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Episodic arc-ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny

Episodic arc-ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny
Episodic arc-ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny
In order to understand the progressive growth of continental margins and the evolution of continental crust, we must first understand the formation of allochthonous ophiolitic and island-arc terranes within ancient orogens and the nature of their accretion. During the early Paleozoic closure of the Iapetus Ocean, diverse sets of arc terranes, oceanic tracts, and ribbon-shaped microcontinental blocks were accreted to the passive continental margin of Laurentia during the Grampian-Taconic orogeny. In the northern Appalachians in central Newfoundland, Canada, three distinct phases of arc-ophiolite accretion have been recognized. New field mapping, high-resolution airborne geophysics, whole-rock and Nd-isotope geochemistry, and U-Pb zircon geochronology within the Tyrone Volcanic Group of Northern Ireland have allowed all three episodes to now be correlated into the British and Irish Caledonides. The Tyrone Volcanic Group (ca. 475–469 Ma) is characterized by mafic to intermediate lavas, tuffs, rhyolite, banded chert, ferruginous jasperoid, and argillaceous sedimentary rocks cut by numerous high-level intrusive rocks. Geochemical signatures are consistent with formation within an evolving peri-Laurentian island-arc/backarc, which underwent several episodes of intra-arc rifting prior to its accretion at ca. 470 Ma to an outboard peri-Laurentian microcontinental block. Outriding microcontinental blocks played a fundamental role within the orogen, explaining the range of ages for Iapetan ophiolites and the timing of their accretion, as well as discrepancies between the timing of ophiolite emplacement and the termination of the Laurentian Cambrian–Ordovician shelf sequences. Accretion of the Tyrone arc and its associated suprasubduction-zone ophiolite represents the third stage of arc-ophiolite emplacement to the Laurentian margin during the Grampian-Taconic orogeny in the British and Irish Caledonides.
0016-7606
1702-1723
Hollis, Stephen P.
8b432927-f15a-469c-979b-4b98714b4b5e
Roberts, Stephen
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Cooper, Mark R.
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Earls, Garth
2cbfc172-8668-4180-8950-e2fbd27df51e
Herrington, Richard
6466a9c1-3e23-40a4-a1e5-a5ce15f5a43d
Condon, Daniel J.
badc146b-cda6-444a-866b-1d78a0e12ad9
Cooper, Matthew J.
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Archibald, Sandy M.
f8079c8d-15a4-44ad-b951-48300d4c24e1
Piercey, Stephen J.
f7f07830-ee80-4158-8438-799e38795f78
Hollis, Stephen P.
8b432927-f15a-469c-979b-4b98714b4b5e
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
Cooper, Mark R.
68d782fa-c882-41e0-a21e-b1a88bf34f99
Earls, Garth
2cbfc172-8668-4180-8950-e2fbd27df51e
Herrington, Richard
6466a9c1-3e23-40a4-a1e5-a5ce15f5a43d
Condon, Daniel J.
badc146b-cda6-444a-866b-1d78a0e12ad9
Cooper, Matthew J.
54f7bff0-1f8c-4835-8358-71eef8529e7a
Archibald, Sandy M.
f8079c8d-15a4-44ad-b951-48300d4c24e1
Piercey, Stephen J.
f7f07830-ee80-4158-8438-799e38795f78

Hollis, Stephen P., Roberts, Stephen, Cooper, Mark R., Earls, Garth, Herrington, Richard, Condon, Daniel J., Cooper, Matthew J., Archibald, Sandy M. and Piercey, Stephen J. (2012) Episodic arc-ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny. Geological Society of America Bulletin, 124 (11-12), 1702-1723. (doi:10.1130/B30619.1).

Record type: Article

Abstract

In order to understand the progressive growth of continental margins and the evolution of continental crust, we must first understand the formation of allochthonous ophiolitic and island-arc terranes within ancient orogens and the nature of their accretion. During the early Paleozoic closure of the Iapetus Ocean, diverse sets of arc terranes, oceanic tracts, and ribbon-shaped microcontinental blocks were accreted to the passive continental margin of Laurentia during the Grampian-Taconic orogeny. In the northern Appalachians in central Newfoundland, Canada, three distinct phases of arc-ophiolite accretion have been recognized. New field mapping, high-resolution airborne geophysics, whole-rock and Nd-isotope geochemistry, and U-Pb zircon geochronology within the Tyrone Volcanic Group of Northern Ireland have allowed all three episodes to now be correlated into the British and Irish Caledonides. The Tyrone Volcanic Group (ca. 475–469 Ma) is characterized by mafic to intermediate lavas, tuffs, rhyolite, banded chert, ferruginous jasperoid, and argillaceous sedimentary rocks cut by numerous high-level intrusive rocks. Geochemical signatures are consistent with formation within an evolving peri-Laurentian island-arc/backarc, which underwent several episodes of intra-arc rifting prior to its accretion at ca. 470 Ma to an outboard peri-Laurentian microcontinental block. Outriding microcontinental blocks played a fundamental role within the orogen, explaining the range of ages for Iapetan ophiolites and the timing of their accretion, as well as discrepancies between the timing of ophiolite emplacement and the termination of the Laurentian Cambrian–Ordovician shelf sequences. Accretion of the Tyrone arc and its associated suprasubduction-zone ophiolite represents the third stage of arc-ophiolite emplacement to the Laurentian margin during the Grampian-Taconic orogeny in the British and Irish Caledonides.

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More information

Published date: November 2012
Organisations: Geology & Geophysics, Geochemistry

Identifiers

Local EPrints ID: 345448
URI: http://eprints.soton.ac.uk/id/eprint/345448
ISSN: 0016-7606
PURE UUID: e0010224-f4e1-4b38-a4b4-6b4395ec2ee1
ORCID for Stephen Roberts: ORCID iD orcid.org/0000-0003-4755-6703
ORCID for Matthew J. Cooper: ORCID iD orcid.org/0000-0002-2130-2759

Catalogue record

Date deposited: 20 Nov 2012 15:27
Last modified: 26 Nov 2019 02:06

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