Palaeomagnetic secular variation from Holocene lava flows of the Taupo Volcanic Zone (TVZ), New Zealand
Abstract:In order to understand the origin, temporal behaviour and spatial characteristics of Earth’s magnetic field, global data coverage and high resolution age control are required. Previous studies and modelling approaches contain only little data from the southern hemisphere and in particular the Southwest Pacific.
Here we study Holocene records of the direction and intensity of the palaeomagnetic field from volcanic materials sampled within Taupo Volcanic Zone, New Zealand. Altogether we sampled 49 sites on 17 individual basaltic to rhyolitic lava flows of Holocene age. Each individual flow was sampled at a minimum of three sites, allowing a direct comparison of palaeomagnetic and rock magnetic results with location in a lava flow. Estimates of palaeofield directions were obtained from principal component analysis of thermal and alternating field demagnetisation data. Site mean declinations range from 340° (W) to 18° (E) and inclinations range between - 45° and - 85°. The current values in Taupo, New Zealand are: declination 21°, inclination -65°, and intensity 54.5 μT.
Successful palaeointensity estimates were obtained from five flows by combining extensive microwave and thermal experiments following Coe and IZZI Thellier-type protocols. Results were accepted on the basis of stringent quality criteria, agreement between different methods and consistency between sites from each lava flow. Palaeointensities range from 29 to 78 μT.
The new data shows that the local field had a generally more easterly declination and was of higher intensity than suggested by the CALS series world models (e.g. Korte et al, 2011). The latter are predominantly based on northern hemisphere data and lack a full dataset from New Zealand. The implications of the new data on global and regional field models are discussed.