Does the Meguma Terrane Extend into SW England?

Nance, R. Damian; Neace, Erika R.; Braid, James A.; Murphy, J. Brendan; Dupuis, Nicolle E.; Shail, RK

doi:10.12789/geocanj.2014.41.056

Cited by 22 publications

(12 citation statements)

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“…For a comprehensive review of peri-Gondwanan terranes, the reader is referred to Nance et al (2008). The correlation of the Meguma terrane to the Harlech Dome has been discussed by Waldron et al (2011), White et al (2012) and Nance et al (2015). Todd et al 1991).…”

Section: Regional Geology and Review Of Terranes In The British Islesmentioning

confidence: 99%

The provenance of the Devonian Old Red Sandstone of the Dingle Peninsula, SW Ireland; the earliest record of Laurentian and peri-Gondwanan sediment mixing in Ireland

Fairey

Kerrison

Meere

et al. 2018

JGS

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The Lower Old Red Sandstone in southern Ireland is hosted in the Early Devonian Dingle Basin, which lies immediately south of the Iapetus Suture on the Dingle Peninsula, County Kerry. The basin developed as a post-Caledonian pullapart structure prior to Acadian deformation, which in turn was followed by end-Carboniferous Variscan deformation. Detrital zircon U-Th-Pb geochronology is complemented by mica Ar-Ar and apatite U-Pb geochronology to gain a comprehensive understanding of the provenance of the Lower Devonian Lower Old Red Sandstone of the Dingle Basin and assess contributions of major tectonic components (e.g. Laurentia, Ganderia). Sedimentary rocks in the Lower Old Red Sandstone have similar detrital zircon age distributions, which are dominated by c. 1.2 Ga zircons as well as late Neoproterozoic grains. This indicates a dominant contribution of detritus of Laurentian affinity as well as contributions from westerly and southerly derived Ganderian detritus. Caledonian uplift of the area north of the Iapetus Suture would have facilitated a large contribution of (peri-)Laurentian material. The Upper Old Red Sandstone on the Dingle Peninsula has a distinctly different detrital zircon character including few late Neoproterozoic zircons and abundant zircons of c. 1.05 Ga age, indicating sediment derivation only from Laurentia and no recycling from the Lower Old Red Sandstone.

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Section: Regional Geology and Review Of Terranes In The British Islesmentioning

confidence: 99%

The provenance of the Devonian Old Red Sandstone of the Dingle Peninsula, SW Ireland; the earliest record of Laurentian and peri-Gondwanan sediment mixing in Ireland

Fairey

Kerrison

Meere

et al. 2018

JGS

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“…Since pre-Devonian basement is not exposed in SW England, it is not possible to identify a correlative high-grade greywacke-pelite source for major and trace element modelling of partial melting and differentiation. The greywacke sandstones of the upper plate-derived peri-Gondwanan Gramscatho Group were used as a compositional proxy (Floyd and Leveridge, 1987;Scott et al, 2003;Nance et al, 2015). The original source comprised 45% quartz, 35% plagioclase, 13% biotite, 3% garnet, 2% alkali feldspar, 1% muscovite and 1% aluminosilicates which lies within the compositional constraints for the Gramscatho Formation (Floyd and Leveridge, 1987) and greywacke material (e.g.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

