Abstract: Thirteen pumice samples from the D and E ignimbrite units of Kalymnos Tuff have been analyzed for their biotite and feldspar phenocryst mineral chemistry and for bulk major and 20 trace, including 14 Rare Earth elements, to define and compare their petrochemistry with the Kos Plateau Tuff (KPT). For the same purpose major element analyses were obtained from Kalymnos Tuff and KPT glasses. Both KPT and Kalymnos pumice lapilli are rhyolites characterized by a well-developed âsilkyâ texture and roundish quartz. Phenocrysts of biotite and feldspars (sanidine, oligoclase) from both tuffs display compositional overlap. Crystals are characterized by undulatory extinction (quartz), fractures (sanidine, oligoclase) and bent cleavages (biotite) due to the explosive origin of their host. Both tuffs show well-defined petrogenetic trends and extensive compositional overlaps on major and trace element variation diagrams suggesting that they are consanguineous. However, D ignimbrite samples are more evolved than those obtained from E ignimbrite as indicated from major elements, alkali earths (Ba, Rb, Sr), immobile (Zr, Y), compatible (V) and hygromagmatophile trace element (Th) distributions. This evidence indicates a stratified magma chamber under a ~16 Km caldera superstructure which is mostly submarine.
Abstract: To model the morphotectonic evolution of Nisyros stratovolcano in the Aegean Volcanic Arc (36° 35ⲠN, 27° 10ⲠE), a 30 m resolution ASTER GDEM was used. Nisyros is characterized by a relative pristine volcanic terrain. Elevation, slope and aspect images, the corresponding frequency distributions and rose diagrams enabled the geomorphometric analysis of Nisyros revealing the major geomorphological structures that are associated to both endogenetic and exogenetic processes acting on the island either new or previously reported in the literature. New elements include the number, loci of issue, relative age, ogive structures of the voluminous precalderan Nikia flows and their contact relationships with the Avlaki flows. The tectonic control, fine feature morphology and flow paths of lavas and smaller domes associated with the main postcalderan domes become visually apparent. Particularities of the hydrographic network accentuate and bring forward non-mapped radial faults. Intense landslide scarring and the volcanic stratigraphy of the intact units were revealed in the northeastern quadrant of Nisyros. Major, new volcano-tectonic features include the division of the island into three northwesterly trending sectors and the dipping of Nisyros towards the southeast as a result of segmentation by two major ring faults the Kos Ring Fault (KRF) and Perigussa Ring trapdoor Fault (PRF) which represent ring faults of the Kos sagging-caldera. The ASTER GDEM has provided suitable thematic information content in the geomorphometric analysis of Nisyros and therefore it offers a reconnaissance tool in the geomorphological analysis of a volcanic landscape.
Abstract: The Hellenic Peninsula and the adjacent Aegean and Ionian seas are segmented into regions on the basis of Terra satellite-MODIS instrument derived land surface temperatures (LST) to test if they can be used in the field reconnaissance for potential geothermal targets, each region representing a different thermal signature. The method has been used successfully to identify hot spot and geothermal activity in the Afar Triangle and in the Red Sea. Night monthly average LST values per pixel, since 2001, are used in this work for geothermal field identification. Average LST seasonal variability is expressed by a common centroid curve of pixel cluster. Clusters were subsequently ranked in increasing LST according to their centroids. Cluster-2 represents by far the Aegean volcanic arc (AVA) which comprises the high enthalpy (320 and 350°C, respectively) geothermal fields of Milos and Nisyros. The interpretation of LST terrain segmentation into sub-clusters of Cluster-2 is consistent with thermal anomalies related to the volcano-islands of the AVA, the occurrence of thermal anomalies related to granodiorite plutons in the Cyclades and to the volcano-related anomalies of the Dodecanese Province. We conclude that the identification of such thermal anomalies obtained by a combination of remote sensing (LST), regional geology and field data (borehole, thermal spring and subsurface hydrothermal reservoir temperatures) can be a particularly useful exploration tool for localizing geothermal anomalies.
Abstract: Scheelite (CaWO4) mineralization has developed as disseminations, veinlets and mainly pods within garnet-pyroxene
skarn and hornfelses in two locations within the contact aureole of a syntectonic calc-alkaline granodiorite to leucogranite pluton
on the island of Tinos, Hellas. The pluton was emplaced during a transition from compression (granodiorite) to extension (leucogranite).
Opening of conduits assisted by carbofracturing allowed fl uid circulation during extension, which resulted in a change
of character of contact metamorphism from thermal-isochemical to infi ltration metasomatism. During infi ltration metasomatism
ion exchange involved the plutonic and the country rocks and was intensifi ed by carbofracturing resulting from the pyrometasomatic
loss of CO2 from the marbles. Skarn formation may have been initiated due to thermal effects of the pluton with local mass
transfer in the host schists and marbles. The Tinos tungsten skarn is an oxidized skarn that retains relics of an earlier less oxidized
stage probably mirroring a change in the redox conditions of the leucogranite. Skarn pyroxene is diopside, however, hedenbergite
has been preserved locally. Cores of garnet megacrysts from an early skarn formation are rich in grossular component and exhibit
sector-zoning, characteristic of growth under contact metamorphic conditions at log fO2 that ranged between â19.8 and â22.9. Garnet
overgrowths from a later stage are predominantly andradite and display euhedral crystal boundaries, oscillatory zoning, zonal
anisotropy and growth as open space fi llings, which are features typical of hydrothermal garnet. Scheelite crystals are enclosed
within and display equilibrium boundaries to hydrothermal garnet. They have primary fl uid inclusions with an average homogenization
temperature Th of 375 °C and salinity of ~14 wt% NaCl equivalent. Th of primary fl uid inclusions in the coexisting hydrothermal
garnet ranges from 310 to 340 °C, of primary inclusions in quartz from quartz-calcite veinlets formed by carbofracturing
from ~ 400 to 375 °C and salinity ~14 wt% NaCl equivalent. These quartz-calcite veinlets cut mainly the early garnet cores, rich
in the grossular component, but rarely the hydrothermal andraditic garnet overgrowths, indicating that scheelite mineralization is
associated with the late leucogranitic phase of the Tinos pluton.
