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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]

Granitoids, as a major component of the Earth's crust, have large K isotopic variations (δ41K = −1.0‰ to 0.4‰), but K isotope fractionation during granite differentiation is poorly constrained. Here, we examined K isotopic compositions of a suite of well-characterized crustal igneous rocks (quartz diorite, granodiorite and monzogranite) from the Tagong pluton, northeastern Tibetan Plateau. The rocks display increasing δ41K in the following order: quartz diorite (δ41K = −0.798‰ to −0.538‰) < granodiorite (δ41K = −0.520‰ to −0.378‰) < monzonite granite (δ41K = −0.439‰ and − 0.436‰). The δ41K values are positively correlated with SiO 2 and K 2 O contents and negatively with MgO and Al 2 O 3 contents, indicating up to ∼0.42‰ fractionation during magmatic differentiation. Taking into account mineral assemblage, fractional crystallization of K-rich phases (mica and K-feldspar) likely plays a dominant role in K isotopic variation. In addition, mafic microgranular enclaves (MMEs) commonly occurring in granitoid rocks show comparable δ41K values (−0.489‰ to −0.416‰) to their corresponding host rocks, implying their schlieren origin. These features demonstrate that K isotope heterogeneity of the crust could have been induced by magma differentiation in addition to source control. • K isotope fractionation during granite differentiation. • Fractional crystallization probably controlled fractionation of K isotopes. • Schlieren origin of mafic microgranular enclaves from perspective of K isotopes. • Contribution of magma differentiation to K isotopic heterogeneity of the crust. [ABSTRACT FROM AUTHOR]

Determining the geochronological framework and geochemical nature of magmatism associated with orogenic processes is crucial to decipher the evolution of orogenic belts. The Himalayan orogen has recorded considerable information regarding deformation, metamorphism, and magmatism related to orogenic processes. Here, we identify four stages of granitic magmatism on the basis of monazite U–Th–Pb dating of rocks from the Lhagoi Kangri dome, north Himalayan antiform, southern Tibet: middle Eocene (42–40 Ma), late Eocene (ca. 36 Ma), Oligocene (ca. 26 Ma), and Miocene (16–13 Ma). The middle Eocene tourmaline-bearing leucogranite is characterized by (1) relatively high SiO 2 (78.7 wt%), Al 2 O 3 (12.6 wt%), and Na 2 O (6.3 wt%) contents; (2) enrichment in light rare earth elements (LREEs), depletion in heavy REEs, high abundances of REEs, and pronounced negative Eu anomalies; and (3) relatively low values of whole-rock Sr Nd isotope compositions (87Sr/86Sr(t) = 0.72101 and εNd(t) = −9.8). And the coeval garnet–bearing two–mica granite has a pronounced negative Eu anomaly (Eu/Eu* = 0.07) and a significate lanthanide tetrad effect (TE 1,3 = 1.46). These geochemical data suggest that these leucogranites underwent fractional crystallization. They provide a robust evidence for that anatexis of the lower crust of Indian plate began at 42–40 Ma in the central Himalayan orogen. The Oligocene and Miocene two–mica granites share broadly similar geochemical characteristics, such as moderate REE contents and weak negative Eu anomalies, and are distinct from the garnet-bearing muscovite leucogranite. Whole-rock Sr Nd isotope compositions of the Oligocene and Miocene leucogranites differ from those of the middle Eocene leucogranites, with higher 87Sr/86Sr(t) ratios (0.73524–0.74188) and lower εNd(t) values (−14.7 to −13.7). These geochemical data indicate that the Oligocene and Miocene leucogranites are products of muscovite-dehydration melting of metasedimentary rocks. The garnet-bearing muscovite leucogranite shows the REE tetrad effect, which suggests that it is more evolved than the coeval two–mica granite. We therefore infer that the variations in age and isotopic characteristics of the studied leucogranites were caused by a change in melt source resulting from the compression–extension evolution of the Himalayan collisional orogenic system. • Four-stage emplacement of leucogranites were identified in the Lhagoi Kangri dome. • The age and isotopic variations of leucogranites result from a change in melt source. • Middle Eocene leucogranites reveal a long-lived anatexis in the Himalayan orogen. [ABSTRACT FROM AUTHOR]