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TitleThe age of Salinic deformation constrained by 40Ar/39Ar dating of multiple cleavage domains: Bathurst Supergroup, New Brunswick Appalachians
AuthorKellett, D AORCID logo; van Staal, C; Wilson, R A; Rogers, N
SourceAmerican Journal of Science vol. 317, 2017 p. 338-368,
Alt SeriesEarth Sciences Sector, Contribution Series 20160060
PublisherAmerican Journal of Science (AJS)
Mediapaper; on-line; digital
File formatpdf
ProvinceNew Brunswick
NTS21A; 21B; 21G; 21H; 21I; 21J; 21O; 21P
Lat/Long WENS -68.0000 -64.0000 48.0000 44.0000
Subjectsgeochemistry; geochronology; igneous and metamorphic petrology; mineralogy; structural geology; tectonics; orogenies; orogenesis; deformation; felsic volcanic rocks; tectonic evolution; argon argon dates; argon argon dating; mica; plutons; mafic volcanic rocks; Phanerozoic; Paleozoic; Devonian; Silurian; Ordovician; Cambrian; Precambrian; Proterozoic
Illustrationslocation maps; geological sketch maps; photographs; stratigraphic columns; tables; photomicrographs; graphs
ProgramTargeted Geoscience Initiative (TGI-4) Volcanogenic Massive Sulfide Ore Systems
Released2017 04 11
AbstractIn the New Brunswick Appalachians, polydeformed felsic volcanic rocks of the Bathurst Supergroup record four cleavage-forming tectonic events, of which D1 and D2 record subduction-related underplating of buoyant elements of the Tetagouche backarc basin and subsequent collision between composite Laurentia and the Gander margin, respectively, during the Salinic orogenic cycle. Here we present an integrated approach to dating multiple cleavage domains in which we performed step heat 40Ar/39Ar analyses, microstructural observations and mineral-chemistry analysis on a suite of samples, as well as in situ 40Ar/39Ar analysis on two samples from the suite with clear S1 and S2 cleavage relationships. We use this dataset to characterize the complex relationships between S1 and S2 white mica between samples at different structural settings across the supergroup. We refine the timing of S1 white mica growth, and hence M1-D1 of the Salinic cycle in the Bathurst Supergroup to ca. 452 to 437 Ma, and S2 white mica growth (also D2) to ca. 427 to 418 Ma. New and published data indicate local thermal resetting of white mica at ca. 411 Ma, which we interpret to indicate a buried intrusion, likely a component of the Central plutonic belt. Delineation of the two white mica age components, particularly within a single sample, was informed by both spatially-controlled analysis (in situ 40Ar/39Ar), and the higher age precision of step heat 40Ar/39Ar analyses.
Summary(Plain Language Summary, not published)
Rocks involved in plate collisions can record multiple episodes of deformation. If the rocks do not experience too high temperatures (e.g. <400 C), they may preserve new platy minerals such as white mica grown during each deformation episode. White mica is a particularly useful mineral as it can be dated using a method called 40Ar/39Ar geochronology. However, it is difficult to separate out white mica from different deformation episodes in a single rock, and mixed, meaningless age data may be the result. Here we integrate two types of Ar/Ar geochronology, one with high age precision and one with high spatial precision, to obtain ages for two deformation events in the Bathurst Supergroup, rocks which host the Bathurst Mining camp massive sulphide deposits. We show the value of combining both methods and incorporating complementary microstructural observations and mineral chemistry. We use our results to refine the timing of deformation episodes 1 and 2 of the Salinic orogeny in New Brunswick.

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