The South Aegean Active Volcanic Arc: Present Knowledge and Future Perspectives, Milos Conferences

401 Pages·2005·48.02 MB·English

by  Michael Fytikas and Georges E. Vougioukalakis (Eds.)

THE SOUTH AEGEAN ACTIVE
VOLCANIC ARC
PRESENT KNOWLEDGE AND
FUTURE PERSPECTIVES
This Page is Intentionally Left Blank
THE SOUTH AEGEAN ACTIVE
VOLCANIC ARC
PRESENT KNOWLEDGE AND
FUTURE PERSPECTIVES
Edited by
Michael Fytikas
Aristotle University
Thessaloniki, Greece
and
Georges E. Vougioukalakis
Institute for Geology and Mineral Exploration
Athens, Greece
2005
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THE SAAVA 2003 CONFERENCE
INTERNATIONAL PROGRAM COMMITTEE
Prof. Michael FYTIKAS, Aristotle University of Thessaloniki (GR) - Chair
Prof. Jon DAVIDSON, University of California (US)
Prof. Lorella FRANCALANCI, University of Florence, (IT)
Prof. F. INNOCENTI, Universita' di Pisa (IT)
Prof. Joerg KELLER, University of Freiburg (DE)
Prof. X. Le PICHON, Universite' P. Et M. Curie (FR)
Prof. Dimosthenis MOUNTRAKIS, Aristotle University of Thessaloniki (GR)
Prof. Vassilios PAPAZACHOS, Aristotle University of Thessaloniki (GR)
Prof. Georgia PE-PIPER, University of Saint Marry's (CA)
Assoc. Prof. Nikolaos SKARPELIS, University of Athens (GR)
Prof. Steve SPARKS, University of Bristol (UK)
Dr. Georges VOUGIOUKALAKIS, Institute of Geology & Mineral Exploration (GR)
LOCAL ORGANISING COMMITTEE
Emmanuel VOULGARIS "Milos Conference Center - George Eliopoulos"- Chair
Michael FYTIKAS, Aristotle University of Thessaloniki
Athanasios KEF ALAS, S&B Industrial Minerals S.A.
Kostas KONSTANTINIDIS, Heliotopos Conferences
ORGANIZERS
The "Milos Conference Center - George Eliopoulos" and Heliotopos Professional
Congress Organizers jointly organized this Conference within the framework of "Milos
Conferences".
The Conference was under the auspices of the Aristotle University of Thessaloniki, the
International Association of Volcanology and Chemistry of the Earth's Interior
(IAVCEI), the Geological Society of Greece and the Institute of Geology and Mineral
Exploration of Greece.
VI
VENUE
The Conference was held at the "Milos Conference Center - George Eliopoulos" on
Milos island, Greece.
CONFERENCE SECRETARIA T
Heliotopos Professional Congress Organizers
28, Ypsilantou str.
GR-172 36, Dafni, Athens, Greece
Tel: [phone], Fax: [phone]
E-mail: [email protected]
http://heliotopos.conferences.gr
Vll
PREFACE
Our knowledge about of South Aegean Active Volcanic Arc (SAAVA) has grown
substantially during the past 15 years. Therefore the time was ripe for reviewing past
achievements and setting new goals for the future.
This book is a collection of selected papers from the Conference "The South Aegean
Active Volcanic Arc: Present Knowledge and Future Perspectives" held in September
2003 in the framework of "Milos Conferences" at the "Milos Conference Center -
George Eliopoulos" in Milos island, Greece. The aim of the conference was to serve as
a forum for the presentation and constructive discussion of the state of the art and
emerging issues on the South Aegean Volcanic Arc.
The Aegean area is one of the most rapidly deforming parts of the Alpine -
Himalayan mountain belt delineated by the extremely high number of the seismic events
occurring in this area. Deformation seems to be dominated by the effects of the
westward motion of the Anatolian block, the south-westward motion of the southern
Aegean and the vertical-rotational movements of big lithosphere portions.
