Abstract
"Residual gravity anomalies", RGA, in the north Pacific are calculated from the explosion seismic results and examined as a function of the sea-floor age deduced from the geomagnetic anomalies. The RGA, which implies the mass anomaly in the upper mantle, increases systematically as the age increases; this suggests gradual cooling of the upper mantle away from the midocean ridges.
The RGA in the Hawaii region, which is smaller than predicted by the standard RGA vs. age curve by about 100 mgal, implies hot material beneath this region. On the other hand, the RGA in the Parece Vela Basin is larger than predicted by the standard curve by about 100 mgal. This deviation can be expected if the upper mantle material beneath the marginal seas is of higher density than that beneath the normal ocean.
The thickness of the "plate" inferred from the RGA is approximately proportional to the square root of the age.
