The reliability of palaeomagnetic data from basalts with low curie temperature(TC<90°C)

Abstract

Domain structure observations of Tertiary basalts from the Southern Alps with low Curie temperatures (TC < 90°C) reveal that: 1. (a) Most of the larger ore grains are paramagnetic at room temperature and cannot contribute anything to remanence. 2. (b) Optically homogenous titanomagnetites can have a range of Curie temperatures of more than 100°C between the centre and the margin. 3. (c) Only marginal zones of the larger ore grains and all small particles with a diameter of less than about 5–10 μm are the ferrimagnetic carriers of remanence. The phase with higher TC is believed to have been formed by maghemitization during or immediately after the formation of the rock. It could not be decided whether the remanence is mainly an original TRM or a subsequently formed CRM. 4. (d) Despite of the close vicinity between ambient temperature and blocking temperatures only negligible components of viscous remanent magnetization in the direction of the present field have been found. 5. (e) The paleomagnetic data are believed to correlate, perhaps not exactly, with the age of the rock but with the time of volcanic activity in the region i.e. Oligocene.