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Himalayan leucogranites are widely distributed in the North Himalayan gneiss dome (NHGD) and at the top of the Greater Himalayan Crystalline Complex (GHC) and are generally controlled by detachment faults. The ages of these prekinematic, synkinematic, and postkinematic leucogranites can be used to limit the activity of detachment structures (such as the South Tibetan Detachment System, STDS). Research on the STDS activity time in the eastern Himalayas is relatively sparse. In this study, the zircon and monazite U–Th–Pb geochronology of synkinematic and postkinematic leucogranites, which are affected by the STDS and NHGD, in four areas (Lhozhag, Kuju, Xiaozhan, and Cuonadong) in Shannan City, Tibet, China, was measured. The results show that the oldest synkinematic two‐mica granite from Lhozhag, which is affected by the STDS, is 24–25 Ma, so the time of STDS activity is at or slightly earlier than 25 Ma. The youngest synkinematic leucogranite is the garnet‐bearing muscovite granite in Cuonadong at 18.4 Ma. The oldest undeformed postkinematic leucogranite (not affected by the STDS) is the muscovite granite in Xiaozhan at 17.4 Ma. Therefore, the end of STDS activity can be limited to 18.4–17.4 Ma. The STDS includes three forms: detachment fault in the NHGD (northern extension of the STDS), the inner STDS between the GHC and Tethyan Himalayan Sequence, and the outer STDS at the bottoms of synformal klippes. In this paper, the active time limits of the above three kinds of detachment zones are comprehensively summarized. Based on this work, the northward extension (ductile deformation) time of the STDS in the region is considered to be 28–17 Ma. The exhumation of the GHC is mainly controlled by in‐sequence shearing: first, the South Tibet Thrust system (predecessor of the STDS) at the top of the GHC thrust southward at 45–28 Ma, then the High Himalayan Discontinuity fault in the middle of the GHC forms south‐vergent ductile thrusts at 28–17 Ma, and finally, the Main Central Thrust at the bottom of the GHC thrust southward at 17–9 Ma. [ABSTRACT FROM AUTHOR]

The Duolong porphyry Cu-Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au) was recently discovered in the southern Qiangtang terrane, central Tibet. Here, new whole-rock elemental and Sr-Nd-Pb isotope and zircon Hf isotopic data of syn- and post-ore volcanic rocks and barren and ore-bearing granodiorite porphyries are presented for a reconstruction of magmas associated with Cu-Au mineralization. LA-ICP-MS zircon U-Pb dating yields mean ages of 117.0 ± 2.0 and 120.9 ± 1.7 Ma for ore-bearing granodiorite porphyry and 105.2 ± 1.3 Ma for post-ore basaltic andesite. All the samples show high-K calc-alkaline compositions, with enrichment of light rare earth elements (LREE) and large ion lithophile elements (LILE: Cs and Rb) and depletion of high field strength elements (HFSE: Nb and Ti), consistent with the geochemical characteristics of arc-type magmas. Syn- and post-ore volcanic rocks show initial Sr ratios of 0.7045-0.7055, εNd(t) values of −0.8 to 3.6, (206Pb/204Pb)t ratios of 18.408-18.642, (207Pb/204Pb)t of 15.584-15.672 and positive zircon εHf(t) values of 1.3-10.5, likely suggesting they dominantly were derived from metasomatized mantle wedge and contaminated by southern Qiangtang crust. Compared to mafic volcanic rocks, barren and ore-bearing granodiorite porphyries have relatively high initial Sr isotopic ratios (0.7054-0.7072), low εNd(t) values (−1.7 to −4.0), similar Pb and enriched zircon Hf isotopic compositions [εHf(t) of 1.5-9.7], possibly suggesting more contribution from southern Qiangtang crust. Duolong volcanic rocks and granodiorite porphyries likely formed in a continental arc setting during northward subduction of the Bangong-Nujiang ocean and evolved at the base of the lower crust by MASH (melting, assimilation, storage and homogenization) processes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Bangong- Nujiang suture ( BNS) between the Lhasa and Qiangtang terranes is an important boundary and its petrogenesis is controversial. Diabase from the accretionary prism in the southern Qiangtang terrane yields a zircon U- Pb age of 181.3 ± 1.4 Ma. All the diabases show tholeiitic basalt compositions, gentle enrichment patters of light rare earth elements ( REE), variable enrichment in incompatible element concentrations (e.g. Th and Rb), and no anomaly in high field strength elements (e.g. Nb and Ta), similar to that of enriched mid-ocean ridge basalt ( E- MORB). They have relatively homogeneous whole rock Nd (ε Nd(t) = 7.3-9.1) and zircon Hf- O isotopic compositions (ε Hf(t) = 14.8-16.1, and δ18 O = 4.57-6.12‰), possibly indicating melting of the depleted mantle and no significant crustal contamination during the petrogenesis. The element variations suggest that the diabases were formed by plume-ridge interaction at a mid-ocean ridge within the Bangong- Nujiang ocean. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Jigongcun Mo deposit formed during the early Miocene. • High Re concentrations are due to isovalent Re substitution for Mo in molybdenite. • Relatively oxidized fluids caused Re enrichment in the Jigongcun deposit. The Jigongcun Re-rich quartz vein-type Mo deposit is located in the Gangdese porphyry Cu belt, southern Tibet, China. The stratiform and lenticular orebodies are hosted within the quartz veins and are controlled by the NW-/EW-trending faults. In this study, we have identified four hydrothermal stages, namely the (1) pre-ore stage (stage Ⅰ) characterized by the development of thick Mo-free quartz veins; (2) stage Ⅱ, mainly forming thick quartz veins with Re-rich massive molybdenite (Mo1-type; mean = 1811 ppm) and bladed molybdenite (Mo2-type; mean = 1312 ppm); (3) stage III, mainly forming quartz veins with Re-barren bladed molybdenite (Mo3-type) and abundant galena and pyrite; (4) the post-ore stage (stage Ⅳ) characterized by formation of thick ore-barren quartz–calcite veins. Both electron probe micro-analysis and in situ laser ablation–inductively coupled plasma–mass spectrometry analysis of different types of molybdenite show that high Re concentrations are due to isovalent Re substitution for Mo in molybdenite. Fluid evolution during the four stages of mineralization was constrained by a detailed fluid inclusion study. Fluid inclusions during the formation of the early pre-ore stage indicate relatively high-temperature (311–337 °C), high-pressure (1300–1600 bars), low-salinity (0.2–2.6 wt% NaCl-equiv.), and CO 2 -rich hydrothermal fluids. Fluid immiscibility assemblages in CO 2 -rich inclusions coexisting with aqueous inclusions occur in quartz–K-feldspar veins of stage Ⅱ, and likely record phase separation at a temperature of 262–300 °C and pressure of 900–1100 bars, with the precipitation of Re-rich molybdenite. The subsequent fluid mixing occurs at a temperature of 220–271 °C, with the precipitation of Re-barren molybdenite at stage III. H–O–S isotope compositions show that sulfur and ore-forming fluids are derived from a deep-seated igneous source. Re-Os dating of molybdenite samples yielded an isochron age of 22.0 ± 0.4 Ma, indicating that the Jigongcun deposit formed in the Early Miocene, which is earlier than most of the porphyry Cu deposits in the Gangdese porphyry Cu belt. Combined our new geochemical and isotopic results with previous regional investigations, we suggest that the Re-rich Mo mineralization of Jigongcun deposit may be related to the Early Miocene northward subduction of the Indian continental plate. [ABSTRACT FROM AUTHOR]

