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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: [email protected]
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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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References

Berger, A.R. and Pitcher, W.S. (1970) Structures in granitic rocks: a commentary and a critique on granite tectonics. Proc. Geol. Assoc., 81, 441–61.CrossRefGoogle Scholar
Bouchez, J-L., Delas, C., Gleizes, G., Nedelec, A. and Cuney, M. (1992) Submagmatic microfractures in granites. Geology, 20, 35–8.2.3.CO;2>CrossRefGoogle Scholar
Claxton, C.W. (1970) Some observations on the assimilation of basic xenoliths by acid magma in the galway granite, Co. Galway, Eire. Scientific Proc. Royal Dubli. Soc., 3, 247–55.Google Scholar
Coats, J.S. and Wilson, J.R. (1971) The eastern end of the Galway Granite. Mineral. Mag., 38, 138–51.CrossRefGoogle Scholar
Crowley, Q. and Feely, M. (1997) New perspectives on the order and style of granite emplacement in the Galway Batholith, western Ireland. Geol. Mag., 134 (4), 539–48.CrossRefGoogle Scholar
Didier, J. and Barbarin, B. (1991) The different types of enclaves in granites – nomenclature. Pp. 19–24 in: Enclaves and Granite Petrology (Didier, J. and Barbarin, B., editors). Developments in Petrology, 13, Elsevier, Amsterdam.Google Scholar
El Desouky, M., Feely, M. and Mohr, P.M. (1996) Diorite-granite magma mixing along the axis of the Galway Granite batholith, Ireland. J. Geol. Soc., 153, 361–74.CrossRefGoogle Scholar
Feely, M. and Madden, J.S. (1987) The spatial distribution of K, U, Th and surface heat production in the Galway Granite, Connemara, western Ireland. Irish J. Earth Sci., 8, 155–64.Google Scholar
Feely, M., McCabe, E. and Kunzendorf, H. (1991) The evolution of REE profiles in the Galway Granite, western Ireland. Irish J. Earth Sci., 11, 71–89.Google Scholar
Friedrich, A.M., Bowring, S.A., Martin, M.W. and Hodges, K.P. (1999) Short-lived continental magmatic arc at Connemara, western Irish Caledonides: Implications for the age of the Grampian orogeny. Geology, 27, 27–30.2.3.CO;2>CrossRefGoogle Scholar
Graham, N.T. (1997) Fabric studies in the Galway Granite, Ireland. D.Phil. thesis, Univ. Oxford.Google Scholar
Hibbard, M.J. (1987) Deformation of incompletely crystallised magma systems: granite gneisses and their tectonic implications. J. Geol., 95, 543–61.CrossRefGoogle Scholar
Hibbard, M.J. and Watters, R.J. (1985) Fracturing and dyking in incompletely crystallised granitic plutons. Lithos, 18, 1–12.CrossRefGoogle Scholar
Klemperer, S.L., Ryan, P.D. and Snyder, D.B. (1991) A deep seismic reflection transect across the Irish Caledonides. J. Geol. Soc., 148, 149–64.CrossRefGoogle Scholar
Lawrence, G. (1975) The use of Rb/Sr ratios as a guide to mineralisation in the Galway Granite, Ireland. Proc. Geol. Exploration Symposium (Vancouver). Elsevier, Amsterdam, pp. 353–70.Google Scholar
Leake, B.E. (1974) The crystallisation history and mechanism of emplacement of the western part of the Galway Granite, Connemara, western Ireland. Mineral. Mag., 39, 498–513.CrossRefGoogle Scholar
Leake, B.E. (1978) Granite emplacement: the granites of Ireland and their origin. Pp. 221–248 in: Crustal Evolution in Northwest Britain and Adjacent Regions (Bowes, D.R. and Leake, B.E., editors). Geol. J. (spec. issue), 10.Google Scholar
Leake, B.E. (1989) The metagabbros, orthogneisses and paragneisses of the Connemara complex, western Ireland. J. Geol. Soc., 146, 575–96.CrossRefGoogle Scholar
Leake, B.E. and Leggo, P.J. (1963) On the age relations of the Connemara migmatites and the Galway Granite, west of Ireland. Geol. Mag., 100, 193–205.CrossRefGoogle Scholar
Leggo, P.J., Compston, W. and Leake, B.E. (1966) The geochronology of the Connemara Granites and its bearing on the antiquity of the Dalradian series. Q.J.G.S. Lond., 122, 91–118.CrossRefGoogle Scholar
Madden, J.S. (1987) Gamma-ray spectrometric studies of the Main Galway Granite, Connemara, west of Ireland. Ph.D. thesis, National Univ. Ireland.Google Scholar
Max, M.D., Long, C.B. and Geoghegan, M. (1978) The Galway Granite. Bull. Geol. Surv. Ireland, 2, 223–33.Google Scholar
Max, M.D., Ryan, P.D. and Inamdar, D.D. (1983) A magnetic deep structural geology interpretation of Ireland. Tectonics, 2, 431–51.CrossRefGoogle Scholar
McKie, D. and Burke, K. (1955) The geology of the islands of south Connemara. Geol. Mag., 92, 487–98.CrossRefGoogle Scholar
Murphy, T. (1952) Measurements of gravity in Ireland: Gravity survey of central Ireland. Dublin Inst Adv. Stud., Geophys. Mem., 2.Google Scholar
Patino Douce, A.E. and Beard, J.S. (1995) Dehydration melting of biotite gneiss and quartz amphibolite from 3 to 15 kbar. J. Petrol., 36, 707–38.CrossRefGoogle Scholar
Pitcher, W.S. and Berger, A.R. (1972) The Geology of Donegal – a Study of Granite Emplacement and Unroofing. Wiley Interscience, Chichester.Google Scholar
Rushmer, T. (1991) Partial melting of two amphibolites: contrasting experimental results under fluid absent conditions. Contrib. Mineral. Petrol., 107, 41–59.CrossRefGoogle Scholar
Streckeisen, A.L. (1976) To each plutonic rock its proper name. Earth Sci. Rev., 12, 1–33.CrossRefGoogle Scholar
Vance, J.A. (1969) On synneusis. Contrib. Mineral. Petrol., 24, 7–29.CrossRefGoogle Scholar
Vance, J.A. and Gilreath, J.P. (1967) The effect of synneusis on phenocryst distribution patterns in some porphyritic igneous rocks. Amer. Mineral., 52, 529–36.Google Scholar
Vogt, J.H.L. (1921) The physical chemistry of the crystallization and magmatic differentiation of igneous rocks. J. Geol., 28, 318–50.CrossRefGoogle Scholar
Wickham, S.M. (1987) The segregation and emplacement of granite magmas. J. Geol. Soc., 144, 281–97.CrossRefGoogle Scholar
Williams, D.M., Armstrong, M.A. and Harper, D.A.T. (1988) The age of the South Connemara Group, Ireland, and its relationship to the Southern Uplands Zone of Scotland and Ireland. Scott. J. Geol., 24, 279–87.Google Scholar