Structural and Geochronological Investigations of Neoproterozoic Rifting in Southwestern Laurentia

摘要寒武纪大爆发及其新元古代前兆发生在异常环境扰动的背景下，包括冷暖气候之间的极端波动，可能的真极地漫游，以及超大陆的重组和最终解体。构造事件可能是气候和极移事件的主要原因。尽管在过去的十年中取得了重大进展，但由于缺乏可靠的全球相关性以及与中生代相当的裂谷和大陆板块运动的年表，对大多数这些继承的绝对年龄控制的缺乏严重限制了新想法的测试。PI建议继续进行地质测绘、地层学研究和对劳伦西亚西南部相对完整的新元古代序列进行U/Pb测年的计划。到目前为止，他已经建立了一个基本的结构和地层框架，在一个关键领域，该部分记录了两个主要的冰期和他们的帽碳酸盐序列（可能与澳大利亚的Sturtian和Marinoan事件相关），以及导致西南劳伦被动边缘发展的构造作用。此外，他还在该层序中发现了三个新的灰层，并在新元古代的十多个主要砂体中发现了丰富的自生磷钇矿。他将尝试用常规的TIMS分析和微束分析技术对锆石和磷钇矿进行测年。这个项目的更广泛的影响包括：i）在加州理工学院培养一名地质学博士生; ii）多个机构的参与，包括圣安德鲁斯大学、加州大学洛杉矶分校、麻省理工学院和亚利桑那大学的研究工作，包括改进确定砂岩中自生矿物年代的国家基础设施;特别是在这项研究过程中制定磷钇矿分析标准，如果我们成功，将立即使世界各地的许多研究人员受益; iii）在死亡谷国家公园向公众进行演讲，这将有助于公众更好地了解公园自然资源的重要性; iv）研究可能有助于了解生物圈如何对极端的全球变化作出反应，从而有助于关于全球变暖和相关问题的国际辩论。

AbstractThe Cambrian explosion and its Neoproterozoic precursors occurred in a context of extraordinary environmental perturbations, including extreme fluctuations between warm and cold climate, possible True Polar Wander, and the reorganization and eventual breakup of a supercontinent. The tectonic events may have been primary causes of both climatic and polar wander events. Despite significant progress over the last decade, the lack of absolute age control on most of these successions has severely limited testing new ideas owing to a lack of reliable global correlations and a chronology of rifting and continental plate motions on a par with the Phanerozoic. The PI proposes to continue a program of geological mapping, stratigraphic studies, and U/Pb dating of the relatively complete Neoproterozoic succession in southwestern Laurentia. Thus far, he has established a rudimentary structural and stratigraphic framework in a key area where the section records two major glacial intervals and their cap carbonate sequences (presumably correlative with the Sturtian and Marinoan events in Australia), as well as tectonism that led to the development of the southwest Laurentian passive margin. In addition, he has discovered three new ash horizons within this sequence, and found abundant authigenic xenotime in some ten major sand bodies spanning the Neoproterozoic. He will attempt to date these units with conventional TIMS analysis and microbeam analytical techniques on both zircon and xenotime.The broader impacts of this project include: i) graduate training of a doctoral student in geology at Caltech; ii) involvement of multiple institutions, including St. Andrews University, UCLA, MIT and the University of Arizona in the research effort, including improvement of national infrastructure for dating authigenic minerals in sandstones; in particular, development of a xenotime analytical standard in the course of this research, if we are successful, will be of immediate benefit to many researchers around the world; iii) presentations to the public in Death Valley National Park, which will contribute to greater public understanding of the significance of the natural resources in the park; and iv) the research may contribute to understanding how the biosphere responds to the extremes of global change, and therefore contribute to evolving international debate regarding global warming and related issues.