Evidence from a Gabbro-Diorite Complex in the Gangdese Magmatic

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GEOSPHERE Identification of a new source for the Triassic Langjiexue Group: Evidence from a gabbro-diorite complex in the Gangdese magmatic

GEOSPHERE, v. 16, no. 1 belt and zircon microstructures from sandstones in the Tethyan https://doi.org/10.1130/GES02154.1 Himalaya, southern Tibet 16 figures; 1 set of supplemental files Xuxuan Ma1,2, Zhiqin Xu3, Zhongbao Zhao1, and Zhiyu Yi1 1 CORRESPONDENCE: [email protected] Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China 2Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA 3State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China CITATION: Ma, X.X., Xu, Z.Q., Zhao, Z.B., and Yi, Z.Y., 2020, Identification of a new source for the Triassic Langjiexue Group: Evidence from a gabbro-diorite complex in the Gangdese magmatic belt and zircon ABSTRACT began no later than the Middle Triassic. Arc-affin- During the past decades, progress has been microstructures from sandstones in the Tethyan Hima- laya, southern Tibet: Geosphere, v. 16, no. 1, p. 407– ity magmatic rocks supplied some materials to the achieved on understanding the formation of the 434, https://doi.org/10.1130/GES02154.1. Considerable debate persists as to the Triassic Langjiexue Group. This scenario sheds new light Himalayan-Tibetan orogen. However, many basic paleogeographic framework of the Neotethys and on the provenance of the Langjiexue Group and the questions remain open to debate. This study Science Editor: Shanaka de Silva the origin of the Late Triassic Langjiexue Group in Triassic paleogeography of the Neotethyan realm. focuses on the following issues: (1) the timing for Associate Editor: Christopher J. Spencer the Tethyan Himalaya. Triassic magmatic rocks in initial subduction of the Neotethyan oceanic lith- the Gangdese belt and Late Triassic Langjiexue sed- osphere; and (2) the tectonic setting of the Late Received 7 May 2019 Revision received 10 September 2019 iments play a pivotal role in addressing these issues. ■■ INTRODUCTION Triassic Langjiexue Group in the Tethyan Himalaya, Accepted 2 December 2019 Geochronological, petrological, and geochemical in other words, the provenance for the sediments analyses have been performed on the Middle Tri- An ongoing continent-continent collisional oro- of the Langjiexue Group. Published online 19 December 2019 assic gabbro-diorite complex (with crystallization gen, the Himalayan-Tibetan orogen, has attracted Recent studies have revealed that voluminous ages of ca. 244–238 Ma) from the Gangdese belt. much attention among the geological community calc-alkaline igneous rocks are exposed in the These plutonic rocks are characterized by relatively (Fig. 1; Yin and Harrison, 2000; Spencer et al., 2012). Gangdese magmatic belt, with ages ranging from

low MgO and high Al2O3 contents, calc-alkaline The Indo-Asian collision took place at ca. 60–50 Ma, Middle Triassic to Late Cretaceous (Ma et al., 2018a; trends, and depletion of Nb, Ta, and Ti, resem- triggering the uplift of the Tibetan Plateau (Ding et al., Wang et al., 2016a). The Middle Triassic to Jurassic bling low-MgO high-alumina basalts or basaltic 2016; Hu et al., 2015; Jin et al., 2018; Sun et al., 2016; magmatic rocks are ascribed to southward sub- andesites. These plutonic rocks exhibit depleted Zhu et al., 2015). However, the pre-plateau history of duction of the Bangong-Nujiang Tethyan oceanic

whole-rock εNd(t) values of ~+5 and zircon εHf(t) values the Lhasa terrane, especially the evolutionary history lithosphere beneath the Lhasa terrane (Zhu et al., peaking at ~+14. These features resemble those of of the Neotethyan Ocean, remains enigmatic (Li et al., 2013; Yang et al., 2017), or to the northward sub- rocks in a subduction-related arc setting. 2010; Zhu et al., 2010). The Gangdese magmatic belt, duction of the Neotethyan oceanic slab beneath the We also completed detrital zircon U-Pb dating located in the southern margin of the Lhasa terrane, Lhasa terrane (Guo et al., 2013b; Kang et al., 2014; and microstructure analysis for the sandstones of documents voluminous Middle Triassic to Late Cre- Ma et al., 2018a; Wang et al., 2016a). Whether the the Langjiexue Group in the Tethyan Himalaya. Zir- taceous subduction-related igneous activity (Ji et al., southward or northward model is correct, these con grains with ages >300 Ma are dominated by 2009; Meng et al., 2016a, 2019a; Mo et al., 2005a; results suggest that these magmatic rocks were preweathered and weathered surfaces as well as Wang et al., 2016a), indicating that the Gangdese generated in a convergent margin setting either fairly rounded to completely rounded scales, indi- magmatic belt experienced a protracted history prior as an active continental margin or intra-oceanic cating a high degree of polycyclicity. In contrast, to the Indo-Asian collision. Thus, study of the mag- arc. About 40% of the modern convergent margin 300–200 Ma ones are characterized by fresh sur- matic rocks in the Gangdese magmatic belt is very around the globe is interpreted as intra-oceanic faces and completely unrounded to poorly rounded important for deciphering the subduction-accretion subduction zones (Larter and Leat, 2003). This scales, indicating nearby sources. Collectively, our orogeny of the Gangdese magmatic belt and the raises the questions of whether an intra-oceanic This paper is published under the terms of the data, combined with published results, support framework of the Neotethyan realm before the final subduction system developed within the eastern CC‑BY-NC license. that the subduction initiation of the Neotethys collision and formation of the Tibetan Plateau. Neotethyan realm, and whether some intra-oceanic

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N 75°E 80°E 85°E 90°E 95°E 100°E 105°E LGR: Longgar rift ATF: Altyn Tagh fault Normal fault NTR: Nyima-Tingri rift HYF: Haiyuan fault Strike-slip fault XDR: Xainza-Dingjye rift JLF: Jiali fault Thrust fault elt YGR: Yadong-Gulu rift KF: Karakoram fault Suture zone enic b LST: Longmen Shan thrust rog MBT: Main Boundary thrust Eclogite zone sian o BNS: Bangong-Nujiang suture ral A XSF: Xianshuihe fault Cent AKS: Anymaqen-Kunlun suture IYS: Indus–Yarlung Tsangpo suture 40°N North China JSS: Jinsha suture LS: Longmu Co–Shuanghu suture SQS: South Qilian suture North Pamir Tarim block block SS: Shyok suture Central Pamir Qilian terrane TS: Tanymas suture Q K F im Qa South Pamir AT an T ida HY F K agh m b SQ F m te unl as S a rr un t in S or an erra T ak e AKS ne ar Kohistan K Songpan-Gan ze ﬂysch complex 35°N SS Ladakh North Qiangtang J H B So SS i S NS uth Q m hi iangt a qu ang l an Gaize Shuanghu Amdo LS ay he a X T n f SF S o L ld Lhasa terrane -t IY Sumdo 30°N hr S JLF us R t b G L Linzhi

e R Xigaze Lhasa

lt T R R

N G India M D B Y South China T X block 0 500 km Figure 2

Figure 1. Tectonic map of the Tibetan Plateau showing the study location (modified after Kapp and Guynn [2004] and Yin and Harrison [2000]).

arc rocks are preserved in the Gangdese mag- configuration for the eastern Neotethyan realm, as the eastern Neotethyan realm, especially the Cim- matic belt. well as the possible source for the Langjiexue Group. meride and the northern Gondwana landmasses. The Late Triassic Langjiexue Group, exposed in The foregoing issues are closely related to the In this study, we discuss new results from the the Tethyan Himalaya belt, plays a pivotal role in opening of the Neotethyan Ocean. Based on the ca. 240 Ma gabbro-diorite complex in the Gang- reconstructing the framework of the Neotethyan paleogeographic reconstruction of the Pangea dese magmatic belt and microstructures of detrital realm. However, its tectonic affinity has been hotly supercontinent and the Neotethyan realm, the Neo- zircon grains of sandstones from the Late Triassic debated for decades. Models proposed to explain tethys has been suggested to have opened in the Langjiexue Group in the Tethyan Himalaya. Based the formation of the Langjiexue Group include basin- early Permian (Angiolini et al., 2003; Garzanti et al., on our combined analyses of regional geology, we fill during the initial rifting between the Indian and 1996; Kroner et al., 2016). However, as remnants propose the existence of another possible source Lhasa blocks (Dai et al., 2008; Webb et al., 2012), of the Neotethyan oceanic lithosphere, the Indus– in the Gangdese magmatic belt, which partly pro- forearc basin deposition due to the northward Yarlung Tsangpo ophiolites, whose formation is vided some source materials for the Langjiexue subduction of the Neotethyan oceanic lithosphere attributed to forearc extension, mainly fall into an sandstones. beneath the Lhasa terrane or an intra-oceanic arc age range of 130–120 Ma (Wu et al., 2014; Liu et al., (Li et al., 2010), passive continental margin deposi- 2016; Maffione et al., 2015; Xiong et al., 2017). Fur- tion along the northern or northwestern margin of thermore, the opening of the Neotethys has been ■■ GEOLOGICAL SETTING the Gondwana landmass (Cai et al., 2016; Cao et al., proposed to have been a byproduct of the south- 2018; Fang et al., 2018; Wang et al., 2016b; Meng et al., ward subduction of the Bangong-Nujiang Tethys Tectonic Framework 2019b), and a multi-source model within the Neo- during the Late Triassic (Zhu et al., 2013; Yang et al., tethys (Li et al., 2016; Zhang et al., 2017). Thus this 2017). These debates necessitate more work to con- The Tibetan Plateau was formed through the question has been hindering our full understanding strain the opening of the Neotethys. This dispute sequential accretion of terranes to the southern of the reconstruction of the Triassic paleogeographic hampers our recognition of the tectonic regime for margin of the Asian continent (Yin and Harrison,

2000). From north to south, these terranes include east-west–trending Gangdese magmatic belt, Lee et al., 2009b). The post-collisional (30–13 Ma) the Songpan-Ganze, Qiangtang, Lhasa, and Tethyan 2500 km in length and ~100 km in width, is located igneous rocks within the Gangdese magmatic belt Himalayan terranes separated by the Jinsha, Ban- immediately north of the Indus–Yarlung Tsangpo consist of S-type granites, adakites, basaltic dikes, gong-Nujiang, and Indus–Yarlung Tsangpo suture suture zone (Fig. 2; Yin and Harrison, 2000). Dia- and ultrapotassic to potassic volcanics (Chung et al., zones (Fig. 1; Zhang et al., 2014; Leary et al., 2016). basic gabbros, diorites, and granitoids, as well as 2005). Post-collisional porphyry-type Cu deposits Among these accreted terranes, the Lhasa terrane their eruptive equivalents, are tightly dispersed have been identified in the Gangdese magmatic belt is considered to have been the last block to aggre- within the Gangdese magmatic belt. Temporally, (Hou et al., 2015; Lu et al., 2015; Yang et al., 2016). gate with the Asian continent before the Indo-Asian the igneous rocks across the whole belt span a large collision (Yin and Harrison, 2000; Tapponnier et al., age range from 237 to 13 Ma (Ji et al., 2009; Wang 2001). Recent studies suggest that the Lhasa terrane et al., 2018; Meng et al., 2019a). These voluminous Tethyan Himalaya is not intact, and several suture zones are proposed magmatic rocks belong to four major flareups at within the Lhasa terrane, such as the Shiquanhe– 237–160 Ma, 100–80 Ma, 65–40 Ma, and 30–13 Ma. South of the Indus–Yarlung Tsangpo suture Yunzhug–Namu Tso and Sumdo ophiolite belts (Pan The first flareup has been suggested to have sub- zone, the Himalayan orogen is composed of, et al., 2012; Yang et al., 2007; Zeng et al., 2018). duction-related calc-alkaline affinity, owing to the from south to north, the Lesser Himalaya, Greater The Lhasa terrane is separated from the Tethyan subduction of the Neotethyan oceanic lithosphere Himalaya, and Tethyan Himalaya (Yin, 2006; Guil- Himalayan terrane by the Indus–Yarlung Tsangpo (Lang et al., 2017; Meng et al., 2016a). Two different lot et al., 2008; Xu et al., 2013; Leary et al., 2017). ophiolite belt, whose formation ages cluster around models have been proposed for the 100–80 Ma mag- The Greater Himalayan rocks are considered to be 130–120 Ma (Liu et al., 2016; Xiong et al., 2017). matic flareup: one is ridge subduction (Guo et al., Indian basement that has been exhumed along 2013a; Zhang et al., 2010), and the other is extension the Main Central thrust (DeCelles et al., 2000). The due to slab rollback (Ma et al., 2015). The 65–40 Ma Tethyan Himalaya is separated from the Greater Gangdese Magmatic Belt magmatic flareup, represented by the Linzizong vol- Himalaya to the south by the Southern Tibet canic rocks and Quxu batholith, resulted from slab detachment system (Yin and Harrison, 2000). The The Gangdese magmatic belt occupies the rollback and breakoff associated with the Indo-Asian Tethyan Himalaya comprises southern and north- southern margin of the Lhasa terrane. The collision (Ding et al., 2003; Mo et al., 2003, 2005b; ern subzones, divided by the Gyirong-Kangmar

88°E 90°E 92°E 94°E 30° Gongbujiangda 220 Ma appinite Sumdo N (Ma et al., 2018b) 229 Ma granite 240 Ma gabbro- 226 Ma diorite (Meng et al., 2018) diorite (this study) 245 Ma andesite (Ji W.Q., personal (Wang et al., 2018) Nanmulin commun.) ca. 230 Ma volcanics Lhasa (Wang et al., 2016a) Dazhuqu Nymo Quxu Zedong Xigaze D2

Liuqu Langxian Bainang D1 Qusong 29° Renbu Qiongjie N Yardoi Jiangzi N Figure 3A Greater 0 100 km Yumen mélange Himalaya Kangma zone

Lake Quaternary Batholith Gabbro- Ophiolite Mélange Dazhuqu Xigaze Jurassic- Late Triassic Triassic Jurassic or Gangdese Greater Sampling N-vergent E- or SE-vergent diorite conglomerate forearc Cretaceous Langjiexue Gr. Changguo Cretaceous basement Himalaya location fold (D1) fold (D2) basin sediments volcanics Bima Fm.

