experimental and thermodynamic constraints on mineral equilibrium inpantelleritic magmas abstract crystallization experiments on two pantellerites from pantelleria italy provide new evidence for the relationships between mineral phases in pantelleritic rocks as well as the influence of temperature and redox conditions on mineral assemblages experiments were performed at 1 kbar with temperature ranging between 750 900 c and fluid saturation conditions with xh2o h2o h2o co2 between 0 and 1 redox conditions were fixed at or slightly below the fmq buffer results show that at temperature of 900 c pantelleritic magmas are well above the liquidus regardless their water content we also observed a decrease in liquidus temperature 800 c with increasingly reducing conditions mineral assemblages of the natural rocks have been successfully reproduced particularly the relationship between fayalite and aenigmatite which appear to be strongly controlled by melt peralkalinity temperature and redox conditions this is the first time that fayalitic olivine have been synthetized in experimental studies on pantellerites which was found to be stable only for temperatures 750 c while amphibole can be stable at temperatures as high as 800 c at high ff2 experimental results have been compared with the composition of mineral phases as well as with the results obtained from mineral equilibrium geothermometry and oxygen barometry studies on pantelleritic lava and tuffs from pantelleria italy eburru kenya and menengai kenya petrological characteristics appear similar at different locations worldwide with typical assemblages of anorthoclase and sodian clinopyroxene with variable fayalite aenigmatite fe ti oxides and amphibole

holocene hydrological changes in south western mediterranean as recorded by lake level fluctuations at lago preola a coastal lake in southern sicily italy abstract this paper presents a high resolution lake level record for the holocene at lago preola sicily southern italy based on a specific sedimentological approach with a chronology derived from ams radiocarbon dates it gives evidence of three major successive palaeohydrological periods with 1 a pronounced dryness during the early holocene until ca 10300 cal bp 2 a highstand from ca 10300 to 4500 cal bp and 3 a marked lowstand from 4500 cal bp to present large amplitude lake level fluctuations characterise two transition phases at ca 10300 9000 and 6400 4500 cal bp period 2 was interrupted between 8300 and 7000 cal bp by a dry phase that was punctuated to ca 7300 cal bp by the deposition of a tephra from neighbouring pantelleria island comparisons of the preola record with other palaeohydrological records along north south and west east transects in the mediterranean show contrasting patterns of hydrological changes north south of around 40 n latitude the records highlight a mid holocene period characterised by lake level minima maxima humid mid holocene conditions over the mediterranean south of 40 n were probably linked to a strong weakening of the hadley cell circulation and of monsoon winds we suggest that the maximum of humidity in the mediterranean during the mid holocene was characterised by humid winters to the north of 40 n and humid summers to the south on a multi centennial scale the high resolution palaeohydrological reconstructions in the central mediterranean area reveal a strong climate reversal around 4500 4000 cal bp with contrasting changes in the hydrological cycle in addition to seasonal and inter hemispherical changes related to orbital forcing this major oscillation might be related to non linear responses of the climatic system to the gradual decrease in summer insolation at northern latitudes another major climate oscillation around 7500 7000 cal bp may have resulted from the combined effects of 1 a strong rate of change in insolation and 2 variations in solar activity finally comparisons of the preola lake level record with sicilian pollen records suggest a strong influence of moisture availability on vegetation development in sicily very dry early holocene conditions probably prevented the expansion of coastal evergreen forests while decreasing moisture availability since the onset of the late holocene may have exacerbated effects of intensive land use

estimation of magma depth for resurgent domes an experimental approach post collapse resurgence is a phenomenon affecting many calderas attributed to a renewed magma rise the process is still poorly understood and the associated source parameters remain poorly constrained a set of experiments has been conducted to gain insight into the structural evolution of caldera resurgent domes a sand plaster mixture was chosen as an analogue for the brittle pile of volcanic rocks and silicone putty simulates the ductile behavior of the intruding magma resurgence is driven by the vertical uplift of the silicone with variable shape and depth similarity conditions are achieved through eight dimensionless numbers which are of the same order of magnitude in both nature and experiments results show that extension due to doming is in many cases accommodated by one axial graben opposite master faults of this graben intersect at depth at the junction with the rising viscous silicone the simplicity of the geometry of the whole analogue system provides equations which allow the estimation of the silicone depth from surface parameters these equations are then used in some field examples to assess the magma depth beneath natural resurgent domes

the eruptive history and magmatic evolution of aluto volcano new insights into silicic peralkaline volcanism in the ethiopian rift the silicic peralkaline volcanoes of the east african rift are some of the least studied volcanoes on earth here we bring together new constraints from fieldwork remote sensing geochronology and geochemistry to present the first detailed account of the eruptive history of aluto a restless silicic volcano located in a densely populated section of the main ethiopian rift prior to the growth of the aluto volcanic complex before 500 ka the region was characterized by a significant period of fault development and mafic fissure eruptions the earliest volcanism at aluto built up a trachytic complex over 8 km in diameter aluto then underwent large volume ignimbrite eruptions at 316 19 ka and 306 12 ka developing a 42 km2 collapse structure after a hiatus of 250 ka a phase of post caldera volcanism initiated at 55 19 ka and the most recent eruption of aluto has a radiocarbon age of 0 40 0 05 cal ka bp during this post caldera phase highly evolved peralkaline rhyolite lavas ignimbrites and pumice fall deposits have erupted from vents across the complex geochemical modelling is consistent with rhyolite genesis from protracted fractionation 80 of basalt that is compositionally similar to rift related basalts found east of the complex based on the style and volume of recent eruptions we suggest that silicic eruptions occur at an average rate of 1 per 1000 years and that future eruptions of aluto will involve explosive emplacement of localised pumice cones and effusive obsidian coulees of volumes in the range 1 100 106 m3

