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We present new distal records of tephra deposits that overly the Kos ignimbrite in seven locations of Datça peninsula. Tephra in one of these locations were previously associated with Nisyros Kyra sub-unit based only on the field characteristics. We use different proxies such as field observations, petrography, mineral, glass, and whole-rock chemistry in order to characterize and correlate the previously and recently identified pumice fall deposits on Datça. The total thickness of the fall deposit reaches to 3.5 m. The size of the pumice clasts is generally within the range of lapilli, and they have vitrophyric texture consisting mainly of plagioclase (andesine to labradorite) with scarce clinopyroxene (diopside to augite), olivine (Fo 48–50 ), amphibole (magnesio-hastingsite), and biotite crystals. Amphibole is a ubiquitous phenocryst in all Datça tephra units and used as a criterion for the correlation. Glass major element analyses by EMPA reveal two different groups with andesitic and dacitic compositions. Difference in silica content (up to ca. 4 wt%) detected in the same specimen also designates the heterogeneity in pumice glass. This heterogeneity in glass composition is also supported by the frequent occurrence of banded pumice clasts in Datça tephra. Whole-rock composition of the pumice is mainly andesitic with calc-alkaline affinity. Multi-element patterns on primitive-mantle normalized diagram display typical arc-magmatism signature (i.e. depletion in Nb, Ta, Ti, and P). In order to check and eliminate the potential alternatives, we compared the distal deposits on Datça not only with Kyra, but also with other Nisyros tephra units. Yet, Kyra is the only unit that has comparable depositional characteristics, calcic amphibole crystals, andesitic-dacitic glass and whole-rock chemistry, and distal tephra deposits on neighboring islands (Tilos and Chalki). Therefore, we associate Datça tephra deposits with some proximal Kyra subunits of intermediate composition. However, if further geochemical (especially glass and mineral chemistry) data are provided for the Lakkí and Melisserí tephra units, a more thorough tephra correlation will be possible. Finally, our results may have implications on Nisyros tephra dispersal and geochemical characterization. [ABSTRACT FROM AUTHOR]

Abstract: The Greek island of Nisyros is the source of tephra found in distal settings throughout the Aegean. In this contribution, we define geochemical fingerprints for the Lower and Upper Pumice eruptions of Nisyros based on micron-beam major (EMPA) and trace (LA-ICP-MS) element data. These two eruptions are compositionally distinct from each other. The high phenocryst content of proximal Lower and Upper Pumice tephra means that the differences between the two magmas are masked in whole-rock analyses. We demonstrate that all previous reports of distal marine and continental tephras correspond to the younger Upper Pumice not the older Lower Pumice. This has important implications for the marine tephrochronology of the Mediterranean and for the age of the Upper and Lower Pumice eruptions. We suggest an age of at least 47ka for the Upper Pumice and an older, unconstrained age for the Lower Pumice. [Copyright &y& Elsevier]

Abstract: In this work, we investigated the water–rock interaction processes taking place in the hydrothermal reservoir of Nisyros through both: (1) a review of the hydrothermal mineralogy encountered in the deep geothermal borehole Nisyros-2; and (2) a comparison of the analytically-derived redox potentials and acidities of fumarolic-related liquids, with those controlled by redox buffers and pH buffers, involving hydrothermal mineral phases. The propylitic zone met in the deep geothermal borehole Nisyros-2, from 950 to 1547m (total depth), is characterised by abundant, well crystallised epidote, adularia, albite, quartz, pyrite, chlorite, and sericite–muscovite, accompanied by less abundant anhydrite, stilpnomelane, wairakite, garnet, tremolite and pyroxene. These hydrothermal minerals were produced in a comparatively wide temperature range, from 230 to 300°C, approximately. Hydrothermal assemblages are well developed from 950 to 1360m, whereas they are less developed below this depth, probably due to low permeability. Based on the R H values calculated for fumarolic gases and for the deep geothermal fluids of Nisyros-1 and Nisyros-2 wells, redox equilibrium with the (FeO)/(FeO1.5) rock buffer appears to be closely attained throughout the hydrothermal reservoir of Nisyros. This conclusion may be easily reconciled with the nearly ubiquitous occurrence of anhydrite and pyrite, since R H values controlled by coexistence of anhydrite and pyrite can be achieved by gas separation. The pH of the liquids feeding the fumarolic vents of Stephanos and Polybote Micros craters was computed, by means of the EQ3 code, based on the Cl–δD relationship which is constrained by the seawater–magmatic water mixing occurring at depth in the hydrothermal–magmatic system of Nisyros. The temperature dependence of analytically-derived pH values for the reservoir liquids feeding the fumarolic vents of Stephanos and Polybote Micros craters suggests that some unspecified pH buffer fixes the acidity of these reservoir liquids at values of 4.72–4.85 and 4.88–5.23, respectively. Many of these pH values are lower than those expected for the full-equilibrium condition, although they are close to those of the reservoir liquids of Nisyros-1, 5.16, and Nisyros-2, 4.87. It is likely that this excess of acidity-producing species, chiefly CO2, promotes release of Fe(II) and Fe(III) to the reservoir liquids through rock dissolution, permitting the attainment of redox equilibrium with the (FeO)/(FeO1.5) rock buffer, as already suggested by the late Werner Giggenbach. [Copyright &y& Elsevier]

Abstract: A composite 40.2 m sediment sequence from Megali Limni, Lesvos Island, Greece, spanning the interval from 22 to 62 ka BP, contains six Pleistocene tephra layers, which can be identified on the basis of their major and trace elemental compositions. The youngest tephra deposit correlates with the 22 ka Y-2 marker, erupted during the Cape Riva eruption of Santorini. The second tephra originates from the Campanian area in Italy and corresponds to the Campanian Ignimbrite eruption (the 39 ka Y-5 marker). The next two layers are compositionally identical, and originate from Eastern islands of the Hellenic Arc; they could potentially correspond to the Upper and Lower Pumice eruptions of Nisyros or some other previously unidentified eruption from Yali. The fifth stratum corresponds to the Y-6 marker, which erupted during the Green Tuff eruption of the Pantelleria Island. The source of the last tephra layer is either the Yali–Nisyros complex or Central Anatolia; no specific corresponding eruption has yet been found. Long distal tephra sequences within terrestrial settings are rare in the eastern Mediterranean and the Megali Limni record contains the most complete sequence to date. Moreover, its age model, based on independent chronologies such as AMS and conventional radiocarbon dates and high-resolution pollen stratigraphy, provides new ages for these eruptions and places them within the context of the millennial-scale palaeoenvironmental variability of the last glacial period. Finally, the recognition of the Pantelleria tephra in this locality considerably extends the confirmed Northerly and Easterly distribution of this widespread and distinctive unit, while the existence of the Nisyros–Yali tephras on Lesvos refutes the current belief of limited tephra dispersal and small magnitude of these eruptions. [Copyright &y& Elsevier]