Heat flow study of the Emeishan large igneous province region: Implications for the geodynamics of the Emeishan mantle plume

Accepted Manuscript Heat flow study of the Emeishan large igneous province region: Implications for the geodynamics of the Emeishan mantle plume

Qiang Jiang, Nansheng Qiu, Chuanqing Zhu PII: DOI: Reference:

S0040-1951(17)30530-9 https://doi.org/10.1016/j.tecto.2017.12.027 TECTO 127734

To appear in:

Tectonophysics

Received date: Revised date: Accepted date:

11 July 2017 27 December 2017 29 December 2017

Please cite this article as: Qiang Jiang, Nansheng Qiu, Chuanqing Zhu , Heat flow study of the Emeishan large igneous province region: Implications for the geodynamics of the Emeishan mantle plume. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Tecto(2017), https://doi.org/ 10.1016/j.tecto.2017.12.027

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ACCEPTED MANUSCRIPT Heat flow study of the Emeishan large igneous province region: Implications for the geodynamics of the Emeishan mantle plume

Qiang Jiang1, 2, Nansheng Qiu1, 2*, Chuanqing Zhu1, 2

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1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum,

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Beijing, China.

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2. Research Centre for Basin and Reservoir, China University of Petroleum, Beijing, China.

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*Corresponding author: Nansheng Qiu ([email protected])

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Abstract

The Emeishan large igneous province (ELIP) is widely considered to be a

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consequence of a mantle plume. The supporting evidence includes rapid emplacement,

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voluminous flood basalt eruptions, and high mantle potential temperature estimates. Several studies have suggested that there was surface uplift prior to the eruption of the

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Emeishan flood basalts. Additionally, the plume’s lateral extent is hard to constrain

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and has been variously estimated to be 800–1400 km in diameter. In this study, we analyzed present-day heat flow data and reconstructed the Permian paleo-heat flow using vitrinite reflectance and zircon (U-Th)/He thermochronology data in the ELIP region and discussed implications for the geodynamics of the Emeishan mantle plume. The present-day heat flow is higher in the inner and intermediate zones than in the outer zone, with a decrease of average heat flow from 76 mW/m2 to 51 mW/m2. 

Present address: Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA

6845, Australia 1

ACCEPTED MANUSCRIPT Thermal history modeling results show that an abnormal high paleo-heat flow of 90-110 mW/m2 was caused by the Emeishan mantle plume activity. Based on the present-day heat flow data, we can calculate that there is lithospheric thinning in the central ELIP region, which may be due to the destruction of the lithosphere by mantle

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plume upwelling and magmatic underplating. The Permian paleo-heat flow anomaly

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implies that there was a temperature anomaly in the mantle. The ascending

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high-temperature mantle plume and the thinned lithosphere may have induced the large-scale uplift in the ELIP region. According to the range of the surface heat flow

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anomaly, it can be estimated that the diameter of the flattened head of the Emeishan

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mantle plume could have reached ~1600–1800 km. Our research provides new insights into the geodynamics of the Emeishan mantle plume through study of heat

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flow.

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Key words: Emeishan large igneous province; Heat flow; Mantle plume; Thermal

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history; Thermochronology

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1. Introduction

The existence of mantle plumes is a highly debated issue that has inspired new and innovative approaches to explain the formation, tectonic significance, metallogeny, and environmental impacts of voluminous and rapidly emplaced flood basalt provinces and oceanic plateaus (White and McKenzie, 1989; Campbell and Griffiths, 1990; Larson, 1991; Courtillot et al., 1999; Wignall, 2001; Zhou et al., 2005). Mantle plumes are generally thought to originate from the core-mantle

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ACCEPTED MANUSCRIPT boundary, where hot deep mantle materials move upward due to thermal buoyancy, forming a large mushroom-shaped head followed by a narrower feeder conduit. This mantle plume then collides with the base of the lithosphere, interacting with materials there (e.g. Campbell and Griffiths, 1990; Campbell, 2005; Sleep, 2006; Bryan and

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Ernst, 2008). Many surface phenomena, such as large-scale surface uplifts (He et al.,

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2003a; Saunders et al., 2007; Sahu et al., 2013) and heat flow, gravity and geoid

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anomalies (Courtney and White, 1986; Von Herzen et al., 1989; Sleep, 1990; Harris and McNutt, 2007) near ocean hotspots or continental large igneous provinces

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correspond to these deep mantle and crustal processes and are believed to result from

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mantle plume activity.

Mantle plumes are essentially processes of upward mass and heat transport from

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the deep core and mantle to the shallow lithosphere and surface of the Earth, and are a

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very important heat-loss mechanism for the Earth (Davies and Richards, 1992; Hill, 1993). Multiple studies have focused on thermal aspects of mantle plumes, such as

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theoretical analysis of plume thermal structure (Loper and Stacey, 1983; Farnetani and

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Richards, 1994; Campbell and Davies, 2006; Mittelstaedt and Tackley, 2006; Farnetani and Hofmann, 2009), estimation of Earth heat loss amounts through plumes (Davies, 1988, 1999; Sleep, 1990; Hill et al., 1992), calculation of the melting temperatures of primitive magma that formed exposed basalts (Xu et al., 2001; Zhang et al., 2006; Ali et al., 2010), and measurement and modeling of surface heat flow at the top of mantle plumes (Von Herzen et al., 1982; Courtney and White, 1986; DeLaughter et al., 2005; Harris and McNutt, 2007). Although consensus has been

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ACCEPTED MANUSCRIPT reached on some of these issues, there is still a debate among surface phenomena and thermal-related research of mantle plumes, such as whether a mantle plume would induce an elevated surface heat flow. For example, heat flow measurements in some oceanic hotspot swells, such as the Hawaii hotspot (Von Herzen et al., 1982;

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DeLaughter et al., 2005; Harris and McNutt, 2007) and the Iceland hotspot (Stein and

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Stein, 2003), show that no heat flow anomaly is expected in these regions, whereas

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the surface heat flow on top of the Neogene Yellowstone mantle plume shows an apparent anomaly (Morgan and Gosnold, 1989; Pierce and Morgan, 2009).

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The middle-late Permian Emeishan large igneous province (ELIP) in southwest

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China is one of the most important and best-studied continental flood basalts in the world, and is believed to have contributed to the end-Guadalupian mass extinction

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(Wignall, 2001; Ali et al., 2005). Geochemical, geophysical and sedimentological

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evidence indicates that the ELIP resulted from ancient mantle plume activity (e.g. Chung and Jahn, 1995; Xu et al., 2004; Zhang et al., 2006, 2008; Li et al., 2015). It

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has been suggested that the mantle plume upwelling induced a large-scale surface

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uplift in the ELIP region before the initiation of Emeishan volcanism. Supporting evidence includes the differential erosion and paleokarst of the Maokou Formation, which directly underlies the Permian basalts (He et al., 2003a, 2010). In addition, He et al. (2003a) and Xu et al. (2007) further suggested that the mantle excessive temperature was ~200°C based on the amount of surface uplift. However, debate arose over the existence of surface uplift because of the recognition of submarine hydromagmatic deposits (Utskins Peate and Bryan, 2008, 2009) and a lack of

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ACCEPTED MANUSCRIPT depositional evidence for the karstification of the Maokou limestone (Utskins Peate et al., 2011). Also, further studies have been conducted on conodont age dating of the Maokou Formation and volcanological observations and interpretations of the basalt sequence in the inner zone to prove the syn-volcanic marine sedimentary environment

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(Sun et al., 2010; Zhu et al., 2014; Jerram et al., 2016).

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Additionally, there has been little research on the Emeishan mantle plume’s

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lateral extent, which is a critical parameter in the mantle plume model. It is generally believed that the Emeishan flood basalts cover ~2.5×105 km2 area in southwest China,

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but it is difficult to constrain the scale of the Emeishan mantle plume based only on

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the distribution of outcrop basalts because of disruption by tectonic movements and intensive erosion. Also, there are many basalts covered by sedimentary strata as

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revealed by oil exploration boreholes in the Sichuan Basin (Tian et al., 2017). He et al.

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(2006) estimated the diameter of the plume head to be ~800–1000 km based on the range of surface uplift. Recently, Li et al. (2017) proposed that the diameter of the

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ELIP could have reached ~1200–1400 km based on the distribution of Permian basalt

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in the Yanghe area of the Sichuan Basin that is geochemically comparable to Emeishan basalt. In general, these estimates of the size of the Emeishan mantle plume head are relatively small compared with the results of fluid dynamical and numerical models reported by Griffiths and Campbell (1991), and some researchers doubt the plume’s ability to trigger the end-Guadalupian mass extinction event because of its small size and dominantly submarine eruption environment (Ali et al., 2005; Li et al., 2017).

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ACCEPTED MANUSCRIPT Surface heat flow is the most direct signal of the temperature variation and geodynamical processes in the Earth’s interior, making it a critical parameter for studying the thermal state and structure of the lithosphere and mantle. In this paper, we studied present-day heat flow and modeled Permian paleo-heat flow based on

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the geodynamical processes of the Emeishan mantle plume.

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various paleogeothermal indicators in the ELIP area to further our understanding of

2. Geological setting

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The ELIP is located in southwest China, and Permian Emeishan basalts cover a

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rhombic area of about 2.5×105 km2. Its northwestern boundary is the Longmen Shan fold belt and the Ailao Shan-Red River Fault is its southwestern boundary (Fig.

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1).The thickest point of the basalts, at 2–3 km thick, is in the Yanyuan-Lijiang area,

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and the basalts gradually thin to the east and north (Fig. 2). Geochronological studies of the ELIP, using methods such as U-Pb zircon-grain radiometric techniques,

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stratigraphic correlation, fusulinid foraminifera tests, and conodont biostratigraphy

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measurements suggest that the emplacement of the Emeishan basalts initiated around 259 Ma and lasted for only a few million years (e.g. He et al., 2003a; Ali et al., 2004; Shellnutt et al., 2008, 2012; Sun et al., 2010; Zhong et al., 2014). The ELIP is considered to be a mantle plume-derived large igneous province based on evidence from geological, geochemical, and geophysical studies (e.g. Chung and Jahn, 1995; Xu et al., 2004; Zhang et al., 2006, 2008; Li et al., 2015). Biostratigraphic correlations and paleokarst characteristics of the Maokou limestone

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ACCEPTED MANUSCRIPT that immediately underlies the Emeishan basalts suggest that a significant crustal doming and surface uplift resulted from the impingement of the plume head on the lithosphere. The doming area was divided into inner, intermediate, and outer zones according to amounts of erosion and surface uplift. The magnitude of uplift in the

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inner zone was estimated to be 450–1000 m (He et al., 2003a, 2010) (Fig. 1). Despite

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the ELIP being regarded as the best example of plume-induced surface uplift

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(Campbell, 2005), it is still a contentious issue because of a large amount of geological evidence to the contrary (e.g. Utskins Peate and Bryan, 2008, 2009; Sun et

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al., 2010; Utskins Peate et al., 2011; Zhu et al., 2014). An alternative hypothesis

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proposed by Shellnutt (2014) suggestes a “topographic high” in the inner zone that conforms well with the stratigraphic relationships and the crustal structure in the ELIP

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region. Geochemical data indicates that the basalts were produced by partial melting

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of plume with minor lithospheric mantle and upper crust (Chung and Jahn, 1995; Xu et al., 2001), and that initial melt temperature can have reached as high as

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1500–1690°C, suggesting a 100–350°C thermal anomaly (Xu et al., 2001; Zhang et

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al., 2006; Ali et al., 2010). Borehole vitrinite reflectance data led to an estimated abnormally high paleogeothermal gradient of as high as ~43°C/km, which was attributed to the thermal effect of the Emeishan mantle plume (Zhu et al., 2010, 2016a). Tectonically, the ELIP is in the western margin of the Yangtze Block, which is an ancient craton in southern China (Fig. 1). The Yangtze Craton has experienced two important periods of tectonism, the Indosinian period and the Himalayan period. The

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ACCEPTED MANUSCRIPT Indosinian tectonism is associated with the Indochina-South China collision, whereas the Himalayan tectonism is associated with the India-Eurasian collision. The faulting and uplift related to these tectonic movements may have extensively modified and reshaped the distribution of the Emeishan basalts. Marine carbonate rocks and shales

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were deposited before the middle Triassic in the craton stage and terrestrial clastic

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rocks were dominated from the late Mesozoic to the Cenozoic in the western Yangtze

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Block (Fig. 2a).

