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The Riviere des Plante Ophiolitic Melange; Tectonic Setting and Melange Formation in the Quebec Appalachians

Pierre A. Cousineau
The Journal of Geology
Vol. 99, No. 1 (Jan., 1991), pp. 81-96
Stable URL: http://www.jstor.org/stable/30068767
Page Count: 16
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Riviere des Plante Ophiolitic Melange; Tectonic Setting and Melange Formation in the Quebec Appalachians
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Abstract

The Rivière des Plante ophiolitic Melange (RPOM) is the largest and best exposed of the three known ophiolitic melanges that contain blocks of Chain Lakes Massif (CLM). All three lie along the Baie Verte-Brompton line, which marks the suture between the continental rocks of the Humber zone and the oceanic rocks of the Dunnage zone. The ophiolitic melange is composed of: serpentinized ultramafic rocks, some of which are sheared and/or carbonatized; blocks of amphibolitized gabbro; basalt; volcanogenic breccia; and conglomerates. It also contains "continental" K-rich granitoid rocks and high-grade metamorphic (upper amphibolite facies) rocks. The RPOM is part of the Saint-Daniel Melange, an accretionary prism onto which the RPOM has been technically emplaced. The CLM was part of a terrane accreted to the Laurentian margin during the Taconian orogeny. Blocks of the CLM along the Baie Verte-Brompton line are interpreted as fragments of this terrane caught within the suture zone. It is proposed that the CLM could be the equivalent of Grenville-derived greywacke originally laid down during the phase of continental rifting that led to the formation of the Iapetus Ocean and was later tectonized and metamorphosed during the Taconian and Acadian orogenies. The RPOM would represent the relic of a serpentinite diapir that rose within a deep oceanic fault. The presence of continental rocks like the CLM suggest that a continental magmatic arc was put in contact with an oceanic crust along this fault.

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