three dimensional p wave velocity image under the carpathian arc abstract an inversion of p wave travel time residuals from selected earthquakes in the distance range 30 98 to two seismic station networks was used to model p wave velocity anomalies down to 250 km depth in the first inversion experiment a region between 43 5 47 5 n and 21 29 e was modelled using 35 seismic stations while in the second one a region between 44 47 n and 25 29 e was modelled using 19 seismic stations the 4 layer block model of the first inversion offers 19 reduction in residual variance while the 5 layer block model of the second one offers 26 reduction the rest being explained by noise and smaller scale heterogeneities the obtained velocity anomalies correlate remarkably well with the gravity anomalies and with the tectonic model for the vrancea region of fuchs et al 1979

slab break off abrupt cut or gradual detachment new insights from the vrancea region se carpathians romania slab break off is a plate tectonic process which does not only return lithospheric material into the deeper mantle but also has severe effects on surface movements and seismic hazard slab pull induced seismicity is reduced when the subducted slab decouples from the overlying crust in the vrancea region se carpathians strong earthquakes frequently occur at intermediate depths 70 180 km in a laterally small volume while the crust shows low but distributed seismicity the stress pattern shows similar partitioning with vertical extension in the slab and no preferred orientation in the overlying crust both features indicate a decoupling between slab and overlying crust either by slab break off or delamination however the strong vertical elongation of the slab requires that the upper end of the slab is fixed vertically thus a soft coupling is assumed that is strong enough to enable elongation of the slab but weak enough to inhibit quasi static stress transfer to the overlying crust

geochemistry and tectonic development of cenozoic magmatism in the carpathian pannonian region this review considers the magmatic processes in the carpathian pannonian region cpr from early miocene to recent times as well as the contemporaneous magmatism at its southern boundary in the dinaride and balkans regions this geodynamic system was controlled by the cretaceous to neogene subduction and collision of africa with eurasia especially by adria that generated the alps to the north the dinaride hellenide belt to the east and caused extrusion collision and inversion tectonics in the cpr this long lived subduction system supplied the mantle lithosphere with various subduction components the cpr contains magmatic rocks of highly diverse compositions calc alkaline k alkalic ultrapotassic and na alkalic all generated in response to complex post collisional tectonic processes these processes formed extensional basins in response to an interplay of compression and extension within two microplates alcapa and tisza dacia competition between the different tectonic processes at both local and regional scales caused variations in the associated magmatism mainly as a result of extension and differences in the rheological properties and composition of the lithosphere extension led to disintegration of the microplates that finally developed into two basin systems the pannonian and transylvanian basins the southern border of the cpr is edged by the adria microplate via sava and vardar zones that acted as regional transcurrent tectonic areas during miocene recent times major trace element and isotopic data of post early miocene magmatic rocks from the cpr suggest that subduction components were preserved in the lithospheric mantle after the cretaceous miocene subduction and were reactivated especially by extensional tectonic processes that allowed uprise of the asthenosphere changes in the composition of the mantle through time support geodynamic scenarios of post collision and extension processes linked to the evolution of the main blocks and their boundary relations weak lithospheric blocks i e alcapa and western tisza generated the pannonian basin and the adjacent styrian transdanubian and z rand basins which show high rates of vertical movement accompanied by a range of magmatic compositions strong lithospheric blocks i e dacia were only marginally deformed where strike slip faulting was associated with magmatism and extension at the boundary of adria and tisza dacia strike slip tectonics and core complex extension were associated with small volume miocene magmatism in narrow extensional sedimentary basins or granitoids in core complex detachment systems along older suture zones sava and vardar accommodating the extension in the pannonian basin and afterward pliocene quaternary inversion magmas of various compositions appear to have acted as lubricants in a range of tectonic processes

the effects of secular disequilibrium on u th he systematics and dating of quaternary volcanic zircon and apatite the u th he dating method applied to u rich phases such as zircon and apatite has sufficient sensitivity and precision to be of potential use for dating relatively recent geologic events such as volcanic eruptions however in phases with crystallization ages less than 1 ma chemical fractionation within the 238 u decay series may modify the he ingrowth rate causing he ages computed from the secular equilibrium age equation to be incorrect the resulting systematic error depends on the 230 th 238 u activity ratio of the dated phase when it is erupted and on the eruption age zircons which exclude th relative to u will likely have secular equilibrium he ages that underestimate the eruption age by up to a few tens of decreasing with increasing eruption age apatites tend to accommodate u and th with little fractionation so apatite secular equilibrium he ages will be nearly concordant with eruption age if minerals are erupted immediately after crystallization the disequilibrium effect can be reasonably accounted for based on th u systematics however crystals are likely to reside for unknown but potentially long periods in a magma chamber such that the degree of secular disequilibrium will be reduced prior to the onset of he accumulation u th he analyses of co genetic phases that fractionate the u th ratio differently like apatite and zircon can be used to better constrain eruption age as well as to provide insights into magma chamber residence time we illustrate this approach with u th he analyses of zircons and apatites of the pleistocene age rangitawa tephra new zealand

