The Petrology And Geochemistry Study About The Mafic-Ultramafic Rocks In The Southern Altyn Fault, XinJiang

As the northern boundary of Qinghai-Tibet Plateau, the Altyn fault has a consuming tectonic activity, and has been experienced a multi-stage magmatic activity, mafic-ultramafic magmatism development. For a long time, there are different viewpoint about the characteristics,composition and age of the mafic- ultramafic intrusion in the Altyn fault, which caused the large differences about the tectonic and magma evolution, These different views also affect the development of regional prospecting.In this paper, on the basis of previous studies, closely integrated regional geological survey results of the new information,we choose Yuemakeqi and Changshagou in southern Altyn fault as the studying object,and study on the rock petrogenesis, rock composition series and the isotope age of mafic-ultramafic rock.Comprehensive use of petrology, geochemistry, isotope age research methods, discuss the composition,character and the age , restoration and reconstruction the tectonic and magma evolution history about the southern Altyn fault. The main understanding at this stage are as follows:1. Yuemakeqi rock body is a slide of ophiolite that involved in the Altun fault. It is composed of ultrabasic rocks, basalt and gabbro. And ultrabasic rocks and gabbro contact with a fault, the ultrabasic rocks,gabbro and basalt constitute a complete ophiolite unit.2. Changshagou rock body is made up of Qingshuiquannan rocks,Middle Changshagou rocks,Qingshuiquanbei rocks,Huangtuquan rocks . They are contact with each other with a fault .These four rocks become some blocks that involved in Altun fault . Among them, Qingshuiquannan mafic-ultramafic rock formed in the initial ocean basin environment, with ophiolite characteristics. The middle Changshagou mafic-ultramafic rock is intrusive rock and it formed continental rift environment. Qingshuiquanbei mafic-ultramafic rock is formed in the continental rift environment, but, compared to the The middle Changshagou mafic-ultramafic rock it has different character,because it has been mixed by the crust.3.By zircon U-Pb dated, the age of Yuemakeqi basic-ultrabasic rock is about 500.7±1.9Ma,and is the product of magmatic activity in the late Cambrian, the granite behind Yuemakeqi basic-ultrabasic rock belong to Early Ordovician,its zircon U-Pb dating is 466.0±6.1Ma,it is a subsequent intrusion body relative to the Yuemakeqi basic-ultrabasic rock.The age of the plagioclase amphibolite is 1827±13Ma, belonging to the Mesoproterozoic, they are the oldest part of the basement, but weighted average age of the biotite granite the is 504.0±5.7Ma,These ages that we obtain have an important meaning to make certain the characters of the Changshagou and Yuemakeqi rock and to study the tectonic and magma evolvement.