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Article

Petrogenesis of the Late Jurassic Granodiorite and Its Implications for Tectonomagmatic Evolution in the Nuocang District, Western Gangdeses

by
Junsheng Jiang
1,2,
Shunbao Gao
3,
Bo Bao
1,*,
Peng Hu
1,
Xin Chen
3,
Kan Tian
4,
Pengcheng Huang
3,
Jian Huang
3 and
Xinran Guo
5
1
Wuhan Center, China Geological Survey (Central South China Innovation Center for Geosciences), Wuhan 430205, China
2
Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring (Central South University), Ministry of Education, Changsha 410012, China
3
Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China
4
Department of Urban and Rural Planning and Architectural Engineering, Guiyang University, Guiyang 550005, China
5
The Geological Science Education Center of Guangdong, Guangzhou 510000, China
*
Author to whom correspondence should be addressed.
Minerals 2022, 12(8), 1058; https://doi.org/10.3390/min12081058
Submission received: 2 August 2022 / Revised: 13 August 2022 / Accepted: 15 August 2022 / Published: 21 August 2022
(This article belongs to the Special Issue Tectono-Magmatic Evolution and Metallogeny of Tethyan Orogenic Belts)
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Abstract

:
The Gangdese magmatic rocks of the southern Lhasa terrane, are generally thought to be an important window to witness the formation and evolution of the Neo-Tethys oceanic opening, subduction, and closure, and India-Eurasian continental collision. We investigated a new occurrence of granodiorite in the Nuocang district of western Gangdese, southern Lhasa terrane, and conducted a series of analyses on their petrology, chronology, and geochemistry. The Nuocang granodiorites have the zircon U-Pb ages of 151–154 Ma, which suggest that Late Jurassic granitoids are present in the western Gangdese of southern Lhasa terrane. They are relatively high in SiO2, Al2O3, low K2O, Na2O, and Sr/Y ratios, enrichments of LILE and LREE, and depletion of HFSE, with the positive correlation between Rb and Th, and negative correlations between SiO2 and P2O5, Rb, and Y, showing the features of I-type granites. The relatively high (87Sr/86Sr)i values from 0.712231 to 0.712619, low εNd(t) values from −9.56 to −8.99, together with the negative εHf(t) values from −10.8 to −5.0 (mean value −8.9) suggested that the Nuocang granodiorites probably sourced from the partial melting of the ancient Lhasa terrane, with parts of mantle materials involving in. Combined with the previous geochronology and geochemical data of Mesozoic magmas in the Gangdese belt, as well as the Late Jurassic granodiorite, in this paper, we propose that the Nuocang granodiorites formed in a continental margin arc environment triggered by the northward subduction of Neo−Tethys oceanic crust.

1. Introduction

The Lhasa terrane, as an important part of the Qinghai-Tibet Plateau, is distributed between the Bangong-Nujiang and Yarlung-Zangbo suture zones (Figure 1). Since the Mesozoic period, it has undergone a complex geological process, including the southward subduction of the Bangong-Nujiang oceanic lithosphere, the collision of the Lhasa and Qiangtang terrane, the northward subduction of the Neo-Tethys Ocean, and the continental collision of India and Eurasia, which formed a unique geological landscape in the world [1,2,3,4]. The Gangdese magmatic belt within the southern Lhasa terrane was mainly composed of large areas of Gangdese batholith and comagmatic volcanic rocks. So far, numerous researchers have conducted a series of detailed investigations on the petrogenesis and the tectonic evolution of the Cretaceous-Tertiary intrusions within the Gangdese magmatic belt and arrived at a consensus that the Neo-Tethys oceanic crust has subducted northward in Cretaceous, and take the continental collision of India and Eurasia in Paleocene [5,6,7,8,9]. While there are only a few pre-Cretaceous magmatic rocks occurring in the Gangdese belt [10,11,12,13,14], their petrogenesis and tectonic setting are still under debate. Some researchers argued that the pre-Cretaceous magmatic rocks in the Gangdese belt can be correlated with the southward subduction of the Bangong-Nujiang oceanic crust [4,15,16], while others suggested that they are the products of the northward subduction of Neo-Tethys oceanic crust [11,14,17,18]. Most of these pre-Cretaceous magmatic rocks discovered in the Gangdese belt show affinity with the growth and reworking of the juvenile crust [1,5,17,19]. In recent years, the ancient Lhasa crust has also been identified in some areas within the Gangdese belt of southern Lhasa terrane [20,21]. Thus, whether the magmatic source of pre-Cretaceous magmatic rocks in the Gangdese belt contains the ancient Lhasa crust components is still unclear.
In this study, we first discovered the Late Jurassic granodiorite in the Nuocang district of western Gangdese, southern Lhasa terrane. We present U-Pb zircon ages, Sr-Nd-Hf isotopic composition, as well as mineralogical and whole-rock geochemical data on the Nuocang Jurassic granodiorites in order to reveal the petrogenesis, tectonic evolution, and geodynamic model during Late Jurassic in western Gangdese of southern Lhasa terrane.

