Deciphering multiple Mesoproterozoic and Paleozoic events recorded in zircon and titanite from the Baltimore Gneiss, Maryland: SEM imaging, SHRIMP U-Pb geochronology, and EMP analysis

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dc.contributor.authorAleinikoff, John N.
dc.contributor.authorHorton, J W
dc.contributor.authorDrake, Avery Ala
dc.contributor.authorWintsch, R P
dc.contributor.authorFanning, Christopher
dc.contributor.authorKeewook, Yi
dc.date.accessioned2015-12-13T23:08:01Z
dc.date.available2015-12-13T23:08:01Z
dc.date.issued2004
dc.date.updated2016-02-24T09:47:31Z
dc.description.abstractThe Baltimore Gneiss, exposed in antiforms in the eastern Maryland Piedmont, consists of a suite of felsic and mafic gneisses of Mesoproterozoic age. Zircons from the felsic gneisses are complexly zoned, as shown in cathodoluminescence imaging; most zircon grains have multiple overgrowth zones, some of which are adjacent and parallel to elongate cores. Sensitive high-resolution ion microprobe (SHRIMP) analyses of oscillatory-zoned cores indicate that the volcanic protoliths of the felsic gneisses crystallized at ca. 1.25 Ga. These rocks were subsequently affected by at least three Mesoproterozoic growth events, at ca. 1.22, 1.16, and 1.02 Ga. Foliated biotite granite intruded the Baltimore Gneiss metavolcanic sequence at ca. 1075 Ma. The Slaughterhouse Granite (renamed herein) also is Mesoproterozoic, but extremely discordant U-Pb data from high-U, metamict zircons preclude calculating a precise age. The 1.25 Ga rocks of the Baltimore Gneiss are coeval with rocks emplaced in the Grenville Province during the Elzevirian orogeny, and the 1.22 Ga zircon overgrowths are coincident with a later stage of this event. Younger zircon overgrowths formed during the Ottawan phase of the Grenville orogeny. Backscattered electron imaging of titanites from felsic gneisses and foliated biotite granite reveals that many of the grains contain cores, intermediate mantles, and rims. Electron microprobe traverses across zoned grains show regular variations in composition. SHRIMP ages for titanite from the foliated biotite granite are 374 ± 8, 336 ± 8, and 301 ± 12 Ma. The ca. 374 Ma age suggests growth of titanite during a thermal event following the Acadian orogeny, whereas the late Paleozoic titanite growth ages may be due to greenschist-facies replacement reactions associated with Alleghanian metamorphism and deformation.
dc.identifier.isbn0813711975
dc.identifier.urihttp://hdl.handle.net/1885/86469
dc.publisherGeological Society of America Inc
dc.relation.ispartofProterozoic tectonic evolution of the Grenville orogen in North America
dc.relation.isversionof1st Edition
dc.subjectKeywords: Baltimore Gneiss; Grenville; SHRIMP U-Pb geochronology; Titanite; Zircon
dc.titleDeciphering multiple Mesoproterozoic and Paleozoic events recorded in zircon and titanite from the Baltimore Gneiss, Maryland: SEM imaging, SHRIMP U-Pb geochronology, and EMP analysis
dc.typeBook chapter
local.bibliographicCitation.lastpage434
local.bibliographicCitation.placeofpublicationBoulder, Colorado
local.bibliographicCitation.startpage411
local.contributor.affiliationAleinikoff, John N., US Geological Survey
local.contributor.affiliationHorton, J W, US Geological Survey
local.contributor.affiliationDrake, Avery Ala, US Geological Survey
local.contributor.affiliationWintsch, R P, Indiana University
local.contributor.affiliationFanning, Christopher, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationKeewook, Yi, Korea Institute of Geology, Mining & Materials
local.contributor.authoremailu4029993@anu.edu.au
local.contributor.authoruidFanning, Christopher, u4029993
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.absfor040304 - Igneous and Metamorphic Petrology
local.identifier.ariespublicationMigratedxPub15362
local.identifier.doi10.1130/0-8137-1197-5.411
local.identifier.scopusID2-s2.0-77957017278
local.identifier.uidSubmittedByMigrated
local.type.statusPublished Version

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