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Timing, relations and cause of plutonic and volcanic activity of the Siluro-Devonian post-collision magmatic flare-up in the Grampian Terrane, Scotland [abstract]

Neilson, J; Kokelaar, P; Crowley, Quentin George. 2008 Timing, relations and cause of plutonic and volcanic activity of the Siluro-Devonian post-collision magmatic flare-up in the Grampian Terrane, Scotland [abstract]. In: Highland Workshop, Edinburgh, 2008.

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Abstract/Summary

Siluro-Devonian high-K calc-alkaline magmatism in the Grampian Terrane initiated at ~430 Ma, just when subduction of oceanic lithosphere ceased. It followed subduction of the leading edge of continental Avalonia beneath the margin of Laurentia and it persisted for 22-25 million years. Previous U-Pb zircon age data record the earliest plutonic crystallisation at ~429-428 Ma (Rogers and Dunning 1991). New highprecision ID-TIMS U-Pb dating of magmatic zircons yields 425.0 ± 0.7 Ma for the Lorn Lava Pile, 422.5 ± 0.5 Ma for the Rannoch Moor Pluton, 419.4 ± 4.8 Ma for a Fault-Intrusion at Glencoe caldera volcano, 418.0 ± 0.5 Ma for the Clach Leathad Pluton, which cuts Glencoe, 415.0 ± 0.4 Ma for the Cruachan Intrusion of the Etive Pluton and 408.1 ± 0.4 Ma for the Inner Starav Intrusion of the Etive Pluton. The Etive Pluton was assembled in ~8 million years and together with the Clach Leathad and Rannoch plutons constitutes the Lochaber Batholith, which formed in 14 million years. The Etive Dyke Swarm was mostly formed within ~3-4 million years and was part of the plumbing of a large volcano (Etive Volcano; ≥2000 km3) that was intruded by the Etive Pluton and then almost entirely removed by uplift and erosion. The postcollision magmatism is described in terms of a magmatic flare-up that resulted from breakoff of the subducted oceanic lithosphere and consequent rise of asthenosphere, which led to partial melting of LILE- and LREE-enriched lithospheric mantle and mafic-to-intermediate lowermost crust. Large volumes (1000s of km3) of andesite and dacite were erupted repeatedly throughout the flare-up but were rapidly removed by contemporaneous uplift and erosion. This essential volcanic counterpart to the ‘Newer Granite’ plutons has not previously been fully recognised; it is probable that centred volcanoes preceded the plutons widely, from Shetland to Donegal. Most intermediate magmas formed by partial melting of mafic-to-intermediate lowermost crust that derived its high Ba-Sr qualities via a previous partial melting of the LILEenriched lithospheric mantle, possibly at ~1.8 Ga. This crustal recycling was caused by heat and volatile addition from underplated mantle melts (parental appinitelamprophyre magmas) and involved uplift related to the rise of asthenosphere through the slab break.

Item Type: Publication - Conference Item (Paper)
Programmes: BGS Programmes > NERC Isotope Geoscience Laboratory
NORA Subject Terms: Earth Sciences
Date made live: 02 Jul 2008 13:18
URI: http://nora.nerc.ac.uk/id/eprint/3438

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