Late Neoproterozoic Avalonian and related peri-Gondwanan rocks of the Newfoundland Appalachians

Abstract

Distinct groupings of late Neoproterozoic tectonomagmatic and depositional events at 760 Ma, 685-670 Ma, 635-590 Ma and 590-545 Ma are recognized within the peri-Gondwanan margin of the Newfoundland Appalachians. This pre-Iapetan orogenic activity resulted in amalgamation of distinctive tectonic packages prior to deposition of a shale-rich platformal cover of terminal Neoproterozoic to Early Ordovician age, east of the Appalachian central mobile belt. The late Neoproterozoic successions chronicle, in part, the development of segments of a larger peri-Gondwanan orogenic system that was dispersed prior to, and variously reworked during, the protracted evolution of the southern Iapetus Ocean.The oldest orogenic events yet identified in the Newfoundland Avalonian belt occurred at and prior to 760 Ma and are manifest by the accumulation of submarine mafic volcanic rocks, the emplacement of oceanic gabbros, and the associated deposition of unique clastic and carbonate olistostromes. As early as 685 Ma, arc-related volcanic and associated arc-root plutonic complexes of felsic to intermediate composition developed along the orogenic belt in an overall contractional environment. These complexes, which are preserved together with amphibolite gneisses and associated intrusive rocks, were inhomogeneously deformed and then uplifted prior to the onset of widespread (635-590 Ma) volcanism, marine sedimentation, and coeval calc-alkaline plutonism, the products of which were deposited upon or emplaced into the 685-670 Ma basement. Locally, pre-600 Ma rocks have been inhomogeneously deformed prior to a complex volcanic, plutonic, and structural event (590-545 Ma), partly extensional and partly contractional in nature, during which the classical Ediacaranbearing and younger sedimentary successions of the Avalonian belt accumulated.Diverse tectonic elements that evolved prior to the Cambrian were variably dispersed at several times, perhaps most significantly during late Neoproterozoic orogenesis. Pronounced terminal Neoproterozoic and early Paleozoic tectonothermal events were recorded on the inboard Iapetan margin of the belt, while elsewhere, terminal Neoproterozoic through Cambro-Ordovician platformal sediments were deposited, in most cases without apparent hiatus. These contrasting peri-Gondwanan terranes were reamalgamated and again dispersed during complex transpressional orogenesis of Silurian age related to closure of the Iapetus Ocean, and ensuing collision of Gondwanan and Laurentian elements of the Appalachian orogen.

Neoproterozoic?Early Paleozoic evolution of peri-Gondwanan terranes: implications for Laurentia-Gondwana connections

“…605 Ma in mainland Nova Scotia , between 575 Ma and 560 Ma in southern Cape Breton Island (Bevier et al 1993), at ca. 570 Ma in Newfoundland (O'Brien et al 1996), and in the interval 570-560 Ma in Britain (Tucker and Pharoah 1991). Although the transition was locally accompanied by deformation and metamorphism, no evidence exists for the regional orogenesis, crustal shortening, and crustal thickening and uplift characteristic of continental collision zones.…”

“…However, its cessation was diachronous, terminating at ca. 590 Ma in New England (Kaye and Zartman 1980;Zartman 1985, 1992;Thompson et al 1996;Thompson and Bowring 2000), 600 Ma in southern New Brunswick (Bevier and Barr 1990;Barr et al 1994;Currie and McNicoll 1999), 605 Ma in mainland Nova Scotia (Doig et al 1991;Murphy et al 1997;, 575 Ma in southern Cape Breton Bevier et al 1993), 585 Ma in Newfoundland (Krogh et al 1988;O'Brien et al 1996), and 600 Ma in the British Isles (e.g., Tucker and Pharaoh 1991;Horµk 1993;Noble et al 1993).…”

“…683 Ma Tickle Point Formation and ca. 673 Ma Furby's Cove Intrusive Suite in southern Newfoundland (Swinden and Hunt 1991;O'Brien et al 1996). The rift ophiolite volcanics of the Burin Group in Newfoundland (Strong et al 1978) may extend this early Avalonian magmatic activity to ca.…”

“…650 Ma in various parts of Avalonia, including coastal Maine (Stewart and Tucker 1998) and the Malvern Plutonic Complex (Strachan et al 1996b). Amphibolite facies metamorphism of pre-630 Ma age may also be present in central Cape Breton Island ) and southern Newfoundland (O'Brien et al 1996), and some form of accretion is implicated by the ophiolitic rocks of the ca. 760 Ma Burin Group ).…”

“…Coeval sedimentary successions that are dominated by volcanogenic turbidites are locally associated with these arcrelated magmatic rocks, and have been attributed to deposition in a variety of intra-arc, interarc and back arc basins (e.g., Pe-Piper and Murphy 1989;Pauley 1990;Smith and Socci 1990;O'Brien et al 1996;Murphy et al 1999). This magmatic activity and the generation of arc-related basins are interpreted to reflect oblique subduction beneath the northern Gondwanan margin.…”