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Article

The First Discovery of A1-Type Granite in the Meibaqieqin Region, Central Lhasa Terrane, Xizang

by
Yi Yang
1,
Junkang Zhao
2,*,
Ke Gao
2,*,
Zhi Zhang
3,
Shuai Ding
2,
Jiansheng Gong
2,
Jianyang Wu
3,
Peiyan Xu
3 and
Yingxu Li
3
1
College of Engineering, Tibet University, Lhasa 850000, China
2
Zijin Mining Group Southwest Geological Exploration Co., Ltd., Chengdu 610059, China
3
Chengdu Center, China Geological Survey (Geoscience Innovation Center of Southwest China), Chengdu 610218, China
*
Authors to whom correspondence should be addressed.
Minerals 2025, 15(10), 1093; https://doi.org/10.3390/min15101093
Submission received: 24 August 2025 / Revised: 15 October 2025 / Accepted: 15 October 2025 / Published: 21 October 2025
(This article belongs to the Special Issue Tectonic Evolution of the Tethys Ocean in the Qinghai–Tibet Plateau)
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Versions Notes

Abstract

This study documents the first A1-type granite identified on the southern margin of the central Lhasa terrane: a two-mica syenogranite pluton in the Meibaqieqin region. Because A-type granite provides sensitive records of crustal melting and lithospheric extension, this pluton offers important insights into magmatic processes and tectonic evolution along the southern margin of the Lhasa terrane. We analyzed two sample suites collected from different sites within the same pluton using zircon U–Pb geochronology and Hf isotopes, whole-rock geochemistry and Nd isotope. Zircon U–Pb weighted mean ages were 130.5 ± 0.7 Ma and 130.0 ± 0.7 Ma, placing emplacement in the Early Cretaceous. Zircon εHf(t) values ranged from −11.29 to −9.00 and −11.04 to −7.27, with two-stage Hf model ages (TDM2) of 1.76–1.90 Ga and 1.65–1.89 Ga. Whole-rock εNd(t) values clustered between −11.77 and −11.36, yielding two-stage Nd model ages (TNdDM2) of 1.85–1.88 Ga. Geochemically, the pluton is high-K calc-alkaline. These isotopic signatures indicate derivation predominantly from ancient crustal sources with a little mantle material. Chondrite-normalized REE patterns are overall right-inclined and display a V-shaped profile. Together with trace-element characteristics, these features support classification as A1-type granite. Regional comprehensive data suggest that pluton emplacement was controlled mainly by lithospheric extension related to northward subduction of the Neo-Tethyan oceanic plate, with a lesser contribution from southward subduction along the Bangongco–Nujiang suture. The source characteristics and geodynamic context differ markedly from A2-type granites on the northern margin of the central Lhasa terrane, which reflect distinct magmatic sources and tectonic regimes.

1. Introduction

The Lhasa terrane, a key component of the Tibetan Plateau, underwent northward subduction of the Neo-Tethyan oceanic crust and southward subduction of the Bangongco–Nujiang oceanic crust, followed by collisions with the Indian continent and the Qiangtang terrane [1,2,3,4,5,6,7]. These processes produced large-scale Mesozoic–Cenozoic magmatism, forming the Gangdese batholith [5]. The southern batholith is dominated by diorite, granodiorite, and porphyritic biotite granite, with subordinate biotite and two-mica granite, mostly emplaced between ca. 65 and 40 Ma [8]. The Lhasa terrane is subdivided into the north, central, and south Lhasa terranes, separated by the Shiquanhe–Namco ophiolite belt and the Luobadui–Milashan fault [4,5,6,9].
A-type granite, originally defined as alkaline, relatively anhydrous, and anorogenic [10], covering almost all granite types except typical I- and S-type granites [11,12], commonly forms in rift zone and within stable continental blocks [13,14]. It includes two subtypes: A1, typically associated with intraplate extension or rift zone, and A2, commonly linked to post-collisional plate-margin extension [15,16]. Because of their diagnostic geochemical and tectonic signatures, A-type granites are key to understanding extensional magmatism and regional tectonic evolution [10,15,17,18,19].
In the northern Lhasa terrane, numerous Early Cretaceous A-type granites have been identified, offering critical constraints on the evolution of the Bangongco–Nujiang Ocean and the Shiquanhe–Namco ophiolite belt. Examples include the Shenza biotite granite [20], the Zhaduding monzogranite in Gaer County (ca. 104 Ma [21]), the Asa porphyritic granite (ca. 107–106 Ma [22]), the Qusanggele granite in Nima County (ca. 101 Ma [23]), and the Kongcuo granite (ca. 105 Ma [24,25]) (Figure 1b). However, these plutons are largely confined to the North Lhasa terrane and the northern margin of the central Lhasa terrane. To date, no A-type granite has been reported along the southern margin of the central Lhasa terrane. Previous studies attribute the northern A-type magmatism mainly to southward subduction of the Bangongco–Nujiang oceanic crust and subsequent post-collisional extension [20,22,23]. In contrast, few extensional granites have been documented in the southern Lhasa terrane, and the petrogenesis and tectonic setting of any A-type granites there remain poorly constrained.
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Figure 1. Tectonic Map of the Tibetan Plateau (a) and pluton distribution sketch (b), Lhasa terrane, Xizang. Age data of A-type granite and rhyolites from [20,21,22,23,24,25,26]. Figure 2 illustrates the tectonic location of the geological map of the study area.
Figure 1. Tectonic Map of the Tibetan Plateau (a) and pluton distribution sketch (b), Lhasa terrane, Xizang. Age data of A-type granite and rhyolites from [20,21,22,23,24,25,26]. Figure 2 illustrates the tectonic location of the geological map of the study area.
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Figure 2. Geological map in the Meibaqieqin region, central Lhasa terrane.
Figure 2. Geological map in the Meibaqieqin region, central Lhasa terrane.
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During the past two years of geological surveys, we identified an A1-type two-mica syenogranite along the southern margin of the central Lhasa terrane. This study integrates field mapping, petrography, geochronology, whole-rock geochemistry, and isotope analyses to investigate its petrogenesis, source characteristics, and tectonic setting. As the first reported A1-type granite from the central Lhasa terrane, our results provide new evidence for Early Cretaceous magmatism and geodynamics in the region.

2. Geological Background

The Lhasa terrane is situated between the Yarlung Tsangpo suture zone and the Bangongco-Nujiang suture zone, formed by the northward subduction of the Yarlung Tsangpo oceanic crust, the southward subduction of the Bangongco-Nujiang oceanic crust, and subsequent collision processes. Extensive tectonic evolution of the Lhasa Terrane driven by east–west–trending internal structures and subsidiary faults has been documented by numerous studies [2,27]. Building on the discovery of oceanic subduction–type eclogites in the Sumdo area, Yang et al. (2006) partitioned the terrane into the southern and northern Lhasa terranes [28]. Zhu et al. (2011) subsequently refined this framework, recognizing three regions—the Northern Lhasa terrane, Central Lhasa terrane, and Southern Lhasa terrane—on the basis of variations in the cover and basement, with boundaries defined by the Shiquanhe–Shenzha-Jiali ophiolitic belt (SSJ) and the Luobadui–Milashan fault (LMF) [5]. This study focuses on the southern part of the central Lhasa terrane (Figure 1b).
The study area lies north of Meibaqieqin Township, Angren County, Shigatse City, immediately north of the Luobadui–Milashan fault belt, within the southern margin of the Central Lhasa terrane. The stratum includes: Carboniferous Yongzhu Formation, Upper Carboniferous–Lower Permian Laga Formation, Lower Permian Angjie Formation, Middle Permian Xiala Formation, Paleocene Dianzhong Formation, Eocene Nianbo Formation, Pliocene Wuyu Group, Quaternary deposits.
Magmatic rocks are widespread in the study area and are dominated by intrusions, with a small amount of volcanics. Magmatism spans three main stages—Early Cretaceous, Late Cretaceous, and Paleogene—with the Cretaceous representing the most intense phase and dominated by felsic compositions. Volcanism is best developed in the Paleogene Linzizong Group, followed by the Neogene Wuyu Group. The authors conducted mapping through conventional geological surveys and drew the geological map of the study area.

