Boulder, Colo., USA – Geosphere articles posted online 17 Mar. 2014 include additions to two series: "CRevolution 2: Origin and Evolution of the Colorado River System II" and "Origin and Evolution of the Sierra Nevada and Walker Lane." Other articles present new seismic data for the Slate Range of California, USA; the first detailed geologic map from the Likhu Khola region of east central Nepal; and a review of pre-21st century ideas about the origin of Grand Canyon.
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Middle Miocene to recent exhumation of the Slate Range, eastern California, and implications for the timing of extension and the transition to transtension
J. Douglas Walker et al., Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA. Published online 17 Mar. 2014; http://dx.doi.org/10.1130/GES00947.1.
Faulting in western North America reflects the interaction of the Pacific tectonic plate with the North American one. This paper by J. Douglas Walker of the University of Kansas and colleagues presents new data on how these plates have interacted over the past 15 million years. New data for the Slate Range of California shows that there was a change at about four million years ago in the style of faulting -- a change from a style similar to the Basin and Range to one more like the San Andreas fault. This occurred about six million years after a major change in the motion of the Pacific relative to North America. This suggests that the North American continent absorbed the change for a time before fully following it.
Zircon age and oxygen isotopic correlations between Bouse Formation tephra and the Lawlor Tuff
Janet C. Harvey, Department of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Boulevard, Pasadena, California 91125, USA. Published online 17 Mar. 2014; http://dx.doi.org/10.1130/GES00904.1. Series: "CRevolution 2: Origin and Evolution of the Colorado River System II."
From the abstract: The Bouse Formation in the lower Colorado River trough holds an important record of the onset of the modern drainage patterns in the southwestern United States. It comprises calcareous and clastic infill deposited during flooding of several basins, including the Bristol and Blythe subbasins of Lake Bouse. An intercalated ash bed, which is key to constraining its depositional age, is exposed in two locations, Buzzards Peak and Amboy…
A pre-21st century history of ideas on the origin of the Grand Canyon
Wayne Ranney, 255 E. Hutcheson Drive, Flagstaff, Arizona 86001, USA. Published online 17 Mar. 2014; http://dx.doi.org/10.1130/GES00960.1. Series: "CRevolution 2: Origin and Evolution of the Colorado River System II."
The Grand Canyon has been studied scientifically for more than 150 years, but to date no resolution has been achieved with regards to its specific age or mode of formation. Celebrated and illustrious geologists have contributed ideas to the ongoing debate, including John Strong Newberry, John Wesley Powell, Clarence Dutton, and Charles Walcott. Many of their ideas were revolutionary and helped set the stage for more modern studies. In this paper, author Wayne Ranney takes a sequential look at these ideas, providing a necessary background for anyone wishing to understand how Earth's most recognized landform came to be.
Mechanics of relative and absolute displacements across normal faults, and implications for uplift and subsidence along the eastern escarpment of the Sierra Nevada, California
Stephen J. Martel et al., Department of Geology and Geophysics, University of Hawaii, Honolulu, Hawaii 96822, USA. Published online 17 Mar. 2014; http://dx.doi.org/10.1130/GES00968.1. Series: "Origin and Evolution of the Sierra Nevada and Walker Lane."
A broad range of mechanical analyses shows that the faulting along the east side of the Sierra Nevada has dropped the surface east of the range much more than the range itself has been uplifted. This means the height of the range is ancient. The impressive eastern escarpment of the Sierra Nevada thus is a geologically young feature on an old range.
Tectonostratigraphy, deformation, and metamorphism of the Himalayan mid-crust exposed in the Likhu Khola region, east-central Nepal
Richard From and Kyle Larson, Department of Geological Sciences, 114 Science Place, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada. Published online 17 Mar. 2014; http://dx.doi.org/10.1130/GES00938.1.
This study presents the first detailed geologic map from the Likhu Khola region of east central Nepal with integrated descriptions of the lithological, structural, and metamorphic character of these rocks. These data are the critical building blocks for future research in the region. Richard From and Kyle Larson of the University of Saskatchewan interpret the rocks in the study area as being part of the exhumed metamorphic core of the Himalayan orogen in the hanging wall of the Main Central thrust. This differs from previous reconnaissance scale studies, which included the study area that placed the Main Central thrust within the study area. The current data from the Likhu Khola region as a whole supports an evolution of the Himalayan metamorphic core that includes components of spatially and temporally distinct yet compatible lateral mid-crustal flow and wedge taper deformation.
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