Geochemical Characteristic of Granite in the Binggou Area of the Altun Mountains and Its Implications for Geological Structure Evolution
This study presents a detailed petrological,geochemical,and zircon SHRIMP U-Pb geochronological investi-gation of the granite sequences exposed with in the Binggou Tectonic Magmatic Belt in Arjin mountains.The geochemi-cal characteristics show that the granites are characterized by high Si and Na,low Fe,Mg and Ca,and the aluminum satu-ration index(A/CNK)is 0.88-1.01,which is in the metaluminous"Ⅰ"type granite;they are enriched in Rb,Th,and LREE,and are deficient in Ta,Nb,Zr,Hf,and HREE;they mostly have negative europium anomalies,and their δEu val-ues range from 0.52 to 0.62.The zircon U-Pb dating results show that among the intrusive rocks in the Binggou se-quence,granodiorite is(410.7±11.9)Ma,diorite is(418.5±9.6)Ma,and gabbro is(449.5±10.9)Ma.Combined with the regional geologic data,geochemical characteristics,and tectonic interpretation,it is revealed that the granite body should have formed in the post-collisional extension stage,and it is thought that the same collision and extrusion stage of the orogeny was transferred to the post-collisional stage,and the same collision and extrusion stage was transferred to the post-collisional stage,and the same collision and extrusion stage was transferred to the post-collisional stage.It is be-lieved that the transition from co-collision and extrusion to post-collision and extension was around 440 Ma,and the post-collision and extension and alkaline magmatism lasted for about 30 Ma from 440 Ma to 410 Ma.The closure of the an-cient Altun Ocean basin in the north of the late ordovician epoch led to the formation of a large scale subtractive tectonic magmatic belt at the active plate margin(island-arc or active continental margin)in the limited ocean basin orogenic belt(the intrusive rocks in the Binggou sequence).
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