Stability of zircon u-pb systematics in a greenschist-grade mylonite - an example from the rockfish valley fault zone, central Virginia, USA

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dc.contributorVirginia Techen
dc.contributor.authorWayne, D. M.en
dc.contributor.authorSinha, A. K.en
dc.contributor.departmentGeosciencesen
dc.coverage.countryUnited Statesen
dc.coverage.stateVirginiaen
dc.date.accessed2014-06-26en
dc.date.accessioned2014-06-27T14:45:40Zen
dc.date.available2014-06-27T14:45:40Zen
dc.date.issued1992-09en
dc.description.abstractThe mid-Paleozoic, greenschist-grade Rockfish Valley Fault Zone (RVFZ) of central Virginia cuts the Grenville-aged Pedlar River Charnockite Suite (PRCS) and contains zircons that underwent brittle failure during ductile deformation. Electron microprobe analyses and scanning electron microscope (SEM) backscattered electron (BSE) imaging show that zircons from the protolith PRCS are concentrically zoned (with alternating U-Hf-rich and U-Hf-poor bands), and contain numerous radial microcracks. Zircons from the RVFZ mylonite are unzoned, fragmented, show no internal microfractures, and have low U and Hf concentrations relative to the PRCS zircons. U-Pb isotopic studies of zircons from the mylonites and from the charnockitic protolith demonstrate that no preferential Pb loss occurred in the zircons from the mylonite, and that the Pb-207/Pb-206 ages of the mylonite zircons are identical to those of the protolith zircons. The loss of primary zoning from the zircons of the RVFZ ultramylonites can be explained by the physical removal of microfractured, U-rich, alpha-damaged zircon domains as the result of brittle failure and disaggregation during mylonitization. Mechanically resistant (low-U) portions of zircon grains tended to remain intact in the mylonite. Thus, it may not always be possible to predict whether or not the zircon U-Pb system has been disturbed by mylonitization by using physical criteria (e.g., grain size reduction, obliteration of primary zoning textures) alone. Evidently, fluids present during mylonitization accomplished the hydration of primary mineral assemblages, but did not chemically interact with zircons, and their primary U-Pb and Pb-Pb ages were preserved.en
dc.description.sponsorshipNSF (EAR 8416575)en
dc.description.sponsorshipDOE (Division of Basic Energy Research, Contract DE-FGO5-88-ER13951)en
dc.identifier.citationDavid M. Wayne and A. Krishna Sinha. "Stability of Zircon U-Pb Systematics in a Greenschist-Grade Mylonite: An Example from the Rockfish Valley Fault Zone, Central Virginia, USA," The Journal of Geology, Vol. 100, No. 5 (Sep., 1992), pp. 593-603. http://www.jstor.org/stable/30068531en
dc.identifier.issn0022-1376en
dc.identifier.urihttp://hdl.handle.net/10919/49142en
dc.identifier.urlhttp://www.jstor.org/stable/30068531en
dc.language.isoen_USen
dc.publisherUniversity of Chicago Pressen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectblue ridgeen
dc.subjectrocksen
dc.subjectcrystallineen
dc.subjectdeformationen
dc.subjectmineralsen
dc.subjectmodelen
dc.subjectageen
dc.subjectgeologyen
dc.titleStability of zircon u-pb systematics in a greenschist-grade mylonite - an example from the rockfish valley fault zone, central Virginia, USAen
dc.title.serialJournal of Geologyen
dc.typeArticle - Refereeden

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