The north Patagonian batholith at Paso Puyehue (Argentina-Chile). SHRIMP ages and compositional features

ARAGÓN EUGENIO; CASTRO, ANTONIO; DÍAZ-ALVARADO, JUAN; LIU, D, -Y.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2011 vol. 2011 p. 1 - 8

0895-9811

         New U-Pb SHRIMP zircon ages together with a geochemical and isotopic (Sr and Nd) study has been carried out on granitoids and host volcanics of the North Patagonian batholith at Paso Puyehue, close to the Argentinean-Chilean border. The results yield ages of 18.0 ±1 Ma for the gabbros and 12.0 ±0.3 Ma for the granodiorites. An age of 125.0 ±2 Ma was obtained for the host volcanic rock, and an age of 21.7 ±1.8 Ma for the basaltic trachy-andesite. The intrusive suite is formerd by dominant hornblende-biotite granodiorite and subordinate hornblende gabbros and diorites. These form a typical metaluminous calc-alkaline series. The time-isotopic magmatic evolution of plutonic an volcanic rocks shows an Early Eocene beginning of isotopic mélanges of primitive and more crustal compositions with no spatial constrains. This isotopic mélange is coeval to the presence of the Aluk-Farallon-SAM triple junction at this latitude and to synextensional widespread magmatism as the calc-alkaline magmatism locus shifts from the North Patagonian batholith plutons to the back-arc bimodal Eastern Paleogene-Eogene volcanic Belt made of a large calc-alkaline ignimbrite flare-up with basalts of OIB affinity. Considerations are made for the possibility of a Paleogene slab window by slab detachment, and the development of a new subduction front since the beginning of Nazca Plate development at the 23 Ma major ocean plate rearrangements.