EARLY PALEOZOIC ARC SYSTEMS IN THE NORTHERN APPALACHIANS: AN INTRODUCTION

Detailed thematic investigations with high quality age data are making it progressively more evident that the northern Appalachians contain numerous, generally short-lived (10-20 m.y.), arcs. The arcs formed between the Early Cambrian and Late Silurian. Geology and paleogeographic data indicate that these arcs represent different tectonic systems in the Iapetus Ocean. Newfoundland is particularly well endowed with a large number of well exposed arcs and it is tempting to use it as a template for New England with its extensive cover of Siluro-Devonian rocks and relative paucity of age data Although some arc systems can be traced for long distances along the orogen, others are not so easily correlated and may only have local significance. Suprasubduction (ssz) zone rocks of the peri-Laurentian Baie Verte Oceanic Tract (507-485 Ma) and Notre Dame arc (488-460 Ma) can be traced from Newfoundland into southern New England and their accretion to Laurentia is at least in part responsible for the Taconic orogenesis in western New England. Other peri-Laurentian arc systems (further outboard at 30oS?) such as the Arenig Annieopsquotch accretionary tract with its ssz ophiolites (480-468 Ma) and narrow slices of ensialic arc rocks (473-460 Ma) are either absent or can only locally be recognized (e.g., Ascot-Weedon?). The extent of the peri-Gondwanan arcs is also problematic. The Cambrian elements (513-488 Ma) of the Victoria/Penobscot arc-backarc system are well preserved in Newfoundland, but potential correlatives of these rocks are only recognized in southern New Brunswick and coastal Maine. It requires a complex tectonic model to accommodate these into one system. The overlying Middle Ordovician Victoria/Exploits arc-backarc system can reasonably be traced into the Popelogan-Tetagouche system in New Brunswick and northern Maine, but it is unclear whether they continue into the on-strike, generally slightly younger Bronson Hill arc. Two coeval Silurian arcs formed during final closure of the Tetagouche-Exploits basin and the docking of Avalon and/or Meguma, respectively. Slab break-off of the associated two slabs may be responsible for some, but possibly not all of the abundant Late Silurian/Early Devonian magmatism.