The most recent major explosive eruption of the Santorini volcano in Greece—around 3600 years before present (B.P.), often referred to as the Minoan eruption—is one of the largest volcanic events known in historical time and has been the subject of intense volcanological and archeological studies [Druitt et al., 1999]. The submarine volcano Kolumbo, located seven kilometers northeast of Santorini and associated with Santorini's tectonic system, erupted explosively in 1650 A.D., resulting in fatalities on the island of Thera [Fouqué, 1879]. A large fraction of the erupted products from the Minoan eruption has been deposited in the sea but, up to now, only has been studied in distal marine sediments.
As part of a collaborative project between the University of Rhode Island (Narragansett), the Hellenic Centre of Marine Research (Athens, Greece), and the Institute of Geology and Mineral Exploration (Athens), a marine geological survey was conducted around Santorini from April to June 2006. he new work now shows that the volume of the Minoan eruption may be comparable to that of the largest known historical eruption, the 1815 eruption of Tambora in Indonesia [Sigurdsson and Carey, 1989]; provides insights into the depositional processes and size of the Minoan eruption; and led to the discovery of important submarine hydrothermal vents with active mineralization.
Based on detailed field, petrographic, chemical, and isotopic data, this paper shows that the youngest magmas of the active Nisyros volcano (South Aegean Arc, Greece) are an example of transition from rhyolitic to less evolved magmas by multiple refilling with mafic melts, triggering complex magma interaction processes. The final magmatic activity of Nisyros was characterized by subPlinian caldera-forming eruption (40 ka), emplacing the Upper Pumice (UP) rhyolitic deposits, followed by the extrusion of rhyodacitic post-caldera domes (about 31-10 ka). The latter are rich in magmatic enclaves with textural and compositional (basaltic-andesite to andesite) characteristics that reveal they are quenched portions of mafic magmas included in a cooler more evolved melt. Dome-lavas have different chemical, isotopic, and mineralogical characteristics from the enclaves. The latter have lower 87 Sr/ 86 Sr and higher 143 Nd/ 144 Nd values than dome-lavas. Silica contents and 87 Sr/ 86 Sr values decrease with time among dome-lavas and enclaves. Micro-scale mingling processes caused by enclave crumbling and by widespread mineral exchanges increase from the oldest to the youngest domes, together with enclave content. We demonstrate that the dome-lavas are multi-component magmas formed by progressive mingling/mixing processes between a rhyolitic component (post-UP) and the enclave-forming mafic magmas refilling the felsic reservoir (from 15 wt.% to 40 wt.% of mafic component with time). We recognize that only the more evolved enclave magmas contribute to this process, in which recycling of cumulate plagioclase crystals is also involved. The post-UP end-member derives by fractional crystallization from the magmas leftover after the previous UP eruptions. The enclave magma differentiation develops mainly by fractional crystallization associated with multiple mixing with mafic melts changing their composition with time. A time-related picture of the relationships between dome-lavas and relative enclaves is proposed, suggesting a delay between a mafic magma input and the relative dome outpouring. We also infer that the magma viscosity reduction by re-heating allows dome extrusion without explosive activity.
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