Tracing deep fluids in the Bozhong Sag: Evidence from integrated petrography and geochemistry data

Journal Pre-proof Tracing deep fluids in the Bozhong Sag: Evidence from integrated petrography and geochemistry data Zilong Zhao, Zhenliang Wang, Deying Wang, Feilong Wang, Shengdong Xiao, Liwen Zhu, Xuhui Gao PII:

S0264-8172(19)30606-3

DOI:

https://doi.org/10.1016/j.marpetgeo.2019.104154

Reference:

JMPG 104154

To appear in:

Marine and Petroleum Geology

Received Date: 2 October 2019 Revised Date:

27 November 2019

Accepted Date: 27 November 2019

Please cite this article as: Zhao, Z., Wang, Z., Wang, D., Wang, F., Xiao, S., Zhu, L., Gao, X., Tracing deep fluids in the Bozhong Sag: Evidence from integrated petrography and geochemistry data, Marine and Petroleum Geology (2019), doi: https://doi.org/10.1016/j.marpetgeo.2019.104154. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

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Tracing deep fluids in the Bozhong Sag: Evidence from integrated petrography and geochemistry data

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Zilong Zhao a,b, Zhenliang Wang a,b*, Deying Wang c, Feilong Wangc, Shengdong Xiao a,b, Liwen Zhu a,b , Xuhui Gao a,b

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Abstract: The Bozhong Sag is a mature exploration area for petroleum in the Bohai Bay basin, China,

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which is a typical oil-bearing basin and hosts the Penglai (PL) 19-3, and Qinhuangdao (QHD) 32-6

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giant oil fields (Xue, 2018). Despite 60 years of hydrocarbon exploration in the basin, only few large

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gas fields have been discovered. The discovery of the Bozhong (BZ) 19-6 gas field not only indicated

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that the Bozhong Sag has great potential for natural gas exploration, but also raised questions regarding

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the formation of large-scale natural gas fields in typical oil-prone basins and in sapropelic source rocks.

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The present study therefore performs a detailed investigation of the sources and migration pathways of

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the deep fluids in the Bozhong Sag area as a means of shedding light into this scientific challenge.

a

State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, Shaanxi 710069, China Department of Geology, Northwest University, Xi’an, Shaanxi 710069, China c Bohai Petroleum Institute of CNOOC (China) Co. Ltd. Tianjin Branch, Tianjin 300459, China * Corresponding author：Department of Geology, Northwest University, 229 North Taibai Road, Xi’an, Shaanxi 710069, b

China. E-mail: [email protected] (Z. Wang)

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The Bozhong Sag is located in the thinnest crust and tectonic transition zone of the Bohai Bay

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basin. Intense extension and thinning of lithosphere led to the upward ejection of deep crust and mantle

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materials under diapirism. Improvements in this tectonic setting and the fluid migration path occurred

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as a result of early faults that were formed by compressive thrust in the Indosinian-Yanshan orogenies

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in addition to a process of extensional development and reactivation of Himalayan faults. We obtained

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cores from 13 wells in the Bozhong Sag, and subsequently observed their petrography and analyzed

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samples for fluid inclusions. Also, volcanic rock samples were analyzed for major and trace elements,

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and carbonate rock samples were analyzed for δ13C, δ18O, and

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and He isotopic data were are also discussed. Our results showed that petrography was characterized by

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thermal fading and hydrothermal breccia around fractures filled with quartz and calcite. Deep fluid

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activity was mainly reflected by petrographic assemblages of quartz, ankerite, pyrite, plus calcite and

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volcanic eruptive rocks that were i) enriched with large ion-lithophile elements (LILE), ii) enriched

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with light rare-earth elements (LREE), iii) relatively deficient in high-field strength elements (HFSE),

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and iv) relatively deficient heavy rare-earth elements (HREE). Thermal anomaly events were reflected

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by the homogenization temperature of fluid inclusions, and characteristics of magmatic hydrothermal

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fluids were exhibited by δ13C, δ18O, and 87Sr/86Sr. Our findings indicated that deep fluids were mainly

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derived from the deep parts of the upper mantle, and that they were slightly contaminated by crustal

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materials. Combining our results with those of previous studies on deep xenoliths and xenolithic fluid

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compositions in eruptive rocks of eastern China (Zhang et al., 1999; Han et al., 2008), we interpreted

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Sr/86Sr. Previously reported δ13CCO2

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that deep fluid properties in the study region were characterized by high H2 and low total volatile gases.

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We conclude that the deep fluids in the Bozhong Sag was mainly derived from deep material in the

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upper mantle, and that the fluid activity pattern was aided by the deep fracture-fault systems in addition

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to central and fissure-type wide-area eruption activities. Keywords: Deep fluids; Bozhong Sag; Mineral assemblage of quartz, ankerite, pyrite, calcite; REE; Fluid inclusions; δ13C and δ18O; 87Sr/86Sr; R/Ra

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1. Introduction

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The term ‘deep fluids’ refers to mantle-derived volatile fluids below the basement of sedimentary

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basins, fluids produced by rock dehydration during plate subduction, and deep circulation fluids that

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are driven by mantle-derived heat sources (Fyfe, 1997). The deep fluids are an important carrier of

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matter and energy, which consists of stable elements of C, H, O, N, S, rare gas elements of He, Ne, Ar,

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Kr, Xe, Rn, etc. Meanwhile, it is rich in major elements such as Si, Al, Fe, Mn, Mg, Cu, P, as well as

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trace elements such as V, Cr, etc. And its temperature is higher than that of the strata through the

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surrounding rocks (e.g. Hu, 2016; Liu et al., 2019). Furthermore, on the one hand, the deep fluids are

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an important H2 source, which can optimize the composition of hydrocarbon source rocks and

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accelerate the maturation of source rocks through the addition of exogenous hydrogen (Murchison and

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Raymond, 1989; George, 1992; Liu et al., 2018). On the other hand, it can promote the

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organic-inorganic interactions, thus improving the oil-gas reservoir space (Lavoie et al., 2005; Smith,

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2006; Li, 2016) and the efficiency of oil-gas migration and accumulation (Jin et al., 2004, 2013; Liu et

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al., 2019). Expulsion and migration of deep fluids is closely related to pore-fluid pressure produced by

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diapirism (Qi and Yang, 2010; Klaucke et al., 2016). The evolution and development of anticlinal

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ridges can provide a local extensional environment for the upward migration of deep fluids, but can

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also control the path and scale of fluid migration (e.g. Argentino et al., 2019; Yamada et al., 2014;

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Laird and Morley, 2011). There are many petrographic indicators in rocks that can be used to identify

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deep fluid activities, including thermal fading (TFa) and hydrothermal breccia (HBr) features, which

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can be observed around fractures when deep fluids have higher temperatures and lower pressure than

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the host rocks (e.g. Jébrak, 1997; Jin et al., 2006; Wu et al., 2007; Jin et al., 2015; Fang et al., 2016).

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Multistage structural development were extraordinarily documented by fluids responsible for

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precipitation of veins, which reflect the complicated deformational and thermal history of the area (e.g.

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Kenis et al., 2000; Noten et al., 2011; Slobodník et al., 2012). Authigenic albite with a crystallization

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temperature concentrated between 90-110 °C is a typical hydrothermal mineral, and pyrite in

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fault-fracture systems is the product of deep hydrothermal activity (Mills and Elderfield, 1995; Chen,

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2008; Li et al., 2012). The precipitation of saddle dolomite has been confirmed to originate from the

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dissolution of dolomite during deep fluid activity (Zhang et al., 2008; Shu et al., 2012). A certain

2

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amount of Mg2+ can be obtained from magmatic intrusions through fluid-rock interactions, and

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hydrothermal dolomitization occurs along fault-fracture systems (e.g. Davies and Smith, 2006;

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Jacquemyn et al., 2014; Liu et al., 2019). Calcite, quartz, and other minerals are common minerals that

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indicate deep fluid activity, and their mineral assemblages are determined by the composition of deep

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fluids and fluid-rock interactions (e.g. Jin et al., 2006; Zhu et al., 2008; Hu, 2016). For example,

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quartz-siderite-pyrite-ankerite (Jin et al., 2006; Zhu et al., 2008, 2013; Qin et al., 2017), quartz-ankerite

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(Liu et al., 2008; Hu, 2016; Jin et al., 2019), quartz-kaolinite-pyrite± illite (e.g. Allibone, 1998;

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Bongiolo et al., 2011) and albite-montmorillonite-chlorite (Fontana et al., 2017; Lopes et al., 2019).

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Volcanic eruption and magma intrusion activities are direct manifestations of deep fluid activity

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(e.g. Zanon and Viveiros, 2019; Troise et al., 2019; Liu et al., 2014). Data on major and trace elements,

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isotopes, and the fluid composition in mantle xenoliths provide key information for judging the

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formation environment and properties of deep fluids (e.g. Zhang et al., 2008; Emel’yanova and Lelikov,

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2016; Columbu, 2018). Trace element geochemistry has been used to reconstruct fluid environments

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during the formation of carbonate cements (e.g. Feng et al., 2009; Wang et al., 2018; Zwicker et al.,

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2018). The rare-earth elements (REE) are a group of elements with similar geochemical properties that

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reflect changes in the compositions of deep fluids and allow geochemical processes of fluids to be

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traced (e.g. Elderfield and Sholkovitz, 1987; Hu et al., 2009; Himmler et al., 2013). The stable C and O

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isotopes (i.e., δ13C and δ18O) of carbonate cements in fractures can be used to identify minerals

93

separated from igneous and metamorphic rocks (Peter, 1977; Hu et al., 2018), in addition to their

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origins (Wang and Zhang, 2001; Slobodník et al., 2012) and genesis (e.g. Zheng et al., 1997; Huang et

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al., 2017; Liang et al., 2019). The Sr signature of ocean water is assumed to be homogeneous at any

96

given point in time because the residence time of Sr in seawater is far longer than the ocean mixing

97

time (McArthur et al., 1992). Meanwhile, the

98

fluid-rock interactions, thus providing useful information about their sources and migration pathways

99

(e.g. Argentino et al., 2019; Joseph et al., 2012). Fluid inclusions can be used for paleotemperature

100

reconstructions and to trace paleo-fluid composition during the time of mineral formation (e.g. Fall et

101

al., 2012; Nomura et al., 2014; Biehl et al., 2016; Permanyer et al., 2018). Moreover, Traces of deep

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fluid activity can exist when the homogeneous temperature of fluid inclusions is higher than the highest

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temperature reached by the strata in which the fluid is located (e.g. Florian et al., 2016; Zhao et al.,

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2018). Organic and inorganic origins of CO2 can be distinguished according to the statistical

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relationship of δ13CCO2 (Dai et al., 1996). Namely, an organic origin is marked by an enrichment in

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light C isotopes (δ13CCO2 < -10‰), whereas an inorganic origin is indicated by an enrichment in heavy

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C isotopes (δ13CCO2 > -8‰). However, the inorganic origin of CO2 from the crust-mantle cannot be

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distinguished by the statistical relationship of δ13CCO2. The isotopic composition of He in natural gas

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that is associated with CO2 is a sensitive index for distinguishing mantle-derived and crust-derived

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Sr/86Sr ratio of deep fluids reflects fluid mixing and

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fluids (Jenden et al., 1988; Dai et al., 1996). The R/Ra ratio of He (Table 1) that is associated with i)

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CO2 formed in mantle-derived magma is > 2, ii) CO2 formed in the crust-mantle mixing origin ranges

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from 1-2, and iii) a crustal origin is < 1 (He et al., 2005; Hu et al., 2009).

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The Bozhong Sag in the Bohai Bay basin is one of the earlier mature exploration areas in eastern

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China, yet after 60 years of exploration, no large natural gas fields had been discovered. Sapropel type

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and mixed type of oil-prone source rocks are the main types of hydrocarbon source rocks that have

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been understood to be lesser conducive to the formation of large natural gas reservoirs (Hu et al., 1986;

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Jiang, 1999; Lai et al., 2000). However, the successful discovery of 100 billion cubic meters of large

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gas fields (BZ19-6) suggests that the Bozhong Sag has great potential for natural gas exploration (Fig.

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1). A major question that is of particular interest to the oil-gas industry and scientific community exists

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regarding how sapropelic source rocks might generate large-scale natural gas. Hydrogen-rich deep fluid

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activity has become a reasonable explanation for the generation of large-scale natural gas from

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sapropel-type source rocks within the current experimental range, and the gas production rate can

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reportedly be increased by more than 147% (Jin et al., 2002). Therefore, investigating whether there is

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deep fluid activity in the Bozhong Sag is a key to solving this question.

