The evolution of quartz veins during the tectonometamorphic development of the Brusque Metamorphic Complex, Brazil

Abstract

Microstructural analysis and characterization of quartz veins hosted in rocks from the Brusque Metamorphic Complex in the region of Brusque, State of Santa Catarina, have been performed to establish the relations between fluid regimes, tectonic styles and deformation/recrystallization mechanisms. The analysis was based on observations of structural overprinting, spatial structural relations, the origin of the quartz veins and microtectonics studies. Five types of veins were identified: meter-long veins parallel to the regional foliation (V1-veins); massive, meterwide veins present in thermal aureoles (V2-veins); millimeter-wide, erratic veins, also present in thermal aureoles (V3-veins); tabular, undeformed and NW striking (V4-veins); millimeter-wide erratic veins restricted to brittle reactivation of strike-slip shear zones (V5-veins). The regional foliation, developed under garnet zone metamorphic conditions, was more effective in vein production when compared to the steeply dipping mylonitic foliation corridors developed under chlorite zone conditions. Pressure solution was the main deformation mechanism during the regional foliation development. However, granoblastic and decussate textures in hornfels reveal an influence of grain boundary area reduction mechanism. The granoblastic texture in hornfels would have inhibited fluid circulation during dehydration reactions, increasing fluid pressure and promoting massive (V2-veins) and erratic hydraulic fracture-related (V3) veins. In dextral NEtrending strike-slip shear zones, tabular quartz veins (V4-veins) are parallel to tension gashes. Reactivation of strike-slip shear zones under brittle conditions has produced local brecciated millimeter-wide quartz veins (V5-veins). This study underscores the important role of fluids during orogenic evolution near the brittle-plastic transition of the crust, and demonstrates how combined vein and microtextural analysis can reveal the tectonometamorphic history of lowgrade metamorphic rocks.