Spatio-temporal variation in rock exhumation linked to large-scale shear zones in the southeastern Tibetan Plateau

Abstract

Crustal-scale shear zones are believed to have played an important role in the tectonic and landscape evolution of orogens. However, the variation of long-term rock exhumation between the interior of shear zones and adjacent regions has not been documented in detail. In this study, we obtained new zircon U-Pb, biotite 40Ar/39Ar, zircon and apatite (U-Th)/He data, and conducted inverse thermal history modeling from two age-elevation profiles (the Pianma and Tu’er profiles) in the southeastern Tibetan Plateau. Our goal is to constrain the exhumation history of the Gaoligong and Chongshan shear zones and adjacent regions, so as to explore the effect of the shear zones on exhumation and their thermal effect on cooling that should not be ignored. Our results suggest that during the interval of 18–11 Ma the exhumation rates of rocks within the Gaoligong shear zone are anomalously high compared with those outside of. The rapid cooling during 18–11 Ma appears to be restricted to the shear zone, likely due to localized thermal effects of shearing and exhumation. After 11 Ma, both the areas within and outside of the shear zones experienced a similar two-stage exhumation history: slower cooling until the early Pliocene, and then a rapid increase in cooling rate since the early Pliocene. Our results indicate a synchronized exhumation but with spatially varied exhumation rates. Our study also highlights the important role of large-scale shear zones in exposing rocks, and thus the importance of the structural context when interpreting thermochronological data in the southeastern margin of the Tibetan Plateau.