Basic magmatism in Eastern Sierras Pampeanas (Córdoba, Argentina): the magmatic record of Late Carboniferous extension

CAPRANO, J.; COLOMBO, F.; BALDO, EDGARDO; WEMMER, KLAUS

Oviedo

Congreso; VIII Congreso Geológico Español; 2012

Universidad de Oviedo

During the Late Paleozoic, part of central and western Argentina underwent regional extension,with the formation of extensive continental basins behind the arc at proto-Pacific margin of Gondwana.We describe here a dike (chemically classified as shoshonite) intruded in a granite of the Achalabatholith (Córdoba province, 31º 23.8ºS - 64º 32.9º W). The dike, dated at 309±7 and 308±6 Ma (K/Ar), is representative of the magmatism that took place synchronously with this regional extension. It is composed of microphenocrysts of plagioclase in a groundmass of more sodic plagioclase, sanidine, quartz, ilmenite, magnetite, titanite and fluorapatite, with devitrified glass. The shoshonite has about 51.5 wt.% SiO2, and shows the chemical attributes typical of oceanic island basalts. The low content of MgO(<3.1 wt.%) and very low Cr and Ni show that it is not a primary magma. It carries many different xenoliths: anorthoclase, kaersutite, ilmenite and apatite xenocrysts, xenoliths of granulite-grade metapelites, orthopyroxene-rich enclaves and syenite or anorthosite enclaves. This dike is important because indicates extensional processes further South from the previously known extensional area. In addition, the granulitic xenoliths confirm that in this area the Achala batholith is underlain by high-grade metamorphic rocks.