24 D7. Structural Geology, Geophysics, Tectonics, and Petrology Contributions (Posters)

Saturday, 29 March 2025
8:30 AM - 5:30 PM
North Great Hall

FLUID EVOLUTION AND TRAPPING CONDITIONS IN THE NORTHERN PART OF THE LACKAWANNA SYNCLINORIUM

Paper number: 24-11
Program: Technical Sessions
Time: 8:30 AM – 5:30 PM

Authors

Abstract

Earlier work examined fluid inclusion microthermometry of fluid inclusions in quartz veins from Pennsylvanian rocks of the Southern and Middle Anthracite Fields, and supports a deep burial model of coalification in favor of focused orogenic hot fluid flow. High-temperature (250 to 255 °C) trapping of CH4 ± CO2 saturated aqueous fluids and CH4 ± CO2 fluid inclusions indicate fluid trapping at depths of 11.5 to 13.4 km under a cover of Pennsylvanian to Permian(?) syntectonic load. In the folded rocks to the south of the Southern Anthracite belt near the Blue Mountain Structural Front, CH4 ± CO2 fluid inclusions indicate a sediment load that was up to 16.3 km thick.

The Lackawanna Synclinorium, known as the Northern Anthracite Field, is located 50 to 100 km to the north of the Southern Field and is an over 120 km long synclinal trough that has been interpreted as a salt-collapse structure. Preliminary analysis of CH4 ± CO2 fluid inclusions in quartz veins from the Pottsville Fm. give minimum homogenization values (ThH) of -100.8 to -80.0 °C and contain 12 to 15% CO2 for one vein and 7.0 to 10.0 % CO2 for another. The CH4 ± CO2 fluid inclusions examined so far indicate fluid tapping at conditions less than lithostatic, suggesting hydrofracturing of the fluid system and rapid drop in pore-fluid pressure resulting of degassing of formation fluids. Aqueous fluid inclusions from the Pottsville Fm. have homogenization values (ThA) of 172.3 to 178.5 °C with ice melting temperatures (TmIce) of -7.7 to -5.7 (8.8 to 11.3 wt. % NaCl equiv. salinity). These salinities are much higher than those determined from the Pennsylvanian rocks in the more southern Anthracite fields which range from 0 to 3%. Fluid trapping depths are estimated to be 6.2 to 7.8 km. Published vitrinite reflectance values in Pennsylvanian rocks in the northern part of the Lackawanna Synclinorium are <4.0 (<235 °C).

Aqueous fluid inclusions from rare quartz veins the Devonian-Mississippian Spechty Kopf Fm. have ThA values of 122.1 to 131.6 °C and TmIce of -9.8 to -5.7 (8.8 to 13.7 wt. % NaCl equiv. salinity). Pressure-corrected trapping temperatures are 150 to 275 °C and indicate trapping depths of 5.2 to 12.8 km. At this point, it is uncertain whether coalification in the northern part of the Lackawanna Synclinorium area is due to burial or focused hot fluid flow.

Geological Society of America Abstracts with Programs. Vol. 57, No. 3

doi: 10.1130/abs/2025NE-408510

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.