Abstract: In Serifos island a mid-Miocene pluton was emplaced syntectonically at ca. 11 Ma in a northeasterly trending fault zone
within schist and marble of the Cycladic Blueschist Unit. The central mass of the pluton consists mainly of hornblende-biotite
granodiorite and less tonalite, its border facies is granodiorite to granite. Associated dykes are mainly granodioritic. Amphibole
geothermobarometry indicates pluton emplacement at initial maximum P â 3.1 ± 0.6 kbar and T between 748° to 718 °C under
hypersolvus conditions. Magnetiteâhematite ores, which have been mined since antiquity, occur in the proximity of the Serifos
pluton. Most of iron oxide ores are located in marble within the contact metamorphic aureole and have been considered as skarn
deposits. However, a few iron oxide and base metal sulfi de deposits occur outside the contact aureole. The trace element (V, Ti, Ni)
characteristics of the iron ores suggest a sedimentary provenance. The sulfi de ores are folded and because the geochemistry of some
of the schists of the encasing Blueschist Unit shows them to be of possible metavolcanic origin, on alternative exhalite genesis is
suggested for these Serifos ores.
Abstract: Twenty pumice samples from the D and E ignimbrite units of Kos Plateau and Tilos Tuffs have been analyzed for major and 37 trace elements, including 14 Rare Earth elements to provide evidence for their geochemical insignia. Tilos island lies roughly 50 km from Kos and the identity of these two tuffs has been previously established in the literature on physical volcanology arguments (Allen 2001). Kos and Tilos tuff samples form a cluster of calcalkaline rhyolites transgressing the peraluminous-metaluminous boundary in ACNK-ANK space. Both pumices display well-defined partly overlapping trends, with D samples being more evolved than E, on variation diagrams for major elements, alkali earths (Ba, Rb, Sr), immobile (Zr, Y), compatible (V), highly incompatible (Pb, Th) and hygromagmatophile (Sb) trace elements.
It has been suggested by Allen (2001) that the KPT has been erupted 161 Ka ago (Smith et al. 1996) ago, from a superstructure now outlined by the remains of a â¼16 km caldera which is mostly submarine. Pyroclastic density currents traveled either on land (Pe-Piper et al. 2005), or crossed open sea (Bohla 1987, Allen 2001) and deposited tuffs on Tilos, Kalymnos, on the coasts of Asian Minor and other islands in the area. The apron of this ash has traveled 300 km to the south and is thought to be equivalent with the W-3 submarine tephra layer (Federman & Carey 1980, Keller 1980, Vinci 1985).
Our studies using Landsat-TM remotely sensed imagery, subaqueous distribution of hydrothermal vents and tectonic data of ring and radial faults collected on land, has indicated a caldera superstructure very similar to that proposed by Allen (2001) which "nests" smaller caldera-depressions (Kefalos, Zini, Yali, Perigusa-Pachia) or has them attached as "satellite" (Nisyros caldera) structures (St. Seymour et al. 2006). It has been proposed that these calderas represent the physical expression of interconnected magma chambers (St. Seymour 1996), satellites to a larger, active subvolcanic chamber underlying the area between Kos and Nisyros (Papadopoulos et al. 1998, Lagios et al. 2005).
Abstract: Nisyros is characterised by a high enthalpy geothermal system. Numerous thermal springs are concentrated near the coastline with temperatures of 27°-43°C. Isotopic composition of Nisyros thermal water samples reveals mixing between seawater with magmatic water and geothermal steam and the possible involvement of groundwater and/or meteoric water. Combined silica and K2/Mg geothermometry indicates temperatures of 90°-140°C while deep geothermal fluids display temperatures of 245°C and steam heated samples approximately 210°C. We have calculated the initial temperature of the hot component of mixing using the diagram of dissolved SiO2 versus enthalpy. We propose that the geothermal system of Nisyros consists of two major reservoirs. A deeper one (1400-1800 m) with temperatures greater than 245°C which is the result of mixing between seawater and primary geothermal fluid and hosts hot waters of high enthalpy which cool adiabatically and ascend, due to separation of vapours, to the shallow reservoir (0-500m) of lower enthalpy. In this mixing occurs mixing between seawater and geothermal vapours and/or underground water or meteoric water with a hot water component of approximately 180°-220°C. The latter is derived from the ascent of the high enthalpy waters into the shallow reservoir which represents the mixing zone of the geothermal system and is characterised by lower enthalpy compared to the deeper reservoir displaying temperatures of 90°-140°C whilst the temperature of the separated vapours are approximately 225°C.
Abstract: Nisyros represents the ideal candidate of a Mediterranean volcano for a pilot study on sustainable
development. Nisyros was a renown Loutropolis in the past for its baths used for medicinal purposes. In this
work, we present a preliminary survey of the thermal and mineral waters of the island. We present chemical
data revealing seawater and geothermal water mixing processes. The aim of this work is to evaluate the water
character and include thermal and mineral waters of Nisyros volcano in the sustainable development plan
proposed for the establishment of Nisyros to the status of a National Park and as an attraction pole for
âalternative tourismâ. However, the use that agrees with the promotion of the volcano to a Natural Park with
the consensus of the permanent inhabitants, is their use for baths and in Spa centers. This target will redirect
economy towards âalternative tourismâ and restore Nisyros to its ancient status of a renown Loutropolis.
Abstract: Nisyros represents the ideal candidate of a Mediterranean volcano for a pilot study on sustainable
development. Nisyros was a renown Loutropolis in the past and its baths, for medicinal purposes. In this work
we present a preliminary survey of the thermal and mineral waters of the island. We present chemical data
revealing seawater and geothermal water mixing processes with the aim to evaluate their water character and
include thermal and mineral waters of Nisyros volcano in the sustainable development plan proposed for the
establishment of Nisyros to the status of a National Park and as an attraction pole for âalternative tourismâ.
However, the use that dovetails with promotion of the volcano to a Natural Park and that most of the
permanent inhabitants wish for, is their use for baths and in Spa centers, targeting the redirection of the
economy towards âalternative tourismâ and restoring Nisyros to its ancient status of a renown Loutropolis.
Abstract: Nisyros represents the ideal candidate of a Mediterranean volcano for a pilot study in sustainable
development: it is a geotope with rare fauna and flora, as well as, rock exposures that illustrate a host of
volcanic phenomena taking place during the evolution of a subduction related-stratovolcano. Nisyros with a
population of 916 permanent habitants survives due to its quarrying of pumice and perlite stone from the
nearby island of Yali and to transit tourism from the island of Kos. Fresh water is a rare commodity on
Nisyros. However, the island contains all the solutions that will set it in a sustainable orbit: (i) Inexpensive
wind and solar energy and a high enthalpy geothermal field that could provide electricity and also power a
much needed second desalination plant to revive the southern part of the island. (ii) It was a renown
Loutropolis in the past and its baths, for medicinal purposes, they can be developed into Spa-Centers. (iii) It
has an important geopolitical position lying 16.7km off the coast of Asian Minor. Due to its rich cultural and
physical heritage we propose here the sustainable development of Nisyros into a National Park. The island will
act as a pole of attraction for alternative tourism and ecotourism. Five ânature itinerariesâ with the purpose to
expose and educate visitors to the stunning workings of an active volcano and to rare species of fauna and
indigenous flora, are presented here. The National Park of Nisyros will co-host a Volcano Observatory and a
Cultural and Natural Museum.
Abstract: The interdependence of volcanism and tectonism has been focused upon in the last decade as a result ofpreviously accumulated evidence, as well as, due to the application ofremote sensing techniques in both these fields. Volcanoes depend on tectonic features such as faults for their positioning and operation and on petrotectonic environmentfor the chemistry oftheir magmas. Faults provide the plumbing system for magma ascent and therefore volcano localisation and distribution in space greatly depends on the tectonic pattern ofan area. On the other hand, volcanoes locally imprint their volcanotectonic features such as radial and ring faults which result from cycles of magma replenishment (inflation) and evacuation (deflation) of magmatic reservoirs (magma chambers). Under this light, the area in the easternmost extremity of the Aegean Arc is being reconsidered. Our main preliminaryfindings ofongoing research in the area, using field and remote sensing methods indicate localization of volcanic activity on Kos and on the Datca Peninsula of Asian Minor since Miocene due to the northboundingfaults oftheDatcaGraben. Localisation ofvolcanicvents andcalderasin the Kos-Nisyros area follows intersection of a major tectonic line of northnorthwesterly trending faults the 'Kos-Nisyros-Tilos Line' withN50oE,N30oE and N200W trending faults. On the well-preserved volcano ofNisyros the architecture of the volcanic edifice has significantly been affected by 'trap-door' volcanotectonics ofa major volcanic infrastructure in the area namely the Kos-Caldera.
Abstract: Remote sensing techniques using SPOT,
LANDSAT-TM and ASTER satellite images, as
well as Digital Elevation Models (DEM) have been
used to identify caldera structures in the
Quaternary Volcanic Arc and in the Miocene
volcanic field of Lesvos in the Aegean Sea.
Erosion and fault tectonics in Lesvos and
inundation by sea-water in Milos and Kos have
rendered the caldera structures difficult to identify.
Abstract: Low sulfidation epithermal Au-Ag-Te deposits constitute important sources of precious metals. Epithermal Au-Ag-Te mineralization at Panormos Bay is unusual in that is genetically related to plutonic calc-alkaline rocks rather than intrusive rocks. It is hosted in marbles, approximately 15 km from the western border of Tinos pluton. The mineralization is associated with a stockwork of early milky and late clear quartz syntaxial veins, filling a conjugate system of strike-slip faults. Any attempt to model the genesis of the Panormos Bay mineralization, must take into consideration its overall spatial and temporal association with the Tinos calcalkaline pluton (especially its leucogranitic phase), the diverse set of sulfides, sulfosalts, tellurides and native metals which are related to the multiple metal sources, the distance over which the hydrothermal fluids traveled to the site of deposition, and the corrosive nature of the low pH (3,3) fluid that carried F, Cl, CO2, H2S and B.
The high permeability of the marble host at Tinos permitted inflow of cooler, meteoric waters into the host. Subsequent mixing with and cooling of hydrothermal fluids, as indicated by stable isotope (S, C, O and H) and fluid inclusion studies, resulted in condensation of the metalliferous vapors and tellurium and gold ligands into the aqueous phase. The high reactivity of the marble provided an important mechanism that controlled ore precipitation. CO2 effervescence which caused a pH shift towards neutral conditions resulted in the destabilization of bisulfide complexes, the release of H2S and the precipitation of precious metal tellurides. Hydraulic fracturing and carbofracturing allowed conduits to remain open, permitting fluids to flow and volatiles to escape.
Abstract: Nisyros volcano is a rare natural monument in the stage of neglect, which would have been severe in the absence of tourists from Kos and the renewed scientific interest in the area. Quaternary volcanism in Nisyros occurred in two cycles: one andesitic stratovolcano-building and a second intensely explosive which resulted in caldera formation. Several phreatic craters and fumaroles are situated on the caldera floor and hot springs are located mainly on the southern and northern coasts. Two aquifers, a deep (330 degrees centigrade) and a shallow (170 degrees centigrade), are reported in the literature. In 1973 a project was launched generating electricity from geothermal energy. For Nisyros to develop in a sustainable direction, it has to overcome the challenges of adequate quantities of quality water and easily accessible cheap energy. Our plan for water and energy management of Nisyros would include additional desalination capacity by taking advantage of geothermal and other âsoftâ energy sources (RES). These could also be used for heating of buildings, greenhouses and as sources for electricity. Water management research applying to the seasonal needs of the island, would include management of desalination and physical water sources such as rainfall, runoff and underground water reservoirs. With the proper water and energy management, the extreme natural beauty of volcanological sites, the great variety of ornithological species and rare fauna could promote the island to the status of a National Park.
The Nisyros of the past was a renown city for its baths. The development of the hot spring into Spa Centers would re-establish Nisyros to its ancient status and an important attraction pole for ecotourism. Finally, we propose the establishment of an institute to monitor the RES applications, act as a Volcanological Observatory and as Museum of physical history and volcanological education.
Abstract: The Kos - Nisyros study area is located at the easternmost edge of the active Quaternary volcanic arc of the southern Aegean Sea and includes the islands of Kos and Nisyros and the islets of Gyali, Strongyli, Pachia and Pyrgoussa. The volcanic activity of Kos island is characterized by Upper â Miocene ignimbrite deposits and Pliocene - Pleistocene volcanic products such as volcanic domes, the Kefalos pyroclastic sequence of hydromagmatic tuffs and the large-scale pyroclastic formation Kos Plateau Tuff (KPT) deposits which is also found on the Kalymnos, Pserimos and Tilos islands. Nisyros is a calcalkaline stratovolcano which consists of Pliocene volcanic products such as andesite and basaltic andesite lavas that are overlain by pyroclastic deposits, lava flows and lava domes of dacitic â rhyodacitic composition. The islets of Gyali, Strongyli, Pachia and Pyrgoussa represent Pliocene lava domes of rhyolitic (Gyali), andesitic (Strogyli) and dacitic composition (Pachia and Pyrgoussa) On these domes, pyroclastic deposits of the Upper Pumice unit of Gyali (in Strogyli) and pyroclastic deposits of the Kos Plateau Tuff (KPT) and Panayia Kyra formation (in Pachia and Pyrgoussa) have been identified.
In this thesis, the volcanic products of the Kos-Nisyros area are examined using mineral chemistry, geochemical and petrographical methods, while volcanic structures and morphological features are identified and mapped using remote sensing techniques. The aim of this thesis is to understand the volcanic evolution of the study area, by drawing conclusions regarding the consanguineous relationship of the magmatic products, magma mixing phenomena and the magma chamber system of the area, as well as, the surface expression of this magma chamber system in the form of caldera structures.
For this purpose, in this thesis, it is investigated the consanguineous relationship of the Kos Tuff (Kos Plateau Tuff) found on Kos, Tilos and Kalymnos islands, as well as, the geochemical differentiation of the most violent and explosive ignimbrite units D and E of the Kos Tuff, confirming the stratigraphic correlation of these deposits as it was previously presented by physical volcanology data. The petrochemical study of the Kos - Nisyros area as a single "volcanic complex" reveals that the volcanism of the study area is divided into a Miocene and a Pliocene â Pleistocene activity. The Miocene activity is characterized by magmatic and volcanic products such as the monzonite of Kos and the Miocene ignimbrites of Kos and the Pliocene â Pleistocene volcanic activity consists of volcanic products such as lava domes and pyroclastic deposits from Kos, Gyali and Nisyros volcanoes where it is revealed the consanguineous magmatic relationship of these Pliocene â Pleistocene products. Using âNomarskiâ interferometry method it is revealed that magma mixing/mingling phenomena are unquestionable for the magma chamber system of Nisyros and provide evidence that these phenomena were active throughout the volcanic evolution of Nisyros volcano. Field observations and remote sensing methods revealed caldera structures in the Kos - Nisyros area which are identified and classified according to new perceptions regarding the volcanic evolution. The volcanic structures of Nisyros volcano are examined using remote sensing methods such as satellite image and digital elevation models interpretation, as well as, the geomorphometric analysis of the Nisyros terrain in combination with geomorphotectonic features of the volcano as presented by other researchers and new perceptions on the volcanic evolution. It is also presented a model of proto-caldera, caldera and post-caldera evolution of Nisyros volcano based on new perceptions on the volcanic evolution in relation to the stratigraphic evolution. Finally, it is studied the subvolcanic magma chamber system of the Kos - Nisyros area, as well as, mixing phenomena in the volcano of Nisyros using the âNomarskiâ interferometry method and the distribution of major, trace and rare earth elements revealing the consanguineous nature of these volcanic centers by providing the widest volcanic area of Kos - Nisyros as a major volcanic center characterized by a complex caldera system.