2. Geological Background

The Tibet plateau, the highest plateau in the world, is composed of the Songpan-Ganze, Qangtang, Lhasa, and Tethyan Himalaya terranes bounded by the Jinsha, Bangong-Nujiang, and Yarlung-Zangbo suture zones from north to south (Figure 1a, [22]). The Lhasa Terrane, separated by the Shiquanhe-Namtso Mélange Zone (SNMZ) and the Luobadu-Milashan Fault (LMF), is divided into three parts of northern, central, and southern terranes (Figure 1b; [4]). The southern and northern Lhasa terranes are generally thought to be the accreting terranes with juvenile crust, which were triggered by the northward subduction of the Neo-Tethys oceanic crust and the northward subduction of the Bangong-Nujiang oceanic crust, whereas the central Lhasa is composed of Archean-Proterozoic Nyainqentanglha basement rocks [4].
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Figure 1. (a) Simplified structural map of China; (b) tectonic framework of the Himalayan-Tibetan plateau; (c) Simplified geologic map of the Lhasa terrane showing the major tectonic subdivisions, distribution of Mid-Late Jurassic granitoids [4,5,7,11,16,23,24,25,26] and position of the study area [4]. IYZSZ—Indus-Yarlung Zangbo Suture Zone; LMF—Luobadui-Milashan Fault; GLZCF−Gar-Lunggar−ZhariNam Tso−Comai Fault; SNMZ—Shiquan River-Nam Tso Mélange Zone; BNSZ—Bangong-Nujiang Suture Zone; NL—northern Lhasa terrane; CL—central Lhasa terrane; SL—southern Lhasa terrane; NC—Nuocang granodiorite in this study; XDL—Xiadingle intrusion; CQ—Cuoqin intrusion; JB—Jiangba intrusion; YH—Yanhu rhyolite; XB—Xiongba intrusion; XRC—Xurucuo intrusion; WB—Wenbu intrusion; SMG—Songmuguo intrusion; YXL—Yangxionglel intrusion; XTM—Xietongmen intrusion; TB—Tanabai intrusion; WB—Wobu intrusion; DZQ—Dazhuqu intrusion; NM—Nymo intrusion; DZ—Dazi intrusion; ZD—Zedong intrusion.
Figure 1. (a) Simplified structural map of China; (b) tectonic framework of the Himalayan-Tibetan plateau; (c) Simplified geologic map of the Lhasa terrane showing the major tectonic subdivisions, distribution of Mid-Late Jurassic granitoids [4,5,7,11,16,23,24,25,26] and position of the study area [4]. IYZSZ—Indus-Yarlung Zangbo Suture Zone; LMF—Luobadui-Milashan Fault; GLZCF−Gar-Lunggar−ZhariNam Tso−Comai Fault; SNMZ—Shiquan River-Nam Tso Mélange Zone; BNSZ—Bangong-Nujiang Suture Zone; NL—northern Lhasa terrane; CL—central Lhasa terrane; SL—southern Lhasa terrane; NC—Nuocang granodiorite in this study; XDL—Xiadingle intrusion; CQ—Cuoqin intrusion; JB—Jiangba intrusion; YH—Yanhu rhyolite; XB—Xiongba intrusion; XRC—Xurucuo intrusion; WB—Wenbu intrusion; SMG—Songmuguo intrusion; YXL—Yangxionglel intrusion; XTM—Xietongmen intrusion; TB—Tanabai intrusion; WB—Wobu intrusion; DZQ—Dazhuqu intrusion; NM—Nymo intrusion; DZ—Dazi intrusion; ZD—Zedong intrusion.
Minerals 12 01058 g001
Magmatic activity widely developed in the southern Lhasa terrane, which consists of the famous Gangdese magmatic belt. It is dominantly comprised of voluminous Late Cretaceous-Tertiary Gangdese batholith (103–80 Ma; 65–40 Ma; [5]), Paleocene−Eocene Linzizong volcanic rocks (65–45 Ma; [27,28]), and Oligocene-Miocene granitoids (33–13 Ma; [29,30]). Additionally, the Early Mesozoic granitoids (205–152 Ma; [31]), and the volcanic rocks of the Early Jurassic Yeba Formation and the Late Jurassic-Early Cretaceous Sangri Group [12,32], are sporadically distributed in the southern Lhasa terrane. The central Lhasa terrane is generally thought to represent a microcontinent that experienced multi-metamorphic events during the Neoproterozoic. The overlying strata include Carboniferous-Permian and Upper Jurassic−Lower Cretaceous sedimentary rocks, with large numbers of acidic volcanic rocks and Late Triassic-early Cretaceous granitoids that are distributed near the Luobadui-Milashan Fault. The northern Lhasa subterrane is characterized by juvenile crust, with the overlying Middle Triassic to Cretaceous sedimentary rocks and an abundance of early Cretaceous medium-K calc-alkaline arc volcanic rocks and granitoids (Figure 1c).
As described above, the Mid-Late Jurassic intrusions predominantly developed in the central terrane (e.g., Xurucuo, Xiongba, Jiangba, Yangxiongle, Xiadingle, Wenbu, and Cuoqin areas; [7,16,23,33,34] and northern Lhasa terrane (e.g., Chayu, Ranwu, Sama, Bange areas; [1,34,35]). The Nuocang granodiorite in this paper is distributed in the western part of the Gangdese magmatic belt, which is firstly described in the southern Lhasa terrane. The Nuocang granodiorite was traditionally thought to be formed in the Eocene and coexisted with the Lizizong volcanic rocks of the Pana Formation [36]. In this study, we provided U-Pb ages of zircons from the Nuocang granodiorite samples and determined it was the product of Late Jurassic magmatism. It is exposed on the northern side of the Nuocang deposit, with an irregular-elliptical shape and an area of about 0.5 km2. They intruded on the siltstone and sandstone of the early Permian Angjie Formation (Figure 2).

3. Sampling and Petrography

Six samples of granodiorites were collected from the Nuocang district. The granodiorites, occurring as the stock in this district, are grey-white, with a fine-grained granitic texture (Figure 3a,b). They are composed of plagioclase (55 vol%, 0.5–4 mm), K-feldspar (7 vol%, 0.5–2 mm), quartz (18 vol%, 0.3–2 mm), amphibole (12 vol%, 0.5–1.5 mm), and biotite (7 vol%, 0.5–1.5 mm), with small amounts of zircon, monazite, apatite, and titanite (Figure 3c).

4. Analytical Methods

4.1. Zircon U–Pb Dating and Lu-Hf Isotopic Analyses

Before the U-Pb dating, zircon grains were polished for the purpose of showing the crystal’s shape, and their internal structure was studied by transmitted and reflected light microscopy and cathodoluminescence. Zircon grains of the Nuocang granodiorites (NCNYT3 and NCNYT5) are colorless with few inclusions and exhibit oscillatory zoning (Figure 4). U-Pb dating and trace element analyses of zircon were simultaneously conducted on the LA-ICP-MS at the Wuhan Sample Solution Analytical Technology Co., Ltd. Laser sampling was performed on a GeoLasPro laser ablation system (Coherent, Santa Clara, CA, USA), and ion-signal intensities were used by an Agilent 7700e ICP-MS instrument (Agilent, Santa Clara, USA) to acquire. Sample mounts were carried by Helium, and Argon was mixed by a T-connector before entering the ICP. Zircon 91,500 and glass NIST610 were used as external standards for U-Pb dating and trace element calibration, respectively. ICPMSDataCal (10.1, Yongsheng Liu, Wuhan, China) was used to calculate for trace element analysis and U-Pb dating [37]. The age diagrams and their calculations were used by the ISOPLOT [38].
Hf isotopic analyses were conducted on a Neptune Plus MC-ICP-MS in combination with a Geolas HD excimer ArF laser ablation system in the Wuhan Sample Solution Analytical Technology Co., Ltd. The 179Hf/177Hf and 173Yb/171Yb ratios normalized to 0.7325 and 1.132685 [39] in order to calculate the mass bias of Hf (βHf) and Yb (βYb). 176Lu/175Lu = 0.02656 and 176Yb/173Yb = 0.79639 were used to calculate the instrumental mass bias of Hf and Yb isotope ratios, respectively.

4.2. Whole-Rock Geochemical Analysis

The Nuocang granodiorite samples selected for major and trace elemental analyses were conducted at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan. The granodiorites were powdered into less than 200 mesh by a tungsten carbide ball mill, and finally, weighing ~0.5 g was selected for pulping. Major elements were analyzed by XRF, with an analytical uncertainty of <5%. Trace elements were measured with an Agilent 7500a ICP-MS. The analytical precision is better than 5% for elements with concentrations >10 ppm and less than 10% for those <10 ppm. The detailed analytical procedures are stated in [37].

4.3. Sr-Nd Isotopes

Sr-Nd isotopic measurements were conducted on the isotope dilution thermal ionization MS (TIMS) with a Triton Ti TIMS in the Zhongnan Mineral Resources Supervision and Test Center for Geoanalysis, Wuhan Center, China Geological Survey. The mixture of HF, HNO3, and HClO4 in Teflon bombs was used to dissolve the samples for Sr and Nd isotopic analyses. 86Sr/88Sr of 0.1194 and 146Nd/144Nd of 0.7219 were generally taken as the mass fractionation corrections [40].

5. Results

5.1. Zircon U-Pb Ages and Lu-Hf Isotopes

The length of zircon grains of Nuocnag granodiorites varies from 40 μm to 120 μm, with the 4:1 to 1:1 length-to-width ratios. The majority of the zircon grains in this study show clear oscillatory zoning, with no inherited core and metamorphic rim. Uranium contents of 542−1952 ppm, Th contents of 243−1369 ppm, with Th/U ratios of 0.37−0.70, suggesting a magmatic origin [41]. Zircons of NCNYT3 (18 spots) and NCNYT5 (20 spots) samples have 206Pb/238U ages ranging from 150.8 to 162.8 Ma and from 140.9 to 152.4 Ma, with weighted mean ages of 154.3 ± 1.3 Ma (2σ), and 150.9 ± 1.3 Ma (2σ), respectively (Figure 4, Table 1).
Ten Lu-Hf isotopic analyses were conducted on the NCNYT3 sample, with the 176Lu/177Hf ratios of 0.001113–0.002631 and 176Hf/177Hf ratios of 0.282109–0.282560, yielding εHf(t) values from −10.8 to −5.0 (Table 2).

5.2. Major and Trace Elements

Major and trace element data of Nuocang granodiorites are listed in Table 3. They have narrow ranges of SiO2 (64.37–65.02 wt%), low K2O (1.58–2.09 wt%) and Na2O (2.13–2.26 wt%), moderate MgO (1.73–1.77 wt%), and high Al2O3 (16.15–16.39 wt%), indicating the medium K calc-alkaline and peraluminous characteristics (Figure 5a–c). The rare earth elements composition in this study is less variable, with REEs of 97.0–111.0, LREE/HREE of 6.12–7.19, (La/Yb)N of 6.5–8.3, and δEu values of 0.77–0.81 (average = 0.79). The REE pattern revealed the enrichment in LREEs and depletion in HREEs (Figure 6a; [41]). The Nuocang granodiorite samples are enriched in the Rb, K, Zr, Hf, U, and Th but depleted in Sr, Ba, Nb, Ti, and P (Figure 6b). Sr/Y ratios of 9.7–11.4, with Y contents of 16.0– 20.9 ppm, indicate typical arc magmatic rocks [42].

5.3. Sr-Nd Isotopes

Sr-Nd isotopic results of Nuocang granodiorites are shown in Table 4. They have nonradiogenic or negative isotope compositions, with the 87Sr/86Sr ratios ranging from 0.714343 to 0.714578 and 143Nd/144Nd ratios ranging from 0.512066 to 0.512098, corresponding to (87Sr/86Sr)i ratios of 0.712231–0.712619 and εNd(t) values from −9.56 to −8.99. Their two-stage Nd model ages (T2DM) range from 1.45 to 1.49 Ga.

6. Discussion

6.1. The Mid-Late Jurassic Magmatism in the Gangdese of Southern Lhasa Terrane

The previous research on the magmatic rocks of Lhasa terrane suggests that the Mid-Late Jurassic magmatism dominantly occurred in the central (e.g., Yangxiongle intrusion, 142.0 Ma, [23]; Wenbu intrusion, 154.5 Ma, Xie Guogang et al., unpublished data; Xiadingle intrusion, 153.1 Ma, Liu Dengzhong et al., unpublished data; Xiongba intrusion, 149.0 Ma; and Jiangba intrusion, 170 Ma; [7]; Cuoqin granite, 152.0 Ma; and Yanhu rhyolite, 146.0 Ma, [4]; Xurucuo, 155.1 and 155.7 Ma, [16]) and northern part of Lhasa terrane (e.g., Nierong intrusion, 175 Ma, [47]; Darucuo andesite, 165.0 Ma, [15]). However, the Gangdese Batholith and volcanic rocks in the Gangdese of the southern Lhasa terrane predominantly consist of Paleocene-Eocene, Miocene, and Cretaceous magmatic rocks [9,27]. Recent work has identified the presence of the Mid-Late Jurassic magmatic rocks in the eastern Gangdese of southern Lhasa terrane, such as the Xietongmen (177 Ma, [26]), Tangbai (180 Ma, [11]), Wobu (166 Ma, [26]), Dazhuqu (174 Ma, [5]), and Nymo intrusions (178 Ma, [9,27]). In addition, the intrusions that occurred in the Zedong area were formed in the Late Jurassic (160–155 Ma; [26]), which possibly represent a slice of magmatic arc developed on the southern margin of the Lhasa Terrane [26]; Figure 1c). Correspondingly, the volcanic rocks of the Sangri Formation formed in the same period widely developed in the southern Lhasa terrane, with a wide age range of 195–137 Ma [12]. In this study, we identified the Late Jurassic intrusion in the Nuocang district for the first time, which expands the distribution of the Mid-Late Jurassic magmatism in the southern Lhasa terrane.