eruptive history of a low frequency and low output rate pleistocene volcano ciomadul south harghita mts romania based on a new set of k ar age data and detailed field observations the eruptive history of the youngest volcano in the whole carpathian pannonian region was reconstructed ciomadul volcano is a dacitic dome complex located at the southeastern end of the c limani gurghiu harghita neogene volcanic range in the east carpathians it consists of a central group of extrusive domes the ciomadul mare and haramul mare dome clusters and the koves ponk dome surrounded by a number of isolated peripheral domes some of them strongly eroded balvanyos puturosul and others topographically well preserved haramul mic dealul mare one of the domes dealul cet ii still preserves part of its original breccia envelope a large number of bread crust bombs found mostly along the southern slopes of the volcano suggest that the dome building activity at ciomadul was punctuated by short vulcanian type explosive events two late stage explosive events that ended the volcanic activity of ciomadul left behind two topographically well preserved craters disrupting the central group of domes the larger diameter shallower and older mohos phreatomagmatic crater and the smaller deeper and younger sf ana sub plinian crater phreatomagmatic products of the mohos center including accretionary lapilli bearing base surge deposits and poorly sorted airfall deposits with impact sags are known close to the eastern crater rim a key section studied in detail south of b ile tusnad shows the temporal succession of eruptive episodes related to the sf ana sub plinian event as well as relationships with the older dome building stages the age of this last eruptive event is loosely constrained by radiocarbon dating of charcoal pieces and paleosoil organic matter at ca 27 35 ka the age of the mohos eruption is not constrained but we suggest that it is closely related to the sf ana eruption the whole volcanic history of ciomadul spans over ca 1 myr starting with the building up of peripheral domes and then concentrating in its central part ciomadul appears as a small volume ca 8 74 km3 and very low frequency and low output rate volcano ca 9 km3 myr at the terminus of a gradually diminishing and extinguishing volcanic range a number of geodynamically active features strongly suggest that the magma plumbing system beneath ciomadul is not completely frozen so future activity cannot be ruled out

neogene quaternary magmatism and geodynamics in the carpathian pannonian region a synthesis in the carpathian pannonian region in neogene times westward dipping subduction in a land locked basin caused collision of two lithospheric blocks alcapa and tisia with the southeastern border of the european plate calc alkaline and alkaline magmatism was closely related to subduction rollback collision and extension from the spatial distribution of the magmatic activity four segments can be defined western segment magmatism occurring on the alcapa block central segment magmatism occurring on both alcapa and the tisia blocks south eastern segment and interior segment both on the tisia block most calc alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment assimilation and fractionation processes at shallow crustal levels occurred in most of the segments strongly masking the deeper source processes long term subduction rollback and or delamination led to contamination of the asthenosphere beneath the western segment here large volume partial melts of the contaminated mantle caused underplating and crustal anatexis leading to mixing of mantle derived calc alkaline magmas with crustal melts in the central segment calc alkaline magmas were formed by subduction and rollback followed by back arc extension and slab breakoff avariable mantle source is indicated in the back arc setting and larger amount of fluid induced metasomatism source enrichment and assimilation nearer to the trench in the interior segment evolution from typical calc alkaline magmas to adakite like ones was related to extension due to fast rotations and transtensional tectonics here calc alkaline magmas formed by decompression melting of a heterogeneous crust mantle lithosphere while adakite like melts resulted from fliud dominated melting of the lithosphere along the south eastern segment slab breakoff was responsible for the generation of typical calcalkaline magmas but in the extreme south of the segment shallow level tearing of the slab followed breakoff strike slip tectonics allowed the rise of hot asthenosphere and generation of adakite like magmas via slab melting along the torn edge of the east european plate alkalic basaltic volcanism with an oib like asthenosphere source followed the calc alkaline stage

40ar 39ar geochronology of magmatic activity magma flux and hazards at ruapehu volcano taupo volcanic zone new zealand we have determined precise eruption ages for andesites from ruapehu volcano in the tongariro volcanic centre of the taupo volcanic zone tvz using 40ar 39ar furnace step heating of separated groundmass concentrates the plateau ages indicate several eruptive pulses near 200 134 45 22 and 300 m section of lavas in whangaehu gorge as well as some lavas in ohinepango and waihianoa catchments on eastern ruapehu and this suite of lavas belongs to the waihianoa formation this pulse of activity is not represented on nearby tongariro volcano indicating that the two volcanoes have independent magmatic systems a younger group of lavas yields dates between 50 and 20 ka and includes lava flows from the turoa skifield and in the ohinepango and mangatoetoenui catchments and is consistent with two pulses of magmatism around the time of the last glacial maximum relating it broadly to the mangawhero formation syn and post last glacial activity lavas with ages 15 ka are assigned to the whakapapa formation and include the voluminous flows of the rangataua member on southern ruapehu magma flux integrated over 1000 yr periods averages 0 6 km3 ka 1 assuming a volcano lifespan of 250 ka fluxes for the te herenga waihianoa and mangawhero formations are consistent at 0 93 0 9 and 0 88 km3 ka 1 respectively these fluxes are broadly comparable with those measured at other modern andesite arc volcanoes e g ngauruhoe 0 88 merapi 1 2 and karymsky 1 2 km3 ka 1 the relatively low flux 0 17 km3 ka 1 calculated for the whakapapa formation may derive from underestimates of erupted volume arising from an increase in phreatomagmatic explosive eruptions in postglacial times however using volume estimates for the 1995 1996 eruptions and a recurrence interval of 25 yr has yielded an integrated 1000 yr flux of 0 8 km3 ka 1 in remarkable agreement to estimates for the prehistoric eruptions overall ruapehu shows consistency in magma flux but at time scales of the order of one hundred to some thousands of years field evidence suggests that short bursts of activity may produce fluxes up to twenty times greater this is significant from the perspective of future activity and hazard prediction

