Recent craton growth by slab stacking beneath Wyoming

Abstract

Seismic tomography images high-velocity mantle beneath the Wyoming craton extending to >250 km depth. Although xenoliths and isostatic arguments suggest that this mantle is depleted of basaltic component, it is not typical craton: its NE elongate shape extends SW of the Wyoming craton; xenoliths suggest that the base of Archean mantle was truncated from ∼180–200 to ∼140–150 km depth since the Devonian, and that the deeper mantle is younger than ∼200 Ma. The Sevier–Laramide orogeny is the only significant Phanerozoic tectonic event to have affected the region, and presumably caused the truncation. Apparently, the base of the Wyoming craton was removed and young, depleted mantle was emplaced beneath the Wyoming craton during the Sevier–Laramide orogeny. We suggest that the Wyoming craton experienced a ∼75 Ma phase of growth through a three-stage process. First, flat-slab subduction removed 40–50 km off the base of the Archean Wyoming craton. This was followed by emplacement of basalt-depleted ocean plateau mantle lithosphere of the Shatsky Rise conjugate, which arrived in the early Laramide. The geologic recorded of vertical motion in the Wyoming region suggests that the plateau's crust escaped into the Earth's interior at 70–75 Ma. Initiation of Colorado Mineral Belt magmatism at this time may represent a slab rupture through which the ocean crust escaped.