Heterogeneous sources of the Triassic granitoid plutons in the southern Qinling orogen: An E-W tectonic division in central China

Authors

  • Xianquan Ping,

    1. State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan, China
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  • Jianping Zheng,

    Corresponding author
    • State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan, China
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  • Junhong Zhao,

    1. State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan, China
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  • Huayun Tang,

    1. State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan, China
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  • W. L. Griffin

    1. ARC Centre of Excellence for Core to Crust Fluid Systems/GEMOC, Department of Earth and Planetary Sciences, Macquarie University, New South Wales, Australia
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Corresponding author: Dr. J. Zheng, State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China. (jpzheng@cug.edu.cn)

Abstract

[1] The Qinling orogen is an important orogenic belt formed by the collision between the North and South China blocks along the Mianlue suture during the Triassic. The orogen is customarily divided into the western and eastern Qinling terranes. However, the boundary has long been a matter of debate. There are many Triassic granitoid plutons in the orogen, especially in South Qinling, along the southern part of the Shangdan suture. Systematic analysis of U-Pb ages and Hf isotopes in zircons frxom six granitoid plutons, including Guangtoushan, Gaoqiaopu, Xiba, Laocheng, Dongjiangkou, and Zhashui from west to east, allows us to trace their formation ages and source regions. All plutons yield ages that vary only from 218 to 211 Ma. However, zircon Hf-isotope data for these Triassic plutons cluster in two distinct groups. Granitoids from the western segment (i.e., Guangtoushan, Gaoqiaopu, and Xiba) of the South Qinling belt have negative εHf(t) values (−20.9 to −5.2) and relatively old two-stage Hf model ages (1.58 to 2.57 Ga). In contrast, those from the eastern segment (i.e., Laocheng, Dongjiangkou, and Zhashui) show higher εHf(t) values (−5.4 to +6.8) and younger two-stage Hf model ages (0.82 to 1.60 Ga). Integrating these analyses with published Sr-Nd-Pb-Hf isotopic data, we suggest that the division between the western and eastern South Qinling segments is located near the Taibai-Chenggu line, between the Baoji-Chengdu railway and 108°E longitude. The integrated data suggest that the western South Qinling segment separated from the North China block during the Paleoproterozoic and early Mesoproterozoic and then switched into continental convergence with the eastern South Qinling segment (northern margin of the Yangtze block) during the late Mesoproterozoic to early Neoproterozoic; finally, the two segments amalgamated during the late Neoproterozoic.

1 Introduction

[2] Granitoid plutons make up significant parts of large orogenic belts, such as the Alpine-Himalayan orogenic belt [Harris et al., 1986; Barbarin, 1999; Bonin, 2004] and the Qinling-Dabie-Sulu orogenic belt [Zhang et al., 1997c, 2001; Dong et al., 2011]. Most granitoids formed from partial melting of the deep crust; therefore, their chemical and isotopic compositions can be used to trace the nature of the deep crust beneath orogenic belts [DePaolo, 1981; Chappell et al., 1987, 1988; Harris et al., 1990; Whalen, et al., 1995; Kemp and Hawkesworth, 2003] and to identify terrane boundaries [Chappell et al., 1988; Kistler, 1990; Persson et al., 1995; Mellqvist et al., 1999; Manya, 2011; Zhu et al., 2011a; Foster et al., 2012]. The incorporation of U and Hf, exclusion of Pb and Lu, and the high closure temperature for rapid diffusion of Pb in the zircon crystal lattice make it the ideal mineral to investigate magma genesis in terranes of continental affinity [Watson, 1996; Watson and Cherniak, 1997]. These isotopic systems typically remain undisturbed during low-temperature high-pressure metamorphism [Zheng et al., 2005], and disturbances such as Pb loss can be identified in many instances by evaluating U-Pb data in a concordia plot [Mezger and Krogstad, 1997]. Therefore, Hf isotopes of zircon from granitoid rocks represent a powerful tool for revealing the nature of the deep crust [Griffin et al., 2002; Belousova et al., 2006; Hawkesworth and Kemp, 2006; Kemp et al., 2007; Kurhila et al., 2010; Zhu et al., 2011a; Foster et al., 2012].

[3] The Qinling orogen separates the South China block from the North China block and links the Kunlun and Qilian orogens to the west with the Dabie-Sulu orogen to the east (Figure 1a). The orogen can be subdivided into North Qinling and South Qinling [Meng and Zhang, 2000; Zhang et al., 2001]. Moreover, the orogen is commonly divided into western and eastern segments on the basis of the regional geology and geophysics [Zhang et al., 1995, 1996a, 2001, 2002a, 2011; Yuan, 1996]. There is a general consensus that the boundary between North Qinling and South Qinling is located at the Shangdan suture. However, the position of the boundary between the western and eastern segments has long been a matter of debate. Zhang et al. [2001, 2007a] suggested that the boundary is roughly located at the Baoji-Chengdu railway (Line 1 in Figures 1b and 1c), whereas Zhang et al. [2002a] proposed that the boundary is roughly along the 108°E longitude (Line 2 in Figures 1b and 1c).

Figure 1.

(a) Simplified geological map of China, showing the major tectonic units (modified from Zheng et al. [2010]). (b) Simplified geological map with the distribution of the Triassic granitoids in the Qinling orogen (modified from Zhang et al. [2006, 2007a, 2008])—Line 1: the Baoji-Chengdu railway proposed by Zhang et al. [2001, 2007a], Line 2: the 108°E longitude proposed by Zhang et al. [2002a], and Line 3: the Taibai-Chenggu line. (c) Cross section showing Lines 1 and 2 in Figure 1b (modified from Zhang et al. [1995] and Meng and Zhang [2000]); the vertical scale is the same as the horizontal scale. (d) Schematic cartoon showing the tectonic evolution of the Qinling orogen (modified from Meng and Zhang [1999] and Dong et al. [2011])—a. the Proto-Tethyan Qinling ocean separated South Qinling (northern margin of the South China block) from North Qinling (southern margin of the North China block) between late Proterozoic and early Paleozoic time; b. subduction of the Proto-Tethyan ocean beginning in the early Paleozoic generated an arc-trench system and a back-arc basin in the North Qinling region, which then evolved into the southern active continental margin of the North China block; c. coeval with the early Paleozoic collision at the Shangdan suture, the southern edge of South Qinling started to be gradually rifted away from the South China block; d. South Qinling was separated from the South China block during the middle Paleozoic by the Paleo-Tethyan Qinling ocean; e. the Paleo-Tethyan Qinling ocean is assumed to have started to subduct in the Permian; and f. collision between South Qinling and South China block apparently took place in the Triassic and resulted in the formation of the Mianlue suture. Abbreviations in a, b, c, and d: NC = North China block, YZ = Yangtze block, SC = South China fold belt, KL = Kunlun mountains, QLS = Qilian orogen, QL = Qinling orogen, DB = Dabie orogen, JS = Jinshajiang suture, A-MS = A'nimaque-Mianlue suture, SPGZ = Songpan-Ganzi orogen, DEZ = Daerzang, MW = Meiwu, WQ = Wenquan, LB* = Luoba, MSL = Mishuling, GTS = Guangtoushan, GQP = Gaoqiaopu, LB = Liuba, XB = Xiba, HY = Huayang, WL = Wulong, XCH = Xichahe, LC = Laocheng, YZB = Yanzhiba, DJK = Dongjiangkou, ZS = Zhashui, CP = Caoping, SHW = Shahewan, NCB = North China Block, SCB = South China Block, NQ = North Qinling, SQ = South Qinling, BK = Bikou Terrane, SS = Shangdan suture, and MS = Mianlue suture. Zircon U-Pb age and εHf(t) value data sources in b: WL from Qin [2010]; YZB from Jiang et al. [2010]; CP and SHW from Gong et al. [2009a, 2009b]; and GTS, GQP, XB, LC, DJK, and ZS from this study.

[4] The location of the east/west division of South Qinling is a key to understanding its tectonic evolution and for mineral exploration. For example, the western segment is characterized by Pb-Zn deposits, whereas the eastern segment contains Hg-Sb and Ba deposits [He, 2008; Chen, 2010]. Triassic granitoids are widely exposed in the Qinling orogen, but especially along the southern Shangdan suture juxtaposing the North Qinling and South Qinling [Zhang et al., 2001, 2007a, 2008; Dong et al., 2011]. This distribution provides a good opportunity to isotopically delineate the boundary, at the surface, between the western South Qinling segment (WSQ) and eastern South Qinling segment (ESQ). In addition, these data can provide important boundary conditions for evaluating continent-continent collision models for the Qinling orogen.

[5] In this study, we present zircon U-Pb ages and Hf isotopic data for six granitoid plutons from the western and eastern segments of the South Qinling orogen. Integrated with previously published whole-rock Sr-Nd-Pb isotopic data, our new data enable us to quantify the nature of the lower crust beneath these two segments and then to identify two distinct terranes and their boundary, which may have implications for the evolution of South Qinling and the tectonic evolution of the Qinling orogen as a whole.

