HR: 0830h
AN: V51G-0366    [PDF]
TI: 40Ar/39Ar Geochronology of Hypabyssal Igneous Rocks in the Western Amazon Basin of Peru: a Record of Thermal History, Structure, and Alteration
AU: * Prueher, L
EM: lprueher@usgs.gov
AF: USGS, MS 974 POB 25046 Denver Federal Center, Lakewood, CO 80225
AU: Snee, L
EM: lsnee@usgs.gov
AF: USGS, MS 974 POB 25046 Denver Federal Center, Lakewood, CO 80225
AB: Hypabyssal dacites located in the western Amazon basin of Peru record the thermal, tectonic, and alteration history of the area. The dacites were emplaced into the foreland of the Andean fold and thrust belt, and are the only known intrusions along the deformation front in Peru. Deformation in the fold and thrust belt occurred approximately 16 Ma. Preliminary 40Ar/39Ar geochronology on three hornblende separates yields crystallization ages of 12 Ma, younger than the folding and faulting. The dacites are located within a domed area, which includes Cretaceous shales and sandstones of the Chonta and Vivian formations and Tertiary shales, sandstones and tuff of the Pozo, Yahuarango and Chambria formations. Petrographic evidence shows that the dacites are not deformed, but locally underwent quartz-sericite-pyrite alteration during later hydrothermal activity. Argon geochronology on hornblende and potassium feldspar will define cooling history and age of the intrusions. Argon geochronology on sericite will provide a minimum age of the hydrothermal alteration. Seismic data are being examined to determine if the rocks form a stock-like feature or a laccolith similar to that observed in the Henry Mountains, Utah, which represent analogous igneous rocks in a similar setting.
DE: 1035 Geochronology
DE: 8499 General or miscellaneous
DE: 9360 South America
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting