Document Type

Article

Journal/Book Title/Conference

Journal of Geology

Volume

110

Publisher

University of Chicago

Publication Date

2002

First Page

305

Last Page

324

Abstract

Kinematic data associated with both Laramide‐age and ‐style and Rio Grande rift‐related structures show that the latest Cretaceous to Neogene interaction between the Colorado Plateau and the North American craton was dominantly coupled with a component of dextral shear. Consistent with earlier studies, minor‐fault data in this study yielded results of varied kinematics. Inverted to a common northeast‐oriented hemisphere, the mean trend of kinematic shortening associated with Laramide‐age structures is 056∘±6" role="presentation" style="box-sizing: border-box; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative;">056∘±6056∘±6

°. Inverted to a common west‐oriented hemisphere, the mean trend of kinematic extension associated with Neogene rifting is 300∘±34" role="presentation" style="box-sizing: border-box; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative;">300∘±34300∘±34

°. The observed dispersion in these directions suggests multiphase deformation, particularly during rifting, along the margin of the plateau since the latest Cretaceous. These data were evaluated using a simple two‐dimensional transcurrent kinematic model; assuming a minimal importance of strain partitioning, a mean trend of convergence between the Colorado Plateau and the North American craton was estimated to be 055∘±5" role="presentation" style="box-sizing: border-box; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative;">055∘±5055∘±5

°. Subsequent Rio Grande rifting, which separated the plateau from the craton, was associated with a mean divergence trend of 307∘±5.8" role="presentation" style="box-sizing: border-box; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative;">307∘±5.8307∘±5.8

°. Analysis of paleomagnetic data from Pennsylvanian to Triassic red beds along the eastern margin of the plateau and from rocks within the rift indicate clockwise rotations of uplifted blocks. Given the lack of regional strike‐slip and dip‐slip faults of common trends, the consistent clockwise rotations support an absence of strain partitioning. Correspondingly, for the north‐south‐trending eastern margin of the plateau, the apparently clockwise‐rotated paleomagnetic data are consistent with dextral transpressive shear between the plateau and the craton. Previous data indicating counterclockwise rotations of crust within parts of the Española rift basin are, if reliable, consistent with dextral transtensive shear. Overall, the transition from latest Cretaceous/Early Cenozoic shortening to Cenozoic extension seems characterized by a quasi‐continuous change from dextral transpressive to dextral transtensive deformation. This interpretation for the kinematic history of the eastern margin of the plateau demonstrates the importance of a dextral shear coupling between the craton and the Farallon plate system—a conclusion rarely implied by previous models of Cenozoic multistress field tectonics during deformation of the Cordilleran foreland.

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