6.2. Petrogenesis of Nuocang Granitoid Rocks

Traditionally, four types of granite (I, S, M, and A) have been divided based on mineralogical and geochemical characteristics [48]. A-type granitoids were first excluded since the Nuocang granodiorites lack anhydrous minerals and depletion of high field-strength elements (Figure 6b), with relatively low magmatic crystallization temperatures of 697–804°C (the Zr-saturation temperature of 697–733 °C [49], and the Ap-saturation temperature ranging from 795 to 804 °C [50]; A-type granite is usually higher than 850 °C [51]). The Nuocang granodiorites, together with other Jurassic granitoids in the Lhasa terrane, show features of calc-alkaline to high-K calc-alkaline. The granodiorites have high Al2O3 (16.13–16.39), with the A/CNK values of 1.07– 1.16, showing similarities with S-type granite [52]. However, the positive correlation between Rb and Th and negative correlation between Rb and Y (Figure 7a,b) are similar to these I-type granitoids in the central Lhasa terrane [7,16,52]. Moreover, The Nuocang granodiorites and other Jurassic granite in the Lhasa terrane totally fall in the I-type granite scope, indicating that they should be I-type granite rather than S-type (Figure 7c,d).
Three formation mechanisms for the I-type granite have been proposed: (1) extensive fractional crystallization of mantle-derived magmas, probably accompanied by crustal assimilation [54,55], (2) partial melting of crustal materials [56], and (3) magma mixing mechanism of the mantle- and crust-derived magmas [57,58]. Magmas generated by fractional crystallization of mantle-derived parental magmas generally show relatively high εNd(t) and εHf(t) values and develop the mafic to felsic magmatic rocks in the surroundings [54,55]. The Nuocang granodiorites show lower εNd(t) values (from −9.56 to −8.99) and εHf(t) values (from −10.8 to −5.0), with no mafic intrusions in the surrounding area. Moreover, the variation of La/Nd values versus SiO2 (Figure 8a) and linear relation on the La/Sm versus La plot (Figure 8b) correspond to the partial melting process.
The lower Sm/Yb (mean 1.73) and La/Sm ratios (mean 5.97) of Nuocang granodiorites were plotted into the range of pyroxene-dominated residual mineralogy in the discrimination diagram (Figure 8c), suggesting a relatively low-pressure condition and shallow magma source [59]. Hence, the partial melting of crustal materials possibly contributed to the magma source of Nuocang granodiorites.
Minerals 12 01058 g008 550
Figure 8. (a) La/Nb vs. SiO2 diagram; (b) La/Sm vs. La diagram; (c) La/Sm vs. Sm/Yb diagram [60]. Data are from the same source as Figure 5.
Figure 8. (a) La/Nb vs. SiO2 diagram; (b) La/Sm vs. La diagram; (c) La/Sm vs. Sm/Yb diagram [60]. Data are from the same source as Figure 5.
Minerals 12 01058 g008
Isotopically, the Nuocang granodiorites show negative Hf isotope values (from −10.8 to −5.0), and old TDMc values (from 1.52 to 1.88 Ga) of the igneous rocks, plot into the area of Middle Jurassic granitoids summarized by researchers, suggesting the Archean-Proterozoic Nyainqentanglha basement rocks of ancient Lhasa crust may exist in the Nuocang district (Figure 9a). This viewpoint also has been identified by the Late Cretaceous granite porphyry nearby (Hf isotope values: from −22.0 to −6.0; [21]). Similarly, the Nuocang granodiorites display remarkably high (87Sr/86Sr)i (from 0.712231 to 0.712619), low εNd(t) (from −9.56 to −8.99) values, and old TDM2(Nd) ages (from 1.45 to 1.49 Ga; Figure 9b), strongly suggest that the ancient Lhasa crust exists in the Nuocang district. This supports the interpretation suggesting that there exists an ancient Lhasa crust in western Gangdese (83–87° E) and southern Lhasa terrane by [20].
Notably, the εHf(t) values of Nuocang granodiorites show a heterogeneous feature (vary from −10.8 to −5.0), indicating a magma mixing with mantle-derived sourced compositions [51]. The Sr-Nd isotopic data plotted along the mixing lines of the mantle-derived and the ancient Lhasa crustal materials (Figure 9b) in the 87Sr/86Sr(i) vs. εNd(t) diagram, together with the Mg# (38–39), lower (La/Yb)N (6.52–8.32) and (Gd/Yb)N (1.40–1.54) ratios, also revealing the involving input of mantle melt. Consequently, we proposed that the Nuocang granodiorites originated from the partial melting of ancient Lhasa crust, with the contribution of mantle-derived melt.

