Caracterização petrográfica e geoquímica dos mármores da formação Nhamessolo na Localidade de Mungári, província de Manica

Abstract

With the aim of contributing to the petrogenetic correlation between the marbles of the Nhamessolo Formation and the Rushinga Group, 14 samples were selected, of which 11 are from the Nhamessolo Formation and 3 from the Monte Pitão Formation of the Rushinga Group, collected as part of the geological mapping project at a scale of 1:50,000 of Sheet 712 developed by the Geological Research Services (SPG) of INAMI, for the petrographic, geochemical and isotopic study of carbon and oxygen.

The marbles of the Nhamessolo Formation vary from pure calcitic to pure silicatic, while those of the Monte Pitão Formation are pure calcite-dolomitic, according to the classification diagram of Storey and Vos (1981). Both Formations were subjected to two distinct metamorphic events, the first related to contact metamorphism, evidenced by the presence of high-grade minerals such as olivine, diopsides, tremolite, and phlogopite, and the second, related to hydrothermal metamorphism between 500-600 °C, evidenced by the presence of alteration minerals such as serpentine. The carbon and oxygen isotopic signatures of the marbles of the Nhamessolo Formation are consistent with a protolith formed in an impure and open environment prone to the deposition of siliceous material and organic matter, which during metamorphism triggered reactions that formed a variety of accessory minerals. On the other hand, the little variety in the accessory minerals of the Monte Pitão Formation indicates that it originates from a protolith formed in an environment with little interaction with siliceous material. In general terms, the marbles of the Nhamessolo Formation show petrographically variable characteristics, containing calcite as the main constituent followed by dolomite. Olivine, phlogopite, diopside, clay minerals, orthopyroxene, and graphite occur as accessory minerals in some samples.(TRADUÇÃO NOSSA)