field occurrences and nd isotopic characteristics of the meta mafic ultramafic rocks from the caozhuang complex eastern hebei implications for early archean crustal evolution of the north china craton abstract crust mantle differentiation and growth of early crust are critical issues in the field of solid earth science and the proper understanding of how earth evolved during eoarchean paleoarchean greatly relies on these issues the caozhuang complex one of the oldest rock units in the north china craton ncc is located in eastern hebei and composed of the caozhuang supracrustal rocks and the huangbaiyu orthogneisses the caozhuang supracrustal rocks are considered to be the oldest sedimentary sequences in the ncc into which the huangbaiyu grey gneisses with 3 3 ga zircon ages intruded in previous studies the caozhuang supracrustal rocks are represented by fuchsite bearing quartzites with 3 8 ga detrital zircons and metamorphosed mafic rocks amphibolites with 3 5 ga single stage nd model age relative to depleted mantle tdm nd here we present our new study on meta mafic ultramafic rocks of the caozhuang supracrustal sequence in accordance with detailed large scale field mapping petrology elemental and sm nd isotopic analyses and then discuss the possible crust mantle differentiation events that could take place during eoarchean and paleoarchean in the caozhuang area the meta mafic ultramafic rocks can be subdivided into two groups based on field occurrence group one rocks are amphibolites and hornblendites that occur as layers or slabs only in sedimentary sequences which are typically accompanied by banded iron formations bifs by contrast group two never coexists with bifs and they mainly occur as amphibolites and hornblendites lenses or deformed dykes and sills in supracrustal sequences and orthogneisses with blastophitic textures preserved sm nd isotopic analyses show that rocks from group one have a sm nd isochron age of 3580 98 ma and end t of 0 5 to 1 3 corresponding to tdm nd of 3 7 3 5 ga while group two rocks yield a sm nd isochron age of 3179 90 ma and end t between 4 6 and 6 6 corresponding to tdm nd of 3 3 3 1 ga geochemical characteristics of the two groups such as moderate mg negative correlation between fe2o3t and mgo and positive correlation between ni and mgo suggest they both experienced fractional crystallization of ferromagnesian minerals dominated by olivine and clinopyroxene during emplacement of magma s and combined with the flat hrees patterns and n morb like trace element spider diagrams and positive end t values it could be indicated that they could be partial melting products of ancient depleted mantle in the spinel stability fields based on the consistent whole rock sm nd isochron ages with tdm nd we suggest that two episodes of crustal growth occurred during 3 7 3 5 ga in late eoarchean and 3 3 3 1 ga in late paleoarchean in the caozhuang area the depleted characteristics of group one indicate lithospheric mantle in the caozhuang area might have been depleted before 3 7 3 5 ga and the sm nd isochron ages of group one basic volcanic rocks constrained that caozhuang supracrustal sequence may have deposited during 3 7 3 5 ga basic dykes or sills with tdm nd of 3 3 3 1 ga and time equivalent ttg gneisses represent a significant thermal event in late paleoarchean the meta mafic ultramafic rocks in the caozhuang complex are an important window to reveal and understand the early crustal evolution of the ncc which probably has global significance

the complex tectonic evolution of the craton adjacent northern margin of the palaeoproterozoic ketilidian orogen southeastern greenland evidence from the geochemistry of mafic to intermediate and granitic intrusions abstract the archaean thrym complex exposed in southeastern greenland is part of the north atlantic craton its southernmost part is in a transitional zone containing archaean orthogneiss to the north and palaeoproterozoic paragneiss and granitic rocks to the south that are part of the ketilidian orogen this 50 km wide transitional zone includes ca 2830 ma orthogneiss that is similar in age to orthogneiss in the central and northern parts of the complex and ca 2740 ma orthogneiss that is synchronous with the ca 2790 2700 ma skjoldungen orogeny a significant difference between this zone and the complex to the north is the presence of greenschist facies sedimentary rocks unconformably overlying orthogneiss and intruded by ca 1820 1800 ma granitic and mafic to intermediate intrusions these intrusions are within the ca 1854 1799 ma age range of the julianehab igneous complex with suites both older and younger than ca 1830 ma that are not restricted to specific zones within the ketilidian orogen the geochemistry of the palaeoproterozoic mafic to intermediate rocks in the transitional zone shows contamination by orthogneiss from the thrym complex and emplacement within an oceanic continental transition in a within plate setting unrelated to subduction in contrast the palaeoproterozoic granites were sourced entirely from archaean orthogneiss of the thrym complex making them technically i type granites that have inherited their petrogenetic signature from the orthogneiss as a result the palaeoproterozoic granites and intermediate to mafic igneous rocks have similar chondrite normalised patterns to the orthogneiss in the archaean complex this demonstrates that discrimination diagrams cannot be assumed to be unequivocal for the rocks studied unless the geochemistry of the source rocks is also known

on the origin and post depositional history of widespread massive ash deposits the case of intermediate brown tuffs ibt of lipari aeolian islands italy abstract we analysed a widespread massive ash unit outcropping on the island of lipari which belongs to the intermediate brown tuffs ibt succession of the aeolian islands italy the use of a multidisciplinary approach that integrates textural petrological and pedological methods allows us to discriminate between syn eruptive and post depositional features the deposits are dominated by uncrystallised blocky glass fragments of homogeneous shoshonitic composition confirming a provenance from hydromagmatic eruptions on the island of vulcano many glass fragments are surrounded by a coating separated by a thin void of syn eruptive origin due to alteration by aggressive acid gases in the eruptive cloud the lack of this coating in the northern part of lipari can be explained as a progressive dispersion of the gases far from the vent and or to post depositional processes the degree of soil development significantly increases from south soil profiles p1 and p2 at valle muria to north p3 and p4 at madoro and chiesa vecchia sites respectively as a response to a decrease in slope steepness which has brought about a progressive deepening of the pedogenetic front on gentler landforms and conversely its rejuvenation on steep slopes the relatively poor to moderate degree of pedogenic evolution of the studied ibt unit is consistent with its emplacement during part of the last glacial period

field relationship of high grade neo to mesoarchaean rocks of south east greenland tectonometamorphic and magmatic evolution abstract south east greenland forms part of the north atlantic craton and is characterized by migmatitic orthogneisses narrow bands of mafic granulite ultramafic and possible meta sedimentary rocks and alkaline carbonatitic intrusive rocks mafic granulite meta sedimentary and ultramafic rocks form the basement for the emplacement of granitic intrusions at ca 2865 ma that lasted episodically until ca 2790 ma and continuously during 2750 2700 ma the area is structurally complex with evidence of at least seven deformation events including reclined and mushroom like fold interference patterns an older 2790 ma foliation formed in granitic rocks and the basement during the timmiarmiut orogeny dt deformation associated with the ca 2790 2700 ma skjoldungen orogeny folded this early foliation and is associated with a penetrative foliation that is refolded progressively in a northeast southwest oriented stress field the orientation of the stress field progressively rotated into a northnorthwest southsoutheast orientation during the last stages of the orogeny the orogeny is also characterized by syn deformational anatexis at granulite facies at approximately 800 c and 5 8 kbar ca 2790 2740 ma which decreased to the amphibolite facies at ca 2730 ma the late to post tectonic granite and alkaline rocks assigned to the skjoldungen alkaline province intruded the central northern part around 2710 ma this was followed by north south extensional deformation during the singertat stage forming discrete shear zones at greenschist facies grades which is coeval with the emplacement of pegmatite ijolite and carbonatite emplacement during ca 2680 2650 ma similar lithology and tectonic processes in the tasiusarsuaq terrane of southern west greenland and the lewisian complex in scotland suggest a possibly large archaean terrane at that time which taking the present size at least covered around 500 600 km in an east west direction and approximately 200 km in a north south direction

wet surge deposits at la fossa di vulcano depositional and eruptive mechanisms abstract wet surge deposits of different volcanic cycles of the recent fossa activity at vulcano have been measured on a bed by bed basis with data recorded to millimeter detail the wet surge layers are varicoloured with variable thickness with the most recurrent thickness being about 1 cm the beds consist of fine ash without internal structures textural features include a accretionary lapilli of maximum size of 0 5 cm dispersed thoroughout the layer or forming continuous layers of submillimeter size b vesiculated layers which represent 10 to 65 of the total deposit vesicles have different shapes and smooth walls varying in volume from 1 to 15 20 c soft sediment types of bedding deformation such as gravity flowage ripples load cast and slumps the slope angle has not influenced either the concentration and size of the accretionary lapilli or the shape size and distribution of vesicles only the thickness of the layers decreases with distance from the vent sem investigations show features indicating the hydromagmatic origin of the deposits and stressing the role of the fluid phase noteworthy is the presence of vesiculated grains produced by magmatic exsolution which show chilling effects on the internal walls of the broken bubbles grain size analyses reveal that the layers are not graded and most of the samples have a median size finer than 50 m the grain size distributions are frequently polymodal suggesting several closely timed explosions as all the beds exhibit the same textures grain size and particle morphology a single mechanism can explain their deposition the depositional unit formed at the base of the cloud through the lateral expansion on the ground of a sticky muddy medium consisting of ash and fluid in general each layer lost its plasticity before the deposition of the next layer the deposition occurred in a nearly continuous sequence without periods of rest long enough to permit erosional discontinuity the eruptions are hydromagmatic and occur where magma at least partially fragmented comes into effective contact with subsurface water the process follows a model suggested by wohletz 1983b 1986 developing in more than one fragmentation event in the turbulent surge cloud both severe hydration and alteration of glassy grains and the formation of accretionary lapilli occur

new unspiked k ar ages of volcanic rocks of the central and western sector of the aeolian islands reconstruction of the volcanic stages abstract a geochronological study of the filicudi salina lipari and vulcano islands aeolian archipelago using the unspiked potassium argon technique provides new age data which combined with stratigraphic correlation better constrain the temporal evolution of volcanism the unspiked k ar age of the oldest exposed lavas on filicudi 219 5 ka is significantly younger than the previous estimation of 1 02 ma in the general context of aeolian volcanism this new date suggests that the volcanism of the western sector of the aeolian archipelago is younger than previously thought geochronological data point out on the rapid transition from calc alkaline to potassic volcanism the distribution of the k ar ages within the salina lipari vulcano group shows that the volcanism started on lipari and propagated over time northward on salina and southward on vulcano geochronological and geophysical data suggest that the onset of volcanism in the central sector of the aeolian arc may be due to a mantle upwelling structure located below lipari a change in the style of the eruptions occurred in the salina lipari vulcano system at about 100 ka from the present low energy magmatic eruptions occurred between 188 and about 100 ka from about 100 ka to the present higher energy eruptions and low energy events due to magma water interaction also occurred this change in the style of activity together with the appearance of evolved products i e rhyolites during the last 50 ka is consistent with the formation of magmatic reservoirs located at shallower depth with respect to those of the 188 100 ka period the new geochronological data and available petrological models reveal that a change in the deep source of the primary magmas occurred in a relatively short time interval

magnetic fabric and remanent magnetization of pyroclastic surge deposits from vulcano aeolian islands italy abstract tufi di grotte dei rossi inferiori are unwelded fine grained pyroclastic deposits of hydromagmatic origin emplaced between 21 and 11 8 6 ka at vulcano aeolian islands italy by deposition through surges spreading laterally from inside the la fossa caldera in this study the deposit s magnetic properties were investigated and interpreted in terms of eruptive and emplacement dynamics rock magnetism data were supplemented by grain size and textural characteristic analyses as well as scanning electron microscope sem investigations curie point measurements isothermal remanent magnetization and microprobe analyses showed that magnetization is carried by low ti titanomagnetite the size of the grains ranges from about 20 to 300 micrometres their shape from equidimensional to highly elongated the magnetic fabric is typical of fine grained pyroclastics foliation is well developed and in most sites lineation is directed towards the source area of the la fossa caldera the remanent magnetization consists of two components whose blocking temperature spectra partially overlap the direction of the low temperature component is close to that of the axial dipole and consistent with the palaeosecular variation curve for the aeolian islands the high temperature component is systematically shallowed and close to the direction of the magnetic lineation the overall results suggest that the high temperature component was acquired before and the low temperature component after the actual deposition of grains immediately after eruption the grains cooled and moved as free particles in the turbulent cloud during the expansion of the surge flows those particles with high blocking temperatures acquired a thermal remanence they were then deposited and shear at the very base of the flow oriented them and imprinted the rock s fabric and high temperature magnetization component volcanological and magnetic data suggest turbulent transportation and traction deposition of particles finally the rock cooled down and acquired the low temperature magnetization according to this model remanence acquisition in pyroclastic rocks deposited at temperatures lower than the curie point of their ferromagnetic grains depends on both the fluid dynamic forces and cooling history and must therefore be more complex than in pyroclastics deposited at higher temperatures such as welded ignimbrites

dynamics of vulcano island tyrrhenian sea italy investigated by long term 40 years geophysical data abstract vulcano island is a composite volcanic edifice located in the south central sector of the aeolian archipelago tyrrhenian sea italy historic activity has been characterized by frequent transitions from phreatomagmatic to minor magmatic activity the last eruption in 1888 90 saw powerful explosive pulses and this eruption defines what we call vulcanian also for other volcanoes since then volcanic activity has been in the form of fumarolic emanations of variable intensity and temperature mainly concentrated at la fossa crater we investigated vulcano dynamics through ca 40 years of ground deformation and seismicity data collected by the discrete and continuous ingv monitoring networks we considered levelling gps edm seismic and tilt data edm and levelling measurements began in the middle of the 1970s since the late 1990s the edm benchmarks have been measured using gps we performed a data inversion identifying for the 1999 2013 period the action of a deflating magmatic source located under vulcanello at 4 5 km a s l just at the top of a wide regional tectonic tabular source we analyzed data on different time space scales distinguishing the dynamics of different sectors of vulcano piano vulcanello la fossa cone and caldera and three periods 1974 1984 1984 1999 1999 2013 and the time evolution of the dynamics of the island we also show how the regional tectonic stress plays an important role in the transition of the volcanic system from a phase of stability to one of unrest inducing the heating and expansion of shallow hydrothermal fluids

cryptotephra from lipari volcano in the eastern gulf of taranto italy as a time marker for paleoclimatic studies we present the first tephroanalysis based on geochemical fingerprinting of volcanic glass shards from eastern apulian shelf sediments in the gulf of taranto italy high sedimentation rates in the gulf are ideal for high resolution paleoclimate studies which rely on accurate age models cryptotephrostratigraphy is a novel tool for the age assessment of marine sediment cores in the absence of discrete tephra layers high resolution quantitative analysis of glass shard abundance in the uppermost 45 cm of a gravity core identified two cryptotephras microprobe analysis of glass shards supported by an accelerator mass spectrometry 14c based age model identified the pronounced primary cryptotephra at 36 cm bsf below sea floor as the felsic ad 776 monte pilato eruption on the island of lipari whereas the thinner mafic tephra layer at 1 5 cm bsf is associated with the ad 1944 eruption of somma vesuvius identifying these tephra layers provides an additional 14c independent stratigraphic framework for further paleoclimatic studies allowing us to link mediterranean climate and hydrology to orbital variation and large scale atmospheric processes our results underline the importance of qualitative tephrostratigraphy in a highly geodynamic region where solely quantitative approaches have demonstrated to bear a high potential for false correlations between tephra layers and eruptions

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

transition from calc alkaline to potassium rich magmatism in subduction environments geochemical and sr nd pb isotopic constraints from the island of vulcano aeolian arc the problem of mantle metasomatism vs crustal contamination in the genesis of arc magmas with different potassium contents has been investigated using new trace element and sr nd pb isotopic data on the island of vulcano aeolian arc the analysed rocks range in age from 120 ka to the present day and cover a compositional range from basalt to rhyolite of the high k calc alkaline hkca to shoshonitic sho and potassic ks series older vulcano products 30 ka consist of hkca sho rocks with sio2 48 56 they show lower contents of k2o rb and of several other incompatible trace element abundances and ratios than younger rocks with comparable degree of evolution 87sr 86sr ranges from 0 70417 to 0 70504 and increases with decreasing mgo and compatible element contents 206pb 204pb ratios display significant variations 19 31 to 19 76 and are positively correlated with mgo 143nd 144nd 0 512532 0 512768 207pb 204pb 15 66 15 71 and 208pb 204pb 39 21 39 49 overall geochemical and isotopic data suggest that the evolution of the older series was dominated by assimilation fractional crystallisation afc with an important role for continuous mixing with mafic liquids magmas erupted within the last 30 ka consist mostly of sho and ks intermediate and acid rocks with minor mafic products except for a few acid rocks they display moderate isotopic variations e g 87sr 86sr 0 70457 0 70484 206pb 204pb 19 28 19 55 but 207pb 204pb 15 66 15 82 which suggest an evolution by fractional crystallisation or in some cases by mixing with little interaction with crustal material the higher sr isotopic ratios 87sr 86sr 0 70494 0 70587 of a few low volume intermediate to acid rocks support differentiation by afc at shallow depths for some magma batches new radiogenic isotope data on the aeolian islands of alicudi and stromboli as well as new data for lamproites from central italy are also reported in order to discuss along arc compositional variations and to evaluate the role of mantle metasomatism geochemical and petrological data demonstrate that the younger k rich mafic magmas from vulcano cannot be related to the older hkca and sho ones by intra crustal evolutionary processes and point to a derivation from different mantle sources the data from alicudi and stromboli suggest that even though interaction between magma and wall rocks of the calabrian basement during shallow level magma evolution was an important process locally a similar interpretation can be extended to the entire aeolian arc

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

on the use of unconformities in volcanic stratigraphy and mapping insights from the aeolian islands southern italy abstract the approach to volcanic stratigraphy and mapping in the aeolian islands has found the concept of unconformity bounded units ubus extremely useful for purposes of stratigraphic classification and correlation volcanic unconformities erosive and collapse unconformities relative to processes of internal modification of a volcano are classified separately from sea level driven unconformities the erosive unconformities formed during periods of volcanic quiescence are generally characterized by angular relationships and lithological change between the products below and above an unconformity and may be associated with paleosols or epiclastic horizons the collapse unconformities related to calderas and lateral collapses represent surfaces of structural truncation along the collapse borders passing outside of the collapse to erosive unconformities developed during the corresponding repose periods instead the sea level driven unconformities are marine and subaerial erosive surfaces bounding in pairs the depositional cycles relative to sea level highstands which are recorded in raised marine terraces most unconformities can be correlated on a variable scale from local volcanic island to regional inter island by means of careful stratigraphic analysis targeted to identify the corresponding stratigraphic hiatus in the volcanic successions in different points of observation this helps to solve the problems arising from the difficult recognition of the unconformities in the field moving away from the type locality due to their variable features a practical nomenclature scheme for a hierarchy of ubus to be applied in volcanic areas can be established on the basis of the areal magnitude of the bounding unconformities and their importance in the volcano history passing through a slight modification of the international stratigraphic guide s rules combined with lithostratigraphic units mapped rock bodies and lithosomes eruptive centres the ubus provide a useful stratigraphic synthesis of a volcanic area by means of a framework of time stratigraphic unconformable surfaces moreover ubus can be directly interpreted in terms of volcanic activity units with a time stratigraphic significance thus providing the key elements for the eruptive history of a volcano and the definition of its event stratigraphy

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

quantitative hazard assessment of phreatomagmatic eruptions at vulcano aeolian islands southern italy as obtained by combining stratigraphy event statistics and physical modelling abstract the detailed analysis of stratigraphy allowed the reconstruction of the complex volcanic history of la fossa di vulcano an eruptive activity mainly driven by superficial phreatomagmatic explosions emerged a statistical analysis of the pyroclastic successions led to the identification of dilute pyroclastic density currents base surges as the most recurrent events followed by fallout of dense ballistic blocks the scale of events is related to the amount of magma involved in each explosion events involving about 1 million cm 3 of magma occurred during recent eruptions they led to the formation of hundreds of meters thick dilute pyroclastic density currents moving down the volcano slope at velocities exceeding 50 m s the dispersion of density currents affected the whole vulcano porto area the vulcanello area they also overrode the fossa caldera s rim spreading over the piano area for the aim of hazard assessment deposits from la fossa cone and la fossa caldera were studied in detail to depict the eruptive scenarios at short term and at long term by means of physical models that make use of deposit particle features the impact parameters have been calculated they are dynamic pressure and particle volumetric concentration of density currents and impact energy of ballistic blocks a quantitative hazard map based on these impact parameters is presented it could be useful for territory planning and for the calculation of the expected damage

pyroclastic surges of the pleistocene monte guardia sequence lipari island italy depositional processes the 20 16 ka monte guardia sequence of lipari island southern italy is a complex succession of silicic pyroclastic surge deposits produced in part by hydromagmatic explosions near sea level most surges were directed to the east north east and north of the vent and climbed the 12 southern slopes of monte sant angelo in the central part of the island a series of thin distinctive key bed sets containing oxidized ash and accretionary lapilli allow a detailed correlation of sections and the lateral tracing of deposits of single pyroclastic surges across the island facies analysis reveals that the proximal to distal facies changes are different from those suggested by a previous study based on a statistical approach to lateral facies distribution single dry surge deposits evolve downcurrent from 1 beds of disorganized medium to coarse grained lapilli containing scattered blocks to 2 bipartite disorganized stratified beds of fine to coarse grained lapilli with ash matrix to 3 dunes formed of coarse grained ash to medium grained lapilli to 4 planar beds of fine grained lapilli this facies sequence is similar to published models for some korean surge deposits and records decelerating surges which experienced a downflow decrease in turbulence particle concentration and suspended load fall out rate and an increase in traction processes as the monte guardia surges climbed the opposing slopes of monte sant angelo they bifurcated into eastern and western tongues which experienced rapid deceleration leading to a rapid downcurrent thinning and fining of the surge deposits two fluid dynamical approaches suggest that monte guardia surges travelled at speeds of more than 75 85 m s 1 before climbing monte sant angelo flows with this vigour and distribution are capable of destroying animal and plant populations on lipari

an approach for investigating the depositional mechanism of fine grained surge deposits the example of the dry surge deposits at la fossa di vulcano abstract fine grained thinly laminated surge deposits have been studied in order to understand the physical properties of pyroelastic deposits with a large tractional component and to investigate on type and number of laminae deposited from a single surge cloud the examples are taken from the dry surge deposits of the fossa cone vulcano island where there is a good knowledge of the stratigraphy good exposures of the deposits and an absence of secondary structures analysis of texture and structure allows all the bed facies to be grouped into 4 principal types type 1 is made up of a loose coarse and medium ash in dark grey gently undulating laminae sometimes with cross laminae that alternate with pale grey laminae type 2 consists of grey ash in beds characterized by limited lateral continuity normal grading and a flat non erosive base type 3 is made up of submillimeter ochreous laminae plane parallel or gently undulating type 4 consists of massive beds of fine ash ochre in colour characterized by notably lateral continuity and constant thickness determination of the nature morphology and size of the grains shows that a close relationship exists between the relative abundance and shape of components and the textural and grain size characteristics of the bed facies the results suggest that a single surge event could deposit either a set of plane parallel to transverse laminae as type 1 and type 3 or a pair of laminated beds as type 2 and 4 depending on the flow velocity the effective grain size and density of the solid phase and the particle concentration in the eruptive cloud the almost complete lack of lithics suggests that magma water interaction occurred in sub surface conditions across a fragmented magma surface the efficiency of the interaction was primarily controlled by the ascent velocity of the magma in the conduit and its physical properties