voluminous lava like precursor to a major ash flow tuff low column pyroclastic eruption of the pagosa peak dacite san juan volcanic field colorado abstract the pagosa peak dacite is an unusual pyroclastic deposit that immediately predated eruption of the enormous fish canyon tuff 5000 km3 from the la garita caldera at 28 ma the pagosa peak dacite is thick to 1 km voluminous 200 km3 and has a high aspect ratio 1 50 similar to those of silicic lava flows it contains a high proportion 40 60 of juvenile clasts to 3 4 m emplaced as viscous magma that was less vesiculated than typical pumice accidental lithic fragments are absent above the basal 5 10 of the unit thick densely welded proximal deposits flowed rheomorphically due to gravitational spreading despite the very high viscosity of the crystal rich magma resulting in a macroscopic appearance similar to flow layered silicic lava although it is a separate depositional unit the pagosa peak dacite is indistinguishable from the overlying fish canyon tuff in bulk rock chemistry phenocryst compositions and 40ar 39ar age the unusual characteristics of this deposit are interpreted as consequences of eruption by low column pyroclastic fountaining and lateral transport as dense poorly inflated pyroclastic flows the inferred eruptive style may be in part related to synchronous disruption of the southern margin of the fish canyon magma chamber by block faulting the pagosa peak eruptive sources are apparently buried in the southern la garita caldera where northerly extensions of observed syneruptive faults served as fissure vents cumulative vent cross sections were large leading to relatively low emission velocities for a given discharge rate many successive pyroclastic flows accumulated sufficiently rapidly to weld densely as a cooling unit up to 1000 m thick and to retain heat adequately to permit rheomorphic flow explosive potential of the magma may have been reduced by degassing during ascent through fissure conduits leading to fracture dominated magma fragmentation at low vesicularity subsequent collapse of the 75 35 km 2 la garita caldera and eruption of the fish canyon tuff were probably triggered by destabilization of the chamber roof as magma was withdrawn during the pagosa peak eruption

a paleopedological and ichnological approach to interpreting spatial and temporal variability in early permian fluvial deposits of the lower dunkard group west virginia u s a abstract lower permian asselian deposits of the washington formation dunkard group in west virginia u s a represent proximal to distal expressions of a migrating anastomosing river and associated floodplain environments these deposits are part of the upper fluvial plain province of the dunkard basin characterized by thick to thin sandstone bodies shales and paleosols the paleosols and associated ichnofossils record a wealth of paleoenvironmental paleoecological and paleoclimatic data which improve our understanding of the autogenic and allogenic processes that result in the spatial and temporal variability of ancient fluvial systems this study integrates field and laboratory analysis of paleosols and ichnofossils including macro to micromorphology bulk geochemistry and clay mineralogy to better understand variations in soil forming processes across this early permian floodplain nine different pedotypes were identified including proximal poorly developed entisols and inceptisols poorly drained histosols and thick moderately to well drained inceptisols and vertisols lateral differences in paleosol properties were minor compared to the diversity of paleosols present in the vertical exposure and were largely a result of localized variations in drainage and topography differences in the properties of the paleosols in the vertical succession could not be explained by variable drainage due to position on the floodplain cyclicity was largely controlled by avulsion but was overprinted by changes in climate while climatic drying during the early permian as a general trend is well established smaller scale fluctuations between wet and dry intervals contributed significantly to observed paleosol properties dominance by calcareous vertisols in the upper fluvial plain facies province and their representation of strongly seasonal conditions are consistent with previous research however thorough investigation of the paleosols suggests that more humid conditions existed than the arid to semiarid climate that has been suggested

the gold flat tuff nevada insights into the evolution of peralkaline silicic magmas the gold flat tuff is the youngest 9 15 ma ash flow sheet erupted from the black mountain volcanic centre southwest nevada usa this paper explores some aspects of the very complex nature of the tuff s magmatic plumbing system the main body of the deposit is a mixed magma product comprising pantelleritic and comenditic melts derived from independently evolving reservoirs and antecrysts and enclaves derived from a range of basic to intermediate sources metre scale cognate xenoliths point to the presence of alkali feldspar accumulation zones the pantellerite contains phenocrysts of fluorite and chevkinite ce the inferred intermediate magma component contains perrierite ce phenocrysts the pantellerite has unusually high contents of f 2 2 wt f cl 2 9 wt and zro 2 1 04 wt the high halogen contents may have influenced the evolution of the strongly peralkaline magma the crystallization conditions are poorly constrained but those for the pantelleritic magma may have been close to water saturation 4 wt melt water at temperatures 740 c and fo 2 around fmq