morphometrical and geochronological constraints on the youngest eruptive activity in east central europe at the ciomadul csomad lava dome complex east carpathians abstract the timing of late pleistocene volcanic activity of the ciomadul csomad dacitic lava dome complex site of the youngest eruptions in the carpathians has been constrained by morphometric analysis and radiometric chronology pelean domes and asymmetric domes coulees built up the volcano including the central edifice that hosts the youngest twin craters of mohos mohos peat bog and lake st ana szent anna a comparative digital elevation model dem based morphometric analysis of lava domes 29 worldwide examples including 5 domes from ciomadul shows that it is the mean slope of the upper dome flank that correlates best with age although the logarithmic relationship is only moderately strong r 0 80 slope characteristics of the ciomadul domes fit to those of 10 100 ka old domes these young ages contradict the previous k ar dates giving as old as 1 ma ages on a number of domes but are supported by ongoing u pb and u th he zircon dating the latter methods constrain the whole volcanic activity to the past 250 ka and the emplacement of most lava domes within the period of 150 100 ka the volcanism at ciomadul produced alternating effusive and explosive eruptions including lava dome collapses and successive crater formations the latest possibly subplinian explosive event formed the well preserved st ana crater radiocarbon dating of organic remains from a sediment core that reached 11 m into the lacustrine infill of st ana suggests that the crater was formed prior to 26 000 years bp

new seismic and tomography data in the southern part of the harghita mountains romania southeastern carpathians connection with recent volcanic activity the southern part of the southeastern carpathians represents the site of the most recent volcanic eruptions of the entire carpathian pannonian region the products of these eruptions range from 42 to 10 ka radiocarbon ages in the south harghita mountains high k calc alkaline rocks with adakite like features and at 1 2 0 6 ma k ar ages in the persani mountains alkali basalts they were emplaced in a post collisional regime ciomadul volcano is located at the southernmost part of the nw se oriented c limani gurghiu harghita range crossing the inner part of the southeastern carpathians and in the rough proximity of the vrancea seismic zone at ca 60 km toward nw its magma generation is attributed to geodynamic events closely related to the seismogenic area a number of particular geophysical and geochemical features located in the study region including 1 the abrupt attenuation of the seismic waves originating from the vrancea intermediate depth foci 2 the most intense heat flow anomaly in romania 3 the most prominent 3he 4he anomaly measured in natural postvolcanic gas emanations are all in favor of the hypothesis of a still existing hot local magma chamber data acquired during recent seismic monitoring of the vrancea zone and its neighborhoods suggest an enhancement of the local seismicity beneath the southern edge of the south harghita mts both at crustal and subcrustal levels at the same time recent tomography images obtained using local earthquake data correlate well with the presence of a vertically extended low velocity zone coming from the upper mantle to the assumed magmatic chambers located in the crust the present data supporting the presence of an active crustal magma chamber beneath ciomadul allow us to consider that future volcanic activity at this volcano cannot be discarded

magma eruption rates constrained by 40ar 39ar chronology and gis for the ceboruco san pedro volcanic field western mexico 40ar 39ar geochronology is coupled with quantitative volume determinations utilizing field mapping digital elevation models orthophotos and geographic information system gis software to constrain magma eruption rates at the ceboruco san pedro volcanic field 1600 km2 in the western trans mexican arc ages are reported for 40 volcanic units including volcan ceboruco an active andesitic stratovolcano peripheral domes shields cinder cones and fissure fed flows after a hiatus of 3 m y volcanic activity recommenced to produce 80 5 3 5 km3 of magma at a rate of 63 m3 km2 per year over the past 0 8 m y however 75 of this volume erupted in the past 100 k y including the 51 2 5 km3 of volcan ceboruco equivalent to an eruption rate of 377 m3 km2 per year there have been at least two stages of cone building activity at volcan ceboruco the main edifice is composed of 38 km3 of precaldera andesites the youngest dated at 45 8 ka their eruption was followed by a hiatus interrupted by a plinian eruption at 1 ka the plinian eruption and subsequent lava flows are andesite to dacite in composition and constitute 13 km3 of the total volume of volcan ceboruco overall the relative proportions of lava types erupted in the past 0 8 m y are 18 19 basaltic andesite 56 60 andesite 18 22 dacite and 3 rhyolite the peripheral lavas are each of small volume geochemically diverse and show little evidence of prior storage in an upper crustal chamber the eruptive sequence proportions of lava types phenocryst assemblages textures and geochemistry imply that the lavas do not reflect the differentiation of a single parental liquid in a long lived magma chamber the distinct geochemical signatures were present prior to magma emplacement in the upper crust whereupon subsequent degassing and crystallization led to variable phenocryst abundances and assemblages