remote sensing of geomorphology and facies patterns on a modern carbonate ramp arabian gulf dubai u a e abstract the occurrence of power law relationships in the spatial distribution of sedimentary lithotopes has been identified in both modern and ancient carbonate depositional bodies in this study facies patterns and their spatial relationships are investigated quantitatively in an arabian gulf shallow subtidal carbonate ramp setting using a synergy of ikonos satellite imagery and vessel based acoustic bathymetry survey three dimensional reconstruction of the facies distribution on the seabed enabled quantification of relationships between eight dominant facies classes and the association of particular lithotopes to water depth fractal behavior was investigated using a combination of boundary and patch based metrics and the spatial distribution of early diagenetically cemented hardgrounds and unconsolidated carbonate sand were shown to display strong fractal properties in contrast we show that landscape scale processes can be treated as essentially deterministic and facies neighborhood patterns are strongly probabilistic identifying that the heterogeneity of shallow subtidal carbonate facies scales with a power law within certain thresholds has the potential to serve as a tool in environmental reconstruction in the ancient where information on the lateral persistence of facies units is difficult to obtain the findings are relevant to the interpretation of stratigraphic sequences and paleo depth analysis

geological evidence for recurrent collapse driven phreatomagmatic pyroclastic density currents in the holocene activity of stromboli volcano italy abstract we present a multidisciplinary geological study of lithified to unconsolidated ash rich lapilli tuff deposits bearing accretionary lapilli that crop out in scattered sites along the lower slopes of the stromboli volcano southern italy these deposits are related to three pyroclastic successions called semaforo nuovo secche di lazzaro and semaforo labronzo with distinctive lithologic and volcanologic features and different stratigraphic position within the neostromboli volcano stratigraphy holocene their juvenile clasts have slightly different major and trace element compositions whole rock and glass isotopic ratios and mineralogical characteristics although they are all within the most evolved high k shoshonites typical of neostromboli the three successions are independently recognized in distinct sectors of the volcano displaying an asymmetric areal distribution that is interpreted as the result of directed pyroclastic density currents and minor fallout generated from summit eruptive vents lithological characteristics and morphoscopic features of ash particles indicate phreatomagmatic fragmentation combined with mechanisms of volatile exsolution or decompression which is atypical with respect to the dominant strombolian effusive eruptive behaviour of stromboli during the holocene we suggest that the three phreatomagmatic eruptions are linked to different major lateral collapses associated to flank fissure eruptions that occurred along the nw dipping sciara del fuoco collapsed flank it is argued that the collapses have unloaded the magmatic and hydrothermal system enabling magma water interaction and explosive decompression of a shallow magma reservoir the recurrent collapse eruption link with generation of directed pdcs able to reach the lower slopes of the volcano highlights a previously underestimated source of volcanic hazard at stromboli

petrology and geochemistry of volcanic rocks from the island of panarea implications for mantle evolution beneath the aeolian island arc southern tyrrhenian sea abstract major trace element and radiogenic isotope sr nd pb data are reported for a suite of rocks from the panarea volcano a large structure that is largely hidden below sea level and outcrops only as a group of small islands between lipari vulcano and stromboli in the eastern aeolian arc the exposed rocks mostly consist of high potassium calc alkaline hkca andesites dacites and some rhyolites shoshonitic basalts have been collected from submarine centres mafic calc alkaline ca rocks occur as thin layers of late erupted strombolian scoriae major and trace element data are scattered but define generally linear trends on inter element diagrams sr isotope ratios do not display significant increase with evolution although rough positive trends of 87sr 86sr versus sio2 and rb sr can be recognised within some units the mafic rocks display varying enrichment in potassium from ca to shoshonitic compositions and are characterised by variable abundances of incompatible trace elements which increase with potassium there is an increase of 87sr 86sr ratios and a decrease of 143nd 144nd and 206pb 204pb ratios from ca to hkca and shoshonitic mafic rocks the scattered and incomplete nature of the outcrops make it difficult to constrain magmatic evolution at panarea geochemical and isotopic data suggest that afc and mixing were important evolutionary processes however geochemical modelling does not support the possibility that the first order compositional variations observed in the mafic rocks are the result of these processes and suggests a genesis in a heterogeneous mantle source recent studies have highlighted strong differences in terms of incompatible trace element ratios and isotopic signatures between the western central and the eastern aeolian arc rocks from the western islands alicudi filicudi salina vulcano have typical magmatic arc geochemical signatures and relatively unradiogenic sr isotope compositions by contrast the eastern island of stromboli has a more radiogenic sr isotope signature and shows trace element abundances and ratios that are intermediate between arc and intraplate compositions panarea mafic rocks have geochemical and isotopic signatures that are intermediate between those observed in the two sectors of the arc the late erupted ca scoriae of panarea have trace element and isotopic compositions similar to those of the mafic rocks from the western islands of filicudi and alicudi whereas the hkca and shoshonitic mafic rocks have isotopic and trace element signatures that are closer to those of stromboli this reflects the particular position of panarea which is sited midway between the western central arc and stromboli according to some recent views subduction of the ionian sea plate is actively occurring beneath the eastern aeolian arc with rollback of the subduction zone toward the southeast the tindari letoianni malta escarpment fault zone is considered to be the boundary between the active subducting plate in the east and the african plate and western aeolian arc in the west it is suggested that the rollback of the ionian plate generated inflow of mantle material from below the western arc into the mantle wedge above the subducting ionian slab this situation generated a hybrid mantle beneath panarea which resulted in a mixture of western type and resident eastern arc mantle materials the latter had a composition akin to the source of stromboli magmas early hkca and shoshonitic magmatism tapped such a hybrid source whereas the younger ca activity has been derived from melting of unmodified western type mantle material the late eruption of ca rocks with a composition similar to western arc can be explained by assuming that a continuing inflow process had increased the amount of western type mantle with time thus favouring the late appearance of ca magmas this hypothesis accounts for the overall decrease of potassium with time which is the opposite of the trend observed in other aeolian islands

assimilation and high pressure fractional crystallization afc recorded by paleo proterozoic mafic dykes southeast greenland abstract the northern margin of the nagssugtoqidian mobile belt in southeast greenland exposes a suite of moderately fractionated fe rich tholeiitic dykes of paleo proterozoic age the dykes were intruded during extension of the crust prior to the development of the nagssugtoqidian mobile belt although the dykes recrystallized under amphibolite facies conditions during proterozoic orogenesis they suffered little deformation excluding two very evolved samples the compositions range between 7 8 4 6 wt mgo 44 5 52 9 wt sio2 and 1 8 6 9 wt total alkalis one group of mafic dykes shows distinct mantle normalized trace element patterns with high abundance of low field strength elements and light rare earth elements and low abundances of high field strength elements these characteristics are consistent with a process of fractional crystallization coupled with assimilation of the regional granulitic crust relatively high rates of assimilation to fractional crystallization 0 7 are required to generate the level of incompatible trace elements this points to lower crustal conditions and the assimilation is believed to have taken place at the base of the continental crust trace element variations indicate fractionation at high pressure involving clinopyroxene as the main extracted phase we evaluate two fractionation models corresponding to a pressure of 0 9 and 1 5 gpa respectively and show that the trace element variations require polybaric fractionation at pressures from a maximum of 1 5 gpa to a minimum of 0 9 gpa

computer simulation of transport and deposition of the campanian y 5 ash analyses of grain size and modal composition of the campanian tuff ash layer y 5 from 11 deep sea cores have been carried out this layer represents ash fall that has been correlated with the 38 000 y b p campanian ignimbrite thunell et al 1979 a deposit formed by the largest eruption documented in the mediterranean region during the late pleistocene barberi et al 1978 the bulk deposit is bimodal in grain size and dominated by glass shards the calculated mean grain size of the coarse mode of the individual size distributions decreases with distance from the source and progressively approaches a near constant fine mode of approximately 13 microns distal samples are unimodal in grain size these data combined with a set of vertical profiles of wind 10 year average have been used as input to a computer model that simulates fallout of tephra modelling indicates that the downwind variation of grain size of the coarse mode can be accurately reproduced with transport of ash between 5 and 35 km the observed fine mode of the deposit cannot however be generated by transport of ash as individual particles at these elevations such transport would result in deposition of virtually all of the fine ash beyond the studied area deposition of fine ash within the studied distance of 1600 km from source can only occur by fallout as particle aggregates from a high eruption plume or as individual particles from co ignimbrite ash clouds with a maximum elevation of 3 km the large volume of ash in the fine mode 70 wt and the irregularity in azimuth of low level winds argue against major low level transport of co ignimbrite ash rather the ash may have been derived from both a plinian eruption column and high altitude clouds of co ignimbrite ash with settling of fine ash as particle aggregates

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

pre break up palaeostress state along the east greenland margin this paper describes intraplate deformation and the palaeostress state along the east greenland margin during the paleocene between 65 and 55 myr ago prior to the onset of the ne atlantic spreading it is shown that the pre break up deformation is the result of dip oblique strike slip tectonics in the se and compressive tectonics in the north the reduced palaeostress tensors derived from inversion of the fault slip data show that the maximum horizontal stress 1 is compressive and the orientations of 1 change from ene wsw in the south to nne ssw in the north the reconstructed palaeostress trajectory map demonstrates that the 1 orientations reflect the plate motion path and define small circles whereas the trends of the minimum horizontal stress 3 converge and cluster around an area in the arctic that is interpreted as the rotation pole of greenland the intraplate deformation folding and uplift that affected the greenland and european margins the barents sea and the north sea during the paleocene can be explained by the counter clockwise rotation of greenland the present paper calculates the pole of rotation of greenland using the kinematics of brittle faults along the plate margin and the palaeostress derived from inversion of fault slip data analysis as an indicator of motion path

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

timing of magmatism and metamorphism in the gruinard bay area of the lewisian gneiss complex comparison with the assynt terrane and implications for terrane accretion reply u pb zircon data from selected gneiss samples provide estimates of the timing of igneous protolith emplacement and granulite facies metamorphism in the gruinard bay badcall bay and lochinver areas of the mainland lewisian gneiss complex of north west scotland zircons from the gneisses contain complex zoning patterns making them amenable to shrimp ion microprobe analysis with inherited zircon distinguishable from magmatic growth and metamorphic recrystallisation from gruinard bay a tonalitic granulite yielded a protolith age of 2 825 8 ma for oscillatory zoned zircon cores with recrystallised low u rims preserving an age of 2 733 12 ma an inherited 2 905 15 ma age component was recognised in a sample of trondhjemitic gneiss the protolith of which is estimated to have been emplaced at 2 858 11 ma low u rims yielding an age of 2 729 20 ma are also present which together with the rim age from the granulite are considered to date granulite facies metamorphism in the gruinard region for comparison with the gruinard bay gneisses a trondhjemitic partial melt and trondhjemite sheet were analysed from the granulite facies rocks at badcall bay in the assynt terrane age data do not show definitive relationships with zoning patterns in the zircons and show a spread along concordia typical of previous ion microprobe age data from the scourie gneisses both samples do however show a significant isotopic disturbance at 2 480 ma the most recent estimate for the badcallian metamorphism protolith ages for components of the assynt terrane range between ca 2 900 and 3 030 ma and appear to be older than the 2 860 2 825 ma gneiss protoliths from the gruinard bay area the timing of granulite facies metamorphism also appears to be different between the two areas suggesting that the two granulite regions of the mainland may not be related as previously thought instead they are interpreted in terms of a terrane accretion model whereby the two areas evolved as separate blocks prior to their juxtaposition during the palaeoproterozoic the boundary between the two terranes is thought to lie to the south of lochinver corresponding with the strathan line because of the observed 2 480 ma age signature to the north and 2 730 ma signature to the south by defining a new mainland terrane the gruinard terrane the number of mainland blocks which includes the assynt central rhiconich northern and southern terranes has been expanded

fragmentation versus transportation mechanisms in the pyroclastic sequence of monte pilato rocche rosse lipari italy abstract monte pilato is a rhyolitic pumice cone formed about 1400 years ago during the last volcanic activity which occurred at lipari its activity consisted of numerous explosive episodes ending with the extrusion of the rocche rosse obsidian lava flow we have identified nine different pyroclastic lithofacies of which four main lithofacies represent 90 of the erupted products they include 1 deposits consisting of decimeters to meters thick well sorted graded beds of pumice lapilli which are of fall origin 2 massive deposits consisting of decimeters thick beds of pumice lapilli in an ash matrix interpreted as being of pyroclastic flow origin 3 deposits of centimeters thick ash beds of surge origin 4 decimeter thick fine ash layers with scattered subcentimetric accretionary lapilli of turbulent flow origin the complex grain size distributions of the main lithofacies were distinguished using a multivariate statistic analysis r mode factor analysis variations of the grain size characteristics in relation to the distance from the vent area have been investigated in order to discriminate the roles played by fragmentation and transportation processes in the lithofacies 1 fall deposits the grain size distribution is always unimodal and varies from a rosin type distribution near the vent to a gaussian one in the distal outcrops this is caused by the transport process and the different particle trajectories in lithofacies 2 3 and 4 the grain size distributions are always polymodal the polymodality is not caused by preferential processes occurring during transportation but seems rather to be connected with the original fragmentation of the pyroclastic material the pumice lapilli present both in lithofacies 1 and 2 have mean vesicularity index values always in excess of 65 and the value is homogeneous throughout the sample these data suggest that for these two lithofacies the pumice lapilli originated from exsolution of magmatic gases in contrast the fine ash particles in lithofacies 2 and also the main mode of lithofacies 3 and 4 deposits show typical features of hydromagmatic fragmentation processes the grain size population is always centered at 4 5 0 032 0 064 mm and interestingly the same grain size has been obtained recently zimanowski et al 1991 for fragments produced by experimental magma water interaction field and laboratory data suggest that during monte pilato rocche rosse eruptions magmatic and hydromagmatic mechanisms were frequently operative at the same time

high precision u pb dating of complex zircon from the lewisian gneiss complex of scotland using an incremental ca id tims approach abstract a novel approach of thermally annealing and sequentially partially dissolving single zircon grains prior to high precision isotope dilution thermal ionization mass spectrometry id tims is presented this technique is applied to complex zircon from the precambrian lewisian gneiss complex of scotland up to six partial dissolutions were conducted at incrementally higher temperatures and analysed at each successive step id tims analyses reveal the portions of zircon affected by the lowest temperature partial dissolution step have suffered pb loss successively higher temperature partial dissolution steps yield a series of analyses from the younger domains followed by mixing trajectories with older components presumably from the inner domains specifically for a partially retrogressed granulite tonalite gneiss from the central block assynt high grade metamorphic zircon ages of c 2500 ma and c 2700 ma are resolved with a protolith age of c 2860 ma also recognised this unequivocally demonstrates two separate episodes of high grade metamorphism affected rocks from this region the c 2700 ma age provides a minimum age constraint on the highest pressure event known from archean crustal rocks using this technique of pseudo spatial resolution coupled with high precision analysis it is possible to recognise discrete pb loss and multiple stages of zircon growth or isotopic resetting within single grains to within 0 1 0 2 error 2 on individual 207pb 206pb ages this method has relevance to u pb zircon geochronology where conventional micro beam techniques are unable to resolve between separate ages within single grains

interference fold patterns in regional unidirectional stress fields a result of local kinematic interactions abstract folds are commonly found in association with ductile shear zones however superimposed folding contemporaneous with shearing is rarely reported here we describe a macroscopic fold interference pattern with geometry intermediate between types 1 and 2 related to development of adjacent transcurrent shear zones the interference fold pattern is located in a compartment bounded on the eastern side by an ene trending dextral shear zone that connects with a ne trending sinistral shear zone and on the western side by a ne trending sinistral shear zone a first folding episode produced nw trending sw verging inclined folds and a later one ne trending upright folds folds of the first event are attributed to a local contractional strain field induced by the growth of the shear zones with opposed kinematics whereas the later folding episode and nucleation of the western shear zone reflects regional nw se contraction folding of a macro scale nw trending fold by ne trending folds produced the fold interference structure in contrast with most cases of types 1 and 2 fold interference patterns in the present case no change on the orientation of regional stress axes is required

changes of the geomagnetic field vector obtained from lava sequences on the island of vulcano aeolian islands sicily abstract a combined geochronologic k ar and palaeomagnetic study has been conducted on five volcanic sections 70 flows on the island of vulcano the sections span the interval from 15 2 to 135 4 ka with large hiatuses rock magnetic investigations indicate that the natural remanent magnetisation nrm is carried by titanomagnetites in the four oldest sections with a contribution from high coercivity magnetic minerals in the youngest section palaeomagnetic directions obtained by thermal demagnetisation document a large magnetic excursion at around 110 ka with virtual geomagnetic poles vgps that lie over eastern siberia these directions may represent a volcanic record of the termination of the blake event only about 15 of the samples from 19 flows proved suitable for palaeointensity thellier and thellier determinations these measurements indicate that the geomagnetic field has varied at vulcano between 16 and 53 t in the explored time interval when combined with previous results obtained at mt etna for the period from 140 to 60 ka tric et al 1994 phys earth planet inter 85 113 129 these results document a broad low at around 115 ka the palaeointensity values from vulcano and etna are consistent with global values suggesting the presence of a dominant dipole field contribution these values on the other hand are significantly smaller than those recently obtained from la reunion in the southern hemisphere this suggests that large long lived non dipolar components of the geomagnetic field may be present at la reunion in the interval from 130 to 90 ka these observations are consistent with the fact that the vgp angular dispersion calculated from non excursional data is significantly smaller at vulcano than at la reunion

event stratigraphy of a caldera forming ignimbrite eruption on tenerife the 273 ka poris formation the 273 ka poris formation in the bandas del sur group records a complex compositionally zoned explosive eruption at las canadas caldera on tenerife canary islands the eruption produced widespread pyroclastic density currents that devastated much of the se of tenerife and deposited one of the most extensive ignimbrite sheets on the island the sheet reaches 40 m thick and includes plinian pumice fall layers massive and diffuse stratified pumiceous ignimbrite widespread lithic breccias and co ignimbrite ashfall deposits several facies are fines rich and contain ash pellets and accretionary lapilli eight brief eruptive phases are represented within its lithostratigraphy phase 1 comprised a fluctuating plinian eruption in which column height increased and then stabilized with time and dispersed tephra over much of the southeastern part of the island phase 2 emplaced three geographically restricted ignimbrite flow units and associated extensive thin co ignimbrite ashfall layers which contain abundant accretionary lapilli from moist co ignimbrite ash plumes a brief plinian phase phase 3 again dispersing pumice lapilli over southeastern tenerife marked the onset of a large sustained pyroclastic density current phase 4 which then waxed phase 5 covering increasingly larger areas of the island as vents widened and or migrated along opening caldera faults the climax of the poris eruption phase 6 was marked by widespread emplacement of coarse lithic breccias thought to record caldera subsidence this is inferred to have disturbed the magma chamber causing mingling and eruption of tephriphonolite magma and it changed the proximal topography diverting the pyroclastic density current s down the guimar valley phase 7 phase 8 involved post eruption erosion and sedimentary reworking accompanied by minor down slope sliding of ignimbrite this was followed by slope stabilization and pedogenesis the fines rich lithofacies with abundant ash pellets and accretionary lapilli record agglomeration of ash in moist ash plumes they resemble phreatomagmatic deposits but a phreatomagmatic origin is difficult to establish because shards are of bubble wall type and the moisture may have arisen by condensation within ascending thermal co ignimbrite ash plumes that contained atmospheric moisture enhanced by that derived from the evaporation of seawater where the hot pyroclastic currents crossed the coast ash pellets formed in co ignimbrite ash clouds and then fell through turbulent pyroclastic density currents where they accreted rims and evolved into accretionary lapilli

age and geochemistry of tephra layers from ischia italy constraints from proximal distal correlations with lago grande di monticchio unraveling the eruptive history of the island of ischia southern italy is problematic due to its burial caldera collapse resurgent uplift and erosion here we present new major and trace element glass data for 39 75 ka proximal tephra deposits including those of the caldera forming monte epomeo green tuff megt eruption correlations with the distal tephra archive preserved at lago grande di monticchio lgdm are used to constrain the timing of as yet undated eruptive events out of 13 lgdm tephras analysed from the 39 104 ka time window glass geochemical data show that all are compositionally consistent with the explosive volcanic eruptions of ischia whilst 5 of them can be correlated with specific proximal deposits pre megt pyroclastic sequences comprise three compositional groups these groups occur repeatedly in sucessive eruptions proximal distal correlations indicate that the porticello eruption occurred at 59 2 ka and the tisichiello eruption probably occurred at 76 3 ka the megt eruption is correlated with lgdm tm 19 which has been directly dated at 55 2 ka post megt tephras form compositional groups that overlap with the pre megt but are displaced to lower feo and tio2 and lower incompatible element contents proximal distal correlations indicate that the schiappone and pietre rosse eruptions occurred at 50 6 2 0 ka and 45 6 ka respectively tephra from the megt eruption span a wide compositional range broadly overlapping the three pre megt compositional groups but are displaced to higher nd and y and contain an additional less evolved glass population glass geochemistry is used to recognise and confirm distal equivalents of the megt at lgdm tm 19 and in the ionian y 7 adriatic prad 1870 and tyrrhenian c 18 md 28 seas distal occurences of megt tephra define a dispersal axis to the south southeast and are found as far as 540 km from ischia making the megt one of the most widely dispersed late quaternary pyroclastic deposit erupted in the campanian region we estimate a volume of approximately 40 km3 for the fallout portion of the megt pyroclastic sequence on the basis of proximal and distal deposit thicknesses

late quaternary ancient shorelines at lipari aeolian islands stratigraphical constraints to reconstruct geological evolution and vertical movements indicators of three fossil shorelines located at elevations of 43 45 m asl i order 23 27 m ii order and about 12 m iii order are recognized on the island of lipari detailed evaluation of the stratigraphic relationships to the volcanic substratum allows their correlation with late quaternary eustatic highstands of tyrrhenian age corresponding to marine oxygen isotope substages 5e 124 ka 5c 100 ka and 5a 81 ka marine deposits related to the ancient shorelines represent useful stratigraphic markers as related unconformities constrain the geological evolution of lipari this is interpreted as a result of two main stages of volcanic activity pre and post tyrrhenian spaced out by one stage characterized by prevalent marine erosional episodes tyrrhenian chronological and altimetrical data concerning the ancient shorelines have been used to estimate the vertical mobility of the volcanic edifice of lipari which is characterized by a continuous uplift at an average rate of 0 34 mm a during the last 125 ka this estimation is fully concordant with the values obtained during the same time period from the nearby islands of filicudi 0 31 mm a and salina 0 36 mm a suggesting a similar uplift trend induced by the prevalence of regional tectonic processes

