T139 State-of-the-Art and Future Directions in Petrology and Petrochronology II: A Session in Honor of Chris Yakymchuk, University of Waterloo, GSA MGPV Early Geological Career Awardee for 2024

Monday, 23 September 2024
1:30 PM - 5:30 PM
206B

MECHANISMS OF CO2-BEARING FLUID INFILTRATION INTO DRY ROCKS IN MÉLANGE, NORTHEASTERN CONNECTICUT, USA

Paper number: T139-6
Program: Technical Sessions
Time: 2:35 PM – 2:50 PM

Authors

Abstract

The infiltration of aqueous fluids plays a major role in the global cycling of carbon and influences metamorphic CO2 fluxes. Aqueous fluids infiltrating metacarbonate rocks may lead to the release of CO2 during metamorphism, whereas CO2-bearing fluids infiltrating silicate rocks may deposit carbonate minerals and sequester CO2 at depth. It is therefore necessary to understand the mechanisms by which these fluids infiltrate and interact with rocks along their flow paths, in particular initially dry rocks lacking a preexisting fluid-filled porosity. Here, we focus on Acadian–Neoacadian age mélange in northeastern Connecticut, USA1, containing initially dry mafic–ultramafic blocks that have been variably hydrated and carbonated by a large-scale vein forming event that introduced matrix fluids to the blocks. The veins contain carbonate minerals (primarily dolomite–ankerite and magnesite–siderite), indicating the presence of CO2 in the fluid, and silicate minerals including quartz, garnet, and kyanite. The blocks lack carbonate phases, so the CO2 must have been introduced by the fluids. The growth of euhedral crystals into open spaces suggests fluid flow through cracks, but carbonated selvages surrounding the veins indicate that pervasive infiltration into the blocks also occurred. Petrographic observations reveal the growth of small kyanite and sometimes carbonate and staurolite crystals along plagioclase grain boundaries in the selvages, indicating that pervasive infiltration of water and CO2 likely initiated along these grain boundaries. Extensive interface-coupled dissolution-reprecipitation (ICDR) textures are observed in plagioclase. ICDR is a process by which a disequilibrium mineral phase is epitaxially replaced by a more stable phase due to fluid-mineral interaction. This process produces an extensive micro–nanoporosity network, which could facilitate further fluid ingress and subsequent CO2 mineralization. Thus, we posit that channelized flow introduced matrix fluids to the blocks, whereas migration of fluid along grain boundaries and nanoporosity resulting from ICDR processes allowed for CO2 and H2O ingress at the grain scale. Together, these processes facilitated CO2-bearing fluid infiltration and associated carbonate mineralization in these mélange blocks.

  1. Tassara, S., et al. Geology 49, 168-173 (2021).

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404872

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