282-2 Fluid Infiltration Drives Metamorphism, Carbon Loss, And Metasomatism In A Proterozoic Contact Aureole

Session: Crustal Petrology, Part II

Presenting Author:

Authors:

Abstract:

The generation and movement of fluid in metamorphic terranes is a dominant control on mineral equilibria, metasomatism, and heat transfer. The degree and nature of fluid infiltration may enhance or suppress the extent of metamorphism (Ferry, 1991) while metamorphic reactions may, in turn, contribute to crustal fluid flow through devolatilization reactions (Baumgartner and Valley, 1986). Here, we look at the infiltration of fluids released during emplacement of the Tudor gabbro and its effect on the metamorphic evolution of contact aureole rocks.

The Tudor Gabbro was emplaced in calcareous host rocks of the Grenville Supergroup at ~1.2 Ga, predating at least one regional metamorphic event of the Grenvillian orogeny. The Tudor gabbro is dominantly clinopyroxene + plagioclase + magnetite + ilmenite with retrograde amphibole, biotite, and epidote. Minor calcite is present as inclusions within the pyroxenes and feldspars in the outer part of gabbro. The country rock consists of a carbonate + biotite + feldspar marble; approaching the gabbro a successive tremolite-in, titanite-in, clinopyroxene-in, hornblende-in, K-feldspar-in, and finally a biotite-out isograd record prograde reactions.

We constructed Temperature-activity of CO₂ and Pressure-Temperature pseudosections to understand the temperature – fluid evolution of the contact aureole. Thermodynamic modelling reveals high temperature amphibole and epidote bearing assemblages are possible only through infiltration of water rich fluid (achieving a_CO2 ≲ 0.25) at peak temperatures ≥ 700°C. Lower grade rocks, on the other hand, show possible metamorphic evolution in a closed, rock-dominated system. Stable isotopic evidence shows minimal variation in δ¹³C in the aureole while larger variability in δ¹⁸O suggests fluid infiltration. Ultimately, we find that fluid-infiltration and contact metamorphism drove > 90% carbon loss in the highest-grade rocks of the contact aureole.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5601

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