The Petrology and Origin of the Tertiary Lundy Granite (Bristol Channel, UK)

Thorpe, R. S.; Tindle, A. G.; Gledhill, A.R

doi:10.1093/petrology/31.6.1379

Cited by 26 publications

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“…Sample LUN 69 has the highest Eu anomaly of the analysed trachyte/rhyolite samples with Eu/Eu* = 0.18. Although the REE pattern resembles that in the Lundy granites (Thorpe et al 1990; Figure 5) the Zr concentrations (294, 371 ppm) are much higher than those of the granite samples (Zr = ~4 0 -8 0 ppm; Thorpe et u/. 1990).…”

Section: Geochemistrymentioning

confidence: 76%

“…There is no isotopic reason to propose contamination by Archaean (Lewisian) or other younger Proterozoic crustal rocks that have been suggested to characterize the lower crust below southern Britain (Thorpe et al 1984(Thorpe et al , 1990Hampton and Taylor 1983 Figure 7 shows enrichment of the stable incompatible element Th by a factor of about five (i.e. up to = 80% fractional crystallization) with depletions of trace elements representing fractionation of plagioclase (Sr), apatite (P) and Fe-Ti oxide (Ti).…”

Section: A Doleritesmentioning

confidence: 99%

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Petrology and petrogenesis of a tertiary bimodal dolerite‐peralkaline/subalkaline trachyte/rhyolite dyke association from Lundy, Bristol Channel, UK

Thorpe

Tindle

1992

Geological Journal

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The island of Lundy forms the southernmost igneous complex of the British Tertiary Volcanic Province (BTVP) and consists of granite ( = 90%)) emplaced into deformed Devonian sedimentary rocks (Pilton Shale) and associated with a swarm of dykes of doleriteibasalt, minor trachyte and rhyolite composition. The dolerites are of varied olivine basalt composition and are associated with peralkaline trachyte and subalkalineiperalkaline rhyolite with alkali feldspar and quartz f alkali amphibole f pyroxene mineralogy. The dyke swarm is therefore an anorogenic bimodal doleritei basalt--trachyte/rhyolitc BTVP association. Although the dyke association is bimodal in major element terms between doleriteibasalt and minor trachyteirhyolite, the mineralogy and trace element geochemistry indicate that the dykes may be regarded as a cogenetic dolerite-peralkaline trachyteirhyolite association with minor subalkaline rhyolites.Sr and Nd isotope data indicate derivation of these magmas from a similar BTVP mantle source (with or without minor contamination by Pilton Shale, or possibly Lundy granite).The petrogenesis of the Lundy dyke association is therefore interpreted in terms of extensive fractional crystallization of basaltic magma in a magma chamber of complex geometry below the (exposed) Lundy granite. Fractional crystallization of a representative dolerite magma (olivine f clinopyroxene k plagioclase) yields trachyte magma from which the crystallization of alkali feldspar (anorthoclase) & plagioclase (oligoclase) + Fe-Ti oxide + apatite results in peralkaline rhyolite. Rarer subalkaline rhyolites result from fractionation from a similar dolerite source which did not achieve a peralkaline composition so allowing the crystallization and fractionation of zircon. The basalt-(minor trachyte)/rhyolite bimodality reflects rapid crystallization of basalt magma to trachyte (and rhyolite) over a relatively small temperature interval (mass fraction of melt, F = t 0 . 1 5 ) . The rapid high level emplacement of basalt, trachyte and rhyolite dyke magmas is likely to have been associated with the development of a substantial composite bimodal basalt--(minor trachyte)/rhyolite volcano above the BTVP Lundy granite in the Bristol Channel.

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Section: Geochemistrymentioning

confidence: 76%

Section: A Doleritesmentioning

confidence: 99%

Petrology and petrogenesis of a tertiary bimodal dolerite‐peralkaline/subalkaline trachyte/rhyolite dyke association from Lundy, Bristol Channel, UK

Thorpe

Tindle

1992

Geological Journal

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“…It has been suggested that intrusion of the Lundy Granite at the end of the Mid-Paleocene (58.7 ± 1.6 Ma; Thorpe et al 1990) Carlingford (61.4 ± 0.8 Ma) intrusive complexes (dates from Gamble et al 1999;Mitchell et al 1999) are located on the NNW-trending fault zone, south of Lough Neagh, that controlled the development of the Lough Neagh pull-apart (Fig. 3).…”

