geodynamic implications of earthquake data in the southern tyrrhenian sea abstract data from short period seismic stations operating in calabria sicily and the aeolian islands have been used to investigate earthquake properties of the southern tyrrhenian lithosphere the results have been analyzed taking into account other geophysical and geological information available in the literature for the same region with the main purpose of contributing to the definition of local geodynamic processes space distribution and focal mechanisms of earthquakes support the hypothesis of southeastward migration of the southern tyrrhenian lithosphere shared by several authors in their tectonic modelling of the area we find that most seismicity appears to be related to two main faults crossing the aeolian island archipelago sisifo and vulcano and propose that these faults are important dislocation structures associated with the lithosphere migration process we also give a detailed picture of the seismic behaviour of the above mentioned fault systems by analyzing the earthquake depth distribution focal mechanisms seismic clustering and strain release some degree of activity was also detected at the eastern boundary of the southern tyrrhenian area calabrian arc in particular our results demonstrate that in this highly stressed zone of contact between different tectonic units tyrrhenian and ionian basins strain is released under seismic form up to depths of the order of 25 km in the crust and not just in the shallowest structures as proposed by other authors

calcium isotope constraints on the marine carbon cycle and caco3 deposition during the late silurian ludfordian positive δ13c excursion abstract this study investigates calcium isotope variations 44 40 ca in late silurian marine carbonates deposited in the prague basin czech republic which records one of the largest positive carbon isotope excursion cie of the entire phanerozoic the mid ludfordian cie which is associated with major climatic changes abrupt cooling and global sea level fluctuations our results show that during the onset of the cie when 13 c increases rapidly from 0 to 8 5 44 40 ca remains constant at about 0 3 0 1 relative to nist 915a while 87sr 86sr in well preserved carbonates are consistent with a typical ludfordian seawater composition ranging from 0 70865 to 0 70875 such decoupling between 13 c and 44 40 ca trends during the onset of the cie is consistent with the expected order of magnitude difference in the residence times of ca 10 6 yr and c 10 5 yr in the open ocean suggesting that the mid ludfordian cie was caused by processes where the biogeochemical pathways of c and ca in seawater were mechanistically decoupled these processes may include i near shore methanogenesis and photosynthesis ii changes in oceanic circulation and stratification and or iii increased production and burial of organic c in the global ocean the latter however is unlikely due to the lack of geological evidence for enhanced organic c burial and also because of unrealistic parameterization of the ocean c cycle needed to generate the observed cie over the relatively short time interval in contrast higher up in the section where 13 c shifts back to pre excursion baseline values there is a correlated shift to higher 44 40 ca values such coupling of the records of ca and c isotope changes in this part of the study section is inconsistent with the abovementioned differences in oceanic ca and c residence times indicating that the record of 44 40 ca changes does not faithfully reflect the evolution of the oceanic ca reservoir but rather some local processes in the prague basin these can be related to restricted elemental sediment cycling involving mixing of isotopically distinct ca sources and carbonate polymorphs calcite vs aragonite and or possible kinetic ca isotope effects due to changes in the rate of marine carbonate formation evidence supporting the kinetic effect in the studied mid ludfordian carbonates is indicated by correlated 44 40 ca and sr concentration data r s 0 76 p 0 001 n 41 yielding a slope of 0 00097 which is indistinguishable from the kinetic slope of abiotic calcite precipitation kinetic processes are integral to the model of rapid carbonate precipitation recently proposed by kozlowski 2015 to explain the origin of the mid ludfordian cie involving intense methanogenesis photosynthesis in near shore settings coupled with rapid caco3 precipitation i e massive whitings events and eustatically controlled carbonate hypersaturation of seawater more ca isotope studies are needed to shed light on the question of whether kinetics or mineralogy controls the coupled variations in carbonate 44 40 ca and 13 c records observed in this study and other large positive cies in geological record

volcanism and aseismic slip in subduction zones the spatial and temporal relationship of volcanism to the occurrence of large earthquakes and convergent plate motion is examined the number of volcanic eruptions per year in a convergent zone is found to be linearly related to the aseismic slip component of plate motion if the aseismic slip rate is low coupling between converging plates is strong then the primary manifestation of tectonic activity is the occurrence of large earthquakes with only infrequent volcanic activity if however the aseismic slip rate is high coupling is weak then there are few large earthquakes and volcanism is the principal manifestation of tectonic activity this model is consistent with the spatial distribution of large earthquakes and active volcanoes in the circum pacific area it is tested by examining the extent of volcanic activity in the rupture zones of the 1952 1973 sequence of earthquakes in the japan kurile islands area the number of volcanic euptions along these zones during the interval between large earthquakes is used to compute the aseismic slip rates for these segments based on the relationship developed in this study the aseismic slip rates so computed agree with those determined from the earthquake history of the area and rates of plate motion themore agreement suggests that in the interval between large earthquakes the aseismic plate motion is manifested in a specific number of volcanic eruptions therefore in areas with adequate historial data it should be possible to use the model developed in this study to monitor volcanic eruptions for long term prediction of large earthquakes less

