u pb geochronological constraints for paleoproterozoic evolution of the core zone southeastern churchill province northeastern laurentia abstract the core zone of the southeastern churchill province northeastern laurentia is a composite of paleoproterozoic lithotectonic domains assembled in the vise between obliquely colliding archean superior and north atlantic cratons between ca 1860 and 1810 ma detailed geological and u pb geochronological studies of domains in the southern core zone highlight significant differences in archean and paleoproterozoic geology between domains and constrain timing and models for paleoproterozoic assembly in the south central part of the core zone crossroads and orma domains consist of late archean granite greenstone terrane crust crossroads domain also contains a significant number of granite charnockite intrusions belonging to the 1840 1810 ma de pas batholith magmatism pre dates and overlaps with ca 1820 1775 ma high grade metamorphism and attendant deformation in marked contrast orma domain which occurs to the east of crossroads domain contains only local evidence of paleoproterozoic de pas related intrusions and appears to have mainly escaped paleoproterozoic metamorphism and penetrative deformation a model compatible with available data suggests the de pas batholith is a continental magmatic arc formed above an east dipping subduction zone paleoproterozoic metamorphism and deformation is concentrated in regions contiguous with arc magmatism west of crossroads domain and separated from it by the lac tudor shear zone mckenzie river domain is dominated by archean orthogneiss 80 m y older than gneisses in crossroads and orma domains minor amounts of paleoproterozoic supracrustal rocks absent in domains to the east and 1815 ma tonalite it does not contain de pas intrusions u pb geochronology suggests juxtaposition of the mckenzie river domain with domains to the east may have occurred around 1810 ma one possible model envisages the mckenzie river domain as a piece of reassembled superior craton crust incompletely rifted from the superior margin during ca 2 17 ga rifting domains occurring east of the lac tudor shear zone are interpreted to be exotic with respect to the superior craton

u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

new chronological constraints for middle palaeolithic mis 6 5 3 cave sequences in eastern transylvania romania abstract the middle to upper palaeolithic transition is one of the crucial periods of change in the prehistory of europe due to the full emergence continent wide of modern human lithic technologies and detrimental of neanderthal survival knowledge about the transition is growing however the evidence for cultural and technological developments for the middle palaeolithic in the carpathian lower danube basin is still rather sparse here we discuss latest findings arising from a chronological investigation of middle palaeolithic assemblages within the varghis karst eastern transylvania romania combining our first chronological results with information from previous excavations we can distinguish two main stages of habitation albeit middle palaeolithic lithics and faunal remains appear scattered throughout the investigated profile within the abri 122 rock shelter in order to augment the typological cultural considerations we applied direct radiocarbon dating on bones and charcoal from within the occupation layers radiocarbon dating of bones suggests that the middle palaeolithic sequence is older than the upper dating limit of the method whereas direct luminescence ages on the lowermost productive horizon and immediately above it indicate surprisingly old ages of ca 106 141 ka osl optically stimulated or 99 174 ka irsl infrared stimulated multiple protocol dating of charcoal found within the two habitation layers produced ages 38 14 c ka bp also suggesting that the lowermost lithic rich horizon pertains to the middle palaeolithic industries overall the recovered lithics currently forming one of the most significant collections for romania are fully consistent with two main habitation phases connected to middle palaeolithic cultural affinities the occurrence of a volcanic ash layer within ursului cave and originating from the ciomadul volcanic complex carpathians is first reported here recently dated to 43 50 ka it might represent an important marker horizon providing that it is identified within other palaeolithic cave assemblages

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research

evidence for transition from a continental forearc to a collisional pro foreland basin in the eastern trans hudson orogen detrital zircon provenance analysis in the labrador trough canada abstract the new quebec orogen nqo is the best preserved supracrustal belt of the deeply eroded paleoproterozoic trans hudson orogen and thus constitutes an exceptional window to investigate one of the most ancient wilson cycle sedimentary records within the manikewan paleo ocean it consists of a paleoproterozoic supracrustal belt that underwent reworking when the superior craton collided with an archean to paleoproterozoic microcontinent core zone terrane during the trans hudsonian orogeny within the nqo the western and central parts of the labrador trough comprise greenschist facies sedimentary and volcanic sequences kaniapiskau supergroup inferred to represent the rifted margin of the superior craton whereas the laporte group eastern part composed of similar successions but metamorphosed to higher grades remains of unclear origin competing models purport that the laporte group is either a deeper higher grade exposure of the kaniapiskau supergroup or an exotic terrane large scale sampling petrography and shrimp u pb detrital zircon geochronology provide insights to elucidate the sedimentary provenance and depositional environments for both zones kaniapiskau supergroup detrital zircons yield ages older than 2 5 ga showing a signature typical of the archean superior craton with a main peak at 2 72 ga there is a gap of more than 150 ma between detrital zircon ages and the interpreted depositional age suggesting a divergent environment like a rift and passive margin in contrast detrital zircons from the laporte group yield ages as young as 1834 2 4 ma and a dominant age peak at 1 84 ma the presence of age peaks at 2 2 2 4 ga suggests that the core zone exotic terrane is the main source area and the metamorphic monazite ages previously dated at 1793 2 ma point to a relative short depositional time the presence of an andean type magmatic arc in the western part of the core zone terrane supports the interpretation of an eastward subduction at 1860 1830 ma furthermore a lag time between crystallization and deposition ages within the laporte group points to convergent and collisional settings with a 40 ma transition from continental forearc basin to collisional pro foreland basin marking the consolidation of the columbia supercontinent in northeastern laurentia

first evidence of a distal early holocene ash layer in eastern mediterranean deep sea sediments derived from the anatolian volcanic province article i nfo a hitherto unknown distal volcanic ash layer has been detected in a sediment core recovered from the southeastern levantine sea eastern mediterranean sea radiometric stratigraphic and sedimentological data show that the tephra here termed as s1 tephra was deposited between 8970 and 8690 cal yr bp the high silica rhyolitic composition excludes an origin from any known eruptions of the italian aegean or arabian volcanic provinces but suggests a prevailing central anatolian provenance we compare the s1 tephra with proximal to medial distal tephra deposits from well known mediterranean ash layers and ash fall deposits from the central anatolian volcanic field using electron probe microanalyses on volcanic glass shards and morphological analyses on ash particles we postulate a correlation with the early holocene dikkartin dome eruption of erciyes dag volcano cappadocia turkey so far no tephra of the central anatolian volcanic province has been detected in marine sediment archives in the eastern mediterranean region the occurrence of the s1 tephra in the south eastern part of the levantine sea indicates a wide dispersal of pyroclastic material from erciyes dag more than 600 km to the south and is therefore an important tephrostratigraphical marker in sediments of the easternmost mediterranean sea and the adjacent hinterland

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

geophysics of proposed proterozoic sutures in canada abstract sutures have been identified or proposed at several sites in the canadian shield although many authors have suggested that some form of primitive plate tectonic processes have played a major role in the formation of the archean crust of the superior structural province proterozoic sutures resembling phanerozoic examples have been proposed only within the younger churchill and grenville provinces and at or near the boundaries between the older superior and slave provinces and the younger provinces gravity magnetic seismic and paleomagnetic data related to three proposed sutures in the latter category have been interpreted and generally support the view that the shield comprises a mosaic of once separated but now joined cratonic blocks the sutures vary in complexity from wide zones containing distinctive rocks formed at ancient accreting and consuming plate margins to cryptic sutures marked only by abrupt changes in metamorphism and zones of cataclasis paired negative and positive gravity anomalies associated with these sutures have been interpreted in terms of juxtaposed crustal blocks of different density and thickness magnetic anomaly patterns change abruptly at structural province boundaries available seismic results support the concept of thickened crust in the younger province as derived from gravity modelling most authors prefer interpretation of proterozoic pole positions in terms of one plate models but in some cases the interpretation of paleomagnetic data is equivocal and two plate models have been proposed

eruptive history of the late quaternary ciomadul csomad volcano east carpathians part i timing of lava dome activity located at the southern tip of the intra carpathian volcanic range in romania and composed of a dozen dacitic lava domes the ciomadul csomad volcanic complex is the youngest eruptive centre of the carpatho pannonian region whereas in the last decade the explosive history of ciomadul since 50 ka has been well constrained by numerous studies the chronology of the dome sequence still lacks robust chronological constraints and an extended analysis of all available data here we apply a detailed k ar dating approach to refine the chronology of the lava dome eruptions using the unspiked k ar cassignol gillot technique our dating focused on the most voluminous central part of the lava dome complex new eruption ages were determined following a strict separation of 10 g of groundmass from about 3 kg of unaltered sample rocks thereby isolating material whose cooling was contemporaneous with the eruption the newly applied methodology mainly consisting of a double full preparation first at larger grain size 0 4 mm and then at 100 m provides an appropriate procedure to separate suitable material to obtain the k ar age of the eruption i e the sample s groundmass in which there is no risk of the presence of older inherited crystals our new geochronological data set gives an improved insight into the temporal construction of the ciomadul volcanic complex where due to the method applied here all ages are younger than those from previous studies that used whole rock k ar ages our new results show that ciomadul s volcanic activity began with the construction of the south eastern peripheral domes from ca 850 ka to 440 ka after a ca 250 ky long repose period the activity resumed in the northern part at around 200 ka with subsequent domes emplaced between 200 and 130 ka aligned roughly north south in the western central part of the complex following a 30 ky long quiescence period the eastern central domes formed between 100 and 60 ka in addition to the chronological history of lava dome volcanism we also investigated the sequence of crystallization of mineral phases present in the lavas with respect to the modification of eruption ages ages obtained on pure minerals plagioclase amphibole and biotite are systematically older than those obtained on groundmass showing that most of them formed up to 1 85 myr before eruption in a long lived pre ciomadul magmatic system crystal size distribution csd data support the age contrasts between juvenile groundmass and older inherited minerals after injection of new magma and convective mixing with crystal clots ascent of the resulting mixture led to eruptions of material representing contrasting ages