Section: Discussionmentioning

confidence: 99%

Lough Neagh: the site of a Cenozoic pull-apart basin

Quinn

2006

SJG

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SynopsisThe Lough Neagh Basin in Northern Ireland is the site of a Cenozoic depocentre defined by gravity measurements and a thick succession of Paleocene basaltic lavas and Upper Oligocene clays. Much of the Cenozoic outcrop is concealed by Lough Neagh, but the rhombic outline of the lough provides some indication of the underlying structural control of the depocentre. Several authors have inferred that a Cenozoic pull-apart basin lies within the Lough Neagh area and suggest it is one of a number of transtensional basins, including the Bovey and Petrockstow basins in SW England, associated with NW to NNW-trending strike-slip fault zones. Solid geology maps and gravity data show that the structure of the Lough Neagh Basin is dominated by a segmented, orthogonal pattern of offset NNW and NE-trending faults. It is proposed that pull-apart basin formation took place in the Mid-Paleocene by dextral movement on these offset faults. The potential link between strike-slip tectonics and Cenozoic volcanism in the north of Ireland is briefly considered.

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“…Meighan 1979, Meighan et al 1984, Thorpe et al 1990), although it must be noted that Stone (1988Stone ( , 1990) assigns general S-type status to the Lundy intrusions. The paucity of published isotopic data factor (Table 3) is particularly serious for parts of this sector, especially for O. Recognising this and the importance of information for several isotopic systems, new data for Arran (O) and northeastern Ireland (O, Nd, Sr) are summarised and discussed in relation to the northern sector.…”

Section: New Isotopic Data For the S Sector Of The Btipmentioning

confidence: 99%

“…Sr-Nd-Pb) has been particularly revealing, but unfortunately there is a gross geographic imbalance here: for Skye (Table 3) there is a profusion of data (Sr, Pb, Nd, O, H, C and recently (Dickin et al 1987) Ce isotopic ratios) for the Table 3 Published isotopic coverage for some BTIP central complexes and the isotopic ranges for its granites. There are no published U-Pb zircon studies Data sources: Harrison et al (1987) for Ailsa Craig, Harding et al (1984) for St Kilda, Thorpe et al (1990) for Lundy, this study and numerous others cited in the references. on July 5, 2015 specialpapers.gsapubs.org Downloaded from acid and basic rocks.…”

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confidence: 99%

Anorogenic granite magma genesis: new isotopic data for the southern sector of the British Tertiary Igneous Province

Meighan

Fallick²,

McCormick³

1992

Geological Society of America Special Papers

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It is now generally accepted that British Tertiary granites contain crustal and mantle components. Genesis principally by differentiation of crustally contaminated basaltic magmas is widely held and silicic melts with some remarkable trace element similarities were generated within different upper crust along the St Kilda/Skye -Carlingford zone.New whole-rock (and mineral) O isotope data for the southern sector of the province (N Arran, Ailsa Craig, Mourne Mountains, Slieve Gullion, etc) reveal that <5 18 0 lies in the range +5-1 to -i-9-7%o for most of the analysed granites, meteoric water-rock interaction having been in general less intensive than at Skye and Mull. Nevertheless, highly '"O-depleted country rocks (with ¿ IK O < 0) exist adjacent to the N Arran and Mourne Mountains granite plutons. There is as yet no evidence for the existence of low -18 0 granitic melts in this southern sector where magmatic <5 ls O compositions (up to c. +9-5%o) can be inferred for some of the intrusions.New Nd (and Sr) isotope data indicate that although there is some similarity in initial 87 Sr/ 86 Sr ratios between the northern and southern sector granites, in northeastern Ireland initial e Nd values for the analysed Tertiary acid major intrusions range from -3-9 to -4-5. This is in marked contrast to the Skye granites, some of which have values below -20, reflecting the involvement of different lithosphere.

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The Petrology and Origin of the Tertiary Lundy Granite (Bristol Channel, UK)

Cited by 26 publications

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Petrology and petrogenesis of a tertiary bimodal dolerite‐peralkaline/subalkaline trachyte/rhyolite dyke association from Lundy, Bristol Channel, UK

Petrology and petrogenesis of a tertiary bimodal dolerite‐peralkaline/subalkaline trachyte/rhyolite dyke association from Lundy, Bristol Channel, UK

Lough Neagh: the site of a Cenozoic pull-apart basin

Anorogenic granite magma genesis: new isotopic data for the southern sector of the British Tertiary Igneous Province

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