Extensional Domains of the Northwestern Basin and Range Province
Abstract
Compilation of new and existing geologic, geochronologic, and thermochronologic data reveal that broad regions of northern Nevada have significantly different Tertiary histories in terms of timing and amount of extension. Definition of these different extensional domains allows better insight into the regional relationship of magmatism to extension and points to zones that acted as boundaries between areas that extended at different times. Much of central Nevada (roughly lat. 38-40) is blanketed by thick sections of Oligocene-Early Miocene volcanic rocks. Prominent unconformities in these sections indicate that parts of central Nevada underwent episodic and variable amounts of extensional faulting and tilting from Oligocene to Early Miocene time. Subsequently, rapid slip occurred along range-bounding faults at ~17-15 Ma. Despite apparently synchronous and rapid extension across an area stretching from the Wasatch front to the Wassuk Range east of the Sierra Nevada, volcanic rocks were erupted only locally in central Nevada at this time. In contrast, the Oligocene to Early Miocene volcanic rocks in northwestern Nevada are capped by the voluminous 17-15 Ma basalt-rhyolite sequence associated with the Northern Nevada Rift and the Yellowstone hot spot. The absence of angular unconformities in the volcanic section demonstrates that no faulting and tilting took place over the interval 30-15 Ma. The only extension to occur in this large region formed the modern ranges and was of low magnitude. Apatite fission-track data indicate that faulting was ongoing at 7-10 Ma, postdating both bimodal volcanism and rapid extension in central Nevada. Regions with possibly similar, but less well-documented, histories include the region of northwestern Nevada stretching from the Pine Forest Range to the Warner Range in northern California, and the region south of I-80 characterized by Northern Nevada Rift-related basalts now cut and tilted by modern range-bounding faults. This new compilation suggests that rapid 17-15 Ma extension in central Nevada was coeval with bimodal Yellowstone hot spot/Northern Nevada Rift volcanism to the north, but, despite being the locus of active volcanism during this interval, the crust in northwestern Nevada remained unextended until 5-8 million years later. The difference in the timing and amount of extension between these areas implies that an east-west trending shear or accommodation zone separated rapidly extending crust in central Nevada from unextended crust in northwestern Nevada during Middle Miocene extension.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.T31E0876C
- Keywords:
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- 8000 STRUCTURAL GEOLOGY (New field;
- replaces single entry 8165);
- 8109 Continental tectonics: extensional (0905)