Aeromagnetic evidence for a volcanic caldera(?) complex beneath the divideof the West Antarctic Ice Sheet

A 1995-96 aeromagnetic survey over part of the Sinuous Ridge (SR) beneath t he West Antarctic Ice Sheet (WAIS) divide shows a 70-km diameter circular p attern of 400-1200-nT anomalies suggesting one of the largest volcanic cald era(?) complexes on earth. Radar-ice-sounding (RIS) shows the northern part of this pattern overlies the SR, and extends south over the Bentley Subgla cial Trench (BST). Modeled sources of all but one the caldera(?) anomalies are at the base of < 1-2-km thick ice and their volcanic edifices have been glacially removed. The exception is a 700-m high, 15-km wide "volcano" pro ducing an 800-nT anomaly over the BST. "Intrusion" of this "volcano" beneat h 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice. The background area (-300 to -5 00-nT) surrounding the caldera(?) is possibly caused by a shallow Curie iso therm.