Decompression experiments in rhyolitic melts at high temperatures, low water: application to the Parana volcanism

• Grant number: 19/13193-8
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• Start date: September 16, 2019
• End date: December 15, 2019
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Valdecir de Assis Janasi
• Grantee: Liza Angélica Polo
• Supervisor: Max Schmidt
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: Swiss Federal Institute of Technology Zurich, Switzerland
• Associated to the scholarship: 17/15540-1 - Experimental simulation of the conditions of formation of silicic volcanic rocks in the Paraná Magmatic Province: a contribution of the Brazilian experimental petrology to the modern volcanology, BP.PD

Abstract

The purpose of this BEPE project is to perform experiments to investigate the role of decompression, cooling rate and water activity on the kinetics of the crystallization of rhyolites from the Paraná Magmatic Province (PMP) using the laboratory facilities of the Institute of Geochemistry and Petrology at ETH Zurich, Switzerland. The target rhyolite belongs to the Santa Maria (SMr) volcanic unit of PMP, exposed over an area of ca. 12,300 km² (volume of ca. 4,500 km³) in the central-northern region of Rio Grande do Sul state, Brazil. Besides the exceptional dimension of this volcanic unit, it is particular interesting due to its physicochemical properties, such as high temperatures (950-1000ºC), low water contents in the melt (<1%) and moderate viscosities (104-107 Pa·s).The experimental grid of this project aims to reproduce the physico-chemical conditions (T, P, % H2O and ’O2) required for crystallization and/or stabilization of the main crystalline phases of the pre- and sin-eruptive stages. The experimental crystallization of a similar mineral assemblage on synthesized glass and their comparison with composition of natural phases will be used to confirm the near liquidus temperatures and the low water contents of this magma, according to estimates from previous studies. The role of decompression and H2O activity will be investigated using different water contents (0, 1 and 2 wt%) in experiments with varied pressures (i.e. from 200 up to 5 MPa).Experimental studies on similar rocks are nearly absent in the literature, and thus the results will be relevant to better constrain degassing and crystallization and how they affect the rheology of high-temperature silicic magmas during their ascent to the surface, which in turn is reflected in the eruptive style (explosive or effusive) and in the morphology of resulting volcanic deposits.