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Earth System Processes - Global Meeting (June 24-28, 2001)

Paper No. 0
Presentation Time: 10:40 AM

THE TIME LAG BETWEEN MOUNTAIN BUILDING AND PRECIPITATION-DRIVEN EROSION IN THE EASTERN GREATER CAUCASUS


HOVIUS, Niels, Department of Earth Sciences, Univ of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom, VALDES, Paul, Dept. of Meteorology, Univ of Reading, Earley Gate, Whiteknights, Reading, RG6 6BB, United Kingdom, WEISSEL, Jeffrey, Lamont-Doherty Earth Observatory, Columbia Univ, Route 9W, Palisades, NY 10964, ALLEN, Mark, CASP, West Building, Gravel Hill, Huntingdon Road, Cambridge, CB3 0DJ, United Kingdom and ISMAIL-ZADEH, Arif, Geological Institute, Azerbaijan Academy of Sciences, Baku, Azerbaijan, nhovius@esc.cam.ac.uk

Compressional deformation of the Earth's lithosphere commonly results in the building of mountains because erosion lags behind the onset of rock uplift. This time lag can be observed in the Greater Caucasus. We have documented the gradual increase of orogenic relief and orographic precipitation, and the concomitant transition from 'constructional' to 'erosional' topography that is manifest in the eastern part of the range.

Uplift of the Greater Caucasus is driven by convergence of the Arabian and Eurasian plates, and started at about 5 Ma. Since then, the mountain belt has propagated both eastward and westward from a centre located near its present culmination. Currently, the eastern tip of the Greater Caucasus is located in Azerbaijan, where structure and topography plunge towards the Caspian Sea. There, the Caucasian chain evolves from the wave-beveled top of a folded sequence of Tertiary sediments to a 4 km high, two-sided fold-and-thrust belt, over a distance of 250 km. The easternmost part of the range is extremely arid, with sparse, structurally entrained drainage. Further west, a regular pattern of transverse streams drains the mountain belt, delivering orogenic detritus to the Caspian shelf. The transition from 'constructional' to 'erosional' topography occurs where orogenic relief is about 1.5 km.

We have used a high-resolution digital elevation model and local precipitation records to calculate the distribution of stream power within the eastern Greater Caucasus. In addition, regional scale climate models have been run to calculate Holocene optimum and Late Glacial Maximum precipitation across the range. The onset of sedimentation on the Caspian shelf and the appearance of transverse streams record the minimum conditions required for effective erosion. Where these conditions have been met, through the tectonic construction of relief and the orographic forcing of precipitation, a feedback between erosion and tectonics is established.

Session No. 38

T13. Time Scales of Denudation: From Catchment to Continent
Wednesday, 27 June 2001: 10:00 AM-4:30 PM
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