EAR-PF: Unraveling the Paleogene exhumation history of the Orocopia Schist in west-central Arizona

EAR-PF：揭示亚利桑那州中西部 Orocopia 片岩的古近纪发掘历史

• 批准号: 1952764
• 负责人: Nikki Seymour
• 金额: $ 17.4万
• 依托单位: Seymour, Nikki M
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-08-01 至 2022-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1952764&HistoricalAwards=false
• 关键词: EAR; PF; Unraveling; Paleogene; exhumation

pDr. Nikki M. Seymour has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education plans at Stanford University and the University of California Santa Cruz under the mentorships of Dr. Martin Grove and Dr. Jeremy Hourigan respectively. This research project will determine the exhumation history of the northern Plomosa Mountains, located in west-central Arizona. The rocks exposed in the Plomosas originated as sediments deposited on the Pacific Ocean floor west of California and were subducted and added to the base of the North American continent during the late Cretaceous-Paleogene Laramide Orogeny, a period of shallow-angle subduction from ~90-50 Ma that has been tied to the end of Sierra Nevada magmatism, construction and subsequent collapse of high plateaus, uplift of basement-cored mountain ranges, and extensive volcanism. The top of the Orocopia Schist was exposed at the surface by the Plomosa detachment fault between ~21-15 Ma, meaning it would have been exposed at the surface after traveling more than 40 km through the crust to reach shallow crustal levels in the latest Cretaceous-Paleogene (~73-23 Ma). The thermal history that follows the buildup of sediment at the base of the crust during shallow-angle subduction can reveal how these rocks moved through the crust. This project will study metamorphic zircon rims from the Orocopia Schist to document the timing of sediment subduction and addition to the bottom of North America. However at present there are no constraints on the history that brought these rocks to the shallow crust prior to Miocene faulting (~21-15 Ma). As part of the broader impacts of this project Dr. Seymour will coordinate with San Francisco-based software developers to expand the capabilities of the Augmented Reality Topographic Sandbox to integrate geologic maps. Successfully integrating maps with topography in the sandbox will allow students to experiment with the 3D geometries of sedimentary formations and structures and will be widely applicable throughout all levels of geoscience education./ppDetermining the exhumation history of the Orocopia Schist (OS) is critical to understanding the transition from Cretaceous shortening to Miocene extension, as well as the processes driving sediment underplating, accretion, and syn-subduction exhumation. Dr. Seymour will systematically investigate the temporal and thermal evolution of the Orocopia Schist subduction complex using meso- and microstructural, geo- and thermochronological, petrological, and geochemical analyses to understand (1) at what depth the OS was accreted and understand the processes that exhumed it, (2) the age and geochemical affinity of the crystalline gneiss that structurally overlies the OS and the significance of its tectonic contact with the OS, and (3) the exhumation histories of the gneiss and OS. Methods will include detailed mapping and microstructural study of the OS and the overlying gneiss at key locations to document crucial cross-cutting relationships, dating of syn-kinematic phases with clear kinematic context such as titanite for U-Pb and hornblende, phengite, and biotite for Ar/Ar thermochronology, and thermobarometry using Titanium-in-quartz, Raman spectroscopy of carbonaceous material, and oxygen stable isotope ratios for thermometry and garnet-biotite-plagioclase-quartz chemistries for barometry. This approach will document the number and significance of fabric generations preserved in the Orocopia Schist, and determine whether the presently exposed mylonitic fabric is related to Paleogene metamorphism, Miocene extension, or preserves elements of both. Comparing these results to the thermal history of the crystalline gneiss will provide critical details to tectonic relationship between the two rock types. Particular attention will be paid to whether the schist and gneiss share any portion of their thermal history, and if so, at what point their histories evolved together. A shared thermal history between the OS and gneiss would provide insights into the geodynamic processes that control subduction complex exhumation during or shortly following shallow-slab subduction. These observations have implications for (1) the regional tectonics of the southwestern USA, (2) the extent of subduction underplating during shallow-angle subduction, and (3) the geodynamic processes that control subduction complex exhumation during or shortly following flat-slab subduction./ppThis award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria./p

