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The AAPG/Datapages Combined Publications Database
Geochemical and structural analysis techniques were integrated in an investigation of epigenetic mineralization on fault zones to develop an evolutionary model for the post-Paleozoic history of the northern Appalachian basin. Analysis of faults in outcrop, excavations, and oriented drill cores revealed the occurrence of strike-slip and dip-slip faults which are representative of a fabric which is persistent in style, orientation, and magnitude across New York State. The elements of this fabric do not decrease in frequency with distance from the Allegheny structural front nor do they fan around the centers of deformation as do the Allegheny structures. Indeed the west-northwest trends of the normal faults and the acute bisectrix of the conjugate strike-slip faults are para lel with the short axis of the Appalachian basin. Their formation is attributed to the stresses produced during the asymmetric uplift of the basin in post-Paleozoic time.
Mississippi Valley-type epigenetic mineralization was deposited along these fault zones where they served as the dominant channels for circulating fluids within the well-cemented sandstones. Homogenization of fluid inclusions in vein minerals revealed an intermittent range of depositional temperatures from that typical of the peak of diagenesis in deep sediments, 170°C, to as low as 70°C. The higher temperatures may reflect waning of an elevated heat-flow regime produced by dehydration during diagenesis. The temperatures between 112 and 70°C are attributed to cooling during uplift.
Strike-slip faulting was initiated at temperatures near 170°C as indicated by syntectonic deposition of high-temperature calcite. Normal faulting did not occur until the hydrothermal brines had cooled to 112°C. Minor deformation and entrapment of secondary fluid inclusions continued to 70°C. The timing of tectonic events can be estimated by several techniques which generally indicate a late Paleozoic to early Mesozoic age for strike-slip faulting and a late Mesozoic to Cenozoic age for normal faulting.
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