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Brittle Deformation in the Hylas Zone, eastern Piedmont, Virginia
Hollis, John
Hollis, John
Abstract
The Hylas mylonite zone is a dextral transpressive shear zone in the eastern Piedmont of Virginia. It formed during the Alleghanian orogeny ~320-260 Ma, and separates the Goochland terrane on the west from the Triassic Richmond and Taylorsville basins to the east. The zone is composed of ultra mylonite to barely mylonitic granites and gneisses, and has undergone significant deformation since its formation. The Hylas zone has three major facture sets, an ENE set of mineralized shear fractures, likely formed during the later stages of the Alleghanian orogeny; a NNE set of extension fractures and normal faults likely formed during early Mesozoic rifting, which opened the Richmond and Taylorsville basins as well as rotating sections of the Hylas zone, preserved in the orientation of the foliations. This set is cut by a NNW set of extension fractures and smaller normal faults, subparallel to a swarm of Jurassic Diabase dikes, making them likely of Jurassic age. Also present in the Hylas zone are pseudotachylite veins, which are a frictional melt which can be formed from slip along a fault surface, and can also allow isotopic dating of fault slip. Another potential avenue for absolute dating is zeolite minerals found in cataclasite along fault planes.
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2012-01-01
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Bailey, Christopher M.
Department
Geology