an experimental study of the kinetics of decompression induced crystallization in silicic melt 1 experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression pinatubo dacite was held at 780 c 220 mpa fo2 nno 2 h2o saturated conditions for an equilibration period decompressed to final pressures pf ranging from 175 to 5 mpa and then held for 0 3 931 hours according to the plagioclase liquidus curve in ph2o t space for the relevant melt composition these decompressions impose effective undercoolings teff of 34 266 c growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 pf 150 mpa teff 34 93 c and equilibrium crystal modes are achieved in 168 hours microlite nucleation is the dominant transformation process for 10 pf 50 mpa teff 125 241 c and chemical equilibrium is not attained by 168 hours under these conditions slow steady decompressions typically produced normally zoned euhedral and planar faceted feldspar crystals although anhedral morphologies were produced at very low pf contrary to expectation slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure although counterintuitive these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth controlled by teff and melt viscosity experienced during each decompression path analysis of liquid to solid transformation kinetics using ttt style diagrams shows that crystallization occurs most rapidly at 100 mpa by a crystal growth mechanism the next most efficient crystallization conditions are at 25 mpa in a crystal nucleation dominated regime

crystal poor rhyolites and rhyodacites from volcan tepetiltic mexico evidence for melt formation crystallization and eruption over short timescales abstract a detailed petrologic study is presented for six rhyolite and rhyodacite pumices that erupted from volcan tepetiltic in western mexico to determine the pre eruptive conditions of the magma reservoir as the volcano exited a 180 kya hiatus of activity rhyolite pumices are crystal poor 6 7 and minimally saturated in seven mineral phases plagioclase titanomagnetite ilmenite apatite quartz orthopyroxene clinopyroxene hornblende zircon in all samples plagioclase is the most abundant phenocryst phase and spans a range of composition of 20 30 mol an in each sample pre eruptive temperatures determined from two fe ti oxide geo thermometry range from 703 to 857 c maximum pre eruptive h2o contents determined from plagioclase hygrometry range from 5 0 8 9 wt where the most calcic plagioclase compositions correspond to the highest water contents comparison of compositions textures and sr and ba concentrations in plagioclase are used to determine phenocrysts from xenocrysts through comparison with experiments xenocrysts are identified in one sample comp 48 comparison of plagioclase abundances textures and sizes with those grown in the run products of experiments from the literature reveals that 1 the pumices were all likely super heated prior to crystallization 2 they experienced a low degree of undercooling induced by either degassing or cooling and 3 four of the pumices those with

a thermodynamic model for the plagioclase liquid hygrometer thermometer a new thermodynamic model for the plagioclase liquid exchange reaction between the albite naalsi 3 o 8 and anorthite caal 2 si 2 o 8 components is presented which can be used as a plagioclaseliquid hygrometer or thermometer the model incorporates calorimetric and volumetric data for the pure liquid and crystalline components which permits the effect of temperature and pressure on the exchange reaction to be calculated independently from the effect of composition this allows a more accurate assessment of the effect of melt composition including dissolved water concentration on the exchange reaction from plagioclase liquid equilibrium experiments activity composition relations for the plagioclase solid solution are taken from holland and powell 1992 the new hygrometer is calibrated on 71 plagioclase liquid experiments of which 45 are hydrous and 26 are anhydrous three filters were applied to the phase equilibrium data 1 crystallanities 30 2 pure h 2 o fluidsaturated and 3 compositional totals including h 2 o component of 97 101 for hydrous quenched glasses the final data set spans a wide range of liquid compositions 46 74 wt sio 2 plagioclase compositions an 93 an 37 temperatures 825 1230 c pressures 0 300 mpa and dissolved melt water concentrations 0 7 wt h 2 o the standard error of estimate see for the model is 0 32 wt h 2 o and all liquid compositions are fitted equally well when the model is used as a thermometer all measured temperatures are recovered equally well within 14 c on average the model is only recommended for applications that fall within the compositional bounds of the calibration data set i e metaluminous basalts through rhyolites in equilibrium with an 95 an 35 it is not yet calibrated for rhyolites crystallizing plagioclase more sodic than an 30 owing to an absence of phase equilibrium experiments on rhyolites that pass the required filters the new plagioclase liquid hygrometer thermometer is available as a visual basic program that runs on excel 2004