6.3. Implication for the Jurassic Neo-Tethys Geodynamic Model in the Gangdese of Southern Lhasa Terrane

As widely accepted that the Neo-Tethys Oceanic opening started from Carboniferous-Early Permian time [61,62], and the Lhasa terrane separated from Gondwanaland before Triassic [63]. Subsequently, the crustal accretion and tectonic-magmatic evolution of Lhasa terrane from Triassic to Cretaceous was triggered by the southward subduction of Bangong-Nujiang oceanic crust and northward subduction of Neo-Tethys oceanic crust [64,65]. However, the Mesozoic tectonic-magmatic evolutional model in the Gangdese of southern Lhasa terrane has always been debated. These competing models include (1) the southward subduction of the Bangong-Nujiang oceanic crust that formed in a back-arc extensional setting [4,16,64,66] and (2) the northward subduction of Neo-Tethys oceanic crust [1,5,10,12,14] that represents an Andean-type continental margin. Previous researchers proposed that the initial Neo-Tethys subduction began in the early Cretaceous based on that the dating of remnant ophiolites in the Yarlung Zangbo suture was Late Jurassic [67]. Thus, some scholars proposed that the Gangdese magmatism formed in a back-arc environment during the Mid-Late Triassic-Jurassic [64].
However, extensive Mid-Late Triassic–Jurassic magmas, such as the volcanic rocks of Yeba Formation and Sangri Group and the coeval intrusions, have been identified in the Gangdese of southern Lhasa terrane, which formed a continuous E–W-trending liner magmatic belt adjacent to the Yarlung Zangbo suture zone [1,11,12,17,66]. These Mid-Late Triassic-Jurassic magmatic rocks are featured by the subducted magmas that formed in a continental arc setting, showing the affinity with the northward subduction of the Neo-Tethys ocean [10,14,17]. The Nuocang granodiorites show enrichment in LREE and LILEs, and depletion in HREE and HFSEs, which are typical of arc-related magmatic rocks [68]. Additionally, on the trace element discrimination diagram, all the samples plot within the arc field (Figure 10a,b) [69]. The Th/Ta ratios of Nuocang granodiorites are greater than 6 (mean value = 10.75), which suggests an active continental margin setting (Figure 10c).
Therefore, we proposed that Nuocang granodiorites formed in an active continental margin setting associated with the subduction of Neo-Tethys oceanic crust during the Late Jurassic. During the Late Jurassic, the northward subduction of Neo-Tethys oceanic crust induced the partial melting of a depleted mantle wedge that had been metasomatized by subduction-related fluids and generated the initial basaltic magmas. With the upwelling of basalt magmas, it underplated and produced significant thermal perturbation to cause the partial melting of the overlying ancient Lhasa crust in the Nuocang district. Partial melting of ancient Lhasa crust, mixing with the mantle materials, was responsible for the Nuocang granodiorites (Figure 11a,b).

7. Conclusions

(1)
Zircon U-Pb dating of two Nuocang granodiorites shows weighted mean ages of 151–154 Ma, firstly revealing that the Late Jurassic granitoids also occurred in the western Gangdese of southern Lhasa terrane.
(2)
Major and trace elements and Sr-Nd-Hf isotopic data indicate that the Nuocang granodiorites were sourced from the partial melting of ancient Lhasa crust, with the contribution of mantle-derived materials involved during their generation.
(3)
The Nuocang granodiorites possibly formed in an active continental margin setting. They record the late Jurassic magmatism in western Gangdese, which were the product of the northward subduction of the Neo-Tethys oceanic crust beneath the Lhasa terrane.

Author Contributions

J.J., B.B., and S.G. conceived this contribution and conducted all field and analytical work, assisted by P.H. (Peng Hu), X.C., K.T., P.H. (Pengcheng Hu), J.H., and X.G. The manuscript was written by J.J., B.B., and S.G., with contributions from P.H. (Peng Hu), X.C., K.T., P.H. (Pengcheng Hu), J.H., and X.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research is supported by the Open Research Fund Program (2021YSJS09) of the Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring (Central South University), Ministry of Education, the China Geological Survey (DD20221802, DD20201153, DD20190443, DD20190159-33, DD20160027-2), National Key Research and Development Program of China (No. 2016YFC0600300), and Commonwealth Project from the Ministry of Land and Resources (201511015).

Data Availability Statement

Not Applicable.

