The late Paleozoic volcanic rocks of the northern Canadian Cordillera lying between Ancestral North America to the east and the accreted terranes of the Omineca belt to the west record early arc and rift magmatism along the paleo-Pacific margin of the North American craton. The Mississippian to Permian volcano-sedimentary Klinkit Group extends discontinuously over 250 km in northern British Columbia and southern Yukon. The two stratotype areas are as follows: (1) in the Englishman Range, southern Yukon, the English Creek Limestone is conformably overlain by the volcano-sedimentary Mount McCleary Formation (Lower Clastic Member, Alkali-Basalt Member and Volcaniclastic Member), and (2) in the Stikine Ranges, northern British Columbia, the Screw Creek Limestone is conformably overlain by the volcano-sedimentary Butsih Formation (Volcaniclastic Member and Upper Clastic Member). The calc-alkali nature of the basaltic volcaniclastic members of the Klinkit Group indicates a volcanic-arc setting ((La/Yb)N = 2.77–4.73), with little involvement of the crust in their genesis (εNd = +6.7 to +7.4). Alkali basalts in the Mount McCleary Formation ((La/Yb)N = 12.5–17.8) suggest periodic intra-arc rifting events. Broadly coeval and compositionally similar volcano-sedimentary assemblages occur in the basement of the Mesozoic Quesnel arc, north-central British Columbia, and in the pericratonic Yukon–Tanana composite terrane, central Yukon, suggesting that they all represent pieces of a single long-lived, late Paleozoic arc system that was dismembered prior to its accretion onto Ancestral North America. Therefore, Yukon–Tanana terrane is possibly the equivalent to the basement of Quesnel terrane, and the northern Quesnel terrane has a pericratonic affinity.

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Volcaniclastic and overlying dark sedimentary rocks of the Klinkit assemblage (NTS 104-O/11) are the youngest of several arc remnants that lie between the Cassiar Platform and Cache Creek terrane in the British Columbia-Yukon border area. New U-Pb geochronological and micropaleontological data indicate Late Carboniferous (or younger) to Late Triassic age for the assemblage. Limestone at the base of the Klinkit assemblage contains Bashkirian conodonts. Intrusive rocks, more deformed than the Klinkit assemblage, are ca. 340 Ma and ca. 320 Ma. A tuff, probably correlative with the Klinkit assemblage, yielded an Early Permian (ca. 281 Ma) date. Middle to Late Triassic conodonts were recovered from the argillaceous upper unit. We conclude that Klinkit volcanism, begun in the Late Carboniferous, continued through Permian time and was followed by Triassic clastic sedimentation. Correlative late Paleozoic volcanic centres and Triassic sedimentary rocks in the pericratonic belt are found in central Yukon and north-central British Columbia.

The Yukon-Tanana terrane in the northern Canadian Cordillera records the development of a series of midto late Paleozoic arc systems, punctuated by intra-arc deformation, uplift, and episodic rifting coeval with back-arc extension, built upon a metasedimentary basement of northwestern Laurentian affinity. In central Yukon, the Little Kalzas formation records the development of one of these Mississippian continental arcs, whereas the Little Salmon formation records the development of an intra-arc rift basin within a continental arc. The Little Salmon formation lower succession comprises mainly volcaniclastic rocks derived from erosion of Early Mississippian and older units, including rocks of the Little Kalzas continental arc. Above a medial limestone member, the upper succession of the Little Salmon formation includes alkali basalt, breccia, and crystal and ash tuffs in the north and predominantly epiclastic rocks interbedded with crystal and ash tuffs in the south. The alkali basalts have the geochemical characteristics of ocean-island basalts and their positive ε Nd 340 (+7.3) and low 87 Sr/ 86 Sr values (0.705) suggest a primitive magma source with little or no involvement of continental crust. The transition between the northern and southern facies of the upper succession of the Little Salmon formation coincides with a northeast-trending synvolcanic fault inferred to have controlled alkali basalt eruptions and deposition of Mn-bearing exhalite in the north and basin plain sedimentation in the south. The environment of deposition of the Little Salmon formation resembles that of the modern Sumisu rift in the Izu-Bonin-Mariana arc system or the early stages of development of the Japan island-arc system. Résumé :Le terrane de Yukon-Tanana dans le nord de la Cordillère canadienne enregistre le développement d'une série de systèmes d'arc, du Paléozoïque moyen à tardif, ponctuée par une déformation intra-arc, un soulèvement et de la distension épisodique contemporains avec une extension d'arrière-arc édifiée sur un socle métasédimentaire qui comporte des affinités avec le nord-ouest de Laurentia. Dans le centre du Yukon, la Formation de Little Kalzas enregistre le développement de l'un de ces arcs continentaux datant du Mississippien alors que la Formation de Little Salmon enregistre le développement d'un bassin de distension intra-arc à l'intérieur d'un arc continental. La succession inférieure de Little Salmon comprend des roches surtout volcano-clastiques qui proviennent de l'érosion d'unités datant du Mississippien précoce et plus anciennes, incluant les roches de l'arc continental de Little Kalzas. Au-dessus d'un membre de calcaire médian, la succession supérieure de la Formation de Little Salmon comprend un basalte alcalin, des brèches et des tufs cendrés et cristallins au nord ainsi que des roches surtout épiclastiques interlitées avec des tufs cendrés et cristallins au sud. Les basaltes alcalins ont les caractéristiques géochimiques de basaltes d'îles océaniques; leurs valeurs positives ε Nd 340 (+7,3) et le...