  The areal centroids of the youngest polar deposits on Mars are offset from
those of adjacent paleopolar deposits by 5-10 degrees. We test the hypothesis
that the offset is the result of true polar wander (TPW), the motion of the
solid surface with respect to the spin axis, caused by a mass redistribution
within or on the surface of Mars. In particular, we consider TPW driven by
late-stage volcanism during the late Hesperian to Amazonian. There is
observational and qualitative support for this hypothesis: in both North and
South, observed offsets lie close to a great circle 90 degrees from Tharsis, as
expected for polar wander after Tharsis formed. We calculate the magnitude and
direction of TPW produced by mapped late-stage lavas for a range of
lithospheric thicknesses, lava thicknesses, eruption histories, and prior polar
wander events. If Tharsis formed close to the equator, the stabilizing effect
of a fossil rotational bulge located close to the equator leads to predicted
TPW of <2 degrees, too small to account for observed offsets. If, however,
Tharsis formed far from the equator, late-stage TPW driven by low-latitude,
late-stage volcanism would be 6-33 degrees, similar to that inferred from the
location of paleopolar deposits. 4.4+/-1.3x10^19 kg of young erupted lava can
account for the offset of the Dorsa Argentea Formation from the present-day
south rotation pole. This mass is consistent with prior mapping-based estimates
and would imply a mass release of CO2 by volcanic degassing similar to that in
the atmosphere at the present time. The South Polar Layered Deposits are offset
from the spin axis in the opposite sense to the other paleopolar deposits. This
can be explained by an additional contribution from a plume beneath Elysium. We
conclude with a list of observational tests of the TPW hypothesis.
