Dikes And It's Tectonic Implications In Rongbu Area,southern Tibet

The Rongbu area is located in the southern Tibet and clamped between the Qiongduojiang faults and the Rongbu-Gudui faults.A large number of mafic and acidic dikes are widely developed in this area.This paper relies on the“4 Geological Surveys of Tibetan Rongbu area 1?50000(H46E020003,H46E020004,H46E020005,H46E020006)”of Cheng Du geological survey center of the Geological Survey of China.The paper obtained the following understanding by researching on petrology,geochemistry,and chronology of the intrusive veins in this area:There are mafic dikes exposed in Rongbu area.The main rock types are diabase-porphyrite,gabbro-diabase,gabbro,etc.They are distributed in NW-SE direction with different sizes,consistent with the extension direction of regional faults.Cluster distribution.The contact relationship between veins and surrounding rocks is obvious,and most of them have condensation edges.The content of Si₂O is decrease gradually from deep intrusive gabbro veins to shallow intrusive diabase-porphyrite.The content of Al₂O₃ in diabase-porphyrites was significantly higher than that of gabbro-diabases and gabbros,reflecting the nature of the magma sources and pressure melting are differences.The diabase-porphyrite dikes is consistent with the MORB geochemical elemental content,while the gabbro-diabase and gabbro dikes have typical oceanic island basalt(OIB)features.According to the comparative analysis of rare earth and trace elements of the regional volcanic rocks and dikes,the dikes and the same period of mafic magmatic rocks are products of the same origin and the different shapes,southern Tibet.The acidic dikes mainly include granitic aplite,granodiorite-porphyry,etc.in the Rongbu area.The outcrop scale ranges from dozens of meters to hundreds of meters.The boundaries between veins and surrounding rocks are very clear,most of the visible baking side.Mainly presented as NW-SE,with some along the fault zone.Constant geochemical analysis shows that the dikes are characterized by peraluminous S-type granites.The total amount of rare earth elements(38.7×10-6?88.71×10-6)is low,which is enriched in light rare earth elements and is depleted in large ion lithophilic elements(LIVEs)such as Sr,Ba,and Th,enriching in high field strength element(HFSE)such as Ta,Hf,Y and Zr.The analysis of trace elements such as Rr,Ba,and Sr shows that the source rocks of the acidic dikes may come from the upper part of the earth's crust.They have the characteristics of argillaceous rock source regions and contain a small amount of sandy components.The mafic dikes ages were 147.3±3.6 Ma(MSWD=1.3)and 137.3±1.6 Ma(MSWD=0.54),and the formation age was Late Jurassic-Early Cretaceous.The tectonic setting of the study area is in the extension and expansion of the late Neo-Tethys Oceanic,a large number of mafic magmas have become emplaced with regional faults and fissures,forming mafic dikes and rock walls that are distributed along the tectonic line.The age of the acidic dikes is 41.5±6.1Ma(MSWD=20).The tectonic setting is in the collisional orogeny stage between the Indian plate and the Eurasian plate at the Paleogene Eocene.The upper part of the crust is partially melted and produced a series of acidic intrusive dikes that are characterized by S-type granites.