2 Geological Background and Sample Descriptions

[6] The geological framework of the Qinling orogen developed from the Paleozoic to Early Jurassic interaction among three blocks, the North China block (which includes the North Qinling), South Qinling and the South China block (Figure 1a), separated by the Shangdan suture (including the Linxia-Zhangxian-Wushan fault to the west) and the Mianlue suture [Meng and Zhang, 2000; Ratschbacher et al., 2003]. The Qinling orogen was the end result of a prolonged continental divergence and subsequent convergence between the North and South China blocks (Figure 1d). From late Neoproterozoic to early Paleozoic time, South Qinling formed the northern margin of the South China block, and the future North Qinling occupied the southern margin of the North China block, separated from the South Qinling-South China block by a Proto-Tethyan Qinling Ocean (stage a in Figure 1d). The North Qinling region evolved into an active convergent margin when the proto-Tethyan Qinling Ocean basin was subducted northward during the early Paleozoic (stage b in Figure 1d). Collision between South Qinling and North Qinling took place in the middle Paleozoic along the Shangdan suture [Enkin et al., 1992; Kröener et al., 1993; Zhang et al., 1994; Lerch et al., 1995; Xue et al., 1996; Yin and Nie, 1996; Hacker et al., 2004] (stage c in Figure 1d). Synchronously with the collision, rifting occurred along the southern boundary of South Qinling, followed by the opening of the Paleo-Tethyan Qinling Ocean which comprised the easternmost part of the Paleo-Tethys Ocean during the late Paleozoic, resulting in the rifting of the South China block from South Qinling [Lai et al., 1992] (stage d in Figure 1d). Subduction of the Paleo-Tethyan Qinling ocean is assumed to have started in the Permian [Dong et al., 2011] (stage e in Figure 1d) and resulted in the development of island-arc calc-alkalic volcanic rocks [Lai and Zhang, 1996]. Collision of the South Qinling and South China block occurred in the Triassic along the Mianlue suture (stage f in Figure 1d). The Triassic collision resulted in widespread compressional deformation and magmatism throughout the Qinling orogen and led to the final amalgamation of the North and South China blocks [Meng and Zhang, 2000; Zhang et al., 2001].

[7] South Qinling is characterized by south-vergent thrusts and folds making up an imbricated thrust-fold system [Zhang et al., 2001] (Figure 1c), which was mainly developed during Late Triassic to Late Jurassic time [Meng and Zhang, 2000; Dong et al., 2011]. The basement of South Qinling mainly contains Mesoproterozoic to Neoproterozoic rifting-related volcanic and sedimentary rocks that underwent greenschist-facies metamorphism [Zhang et al., 1995] with minor Neoarchean to Paleoproterozoic rocks [Zhang et al., 2002c]. The Phanerozoic cover consists mainly of a sequence of Cambrian to Triassic, mostly Devonian-Cretaceous, sedimentary rocks.

[8] The widely exposed granitic plutons in the South Qinling orogen are thought to be the result of the continent-continent collision between the South Qinling and South China block [Lu et al., 1998; Sun et al., 2002; Zhang et al., 2008; Jiang et al., 2010; Dong et al., 2011; Zhu et al., 2011b]. These plutons are distributed approximately parallel to the Shangdan suture (Figure 1b). Bounded by the narrowest part (107°E–108°E longitude) of the South Qinling orogen, these granitoids can be geographically divided into the western South Qinling segment and eastern South Qinling segment. From west to east, the granitoids from the western South Qinling segment include the Daerzang, Meiwu, Luoba, Wenquan, Mishuling, Guangtoushan, Gaoqiaopu, Liuba, Xiba, and Huayang bodies, while those from the eastern South Qinling segment include the Wulong, Laocheng, Xichahe, Yanzhiba, Dongjiangkou, Zhashui, Caoping, and Shahewan plutons (Figure 1b). These granitoids mostly display I-type compositions and are thought to be the result of partial melting of the mafic lower crust [Zhang et al., 2002b, 2007b; Qin et al., 2007a, 2008a, 2008b, 2009, 2010; Cao et al., 2010; Wang et al., 2011; Zhu et al., 2011b]. They were emplaced during the Middle to Late Triassic (233–206 Ma) [Qin et al., 2007b, 2008b, 2009; Wang et al., 2007, 2011; Zhang et al., 2007a, 2007b; Gong et al., 2009a; Cao et al., 2010], slightly postdating the peak UHP metamorphic ages of 240 to 225 Ma [Zheng et al., 2003; Wan et al., 2005] and implying that they mostly formed in a post-collisional setting. The representative plutons studied in this project include the Guangtoushan, Gaoqiaopu, and Xiba bodies in the western segment and the Laocheng, Dongjiangkou and Zhashui plutons in the eastern segment (from west to east); they are described below (Table 1).

Table 1. Petrography of the Samples From the Six Plutons in the South Qinlinga
PlutonLithologyTexturePlagioclase (Volume Content)K-FeldsparQuartzBiotiteHornblendeAccessory
  1. a

    Ap: apatite; Ttn: titanite; Zrn: zircon; Opa: opaque minerals.

GuangtoushanQuartz diorite (GTS01)Porphyritic65%±9%±14%±10%± Ap, Zrn, Opa
GaoqiaopuQuartz diorite (GQP01)Porphyritic60%±14%±5%±10%±10%±Ap, Zrn, Opa
XibaQuartz monzonite (XB01)Porphyritic45%±27%±15%±2%±10%±Ap, Ttn, Zrn, Opa
LaochengSyenogranite (LC01)Porphyritic10%±50%±35%±4%± Ap, Zrn, Opa
DongjiangkouMonzogranite (DJK01)Porphyritic40%±30%±20%±4%±5%±Ap, Ttn, Zrn, Opa
ZhashuiMonzogranite (ZS01)Granitic36%±30%±25%±6%±2%±Ttn, Ap, Zrn, Opa

Guangtoushan Pluton

[9] The Guangtoushan pluton is a nearly equiaxial batholith lying north of the Mianlue suture and has an outcrop area of about 900 km2. It mainly intruded into metamorphosed Early Paleozoic clastic rocks. The Guangtoushan pluton mainly consists of quartz diorite and granodiorite. These rocks are composed of plagioclase (40–65%) + alkali feldspar (5–20%) + quartz (10–25%) + biotite (5–10%) ± hornblende (1–3%), with a porphyritic texture. The quartz diorite (sample GTS01) consists of plagioclase (65%), alkali feldspar (9%), quartz (14%), and biotite (10%) (Figure 2a) with accessory apatite, magnetite, and zircon.

Figure 2.

Photomicrographs of the samples from the granitoid plutons in the western and eastern South Qinling segments. (a) Quartz diorite (GTS01) from the GTS, (b) quartz diorite (GQP01) from the GQP, (c) quartz monzonite (XB01) from the XB, (d) syenogranite (LC01) from the LC, (e) monzogranite (DJK01) from the DJK, and (f) monzogranite (ZS01) from the ZS. Q: Quartz, Kf: Alkali feldspar, Pl: Plagioclase, Bi: Biotite, and Hb: Hornblende.

Gaoqiaopu Pluton

[10] The Gaoqiaopu pluton is a small ellipsoidal body with an outcrop area of about 5 km2. It intruded into metamorphosed Devonian-Carboniferous strata, which mainly consist of sandstone, limestone, schist, and marble. It mainly consists of quartz diorite and granodiorite. Granodiorites are made up of plagioclase (40–60%) + alkali feldspar (10–25%) + quartz (5–20%) + biotite (5–10%) + hornblende (5–10%). The quartz diorite (sample GQP01) consists of plagioclase (60%), alkali feldspar (14%), quartz (5%), biotite (10%), and hornblende (10%) (Figure 2b) with accessory apatite, zircon, and magnetite.

Xiba Pluton

[11] The Xiba pluton is lensoidal in shape, cropping out over about 150 km2. It intruded into Devonian metasiltstone and carbonate strata. The pluton mainly consists of quartz monzonite, monzogranite, granite, and granodiorite. These rocks consist of alkali feldspar (25–40%) + plagioclase (15–35%) + quartz (15–30%) + hornblende (5–10%) + biotite (1–3%). The quartz monzonite (sample XB01) is mainly composed of plagioclase (45%), alkali feldspar (27%), quartz (15%), biotite (2%), and hornblende (10%) (Figure 2c) with accessory apatite, zircon, and magnetite.

Laocheng Pluton

[12] The Laocheng pluton covers an area of about 520 km2. It intruded into Cambrian-Ordovician metasedimentary strata in the east and Devonian strata in the north and south, which mainly include sandstone, schist, slate, phyllite, limestone, and marble [Zhang, 1992]. The pluton is mostly composed of syenogranite, granodiorite, and quartz diorite. These rocks are composed of plagioclase (10–60%) + alkali feldspar (10–50%) + quartz (15–35%) + biotite (4–10%) ± hornblende (1–3%), with a porphyritic texture. The syenogranite (sample LC01) mainly consists of alkali feldspar (50%), quartz (35%), plagioclase (10%), and biotite (4%) (Figure 2d). Accessory minerals are apatite, zircon, and magnetite.