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The objective of the present study is to improve our systematic understanding of the activity of

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deep fluids in the Bozhong Sag by integrating information from drilling cores, microscopic slices, and

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isotopic evidence. We first present a summary of the petrographic assemblage characteristics that

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reflect the deep fluid activity in the sag in terms of i) the possible fluid migration pathways, ii) the

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characteristics of fractures and surrounding rock cements, and iii) the types of mineral assemblages.

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We then corroborate these information with geochemical evidence including the major and trace

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elemental compositions of volcanic rocks, fluid inclusions, and δ13C, δ18O, and 87Sr/86Sr in the cements

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of fractures and surrounding rocks. We interpret and confirm our findings within the context of other

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studies on CO2 and He, the Cenozoic tectonic characteristics, the multi-stage evolution of deep and

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large faults, and the background kinematic mechanism in the Bozhong Sag. Finally, we use our

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findings to propose a comprehensive model of deep fluid activity in the Bozhong Sag, which provides

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new insights for understanding the generation of large-scale natural gas from sapropelic source rocks.

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2. Geological setting

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2.1. Regional tectonics and evolution

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The Bozhong Sag is a secondary tectonic unit in the Bozhong depression of the Bohai Bay basin

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(Fig. 1). The regional structure is located at the intersection of the Paleo-Asian Ocean, the Tethyan

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Ocean, and the Pacific tectonic system, which has undergone multi-stage tectonic superimposition and

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evolution (e.g. Li et al., 2010; Tian et al., 2017). During the Indosinian tectonic period, a nearly

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north-south trending compressive stress field was formed through the shear closure of the North China

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Plate and the Yangtze Plate (Yu et al., 2002; Wu et al., 2007), thus resulting in the absence of Mesozoic 4

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sediments and intense denudation of the Paleozoic sediments (Fig. 2). When the Paleo-Pacific Plate

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subducted to the west, and the North China Plate shifted from the Tethyan Ocean tectonic system tract

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to the littoral Pacific tectonic system tract, a relatively strong left-lateral shear resulted (Zhou et al.,

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2003; Qi and Yang, 2010). Under this stress mechanism, the buried mountain tectonic belt was greatly

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uplifted, weathered and intensely denuded in the region of the Bozhong Sag, thereby forming an

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obvious truncated unconformity surface (Fig. 2). During the Himalayan period, the Bozhong Sag was

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subjected to a dual stress field of the north to south extension and north to east right shear due to the

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combined effects of the low-angle and high-speed northwest oblique subduction of the Pacific Plate

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and the northward convergence and collision of the Indian Plate (Xu et al., 2019; Xiao et al., 2019).

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The Bozhong Sag experienced a synrift stage from the Paleocene to the Oligocene (65.0-24.6 Ma). The

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Guantao and Minghuazhen Formations (24.6-5.1 Ma) experienced a post-rift stage and a neotectonic

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movement stage (5.1-0 Ma), which were influenced jointly by the Zhangjiakou-Penglai strike-slip fault

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zone, the Qinhuangdao-Lvshun sinistral strike-slip fault zone, and the Tanlu dextral strike-slip fault

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zone (24.6-0 Ma) in the late Himalayan period (e.g. Li, 1979; Qi et al., 1995; Gong et al., 2007). In

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summary, the tectonic evolution of the Bozhong Sag can be divided into three main periods: 1) a

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tectonic uplift period (Middle Jurassic to Late Cretaceous), 2) a synrift period, including synrift I (the

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Kongdian Formation (Ek), the 4th member of Shahejie Formation (E2s4)); Synrift II (the 3rd member of

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the Shahejie Formation (E2s3)), and Synrift III (the 2nd member of the Shahejie Formation (E3s2) and

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the 1st member of the Dongying Formation (E3d1)), and 3) a post-rift period, including post-rift I (the

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Guantao Formation (N1g), the lower member of the Minghuazhen Formation (N1mL)); and post-rift II

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(the upper member of the Minghuazhen Formation (N2mu) until present day) (Fig. 2).

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2.2. Stratigraphic characteristics

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The Bozhong Sag and lower uplift are mainly bounded by faults and are controlled by the steep

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slope zone of boundary faults. The study area is surrounded by the eastern Bodong lower uplift, the

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southern and southeastern Bonan lower uplift, the Chengbei lower uplift, the western Shaleitian lower

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uplift, and the northern Shijiutuo lower uplift (Fig. 1). The oil and gas bearing strata from bottom to top

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mainly include Archean-Proterozoic (Ar-Pt) granites, conglomerates of the Ek, medium-fine

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sandstones of E3s2 and the 1st member of the Shahejie Formation (E3s1), medium sandstones of E3d1 and

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the 2nd member of the Dongying Formation (E3d2), and the sandstone reservoirs of the Guantao and

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Minghuazhen Formations (Fig. 2). The total organic carbon (TOC) of the source rocks in E2s3, E3s1,

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and 3rd member of the Dongying Formation (E3d3) of the Bozhong Sag are 0.29%-6.07%,

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0.46%-6.15%, and 0.35%-3.13%, respectively. The hydrocarbon generation potentials (S1 + S2) of E2s3,

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E3s1, and E3d3 are 0.67-35.89 mg/g, 1.03-32.99 mg/g, and 0.15-22.16 mg/g, respectively, and the

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hydrogen index (HI) are 98-557 mg/g, 15-843 mg/g, and 9-953 mg/g, respectively (Xie et al., 2018;

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Jiang et al., 2019).

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3. Samples and methods

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3.1. Sample preparation

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According to the distribution range and horizon distribution of natural gas wells in the Bozhong

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Sag, as well as the gas content of drilling cores, 13 typical wells were selected for coring. Selective

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systematic sampling was carried out at A3, A4, and A7 wells with long coring and complete horizons in

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the sag area in order to represent all important stratigraphic units (Fig. 1). Structural positions of the

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hydrothermal veins have been documented in the core house and sampled for a detailed petrographic

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study using incident and transmitted light. Based on the petrographic investigation, vein and

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surrounding rock samples were sampled by a Relion MSS microsampling instrument and a Nikon

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SMZ1270 stereomicroscope. Samples were selected for determining i) the major and trace elements in

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volcanic eruptive rocks, ii) fluid inclusions, and iii) δ13C and δ18O, and

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cements of fractures and surrounding rocks. Geochemical data of δ13CCO2 and He isotopes (R/Ra)

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reported in other studies were also collected and systematically sorted (Table 1).

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3.2. Experiments and analytical methods

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3.2.1. Petrographic observation

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Sr/86Sr isotopes in calcite

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The characteristics of fractures and intergranular pore cements that are connected with fractures

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are the focus of this study. Thin sections were observed with a ZEISS Axio Scope A1 dual-channel

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transmission-reflection light microscope. Petrographic characteristics and assemblage types were

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observed at different objective multiples (2.5X, 5X, 10X, 20X, 50X, and 100X). Different types of

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carbonate cements were distinguished by staining thin sections using potassium ferricyanide and

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alizarin red. Cathodoluminescence microscopy was applied to distinguish multiple vein generations

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(Kolchugin et al., 2016; Wei et al., 2018) or to reveal recrystallization and alteration of surrounding

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rocks (Frelinger et al., 2015; Rebelo et al., 2016). The cathodoluminescence thin slices were excited by

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a Beacon Innovation International Incorporation (BII) CLF-1 cathodoluminescence instrument and

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analyzed with a Nikon LV100N POL transmission microscope. The power supply was 100-230 V (10

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A), the output voltage/current was 40 KV/2 mA. The vacuum was used at 0.003 mbar, and the stepping

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platform is controlled by six speed modes. The working environment temperature was 21 °C and the

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humidity was 50%. A smooth, clean surface was used as the observation surface, and the naturally

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dried samples were put into the ion sputtering apparatus for coating gold. Microscopic minerals were

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analyzed by a FEI Quanta 400 field emission gun (FEG) environmental scanning electron microscope

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(SEM). The accelerating voltage was 30-500 KV, the astigmatism was ≤ 50 µm, the magnification was

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between 7 to 1 000 000 times, and the image resolution was ≤ 3.5 nm.

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3.2.2. Analysis of major and trace elements 6

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The collected volcanic eruptive rock samples were all Mesozoic and included andesite and tuff.

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Andesite samples with a weak alteration were selected for testing. After pollution-free crushing and

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shrinkage, 300 g of each sample was grinded to 75 µm for chemical analysis. Trace elements and REE

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were handled using 1 ml HF plus 0.5 ml HNO3 sealed solution in an oven at 190 °C for 24 hours (Zhao

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et al., 2016; Li et al., 2018). The insoluble residues were dissolved at 130 °C in 5 ml 30% (v/v) HNO3

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for 3 hours and then diluted to 25 ml (Chen et al., 2016). The major and trace elements were analyzed at

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the ALS Minerals-ALS Chemex (Guangzhou, China) using a Elan 9000 inductively coupled plasma

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mass spectrometer (ICP-MS) (Perkin Elmer, U.S.A) for trace elements, and a Axios X-ray fluorescence

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spectrometer (XRF) (PAN analytical, the Netherlands) for major elements. The analytical accuracies of

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each element were better than 5%.

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3.2.3. Fluid inclusions testing

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Doubly polished sections were prepared for fluid inclusion analyses. After initial microscopic

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evaluation of the sections, the types and characteristics of fluid inclusions were observed by a ZEISS

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Axio Scope A1 dual-channel fluorescence-transmission light microscope, and homogenization

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temperatures were measured using a Linkam THMS600G freezing-heating stage. The stage enables

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measurements within the range of -196-600 °C. The initial heating rate was 5 °C/min, and the stage was

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adjusted to 1 °C/min when a homogeneous state was approached. The precision of temperature

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measurement is better than ± 0.5 °C for ice-melting temperatures, and better than ±1 °C for total

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homogenization temperatures. Fluid inclusion analysis was completed at the State Key Laboratory of

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Continental Dynamics and the Analytical Experimental Center of the Department of Geology,

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Northwest University, China.

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3.2.4. Analyses of δ13C, δ18O, and Sr

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δ13C and δ18O of the vein calcites and their host-rocks were analysed in the State Key Laboratory

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of Continental Dynamics and the Analytical Experimental Center of the Department of Geology,

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Northwest University, China. Samples were performed by crushing with agate mortar into powder

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(particle size 75 µm). The carbonate powders were reacted with 10% H2O2 and then absorbed by

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acetone. Samples were then dried for 4 hours at 105 °C in an oven before being put into sampling

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bottles. CO2 was produced using the phosphoric acid method (McCrea, 1950) in a Thermo Fisher

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GasBench II multi-function gas generator, and analyzed using a Thermo Finnigan MAT 253 gas stable

242

isotope ratio mass spectrometer. Results are reported in standard δ notation relative to the

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Vienna-PeeDee Belemnite (V-PDB) standard. Precision was 0.1‰ (1σ) for both δ13C and δ18O.

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Sr sample processing and testing were completed at the Analytical and Testing Research Center of

245

the Beijing Research Institute of Uranium Geology. Splits of powdered samples (particle size < 150 µm)

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were decomposed with ultra-pure acid (HNO3, HF and HClO4; analytical reagent acids were

247

double-distilled) at 160-180 °C in sealable tubes. First, 6 ml (1:1) of HNO3 was added to the tubes in

248

which each filter was placed, which were then closed and placed in an ultrasonic bath for at least 7

249

40 min. The solutions were then heated for 24  hours at 180 °C on a hot plate. Then, 1 mL concentrated

250

HNO3 was added to each dissolved sample and the solutions were evaporated to near-dryness at 140 °C

251

in an electric hot plate. Finally, 3 ml (1:2) of HNO3 was added to the solutions, and the samples were

252

heated at 130 °C for 4  hours. After digestion following the process described above, the elements Sr in

253

the samples were successively separated (Du et al., 2017, 2019). A Phoenix thermal surface ionization

254

mass spectrometer was used for Sr analysis and testing. The

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fractionation to 86Sr/88Sr =0.1194. External reproducibility was controlled by repeated analyses of the

256

NBS 987 strontium isotopic standard (2σ, n = 10), which has a recommended value of 0.71025, was

257

0.71025 ± 0.00003.

