GEOCHEMISTRY OF THE ANNIDALE GROUP - IMPLICATIONS FOR THE TECTONIC SETTING OF LOWER ORDOVICIAN VOLCANISM IN SOUTHWESTERN NEW-BRUNSWICK

Chemical analyses from volcanic rocks in the Lower Ordovician Annidale Group in southern New Brunswick indicate that it contains two main su ites. The volumetrically more abundant suite is bimodal, and consists of within-plate tholeiitic basalt and rhyolite. The other suite contai ns rocks that exhibit features indicative of oceanic or possibly subdu ction-related magmatism. The chemistry of the former suite is consiste nt with the current interpretation that Ordovician volcanism in southw estern New Brunswick occurred in a back-are basin. The latter suite, s ituated near the highly-sheared southeastern margin of the Annidale Gr oup, apparently contains remnants of a different magmatic series near the suture zone between the Gander Zone and the surface expression of the Avalon Zone to the southeast.