Dongjiangkou Pluton

[13] The Dongjiangkou pluton covers an area of at least 365 km2 and intruded into Devonian quartzites. Rocks from the pluton include monzogranite with mafic microgranular enclaves. The monzogranite (sample DJK01) is mainly composed of plagioclase (40%), alkali feldspar (30%), quartz (20%), hornblende (5%), and biotite (4%) (Figure 2e) with accessory apatite, titanite, magnetite, and zircon.

Zhashui Pluton

[14] The Zhashui pluton crops out over 264 km2 and intruded into Early Paleozoic metamorphic clastic rocks. The pluton mainly consists of monzogranite with mafic microgranular enclaves. The mineral assemblage of the monzogranite (sample ZS01) includes plagioclase (36%), alkali feldspar (30%), quartz (25%), biotite (6%), and hornblende (2%) (Figure 2f). Accessory minerals are titanite, apatite, zircon, and magnetite

3 Analytical Methods

[15] Zircons were extracted from whole-rock samples using standard techniques of density and magnetic separation in the laboratory of the Langfang Regional Geological Survey, Hebei Province, China. Zircon grains were mounted in epoxy disks and polished to approximately half their thickness. Transmitted light, reflected light, and cathodoluminescence (CL) images were collected on a microscope and a JXA-8100 electron microscope, respectively, at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan), China. Representative CL images are shown in Figure 3.

Figure 3.

Cathodoluminescence (CL) images of representative zircons from the six plutons in the western and eastern South Qinling segments. Circles indicate the location of U-Pb and Hf-isotope analysis, and the numbers inside and outside the circles refer to the εHf(t) values and the apparent 206Pb/238U ages, respectively.

[16] Simultaneous in situ determinations of U-Pb age, trace element, and Hf isotope composition on the same spots of single zircon grains were carried out in the State Key Laboratory of Continental Dynamics at Northwest University (Xi'an), China. The combined determinations were performed using a GeoLas 2005 laser-ablation system with a COMPexPro 102 UV 193 nm ArF excimer laser, coupled to an Elan 6100DRC Q-ICPMS and a Nu Plasma HR MC-ICPMS. The laser ablation used a beam diameter of 44 µm, a pulse rate of 10 HZ, and energy density of 15–20 J/cm2. The detailed analytical procedures, conditions, and data acquisition parameters are described by Yuan et al. [2004, 2008]. The measured 207Pb/206Pb, 206Pb/238U, and 208Pb/232Th ratios were processed using the GLITTER® software (version 4.4) [Griffin et al., 2008], and common-Pb contents were evaluated using the method of Anderson [2002]. The data were treated with the ISOPLOT program of Ludwig [2003]. Uncertainties of individual analysis were reported with 1σ, but weighted average ages were calculated at 2σ level. Results of U-Pb analyses are shown in Table 2.

Table 2. U-Pb Data for Zircons From the Six Plutons in the South Qinling
Analysis SpotContent (ppm)RatiosAges(Ma)
ThUTh/U207Pb/206Pb1σ207Pb/235U1σ206Pb/238U1σ208Pb/232Th1σ207Pb/206Pb1σ207Pb/235U1σ206Pb/238U208Pb/232Th1σ
Western South Qinling Segment
Sample GTS01 (33°13′2″N, 106°44′54″E, 656 m; Guangtoushan pluton)
11854110.450.05120.00150.23510.00670.03330.00030.01030.000224851214621122075
22434840.500.04910.00130.22470.00570.03320.00030.00980.000215243206521021974
33575480.650.05030.00110.22900.00510.03300.00020.01060.000221139209420912133
42055680.360.05090.00130.23460.00570.03360.00030.01010.000223540214521322044
53114880.640.05180.00670.23140.02960.03240.00050.01020.00032772882112420532056
62356010.390.05120.00120.23480.00610.03310.00030.01030.000225243214521022074
73184800.660.05100.00140.23460.00630.03340.00030.01020.000224247214521222063
82457010.350.05200.00180.24280.00810.03390.00030.01060.000128482221721522142
91883980.470.05250.00150.24060.00710.03330.00030.01010.000230652219621122045
102726570.410.05300.00090.24850.00470.03390.00030.01060.000233028225421522124
112114220.500.05420.00220.25430.00970.03400.00040.01060.000138091230821622142
123027580.400.05000.00120.22660.00510.03290.00030.01020.000219538207420922053
132425060.480.05350.00290.23980.01270.03250.00030.01020.00013511252181020622041
142176570.330.05160.00110.23750.00510.03340.00030.01090.000226934216421222204
151905880.320.05270.00230.23310.01000.03210.00030.01010.0001315103213820422022
163015470.550.05130.00130.23150.00590.03270.00030.01010.000225442211520822024
174237740.550.05420.00150.24670.00740.03290.00030.01050.000238149224620922123
183356310.530.05060.00110.23100.00520.03310.00030.01080.000222136211421022163
193288240.400.05690.00110.26710.00560.03400.00030.01230.000248931240421522484
203956130.640.06250.00200.29770.00960.03450.00030.01290.000369255265821922605
213447360.470.06440.00220.30450.01020.03430.00030.01510.0005755562708218230310
2224788702.850.07540.00190.28640.01160.02700.00070.00560.0004107943256917241138
233146960.450.05470.00210.25850.00980.03430.00030.01070.000140089233821722151
245228180.640.07140.00340.32370.01490.03290.00030.01000.0001968982851120922002
252274820.470.05090.00130.23440.00590.03340.00020.01060.000223645214521212133
263698230.450.05070.00170.24050.00750.03440.00040.01090.000122578219621822182
271914310.440.05060.00160.23490.00740.03370.00020.01060.000122476214621322131
282767220.380.04960.00100.22310.00450.03260.00020.01000.000217535204420712023
292794680.600.04910.00150.22420.00600.03340.00030.01080.000315445205521122165
302636440.410.05220.00130.24130.00590.03340.00030.01060.000229541220521222134
315257880.670.06210.00650.29760.03080.03480.00050.01070.00016772332642422032152
323027680.390.05030.00100.23660.00460.03400.00030.01100.000220830216421622213
333195310.600.05110.00140.24000.00600.03410.00030.01100.000224443218521622223
343227070.460.05050.00100.23690.00420.03400.00030.01100.000221728216321522203
353055310.570.05170.00140.24150.00610.03390.00030.01120.000227343220521522254
362033390.600.05140.00150.23430.00670.03310.00030.01070.000225749214621022164
372384140.580.05390.00140.25430.00640.03430.00030.01100.000236541230521822214
382636910.380.05100.00110.23700.00520.03370.00030.01110.000224133216421422244
395896990.840.05310.00120.24400.00600.03320.00030.01040.000133441222521122083
403597050.510.05270.00130.24510.00590.03380.00030.01060.000231640223521422134
412214910.450.05660.00140.26240.00710.03350.00030.01210.000247646237621222424
Sample GQP01 (33°46′52″N, 106°49′48″E, 1239 m; Gaoqiaopu pluton)
1437417325.250.07810.00220.78360.03040.07530.00270.00190.00021148345881746816394
2108317510.620.05250.00150.24500.00660.03390.00030.00470.00043074722352152948
32385620.420.07320.00430.81450.04640.08070.00110.02440.000310181226052650164875
4178411851.510.05840.00120.24730.00530.03080.00020.00180.00015433322441951371
53283990.820.07180.00310.30450.01430.03060.00040.01010.00069817427011194220311
6882700.330.06350.00580.28890.02610.03300.00040.01010.00017262012582120932032
71132260.500.05650.00250.26750.01180.03440.00030.01220.000447181241921822457
81221770.690.05230.00280.24790.01370.03440.00040.01110.00033001052251121832236
92174160.520.05210.00250.24160.01120.03360.00040.01060.0001290111220921322122
101812580.700.05110.00330.23280.01470.03300.00030.01040.00012461472131221022091
111105240.210.05160.00120.24080.00570.03380.00020.01170.000426942219521412349
12591420.410.05250.00220.25240.01030.03510.00050.01240.000430668229822232498
133993541.130.06690.00210.31100.00980.03360.00030.00800.0007834492758213216014
141412020.700.05700.00210.28330.01060.03600.00050.00870.000448957253822831758
151692250.750.05150.00300.23890.01390.03360.00030.01060.00012641372181121322131
161712720.630.05640.00940.26070.04330.03350.00060.01040.00034693592353521342106
177553851.960.06900.00340.27910.01130.03000.00040.00200.00028986425091902405
184372381.840.05410.00220.19630.00810.02630.00040.00290.00043736418271673598
191311820.720.05050.00230.23720.01050.03410.00040.01080.000322082216921622176
202697570.360.05710.00140.27680.00530.03540.00040.00950.000249425248422421904
21762580.300.12990.00126.74660.08490.37490.00320.10730.0013209611207911205215206123
221362180.620.05250.00180.24630.00850.03420.00040.00970.000230857224721731965
231151870.620.05000.00220.23820.01010.03470.00040.01100.000319779217822022206
242022840.710.05410.00200.25700.00970.03440.00030.01010.000337668232821822045
Sample XB01 (33°47′46″N, 107°11′8″E, 1203 m; Xiba pluton)
11621810.890.05230.00270.25390.01280.03540.00050.01150.0003300902301022432326
21461610.900.05440.00320.24860.01430.03330.00040.01040.00043881062251221132098
374960.770.05430.00510.24850.02300.03410.00060.01080.00053821782251921642179
41413510.400.04850.00200.22600.00950.03360.00040.01020.000312575207821322066
52672631.010.05280.00240.25910.01120.03590.00050.01150.000331972234922732325
61312170.600.05340.00290.25290.01360.03430.00040.01100.00043451012291121732207
71601601.000.05320.00310.25230.01330.03580.00160.01070.00033375422811227102166
8971640.590.05120.00330.23570.01510.03380.00050.01180.00042481202151221432389
91813280.550.04920.00360.20430.01420.03040.00060.01010.00031561231891219332027
10701100.640.06130.00400.28830.01760.03530.00060.01150.000564910325714223423210
11801730.460.05050.00420.23500.01900.03410.00050.01050.000521815621416216321110
12991330.750.05160.00340.24900.01630.03560.00050.01190.00042671242261322532408
131472590.570.05240.00230.25370.01130.03490.00030.01180.000330486230922122376
141091710.640.05440.00410.25180.01800.03390.00070.00990.000538912322815215419810
15821600.510.14460.00254.67380.09550.23390.00270.06470.0020228320176317135514126738
161001650.610.05230.00330.24890.01570.03490.00060.01150.00052961142261322142309
174123881.060.05390.00220.25940.01120.03480.00040.01090.000236976234922122204
181201670.720.05350.00220.25350.01020.03460.00040.01120.000335072229821922246
191974240.460.05380.00180.25310.00830.03420.00040.01100.000236255229721722205
202052210.930.05380.00300.25720.01430.03630.00150.01090.00033635823212230102195
211153210.360.05210.00210.23880.00930.03330.00050.01040.000329162217821132096
223543950.900.06120.00390.27260.01630.03270.00050.01040.00036471022451320832086
231422780.510.05350.00230.25400.01000.03480.00050.01130.000335063230822132266
241521491.020.05580.00320.26050.01530.03410.00040.01080.00034451092351221632186
251581940.810.05290.00290.24620.01350.03400.00050.01100.0003326972231121532226
261161590.730.05440.00440.26310.02100.03510.00050.01100.00013871862371722232202
271061780.600.05420.00350.27040.01720.03620.00040.01130.00013781492431422932272
 
Eastern South Qinling Segment
Sample LC01 (33°21′31″N, 108°15′32″E, 525 m; Laocheng pluton)
12987830.380.05240.00130.24610.00590.03400.00020.01060.000230242223521522134
22025810.350.04930.00190.23380.00790.03460.00040.01210.000316456213621932437
32147400.290.05090.00120.24330.00570.03460.00030.01130.000223839221521922275
41777030.250.04840.00130.22770.00580.03410.00020.01090.000311848208521612195
52815020.560.05590.00140.26830.00720.03480.00040.01210.000344737241622032435
629500.590.06160.00620.29020.02850.03540.00090.01120.000766116725922224622613
73796540.580.05110.00110.24030.00510.03410.00020.01110.000224636219421612235
82276700.340.05930.00280.29860.01360.03650.00050.01130.00015771052651123132272
96696531.020.05260.00120.24590.00570.03390.00020.01040.000131140223521522093
102256310.360.05150.00110.23660.00510.03330.00030.01010.000226435216421122034
1140913170.310.05160.00170.25200.00750.03540.00040.01110.000126775228622432242
123768430.450.05070.00170.24480.00780.03500.00030.01100.000122878222622222221
1347811940.400.05190.00090.24390.00470.03390.00020.01080.000128031222421512163
Sample DJK01 (33°39′36″N, 108°38′58″E, 794 m; Dongjiangkou pluton)
1501180.430.12340.00412.72000.08360.15990.00200.04570.00052006601334239561190310
23704470.830.05420.00160.26560.00820.03540.00040.01110.000237951239722422224
31881521.240.05500.00240.26400.01160.03480.00050.01000.000341371238922132015
4641140.570.04890.00300.22780.01440.03380.00060.00990.00041431122081221431988
54207050.600.09300.00073.15430.02670.24490.00120.05920.0012148891446714126116223
62363450.680.05280.00210.24530.00920.03390.00030.00980.000232168223821521974
73443810.900.05730.00190.26980.00870.03420.00030.01020.000250355243721722043
81211141.060.05570.00280.26040.01280.03420.00050.01070.0003439862351021732155
91531680.910.05110.00220.23580.01010.03370.00040.01030.000224376215821432064
101631730.940.07060.00171.17340.03590.11960.00170.04200.000694639788177281083211
1184960.870.05200.00350.24330.01710.03390.00050.01010.00032841332211421532047
121411440.980.05660.00300.26730.01410.03460.00050.01120.0003477922411121932266
131741731.000.05460.00280.24680.01180.03350.00050.01030.0002395822241021232074
14781190.660.05330.00310.24800.01410.03390.00050.01190.001134310322511215323821
1512550.230.11570.01283.77470.37790.23660.01090.06810.00311891207158780136957133159
16885130.170.09910.00103.23440.05940.23540.00310.05750.0020160817146514136316112937
17992060.480.15910.00185.50920.19480.24760.00710.07470.0025244627190230142636145547
182804100.680.05430.00180.26270.00810.03530.00050.01150.000238544237722432304
197459310.800.05880.00100.53580.01090.06630.00120.01900.000555820436741473809
Sample ZS01 (33°40′14″N, 109°06′46″E, 802 m; Zhashui pluton)
13194830.660.054910.005280.251820.024030.033260.000390.010380.00014092202281921122092
2233214451.610.058620.001520.248070.00560.030760.000230.008050.0001955336225519511624
33144760.660.053290.003680.243210.01660.03310.000370.010370.000083411602211421022082
41623700.440.050150.002760.235830.012610.034110.000440.010760.000112021272151021632162
54485880.760.055310.001650.258630.007580.033890.000270.010380.0001942551234621522094
62293600.640.048940.005450.22960.025270.034020.000590.010770.000421452472102121642168
73184970.640.050640.003710.25060.018220.035890.000310.011310.000122251682271522722272
8540324312.220.055350.001190.254590.004940.03330.000270.009480.0001342629230421121913
96625351.240.068760.002030.359720.010110.038040.000450.01380.0002489239312824132775
101381161.180.0550.007450.250830.033810.033070.000460.010320.000144123062272721032083
113863801.020.071770.003160.344590.012350.035660.000540.013960.0002897948301922632806
125364061.320.053010.004010.248470.018630.0340.000340.010660.000073291742251521622141
136467450.870.055940.002160.258220.009590.03340.000430.011120.0002545059233821232235
14302714432.100.084840.003790.445540.025480.036450.000620.010210.00031312853741823142056

[17] We used the 176Lu decay constant of 1.865 × 10−11 yr−1 [Scherer et al., 2001] for calculating the Hf isotopic data. Initial 176Hf/177Hf ratios, expressed as 176Hf/177Hfi, were calculated back to the time of zircon crystallization. εHf(t) was computed relative to a present-day chondritic reservoir with a 176Hf/177Hf ratio of 0.282772 and 176Lu/177Hf of 0.0332 [Blichert-Toft and Albarède, 1997]. The depleted-mantle model ages (TDM1) were calculated using the measured Lu/Hf ratios and the present-day 176Hf/177Hf ratio of 0.28325 and 176Lu/177Hf of 0.0384 [Griffin et al., 2000] of depleted mantle (DM). The average crustal model ages (TDM2) were obtained under the assumption that the protolith of the host rock of a given zircon was derived from the depleted mantle and had the composition of the average continental crust with 176Lu/177Hf = 0.015 [Griffin et al., 2002]. The zircon Hf isotope results are given in Table 3.

