ONE NEOPROTEROZOIC GLACIATION, TWO EPISODES OF EXTENSION, AND ONE RIFT RECORDED AT GATAGA MOUNTAIN IN NORTHERN BRITISH COLUMBIA

In Northern British Columbia, mafic flows, felsic flows, and volcaniclastic deposits of the Gataga Volcanics are exposed at Gataga Mountain. A previous study reported a bulk fraction U/Pb TIMS age of 689.1 ± 4.6 Ma (Ferri et al., 1999) from a rhyolite within the volcanic stack. This age has been cited as a constraint on rift-related magmatism on the western margin of Laurentia. Additionally, recent age constraints on the Sturtian glaciation (716.5-662.4 Ma; Rooney et al., 2013) suggest that these volcanics were erupted during glaciation, however, no glacial deposits were previously identified. Here we present preliminary U/Pb single grain zircon ages, new stratigraphic and mapping relationships, and carbon isotope chemostratigraphic data to better understand the tectonic evolution of the western margin of Laurentia during the breakup of Rodinia, and to provide new age constraints on Cryogenian glaciations. We have distinguished three sequences exposed in the Gataga area, the Frog quartzite, the Gataga Volcanics, and the Matulka Group. The oldest rocks, the informal Frog quartzite, consist predominantly of cross-bedded shoreface sandstone and include a horizon with mud-cracks, indicative of non-glacial deposition. The overlying Gataga Volcanics are over 1 km thick, with volcaniclastic breccia common throughout. We identified multiple potentially glaciogenic matrix-supported diamictite units with cosmopolitan clasts, although definitive evidence for glaciation is lacking. Iron formation was identified above one of the diamictite units near the base of the volcanics. It is possible that the Gataga Volcanics were erupted in a sub-ice environment, however, the tightly folded, strongly foliated, metamorphosed nature of the volcanics makes it challenging to distinguish sub-ice from sub-aqueous explosive volcanic facies. Overlying the volcanics is the Matulka Group, a mixed carbonate-siliciclastic succession with minor basalt that is chemically distinct from the Gataga Volcanics. The Matulka Group appears to correlate with the late Ediacaran Hyland Group. We suggest that the iron formation is correlative with that in the Rapitan Formation to the north, and together represent narrow Cryogenian basins that formed 100 Ma prior to the unconformably overlying Ediacaran sequence.