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Plagioclase-rich microgranular inclusions from the late-Caledonian Galway Granite, Connemara, Ireland

Published online by Cambridge University Press:  25 June 2018

N. T. Graham ,
M. Feely  and
B. Callaghan
N. T. Graham
Affiliation:
Department of Earth Sciences, Parks Road, University of Oxford, England
M. Feely*
Affiliation:
Department of Geology, National University of Ireland, Galway, Ireland
B. Callaghan
Affiliation:
Department of Geology, National University of Ireland, Galway, Ireland
*
*E-mail: martin.feely@nuigalway.ie
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Abstract

We report on the occurrence, petrology and geochemistry of recently recognized leucocratic plagioclase-rich microgranular inclusions hosted by two granite facies in the late-Caledonian Galway Granite, Connemara, Ireland. They have been recorded at 66 localities along an ESE trending, 4 km wide corridor which incorporates the contact zone between their host granites (i.e. The Megacrystic Granite and the Mingling and Mixing Zone Granodiorite). The inclusions are discoidal in shape and oriented parallel to the general ESE trending foliation in the granites with the most elongate (6.0 × 0.6 cm) occurring in zones of strongest fabric intensity. Contacts between the inclusions and the host granite are sharp with no chilled margin visible. They display a fine-grained (<1 mm) interlocking texture with occasional crystals of plagioclase ranging up to 2 mm in length. Microprobe analysis shows that the plagioclase is essentially oligoclase (An22–32) in composition and is similar to that (i.e. An21–30) occurring in the host granites. Furthermore, the oligoclase accounts for between 61 and 78% of the mode which is reflected in the major element chemistry of the inclusions. Other minerals (in decending order of abundance) include K-feldspar, quartz, biotite and magnetite. The origin of the inclusions is unclear. However, the results of the microprobe analysis provide evidence of a link between them and their host granites.

Keywords

Galway granitemicrogranular inclusionsoligoclasesynneusismelt segregation
Type
Research Article
Information
Mineralogical Magazine , Volume 64 , Issue 1 , February 2000 , pp. 113 - 120
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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