Geological Magazine

Original Article

Long-lived granite-related molybdenite mineralization at Connemara, western Irish Caledonides

MARTIN FEELYa1 c1, DAVID SELBYa2, JON HUNTa1 and JAMES CONLIFFEa3

a1 Earth and Ocean Sciences, Quadrangle Building, School of Natural Sciences, National University of Ireland, Galway, Ireland

a2 Department of Earth Sciences, Durham University, Durham DH1 3LE, UK

a3 Department of Earth Sciences, Memorial University, St Johns, Newfoundland, Canada

Abstract

New Re–Os age determinations from the Galway Granite (samples: KMG = 402.2 ± 1.1 Ma, LLG = 399.5 ± 1.7 Ma and GBM = 383.3 ± 1.1 Ma) show that in south Connemara, late Caledonian granite-related molybdenite mineralization extended from c. 423 Ma to c. 380 Ma. These events overlap and are in excellent agreement with the published granite emplacement history determined by U–Pb zircon geochronology. The spatial distribution of the late-Caledonian Connemara granites indicates that initial emplacement and molybdenite mineralization occurred at c. 420 Ma (that is, the Omey Granite and probably the Inish, Leterfrack and Roundstone granites) to the N and NW of the Skird Rocks Fault, an extension of the orogen-parallel Southern Uplands Fault in western Ireland. A generally southern and eastward progression of granite emplacement (and molybdenite mineralization) sited along the Skird Rocks Fault then followed, at c. 410 Ma (Roundstone Murvey and Carna granites), at c. 400 Ma (Errisbeg Townland Granite, Megacrystic Granite, Mingling Mixing Zone Granodiorite, Lough Lurgan Granite and Kilkieran Murvey Granite) and at c. 380 Ma (Costelloe Murvey Granite, Shannapheasteen and Knock granites). The duration of granite magmatism and mineralization in Connemara is similar to other sectors of the Appalachian–Caledonian orogeny and several tectonic processes (e.g. slab-breakoff, asthenospheric flow, transtension and decompression) may account for the duration and variety of granite magmatism of the western Irish Caledonides.

(Received September 01 2009)

(Accepted March 02 2010)

(Online publication April 22 2010)

Keywords:

  • molybdenite;
  • granite;
  • Connemara;
  • Caledonides;
  • Re–Os chronometry

Correspondence:

c1 Author for correspondence: martin.feely@nuigalway.ie

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