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

an overview of the upb geochronology of the paleoproterozoic torngat orogen northeastern canada abstract the paleoproterozoic torngat orogen northern labrador and northeastern quebec canada is the result of oblique collision between the nain north atlantic and rae cratons a comprehensive set of u pb ages allows the chronology of events to be closely bracketed subduction occurred below the nain craton from ca 1910 1870 ma and collision between the cratons may have occurred between 1869 and 1844 ma sinistral deformation continued along the intervening abloviak shear zone until ca 1824 ma and convergence was ultimately impeded by the partial subduction of the southern rae craton post collisional isostatic uplift of the southern rae craton initiated deformation in the komaktorvik zone ca 1798 ma a prominent bend in the abloviak shear zone may be the result of differential uplift of the western side of the orogen in the south sinistral strike slip and east as well as west side up deformation continued episodically in the komaktorvik zone until at least 1710 ma the tectonic development of the orogen can be explained in terms of modern plate tectonic processes

impact of volcanism on the evolution of lake van ii temporal evolution of explosive volcanism of nemrut volcano eastern anatolia during the past ca 0 4ma thirty two new single crystal ages document 400 000 years of widespread explosive volcanism of historically active nemrut volcano towering over huge alkaline lake van eastern anatolia the dated deposits were selected to monitor the volcanic and compositional evolution of nemrut volcano through time and thus to provide a rigorous temporal framework for the tephra record of the paleovan drilling project tephra samples were taken from large volume deposits or those that occur in medial to distal localities well exposed stratigraphic sections or from the initial phase of an eruptive sequence mainly fallout deposits were chosen because most ignimbrites show more complex and corroded feldspar populations owing to compositional zoning and magma mixing moreover fallout deposits held the promise to be more clearly identifiable with and correlatable to 300 tephra layers in the paleovan drill cores even though commonly in amounts marginal or insufficient in thickness to allow well supported single crystal dating the crystals dated are dominantly anorthoclase the main phenoctyst phase in the trachytic to rhyolitic slightly to strongly peralkaline nemrut magmas ages obtained so far range from ca 400 ka to ca 30 ka for nemrut volcano the causes of significant changes in the frequency volume and composition of tephra layers per unit time are discussed in terms of external erosion climate changes geodynamic factors and internal forcing changes in magma supply and composition and incubation periods preceding large volume rhyolitic eruptions for example the low frequency of tephra layers deposited prior to ca 200 ka may be due to low explosive activity severe erosion between mis 9 and mis 11 or both nevertheless the overall frequency of explosive eruptions appears to have increased during the past ca 200 ka we also recognize a slight peak in explosive eruptions during warm periods e g mis 5 and mis 7 and speculate on lithospheric unloading triggering increased partial melting or magma reservoir unloading following massive glacier melting the ages of 5 dated ignimbrites span ca 250 000 years suggesting that nemrut volcano went through a polycyclic evolution with multiple caldera collapses and major pyroclastic flow eruptions the oldest dated so far as 265 ka the widely held view of the impressive nemrut caldera now dated to have formed at ca 30 ka as the main paroxysmal event during the evolution of the volcano is no longer tenable distinct and coherent compositional characteristics especially in trace element concentrations characterize several groups of trachytic tephras we speculate that the growth of nemrut volcano caused the isolation of the lake van basin on account of their mineralogical anorthoclase hedenbergite fayalite aenigmatite and alkalic chemical compositions and large volume dated nemrut fallout tephras are likely to represent excellent markers in lakes and other sites of paleoclimatological or archeological interest in neighboring countries to the northeast of lake van as far as the caspian sea in what may be called the east anatolian tephra province

vegetation cover and geomorphodynamics on abandoned fields in the central ebro basin spain abstract a dense vegetation cover is the key to soil erosion control on abandoned fields in semi arid environments in the study area maria de huerva in the semi arid central ebro basin spain investigations were carried out on two abandoned fields of different ages 5 and approx 75 years young fallow land abandoned field for a period of 5 years 1994 1998 the vegetation cover and the intensity of geomorphodynamics were recorded on two 24 36 m unbounded test plots for 8 5 specific dates based on the states of vegetation cover and geomorphodynamics at two points change maps were developed these change maps were combined to change relation maps it can be seen that an increase in vegetation cover does not generally lead to a stabilisation in the geomorphodynamic process activity

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

the intav intercomparison of electron beam microanalysis of glass by tephrochronology laboratories results and recommendations abstract the international focus group on tephrochronology and volcanism intav of the international union for quaternary research inqua has conducted an intercomparison of tephrochronology laboratories with electron beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries this assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community the intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation participating laboratories were each supplied with a mount containing three samples for analysis 1 rhyolitic lipari obsidian id3506 2 phonolitic sheep track tephra from mt edziza british columbia canada and 3 basaltic laki 1783 a d tephra a fourth sample rhyolitic old crow tephra was also distributed most laboratories submitted extensive details of their analytical procedures in addition to their analytical results most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration approximately two thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance despite substantial variety in procedures and calibration standards most mean concentrations compare favorably between laboratories and with other data typically four or fewer data contributions had means for a given element on a given sample that differed by more than 2 standard deviations from the overall means obtaining accurate na 2 o concentrations for the phonolitic tephra proved to be a challenge for many laboratories only one half of the data sets had means within 1 standard deviation of the 8 2 wt na 2 o value obtained by other methods one mean is higher and 14 are lower three of the data set means fall below 7 wt na 2 o most submissions had relative precision better than 1 5 for the major elements for low abundance elements the precision varied substantially with relative standard deviations as small as 10 and as large as 110 because of the strong response to this project the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories finally recommendations are provided for improving accuracy precision and reporting of electron beam microanalytical data from glasses

u pb ages for late magmatism and regional deformation in the shebandowan belt superior province canada five precise u pb zircon and titanite ages from different lithologic units of the shebandowan greenstone belt in the western wawa subprovince of the superior province put tight constraints on the time of late archean magmatism and of two major deformation events a porphyry sill from the older supracrustal sequence has an age of 2733 3 ma another porphyritic rock a trondhjemite occurring as a clast in a conglomerate of the unconformably overlying timiskaming type supracrustal sequence formed 2704 2 ma ago and defines a maximum age for the deposition of the timiskaming type sequence an alkalic volcanic rock from this sequence has been directly dated at in accord with the above constraint and with another probable maximum age of deposition given by the date of 2696 2 ma for the shebandowan lake pluton a first deformation event d1 was related to a predominantly vertical tectonic regime and occurred during or before intrusion of the shebandowan lake pluton at 2696 2 ma the second deformatio

marine tephra from the cape riva eruption 22 ka of santorini in the sea of marmara abstract a discrete tephra layer has been discovered in three marine sediment cores from the sea of marmara eastern mediterranean the rhyodacitic glass chemistry and the stratigraphical position suggest a santorini provenance and in particular a correlation with the marine y 2 tephra that is known from the southern aegean sea and eastern levantine basin this tephra represents the distal facies of the cape riva eruption of santorini which has been dated by 14c on land at 21 950 cal yr bp hitherto the y 2 tephra has been detected only in marine sediment cores recovered south to southeast of its volcanic source the new occurrence in the sea of marmara approximately 530 km nne of the santorini eruptive centre suggests a more north easterly dispersal of fallout products of the cape riva eruption than previously supposed

thermobarometric modelling of zircon and monazite growth in melt bearing systems examples using model metapelitic and metapsammitic granulites u pb age data collected from zircon and monazite are used to draw fundamental inferences about tectonic processes in the earth despite the emphasis placed on zircon and monazite ages the understanding of how to relate the timing of growth of zircon and monazite to an evolving rock system remains in its infancy in addition few studies have presented large datasets of geochronological data from zircon and monazite occurring in the same metamorphic rock sample such information is crucial for understanding the growth of zircon relative to monazite in a systematic and predictive manner as per this study the data that exist support the generally held conception that zircon ages tend to be older than monazite ages within the same rock here experimental data for zircon and monazite saturation in melt bearing rocks are integrated with phase diagram calculations the calculations constrain the dissolution and growth behaviour of zircon and monazite with respect to evolving pressure temperature and silicate mineral assemblages in high grade melt bearing metasedimentary rocks several key results emerge from this modelling first that in aluminous metapelitic rocks i e garnet cordierite sillimanite assemblages zircon ages are older than monazite ages in the same rock second that the growth rate of accessory minerals is nonlinear and much higher at and near saturation than at lower temperatures and third that the difference in zircon and monazite ages from the same rock may be ascribed to differences in the temperature s at which zircon and monazite grow rather than differences in closure temperature systematics using our methodology the cooling rate of granulites from the reynolds range central australia have been constrained at 4 c myr 1 this study serves as a first pass template on which further research in applying the technique to a field study can be based

the matuyama brunhes boundary in loess sections in the south of the east european plain and their correlation on the basis of palaeomagnetic and palaeopedologic data abstract the matuyama brunhes boundary mbb in loess sections of the east european plain one of the greatest areas of global loess distribution is a highly debatable issue the ambiguity of the mbb position here results from the complexity of loess soil magnetization processes and an apparent delay in loess remanence acquisition and from the uncertainties of pedostratigraphic interpretations in the don glaciation area the mbb is unanimously placed below the don moraine although the exact position is still controversial in the sites of the northern azov sea the mbb is however placed in the loess horizon considered to be the equivalent of the don moraine in the north the inconsistency of this interpretation is demonstrated by detailed magnetostratigraphic and pedostratigraphic studies in the western sites of zaporozh e dnieper basin novaya etuliya lower danube basin and roxolany lower dniester basin in all these sites albeit with certain minor discrepancies the mbb is found two or three interglacial palaeosols below the don loess which is overlain by the good stratigraphic marker of the vorona pedocomplex a thick polygenetic red brown palaeosol formed supposedly in a mediterranean climate here the mbb is placed in a quadruple soil unit termed roxolany loess soil suite which consists of four closely spaced strongly calcareous soils occupying an interval between the don loess on top and the earlier well developed bobrov loess with reversed matuyama magnetization the roxolany suite can possibly be correlated with the three palaeosols of the pre don ilyinka unit of the russian unified stratigraphic scheme and thus confirms the interpretation of the mbb in the central areas of the east european plain as to the interval between the ternovka second pre don palaeosol and the troitsk third pre don palaeosol

pedosedimentary division rock magnetism and chronology of the loess palaeosol sequence at roxolany ukraine abstract the loess mantle of the viii dniestre terrace at roxolany in the black sea area of ukraine is subdivided into six units which encompass the following palaeosol taxons pedocomplexes pk with evidence for several soil forming and sedimentary episodes incipient monogenetic palaeosols and horizons of carbonate concretions these cyclical loess palaeosol units provide a depositional record from the end of the matuyama chron through the holocene the detailed pedosedimentary subdivision of loesses at roxolany is generally consistent with magnetic susceptibility depth functions and seems to reflect global climatic variations earlier chronologies guidebook of the international geological congress xxvii session 1984 are re estimated on the basis of a revised position of the matuyama brunhes boundary and by detailed rock magnetic and micromorphological studies the strongly developed chernosem of pk 4 at approximately 22 m depth showing features of rubefication and the highest magnetic susceptibility value is viewed as a good stratigraphic marker of the late cromerian and seems to represent the climatic optimum of the brunhes chron oxygen isotope stage 13 the uppermost pk 2 is represented in the lower part by a chernosem analogous to surface soils of the area and is argued to be no younger than the last interglacial oxygen isotope stage 5e the poor preservation of pk 2 seems to result from processes of soil degradation and deflation at the time of interglacial glacial transition the closely spaced palaeosols between pk 2 and pk 4 seem to relate to three independent interglacials highest resolution of the palaeoclimatic record is found at the final matuyama chron from pk 9 to pk 8 and in incipient soils that contain either humic horizons with enhanced magnetic susceptibility or only horizons of large carbonate concretions

reply to comment on the paper by galaś a impact of volcanic eruptions on the environment and climatic conditions in the area of poland central europe earth science reviews vol 162 2016 58 64