Figure 2. Simplified map of the Gangdese magmatic belt and the Tethyan Himalaya showing the sampling location.

thrust. The Mesozoic–Cenozoic strata in the Tethyan by the Kerguelen plume in the Indian plate due to were obtained at the Key Laboratory of Mineral Himalaya can be divided into the Langjiexue Group the rifting of the Gondwana landmass (Zhu et al., Resources Evaluation in Northeast Asia, Ministry (Upper Triassic) and Lure (Lower Jurassic), Zhela 2009). Recently, Ao et al. (2018) proposed that these of Land and Resources of China, Jilin University (mid-Jurassic), Sangxiu (Upper Jurassic), Lakang dikes were probably formed in the Neotethyan (Changchun, China). The instrument coupled a (Lower Cretaceous), and Zongzhuo (Upper Creta- Ocean and hosted in the Langjiexue Group strata quadrupole ICP-MS (Agilent 7900) and 193 nm ArF ceous) formations (Ao et al., 2018). The southern during accretion in the Tethyan Himalayan prism. excimer laser (COMPexPro 102, Coherent) with zone is characterized by shallow-water carbonates an automatic positioning system. For the pres- and clastic sediments, whereas the northern zone ent work, laser spot size was set to 32 μm, laser is dominated by deep-water turbidites, shales, and ■■ ANALYTICAL METHOD energy density at 10 J/cm2, and repetition rate at cherts (Wang et al., 2016b). In the northern zone, the 8 Hz. Laser sampling used a 30 s blank, 30 s sam- Late Triassic Langjiexue Group sediments dominate Geochronology pling ablation, and 2 min sample-chamber flushing and occupy a huge area (Fig. 2). after the ablation. The ablated material was carried The Langjiexue Group was tectonically dis- Zircon U-Pb ages presented in this paper were into the ICP-MS by a high-purity helium gas stream placed to the south of the eastern Indus–Yarlung obtained in two laboratories. Zircon U-Pb ages of with a flux of 1.15 L/min. The whole laser path was Tsangpo suture zone (Fig. 2). It was thrust to the the gabbro-diorite complex were measured by fluxed with Ar (600 mL/min) in order to increase south over the Nieru Formation and Jurassic–Cre- using an Agilent 7500a inductively coupled plasma energy stability. The counting time was 20 ms for taceous strata of Tethyan Himalaya along the nearly mass spectrometer (ICP-MS) attached to a Coher- 204Pb, 206Pb, 207Pb, and 208Pb; 15 ms for 232Th and east-west–trending Lazi-Qiongduojiang-Zara thrust ent 193 nm laser ablation system at the State Key 238U; 20 ms for 49Ti; and 6 ms for other elements. and was thrust northward over the Indus–Yarlung Laboratory for Mineral Deposits Research, Nanjing Calibrations for the zircon analyses were carried Tsangpo ophiolites along the east-west–trending University (Nanjing, China). The laser light beam out using NIST 610 glass as an external standard Greater Counter thrust in the north (Fang et al., had a diameter of ~32 μm with a repetition rate and Si as an internal standard. U-Pb isotope frac- 2018; Yin, 2006). This group is mainly composed of 5 Hz under a 70% energy condition. Isotope tionation effects were corrected using zircon 91500 of feldspar and/or lithic sandstone, siltstone, slate, mass fractionation was normalized through exter- (Wiedenbeck et al., 1995) as an external standard. and shale, deposited in a bathyal-abyssal sub- nal standard GEMOC GJ-1 with 207Pb/206Pb age = Zircon standard Plesovice (337 Ma) was also used marine fan environment (Zhang et al., 2015a). 608.5 ± 1.5 Ma (Jackson et al., 2004). The analyti- as a secondary standard to supervise the devia- The Langjiexue Group was subjected to intense cal accuracy was monitored through the Mud Tank tion of age measurement (Sláma et al., 2008). The deformation, characterized by the south-north zircon standard, which has an intercept age of 732 analytical results of detrital zircon U-Pb ages are convergence resulting in southward and north- ± 5 Ma (Black and Gulson, 1978). Zircon analyses presented in Table S2 (footnote 1), whereas the ward thrusts and east-west–trending axial planes were carried out in runs of 15 analyses including trace elemental results of magmatic zircon grains of folds (Fig. 3B; Li et al., 2010). Although strongly five zircon standards and up to 10 sample spots. from the plutonic rocks in the Gangdese belt and deformed, the Langjiexue Group only experienced The U-Pb dating results were calculated through the the detrital zircon grains from the sandstones of low- to medium-grade greenschist facies metamor- online software package GLITTER (ver. 4.4; http:// the Langjiexue Group in the Tethyan Himalaya are

Table S1. Zircon U-Pb dating results of the gabbro-diorite complex in the Gangdese magmatic belt, southern Tibet, China MEASURED RATIOS UNCORRECTED AGES (Ma) COMMON LEAD Concordance limit (ns) CORRECTED RATIOS CORRECTED AGES (Ma) Calculated concentration (ppm) Observed Correction Concordance Analysis 207 206 207 235 206 238 208 232 238 232 Assumed 207 206 207 235 206 238 208 232 Comment 206 Discordance 207 206 207 235 206 238 208 232 rr 238 232 207 206 207 235 206 238 208 232 Th U Th/U Pb/ Pb Pb/ U Pb/ U Pb/ Th U/ Th discordance Pb/ Pb Pb/ U Pb/ U Pb/ Th type % common Pb Pb/ Pb Pb/ U Pb/ U Pb/ Th U/ Th Pb/ Pb Pb/ U Pb/ U Pb/ Th (100%) 1s 1s 1s 1s 1s rt Central Min. rim 1s 1s 1s 1s 1s Central Min. rim 1s 1s 1s 1s 1s 1s 1s 1s stdgj01 0.05995 0.00079 0.80071 0.01278 0.09688 0.00136 0.02925 0.00189 80.53841 0.13797 0.9 -1 . 602 15 597 7 596 8 583 37 None Concordant . . -1 . 0.05995 0.00079 0.80071 0.01278 0.09688 0.00136 0.02925 0.00189 0.9 80.54 0.14 602 15 597 7 596 8 583 37 7.5 311.4 0.0 100.2 stdgj02 0.06045 0.0008 0.81851 0.01319 0.09821 0.0014 0.03301 0.00194 80.00618 0.13532 0.9 -2.7 . 620 16 607 7 604 8 656 38 None Concordant . . -2.7 . 0.06045 0.0008 0.81851 0.01319 0.09821 0.0014 0.03301 0.00194 0.9 80.01 0.14 620 16 607 7 604 8 656 38 7.7 319.4 0.0 100.5 phism (Li et al., 2016). www.glitter -gemoc.com/). Zircon U and Th concen- presented in Table S3 (footnote 1). mt01 0.06507 0.00128 1.08327 0.02289 0.12075 0.0018 0.03668 0.00147 1.80506 0.00783 0.9 -5.7 -0.3 777 22 745 11 735 10 728 29 None Common Pb < det. lim. -0.06 . -5.7 -0.3 0.06507 0.00128 1.08327 0.02289 0.12075 0.0018 0.03668 0.00147 0.9 1.81 0.01 777 22 745 11 735 10 728 29 52.1 48.5 1.1 101.4 xm82-01 0.0531 0.00112 0.27714 0.00631 0.03785 0.00059 0.01112 0.00051 0.84716 0.00144 0.9 -28.6 -15.7 333 26 248 5 239 4 224 10 None Common Pb < det. lim. -1.01 . -28.6 -15.7 0.0531 0.00112 0.27714 0.00631 0.03785 0.00059 0.01112 0.00051 0.9 0.85 0.01 333 26 248 5 239 4 224 10 725.5 317.2 2.3 103.8 xm82-02 0.05079 0.00129 0.27109 0.00696 0.03871 0.00057 0.01248 0.00072 1.03654 0.00224 0.9 6 . 231 33 244 6 245 4 251 14 None Concordant . . 6 . 0.05079 0.00129 0.27109 0.00696 0.03871 0.00057 0.01248 0.00072 0.9 1.04 0.01 231 33 244 6 245 4 251 14 364.6 195.0 1.9 99.6 xm82-03 0.05101 0.00086 0.27454 0.00516 0.03903 0.00056 0.01225 0.00051 1.48385 0.00231 0.9 2.4 . 241 20 246 4 247 3 246 10 None Concordant . . 2.4 . 0.05101 0.00086 0.27454 0.00516 0.03903 0.00056 0.01225 0.00051 0.9 1.48 0.01 241 20 246 4 247 3 246 10 492.1 376.8 1.3 99.6 xm82-04 0.05295 0.00129 0.27709 0.0069 0.03795 0.00056 0.01156 0.00056 1.03941 0.00264 0.9 -27 -8.3 327 31 248 5 240 3 232 11 None Common Pb < det. lim. -0.37 . -27 -8.3 0.05295 0.00129 0.27709 0.0069 0.03795 0.00056 0.01156 0.00056 0.9 1.04 0.01 327 31 248 5 240 3 232 11 264.0 141.6 1.9 103.3 xm82-05 0.05035 0.00077 0.26662 0.00465 0.03839 0.00054 0.01107 0.00044 1.46767 0.00215 0.9 15.3 . 211 18 240 4 243 3 223 9 None Common Pb < det. lim. -0.83 . 15.3 . 0.05035 0.00077 0.26662 0.00465 0.03839 0.00054 0.01107 0.00044 0.9 1.47 0.01 211 18 240 4 243 3 223 9 563.0 426.4 1.3 98.8 xm82-06 0.05161 0.00109 0.27661 0.00615 0.03887 0.00057 0.01185 0.00052 1.22702 0.0029 0.9 -8.5 . 268 26 248 5 246 4 238 10 None Concordant . . -8.5 . 0.05161 0.00109 0.27661 0.00615 0.03887 0.00057 0.01185 0.00052 0.9 1.23 0.01 268 26 248 5 246 4 238 10 258.0 163.4 1.6 100.8 xm82-07 0.05174 0.00106 0.27519 0.00598 0.03857 0.00056 0.01148 0.00051 1.19447 0.00279 0.9 -11.1 . 274 25 247 5 244 3 231 10 None Concordant . . -11.1 . 0.05174 0.00106 0.27519 0.00598 0.03857 0.00056 0.01148 0.00051 0.9 1.19 0.01 274 25 247 5 244 3 231 10 270.9 167.0 1.6 101.2 xm82-08 0.0528 0.001 0.28516 0.00578 0.03916 0.00056 0.0114 0.00049 1.04494 0.00225 0.9 -23.1 -11.1 320 22 255 5 248 3 229 10 None Common Pb < det. lim. -0.95 . -23.1 -11.1 0.0528 0.001 0.28516 0.00578 0.03916 0.00056 0.0114 0.00049 0.9 1.04 0.01 320 22 255 5 248 3 229 10 366.6 197.6 1.9 102.8 xm82-09 0.05288 0.00128 0.30417 0.00769 0.04171 0.00066 0.01121 0.0007 1.44029 0.00237 0.9 -19 -0.6 324 30 270 6 263 4 225 14 None Common Pb < det. lim. -1.42 . -19 -0.6 0.05288 0.00128 0.30417 0.00769 0.04171 0.00066 0.01121 0.0007 0.9 1.44 0.01 324 30 270 6 263 4 225 14 455.5 338.5 1.3 102.7 xm82-10 0.05189 0.00111 0.28018 0.00624 0.03915 0.00057 0.01175 0.00062 1.08907 0.00223 0.9 -12 . 281 26 251 5 248 4 236 12 None Concordant . . -12 . 0.05189 0.00111 0.28018 0.00624 0.03915 0.00057 0.01175 0.00062 0.9 1.09 0.01 281 26 251 5 248 4 236 12 388.8 218.5 1.8 101.2 xm82-11 0.05049 0.00148 0.26947 0.00802 0.0387 0.00063 0.01075 0.0007 1.35063 0.00279 0.9 12.7 . 218 40 242 6 245 4 216 14 None Concordant . . 12.7 . 0.05049 0.00148 0.26947 0.00802 0.0387 0.00063 0.01075 0.0007 0.9 1.35 0.01 218 40 242 6 245 4 216 14 308.0 214.7 1.4 98.8 xm82-12 0.0518 0.00109 0.27392 0.00605 0.03835 0.00056 0.01113 0.00058 1.02346 0.00213 0.9 -12.5 . 277 26 246 5 243 3 224 12 None Concordant . . -12.5 . 0.0518 0.00109 0.27392 0.00605 0.03835 0.00056 0.01113 0.00058 0.9 1.02 0.01 277 26 246 5 243 3 224 12 400.3 211.4 1.9 101.2 xm82-13 0.05385 0.00119 0.28644 0.00657 0.03858 0.00055 0.01185 0.00061 1.08562 0.00279 0.9 -33.7 -21.4 365 27 256 5 244 3 238 12 None Common Pb < det. lim. -0.23 . -33.7 -21.4 0.05385 0.00119 0.28644 0.00657 0.03858 0.00055 0.01185 0.00061 0.9 1.09 0.01 365 27 256 5 244 3 238 12 246.8 138.2 1.8 104.9 xm82-14 0.05358 0.00101 0.28439 0.00557 0.03849 0.00052 0.01221 0.00075 0.71332 0.00125 0.9 -31.7 -22.4 353 22 254 4 243 3 245 15 None Common Pb < det. lim. 0.24 . -31.7 -22.4 0.05358 0.00101 0.28439 0.00557 0.03849 0.00052 0.01221 0.00075 0.9 0.71 0.01 353 22 254 4 243 3 245 15 810.9 298.5 2.7 104.5 xm82-15 0.05274 0.00168 0.2757 0.00875 0.03792 0.00064 0.00938 0.00074 1.31257 0.00258 0.9 -24.9 . 318 42 247 7 240 4 189 15 None Concordant . . -24.9 . 0.05274 0.00168 0.2757 0.00875 0.03792 0.00064 0.00938 0.00074 0.9 1.31 0.01 318 42 247 7 240 4 189 15 348.2 235.8 1.5 102.9 stdgj03 0.0602 0.00107 0.80717 0.01539 0.09726 0.0014 0.03225 0.0025 79.65983 0.13047 0.9 -2.1 . 611 19 601 9 598 8 642 49 None Concordant . . -2.1 . 0.0602 0.00107 0.80717 0.01539 0.09726 0.0014 0.03225 0.0025 0.9 79.66 0.13 611 19 601 9 598 8 642 49 8.3 340.7 0.0 100.5 Traditionally, the Langjiexue Group consists of trations were calculated by comparing the relative For all analyses, isotopic ratios and element stdgj04 0.06003 0.00113 0.81172 0.01622 0.09809 0.00143 0.02977 0.00249 79.63862 0.12894 0.9 -0.3 . 605 21 603 9 603 8 593 49 None Concordant . . -0.3 . 0.06003 0.00113 0.81172 0.01622 0.09809 0.00143 0.02977 0.00249 0.9 79.64 0.13 605 21 603 9 603 8 593 49 8.5 348.6 0.0 100.0 GPS 29°19 21.04 N 89°53 00.05 E