The Sichuan Basin, which is bounded by the Longmen Shan fold belt in the

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northwest and the Emeishan-Liangshan fold belt in the southwest, is a large

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petroliferous sedimentary basin in the northwestern portion of the Yangtze Block. Its southwest edge is about 200 km from the ELIP’s center (Fig. 1). Several localized

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outcrops of Permian basalts have been reported in the southwestern and central areas

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of the basin (e.g. Xiong et al., 2011; Li et al., 2017). Additionally, boreholes in the southwestern and northeastern Sichuan Basin penetrated the Permian basalts (Tian et

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al., 2017) (Fig. 1). The Sichuan Basin was part of the Yangtze carbonate platform in

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the Paleozoic and the Early Triassic collision between the North China and South China Block terminated marine deposition. The basin experienced extensive uplift and erosion during the Triassic collision and the Cenozoic India-Eurasia collision; however, faults and folds were relatively rare in many areas except its eastern portion. In general, the Sichuan Basin is relatively stable tectonically compared with other parts of the ELIP.

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ACCEPTED MANUSCRIPT 3. Present-day heat flow in the ELIP region Present-day heat flow, which is the last episode of thermal evolution, can be viewed as a starting point for thermal history modeling. It is also an important parameter that can reflect the crust and mantle’s thermal structure. We collected 80

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previously measured heat flow data from published papers and constructed a contour

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map of the ELIP region (Fig. 3). According to Beck and Balling (1988), a valid heat

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flow value should be calculated using the equilibrium temperature gradient and thermal property values of rocks from corresponding intervals. Temperature

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measurements for an equilibrium temperature gradient should be in near steady state,

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devoid of influence by factors such as underground water, topography, and climate change. The heat flow data in the Panzhihua-Xichang (Panxi) region (Wang and

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Huang, 1987), Yunnan (Wu et al., 1988; Wang et al., 1990), and the Sichuan Basin

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(Huang and Wang, 1991; Han and Wu, 1993; Xu et al., 2011) are high quality because they can meet these standards. However, heat flow data in the Guizhou and Guangxi

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regions from Wang et al. (1990) are lower quality because the calculations of these

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data used bottom-hole temperature data or thermal property values from nearby wells. Despite this, we still used the estimated heat flow data in these regions because they were relatively far away from the center of the ELIP but can still provide some information on heat flow distribution patterns for the ELIP region. We did not use the heat flow values measured by Wang and Huang (1987) from wells ZK 823 and ZK 7405 in the Panxi region in this study because of the shallow borehole depth. The heat flow in the inner and intermediate zones is relatively high, whereas heat

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ACCEPTED MANUSCRIPT flow gradually decreases as distance from the center of the ELIP increases. The average heat flow for the inner, intermediate, and outer zones is 76.4 mW/m2, 76.0 mW/m2, and 51.4 mW/m2, respectively.

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4. Thermal history modeling

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4.1 Analytical method and basic geological data

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There are generally two kinds of methods for studying the paleothermal conditions of strata: 1) model the thermal history based on paleogeothermal indicators,

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such as vitrinite reflectance (Ro) (Lerche et al., 1984; Qiu et al., 2014), apatite and

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zircon fission track, and (U-Th)/He thermochronology (Gleadow and Brooks, 1979; Qiu et al., 2008); or 2) calculate the paleotemperature using thermo-mechanical

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models, such as the McKenzie model for extensional basins (McKenzie, 1978) and

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the Falvey-Middleton model for extensional and compressional basins (Falvey and Middleton, 1981). We chose to use paleogeothermal indicators to reconstruct the

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thermal history in this study because of the research area’s multi-stage and complex

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structural-thermal evolution. Vitrinite reflectance is the most commonly used paleogeothermal indicator in thermal history modeling. Vitrinite reflectance values largely depend on the temperature and duration of heating that organic matter has experienced, and the EASY%Ro chemical kinetic model is the most commonly used model for illustrating their relations (Sweeney and Burnham, 1990). In this study, we combined a paleotemperature gradient-based method (Duddy et al., 1991; Bray et al., 1992;

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ACCEPTED MANUSCRIPT Feinstein et al., 1996; O’Sullivan, 1999) and paleo-heat flow-based method to model the thermal history. There are four main steps in this method (Fig. 4). 1) The borehole’s burial history is reconstructed. 2) The borehole’s sedimentary strata is divided into several structural layers bounded by unconformities, and structural layers

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that have experienced the maximum paleotemperature simultaneously can be regarded

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as a united subsection. 3) From top to bottom, a heat flow value is assumed for each

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layer and the paleogeothermal indicator values are calculated based on Sweeney and Burnham’s (1990) EASY%Ro model. 4) If the calculated value conforms well the

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measured value, the assumed paleo-heat flow value will be accepted for this period of

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time, otherwise another paleo-heat flow value will be tried. Thus the paleo-heat flow evolution history for this well is determined. Thermodel for Windows software (Hu et

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al., 1998, 2001) was used in the calculation of paleo-heat flow history. More detailed

et al. (1998, 2001).

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assumptions and principles of this method can be found in Bray et al. (1992) and Hu

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We divided the thermal history modeling based on Ro data into two cases

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according to the characteristics of borehole Ro-depth profiles (Fig. 4). For boreholes with Ro profiles displayed as a succession of two different gradients, we divided the borehole strata into two subsections, with the lower subsection having experienced a higher paleogeothermal gradient than the upper one. For boreholes that have continuous Ro profiles, the upper and lower subsection experienced the maximum paleogeothermal gradient at the same time and the calculated paleogeothermal gradient can be considered the maximum value that the well has experienced.

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ACCEPTED MANUSCRIPT Zircon (U-Th)/He (ZHe) thermochronology is an important tool for studying thermal history (e.g. Armstrong, 2005; Qiu et al., 2008, 2011; Chang et al., 2012). The (U-Th)/He dating technique is developed based on measuring 4He accumulation in minerals produced by uranium and thorium decay. Diffusion experiments show that

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the ZHe thermochronometer has a sensitivity range of 130–200°C (Reiners, 2005;

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Wolfe and Stockli, 2010). In this study, we applied the zircon model of Guenthner et

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al. (2013) to model the ZHe age, and when the modeled ZHe age correlated well with the measured value, we accepted the supposed time-temperature path as correct, thus

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giving us the sample’s thermal history. For each sample, we tried 2000

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time-temperature paths using Monte Carlo inversion techniques by means of the HeFTy software package. In addition, we reconstructed the sample’s burial history

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based on a variety of parameters, such as strata thickness, the eroded thickness at each

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unconformity, and the timing of tectonic thermal events constrained by the ZHe ages. Therefore, we could calculate the paleogeothermal gradient and paleo-heat flow at

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each geological time from the sample’s modeled paleotemperature and reconstructed

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paleo-burial depth.

In addition to paleogeothermal indicators, there are a variety of geological data essential in thermal history modeling, such as stratigraphic and lithologic data, present-day surface temperature, geothermal gradients and heat flow. Lithologic data such as heat conductivity, heat production, and rock density, and present-day temperature and heat flow were cited from previous publications (Wang and Huang, 1987; Huang and Wang, 1991; Xu et al., 2011). We obtained the original rock

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ACCEPTED MANUSCRIPT porosity data and compaction factor from well-logging data according to the model proposed by Sclater and Christie (1980). The surface temperature was assumed to be 15°C throughout geological time. 4.2 Vitrinite reflectance data

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As a kind of thermal maturity indicator for organic matter, a great deal of

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vitrinite reflectance data in the ELIP region, especially in the Sichuan Basin and its

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periphery, has been measured by local oil companies for oil and gas prospecting over recent decades. In this study, we collected borehole and outcrop Ro data from the

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database of the Southwest Petroleum Branch of Sinopec and previously published

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literature. Figure 5 shows Ro data from Sichuan Basin boreholes, some of which (well NJ, T1, H1, W28, and MA1) show a discontinuity in the boundary between the

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middle and upper Permian. The slopes of the Ro profiles in the lower part are steeper

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than those of the upper part in these wells, implying that the lower part has experienced a higher thermal state than the upper part. For these wells, we divided the

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strata into two subsections for thermal history modeling: the lower subsection which

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includes strata from the base to the middle Permian and the upper subsection which includes strata from the middle Permian to the surface. Outcrop Ro data collected from the Southwest Petroleum Branch of Sinopec and stratigraphic data were used to construct outcrop Ro profiles (Fig. 6). These outcrops are located in the northwestern and southwestern margins of the Sichuan Basin and the Huayingshan area of the central Sichuan Basin (Fig. 1). The Permian basalt cropped out in some of the sections closer to the ELIP, such as the Huayingshan,

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ACCEPTED MANUSCRIPT Changning, Emei and Ganluo sections. In these sections, the Ro values from strata that are very close to the basalt sequence are greater than the trend values (solid lines in the Ro-depth profiles in Fig. 6). However, in sections relatively far away from the ELIP and without basalt exposure, such as the Guangyuan, Wangcang and Nanjiang

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sections, this phenomenon does not exist (Fig. 6). Thus, the high Ro values from

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strata near the basalts can be considered evidence of direct heating from the cooling

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process of the Emeishan basalts. The Ro values in Permian strata in the Guangyuan Section are relatively small (Fig. 6a), but many other maturity indicators show that the

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organic matter in this area is now in high-over maturity stage. Xie et al. (2003)

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suggested that these low Ro values were due to the hydrogen-rich vitrinite source matter.