review of neogene and quaternary volcanism of the carpathian pannonian region abstract development of the pannonian basins as well as thrusting and folding of the carpathians was accompanied by widespread volcanic activity this volcanism can be divided into three main genetic types 1 1 early miocene mainly acidic volcanism tuffs and ignimbrites the recent spatial separation of these volcanics may be due to large right lateral displacement along the mid hungarian shear zone during the early miocene 2 2 middle miocene pliocene calc alkaline mainly intermediate stratovolcanic complexes in the inner western carpathians and in the east carpathians related to a subducted oceanic slab their geochemical compositions show a transitional character between active continental margin and island arc type magmatic rocks the thickness of the crust increased with time and from west to east beneath this volcanic arc 3 3 pliocene pleistocene alkali basaltic volcanism was related to an upwelling then cooling asthenospheric dome this is thought to have initiated the thermal regime from which these melts ascended the compositional difference in space and in time might reflect the existence of local individual small sized diapiric bodies as well as several processes e g fractional crystallization mixing which modified the original magma the eruption of these basaltic melts was temporally associated with the final phase of development of the pannonian basin this volcanism was associated with recent uplifts and tectonic rejuvenation of the area

amphibole perspective to unravel pre eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes a case study from ciomadul volcano se carpathians ciomadul is the youngest volcano in the carpathian pannonian region produced crystal rich high k dacites that contain abundant amphibole phenocrysts the amphiboles in the studied dacites are characterized by large variety of zoning patterns textures and a wide range of compositions e g 6 4 15 wt al2o3 79 821 ppm sr often in thin section scale and even in single crystals two amphibole populations were observed in the dacite low al hornblendes represent a cold 900 c mafic magma amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage 8 12 km this was also the place where the erupted dacitic magma was formed during the remobilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple zoned and composite amphiboles this includes reheating by 200 c and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population including pargasites breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes suggesting that pre eruptive heating and mixing could take place within days or weeks before the eruption the decompression rim of pargasites suggests around 12 days of magma ascent in the conduit several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the ciomadul but in our dacite the two amphibole population can be found even in a single crystal composite amphiboles our study indicates that high al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone thus they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes the simple zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the al tschermak substitution can be recognized suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation

re anchoring the late pleistocene tephrochronology of new zealand based on concordant radiocarbon ages and combined 238u 230th disequilibrium and u th he zircon ages abstract the caldera forming rotoiti eruption from okataina volcano was one of the largest rhyolite events of the last 100 ka in the taupo volcanic zone new zealand its associated widespread tephra layer rotoehu tephra is a significant time marker in terrestrial marine paleoclimate correlation studies in the sw pacific however the accurate and precise age of this eruption and of the subsequent smaller volume earthquake flat eqf eruption has been the subject of controversy despite numerous studies we have applied combined 238u 230th disequilibrium and u th he dating of zircon from rotoiti and eqf deposits and obtained overlapping ages of 45 1 7 3 3 ka and 45 1 6 2 9 ka respectively these results are supported by new and published high precision radiocarbon data bracketing the age of the rotoiti eruption between 44 8 0 3 and 47 5 2 1 ka cal bp these age data are also in good agreement with a range of previously published estimates based on paleoclimate palynology luminescence dating of enclosing sediment and sedimentation rates in terrestrial and marine settings however these results are at variance with a commonly quoted age of 60 ka largely constrained by a single 40ar 39ar age of an overlying glassy lava flow at a distal tephra site this study demonstrates the potential for combined 238u 230th disequilibrium and u th he dating of zircon in tephra and other volcanic deposits to provide age control in the 40 100 ka time interval a period difficult to constrain using more traditional radiocarbon k ar and 40ar 39ar methods

potassium argon geochronology of a basalt andesite dacite arc system the mount adams volcanic field cascade range of southern washington high precision k ar dating and detailed mapping have established an eruptive chronology for a cascade stratovolcano and its surrounding array of coeval basaltic centers mount adams is a 200 km 3 andesitic cone that stands at the center of a coeval 1250 km 2 quaternary volcanic field that contains 60 discrete vents k ar ages were measured for 74 samples from 63 of the 136 volcanic units defined in the course of the mapping within analytical error there are no discrepancies between k ar ages and stratigraphic sequence major activity began in the area ca 940 ka and inception of the central stratovolcano took place at ca 520 ka a plot of cumulative volume erupted versus time shows that between 940 and 520 ka the eruptive rate was 3 k y and 80 of the products were basaltic andesites are volumetrically dominant and were emplaced in three main cone building episodes centered at 500 450 and 30 ka at eruptive rates of 1 6 5 km 3 k y at a lower rate of 0 05 0 1 km 3 k y the magmatic system remained almost continuously active between the main pulses although breaks in activity as long as 30 k y are permitted by the k ar data andesitic dacitic activity in the focal region and dominantly basaltic activity on the periphery have coexisted for 520 k y and their products are interstratified the last main episode of cone construction occurred ca 40 10 ka the oldest andesite identifiably derived from within the present day edifice having an age of 33 14 ka andesites forming the south summit rim and the true summit have ages of 13 8 ka and 15 8 ka respectively the time volume composition data bear upon several fundamental questions concerning the long term behavior of arc volcanoes stratovolcanoes commonly grow in spurts but can stay active between the widely spaced episodes of peak productivity large stratocone systems may remain active for half a million years subdivision of complex stratovolcanoes into eruptive or constructional stages without detailed mapping geochronology and compositional data should be treated skeptically discussion of volumetric eruptive rates can be misleading without an adequate time scale stratovolcanoes need never develop large upper crustal magma chambers basalt erupts peripherally but its ascent is suppressed beneath stratovolcanoes by deep crustal domains of magma storage and hybridization that form where concentrated injection of basalt amplifies crustal melting