stdgj07 0.06009 0.00085 0.80789 0.01268 0.09752 0.00124 0.02888 0.00209 78.04461 0.14482 0.9 -1.2 . 607 15 601 7 600 7 575 41 None Concordant . . -1.2 . 0.06009 0.00085 0.80789 0.01268 0.09752 0.00124 0.02888 0.00209 0.9 78.04 0.14 607 15 601 7 600 7 575 41 8.8 363.8 0.0 100.2 stdgj08 0.06012 0.00086 0.81032 0.01275 0.09777 0.00125 0.03266 0.00219 75.76232 0.14208 0.9 -1.1 . 608 15 603 7 601 7 650 43 None Concordant . . -1.1 . 0.06012 0.00086 0.81032 0.01275 0.09777 0.00125 0.03266 0.00219 0.9 75.76 0.14 608 15 603 7 601 7 650 43 8.9 356.2 0.0 100.3 mt04 0.06385 0.00132 1.03338 0.02194 0.11738 0.00161 0.03556 0.00157 1.69213 0.0076 0.9 -3 . 737 23 721 11 715 9 706 31 None Concordant . . -3 . 0.06385 0.00132 1.03338 0.02194 0.11738 0.00161 0.03556 0.00157 0.9 1.69 0.01 737 23 721 11 715 9 706 31 69.2 62.2 1.1 100.8 xm84-01 0.05115 0.00092 0.27109 0.00519 0.03844 0.00051 0.01071 0.0004 1.48308 0.00298 0.9 -1.8 . 248 22 244 4 243 3 215 8 None Concordant . . -1.8 . 0.05115 0.00092 0.27109 0.00519 0.03844 0.00051 0.01071 0.0004 0.9 1.48 0.01 248 22 244 4 243 3 215 8 394.0 310.1 1.3 100.4 xm84-02 0.05108 0.00139 0.2685 0.00743 0.03813 0.00058 0.01096 0.00058 1.36763 0.0029 0.9 -1.4 . 244 36 241 6 241 4 220 12 None Concordant . . -1.4 . 0.05108 0.00139 0.2685 0.00743 0.03813 0.00058 0.01096 0.00058 0.9 1.37 0.01 244 36 241 6 241 4 220 12 384.8 279.3 1.4 100.0 xm84-03 0.05081 0.00124 0.26787 0.00674 0.03824 0.00057 0.011 0.00061 1.41101 0.00246 0.9 4.2 . 232 32 241 5 242 4 221 12 None Concordant . . 4.2 . 0.05081 0.00124 0.26787 0.00674 0.03824 0.00057 0.011 0.00061 0.9 1.41 0.01 232 32 241 5 242 4 221 12 549.2 411.2 1.3 99.6 xm84-04 0.05135 0.00081 0.27018 0.00464 0.03817 0.0005 0.01126 0.00046 0.91267 0.00138 0.9 -6 . 257 18 243 4 241 3 226 9 None Concordant . . -6 . 0.05135 0.00081 0.27018 0.00464 0.03817 0.0005 0.01126 0.00046 0.9 0.91 0.01 257 18 243 4 241 3 226 9 1138.6 551.4 2.1 100.8 xm84-05 0.05207 0.00106 0.27209 0.00566 0.0379 0.0005 0.01214 0.00069 2.22855 0.00419 0.9 -17.2 -0.2 288 25 244 5 240 3 244 14 None Common Pb < det. lim. 0.13 . -17.2 -0.2 0.05207 0.00106 0.27209 0.00566 0.0379 0.0005 0.01214 0.00069 0.9 2.23 0.01 288 25 244 5 240 3 244 14 299.4 354.0 0.8 101.7 xm84-06 0.05252 0.00192 0.27692 0.00998 0.03824 0.00066 0.01174 0.00099 1.63738 0.00344 0.9 -21.9 . 308 51 248 8 242 4 236 20 None Concordant . . -21.9 . 0.05252 0.00192 0.27692 0.00998 0.03824 0.00066 0.01174 0.00099 0.9 1.64 0.01 308 51 248 8 242 4 236 20 326.4 283.6 1.2 102.5 xm84-07 0.05103 0.00114 0.26982 0.00631 0.03835 0.00056 0.01097 0.00069 0.98976 0.00144 0.9 0.2 . 242 28 243 5 243 3 221 14 None Concordant . . 0.2 . 0.05103 0.00114 0.26982 0.00631 0.03835 0.00056 0.01097 0.00069 0.9 0.99 0.01 242 28 243 5 243 3 221 14 1119.6 588.0 1.9 100.0 xm84-08 0.05204 0.001 0.27413 0.00555 0.03821 0.00052 0.01121 0.00054 1.21146 0.00252 0.9 -16.1 -0.5 287 23 246 4 242 3 225 11 None Common Pb < det. lim. -0.76 . -16.1 -0.5 0.05204 0.001 0.27413 0.00555 0.03821 0.00052 0.01121 0.00054 0.9 1.21 0.01 287 23 246 4 242 3 225 11 452.1 290.7 1.6 101.7 xm84-09 0.05073 0.00175 0.267 0.00913 0.03817 0.00063 0.01174 0.00108 1.15321 0.00226 0.9 5.8 . 229 49 240 7 241 4 236 22 None Concordant . . 5.8 . 0.05073 0.00175 0.267 0.00913 0.03817 0.00063 0.01174 0.00108 0.9 1.15 0.01 229 49 240 7 241 4 236 22 533.6 326.5 1.6 99.6 xm84-10 0.05103 0.00109 0.26858 0.00581 0.03818 0.00051 0.01221 0.00087 0.97011 0.00168 0.9 -0.3 . 242 26 242 5 242 3 245 17 None Concordant . . -0.3 . 0.05103 0.00109 0.26858 0.00581 0.03818 0.00051 0.01221 0.00087 0.9 0.97 0.01 242 26 242 5 242 3 245 17 813.2 418.6 1.9 100.0 xm84-11 0.05235 0.00136 0.27823 0.00724 0.03855 0.00056 0.01148 0.00097 0.81484 0.0013 0.9 -19.3 . 301 34 249 6 244 3 231 19 None Concordant . . -19.3 . 0.05235 0.00136 0.27823 0.00724 0.03855 0.00056 0.01148 0.00097 0.9 0.81 0.01 301 34 249 6 244 3 231 19 1135.1 490.8 2.3 102.0 the Jiangxiong, Jiedexiu, Zhangcun, and Songre signal intensity between the standard zircon GJ-1 concentrations of zircon grains were calculated xm84-12 0.05071 0.00131 0.26766 0.00688 0.03829 0.00054 0.01319 0.00109 1.14982 0.00238 0.9 6.5 . 228 34 241 6 242 3 265 22 None Concordant . . 6.5 . 0.05071 0.00131 0.26766 0.00688 0.03829 0.00054 0.01319 0.00109 0.9 1.15 0.01 228 34 241 6 242 3 265 22 477.5 291.4 1.6 99.6 xm84-13 0.05136 0.00135 0.26955 0.00718 0.03807 0.00056 0.01144 0.00086 1.13103 0.00223 0.9 -6.4 . 257 35 242 6 241 3 230 17 None Concordant . . -6.4 . 0.05136 0.00135 0.26955 0.00718 0.03807 0.00056 0.01144 0.00086 0.9 1.13 0.01 257 35 242 6 241 3 230 17 536.2 321.8 1.7 100.4 xm84-14 0.05272 0.00117 0.28472 0.00649 0.03917 0.00055 0.01216 0.00072 1.38822 0.00374 0.9 -22.2 -4.5 317 28 254 5 248 3 244 14 None Common Pb < det. lim. -0.1 . -22.2 -4.5 0.05272 0.00117 0.28472 0.00649 0.03917 0.00055 0.01216 0.00072 0.9 1.39 0.01 317 28 254 5 248 3 244 14 234.5 172.7 1.4 102.4 xm84-15 0.05205 0.00108 0.27235 0.00585 0.03795 0.00052 0.01145 0.00072 1.14105 0.00247 0.9 -16.8 . 288 26 245 5 240 3 230 14 None Concordant . . -16.8 . 0.05205 0.00108 0.27235 0.00585 0.03795 0.00052 0.01145 0.00072 0.9 1.14 0.01 288 26 245 5 240 3 230 14 441.7 267.4 1.7 102.1 stdgj09 0.06056 0.00106 0.80927 0.01494 0.09693 0.00127 0.03169 0.00288 77.98914 0.16017 0.9 -4.6 . 624 19 602 8 596 7 631 56 None Concordant . . -4.6 . 0.06056 0.00106 0.80927 0.01494 0.09693 0.00127 0.03169 0.00288 0.9 77.99 0.16 624 19 602 8 596 7 631 56 7.2 297.0 0.0 101.0 stdgj10 0.05975 0.00104 0.80886 0.01489 0.0982 0.0013 0.02976 0.00272 79.53092 0.16175 0.9 1.6 . 595 19 602 8 604 8 593 53 None Concordant . . 1.6 . 0.05975 0.00104 0.80886 0.01489 0.0982 0.0013 0.02976 0.00272 0.9 79.53 0.16 595 19 602 8 604 8 593 53 7.2 302.9 0.0 99.7 GPS 29°19 19.55 N 89°52 54.63 E

stdgj03 0.06049 0.00084 0.81227 0.01279 0.0974 0.00128 0.03166 0.00185 79.56472 0.14211 0.9 -3.7 . 621 15 604 7 599 8 630 36 None Concordant . . -3.7 . 0.06049 0.00084 0.81227 0.01279 0.0974 0.00128 0.03166 0.00185 0.9 79.56 0.14 621 15 604 7 599 8 630 36 7.7 327.8 0.0 100.8 stdgj04 0.05976 0.00083 0.80653 0.01269 0.0979 0.00128 0.0298 0.00187 78.59283 0.13986 0.9 1.2 . 595 15 601 7 602 8 594 37 None Concordant . . 1.2 . 0.05976 0.00083 0.80653 0.01269 0.0979 0.00128 0.0298 0.00187 0.9 78.59 0.14 595 15 601 7 602 8 594 37 7.9 330.2 0.0 99.8 mt02 0.09092 0.0016 1.50064 0.02806 0.11972 0.00169 0.04449 0.00159 1.86835 0.00829 0.9 -52.4 -50.9 1445 17 931 11 729 10 880 31 Disc OK 1.99 0.34 -36.3 -23.6 0.07578 0.00371 1.22605 0.05716 0.11734 0.00177 0.03529 0.00048 0.74 1.87 0.01 1089 101 813 26 715 10 701 9 53.2 53.1 1.0 113.7 xm85-01 0.053 0.00119 0.27782 0.00653 0.03802 0.00057 0.01027 0.00045 1.1122 0.00203 0.9 -27.3 -11.7 329 28 249 5 241 4 207 9 None Common Pb < det. lim. -1.76 . -27.3 -11.7 0.053 0.00119 0.27782 0.00653 0.03802 0.00057 0.01027 0.00045 0.9 1.11 0.01 329 28 249 5 241 4 207 9 527.1 313.0 1.7 103.3 xm85-02 0.05481 0.0015 0.29499 0.00823 0.03904 0.00062 0.01059 0.00051 2.03366 0.00477 0.9 -39.7 -25.8 404 35 262 6 247 4 213 10 None Common Pb < det. lim. -0.93 . -39.7 -25.8 0.05481 0.0015 0.29499 0.00823 0.03904 0.00062 0.01059 0.00051 0.9 2.03 0.01 404 35 262 6 247 4 213 10 175.1 190.1 0.9 106.1 xm85-03 0.0509 0.00073 0.27043 0.00438 0.03853 0.00051 0.01313 0.00047 0.71623 0.00087 0.9 3.2 . 236 17 243 4 244 3 264 9 None Concordant . . 3.2 . 0.0509 0.00073 0.27043 0.00438 0.03853 0.00051 0.01313 0.00047 0.9 0.72 0.01 236 17 243 4 244 3 264 9 1853.7 708.8 2.6 99.6 xm85-04 0.05082 0.00105 0.2723 0.00604 0.03886 0.00059 0.00938 0.00051 0.97611 0.00111 0.9 5.7 . 233 25 245 5 246 4 189 10 None Concordant . . 5.7 . 0.05082 0.00105 0.2723 0.00604 0.03886 0.00059 0.00938 0.00051 0.9 0.98 0.01 233 25 245 5 246 4 189 10 1553.7 809.7 1.9 99.6 xm85-05 0.05131 0.00081 0.2733 0.00473 0.03863 0.00051 0.01159 0.00045 0.74458 0.00112 0.9 -4.2 . 255 19 245 4 244 3 233 9 None Concordant . . -4.2 . 0.05131 0.00081 0.2733 0.00473 0.03863 0.00051 0.01159 0.00045 0.9 0.74 0.01 255 19 245 4 244 3 233 9 1154.5 458.9 2.5 100.4 xm85-06 0.05143 0.0012 0.27879 0.0067 0.03931 0.00057 0.01113 0.0005 1.50729 0.00359 0.9 -4.5 . 260 30 250 5 249 4 224 10 None Concordant . . -4.5 . 0.05143 0.0012 0.27879 0.0067 0.03931 0.00057 0.01113 0.0005 0.9 1.51 0.01 260 30 250 5 249 4 224 10 228.5 183.9 1.2 100.4 Formations. However, an increasing number of (U = 330 ppm, Th = 8 ppm) and the zircon samples using GLITTER. Concordia ages and diagrams xm85-07 0.05362 0.00211 0.28535 0.01091 0.03859 0.00065 0.01238 0.00119 1.14995 0.00275 0.9 -31.8 . 355 56 255 9 244 4 249 24 None Concordant . . -31.8 . 0.05362 0.00211 0.28535 0.01091 0.03859 0.00065 0.01238 0.00119 0.9 1.15 0.01 355 56 255 9 244 4 249 24 297.0 182.3 1.6 104.5 xm85-08 0.05042 0.00178 0.26445 0.00914 0.03807 0.00063 0.01449 0.00187 0.80655 0.00085 0.9 12.5 . 214 50 238 7 241 4 291 37 None Concordant . . 12.5 . 0.05042 0.00178 0.26445 0.00914 0.03807 0.00063 0.01449 0.00187 0.9 0.81 0.01 214 50 238 7 241 4 291 37 2171.2 934.9 2.3 98.8 xm85-09 0.05231 0.00123 0.27648 0.00651 0.03833 0.00053 0.01223 0.00079 1.13029 0.0022 0.9 -19.3 . 299 29 248 5 242 3 246 16 None Concordant . . -19.3 . 0.05231 0.00123 0.27648 0.00651 0.03833 0.00053 0.01223 0.00079 0.9 1.13 0.01 299 29 248 5 242 3 246 16 457.1 275.8 1.7 102.5 xm85-10 0.05239 0.0011 0.27494 0.00594 0.03806 0.00052 0.01139 0.00057 1.30246 0.00285 0.9 -20.8 -3.5 302 26 247 5 241 3 229 11 None Common Pb < det. lim. -0.5 . -20.8 -3.5 0.05239 0.0011 0.27494 0.00594 0.03806 0.00052 0.01139 0.00057 0.9 1.3 0.01 302 26 247 5 241 3 229 11 313.4 217.9 1.4 102.5 xm85-11 0.05276 0.00131 0.27976 0.00711 0.03846 0.00057 0.01189 0.00072 1.19151 0.00252 0.9 -24.1 -2.8 318 32 250 6 243 4 239 14 None Common Pb < det. lim. -0.16 . -24.1 -2.8 0.05276 0.00131 0.27976 0.00711 0.03846 0.00057 0.01189 0.00072 0.9 1.19 0.01 318 32 250 6 243 4 239 14 366.3 233.0 1.6 102.9 xm85-12 0.05104 0.0012 0.26971 0.00661 0.03832 0.00058 0.01349 0.00114 0.79812 0.00087 0.9 -0.1 . 243 30 242 5 242 4 271 23 None Concordant . . -0.1 . 0.05104 0.0012 0.26971 0.00661 0.03832 0.00058 0.01349 0.00114 0.9 0.8 0.01 243 30 242 5 242 4 271 23 2047.8 872.5 2.3 100.0 xm85-13 0.05193 0.00284 0.27504 0.01453 0.03844 0.00087 0.00586 0.00087 0.93218 0.00139 0.9 -14.2 . 282 79 247 12 243 5 118 17 None Concordant . . -14.2 . 0.05193 0.00284 0.27504 0.01453 0.03844 0.00087 0.00586 0.00087 0.9 0.93 0.01 282 79 247 12 243 5 118 17 938.4 467.0 2.0 101.6 xm85-14 0.05126 0.00086 0.27057 0.00491 0.03828 0.00051 0.01173 0.00066 0.96915 0.00127 0.9 -4.2 . 253 20 243 4 242 3 236 13 None Concordant . . -4.2 . 0.05126 0.00086 0.27057 0.00491 0.03828 0.00051 0.01173 0.00066 0.9 0.97 0.01 253 20 243 4 242 3 236 13 1175.6 608.3 1.9 100.4 xm85-15 0.05115 0.00123 0.27057 0.00673 0.03836 0.00059 0.01317 0.00122 0.63727 0.00072 0.9 -2 . 248 30 243 5 243 4 264 24 None Concordant . . -2 . 0.05115 0.00123 0.27057 0.00673 0.03836 0.00059 0.01317 0.00122 0.9 0.64 0.01 248 30 243 5 243 4 264 24 2397.6 815.7 2.9 100.0 stdgj05 0.06033 0.00093 0.80191 0.01351 0.09641 0.00126 0.02927 0.00219 75.47329 0.13476 0.9 -3.8 . 615 17 598 8 593 7 583 43 None Concordant . . -3.8 . 0.06033 0.00093 0.80191 0.01351 0.09641 0.00126 0.02927 0.00219 0.9 75.47 0.13 615 17 598 8 593 7 583 43 8.1 328.0 0.0 100.8 stdgj06 0.05988 0.00101 0.81463 0.01477 0.09868 0.00133 0.03327 0.00274 75.62695 0.13384 0.9 1.3 . 599 19 605 8 607 8 662 54 None Concordant . . 1.3 . 0.05988 0.00101 0.81463 0.01477 0.09868 0.00133 0.03327 0.00274 0.9 75.63 0.13 599 19 605 8 607 8 662 54 8.3 333.9 0.0 99.7 GPS 29°19 18.93 N 89°52 51.23 E