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4.3 Zircon (U-Th)/He (ZHe) thermochronology

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4.3.1 Sample strategy and experiments To study the Permian thermal history of the ELIP region, thermochronology

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samples must be collected from strata before the Permian. However, the Paleozoic

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strata in the western Yangtze Block are dominated by carbonate rocks, and clastic rocks are only found in some thin Cambrian, Ordovician, and Devonian layers. We collected seven outcrop sandstone and igneous rock samples from these thin layers in the Sichuan Basin’s western and southern margins (Fig. 7). The Paleozoic strata were deeply buried during the Mesozoic and may have experienced much higher temperatures than the partial retention zone of apatite (U-Th)/He (40–80°C, Wolf et al., 1996, 1998) and the annealing temperature of apatite fission track (60–110°C;

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ACCEPTED MANUSCRIPT Green et al., 1989). Thus in this study we tested ZHe, which has a higher temperature sensitivity range (130–200°C; Wolfe and Stockli, 2010; Guenthner et al., 2013) were tested in this study. We separated zircon grains from rock samples using conventional mineral separation techniques. Measurements of ZHe ages were carried out at the

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University of Melbourne following the same procedures described by Tian et al.

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(2012). For each sample, two or three apatite and zircon grains were tested (Table 1).

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4.3.2 Zircon (U-Th)/He age interpretation

There are 20 ZHe ages obtained from seven samples in the research area (Fig. 7)

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with an age range of 4.5–683.8 Ma, which reflects the rather complicated tectonic

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thermal history of these areas.

Six samples come from the Longmen Shan fold-thrust belt. From west to east,

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the Longmen Shan can be divided into three NW-dipping fault zones: the

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Wenchuan-Maowen Fault (WMF), the Yingxiu-Beichuan Fault (YBF), and the Guanxian-Anxian Fault (GAF) (Fig. 7). Previous research indicates that the YBF is

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the thrust boundary between the Sichuan Basin and the Longmen Shan fold-thrust belt,

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which is characterized as having a much higher exhumation rate and tectonic uplift of the hanging wall of the YBF than the footwall wall (Burchfiel et al., 1995; Godard et al., 2009; Tian et al., 2013; Gao et al., 2016). This phenomenon is also evident in our newly tested ZHe ages. For example, the ZHe ages of DY-10 and QP-4, which are in the YBF hanging wall are very young, which reflects the YBF’s Cenozoic uplift and cooling history. The locations of BC-3 and GX-8 are very close, but the ZHe ages of BC-3, which lies in the YBF hanging wall are younger than the GX-8, which lies in

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ACCEPTED MANUSCRIPT the YBF footwall, reflecting a differential tectonic uplift across the YBF. Samples SS-1 and SS-3, which are in the footwall of these thrust faults are much older than other samples, which may reflect the early tectonic thermal event in these areas. The ZHe ages of some grains from samples SS-1 and SS-3 are older than the strata age,

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perhaps because of the sedimentary source of the samples.

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From north to south along its strike, the Longmen Shan can be divided into

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northern, central, and southern segments according to Li et al. (2012). Fission track thermochronology data shows that the northern segment of the Longmen Shan

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experienced more rapid cooling during the Mesozoic. On the contrary, the central and

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southern segments of the Longmen Shan underwent more extensive and rapid exhumation and uplift during the Cenozoic (Li et al., 2012), which is in accordance

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with geomorphic variations along the strike of the Longmen Shan (Fig. 7). (U-Th)/He

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thermochronology data in this study shows that the ZHe ages gradually decrease from the northern segment to the central and south segments, which conforms well to

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previous results revealed by fission track thermochronology and geomorphic data (Li

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et al., 2012; Gao et al., 2016). As a result, the thermal history information of Permian is better preserved in the northern segment of the Longmen Shan and the YBF footwall. 4.4 Thermal history modeling results A large volume of research has focused on the Sichuan Basin’s thermal history and the thermal effect of the ELIP (e.g. Lu et al., 2007; He et al., 2014; Zhu et al., 2016a, 2016b). However, based on borehole Ro data (Lu et al., 2007; Yang et al.,

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ACCEPTED MANUSCRIPT 2015; Zhu et al., 2016b) and (U-Th)/He thermochronology (Qiu et al., 2008; Qin et al., 2010), these works were mainly centered on the Meso-Cenozoic thermal history of the northern and eastern parts of the Sichuan Basin far away from the ELIP where petroleum resources are abundant, or the western Sichuan foreland basin where the

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Paleozoic strata were deeply buried in the Meso-Cenozoic so that traditional

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paleogeothermal indicators are less capable of revealing the thermal history in early

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geological times (He et al., 2014; Zhu et al., 2015). A few publications reported possible links between the thermal effects of the ELIP and the thermal anomaly in the

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Sichuan Basin based on thermal history modeling of several boreholes (Zhu et al.,

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2010, 2016a) and geodynamical models (He et al., 2011). In this paper, the Ro data of 13 wells from various part of the Sichuan Basin and zircon (U-Th)/He

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thermochronology which has a relatively high temperature range sensitivity were used

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to decipher the Permian thermal regimes of the ELIP region. Fig. 8 shows the thermal history reconstruction of wells NJ and YS2 in the

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Sichuan Basin. Well NJ is in the central Sichuan Basin and well YS2 is in the

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southern Sichuan Basin (Fig. 5). The burial history of these wells was reconstructed and the eroded thickness at each unconformity referred to Zeng (1988) and Zhu et al. (2009). The Ro profile of well NJ shows a broken style, with a higher gradient in the lower subsection and a lower gradient in the upper subsection. Calculations show that the lower subsection experienced a maximum paleo-heat flow of 75.3 mW/m2. The calculated paleo-heat flows of other wells with a similar Ro profile, including well T1, H1, W28, and MA1, range between 66.2 and 113.9 mW/m2 (Fig. 9). This was the heat

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ACCEPTED MANUSCRIPT flow value that happened in the study area before the late Permian. Considering that the Paleozoic Yangtze Block was a part of the South China Craton, which was characterized by a stable tectonic setting and moderate heat flow, the most intense thermal event the lower subsection could have experienced was the Permian

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Emeishan volcanic magmatism, therefore the estimated paleo-heat flow most likely

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happened during that period.

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The Ro profile of well YS2 is relatively continuous (Fig. 8b), and the estimated maximum paleo-heat flow for this well is 78.6 mW/m2. The calculated paleo-heat

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flows of other wells with continuous Ro profiles, such as wells L4, CY84, WK1, JS1,

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LS1, Z12 and X14, range between 62.5 and 83.6 mW/m2, with an average of 73.0 mW/m2. This estimated heat flow is the maximum heat flow that these wells have

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experienced, which means that this heat flow could have happened during the

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Permian Emeishan volcanism or the Meso-Cenozoic tectonic events. As stated above, the major tectonic events that the Sichuan Basin experienced during the

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Meso-Cenozoic were periods of uplift and erosion induced by the early Triassic North

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China-South China collision and the Cenozoic Indian-Eurasian collision. Faults and folds developed in the eastern part of the basin but are relatively rare in other areas. Thermal history modeling results from previous research indicate that the early Triassic paleo-heat flow in the eastern Sichuan Basin was 51–66 mW/m2 and the paleo-heat flow did not exceed 55 mW/m2 during the Cenozoic (Qiu et al., 2008; Zhu et al., 2016b). Thus, the most likely cause for the calculated heat flow is the Permian Emeishan volcanism.

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ACCEPTED MANUSCRIPT We used the software package HeFTy to model the time-temperature paths of the ZHe samples. For samples with a young ZHe age, such as the Cambrian sample BC-3 (Fig. 10), the paleotemperature of early time cannot be well constrained as the thermal information may have been erased by temperatures higher than the confined

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temperature of zircon (U-Th)/He. The Devonian samples GX-8 and SS-1 experienced

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a maximum temperature of 150–160°C during the Permian (Fig. 10). We

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reconstructed the burial history of the thermochronology samples based on strata thickness and the eroded thickness at each unconformity (Fig. 11) (Editorial

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Committee of Regional Stratigraphic Table of Sichuan Province, 1978; Zhu et al.,

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2009). The thermal gradients during the Permian can be estimated according to the sample’s paleotemperature and the corresponding paleodepth. The Permian thermal

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gradient of samples GX-8 and SS-1 was 30-33°C/km, and the heat flow at this time

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was about 75–82 mW/m2 (the average rock thermal conductivity is about 2.5 W/mK for the western Sichuan Basin according to Huang and Wang (1991) and Xu et al.

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(2011)), which conforms well with vitrinite reflectance results.

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The reconstructed heat flow evolution history of thirteen wells and two outcrop samples are shown in Fig. 9. The heat flow was relatively low in Caledonian period (50-60 mW/m2). A heat flow peak as high as 90-110 mW/m2 happened in late Permian and the average value of the heat flow peak was 78 mW/m2. The heat flow decreased rapidly to 65-45 mW/m2 since Mesozoic. The uncertainties and reliability of the modeled thermal history mainly depend on measurement errors of thermal indicators and consistency between the calculated

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ACCEPTED MANUSCRIPT and measured values (Figs. 8b, 8d). Measurement errors may increase Ro data and ZHe thermochronology data uncertainties. Errors were generally smaller than ±10% for Ro data and smaller than ±6.2% for ZHe data in this study (Table 1). Increasing or decreasing the heat flow values by 10% would result in a great inconsistency between

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the calculated and measured Ro values, whereas a 5% adjustment of the heat flow

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would be largely consistent between the two. The goodness-of-fit (GOF) in our ZHe

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thermal history modeling is 1.0 (Fig. 10), which indicates that the model and the data match well. Overall, the accuracy of the modeled paleo-heat flow is about ±5%. For

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more detailed discussions on the uncertainties of thermal history research using

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paleogeothermal indicators, refer to Li et al. (2010) and Qiu et al. (2011).

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5. Discussion

plume activity

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5.1 Present-day heat flow, thermal lithospheric structure and implications for mantle

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The heat flow values in the inner and intermediate zones are much higher than

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the heat flow value of the outer zone, except for a low-value area with a minimum value of 45.6 mW/m2 near Panzhihua (Fig. 3). In fact, the heat flow in the Panxi region measured by Wang and Huang (1987) varies greatly from 90 mW/m2 to 40 mW/m2 within a small area (Fig. 3). Several factors may have contributed to this variation. First, the depth of boreholes used in the heat flow measurements in this area was relatively shallow, with no boreholes exceeding 1 km, so these heat flow data may not fully reflect the thermal state of the crust and mantle. In addition, several

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ACCEPTED MANUSCRIPT north-south trending major faults were developed in this area, which have greatly modified and reshaped the distribution of the Emeishan basalts (Fig. 2b). These faults also may have affected heat flow distribution patterns in these areas. For example, Huang and Wang (1988) found that surface heat flow values did not have a good

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linear relationship with rock heat production in the Panxi region (Fig. 2 in Wang and

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Huang, 1987), and they discussed the influence of these faults on the heat flow values.

