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-Costa Rasa, on the island of Lipari (Aeolian Archipelago). The lava flow sequence is about 10 m thick and has been sampled in detail. Magnetic properties 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 and AF demagnetization have shown the presence of secondary magnetization components. These were removed mostly at 450 degrees-500 degrees C or 20-30 mT, indicating a highly stable ChRM with directions from transitional to reverse. Where a ChRM could not be isolated by application of the demagnetization techniques, the converging remagnetization circles method gave a mean ChRM value fully comparable with that obtained from other methods. Ar-40/Ar-39 determinations were performed on two lava flows, in the lower and upper parts of the sequence. The former shows a transitional ChRM direction and a whole-rock age of 157 +/- 12 ka, the latter a reverse direction, a whole-rock age of 143 +/- 17 ka and a ground-mass age of 128 +/- 23 ka. The radiometric data and the reconstructed stratigraphy, which indicate ages of 150 +/- 10 ka and 104 +/- 3.5 ka, respectively, for the volcanic units at the bottom and top of the Monte Chirica-Costa Rasa unit, suggest that the reverse directions recorded in Lipari are related to the Blake event.