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When and where did India-Asia collide and what happened since then? A new synthesis

Event Type: 
Event Date: 
18 August 2017 - 8:00am
EOS Seminar Room - N2-01B-28
Xixi Zhao
About the speaker: 

As a paleomagnetist, Dr. Xixi Zhao interpret fossil magnetizations in rocks and sediments from the continents and oceans. These natural archives hold a record of the geomagnetic field in the geological past, and shed light on the motions of the continents. The paleomagnetic record also reveals the history of numerous reversals of polarity that Earth's magnetic field has undergone throughout geologic time. Dr. Zhao’s research interests have concentrated on paleomagnetic and rock magnetism, and their application to the history of Earth's magnetic field, tectonics, magnetostratigraphy, and geologic problems. His research foci include several tectonic projects both in China and overseas, including basin development, conjugate faulting and rotations, and uplift history of Tibetan plateau, tectonic history of Junggar and Qaidam basins of northwestern China, and tectonics and paleogeographic reconstruction of the Parana Basin of Brazil and Permo-Carboniferous apparent polar wander of South America. Dr. Zhao is currently a Distinguished Researcher at College of Marine and Earth Science, Tongji University and a Recalled-Research Geophysicist at the Center for Studies of Imaging and Dynamics of the Earth (CSIDE), Institute of Geophysics and Planetary Physics (IGPP), UC Santa Cruz.

About the event: 

Two critical questions involving the geodynamic evolution of the Tibetan plateau are (i) how and when India collided with Asia and (ii) when did a compression-dominated tectonic regime change to an extension-dominated tectonic regime on the plateau and how does this timing correlate with double thickening of the crust? In this synthesis, we provide new paleomagnetic evidence for the timing, magnitude, and partitioning of intra-Asian convergence. Our study suggests 1) the age and locus of the initial India-Asia collision are at ~50 Ma and ~24ºN, respectively; 2) Tibet resisted India’s northward push during the first ~16 Ma of initial impact from the collision and experienced little latitudinal displacement; and 3) Sometime a little after 34 Ma, Greater India was consumed and thicker Indian Craton subsequently made contact with Asia, resulting in ~6ºnorthward drift of Asia. Our synthesis results imply a first-order constraint of 900–1100 km north-south shortening concentrated within the interval from 53 to 26 Ma. This suggests that a fundamental change at ~26 Ma occurred in the geodynamics of the Tibetan Plateau marked by a reduction in large-scale convergence and compressive deformation. The implication is that significant regional uplift of the proto-Tibetan Plateau occurred within the ~55–26 Ma interval. The paleolatitude, paleoclimate, and topography of south central Tibet seen at present were likely established around 26 Ma.