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-fl ow 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-fl ow 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-fl ow values at two different times, ca. 25 Ma and the present. Using a fi rst-order model for temperature-depth profi les, these two heat-fl ow 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 fl ow 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 fl ow to increase. Derived Neogene lithosphere thinning of ~100 km leads one to consider lithosphere displacement of the same order. If the presented fi nite-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-fl ow rise in the area, as well as the nearuniform heat fl ow over large regions of the plateau interior identifi ed by low-noise heatfl ow data.

Timing of the Cenozoic “Great Hydration” event beneath the Colorado Plateau: Th-Pb dating of monazite in Navajo volcanic field metamorphic eclogite xenoliths

“…An additional uplift of ~700 m in the Oligocene was attributed to mantle upwelling (also see Reiter, 2014). The 28 Ma age for monazite growth in our samples is in agreement with the Oligocene uplift of the Liu and Gurnis (2010) and Reiter (2014) models.…”

“…An additional uplift of ~700 m in the Oligocene was attributed to mantle upwelling (also see Reiter, 2014). The 28 Ma age for monazite growth in our samples is in agreement with the Oligocene uplift of the Liu and Gurnis (2010) and Reiter (2014) models. We argue that these ages represent the part of the Great Hydration event in which the peridotite in the mantle lith-osphere of the central plateau was partially hydrated to antigorite, chlorite, and amphibole.…”

Heat Flow Data in an Area of the Eastern Southern Basin and Range in Arizona Contribute to an Analysis of Neogene Lithosphere Thinning Greater than 100 Km

“…Geothermal information providing subsurface temperature estimates relevant to a past geologic time can be considered with present heat flow data to estimate the related past lithosphere thickness as well as lithosphere thinning over the corresponding geologic interval. For example, mineralogy and heat flow studies were used to estimate heat flow~25 Ma for the Four Corners Area of the Colorado Plateau [1,2] and to suggest Neogene lithosphere thinning of 100 km for the area. A heat flow-temperature-depth expression, the same as in this study, was used to match upper man-tle depth-temperature estimates at~25 Ma consistent with the mineralogy data relevant at~70 and~140 km depth [1,2].…”

“…For example, mineralogy and heat flow studies were used to estimate heat flow~25 Ma for the Four Corners Area of the Colorado Plateau [1,2] and to suggest Neogene lithosphere thinning of 100 km for the area. A heat flow-temperature-depth expression, the same as in this study, was used to match upper man-tle depth-temperature estimates at~25 Ma consistent with the mineralogy data relevant at~70 and~140 km depth [1,2]. From this analysis, a heat flow estimate of 47 mW m -2 for 25 Ma was possible, and therefore, an estimate of lithosphere thickness could be made [1].…”

“…A heat flow-temperature-depth expression, the same as in this study, was used to match upper man-tle depth-temperature estimates at~25 Ma consistent with the mineralogy data relevant at~70 and~140 km depth [1,2]. From this analysis, a heat flow estimate of 47 mW m -2 for 25 Ma was possible, and therefore, an estimate of lithosphere thickness could be made [1]. Heat flow analyses also provided estimates of present lithosphere thickness from the present heat flow data for the Colorado Plateau, which was consistent with seismic studies [1].…”