quantitative nannofossil correlation to open ocean deep sea sections from plio pleistocene boundary at vrica italy although numerous studies have been performed on material from the vrica section southern italy1 3 with a view to establishing its suitability as a type section for the plio pleistocene boundary these studies have failed either to establish the age of the boundary or to achieve accurate correlation to other regions we report here quantitative studies of selected nannofossil species in this section which unambiguously correlate it with open ocean piston cores in which an accurate chronology has been established the age of the plio pleistocene boundary as proposed by colalongo et al 4 is estimated to be 1 6 myr

periodicities of caco3cycles in the pliocene of sicily discrepancies with the quasi periods of the earth s orbital cycles a high resolution caco3 record in combination with a detailed magnetostratigraphy is presented for the rhythmically bedded marly sequence of the pliocene trubi formation on sicily italy magnetostratigraphic age calibration and subsequent spectral analysis of the variatrions in caco3 content yield a remarkably consistent discrepancy between the resulting periodicities and the corresponding quasi periods of the earth s orbital cycles this discrepancy can only be explained by assuming that ages assigned to polarity reversal boundaries in the geomagnetic polarity time scale lack sufficient precision a new polarity time scale is presented for the major part of the gilbert and gauss chron using the radiometrically dated gilbert gauss chron boundary at 3 40 ma as an age reference point and extrapolating an average quasi period of 21 7 kyr of the precession cycle as the periodicity of small scale colour annex caco3 cycles

unraveling tectonic and climatic controls on synorogenic growth strata northern apennines italy we develop a new high resolution stratigraphic age model to unravel the contributions of tectonic and climatic processes on early to late pleistocene synorogenic growth strata we capitalize on excellent continuous exposures along the flank of the po foreland in northern italy to elucidate hydrologic geomorphic and sedimentologic processes that are regularly attributed to but rarely proven to be caused by glacial interglacial climatic changes and unsteady rock uplift we perform our analysis on the enza section a succession of marine and terrestrial strata exposed along the enza river between parma and reggio emilia northern italy bedding in the enza section displays synorogenic growth strata geometry with bedding dips that range from 2 to 55 that becomes progressively shallower upsection we develop an age model that incorporates biostratigraphy magnetostratigraphy rock magnetic cyclostratigraphy cosmogenic radionuclide burial dating and optically stimulated luminescence dating and shows that the enza section spans the interval between 0 04 and 1 65 ma furthermore the age model pins the time of deposition for several lithostratigraphic units of regional significance and shows that sediment accumulation was unsteady ranging from 14 31 cm k y in the marine part of the section to 5 362 cm k y in the overlying littoral and terrestrial part of the section unsteady deposition is most pronounced in the terrestrial deposits where thick fluvial gravel packages accumulated in short 10 15 k y time periods that coincide with quaternary glacial intervals there is direct evidence for a dominant tectonic control in the older marine part of the section here sediment accumulation rates on the limb of the fold growing along this portion of the northern apennine mountain front show that between 1 07 and 1 65 ma repetitive progradation of neritic sand units directly followed pulses of rapid punctuated uplift in contrast the cyclic terrestrial facies variations in the enza section reveal that once the section became emergent at ca 1 ma and uplift slowed climate was the dominant control on sediment production and deposition

geochemistry of the palitana flood basalt sequence and the eastern saurashtra dykes deccan traps clues to petrogenesis dyke flow relationships and regional lava stratigraphy recent studies of large mafic dyke swarms in the deccan traps flood basalt province india indicate that some of the correlative lava flows reached several hundred kilometers in length here we present field petrographic mineral chemical and whole rock geochemical including sr nd isotopic data on the palitana lava sequence and nearby dykes in the saurashtra region of the northwestern deccan traps these rocks are moderately evolved many with low ti nb characteristics we infer that most dykes are notably and systematically less contaminated by ancient continental crust than the palitana flows but four dykes are equally or significantly more contaminated with some of the most extreme sr nd isotopic compositions seen in the entire deccan traps initial end is as low as 18 0 a bhimashankar type and a poladpur type dyke are present several hundred kilometers from the type section of these magma types in the western ghats escarpment we find no geochemical correlations between the palitana sequence and three subsurface sequences in ne saurashtra containing abundant picritic rocks surface lavas previously studied from saurashtra or the western ghats sequence intriguingly the eastern saurashtra dykes cannot have been feeders to any of these lava sequences feeder dykes of these sequences may be located in southwestern or central saurashtra or in the dhule nandurbar dediapada areas across the gulf of cambay 200 300 km east of palitana our results indicate polycentric flood basalt eruptions not only on the scale of the deccan traps province but also within the saurashtra region itself

