Definition of volatile budgets of magmas that generated Palmas-type silicic rocks - Paraná-Etendeka Magmatic Province

• Grant number: 24/10966-4
• Support Opportunities: Scholarships in Brazil - Master
• Start date: November 01, 2024
• End date: October 31, 2026
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Adriana Alves
• Grantee: Eduardo Chiappetta Spera
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 19/22084-8 - The Paraná Magmatic Province: petrogenesis, chronology and environmental impact of Cretaceous tholeiitic, alkaline and silicic magmatism in the Brazilian Platform, AP.TEM

Abstract

The Paraná-Etendeka Magmatic Province (PEMP), aim of this study, has the largest preserved volume of silicic lavas among the continental LIPs on the planet. Divided into two groups according to Ti content, there are the silicic lavas of the Palmas type (low-Ti) and those of the Chapecó type (high-Ti). The eruptive style of the PEMP silicic lavas is the scene of discussions and controversies. Because of the high textural similarity between silicic lava flows and highly welded ignimbrites, their distinction becomes uncertain. In addition to this factor, the high rate of weathering and the limited number of continuous outcrops are adverse factors for the interpretation of such rocks. Recent studies suggest a predominantly effusive eruptive style for the lavas based on the low viscosity and high temperature (~1000ºC) during the eruption and on the presence of effusive structures. On the other hand, when comparing with the silicic rocks of the Etendeka portion of the PEMP, some authors suggest an explosive origin and classify the rocks as highly welded ignimbrites originating from the Messum complex.The placement of a LIP is accompanied by a significant release of gases and particulate matter into the atmosphere. In subaerial conditions, the ejection of ash and SO2 is linked to short-term global cooling, while CO2 gas is linked to long-term global warming. The oceanic anoxic event and global cooling during the Valanginian may have been influenced by the placement of the PEMP, given its contemporaneity, however, the degree of influence and chronological accuracy have not yet been properly established. Estimates of the content of volatiles exhaled by a magmatic province, in order to evaluate its climatic effects, are made by determining concentrations in melt inclsuons, the effectiveness of degassing and the volume of lava produced. The present project aims, primarily, to acquire data that assist in the interpretation of the eruptive style of Palmas-type silicic rocks. These data, however, can be used as a basis for calculating the exhalative potential of magmas and the results will, therefore, be directly used in the construction of knowledge about the potential climatic effects of the province's silicic rocks.By combining the data to be obtained by petrography (optical microscopy, electron microscopy and cathodoluminescence) with CSD studies, the aim is to identify characteristics of the crystallization environments, such as: pressure, crystallization rates, residence periods, evidence of mixing of magmas among others. Depending on each of these parameters, the evolutionary history of magma can be developed, from a certain depth to the surface. Analyses will be carried out using Raman spectrometry and electron microprobes on clinopyroxene crystals, apatite and non-homogenized melt inclusions present in plagioclase crystals, with the aim of characterizing the nature and content of their volatiles. In addition, analyses will be carried out using Fourier transform infrared spectrometry (FTIR) on plagioclase and pyroxene, with the intention of quantifying the water content in the magma. From the joint interpretation of all these data, we intend to contribute to a better understanding of the eruptive style of PEMP silicic lavas and the volatiles exhaled from them.