an 18 m thick volcaniclastic interval in pantelleria trough sicily channel deposited from a large gravitative flow during the green tuff eruption abstract a 30 m long piston core from the floor of pantelleria trough penetrated an 18 m thick volcaniclastic interval under and overlain by hemipelagic sediments the distribution and thickness of the interval is mapped in 3 5 khz profiles across the trough core sediments have been analysed for grain size carbonate content detrital petrology and physical properties such as bulk density and magnetic susceptibility chemical analyses of tephra and included minerals have been made by electron microprobe the volcaniclastic interval is correlated with the youngest large explosive eruption on pantelleria the 50 ka green tuff ignimbrite eruption on the basis of the sedimentation rate of overlying sediment calcareous nannofossil and foraminiferal biostratigraphy a calibrated radiocarbon age of 43 47 2 ka possibly infinite in the underlying marls and many similarities in tephra and mineral chemistry and abundance the lower 8 m of the volcaniclastic interval consists of poorly sorted massive units of lapilli tuff interpreted as resulting from the direct flow of a pyroclastic flow into the sea with the energetic hyperconcentrated flows crossing the length of pantelleria trough and eventually freezing on the low gradients the overlying 10 m thick turbidite probably developed from the dilute turbulent pyroclastic flow of the co ignimbrite cloud and the resulting turbulent subaqueous flow eroded bioclastic material from the shelf and deposited a well graded bed from sand through silt to mud the poorer sorting of the volcaniclastic interval compared with the green tuff ignimbrite on land supports the concept that ignimbrite deposits are sorted by aggrading bed processes

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

glass chemistry in volcaniclastic sediments of odp leg 107 site 650 sedimentary sequence provenance and chronological implications abstract a detailed chemical investigation of volcanic glass fragments from volcaniclastic strata 6 tephras 1 volcanic debris flow 12 volcanic turbidites of odp leg 107 site 650 sedimentary sequence leads to a varied pattern in terms of both provenance and age constraints the six analyzed tephra strata indicate a provenance from at least three different volcanic provinces aeolian campanian and sicilian channel pantelleria island the older tephra strata 021 018 012 have a large amount of orogenic rhyodacite rhyolite deposits that may be attributed to the aeolian province although no subaerial coeval volcanic activity of similar composition has so far been documented in the aeolian arc tephra 007 is related to the pantelleria island activity and particularly to an ignimbrite episode dated circa 130 ka tephra strata 005 and 003 have a clear campanian provenance and are correlated with analogous tephra layers observed in the tyrrhenian and ionian seas dated circa 107 and 60 ka respectively in the oldest portion of the sequence from 1 3 to 0 13 ma the volcaniclastic sediments were only derived from the aeolian domain whereas in the latest 130 ka the campanian influx becomes much more predominant therefore a general k enrichment trend is observed in the temporal sequence of all the analyzed samples almost 700 point analyses which may be related both to a variation in the source area and to the specific pleistocene magmatic evolution of the peri tyrrhenian volcanic provinces

paleomagnetic dating of the most recent silicic eruptive activity at pantelleria strait of sicily we report on the paleomagnetism of ten sites in the products of the most recent silicic eruptive cycle of pantelleria strait of sicily previously radiometrically dated at 5 10 ka our comparison with proxies for geomagnetic field directions allows us to narrow considerably the time window during which these eruptions occurred the strongly peralkaline composition causes the magmas to have low viscosities locally resulting in strong agglutina tion of proximal fall deposits this allows successful extraction of paleomagnetic directions from the explosive phases of eruptions one of our sites was located in the serra della fastuca fall deposit produced by the first explosive event of the eruptive cycle the other nine sites were located in the most recent explosive pumice fall and agglutinate from cuddia del gallo and cuddia randazzo and effusive khaggiar lava products the very similar paleomagnetic directions gathered from eight internally consistent sites were compared to reference geomagnetic field directions of the last 5 10 ka directions from cuddia del gallo agglutinate and khaggiar flows translate into 5 9 to 6 2 ka ages whereas the fastuca pumices yield a slightly older age of 6 2 6 8 ka hence the most recent silicic eruptive cycle lasted at most a millennium and as little as a few centuries around 6 0 ka paleomagnetically inferred ages are in good agreement with published and calibrated by us 14 c dates from paleosols charcoals sampled below the studied volcanic units whereas k ar data are more scattered and yield 30 older ages our data show that the time elapsed since the most recent silicic eruptions at pantelleria is comparable to the quiescence period separat ing the two latest volcanic cycles

prolonged history of silicic peralkaline volcanism in the eastern pacific ocean socorro island mexico is an alkaline and peralkaline volcanic island located in the eastern pacific ocean on a mid ocean ridge spreading center that was abandoned at 3 5 ma silicic peralkaline rocks comprise up to 80 of the surface of the island rendering socorro virtually unique in the pacific ocean precise replicate 40ar 39ar ages of 21 peralkaline trachytes and rhyolites reveal a history of episodic volcanic activity from 540 to 370 ka that may have culminated with caldera formation repose periods between these episodes may have had maximum duration of 30 kyr after up to 200 kyr of quiescence 40ar 39ar ages indicate that postcaldera silicic peralkaline activity commenced by 180 ka forming the cerro evermann formation postcaldera mafic alkaline lavas of the lomas coloradas formation erupted dominantly between 70 and 150 ka based upon relative age relations the dominant lithology of precaldera and syncaldera silicic peralkaline deposits on socorro is nonfragmental and nonvesicular and lacks lithic fragments and fiamme despite this numerous lines of evidence including welding zonation presence of a proximal ignimbrite or co ignimbrite deposit association with a caldera and compositional heterogeneity within eruptive units suggest that they are dominantly ash flow tuffs a change in eruptive style from predominantly explosive to predominantly effusive followed caldera formation and suggests that a change in the efficacy of magma degassing may be linked to caldera formation on the basis of the presence of a caldera the magma chamber associated with socorro island is shallow and probably resides within the upper oceanic crust or the edifice this together with a prolonged history of silicic magmatism indicates that intrusion of mafic magma maintained thermal viability of the magmatic plumbing system the minimum calculated growth rate for the entire volcanic edifice 7 10 4 km3 yr exceeds those of nonhotspot off axis volcanoes in the pacific by almost an order of magnitude eruption rates for subaerial phases on socorro may be several orders of magnitude smaller than this growth rate and are comparable to subaerial eruption rates of isolated ocean islands related to mantle plumes