episodes of dormancy and eruption of the late pleistocene ciomadul volcanic complex eastern carpathians romania constrained by zircon geochronology abstract ciomadul is the youngest volcanic system in the carpathian pannonian region recording eruptive activity from ca 1 ma to 30 ka based on combined zircon u th and u th he geochronology ciomadul volcanism is divided into two main eruptive periods old ciomadul 1 ma 300 ka ocep and young ciomadul eruptive period 160 30 ka ycep ocep activity comprises eruptive epochs 1 3 whereas new ages for eight lava domes and four pyroclastic units belonging to the ycep lead to its further subdivision into two eruptive epochs eruptive epochs 4 and 5 the extrusion of most of the lava domes occurred between 160 and 90 ka eruptive epoch 4 during three eruptive episodes at ca 155 ka 135 ka and 95 ka eruptive episodes 4 1 4 2 and 4 3 respectively along a ne sw lineament which is perpendicular to the regional nw se trend of the c limani gurghiu harghita volcanic chain eruptive epoch 5 occurred after a ca 40 kyr of quiescence at ca 55 30 ka and is mainly characterized by explosive eruptions with a minor lava dome building activity all of the dated pyroclastic outcrops together with the lava dome of piscul pietros belong to the older eruptive episode 5 1 with an eruption age of 55 45 ka the eruption centers of eruptive epoch 5 are located at the junction of the conjugated nw se and ne sw lineaments defined by the older eruptive centers the whole rock geochemistry of all studied samples is fairly homogeneous sio2 63 69 wt k2o 3 4 wt it also overlaps with the composition of the lava domes of the old ciomadul eruptive period implying a monotonous geochemical characteristic for the past 1 myr the eruption rates for the ciomadul volcanism were determined based on the erupted lava dome volume calculations supplemented with the eruption ages the activity peaked during the eruptive epoch 4 160 90 ka having an eruption rate of 0 1 km3 kyr in comparison these values are 0 05 km3 kyr for the ycep 160 30 ka and 0 01 km3 kyr for the overall ciomadul volcanism 1 ma 30 ka based on the geochemical characteristics the quiescence periods and the lifetime of the complex as well as the relatively small amount of erupted material this volcanic system can be placed in a subduction related post collisional geodynamic setting which shows strong chemical similarities to continental arc volcanism the commonly found long repose times between the active phases suggest that the nature of a volcano cannot be understood solely based on the elapsed time since the last eruption instead comprehensive geochronology coupled with the understanding of the magma storage behavior could be a base of hazard assessment for volcanic fields where the last eruptions occurred several 10 s of thousand years ago and therefore they are not considered as potentially active

uranium series accessory crystal dating of magmatic processes complex and protracted crystallization histories over geologic timescales are recorded in accessory minerals e g zircon allanite although magmatic crystallization was traditionally assumed to occur essentially instantaneously for the purposes of interpreting mineral geochronometers with low absolute time resolution for ancient samples it emerged relatively recently that magmatic crystallization can occur over extended durations this discovery arose from applying high spatial resolution accessory mineral dating techniques for uranium series isotopes to young volcanic and cognate plutonic rocks the emerging pattern from these studies is that individual crystals and crystal populations record crystallization episodes lasting from 1 000 to many hundreds of thousands of years accessory mineral dating of volcanic rocks and cognate plutonic xenoliths opens new research avenues for crystal age fingerprinting that correlates pyroclastic deposits lavas and plutonic rocks by using characteristic age dis

geochemical response of magmas to neogene quaternary continental collision in the carpathian pannonian region a review the carpathian pannonian region contains neogene to quaternary magmatic rocks of highly diverse composition calcalkaline shoshonitic and mafic alkalic that were generated in response to complex microplate tectonics including subduction followed by roll back collision subducted slab break off rotations and extension major element trace element and isotopic geochemical data of representative parental lavas and mantle xenoliths suggests that subduction components were preserved in the mantle following the cessation of subduction and were reactivated by asthenosphere uprise via subduction roll back slab detachment slab break off or slab tearing changes in the composition of the mantle through time are evident in the geochemistry supporting established geodynamic models magmatism occurred in a back arc setting in the western carpathians and pannonian basin western segment producing felsic volcaniclastic rocks between 21 to 18 ma ago followed by younger felsic and intermediate calc alkaline lavas 18 8 ma and finished with alkalic mafic basaltic volcanism 10 0 1 ma volcanic rocks become younger in this segment towards the north geochemical data for the felsic and calc alkaline rocks suggest a decrease in the subduction component through time and a change in source from a crustal one through a mixed crustal mantle source to a mantle source block rotation subducted roll back and continental collision triggered partial melting by either delamination and or asthenosphere upwelling that also generated the younger alkalic mafic magmatism in the westernmost east carpathians central segment calc alkaline volcanism was simultaneously spread across ca 100 km in several lineaments parallel or perpendicular to the plane of continental collision from 15 to 9 ma geochemical studies indicate a heterogeneous mantle toward the back arc with a larger degree of fluid induced metasomatism source enrichment and assimilation on moving north eastward toward the presumed trench subduction related roll back may have triggered melting although there may have been a role for back arc extension and asthenosphere uprise related to slab break off calc alkaline and adakite like magmas were erupted in the apuseni mountains volcanic area interior segment from15 9 ma without any apparent relationship with the coeval roll back processes in the front of the orogen magmatic activity ended with oiblike alkali basaltic 2 5 ma and shoshonitic magmatism 1 6 ma lithosphere breakup may have been an important process during extreme block rotations 608 between 14 and 12 ma leading to decompressional melting of the lithospheric and asthenospheric sources eruption of alkali basalts suggests decompressional melting of an oib source asthenosphere mixing of asthenospheric

