Anelast ic tomography: a new perspective on upper mantle thermal structure

Anelastic tomography provides new insights into the thermal structure of the earth's upper mantle. Lateral variations in Q are largest in the upper 300 km, but remain significant down to at least 500-600 km. They correlate with the distribution of plates in the upper 300 kin, in agreement with cooling plate models and with the distribution of hotspots at greater depths. Two major upwellings are revealed under Hawaii and northeastern Africa, which may originate at the bottom of the transition zone or deeper. Low Q structure beneath the main ridge systems, on the other hand, does not appear to extend vertically below about 300 km.