early silurian wenlockian δ13c profiles from the cape phillips formation arctic canada and their relation to biotic events geochemical data from the cape phillips formation arctic canada are examined in association with three silurian biotic crises in the graptolite community the early wenlockian ireviken mid wenlockian cyrtograptus lundgreni and end wenlockian colonograptus ludensis extinction events positive 13corg excursions are associated with the ireviken and c lundgreni events but not the co ludensis event the ireviken and c lundgreni excursions are recognized worldwide and are herein interpreted to be the result of carbonate weathering in response to eustatic sea level drop the c lundgreni excursion is of greater magnitude in the more proximal basin margin section at abbott river cornwallis island and is explained by the amplification of a more strongly positive 13c signature in shallower parts of an epeiric basin during increased exposure and weathering of the carbonate shelf excursion c5 within the c praedeubeli c deubeli zone is also of regional significance as it occurs in both the abbott r

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

carbon isotope excursion near the wenlock ludlow silurian boundary in the anglo welsh area oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from several exposures that show the boundary between the wenlock and ludlow series in the classic silurian areas of wales the welsh borderland and the west midlands of england our data indicate a monotonic decline in 13 c from positive to negative values across the boundary between the much wenlock limestone formation wenlock series and the lower elton formation ludlow series and correlatives in all sites investigated a slightly earlier negative excursion is also present in the upper wenlock strata of two of these localities both negative 13 c excursions appear to be contemporaneous with episodes of increased ocean ventilation and eustatic sea level lowstand postulated by kemp at least one and possibly both of the late wenlock carbon isotope depletions can also be related to the decline in pelagic graptolite diversity the distribution of the carbon isotope depletion in both carbonate platform and off shelf facies implies that this trend is unlikely to have been caused by local diagenetic alteration isotope chemostratigraphy may also provide an extra correlation tool that can be integrated with traditional biostratigraphic methods for silurian strata

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

dating of the upper pleistocene holocene volcanic activity of la palma using the unspiked k ar technique abstract combined unspiked k ar dating and detailed mapping have established the eruptive chronology of the cumbre vieja volcano in the canary islands the cv volcano is a large polygenetic volcano subaerial area 220 km2 subaerial volume 125 km3 elevation above sea level 2000 m which rests on the southern flank of the older taburiente cumbre nueva volcano we defined two stratigraphic units by their relationship to the development of coastal cliffs developed around the cumbre vieja volcano a cliff forming series and a scree forming series which is draped over the cliffs and forms the coastal platforms at their bases k ar ages were measured from 20 samples from the two series there are no discrepancies between k ar ages and the stratigraphy the k ar ages of one flow compare well with 14 c determinations 14 c 3 2 0 1 ka k ar 4 2 ka the ages of the scree forming series range from 3 2 ka to 21 2 ka the cliff forming series ages range from 20 2 ka to 123 3 ka but as the base of the sequence is not exposed the growth of the cumbre vieja volcano must have begun substantially earlier the boundary between the two coincides with the low sea level stand in the last glacial maximum which we infer to have been a period of intense coastal erosion dated samples from the upper part of the taburiente cumbre nueva volcano range in age from 853 10 ka to 566 8 ka the age of the youngest taburiente cumbre nueva volcano sample provides an upper bound on the age of the subsequent cumbre nueva giant lateral collapse

relationships among crustal structure volcanism and strike slip tectonics in the lipari vulcano volcanic complex aeolian islands southern tyrrhenian sea italy abstract the lipari vulcano volcanic complex lvvc aeolian arc southern tyrrhenian sea italy develops along a strike slip fault system that bisects the aeolian arc the lvvc crustal structure is investigated by applying seismic methods to two data sets p wavefronts generated by local and distant events constrain the shallow velocity structure dss data provide shape and depth of the main crustal discontinuities the obtained velocity model shows that the lvvc shallow structure is characterized by the presence of two sharp lateral discontinuities the northern discontinuity bounds a low velocity basin like structure including the la fossa caldera and mt guardia caldera depressions the southern discontinuity coincides with the southern boundary of a high velocity diffractor located beneath the la fossa cone direct modeling of dss data define three crustal discontinuities showing a complex geometry the intra crustal interfaces and the moho discontinuity show an upheaval beneath the lvvc central sector the estimated crustal velocities are lower than those generally reported for the continental crust this feature is due to the high heat flux and fluid circulation affecting the lvvc area the ratio between the thickness of the upper and lower crust and the presence of the moho upheaval are consistent with that reported for continental areas affected by extensional strain the collected geophysical data combined with volcanological and structural information indicate that a the mt guardia and la fossa caldera depressions represent the surface expression of a single structure whose formation is mainly due to tectonic processes b the lvvc crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from arc related to rift volcanism in addition results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio between magmatic overpressure and tectonic stress this suggests a passive mechanism of mantle upwelling the mantle upwelling is due the post collisional normal strike slip tectonics affecting the aeolian arc

