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Subduction of Indian continental lithosphere during the Asia-India collision played an important role in the formation and evolution of the Himalaya-Tibetan orogen. However, the geometry of early Indian continental subduction remains debated. Given that the Indian continent is characterized by enriched isotope ratios (87Sr/86Sr > 0.730, εNd(t) < −10), relative to those in subducted oceanic materials (87Sr/86Sr < 0.704, εNd(t) ≈ +8), changes in the composition of magmatic rocks with time, in particular their radiogenic isotope ratios, is used to constrain the timing and nature of continental subduction. This study reports the field relations, zircon U-Pb ages and geochemical composition of a syn-collisional batholith that crosscuts the central Indus-Yarlung Zangbu suture in the Saga area of southern Tibet. Zircon U/Pb ages for the batholith mainly range from 50 to 46 Ma. Samples from the Lopu Range batholith have enriched zircon Hf (εHf(t) = −0.4 to −8.6) and whole rock 87Sr/86Sri = 0.7094–0.7121 and εNd(t) = −7.3 to −9.8, suggesting that they were derived from a mixture of juvenile Gangdese and isotopically enriched Indian crustal materials. This result indicates that subduction of Indian crustal rocks occurred before 50 Ma in the central Himalaya. The geochemical composition and distribution of high volume ca. 51 Ma magmatism in the Gangdese belt, combined with thermal models of the subduction zone, suggests a steepening of the subducted Indian continental lithosphere occurred between the onset of India-Asia collision (59 Ma) and 46 Ma in the central-eastern Himalaya.

The petrogenesis of biotite granites, which may be metaluminous or peraluminous in composition, is a subject of debate. In this study, we present new zircon U-Pb geochronology and O-Hf isotopic, and whole-rock major and trace element, and Sr-Nd isotopic data for biotite granites in the Langla–Laqinpu area of northern Lhasa Terrane, central Tibet. The rocks are distributed along the eastern segment of the Bangong–Nujiang Tethys Ocean suture, and were emplaced during the late Early Cretaceous (ca.119 Ma). The biotite granites are peraluminous, and have high SiO2 (67.5–72.4 wt%) and low MgO (0.57–1.20 wt%) and CaO (2.36–4.38 wt%) contents with variable K2O/Na2O ratios (0.77–1.32), and show geochemical affinity with the upper-continental crust, e.g., enrichment of Rb, Th, U, K and Pb, depletion of Nb, Ta, Ti, P, Eu, and Sr. They are characterized by relatively high initial 87Sr/86Sr ratios ((87Sr/86Sr)i = 0.7098–0.7137) and low eNd(t) values (−8.4 to −10.3), and high zircon δ18O values (8.29–13.47‰) and variable eHf(t) values (−0.02 to −21.36), indicating they were derived through partial melting of a crustal source consisting of metagreywackes with or without minor metaigneous rocks. Taking into account all available regional geological data, we suggest that the Bangong–Nujiang Tethys Ocean may undergo diachronous closure–although the eastern segment may have been closed by the late Early Cretaceous, its western and western–middle segments may still have been at least partially open and active at that time. The Langla–Laqinpu biotite granites were probably generated in post-collisional setting, following slab break-off after closure of the Bangong–Nujiang Tethys Ocean.

