Geodynamic implications of xenolith geotherms

Studies of xenolith suites yield depth‐temperature arrays for the lithosphere at the time of eruption. These studies constrain the conductive heat flow through the lithosphere and limit the temperature range across the rheological boundary layer to <300 K. Numerical models of convection illustrate features that may be found within suites of samples. An individual dike may sample the geotherm along a finite length of its strike having variable geotherms, causing scatter in the depth‐temperature array. In a suite from the Slave Province of Canada, local heating within a deep stockwork is a more likely cause of scatter. Plume material ponded beneath a craton may yield a linear array extrapolating to the shallow geotherm without any noticeable kink or curvature. This situation existed beneath Lesotho in South Africa at ∼90 Ma. Convection at the base of the lithosphere may produce stress concentrations that trigger dike formation. Dikes may stagnate and form stockworks in low‐stress regions above the thermal boundary layer.