Cretaceous Tectonic Magma Evolution In The Southern Qinghai-Tibet Plateau

In this study,According to the 1/25 million regional geological survey,1/5 million regional geological survey / mineral survey,relevant scientific research reports,published papers,dissertations and accumulated chronology and petrochemical information of research area accumulated by mentor team nearly 20 years,the paper accurately determine the age of the Cretaceous magmatic rocks and check the rationality of the main chemical elements in the study area.On the basis of the above,the paper determine the chemical type of rock,identify the rock assemblage of TTG and high Mg combinations,and then explore the evolution of Cretaceous tectonic magma from the angle of rock assemblage and its evolution.We got some basic knowledges as follows:(1)During the early Cretaceous period,the TTG combination was extensively developed and strip-shaped distributed.The TT combination was mainly distributed in the south gangdise area and the Himalayan zone,followed by sporadic distribution in the North Gangdise with characteristics of striped distribution along edge and axis.The GG combination is mainly distributed in the middle and northern Gangdise,with characteristics of striped distribution along edge and axis.These reflect the subduction of the ocean of Yarlung Zangbo River to the north,as well as the different levels and degrees of partial melting effect of the passive land source on the side of the Inchong plate.(2)During Late Cretaceous,magmatic activity is still extensive,but weaker than those of the Early Cretaceous in degree and intensity.The TT combination is distributed in the Nangangsi belt,which is characterized by sporadic distribution along the axis and GG combination is more widely distributed in the Ganggans and the North Gangdise belt.These reflecting the subduction of the ocean of Yarlung Zangbo River northward with gradually weakening degree,and characteristics of difference deep melting of the front of magma arc along the edge or the axis.(3)During the Early Cretaceous,the spatial distribution of the magmatic rocks in the Gangdese zone is characterized by south-neutral and north-acidity,and the granite is characterized by the south "I-S"-the north "S" in the rock type distribution.Rock series distribution is characterized by the low potassium in the south and high potassium in the north.Volcanic rocks,exposed at himalayan zone,may be the products of the stretch and stretching of side of the passive continental margin draged by the front of the oceanic crust.All of these indicate that the ocean of Yarlung Zangbo river was subducting northward and was in the main subduction period during the Early Cretaceous.During the Late Cretaceous,the spatial distribution of the magmatic rocks in the Gangdese zone is characterized by south-neutral and north-acidity,and the granite is characterized by the south "I-S"-the north "S" in the rock type distribution.Rock series distribution is characterized by the low potassium in the south and high potassium in the north.There is less distribution of rock mass in the Himalayan belt,may be in the oceanic crust drag and drop,because of the relatively weak of passive edge.All of these indicate that the ocean of Yarlung Zangbo river was subducting northward.The magmatic activity During early Cretaceous is stronger than that During Late Cretaceous,that indicating more stronger subducting of the oceanic crust during Early Cretaceous.subducting of the oceanic has a tendency to weaken during the Late Cretaceous.On the whole,the Cretaceous oceanic crust was subducting northward during the Cretaceous period.