CARBONATE CLUMPED ISOTOPE EVIDENCE FOR PALEOELEVATIONS AND TECTONICS IN CENTRAL TIBET

To better understand the topographic growth and tectonic history of the Central Tibetan Plateau, we obtained more than 50 clumped isotope temperatures of lacustrine carbonates from the Lunpola, Nima, and Gerze basins, using a new rapid and precise system of tunable infrared laser differential absorption spectrometer (TILDAS). In the Lunpola Basin, a >10 °C temperature decrease is observed between the middle Niubao Member (~40–36 Ma) and the Dingqinghu Formation (~20–17 Ma), which is consistent with more than 1 km surface uplift during the Oligocene and/or early Miocene after consideration of global temperature change. In the Nima Basin, the clumped isotope temperatures of late Oligocene (~25 Ma) lacustrine micrites are 48–65 °C, higher than plausible Earth’s surface temperatures; in addition, the diagenetic vein calcites show much higher temperatures of 132–141 °C. In the Gerze Basin, late Eocene (~38–36 Ma) lacustrine micrites also show higher temperatures of 42–54 °C, while the diagenetic vein calcites show lower temperatures of 20–30 °C, indicating at least two stages of diagenesis. To explore whether solid-state reordering and/or open(closed) system cryptic-recrystallization could explain the higher clumped isotope temperatures (42–65 °C) of the lacustrine micrites, additional work, including carbonate U-Pb dating, scanning microscope analysis, and modeling of solid-state reordering are underway. The resolution of this issue is important as differential preservation of the primary stable isotopic values will have different implications for previous stable isotope-based paleoaltimetry results in this region.