Acknowledgments

Staff at Wuhan Sample Solution Analytical Technology Co., Ltd., Zhongnan Mineral Resources Supervision and Test Center for Geoanalysis, Wuhan Center, China Geological Survey, and the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan are gratefully acknowledged for assistance with the instrument operation. We thank the reviewers for the journal Minerals.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Figure 2. Simplified geological map of the Nuocang district, southern Lhasa terrane (modified after [36]).
Figure 2. Simplified geological map of the Nuocang district, southern Lhasa terrane (modified after [36]).
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Figure 3. Outcrop photograph (a), typical hand specimen photographs (b), and microphotographs (c) of Nuocang granodiorite. Amp—amphibole; Pl—plagioclase; Qtz—quartz.
Figure 3. Outcrop photograph (a), typical hand specimen photographs (b), and microphotographs (c) of Nuocang granodiorite. Amp—amphibole; Pl—plagioclase; Qtz—quartz.
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Figure 4. LA-ICP-MS U-Pb concordia diagrams and weighted mean ages for the Nuocang granodiorite samples NCNYT3 (a) and NCNYT5 (b). The insets show typical CL images of zircon grains with 238U/206Pb ages. The white scale bar in the CL images is 100 μm.
Figure 4. LA-ICP-MS U-Pb concordia diagrams and weighted mean ages for the Nuocang granodiorite samples NCNYT3 (a) and NCNYT5 (b). The insets show typical CL images of zircon grains with 238U/206Pb ages. The white scale bar in the CL images is 100 μm.
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Figure 5. (a) K2O + Na2O vs. SiO2 diagram [43]; (b) K2O vs. SiO2 diagram [44]; (c) A/NK vs. A/CNK diagram [45]; (d) Sr/Y vs. Y diagram [45]. Data sources: Nuocang granodiorites from this study; Xurucuo granitoids [16]; Yangxiongle granitoids [23]; Yanhu and Cuoqin granitoids [4].
Figure 5. (a) K2O + Na2O vs. SiO2 diagram [43]; (b) K2O vs. SiO2 diagram [44]; (c) A/NK vs. A/CNK diagram [45]; (d) Sr/Y vs. Y diagram [45]. Data sources: Nuocang granodiorites from this study; Xurucuo granitoids [16]; Yangxiongle granitoids [23]; Yanhu and Cuoqin granitoids [4].
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Figure 6. Chondrite normalized REE distribution diagram (a) and primitive mantle normalized trace element spider diagram (b) [46] for Nuocang granodiorites. Data are from the same source as Figure 5.
Figure 6. Chondrite normalized REE distribution diagram (a) and primitive mantle normalized trace element spider diagram (b) [46] for Nuocang granodiorites. Data are from the same source as Figure 5.
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Figure 7. (a) P2O5 vs. SiO2 diagram; (b) Th vs. Rb diagram; (c) Y vs. Rb diagram; (d) TFeO/MgO vs. Zr+Nb+Ce+Y diagram [53].
Figure 7. (a) P2O5 vs. SiO2 diagram; (b) Th vs. Rb diagram; (c) Y vs. Rb diagram; (d) TFeO/MgO vs. Zr+Nb+Ce+Y diagram [53].
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Figure 9. (a) εHf(t) vs. U-Pb age diagram of zircons from the Nuocang granodiorites; (b) 87Sr/86Sr(i) vs. εNd(t) for the Nuocang granodiorites. CL- the Hf values of granitoids in the central Lhasa terrane; SL- the Hf values of granitoids in the southern Lhasa terrane; The Yarlung Zangbo Mid-ocean ridge basalts (MORB) is from [4]: εNd(t) = +7.0, Nd = 1.2 ppm; The mantle-derived basaltic magmas (represented by the Dazi basalt; [59]): (87Sr/86Sr)i = 0.7043, εNd(t) = +5.2, Sr = 291 ppm, Nd = 9.6 ppm; Ancient crustal (represented by a strongly peraluminous granites from the central Lhasa terrane; [4]): (87Sr/86Sr)i = 0.7402, εNd(t) = −15.4, Sr = 131 ppm, Nd = 43.40 ppm. The central Lhasa terrane is from [4,20].
Figure 9. (a) εHf(t) vs. U-Pb age diagram of zircons from the Nuocang granodiorites; (b) 87Sr/86Sr(i) vs. εNd(t) for the Nuocang granodiorites. CL- the Hf values of granitoids in the central Lhasa terrane; SL- the Hf values of granitoids in the southern Lhasa terrane; The Yarlung Zangbo Mid-ocean ridge basalts (MORB) is from [4]: εNd(t) = +7.0, Nd = 1.2 ppm; The mantle-derived basaltic magmas (represented by the Dazi basalt; [59]): (87Sr/86Sr)i = 0.7043, εNd(t) = +5.2, Sr = 291 ppm, Nd = 9.6 ppm; Ancient crustal (represented by a strongly peraluminous granites from the central Lhasa terrane; [4]): (87Sr/86Sr)i = 0.7402, εNd(t) = −15.4, Sr = 131 ppm, Nd = 43.40 ppm. The central Lhasa terrane is from [4,20].
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Figure 10. (a) Rb vs. Y + Nb [69]; (b) Y vs. Zr; (c) Th/Ta vs. Y [70]. Data are from the same source as Figure 5.
Figure 10. (a) Rb vs. Y + Nb [69]; (b) Y vs. Zr; (c) Th/Ta vs. Y [70]. Data are from the same source as Figure 5.
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Figure 11. (a) Cartoon model of multiple terranes and island arcs in Late Jurassic, Lhasa Terrane; (b) cartoon showing dynamic model of the Neo–Tethys ocean subduction and formation of Nuocang granodiorites during the Late Jurassic, southern Lhasa terrane.