A-type granites have been the focus of considerable research due to their distinctive major- and trace-element signatures and tectonic significance. However, their petrogenesis, magmatic source and tectonic setting remain controversial, particularly for aluminous A-type granites. The earliest Cretaceous (ca. 140 Ma) Comei granite in the eastern Tethyan Himalaya is associated with coeval oceanic island basalt (OIB)-type mafic lava, and has A-type granite geochemical characteristics including high 10,000 × Ga/Al (up to 6), FeOtotal/MgO (4.6–6.1) and (Na2O + K2O)/Al2O3 (0.50–0.61) ratios but low CaO (0.6–1.6 wt%) and Na2O (1.8–2.6 wt%) contents. The Comei granite also has variable peraluminous compositions (A/CNK = 1.00–1.36) along with zircon δ18O, εNd(t) and initial 87Sr/86Sr values of 8.2‰ to 9.3‰, − 13.0 to − 12.4 and 0.7238 to 0.7295, respectively. This range of compositions can be interpreted as the interaction between high-temperature upwelling OIB type basaltic magmas and a shallow crustal (< 5 kbar) metapelitic source. The Comei granite and coeval OIB type basaltic rock could represent the earliest stage (145–140 Ma) of a large igneous event in eastern Tethyan Himalaya, which may well have been triggered by pre-breakup lithospheric extension prior to the arrival of the Kerguelen plume head.

High-silica granites are common in collisional orogenic belts. However, the petrogenesis of such granites and the geodynamic processes associated with their emplacement are debated. In this study, we present zircon U–Pb ages and Hf isotopes, and whole-rock geochemical and Sr–Nd isotopic compositions for biotite granites from the Jiang Co area, in the Bangong–Nujiang suture zone, central Tibet. Zircon U–Pb dating reveals that the Jiang Co granites were emplaced during the late Early Cretaceous (ca.114 Ma). These granites are characterized by high and variable SiO2 (69.7–78.2 wt%) and K2O (4.7–8.4 wt%), and low MgO (0.09–1.25 wt%) and P2O5 (

The nature and pre‐Cenozoic evolution history of crust in southern Lhasa, which is crucial for our understanding of Indo‐Asian continental collision and Tibetan uplift during the Cenozoic, remains controversial due to a “missing” pre‐Mesozoic magmatic record. In this contribution, we report petrological and geochemical data for newly identified Paleozoic bimodal magmatism in the Zhengga area of southern Tibet. The magmatism comprises Late Devonian‐Early Carboniferous (366–353 Ma) amphibolite and two‐mica gneissic granite. The protoliths of the Zhengga amphibolite were gabbro and diorite with low SiO2 and high MgO, Cr, and Ni contents with high eNd(t) values of +3.3 to +8.0, variable and positive zircon eHf(t) of +0.9 to +11.2, and low zircon δ18O of 5.7 ± 0.2‰. These protoliths are proposed to have formed by decompression melting of asthenosphere during intracontinental back‐arc extension. In contrast, the granite has relatively high SiO2 and low MgO contents with much lower eNd(t) of −8.6 to −7.3, variable and negative zircon eHf(t) of −10.4 to −1.3, and high zircon δ18O of 9.4 ± 0.2‰ values and was most likely derived from an ancient metasedimentary source. This magma subsequently underwent recharge with minor amounts mafic magma followed by fractional crystallization of K‐feldspar in middle‐upper crust (~10–20 km) magma chambers. Using our new data, in combination with Nd‐Hf isotopes, we present the first comprehensive picture of crustal evolution in southern Lhasa. The southern Lhasa sub‐block is likely to have been a microcontinent that underwent extensive Phanerozoic crustal reworking and growth, rather than a Mesozoic‐Early Tertiary juvenile accretionary arc terrane.

