Lithostratigraphy and lithogeochemistry of Ediacaran alkaline basaltic rocks of the Musgravetown Group, Bonavista Peninsula, northeastern Newfoundland, Canada: an extensional volcanogenic basin in the type-Avalon terrane

Volcanic rocks of the Ediacaran Musgravetown Group on Bonavista Peninsula, Avalon terrane, Newfoundland, include basal ca. 600 Ma calc-alkaline basalt succeeded by continental tholeiite and alkaline rhyolite 592 Plate Cove volcanic belt (Bull Arm Formation), indicating a change from subduction-related to extensionrelated tectonic regimes during that interval. Alkalic basalts northeastern (Dam Pond area) southwestern (British Harbour Peninsula occur below above, respectively, 580 glacial Trinity facies. Dam occurs in structural dome intercalated with flanked fine-grained, siliciclastic deposits (Big Head Formation) overlain The British above facies, an upward- coarsening sandstone sequence (Rocky red beds Crown Hill Formation (uppermost Group). Rocky Big formations are likely stratigraphically interfingered proximal distal deposits, derived erosion Bull older Avalonian assemblages.The have lower SiO2, Zr, FeOT, P2O5, TiO2 higher Mg#, Cr, V, Co Ni contents, therefore more primitive than FeOT-, TiO2-, P2O5-rich basalts. Large-ionlithophile rare-earth-element concentrations ratios indicate both suites originated low degree partial melts deep, weakly garnet-bearing, undepleted asthenospheric peridotite sources, magma conduits focused along regional extensional faults. protracted episodic extension-related activity is consistent geodynamic setting evolved mature arc into basins slowly waning magmatism, possibly involving slab rollback delamination followed magmatic underplating. duration variation volcanism sedimentation should be elevated Supergroup order facilitate future correlation its constituent parts other basins.