Geophysical data record a thinned continental crust in all the Aegean area and an
anomalous heat flow, implying a complex geodynamic - geotectonic situation.
Calc-alkaline volcanic activity was manifested at Plio-Quaternary, along a restricted
belt which extends in an arc form, from Susaki (near the Korinth isthmus) to the west to
Nisyros island to the east, the so-called South Aegean Active Volcanic Arc (SAAVA).
This arc hosts the active (Methana and Santorini) and potentially active (Milos and
Nisyros) Hellenic volcanic centres. The correspondence of the active volcanic arc
location over a Benioff zone depth of about 130 km is evidence for a role of subduction
in the genesis of the arc.
The volcanism is voluminous, with individual stratovolcanoes having volumes
above sea level of the order of 10-40 km3. The main volcanic centres in the central part
of the arc appear to be associated with big tectonic lineaments and active faults trending
NE.
The products of this volcanism form a typical calc-alkaline association which
displays a continuous evolution from basalts to rhyolites. Their chemical characteristics
are closely comparable with those of the volcanics of island arcs sited on thin
continental margins.
The huge magmatic and hydrothermal activity created economic deposits and
formations in most of the Aegean volcanic fields.
The 22 papers that are included in this volume review most of the above
characteristics of the SAAVA, presenting and discussing also new data and ideas.
The three first papers (Mountrakis; Ranguelov; Kassaras et al.) discuss the
tectonic- geodynamic setting and the present upper mantle structure of the Aegean area.
The forth paper, by Papazachos et al., present an interesting interpretation of the data
on spatial distribution of intermediate focal depth earthquakes, fault plane solutions and
Vlll
deep velocity structure, to further investigate active tectonics related to the deep
structure of the southern Aegean volcanic arc. A low seismicity part (110 - 140km) of
the subducted east Mediterranean lithospheric slab, that is sited under the volcanic arc,
geochemical data and tomographic results lead them to suggest that the primary magma
reservoir of the Hellenic volcanic arc is in the mantle wedge between the subducted
Mediterranean and the overriding Aegean slabs, at depths 60 - 90km. The genesis of
earthquakes at the shallow part of the subducted Mediterranean slab is attributed to
dehydration embrittlement of basalt, the low seismicity at intermediate depths is due to
increase of temperature and confining pressure and the increase again of seismicity in
the lower active part of the slab to a second dehydration embrittlement of hydrous
eclogite.
The next two papers deal with the general volcanological, petrological and tectonic
characteristics of the SAAVA. Francalanci et al. present an extensive review of the
volcanological, chemical and isotope data, using a large amount of new field and
laboratory data. They conclude that volcanic center location was controlled by large
tectonic lineaments, most of them still active, trending E-W to NW-SE for the western
part and mainly NE-SW for the central and eastern parts of the arc. Volcanic fields
developed along ellipse shaped areas with the longest axis oriented perpendicular to the
subduction front. Volcanic activity is clearly controlled by both the active tectonic
lineaments and the subduction kinematics dynamics, nevertheless, it is difficult to apply
a simple evolutionary model, as the whole area is a patchwork of fragmented crustal
blocks which move one respect to the other in a very complex relationship. Partial
melting of a MORB-like astenospheric mantle, metasomatised by prevailing subducted
sediments, is thought to produce the entire spectrum of parental magmas of SAAVA.
Slab-derived fluids are generally reduced. Total amount of subducted sediments
involved in the magma genesis decreases from West to East. Pe-Piper and Piper,
reviewing also a large amount of magmatological and tectonic data, conclude that two
principal volcanic associations, together with a third minor association, occur in the
South Aegean active volcanic arc, differing in magma type, age, spatial distribution,
relationship to faulting, and petrogenesis. Variation in magmatism is related to changes
in tectonics during the evolution of the arc, as a result of collision of African continental
crust with the Aegean-Anatolian microplate, that set up changing patterns of strike-slip
faulting in the arc. The ultimate cause of magmatism in the South Aegean active
volcanic arc is concluded to be the subduction-related release of hydrous volatiles, but
there are important differences between the petrogenesis of the older western and
younger eastern parts of the arc.
