A number of geophysical arguments point out the possibility that global mantle convection could have been extremely sluggish or even absent during a large part of Martian history. This implies that early mantle thermal anomalies produced during planetary formation might not have been quickly erased by vigorous convection. One likely mechanism of early thermal inhomogeneity is large impacts at the end of heavy bombardment. We suggest that Tharsis province might be related to such an impact-induced thermal anomaly rather than a convective plume. The shape of the present-day geoid for our preferred model is in good agreement with the geoid measured by Mars Global Surveyor (MGS).