Skip to content

Research at St Andrews

Late Caledonian transpression and the structural controls on pluton construction; new insights from the Omey Pluton, western Ireland

Research output: Contribution to journalArticle


William McCarthy, R. John Reavy, Carl T. Stevenson, Michael S. Petronis

School/Research organisations


The Galway Granite Complex is unique among the British and Irish Caledonian granitoid terranes, as it records punctuated phases of magmatism from approximate to 425-380 Ma throughout the latest phase of the Caledonian Orogeny. Remapping of the Omey Pluton, the oldest member of this suite, has constrained the spatial distribution and contact relationships of the pluton's three main facies relative to the nature of the host rock structure. The external contacts of the pluton are mostly concordant to the limbs and hinge of the Connemara Antiform. New AMS data show that a subtle concentric outward dipping foliation is present, and this is interpreted to reflect pluton inflation during continued magma ingress. Combined field, petrographic and AMS data show that two sets of shear zones (NNW-SSE and ENE-WSW) cross-cut the concentric foliation, and that these structures were active during the construction of the pluton. We show that regional sinistral transpression at approximate to 420 Ma would have caused dilation along the intersection of these two fault sets, and suggest that this facilitated centralised magma ascent. Lateral emplacement was controlled by the symmetry of the Connemara Antiform to ultimately produce a discordant phacolith. We propose that regional sinistral transpression at approximate to 420 Ma influenced the siting of smaller intrusions over NNW-SSE faults, and that the later onset of regional transtension caused larger volumes of magma to intrude along the E-W Skird Rocks Fault at approximate to 400 Ma.



Original languageEnglish
Pages (from-to)11-28
Number of pages18
JournalEarth and Environmental Science Transactions Of The Royal Society Of Edinburgh
Issue number1
Publication statusPublished - Dec 2015

    Research areas

  • Anisotropy of magnetic susceptibility, anticline, ascent and emplacement, Caledonian granite, flow, fold, Galway Granite Complex, microstructure, phacolith, transpression, HYDROTHERMAL FLUID CIRCULATION, RE-OS CHRONOMETER, GALWAY-GRANITE, MAGNETIC-SUSCEPTIBILITY, CRYSTALLIZATION HISTORY, IRISH CALEDONIDES, DEFORMED ROCKS, NW SCOTLAND, CONNEMARA, EMPLACEMENT

Discover related content
Find related publications, people, projects and more using interactive charts.

View graph of relations

Related by author

  1. Structural signatures of igneous sheet intrusion propagation

    Magee, C., Muirhead, J., Schofield, N., Walker, R. J., Galland, O., Holford, S., Spacapan, J., Jackson, C. A-L. & McCarthy, W., Aug 2019, In : Journal of Structural Geology. 125, p. 148-154 7 p.

    Research output: Contribution to journalArticle

  2. Lateral magma flow in mafic sill complexes

    Magee, C., Muirhead, J. D., Karvelas, A., Holford, S. P., Jackson, C. A. L., Bastow, I. D., Schofield, N., Stevenson, C. T. E., McLean, C., McCarthy, W. & Shtukert, O., Jun 2016, In : Geosphere. 12, 3, p. 809-841 33 p.

    Research output: Contribution to journalArticle

  3. Paleomagnetic, anisotropy of magnetic susceptibility, and geochronologic data from the Buena Vista intrusion, north-central New Mexico

    Petronis, M., Castillo, G., Lindline, J., Zebrowski, J., McCarthy, W., Lemen, D. & McIntosh, W., Dec 2015, Geology of the Las Vegas Region: Guidebook. Vol. 66. p. 193 204 p.

    Research output: Chapter in Book/Report/Conference proceedingChapter

  4. Distinguishing diapirs from inflated plutons: an integrated rock magnetic fabric and structural study on the Roundstone Pluton, western Ireland

    McCarthy, W., Petronis, M. S., Reavy, R. J. & Stevenson, C. T., Sep 2015, In : Journal of the Geological Society. 172, 5, p. 550-565 16 p.

    Research output: Contribution to journalArticle

Related by journal

ID: 245138481