late archaean granites a typology based on the dharwar craton india abstract extensive field work in the eastern dharwar craton associated with petrographic and geochemical major and trace elements investigations allows four main types of late archaean granitoids to be distinguished 1 na rich granitoids of trondhjemitic tonalitic and granodioritic composition ttg that are characterised by strongly fractionated ree patterns and low hree contents and generally interpreted as slab melts generated by partial melting of metamorphosed hydrated basalt most likely in a subduction environment 2 sanukitoids which are k and mg rich monzonites and granodiorites with ttg like ree patterns associated with marked lile enrichment and considered to result from the reaction of slab melts generated in a subduction environment with and assimilation of mantle wedge peridotite 3 uncommon high hfse mg and k granites with strongly ree and lile enrichment that probably formed by partial melting of an enriched mantle source unlike in the genesis of sanukitoids in this case the slab melt is considered to be wholly consumed by reaction with mantle minerals resulting in mantle enrichment subsequent melting of this enriched mantle probably in a post subduction setting gives rise to high hfse mg and k magmas as demonstrated for the closepet granite dharwar craton the hot mantle derived magma can induce melting of continental crust and then mix with the anatectic products 4 k rich mg poor anatectic biotite granites with ree patterns that are less fractionated and show negative eu anomalies these granites result from the remelting of old basement or recently accreted plutons both with ttg compositions such anatexis can occur either in a subduction or in a post subduction environment this typology based on the well exposed dharwar craton can be extended to late archaean granitoids from all over the world about such 500 analysis were compiled and a number of discriminant diagrams based on both major and trace elements are proposed the most likely tectonic setting for the observed rock types is an accretionary orogen with accretion of continental blocks above a subduction system followed by thermal reworking of the newly accreted continental material however it has been found that archaean subduction related granitoids are significantly different from their modern counterparts implying progressive changes in the modes of magma generation at convergent margins from the archaean to the present

the campanian ignimbrite and codola tephra layers two temporal stratigraphic markers for the early upper palaeolithic in southern italy and eastern europe tephra layers from archaeological sites in southern italy and eastern europe stratigraphically associated with cultural levels containing early upper palaeolithic industry were analysed the results confirm the occurrence of the campanian ignimbrite tephra ci ca 40 cal ka bp at castelcivita cave southern italy temnata cave bulgaria and in the kostenki borshchevo area of the russian plain this tephra originated from the largest eruption of the phlegrean field caldera represents the widest volcanic deposit and one of the most important temporal stratigraphic markers of western eurasia at paglicci cave and lesser sites in the apulia region we recognise a chemically and texturally different tephra which lithologically chronologically and chemically matches the physical and chemical characteristics of the plinian eruption of codola a poorly known late pleistocene explosive event from the neapolitan volcanoes likely somma vesuvius for this latter we propose a preliminary age estimate of ca 33 cal ka bp and a correlation to the widespread c 10 marine tephra of the central mediterranean the stratigraphic position of both ci and codola tephra layers at castelcivita and paglicci help date the first and the last documented appearance of early upper palaeolithic industries of southern italy to ca 41 40 and 33 cal ka bp respectively or between two interstadial oscillations of the monticchio pollen record to which the ci and codola tephras are physically correlated corresponding to the greenland interstadials 10 9 and 5 in eastern europe the stratigraphic and chronometric data seem to indicate an earlier appearance of the early upper palaeolithic industries which would predate of two millennia at least the overlying ci tephra the tephrostratigraphic correlation indicates that in both regions the innovations connected with the so called early upper palaeolithic encompassing subsistence strategy and stone tool technology appeared and evolved during one of the most unstable climatic phases of the last glacial period on this basis the marked environmental unpredictability characterising this time span is seen as a potential ecological factor involved in the cultural changes observed

marine continental tephra correlations volcanic glass geochemistry from the marsili basin and the aeolian islands southern tyrrhenian sea italy abstract major minor and trace element analysis of volcanic glass in proximal and distal it is evident that correlation of proximal continental and distal marine tephras at a high level of confidence requires a full complement of major minor and trace element data in conjunction with considerations of the mineralogy and morphology of juvenile deposits these data help define petrological lineages such that precise provenance can be established whilst a precise proximal distal match must be based on identical major minor and trace element concentrations it is clear that resurgent activity from a single volcano can produce magmas with identical compositions in such cases stratigraphic relationships must complement any geochemical study occasionally proximal stratigraphies may be unrepresentative of the complete eruptive history because of a lack of exposure due to burial by more recent effusive and explosive activity or sector collapse which can remove vital stratigraphy particularly on volcanic islands

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system

tectonic and volcanic evolution of panarea aeolian islands italy abstract based on new geophysical volcanological structural and radiometric data a morphological structural reconstruction of the submarine part of the panarea volcanic edifice is provided and a model for the evolution of the entire complex is proposed panarea is a small part of a much larger submarine edifice whose overall shape is one of a truncated cone with an eastern protrusion the base of the cone is about 1500 m below sea level it has a diameter of about 23 km and an area of 460 km2 several lobes are present on the steep eastern slopes of the cone and the wide submarine top is of a morphology which is more complex than previously thought the evolution of the panarea volcanic complex occurred in three stages 1 1 development of a central volcano in the western sector of the complex the island of panarea represents the top of this volcano 2 2 eastward shifting of volcanic activity producing development of the lobed eastern sector of the complex 3 3 extensive caldera collapse of the central part of the complex and emplacement within the collapsed area of domes and lava bodies of various affinities some of which are basaltic ne sw oriented structures seem to have had a fundamental role during the development of the panarea volcanic complex these structures have been active until recent times and are of regional significance indeed the evolution of nearby stromboli has been controlled by the ne sw trending structures panarea and stromboli also display similar magnetic anomaly trends geochemical affinities and temporal relationships in volcanism

tyrrhenian sea tephrochronology of the oxygen isotope record for the past 60 000 years abstract a chronology of the marine oxygen isotope record of the past 60 ka is proposed by correlating eight marine ash layers with terrestrial volcanic deposits dated by the 14c and or k ar methods detailed oxygen isotope analyses were made on the planktonic foraminifera of three cores collected in the central tyrrhenian sea the origin of the ash layers was determined by major and trace elements analyses then the major pyroclastic terrestrial deposits were sampled and analysed in order to provide land sea correlations two ash layers occurred during the warm event that followed the first step of the deglaciation and which was dated at 12 6 0 5 ka b p another ash layer is present near the last glacial maximum that we have dated at 17 5 0 3 ka b p during isotopic stage 3 five ash layers were recognized and dated which allowed us to assign ages to the isotopically light oxygen peaks warmer interstadials at 31 1 5 ka and 33 4 1 6 ka denekamp at 37 5 2 ka hengelo and successively at 49 2 ka 52 4 2 2 ka 57 2 2 ka and 60 5 2 2 ka moershoofd complex

leaching procedure used in dating young potassic volcanic rocks by the 226ra 230th method a method for determining the ages of shoshonitic volcanics erupted within the last 5000 years is presented and assessed this method is based on 226ra 230th radioactive disequilibrium and on a leaching procedure and counting of volcanics containing th enriched rainitial depleted mineral phases detected by microprobe analyses k is used as a ra stable chemical analogue the data are plotted on 226ra 228ra k 228ra osmond type diagrams in order to evaluate the 226raradiogenic230th activity ratio of the th enriched rainitial depleted phases four samples of volcanics from vulcano island southern italy gave ages consistent with historical reports andk ar chronology

testing the model of late archean terrane accretion in southern west greenland a comparison of the timing of geological events across the qarliit nunaat fault buksefjorden region abstract the prevailing tectonic model for the archean gneiss complex of southern west greenland holds that terranes with different metamorphic histories and protolith ages were juxtaposed between 2 80 and 2 72 ga this model was tested by using detailed mapping and u pb geochronology to compare the timing of geological events across the qarliit nunaat fault the boundary between terranes in the buksefjorden region the fault was interpreted as a terrane boundary mostly because it is a narrow zone of mylonitic rocks that separates granulite or retrograde amphibolite facies gneisses of the tasiusarsuaq terrane tt from prograde amphibolite facies gneisses of the akulleq terrane at and it separates tonalitic gneisses of different age 3 87 3 60 and 2 80 ga in the at versus 2 92 2 86 ga in the tt dating of similar homogeneous gneisses in each terrane yielded ages of 2843 3 ma in the tt tonalite and 2824 2 ma in the at granodiorite ikkattoq gneiss granulite facies metamorphism in the tt is thought to have coincided with intrusion of a 2805 2 ma orthopyroxene pegmatite and zircon and titanite from nearby amphibolitic gneiss yielded ages of 2779 2 and 2660 10 ma respectively metamorphic minerals in the at are younger zircon and titanite from amphibolitic gneiss are 2717 3 and 2510 10 ma respectively and monazite from pelitic schist is 2732 5 and 2708 4 ma a concordant pegmatite layer that underwent a substantial amount of shearing along the qarliit nunaat fault was dated at 2725 2 other pegmatites that intruded relatively late in the structural history crystallized at 2710 2 in the tt and 2541 2 ma in the at these results support the prevailing tectonic model by showing that i similar homogeneous gneisses in each terrane are different age ii 2805 ma granulite facies metamorphism in the tt predated 2740 2700 ma amphibolite facies metamorphism in the at and iii shearing along the terrane boundary occurred after 2725 ma

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

the neoarchean ultramafic mafic complex in the yinshan block north china craton magmatic monitor of development of archean lithospheric mantle abstract neoarchean ultramafic mafic complexes are critical for characterizing the embryonic continental lithosphere and hence for arbitrating the extrapolation of plate tectonics into the archean geology this geochronological and geochemical study documents the newly identified amphibolite to granulite facies xiwulanbulang xwlbl ultramafic mafic complex in the yinshan block north china craton ncc it is composed mainly of meta gabbro hornblendite and serpentinite sims u pb zircon dating on the later granite constrains a minimum formation age of 2581 ma for the complex whereas the metamorphic zircons from the hornblendite and coexisting kyanite garnet gneiss yield a metamorphic age of 2 50 ga the dominant meta gabbros in the complex show an morb composition and characterized by an lree depleted to flat ree pattern yet possessing prominent nb zr and ti depletions which suggest dual geochemical features combined with their depleted nd t isotope compositions 1 77 to 2 23 and regional high temperature high mg basaltic magmatism we suggest that they may have been produced by interaction of the upwelling asthenosphere with the metasomatized lithospheric mantle minor hornblendites pyroxenites that occurred in the complex display high mgo 13 6 20 2 wt cao 7 5 13 8 wt cr 475 2049 ppm and ni 154 859 ppm contents reflecting they have originated either as a crystal mush magma or high degree partial melts of a mantle source they show moderately fractionated ree patterns la yb n 2 9 10 7 but depleted nd t 1 48 to 3 53 and zircon hf t up to 7 3 values considering their negative anomalies for nb zr and ti relative to neighboring ree we suggest that the mantle source of the hornblendites was refractory depleted peridotite that experienced prior basaltic magma extraction followed by metasomatism of subduction related fluids systematic variations trend in both major and trace elements between the hornblendites and the associated serpentinites support their genetic linkage high cao 0 7 6 9 wt and al2o3 3 9 6 9 wt contents but low mg 79 85 imply that the serpentinites were likely the cumulates segregated from the coexisting hornblendite pyroxenite magma instead of mantle peridotite taking into full account the regional tectono thermal events we conclude that the xwlbl ultramafic mafic complex was produced in a neoarchean subduction related zone which was more likely trigged by the upwelling asthenosphere mantle as a result of rollback of subducted oceanic lithosphere

shrimp u pb zircon geochronology of the late archaean ruinnaesset syenite skjoldungen alkaline province southeast greenland abstract a sample of the ruinnaesset syenite of the southeast greenland skjoldungen alkaline province contains a homogeneous population of zircons up to 1 mm diameter that are devoid of new overgrowths and old inherited cores u pb isotopic analyses of these zircons form a single population with weighted mean 207 pb 206 pb and 206 pb 238 u ages of 2699 4 ma and 2690 20 ma 2 respectively these dates are interpreted as giving the time of crystallisation of the syenite

