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 ELSEVIER Amsterdam - Boston - Heidelberg - London - New York - Oxford Paris - San Diego - San Francisco - Singapore - Sydney - Tokyo ELSEVIER B.V. ELSEVIER Inc. ELSEVIER Ltd ELSEVIER Ltd Radarweg 29 525 B Street, Suite 1900 The Boulevard, Langford Lane 84 Theobalds Road P.O. Box 211, 1000 AE Amsterdam San Diego, CA 92101-4495 Kidlington, Oxford OX5 1GB London WC1X8RR The Netherlands USA UK UK © 2005 Elsevier B.V. All rights reserved. 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British Library Cataloguing in Publication Data A catalogue record is available from the British Library. ISBN: 0-444-52046-5 © The paper used in this publication meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper). Printed in The Netherlands. Working together to grow libraries in developing countries www.elsevier.com | www.bookaid.org | www.sabre.org ELSEVIER P°°!F££? Sabre Foundation t 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: +302109730697, Fax: +302109767208 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