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To better understand of the main controlling factors of heat flow distribution patterns in the ELIP region, we calculated the thermal structure and lithospheric

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thickness of an east-west transect from Huili to Qingzhen that cuts through the inner,

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intermediate, and outer zones (Fig. 12a). These calculations were based on heat flow data extracted from Fig. 3, crustal structure data from Deng et al. (2014) and Chen et

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al. (2015), and rock thermal properties from Wang and Huang (1987). The

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temperature-depth curve within a lithosphere depth interval can be estimated based on surface heat flow and the one-dimensional heat flow conduction equation, and the

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thermal lithospheric thickness can be calculated using the depth of the intersection

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between the temperature-depth curve and the mantle adiabatic or dry basalt solidus line (Fig. 12b) (Pollack and Chapman, 1977; Rudnick et al., 1998; Qiu et al., 2014). The results revealed thermal lithospheric thickness increase and decreasing crustal thickness from the inner and intermediate zones to the outer zone (Fig. 12c). Although the crustal thickness variations in the ELIP region may have some influence on the heat flow distribution patterns, this contribution is subordinate because the thickened crust in the inner zone was due to underplating of mafic igneous rocks (Chen et al.,

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ACCEPTED MANUSCRIPT 2015) which usually have low radiogenic heat production (Vilà et al., 2010). For example, a 10 km-thick underplated basaltic layer in the crust results in an additional surface heat flow of only 3.58 mW/m2 (Radiogenic heat production value refers to Vilà et al. (2010)). Thus, the heat flow and lithospheric structure variations in the

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ELIP region must have a deep origin.

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The formation of a large igneous province and mantle plume activity were

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associated with the impingement of hot rising mantle materials on the base of the lithosphere and with extensive magmatic underplating. This would impose a

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destructive effect on the lithosphere, resulting in lithospheric thinning, which has been

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tested by geochemical modeling of plume-related lavas from the Isle of Mull (Kerr, 1994). Because of the tectonic movements over geological time, mantle temperature

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anomalies and mantle plume upwelling may not currently exist at the bottom of the

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lithosphere in the ELIP region as revealed by receiver function analysis and other geophysical studies (He et al., 2014). However, mantle plume influence may still have

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been kept as a form of modification of the ELIP region’s lithospheric structure. The

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relatively higher heat flow and corresponding thinner lithosphere in the inner and intermediate zones can thus be viewed as the influence of the Emeishan mantle plume.

Rare Earth Element (REE) in basalts is a sensitive indicator of lithospheric thickness (McKenzie and O’Nions, 1991; Kerr, 1994; Xu et al., 2001). The high Ce/Yb ratios of the high-Ti basalts mainly in the outer zone indicate melting regimes under a thick lithosphere and garnet as the dominant residual phase, whereas the low

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ACCEPTED MANUSCRIPT Ce/Yb ratios of the low-Ti basalts in the inner and intermediate zone correspond to a thin lithosphere and spinel control (Xu et al., 2001). Based on REE inversion, Xu et al. (2001) suggested that the mantle melting for the low-Ti lavas started from a depth as low as 60 km, whereas a depth of 75 km for the high-Ti lavas was estimated. This

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indicates that the lithosphere might have been as thin as 60 km in the inner and

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intermediate zone and 75 km in the outer zone in late Permian. The modeling results

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of a thinner lithosphere in the inner and intermediate zone and a thicker lithosphere in the outer zone are compatible with the lithospheric thickness variations calculated in

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this study, while the lithospheric thickness differences between Permian (Xu et al.’s

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(2001) results) and present-day (our calculations) can be explained by lithospheric thickening due to thermal decay and re-equilibration of the Emeishan mantle plume

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since late Permian.

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Cenozoic tectono-magmatic events, on the other hand, may have also influenced the study area’s heat flow distribution pattern. A series of reactivated fault systems

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and strike-slip fault systems (e.g. Wang and Burchfiel, 2000; Wang et al., 2001), and

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the Eocene to Miocene carbonatite-syenite magmatism (Hou et al., 2009) happened in the Panxi region due to the Indian-Eurasian plate collision at 65-55 Ma. These faulting and magmatic activities may partly account for the uneven heat flow distribution in the study area as discussed above. Nevertheless, our results suggest that the higher heat flow in the inner and intermediate zones is mainly controlled by a thinner lithosphere, particularly a thinner lithospheric mantle, in these regions. It is less likely that the Cenozoic tectonic activity significantly influenced the lithospheric

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ACCEPTED MANUSCRIPT mantle thickness in the ELIP region and the Emeishan mantle plume model is essential in explaining these phenomena. In addition to heat flow, various geophysical parameters also show a similar pattern in the ELIP region. Deng et al. (2014, 2016) and Shi et al. (2015) investigated

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the residual gravity and density anomalies of the ELIP and found that the maximum

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values were located in the inner zone and that the value gradually decreases toward

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the surrounding area. This can be attributed to mafic rocks originating from magmatic intrusions and magmatic underplating caused by the Emeishan mantle plume. Chen et

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al. (2015) and Xu et al. (2015) proposed the plume-modified crust of the ELIP based

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on crustal geophysical characteristics such as high P-wave velocity, high Vp/Vs ratios, and a thickened crust. These geophysical properties can be viewed as evidence of the

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influence of the fossil mantle plume on the lithosphere in the ELIP region.

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In addition to Emeishan flood basalts, the Neoproterozoic Kangdian basalts, which were also thought to be derived from a fossil mantle plume (Li et al., 2002), are

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exposed in the Panxi region. It seems possible that the Neoproterozoic mantle plume

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also affected the region. However, aside from the Kangdian basalts, there are at least 14 contemporaneous basaltic successions in southern China, such as the Yiyang komatiitic basalts in the central South China Block (Wang et al., 2007), the Bikou basalts in the northwestern Yangtze Block (Wang et al., 2008) and the Mamianshan alkaline basalts in the Cathaysia Block (Li et al., 2005). These basaltic rocks were thought to be derived from a single mid-Neoproterozoic mantle plume beneath the South China Block (Wang et al., 2009 and references therein). It is less likely that this

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ACCEPTED MANUSCRIPT mid-Neoproterozoic mantle plume caused greater lithospheric thinning in the western segment of the Huili-Qingzhen transect, which was farther to the center of the Yangtze Block, than in the eastern segment of the transect. In contrast, the Emeishan mantle plume model can better explain this thickness variation.

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In summary, after considering the destruction effect caused by plume-lithosphere

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interaction, thermal decay and re-equilibration, and ruling out the possible influence

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of the Neoproterozoic mantle plume and the Meso-Cenozoic tectonic activities, we suggest it is reasonable to attribute the heat flow and lithospheric thickness variations

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in the ELIP region to the Emeishan mantle plume activity.

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5.2 Abnormal Permian heat flow and its relation with the Emeishan mantle plume The vitrinite reflectance data from outcrop samples in the southern and

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southwestern Sichuan Basin (Fig. 6), and the Wulong area of the southeastern edge of

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the Sichuan Basin (Yang et al., 2015), show an apparent influence of the thermal effect of the Emeishan basalts on the maturity of organic matter in sedimentary strata.

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Thermal history modeling using Ro and ZHe thermochronology data indicates an

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extensive surface heat flow anomaly with an average value of 20 mW/m2 during the late Permian in the ELIP area. This correlates well with the temporal and spatial distributions of Emeishan flood basalt volcanism and geodynamical models of the Emeishan mantle plume have similar results (He et al., 2011). The cooling of basalts passing through the crust would release large amounts of heat, which could have influenced the heat flow. The Emeishan basalts were possibly derived from the Emeishan mantle plume which is supported by large volume of

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ACCEPTED MANUSCRIPT geological evidence (e.g. Chung and Jahn, 1995; Xu et al., 2004; Zhang et al., 2006, 2008; Li et al., 2015), or from lithospheric rifting that happened in the early Permian and late Permian in the study area (Luo et al., 1990; He et al., 2011). The paleo-heat flow influenced by the extension and rifting would not exceed 60–62 mW/m2,

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whereas a heat flow value of 80–100 mW/m2 could be reached when the plume model

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was involved (He et al., 2011). In this study, the thermal history modeling based on

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multiple paleogeothermal indicators indicated a high heat flow of 80–110 mW/m2 in the late Permian. Thus, the plume head with abnormal high mantle potential

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temperature and plume-derived basalts were the most likely causes of the high heat

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flow.

There is still some disagreement as to whether mantle plume activity would

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trigger an apparent surface heat flow anomaly. For instance, some early measurements

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of heat flow across oceanic hotspots such as the Hawaii swell (Von Herzen et al., 1982; Crough, 1983), the Cape Verde swell (Courtney and White, 1986) and Bermuda

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(Detrick et al., 1986) show an anomaly of 20-25% compared with normal oceanic

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heat flow. Later measurements of heat flow data and new thermal models suggested an absence of significant heat flow anomalies at these hotspot swells (Von Herzen et al., 1989; DeLaughter et al., 2005; Harris and McNutt, 2007). No distinct higher seafloor heat flow exists near the Iceland mantle plume either (Stein and Stein, 2003). In contrast to the cases of oceanic hotspots, research on several continental large igneous provinces seems to show a different scenario. For example, the heat flow of a north-south transect from northeastern Washington to southeastern Nevada across the

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ACCEPTED MANUSCRIPT Neogene Yellowstone mantle plume in the western United States shows a maximum value of 105 mW/m2 and an anomaly of 20 mW/m2 on top of the relict plume head (Pierce and Morgan, 2009). Numerical modeling of the paleo-heat flow history of a borehole near the early Cretaceous Paraná-Etendeka large igneous province in central

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South America shows an increase of about 10 mW/m2 associated with basalt

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volcanism (Hurter, 1992). Xu and Qiu (2017) proposed that the end-Permian Siberian

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mantle plume triggered an added heat flow of 5 mW/m2 in the Siberian Craton based on mantle xenolith thermobarometry data. In this study, we provided robust evidence

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for the existence of an abnormal surface heat flow associated with the late Permian

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Emeishan mantle plume, based on a large number of paleo-thermal indicators in the ELIP region. Thus, it seems to be a universal phenomenon that heat brought up from

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deep core and mantle by mantle plumes and associated basalts would add heat flow at

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the Earth’s surface, whereas the absence of heat flow anomalies at ocean swells and hotspots can be explained by the continuous relative motion between the hot plume

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water.

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root and the oceanic lithosphere, and heat convection and dissipation through cold sea

5.3 Abnormal paleo-heat flow, mantle temperature anomaly, and pre-volcanism uplift The ELIP has been regarded as a classical example of crustal domal uplift resulting from mantle plume upwelling before massive basalt eruption to the surface (Xu et al., 2004; Campbell, 2005; Saunders et al., 2007). Biostratigraphic and sedimentologic studies have revealed a paleokarst on top of the Maokou Formation and differential erosion of the formation, which were attributed by He et al. (2003a,

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ACCEPTED MANUSCRIPT 2010) to the transient uplift in response to the Emeishan mantle plume. There is, however, an increasing number of geological indicators that contradict a large-scale pre-volcanism surface uplift and suggest a moderate, or even an absence of, regional uplift in the ELIP region. For example, the discovery of mafic hydromagmatic

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deposits formed in shallow marine environments (Utskins Peate and Bryan, 2008) and

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the conodont biostratigraphic evidence of deep-water facies at the time of the

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Emeishan volcanism in the ELIP region (Sun et al., 2010) preclude the possibility of subaerial erosion, thus the existence of surface uplift. Recent volcanological

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observations revealed a submarine-to-subaerial transition was attributed to the

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infilling in the inner zone by gradual emplacement of massive magmatic products rather than pre-volcanism uplift (Zhu et al., 2014).

