Volcan Sollipulli is a Quaternary stratovolcano situated at 38'50'S in the Southern Volcanic Zone of the Andes of Chile, about 25 km east of the volcanic front. The volcano is capped by a large (25 km2 approx. ) ice-filled caldera. Sollipulli is unusual in this region of predominantly basic to intermediate magmatism in that it has erupted a wide range of magmas from high-MgO (9%) basalt to rhyolite (74% Si02). The last major eruption, the Alpehue eruption, occurred at about 2,900 B. P, ejecting about 4.7 km3 (D. R. E) of homogeneous high-Si dacite pumice, forming an extensive plinian airfall deposit and ignimbrite. The caldera predates the Alpehue eruption and is believed to have formed by passive subsidence combined with erosion rather than by catastrophic collapse. Withdrawal of magma from beneath the centre of the structure and effusive eruption induced subsidence. Magma mixing, fractional crystallisation and crustal assimilation are important evolutionary mechanisms. Some mixed dacite lavas contain primitive basaltic magmatic inclusions with diktytaxitic textures indicative of rapid quenching. Strongly resorbed, reverse zoned sodic plagioclase of dacitic origin occurs in basic inclusions and high-Mg olivine occurs in dacites. Other sequences appeart o have evolved predominantly by fractional crystallisation with some crustal assimilation. The amount of crustal assimilation increasesw ith decreasinga gei n somec ases. Older Sollipulli basic magmash ave evolved as small batchesp redominantlya t moderatet o high pressurein the mid-lower crust whereas younger basic magmas have experienced protracted upper crustal histories in a large magma chamber, fractionating and assimilating crust to produce abundant high-Si dacite. Sollipulli magmas have an anhydrous mineralogy except for the occurrence of very minor amphibolei n somem ixed rocks. Magma temperaturesra ngef rom about 118 0'C in basalts to about 900'C in dacites. The most primitive samples represent hot and relatively water-poor (<1-2% H20) high-Al basaltic magmas. Crystal-rich andesitesa nd dacites record lower temperaturesth an crystal-poore quivalents. The cooler porphyritic magmas appear to have assimilated more crust than the hotter crystal-poor magmas. Most magmas have evolved at oxygen fugacities close to the NNO buffer curve. Large volcanic front centres in the region erupt magmas with lower incompatible elementa bundancea nd higher Ba/Nb than magmase rupteda t minor monogeneticc entresa, nd at stratovolcanoesto the easto f the front, which have incompatiblee lements ignatures transitional towards back-arc alkaline magmas (e. g. high Nb, Ce/Y). Older Sollipulli magmas also have high Ce/Y and Nb similar to magmas at some monogenetic centres but have lower Ti and Y. Younger Sollipulli magmas have even lower Ti and Y. Sollipulli basic magmasa re also characterisedb y higher Mg/Ni than all regional magmas. The simplest explanation is that the high Nb, Ce/Y magmas have assimilated enriched mantle lithosphere. The Ti, Y, Mg/Ni systematics suggest that the Sollipulli magmasa re generated by higher degrees of melting of a similar MORB-source-type mantle than the regional magmas. In the case of the younger Sollipulli magmas, generation from mantle which was slightly depleted during the earlier phase is also possible but the older magmas show no evidence in their spinel compositions for derivation from refractory mantle.

