Heat-flow data in the Four Corners area suggest Neogene crustal warming resulting from partial lithosphere replacement in the Colorado Plateau interior, southwest USA

Abstract

The uplift of the Colorado Plateau is of great geologic interest, and low-noise terrestrial heat-flow data can provide boundary conditions that should be met by proposed models of uplift. The structural continuity of the plateau interior with respect to the neighboring Basin and Range and Southern Rocky Mountains implies a distinctive Neogene lithosphere-crustal evolution. The Four Corners area represents a unique location in the Colorado Plateau interior, and likely the world, where both heat-flow data with little variability, and mineralogy studies relating to pre-Neogene lithosphere temperatures, are available. Together these studies allow one to calculate data-derived heat-flow values at two different times, ca. 25 Ma and the present. Using a first-order model for temperature-depth profiles, these two heat-flow values imply ∼100 km of Neogene lithosphere-asthenosphere boundary (LAB) shallowing in the study area. If crustal radiogenic heat remains constant, the calculated Neogene increase in heat flow of ∼17 mW m –2 will be produced below the Moho. Several mechanisms are considered that might cause the LAB to shallow and the near-surface heat flow to increase. Derived Neogene lithosphere thinning of ∼100 km leads one to consider lithosphere displacement of the same order. If the presented finite-difference model approximates Neogene thermal phenomena in the Four Corners, then partial lithosphere replacement of the upper-mantle lithosphere appears to be the most suitable cause of the heat-flow rise in the area, as well as the near-uniform heat flow over large regions of the plateau interior identified by low-noise heat-flow data.