Fast geochemical changes and rapid lava accumulation at Stromboli Island (Italy) inferred from K-Ar dating and paleomagnetic variations recorded at 60 and 40 ka

Forty-three lava flows from the Vallone di Rina (Stromboli, Aeolian Islands, Italy) have been investigated for paleomagnetic, geochemical and K-Ar analyses. K-Ar dating shows that two fast building stages occurred at 62±1 and 40±2 ka. The comparison with archeomagnetic variations for the last 2 kyr shows that the time interval covered by the Vallone di Rina section is at the most a few thousand years, most probably on the order of a few hundred years. Such high accumulation rate can be related to the Stromboli volcanic history, which is marked by five to seven successive collapses. The rapid effusion rate of these Paleo-Stromboli (PST) II lavas suggests that they have been erupted shortly after the Paleo-Stromboli I collapse in response to pressure release due to instantaneous deloading. Their age of 62±1 ka is thus interpreted here as the age of the Paleo-Stromboli I collapse event. Similarly, the age of 40±2 ka obtained for lavas from Paleo-Stromboli III can be related with another collapse event. As previously recognized, major and trace elements of these lava flows show that they are compatible with magma sources of metasomatized mantle origin and various crustal levels of melting and mixing. They display recurrent jumps from calc-alkaline to high-K calc-alkaline and shoshonitic series within a very short time span, which suggest that several magmatic systems were operating simultaneously. Finally, we have shown that the combined approach of absolute dating provided by the K-Ar Cassignol technique, together with high-resolution paleomagnetic data compared to historical variations, can constrain, for high extrusion rates, the relative lava emplacements to within a few hundred years.