• The Mingsai deposit formed during the Miocene (16.03 ± 0.31 Ma). • The sulfur of the Au-bearing pyrite has a deep source. • The Mingsai deposit is an orogenic-type Au deposit. Mingsai is a newly discovered Au deposit located in the eastern part of the Tethys Himalayan Au–Sb polymetallic metallogenic belt. The stratiform and lenticular orebodies are hosted within Middle Jurassic metamorphic tuff and quartz-sericite veins and controlled by an interlayer-gliding fracture zone with extensive hydrothermal alteration. In this study, at least three alteration/mineralization stages of the deposit were recognized as follows: (1) pre-ore stage (Stage Ⅰ), forming mainly ore-barren fine quartz veins without sulfides; (2) main ore stage (Stage Ⅱ), forming mainly thick quartz veins with abundant coarse-grained or fine-grained euhedral and subhedral Au-bearing pyrite, arsenopyrite and sericite; and (3) post-ore stage (Stage III), which is characterized by formation of thick barren quartz–calcite veins with few sulfides. Three types of fluid inclusions were identified as follows: (1) pure carbonic (V-type) inclusions, (2) aqueous-carbonic (C-type, including three-phase C1-type and two-phase C2-type) inclusions and (3) aqueous (L-type) inclusions. Fluid inclusions during the pre-ore stage are mainly C1-type, C2-type and V-type. The main ore stage contains mainly C1-type, C2-type, L-type and limited V-type, whereas the post-ore stage contains mainly L-type (with limited C2-type) fluid inclusions. From stages Ⅰ to III, microthermometric data show homogenization temperatures of 292–362 °C (mean = 309 °C), 247–320 °C (mean = 285 °C), and 206–272 °C (mean = 244 °C), respectively, and fluids with salinities of 0.2–8.3 (mean = 2.8) wt% NaCl equiv., 0.2–13.1 (mean = 5.8) wt% NaCl equiv., and 0.8–15.2 (mean = 8.3) wt% NaCl equiv., respectively. The δD values of the fluids from stages I to III range from −129.1‰ to −131.8‰, −137.5‰ to −137.4‰, and −143.6‰ to −138.6‰, respectively. The δ18O H2O values of the fluids from stages Ⅰ to III range from 13.3‰ to 13.6‰, 13.0‰ to 13.2‰, and 11.0‰ to 11.9‰, respectively. The δD and δ18O H2O values may reflect meteoric water involvement in ore-forming fluids sourced from either crustal metamorphism or mantle devolatilization. Fluid mixing is the crucial mechanism that controlled the deposition of the Au-bearing sulfides. In situ δ34S values of the Au-bearing pyrite range from 1.06‰ to 2.41‰, whereas δ34S values of the barren pyrite from the slate range from 8.19‰ to 15.86‰, indicating that sulfur of the Au-bearing pyrite has a deep source. The 40Ar–39Ar plateau age of hydrothermal ore-bearing sericite from the main ore stage is 16.03 ± 0.31 Ma, indicating that the mineralization time of the deposit is Miocene, which is different from other major gold deposits (Eocene) in the Tethys Himalayan Au–Sb polymetallic metallogenic belt. Consequently, taking the data together, it is suggested that the Mingsai is an orogenic-type Au deposit in the Tethys Himalayan Au–Sb polymetallic metallogenic belt. [ABSTRACT FROM AUTHOR]

Abstract This paper presents new geochronological and geochemical (whole-rock major and trace elements and Sr–Nd–Pb isotopes) data on intrusive rocks exposed in the Qiongduojiang area, the northern part of the Tethyan Himalaya. The Qiongduojiang intrusive rocks are mainly composed of mafic rocks (diabase and gabbro) with subordinate felsic rocks (monzonite), indicating bimodal component characteristics. In zircon U-Pb dating of monzonite, diabase and gabbro samples, the weighted mean ages of magma emplacement were determined to be 230.5 ± 2.9 Ma to 227.4 ± 4.7 Ma, showing Middle–Late Triassic magmatic activity in the northern part of the Himalayan belt. The monzonitic rocks share most of the geochemical features of A-type granites, and their Nd isotopic compositions are consistent with those of coeval diabase rocks. This suggests that they are likely generated by mantle-derived magmas, which had assimilated significant amounts of continental crust. The gabbro samples exhibit the geochemical composition of ocean island basalt (OIB) features and therefore assumingly originate from a depleted mantle source with insignificant crustal contamination. In contrast, the diabase samples display enriched mid-ocean ridge basalt (E-MORB) features and were derived from spinel bearing peridotite that was metasomatised by OIB-like components with limited crustal contamination. The Qiongduojiang bimodal magmas can be considered as the products of the opening of the Neo-Tethyan ocean. Considering the magmatic petrology, paleomagnetism and paleontology data, we further propose that the Neo-Tethyan ocean began opening before ~230 Ma. Highlights • The Middle-Late Triassic intrusive rocks (230.5–227.4 Ma) are exposed in Tethyan Himalayan belt. • They are characterised by bimodal composition (monzonite, diabase, and gabbro). • The Neo-Tethys ocean initial opening commenced prior to ~230 Ma. [ABSTRACT FROM AUTHOR]