the mid homerian silurian biotic crisis in offshore settings of the prague synform czech republic integration of the graptolite fossil record with conodonts shelly fauna and carbon isotope data abstract the middle homerian biotic crisis resulted in the almost complete eradication of graptolites the shale dominated kosov quarry section central bohemia preserves the most complete graptolite record across the crisis in peri gondwanan europe the pre extinction graptolite assemblage of the upper lundgreni biozone composed of ten species vanished in three extinction phases recognized in an interval 1 6 m thick the crisis commenced with the increasing dominance of generalist taxa and subsequent extinction of several abundant species including cyrtograptus lundgreni the second phase coincided with the extinctions of genera cyrtograptus and testograptus whereas long ranging generalist monograptids prevailed before they became extinct as the crisis culminated in its third phase in the flemingii biozone the lower part of the overlying parvus biozone contains only pristiograptus parvus which became abundant in the upper part of the biozone together with incoming gothograptus nassa the recovery interval is marked by a moderate diversification of monograptids and retiolitids the extinction did not affect the diversity of pelagic cephalopods although their abundance was reduced a bivalve dominated benthic fauna disappeared throughout the extinction interval and re appeared not earlier than in the latest homerian it was temporarily replaced by a time specific fauna of anachronistic trilobites and brachiopods the extinction interval coincided with sea level fall indicated by limestone slump beds in a generally shaly succession the post extinction interval corresponds with a lowstand systems tract with deposition of condensed shelly limestone and burrowed shale a positive carbon isotope excursion started in the flemingii biozone and 13c values increased up to the lower parvus biozone above which the plateau of the first peak started the beginning of the graptolite extinction predated the early phase of the late homerian carbon isotope excursion the terminal phase of the extinction nevertheless coincided with the onset of the carbon isotope excursion and change in benthic fauna

juan de fuca plate aseismic subduction at 1 8 cm yr volcanic activity in the cascades in historic times suggests that the juan de fuca plate is underthrusting aseismically at about 1 8 cm yr this rate of underthrusting is identical to the rate computed from sediment studies

the role of the crust in the magmatic evolution of the island of lipari aeolian islands italy volcanic rocks on the island of lipari show the entire range of sr nd pb isotopic compositions displayed by other islands in the aeolian archipelago the rapid isotopic evolution of subaerial volcanic rocks on lipari towards crustal values together with the appropriate isotopic composition of the neighbouring calabrian crust serre indicate that many geochemical characteristics observed in the lavas can be attributed to contamination and mixing with crustal materials and melts interpretation of the data is complicated by the fact that underplating onto the crust mantle boundary and the specific lithologies present in the crustal section differ underneath each individual sector of the island in the central and northern parts of the island metapelitic rocks were incorporated to provide the more radiogenic sr isotopic compositions of some lavas the products from m guardia in the southern part of lipari where activity is restricted to the last 30 40 ka bear geochemical similarities to the island of vulcano where it is proposed that considerable remobilization of the crust took place in the presence of mafic mantle derived melts on lipari the petrogenetic processes of magma mixing and assimilation dominate over fractional crystallization and the observed increase of k2o over na2o can be correlated with contributions from metapelitic crustal lithologies it is suggested that the variability in isotopic composition and the budget of alkalis na2o versus k2o in the lavas can be explained by invoking a heat source from an intruding asthenospheric morb type mantle into a cooler lithospheric crust mantle during the opening of the tyrrhenian basin

