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Article

Genesis of Early Cretaceous Magmatism in the Western Gangdese Belt, Southern Tibet: Implications for Neo-Tethyan Oceanic Slab Subduction

by
Jiqing Lin
1,2,
Ke Gao
3,*,
Zizheng Wang
4,*,
Zhongbiao Xu
1 and
Yongping Pan
1
1
School of Geographical Sciences and Tourism, Zhaotong University, Zhaotong 657000, China
2
Jinsha River Research Center, Zhaotong 657000, China
3
Zijin Mining Group Southwest Geological Exploration Co., Ltd., Chengdu 610059, China
4
Chengdu Center, China Geological Survey, Chengdu 610081, China
*
Authors to whom correspondence should be addressed.
Minerals 2025, 15(11), 1143; https://doi.org/10.3390/min15111143 (registering DOI)
Submission received: 22 September 2025 / Revised: 22 October 2025 / Accepted: 23 October 2025 / Published: 30 October 2025
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Abstract

Research on the Mesozoic–Cenozoic magmatism and the tectonic framework within the Lhasa Terrane is voluminous. However, the sparse documentation of Early Cretaceous magmatism in this region fuels ongoing debate over the prevailing tectonic regime during this time period (i.e., normal subduction vs. flat subduction). The present study investigates the Luerma pyroxenite and Boyun granitoid in the Western Lhasa Terrane through zircon U-Pb dating, whole-rock geochemistry, mineral chemistry, and Sr-Nd-Hf isotopes. The findings date the formation of Luerma pyroxenite at 115 Ma and Boyun granites at 113 Ma to the Early Cretaceous period (115–113 Ma). SiO2 content of pyroxenite is relatively low (34.27–44.16 wt.%), characterized by an enrichment in large ion lithophile elements (LILEs), light rare earth elements (LREEs), and a depletion in heavy field strength elements (HSFEs), indicative of a metasomatic origin. The εNd (t) and εHf (t) values of the Early Cretaceous ultrabasic rocks range from +2.1 to +2.7 and −0.8 to +10.1, respectively, suggesting their derivation from an enriched mantle source with asthenospheric material incorporation. The Early Cretaceous granodiorites and their mafic enclaves belong to the high-K calc-alkaline series, and show enrichment in LILEs (e.g., Rb, Ba, U, and Th) and depletion in HFSEs (e.g., Nb, Ta, Ti, and Zr). The acidic rocks and their developed mafic enclaves exhibit the geochemical characteristics of trace elements found in island arc magmas. Their εNd (t) values are (−6.0–−5.0), while their εHf (t) values are (−11.7–−1.8); the MMEs εHf (t) values are (−4.1–+0.9). In summary, the Early Cretaceous pyroxenite in the Gangdese Belt originated from a combination of asthenospheric and enriched lithospheric mantle melts, while the granitoids were generated by partial melting of the mantle wedge, a process driven by metasomatism resulting from the slab-derived fluids. At the same time, heat from upwelling mantle-derived melts induced the partial melting of lower crustal materials, leading to the formation of acidic magmas through varying degrees of mixing with basic magmas. This study suggests that Early Cretaceous magmatic activity occurred within a northward subduction setting, characterized by the rotation and fragmentation of the Neo-Tethys oceanic crust.

1. Introduction

The Qinghai–Tibet Plateau, known as the third pole, is the world’s highest plateau and features the largest, most prominent orogenic belt. Its complex evolutionary history within the Tethys realm showcases multiple landmasses, multiple island arc frameworks, and dynamic processes of multiple ocean basins, multiple subductions, multiple collisions, and multiple orogenies. Bounded by the Jinsha Jiang Suture Zone to the north and by the Bangong Co-Nujiang Suture Zone and Yarlung Tsangpo Suture Zone to the south, the plateau comprises several geological terranes, including Songpan-Ganzi Terrane, Qiangtang Terrane, Lhasa Terrane, and Himalaya Terrane [1,2] (Figure 1a).
The Lhasa Terrane, also referred to as the Gangdese tectonic magmatic belt, occupies a critical position in the southern region of the Qinghai–Tibetan Plateau [4]. This region is distinguished by an abundance of Mesozoic–Cenozoic magmatic rocks, which account for approximately 80% of its total magmatic rock composition [4]. Characterized by significant crustal growth and reworking [5], these magmatic rocks are pivotal for understanding the region’s geological history. The varied and complex magmatic rock types in the Gangdese orogenic belt, along with their temporal and spatial migration patterns, provide key insights into the formation processes of the Gangdese Belt and the tectonic evolution of the Tethys Ocean. This includes critical phases such as the ocean-continental transition, collision orogeny, and intracontinental convergence [6]. Recent advancements in research techniques and analytical testing have led to considerable breakthroughs in understanding Cenozoic magmatism within the Gangdese Belt. This magmatism resulted from Indo-Eurasian plate collision and subsequent orogenic processes. However, Mesozoic magmatic rocks, particularly those of Early Cretaceous age, are generally scarce in the southern Gangdese Belt. This gap has led to diverse interpretations of the area’s tectonic history. According to previous studies, Late Jurassic to Late Cretaceous magmatism (150–65 Ma) [7,8,9,10,11] can be broadly categorized into two stages: Early Cretaceous (150–109 Ma) and Late Cretaceous (109–65 Ma). To date, investigations into Late Jurassic to Early Cretaceous magmatism (150–130 Ma) in the southern Gangdese region have been limited; volcanic rocks from this period (137–130 Ma) only identified in the Sangri Group, specifically in the Liqiongda and Mamen areas [7,8]. The Liqiongda area exhibits a bimodal volcanic rock assemblage, which includes basalt, basaltic andesite, and rhyolite, while the Mamen area is characterized by adakitic andesites [7]. Further research on the late Early Cretaceous (130–109 Ma) have only been shed some light on the lithographical characteristics of the Gangdese Belt, revealing more about its complex geological history. Wang et al. (2013) [9] identified Early Cretaceous diorite (122 Ma) in Nang County, characterized by low SiO2 and high Al2O3 and MgO contents, along with an enrichment in Na, LREEs, and depletion in HREEs. The presence of clinopyroxene and magmatic epidote indicates that the parental magma of these rocks was rich in water [9]. Despite the scarcity of granitic batholith from this period, a large number of 130–80 Ma detrital zircons have been found in the sediments of the Xigaze Basin. These zircons, notable for their high 176Hf/177Hf ratios, positive εHf (t) values, and isotopic characteristics similar to those of the Gangdese batholith, imply a primary derivation from the Gangdese batholith. This suggests that large-scale magmatic activity may have occurred in the Gangdese batholith (130–109 Ma), leading to the erosion of Early Cretaceous magmatic rocks during subsequent uplift phases [10]. The absence of granitic batholith outcrops from this period and early research findings suggest that the tectonic setting of the Neo-Tethys Ocean during the Early Cretaceous period of the Neo-Tethys Ocean was dominated by flat subduction or low angle subduction [8]. Contrasting earlier interpretations of flat subduction, the discovery of water-rich diorite masses in Nang Country and the widespread distribution of detrital zircons distributed in the Xigaze Basin during this period, suggest a scenario of normal high-angle subduction for the Neo-Tethys Ocean, as opposed to flat subduction [9]. The mechanisms triggering oceanic subduction include arc-continent and continent–continent collisions, and the collision between the Lhasa Terrane and the Qiangtang Terrane during the Late Jurassic–Early Cretaceous [11].
The present study aims to shed light on the Early Cretaceous tectono-magmatic processes in the Gangdese Belt, and to provide constraints for these processes, by focusing on the Luerma pyroxenite and Boyun granitoids in combination with existing data on Early Cretaceous magmatic rocks in the Gangdese Belt. In order to provide constraints for the Early Cretaceous tectono-magmatic processes in the Gangdese Belt. Additionally, the study intends to discuss the genesis of these magmatic rocks and their tectonic evolution characteristics in the Gangdese Belt.

2. Regional Geology

The Gangdese Belt has undergone extensive development as a result of internal east–west structures and secondary faults, as documented in several studies [4,12,13,14]. Zhu et al. (2011) [15] refined the subdivision of the Gangdese Belt (Lhasa Terrane) into three distinct regions: the Southern Gangdese Belt, the Central Gangdese Belt, and the Northern Gangdese Belt, from south to north. This classification was based on variations in the terrane’s cover layer and basement, delineated by the Shiquan River–Namtso ophiolitic melanomy belt (SNMZ) and the Luoba Dui-Milashan fault (LMF). The focus of this study lies within the western section of the Gangdese Belt (Figure 1b). Geologically, the structural orientation within this region follows an NWW-SEE trend, while the predominant lithological units consist of Carboniferous and Permian sedimentary rocks, encompassing the Lower Carboniferous Yongzhu Formation (C1y) and Upper Carboniferous to Lower Permian Laga Formation (C2P1l).

