Geology and tectonic significance of the metavulcano-sedimentary rocks of the Coxilha do Batovi Complex, Dom Feliciano Belt (São Gabriel, RS).

Abstract

The Coxilha do Batovi Complex (CCB) is a Precambrian metavolcano-sedimentary sequence, exposed in a structural framework south of the town of São Gabriel. To understand the structural evolution of the complex, an integrated study of stratigraphy, sedimentology, petrographic analysis, structural geology and metamorphic petrology was carried out. The CCB is located at the southwestern end of the Taquarembó Terrane boundary, over the NW-SE direction Ibaré Shear Zone. The CCB is composed of fine to medium quartzitic and arkosean meta-sandstones and metapelites, with a subordinate occurrence of marbles, metavolcanic rocks, banded iron formations and metagranites. The rocks of the CCB record a complex structural fabric, resulting from a long history of progressive deformation associated to a low grade orogenic metamorphism, of greenschist facies conditions. The original thickness of the sedimentary package is multiplied by the action of isoclinal folds and by the crenulation and transposition of the main schistosity. In less deformed portions, are preserved primary structures such as plane-parallel stratification, trough cross-bedding, and low-angle planar cross-bedding. The measured and interpreted columnar profiles suggest a prograding sequence, composed of a thick package of meta-sandstones that grade to a rhythmic intercalation with metapelites superimposed by another thick package of meta-sandstones. The CCB rocks represent quartzitic and carbonate siliciclastic sediments likely deposited in a delta environment in an intracratonic or passive margin basin. The rocks of the complex are deformed by the action of a regional shortening of NE-SW direction, associated with the formation of foliations S₁ and S₂, whose maximum deformation performance generated the Ibaré Shear Zone.