PALEOMAGNETISM OF THE ESTEREL ROCKS - A REVISIT 22 YEARS AFTER THE THESIS OF ZIJDERVELD,HANS

For his PhD. thesis, Zijderveld (1975) studied the paleomagnetism of t he Permian Esterel rocks (southern France). High-quality thermal and a lternating-field demagnetization diagrams were interpreted to determin e the direction of the characteristic natural magnetization. For the E sterel volcanics, a mean direction of Dec = 206.5 degrees, Inc = -23 d egrees, alpha(95) = 5.7 degrees, k = 112 was found for this magnetizat ion. The dispersion in this mean is remarkably low. Only the declinati on of the Reyran Rhyolite in the Reyran River quarry clearly deviated from this mean. This deviating direction is not found in our samples, taken at the same site. As many faults occur in this quarry, it is sug gested that Zijderveld sampled this rhyolite on a small rotated block. To verify whether the small dispersion in the mean paleomagnetic dire ction of the Esterel rocks has a geomagnetic or a rock-magnetic origin , two conglomerate tests were carried out. One of these might be inter preted as positive. The results of the other conglomerate test (Agay F ormation) are ambiguous: four of the six measured boulders show direct ions close to the mean paleomagnetic direction of the Esterel rocks. R ock-magnetic measurements show that the remanence is carried by a magn etite and a hematite fraction. The low dispersion in the paleomagnetic directions, the conglomerate tests, and hematite as remanence carrier suggest that the characteristic remanence in the Esterel volcanics wa s not instantaneously acquired during cooling, but might be affected b y remagnetization due to weathering.