Collaborative Research: Deciphering Subduction Dynamics: Case Study of the Catalina Schist

俯冲带发生在两个构造板块会聚的地方，其中一个板块被推入地幔，是地球上许多重要过程的所在地，包括地球上一些最致命的地震和火山链的产生。在俯冲板块与地幔的界面处，发生了显著的热传递和物理化学交换。为了更好地了解地壳和地幔物质如何在俯冲带内移动和相互作用，研究从这一过程中挖出的岩石至关重要。拟议中的工作将通过确定这些挖出的岩石在俯冲带本身经历的温度和压力历史来限制物质如何在俯冲带内移动。在这项工作中，主要的研究人员将分析岩石中金红石和钛铁矿的化学成分，这些岩石来自一个典型的俯冲地区，即加州南部的卡塔利纳片岩。然后，他们将把记录的历史与俯冲带内物质行为的不同模型预测的历史进行比较。除了该项目的科学目标外，该奖项还支持STEM学科的研究生和本科生教育，有助于扩大科学中代表性不足的群体，以及矿物学和岩石学本科课程的发展。该项目正在促进参与这项工作的伙伴机构之间的新合作，并促进微量元素/地质年代学实验室之间直接交流科学方法和分析标准。该项目的成果正通过研究出版物和演示文稿向科学界传播，数据正在适当的社区数据库中存档。该项目将利用温压法和地质年代学的新发展，以加州圣卡塔利纳岛上的卡塔利纳片岩为典型实例，更好地了解俯冲带构造。这项工作将提供新的、高精度的压力-温度-时间（P-T-t）约束，以前所未有的地理范围和精度严格测试构造模型。拟议的研究解决广泛的地球动力学问题，例如，在何种程度上流在俯冲通道的时间变化和影响俯冲热演化？此外，主要研究人员将继续开发岩石学和年代学工具，广泛推进其他领域的岩石成因研究。本研究将解决俯冲带构造演化中的两个主要问题：（1）混杂岩基质渐进变质过程中混杂岩流动的规模如何？(2)什么构造过程产生了独特的高温俯冲相关岩石？已经普遍提出了许多不同的模型。将收集四组基本数据：（1）将在一个已绘制好地图的混杂岩区和沿着三个关键断面收集样本。(2)电子探针分析将提供压力-时间估计，并确定特定的钛铁矿和金红石颗粒和微量元素分析领域。(3)亚晶粒尺度（50-100微米点）上的激光烧蚀电感耦合质谱（LA-ICPMS）将分别限制温度和时间。(4)矿物包裹体的拉曼光谱将限制包埋压力在包埋压力-温度路径上，由此产生的数据将用于测试构造模型，通过表征混杂带内的压力-温度-时间均匀性（混合尺度）程度和整个结构的压力-温度-时间趋势。所有数据将永久存档在MetPetDB中。

Subduction zones, which occur where two tectonic plates converge and one plate is thrust down into Earth's mantle, are the location of many important processes on Earth, including the generation of some of Earth's deadliest earthquakes and chains of volcanoes. At the interface between the subducting plate and the mantle significant heat transfer and physical and chemical exchange occur. To better understand how crustal and mantle materials move and interact within subduction zones, it is critically important to study rocks exhumed from this process. The proposed work will constrain how material moves within subduction zones by determining the temperature and pressure histories that these exhumed rocks experienced while in the subduction zone itself. For this work the principle investigators will analyze the chemical composition of the minerals rutile and titanite in rocks from a classic subduction locality, the Catalina Schist of southern California. They will then compare the recorded histories with histories predicted by different models for material behavior within subduction zones. In addition to the scientific goals of the project, this award is supporting the eduction of graduate and undergraduate students in an STEM discipline, is contributing to broadening of underrepresented groups in science, and the development of undergraduate course curricula in mineralogy and petrology. The project is facilitating a new collaboration between the partnering institutions involved in this effort, and is contributing direct exchange of scientific methods and analytical standards between trace element/geochronology laboratories. The results that derive from this project are being disseminated to the scientific community through research publications and presentations, and the data are being archived in appropriate community databases. This project will exploit new developments in thermobarometry and geochronology to better understand subduction zone tectonics, using exposures of Catalina Schist on Santa Catalina Island, California, as a type example. The work will provide new, high-precision Pressure-Temperature-time (P-T-t) constraints that critically test tectonic models with unprecedented geographic scope and precision. The proposed research addresses broad geodynamic questions, e.g. to what degree does flow in the subduction channel change temporally and affect subduction thermal evolution? In addition, the principle investigators will continue to develop petrologic and chronologic tools that broadly advance petrogenetic research in other fields. This research will address two main issues in the tectonic evolution of subduction zones: (1) What is the scale of melange flow as melange matrix progressively metamorphoses? (2) What tectonic processes produced distinctive high-Temperature subduction-related rocks? Numerous different models have been generally proposed. Four basic sets of data will be collected: (1) Samples will be collected over a well-mapped area of melange and along three key transects. (2) Electron microprobe analysis will provide Pressure-Time estimates and identify specific titanite and rutile grains and domains for trace element analysis. (3) Laser-ablation Inductively-coupled-mass spectrometry (LA-ICPMS) on a sub-grain scale (50-100 micron spots) will constrain temperature and time, respectively. (4) Raman spectroscopy of mineral inclusions will constrain entrapment pressures on the prograde Pressure-Temperature path. The resulting data will be used to test tectonic models by characterizing the degree of Pressure-Temperature-time homogeneity (scale of mixing) within a melange zone and Pressure-Temperature-time trends across structure. All data will be permanently archived with MetPetDB.