Zircon U–Pb age, geochemical, and Sr–Nd–Hf isotopic constraints on the origin of mafic dykes in the Shaanxi Province, North China Craton, China

    Zircon U-Pb age, geochemical, and Sr-Nd-Hf isotopic constraints on the origin of mafic dykes in the Shaanxi Province, North China Craton, China Shen Liu, Caixia Feng, Bor-ming Jahn, Ruizhong Hu, Shan Gao, Ian M. Coulson, Guangying Feng, Shaocong Lai, Chaogui Yang, Yuhong Yang PII: DOI: Reference:

S0024-4937(13)00137-0 doi: 10.1016/j.lithos.2013.04.020 LITHOS 2977

To appear in:

LITHOS

Received date: Accepted date:

25 February 2013 24 April 2013

Please cite this article as: Liu, Shen, Feng, Caixia, Jahn, Bor-ming, Hu, Ruizhong, Gao, Shan, Coulson, Ian M., Feng, Guangying, Lai, Shaocong, Yang, Chaogui, Yang, Yuhong, Zircon U-Pb age, geochemical, and Sr-Nd-Hf isotopic constraints on the origin of mafic dykes in the Shaanxi Province, North China Craton, China, LITHOS (2013), doi: 10.1016/j.lithos.2013.04.020

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ACCEPTED MANUSCRIPT Zircon U-Pb age, geochemical, and Sr-Nd-Hf isotopic constraints on the origin of mafic dykes in the Shaanxi

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Province, North China Craton, China

Shen Liua, Caixia Fenga, Bor-ming Jahnb, Ruizhong Huc, Shan Gaod, Ian M. Coulsone,

a

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Guangying Fengf, Shaocong Laia, Chaogui Yangc, Yuhong Yangc

State Key Laboratory of Continental Dynamics and Department of Geology,

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Northwest University, Xi’ an 710069, China

Department of Geosciences, National Taiwan University, Taipei, Taiwan

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State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry,

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b

Chinese Academy of Sciences, Guiyang 550002, China State Key Laboratory of Geological Processes and Mineral Resources, China

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d

University of Geosciences, Wuhan 430074, China Solid Earth Studies Laboratory, Department of Geology, University of Regina,

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e

Regina, Saskatchewan, S4S 0A2, Canada f

Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037,

China

* Corresponding author. Tel: +86 29 88300226; Fax: +86 29 88300226 E-mail address: [email protected]; [email protected] (Shen Liu) *

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ACCEPTED MANUSCRIPT Abstract Mafic dolerite dykes form a series of swarms that are widespread across the North

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China Craton (NCC). We present U-Pb zircon ages, geochemical data, and Sr-Nd-Hf

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isotopic data for representative samples of the Shaanxi dolerite dykes in the southern NCC. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon analyses for three samples yield ages ranging from 448.1 ± 1.2 to 489.6

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± 0.9 Ma (i.e., Cambro-Ordovician). The dolerites are characterized by a wide range

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of rock compositions. They display enrichments in light rare earth element (LREEs) and large ion lithophile element (LILE) (i.e., Ba, U, K and Pb), as well as depletion in

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high field strength (HFSE) (Nb, Ta, Hf and Ti). The mafic dykes have relatively

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uniform (87Sr/86Sr)i ranging from 0.7049 to 0.7076, (176Hf/177Hf)i from 0.282187 to

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0.282236, low εNd (t) values, from -4.1 to -4.9, εHf (t) values of between −7.9 and −9.8, for zircon, and high hafnium model ages (TDM1 = 1366-1535 Ma, TDM2 = 1924-2081

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Ma). These results suggest that the dykes are derived by partial melting of an enriched, lithospheric mantle source. The magmas underwent fractionation of olivine, pyroxene, plagioclase, and Ti-bearing phases (rutile, ilmenite, titanite), along with crustal contamination. The formation of the Shaanxi Province, NCC mafic dykes can be attributed to the collision between the NCC and south Qinling Block. Specifically, these magmas formed as a result of crustal thinning in response to extension that followed this collision.

Keywords: Palaeozoic, mafic dykes, petrogenesis, Shaanxi Province, NCC

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ACCEPTED MANUSCRIPT 1. Introduction The NCC is composed of three Archaean tectonic units: an Eastern Continent

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(EC, > 2500 Ma), a Western Continent (WC, > 2500 Ma), and a Middle Continent

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(Zhao et al., 2002; Kusky and Li, 2003), and many provinces (e.g., Jilin, Liaoning, Beijing, Inner Mongolia, Hebei, Shanxi, Shandong and Shaanxi,) are located within this ancient cratonic part of China (Fig. 1a). Swarms of more than six hundred mafic

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dykes (that include dolerite, dolerite-porphyry and lamprophyre) are widespread in

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the NCC, commonly occurring as NE-NW-WE-trending swarms (Liu et al., 2008a, b, 2009, 2012a, b, c, d; 2013). It is generally accepted that these mafic dykes formed as

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a result of considerable extension of the continental lithosphere (Hall, 1982; Hall and

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Fahrig, 1987; Tarney and Weaver, 1987; Zhao and McCulloch, 1993). Therefore,

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studies of the NCC mafic dyke swarms can provide critical insights in our understanding of the generation of extensive mafic magmatism, and also valuable

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information concerning the lithospheric evolution (extensional process, mantle source, and temporal and spatial evolution) relating to the break up of the NCC (e.g., Liu, 2004, Liu et al., 2006, 2008a, b, 2009, 2012a, b, c, d, 2013), as well as to mineralization present across the NCC. Although there is some published work on the NCC mafic dykes these studies have focused mainly on the Mesozoic (e.g., Zhang and Sun, 2002; Yang et al., 2004; Liu, 2004, Liu et al., 2006, 2008a, b, 2009, 2012b, c, d, 2013) and Precambrian (e.g., Hou et al., 2006, 2008; John et al., 2010; Li et al., 2010; Peng, 2010; Peng et al., 2005, 2007, 2008, 2010, 2011a, b; Liu et al., 2012a) NCC mafic dyke swarms.

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ACCEPTED MANUSCRIPT However, little is known about Paleozoic mafic dykes that are also present. Furthermore, it is generally accepted that significant lithospheric extension occurred

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during the early Paleozoic in the southern Shaanxi Province; however, the extent of

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this extension and its timing are still unclear. There is also considerable controversy relating to the timing (Paleozoic or Mesozoic) of collision between the NCC and Yangtze Block. Consequently, the investigation of Palaeozoic crustal extension and

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related mafic magmatism, through investigation of NCC mafic dyke swarms can

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provide significant information on a wide range of geological issues. In this paper we present new Laser ablation inductively coupled plasma mass

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spectrometry (LA-ICP-MS) zircon U-Pb ages, petrography, major, trace element and

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Sr-Nd-Hf isotopic data for NCC mafic dykes in the Shaanxi region. In doing so we will:

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(1) constrain the emplacement age(s) of the mafic dykes; (2) determine their petrogenesis; and (3) understand the evolution of the lithospheric mantle beneath the

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southern NCC.

2. Geological setting and petrography The NCC comprises two Archaean blocks, an eastern and a western block, that are separated by a 1.8 Ga N-S trending Proterozoic orogenic belt (Middle continent) (Zhao et al., 2001) (Fig. 1a). Two geological sutures occur in the southern Shaanxi Province, i.e., the Mian-Lue suture and Shang-Dan suture. The more southerly, Mian-Lue suture mainly comprises an ophiolitic mélange, ancient gneiss, granite, mafic volcanic rocks, and mafic dykes, whereas for the northerly Shang-Dan suture,

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ACCEPTED MANUSCRIPT rock types include ophiolite, volcanic rocks, dolomite, and cherts (Shaanxi Province bureau of geology and mineral resources, 1989).

