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

俯冲带发生在两个构造板块汇合的地方，其中一个板块被推入地幔，是地球上许多重要过程的发生地，包括地球上一些最致命的地震和火山链的产生。在俯冲板块与地幔之间的界面处，发生了大量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掘出来的岩石至关重要。拟议的工作将通过确定这些被挖掘出的岩石在俯冲带本身所经历的温度和压力历史来限制物质在俯冲带内的移动。在这项工作中，主要研究人员将分析来自南加州卡塔利娜片岩这一典型俯冲位置的岩石中矿物金红石和钛矿的化学成分。然后，他们将把记录的历史与不同模型预测的俯冲带内物质行为的历史进行比较。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的教育，有助于扩大科学领域代表性不足的群体，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科学方法和分析标准的直接交流。从这个项目获得的成果正在通过研究出版物和报告向科学界传播，数据正在适当的社区数据库中存档。本项目将利用热气压学和地质年代学的新进展，以加利福尼亚圣卡塔利娜岛的卡塔利娜片岩的暴露为例，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对构造模型进行严格测试。拟议的研究解决了广泛的地球动力学问题，例如，在多大程度上，俯冲通道内的流动在时间上发生了变化，并影响了俯冲热演化？此外，主要研究人员将继续开发岩石学和年代学工具，以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)在混杂岩基质逐渐变质过程中，混杂岩流的规模是多少？(2)哪些构造过程产生了独特的高温俯冲相关岩石？人们普遍提出了许多不同的模型。将收集四组基本数据：(1)样本将在一个绘制良好的混杂区域和三个关键样带上收集。(2)电子探针分析将提供压力-时间估计，并确定特定的钛矿和金红石颗粒和痕量元素分析域。(3)亚晶粒尺度（50-100微米）激光烧蚀电感耦合质谱法（LA-ICPMS）将分别限制温度和时间。(4)包裹体拉曼光谱对压力-温度进行路径的包裹压力有一定的约束。所得数据将用于通过描述混合带内的压力-温度-时间均匀性程度（混合规模）和跨构造的压力-温度-时间趋势来测试构造模型。所有的数据都将被永久的保存在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.