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The Baingoin batholith is one of the largest granitic plutons in the North Lhasa terrane. Its petrogenesis and tectonic setting have been studied for decades, but remain controversial. Here we report data on geochronology, geochemistry and isotopes of Early Cretaceous granitoids within the Baingoin batholith, which provide more evidence to uncover its petrogenesis and regional geodynamic processes. The Early Cretaceous magmatism yields ages of 134.4–132.0 Ma and can be divided into I‐type, S‐type and highly fractionated granites. The I‐ and S‐type granites exhibit medium SiO2, high K2O/Na2O with negative εNd(t) and εHf(t) values, whereas, the albite granites have very high SiO2 (79.04%–80.40%), very low K2O/N2O, negative εNd(t) and a large variation in εHf(t). Our new data indicate that these granitoids are derived from unbalanced melting in a heterogeneous source area. The granodiorites involved had a hybrid origin from partial melting of basalt‐derived and Al‐rich rocks in the crust, the porphyritic monzogranites being derived from partial melting of pelitic rocks. The albite granites crystallized from residual melt separated from K‐rich magma within the 'mush' process and underwent fractionation of K‐feldspar. We believe that the Early Cretaceous magmatism formed in an extensional setting produced by the initial and continuous rollback of a northward‐subducting slab of the NTO. [ABSTRACT FROM AUTHOR]

There were multiple episodes of magmatism in the Southern Da Hinggan Mountains during the Late Jurassic to Early Cretaceous, and an in-depth study of the petrogenesis and evolutionary process is of great geological significance to reveal the Mesozoic geodynamic background and mineralization. In this paper, LA-ICP-MS zircon U-Pb dating and whole-rock geochemistry for medium-grained adamellite, fine-grained adamellite and granite peg-matite in Hailiute area were carried out. The zircon 206Pb/238U weighted average ages of the medium-grained adam-ellite, fine-grained adamellite and granite pegmatite are 142.0 ± 0.7 Ma, 141.2 ± 1.1 Ma and 139.7 ± 2.4 Ma respectively, belonging to the Early Cretaceous. They have high SiO2 and total alkali contents, and their A/CNK value is 1.01 ~ 1.18, with an average value of 1.09, which is weak peraluminous. They are characterized by enrichment of large ion lithophile elements such as Rb, Th and K and depletion of high field strength elements including Ba, Sr, P and Ti, with extremely negative Eu anomalies (δEu = 0.012~0.040). The Zr+Nb+Ce+Y value of them is between 38. 25x10-6 and 258. 2x10-6, less than 350x10-6. The zircon saturation temperature of them is 723X1 to 778X1. The primary muscovite and alkaline-mafic minerals Eire not found among them. The magma experienced the fractional crystallization of plagioclase and K-feldspar during its evolution. The Zr/Hf, La/Ta and La/Nb of them are lower than the range of normal granite, however Nb/Ta and Y/Ho of them are in the area of normal granite. The parameters of tetrad effect of rare earth element (TE1,3) of them is between 1.18 and 1.34, greater than 1.1. In conclusion, the Hailiute granite belongs to early Cretaceous highly differentiated I-type granite. It has weak interaction between melt and fluid in the process of crystallization differentiation, which can promote the formation of tungsten, tin and rare metals minerals. [ABSTRACT FROM AUTHOR]

