16-34 Fluid Inclusion Determined Trapping Conditions in the Lackawanna Synclinorium

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

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Abstract:

The Lackawanna Synclinorium is a 120 km long trough-shaped geologic structure in northeastern Pennsylvania that contains significant anthracite coal deposits. This structure, known as the Northern Anthracite Field, has been interpreted as forming from either thin-skinned Alleghenian tectonics or as a salt-collapse structure. The presence of anthracite-grade coal within the Lackawanna Synclinorium indicates higher burial temperatures than those found in nearby rocks outside of the Synclinorium. As a result, two hypotheses for explaining the formation of this anthracite have emerged. The first is that the Northern Anthracite Field formed at a relatively high burial depth of over 10 km, leading to the high temperature and pressure needed for anthracite formation. The second hypothesis proposes a relatively low burial depth closer to 6 km with high-temperature fluids passing through the structure during formation, leading to anthracitization.

This study aims to determine which of these hypotheses is correct by conducting fluid inclusion microthermometry of quartz veins found throughout the Lackawanna Synclinorium. By analyzing the temperatures at which multi-phase fluid inclusions homogenize within the quartz veins, an estimation of the depth and temperature conditions of vein formation can be made. Preliminary analysis indicates the presence of both CH4 ±CO2 fluid inclusions and aqueous fluid inclusions. Methane inclusions give minimum homogenization values (ThH) of -86.7°C and aqueous inclusions that homogenize (ThA) at 149.2°C, with large deviations throughout the synclinorium due to apparent variable formation depth and salinity. While salinity differs from site to site, the average salinity of the aqueous inclusions is high, nearing 10%. These results will determine the burial depth of the anthracite and improve our models for anthracite formation within the Lackawanna Synclinorium.

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