volcanological and magmatological evolution of stromboli volcano aeolian islands the roles of fractional crystallization magma mixing crustal contamination and source heterogeneity the present paper reports the results of a detailed stratigraphical petrological and geochemical investigation on the island of stromboli aeolian arc southern tyrrhenian sea major and trace element data determined on a large quantity of samples from well established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known the activity of the exposed part of stromboli which occurred over a time span of about 100 000 years started with the emission of high k calc alkaline hkca volcanics which were covered by calc alkaline ca shoshonitic sho high k calc alkaline hkca and potassic ks products the most recent activity consists of hkca lavas and the present day sho basaltic volcanics emitted by mildly explosive strombolian activity most of the products are lavas with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity the transition from the sho to the ks cycle was associated with the collapse of the upper part of the volcanic apparatus the transition from ks to the present day sho activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the sciara del fuoco depression the rock series cropping out at stromboli show variable enrichment in potassium incompatible trace elements and radiogenic sr which increase from ca through hkca and sho up to ks rocks major trace element and sr isotopic data agree in indicating that the hkca and sho series evolved by crystal liquid fractionation starting from different parental liquids whereas crustal assimilation appears to have been the leading process during the evolution of ks volcanics mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic sr by addition via subduction of different amounts of crustal material geochemical data however are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization assimilation and mixing of a ca magma in a deep sited magma chamber the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization hkca and sho series and by assimilation of crustal material ks the occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of stromboli is the result of processes occurring within the volcanic system

tephrostratigraphy study for the last 18 000 14 c years in a deep sea sediment sequence for the south adriatic abstract a detailed tephrostratigraphy supported by accelerator mass spectrometry ams 14c dating and isotopic and geochemical analyses has been carried out for a deep sea core collected from the southern adriatic sea which spans the last 18 14c kyr fourteen ash layers have been recognized in the marine core and the origin was determined by comparing their age and geochemistry with tephra detected in terrestrial deposits the geochemical signatures of marine ash layers indicate a prevailing campanian and subordinate etnean and eolian provenances collectively they are attributed to sources in the phlegraean fields lam lagno amendolare ln1 ln2 gm1 c 2 nyt neapolitan yellow tuff c 1 agnano pomici principali ams pf agnano monte spina ast astroni somma vesuvius l9 pomici di base l8 greenish mount etna et1 y1 biancavilla ignimbrite lipari e 1 gabellotto fiumebianco and palinuro seamount pal 1 some of these eruptions have been detected for the first time in marine cores astroni lam l9 l8 and three were detected and dated by marine tephra ln1 ln2 and pal 1 providing new more precise stratigraphic markers for the last 18 kyr in the south adriatic marine record

provenance of volcaniclastic beach sand in a magmatic arc setting an example from lipari island aeolian archipelago tyrrhenian sea lipari an active volcanic island in the aeolian magmatic arc is an excellent area to determine the effects of multiple source lithology climate weathering transport and depositional environment on epiclastic sand composition volcaniclastic sand samples from 12 modern beaches were petrographically characterized using the gazzi dickinson method and the proportions of source rocks in combination with topography in associated coastal drainage basins were quantified using gis several types of bedrock in the 12 drainage basins that are the likely prominent sources for sand at each sampled beach were recognized and divided into two categories of provenance lithotypes lavas and pyroclastic rocks ranging in composition from basaltic andesitic to andesitic to rhyolitic volcanic lithic fragments from lipari beach sand consist of colourless and black glassy volcanic fragments with lathwork felsitic vitric and microlitic textures moreover high amounts of detrital less durable minerals such as pyroxene olivine and fe oxides illustrate how the analysed sands preserve the source rock s provenance signals applying the concept of sand generation index we see that these lithotypes have different propensities to create detritus in terms of both grain size and composition clastic contribution from pyroclastic rock outcrops such as pumice is not found in the size ranges studied suggesting that these pumiceous source rocks probably only produce gravel or very fine sand and silt this finding has implications for the stratigraphic record because pumice clasts ranging from medium to fine grain size could be underrepresented in older volcaniclastic deposits and overrepresented in other size fractions

arc generated blocks with crustal sections in the north atlantic craton of west greenland crustal growth in the archean with modern analogues abstract the ca 700 km long archean craton of west greenland consists of six meso neoarchean ca 3000 2720 ma shear zone bounded crustal blocks that display similar cross sections from south to north ivittuut kvanefjord bjornesund sermilik fiskefjord maniitsoq each block has a southerly upper and a northerly lower zone thus each faces upwards to the south upper zones have prograde amphibolite facies mineralogy and have never been in the granulite facies whereas lower zones reached granulite facies and were partly retrogressed to amphibolite facies upper and lower zones consist predominantly of tonalite trondhjemite granodiorite ttg orthogneisses geochemistry suggests generation by slab melting in subduction settings of island arcs and active continental margins the gneisses contain km thick metavolcanic amphibolite layers typically bordered by km thick layers containing anorthosite and leucogabbro most upper zones contain upper greenschist to amphibolite facies metavolcanic belts including volcaniclastic andesitic rocks the two most prominent metavolcanic belts in the fiskefjord block at qussuk andesitic volcaniclastic rocks garde a a 2007 a mid archaean island arc complex in the eastern akia terrane godthabsfjord southern west greenland journal of the geological society london 164 565 579 and ivisaartoq mafic ultramafic rocks and anorthosite leucogabbro from upper and lower parts of a supra subduction zone system polat a frei r appel p w u dilek y fryer b ordonez calderon j c yang z 2008 the origin and compositions of mesoarchean oceanic crust evidence from the 3075 ma ivisaartoq greenstone belt sw greenland lithos 100 293 321 have island arc geochemical signatures the 2 km thick fiskenaesset complex bjornesund block comprises chromite layered anorthosites leucogabbros and gabbros and local pillow bearing roof pendants from overlying metavolcanic amphibolite the style of deformation changes downwards within crustal blocks upper zones are characterised by linear metavolcanic belts deformed by mostly one major phase of isoclinal folding and lower zones by kilometre scale double triple fold interference patterns everywhere ttg protoliths have intruded anorthositic and volcanic rocks typically along ductile shear zones often so extensively that only anorthositic or amphibolitic lenses are preserved the meso neoarchean crust was thickened by a combination of thrusting isoclinal folding and continued ttg injection dissimilarities in the proportions of anorthositic and metavolcanic rocks in the six blocks suggest that they evolved in several different microcontinents but by similar processes these crustal blocks provide an exceptional example of how continents evolved in the meso neoarchean comparable archean examples in kapuskasing and pikwitonei canada and modern analogues in fiordland new zealand kohistan himalayas southern california batholith peruvian andes and hidaka japan demonstrate that processes of continental growth from island arc to continental arc magmatism and by implication to continental collision were broadly similar throughout most of earth history

adjacent terranes with ca 2715 and 2650 ma high pressure metamorphic assemblages in the nuuk region of the north atlantic craton southern west greenland complexities of neoarchaean collisional orogeny abstract in the gneiss complex of the nuuk region of the north atlantic craton in southern west greenland terrane juxtaposition was followed by neoarchaean folding under amphibolite facies conditions with widespread low pressure recrystallisation 5 kbar and 550 700 c the complex metamorphic overprinting requires that the p t history related to actual terrane assembly has to be extracted from very small relicts of older metamorphic assemblages combined with the u pb dating petrology and geochemistry of metamorphic zircons in the south of the region the faeringehavn terrane eoarchaean orthogneisses is tectonically overlain by a supracrustal package of amphibolites and paragneisses ca 2840 ma felsic volcano sedimentary protoliths this package is juxtaposed against a higher tectonic level represented by the tre brodre terrane 2825 ma orthogneisses and the tasiusarsuaq terrane 2920 2810 ma orthogneisses the terranes were assembled by 2710 2720 ma as shown by dating of granitic sheets intruded along the terrane boundary mylonites in the faeringehavn terrane and in the overlying 2840 ma supracrustal package relict early high pressure assemblages 12 8 kbar 700 750 c are clinopyroxene garnet plagioclase quartz hornblende in mafic rocks and garnet kyanite rutile bearing assemblages in paragneisses these are commonly replaced by lower pressure assemblages 7 5 kbar such as cordierite sillimanite garnet in paragneisses and hornblende plagioclase quartz garnet in mafic rocks in situ partial melting took place during both low and high pressure regimes metamorphic zircon in the high and low pressure assemblages yields dates of ca 2715 ma mostly with errors of the kapisilik terrane 3050 2960 ma orthogneisses and another supracrustal assemblage of amphibolites and ca 2800 ma quartzo feldspathic metasedimentary rocks are exposed north of the faeringehavn terrane and within fold cores along its western margin are bounded by folded neoarchaean mylonites the kapisilik terrane and this supracrustal assemblage include high pressure metamorphic remnants in amphibolites and metasediments metamorphic segregations with garnet clinopyroxene and kyanite respectively that formed at ca 2650 ma these remnants are overprinted by high temperature but lower pressure metamorphic events at ca 2630 2610 and 2580 ma thus remnants of early metamorphism reveal mutually exclusive ca 2715 and 2650 ma high pressure events in adjacent tectonically juxtaposed terranes repeated high pressure metamorphism in adjacent terranes is observed in younger complex collisional orogens

u pb zircon systematics at gruinard bay northwest scotland implications for the early orogenic evolution of the lewisian complex the gruinard bay area of the mainland lewisian complex comprises a metamorphosed suite of archaean trondhjemites and minor granites enclosing remnants of older tonalitic gneiss and mafic to ultramafic enclaves the u pb zircon dating yields ages of 2731 14 ma and 2728 2 ma for two trondhjemite and 2732 4 ma for one granite sample also revealing the presence of large amounts of inherited xenocrystic zircons although the region has been pervasively overprinted by retrogressive events in amphibolite to greenschist facies the textural relations between biotite hornblende quartz and titaniferous minerals indicate that these minerals are pseudomorphs of pyroxene and high ti amphibole formed in hornblende granulite facies structural relations link this metamorphism to a steep northeast trending fabric coeval with the intrusion of the trondhjemites dated at 2730 ma dating of zircon in amphibolite and tonalite enclaves yields complex internal isotopic relations with apparent ages ranging from 2825 to 2740 ma this age range reflects new growth during the 2730 ma metamorphic metasomatic events superimposed on older zircon phases which include combinations of xenocrystic cores and magmatic and or metamorphic growth phases whose mode of formation cannot clearly be resolved by imaging techniques e g cathodoluminescence alone a pegmatitic vein that escaped the d3 strain and related isotopic disturbances yields a precise age of 2792 2 ma which constrains to some degree the earliest orogenic events in the area age relationships displayed in the central block at scourie badcall and in the gruinard bay area indicate that petrogenetic events in both areas were comparable about 2800 ma and that both areas underwent trondhjemitic magmatism about 2730 ma in contrast at gruinard bay there is no isotopic evidence for a period of high grade metamorphism and magmatism at 2490 2480 ma that drastically affected the scourie block indicating that at this stage the two regions occupied different levels of the crust

morpho bathymetric and seismo stratigraphic analysis of the insular shelf of salina aeolian archipelago to unveil its late quaternary geological evolution abstract the distribution and morphological characteristics of the shelves around salina island have been analyzed and integrated with observations from onshore geological field studies in order to improve knowledge about its evolution and to demonstrate how shelf width depth can be used as proxies for reconstructing the development of the volcanic edifice insular shelves form essentially through marine erosion of volcanic centres during stages of reduced or inactive volcanism and are representative of their original extension shelves having larger widths commonly 1000 m and deeper edges over 125 m depth experienced wave erosion during successive cycles of sea level fluctuations and subsidence after their formation thus being indicative of a relatively older age of the eroded volcanic centres accordingly we document offshore salina the occurrence of presently submerged and largely dismantled volcanic centres namely pizzo capo north and fossa delle felci south predating the oldest subaerial products exposed on the adjacent coastal sectors these offshore centres have subsided after their erosion and are no more documented on land furthermore the finding of the largest and deepest shelf around the subaerial remnants of pizzo di corvo volcanic edifice allows relating it to an earlier stage of evolution of salina shedding light on contradictory radiometric ages on land narrower shelves commonly on the whole our results show the importance of integrated field and marine studies to unravel the geological evolution of insular volcanoes and to obtain inferences on their vertical mobility

