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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]

[Display omitted] • Skarn-type mineralization of the Cuonadong Sn-W-Be polymetallic deposit occurred at ca. 15 Ma. • Skarn-hosted scheelite can be divided into an older type 1 scheelite and a younger type 2 scheelite. • The ore-forming fluid was exsolved from the Cuonadong Miocene leucogranite. • Geochemically and isotopically, the ore-forming fluid was modified by intense fluid-rock interaction during skarnization and greisenization. The Cuonadong Sn-W-Be polymetallic deposit is the first rare-metal deposit with an extraordinary metallogenic potential that has been discovered in the Tethyan Himalayan metallogenic belt. The deposit shows a wide range of different mineralization types, including greisen-, pegmatite-, skarn-, and hydrothermal vein-type mineralization. Of these mineralization types, the skarn-type has the largest inferred resources. In order to constrain the source and evolution of the ore-forming fluid, we conducted a detailed study of the skarn-hosted scheelite, including cathodoluminescence imaging, in-situ trace elemental analysis, and bulk Sr isotope analysis. In addition, bulk Sr isotope analysis of fluorite, phlogopite 40Ar-39Ar dating, and marble whole-rock geochemical analysis were also conducted. Phlogopite 40Ar-39Ar dating indicates that the skarn was formed at ca. 15 Ma, which is close to the formation age of the Cuonadong muscovite granite reported in previous studies. Cathodoluminescence images indicate that skarn-hosted scheelite can be subdivided into an older type 1 scheelite and a younger type 2 scheelite. Type 1 scheelite is characterized by a negative Eu anomaly, whereas type 2 scheelite shows a positive Eu anomaly. Considering the close temporal and spatial relationship between the Cuonadong Miocene leucogranite and the ore-bearing skarn, and their similar lanthanide tetrad effect as observed in the REE patterns, we propose that the negative Eu anomaly was inherited from the Cuonadong Miocene leucogranite, while the positive Eu anomaly resulted from the addition of Eu2+ to the ore-forming fluid during greisenization. Sr isotope data show that the fluorite (87Sr/86Sr) i value of 0.728885 is within the range of the Cuonadong Miocene leucogranite (87Sr/86Sr) i values, while scheelite (87Sr/86Sr) i values (0.709717–0.713480) are similar to those of the Cuonadong marble (0.709525–0.712146). Since scheelite is intergrown with fluorite, we propose that the hydrothermal fluid that exsolved from the Cuonadong Miocene leucogranite is responsible for formation of both fluorite and scheelite. Water-rock interaction between this magma-derived fluid and the marble is responsible for the loss of the scheelite magmatic Sr isotopic signature. [ABSTRACT FROM AUTHOR]

• Cuonadong is the firstly discovered W-Sn-Be-Rb deposit in Himalayan. • Zircon and cassiterite U-Pb and muscovite Ar-Ar ages (15.5–14.3 Ma) are similar. • E-W extension of the NSTR initiated at ca. 18–14 Ma. • Himalaya leucogranites belong to Sn granite. The Cuonadong deposit is located in the Cuonadong gneiss dome of the eastern Tethyan Himalaya and is characterized as a large- to superlarge-scale Sn polymetallic deposit in the Himalaya orogen. The mineralization pattern includes skarn W-Sn mineralization in the strong shear zone of the dome mantle, hydrothermal Sn-W veins controlled by north-south-trending rifts (NSTRs), and Be-Rb mineralization in pegmatitic leucogranite. The results of this study show that the zircon U-Pb age of undeformed (postkinematic) leucogranites is 15.5 ± 0.1 Ma (n = 28, MSWD = 1.4), the cassiterite U-Pb age of the vein-type Sn-W orebody is 14.3 ± 0.5 Ma (n = 40, MSWD = 3.2), and the muscovite Ar-Ar age of beryl-bearing pegmatitic leucogranite is 15.2 ± 0.2 Ma (MSWD = 1.5). The isotopic dating results demonstrate that the Cuonadong Sn-W-Be-Rb mineralization has a close genetic relationship with the Miocene (ca. 16–14 Ma) leucogranite magmatic hydrothermal activity in the Cuonadong dome. The deformed (synkinematic) two-mica granite (18 Ma) was cut by the Sn-W ore veins (14 Ma) faulted by NSTRs, indicating that the E-W-trending extension of the NSTRs initiated at ca. 18–14 Ma. The Himalaya leucogranite belongs to a highly fractionated granite with high Sn content (>15 ppm). In conclusion, the Himalaya leucogranite is considered to be tin granite in this study, and therefore, the Himalaya presents high potential for Sn polymetallic mineralization prospecting. [ABSTRACT FROM AUTHOR]

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]

Several giant industrial-grade rare-metal deposits have been discovered in the Himalaya most recently. However, the mechanism of how rare-metals mineralization formed in the prototype of the collisional belt is poorly understood, mainly due to insufficient studies on mineralogy, petrology and emplacement conditions. In this study, we have reported the whole-rock and mineral compositions of spodumene pegmatites, leucogranite, skarns and P-T paths of metapelites from Lhozhag, eastern Himalaya. Four spodumene pegmatite veins were studied that are enriched in lithium, beryllium, cesium and tantalite (Li-Cs-Ta subtype), mainly hosted by minerals of spodumene, petalite, elbaite, lepidolite, zinnwaldite, and margarite. Li-Be margarite is first reported from the Himalaya, and its lithium and beryllium come from the breakdown of spodumene and beryl. The surrounding skarns are enriched in lithium, beryllium, and tin, mainly hosted by minerals of vesuvianite, scapolite and garnet. Petrography and P-T estimates from the andalusite-staurolite phyllites suggest two stages of metamorphism that earlier Barrovian metamorphism was superimposed by Buchan metamorphism at conditions of 3.1 ± 0.3 kbar and 535°C or 580°C (52–56°C/km) during leucogranite emplacement. Combined with zircon and monazite saturation temperatures and conditions of Buchan metamorphism, the leucogranites should have undergone a first-stage isothermal decompression to crystallization conditions at ∼3.1 kbar and 650–720°C and a second-stage isobaric cooling at ∼3.1 kbar. The pegmatite probably underwent a similar P-T evolution supported by the appearance of two-stage growth of spodumene (Spd-1 and Spd-2 + Qz), petalite corona around spodumene, and cymatolite. The leucogranites/pegmatites have emplaced into the surficial Tethyan Himalayan Sequence simultaneously, causing contact metamorphism, skarnization and undercooling, which may have facilitated rare-metals mineralization in the pegmatites and skarns during the emplacement stage. We suggest that the pegmatites and skarns in Lhozhag, eastern Himalaya have enormous potential for rare-metals exploration. [Display omitted] • Detailed mineralogy and petrology of the spodumene pegmatites in Lhozhag are presented. • Li-Be margarite is reported for the first time in the Himalaya. • Leucogranites/pegmatites emplaced into THS, causing contact metamorphism and undercooling. • P-T conditions of contact metamorphism were ∼ 3.1 kbar and 535–580°C. • Lhozhag in eastern Himalaya has enormous potential for rare-metals exploration. [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]

[Display omitted] • The Cuonadong composite leucogranites resulted from at least three-period magmatism from Oligocene to Miocene. • The Cuonadong skarn contains multiple generations, and the age and composition of titanite from skarn record three-stage hydrothermal events. • Miocene Sn-rich titanite coexisting with garnet and interstitial cassiterite implies that hydrothermal Sn metasomatism occurred after garnet crystallization. The newly discovered Cuonadong Sn-W-Be skarn deposit is related to fractionated leucogranitic intrusions hosted in the Cenozoic Himalayan gneiss dome, Tibet, however, temporal and genetic relationships between composite magmatism, skarn and mineralization remain unclear. Based on age and compositional features, three types of titanite were identified: Ttn1 and Ttn2 in the diopside-dominated skarn and adjacent greisenized granitic dike, and Ttn3 (subdivided into Ttn3a and 3b) in the Sn-mineralized garnet skarn. Ttn1 has a higher Ti content and yielded a U-Pb age of ∼35 Ma, consistent with the U-Pb ages of monazite from the pegmatitic granite (35.0 ± 0.6 Ma). Younger, recrystallized Ttn2 (∼28–27 Ma) is characterized by higher Al, F, Ta, Nb, Sn and Y contents and was likely formed by interaction between early Ttn1 and late fluids as indicated by the monazite U-Pb age of two-mica granite (28.8 ± 0.3 Ma). These two types of hydrothermal titanite are confined to the Oligocene unmineralized skarn and adjacent greisenized granitic dike. Titanite from the garnet-bearing Sn-mineralized skarn (Ttn3) provides the age of mineralization (16.8 ± 1.6 Ma), slightly younger than the emplacement age of the Miocene granite (monazite U-Pb age: 19.9 ± 0.3 Ma and columbite: 19.0 ± 0.4 Ma). The Sn-rich Ttn3b coexisting with garnet and interstitial cassiterite shows a deficit of Y and HREE and a high (Dy) N /(Yb) N ratio, implying that hydrothermal Sn metasomatism of Ttn3 occurred after garnet crystallization. Overall, our results shows that the Cuonadong multigenerational skarns were generated during three episodic magmatic-hydrothermal events, and mineralization occurred in the Miocene. [ABSTRACT FROM AUTHOR]