Stable isotopic constraints on the tectonic, topographic, and climatic evolution of the northern margin of the Tibetan Plateau

This study presents oxygen and carbon isotopic records from lacustrine, paleosol, alluvial, and fluvial carbonate sampled in thirteen Cenozoic sedimentary sections that span the northern margin of the Tibetan Plateau. Isotopic analyses of 1475 carbonate samples yield delta O-18 values that range from 13.1 to 38.9 parts per thousand (SMOW), and delta C-13 values range from -11.5 to 3.7 parts per thousand (PDB). Based on these analyses, we see two isotopic trends regionally. We interpret a Paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region's drainages as they tapped waters from a growing Tibetan Plateau to the south of the study area. We interpret a Neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters, which increased basin isolation, aridity, and temperatures. The timing of inferred initiation of uplift in this region is consistent with structural, thermochronological, and sedimentological evidence for a tectonic transition in the early and middle Miocene from accommodation of India-Eurasia convergence through extrusion along the Allyn Tagh fault to accommodation of convergence through active shortening and mountain building in this region. This study also supports tectonic models for the differential uplift of the Tibetan Plateau, in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central Tibetan Plateau. (C) 2009 Elsevier B.V. All rights reserved.