Figure 11. (a) Cartoon model of multiple terranes and island arcs in Late Jurassic, Lhasa Terrane; (b) cartoon showing dynamic model of the Neo–Tethys ocean subduction and formation of Nuocang granodiorites during the Late Jurassic, southern Lhasa terrane.
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Table
Table 1. Zircon LA-ICP-MS U-Pb dating result of Nuocang granodiorite.
Table 1. Zircon LA-ICP-MS U-Pb dating result of Nuocang granodiorite.
Sample No.Spot No.ThUTh/U207Pb/206Pb207Pb/235U206Pb/238U208Pb/232Th207Pb/235U206Pb/238U
ppmppmRatio1σRatio1σRatio1σRatio1σAge (Ma)1σAge (Ma)1σ
NCN-YT3NCN-YT3-01258.60 656.15 0.39 0.04950.00210.16050.00670.02370.00040.04950.0021151.15.878640586150.82.234167613
NCN-YT3-02243.45 651.98 0.37 0.04960.00190.16300.00610.02400.00030.04960.0019153.45.310753674152.72.187709109
NCN-YT3-03306.15 733.49 0.42 0.04930.00200.16300.00640.02410.00030.04930.0020153.35.592835286153.72.020804024
NCN-YT3-041368.64 1951.75 0.70 0.04970.00140.16500.00440.02420.00030.04970.0014155.03.804911278154.01.802496621
NCN-YT3-05488.89 1042.87 0.47 0.05030.00180.16520.00590.02380.00030.05030.0018155.25.169909843151.91.755247831
NCN-YT3-06381.17 885.83 0.43 0.05100.00200.16970.00650.02440.00040.05100.0020159.15.641800081155.42.206600206
NCN-YT3-07370.03 787.74 0.47 0.04950.00210.16070.00640.02380.00030.04950.0021151.35.622669297151.52.064477891
NCN-YT3-08443.84 1007.72 0.44 0.04960.00220.16470.00710.02450.00040.04960.0022154.86.161094504156.02.208237054
NCN-YT3-09259.36 542.46 0.48 0.05060.00260.16480.00750.02410.00040.05060.0026154.96.543424564153.42.331191049
NCN-YT3-11368.28 787.98 0.47 0.05010.00240.16680.00740.02440.00030.05010.0024156.76.442724526155.42.201532889
NCN-YT3-13895.79 1526.41 0.59 0.04800.00160.16070.00560.02420.00030.04800.0016151.44.914979083154.31.916805401
NCN-YT3-14254.43 583.03 0.44 0.05120.00200.16990.00680.02410.00030.05120.0020159.35.899657767153.72.078019071
NCN-YT3-151080.34 1639.74 0.66 0.04970.00140.16680.00470.02430.00030.04970.0014156.74.120652056155.01.742173735
NCN-YT3-16458.25 844.57 0.54 0.04990.00220.16310.00660.02380.00030.04990.0022153.45.751187756151.52.031091286
NCN-YT3-18426.78 972.84 0.44 0.05000.00200.16590.00600.02420.00030.05000.0020155.95.253441493154.41.844105038
NCN-YT3-19815.99 1246.69 0.65 0.05060.00170.16940.00590.02420.00030.05060.0017158.95.086706758154.21.871192917
NCN-YT3-21869.70 1444.21 0.60 0.05010.00200.17600.00680.02560.00030.05010.0020164.65.856328883162.82.090853914
NCN-YT3-23335.23 748.48 0.45 0.05000.00250.16740.00800.02470.00030.05000.0025157.16.935594206157.22.037402207
NCN-YT5NCN-YT5-01279.33 690.59 0.40 0.050170.003220.156570.009010.023200.000350.050170.00322147.77.915054148147.92.206005581
NCN-YT5-03403.97 817.81 0.49 0.052260.002260.171360.007120.024110.000310.052260.00226160.66.175466477153.61.962492186
NCN-YT5-04312.18 692.27 0.45 0.049340.002170.167680.007120.024900.000350.049340.00217157.46.1947696158.62.209765425
NCN-YT5-05348.26 840.72 0.41 0.049590.002360.156930.006930.023440.000320.049590.00236148.06.083826678149.42.001305011
NCN-YT5-06456.80 1013.02 0.45 0.049360.002070.160670.006370.023960.000340.049360.00207151.35.571610871152.72.126633394
NCN-YT5-07295.09 748.58 0.39 0.049900.002300.160080.007410.023440.000350.049900.00230150.86.488635488149.32.204384254
NCN-YT5-08416.44 907.85 0.46 0.050840.002900.161300.007700.023690.000340.050840.00290151.86.736998527150.92.166674393
NCN-YT5-09575.48 1050.06 0.55 0.049300.002020.154570.006340.022800.000290.049300.00202145.95.579278375145.31.825797051
NCN-YT5-10261.94 662.29 0.40 0.052480.002350.173720.007270.024360.000370.052480.00235162.66.293287554155.22.342009655
NCN-YT5-11346.37 769.47 0.45 0.049230.002260.156810.006960.023390.000330.049230.00226147.96.109559884149.02.055673905
NCN-YT5-12346.64 895.59 0.39 0.049210.001880.162280.006080.023900.000340.049210.00188152.75.310899944152.22.119258927
NCN-YT5-13307.73 820.19 0.38 0.049520.002050.156680.006220.023120.000300.049520.00205147.85.464077401147.41.887466747
NCN-YT5-14340.90 761.79 0.45 0.052280.002270.170670.007260.023860.000320.052280.00227160.06.296839221152.02.019284285
NCN-YT5-17328.08 682.89 0.48 0.049440.002220.158000.006830.023450.000320.049440.00222149.05.987072839149.42.004429465
NCN-YT5-18278.66 659.22 0.42 0.049970.002330.159490.007260.023520.000330.049970.00233150.36.357828411149.92.107184755
NCN-YT5-19293.62 644.80 0.46 0.050590.002420.162030.007300.023760.000310.050590.00242152.56.379606547151.41.941662278
NCN-YT5-20476.04 859.00 0.55 0.049820.002110.161320.006620.023840.000310.049820.00211151.95.79314197151.91.925953949
NCN-YT5-22531.88 1060.19 0.50 0.049700.001880.162780.006010.023990.000290.049700.00188153.15.245983248152.81.81947249
NCN-YT5-24444.32 849.10 0.52 0.049730.002020.158610.006120.023460.000290.049730.00202149.55.366659227149.51.837156843
NCN-YT5-25458.12 1046.00 0.44 0.049280.001710.162150.005600.023920.000280.049280.00171152.64.892766152152.41.793306592
Table
Table 2. Hf isotope analysis result of Nuocang granodiorite.
Table 2. Hf isotope analysis result of Nuocang granodiorite.
Spot No.176Hf/177Hf1σ176Lu/177Hf1σ176Yb/177Hf1σageεHf(t)T2DM (Ma)
