SYMMETRICAL GRAVITY ANOMALIES AS EVIDENCE OF VARIATION OF THE SPREADING VELOCITY ON MID-OCEAN RIDGES

Abstract

Visual inspection of records, followed by the mathematical analysis, of the geophysical field of the ocean have long ago revealed a symmetry of several geophysical variables with respect to the axes of the mid-ocean ridges (MOR). In the gravity field the general symmetry shows up in the Bouguer anomalies, whose amplitudes increase steadily in the direction from the center lines of the ridges toward the trenches, and conform to the generalized relief of the bottom. To find out whether there exist symmetrical shapes in the sea floor relief and what is their connection with the symmetric gravity anomalies, the authors carried out correlation tests where a zone of the relief was used as the reference anomaly signal. It turned out that the symmetry is either absent or the gravity effect of the relief does not induce the observed amplitudes of the symmetric gravity anomalies. The totality of their data suggests that the local symmetries of the gravity field anomalies their are not caused by random density inhomogeneities in the lower crust but are connected with certain definite changes in the velocities of spreading of the seafloor.