Fluid inclusions study on the Parapente Granite, Gaspar (SC): implications to the tectonic evolution of the Itajaí-Perimbó Shear Zone

Abstract

By placing the Brusque Metamorphic Complex rocks in contact with the Itajaí Basin rocks, the Itajaí-Perimbó Shear Zone delimits the boundary between the Central and Outer areas of the Dom Feliciano belt in the Santa Catarina Shield. The evolution of this crustal scale structure can be investigated by the study of the Parapente granite, which outcrops in the city of Gaspar, through the shear zone. The crystallization age of 843 Ma makes this type A granite an excellent strain marker related to the operation of the shear zone. To estimate temperature, pressure and depth conditions strain related, there were analyzed fluid inclusions in three quartz types from the Parapente granite. The minimum trapping temperatures and the mean pressures and depths obtained by fluid inclusions are: 220-190ºC, 6 kbar and 23 km, for quartz I, from the less deformed granite facies, considered earlier; 160-130ºC, 4 kbar and 14 km, for quartz II, from the phyllonite, formed in the most recent stage of the shear zone evolution; and 260-220ºC, 190-170ºC, <12 km and <3 kbar, for the quartz III, from a vein that cuts the shear zone foliation. The variation in depth evidenced by the formation of quartz I and II shows that the shear zone operated initially as a thrust fault, rising in almost 10 km the Parapente granite in intermediate crustal levels. All the three quartz types present low salinities fluid inclusions, showing that the Itajaí-Perimbó Shear Zone was duct for fluids over a long period.