En echelon Miocene rifting in the Southwestern United States and model for vertical-axis rotation in continental extension

Two areas of intense early Miocene crustal extension in the southwestern United States, the Colorado River trough and the central Mojave Desert, are separated by a weakly deformed area in the eastern Mojave Desert. We propose that these areas form a left-stepping en echelon rift system linked by a d...

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Bibliographic Details
Published in:Geology (Boulder) 1991-12, Vol.19 (12), p.1165-1168
Main Authors: Bartley, John M, Glazner, Allen F
Format: Article
Language:English
Subjects:
California
Cenozoic
Colorado River basin
continental crust
crust
Deserts
en echelon faults
extension
faults
Geology
lower Miocene
Miocene
Mojave Desert
Neogene
paleomagnetism
patterns
rift zones
rifting
Rivers
rotation
shear
Southwestern U.S
structural geology
tectonics
terranes
Tertiary
thin-skinned tectonics
United States
upper crust
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Summary:Two areas of intense early Miocene crustal extension in the southwestern United States, the Colorado River trough and the central Mojave Desert, are separated by a weakly deformed area in the eastern Mojave Desert. We propose that these areas form a left-stepping en echelon rift system linked by a ductile detachment at depth. The en echelon geometry explains the southward loss of displacement in the central Mojave Desert and northward loss of coeval displacement in the Colorado River trough, and it incorporates seismic reflection evidence that, mid-crustal Tertiary extensional mylonites continue beneath the weakly deformed area. This geometry also explains clockwise paleomagnetic declination anomalies from lower Miocene rocks as recording thin-skinned, detached rotations; large- scale block rotations are not required. Obliquity of the northeast-trending crustal-extension vector to the east-west-trending early Miocene synextensional volcanic belt may have caused the en echelon pattern to develop.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(1991)019<1165:EEMRIT>2.3.CO;2