3. Petrographic Characteristics

The Boyun pluton is located in the transition area between the Southern Gangdese Belt and the Central Gangdese Belt. The region has experienced significant magmatic activity from the Early Cretaceous to the Neogene. A feature of this activity is the Boyun pluton, of Early Cretaceous age. This pluton covers an extensive area of about 43 km2, and is irregularly distributed across the landscape. It intrudes into the clastic rock strata of the Lower Carboniferous Yongzhu Formation (C1y), and is partially overlain by Quaternary. Numerous gabbro diorite enclaves are present within this pluton. These enclaves vary widely in size, ranging from several centimeters to tens of centimeters in diameter, and are predominantly elliptical. The contact boundary between these diorite enclaves and host rocks can be either complete or transitional, accompanied by the development of light-colored feldspathic halos within their contact zone. Diorite enclaves display K-feldspar megacrysts and quartz porphyry (Figure 1b).
The present study, a selection of ten host granodiorites and four MMES samples were collected for analysis. The granodiorites (K1γδ) exhibit shades of gray, light gray, and locally light greenish-gray coloration, characterized by a medium-fine granitic structure as well as massive structure (Figure 2a,b). Its mineral composition primarily consists of plagioclase (55–60%), quartz (20–25%), and a minor amount of K-feldspar (8–15%). Additionally, secondary minerals such as magnetite, apatite, zircon, and titanite are present with occasional occurrences of epidote (Figure 2c,d).
The MMEs have a distinct composition and are predominantly made up of plagioclase, amphibole, a small amount of pyroxene, quartz, and biotite. Among them, plagioclase constitutes approximately 65%, accompanied by amphibole (20–30%), quartz (1–5%), and clinopyroxene (<5%). Additionally, these enclaves contain minor quantities of biotite, K-feldspar, apatite, and opaque minerals (<2%) (Figure 2c). Acicular apatite can be seen in the MMEs, indicative of rapid cooling and quenching (Figure 2e,f).
The pyroxenite veins in the Luerma area of the southern Gangdese Belt have a limited extent, with their total surface exposure not exceeding 2 m2. These veins are primarily located within late Triassic gabbro fractures (Figure 3a,b). The pyroxenite exhibits a hypidiomorphic granular texture, and displays blocky and vein-like structures. Compositionally, it is largely made up of clinopyroxene (70–75%), amphibole (5–7%), biotite (~2–3%), chlorite (~1%), and magnetite (15–18%) (Figure 3c). The clinopyroxene grains are mainly 0.2 to 1 mm in size, showing a hypidiomorphic morphology with short columnar and granular shapes. Amphibole occurs as green or brown-green elongated columns, measuring generally less than 0.2 mm in length, displaying evident other—hemidiomorphic columnar forms without polychromatic characteristics. The ferrous minerals occur as black opaque grains with other—hemidiomorphic granular textures.

4. Analytical Methods

4.1. Isotope Geochronology

Zircon U-Pb isotope and trace element analyses were performed using LA-ICP-MS at Beijing Zhongke Mine Research and Testing Technology Co., Ltd. (Beijing, China). The analyses utilized an Agilent 7500 ICP-MS (Agilent Technologies Inc., Santa Clara, CA, USA) paired with an ESI NWR laser denudation system. A 193 nm laser was used to denudate the zircon particles. The specific experimental process is shown in [16], data processing was performed using the ICP-MS Data Cal software (V9.5) [17].

4.2. Whole-Rock Major and Trace Element Analysis

The whole-rock major elements were determined by fusing X-ray fluorescence spectrometry (XRF) at Beijing Zhongke Mining Research and Testing Technology Co., Ltd. The instrument used was the Shimadzu XRF-1800 (Shimadzu Corporation, Kyoto, Japan), All samples were cleaned, ground to pass a 200-mesh sieve, and dried in an oven. A 1 g aliquot of each sample was weighed into a crucible and baked in a muffle furnace at 1000 °C for 1 h to determine the loss on ignition (LOI). Subsequently, 5.85 g of a mixed flux (lithium borate, lithium metaborate, and lithium fluoride) and 0.65 g of the sample were accurately weighed, placed into a platinum crucible, and mixed uniformly. After adding 2–3 drops of saturated ammonium bromide, the mixture was fused in a high-frequency fusion machine to prepare a homogeneous glass disk. Major element analysis was performed using a Shimadzu XRF-1800 X-ray fluorescence spectrometer, with an analytical precision better than 2%. The determination of trace element content within the whole rock samples was conducted using an Agilent 7500. The main steps are as follows: (1) Accurately weigh 50 mg of 200-mesh powder sample and put it into a cleaned and air-dried Teflon digestion tank for sample digestion. (2) Add 1 mL of HF, heat to 150 °C, and evaporate to dryness to remove Si from the sample. (3) Add 1.0 mL of HF and 0.6 mL of HNO3, place the Teflon digestion tank in a steel sleeve, heat to 190 °C, and maintain the temperature for more than 96 h. Then, open the digestion tank and evaporate the solution to a milky droplet state to remove excess HF from the sample. (4) Add 1 mL of concentrated nitric acid and heat to evaporate to a milky droplet state (repeat this process twice). (5) Continue to add 1.6 mL of HNO3, and keep it warm at 140 °C for 3–5 h. After cooling, transfer the sample solution to a 50mL centrifuge tube. Finally, add 1 mL of 500 ng/g Rh internal standard to the centrifuge tube and dilute to the 50 mL mark. (6) After shaking evenly, send it to an inductively coupled plasma mass spectrometer (Agilent 7500 ICP–MS) for testing. The analysis precision of most elements is better than 5%, and the analysis precision of elements with lower concentrations is within 5–10%.

4.3. Zircon Lu-Hf Isotope

The Lu-Hf isotope analyses carried out is laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Incorporating a laser denudation multi-receiver inductively coupled plasma mass spectrometer. The laser sampling system of this setup is an NWR 213 nm solid-state laser (New Wave Research Inc., Fremont, CA, USA). The analysis itself was conducted using a multi-receiver plasma mass spectrometer (NEPTUNE plus) (Thermo Fisher Scientific Inc., Waltham, MA, USA). The process began with the careful selection of appropriate zircon sections, guided by analysis of three distinct types of zircon imagery. The NWR 213 nm solid laser was used to denude the zircon. The parameters set for the laser ablation included a spot beam diameter of approximately 55 μm, an energy density of 7–8 J/cm2, and a frequency of 10 Hz. Following laser denudation, the material was fed into a Neptune Plus (MC-ICPMS) with high purity He as carrier gas, and the receiver configuration was the same as that for the solution injection.

4.4. Whole-Rock Sr-Nd Isotopes

The Sr and Nd isotope analyses were performed at Beijing Zhongke Mine Research and Testing Technology Co., Ltd., utilizing the Neptune plus type MC-ICP-MS. To ensure accuracy in the measurement of Sr isotopes, an index equation of 88Sr/86Sr = 8.375209 was applied, designed to correct for any fractionation of the Sr isotope instrument. Similarly, the Nd isotopic fractionation was corrected using an index equation with 146Nd/144Nd = 0.7219. The detailed experimental procedures and methodologies were based on the guidelines provided by [18].

4.5. Mineral Major Elements Analysis

The analysis of mineral chemistry was carried out at Southwest Petroleum University, employing a JOEL JXA-8230 (JEOL Ltd., Tokyo, Japan) electron microprobe analysis (EMPA). The conditions set for these analyses included an acceleration voltage of 15.0 KV, a probe beam current of 10 nA, and a spot beam diameter typically set to 1 μm.

5. Results

5.1. Zircon U-Pb Geochronology

The zircon U-Pb dating analysis included samples from two granodiorites (BY01, BY02), one MME (BY-2), and one pyroxenite (LRM-4). The results, detailed in Table 1, reveal that the zircons from all collected samples are predominantly euhedral and transparent, with typical oscillatory zoning CL textures. Their length to width ratios (1:1–5:1) (Figure 4a–d), are indicative of their magmatic origin [19]. Zircons extracted from the granodiorite samples (BY01, BY02) and gabbro diorite enclaves (BY-1) have high Th/U ratios (>0.3). These samples yield weighted mean 206Pb/238U ages of 114 ± 1 Ma, 113 ± 1 Ma, and 114 ± 1 Ma, respectively, placing their formation in the Early Cretaceous. Similarly, the zircons from pyroxenite (LRM-4) have high Th/U values (>0.7, see Table 1) and yield weighted mean 206Pb/238U ages of 115 ± 1 Ma.
The above Early Cretaceous rocks are the first discovered and reported Early Cretaceous magmatic activity in the western part of the Gangdese Belt, and this discovery is significant in the geological understanding of the region.