Table 3. Lu-Hf Isotope of Zircons From the Six Plutons in the South Qinling
Spot176Hf/177Hf2σ176Yb/177Hf2σ176Lu/177Hf2σZircon U-Pb age (Ma)176Hf/177HfIaεHf(t)b1σTDM1(Ga)c1σTDM2 (Ga)d1σ
  1. a

    176Hf/177Hfi = (176Hf / 177Hf)S − (176Lu / 177Hf)S × (eλt − 1)

  2. b

    εHf(t) = ((176Hf / 177Hf)S − (176Lu / 177Hf)S × (eλt − 1)) / ((176Hf / 177Hf)CHUR,0 − (176Lu / 177Hf)CHUR × (eλt − 1)) − 1) × 10000

  3. c

    TDM1(Ga) = 1 / λ × ln(1 + ((176Hf / 177Hf)S − (176Hf / 177Hf)DM) / ((176Lu / 177Hf)S − (176Lu / 177Hf)DM))

  4. d

    TDM2(Ga) = 1 / λ × ln(1 + ((176Hf / 177Hf)S,t − (176Hf / 177Hf)DM,t) / ((176Lu/ 177Hf)S − (176Lu/ 177Hf)DM)) + t / 1000

  5. t = the apparent age of zircon (when t (206Pb/238U age) is greater than 1.0 Ga, it is 206Pb/207Pb age; in contrast, it is 206Pb/238U age)

Western South Qinling Segment
Sample GTS01 (Guangtoushan pluton)
10.2823570.0000210.0141650.0001000.0005830.0000042110.282355−10.10.41.250.011.890.02
20.2823920.0000250.0159000.0001410.0006650.0000062110.282389−8.90.41.210.021.810.03
30.2823360.0000230.0252030.0002370.0010320.0000092110.282332−10.90.41.300.021.940.03
40.2824810.0000220.0149370.0003130.0006650.0000142110.282479−5.80.41.080.021.620.02
50.2822690.0000220.0227240.0002640.0009180.0000102110.282266−13.30.41.380.022.090.02
60.2824930.0000230.0108690.0001330.0004800.0000062110.282491−5.30.41.060.021.590.03
70.2823500.0000230.0185600.0002680.0007870.0000092110.282347−10.40.41.270.021.910.03
80.2823580.0000280.0181590.0002730.0007780.0000122110.282355−10.10.51.260.021.890.03
90.2824290.0000200.0110750.0000630.0004880.0000032110.282427−7.60.31.150.011.730.02
100.2824000.0000260.0140950.0001130.0006210.0000052110.282397−8.60.51.190.021.800.03
110.2823520.0000240.0166310.0000640.0007010.0000032110.282349−10.30.41.260.021.900.03
120.2824180.0000210.0166220.0003720.0007290.0000162110.282415−8.00.41.170.011.760.02
130.2823720.0000240.0172460.0003980.0007500.0000162110.282369−9.60.41.240.021.860.03
140.2823620.0000250.0161240.0002810.0007080.0000132110.282359−10.00.41.250.021.880.03
150.2822930.0000250.0170170.0004830.0007170.0000172110.282290−12.40.41.350.022.040.03
160.2823820.0000210.0192120.0002780.0008010.0000112110.282379−9.30.41.220.011.840.02
170.2823150.0000240.0217100.0005110.0009180.0000202110.282312−11.60.41.320.021.990.03
180.2823800.0000250.0217610.0001810.0009370.0000072110.282376−9.40.41.230.021.840.03
190.2823660.0000240.0138380.0000380.0006050.0000012110.282363−9.80.41.240.021.870.03
200.2822820.0000240.0244660.0005770.0010210.0000232110.282278−12.90.41.370.022.060.03
210.2824040.0000250.0195090.0000910.0008320.0000052110.282401−8.50.41.190.021.790.03
220.2823080.0000340.0302540.0010640.0011810.0000422110.282304−11.90.61.340.022.000.04
230.2823370.0000240.0163020.0002010.0006950.0000102110.282334−10.90.41.280.021.940.03
240.2822660.0000250.0206310.0001350.0008770.0000062110.282262−13.40.41.390.022.100.03
250.2823770.0000250.0159820.0000930.0007050.0000032110.282374−9.40.41.230.021.850.03
260.2823170.0000240.0180520.0001310.0007600.0000052110.282314−11.60.41.310.021.980.03
270.2824560.0000200.0111300.0001420.0004890.0000062110.282454−6.60.41.110.011.670.02
280.2824090.0000190.0195870.0001950.0008500.0000092110.282406−8.30.31.190.011.780.02
290.2822970.0000220.0194680.0001230.0008270.0000052110.282294−12.30.41.340.022.030.02
300.2824180.0000210.0155990.0002700.0006760.0000122110.282415−8.00.41.170.011.760.02
310.2822320.0000320.0294300.0006450.0011420.0000212110.282227−14.60.61.450.022.170.04
320.2823690.0000210.0153500.0001350.0006670.0000062110.282367−9.70.41.240.011.860.02
330.2823630.0000230.0256820.0001990.0010580.0000072110.282359−10.00.41.260.021.880.03
340.2824550.0000210.0122110.0000720.0005530.0000022110.282453−6.60.41.110.011.670.02
350.2823340.0000190.0233460.0004580.0009890.0000192110.282330−11.00.31.300.011.950.02
360.2824220.0000190.0170750.0001470.0007120.0000062110.282419−7.80.31.160.011.750.02
370.2824220.0000200.0160080.0002430.0006730.0000102110.282419−7.80.41.160.011.750.02
380.2824080.0000210.0138580.0001600.0006080.0000072110.282406−8.30.41.180.011.780.02
390.2823540.0000220.0231330.0006830.0009790.0000272110.282350−10.30.41.270.021.900.02
400.2824880.0000250.0167110.0000930.0007370.0000042110.282485−5.50.41.070.021.600.03
410.2823840.0000230.0115040.0001030.0005000.0000042110.282382−9.20.41.210.021.830.03
Sample GQP01 (Gaoqiaopu pluton)
10.2823020.0000330.0332830.0002650.0013360.0000094680.282290−6.80.61.350.021.880.04
20.2821820.0000320.0233120.0000800.0008990.0000032150.282178−16.30.61.510.022.280.03
30.2817760.0000330.0340980.0002220.0014280.0000095010.281762−24.70.62.100.023.030.04
40.2822160.0000310.0153100.0000990.0006120.0000042150.282213−15.10.51.450.022.200.03
50.2820900.0000290.0243430.0003480.0009210.0000132150.282087−19.50.51.630.022.480.03
60.2823080.0000320.0141980.0002600.0006290.0000092150.282306−11.80.61.320.022.000.04
70.2823520.0000270.0123170.0000990.0004770.0000042150.282350−10.20.51.250.021.900.03
80.2824590.0000200.0124120.0003960.0004700.0000142150.282457−6.40.41.110.011.660.02
90.2823680.0000270.0192200.0001150.0007260.0000042150.282365−9.70.51.240.021.870.03
100.2822730.0000280.0183840.0002890.0006890.0000112150.282270−13.00.51.370.022.080.03
110.2824260.0000250.0204540.0002030.0008940.0000082150.282422−7.70.41.170.021.740.03
120.2824400.0000260.0107370.0001650.0004580.0000092150.282439−7.10.51.130.021.700.03
130.2823250.0000250.0159890.0001170.0006000.0000042150.282322−11.20.41.300.021.960.03
140.2824780.0000240.0144770.0001870.0005450.0000072150.282476−5.80.41.080.021.620.03
150.2824410.0000250.0236680.0003860.0008890.0000152150.282438−7.10.41.140.021.700.03
160.2823870.0000260.0196520.0003110.0007310.0000112150.282384−9.00.51.210.021.820.03
170.2823020.0000230.0098810.0002400.0004330.0000102150.282300−12.00.41.320.022.010.02
180.2824940.0000230.0123800.0007010.0004720.0000252150.282493−5.20.41.060.021.580.03
190.2824380.0000220.0189340.0002640.0007090.0000102150.282435−7.20.41.140.021.710.02
200.2823820.0000230.0219250.0001800.0009330.0000072150.282378−9.20.41.230.021.840.03
210.2813080.0000220.0322960.0003010.0012280.00000920960.281259−6.70.42.730.013.140.02
220.2824870.0000210.0161520.0002520.0006030.0000092150.282484−5.50.41.070.011.600.02
230.2823340.0000230.0128660.0004710.0004870.0000172150.282332−10.90.41.280.021.940.03
240.2824660.0000210.0195670.0002650.0007260.0000102150.282463−6.20.41.100.011.650.02
Sample XB01 (Xiba pluton)
10.2821870.0000330.0206810.0008120.0006200.0000242180.282185−16.00.61.490.022.260.04
20.2822550.0000220.0210780.0003110.0006330.0000082180.282252−13.60.41.390.022.110.02
30.2820470.0000230.0140710.0002360.0004300.0000072180.282045−20.90.41.670.022.570.02
40.2823100.0000400.0150110.0000560.0005150.0000012180.282308−11.60.71.310.031.990.04
50.2822330.0000240.0316090.0006950.0009410.0000192180.282229−14.40.41.440.022.170.03
60.2824090.0000260.0137550.0000560.0004360.0000012180.282407−8.10.51.180.021.770.03
70.2824500.0000240.0212960.0001690.0006390.0000042180.282447−6.70.41.120.021.680.03
80.2821550.0000240.0126870.0000580.0004130.0000012180.282153−17.10.41.520.022.330.03
90.2821970.0000250.0193290.0003100.0006170.0000092180.282194−15.70.41.470.022.240.03
100.2822870.0000240.0120390.0001520.0003840.0000042180.282286−12.40.41.340.022.040.03
110.2824440.0000240.0107460.0000690.0003550.0000022180.282442−6.90.41.120.021.690.03
120.2821730.0000210.0139340.0001900.0004310.0000052180.282171−16.50.41.500.012.290.02
130.2822820.0000230.0156300.0001060.0005010.0000042180.282280−12.60.41.350.022.050.03
140.2821170.0000410.0168560.0005370.0005290.0000152180.282115−18.50.71.580.032.420.04
150.2822480.0000230.0126760.0000870.0004000.00000222830.28182117.50.51.950.021.730.03
160.2823770.0000370.0423330.0009420.0012430.0000262180.282247−13.80.41.400.022.130.03
170.2823140.0000390.0189470.0001330.0005770.0000042180.282372−9.40.61.240.031.850.04
180.2822020.0000360.0152470.0000460.0004980.0000032180.282312−11.50.71.310.031.980.04
190.2822740.0000260.0280830.0004320.0008300.0000122180.282200−15.50.61.460.022.230.04
200.2821560.0000240.0113420.0001140.0003810.0000032180.282271−12.90.51.370.022.070.03
210.2823660.0000230.0191650.0004690.0005660.0000132180.282155−17.10.41.520.022.330.03
220.2822340.0000350.0125260.0000530.0004000.0000022180.282364−9.70.41.240.021.870.03
230.2823380.0000280.0249670.0000540.0007030.0000012180.282233−14.30.61.410.022.160.04
240.2821950.0000220.0225840.0001590.0006740.0000042180.282335−10.70.51.280.021.930.03
250.2824140.0000230.0183760.0002980.0005570.0000092180.282193−15.70.41.480.022.250.02
260.2823980.0000230.0138110.0001150.0004200.0000042180.282411−8.00.41.170.021.760.03
270.2818420.0000270.0148780.0001540.0004740.0000042180.282396−8.50.41.190.021.800.03
 
Eastern South Qinling Segment
Sample LC01 (Laocheng pluton)
10.2826040.0000240.0193110.0001230.0006910.0000052160.282601−1.30.40.910.021.340.03
20.2825480.0000230.0225160.0001230.0007940.0000052160.282545−3.30.40.990.021.470.03
30.2827090.0000180.0165470.0000790.0006120.0000022160.2827062.40.30.760.011.100.02
40.2826720.0000270.0220040.0002030.0007630.0000072160.2826691.10.50.820.021.190.03
50.2823630.0000420.0012300.0000440.0000280.0000012160.282362−9.70.71.230.031.870.05
60.2826680.0000270.0285790.0002920.0010240.0000112160.2826640.90.50.830.021.200.03
70.2826650.0000250.0189220.0001630.0006770.0000042160.2826620.80.40.830.021.200.03
80.2827820.0000270.0463170.0004290.0014860.0000112160.2827764.90.50.680.020.940.03
90.2826770.0000190.0172050.0000840.0006680.0000032160.2826741.30.30.810.011.170.02
100.2825730.0000260.0265260.0001430.0009800.0000052160.282569−2.40.40.960.021.410.03
110.2825730.0000270.0211450.0002110.0007100.0000072160.282571−2.40.50.950.021.410.03
120.2826080.0000230.0219920.0005490.0007930.0000202160.282605−1.20.40.910.021.330.03
Sample DJK01 (Dongjiangkou pluton)
10.2815720.0000340.0145800.0000970.0004710.0000039560.281563−21.70.62.320.023.190.04
20.2824230.0000330.0156930.0001240.0005510.0000032180.282421−7.60.61.160.021.740.04
30.2824360.0000380.0149260.0004480.0004600.0000132180.282435−7.20.71.140.031.710.04
40.2826600.0000230.0148090.0000930.0005820.0000022180.2826580.70.40.830.021.210.03
50.2816050.0000320.0216560.0006370.0007640.00001814880.281583−9.00.62.290.022.820.04
60.2826440.0000250.0123980.0000460.0004760.0000012180.2826420.20.40.850.021.240.03
70.2825410.0000250.0219250.0004540.0008020.0000172180.282538−3.50.41.000.021.480.03
80.2825280.0000250.0147930.0000290.0005040.0000022180.282526−3.90.41.010.021.510.03
90.2824860.0000250.0175100.0002820.0006590.0000092180.282483−5.40.41.080.021.600.03
100.2823410.0000340.0310550.0005550.0010990.0000207280.2823260.30.61.290.021.640.04
110.2825260.0000220.0225580.0002230.0007790.0000052180.282522−4.00.41.020.021.510.02
120.2825890.0000200.0151030.0004690.0005210.0000152180.282587−1.70.30.930.011.370.02
130.2825490.0000210.0171730.0003700.0005960.0000122180.282546−3.20.40.990.011.460.02
140.2825810.0000220.0072070.0000110.0002560.0000012180.282580−2.00.40.930.021.380.03
150.2816630.0000250.0590430.0008280.0019950.00002218910.281383−7.00.62.550.023.000.04
160.2819460.0000490.0204560.0000770.0007430.00000716080.281602−5.60.42.290.022.700.03
170.2825080.0000220.0211250.0001390.0008000.00000424460.28191224.50.91.820.031.400.06
180.2824630.0000290.0482890.0012500.0016530.0000342180.282505−4.70.41.050.021.550.02
190.2813950.0000360.0094600.0001660.0003560.0000074140.282450−2.30.51.140.021.550.03
Sample ZS01 (Zhashui pluton)
10.2823950.0000400.0194520.0002780.0007930.0000122130.282392−8.80.71.210.031.810.04
20.2826360.0000270.0287310.0010280.0011400.0000372130.282631−0.30.50.880.021.270.03
30.2824540.0000320.0172930.0004090.0007400.0000162130.282451−6.70.61.120.021.680.04
40.2827610.0000330.0204060.0003590.0007740.0000122130.2827574.20.60.690.020.990.04
50.2826760.0000240.0245420.0003690.0009490.0000142130.2826731.20.40.820.021.180.03
60.2825630.0000230.0180550.0001870.0007190.0000062130.282560−2.80.40.970.021.430.03
70.2826280.0000230.0381380.0015760.0011790.0000452130.282623−0.60.40.890.021.290.03
80.2828370.0000360.0445220.0012060.0014800.0000422130.2828316.80.60.600.030.820.04
90.2825830.0000410.0195620.0006460.0006830.0000182130.282580−2.10.70.940.031.390.05
100.2825430.0000230.0164090.0002440.0006050.0000082130.282541−3.50.40.990.021.470.03
110.2827040.0000210.0290450.0004910.0010740.0000162130.2827002.10.40.780.011.120.02

4 Zircon Morphology and Geochronology

4.1 Plutons in the Western Segment

[18] Zircons in granitoid samples (GTS01, GQP01, and XB01) from the western South Qinling segment are mostly euhedral, prismatic, transparent, and colorless, ranging from 100 to 300 µm in length. However, zircons from samples GTS01 and XB01 mostly have greater width-to-length ratios (1 : 2 to 1 : 3) than those from sample GQP01 (1 : 3.5 to 1 : 5). In CL images, the former exhibit well-developed oscillatory zoning (Figures 3a and 3c) without inherited cores, while the latter have weak zoning (Figure 3b) and some have core-rim structures. The zircons from different samples show Th and U concentrations ranging from 59 to 1083 ppm and 96 to 1751 ppm, respectively, and their Th/U ratios vary from 0.21 to 1.06, indicating a magmatic origin.

[19] Thirty-two zircon analyses from sample GTS01 form a tight cluster on Concordia and yield a weighted mean 206Pb/238U age of 211 ± 1 Ma (MSWD = 3.2, 2σ) (Figure 4a), representing the crystallization age of this pluton. The age is slightly younger than the emplacement age (216 ± 2 Ma) of this pluton obtained by Sun et al. [2002].

Figure 4.

U-Pb Concordia diagrams for zircons from the six plutons in the western and eastern South Qinling segments.

[20] Twelve zircon analyses from sample GQP01 yield a weighted mean 206Pb/238U age of 215 ± 2 Ma (MSWD = 2.4, 2σ) (Figure 4b), which represents the emplacement age of the Gaoqiaopu pluton. The emplacement age is identical with that of the Guangtoushan pluton within error. One old core (spot GQP01-21) with an age of 2096 ± 11 Ma has a Th/U ratio of 0.30, indicating a magmatic origin.

[21] Twenty-five zircon analyses from sample XB01 form a coherent group with a weighted mean 206Pb/238U age of 218 ± 3 Ma (MSWD = 5.6, 2σ) (Figure 4c), representing the emplacement age of the pluton, consistent with a previous determination by Zhang et al. [2009].

