Ordovician tectonic evolution of the southern Long Range Mountians, Newfoundland

Hall, Lindsay Anne Forsyth (1998) Ordovician tectonic evolution of the southern Long Range Mountians, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The rocks of the southern Long Range Mountains consist of metamorphosed mafic, ultramafic, sedimentary and felsic intrusive rocks and granite plutons. The mafic and ultramafic rocks constitute the Long Range Mafic-ultramafic Complex, the oldest rocks in the area. Pelitic to psammitic metasedimentary rocks with entrained fragments of the Long Range Mafic-ultramafic Complex comprise the Mischief Mélange. The Cape Ray Igneous Complex consists of deformed and metamorphosed tonalitic, granitic and granodioritic rocks which cut the Long Range Mafic-ultramafic Complex and the Mischief Mélange. This complex includes the Cape Ray Granite (488 (+/-3) Ma), Long Pond Tonalite (472 (+/-2) Ma) and the younger Staghill Orthogneiss which intrudes the other members of this complex and cuts features of early deformation. Four plutons, the Pin (449 (+2/-3) Ma), Red Rocks, Strawberry (384 (+/-2) Ma) and Dragon Lake granites and dykes associated with them cut all older rocks and structures. -- The rocks of the southern Long Range Mountains record Ordovician orogenesis, namely, the generation of an ophiolite suite (the Long Range Mafic-ultramafic Complex), its obduction and association with a mélange (the Mischief Mélange), the generation of a continental arc (the Cape Ray Igneous Complex) and further obduction and plutonism (granites). Amphibolite grade peak metamorphism pre-dates the intrusion of the Staghill Orthogneiss, however, the rocks remained in a deformational and metamorphic regime during and after the emplacement of the Staghill Orthogneiss. Dated at 449 Ma, the post-tectonic Pin Granite provides a lower limit for the cessation of penetrative deformation in this area. Plutonism was renewed in at least one distinct event with emplacement of the 384 (+/-2) Ma Strawberry Granite. -- Rocks of the southern Long Range Mountains occur in the hanging wall of the Long Pond Thrust, a southeast dipping thrust which intersects the escarpment of the much younger Cabot Fault. To the southeast the rocks are bounded by the Cape Ray Fault that dips southeast and separates Gondwanan and Laurentian elements of the earlier Iapetus Ocean.

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