【作者】 刘征华；

【导师】 张传恒；

【作者基本信息】 中国地质大学（北京） ， 构造地质学， 2009， 硕士

【摘要】 扬子陆块北缘毛堂群记录了Rodinia裂解事件的重要地质信息,对约束扬子陆块裂解过程,研究扬子古陆的演化具有重要意义。经过野外地质调查,结合SHRIMP法和LA-ICP-MS法锆石U-Pb同位素测年,及岩石化学数据综合分析,获得如下主要认识:(1)毛堂群形成于760±10Ma,即新元古代中晚期,且其岩浆活动持续时间较长,上限可能在600Ma左右。(2)毛堂群形成于大陆板内裂谷环境。(3)毛堂群酸性火山岩系显示出壳源特点,原岩可能是上部陆壳岩石的重熔产物;其基性火山岩系显示出幔源特点,是源自大陆岩石圈之下的地幔柱,并在上升过程中与大陆岩石圈相互作用,受到了不同程度的地壳混染,可能产生于60-80km深的尖晶石-石榴子石过渡带,源区的部分熔融程度可能较高。(4)毛堂群火山岩锆石测年结果显示,该区域存在与扬子克拉通内部和陆缘区时代相同的830～780Ma岩浆事件记录,指示了区域内存在晋宁期基底岩系,表明毛堂群所属的南秦岭武当地区是扬子克拉通北缘的组成部分。(5)区域地层对比表明毛堂群与武当山群和耀岭河群不具有简单的相似可比性。毛堂群姚营寨组形成时代与峡东莲沱组底部相当,更完整地记录了扬子克拉通南华纪初期的区域拉张-沉积事件;马头山组与峡东南沱组不能直接对比,可能代表发生于扬子克拉通北缘的另一次重要的构造-岩浆事件。(6)毛堂群裂谷火山活动是波及中亚-东亚(包括中国中-西部和华南)、澳大利亚、北美、非洲南部和南极的一次全球性的由地幔柱活动引发的裂谷火山事件群的组成部分。这次具有全球规模的裂谷火山事件群应当就是Rodinia超大陆裂解过程的响应。(7)扬子陆块北缘在760±10Ma时,被动裂谷开始启动,于600Ma左右,裂谷活动趋于结束,出现稳定的陆源碎屑沉积和大量的浅水碳酸岩沉积,被动大陆边缘形成,扬子克拉通新元古代陆内裂解结束。更多还原

【Abstract】 The Maotang group in the northern margin of the Yangtze block recorded important information of Rodinia breakup. These data could be helpful in constraining the breakup process of the Yangtze block, and thus make great significance in understanding the evolution of Yangtze block.In comprehensive analysis of field observation, SHRIMP and LA-ICP-MS zircon U-Pb dating and whole rock geochemistry data, we could obtain the following conclusions:1. Maotang group was formed in rifting envirenment of the inner continent during middle Neoproterozoic. The magmatic activity continnued for a long period, and ended at about 600Ma.2. The felsic volcanic formation from Maotang group was characterized by crust source, with primitive rocks possibly derived from the remelting of the upper crust; the basic volcanic formation, Maotang group was characterized by mantle source, and was indicated to be the production of mantle plume contaminated by crust in various degree during ascending. The mantle plume could be sourced from the transition zone from spinel phase to garnet phase, with a relative high degree of paritial melting.3. Zircon dating of the vocanic rocks from Maotang group indicate that this area exist a similar magmatic event to the inner and margin of the Yangtze block at 830～780Ma. This indicates the existence of the basement of the Jinningian in this area, which suggest that the area from the south part of the Qinling to the Wudang where the Maotang group occurred should be a part of the north margin of the Yangtze block.4. Regional stratigraphic correlation indicates that the Maotang group, Wudangshan group and Yaolinghe group could be correlated. The Yaoyingzhai formation of Maotang group is similar to the Liantuo formation in the Xiadong area, and recorded more information of the extension and sedimentation event of the Yangtze block at the beginning of the Neoproterozoic Nanhua Period. The Maotoushan foramtion could not be correlated with the Nantuo foramtion in the Xiadong area, and could represent another tectonic-magmatic event in the north margin of the Yangtze block.5. The vocanic event indicated by the Maotang formation is a part of the globle rifting and volcanic activity event which is thought to be triggered by mantle plume and affect areas such as Middle Asia-East Asia (including the middle and west part of China and the South China), Austrilia, north America, the south part of the Africa and Antarctic.6. The passive rifting in the north margin of the Yangtze block began at 760±10Ma and finished at about 600Ma. The appearence of stable land clastic sedimentation and carbonate deposition in shallow water indicate the formation of the passive continental margin and the finish of the Yangtze block breakup in Neoproterozoic.更多还原