Palaeomagnetic study of Oligocene (24–30 Ma) lava flows from the Kerguelen Archipelago (southern Indian Ocean): directional analysis and magnetostratigraphy

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

“…We carried out a palaeointensity study on three Oligocene (28– 30 Ma) volcanic sections from the Kerguelen Archipelago (southern Indian Ocean). It complements the palaeosecular variation directional study already achieved on the same sections: Mont des Ruches, Mont des Tempêtes, and Mont Rabouillère (Plenier et al 2002). Out of the 57 studied units, we considered 32 suitable for palaeofield strength determination experiments when at least three of their samples pass the following selection criteria: angle between NRM and ChRM ≤15° (or secondary component quickly demagnetized), NRM dispersion not too large, viscosity index <5 per cent, stable susceptibility at room temperature after each demagnetization step of a sister sample and reversible susceptibility in temperature curves.…”

“…1). For the reasons developed in Plenier et al (2002), the palaeomagnetic sections do not correspond exactly to the previously‐dated sections (Yang et al 1998; Nicolaysen et al 2000; Doucet et al 2002), but they appear to be correlated. Usually, seven samples were drilled in each successive lava flow using a gas‐powered drill and oriented with both solar sightings and magnetic compass with a clinometer.…”

“… 1 indicates flows which have been grouped together in Plenier et al 's (2002) directional analysis. Flows are listed in stratigraphic order with the youngest on top, oldest on the bottom.…”

“…To be sure of the thermal stability of the samples during successive heating in the laboratory, we used the low‐field magnetic susceptibility ( k 0 ) measured at room temperature after each thermal demagnetization step performed in air for the sister specimen previously studied in the palaeodirection determination (Plenier et al 2002). A favourable sample for palaeointensity determination should have a relatively constant k 0 value during most of the demagnetization procedure.…”

“…We performed in a previous study (Plenier et al 2002), a quantitative bootstrap test for a common mean on successive magnetic directions in order to identify non‐independent records. We concluded in particular that the Ruc14 and Ruc15 flows may represent two contemporaneous records of the palaeofield (Table 1).…”