3. Petrology

The two-mica syenogranite that intrudes the Lower Permian Angjie Formation and is well exposed. The upper part of the pluton is overlain by volcanic strata of the Paleocene Dianzhong and Eocene Nianbo formations (Figure 2). The two-mica syenogranite is in an intrusive contact relationship with syenogranite and monzonitic granite. The exposed area of the pluton is approximately 42 km2. Two sample sets were collected from the same pluton and show similar petrography. The main mineral assemblage comprises quartz (24%–27%), K-feldspar (50%–53%), plagioclase (13%–15%), muscovite (4%–6%), and biotite (3%–5%), with accessory zircon, monazite, and apatite (Figure 3). K-feldspar locally replaces plagioclase, preserving plagioclase relicts enclosed within K-feldspar. Figure 3a,b show that the mineral composition mainly consists of K-feldspar and plagioclase, with some plagioclase being replaced by K-feldspar; quartz grains mainly exhibit subhedral structure; biotite and muscovite display alteration transitional distribution with K-feldspar.

4. Results

4.1. Whole-Rock Geochemistry

Two groups of samples were collected from the same pluton representing two-mica syenogranites, showing consistent petrogeochemical features (Table 1). See Appendix A for the analytical methods. Loss on ignition (LOI) is 0.54–1.51 wt.%, indicating weak alteration and reliable geochemical data. The rocks have SiO2 = 73.97–76.97 wt.%, K2O + Na2O = 8.12–8.72 wt.%, and Al2O3 = 12.00–13.64 wt.%, i.e., high-silica, alkali-rich, and relatively low Al. In the TAS diagram, all samples plot in the granite domain and are subalkaline [29] (Figure 4a). The aluminum saturation index (A/CNK) is 0.95–1.14; in the A/CNK–A/NK diagram, samples fall in the metaluminous to peraluminous domain [30] (Figure 4b). The Rittmann index (σ) is 1.97–2.38 (<3.3), consistent with calc-alkaline affinity; the SiO2–K2O plot places all samples in the high-K calc-alkaline field [31] (Figure 4c).
Total rare earth elements are 134–244 μg/g, with LREE/HREE = 6.91–9.44 and LaN/YbN = 2.86–8.21. Chondrite-normalized REE patterns show LREE enrichment, obviously negative Eu anomalies (Eu/Eu* = 0.16–0.40), and strong LREE–HREE fractionation (Figure 5a). Primitive mantle-normalized spidergram shows enrichment in large ion lithophile elements (e.g., Rb, Zr, Th, U, Hf) and depletion in high field strength elements (e.g., Sr, Ba, Ti, and P), consistent with A-type granite signatures (Figure 5b). In addition, the Rb/Sr ratios of the two-mica syenogranite vary from 10.9 to 53, with average of 25.8.

4.2. Whole-Rock Nd Isotopes

Eight Nd isotope analyses yielded εNd(t) values of −11.77 to −11.36 at 130 Ma, with (143Nd/144Nd)i = 0.511867–0.511888 and two-stage model ages (TNdDM2) of 1.85–1.88 Ga (Table 2).

4.3. U-Pb Zircon Geochronology

Zircon U-Pb dating was conducted on two two-mica syenogranite samples (ZGL01 and ZGL02; Table 3). Most zircons are short prismatic grains, 90–210 μm long and 60–130 μm wide, with aspect ratios of 1–2. Cathodoluminescence images show clear oscillatory zoning, consistent with magmatic zircon [35] (Figure 6). Zircons from the two-mica syenogranite exhibit high U and Th contents, and the U-Pb dating results show good concordance, differing from other types of zircon. There are a few detrital zircons in this study. The zircon cores appear dark gray in CL images with relatively low transparency. The margins of the zircons show obvious corrosion rims with embayed morphology. This indicates that the cores underwent thermal metamorphism and metasomatism under magmatic processes. Fractures are well-developed.
A total of 24 zircon U-Pb isotope data points were obtained from sample ZGL01, with 206Pb/238U ages concentrated between ca. 129.8~132.6 Ma. On the U-Pb age concordia diagram, the data points distribute near the concordia line, yielding a weighted mean age of 130.5 ± 0.7 Ma (MSWD = 1.3) for this sample (Figure 7). Sample ZGL02 yielded 25 U-Pb 206Pb/238U ages ranging between 128.1 and 131.4 Ma, and a weighted mean age of 130 ± 0.7 Ma (MSWD = 0.17). These two age values accurately represent the crystallization age of this pluton, indicating large-scale magmatic activity during the Cretaceous in this region.

4.4. Zircon Hf Isotopes

The zircon crystallization ages were used to calculate εHf(t) values and two-stage model ages. Zircon Hf isotopes were measured at 22 and 23 spots from samples ZGL01 and ZGL02, respectively. Hf spots coincide with the U-Pb analytical sites (Table 4), and both samples show similar isotopic compositions. In total, 45 spots yield initial 176Hf/177Hf ratios of 0.282382–0.282446. For ZGL01, εHf(0) values range from −13.79 to −11.53 and εHf(t) from −11.29 to −9.03; single-stage Hf model ages (TDM) are 1.18–1.34 Ga and two-stage model ages (TDM2) are 1.76–1.90 Ga. For ZGL02, εHf(0) ranges from −13.67 to −9.83 and εHf(t) from −11.04 to −7.27; TDM values are 1.13–1.34 Ga and TDM2 values are 1.65–1.89 Ga.

5. Discussion

5.1. Genetic Type

Granites are commonly grouped into I-, S-, and A-types based on geochemistry and petrogenesis. A-type granites are typically alkaline or peralkaline, rich in high field strength elements (Nb, Ta, Zr, Hf), and formed at relatively high temperatures; they also show elevated Ga/Al and FeOT/MgO ratios [13,16,17]. Petrologists further subdivide A-type granites into A1 and A2 subtypes that reflect different tectonic environments and chemical features [15]. Because of these attributes, A-type granites are valuable records of extensional magmatism and regional tectonics.
The two-mica syenogranite investigated here is rich in K-feldspar and biotite. Major elements indicate high K, high total alkalis, and Mg depletion. The aluminum saturation index is classified as weakly peraluminous (A/CNK = 0.95–1.14; A/NK = 1.12–1.19; see Figure 4b and Table 1), which aligns with typical A-type compositions [13,36], higher than those of typical I-type granites. The differentiation index (DI) is 93.4–96.1, implying strong magmatic differentiation. Rare earth element patterns show significantly negative Eu anomalies (Eu/Eu* = 0.16–0.40) and positive Ce anomalies (Ce/Ce* = 1.04–2.66), with light REE strongly enriched over heavy REE (LREE/HREE = 6.91–9.44). Chondrite-normalized REE plots display right-inclined, concave-upward patterns. Primitive mantle-normalized spidergrams show enrichment in Rb, Th, U, Zr, Hf and depletion in Sr, Ba, Ti, P. The above geochemical characteristics are consistent with the typical features of A-type granites [13,14]. In addition, they display high (10,000 Ga/Al) ratios (Figure 8a–d). On multiple discrimination diagrams, all samples plot within the A-type field (Figure 8a–d). A1-type granites have very low Y/Nb and Rb/Nb ratios, while A2-type granites are the opposite [15]. The two-mica Syenogranite are consistent with the A1-type granite (Y/Nb ratio < 1.2), with their Y/Nb ratios varying from 0.34 to 1.01. Compared with published Early Cretaceous A-type granites in the Lhasa terrane, the Meibaqieqin two-mica syenogranite has relatively low Y/Nb (0.34–1.01) and Rb/Nb (9.24–17.66). In the Y–Nb–Ce discrimination diagrams of A-type granites proposed by Eby [14] (Figure 8e), the two-mica syenogranites plot in the A1 subfield. Moreover, the two-mica syenogranites samples plot in the scope of A1 subtype and overlap with the OIB field in the Y/Nb vs. Ce/Nb diagram [14,15] (Figure 8f). All of the above characteristics indicate that the two-mica syenogranite belongs to type A1 granite.

5.2. Magmatic Sources and Petrogenesis

Several genetic models have been put forward for A-type granites, including partial melting of lower crust [17,28], melting of high-grade (granulite-facies) crustal protoliths [37,38], and mingling or mixing of crustal melts with mantle-derived magmas [28,39]. Despite different origins, A-type granites commonly exhibit high SiO2, high total alkalis, low Ca and Mg, and relatively high (Na2O + K2O)/Al2O3, FeOT/MgO, and Ga/Al [13,40,41,42]. Eby linked A1-type granites to intraplate or rift-related settings, whereas A2-type granites reflect post-collisional reworking and melting of continental crust [14]. In the Lhasa terrane, A2-type granites are commonly explained by interaction between mantle-derived mafic magmas and partially melted juvenile lower crust [21,24,25]. The two-mica syenogranite is the first discovered A1-type granite in the Lhasa terrane. Although it shares some similar geochemical characteristics with A2-type granite, its material source and genesis require further in-depth research.
Low Y/Nb ratios are characteristic of oceanic island, intraplate, and rift zone magmas derived from OIB-type mantle sources [15]. Magmas derived from arc-type sources (lithospheric mantle altered by subduction-related fluids) or dominantly from continental crust typically exhibit high Y/Nb ratios, reflecting the high ratio in continental crust [15]. Therefore, A1-type suites with lower Y/Nb ratios are interpreted as differentiates of mantle-derived melts similar to ocean island basalt (OIB). The two-mica syenogranite exhibits low Y/Nb ratios, possibly indicating a genesis of magmatic differentiation driven by mantle-derived material. The high alkaline characteristics and low Y/Nb and Y/Ta ratios all indicate that the two-mica syenogranite belongs to the A1 type, which is considered to be formed by derivatives of enriched OIB mantle sources [15,16]. However, several trace-element ratios indicate substantial crustal involvement. Nb/Ta = 6.74–9.92 and Ce/Pb = 1.88–3.74 approach continental crust values (Nb/Ta ≈ 11–12; Ce/Pb ≈ 4) and are well below primitive mantle values (Nb/Ta ≈ 17.5; Ce/Pb ≈ 9) [43,44]. High Rb/Sr (10.9–59.0) and low Cr (1.09–7.01 μg /g) also point to evolved, crustal sources. The Sm/Nd ratios of the samples range from 0.17 to 0.22, which are slightly lower than the characteristic values corresponding to the crust (0.3), indicating the magma source region contains material not only from the crust [45]. The Zr/Nb ratio ranges from 1.13 to 5.05, with an average value of 3.72, which is significantly lower than the corresponding ratio of continental crust (16.2) [46]. Nb/U = 5.62–8.22 is far lower than the primitive mantle ratio (~33.6) and typical of continental crust [47]. Strong Eu anomalies and depletion in Sr and Ba (Figure 7) suggest residual or fractionating plagioclase and melting of plagioclase-rich, garnet-poor sources [48]. La/Nb = 0.46–1.58 also supports a crustal component [49]. The strong depletion of Ba and Sr in the two-mica syenogranite (Figure 5b) also reflects that it may be a product of low-degree partial melting of crustal materials [50]. The Th/Ta ratio in granitic rocks is significant for indicating magma–crust interaction, as mantle-derived rocks exhibit Th/Ta ratios of ≈2—lower than those of the upper crust (Th/Ta ≈ 6.9) and lower crust (Th/Ta ≈ 7.9) [51]. Samples of two-mica syenogranites yield an average Th/Ta value of ≈12.86. The two-mica syenogranite was derived from crust-generated magma, possibly. In short, these characteristics indicate that the tectonic affinity of two-mica syenogranite reflects an extensional setting (intraplate and rift zone), while the magma itself is primarily derived from partial melting of ancient continental crust, with the driving force for partial melting possibly originating from shallow mantle magmatism.
Zircon Hf isotopes, owing to zircon’s high closure temperature and low Lu/Hf, are robust tracers of magma sources and crustal evolution [39,52]. Positive εHf(t) values generally indicate juvenile crust or depleted mantle sources, whereas negative εHf(t) values point to derivation from older continental crust [53,54]. The A1-type granites studied here yield zircon εHf(t) values of −11.28 to −7.26 (average −9.83) and two-stage Hf model ages (TDM2) of 1.65–1.90 Ga. In the age vs. εHf(t) diagram (Figure 9a), all analyses plot below the chondritic (CHUR) evolution curve, between Paleoproterozoic (ca. 1.6–2.0 Ga) crustal evolution lines, indicating predominantly Paleoproterozoic crustal sources. Whole-rock εNd(t) values of −11.75 to −11.36 further support derivation from ancient crust with limited juvenile input (Figure 9b). To compare source characteristics through time, we compiled published Hf isotope data for A-type granites across Lhasa terrane. Three main emplacement pulses occur at ca. 130 Ma, ca. 114 Ma, and ca. 105 Ma (Figure 9a). The younger A2-type granites (ca. 114 Ma and ca. 105 Ma), chiefly along the northern margin of the central Lhasa terrane, show increased mantle contributions relative to the ca. 130 Ma magmatism, which is dominated by crustal signatures [20,21,22,23,24,25,26,33] (Figure 9a). As mentioned above, both the zircon εHf(t) values and whole-rock εNd(t) values of the two-mica syenogranite indicates the involvement of crustal materials in the magma source. The whole-rock geochemical data also indicate characteristics of crustal material participation in petrogenesis.
The characteristics of trace elements such as Th, La, Sm, and Nd can be used to discriminate whether the petrogenetic process is fractional crystallization or partial melting [55]. In the La vs. La/Sm and La vs. La/Yb diagrams (Figure 10a,b), the samples define positive correlations consistent with partial melting. Experimental studies on pelites, greywackes, and mafic protoliths demonstrate contrasting melt chemistries [48,56,57]. The low CaO + FeOT + TiO2 contents of our samples resemble melts derived from pelitic sources (Figure 10c).
This evidence indicates that the two-mica syenogranite was generated mainly by partial melting of ancient continental crust, with a pelitic-dominated source and some mantle input. This differs from A2-type granites along the northern margin of the central Lhasa terrane, which reflect stronger crust–mantle interaction.
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Figure 9. Plot of age vs. εHf(t) ((a), after [58]) and age vs. εNd(t) (b) for the two-mica syenogranite. The cited data is the same as that in Figure 6.
Figure 9. Plot of age vs. εHf(t) ((a), after [58]) and age vs. εNd(t) (b) for the two-mica syenogranite. The cited data is the same as that in Figure 6.
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Figure 10. Genetic types and source discrimination diagrams of two-mica syenogranite. (a) La vs. La/Sm diagram, (b) La vs. La/Yb diagram, (c) CaO + FeO + TiO2 vs. CaO/(FeOT + MgO + TiO2) diagram.
Figure 10. Genetic types and source discrimination diagrams of two-mica syenogranite. (a) La vs. La/Sm diagram, (b) La vs. La/Yb diagram, (c) CaO + FeO + TiO2 vs. CaO/(FeOT + MgO + TiO2) diagram.
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5.3. Tectonic Setting

A-type granites typically form in extensional settings, including intraplate, post-collisional, and back-arc environments [13,15]. The A-type granites are usually regarded as a marker of crustal extension [13,17]. In the Lhasa terrane, three A-type episodes are recognized at ca. 130 Ma, ca. 114 Ma, and ca. 105 Ma [20,21,22,23,24,25]. Discrimination diagrams categorize the Meibaqieqin two-mica syenogranite (ca. 130 Ma) as A1-type, consistent with intraplate extensional magmatism (Figure 11). By contrast, the ca. 114 Ma and ca. 105 Ma A-type granites are A2-type and are linked to southward subduction of the Bangongco–Nujiang oceanic crust and post-collisional extension in northern Lhasa [20,22,23].
As analyzed above, the two-mica syenogranite is situated in the southern margin of the central Lhasa terrane, showing clear differences from the continent-continent collision-related A2-type granites in the northern margin of the central Lhasa terrane. Around 130 Ma, the Bangongco-Nujiang oceanic crust was undergoing southward subduction, while the Neo-Tethyan oceanic crust was subducting northward. Which subduction event is more closely related to the samples studied in this research? Recent studies on the Shiquanhe-Namco ophiolitic mélange belt suggest that this belt is a back-arc basin formed during the subduction of the Bangongco-Nujiang Ocean [5,59,60]. Its small scale and rapid evolution imply that the subduction in this basin is not related to the large-scale magmatic activity in the central-northern part of the Lhasa terrane [61]. This paper posits that the northward subduction of the Neo-Tethyan oceanic crust had a stronger influence than the southward subduction of the Bangongco-Nujiang oceanic crust and the Shiquanhe-Namco small oceanic basin crust. The main evidence includes: (1) In the early Early Cretaceous, the Lhasa terrane had a bidirectional subduction system [2], which included the southward subduction of the Bangongco-Nujiang oceanic crust, and the northward subduction of the Neo-Tethyan oceanic crust. This bidirectional subduction led to the formation of the Zenong Group volcanic arc, Coqin-Duowa back-arc basin, Longgar-Nyainqentanglha magmatic arc, and south Gangdese magmatic arc from north to south, respectively [2]. This also created an extensional tectonic environment in the southern Lhasa terrane, distinctly different from the post-collisional A2-type granites in the northern Lhasa terrane because of Shiquanhe-Namco small oceanic basin. (2) The influence of the northward subduction of the Neo-Tethys oceanic plate is comparable to that of the southward subduction of the Bangongco-Nujiang oceanic crust, therefore the distance between the location of plutons and the subduction zone is related to the strength of tectonic influence indication [62]. The A1-type granite discovered in the Meibaqieqin region is situated in the southern area of the central Lhasa terrane, approximately 80 km from the Yarlung Zangbo suture zone and nearly 300 km from the Bangongco-Nujiang suture zone. This proximity suggests that the influence of the southern Neo-Tethyan ocean subduction is more significant. (3) The volcanic rocks from the Duoni Formation and Zenong Group in the central-northern Lhasa terrane to the Early Cretaceous volcanic rocks on the southern side of the central Lhasa terrane also show that the lithologic assemblage transformed from calc-alkaline series to predominantly high-K calc-alkaline and minor shoshonitic series, indicating that the subduction zone depth deepened from north to center, with subduction polarity from north to south, and ages showing a trend of becoming younger from north to center. The volcanic rocks from the Yeba Formation and Sangri Group in the southern Lhasa terrane to the Early Cretaceous volcanic rocks on the southern side of the central Lhasa block show lithologic assemblages that transformed from tholeiitic to calc-alkaline series to high-K calc-alkaline and shoshonitic series, with ages showing a trend from old to young, indicating that the subduction zone depth deepened from south to center, with subduction polarity from south to north, suggesting possible constraints from bidirectional subduction during the Early Cretaceous. The distribution characteristics of different rock series indicate that the northern part of the central Lhasa terrane was more influenced by southward subduction of the Bangongco-Nujiang oceanic crust, while the southern part of the central Lhasa terrane was more influenced by northward subduction of the Neo-Tethyan oceanic crust [62]. Around 130 Ma, the Neo-Tethyan oceanic crust was in a northward subduction stage, forming extensive arc magmatic rock distributions in the southern Lhasa block. At this time, the Bangongco-Nujiang oceanic crust experienced bidirectional subduction. Due to north-south extensional tectonic setting, the Shiquanhe- Namco back-arc ocean basin was formed. The northward subduction of the Neo-Tethyan Ocean did not form a typical back-arc small ocean basin. Instead, its tectonic stress created back-arc rift zones or intraplate hotspots. Lithospheric thinning led to asthenospheric mantle upwelling, providing heat sources for petrogenesis. Magmatic materials metasomatically enriched the lower crust to form primitive magmas, which underwent magmatic evolution and intruded into the shallow crust to form this special type of granite.
Thus, it is evident that the northward subduction of the Neo-Tethyan Ocean played a major role in the extensional tectonic setting in the southern part of the Lhasa terrane. This was the key dynamic factor for the formation of intraplate granites in the Meibaqieqin region, whereas the southward subduction of the Shiquanhe-Namco back-arc basin and the Bangongco-Nujiang oceanic crust had relatively minor influences.

6. Conclusions

  • The crystallization age of the two-mica syenogranite is ca. 130 Ma, representing a large-scale Early Cretaceous magmatism in the Meibaqieqin region and its periphery.
  • Geochemical and isotopic data indicate that the two-mica syenogranite is a high-K calc-alkaline, A-type granite, with magmatic source materials derived from ancient crustal materials, formed through partial melting of pelitic rocks driven by mantle-derived magma.
  • The Meibaqieqin A1-type granite was formed in intraplate extensional tectonic setting, primarily influenced by the northward subduction of the Neo-Tethyan oceanic crust, with relatively minor influence from the southward subduction of the Bangongco-Nujiang oceanic crust. The petrogenesis of two-mica syenogranite is related to the extensional tectonic setting formed by subduction, and this petrogenetic environment is distinctly different from the post-collisional extensional environment of A2-type granites.

Author Contributions

Writing—original draft, Y.Y. and J.Z.; Writing—review & editing, K.G. and Y.Y.; resources, K.G. and Z.Z.; Conceptualization, K.G.; Funding acquisition, J.Z., J.G. and S.D.; investigation, J.W., Y.L. and P.X. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Deep Earth Probe and Mineral Resources Exploration—National Science and Technology Major Project (2024ZD1003205, 2024ZD1003206, 2024ZD1003207), Key Research and Development Program Project of Tibet Science and Technology Department (XZ202501ZY0102), Central Guidance Fund for Local Science and Technology Development Projects (XZ202301YD0030C), China Geological Survey Projects (DD20242518, DD20240069, DD202402028).

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors are thankful to the reviewers and scientific editor, whose constructive criticism and recommendations helped us to significantly rework and improve the manuscript.

Conflicts of Interest

Junkang Zhao, Ke Gao, Shuai Ding and Jiansheng Gong were 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.

Appendix A. Analytical Methods

Appendix A.1. Whole-Rock Major and Trace Element Analyses

Whole-rock major elements were determined after fusion. The flux consisted of lithium tetraborate, lithium metaborate, and lithium fluoride mixed in a 45:10:5 ratio. Ammonium nitrate and lithium bromide served as the oxidant and release agent, respectively. Fusions were carried out at 1050 °C for 15 min. Major elements were analyzed on a Rigaku ZSX Primus II wavelength-dispersive XRF with a 4.0 kW end-window Rh target X-ray tube, operated at 50 kV and 60 mA. All oxides were measured on Kα lines. Calibration used Chinese national reference materials (rock: GBW07101–14 [63]; soil: GBW07401–08 [64]; stream sediment: GBW07302–12 [65]). Data were corrected using the theoretical α-coefficient method, and the relative standard deviation (RSD) was <2%.
Whole-rock trace elements were measured by ICP-MS (Agilent 7700e) at Wuhan Sample Solution Analytical Technology Co., Ltd. (Wuhan, China). The digestion procedure was: (1) Dry 200-mesh powders at 105 °C for 12 h; (2) Accurately weigh 50 mg into a Teflon bomb; (3)Add 1 mL HNO3 and 1 mL HF slowly; (4)Place the bomb in a stainless-steel jacket and heat at 190 °C in an oven for >24 h; (5) After cooling, open the bomb, evaporate at 140 °C to incipient dryness, add 1 mL HNO3, and evaporate to dryness again; (6) Add 1 mL HNO3, 1 mL MQ water, and 1 mL of 1 µg/g In internal standard solution; reseal and heat at 190 °C for >12 h; (7) Transfer the solution to a polyethylene bottle and dilute with 2% HNO3 to a final mass of 100 g.

Appendix A.2. Nd Isotopic Ratio Measurements

Nd isotope ratios were obtained using a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Dreieich, Germany) at Wuhan Sample Solution Analytical Technology Co., Ltd. The double-focusing instrument was fitted with seven fixed electron-multiplier ICs and nine Faraday cups with 1011 Ω resistors. A high-capacity dry interface pump (120 m3 h−1), an H skimmer cone, and the standard sample cone were used to enhance sensitivity. An Alfa Aesar Nd single-element solution was used for tuning. A 200 µg/L GSB 04-3258-2015 standard was analyzed routinely to assess accuracy and reproducibility; typical 142Nd+ intensities exceeded ~2.5 V. Data were collected in static mode at low resolution in ten blocks of ten cycles, with 4.194 s per cycle, for a total of ~7 min per analysis.
Instrumental mass discrimination was corrected using the exponential law [66], with internal normalization to 146Nd/144Nd = 0.7219 [67]. Samarium was effectively removed by ion exchange; any residual 144Sm+ was corrected following Lin et al. [67]. Data reduction for Nd isotope ratios was performed with Iso-Compass software [68]. One GSB 04-3258-2015 standard was measured after every seven unknowns [69]. The measured 143Nd/144Nd for GSB 04-3258-2015 was 0.512440 ± 6 (2SD, n = 31), identical within error to the published value of 0.512438 ± 6 (2SD) [69]. USGS reference materials BCR-2 (basalt) and RGM-2 (rhyolite) yielded 0.512641 ± 11 (2SD, n = 82) and 0.512804 ± 12 (2SD, n = 80), respectively, consistent with published values [70].

Appendix A.3. Zircon U-Pb Dating

Zircon U-Pb ages were acquired by LA–ICP–MS at Wuhan Sample Solution Analytical Technology Co., Ltd. (Wuhan, China). Instrumental parameters for the laser ablation system, ICP–MS, and data reduction followed Zong et al. [71]. Ablation used a GeolasPro platform equipped with a COMPexPro 102 ArF excimer laser (193 nm, maximum energy 200 mJ) and a MicroLas optical system (Agilent Technologies, Bremen, Germany). Ion signals were measured on an Agilent 7900 ICP–MS. The system includes a wire-type signal-smoothing device [72]. In this study, the laser spot diameter was 30 µm and the repetition rate was 6 Hz. Zircon 91500 and NIST SRM 610 glass were used as external standards for U–Pb dating and trace-element calibration, respectively [73]. Off-line background selection/integration, time-drift correction, and quantitative calibration for both trace elements and U–Pb data were performed with the Excel-based ICPMSDataCal 10 software [74,75]. Concordia plots and weighted mean values were calculated using Isoplot/Ex_ver3 [76].

Appendix A.4. Zircon Hf Isotope

Experiments of in situ Hf isotope ratio analysis were conducted using a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Dreieich, Germany) in combination with a Geolas HD excimer ArF laser ablation system that was hosted at the Wuhan Sample Solution Analytical Technology Co., Ltd., Wuhan, China. A “wire” signal smoothing device is included in this laser ablation system, by which smooth signals are produced even at very low laser repetition rates down to 1 Hz [73]. Helium was used as the carrier gas within the ablation cell and was merged with argon (makeup gas) after the ablation cell. Small amounts of nitrogen were added to the argon makeup gas flow for the improvement of sensitivity of Hf isotopes [77]. Compared to the standard arrangement, the addition of nitrogen in combination with the use of the newly designed X skimmer cone and Jet sample cone in Neptune Plus improved the signal intensity of Hf, Yb and Lu by a factor of 5.3, 4.0 and 2.4, respectively. All data were acquired on zircon in single spot ablation mode at a spot size of 44 μm. The energy density of laser ablation that was used in this study was ~7.0 J cm−2. Each measurement consisted of 20 s of acquisition of the background signal followed by 50 s of ablation signal acquisition. Detailed operating conditions for the laser ablation system and the MC-ICP-MS instrument and analytical method are the same as description by Hu et al. [77].
The major limitation to accurate in situ zircon Hf isotope determination by LA-MC-ICP-MS is the very large isobaric interference from 176Yb and, to a much lesser extent 176Lu on 176Hf. It has been shown that the mass fractionation of Yb (βYb) is not constant over time and that the βYb that is obtained from the introduction of solutions is unsuitable for in situ zircon measurements [78]. The under- or over-estimation of the βYb value would undoubtedly affect the accurate correction of 176Yb and thus the determined 176Hf/177Hf ratio. We applied the directly obtained βYb value from the zircon sample itself in real-time in this study. The 179Hf/177Hf and 173Yb/171Yb ratios were used to calculate the mass bias of Hf (βHf) and Yb (βYb), which were normalized to 179Hf/177Hf = 0.7325 and 173Yb/171Yb = 1.132685 [79] using an exponential correction for mass bias. Interference of 176Yb on 176Hf was corrected by measuring the interference-free 173Yb isotope and using 176Yb/173Yb = 0.79639 [79] to calculate 176Yb/177Hf. Similarly, the relatively minor interference of 176Lu on 176Hf was corrected by measuring the intensity of the interference-free 175Lu isotope and using the recommended 176Lu/175Lu = 0.02656 [80] to calculate 176Lu/177Hf. We used the mass bias of Yb (βYb) to calculate the mass fractionation of Lu because of their similar physicochemical properties. Off-line selection and integration of analyte signals, and mass bias calibrations were performed using ICPMSDataCal 10 [75].

Appendix A.5. Calculation Formula of Zircon Hf Isotope

εHf(t) = 10,000 × (((176Hf/177Hf)S − (176Lu/177Hf)S × (eλt − 1))/((176Hf/177Hf)CHUR,0 − (176Lu/177Hf)CHUR × (eλt − 1)) − 1); TDMC = TDM − (TDM − t) × ((fcc − fs)/(fcc − fDM)); TDM = 1/λ × ln(1 + ((176Hf/177Hf)S − (176Hf/177Hf)DM)/((176Lu/177Hf)S − (176Lu/177Hf)DM)); fLu/Hf = (176Lu/177Hf)S/(176Lu/177Hf)CHUR − 1; λ = 1.867 × 10−11 year−1 [81]; (176Lu/177Hf)S and (176Hf/177Hf)S are the measured values of the samples; (176Lu/177Hf)CHUR = 0.0336 and (176Hf/177Hf)CHUR,0 = 0.282785 [82]; (176Lu/177Hf)mean crust = 0.015 [83]; (176Lu/177Hf)DM = 0.0384 and (176Hf/177Hf)DM = 0.28325 [84]; fcc = ((176Lu/177Hf)mean crust/(176Lu/177Hf)CHUR) − 1; fs= fLu/Hf; fDM = ((176Lu/177Hf)DM/(176Lu/177Hf)CHUR) − 1; t = crystallization time of zircon.

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Minerals 15 01093 g003
Figure 3. Hand specimens (a,b) and microphotograph (c,d) of the two-mica syenogranite in the Meibaqieqin region, central Lhasa terrane. Qtz-Quartz, Bt-Biotite, Kfs-k-feldspar, Pl-Plagioclase Ms-muscovite. Sample locality for photo (a,c) is E 87°26′22″ and 30°16′05″ (ZGL01); Sample locality for photo b, d is E 87°25′34″ and 30°16′23″ (ZGL02).
Figure 3. Hand specimens (a,b) and microphotograph (c,d) of the two-mica syenogranite in the Meibaqieqin region, central Lhasa terrane. Qtz-Quartz, Bt-Biotite, Kfs-k-feldspar, Pl-Plagioclase Ms-muscovite. Sample locality for photo (a,c) is E 87°26′22″ and 30°16′05″ (ZGL01); Sample locality for photo b, d is E 87°25′34″ and 30°16′23″ (ZGL02).
Minerals 15 01093 g003
Minerals 15 01093 g004
Figure 4. TAS diagram ((a), after [29]), A/NK vs. A/CNK diagram ((b), after [30]), K2O vs. SiO2 diagram ((c), after [31,32]) of the two-mica syenogranite in the Meibaqieqin region. A-type granite from central Lhasa terrane from [20,21,22,23,24,25,26,33].
Figure 4. TAS diagram ((a), after [29]), A/NK vs. A/CNK diagram ((b), after [30]), K2O vs. SiO2 diagram ((c), after [31,32]) of the two-mica syenogranite in the Meibaqieqin region. A-type granite from central Lhasa terrane from [20,21,22,23,24,25,26,33].
Minerals 15 01093 g004
Minerals 15 01093 g005
Figure 5. Chondrite-normalized REE patterns (a) and primitive mantle-normalized trace element patterns (b) of the two-mica syenogranite in the Meibaqieqin region [34]. A-type granite from northern Lhasa terrane from [24,25].
Figure 5. Chondrite-normalized REE patterns (a) and primitive mantle-normalized trace element patterns (b) of the two-mica syenogranite in the Meibaqieqin region [34]. A-type granite from northern Lhasa terrane from [24,25].
Minerals 15 01093 g005
Minerals 15 01093 g006
Figure 6. Zircons CL images of the two-mica syenogranite in the Meibaqieqin region.
Figure 6. Zircons CL images of the two-mica syenogranite in the Meibaqieqin region.
Minerals 15 01093 g006
Minerals 15 01093 g007
Figure 7. U-Pb concordia diagrams and weighted mean 206Pb/238Pb age diagrams for the two-mica syenogranite in the Meibaqieqin region.
Figure 7. U-Pb concordia diagrams and weighted mean 206Pb/238Pb age diagrams for the two-mica syenogranite in the Meibaqieqin region.
Minerals 15 01093 g007
Minerals 15 01093 g008
Figure 8. Discrimination diagrams for the two-mica syenogranite in the Meibaqieqin region. Diagram (a–d), after [13]; Diagram (e,f), after [15]. The cited data is the same as that in Figure 6.
Figure 8. Discrimination diagrams for the two-mica syenogranite in the Meibaqieqin region. Diagram (a–d), after [13]; Diagram (e,f), after [15]. The cited data is the same as that in Figure 6.
Minerals 15 01093 g008
Minerals 15 01093 g011
Figure 11. Tectonic discrimination diagrams for the two-mica syenogranite. (a) Yb vs. Ta diagram; (b) Y vs. Nb diagram.
Figure 11. Tectonic discrimination diagrams for the two-mica syenogranite. (a) Yb vs. Ta diagram; (b) Y vs. Nb diagram.
Minerals 15 01093 g011
Table 1. Major (wt.%), trace and TREE (μg/g) element data of the two-mica syenogranite in the Meibaqieqin region.
Table 1. Major (wt.%), trace and TREE (μg/g) element data of the two-mica syenogranite in the Meibaqieqin region.
SampleZGL01-1ZGL01-2ZGL01-3ZGL01-4ZGL01-5ZGL02-1ZGL02-2ZGL02-3ZGL02-4ZGL02-5
SiO273.9776.3775.2776.9775.8876.4675.2374.8474.8476.06
Al2O312.6012.0012.8712.0212.1112.2713.6412.9913.1312.32
TFe2O31.260.511.240.370.541.090.651.100.750.99
CaO1.171.060.570.921.000.440.230.320.270.39
MgO0.180.180.140.090.110.130.140.210.130.14
K2O5.295.095.275.195.095.004.715.215.195.01
Na2O3.333.033.143.143.033.273.953.213.533.24
P2O50.010.010.020.010.010.010.010.020.010.01
MnO0.050.020.050.020.020.020.040.030.050.02
TiO20.140.120.150.120.120.120.030.130.090.12
LOI1.511.090.570.771.240.770.580.940.550.54
K2O + Na2O8.638.128.418.338.128.278.668.428.728.25
DI93.3894.2394.3995.3394.2895.5696.0195.196.195.7
σ2.381.972.182.031.992.042.312.212.372.05
10,000 Ga/Al3.693.893.534.053.833.574.633.884.513.99
A/NK1.121.141.181.121.151.141.181.191.151.15
A/CNK0.950.971.080.970.991.061.141.141.11.08
Sr21.637.831.330.134.914.914.922.314.415.4
Ba67.612811266.284.269.046.664.140.055.2
V2.457.166.961.461.385.264.927.784.604.24
Zr16015817516116617176.0141133158
As7.183.098.521.603.650.630.981.470.930.35
Li17.69.3841.48.348.3546.112958.015542.5
Be3.653.623.523.763.443.575.055.735.054.38
Sc1.943.472.434.063.252.897.624.418.022.86
Cr2.413.863.651.131.391.152.387.011.391.09
Co0.600.610.870.270.720.170.360.840.390.79
Ni1.261.612.050.400.590.470.863.170.400.29
Cu7.3213.81414.854.351.892.975.2521.51.75
Zn31.426.339.021.525.730.322.836.728.227.5
Ga24.624.724.025.824.523.233.426.731.326.0
Rb336514341537445395791491847403
Y22.643.524.748.343.435.523.232.729.733.9
Nb36.443.034.550.643.636.267.434.348.036.8
Cs4.215.375.345.554.725.0412.19.4514.005.28
La22.559.119.160.962.034.930.954.451.145.0
Ce93.610294.0106.811091.162.9106105104
Pr4.719.763.9410.310.27.635.4710.49.559.98
Nd15.228.912.630.130.724.715.132.328.432.3
Sm3.235.442.755.635.704.572.525.644.875.80
Eu0.340.300.350.280.280.340.170.420.290.39
Gd2.895.242.625.395.313.832.164.583.904.51
Tb0.530.860.580.880.880.680.390.760.630.71
Dy3.635.263.665.565.554.732.874.804.144.44
Ho0.981.310.951.431.381.250.831.181.081.15
Er3.314.573.505.145.004.753.484.444.224.33
Tm0.540.750.590.850.780.820.700.720.770.70
Yb3.555.144.805.855.425.555.554.905.665.03
Lu0.570.840.631.080.890.870.960.770.960.75
Ta3.944.874.115.714.404.019.994.345.864.24
Pb30.130.050.029.336.928.434.030.639.927.8
Th56.386.152.884.474.756.428.249.146.567.7
U3.0010.03.0018.723.04.355.304.456.303.51
Hf4.033.714.444.154.074.512.873.523.844.13
Rb/Sr15.6013.6010.9117.8212.7626.5952.9921.9759.0326.22
Y/Nb0.621.010.710.950.990.980.340.950.620.92
Rb/Nb9.2411.979.8810.5910.2110.9211.7514.3017.6610.95
Ce/Nb2.572.372.722.112.522.520.933.102.182.83
Nb/Ta9.248.828.398.879.929.026.747.908.188.68
Ce/Pb3.113.401.883.652.983.211.853.462.623.74
Zr/Nb4.413.685.053.193.804.731.134.112.774.30
La/Nb0.621.370.551.201.420.960.461.591.061.22
Th/Ta14.317.6612.8314.7717.0014.062.8211.317.9315.96
La/Sm6.9510.876.9510.8210.897.6312.249.6410.497.76
La/Yb6.3211.503.9810.4211.456.295.5711.109.038.93
Ce/Ce*2.231.042.661.051.071.371.191.091.161.20
Eu/Eu*0.340.170.400.160.160.250.220.250.200.23
ΣREE155.5229.4150.2240.16244.25185.7134231.4220.2219.1
LREE/HREE8.728.577.678.178.697.266.919.449.319.14
LaN/YbN4.548.252.867.478.214.513.997.966.486.41
Notes: Eu/Eu* = 2 × EuN/(SmN + GdN); Ce/Ce* = 2 × CeN/(LaN + PrN); σ = (Na2O + K2O)2/(SiO2 − 43) (wt.%); Differentiation Index (DI) = Qz + Or + Ab + Ne + Lc + Kp.
Table 2. Nd isotopic data of the two-mica syenogranite in the Meibaqieqin region.
Table 2. Nd isotopic data of the two-mica syenogranite in the Meibaqieqin region.
SampleSm (μg/g)Nd (μg/g)147Sm/144Nd143Nd/144Nd(143Nd/144Nd)iεNd(0)εNd(t)fSm/NdTDMTNdDM2
ZGL01-13.2315.20.1290.5119780.511868−12.87−11.75−0.3421061879
ZGL01-25.4428.90.11370.511970.511873−13.03−11.65−0.4217971872
ZGL01-32.7512.60.13170.5120.511888−12.45−11.36−0.3321341847
ZGL01-45.6330.10.11310.5119670.51187−13.09−11.71−0.4317911876
ZGL02-14.5724.70.1120.5119660.51187−13.11−11.71−0.4317731876
ZGL02-22.5215.10.10110.5119590.511873−13.25−11.65−0.4916121874
ZGL02-35.6432.30.10570.5119750.511885−12.93−11.42−0.4616581855
ZGL02-44.8728.40.10380.5119560.511867−13.3−11.77−0.4716551881
Table 3. LA-ICP-MS U-Pb data for zircon from the two-mica syenogranite in the Meibaqieqin region, central Lhasa terrane.
Table 3. LA-ICP-MS U-Pb data for zircon from the two-mica syenogranite in the Meibaqieqin region, central Lhasa terrane.
SpotPbThUTh/U207Pb/206Pb207Pb/235U206Pb/238U207Pb/235U206Pb/238UConcordance
(μg/g)(μg/g)(μg/g)Ratio1σRatio1σRatio1σAge1σAge1σ
ZGL01-1729727161.360.04840.00350.13700.00870.02050.0004130.47.8131.12.899%
ZGL01-2334403161.390.05550.00600.15290.01350.02060.0004144.511.9131.32.490%
ZGL01-3659157511.220.05010.00340.14080.00870.02050.0003133.87.7130.81.897%
ZGL01-4526855101.340.04670.00380.13250.00900.02040.0002126.48.1130.11.597%
ZGL01-5169233418331.270.04920.00260.13820.00680.02040.0002131.56.1129.91.398%
ZGL01-68310909911.100.04910.00330.13790.00860.02030.0003131.17.7129.81.698%
ZGL01-7344863521.380.04920.00550.13620.01370.02030.0003129.612.2129.81.799%
ZGL01-8403117970.390.05210.00370.15130.01080.02080.0003143.19.6132.62.292%
ZGL01-9588226091.350.05030.00440.13950.01030.02060.0004132.69.2131.22.398%
ZGL01-10557315631.300.04700.00410.13300.01030.02050.0002126.89.2130.71.396%
ZGL01-11517595081.490.04740.00430.13150.01060.02040.0003125.59.5130.01.896%
ZGL01-12517394801.540.05170.00420.14650.01040.02060.0003138.89.2131.11.694%
ZGL01-13507074841.460.04860.00460.13640.01200.02050.0003129.810.7130.92.199%
ZGL01-14699438141.160.04730.00380.13300.01000.02040.0002126.89.0130.41.497%
ZGL01-15669267051.310.04900.00430.13780.01100.02050.0003131.09.8131.01.699%
ZGL01-16527754181.850.05060.00530.14250.01470.02050.0003135.213.1130.51.796%
ZGL01-1795126211641.080.04630.00290.13140.00820.02040.0002125.47.4130.41.596%
ZGL01-18324383281.340.05390.00580.15130.01330.02060.0003143.111.8131.41.791%
ZGL01-19608287121.160.05270.00400.14610.00970.02040.0002138.58.6129.91.593%
ZGL01-20506785091.330.05060.00520.14260.01440.02040.0003135.312.8130.41.796%
ZGL01-21284192851.470.05150.00640.14090.01560.02040.0003133.813.9130.21.997%
ZGL01-22618625981.440.05210.00420.14800.01120.02060.0003140.19.9131.11.893%
ZGL01-23496655371.240.04820.00410.13770.01100.02040.0002131.09.8130.11.599%
ZGL01-24506177020.880.05030.00380.14410.01030.02050.0003136.79.1130.91.995%
ZGL02-1568335821.430.04770.00340.13540.00860.02050.0003128.97.7130.61.898%
ZGL02-2365064221.200.04490.00420.12640.01090.02050.0003120.89.9130.51.892%
ZGL02-3355053671.380.05160.00460.14590.01200.02050.0003138.310.6130.81.894%
ZGL02-4365464141.320.04740.00400.12890.00880.02020.0004123.17.9129.12.495%
ZGL02-5283773661.030.05140.00450.14590.01200.02050.0003138.310.6131.02.094%
ZGL02-67811367861.450.04840.00300.13760.00870.02030.0003130.97.7129.61.799%
ZGL02-7263772981.270.05120.00490.14200.01200.02050.0004134.810.6130.52.296%
ZGL02-8375194251.220.05130.00420.14260.01020.02040.0003135.49.0130.12.095%
ZGL02-9527475891.270.04900.00360.13840.00990.02040.0003131.68.9130.41.899%
ZGL02-10376302552.470.04670.00530.12900.01280.02010.0003123.211.5128.11.896%
ZGL02-11304213401.240.04470.00410.12530.01010.02030.0003119.99.1129.61.692%
ZGL02-127411597511.540.05080.00340.14220.00940.02030.0003135.08.4129.72.095%
ZGL02-13284213001.400.05300.00570.15150.01470.02060.0003143.312.9131.12.091%
ZGL02-157711748101.450.04550.00330.12730.00860.02020.0003121.77.8129.21.994%
ZGL02-16287615541.370.04410.00420.12490.01130.02030.0003119.510.2129.31.892%
ZGL02-188712239691.260.04670.00350.13040.00930.02030.0002124.58.3129.31.496%
ZGL02-19436144301.430.04930.00440.13790.01120.02030.0002131.210.0129.41.598%
ZGL02-20486794771.420.05420.00450.15280.01120.02060.0003144.49.9131.42.190%
ZGL02-21314193221.300.05200.00470.14590.01120.02040.0003138.39.9130.01.993%
ZGL02-229214286132.330.04900.00400.13940.01050.02040.0002132.59.4130.21.498%
ZGL02-23496655241.270.05430.00580.14860.01390.02050.0003140.612.3130.62.192%
ZGL02-24495956720.890.05120.00390.14530.01050.02060.0003137.89.3131.11.795%
ZGL02-257310696031.770.04700.00420.13180.01100.02040.0003125.79.8130.31.896%
ZGL02-26355133701.390.04830.00460.13770.01150.02040.0003131.010.3129.91.999%
ZGL02-28395703461.650.04970.00510.14040.01310.02030.0003133.411.6129.72.097%
