LATE PALEOGENE ARC-RELATED VOLCANISM IN THE NORTH PATAGONIAN ANDES (39-41ºS)

IANNELLI, SOFÍA B.; FOLGUERA, ANDRÉS; LITVAK, VANESA D.; RAMOS, MIGUEL; FERNÁNDEZ PAZ, LUCÍA

Santiago

Simposio; Primer Simposio de Tectónica Sudamericana; 2016

Asociación tectónica Sudamericana (ATECSUD)

Paleogene to Neogene arc-related volcanism in the North Patagonian Andes have been considerably influenced by variations in subduction parameters, which constrains their geochemical signature. This magmatism is developed to the east of the present volcanic arc as two distinctive volcanic belts (Pilcaniyeu and El Maitén) which have evolved partially diachronously showing contrasting petrological and geochemical characteristics. Our study focus on Eocene and Oligocene arc-related volcanics rocks particularly exposed where both magmatic belts converge. Bimodal Eocene sequences nearby Filo Hua Hum lake area show tholeiitic signature and low influence from subduction-derived fluids; while foreland volcanic temporal equivalents were reported as typical intraplate-derived magmas. Oligocene magmatism analyzed in Auca Pan depocenter comprises intermediate volcanic lavas that show a clear calc-alkaline magmatic source and higher melting degrees, resulted from a more evolved volcanic arc. In comparison, further difference in the evolution of this volcanic arc is registered in the younger magmatic products (< 28 Ma) from Cura Mallín and Abanico basins, as they show the highest influence from slab-derived components, with tholeiitic sources. These differences in geochemical signature from arc-related sequences after 28 Ma are possibly associated to changes in subduction parameters due to Farallon breakup and the beginning of orthogonal subduction convergence.