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

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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.