Table 4. Hf isotopic compositions of zircons from the two-mica syenogranite in the Meibaqieqin region, central Lhasa terrane.
Table 4. Hf isotopic compositions of zircons from the two-mica syenogranite in the Meibaqieqin region, central Lhasa terrane.
Spot176Yb/177Hf1σ176Lu/177Hf1σ176Hf/177Hf1σAge (Ma)IHfεHf(0)εHf(t)TDMTDM2fLu/Hf
ZGL01-10.0649410.0005770.0016700.0000180.2823990.000013131.10.282395−13.18−10.4712271852−0.95
ZGL01-20.0861680.0023560.0018830.0000350.2824360.000015131.30.282432−11.88−9.1611811770−0.94
ZGL01-30.1028410.0004640.0023230.0000180.2824120.000016130.80.282407−12.72−10.0512291824−0.93
ZGL01-40.0897860.0006290.0022470.0000240.2823980.000014130.10.282392−13.23−10.5812481857−0.93
ZGL01-50.0977620.0006810.0024910.0000080.2824100.000013129.90.282404−12.80−10.1512381830−0.92
ZGL01-60.0855600.0008980.0021120.0000020.2823970.000016129.80.282392−13.26−10.5812441857−0.94
ZGL01-70.0516770.0010960.0012660.0000190.2824190.000014129.80.282416−12.48−9.7311851804−0.96
ZGL01-80.0940330.0006020.0023100.0000150.2824200.000013132.60.282415−12.44−9.7612171806−0.93
ZGL01-90.0812560.0003960.0020720.0000020.2824100.000013131.20.282405−12.79−10.1212241828−0.94
ZGL01-100.0728250.0003200.0018330.0000140.2824020.000014130.70.282398−13.07−10.3712271844−0.94
ZGL01-110.0909990.0018070.0021990.0000510.2824300.000015130.00.282425−12.08−9.4111991784−0.93
ZGL01-120.0892610.0015380.0020450.0000310.2824230.000012131.10.282418−12.33−9.6612041798−0.94
ZGL01-130.0976690.0005400.0021850.0000200.2824340.000015130.90.282429−11.95−9.2711931775−0.93
ZGL01-140.0768260.0003250.0018180.0000080.2824010.000013130.40.282396−13.14−10.4412301849−0.95
ZGL01-150.0721020.0003190.0017880.0000100.2824320.000014131.00.282428−12.02−9.3011831777−0.95
ZGL01-160.0964010.0016420.0022070.0000280.2824030.000016130.50.282398−13.04−10.3712381843−0.93
ZGL01-170.1557630.0041770.0041790.0001170.2823820.000014130.40.282372−13.79−11.2813421902−0.87
ZGL01-180.0844080.0012490.0020830.0000400.2824130.000016131.40.282408−12.68−10.0112201821−0.94
ZGL01-190.0834140.0010030.0020750.0000130.2824180.000015129.90.282412−12.54−9.8712141812−0.94
ZGL01-200.0620560.0007350.0015160.0000050.2823880.000016130.40.282385−13.57−10.8212371875−0.95
ZGL01-210.1825020.0080260.0040880.0001260.2824460.000019130.20.282436−11.53−9.0212411759−0.88
ZGL01-220.0927320.0017820.0023190.0000490.2824350.000013131.10.28243−11.91−9.2311961773−0.93
ZGL02-10.1069460.0003950.0025030.0000220.2824330.000012130.60.282427−11.98−9.3512051779−0.92
ZGL02-20.0678300.0001830.0016150.0000040.2824070.000012130.50.282403−12.91−10.2012141834−0.95
ZGL02-30.0576460.0009370.0012980.0000110.2824320.000013130.80.282429−12.03−9.2811681776−0.96
ZGL02-40.0722880.0003750.0017170.0000090.2824080.000016129.10.282403−12.89−10.2012161832−0.95
ZGL02-50.0941550.0004630.0022170.0000130.2824300.000014131.00.282425−12.09−9.4212001785−0.93
ZGL02-60.0929700.0029900.0023680.0000820.2823930.000014129.60.282387−13.41−10.7712591868−0.93
ZGL02-70.0562640.0005800.0013170.0000140.2824110.000013130.50.282407−12.78−10.0611991824−0.96
ZGL02-80.0647810.0002440.0015560.0000020.2824300.000014130.10.282426−12.10−9.3911791782−0.95
ZGL02-90.0728940.0005770.0017830.0000050.2824240.000012130.40.282419−12.32−9.6311961798−0.95
ZGL02-100.1439200.0016000.0031220.0000150.2824940.000014128.10.282486−9.83−7.2611361647−0.91
ZGL02-110.0830860.0005300.0018320.0000070.2824200.000012129.60.282415−12.46−9.7712021805−0.94
ZGL02-120.1236620.0018340.0030340.0000460.2824150.000014129.70.282408−12.63−10.0212501823−0.91
ZGL02-130.0709750.0006540.0015550.0000060.2824340.000013131.10.28243−11.97−9.2411741774−0.95
ZGL02-150.0788060.0007240.0019690.0000240.2824140.000012129.20.282409−12.66−9.9912151819−0.94
ZGL02-180.0875610.0003790.0019070.0000100.2824250.000013129.30.282421−12.26−9.5611971794−0.94
ZGL02-190.0642020.0003000.0015840.0000130.2824130.000017129.40.282409−12.69−9.9912041820−0.95
ZGL02-200.0859970.0020790.0020090.0000350.2824730.000014131.40.282468−10.59−7.9011321688−0.94
ZGL02-210.0597030.0008360.0013650.0000070.2824130.000013130.00.28241−12.69−9.9511971819−0.96
ZGL02-220.1365690.0023740.0029930.0000390.2824460.000015130.20.282439−11.52−8.9312021752−0.91
ZGL02-230.0981170.0010780.0026890.0000520.2823860.000015130.60.282379−13.67−11.0512811887−0.92
ZGL02-240.0606800.0014260.0014130.0000240.2824060.000013131.10.282403−12.93−10.2012081834−0.96
ZGL02-250.0886600.0010480.0021100.0000190.2824110.000018130.30.282406−12.76−10.0912241827−0.94
ZGL02-260.0627620.0003510.0015040.0000140.2823880.000015129.90.282384−13.58−10.8712371875−0.95
Note: The calculation formula is presented in Appendix A.5.
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Yang, Y.; Zhao, J.; Gao, K.; Zhang, Z.; Ding, S.; Gong, J.; Wu, J.; Xu, P.; Li, Y. The First Discovery of A1-Type Granite in the Meibaqieqin Region, Central Lhasa Terrane, Xizang. Minerals 2025, 15, 1093. https://doi.org/10.3390/min15101093

AMA Style

Yang Y, Zhao J, Gao K, Zhang Z, Ding S, Gong J, Wu J, Xu P, Li Y. The First Discovery of A1-Type Granite in the Meibaqieqin Region, Central Lhasa Terrane, Xizang. Minerals. 2025; 15(10):1093. https://doi.org/10.3390/min15101093

Chicago/Turabian Style

Yang, Yi, Junkang Zhao, Ke Gao, Zhi Zhang, Shuai Ding, Jiansheng Gong, Jianyang Wu, Peiyan Xu, and Yingxu Li. 2025. "The First Discovery of A1-Type Granite in the Meibaqieqin Region, Central Lhasa Terrane, Xizang" Minerals 15, no. 10: 1093. https://doi.org/10.3390/min15101093

APA Style

Yang, Y., Zhao, J., Gao, K., Zhang, Z., Ding, S., Gong, J., Wu, J., Xu, P., & Li, Y. (2025). The First Discovery of A1-Type Granite in the Meibaqieqin Region, Central Lhasa Terrane, Xizang. Minerals, 15(10), 1093. https://doi.org/10.3390/min15101093

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