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Evidence for a late Cambrian juvenile arc and a buried suture within the Laurentian Caledonides of Scotland: Comparisons with hyperextended Iapetan margins in the Appalachian Mountains (North America) and Norway
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2019 (English)In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 47, no 8, p. 734-738Article in journal (Refereed) Published
Abstract [en]

Uranium-lead (U-Pb) zircon dating establishes a late Cambrian (Drumian) protolith age of 503 ± 2 Ma for a trondhjemitic gneiss of the calc-alkaline Strathy Complex, northern Scottish Caledonides. Positive εHf and εNd values from trondhjemitic gneisses and co-magmatic amphibolites, respectively, and an absence of any inheritance in zircon populations support published geochemistry that indicates a juvenile origin distal from Laurentia. In order to account for its present location within a stack of Laurentia-derived thrust sheets, we interpret the complex as allochthonous and located along a buried suture. We propose that a microcontinental ribbon was detached from Laurentia during late Neoproterozoic to Cambrian rifting; the intervening oceanic tract closed by subduction during the late Cambrian and formed a juvenile arc, the protolith of the Strathy Complex. The microcontinental ribbon was reattached to Laurentia during the Grampian orogeny, which transported the Strathy Complex as a tectonic slice within a nappe stack. Peak metamorphic conditions for the Strathy Complex arc (650–700 °C, 0.6–0.75 GPa) are intermediate in pressure between those published previously for Grampian mineral assemblages in structurally overlying low-pressure migmatites (670–750 °C, <0.4 GPa) that we deduce to have been derived from an adjacent backarc basin, and structurally underlying upper amphibolite rocks (650–700 °C, 1.1–1.2 GPa) that we interpret to represent the partially subducted Laurentian margin. This scenario compares with that of the northern Appalachian Mountains and Norway where microcontinental blocks are interpreted to have their origins in detachment from passive margins of the Iapetus Ocean during Cambrian rifting and to have been re-amalgamated during Caledonian orogenesis.

Place, publisher, year, edition, pages
2019. Vol. 47, no 8, p. 734-738
National Category
Geology
Research subject
The changing Earth
Identifiers
URN: urn:nbn:se:nrm:diva-3589DOI: 10.1130/G46180.1OAI: oai:DiVA.org:nrm-3589DiVA, id: diva2:1375502
Conference
12/5/2019
Available from: 2019-12-05 Created: 2019-12-05 Last updated: 2019-12-06Bibliographically approved

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Publisher's full texthttps://doi.org/10.1130/G46180.1

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