Emissions from Paraná-Etendeka Magmatic Province: evaluating the silicic and thermogenic gases

Author(s)

Melina Cristina Borges Esteves

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Geociências (IG/BT)
• Defense date: 2024-08-09

Examining board members

Adriana Alves; Letícia Freitas Guimarães; André Luiz Silva Pestilho; Eleonora Maria Gouvêa Vasconcellos

• Advisor: Adriana Alves

Abstract

Brazil hosts one of the world\'s most significant Continental Flood Basalts (CFBs), the Paraná-Etendeka Magmatic Province (PMP), associated with the breakup of the Gondwana Supercontinent and the opening of the Atlantic Ocean. The temporal coincidence between the emplacement of CFBs and global environmental changes emphasizes the potential role that volcanic emissions can exert on atmospheric composition, potentially leading to significant climate and ecosystem disturbances. Although the role of volcanic activity is uncontroversial, the limited data on PMPs magmatic volatiles, especially the silicic magmatism, have made it challenging to assess the potential environmental impacts associated. Additionally, the severity of the environmental disturbance during LIP events may also lie directly on the composition of the gases generated in their respective volcanic basins. Here we bridge these two gaps by first estimating the original volatile budgets of the high-Ti silicic rocks using melt inclusions (MIs) entrapped in plagioclase macrocrysts and the halogen signatures of apatite crystals and second investigating the thermal degassing of sedimentary samples from the Amazonas (CAMP) and Paraná (PMP) Basins. The analyzed MIs bear pre- entrapment crystals, daughter crystals, and fluid-bearing shrinkage bubbles, and they are characterized by silica-rich compositions (69 to 74 SiO2 wt%, on a dry basis), with low Cl and S (up to 363 and 314 ppm, respectively). Apatite crystals are fluorapatite, with consistently high fluorine (F>3.5 wt%) but low chlorine contents (Cl<2000 ppm). Using thermodynamically constrained equations we estimated the exchange reactions that control volatile partitioning, and approximated halogen contents of the equilibrium melt (F ~2800, Cl ~1400 ppm, and H2O ~0.5 wt%). Forward models using the aforementioned data as input closely reproduce apatite compositional trends, allowing insights into the depth of magma storage (c.a. 2 kbar) based on fluid/melt Cl partitioning and on Cl/H2O of equilibrium melt. The depolymerizing nature of F combined with high Rheological Agpaitic Indexes calculated from whole rock data imply an effusive eruptive style, with a passive degassing of F as high as 6.5 Gt, at least 2.1 Gt of Cl, and ~0.5 Gt of S. Experiments reveal significant geochemical and mineralogical alterations, with synthetic fluid inclusions indicating the release of volatiles such as CO2, CH4, N2, H2S, and H2O primarily through decarbonation, dehydration, and cracking of organic matter. Isotopic analysis shows a shift in 13C values, highlighting the impact of thermal processes on isotopic fractionation. Metamorphic reactions and associated fluids are treated to estimate basin-scale devolatilization. Even under conservative degassing effectiveness, the upscaling of our experimental results indicates the generation of 3200 Gt C in the Paraná- Etendeka Province and 14200 Gt C in the CAMP. We emphasize that factors beyond organic matter abundance, such as their quality, gas speciation, and production potential, would have controlled the volume of thermogenic gasses associated with the emplacement of the studied LIPs. The effects of the volcanic-related halogen are likely local due to rapid removal from the atmosphere through rainfall. Additionally, the absence of hydrothermal vent complexes in the PMP suggests that methane generated during metamorphism may have been stored within the geological formations rather than released into the atmosphere, both factors probably contribute to the lack of a significant global paleoenvironmental event linked to Paraná-Etendeka Province. (AU)

• FAPESP's process: 18/19713-0 - Environmental impacts produced through magma-sediment interactions in the Paraná-Etendeka Magmatic Province
• Grantee: Melina Cristina Borges Esteves
• Support Opportunities: Scholarships in Brazil - Doctorate