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Volcanic facies architecture and evolution of Milos, Greece

Stewart, AL 2003 , 'Volcanic facies architecture and evolution of Milos, Greece', PhD thesis, University of Tasmania.

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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
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).

Item Type: Thesis - PhD
Authors/Creators:Stewart, AL
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