Geomagnetic paleosecular variation recorded in Plio-Pleistocene volcanic rocks from Possession Island (Crozet Archipelago, southern Indian Ocean)
Résumé
Possession Island, in the Crozet Archipelago, consists of volcanic units erupted mainly between ~5 and 0.5 Ma. A paleomagnetic sampling was carried out along several sections distributed near the northern, eastern, and southeastern coasts. A total of 45 independent flows were sampled (320 samples). For each flow a precisely defined characteristic remanence direction was usually isolated after a careful progressive cleaning in alternating fields. However, particularly complex remanence behavior is often observed. The magnetostratigraphy of the lava pile is quite simple, with reversed rocks in the lower part and normal units in the upper part of two sections. A third section is of normal polarity throughout its whole thickness, including three excursional directions. We did not find any intermediate directions between the normal and reverse magnetozones. Thus we have no evidence for the recording of the Matuyama-Brunhes transition expected from a previous study (Watkins, 1972). The amplitude of paleosecular variation, estimated from between-flow dispersion from the field of an axial dipole, is 11.8 with 95% confidence limits between 9.3 deg and 14.0 deg. This value is consistent with the general anisotropic statistical model for paleosecular variation of Constable and Johnson, 1999.
Domaines
Géophysique [physics.geo-ph]
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