Absolute palaeointensity of Oligocene (28-30 Ma) lava flows from the Kerguelen Archipelago (southern Indian Ocean)

We report palaeointensity estimates obtained from three Oligocene volcanic sections from the Kerguelen Archipelago (Mont des Ruches, Mont des Tempetes, and Mont Rabouillere). Of 402 available samples, 102 were suitable for a palaeofield strength determination after a preliminary selection, among which 49 provide a reliable estimate. Application of strict a posteriori criteria make us confident about the quality of the 12 new mean-flow determinations, which are the first reliable data available for the Kerguelen Archipelago. The Virtual Dipole Moments (VDM) calculated for these flows vary from 2.78 to 9.47 10 (22) Am-2 with an arithmetic mean value of 6.15 +/- 2.1 10(22) Am-2. Compilation of these results with a selection of the 2002 updated IAGA palaeointensity database lead to a higher (5.4 +/- 2.3 10(22) Am-2) Oligocene mean VDM than previously reported (Goguitchaichvili et al. 2001; Riisager 1999), identical to the 5.5 +/- 2.4 10(22) Am-2 mean VDM obtained for the 0.3-5 Ma time window. However, these Kerguelen palaeointensity estimates represent half of the reliable Oligocene determinations and thus a bias toward higher values. Nonetheless, the new estimates reported here strengthen the conclusion that the recent geomagnetic field strength is anomalously high compared to that older than 0.3 Ma.