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Mark A. Evans - One of the best experts on this subject based on the ideXlab platform.
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Fate of ‘warm’ migrating fluids in the central Appalachians during the Late Paleozoic Alleghanian Orogeny
Journal of Geochemical Exploration, 2003Co-Authors: Mark A. Evans, G.c. HobbsAbstract:Abstract Middle to Upper Devonian elastic rocks throughout the Valley and Ridge province in the central Appalachians contain evidence for fluid migration during the Late Paleozoic Alleghanian Orogeny. Fluid inclusion microthermometry of vein minerals indicate that the migrating fluid was a ‘warm’ (160 to >220 °C) CH 4 -saturated NaCl-CaCl 2 brine. However, rocks in the same stratigraphic interval immediately forelandward of the Valley and Ridge contain veins that have significantly different fluid inclusions, indicating that the ‘warm’ fluids did not significantly migrate into the rocks of the Appalachian Plateau province. The ‘warm’ fluids are interpreted to have migrated to the paleosurface as hot springs during the Late Paleozoic. Stable and strontium isotope chemistry of the vein minerals suggests that some infiltration of the 'warm' fluids into the easternmost Plateau province did occur. This indicates that wholesale flushing of a foreland during an Orogeny may not be as common as originally thought.
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fluid inclusion and stable isotope analyses of veins from the central appalachian valley and ridge province implications for regional synorogenic hydrologic structure and fluid migration
Geological Society of America Bulletin, 1999Co-Authors: Mark A. Evans, Denise A BattlesAbstract:Fluid inclusion microthermometric analyses and O and C stable isotopic analyses of vein minerals are used to determine the chemistry and trapping conditions of fluids present in the central Appalachian fold-and-thrust belt during the late Paleozoic Alleghanian Orogeny. The upper Paleozoic rock section contains three regional hydrostratigraphic systems based on fluid chemistry and temperature. The Ordovician Trenton Formation through the Devonian Helderberg Group was a regional aquitard and was dominated by high-salinity, CH 4 -saturated, in situ fluids. The Devonian Oriskany Formation through the lower portion of the Chemung Formation was a regional aquifer system and underwent an influx of warm migrating fluids. The upper portion of the Devonian Chemung through Pocono Formations was also a regional aquifer, but it was dominated by an influx of meteoric water that mixed with in situ fluids. The migrating fluid was a warm (160 to >220 °C) CH 4 -saturated NaCl-CaCl 2 brine that was stratigraphically restricted to the Oriskany Formation through the lower portion of the Chemung Formation, although there is evidence for infiltration into lower stratigraphic units. Two separate fluid migration events are recorded in the rocks. The first event is either late synfolding to postfolding, and the second event is postfolding. Approximately 2‐4 km of overburden were removed by erosion between the two migration events. The source of the warm migrating fluids is still unknown. However, the most likely source would be fluids that were tectonically driven through the fold-and-thrust belt by large-scale, out of sequence thrusting in the hinterland. The migrating fluids were transported far into the foreland where they may have been directly responsible for (1) flushing of hydrocarbons from the upper Paleozoic of the Valley and Ridge into the Plateau province and (2) elevated thermal maturation indicators in the Valley and Ridge and Plateau provinces.
Arthur G Goldstein - One of the best experts on this subject based on the ideXlab platform.
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a shear zone origin for Alleghanian permian multiple deformation in eastern massachusetts
Tectonics, 1994Co-Authors: Arthur G GoldsteinAbstract:The area around Worcester, Massachusetts, has been used to determine which deformational and metamorphic features are due to the Alleghanian (Permian) Orogeny and which are pre-Alleghanian. Isolated, fault-bounded inliers of Carboniferous rocks display evidence of a single metamorphism and the formation of two prominent cleavages. The first cleavage formed synchronously with metamorphism. Pre-Carboniferous metasedimentary rocks have been affected by two metamorphisms and contain three prominent cleavages. The initial cleavage formed during the first metamorphism and the second cleavage formed during the second, retrogressive metamorphism. Thus the second two cleavages and the second metamorphism in pre-Carboniferous rocks are interpreted as Alleghanian. Normal displacements on two distinct faults are bracketed by the formation of the first and second Alleghanian cleavages. The initial faulting, along the newly defined Wachusett mylonite zone (WMZ), formed a wide zone of ductile mylonites which dips moderately to the northwest and contains elongation lineations which trend northwest. The second faulting, along the Clinton-Newbury fault (CNF) occurred along a steeply inclined plane which cuts the WMZ mylonites and contains a thin zone of phyllonites and mylonites which have elongation lineations which trend west. Alleghanian cleavages and metamorphism are confined to a mappable zone which is approximately 15 km wide where well defined. This zone is interpreted as a ductile shear zone which moved twice, forming the first and second Alleghanian cleavages. Early-formed, pre-Alleghanian metamorphic minerals are retrograded to hydrous phyllosilicates, and new hydrous minerals formed in the shear zone, indicating that it was a pathway for fluid flow. The initial motion was left-lateral with a thrust component. The second cleavage formed during top-to-the-northwest normal displacements. Thus the history of Alleghanian tectonism in this area began with sinistral faulting and then included three displacements along normal faults or shear zones. This suggests that the strain history included two distinct episodes, with the second experiencing slightly different strain orientations at different times, resulting in first WMZ normal motion, then CNF normal motion and finally normal displacements related to the second Alleghanian cleavages. This history agrees well with other work on the nature of the Alleghanian Orogeny in the northeast United States.
Terry Engelder - One of the best experts on this subject based on the ideXlab platform.