The 8-9 million year old volcanic complex of Oxnadalur is host to large-volume basalt flows, small and large volume rhyolite ash and lava flows, and a gabbroic intrusion. Both the plagioclase and pyroxene phenocrysts of the basalt are larger in size in the younger flows. The rhyolite ashes contain no primary crystals, but numerous basalt xenoliths and pumice fragments. The rhyolite lava flows are banded, with only the oldest containing phenocrysts of sanidine and plagioclase. One rhyolite flow is a mingled hybrid of two glasses, each containing plagioclase, pyroxene, and hornblende. Whole rock major and trace element analyses indicate a mixing trend among all of the units in the complex; yet abundant xenoliths in the ashes make this less data less dependable. In situ major and trace element analyses were performed via electron microprobe show two distinct populations in the variation diagrams, with the basalts and rhyolites separated by a compositional gap. Electron microprobe analyses also show that the plagioclase of the basalts and the gabbro are normally zoned with distinct calcic cores and sodic rims; this is also true for the mingled hybrid flow. Rare earth element analyses done via laser ablation inductively coupled plasma mass spectrometry, show that the phenocrysts are enriched in the light and depleted in the heavy rare earth elements. Rare earth element abundances in the glasses have a trend similar to that of ocean island basalt rather than that of mid ocean ridge basalt. Plagioclase geothermometry and amphibole geobarometry indicate that the magma chambers were replenished by new batches of melt and may have existed at a shallow level in the crust just prior to being erupted. Oxygen isotope ratios are depleted compared to those of typical mid ocean ridge basalts, typically indicating that the source melt was partially melted from a hydrothermally altered layer in the crust. As the δ18O values are whole rock, the depletion may be the result of any sub solidus interaction with low δ18O water. The data indicate that multiple shallow reservoirs evolved separately, with limited communication while being intruded by new magma throughout the lifespan of the complex.

Rapakivi and alkali feldspar phenocrysts from the Deer Isle Granite Complex were investigated using in situ trace element and Pb isotope geochemistry to see if magma mixing or isothermal decompression was responsible for their formation. Pb isotope and trace element profiles, along with CL imagery of quartz phenocrysts, indicate compositional changes in the magma chamber occurred during rapakivi and alkali feldspar growth. Repeated episodes of magma mixing/replenishment by relatively isotopically primitive and LREE enriched magmas (along with hybridized variations with the host magma) created localized disequilibration. Alkali feldspar phenocrysts proximal to these zones of thermal perturbation were first resorbed and then mantled by plagioclase. Entrainment back into this zone of mixing caused multiple mantles of plagioclase to form on some phenocrysts. For grains more distal to these zones of mixing, complete disequilibration of the grain did not occur and continued growth resulted in Ba-rich alkali feldspar mantles over Ba-poor alkali feldspar cores. As crystallization of the chamber continued along solidification fronts, batches of cooler crystal-rich magmas settled en masse to the floor. Disaggregation of these batches during settling, and subsequent accumulation on the chambers floor, brought grains with disparate crystallization histories together. Filter pressing of the cumulate pile flushed highly evolved fluids out from interstitial pores. Small amounts of evolved liquid, trapped interstitial to the cumulate, formed LREE depleted albitic rims on some grains. The crystallization, transportation and juxtaposition of rapakivi, mantled alkali feldspar and plagioclase phenocrysts suggests that a relatively large and active magma chamber, periodically recharged by batches of melt, must have existed.

Widespread base- and precious-metal anomalies, altered porphyry intrusions and oxidized veins occur in a portion of the Sulphur Springs Range, Nevada (adjacent to the Au-producing Carlin Trend). Some of the Eocene-Oligocene intrusions and cogenetic volcanic rocks in the range exhibit evidence of magma mixing and invite comparisons with other mineralized, Eocene mixed magma systems like the Bingham porphyry Cu deposit 300 km farther to the east. The Sulphur Springs igneous suite ranges compositionally through rhyolite, dacite, andesite and basaltic andesite but is less alkaline than the Bingham volcanic suite. However, the alkali content of the Sulphur Springs suite is similar to other Eocene igneous rocks along the Carlin Trend. The unusual geochemical signature of the Bingham igneous suite, enrichment in Cr, Ni, and Ba, is generally not found in the unaltered Sulphur Springs suite, with the exception of a set of altered mafic and intermediate dikes found in the core of the Sulphur Springs Range. The Bingham and Sulphur Springs volcanic suites both show extensive mixing of mafic magma with more silicic magma to create magma with intermediate compositions. The Bingham suite demonstrates mixing mineralogically by the presence of altered olivine and pyroxene in intermediate composition rocks. One of the disequilibrium Sulphur Springs rocks vividly expresses magma mixing as “andesite" - containing plagioclase, biotite, clinopyroxene, orthopyroxene, olivine, and amphibole coexisting with heavily resorbed megacrysts of quartz and K-feldspar. The Sulphur Springs mixed magma also contains abundant late-stage accessory magnetite and resorbed and oxidized garnet. The most likely parental magmas for this rock are a garnet-bearing quartz porphyry and olivine-bearing basaltic andesite which are both present in the range. Questions these data raise include: 1) Was there an unusual tectonic setting during the Eocene of the western United States that promoted both magma mixing and base- and precious-metal mineralization? 2) How vital might mixing processes and mafic magma be in delivering large amounts of S and chalcophile metals from deeper magmas to the shallow crust and eventual ore deposits?