5.2. Whole-Rock Geochemistry

5.2.1. Whole-Rock Oxides and Trace Elements

The analytical results of major and trace elements for the representative samples of the Early Cretaceous intrusive rocks are presented in Table 2 and Table 3. The magmatic activity in the study area during the Early Cretaceous mainly comprises ultrabasic and acidic rocks (Figure 5a). Ultrabasic rocks are pyroxenites, while acidic rocks consist of granodiorites with well developed mafic enclaves. Pyroxenites have low SiO2 contents (34.27–44.16 wt.%), high Fe2O3 contents (10.06–19.66 wt.%), high MgO contents, and Mg# (10.81–15.29 wt.% and 52–76, respectively).
Granodiorites have high SiO2 contents (62.24–65.41 wt.%), total alkali contents (5.16–6.91 wt.%). Their MgO contents (2.01–3.08 wt.%) and Mg# values (48–56) are moderate. In the K2O–SiO2 diagram (Figure 5b), these granodiorites fall into the high calc-alkaline series, with A/CNK values of 0.9–1.0, exhibiting metaluminous characteristics (Figure 5c). MMEs have lower SiO2 contents (53.73–54.63 wt.%), high Fe2O3 and MgO contents (9.07–9.31 wt.% and 5.05–5.83 wt.%, respectively), and medium Mg# (52–56). They fell into the gabbro-diorite field on the TAS diagram (Figure 5a) and high K-calc-alkali field on the K2O–SiO2 diagram (Figure 5b), and also exhibit metaluminous characteristics (Figure 5c), with A/CNK values of 0.75–0.80.
In the trace element diagram, the granodiorite samples exhibit patterns typical of arc magmatism, including pronounced enrichment in LILEs (such as Ba, K, etc.) and relative depletion of high field strength elements (HFSEs, such as Nb, etc.) (Figure 6b). The rare earth elements (REEs) partitioning of these granodiorites is depicted by a right-leaning curve on the REEs diagram (Figure 6a), with a relatively obvious negative Eu anomaly (δEu = 0.57–0.88) and a (La/Yb)N ratio of 6.24–13.09, indicating fractionation processes that favor LREEs over HREEs. These granodiorites have low Sr/Y ratios (9.60–15.24), 18.47–28.88 ppm for Y, and 1.96–2.97 ppm for Yb. These geochemical signatures suggest that the granodiorites lack adakitic traits. Additionally, these granodiorites have low Zr + Nb + Ce + Y values (108–292 ppm). When plotted on an FeOT/MgO versus Zr + Nb + Ce + Y diagram (Figure 5d), all samples fell into the undifferentiated I-type granitic field.
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Figure 5. (a) Total alkalis versus silica diagram [20], the line that separates between the alkaline and sub-alkaline series [21]; (b) K2O versus SiO2 diagram [22]; (c) A/NK [Al2O3/(Na2O + K2O)] versus A/CNK [Al2O3/(CaO + Na2O+ K2O)] diagram [23]; (d) FeOT/MgO–(Zr + Nb + Ce + Y) diagram [24].
Figure 5. (a) Total alkalis versus silica diagram [20], the line that separates between the alkaline and sub-alkaline series [21]; (b) K2O versus SiO2 diagram [22]; (c) A/NK [Al2O3/(Na2O + K2O)] versus A/CNK [Al2O3/(CaO + Na2O+ K2O)] diagram [23]; (d) FeOT/MgO–(Zr + Nb + Ce + Y) diagram [24].
Minerals 15 01143 g005
The MMEs samples show geochemical signatures that closely parallel those of their host granodiorite rocks, marked by an enrichment in LILEs and a depletion in HFSEs (such as Nb, Ta, and Ti) (Figure 6d). In the REEs partition mode diagram, the MMEs exhibit a right-leaning partition pattern (Figure 6c), indicative of fractionation favoring LREEs over HREEs. A relatively obvious negative Eu anomaly (δEu = 0.44–0.82), and a (La/Yb) N ratio of 3.78–6.67, highlight a significant fractionation of HREEs. These MMEs have low Sr/Y ratios (4.62–13.91), high Y contents (19.36–59.87 ppm), and Yb contents (2.37–6.34 ppm). These geochemical features indicate that, like their host rocks, the MMEs do not possess the characteristic markers of adakitic rocks.
The pyroxenite samples from the study area exhibit distinct “bell-shaped” patterns in their REE partition diagrams (Figure 6e), indicative of metasomatic processes. This particular shape aligns with the findings of [25], who summarized that the Early Cretaceous pyroxenite in the study area has metasomatic characteristics. The total REE content (∑REE) (59–228 ppm) of these pyroxenite samples. They display pronounced LREE enrichment and HREE depletion, with (La/Yb)N ratios (5.13–12.82), and weak negative Eu anomalies (δEu = 0.85–0.87). In trace element spider diagrams (Figure 6f), the pyroxenite samples show pronounced enrichment in LILEs and a notable depletion in HFSEs (such as Rb, etc.). They also exhibit a depletion in radioactive elements such as Th and U.
Minerals 15 01143 g006
Figure 6. Chondrite-normalized REE patterns (a,c,e) and primitive mantle-normalized trace element diagrams (b,d,f) for Early Cretaceous magmatic rock, the compositions of chondrite and primitive mantle refer to [26], genetic data of pyroxenite according to [25].
Figure 6. Chondrite-normalized REE patterns (a,c,e) and primitive mantle-normalized trace element diagrams (b,d,f) for Early Cretaceous magmatic rock, the compositions of chondrite and primitive mantle refer to [26], genetic data of pyroxenite according to [25].
Minerals 15 01143 g006

5.2.2. Sr–Nd Isotopic Compositions

The whole-rock Sr-Nd isotope analysis conducted on samples from Boyun and Luerma included two granodiorite samples and four pyroxenite samples (Figure 7a). The results, displayed in Table 4, reveal distinct differences between the granodiorite and pyroxenite samples. The four pyroxenite samples exhibit 87Sr/86Sr values from 0.70413 to 0.70650. Using the U-Pb zircon ages of approximately 115 Ma determined in this study, the initial strontium ratio 87Sr/86Sri varies from 0.70401 to 0.70514. The εNd (t) values range between +2.1 and +2.7, and the two-stage model age (TCDM) falls between 695 and 742 Ma. In contrast, the two granodiorite samples have higher 87Sr/86Sr ratios, between 0.70876 and 0.70992, and the εNd (t) values were calculated based on the U–Pb zircon ages (ca. 113 Ma) determined in this study. The values of 87Sr/86Sri are 0.70669–0.70783, and the εNd (t) values are −6.0–−5.0. The calculated model ages TCDM indicate an age lying between 1318 and 1403 Ma.

5.2.3. Lu-Hf Isotopes

Zircons from two granodiorites (BY01, BY02), one MME (BY-1), and one pyroxenite (LRM-4) were chosen for Hf isotope analysis, and the results are listed in Table 5. For the granodiorite samples, the 176Hf/177Hf ratio is between 0.282373 and 0.282651, and the εHf (t) value of zircon calculated based on the U–Pb zircon ages (ca. 113 Ma) ranges from −11.7 to −1.8. These values translate to model ages TCDM of 1292 to 1916 Ma, which is similar to the Hf isotopic composition of the basement zircons in the Central Gangdese Belt (Figure 7b). The 176Hf/177Hf ratios of the MMEs range from 0.282587 to 0.282729, the εHf (t) values are calculated based on the U–Pb zircon ages (ca. 114 Ma), which range from −4.1 to +0.9, and the model ages TCDM range from 1117 Ma to 1437 Ma. The pyroxenite samples have 176Hf/177Hf ratios between 0.282688 and 0.282717, the εHf (t) values calculated based on the U–Pb zircon ages (ca. 115 Ma) range between −0.7 and +0.5, and the model ages TCDM range from 1144 to 1215 Ma.

5.2.4. Mineral Chemistry

The EMPA of clinopyroxene in pyroxenite from the Early Cretaceous period in Luerma, as outlined in Table 6, provides mineralogical and geochemical insights into these rocks. Pyroxenite (LRM-3) is mainly composed of clinopyroxene, based on its microscopic characteristics. Analyses show high CaO contents (23.14–23.65 wt.%), Al2O3 contents (5.89–7.30 wt.%), FeO contents (7.06–7.99 wt.%), and low MgO contents (11.78–12.79 wt.%). Its Mg# values are (73–76) in the composition of clinopyroxene. As shown in the composition diagram, the clinopyroxene composition falls within the diopside series (Wo = 48.90–50.10 × 10−6, En = 35.30–37.10 × 10−6, Fs = 11.80–13.40 × 10−6) (Figure 8).
In the present study, clinopyroxene from the pyroxenites in this work was compared with that from metasomatic pyroxenites, cumulate pyroxenites, and subducted oceanic crust metamorphic pyroxenites in the Mg#–Cr2O3 and Mg#–Al2O3 diagrams. The results show that the clinopyroxene from the pyroxenites in this study falls within the field of metasomatic pyroxenites (Figure 9).

6. Discussion

6.1. Petrogenesis of the Early Cretaceous Granodiorite

The classification of granites into I-type, S-type, A-type, and M-type is a fundamental scheme widely accepted in geological research [24,32,33]. In the context of the Gangdese belt’s Mesozoic subduction setting, the formation of M-type granite, typically associated with mantle differentiation and commonly found in oceanic settings alongside ophiolites [34], is considered highly unlikely. This is because M-type granites belong to the low-K tholeiitic series, which is inconsistent with the area’s subduction tectonic regime. Therefore, the classification of granite types in this study primarily focuses on distinguishing between A-type, I-type, and S-type granites. In terms of mineralogical characteristics, the Early Cretaceous granodiorites are mainly composed of minerals such as plagioclase, quartz, amphibole, and biotite. In terms of chemical composition, all samples have an A/CNK ratio of less than 1.0 (0.90–1.00), indicating that they are metaluminous. This is clearly inconsistent with the characteristics of S-type granites summarized by Chappell and White (1974), which contain aluminous minerals (such as muscovite, cordierite, and garnet) and exhibit a strongly peraluminous nature (A/CNK > 1.1) [32]. Additionally, A-type granites usually have high zircon saturation temperature and high (Zr + Nb + Ce + Yb) contents (>350 ppm), which are obviously inconsistent with the trace element geochemical characteristics of the granodiorites in this study. The granodiorites’ positioning in the FeOT/MgO–(Zr + Nb + Ce + Yb) diagram (Figure 5d), and the P2O5–SiO2 diagram (Figure 10), both support their classification as an I-type granite.
High temperature and pressure experiments show that the partial melting of mantle peridotite typically yields basaltic magma, and cannot directly produce granitic rock magma [36]. Further supporting this, Jiang et al. (2006) elaborated on the geochemical signatures of magma derived from partial melting of the metasomatic mantle wedge, characterizing these magmas as having shoshonitic affinities [37]. The geochemistry of the granodiorite in the study area, marked by high K calc-alkaline series, and enriched Sr-Nd-Hf isotopic composition, differs markedly from those typically associated with mantle rocks. This discrepancy leads to the conclusion that the granodiorites’ origins from low-degree partial melting of a metasomatic mantle wedge are highly improbable. Additionally, the crystallization differentiation of basaltic magmas often forms tholeiite rocks, which are inconsistent with the high K calc-alkaline series exhibited by the granodiorites in this area. The absence of a significant presence of contemporaneous basic rocks in the study area further reduces the likelihood that the granodiorite is formed by the crystallization differentiation of basaltic magma.
The contemporaneous formation of the Boyun granodiorites and MMEs constitutes classic evidence of magma mixing [38]. Prographically K-feldspar phenocrysts and quartz developed in the dioritic enclaves (Figure 2b), this disequilibrium mineral assemblage serves as an indicator of mixing between two magmas with distinct compositions. Furthermore, variations in the Hf isotopic composition of zircons within the granodiorites (spanning 10ε units) and their more depleted Sr-Nd isotopic composition than that of the old and mature crust hint at the involvement of mantle-derived material in the magmatic source region. The granodiorites in the study area contain MMEs similar to the contemporaneous granodiorite petrography of the Gangdese Belt [38,39,40]. Zircon U-Pb dating of gabbro diorite enclaves shows that they are coeval. Zhang et al. (2012) studied the Early Cretaceous granodiorites of the Cuoqin Maiga pluton in the Central Gangdese Belt, and concluded that the ferrimafic enclaves and host granitic rocks were the products of the mixing coevally emplaced of ferrimafic and felsic magma [39].
In the Y/Nb–Yb/Ta diagram (Figure 11a), the granitoid samples plot in the field of low crust and depleted mantle, but close to the average crust, strongly suggesting that crustal sources play a very crucial role in the formation of Early Cretaceous magmatic rock in Boyun area. MMEs and their host granites share the same geochemical characteristic, indicating a close relationship with magma mixing processes. Moreover, all the granitoid samples exhibit a positive linear correlation observed in the MgO-FeOT diagram (Figure 11b), indicative of magma mixing.
The granodiorites in the study area exhibit characteristics typical of magmatic arc granites, including a negative Eu anomaly, enrichment in LILEs, and deficit in HFSEs (Nb, Ta, Ti). The Nb/Ta ratios (6.6–10.6), which are significantly lower than those of chondrite (~17.6, [26]), and the Sr content are relatively low. These geochemical traits indicate that the granodiorites formed in association with the dehydration of amphibolite-facies subducted slabs [44]. As hydrous minerals in the oceanic crust dehydrate, water-rich fluids induce metasomatism of the mantle wedge, forming hydrous minerals. This process lowers the mantle solidus temperature and subsequently induces partial melting of the mantle wedge, generating arc magmas characterized by depletion in HFSEs (Nb, Ta, Ti) and HREEs, and enrichment in LILEs and LREEs [45]. The melting, assimilation, storage, and homogenization of the ancient crystalline lower crust play a crucial role in the development of magma chambers in the shallow crust and the eventual emplacement of granitic magmas at the surface.

6.2. Petrogenesis of the Early Cretaceous MMES

The presence of mafic enclaves within the granodiorites of the western of Gangdese Belt provides crucial insights into the origin and dynamic processes of host granodiorites. Currently, there are four types of mafic enclaves: (1) xenolith of surrounding rock; (2) solid refractory residues in the source region; (3) cognate cumulus crystals formed during the early crystallization of granitic magma; and (4) products of mixing between mantle-derived mafic magma and crust-derived granitic magma [46,47,48,49,50,51].
The MMEs in the granodiorites exhibit ellipsoidal or spherical shapes and fine-grained textures, which strongly suggest a magmatic origin (Figure 3 and Figure 4b). This conclusion is further supported by the presence of oscillatory zoning in zircons (observed in CL images), which rules out the possibility that the MMEs are solid refractory residues. The MMEs share the same crystallization age as the host granodiorites, directly implying a coeval formation, suggesting that the enclaves and the surrounding granodiorites magma belonged to the same magmatic system during crystallization. This temporal relationship effectively eliminates the possibility that the MMEs are xenoliths of surrounding rocks, which would have an external origin and potentially a different age of formation. The absence of cumulus or metamorphic textures in the MMEs indicates they are neither products of early crystallization in granitic magma nor remnants of metamorphism. Specific textural features, such as plagioclase macrocrystals and acicular apatite, reflect quenching effects caused by rapid cooling. Such quenched textures are typical of high-temperature magmas that undergo sudden cooling, often due to magma mixing [39]. The similar Mg# values (53–57) in the MMEs and host granodiorites (49–57) suggest a shared magmatic lineage, implying their likely genesis via magmatic mixing [52]. In the FeOT-MgO diagram, the MMEs show an obvious positive linear correlation, consistent with the trend of magma mixing (Figure 11b). Current studies have shown that MORB mafic magmas have positive anomalies of Nb, Ta, and Ti and negative Pb anomalies [53]. The geochemical characteristics of the gabbro diorite enclaves, particularly their negative Nb, Ta, and Ti anomalies (Figure 6d) and low Nb/U and Ce/Pb, differentiate them from typical MORB (Nb/U, 47 ± 10; Ce/Pb, 25 ± 5; [53]), suggesting that the gabbro diorite enclaves may not originate from the MORB-type asthenospheric mantle. The MMEs have enriched Hf isotopic compositions (εHf (t)= −4.1–+0.9) and two-stage model ages (TcDM = 1118–1438 Ma) that are significantly lower than the basement age of the Central Lhasa Terrane (Figure 7b), combined with high K2O contents (1.69–2.20wt.%), relatively low TiO2 contents (0.78—0.81wt.%), enrichment in LILEs (Cs, Rb, K, Th, U, Ba) and LREEs, and depletion in HREEs and HFSEs (Nb, Ta, Sr, P, Ti), indicating that these rocks formed via partial melting of an enriched mantle metasomatized by subduction-related fluids in an arc setting [54] (Figure 6b). Compared to the host granodiorites, the MMEs have higher MgO contents (5.05—5.83wt.%), Cr contents (123.8–275.7 ppm), and Ni contents (29.1–43.8 ppm), indicating a significant mantle contribution to their magmatic source. To further understand the proportion of mantle and crust in the source, the magmatic mixing process was quantitatively estimated using the εHf (t)-Hf/1000 diagram (Figure 12). The results show that the mantle-derived components account for approximately 50%–60% of MMEs, compared to 0–60% in the granodiorites. This substantial variation in mantle contribution between the MMEs and the host granodiorites suggests a complex magmatic system, where different batches of magma interacted and mixed to varying degrees.
In summary, the Early Cretaceous MMEs and the host granodiorites exhibit remarkable geochemical similarities, which may indicate that the Early Cretaceous MMEs are derived from partial melting of the mantle wedge induced by subduction fluids. Simultaneously, the influx of mantle-derived melt provides heat that induces partial melting of lower crustal material, leading to the formation of acidic magma. This magma subsequently mixes with basic magma in varying proportions, giving rise to granodiorite magmatic activity accompanied by extensive mafic enclaves.

6.3. Petrogenesis of the Early Cretaceous Pyroxenite

The pyroxenites mentioned above can be further divided into silica-saturated and silica-unsaturated types based on their SiO2 contents. The pyroxenites have low SiO2 contents (34.27–44.16 wt.%). According to the CIPW, there is no quartz (Qz) in the pyroxenites, indicating they are silicon unsaturated pyroxenites. It is generally accepted that the source of silico-unsaturated pyroxenites mainly includes mantle peridotites, recycled crust, early formed pyroxenite, or a mixture of these sources [55,56,57]. The pyroxenite samples in this study have relatively high K2O contents (1.04–1.37 wt.%). Petrological experiments show that the solubility of K2O in pyroxenites increases significantly with the increase in pressure, reaching 1.4–1.9 wt.% at 60 × 108–125 × 108 Pa [58,59,60]. Furthermore, the high Mg# values (75), which are close to the Mg# values (76) of melts derived from the partial melting of mantle peridotites [61], suggest a strong mantle influence. Bowman and Ducea (2023) conducted a statistical analysis on the Zn/Fe ratios of Pliocene-Holocene primitive arc magmas (with MgO contents of 7–17 wt.%) from 20 typical continental/oceanic arcs worldwide [62]. Their results indicate that the whole-rock Zn/Fe ratio has been proven to be an effective compositional indicator for distinguishing between magmas derived from peridotite and pyroxenite. Melts sourced from pyroxenite generally have a Zn/Fe ratio (×104) > 12, and can even reach 20, whereas the vast majority of melts derived from peridotite have a Zn/Fe ratio (×104) < 12. The pyroxenite samples in this study have Zn/Fe ratios (×104) of 7.22–9.53, suggesting their source is peridotite. Arc crust thickening causes the mantle wedge to migrate to regions of higher pressure and lower temperature, which reduces the degree of peridotite melting and, thus, increases the contribution of pyroxenite sources. However, considering that the Gangdese magmatic arc experienced significant thickening during the Early Cretaceous, the presence of pyroxenite in the source region of the pyroxenites in this study would have resulted in a relatively high Zn/Fe ratio (×104). The fact that the Zn/Fe ratios (×104) of the pyroxenite samples in this study are significantly < 12 indicates their source is mainly mantle peridotite. Additionally, the small size of the pyroxenites in this study suggests that the melting of deep-seated peridotite weakened with the crustal thickening during the Early Cretaceous.
Clinopyroxene data from the pyroxenites, particularly in Mg# vs. Cr2O3 and Mg# vs. Al2O3 variation diagrams, fall within the metasomatic pyroxenite region (Figure 9). Furthermore, the pyroxenites exhibit variability in the whole rock composition, and the rare earth partition patterns are similar to those summarized by [25] for metasomatic-origin pyroxenites. In addition, the pyroxenites have εNd (t) values of +2.1–+2.7 and εHf (t) values of −0.7–+0.5, indicating some degree of Sr-Nd and Hf isotopic decoupling. In subduction zones, fluids released from the dehydrating subducting slabs play a critical role in metasomatizing the overlying mantle wedge. These fluids are more efficient at transporting LREEs and LILEs than HFSEs, leading to the mantle wedge containing more non-radioactive Nd and less Hf after fluid metasomatism. This results in Sr–Nd–Hf isotopic decoupling [63]. Such decoupling suggests the source was significantly influenced by metasomatism from dehydrating subduction slab fluids. During magma differentiation and crystallization, the geochemical behavior of REEs is mainly controlled by apatite, titanite, and xenotime. The absence of these minerals in the pyroxenites means both HREEs and LREEs behave as incompatible elements during parental magma evolution. Thus, the HREE/LREE ratios of the samples reflect the parental magma composition. The pyroxenites have (La/Yb)N values (5.06–12.66), and (La/Gd)N values (1.11–2.06). These values exceed those of E-MORB ((La/Yb)N = 1.88, (La/Gd)N = 1.86) but are comparable to those of OIB ((La/Yb)N = 12.13, (La/Gd)N = 4.25) [26]. Suggesting a significant contribution of asthenospheric material to their source. Sr-Nd isotopic compositions are mainly related to metasomatic melt [25]. The pyroxenites have an εHf (t) value of −0.67–+0.49, which suggests the presence of an enriched mantle in the study area. This enrichment is further supported by significant Middle Permian magmatic activity in the region, such as the Meta-Gabbro (262 Ma) in the Yawa area [27] and the abundant zircons with a crystallization age of 259 Ma in the late Triassic Gabbro in this study. These findings indicate that the mantle lithosphere in the study area experienced metasomatism by Si- and Zr-rich fluids during the Middle Permian, leading to the formation of an enriched lithospheric mantle.

