HR: 1340h
AN: PP23A-1400    [Abstracts]
TI: Geochronology of Tropical Alpine Glaciations From the Cordillera Huayhuash, Peru
AU: * Hall, S R
EM: shall@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Science Dept., 1156 High St., Santa Cruz, CA 95064 United States
AU: Farber, D L
EM: farber2@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550-9234 United States
AU: Rodbell, D T
EM: rodbelld@union.edu
AF: Union College, Geology Department, Schenectady, NY 12308-2311 United States
AU: Finkel, R C
EM: rfinkel@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550-9234 United States
AU: Ramage, J M
EM: ramage@lehigh.edu
AF: Lehigh University, Earth and Environmental Sciences, 31 Williams Hall, Bethlehem, PA 18015 United States
AU: Smith, J A
EM: jasmit10@mailbox.syr.edu
AF: Syracuse University, Department of Earth Sciences, 204 Heroy Geology Laboratory, Syracuse, NY 13244 United States
AU: Mark, B G
EM: mark.9@osu.edu
AF: The Ohio State University, Department of Geography, 1136 Derby Hall, 154 North Oval Mall, Columbus, OH 43210 United States
AU: Seltzer, G O
EM: goseltze@mailbox.syr.edu
AF: Syracuse University, Department of Earth Sciences, 204 Heroy Geology Laboratory, Syracuse, NY 13244 United States
AB: The Cordillera Huayhuash of the Central Peruvian Andes (10.3$\deg$S, 76.9$\deg$W) is an ideal range to study regional climate signals and variations in paleo-ice volumes. Located between the Cordillera Blanca to the north and the Junin region to the south, the range trends nearly north-south with modern glaciers confined to the high peaks ($>$4800 m). Cross-cutting relationships, geomorphology, and correlation with surface exposure dated moraines in the nearby Cordillera Blanca suggest the region preserves a rich record of tropical glaciation. In order to determine the glacial chronology we mapped and dated glacial features of the Jahuacocha valley (which drains the western side of the range) and two eastern drainages, the Mitococha valley, and the Carhuacocha valley. At each locality we used ASTER data, aerial photographs, and GPS to map glacial features both within main valleys and tributaries. We sampled quartz-bearing erratics on moraine crests as well as ice-polished bedrock surfaces for exposure age dating using in situ produced cosmogenic $^{10}$Be and $^{26}$Al. In the Jahuacocha valley, the greatest ice extent reached an elevation of $\sim$4090m and moraine crest boulders yield and age of $\sim$11.2 $\pm$0.6 ka suggesting a significant late Glacial ice advance or stillstand. A younger cluster of moraines exists $\sim$1 km up-valley at an elevation of $\sim$4100m. These moraines, dated at $\sim$8.0 $\pm$1.0 ka, suggest an early Holocene advance. In the Mitococha valley, a young moraine and polished bedrock dated at $\sim$0.2 ka and $\sim$11.4 $\pm$0.4 ka respectively span the late Glacial through recent. The late Glacial features of this eastern drainage occur at an elevation of $\sim$4100m while the recent events occur at an elevation of $\sim$4380m. Our preliminary results suggest that all three valleys experienced a very similar glacial history with minor differences likely due to the variations in valley morphology. Comparing the chronology of glaciation in the Cordillaera Huayhuash with that in regions to the south and north will provide a means of evaluating the degree of synchroneity of glaciation and climate change across 5$\deg$ of latitude in the tropics.
DE: 9360 South America
DE: 5416 Glaciation
DE: 1620 Climate dynamics (3309)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting