CARACTERIZAÇÃO LITOLÓGICA E EVOLUÇÃO METAMÓRFICA DA PORÇÃO LESTE DO COMPLEXO METAMÓRFICO BRUSQUE, SANTA CATARINA

Abstract

The eastern portion of the Brusque Metamorphic Complex comprises dominantly metassedimentary rocks, with subordinate metavolcanics. Sheets of peraluminous leucogranites are concordantly intrusive in this sequence, as well as larger granitic bodies, as the Compra Tudo, Valsungana and Serra dos Macacos granitoids. Regional deformation and orogenic metamorphism are here interpreted as polyphase events of Neoproterozoic age associated to continental collision. A younger metamorphic event is related to heat transfer from granitic magmas and to the development of ductile shear zones. Protoliths are dominantly marine sediments probably deposited in rift systems evolving towards continental margin enviroments. No evidence of ancient oceanic crust is found. Turbidites are characterized by systematically alternate pelites, feldspathic sandstones and quartz sanstones, with minor amounts of limestone and marble. Massive metavolcanic rocks of tholeiitic affinity are interpreted as former subaqueous basalt flows. Minor occurrences of chemical exhalative interflows are found as banded iron formations. Metamorphic evolution is complex and intimately related to deformation events. M1 e M2 metamorphic events are related to low-pressure, regional orogenic metamorphism synchronous to the development of foliations S1 and S2 . Both were formed during continental collision, which caused important tectonic interleaving of the volcano-sedimentary sequence. Temperature conditions range from those of the greenschist facies to lower amphibolite, marked by chlorite, biotite, garnet, andaluzite and cordierite zones. Metamorphic zoning pattern is complex, with repetition and incompatibility of zones due to tectonic interleaving. M3 metamorphic event is related to the intrusion of syn-transcurrence (D3), Neoproterozoic Valsungana and Serra dos Macacos granites, which develop contact metamorphic aureoles containing pelitic and calc-silicate rocks formed under albite-epidote hornfels to pyroxene hornfels facies conditions. Mylonitic rocks formed under greenshist facies conditions are found along the Major Gercino and Itajaí- Perimbó shear zones.