The ore-related Sn granites in the Youjiang basin (YJB; ~ 4.0 Mt Sn) and W granites in the Jiangnan tungsten belt (JNB; ~ 6.0 Mt WO3) in south China were studied to decipher regional-scale controls on whether Sn or W is most likely to be associated with highly fractionated reduced granitic magmas. Both Sn and W mineralization-related magmas were derived from partial melting of metasedimentary rocks. Although Sn and W behave similarly during fractional crystallization and therefore become enriched in highly evolved reduced granites, there is commonly a clear distinction between Sn-dominated and W-dominated systems. For example, the YJB hosts world-class Sn deposits that lack accompanying economic W, whereas the JNB hosts world-class reduced W deposits that lack accompanying economic Sn. This difference may be related to conditions of source melting, such that W is mobilized into initial granitic magmas when partial melting of metasedimentary rocks occurs at lower temperature, whereas melts that form at higher temperature may have higher Sn concentrations. The later have low W concentrations because W has already been lost at the lower temperature melting event. Results from this study reveal that the W-related granites in the JNB were derived from metasedimentary rocks that had never experienced a previous episode of high-grade metamorphism or melting. The melts were enriched in W but depleted in Sn and formed W-only ores after extensive fractional crystallization. In contrast, the granites in the YJB were derived from melting of metasedimentary rocks that had undergone previous episodes of high-grade metamorphism or melting and formed Sn-only ores after extensive fractional crystallization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Early Jurassic highly fractionated S-type granites near Damxung in south Tibet. • Fractional crystallization produced the compositional diversity. • The magmatism is attributed to the rollback of Neo-Tethyan slab. The Gangdese orogenic belt in southern Tibet records a succession of arc-trench-basin assemblages formed by the Neo-Tethyan subduction and the subsequent India-Asian collision. However, the geochronology and geodynamics of S-type granites in the northern part of the Gangdese belt are disputed. This paper describes ~190 Ma S-type granitoids outcropped in the Nyainqêntanglha Range, South Tibet, focusing on their petrogenesis and their relationship with contemporaneous magmatism. There are three distinct groups of granitoids, based on field relationships, petrology, and geochemistry. The coarse-grained Group I and II granitoids are large, sheet-like bodies and exhibit high contents of incompatible elements and negative Eu anomalies. The fine-grained Group III granites form small laccoliths and have low REE contents and positive Eu anomalies. The negative ε Nd (t) and ε Hf (t) values, abundant inherited zircons, moderately light REE and LILE enrichment, and HFSE depletion indicate that the Damxung granitoids were derived mainly by the partial melting of a metapelitic source. Further studies proposed that group I and II samples with high contents of incompatible elements and negative Eu anomalies represent fractionated melts, whereas group III samples with low REE contents and positive Eu anomalies represent cumulates. The age distribution pattern of inherited zircons supports the interpretation that the Lhasa terrane rifted away from the northern margin of the Indian plate. Considering previously published data in the Lhasa terrane, we suggest that the Early Jurassic magmatism could be related to a period of subducted oceanic slab roll-back, which provides new insights into the evolution process of the Neo-Tethyan ocean realm. [ABSTRACT FROM AUTHOR]

The widespread W-(Mo)-Sn-Nb-Ta polymetallic mineralization in Southeast (SE) China is genetically associated with Mesozoic highly fractionated granitic rocks. Such rocks have enigmatic mineralogical and geochemical features, making its petrogenesis an intensely debated topic. To better understand the underlying magma evolution processes, petrography, garnet chemistry and whole-rock major and trace element data are reported for Jurassic highly fractionated granitic rocks and associated microgranite and aplitepegmatite dikes from Macao and compared with coeval similar granitic rocks from nearby areas in SE China. Despite the fact that the most evolved rocks in Macao are garnet-bearing aplite-pegmatite dikes, the existence of coeval two-mica and garnet-bearing biotite and muscovite granites displaying more evolved compositions (e.g, lower Zr/Hf ratios) indicates that the differentiation sequence reached higher degrees of fractionation at a regional scale. Although crystal fractionation played an important role, late-stage fluid/melt interactions, involving F-rich fluids, imparted specific geochemical characteristics to Macao and SE China highly fractionated granitic rocks such as the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of trace elements, leading, for example, to non-chondritic Zr/Hf ratios, Rare Earth Elements (REE) tetrad effects and Nb-Ta enrichment and fractionation. Such process contributed to the late-stage crystallization of accessory phases only found in these highly evolved facies. Among the latter, two populations of garnet were identified in MGI (Macao Group I) highly fractionated granitic rocks: small grossular-poor euhedral grains and large grossular-rich skeletal garnet grains with quartz inclusions. The first group was mainly formed through precipitation from highly evolved Mn-rich slightly peraluminous melts under low-pressure and relatively low temperature (∼700 °C) conditions. Assimilation of upper crust metasedimentary materials may have contributed as a source of Mn and Al to the formation of garnet. The second group has a metasomatic origin related to the interaction of magmatic fluids with previously crystallized mineral phases and, possibly, with assimilated metasedimentary enclaves or surrounding metasedimentary strata. The highly fractionated granitic rocks in Macao represent the first stage in the development of granite-related W-(Mo)-Sn-Nb-Ta mineralization associated with coeval more evolved lithotypes in SE China. [ABSTRACT FROM AUTHOR]

