CRUSTAL XENOLITHS, THEIR ZIRCONS AND APATITES: INVESTIGATING THE CONTINENTAL BASEMENT BENEATH THE CENTRAL ANDES
Whole-rock geochemical data confirms compositional heterogeneity between the sampled xenoliths, as expected based on observed lithological and mineralogical variations. New U-Pb zircon ages from igneous xenoliths record plutonism associated with Neogene (and younger) arc magmatism while previously dated zircons in metamorphic xenoliths range from the Devonian to the Paleoproterozoic (McLeod et al., 2013, GSA Bull. v. 125). Preliminary apatite REE data from two igneous xenoliths display variable but distinct geochemical characteristics (n=73): e.g. LaN/CeN (average 0.74 vs. 0.99), Eu anomalies range from 0.23-0.39 vs. 0.57-0.77, LREE signatures: LaN/SmN at 0.36-2.6 vs. 1.77-2.71, and variable HREE depletion: GdN/LuN 3.95-16.18 vs. 2.78-9.57, respectively. It is anticipated that this new dataset will allow crustal domain boundaries beneath Pampa Aullagas and Quillacas to be evaluated, potentially leading to a renewed understanding of the tectonic block arrangement of the region. Ultimately, the bulk geochemical data combined with in-situ analysis of accessory phases will yield vital insights into the processes and events that have established the continental basement on which the modern-day Andean Cordillera is constructed.