The next paper, by Schuiling, considering the Milos case, carries out some
interesting calculations on the gas flow rates in volcanic areas and the provenance of
these gasses.
Santo is presenting in the eighth paper a detailed study of the Nea Kameni
(Santorini) plagioclase phenocrysts, with useful results for both the magmatic evolution
and the volcanic hazard assessment of the most active SAAVA center.
IX
The next eight papers deal with the volcanic hazard assessment and the monitoring
efforts of the active SAAVA centers. The editors (Vougioukalakis and Fytikas) present
an extensive review on the volcanic hazard assessment and the monitoring state of the
SAAVA centers. Dimitriadis et al. and Stiros et al. present the results of the seismic and
geodetic monitoring of the Santorini volcano. Dimitriadis et al. located two clusters of
epicenters in the broader area of the Santorini Volcano. The first cluster is located in the
Santorini caldera and is associated with the volcanic processes in the Kameni Islands.
The second (larger) cluster is located NE of the Santorini Island group, at the Kolumbo
submarine volcano, and is connected with the volcanic processes at this center. These
clusters can be appropriately associated with the two main tectonic faults in the area
under study. The first one (N60°E direction) corresponds to the continuation of the
Amorgos fault in the area, while the secondary tectonic line (EW direction) is probably
related with the southern edge of a submarine graben, which is located between the
islands of Amorgos and Santorini. Between June 1994 and May 2003, Stiros et al.(a)
registered a small-scale (up to 10cm), gradual inflation of the northern part of the
caldera (between Nea Kameni and Thirasia), possibly associated with magma ascent
along a dyke. Papadopoulos and Orfanogiannaki carried out a long-term prediction of
the next eruption in Santorini volcanic field from conditional probability estimates.
Regarding Nisyros volcano, Stiros et al. (b), through a detailed geomorphological
and biological study of the coasts of Nisyros and of the nearly Kos Island, combined
with radiocarbon analysis of collected samples, provide evidence of land uplift along
the northern and western coast of Nisyros Island, at a minimum, though increasing rate
of 1.7 mm/yr during the last 2,000-3,000 years. This uplift correlates with late
Quaternary uplift deduced from coastal and volcanological data, and reflects a new
tendency for topography build-up due to caldera inflation, and consequently to potential
for a new volcanic unrest. Galanopoulos and Kolettis present a DC resistivity study in
order to investigate the formation of a 600 m long and 15-20 m deep fissure on the
Nisyros caldera floor. The derived electrical models are compatible with the local
geology and support the idea that the formation of the fracture is directly related with
subsidence phenomena within the top 100 m depths. Di Filippo and Toro registered
between 2001-2003, through monitoring with a microgravity network, variations that
largely exceeded the measuring errors, suggesting that such variations are to be ascribed
to mass variations of the volcanic complex. Teschner et al. present the results of a real
time monitoring of gas-geochemical parameters in Nisyros fumaroles, during 2003.
The next two articles deal with hydrothermal deposits and processes in the SAAVA.
Glasby et al. present a thorough study on the Vani manganese deposit (Milos island), a
fossil stratabound hydrothermal deposit formed by the penetration of hydrothermal
fluids through a lithified pyroclastic tuff. Two types of deposit have been recognized:
"high-temperature" hydrothermal Mn deposits formed initially when the hydrothermal
fluids penetrated faults and fissures within the volcaniclastic sandstone and bedded
hydrothermal Mn deposits formed subsequently as the cooling hydrothermal fluids
migrated along the bedding planes of the volcaniclastic sandstone. Both are late-stage,
low-temperature deposits. Papoulis et al. present a study of the hydrothermal alteration