Abstract

The Gold Butte block of southeastern Nevada appears to be a cross section through the upper ∼17 km of Colorado Plateau crust, tilted eastward and tectonically denuded via top-to-the-west normal faulting in Tertiary time. The east side of the block exposes a steeply dipping cratonic Paleozoic section 2 to 3 km thick; Proterozoic basement to the west is continuously exposed for an apparent thickness of ∼15 km structurally below the basal Cambrian unconformity. Apatite fission track dating and confined track-length distributions have been used to determine the time of unroofing of the Gold Butte block and hence the timing of one episode of extension in this part of the Basin and Range province. Samples collected in an east-west transect along the block indicate an abrupt transition from a period of relative thermal and tectonic stability to the onset of rapid cooling. The fission-track data indicate that the unroofing of the Gold Butte block was rapid and that the crustal section was brought to within a few kilometres of the surface at ca. 15 Ma.

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