Simons

Shail

Andersen

2016

Lithos

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The Early Permian Cornubian Batholith was generated during an extensional regime following Variscan convergence within the Rhenohercynian Zone of SW England. Its component granites can be classified, using mineralogical, textural and geochemical criteria, into five main types, all of which are peraluminous (A/CNK >1.1): G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz). G1 granites formed through up to 20% muscovite and minor biotite dehydration melting of a metagreywacke source at moderate temperatures and pressures (731-806°C, >5 kbar). Younger G3 granites formed through higher temperature, lower pressure (768-847°C, <4 kbar) biotite-dominated melting of a similar source. Partial melting was strongly influenced by the progressive lower-mid crustal emplacement of mafic igneous rocks during post-Variscan extension and a minor (<5-10%) mantle-derived component in the granites is possible. Two distinct fractionation series, G1-G2 and G3-G4, are defined using whole rock geochemical and mineral chemical data.Variations in the major elements, Ba, Sr and Rb indicate that G1 and G3 granites underwent 15-30% fractionation of an assemblage dominated by plagioclase, alkali feldspar and biotite to form, more evolved G2 and G4 granites respectively. Decreasing whole rock abundances of Zr, Th and REE support fractionation of zircon, monazite, apatite and allanite. Subsolidus alteration in G2 and G4 granites is indicated by non-primary muscovite and tourmaline and modification of major and trace element trends for G3-G4 granites, particularly for P 2 O 5 and Rb. Topaz (G5) granites show low Zr, REE and extreme enrichment in Rb (up to 1530 ppm) and Nb (79 ppm) that cannot be related in a straightforward manner to continued differentiation of the G1-G2 or G3-G4 series. Instead, they are considered to represent partial melting, mediated by granulite facies fluids, of a biotite-rich restite following extraction of

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“…However, there are several indirect lines of evidence that indicate, whilst SW England basement is of peri-Gondwanan provenance (e.g. Cocks & Torsvik 2006), it might not be exclusively Avalonian: (1) εNd values for SW England granites are rather more negative than those for typical Avalonian basement, overlapping with values for Armorica/Saxothuringia (Shail and Leveridge 2009); (2) εNd isotopic signatures of Devonian sedimentary rocks in southern SW England, the South Portuguese Zone and the isotopically more juvenile plutons they host, are similar to those for the Meguma terrane in Nova Scotia (Nance et al 2015); (3) Sr and Nd isotopic compositions of Early Permian lamprophyres and basalts change between northern and southern SW England, approximately corresponding to the southern margin of the Culm Basin; this has been interpreted as the trace of a pre-Devonian terrane boundary, between Avalonia and Armorica, in the lithospheric mantle (Dijkstra & Hatch 2018). In addition, northerly dipping reflectors, tentatively classified as 'Caledonian', have been recognized in the lower crust and mantle below SW England (Bois et al 1990;.…”

Section: Pre-devonian Basementmentioning

confidence: 96%

Late Paleozoic extensional reactivation of the Rheic–Rhenohercynian suture zone in SW England, the English Channel and Western Approaches

Alexander¹,

Shail

Leveridge³

2019

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The Rheic Ocean is a persistent feature of Paleozoic palaeogeographies whose closure contributed to the development of the Variscan orogen and formation of Pangaea. Geological and geophysical data indicate repeated episodes of Paleozoic rifting and plate convergence around SW England and the adjacent offshore areas. SW England occupied a lower plate position during the Devonian-Carboniferous, on the northern passive margin of the short-lived Rhenohercynian Ocean that had formed near a recently closed segment of the Rheic Ocean. Variscan plate convergence resulted in the development of the composite southwardsdipping Rheic-Rhenohercynian suture zone by the latest Devonian and inversion of the lower plate basins during the Carboniferous. Early Permian NNW-SSE extensional reactivation of this suture zone controlled the development of the Western Approaches Basins in its hangingwall and provides an excellent example of Wilson Cycle structural inheritance. The onshore expression of this episode includes shear zones and detachment faults consistent with top-to-the SSE extensional reactivation of Variscan thrust faults. There is a progression to higher-angle brittle extensional faults that cutout earlier structures. Exhumation of the lower plate was accompanied by Early Permian mantle and concomitant crustal partial melting, the construction of the Cornubian Batholith, and W-Sn-Cu fracture-hosted mineralisation.

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Does the Meguma Terrane Extend into SW England?

Cited by 22 publications

References 100 publications

The provenance of the Devonian Old Red Sandstone of the Dingle Peninsula, SW Ireland; the earliest record of Laurentian and peri-Gondwanan sediment mixing in Ireland

The provenance of the Devonian Old Red Sandstone of the Dingle Peninsula, SW Ireland; the earliest record of Laurentian and peri-Gondwanan sediment mixing in Ireland

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

Late Paleozoic extensional reactivation of the Rheic–Rhenohercynian suture zone in SW England, the English Channel and Western Approaches

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