An early history of pure shear in the upper plate of the raft river metamorphic core complex- black pine mountains, southern Idaho

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Journal Article: An early history of pure shear in the upper plate of the raft river metamorphic core complex- black pine mountains, southern Idaho

Abstract
Although commonly obscured by simple shear, pure shear fabrics occur locally within many metamorphic core complexes. The cover rocks to the Raft River metamorphic core complex exposed within the Black Pine Mountains display an early coaxial strain history which developed prior to the formation of low-angle fault-bounded allochthons. At higher structural levels this is documented by pressure shadows with straight sutures, and oppositely-rotated antitaxial calcite veins. These rocks were sub-horizontally extended parallel to bedding, by up to 160%, in an ≈ E-W direction. The marbles of the lowest exposed levels exhibit well-developed crystallographic preferred orientation fabrics. Calcite c- and a-axis pole figures are symmetric to slightly asymmetric, with obliquities ranging from 0° to 8°, which indicate that the percent pure shear ranges between 100 and 76%. Initial constraints on the timing of this layer-parallel extension suggest that extension was occurring locally within the Sevier belt hinterland during the late Cretaceous. These data, coupled with previous studies, suggest that pure shear might be a much more common component of strain in rocks deformed in extensional environments than is generally acknowledged.

Authors 
Wells, M.L.; Allmendinger and R.W.  








Published Journal 
Journal of Structural Geology, 1/1/1990





DOI 
http://dx.doi.org/10.1016/0191-8141(90)90059-8


 

Citation

Wells, M.L.; Allmendinger, R.W.  . 1/1/1990. An early history of pure shear in the upper plate of the raft river metamorphic core complex- black pine mountains, southern Idaho. Journal of Structural Geology. (!) .


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