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Pre-volcanism transient uplift is essentially a consequence of the variations in the

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mantle’s thermal structure and the overlying lithosphere. Several factors are predicted to have contributed to the uplift, such as the ascending mantle plume with abnormally

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high temperature and the reheated and thinned lithosphere that passes over the plume

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(Saunders et al., 2007). He et al. (2003a) and Xu et al. (2007) estimated the mantle excessive temperature to be in the order of ~200°C based on the amount of uplift in the ELIP area on the basis of the relationship between the extent of mantle excess temperature and the amount of surface uplift derived from fluid dynamical and numerical models by Griffiths and Campbell (1991). This abnormal temperature correlates well with petrological and geochemical studies of Emeishan basalts (Xu et al., 2001; Zhang et al., 2006; Ali et al., 2010). Geodynamical modeling of the

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ACCEPTED MANUSCRIPT Emeishan mantle plume suggested that such a mantle temperature anomaly would result in a surface heat flow anomaly of ~20 mW/m2 (He et al., 2011). Our results on paleo-heat flow using multiple paleogeothermal indicators can be viewed as verifying the geodynamical modeling results and thus can be evidence of mantle temperature

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anomalies. As a result, the ascending mantle plume with high temperature and thinned

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lithosphere revealed in this study may have induced the large-scale surface uplift in

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the ELIP region.

5.4 A larger lateral extent of the head of the Emeishan mantle plume?

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There are many difficulties in measuring the lateral extent of Emeishan mantle

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plume due to the intensive modification and disruption of the Emeishan flood basalts by tectonic movements and erosion. It is generally believed that the northwestern

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boundary of the Emeishan basalts is the Longmen Shan thrust-belt fault; however,

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Xiao et al. (2004) proposed that the Permian basalts in the Songpan-Ganze Block were part of the ELIP. Permian magmatic rocks further south in the Tu Le Basin and

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Phan Si Pan Uplift in northwestern Vietnam (Fig. 1) also have close relationships with

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the Emeishan basalts according to petrological, geochemical, and geochronological data (Tran et al., 2015). But this distribution may have been modified by the extrusion of Indochina relative to southern China in response to the Cenozoic collision of the Indian and Eurasian tectonic plates, and thus cannot be used to constrain the original range of the Emeishan basalts. The latest estimates of the diameter of the Emeishan mantle plume are ~1200–1400 km according to the geochemical study of Yanghe basalts in the Sichuan Basin (Li et al., 2017). Whether this estimate represents the

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ACCEPTED MANUSCRIPT maximum extent of the plume head still remains to be tested. For example, many oil exploration boreholes drilled in the northeastern Sichuan Basin penetrated the Permian basalts (Fig. 1) (Tian et al., 2017). In addition to the distribution of Emeishan basalts, there are several indirect

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estimations of the plume head diameter. For example, estimates based on the plume

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model of Campbell and Griffiths (1990) show that the plume tail diameter is

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approximately equal to the width of the deep erosion zone and that the plume head is twice the diameter of the plume tail. He et al. (2003b) proposed that the head of the

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Emeishan mantle plume could have reached 800 km in diameter. Later He et al. (2006)

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revised their estimation and suggested a diameter of 800–1000 km according to the location of the carbonate gravity flow and deep sea trench caused by the dynamic

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uplift. The mantle plume hypothesis suggested that the diameter of the mushroom

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head of mantle plume originating at the core-mantle boundary can enlarge to ~2000 km when it reaches the bottom of a rigid lithosphere and can produce thermal

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anomalies 2000 km or more across (Griffiths and Campbell, 1990). This conclusion is

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in good agreement with the extent of the Karoo and Deccan flood basalt provinces and the Iceland mantle plume (White and McKenzie, 1989; Campbell and Griffiths, 1990). However, when compared with previous results on the size of the Emeishan mantle plume, the latter seems to be quite small. Our research on the thermal effect of the Emeishan mantle plume could possibly provide some constraints for the lateral extent of the plume head. When the plume head, which had an abnormally high mantle temperature, became flattened at the base

30

ACCEPTED MANUSCRIPT of the rigid lithosphere, it would result in a rise of heat flow at the Earth’s surface. The size of the plume head can thus be constrained by the range of the surface heat flow anomaly. The range of the abnormally high heat flow in the Sichuan Basin seems to be larger than Li et al.’s (2017) estimation of ~1200–1400 km. The Ro data in the

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Huayingshan section, which is very close to the Yanghe area, indicates an apparent

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influence of the thermal effect of the Emeishan mantle plume because the gradient of

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the Ro-depth profile of the Paleozoic strata is steeper than that of the post-late Permian strata (Fig. 6). In addition, the thermal history modeling of ZHe in the

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northwestern Sichuan Basin and Ro data from boreholes in the northeastern Sichuan

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Basin which are farther from the center of the ELIP than the Yanghe area also show an abnormally high heat flow. As a result, the diameter of the flattened plume head may

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have reached ~1600–1800 km, which is larger than previous estimations.

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We note that our estimation of the size of the Emeishan mantle plume is a possible scenario. This conclusion can be further tested in the following manner. First,

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a detailed paleo-heat flow study in the northern and eastern Sichuan Basin that uses

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more vitrinite reflectance and thermochronology data will provide better constraints on the range of the Emeishan mantle plume’s thermal impact. In addition, geochemical and isotopic analysis of Permian basalts in the northeastern Sichuan Basin could place fundamental constraints on their relationship with the Emeishan mantle plume and provide a better understanding of the lateral extent of Emeishan volcanism.

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ACCEPTED MANUSCRIPT 6. Conclusions We reached the following conclusions in this study. (1) A compilation of present-day heat flow data and calculations of thermal lithospheric thickness indicate that from the inner and intermediate zones to the outer

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zone of the ELIP, the average heat flow value decreases gradually from 76 mW/m2 to

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51 mW/m2, whereas the lithospheric thickness increases from 118 km to 153 km.

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These characteristics can be viewed as evidence of lithospheric thinning and destruction by the impingement of hot rising mantle materials on the base of the

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lithosphere and extensive magmatic underplating caused by the Emeishan mantle

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plume.

(2) Thermal history modeling based on vitrinite reflectance and zircon

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(U-Th)/He thermochronology data revealed a surface heat flow peak of 90-110

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mW/m2 during the late Permian in the ELIP region, which can be viewed as evidence of the temperature anomaly associated with the mantle plume activity. This

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temperature anomaly and related lithospheric thinning may have caused the

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pre-volcanism surface uplift in the ELIP region. The diameter of the flattened head of the Emeishan mantle plume may have reached ~1600–1800 km based on the range of surface heat flow anomalies.

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ACCEPTED MANUSCRIPT 7. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (No. 41690133 and No. 41125010), National Science and Technology Major Project (2016ZX05007-003) and the Training foundation for the Science and

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Technology New Star and Leading Talent of Beijing (Z171100001117163). The

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Sinopec Southwest Oil and Gas Field Company is gratefully acknowledged for

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providing vitrinite reflectance data. Special thanks are extended to Greg Shellnutt and an anonymous reviewer for their thoughtful and constructive reviews which have

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greatly improved the early version of this paper.

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ACCEPTED MANUSCRIPT References Ali, J.R., Lo, C., Thompson, G.M., Song, X., 2004. Emeishan Basalt Ar-Ar overprint ages define several tectonic events that affected the western Yangtze Platform in the Mesozoic and Cenozoic. Journal of Asian Earth Sciences 23, 163-178.

PT

Ali, J.R., Thompson, G.M., Zhou, M., Song, X., 2005. Emeishan large igneous

RI

province, SW China. Lithos 79, 475-489.

SC

Ali, J.R., Fitton, J.G., Herzberg, C., 2010. Emeishan large igneous province (SW China) and the mantle-plume up-doming hypothesis. Journal of the Geological

NU

Society 167, 953-959.

MA

Armstrong P.A., 2005. Thermochronometers in Sedimentary Basins. Reviews in Mineralogy and Geochemistry 58, 499-525.

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Beck, A.E., Balling, N. 1988. Determination of virgin rock temperature. In: Haenel,

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R., Rybach, L., Stegena, L. (Eds.), Handbook of terrestrial heat flow density determination. Kluwer Academic Publishers, Dordrecht, Netherlands, pp. 59–86.

CE

Bray, R.J., Green, P.F., Duddy, I.R., 1992. Thermal history reconstruction using

AC

apatite fission track analysis and vitrinite reflectance: a case study from the UK East Midlands and Southern North Sea. Geological Society London Special Publication 67, 3-25. Bryan, S.E., Ernst, R.E., 2008. Revised definition of Large Igneous Provinces (LIPs). Earth-Science Reviews 86, 175-202. Burchfiel, B.C., Chen, Z., Liu, Y., Royden, L.H., 1995. Tectonics of the Longmen Shan and adjacent regions, Central China. International Geology Review 37,

34

ACCEPTED MANUSCRIPT 661-735. Campbell, I.H., Griffiths, R.W., 1990. Implications of mantle plume structure for the evolution of flood basalts. Earth and Planetary Science Letters 99, 79-93. Campbell, I.H., 2005. Large igneous provinces and the mantle plume hypothesis.

PT

Elements 1, 265-269.

RI

Campbell, I.H., Davies, G.F., 2006. Do mantle plumes exist? Episodes 29, 162-168.

SC

Chang, J., Qiu, N., Li, J., 2012. Tectono-thermal evolution of the northwestern edge of the Tarim Basin in China: Constraints from apatite (U–Th)/He thermochronology.

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Journal of Asian Earth Sciences 61, 187-198.

MA

Chen, Y., Xu, Y., Xu, T., Si, S., Liang, X., Tian, X., Deng, Y., Chen, L., Wang, P., Xu, Y., Lan, H., Xiao, F., Li, W., Zhang, X., Yuan, X., Badal, J., Teng, J., 2015.

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Magmatic underplating and crustal growth in the Emeishan Large Igneous Province,

PT E

SW China, revealed by a passive seismic experiment. Earth and Planetary Science Letters 432, 103-114.

CE

Chung, S.-L., Jahn, B., 1995. Plume-lithosphere interaction in generation of the

AC

Emeishan flood basalts at the Permian-Triassic. Geology 23, 889-892. Courtillot, V., Jaupart, C., Manighetti, I., Tapponnier, P., Besse, J., 1999. On causal links between flood basalts and continental breakup. Earth and Planetary Science Letter 166, 177-195. Courtney, R.C., White, R.S., 1986. Anomalous heat flow and geoid across the Cape Verde Rise: evidence for dynamic support from a thermal plume in the mantle. Geophysical Journal International 87, 815-867.

35

ACCEPTED MANUSCRIPT Crough, S.T., 1983. Hotspot Swells. Annual Review of Earth and Planetary Sciences 11, 165-193. Davies, G.F., 1988. Ocean bathymetry and mantle convection: 1. Large-scale flow and hotspots. Journal of Geophysical Research: Solid Earth 93, 10467-10480.