6.4. Geodynamic Tectonic Implications

The above studies indicate that the Early Cretaceous granodiorites originated from the partial melting of the lower crust and underwent magmatic mixing with enriched mantle-derived mafic magma, forming the mafic enclaves within the granodiorites of the Gangdese Belt. These rocks constitute an extensive magmatic belt extending ~1000 km east–west across the Shiquan River-Namtso Ophiolitic Melange Zone (SNMZ) and spanning from south to north. Studies have shown that the magmatic assemblages within this belt are predominantly calc-alkaline I-type granitoids, characterized by the presence of MMEs. The magmatic suite also includes small amounts of mafic rocks and S-type granites [15,38,39,64]. Additionally, in recent years, some Early Cretaceous magmatic rocks have been reported in the southern Gangdese Belt. Zhu et al. (2009) identified adakites in the Mamen area with a U-Pb age of 136.5Ma [7]. Wang et al. (2017) reported basalt, basaltic andesite, and rhyolite in the Liqiongda area with a U-Pb age of 137–130 Ma [8]. The geochemical signatures of these Early Cretaceous magmatic rocks, characterized by enrichment of LILEs and LREEs, and depletion in HREEs, support their formation in an arc tectonic setting associated with subduction. However, the specific oceanic domain associated with the subduction that formed these magmatic rocks remains debated among geologists. Some scholars argue that the Early Cretaceous magmatism of the central and northern Gangdese Belt is related to the southward subduction of the Bangong River-Nujiang Tethys oceanic, followed by slab rollback and breakoff [7,12,13,15,38,39,64]. Others suggest it is related to the northward subduction of the Neo-Tethys Ocean [8,65,66,67,68,69]. Based on existing data, it is difficult to systematically distinguish which ocean is associated with the Early Cretaceous magmatic activity in terms of geochemical characteristics. Therefore, further discussion of Early Cretaceous magmatic activity characteristics in the central, southern, and northern Gangdese Belt is necessary.
Pyroxenites characterized by enrichment in LILEs and LREEs, and depletion in HREEs, support their formation in an arc tectonic background. In the Ta/Hf-TH/Hf diagram (Figure 13a), the Early Cretaceous MMEs mainly plot in the IV3 zone (incipient continental rift basalt). Meanwhile, in the Nb-Y diagram (Figure 13b), the Early Cretaceous granodiorites plot in the island arc volcanic field, supporting their formation in an island arc setting. These results indicate that the Early Cretaceous magmatic activity in the Gangdese Belt may be related to the northward subduction of the Neo-Tethys Ocean.
At present, there are two hypotheses regarding the northward subduction pattern of the Early Cretaceous Neo-Tethys Ocean: (1) The Yarlung—Zangbo Ocean subducted northward in a low angle or flat plate pattern [8,66,67,69,72,73]; (2) The Yarlung—Zangbo Ocean subducted at a normal angle [7,9]. He (2015) studied the OIB ophiolite in the Zhongba area (with a formation age of 160Ma) [74] and concluded that it formed at a mid-ocean ridge spreading center under the influence of mantle plumes. This finding indicates the presence of a spreading mid-ocean ridge along the western margin of the Gangdese Belt during the Late Jurassic. However, Zhang et al. (2019), through studying the Lazi ophiolitic melange in the middle of the Yarlung Tsangpo Ophiolitic Belt, suggested that the Neo-Tethys ridge expansion had reached the late stage at ~130 Ma [75].
Therefore, this paper proposes that a ridge subduction event occurred in the Neo-Tethys Ocean at the end of the Late Jurassic. Due to the greater buoyancy of the ridge subduction compared to normal ocean crust, the subduction plate angle became flatter, leading to flat subduction [76]. This process continued into the late Early Cretaceous, during which the ongoing flat subduction of the oceanic plates could have caused the plates to rotate or break off. Such plate rotation or detachment events would trigger asthenospheric upwelling, initiating coeval mafic and intermediate-felsic magmatic activity [77], which is often accompanied by magmatic mixing. Similar geological scenarios have been observed elsewhere; for example, the widely distributed Eocene magmatic activity in the eastern Gangdese Belt, which formed against a backdrop of slab break-off and featured coeval mafic magmatism, intermediate-felsic magmatism, and magma mixing [78]. Considering the subduction characteristics of regional stratigraphy, structures, magmatic rocks, and oceanic slabs at different stages, combined with the existing research data, the paper suggests that the association of Early Cretaceous pyroxenite, granodiorite, MMEs in the Gangdese Belt may have formed in a tectonic setting of plate rotation or break-off following flat subduction.
Based on the magmatic activity characteristics of the Gangdese Belt from the Late Jurassic to Late Early Cretaceous, this study concludes that the tectonic magmatic evolution of the Gangdese Belt during this period can be divided into three stages (Figure 14): First stage (~150 Ma): Normal subduction of the Neo-Tethyan Ocean; Second stage (150–130 Ma): Flat plate subduction of the Neo-Tethys Ocean; Third stage (130~110 Ma): Rotation and eventual break-off of the Neo-Tethys oceanic plate.
During the first stage (~150 Ma), the normal subduction of the Neo-Tethys Ocean was marked by the widespread distribution of Late Triassic-Late Jurassic calc-alkaline magmatic rocks across the central and southern Gangdese Belt [40,64,68,79] (Figure 15a). The presence of these rocks indicates that Neo-Tethys Ocean subduction during this period occurred in a typical subduction tectonic setting. Transitioning to the second stage (150–130 Ma), characterized by flat subduction of the Neo-Tethys Ocean (Figure 15b), magmatic activity in the Gangdese Belt decreased significantly. A key feature of flat subduction is that continuous subduction leads to crustal shortening and thickening. Evidence of this tectonic regime is observed in the Late Jurassic–Early Cretaceous, when strong north–south compression affected the Gangdese Belt, shortening the Lhasa Terrane by nearly 60% [80], and forming numerous active faults and fold structures within the terrane [80,81]. Tang et al. (2020) provided further evidence for this tectonic regime through the analysis of detrital zircons from river sands in the inner part of the Gangdese batholith [82], concluding that significant crustal thickening occurred in the southern Gangdese Belt around 150–130 Ma. Additionally, a study of paleo-granites in the Wenbu and Nianqing Tanggula areas [81] concluded that the magmatic activity during this period was influenced by the tectonic environment of crustal compression and thickening.
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Figure 14. Plot of εHf (t) versus age (Ma) for Early Jurassic—Early Cretaceous magmatic rocks in Gangdese Belt (southern Gangdese Belt: [5,7,8,68,83], central Gangdese Belt: [14,40,69,82,84,85], northern Gangdese Belt: [14,38,86].
Figure 14. Plot of εHf (t) versus age (Ma) for Early Jurassic—Early Cretaceous magmatic rocks in Gangdese Belt (southern Gangdese Belt: [5,7,8,68,83], central Gangdese Belt: [14,40,69,82,84,85], northern Gangdese Belt: [14,38,86].
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Wang et al. (2017) [8] conducted a comprehensive study of bimodal volcanic rocks in the Liqiongda area, southern Gangdese Belt, combined with data on Mamen adakites, and concluded that these magmatic rocks share similar genetic characteristics with adakites and high-Al basalts distributed in the Aleutian–Kamchatka subduction zone, formed flat subduction conditions. All this evidence supports the argument that the northward subduction of the Neo-Tethys Ocean during the Early Cretaceous was flat subduction. In the third stage (130~110 Ma), characterized by the rotation and eventual breaking off of the flatly subducted Neo-Tethys oceanic plate, significant geological processes were initiated (Figure 15c). The detachment or rotation of the subducting slab facilitated the upwelling of asthenospheric material, providing the heat and materials necessary for the partial melting of the lithospheric mantle and the formation of mafic magma. The thermal impact of the ascending hot mafic magma beneath the ancient crust promoted crustal materials melting and induced magma mixing. The resulting magmatism is typified by calc-alkaline I type granites (accompanied by numerous MMEs), which formed mainly by the remelting of ancient crustal materials with input from mantle materials. Meanwhile, asthenosphere upwelling driven by flat subduction, slab rotation, and break-off, plays a crucial role in the genesis of Early Cretaceous pyroxenites, which exhibit geochemical characteristics of both asthenosphere and lithospheric mantle materials (Figure 15d).
In summary, the Early Cretaceous mafic and felsic magmatic activity in the western Gangdese Belt is closely related to the northward subduction of the Neo-Tethys Ocean; this magmatism may have formed in a tectonic setting of plate rotation or break-off following oceanic plate subduction.
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Figure 15. Geodynamic—petrogenetic model for the Early Cretaceous arc magmatism from western of Gangdese Belt.
Figure 15. Geodynamic—petrogenetic model for the Early Cretaceous arc magmatism from western of Gangdese Belt.
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7. Conclusions

From a few samples, two igneous rock types were studied in the western Gangdese Belt. Our main conclusions are summarized as follows:
(1) Geochemical data and zircon U-Pb dating results indicate that the Boyun granitoids and Luerma pyroxenites formed in the Early Cretaceous (115 Ma–113 Ma).
(2) Early Cretaceous Boyun MMEs are products of magma mixing between mantle material and ancient crust, as suggested by our field observations. The host granite’s parental melts are mainly derived from partial melting of the ancient crust, but modified by subsequent contamination with enriched mantle material.
(3) Luerma pyroxenites have low SiO2 contents (34.27–44.16 wt.%), high Fe2O3 contents (10.06–19.66 wt.%), high MgO contents (10.81–15.29 wt.%), high K2O (1.04–1.37 wt.%), and values of Mg# (52–76). Additionally, the observed decoupling between Nd isotopes and zircon Hf isotopic compositions further supports that these pyroxenites originated from mixed melts, reflecting the interaction between asthenospheric mantle and enriched lithospheric mantle.
(4) The Late Jurassic–Early Cretaceous tectonic evolution of the Neo-Tethys Ocean can be divided into the following three distinct stages: first stage (~150 Ma), normal subduction of the Neo-Tethyan Ocean; second stage (150–130 Ma), flat plate subduction of the Neo-Tethys Ocean; third stage (130–110 Ma), rotation and break-off of the Neo-Tethys oceanic plate.

