下扬子PTB界线深水相区粘土岩的火山成因研究及其对LPME的指示意义

发布时间：2018-04-08 21:19

本文选题：二叠—三叠纪界线(PTB)　切入点：粘土岩　出处：《地质学报》2016年04期

【摘要】：全球,尤其是特提斯域二叠—三叠纪之交(PTB)剖面中普遍发育火山成因的粘土岩,对理解晚二叠世末生物大灭绝(LPME)的触发机制及相关基础地质问题具有重要意义。本文报道了在华南下扬子区新发现两条深水PTB剖面(皖南牛山和蔡村)的粘土岩工作,包括岩石学、矿物学和全岩地球化学等,填补了区域研究空白。研究结果发现,粘土岩主要由伊利石等粘土矿物,以及石英、岩浆锆石、长石等斑晶矿物组成。在地球化学上具有高K_2O、低Na_2O、相对富集大离子亲石元素(LILE)、相对亏损高场强元素(HFSE)等特征。据此,认为这些粘土岩为火山成因的钾质斑脱岩,其原岩可能为中酸性流纹英安岩,具有弧岩浆作用的源区背景。对比华南其他地区已发现的PTB界线粘土岩,发现它们成因类似,可能来源于古特提斯洋周缘陆陆碰撞,抑或是泛大洋俯冲潘吉亚大陆东缘(包括华南板块)所导致的长英质火山岩浆喷发,且具有多期多源性特点。PTB时期全球活跃的火山岩浆活动(包括镁铁质火山作用和华南地区火山灰所指征的长英质火山作用)可能是导致LPME的主要原因。
[Abstract]:Volcanogenic clay rocks are widely developed in the global, especially in the Tethys Permian-Triassic (PTB) section, which is of great significance for understanding the trigger mechanism and related basic geological problems of LPMEs in late Permian.In this paper, two new deep water PTB profiles (Niushan and Cai village) have been discovered in Lower Yangtze area, South China, including petrology, mineralogy and whole rock geochemistry, which fill the gaps in regional research.The results show that the clay rocks are mainly composed of Illite and other clay minerals, as well as quartz, magmatic zircon, feldspar and other porphyry minerals.Geochemistry is characterized by high K _ 2O, low Na _ 2O, relative enrichment of large ion lithophile element Lilei, and relative depletion of high field strength element (HFSE).Therefore, it is considered that these clay rocks are volcanic origin kalitic porphyry, and their original rocks may be intermediate-acid fluid-striped dolomite with arc magmatism source area background.Comparing with the PTB boundary clay rocks found in other parts of South China, it is found that they are of similar origin and may have originated from the continental collision around the PaleoTethys ocean.Or the felsic volcanic magma eruption caused by the pan-ocean subduction of the eastern margin of the Pangea continent (including the South China plate),The global active volcanic magmatism (including magnesite volcanism and felsic volcanism indicated by volcanic ash in South China) may be the main cause of LPME.
【作者单位】：南京大学地球科学与工程学院;
【基金】：国家重点自然科学基金项目(编号:41230312)资助的成果
【分类号】：P588.22

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