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

蛇绿岩是侵位到大陆上的洋壳和上地幔的碎片。蛇绿岩的形成是板块构造的基本组成部分，可能与新俯冲带的形成有关。最近高精度U-Pb测年的应用提高了我们对世界上最大和研究得最好的蛇绿岩--塞梅尔蛇绿岩（阿曼-阿拉伯联合酋长国）的形成和侵位的认识。该项目将扩大最近的工作，对蛇绿岩下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。研究结果将解决长期存在的关于蛇颈龙起源的争论，并为蛇颈龙如何用于理解现代洋中脊、俯冲带以及潜在的俯冲开始提供新的见解，这是一个关键但知之甚少的构造过程。该研究将通过地球科学研究生培训，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促进预期的社会成果。一个薄的角闪岩-麻粒岩相变质岩的底部位于塞梅尔和其他特提斯蛇绿岩之下。作为俯冲板块的残留物，单一出露可以用来更好地理解蛇绿岩的形成和仰冲作用。最近的数据从两个大曝光的变质鞋底下面的塞梅尔蛇绿岩产生了令人惊讶的结果，表明，最早的唯一的变质作用是同步或早于蛇绿岩地壳的形成，变质作用是穿时的沿着蛇绿岩的长度，跨越1.3马，与目前的模式。这些数据，结合现有的地球化学约束和估计的变质压力从唯一的，最好的解释形成的蛇绿岩在超俯冲带设置，与变质作用的唯一的岩石发生在俯冲板。为了更好地了解这些结果对蛇绿岩起源的影响，项目科学家将在整个塞梅尔蛇绿岩的变质鞋底暴露处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会聚边缘的俯冲和折返过程提供变革性的见解。

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.