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The mafic dykes are widespread in the Shaanxi Province and study area is

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situated in the southern section of the Province, southern NCC, near to the Shang-Dan suture (Fig. 1). . The country rocks in the area include predominantly, monzonite and granite, gabbro and peridotite, and gneiss, and, although the mafic

gabbro-peridotite

(Fig.1b).

Individual

mafic

dykes

are

vertical

and

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and

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dykes intrude all of these lithologies, they principally occur within monzonite-granite

NE-NW-NS-trending (Fig. 1c); they are commonly 20 m-1.2 km wide and 0.6-12.5 km

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in length (Fig. 1b). Representative photomicrographs of the mafic dykes in the

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vicinities of Jiuchaigou, Jinlonghe and Dashejian are provided in Fig. 2. The mafic

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dykes outcrop as linear features, and the dyke rocks are all dolerite with a typical doleritic texture.

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The dykes are massive, locally vesicular, and structure, fine to medium granularity, and dark-grey or grey-green in colour. In addition, the dykes mainly contain sub- to anhedral clinopyroxene (30-50 %), elongate to columnar plagioclase (30-45 %), and minor olivine, biotite, quartz, apatite, magnetite and llmenite (<12 %). Generally, the clinopyroxene is altered to a mixture of chlorite, amphibole and carbonate minerals, whereas plagioclase locally is replaced by albite, epidote and kaolinite. Rarely, small and altered granite xenoliths occur within the mafic dykes. Dolerite dykes from Jiuchaigou are vertical in outcrop, trend NW, and are typically 6.0-30 m wide and ~ 350m long. These grey-green coloured dykes chiefly comprise 30-35 %

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ACCEPTED MANUSCRIPT medium-grained phenocrysts of clinopyroxene (2-4 mm) and lath-shaped plagioclase (2-3 mm), within a 65-70 % groundmass of clinopyroxene, plagioclase and minor

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magnetite. In contrast, dolerite from Jinlonghe and Dashejian are also vertical, trend

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NW-NE, are 1.5-4.0 m wide, and 40-150m long, and comprise 25-40 % medium-coarse grained phenocrysts of clinopyroxene (2-4 mm) and plagioclase (2-3

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mm), in a 60-75 % matrix of clinopyroxene, plagioclase, minor magnetite and chlorite.

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3. Analytical procedures

3.1. U-Pb dating by LA-ICP-MS methods

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Zircon was separated from three samples (JLH-1, DSJ-1, and JCG-2) using

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conventional heavy liquid and magnetic techniques at the Langfang Regional

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Geological Survey, Hebei Province, China. Zircon separates were examined under transmitted and reflected light, as well as by cathodoluminescence petrography (CL)

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at the State Key Laboratory of Continental Dynamics, Northwest University, China to observe their external and internal structures. Laser-ablation techniques were employed for zircon age determinations (Table 1- supplemental table; Fig. 3) using an Agilent 7500a ICP-MS instrument equipped with a 193 nm excimer laser at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geoscience, Wuhan, China. Zircon # 91500 was used as a standard, and NIST 610 was used to optimise the results. A spot diameter of 24 μm was used.

Prior to

LA-ICP-MS zircon U-Pb dating, the surfaces of the grain mounts were washed in dilute HNO3 and pure alcohol to remove any potential lead contamination. Details of

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ACCEPTED MANUSCRIPT the analytical methodology have been described in Yuan et al. (2004) and Liu et al. (2010). Corrections for common Pb were performed following Andersen (2002). Data

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were processed using the GLITTER and ISOPLOT programs (Ludwig, 2003) (Table

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1- supplemental table; Fig. 3). Errors for individual analyses by LA-ICP-MS were quoted at the 95 % (1σ) confidence level.

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3.2. Major elemental and trace elemental analyses

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Eighteen samples were analyzed for major and trace element and Sr-Nd isotopes. Whole-rock samples were trimmed to remove altered surfaces, cleaned with

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de-ionised water, and then crushed and powdered using an agate mill. Major

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elements were determined using a PANalytical Axios-advance (Axios PW4400)

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X-ray fluorescence spectrometer (XRF) at the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences. Fused

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glass discs were utilsed and the analytical precision was better than 5 %, as determined based on the Chinese National standards: GSR-1 and GSR-3 (Table 2). Loss on ignition (LOI) was obtained using 1 g of powder heated to 900°C for 2 hour. Trace elements were analysed by plasma optical emission mass-spectrometry (MS) and ICP-MS at the National Research Center of Geo-analysis, Chinese Academy of Geosciences. The discrepancy among triplicates was less than 5 % for all elements. Analysis results of the international standards OU-6 and GBPG-1 were in agreement with the recommended values (Table 3).

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ACCEPTED MANUSCRIPT 3.3 Sr-Nd isotopic analyses For the analysis of Rb-Sr and Sm-Nd isotopes, sample powders were spiked with

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mixed isotope tracers, dissolved in Teflon capsules with HF+HNO3 acids, and

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separated by conventional cation-exchange techniques. Isotopic measurements were performed using a Finnigan Triton Ti thermal ionization mass spectrometer at the State Key Laboratory of Geological Processes and Mineral Resources, China

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University of Geosciences, Wuhan, China. Procedural blanks were < 200 pg for Sm

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and Nd, as well as < 500 pg for Rb and Sr. Mass fractionation corrections for Sr and Nd isotopic ratios were based on

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Sr/88Sr = 0.1194 and

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Nd/144Nd = 0.7219,

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respectively. Analyses of standards yielded the following results: NBS987 gave Sr/86Sr = 0.710246 ± 16 (2σ) and La Jolla gave

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87

143

Nd/144Nd = 0.511863 ± 8 (2σ).

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The analytical results for Sr-Nd isotopes are presented in Table 4.

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3.4. In situ zircon Hf isotopic analysis In situ, zircon Hf isotopic analyses were conducted using a Neptune multiple collector (MC)-ICP-MS, equipped with a 193 nm laser, at the Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing, China. During the analysis, a laser repetition rate of 10 Hz at 100 mJ was used, as were spot sizes of 32 and 63 μm. Details of the analytical technique are described in Wu et al. (2006). During the analysis, the

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Hf/177Hf and

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Lu/177Hf ratios of the standard zircon (91500) were

0.282300 ± 15 (2σn, n = 24) and 0.00030, similar to the commonly accepted 176

Hf/177Hf ratio of 0.282302 ± 8 and 0.282306 ± 8 (2σ) measured using the solution

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ACCEPTED MANUSCRIPT method (Goolaerts et al., 2004). The analytical results are listed in Table 5

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(supplemental table).

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4. Results 4.1. Zircon U-Pb ages

Euhedral zircon grains in samples JLH-1, DSJ-1, and JCG-2 are clean and

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Pb/238U age of 450.9 ± 1.2 Ma (1σ) (95 % confidence interval) for

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weighted mean

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prismatic, with magmatic oscillatory zoning (Fig. 3). A total of 12 grains provided a

JLH-1; 10 grains have a weighted mean

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Pb/238U age of 448.1 ± 1.2 Ma (1σ) (95 %

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confidence interval) for DSJ-1, and 15 grains gave a weighted mean 206Pb/238U age of

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489.6 ± 0.9 Ma (1σ) (95 % confidence interval) for JCG-2 (Table 1- supplemental

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table; Fig. 3a-c). These determinations are the best estimates of the crystallisation

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ages of the dolerite dykes. There was no inherited zircon characteristics observed.

