| Central Asian orogenic belt(CAOB),one of the largest hyperplastic orogenic belts in the Phanerozoic,lies between the Siberia plate and Northern china-Tarim plate.Kalamaili orogenic belt was formed by the collisional suture of Junggar plate and Siberia plate,which is located in the northeastern margin of the Junggar Basin and an important part of the Central Asian Orogenic Belt.Laoyaquan Granite is located in the northern Kalamaili orogenic belt,belonging to the same tectonic unit with Kalamaili ophiolite belt,and which is the largest alkaline granite in the Eastern Junggar.So it is of considerable geological significance for the researching of East Junggar region and even the evolution of Central Asian Orogenic Belt.This thesis has studied the regional geology,petrogeochemistry,and isotopic chronology of Laoyaquan granite.The main conclusions as following:1.Through field geological study,Laoyaquan Granite intruded into Lower Carboniferous Nalinkala formation.Granite is a composite body,consisting of porphyritic granite,coarse-grained granite and fine-grained granite,of which the coarse is the largest outcropping.LA-ICP-MS zircon U-Pb age of the porphyritic granite is 317.6±3.3Ma;LA-ICP-MS zircon U-Pb age of coarse-grained granite is 310.3±3.2Ma;LA-ICP-MS zircon U-Pb age of fine-grained granite is308.4±2.8Ma,all were formed in Late Carboniferous.2.Fine-grained granite has a high content of SiO2(76.95-77.44wt.%),low in Mg O(0.03-0.07wt.%),and TiO2(0.03-0.06wt.%),Al2O3(12.33-12.79wt.%);alkali rich,(Na2O+K2O=8.30-8.83wt.%),K2O>Na2O;A/NKC=1.00-1.03;weak peraluminous,high Rb(327×10-6-413×10-6),Y(30.6×10-6-138×10-6)and Yb(4.75×10-6-13.80×10-6),low Sr(2.88×10-6-7.83×10-6)and Ba(5.50×10-6-22.4×10-6),10000×Ga/Al=3.1-3.8,Y/Nb=1.6-12.2.Rb,Th,K,Pb,Nd and Hf are enriched in trace element spider diagram,while Ba,Nb,Sr,P,Ti and Eu are depleted;?REE=108.1×10-6-283.8×10-6,REE patterns diagram exhibits a plat“V”shape,LREE/HREE=0.49-1.39,(La/Yb)N=0.90-2.30,LREE is slightly enriched,?Eu=0.01-0.04,exhibiting strong negative anomaly.The geochemical characteristics of the above indicated that Laoyaquan granite exhibit the characteristics of weak aluminum high-K calc-alkaline series of A2-type granites.3.By field work and geochemistry study,combined with previous research results,it is determined that Laoyaquan granite was formed under post-collision extensional stretching tectonic setting and it is A2-type composite granite with a high degree of partial melting produced by multiple intrusion of homologous magma caused by partial melting heated by underplating basaltic magma. |
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