CAREER: Rheological Evolution of Subduction Interface Shear Zones: Insights From Exhumed Subduction Complexes

University Of Texas At Austin, Austin TX

Investigators

Abstract

Geophysical data from subduction zones worldwide illustrate that subduction interfaces are rheologically complex and heterogeneous. Observations of exhumed remnants of subduction interface shear zones yield fundamental insight into the processes that control this complexity. The scientific objective of this project is to systematically investigate the rheological properties and evolution of the subduction interface using exhumed rocks. Specifically, the project will investigate the heterogeneity of deformation within subduction interface shear zones and the nature of changes in deformational styles and mechanisms as rocks are progressively subducted to depth. The research component of this project will focus on three exhumed subduction shear zones that each record prograde deformation and that together represent a wide range of pressure-temperature conditions. The field sites include the: 1) Chugach accretionary complex, Alaska (T = 150-300 degrees C, P = 2-5 kilobars), 2) the Condrey Mountain Window, southern Klamath Mountains, northern California (T = 300-420 degrees C, P = 5-7 kilobars), and 3) the Cycladic Blueschist Unit in Syros Island, Greece (T = 450-550 degrees C, P = 2-15 kilobars). The project uses a wide range of structural, microstructural, and petrological tools to track macro-scale distributions of strain, degrees and mechanisms of strain localization, fluctuations in fluid pressures and strain rates, microphysical mechanisms of rock creep, effects of metamorphic reactions on deformation, and sources of anisotropy, in rocks that have been cycled through the subduction process. The research involves: 1) identifying domains in each field area that represent deformation under prograde conditions; 2) documenting macro-scale strain distributions; 3) determining the microphysical mechanisms of rock creep in different rock and mineral phases; and 4) synthesizing the field and microstructural observations in the context of subduction zone mechanics. The integrated educational objective of this CAREER award is to establish a five-year mentoring and research program at the University of Texas ? the Jackson School of Geosciences-Catalyst (JSGC) ? aimed at ethnic and racial minorities and first-generation college students in the Earth Sciences. JSGC will provide 1) mentoring, community support, and career advice for undergraduates through mentorship pairing, monthly meetings, social events, and field trips; and 2) financial support for members while simultaneously enhancing their undergraduate research experience through summer internships, senior thesis projects and participation in field-based team research. The JSGC program is designed to increase retention and completion rates of underrepresented minorities in STEM fields and to prepare and encourage these students to go on to graduate school. Processes in the zone between a subducting oceanic plate and the overriding plate ? the subduction zone interface - are responsible for a all-too-familiar yet poorly understood phenomena such as large devastating earthquakes as well as other more enigmatic events such as episodic slip and tremor. This project aims to improve understanding of this zone through a systematic study of terranes that were exhumed from the depths of the interface by various tectonic processes. These terranes provide an unusual opportunity to understand the geologic processes associated with the various phenomena along the subduction zone interface. Additionally, the project will advance desired societal outcomes through: (1) full participation of women and underrepresented minorities in STEM through support of an early career Hispanic female PI, a female graduate student, and, most notably, a robust plan to provide mentoring, and research and professional development opportunities to underrepresented minorities majoring in Earth Science, thus directly contributing to retention and promotion of underrepresented minorities in STEM fields; (2) development of a diverse, globally competitive STEM workforce through undergraduate and graduate student training with emphasis on mentoring students from underrepresented groups in Earth science; and (3) increased partnerships through international collaboration.