early silurian sea level changes global sea level fluctuated markedly during the early silurian probably as a result of the waxing and waning of ice sheets in the south american portion of gondwana the highest sea levels of the silurian are recorded by the telychian upper crispus lower griestoniensis and spiralis lower lapworthi biozones other highstands occurred in the early aeronian during the convolutus zone mid aeronian guerichi zone and late turriculatus zone early telychian and early sheinwoodian low sea levels characterized much of the argenteus and sedgwickii zones aeronian the utilis subzone late guerichi early turriculatus zones early telychian the late telychian commencing in the mid lapworthi zone and after a period of apparently only small amplitude sea level fluctuations in the late sheinwoodian and earliest homerian the mid late homerian in particular the early nassa zone facies and faunal changes in the lower silurian do not support the p and s model of jeppsson and others but are consistent with the sea level changes proposed herein mid telychian marine red beds appear to have been deposited during a minor sea level fall immediately after a period of very high sea levels rather than during a transgressive episode as previously suggested comparison of the sea level curve presented herein with those constructed in the past is hampered by the lack of precision currently possible in the correlation of early silurian deep water graptolitic and shallow water shelly sequences improving the precision of this correlation should be a priority for future research

the homerian late wenlock silurian carbon isotope excursion from perunica does dolomite control the magnitude of the carbon isotope excursion the 13ccarb records from two geographically close sections of the shallow water kozel limestone member late wenlock motol formation perunica microplate significantly differ in the magnitude of the homerian carbon isotope excursion as well as in their dolomite content the present paper tests a hypothesis as to whether a difference of about 2 in the magnitude of the 13ccarb anomaly is caused by the different content of dolomite which could be enriched in both 13c and 18o relative to coexisting calcite as has been suggested by experimental data the new data obtained reveal that the 18o composition of calcite and dolomite was probably controlled by the pore fluid composition during limestone diagenesis and that both carbonates seem to be close to equilibrium in oxygen isotope composition on the other hand the 13c values of dolomite are similar to those of calcite and thus the carbon isotope composition of both carbonates was probably determined by the precursor carbonate composition moreover

volcanological and geochemical evolution of filicudi aeolian islands south tyrrhenian sea italy this paper reports on field petrological geochemical and isotopic characteristics of volcanic rocks from filicudi island aeolian arc southern tyrrhenian sea with particular attention to the recognition of temporal and geochemical variations of magma activity the filicudi volcano consists of basaltic basaltic andesitic and high k andesitic lavas and pyroclastic deposits it represents the emergent part of a complex structure parallel to the main regional structural lineaments stratigraphic investigations and dating have defined four main cycles of activity interrupted by periods of quiescence the main stratigraphic sequences reconstructed on filicudi display irregular variations of rock evolution over time with recurrent reversals to more basic compositions magmas erupted from different vents during the first three cycles of activity display overall similar petrological and geochemical characteristics some major and trace elements define slightly scattered correlations with silica sr abundances are particularly scattered with a large range of values in basic rocks sr isotope ratios range between 0 704270 and 0 704740 and do not exhibit good correlations with geochemical parameters fractional crystallization associated with several episodes of mixing processes and crust assimilation are considered to be responsible for the complex evolution of the filicudi magma mafic magmas erupted during the last cycle of activity at la canna centre show increasing k na mg al rb sr and decreasing ba nb ba rb ratios in respect to the older basalts these characteristics are considered to reflect a derivation from a different mantle source

inherited argon in a pleistocene andesite lava 40ar 39ar incremental heating and laser fusion analyses of plagioclase by using 40 ar 39 ar incremental heating and laser fusion techniques xenocrystic plagioclase was discovered in a late pleistocene andesitic lava that erupted through the andean cordillera inherited argon in the xenocrysts is as much as 450 times older than the host lava the age of which is independently known and is an obstacle to dating the lava by using a whole rock sample the xenocrysts are impossible to identify from petrography or chemical parameters such as their k ca ratios holocrystalline groundmass carefully separated from plagioclase and other phenocrysts gives an accurate 40 ar 39 ar age for the lava the xenocrysts could not have been degassed for more than several days in the magma and probably were assimilated from paleozoic rocks buried under kilometers of mesozoic and tertiary arc rocks composing the cordillera in central chile the required magma ascent velocity on the order of kilometers day is extraordinarily high compared to the 10 4 km day minimum implied by the 226 ra excess in continental arc lavas these data permit magma migration and storage in the mantle and lower crust for as much as thousands of years followed abruptly by rapid ascent to the surface

