U–Pb zircon geochronology of Lower Jurassic and Paleozoic Stikinian strata and Tertiary intrusions, northwestern British Columbia

Abstract

New U–Pb zircon ages are reported from western Stikinia. Devonian and Pennsylvanian ages of volcanic rocks at Oweegee dome confirm the presence of pre-Permian strata, and with Paleozoic and Triassic detrital zircons from Lower Jurassic sandstone, they help to demonstrate pre-Lower Jurassic deformation and uplift. The absence of pre-Paleozoic inherited zircon from all samples is consistent with Nd–Sr isotopic data which suggest that Stikinia consists mainly of juvenile crust. U–Pb ages for posttectonic intrusions suggest that structures in Skeena Fold Belt in the Kinskuch area formed prior to Eocene time. Five ages for felsic volcanic rocks from stratigraphically well-constrained upper parts of the Hazelton arc are approximately 196–199 Ma and suggest near-contemporaneity for cessation of volcanism in the areas studied. The Sinemurian or late Sinemurian – early Pliensbachian ages are older than previously reported U–Pb and biostratigraphic ages for presumed correlative rocks to the west, and westward-migrating volcanism is implied. Together with Toarcian fossils from overlying sandstone, the new ages suggest that a hiatus of moderate duration preceded regionally extensive sedimentation.

Logan Medallist 1. Seeking the Suture: The Coast-Cascade Conundrum

“…Initiation of the mainly Jurassic arc successions of Wrangellia and Stikinia was in the latest Triassic: the oldest U/Pbdate from the Bonanza volcanics in Wrangellia on Vancouver Island is ~204 Ma, although fossil ages from the succession indicate the lowest part is slightly older (Graham Nixon, personal communication 2014); the oldest date from the Hazelton volcanics in Stikinia is ~203 Ma (Joanne Nelson, personal communication 2013); and that from the Talkeetna volcanics in Wrangellia composite terrane of southern Alaska is 207 Ma (Pálfy et al 1999;Amato et al 2007). Furthermore, in and near the eastern Coast Mountains between latitudes 54°30' and 57°, folds and thrust faults of latest Triassic age (> 203 Ma) involve Permian and Triassic Stikinian strata (Brown and Greig 1990;Greig and Gehrels 1995). Early Jurassic (~185 Ma) uplift and deep erosion of the Stikinian arc near latitude 60° was speculatively related by Johannson et al (1997) to processes accompanying strike-slip faulting.…”

A detrital record of Mesozoic island arc accretion and exhumation in the North American Cordillera: U-Pb geochronology of the Kahiltna basin, southern Alaska

“…The oldest known magmatic source areas associated with the Intermontane belt include an isolated suite of Cambrian–Ordovician rocks in western British Columbia [ Okulitch , 1985]. Some of the most widespread Paleozoic magmatic sources areas in the Intermontane belt consist of Late Devonian–Mississippian rocks (365–320 Ma) associated with the Quesnellia‐Slide Mountain terrane in southwest Yukon and western British Columbia and Stikinia terrane of southwest British Columbia [ Mortensen , 1990; Greig and Gehrels , 1995; Johnston et al , 1996]. Additional Paleozoic sources include Late Devonian–Mississippian augen gneiss and orthogneiss (380–330 Ma) of the Yukon‐Tanana composite terrane in east central Alaska and western Yukon [ Dusel ‐ Bacon and Aleinikoff , 1985; Aleinikoff et al , 1986; Mortensen , 1990; Johnston et al , 1996; Day et al , 2003].…”

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 unimodal detrital zircon age distribution (peak age of 368 Ma) in sample 081115KR‐01 suggests a local source of sediment that was relatively proximal to the area of deposition (i.e., not a regional watershed with multiple sources of sediment); likely sources are the felsic intrusive and extrusive rocks with documented U‐Pb zircon ages of 376–353 Ma that have been reported in the Totatlanika schist (or the equivalent Wood River assemblage) and Healy schist in east‐central Alaska (Dusel‐Bacon et al, , ). Additional potential igneous sources along the western Northern Cordillera, but currently more distal to our study area, include a suite of Late Devonian‐Mississippian magmatic sources with zircon ages of 365–320 Ma that correlate with the Quesnellia‐Slide Mountain terrane in southwestern Yukon and western British Columbia, along with similar Paleozoic ages from the Stikine terrane of southwestern British Columbia (Figure ) (Currie, ; Greig & Gehrels, ; Gunning et al, , ; Johnston et al, ; Mortensen, ).…”