geochemistry of thermal fluids on the volcanic isle of pantelleria southern italy abstract chemical analyses of thermal springs and gas emissions on the volcanic island of pantelleria southern italy suggest the presence at depth of a na cl thermal aquifer near 100 c 80 90 of the water in this aquifer is fed by rainfall and the remainder of the mixture is seawater chemical analyses of the gas emissions reveal that below this shallow aquifer a deeper hydrothermal degassing system 150 c may exist rising co 2 causes alterations of the upper aquifer host rocks mostly pantellerites favors formation of na hco 3 type waters and causes eventual rpecipitation of caco 3 and coprecipitation of mgco 3 and silica comparison of the present chemical data with older data from the literature suggests that the shallow pantelleria thermal aquifer has increased in salinity and decreased in temperature during the last 25 a both effects were apparently caused by increased flow of recent seawater into the system because of increased ground water abstraction in the northern part of the island

nested calderas and trapdoor uplift at pantelleria strait of sicily pantelleria is dominated by a caldera 6 km in diameter that formed 55 000 yr ago during eruption of a rheomorphic fall deposit that is zoned from pantellerite to trachyte trachytic lavas then built a shield that nearly filled the caldera magma subsequently reinflated the shallow reservoir and raised the northwest half of the trachyte shield 275 m creating montagna grande by trapdoor uplift the lid eventually failed and pantellerite magma erupted as domes flows and pumice cones along the trapdoor faults and their hingeline we have identified a second caldera 93 000 yr old within which the younger caldera is nested a still older structure may encircle them both replenishment of magma reservoirs beneath calderas can promote dilatant reactivation of older subsidence structures resulting in multicyclic collapses that reuse these structures and produce nested calderas

an experimental investigation on mass failures occurring in a riverbank composed of sandy gravel abstract this paper reports the results and interpretation of laboratory experiments carried out on a model of a relatively coarse sandy gravel riverbank with the aim of investigating the basic processes and possible factors of instability after a series of initial tests three main experiments were carried out in a glass walled tank where a bank model was built with bank angles varying from 75 to 90 bank height of 70 cm and same sediment mixture 60 gravel 40 sand but with the addition of 1 of cement in the third experiment only during the experiments the bank was subject to a given hydrograph associated with a static oscillation of the water level and corresponding variations in pore water pressures were measured results show the occurrence of a large variety of processes including erosion and failures because of loss of matric suction cantilever slab and slide failures and granular flows during the ascending phase of the hydrograph bank instability was related to a superimposition of initial geometric factors and progressive reduction of apparent cohesion during the rising water stage apparent cohesion was sufficient to maintain a stable bank in loose material but only for low bank height and or slopes whereas a limited percentage of cement is able to explain a markedly different response in terms of stability and mechanisms of failure

relationships between magmatism and tectonics in a continental rift the pantelleria island region sicily channel italy abstract field geological data of the pantelleria island a large late quaternary volcano located in the sicily channel rift zone integrated with offshore geophysical information are used to derive the structural setting of the island and the surrounding region and to analyse the relationships between tectonics and magmatism field work shows that the principal faults exposed on the island fall into two systems trending nne ssw and nw se mapped faults from offshore multichannel seismic profiles show similar trends and some of them represent the offshore extension of the pantelleria island structures the nw se faults bound the pantelleria graben one of the three main depressions formed since the late miocene early pliocene within the african continental platform which compose the sicily channel rift zone a 3 d moho depth geometry derived from inversion of bouguer gravity data shows a significant uplift of the discontinuity up to 16 17 km beneath the westernmost part of the pantelleria graben and beneath the pantelleria island it lows rapidly to 24 25 km away from the graben north eastward and south westward the moho uplift could explain the presence of a shallow magma chamber in the southern part of the island where processes of magmatic differentiation are documented geological and geophysical data suggest that the northwestern part of the sicily channel is presently dominated by a roughly e w directed extensional regime crustal cracking feeding the quaternary volcanism could be also related to this extensional field that would be further responsible for the development of the n s trending volcanic belt that extends in the sicily channel from lampedusa island to the graham bank this mode of deformation is confirmed also by geodetic data this implies that in the northwestern part of the sicily channel the e w extension replaced the ne sw crustal stretching that originated the nw trending tectonic depressions constituting the rift zone

formation of the green tuff pantelleria the strongly peralkaline green tuff pantelleria is an example of a thin densely welded air fall tuff which mantles an area of at least 85 km2 offshore the tuff is correlated with the y 6 ash layer in the central mediterranean sea and the total volume of the eruption is estimated at 7 km3 d r e new petrological data suggests that the tuff was erupted from a zoned magma chamber containing a cooler more fractionated upper zone relative to be bulk of the magma analysis of the distribution of accessory lithic fragments in terms of existing models of eruption dynamics indicates emplacement by a plinian type eruption it is shown that due to the low viscosity of pantelleritic ejecta dense welding can occur at moderate tephra accumulation rates and a rate of the order of 1 cm minute is suggested for the green tuff this yields an estimate for the eruption duration of rather less than one day it is predicted that welded tuff should be formed during large plinian eruptions of pantelleritic magma and therefore that welded airfall tuffs should be common in areas of peralkaline volcanism

