Oxygen and clumped isotope evidence for late Paleogene high elevations of the east-central Tibetan Plateau
Abstract
The topographic growth history of the Tibetan Plateau is fundamental to our understanding of geodynamic processes driving surface uplift, and its role in modulating both regional and global climate. Reconstruction of paleoelevations of the central Tibetan Plateau has been a long-standing challenge because stable isotope-based paleoaltimeters such as δ18O and δD are subject to the influence of multiple vapor sources as well as uncertainties in paleotemperature. Therefore, in this study, we use both carbonate clumped isotope geothermometry and modified stable isotope-based paleoaltimetry to reconstruct the Cenozoic paleoelevations of the Nangqian basin in the east-central Tibetan Plateau. Three late Paleogene (37.2-24.0 Ma) lacustrine carbonate samples collected at present-day elevations of 3.8 km yield clumped isotope temperatures between 25.3 and 28.3°C. Because modern warm-season lake surface water temperature on the south-central Tibetan Plateau at the sampling elevation is 17°C, and given a global cooling of 6°C since the latest Eocene, we infer that the Nangqian basin was at an elevation of 3200±400 m during the late Paleogene. By separately considering Rayleigh distillation of the two major moisture sources in the Nangqian region and proportional mixing determined by single particle back trajectory analysis, we reconstruct modern elevation of the study area within errors. This suggests paleoelevation of the Nangqian basin can be estimated if the predominant vapor sources and their relative contributions can be determined. Recent paleoclimate modeling has suggested that the atmospheric circulation patterns on the Tibetan Plateau may have been broadly similar to present during the late Eocene. We use this modified stable isotope-based paleoaltimetry, with clumped isotope geothermometry constrained paleotemperature, to estimate the paleoelevation. Results also show that the Nangqian basin was at 3136 (+520/-390) m during the late Paleogene. Our results that the east-central Tibetan Plateau had obtained high elevation ( 3200 m) during the late Paleogene are consistent with geodynamic models that indicate early-middle Eocene upper crustal shortening, but not late Miocene lower crustal flow, as the dominant driver for surface uplift of the east-central Tibetan Plateau.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.T43A0668L
- Keywords:
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- 3355 Regional modeling;
- ATMOSPHERIC PROCESSES;
- 8110 Continental tectonics: general;
- TECTONOPHYSICS;
- 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS