COLLABORATIVE RESEARCH: STRAIN LOCALIZATION, SHEAR ZONE CONNECTIVITY, AND MAGMA-DEFORMATION INTERACTIONS BY DEPTH WITHIN A 65 KM THICKTRANSPRESSIONAL CONTINENTAL ARC

It is poorly understood how deformation becomes localized into high-strain shear zones and how deformation is achieved and sustained deep within the roots of continental arcs during episodes of shortening, magmatism, metamorphism, and anatexis. This problem is important to investigate, not only for determining how different weakening mechanisms contribute to strain localization within the lithosphere, but also for understanding how arc magmatism and deformation interact to form and modify continental crust. A secondary problem is that there is strong disagreement over how competing weakening mechanisms promote and maintain strain localization in arcs as magmas crystallize, melts are mobilized, and thermal conditions change. To solve these problems, co-PIs Miranda (CSUN) and Klepeis (University of Vermont) propose a coordinated field and microstructural study of strain localization processes, deformation mechanisms, and shear zone connectivity within the lower crust of a Cordilleran arc located in Fiordland, New Zealand. In Fiordland, a magmatic flare-up at ~118-115 Ma produced a deep crustal batholith in the lower crust, where the batholith is both enveloped and transected by a number of high-strain shear zones. The batholith and its shear zones are the target of our planned study. Key objectives of our work include: 1) determining how high-strain zones connect laterally and vertically within a compositionally and rheologically stratified lower arc crust, 2) evaluating how temporal and spatial variations in melt supply and other factors influence shear zone development in lower arc crust, 3) determining how lower crustal heterogeneities influence shear zone initiation, and 4) identifying the deformation mechanisms and weakening processes that lead to strain localization. We propose a 3-year study in which we use field observations and microstructural, electron backscatter diffraction (EBSD), geochronologic and thermochronologic analyses to address our objectives and investigate the process of shear zone development within a Cordilleran arc. This work will support 3 CSUN and 3 Univ. Vermont MS students, and 3 CSUN undergraduates. As part of the broader impacts of our proposed work, we propose an innovative summer workshop at CSUN for underrepresented undergraduate geology students from southern California universities. In the workshop, we will provide a hands-on, guided research experience emphasizing the collection and processing of EBSD data as a way of sparking student interest in research and grad school, creating a pipeline for recruitment to CSUN and Univ. of Vermont.