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Geophysical and Geochemical Evidence for Deep Temperature Variations Beneath Mid-Ocean Ridges

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Science  04 Apr 2014:
Vol. 344, Issue 6179, pp. 80-83
DOI: 10.1126/science.1249466

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Deep, Driving Temperatures

Convection in Earth's mantle is largely controlled by the physical properties of the mantle such as density and viscosity. Because these factors are influenced by both temperature and composition, it has been difficult to ascribe one as the primary control over mantle convection or explain the long-wavelength features associated with mid-ocean ridges. Examining correlations between a global seismic velocity model with constraints on the depth and geochemical signature of mid-ocean ridges, Dalton et al. (p. 80; see the Perspective by Kelley) suggest that large temperature variations extending into the upper mantle explain most of the geophysical and geochemical observations. Moreover, the analysis provides support for deeply rooted mantle plumes as the source of hot spot volcanism.

Abstract

The temperature and composition of Earth’s mantle control fundamental planetary properties, including the vigor of mantle convection and the depths of the ocean basins. Seismic wave velocities, ocean ridge depths, and the composition of mid-ocean ridge basalts can all be used to determine variations in mantle temperature and composition, yet are typically considered in isolation. We show that correlations among these three data sets are consistent with 250°C variation extending to depths >400 kilometers and are inconsistent with variations in mantle composition at constant temperature. Anomalously hot ridge segments are located near hot spots, confirming a deep mantle-plume origin for hot spot volcanism. Chemical heterogeneity may contribute to scatter about the global trend. The coherent temperature signal provides a thermal calibration scale for interpreting seismic velocities located distant from ridges.

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