Crustal reworking in the collisional zones is commonly considered as an important process to result in continental crust differentiation and maturation. However, the reworking mechanism remains unclear. Here, a combined study of zircon SIMS U–Pb age, whole-rock major and trace element, Sr–Nd–Hf and zircon Hf–O isotopic geochemistry was carried out for the Duoma–Namuqie (DM–NMQ) granite porphyry intrusions, including DM, NMQ I, II and III intrusions, in southern Qiangtang, central Tibet. Zircon SIMS U–Pb dating yielded ages of 79–76 Ma, suggesting that they were formed in the later stage of Late Cretaceous. The DM granite porphyries are metaluminous to peraluminous with slightly low SiO2 (69.2–71.4 wt%) and high MgO (0.67–0.79 wt%) contents. They are depleted in high-field-strength elements (HFSEs) and enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs), and show weakly negative Eu anomalies. The NMQ III granite porphyries show similar elemental features to the DM granite porphyries, but have relatively high SiO2 (69.8–72.2 wt%) and low MgO (0.25–0.28 wt%) contents. Both of them belong to I-type granites. The NMQ I and II granite porphyries are relatively differentiated with high SiO2 (76.4–77.9 wt%), low MgO (0.11–0.16 wt%) contents, and significantly negative Eu anomalies. Extremely low LREE contents and notable REE tetrad effect can be observed in the NMQ II granite porphyries. The NMQ I and II intrusions are fractionated I-type granites. The whole-rock Sr–Nd–Hf and zircon Hf–O isotope data exhibit an enriched trend from the DM granite porphyries ((87Sr/86Sr)i = 0.7049–0.7050, eNd(t) = 1.2–1.6, eHf(t)whole-rock = 9.9–12.0, eHf(t)zircon = 7.4–11.5, δ18O = 6.2–7.1‰) to the NMQ III granite porphyry ((87Sr/86Sr)i = 0.7058–0.7067, eNd(t) = −0.9 to −1.1, eHf(t)whole-rock = 7.0–7.4, eHf(t)zircon = 2.7–9.5, δ18O = 7.2–7.6‰) to the NMQ I and II granite porphyries (eNd(t) = −3.0 to −4.3, eHf(t)whole-rock = 5.3–6.6, eHf(t)zircon = 1.5–7.4, δ18O = 6.6–9.2‰). We suggest that the DM–NMQ granite porphyries were mainly derived by partial melting of the juvenile mafic lower crust with variable volumes of ancient crustal components involved in their magma sources. The way in which these granite porphyries were formed provides evidence for the crustal differentiation and maturation in a post-collisional extensional setting triggered by the far-field rollback of the subducted Neo-Tethys oceanic slab

Arc magmas are generated by complex geological processes in subduction settings. Due to the complexity of source materials and geological processes, the genesis of arc magmatic rocks can be difficult to disentangle. Here, we report on diorites from the Kenama area of the middle-eastern part of the Bangong–Nujiang suture zone in central Tibet. New SIMS and LA–ICP–MS zircon U Pb dating for three diorite samples indicates that they crystallized during the early Late Jurassic (ca. 161 Ma). The diorites can be divided into two groups based on whole-rock major element compositions and mineralogical characteristics: Group I diorites with relatively low SiO2 (47.6–53.4 wt%), and high MgO (4.97–9.10 wt%) and amphibole contents (50–54 vol%); and Group II diorites with slightly higher SiO2 (56.9–59.5 wt%), and low MgO (2.9–3.8 wt%) and amphibole contents (25–30 vol%). The Group I diorites exhibit relative enrichment in light rare earth element (LREE) ((La/Yb)N = 5.7–10.5) with slightly negative Eu anomalies, and are characterized by enrichment of large ion lithophile elements (LILEs; K, Rb, Ba, Th, and U), the depletion of high field strength elements (HFSEs; Nb, Ta, Zr, Hf, and Ti). The Group I diorites have relatively high initial 87Sr/86Sr ratios (0.7073–0.7094), variably negative eNd(t) values(−10.3 to −5.9), negative zircon eHf(t) values (−14.8 to–4.4), and slightly elevated δ18O values (6.5‰–7.3‰). The Group II diorites show similar trace element characteristics to Group I. They also have high initial 87Sr/86Sr ratios (0.7083–0.7087), uniformly negative eNd(t) values (−9.5 to −9.0), negative zircon eHf(t) values (−10.3 to −4.2), and elevated δ18O values (6.6‰–7.5‰). Amphiboles from Group I and Group II diorites have low Al2O3 contents (3.6–9.9 wt% and 5.6–8.5 wt%, respectively), and formed at similar P–T conditions (751–871 °C and 69–226 MPa and 745–832 °C and 77–162 MPa, respectively). On primitive mantle-normalized spider diagrams, these low-Al amphibole grains have slightly convex upward REE patterns with distinctly negative anomalies in Pb, Sr, Eu, Zr, Hf, and Ti, suggesting that amphiboles from both groups crystallized from the similar arc magmas after plagioclase and magnetite crystallization. These mineralogical, geochemical and isotopic characteristics suggest that both groups of Kenama diorites probably originated from an enriched lithospheric mantle metasomatized by subducted oceanic sediment-derived melts. Their parental magmas may have similar geochemical characteristics and underwent varying degrees of accumulation and fractional crystallization. The Group I diorites were likely generated by accumulation of amphibole and fractional crystallization of olivine, clinopyroxene, and plagioclase from mafic magmas, and the Group II diorites were formed by the fractional crystallization of clinopyroxene and plagioclase from mafic magmas that were geochemically similar to the Group I diorites. In combination with regional geology, in particular adjacent ophiolites, high-magnesian andesitic rocks and Cretaceous sedimentary rocks, we conclude that all of the Kenama diorites were probably generated in an early Late Jurassic arc setting related to the subduction of the Bangong–Nujiang Tethys oceanic lithosphere.

