Determining the rates and conditions of subduction initiation beneath the Samail Ophiolite

俯冲带是地球表面和深部之间化学交换的主要场所。了解俯冲是如何开始和演化的，对于描述这种交换的性质是很重要的。地质记录包含了以蛇绿岩形式的俯冲起始的丰富档案，蛇绿岩是位于大陆上的洋壳和地幔碎片。这些蛇绿岩通常含有一层薄薄的岩石，被涂抹并焊接到它们的底部（“变质底部”），这些岩石被认为是新形成的俯冲带中俯冲物质的第一次增加，即，当盘子开始下沉的时候该提案旨在描述这些最早的俯冲岩石的热和化学记录，沿着Samail蛇绿岩（阿曼/阿联酋）的基础，以确定在Samail系统开始俯冲的速率和条件。这些数据将根据地球动力学模型进行严格的测试，以了解导致俯冲开始的构造环境和物理参数。这些数据还将用于追踪地表和地球深部之间与俯冲有关的化学交换的最早阶段。该项目由两名早期职业科学家带头;支持两名本科生的教育，技术和专业发展;并资助为公众开发一个关于蛇类的虚拟博物馆展览。该研究预计将确定：i）Samail鞋底中高温变质作用的持续时间，ii）鞋底中的变质条件和质量流路径（P-T-t），和iii）（i）和（ii）沿蛇绿岩长度的沿着变化。分析工作将在以前从Samail变质鞋底收集的石榴石斜长角闪岩上进行。我们将收集石榴石，单斜辉石，钛相微量元素斑点和地图（LA-ICPMS）;定量石榴石和单斜辉石主元素地图（EPMA）;散装岩石的主要和微量元素数据（XRF，ICPMS）;和应变石英和锆石夹杂物在石榴石的拉曼光谱。这些数据将用于传统的单元素（例如，锆在钛铁矿），和弹性热压法来表征P-T路径所经历的每一个研究的样品，以及微量和主要元素配置文件的石榴石和单斜辉石的扩散建模，以约束T-T的历史。这些数据也将被用来测试从不同的地质年代学技术变质时间尺度的数量级差异之间，可能支持长期的“被迫”俯冲启动或短期的“自发”俯冲initiation.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Subduction zones are the primary loci of chemical exchange between the surface and the deep Earth. Understanding how subduction initiates and evolves is important for characterizing the nature of this exchange. The geological record contains a rich archive of subduction initiation in the form of ophiolites, which are pieces of oceanic crust and mantle emplaced on continents. These ophiolites often contain a thin veneer of rocks smeared out and welded to their base (“metamorphic soles”) that are thought to represent the first increments of subducted material in a newly formed subduction zone, i.e., when a plate first begins to sink. This proposal seeks to characterize the thermal and chemical record of these earliest subducted rocks along the base of Samail Ophiolite (Oman/UAE) to determine the rates and conditions at which subduction started in the Samail system. These data will be critically tested against geodynamic models to understand the tectonic settings and physical parameters leading to subduction initiation. The data will also be used to trace the earliest phases of subduction-related chemical exchange between the surface and the deep Earth. The project is spearheaded by two early career scientists; supports the educational, technical, and professional development of two undergraduate students; and funds the development of a virtual museum exhibit about ophiolites for the general public.The research is expected to identify: i) the duration of high-T metamorphism in the Samail sole, ii) metamorphic conditions and mass flow paths (P-T-t) in the sole, and iii) variations in (i) and (ii) along the length of the ophiolite. Analytical work will be performed on garnet amphibolites previously collected from the Samail metamorphic sole. We will collect garnet, clinopyroxene, and Ti-phase trace-element spots and maps (LA-ICPMS); quantitative garnet and clinopyroxene major-element maps (EPMA); bulk-rock major and trace-element data (XRF, ICPMS); and Raman spectra on strained quartz and zircon inclusions in garnet. These data will be used for conventional, single-element (e.g., Zr-in-titanite), and elastic thermobarometry to characterize P-T paths experienced by each of the studied samples, as well as diffusion modelling of trace- and major-element profiles in garnet and clinopyroxene to constrain T-t histories. These data will also be used to test between order-of-magnitude differences in metamorphic timescales from different geochronological techniques, potentially supporting either long-term “forced” subduction initiation or shorter-term “spontaneous” subduction initiation.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.