Abstract: Mesozoic intermediate–felsic intrusions are widely distributed in the southern Qiangtang terrane, central Tibet. Zircon U–Pb dating shows that these intrusions formed in two periods in the Jurassic (169–150Ma) and Cretaceous (127–113Ma). They mostly belong to the high-K calc-alkaline series, and show strong enrichments in large ion lithophile elements (e.g., Cs, Rb, and K), depletions in Nb, Ta, and Ti, and negative Ba anomalies on primitive mantle-normalized diagrams. P2O5 contents decrease with increasing SiO2 content, and Th contents increase with increasing Rb content, consistent with the evolution trend of I-type magmas. These intrusions show a wide range of zircon εHf(t) values from −19.4 to 11.2, including in rocks with similar SiO2 contents, suggesting variable contributions from mantle and Qiangtang crustal sources. Fine-grained mafic to intermediate igneous enclaves in Jurassic intrusions have similar zircon U–Pb ages and similar or slightly higher zircon εHf(t) values to the host rocks, suggesting that the enclave magmas were derived from mixed magmas at depth and injected into more evolved magmas in upper crustal magma chambers. Magma mixing is also supported by the wide range of zircon Hf isotopic compositions (εHf(t)=−19.4 to 2.5) from within individual Jurassic and Cretaceous intrusions, and Jurassic enclaves. The Jurassic–Cretaceous magmas likely formed in a continental arc setting during subduction of the Bangong–Nujiang ocean between 170 and 110Ma, and evolved in the upper plate crust by MASH processes. [Copyright &y& Elsevier]

Rare-metal pegmatite represents the most differentiated magmatic system on earth, containing high concentrations of rare metals (Li, Rb, Cs, Be, Ta, Nb, and Sn) and fluxing components. Recent studies have shown that the Himalayan leucogranite–pegmatite system has considerable potential for rare-metal mineralization. A new spodumene pegmatite-type Li deposit (Gabo) was recently discovered in the Lhozhag region of the eastern Himalaya. However, the lack of precise geochronological and isotopic constraints on the crystallization timing and chemical affinity between spodumene pegmatites and nearby leucogranite has precluded definitive statements on their petrogenetic link. In this study, systematic monazite, xenotime, and columbite group mineral U–(Th)–Pb dating and Li–Nd–Hf isotope analysis were performed on the spodumene pegmatite and nearby leucogranite (Lhozhag pluton). Columbite group mineral LA-ICP-MS U Pb dating of spodumene pegmatite indicates that the timing of lithium mineralization occurs at ca. 20–18 Ma, which is consistent with the magmatic crystallization age of the Lhozhag pluton (ca. 19 Ma) within the error margin, as constrained by monazite and xenotime U–(Th) Pb dating. The Nd Hf isotope analysis also indicates a chemical affinity between the Lhozhag pluton and spodumene pegmatite. Given the consistency in crystallization ages, Nd Hf isotopic compositions, and close field spatial relationship, the leucogranite probably represents the parent magma of spodumene pegmatites. The continuous evolutionary trend in the composition of spodumene pegmatites, as observed on the spodumene (Spd)– albite (Ab)–orthoclase (Or)–quartz (Qz)–H 2 O phase diagram, suggests that the enrichment of Li in pegmatite is result from fractional crystallization. Li isotopic analysis shows that the spodumene pegmatite has a δ7Li value of −2.5‰ to +3.3‰, slightly higher than that of the Lhozhag pluton (−2.4‰ to +1.0‰), providing additional support for their fractional crystallization links. These findings warrant a more comprehensive assessment of the lithium potential within the Himalayan orogenic belt. [Display omitted] • Lhozhag leucogranite pluton formed at ca. 19 Ma. • Gabo Spodumene pegmatites formed at ca. 20–18 Ma. • A genetic link between Lhozhag pluton and Gabo Spodumene pegmatites was revealed. • The spodumene pegmatites formed by multi-stage fractional crystallization from Lhozhag pluton. [ABSTRACT FROM AUTHOR]

