| The Kamai granite is located in Gongjue County,eastern Tibet,and the tectonic location belongs to the Qiangtang-Sanjiang orogenic system?primary tectonic unit?,Jiangda-Lvchun volcano-magmatic arc?secondary tectonic unit?,and Jiangda-Weixi land Marginal arc?third-level tectonic unit?,the Kamai granite body is exposed in the north-central part of the Jiangda-Weixi continental arc,the product of the westward subduction of the continental margin volcanic arc system Jinshajiang ocean basin in the study area.The action is strong,accompanied by large-scale magmatism.In this paper,the kamai granite in Gongjue County,eastern Tibet is taken as the research object.Through field investigation,the actual spatial distribution of the rock mass is understood,and the mineral composition of the rock mass is understood in conjunction with the characteristics of the mirror.Then,through the zircon U-Pb chronological characteristics,the earth Geochemical characteristics,combined with the regional geological background of the study area,discuss the genetic type of the rock mass,the nature of the source area,the structural background and the mineralization of the rock mass.The Carmelite granite body is dominated by a large area of exposed rock base,and its main lithology is monzonite granite.After field geological survey,it is found that the rock body is mainly distributed in the direction of NNW-SSE,and the exposed area is about 200km2.The fresh surface is off-white,with weak weathering degree,and intrusive contact with the surrounding rock.According to the thin section identification,the rock mass is mainly composed of plagioclase,potash feldspar,quartz,hornblende,biotite and other minerals.The three zircon U-Pb isotope test results were 198±1Ma?MSWD=3.7?,196±1Ma?MSWD=2.8?,and 197±2Ma?MSWD=4.9?,It indicates that the diagenesis of the Kamai granite body in Gongjue County,eastern Tibet is Early Jurassic.The rock mass in the study area has a high content of Si O2?63.38%-75.24%?,with an average value of 70.6%.It is an acid rock,with a K2O content of?3.12%-5.79%?and a Na2O content of?2.72%-4.02%?,relative Rich in potassium and poor in sodium,the rock aluminum saturation index A/CNK value is 0.9-1.24,the average value is 1.01,which belongs to quasi-aluminum-weak peraluminous granite,and the Ritman index?=2.19-3.64,which is calcium and alkaline—Alkaline rock.The high acidity of the rock indicates strong differentiation and evolution.The trace elements are enriched by K,Rb and other large ion philophile elements,depleted Nb,Ta and other high field strength elements,the total amount of rare earth elements??REE?is between 94.75×10-6-203.36×10-6,light and heavy rare earth The ratio?LREE/?HREE is between 7.11-17,light rare earth elements are relatively enriched,and heavy rare earth elements are relatively depleted.The?Eu value is between 0.5 and 0.87,with an average value of 0.67.It has a weak negative Eu anomaly and similar geochemical properties.The source rock may be a mixture of crust-derived materials and mantle-derived materials.The granite in the study area was formed in the collision environment,reflecting the geodynamic background of continental collision.The Jintejiang Gutti Ocean was closed before the Late Triassic.There are several types of minerals related to the Triassic granite and the volcanic arc on the Jiangda-Weixi continental margin.Based on the analysis of available data,the granite in the study area may have prospects for rare earth minerals such as W,Sn,Mo,Bi,and Be. |
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