The Mato Perso Conduit System: evidence of silicic magma transport in the southern portion of the Paraná-Etendeka LIP, Brazil

Abstract

The Mato Perso Conduit System is described from a ~ 120 km2 area in south Brazil exposing silicic volcanics of the Paraná-Etendeka LIP. A volcanic succession is defined by basaltic flows covered by flat-lying oxidized vitrophyres, banded vitrophyres cutting the lower lavas and grey flat-lying vitrophyres covering all the units. Flow morphologies determined by the recognition of structures, textures, and vesicle distribution were observed. Oxidized vitrophyres display massive flat-lying banded cores and flow tops from vesicular to frothy. Grey flat-lying vitrophyres have sharp contacts in the top of both basalt flows and oxidized vitrophyres, locally exhibit basal breccia and have a flat-lying foliation. Conduits are represented by banded vitrophyres and breccias, which outcrop in a 6 km wide, NW-SE oriented segment downthrown by normal faults towards the Antas River. The interpretation of the units on the geological map scale indicates intrusive contact relations. Recognition of dike-like structures in banded vitrophyres and dykes of oxidized vitrophyre are evidence of felsic magma transport. Based on field observations, we propose the emplacement of subaerial oxidized and grey vitrophyres fed by a fault-related conduit system. Sustained high temperature magmatic systems ensure the silicic lavas have a low viscosity and travel great distances.