Abstract
Summary Magnetic, petrologic and mineralogic measurements were made on fifty-six samples taken on a regular grid from across the transverse surface of a single prism of columnar basalt. No systematic variations were found in the density, petrology and gangue mineralogy which reflect the uniformity of the primary magma. Systematic variations related to the column’s shape of about 40% were found in the remanence intensities, magnetic hysteresis and thermomagnetic properties which reflect systematic variations in the oxygen and titanium content of the titanomagnetite. The amount of scatter in the directions of the remanence and of the axes of the ellipse of susceptibility anisotropy is significant and is strongly related to the column’s shape; it may reflect the tensional stresses or rate of cooling. The magnitude of the anisotropy of susceptibility is unrelated to the column’s shape but reflects a systematic viscous flow pattern in the primary magma. This study indicates that care must be taken in sampling columnar basalts for palaeomagnetic studies and that a continuous contraction hypothesis best explains the genesis of the columns.
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