tectonic significance of changes in post subduction pliocene quaternary magmatism in the south east part of the carpathian pannonian region the south eastern part of the carpathian pannonian region records the cessation of convergence between the european platform moesia and the tisza dacia microplate plio quaternary magmatic activity in this area in close proximity to the vrancea zone shows a shift from normal calc alkaline to much more diverse compositions adakite like calc alkaline k alkalic mafic na alkalic and ultrapotassic suggesting a significant change in geodynamic processes at approximately 3 ma we review the tectonic setting timing petrology and geochemistry of the post collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration the calc alkaline volcanism 5 3 3 9 ma marks the end of normal subduction related magmatism along the post collisional c limani gurghiu harghita volcanic chain in front of the european convergent plate margin at ca 3 ma in south harghita magma compositions changed to adakite like calc alkaline and continued until recent times 0 03 ma interrupted at 1 6 1 2 ma by generation of na and k alkalic magmas signifying changes in the source and melting mechanism we attribute the changes in magma composition in front of the moesian platform to two main geodynamic events 1 slab pull and steepening with opening of a tear window adakite like calc alkaline magmas and 2 renewed contraction associated with deep mantle processes such as slab steepening during post collisional times na and k alkalic magmas contemporaneous post collisional volcanism at the eastern edge of the pannonian basin at 2 6 1 3 ma was dominated by na alkalic and ultrapotassic magmas suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the adriatic indentation similar timing magma chamber processes and volume for k alkalic shoshonitic magmas in the south apuseni mountains 1 6 ma and south harghita area at a distance of ca 200 km imply a regional connection with the inversion tectonics

observations on shelf and subtidal channel flow implications of sediment dispersal seaward of the keum river estuary korea although much of the fine grained sediment in the south eastern yellow sea is attributed to discharge from the keum river dispersal of these sediments by tide or wind has never been determined by direct current measurements in this paper we provide in situ observations of currents in two dispersal systems immediately seaward of the keum river entrance one of these is a subtidal channel system that defines flow from the shallow subtidal region seaward to the shelf and the other is the inner shelf mudstream where mixing is maintained primarily by tides subtidal channels have moderate current speeds but low suspended sediment concentrations instantaneous current speeds during spring tide were of the order 100 cm s 1 and suspended sediment concentrations were typically less than 10 mg l 1 at the surface and 40 mg l 1 at the bottom under fair weather conditions subtidal channels play a negligible role in offshore sediment dispersal since sediment concentrations during flood appear to equal or exceed those during ebb instantaneous currents at two stations on the shelf were of the same order as those in subtidal channels but displayed net flow to the south at speeds of 7 8 and 3 8 cm s 1 we speculate that subtidal channels provide the conduits for transporting sediments directly offshore during winter monsoons on an annual time scale one model for sedimentation would be low sediment influx from rivers but high influx from tidal flats to the coast during winter when north winds generate large waves in the yellow sea and the reverse in summer when winds from the south produce little wave activity coastal muds would thus be eroded in winter and replenished by high river discharge in summer further it is reasonable to assume that residual flow to the south would strengthen in winter as the monsoon season progressed thus the introduction of resuspended tidal flat sediments would coincide with the best developed dispersal system

slab in the wrong place lower lithospheric mantle delamination in the last stage of the eastern carpathian subduction retreat a model with a new type of delamination of the lower lithospheric mantle is proposed to explain the pliocene to recent tectonic evolution of the eastern carpathians we suggest that after the continental collision in middle miocene time break off of the west dipping subducting slab occurred at a depth of 70 km slab break off propagated horizontally toward the east inducing lithospheric delamination and movement of the vrancea slab into its present position delamination was followed by rapid asthenospheric rise resulting in magma generation and the explosive alkaline basaltic magmatism of the persani mountains contamination of the former subduction related magmatic reservoirs with the alkalic basaltic material and differentiation processes produced the harghita calc alkaline and shoshonitic rocks the asthenospheric rise induced crustal uplift which is the triggering mechanism for extension and formation of the brasov gheorghieni hinterland basins the extension was accommodated by shortening and folding in the foreland the vertical vrancea slab appears in our model as a segment of delaminated lower lithospheric mantle that is seismically active due to the ongoing pull of the eclogitized oceanic crust the model explains the displaced and shallow position of the slab relative to the eastern carpathian suture zone

