Paleointensity Determinations with Measurements at High Temperature.

Abstract

Paleointensity determinations following the principle of the Konigsberger Thellier Thellier (KTT) method, but with measurement at high temperatures have been carried out. The high temperature measurements were made with a continuous thermal demagnetization system, which operates as a modification of a 2G horizontal access cryogenic magnetometer. The high temperature measurements permit comparison of the NRM lost and TRM acquired within temperature stages incrementally, rather than in the cumulative manner of the KTT method. When this approach was applied to a Hawaii 1960 lava erupted in a known geomagnetic field intensity, the NRM/TRM ratio for one specific temperature range of 400-450° C gave anomalously high values, while the expected NRM/TRM ratios were obtained from all other temperature ranges. This anomalous behavior is related to the destruction of a phase carrying NRM in this temperature range. The advavantage of making measurements at high temperature is that it permits independent determinations of the incremental ratio of NRM lost/TRM gained. This ability to isolate anomalous temperature ranges may permit reliable intensity determinations in materials, such as lunar rocks and meteorites, whose complicated behaviour on heating has precluded intensity determinations in the past.