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4. Results

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4.1. Petrographic assemblage characteristics

87

Sr/86Sr ratios were corrected for mass

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The activities of deep fluids, changes in temperature and pressure conditions, and interactions with

261

surrounding rocks can all result in the formation of special features in or around fractures. Observation

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of cores (Fig. 3) indicated that the reservoir space in the natural gas reservoir is dominated by multiple

263

fracture systems. Fracture filling was mainly characterized by quartz and calcite minerals (Fig. 3a, 3b),

264

and fractures of cross-cutting relationships were filled with calcite in Ordovician dolomite with a

265

calcite vein width of 0.3-1.1 cm (Fig. 3b). TFa and HBr exist around the fractures, meanwhile, the

266

unfilled parts of the fractures were occupied by oil and solid bitumen (Fig. 3).

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Deep fluid activity can be traced by the characteristics of mineralogical petrographic assemblages

268

(Stoffregen, 1987; Jin et al., 2006). Based on the microscopic observation of more than 300 thin

269

sections, two petrographic assemblages of fracture filling minerals were determined. Assemblage I was

270

characterized by pyrite (Fig. 4a, 4b, 4e), orange banded calcite (Fig. 4c, 4d), plus light-green cathodic

271

apatite (Fig. 4c). The calcite and pyrite were directionally filled in veins (Fig. 4d, 4e), with beaded

272

apatite accompanied by pyrite. Assemblage II was characterized by crackle quartz (Fig. 4f), ankerite

273

(Fig. 4f), plus pyrite (Fig. 4g). The long axis direction of crackle quartz and ankerite was consistent

274

with the extension direction of the fractures (Fig. 4f). Saddle-shaped dolomite and pyrite occurred in a

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massive form in the fracture-pore system (Fig. 4g). These observations indicated that crackle quartz,

276

ankerite, saddle-shaped dolomite, and pyrite were derived from fluids migrating upwards through

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fractures.

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Authigenic albite was found in the dissolution pores of potassium feldspar grains (Fig. 4h), and

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quartz, filamentous illite, and villous pyrite filled the intergranular pores of ankerite (Fig. 4i). The

280

characteristics of the petrographic assemblages suggest that deep fluids migrated dominantly through

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the fault-fracture system, and were exposed to rapid charging activities of the central type and fissure

282

type eruptions. HBr (Fig. 3b, 4d) and TFa (Fig. 3b) occurred near the fracture surfaces due to the high

283

temperature of the deep fluids, and at almost the same time, the crackle quartz and ankerite migrated 8

284

along the fault system within the deep fluids. A gradual weakening of the deep fluid activity occurred

285

as fluid velocity slowed and temperatures and pressures decreased. Albite and saddle dolomite

286

precipitated as the last phases following the decrease in temperature and pressure along the fracture

287

system (Fig. 4h, 4i).

288

4.2. Major and trace elements

289

Percentage contents of oxides in the Mesozoic volcanic rock samples were ranked as follows:

290

SiO2 (56.76%-69.85%) > Al2O3 (12.38%-19.65%) > Na2O (4.54%-5.69%) > Fe2O3 (2.39%-4.59%) >

291

K2O (1.72%-4.11%) > CaO (0.91%-2.88%) > MgO (0.45%-1.79%) > TiO2 (0.18%-1.03%). The ranges

292

of Na2O and K2O suggest these samples belong to the high K calc-alkaline magma series (Fig. 5a). The

293

total alkali content (K2O + Na2O) ranged from 4.70% to 8.98%. According to the silica-alkali

294

classification plate of volcanic rocks (Fig. 5b), the samples fall into the areas of trachyandesite,

295

trachyte, and trachydacite. CIPW norm calculation results showed that all samples contained olivine or

296

quartz standard minerals to varying degrees, and that the samples were a set of SiO2

297

saturated-supersaturated volcanic rocks.

298

The Mesozoic volcanic rock samples showed an enrichment of LILE and LREE, and a relatively

299

depletion of HFSE and HREE on the original mantle normalization map of incompatible elements (Fig.

300

6). Trace elements analyses showed that the samples were enriched Cs (0.58 × 10-6 to 1.54 × 10-6) and

301

Ba (768 × 10-6 to 2540 × 10-6). There were relatively higher contents of REE in the samples (∑REE =

302

115 × 10-6 to 235 × 10-6). The volcanic rocks had no apparent anomalies of Eu (δEu = 0.18-0.21) or Ce

303

(δCe = 0.23-0.25) (Fig. 6a). The Nb/Ta (16-21) and Zr/Hf (34-42) ratios of relatively HFSE were

304

similar to those reported by Sun and McDonough (1989) for the original mantle (Nb/Ta = 17, Zr/Hf =

305

36). The Nb contents (5.4 × 10-6 to 14.5 × 10-6) of our samples were higher than of that reported for

306

normal mid-ocean ridge basalts (N-MORB) (2.3 × 10-6), and were more like that of enriched mid-ocean

307

ridge basalts (E-MORB) (8.3 × 10-6 (Sun and McDonough, 1989)). Samples showed obvious negative

308

anomalies of Nb and Ta, and the La/Nb ratio was 2.8-6.4 (Fig. 6b). The major and trace data

309

characteristics of the eruptive rock samples suggest that the mantle-derived magma may have intruded

310

during the process of evolution in the Bozhong Sag.

311

4.3. Fluid inclusions

312

Thermal anomaly information and deep fluid composition can be captured in detail by fluid

313

inclusions (Lüders et al., 2012; Chen et al., 2015; Wang et al., 2019). Formation temperatures higher

314

than the normal geothermal gradient can be obtained to varying degrees during the homogenization

315

temperature measurement of fluid inclusions (hydrocarbon inclusions and brine inclusions) in fracture

316

vein cements, feldspar, and quartz grains (Fig. 7). On the basis of the current measured geothermal

317

gradient and the simulation results of a single well burial thermal evolution in typical tectonic blocks in

318

the Bozhong Sag (Hu et al., 2001; Zou et al., 2011), samples with the maximum temperatures in the

319

strata beyond the actual burial depth in the tectonic blocks of BZ-19, BZ-21, Caofeidian (CFD) -18, 9

320

and QHD-36 account for 66.81%, 24.53%, 71.23%, and 37.90% of the total number of analyzed fluid

321

inclusion samples from this study, respectively (Fig. 8). The homogeneous temperature of these

322

secondary fluid inclusions was higher than the actual geothermal gradient and the temperature that the

323

strata can reach under the condition of burial depth, which cannot fully represent the different degrees

324

of abnormal thermal events occurring in the tectonic blocks. However, the relative values suggest that

325

the different tectonic blocks in the Bozhong Sag underwent high temperature activities in relation to the

326

deep fluids to varying degrees. Our findings are supported by those of another study, which analyzed

327

the fluid compositions of 20 alkaline volcanic and lherzolite xenoliths in eastern China, and concluded

328

that deep mantle-derived fluid compositions were characterized by high H2 content and low total

329

volatile gases (Zhang et al., 1999; Han et al., 2008). Fluid inclusions containing CO2 and H2 were

330

discovered in the actic area of the north part of the Bozhong Sag, which have the same petrographic

331

characteristics and a large number of paragenesis with hydrocarbon inclusions (Wang et al., 2012,

332

2019). It is further confirmed that the deep fluids in the Bozhong Sag can provide a large-scale H2 for

333

source rocks, and might also have a certain coupling relationship with hydrocarbon accumulation.

334

4.4. δ13C and δ18O

335

The composition of stable C and O isotopes in fracture filling calcite samples and surrounding

336

rock samples from BZ-19, BZ-21, and QHD-36 tectonic blocks were analysed (Fig.9). The value of

337

δ13C ranged from -10.9‰ to 9.4‰ (mean = -0.1‰; standard deviation (SD) = 3.6‰; number of

338

samples (n) = 46), whereas the δ18O composition ranged from -25.0‰ to -7.6‰ (mean = -16.2‰, SD =

339

4.1‰, n = 46). δ13C values in samples from the surrounding rocks ranged from -7.5‰ to 9.2‰ (mean =

340

0.5‰, SD = 3.3‰, n = 46), and δ18O ranged from -24.2‰ to -6.0‰ (mean = -12.1‰, SD = 3.5‰, n =

341

46). It can be seen that the isotopic composition of calcite filled fractures was generally lower than of

342

that of the surrounding rocks. According to the principle of oxygen isotope fractionation (Zheng and

343

Chen, 2000), δ18O in water would be greatly consumed. Light δ18O signatures of carbonate cements

344

may derive from diagenetic alteration as well as from high temperature conditions during carbonate

345

precipitation. On the basis of δ13C data and the findings of other studies (e.g. Peter, 1977; Jin et al.,

346

2015), we interpret that fracture-filled calcite in the Bozhong Sag should belong to carbonate rocks

347

formed by magmatic hydrothermal veins. Figure 9 shows that δ13C and δ18O values from calcite cement

348

samples were relatively lower between zone C and zone D. This also suggests that the calcite filling in

349

fractures was formed by relatively high-temperature hydrothermal fluids (Fig. 9). After a continuous

350

decrease in temperature, pressure, and flow rate in the reservoir, calcite supersaturation led to the

351

precipitation of calcite in the fracture to form vein-like calcite filling.

352

Figure 9 shows that the negative δ13C values of samples may be caused by the combination of CO2

353

released by thermal decarboxylation of organic matter in source rocks with Ca2 + and Mg2 + in the deep

354

fluids to form carbonate minerals (e.g. Curtis et al., 1972; Suess and Whiticar, 1989; Longstaffe, et al.,

355

2003; Cui et al., 2012; Guo et al., 2014). Meanwhile, the hydrocarbon source foundation of 10

356

mature-high mature stages (e.g. Yang and Li, 2012; Jiang et al., 2016) and the geological background

357

of the well-developed fault-fracture migration and accumulation (e.g. Xu et al., 2016; Wang et al.,2016;

358

Xue, 2018), which all revealed that the organic acids had been charged in a large scale. The negative

359

δ13C values can also be caused by diagenesis, but the result of this genetic mechanism is that the

360

negative δ13C is accompanied by the light δ18O (Lan et al., 2016). Then the δ18O of samples with the

361

negative δ13C is relatively heavy (Fig. 9), and further studies confirm that the carbonate rocks from

362

deep fluids themselves have relatively heavy δ18O characteristics (Spencer, 1987; Jin et al., 2013;

363

Wang et al., 2017), which can be up to 12‰ (Zheng and Chen, 2000). Therefore, the negative δ13C

364

caused by diagenesis is weak in the study area.

365

4.5. Sr isotopes

366

Sr isotope results showed (Fig. 10a) the calcite minerals in a vein body in the BZ-29 block had

367

relatively high 87Sr/86Sr values, and ranged from 0.7099-0.7208. The vein calcite minerals in both the

368

BZ-29 and CFD-18 tectonic blocks (87Sr/86Sr 0.7124-0.7208) were relatively higher than the

369

surrounding rocks (87Sr/86Sr 0.7095-0.7125), thus indicating fluid-rock interactions during fluid

370

migration through siliciclastic units and/or the granitic basement. The ratio of

371

fractured vein body in the BZ-21 block (87Sr/86Sr 0.7093-0.7098) and the surrounding rocks (87Sr/86Sr

372

0.7092-0.7099) were similar, thus suggesting that there was a strong material exchange between the

373

deep fluids and surrounding rocks. Sr from crustal sources is rich in Rb, and can have a high 87Sr/86Sr

374

ratio, with the global average crustal 87Sr/86Sr ratio reported as 0.7119 (Palmer and Edmond, 1989). Sr

375

from mantle sources has been understood to be mainly supplied by deep hydrothermal systems in

376

mid-ocean ridges, with poor Rb and low

377

reported as 0.7035 (Palmer, 1985). Fractured vein carbonate cements were filled by deep

378

mantle-derived fluids with relatively high Sr isotope ratios. Partial fractionation of Sr isotopes recorded

379

in the surrounding rock samples (Fig. 10a) indicated that the surrounding rocks were affected by deep

380

crust-derived materials with relatively higher

381

isotopic composition of Ordovician seawater was relatively homogeneous (global mean = 0.7091)

382

(Denison et al., 1994). However, the Sr isotope of Ordovician surrounding rocks in the Bozhong Sag

383

exceeded this mean (Fig. 10a), which further suggests that the source of Sr to the calcite in the

384

surrounding rocks is not entirely from Ordovician seawater (Fig. 10b), but possibly supplied from

385

Cambrian or Precambrian mantle-derived fluids.

