Formation of the metamorphic sole of the Semail ophiolite: High-precision U-Pb dating of the preserved remnants of a subducted slab

Semail 蛇绿岩变质底的形成：俯冲板片保存遗迹的高精度 U-Pb 测年

• 批准号: 1650407
• 负责人: Matthew Rioux
• 金额: $ 23.11万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-04-15 至 2022-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1650407&HistoricalAwards=false
• 关键词: Formation; metamorphic; sole; Semail; ophiolite

Ophiolites are pieces of oceanic crust and upper mantle that have been emplaced onto the continents. The formation of ophiolites is a fundamental component of plate tectonics, potentially related to the initiation of new subduction zones. Recent application of high-precision U-Pb dating has advanced our understanding of the formation and emplacement of the Semail (Oman-United Arab Emirates) ophiolite, the largest and best studied ophiolite in the world. This project will expand on the recent work, undertaking detailed high-precision dating of metamorphic rocks persevered below the ophiolite, which likely formed at depths greater than 35 km within a subduction zone. The results will address long-standing debates regarding the origin of ophiolites, and provide new insight into how ophiolites can be used to understand modern mid-ocean ridges, subduction zones, and potentially the initiation of subduction, a critical but poorly understood tectonic process. The research will advance desired societal outcomes by graduate student training in the earth sciences, involvement of Omani students, public outreach, and fostering collaborations between scientists from the United States, the United Kingdom, Oman, and the United Arab Emirates.A thin sole of amphibolite- to granulite-facies metamorphic rocks underlies the Semail and other Tethyan ophiolites. As preserved remnants of the underthrust plate, sole exposures can be used to better understand the formation and obduction of ophiolites. Recent data from two large exposures of the metamorphic sole below the Semail ophiolite yielded surprising results, indicating that that the earliest sole metamorphism was synchronous with or pre-dated formation of the ophiolite crust and that metamorphism was diachronous along the length of the ophiolite, spanning 1.3 Ma, contrary to current models. These data, combined with existing geochemical constraints and the estimated metamorphic pressures from the sole, are best explained by formation of the ophiolite in a supra-subduction zone setting, with metamorphism of the sole rocks occurring in a subducted slab. To better understand the implications of these results to the origin of ophiolites, the project scientists will carry out high-precision isotope dilution-thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon dating at exposures of the metamorphic sole throughout the Semail ophiolite. The new dataset from the sole of the ophiolite has the potential to provide transformative insight into the formation and emplacement of ophiolites, and to processes of subduction and exhumation at convergent margins.

蛇绿岩是已经沉积到大陆上的洋壳和上地幔碎片。蛇绿岩的形成是板块构造的基本组成部分，可能与新俯冲带的启动有关。最近高精度 U-Pb 测年的应用加深了我们对 Semail（阿曼-阿拉伯联合酋长国）蛇绿岩（世界上最大且研究最深入的蛇绿岩）形成和就位的了解。该项目将扩展最近的工作，对蛇绿岩下方持续存在的变质岩进行详细的高精度测年，蛇绿岩可能形成于俯冲带内超过 35 公里的深度。研究结果将解决有关蛇绿岩起源的长期争论，并为如何利用蛇绿岩来了解现代大洋中脊、俯冲带以及潜在的俯冲起始（一个关键但知之甚少的构造过程）提供新的见解。该研究将通过地球科学方面的研究生培训、阿曼学生的参与、公众宣传以及促进来自美国、英国、阿曼和阿拉伯联合酋长国的科学家之间的合作来推进预期的社会成果。角闪岩到麻粒岩相变质岩位于 Semail 和其他特提斯蛇绿岩之下。作为逆冲板块保存下来的残余物，唯一的暴露可用于更好地了解蛇绿岩的形成和仰冲。最近，来自 Semail 蛇绿岩下方变质底部的两次大型暴露的数据产生了令人惊讶的结果，表明最早的唯一变质作用与蛇绿岩地壳的形成同步或早于蛇绿岩地壳的形成，并且变质作用沿着蛇绿岩的长度是历时的，跨越1.3 Ma，与当前模型相反。这些数据，结合现有的地球化学限制和估计的底部变质压力，可以最好地解释为在超俯冲带环境中形成蛇绿岩，并且底部岩石的变质作用发生在俯冲板片中。为了更好地了解这些结果对蛇绿岩起源的影响，该项目科学家将对整个 Semail 蛇绿岩变质底的暴露部位进行高精度同位素稀释热电离质谱 (ID-TIMS) U-Pb 锆石定年。来自蛇绿岩底部的新数据集有可能为蛇绿岩的形成和就位以及汇聚边缘的俯冲和折返过程提供变革性的见解。

项目成果

The Origin of Felsic Intrusions Within the Mantle Section of the Samail Ophiolite: Geochemical Evidence for Three Distinct Mixing and Fractionation Trends

• DOI: 10.1029/2020jb020760
• 发表时间: 2021-03
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: M. Rioux;M. Benoit;I. Amri;G. Ceuleneer;J. Garber;M. Searle;Kayla Leal

One line on the map: A review of the geological history of the Semail Thrust, Oman-UAE mountains

• DOI: 10.1016/j.jsg.2022.104594
• 发表时间: 2022-05
• 期刊: Journal of Structural Geology
• 影响因子: 3.1
• 作者: M. Searle;M. Rioux;J. Garber

Petrochronology of Wadi Tayin Metamorphic Sole Metasediment, With Implications for the Thermal and Tectonic Evolution of the Samail Ophiolite (Oman/UAE)

• DOI: 10.1029/2020tc006135
• 发表时间: 2020-12-01
• 期刊: TECTONICS
• 影响因子: 4.2
• 作者: Garber, Joshua M.;Rioux, Matthew;Searle, Michael P.
• 通讯作者: Searle, Michael P.

High‐Precision U‐Pb Zircon Dating of Late Magmatism in the Samail Ophiolite: A Record of Subduction Initiation

萨迈伊蛇绿岩晚期岩浆活动的高精密 U-Pb 锆石定年：俯冲起始记录

• DOI: 10.1029/2020jb020758
• 发表时间: 2021
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Rioux, Matthew;Garber, Joshua M.;Searle, Michael;Kelemen, Peter;Miyashita, Sumio;Adachi, Yoshiko;Bowring, Samuel
• 通讯作者: Bowring, Samuel

Dating Continental Subduction Beneath the Samail Ophiolite: Garnet, Zircon, and Rutile Petrochronology of the As Sifah Eclogites, NE Oman

萨梅尔蛇绿岩下方大陆俯冲年代测定：阿曼东北部 As Sifah 榴辉岩的石榴石、锆石和金红石岩石年代学

• DOI: 10.1029/2021jb022715
• 发表时间: 2021
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Garber, Joshua M.;Rioux, Matthew;Searle, Michael P.;Kylander‐Clark, Andrew R.;Hacker, Bradley R.;Vervoort, Jeff D.;Warren, Clare J.;Smye, Andrew J.
• 通讯作者: Smye, Andrew J.