Paper No. 6
Presentation Time: 3:00 PM
THE SERENDIPITOUS LINK BETWEEN CALEDONIAN - APPALACHIAN ECLOGITES AND OPHIOLITES
In 1959 eclogitized metagabbros were found as mafic boudins within Moinian psammites of Western Ireland. On the assumption that the Caledonian rocks of Ireland, the western 'orthotectonic' belt, should continue into Newfoundland, a search for eclogites was initiated in 1963, and in the following year four eclogite localities were indeed found in psammites of the Fleur de Lys Supergoup. Following Wilson's formulation of the idea of a Proto-Atlantic ocean in 1966, Fritz and Stevens seized on the idea that the emplacement of the Bay of Islands Taconic allochthons was related to the closure of the Proto-Atlantic, and by 1968 the discovery of detrital chromite in units of the allochthonous flysch led to the proposition that the ophiolites were an integral part of the transported sequence. The insight that the ophiolites were oceanic material followed from two chance events. The first was the chance discovery - while searching for articles on Alpine eclogites in the relatively obscure Swiss journal Schweitzerische Petrographische Mitteilung - of Ben Reinhardt's article on the oceanic origin of 'sheeted diabase' in the Oman ophiolite, and the second the finding while mapping along the coast of the Burlington Peninsula of a 'sheeted diabase' unit in the Betts Cove ophiolite, just as described by Reinhardt . At that point the idea that the Newfoundland ophiolites were allochthonous and of oceanic origin became fixed as a point of reference for all future tectonic studies in the Appalachians. Recent age-dating studies on the age of the ophiolites of Papua and Oman, and their associated dynamothermal aureoles and 'eclogite extrusion spots', fits well with earlier suggestions that 'The existence of high temperature aureoles implies that at the time of their emplacement they were relatively hot, and that the age of the ophiolites should not differ greatly from that of their emplacement', and, further, that they may have been emplaced during the closing of the Appalachian ocean, while the ridge was positioned close to the continental margin or was newly developing within the margin.'. Whether the eclogite-bearing Fleur de Lys and Belvedere Mountain (Vermont) terrains also represent rapidly developed "spot extensions", or whether they are related to periods of late Taconic or Siluro-Devonian extension, remains yet to be argued.