volcanic evolution of volcan aucanquilcha a long lived dacite volcano in the central andes of northern chile volcan aucanquilcha northern chile has produced 37 km3 of dacite 63 66 wt silica mainly as lavas with ubiquitous magmatic inclusions 59 62 wt silica over the last 1 million years a pyroclastic flow deposit related to dome collapse occurs on the western side of the edifice and a debris avalanche deposit occurs on the eastern side the 6 000 m high edifice defines a 9 km e w ridge and lies at the center of a cluster of more than 15 volcanoes the aucanquilcha volcanic cluster that has been active for at least the past 11 million years the e w alignment of vents is nearly orthogonal to the arc axis a majority of volcan aucanquilcha was constructed during the first 200 000 years of eruption whereas the last 800 000 years have added little additional volume the peak eruptive rate during the edifice building phases was 0 16 km3 ka and the later eruptive rate was 0 02 km3 ka comparable dacite volcanoes elsewhere show a similar pattern of high volcanic productivity during the early stages and punctuated rather than continuous activity volcan aucanquilcha lavas are dominated by phenocrysts of plagioclase accompanied by two populations of amphibole biotite clinopyroxene fe ti oxides and or orthopyroxene accessory phases include zircon apatite and rare quartz and sanidine one amphibole population is pargasite and the other is hornblende the homogeneity of dacite lava from volcan aucanquilcha contrasts with the heterogeneity 52 66 wt silica at nearby volcan ollague which has been active over roughly the same period of time we attribute this homogeneity at aucanquilcha to the thermal development of the crust underneath the volcano resulting from protracted magmatism there whereas volcan ollague lacks this magmatic legacy

40ar 39ar chronology and paleomagnetism of quaternary basaltic lavas from the persani mountains east carpathians abstract quaternary volcanism in the persani mountains forms an na alkali basaltic province inside the bend area of the carpathians in the southeastern part of europe previous k ar ages and paleomagnetic data reveal several transitional virtual geomagnetic poles which were tentatively associated with the cobb mountain subchron and a brunhes chron excursion we report a new paleomagnetic and rock magnetic study coupled with 40ar 39ar geochronology to better constrain the age of geomagnetic reversals or excursions that might be recorded and the timing of volcanism of the paleomagnetic directions obtained from sampled lava flows 4 are reversed polarity 19 are normal polarity and 16 have transitional polarity 40ar 39ar plateau ages determined from incremental heating experiments on groundmass indicate that two of the reversely magnetized lavas erupted at 1142 41 and 800 25 ka four of the normally magnetized lavas erupted at 1060 10 1062 24 684 21 and 683 28 ka and two transitionally magnetized lavas formed at 1221 11 and 799 21 ka both the new 40ar 39ar ages and the paleomagnetic data suggest at least five episodes of volcanic activity with the most active periods during the jaramillo and brunhes chrons this results shows that the last phases of alkalic and calc alkaline magmatism in the south east carpathians were contemporaneous the age of the older transitionally magnetized lava flow is within error of recent unspiked k ar and astrochronologic ages for the reversal that defines the onset of the cobb mountain normal polarity subchron the age of the younger transitional lava is similar to that of an excursion that preceded the matuyama brunhes polarity reversal and which has come to be known as the matuyama brunhes precursor omitting the excursion data the dispersion of the virtual geomagnetic poles around 19 is larger than the expected value around 45 n from the global compilation but closer to the value obtained only from the time averaged geomagnetic field initiative studies

geology and eruptive history of unzen volcano shimabara peninsula kyushu sw japan abstract during the past 500 thousand years unzen volcano an active composite volcano in the southwest japan arc has erupted lavas and pyroclastic materials of andesite to dacite composition and has developed a volcanotectonic graben the volcano can be divided into the older and the younger unzen volcanoes the exposed rocks of the older unzen volcano are composed of thick lava flows and pyroclastic deposits dated around 200 300 ka drill cores recovered from the basal part of the older unzen volcano are dated at 400 500 ka the volcanic rocks of the older unzen exceed 120 km3 in volume the younger unzen volcano is composed of lava domes and pyroclastic deposits mostly younger than 100 ka this younger volcanic edifice comprises nodake myokendake fugendake and mayuyama volcanoes nodake myokendake and fugendake volcanoes are 100 70 ka 30 20 ka and

eruptive history and petrologic evolution of the albano multiple maar alban hills central italy a comprehensive volcanological study of the albano multiple maar alban hills italy using i 40ar 39ar geochronology of the most complete stratigraphic section and other proximal and distal outcrops and ii petrographic observations phase analyses of major and trace elements and sr and o isotopic analyses of the pyroclastic deposits shows that volcanic activity at albano was strongly discontinuous with a first eruptive cycle at 69 1 ka producing at least two eruptions and a second cycle with two peaks at 39 1 and 36 1 ka producing at least four eruptions contrary to previous studies we did not find evidence of magmatic or hydromagmatic eruptions younger than 36 1 ka the activity of albano was fed by a new batch of primary magma compositionally different from that of the older activity of the alban hills moreover the ree and 87sr 86sr data indicate that the albano magma originated from an enriched metasomatized mantle according to the modeled liquid line of descent this magma differentiated under the influence of magma limestone wall rock interaction our detailed eruptive and petrologic reconstruction of the albano maar evolution substantiates the dormant state of the alban hills volcanic district

