Magnetic properties of a columnar basalt from central Mexico

Abstract

The variation of low‐field magnetic susceptibility with low temperature (between ˜77°K and ˜300°K) observed for a vertical columnar basalt from central Mexico shows a rare pattern for continental basalt ‐ i.e. susceptibility decreases with temperature to about 40‐70% of room‐temperature value, and then increases up to about 60‐100% at 77°K. These results combined with other rock‐magnetic measurements, including AF and thermal demagnetization, IRM experiments, Lowrie‐Fuller tests, thermomagnetic analysis, and optical and SEM observations suggest the presence in the columnar basalt of predominantly single domain and pseudo‐single domain titanomagnetites with composition around TM60, and a small amount of very fine‐grained particles.