386

4.6. CO2 and Helium isotopes

87

87

Sr/86Sr between the

Sr/86Sr ratios, with the global average mantle

87

87

Sr/86Sr

Sr/86Sr ratios. Other studies have reported that the Sr

387

Figure 11a shows data reported by another study (Table 1), which found a low CO2 content in the

388

Laizhou Bay Sag and Liaodong uplift in the Bohai Bay basin, and concluded that this was of an organic

389

origin. The CO2 content in 95% of the samples was < 1% (mean = 0.44%) and the δ13CCO2 was < -10‰.

390

Studied have found that the CO2 content in the Bozhong Sag ranged from 0% to 89.1%, and were

391

mostly > 15%, and that the δ13CCO2 value ranged from -1.70‰ to -33.96‰. With the exception of two 11

392

gas samples from the BZ-29 oil field, all other gas samples (δ13CCO2 > -8‰) were determined as being

393

mainly of an inorganic origin (Fig. 11a, Table 1). The BZ-21 block is gas-bearing and has a larger

394

depth (5141 m) than other blocks in the sag, and reportedly also has higher temperatures (up to 180 °C),

395

a relatively high CO2 content (48.92%), a δ13CCO2 of -3.2‰, and a R/Ra ratio (i.e., He isotopes) of 6.41.

396

The QHD-29 is an oil field with a reportedly high CO2 content and large resource reserves, meanwhile,

397

the R/Ra ratio of gas samples were 4.44 and 3.92 (Fig. 11b, Table1). Therefore, it can be hypothesized

398

that much of the CO2 in the Bozhong Sag is of an inorganic origin from mantle-derived magma.

399

5. Discussion

400

5.1. Dynamics during the Cenozoic and diapirism of magma

401

The Cenozoic dynamic mechanism of the Bohai Bay basin has been discussed by many scholars

402

(e.g. Qi et al., 1995; Wu and Zhou, 2000; Ji, 2002; Sun et al., 2008; Xu et al., 2011). The current

403

consensus is that the crustal thinning was caused by mantle uplift from the subduction of the Pacific

404

Plate to the Eurasian Plate, and that the superimposed strike-slip process formed the Cenozoic rift

405

basin. Further studies have suggested that the Cenozoic basin in Bohai Bay is affected by two dynamic

406

mechanisms (e.g. Qi et al., 2010; Teng et al., 2014; Zhou et al., 2019). The first dynamic force was

407

derived from the bottom of the lithosphere. Crustal extension caused by the mantle thermal diapir

408

resulted in an extensional tectonic deformation of the crust, and subsequently controlled the deep

409

thermal fluid activity. The second dynamic force was a lateral force transferred from the plate boundary

410

interaction to the plate, which resulted in the development of a strike-slip structural deformation along

411

deep faults in the basin (Fig. 12).

412

As previously mentioned, the Bozhong Sag is located at the intersection of the Tanlu strike-slip

413

fault, the Zhangjiakou-Penglai fault, and the Qinhuangdao-Lvshun fault (Fig. 1), which marks the end

414

of the development and evolution of the whole Bohai Bay basin. The minimum depth of the Moho

415

surface between the crust and the mantle in the Bozhong Sag is only ~25 km (Zhu and Mi, 2010),

416

which is the thinnest crustal thickness area in the Bohai Bay basin. A large number of centripetal faults

417

developed during the Paleogene period in the basin, which indicates extensive extensional action

418

existed widely in the Bozhong Sag. The dynamic mechanism of extensional action may be derived

419

from the thermal action of the lithosphere or from plate creep dispersion. This dynamic mechanism also

420

better explain the following phenomena. During the Paleogene rifting stage, an intense thermal

421

expansion occurred at the bottom of the lithosphere, and the crust-mantle materials were ejected

422

upward under diapir action (Fig. 12). Meanwhile, both physical simulation and mathematical models

423

confirm that the deep fluids is mainly controlled by heat conduction under the background of deep

424

fault-fracture systems (e.g. Xu et al., 2000; Cloetingh et al., 2010; Scheck-Wenderoth et al., 2014).

425

Different structural form make the thermal conductivity of rocks change in vertical and horizontal

426

directions, and then the heat flow is redistributed after refraction (Franz and George, 1966; Xiong and 12

427

Zhang, 1984; Chang et al., 2016; Zhang et al., 2017). The high geothermal gradient is positively

428

correlated with the high thermal resistance mudstone caprocks and the high thermal conductivity

429

bedrock configuration (Xiong and Gao, 1982; Chen et al., 1984; Lin and Gong, 2005; Wang et al.,

430

2019). The coupling of the above special dynamic background, heat conduction mechanism and deep

431

stratigraphic structure led to a relatively high geothermal flux in the Bozhong Sag. The average

432

geothermal heat flow in the sag has been reported as being 60-65 mW/m2, but this can exceed 70

433

mW/m2 in the lower uplift areas around the sag (Zhu, 2009). Hence, the regional tectonic background

434

and diapirism of magma laid an improved material foundation for deep fluid activities.

435

5.2. Multi-stage evolution of deep faults

436

The formation time and dynamic mechanisms of deep fault-fracture systems have become core

437

aspects for studying deep fluid activities. The North China Plate was subjected to the Caledonian and

438

Hercynian movements during the pre-Indosinian period (Song, 1999; Wu et al., 2007), and the strata

439

formed gentle folds in the form of vertical subsidence (Fig. 13a). During the Indosinian to early

440

Yanshan periods, the North China Plate and Yangtze Plate were squeezed in an almost north to south

441

direction, thereby forming a large number of nearly east-west thrusting faults (Fig. 13b, 13c). With an

442

increase in the compressive and torsional stress in the south to north direction, the uplift of the fold was

443

subjected to different degrees of denudation, thus resulting in the basement being exposed to the

444

surface and the formation of angular unconformity (Fig. 13c). In the mid-Yanshan period, the stress

445

field in the Bozhong Sag changed from the previous compression-shear stress field to a tension-shear

446

stress field. The near-east to west trending faults that formed in the early stage were extensional and

447

reversed (Fig. 13d), and the strike-slip faults were large-scale left-lateral strike-slip extensions.

448

Nevertheless, during the late Yanshan period, the sag shifted into a near north to south compressive

449

stress field. The faults reversed and the Bozhong Sag uplifted differently, and formed a north high and

450

south low tectonic framework (Fig. 13e). Since the Himalayan epoch, the Bozhong Sag has

451

experienced dual stress fields of the north to south extension and a north to east right shear. As a result,

452

the deep fault-fracture system developed and the pre-existing faults were extended and activated (Fig.

453

13f). Multi-stage evolution of deep faults, especially the concentrated development and reactivation of

454

faults since neotectonic movement, provide an advantageous channel for the upward movement of the

455

deep fluids.

456

5.3. Deep fluid activity pattern

457

Studies have confirmed that the main eruption time of magmatic rocks in the Bozhong Sag was

458

the sedimentary period of the Dongying Formation, and that the eruption intensity was the largest

459

during the late Oligocene, which was dominated by the Hawaiian volcanic eruption pattern (Zhu et al.,

460

2014; Guo et al., 2016). Meanwhile, the strike-slip of the fault zone triggered the development of a

461

secondary fault-fracture system, magmatism, and volcanic activity (e.g. Han et al., 2008; Zhou et al.,

462

2019; Fedorik et al., 2019). The deep coupling of the late Oligocene deep fluids and the concentrated 13

463

development and reactivation of the Himalayan deep faults laid the material foundation and channel

464

background for the deep fluids in the Bozhong Sag. The dynamic background of the upward eruption

465

of the crust-mantle material under diapir action developed after an intense thermal expansion at the

466

bottom of lithosphere. The petrographic assemblage of quartz, ankerite, pyrite, plus calcite mainly

467

reflects local deep fluid activity. The phenomena of TFa and HBr around the fracture-fault margin

468

partly reflects the local energy exchange between the high-temperature deep fluids and the surrounding

469

rocks. Since LILE and LREE were relatively enriched, and HFSE and HREE were relatively deficient

470

in the volcanic rock samples, we interpret this as reflecting that the deep fluid activities originated from

471

mantle-derived materials. The thermal anomaly events that were reflected by the homogenization

472

temperature of the fluid inclusions, and magmatic hydrothermal fluids (exhibited by C and O isotopes,

473

Sr, CO2, and R/Ra) suggest that the deep fluids were mainly derived from the deep part of the upper

474

mantle and that they were slightly contaminated by crustal materials. In summary, the deep fluid

475

activity pattern in the Bozhong Sag was mainly derived from the deep material in the upper mantle, and

476

with the aid of the deep fault-fracture system, central and fissure-type wide-area eruption activities took

477

place (Fig. 14).

478

6. Conclusions

479

Based on the Cenozoic tectonic background and the multi-stage evolution and dynamic

480

mechanisms of deep faults in the Bozhong Sag, we traced in detail the sources and migration pathways

481

of the deep fluids using petrography and geochemistry data. The following conclusions were drawn.

482

(1) The bottom of the lithosphere in the Bozhong Sag has undergone intense thermal expansion,

483

with crustal and mantle materials having been ejected upward under diapir action. Deep faults mainly

484

underwent compression thrust in the early period of the Indosinian-Yanshan orogenies, and a process

485

of extension and reactivation of Himalayan faults also occurred. These factors provided an improved

486

source and better migration pathways for deep fluid activities.

487

(2) Deep fluid activity was reflected by petrographic assemblages of quartz, ankerite, pyrite, plus

488

calcite, thermal anomaly events were reflected by the homogenization temperature of fluid inclusions,

489

and characteristics of magmatic hydrothermal fluids were exhibited by REE, δ13C, δ18O, and 87Sr/86Sr.

490

The deep fluid activity pattern in the Bozhong Sag was mainly originated from the upper mantle

491

material that was slightly mixed with crustal materials, and a deep fault-fracture system assisted the

492

eruption of the deep fluids in a manner of central and fissure-type activities.

493

Acknowledgments

494

This work was supported by funding from the Key Project of National Sciences and Technologies

495

(Grant No. 2017ZX05008-004-004). Anonymous reviewers and editor gave constructive comments and

496

advice that were greatly appreciated for improving our manuscript. 14

497

References

498

Allibone A., 1998. Synchronous deformation and hydrothermal activity in the shear zone hosted high-sulphidation

499

Au-Cu deposit at Peak Hill, NSW, Australia. Mineralium Deposita. 33(5), 495-512.

500

Argentino C., Conti S., Crutchley G. J., Fioroni C., Fontana D., Johnson J. E., 2019. Methane-derived authigenic

501

carbonates on accretionary ridges: Miocene case studies in the northern Apennines (Italy) compared with modern

502

submarine counterparts. Marine and Petroleum Geology. 102, 860-872.

503

Argentino C., Lugli F., Cipriani A., Conti S., Fontana D., 2019. A deep fluid source of radiogenic Sr and highly dynamic

504

seepage conditions recorded in Miocene seep carbonates of the northern Apennines (Italy). Chemical Geology. 522,

505

135-147.

506 507

Biehl B. C., Reuning L., Schoenherr J., Lewin A., Leupold M., Kukla P. A., 2016. Do CO2-charged fluids contribute to secondary porosity creation in deeply buried carbonates?. Marine and Petroleum Geology. 76, 176-186.

508

Bongiolo E. M., Renac C., Mexias A. S., Gomes M. E. B., Ronchi L. H., Patrier-Mase P., 2011. Evidence of Ediacaran

509

glaciation in southernmost Brazil through magmatic to meteoric fluid circulation in the porphyry-epithermal Au-Cu

510

deposits of Lavras do Sul. Precambrian Research. 189(3-4), 404-419.

511 512 513 514

Bruckschen P., Oesmann S., Veizer J., 1999. Isotope stratigraphy of the European Carboniferous: proxy signals for ocean chemistry, climate and tectonics. Chemical Geology. 161(1-3), 127-163. Chang J., Qiu N., Zhao X., Xu W., Xu Q., Jin F., Han C., Ma X., Dong X., Liang X., 2016. Present-day geothermal regime of the Jizhong depression in Bohai Bay basin, East China. Chinese Journal of Geophysics. 59(3), 1003-1016.

515

Chen C., Mu C., Zhou K., Liang W., Ge X., Wang X., Wang Q., Zheng B., 2016. The geochemical characteristics and

516

factors controlling the organic matter accumulation of the Late Ordovician-Early Silurian black shale in the Upper

517

Yangtze Basin, South China. Marine and Petroleum Geology. 76, 159-175.

