New geochronological data are presented and discussed together with field data in order to reconstruct the geo-volcanological evolution of Panarea Island. Attention is focused on the discrepancies between geochronological data compared with field evidence. Field data provide evidence that the Panarea dome was continuously built up without a significant break in volcanic activity. Continuous extrusion of new magma allowed the dome to emerge subaerially. Subaerial effusive activity followed with the alternation of exogenous and endogenous phases of growth that led to the formation of radial and tangential lava lobes and plugs. The younger volcanic products are represented by a thick succession of pyroclastic products discontinuously outcropping all over the island, dated here for the first time. Samples were dated through the U/Th disequilibrium method, which is also able to provide information on the geological processes at the origin of U–Th fractionation. The chronology of the volcanic events at Panarea suggests that the volcanic activity developed through two main phases. Effusive activity mainly characterized the first phase of the dome growth, while during the second phase explosive activity prevailed. The second phase occurred from 3177 to 2072 ka. Assessing the age of the first phase is more difficult. The age of 155712 ka, which is in the same time span obtained from K/Ar or Ar/Ar methods, is not consistent with field evidence. Furthermore, although the alignment of the points on the isochron is very good, the initial value of the 230Th/232Th ratio is very low and does not have a clear meaning. Our data strongly suggest that the age of 155712 ka is not realistic. Two alternative scenarios are proposed, implying a revision of the geological and geochronological evolution of the island together with the significance of the marine terraces on Panarea.
Dolfi, D., DE RITA, D., Cimarelli, C., Mollo, S., Soligo, M., Fabbri, M. (2007). Dome growth rates, eruption frequency and assessment of volcanic hazard: insights from new U/Th dating of the Panarea and basiluzzo dome lavas and pyroclastics, Aeolian islands, Italy. QUATERNARY INTERNATIONAL, 162-163, 182-194 [10.1016/j.quaint.2006.05.035].
Dome growth rates, eruption frequency and assessment of volcanic hazard: insights from new U/Th dating of the Panarea and basiluzzo dome lavas and pyroclastics, Aeolian islands, Italy
DE RITA, Donatella;SOLIGO, Michele;
2007-01-01
Abstract
New geochronological data are presented and discussed together with field data in order to reconstruct the geo-volcanological evolution of Panarea Island. Attention is focused on the discrepancies between geochronological data compared with field evidence. Field data provide evidence that the Panarea dome was continuously built up without a significant break in volcanic activity. Continuous extrusion of new magma allowed the dome to emerge subaerially. Subaerial effusive activity followed with the alternation of exogenous and endogenous phases of growth that led to the formation of radial and tangential lava lobes and plugs. The younger volcanic products are represented by a thick succession of pyroclastic products discontinuously outcropping all over the island, dated here for the first time. Samples were dated through the U/Th disequilibrium method, which is also able to provide information on the geological processes at the origin of U–Th fractionation. The chronology of the volcanic events at Panarea suggests that the volcanic activity developed through two main phases. Effusive activity mainly characterized the first phase of the dome growth, while during the second phase explosive activity prevailed. The second phase occurred from 3177 to 2072 ka. Assessing the age of the first phase is more difficult. The age of 155712 ka, which is in the same time span obtained from K/Ar or Ar/Ar methods, is not consistent with field evidence. Furthermore, although the alignment of the points on the isochron is very good, the initial value of the 230Th/232Th ratio is very low and does not have a clear meaning. Our data strongly suggest that the age of 155712 ka is not realistic. Two alternative scenarios are proposed, implying a revision of the geological and geochronological evolution of the island together with the significance of the marine terraces on Panarea.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
