GEOMAGNETIC-FIELD INTENSITY BETWEEN 70000 AND 130000 YEARS BP FROM A VOLCANIC SEQUENCE ON LA REUNION, INDIAN-OCEAN

A detailed paleointensity study was made of a sequence of 70 successiv e lava flows of the Piton des Neiges volcano on the island of La Reuni on (Indian Ocean). Radiometric dating brackets the age of this sequenc e between 130 +/- 3 ka and 72 +/- 3 ka. Rock magnetic investigations s how that titanomagnetites in the pseudo single domain range are the ma in magnetic carrier of the Natural Remanent Magnetisation (NRM). Over 350 samples were used for paleointensity determinations carried out wi th the Thellier method in vacuum or in an argon atmosphere. Of these, 89 samples yielded reliable results, with within-flow scatter often lo wer than 20%. These results indicate that the geomagnetic field intens ity has varied at La Reunion between 13 and 65 mu T during the period of time explored. The average value, 42 mu T, is higher than the prese nt field at La Reunion (35 mu T). The results from the upper part of t he section are consistent with previous results obtained for the 82-98 ka period also at La Reunion [1] and document a broad low around 95 k a, not associated with large directional changes. On a larger geograph ic scale, the paleointensity values from La Reunion are significantly higher than those obtained from Mount Etna [2]. Precise comparison is, however, difficult because of the lack of detail in the Etna results. In the lower part of the section, a marked intensity low, coinciding with significant deviation from the dipole field direction is observed at 115 ka and could correspond to the end of the Blake event.