Geochemical Characteristics And Diagenetic Age Of The Leucogranites In The Cuonadong,Tibet

Himalayan leucogranites has been a hotspot in geosciences since its discovery.The CuoNadong dome is a newly discovered leucogranites in recent years,and it has been found in recent years to have a huge potential for W-Sn and rare metal ore.In this paper,the geochemical characteristics,U-Pb chronology,and biotense analysis of biotite in the leucogranites of the CuoNadong were studied.Based on the previous research results,the formation age and cause of the leucogranites were discussed.The formation of dynamic factors.The leucogranites rock is located in the eastern part of the Tethys Himalayan leucogranites belt,close to the southern Tibet detachment fault.After analysis of the geochemical characteristics of the leucogranites in the CuoNadong dome,the content of SiO₂ is 74.73%⁷2.15%,the content of K₂O is 1.9%⁴.9%,and the CaO/Na₂O is 0.075⁰.28.The leucogranites of CuoNadong dome belongs to high potassium calcium alkaline aluminum Granite,Rb/Sr content is 3.46⁵9.41>0.9,higher differentiation coefficient?DI??91.04⁹4.89?,low consolidation coefficient?SI??0.36².39?,Zr/Hf?0.07⁰.86?is much lower than Zr/Hf?36.24?in the original mantle,light and heavy rare earth ratio?1.22⁹.61?,Zr?2.4⁴.5?is much lower than the content of chondrite,so it has obvious characteristics of high-differentiated S-type granite.In this paper,the formation age of the leucogranites is determined to be 20.04±0.36 Ma²3.13±0.21 Ma,which belongs to Miocene leucogranites.Combined with previous studies,we believe that the metamorphic deformation of the leucogranites can be divided into three phases:the first phase occurs at 44-23.7 Ma,mainly for the crustal thickening extrusion deformation;the second phase occurs at 23-14 Ma.A large number of light-colored granites were formed;the third period occurred from 14Ma to the present,which was mainly caused by the collapse of the Qianlong uplift,the formation of the north-south rift and the formation of pale granite.The Nd model age indicated by the Sr-Nd isotope is within the Nd model age of the high Himalayan crystalline rock series.The combination of I_Sr–?_Nd?t?can indicate that the source rock is a metamorphic rock in the high Himalayan crystalline rock series.The biomimetic data of the biotite is calculated to be 470-643.3°C,the oxygen fugacity is-17.5 to-19.5,the consolidation pressure is 4.15 to 5.97 Kbar,and the static rock pressure gradient is 0.0218 to 0.02315 GPa*Km^-1,calculated to have the shallowest formation depth of 2.26 Km.The leucogranites of the CuoNadong is lower in temperature and pressure than the general granite,and the oxygen fugacity is lower,indicating that the leucogranites of the CuoNadong is formed in the reducing environment,and partial melting occurs due to structural decompression.The leucogranites source rock is a high Himalayan crystalline rock system,and the Indian plate collides with the Eurasian plate to cause the crust to thicken.The opening of the South Tibet detachment system causes the pressure to decrease,and the structural decompression triggers the source region to have white clouds.The mother dehydrates and melts,and the formed magma rises along the tectonic channel and undergoes a high degree of crystallization differentiation,eventually forming a leucogranites.