New U-Pb age constraints for the Laxford Shear Zone, NW Scotland: Evidence for tectono-magmatic processes associated with the formation of a Paleoproterozoic supercontinent

Goodenough, Kathryn; Crowley, Quentin; Krabbendam, Maarten; Parry, Sara

doi:10.1016/j.precamres.2013.04.010

Cited by 48 publications

(83 citation statements)

References 57 publications

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“…The Lewisian Gneiss Complex comprises mid-late Archaean tonalite-trondhjemite-granodiorite (TTG) gneisses, with minor mafic-ultramafic and metasedimentary components, that have been reworked by several Late Archaean and Palaeoproterozoic tectonic events (e.g., Bridgwater et al, 1973;Park & Tarny, 1987;Park, 1994;Park, 1995;Baba, 2002;Kinny et al, 2005a;Park, 2005;Goodenough et al, 2013).…”

Section: Palaeoproterozoic Lewisian Gneiss Complex Makes Up the Britimentioning

confidence: 99%

“…Goodenough et al, 2013 andreferences therein, andvan Gool et al, 2002) and Palaeoproterozoic extension and rifting forming the c. 2.4 Ga Scourie Dyke Swarm. Therefore, the lithospheric keel underlying Loch Roag and the wider Lewisian (NAC) of Scotland has experienced a series of tectono-magmatic and metasomatic events, some or all of which may have modified its 'sulphur-budget' (Hughes et al, 2016).…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

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Paradoxical co-existing base metal sulphides in the mantle: The multi-event record preserved in Loch Roag peridotite xenoliths, North Atlantic Craton

Hughes

McDonald

Loocke

et al. 2017

Lithos

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT AbstractThe role of the subcontinental lithospheric mantle as a source of precious metals for mafic magmas is contentious and, given the chalcophile (and siderophile) character of metals such as the platinumgroup elements (PGE), Se, Te, Re, Cu and Au, the mobility of these metals is intimately linked with that of sulphur. Hence the nature of the host phase(s), and their age and stability in the subcontinental lithospheric mantle may be of critical importance. We investigate the sulphide mineralogy and sulphide in situ trace element compositions in base metal sulphides (BMS) in a suite of spinel lherzolite mantle xenoliths from northwest Scotland (Loch Roag, Isle of Lewis). This area is situated on the margin of the North Atlantic Craton which has been overprinted by a Palaeoproterozoic orogenic belt, and occurs in a region which has undergone magmatic events from the Palaeoproterozoic to the Eocene.We identify two populations of co-existing BMS within a single spinel lherzolite xenolith (LR80) and which can also be recognised in the peridotite xenolith suite as a whole. Both populations consist of a mixture of Fe-Ni-Cu sulphide minerals, and we distinguished between these according to BMS texture, petrographic setting (i.e., location within the xenolith in terms of 'interstitial' or within feldspar-spinel symplectites, as demonstrated by X-ray Computed Microtomography) and in situ trace element composition. Group A BMS are coarse, metasomatic, have low concentrations of total PGE (< 40 ppm) and high (Re/Os) N (ranging 1 to 400). Group B BMS strictly occur within symplectites of spinel and feldspar, are finer-grained rounded droplets, with micron-scale PtS (cooperite), high overall total PGE concentrations (15-800 ppm) and low (Re/Os) N ranging 0.04 to 2. Group B BMS sometimes coexist with apatite, and both the Group B BMS and apatite can preserve rounded micron-scale Ca-carbonate inclusions indicative of sulphide-carbonate-phosphate immiscibility. This carbonate-phosphate metasomatic association appears to be important in forming PGE-rich sulphide liquids, although the precise mechanism for this remains obscure. As a consequence of their position within the symplectites, Group B BMS are particularly vulnerable to being incorporated in ascending A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTmantle-derived magmas (either by melting or physical entrainment). Based on the cross-cutting relationships of the symplectites, it is possible to in...

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Section: Palaeoproterozoic Lewisian Gneiss Complex Makes Up the Britimentioning

confidence: 99%

Section: Accepted M Manuscriptmentioning

confidence: 99%

Paradoxical co-existing base metal sulphides in the mantle: The multi-event record preserved in Loch Roag peridotite xenoliths, North Atlantic Craton

Hughes

McDonald

Loocke

et al. 2017

Lithos

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“…The oldest protoliths of the Lewisian Gneiss Complex may span the Paleo-, Meso-and Neo-Archean (Corfu et al, 1998;Friend and Kinny, Gondwana Research xxx (2014) 2001; Love et al, 2010;Goodenough et al, 2013). They have been variably affected by a Neo-Archean granulite event termed the Badcallian (Park, 1970) and two lower grade Paleoproterozoic events termed the Inverian (Evans, 1965) and Laxfordian (Sutton and Watson, 1950).…”

