Late precambrian volcaniclastic deposits of the avalonian eastport basin (newfoundland appalachians): petrofacies, detrital clinopyroxene geochemistry and palaeotectonic implications

Abstract

The Eastport basin contains over 5 km of well-preserved, marine volcaniclastic deposits, that comprise parts of the late Precambrian (Avalonian) Connecting Point and Love Cove groups of the eastern Newfoundland Appalachians. Basin infilling was dominated by deep-sea resedimentation of pyroclastic and epiclastic sediments. Four petrographically and texturally distinct petrofacies have been designated, viz.-tuffs, tuffaceous sandstones and conglomerates, feldspathic sandstones and conglomerates, polymict sandstones and conglomerates. A broad compositional spectrum of volcanogenic detritus, a copious supply of pyroclastic basaltic, andesitic, dacitic and rhyolitic ejecta, and the ubiquity of trace plutonic and metamorphic rock fragments are diagnostic provenance attributes of the basin-fill and these indicate derivation from an evolved magmatic arc, developed on a transitional or possibly continental crust. Detrital calcic clinopyroxenes and calcic amphiboles from the upper part of the Connecting Point Group are low in Ti and Al, display calc-alkaline and calc-alkaline to tholeftic affinity of the parental magma and plot in the field of orogenic basalts. Discriminant function analysis demonstrates that basalts and andesites were the main source of the detrital clinopyroxene. The clinopyroxene major-element chemistry is consistent with the evolved-volcanic-arc provenance suggested by petrographic data. Both datasets independently support other sedimentological and stratigraphic evidence that the Eastport basin records sedimentation adjacent to an active Avalonian-Cadomian volcanic arc, the remnants of which are preserved in part within the presently adjacent, predominantly volcanic Love Cove Group.