New Look at Pueblo Mountains Shows Movement, Pinpoints Timing

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New Look at Pueblo Mountains Shows Movement, Pinpoints Timing

New data suggest that motion on a sheer zone in the Pueblo
Mountains on the Oregon-Nevada border occurred approximately 95
million years ago, in the Cretaceous period. The findings oppose
previous proposals that movement occurred 155 million years ago in
the Jurassic period.

In the study, Mary Anne Brown,a graduate student in geology and
geophysics at Rice University, found that in the northeast-trending
sheer zone-a broad fault zone below the surface of the earth-hotter,
deeper rocks were moved up from the southeast toward the northwest.

Brown presented the research at the 1996 Cordilleran Section
Meeting of the Geological Society of America in Portland on April
24. Her paper is entitled, “Structural Evolution and Timing of a NE-
Trending Shear Zone in the Pueblo Mountains, Northwest Nevada-
Southeast Oregon.”

Brown sees similarities in the orientation of the sheer zone and
the timing of the movement with other zones near the Oregon-Idaho
border to the north, which may have implications for the tectonic
history of the region.

Contact: Mary Anne Brown, at (713) 527-8750, ext. 2519, or
Lia Unrau, News Editor, Rice University News Office, at (713)
831-4793, by e-mail at unrau@rice.edu.

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