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Structural characteristics and Re–Os dating of quartz-pyrite veins in the Lewisian Gneiss Complex, NW Scotland : evidence of an Early Paleoproterozoic hydrothermal regime during terrane amalgamation.

Vernon, R. and Holdsworth, R.E. and Selby, D. and Dempsey, E. and Finlay, A.J. and Fallick, A.E. (2014) 'Structural characteristics and Re–Os dating of quartz-pyrite veins in the Lewisian Gneiss Complex, NW Scotland : evidence of an Early Paleoproterozoic hydrothermal regime during terrane amalgamation.', Precambrian research., 246 . pp. 256-267.

Abstract

In the Archaean basement rocks of the Assynt and Gruinard terranes of the mainland Lewisian Complex in NW Scotland, a regional suite of quartz-pyrite veins cross-cut regional Palaeoproterozoic (Badcallian, ca. 2700 Ma; Inverian, ca. 2480 Ma) fabrics and associated Scourie dykes. The quartz veins are overprinted by amphibolite-greenschist facies Laxfordian deformation fabrics (ca. 1760 Ma) and later brittle faults. The hydrothermal mineral veins comprise a multimodal system of tensile/hybrid hydraulic fractures which are inferred to have formed during a regional phase of NW-SE extension. The almost orthogonal orientation of the quartz veins (NE-SW) to the Scourie dykes (NW-SE) are incompatible and must result from distinct paleostress regimes suggesting they are related to different tectonic events. This hypothesis is supported by Rhenium–Osmium dating of pyrite that yields an age of 2249 ± 77 Ma, placing the vein-hosted mineralisation event after the oldest published dates for the Scourie Dykes (2420 Ma), but before the youngest ages (1990 Ma). Sulphur isotope analysis suggests that the sulphur associated with the pyrite is isotopically indistinguishable from primitive mantle. The presence of the ca. 2250 Ma quartz-pyrite veins in both the Assynt and Gruinard terranes confirms that these crustal units were amalgamated during or prior to Inverian deformation. The absence of the veins in the Rhiconich Terrane is consistent with the suggestion that it was not finally amalgamated to the Assynt Terrane until the Laxfordian.

Item Type:Article
Keywords:Re–Os geochronology, Lewisian Complex, Palaeoproterozoic, Quartz-pyrite veins, Scourie dykes, Terranes.
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1016/j.precamres.2014.03.007
Publisher statement:NOTICE: this is the author’s version of a work that was accepted for publication in Precambrian Research,. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Precambrian Research, 246, June 2014, 10.1016/j.precamres.2014.03.007.
Date accepted:13 March 2014
Date deposited:12 January 2015
Date of first online publication:21 March 2014
Date first made open access:No date available

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