Sustainable development of Nisyros volcano represents a management tool which combines the volcanic evolution with the environmental preservation and can promote volcanic regions as geotopes. The investigation of the present conditions of the island reveals, despite the fact that Nisyros is characterized by a strong environmental, energy, social, cultural and economic potential, it remains undeveloped and unexploited due to lack of an integrated sustainable development management plan, based on which, decisions should be equal, equivalent simultaneously and in harmony. Based on the study of the Nisyros water resources, the energy potential from renewable energy sources, the management of natural and urban environment of the volcano of Nisyros and the study of the positive and/or negative effects of the mining industry in Gyali volcanic islet it is proposed an integrated sustainable development according to the views and the perspectives of the local community. From this intergraded plan are generated recommendations for an integrated management of the volcano of Nisyros which satisfy equal, equivalent, simultaneously and in harmony the principles of sustainable development aiming to refocus the local economy, the management of natural and urban environment and the social development.
Abstract: Mantle hotspots appear to announce lingering diapiric activity at lithospheric triple junctions which results in the breaking of continents, the motion of plates and the formation of new oceans. They are longed-lived phenomena, with average durations extending to 100 Ma (SEARS 2004). Africa is a continent on the eve of its dispersal. Major hotspots are hosted by Africa and many African continental fragments have accreted onto Europe during the formation of the Tethys oceans. The eastern half of this continent is presently in the break-up stage (East African Rift, Afar triple junction and the opening of Red Sea). The Red Sea event was initiated in early Miocene. Today at the height of the Gulf of Aqaba a triple junction has been formed, its eastern branch continuing as the Dead Sea fault. This fault joins to the north with the EAF fault and the Bilitis-Zagros suture zone. It is a consensus in the literature that the western branch of the Y (Suez branch) dies-out shortly upon entering the Mediterranean Sea. However, accumulating circumstantial evidence indicates that this may not be the case. Manifestation of Excess Mass (EM) and Excess Mass Stress (EMS) has been interpreted by TASSO (1998) as mantle upwelling and diapism in the northeastern Aegean, based on geophysical data. Processing of remote sensing data by our group, indicates a thermal anomaly just outside the island of Rhodes of geometry very similar to that of the thermal anomalies present in the Red Sea. Continuation of the Suez branch up into the northeastern Aegean agrees also with the estimated splitting dates of the Aegean region given by DERMITZAKIS (1990) and ANASTASAKIS and DERMITZAKIS (1990) and may explain the Rhodes thermal anomaly, as well as, the chemical and isotopic insignia of Miocene-Early Pliocene volcanism in eastern Aegean and western Anatolia.
Abstract: Thirty six pumice samples from the Kos Plateau, Tilos and Kalymnos Tuffs have been analyzed for major, 23 trace and 14 Rare Earth elements to provide evidence for their geochemical insignia. Tilos island lies roughly 50 km southeast from Kos and Kalymnos and the identity of these tuffs has been previously established in the literature on physical volcanology arguments (Allen 2001). Kos, Tilos and Kalymnos tuff samples form a cluster of calcalkaline rhyolites transgressing the peraluminous-metaluminous boundary in ACNK-ANK space. Both pumices display tightly overlapping trends on variation diagrams for major elements, alkali earths (Ba, Rb, Sr), immobile (Zr, Y, Nb), compatible (V) and highly incompatible (Pb, Th) trace elements. It has been suggested by Allen (2001) that the KPT has been erupted 161.000 (Smith et al., 1996) years ago, from a superstructure now outlined by the remains of a ~16 km caldera which is mostly submarine. Pyroclastic density currents traveled either on land (Pe-Piper et al. 2005), or crossed open sea (Bohla 1987; Allen 2001) and deposited tuffs on Tilos, Kalymnos, on the coasts of Asian Minor and other islands in the area. Our studies using Landsat-TM remotely sensed imagery, subaqueous distribution of hydrothermal vents and tectonic data of ring and radial faults collected on land, has indicated a caldera superstructure very similar to that proposed by Allen (2001) which ânestsâ smaller caldera-depressions (Kefalos, Zini, Yali, Perigusa-Pachia) or has them attached as âsatelliteâ structures (Nisyros caldera) (St. Seymour et al., 2006). It has been proposed that these calderas represent the physical expression of interconnected magma chambers (St. Seymour 1996), satellites to a larger, active subvolcanic chamber (Papadopoulos et al. 1998; Lagios et al. 2005) underlying the area between Kos and Nisyros.
Abstract: Milos, in the Quaternary Aegean Arc, renowned since pre-historic times for its trading of obsidian stone, is a complex of stratovolcanoes. Milos is an advanced hydrothermal stage and for this reason it is a worldâs known producer of commercial clay minerals and a high enthalpy geothermal field. The excellent plumbing of the hydrothermal system is attributed to intense faulting due to crustal thinning, which is also the reason of the partially submerged, difficult to identify, caldera systems. Such a partially inundated superstructure, the âApolloniaâ caldera, lies on the north-eastern part of Milos which encompasses also the western coast of Kimolos island, with the âFylakopiâ and âSaracenecoâ nested calderas within it. The volcanosedimentary succession exposed on the shores of Saraceneco Basin, consists of four depositional cycles of inversely graded pumice lapilli, intercalated with diatomites, with sedimentary structures indicative of deposition in shallow waters. The cycles of volcanosedimentation are separated by seismoturbidite horizons which signified resuming of explosive volcanic activity after a hiatus. The stratigraphic upwards evolution of the lapilli geochemistry was examined via major, 30 trace and 14 Rare Earth elements. All the lapilli are calk-alkaling rhyolites in composition, however, there is an overall upsection differentiation of the pumices towards more acid compositions. The significance of second order geochemical cycles within each major sedimentary cycle is discussed in this work, as well as, the comparative geochemistry of the Saraceneco pumice clasts and the products of the Bombarda volcano to the south.
