Idade U-Pb e Geoquímica do Traqui-Andesito Toleítico de Gouveia (MG) Comparadas com Rochas Básicas Toleíticas Regionais Pedro Lessa e Formiga: Fragmentos de uma Large Igneous Province (LIP) Toniana

Abstract

In Gouveia (MG), a tholeiitic high-K trachy-andesitic subvolcanic rock, with phenocrysts of plagioclase and sa-nidine, and a matrix rich in feldspars, biotite, magmatic epidote and quartz, outcrops in the form of irregular bodies and subverticalized dykes. The U-Pb age of 938.5 +/- 4.5 Ma found for the Gouveia trachy-andesite is practically the same as for the regional metabasic rocks of the Pedro Lessa suite (933 +/- 20 Ma) and the Formiga dykes (940 + / - 50 Ma), poin-ting to the grouping of all these rocks in the same magmatic event. The combined treatment of the geochemistry of the trachy-andesitic rock with that of the regional Pedro Lessa and Formiga rocks, reveals cogeneticity among these litho-types. The basaltic magma that generates these rocks, with an OIB signature (typical of mantle plume), would came from partial melting of a garnet-bearing peridotite, passed through lithospheric contamination and differentiated through the fractional crystallization process until the investigated trachy-andesite. This basic/intermediate magmatism of Tonian age is inserted in the magmatic context of a large igneous province (LIP) rebuilt in São Francisco and Congo cratons.