Provenance analysis of the Dezadeash Formation (Jurassic–Cretaceous), Yukon, Canada: implications regarding a linkage between the Wrangellia composite terrane and the western margin of Laurasia

Abstract

The Mesozoic convergence of the allochthonous Wrangellia composite terrane (WCT) with the western margin of Laurasia coincided with the construction of the Chitina magmatic arc on the WCT, and the dispersal of volcanic flows and sediment gravity flows into an adjacent flysch basin. The basin, preserved as the Gravina–Nutzotin belt, includes the Dezadeash Formation in southwest Yukon, the Nutzotin Mountains sequence in southern Alaska, and the Gravina belt in southeastern Alaska. The Dezadeash Formation is a submarine fan system comprising stacked channel-lobe transition and lobe deposits interposed with overbank deposits. Conglomerate pebble-counts, sandstone point-counts, detrital zircon ages, and major element, trace element, rare earth element, and Sm–Nd isotopic geochemistry of sandstone, mudstone, and hemipelagite beds suggests that the deposits consist mainly of first-cycle volcanogenic detritus shed from the undissected Chitina arc, in addition to material eroded from the WCT. The arc was constructed of undifferentiated magma sourced from the depleted mantel, as well as older crustal material attributed to the WCT proxying for continental crust. The compositional provenance results, together with published paleocurrent data for the Dezadeash Formation and compositional and directional provenance indicators from the Nutzotin Mountains sequence and Gravina belt, does not require a sediment source from Laurasia. The provenance record is compatible with deposition of the Gravina–Nutzotin belt in a convergent plate margin setting.

Detrital zircon geochronology along a structural transect across the Kahiltna assemblage in the western Alaska Range: Implications for emplacement of the Alexander-Wrangellia-Peninsular terrane against North America

“…Detrital zircon geochronological data for sandstone samples from the Kahiltna assemblage have been published from the central Alaska Range (Hampton et al, 2007(Hampton et al, , 2010 and from the western Alaska Range (Kalbas et al, 2007;Bradley et al, 2009;Hults et al, 2013). Similar analyses have also been published for the Nutzotin basin (Hults et al, 2013), the Dezadeash basin (Lowey, 2019) and the adjacent Kluane schist (Israel et al, 2011), and for Gravina basin strata (Yokelson et al, 2015, and references therein). All these studies identified a distinct contrast in detrital zircon populations A B Structure section line (Fig.…”

“…Trimble samples generally have 0%-5% Precambrian grains, and no samples have a statistically significant Precambrian age population. The Late Jurassic age populations are correlative with volcanic and plutonic rock ages within the "Chitina arc" sequence of the Alexander-Wrangellia-Peninsular terrane from the Wrangell Mountains down into southeastern Alaska (Plafker et al, 1989;Trop and Ridgway, 2007;Beranek et al, 2017;Lowey, 2019). The Early Jurassic ages are well represented in both intermediate volcanic and felsic plutonic rocks within the Alexander-Wrangellia-Peninsular terrane ("Alexander-Wrangellia-Peninsular igneous" in Fig.…”

“…Laurentian basement and cover the eastern Alaska Range near the Canadian border (Manuszak et al, 2007), as the Dezadeash Formation and the adjacent Kluane schist (offset by Cenozoic dextral displacement across the Denali fault: Fig. 1) in Yukon, Canada (Eisbacher, 1976;Lowey, 1998Lowey, , 2019Mezger et al, 2001;Israel et al, 2011), and then to the southeast through southeastern Alaska in the Gravina basin (Berg et al, 1972;Brew and Karl, 1988;Rubin and Saleeby, 1991). Southwest of the Alaska Range, the northwestern part of the Kahiltna assemblage strikes southwest into the Upper Cretaceous Kuskokwim Group, whereas the southeastern part of the Kahiltna assemblage trends southwest into Upper Jurassic and Lower Cretaceous strata of the Koksetna River sequence (Wallace et al, 1989;Wilson et al, 2015).…”

Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

“…Nutzotin Mountains strata are locally in depositional contact with the Wrangellia-Alexander terrane and in other areas have been thrust southward (present-day coordinates) over Wrangellia along south-verging thrust faults (Richter, 1976;Manuszak et al, 2007). Sedimentological and detrital data from the Nutzotin Mountains sequence and Dezadeash Formation reflect a provenance from sources within the Wrangellia-Alexander terrane (Manuszak et al, 2007;Lowey, 2011;Fasulo et al, 2018;Lowey, 2018), similar to the southern Kahiltna assemblage. Manuszak et al (2007) infer that the Nutzotin strata accumulated in a compressional basin setting linked to Late Jurassic-Early Cretaceous shortening, uplift, and unconformity development documented in the Wrangellia composite terrane south of the Nutzotin basin (Trop et al, 2002).…”

Geology, U‐Pb Geochronology, and Hf Isotope Geochemistry Across the Mesozoic Alaska Range Suture Zone (South‐Central Alaska): Implications for Cordilleran Collisional Processes and Tectonic Growth of North America

“…The absence of detrital zircon ages from the regionally extensive Late Cretaceous arc rocks in the Jurassic‐Cretaceous basins in eastern Alaska (Figures D and E) and southeastern Alaska (Figures G and H) suggest that deposition may have ended earlier in these basins relative to the basins in south‐central Alaska. As part of the Jurassic‐Cretaceous basins, the Dezadeash Formation within the Dezadeash basin in Yukon, Canada also shows an absence of Late Cretaceous detrital zircon ages (Lowey, ). Lowey () presents new U‐Pb analyses of detrital zircons from the Dezadeash Formation that range from ~2111–145 Ma, with Mesozoic ages as the most abundant and a youngest dominant peak age at ~157 Ma (Figure A in Lowey, ).…”