Pdr。 Nikki M. Seymour分别获得了斯坦福大学和加利福尼亚大学圣克鲁斯分别在马丁·格罗夫（Martin Grove）博士和杰里米·霍米尼尼（Jeremy Hourigan）博士的指导下，在斯坦福大学和加利福尼亚大学圣克鲁斯分校进行研究和教育计划。该研究项目将确定位于亚利桑那州中西部的北部Plomosa山的挖掘历史。暴露在plomosas中的岩石起源于在加利福尼亚州以西的太平洋地板上沉积的沉积物，并在白垩纪晚期的laramide造山心上被俯冲，并添加到北美大陆的底部，这是一个浅层山脉的浅色山顶，与高高的山脉融合了高高的Magifter and Magifter and Magifter and Magmatism and collat​​e and Magmatism collastians and collat​​e and Magmatism，地下室的山脉和广泛的火山范围。 Orocopia片岩的顶部通过约21-15 Ma之间的Plomosa脱离断层在表面暴露在表面上，这意味着它在经过约40公里以上的地壳上行驶后将在表面暴露在表面上，以达到最新的白垩纪 - 甲壳虫（约73-23 mA）中的浅层地壳水平。在浅角俯冲期间，在地壳底部积聚在地壳底部的沉积物堆积之后的热历史可以揭示这些岩石如何穿过地壳。该项目将研究来自Orocopia片岩的变质锆石轮辋，以记录沉积物俯冲的时机并在北美底部增加。但是，目前，在中新世断层（〜21-15 Ma）之前，对历史没有任何限制，将这些岩石带到了浅层地壳上。作为该项目的更广泛影响的一部分，西摩博士将与位于旧金山的软件开发人员进行协调，以扩大增强现实现实地形沙盒的功能以整合地质图。 Successfully integrating maps with topography in the sandbox will allow students to experiment with the 3D geometries of sedimentary formations and structures and will be widely applicable throughout all levels of geoscience education./ppDetermining the exhumation history of the Orocopia Schist (OS) is critical to understanding the transition from Cretaceous shortening to Miocene extension, as well as the processes driving sediment underplating, accretion, and合成挖掘。 Dr. Seymour will systematically investigate the temporal and thermal evolution of the Orocopia Schist subduction complex using meso- and microstructural, geo- and thermochronological, petrological, and geochemical analyses to understand (1) at what depth the OS was accreted and understand the processes that exhumed it, (2) the age and geochemical affinity of the crystalline gneiss that structurally overlies the OS and the其与OS的构造接触的意义，以及（3）片麻岩和OS的发掘历史。 Methods will include detailed mapping and microstructural study of the OS and the overlying gneiss at key locations to document crucial cross-cutting relationships, dating of syn-kinematic phases with clear kinematic context such as titanite for U-Pb and hornblende, phengite, and biotite for Ar/Ar thermochronology, and thermobarometry using Titanium-in-quartz, Raman spectroscopy of carbonaceous material,和氧气稳定的同位素比，用于调节体的温度计和石榴石 - 生物岩 - 泛岩 - 石英化学剂。这种方法将记录留在Orocopia片岩中保存的织物世代的数量和意义，并确定目前暴露的mylonitic织物是否与古近年的变质，中新世扩展或保留两者的元素有关。将这些结果与晶体片麻岩的热历史进行比较，将为两种岩石类型之间的构造关系提供关键细节。特别关注片岩和片麻岩是否共享其热史的任何部分，如果是的话，他们的历史在什么时候也会发展在一起。 OS和片麻岩之间的共有热历史将提供有关控制俯冲过程在浅板俯冲期间或不久后控制俯冲复合物挖掘的洞察力的见解。这些观察结果对（1）美国西南部的区域构造学具有影响，（2）俯冲俯冲期间的俯冲程度，以及（3）控制俯冲式复杂挖掘的地球动力学过程，或在平面俯冲后不久以来都通过评估了NSF的构建范围，并反映了NSF的构建范围。更广泛的影响评论标准/