rheomorphism of welded tuffs abstract peralkaline welded tuffs from the islands of gran canaria canary islands and pantelleria italy show abundant evidence for post depositional flow it is demonstrated that rheomorphism or secondary mass flowage can occur in welded tuffs of ignimbrite and air fall origin the presence of a linear fabric is taken as the diagnostic criterion for the recognition of the process deposition on a slope is an essential condition for the development of rheomorphism after compaction and welding internal structures produced during rheomorphic flow can be studied by the methods of structural geology and show similar dispositions to comparable features in sedimentary slump sheets it is shown that secondary flowage can occur in welded tuffs emplaced on gentle slopes provided that the apparent viscosity of the magma is sufficiently low compositional factors favor the development of rheomorphism in densely welded tuffs of peralkaline type

the pantelleria caldera geothermal system data from the hydrothermal minerals abstract this paper proposes on the basis of petrographic and mineralogic data on cutting and cores from two deep wells pantelleria 1 and pantelleria 2 the first model of the active hydrothermal system of the island of pantelleria phyllosilicates were studied in detail because they are considered key minerals in the identification of hydrothermal processes the results of these studies emphasize differences between the intracaldera and pericaldera areas of the island within the 45 ka caldera there is a high temperature 240 260 c at 600 800 m depth active hydrothermal system with five zones of characteristic alteration minerals with increasing depth rocks are unaltered to a depth of 200 m contain smectite and mixed layer chlorite smectite c s between 200 and 380 m chlorite illite chalcedony and quartz from 380 to 500 m albite adularia and saponite from 500 to 680 m mixed layer biotite vermiculite from 680 m to the depth drilled 1100 outside the caldera but near the rim a low temperature and low permeability

tephra correlations and climatic events between the mis6 5 transition and the beginning of mis3 in theopetra cave central greece abstract three cryptotephra layers associated with important periods of climatic change were identified in the middle palaeolithic sequence of theopetra cave greece the lower cryptotephra layer thp tii5 is correlated with the p 11 pantellerian eruption dated to 128 131 ka this cryptotephra postdates a thick sequence of combustion layers that show a complex vegetation succession quite similar to that of the last deglaciation succession in the cave two other cryptotephras thp tii10 and thp tii12 are correlated with the nisyros upper pumice and the pantellerian y6 green tuff dated to 50 ka and 45 7 ka respectively this sequence confirms the position of the nisyros upper tephra below the pantellerian green tuff in the volcanic event stratigraphy of the mediterranean moreover these two upper cryptotephras bracket an extended combustion layer with interstadial vegetation characteristics that may be coincident with the complex greenland interstadial 13 14 on the basis of this new chronology it can be deduced that the intensity of occupation and presence or absence of humans in the cave were closely related to climatic changes in addition a remarkable similarity in the pattern of occupational intensity during the last two deglaciations can be suggested

paleomagnetism of pleistocene volcanic rocks from pantelleria island sicily channel italy abstract a paleomagnetic investigation has been carried out on pleistocene volcanic rocks from pantelleria in the sicily channel this island is characterised by a bimodal volcanism of peralkaline rhyolite to trachyte and basalt composition the radiometric data indicate that volcanic activity started around 324 ka bp samples have been collected from 30 sites in 16 volcanic units spanning activity during the last 150 ka magnetic properties vary systematically with lithotype and indicate high ti titanomagnetite to magnetite as the main carriers of magnetisation stable characteristic remanent magnetisation chrm directions isolated by alternating fields af demagnetisation show normal polarity consistent with emplacement during the brunhes chron and vary within the paleosecular variation psv range however the inclinations are low as compared with the geocentric axial dipole gad inclination at pantelleria especially for volcanic units younger than 50 ka the mean chrm direction computed from 27 sites is d 358 8 i 46 9 k 30 95 5 2 and the inclination anomaly is i 8 1 both tectonic movements and the presence of large magnetic anomalies around the island of pantelleria fail to explain this low inclination which may therefore be related to a significant long lived non dipolar field contribution in the area over the past 150 kyr

1200 years of decadal scale variability of mediterranean vegetation and climate at pantelleria island italy a new sedimentary sequence from lago di venere on pantelleria island located in the strait of sicily between tunisia and sicily was recovered the lake is located in the coastal infra mediterranean vegetation belt at 2 m a s l pollen charcoal and sedimentological analyses are used to explore linkages among vegetation fire and climate at a decadal scale over the past 1200 years a dry period from ad 800 to 1000 that corresponds to the medieval warm period wmp is inferred from sedimentological analysis the high content of carbonate recorded in this period suggests a dry phase when the ratio of evaporation precipitation was high during this period the island was dominated by thermophilous and drought tolerant taxa such as quercus ilex olea pistacia and juniperus a marked shift in the sediment properties is recorded at ad 1000 when carbonate content became very low suggesting wetter conditions until ad 1850 1900 broadly this period coincides with the little ice age lia which was charact

the pantelleria graben sicily channel central mediterranean an example of intraplate passive rift abstract we present new high resolution swath bathymetric data and multichannel seismic profiles acquired in the pantelleria graben one of the three main tectonic depressions forming the sicily channel rift zone this region experienced a late miocene early pliocene continental extension with the development of nw trending fault bounded troughs later accompanied by widespread volcanic manifestations data support the interpretation that the pantelleria graben evolution was dominated by two tectonic phases a lithospheric scale continental rifting early pliocene in which the whole graben was formed and a successive phase late pliocene pleistocene characterized by a magma assisted extensional mechanism ascending magmas within the graben floor seem to migrate from the s e sector of the depression toward the n w sector which is almost entirely floored by igneous material and where the volcanic edifice of the pantelleria island is emerged the volcanic activity is presently concentrated north of the pantelleria island the tectonic evolution of the pantelleria graben characterized by the chronological sequence of events rifting doming volcanism can be referred to as a passive rifting model crustal stretching and subsequent fault development and rifting within the pelagian block may have been controlled by slab pull forces of the northward subducting african slab