eruptive history of chimborazo volcano ecuador a large ice capped and hazardous compound volcano in the northern andes abstract new fieldwork radiometric and whole rock chemical data permit the reconstruction of the main eruptive stages of the chimborazo compound volcano the highest summit of the northern andes chimborazo is composed of three successive edifices the basal edifice ch i was active from 120 to 60 ka and resulted in a large mostly effusive edifice which was built up during two stages of cone building terminating with the formation of a dome complex this edifice was affected by a huge sector collapse around 65 60 ka which produced a major debris avalanche that spread out into the riobamba basin covering about 280 km2 with an average thickness of 40 m and a total volume of 10 12 km3 after the emplacement of the riobamba debris avalanche eruptive activity resumed at the eastern outlet of the avalanche scar and was responsible for the construction of a less voluminous intermediary edifice ch ii whose current remnants are the politecnica and martinez peaks this edifice developed from 60 to 35 ka lastly eruptive activity shifted to the west leading to the construction of the morphologically well preserved young cone ch iii which currently forms the highest summit whymper the average eruptive rate of chimborazo volcano is 0 5 0 7 km3 ka however looking at the three successive edifices individually we estimate that there has been a progressive decrease in magma output rate from the basal edifice 0 7 1 0 km3 ka through the intermediary edifice 0 4 0 7 km3 ka to the young cone 0 1 km3 ka however during the main cone building stages the peak eruption rates are markedly higher indicating significant variations in the magma output rate during the lifespan of this arc volcano during the holocene the chimborazo eruptive activity consisted of small volume explosive events that occurred at quite regular intervals between about 8000 and 1000 yr ago since the last eruption occurred between the early part of the 5th century and the end of the 7th century and the average time interval between the events is about 1000 yr chimborazo must be considered as a potentially active volcano the presence of a thick ice cap covering the summit its steep flanks and its position above the populated lowland area of riobamba and ambato are factors that result in a high potential risk

interplay of tectonics and neogene post collisional magmatism in the intracarpathian region abstract distribution of the neogene calc alkaline magmatism of the carpathian arc is directly related in space and time to the kinematics of the two major terranes of the intracarpathian area alcapa tisia getia along the south eastern border of the european plate in the west carpathians and adjacent areas the volcanic activity occurred between 20 11 ma with large volumes of both acidic and intermediate rocks generally distributed randomly sometimes transversally to the orogenic belt and as rare small occurrences along the flysch belt in the east carpathians the volcanic rocks are distributed along the northern margin of the zemplin block the north easternmost part of the alcapa and eastward along the front of the getic block at the contact with european plate between tokaj slanske vihorlat up to northern calimani mountains the magmatism occurred between 14 9 ma and along the calimani harghita chain between 9 0 2 ma the calc alkaline magmatic rocks of the apuseni mountains are located in the interior of the tisia block and occurred between 14 9 ma the generation of the calc alkaline magmatism is considered here as the result of complex interplay between plate roll back and lithospheric detachment tectonic processes and the break off of the subducted plate mostly in a post collisional setting 1 the magmatites of the western carpathians and the pannonian basin were generated in direct relation to subduction roll back processes over the downgoing slab during the period of lateral extrusion and back arc extension in this area characterized by maximum crustal shortening we can infer further delamination processes to explain the generation of magmas 2 the magmatic rocks from the northern sector of the east carpathians tokaj slanske vihorlat up to the northern calimani mountains resulted after subduction roll back processes and an almost simultaneous break off of the descending plate all along the arc segment during main clockwise rotation of the intracarpathian terranes 3 in the eastern sector of the east carpathians calimani up to harghita mountains the magmatic rocks were generated through partial melting of the subducted slab followed by gradual break off of the subducted plate along strike north to south 4 the apuseni mts magmatic activity resulted in transtensional tectonic regime by decompressional melting of lithospheric mantle during the translation and rotation of tisia getia block

source duration scales with magnitude differently for earthquakes on the san andreas fault and on secondary faults in parkfield california we used a comparison of source time function pulse widths to show that a group of earthquakes on the san andreas fault near parkfield have a constant duration over a magnitude range of 1 4 3 7 earthquakes on secondary faults have an increase in duration with magnitude which is the expected relationship for the usual observation of constant stress drop the constant duration suggests that fault area is the same regardless of magnitude and that variations in stress drop are due entirely to variations in slip calculated stress drop values on secondary faults range from 0 31 to 14 mpa and stress drop values on the san andreas fault range from 0 18 to 63 mpa the observation of constant duration on the san andreas fault is consistent with a model of a locked asperity in a creeping fault the differences in durations between the events on the san andreas fault and on secondary faults suggest that earthquakes on the san andreas fault are inherently different we speculate that faults with more cumulative displacement have earthquakes that may rupture differently furthermore the differences in source properties between the two populations might be explained by differences in fault surface roughness online material station subsets used to evaluate cross fault seismic velocity contrasts

evolution and volcanic hazards of taapaca volcanic complex central andes of northern chile taapaca volcanic complex is a large dacitic volcano 35 km 3 located in the western border of the active zone of the central andes of northern chile apart from early poorly preserved silicic andesites taapaca volcanic complex has generated remarkably similar porphyritic hornblende biotite dacites with distinctive sanidine megacrysts for at least 1 5 ma the main products of the volcano are dacite lavas and domes with associated block and ash flow deposits there have also been several sector collapses to generate debris avalanches which are closely associated with volcanic blasts and episodes of dome growth four stages of evolution are recognized with volcanism occurring in short bursts between much longer periods of dormancy volcanism has built a substantial stratovolcano and has migrated 4 5 km towards the sw with time late pleistocene to holocene activity has involved at least three sector collapses of the hydrothermally altered flanks and domes volcanic blasts block and ash flows debris avalanches and lahars have been distributed down the southwestern flanks these areas are the main populated part of the chilean altiplano and the location of the main road between bolivia and the pacific ocean coast a future eruption will threaten these areas and the regional economy