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The construction of the Donegal composite batholith, Irish Caledonides: temporal constraints from U-Pb dating of zircon and titanite

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Magmatic and tectonic processes can transport large volumes of magma generated in the deep crust as discrete pulses to shallower crustal depths, resulting in the incremental construction of large composite batholiths over thousands to tens of millions of years. The Silurian to early Devonian Donegal composite batholith in Ireland is a classic example for which regional geological syntheses and lithogeochemical data show emplacement was syn- and post-kinematic with respect to the terminal phases (ca. 437-415 Ma) of the Caledonian orogeny. We used U-Pb dating of zircon and titanite to investigate the construction of the batholith over time. Imaging of these minerals reveals complex, zoned grains with distinct autocrystic (growth during pluton emplacement), as well as inherited domains comprising antecrysts (growth during lower crustal incubation), and xenocrysts (incorporated from wall rocks). To determine the age(s) of emplacement and of inherited domains, discrete growth zones were targeted for dating using LA44 ICP-MS (laser ablation inductively coupled plasma mass spectrometry). Taken together, the zircon and titanite U-Pb isotopic data indicate that batholith emplacement occurred over at least 30 myr, between ca. 430 Ma and 400 Ma, bracketed by emplacement of the ca. 427-423 Ma Ardara pluton and the latest phases in the Main Donegal and Trawenagh Bay plutons (ca. 400 Ma). Although apparently volumetrically minor, U-Pb data from spatially associated mafic rocks (appinite suite, lamprophyre dikes, and mafic enclaves in granitoid plutons) yield ages ranging from ca. 431-416 Ma, which indicates ongoing mafic magmatism during emplacement of much of the Donegal composite batholith.
Original languageEnglish
Number of pages20
JournalBulletin of the Geological Society of America
Early online date3 Mar 2021
DOIs
Publication statusEarly online - 3 Mar 2021

Documents

  • The construction of the Donegal composite batholith

    Rights statement: Donnelly B. Archibald, Lauren M.G. Macquarrie, J. Brendan Murphy, Robin A. Strachan, Chris R.M. McFarlane, Mark Button, Kyle P. Larson, Joseph Dunlop; The construction of the Donegal composite batholith, Irish Caledonides: Temporal constraints from U-Pb dating of zircon and titanite. GSA Bulletin 2021; doi: https://doi.org/10.1130/B35856.1.

    Accepted author manuscript (Post-print), 3.98 MB, PDF document

    Due to publisher’s copyright restrictions, this document is not freely available to download from this website until: 3/02/22

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