stdgj05 0.06054 0.00086 0.80289 0.01255 0.09622 0.00122 0.02916 0.00189 75.40149 0.13899 0.9 -5.2 . 623 15 598 7 592 7 581 37 None Concordant . . -5.2 . 0.06054 0.00086 0.80289 0.01255 0.09622 0.00122 0.02916 0.00189 0.9 75.4 0.14 623 15 598 7 592 7 581 37 8.1 328.6 0.0 101.0 stdgj06 0.05972 0.00085 0.8154 0.01297 0.09905 0.00129 0.03173 0.00186 75.67724 0.1375 0.9 2.7 . 593 16 605 7 609 8 631 36 None Concordant . . 2.7 . 0.05972 0.00085 0.8154 0.01297 0.09905 0.00129 0.03173 0.00186 0.9 75.68 0.14 593 16 605 7 609 8 631 36 8.3 338.2 0.0 99.3 mt03 0.06414 0.00146 1.04759 0.02412 0.1185 0.00165 0.0343 0.00148 1.80936 0.00855 0.9 -3.5 . 746 26 728 12 722 10 682 29 None Concordant . . -3.5 . 0.06414 0.00146 1.04759 0.02412 0.1185 0.00165 0.0343 0.00148 0.9 1.81 0.01 746 26 728 12 722 10 682 29 51.2 50.1 1.0 100.8 xm86-01 0.05128 0.00092 0.26797 0.00519 0.0379 0.00052 0.01046 0.00038 1.04884 0.00176 0.9 -5.5 . 253 22 241 4 240 3 210 8 None Concordant . . -5.5 . 0.05128 0.00092 0.26797 0.00519 0.0379 0.00052 0.01046 0.00038 0.9 1.05 0.01 253 22 241 4 240 3 210 8 702.1 398.2 1.8 100.4 studies suggest that the coeval Nieru Formation using the Microsoft Excel program Data Templat- were obtained using Isoplot/Ex (ver. 3.0) (Ludwig, xm86-02 0.05237 0.00113 0.27466 0.00623 0.03805 0.00055 0.01113 0.00052 1.42707 0.00246 0.9 -20.6 -1.8 302 27 246 5 241 3 224 10 None Common Pb < det. lim. -0.67 . -20.6 -1.8 0.05237 0.00113 0.27466 0.00623 0.03805 0.00055 0.01113 0.00052 0.9 1.43 0.01 302 27 246 5 241 3 224 10 487.6 376.3 1.3 102.1 xm86-03 0.05323 0.00117 0.27306 0.00631 0.03721 0.00055 0.01061 0.00052 0.93402 0.00142 0.9 -31 -17.1 339 27 245 5 236 3 213 10 None Common Pb < det. lim. -1.33 . -31 -17.1 0.05323 0.00117 0.27306 0.00631 0.03721 0.00055 0.01061 0.00052 0.9 0.93 0.01 339 27 245 5 236 3 213 10 952.6 481.1 2.0 103.8 xm86-04 0.05104 0.00088 0.26297 0.00488 0.03738 0.0005 0.01077 0.00039 1.17133 0.0021 0.9 -2.6 . 243 21 237 4 237 3 217 8 None Concordant . . -2.6 . 0.05104 0.00088 0.26297 0.00488 0.03738 0.0005 0.01077 0.00039 0.9 1.17 0.01 243 21 237 4 237 3 217 8 547.0 346.4 1.6 100.0 xm86-05 0.05235 0.00121 0.27198 0.00661 0.03768 0.00057 0.01059 0.00063 0.745 0.00092 0.9 -21.1 -0.3 301 29 244 5 238 4 213 13 None Common Pb < det. lim. -1.93 . -21.1 -0.3 0.05235 0.00121 0.27198 0.00661 0.03768 0.00057 0.01059 0.00063 0.9 0.75 0.01 301 29 244 5 238 4 213 13 1832.2 738.1 2.5 102.5 xm86-06 0.04857 0.0016 0.25804 0.00839 0.03854 0.0006 0.01138 0.00081 1.64737 0.00361 0.9 93.5 56.7 127 47 233 7 244 4 229 16 None Initially inv. disc. . . 93.5 56.7 0.04857 0.0016 0.25804 0.00839 0.03854 0.0006 0.01138 0.00081 0.9 1.65 0.01 127 47 233 7 244 4 229 16 260.4 232.0 1.1 95.5 xm86-07 0.05004 0.00097 0.26002 0.00522 0.0377 0.00049 0.01202 0.00057 1.32677 0.00254 0.9 21.5 7 197 24 235 4 239 3 242 11 None Initially inv. disc. . . 21.5 7 0.05004 0.00097 0.26002 0.00522 0.0377 0.00049 0.01202 0.00057 0.9 1.33 0.01 197 24 235 4 239 3 242 11 423.7 304.0 1.4 98.3 xm86-08 0.05197 0.00103 0.2718 0.00561 0.03794 0.00052 0.01148 0.00053 1.35845 0.0027 0.9 -15.8 . 284 24 244 4 240 3 231 11 None Concordant . . -15.8 . 0.05197 0.00103 0.2718 0.00561 0.03794 0.00052 0.01148 0.00053 0.9 1.36 0.01 284 24 244 4 240 3 231 11 385.4 283.1 1.4 101.7 xm86-09 0.05154 0.00087 0.26955 0.0049 0.03794 0.0005 0.01119 0.00052 0.70242 0.00101 0.9 -9.6 . 265 20 242 4 240 3 225 10 None Concordant . . -9.6 . 0.05154 0.00087 0.26955 0.0049 0.03794 0.0005 0.01119 0.00052 0.9 0.7 0.01 265 20 242 4 240 3 225 10 1433.4 544.4 2.6 100.8 xm86-10 0.05138 0.00085 0.26739 0.00477 0.03775 0.0005 0.01147 0.00054 1.22561 0.00173 0.9 -7.5 . 258 19 241 4 239 3 231 11 None Concordant . . -7.5 . 0.05138 0.00085 0.26739 0.00477 0.03775 0.0005 0.01147 0.00054 0.9 1.23 0.01 258 19 241 4 239 3 231 11 848.6 562.4 1.5 100.8 xm86-11 0.05124 0.00098 0.2643 0.00537 0.03741 0.00052 0.01029 0.00055 0.87825 0.00128 0.9 -6 . 252 23 238 4 237 3 207 11 None Concordant . . -6 . 0.05124 0.00098 0.2643 0.00537 0.03741 0.00052 0.01029 0.00055 0.9 0.88 0.01 252 23 238 4 237 3 207 11 1110.0 527.1 2.1 100.4 xm86-12 0.05414 0.00143 0.27678 0.00746 0.03708 0.00057 0.00908 0.00053 1.21159 0.00233 0.9 -38.4 -23.4 377 34 248 6 235 4 183 11 None Common Pb < det. lim. -2.58 . -38.4 -23.4 0.05414 0.00143 0.27678 0.00746 0.03708 0.00057 0.00908 0.00053 0.9 1.21 0.01 377 34 248 6 235 4 183 11 459.5 301.0 1.5 105.5 xm86-13 0.04979 0.00083 0.25586 0.0046 0.03728 0.00049 0.01108 0.00056 0.75921 0.00108 0.9 27.9 11.2 185 20 231 4 236 3 223 11 None Initially inv. disc. . . 27.9 11.2 0.04979 0.00083 0.25586 0.0046 0.03728 0.00049 0.01108 0.00056 0.9 0.76 0.01 185 20 231 4 236 3 223 11 1340.1 550.2 2.4 97.9 xm86-14 0.05167 0.00091 0.2654 0.00498 0.03725 0.0005 0.01042 0.00052 0.99478 0.00167 0.9 -13.2 . 271 21 239 4 236 3 210 10 None Concordant . . -13.2 . 0.05167 0.00091 0.2654 0.00498 0.03725 0.0005 0.01042 0.00052 0.9 0.99 0.01 271 21 239 4 236 3 210 10 739.6 397.8 1.9 101.3 xm86-15 0.05187 0.00118 0.26858 0.00631 0.03755 0.00055 0.01041 0.00069 1.10199 0.00176 0.9 -15.3 . 280 28 242 5 238 3 209 14 None Concordant . . -15.3 . 0.05187 0.00118 0.26858 0.00631 0.03755 0.00055 0.01041 0.00069 0.9 1.1 0.01 280 28 242 5 238 3 209 14 731.9 436.1 1.7 101.7 stdgj07 0.05992 0.00098 0.80532 0.01415 0.09748 0.00128 0.02885 0.00237 78.38576 0.14431 0.9 -0.2 . 601 18 600 8 600 8 575 47 None Concordant . . -0.2 . 0.05992 0.00098 0.80532 0.01415 0.09748 0.00128 0.02885 0.00237 0.9 78.39 0.14 601 18 600 8 600 8 575 47 7.8 329.4 0.0 100.0 stdgj08 0.06021 0.00096 0.81103 0.01401 0.09771 0.00128 0.0327 0.00242 75.76306 0.14068 0.9 -1.8 . 611 18 603 8 601 8 650 47 None Concordant . . -1.8 . 0.06021 0.00096 0.81103 0.01401 0.09771 0.00128 0.0327 0.00242 0.9 75.76 0.14 611 18 603 8 601 8 650 47 7.9 323.8 0.0 100.3 GPS 29°19 18.93 N 89°52 46.12 E in the Kangma region, situated at the southern ev2b from the Australian Research Council National 2003). A common-Pb correction was applied using margin of the Langjiexue Group, also belongs to Key Centre for Geochemical Evolution and Metal- LA-ICPMS Common Lead Correction (ver. 3.15, 1 Supplemental Materials. Includes whole rock geo- this group. This formation shares similar stratal logeny of Continents (GEMOC). Each rock sample http://gemoc.mq .edu .au /TerraneChron /CommonPb. chemical, zircon U-Pb dating and Hf results of gabbro- assemblages and lithological features as well as was subject to one or several runs of 15 analyses. html), following the method of Andersen (2002). dioritic samples, as well as detrital zircon U-Pb ages fossil types (Cai et al., 2016; Li et al., 2010; Li et al., The analytical results are presented in Table S1 of The analytical data are presented on U-Pb con- and Hf isotopes of Langjiexue Group sandstones in 1 Tethyan Himalaya from this study and many other 2016). The Langjiexue Group is characterized by the Supplemental Materials . cordia diagrams with 2σ errors. The mean ages published papers. Detailed analytical methods and extensive ca. 130 Ma diabase dikes or intrusions Detrital zircon laser ablation (LA) ICP-MS are weighted means at the 95% confidence level metadata, as well as additional figures. Please visit (Fig. 3D), showing close affinity to oceanic island U-Pb geochronology and trace elements from (Ludwig, 2003). More detailed analytical parame- https://doi.org/10.1130/GES02154.S1 or access the full-text article on www.gsapubs.org to view the Sup- basalt (OIB)–type rocks (Zhu et al., 2009). These OIB sandstones, as well as trace elements for the mag- ters of zircon U-Pb dating can be seen in Text S1 plemental Materials. dikes were first proposed to have been generated matic zircon grains of the gabbro-diorite complex, (footnote 1).

29°24′N A

Yarlung-Tsangpo river Gabbro-diorite complex Dazhuqu

Renbu B m17-52 m17-08

E ′ m17-51 4

9 C

m17-53 N 0 10 20 km

Jiangzi 3-D DEM map,DEM data are 28°54′N collected from CGIAR-CSI

E W diabase block conjugate veins N 1 Gabbro- diorite complex D2 2

3 gabbro D1 2 vein backpack 70°

A m17-51 C 5 B m17-52 SE km m17-08

Basement of Tethyan Himalaya? Gangdese batholith? 0 0 6 km Gabbro- Gangdese Late Cretaceous Eocene Jurassic Dazhuqu Mélange Late Triassic Ultramaﬁc Diabase diorite batholith granitoid pluton granite Bima Fm. conglomerate zone Langjiexue Gr. block

Figure 3. Simplified map of the sampling location, Tethyan Himalaya, southern Tibet. (A) Three-dimensional (3-D) map of the studied area, showing sampling locations (red stars). DEM—digital elevation model; CGIAR-CSI—CGIAR Consortium for Spatial Information. (B) Cross-section for the studied area including the Langjiexue Group in the Tethyan Himalaya and the gabbro-diorite complex in the Gangdese belt (see A for location). (C) Gabbro-diorite complex intruded by later gabbroic and granitic dikes (numbering showing the intruded sequence, with number 1 as the first intrusion, and number 3 as the last intrusion). (D) Diabase featuring conjugate veins within the Langjiexue Group. (E) Cartoon showing two deformation events.

Zircon Hf Isotopic Analysis from the sample matrix. Neodymium was sepa- calculation procedures can be referenced in Ma rated from other REEs on the second column with et al. (2018b). The analytical results are presented Zircon Hf isotopes were analyzed using a 193 nm Teflon powder coated in Eichrom Ln-Spec resin. The in Table S7 (footnote 1). laser attached to a Neptune multi-collector (MC) Sr- and Nd-bearing elutions were dried and redis-

ICP-MS (Thermo Finnigan, Bremen, Germany) at solved in 1.0 ml 2 wt% HNO3. Small aliquots of each Key Laboratory of Deep-Earth Dynamics, Institute of were measured using an Agilent Technologies 7700x Detrital Zircon Microstructural Classification Geology, Chinese Academy of Geological Sciences quadrupole ICP-MS to determine the contents of Sr (CAGS; Beijing, China). MC-LA-ICP-MS analyses and Nd. Diluted solutions (50 ppb Sr, 50 ppb Nd, Approximately 150 zircon grains of each sam- were carried out with a beam size of ~32 μm. A decay doped with 10 ppb Tl for both) were introduced into ple were mounted on double-sided tape on a glass constant for 176Lu of 1.867 × 10−11 yr–1 (Söderlund et al., a Nu Instruments Nu Plasma II MC-ICP-MS through disk. After carbon coating, these detrital zircon 2004) was adopted to analyze initial 176Lu/177Hf ratios, a Teledyne Cetac Technologies Aridus II desolvat- grains were analyzed for surface microstructures while chondritic values of 176Lu/177Hf = 0.0336 and ing nebulizer system. Sr-Nd isotope analyses were (roundness and surface textures) at the Institute of 176 177 Hf/ Hf = 0.282785 were chosen to obtain the εHf(t) carried out at Nanjing FocuMS Technology (Nanjing, Geology, CAGS (Beijing, China) using a FEI NOVA values (Bouvier et al., 2008). The single-stage model China). Detailed measurement and calculation proce- NANOSEM 450 scanning electron microscope

age (TDM) was calculated relative to the depleted dures are presented in Zhu et al. (2017). The analytical (SEM). Magnification scales ranged from ~100× to mantle with a present-day 176Hf/177Hf = 0.28325 and results are presented in Table S6 (footnote 1). 460×. The SEM worked in secondary electron mode 176Lu/177Hf = 0.0384. A two-stage continental model under high vacuum with 10 or 15 kV voltage and a C age (TDM ) was calculated by projecting the initial working distance of ~5 mm. After the SEM analyses, 176Hf/177Hf of zircon back to the depleted-mantle Mineral Electron Microprobe Analysis cathodoluminescence (CL) images were obtained. growth curve using 176Lu/177Hf = 0.015 for the average The detailed analytical method for CL images will continental crust (Griffin et al., 2000). The analytical Representative hornblende and plagioclase min- not be presented here. results are presented in Table S4 (footnote 1). erals were selected from thin sections for electron Detrital zircon morphology (roundness) fea- microprobe analyses (EMPA). Mineral compositions tures were categorized using parameters of Gärtner were measured using a JEOL JXA-8230 electron et al. (2013). The I–X roundness scale reveals the Whole-Rock Geochemistry microprobe (20 nA beam current, 5 μm beam spot, smoothing of crystal edges and abrasion of crystal 15.0 kV accelerating voltage) at the Institute of faces: a roundness of I emphasizes that the crystal The whole-rock elemental results were deter- Mineral Resources, CAGS (Beijing, China). The ana- is completely unrounded, whereas a roundness mined at ALS Laboratory (ALS Mineral–ALS Chemex; lytical results are presented in Table S7 (footnote 1). of X implies that the crystal is completely rounded. Guangzhou, China). Oxide abundances were mea- Crystal surface textures were classified using the sured by a PANalytical Axios X-ray fluorescence standards of Finzel (2017) and Vos et al. (2014). The spectrometer with analytical precision of better than Hornblende-Plagioclase Geothermometry analytical results of zircon CL and SEM images are 5%. Trace and rare earth elements (REEs) were mea- presented in Text S2 (Fig. S1 [footnote 1]). sured using ICP-MS; relative standard deviations are Hornblende and hornblende-plagioclase geo- <10% for trace elements and <7% for REEs. Analytical thermometry are used based on the values of Si procedures are described by Qi et al. (2000), and the and Al cations in the tetrahedral positions (Blundy ■■ RESULTS results are presented in Table S5 (footnote 1). and Holland, 1990; Holland and Blundy, 1994; Ridolfi and Renzulli, 2012). Blundy and Holland (1990) Petrography proposed an empirical hornblende-plagioclase ther- Whole-Rock Sr-Nd Isotopic Analysis mometer based on the edenite-tremolite reaction Gabbro-Diorite Complex in the Gangdese Belt for quartz-bearing intermediate to felsic igneous For whole-rock Sr-Nd isotopic analysis, rock rocks. Later on, Holland and Blundy (1994) reported The gabbro-diorite complex, located in the powders were decomposed using a high-pressure thermometer A (tremolite-edenite reaction) for southern margin of the Gangdese magmatic belt, polytetrafluoroethylene (PTFE) bomb. Strontium and quartz-bearing metabasites and thermometer B shows varied petrographic structures such as neodymium were purified from the same digestion (richterite-edenite reaction) for quartz-free igne- hornblende cumulate layers, huge phenocrysts, solution by two-step column chemistry. In the first ous rocks. The hornblende thermometer of Ridolfi magmatic flow banding, and equigranular features exchange column, Bio-Rad AG 50W-X8 and Eichrom and Renzulli (2012) was also used to obtain the (Fig. 4). In all structures, hornblende dominates as Sr-Spec resins were used to separate Sr and REEs crystallization temperature of the pluton. Detailed the main mafic mineral, with plagioclase occupying

