University of Tasmania
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Volcanic facies architecture and evolution of Milos, Greece

posted on 2023-05-26, 00:00 authored by Stewart, AL
The volcanic island of Milos Island, Greece, is a relatively small (-151 km') but significant portion of the active Southern Aegean Volcanic Arc, Milos comprises an Upper Pliocene-Pleistocene, thick (up to 700 m), and compositionally and texturally diverse succession of calc-alkaline, volcanic and sedimentary rocks that record a transition from a relatively shallow but dominandy below-wave-base submarine setting to a subaerial one. The shallow marine part of the succession hosts several significant epithermal gold deposits. Twenty-two main submarine and twelve subaerial volcanic, sedimentary and intrusive facies have been identified, and arranged into eleven compositionally and texturally distinct facies associations. The principal volcanic facies are (1) coherent rhyolite, dacite, andesite, basaltic andesite Oavas, domes, cryptodomes, dykes and sills), and associated autedastic facies (autobreccia, hyalodastite and intrusive hyalodastite); (2) submarine and subaerial pyrodastic deposits; and (3) volcanogenic sedimentary facies. The volcanic and intrusive facies are interbedded with a sedimentary facies association comprising sandstone and/or fossiliferous mudstone mainly derived from erosion of preexisting volcanic deposits. The main facies associations are interpreted to have conformable, disconformable, and interfingering contacts, and there are no mappable angular unconformities or disconformities whhin the volcanic succession. The facies architecture indicates depositional environments evolved from below to above the wave base to subaerial in most areas, except at the southeastern sector of the island where more uniform subaerial environments dominated. The architecture of the dominantly felsic-intermediate volcanic succession reflects contrasts in eruption style) proximity to source, depositional environment and emplacement processes. The volcanic facies architecrure comprises interfingering proximal (near vent), medial (volcano flanks), and distal (volcano margin) facies associations related mainly to submarine and subaerial felsic cryptodome-pumice cone volcanoes, dacitic to basaltic andesite lava domes and pyroclastic cones. Submarine felsic cryptodome-pumice cone volcanoes are the most voluminous and common type of volcano identified. Submarine explosive eruptions from these centres generated pumiceous gravity-current deposits and thick beds of very coarse, water-settled pumice. In proximal sections, thick felsic pumice breccia intervals were intruded by compositionally similar, porphyritic, rhyolitic and New SHRIMP V-Pb data from four major volcanic facies, in combination with detailed mapping and facies analysis, have enabled construction of an enhanced, internally consistent time-stratigraphic framework for the evolution of Milos. The volcanic activity began at 2.66 ± 0.07 Ma and has been more or less continuous since then. Subaerial emergence probably occurred at 1.44 ± 0.08 Ma, in response to a combination of volcanic constructional processes and fault-controlled volcano-tectonic uplift. Recent phreatic craters are the youngest (200 Be-200 AD) expressions of volcanism, and are spatially associated with an active, high-enthalpy geothermal field. The succession contains several significant epithermal, precious and base metal deposits that display a range of textural, mineralogical, and compositional characteristics. The majority of these epithermal ores occur within and at the top a single, submarine felsic cryptodome-pumice cone volcano near the stratigraphic base of the succession. The palaeogeography during mineralisation probably comprised scattered islands (volcanic domes) flanked by shallow-marine areas. A modern analogue for rhe setting of the epithermal- style mineralisation is the shallow submarine to subaerial volcanic complex of the island of Panarea, in the active Aeolian volcanic arc (Tyrrhenian Sea, Italy).


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