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

the latest explosive eruptions of ciomadul csomad volcano east carpathians a tephrostratigraphic approach for the 51 29 ka bp time interval abstract the most recent mainly explosive eruptions of ciomadul the youngest volcano in the carpatho pannonian region have been constrained by detailed field volcanological studies major element pumice glass geochemistry luminescence and radiocarbon dating and a critical evaluation of available geochronological data these investigations were complemented by the first tephrostratigraphic studies of the lacustrine infill of ciomadul s twin craters st ana and mohos that received tephra deposition during the last eruptions of the volcano our analysis shows that significant explosive activity collectively called eppa early phreatomagmatic and plinian activity started at ciomadul in or around the present day mohos the older crater at 51 ka bp these eruptions resulted in a thick succession of pyroclastic fall deposits found in both proximal and medial distal localities around the volcano characterized by highly silicic rhyolitic glass chemical compositions ca 75 2 79 8 wt sio 2 the eppa stage was terminated by a subplinian plinian eruption at 43 ka bp producing pumiceous pyroclastic fall and flow deposits of similar glass composition probably from a proto st ana vent located at or around the younger crater hosting the present day lake st ana after a quiescent period with a proposed lava dome growth in the st ana crater a new explosive stage began defined as mpa middle plinian activity in particular a significant two phase eruption occurred at 31 5 ka bp producing pyroclastic flows from vulcanian explosions disrupting the preexisting lava dome of sf ana and followed by pumiceous fallout from a plinian eruption column related pyroclastic deposits show a characteristic less evolved rhyolitic glass composition ca 70 2 74 5 wt sio 2 and occur both in proximal and medial distal localities up to 21 km from source the mpa eruptions that may have pre shaped a crater similar to but possibly smaller than the present day st ana crater was followed by a so far unknown but likewise violent last eruptive stage from the same vent creating the final morphology of the crater this stage referred to as lspa latest st ana phreatomagmatic activity produced pyroclastic fall deposits of more evolved rhyolitic glass composition ca 72 8 78 8 wt sio 2 compared to that of the previous mpa stage according to radiocarbon age constraints on bulk sediment charcoal and organic matter from lacustrine sediments recovered from both craters the last of these phreatomagmatic eruptions that draped the landscape toward the east and southeast of the volcano occurred at 29 6 ka bp some 2000 years later than the previously suggested last eruption of ciomadul

early holocene volcanic ash fallout in the yammouneh lacustrine basin lebanon tephrochronological implications for the near east article i nfo a volcanic ash layer tyam 1 was identified in holocene sediments from the yammouneh paleo lake lebanon the ash layer consisted of colourless shards the major elemental chemistry of the glass as determined by electron microprobe analyses indicates a rhyolitic composition radiocarbon dating of detrital wood fragments located in the ash layer suggests an age of approximately 8 6 ka cal bp the timing of the layer and a chemical comparison with other published data suggest that tyam 1 likely originated from anatolia and likely corresponds to early holocene z3 z4 z5 tephras the preliminary results provided in this manuscript suggest a new stratigraphical and chronological marker for the continental records of lebanon and neighbouring regions

impact of volcanism on the evolution of lake van i evolution of explosive volcanism of nemrut volcano eastern anatolia during the past 400 000 years the historically active nemrut volcano 2 948 m asl eastern anatolia rising close to the western shore of huge alkaline lake van has been the source of intense plinian eruptions for 530 000 years drilled lake sediments about 40 widespread newly recognized trachytic and less common rhyolitic fallout tephras and ca 12 interbedded ignimbrites sourced in nemrut volcano are documented in stratigraphic traverses throughout an area of 6 000 km2 mostly west of lake van phenocrysts in the moderately peralkaline trachytes and rarer large volume comenditic rhyolites comprise anorthoclase hedenbergite augite fayalite and especially in trachytic units augite minor aenigmatite apatite and quartz and rare chevkinite and zircon dacitic to rhyolitic tephras from nearby calcalkalic suphan volcano 4 058 m asl locally interbedded with nemrut tephras are characterized by disequilibrium phenocryst assemblages biotite augitic clinopyroxene and hypersthene minor olivine common crystal clots and or in some deposits amphibole the magma volume dre of the largest nemrut tephra sheet ap 1 described in detail may exceed 30 km3 extreme facies and systematic compositional changes are documented in the ca 30 ka nemrut formation nf deposits formed from one large and complex eruption thick rhyolitic fallout overlain by ignimbrite welded agglutinate overbank surge deposits and final more mafic fallout deposits common evidence of magma mixing in nemrut ignimbrites reflects eruption from compositionally zoned magma reservoirs several young cekmece formation trachytes overlying ca 30 ka old nf deposits and the late trachytes of the nf deposits show compositional affinities to tephra from suphan volcano possibly due to temporary influx of suphan magmas into the nemrut system following the evacuation of 10 km3 magma dre during the caldera forming nf eruption axes of large fallout fans are dominantly sw ne but w e in the younger sheets resembling the direction of the present dominant wind field growth of nemrut volcanic edifice and its peripheral domes since before 0 5 ma in the hinge area between the van and mus tectonic basins is likely to have been the major factor in isolating lake van basin thus initiating the origin and subsequent alkaline evolution of the lake this alkalinity was later significantly controlled by climate forcing internal forcing mechanisms volcanic and geodynamic may also have contributed to major lake level changes in addition to climate forcing

roxolany and novaya etuliya key sections in the western black sea loess area magnetostratigraphy rock magnetism and paleopedology abstract loess paleosol sequences in the western black sea area at roxolany 48 m thick and novaya etuliya 30 m thick were studied using paleo and rock magnetic methods in conjunction with micromorphology and mossbauer investigations although seemingly complete the sites show variability in the type and number of loess paleosol cycles and inconsistency of the matuyama brunhes boundary mbb stratigraphic position at roxolany nine pedocomplexes pk and several incipient paleosols alternating with thick loesses were observed with the mbb being located between pk 6 and pk 7 at novaya etuliya 13 pks occur upon terrace xii with khapry fauna and with the mbb in the upper part of pk 7 and the jaramillo subchron within the lower part of pk 8 the depth functions of rock magnetic properties organic carbon content c org both for bulk samples and for clay extracts along with micromorphology and mossbauer spectra allowed objective identification of individual soils within pks and maximizing the resolution of paleopedological reconstructions of global climatic stages the mossbauer studies demonstrate that paleosols are basically enriched in ferric montmorillonite oxidized magnetite ultrafine iron hydroxides and hematite are intimately associated with clay minerals in contrast fe compounds in loess consist mainly of ferrous silicates these data indicate that the paleosol magnetism is basically of bio chemogenic origin and is related to pedogenic transformation of fe compounds in a changing environment while loess magnetism is primarily detrital pedogenic magnetically soft and partly oxidized magnetite may also originate during or even after burial this ensuing transformation of fe minerals in paleosols seems to be crucial for the understanding of the timing of natural remanent magnetization nrm in subaerial sediments given that paleosols formed on the similar parent material loess their typological variability seems to depend on climate and or chronology hence the different paleosol types from roxolany and novaya etuliya provide key information for intra and inter regional correlation of loess soil sequences and represent valid paleoclimatic proxies

review of crustal architecture and evolution in the ungava peninsula baffin island area connection to the lithoprobe ecsoot transect within the trans hudson orogen in northern quebec and southern baffin island parautochthonous archean basement and paleoproterozoic cover as well as allochthonous accreted paleoproterozoic units are exposed in a series of antiformal culminations and complementary synclinoria the parautochthonous rocks of the superior province margin and two assemblages of accreted paleoproterozoic units ungava and meta incognita crustal terranes define a basic tripartite crustal architecture which is characterized by polyphase deformation and metamorphic histories early structures and mineral assemblages are recognized in all three crustal components and shown to be temporally distinct the earlier structures and assemblages are overprinted by younger elements and mineral assemblages that are related to at least three regional contraction episodes and one thermal event that are common to all crustal components of the orogen close correlation of regional aeromagnetic data in northern quebec and southern baffin island with the three crustal components offers a first order approximation of the distribution of basement lithological units across hudson strait continuation of the aeromagnetic domains beneath ungava bay to northeastern quebec and northern labrador allows for the southward extrapolation of the tripartite trans hudson orogen crustal architecture into the lithoprobe eastern canadian shield onshore offshore transect 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

