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

俯冲带是地表和地球深处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。地质记录包含了丰富的俯冲起源档案，蛇绿岩是部署在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，涂在它们的底部(“变质底”)，被认为是新形成的俯冲带中俯冲物质的第一次增量，也就是当一个板块开始下沉时。这项建议旨在描述这些最早俯冲的岩石沿Samail蛇绿岩(阿曼/阿联酋)底部的热和化学记录，以确定Samail系统开始俯冲的速度和条件。这些数据将根据地球动力学模型进行关键测试，以了解导致俯冲开始的构造环境和物理参数。这些数据还将被用来追踪地表和地球深处之间与俯冲相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，并资助开发一个面向公众的蛇绿岩虚拟博物馆展览。研究有望确定：i)Samail鞋底的高温变质作用持续时间，ii)鞋底的变质条件和物质流动路径(P-T-t)，以及iii)(I)和(Ii)沿蛇绿岩长度的变化。将对以前从Samail变质鞋底收集的石榴石角闪岩进行分析工作。我们将收集石榴石、单斜辉石和钛相微量元素斑点和图解(LA-ICPMS)；石榴石和单斜辉石主量元素定量图解(EPMA)；块状岩石主量元素和微量元素数据(XRF、ICPMS)；以及石榴石中应变石英和锆石包裹体的拉曼光谱。这些数据将用于常规、单元素(例如，锆钛铁矿)和弹性温压测量，以表征每个研究样品经历的P-T路径，以及石榴石和单斜辉石中痕量和主要元素剖面的扩散模拟，以约束T-T历史。这些数据还将被用来测试不同地质年代学技术在变质时间尺度上的数量级差异，潜在地支持长期的“强迫”俯冲启动或短期的“自发”俯冲启动。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.