Structural and Geochronological Investigations of Neoproterozoic Rifting in Southwestern Laurentia

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，包括气候温暖和寒冷之间的极端波动，可能的真极移，以及超大陆的重组和最终的解体。构造事件可能是气候和极地漂移事件的主要原因。尽管在过去十年中取得了重大进展，但由于缺乏可靠的全球对比和与显生宙相同的裂谷和大陆板块运动年表，对这些序列中的大多数缺乏绝对年龄控制，严重限制了对新想法的测试。PI建议继续对劳伦西亚西南部相对完整的新元古代序列进行地质填图、地层学研究和U/Pb测年。到目前为止，他已经在一个关键区域建立了初步的构造和地层格架，该剖面记录了两个主要的冰川区间及其盖层碳酸盐序列(可能与澳大利亚的Sturtian和Marinoan事件相关)，以及导致劳伦斯西南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火山灰层位，并在横跨新元古代的约10个主要砂体中发现了丰富的自生辉长岩。他将尝试用常规的TIMS分析和微束分析技术来确定这些单元的年龄。这个项目的更广泛的影响包括：i)加州理工大学地质学博士研究生的培训；ii)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在内的多个机构参与研究工作，包括改善国家基础设施，以确定砂岩中自生矿物的年龄；特别是，在这项研究过程中开发出一个Xe-time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介绍情况，这将有助于公众更好地了解该公园自然资源的重要性；以及iv)这项研究可能有助于了解生物圈如何应对极端的全球变化，从而有助于推动关于全球变暖及相关问题的不断演变的国际辩论。

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.