changing modes and rates of mafic magma supply at pantelleria sicily channel southern italy new perspectives on the volcano factory drawn upon olivine records

cooling and crystallization recorded in trachytic enclaves hosted in pantelleritic magmas pantelleria italy implications for pantellerite petrogenesis abstract this study focuses on the comenditic trachyte enclaves hosted in pantelleritic lava and pumices emplaced during one of the most recent eruptive events at pantelleria 6 ka enclaves range from mm sized fragments to dm sized blocks with spheroidal to amoeboid shapes and characteristic globular surfaces they are crystal rich with 30 vol large anorthoclase less abundant fe rich olivine clinopyroxene and fe ti oxides vesicles ranging from a few mm to 1 2 cm in size are distributed throughout the enclave and are commonly filled with microlite free vesicular glass the groundmass presents spectacular textures including fine to coarse spherulites and hopper and skeletal microlites mostly anorthoclase with 10 35 vol residual glass and 10 15 vol small vesicles 2 accordingly the microlite composition is close to that of the host pantellerite these textures were acquired during a magma mixing event prior to the eruption i a vapor saturated comenditic trachyte magma intruded the shallower cooler pantellerite magma body triggering a first degassing event first boiling and rapid crystallization with a high degree of undercooling t 100 150 c ii vapor exsolution induced by rapid crystallization second boiling produced the microvesicular groundmass and iii vapor pressure forced the residual pantelleritic liquid to migrate into the large vesicles and or outside the enclaves based on this interpretation these enclaves can be used as a natural laboratory for identifying the chemical and physical processes driving the evolution of silicic magmas at pantelleria in particular they can be used to assess whether pantellerite melts can be obtained from comenditic trachytes after extensive crystallization followed by gas driven filter pressing and consequent pantellerite melt segregation

recent volcanic history of pantelleria a new interpretation abstract the island of pantelleria is located in the pantelleria rift between sicily and africa this rift is floored by a 20 km thick continental type crust that is characterized by horsts and grabens formed by nw se tensional faults and ne sw shear faults several faults and fractures that intersect the island follow these regional trends prominent volcano tectonic features on the island include two calderas the younger being related to the eruption of the green ignimbrite and the uplifted montagna grande block pantelleria mostly consists of peralkaline silicic rocks with minor trachytes and basalts volcanism on the island is characterized by both explosive and effusive activity reconstruction of the volcanic history of the island since the eruption of the green ignimbrite is based on geological and geochronological data the eruption of the green ignimbrite 50 000 y b p was followed by collapse of the monastero caldera that has been the site of most of the subsequent acid volcanism the montagna grande volcanic complex 35 000 y b p fills the central part while the lower pantelleritic lava flows 16 000 y b p erupted along its rim very probably the young mt gelfiser and khaggiar domes are also located on the caldera rim the montagna grande block rose within the caldera at an estimated average rate between 1 0 and 1 5 cm y for about 20 000 y subsequent pumice cones 9 000 y b p endogenous domes and lava flows also erupted inside this caldera among the main acid volcanic units younger than the green ignimbrite only the mt gelkhamar endogenous dome is not linked to this caldera in the last 50 000 years basaltic activity only occurred in the northern part of the island the basaltic vents are aligned parallel with the main tensional trends of the rift at least two phases have been recognized the older is about 29 000 y b p and the younger is a few thousands of years old a change occurred in the eruptive style after the eruption of the green ignimbrite and collapse of the monastero caldera explosive activity diminished and extrusion of lava became dominant

a revision of the structure and stratigraphy of pre green tuff ignimbrites at pantelleria strait of sicily abstract at pantelleria peralkaline silicic magmas were erupted across a range of eruptive typologies and magnitudes pyroclastic flows plinian to strombolian pumice fallout and lava flows in this paper we focus on the intermediate cycle of eruptive activity which is bracketed by ignimbrite units slightly older than the two caldera collapses which marked the volcanological activity of the island this age interval 180 85 ka was punctuated by six ignimbrite forming eruptions silicic and variably peralkaline for a cumulative erupted magma volume of approximately 6 km 3 dense rock equivalent based on new 40 ar 39 ar na k feldspar ages and petrographic data we propose an updated volcanostratigraphic scheme for these welded and rheomorphic ignimbrites that can be summarised as follows i the age of the old la vecchia caldera collapse is now tightly constrained between 140 and 146 ka and the caldera forming eruption can be traced to a lithic rich welded tuff breccia that outcrops in two opposite sectors of the island south west and north east ii four ignimbrite units previously considered unrelated are now merged in two distinct eruptive paroxysmal events at 107 and 85 ka in particular the 85 ka eruptive event is comparable in magnitude to the younger caldera forming green tuff plinian eruption iii the recurrence patterns of the 107 and 85 ka eruptions compared to the green tuff allow us to qualitatively assess that the climax in production of low temperature silicic and peralkaline melt was focused in the age interval 85 45 ka