Section: Regional Geologymentioning

confidence: 99%

“…Moorbath et al, 1969;Hamilton et al, 1979;Rollinson and Windley, 1980;Whitehouse and Moorbath, 1986;Heaman and Tarney, 1989;Coward, 1990;Whitehouse and Bridgwater, 2001;Rollinson, 2012;Johnson et al, 2013). The Lewisian gneisses, are predominantly tonalite-trondhjemite-granodiorite (TTG) gneisses but also feature gneisses of sedimentary origin, metamorphosed ultramafic rocks, mafic dykes and alkali granitoids, all of which are variably deformed and metamorphosed (Tarney and Weaver, 1987;Goodenough et al, 2013;MacDonald et al, 2013). Collectively these lithologies form part of a now-fragmented Precambrian terrane in the North Atlantic, which includes basement rocks in Scandinavia, Greenland and North America (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Tectonothermal events, including formation of early granulites retrogressed during a later amphibolite facies event, recorded by the Lewisian gneisses are also found in many cratons worldwide Santosh et al, 2013;Jiang et al, 2013;Rekha et al, 2013;Verma and Verma, 2013) and appear to represent periods of significant crustal growth. Recent paleogeographic reconstructions have placed the North Atlantic Craton proximal to the Dharwar Craton of India in Paleoproterozoic times (Nilsson et al, 2013) and have linked Lewisian rocks to formation of the supercontinent Columbia (Baba, 2002;Goodenough et al, 2013). Understanding the geological evolution of the Lewisian Gneiss Complex exposed in NE Scotland therefore affects our understanding of a much broader geographic area and is pertinent to the study of global tectonic processes and crustal growth in Archean and Proterozoic times.…”

Section: Introductionmentioning

confidence: 99%

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High-precision U–Pb dating of complex zircon from the Lewisian Gneiss Complex of Scotland using an incremental CA-ID-TIMS approach

2015

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Metasomatism and the crystallization of zircon megacrysts in Archaean peridotites from the Lewisian complex, NW Scotland

Faithfull

Dempster

MacDonald

et al. 2018

Contrib Mineral Petrol

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Zircon megacrysts are locally abundant in 1–40 cm-thick orthopyroxenite veins within peridotite host rocks in the Archaean Lewisian gneiss complex from NW Scotland. The veins formed by metasomatic interaction between the ultramafic host and Si-rich melts are derived from partial melting of the adjacent granulite-facies orthogneisses. The interaction produced abundant orthopyroxene and, within the thicker veins, phlogopite, pargasite and feldspathic bearing assemblages. Two generations of zircon are present with up to 1 cm megacrystic zircon and a later smaller equant population located around the megacryst margins. Patterns of zoning, rare earth element abundance and oxygen isotopic compositions indicate that the megacrysts crystallized from crustal melts, whereas the equant zircon represents new neocryst growth and partial replacement of the megacryst zircon within the ultramafic host. Both zircon types have U–Pb ages of ca. 2464 Ma, broadly contemporaneous with granulite-facies events in the adjacent gneisses. Zircon megacrysts locally form > 10% of the assemblage and may be associated to zones of localized nucleation or physically concentrated during movement of the siliceous melts. Their unusual size is linked to the suppression of zircon nucleation and increased Zr solubility in the Si-undersaturated melts. The metasomatism between crustal melts and peridotite may represent an analog for processes in the mantle wedge above subducting slabs. As such, the crystallization of abundant zircon in ultramafic host rocks has implications for geochemistry of melts generated in the mantle and the widely reported depletion of high field strength elements in arc magmas.

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New U-Pb age constraints for the Laxford Shear Zone, NW Scotland: Evidence for tectono-magmatic processes associated with the formation of a Paleoproterozoic supercontinent

Abstract: 11The Lewisian Gneiss Complex in north-west Scotland is a part of the extensive network of

Cited by 48 publications

References 57 publications

Paradoxical co-existing base metal sulphides in the mantle: The multi-event record preserved in Loch Roag peridotite xenoliths, North Atlantic Craton

Paradoxical co-existing base metal sulphides in the mantle: The multi-event record preserved in Loch Roag peridotite xenoliths, North Atlantic Craton

High-precision U–Pb dating of complex zircon from the Lewisian Gneiss Complex of Scotland using an incremental CA-ID-TIMS approach

Metasomatism and the crystallization of zircon megacrysts in Archaean peridotites from the Lewisian complex, NW Scotland

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