Differential incision of the Grand Canyon related to Quaternary faulting; constraints from U-series and Ar/Ar dating
Pederson, Joel; Karlstrom, Karl; Sharp, Warren; McIntosh, William (2002) Differential incision of the Grand Canyon related to Quaternary faulting; constraints from U-series and Ar/Ar dating. Geology Boulder, vol.30, no.8, pp.739-742, Aug 2002
| Authors | Pederson, Joel; Karlstrom, Karl; Sharp, Warren; McIntosh, William |
|---|---|
| Year | 2002 |
| Title | Differential incision of the Grand Canyon related to Quaternary faulting; constraints from U-series and Ar/Ar dating |
| Source | Geology Boulder, vol.30, no.8, pp.739-742, Aug 2002 |
| ISSN | 0091-7613 |
| GeoRef | 2002-079349 |
| Keywords | absolute age; active faults; Ar/Ar; Arizona; basalts; Basin and Range Province; basin range structure; carbonate rocks; Cenozoic; Coconino County Arizona; Colorado River; dates; faults; fluvial features; Grand Canyon; igneous rocks; incised-valley systems; Mohave County Arizona; neotectonics; normal faults; North America; Quaternary; rivers; sedimentary rocks; slip rates; tectonics; Toroweap Fault; travertine; United States; uranium disequilibrium; volcanic rocks |
| Notes | With GSA Data Repository Item 2002085 |
| DOI | 10.1130/0091-7613(2002)030<0739:DIOTGC>2.0.CO;2 |
Abstract
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 approximately 500 k.y., based on measurements of bedrock incision combined with U-series and super 40 Ar/ super 39 Ar ages. River incision rates downstream of the Toroweap fault in the western Grand Canyon are about half the approximately 140 m/m.y. incision rate calculated for a distance of at least 200 km upstream of the fault. We hypothesize that this differential incision is due to west-down slip on the Toroweap fault of 94 + or - 6 m/m.y. based on measured offset of the newly dated Upper Prospect basalt flow, which is the major middle-late Quaternary slip evident along the river. Regional incision has been driven mostly by base-level fall related to drainage reversal off the Colorado Plateau ca. 6 Ma. Because local normal faulting is lower in rate than this regional incision and is likely an expression of Basin and Range extension and subsidence rather than uplift, this is a case where active faulting diminishes, but does not drive, incision. Quaternary incision rates are insufficient to have carved the Grand Canyon in 6 m.y., suggesting either that rates have decreased through time as the original base-level signal has attenuated, or that some component of the canyon relief we see today existed prior to Colorado River integration.