the interstitial space between hornblende phe- E nocrysts (Fig. 5). In addition, plagioclase occurs as small laths, and crosscuts and postdates the horn- intrusive complex Bima volcanic rocks lithic fragment blende. The main body of the pluton is equigranular, with rock composition akin to gabbro, diorite, and granodiorite, but still marked by abundant hornblendes. The rock type of gabbro to granodiorite Bima volcanic rocks combined with the mineral structures (phenocrysts to equigranular) and the hornblende cumulate layers and plagioclase layers reveal that the pluton was most likely formed through a fractional crys- pluton 600 m Yarlung-Tsangpo river tallization process. Abundant hornblendes suggest that the magma source of the pluton was wet (Mur- E phy, 2013). Two later dikes that intruded the pluton have also been observed (Fig. 3C).

dioritic suite Sandstones of the Langjiexue Group porphyritic texture Hbl phenocryst The Langjiexue Group in the Renbu region gabbroic suite (Fig. 2) mainly consists of interbedded dark mud- G stones and sandstones formed in a submarine fan environment (Zhang et al., 2015a). These strata have Hbl cumulate layer been strongly deformed, showing fold and thrust structures (Fig. 3B) with muscovites oriented along Pl layer cleavage planes (Figs. 5E–5F). According to our detailed field work, we find that these north-verging folds with east-west–trending axial planes experienced a second structural event (east-west–verging folding), evidenced by varying hinge orientations (Fig. 3E). The second deformation event was Hbl phenocryst Magmatic ﬂow structure probably associated with the east-west–trending orogen-parallel extrusion of the Himalayan terranes Figure 4. Representative field photos for the gabbro-diorite complex, Gangdese magmatic belt, southern Tibet. (A) Google in the late Oligocene and Miocene (Xu et al., 2013). Earth map showing the intrusive complex with the Bima Formation volcanic rocks (N29˚19′19″, E89˚52′43″). (B) Contact between the intrusive complex and the overlying Bima Formation (N29˚19 19 , E89˚53 33 ). (C) Huge hornblende (Hbl) pheno The extrusion was probably triggered by the ~20° ′ ″ ′ ″ cryst (N29˚20′33″, E89˚51′51″). (D) Hornblende phenocryst assemblage showing cumulate structure (N29˚19′19″, E89˚52′53″). clockwise vertical-axis rotation during the early (E) Equigranular textures of hornblende and plagioclase for the dioritic suite of the gabbro-diorite complex (N29˚19′19″, Miocene (Antolín et al., 2011). The diabase dikes E89˚52′53″). (F) Hornblende (Hbl) phenocrysts accumulated in a cumulate layer (N29˚20′33″, E89˚51′51″). (G) Magmatic flow hosted within the sedimentary rocks are cut by con- structure (Pl—plagioclase) (N29˚20′33″, E89˚51′51″). jugate quartz veins (Fig. 3D) whose formation could be closely associated with the later deformation event. The orientations of these conjugate quartz Zircon U-Pb Dating Results gabbro-diorite complex have broad, banded veins indicate the same direction of shortening as zoning, whereas a few show oscillatory zoning the second folds. In spite of intense deformation Zircon U-Pb Ages of the Gabbro-Diorite (Fig. 7). Most of these zircon grains display euhe- (Fig. 6), the graded sandstones of the Langjiexue Complex dral prismatic shapes with aspect ratios of ~2:1 Group exhibit clear Bouma sequences. The sand- (~100–200 µm in length and ~50–100 µm in width; stones have subangular plagioclases and quartz, Cathodoluminescence (CL) images reveal Fig. 7). No obvious metamorphic overgrowths and abundant in lithic volcanic fragments. that most of the examined zircon grains of the were present, and all of the zircon grains show

Hbl Hbl Hbl

Hbl Pl Hbl Hbl Hbl Pl 500 µm 2 mm

Figure 5. Representative photomicrographs of the studied gabbro-diorite complex in the Gangdese Qtz magmatic belt and sandstones in the Tethyan Qtz Himalaya, southern Tibet. Abbreviations: Hbl— Pl Hbl hornblende; Pl—plagioclase; Qtz—quartz; Lv—lithic volcanic fragment; Ms—muscovite. (A) Hornblende assemblage in the intrusive complex. Hornblende Pl accounts for ~95% or more. (B) Hornblende phenocrysts with small plagioclase laths occurring as Pl Hbl the interstitial phase in the gabbro-diorite complex. (C) Euhedral hornblende phenocryst with plagioclases occupying the interstitial space in the Hbl gabbro-diorite complex. (D) Equigranular texture of hornblende and plagioclase in the dioritic gabbro-di- Hbl orite complex. (E) Sandstone including many lithic volcanic fragments. (F) Sandstone including lithic volcanic fragments and muscovites. 200 µm 100 µm E Ms Lv Qtz Qtz Lv Lv

Qtz Lv Ms

Pl Qtz Qtz Pl Lv Ms

100 µm 100 µm

high Th/U ratios between 0.8 and 2.7 (with a peak at ~1.6), typical of magmatic zircon grains. These te S features suggest that these zircon grains are of mera nglo magmatic origin (Corfu et al., 2003). Fifteen (15) qu co azhu zircon U-Pb age analyses of samples xm82, xm84, D xm85, and xm86 yield weighted mean ages of 244 ± 1.7 (mean square of weighted deviates [MSWD] = 0.68), 242.2 ± 1.6 (MSWD = 0.42), 243.3 ± 1.8 Renbu mélange (MSWD = 0.37) and 238.3 ± 1.6 Ma (MSWD = 0.48), respectively (Fig. 7).

utility pole Zircon U-Pb Ages of the Sandstones in the Langjiexue Group E N ultramaﬁc block Detrital zircon grains extracted from the sandstones of the Langjiexue Group in the Renbu region were analyzed for U-Pb dating. A total of 308 zircon

1 m grains have been dated (77 grains from each of four Dazhuqu conglomerate sandstone samples). Generally, discordance filters Langjiexue Fm in literature vary from 1% to 30% depending on the 30 cm serpentine utility pole level of interpretation desired and the data process- NE G NE H NE ing precision (Spencer et al., 2016, 2017). In the present study, we choose 20% discordance as the filter based on the following reasons: (1) LA-ICP-MS has lower analytical precision than secondary ion mass spectrometry (SIMS) or thermal ionization mass spectrometry (TIMS), thus it should be acceptable within larger discordance; (2) a filter of 20% versus 10% would not have big impact on the sta- sandstone 1 m sandstone SW NE tistical analysis for the dated zircon in the present study; and (3) a large number of detrital zircon ages of the Langjiexue Group have been published in previous work, which could be used as a compel- ling comparison to the results of our present study. Among the 308 zircon grains, 297 passed a concordance filter of 80%–100% concordance. In addition, we have adopted the evaluation rule of discor- 2 m sandstone dance in Spencer et al. (2016, 2017) to filter the Figure 6. Representative field photos, southern Tibet. (A) Contact between the Dazhuqu conglomerate and the Renbu mélange 297 zircon U-Pb ages (with concordance between zone (N29˚17′23″, E89˚48′05″). (B) Dazhuqu conglomerate (N29˚17′41″, E89˚47′47″). (C) An ultramafic block within the mélange 80%–100%). The plots reveal that only 279 zircon (N29˚15′5.5″, E89˚49′32.6″). (D) Ultramafic rock that has been serpentinized (N29˚15′5.5″, E89˚49′32.6″). (E) North-verging grains fall along the 206Pb/238U versus 207Pb/235U 1:1 fold of the Langjiexue Group (N29˚10′08″, E89˚56′57.7″). (F) Graded sandstone showing the Bouma sequence (N29˚11′33.3″, E89˚53′25.6″). (G) Northeast-verging fold of the Langjiexue Group (N29˚11′33.3″, E89˚53′25.6″). (H) Graded sandstone showing age line, with 18 falling off the line (Fig. S2 in Text the Bouma sequence (N29˚08′57″, E89˚58′22.7″). (I) Folded strata of the dark mudstone of the Langjiexue Group (N29˚08′57″, S2 [footnote 1]). The remaining 279 ages exhibit E89˚58′22.7″). (J) Folded strata of the Langjiexue Group in the Chongzi region, Jiangzi County (N28˚59′19.7″, E89˚25′35.6″). a wide range from Mesoarchean to Late Triassic (K) Thick sandstone stratum showing the sampling location for m17-53 (N28˚59′19.7″, E89˚25′35.6″). (3190–201 Ma) (Fig. 8A), indicating multiple sources and a variety of rock types in the provenance.

280 data-point error symbols are 1σ data-point error symbols are 1σ xm82 xm84 270 244 ± 1.7 Ma [0.71%] 95% conf. 242.2 ± 1.6 Ma [0.67%] 95% conf. Wtd by data-pt errs only, 0 of 14 rej. Wtd by data-pt errs only, 0 of 15 rej. MSWD = 0.68; Probability = 0.79 MSWD = 0.42; Probability = 0.97 ) 260 a (uncertainties are 2σ) (uncertainties are 2σ) M

e ( 250 g U a 8 3

2 240 / b P 6 0 2 230

220 Figure 7. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb 210 weighted mean ages for the plutonic suite. Percent- age values shown in the square brackets are the 280 xm85 xm86 relative errors. Abbreviations: MSWD—mean square 243.3 ± 1.8 Ma [0.75%] 95% conf. 238.3 ± 1.6 Ma [0.67%] 95% conf. weighted deviation; conf.—confidence; errs—errors; 270 Wtd by data-pt errs only, 0 of 15 rej. Wtd by data-pt errs only, 0 of 15 rej. pt—point; rej.—rejected; Wtd—weighted. MSWD = 0.37; Probability = 0.98 MSWD = 0.48; Probability = 0.94 260 (uncertainties are 2σ) (uncertainties are 2σ) ) a data-point error symbols are 1σ data-point error symbols are 1σ M

e ( 250 g U a 8 3

2 240 / b P 6 0 2 230

220

210 Analyzed spot Analyzed spot

Several prominent age populations exist: Mesoar- the empirical equation of Spencer et al. (2016). In Whole-Rock Major and Trace Elemental chean (3200–3100 Ma), early Paleoproterozoic their study, the best-fit trendlines reveal an empiri- Results of the Gabbro-Diorite Complex (2500–2400 Ma), late Paleoproterozoic–early Meso- cal crossover point of 207Pb/206Pb and 206Pb/238U ages proterozoic (1755–1500 Ma), early Neoproterozoic at ca. 1.5 Ga. Thus, the 207Pb/206Pb ages are used All of the analyzed rock samples from the gab- (1000–800 Ma), late Neoproterozoic–early Paleo- as the best ages for zircons older than ca. 1.5 Ga, bro-dioritic suite plot in the subalkaline field of zoic (620–420 Ma), and early Permian–Late Triassic and the 206Pb/238U ages are used as the best ages gabbro to granodiorite with major oxide abundances

(299–201 Ma) (Fig. S3 in Text S2 [footnote 1]). for younger ones (Spencer et al., 2016). The distri- as follows: SiO2 = 51.85–59.28 wt%, Al2O3 = 15.14– T T In addition, a large number of published detrital bution patterns of these collected detrital zircon 17.52 wt%, Fe2O3 ( means total iron) = 5.98–10.69

zircon U-Pb ages for the Langjiexue Group have U-Pb ages have been evaluated by kernel density wt%, MgO = 2.7–6.4 wt%, CaO = 4.8–9.41 wt%, TiO2

been collected and compiled in the Table S2 (foot- estimation (KDE) plotting according to the method = 0.45–0.51 wt%, and total alkali (Na2O + K2O) = 4.14– note 1). The age of the cutoff between 207Pb/206Pb of Vermeesch (2012) and Vermeesch et al. (2016) 7.49 wt% (Fig. 9). Such oxide abundances resemble and 206Pb/238U ages is chosen as 1.5 Ga according to (Fig. 8B). those of low-MgO high-alumina basalts or andesites

(Sisson and Grove, 1993b). These chemical charac- of 87Sr/86Sr ratios (0.703714–0.704119) and initial teristics, together with FeO*/MgO (asterisk means 87Sr/86Sr ratios of 0.703432–0.703739. In addition, Detrital zircon U-Pb ages total) ratios from 1.24 to 2.19 (Fig. 9B), FeO*/MgO the plutonic rocks are characterized by positive εNd(t) of sandstones from T T versus SiO2, and TiO2 versus FeO /MgO ( means values ranging from +4.5 to +5.5 (Fig. 11C). Langjiexue Group, 0.0015 total) (Figs. 9B–9C), indicate typical calc-alkaline Tethyan Himalaya features. Diagrams of ε versus SiO , Cr versus Data are compiled from Nd(t) 2 the present study Mg# (molecular MgO/(MgO + FeOT)*100), and La/ Mineral Geochemical Results from the n = 279/308 Sm versus La reveal that these studied rocks exhibit Gabbro-Dioritic Rocks 0.0010 a gradual variation trend (Figs. 9D–9F), which, with

the variation of mineral structures and rock types in The magmatic amphibole (hornblende) and Kernel density estimation 0.0005 the field and the wide range of SiO2, indicates that plagioclase pairs in the plutonic rock of sample they were formed through a continuous fractional xm83 were selected for EMPA analysis. Accord- crystallization process. ing to the nomenclature of Leake et al. (1997), the ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| ||||||||||||| || | | | | | ||| | |||| || |||| In chondrite-normalized REE patterns, all sam- amphiboles fall into the magnesiohornblende field 0.0000 0 1000 2000 3000 4000 ples have similar enrichment in light REEs with (Fig. 11D). These hornblendes are characterized by

(La/Yb)N (N stands for chondrite-normalized) = 4.25– CaA (Ca in the A site) <0.50, (Na + K)A <0.50, and 0.0025 8.05 and weak negative Eu anomalies (Fig. 10A). Ca >1.50 on the M4 sites. Therefore, the selected Detrital zircon U-Pb ages In the primitive mantle–normalized spidergram, hornblendes are typical of magmatic calcic amphi- of sandstones from Langjiexue Group, these rocks display a strong Pb enrichment and boles. The analyzed plagioclases exhibit a narrow 0.0020 Tethyan Himalaya negative Nb, Ta, and Ti anomalies, similar to the range of anorthite (An) and albite (Ab) values. In Data are compiled from western Aleutian high-Al basalt (Fig. 10B). Popu- the calculations of hornblende-plagioclase geo- references 0.0015 n = 7019 lar discrimination diagrams (Condie, 1989; Pearce thermometry, the mean composition of all of the et al., 2005; Plank, 2005) are employed to distin- plagioclases was adopted. The geothermometry guish the tectonic setting of the studied plutonic yields a ~720 °C crystallization temperature for the 0.0010 Kernel density estimation rocks. These rocks plot within the intra-oceanic gabbro-dioritic pluton.

