Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The Toodoggone Formation in Toodoggone River map area, north-central British Columbia, is an Early and Middle Jurassic time-stratigraphic Hazelton Group unit. Detailed mapping defined six subaerial lithostratigraphic members in the zeolite metamorphic facies. The High-K (3.1% K{dollar}\sb2{dollar}O at 57.5% SiO{dollar}\sb2{dollar}), calc alkaline latite and dacite volcanics are characterized by {dollar}\pm{dollar} sanidine - quartz - biotite - hornblende phenocysts. Basalt and rhyolite occur only as late dykes. Toodoggone strata occupy an elongate volcanic depression; they unconformably overlie submarine, arc volcanic and sedimentary rocks of the Permian Asitka and Late Triassic Takla Groups, and are capped unconformably by continental, Late Cretaceous clastic rocks of the Sustut Group.;Potassium-argon dates from the four volcanic members show two discrete cycles of volcanism. Shallow marine clastic rocks with middle to upper Toarcian fossils were deposited locally during the lull between cycles. The lower cycle (204 Ma to 197 Ma) began with widespread plateau-forming eruptions of dacite ash-flows, which are in part synchronous and superseded by latite flows and lahars that built stratovolcanoes. Possible comagmatic granodiorite and quartz monozonite plutons were emplaced during this period. The upper cycle began by 189 Ma with mainly dacite air-fall deposits. It culminated at about 182 Ma with voluminous outpourings of ash-flow tuffs and accompanying asymmetric collapse that produced the Central Toodoggone Depression.;The Toodoggone Formation is interpreted to record island arc magmatism. This arc magmatism resembles modern continent margin arc successions both in style and composition, hence it is believed that a thick, continent-like substrate underlies the Toodoggone area. The Toodoggone arc segment may be east-facing and related to steep, oblique westward subduction with a protracted history of intra-arc extension and shallow crustal subsidence. Extension and magmatism in Toodoggone map area is strikingly similar to large-scale extension and volcanic-sedimentary events in the McConnell Creek and Hazelton areas. This suggests consistent Jurassic tectonic evolution in these areas within a common, east-facing island arc developed along the east margin of the allochthonous Stikine terrane.



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