Cenozoic thermal and topographic evolution of the northern Great Basin, western U.S.

It is often argued that late Mesozoic crustal shortening beneath the Great Basin, western U.S., produced extremely thick (60-70+ km) crust that supported a high (> 3 km) plateau, the Nevadaplano. According to this concept, gravitational collapse led to extension that began in the Late Cretaceous and eventually produced the Basin and Range province (BRP). Unfortunately, this model does not explain how ultra-thick crust was thinned to its present 30 km, given estimates of only 50% extension during BRP faulting.

Sedimentary rocks deposited across the retro-arc region record Late Cretaceous and Cenozoic tectonism and topography, which serve as proxies for elevation and crustal thickness. New U-Pb detrital zircon dates improve ages of strata sampled for stable isotope paleoaltimetry and paleoclimate studies of the Elko Basin area, northeast Nevada. We also report new δ¹⁸O and δ¹³C measurements from 20 samples. The data show a minor increase in δ¹⁸O (2‰) sometime between the Late Cretaceous and 46 Ma, followed by a 12‰ decrease between ca. 38-24 Ma, and finally a 4‰ increase between 10-3 Ma. If a portion of the δ¹⁸O record indicates elevation changes (rather than purely climate), then a substantial elevation increase occurred at these latitudes between late Eocene and late Oligocene time, contradicting the Nevadaplano model. The new data suggest moderate Mesozoic crustal thickening (perhaps to 45 km), followed by thermal uplift due to Eocene-Oligocene asthenospheric upwelling and south-sweeping volcanism associated with removal of the shallow Laramide slab. Sedimentation began ca. 46 Ma and ended at 38 Ma in the Elko Basin, when volcanism arrived. Across the Great Basin, volcanic material in E- and W-draining paleovalleys youngs southward. We propose that deposition occurred in a trough ahead of the migrating thermal bulge. Thus, the N-S paleodivide inferred to have traversed Nevada in Eocene-Oligocene time may have been time-transgressive.

Following volcanism, crustal temperatures remained elevated for up to 10 Ma. Minor sedimentation began in latest Oligocene time, perhaps heralding the onset of extension, and accelerated markedly ca. 17 Ma. Extension was driven by thermally elevated, weakened crust, but boundary conditions were also critical, including plate motions and the final removal of the Laramide slab.