Antler orogeny and foreland basin: A model

Abstract

The Antler orogeny occurred in Mississippian time at a passive margin of the sialic North American continent in Nevada and probably in Idaho. Its principal events were the emplacement of an extensive allochthon of oceanic rocks on the continental shelf, subsidence of an elongate foreland basin, and maintenance of highlands in the interior region of the allochthon during and after subsidence of the foreland basin. The orogeny was apparently not accompanied by thermal phenomena or large crustal shortening. We follow earlier models by assuming that the orogeny was initiated by collision of an arc system with North America. Our proposal holds that a large accretionary prism of the probably far-traveled arc system was underthrust by the continental slope and outer shelf and became the Roberts Mountains allochthon. The Antler magmatic arc, now unexposed, thermally contracted after collision and was largely or entirely subducted in a later (Triassic) arc-continent collision. The Antler foreland basin was created by vertical loading and downflexing of the continental shelf by the allochthon, and sediment from subaerial regions of the allochthon ultimately filled and broadened the foreland basin. Quantitative models using the theory of a loaded thin elastic plate above a dense fluid provide reasonable agreement between calculated widths, depths, and asymmetry of plate deflections and the Antler foreland basin. Models predict that a flexural bulge of low amplitude migrated continentward ahead of the foreland basin during arc-continent closure. Certain stratigraphic phenomena in pre-foreland basin strata of central Nevada may record the passage of the bulge.