geochronology and isotopic variation of the early archaean amitsoq gneisses of the isukasia area southern west greenland abstract relatively unaltered samples of the amitsoq gneiss complex in the isukasia area were identified and analysed despite the effects of metamorphism and local proterozoic hydrothermal alteration and contamination the parents of the three lithologies that make up the amitsoq gneisses of the area were emplaced over about 320 ma taking a weighted average of dates from u pb on zircons rb sr on wr sm nd on wr and pb pb on wr the most probable ages of intrusion are grey gneisses at 3690 50 ma white gneisses at 3590 40 ma and pegmatitic gneisses at 3370 60 ma the rb sr isochron initial 87 sr 86 sr ratios for the grey white and pegmatitic gneisses are 0 7006 1 0 7016 1 and 0 8248 3 respectively the corresponding average nd t values are 1 0 0 7 and 0 2 since the ree chemistry of the rocks that were the direct parents of the grey gneisses is not known the 1 0 average nd t of the grey gneisses need not imply generation from a depleted mantle the sr initial ratio and nd t values for the white and pegmatitic gneisses are compatible with consecutive derivation at two discrete intervals by partial melting of crust mainly comprised of rocks similar to the grey gneisses the progressive evolution of nd with t for the amitsoq gneisses in the early archaean shows that values of nd t near zero in granitoids do not necessarily indicate derivation from the undepleted mantle chur

three dimensional structure of the torngat orogen ne canada from active seismic tomography the crustal velocity structure and the moho depth of the proterozoic torngat orogen ne canada is determined by active seismic tomography using travel times of crustal turning rays and moho reflections the orogen developed during oblique convergence of the archean superior and nain provinces which trapped an interior belt of archean crust core zone between them with the torngat orogen evolving between the core zone and the nain province beneath the central orogen a crustal root is found with a preserved depth of 52 km and a width of 100 km to the north the root shallows to 44 km and narrows to a width of 45 km the root correlates with a set of major late orogenic shear zones that accommodated oblique convergence of the superior and nain provinces this correlation suggests that the transpressional shearing focused strain in the region of the root and contributed to the crustal thickening absence of postorogenic magmatic activity prevented reworking or thermal relaxation of the root the lack of late magmatism is probably related to the depleted and refractory nature of the archean lithosphere underlying the orogen upper crustal velocities are lowest in the core zone 5 7 km s at the surface and are compatible with laboratory measurements carried out on gneissic rock samples from that area higher velocities in the nain province 5 9 km s correlate with felsic gneiss and anorthosite rock samples a high velocity region immediately to the north of the crustal root is associated with a moho uplift 34 km this is explained by extension along the ungava transform fault and possibly in hudson strait at 55 ma when rifting in the labrador sea was transferred into baffin bay

rb sr and u pb isotope studies on migmatites from the schwarzwald germany constraints on isotopic resetting during variscan high temperature metamorphism mineral and isotope studies were undertaken on migmatites from the schwarzwald moldanubian zone of the variscan belt the aims of the study were to date the migmatite formation and to determine the processes involved in migmatization in order to evaluate their influence on isotopic resetting textural evidence and the comparison of mineral compositions from leucosomes and mesosomes of two centimetre scale migmatite profiles respectively suggest that migmatitic textures and mineral assemblages were formed by metamorphic segregation deformation enhanced mass transport rather than by partial melting anatexis the results of rb sr thin slab dating on these profiles indicate that sr isotopes were not completely reset during migmatization no true isochron ages but ages of approximate isotopic homogenization were obtained on the thin slabs by calculating 87sr 86sr ratios back to various stages in their evolution the coincidence of these rb sr data with u pb ages of monazites from migmatites and non migmatitic gneisses shows that gneisses and migmatites were formed during the same high temperature event in the carboniferous 330 335 ma the observation that high temperature metamorphism failed to equilibrate sr isotopes on the centimetre scale imposes limitations on the use of conventional whole rock isochron techniques in dating migmatites

is the cape smith belt northern quebec a klippe the cape smith belt is one of the most interesting and controversial of the proposed geosutures in the canadian shield a new tectonic model is presented in which the mafic ultramafic thrust sheets of the belt constitute a klippe 20 000 km2 in area separated from underlying basement of superior province and its thin autochthonous cover by a continuous decollement exposed along the north margin and the plunging eastern end of the belt thrusting is directed southward and the entire stack is folded into a regional antiform north of the belt and synform the belt itself it is proposed that the decollement is rooted 30 90 km north of the belt in a zone paralleling sugluk inlet across which there is a major positive deflection in the bouguer gravity field an abrupt switch from broad north south to narrow east west magnetic anomalies and a change in metamorphic grade from amphibolite to granulite facies from south to north in the model this zone is a north dipping ductile shear zone juxtaposing cru

the marine isotope stage 1 5 cryptotephra record of tenaghi philippon greece towards a detailed tephrostratigraphic framework for the eastern mediterranean region abstract the iconic climate archive of tenaghi philippon tp ne greece allows the study of short term palaeoclimatic and environmental change throughout the past 1 3 ma to provide high quality age control for detailed palaeoclimate reconstructions based on the tp archive crypto tephra studies of a peat core tp 2005 have been carried out for the 0 130 ka interval the results show that the tp basin is ideally positioned to receive tephra fall from both the italian and aegean arc volcanic provinces two visible tephra layers the santorini cape riva y 2 c 22 ka and the campanian ignimbrite ci y 5 c 39 8 ka tephras and six primary cryptotephra layers namely the early holocene e1 tephra from the aeolian islands c 8 3 ka the campanian y 3 c 29 ka and x 6 tephras c 109 5 ka as well as counterpart tephras tm 18 1d c 40 4 ka tm 23 11 c 92 4 ka and tm 33 1a c 116 7 ka from the lago grande di monticchio sequence southern italy were identified along with repeatedly redeposited y 2 and ci tephra material bayesian modelling of the ages of seven of the primary tephra layers 60 radiocarbon measurements and 20 palynological control points have been applied to markedly improve the chronology of the tp archive this revised chronology constrains the age of tephra tm 18 1d to 40 90 41 66 cal ka bp 95 4 range several tephra layers identified in the tp record form important isochrons for correlating this archive with other terrestrial e g lago grande di monticchio sulmona basin and lake ohrid and marine e g adriatic sea core prad 1 2 and aegean sea core lc21 palaeoclimate records in the mediterranean region

u pb geochronology of archean magmatism and basement reactivation in the carajas area amazon shield brazil abstract the archean carajas subprovince is a metallogenic district bif bauxite cu ni mn au located in the easternmost amazonian craton in brazil the main conclusions from a u pb study of the itacaiunas supergroup and a locality in the xingu complex are the following the xingu basement complex the oldest unit underwent migmatization at 2859 2 ma and also grew new zircon at 2851 4 ma the luanga mafic intrusion is 2763 6 ma old and coeval with the 2759 2 ma felsic volcanics of the grao para group amphibolites from the salobo group contain 2851 ma zircons were metamorphosed 2761 3 ma and intruded by granitic veins ca 2758 ma at the time of grao para magmatism and also grew new zircon at 2732 2742 ma the data indicate that the salobo group is part of the xingu complex and not of the itacaiunas supergroup as heretofore believed the pojuca group possibly coeval with the salobo group was metamorphosed at 2732 3 ma a late archean reactivation event of regional extent is marked by titanite growth at 2581 5 ma in the mirim area intrusion of the old salobo granite at 2573 2 ma new zircon growth in salobo group amphibolites at 2555 4 3 ma and monazite growth in a metamorphosed iron formation at 2551 2 ma in addition k metasomatism associated with shear zones formed titanite in salobo group amphibolites at 2497 5 ma and new titanite at 2519 5 ma in the xingu complex events in the 2581 2497 ma interval are probably associated with the latest activity of a wnw ese sinistral shear system which could also be responsible for the establishment of a transtensional basin filled by the volcano sedimentary sequence of the grao para bahia and rio fresco groups finally undeformed proterozoic granitoid intrusions were dated at 1883 2 ma cigano 1883 5 2 ma musa 1880 2 ma carajas and 1874 2 ma pojuca

electron microprobe dating of monazites from high grade gneisses and pegmatites of the kerala khondalite belt southern india monazites of five samples one leptynitic garnet biotite gneiss one khondalite one augen gneiss and two pegmatites from the central and northern part ponmudi unit of the kerala khondalite belt kkb in southern india were analyzed with the electron microprobe dating technique monazites in the augen gneiss and the pegmatites yield grain sizes between 200 800 m th abundances are rather low 10 wt and the distribution of th u and pb within single grains is fairly homogeneous contrasting to this monazites in the leptynitic gneiss and the khondalite are small 150 m they often display very complex th u pb patterns and contain high th concentrations up to 20 wt the statistical treatment of individual ages from the investigated samples revealed three populations of lower proterozoic 1 9 ga upper proterozoic 580 ma and ordovician age 470 ma as well as mid proterozoic ages between 0 8 1 7 ga which are not regarded to be of geological significance lower proterozoic ages are preserved in the cores of monazites from leptynitic gneisses and khondalites they fairly agree with sm nd model ages for similar rocks of the kkb and give a minimum age for first monazite growth or complete homogenization the prominent pan african population with mean values between 540 and 580 ma is present in the leptynitic gneiss the khondalite and the augen gneiss and in line with published isotope ages for the kkb the ordovician population finally marks the emplacement of granitic pegmatites subsequent to the pan african high grade metamorphic event there is an obvious discrepancy between khondalites and leptynitic gneisses on the one hand and augen gneisses on the other concerning the presence of lower proterozoic ages while these are abundant in the former often rimmed by upper proterozoic ages they are completely absent in the latter it appears unlikely that lower proterozoic ages were completely reset during a pan african event exclusively in the augen gneisses while they were preserved in leptynitic gneisses and khondalites it is further concluded that the augen gneisses are of magmatic origin and were derived from porphyritic granites thus the upper proterozoic age of 605 37 ma calculated for the investigated sample approximates the time of magma emplacement which slightly precedes the peak stage of pan african high grade metamorphism in the kkb and of monazite crystallization from the granitic melt a characteristic feature of the investigated monazites is the resetting of lower proterozoic and pan african ages to significantly younger values due to partial pb loss monazites not shielded by other minerals e g garnet suffered selective mobilization of pb along fractures or at their rims while th and u concentrations remained almost unchanged the results presented in this study indicate that this was mainly due to fluid rock interaction it is concluded that thermal diffusion of pb even at the suggested temperatures of 900 c only had minor influence on the th u pb composition in monazite and that the closure temperature for this system must be significantly higher than previously assumed 750 c

le batholite de de pas nouveau quebec infrastructure composite d arc magmatique proterozoique the de pas batholith in new quebec is a mass of granitoids elongated in a n s direction covering 7000 km2 in the southeastern part of the archean rae province it is located between the paleopro