a rapid mechanism to remobilize and homogenize highly crystalline magma bodies the largest products of magmatic activity on earth the great bodies of granite and their corresponding large eruptions have a dual nature homogeneity at the large scale and spatial and temporal heterogeneity at the small scale this duality calls for a mechanism that selectively removes the large scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal rich viscous conditions seemingly resistant to mixing here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization unzipping of highly viscous crystal rich mushes we demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning what distinguishes our model is the recognition that the process has two stages initially a stiff mushy magma is reheated from below producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer when the thickening mobile layer becomes sufficiently buoyant it penetrates the overlying viscous mushy magma this second stage rapidly exports homogenized material from the lower mobile layer to the top of the system and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption the agreement between calculated and observed unzipping rates for historical eruptions at pinatubo and at montserrat demonstrates the general applicability of the model this mechanism furthers our understanding of both the formation of periodically homogenized plutons crust building and of ignimbrites by large eruptions

phase relations in silicic systems at one atmosphere pressure an important control on magma rheology is the extent to which the magma crystallizes during ascent as a result of the effective undercooling created by volatile exsolution to assess this undercooling we need to know the final anhydrous one atmosphere phase relations of silicic magmas for this reason we have performed one atmosphere controlled fo2 crystallization experiments on dacitic to rhyolitic melt compositions 67 78 wt sio2 and determined equilibrium phase assemblages melt fractions and some phase compositions over a range of temperatures experiments were run at oxygen fugacities between nno 1 and nno 2 and temperatures of 1 000 to 1 250 c constant phase compositions and sample crystallinities in runs longer than 3 5 days suggest that these runs closely approached compositional equilibrium additionally melting experiments with similar compositions yielded results closely resembling those obtained in crystallization experiments all samples have liquidus temperatures between 1 250 and 1 200 c with plagioclase the liquidus phase for the two most mafic samples and quartz for the most silicic sample when associated glass compositions are projected into the qz ab or system they define a revised one atmosphere quartz feldspar cotectic 5 10 less quartz normative than previously estimated glass compositions from each sample plot along this cotectic between 1 100 and 1 000 c consistent with the plagioclase quartz co crystallization textures found in runs at these temperatures this cotectic constrains glass compositions to a maximum silica content of 76 1 wt sio2 reported glass compositions in excess of 77 wt sio2 in volcanic samples suggest non equilibrium crystallization perhaps a consequence of large melt undercoolings

late gauss to early matuyama invasions of neogloboquadrina atlantica in the mediterranean and associated record of climatic change a well dated high resolution record of climatic change is presented for the late pliocene mediterranean principal component analysis on abundances of 14 planktonic foraminiferal species reveals a series of late gauss to early matuyama surface water cooling events which can be correlated with north atlantic glacial isotope stages 108 to 94 the abundance record of the benthic foraminifer trifarina angulosa suggests lowered bottom water temperatures at times of surface water cooling the record of surface water oxygen and carbon isotopes shows an inverse pattern with 18o maxima and 13c minima at times of cool sea surface temperature conditions concomitant decrease in p b value and increased admixtures of clastic material suggest that late gauss to early matuyama surface water cooling events in the mediterranean are accompanied with glacioeustatic sea level low stands major surface water cooling events are associated with invasions of neogloboquadrina atlantica this north atlantic mid to high latitude species is at 2 55 ma close to the gibraltar portal whereafter it could invade the mediterranean repeatedly during periods of climatic cooling until it disappears from all over the north atlantic and mediterranean at the end of glacial stage 96

