Genesis of Himalayan leucogranite and its potentiality of rare-metal mineralization

The Himalayan leucogranite attracts the attention of the world and has important theoretical and prospecting significances, but its genesis is controversial. In this paper, the geochemistry of whole rock main and trace elements, Sr-Nd-Pb-Hf isotopes, in-situ U-Pb ages of zircon/monazite/xenotime and other accessory minerals, and zircon Hf isotopes of secondary minerals from more than 2000 samples have been reviewed, in order to comprehensively summarize the research progresses and status of Himalayan leucogranites. The Himalayan leucogranites are divided into two zones.The northern zone is mainly exposed in the Tethyan Himalayas and gneiss dome, and the southern zone is mainly developed in the top of the Great Himalayan Copmlex and the Western-Eastern Himalayan Syntaxis. From north to south, the petrogenetic ages become younger gradually. There are two-mica granites and (garnet-tourmaline) muscovite granites in the northern and southern zones, and two stages (Eocene and Miocene) intermediate-basic dikes and adakite rocks are mainly developed in the northern zone. 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, which are mainly related to the separation of the New Tethyan oceanic plate, the low angle subduction, detachment or retraction, the north-south tearing (north-south-trending rift) of the Indian continental plate, and the rapid uplift of the Himalayan syntaxes, respectively. The Himalayan leucogranites originated from the incongruent (disequilibrium) partial melting of the Great Himalayan Complex and underwent highly differentiated evolution of mineral separation crystallization. The leucogranites are characterized by high Si, K, Na, low Ca, Fe, Mg, Ti, Mn, strong peraluminite, low total rare earth elements, obvious negative Eu anomaly, high Rb/Sr, Y/Ho values, and low Th/U, Nb/Ta, Zr/Hf, K/Rb values. As the petrogenetic ages become younger, the Sr-Nd-Pb-Hf isotopes show that the proportion of older crustal material in the magmatic source area increases gradually. The enrichment coefficients of rare elements such as Li, Be, W, Sn, Ta, Cs and Rb in the Himalayan leucogranite are greater than 10 relative to the total crustal value, and they belong to LCT-type pegmatite. The Cenozoic leucogranite belt of the Himalayas is expected to be a new world-class Li-Be-Sn-W-Ta rare metal metallogenic belt.