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

Research output: Contribution to journalArticle

Author(s)

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

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Abstract

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.

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Details

Original languageEnglish
Pages (from-to)11-28
Number of pages18
JournalEarth and Environmental Science Transactions Of The Royal Society Of Edinburgh
Volume106
Issue number1
DOIs
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

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