EVIDENCE FOR THE BLAKE EVENT IN VOLCANIC-ROCKS FROM LIPARI (AEOLIAN ARCHIPELAGO)

Palaeomagnetic and geochronological measurements have been carried out on the late Pleistocene basaltic-andesitic unit of Monte Chirica-Cost a Rasa, on the island of Lipari (Aeolian Archipelago). The lava flow s equence is about 10 m thick and has been sampled in detail. Magnetic p roperties are rather uniform; Curie temperatures of 540 degrees to 580 degrees C, and the saturation IRM reached at applied values of 0.1 T point to titanomagnetite as the main magnetization carrier. Thermal an d AF demagnetization have shown the presence of secondary magnetizatio n components. These were removed mostly at 450 degrees-500 degrees C o r 20-30 mT, indicating a highly stable ChRM with directions from trans itional to reverse. Where a ChRM could not be isolated by application of the demagnetization techniques, the converging remagnetization circ les method gave a mean ChRM value fully comparable with that obtained from other methods. Ar-40/Ar-39 determinations were performed on two l ava flows, in the lower and upper parts of the sequence. The former sh ows a transitional ChRM direction and a whole-rock age of 157 +/- 12 k a, the latter a reverse direction, a whole-rock age of 143 +/- 17 ka a nd a ground-mass age of 128 +/- 23 ka. The radiometric data and the re constructed stratigraphy, which indicate ages of 150 +/- 10 ka and 104 +/- 3.5 ka, respectively, for the volcanic units at the bottom and to p of the Monte Chirica-Costa Rasa unit, suggest that the reverse direc tions recorded in Lipari are related to the Blake event.