The Himalaya-Tibetan orogen has become the paradigm for continental collision and is central to deciphering continental tectonics. Neogene extension in the orogen is not predicted by plate tectonic theory, and its significance is widely debated. In the Himalaya, north-south extension is restricted to the Southern Tibetan Detachment System (STDS), which juxtaposes the High Himalayan Crystalline ...

Incision of the Colorado River in the Grand Canyon, widely thought to have happened between ca. 6 and 1.2 Ma, has continued at variable rates along the canyon over the past ;500 k.y., based on measurements of bedrock incision combined with U-series and 40Ar/ 39Ar ages. River incision rates downstream of the Toroweap fault in the western Grand Canyon are about half the ;140 m/m.y. incision rate ...

Models of how high elevations formed across Tibet predict: (a) the continuous thickening of a "viscous sheet"; (b) time-dependent, oblique stepwise growth; and (c) synchronous deformation across Tibet that accompanied collision. Our new observations may shed light on this issue. Here, we use 40Ar/39Ar and (U-Th)/He thermochronology from massifs in the hanging walls of thrust structures along th...

In a reconnaissance study, we investigated the potential of γ-ray induced production 38ArK from 39K for geochronological applications. For this purpose, various age monitors commonly in use established 40Ar/39Ar-method were co-irradiated 60 h at 17.6 MeV maximum energy ELBE facility, Dresden-Rossendorf, Germany. Because available was low, total depressed, leading to low J38-values (2.1–4.1) × 1...

An 40Ar/39Ar chronology of in-situ to near insitu volcanic ashfall deposits indicates that the surficial stratigraphy of Arena Valley extends back at least to middleMiocene time. Wet-based glacial ice occupied part of Arena Valley more than 11.3 Ma ago. Thick, northeast-flowing ice subsequently engulfed Arena Valley, again more than 11.3 Ma ago. Only minor glacier expansion occurred during Plio...

The geomorphic character of major river drainages in the Himalayan foothills of central Nepal suggests the existence of a discrete, west-northwest–trending break in rock uplift rates that does not correspond to previously mapped faults. The 40Ar/39Ar thermochronologic data from detrital muscovites with provenance from both sides of the discontinuity indicate that this geomorphic break also corr...

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 infi ll deposited during fl ooding 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 i...