The multimethod palaeointensity approach applied to volcanics from Terceira: full-vector geomagnetic data for the past 50 kyr

Abstract

The island of Terceira (38.5°N, 27.2°W) in the Azores Archipelago boasts a wealth of well-dated recent volcanic products; it is therefore the ideal location to improve the resolution of the full-vector geomagnetic field record for the Mid-Atlantic Ocean. We investigated 21 (sub-)sites sampled from 10 different cooling units; six of these cooling units are from the Holocene, the other four are approximately coeval with the age of known geomagnetic excursions. After successfully determining the palaeodirections from all but one site, we applied the multimethod palaeointensity approach to all sites. Here, we used three different palaeointensity methods: the IZZI-Thellier protocol, the Multispecimen technique, and the calibrated pseudo-Thellier method. For the Holocene sites four robust palaeointensity estimates were obtained, they mostly agree with data from the nearby island of São Miguel and data from the Iberian Peninsula and West Africa. Two older sites, dated at 25.7 and 46.3 ka, produced low palaeointensities: 24.4 and 24.1 μT, respectively. As both the IZZI-Thellier and pseudo-Thellier methods yielded technically acceptable results for these sites we used them to improve the pseudo-Thellier calibration relation and establish its applicability to lower palaeointensities. Sixty per cent of all sampled cooling units/ages in our study yielded a technically successful palaeointensity estimate; this unusually high success rate is attributed both to our sampling strategy and the implementation of the multimethod approach.