18 Crossing Borders: Large-scale tectonic models of the North American Cordillera

This session focusses on the Phanerozoic evolution of the North American Cordillera, soliciting studies that address large-scale tectonic models associated with obliquely convergent and divergent movement along the margin.

Thursday, 23 April 2026
8:00 AM - 12:00 PM
LMH, Isla Carmen

The one-two punch of the Sevier-Laramide orogeny: The left-lateral Intermontane superterrane movement

Paper number: 18-11
Program: Technical Sessions
Time: 11:20 AM – 11:40 AM

Authors

Abstract

We present a model for the first phase of the Sevier-Laramide orogeny in the western United States, from 130-105 Ma, caused by the southward movement of the Intermontane terrane.  Southward movement of the Intermontane terrane is constrained by paleomagnetic data from Quesnellia, Stikinia, and Blue Mountain terranes, and is corroborated by sinistral motion on margin parallel faults (e.g., Pasayten).  In northern Nevada, a promontory inherited from rifting associated with the breakup of Rodinia blocked the southward movement of the Intermontane terrane.  The collision of the Intermontane terrane with this promontory led to deformation in the central Cordillera, more localized than younger deformation. The following effects occur from west-to-east.  The Klamath mountains are pushed westward, offsetting their previous position as a continuation of the northern Sierra Nevada.  The Blue Mountains of Oregon are rotated ~30° clockwise when pushed against the promontory.  Deformation in the hinterland occurs in the Salmon River belt in Idaho, the Ruby Mountains-East Humboldt Range resulting in the northward increasing barometric gradient, and the Raft River-Albion-Grouse Creek mountains of Utah-Idaho with 132-138 Ma tectonic burial.  These results are consistent with the timing of the basal conglomerate of the Kootenai Fm of Montana, interpreted as recording regional uplift and erosion.  Contraction in the foreland occurs in the Sevier fold-and-thrust belt in Montana, Wyoming, and northern Utah.  The deformation associated with the southward translation continues through 105 Ma.  A compelling aspect of this model is the ~105-100 Ma top-to-the-north, extensional deformation documented in the Raft River-Albion-Grouse Creek mountains.  This extension is interpreted to result from the switch from contraction on the northern edge of the California promontory caused by southward motion of Insular Superterrane, to extension indicating the initial phase of opening of the Columbia embayment.  Subsequent Cretaceous deformation is associated with the 100 Ma oblique collision of the Insular superterrane and northward terrane translation, which also resulted in ~1000 km northward movement of the Intermontane superterrane.  Therefore, we argue the Sevier (sensu stricto) orogeny was the first blow of a “one-two punch” orogeny cause by southward movement of the Intermontane superterrane, effectively colliding with the northern margin of Precambrian promontory, and subsequent northward collision and movement of the Intermontane terrane colliding with the entire North American margin in the central Cordillera.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410853

© Copyright 2026 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.