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Davies, G.F., Richards, M.A., 1992. Mantle convection. The Journal of Geology 100,

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151-206.

SC

Davies, G.F., 1999. Dynamic Earth: Plates, plumes and mantle convection. Cambridge University Press, Cambridge, UK.

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DeLaughter, J.E., Stein, C.A., Stein, S., 2005. Hotspots: A view from the swells.

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Geological Society of America Special Paper 388, 257-278. Deng, Y., Zhang, Z., Mooney, W., Badal, J., Fan, W., Zhong, Q., 2014. Mantle origin

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of the Emeishan large igneous province (South China) from the analysis of residual

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gravity anomalies. Lithos 204, 4-13. Deng, Y., Chen, Y., Wang, P., Essa, K.S., Xu, T., Liang, X., Badal, J., 2016. Magmatic

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underplating beneath the Emeishan large igneous province (South China) revealed

AC

by the COMGRA-ELIP experiment. Tectonophysics 672-673, 16-23. Detrick, R.S., Von Herzen, R.P., Parsons, B., Sandwell, D., Dougherty, M., 1986. Heat flow observations on the Bermuda Rise and thermal models of midplate swells. Journal of Geophysical Research Solid Earth 91, 3701–3723. Duddy, I.R., Green, P.F., Hegarty, K.A., Bray, R.J., 1991. Reconstruction of thermal history in basin modelling using apatite fission track analysis: what is really possible? Proceedings Offshore Australia Conference, Australia, pp. 25-38.

36

ACCEPTED MANUSCRIPT Editorial Committee of Regional Stratigraphic Table of Sichuan Province, 1978. Regional stratigraphic table of SW China, Sichuan Province. Geological Publishing House, Beijing, China. (in Chinese) Falvey, D.A., Middleton, M.F., 1981. Passive continental margins: Evidence for

PT

pre-break up deep crustal metamorphic subsidence mechanism. Oceanologica Acta

RI

4, 103-114.

SC

Farley, K.A., Wolf, R.A., Silver, L.T., 1996. The effects of long alpha-stopping distances on (U-Th)/He ages. Geochimica et Cosmochimica Acta 60, 4223-4229.

NU

Farnetani, C.G., Richards, M.A., 1994. Numerical investigations of the mantle plume

MA

initiation model for flood basalt events. Journal of Geophysical Research: Solid Earth 99, 13813-13833.

D

Farnetani, C.G., Hofmann, A.W., 2009. Dynamics and internal structure of a lower

PT E

mantle plume conduit. Earth and Planetary Science Letters 282, 314-322. Feinstein, S., Kohn, B.P., Steckler, M.S., Eyal, M., 1996. Thermal history of the

CE

eastern margin of the Gulf of Suez, I. reconstruction from borehole temperature and

AC

organic maturity measurements. Tectonophysics 266, 203-220. Gao, M., Zeilinger, G., Xu, X., Tan, X., Wang, Q., Hao, M., 2016. Active tectonics evaluation from geomorphic indices for the central and the southern Longmenshan rang on the Eastern Tibetan Plateau, China. Tectonics 35, 1812-1826. Gleadow, A.J.W., Brooks, C.K., 1979. Fission track dating thermal histories and tectonics of igneous intrusions in East Greenland. Contributions to Mineralogy and Petrology 71, 45-60.

37

ACCEPTED MANUSCRIPT Godard, V., Pik, R., Lavé, J., Cattin, R., Tibari, B., Sigoyer, J. de, Pubellier, M., Zhu, J., 2009. Late Cenozoic evolution of the central Longmen Shan, eastern Tibet: Insight from (U-Th)/He thermochronometry. Tectonics 28, TC5009. Green, P.F., Duddy, I.R., Laslett, G.M., Hegrrty, K.A., Gleadow, A.J.W., 1989.

PT

Thermal annealing of fission tracks in apatite: 4. Quantitative modelling techniques

RI

and extension to geological timescales. Chemical Geology 79, 155-182.

Earth and Planetary Science Letters 99, 66-78.

SC

Griffiths, R.W., Campbell, I.H., 1990. Stirring and structure in mantle starting plumes.

NU

Griffiths, R.W., Campbell, I.H., 1991. Interaction of mantle plume heads with the

MA

Earth's surface and onset of small-scale convection. Journal of Geophysical Research 96, 295-310.

D

Guenthner, W.R., Reiners, P.W., Ketcham, R.A., Nasdala, L., Giester, G., 2013.

PT E

Helium diffusion in natural zircon: Radiation damage, anisotropy, and the interpretation of zircon (U-Th)/He thermochronology. American Journal of Science

CE

313, 145-198.

AC

Han, Y., Wu, C., 1993. Geothermal gradient and heat flow values of some deep wells in Sichuan Basin. Oil and Gas Geology 14, 80-84. (in Chinese with English abstract)

Harris, R.N., McNutt, M.K., 2007. Heat flow on hot spot swells: Evidence for fluid flow. Journal of Geophysical Research: Solid Earth 112, B03407. He, B., Xu, Y., Chung, S., Xiao, L., Wang, Y., 2003a. Sedimentary evidence for a rapid, kilometer-scale crustal doming prior to the eruption of the Emeishan flood

38

ACCEPTED MANUSCRIPT basalts. Earth and Planetary Science Letters 213, 391-405. He, B., Xu, Y., Xiao, L., Wang, K., Sha, S., 2003b. Generation and spatial distribution of the Emeishan large igneous province: New evidence from stratigraphic records. Acta Geologica Sinica 77, 194-202. (in Chinese with English abstract)

PT

He, B., Xu, Y.-G., Wang, Y.-M., Luo, Z.-Y., 2006. Sedimentation and lithofacies

RI

paleogeography in southwestern China before and after the Emeishan flood

SC

volcanism: New insights into surface response to mantle plume activity. The Journal of Geology 114, 117-132.

NU

He, B., Xu, Y.-G., Guan, J.-P., Zhong, Y.-T., 2010. Paleokarst on the top of the

MA

Maokou Formation: Further evidence for domal crustal uplift prior to the Emeishan flood volcanism. Lithos 119, 1-9.

D

He, C., Santosh, M., Wu, J., Chen, X., 2014. Plume or no plume: Emeishan Large

PT E

Igneous Province in Southwest China revisited from receiver function analysis. Physics of the Earth and Planetary Interiors 232, 72-78.

CE

He, L., Xu, H., Wang, J., 2011. Thermal evolution and dynamic mechanism of the

AC

Sichuan Basin during the Early Permian-Middle Triassic. Science China Earth Sciences 54, 1948-1954. He, L., 2014. Permian to Late Triassic evolution of the Longmen Shan Foreland Basin (Western Sichuan): Model results from both the lithospheric extension and flexure. Journal of Asian Earth Sciences 93, 49-59. Hill, R.I., 1993. Mantle plumes and continental tectonics. Lithos 30, 193-206. Hill, R.I., Campbell, I.H., Davies, G.F., Griffiths, R.W., 1992. Mantle Plumes and

39

ACCEPTED MANUSCRIPT Continental Tectonics. Science 256, 186-193. Hou, Z., Tian, S., Xie, Y., Yang, Z., Yuan, Z., Yin, S., Yi, L., Fei, H., Zou, T., Bai, G., Li, X., 2009. The Himalayan Mianning–Dechang REE belt associated with carbonatite–alkaline complexes, eastern Indo-Asian collision zone, SW China. Ore

PT

Geology Reviews 36, 65-89.

RI

Hu, S., Zhang, R., Zhou, L., 1998. Methods of thermal history reconstruction for

SC

oil-gas basin. Petroleum Explorationist 3, 52–54. (in Chinese with English abstract) Hu. S., O’Sullivan, P.B., Raza, A., Kohn, B.P., 2001. Thermal history and tectonic

NU

subsidence of the Bohai Basin, northern China: a Cenozoic rifted and local

MA

pull-apart basin. Physics of the Earth and Planetary Interiors 126, 221-235. Hu, S., Fu, M., Yang, S., Yuan, Y., Wang, J., 2007. Palaeogeothermal response and

D

record of Late Mesozoic lithospheric thinning in the eastern North China Craton. In:

PT E

Zhai, M., Windley, B.F., Kusky, T.M., Meng, Q. (Eds), Mesozoic Sub-Continental Lithospheric Thinning Under Eastern Asia. Geological Society, London, Special

CE

Publications 280, 267-280.

AC

Huang, S., Wang, J., 1988. Heat flow pattern in Panxi Paleorift zone, SW China and its mechanical implications. Acta Seismologica Sinica 10, 289-299. (in Chinese with English abstract) Huang, S., Wang, J., 1991. Several heat flow values from deep drill holes in the northwest depression of the Sichuan Basin, SW China. Chinese Science Bulletin 36, 47-51. Hurter, S.J., 1992. Heat flow, thermal structure and thermal evolution of the Parana

40

ACCEPTED MANUSCRIPT Basin, southern Brazil. Ph.D. thesis, The University of Michigan. Jerram, D.A., Widdowson, M., Wignall, P.B., Sun, Y., Lai, X., Bond, D.P.G., Torsvik, T.H., 2016. Submarine palaeoenvironments during Emeishan flood basalt volcanism, SW China: Implications for plume–lithosphere interaction during the Middle

Permian

(‘end

Guadalupian’)

extinction

event.

PT

Capitanian,

RI

Palaeogeography, Palaeoclimatology, Palaeoecology 441, 65-73.

SC

Kerr, A.C., 1994. Lithospheric thinning during the evolution of continental large igneous provinces: A case study from the North Atlantic Tertiary province. Geology

NU

22, 1027-1030.

MA

Larson, R.L., 1991. Geological consequences of superplumes. Geology 19, 963-966. Lerche, I., Yarzab, R.F., Kendall, C. G. St. C., 1984. Determination of paleoheat flux

D

from vitrinite reflectance data. AAPG Bulletin 68, 1704-1717.

PT E

Li, H., Zhang, Z., Ernst, R., Lü, L., Santosh, M., Zhang, D. and Cheng, Z., 2015. Giant radiating mafic dyke swarm of the Emeishan Large Igneous Province,

CE

Identifying the mantle plume centre. Terra Nova, 27, 247-257.

AC

Li, H., Zhang, Z., Santosh, M., Lü, L., Han, L., Liu, W., 2017. Late Permian basalts in the Yanghe area, eastern Sichuan Province, SW China: Implications for the geodynamics of the Emeishan flood basalt province and Permian global mass extinction. Journal of Asian Earth Sciences 134, 293-308. Li, M., Wang, T., Chen, J., He, F., Yun, L., Akbar, S., Zhang, W., 2010. Paleo-heat flow evolution of the Tabei Uplift in Tarim Basin, northwest China. Journal of Asian Earth Sciences 37, 52-66.

41

ACCEPTED MANUSCRIPT Li, X., Li, Z.-X., Zhou, H., Liu, Y., Kinny, P.D., 2002. U–Pb zircon geochronology, geochemistry and Nd isotopic study of Neoproterozoic bimodal volcanic rocks in the Kangdian Rift of South China: implications for the initial rifting of Rodinia. Precambrian Research 113, 135-154.

