Geology and petrochemistry of the Ordovician volcano-plutonic Robert's Arm Group, Notre Dame Bay, Newfoundland

Abstract

The Robert's Arm Group is a Middle Ordovician.fault-bounded, spilitized. bimodal volcanic to shallow plutonic assemblage within the northern Dunnage tectonostratigraphic zone. On the north it is nonconformably overlain by Silurian Springdale Group red beds, and both are separated from the Lower Ordovician Lushs Bight ophiolitic terrane by the Lobster Cove Fault. The group itself is complexly faulted and comprises an older terrane of tholeiitic to alkaline basalt slices overlain by one of more calc-alkaline slices. The tholeiitic basalts are interleaved with fine elastics of Cresent Lake Formation and with quartz-phyric felsites accompanied by substantial pyroclastics, whereas the calc-alkaline terrane includes quartz-amygdaloidal felsites with less common pyroclastics, concentrated in major centres that locally grade into granite. Erratic lithium enrichment of the basalts is spatially related to the basal fault contact of the group but spreads upward where deformation of underlying shales is strongest and disruption of the overlying basalts is greatest. The Robert's Arm Group evolved at the outer edge of a back arc basin beginning with deep water eruption of tholeiitic basalts before abduction of ophiolite in western Newfoundland. Subsequent more calc-alkaline volcanism occurred in neritic to littoral environments likely about the time of continental collision. After southeastward thrusting of Robert's Arm Group and deposition of Springdale Group, the dips of both were steepened by Devonian tectonism. Oroclinal bending of the basalts accompanied late right lateral movements on the Lobster Cove Fault. Alkaline dykes of presumed Mesozoic age were emplaced during opening of the modern Atlantic Ocean.

From Large Zones to Small Terranes to Detailed Reconstruction of an Early to Middle Ordovician Arc–Backarc System Preserved Along the Iapetus Suture Zone: A Legacy of Hank Williams

“…This was followed by addition and imbrication of Darriwilian arc terranes during collision with the peri-Gondwanan Popelogan -Victoria arc. The structure and development of the individual terranes has been described in detail in other publications (Bostock 1988;Kerr 1996;Dec et al 1997;O'Brien 2003O'Brien , 2007Zagorevski et al 2006Zagorevski et al , 2010aZagorevski and Rogers 2009 Williams and Payne 1975;Dunning 1987;Dunning et al 1987;Szybinski 1995;Swinden 1996;O'Brien 2003;Lissenberg et al 2005c;Cutts et al 2012). Collectively, these are interpreted as a remnant infant arc.…”

“…The structurally underlying Buchans Group comprises calc-alkaline basaltic and rhyolitic rocks of continental arc affinity, along with locally abundant granitoid-bearing conglomerate and debris flows, constituting the Lundberg, Ski Hill and Buchans River formations, respectively (Thurlow and Swanson 1987;van Hees et al 2012 Bostock 1988;Kerr 1996). 12-14.…”

“…Simplified geology of the Buchans (A) and Robert's Arm (B) areas (geology modified from Whalen et al (2013) and Bostock (1988), respectively). Geochronology is compiled from Dunning et al 1987;Kerr and Dunning 2003;Zagorevski et al 2006;Coombs et al 2012;Whalen et al 2013 and this paper (see Appendix 2).…”

“…1; e.g. Pickett 1987;Bostock 1988;Swinden et al 1989). Subsequent detailed investigations of the AAT, focusing on the differences and/or changes in tectonic setting and structure over time between different areas, implied a greater complexity, as each one of these slivers, in essence, was shown to constitute a discrete terrane (Fig.…”

“…Subsequent detailed investigations of the AAT, focusing on the differences and/or changes in tectonic setting and structure over time between different areas, implied a greater complexity, as each one of these slivers, in essence, was shown to constitute a discrete terrane (Fig. 1;Bostock 1988;Zagorevski et al 2006Zagorevski et al , 2010aZagorevski and Rogers 2009).…”