518 519 520 521

Chen H., Lu Z., Cao Z., Han J., Yun L., 2015. Hydrothermal alteration of Ordovician reservoir in northeastern slope of Tazhong uplift, Tarim Basin. Acta Petrolei Sinica. 37(1), 43-63. Chen M., Huang G., Wang J., Deng X., Wang J., 1984. A preliminary research on the geothermal characteristics in the Bohai sea. Scientia Geologica Sinica. 4, 392-401.

522

Chen S., 2008. Mineralogy petrology. China University of Petroleum Press, Shandong.

523

Cloetingh S., Wees J. D. V., Ziegler P. A., Lenkey L., Beekman F., Tesauro M., Förster A., Norden B., Kaban M.,

524

Hardebol N., Bonté D., Genter A., Guillou-Frottier L., Voorde M. T., Sokoutis D., Willingshofer E., Cornu T.,

525

Worum G., 2010. Lithosphere tectonics and thermo-mechanical properties: An integrated modelling approach for

526

Enhanced Geothermal Systems exploration in Europe. Earth-Science Reviews. 102(3-4), 159-206.

527 528

Columbu S., 2018. Petrographic and geochemical investigations on the volcanic rocks used in the punic-roman archaeological site of nora (sardinia, Italy). Environmental Earth Sciences. 77(16), 577.

529

Cui H., Guan P., Jian X., 2012. Magmatic hydrothermal fluids-formation water compound system and diagenetic

530

response of carbonate reservoir rocks in Northern Tarim Basin. Acta Scientiarum Naturalium Universitatis

531

Pekinensis. 48(3), 433-443.

15

532 533 534 535

Curtis C. D., Petrowski C., Oertel G., 1972. Stable carbon isotope ratios within carbonate concretions: a clue to place and time of formation. Nature. 235(5333), 98-100. Dai J., Song Y., Dai C., Wang D., 1996. Geochemistry and accumulation of carbon dioxide gases in China. AAPG Bulletin. 80(10), 1615-1626.

536

Dai J., Fu C., Guan D., 1997. New progress on natural gas. Petroleum Industry Press, Beijing.

537

Davies G. R., Smith L. B., 2006. Structurally controlled hydrothermal dolomite reservoir facies: An overview. AAPG

538 539 540

Bulletin. 90(11), 1641-1690. Denison R. E., Koepnick R. B., Burke W. H., Hetherington E. A., Fletcher A., 1994. Construction of the Mississippian, Pennsylvanian and Permian seawater 87Sr/86Sr curve. Chemical Geology. 112(1-2), 145-167.

541

Du Z., Xiao C., Liu Y., Yang J., Li C., 2017. Natural vs. anthropogenic sources supply aeolian dust to the Miaoergou

542

Glacier: Evidence from Sr–Pb isotopes in the eastern Tienshan ice core. Quaternary International. 430(Part B),

543

60-70.

544

Du Z., Xiao C., Dou T., Li S., An H., Liu S., Liu K., 2019. Comparison of Sr-Nd-Pb isotopes in insoluble dust between

545

northwestern China and high-latitude regions in the Northern Hemisphere. Atmospheric Environment. 214,

546

https://doi.org/10.1016/j.atmosenv.2019.116837.

547 548 549 550

Elderfield H., Sholkovitz E. R., 1987. Rare earth elements in the pore waters of reducing nearshore sediments. Earth and Planetary Science Letters. 82(3-4), 280-288. Emel’yanova, T. A., Lelikov E. P., 2016. Geochemistry and petrogenesis of the Late Mesozoic-Early Cenozoic volcanic rocks of the Okhotsk and Japan marginal seas. Geochemistry International. 54(6), 509-521.

551

Fall A., Eichhubl P., Cumella S. P., Bodnar R. J., Laubach S. E., Becker S. P., 2012. Testing the basin-centered gas

552

accumulation model using fluid inclusion observations: Southern Piceance Basin, Colorado. AAPG Bulletin. 96(12),

553

2297-2318.

554 555

Fang W., 2016. On tectonic system of hydrothermal breccia: Objective, methodology and lithofacies-mapping applications. Geotectonica et Metallogenia. 40(2), 237-265.

556

Fedorik J., Zwaan F., Schreurs G., Toscani G., Bonini L., Seno S., 2019. The interaction between strike-slip dominated

557

fault zones and thrust belt structures: Insights from 4D analogue models. Journal of Structural Geology. 122, 89-105.

558

Feng D., Chen D., Peckmann J., 2009. Rare earth elements in seep carbonates as tracers of variable redox conditions at

559

ancient hydrocarbon seeps. Terra Nova. 21, 49-56.

560

Florian D., Kerkhof A., Sosa G., Leiss B., Wiegand B., Vollbrecht A., Sauter M., 2016. Fluid inclusion and microfabric

561

studies on Zechstein carbonates (Ca2) and related fracture mineralizations-New insights on gas migration in the

562

Lower Saxony Basin (Germany). Marine and Petroleum Geology. 77, 300-322.

563

Fontana E., Mexias A. S., Renac C., Nardi L. V. S., Lopes R. W., Barats A., Gomes M. E. B., 2017. Hydrothermal

564

alteration of volcanic rocks in Seival Mine Cu-mineralization-Camaquã Basin-Brazil (part I): Chloritization process

565

and geochemical dispersion in alteration halos. Journal of Geochemical Exploration. 177, 45-60.

566 567

Franz S., George C. W., 1966. Temperature distribution in salt domes and surrounding sediments. Geophysics. 31(2), 346-361. 16

568 569

Frelinger S. N., Ledvina M. D., Kyle J. R., Zhao D., 2015. Scanning electron microscopy cathodoluminescence of quartz: Principles, techniques and applications in ore geology. Ore Geology Reviews. 65(4), 840-852.

570

Fyfe W. S., 1997. Deep fluids and volatile recycling: crust to mantle. Tectonophysics. 275(1), 243-251.

571

George S. C., 1992. Effect of igneous intrusion on the organic geochemistry of a siltstone and an oil shale horizon in the

572 573 574

Midland Valley of Scotland. Organic Geochemistry. 18(5), 705-723. Gong Z., Cai D., Zhang G., 2007. Dominating action of Tanlu Fault on hydrocarbon accumulation in eastern Bohai Sea area. Acta Petrolei Sinica. 28(4), 1-10.

575

Guo J., Zeng J., Song G., Zhang Y., Wang X., Meng W., 2014. Characteristics and origin of carbonate cements of

576

Shahejie Formation of central uplift belt in Dongying Depression. Earth Science-Journal of China University of

577

Geosciences. 39(5), 565-576.

578

Guo T., Yang B., Chen L., Yang H., Wang X., Liu Q., Tu X., 2016. 3D fine description of magmatic rocks: the

579

discovery of BZ34-9 oilfield in the southern slope of Huanghekou sag. China Offshore Oil and Gas. 28(2), 71-77.

580

Han Z., Yan B., Tang L., 2008. Tectonic evolution and volcanic activities of Bohai sea and its adjacent areas in

581 582 583 584 585

Meso-Cenozoic. Transactions of Oceanology and Limnology. (2), 30-36. Hao F., Zhou X., Zhu Y., Yang Y., 2009. Mechanisms for oil depletion and enrichment on the Shijiutuo uplift, Bohai Bay Basin, China. AAPG Bulletin. 93(8), 1015-1037. He J., Xia B., Liu B., Zhang S., 2005. Origin, migration and accumulation of CO2 in East China and offshore shelf basins. Petroleum Exploration and Development. 32(4), 42-49.

586

Himmler T., Haley B. A., Torres M. E., Klinkhammer G. P., Bohrmann G., Peckmann J., 2013. Rare earth element

587

geochemistry in cold-seep pore waters of Hydrate Ridge, northeast Pacific Ocean. Geo-Marine Letters. 33(5),

588

369-379.

589 590 591 592

Hu A., Dai J., Yang C., Zhou Q., Ni Y., 2009. Geochemical characteristics and distribution of CO2 gas fields in Bohai Bay Basin. Petroleum Exploration and Development. 36(2), 181-189. Hu J., Xu S., Tong X., 1986. Formation and distribution of complex petroleum accumulation zones in Bohaiwan Basin. Petroleum Exploration and Development. 13(1), 1-8.

593

Hu S., O’Sullivan P. B., Raza A., Kohn B. P., 2001. Thermal history and tectonic subsidence of the Bohai Basin,

594

northern China: a Cenozoic rifted and local pull-apart basin. Physics of the Earth and Planetary Interiors. 126,

595

221-235.

596

Hu T., Pang X., Jiang S., Wang Q., Zheng X., Ding X., Zhao Y., Zhu C., Li H., 2018. Oil content evaluation of

597

lacustrine organic-rich shale with strong heterogeneity: A case study of the Middle Permian Lucaogou Formation in

598

Jimusaer Sag, Junggar Basin, NW China. Fuel. 221, 196-205.

599 600

Hu W., 2016. Origin and indicators of deep-seated fluids in sedimentary basins. Bulletin of Mineralogy, Petrology and Geochemistry. 35(5), 817-826.

601

Hu Z., Zheng R., Hu J., Wen H., Li Y., Wen Q., Xu F., 2009. Geochemical characteristics of rare earth elements of

602

Huanglong Formation dolomites reservoirs in Eastern Sichuan-Northern Chongqing area. Acta Geologica Sinica.

603

83(6), 782-790. 17

604

Huang S., Huang K., Zhong Y., Li X., Mao X., Hu Z., Liu S., Zhang M., Wu W., 2017. Carbon isotope composition and

605

comparison of Lower Triassic marine carbonate rocks from Southern Longmenxia section in Guang’an, Sichuan

606

Basin. Science China Earth Sciences. 60(1), 80-94.

607 608 609 610 611 612 613 614 615 616

Jacquemyn C., Desouky H. E., Hunt D., Casini G., Swennen R., 2014. Dolomitization of the Latemar platform: Fluid flow and dolomite evolution. Marine and Petroleum Geology. 55, 43-67. Jenden P. D., Kaplan I. R., Roreda R., Craig H., 1988. Origin of nitrogen-rich gases in the California Great Valley: evidence from heileum carbon and nitrogen isotope ratios. Geochemica et Comochimica Acta. 52(4), 851-861. Jébrak M., 1997. Hydrothermal breccias in vein-type ore deposits: A review of mechanism, morphology and size distribution. Ore Geology Reviews. 12(3), 111-134. Ji Y., 2002. Characteristics and seismic interpretation of strike-slip faults in China offshore basins. China Offshore Oil and Gas (Geology). 16(5), 355-357. Jiang F., Pang X., Bai J., Zhou X., Li J., Guo Y., 2016. Comprehensive assessment of source rocks in the Bohai Sea area, eastern China. AAPG Bulletin. 100(6), 969-1002.

617

Jiang X., Liu L., Sun H., Huang S., Geng M., Chen S., Li N., Shen P., 2019. Differential distribution of high-quality

618

lacustrine source rocks controlled by climate and tectonics: a case study from Bozhong sag. Acta Petrolei Sinica.

619

40(2), 165-175.

620 621 622 623 624 625

Jiang Y., 1999. Characteristics and formation conditions of natural gas accumulation areas in Bohai Bay Basin. Journal of China University of Petroleum (Edition of Natural Sciences). 23(5), 9-13. Jin Q., Mao J., Du Y., Huang X., 2015. Fracture filling mechanisms in the carbonate buried-hill of Futai oilfield in Bohai Bay basin, East China. Petroleum Exploration and Development. 42(4), 454-462. Jin X., Liu X., Hao Y., Wang J., Wang F., 2019. Reformation of the volcanic hydrothermal fluid activities to the carbonate reservoir in CF Oilfield. Petroleum Geology and Oilfield Development in Daqing. 38(1), 42-50.

626

Jin Z., Zhang L., Yang L., Hu W., 2002. Primary study of geochemical features of deep fluids and their effectiveness on

627

oil/gas reservoir formation in sedimental basins. Earth Science-Journal of China University of Geosciences. 27(6),

628

659-665.

629 630

Jin Z., Zhang L., Yang L., Hu W., 2004. A preliminary study of mantle-derived fluids and their effects on oil/gas generation in sedimentary basins. Journal of Petroleum Science and Engineering. 41(1-3), 45-55.

631

Jin Z., Zhu D., Hu W., Zhang X., Wang Y., Yan X., 2006. Geological and geochemical signatures of hydrothermal

632

activity and their influence on carbonate reservoir beds in the Tarim Basin. Acta Geologica Sinica. 80(2), 245-253.