PT

Li, X.-W., Li, X.-H., Li, Z.-X., 2005. Neoproterozoic bimodal magmatism in the

RI

Cathaysia Block of South China and its tectonic significance. Precambrian

SC

Research 136, 51-66.

Li, Z., Liu, S., Chen, H., Deng, B., Hou, M., Wu, W., Cao, J., 2012. Spatial variation

NU

in Meso-Cenozoic exhumation history of the Longmen Shan thrust belt (eastern

MA

Tibetan Plateau) and the adjacent western Sichuan basin: Constraints from fission track thermochronology. Journal of Asian Earth Sciences 47, 185–203.

D

Loper, D.E., Stacey, F.D., 1983. The dynamical and thermal structure of deep mantle

PT E

plumes. Physics of the Earth and Planetary Interiors 33, 304-317. Lu, Q., Ma, Y., Guo, T., Hu, S., 2007. Thermal history and hydrocarbon generation

CE

history in western Hubei-eastern Chongqing area. Chinese Journal of Geology 42,

AC

189-198. (in Chinese with English abstract) Luo, Z., Jin, Y., Zhao, X., 1990. The Emei Taphrogenesis of the upper Yangtze Platform in south China. Geological Magazine 127, 393-405. McKenzie, D., 1978. Some remarks on the development of sedimentary basins. Earth and Planetary Science Letter 40, 25-32. McKenzie, D., O’Nions, R.K., 1991. Partial melt distributions from inversion of rare earth element concentrations. Journal of Petrology 32, 1021–1091.

42

ACCEPTED MANUSCRIPT Mittelstaedt, E., Tackley, P.J., 2006. Plume heat flow is much lower than CMB heat flow. Earth and Planetary Science Letters 241, 202-210. Morgan, P., Gosnold, W.D., 1989. Heat flow and thermal regimes in the continental United States. Geological Society of America Memoirs 172, 493-522. P.B.,

1999.

Thermochronology,

denudation

and

variations

in

PT

O’Sullivan,

RI

palaeosurface temperature: a case study from the North Slope foreland basin,

SC

Alaska. Basin Research 11, 191–204.

Pierce, K.L., Morgan, L.A., 2009. Is the track of the Yellowstone hotspot driven by a

NU

deep mantle plume? —Review of volcanism, faulting, and uplift in light of new

MA

data. Journal of Volcanology and Geothermal Research 188, 1-25. Pollack, H.N., Chapman, D.S., 1977. On the regional variation of heat flow,

J.,

Wang,

J.,

Qiu,

N.,

PT E

Qin,

D

geotherms, and lithospheric thickness. Tectonophysics 38, 279-296. McInnes,

B.I.A.,

Tao,

C.,

2010.

New

paleo-geothermometers for the inversion of dynamic thermal evolution history of

CE

marine sequences in South China— (U-Th)/He age and closure temperature of

AC

apatite and zircon. Oil & Gas Geology 31, 277–287. (in Chinese with English abstract)

Qiu, N., Qin, J., McInnes, B.I.A., Wang, J., Tenger, Zhen, L., 2008. Tectonothermal evolution of the northeastern Sichuan basin: Constraints from apatite and zircon (U-Th)/He ages and vitrinite data. Geological Journal of Chinese Universities 14, 223-230. (in Chinese with English abstract) Qiu, N., Jiang, G., Mei, Q., Chang, J., Wang, S., Wang, J., 2011. The Paleozoic

43

ACCEPTED MANUSCRIPT tectonothermal evolution of the Bachu Uplift of the Tarim Basin, NW China: constraints from (U-Th)/He ages, apatite fission track and vitrinite reflectance data. Journal of Asian Earth Sciences 41, 551-563. Qiu, N., Zuo, Y., Chang, J., Li, W., 2014. Geothermal evidence of Meso-Cenozoic

PT

lithosphere thinning in the Jiyang sub-basin, Bohai Bay Basin, eastern North China

RI

Craton. Gondwana Research 26, 1079-1092.

SC

Reiners, P.W., 2005. Zircon (U–Th)/He thermochronometry. Reviews in Mineralogy and Geochemistry 58, 151–179.

NU

Rudnick, R.L., McDonough, W.F., O’Connell, R.J., 1998. Thermal structure,

MA

thickness and composition of continental lithosphere. Chemical Geology 145, 395-411.

D

Sahu, H.S., Raab, M.J., Kohn, B.P., Gleadow, A.J.W., Kumar, D., 2013. Denudation

PT E

history of Eastern Indian peninsula from apatite fission track analysis: Linking possible plume-related uplift and the sedimentary record. Tectonophysics 608,

CE

1413-1428.

AC

Saunders, A.D., Jones, S.M., Morgan, L.A., Pierce, K.L., Widdowson, M., Xu, Y.G., 2007. Regional uplift associated with continental large igneous provinces: the roles of mantle plumes and the lithosphere. Chemical Geology 241, 282-318. Sclater, J.G., Christie, P.A.F., 1980. Continental stretching: An explanation of the Post-Mid-Cretaceous subsidence of the central North Sea Basin. Journal of Geophysical Research Atmospheres 85, 3711-3739. Shellnutt, J.G., Zhou, M.-F., Yan, D.-P., Wang, Y., 2008. Longevity of the Permian

44

ACCEPTED MANUSCRIPT Emeishan mantle plume (SW China): 1Ma, 8Ma or 18Ma? Geological Magazine 145, 373-388. Shellnutt, J.G., Denyszyn, S.W., Mundil, R., 2012. Precise age determination of mafic and felsic intrusive rocks from the Permian Emeishan large igneous province (SW

PT

China). Gondwana Research 22, 118-126.

RI

Shellnutt, J.G., 2014. The Emeishan large igneous province: A synthesis. Geoscience

SC

Frontiers 5, 369-394.

Shi, L., Lou, H., Wang, Q., Lu, H., Xu, W., 2015. Gravity field characteristics and

NU

crust density structure in the Panxi region, China. Chinese Journal of Geophysics

MA

58, 2402-2412. (in Chinese with English abstract)

Sleep, N.H., 1990. Hotspots and mantle plumes: Some phenomenology. Journal of

D

Geophysical Research: Solid Earth 95, 6715-6736.

PT E

Sleep, N.H., 2006. Mantle plumes from top to bottom. Earth-Science Reviews 77, 231-271.

CE

Stein, C.A., Stein, S., 2003. Mantle plumes: heat-flow near Iceland. Astronomy &

AC

Geophysics 44, 1.08-1.10(1). Sun, Y, Lai, X., Wignall, P.B., Widdowson, M., Ali, J.R., Jiang, H., Wang, W., Yan, C., Bond, D.P.G., Védrine, S., 2010. Dating the onset and nature of the Middle Permian Emeishan large igneous province eruptions in SW China using conodont biostratigraphy and its bearing on mantle plume uplift models. Lithos 119, 20-33. Sweeney, J.J., Burnham, A.K., 1990. Evaluation of a simple model of vitrinite reflectance based on chemical kinetics. AAPG Bulletin 74, 1559-1571.

45

ACCEPTED MANUSCRIPT Tian, Y., Qiu, N., Kohn, B.P., Zhu, C., Hu, S., Gleadow, A.J.W., McInnes, B.I.A., 2012. Detrital zircon (U–Th)/He thermochronometry of the Mesozoic Daba Shan Foreland Basin, central China: Evidence for timing of post-orogenic denudation. Tectonophysics 570-571, 65-77.

PT

Tian, Y., Kohn, B.P., Gleadow, A.J.W., Hu, S., 2013. Constructing the Longmen Shan

RI

eastern Tibetan Plateau margin: Insights from low-temperature thermochronology.

SC

Tectonics 32, 576-592.

Tian, J., Lin, X., Guo, W., Zhang, X., Huang, P., 2017. Geological significance of oil

NU

and gas in the Permian basalt eruption event in Sichuan Basin, China. Journal of

Chinese with English abstract)

MA

Chengdu University of Technology (Science & Technology Edition) 44, 14-20. (in

D

Tran, T.H., Lan, C., Usuki, T., Shellnutt, J.G., Pham, T.D., Tran, T.A., Pham, N.C.,

PT E

Ngo, T.P., Izokh, A.E., Borisenko, A.S., 2015. Petrogenesis of Late Permian silicic rocks of Tu Le basin and Phan Si Pan uplift (NW Vietnam) and their association

AC

1-19.

CE

with the Emeishan large igneous province. Journal of Asian Earth Sciences 109,

Utskins Peate, I., Bryan, S.E., 2008. Re-evaluating plume-induced uplift in the Emeishan large igneous province. Nature Geoscience 1, 625-629. Utskins Peate, I., Bryan, S.E., 2009. Reply to pre-eruptive uplift in the Emeishan. Nature Geoscience 2, 531e532. Utskins Peate, I., Bryan, S.E., Wignall, P.B., Jerram, D.A., Ali, J.R., 2011. Comment on ‘Paleokarst on the top of the Maokou Formation: further evidence for domal

46

ACCEPTED MANUSCRIPT crustal uplift prior to the Emeishan flood volcanism’. Lithos 125, 1006e1008. Vilà, M., Fernández, M., Jiménez-Munt, I., 2010. Radiogenic heat production variability of some common lithological groups and its significance to lithospheric thermal modelling. Tectonophysics 490, 152-164.

PT

Von Herzen, R.P., Detrick, R.S., Crough, S.T., Epp, D., Fehn, U., 1982. Thermal

SC

Geophysical Research: Solid Earth 87, 6711-6723.

RI

origin of the Hawaiian swell: Heat flow evidence and thermal models. Journal of

Von Herzen, R.P., Cordery, M.J., Detrick, R.S., Fang, C., 1989. Heat flow and the

NU

thermal origin of hot spot swells: the Hawaiian swell revisited. Journal of

MA

Geophysical Research: Solid Earth 94, 13783-13799. Wang, E., Burchfiel, B.C., 2000. Late Cenozoic to Holocene deformation in

D

southwestern Sichuan and adjacent Yunnan, China, and its role in formation of the

112, 413-423.

PT E

southeastern part of the Tibetan Plateau. Geological Society of America Bulletin

CE

Wang, J., Huang, S., 1987. Linear relationship between heat flow and heat production

AC

in Panxi Paleorift Zone, southwestern China. Geophysical Research Letters 14, 272-274.

Wang, J., Huang, S., Huang, G., Wang, J., 1990. Basic characteristics of the earth's temperature distribution in China. Geological Publishing House, Beijing, China. (in Chinese) Wang, J.-H., Yin, A., Harrison, T.M., Grove, M., Zhang, Y.-Q., Xie, G.-H., 2001. A tectonic model for Cenozoic igneous activities in the eastern Indo–Asian collision

47

ACCEPTED MANUSCRIPT zone. Earth and Planetary Science Letters 188, 123-133. Wang, X.-C., Li, X.-H., Li, W.-X., Li, Z.-X., 2007. Ca. 825 Ma komatiitic basalts in South China: First evidence for >1500 °C mantle melts by a Rodinian mantle plume. Geology 35, 1103-1106.

