The Genesis of the Cornubian Batholith (South-West England): the example of the Carnmenellis Pluton

Charoy, B.

doi:10.1093/petrology/27.3.571

Cited by 100 publications

(71 citation statements)

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“…The major and trace element geochemistry of the Cornubian granites has been fairly well established and this study is broadly in agreement with previous studies (e.g. Charoy, 1986;Stone, 1992;Manning et al, 1996;Stone, 2000;Chappell and Hine, 2006;Müller et al, 2006a) (Supplementary Table 2). …”

Section: Accepted M Manuscriptsupporting

confidence: 92%

“…Huang and Wyllie, 1981;Monier and Robert, 1986;Clarke, 1995). The current mineral assemblage of the granites must therefore correlate to reactions involving muscovite and cordierite for G1 and G3 granites respectively (see also Charoy, 1986;Villaseca et al, 2008). The presence of F and B within the granite melts shifts the system minimum towards lower temperatures where andalusite and white mica become…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

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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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Section: Accepted M Manuscriptsupporting

confidence: 92%

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 close similarity between biotite and host rock REE patterns in the Lundy samples compares with the similarities in the Carnmenellis (Charoy, 1986;Stone, 1987) and Isles of Scilly (Stone and Exley, 1989) samples, where both rock and biotite patterns mirror the accessory mineral patterns. Accessory minerals, mainly those included in biotite, were examined with the aid of a Philips 501B SEM fitted with a LINK Systems microanalyser.…”

Section: Comparison With Other Tertiary Granites and Cornubian Granitesmentioning

confidence: 58%

“…Similar source rocks to those envisaged for the Cornubian granites, such as a pelitic/semipelitic (greywacke) source that had retained incompatible elements and not been involved in an earlier fusion event might provide suitable source material. On the basis of REE modelling, Charoy (1986) concluded that the Carnmenellis granite magma in the Cornubian batholith could have been derived by c. 30% melting of Brioverian source rocks. Such a source for the Lundy granite is consistent with presently available isotope data (Hampton and Taylor, 1983), but <30% melting would give CeN/YbN ratios of c. 20 or more and would not produce any REE pattern from which the Lundy rocks could have evolved unless there was a major input of HREE, or total REE followed by marked LREE fractionation to give a flat pattern.…”

Section: Discussionmentioning

confidence: 99%

The Lundy granite: a geochemical and petrogenetic comparison with Hercynian and Tertiary granites

Stone

1990

Mineral. mag.

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New chemical data show that the two main granite types (G1 and G2) cannot be discriminated, but that microgranite sheets/dykes (G3) are significantly different and more evolved, largely as a result of biotite, accessory mineral, and plagioclase fractionation. The Lundy granite is similar to other Tertiary granites of Scotland and Ireland, in age, setting, possible high-temperature mineralogy, relationship to basic magmatism, and REE patterns. These features and a highly evolved chemistry suggest derivation from an unexposed more 'primitive' granite that, in turn, had a basaltic parentage. However, similarities with the nearby S-type Hercynian granites, such as high aluminium saturation index (and normative corundum), high trace alkali, Nb, and F contents, low Zr, and high initial Sr ratio suggest a significant crustal component. The problem is resolved by proposing either mixing of silicic magma derived by strong fractionation of basaltic magma with anatectic magma from a pelitic/semi-pelitic crustal source, or fractionation of basaltic magma heavily contaminated by assimilated crustal material. Both origins would yield the high REE contents and fiat REE patterns of a 'primitive' granite magma. Fractionation, perhaps of hornblende initially, and later, of biotite and accessory minerals together with feldspars, would produce the small volume of highly fractionated Lundy granite.

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“…Several lines of evidence indicate that evaporites may represent a significant B inventory for magmatic melt/fluid systems. For example, the high boron, lithium, and alkali concentrations of the Cornubian batholiths of SW England are compatible with source rocks of these granites containing non-marine evaporites (Charoy, 1986). Extremely high Cl/Br and Cl/I ratios and sulfate concentrations are reported for the magmatic fluids forming the quartz-fluorite veins in the granitic pluton at Capitan Mountains, New Mexico (Campbell et al, 1995).…”

Section: Disscusions On Possible Primary Boron Sources For the Granitementioning

confidence: 88%

Chemical and boron isotopic compositions of tourmaline from the Lavicky leucogranite, Czech Republic

et al. 2003

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Abundant tourmaline occurs in the Lavicky leucogranite, Czech Republic as spherical to ovoid quartztourmaline orbicules, typically 5 to 7 cm in diameter. The tourmalines also occur as fine-grained quartztourmaline veins (<1 cm thick) that cut the orbicule-rich granite. Electron microprobe analyses reveal that tourmaline from the quartz-tourmaline orbicules is Fe-rich schorl with a range of Fe/(Fe+Mg) ratio 0.62 to 0.77 and Na/(Na+Ca) ratio 0.82 to 0.95. In contrast, tourmaline from quartz-tourmaline veins is Mg-rich dravite with a range of Fe/(Fe+Mg) ratio 0.23 to 0.45 and Na/(Na+Ca) ratio 0.67 to 0.90. Very low δ 11 B values of -37.3 to -32.1‰ are found in the tourmalines from the orbicules, whereas tourmalines from the veins display relatively higher δ 11 B values of -28.2 to -21.3‰. The overall large δ 11 B variation is suggested to reflect mixing of different boron sources and boron isotope fractionation during magmatic degassing and magmatic-hydrothermal evolution at late solidus to early subsolidus stages of granite crystallization. Only non-marine evaporites show very negative δ 11 B values (<-20‰) in all natural boron reservoirs, hence, the very low δ 11 B values of the quartz-tourmaline orbicules likely indicate a major contribution of boron from non-marine evaporites that probably exist in the magma source regions or assimilated into the magma during its ascent. Quartz-tourmaline orbicules may have formed during a transition from magmatic to hydrothermal processes, whereas the vein tourmalines formed by mixing of the exsolved magmatic-hydrothermal fluids with an external fluid rich in Ca and Mg and having higher δ 11 B than the exsolved magmatic fluids.

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The Genesis of the Cornubian Batholith (South-West England): the example of the Carnmenellis Pluton

Cited by 100 publications

References 0 publications

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

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

The Lundy granite: a geochemical and petrogenetic comparison with Hercynian and Tertiary granites

Chemical and boron isotopic compositions of tourmaline from the Lavicky leucogranite, Czech Republic

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