Studies of high-pressure xenoliths suggest that mafic rocks are dominant in the lower crust and abundant in the uppermost mantle, beneath most continental areas. Xenolith data allow construction of geotherms and stratigraphic profiles and provide lithological constraints and physical parameters for realistic interpretations of geophysical data. In continental regions of high heat flow, the Moho, as defined by seismic refraction data, may lie deeper than the crust/mantle boundary. The seismic differences recorded for cratonic vs. “hot” lower crust/upper mantle sections may be explained by temperature variations alone and do not require large lithological differences.

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