THE W (Sn-Mo)-SPECIALIZED CATINGA SUITE AND OTHER GRANITOIDS OF THE BRUSQUE GROUP, NEOPROTEROZOIC OF THE STATE OF SANTA CATARINA, SOUTHERN BRAZIL

Abstract

The petrographic, geochemical and isotopic data on the granitoids intrusive in the Brusque Group, State of Santa Catarina, southern Brazil, are presented in this paper. These are late- to post-tectonic rocks, being the most evolved ones those that constitute the Catinga Suite. The granitoids intrusive in the southern domain of the Brusque Group are grayish rocks, in which biotite (when present) is practically the only mafic mineral. They are rather reduced, slightly alkalic, transitional between meta-and peraluminous. An acid subvolcanic pluton, the Ribeirão da Velha pluton, has similar petrographic and geochemical characteristics, and seems to be genetically related to these granitoids. LREE fractionation relative to HREE is incipient for the Catinga suite, and the REE patterns showing strong negative Eu anomaly. Initial 87 Sr/ 86 Sr ratios, from the literature for these granitoids are around 0.721 (São João Batista granitoid) and the only available IDM model age (Valsungana granitoid) points to a genesis from a continental crust of ca. 2020 Ma old. Gneiss-migmatitic rocks such as those that occur in the eastern portion of Brusque Group domain and as enclaves in the Nova Itália granitoid are strong candidates for protoliths of these granitoids. Little available information on the granitoids intrusive in the northern domain of the Brusque Group reports the presence of pink K-feldspar hornblende granitoids (Faxinai pluton) and light pink K-feldspar biotite granitoid (Guabiruba pluton). These granitoids are more enriched in K and more oxidized than those in the southern domain, and the LREE fractionation relative to HREE is strong, with the REE patterns showing incipient negative Eu anomaly. It is suggested that part of the Au concentrations found in the northern domain may be genetically associated with the granitoids, since they present characteristics favorable to promote Au mineralizations than the granitoids in the southern domain. Distinct protoliths and evolutionary processes from south to north within the Brusque Group domain, late to post-collisional conditions and the influence of a thick continental crust during the Neoproterozoic are the factors responsible for the generation of such a variety of granitoids in Brusque Group domain. Keywords: