Paleomagnetic evidence for en echelon crustal extension and crustal rotations in western Montana and Idaho

Article Abstract:

Paleomagnetic data from western Montana's Bitterroot metamorphic core complex show that the 26-degree change in strike of the dikes across the complex are due to tectonic rotation. Analysis indicates that while sliding out in a northeastward direction from underneath the Skalkaho slab, the Bitterroot dome rotated slightly in a counterclockwise direction, while the upper plate experienced a clockwise rotation near its northern edge. En echelon extensional detachments on either side of the slab explain this occurence. Eocene ductile/brittle extension stretches from British Columbia to south central Idaho.

Montana, Dikes (Geology), Domes (Geology)

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Implications of paleomagnetic data on Miocene extension near a major accommodation zone in the Basin and Range province, northwestern Arizona and southern Nevada

Article Abstract:

Paleomagnetic analysis of a northern Colorado River extensional corridor sheds light on the structure of a Miocene accommodation zone. Little vertical axis rotation is evident in the zone indicating that neither distributed strike-slip displacement nor major movement between opposing tilt blocks occured. Lower plate rock and mylonite distribution indicates shoaling of structural levels toward the accommodation zone. Upper crustal extension also declines in the same direction. The results suggest that the zone is a consistent barrier between conjugate Miocene normal faults.

Geology, Stratigraphic, Stratigraphy, Miocene Epoch, Faults (Geology), Great Basin

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Cenozoic crustal rotations in the Mojave Desert from paleomagnetic studies around Barstow, California

Article Abstract:

A paleomagnetic study of Mojave Desert around Barstow, California reveals 55-75 degrees clockwise rotation of the region in the earliest Miocene period, 23 degrees counter-clockwise rotation in the Early Miocene and no rotation after 18 Ma. This shows that Miocene extension in Majove Desert is similar to the extension in the Colorado river. The inclination of Oligocene-Miocene Oroclinical toward the southern Sierra Nevada caused the earlier clockwise rotation, while the early Miocene detachment faulting in the Mojave Desert resulted in counter-clockwise rotation.

Mojave Desert

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