Discussion on ‘The sole of an ophiolite: the Ordovician Bay of Islands Complex, Newfoundland’ Journal , 170, 2013, pp. 715–722

Abstract

Dewey & Casey (2013) present a model for generation of the Bay of Islands Complex and its metamorphic sole that is anchored on intra-oceanic subduction initiation at a ridge–transform boundary. Several aspects of this model are inconsistent with a wealth of geological relationships and cannot readily accommodate the geological complexity of associated units in Newfoundland. Their model presents an alternative to the models of Waldron & van Staal (2001) and van Staal et al . (2007, 2013), which propose formation of the Baie Verte oceanic tract, including the Bay of Island Complex, after a Late Cambrian collision between an oceanic arc (Lushs Bight oceanic tract) and the Dashwoods microcontinent. In these models, the Baie Verte oceanic tract formed following subduction initiation in the seaway trapped between the Laurentian margin and the Dashwoods microcontinent. This subduction generated the continental Notre Dame Arc. Herein, we address some aspects of the Dewey & Casey (2013) model and discuss its tectonic implications. The model of intra-oceanic subduction initiation conflicts with the observation that the c . 489–485 Ma Baie Verte oceanic tract formed coevally with formation of the first phase ( c . 490–476 Ma) of the continental Notre Dame Arc (Dube et al . 1996; van Staal et al . 2007; Table 1). In addition, the Baie Verte oceanic tract formation was preceded by a slightly older arc ( c . 510–500 Ma Lushs Bight oceanic tract) that collided with the Dashwoods microcontinent (≥493 Ma; see below). The relationships to the older arc and its accretion to Dashwoods are crucial to understanding the formation of the Baie Verte oceanic tract, because the Bay of Islands Complex, at least in part, spread within rocks generally assigned to the Lushs Bight oceanic tract (e.g. Kurth et al . 1998), indicating that ophiolite formation …