Early Cretaceous to present latitude of the central proto-Tibetan Plateau: A paleomagnetic synthesis with implications for Cenozoic tectonics, paleogeography, and climate of Asia

Abstract

Published paleomagnetic data from well-dated sedimentary rocks and lavas from the Lhasa terrane have been reevaluated in a statistically consistent framework to assess the latitude history of southern Tibet from ca. 110 Ma to the present. The resulting apparent polar wander path shows that the margin of the Lhasa terrane has remained at lat ∼20° ± 4°N from ca. 110 to at least 50 Ma and has drifted northward to its present latitude of 29°N since the early Eocene. This latitude history provides a paleomagnetically determined collision age between the Tibetan Himalaya and the southern margin of Asia that is ca. 49.5 ± 4.5 Ma, if not a few millions of years earlier after considering reasonable estimates for shortening within the suture zone. This collision occurred at lat ∼21° ± 4°N, or perhaps ∼2° lower if an average-size forearc is considered. These paleomagnetic data indicate 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 and thickening within Asia calculated from structural geologic studies. Thus, a substantial amount of the shortening within, and therefore surface uplift of, the Tibetan Plateau predates the Tibetan Himalaya-Lhasa collision. These conclusions suggest that the Tibetan Plateau is similar to the Altiplano of the Andes, in that most of the plateau developed at subtropical latitudes above an oceanic subduction zone in the absence of a continent-continent collision. A direct implication of these findings is that 1700 ± 560 km or more post-50 Ma India-Asia convergence was partitioned into the lower plate of the orogenic system (i.e., units of Indian affinity). Recent paleomagnetic and plate tectonic analyses suggested significant extension of Greater India lithosphere after breakup from Gondwana but prior to collision with the southern margin of Asia. Cretaceous extension within Greater India was inferred to open an oceanic Greater India Basin, which would have maintained a deep tropical water mass along the southern edge of greater Asia throughout most of the Paleogene. We suggest ways in which future climate models can incorporate this paleogeography to more accurately explore how Paleogene atmospheric processes interact with or are modified by the juxtaposition of a tropical ocean basin and the high uniform topography of the Tibetan Plateau.