Author Contributions

Conceptualization, J.L. and K.G.; methodology, J.L.; software, J.L.; validation, J.L., K.G. and Z.W.; formal analysis, Z.X.; investigation, Y.P.; resources, J.L.; data curation, J.L.; writing—original draft preparation, J.L.; writing—review and editing, J.L.; visualization, Z.X.; supervision, Z.W.; project administration, Y.P.; funding acquisition, J.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Yunnan Fundamental Research Projects of Department of Science and Technology of Yunnan Province (NO. 202401AU070073).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Acknowledgments

We would like to express our gratitude to Ding Feng and Chen Cuihua of Chengdu University of Technology for their guidance in the process of writing this paper. We also extended our thanks to the anonymous reviewers for their valuable comments and suggestions, which significantly improved the quality of the paper.

Conflicts of Interest

Author Ke Gao was employed by the Zijin Mining Group Southwest Geological Exploration Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Distribution of magmatic rocks in the western Gangdese Belt. (a) Tectonic map of the Qinghai-Tibet Plateau and its adjacent areas; (b) Location map of the magmatic rock belt in the Lhasa Terrane [3]; (c) Sketch map of regional geology in the Boyun area; (d) Sketch map of regional geology in the Lurma area; (e) Sketch Map of the Lurma Composite Intrusion (Late Triassic-Early Cretaceous).
Figure 1. Distribution of magmatic rocks in the western Gangdese Belt. (a) Tectonic map of the Qinghai-Tibet Plateau and its adjacent areas; (b) Location map of the magmatic rock belt in the Lhasa Terrane [3]; (c) Sketch map of regional geology in the Boyun area; (d) Sketch map of regional geology in the Lurma area; (e) Sketch Map of the Lurma Composite Intrusion (Late Triassic-Early Cretaceous).
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Figure 2. Field photographs and photomicrographs of the Boyun granitoid rocks: (a) remote view of the Boyun pluton; (b) outcrop photograph of MMEs; (c) outcrop photograph of granodiorite; (d) hand specimen and photomicrographs of granodiorite; (e) hand specimen photograph of MMEs; (f) photomicrograph of MMEs. Pl—plagioclase; Amp—amphibole; Bt—biotite; Qz—quartz; Kfs—K-feldspar.
Figure 2. Field photographs and photomicrographs of the Boyun granitoid rocks: (a) remote view of the Boyun pluton; (b) outcrop photograph of MMEs; (c) outcrop photograph of granodiorite; (d) hand specimen and photomicrographs of granodiorite; (e) hand specimen photograph of MMEs; (f) photomicrograph of MMEs. Pl—plagioclase; Amp—amphibole; Bt—biotite; Qz—quartz; Kfs—K-feldspar.
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Figure 3. Field photographs and photomicrographs of the Luerma pyroxenite: (a) remote view of pyroxenite vein; (b) outcrop photographs of the pyroxenite vein; (c,d) photomicrographs of the pyroxenite. Cpx—clinopyroxenite; Bt—biotite; Mag—magnetite; Amp—amphibole.
Figure 3. Field photographs and photomicrographs of the Luerma pyroxenite: (a) remote view of pyroxenite vein; (b) outcrop photographs of the pyroxenite vein; (c,d) photomicrographs of the pyroxenite. Cpx—clinopyroxenite; Bt—biotite; Mag—magnetite; Amp—amphibole.
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Figure 4. Cathodoluminescence (CL) images and concordia plots for zircons: (a,b) granodiorite from Boyun pluton; (c) MMES from Boyun pluton; (d) pyroxenite from Luerma. U–Pb analysis spots are shown by solid circles, and Hf isotope spots are shown by the dashed circles.
Figure 4. Cathodoluminescence (CL) images and concordia plots for zircons: (a,b) granodiorite from Boyun pluton; (c) MMES from Boyun pluton; (d) pyroxenite from Luerma. U–Pb analysis spots are shown by solid circles, and Hf isotope spots are shown by the dashed circles.
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Figure 7. εNd (t) vs. 87Sr/86Sri (a) and εHf (t)vs. Age (Ma); (b) diagrams for Luerma pyroxenite and Boyun granitoid. Data sources are as follows: Yawa Permian (~262 Ma) basaltic intrusions data [27], Early Cretaceous magmatic rock data [8], central and southern Gangdese Belt magmatic rock isotope data [28].
Figure 7. εNd (t) vs. 87Sr/86Sri (a) and εHf (t)vs. Age (Ma); (b) diagrams for Luerma pyroxenite and Boyun granitoid. Data sources are as follows: Yawa Permian (~262 Ma) basaltic intrusions data [27], Early Cretaceous magmatic rock data [8], central and southern Gangdese Belt magmatic rock isotope data [28].
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Figure 8. Data for clinopyroxene from pyroxenite plotted on the enstatite-ferrosilite–diopside–hedenbergite quadrilateral of [29].
Figure 8. Data for clinopyroxene from pyroxenite plotted on the enstatite-ferrosilite–diopside–hedenbergite quadrilateral of [29].
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Figure 9. (a) Pyroxenites Mg# vs. Cr2O3 diagram; (b) Pyroxenites Mg# vs. Al2O3 diagram. Data for Metasomatic pyroxenite, cumulate pyroxenite and Eclogite—facies pyroxenite formed by metamorphism of subducted oceanic crust from [30,31].
Figure 9. (a) Pyroxenites Mg# vs. Cr2O3 diagram; (b) Pyroxenites Mg# vs. Al2O3 diagram. Data for Metasomatic pyroxenite, cumulate pyroxenite and Eclogite—facies pyroxenite formed by metamorphism of subducted oceanic crust from [30,31].
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Figure 10. SiO2 vs. P2O5 variation diagram of granite evolution trend diagram [35].
Figure 10. SiO2 vs. P2O5 variation diagram of granite evolution trend diagram [35].
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Figure 11. (a) Y/Nb-Yb/Ta diagram; (b) FeOT-MgO diagram [41]. Data for BBC and LCC are from [42]; Data for DM is from [43]. BBC—Bulk Continental Crust; LCC—Lower Continental Crust.
Figure 11. (a) Y/Nb-Yb/Ta diagram; (b) FeOT-MgO diagram [41]. Data for BBC and LCC are from [42]; Data for DM is from [43]. BBC—Bulk Continental Crust; LCC—Lower Continental Crust.
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Figure 12. εHf (t)-Hf/1000 modeling diagram of magma mixing [38].
Figure 12. εHf (t)-Hf/1000 modeling diagram of magma mixing [38].
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Figure 13. (a) Ta/Hf-Th/Hf diagram [70]; (b) Y-Nb diagram [71]. I—N-MORB zone at the plate divergent margin; II1—Oceanic island arc basalt zone; II2—Continental margin island arc + Continental margin volcanic arc; III—Oceanic Intraplate Island zone; IV1—Intracontinental rift + continental margin rift tholeiitic basalt; IV2—Intracontinental rift alkali basalt; IV3—Incipient continental rift basalt; V—Mantle Plume Basalt Zone; WPG-Within plate granite; VAG—Volcanic arc granite; Syn-COLG—Synclonic granite; ORG—Ocean ridge plagiogranite.
Figure 13. (a) Ta/Hf-Th/Hf diagram [70]; (b) Y-Nb diagram [71]. I—N-MORB zone at the plate divergent margin; II1—Oceanic island arc basalt zone; II2—Continental margin island arc + Continental margin volcanic arc; III—Oceanic Intraplate Island zone; IV1—Intracontinental rift + continental margin rift tholeiitic basalt; IV2—Intracontinental rift alkali basalt; IV3—Incipient continental rift basalt; V—Mantle Plume Basalt Zone; WPG-Within plate granite; VAG—Volcanic arc granite; Syn-COLG—Synclonic granite; ORG—Ocean ridge plagiogranite.
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Table 1. LA-ICP-MS U-Pb isotopic dating of the Boyun granitoids and Luerma pyroxenite in the western Gangdese Belt.
Table 1. LA-ICP-MS U-Pb isotopic dating of the Boyun granitoids and Luerma pyroxenite in the western Gangdese Belt.
SampleThUTh/U207Pb/206Pb1δ207Pb/235U1δ206Pb/238U1δ207Pb/206Pb1δ207Pb/235U1δ206Pb/238U1δ
LRM-4 (Proxenite)
LRM-4-13203041.050.04990.00160.12080.00420.01760.00031876911641122
LRM-4-23303580.920.04920.00140.11980.00350.01770.00021677311531131
LRM-4-55634461.260.05320.00260.13340.00670.01820.000434510512761173
LRM-4-65595161.080.05320.0020.12980.00480.01770.00023458212441131
