Middle Ordovician disorganized arc rifting in the peri-Laurentian Newfoundland Appalachians: implications for evolution of intra-oceanic arc systems

Abstract

The Annieopsquotch Accretionary Tract comprises a tectonic collage of Ordovician peri-Laurentian terranes that formed during closure of Iapetus Ocean and imbricated beneath the composite margin of Laurentia. New zircon U–Pb geochronological data ( n = 8) for felsic volcanic rocks representing three distinct tectonostratigraphic units (the Mary March Brook group, the Buchans Group and the Red Indian Lake Group) indicate deposition over a short interval between 465 and 462 Ma. These tectonostratigraphic units are characterized by submarine mafic and felsic magmatism, and sedimentation typical of intra-oceanic arc systems. New and compiled whole-rock geochemical ( n = 315) and Sm–Nd isotopic ( n = 33) data for mafic and felsic volcanic rocks indicate that these tectonostratigraphic units formed in tholeiitic island arc to calc-alkaline arc settings. Isotopic (ε Nd −11.2 to +6; T DM 1.0–2.4 Ga) and zircon inheritance data (0.5–3.4 Ga) are consistent with presence of Laurentian continental crust in the basement. Relationships within and between these and adjacent tectonostratigraphic units in the Annieopsquotch Accretionary Tract suggest that they represent imbricated slices of a submarine arc that experienced disorganized arc rifting, similar to sectors of the modern Tonga–Kermadec and Izu–Bonin–Mariana arcs. The recognition of disorganized spreading in the Annieopsquotch Accretionary Tract has significant implications for along-strike correlations within the Appalachian orogen, as the nature of the arc systems is expected to differ significantly along-strike. The presence of a clear isotopic and inheritance signature of peri-Laurentian continental crust within the Annieopsquotch Accretionary Tract submarine arc system is consistent with the discoveries of older arc and continental basement in modern intra-oceanic arc systems. Supplementary materials: Geochronological analytical procedures and data, summary of geochemical data and isotopic data are available at http://www.geolsoc.org.uk/SUP18860 .

First evidence of Lower–?Middle Ordovician (Floian–?Dapingian) brachiopods from the Peruvian Altiplano and their paleogeographical significance

“…As discussed in the preceding, the Peruvian assemblage studied here also shows clear links with several terranes, of probable Gondwanan origin (Murphy et al, 1999; Zagorevski et al, 2015; Reusch et al, 2018), located at intermediate (Ganderia and Monian composite terranes) and low (Moretown, Dashwoods, and Midland Valley–Mayo terranes) latitudes between Gondwana and Laurentia (see Johnson et al, 1991 and Cutts et al, 2011 for paleogeographic position of Dashwoods Terrane) during Floian-Dapingian times. Villas et al (2015) proposed the existence during Sandbian times (early Late Ordovician) of intermediate islands in the Rheic Ocean between the Peruvian Altiplano and Avalonia, permitting dispersal following the Southern Westerlies currents (Pohl et al, 2016) and island hopping of brachiopod species with low dispersal potential (short larval period) to overcome the presumably large distances between those terranes.…”

The Österplana Fossil Meteorites and… What Else? Terrestrial Cr-Spinels and Zircons in the Ordovician Limestones of the Thorsberg Quarry (Sweden)

“…At the same time, Refs. [71][72][73][74] showed that the Canadian Appalachians comprise a tectonic collage of Ordovician peri-Laurentian terranes that formed during the closure of the Iapetus Ocean and imbricated beneath the composite margin of Laurentia, and is comprised in the 470-460 Ma interval.…”