age and petrology of the late pleistocene brown tuffs on lipari italy late pleistocene volcanic products on lipari consist mainly of pyroclastic surge deposits monte guardia sequence and fine grained brown tuffs radiometric age determination on carbon from thin soils at the top of the tuffs indicate that they have several ages of emplacement ranging from more than 35 000 to 16 800 years ago chemical and microprobe data on glass and mineral fragments from these tuffs show that they belong to a shoshonite or high k series this composition is compatible with an origin related to the magma system of vulcano but not with the magma system on lipari

the stratigraphic role of marine deposits in the geological evolution of the panarea volcano aeolian islands italy using reconstructed unconformity bounded stratigraphy the geological evolution of panarea and surrounding islets can be described in terms of the interaction between the growing volcano and sea level fluctuations from the recognition of marine deposits corresponding to marine oxygen isotope stage mis 5 and of widespread brown tuff type pyroclastic deposits on panarea two first order unconformities u i and u ii of regional stratigraphic significance can be correlated with the island of lipari and adopted as a means of correlation on an inter island scale in the aeolian volcanic district then two second order and three third order unconfomities consisting of erosional surfaces related to minor sea level fluctuations or to subaerial reworking operating during the phases of volcanic inactivity are introduced the construction of the volcanic edifice occurred during seven successive eruptive epochs of local volcanic activity between 150 and 10 ka with intervening dormant periods characterized by the activation of reworking processes in subaerial and marine environments and by the emplacement of widespread pyroclastic deposits of external provenance

volcanic history of lipari aeolian islands italy during the last 10 000 years abstract examination of the volcanic stratigraphy of deposits younger than 10 000 years on lipari indicates four principal periods of volcanic activity related to specific centers the products from each different volcanic center are defined as volcano stratigraphic unit vsu from the oldest these are the canneto dentro gabellotto fiume bianco forgia vecchia and monte pilato rocche rosse vsus the study of textures and dispersal of the deposits permitted the vents to be localized and the recent volcanic history of lipari to be reconstructed the oldest event formed a small explosion breccia cone with a final obsidian lava in the canneto dentro area immediately afterward a complex series of explosions produced the widespread dry surge deposits of the gabellotto fiume bianco sequence this activity ended with the extrusion of a domical lava flow the renewal of activity occurred in the pirrera area with an explosive eruption that produced explosion breccia deposits the last eruptions from this vent were coeval with the first eruption of m pilato the rim of the explosion breccia cone was partially destroyed by the forgia vecchia lava flow m pilato cone grew in a very short period of time due to a continuous swarm of explosive events after a short repose time a series of more energetic and superficial explosions occurred through a vent slightly to the south the extrusion of the rocche rosse lava flow about 729 a d ended this cycle of activity all the volcanic centers follow a quite similar stochastic pattern starting with a fall or surge eruption and ending with effusion of viscous rhyolitic lavas the four centers are aligned along either nw se or ne sw fault systems according to the structural pattern of the island they can be placed into two groups the canneto dentro gabellotto centers and the forgia vecchia m pilato centers a long quiescence 3 500 years separates the activity of these two groups while inside of each the activities were nearly contemporaneous or in rapid succession

deformation of the 125 ka marine terrace in italy tectonic implications in peninsular italy marine terraces and shorelines created during oxygenisotope substage 5e known historically as the tyrrhenian highstand provide a reliable and homogeneous datum of vertical motions during the past 125 000 years published accounts of 121 locations on the tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates the data show arching of southern italy between the tyrrhenian and the adriatic coasts and of the calabrian arc between the sangineto and the longi taormina tectonic lineaments at rates of up to 1 2 mm yr for the past 125 ka they also suggest that the present configuration of the southern apennines is the product of post early pleistocene regional uplift superimposed on tortonian to early pleistocene thrusting uplift patterns are characterised by different wavelength in different geodynamic settings suggesting a close link with the depth of the causative tectonic sources

u pb isotopic evidence for the accretion of different crustal blocks to form the lewisian complex of northwest scotland single zircon and titanite u pb shrimp data presented for tonalite trondhjemite granodiorite ttg suite gneisses and an ultramafic rock from the northern and central regions of the lewisian complex of northwest scotland show that protolith ages of tonalitic gneisses in the northern region 2800 2840 ma are significantly younger than those in the central region 2960 3030 ma further evidence of a major 2490 2480 ma metamorphic event in the central region is documented by a metamorphic zircon associated with a granulite facies ultramafic body a dioritic gneiss from the northern region has also been dated at c 2680 ma the northern region therefore does not comprise reworked central region rocks and consequently the old models for the evolution of the lewisian which were based upon this concept need replacing it is instead proposed that two distinct crustal blocks now the northern and central regions were tectonically juxtaposed along a boundary corresponding to the laxford front juxtaposition would appear to have occurred in proterozoic times as it must have postdated the 2490 2480 ma inverian metamorphism recorded only in the central region and the emplacement of granite sheets restricted to the northern side of the boundary the first recorded event common to both regions is resetting of titanite ages associated with c 1750 ma laxfordian amphibolite facies metamorphism zircon inheritance in rocks of both regions is scarce within one zircon from the northern region a c 3550 ma core was found this represents the oldest known material from the region

the influence of variable topography on the depositional behaviour of pyroclastic density currents the examples of the upper pollara eruption salina island southern italy abstract stratigraphic reconstruction of the upper pollara eruption has allowed for the inference of eruptive mechanisms and the distillation of a sedimentological model for pyroclastic density currents pdcs moving across variable topography the pre eruptive topography in the study area was characterised by a tuff ring like morphology with both inward and outward dipping slopes highly viscous moderately porphyritic dacitic to rhyolitic magmas fed the eruption which was characterised by a vulcanian eruptive style the stratigraphic succession was divided into five eruption units eus which result from different phases of the eruption separated by stases sustained columns occurred only during eu1 while pdc generation dominates eu2 5 lithofacies analysis of the pdc deposits indicates the prevalence of massive coarse grained deposits on the inner slopes of the pollara crater which are interpreted as the deposits of a flow boundary zone dominated by granular flow or fluid escape regimes dune bedded massive to stratified lithofacies dominate the outer slopes of the pollara crater and are interpreted as the deposits of pdcs with flow boundary zones in which traction played a major role thin massive pdc deposits are exposed on the sub horizontal malfa terrace and are interpreted as representative of flow boundary zones dominated by a granular flow regime the occurrence of stacked deposits indicates that most of the pdcs were characterised by unsteady pulsatory behaviour with development of trains of pulses during their transport the downcurrent lithofacies transitions observed for the upper pollara deposits have finally been compared with other similar lithofacies associations which have been described for short lived pdcs at tuff rings in order to discuss the influence of pre eruptive topography on lithofacies association

geodynamic setting and deformation history of an archaean terrane at mid crustal level the tasiusarsuaq terrane of southern west greenland abstract the neoarchaean tasiusarsuaq terrane is situated in the north atlantic craton approximately 50 km south of the capital nuuk and extends for 400 km to the south to the frederikshab isblink it mainly consists of granulite facies and commonly migmatitic grey gneiss narrow supracrustal belts and volumetrically minor late tectonic granites the supracrustal belts have a lithological association of picritic komatiitic and basaltic rocks together with ultramafic dykes and sills with geochemical characteristics typical of an arc type setting the grey gneiss is tonalitic to granodioritic in composition and was emplaced between ca 2 92 and 2 82 ga into crust that is probably represented by the supracrustal rocks the gneiss in turn was intruded by granite dykes at ca 2830 ma 2800 ma and by tonalitic dykes at ca 2770 ma both probably are the result of partial melting of the thickened crust late tectonic tonalitic pegmatites intruded at 2673 5 ma at amphibolite facies conditions the structural evolution from the granulite facies peak to amphibolite facies levels is characterised by three deformation stages d 1 fabrics form only relics in low strain domains of the dominant nw vergent d 2 fold and thrust structures syn tectonic granite and tonalitic dykes date the d 2 thrusting to have occurred between ca 2800 ma and 2700 ma contemporaneously with near isobaric cooling the subsequent d 3 deformation still in the amphibolite facies is marked by e w to ne sw shortening forming upright folds and near vertical strike slip shear zones at ca 2670 2630 ma the final exhumation of the terrane likely occurred first during the proterozoic and was probably mainly driven by erosion the granulites of the tasiusarsuaq terrane formed at an orogenic margin in a compressive regime a first orogenic cycle 2 8 2 7 ga here termed the tasiusarsuaq orogeny resulted in thrusting of the terrane on a rigid foreland represented by the faeringehavn terrane in the north the tasiusarsuaq granulites were further affected by a second archaean orogeny 2 67 2 58 ga the kapisilik orogeny which caused transcurrent deformation and only insignificant exhumation to mid crustal levels significantly there is no evidence that the exhumation of the granulite facies tasiusarsuaq terrane was driven by archaean extension in contrast to many modern situations where granulites are exhumed by extension related to magmatic underplating and delamination of the lithosphere the thickened tasiusarsuaq terrane was possibly stabilised due to the low density differences and equilibration by melt extrusion during granulite facies metamorphism stabilisation of the crust and lack of lithospheric delamination is therefore regarded as being more common in archaean orogens compared to younger orogens

monte guardia sequence a late pleistocene eruptive cycle on lipari italy this paper documents a complex sequence of interbedded lapilli fall base surge and pyroclastic flow deposits here named the monte guardia sequence that erupted from volcanic centers in the southern part of lipari aeolian island arc radiocarbon data from ash flow tuffs above and below this sequence bracket its eruption between 22 600 and 16 800 years ago geologic evidence however suggests that this single eruptive cycle had a more restricted duration of years to tens of years the basis for our interpretations comes from data measured at 38 detailed sections located throughout the island the monte guardia sequence rests on a series of lower rhyolitic endogenous domes in the southern part of lipari and it covers the oldest lavas lahars and pyroclastic flows in the north only in the northeast part of the island is it covered by younger deposits which there consist of lapilli tuffs and lavas of the monte pilato rhyolitic cycle the deposit ranges in thickness from more than 60 m surrounding the vents in the south to less than a few decimeters at 10 km distance in the north throughout most of the island the monte guardia sequence overlies a thin andesitic lapilli fall layer which is a key bed for correlation this lapilli tuff probably erupted from a volcanic center on another island of the aeolian arc possibly salina the principal activity of the monte guardia sequence started with an explosion that formed a continuous breccia blanket covering most of the island some pumiceous blocks within this breccia are composed of alternating bands of acidic and andesitic composition suggesting that the initiation of pyroclastic activity could have been triggered by magma mixing typical monte guardia sequence consists of explosive products that grade from magmatic pumice fall to phreatomagmatic base surge character the eruptive cycle is characterized by a number of energy decreasing megarhythms that start with a lapilli fall bed and end with a base surge set that progresses through sand wave massive and planar beds isopach maps of the fall and surge deposits indicate that both types were directed to the northwest by prevailing winds existing topographic relief was an additional factor that affected the emplacement of surge products at the end of the cycle andesitic pyroclastic flows and rhyolitic endogenous domes were emplaced above the monte guardia deposits near the vent