NCN-YT5-050.282405 0.000023 0.001591 0.000006 0.060679 0.004838 149 −9.86 1823
NCN-YT5-060.282429 0.000021 0.001375 0.000007 0.025070 0.000139 153 −8.93 1768
NCN-YT5-080.282425 0.000029 0.001222 0.000014 0.027063 0.000261 151 −9.07 1775
NCN-YT5-090.282427 0.000027 0.001708 0.000021 0.054536 0.000378 145 −9.18 1778
NCN-YT5-110.282377 0.000025 0.001399 0.000007 0.018755 0.000416 149 −10.84 1885
NCN-YT5-120.282421 0.000029 0.001428 0.000017 0.084494 0.002635 152 −9.21 1785
NCN-YT5-130.282385 0.000030 0.001571 0.000006 0.029334 0.000315 147 −10.63 1870
NCN-YT5-140.282439 0.000028 0.001016 0.000004 0.037709 0.000561 152 −8.54 1743
NCN-YT5-190.282439 0.000036 0.001348 0.000006 0.023860 0.000727 151 −8.60 1746
NCN-YT5-220.282460 0.000038 0.001383 0.000015 0.028526 0.000683 153 −7.83 1699
NCN-YT5-240.282541 0.000038 0.001368 0.000020 0.031809 0.000406 150 −5.04 1520
Table
Table 3. Major and trace element analysis result of Nuocang granodiorite (major elements: wt%; trace elements: ppm).
Table 3. Major and trace element analysis result of Nuocang granodiorite (major elements: wt%; trace elements: ppm).
Sample No.NCN-YT1NCN-YT2NCN-YT3NCN-YT4NCN-YT5NCN-YT6
SiO265.02 64.94 64.48 64.37 64.87 64.68
Al2O316.23 16.13 16.21 16.39 16.22 16.15
Fe2O30.93 0.92 1.02 0.77 0.94 0.78
FeO4.17 4.15 4.12 4.33 4.23 4.27
CaO4.95 4.91 4.91 5.39 4.48 4.90
MgO1.75 1.73 1.76 1.77 1.77 1.74
K2O1.58 1.91 2.09 1.77 1.99 2.07
Na2O2.14 2.12 2.21 2.17 2.26 2.13
TiO20.56 0.55 0.58 0.58 0.58 0.55
P2O50.10 0.10 0.09 0.10 0.09 0.09
MnO0.09 0.09 0.09 0.09 0.09 0.08
LOI1.81 1.79 1.78 1.59 1.81 1.88
Total99.34 99.34 99.34 99.32 99.33 99.33
TFe2O35.57 5.53 5.59 5.58 5.64 5.53
Mg#0.38 0.38 0.38 0.39 0.38 0.38
A/CNK1.14 1.11 1.09 1.07 1.16 1.10
A/NK3.10 2.90 2.75 2.99 2.76 2.81
Rb54.98 74.27 78.66 63.06 74.14 76.69
Ba275.48 292.48 316.57 289.71 282.99 297.35
Th9.51 11.07 9.12 8.89 9.04 9.15
U1.26 1.23 1.19 0.95 1.17 1.20
Nb7.23 8.14 7.12 7.19 7.34 6.72
Sr202.11 203.01 222.51 196.14 220.56 212.21
Zr129.56 125.34 127.99 133.67 131.42 127.50
Hf3.23 3.23 3.06 3.57 3.57 3.40
La23.36 22.60 19.45 21.42 20.17 23.44
Ce43.57 42.84 37.46 40.90 39.57 44.18
Pr5.58 5.32 4.84 5.19 4.87 5.66
Nd19.37 18.48 17.19 18.14 17.34 19.51
Sm3.86 3.53 3.53 3.62 3.60 3.72
Eu1.01 0.93 0.94 0.98 0.92 0.94
Gd3.75 3.71 3.63 3.79 3.62 3.77
Tb0.62 0.61 0.61 0.61 0.60 0.62
Dy3.73 3.66 3.69 3.68 3.62 3.70
Ho0.78 0.75 0.75 0.74 0.73 0.73
Er2.20 2.14 2.16 2.06 2.03 2.09
Tm0.34 0.33 0.33 0.32 0.33 0.32
Yb2.16 2.18 2.14 2.07 2.09 2.02
Lu0.34 0.33 0.33 0.31 0.32 0.30
Y20.92 19.49 19.79 19.80 19.40 19.66
ΣREE110.66 107.41 97.03 103.83 99.81 111.01
LREE96.75 93.70 83.40 90.24 86.47 97.45
HREE13.91 13.71 13.63 13.58 13.34 13.55
LREE/HREE6.95 6.83 6.12 6.64 6.48 7.19
LaN/YbN7.77 7.43 6.52 7.42 6.93 8.32
δEu0.81 0.79 0.81 0.81 0.78 0.77
δCe0.94 0.96 0.95 0.95 0.98 0.94
Zr-saturation
T (°C)avrg		719711709709722711
Ap-saturation
T (°C)		804803797795802799
Table
Table 4. Sr–Nd isotopic data for the Nuocang granodiorites.
Table 4. Sr–Nd isotopic data for the Nuocang granodiorites.
Sample No.Age (Ma)87Rb/86Sr87Sr/86Sr±2σ(87Sr/86Sr)i147Sm/144Nd143Nd/144Nd±2σ(143Nd/144Nd)iεNd(t)T2DM(Ma)
NCN-YT11540.7875800.714343 0.0000060.7126190.12030 0.5120840.0000020.51196278−19.311468
NCN-YT21541.0591800.714550 0.0000080.7122310.11544 0.5120660.0000090.511949671−9.561486
NCN-YT31541.0235000.714524 0.0000080.7122830.12399 0.5120980.0000050.511973061−9.111454
NCN-YT41510.9308300.714518 0.0000120.7124800.12047 0.5120970.0000030.511975611−9.061451
NCN-YT51510.9731900.7144830.0000090.7123530.12554 0.5120980.0000070.5119715−9.141456
NCN-YT61511.0462900.7145780.0000070.7122870.11523 0.5120950.0000050.511978886−8.991446
Note: εNd (t) = [(143Nd/144Nd) sample(t)/(143Nd/144Nd) CHUR(t) − 1] × 10−4; TDM2 = 1/λ × {1 + [(143Nd/144Nd)sample − ((147Sm/144Nd)sample − (147Sm/144Nd)crust) × (eλt − 1) − (143Nd/144Nd)DM]/((147Sm/144Nd)crust − (147Sm/144Nd)DM)}. (147Sm/144Nd)CHUR = 0.1967, (143Nd/144Nd)CHUR = 0.512638, (147Sm/144Nd)DM = 0.2137, (143Nd/144Nd)DM = 0.51315, (147Sm/144Nd)crust = 0.1012.
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Jiang, J.; Gao, S.; Bao, B.; Hu, P.; Chen, X.; Tian, K.; Huang, P.; Huang, J.; Guo, X. Petrogenesis of the Late Jurassic Granodiorite and Its Implications for Tectonomagmatic Evolution in the Nuocang District, Western Gangdeses. Minerals 2022, 12, 1058. https://doi.org/10.3390/min12081058

AMA Style

Jiang J, Gao S, Bao B, Hu P, Chen X, Tian K, Huang P, Huang J, Guo X. Petrogenesis of the Late Jurassic Granodiorite and Its Implications for Tectonomagmatic Evolution in the Nuocang District, Western Gangdeses. Minerals. 2022; 12(8):1058. https://doi.org/10.3390/min12081058

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Jiang, Junsheng, Shunbao Gao, Bo Bao, Peng Hu, Xin Chen, Kan Tian, Pengcheng Huang, Jian Huang, and Xinran Guo. 2022. "Petrogenesis of the Late Jurassic Granodiorite and Its Implications for Tectonomagmatic Evolution in the Nuocang District, Western Gangdeses" Minerals 12, no. 8: 1058. https://doi.org/10.3390/min12081058

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