EVALUATING TECTONIC MODELS FOR THE FORMATION OF THE CANADIAN CORDILLERA USING MULTIVARIATE STATISTICAL ANALYSIS OF CONODONT FAUNAS FROM THE QUESNEL AND STIKINE TERRANES IN BRITISH COLUMBIA

The Canadian Cordillera is a composite of crustal terranes with various stratigraphic and tectonic histories. The relationships between these terranes, and their relative positions throughout the late Paleozoic and Mesozoic, are an ongoing field of research. In British Columbia and southern Yukon, the oceanic Cache Creek terrane is structurally juxtaposed between the island arc Stikine and Quesnel terranes. Previous studies have concluded that the Quesnel and Stikine terranes were originally part of the same arc, and were emplaced in their current configuration either through rotation (“entrapment” hypothesis) or by strike-slip faulting (“escape” hypothesis).

The two competing tectonic models are mutually exclusive. The “escape” hypothesis requires that the Stikine terrane was originally located to the south of the Quesnel terrane, before being moved northward by strike-slip faulting. In contrast, the “entrapment” hypothesis requires that the Stikine terrane was originally located to the north of the Quesnel terrane, before moving southward due to rotation. The present study utilizes multivariate statistical analysis of conodont faunas from the Quesnel and Stikine terranes to discriminate between the competing models. Such analysis allows the degree of similarity between faunas to be determined during the Late Triassic, prior to the time when both terranes are thought to have accreted to the North American margin in the Early-Middle Jurassic. In the “escape” hypothesis, the fauna from the northern part of the Stikine terrane should be most similar to that of the southern part of the Quesnel terrane, and in the “entrapment” hypothesis, the southern part of the Stikine terrane should be most similar to the northern part of the Quesnel terrane.

By comparing the Late Triassic conodont faunas from the terranes to those of the North American margin, it is also possible to constrain the latitude at which accretion took place. Abundant Late Triassic collections from British Columbia in the north and Nevada in the south provide a standard for the composition of relatively “high-latitude” and “low-latitude” conodont faunas at this time. Comparison with this standard gives an indication of how much lateral movement of terranes has occurred since accretion.