4.2. Major and trace elements Geochemical data on the mafic dykes in the study area are presented in Tables 2 and 3. The dolerite samples exhibit a wide range of geochemical compositions, falling into both the alkaline (JLH and DSJ) and calc-alkaline fields (JCG) in terms of the total alkali-silica (TAS) diagram (Fig. 4a); rock types include basaltic andesite, basaltic trachy-andesite, andesite, and trachy-andesite. The JLH and DSJ dyke samples also display an affinity to shoshonitic compositions, whereas JCG samples are again calc-alkaline, in terms of Na2O vs. K2O (Fig. 4b). The dykes display regular

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ACCEPTED MANUSCRIPT trends of decreasing TiO2, Fe2O3, and MgO with increasing SiO2 (Fig. 5b, c, d) and are also characterized by LREE enrichment and HREE depletion, with a wide range

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in La/Yb ratios and EuN/Eu* (Table 3 and Fig. 6a). On primitive mantle-normalised

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trace element diagrams, the mafic samples show enrichment in LILEs (i.e., Ba, U, K, and Pb) and depletion in HFSEs (i.e., Nb, Ta, Hf, and Ti) (Fig. 6b).

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4.3. Sr-Nd isotopes

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Sr-Nd isotopic data have been obtained from (twelve) representative mafic dyke samples (Table 4). The dykes show very different (87Sr/86Sr) i values ranging from

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0.7049 to 0.7076, and relatively little variation in εNd (t) values from -4.1 to -4.9. The

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Sr-Nd isotopic compositions (Fig. 7) are also comparable to those of early Palaeozoic

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mafic rocks determined previously for the NCC.

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4.4. Zircon Hf isotopes

Three samples of zircon dated by U-Pb methods were also analysed for their Lu-Hf isotopes, and the results are presented in Table 5 (supplemental table). Sixteen spot analyses were obtained for the zircon sample, JLH-1, yielding variable εHf (t) values of between -8.6 and -9.0 (Fig. 8a), with two-stage model ages (TDM2) of 1968 to 1997 Ma (Fig. 8d), and giving initial

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Hf/177Hf ratios ranging from 0.282236 to

0.282249. Fifteen spot analyses were made for sample DSJ-1. The determined negative ε

Hf

(t) values for this zircon vary between -7.9 and -8.2 (Fig. 8b),

corresponding to TDM2 model ages in the range 1924 to 1944 Ma (Fig. 8e). This

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ACCEPTED MANUSCRIPT sample has an initial

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Hf/177Hf ratio that varies between 0.282261 and 0.282271.

Fifteen spot analyses were also performed on zircon from sample JCG-2. The (t) values for this dyke vary between -9.4 and -9.9 (Fig. 8c),

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Hf

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determined negative ε

sample has initial

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corresponding to TDM2 model ages in the range of 2049 to 2081 Ma (Fig. 8f). This 176

Hf/177Hf ratios that vary between 0.282187 and 0.282200. The

zircon Hf isotopic results also suggest an enriched mantle source region for the mafic

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dykes.

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5. Genetic discussion

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5.1. Mantle source

The Paleozoic Shanzi Province mafic dykes are characterised by low SiO2

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contents (50.3-55.7 wt. %), suggesting that the mafic dykes were derived from an ultramafic source. This is supported in the high MgO contents (4.5-10.4 wt. %) and

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Mg# (55-70) in the mafic dykes from JLH1-10 and DSJ1-9. Crustal rocks can be ruled out as possible sources, as partial melting of any of the crustal rocks (e.g., Hirajima et al., 1990) and lower crustal intermediate granulites (Gao et al., 1998) in the deep crust would produce high-Si, low-Mg liquids (i.e., granitoid liquids; Rapp et al., 2003). The high initial

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Sr/86Sr ratios and negative ε Nd (t) and zircons ε

Hf

(t) values (Tables

4 and 5- supplemental table) for the mafic dykes are consistent with derivation from an enriched lithospheric mantle source rather than an asthenospheric mantle-source, with a depleted Sr-Nd isotopic composition, such as MORB.

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ACCEPTED MANUSCRIPT 5.2. Crustal contamination Crustal contamination might cause significant depletion in Nb-Ta and enriched

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Sr-Nd isotopic signatures in basaltic rocks. The dolerites are characterised by

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negative Nb-Ta anomalies, high Sr isotopic composition and negative  Nd (t) (Table 3), this could imply a crustal component in the magma genesis of the mafic dykes. Further support for this is given in their low Nb/U ratios (2.4-11.03) (cf. Nb/U= 9.0-21

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for crust, and Nb/U= 47 for primitive mantle), and Ta/La ratios (0.013-0.026) (cf.

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Ta/La= 0.06 for primitive mantle). Moreover, crustal assimilation would cause significant variation in Sr-Nd isotopes, and result in a positive correlation between

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MgO and εNd (t) values (-4.1 to -4.9), features that are also observed in these

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dolerites (Table 4; Fig. 7 and 9b). There is no correlation between MgO and Sr

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isotopic rations (Fig. 9a); however this does not rule out crustal contamination, because MgO contents are not solely associated with crustal contamination, but also

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with fractionation of ferromagnesian phases during magma evolution. In summary, the geochemical and isotopic signatures of the dolerites indicate that crustal contamination occurred.

5.3. Fractional crystallisation For the studied rocks, JLH1-10 and DSJ19 mafic dyke samples have high Mg# (55-70) (Table 2), which is inconsistent with significant fractionation. However, the JCG1-7 samples contains lower MgO (< 4.0 wt. %), Cr (< 21 ppm) and Ni (< 8.0 ppm) (Tables 1 and 2; Fig. 5d), implying that they were derived by fractional crystallisation.

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ACCEPTED MANUSCRIPT Furthermore, SiO2 shows a negative correlation with TiO2, Fe2O3, and MgO for all rocks (Fig. 5a, c, and d), indicating that the mafic dykes were likely the result of

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olivine, pyroxene-dominated and Ti-bearing phases (rutile, ilmenite, titanite)

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fractionation of a more mafic parental magma. Similarly, the separation of plagioclase and Ti-bearing phases could account for the observed negative Eu, Nb and Ta anomalies in chondrite-normalized REE patterns and primitive-mantle-normalised

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trace element patterns (Fig. 6a and b). Additionally, in EuN/Eu* vs. Sr and Ba related

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plots (online appendix), the dolerites show a combined vector of K-feldspar and plagioclase fractionation, however, this also indicates that plagioclase fractionation

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was more important than K-feldspar in controlling Sr and Ba abundances (Table 3).