PT

Wang, X.-C., Li, X.-H., Li, W.-X., Li, Z.-X., Liu, Y., Yang, Y.-H., Liang, X.-R., Tu,

RI

X.-L., 2008. The Bikou basalts in the northwestern Yangtze block, South China:

SC

Remnants of 820–810 Ma continental flood basalts? Geological Society of America Bulletin 120, 1478-1492.

NU

Wang, X.-C., Li, X.-H., Li, X.-W., Li, Z.-X., 2009. Variable involvements of mantle

MA

plumes in the genesis of mid-Neoproterozoic basaltic rocks in South China: A review. Gondwana Research 15, 381-395.

D

White, R., McKenzie, D., 1989. Magmatism at rift zones: The generation of volcanic

PT E

continental margins and flood basalts. Journal of Geophysical Research Atmospheres 94, 7685-7729.

CE

Wignall, P.B., 2001. Large igneous provinces and mass extinctions. Earth-Science

AC

Reviews 53, 1-33.

Wolf, R.A., Farley, K.A., Silver, L.T., 1996. Helium diffusion and low-temperature thermochronometry of apatite. Geochimica et Cosmochimica Acta 60, 4231-4240. Wolf, R.A., Farley, K.A., Kass, D.M., 1998. Modeling of the temperature sensitivity of the apatite (U–Th)/He thermochronometer. Chemical Geology 148, 105-114. Wolfe, M.R., Stockli, D.F., 2010. Zircon (U–Th)/He thermochronometry in the KTB drill hole, Germany, and its implications for bulk He diffusion kinetics in zircon.

48

ACCEPTED MANUSCRIPT Earth and Planetary Science Letters 295, 69–82. Wu, Q., Zu, J., Xie, Y., Wang, D., 1988. Characteristics of geothermal field in Yunnan region. Seismology and Geology 10, 177-183. (in Chinese with English abstract) Xiao, L., Xu, Y., Xu, J., He, B., Franco, P., 2004. Chemostratigraphy of flood basalts

PT

in the Garzê-Litang region and Zongza Block: Implications for western extension

RI

of the Emeishan large igneous province, SW China. Acta Geologica Sinica 78,

SC

61-67.

Xie, B., Wang, L., Zhang, J., Chen, J., 2003. Vertical distribution and geochemical

NU

behaviours of the hydrocarbon source rocks in the north section of Longmen

MA

Mountains. Natural Gas Industry 23, 21-23.

Xiong, L., Zhang, B., He, L., Yang, Y., Zou, J., Ran, F., Pei, S., 2011. Eruption setting

D

and distribution of the Permian basalt at the southwest end of the west Sichuan

PT E

Depression. Acta Geologica Sichuan 31, 260-265. (in Chinese with English abstract)

CE

Xu, M., Zhu, C.-Q., Tian, Y.-T., Rao, S., Hu, S.-B., 2011. Borehole Temperature

AC

Logging and Characteristics of Subsurface Temperature in the Sichuan Basin. Chinese Journal of Geophysics 54, 224-233. Xu, T., Zhang, Z., Liu, B., 2015. Crustal velocity structure in the Emeishan large igneous province and evidence of the Permian mantle plume activity. Science China Earth Sciences 58, 1133-1147. Xu, W., Qiu, N., 2017. Heat flow and destabilized Cratons: a comparative study of the North China, Siberian and Wyoming Cratons. International Geology Review 59,

49

ACCEPTED MANUSCRIPT 898-918. Xu, Y., Chung, S.-L., Jahn, B., Wu, G., 2001. Petrologic and geochemical constraints on the petrogenesis of Permain-Triassic Emeishan flood basalts in southwestern China. Lithos 58, 145-168.

PT

Xu, Y.-G., He, B., Chung, S.-L., Menzies, M.A., Frey, F.A., 2004. Geologic,

RI

geochemical, and geophysical consequences of plume involvement in the Emeishan

SC

flood-basalt province. Geology 32, 917-920.

Xu, Y.-G., He, B., Huang, X., Luo, Z., Chung, S.-L., Xiao, L., Zhu, D., Shao, H., Fan,

NU

W.-M., Xu, J., Wang, Y.-J., 2007. Identification of mantle plumes in the Emeishan

MA

Large Igneous Province. Episodes 30, 32-42.

Yang, P., Yin, F., Yu, Q., Wang, Z., Liu, J., Zhang, D., Zhang, D., 2015. Evolution

D

anomaly of organic matter and characteristics of palaeogeothermal field in the

PT E

southeast edge of Sichuan Basin. Natural Gas Geoscience 26, 1299-1309. (in Chinese with English abstract)

CE

Zeng, D., 1988. A preliminary study on the restoration for the various denuded

AC

sequences of Sichuan Basin. Experimental Petroleum Geology 10, 134-141. (in Chinese with English abstract) Zhang, Y., Luo, Y., Yang, C., 1988. Panxi rift. Geological Publishing House, Beijing, China. (in Chinese) Zhang, Z., Mahoney, J.J., Mao, J., Wang, F., 2006. Geochemistry of Picritic and Associated Basalt Flows of the Western Emeishan Flood Basalt Province, China. Journal of Petrology 22, 1997-2019.

50

ACCEPTED MANUSCRIPT Zhang, Z., Zhi, X., Chen, L., Saunders, A.D. and Reichow, M.K., 2008. Re-Os isotopic compositions of picrites from the Emeishan flood basalt province, China. Earth and Planetary Science Letters, 276, 30-39. Zhong, Y.-T., He B., Mundil, R., Xu, Y.-G., 2014. CA-TIMS zircon U-Pb dating of

PT

felsic ignimbrite from the Binchuan section: Implications for the termination age of

RI

Emeishan large igneous province. Lithos 204, 14-19.

SC

Zhou, M.-F., Robinson, P.T., Lesher, C.M., Keays, R.R., Zhang, C.-J., Malpas, J., 2005. Geochemistry, Petrogenesis and Metallogenesis of the Panzhihua Gabbroic

NU

Layered Intrusion and Associated Fe–Ti–V Oxide Deposits, Sichuan Province, SW

MA

China. Journal of Petrology 46: 2253-2280.

Zhu, B., Guo, Z., Liu, R., Liu, D., Du, W., 2014. No pre-eruptive uplift in the

D

Emeishan large igneous province: New evidences from its ‘inner zone’, Dali area,

PT E

Southwest China. Journal of Volcanology and Geothermal Research 269, 57-67. Zhu, C., Xu, M., Shan, J., Yuan, Y., Zhao, Y., Hu, S., 2009. Quantify the denudations

CE

of major tectonic events in Sichuan Basin: Constrained by the paleothermal records.

AC

Geology in China 36, 1269-1277. (in Chinese with English abstract) Zhu, C., Xu, M., Yuan, Y., Zhao, Y., Shan, J., He, Z., Tian, Y., Hu, S., 2010. Palaeogeothermal response and record of the effusing of Emeishan basalts in the Sichuan basin. Chinese Science Bulletin 55, 949-956. Zhu. C., Qiu, N., Jiang. Q., Hu, S., Zhang, S., 2015. Thermal history reconstruction based on multiple paleo-thermal records of the Yazihe area, Western Sichuan Depression, SW China. Chinese Journal of Geophysics 58, 3660-3670.

51

ACCEPTED MANUSCRIPT Zhu, C., Hu, S., Qiu, N., Jiang, Q., Rao, S., Liu, S., 2016a. Geothermal constraints on Emeishan mantle plume magmatism: paleotemperature reconstruction of the Sichuan Basin, SW China. International Journal of Earth Sciences. doi: 10.1007/s00531-016-1404-2.

PT

Zhu, C., Qiu, N., Cao, H., Rao, S., Hu, S., 2016b. Paleogeothermal reconstruction and

AC

CE

PT E

D

MA

NU

SC

Sichuan Basin. Journal of Earth Science 27, 796-806.

RI

thermal evolution modeling of source rocks in the Puguang gas field, northeastern

52

ACCEPTED MANUSCRIPT Table 1. Single grain zircon (U-Th)/He dating results. Sample

Lab.

Strat.

No.

Elev.

4

(m)

(ncc)

He

U ppm

Th ppm

a

[eU]

b

FT

ppm

Corrected

Error

age (Ma)

(±1s)

13387

D

870

353.3

344.3

48.1

355.6

0.82

683.8

42.4

SS-1

13388

D

870

108.2

573.4

391.9

665.5

0.77

260.7

16.2

SS-1

13389

D

870

73.4

263.2

255.9

SS-3

13390

O

894

46.6

698.1

358.6

SS-3

13391

O

894

32.1

257.1

SS-3

13392

O

894

41.8

426.9

GX-8

13426

D

575

84.7

GX-8

13427

D

575

GX-8

13428

D

575

EM-1

13429

Granite

714

EM-1

13430

Granite

EM-1

13431

BC-3

13432

0.76

341.9

21.2

782.4

0.71

212.8

13.2

184.8

300.6

0.72

304.7

18.9

105.2

0.67

503.7

31.2

308.6

435.5

0.79

211.1

13.1

NU

451.7

43.1

308.7

218.2

359.9

0.74

258.5

16.0

30.1

206.4

140.6

239.4

0.77

197.6

12.2

4.876

1235.4

714.5

1403.3

0.75

5.2

0.3

714

7.906

679.0

1384.0

1004.2

0.77

8.7

0.5

Granite

714

8.836

1957.6

1498.2

2309.7

0.79

4.5

0.3

CE

SC

323.4

RI

PT

SS-1

Є

716

5.8

220.8

96.9

243.6

0.67

124.4

7.7

13434

Є

716

4.6

87.6

61.3

102.0

0.71

136.3

8.4

MA

D

QP-4

AC

PT E

363.0

13435

Granite

1097

13.8

169.8

105.4

194.6

0.82

28.8

1.8

QP-4

13436

Granite

1097

7.3

149.2

101.2

172.9

0.84

19.5

1.2

QP-4

13437

Granite

1097

14.0

160.6

86.6

180.9

0.84

28.6

1.8

DY-10

13438

Gabbro

1280

21.5

764.8

150.2

800.1

0.80

26.6

1.6

DY-10

13439

Gabbro

1280

5.7

378.4

159.3

415.8

0.78

19.2

1.2

BC-3

53

ACCEPTED MANUSCRIPT

DY-10

Gabbro

1280

7.2

982.9

230.7

1037.1

0.73

Effective uranium concentration (U ppm+0.235 Th ppm).

PT E

D

MA

NU

SC

RI

PT

FT is the a-ejection correction after Farley et al. (1996).

CE

b

AC

a

13440

54

15.4

1.0

ACCEPTED MANUSCRIPT Highlights 

The regional heat flow is examined to trace the after effects of the Emeishan mantle plume.



Paleogeothermal indicators were used to constrain the thermal effect of the Emeishan large igneous province. New geothermal evidence for the pre-volcanism uplift and implications for the

CE

PT E

D

MA

NU

SC

RI

PT

lateral extent of the Emeishan mantle plume.

AC



55

Graphics Abstract

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12