LRM-4-1066210240.650.05240.00110.12790.00290.01770.00023024412231131
LRM-4-112122920.730.04870.00380.1230.01030.01820.000320010611891162
LRM-4-125975281.130.05160.00260.12710.00690.01790.000433311912161143
LRM-4-133763521.070.05290.00370.13270.00860.01830.000332415512781172
LRM-4-156705561.210.05480.00160.13650.00390.01820.00034066313031162
LRM-4-192352470.950.05250.00520.13010.01320.01790.0003309228124121142
LRM-4-207725611.380.05460.00280.13440.00660.01790.000239411512861141
LRM-4-234944301.150.05470.00250.13020.00560.01740.000246710212451112
LRM-4-244043441.170.05850.00610.13940.01320.01750.0004550231132121122
BY01 (Granodiorite)
BY01-11992470.80.07360.00350.18080.00880.01790.000310319716981142
BY01-24314281.010.06830.01980.12550.00730.0180.000587763012071153
BY01-42543570.710.05120.00230.12850.00620.01820.000425410412361162
BY01-63974220.940.05430.00350.13430.00820.01810.000338914612871162
BY01-72653700.720.0470.00250.11470.0060.01770.00035012611051132
BY01-82753290.840.05120.00270.12520.00650.01780.000325012212061142
BY01-95584841.150.04820.0020.11810.00490.01780.000310910111341142
BY01-102633220.820.05570.00240.13310.00580.01730.000244312912751112
BY01-111031990.520.05320.00290.13360.00810.01810.000433912612771162
BY01-121222140.570.04650.0030.11570.0070.01810.00042014811161162
BY01-131802520.710.0570.0030.14260.00730.01820.000349411713561172
BY01-142283420.670.05090.0030.12590.0070.0180.000323913512061152
BY01-171522430.620.05260.0040.12670.00950.01760.000332217412191122
BY01-183073710.830.05850.00350.14910.0110.0180.0003546130141101152
BY01-192023040.660.05590.00320.13460.00790.01750.000345612512871122
BY01-204024710.850.04940.00160.12020.0040.01760.00021697111541131
BY01-215416240.870.04890.00170.11990.00420.01780.00031468611541142
BY01-223708620.430.04660.00130.11320.00340.01760.0002286710931121
BY01-241532560.60.05480.00280.13410.0070.01790.000346711712861142
BY01-251063170.330.05470.00290.13620.00720.01810.000346711913061162
BY02 (Granodiorite)
BY02-11912590.740.05850.00420.14540.01010.01810.000555015613891163
BY02-23353800.880.04670.00260.11580.00630.01810.00033513011161162
BY02-32983810.780.050.00240.12470.00590.01820.000319511311951162
BY02-43874370.890.04860.0030.11870.00680.01780.000313220211461142
BY02-56575271.250.05180.00270.12820.00660.0180.000327612212261152
BY02-668111480.590.05470.0020.13520.00460.0180.00043987912941153
BY02-92112180.970.05160.0050.12820.01240.01790.0004333222122111142
BY02-102213260.680.04980.00220.12480.00510.01830.000318310211951172
BY02-113033810.80.04630.00240.11340.00570.01790.0003912210951142
BY02-123333890.860.05270.00280.12850.00690.01770.000331712212361132
BY02-133724800.780.04730.00410.11340.01070.01720.000465193109101103
BY02-143513980.880.04960.00260.12120.00610.01780.000317612511661132
BY02-1551351110.05150.0050.12470.01260.01750.0004265221119111122
BY02-162453030.810.05860.00310.14540.00840.01790.000555411613871143
BY02-172793140.890.0550.0030.13530.00750.01780.000240912212971141
BY02-193543521.010.04790.00230.11640.00580.01760.00039811111251132
BY02-203804060.940.05250.00250.12720.00620.01760.000330910912261122
BY02-212943460.850.05280.00290.12480.00660.01720.000232012611961102
BY02-224645200.890.04660.00190.11020.00490.01710.0003339110641092
BY02-233573800.940.04920.00250.11870.0060.01750.000316712011451122
BY02-242893910.740.05640.0040.13980.01070.01790.000347815613391142
BY02-255405111.060.0470.00210.11470.0050.01780.00035010411051132
BY-1 (MMEs)
BY-1-12012410.830.05130.00220.12790.00560.01820.000225410012251161
BY-1-22062670.770.04750.00220.1170.00550.01790.00027211711251152
BY-1-31972080.950.05660.00580.14290.01510.01840.0005476234136131173
BY-1-53373520.960.05270.00220.13390.0060.01850.00023229412851181
BY-1-63283400.970.05210.00160.13090.00440.01830.00032877512541172
BY-1-71601940.830.05930.0030.14520.0070.01790.000357610913861152
BY-1-91892230.850.04770.00210.11740.00530.01790.00028710011351141
BY-1-102862761.030.05160.00190.12610.00410.01790.00023338312141151
BY-1-1110005071.970.05660.00280.13670.00670.01760.000247611113061122
BY-1-122052150.950.04830.0030.12010.00750.01810.000312213111571162
BY-1-142942631.120.04990.00330.12180.0080.01770.000219115411771131
BY-1-154183421.220.05080.00260.12750.00660.01830.000323211712261172
BY-1-163162941.080.05240.00250.13010.00730.01790.000330210912471142
BY-1-182582551.010.0550.00370.13530.0090.0180.000340915212981152
BY-1-192492321.070.0550.00220.13580.00520.01810.00034139112951162
BY-1-203692971.240.05030.0020.12330.00490.01790.00032098811841142
BY-1-212903110.930.04860.0020.12280.00540.01830.00031289611851172
BY-1-222602371.10.05710.00350.1390.00810.01780.000449414013271142
BY-1-231752520.690.04990.00210.12140.00460.01790.00031879811641142
BY-1-243122821.110.05570.00230.13580.00560.01770.00024399112951131
BY-1-252012060.980.05730.00590.14330.01640.01810.0005506228136151153
Table 2. Whole-rock oxides (wt.%) and trace elements (ppm) of the Boyun Granodiorite in the western Gangdese Belt.
Table 2. Whole-rock oxides (wt.%) and trace elements (ppm) of the Boyun Granodiorite in the western Gangdese Belt.
SampleBY01-1BY01-2BY02-1BY02-2BY-4BY-5BY-6BY-7BY-8BY-9
Granodiorite
SiO262.2462.3564.3164.2664.864.1263.7965.4163.7865.03
TiO20.610.610.680.680.450.520.550.4530.5540.476
Al2O31615.9214.3714.4515.815.8715.8615.5715.2716.03
Fe2O35.395.345.685.624.384.865.044.255.374.18
MnO0.10.10.10.10.10.110.110.0910.1240.096
MgO2.742.733.053.082.082.322.332.012.672.1
CaO5.45.3955.074.44.514.834.144.584.26
Na2O2.682.672.092.122.83.032.972.693.23.48
K2O3.173.163.083.063.572.722.944.222.592.18
P2O50.170.170.160.170.120.150.150.1350.170.136
LOI1.081.051.221.221.431.71.330.951.611.98
SUM99.5899.599.7499.8299.9299.9199.9199.9299.9299.95
K2O + Na2O5.855.835.165.186.375.755.916.915.795.66
Mg#51515252494948495056
SC16.5516.7919.4419.3511.0513.2912.2711.3516.7112.28
V95.195.4393.7192.8170.3482.1182.0467.8393.9175.53
Cr5154.7873.0471.9145.0339.536.4931.5147.6535.36
Co14.113.8114.1214.1410.3411.1312.1310.0712.028.87
Ni12.051315.1914.2110.9812.2912.179.8114.9511.81
Ga17.1717.3918.1217.8214.8815.2615.6613.9414.8315.28
Rb136.53136.3124.67125.76147.25121.88139.24161.2115.85126.08
Sr305.94306.68277.81276.37292.57283.85285.55281.52263.75290.73
Y26.3826.3428.8828.5619.1821.7420.6518.4726.6819.84
Zr132133.04159.28152.2539.6692.8980.8656.6583.0670.37
Nb7.857.958.388.345.666.056.925.496.325.62
Ba267.56268.45315.97316.01255.45211.28211.01373.2224.25202.47
La24.1624.1751.6952.1322.3828.6723.3418.7638.8429.76
Ce52.0151.995.9396.7243.6953.7846.8637.6171.9354.51
Pr6.116.069.899.95.26.085.464.667.965.97
Nd23.5523.4334.6934.6120.1522.621.8619.1231.0723.73
Sm4.994.956.116.133.974.34.063.765.64.23
Eu1.171.191.151.110.9710.920.921.121.15
Gd4.574.655.455.43.413.833.793.394.93.79
Tb0.70.70.810.80.560.60.60.530.80.58
Dy4.34.334.884.853.253.623.463.264.633.36
Ho0.90.90.990.980.640.720.70.630.910.66
Er2.622.632.832.811.972.212.21.922.782.08
Tm0.420.420.450.440.310.340.340.30.420.32
Yb2.742.782.972.8622.22.261.962.852.07
Lu0.420.430.440.430.330.360.370.330.460.34
Hf3.683.774.44.251.552.943.062.242.882.4
Ta0.810.830.790.80.740.811.10.830.740.85
Pb11.7711.9114.0114.0510.869.310.2412.658.799.97
Th14.6415.4320.921.081522.0118.4713.5424.1819.51
U2.422.511.21.32.022.262.221.892.222.14
∑REE12912921822010813011797175132
LREE1121121992019611610385157119
HREE17171919121414121813
LREE/HREE6.726.6310.610.87.738.387.476.888.829.05
δEu0.750.760.610.590.810.750.720.790.650.88
Note: Mg# = 100 × Mg2+/(Mg2+ + Fe2+) (atomic number). δEu = 2 × EuN/(SmN + GdN).
Table 3. Whole-rock major (wt.%) and trace (ppm) elemental compositions of Boyun MMEs and Luerma pyroxenite in the western Gangdese Belt.
Table 3. Whole-rock major (wt.%) and trace (ppm) elemental compositions of Boyun MMEs and Luerma pyroxenite in the western Gangdese Belt.
SampleLRM-5LRM-6LRM-7LRM-8BY-6-1BY-7-1BY-8-1BY-9-1
PyroxenitePyroxenitePyroxenitePyroxeniteMMEsMMEsMMEsMMEs
SiO244.1634.7134.5434.2754.153.7353.8154.63
TiO21.352.212.232.130.780.810.810.8
