Erosion in northwest Tibet from in-situ-produced cosmogenic ¹⁰Be and ²⁶Al in bedrock

【作者】 孔屏； David Fink；

【Author】 Ping Kong,~(1,2,*) Chunguang Na,~1 David Fink,~3 Lin Ding~2 and Feixin Huang~2 1 State Key Laboratory of Lithosphere Tectonic Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,PO Box 9825, Beijing 100029,China 2 Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing 100029,China 3 ANSTO-Environment,Australian Nuclear Science and Technology Organisation,Menai,NSW 2234,Australia

【机构】 State Key Laboratory of Lithosphere Tectonic Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences； Institute of Tibetan Plateau Research,Chinese Academy of Sciences； ANSTO-Environment,Australian Nuclear Science and Technology Organisation,Menai,NSW 2234,Australia；

【摘要】 <正>Concentrations of in-situ-produced cosmogenic nuclides ¹⁰Be and ²⁶Al in quartz were measured by accelerator mass spectrometry for bedrock basalts and sandstones located in northwest Tibet The effective exposure ages range between 23 and 134 ka(¹⁰Be) and erosion rates between 4-0 and 24 mm ka^-1.The erosion rates are significantly higher than those in similarly arid Antarctica and Australia,ranging between 0-1 and 1 mm ka^-1,suggesting that precipitation is not the major control of erosion of landforms.Comparison of erosion rates in arid regions with contrasting tectonic activities suggests that tectonic activity plays a more important role in controlling long-term erosion rates.The obtained erosion rates are,however, significantly lower than the denudation rate of 3000-6000 mm ka^-1 beginning at c.5- 3 Ma in the nearby Godwin Austen（K2） determined by apatite fission-track thermochronology. It appears that the difference in erosion rates within different time intervals is indicative of increased tectonic activity at c.5-3 Ma in northwest Tibet.We explain the low erosion rates determined in this study as reflecting reduced tectonic activity in the last million years.A model of localized thinning of the mantle beneath northwest Tibet may account for the sudden increased tectonic activity at c.5-3 Ma and the later decrease.Copyright ? 2006 John Wiley & Sons,Ltd.更多还原

【Abstract】 Concentrations of in-situ-produced cosmogenic nuclides ¹⁰Be and ²⁶Al in quartz were measured by accelerator mass spectrometry for bedrock basalts and sandstones located in northwest Tibet The effective exposure ages range between 23 and 134 ka(¹⁰Be) and erosion rates between 4-0 and 24 mm ka^-1.The erosion rates are significantly higher than those in similarly arid Antarctica and Australia,ranging between 0-1 and 1 mm ka^-1,suggesting that precipitation is not the major control of erosion of landforms.Comparison of erosion rates in arid regions with contrasting tectonic activities suggests that tectonic activity plays a more important role in controlling long-term erosion rates.The obtained erosion rates are,however, significantly lower than the denudation rate of 3000-6000 mm ka^-1 beginning at c.5- 3 Ma in the nearby Godwin Austen（K2） determined by apatite fission-track thermochronology. It appears that the difference in erosion rates within different time intervals is indicative of increased tectonic activity at c.5-3 Ma in northwest Tibet.We explain the low erosion rates determined in this study as reflecting reduced tectonic activity in the last million years.A model of localized thinning of the mantle beneath northwest Tibet may account for the sudden increased tectonic activity at c.5-3 Ma and the later decrease.Copyright ? 2006 John Wiley & Sons,Ltd.更多还原