HR: 16:30h
AN: T32E-03    [PDF]
TI: Applying low temperature thermochronology to resolve the climatic, erosional and tectonic controls on the geomorphic development of the southern Andes
AU: * Thomson, S N
EM: stuart.thomson@yale.edu
AF: Department of Geology and Geophysics, Yale University P.O.Box 208109, New Haven, CT 06520-8109 United States
AU: Tomkin, J H
EM: tomkin@geol.lsu.edu
AF: Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803 United States
AU: Reiners, P W
EM: peter.reiners@yale.edu
AF: Department of Geology and Geophysics, Yale University P.O.Box 208109, New Haven, CT 06520-8109 United States
AU: Brandon, M T
EM: mark.brandon@yale.edu
AF: Department of Geology and Geophysics, Yale University P.O.Box 208109, New Haven, CT 06520-8109 United States
AB: The southern Andes are an ideal orogen in which to study the interplay between tectonics, variable climate, and glacial erosional processes on the geomorphic development of mountains. They represent a mid- to high-latitude high relief mountain chain developed largely since late Cenozoic times in a relatively simple non-collisional convergent margin tectonic setting perpendicular to the prevailing mid-latitude westerly weather systems. An orographically induced rainshadow is well developed with the leeward (east) side receiving less than 10 % the precipitation of the windward (west) side. Preliminary new apatite (U-Th)/He (AHe) low temperature thermochronologic data have been obtained from samples previously analysed using the fission track (AFT) method to investigate in more detail variations in late Cenozoic cooling and hence erosional denudation both along strike and across the southern Andes. The cooling histories indicated by the AHe ages agree well with earlier AFT results, and indicate increased amounts of late Cenozoic erosional denudation on the windward side, with the youngest ages and amounts of exhumation apparently increasing toward the present day topographic divide. The AHe ages, when combined with AFT thermal modelling, also provide a well constrained age of ca. 8 Ma for the onset of accelerated denudation close to the present day topographic divide at ca. 47-48$\deg$S. With the acquisition of a more detailed low temperature thermochronologic AHe data we aim to test geodynamic models that predict the effects of variable climate (orographic precipitation), glacial and fluvial erosion, and tectonic uplift in a steady state orogenic wedge similar to the situation in the southern Andes. Such models imply similar topographic expression, but different spatial erosion responses to tectonic uplift in an orogenic wedge dependent on whether fluvial or glacial processes were the dominant erosion mechanism. Such differences should be better resolvable with the higher precision and lower temperatures (and hence nearer surface denudation record) provided by AHe data.
DE: 8102 Continental contractional orogenic belts
DE: 9360 South America
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: 2003 Fall Meeting