Collaborative Research: Mesoproterozoic Tectonics of Inboard Southwestern Laurentia: Insight Into Assembly and Configuration of Rodinia From Study of Sedimentary Successions

该项目正在研究美国西部的中元古代(1300-1000 Ma)沉积岩，以检验有争议的罗迪尼亚假说的各个方面。正在测试的假设是，在暴露良好的沉积序列中保存下来的劳伦蒂斯西南部的内侧沉积和构造记录，可以用来了解周围板块边缘的应力、劳伦蒂斯西南部的排水模式和盆地的性质，以及可能的外部碎屑来源的年龄。这项研究包括构造、岩石学和地质年代学研究，目的是对比几个关键地区和单元的来源，并确定其来源。这些地区代表了曾经广泛的沉积序列的保存遗迹；它们暴露得很好，但距离很远，缺乏可靠的地质年代学阻碍了对比。这项研究集中在阿帕奇组(亚利桑那州)、昂卡组(大峡谷)、水晶泉组(死亡谷)和拉诺拉组(德克萨斯州)。研究人员正在重建区域克拉通内盆地和构造模式，并寻找可能的外部碎屑来源的“指纹”。年代学研究包括：火山灰层的精密U-Pb定年、碎屑锆石的U-Pb定年、独居石颗粒的新型原位U-Pb微探针定年、云母粒的Ar-Ar激光定年。沉积-构造研究正在通过寻找跨断层的相变化和与同构造岩浆作用的关系来评估哪些断层在沉积期间是活动的。岩石学研究强调使用标准岩石学技术的硅质碎屑岩的来源。涉及与沉积构造有关的地质年代学的详细区域测试正在更好地了解劳伦西亚西部的构造环境，从而更好地了解从1.3-1.0Ga与劳伦西亚碰撞的最有可能的相邻外侧大陆块。

This project is investigating Mesoproterozoic (1300-1000 Ma) sedimentary rocks in the western U.S. to test aspects of the controversial Rodinia hypotheses. The hypothesis being tested is that the inboard record of sedimentation and tectonics in southwestern Laurentia, preserved in well-exposed sedimentary successions, can be used for understanding stresses at the surrounding plate margins, nature of drainage patterns and basins in southwestern Laurentia, and the age of possible outboard sources of detritus. The research involves structural, petrologic, and geochronologic study aimed at correlation of, and characterizing provenance for, several key areas and units. These areas represent preserved remnants of once more extensive sedimentary successions; they are well exposed, but widely separated, and correlations have been hampered by a lack of reliable geochronology. The study concentrates on the Apache Group (Arizona), Unkar Group (Grand Canyon), Crystal Spring Formation (Death Valley), and Lanora Formation (Texas). The researchers are reconstructing the regional intracratonic basinal and tectonic patterns and searching for a "fingerprint" of possible outboard sources of detritus. The geochronological studies involve: dating ash beds using precise U-Pb geochronology, U-Pb dating of detrital zircons, new in situ U-Pb microprobe dating of monazite grains, and Ar-Ar laser dating of mica grains. Sedimentary-tectonic studies are evaluating which faults were active during deposition by looking for facies changes across faults and relationships to syntectonic magmatism. Petrologic studies are emphasizing provenance of siliciclastic rocks using standard petrologic techniques. Detailed regional tests involving geochronology linked to sedimentary tectonics are providing better understanding of the tectonic setting of western Laurentia and hence the most likely adjacent outboard continental masses that collided with Laurentia from 1.3-1.0 Ga.