temporal evolution of a three component system the island of lipari aeolian arc southern italy the volcanic products from lipari define an evolutionary trend with a high gradient of k enrichment similar to the calc alkaline to potassic volcanism of other islands in the aeolian arc stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages the first stage from 223 to 42 ka consists of six eruptive cycles and is characterized by basalts and basalt andesites showing progressive increase in both sio2 and k2o contents with time the second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products fractional crystallization assimilation and mixing models suggest that the geochemistry of lipari volcanism evolved with time by a complex interplay between two mantle derived components one sub alkaline and the other alkaline in addition to crustal melts and or crustally derived materials a petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro and microscopic features melts from the crustal and mantle end members are almost always present in the system but the relative proportions appear to vary with time the sub alkaline mantle component source of tyrrhenian tholeiites is an important contributor to the early evolution of the volcanism in lipari input from the alkaline mantle component source of the roman comagmatic province increases with time and the crustal component becomes dominant in the later activity the preferred petrogenetic model for the temporal evolution of the volcanic system in lipari involves melting initially caused by an increase in the thermal input related to the opening of the tyrrhenian sea and or to subduction processes the quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts

timing of late archaean terrane assembly crustal thickening and granite emplacement in the nuuk region southern west greenland abstract a breakthrough in understanding the structural and metamorphic evolution of archaean gneiss complexes occurred with the recognition that the nuuk region of southern west greenland comprised separate terranes assembled in the late archaean from northwest to southeast these are the akia 3220 2970 ma akulleq 3870 3600 and 2820 ma and tasiusarsuaq 2920 2860 ma terranes the minimum time of assembly is recorded by the first event common to all component terranes using shrimp u pb zircon geochronology the oldest events common to all terranes including emplacement of crustally derived granites contemporaneous metamorphism and anatexis have been dated at 2710 2725 ma in the akulleq terrane areas where in situ diatexite formed abundant granitoid sheets were intruded and common growth of metamorphic zircon mostly low th u in most lithologies occurred in the akia and tasiusarsuaq terranes there was only intrusion of a lesser number of 2720 ma granitoid sheets because metamorphic zircons of that age have not been found the 2720 ma event is interpreted as marking or shortly following terrane assembly when the diverse components of the akulleq terrane were tectonically juxtaposed with the other two this new documentation of metamorphic and associated igneous events within an accreting cratonic region is an illustration that the stabilisation of extensive areas of archaean gneisses can be due to accretionary tectonics long after the individual components were first formed

stratigraphy and significance of brown tuffs on the aeolian islands southern italy abstract brown tuffs bt are volcaniclastic ash deposits prominently represented in the stratigraphic profiles of all the aeolian islands and capo milazzo on the northern coast of sicily detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period ca 80 ka bp up to 4 5 ka bp age of the overlying punte nere pyroclastic products on vulcano the most complete bt succession is documented on lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers local volcanic products paleosols and epiclastic deposits and the occurrence of local erosive surfaces inter island occurrence of ischia tephra a widely known tephra layer in the aeolian archipelago dated at 56 ka bp and monte guardia pyroclastics from lipari dated at 22 20 ka bp subdivides the bt succession in upper ubt intermediate ibt and lower bt units lbt which can be correlated at regional level the lbt was emplaced between 80 and 56 ka bp the ibt between 56 and 22 ka bp and the ubt between 20 and 4 5 ka bp on the basis of stratigraphy similarity in lithology and textural features morphology of glass fragments composition and consistency of thickness and grain size variations ubt units correlate with piano grotte dei rossi tuffs on vulcano island they were generated by pulsating hydromagmatic explosive activity giving rise to pyroclastic density currents spreading laterally from a source located inside the la fossa caldera on vulcano island composition is in agreement with this hypothesis since ubt compositional features match those of vulcano magmas erupted in that period the effect of co ignimbrite ash clouds or associated fallout processes from sustained eruptive columns is seen to explain the presence of ubt in areas further away from the suggested source e g salina and lipari islands and capo milazzo the origin of ubt exposed on panarea island is still a matter of debate due to contrasting compositional data due to large uniformity of lithological textural and componentry characters with respect to the ubt the lower portions of the bt succession lbt ibt are considered to be the result of recurrent large scale hydromagmatic eruptions of similar type moreover for the ibt units the correlation with monte molineddo 3 pyroclastics of vulcano island on the basis of lithological compositional and stratigraphic matching again suggests source s related to the vulcano plumbing system and located within the la fossa caldera

re evaluating ambiguous age relationships in archean cratons implications for the origin of ultramafic mafic complexes in the lewisian gneiss complex abstract archean ultramafic mafic complexes have been the focus of important and often contentious geological and geodynamic interpretations however their age relative to the other components of archean cratons are often poorly constrained introducing significant ambiguity when interpreting their origin and geodynamic significance the lewisian gneiss complex lgc of the northwest scottish mainland a high grade tonalite trondhjemite granodiorite ttg terrane that forms part of the north atlantic craton nac contains a number of ultramafic mafic complexes whose origin and geodynamic significance have remained enigmatic since they were first described previous studies have interpreted these complexes as representing a wide range of geological environments from oceanic crust to the sagducted remnants of archean greenstone belts these interpretations which are often critically dependent upon the ages of the complexes relative to the surrounding rocks have disparate implications for archean geodynamic regimes in the nac and globally most previous authors have inferred that the ultramafic mafic complexes of the lgc pre date the ttg magmas this fundamental age relationship is re evaluated in this investigation through re mapping of the geodh nan sgadan complex where tonalitic gneiss reportedly cross cuts mafic rocks and new mapping of the 7 km2 ben strome complex the largest ultramafic mafic complex in the lgc alongside detailed petrography and spinel mineral chemistry this new study reveals that despite their close proximity in the lgc 12 km the ben strome and geodh nan sgadan complexes are petrogenetically unrelated indicating that the lgc and thus nac records multiple temporally and or petrogenetically distinct phases of ultramafic mafic archean magmatism that has been masked by subsequent high grade metamorphism moreover field observations and spinel mineral chemistry demonstrate that the ben strome complex represents a layered intrusion that was emplaced into a ttg dominated crust further to representing a significant re evaluation of the lgc s magmatic evolution these findings have important implications for the methodologies utilised in deciphering the origin of archean ultramafic mafic complexes globally where material suitable for dating is often unavailable and field relationships are commonly ambiguous

structure of the palaeoproterozoic nagssugtoqidian orogen south east greenland model for the tectonic evolution abstract the palaeoproterozoic nagssugtoqidian orogen extends over 250 km along the east coast of greenland around the settlement of tasiilaq the orogen includes archaean rocks from the adjoining rae craton to the north and the north atlantic craton to the south and palaeoproterozoic rocks the rae craton consists of orthogneiss and amphibolite included in the schweizerland and kuummiut terranes and is tectonically overlain in the kuummiut terrane by ca 2100 2200 ma units that include marble meta pelite and psammite and amphibolite assigned to the helheim and kuummiut units the kuummiut terrane was probably subducted underneath the se trending ca 1885 ma ammassalik intrusive complex which has a high temperature metamorphic halo and is characterised by a change from sinistral faulting to pure shear deformation the southern isortoq terrane consists of medium pressure amphibolite facies bimodal meta volcanic and the rocks of the kuummiut terrane were tectonically imbricated in ene verging structures during ca 1870 ma high pressure metamorphism this was followed by ne sw convergence and close to orthogonal extrusion in the weakened crust which is characterised by partial melting during decompression the rocks of the isortoq terrane were imbricated in a se vergent thrust and ramp system either during oblique subduction of the kuummiut terrane or an earlier tectonic stage elsewhere ne sw compression as in the northern terranes formed sw vergent thrust systems and folds this was most likely caused by a change in the regional stress field during collision between ca 1870 and 1820 ma in the north the schweizerland terrane was juxtaposed to the kuummiut terrane in southeasterly direction causing refolding of earlier structures in the lower amphibolite facies this hinteland type of deformation was possibly related to tectonism in western greenland the latest recognised deformation event was during ca 1740 1680 ma associated with ne sw extension which is interpreted as orogenic collapse the complex structural evolution of the orogen was caused by oblique convergence during wsw directed subduction the convergence of irregularly shaped cratons and the change of the regional stress field from ene wsw to nw se during progressive collisional tectonics between the two archaean cratons

composite detrital and thermal remanent magnetization in tuffs from aeolian islands southern tyrrhenian sea revealed by magnetic anisotropy this paper reports on the complex relation between rock emplacement and remanence acquisition in tuffs deposited by pyroclastic density currents disclosed by systematic measurements of the anisotropy of magnetic susceptibility and natural remanent magnetization nrm thermal demagnetization shows that the nrm consists of two components with different blocking temperature spectra the direction of the low temperature component is consistent with the geocentric axial dipole value whereas the high temperature component has dispersed directions the magnetic fabric is oblate the magnetic foliation is close to the bedding and the lineations are generally dispersed along a girdle within the foliation plane the directions of the magnetic lineation and the high temperature remanence component of individual specimens are close to each other this correspondence suggests that the high blocking temperature grains acquired a remanence aligned to their long dimension before deposition while cooling within the explosive cloud and the moving pyroclastic current thereafter during deposition the traction processes at the base of the current oriented the grains along the flow direction and affected both fabric and high temperature remanence this nrm component results from mechanical orientation of previously magnetized grains and is thus detrital in origin a second thermal component was then acquired during the cooling of the low blocking temperature grains after deposition these results show that nrm in fine grained pyroclastic rocks is affected by the earth s magnetic field as well as the emplacement processes and that magnetic fabric data are essential to unravel its complex nature

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

eruptive and emplacement mechanisms of widespread fine grained pyroclastic deposits on vulcano island italy tufi di grotte dei rossi inferiori are thick ash deposits representing the most voluminous stratigraphic unit on vulcano island the deposits are related to hydromagmatic eruption which occurred under shallow water inside a caldera depression grain size data and results of sem investigation allow the character of the transporting medium solid material concentration in the cloud during the lateral expansion and the nature and role of the fluids present at the time of deposition to be constrained we suggest that the eruption was characterized by closely timed hydromagmatic pulses giving rise to eruption clouds rich in water vapor and steam the coarser material was not significantly transported in the eruptive cloud and it probably deposited in the caldera depression area the finer material was extensively transported in the cloud creating turbulent flows which surmounted the caldera rim barrier and dispersed in a southward direction forming widespread deposits in the piano area lower concentrated flows produced laminated deposits of more limited dispersion whereas higher concentrated flows formed more dispersed thicker massive layers

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

conditions of archean granulite metamorphism in the godthab fiskenaesset region southern west greenland the nordlandet peninsula akia terrane and the tasiusarsuaq terrane in southern west greenland were metamorphosed to granulite facies at 3 0 and 2 8 ga respectively temperatures of metamorphism are estimated using magnetite ilmenite garnet orthopyroxene garnet clinopyroxene and garnet biotite thermometers barometry has been carried out in the two terranes using eight different garnet barometers a uniform set of activity models for all minerals including the garnet activity model of newton et al 1986 is applied to each barometer in order to permit comparison pressure estimates using the different barometers are generally quite consistent 1 5 kbar use of the newton et al 1986 garnet activity data results in pressures similar to those obtained using other garnet activity models peak metamorphic conditions on the nordlandet peninsula are estimated to have been 800 50 c 7 9 1 0 kbar values of logfo2 are estimated to have been 1 1 to 2 0 above the quartz magnetite fayalite buffer from assemblages of magnetite ilmenite and quartz magnetite ferrosilite peak metamorphic conditions in the tasiusarsuaq terrane are estimated to have been 780 50 c 8 9 1 0 kbar estimates of fh2o and fco2 using biotite amphibile grossular anorthite and grossular scapolite equilibria are low in both terranes these results suggest that granulite metamorphism was fluid absent in both terranes and that the metamorphism in the akia terrane and possibly also in the tasiusarsuaq terrane was initiated by the injection of large volumes of magma into the lower crust