Abstract: Milos island, in the central Aegean Archipelago, is a complex volcanic field consisting of a multitude of coalesced andesitic and felsic volcanic centers, which partakes of the Aegean Volcanic Arc. The arc is the result of collision of the African plate with the Aegean microplate, due to closure of the Tethys Ocean. Milos, which is presently at the hydrothermal stage, has been inhabited since ancient times and is renown for the statue of Aphrodite (Venus) of Milos (now in the museum of Louvre), international exports of industrial minerals (kaoline, montmorillonite), epithermal Au mineralization (Prophet Helias Dome, west part of the island) and for attracting visitors. Volcanism was initiated ~1.6 Ma ago and was initially pyroclastic-submarine in character. The subaerial phase included extensive andesitic to felsic volcanic products in the form of lavas, lava domes and pyroclastic covers, but no report of caldera structures existed with the exception of the younger center of Fyriplaka which is still visible by air. Recent geophysical evidence, however, is permissive of the presence of calderas on Milos. We have investigated the case of Milos calderas using remote sensing techniques combined with geological field research. Study of Landsat-TM imagery geometrically corrected and introduced in a GIS framework, assisted by the study of a digitized elevation model (DEM) of the island including the sea strait of Adamas Bay, revealed seven caldera structures on Milos: Five overlapping calderas encompassing the Zephyria geothermal field (where an electric plant was constructed in the past) and the whole Adamas Bay Strait which includes four more overlapping calderas indicative of migration of the magmatic chamber in a northwesterly direction, congruent with the local tectonic structures. A fifth caldera (Apollonia) includes a very actively exploited area for clay minerals, reflecting the intense alteration of volcanic products associated with caldera structures. However, most impressive is the partly submerged Sarakeneco Caldera, which occupies most of the northeastern shores of the island. It is marked by pumice pyroclasts up to 3.5 meters long and numerous conspicuous radial caldera faults now occupied by streams. Satellite imagery further reveals that the Sarakeneco caldera is part of a superstructure that also includes the volcanic island of Kimolos (âChalk Islandâ) north of Milos.
Abstract: The largest low-sulfidation epithermal gold-telluride deposits in the world (e.g., Emperor, Fiji; Cripple Creek, U.S.A.) occur in intrusive volcanic rocks of alkaline or calc-alkaline affinity. By contrast, unexploited Au-Ag-Te mineralization at Panormos Bay, Greece, is relatively unusual in that it is genetically related to a F- and B-bearing granite (Tinos leucogranite). The Panormos Bay vein system, which is hosted in Miocene marbles, is composed primarily of thirty nearly parallel, high-angle quartz veins that extend for at least 500 m. In places, gold mineralization occurs in breccias. Zones of chlorite, talc, and muscovite-albite-tourmaline alteration, up to 50 cm wide, are associated with precious metal-bearing milky and clear quartz veins. The Au-Ag-Te mineralization is developed in stage V of eight hydrothermal stages. Stage V consists of three sub-stages (early, middle, and late) that are characterized by Ag-, Cu-, and Au-bearing tellurides, respectively. Hessite, sylvanite, altaite, native tellurium, stützite, and Cu-bearing cervelleite characterize the early stage whereas melonite, rickardite, vulcanite, weissite, and native tellurium are present in the middle stage. Late stage V contains rickardite, kostovite, krennerite, petzite, and calaverite. Fluid inclusion studies suggest that hydrothermal mineralization was deposited under hydrostatic pressures at a minimum depth of 1km from moderate-temperature (155o-321oC), low to moderately saline (0.2 to 6.3 equiv. wt % NaCl), effervescing, CO2-bearing fluids that contained appreciable amounts of CaCl2 and MgCl2. Calculated isotope compositions of δ18O = -3.3 to 5.1 per mil and δD of -73 to -62 per mil for waters in equilibrium with muscovite, quartz, and talc are consistent with ore fluids being derived from the Tinos granite that subsequently mixed with a more dilute, low temperature meteoric fluid. Calculated δ13CCO2 (-2.0 to -0.3 per mil) and δ34SH2S (-10.5 to 0.8 per mil) compositions of the ore fluids indicate an igneous source of carbon and sulfur, which were highly exchanged with a meta-sedimentary source. Epithermal gold mineralization at Panormos Bay is one of several granite-related gold occurrences (including nearby Apigania Bay) in Greece.
Abstract: The interdependence of volcanism and tectonism has been focused upon in the last decade as a result of previously accumulated evidence, as well as, due to the application of remote sensing techniques in both these fields. Volcanoes depend on tectonic features such as faults for their positioning and operation and on petrotectonic environment for the chemistry of their magmas. Faults provide the plumbing system for magma ascent and therefore volcano localisation and distribution in space greatly depends on the tectonic pattern of an area. On the other hand, volcanoes locally imprint their volcanotectonic features such as radial and ring faults which result from cycles of magma replenishment (inflation) and evacuation (deflation) of magmatic reservoirs (magma chambers).
Under this light, the area in the easternmost extremity of the Aegean Arc is being reconcidered. Our main preliminary findings of ongoing research in the area, using field and remote sensing methods indicate localization of volcanic activity on Kos and on the Datca Peninsula of Asian Minor since Miocene due to the north-bounding faults of the Datca Graben. Localisation of volcanic vents and calderas in the Kos-Nisyros area follows intersection of a major tectonic line of north-northwesterly trending faults the âKos-Nisyros-Tilos Lineâ with N50oE, N30oE and N20oW trending faults. The classification of calderas in our study area according to P.W. Lipman, 1995 agrees with the clues that on the well-preserved volcano of Nisyros the architecture of the volcanic edifice has significantly been affected by âtrap-doorâ volcanotectonics of a major volcanic infrastructure in the area, with downsag caldera of Kos.
Abstract: Scheelite (CaWO4) mineralization has developed as disseminations, veinlets and mainly pods within garnet-pyroxene skarn and hornfelses in two locations within the contact aureole of a syntectonic calc-alkaline granodiorite to leucogranite pluton on the island of Tinos, Hellas. The pluton was emplaced during a transition from compression (granodiorite) to extension (leucogranite). Opening of conduits assisted by carbofracturing allowed fl uid circulation during extension, which resulted in a change of character of contact metamorphism from thermal-isochemical to infi ltration metasomatism. During infi ltration metasomatism ion exchange involved the plutonic and the country rocks and was intensifi ed by carbofracturing resulting from the pyrometasomatic loss of CO2 from the marbles. Skarn formation may have been initiated due to thermal effects of the pluton with local mass transfer in the host schists and marbles. The Tinos tungsten skarn is an oxidized skarn that retains relics of an earlier less oxidized stage probably mirroring a change in the redox conditions of the leucogranite. Skarn pyroxene is diopside, however, hedenbergite has been preserved locally. Cores of garnet megacrysts from an early skarn formation are rich in grossular component and exhibit sector-zoning, characteristic of growth under contact metamorphic conditions at log fO2 that ranged between â19.8 and â22.9. Garnet overgrowths from a later stage are predominantly andradite and display euhedral crystal boundaries, oscillatory zoning, zonal anisotropy and growth as open space fi llings, which are features typical of hydrothermal garnet. Scheelite crystals are enclosed within and display equilibrium boundaries to hydrothermal garnet. They have primary fl uid inclusions with an average homogenization temperature Th of 375 °C and salinity of ~14 wt% NaCl equivalent. Th of primary fl uid inclusions in the coexisting hydrothermal garnet ranges from 310 to 340 °C, of primary inclusions in quartz from quartz-calcite veinlets formed by carbofracturing from ~ 400 to 375 °C and salinity ~14 wt% NaCl equivalent. These quartz-calcite veinlets cut mainly the early garnet cores, rich in the grossular component, but rarely the hydrothermal andraditic garnet overgrowths, indicating that scheelite mineralization is associated with the late leucogranitic phase of the Tinos pluton.
Abstract: Mantle hotspots appear to announce lingering diapiric activity at lithospheric triple junctions which results in the breaking of continents, the motion of plates and the formation of new oceans. They are longed-lived phenomena, with average durations extending to 100 Ma (SEARS 2004). Africa is a continent on the eve of its dispersal. Major hotspots are hosted by Africa and many African continental fragments have accreted onto Europe during the formation of the Tethys oceans. The eastern half of this continent is presently in the break-up stage (East African Rift, Afar triple junction and the opening of Red Sea). The Red Sea event was initiated in early Miocene. Today at the height of the Gulf of Aqaba a triple junction has been formed, its eastern branch continuing as the Dead Sea fault. This fault joins to the north with the EAF fault and the Bilitis-Zagros suture zone. It is a consensus in the literature that the western branch of the Y (Suez branch) dies-out shortly upon entering the Mediterranean Sea. However, accumulating circumstantial evidence indicates that this may not be the case. Manifestation of Excess Mass (EM) and Excess Mass Stress (EMS) has been interpreted by TASSO (1998) as mantle upwelling and diapism in the northeastern Aegean, based on geophysical data. Processing of remote sensing data by our group, indicates a thermal anomaly just outside the island of Rhodes of geometry very similar to that of the thermal anomalies present in the Red Sea. Continuation of the Suez branch up into the northeastern Aegean agrees also with the estimated splitting dates of the Aegean region given by DERMITZAKIS (1990) and ANASTASAKIS and DERMITZAKIS (1990) and may explain the Rhodes thermal anomaly, as well as, the chemical and isotopic insignia of Miocene-Early Pliocene volcanism in eastern Aegean and western Anatolia.
