Petrology, Geochronology And Geochemistry Of Central And Eastern Section Leucogranites Of North Himalayan Domes Belt

The North Himalayan antiform of South Tibet consist of a series of gneiss domes, which aremostly intruded by leucogranite.The leucogranite types of this domes belt are mostly two-micagranite and muscovite-granite. The major elements composition is the same, with rich SiO₂（69.5～77.26%）, Al₂O₃（13.61～17.21%）, low MgO+FeO^T （0.12～3.53%）, and A/CNK>1.1.The leucogranites in eastern section of North Himalayan, which are represented by Quedang,Dala, Yardoi, Rongbo and Gengre have lower k₂O/Na₂O ratios （<1）, but the leucogranite fromcentral section of North Himalayan （such as Quzhen, Sakya, Makya, Kudui and La-track Kangri）have high ratios （k₂O/Na₂O>1）. Both trace elements show different features, the rocks from theeastern section have adakite-like nature with high Sr, low Y, low HREE, without Eu anomaly,but the rocks form central section have low Sr, low Y, low HREE and Eu negative anomaly.Based on geochronology, the rocks from eastern section were formed during35.3～44Ma, whilethe rocks in the central section formed furing8.6to27Ma. This thesis further compared theleucogranites from eastern and central section by their age and geochemical characteristics. Theresults show that their age differences may be related to their different tectonic evolutionprocesses, whereas the difference between the geochemical properties are subject to the strongcontrolling of the source region of inconsistent structure evolution and depth. After the collisionbetween India and Asia in44～35Ma, due to crustal thickening, the India plate side, the HHcrystalline rock series （mainly hornblende with minor metapelites） occur partial melting at30kmdepth, which later formed adakitic-like rocks in the eastern section. Subsequently, strated from³5Ma, some partial melting event may lead to start the STDS, thereby promoting the NHchange from shortening and thickening to extensional collapse, and further led to the domeexhumation during27Ma to8.6Ma. In the mean time, and metaoelites muscovite dehydrationmelting at10km depth took place and later formed the leucogranite in the middle section.