Geochronology of the Buchans, Roberts Arm, and Victoria Lake groups and Mansfield Cove Complex, Newfoundland

Abstract

Volcanic groups of the Central Mobile Belt of the Newfoundland Appalachians have previously been subdivided into "early" and "late" arc sequences, separated in time by a quiescent Caradocian stage defined in some areas by fossil-bearing black shales.New U–Pb zircon ages of [Formula: see text] and 473 ± 2 Ma for rhyolites of the Buchans and Roberts Arm groups, respectively, show them to be correlative early Ordovician sequences. These ages serve to refute both the previous Rb–Sr whole-rock isochron ages of 447 Ma and the idea that these groups were "late arc" sequences. These new ages corroborate evidence from late Arenig – early Llanvirn conodonts in the Buchans Group and calibrate this fossil occurrence.A new U–Pb zircon age of 479 ± 3 Ma from plagiogranite of the Mansfield Cove Complex immediately west of the Roberts Arm Group shows that this plutonic body is only slightly older than the adjacent volcanic rocks and not Hadrynian as previously supposed. Local field relationships suggest this body may represent part of a disrupted ophiolite. It is coeval with the ophiolitic Annieopsquotch Complex along a strike to the south and may form part of a belt of rocks derived from early Ordovician ocean floor that is discontinuously exposed along the western boundary of the Buchans – Roberts Arm Belt.Zircons from rhyolite at the northeast termination of the Tulks Hill volcanics, part of the extensive Victoria Lake Group, give an age of [Formula: see text]. This dated sequence contains limestone previously dated as Llanvirn–Llandeilo by conodonts. This part of the group is therefore younger than the Buchans Group, and the designations "early" and "late" arc are not appropriate. The thrusting that juxtaposed these groups is no longer constrained to be of Silurian age but could have been middle to late Ordovician. Precambrian zircons included in the Victoria Lake Group rhyolite could have been incorporated from associated sedimentary rocks and suggest that the group may have formed in a tectonic setting transitional between oceanic and continental and received detritus from several sources.

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.…”

“…1), Floian volcanic rocks (ca. 471 Ma; Dunning et al 1987;G. Dunning, personal communication 2012) occur within Darriwilian (Whalen et al 2013) debris flows that host volcanogenic massive sulphide deposits (e.g.…”

“…Dunning and Krogh 1985;Zagorevski and van Staal 2011), indicating that it is a composite terrane. On the basis of age, structure, and tectonic setting, van Staal et al (1998) grouped the easternmost units of the Notre Dame subzone, including the Annieopsquotch ophiolite belt (Dunning 1987;Dunning et al 1987), into the Annieopsquotch accretionary tract (AAT), a southeast facing accretionary complex composed of slivers of arc and backarc rocks ( Fig. 1; e.g.…”

Tectonic implications of early silurian thrust imbrication of the northern exploits subzone, Central Newfoundland

“…Cross-cutting plutonic rocks presumably of the Hodges Hill Complex show that thrusting ended in the New Bay Pond area by Late Silurian-Early Devonian. Further south in the Buchans area, thrusts involve 473 + 3/-2 Ma and 462+4/ -2 Ma rocks (Whalen et al, 1987;Dunning et al, 1987), and a 429+3 Ma pluton cuts rocks of one thrust sheet (Whalen et al, 1987). It is unknown, however, whether or not this pluton is allochthonous.…”

Early Silurian paleolatitude for central Newfoundland from paleomagnetism of the Wigwam Formation: Discussion

“…These include the Lush's Bight, Catcher's Pond and Roberts Arm Groups. The latter has yielded a U-Pb zircon age of 473 + 2 Ma [14].…”