TY - JOUR
T1 - Use of clay-mineral alteration patterns to define syntectonic permeability of joints (cleat) in Pennsylvania anthracite coal
AU - Daniels, E. J.
AU - Marshak, S.
AU - Altaner, S. P.
N1 - Funding Information:
We thank Jane Eggleston for help with field work, Alden Carpenter, Craig Bethke and Richard Hay for helpful discussions, Byron Kulander, Terry Engelder and an anonymous reviewer for helpful comments on the manuscript. This research was supported by NSF grants EAR 87-07319 and EAR 89-15792, and a GSA student research grant.
PY - 1996/10/15
Y1 - 1996/10/15
N2 - Joints (cleat) in Pennsylvania anthracite contain two distinct clay-mineral assemblages, both of which formed by alteration of preexisting kaolinite at peak metamorphic conditions during the Alleghanian orogeny. The first assemblage, NH4-illite or pyrophyllite ± quartz, formed by reaction of kaolinite with methane-rich fluids derived from within the coal. The second assemblage, sudoite ± tosudite ± rectorite ± berthierine, formed by the reaction of kaolinite with ferromagnesian-bearing hydrothermal fluids which must have come from outside the coal. In an earlier paper, we suggested that the first assemblage indicated clay diagenesis in low-permeability environments, and that the second assemblage indicated clay diagenesis in high-permeability environments. If this premise is correct, then the distribution of clay-mineral alteration assemblages serves to define syntectonic permeability variations in coal cleat. The first assemblage dominates in the coal matrix itself, in isolated cleat, in cleat that parallel the regional trend of Alleghanian folds, and in the mirror portions of cleat oriented perpendicular to the fold trends, suggesting that these regions are low-permeability environments. The second assemblage dominates in the hackle fringe of interconnected cleat that trend perpendicular to the strike of the Appalachian orogen, suggesting that these regions are high-permeability environments. Our results emphasize that syntectonic cleat permeability is a function of cleat orientation, macroscopic cleat interconnectivity and orientation, as well as microscopic cleat-surface morphology.
AB - Joints (cleat) in Pennsylvania anthracite contain two distinct clay-mineral assemblages, both of which formed by alteration of preexisting kaolinite at peak metamorphic conditions during the Alleghanian orogeny. The first assemblage, NH4-illite or pyrophyllite ± quartz, formed by reaction of kaolinite with methane-rich fluids derived from within the coal. The second assemblage, sudoite ± tosudite ± rectorite ± berthierine, formed by the reaction of kaolinite with ferromagnesian-bearing hydrothermal fluids which must have come from outside the coal. In an earlier paper, we suggested that the first assemblage indicated clay diagenesis in low-permeability environments, and that the second assemblage indicated clay diagenesis in high-permeability environments. If this premise is correct, then the distribution of clay-mineral alteration assemblages serves to define syntectonic permeability variations in coal cleat. The first assemblage dominates in the coal matrix itself, in isolated cleat, in cleat that parallel the regional trend of Alleghanian folds, and in the mirror portions of cleat oriented perpendicular to the fold trends, suggesting that these regions are low-permeability environments. The second assemblage dominates in the hackle fringe of interconnected cleat that trend perpendicular to the strike of the Appalachian orogen, suggesting that these regions are high-permeability environments. Our results emphasize that syntectonic cleat permeability is a function of cleat orientation, macroscopic cleat interconnectivity and orientation, as well as microscopic cleat-surface morphology.
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U2 - 10.1016/S0040-1951(96)00019-4
DO - 10.1016/S0040-1951(96)00019-4
M3 - Article
AN - SCOPUS:0030441940
SN - 0040-1951
VL - 263
SP - 123
EP - 136
JO - Tectonophysics
JF - Tectonophysics
IS - 1-4
ER -