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Cenozoic Extensional Processes And Tectonics In The Northern Rocky Mountains, Susanne U. Janecke

Susanne U. Janecke

Extension has shaped the crust of the Northern Rocky Mountains for more than a billion years. Rifting produced the Belt basin shortly after 1.5 Ga and initiated the Paleozoic passive margin. Mesozoic to early Cenozoic convergence pro-duced the Cordilleran fold-and-thrust belt, the uplifts of the Rocky Mountain foreland (Laramide) and an unusually broad Challis arc in the northern Rocky Mountains. The struc-tural grain of the contractional belts, basement features, and the rheology of the Idaho batho-lith influenced the locus, kinematics and ge-ometry of the >55 m.y. of extension that fol-lowed. Sparse data suggest that extension may have begun in the …