FIRST ZIRCON U-Th-Pb SHRIMP AGES OF THE FELSIC ALKALINE MAGMATISM OF THE SIERRA DE LOS CHACAYS VOLCANIC COMPLEX, PATAGONIA, ARGENTINA

CORDENONS, P. D.; SANTOS S. JOAO ORESTES; SALANI, F. M.

San Pablo

Simposio; 9th Southamericam Symposium on Isotope Geology; 2014

On the northern portion of the Extra-Andean Patagonia lies an extensive alkaline basaltic plateau defined as the Somún Curá Magmatic Province, spanning for more than 25.000 km2. These Cenozoic volcanic rocks are the region?s widest and the farthest (~450 km) from the current Nazca-South American trench, posing an intriguing geodynamic environment (Remesal et al. 2011). The Sierra de los Chacays Volcanic Complex (SCVC) is a large bimodal alkaline magmatic manifestation that delimits the southern portion of this basaltic plateau. It is conformed by several dismantled central edifices and many minor cones and domes that configure a NE-SW trend, all regarded as part of a post-plateau stage. Two key locations within the SCVC were selected for geochronologic studies: the southwestern ranges near Chacay Oeste (CHO), and the northeastern highs known as Sierra Aguada la Noche (SAN). Both sites show mainly trachytic and rhyolitic cores surrounded by basaltic flows, interpreted as complexes of central volcanic constructions and associated peripheral apparatus. Whereas SAN shows a well preserved volcanic edifice with a ~3 km wide central depression, CHO site displays mainly necks, dikes and dissected flows configuring a rough topography. One trachyte of each location was processed for zircon U-Th-Pb SHRIMP analysis at Curtin University of Technology, Perth, Australia.