STRUCTURE OF A HYPOVOLCANIC ACID COMPLEX INFERRED FROM MAGNETIC-SUSCEPTIBILITY ANISOTROPY MEASUREMENTS - THE WESTERN RED HILLS GRANITES (SKYE, SCOTLAND, THULEAN IGNEOUS PROVINCE)

The geochemistry and the injection mechanism of hypovolcanic ring dyke s have been extensively studied, but such is not the case for their in ternal fabric. The Tertiary Western Red Hills epigranites of the Isle of Skye are a classic example of such intrusions. Using anisotropy of magnetic susceptibility measurements, we present the first structural data of their internal magmatic fabric. The magnetic foliations, equat ed with the magmatic flow planes, have strikes which roughly follow th e walls of the different intrusions. They dip steeply toward the conve x wall of each intrusion. The lineations, or maximal magnetic suscepti bility axes, generally have shallow plunges, except in the latest gran ite intrusion. These structures appear to be related to the compressio nal deformation of each intrusion toward the end of its crystallizatio n. This shortening would be a consequence of a radial and compressive stress field acting after each injection of magma. This radial stress field is interpreted as the effect of high magma pressures originating from the acid magma chamber underlying the ring-dyke complex at a sha llow depth.