Elizabeth Castle forms part of the South-East Granite Complex of Jersey, Channel Islands and is one of several multi-magma complexes in the region. The rocks have calc-alkaline signatures indicative of a subduction zone setting. In the western half of the Elizabeth Castle complex, the outcrops are wholly granophyre, while to the east, granophyre and minor monzogranite are intimately associated with diorite. The dioritic rocks form part of a layered series which is preserved at several localities. The layered diorites were initially intruded by multiple sub-horizontal granitic sheets. All contacts between the diorite and the granitic sheets are crenulate, indicating that the two were present as coexisting magmas. Fine-grained, dark margins in the diorites contain quench textures such as spherulitic plagioclase and acicular apatite, and are interpreted as chilled margins. At many contacts a narrow tonalitic marginal zone, with acicular amphiboles, is present. Field relationships suggest that this is a hybrid produced by interaction between coexisting dioritic and granitic magmas and this is confirmed by modelling based on geochemical data. It is proposed that within the marginal zones the presence of volatile-rich fluids, increased temperatures and a decrease in viscosity promoted chemical diffusion across the dioritegranite interface. The transfer of elements, together with the presence of volatiles, promoted the growth of hydrous mafic phases and suppressed crystallization of alkali feldspar. At the same time, fluid infiltration modified the composition of the dioritic magma. Field evidence indicates that these processes took place in a narrow time frame prior to further granitic intrusion. Parts of the sheeted complex were extensively disrupted by the later granitic intrusions, producing large areas rich in dioritic enclaves. Within these disrupted areas a grey inhomogeneous rock is encountered. Field and petrographic evidence suggest that this is a hybrid rock produced by the physical mixing of dioritic and granitic magmas. Linear chemical trends confirm this interpretation. Minor intrusions comprising red granite dykes, basic dykes, composite dykes and aplite sheets cut the complex.

Fractional crystallization, magma mixing, assimilation of continental crust, and how those processes modify volatile budgets, control the evolution of magma. As a consequence, the understanding of these processes, their magnitudes, and timescales is critical for interpreting ancient magma systems, their eruptions, and the potential future volcanic activity. In this dissertation I present the results of three projects. The first explores how magmatic processes affect magma reservoirs and eruption dynamics. The second explores where in the storage system and how often these processes occur. The third explores how volatile budgets are modified by processes such as crystallization, mixing, and assimilation. Volcán Popocatépetl (central México) erupted ~14100 14C yr BP producing the Tutti Frutti Plinian Eruption (TFPE). The eruption tapped two different silicic magmas that mixed just prior and during the eruption. The influx of mass and volatiles generated during the mixing of both magmas overpressured the reservoir, which was weakened at the top. The weakened reservoir relaxed while magma was tapped and collapsed to form a caldera at the surface. Although it is known that fractional crystallization, mixing, and assimilation can greatly modify magmas, the frequency and intensity of these events is not known. I investigated the magmatic processes responsible for the evolution of magmas erupted during five Plinian events of Popocatépetl volcano. Results show that during the last 23 ky magma was stored in two different zones, and was variably modified by replenishments of mafic magma. Interestingly, little evidence for large mafic inputs triggering explosive eruptions was found. Each of these processes alters the abundances of volatiles and introduces different