【作者】 孙吉明；

【导师】 徐学义；

【作者基本信息】 长安大学 ， 地球化学， 2008， 硕士

【摘要】 阿尔金断裂作为青藏高原的北部边界,构造活动强烈,经历了多期岩浆活动,镁铁—超镁铁质岩发育。长期以来,阿尔金南缘断裂带镁铁—超镁铁质岩的性质、组成和形成时代存在着不同的认识,致使对阿尔金断裂带的构造岩浆演化也存在较大的分歧,这些不同认识和分歧影响了区域找矿的开展。本文在前人研究的基础上,密切结合区域地质调查的新成果资料,选择阿尔金南缘断裂的约马克其岩体和长沙沟岩体为研究对象,开展镁铁—超镁铁质岩体岩石成因、岩石组合系列、同位素年代学等方面的研究。综合运用岩石学、地球化学、同位素地质年代学等研究方法,探讨约马克其和长沙沟镁铁—超镁铁质岩体的组成、性质、形成时代,恢复重建阿尔金南缘断裂带构造岩浆演化历史。取得的主要认识如下:1约马克其岩体是卷入到阿尔金断裂带中的蛇绿岩片,该蛇绿岩片由超基性岩、辉长岩和玄武岩组成,其中超基性岩和辉长岩呈断层接触,它们共同构成了一个完整的蛇绿岩单元。2长沙沟岩体由清水泉南、长沙沟中段、清水泉北和黄土泉四个镁铁质岩块组成,彼此间呈断层接触,它们均卷入到阿尔金活动带以构造岩块的形式产出。其中,清水泉南镁铁—超镁铁质岩体形成于由裂谷向大洋转化的初始洋盆环境,具有蛇绿岩的特征。长沙沟中段镁铁—超镁铁质岩体为形成于大陆裂谷环境的侵入岩。清水泉北镁铁—超镁铁质岩体也形成于大陆裂谷环境,受到地壳一定程度的混染作用而区别于长沙沟镁铁—超镁铁质岩。3年代学研究表明:约马克其基性—超基性岩块锆石U-Pb年龄是500.7±1.9Ma,为晚寒武世岩浆活动的产物;清水泉南岩块的斜长角闪岩锆石U-Pb年龄为1827±13Ma,属于中元古代;清水泉岩块中的片麻状黑云母花岗岩U-Pb年龄为504.0±5.7Ma,这些年龄取得对确定长沙沟和约马克岩镁铁—超镁铁岩体的性质和研究阿尔金南缘断裂带的构造岩浆演化具重要意义。更多还原

【Abstract】 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.更多还原