Early Cambrian U-Pb zircon age and Hf-isotope data from the Guasay¨¢n pluton,

DAHLQUIST, J.A.; VERDECCHIA, S.; BALDO, E.G.; BASEI, M.A.S.; ALASINO, P.H.; UR¨¢N, G.A. ; RAPELA, C.W.; CAMPOS NETO, M; ZANDOMENI, P.S.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2016 vol. 43 p. 137 - 150

0718-7092

AnEarly Cambrian pluton, known as the Guasay¨¢n pluton, has been identified in thecentral area of Sierra deGuasay¨¢n, northwestern Argentina. A U¨CPb zircon Concordia ageof533 ¡À 4 Ma was obtained by LA-MC-ICP-MS and represents the first report ofrobustly datedEarly Cambrian magmatism for the northwestern Sierras Pampeanas. The pluton was emplaced in low-grade metasedimentaryrocks and its magmatic assemblage consists of K-feldspar(phenocrysts) + plagioclase + quartz + biotite, with zircon, apatite, ilmenite, magnetite and monazite as accessoryminerals. Geochemically, the granitic rock is ametaluminoussubalkaline felsic granodiorite with SiO2 =69.24%, Na2O+K2O =7.08%,CaO= 2.45%, Na2O/K2O =0.71 and FeO/MgO = 3.58%. Rare earth element patternsshowmoderate slope (LaN/YbN =8.05) with a slightly negative Eu anomalies (Eu/Eu* =0.76).Wereport the first in situ Hfisotopes data (¦ÅHft =-0.12 to -4.76) from crystallizedzirconsin the Early Cambrian granites of the Sierras Pampeanas, helping to constrainthemagmasource and enabling comparison with other Pampean granites. The Guasay¨¢n plutonmightprovide a link between Early Cambrian magmatism of the central SierrasPampeanasandthat of the Eastern Cordillera, contributing to define the western boundary ofthePampean paleo-arc.