types of volatiles to the system. Hence, the volatile budget of magma can have a rich and complex history. To investigate how volatile budgets evolve in active magma systems, I analyzed the abundances of volatiles (H2O, CO2, F, Cl, and S) in numerous glass inclusions trapped in phenocrysts. Results show that the magmas that produced the last five Plinian eruptions at Popocatépetl volcano evolved by crystallization and magma mixing, assimilation of the local carbonate basement is not chemically appreciable. Mixing with mafic magmas added substantial CO2 and S to the system, dewatered the magma, yet produced little change in the F contents of the magmas. / text

Master of Science / Department of Geology / Matthew E. Brueseke / Previous studies of the northern Great Basin have indicated that mid-Miocene epithermal gold and silver ore deposits distributed regionally are temporally related to the magmatic activity associated with the onset of widespread extension and the Yellowstone hotspot (Saunders and Crowe, 1996; Kamenov et al., 2007). This study is focused on the volcanic rocks and ore deposits from the Silver City district (SCD), ID to address the petrogenesis and magmatic evolution that was influential in forming local precious metal deposits. The goal is to understand the tectonomagmatic conditions that contributed to the petrogenesis of the volcanic suite in the Silver City district, which can be used to provide details on the relationship between coeval mid- Miocene magmatism and mineralization across the northern Great Basin and Oregon Plateau. In order to better constrain the magmatic evolution of the SCD and potential sources of the precious metals, we have undertaken detailed sampling of local crust and mid-Miocene volcanic units to constrain their physical, geochemical, isotopic, and geochronological characteristics, as well as provide constraints on the petrogenesis of the mid-Miocene volcanic package. Prior studies of the local volcanism have yielded K-Ar and [superscript]40Ar/[superscript]39Ar ages of ~16.6 to 14 Ma (Bonnichsen, 1983), while others have dated adularia from one SCD mineral vein and obtained [superscript]40Ar/[superscript]39Ar ages of between 15.6 and 16.3 Ma (Hames et al., 2009; and Aseto et al., 2011). Field observations are consistent with earlier work (Lindgren, 1900; Asher, 1968; Pansze, 1975; Halsor et al., 1988; Bonnichsen and Godchaux, 2006; Camp and Ross, 2009) and reveal a sequence of basalt consisting of regionally prevalent Steens Basalt that pre-dated precious metal mineralization. Some of the basalt appears to have been erupted locally, based on the presence of mafic dikes and thick pyroclastic deposits similar to other regional mid-Miocene magmatic systems. Stratigraphically overlying this lower basalt suite is a complex package of rhyolite flows and domes, thin silicic pyroclastic units, additional basaltic lava flows, intermediate lava flows, and mafic/silicic shallow intrusives. Geochemical analysis indicates that the basaltic and basaltic andesite lava flows are locally erupted flows of Steens Basalt while the intermediate and silicic volcanism in SCD can be classified into nine distinct units including two andesites, one dacite, four rhyolites and two rhyolite tuffaceous units. Geochemical modeling suggest that the intermediate and silicic magmas were formed by a combination of open system processes, including low pressure partial melting and assimilation of mid to upper crustal granitoid basement rock, and magma mixing between silicic and basaltic endmembers. The formation of silicic volcanism in the SCD is similar to other regional mid-Miocene silicic volcanic systems (e.g. Santa Rosa-Calico volcanic field and Jarbidge Rhyolite). Based on new [superscript]40Ar/[superscript]39Ar geochronology of both volcanic units and epithermally emplaced mineralization, SCD volcanism appears to have erupted over a relatively short amount of time that overlaps with local epithermal Au-Ag mineralization.