arc fields, as shown in the Th/Nb versus La/Nb, La 0.0005 versus Th, La/Yb versus Th/Yb, and Th/Yb versus |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||

Ta/Yb diagrams (Figs. 10C–10F). Microstructures of Detrital Zircon Grains of 0.0000 0 1000 2000 3000 4000 the Langjiexue Group Zircon U-Pb age (Ma)

Figure 8. Kernel density estimation (KDE) for detrital zircon Zircon Hf Isotopic Results of the Gabbro- Based on the roundness classification of Finzel grains of the Langjiexue Group in the Tethyan Himalaya. (A) Age Diorite Complex (2017), all of the analyzed grains from the sand- KDE visualization of zircon grains from sandstones in this study. stones of the Langjiexue Group in the Tethyan (A total of 308 U-Pb ages of detrital zircon grains have been yielded, but only 279 ages passed the discordance filter). (B) KDE Dated zircon grains of the gabbro-dioritic rocks Himalaya are classified using a I–X roundness scale. visualization of published ages for zircon grains from sand- are also employed for Hf isotopic determination. It is clear that the Precambrian zircon grains are stones in the Langjiexue Group, Tethyan Himalaya, southern Tibet, compiled from Aikman et al. (2008), Cai et al. (2016), Cao The εHf(t) values range from +10 to +16 (with a peak at more rounded, above IV on the roundness scale. In et al. (2018), Fang et al. (2018), Li et al. (2010, 2016), Wang et al. ~+14), corresponding to the depleted mantle modal contrast, the zircon grains with ages of 300–200 Ma (2016b), Webb et al. (2012), and Metcalf and Kapp (2019). ages of 500–240 Ma (with a peak at ca. 300 Ma) are less rounded, ranging from I to IV on the round- (Figs. 11A–11B). ness scale (Fig. 12). Similarly, the zircon grains of 300–200 Ma have fresh surface microstructures ■■ DISCUSSION compared to the Precambrian zircon grains. No Whole-Rock Sr-Nd Results of the Gabbro- obvious chemical or mechanical impact features Petrogenesis and Tectonic Setting of the Dioritic Rocks could be seen from these younger zircon grains Gabbro-Dioritic Rocks (Fig. 13). In contrast, the older ones show com- Initial isotopic ratios were calculated for the mon chemical (scaling, weathered surfaces) and The intrusive complex consists of a group crystallization age of the plutonic rocks. The results mechanical (upturned plates, abrasion features, of coeval plutons and hypabyssal rocks that show that these samples have a narrow range fracture faces, conchoidal fractures) features. range from mafic to felsic in composition but

18 4 Ultrabasic Basic Intermediate Acid 15 c Nepheline iti 3 lei syenite ho 12 Quartz T

) syenite O

% Syenite g t w M / 9 Granite * 2 ne O ( Syeno-diorite

O i

2 l e ka F al Ijolite Quartz c- 6 Alkali gabbro diorite al

O + K Granodiorite C 2

a Gabbro

N Diorite 1 3 Alkaline Subalkaline 0 0 35 40 45 50 SiO2 (wt%) 60 65 70 75 45 50 SiO2 (wt%) 60 65 3 20 Cru 2.5 sta 15 l co nta mi Figure 9. Geochemical variation diagrams nat 2 ion for plutonic rocks of the gabbro-diorite

) 10 Fractional crystallization complex in the Gangdese magmatic belt.

% (A) Total alkalis versus silica (after Wilson, t

c ) iti t ( w 1.5 lei 1989). (B) FeO*/MgO versus silica (asterisk o d ( h 2 T N means total); tholeiitic and calc-alkaline ɛ O

i 5 fields from Miyashiro (1974). (C) TiO2 versus T 1 FeOT/MgO (T means total) (after Miyashiro, C alc 1974). (D) Whole-rock epsilon Nd versus -al SiO for the plutonic rocks. (E) Cr versus kal 2 in 0 T 0.5 e Mg# [molecular MgO/(MgO + FeO ) × 100]. (F) La/Sm versus La.

0 −5 0 1 T/ 3 4 50 52 54 56 58 60 FeO MgO SiO2 (wt%) 60 6 E g n i 50 t n l o e i t a z l m 40 i a l 4 i l t r ) a n t a io m s t P a

p z y m li

p l r S a 30 / st

a y

r ( l c r

a L l c C a n on o ti i c 20 t 2 ra c F a r F 10

0 0 30 40 50 60 0 10 20 30 40 Mg# La (ppm)

1000 1000 e l t n e a t

i 100 100 r Aleutian HAB Aleutian HAB e m d v n i o t i h c m / i e r l p p / e m l a 10 p 10 S m a S

1 1 La Ce Pr Sm Eu Dy Ho Er Tm Lu Rb Th Nb La Pb Sr Zr Sm Ti Tb Y Er Yb Figure 10. Geochemical characteristics of Nd Gd Tb Yb Ba U Ta Ce Pr Nd Hf Eu Gd Dy Ho Tm Lu 4 25 the samples from the gabbroic-dioritic intrusive complex. (A,B) Chondrite-nor- .3 .2 malized rare earth element patterns (A) and a = 0 primitive mantle–normalized element di- L a = 0 c / L r h h/ 20 agram (B). Aleutian high-Al basalt (HAB) 3 T T n a a data are from Singer et al. (2007). The chon- h a t drite and primitive mantle standard values a n ) are from Boynton (1984) and Sun and Mc- 15 A b m a Donough (1989), respectively. (C, D) Th/ p c N n r /

p a 2 i Nb versus La/Nb diagram (C) and La ver- h r k a a o a ( T .1 m sus Th diagram (D) (Plank, 2005). Mariana a = 0 L 10 M k h/L Anatahan data (gray) and Aleutian Okmok T an O ti data (pink) are compiled from Wade et al. u le (2005) and Kelemen et al. (2003), respec- 1 A 5 tively. (E) La/Yb versus Th/Yb diagram Intra-oceanic arcs (after Condie, 1989). (F) Th/Yb versus Ta/ (Aleutians, Antilles, Marianas) Yb diagram (after Pearce et al., 2005) (with 0 0 the small insert diagram showing the differ- 0 10 20 0 1 2 3 Th (ppm) 5 6 7 ent trends for igneous rocks from different La/Nb settings). Abbreviations: CA—calc-alkaline; 10 l 1000 ta e TH—tholeiitic; C—crustal contamination; F— en rc n u E ti o fractional crystallization; S—subduction on s in le s lt components; W—within-plate enrichment. c g t a r ve c r n s ti a a a in a c g A d m e b ar e t m h la l m c p a 1 ri - 100 t n ra en E t in In nt b

o b C Y CA Y / / a

h TH L T

Oceanic e rc 10 island arc u C 0.1 o e s S tl W an Island arc F d m te le Primitive island arc ep 1 D 0.1 1 10 100 1000 0.01 Th/Yb 0.01 0.1 Ta/Yb 1 10

9 Peaking at ~14 14 8 12 Peaking at ~300 Ma 7 Samples xm82 + Samples xm82 + xm84 + xm85 + y xm84 + xm85 + 10 t y i xm86 t l 6 xm86 i i l b n = 60 i n = 60 a b b 5 a 8 o b r o r

e p 4 v e p 6 i v t i a t l a e

3 l e R 4 R 2

1 2

0 0 8 10 12 14 16 18 20 0 100 200 300 400 500 600 700 Zircon ɛHf(t) Zircon Hf T D M age (Ma)

15 CaM4≥1.50;(Na + K)A <0.50; CaA<0.50 Neotethyan 1.0 Figure 11. Geochemical features for the samples ophiolites from the gabbro-dioritic intrusive complex. (A) Histo- Magnesiohornblende 10 grams of zircon epsilon Hf isotopes. (B) Histograms

of zircon depleted mantle model ages (TDM). (C) Bulk M rock Sr-Nd isotopes for the gabbro-diorite complex; 5 a Tschermakite n ) data for the Neotethyan ophiolites are from Xu and +

t 2

l e Castillo (2004) and Zhang et al. (2005). (D) Classifica- e a )

t tion of hornblendes according to the nomenclature ( d r g + F N 0 0.5 r of Leake et al. (1997). (E) Cr versus Y (after Siddiqui ɛ

a M (

y / et al., 2017). DM and PM represent depleted mantle g and primitive mantle, respectively. %melt describes M −5 amount of melt of depleted mantle, %cryst indicates Ferrohornblende Ferrotschermakite fractional crystallization process. The black dashed line shows fractional crystallization of ca. 20% melt −10 of the depleted mantle.) (F) Ce-Yb geochemical dis- criminant diagram (after Hawkesworth et al., 1993). Marine sediments 0 Abbreviations: CVZ—Central Volcanic Zone; SVZ— −15 7.50 7.00 6.50 6.00 Si (p.f.u.) Southern Volcanic Zone; p.f.u.—per formula unit; 0.70 0.71 87 86 0.73 ( Sr/ Sr)i 0.72 i—initial. 120 DM PM E Aeolian Is. 90 100 1000 Melt (%) Philippines 20 10 5 50 80 Andes )

m CVZ ) p m p 100 p Grenada p

r ( 60 C e ( C Andes Aleutians. 40 SVZ

10 New Britain N. Lesser Antilles 20 Crystallization (%) Marianas S. Sandwich Is. Tonga-Kermadec 1 0 1 10 100 0 1 2 3 4 5 6 Y (ppm) Yb (ppm)

II III VII IV I V III V VI IV I V

V IV III V I B

VI IX VI I IV IV

m17-08-2 m17-51-2

VI B IX IV VI V VII IV

VI X VI V V II IV III

III V VI V VIII VII V V

II V X X VI B IX VI

m17-52-2 m17-53-2

220 Ma 220 Ma 246 Ma IV III 269 Ma 268 Ma 208 Ma 249 Ma II 289 Ma I II II I 237 Ma III 150µm I m17-08-2 221 Ma I I II II 291 Ma 225 Ma 211 Ma 266 Ma 211 Ma I I II I 253 Ma 209 Ma m17-51-2

I I I I I m17-52-2 214 Ma 210 Ma 234 Ma 251 Ma 255 Ma I - completely unrounded IV - poorly rounded VII - well rounded X - completely rounded II - almost completely unrounded V - fairly rounded VIII - very well rounded B - broken III - very poorly rounded VI - rounded IX - almost completely rounded

Figure 12. Scanning electron microscope images of representative zircon grains from each sample of sandstones from the Langjiexue Group, showing grain roundness characteristics. The roundness classification is from Finzel (2017); grains with higher numbers are more rounded. In the lower part of the figure, each zircon is shown with both scanning electron microscope image and cathodoluminescence image. The red circles represent the U-Pb dating spots, with the corresponding ages shown nearby.

are dominated by hornblende gabbro to diorite. 570 Ma 289 Ma 1726 Ma The most common mafic mineral in this suite is Fs Pw Af Cr hornblende, which typically occurs as both large Fs prismatic phenocrysts and small crystals in the Fs Up Up matrix. No pyroxene was found in field exposures 211 Ma or in the thin sections of the studied rocks. In addition, plagioclase commonly occurs as small laths 790 Ma 2287 Ma Fs Fs Up between the hornblende phenocrysts, and cross- Pw cuts and postdates the hornblende minerals. These Af observations are congruent with the importance of Cr m17-08 Pw 221 Ma water in the early paths of magma differentiation; 208 Ma the presence of water suppressed the early crystal- 607 Ma 908 Ma 541 Ma lization of plagioclase when olivine and pyroxene Fs fractionated (Feig et al., 2006; Grove et al., 2012; Ws Pw Ws Ws Smith et al., 2009; Wan et al., 2013). These plutonic rocks plot in the calc-alkaline Fs field, rather than the tholeiitic field (Figs. 9B–9C), 253 Ma Ws Pw supporting a dominant role of magmatic water 851 Ma Fs (Zimmer et al., 2010). Once magma is wet, the Cr magmatic water would lead to the crystalliza- 639 Ma Fs tion of calcic plagioclase while reducing the total Af proportion of plagioclase in the mineral assem- Cr Fs blage, thereby facilitating the development of 211 Ma the calc-alkaline differentiation trend (Sisson and Grove, 1993a). m17-51 Generally, the crystallization temperature of 642 Ma a normal basaltic magma is very high. However, if the magma is water saturated, the crystallization temperature would be significantly reduced Pw Cr Fs Ch (Lee et al., 2009a; Wan et al., 2013). The various geothermometers employed in this study yield Be Vp Ch similar crystallization temperature ranges for the Ch 732 Ma 952 Ma 756 Ma gabbro-diorite complex (Fig. 14). The Zr–in–whole rock geothermometer yields a weighted mean 2818 Ma Fs: fresh surfaces 577 Ma Cr: craters crystallization temperature of ~713 °C (Table S8 l Ff: fracture faces a

c [footnote 1]). Hornblende and hornblende-pla- i Ch: conchoidal fracture Ff n a Vp: V-shaped cracks gioclase geothermometers present a weighted

Surface textures h

Up c Af: abrasion features e mean crystallization temperature of ~720 °C. The Ws Up: upturned plates Ff Be: bulbous edges Ti-in-zircon geothermometer calculated ~720 °C l M

a for the gabbro-diorite complex (Table S9). Taken c m17-52 i m together, we find that the crystallization tempera- e Pw: preweathered surface h

C Ws: weathered surface ture of the gabbro-diorite complex is sharply lower than that of normal basaltic magma. Furthermore, Figure 13. Scanning electron microscope images of representative grains from the studied sandstones showing surface micro the high alumina contents (15%–17%) of these textures. The identification standards for microtextures are from Finzel (2017). calc-alkaline rocks, potentially controlled by the delay of plagioclase nucleation, also support a high

water content in the magma (Crawford and Falloon, C ° r (

1987; Kelley et al., 2010). e t

e 800

The water content in continental crust is <0.001 m

o 713 m wt%, and <0.1 wt% in the asthenospheric and r e 600 h

lithospheric mantle (Williams and Hemley, 2001). k t c However, a high amount of water (>3 wt%) within o 400 e r l o

the magma is needed for the crystallization of horn- h

w 200 –

blende (Grove et al., 2012; Sisson and Grove, 1993a). n i

– r 5 10 15 20 Generally, the H2O of arc magma is generated by Z 0 the dehydration of hydrous minerals, which are Number of analyzed samples 800 carried down by the subducting oceanic slab. The )

C 720 water is released into the overlying mantle wedge, ° 700 r (

e Figure 14. Geothermometers of crystalli-

where melting initiates and ascends as hydrous t 600 e zation temperature for the gabbro-diorite

magma (Grove et al., 2012). Therefore, a subduction m

o Hbl-Pl thermometer of Blundy and Holland (1990) complex. (A) Zr–in–whole rock thermome-

zone is the best locus to form these magmas, where m ter yielding crystallization temperature of r 400 Hbl thermometer of Ridolﬁ and Renzulli (2012) e

additional hydration for the magma can occur from h Hbl-Pl thermometer equation A (with quartz) of ~713 °C. The equation is from Watson and

l t Holland and Blundy (1994) Harrison (1983). (B) Hornblende (Hbl)–pla- P

the mantle wedge metasomatized by subduction -

l 200 Hbl-Pl thermometer equation B (with or without quartz) gioclase (Pl) and hornblende thermometers slab-derived fluid (Grove et al., 2012; Hirschmann, b of Holland and Blundy (1994) revealing ~720 °C crystallization tempera- H 2006; Murphy, 2013). 5 10 15 20 ture. (C) Ti-in-zircon thermometer yielding 0 ~720 °C crystallization temperature. The Zircon grains of gabbro-dioritic rocks show Number of analyzed samples equation is from Watson et al. (2006). highly positive εHf(t) values (+10 to +16, with a peak 1000 at ~+14; Fig. 11A). Correspondingly, the zircon Hf ) C

