Assinatura mantélica de isótopos de carbono e oxigênio em cristais de calcita de rochas Foid-Sieníticas da Província Alcalina do Sul do estado da Bahia

Abstract

MANTELIC SIGNATURE OF CARBON AND OXIGEN ISOTOPES OF CALCITE CRISTALS FROM FOID-SIENITIC ROCKS OF THE ALKALINE PROVINCE OF SOUTHERN BAHIA, BRAZIL The South Bahia Alkaline Province (SBAP), with Neoproterozoic age (739 - 676 Ma), is a magmatic association formed by four batholiths and several stocks, predominantly composed by foid-syenitic rocks. In these rocks calcite crystals can occur disseminated, form aggregates, fill micro-fractures and as centimetric dykes. C and O isotopic data of calcite range between δ13CPDB -4,84 º/oo and - 7,35 º/oo, δ18OSMOW 6,47º/oo and 7,17 º/oo , which are similar values to those observed in carbonates crystallized from primary igneous carbonatitic magmas, with δ13CPDB data close to those reported for the mantle. These data permit to infer that the evolution of these alkaline intrusions took place in a closed system, preserving the C and O mantle signature even in late-magmatic minerals, such as calcite.