distribution and chemical composition of tephra layers from eastern mediterranean abyssal sediments abstract most cores of late quaternary sediments from the eastern mediterranean sea contain many ash layers glass shards from discrete layers have been analysed chemically for major elements the layers from different cores have been correlated and unambiguously related to known volcanic events on the basis of the chemical data most of the layers are derived from explosive eruptions of the santorini volcanic complex other layers have their source in other volcanoes of the hellenic arc yali nisyros kos one layer originated from the campanian area italy

vegetation and environmental responses to climate forcing during the last glacial maximum and deglaciation in the east carpathians attenuated response to maximum cooling and increased biomass burning the carpathian mountains were one of the main mountain reserves of the boreal and cool temperate flora during the last glacial maximum lgm in east central europe previous studies demonstrated lateglacial vegetation dynamics in this area however our knowledge on the lgm vegetation compo sition is very limited due to the scarcity of suitable sedimentary archives here we present a new record of vegetation fire and lacustrine sedimentation from the youngest volcanic crater of the carpathians lake st anne lacul sf ana szent anna tto examine environmental change in this region during the lgm and the subsequent deglaciation our record indicates the persistence of boreal forest steppe vegetation with pinus betula salix populus and picea in the foreland and low mountain zone of the east carpathians and juniperus shrubland at higher elevation we demonstrate attenuated response of the regional vegetation to maximum global cooling between 22 870 and 19 150 cal yr bp we find increased regional biomass burning that is antagonistic with the global trend increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers we also demonstrate xerophytic steppe expansion directly after the lgm from 19 150 cal yr bp and regional increase in boreal woodland cover with pinus and betula from 16 300 cal yr bp plant macrofossils indicate local 950 m a s l establishment of betula nana and betula pubescens at 15 150 cal yr bp pinus sylvestris at 14 700 cal yr bp and larix decidua at 12 870 cal yr bp pollen data furthermore support population genetic inferences regarding the regional presence of some temperate deciduous trees during the lgm fagus sylvatica corylus avellana fraxinus excelsior our sedimentological data also demonstrate intensified aeolian dust accumulation between 26 000 and 20 000 cal yr bp

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

danube loess stratigraphy towards a pan european loess stratigraphic model abstract the danube river drainage basin is the second largest river catchment in europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments indeed the danube river and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment however this vast loess province lacks a unified stratigraphic scheme european loess research started in the late 17th century in the danube basin with the work of count luigi ferdinand marsigli since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by kukla 1970 1977 in his correlations of loess with deep sea sediments loess palaeosol sequences in the middle and lower reaches of the danube river basin were a key part of this framework and contain some of the longest and most complete continental climate records in europe covering more than the last million years however the very size of the danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits local loess palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes which often change significantly with advances in age dating have limited the number of basin wide studies a unified basin wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records therefore we review the existing stratigraphic schemes and define a new danube basin wide loess stratigraphy based around a synthetic type section of the mosorin and stari slankamen sites in serbia we present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the chinese loess plateau with the oxygen isotope records from deep sea sediments and with classic european pleistocene stratigraphic subdivisions the hierarchy of danubian stratigraphic units is determined by climatically controlled environmental shifts in a similar way to the chinese loess stratigraphic scheme a new unified danube loess stratigraphic model has a number of advantages including preventing confusion resulting from the use of multiple national schemes a more transparent basis and the potential to set pleistocene palaeoenvironmental changes recorded in the danube catchment area into a global context the use of a very simple labelling system based on the well established chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the danube basin loess sites in a wider more accessible context that can be readily correlated world wide this stratigraphic approach also provides for the first time an appropriate framework for the development of an integrated pan european and potentially pan eurasian loess stratigraphic scheme

the southeastern churchill province synthesis of a paleoproterozoic transpressional orogen the paleoproterozoic southeastern churchill province secp is located in the northeastern canadian shield of labrador and quebec the secp formed through the oblique collisions of the archean nain and superior cratons with a third intervening archean block the core zone the belt has a tripartite structure comprising the torngat orogen to formed by nain craton core zone collision in the east the core zone in the centre and the new quebec orogen nqo formed by superior craton core zone collision in the west the secp thus records transpressional development on the flanks of the superior and nain cratons as they indented northwards to form the larger trans hudson nagssugtoqidian orogenic belt to the north principal stages of tectonic development were 1 2 2 2 1 ga crustal rifting of nain and superior cratons 2 ca 1 9 ga subduction under eastern nain craton 3 ca 1 87 1 85 ga collision of nain craton and core zone to form the to 4 1 845 1 820 ga sinistral transpression in the to and subduction under the western core zone and 5 1 82 1 77 ga collision of superior craton and core zone to form the nqo in association with dextral transpression crustal scale cross sections of the secp have been developed from reflection and refraction seismic data the western part of the nqo is dominantly west vergent and associated with an imbricate thick skinned thrust stack that ramps from the base of the crust the core zone is characterized by a 35 40 km thick crust and pervasive east dipping fabrics related to westerly thrusting the to is a narrow doubly vergent belt associated with a 48 km thick crust that forms a crustal root with a moho relief of 12 km the root is interpreted to result from attempted subduction of the core zone under the nain craton possibly as a result of mid crustal wedging by the nain craton the to was the site of intense convergence that resulted in excision of juvenile crust possibly including tectonic removal of the axial magmatic arc as a result the middle to lower levels of the secp consist largely of refractory archean lithosphere this may account for the lack of widespread post collisional plutonism in the secp and the preservation of the to root

loess correlations between myth and reality abstract the correlation of loess sequences across global hemispheric regional and local scales is one of the most fundamental aspects to loess research however despite recent progress in stratigraphic and chronometric methods the correlation of many loess sequences is often still based on untested assumptions over loess deposition preservation soil type and age as such the aim of this overview is to provide an adequate framework for evaluation of the accuracy of loess correlations applied on different temporal and spatial scales across eurasia this opens up possibilities for detailed temporal and spatial environmental reconstructions across the huge loess provinces of the eurasia and provides a framework for future extension of this to north america additionally we evaluate the potential development of appropriate sub millennial scale loess correlations as well as essentially important chronological approaches for establishing valid correlations between different loess records such as current improvements in tephrochronology 14c and luminescence dating techniques

middle upper pleistocene bio climatic and magnetic records of the northern black sea coastal area loess palaeosol sequences are widespread in the northern black sea coastal area unlike the quasi continuous loess palaeosol series in central asia and the loess plateau of china the incomplete geological record of loess palaeosol successions in europe provokes different stratigraphical interpretations for different sections despite a long history of investigation many uncertainties still remain in the geochronology of the regional stratigraphy in this study some of the most representative loess palaeosol sections of moldova the dniester republic southern ukraine and southern russia were examined a multidisciplinary approach was used to establish stratigraphical markers seven palaeosols pedocomplexes are distinguished within the brunhes chron in the loess palaeosol sequence in the studied area the position of the matuyama brunhes m b reversal is drawn at the base of the kolkotova palaeosol complex in the khadzimus section the jaramillo subchron was revealed at the base of the loess formation this magnetostratigraphic framework is confirmed by biostratigraphical data small mammals are valuable serving as very important evidence for long distance correlation paleopedological data combined with magnetic susceptibility profiles provide additional stratigraphic control for a loess palaeosol correlation the results allow us to conclude that the main paleoenvironmental changes occurred ca 1 ma ago when lagoon and alluvial sedimentation was replaced by increasing loess accumulaton during some intervals erosion or variation in the loess sedimentation rate at different sites are responsible for the variability of the loess palaeosol alternation the correlation of the loess palaeosol succession in the brunhes chron with marine oxygen isotope stages suggests that the beginning of the loess palaeosol formation of the middle pleistocene was forced by more pronounced long paleoclimatic cycles than are noticed prior to the m b reversal

palaeowind directions and sources of detrital material archived in the roxolany loess section southern ukraine abstract measurements of the anisotropy of whole rock magnetic susceptibility ams and u pb ages of detrital zircons have been combined to define the palaeowind directions and sources of wind blown dust in the loess palaeosol key section at roxolany southern ukraine zircon dating has also been used to determine the age and provenance of the interbedded roxolany tephra the distribution of ams axes in the loess indicates that the prevailing wind during its accumulation blew from the north west the same as the mean present day summer wind direction measured in the nerby city of odessa the u pb isotopic ages of the detrital zircons mostly range between 0 25 and 2 ga with clusters at 0 28 0 32 0 45 0 58 1 0 and 1 5 ga single neoarchean grains ca 2 7 ga were also found these ages indicate that material from carpathian and podolian sources formed the roxolany loess this material initially was transported by the dniester river then was wind blown form the dniester liman and the lower dniester valley located nw of roxolany most of the pyroclastic zircons from the roxolany tephra gave ages of 470 840 ka with a peak between 500 and 750 ka this age range is consistent with their being derived from the ciomadul volcano in romania

u pb ages for magmatism and deformation in the new quebec orogen the new quebec orogen is a paleoproterozoic fold and thrust belt active from 2 17 to 1 77 ga bordering the eastern margin of the archean superior province the orogen developed on a long lived passive continental margin and comprises two volcanic sedimentary sequences the ages presented in this study help to bracket the magmatic and deformational history of the orogen a glomeroporphyritic gabbro from the hellancourt formation was dated at 1874 3 ma and a rhyodacite from the upper murdoch formation yielded an identical age of 1870 4 ma these data allow the correlation of the two units and indicate that they are 10 14 ma younger than the estimated age for the sokoman formation these ages together with already published work indicate that magmatism related to the younger magmatic event occurred at 1884 1870 ma albitized pelites from the murdoch formation contain euhedral detrital zircons 2707 2690 ma old indicating that the source rocks were archean an undeformed monzonitic intrusion occurr

