LA-ICP-MS Zircon U-Pb Geochronology in the Altar Porphyry Copper Project, Andes Main Cordillera Of San Juan

MAYDAGÁN LAURA; SATO, ANA MARÍA; FRANCHINI, MARTA; LLAMBÍAS, EDUARDO; CHIARADIA, MASSIMO

Brasilia

Simposio; South American Symposium on Isotope Geology; 2010

SSAGI

The U-Pb zircon age of 20 ± 0.3 obtained in a sample of the massive tuff suggests Early Miocene as the youngest age for the Lower Volcanic Complex. The U-Pb zircon age of 10.35±0.32 Ma for the Central Ridge Porphyry of the Upper Subvolcanic Suite indicates a Late Miocene age. Positive  eNd(t) values and the 87Sr/86Sr(t) range of 0.703991-0.704865 for all Altar rocks suggest a mixed mantle-crust component in  their magmas, although  the mantle component might be dominant. Strong correlations of radiogenic isotopes with geochemical parameters in the LVC suggest that the melt experienced  assimilation-fractional-crystallization (AFC) processes. However, their relatively narrow isotopic variability implies that either assimilation was reduced or that assimilated rocks were isotopically similar to the mantle-derived melts. The ~10 Ma age of the USS coincides with the early stages of shallowing of the slab beneath the central Flat Slab segment and with the arrival of the Juan Fernández Ridge to this region (Kay and Mpodozis 2002). The nearly uniform radiogenic isotope data of the USS suggests homogeneous slightly more enriched sources.