Eclogitic rocks of Ireland and Newfoundland

 

               Eclogitic rocks, mostly retrograded to kelyphitic garnet granulites, occur in the cores of amphibolite units in psammitic rocks of the Lough Derg Group of western Ireland.   There are several outcrops where the transition from igneous-textured metagabbro to foliated eclogite can be clearly observed.  Similar eclogites are also preserved in the cores of amphibolite units within psammites of the Fleur de Lys Group of Western Newfoundland.  In both cases, the psammites are bordered to the northwest by continental rocks of the western foreland of the Caledonides, and to the south west by melange and ophiolite units of the Rattling Brook/Baie Verte groups in Newfoundland and the melanges and ophiolites of Clew Bay in Ireland.  The distribution of eclogites in this manner has been used as an argument in favour of correlating the Fleur de Lys Group of Newfoundland with the Moine -Dalradian of Ireland and Scotland.

 

        Map showing eclogite localities in the Fleur de Lys Group

 

        Map showing relative locations of eclogites in the Fleur de Lys Newfoundland and the Moine of Ireland

 

     eclobally.jpg - folded body of mafic rock in white weathering psammites, composed of an internal core of eclogite/garnet-granulite and a dark outer rim of amphibolite, Ballyshannon, Ireland.

     eclofleur.jpg -  mafic body in metaconglomerates; road to Bear Cove, Burlington Peninsula;  lighter coloured interior of the rock is eclogite, the darker margins of the outcrop are amphibolite; .

     eclots.jpg -  intergrowths of garnet and albite (kelyphitic texture); bright white crystal is quartz

     eclofleur2.jpg -  eclogite boudin in possibly graded (east to west) Fleur de Lys psammites.  First recorded outcrop of eclogite in the Newfoundland Appalachians, roadside outcrop near Eclogite Pond, on the road to Westport, Burlington Peninsula. 

     eclofleur3.jpg - contact of extremely tough eclogite (right) with psammitic gneiss (left); Bear Cove road near junction with Westport road.

     eclofleur3ts.jpg -  Atoll garnet; possibly retrogressed garnet that has undergone a second period of euhedral (straight boundaries) growth.  Alternatively, the garnet may have been zoned and the survival of the outer atoll may have been due to the particular chemistry of the rim zone.

     eclostaurofleur.jpg  - psammitic unit within several hundred meters of the eclogite locality at Eclogite Pond; the psammites contain large crystals of what are likely to be staurolite.

 

Suzanne L. Baldwin, Brian D. Monteleone, Laura E. Webb, Paul G. Fitzgerald, Marty Grove & E. June Hill, 2004, Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea. Nature, Sept, v. 431, p. 263-267

      papuaeclogite.jpg - rapidly exhumed 4.3 Ma-old eclogite-bearing core terraine separated from ultramafic rocks by a highly sheared (D2) carapace:

FERNANDO MARTINEZ, ANDREW M. GOODLIFFE & BRIAN TAYLOR, 2001. Metamorphic core complex formation by density inversion and lower-crust extrusion. Nature, 411, (21 June 2001), p.930 - 934.

      papuaeclogite2.jpg - illustration of the concept of core complex formation by density inversion

      papuaeclogite3.jpg - explanation of papuaeclogite2