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Dating Deformation: Thermochronology and Chemical and Mineralogical Changes in the blue Ridge Basement Complex in Virginia
Jenkins, Chelsea E.
Jenkins, Chelsea E.
Abstract
The Blue Ridge province in central and northern Virginia is underlain by Mesoproterozoic basement rocks and a Neoproterozoic to early Cambrian cover sequence. Basement rocks include granitoid gneiss, charnockitic gneiss, and younger charnockite and granite. Rift-related metasedimentary and metavolcanic rocks of Swift Run and Catoctin formations unconformably overlie the basement complex. The Blue Ridge basement and cover sequence experienced greenschist facies deformation during mid to late Paleozoic. 40 Ar/39 Ar analysis indicates this deformation occurred between the Acadian ( 420-380 Ma) and Alleghanian (325-260 Ma) orogenies in the late Devonianearly Carboniferous (Mississippian) during the Neoacadian orogeny (380-340 Ma). In places, charnockitic gneiss near the basement/cover contact has been converted to unakite. Consistency of these changes to a depth of 200m below the contact suggests alteration was not a result of Neoproterozoic contact metamorphism, but rather a product of Paleozoic regional metamorphism.
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2011-01-01
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Geology