Abstract: The Duolong porphyry Cu–Au deposit (5.4Mt at 0.72% Cu, 41t at 0.23g/t Au), which is related to the granodiorite porphyry and the quartz–diorite porphyry from the Bangongco copper belt in central Tibet, formed in a continental arc setting. Here, we present the zircon U–Pb ages, geochemical whole-rock, Sr–Nd whole-rock and zircon in-situ Hf–O isotopic data for the Duolong porphyries. Secondary ion mass spectrometry (SIMS) zircon U–Pb analyses for six samples yielded consistent ages of ~118Ma, indicating a Cretaceous formation age. The Duolong porphyries (SiO2 of 58.81–68.81wt.%, K2O of 2.90–5.17wt.%) belong to the high-K calc-alkaline series. They show light rare earth element (LREE)-enriched distribution patterns with (La/Yb)N =6.1–11.7, enrichment in large ion lithophile elements (e.g., Cs, Rb, and Ba) and depletion of high field strength elements (e.g., Nb), with negative Ti anomalies. All zircons from the Duolong porphyries share relatively similar Hf–O isotopic compositions (δ18O=5.88–7.27‰; εHf(t)=3.6–7.3), indicating that they crystallized from a series of cogenetic melts with various degrees of fractional crystallization. This, along with the general absence of older inherited zircons, rules out significant crustal contamination during zircon growth. The zircons are mostly enriched in δ18O relative to mantle values, indicating the involvement of an 18O-enriched crustal source in the generation of the Duolong porphyries. Together with the presence of syn-mineralization basaltic andesite, the mixing between silicic melts derived from the lower crust and evolved H2O-rich mafic melts derived from the metasomatized mantle wedge, followed by subsequent fractional crystallization (FC) and minor crustal contamination in the shallow crust, could well explain the petrogenesis of the Duolong porphyries. Significantly, the hybrid melts possibly inherited the arc magma characteristics of abundant F, Cl, Cu, and Au elements and high oxidation state, which contributed to the formation of the Duolong porphyry Cu–Au deposit. [Copyright &y& Elsevier]

The Galale Cu Au skarn deposit is located on the southern margin of the Bangong-Nujiang metallogenic belt, Tibet, and the Cu Au mineralization is related to the Late Cretaceous granodiorite. The orebodies occurring as stratiform, lenticular and vein types are hosted within the skarn along the contact between the granodiorite and dolomitic marble or calcitic marble of the Jiega Formation. At least four hydrothermal alteration stages of the deposit have been recognized: prograde magnesian and calcic skarn stage (Stage 1), retrograde skarn stage (Stage 2), hydrosilicate alteration stage (Stage 3), and phyllic alteration stage (Stage 4). Fluid inclusions from skarn rocks and quartz veins are indicative of multiple fluid events. The prograde skarn was formed from a medium-salinity, hot (466–518 °C), high pressure (>1000 bar) homogenous magmatic-hydrothermal fluid, under its possible direct separation from crystallizing magma. The subsequent retrograde skarn was formed from a slightly lower temperatures (370–460 °C) and lower pressure (~800 bar) homogenous magmatic-hydrothermal fluid that could be supplied by crystallizing magma. Sharp drop of pressure (from 800 bar to 300 bar) and significant decrease of temperatures (low to 300 °C) may be related to fracturing and increase of porosity during alteration of skarns, and caused the fluid boiling in hydrosilicate alteration stage. The fluid from the latest phyllic alteration stage is characterized by dominant meteoric water and more lower temperatures (low to 178 °C). Decrease of fluid temperatures and pressures, fluid boiling and changes of redox regime are considered the crucial mechanisms for controlling the precipitation of