electron microprobe observations of pb diffusion in metamorphosed detrital monazites electron microprobe analyses have been made on monazite grains from paragneiss samples in the andalusite sillimanite transition 620 15 c and sillimanite orthoclase 680 15 c zones of the cretaceous ryoke metamorphic belt southwest japan monazites from pelitic gneisses are of metamorphic origin euhedral to subhedral and chronologically homogeneous giving chemical th u total pb isochron chime ages of 98 8 3 3 98 0 3 2 ma two psammitic gneisses of individual metamorphic grade contain both metamorphic monazite grains and detrital ones as old as ca 1700 ma most detrital monazite grains are heterogeneous in the tho2 and uo2 concentrations and have multiple or single rims as young as ca 100 ma several detrital monazite grains are well rounded in form exhibit homogeneous th and u distributions and show a pb diffusion profile in the margin the width of the diffusion zones is approximately constant throughout grains from each psammitic gneiss 18 22 m for 620 c and 48 58 m for 680 c assuming the isothermal diffusion of pb from homogeneous monazite spheres during a 5 ma duration of peak metamorphism we obtain diffusion coefficients of 1 9 0 3 10 21 and 1 5 0 3 10 20 cm2 s at 620 c and 680 c respectively these data derive an activation energy of 2 44 2 85 1 26 105 j mol and a frequency factor of 3 4 10 7 8 5 10 12 2 2 107 cm2 s taking account of uncertainties of 15 c in the temperatures and of 20 in the diffusion coefficients the diffusion parameters obtained from natural samples in this study provide a reliable insight into the closure temperature for pb in monazite that has been poorly understood so far

marker horizons in the loesses of the carpathian basin abstract two tephra horizons are known in the middle and upper pleistocene loesses of the carpathian basin the older bag tephra has been described from numerous loess outcrops in hungary whereas the younger paks tephra has been described only from the brickyard of paks in southern hungary the most characteristic heavy minerals in these horizons are various clinopyroxenes occurring in different proportions the clinopyroxenes of the bag tephra are extremely rich in ca and al while the volcanic glass is rich in k indicating high k andesitic or shoshonitic volcanism based on comparative geochemical analyses the most likely origin of the bag tephra is the roman or the campanian volcanic fields in italy geochemical investigation of the paks tephra is in progress and preliminary results suggest the same source for this younger tephra in contrast to the tephra horizons the correlation of the numerous paleosols in some hungarian loess sections and their paleoenvironmental interpretation is possible only if they are based on very detailed micromorphological studies the age determination of the loesses containing the paleosols directly by thermoluminescence tl and infrared stimulated luminescence irsl and indirectly by 14 c based isotope work should provide a reliable basis for the identification of soil forming periods in different parts of the carpathian basin

u pb geochronology of reactivated archean basement and of hudsonian metamorphism in the northern labrador trough the labrador trough is a proterozoic orogenic belt bordering the eastern margin of the archean superior province the volcano sedimentary sequences of the trough were deformed and metamorphosed during the hudsonian orogeny ca 1800 ma the eastern basement present as domal inliers was remobilized during this orogeny whereas the western basement remained unaffected in this study we present u pb ages of the western and eastern basement of the proterozoic labrador trough orogen between leaf river and koksoak river and of the northernmost extension of the depas batholithic complex farther east from the western basement the leaf bay granodiorite has an age of 2721 3 ma zircon from the gneiss domes of the eastern basement the ages are as follows lac moyer 2883 6 ma zircon 1793 5 ma monazite and 1746 ma minimum age rutile lac boulder an upper intercept age of 2868 8 ma and a lower intercept age of 1783 11 ma zircon titanite regression and an age of 1740 5 ma rutile lac olmst

the roxolany tephra ukraine new evidence for an origin from ciomadul volcano east carpathians we present major element glass data and correlations for the roxolany tephra a so far geochemically unconstrained volcanic ash layer previously described in last glacial marine isotope stage 2 loess deposits of the roxolany loess palaeosol complex in south west ukraine this exceptionally well preserved 2 3 cm thick tephra layer is characterized by a rhyolitic glass composition that is comparable to that of proximal tephra units from ciomadul volcano in the east carpathians central romania the chemistry particularly matches that of the final latest st ana phreatomagmatic activity pyroclastic fall unit of st ana crater that is radiocarbon dated in the proximal mohos coring site moh 2 to 29 6 0 62 cal ka bp the age of the tephra correlative agrees with the newest radiocarbon and infrared optically stimulated luminescence age constraints from overlying palaeosols and tephra embedding loess of the roxolany sequence respectively which place the tephra between ca 33 and 24 cal ka bp and thus confirm the long debated chronostratigraphy of this important environmental archive the occurrence of a distal ciomadul tephra ca 350 km east of its source indicates great potential for further tephra and cryptotephra findings from this volcanic complex in the south eastern mediterranean and black sea region

two billion year old isotopically heavy carbon evidence from the labrador trough canada forty eight samples of bulk carbonates were studied from the dunphy portage alder uve denault and abner formations and the undivided pistolet subgroup in the labrador trough quebec canada the carbonate units occur as a number of thick beds up to 300 m within 100 600 m thick formations they are interbedded with siliciclastic sediments and are composed of crystalline sparry micritic allochemical and stromatolitic dolostones the carbonate rocks are recrystallized and metamorphosed up to amphibolite grade they are chemically dolostones and include chemical or biochemical laminated and massive dolostones dolorudites dolarenites and dololitites which were deposited in shallow water dunphy denault and abner formations to relatively deep water uve formation marine environments reef facies are present in the denault and abner formations the dunphy portage alder and uve formations deposited between 2 17 and 2 14 ga yield isotopically heavy values of 13c pdb ranging from 5 3 to

impact of volcanism on the evolution of lake van eastern anatolia iii periodic nemrut vs episodic suphan explosive eruptions and climate forcing reflected in a tephra gap between ca 14ka and ca 30ka fifteen lateglacial to holocene rhyolitic dominantly primary tephra layers piston cored and drilled icdp paleovan drilling project in western lake van eastern anatolia turkey were precisely correlated to either of the two adjacent and active large volcanoes nemrut and suphan based on shard textures mineralogy and mineral and glass compositions the young peralkaline comenditic to pantelleritic primary rhyolitic nemrut tephras are characterized by anorthoclase hedenbergitic to augitic clinopyroxene fayalitic olivine minor quartz and rare accessory chevkinite and zircon phenocrysts in subalkaline primary rhyolitic suphan tephras are chiefly oligoclase labradorite with minor k rich sanidine in some biotite amphibole hypersthene rare augitic clinopyroxene relatively common allanite and rare zircon two contrasting explosive eruptive modes are distinguished from each other episodic suphan and periodic nemrut the lateglacial suphan tephra swarm covers a short time interval of ca 338 years between ca 13 078 vy bp and 12 740 vy bp eruptions having occurred statistically every ca 42 years with especially short intervals between v 11 reworked and v 14 causes for the strongly episodic suphan explosive behavior might include seismic triggering of a volcano magma system unable to erupt explosively without the benefit of external triggering as reflected in pervasive faulting preceding the suphan tephra swarm seismic triggering may have caused the rise of more mafic trachyandesitic parent magma heating near surface pockets of highly evolved magma that might have formed silicic domes during this stage of volcano evolution resulting in ascent and finally explosive fragmentation of magma essentially by external factors probably significantly enhanced by magma water ice interaction explosive eruptions of the nemrut volcano system interpreted to be underlain by a large fractionating magma reservoir follow a more periodic mode of a long term relatively constant supply of parent magma b evolution by low pressure crystal fractionation resulting in sporadic relatively low volume eruption of trachytic and minor rhyolitic magmas c evolution of a large magma reservoir to the point of highly explosive large volume peralkaline rhyolitic plinian eruptions at temporal intervals of ca 20 40 ky some accompanied by ignimbrites and inferred caldera collapse a striking tephra gap between ca 14 ka and ca 30 ka i e during glacial climate conditions is postulated to be due to climate forcing via lithosphere unloading following deglaciation

u pb geochronology of deformation and metamorphism across a central transect of the early proterozoic torngat orogen north river map area labrador1 the early proterozoic torngat orogen resulted from the oblique collision of the archean nain and southeastern rae provinces and evolved in four stages 0 deposition of platformal supracrustal assemblages followed by subduction related arc magmatism in the margin of the rae province i crustal thickening and nappe tectonics ii sinistral transpression and formation of the abloviak shear zone iii uplift on steeply dipping east verging mylonites along the eastern orogenic front u pb geochronology on zircon and monazite from major rock units and syntectonic intrusions indicates that arc magmatism at ca 1880 ma was followed by 40 ma of deformation and high grade metamorphism from ca 1860 to 1820 subsequent uplift and final cooling occurred ca 1795 1770 ma several ages of mineral growth that correspond to distinct structural and metamorphic events have been recognized 1 1858 1853 ma zircon and monazite dates are interpreted as the minimum age of stage i and peak metamorphic conditions 2

upb geochronology of the western cape smith belt canada new insights on the age of initial rifting and arc magmatism abstract the cape smith belt of northern quebec is the foreland to hinterland transition of the ungava orogen a component of the paleoproterozoic trans hudson orogen of north america u pb ages for rift and volcanic arc related units from the cape smith belt are presented and used to evaluate models of its tectonic evolution a gabbroic sill intrusive into the rift related sediments near the base of the povungnituk group is 2038 2 4 ma old indicating that rifting of the superior province was initiated prior to that time 80 m y earlier than previously reported a granodiorite intrusive into the volcanic rocks of the povungnituk group is dated at 1991 2 ma indicating that magmatism associated with the rifting event was active at that time 30 m y earlier than formerly thought the age of parent group arc related magmatism ranges from 1874 3 4 ma the age of a diorite intrusion to 1860 2 ma the age of another diorite intrusion and of a rhyolite a granodiorite intrusive in the parent group yields an age of 1845 6 ma magmatism of the parent group is thought to be related to northward dipping subduction of the superior province margin below the watts group a gabbroic intrusion in the 2000 ma old watts group is dated at 1858 2 ma these ages are consistent with a tectonic model in which the rocks of the cape smith belt formed in a single continental rift to oceanic progression followed by subduction which led to an arc continent collision a comparison of u pb ages for similar events in different sectors of the trans hudson orogen in canada reveals that early events are diachronous and range from 2169 ma to 2038 ma the main collisional events are coeval in the ungava and new quebec orogens and in some of the western sectors at 1830 1860 ma younger ages of 1800 1820 ma are obtained for the late collisional stages throughout the trans hudson orogen

petrology of the abloviak aillikite dykes new quebec evidence for a cambrian diamondiferous alkaline province in northeastern north america a dozen ultramafic lamprophyre dykes have been identified in the eastern part of ungava bay quebec the dark grey dykes are composed of macrocrysts of olivine and phlogopite featuring tetraferriphlogopite rims these minerals are included in a matrix consisting of fine grained phlogopite olivine spinel and interstitial carbonate the geochemical composition mineral assemblage chemical analyses of the xenocrysts and phenocrysts and sm nd isotopic signature indicate that these rocks are carbonated ultramafic lamprophyre dykes the chemical zonation of the micas and the presence of andradite suggest a complex sequence of crystallization an ar isotope correlation analysis indicates an age of approximately 550 ma the dykes have intruded the tasiuyak gneiss a suite of paleoproterozoic metasedimentary rocks this unit occupies the torngat orogen collision zone between the rae province and the nain province the dykes are considered to have been emplaced within tension gashes during reactivation of major

