Differential Unroofing Across Southeastern Tibet: Geodynamic Links Between Plateau-Scale Tectonics and Landscape Evolution

Abstract:

Detailed documentation of the exhumation history of southeastern Tibet is important for understanding of the coupling of tectonic and geomorphic processes shaping this landscape. We present K-feldspar ⁴⁰Ar/³⁹Ar multi-diffusion domain model analysis and zircon (U-Th)/He thermochronology along both horizontal and vertical traverses within Gangdese batholith to constrain the spatial and temporal pattern of exhumation in the region. In conjunction with thermokinematic modeling we use these data to interrogate patterns of regional erosion and test mechanical models of plateau evolution such as delamination, lithospheric-scale folding, and rifting. Previously reported zircon and apatite (U-Th)/He data from a vertical transect west of the Nari Yun Chu Rift indicate a prolonged period of exhumation between ~20 Ma and 12 Ma. To the east, K-feldspar modeling of a sample on the Nyang River shows a period of rapid cooling between ~18-15 Ma that is consistent with an extended period of rapid exhumation. However, zircon (U-Th)/He data vary by ~30 Ma across an E-W transect through the region, which indicates that either the period of rapid erosion occurred much earlier in the west than in the east, or erosion was faster in the east, and removed significantly more material. These differences in exhumation between the E and W correlate with a documented increase in the depth of the Moho and general decrease in relief from E to W. These spatial correlations suggest linkages between deep geodynamic processes and the development of mountain topography. Variability in km-scale exhumation despite common mountain summit elevations throughout southeastern Tibet indicates that this region underwent a complex and protracted unroofing history. Additional data and modeling will test whether an erosional front propagated through the region or if pulses of erosion resulted from localized tectonic forcing, such as motion on the Nari Yun Chu Rift.