The Crust Role at Paramillos Altos Intrusive Belt: Sr and Pb Isotope Evidence

OSTERA HA; LINARES E; HALLER MJ; CAGNONI M

Pucón

Simposio; III South American Symposium on Isotope Geology; 2001

Paramillos Altos Intrusive Belt (PAIB) is located in the thick-skinned fold-and trust belt of Malargüe, southwestern Mendoza, Argentina. (Geochemical and isotopic studies were carried out to determine the crustal role in their genesis. Different sources in Andean Magmatism have been proposed to account for the geochemical and isotopic patterns. The relative proportion of crust, mantle, sediments and fluids in magma genesis is difficult to assess, although various models attempt to explain the evidence. Sr and Pb isotope ratios at PAlB show different fingerprints for the main units from Early to Late Miocene times. The Sr and Pb patterns of PAIB suggest that different sources were involved in their genesis. The lower- crust is considered the contaminant for the older Lower Miocene units. Minor amounts of upper crust are associated with the PAIC-SAS Middle Miocene units. For each unit, the evolution is controlled mainly by fractional crystallization processes. Therefore, PAIB reflects a change in the type and amount of crustal contamination from Early to Late Miocene times. We propose a model that couples a thicker crust with increasing upper crustal contamination and changing isotope ratios, although an additional component from subducted sediment or a subcontinentally eroded lithosphere could not be discarded.