Field evidence from exposed plutonic rocks indicates that mafic-felsic magma interaction is an important process during the construction and evolution of magma chambers. The exhumed, ~140 Ma, Halfmoon Pluton of Stewart Island, New Zealand is characterized by a sequence of mingled mafic sheets and enclaves preserved within an intermediate-felsic host, and provides a unique opportunity to directly investigate the physico-chemical processes that operate within an arc setting. Interpretation of mingling structures and textures in the field, in combination with extensive petrographic, geochemical and geochronological data, allow for conclusions to be reached regarding the nature of the mafic-felsic magma interactions, and the physical, chemical and thermal processes responsible for the generation and evolution of the calc-alkaline magmas. Detailed documentation and interpretation of mafic-felsic magma mingling structures and textures reveal that the Halfmoon Pluton formed incrementally as the result of episodic replenishments of mafic magma emplaced onto the floor of an aggrading intermediate-felsic magma chamber. Physico-chemical processes identified include fractional crystallization and accumulation of a plagioclase – hornblende – apatite – zircon mineral assemblage, episodic replenishment by hot, wet basaltic magmas, magmatic flow and compaction. Early amphibole and apatite crystallization played an important role in the compositional diversity within the Halfmoon Pluton. Variations in the style of magma mingling preserved within the magmatic “stratigraphy” indicate that processes operating within the chamber varied in space and time. Variations in mineral zoning and composition within hornblende indicate that the Halfmoon Pluton crystallized within a magma in which melt composition fluctuated in response to repeated mafic magma replenishments, fractionation, crystal settling and convection. Mineral assemblages, chemical characteristics, isotopic data and geochronological evidence indicate that the amphibole-rich calc-alkaline Halfmoon Pluton was emplaced into a juvenile arc setting, most probably an island-arc. Data are consistent with a model whereby ‘wet’ amphibole-rich basaltic magmas pond at the crust-mantle interface and episodically rise, inject and mingle with an overlying intermediate-felsic magma chamber that itself represents the fractionated product of the mantle melts.

Field evidence from exposed plutonic rocks indicates that mafic-felsic magma interaction is an important process during the construction and evolution of magma chambers. The exhumed, ~140 Ma, Halfmoon Pluton of Stewart Island, New Zealand is characterized by a sequence of mingled mafic sheets and enclaves preserved within an intermediate-felsic host, and provides a unique opportunity to directly investigate the physico-chemical processes that operate within an arc setting. Interpretation of mingling structures and textures in the field, in combination with extensive petrographic, geochemical and geochronological data, allow for conclusions to be reached regarding the nature of the mafic-felsic magma interactions, and the physical, chemical and thermal processes responsible for the generation and evolution of the calc-alkaline magmas. Detailed documentation and interpretation of mafic-felsic magma mingling structures and textures reveal that the Halfmoon Pluton formed incrementally as the result of episodic replenishments of mafic magma emplaced onto the floor of an aggrading intermediate-felsic magma chamber. Physico-chemical processes identified include fractional crystallization and accumulation of a plagioclase – hornblende – apatite – zircon mineral assemblage, episodic replenishment by hot, wet basaltic magmas, magmatic flow and compaction. Early amphibole and apatite crystallization played an important role in the compositional diversity within the Halfmoon Pluton. Variations in the style of magma mingling preserved within the magmatic “stratigraphy” indicate that processes operating within the chamber varied in space and time. Variations in mineral zoning and composition within hornblende indicate that the Halfmoon Pluton crystallized within a magma in which melt composition fluctuated in response to repeated mafic magma replenishments, fractionation, crystal settling and convection. Mineral assemblages, chemical characteristics, isotopic data and geochronological evidence indicate that the amphibole-rich calc-alkaline Halfmoon Pluton was emplaced into a juvenile arc setting, most probably an island-arc. Data are consistent with a model whereby ‘wet’ amphibole-rich basaltic magmas pond at the crust-mantle interface and episodically rise, inject and mingle with an overlying intermediate-felsic magma chamber that itself represents the fractionated product of the mantle melts.