5.4. Genetic mechanism and model

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The mafic dykes in this study have similar characteristics in terms of geochemistry and isotopes (Sr-Nd-Hf), implying that they have a similar source region. However,

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they do not result from the same episode of magmatism due to different ages. On plots of La vs. La/Sm and K2O vs. Ce/Yb related plots (Fig. 10) presented), all samples distribute along the partial melting trend line, indicating that the mafic dykes were derived from partial melting of enriched mantle. Based on the above discussion, the mafic dykes in this study are derived through the partial melting of an enriched mantle source. A dynamic model, however, is required to decipher the origin of these mafic dykes. At least two competing mechanisms can be envisaged: (1) the contribution of the subducting Yangtze Block; (2) the action of subducted ancient Pacific Plate (i.e., Izanagi Plate). However, it is 13

ACCEPTED MANUSCRIPT generally believed that the final collision between NCC and Yangtze Block occurred during the Triassic (Meng and Zhang, 1999; Zhang et al., 2005), and there was no

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west-trending subduction of an ancient Pacific Plate towards the NCC before the

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early Cretaceous (Xu et al., 1993). As the investigated dykes were emplaced during the early Paleozoic, it is unlikely that their petrogenesis relates to either subducting Yangtze lithosphere or the ancient Pacific Plate. An alternative model, therefore, is

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required to account for the how the mafic dykes were formed.

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The study area lies to the north of the Shang-Dan suture that separates the NCC and south Qinling Block. During the Early Paleozoic (Cambrian), significant collision

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occurred between the NCC and south Qinling Block (Meng and Zhang, 1999).

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Following the terminal phase of collision, this boundary underwent extension and

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gravitational collapse, that resulted in the formation of many extensional basins in this region (e.g., the An’Kang-Ziyang and Wudu-Dibu basins), and also led to alkaline

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magmatism, and the emplacement of swarms of mafic dyke. We propose, therefore, the following genetic model to account for the presence of the investigated Shaanxi Province mafic dykes: a) prior to collision, the NCC and south Qinling were two independent crustal blocks (Fig. 11a, b) Prior to the Ordovician (> 500Ma), collision between the NCC and south Qiling Block occurred resulting in the formation of the Shang-Dan suture. Crustal shortening and collision resulted in thickening of the lithospheric mantle beneath both the NCC and south Qinling Block. The thickened lithosphere led to deformation and regional metamorphism, at the same time in the zone of collision, supracrustal rocks underwent transformation to produce ophiolite

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ACCEPTED MANUSCRIPT (Fig. 11b, c) Density differences in this mélange resulted in gravitational imbalance, leading to the foundering of denser crustal units into asthenosphere.

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Following the terminal stage of collision between the two crustal blocks, relaxation

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and lithospheric extension occurred (Fig. 11c). Lithospheric extension allowed for buoyant upwelling of hot asthenosphere, which locally raised geothermal gradients, causing partial melting of the lithospheric mantle beneath both the NCC and south

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investigated Shaanxi Province dykes.

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Qinling Block. These partial melts represent the parental mafic magmas to the

Foundering of denser crustal units into asthenosphere is supported, moreover, by

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the voluminous coeval magmatism (Shaanxi province bureau of geology and mineral

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resources, 1989), large-scale mineralization (e.g., Shaanxi Province bureau of

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geology and mineral resources, 1989), and the 453 Ma adakitic rocks observed in adjacent areas (e.g., Gujiagou, Nangou and Chenjiagou,), as lithospheric

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foundering would result in all of these features.

6. Conclusions

Based upon geochronological, geochemical, and Sr-Nd and Hf isotopic studies, the following conclusions have been drawn: 1.

U-Pb zircon dating indicates that the studied Shaanxi Province mafic dykes formed between 448.1 ± 1.2 and 489.6 ± 0.9 Ma (i.e., they are late Cambrian-Ordovician).

2.

The mafic dykes are derived from an enriched mantle source, with parental 15

ACCEPTED MANUSCRIPT magmas originating through partial melting of the enriched mantle lithosphere beneath both the southern part of the NCC and the south Qinling Block, in

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response to lithospheric thinning/extension. The parental magmas to the mafic

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dyke swarms underwent crustal contamination and crystal fractionation during ascent that included the following mineral phases: olivine, pyroxene, plagioclase and Ti-bearing phases (rutile, ilmenite, and titanite).

The studied mafic dykes were derived in an extensional setting after the collision

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3.

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between NCC and south Qinling Block.

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Acknowledgements

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The present research was supported by the Knowledge Innovation Project

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(KZCX2-YW-111-03), and the opening project (08LCD08) of State Key Laboratory of Continental Dynamics. The authors’ gratefully acknowledge Lian Zhou for assistance

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with the Sr-Nd isotope analyses, Zhaochu Hu for his help with LA-ICP-MS zircon U-Pb dating, and Jinhui Yang for help with the zircon Hf isotope determination. In addition, editor in chief Andrew Kerr and two anonymous reviewers also are thanked for quickly handling this paper.

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ACCEPTED MANUSCRIPT boundaries in the North China Craton: lithological, geochemical, structural and P-T path constraints and tectonic evolution. Precambrian Research 107, 45-73.

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Zhao, G.C., Wilde, S.A., Cawood, P.A., Sun, M., 2002. SHRIMP U-Pb zircon ages of

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Zhao, J.X., McCulloch, M.T., 1993. Melting of a subduction-modified continental

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Zhou, D.W., Zhang, C.L., Wang, J.L., Liu, L., Dong, Y.P., Liu, Y.Y., Han, S. 1998c. The

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basic dyke swarms in the Wudang block and its geological significance. Chinese

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Science Bulletin 43, 1111-1115.

Zhou, D.W., Zhang, C.L., Zhou, X.H., Sang, H.Q. 1999.

40

Ar-39Ar dating of basic

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dykes from Wudang block and their geology significance. Acta Petrologica Sinica 15, 14-20 (in Chinese with English abstract).

Figure captions:

Fig. 1. a. Simplified tectonic map of the NCC, China. b. Inset geological map of the study area as well as the distributions of the mafic dykes, and dyke samples collected for this study (modified after RGSPS, 1982). Fig. 2 Representative photomicrographs showing the petrographic features of the

24

ACCEPTED MANUSCRIPT mafic dykes from the NCC, China. The samples all display doleritic textures and hence are termed dolerite dykes. Key: Py-pyroxene; Pl-Plagioclase.

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Fig. 3. LA-ICP-MS zircon U-Pb concordia diagrams, and inset CL images of analysed

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zircon grains, for the investigated mafic dykes from the NCC, China. Fig. 4. Classification of the mafic dykes from NCC based upon: (a) TAS diagram. All major elemental data have been recalculated to 100 % on a LOI-free basis (after

NU

Middlemost, 1994; Le Maitre, 2002). (b) K2O versus Na2O diagram. The alkaline

MA

association for JLH and DSJ samples is shown to be shoshonitic, whereas JCG samples are calc-alkaline (after Middlemost, 1972).

D

Fig. 5. Selected variation diagrams of major element oxides versus SiO2 (in wt. %) for

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the mafic dykes from the NCC, China.

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Fig. 6. a) Chondrite-normalized rare earth element (REEs) diagram and b) primitive mantle-normalized incompatible element distribution diagrams for the investigated

AC

mafic dykes from the NCC, China. The normalisation values are from Sun and McDonough (1989). Fig. 7. Initial

Sr/86Sr vs. 

87

Nd

(t) diagram for the studied mafic dykes from the NCC,

China. The field for early Palaeozoic mafic rocks from the NCC (after Yan, 2005; Zhang, 2010) is plotted for comparison. The investigated NCC mafic dykes fall within this field, indicating an enriched mantle source. Fig. 8. Histograms of zircon ε Hf (t) values (a to c) and two-stage Hf model ages (d to f) for the mafic dykes in the NCC, China. Fig. 9. Plots of: (a) initial 87Sr/86Sr ratio and (b)  Nd (t) value versus MgO for the mafic

25

ACCEPTED MANUSCRIPT dykes from the NCC, China. Fig. 10. Plots of (a) La vs. La/Sm and (b) K2O vs. Ce/Yb for the studied mafic dykes.