4.2 Plutons in the Eastern Segment

[22] Zircons in granitoid samples (LC01, DJK01, and ZS01) from the eastern South Qinling segment are mostly euhedral, prismatic, transparent, and colorless, ranging from 50 to 300 µm in length and having width-to-length ratios of 1 : 1.5 to 1 : 3. In the CL images (Figures 3d–3f), zircons from all the granitoid samples show well-developed oscillatory zoning; inherited cores were observed only in a few grains from sample DJK01. All the zircons have Th concentrations from 64 to 5403 ppm and U from 96 to 2431 ppm, leading to a wide range of Th/U ratios from 0.25 to 2.22, consistent with a magmatic origin.

[23] Ten zircon analyses from sample LC01 cluster together and yield a weighted mean 206Pb/238U age of 216 ± 2 Ma (MSWD = 3.0, 2σ) (Figure 4d), representing the emplacement age of the pluton; Jiang et al. [2010] obtained a similar emplacement age (217.6 ± 3.4 Ma) for this pluton.

[24] Twelve zircon analyses from sample DJK01 form a tight cluster on Concordia and yield a weighted mean 206Pb/238U age of 218 ± 3 Ma (MSWD = 2.4, 2σ) (Figure 4e), representing the emplacement age of this pluton, as previously found by Qin et al. [2010]. Additionally, there are three inherited ages of 414 ± 7 Ma (spot DJK01-19), 728 ± 10 Ma (spot DJK01-10), and 1488 ± 9 Ma (spot DJK01-5); they have high Th/U ratios of 0.60, 0.80, and 0.94, respectively, which suggest an igneous origin.

[25] Nine zircon analyses from sample ZS01 form a coherent group and yield a weighted mean 206Pb/238U age of 213 ± 2 Ma (MSWD = 1.3, 2σ) (Figure 4f), which is considered as the age of emplacement of the Zhashui pluton. The age is consistent with the previously measured age (213.6 ± 1.8 Ma) of this pluton [Hu et al., 2004].

5 Zircon Hf-Isotope Compositions

5.1 Plutons in the Western Segment

[26] Zircons from the Guangtoushan pluton have 176Lu/177Hf ratios ranging from 0.000480 to 0.001181 and initial 176Hf/177Hf ratios from 0.28223 to 0.28249 with an average of 0.28237. These values result in negative εHf(t) values ranging from −14.6 to −5.3 with an average of −9.5 (Figure 5). Their single-stage Hf model ages (TDM1) range from 1.06 to 1.45 Ga and two-stage Hf model ages (TDM2) from 1.59 to 2.18 Ga with a weighted mean of 1.85 Ga.

Figure 5.

εHf(t) values corrected to the crystallization ages of zircons from the six plutons in the western and eastern South Qinling segments. Reference lines representing Hf-isotope evolution in chondritic and depleted mantle are from Blichert-Toft and Albarede [1997] and Griffin et al. [2000], respectively.

[27] Zircons from the Gaoqiaopu pluton have similar εHf(t) values (−19.5 to −5.2) to those of the Guangtoushan pluton. Their TDM1 ages vary from 1.06 to 1.63 Ga and TDM2 from 1.58 to 2.48 Ga with a weighted mean of 1.83 Ga. The inherited zircon grain (spot GQP01-21) yields a relatively low εHf(t) of −6.7 and a very old TDM2 age of 3.14 Ga.

[28] Zircons from the Xiba pluton have Hf-isotope compositions similar to those of the Guangtoushan pluton. They exhibit initial 176Hf/177Hf ratios from 0.282045 to 0.282447 and εHf(t) values from −20.9 to −6.7. The TDM1 and TDM2 ages of these zircons range from 1.12 to 1.67 Ga and 1.68 to 2.57 Ga, respectively; the weighted mean TDM2 age is 2.08 Ga.

[29] In summary, the zircons from the western segment yielded negative εHf(t) values of −20.9 to −5.2. The TDM2 ages of these zircons range from 1.58 to 2.57 Ga, with a weighted mean of 1.90 Ga. The frequency of Paleoproterozoic TDM2 ages suggests that the magma source was dominated by Paleoproterozoic or older materials.

5.2 Plutons in the Eastern Segment

[30] Zircons from the Laocheng pluton have high initial 176Hf/177Hf ratios from 0.28255 to 0.28278 and εHf(t) values from −3.3 to 4.9 with one exception of −9.7 (Figure 5). Their TDM1 ages range from 0.68 to 0.99 Ga, and TDM2 ages from 0.94 to 1.47 Ga with a weighted mean of 1.25 Ga, which is significantly younger than those of the western South Qinling segment.

[31] Zircons from the Dongjiangkou pluton have initial 176Hf/177Hf ratios ranging from 0.28248 to 0.28266 and εHf(t) values from −5.4 to 0.7 with two outliers of −7.6 and −7.2. These zircons show TDM1 ages from 0.83 to 1.08 Ga and TDM2 ages from 1.21 to 1.60 Ga with a weighted mean of 1.45 Ga. The grains interpreted as inherited (spots DJK01-5, DJK01-10, and DJK01-19) have εHf(t) values of −9.0, 0.3 and −2.3 and TDM2 ages of 2.82, 1.64, and 1.55 Ga, respectively.

[32] Zircons from the Zhashui pluton have Hf-isotope compositions similar to those of the Laocheng pluton. Eleven analyses show εHf(t) values of −3.5 to 6.8 with two exceptions of −8.8 and −6.7. Their TDM1 ages range from 0.60 to 0.99 Ga and TDM2 ages from 0.82 to 1.47 Ga with a weighted mean of 1.22 Ga.

[33] In summary, zircons from the eastern segment show negative to positive εHf(t) values ranging from −5.4 to 6.8 with five outliers at −6.7, −7.2, −7.6, −8.8, and −9.7, and their TDM2 ages are from 0.82 to 1.60 Ga, which are distinct from those of the western segment.

6 Discussion

6.1 Heterogeneous Sources of the Western and Eastern Segments

[34] Zircons separated from the western South Qinling segment (i.e., Guangtoushan, Gaoqiaopu, and Xiba plutons) yield εHf(t) values in the range of −20.9 to −5.2 with an average of −10.3 and Paleoproterozoic two-stage Hf model ages of 1.58 to 2.57 Ga with a weighted mean of 1.90 Ga (Figure 5), implying that they were derived from a similar source region or have similar mixtures of crustal and mantle-derived melts. They also have whole-rock εNd (t) values ranging from −12.9 to −5.5 and two-stage Nd model ages from 1.46 to 2.08 Ga [Huang and Wu, 1990; Zhang et al., 2002a, 2007b; Tian et al., 2009; Liu et al., 2011]. In addition, one Paleoproterozoic inherited zircon (2096 ± 11 Ma) was found in sample GQP01 from this segment. Therefore, the studied granitoids from the western South Qinling segment were probably generated by partial melting of Paleoproterozoic or older lower crust materials.

[35] In contrast, the granitic rocks from the eastern part of the South Qinling (i.e., Laocheng, Dongjiangkou, and Zhashui plutons) yield zircon εHf(t) values from −5.4 to 6.8 with an average of −0.90 and two-stage Hf model ages ranging from 0.82 to 1.60 Ga with a weighted mean of 1.31 Ga, suggesting that these rocks were derived from a relatively juvenile lower crust. We interpret their source to be predominately Mesoproterozoic or older lower crust, which also is evidenced by their higher whole-rock εNd(t) values from −7.2 to −2.0 and younger two-stage Nd model ages from 1.17 to 1.60 Ga than those of the western part of the South Qinling [Huang and Wu, 1990; Zhu et al., 1998; Zhang et al., 2002a, 2007b; Wang et al., 2007, 2008; Jiang et al., 2010; Qin, 2010; Liu et al., 2011]. One Mesoproterozoic inherited age (1488 ± 9 Ma) in sample DJK01 from this segment supports that interpretation.

[36] The studied granitoids from the two segments of the South Qinling also have different whole-rock Sr and Pb isotopic compositions. The granitoids from the western segment show higher whole-rock initial 87Sr/86Sr ratios, from 0.7061 to 0.7091 [Zhang et al., 2007b; Liu et al., 2011] than those of the eastern segment, which have initial 87Sr/86Sr ratios from 0.7042 to 0.7064 [Huang and Wu, 1990; Zhu et al., 1998; Zhang et al., 2002a, 2007b; Jiang et al., 2010; Qin, 2010; Liu et al., 2011]. The former also have higher 206Pb/204Pb (17.942–18.270), 207Pb/204Pb (15.477–15.576), and 208Pb/204Pb (37.856–38.145) [Zhang et al., 1997a, 1997c, 2007b] than those of the eastern segment (206Pb/204Pb = 17.413–17.742, 207Pb/204Pb = 15.430–15.523, and 208Pb/204Pb = 37.019–37.795) [Zhang et al., 1997a, 2007b; Zhu et al., 1998; Qin et al., 2010]. Therefore, we argue that the granitoids were derived from source regions with strikingly different mean ages.

