Provenance of tectonic history of the Gander Zone in the Caledonian/Appalachian Orogen: Implications for the origin and assembly of Avalon

Abstract

New U-Pb zircon, Nd-Sm, and Sr isotopic data from Gander Zone basement fragments in northern New Brunswick, combined with a review of existing data, support a basement-cover relationship between the Avalonian Bras d'Or-Brookville belt and lower Paleozoic clastic rocks of the Gander Zone. Basement fragments occur as (1) large foliated and unfoliated granodiorite cobbles in a late Arenig to Llanvirn conglomerate of the Vallée Lourdes Formation of the Tetagouche Group and (2) as an allochthonous gabbro sheet (Upsalquitch gabbro), tectonically emplaced on top of the Tetagouche Group during Late Ordovician or Early Silurian thrusting.The granodiorite cobbles of the Vallée Lourdes Formation yielded late Mesoproterozoic (ca. 1.09 Ga) U-Pb zircon crystallization ages and gave an ε Nd (T) of -3.47 and a depleted mantle model age (T DM ) of 2.0 Ga. Xenocrystic zircon grains in the cobbles range in age between ca. 1.16 and 1.55 Ga. Geochemical data from a foliated granodiorite cobble suggest that the magma from which it crystallized formed by mixing of mantle-derived and older (>1.5 Ga) crustal-derived components.The Upsalquitch gabbro has a U-Pb zircon crystallization age of 543 +1/-2 Ma (earliest Cambrian) and is inferred to represent a fragment of the Gander Zone basement. Similar age igneous rocks occur in the Avalonian Bras d'Or-Brookville belt. The Upsalquitch gabbro forms the immediate base to one of the Middle Ordovician basalt suites of the Fournier Group (ca. 464 Ma), which indicates the presence of a significant hiatus. The Fournier Group was deposited in a back-arc basin that formed by splitting a late Arenig magmatic arc built on the Gander Zone. During rifting of the arc the gabbroic basement fragment was tectonically exhumed onto the sea floor by low-angle normal faulting immediately before eruption of the basalts. The gabbro's geochemistry indicates that it was mainly derived from a depleted mantle source. Xenocrystic zircons (ca. 2.6 Ga) in the Upsalquitch gabbro suggest the involvement of old Archean crust, although the presence of the latter is not reflected in the Nd-and Sr-isotopic data.The ages presented in this chapter complement detrital and xenocrystic zircon studies carried out by others in the Gander Zone of New Brunswick and Newfoundland and together indicate that basement to the Gander Zone is mainly made up of Early Cambrian (0.54-0.55 Ga), Neoproterozoic (0.6-0.8 Ga), Mesoproterozoic (1.0-1.55 Ga), and Archean rocks (2.5-2.7 Ga). This range of ages, combined with the isotopic and geochemical data, eliminates Laurentia as a possible basement to the

Crustal Evolution of the Northeast Laurentian Margin and the Peri-Gondwanan Microcontinent Ganderia Prior to and During Closure of the Iapetus Ocean: Detrital Zircon U–Pb and Hf Isotope Evidence from Newfoundland

“…However, at present there are many detailed arguments in the literature that the Ganderian microcontinent separated from the Amazonia craton within western Gondwana from the approximate present position of the Caribbean margin of Colombia (van Staal et al 1996 and references therein). For example: (i) earlier-derived detrital zircon ages having a dominant Mesoproterozoic maximum could be matched with source areas overprinted by the Rondonian -San Ignacio orogeny and with Grenvillian basement inliers in the northern Andes; (ii) Cambrian cover sedimentary rocks in Colombia match coeval Ganderian strata containing trilobites of the same realm; (iii) truncation of Grenvillian inliers against the Caribbean coastline indicates removal of a crustal fragment; and (iv) a marked Cambrian transgression recorded in Colombian sedimentary rocks is interpreted to reflect separation of a large terrane.…”

“…van Staal et al 1996Rogers et al 2006;Hibbard et al 2007). East of the Ganderia microcontinent, another Gondwanaderived microcontinent -Avaloniawas added to the Appalachian terrane collage.…”

“…The Gander Group and its correlatives in New England, New Brunswick and the British Isles (van Staal et al 1996;Fig. 1b) are a distinctive cover sequence to the Ganderian microcontinental basement, which also underlies most of the Exploits Subzone (van der Velden et al 2004;.…”

A Review of Proterozoic to Early Paleozoic Lithotectonic Terranes in New Brunswick, Canada and their Tectonic Evolution during Penobscot, Taconic, Salinic and Acadian Orogenesis

“…However, the recognition that the Early Ordovician Penobscot orogeny, first defined in Maine (Neuman 1967), had affected other parts of the Gander Zone led to a more realistic model for the Early Paleozoic plate tectonic evolution of the northeastern Appalachians (Colman-Sadd et al 1992; van Staal 1994;van Staal et al 1996van Staal et al , 1998van Staal et al , 2003van Staal et al , 2009Hibbard et al 2006). These authors presented evidence that the Gander Zone of Williams (1979) formed part of a peri-Gondwanan microcontinent, referred to as Ganderia, which was separate from the Avalon Zone or Avalonia (Fig.…”

“…Consequently, this paper emphasizes integrating the tectonic evolution of the Ganderian terranes in southern New Brunswick with those in the north. The northern terranes (Miramichi, Elmtree, and Popelogan) are dominated by the previously documented development and destruction of the Tetagouche backarc basin, events that culminated in a younger period of Late Ordovician to Silurian Salinic orogenesis (van Staal 1987(van Staal , 1994van Staal et al 1990van Staal et al , 1996van Staal et al , 1998van Staal et al , 2003Fyffe 1991, 1995).…”