k ar dating young rhyolitic rocks a case study of the sierra la primavera jalisco mexico this study demonstrates the feasibility of dating by the k ar method an eruptive sequence of silicic volcanic rocks with ages close to the limits of conventional 14 c dating forty six conventional k ar analyses of sanidine and glass from rhyolites of the sierra la primavera mexico yielded dates of 5 to 150 ka thousand years one sigma errors range from 3 to 39 ka although the samples contain small amounts of extraneous argon most of the dates are consistent with relative ages determined in the field the exceptions are dates on immediately postcaldera eruptive units which are older than the dates for the caldera producing ash flow tuff a similar result has been obtained on dating tuffs and lavas of some other pleistocene calderas this effect is attributed to incomplete outgassing of the larger amount of extraneous argon dissolved in magma that occupied a position deeper in the chamber than the ash flow tuff magma and that erupted immediately after caldera collapse we present two new error equations one a simple extension of the commonly used equation demonstrates the importance of including a term for the uncertainty in the spectrometer mass discrimination factor in the error equation the second equation is a more rigorous formulation of the propagation of errors in the calculation of the age it yields meaningful error estimates for all proportions of radiogenic 40 ar and because it expresses the error in absolute rather than relative terms it can be used to put an upper limit on the age of a sample when no radiogenic 40 ar has been resolved

the emplacement history of a remarkable heterogeneous chemically zoned rheomorphic and locally lava like ignimbrite tl on gran canaria abstract ignimbrite tl on gran canaria is a complex compositionally zoned rheomorphic tuff that locally exhibits features previously considered to be diagnostic of lavas it is made up of two locally overlapping lobes of ignimbrite that were emplaced during a single eruptive episode the eastern lobe is high grade with rheomorphic zones and localised patches that are lava like the western lobe is extremely high grade more extensively lava like and welded to its top surface both parts are zoned with a basal comendite rich zone grading up through a mixed zone into an upper trachyte rich zone lithic contents and the relative proportions of comendite and trachyte pyroclasts vary with height each comendite rich zone is vitroclastic whereas each trachyte rich zone is partly lava like with local gradations into vitroclastic ignimbrite mixed zones are intermediate in character and locally show compositional banding gradational zoning in massive ignimbrite best seen in lower strain zones and welding fabrics that are pervasively lineated and oblique to bedding suggest that deposition was sustained agglutination was rapid and rheomorphic deformation began during the sustained deposition the viscosity and porosity of the agglutinate varied with height because successively deposited pyroclast populations varied in grainsize composition and temperature the hot agglutinate continued to compact and shear downslope after the density currents had dissipated causing further rheomorphic folding thrusting attenuation and autobrecciation the western lobe locally overlies the partly welded top of the eastern lobe in part because it advanced rheomorphically across it for at least 300 m hot state loading and auto intrusion occurred due to unstable density layering in the chemically zoned agglutinate deformation behaviour changed during cooling and degassing and because of heat transfer between juxtaposed agglutinates and localised retention of dissolved volatiles where there was an overlying impermeable cap

fission track analysis of apatite and zircon defines a burial depth of 4 to 7 km for lowermost upper devonian catskill mountains new york apatite and zircon grains separated from a sandstone layer of earliest late devonian age catskill mountains have been subjected to fission track analysis a 125 m y age obtained on the apatite grains requires a temperature for the sediment of less than 120 c during the past 125 m y at some time prior to 125 m y ago temperatures were above 120 c long enough to cause complete fading of tracks analysis of zircon grains resulted in a fission track age of 320 m y zircon data indicate that the temperature of the sediment layer enclosing the grains did not exceed 175 to 200 c over a 235 rn y period time between sedimentation and 125 m y ago if one assumes a typical geothermal gradient of 25 c km a burial depth of between 4 and 7 km is indicated for the lowermost upper devonian atskill mountains

evidence of magma mixing in the daly gap of alkaline suites a case study from the enclaves of pantelleria italy the island of pantelleria consists of trachytes pantellerites and minor mildly alkaline basalts rocks of intermediate composition falling in the so called daly gap such as mugearites benmoreites and mafic trachytes occur only in the form of enclaves in trachytes and pantellerites inside the main caldera of the island caldera cinque denti which collapsed during the green tuff ignimbrite eruption at 50 ka the enclaves include volcanic subvolcanic and intrusive rock types the enclaves in host trachyte contain traces of glass devitrified glass occurs within enclaves in host pantellerites minerals in the enclaves show regular compositional variations with whole rock silica content glass present in the medium grained samples is interpreted to be the result of incipient melting the major and trace element compositions of the enclaves show regular and linear variations between an evolved mafic magma hawaiite and a felsic end member similar to the green tuff trachyte fractional crystallization modelling of compatible and incompatible trace elements v ni zr la sm lu nb y th does not reproduce the observed trends rocks of intermediate composition within the daly gap can be explained only by magma mixing between an already differentiated mafic magma hawaiite and an anorthoclase rich trachytic melt in the lower and higher parts respectively of a stratified magmatic chamber medium grained enclaves are interpreted as the result of fragmentation of solidified mixing layers in the roof of the magma chamber during the eruption of the green tuff when the collapse of the caldera took place diffusion calculations suggest a residence time of 5 days for the enclaves in their host magmas

