Structural and Geochronological Investigations of Neoproterozoic Rifting in Southwestern Laurentia

寒武纪大爆发及其新元古代前体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，可能的真极漂移，至少一次重大的撞击事件，以及超级大陆的重组和最终分裂。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，但缺乏对关键演替的绝对年龄控制，严重限制了可靠的全球对比和与显生宙相当的裂谷和大陆板块运动年表的发展。在这个项目中，研究人员正在获得碎屑锆石上自生的xentime过度生长的U/Pb年龄，以及碎屑锆石的标准U/Pb年龄，这些碎屑锆石来自于Laurentia西南部（Kingston和Panamint Ranges，南加州）相对完整的新元古代演替的砂岩。这一序列包含了丰富的多次裂谷事件和随后的被动边缘沉降记录，穿插着冰川作用和随后的变暖事件、切口和可能的撞击事件的记录。研究人员对一些关键区域进行了采样，这些区域包含了一些构造和地层对裂谷和冰川作用相对时间的限制，并且正在测试一个最近的假设，即被动边缘序列中的特定砂岩层含有来自阿克拉曼撞击结构的碎屑，这将提供东冈瓦纳和劳伦西亚之间的关键时间相关层，并表明在下沉期间靠近澳大利亚南部和劳伦西亚西南部。

EAR-0107123WernickeThe 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, at least one significant impact event, and the reorganization and eventual breakup of a supercontinent. The tectonic events may have been a primary cause of both climatic and polar wander events. Despite significant progress over the last decade, the lack of absolute age control on key successions has severely limited developing reliable global correlations and a chronology of rifting and continental plate motions on a par with the Phanerozoic. For this project, the investigators are obtaining U/Pb ages of authigenic xenotime overgrowths on detrital zircons, as well as standard U/Pb dating on detrital zircons, on sandstones from the relatively complete Neoproterozoic succession in southwestern Laurentia (Kingston and Panamint Ranges, southern California). This succession contains a rich record of multiple rifting events and subsequent passive margin subsidence, interspersed with a record of glaciations and subsequent warming events, incisions, and a possible impact event. The investigators have sampled key areas that contain a number of structural and stratigraphic constraints on the relative timing of rifting and glaciation, and are testing a recent hypothesis that a particular sandstone horizon in the passive margin sequence contains detritus derived from the Acraman impact structure, which would provide a key time-correlative horizon between East Gondwana and Laurentia, and suggest proximity of southern Australia and southwestern Laurentia during subsidence.