Al2O38.8411.611.5810.8915.9115.516.2816.32
Fe2O310.0619.0419.3619.669.079.259.319.25
MnO0.1610.2010.2090.2150.240.230.230.24
MgO15.2911.4511.3810.815.75.835.055.53
CaO15.9614.814.815.647.317.146.897.06
Na2O0.3571.331.331.263.073.173.663.4
K2O1.371.171.161.042.072.22.191.69
P2O50.0432.512.322.920.150.170.220.21
LOI2.350.881.011.061.531.91.470.77
SUM99.9499.999.9299.999.9299.9399.9299.91
K2O + Na2O1.732.52.492.35.145.375.855.09
Mg#7655545255565254
SC93.1371.3668.4571.7422.2722.4836.9524.76
V291.65683.27677.88723.09159.63159.97191.52168.54
Cr197.072.211.143.33275.75247.62123.85141.07
Co54.2470.0971.1472.2724.324.7222.6121.88
Ni85.0519.4518.8919.5843.3443.7829.1542.33
Ga11.7517.7517.3818.318.5918.4418.6817.53
Rb5814.1412.2815.17183.77178.87158.19111.24
Sr201.96531.34558.75540.39251.14253.97276.71269.37
Y11.6528.7128.1231.2224.4526.3559.8719.36
Zr57.8294.9593.03100.872.5793.7898.99103.35
Nb2.024.555.634.1612.6613.0511.658.4
Ba235.59124.33124.9113.61168.11172.98210.76177.25
La5.6529.3328.4431.220.6727.4233.4222.08
Ce17.4871.2370.0377.4851.564.1785.4749.51
Pr3.1211.0211.2111.836.868.112.126.15
Nd16.8558.4959.7761.226.5531.1449.3423.93
Sm4.7314.2113.8814.245.125.6311.083.97
Eu1.313.793.653.840.860.881.581
Gd4.4612.5412.3313.284.234.5310.883.48
Tb0.581.491.481.570.660.711.730.54
Dy2.86.766.686.854.064.5610.193.09
Ho0.451.081.111.10.830.942.070.63
Er1.092.552.592.522.52.785.831.91
Tm0.140.310.310.310.430.450.910.32
Yb0.791.751.761.753.373.486.342.37
Lu0.120.240.250.260.540.590.960.41
Hf2.44.174.344.142.623.184.133.3
Ta0.290.410.450.361.321.341.420.91
Pb1.952.062.392.268.538.116.586.58
Th2.081.752.352.2110.6512.4111.916.21
U0.551.251.140.822.112.492.411.59
∑REE59215214228129155232120
LREE49188187200112137193107
HREE1027272817183913
LREE/HREE4.717.047.057.236.717.614.968.37
δEu0.870.870.850.850.570.530.440.82
Note: Mg# = 100 × Mg2+/(Mg2+ + Fe2+) (atomic number). δEu = 2 × EuN/(SmN + GdN).
Table 4. Whole-rock Sr-Nd isotopic compositions of Boyun granitoid and Luerma pyroxenite in the western southern Lhasa Terrane.
Table 4. Whole-rock Sr-Nd isotopic compositions of Boyun granitoid and Luerma pyroxenite in the western southern Lhasa Terrane.
SampleLRM-5LRM-6LRM-7LRM-8BY01BY02
PyroxenitePyroxenitePyroxenitePyroxeniteGranodioriteGranodiorite
Age (Ma)115115115115113113
87Sr/86Sr0.70650.704140.704130.704160.708760.70992
87Rb/86Sr0.83160.07710.06370.08131.28691.2995
(87Sr/86Sr)i0.705140.704010.704020.704030.706690.70783
143Nd/144Nd0.512720.512730.512730.512730.512260.51232
147Sm/144Nd0.16970.14690.14030.14070.10620.1149
(143Nd/144Nd)t0.51260.512620.512630.512620.512420.51245
εNd (t)2.12.42.72.6−6−5
TDM1 (Ma)148097487288312611280
TDM2 (Ma)74271469570114031318
Table 5. LA-MC-ICP-MS zircon Lu-Hf isotopc compositions of Boyun granitoid and Luerma pyroxenite in the western Gangdese Belt.
Table 5. LA-MC-ICP-MS zircon Lu-Hf isotopc compositions of Boyun granitoid and Luerma pyroxenite in the western Gangdese Belt.
SampleAge (Ma)176Yb/177Hf176Lu/177Hf176Hf/177Hf2δεHf (t)TDM1TDM2fLu/Hf
BY-1 (MMEs)
BY-1-11160.0257640.001090.2826630.000015−1.48361264−0.97
BY-1-111120.0199650.0008140.2826340.000016−2.58711331−0.98
BY-1-131170.0287320.001170.2826910.000016−0.47981201−0.96
BY-1-161140.0212710.000940.2826980.000017−0.27841186−0.97
BY-1-181150.0271390.001190.2827290.0000160.97451117−0.96
BY-1-21150.0194770.0008320.2826380.000015−2.38651319−0.97
BY-1-211170.0292890.0012290.2827080.0000170.27761164−0.96
BY-1-221140.0251340.0010460.2826960.000017−0.37891192−0.97
BY-1-231140.0254670.0010080.2825870.000016−4.19421437−0.97
BY-1-51180.0150920.0006510.2826820.000017−0.68001218−0.98
BY-1-61170.0275370.0011550.2826830.000014−0.78101220−0.97
BY-1-91140.0215520.0009120.2826980.000016−0.27821184−0.97
BY01 (Granodiorite)
BY01-011140.0204030.0008020.2824530.000015−8.911241737−0.98
BY01-031130.0295590.0010910.2825340.000014−610181556−0.97
BY01-051140.0211750.0007640.2823920.000012−1112071872−0.98
BY01-091140.0342180.0012290.2825360.000016−610201553−0.96
BY01-101110.0312070.0011640.282530.000014−6.210261567−0.96
BY01-121140.0299560.0011850.2824540.000016−8.911341736−0.96
BY01-141150.0410210.0014880.2823730.000021−11.712571916−0.96
BY01-151120.0286750.0010660.2824460.000018−9.111421755−0.97
BY01-191120.0253240.0009720.2824280.000019−9.811641795−0.97
BY01-211140.0489490.0017380.2825630.000021−59941493−0.95
BY01-221120.0246940.0009050.2824480.000018−9.111341749−0.97
BY01-251160.0194080.0007120.2825060.00002−6.910471616−0.98
BY02 (Granodiorite)
BY02-011160.0234830.0009690.2826510.000014−1.88511292−0.97
BY02-081140.03380.0014110.2826480.000015−28651301−0.96
BY02-101170.0231850.0008860.2825390.000019−5.810061542−0.97
BY02-121130.0392840.0014580.2825140.000023−6.810571603−0.96
BY02-141130.0213670.0008230.2826030.000021−3.69141399−0.98
BY02-161140.0274460.0010770.2825790.000016−4.49541454−0.97
BY02-171140.0224220.0008990.2826430.000016−2.18601310−0.97
BY02-181100.0207950.0008270.2825630.000016−59701491−0.98
BY02-201120.0305030.0011410.2824820.000015−7.910921672−0.97
BY02-211100.0187640.0007220.2826410.000019−2.38591316−0.98
LRM-4 (Pyroxenite)
LRM-4-11120.0275070.0011720.2826980.000017−0.27881187−0.96
LRM-4-101130.0454320.0021740.2826880.000019−0.78251215−0.93
LRM-4-111160.0286270.0013470.282710.0000180.37751159−0.96
LRM-4-121140.0271980.0012640.2827170.0000210.57631144−0.96
LRM-4-131170.0249780.0011570.2826960.000018−0.27911190−0.97
LRM-4-151160.0342830.0016390.2827110.0000210.37791157−0.95
LRM-4-21130.0270410.0012880.2826940.000014−0.47971198−0.96
LRM-4-61130.0370510.0015340.2826890.000026−0.68091209−0.95
LRM-4-11120.0275070.0011720.2826980.000017−0.27881187−0.96
Table 6. Electron microprobe analyses of the clinopyroxene in the Luerma pyroxenite (wt.%).
Table 6. Electron microprobe analyses of the clinopyroxene in the Luerma pyroxenite (wt.%).
NO.LRM-3-1-1-1LRM-3-1-1-2LRM-3-1-1-3LRM-3-1-1-4LRM-3-1-1-5LRM-3-1-2-1LRM-3-1-2-2LRM-3-1-2-3LRM-3-1-2-4LRM-3-1-2-5
SiO247.3947.9548.2947.7547.9248.8247.5747.5348.1647.42
TiO21.041.11.141.211.250.961.20.921.061.22
Al2O36.796.96.367.056.735.897.36.216.446.87
FeOT7.417.477.067.727.527.167.787.547.447.99
MnO0.110.140.150.140.150.160.110.170.140.14
MgO12.4212.2612.6312.0112.1612.7911.7812.6712.4111.92
CaO23.2423.6223.6523.1923.2523.4723.3623.1423.3223.42
K2O0.010.010.020.010.010.02000.010.02
Na2O0.470.290.310.470.350.280.340.310.370.36
P2O500.020.030.070.040.030.040.010.070.02
Cr2O30.0500.0100.020.0100.0100
F0000000000
Cl0.020.0100.0100.010.01000
Total98.9599.7699.6399.6399.3999.6199.4898.5199.4199.37
En49.350.149.949.549.749.550.248.949.549.9
Wo36.636.237.135.736.237.535.337.336.635.3
Fs12.312.511.81312.71213.212.612.513.4
AlIVR0.20.20.20.20.20.20.20.20.20.2
Mg#75757674747673757573
Note: Based on 6 oxygen atoms and 4 cations. En = enstatite. Fs = ferrosilite. Wo = wollastonite. Mg# = 100 × Mg2+/(Mg2+ + Fe2+) (atomic number).
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Lin, J.; Gao, K.; Wang, Z.; Xu, Z.; Pan, Y. Genesis of Early Cretaceous Magmatism in the Western Gangdese Belt, Southern Tibet: Implications for Neo-Tethyan Oceanic Slab Subduction. Minerals 2025, 15, 1143. https://doi.org/10.3390/min15111143

AMA Style

Lin J, Gao K, Wang Z, Xu Z, Pan Y. Genesis of Early Cretaceous Magmatism in the Western Gangdese Belt, Southern Tibet: Implications for Neo-Tethyan Oceanic Slab Subduction. Minerals. 2025; 15(11):1143. https://doi.org/10.3390/min15111143

Chicago/Turabian Style

Lin, Jiqing, Ke Gao, Zizheng Wang, Zhongbiao Xu, and Yongping Pan. 2025. "Genesis of Early Cretaceous Magmatism in the Western Gangdese Belt, Southern Tibet: Implications for Neo-Tethyan Oceanic Slab Subduction" Minerals 15, no. 11: 1143. https://doi.org/10.3390/min15111143

APA Style

Lin, J., Gao, K., Wang, Z., Xu, Z., & Pan, Y. (2025). Genesis of Early Cretaceous Magmatism in the Western Gangdese Belt, Southern Tibet: Implications for Neo-Tethyan Oceanic Slab Subduction. Minerals, 15(11), 1143. https://doi.org/10.3390/min15111143

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