Abstract

Two fundamentally different models describing the geometry, kinematics, and mechanism of emplacement of the allochthon of the Heart Mountain detachment have been advocated. The traditional "tectonic denudation model" comprises catastrophic gravity sliding of numerous detached blocks, with widespread subaerial exposure of the detachment by tectonic denudation. In this view, catastrophic volcanism covered the allochthonous blocks and the denuded detachment immediately after emplacement of the slide blocks. The alternative "continuous allochthon model" comprises noncatastrophic gravity spreading of a continuous allochthon, without tectonic denudation of the detachment. In this view, volcanism was noncatastrophic and predominantly coeval with, rather than subsequent to, faulting, and volcanic rocks constitute a large volume of the allochthon. Recent field studies indicate that the continuous allochthon model is geometrically and kinematically in accord with field relationships, analog models, geometric models, and relationships characterizing other detachment complexes, whereas the tectonic denudation model is not similarly substantiated. In particular, the tectonic denudation model is disproven by field relationships which demonstrate that volcanic rocks once thought to postdate faulting were instead tectonically emplaced. In addition, theoretical studies indicate that emplacement of the allochthon envisioned in the continuous allochthon model is mechanically plausible, whereas the catastrophic emplacement of detached blocks envisioned in the tectonic denudation model is mechanically implausible.

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