633

Jin Z., Zhu D., Meng Q., Hu W., 2013. Hydrothermal activites and influences on migration of oil and gas in Tarim Basin.

634

Acta Petrologica Sinica. 29(3), 1048-1058.

635

Joseph C., Torres M. E., Martin R. A., Haley B. A., Pohlman J. W., Riedel M., Rose K., 2012. Using the 87Sr/86Sr of

636

modern and paleoseep carbonates from northern Cascadia to link modern fluid flow to the past. Chemical Geology.

637

334, 122-130.

18

638

Kenis I., Muchez P., Sintubin M., Mansy J. L., Lacquement F., 2000. The use of a combined structural, stable isotope

639

and fluid inclusion study to constrain the kinematic history at the northern variscan front zone (bettrechies, northern

640

france). Journal of Structural Geology. 22(5), 589-602.

641 642

Klaucke I., Berndt C., Crutchley G., Chi W., Lin S., Muff S., 2016. Fluid venting and seepage at accretionary ridges: the Four Way Closure Ridge offshore SW Taiwan. Geo-Marine Letters. 36(3), 165-174.

643

Kolchugin A. N., Immenhauser A., Walter B. F., Morozov V. P., 2016. Diagenesis of the palaeo-oil-water transition

644

zone in a Lower Pennsylvanian carbonate reservoir: Constraints from cathodoluminescence microscopy,

645

microthermometry, and isotope geochemistry. Marine and Petroleum Geology. 72, 45-61.

646

Lai W., 2000. Gas exploration potential in Bohai Sea. China Offshore Oil and Gas. 14(3), 168-173.

647

Laird A. P., Morley C. K., 2011. Development of gas hydrates in a deep-water anticline based on attribute analysis from

648

three-dimensional seismic data. Geosphere. 7(1), 240-259.

649

Lan Y., Huang S., Ma Y., Zhou X., Wei Z., 2016. Genesis of negative carbon and oxygen isotopic composition of

650

carbonate rocks in Lower Miocene Zhujiang Formation, Pearl river mouth Basin. Geological Review. 62(4),

651

915-928.

652

Lavoie D., Chi G., Brennan-Alpert P., Desrochers A., Bertrand R., 2005. Hydrothermal dolomization in the Lower

653

Ordovician Romaine Formation of the Anticosti basin: Significance for hydrocarbon exploration. Bulletin of

654

Canadian Petroleum Geology. 53(4), 454-471.

655

Le Maitre, Bateman R. W., Dudek P., 1989. A classification of igneous rocks and glossary of terms. Recommendations

656

of the International Union of Geological Sciences Subcommission on tne Systematics of igneous rocks. Oxford:

657

Blackwell Scientific Publications. 700-750.

658 659 660 661 662 663 664 665 666 667 668 669

Li D., 1979. The tectonic framework of the petroliferous basins in the Bohai Bay. Petroleum Exploration and Development. 6(2), 51-62. Li D., Li R., Zhu Z., Wu X., Liu F., Zhao B., Wang B., 2018. Influence on lacustrine source rock by hydrothermal fluid: a case study of the Chang 7 oil shale, southern Ordos Basin. Acta Geochimica. 37(2), 215-227. Li J., Zou H., Zhou X., Wei G., Zhuang X., Tian J., 2012. Carbon dioxide origin and the main controls over its distribution in Bohai sea. China Offshore Oil and Gas. 24(2), 19-22. Li R., Duan L., Chen B., Xia B., Li J., 2012. Albitization and hydrothermal diagenesis of Yanchang oil sandstone reservoir, Ordos Basin. Acta Petrologica Et Mineralogica. 31(2), 173-180. Li S., Suo Y., Dai L., Liu L., Jin C., Liu X., Hao T., Zhou L., Liu B., Zhou J., Jiao Q., 2010. Development of the Bohai Bay Basin and destruction of the North China Craton. Earth Science Frontiers. 17(4), 64-89. Li Z., 2016. Research frontiers of fluid-rock interaction and oil-gas formation in deep-buried basins. Bulletin of Mineralogy, Petrology and Geochemistry. 35(5), 807-816.

670

Liang H., Xu F., Xu G., Yuan H., Huang S., Wang Y., Wang L., Fu D., 2019. Geochemical characteristics and origins of

671

the diagenetic fluids of the Permian Changxing Formation calcites in the Southeastern Sichuan Basin: Evidence from

672

petrography, inclusions and Sr, C and O isotopes. Marine and Petroleum Geology. 103, 564-580.

19

673 674 675 676 677 678 679 680

Lin S., Gong Y., 2005. Distribution characteristics of geotemperature field in Jizhong depression, North China. Journal of East China Institute of Technology. 28(4), 359-364. Liu J., Liu Q., Zhu D., Meng Q., Liu W., Qiu D., Huang Z., 2018. The role of deep fluid in the formation of organic-rich source rocks. Natural Gas Geoscience. 29(2), 168-177. Liu P., Zhou M., Wang C., Xing C., Gao J., 2014. Open magma chamber processes in the formation of the Permian Baima mafic-ultramafic layered intrusion, SW China. Lithos. 184-187, 194-208. Liu Q., Zhu D., Meng Q., Liu J., Wu X., Zhou B., Fu Q., Jin Z., 2019. The scientific connotation of oil and gas formations under deep fluids and organic-inorganic interaction. Science China Earth Sciences. 62, 507-528.

681

Liu S., Huang W., Chen C., Zhang C., Li J., Dai S., Qin C., 2008. Primary study on hydrothermal fluids activities and

682

their effectiveness on petroleum and mineral accumulation of Sinian System-Palaeozoic in Sichuan Basin. Journal of

683

Mineralogy and Petrology. 28(3), 41-50.

684

Longstaffe F. J., Calvo R., Ayalon A., Donaldson A., 2003. Stable isotope evidence for multiple fluid regimes during

685

carbonate cementation of the Upper Tertiary Hazeva Formation, Dead Sea Graben, southern Israel. Journal of

686

Geochemical Exploration. 80(2-3), 151-170.

687

Lopes R. W., Renac C., Mexias A. S., Nardi L. V. S., Fontana E., Gomes M. E. B., Barats A., 2019. Mineral

688

assemblages and temperature associated with Cu enrichment in the Seival area (Neoproterozoic Camaquã Basin of

689

Southern Brazil). Journal of Geochemical Exploration. 201, 56-70.

690

Lüders V., Plessen B., Primio R. D., 2012. Stable carbon isotopic ratios of CH4-CO2-bearing fluid inclusions in

691

fracture-fill mineralization from the Lower Saxony Basin (Germany)-A tool for tracing gas sources and maturity.

692

Marine and Petroleum Geology. 30(1), 174-183.

693

McArthur J. M., Burnett J., Hancock J. M., 1992. Strontium isotopes at K/T boundary. Nature. 355(6355), 28-28.

694

McCrea J. M., 1950. On the isotopic chemistry of carbonates and a palaeotemperature scale. Journal of Chemical

695 696 697 698 699

Physics. 18, 849-857. Mills R. A., Elderfield H., 1995. Rare earth element geochemistry of hydrothermal deposits from the active TAG Mound, 26°N Mid-Atlantic Ridge. Geochimica et Cosmochimica Acta. 59(17), 3511-3524. Murchison D. G., Raymond A. C., 1989. Igneous activity and organic maturation in the Midland Valley of Scotland. International Journal of Coal Geology. 14(1-2), 47-82.

700

Nomura S. F., Sawakuchi A. O., Bello R. M. S., Méndez-Duque J., Fuzikawa K., Giannini P. C. F., Dantas M. S. S.,

701

2014. Paleotemperatures and paleofluids recorded in fluid inclusions from calcite veins from the northern flank of

702

the Ponta Grossa dyke swarm: Implications for hydrocarbon generation and migration in the Paraná Basin. Marine

703

and Petroleum Geology. 52, 107-124.

704 705 706 707

Palmer M. R., Elderfield H., 1985. Sr isotope composition of sea water over the past 75 Myr. Nature. 314(6011), 526-528. Palmer M. R., Edmond J. M., 1989. The strontium isotope budget of the modern ocean. Earth & Planetary Science Letters. 92(1), 11-26.

20

708

Permanyer A., Martín-Martín J. D., Kihle J., Márquez G., Marfil R., 2018. Oil shows geochemistry and fluid inclusion

709

thermometry of Mid Cretaceous carbonates from the eastern Basque Cantabrian Basin (N Spain). Marine and

710

Petroleum Geology. 92, 255-269.

711 712 713 714 715 716 717 718 719 720

Peter D., 1977. On the oxygen isotope distribution among mineral triplets in igneous and metamorphic rocks. Geochimica et Cosmochimica Acta. 41(12), 1709-1730. Qi J., Yang Q., 2010. Cenozoic structural deformation and dynamic processes of the Bohai Bay basin province, China. Marine and Petroleum Geology. 27, 757-771. Qi J., Zhang Y., Lu K., Yang Q., 1995. Cenozoic tectonic evolution in Bohai Bay Basin province. Journal of China University of Petroleum (Edition of Natural Sciences). 19(S1), 1-6. Qi J., Zhou X., Wang Q., 2010. Structural model and Cenozoic kinematics of Tan-Lu deep fracture zone in Bohai Sea area. Geology in China. 37(5), 1231-1242. Qin X., Li R., Xi S., Yang T., Cheng J., Zhao B., Wang N., 2017. Hydrothermal alteration and its influence on quality of the Upper Palaeozoic gas reservoirs in eastern Ordos Basin. Natural Gas Geoscience. 28(1), 43-51.

721

Rebelo A. C., Meireles R. P., Barbin V., Neto A. I., Melo C., Ávila S. P., 2016. Diagenetic history of lower Pliocene

722

rhodoliths of the Azores Archipelago (NE Atlantic): Application of cathodoluminescence techniques. Micron. 80,

723

112-121.

724

Scheck-Wenderoth M., Cacace M., Maystrenko Y. P., Cherubini Y., Noack V., Kaiser B. O., Sippel J., Björn L., 2014.

725

Models of heat transport in the Central European Basin System: Effective mechanisms at different scales. Marine

726

and Petroleum Geology. 55, 315-331.

727

Shen W., Xu S., Wang R., Lu J., Yin H., Liao Y., Zhang L., 1998. The study on the isotopic characters and the origin of

728

the CO2-rich gas deposits of Jiyang depression. Journal of Nanjing University (Natural Sciences). 34(3), 308-313.

729

Shu X., Zhang J., Li G., Long S., Wu S., Li H., 2012. Characteristics and genesis of hydrothermal dolomites of Qixia

730

and Maokou Formations in northern Sichuan Basin. Oil & Gas Geology. 33(3), 442-448.

731

Slobodník M., Melichar R., Hurai V., Bakker R. J., 2012. Litho-stratigraphic effect on Variscan fluid flow within the

732

Prague synform, Barrandian: Evidence based on C, O, Sr isotopes and fluid inclusions. Marine and Petroleum

733

Geology. 35, 128-138.

734 735 736 737 738 739 740 741 742 743

Smith L. B., 2006. Origin and reservoir characteristics of Upper Ordovician Trenton-Black River hydrothermal dolomite reservoirs in New York. AAPG Bulletin. 90(11), 1691-1718. Song H., 1999. Characteristics of Yanshan type intraplate orogenic belts and a discussion on its dynamics. Earth Science Frontiers. 6(4), 309-316. Spencer R. J., 1987. Origin of Ca-Cl brines in Devonian formations, western Canada sedimentary basin. Applied Geochemistry. 2(4), 373-384. Stoffregen R. E., 1987. Genesis of acid-sulfate alteration and Au-Cu-Ag mineralization at Summitville, Colorado. Economic Geology. 82(6), 1575-1591. Suess E., Whiticar J. M., 1989. Methane-derived CO2 in pore fluids expelled from the Oregon subduction zone. Palaeogeography, Palaeoclimatology, Palaeoecology. 71(1-2), 119-136. 21

744 745 746 747 748 749

Sun S., Mcdonough W. F., 1989. Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processes. Geological Society of London Special Publications. 42, 313-345. Sun Y., Qi J., Lü Y., Han H., 2008. Characteristics of fault structure and its control to hydrocarbon in Bozhong Depression. Acta Petrolei Sinica. 29(5), 669-675. Teng C., Zou H., Hao F., 2014. Control of differential tectonic evolution on petroleum occurrence in Bohai Bay Basin. Science China Earth Sciences. 44, 579-590.

