Western Tibet: Low-temperature thermochronology data and interpretation on exhumation history.
Abstract
The Tibetan plateau is the highest and largest orogenic plateau in the world. Uplift of the plateau is related to the India-Asia collision. However, recent studies [1] suggest that peneplanation predates collision. This implies that a low-relief, low-elevation surface could have existed prior to the uplift and have therefore gained elevation following the India-Asia collision. Some models of long timescale, regional topographic evolution have been mostly based on low-temperature thermochronometry, but so far most data have been obtained in Central and Southern Tibet, where " plateau " conditions, (i.e. low exhumation rates), seem to have been reached prior to the collision [1,2]. Our study focuses on Western Tibet, where the landscape is internally drained and characterized by high local relief on the order of 2 km. We performed (U-Th)/He dating on 21 granitic samples collected in Western Tibet, between the Karakoram fault and the Pangong Co. Apatite (U-Th)/He ages from a vertical transect in the Rutog granite vary between 13.11 +/- 0.14 and 29.25 +/- 0.31 Ma and reveal a clear ages-elevation correlation. Based on the crystallization age of the sampled granite (74.4 +/- 1.9 Ma, U/Pb on zircons), apatite ages are not related to post-intrusion cooling but rather record exhumation or relief evolution. Mean apparent exhumation rate is ~67 m/Ma, which is significatively higher than rates estimated in central Tibet [1,2]. Western Tibet, as Central Tibet, is currently a cold, arid environment with low rates of river incision; modern exhumation rates are presumably similar to Central Tibet and extremely low (< 0.003 mm/a) [3]. Apparent exhumation rates are at least one-order-of-magnitude greater than modern exhumation rates; this suggests that exhumation slowed down after 13 Ma. A possible hypothesis to explain the cooling age difference between Central and Western Tibet is that internal drainage, responsible for low exhumation rates, was established later in Western Tibet. This area could have had a hydrographic net connected to the sea, and was later modified, probably due to normal motion on the Karakoram fault. Further resarch will involve zircons (U-Th)/He and apatite 4He/3He thermochronometry to constrain older and recent evolution. We will discuss these results and their implications. [1] Hetzel R., Dunkl I., Haider V., Strobl M., von Eynatten H., Ding L., and Frei F.(2011) Peneplain formation in southern Tibet predates the India-Asia collision and plateau uplift, Geology 39, pp. 983-986. [2]. Rohrmann A., Kapp P., Carrapa B., Reiners P., Guynn J., Ding L. and Heizler M. (2012) Thermochronologic evidence for plateau formation in central Tibet by 45 Ma, Geology 40, pp. 187-190. [3]. Lal D., Harris N., Sharma K., Gu Z., Ding L., Liu T., Dong W., Caffee M. and Jull A. (2003) Erosion history of the Tibetan Plateau since the last interglacial: constraints from the first studies of cosmogenic 10Be from Tibetan bedrock, Earth and Planetary Sci. Lett. 217, pp. 33-42.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.T34A..06G
- Keywords:
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- 1140 GEOCHRONOLOGY Thermochronology;
- 8175 TECTONOPHYSICS Tectonics and landscape evolution