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jointing within the outer arc of a forebulge at the onset of the Alleghanian Orogeny
Journal of Structural Geology, 2007Co-Authors: Gary G Lash, Terry EngelderAbstract:The oldest joint set in Devonian rocks of western New York state has an atypical NS strike and predates regionally more abundant NW-striking and ENE-striking joints driven by hydrocarbon-related fluid decompression. The NS joints originated in higher modulus diagenetic carbonate and were driven initially by a different mechanism, either joint-normal stretching and/or thermoelastic contraction. The origin of these joints in higher modulus carbonate concretions indicates the presence of a tensile stress produced by uniform regional extensional strain. Upper Devonian shale hosting the NS joints crops out in that area of the Appalachian Basin where a Morrowan erosional unconformity marks the region of maximum upward lithospheric flexure of an early Alleghanian forebulge. The NS strike of these early joints points to a forebulge stretching axis oriented approximately east-west and associated in time and space with crustal loading that drove both the Northfieldian Orogeny and the underplating of the Bronson Hill Anticlinorium in New England. Ultimately, subsidence of the Morrowan forebulge buried the Upper Devonian shale succession to the oil window during the latter part of the Alleghanian tectonic cycle resulting in the propagation of fluid driven NW- and ENE-trending joints in black shale.
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early jointing in coal and black shale evidence for an appalachian wide stress field as a prelude to the Alleghanian Orogeny
Geology, 2006Co-Authors: Terry Engelder, Amy E WhitakerAbstract:Early ENE-striking joints (present coordinates) within both Pennsylvanian coal and Devonian black shale of the Central and Southern Appalachians reflect an approximately rectilinear stress field with a dimension > 1500 km. This Appalachian-wide stress field (AWSF) dates from the time of joint propagation, when both the coal and shale were buried to the oil window during the 10-15 m.y. period straddling the Pennsylvanian-Permian boundary. The AWSF was generated during the final assembly of Pangea as a consequence of plate-boundary tractions arising from late-stage oblique convergence, where maximum horizontal stress, S-H, of the AWSF was parallel to the direction of closure between Gondwana and Laurentia. After closure, the AWSF persisted during dextral slip of peri-Gondwanan microcontinents, when SH appears to have crosscut plate-scale trans-current faults at around 30{sup o}. Following > 10 m.y. of dextral slip during tightening of Gondwana against Laurentia, the AWSF was disrupted by local stress fields associated with thrusting on master basement decollements to produce the local orocline-shaped Alleghanian map pattern seen today.
G.c. Hobbs - One of the best experts on this subject based on the ideXlab platform.
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Fate of ‘warm’ migrating fluids in the central Appalachians during the Late Paleozoic Alleghanian Orogeny
Journal of Geochemical Exploration, 2003Co-Authors: Mark A. Evans, G.c. HobbsAbstract:Abstract Middle to Upper Devonian elastic rocks throughout the Valley and Ridge province in the central Appalachians contain evidence for fluid migration during the Late Paleozoic Alleghanian Orogeny. Fluid inclusion microthermometry of vein minerals indicate that the migrating fluid was a ‘warm’ (160 to >220 °C) CH 4 -saturated NaCl-CaCl 2 brine. However, rocks in the same stratigraphic interval immediately forelandward of the Valley and Ridge contain veins that have significantly different fluid inclusions, indicating that the ‘warm’ fluids did not significantly migrate into the rocks of the Appalachian Plateau province. The ‘warm’ fluids are interpreted to have migrated to the paleosurface as hot springs during the Late Paleozoic. Stable and strontium isotope chemistry of the vein minerals suggests that some infiltration of the 'warm' fluids into the easternmost Plateau province did occur. This indicates that wholesale flushing of a foreland during an Orogeny may not be as common as originally thought.
Denise A Battles - One of the best experts on this subject based on the ideXlab platform.
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fluid inclusion and stable isotope analyses of veins from the central appalachian valley and ridge province implications for regional synorogenic hydrologic structure and fluid migration
Geological Society of America Bulletin, 1999Co-Authors: Mark A. Evans, Denise A BattlesAbstract:Fluid inclusion microthermometric analyses and O and C stable isotopic analyses of vein minerals are used to determine the chemistry and trapping conditions of fluids present in the central Appalachian fold-and-thrust belt during the late Paleozoic Alleghanian Orogeny. The upper Paleozoic rock section contains three regional hydrostratigraphic systems based on fluid chemistry and temperature. The Ordovician Trenton Formation through the Devonian Helderberg Group was a regional aquitard and was dominated by high-salinity, CH 4 -saturated, in situ fluids. The Devonian Oriskany Formation through the lower portion of the Chemung Formation was a regional aquifer system and underwent an influx of warm migrating fluids. The upper portion of the Devonian Chemung through Pocono Formations was also a regional aquifer, but it was dominated by an influx of meteoric water that mixed with in situ fluids. The migrating fluid was a warm (160 to >220 °C) CH 4 -saturated NaCl-CaCl 2 brine that was stratigraphically restricted to the Oriskany Formation through the lower portion of the Chemung Formation, although there is evidence for infiltration into lower stratigraphic units. Two separate fluid migration events are recorded in the rocks. The first event is either late synfolding to postfolding, and the second event is postfolding. Approximately 2‐4 km of overburden were removed by erosion between the two migration events. The source of the warm migrating fluids is still unknown. However, the most likely source would be fluids that were tectonically driven through the fold-and-thrust belt by large-scale, out of sequence thrusting in the hinterland. The migrating fluids were transported far into the foreland where they may have been directly responsible for (1) flushing of hydrocarbons from the upper Paleozoic of the Valley and Ridge into the Plateau province and (2) elevated thermal maturation indicators in the Valley and Ridge and Plateau provinces.