Testing models of metamorphic sole formation and early subduction evolution in the Easton Metamorphic Suite, Northwest Cascades, Washington

测试华盛顿州西北喀斯喀特伊斯顿变质层组中的变质底形成和早期俯冲演化模型

• 批准号: 1948584
• 负责人: Sean Mulcahy
• 金额: $ 18.51万
• 依托单位: Western Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1948584&HistoricalAwards=false
• 关键词: Testing; models; metamorphic; sole; formation

Subduction zones occur where cold and dense oceanic crust descends beneath warmer buoyant oceanic or continental crust. Active subduction zones are responsible for most of Earth’s large earthquakes and volcanic activity. Ancient subduction zones provide important information on processes operating at great depths that are not observable in active subduction zones, such as compositional changes in the crust through time, the history and correlation of past tectonic events, and the timescales of subduction zone processes. Understanding how subduction zones form and change over time is therefore critical to understanding the Earth and the processes responsible for earthquakes and volcanism. This project will test multiple hypotheses for how subduction zones form and change with time. The research will promote the progress of science by: 1. increasing representation in STEM by recruiting and involving underrepresented undergraduate and graduate students in the project, 2. improving undergraduate and graduate education through new laboratory exercises, new advanced courses, and expanded field opportunities, and 3. developing enhanced STEM expertise through undergraduate and graduate field research and collaboration in multiple laboratories in the U.S.The mechanisms by which subduction zones initiate and evolve towards steady state are not fully understood. Subduction initiation is often preserved in suprasubduction zone ophiolites and metamorphic soles, remnants of a newly subducted plate that was heated by the overlying mantle, scraped off, and accreted to the upper plate during the first ten million years of subduction. This research will address several questions related to early subduction processes, specifically: Does subduction initiate spontaneously via a gravitational instability or is subduction induced by forced convergence? Do inverted metamorphic gradients in metamorphic soles form via downward heat advection or by the progressive accretion of subducted material? Do accreted units within subduction zones cool by thermal relaxation, exhumation within the subduction channel, or underplating and accretion? These questions will be resolved through an investigation of the Easton Metamorphic Suite in the Northwest Cascades of Washington. The region contains Jurassic ophiolite sequences and a Jurassic-Cretaceous metamorphic sole formed during subduction initiation beneath western North America. Combined field mapping, structural and microstructural analysis, metamorphic petrology, and geochronology will determine: 1. the relative timing of suprasubduction zone ophiolite and metamorphic sole formation, 2. the timing and conditions of metamorphism within each unit of the metamorphic sole, and 3. the structural relationship of contacts between subducted units. The results will establish a detailed reconstruction of the subduction history that can be used to test proposed models for early subduction evolution.This 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.

俯冲带发生在寒冷而致密的海洋地壳下降到温暖的浮力海洋或大陆地壳之下的地方。活跃的俯冲带是地球上大部分大地震和火山活动的原因。古俯冲带提供了在活动俯冲带无法观测到的大深度过程的重要信息，如地壳成分随时间的变化，过去构造事件的历史和对比，以及俯冲带过程的时间尺度。因此，了解俯冲带是如何随着时间的推移而形成和变化的，对于了解地球以及地震和火山活动的过程至关重要。该项目将测试俯冲带如何随时间形成和变化的多种假设。这项研究将通过以下方式促进科学的进步：1 .通过招募和让代表性不足的本科生和研究生参与该项目，增加STEM的代表性；2 .通过新的实验练习、新的高级课程和扩大的实地机会来改善本科和研究生教育；通过本科生和研究生的实地研究以及在美国多个实验室的合作，发展增强的STEM专业知识。俯冲带的形成和向稳定状态演变的机制尚未完全了解。俯冲起始通常保存在俯冲上带蛇绿岩和变质岩底中，它们是新俯冲板块的残余物，在俯冲的前1000万年中被上覆地幔加热，被刮掉并吸积到上板块。这项研究将解决与早期俯冲过程相关的几个问题，特别是：俯冲是通过重力不稳定自发地开始的，还是由强迫收敛引起的？变质底的反向变质梯度是通过向下的热平流形成的，还是通过俯冲物质的递进增加形成的？俯冲带内的增生单元是否因热松弛、俯冲通道内的掘出或底板和增生而冷却？这些问题将通过对华盛顿西北瀑布的伊斯顿变质岩组的调查来解决。该地区包含侏罗纪蛇绿岩层序和侏罗纪-白垩纪变质底，形成于北美西部俯冲起生时期。综合野外测绘、构造和微观构造分析、变质岩石学和地质年代学将确定：上俯冲带蛇绿岩与变质底岩形成的相对时间；2 .变质底各单元内变质作用的时间和条件；俯冲单元间接触的构造关系。研究结果将建立详细的俯冲历史重建，可用于检验提出的早期俯冲演化模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Evidence for accretion and underplating of distinct units within regional blueschists of the Easton metamorphic suite, northwest Cascades Washington

华盛顿喀斯喀特西北地区伊斯顿变质岩套区域蓝片岩内不同单元的吸积和底侵的证据

• 发表时间: 2023
• 期刊: Geological Society of America Abstracts with Programs
• 作者: Gates, E.;Mulcahy, S.R.;Schermer, E.L.
• 通讯作者: Schermer, E.L.

JURASSIC AND PALEOGENE FAULTING IN THE EASTON NAPPE OF THE WESTERN NORTHWEST CASCADES THRUST SYSTEM OF WASHINGTON

华盛顿西北瀑布逆冲系统伊斯顿推覆体侏罗纪和古近纪断层

• DOI: 10.1130/abs/2021am-369455
• 发表时间: 2021
• 期刊: Geological Society of America Abstracts with Programs
• 作者: Mulcahy, Sean;Schermer, Elizabeth;Singleton, Kalieh
• 通讯作者: Singleton, Kalieh

SUBDUCTION COMPLEX ROCKS IN NW WASHINGTON: LINKING THE SUBDUCTION RECORD TO JURASSIC-CRETACEOUS OROGENIC EVENTS

华盛顿西北部的俯冲杂岩：将俯冲记录与侏罗纪-白垩纪造山事件联系起来

• DOI: 10.1130/abs/2022cd-373949
• 发表时间: 2022
• 期刊: Geological Society of America Abstracts with Programs
• 作者: Schermer, Elizabeth;Mulcahy, Sean;Cordova, Jeremy;Lang, Katherine E.
• 通讯作者: Lang, Katherine E.

Evidence and timing for multiple cooling mechanisms in a long-lived subduction zone from the Easton metamorphic suite in the northwest Cascades

西北喀斯喀特伊斯顿变质岩套中长寿俯冲带多种冷却机制的证据和时间

• 发表时间: 2023
• 期刊: Geological Society of America Abstracts with Programs
• 作者: Mulcahy, S.R.;Schermer, E.L.;Cordova, J.;Gates, E.
• 通讯作者: Gates, E.

Structural evolution of subduction initiation and early cooling: insights from the Easton metamorphic suite, northwest Washington

俯冲起始和早期冷却的结构演化：来自华盛顿西北部伊斯顿变质岩套的见解

• 发表时间: 2023
• 期刊: Geological Society of America Abstracts with Programs
• 作者: Cunetta, N.;Schermer, E.L.;and Mulcahy, S.R.
• 通讯作者: and Mulcahy, S.R.