Some of Earths largest and most intriguing geologic and geographic features, including the Alpine/Himalayan mountain chain, are the result of continental collision. Because continental collision systems are responsible for profound geologic change throughout a large portion of Earth?s history, understanding their complex dynamics is of fundamental importance to Earth Science. Geologic studies based on the rocks and structures preserved in eroded cores of collisional systems provide critical insights into the fundamental processes of mountain building including metamorphism, melting, deformation, and exhumation. Results of this work will help refine our knowledge, not only of individual processes, but also the extent to which they interact to both construct and destruct large mountain chains. Data from this project will form the basis for the development of curricular materials that will be distributed to middle school teachers and a website devoted to highlighting active geoscience projects in the Himalayas. This project will also support mentoring and education of graduate and undergraduate students, and with the help of the NSF Office of International Science and Engineering will initiate a wide-ranging international collaboration on the science.
The Himalaya provide an exceptional opportunity to investigate the evolution of mid-crustal rocks in an active collisional system. Along the collisional front, the major structures that bound these mid-crustal rocks, the Main Central thrust below and South Tibetan detachment above, are offset or reactivated by young metamorphic domes like the Leo Pargil, the focus of this study. Such domes provide an important opportunity to study the generation of partial melt, the potential feedback between partial melt and exhumation, the affects of shear zone nucleation, and the rheology of the crust during dome formation. The high-grade rocks of the Leo Pargil dome have been exhumed during extension and dome formation within an active convergent setting along orogen-parallel thrust faults and low angle detachment faults that were active until the middle Miocene. In collaboration with US and international academic organizations this project will employ a field-and lab-based interdisciplinary investigation to explore the evolution of these rocks using 1) geologic mapping and detailed microstructural analysis, 2) isotope geochronology (U/Pb, Ar/Ar, [U+Th]/He), and 3) determination of metamorphic P-T-t paths. Results from Leo Pargil will be contrasted with that from other domes along the Himalayan front to generate a high-resolution model for the timing and kinematics of orogen-parallel mid-crustal flow and exhumation along the southern margin of the Tibetan plateau since the middle Miocene.