750

Tian J., Hao F., Zhou X., Zou H., Peng B., 2017. Hydrocarbon generating potential and accumulation contribution of the

751

fourth member of the Shahejie Formation in the Liaodong Bay sub-basin, Bohai Bay basin. Marine and Petroleum

752

Geology. 82, 388-398.

753

Troise C., Natale G. D., Schiavone R., Somma R., Moretti R., 2019. The Campi Flegrei caldera unrest: Discriminating

754

magma intrusions from hydrothermal effects and implications for possible evolution. Earth-Science Reviews. 188,

755

108-122.

756

Noten K. V., Muchez P., Sintubin M., 2011. Stress-state evolution of the brittle upper crust during compressional

757

tectonic inversion as defined by successive quartz vein types (High-Ardenne slate belt, Germany). Journal of the

758

Geological Society. 168(2), 407-422.

759

Wang D., Luo J., Chen S., Hu H., Ma Y., Li C., Liu B., Chen L., 2017. Carbonate cementation and origin analysis of

760

deep sandstone reservoirs in the Baiyun Sag, Pearl river mouth Basin. Acta Geologica Sinica. 91(9), 2079-2090.

761

Wang D., Zhang Y., 2001. A study on the origin of the carbonate cements within reservoirs in the external metamorphic

762

belt of the Bohai Bay oil-gas bearing region. Petroleum Exploration and Development. 28(2), 40-42.

763

Wang Q., Liu L., Niu C., Zang C., Hao Y., Liu X., Feng C., Pang X., 2019. The geological evidences and impacts of

764

deep thermal fluid on lacustrine carbonate reservoir in the actic area of the north part of Bozhong Depression, Bohai

765

Bay basin. Earth Science. 44(8), 2751-2760.

766

Wang Q., Tong H., Huang C., Chen D., 2018. Tracing fluid sources and formation conditions of Miocene

767

hydrocarbon-seep carbonates in the central Western Foothills, Central Taiwan. Journal of Asian Earth Sciences. 168,

768

186-196.

769

Wang Q., Zang C., Zhu W., Zhao G., Yuan Z., Feng C., 2012. The impact of mantle source CO2 on clay minerals of

770

clastic reservoirs in the east part of Shijiutuo symon fault, Bozhong depression. Acta Petrologica Et Mineralogica.

771

31(5), 674-680.

772

Wang Q., Zou H., Hao F., Zhou X., Teng C., Sun Z., Xu S., Tian J., Guo L., 2016. Petroleum charge and entrapment

773

along active faults: Study of the accumulation mechanism of the Qinhuangdao 29 oil field on the slope of the

774

Shijiutuo uplift, Bohai Sea. AAPG Bulletin. 100(10), 1541-1560.

775 776

Wang Y., Hu S., Nie D., Zhang K., Jiang G., Wang Z., 2019. Is the Tan-Lu fault zone a thermal anomaly belt: Constraints from heat flow in its southern section. Chinese Journal of Geophysics. 62(8), 3078-3094.

777

Wei C., Yan Z., Huang Z., Hu Y., 2018. Geochemical characteristics of the hydrothermal dolomite from the Nayongzhi

778

deposit, Northwestern Guizhou, China and their prospecting indication. Acta Mineralogica Sinica. 38(6), 666-674.

22

779

Wu M., Wang Y., Zheng M., Zhang W., Liu C., 2007. The hydrothermal karstification and its effect on Ordovician

780

carbonate reservoir in Tazhong uplift of Tarim Basin, Northwest China. Science China Earth Sciences. 50(S2),

781

103-113.

782 783 784 785 786 787 788 789

Wu X., Zhou J., 2000. The anatomy about the tectonic cause of formation of Bohaiwan Basin. Progress in Geophysics. 15(1), 98-107. Wu Z., Hou X., Li W., 2007. Discussion on Mesozoic Basins patterns and evolution in the eastern north China Block. Geotectonica et Metallogenia. 31(4), 385-399. Xiao S., Lü D., Hou M., Hu H., Huang Z., 2019. Mesozoic tectonic evolution and buried hill formation mechanism in the southwestern Bohai Sea. Natural Gas Industry. 39(5), 34-44. Xie Y., Zhang G., Shen P., Liu L., Huang S., Chen S., Yang S., 2018. Formation conditions and exploration direction of large gas field in Bozhong sag of Bohai Bay Basin. Acta Petrolei Sinica. 39(11), 1199-1210.

790

Xiong L., Gao W., 1982. Characteristics of geotherm in uplift and depression. Acta Geophysica Sinica. 25(5), 448-456.

791

Xiong L., Zhang J., 1984. Mathematical simulation of refract and redistribution of heat flow. Scientia Geologica Sinica.

792 793 794 795 796 797 798

4, 445-454. Xu C., Yu H., Wang J., Liu X., 2019. Formation conditions and accumulation characteristics of Bozhong 19-6 large condensate gas field in offshore Bohai Bay Basin. Petroleum Exploration and Development. 46(1), 25-38. Xu H., Xiong L., Wang J., 2000. Mathematical models of relation between reservoir temperatures and vertical fluid flows. Geological Review. 46(S1), 266-268. Xu J., Zhou B., Ji F., Gao X., Lü Y., Wang M., Chen G., 2011. A primary study on the neotectonic pattern of the Bohai area in China. Acta Petrolei Sinica. 32(3), 442-449.

799

Xu S., Hao F., Xu C., Zou H., Quan Y., 2016. Oil migration through preferential petroleum migration pathway (PPMP)

800

and polycyclic faults: A case study from the Shijiutuo Uplift, Bohai Bay basin, China. Marine and Petroleum

801

Geology. 73, 539-553.

802 803 804 805

Xue Y., 2018. The “catchment ridge” model of hydrocarbon migration in Bohai Sea and its control on Neogene hydrocarbon accumulation. Acta Petrolei Sinica. 39(9), 963-970, 1005. Yamada Y., Baba K., Miyakawa A., Matsuoka T., 2014. Granular experiments of thrust wedges: Insights relevant to methane hydrate exploration at the Nankai accretionary prism. Marine and Petroleum Geology. 51, 34-48.

806

Yang C., 2004. Study on the genesis of CO2 in Huanghua depression. Natural Gas Geoscience. 15(1), 7-11.

807

Yang Y., Li Y., 2012. The geochemical characteristics and distribution of source rocks of the Bozhong Sag in the Bohai

808 809 810

Bay basin. Journal of Mineralogy and Petrology. 32(4), 65-72. Yu F., Qi J., Wang C., 2002. Tectonic deformation of Indosinian Period in eastern part of North China. Journal of China University of Mining & Technology. 31(4), 402-406.

811

Zanon V., Viveiros F., 2019. A multi-methodological re-evaluation of the volcanic events during the 1580 CE and 1808

812

eruptions at São Jorge Island (Azores Archipelago, Portugal). Journal of Volcanology and Geothermal Research. 373,

813

51-67.

23

814

Zhang J., Hu W., Qian Y., Wang X., Zhu J., Zhang H., Su J., Wu S., 2008. Feature and origin of dolomite filling in the

815

Upper Cambrian-Lower Ordovician dolostone of the central uplift, Tarim Basin. Acta Sedimentologica Sinica. 26(6),

816

957-966.

817 818

Zhang M., Wang X., Liu G., Li L., 1999. The composition of the fluids in alkali basalts and mantle-derived xenoliths in eastern China. Acta Geologica Sinica. 73(2), 162-166.

819

Zhang Y., Chang J., Liu N., Liu J., Ma X., Zhao S., Shen F., Zhou Y., 2017. Present-day temperature-pressure field and

820

its implications for the geothermal resources development in the Baxian area, Jizhong depression of the Bohai Bay

821

basin. Natural Gas Industry. 37(10), 118-126.

822

Zhao J., Jin Z., Jin Z., Geng Y., Wen X., Yan C., 2016. Applying sedimentary geochemical proxies for

823

paleoenvironment interpretation of organic-rich shale deposition in the Sichuan Basin, China. International Journal

824

of Coal Geology. 163, 52-71.

825

Zhao Z., Zhao J., Ren H., Li J., Wu W., 2018. Characterization and formation mechanisms of fractures and their

826

significance to hydrocarbon accumulation: A case study of the Lower Ordovician mid-assemblage Formations in the

827

central Ordos Basin, China. Journal of Central South University. 25(11), 2766-2784.

828 829

Zheng L., Feng Z., Xu S., Liao Y., 1997. Genesis of the non-hydrocarbon gas reservoir (CO2, He) in Jiyang depression. Journal of Nanjing University (Natural Sciences). 33(1), 76-81.

830

Zheng Y., Chen J., 2000. Stable isotope geochemistry. Science Press, Beijing.

831

Zhou L., Li S., Liu J., Gao Z., 2003. The Yanshanian structural style and basin prototypes of the Mesozoic Bohai Bay

832 833 834 835 836 837 838

Basin. Progress in Geophysics. 18(4), 692-699. Zhou X., Zhang X., Niu C., Liu H., Huang J., 2019. Growth of strike-slip zone in the southern Bohai Bay Basin and its significances for hydrocarbon accumulation. Oil & Gas Geology. 40(2), 215-222. Zhu D., Jin Z., Hu W., Zhang X., 2008. Effects of deep fluid on carbonates reservoir in Tarim Basin. Geological Review. 54(3), 348-354. Zhu D., Meng Q., Hu W., Jin Z., 2013. Differences between fluid activities in the Central and North Tarim Basin. Geochimica. 42(1), 82-94.

839

Zhu H., Liu Y., Wang Y., Zhou X., Yang X., 2014. Volcanic eruption phases and 3-D characterization of volcanic rocks

840

in BZ34-9 block of Huanghekou Sag, Bohai Bay basin. Earth Science-Journal of China University of Geosciences.

841

39(9), 1309-1316.

842

Zhu W., 2009. Hydrocarbon accumulation and exploration in Bohai Sea. Science Press, Beijing.

843

Zhu W., Mi L., 2010. Atlas of oil and gas basins, China Sea. Petroleum Industry Press, Beijing.

844

Zou H., Gong Z., Teng C., Zhuang X., 2011. Late-stage rapid accumulation of the PL19-3 giant oilfield in an active fault

845

zone during Neotectonism in the Bozhong depression, Bohai Bay. Science China Earth Sciences. 54, 388-398.

846

Zwicker J., Smrzka D., Himmler T., Monien P., Gier S., Goedert J. L., Peckmann J., 2018. Rare earth elements as tracers

847

for microbial activity and early diagenesis: a new perspective from carbonate cements of ancient methane-seep

848

deposits. Chemical Geology. 501, 77-85.

849 24

850 851 852

853 854

Fig. 1. Distribution of sags and lower uplifts and main oil and gas fields in the Bozhong Sag.

855

25

856 857 858

859 860

Fig. 2. Stratigraphic column with the dominant lithology, tectonic events, possible source rocks, and producing reservoir

861

horizons in the Bozhong Sag. Stratigraphic nomenclature is from Hao et al. (2009). Ar. = Archean; E1 = Paleocene;

862

Fm = Formation; N2 = Pliocene; Pre. = Precambrian; Prot. = Proterozoic; PY = Pingyuan.

863

26

864 865 866 1 cm

Q

(a)

2 cm

C

HBr TFa

867

(b)

868

Fig. 3. Core-scale fractures and petrographic assemblage characteristics in the Bozhong Sag. (a) A7, 4685.1m, Archean,

869

metamorphic rocks, the fracture is filled with quartz and the unfilled part is occupied by solid bitumen; (b) A8, 3026.3m,

870

Ordovician, gray dolomite, the mutual cutting fractures are filled with calcite, and the unfilled portion is occupied by oil.

871

Thermal fading (TFa) and hydrothermal breccia (HBr) are observed around the fractures. C = calcite; Q = quartz.

872

27

873 874 875

876 877

Fig. 4. Microscopic characteristics of petrographic assemblages of deep reservoirs in the Bozhong Sag. (a) Thin section

878

of Tr, (b) Re, and (c) Cl, A10, 4429.8m, Archean, Ap, C, plus Py are filled with the fractures; (d) Thin section of Tr,

879

A13, 4361.6m, O, hydrothermal breccia (HBr) are observed around the fractures being filled with the calcite; (e) Thin

880

section of Tr, A12, 2738.4m, Pt/Ar, An plus Q are filled with the fractures; (f) Thin section of Re, A13, 3188.5m, Є, Py

881

is filled with the fractures; (g) Thin section of Tr, A4, 4421m, Archean, An plus Py are filled with the fracture-pore; (h)

882

Thin section of SEM, A4, 4610.1m, Archean, the authigenic albite is found in the dissolution pore of K-feldspar; (i) Thin

883

section of SEM, A3, 3815.1m, E1-2k2, the authigenic quartz, filamentous illite, and velvet pyrite are filled in the ankerite.

