Paraná quartz andesite rings and arcs formed by distal imprint of dune design from the Botucatu paleoerg

Abstract

Rings and arcs in a Paraná Volcanic Province quartz andesite were formed by distal imprint of design of the top of barchan and linear dunes. Hydrothermal jetting occurred in the Lower Cretaceous from the dunes onto the upper amygdaloidal crust of the lava flow in Fronteira Oeste of southernmost Brazil. In one occurrence, hot water overflowed the quartz andesite in a hot spring and deposited sinter quartz. This unique register of the process in the continents was investigated with varied techniques, including satellite images, geological field survey, field gammaspectrometry, petrography and whole-rock geochemistry. We characterized the rings and arcs in the upper crust of the Catalán quartz andesite, design defined by hydrothermal processes, no ring dikes observed. We interpret the evidence as hydrothermal injection of sand and alteration of the upper crust of the quartz andesite, including silicification and deposition of epithermal quartz. The reproduction of the design of the dune tops was generated by focused jetting of hot water and vapor (plus sand) through the top of the dunes. The vertical channel maintained the design of the dune tops distally in the quartz andesite. The quartz andesite crusts now display sand dune design above the massive core in the pampas as a result of a special process in geology.