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Fig. 11. Schematic models for block collision and the origin of the NCC mafic dykes.

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(a) prior to collision between the NCC and the south Qinling blocks. (b) Collision occurred prior to the Ordovician, whereby NCC and the south Qinling Block came together along the Shang-Dan suture, resulting in crustal shortening, deformation

NU

and metamorphism within the collisional belt. (c) After collision, the study area

MA

underwent extension and thinning, leading to asthenospheric upwelling, local raised geotherms and partial melting of mantle lithosphere. These partial melts are

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Table captions:

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D

the parental magmas to the NCC, Shaanxi Province mafic dyke swarms.

AC

Table 1. LA-ICP-MS U-Pb isotopic data for zircons from the mafic dykes in NCC. Table 2. Major element oxides (wt. %) for the mafic dykes in NCC. LOI, loss on ignition. Mg#=100*Mg/ (Mg+Fe) atomic ratio. RV, recommended values; MV, measured values. The values for GSR-1 and GSR-3 are from Wang et al. (2003). Table 3. Trace elements compositions (in ppm) for the mafic dykes from NCC. The values for GBPG-1 are from Thompson et al (2000), and for OU-6 from Potts and Kane (2005). Table 4. Sr-Nd isotopic compositions for the mafic dykes in NCC.

26

ACCEPTED MANUSCRIPT Chondrite Uniform Reservoir (CHUR) values (87Rb/86Sr = 0.0847,

87

Sr/86Sr =

0.7045, 147Sm/144Nd = 0.1967 143Nd/144Nd = 0.512638) are used in our calculations.

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T

Rb = 1.42  10-11 year-1 (Steiger and Jäger, 1977); Sm = 6.54  10-12 year-1

SC R

(Lugmair and Harti, 1978).

AC

CE P

TE

D

MA

NU

Table 5. Lu-Hf isotopic compositions for the mafic dykes in NCC.

27

ACCEPTED MANUSCRIPT

Pb/206Pb

0.0535 0.0559 0.0550 0.0579 0.0565 0.0571 0.0562 0.0560 0.0539 0.0569

TE D

1s

0.0013 0.0017 0.0019 0.0018 0.0018 0.0012 0.0016 0.0015 0.0020 0.0016

1s 0.0159 0.0156 0.0157 0.0162 0.0161 0.0158 0.0157 0.0156 0.0155 0.0159 0.0155 0.0158

207

Pb/235U

1s

206

0.5443 0.5553 0.5493 0.5526 0.5547 0.5602 0.5585 0.5576 0.5544 0.5472

0.0158 0.0162 0.0177 0.0186 0.0171 0.0158 0.0161 0.0156 0.0173 0.0164

28

238

Pb/ U 0.0727 0.0723 0.0726 0.0726 0.0723 0.0727 0.0723 0.0726 0.0723 0.0723 0.0726 0.0723

CR

207

Pb/ U 0.5527 0.5529 0.5434 0.5438 0.5666 0.5468 0.5659 0.5639 0.5589 0.5482 0.5469 0.5567

206

US

Th/U 0.60 0.54 0.69 0.66 0.60 1.05 0.99 1.03 0.88 0.36

1s 0.0013 0.0017 0.0015 0.0014 0.0013 0.0013 0.0013 0.0013 0.0016 0.0022 0.0023 0.0017

Pb/ Pb 0.0568 0.0558 0.0557 0.0539 0.0570 0.0558 0.0571 0.0572 0.0565 0.0566 0.0557 0.0655

235

MA N

Th/U 0.43 0.87 0.42 0.46 0.49 0.44 0.44 0.48 0.44 0.45 0.76 1.02

207

IP

ratios

206

CE P

DSJ01 Spot Th(ppm) U(ppm) Pb(ppm) 1.1 313 518 46.6 2.1 164 303 27.2 3.1 179 258 23.4 4.1 183 276 25.3 5.1 231 381 34.2 6.1 674 640 63.4 7.1 277 281 27.7 8.1 412 402 39.8 9.1 206 234 22.9 10.1 111 308 26.0

Isotopic 207

AC

JLH01 Spot Th(ppm) U(ppm) Pb(ppm) 1.1 570 1336 53.4 2.1 737 849 37.5 3.1 348 818 39.62 4.1 425 919 44.14 5.1 640 1308 52.9 6.1 402 905 46.22 7.1 819 1853 75.8 8.1 763 1599 64.7 9.1 460 1056 42.53 10.1 425 952 38.54 11.1 546 719 31.1 12.1 1157 1136 52.4

T

Table 1

Pb/238U

0.0720 0.0718 0.0718 0.0721 0.0722 0.0720 0.0718 0.0719 0.0720 0.0720

Age(Ma) 1s 0.0007 0.0006 0.0006 0.0009 0.0008 0.0005 0.0009 0.0008 0.0009 0.0007 0.0007 0.0006

207

Pb/206Pb 482 444 439 365 493 443 496 501 470 474 441 790

1s

207

Pb/206Pb 1s 350 41 448 49 192 102 528 54 471 52 495 35 461 51 453 46 366 61 488 49

0.0005 0.0007 0.0010 0.0007 0.0006 0.0006 0.0005 0.0006 0.0008 0.0006

1s 47 48 50 45 43 52 39 42 60 47 46 46

207

Pb/235U 447 447 441 441 456 443 455 454 451 444 443 449

1s 10 10 10 11 10 10 10 10 10 10 10 10

206

Pb/238U 452 450 452 452 450 452 450 452 450 450 452 450

1s 4 4 4 5 5 3 5 5 2 4 4 4

207

Pb/235U 435 448 407 465 455 458 451 450 435 456

1s 9 11 19 12 11 8 10 10 13 11

206

Pb/238U 448 447 448 449 449 448 447 448 448 448

1s 3 4 6 4 4 4 3 4 5 4

ACCEPTED MANUSCRIPT

29

206

Pb/238U 0.0793 0.0792 0.0789 0.0785 0.0789 0.0787 0.0791 0.0787 0.0789 0.0791 0.0789 0.0789 0.0789 0.0790 0.0789

T

1s 0.0127 0.0126 0.0117 0.0188 0.0184 0.0138 0.0136 0.0136 0.0124 0.0116 0.0122 0.0130 0.0120 0.0105 0.0136

IP

Pb/235U 0.6134 0.6128 0.6153 0.6124 0.6176 0.6190 0.6179 0.6205 0.6173 0.6195 0.6155 0.6164 0.6177 0.6178 0.6196

CR

207

US

1s 0.0012 0.0011 0.0011 0.0019 0.0018 0.0014 0.0013 0.0013 0.0011 0.0011 0.0012 0.0012 0.0011 0.0009 0.0013

MA N

Pb/206Pb 0.0568 0.0576 0.0572 0.0572 0.0571 0.0576 0.0572 0.0580 0.0583 0.0575 0.0580 0.0572 0.0582 0.0581 0.0585

TE D

207

CE P

Th/U 0.97 0.96 0.94 0.65 0.62 0.70 0.72 0.46 0.56 0.65 0.43 0.49 0.57 0.65 0.57

AC

JCG01 Spot Th(ppm) U(ppm) Pb(ppm) 1.1 232 238 Total 2.1 799 831 92.0 3.1 1161 1234 136 4.1 1462 2240 228 5.1 416 670 67.4 6.1 399 572 58.9 7.1 816 1127 117 8.1 626 1359 132 9.1 571 1022 102 10.1 758 1166 119 11.1 657 1541 145 12.1 710 1461 141 13.1 886 1562 154 14.1 914 1399 143 15.1 914 1605 156

1s 0.0006 0.0006 0.0006 0.0006 0.0006 0.0006 0.0005 0.0005 0.0005 0.0005 0.0005 0.0006 0.0006 0.0005 0.0006

207

Pb/206Pb 482 514 498 498 496 515 500 529 541 512 531 498 539 532 550

1s 32 31 28 53 52 36 36 36 31 29 30 33 29 26 32

207

Pb/235U 492 498 493 491 495 495 495 496 501 496 499 494 501 501 502

1s 8 8 7 12 12 9 8 8 8 7 8 8 7 6 8

206

Pb/238U 492 492 489 487 489 488 491 488 489 491 490 490 490 490 489

1s 3 4 3 4 3 3 3 3 3 3 3 3 3 3 4

ACCEPTED MANUSCRIPT

Al2O3

Fe2O3

MgO

CaO Na2O

K2O

MnO P2O5 TiO2

IP

SiO2

LOI

Total

Mg#

55.65

15.52

7.41

4.93

5.37

3.66

2.61

0.10

0.52

1.07

2.63

99.47

57

JLH-3

dolerite

54.84

15.82

7.45

4.84

5.65

3.61

2.72

0.10

0.53

1.09

2.33

98.98

56

JLH-6

dolerite

54.74

15.96

7.45

4.53

6.59

3.79

2.13

0.10

0.52

1.06

2.45

99.32

55

JLH-7

dolerite

54.79

15.86

7.24

4.58

6.20

3.82

2.44

0.10

0.51

1.06

2.81

99.41

56

JLH-8

dolerite

55.63

15.53

7.20

4.52

6.24

3.80

1.86

0.10

0.52

1.05

2.92

99.37

55

JLH-10 DSJ-1

dolerite

15.87 12.72

7.55 9.27

4.95 9.48

5.37 6.83

3.40 2.09

3.11 3.77

0.10 0.12

0.53 0.64

1.08 1.27

2.65 1.87

99.43 99.52

56

dolerite

54.82 51.45

DSJ-2

dolerite

51.51 12.63

9.19

10.41 6.65

2.05

3.75

0.12

0.67

1.25

1.57

99.81

69

DSJ-4

dolerite

51.56

12.45

9.03

8.74

6.59

2.09

3.73

0.13

0.65

1.22

3.16

99.35

66

DSJ-5

dolerite

50.79

12.78 11.20

9.68

6.01

2.17

3.69

0.12

0.63

1.25

1.83

100.15

63

DSJ-6

dolerite

50.74

12.59 10.76

10.09

5.99

1.99

3.55

0.12

0.65

1.29

2.16

99.94

65

DSJ-8

dolerite

50.33

12.62

8.98

10.36 6.91

2.11

3.56

0.12

0.66

1.22

2.69

99.56

70

DSJ-9

dolerite

50.60

12.46

8.88

10.26 6.73

2.00

3.58

0.12

0.66

1.20

3.15

99.64

70

JCG-1

dolerite

53.93

18.08

8.44

2.85

6.88

4.10

0.90

0.22

0.35

0.67

2.93

99.35

40

JCG-3

dolerite

53.27

18.22

8.63

3.83

6.91

4.26

0.85

0.21

0.32

0.64

2.34

99.46

47

JCG-5

dolerite

54.09

18.29

7.97

2.96

6.22

4.36

0.85

0.17

0.37

0.58

3.43

99.28

42

JCG-6

dolerite

54.85

18.63

7.86

3.15

6.34

4.44

0.97

0.18

0.31

0.56

2.15

99.44

44

JCG-7 GSR-3 GSR-3

dolerite RV* MV*

54.02 44.64 44.75

18.35 13.83 14.14

7.94 13.4 13.35

2.85 7.77 7.74

6.25 8.81 8.82

4.46 3.38 3.18

0.84 2.32 2.3

0.17 0.17 0.16

0.32 0.95 0.97

0.57 2.37 2.36

3.45 2.24 2.12

99.21 99.88 99.89

42

GSR-1 GSR-1

RV*

72.83

13.4

2.14

0.42

1.55

3.13

5.01

0.06

0.09

0.29

0.7

99.62

MV*

72.65

13.52

2.18

0.46

1.56

3.15

5.03

0.06

0.11

0.29

0.69

99.70

TE D

MA N

US

CR

dolerite

AC

JLH-1

CE P

Sample Rock type

T

Table 2

30

67

ACCEPTED MANUSCRIPT

T

Table 3 JLH-1 JLH-3 JLH-6 JLH-7 JLH-8 JLH-10 DSJ-1 DSJ-2 DSJ-4 DSJ-5 DSJ-6 DSJ-8 DSJ-9 JCG-1 JCG-3 JCG-5 JCG-6 JCG-7 OU-6（RV*）OU-6（MV*）GBPG-1（RV*）GBPG-1（MV*） 131 103 158 166 175 171 168 168 170 174 178 171 171 181 170 161 189 169 143 159 129 96.5