the ores. The δ34S values of the sulfides range from −4.4 to 6, primarily from −0.9 to 1.7, that suggest a magmatic source. The sulfides yield narrow ranges of 206Pb/204Pb ratios (18.141–18.871) and 207Pb/204Pb ratios (15.588–15.701) and a wide range of 208Pb/204Pb ratios (38.359–39.008), indicating a mixed crust-mantle ore-forming metal source. The 40Ar 39Ar plateau age of phlogopite from the chalcopyrite-bearing phlogopite tremolite skarn (Stage III) is 87.5 ± 0.6 Ma, which is consistent with the crystallization age of the Late Cretaceous granodiorite. Consequently, taking the data together suggests that the Galale Cu Au deposit is a typical oxidized Cu Au skarn deposit related to the Late Cretaceous magmatic-hydrothermal systems. • Both the calcic skarn and magnesian skarn have been observed in the Galale deposit. • The timing of mineralization is 87.5 ± 0.6 Ma, indicating that the Galale deposit formed in the Late Cretaceous. • The galale deposit is typical oxidized Cu-Au skarn deposit associated to the collision-related Late Cretaceous magmatism [ABSTRACT FROM AUTHOR]

As prototypes of crust-derived remelted S-type granite, Himalayan leucogranites have considerable relevance in crustal evolution and associated metallogeny. However, given their highly differentiated character, the petrogenesis of these rocks has remained controversial. This study reviews the geochemical and isotopic data from >2000 samples of Himalayan Cenozoic granitoids to evaluate their genesis. The Himalayan leucogranites include two major belts: the northern zone occurs in the Tethyan Himalayas and gneiss domes, and the southern zone is exposed mainly at the top of the Higher Himalayas. The ages of these rocks show a southward younging trend from 49 Ma to 1 Ma. The main rock types are two-mica granites and garnet-tourmaline-bearing muscovite granites, whereas Eocene and Miocene intermediate-mafic and adakitic rocks are developed mainly in the northern belt. The leucogranites originated from incongruent disequilibrium partial melting of the Greater Himalayan Crystalline Complex and underwent a high degree of differentiation and fractional crystallization. The rocks are strongly peraluminous and characterized by high Si, K, and Na; low Ca, Fe, Mg, Ti, and Mn; and low rare earth elements with obvious tetrad effects and negative Eu anomalies. A more striking feature of these granites is their high Rb/Sr and Y/Ho values and low Th/U, Nb/Ta, Zr/Hf, and K/Rb values. The Sr–Nd–Pb–Hf isotopes indicate that the proportion of older crustal material in the magmatic source area gradually increased from the Eocene to the Pliocene. The Cenozoic magmatic activity can be divided into five stages—49-40 Ma, 39–29 Ma, 28–15 Ma, 14–7 Ma, and 6–0.7 Ma—and their geotectonic settings are related to the break-off of the Neo-Tethyan oceanic plate, low-angle underthrusting of the Indian continental lithosphere, break-off or rollback of the Indian plate, tearing of the Indian lithospheric slab or delamination of the lithospheric mantle, and rapid extrusion and uplift of the Eastern and Western Himalayan Syntaxis resulting from flat subduction of the Indian continent, respectively. Stream sediment geochemical data from previous work show high positive anomalies for some rare metals in the Himalayas. The average contents of Li, Be, Sn, Ta and Cs in pegmatite are 2466 ppm, 93 ppm, 29 ppm, 14 ppm and 61 ppm, respectively. All these elements have enrichment coefficients higher than 10 compared to the upper continental crust. Recent progress in ore prospecting shows that the Himalayan Cenozoic leucogranite is emerging as a new world-class rare metal metallogenic belt. [Display omitted] • First comprehensive review of the world-famous Himalayan leucogranites. • The leucogranites originated from partial melting of GHC. • They underwent a high degree of differentiation and fractional crystallization. • They cover five stages: 49–40 Ma, 39–29 Ma, 28–15 Ma, 14–7 Ma, and 6–0.7 Ma. • The Himalayas are emerging as a new world-class rare metal metallogenic belt. [ABSTRACT FROM AUTHOR]