Palaeointensity determinations and rock magnetic properties on basalts from Shatsky Rise: new evidence for a Mesozoic dipole low

IODP Expedition 324 cored igneous rocks from Shatsky Rise, an oceanic plateau in the northwest Pacific Ocean that formed mainly during late Jurassic and Early Cretaceous times. We selected 60 samples from 3 different holes for Thellier-Thellier palaeointensity determinations. Induced and remanent magnetization curves measured at low- and high-temperature suggest a diverse and complex magnetic mineralogy, with large variations in Ti content and oxidation state. Hysteresis and FORC measurements show that most samples contain single-domain magnetic grains. After carrying out the palaeointensity determinations, only 9 samples satisfied all reliability criteria. These gave palaeointensity values between 16.5 and 21.5 mu T, which correspond to average VDM values of (4.9 +/- 0.2) x 10(22) Am-2 for an estimated age of 140-142 Ma. This value is lower than that for the recent field, which agrees with the hypothesis of a Mesozoic Dipole Low.