Collaborative Research: Evaluating the role of terrane accretion on the evolution of indenter corner fault systems, an example from the eastern Himalaya

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

The collision of continental tectonic plates produces some of the highest topography, deepest sedimentary basins, and highest potential for large earthquakes on Earth. To explain how these unique plate boundaries evolve, geologists commonly simulate a collision between a rigid tectonic plate that collides with and indents a weaker tectonic plate. Recent observations from the eastern Himalaya and Alaska instead suggest that indenting plates in nature are not entirely rigid, particularly when they contain pieces of crustal blocks accreted from prior collisions in the geologic past. This implies that active fault systems may also deform (and generate earthquakes) within the indenting plate as well as the indented plate, changing the way geoscientists understand plate boundary faults within continental collision zones. This project will study the complex tectonic setting of the eastern Himalaya, a natural laboratory for testing the hypothesis that prior accreted terranes fundamentally change the active fault systems at the margins of a collision zone. This research will address three Grand Challenges outlined in a 2018 NSF Community Vision Document for Tectonics research and will strengthen international ties between US scientists and researchers at multiple Indian universities and research centers, as well as a local non-governmental organization promoting public scientific literacy. This project will further facilitate knowledge transfer between US and international partners by conducting a formal interlaboratory comparison of analytical methods, co-organizing two workshops for US and Indian undergraduate students, and developing K-12 educational outreach. This project will also support two early career faculty and promote the full participation of two graduate and two undergraduate students who will be recruited through programs designed to broaden participation of traditionally underrepresented groups in the geosciences. Orogenic syntaxes are regions of high crustal strain that accommodate the transition from convergence to strike-slip motion at the margins of an indenting plate collision. For several decades, Tectonics research has focused on strain partitioning within the indented plate of a collision zone, this focus has neglected the important influence of strain partitioning within the indenting plate, and in particular, the role of sliver terrane accretion on the evolution of indenter corner fault intersections. Observations from both the eastern Himalayan and Alaskan orogens suggest that the accretion of sliver terranes along transform faults flanking collision zones can lead to a ‘double collision’ where a once-stable fault intersection changes into an unstable triple junction, altering the kinematics of indenter corner fault systems and the pattern of upper plate deformation. To evaluate the broader influence of terrane accretion on collisional orogenesis, this 3-year project will reconstruct the kinematic history of a triple junction in the eastern Himalayan indenter corner. This project focuses on the kinematic history of the Noa Dihing Fault, a key structure at the center of the eastern Himalaya indenter corner that juxtaposes the Indian-Eurasian collision zone with the subduction zone between Indian and the Burma Terrane, as well as the Burma-Eurasia transform zone. This project will constrain the late Cenozoic kinematic history of the Noa Dihing Fault through a combination of field mapping, zircon U-Pb geochronology, fault kinematic analysis, and thermo-kinematic modeling of apatite fission-track, zircon fission track and 40Ar/40Ar thermochronology in the Noa Dihing Fault hanging wall. Testing this hypothesis that sliver terranes concentrate strain within continental indenter corners will help to explain differences in structural style between indenter corners in the same tectonic setting (e.g. differences in the curvature between the eastern and western Himalayan indenter corners) and also relate similarities between indenter corners in different tectonic settings (e.g. southern Alaska and the eastern Himalaya). This is a new way of thinking about indenter tectonics and could provide a complementary perspective that builds further helps to link research in Alaskan and Himalayan orogens. 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.