a reappraisal of seismicity and eruptions of pantelleria island and the sicily channel italy three main tectonic depressions the pantelleria linosa and malta troughs the expression of a continental rift characterize the sicily channel a region with recent volcanic activity attested by the pantelleria and linosa volcanic islands as well as numerous seamounts to understand the seismic and eruptive behaviour of this area we compare historical and instrumental seismicity retrieved from catalogues with recordings from both a mobile seismic network and a permanent station deployed at pantelleria a review of historical eruptions affecting the sicily channel is also presented recent instrumental seismicity shows that the sicily channel is characterized by a low level of seismicity with earthquakes mainly occurring as isolated events rather than swarms as observed during the few documented eruptive periods the results of a seismic survey in 2006 2007 as well as the signals recorded by a permanent station in 2010 2014 enable stating that also pantelleria is characterized by a very low rate of seismicity the available though scant historical information suggests a recurrence time of about a century for the volcanic activity and that eruptions are usually preceded by seismic swarms in the only historical known eruption of pantelleria in addition to shocks uplifting and increasing fumarole activity were observed notwithstanding the lack of eruptions over the past century and despite the low recent seismic rate we believe that the geophysical monitoring of the sicily channel needs improving since it is an area of potentially high seismic and volcanic hazard given the presence of several active submarine eruptive centres

geology of the peralkaline volcano at pantelleria strait of sicily situated in a submerged continental rift pantelleria is a volcanic island with a subaerial eruptive history longer than 300 ka its eruptive behavior edifice morphologies and complex multiunit geologic history are representative of strongly peralkaline centers it is dominated by the 6 km wide cinque denti caldera which formed ca 45 ka ago during eruption of the green tuff a strongly rheomorphic unit zoned from pantellerite to trachyte and consisting of falls surges and pyroclastic flows soon after collapse trachyte lava flows from an intracaldera central vent built a broad cone that compensated isostatically for the volume of the caldera and nearly filled it progressive chemical evolution of the chamber between 45 and 18 ka ago is recorded in the increasing peralkalinity of the youngest lava of the intracaldera trachyte cone and the few lavas erupted northwest of the caldera beginning about 18 ka ago inflation of the chamber opened old ring fractures and new radial fractures along which recently differentiated pantellerite constructed more than 25 pumice cones and shields continued uplift raised the northwest half of the intracaldera trachyte cone 275 m creating the island s present summit montagna grande by trapdoor uplift pantellerite erupted along the trapdoor faults and their hingeline forming numerous pumice cones and agglutinate sheets as well as five lava domes degassing and drawdown of the upper pantelleritic part of a compositionally and thermally stratified magma chamber during this 18 3 ka episode led to entrainment of subjacent crystal rich pantelleritic trachyte magma as crenulate inclusions progressive mixing between host and inclusions resulted in a secular decrease in the degree of evolution of the 0 82 km3 of magma erupted during the episode

central mediterranean explosive volcanism and tephrochronology during the last 630 ka based on the sediment record from lake ohrid abstract lake ohrid located in the central mediterranean region downwind of the italian volcanoes has great potential for developing a detailed record of the explosive activity of these volcanoes electron microprobe and laser ablation inductively coupled plasma mass spectrometry geochemical analyses of juvenile glass fragments of previously not analysed tephra layers of the deep site sediment record of lake ohrid expand the existing tephrostratigraphy for the interval marine isotope stages 1 16 the geochemical signatures of all tephra layers suggest an origin exclusively from the italian volcanism eight of these tephra layers have potential equivalents in marine and terrestrial archives of the central mediterranean region oh dp 1966 sc5 a7 oh dp 1955 ces1 a2 oh dp 1055 s1 oh dp 1006 s2 oh dp 0997 s3 oh dp 0710 s8 c 51 oh dp 0766 odp5 p 13 oh dp 0505 odp4 nine tephra layers which have not been described so far help to reconstruct the late volcanic activity of mount vulture oh dp 2439 and the paleovulsini oh dp 1998 the pre and post rio rava activity of the roccamonfina volcano oh dp 1911 1812 1733 1640 1527 the early activity of the aeolian arc oh dp 1513 1520 and the bracciano activity of the monti sabatini volcanic district oh dp 1175 the multi proxy dataset and chronology of the deep site sediments allowed definition of the climatostratigraphic position for all tephra layers and constrain the ages of so far unknown and or undated tephra layers the presented data provide a crucial increase of knowledge of the middle pleistocene tephrostratigraphy in the central mediterranean back to 630 ka and allows new insights of the volcanic activity of roccamonfina the roman province the campanian volcanic zone cvz the aeolian arc pantelleria and mount vulture

tephrochronology of the astronomically tuned kc01b deep sea core ionian sea insights into the explosive activity of the central mediterranean area during the last 200 ka abstract we present a major trace and rare earth element characterization of single glass shards from fifteen tephra layers found in the astronomically tuned kc01b deep sea core ionian sea central mediterranean 36 15 25 n 17 34 44 e 3642 m water depth kc01b is considered a reference core for the mediterranean area since it provides a new reliable astronomical tuned timescale for the last 1 112 my lourens 2004 the studied deposits punctuate the marine record in a time span ranging from ca 16 ka to ca 191 ka b p encompassing the climatic zones y x w and v they are related to volcanic activity of the campania plain aeolian islands mt etna and pantelleria island along with major main markers of the central mediterranean area such as y 1 y 5 and x 6 astronomically dated at 16 7 ka 39 1 ka and 110 5 ka respectively the succession contains a number of well preserved deposits which can represent useful inter archive instruments of correlation the campania plain in particular sourced at least nine compositionally homogeneous tephra layers prior to the campanian ignimbrite event the data obtained in this work provide a new detailed analytical reference database for ionian sea tephrochronology and for proximal distal correlation studies they may help to unravel from the marine record the history of poorly known or unknown explosive activity on land since the middle pleistocene along with chemical composition size and dispersal of the products