Cr

79.3

76.2

73.7

73.4

73.1

74.6

425

449

446

425

441

464

457

Ni

36.4

36.2

35.3

36.1

34.5

36.2

377

416

253

356

397

397

384

Ga

17.4

18.2

20.9

20.2

19.5

18.3

16.2

16.2

16.7

16.7

16.4

16.2

15.9

Rb

89.2

89.1

69.3

78.9

61.8

107.0

88.4

85.3

86.3

85.4

86.3

91.4

87.6

Sr

940

979

1160

1090

1080

947

617

590

715

615

603

596

Y

15.7

15.8

16.0

15.7

15.6

16.2

27.6

26.6

26.5

27.6

27.6

27.0

IP

V

15.1

16.1

20.6

17.1

70.8

73.5

181

187

5.58

7.67

7.39

6.07

7.50

39.8

42.5

59.6

60.6

17.9

16.2

15.3

16.1

14.8

24.3

26.5

18.6

20.9

28.1

24.9

20.6

33.4

35.2

120

122

56.2

61.4

619

774

822

518

381

286

131

136

364

377

26.9

28.2

23.1

22.5

23.3

22.0

27.4

26.2

18.0

17.2

CR

13.2

US

Sample

342

92.5

81.2

76.8

80.5

72.8

174

183

232

224

12.2

4.69

3.60

3.83

4.35

4.50

14.8

15.3

9.93

8.74

1110

1049

260

297

258

361

376

477

486

908

921

31.5

30.9

21.1

17.1

15.8

16.8

15.3

33.0

33

53.0

51

68.6

66.6

41.8

32.2

31.4

32.7

31.3

74.4

78

103

105

147

147

150

146

147

150

379

343

337

373

362

354

10.5

10.7

10.6

10.6

10.5

10.7

12.9

12.0

12.3

12.7

12.4

12.1

Ba

1410

1440

1000

1290

825

1450

1519

1049

1069

1049

1059

La

29.0

28.1

28.9

27.8

29.6

29.1

32.9

30.0

33.4

32.4

31.4

Ce

57.4

56.8

59.3

56.5

58.9

59.7

71.6

66.4

73.1

70.4

68.1

7.06

6.75

6.96

7.00

7.06

7.38

9.09

8.50

9.18

8.80

8.64

8.79

8.34

5.18

3.92

3.93

4.07

3.84

7.80

8.1

11.5

11.6

27.1

27.1

27.4

27.7

28.0

27.9

38.0

36.6

39.3

36.7

36.8

37.3

35.9

21.2

16

15.6

17.2

15.8

29.0

30.6

43.3

42.4

Sm

5.04

5.30

5.02

4.93

5.05

5.36

8.13

7.95

8.32

8.09

7.97

7.97

7.86

4.83

3.71

3.72

3.94

3.82

5.92

5.99

6.79

6.63

Eu

1.46

1.44

1.41

1.40

1.46

1.43

2.09

1.97

2.09

2.07

2.01

2.07

2.03

1.62

1.22

1.26

1.33

1.02

1.36

1.35

1.79

1.69

Gd

3.88

4.18

3.90

3.84

3.90

4.33

7.32

7.14

7.33

6.90

6.73

6.90

6.95

4.56

3.81

3.66

3.93

3.56

5.27

5.50

4.74

4.47

Tb

0.62

0.61

0.61

0.58

0.64

0.61

0.99

0.98

1.04

0.99

1.03

0.98

0.95

0.78

0.64

0.64

0.62

0.62

0.85

0.83

0.60

0.59

Dy

3.01

2.87

2.95

2.99

2.92

3.00

5.50

5.42

5.46

5.39

5.62

5.36

5.24

4.56

3.65

3.69

3.74

3.7

4.99

5.06

3.26

3.17

Ho

0.62

0.63

0.63

0.61

0.62

0.62

1.01

1.01

0.98

1.00

1.03

0.99

0.99

1.05

0.89

0.85

0.88

0.85

1.01

1.02

0.69

0.66

Er

1.56

1.56

1.56

1.56

1.55

1.59

2.71

2.63

2.65

2.70

2.72

2.64

2.58

3.13

2.41

2.36

2.48

2.45

2.98

3.07

2.01

2.02

Tm

0.21

0.20

0.22

0.22

0.21

0.22

0.34

Yb

1.33

1.37

1.35

1.33

1.28

1.36

2.33

Lu

0.19

0.19

0.19

0.18

0.19

0.18

0.33

Hf

3.54

3.64

3.61

3.51

3.56

3.68

Ta

0.52

0.54

0.54

0.58

0.53

Pb

8.38

9.79

14.40

12.20

Th

3.45

3.40

3.50

U dEu

0.96

2.64

1.0

（La/Yb）N 15.6

AC

CE P

Pr Nd

TE D

MA N

Zr Nb

0.34

0.32

0.35

0.37

0.34

0.34

0.46

0.37

0.35

0.37

0.36

0.44

0.45

0.30

0.29

2.22

2.14

2.31

2.35

2.24

2.28

3.12

2.38

2.47

2.52

2.51

3.00

3.09

2.03

2.03

0.32

0.30

0.32

0.33

0.33

0.31

0.50

0.38

0.38

0.41

0.38

0.45

0.47

0.31

0.31

10.6

9.56

9.02

10.0

10.4

10.0

9.65

2.37

2.1

1.98

2.01

1.95

4.70

4.86

6.07

5.93

0.52

0.83

0.77

0.74

0.83

0.80

0.80

0.75

0.25

0.21

0.21

0.23

0.20

1.06

1.02

0.40

0.46

11.60

9.22

16.3

14.4

18.9

15.9

15.5

15.1

14.1

10.6

9.3

10.2

15.8

11.8

28.2

32.7

14.1

14.5

3.51

3.49

3.64

5.96

5.68

6.34

6.25

5.59

5.75

5.09

4.23

3.50

3.18

3.27

3.11

11.5

13.9

11.2

11.4

1.22

4.41

1.10

2.00

1.79

1.73

1.79

1.78

1.71

1.73

1.55

1.34

0.92

1.02

1.21

0.77

1.96

2.19

0.90

0.99

0.9

1.0

1.0

1.0

0.9

0.8

0.8

0.8

0.8

0.8

0.9

0.8

1.1

1.0

1.0

1.0

0.8

14.7

15.4

15.0

16.6

15.3

10.1

9.7

11.2

10.1

9.6

10.1

9.7

4.9

5.2

4.6

4.8

4.4

31

ACCEPTED MANUSCRIPT

489.6

5.02 5.05

27.4 28.0

69.3 62

1160 1080

8.13 8.32 7.97 7.97

38.0 39.3

88 86

617 715

36.8 37.3

86.3 91

603 596

4.83 3.71 3.72 3.82

21.2 16.0 15.6 15.8

28 24.9 21 35

774 822 518 286

9 8 10 10 8 8 9 12 10

32

IP

940 979

0.705610 0.705541 0.705096 0.704961 0.707365 0.707043 0.707419 0.707575 0.705710 0.705606 0.705793 0.707402

CR

89 89

2σ (87Sr/86Sr)i

US

27.1 27.1

Sr/86Sr 0.705716 0.705642 0.705163 0.705027 0.707589 0.707238 0.707635 0.707810 0.705742 0.705626 0.705820 0.707481

MA N

448.05

5.04 5.30

87

CE P

450.9

Rb/86Sr 0.2742 0.2630 0.1727 0.1654 0.4138 0.3486 0.4139 0.4434 0.1049 0.0875 0.1149 0.3537

AC

JLH-1 JLH-3 JLH-6 JLH-8 DSJ-1 DSJ-4 DSJ-6 DSJ-8 JCG-1 JCG-3 JCG-5 JCG-7

87

TE D

Sample Age(Ma) Sm(ppm) Nd(ppm) Rb(ppm) Sr(ppm)

T

Table 4

8 12 10

147

Sm/144Nd 7.710 6.854 8.573 8.575 6.84 6.84 7.69 10.25 8.566 6.854 10.28 8.55

143

Nd/144Nd 0.512157 0.512179 0.512163 0.512151 0.512223 0.512227 0.512228 0.512232 0.512198 0.512212 0.512219 0.5122346

2σ (143Nd/144Nd)i εNd(t) -4.5 8 0.489386 12 -4.4 0.512179 -4.3 8 0.512163 -4.5 10 0.512151 -4.2 8 0.492161 -4.1 8 0.512227 12 -4.2 0.512228 8 -4.1 0.512232 9 -4.9 0.484726 10 -4.8 0.512212 8 -4.9 0.512219 10 -4.7 0.512235

ACCEPTED MANUSCRIPT

2σ

176

Lu/177Hf

176

2σ

Hf/177Hf

2σ

IP

Yb/177Hf

Age (Ma)

CR

176

Hf/177Hf

εHf(0)

εHf(t) TDM1(Ma) TDM2(Ma)

