Evaluating tectonic models for the formation of the North American Cordillera using multivariate statistical analysis of Late Triassic conodont faunas

Abstract

The tectonic processes that led to the current configuration of the Quesnel and Stikine terranes within the North American Cordillera are contentious, with competing models favouring either northward, strike-slip movement or southward, rotational movement of the Stikine terrane. Multivariate statistical analysis of Late Triassic conodonts faunas from Canada and the USA has been used to evaluate these competing models and to constrain the movement of terranes relative to the North American continent. Late Carnian to early Norian conodonts are present in both the Stikine and Quesnel terranes, as well as at high and low latitudes on the North American continental margin, in northeastern British Columbia and Nevada respectively. The conodont faunas from each of these four geographic areas have been compared using the Dice, Jaccard, Ochiai and Simpson similarity indices. The highest values of similarity were found to be between the faunas of the Stikine and Quesnel terranes, supporting previous conclusions that these belonged to a single volcanic arc system. The conodont faunas of both of these terranes were more similar to that of northeastern British Columbia than either were to that of Nevada, suggesting that during the Late Triassic the terranes were more likely located at higher latitudes than lower latitudes. Finally, the conodont fauna of the Stikine terrane was significantly more similar to that of Nevada than the fauna of the Quesnel terrane was, which indicates that of the two terranes, the Stikine terrane lay farther south than the Quesnel terrane during the Late Triassic. This interpretation of the orientation of these terranes supports tectonic models that favour northward strike-slip translation of the Stikine terrane, rather than those models that require southward rotation of the terrane.