crystal poor multiply saturated rhyolites obsidians from the cascade and mexican arcs evidence of degassing induced crystallization of phenocrysts a detailed petrological study is presented for six phenocryst poor obsidian samples 73 75 wt sio2 erupted as small volume monogenetic domes in the mexican and cascade arcs despite low phenocryst microphenocryst abundances 2 6 these rhyolites are each multiply saturated with five to eight mineral phases plagioclase orthopyroxene titanomagnetite ilmenite apatite zircon hornblende clinopyroxene sanidine pyrrhotite plagioclase and orthopyroxene phenocrysts identified using phase equilibrium constraints span 30 mol an and 15 mg respectively eruptive temperatures 1 on the basis of fe ti two oxide thermometry range from 779 25 to 940 18 c oxygen fugacities 1 range from 0 4 to 1 4 0 1 log units relative to those along the ni nio buffer with temperature known the plagioclase liquid hygrometer was applied maximum water concentrations calculated for the most calcic plagioclase phenocryst in each sample range from 2 6 to 6 5 wt this requires that the rhyolites were fluid saturated at depths 2 7 km it is proposed that the wide compositional range in plagioclase and orthopyroxene phenocrysts despite their low abundance can be attributed to changing melt water concentrations owing to degassing during magma ascent phase equilibrium experiments from the literature show that higher dissolved water concentrations lead to more fe rich orthopyroxene as well as more calcic plagioclase loss of dissolved water leads to a progressive increase in melt viscosity and phenocrysts often display diffusion limited growth textures e g dendritic and vermiform consistent with large undercoolings caused by degassing a kinetic barrier to microlite crystallization occurred at viscosities from 4 5 to 5 0 log10 pa s for these rhyolites presumably because the rate at which melt viscosity changed was high owing to rapid loss of dissolved water during magma ascent

late pliocene to early pleistocene astronomically forced sea surface productivity and temperature variations in the mediterranean abstract principal component analysis of late pliocene to early pleistocene planktonic foraminiferal abundances from the mediterranean yielded two significant components which represent first order approximations for sea surface productivity and temperature this interpretation is confirmed by the good fit between the score plots and sea surface productivity and sea surface temperature proxy records based on selected eutrophic and temperature sensitive species using present day habitat characteristics spectral analysis revealed significant peaks in the orbital frequency bands of the spectrum suggesting that variations in sea surface productivity and temperature are controlled by the quasi periodic variations in the earth s orbit precession forced variations are reflected primarily in sea surface productivity and to a lesser degree in sea surface temperature maxima in sea surface productivity and temperature in this frequency band occurred at times of sapropel formation the sea surface productivity maxima can be explained by an increased input of river borne nutrients and by the shoaling of the pycnocline and the associated intensification of the deep chlorophyll maximum dcm layer precession forced variations in sea surface temperature are not related to glacial cycles since this frequency component is almost completely absent in ice volume proxy records for this time interval sapropel bound sea surface temperature maxima presumably reflect periods of maximum insolation during the northern hemisphere summer the contrasting winter signal corresponds to minimum insolation values which may be reflected by peak abundances ofgloborotalia inflata obliquity forced variations are reflected primarily in sea surface temperature and not in sea surface productivity these temperature fluctuations correspond with ice volume changes registered in the oxygen isotope record at the north atlantic dsdp site 607 this shows that obliquity forced sea surface temperature variations in the mediterranean are primarily driven by glacial cycles

integrated magnetostratigraphy and biostratigraphy of the upper pliocene lower pleistocene from the monte singa and crotone areas in calabria italy the results of a detailed magnetostratigraphic and biostratigraphic study of late pliocene to early pleistocene marine marl sequences from the monte singa and crotone areas in calabria italy are presented the magnetostratigraphy from the monte singa sequence ranges from below the gauss matuyama boundary up to and including the lower olduvai boundary normal polarities at a level corresponding to isotope stage 81 most probably represent the r union subchron from the lower olduvai boundary upward a reliable magnetostratigraphy could not be established due to increased weathering of the marls resulting in mainly secondary magnetizations the magnetostratigraphy from the composite sequence of the crotone area belongs to a large part of the matuyama chron and includes the olduvai subchron the position of the lower and upper boundaries of the olduvai subzone could be established more precisely than from earlier results moreover the upper boundary of the olduvai subzone poses an ambiguity a relatively long normal polarity interval representing the main olduvai subchron and corresponding to a duration of 115 ka is followed by a short 30 ka reversed subchron and the short 15 ka normal vrica subchron another option and more in accordance with the duration of the olduvai subchron in literature would be to consider the complete n r n polarity succession with a total duration of 160 ka as representing the olduvai subchron implying that this olduvai subchron has a short reversed interval in its upper part linear interpolation and extrapolation yield ages for the most important late pliocene early pleistocene biostratigraphic datum levels an age of 1 69 ma is found for the pliocene pleistocene boundary using the conventional polarity time scale dated with radiometric results however hilgen 1 in correlating the sapropel groups and patterns to the precession curve of the earth s orbit obtained significantly different ages for the polarity transitions of the present study according to this astronomically calibrated polarity time scale the age of the pliocene pleistocene boundary is 1 81 ma