884

An = ankerite; Ap = apatite; Ar = Archean; C = calcite; Cl = cathode luminescence; E1-2k2 = the second member of the

885

Kongdian Formation; O = Ordovician; Pt = Proterozoic; Py = pyrite; Q = quartz; Re = reflection light; SEM = scanning

886

electron microscope; Tr = transmission light; Є = Cambrian.

887

28

888 889 890

891 892

Fig. 5. (a) K2O-SiO2 and (b) (Na2O+K2O)-SiO2 diagrams in Mesozoic volcanic rocks of the Bozhong Sag. Rock type

893

boundaries are from Le Maitre et al. (1989). A = picrobasalt; B = foidite; C1 = tephrite (G1 < 10%) and basanite (G1 >

894

10%); C2 = phonotephrite; C3 = tephriphonolite; D = trachyte and trachydacite; E1 = trachybasalt; E2 = basaltic

895

trachyandesite; E3 = trachyandesite; F = basalt; G1 = basaltic andesite; G2 = andesite; G3 = dacite; H = rhyolite.

896 897

29

898 899 900 1000

1000

(b)

Csample/Cchondrite

Csample/Cchondrite

(a)

100

100

10

1

1 La

901

10

Ce

Pr

Nd Sm Eu Gd Tb

REE

Dy Ho

Er Tm Yb Lu

Cs

U Ba

La Nb

Hf Sr

Dy Eu

Lu Y

Th Rb

Ce Ta

Nd Pr

Sm Zr

Yb Tb

REE

902

Fig. 6. (a) Chondrite-normalized REE distribution pattern and (b) primitive-mantle normalized trace elements spider

903

diagram in Mesozoic volcanic rocks of the Bozhong Sag. REE = rare earth element. Csample = content of sample;

904

Cchondrite = content of chondrite; Normalization values are from Sun and MacDonough (1989).

905

30

906 907 908 (b)

(a)

171.2 aq 121.9

200µm

178.3 221.3 o

200µm

o

o

40µm

20µm

(c)

(d)

800µm

g

127.0

142.5 143.9 aq

aq

156.7 155.8

153.2 aq

aq

o

aq

178.2 aq

g

909

20µm

40µm

910

Fig. 7. Photomicrographs of the petrographic characteristics of fluid inclusions in the typical structural blocks of the

911

Bozhong Sag taken at room temperature (21 °C). (a) Single-phase oil (o) fluid inclusions (Th = 178.3 °C, 221.3 °C) in

912

the quartz veins; (b) Coexisting two-phase aqueous (aq) (Th = 121.9 °C) and single-phase oil (o) fluid inclusions (Th =

913

171.2 °C) in the calcite veins; (c) Coexisting two-phase aqueous (aq) (Th = 142.5 °C, 143.9 °C, 153.2 °C) and

914

single-phase oil (o) fluid inclusions (Th = 127.0 °C) in the feldspathic grains; (d) Coexisting two-phase aqueous (aq) (Th

915

= 155.8 °C, 156.7 °C, 178.2 °C) and single-phase gas (g) fluid inclusions in the quartz grains.

916

31

917 918 919 250

20

(a)

(c) E3d2

Es

Ek

Pt/Ar

E3d2

15

Frequency

Frequency

200

150

N = 699

100

Pt/Ar

Pre.

10

N = 71 5

50

0

100

110

120

130

140

150

160

170

180

Homogenization temperature, Th/℃ ℃

190

200 ＞ 200

30

0 100

110

120

130

140

150

160

170

180

Homogenization temperature, Th/℃ ℃

190

200 ＞ 200

70

(b) 25

E3d2

Es

(d)

60

O

Es

E3d2

20 15

N = 159

Frequency

Frequency

50 40

N = 211 30

10 20 5 0

10

40 50 60 70

920

80 90 100 110 120 130 140 150 160 170 180 190 200 ＞200

Homogenization temperature, Th/℃ ℃

0

70

80

90

100 110 120 130 140 150 160 170 180 190 200 ＞200

Homogenization temperature, Th/℃ ℃

921

Fig. 8. Histogram of homogenization temperature (Th) of secondary inclusions in the typical tectonic blocks of (a)

922

BZ-19, (b) BZ-21, (c) CFD-18, (d) QHD-36. E3d2 = the second member of the Dongying Formation; Es = the

923

Shahejie Formation; Ek = the Kongdian Formation; Pt/Ar = Proterozoic/Archean; Pre. = Precambrian. N = number

924

of samples.

925

32

926 927 928

929 930 931

13

18

Fig. 9. δ C-δ O of fracture-filled calcite and surrounding rocks in the typical tectonic blocks in the Bozhong Sag. Base map is from Wang and Zhang (2001).

932

33

933 934 935 0.722

(a)

(b)

CFD18

Calcite fillings in the fractures BZ21

0.718

87Sr/86Sr

Calcite fillings in the surrounding rocks

0.714

BZ29

0.710

Calcite fillings in the fractures(BZ21) Calcite fillings in the fractures(BZ29) Calcite fillings in the fractures(CFD18) Calcite fillings in the surrounding rocks

0.706 0.700

936 937

0.705

0.710

0.715

0.720

87Sr/86Sr

Fig. 10. (a)

87

0.725

-30

-25

-20

-15

δ 18O/‰, PDB

-10

-5

Sr/86Sr values and (b) cross-plot of Sr and O isotopes of the typical tectonic blocks in the Bozhong Sag.

938

The light gray area is the seawater

939

Bruckschen, et al. (1999)).

87

Sr/86Sr value of the Ordovician (87Sr/86Sr value of the Ordovician is from

940

34

941 942 943

944 945

Fig. 11. (a) CO2-δ13CCO2 and (b) δ13CCO2-R/Ra diagram showing the CO2 origin in the offshore area of the Bohai Bay

946

basin (7 data points of the Liaodong uplift and 1 data point of the Laizhou Bay Sag are from Li et al. (2012); 21 data

947

points of the Huanghua Sag and the Jiyang Sag of the Bohai Bay basin from Li et al. (2012), that all were compared with

948

this study). Base map (a) is from Dai et al. (1997) and that (b) is from He et al. (2005).

949

35

950 951 952

953 954

Fig. 12. A cross sectional model illustrating the dynamics of the Bohai Bay basin during the Cenozoic and diapirism of

955

magma while the hot mantle upwelling. (a) Sectional sketch map of dynamics during the Cenozoic (see AA’ in Fig.

956

1 for location). (b) Relationship between brittle extension in the upper crust and ductile extension in the lower crust

957

and upper mantle (modified from Qi and Yang, 2010).

958

36

959 960 961

962 963 964

Fig. 13. Schematic diagram of the structural evolution history of the typical section in the Bozhong Sag (see BB’ in Fig. 1 for location). (modified from Xu et al., 2019).

965

37

966 967 968

969 970 971

Fig. 14. Schematic illustration showing the deep fluid activity pattern of the Bozhong Sag. TFa = thermal fading; HBr = hydrothermal breccia.

972

38

973 974 975 976

Table 1. Compositions and isotopic characteristics of CO2-rich oil/gas fields from the Bohai Bay basin. R is the 3He/4He

977

of the sample, and Ra is the 3He/4He of the atmospheric standard. Fm = Formation; Ra = 1.400×10-6; Nd = no data; O =

978

Ordovician. Sag Huanghua

Oil/gas field ZhaiZhuangzi

Pingfangwang

Well

Fm

CO2

δ13CCO2

(%)

(‰)

Depth(m)

3

He/4He

R/Ra

Reference Yang(2004)

G-151

E3s1

1632.0-1639.0

98.61

-3.77

Nd

3.62

B4-6-6

E2s4

1469.7-1481.0

72.50

-4.57

3.87

2.76

B4-13-1

E2s4

1453.0-1455.0

72.68

-5.08

3.87

2.76

PQ-12

E2s4

1470.5-1498.0

74.20

-4.36

3.56

2.75

Shen et

P12-61

E2s4

1452.4-1487.6

79.17

-4.50

3.61

2.58

al.(1998); Hu

P13-2

E2s4

1453.6-1483.2

68.85

-4.74

3.59

2.56

et al. (2009)

P13-4

E2s4

1450.8-1486.4

74.92

-4.43

3.55

2.54

P14-3

E2s4

1467.0-1484.6

77.93

-4.32

4.47

3.19

PQ-4

E2s4

1459.4-1474.5

75.33

-4.52

Nd

2.75

P9-3

E2s4

1462.6-1489.2

73.87

-4.47

Nd

2.76

BG-14

O

1980.2-2250.0

96.99

-4.76

Nd

2.00

BG-24

O

Nd

74.65

-4.64

Nd

3.73

H-17

E2s3

1965.1-1980

93.78

-3.41

4.45

3.18

H-17

E2s3

2000.0-2009.6

93.54

-3.35

4.49

3.21

Jiyang Hu et al. Pingnan

(2009)

Huagou

Shen et al.(1998) Dai et al.

Gaoqing

GQ-3

N1g

833.4-834.8

94.35

-4.41

Nd

4.47 (1996) Zhou et al.

BZ21

A-1

O

Nd

48.92

-3.20

Nd

6.41 (2017)

Bozhong

PL19-3-A1

N1g

PL19-3-A2

N1g

QHD29-2-1 QHD29-2-1

1128.5-1150.0

6.74

12.50

Nd

Nd

1349.0-1380.7

39.75

1.70

Nd

Nd

Li et al.

E3s2

3301.0-3308.0

26.83

-5.06

6.21

4.44

(2012)

E3s1

3195.0-3218.0

89.06

-5.92

5.49

3.92

PL19-3

QHD29-2

979

39

980




Petrography and geochemistry data revealed deep fluids migration in the Bozhong Sag.

981




Tectonic background and diapirism of magma laied an improved deep fluids source.

982




983




Multi-stage evolution of deep faults provide a better pathways for upward fluids migration. Tracing of deep fluids may contribute to efficient exploration of natural gas.

40




Petrography and geochemistry data revealed deep fluids migration in the Bozhong Sag.




Tectonic background and diapirism of magma laied an improved deep fluids source.





Multi-stage evolution of deep faults provide a better pathways for upward fluids migration. Tracing of deep fluids may contribute to efficient exploration of natural gas.

1

Contributions Zhao Z. with Wang Z. conceived this study and estimated the sources and migration pathways of deep fluids. Zhao Z. led writing the manuscript. Xiao S., Zhu L. and Gao X. helped perform the analysis with constructive discussions. Wang D. and Wang F. contributed to the petrographic observations and the analysis of δ13C, δ18O, and 87

Sr/86Sr data. All authors contributed to the writing and discussion of the science.

November 27, 2019 Qinhong Hu, Professor; Tiago Alves, PhD Editor; Associate Editor Marine and Petroleum Geology Dear Editors: I wish to submit an Article for publication in Marine and Petroleum Geology, titled “Tracing deep fluids in the Bozhong Sag: Evidence from integrated petrography and geochemistry data.” The paper was coauthored by Zilong Zhao, Deying Wang, Feilong Wang, Shengdong Xiao, Liwen Zhu, and Xuhui Gao. This study reports on a detailed investigation of the sources and migration pathways of deep fluids in the Bozhong Sag using petrography, fluid inclusions, and δ13C, δ18O, and 87Sr/86Sr data. Our study leads on from the discovery of the Bozhong 19-6 gas field, which indicated that the Bozhong Sag has great potential for natural gas exploration. We believe that our study makes a significant contribution to the literature because we conclude that the deep fluid activity pattern in the Bozhong Sag was mainly derived from deep material in the upper mantle, and that central and fissure-type wide-area eruption activities took place. Further, we believe that this paper will be of interest to the readership of your journal because we address a major residual question regarding how sapropelic source rocks might generate largescale natural gas. This manuscript has not been published or presented elsewhere in part or in entirety and is not under consideration by another journal. We have read and understood your journal’s policies, and we believe that neither the manuscript nor the study violates any of these. There are no conflicts of interest to declare. Thank you for your consideration. I look forward to hearing from you. Sincerely, Zhenliang Wang Department of Geology, Northwest University, 229 North Taibai Road, Xi’an, Shaanxi 710069 15249236734 [email protected] (Z. Wang)