Mármores da região de Itaoca (ES) e escarnitos no contato com diques máficos e félsicos : mineralogia e petrogênese.

Abstract

Skarns at the contact of marbles and mafic as well as felsic dikes located in the Itaoca region (Espírito Santo State, eastern Brazil) were investigated in terms of mineralogy and genesis. Marbles and the older mafic dykes were affected by high grade metamorphism of Brasiliano age, as comproved by the presence of spinel. The undeformed younger granitic dykes are post-tectonic. Skarns related to the granite dykes were formed as outcomes of silica addition in marble layers during the intrusion, generating zones composed of i)olivine + carbonate + pyroxene + amphibole ± phlogopite; ii)pyroxene + amphibole ± phlogopite ± scapolite, and iii)pyroxene ± phlogopite. The last mineral association occurs close to the granite and shows the maximum silica enrichment. Evidence of Ca-metassomatism in the granite is shown by the strongly zoned plagioclase crystals, which show central portions with An17 and border zone with An43. Skarns generated at the contact with amphibolite dykes are wider than the former, probably because the original contact metamorphic reaction zones generated during the intusion were reinforced by granulite facies metamorphism. The reaction aureoles display the following mineral associations: i) carbonate ± olivine, ii) carbonate + diopside ± scapolite ± epidote, iii) plagioclase + diopside ± scapolite ± epidote, and iv) amphibole + plagioclase ± phlogopite ± hercinite ± grossularite. The first association belongs to the marble at the contact, and the last to the amphibolite. There are mineralogical and textural evidences for metamorphic and metassomatic reactions due to the migration of Ca, Mg and Si, leading, for example, to the scapolitization of the plagioclase.