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

carbonate platform evolution and conodont stratigraphy during the middle silurian mulde event gotland sweden evidence from sedimentology and conodont biostratigraphy is used to reinterpret the mid homerian late wenlock succession on gotland sweden a new conodont zonation includes from below the ozarkodina bohemica longa zone including five subzones the kockelella ortus absidata zone and the ctenognathodus murchisoni zone two taxa are named ozarkodina bohemica longa and pseudooneotodus linguicornis these new zones are integrated with facies in order to correlate strata and infer the major depositional environments and the controls on deposition during the mid homerian mulde event reef associated and skeletal carbonate deposition predominated before and after the event i e during the uppermost o s sagitta zone and again in the c murchisoni zone these periods are characterized by the expansion of reefs and shoal facies across marls in the topmost slite group on eastern gotland and in the lower parts of the klinteberg formation on western gotland respectively the intervening o b longa and k o absidata zones are initially characterized by rapid facies changes including siliciclastic deposition and later stabilisation of a carbonate depositional system the composition of sediments and depositional rates are closely related to the creation and destruction of accommodation space and reflects a classical case of depositional bias of the carbonate and siliciclastic depositional systems based on coastline migration stratal boundaries and the stratigraphic position of major reef belts several facies associations can be fitted into a sequence stratigraphic model for platform evolution a highstand systems tract hst situation prevailed prior to and during the early part of the event the upper slite group including the lower frjel formation this hst was characterized by prolific skeletal production and regional reef development except for during the latest stage when carbonate production declined at the onset of the mulde event platform growth was inhibited during a following regressive systems tract rst when regional siliciclastic deposition predominated the gannarve member the subsequent lowstand resulted in regional emersion and karstification i e a complete termination of the platform the post extinction transgressive systems tract tst is exclusively composed of non skeletal carbonates the bara member of the halla formation re occurrence of reefs and a prolific skeletal production marks platform recovery during a second hst the remaining halla and the lower klinteberg formations integration of high resolution biostratigraphy and sequence stratigraphy reveals that the major physical control on platform evolution was a 5th order eustatic sea level change during an early part of the mulde event and that the bulk of the strata accumulated when the platform aggraded and prograded during the highstand systems tracts thus silurian oceanic events and associated sea level changes had profound impact on the neritic carbonate system the gotland based middle and late homerian sea level curve shows two rapid regressions both leading to truncation of highstand systems tracts the first lowstand occurred at the very end of the c lundgreni chron and the second at the end of the co ludensis chron the intervening interval was characterized by stillstand or possibly slow transgression

comparison of seismicity parameters in different subduction zones and its implications for the cascadia subduction zone the cascadia subduction zone is a young subduction zone with associated volcanic activity but with no history of large thrust earthquakes associated with it as is characteristic of other subduction zones this has led to questions about the potential for great earthquakes associated with this subduction the seismic potential associated with this subduction has been investigated in this study by examining and comparing the number of shallow earthquakes with magnitude 6 which have occurred in different subduction zones since 1910 this examination shows that all subduction zones exhibit a higher level of activity than cascadia furthermore two of these zones with similar rates of plate motion and age at subduction the rivera plate and southwest japan have not only experienced great earthquakes but show a higher rate of activity than the cascadia zone the activity rate in subduction zones with predominantly aseismic slip is also higher than the activity rate in the cascadia zone earthquake activity in the rupture zones of great earthquakes both before and after the occurrence of great earthquakes is higher than the activity rate in the cascadia zone these results therefore suggest that the low rate of activity in the cascadia zone is unusual and supports the idea that the subduction here is different and that perhaps the potential for great earthquakes cannot be extrapolated simply on the basis of certain similarities between the cascadia zone and other subduction zones with a history of great earthquakes the low rate of earthquake activity in the cascadia zone can however be explained on the basis of the combined effect of low rate of plate motion significant aseismic subduction and young age at subduction the activity rate in the cascadia zone is consistent with the activity rates in other subduction zones if it is assumed that much of the plate motion is accommodated aseismically the seismic slip rate associated with this subduction zone is a small fraction of the rate of plate motion and therefore even if the potential for great earthquakes may exist the return period for great earthquakes will be much longer 2 or 3 times than in other zones with similar characteristics such as the rivera plate or southwest japan

carbon isotope event markers through the wenlock pridoli sequence at ohesaare estonia and priekule latvia abstract the ohesaare borehole in the northern part of the silurian baltic gulf penetrates shallow and deep shelf marlstones limestones and dolostones the priekule borehole in the deep shelf belt of the basin was drilled through marlstones and graptolitic mudstones most of the successions except the upper part are characterized by a high sr ca ratio close to marine calcites suggesting good preservation of carbonate material conodont alteration indices are low 1 2 carbon isotopes were measured using whole rock samples in the ohesaare core section two distinctive 13 c positive excursions were established one in the early wenlock riccartonensis and low rigidus ellesae standard graptolite zones 4 2 and the second in the late wenlock nassa zone 4 6 before and after the latter there are also intervals with low 13 c values the first just above the lundgreni zone 1 8 and another in the ludensis perhaps reaching into nilssoni zone 3 8 in the priekule section the early wenlock 13 c peak is well represented 3 1 but in the late wenlock early ludlow 13 c values show little variation from 2 0 to 1 in this section a high peak of 13 c values 5 9 was determined in the nova beds correlated with the topmost gorstian and lowermost ludfordian ludlow the carbon isotope positive excursions show good correlation with lows of the global sea level curve and with most of the biotic and supposed climatic events glaciation ocean state