0.282249 0.282236

-18.1 -18.6

-8.6 -9.0

1407 1431

1968 1997

-0.97 -0.96

fLu/Hf

0.027249 0.031657

0.000688 0.001251

0.001125 0.001337

0.000028 0.000054

0.282259 0.282247

0.000027 0.000036

3

0.031455

0.000323

0.000499

0.000017

0.282253

0.000032

450.9

0.282248

-18.4

-8.6

1393

1970

-0.98

4

0.023144

0.000342

0.000881

0.000016

0.282253

0.000027

450.9

0.282245

-18.4

-8.7

1406

1976

-0.97

5

0.038465

0.000365

0.001654

0.000016

0.282252

0.000029

450.9

0.282238

-18.4

-9.0

1437

1993

-0.95

6

0.035375

0.000834

0.001445

0.000018

0.282256

0.000034

450.9

0.282244

-18.2

-8.8

1423

1980

-0.96

7

0.043116

0.001126

0.001733

0.000037

0.282260

0.000026

450.9

0.282245

-18.1

-8.7

1429

1977

-0.95

8

0.036264

0.000627

0.001544

0.000028

0.282255

0.000028

450.9

0.282242

-18.3

-8.8

1428

1983

-0.95

9

0.016421

0.000834

0.000624

0.000016

0.282253

0.000027

450.9

0.282248

-18.3

-8.6

1397

1971

-0.98

10

0.028686 0.019317 0.024287 0.028513 0.037539 0.032358 0.361862

0.000749 0.000856 0.000866 0.000254 0.000658 0.000388 0.000685

0.001295 0.000684 0.000896 0.001254 0.001246 0.001236 0.001244

0.000026 0.000015 0.000016 0.000018 0.000027 0.000033 0.000025

0.282254 0.282254 0.282257 0.282256 0.282259 0.282255 0.282251

0.000028 0.000028 0.000029 0.000026 0.000027 0.000027 0.000028

450.9

0.282244

-18.3

-8.8

1420

-0.96

450.9 450.9 450.9 450.9 450.9 450.9

0.282248 0.282249 0.282245 0.282249 0.282244 0.282241

-18.3 -18.2 -18.3 -18.1 -18.3 -18.4

-8.6 -8.6 -8.7 -8.6 -8.8 -8.9

1398 1401 1416 1411 1417 1422

1980 1971 1968 1977 1969 1979 1987

TE D

CE P

AC

US

1 2

11 12 13 14 15 16

450.9 450.9

176

MA N

JLH-1 No.

T

Table 5

-0.98 -0.97 -0.96 -0.96 -0.96 -0.96 2 0

1

33

ACCEPTED MANUSCRIPT

0.282280 0.282291 0.282271 0.282273 0.282275 0.282275 0.282276 0.282276 0.282275 0.282275 0.282275 0.282276 0.282275 0.282276 0.282276

2σ

Age (Ma)

0.000028 0.000026 0.000034 0.000028 0.000028 0.000035 0.000028 0.000026 0.000029 0.000026 0.000026 0.000027 0.000025 0.000029 0.000025

448.1 448.1 448.1 448.1 448.1 448.1 448.1 448.1 448.1 448.1 448.1 448.1 448.1 448.1 448.1

34

176

T

0.000033 0.000029 0.000028 0.000019 0.000032 0.000026 0.000035 0.000031 0.000026 0.000031 0.000024 0.000035 0.000032 0.000025 0.000028

Hf/177Hf

IP

0.001131 0.002761 0.000586 0.000893 0.001745 0.001535 0.001813 0.001644 0.000633 0.001355 0.000691 0.000885 0.001273 0.001266 0.001252

176

2σ

CR

Lu/177Hf

US

0.000019 0.000846 0.000175 0.000063 0.000167 0.000315 0.000586 0.000086 0.000038 0.000088 0.000270 0.000041 0.000259 0.000335 0.000124

176

MA N

0.026560 0.025703 0.031547 0.024054 0.037347 0.036265 0.044015 0.037164 0.015823 0.027861 0.019527 0.024367 0.027862 0.038236 0.032556

2σ

TE D

Yb/177Hf

CE P

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

176

AC

DSJ-1 No.

Hf/177Hf

0.282271 0.282268 0.282266 0.282265 0.282261 0.282262 0.282261 0.282262 0.282270 0.282264 0.282270 0.282268 0.282265 0.282265 0.282265

εHf(0)

εHf(t) TDM1(Ma) TDM2(Ma)

fLu/Hf

-17.4 -17.0 -17.7 -17.6 -17.6 -17.6 -17.5 -17.6 -17.6 -17.6 -17.6 -17.6 -17.6 -17.5 -17.6

-7.9 -8.0 -8.0 -8.1 -8.2 -8.2 -8.2 -8.2 -7.9 -8.1 -7.9 -8.0 -8.1 -8.1 -8.1

-0.97 -0.96 -0.98 -0.97 -0.95 -0.95 -0.95 -0.95 -0.98 -0.96 -0.98 -0.97 -0.96 -0.96 -0.96

1377 1424 1370 1379 1407 1400 1409 1403 1366 1392 1368 1375 1389 1389 1388

1921 1928 1932 1934 1944 1942 1944 1942 1923 1937 1924 1928 1935 1934 1934

ACCEPTED MANUSCRIPT

0.282202 0.282211 0.282203 0.282203 0.282208 0.282205 0.282208 0.282206 0.282208 0.282206 0.282205 0.282208 0.282208 0.282208 0.282202

2σ

Age (Ma)

0.000027 0.000026 0.000032 0.000025 0.000028 0.000033 0.000026 0.000029 0.000025 0.000023 0.000025 0.000026 0.000023 0.000026 0.000025

489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6

35

176

T

0.000028 0.000032 0.000029 0.000026 0.000034 0.000025 0.000031 0.000033 0.000028 0.000027 0.000031 0.000032 0.000026 0.000027 0.000033

Hf/177Hf

IP

0.001214 0.002616 0.000577 0.000915 0.001850 0.001632 0.001912 0.001752 0.000644 0.001425 0.000684 0.000879 0.001367 0.001257 0.001362

176

2σ

CR

Lu/177Hf

US

0.000158 0.000678 0.000457 0.000196 0.000476 0.000075 0.000048 0.000056 0.000135 0.000136 0.000058 0.000767 0.000274 0.000196 0.000276

176

MA N

0.027487 0.026321 0.030547 0.025364 0.038447 0.035863 0.045122 0.036365 0.016196 0.028446 0.018744 0.025462 0.028475 0.037286 0.033668

2σ

TE D

Yb/177Hf

CE P

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

176

AC

DST-1 No.

Hf/177Hf

0.282191 0.282187 0.282197 0.282195 0.282191 0.282190 0.282190 0.282189 0.282202 0.282192 0.282199 0.282200 0.282195 0.282196 0.282190

εHf(0)

εHf(t) TDM1(Ma) TDM2(Ma)

fLu/Hf

-20.2 -19.8 -20.1 -20.1 -19.9 -20.1 -20.0 -20.0 -20.0 -20.0 -20.0 -20.0 -20.0 -20.0 -20.1

-9.8 -9.9 -9.6 -9.7 -9.8 -9.8 -9.8 -9.8 -9.4 -9.7 -9.5 -9.5 -9.6 -9.6 -9.8

-0.96 -0.95 -0.98 -0.97 -0.95 -0.95 -0.95 -0.95 -0.98 -0.96 -0.98 -0.97 -0.96 -0.96 -0.96

1490 1535 1465 1477 1507 1503 1510 1507 1460 1494 1465 1469 1489 1484 1495

2073 2081 2059 2065 2072 2076 2075 2076 2049 2069 2055 2054 2064 2061 2075

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 1a,b

36

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 1c 37

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

Fig. 2

38

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 3

39

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 4

40

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 5

41

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 6

42

Fig. 7

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

43

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 8

44

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 9

45

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 10

46

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Fig. 11

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ACCEPTED MANUSCRIPT

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Graphical abstract

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ACCEPTED MANUSCRIPT Highlights >we analyze U-Pb age, chemical and Sr-Nd-Pb isotopes of the mafic dykes. > We

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give the range of ages from 448.05 Ma to 450.9 Ma. > The mafic dykes were derived

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from enriched mantle beneath the study areas. > The parent magmas experience extensive fractional crystallization. > There appeared fraction of Olivine, pyroxene,

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plagioclase, Ti-bearing phases, etc. during magma ascent.

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