TDM modal ages are centered around ca. 300 Ma °

r ( 800

(Fig. 11B), slightly older than the U-Pb crystalliza- e t

e 720

tion ages of ca. 240 Ma, indicating short crustal m

o 600

residence time and significant contributions of m r e

juvenile addition. Likewise, the whole-rock εNd(t) and h

(87Sr/86Sr) ( stands for initial) cluster around ~+5 and n t 400 i i o c

r xm82 xm84 xm85 xm86 ~0.703570, respectively (Fig. 11C), further suggesting i z - 200 that the magma source of the gabbro-diorite com- n i - i

plex was derived from ~20% melting of the depleted T 5 10 15 20 25 mantle wedge (Fig. 11E). The compositions of horn- 0 Number of analyzed samples blendes fall into the magnesiohornblende field (Leake et al., 1997; Fig. 11D), typical of magmatic calcic amphiboles in I-type plutons, and therefore wt% MgO) and basaltic andesites (BAs, with <5 rocks (Brown et al., 1984). The studied plutonic suggest a subduction setting (Clemens and Wall, wt% MgO) (Crawford and Falloon, 1987; Sisson and rocks have low Nb contents (0.5–1.7 ppm) and low 1984). This conclusion is corroborated by the slightly Grove, 1993b). HABs and BAs are the dominant Rb/Zr ratios (0.09–0.46) (as shown in Table S5 [foot- negative Eu anomaly and the significantly negative igneous products in some modern intra-oceanic note 1]), consistent with rocks in primitive island anomalies of Nb, Ta, and Ti (Figs. 10A–10B), thereby arcs such as the western Aleutians (Kay and Kay, arcs. Furthermore, the Th/La ratios (0.13–0.24; implying that a hydrated mantle wedge is an ideal 1985; Schiano et al., 2004), the Barren arc (north- Table S5) are slightly higher than the ~0.12 values source for the intrusive complex. eastern Indian Ocean) (Luhr and Haldar, 2006), the found in intra-oceanic arc suites (Jolly et al., 2001), As shown in Figures 10A–10B, the plutonic rocks Lesser Antilles (Melekhova et al., 2017), the South but are obviously lower than the >0.45 values found show similar REE and trace element patterns to Sandwich Islands (Crawford and Falloon, 1987), as in the continental-margin Aeolian arc (Ellam et al., the western Aleutian high-alumina basalts and well as the Late Carboniferous Bogda arc, Chinese 1988). These Th/La ratios reflect values similar to andesites. These plutonic rocks have relatively high Tianshan (Xie et al., 2016). In addition, Nb contents those of typical of oceanic arcs, but with a little

Al2O3 and low MgO contents, therefore referred to and the Rb/Zr ratios are very useful indicators for contamination of source material by terrigenous as low-MgO high-alumina basalts (HABs, with <7 identifying the geological setting of the granitoid sediments (Jolly et al., 2001). Likewise, with Ce/Yb

ratios mainly clustering around 14.3–25.5 (Table S5), between our results and published data (Cai et al., have affinity with rocks in an intra-oceanic arc set- the studied plutonic rocks correspond to the low 2016; Wang et al., 2016b; Cao et al., 2018; Fang et al., ting (Ma et al., 2018b). These new findings support Ce/Yb array of Hawkesworth et al. (1993), typical of 2018). Before dispersal of the Pangea superconti- a possibility of northern provenance, whether an modern intra-oceanic arc volcanic rocks. In Figure nent during the late Carboniferous–early Permian, active continental margin arc or an intra-oceanic 11F, all data fall into fields close to those of modern all of the Indian and Australian blocks, as well as arc, which supplied some material to the sand- intra-oceanic arcs, but with some exceptions falling the Cimmeride continental blocks (e.g., Lhasa, Iran stones of the Langjiexue Group. into the Andes Southern Volcanic Zone (SVZ) field, terranes, etc), were integral constituents of the Detrital zircon microstructure (grain shape and revealing a slight involvement of subducted sedi- united Gondwanan landmass. In view of this, all surface texture) is a useful tool to help decipher ments into the magma source. We thus conclude of these continents should have the same or sim- polycyclicity and transport processes (Finzel, 2017; that the intrusive complex most likely represents ilar pre-Permian detrital zircon grains, as shown Gärtner et al., 2013; Vos et al., 2014). Most of 300– a component of a former intra-oceanic arc within by the Grenville (1100–750 Ma) and Pan-African 200 Ma detrital zircon grains in the sandstones of the Neotethys (Figs. 10C–10F). However, a continen- (650–500 Ma) zircon grains in the sandstones the Langjiexue Group in the Tethyan Himalaya fall tal arc affinity for the intrusive complex cannot be from Tethyan Himalaya (Fig. 8). Therefore, the zir- into the range of I (completely unrounded) to IV completely excluded. More geological investiga- con grains with ages >300 Ma may not be useful (poorly rounded) on the roundness scale (Fig. 12). In tions are needed in future work. for identifying a specific provenance in the Pangea contrast, most zircon grains with ages >300 Ma fall supercontinent. We thus focus on zircon grains with in the range of V (fairly rounded) to X (completely ages ranging between 300 and 200 Ma to better rounded), indicating a high degree of rounding. Provenance of Sandstones in the Langjiexue constrain the tectonic setting for the Langjiexue The surface microstructures of these detrital zircon Group Group in the Tethyan Himalaya. The youngest zir- grains are different between these two age popula- con U-Pb age peak of ca. 210 Ma approximates tions. For the zircon grains with ages >300 Ma, the A group of models has been proposed for the the maximum depositional age for the Langjiexue most prominent are preweathered and weathered tectonic setting for the Langjiexue Group (Cai et al., sandstones (Fig. 8). The salient age peaks of ca. surfaces. The preweathered surfaces are marked 2016; Cao et al., 2018; Dai et al., 2008; Fang et al., 210 and 252 Ma necessitate penecontemporaneous by minute pits and etching triggered by acid acting 2018; Li et al., 2010, 2016; Wang et al., 2016b; Webb magmatism in the adjacent region (Li et al., 2010, on the zircon surface (Fig. 13). The preweathered et al., 2012; Zhang et al., 2015a, 2017). Nowadays, 2016; Cai et al., 2016; Wang et al., 2016b; Fang et al., surfaces are then overprinted by weathered fea- the most popular model is a passive continental 2018; Meng et al., 2019b). tures (fractures or abrasion). Furthermore, other margin basin along the northern margin of the Previous studies have argued against an microstructures, including craters, conchoidal Gondwanan landmass (Cai et al., 2016; Wang intra-oceanic arc-derived or Lhasa-derived model fractures, V-shaped cracks, and fracture faces, are et al., 2016b; Cao et al., 2018; Fang et al., 2018). due to the lack of identified Early–Middle Triassic found on the Precambrian zircon grains. These fea- From our perspective, this model is acceptable and magmatic rocks within the Gangdese belt (Cai et al., tures are probably caused by mechanical grinding, reasonable, to some extent. However, one issue 2016; Wang et al., 2016b). However, this is no longer grain-to-grain impacts, or scraping. In contrast, the needs to be dealt with: the scarcity of nearby Tri- the case. Several exposures of Middle–Late Triassic 300–200 Ma zircon grains uniformly feature fresh assic magmatic belt or arc rocks in the northern magmatic assemblages have now been identified surfaces, occasionally with some abrasion features. Gondwanan landmass as the provenance for the in the Gangdese belt, southern Tibet (as shown in These microstructural observations further suggest remarkable Triassic zircon grains of the Langjiexue Fig. 2)—for example, the 237–211 Ma Changguo that the zircon grains of 300–200 Ma were probably Group. The model of a forearc basin along the and Beise volcanic rocks in southern Lhasa (Wang not subjected to long-distance transportation or active continental margin arc of the Lhasa terrane et al., 2016a, 2018), the ca. 220–215 Ma cumulate polycyclic recycled processes. Therefore, a near or along the intra-oceanic arc within the Neotethys appinite in the Quxu region (Meng et al., 2016b; source of 300–200 Ma detrital zircon grains was has been proposed by Li et al. (2010, 2016) and Ma et al., 2018b), the 230–225 Ma Daga granite necessary for the formation of the sandstones of Zhang et al. (2017). However, due to the paucity of (Meng et al., 2018), the 212–206 Kazi granite (Ma the Langjiexue Group in the Tethyan Himalaya. regional geological investigation in the Gangdese et al., 2017a), and the 203–201 Ma Cuijiu igneous However, some studies doubt the conclusion that belt and Tethyan Himalaya terrane, the location of complex (Xu et al., 2019). The Changguo and Beise there is some positive relationship between the the intra-oceanic arc rocks is still an open question. volcanic rocks, Daga granite, and Cuijiu igneous transporting distance and the zircon textural matu- Several salient age peaks are shown in the detri- complex are considered to have been formed in an rity (Garzanti, 2017); different transport systems, tal zircon U-Pb age spectra for the sandstones of active continental margin (Wang et al., 2016a, 2018; even from similar environments, do not have con- the Late Triassic Langjiexue Group in the Tethyan Meng et al., 2018; Xu et al., 2019), while the Quxu sistent length or duration (Zoleikhaei et al., 2016). Himalaya (Fig. 8). There is no obvious difference ca. 215 Ma cumulate appinitic suite is proposed to Consequently, future investigations beyond the

zircon textural maturity are needed to precisely submarine fans (Li et al., 2016; Zhang et al., 2017). the Neotethyan history (Lang et al., 2017; Ma et al., define the transport distance, systems, and prove- This submarine fan basin was near an intra-oce- 2018a; Wang et al., 2017; Yang et al., 2017; Zhu et al., nance of the sandstones in the Langjiexue Group. anic arc (Li et al., 2010, 2016). Taken together, our 2013). One primary question centers on the onset The sandstones of the Langjiexue Group are observations suggest that the Langjiexue Group was of subduction of the Neotethys, namely: When was dominated by fine to medium sand grains of feld- deposited not far from volcanic loci in an intra-oceanic an active continental margin initiated along the spar and lithic sandstone or greywackes. These arc, such as that represented by the 220–215 Ma (Ma southern margin of the Lhasa terrane? During the greywackes consist of angular to subangular et al., 2018b) and ca. 240 Ma intrusive complex of the last decade, ages of 237–170 Ma for calc-alkaline feldspar and quartz as well as lithic fragments (sed- present study in the Gangdese belt. magmatism in the Gangdese magmatic belt have imentary, volcanic, and metamorphic lithics, with The model of a forearc basin along the southern indicated that an active continental margin existed lithic volcanic fragments accounting for ~5%–20%), margin of the Lhasa terrane cannot be excluded along the southern margin of the Lhasa terrane. showing poorly to moderately sorted features of fully for the Langjiexue Group. Regarding this Examples include Middle Triassic–Jurassic volcanic low to moderate compositional and textural matu- model, however, several issues have to be dealt rocks of the Yeba, Bima, and Xiongcun Formations rity (Cai et al., 2016; Wang et al., 2016b; Zhang et al., with. First and foremost, some suture zones should (Kang et al., 2014; Ma et al., 2017b, 2018a; Wei et al., 2017; Meng et al., 2019b). This low to moderate be found between the Langjiexue Group and the 2017; Zhang et al., 2012; Zhu et al., 2008) and their maturity is likely related to short-distance transpor- Indian plate. So far, no such suture zone has been coeval plutonic equivalents (Chu et al., 2006; Ji tation. In addition, the lithic volcanic fragments and reported. Secondly, the Langjiexue Group occupies et al., 2009; Lang et al., 2017; Tafti et al., 2014; Wang subangular plagioclase confirm the existence of a very large area in the Himalayan region and con- et al., 2016a, 2017; Xu et al., 2017, 2019). These find- contemporaneous volcanism adjacent to the depo- tains abundant Precambrian zircon grains, which ings indicate that the southern margin of the Lhasa sition location. Although there is a consensus that requires enough provenance, especially Precam- terrane was subjected to intense Middle Triassic the Langjiexue Group was deposited along or adja- brian basement. Unfortunately, the southern Lhasa to Jurassic magmatism due to subduction of the cent to the northern passive continental margin of subterrane features juvenile crust without obvious Neotethyan oceanic lithosphere (Wu et al., 2010). the Gondwanan landmass (Cai et al., 2016; Wang fingerprints of the Precambrian basement (Ji et al., Li et al. (2010) proposed that the northward et al., 2016b; Cao et al., 2018; Fang et al., 2018), 2009). Furthermore, due to the occurrence of one or subduction of the Neotethyan oceanic lithosphere the detrital zircon U-Pb age histograms exhibit a two suture zones within the Lhasa terrane, we have beneath the Lhasa terrane triggered intense mag- salient age peak of ca. 210 Ma close to the depo- to admit that the Lhasa terrane was not intact during matism in the Lhasa terrane. These arc magmatic sition age of the strata. This feature indicates that the Mesozoic period (Zeng et al., 2018; Zhu et al., rocks probably provided a significant contribution the sediments of the Langjiexue Group were prob- 2018). In such a case, the northern Lhasa subterrane to the Upper Triassic Langjiexue Group flysch in ably deposited in a convergent basin, contrasting could not have provided plentiful material for the the Tethyan Himalaya. Within the Lhasa terrane, with a passive continental margin basin (Cawood formation of the Langjiexue Group. Last but not the Paleotethys (Sumdo Ocean), represented by et al., 2012). Furthermore, whole-rock geochem- least, when did the forearc basin rift away from the the Sumdo eclogite and peridotite, was considered istry, heavy minerals, and framework petrology Lhasa terrane and accrete with the Indian continent? to have been closed before 220–240 Ma (Li et al., consistently imply an orogenic provenance for the No obvious clues have been indicated by previous 2011; Yang et al., 2007). This observation precludes Langjiexue sandstones (Meng et al., 2019b). Taking research. Thus, the model of an intra-oceanic arc the possibility that the Middle Triassic–Jurassic all of these observations together, we interpret that within the Neotethys is more likely to have been magmatism in the Gangdese belt was induced the Langjiexue Group has multiple sources. This another possible source for the Langjiexue Group by southward subduction of the Sumdo oceanic conclusion is in good agreement with the obser- than a forearc basin along the southern margin of lithosphere. The Bangong-Nujiang eclogites are vations of Li et al. (2016): numerous Cr-spinels the Lhasa terrane. We tentatively prefer the inter- mainly distributed along the southern margin of found in the Langjiexue Group exhibit contents in pretation of an intra-oceanic arc system within the the South Qiangtang terrane, immediately north

Al2O3 of 5%–257%, in TiO2 of 0.01%–1.0%, in Cr2O3 Neotethys that supplied some material to the Lang- of the Bangong-Nujiang ophiolitic mélange zone, of 44%–100%, and in Cr# (Cr/(Cr + Al)) of 48%–95%, jiexue Group. suggesting a northerly subduction polarity (Zhang revealing several distinctive parent lithologies. et al., 2015c). Based on paleomagnetic results of How do we incorporate these seemingly para- Triassic rocks from the Lhasa terrane, Zhou et al. doxical tectonic regimes into one reasonable and Possible Triassic Intra-Oceanic Arcs within (2016) proposed that the Bangong-Nujiang Ocean feasible configuration? We contend that the Lang- the Neotethys separating the Lhasa and Qiangtang terranes jiexue Group was deposited adjacent to the passive opened up in the Early–Middle Triassic period and Gondwanan continental margin (Cai et al., 2016; Studies on the formation of the Gangdese continued to expand throughout the Triassic. If cor- Wang et al., 2016b), but associated with deep-ocean magmatic belt play a key role in understanding rect, this precludes southward subduction of the