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

eruptive history of the late quaternary ciomadul csomad volcano east carpathians part ii magma output rates this study which builds on high precision unspiked cassignol gillot k ar age determinations presents an advanced dem based volumetrical analysis to infer long term magma output rates for the late quaternary ciomadul csomad dacitic lava dome complex east carpathians romania the volcanic field of ciomadul developed on the erosional surface of lower cretaceous flysch and 2 ma old andesites and experienced an extended eruptive history from 850 to 30 ka predominantly effusive activity took place during the first stage 850 to 440 ka producing volumetrically minor isolated peripheral domes subsequently after a 250 ky repose interval a voluminous central dome cluster developed in the second stage 200 to 30 ka during the youngest phase of evolution 60 to 30 ka highly explosive eruptions also occurred resulting in the formation of two craters mohos and st ana the calculated 8 00 0 55 km3 total volume of the lava domes which includes the related volcaniclastic 1 57 km3 as well as erosionally removed 0 18 km3 material is in line with dimensions of other medium sized dacitic lava domes worldwide this volume was extruded at an average long term magma output rate of 9 76 km3 my 0 0098 km3 ky however most of the domes 7 53 0 51 km3 were formed in the 200 to 30 ka period implying a significantly increased magma output rate of 37 40 km3 my 0 0374 km3 ky more than 30 times higher than in the first stage within these long term trends individual lava domes of ciomadul e g those with volumes between 0 02 and 0 40 km3 would have been emplaced at much higher rates over a period of years to tens of years the active periods lasting up to hundreds of years would have been followed by repose periods 30 times longer the most recent eruption of ciomadul has been dated here at 27 7 1 4 ka this age which is in agreement with radiocarbon dates for the onset of lake sediment accumulation in st ana crater dates fragmented lava blocks which are possibly related to a disrupted dome this suggests that during the last typically explosive phase of ciomadul lava dome extrusion was still ongoing in a global context the analysis of the volumetric dynamism of ciomadul s activity gives insights into the temporal variations in magma output at lava domes short term day or week scale eruption rates smooth out in long term millenia scale output rates which are tens of times lower

u pb evidence of late archean tectono thermal activity in the southern sao francisco shield brazil the sao francisco craton in eastern brazil is one of the major shield areas in south america in the quadrilatero ferrifero area southern sector of the craton the archean rio das velhas greenstone belt is surrounded by granite gneiss terrane and is overlain by proterozoic sedimentary successions the bonfim metamorphic complex is the only area of the granite gneiss terrane adjacent to the greenstone belt that has been mapped it comprises two gneissic units tonalites and late granitic dykes which crosscut the regional north south shear fabric samples of gneiss two tonalites and a granitic dyke were dated by u pb a zircon core from the alberto flores gneiss yielded a minimum age of 2920 ma whereas the overgrowth is concordant at 2772 6 ma two tonalites from the vicinity of serra da moeda are old and a late dyke yielded an age of these data together with previously published u pb ages show that i greenstone belt volcanism was coeval with granitoid intrusion and with metamorphism of older

petrography geochemistry and nd isotope systematics of metaconglomerates and matrix rich metasedimentary rocks implications for the provenance and tectonic setting of the labrador trough canada the new quebec orogen consists of a supracrustal belt that was reworked when the superior craton collided with the core zone terrane during the paleoproterozoic trans hudson orogeny within the new

the gravity field over the ungava bay region from satellite altimetry and new land based data implications for the geology of the area gravity data were obtained along two transects on the southern coast of ungava bay which provide continuous gravity coverage between leaf bay and george river the transects and the derived gravit

an inter laboratory comparison of the electron probe microanalysis of glass geochemistry abstract tephrochronology commonly relies upon grain discrete analysis of glass shards to reveal the subtle geochemical differences between tephras from past explosive volcanic eruptions the use of electron probe microanalysis for this purpose is widely accepted by tephrochronologists it is widely recognised that both precision and accuracy must be maximised and that rigorous standardisation procedures must be followed in this paper the performances of seven northern european electron microprobe centres are compared using a geochemically homogeneous obsidian secondary standard the results reveal that a number of tephra oriented probe centres could benefit from exercises similar to the programme outlined within in particular it is evident that a number of these centres undertaking tephrochronological investigations have generated geochemical data that may be inadequate in terms of distinguishing between tephras inaccuracy in the determination of sodium is seen to be the main difficulty in recent years the application of distal tephrochronology to stratigraphical problems in the northern european quaternary record has become increasingly common geochemical standardisation is essential at an early stage in the development of a regional tephrochronological framework and we hope exercises such as presented here will encourage the production of reliable tephra geochemical data

fingerprinting the late pleistocene tephras of ciomadul volcano eastern central europe late pleistocene tephras derived by large explosive volcanic eruptions are widespread in the mediterranean and surrounding areas they are important isochronous markers in stratigraphic sections and therefore it is important to constrain their sources we report here tephrochronology results using multiple criteria to characterize the volcanic products of the late pleistocene ciomadul volcano in eastern central europe this dacitic volcano had an explosive eruption stage between 57 and 30 ka the specific petrological character ash texture occurrence of plagioclase and amphibole phenocrysts and their compositions the high k calc alkaline major element composition and particularly the distinct trace element characteristics provide a strong fingerprint of the ciomadul volcano this can be used for correlating tephra and cryptotephra occurrences within this timeframe remarkably during this period several volcanic eruptions produced tephras with similar glass major element composition however they differ from ciomadul tephras by glass trace element abundances ratios of strongly incompatible trace elements and their mineral cargo that serve as discrimination tools we used u th he zircon dates combined with u th in situ rim dates along with luminescence and radiocarbon dating to constrain the age of the explosive eruptions of ciomadul that yielded distal tephra layers but lack of identified proximal deposits

identification and dating of tephra layers from quaternary sedimentary sequences of inner anatolia turkey abstract results presented here are part of a research programme to investigate the environmental evolution in central anatolia during the pleistocene in this study tephra are used as chronostratigraphical markers between lacustrine sequences studied in cores or in sections surrounding eruptive centres of the central anatolian province at different locations in the konya plain and cappadocia tephra have been identified characterized and linked to eruptions of the nearby volcanoes seven different tephra have been clearly identified in lacustrine sequences of the konya plain 14 c dates on shells or organic matter as well as 230 th 234 u ages on gypsum give a chronological framework to the tephra layers in addition the study of the sediment fill of the eski acigol maar near nevsehir has allowed the recognition of several eruptions during late glacial and holocene in the vicinity of acigol the results show the first tephra to be identified in lacustrine sequences of anatolia they also show the cappadocian volcanism to be very young 35 ka this young volcanism is often of a basaltic type and does not include thick differenciated pyroclastic deposits

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

the upper and lower nisyros pumices revisions to the mediterranean tephrostratigraphic record based on micron beam glass geochemistry abstract the greek island of nisyros is the source of tephra found in distal settings throughout the aegean in this contribution we define geochemical fingerprints for the lower and upper pumice eruptions of nisyros based on micron beam major empa and trace la icp ms element data these two eruptions are compositionally distinct from each other the high phenocryst content of proximal lower and upper pumice tephra means that the differences between the two magmas are masked in whole rock analyses we demonstrate that all previous reports of distal marine and continental tephras correspond to the younger upper pumice not the older lower pumice this has important implications for the marine tephrochronology of the mediterranean and for the age of the upper and lower pumice eruptions we suggest an age of at least 47 ka for the upper pumice and an older unconstrained age for the lower pumice

the campanian ignimbrite y5 tephra layer a regional stratigraphic marker for isotope stage 3 deposits in the lower danube region romania a number of volcanic ash layers embedded in pleistocene loess and fluvial deposits of the lower jiu and olt valleys in south western romania have been analyzed for glass chemical compositions and general chronological relations the wds epma chemical analyses document remarkably similar major and minor element compositions at the four investigated sites and total alkali silica diagrams ascribe these volcanic ashes a phonolite to trachyte affinity a comparison with the quaternary carpathian volcanism chemical data refutes this volcanic field as the primary source even though earlier works have tentatively taken some of these volcanic ashes as evidence of volcanic activity in this particular field instead the chemical data suggest an origin in the campi flegrei volcanic province in italy and a comparison with chemical data from proximal and distal outcrops of the campanian ignimbrite y5 tephra confirm that the ash layers presented here are distal occurrences of this widespread tephra layer the campanian ignimbrite y5 tephra is the product of one of the largest late quaternary explosive events in the mediterranean and is consistently dated elsewhere to about 39 40 ka it is one of the most important chronologic stratigraphic markers of western eurasia that provide an independent basis for establishing age depth relationships for the embedding deposits optical luminescence age estimates obtained at two of the investigated sites further confirm that these volcanic ash occurrences represent a regionally synchronous depositional event around 40 ka these results highlight the important role that the campanian ignimbrite y5 tephra could play as marker horizon at sub continental scale providing that more potential tephra locations such as these from the pleistocene sedimentary deposits in the lower danube region are chemically and chronologically constrained

