Development of the Himalayan Superstructure, Northwestern India

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This research seeks to determine the structural evolution of the Himalayan superstructure from the India-Asia suture zone to the deformed foreland. The term 'superstructure' refers to the low-grade upper level of an orogenic system, and contrasts with high-grade 'infrastructure' below. Along most of the Himalayan arc, superstructure rocks are only partially preserved. They occur in the north, but high-grade crystalline rocks occupy a central swath and recently accreted material dominates exposures farther south. However, across the eastern Ladakh - Chamba region of the northwestern Indian Himalaya, superstructure rocks are continuously exposed from the suture zone to the foreland fold-thrust belt. The deformation record preserved in these rocks can be used to address two problems: (1) long-standing controversy over the mechanism that emplaced infrastructure rocks between superstructure rocks and accreted materials, and (2) recent recognition that the Himalayan rock record may preserve far less shortening than that required by plate circuit reconstructions. These issues will be addressed by a research program combining mapping, analytical work, and reconstruction. Surface and remote sensing geological mapping using ASTER data will establish the geological framework across the eastern Ladakh - Chamba superstructure. These results will be complemented by kinematic analysis obtained via microstructural studies and thermal history determined via 40Ar/39Ar geo/thermochronology. New and existing structural, thermal, and chronological data will be integrated via balanced palinspastic reconstruction to explore deformation modes and determine shortening estimates, thereby providing a deformation history capable of testing extrusion models and a revised geological shortening budget to test shortening models. Preliminary analysis suggests that this work may add nearly 500 kilometers to the Himalayan shortening budget, which would represent a greater than 50% increase in preserved geological shortening.Mountain-building processes are commonly explored across systems with ongoing contraction such as the Alps, Andes, and Himalaya. These mountain belts offer good preservation, direct constraints on boundary conditions, and the opportunity to simultaneously interrogate ancient and active deformation. The community of tectonics workers is still working out the regional geometry and kinematics of many parts of these systems, particularly along-strike structural variations. The incompleteness of our first-order knowledge of the Himalaya is highlighted by recent studies of the Himalaya that propose a variety of radical revisions to our understanding of initial India-Asia collision and the emplacement of its high-grade crystalline core. The current project will help address both issues by utilizing an under-explored aspect of the range: the local preservation of a wide span of its lower grade carapace rocks in the western Himalaya. By exploring the deformation history of these rocks, this study is anticipated to provide strong limits on Himalayan kinematic models. Broader impacts of this work include training of a Ph.D. student from an underrepresented group, as well as providing research experience for as many as six undergraduate students. The research team will continue outreach activities to communicate tectonics to broad audiences locally, and internationally through creation of Wikipedia pages.