6.2 The Boundary Between the Western and Eastern Segments

[37] It is generally considered that the South Qinling consists of the western and eastern segments, based on four criteria. (1) Between 106°E and 108°E longitude, the South Qinling exposes shallow crust to the west but deeper crustal levels to the east [Zhang et al., 2001, 2002a]. (2) A series of Mesozoic-Cenozoic rifted-related basins is located to the west of the above zone [Zhang et al., 2001]. (3) East of 108°E, the South Qinling has a thin crust (32 km on average), a flat Moho, a positive gravity anomaly, and a positive seismic velocity anomaly relative to the reference value. In contrast, west of 108°E, the South Qinling has thicker crust (56 km on average) with a mountain root and displays a negative gravity anomaly and a negative seismic velocity anomaly [Zhang et al., 1995, 1996a]. (4) Between 105°E and 108°E longitude, the South Qinling mostly has negative to positive, E-W-trending magnetic anomalies to the west, and only positive magnetic anomalies with a NNE trend to the east [Yuan, 1996].

[38] However, the boundary between the segments has long been a matter of debate. Two end-member models have been proposed describing the nature of the South Qinling. Zhang et al. [2001, 2007a] suggested that the boundary is located around the Baoji-Chengdu railway (Line 1 in Figure 1b). Their evidence includes the following: (1) the nearly North-South striking Sichuan-Yunnan-Helan tectonic belt traverses the area, (2) there is a series of Mesozoic-Cenozoic rifted-related basins, and (3) the Triassic granitoids from the two segments have different whole-rock Sr-Nd-Pb isotopic compositions. However, Zhang et al. [2002a] proposed that the boundary lies roughly along the 108°E longitude (Line 2 in Figure 1b), based on (1) different crustal profiles on its western and eastern sides and (2) geophysical studies indicating that the South Qinling has a thin crust (32 km on average) to the east of the boundary and a thick crust (56 km on average) to the west [Zhang et al., 1996a].

[39] Zircons in granitoids from the western and eastern parts of the South Qinling have different Hf-isotope compositions. The western part has more negative zircon εHf(t) values (−20.9 to −5.2) and older TDM2 ages (1.58 to 2.57 Ga) than the eastern part (most zircon εHf(t) values = −6.0 to 6.8, most TDM2 ages = 0.82 to 1.64 Ga) (Figure 6). These data suggest that the lower crust of the western South Qinling segment is mainly Paleoproterozoic or older, whereas the lower crust of the eastern South Qinling segment is dominated by Mesoproterozoic or older materials.

Figure 6.

Histograms of εHf(t) values and two-stage Hf model ages of zircons from the Triassic granitoids in the western and eastern South Qinling segments. Other data sources: Gong et al. [2009a, 2009b], Jiang et al. [2010], and Qin [2010].

[40] The granitoids from the western and eastern South Qinling segments also have different whole-rock Sr-Nd-Pb isotopic components. The former have more negative εNd (t) values (most less than −6) and higher initial 87Sr/86Sr values (most greater than 0.7065) than those of the eastern South Qinling segment (Figure 7a). Similarly, the granitoids from the western South Qinling segment have more radiogenic Pb isotopic compositions than those from the eastern South Qinling segment (Figures 7b and 7c). Therefore, the western and eastern South Qinling segments may have had distinct basement compositions and belong to different terranes, and their boundary is roughly located between the Xiba and Wulong plutons (Line 3 in Figure 8), as represented by the Taibai-Chenggu line (Line 3 in Figure 1b).

Figure 7.

Plots of isotopic data for the Triassic granitoids in the western and eastern South Qinling segments: (a) εNd(210 Ma) versus (87Sr/86Sr)i, (b) initial 206Pb/204Pb versus initial 208Pb/204Pb, and (c) initial 206Pb/204Pb versus initial 207Pb/204Pb. Abbreviations as in Figure 1b. Data sources: western South Qinling segment, Huang and Wu [1990], Zhang et al. [1997a, 1997b, 1997c, 2002a, 2007a], Qin et al. [2009], Liu et al. [2011], and Zhu et al. [2011]; eastern South Qinling segment, Huang and Wu [1990], Zhang et al. [1996b, 1997b, 2002a, 2007b], Zhu et al. [1998], Wang et al. [2007, 2008], Tian et al. [2009], Jiang et al. [2010], Qin [2010], and Liu et al. [2011].

Figure 8.

A plot of zircon εHf(t) values versus the longitudes of the plutons from the western and eastern South Qinling segments. Abbreviations as in Figure 1b. Data sources: the gray symbols from Gong et al. [2009a, 2009b], Jiang et al. [2010], and Qin [2010]; the colored symbols are from this study.

6.3 Implications for the Crustal Structure and Evolution of South Qinling

[41] Based on regional geology, the western and eastern South Qinling segments have different shallow-crustal compositions [Zhang et al., 2001, 2002a]. Moreover, they have distinct deep-crustal compositions defined on the basis of radiogenic-isotope (i.e., Sr-Nd-Pb-Hf) studies. Finally, geophysical investigations suggest that they have different crustal structures and compositions on the larger scale [Zhang et al., 1995, 1996a, 2011; Yuan, 1996]. Therefore, the western and eastern South Qinling segments possibly show different tectonic affinity.

[42] The Qinling orogen resulted from the interaction of the North and South China blocks [Meng and Zhang, 2000; Zhang et al., 2001]; therefore, the tectonic affinity of the orogen is linked with these two blocks. It is commonly accepted that the eastern South Qinling segment rifted from the South China block during the late Paleozoic [Meng and Zhang, 1999, 2000]. However, the tectonic affinity of the western South Qinling segment remains controversial. Based on whole-rock Nd and Pb isotopic investigations, Zhang et al. [2007a] suggested that the western South Qinling segment had a basement composition similar to that of the South China block, whereas Zheng et al. [2010] proposed that the western segment originally separated from the North China block before the Mesoproterozoic-Neoproterozoic on the basis of zircon U-Pb ages and Hf-isotope studies. Our results indicate that the western and eastern South Qinling segments have distinct basement compositions and that the basement of the western South Qinling segment may have more affinity with the older North China block, rather than the younger South China block. Therefore, South Qinling was generated by the tectonic interaction between two terranes: the western South Qinling segment and the eastern South Qinling segment. Because the two segments display similar Sinian to Paleozoic stratigraphic and sedimentological history [Meng and Zhang, 2000; Zhang et al., 2001], we suggest that they might have been amalgamated toward the end of the Neoproterozoic.

6.4 Supplement for the Tectonic Evolution of the Qinling Orogen

[43] The Phanerozoic tectonic evolution of the Qinling Orogen has been studied extensively in the past decades [Mattauer et al., 1985; Enkin et al., 1992; Kröner et al., 1993; Gao et al., 1995; Lerch et al., 1995; Xue et al., 1996; Meng and Zhang, 1999, 2000; Zhang et al., 2001; Sun et al., 2002; Ratschbacher et al., 2003; Hacker et al., 2004; Wang et al., 2007; Dong et al., 2011; Wu and Zheng, 2012]. However, its tectonic evolution during the Proterozoic has rarely been investigated [Gao et al., 1996; Zhang et al., 2000; Lu et al., 2004; Dong et al., 2008]. Combined with the published literature, this study establishes the Proterozoic tectonic evolution of the Qinling orogen. We suggest that the western South Qinling segment separated from the North China block [Zheng et al., 2010] during the Paleoproterozoic and early Mesoproterozoic [Gao et al., 1996] and then switched into continental convergence with the eastern South Qinling segment (northern margin of the Yangtze block) during the late Mesoproterozoic to early Neoproterozoic [Gao et al., 1996]; finally, the two segments amalgamated during the late Neoproterozoic.

7 Conclusions

[44] The six granitoid plutons from the western and eastern South Qinling segments all formed during the Late Triassic (218–211 Ma). However, their source regions show remarkable differences: the western granitoids were mainly derived from Paleoproterozoic or older lower crust, whereas the eastern plutons represent melting predominantly of Mesoproterozoic mafic crust.

[45] The South Qinling can be divided into western and eastern segments, and the boundary may be located at the Taibai-Chengdu line. South Qinling resulted from the tectonic interaction between two smaller terranes: the western South Qinling segment and the eastern South Qinling segment.

[46] The western South Qinling segment separated from the North China block during the Paleoproterozoic and early Mesoproterozoic and then switched into continental convergence with the eastern South Qinling segment (northern margin of the Yangtze block) during the late Mesoproterozoic to early Neoproterozoic; finally, the two segments joined during the late Neoproterozoic.

Acknowledgments

[47] The authors would like to thank Todd Ehlers (editor), Paul Kapp (associate editor), and three anonymous reviewers for their constructive comments and suggestions. The work was supported by the NSFC (41130315 and 91214204), the 973 project (2012CB416604), and the Geologic inquisitional project (1212011120151). This is contribution 874 from the ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents (www.es.mq.edu.au/GEMOC) and 304 from the ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS).

Ancillary