The South China Block (SCB) is considered to have undergone extensive reworking of continental crust. However, the mechanisms of this crustal reworking are unclear. Here, we report on Late Jurassic (162–155 Ma) two-mica granites and associated diorites and syenite porphyries from the Huolushan–Longyandong area of Guangzhou City, southeastern China. The two-mica granites have high SiO2 contents (69.6–73.6 wt%) and weakly peraluminous to strongly peraluminous compositions. These rocks have enriched Sr–Nd–Hf isotopic compositions ((87Sr/86Sr)i = 0.7094–0.7145; eNd(t) = −10.5 to −9.3; eHf(t) = −12.7 to −4.2). The Huolushan two-mica granites have variable zircon O isotopic compositions (δ18O = 6.8‰–10.4‰), whereas the Longyandong two-mica granites have homogeneous compositions (δ18O = 8.6‰–9.9‰). The Huolushan syenite porphyries have moderate SiO2 (59.6–60.1 wt%) and high alkaline (K2O + Na2O = 9.4–9.8 wt%) contents. Their Sr–Nd–Hf–O isotopic compositions ((87Sr/86Sr)i = 0.7105–0.7119; eNd(t) = −9.9 to −9.8; eHf(t) = −14.1 to −5.9; δ18O = 6.5‰–10.6‰) are similar to those of the Huolushan two-mica granites. The Huolushan diorites have moderate SiO2 contents (59.9–60.4 wt%) and are high-K calc-alkaline and metaluminous with Mg# values of 43.2–43.8. Their Sr Nd isotopic compositions ((87Sr/86Sr)i = 0.7106–0.7109, eNd(t) = −8.8 to −8.6) are less enriched than those of the two-mica granites and syenite porphyries. In addition, the diorites have high zircon δ18O values (7.8‰–8.9‰) and a wide range of zircon eHf(t) values (−13.4 to −5.6). We propose that the Huolushan two-mica granites were derived from a metagreywacke-dominated hybridized source with minor juvenile crustal rocks and that the Longyandong two-mica granites were generated by partial melting of metagreywackes. The Huolushan syenite porphyries were formed by the mixing of metasedimentary-rock-derived felsic magmas and minor enriched-mantle-derived alkaline magmas. The Huolushan diorites were most likely derived by partial melting of mafic lower crust, with the dioritic magmas undergoing assimilation and fractional crystallization (AFC) during ascent. All of these intrusive rocks were likely formed in an extensional intraplate setting. The mantle-derived magmas, which could have been triggered by lithospheric extension, underplated the middle–lower crust and provided heat for crustal reworking and materials for late Mesozoic crustal growth.