Geochemistry of Irish granites

Elsdon, R.; Kennan, P. S.

doi:10.1144/gsl.sp.1979.008.01.86

Cited by 5 publications

(2 citation statements)

References 15 publications

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“…It is a peraluminous twomica granite believed to have been derived from partial melting of an immature, dominantly volcaniclastic protolith (Elsdon & Kennan, 1979). It is a peraluminous twomica granite believed to have been derived from partial melting of an immature, dominantly volcaniclastic protolith (Elsdon & Kennan, 1979).…”

Section: A10 Eastern Irish Granitesmentioning

confidence: 99%

The Newer Granite problem revisited: a transtensional origin for the Early Devonian Trans-Suture Suite

Brown

Ryan

Soper³

et al. 2008

Geol. Mag.

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The origin of the Newer Granites is long-standing problem. In the Caledonian orthotectonic zone the intrusions span the period of late orogenic convergence and uplift, but attempts to relate them as a group to late Iapetan subduction have been unsuccessful. A range of rock types is represented, mainly with I-type affinities, and granodiorite is the most voluminous. In contrast, granitic intrusions south of the Moniaive shear zone in Scotland and also in the north of England have significant S-type characteristics, span the trace of the Iapetus suture and have ages in the range 400-390 Ma, significantly younger than intrusions to the north. We refer to these younger granitic intrusions, along with others of similar character along-strike to the southwest, as the Trans-Suture Suite. We explore the link between the Trans-Suture Suite and recently recognized orogen-wide sinistral transtension in the Early Devonian period. Importantly, the Trans-Suture Suite intrusions are accompanied by an intense suite of lamprophyre dykes, the origin of which is to be sought in extension, decompression and heating of enriched Avalonian sub-continental lithosphere. In some instances the granite intrusions carry clots of lamprophyric origin and the Criffel body is particularly important in being continuously zoned from an I-type with lamprophyric enclaves to an S-type interior. We propose that generation of these lamprophyres during transtension advected heat into the base of the crust to produce the S-type component of the Trans-Suture Suite. Modelling presented shows that generation of voluminous S-type magmas requires the coincidence of several factors: hydrated sub-continental lithospheric mantle preserved during 'soft' collision under the Trans-Suture Suite zone; thermal relaxation to remove any subduction refrigeration; crust composed of juvenile volcanogenic material; and Devonian transtension. Our models suggest that if hydration pre-dated transtension then only small granitic bodies could be produced, unless the zone of lamprophyre generation extends beyond the rift zone. The emplacement of the Trans-Suture Suite intrusions overlapped the Acadian deformation period that succeeded the transtensional episode during which the granite magmas were generated.

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Section: A10 Eastern Irish Granitesmentioning

confidence: 99%

The Newer Granite problem revisited: a transtensional origin for the Early Devonian Trans-Suture Suite

Brown

Ryan

Soper³

et al. 2008

Geol. Mag.

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“…The relatively low initial 87 Sr/ 86 Sr ratio (O'Connor & Bruck, 1978), together with other geochemical evidence, in particular the relatively high Na content of the granite (Sweetman, 1987), suggest derivation from an immature, dominantly volcaniclastic metasedimentary pile (Elsdon & Kennan, 1979). The relatively low initial 87 Sr/ 86 Sr ratio (O'Connor & Bruck, 1978), together with other geochemical evidence, in particular the relatively high Na content of the granite (Sweetman, 1987), suggest derivation from an immature, dominantly volcaniclastic metasedimentary pile (Elsdon & Kennan, 1979).…”

Section: B Age and Sourcementioning

confidence: 99%

Cryptic Sr and Nd isotopic variation across the Leinster Granite, southeast Ireland

Mohr

1991

Geol. Mag.

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Rb-Sr isotope whole-rock data from the end-Caledonian Leinster Batholith define an errorchron age of 464 ± 26 Ma, appreciably older than the accepted emplacement age of c. 405 Ma. This anomalously old age is the consequence of a highly variable initial Sr isotopic composition. Initial Nd ratios and T DM model ages also show a wide range of values. However, these isotopic variations are neither randomly distributed nor related to petrographic changes but instead reflect, in a simple way, geographic position about the axis of the batholith. The isotopic pattern revealed in the Leinster Batholith means that isochron ages obtained from S-type granites may be largely dependent on the sampling scheme adopted. The variable isotopic composition of the granite most likely resulted from either a heterogeneous metasedimentary source or hybridization of coeval, dominantly crustal melts.

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Geological and isotope studies of microtonalite-hosted W-Sn mineralization in SE Ireland

Gallagher

1989

Mineral. Deposita

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Geochemistry of Irish granites

Abstract: Major, trace and isotopic element data are reviewed, in the light of current views on the petrogenesis of Caledonian granite magmas. The information at present available tends to confirm a crustal anatexis model rather than a mantle origin, but more work is needed to confirm this.

Cited by 5 publications

References 15 publications

The Newer Granite problem revisited: a transtensional origin for the Early Devonian Trans-Suture Suite

The Newer Granite problem revisited: a transtensional origin for the Early Devonian Trans-Suture Suite

Cryptic Sr and Nd isotopic variation across the Leinster Granite, southeast Ireland

Geological and isotope studies of microtonalite-hosted W-Sn mineralization in SE Ireland

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