A NEW METHOD FOR DETERMINING MAGNETIZATION DIRECTION FROM GRAVITY ANDMAGNETIC-ANOMALIES - APPLICATION TO THE DEEP-STRUCTURE OF THE WORCESTER-GRABEN (VOL 152, PG 561, 1995)

The aeromagnetic field over the Worcester Graben, a major N-S-oriented , fault-bounded sedimentary basin, shows a large positive anomaly of 1 00 nT amplitude near the town of Tetbury. A new method for the determi nation of the magnetization direction of the causative body was employ ed that searches for the maximum correlation between the observed grav ity anomaly and the pseudogravity anomaly computed for a range of orie ntations of the magnetization vector. The method suggests a vertical m agnetization for the causative body of the Tetbury anomaly. A three-di mensional magnetic model of the body has the form of a cone, elongated N-S, whose base is at 6.0 km and upper surface at 3.1 km as indicated by power spectrum analysis of the anomaly. A two-dimensional model de rived from the gravity field and constrained by the surface geology, b orehole data and existing density measurements cannot simulate the obs erved anomaly over the centre of the graben. However, when the magneti c body is included in the gravity model, the fit is much improved. The western side of the body is probably imaged on a seismic reflection p rofile to the north. The body magnetization vector and the correlation of its possible northern extension with exposed Malvernian rocks sugg est a Precambrian age.