Volcaniclastic gravity flow deposits in the Dezadeash Formation (Jura-Cretaceous), Yukon, Canada: Implications regarding the tectonomagmatic evolution of the Chitina arc in the northern Cordillera of North America

The Chitina arc in the northern Cordillera of North America evolved during the accretion of the Wrangellia composite terrane to the western margin of North America in the Jurassic and Cretaceous. The Dezadeash Formation, a 3000m thick sequence of deepwater turbidites in southwestern Yukon, was deposited as a submarine fan in a backarc basin to the Chitina arc. Only limited geochemistry of altered volcanic rocks associated with the arc are available from southern Alaska. However, three thick volcaniclastic beds occur in the Dezadeash Formation. These consist of fine- to medium-grained vitric to crystal tuffs that are interpreted as resedimented syn-eruptive volcaniclastics. A U–Pb zircon age (149.4±0.3Ma) indicates they are contemporaneous with the Chitina arc. Petrographic examination shows the volcaniclastic rocks are altered mainly by albite and locally calcite, with a chemical index of alteration suggesting the rocks are relatively unweathered, or have undergone only incipient weathering. Harker diagrams indicate that CaO, K2O and Rb were mobile. Based on the Th vs. Co compositional diagram, the volcaniclastic rocks are classified as dacites, and according to various trace element plots they are calk-alkaline and adakite-like in composition. The volcaniclastic rocks plot in the active continental margin field on a variety of tectonic discriminant diagrams, and chondrite-normalized multi-element plots display parallel, listric-shaped profiles with significant light rare-earth element enrichment and minor heavy rare-earth element enrichment. Sm–Nd systematics indicate the volcaniclastic rocks represent mixing of a depleted mantle source and an older crustal source. These data suggest mainly slab dehydration with low pressure fractionation controlled by amphibole, with possibly minor input by slab melting. The Chitina arc has previously been interpreted as an oceanic island arc, and the continental arc signature of volcaniclastic rocks in the Dezadeash Formation, together with a continental arc signature of altered volcanic rocks in southern Alaska, is attributed to arc magmas erupting through Paleozoic volcanic, sedimentary and plutonic rocks of the Wrangellia composite terrane proxying for continental crust. ►Present a Riemannian framework to carry out generic computations on an ODF field. ►Does not require that the ODFs be represented by any fixed parameterization. ►Used Riemannian operations to perform various geometric data processing. ►Generalized Ho