A concordant UPb zircon age of 569.6 ± 5.3 Ma from synrift volcanic rocks of the Hamill Group, southeastern Canadian Cordillera, provides the first direct UPb geochronologic constraint on timing of latest Neoproterozoic rifting along western Laurentia. This age confirms a previous estimate of 575 ± 25 Ma for timing of continental breakup, as derived from the analysis of tectonic subsidence in lower Paleozoic miogeoclinal strata of the North American Cordillera. It also corresponds to the timing of passive margin deposition in the "underlying" Windermere Supergroup of the northern Cordillera, as determined by chemostratigraphic correlations. These timing relationships imply a different breakup history for the northern, as compared to the southern, Cordillera. We propose a model that attempts to explain this paradox of Cordilleran geology. The earlier Neoproterozoic (Windermere-age) rifting event probably records breakup of a continental mass from northern Laurentia followed by development of a passive margin. Accordingly, the Windermere Supergroup of the southern Canadian Cordillera was deposited in an intracontinental rift. The second Neoproterozoic rifting (HamillGog) is interpreted to indicate continental breakup and establishment of a passive margin along western Laurentia.
The Stikine assemblage, the "basement" of Stikinia, extends 500 km along the western flank of the Intermontane Belt, east of younger Coast Belt plutons. Four different stratigraphic successions are characteristic of Lower to Middle Devonian, Carboniferous and Permian rocks in the Stikine and Iskut rivers area. West of Forrest Kerr Creek are penetratively deformed Lower to Middle Devonian island-arc volcaniclastic rocks, coralline limestone, and felsic tuff. Fringing carbonate buildups in an arc setting are best illustrated in the sequence at Round Lake where Lower Carboniferous mafic-dominated, bimodal submarine volcanic rocks grade upward into two distinctive coarse echinoderm limestone units and medial siliceous siltstone and limestone conglomerate. Conodont colour alteration indices for Lower Carboniferous rocks near Newmont Lake indicate an anomalously low-temperature thermal history. Upper Carboniferous -Permian polymictic volcanic conglomerate and Lower Permian limestone overlie these strata there. The Scud River sequence is distinguished by subgreenschist-to greenschist-grade Carboniferous(?) volcanic and sedimentary rocks overlain by a structurally thickened package (greater than 1000 m) of Lower Permian limestone. Local calcalkaline pyroclastic rocks interfinger with limestone near the top of the Scud River sequence. Basinal, shelf, and shallow-water carbonate facies developed in the Early Permian, giving way to calcalkaline volcanism in Late Permian followed by deposition of deep-water chert and argillite.The tectonic setting during the Devonian and Carboniferous is comparable with modem Pacific volcanic arcs and atolls, but there is no modem analogue for the shelf-carbonate accumulation during the Early Permian which characterizes the Stikine assemblage and permits Cordilleran-scale correlations. Permian fusulinid and coral species have very close affinity to those of the McCloud Limestone of the eastern Klamath Mountains, California. Other geologic events common to both Stikinia and the Eastern Klamath terrane are Devonian limestone breccia deposition, Lower Permian limestone accumulation with McCloud faunal affinity, Carboniferous and Permian calcalkaline volcanism, and Upper Permian tuffaceous limestone. Stratigraphic differences include the absence of quartz detritus in Devonian strata and lack of thick Upper Permian volcanic rocks in the Stikine River area. --Les roches de l'assemblage de Stikine, representant le << socle D du terrane de Stikinia, s'ktendent sur 500 krn le long du flanc occidental de la Zone Intermontane, a I'est des roches plus jeunes du Complexe plutonique cBtier. On reconnait quatre successions stratigraphiques diffkrentes caracteristiques formkes de roches du Dkvonien moyen et infkrieur, du Carbonifere et du Permien dans les rkgions des rivibres Stikine et Iskut. A l'ouest du ruisseau Forrest Kerr, affleurent des roches volcanoclastiques d'arc insulaire, profondkment dkformkes, d'lge dCvonien moyen a infkrieur, et des calcaires coralliens et des tufs felsitiques. Des complexes...
This six-day trip presents the geological setting and structural history of the central Intermontane belt, a composite of Late Triassic to Early Jurassic volcanic and plutonic arc rocks and porphyry-related mineral deposits that developed on the fringes of ancestral North America before terrane accretion in late Early Jurassic. The trip comprises transects of southern Stikine, Cache Creek, and Quesnel terranes, with visits to six operating mines: Endako (Thompson Creek Metals Company Inc.), Gibraltar (Taseko Mines Limited), Mount Polley (Imperial Metals Corporation), Highland Valley (Teck Resources Limited), New Afton (New Gold Incorporated), and Copper Mountain (Copper Mountain Mining Corporation).
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