Exhumation of Grand Canyon’s basement along the Great Escarpment of Laurentia

Abstract

The Grand Canyon encompasses two billion years of Earth history, but more than half this record is absent across a regionally extensive erosional surface known as the Great Unconformity. This enigmatic surface has been linked to multi-phase regional tectonics accompanying supercontinent assembly and breakup and to Cryogenian glacial erosion. Although rift-related uplift during the breakup of Rodinia has long been implicated in erosion associated with the Great Unconformity, we argue that exhumation in the Grand Canyon region was focused along a continent-scale rift-flank escarpment. This “Great Escarpment of Laurentia,” initiated ca. 800−750 Ma, occupied a position analogous to major escarpments generated during Mesozoic Gondwana breakup and experienced similar magnitudes of exhumation. Our landscape evolution models simulating rift-driven topography suggest that rocks within several hundred kilometers of this feature endured substantial erosion, reaching 8 km near the escarpment and decreasing to ≤2 km at lateral distances of ∼200 km from its peak. Such differential erosion, evidenced in prior thermochronology models, necessitates exhumation of mid-crustal basement lithologies including along reactivated crustal fault blocks. This model helps explain the variable magnitude of erosion associated with the Great Unconformity in the southwestern United States.