ALONG-AXIS VARIATIONS IN OCEANIC CRUSTAL DENSITY AND THEIR CONTRIBUTION TO GRAVITY-ANOMALIES AT SLOW-SPREADING RIDGES

Gravity data from mill-ocean ridges are routinely used to infer crusta l thickness variations. Commonly, the contribution to the gravity anom aly from mantle density variations are taken into account, but variati ons in crustal density are rarely considered. Wide-angle seismic exper iments conducted in the same locations as detailed gravity surveys on the mid-Atlantic Ridge show that the crustal thickness inferred from g ravity data can deviate substantially from that derived from seismic d ata, particularly in the vicinity of ridge offsets. This discrepancy m ay be partly attributed to unmodeled crustal density variations: at sl ow-spreading ridges, crust formed near ridge offsets has consistently lower velocity than crust formed near segment centers, and a correspon ding density reduction of up to 20% may be inferred.