the lundgreni event in the silurian of the east european platform poland abstract the lundgreni event late wenlock silurian is here interpreted in terms of palaeontologic graptolites microphytoplankton benthos biostratigraphic and geochemical evidence derived from homerian deposits drilled in the bartoszyce well east european platform in poland the lundgreni event in the graptolite record of bartoszyce comprises extinction survival and recovery phases the graptolite extinction proceeded in three steps lundgreni testis and flemingii dubius the testis extinction eliminated the largest number of species only the long lasting pristiograptus dubius survived the combined extinctions and was joined during the survival phase by the opportunistic gothograptus nassa and pristiograptus parvus the graptolite recovery is expressed by the diachronous arrival of new species in association with p dubius all documented phytoplankton taxa survived the lundgreni event phytoplankton frequency and diversity patterns together with total organic carbon toc fluctuations indicate that oligotrophy productivity regime was unsteady during the testis and flemingii dubius extinctions and stable during the early graptolite survival there is no evidence for extinction within benthic fauna assemblages diversified benthos appeared in a great abundance during the early survival phase this records a redox related event of substrate colonization that took place simultaneously with local decline in primary productivity the last two phases of graptolite extinction and the onset of the survival correlate with strong positive anomalies of 18o 13corg and 13ccarb the anomalies coincide with the fall in local primary productivity and the enhanced storage of organic carbon in peri gondwanan upwelling zones sudeten thuringia the stepped graptolite extinction in bartoszyce occurred in an environment that was situated within the low latitude baltica shelf and was markedly stable in terms of bathymetry distance from land and oxic regime this local extinction was most likely caused by catastrophic fluctuations in nutrient supply breaking primary productivity the trophic perturbations on the baltica shelf were coeval with and related to eutrophication of the high latitude upwelling zones of the rheic ocean the postulated spatial fluctuations in the trophic resource continuum may reflect palaeooceanographic changes that accompanied the global late sea level highstand of that time

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

high resolution correlation of the homerian carbon isotope excursion silurian across the interior of the midland platform avalonia uk new 13 c carb and microfacies data from hereford worcestershire and the west midlands allow for a detailed examination of variations in the homerian carbon isotope excursion silurian and depositional environment within the much wenlock limestone formation of the midland platform avalonia uk these comparisons have been aided by a detailed sequence stratigraphic and bentonite correlation framework microfacies analysis has identified regional differences in relative sea level change and indicates an overall shallowing of the carbonate platform interior from hereford worcestershire to the west midlands based upon the maximum 13 c carb values for the lower and upper peaks of the homerian carbon isotope excursion cie the shallower depositional setting of the west midlands is associated with values that are 0 7 and 0 8 higher than in hereford worcestershire at the scale of parasequences the effect of depositional environment upon 13 c carb values can also be observed with a conspicuous offset in the position of the trough in 13 c carb values between the peaks of the homerian cie this offset can be accounted for by differences in relative sea level change and carbonate production rates while such differences complicate the use of cies as a means of high resolution correlation and caution against correlations based purely upon the isotopic signature it is clear that a careful analysis of the depositional environment can account for such differences and thereby improve the use of carbon isotopic curves as a means of correlation

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

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

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

initial plant diversification and dispersal event in upper silurian of the prague basin abstract a relatively rich association of six species of embryophyte plants is known from the upper silurian of the prague basin bohemian massif czech republic all stratigraphically controlled specimens come from the neocolonograptus parultimus neocolonograptus ultimus zone of the p idoli a new genus and species tichavekia grandis psenicka sakala et kraft is established the new combination aberlemnia bohemica schweitzer sakala psenicka et kraft comb nov illustrates its lycophytina affinity the distribution and taphonomy of these plants in the prague basin indicates the proximity of exposed land interpreted to be islands of volcanic origin two local associations show primary differences in vegetated areas of the islands and apparent ecological responses of the primitive vascular plants to their habitats suitable environments in the coastal zones of volcanic islands in the prague basin which was situated at the outer periphery of a broad gondwanan shelf likely represent significant transfer points for an initial dispersion and a first expansion of land plants repeated vegetation of the islands is inferred from the discrete distribution of land plants at different stratigraphic levels these changes are explained partly in context of local changes of the island relief and partly as responses to global climatic and sea level fluctuations and fit environmental dynamics of islands of volcanic origin in general this initial plant diversification and dispersal event ipdde is of considerable significance in the evolution of plants documented from the bohemian massif

