A study of the palaeomagnetism of subglacial basalts, SW Iceland: a comparison with oceanic crust

Subglacial volcanic sequences in Iceland were used as analogues of oceanic crust to get an indication of the degree of primary heterogeneity of magnetic directions that can be expected within subaqueous volcanic sequences erupted in both deep and shallow water. In the Icelandic sequences the degree 6f tilt, brecciation and the amount of hyaloclastite are known so it is possible to test for primary magnetic heterogeneity. We measured magnetic directions of 119 oriented core samples (2.5 cm diameter) collected from five sites in SW Iceland where there is good exposure in Quaternary subglacial volcanic sequences. Sample sites vary from compact pillowed flows (most analogous to deep water volcanic sequences) to pillow breccia with up to 40 per cent interpillow hyaloclastite (more analogous to shallow water sequences). Magnetic directions of multiple samples from 16 individual pillows have angular differences of 2"-66 " with most being less than lo". Of the five sites sampled, two sites have inclinations that approximate that of the centred axial dipole, one site has steeper inclinations and two sites have shallower inclinations. When the sit