New super 40 Ar/ super 39 Ar isotopic dates from Miocene volcanic rocks in the Lake Mead area and southern Las Vegas Range, Nevada
Harlan, Stephen S; Duebendorfer, Ernest M; Deibert, Jack E (1998) New super 40 Ar/ super 39 Ar isotopic dates from Miocene volcanic rocks in the Lake Mead area and southern Las Vegas Range, Nevada. Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre, vol.35, no.5, pp.495-503, May 1998
| Authors | Harlan, Stephen S; Duebendorfer, Ernest M; Deibert, Jack E |
|---|---|
| Year | 1998 |
| Title | New super 40 Ar/ super 39 Ar isotopic dates from Miocene volcanic rocks in the Lake Mead area and southern Las Vegas Range, Nevada |
| Source | Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre, vol.35, no.5, pp.495-503, May 1998 |
| Publisher | National Research Council of Canada, Ottawa, ON, Canada CAN |
| ISSN | 0008-4077 |
| GeoRef | 1999-007756 |
| Keywords | absolute age; Ar/Ar; basalts; Basin and Range Province; basins; Boulder Basin; Cenozoic; Clark County Nevada; clastic rocks; dates; extension tectonics; faults; Gass Peak Formation; Horse Spring Formation; igneous rocks; Lake Mead; Las Vegas Range; Las Vegas Valley; lava; Lovell Wash Member; low-angle faults; magmatism; megabreccia; Miocene; Neogene; neotectonics; Nevada; normal faults; North America; pyroclastics; red beds; sandstone; sedimentary basins; sedimentary rocks; shear zones; structural controls; syntectonic processes; tectonics; Tertiary; tilt; tuff; United States; volcanic rocks |
| DOI | 10.1139/cjes-35-5-495 |
Abstract
New super 40 Ar/ super 39 Ar dates on volcanic rocks interlayered with synextensional Miocene sedimentary rocks in the western Lake Mead area and southern end of the Las Vegas Range provide tight constraints on magmatism, basin formation, and extensional deformation in the Basin and Range province of southern Nevada. Vertical axis rotations associated with movement along the Las Vegas Valley shear zone occurred after 15.67+ or -0.10 Ma 2sigma , based on a super 40 Ar/ super 39 Ar date from a tuff in the Gass Peak formation in the southern Las Vegas Range. Basaltic magmatism in the western Lake Mead area began as early as 13.28+ or -0.09 Ma, based on a date from a basalt flow in the Lovell Wash Member of the Horse Spring Formation. Isotopic dating of a basalt from the volcanic rocks of Callville Mesa indicates that these rocks are as old as 11.41+ or -0.14 Ma, suggesting that volcanic activity began shortly after formation of the Boulder basin, the extensional basin in which the informally named red sandstone unit was deposited. The red sandstone unit is at least as old as 11.70+ or -0.08 Ma and contains megabreccia deposits younger than 12.93+ or -0.10 Ma. This result shows that formation of the Boulder basin was associated with development of topographic relief that was probably generated by movement along the Saddle Island low-angle normal fault. Stratal tilting associated with extension occurred both prior to and after 11.5 Ma.