Abstract
A variety of rock-magnetic, paleomagnetic, ore-microscopy and scanning electron microscopy methods have been used to study the magnetic mineralogy and domain structure in samples of a columnar basalt from San Anton (Cuernavaca, Mexico). The basalt presents a rare unique susceptibility variation behaviour with low temperatures. The susceptibility decreases with temperature to about 40-70% of the room-temperature value, and then increases up to about 60-100% at 77K. Results suggest the presence in the columnar basalts of predominantly single and pseudo-single domain titanomagnetites with composition around TM-60, and a small amount of ultra-fine grained superpara-magnetic particles. The titanomagnetites are low-temperature oxidized. Upon heating, these titanomaghemites invert to an intergrowth of titanomagnetite and ilmenite. This increases saturation magnetization and coercivity.
