Interplinian explosive activity of Santorini volcano (Greece) during the past 150,000 years

Abstract

The eruptive history of Santorini was dominated by twelve major Plinian eruptions. Six of these (Middle Pumice, Vourvoulos, Upper Scoriae 1, Upper Scoriae 2, Cape Riva and Minoan) occurred during the past ∼150 ky. This study focuses on the stratigraphy and geochemistry of the interplinian pyroclastic deposits between 145 ka (Middle Pumice) and 3.6 ka (Minoan). Five interplinian eruptive intervals were identified between these major eruptions and are numbered M8-M12. The Upper Scoriae 1/Upper Scoriae 2 (M10) and Upper Scoriae 2/Cape Riva (M11) intervals are divided into sub-intervals by voluminous interplinian lava formations, the Skaros and Andesites of Oia and Therasia lavas, respectively. Each interval lasted between ∼17 and ∼45 ky and contains pyroclastic deposits of numerous eruptions indicating considerable volcanic activity between the major Plinian events. Most of these interplinian eruptions produced scoria-fall and ash-fall deposits predominantly from subplinian-type eruptions. Surge deposits, resulting from phreatomagmatic activity, are predominant in the Upper Scoriae 1/Skaros sub-interval (M10a). The Andesites of Oia/Cape Riva sub-interval (M11b) is entirely composed of subplinian pumice-fall and ash deposits. Other subplinian pumice-fall deposits occur in the intervals Vourvoulos/Upper Scoriae 1 (M9) and Upper Scoriae 1/Upper Scoriae 2 (M10). The Upper Scoriae 1/Skaros sub-interval (M10a) belongs to one of the longest interplinian intervals (M10) that is characterized by the thickest eruptive units and the largest number of eruptions. A further prominent interplinian pyroclastic formation in northern Thera is the Megalo Vouno cinder cone deposit, which occurred in a time span between the Vourvoulos eruption and the formation of the Skaros lava shield. The interplinian deposits vary from 50 to 70 wt.% SiO 2 and are classified as basalt, basaltic andesite, andesite and dacite with a typical calc-alkaline affinity in accordance with the general characteristics of Santorini. They are dominated by a mafic magma component, exemplified by extensive scoria-fall deposits, which is generally absent or only a minor constituent of the silicic Plinian eruptions. Major and trace element compositional trends indicate a significant role of fractional crystallization in the evolution of the interplinian Santorini magmas, where repeated replenishment of primitive magma appears to have prevented magmatic differentiation towards highly silicic compositions that dominate the Plinian eruptions. Pauses in igneous activity, immediately prior to the Plinian and often caldera-forming eruptions, are inferred to be crucial for the generation of more evolved magma compositions erupted during Plinian events.