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Age and geochemistry of tephra layers from Ischia, Italy : constraints from proximal-distal correlations with Lago Grande di Monticchio.

Tomlinson, E.L. and Albert, P.G. and Wulf, S. and Brown, R.J. and Smith, V.C. and Keller, J and Orsi, G. and Bourne, A.J. and Menzies, M. (2014) 'Age and geochemistry of tephra layers from Ischia, Italy : constraints from proximal-distal correlations with Lago Grande di Monticchio.', Journal of volcanology and geothermal research., 287 . pp. 22-39.


Unraveling the eruptive history of the Island of Ischia (southern Italy) is problematic due to its burial, caldera collapse, resurgent uplift and erosion. Here, we present new major and trace element glass data for 39–75 ka proximal tephra deposits, including those of the caldera-forming Monte Epomeo Green Tuff (MEGT) eruption. Correlations with the distal tephra archive preserved at Lago Grande di Monticchio (LGdM) are used to constrain the timing of as yet undated eruptive events. Out of 13 LGdM tephras analysed from the 39–104 ka time window, glass geochemical data show that all are compositionally consistent with the explosive volcanic eruptions of Ischia, whilst 5 of them can be correlated with specific proximal deposits. Pre-MEGT pyroclastic sequences comprise three compositional groups, these groups occur repeatedly in sucessive eruptions. Proximal-distal correlations indicate that the Porticello eruption occurred at 59 ± 2 ka and the Tisichiello eruption probably occurred at 76 ± 3 ka. The MEGT eruption is correlated with LGdM TM-19, which has been directly dated at 55 ± 2 ka. Post-MEGT tephras form compositional groups that overlap with the pre-MEGT but are displaced to lower FeO and TiO2 and lower incompatible element contents. Proximal-distal correlations indicate that the Schiappone and Pietre Rosse eruptions occurred at 50.6 ± 2.0 ka and 45 ± 6 ka, respectively. Tephra from the MEGT eruption span a wide compositional range, broadly overlapping the three pre-MEGT compositional groups but are displaced to higher Nd and Y and contain an additional less evolved glass population. Glass geochemistry is used to recognise and confirm distal equivalents of the MEGT at LGdM (TM-19) and in the Ionian (Y-7), Adriatic (PRAD 1870) and Tyrrhenian (C-18, MD 28) seas. Distal occurences of MEGT tephra define a dispersal axis to the south-southeast and are found as far as 540 km from Ischia, making the MEGT one of the most widely dispersed late Quaternary pyroclastic deposit erupted in the Campanian region. We estimate a volume of approximately 40 km3 for the fallout portion of the MEGT pyroclastic sequence on the basis of proximal and distal deposit thicknesses.

Item Type:Article
Keywords:Tephrochronology, Volcanic ash, Ischia, Explosive eruptions, Quaternary volcanism, Campanian volcanic area.
Full text:(AM) Accepted Manuscript
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Publisher statement:NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Volcanology and Geothermal Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Volcanology and Geothermal Research, 287, 15 October 2014, 10.1016/j.jvolgeores.2014.09.006.
Date accepted:06 September 2014
Date deposited:14 January 2015
Date of first online publication:19 September 2014
Date first made open access:No date available

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