The Qianlishan complex, located in Hunan Province of South China, is closely associated with intense W-dominated polymetallic mineralization. The Qianlishan complex is composed of three phases: the main-phase porphyritic and equigranular granites, granite porphyry, and mafic dykes. Geochronologically, the zircon U-Pb dating results show that the porphyritic and equigranular granites have ages of approximately 159 and 158 Ma, respectively, similar to those of mafic dykes (approximately 158 Ma), while the granite porphyry was formed later at approximately 145 Ma. Geochemically, the mafic dykes are characterized by calc-alkaline high-Mg andesite (HMA) with high MgO, TiO2, Mg#, and CA/TH index. They exhibit significantly depleted εNd(t) and εHf(t) with high Ba/La, La/Nb, and (La/Yb)N, indicating that they formed from mixing melts of depleted asthenospheric mantle and metasomatized subcontinental lithospheric mantle (SCLM). The main-phase granites are peraluminous and are characterized by high SiO2, low (La/Yb)N ratios, and relative depletion in Ba, Sr, Ti, and Eu. They also display negative correlations between La, Ce, Y, and Rb contents, suggesting that they are highly fractionated S-type granites. Furthermore, they show high εNd(t) and εHf(t), CaO/Na2O ratios, HREE, and Y contents, indicating that they were produced by parental melting of ancient basement mixed with mantle-derived components. In contrast, the granite porphyry shows A-type signature granites, with higher εNd(t) and εHf(t) and CaO/Na2O ratios than the main-phase granites but similar Zr/Nb and Zr/Hf ratios to the mafic dykes, suggesting that they are the products of partial melting of a hybrid source with ancient basement and the mafic dykes. We thus infer that the slab roll-back led to generation of Qianlishan back-arc basalt and HMA and further triggered the formation of the Qianlishan granite.

[Display omitted] • Magmatism and mineralization of the Daxiyingzi deposit occurred at ∼223 Ma. • The Daxiyingzi granites belong to highly fractionated granites. • They are derived from partial melting of ancient crust with injecting of mantle magma. • Be-Rb mineralization occurred in granite pegmatites. A new Rb–Be rare metal deposit has been discovered in the northern margin of the North China Craton in Fuxin City, western Liaoning Province, China. The Daxiyingzi Rb–Be deposit is a granitic pegmatite-type deposit and composed mainly of biotite granite, albite granite, and amazonite granitic pegmatite. Amazonite and beryl are the main ore minerals containing Rb and Be, and occur in the amazonite granitic pegmatite. We present integrated biotite 40Ar/39Ar geochronology, mineralogy, whole-rock geochemistry, and Nd–Pb isotope analyses of the Daxiyingzi ore-bearing granites to better understand their petrogenesis and geodynamic setting. Biotite separates in biotite granite and albite granite yield 40Ar/39Ar ages of 223.27 ± 2.39 and 223.37 ± 2.45 Ma, which we interpret as the metallogenic age of the deposit. The Daxiyingzi granites have high A/CNK ratios (1.01–1.11) and sufficient contents of SiO 2 (74.68–79.42 wt%), total alkali (K 2 O + Na 2 O, 7.89–9.49 wt%), Li (64.0–300 ppm), Be (6.85–10.95 ppm), Nb (38.2–144 ppm), Ta (12.6–109 ppm), and Rb (60.8–1426 ppm). Depletion in Eu, Ba, Sr, P, and Ti and enrichment in Rb, Th, Nb, Ta, Nd, and Hf indicate that the granites are highly fractionated I-type granites. The Nd–Pb isotopic compositions [ε Nd (t) = −2.5 to −4.1; T DM2 = 1320–1202 Ma] of these granites suggest that they were derived from a single magma reservoir in an extensional orogenic setting at ∼223 Ma via high-temperature partial melting of Mesoproterozoic–Neoproterozoic basement and the injection of mantle derived magma. As a peraluminous magmatic polymetallic deposit formed in an orogenic setting, the Daxiyingzi Rb–Be deposit represents a potential new direction for prospecting along the northern margin of the North China Craton. [ABSTRACT FROM AUTHOR]

