Paper No. 7-9
Presentation Time: 10:05 AM
LHASA’S JURASSIC-TO-PALEOCENE LATITUDE: IMPLICATIONS FOR THE CENOZOIC TECTONICS AND CLIMATE OF TIBET
Reconstructing the Tibetan Plateau in terms of its surface uplift, its structural position relative to Eurasia and Greater India, and its latitude is a key first-order step in studying feedbacks between continental convergence, crustal thickening, surface uplift, and plate force balances, as well as those between surface elevation, atmospheric dynamics, erosion, and regional and global climate transitions. Tibet’s geography prior to the Greater India-Asia collision is especially important for understanding the extent to which micro-continent accretion and Neotethyan subduction during the Mesozoic pre-conditioned Tibetan lithosphere to develop into the orogenic system we observe today. Here we review paleomagnetic data from lower Jurassic through lower Paleogene rocks of the Lhasa terrane within a coherent analytical framework; this review expands on Lippert et al. (GSA SpP 2014) and Huang et al. (GRL 2015) to incorporate several new data sets. By testing and accounting for processes that bias the primary magnetic signal in rocks, including undersampling of the geomagnetic field in volcanic rocks, inclination shallowing in sedimentary rocks, and insidious remagnetization, we demonstrate that the southern margin of the Lhasa terrane moved rapidly northward from southerly equatorial latitudes in the Early Jurassic to a stable latitude of 20±4°N from at least 120 Ma until 50 Ma. Our analysis indicates that at most, only 1100±560 km of post-50 Ma India-Asia convergence was partitioned into Asian lithosphere. The lower bound of these paleomagnetic estimates is consistent with the magnitude of upper crustal shortening within Asia calculated from structural geologic studies. Collectively, these results indicate that much of the crustal shortening within the high Tibetan Plateau predates the Greater India-Lhasa collision. Thus, the Tibetan Plateau is similar to plateaus within Cordilleran systems of the Americas in that much of the crustal shortening accumulated at subtropical latitudes above an oceanic subduction zone in the absence of a continent-continent collision. The high tropical latitude of the Gangdese Shan and low subtropical latitude of the proto-Tibetan plateau also must be considered in Cenozoic climate and erosion models and when interpreting environmental and elevation proxies from Tibet.