Paleointensity and Paleodirection Estimates from the Erebus Volcanic Province, Antarctica

Abstract:

The Geocentric Axial Dipole (GAD) hypothesis, that the geomagnetic field may be approximated by a dipole aligned with the spin axis and positioned in the center of the Earth, is important for paleogeographic reconstructions. In an ideal GAD field, the intensity (inclination) would vary with latitude. Higher latitudes would preserve higher intensities (absolute inclinations). Yet paleointensity estimates from 0 - 5 Myr stored in absolute paleointensity databases (i.e. PINT and the MagIC database) lack this dipolar field structure. Instead, all latitudes yield comparable paleointensities- approximately 30 μT. To address whether these seemingly “low” intensities recorded at the high southern latitudes accurately reflect the field over the last 5 Myr or poor temporal sampling and unreliable paleointensity estimates, we conducted an extensive paleomagnetic study in the Erebus Volcanic Province, Antarctica (78° S, 167° E). We present 28 new paleointensity estimates from IZZI modified Thellier-Thellier experiments and 111 paleodirections from AF demagnetized and thermally demagnetized drill cores. The resulting paleopole (128° W, 87° N) and α₉₅ = 5.4° is consistent with a GAD field structure. VGP dispersion (30.93 with 24.85 – 35.14 bootstrap lower and upper confidence bounds) overlaps with estimates for the region based on the field model TK03. The resulting average paleointensity estimate, 33 ± 2.6 μT, is comparable to paleointensities from low and mid latitude studies for the Plio-Pleistocene. The corresponding dipole moment, 45 ± 3.2 ZAm², suggests a weaker average dipole moment over the last 5 Myr than for the modern field, 80 ZAm².