episodic tectonic subsidence of late holocene salt marshes northern oregon central cascadia margin salt marsh subsurface deposits 0 4 m depth in netarts bay a small coastal lagoon of northern oregon record six events of marsh burial in the last several thousand years five of the buried marsh surfaces show sharp nonerosional upper contacts with either anomalous sand layers tsunami deposits or tidal flat mud deposits these sequences indicate episodic abrupt subsidence of the marsh surfaces to low intertidal levels in contrast lower marsh contacts with underlying intertidal muds are gradational indicating gradual uplift and development of the marsh three independent measures of deposit elevation relative to mean tidal level percent organics diatom assemblages and percent eolian sand have been used to estimate vertical displacements of marsh surfaces abrupt subsidence displacements of 1 1 5 m alternate with gradual uplift displacements of the order of 0 5 1 0 m the vertical tectonic movements are interpreted to reflect coseismic strain release abrupt subsidence following interseismic strain accumulation gradual uplift associated with interplate coupling between the juan de fuca plate and the north american plate in the cascadia subduction zone recurrence intervals between subsidence events range from possibly less than 300 years to at least 1000 years with the last dated event likely occurring 300 400 radiocarbon years before present rcybp significant 14c age overlaps of at least four subsidence events recorded at netarts and reported for southern washington and other northern oregon bays at 300 500 1000 1300 1400 1800 and 3000 3300 rcybp suggest the potential for event synchroneity over at least 200 km of the central part of the cascadia subduction zone additional work is needed to test the synchroneity of these episodic events of coseismic subsidence

u pb zircon age constraints on the timing and duration of wenlock silurian paleocommunity collapse and recovery during the big crisis high precision isotope dilution u pb zircon dating was conducted on three volcanic ash fall bentonite samples from the swedish island of gotland and on a fourth bentonite from the west midlands england zircons from the ireviken grotlingbo djupvik gotland and wren s nest hill 15 west midlands bentonites yielded weighted mean pb 206 u 238 ages of 431 83 0 23 0 67 ma 428 45 035 0 73 ma 428 06 0 2110 66 ma and 427 86 032 0 71 ma respectively analytical total uncertainties these biostratigraphically well controlled age dates effectively bracket the wenlock epoch of the silurian period and provide control for the duration of one of the major paleozoic biotic events and associated perturbations to the global carbon cycle the big crisis or lundgreni event graptolites the niulde event conodonts the mulde excursion carbon isotopes these new data suggest an older and shorter duration for the recalibration of the wenlock series and demonstrate that the cascade of biological and chemical events that took place during the big crisis happened on time scales of tens to hundreds of thousands of years less

ordovician and silurian sea water chemistry sea level and climate a synopsis following the cambrian explosion and the appearance in the fossil record of most animal phyla associated with a range of new body plans the ordovician and silurian periods witnessed three subsequent major biotic events the great ordovician biodiversification event the end ordovician extinction the first animal extinction and second largest of the five mass extinctions of the phanerozoic and the early silurian postextinction recovery there are currently no simple explanations for these three major events combined extrinsic geological and intrinsic biological factors probably drove the biodiversifications and radiations and the appearance and disappearance of marine habitats have to be analysed in the frame of changing palaeogeography palaeoclimate and sea water chemistry the present paper reviews the relationships of the three biotic events to chemical and physical processes occurring in the ocean and atmosphere during the ordovician and silurian including sea level changes geochemical proxies 13c 18o 87sr 86sr of the ocean waters and the evolution of the atmosphere oxygen and carbon dioxide content less

the deep structure of the eolian arc filicudi panarea vulcano sector in light of gravity magnetic and volcanological data abstract the magnetic and gravimetric methods of investigation have been applied to the central sector of the eolian arc combined with geovolcanological data for the purpose of defining the structural framework in which the volcanism developed the processing of the magnetic and gravimetric data involved 3d modeling of the volcanic bodies and the application of a depth separation filter in order to subtract from the measured field the effect caused by the subaerial and submarine volcanic edifices and by all surface inhomogeneities magnetic and gravimetric 2 5d modeling on selected profiles has also been done in a joint interpretation of the magnetic and gravimetric data constrained by volcanological knowledge the interpretation of the final maps and profiles has demonstrated the existence of extensional tectonics resulting in the development of horst and graben volcanism occurs in the graben areas in particular the salina lipari vulcano magmatic axis has developed in a very deep articulated graben of lithospheric importance and completely filled by volcanic deposits and intrusive bodies the origin of this structure and of the associated igneous activity is suggested to be related to trans tensional tectonics along a plio pleistocene regional strike slip fault system

dating of quaternary basalts using the cosmogenic 3he and 14c methods with implications for excess 40ar concordant radiocarbon and cosmogenic sup 3 he dates of 3 and 11 ka on basalt flows and associated scoria deposits from the zuni bandera volcanic field in new mexico further substantiate published production rates and latitudinal and altitudinal corrections for sup 3 he identical sup 3 he concentrations in coexisting olivine and clinopyroxene confirm that these two minerals have very similar production rates a cosmogenic sup 3 he date of 57 ka on another flow is concordant with a u series date and is younger than two k ar dates suggesting that this flow contains excess sup 40 ar this excess sup 40 ar is also evident in gases released by vacuum crushing of olivine clinopyroxene fractions from all three flows 27 refs 3 figs 3 tabs

source characteristics of hypothetical subduction earthquakes in the northwestern united states historic earthquake sequences on subduction zones that are similar to the cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern united states based on systematic comparisons of several physical characteristics including physiography and seismicity subduction zones that are deemed most similar to the cascadia subduction zone are those in southern chile southwestern japan and colombia these zones have all experienced very large earthquake sequences and if the cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length then earthquakes of very large size m w 8 1 2 must be considered circumstantial evidence is presented that suggests but does not prove that large subduction earthquakes along the cascadia subduction zone may have an average repeat time of 400 to 500 yr

33 000 yr k ar dating of the volcano tectonic horst of the isle of ischia gulf of naples the gulf of naples corresponds to a tectonic sink connected with recent volcanic activity in the south campanian area phlegrean fields ischia and vesuvius at its extreme northwest the isle of ischia was early recognized as a volcano tectonic horst by rittmann1 previous data2 concluded that its uplift ended around 300 000 yr and that the green tuff formation of which it is predominantly composed had an age of some 700 000 yr but tectonic and morphological studies together with original tephrostratigraphical observations on the slope of the horst led us to do some new k ar datings these revealed that the 780 m uplift of the horst from the sea level is younger than 33 000 yr the green tuff which was considered to be the oldest volcanic unit in the island is now dated at 56 000 yr its eruption following the dismantlement of a first volcanic complex now dated as not older than 130 000 yr

mid ludfordian coeval carbon isotope natural gamma ray and magnetic susceptibility excursions in the mielnik ig 1 borehole eastern poland dustiness as a possible link between global climate and the silurian carbon isotope record abstract the graptolite bearing upper silurian succession of the mielnik ig 1 borehole eastern poland represents a periplatform setting on a neritic carbonate platform located on the palaeocontinent of baltica and records widely recorded positive mid ludfordian carbon isotope excursion cie the initial increase of 13 c values occurs in the uppermost part of the neocucullograptus kozlowskii zone whereas pronounced increase and maximal values 6 74 are noted in the n kozlowskii pseudomonoclimacis latilobus interzone pristiograptus dubius bloom interval the thickness time relation in the section indicates that the main initial shift in carbon isotope ratio of 2 7 occurred over a very short time estimated to be around 4000 years and is coeval with a rapid initiation of deposition of rock forming silt sized detrital dolomite and quartz the cie decline is interpreted as steeper than in inner shelf sections and is coincident with a flooding event in the ps latilobus slovinograptus balticus zone whereas the end of the excursion is coeval with the next flooding surface marked by the ps latilobus uncinatograptus acer graptolite assemblage combined sgr spectral gamma ray facies and faunal records during the cie suggest prolonged sea level lowstand conditions the abundant detrital material dolomite siltstone facies occurring exclusively in the cie interval is noted in microfacies as well as in the geophysics record as pronounced negative excursions in total natural gamma ray and magnetic susceptibility both resulting from dilution by diamagnetic and low radioactivity minerals the perfectly sorted vertically equally sized silt material contains unique constant and low diversified grain assemblage euhedral dolomite quartz minute ooids suggesting its provenance exclusively from the shallower and or emerged parts of the carbonate platform interior the spot findings of graptolites and nautiloids along with delicate parallel lamination of sediments indicates relatively deep environment with absence of traction processes these features along with the lack of dolomite detritus in accompanying redeposited carbonates suggest its derivation by wind with regard to the earlier noted presence of aeolian detritus in the middle ludfordian we suggest dustiness as a plausible driving force of the cie in the hypothesis proposed bioavailable fe bearing dust inflow in concert with antiestuarine circulation on shelfs caused nutrient n p ratio disturbances resulting in methanogenesis in surface layer of the seas the surface layer methanogenesis should resulting in bathymetric gradient of isotope fractionation what is consistent with the cie record coincidence of sea level lowstand low latitude aridity and gustiness of the global climate are in accordance with the hypothetical short lived glaciation in mid ludfordian time

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