partial delamination of continental mantle lithosphere uplift related crust mantle decoupling volcanism and basin formation a new model for the pliocene quaternary evolution of the southern east carpathians romania abstract a geodynamic model is proposed for the mid miocene to quaternary evolution of the southern east carpathians in order to explain the relationships between shallow and deep geological phenomena that occurred synchronously during late collision tectonics in this area an active volcanic zone cross cuts since 2 my the suture between the overriding tisza dacia and subducting european continental plates mafic calc alkaline and alkaline magmas south harghita and persani volcanoes erupted contemporaneously these magmas were supplied by partial melting of the mantle lithosphere of the subducting and not of the overriding plate in an effort to decipher this geodynamically a typical setting of magma generation the spatial and temporal distribution of shallow and deep phenomena was successively examined in order to establish the degree of their interdependence our model indicates that intra mantle delamination of the subducting european plate is the principal cause of a succession of events it caused upwelling of the hot asthenosphere below a thinned continental lithosphere of the carpathians inducing the uplift of the lithosphere and its internal decoupling at the moho level by isostatic and mostly thermal effects during this uplift the crust deformed flexurally whilst the mantle deformed in a ductile way this triggered decompressional partial melting of the uppermost mantle lithosphere flexural deformation of the crust induced its fracturing allowing for the rapid ascent of magmas to the surface as well as reactivation of an older detachment horizon at the base of the carpathian nappe stack above which the brasov ciuc and gheorghieni hinterland basins formed by extension and gravity spreading the rapid subsidence of the focsani foreland basin is controlled by the load exerted on the lithosphere by the delaminated mantle slab that is still attached to it in this model crust mantle decoupling magma genesis and volcanism local near surface hinterland extension are consequences of uplift induced by asthenospheric upwelling triggered by intra mantle delamination this model enables to conceive that delamination induced decoupling began to be efficient 9 4 my ago at the northern end of the east carpathians when the mantle slab dipped westwards since then intra mantle delamination migrated laterally normal to the slab strike and follows the arcuate shape nw se sw of the carpathians nowadays whereas the mantle slab is still actively foundering below the vrancea seismic zone to the se of the most recent volcanic area south harghita persani a significant southwestward shift of the delamination process can be discerned

dynamics of the laschamp geomagnetic excursion from black sea sediments abstract investigated sediment cores from the southeastern black sea provide a high resolution record from mid latitudes of the laschamp geomagnetic polarity excursion age constraints are provided by 16 ams 14c ages identification of the campanian ignimbrite tephra 39 28 0 11 ka and by detailed tuning of sedimentologic parameters of the black sea sediments to the oxygen isotope record from the greenland ngrip ice core according to the derived age model virtual geomagnetic pole vgp positions during the laschamp excursion persisted in antarctica for an estimated 440 yr making the laschamp excursion a short lived event with fully reversed polarity directions the reversed phase centred at 41 0 ka is associated with a significant field intensity recovery to 20 of the preceding strong field maximum at 50 ka recorded field reversals of the laschamp excursion lasting only an estimated 250 yr are characterized by low relative paleointensities 5 relative to 50 ka the central fully reversed phase of the laschamp excursion is bracketed by vgp excursions to the sargasso sea 41 9 ka and to the labrador sea 39 6 ka paleomagnetic results from the black sea are in excellent agreement with vgp data from the french type locality which facilitates the chronological ordering of the non superposed lavas that crop out at laschamp olby in addition vgps between 34 and 35 ka reach low northerly to equatorial latitudes during a clockwise loop inferred to be the mono lake excursion

geochemical evolution of the minto block a 2 7 ga continental magmatic arc built on the superior proto craton abstract a 400 km long by 100 km wide geological transect across the minto block of northeastern superior province reveals five plutonic suites and minor amphibolite to granulite grade supracrustal remnants the oldest regionally significant plutonic rocks include 3 0 0 1 ga foliated to gneissic tonalite characterized by high na k ratios high al contents light ree enrichment and initial gend 1 8 the leaf river plutonic suite is the most widespread with crystallization ages of about 2725 5 ma across the transect the suite comprises massive to foliated pyroxene and hornblende bearing granodiorite tonalite granite diorite and minor gabbro pyroxenite and syn plutonic mafic dykes the rocks are i type calc alkaline have variable na k ratios moderate to high ba and sr contents and ree patterns with variable light ree enrichment depletion of heavy rees with increasing silica and neutral negative or positive eu anomalies initial nd values for the suite range from 0 5 to 1 3 mean 0 4 and initial 87 sr 86 sr ratios isr are 0 7020 the diatexite plutonic suite 2713 ma occurs within a 150 km wide zone and consists of orthopyroxene garnet granodiorite containing 25 50 inclusions of granulite grade mafic supracrustal and tonalitic inclusions the variable major and trace element chemistry of the suite with generally high ni and cr contents reflects heterogeneous source materials and the presence of non liquid components initial nd values are from 0 1 to 1 7 monzogranite and orthopyroxene granite dykes plugs and plutonic masses both 2690 ma comprise the last important plutonic suites both biotite monzogranite and orthopyroxene granite are light ree enriched but the former have negative eu anomalies and the latter positive initial nd values range from 0 7 to 3 2 for monzogranite isr 0 7016 to 0 7067 and 0 7 to 0 2 for orthopyroxene granite isr 0 701 to 0 702 the initial nd and isr values of the 2 7 ga plutonic suites are lower and higher respectively than estimatesf of the contemporaneous depleted mantle suggesting significant and wide scale reworking of older tight ree enriched high rb sr lithosphere early tonalite orthogneiss from goudalie domain may be derived by partial melting of mafic crust at high pressures the lithological and geochemical diversity of the 2725 ma leaf river plutonic suite indicate a range of parental magma compositions and petrogenetic processes but fractional crystallization of mantle derived basaltic melts which had assimilated small amounts of significantly older lower crust may have been the dominant mechanism crustal inclusion charged granodioritic diatexite 2713 ma was probably derived by partial melting of heterogeneous lower crustal materials under relatively dry conditions late biotite monzogranite was generated by partial melting of older sialic crust and orthopyroxene granite by deeper melting or fractional crystallization of more juvenile source materials with garnet as a residual mineral we infer from the presence of coeval mafic dykes in all plutonic suites that heat for melting was ultimately derived from intrusion of basaltic magmas at depth the 2 7 ga magmatism in the minto block occurred during a period of active production and accretion of juvenile oceanic terranes in the southern superior province the northwest directed subduction regime inferred from the southern superior province arc terranes may also have been responsible for the magmatism that acted on 3 ga lithosphere in the northern superior province melting within the mantle wedge beneath the proto cratonic lithosphere and in the lower crust occurred within a tectonic setting similar to that of modem continental magmatic arcs

constraints on the timing of quaternary volcanism and duration of magma residence at ciomadul volcano east central europe from combined u th he and u th zircon geochronology article i nfo high spatial resolutionzircon geochronologywas applied to constrain thetimescalesof volcaniceruptions of the youngest mostly explosive volcanic phase of ciomadul volcano carpathian pannonian region romania com bined u th and u th he zircon dating demonstrates that intermittent volcanic eruptions occurred in a time range of 56 32 ka the reliability of the eruption dates is supported by concordant ages obtained from different dating techniques such as zircon geochronology radiocarbon analysis and infrared stimulated luminescence dating for the same deposits the new geochronological data suggest that volcanism at ciomadul is much youn ger bca 200 ka than previously thought up to 600 ka a dominantly explosive volcanic phase occurred after an apparent lull in volcanism that lasted for several 10 s of ka after a period of lava dome extrusion that defines the onset of the known volcanism at ciomadul at least four major eruptive episodes can be distinguished within the 56 32 ka period among them relatively large sub plinian to plinian explosive eruptions produced distal tephra covering extended areas mostly southeast from the volcano the 38 9 ka tephra overlaps the age of the campanian ignimbrite eruption and has an overlapping dispersion axis towards the black sea region the wide range of u th model ages of the studied zircons indicates prolonged existence of a low temperature b800 c silicic crystal mush beneath ciomadul the main zircon crystallization period was between ca 100 and 200 ka coeval with the older mostly extrusive lava dome building stage of volcanism even the youngest u th model ages obtained for the outermost 4 m rim of individual zircon crystals predate the eruption by several 10 s of ka the zircon age distributions suggest re heating above zircon saturation temperatures via injection of hot mafic magmas prior to eruption intermittent intrusions of fresh magma could play a significant role in keeping the intrusive silicic magmatic reservoir in a partially melted for prolonged period the previous history of ciomadul suggests that melt bearing crystal mush resided beneath the volcano and was rapidly remobilized after a protracted several 10 s of ka lull in volcanism to trigger several eruptions in a comparatively short time window this classifies ciomadul as a volcano with potentially active magma storage pams which we propose to be common among the seemingly inactive volcanoes in volcanic arc regions the potential for reacti vation of these systems should be included into volcanic hazard assessments

the detailed tephrostratigraphy of a core from the south east black sea spanning the last 60 ka one visible volcanic ash layer and 21 non visible cryptotephra horizons have been identified in the m72 5 25 gc1 core from the south east black sea that spans the last 60 ka glass chemistry suggests that the tephras derive from italian hellenic and turkish sources the visible tephra layer is trachytic in composition and has been correlated to the 39 ka campanian ignimbrite super eruption from campi flegrei caldera italy two cryptotephra layers are associated with eruptions from acigol volcano turkey around the last glacial maximum another is linked to activity at erciyes dagi in the early holocene perikartini or karagullu and a cryptotephra layer near the top of the core correlates to the 3 6k cal a bp minoan marine z2 tephra from santorini thera greece this extends the known dispersal area for all these volcanic ash units many other calc alkaline rhyolite layers preserved in the core are likely to be from central anatolian sources but the lack of detailed proximal data for many of the volcanoes in the region prohibits further correlations the tephrostratigraphy and glass compositional data presented here allow the tephra layers to be used to correlate sedimentary archives across the region and help to extend the mediterranean tephrochronology framework towards the east

lower paleozoic tholeiitic dykes from central new brunswick possible evidence for the early opening of an ensialic taconian back arc basin cambrian and early ordovician sedimentary rocks of the lower tetagouche group from the southern miramichi terrane in new brunswick were intruded by a series of mafic dykes the age of dykes is unknown but their stratigraphic context and state of deformation indicate that they were intruded during the taconian orogeny the geochemistry of the dykes shows that they are a cogenetic magmatic suite of basaltic composition 48 55 wt sio2 and tholeiitic affinity the dykes are low in silica and high in tio2 1 5 3 5 wt and feo 8 16 wt magmatic evolution of the suite resulted from processes involving both crystal fractionation and crustal contamination as indicated by depletion of compatible elements important enrichment in high field strength elements and the presence of inherited zircons of precambrian age the most primitive samples resemble mid ocean ridge basalts except for higher alkali contents or continental tholeiites depleted of light rare earth elements in comparison the most evolve