Collaborative Research: Do subduction‐complex metamorphic rocks record the thermal evolution of a subduction zone or periods of anomalous tectonic activity? Baja California

地球板块构造系统的一个基本方面——地球坚硬的外部板块的运动——是俯冲作用：海洋地壳沿着大断层向地球内部下沉。最大的地震，大多数火山灾害，山带的位置，许多重要的金属矿床，大陆本身的存在，以及地球气候在地质时期的平衡，最终都是由俯冲过程控制的。因此，理解俯冲作用是理解地球科学许多方面的关键。然而，研究俯冲很困难，因为它发生在地球表面深处，并且发生了数百万年。这项研究的目的是检查从一个古老的俯冲带带回地球表面的岩石；这些岩石和它们所含的矿物质提供了一个“窗口”来了解发生在俯冲带的化学和物理过程。对这些岩石的详细观察将用于检验关于俯冲带如何运作的竞争性假设。除了实现这一科学目标之外，该项目还通过支持早期职业研究者的研究项目，并通过课堂学习、实地考察、实验室工作和专业会议，为重要STEM学科的本科生、研究生和研究生研究人员提供教育机会、专业发展和指导，从而贡献了重要的社会成果。最后，该项目促进了国际合作，加强了美国和墨西哥学术体系之间的联系。该项目的具体目标是通过使用最先进的热气压计和岩石年代学，量化墨西哥下加利福尼亚半岛中生代俯冲复合体中角闪岩、蓝片岩和榴辉岩的压力-温度-时间历史。之所以选择墨西哥的这个地点进行研究，是因为这些重要的岩石类型的突出暴露，以及独特的地质历史，这些地质历史将深俯冲的岩石带回地球表面进行直接调查。这些变质岩在Vizcaíno半岛（结构上位于约220 Ma Vizcaíno蛇绿岩之下）和Cedros岛（结构上位于约170 Ma Cedros蛇绿岩之下）上以块状和连贯单元的形式出现。项目将评价：(1)俯冲带热结构随时间的演化；(2)变质作用、挖掘和蛇绿岩生成的历史、过程和潜在的构造联系。项目结果将用于检验提出的俯冲开始和随后演化的模型，以及从俯冲带挖掘出的变质岩与区域构造变化之间的关系。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A fundamental aspect of Earth’s plate tectonic system—the movement of Earth’s rigid outer plates—is subduction: the sinking of oceanic crust down into Earth’s interior along large faults. The largest earthquakes, most volcanic hazards, the locations of mountain belts, many critical metal deposits, the existence of the continents themselves, and the balancing of Earth’s climate over geological time are all ultimately controlled by the process of subduction. Understanding subduction is thus key to understanding many aspects of Earth science. However, studying subduction is difficult because it is happening deep below Earth’s surface and occurs over millions of years. The purpose of this study is to examine rocks that have been brought back to Earth’s surface from an ancient subduction zone; these rocks and the minerals they contain provide a “window” into the chemical and physical processes that occur in subduction zones. Detailed observations of these rocks will be used to test competing hypotheses about how subduction zones operate. In addition to this scientific goal, this project contributes to important societal outcomes by supporting the research program of an early career researcher and by providing educational opportunities, professional development, and mentoring for undergraduate students, graduate students, and post-graduate researchers in an important STEM discipline through classroom study, fieldwork, laboratory work, and professional conferences. Finally, this project fosters international collaboration and strengthens ties between the academic systems of the USA and Mexico.The specific goal of this project is to quantify the pressure–temperature–time histories of amphibolite, blueschist, and eclogite from Mesozoic subduction complexes in the Baja California peninsula, Mexico, by using state-of-the-art thermobarometry and petrochronology. This location in Mexico was chosen for the research due to the outstanding exposure of these important rock types and the unique geological history that brought deeply subducted rocks back to the Earth’s surface for direct investigation. These metamorphic rocks occur as blocks in mélange and coherent units on the Vizcaíno peninsula (structurally beneath the c. 220 Ma Vizcaíno ophiolite) and Cedros Island (structurally beneath the c. 170 Ma Cedros ophiolite). The project will evaluate: (1) the evolution of subduction zone thermal structure with time; and (2) the history, processes, and potential tectonic linkages among metamorphism, exhumation, and ophiolite generation. Project results will be used to test proposed models for subduction initiation and subsequent evolution as well as the relationships between exhumation of metamorphic rocks from subduction zones and regional tectonic changes.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.