Western Yunnan, an important constituent of the southeastern segment of the East Tethyan tectonic domain, lies along a transformed orientation from the NWW trending Himalayan–Tethyan segment to the northerly trending Southeast Asian segment. However, the geodynamical setting of the Early Cretaceous tectonothermal magmatism along the Bangong–Nujiang–Lushui–Luxi–Ruili belt as the Tethyan branch in western Yunnan (SW China) remains controversial. The Donghe granitoid, which is located between the Gaoligong and Tengliang belts in the northern Tengchong block, reveals its petrogenesis and its tectonics, both of which play a vital role in resolving previous disputes. Our zircon laser ablation inductively coupled plasma mass spectrometry U–Pb dating of granites from the Donghe batholith yields ages of 119.9 ± 0.9–130.6 ± 2.5 Ma. These granites display features typical of highly fractionated I-type granites: high SiO 2 contents (>71 wt.%), high K contents (K 2 O = 3.88–5.66 wt.%), calc-alkaline character, slight peraluminosity (A/CNK = 1.02–1.16), and a highly differentiated index ranging from 83.6 to 95.6. In addition, as SiO 2 contents increase, the rare earth element (REE) abundances, especially heavy REE abundances, and REE pattern slopes change gradually, but the negative Eu anomalies increase sharply, while the degree of enrichment in Rb, Th, U, and Pb and depletion in Ba, Nb, Sr, P, and Ti are enhanced. These features indicate that K-feldspar, ±plagioclase, ±biotite, ±amphibole, ±apatite, ±sphene/garnet, and ±Fe–Ti oxides such as ilmenite play the major role in the fractional crystallization process. The high initial 87 Sr/ 86 Sr (0.7067 and 0.7079) and negative ε Nd ( t ) values (−8.6 to −10.1), with T 2DM ranging from 1.39 to 1.49 Ga, indicate that the sources were mainly derived from the mature ancient middle to lower crust and minor mantle-derived materials. The initial 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios of 18.462–18.646, 15.717–15.735, and 38.699–39.007, respectively, signify that some subduction-related material such as ocean island volcanic rocks and mature arc primitive rocks may be involved as sources. Based on an analysis of similar zircon saturated temperature and geochemical characteristics of typical highly fractionated I-type granites in SE and SW China, and consideration of the regional geological setting, we suggest that the parent magma may be derived from the ancient middle to lower continental crust and mantle-derived basaltic magma. These were generated in the setting of a westward subducted Lushui–Luxi–Ruili (LLR) Tethyan oceanic slab, where mantle-wedge-derived sources provided enough heat and material to melt the middle to lower ancient crust. Taking into account the temporal–spatial distributions of Early Cretaceous magmatic rocks in the region, we further suggest the existence of an Andean-type active continental margin from the Lhasa block to the Tengchong block along the Bangong–Nujiang–LLR Tethys Ocean during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

Zircon, monazite, and xenotime have proven to be valuable chronometers for various geological processes due to their commonly high-U-Th and low common Pb contents. However, zircons that have crystallized in highly fractionated granites often have such high-U contents that radiation damage can lead to scattered U-Pb ages when measured with secondary ion mass spectrometry (SIMS). In this study, monazite and xenotime were separated from a number of highly fractionated granites at the Xihuashan tungsten mine, Southeast China, for alternative dating methods by SIMS. For monazite analysis, obvious excess Pb signal (mainly from interference of ThNdO) was observed in high-Th (>2 wt%) monazite, which hinders Pb-based common Pb corrections. A Pb-based common Pb correction method was used instead. By employing power law relationships between Pb/U versus UO/U, Pb/Th versus ThO/Th and suitable exponentials, monazites with ThO contents in the range of ~3-19 % do not exhibit this matrix effect. Independent SIMS U-Pb ages and Th-Pb ages of three phases of Xihuashan granite samples were consistent with each other and yielded dates of 158.7 ± 0.7, 158.0 ± 0.7, and 156.9 ± 0.7 Ma, respectively. Xenotime does show marked matrix effects due to variations of U, Th, and Y [or total rare earth element (REE), referred as ΣREE hereafter] contents. Suitable correction factors require end-member standards with extremely high or low U, Th, and Y (or ΣREE) contents. No excess Pb was observed, indicating that the Pb-based common Pb correction method is feasible. Independent Pb/Pb ages can be obtained, although multi-collector mode is necessary to improve precision. The main difficulties with dating xenotime are when high-Th (U) mineral inclusions are ablated. We can identify when this occurs, however, by comparing the measured UO/U and ThO/Th with those in xenotime standards. Three xenotime samples from the first phase of Xihuashan granite yielded a weighted mean Pb/Pb date of 159.5 ± 4.4 Ma (MSWD = 1.0) and a Pb/U date of 159.4 ± 0.9 Ma (MSWD = 1.6), which are consistent with monazite U-Pb and Th-Pb ages from the same granites. This study demonstrates that monazite and xenotime are better SIMS chronometers for highly fractionated granites than zircon, which can yield doubtful ages due to high-U contents. [ABSTRACT FROM AUTHOR]