Strong tectonic and weak climatic control on exhumation rates in the 1
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چکیده
16 17 We have studied the relationships between present day relief, precipitation, stream power, 18 seismic energy, seismic strain rate and long-term exhumation rates for the Venezuelan Andes. 19 Average long-term exhumation rates were determined for seven large catchments in the 20 Venezuelan Andes from fission-track analysis of detrital apatite. A quantitative comparison 21 between eight new detrital apatite fission-track (AFT) age distributions presented here and 22 previously published bedrock AFT age patterns shows that detrital AFT ages can be used for 23 predicting exhumation patterns across the mountain belt. Catchment-averaged exhumation 24 rates estimated from the raw data range from 0.48±0.02 to 0.80±0.26 km Myr-1. Accounting 25 for variable sediment yield and assuming that short-term sediment production rates scale with 26 long-term exhumation rates, these rates vary from 0.33±0.07 to 0.48±0.08 km Myr-1. No 27 variation in rates is observed between the northwestern and southeastern flanks of the 28 mountain belt, despite a threefold increase in precipitation from the northwest to the 29 southeast. Long-term exhumation rates are strongly correlated with relief in the different 30 catchments, but no or negative correlations exist with precipitation data or present-day erosion 31 indexes, while the correlation with seismic energy released by earthquakes is weak to 32 moderate. This lack of correlation may be caused by the insufficient temporal range of the 33 available precipitation and seismicity data, and the different time scales involved in the 34 comparison. Long-term exhumation rates are, however, strongly correlated with seismic strain 35 rates (which take the temporal earthquake magnitude-frequency scaling into account), 36 suggesting that the moderate correlation with seismic energy is indeed related to the different 37 timescales and that tectonic control on exhumation is significant. In contrast, given that 38 precipitation patterns in the Venezuelan Andes should have been installed during Miocene 39 3 times, we suggest that decoupling of relief and exhumation from present-day climate explains 40 the lack of correlation between exhumation and precipitation. 41 42
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