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 right-lateral Insular superterrane oblique collision

Paper number: 18-10
Program: Technical Sessions
Time: 11:00 AM – 11:20 AM

Authors

Abstract

The Sevier-Laramide orogeny in the western United States is constrained by geological data to occur from 130-55 Ma.  We argue that this orogenic event is the result of two separate phases each caused by superterrane movement.  Moreover, the pattern of deformation is highly constrained by the geometry of the rifted Precambrian margin.  The first phase of deformation (Sevier sensu stricto or Sevier-Laramide Phase 1) is caused by the southward movement of the Intermontane terrane, with deformation possibly starting as early as ~144 Ma in western Idaho.  The second phase of deformation (Sevier-Laramide Phase 2) initiates at ~105-100 Ma, and is caused by the oblique collision of the Insular superterrane.  This presentation focusses on the Insular superterrane oblique collision, as there is increasing evidence for a major contractional event along the western margin of the United States and northwestern Mexico at ~100 Ma.  Evidence for deformation at 100 Ma includes the initiation of intra-arc transpressional shear zones, hinterland thickening, thrust-belt activation, and basement-cored block uplifts.  Moreover, paleomagnetic-based reconstructions place the Insular superterrane everywhere outboard of this deformation on North America, and there is major contraction within the Insular superterrane at this time. 

Herein, we focus on the effects of the hit-and-run on the North America margin, in order to provide a pre-100 Ma palinspastic reconstruction.  In particular, we restore Miocene-present movement on the Sierra-Great Valley block, the rotation of the Sierra Nevada “tail”, and ~400 km movement the Franciscan-Great Valley-western (only) Sierra Nevada that occurs from 100-85 Ma.  In central Idaho, we rotate counterclockwise the entire block containing the Idaho batholith and the adjacent Blue Mountain terranes.  The result is that central California – then located in south-central California – was a promontory of the North American margin.  The “space” north of this promontory – a significantly larger version of the Columbia embayment – was likely filled by the Intermontane superterrane, a fragment of which exists in NW Nevada as the Jungo terrane.  It was with this complex geometry of the North American margin that the Insular superterrane collided.

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

doi: 10.1130/abs/2026CD-410855

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