Abstract: One of the most distinct peculiarities of planet Earth that sets it apart from the other stony planets of our Solar System, i.e. Mercury, Venus, Mars and our Moon is that the Earthâs crust undergoes Wilson cycles i.e. it is not continuous and immobile, but consists of crustal plates that are formed at Mid-Ocean Ridges, and progressively moving in a plastic fashion on the upper mantle, they are finally consumed under continental plate margins at subduction zones. When oceanic crust forms at Mid-Ocean Ridges and plates move apart, an ocean forms, as does presently the Atlantic Ocean (Fig. xxx). When oceanic crust is consumed an ocean is closing and eventually disappears under volcanic arcs. The Pacific Ocean presently is consumed under the âRing of Fireâ i.e. under subduction zones around the Pacific, a process marked by hundreds of volcanoes (Fig. xxx) (volcanoes of Andes, Costa Rica, Mexico, Guatemala, Western US, Western Canada, Alaska, the Aleutians, Kamtchaka Peninsula, Japan, New Zealand, Indonesia). Similar events of oceanic consumption and volcanism have happened in the geological past in other part of our planet. For example, recent volcanism in Hellas (recent in geology is a million years!), expressed by the volcanoes of Aegina, Methana, Milos, Santorini, Kos and Nisyros is due to the consumption of the remnants of what it was in the geological past a great ocean i.e. the Tethys Ocean (Fig. xxx). Tethys closed when the African continental plate and the Eurasian plate started moving towards each other. What happens when oceans are consumed and continents collide? At continental collision fronts the Earthâs continental crust which is not rigid, as man perceives it in the limited time span of his life, deforms in a plastic fashion and folds. These crustal folds are actually the mountain ridges we observe and this planetary process is called an orogenesis (Fig. xxx). Recent great mountains such as the Himalayas, the Alps, the Pindos and the great Mountain ridges of Peloponnese and Crete, the Zagros Mountains in Iran are due to this process of continental collisions. Except Himalayas that formed by collision of Eurasian with a detached continental crustal wedge (Fig. xxx) that was connected initially with Africa and Antarctica and then navigated north the other mountain chains reported above form part of the Alpine Orogenesis which had its peak of formation ~ 170-90 million years ago. Such other major orogeneses in the geological past were the Hercynian Orogenesis (390 to ~310 million years) and the Caledonian Orogenesis (488 to ~416million years). The Wilson Cycle and the theory of crustal plates is recent in the geological scientific thought, it was elaborated by Canadian earth scientist Tuzo Wilson in the early 1970âs. However, the initial idea of plate motion was advanced by Alfred Wegener based on his observationsof geometrical, lithological and biological similarities of western Africa and eastern South America. Wegener was ridiculed for his ideas by the âscientific establishmentâ and subsequently died leading a polar expedition alone with his sledge dogs. However, the science of planet Earth i.e. Geology was never the same after Wegener.
Abstract: The island of Milos is a composite, high enthalpy volcanic field occupying the central part of the Quaternary Aegean Arc. Volcanism was initially submarine in character changing into subaerial at ~1.44 Ma. Volcanic products range the compositional spectrum from andesite to rhyolite and have been emitted from numerous centers in the form of domes, lava and volcaniclastics. The younger centers of Fyriplaka and Trachelas still retain their volcanic geomorphology, however, a number of older partly submerged caldera structures have been traced using remote sensing techniques. On the northeastern part of Milos these include the âApolloniaâ superstructure which encompasses also the western coast of Kimolos island, with the âSaracenecoâ and âFylakopiâ nested calderas within it and the âAdamas 2â caldera which is associated with the Bombarda felsic volcanic succession been erupted subaqueously ~1.7 Ma ago at a depth <200m below sea level (Rinaldi and Campos Venuti, 2003). The Bombarda volcanic products have probably spilled over and been deposited in shallow waters in the Saraceneco basin where three depositional cycles of inversely-graded pumice lapilli, intercalated with diatomites, have been recognized. Inversely-graded blocks of pumice have been deposited in channels around the shores of the Saraceneco basin. Deposits of larger pumice blocks up to 3.5m long seem to be related with âmoatsâ which are probably topographic expressions of the radial fault system of the Saraceneco caldera. The evolution of the local volcanic events is examined from the perspective of major and trace element geochemistry of the pumice lapilli in the three volcaniclastic cycles of the Saraceneco site, of the large pumice blocks around the Saraceneco basin and the andesitic fragments of the Fylakopi younger center.
Abstract: Au-Ag tellurides constitute a source of precious metal (second in line of importance for gold) and tellurium extraction. In the 1950âs the sole use of Te was in the production of steel and wrought iron. However, with the evolution of electronics Te became a high-tech metal with applications such as in Cd-Te solar cells, photovoltaic media, Te-Se photocopying, infrared detectors and in non-linear optical systems. In Hellas (Greece), precious metal tellurides are hosted within Oligocene to Miocene magmatic systems as epithermal and porphyry occurrences of varying degrees of sulphidation in two areas: the Northeastern Hellenic and the Cyclades belts. In the Northeastern Hellenic belt the Servomacedonian-Rhodope metallogenic area hosts several major ore deposits of which St. Demetrios (260,000 tones at 3.5 gr/t Au) and Perama Hill (11 million tones at 3.71 gr/t Au) are the most promising for future exploration. Tellurides are the major carriers of gold also in Western Thrace in the epithermal to porphyry type mineralization in Santa Barbara, Mavrokoryfi and Pefka prospects. Lemnos island, immediately south of the North Anatolia Fault (NAF), represents the southward extension of this belt with the quartz stockwork of the Fakos gold telluride prospect which partakes of a shoshonitic monzonite porphyry system. In the Cyclades, unexploited Au-Ag mineralization at Panormos Bay, Tinos island, is genetically related to Miocene fluorine- and boron-bearing leucogranite. The vein system, which is hosted in Mesozoic marbles, is composed primarily of 30 nearly parallel quartz veins that extend for at least 500m. Gold mineralization occurs in breccias which are the products of carbofracturing related to CO2 effervescence of the ore fluid. The Au-Ag-Te mineralization is developed in Stage V of eight mesothermal to epithermal polymetallic stages which precipitated 71 ore and gangue minerals. Stage V consists of early, middle and late substages that are characterized by Ag-, Cu- and Au-bearing tellurides respectively. The Panormos polymetallic mineralization is low-sulphidation (LS), whilst the northeastern occurrences are HS-IS in character. Reconnaissance exploration for tellurides is presently underway in other parts of the Cycladic belt which are host to Miocene granitic intrusions. The geological and physicochemical conditions for Au-Ag telluride formation for the Northeastern Hellenic and Cyclades belts are compared in this work.