Bangong-Nujiang oceanic slab. Given the above intra-oceanic arc setting (Ma et al., 2018b). These These observations necessitate two prerequisites: observations, the likelihood of a Middle Triassic observations, in conjunction with the voluminous one is the existence of an intra-oceanic arc, and the to Jurassic active continental margin in the south- Middle Triassic to Jurassic calc-alkaline rocks other is the free transportation of the intra-oceanic ern Lhasa terrane remains likely, with the catalyst hosted within the Gangdese belt, probably support arc material to the Langjiexue Group. being the northward subduction of the Neotethyan an intra-oceanic subduction system within the Neo- Recently, Huang et al. (2018) documented ca. oceanic slab. tethys. The modern western and northern Pacific 230 Ma bimodal intrusive rocks (diabase and gab- However, the Langjiexue Group has multi- are characterized by a number of intra-oceanic arcs, bro and monzonite) that intruded into the Nieru ple sources, rather than a single source (Li et al., such as the Ryukyu-Luzon, Izu-Bonin-Mariana, and Formation in the southern margin of the Langjiexue 2016). The evidence for this conclusion comes western Aleutian arc systems (Mishin et al., 2008; Group. This bimodal magmatism was most likely from the following: (1) bulk-rock Sr-Nd isotopes of Pearce et al., 2005; Singer et al., 2007; Stern et al., formed in a rifting-related backarc basin, triggered sandstones in the Langjiexue Group (epsilon Nd 2003), and may provide analogues to the Triassic by the southward subduction of the Neotethyan values between −7 and −3) reveal a more depleted Neotethyan framework. oceanic slab. We thus argue that an intra-oceanic source than traditional passive continental margin An intra-oceanic arc setting probably plays a southward subduction system occurred within the sediments (Dai et al., 2008); (2) numerous Cr-spi- pivotal role in the provenance of the Langjiexue Neotethys as early as the Middle Triassic, with an nels of the Langjiexue Group exhibit contents in sandstones in the Tethyan Himalaya (Li et al., 2016; accompanying intra-oceanic arc supplying some

Cr# of 48%–95%, in Cr2O3 of 44%–100%, in Al2O3 Zhang et al., 2017). A Late Triassic northward intra- sediments to the deposition of the Langjiexue

of 5%–257%, and in TiO2 of 0.01%–1.0%, indicat- oceanic subduction setting has been proposed Group under a submarine fan environment (Fig. 16). ing multiple parent lithologies (Li et al., 2016); by Li et al. (2010), in which the Langjiexue Group (3) a large percentage of older detrital zircon was deposited in a forearc basin. Recently, Cao grains (with ages of 3300–300 Ma) imply a prob- et al. (2018) delineated a Middle Triassic northward Opening Timing of the Neotethys able passive continental source (Cai et al., 2016; intra-oceanic subduction mosaic within the Neo- Meng et al., 2019b); (4) a remarkable age popula- tethys. As shown in Ce/Ce* versus Eu/Eu* plots The timing of the opening of the Neotethys tion of 260–200 Ma denotes an active convergent (where Ce and Eu are the chondrite-normalized remains an open question. Based on the late Car- margin (Wang et al., 2016b; Fang et al., 2018); and Ce and Eu concentrations, and Ce* and Eu* are boniferous–early Permian large igneous provinces (5) detrital zircon grains with ages between 260 the averages of the chondrite-normalized La and in the Indian and Australian blocks, as well as coeval and 200 Ma have a large range of zircon epsilon Pr concentrations, and Sm and Gd concentrations, extensive basalts and mafic dikes in southern Tibet, Hf values (−12 to +15) (Li et al., 2010; Wang et al., respectively), many of the 300–200 Ma detrital the Pangea supercontinent was suggested to have 2016b). These observations probably reveal the zircon grains of the Langjiexue sandstones have broken up during the early Permian, which triggered existence of a subduction-related arc as a source close affinity with those of the arc-type gabbro- the initial opening of the Neotethys (Chauvet et al., of the Langjiexue Group. diorite complex in the Gangdese belt (Fig. 15A), 2008; Garzanti et al., 1999; Lapierre et al., 2004; Sto- Combining published results with those from and a Th-Pb diagram (Fig. 15B) shows affinity to janovic et al., 2016; Veevers and Tewari, 1995). our study suggests that neither an active conti- the I-type granitoids, probably indicating a close The cause of subduction initiation is still an nental margin nor a passive continental margin is relationship with the subduction-related arc. Sim- enigmatic puzzle (Stern and Gerya, 2017). In some enough to explain the all sources for the Langjiexue ilarly, many younger detrital zircon grains fall into models, the cause is spontaneous nucleation due Group during the Triassic (Li et al., 2016). Therefore, the volcanic arc basalt field in a U-Er plot (Fig. 15C). to gravitational instability of oceanic lithosphere at it is worth considering whether an intra-oceanic arc Most of the young detrital zircon grains have very a transform or fracture zone or at a passive margin system existed within Neotethys. positive epsilon Hf isotopes (Fig. 15D), revealing (Stern and Gerya, 2017). The subduction initiation Globally, intra-oceanic arcs comprise ~40% of the depleted nature of their magma source. This at a transform or fracture zone was employed to the subduction margins of the Earth (Larter and conclusion is consistent with Li et al. (2016)’s obser- explain the Izu-Bonin-Mariana arc system (Hawkins Leat, 2003). Thus, we wonder: Did the Neotethyan vation: Cr-spinels of the Langjiexue sandstones et al., 1984; Stern and Bloomer, 1992). Subduction is

Ocean have scattered intra-oceanic arcs during the having relatively low TiO2 (0%–2%) and Al2O3 (5%– initiated because two lithospheres of different den- Triassic? New findings reveal the possible existence 30%), in concert with arc-basalt or mantle-peridotite sity are juxtaposed across a transform or fracture of a Middle Triassic intra-oceanic subduction sys- sources (Kamenetsky et al., 2001). To some extent, zone (lithospheric weakness), where old and dense tem in the western section of the Neotethys (Sayit these signatures provide robust constraints for the lithosphere would be depressed beneath the level et al., 2015, 2017; Tekin et al., 2016). Furthermore, conclusion that some of the 300–200 Ma detrital of the asthenosphere (Stern, 2004; Stern and Gerya, the 220–215 Ma cumulate appinite in the Quxu zircon grains of the Langjiexue sandstones in the 2017). Recent numerical modeling reveals that the region, southern Lhasa, was likely formed in an Tethyan Himalaya come from an intra-oceanic arc. denser lithosphere should be at least 30 m.y. older

1000 10000 Syenite pegmatites detrital zircon with age <300 Ma Nepheline syenite detrital zircon with age >300 Ma and syenite pegmatites magmatic zircon grains of I-type granitoids ca. 240 Ma gabbro-diorite 100 Lamproites Larvikites 1000 Syenites ) * m e p C p / 10 Carbonatites e

Mafic rocks h ( C T

100

1 1 Kimberlites 2 Granitoids: 1—aplites; leucogranites; 2—granites; 3 S-type granitoids 3—granodiorites and tonalites 0.1 10 0.001 0.01 0.1 Eu/Eu* 1 10 100 0.1 1 10 100 1000 Pb (ppm) 1000 20 VAB-type DM 15

) t

( 5

f H

)

m CHUR o

p 0 c

p 100

i Z U ( −5 WPB-type −10

detrital zircon grains of Langjiexue −15 Group in Tethyan Himalaya detrital zircon with age <300 Ma detrital zircon grains of Triassic N-MORB-type (compiled from Cao et al., 2018) −20 formations in the Lhasa terrane 10 0 500 1000 1500 2000 2500 3000 3500 4000 4500 10 100 Er (ppm) Zircon age (Ma)

Figure 15. Protolith discrimination of the detrital zircon grains of sandstones from the Langjiexue Group using trace elements. (A) Ce/Ce* versus Eu/Eu* (where Ce and Eu are the chondrite-normalized Ce and Eu concentrations, and Ce* and Eu* are the averages of the chondrite-normalized La and Pr concentrations, and Sm and Gd concentrations, respectively) (after Belousova et al., 2002). (B) Th versus Pb (after Wang et al., 2012). (C) U versus Er (after Schulz et al., 2006). (D) Detrital zircon epsilon Hf versus crystallization age. These zircon Hf isotopic data are compiled from Li et al. (2010, 2016) and Wang et al. (2016b), with most of the Permo-Triassic zircon grains falling into the dashed oval field, showing relatively positive values. Abbreviations: CHUR—chondritic uniform reservoir; DM—depleted mantle; N-MORB—normal mid-ocean-ridge basalt; VAB—volcanic arc basalt; WPB—within-plate basalt.

Paleogeographic framework Middle Triassic (ca. 240 Ma) TR Tectonic regime Bimodal intrusive rocks SW Passive continental margin Northern Tethyan sequence N Equator Nieru Formation? (Langjiexue Group) Intra-oceanic arc O e c o e te a th n y a n Africa LA Neotethys

L IA GI Greater India AU

Figure 16. Paleogeographic reconstruction of the Neotethyan realm during the Middle Triassic (ca. 240 Ma). (A) Intra-oceanic subduction arcs of the Neotethys and the location of the Langjiexue Group. Cartoon of paleogeographic framework of the Neotethyan realm is modified according to Cao et al. (2018), Domeier and Torsvik (2014), Kroner et al. (2016), Li et al. (2016), Stampfli and Borel (2002), Torsvik et al. (2012), Veevers (2004), Xiao et al. (2015), and Zhu et al. (2010). The Middle Triassic intra-oceanic subduction in the western part of the Neotethys is inspired by Sayit et al. (2015, 2017) and Tekin et al. (2016). Different colors of the terranes are used to highlight the differences between them, namely, continent, or intra-oceanic arc terrane, or oceanic basin sediments. The light green polygons are the proposed intra-oceanic arcs within the Neotethyan Ocean. Abbreviations: AU—Australian block; IA—Indian block; LA—Lhasa terrane; TR—Turkey terrane; GI—Greater India; L—Langjiexue Group. (B) Cartoon showing the proposed tectonic regime of the Langjiexue Group and the suspected intra-oceanic arc at ca. 240 Ma (revised from Li et al. [2010] and Cao et al. [2018]). The location of the Langjiexue Group is from Wang et al. (2016b), Cai et al. (2016), Li et al. (2010, 2016), Cao et al. (2018), Fang et al. (2018), and Meng et al. (2019b). The bimodal intrusive rocks are from Cao et al. (2018) and Huang et al. (2018).

than the younger lithosphere for initiation of an 2003; Ji et al., 2005), which is characterized by the are unconformably or disconformably overlain intra-oceanic subduction system (Zhou et al., 2018). admixture of warm- and cold-water faunas in the by earliest Permian coastal-marine conglomerate Based on our interpretation that the ca. 240 Ma Cimmerian province (including Turkey, Iran, South and sandstone in the Lhasa terrane (Zhang et al., gabbro-diorite complex in the present study formed Pamir, Himalaya, Lhasa, Qiangtang, Baoshan, and 2015b; Zhao et al., 2001). This major unconformity in an intra-oceanic arc setting, we suggest that the Sibumasu terranes) (Ueno, 2003; Zhang et al., 2013). probably marks the end of rifting of the Pangea opening of the Neotethys should have been earlier In the western Tethyan Himalaya, sandstones supercontinent, followed by the initial opening than ca. 270 Ma, in concert with the above-men- and conglomerates of lowermost Permian diam- of the Neotethys (Garzanti et al., 1996). This con- tioned published model. ictites rich in bryozoans and brachiopods were clusion is supported by extensive early–middle The earliest Permian Gondwanan glaciation deposited in a shallow marine setting. These clas- Permian rifting-related basalts and diabases in the is documented by diamictites containing palyno- tics paraconformably overlie lowermost Permian Tethyan Himalaya (Zeng et al., 2012; Zhu et al., 2010) flora in Oman, Pakistan, India, Lhasa, Australia, and diamictites in the Spiti Valley (northern India), and and recent paleogeographic reconstructions (Kro- South America, indicating that all of these regions disconformably overlie lower Carboniferous are- ner et al., 2016; Stampfli and Borel, 2002; Torsvik were in the same paleophytogeographic province naceous to carbonate sedimentary rocks in the et al., 2012; Xiao et al., 2015). (Angiolini et al., 2003; Zhang et al., 2015b). How- Pin Valley (northern India) (Garzanti et al., 1996). Taking into account all of the above observa- ever, the succession at the top of the diamictites This unconformity continues into the Lahaul and tions, we thus emphasize that the Neotethys likely is rich in wood logs, indicating glacial retreat and Zanskar regions (northern India). Further east in opened during the middle Permian. However, the concomitant encroachment of a shallow epicon- the Karakoram terrane, pre-Permian strata are geodynamic mechanism for the breaking apart of tinental sea. This is in good agreement with the unconformably overlain by a lowermost Permian the Lhasa terrane from the Gondwana landmass early–middle Permian transition from continen- sandstone (Zanchi and Gaetani, 2011). Similarly, and the subduction initiation of the Neotethys tal to shallow-marine sediments (Angiolini et al., upper Carboniferous mudstone and sandstone remain areas for future work.

■■ CONCLUSIONS realm. We are indebted to Scott Paterson for his invaluable com- Blundy, J.D., and Holland, T.J.B., 1990, Calcic amphibole equi- ments and language polishing on the first draft. Many fruitful libria and a new amphibole-plagioclase geothermometer: discussions with Weiqiang Ji, Guangwei Li, and Jiangang Wang Contributions to Mineralogy and Petrology, v. 104, p. 208– The Middle Triassic (ca. 240 Ma) gabbro-diorite helped to clarify some correlations between the magmatism 224, https://doi.org/10.1007/BF00306444. complex in the Gangdese magmatic belt, south- and sedimentology in southern Tibet. For technical support, Bouvier, A., Vervoort, J.D., and Patchett, P.J., 2008, The Lu-Hf we thank Anlin Ma for data analysis, Peixi Zheng and Zheng and Sm-Nd isotopic composition of CHUR: Constraints ern Tibet, exhibits depleted whole-rock and mineral Wang in zircon dating, Bin Shi in zircon CL and SEM analysis, from unequilibrated chondrites and implications for the isotopic signatures. The plutonic rocks are domi- and Liang Li in whole-rock Sr-Nd analysis. This research was bulk composition of terrestrial planets: Earth and Plane- nated by magmatic hornblende and hornblende co-supported by the Second Comprehensive Scientific Investi- tary Science Letters, v. 273, p. 48–57, https://doi.org/10.1016 phenocrysts with plagioclases occurring as an inter- gation into Qinghai-Tibet Plateau (SQ2019QZKK2703), National /j.epsl.2008.06.010. Natural Science Foundation of China (41502198), Research Grant Boynton, W.V., 1984, Geochemistry of the rare earth elements: stitial phase, which, in conjunction with the lower of Chinese Academy of Geological Sciences (J1703), Fund of Meteorite studies, in Henderson, P., ed., Rare Earth Element crystallization temperature (~720 °C), indicates that China Scholarship Council (201809110055), Postdoctoral Scien- Geochemistry: Amsterdam, Elsevier, p. 63–114, https://doi the magma source was wet. The geochemical char- tific Foundation of China (2016T90122), and Geological Survey .org/10.1016/B978-0-444-42148-7.50008-3. of China (DD20190060). We are indebted to Christopher Spencer, Brown, G.C., Thorpe, R.S., and Webb, P.C., 1984, The geochemical acteristics of the plutonic rocks indicate that the Ryan Leary, and an anonymous reviewer for their thorough characteristics of granitoids in contrasting arcs and com- gabbro-diorite complex was probably formed in and constructive comments that significantly improved this ments on magma sources: Journal of the Geological Society, a subduction-related arc setting, either an active manuscript. We would like to thank Geosphere Science Editor v. 141, p. 413–426, https://doi .org /10 .1144 /gsjgs .141 .3 .0413. Shanaka de Silva for guidance and editorial handling of this Cai, F.L., Ding, L., Laskowski, A.K., Kapp, P., Wang, H.Q., Xu, Q., continental margin arc of the Lhasa terrane or an manuscript and Managing Editor Gina Harlow for kindness and and Zhang, L.Y., 2016, Late Triassic paleogeographic recon- intra-oceanic arc within the Neotethys. efforts on this paper. 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