Η έναρξη της ηφαιστειακής δραστηριότητας εις τον Σαρωνικό Κόλπο έγινε κατά το Άνω Πλειόκαινο και είχε ως αποτέλεσμα την δημιουργία ασβεσταλκαλικών κέντρων όπως τα Μέθανα, η Αίγινα και ο Πόρος. Η ηφαιστειότητα εις το βορειοανατολικό άκρο του Τεταρτογενούς Ηφαιστειακού Τόξου του Αιγαίου είναι αποτέλεσμα της ανάλωσης του Ωκεανού της Τηθύος κάτω από την Ευρασία. Δεδομένου ότι 18000 χρόνια πριν αποτελούσαν το ίδιο χερσαίο ηφαιστειακό συγκρότημα ετέθη το ερώτημα εάν τα προϊόντα τους που καλύπτουν το συστασιακό φάσμα από βασαλτικό ανδεσίτη έως δακίτη (-ρυοδακίτη) είναι "συγγενετικά". Επειδή ακόμη οι λάβες των κέντρων αυτών τυπικά χαρακτηρίζονται από πολυπληθή υποστρόγγυλα "εγκλείσματα" (enclaves) μαφικού μάγματος διερευνήθηκε η δυνατότητα ότι η μείξη μαγμάτων ήταν ενεργή διεργασία κατά τη διαφοροποίησή τους, μία διεργασία η οποία προκαλεί βίαιες ηφαιστειακές εκρήξεις με επακόλουθο ηφαιστειακό κίνδυνο. Οι συμπαγείς στο σύνολό τους τροχιές χημικής διαφοροποίησης οξειδίων των κυρίων στοιχείων και κατανομές ιχνοστοιχείων σε διαγράμματα Harker καθώς και οι παράλληλες συμπαγείς κατατομές Σπανίων Γαιών (REE's) και κατατομές ιχνοστοιχείων (αραχνοδιαγράμματα), όλα τα στοιχεία της έρευνας συνηγορούν ότι τα μαγματικά προϊόντα των τριών υπό εξέταση ηφαιστειακών κέντρων είναι "συγγενετικά". Εκτός από τις πολυπληθείς μακροσκοπικές ενδείξεις των εγκλεισμάτων στις λάβες, άλλες ενδείξεις μείξης παρέχονται από τις "εξωτικές" ορυκτολογικές παραγενέσεις, από τις καταγραφές των μικροϊστών και ορυκτοχημείας πλαγιοκλάστων που έχουν υποστεί την μέθοδο Nomarski, από τις δισχιδείς τροχιές ασυμβάτων ιχνοστοιχείων σε διαγράμματα Harker που συνενώνονται με τις τροχιές υβριδικών μαγμάτων, και τελικά η μαγματική μείξη γίνεται εμφανής από τις παραβολικές κατανομές των λόγων των ασυμβάτων ιχνοστοιχείων οι οποίες παραβολικές κατανομές δεν είναι τυχαίες όπως αποδεικνύουν τα ευθύγραμμα "συνοδά" τους διαγράμματα. Παρά την εμφανή δράση φαινομένων "μαγματικής μείξης" κατά την εξέλιξη των ηφαιστειακών κέντρων της Αίγινας-Μεθάνων-Πόρου η ορατή τους στρωματογραφία δεν βρίθει πυροκλαστικών προϊόντων. Γι' αυτό το λόγο προτείνουμε ότι ο ηφαιστειακός κίνδυνος που προέρχεται από πυροκλαστικές εκρήξεις ιδίως για το ενεργό κέντρο των Μεθάνων, με τελευταία έκρηξη το 230 π.Χ., δεν είναι μεγάλος. Αντίθετα ο ηφαιστειακός κίνδυνος που προέρχεται από εισπνοές τοξικών αερίων ιδίως για τους επισκέπτες των ιαματικών θερμοπηγών, όπως έχουν αποδείξει παρελθόντα ατυχή συμβάντα, είναι σαφώς υπαρκτός. Επειδή τα υπό εξέταση ηφαίστεια τώρα έχουν νησιωτικό χαρακτήρα (Μέθανα), η κατολίσθηση ηφαιστειακών πρανών στην θαλάσσια λεκάνη με επακόλουθη δημιουργία tsunami είναι ένας ηφαιστειακός κίνδυνος στον οποίο είναι τα κέντρα αυτά ιδιαίτερα ευάλωτα. Επειδή οι κατολισθήσεις των ηφαιστειακών πρανών προκαλούνται από την ελάττωση της τριβής και την αύξηση της πίεσης που ασκείται στα τοιχώματα των ρηγμάτων από μάγματα ή υδροθερμικά ρευστά, διαλέξαμε να προσομοιώσουμε κατολίσθηση πρανούς στο πλέον κατακερματισμένο από ρήγματα και πλέον ενεργό κέντρο δηλαδή αυτό των Μεθάνων. Χρησιμοποιώντας την εξίσωση του Murty, (2003) δείξαμε ότι το ύψος Η ενός προκληθέντος από κατολίσθηση tsunami είναι 0.77 m και 0.79 m όταν η κατολίσθηση προσομοιωθεί ότι φτάνει σε βάθος λεκάνης 100 m και 200 m αντίστοιχα. Το ύψος του tsunami θα είναι πολλαπλάσιο του αρχικού όταν φτάσει στον Πειραιά. / The onset of volcanic activity in the Saronic Gulf occured during Upper Pliocene and resulted in calc-alkaline volcanic centers such as Methana, Aegina and Poros located in the northeastern extremity of the Quaternary Aegean Volcanic Arc which is the result of the subduction of Tethys under Eurasia. Since 18000 years ago these 3 centers comprised the same volcanic complex on land one can pose the question if their products which cover the compositional spectra from basaltic andesite to dacite-rhyodacite are "syngenetic". Since the lavas of the centers display abundant subrounded mafic inclusions the question arose if magma mixing was a magmatic process operational during their petrogenesis. Magma mixing is related with explosive magmatic activity and the associated volcanic hazards. The overall integral (integer) (compact) differentiation paths of the major element oxides and the distributions of trace elements in HARKER diagrams, as well as the parallel "compact" profiles of REE and spidergrams all corroborate towards the argument of a syngenetic relationship between the three understudy volcanic centers. In addition to the macroscopic evidence provided by the mafic inclusions in the lavas other lines of evidence point towards magma mixing, such as "exotic" mineral assemblages, the plagioclase record of microtextures and mineral chemistry, the distributions of incompatible trace elements on HARKER diagrams and the parabolic distributions of incompatible trace element ratios with their corresponding linear companion diagrams. In spite of the evidence of operation of mixing phenomena during the petrogenesis of the volcanic centers of Aegina, Methana and Poros in their "exposed" volcanic stratigraphy, pyroclastic deposits are rather sparse. Therefore we suggest that volcanic hazards associated with pyroclastic flows, falls and pyroclastic surges, in the volcanic center of Methana which is still active since it's last eruption was in historic times, 230 BC, is not very probable to occur. On the contrary, volcanic hazard that is related to inhalations of toxic gases especially by visitors of the thermal springs, as evidenced by unfortunate events in the past is a real issue. Also, because these volcanoes have presently insular (Aegina, Poros) or almost insular character (Methana) volcanic hazard associated with landslides and/or debris of volcanic slopes and the ensuing tsunami is highly probable. Since volcanic edifice landslides occur due to reduction of friction and the increase of pressure which is attributed to the intrusion of magma into the faults and fissures transecting the volcanic edifice and/or by the hydrothermal fluids and gases we have chosen to simulate landslide of a volcanic slope in the most dissected by faults and active volcanic center among the three, that of the volcano of Methana. Using the equation of Murty (2003) in this simulation we have shown that the height of a tsunami wave near the site of the volcanic landslide will vary between 0.77 and 0.79 m depending on the depth that the landslide will reach in the marine basin and it will increase in height arriving near the shores of Piraeus and Athens.