The Cenozoic Leucogranites From The Himayalan Orogenic Belt, And Petrogenesis

The leucogranites of Himalayan orogenic belt contains many information about continental collision and uplift of plateau,which an important“Rock Probe”for exploring the deep earth of the Tibet Plateau.Based on the 1:250,000 regional geological survey report in the Himalayas,and combined the latest regional research results,this paper sorts out the distribution characteristics of Himalayan leucogranites bodies,conclude the law of spatio-temporal distribution,summarize the petrology and geochemistry of leucogranites,discuss the petrogenesis of leucogranites.The main results of this paper are as follows:?1?The main lithology of the Tethys Himalayas is two-mica monzogranites.The High Himalayan leucogranites is dominated by tourmaline granite and two-mica granite.During 45-24 Ma,leucogranites were only distributed in the Tethys Himalayan belt,characterized by early sodium-rich and high Sr/Y.Oligocene leucogranites is mainly composed of highly differentiated garnet granite associated with tourmaline granites.Miocene can be divided into two stages:?1?14-21 Ma:Tethyan Himalayan belt is a two-mica granites distributed in the middle part of the belt,while generally developed in the high Himalayan belt From West to east,it is tourmaline-two-mica granite--tourmaline-muscovite granites--two-mica monzogranites.?2?7-12Ma:Two mica granites and tourmaline-muscovite granites are exposed at the same time.?2?Two mica granites in the eastern part of the Tethys Himalayan belt has a very low Rb/Sr ratio and is formed by amphibole dehydration and melting.The granite at the western end of the middle section is mainly caused by fluid-absent muscovite dehydration melting,while the granite at the eastern end is mostly caused by the dehydration melting.Garnet granites undergo a high degree of plagioclase crystallization.The light granite in the high Himalayan belt has a high Rb/Sr ratio as a whole.Tourmaline granite is formed by fluid-absent muscovite melting,while two mica granites is formed by fluid-absent biotite melting,and its age is concentrated in 15-20 Ma.The¹2Ma and low Rb/Sr mica granite is the origin of mica hydromelting?3?The Eocene leucogranites may be formed by partial melting of the thicker basaltic amphibolite in the lower crust.The source area of pale granite in the high Himalayan belt is very similar to that in the Tethys Himalayan belt,which may all come from the high Himalayan crystalline rock series.The tourmaline granite and the two mica granite do not show any obvious difference.They are all formed by partial melting of meta-argillaceous rocks of the high Himalayan crystalline rock series.The higher ⁸⁷Sr/⁸⁶Sr ratio of leucogranites in the middle part of the Himalayan orogenic belt may be influenced by felsic materials.