13-11 Inherited Passive Margin Architecture Controls Antler Foreland Basin Evolution

Session: Toe to Toe: Cordilleran Systems from Trench to Retroarc Domains

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Abstract:

The Devonian-Mississippian Antler Orogeny was the first in a series of mountain building events that occurred along the western margin of the North American continent in present day Nevada, California, and Idaho. Deformation associated with the Antler orogeny is best expressed along the Roberts Mountain thrust which emplaced the Roberts Mountain allochthon (RMA), comprised of Cambrian-Devonian deep-water marine siliciclastic and oceanic volcanic rocks, ~100 km eastward above continental-shelf carbonates and siliciclastic rocks of the western Laurentian passive margin. Shortening and associated crustal thickening during the RMA emplacement resulted in the formation of the adjacent 2 km thick Antler Foreland basin sedimentary sequence. However, the provenance and paleogeographic origin of the RMA strata, as well as the tectonic driver of the Antler Orogeny, remains debated due to an abundance of conflicting geochronological, structural, and sedimentological datasets. Here we integrate new and existing detrital zircon U-Pb datasets from Ordovician to Permian rocks across Nevada and eastern California to resolve the sediment provenance of the RMA and Antler foreland basin during the tectonic mode shift from a passive to convergent margin. Detrital zircon U-Pb results from Ordovician strata in the RMA and Laurentian passive margin sequence share a similar reworked Archean cratonic source. By the Silurian-early Devonian the deep-water RMA strata and shallow marine passive margin sediment show along strike mixing of cratonic sources. The asymmetric geometry of the Neoproterozoic to Devonian rift margin of western Laurentia is characterized by northwest striking extensional segments subdivided by northeast striking transform segments, which structurally controlled the sediment routing of shallow marine passive margin sedimentary sequences and deep-water equivalents in the RMA during late phase extension. Contraction related to the Antler Orogeny drove tectonic inversion and sedimentary recycling of the deep-water passive margin deposits of the RMA into the proximal foreland basin deposits. Pennsylvanian-Permian overlap deposits exhibit a provenance shift to greater contribution of western hinterland sources. The zigzag nature of Roberts Mountain Thrust and associated hinterland provinces is the consequence of inherited passive margin architecture, which subsequently controlled the sediment routing pathways and evolution of the Antler foreland basin of California and Nevada.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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