can bed load transport drive varying depositional behaviour in river delta environments abstract understanding the processes and conditions at the time of deposition is key to the development of robust geological models which adequately approximate the heterogeneous delta morphology and stratigraphy they represent we show how the mechanism of sediment transport the proportion of the sediment supply transported as bed load vs suspended load impacts channel kinematics delta morphology and stratigraphy to at least the same extent as the proportion of cohesive sediment supply this finding is derived from 15 synthetic delta analogues generated by processes based simulations in delft3d the model parameter space varies sediment transport mechanism against proportions of cohesive sediment whilst keeping the total sediment mass input constant proximal morphology and kinematics previously associated with sediment cohesivity are also produced by decreasing the proportion of bed load sediment transport however distal depositional patterns are different for changes in sediment transport and sediment load cohesivity changes in sediment transport mechanisms are also shown to impact clinoform geometry as well as the spatiotemporal scale of autogenic reorganisation through channel avulsions we conclude that improving insight into the ratio of bed load to suspended load is crucial to predicting the geometric evolution of a delta

a refined pliocene to early pleistocene chronostratigraphic frame at odp hole 653a west mediterranean abstract two planktonic foraminiferal oxygen isotope records of odp hole 653a tyrrhenian sea are presented for the time period extending from approximately 0 8 to 3 0 ma six generally accepted synchronous bioevents were used to precise the oxygen isotope chronology and to identify the oxygen isotope stages 22 down to 114 subsequently this oxygen isotope chronology was used to determine the synchronism or diachronism of various other biostratigraphic events with those recorded in the singa and ficarazzi land sections italy and those in other dsdp odp sites new results concern the diachronity of the fod of the planktonic foraminiferal species n atlantica g truncatulinoides truncatulinoides and g inflata between odp hole 653a and the italian landsections because many species entered the mediterranean in short term fluxes strongly related to the southward migration of cool north atlantic surface waters their time distribution through the pliocene pleistocene generally corresponds to alternated intervals of presence and absence this should explain most of the apparently diachronous appearances and disappearances alternating presence absence patterns are of less importance for the various nannofossil events the lod of d surculus occurs during the transition of stage 100 to 101 in both odp hole 653a and the singa section which is in perfect agreement with the disappearance of this species from the open ocean the lod of d pentaradiatus in the mediterranean occurs in stages 100 99 which seems to be consistent with the extinction of this species in the southern hemisphere g oceanica which corresponds to the 4 m gephyrocapsa spp m is recorded in stages 65 to 64 at odp hole 653a the gephyrocapsa spp 5 5 m first occurred in stage 51 at hole 653a which fits within the uncertainty interval for this event stretching from stage 51 to 47 in the open ocean and seems therefore a useful tool for conventional biostratigraphy in the mediterranean

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

experimental study of liquid evolution in an fe rich layered mafic intrusion constraints of fe ti oxide precipitation on the t f o 2 and t ϱ paths of tholeiitic magmas the newark island layered intrusion a composite intrusion displaying a similar fractionation sequence to the skaergaard has both dikes which preserved liquids fed into the intrusion and chilled pillows of liquids resident in the chamber this study reports experimentally determined one atmosphere liquid lines of descent of these compositions as a function of oxygen fugacity which varies from qfm quartz fayalite magnetite to 0 5 log10 units above iw iron wustite these experiments reveal a strong oxygen fugacity dependence on the order of appearance and relative abundances of the fe ti oxide minerals titanomagnetite saturates prior to ilmenite at qfm but the order is reversed at lower oxygen fugacities in the layered series of the newark island intrusion ilmenite arrives shortly before titanomagnetite and the titanomagnetite ilmenite ratio decreases monotonically after the cumulus appearance of titanomagnetite comparison of the crystallization sequence in the intrusion with that of the experiments requires that the oxygen fugacity in the intrusion increased relative to qfm before titanomagnetite saturation and decreased afterward but always remained between the qfm and iw buffers similar trends in the modes of the fe ti oxides ilmenite and titanomagnetite in the skaergaard kiglapait and somerset dam intrusions along with fe2o3 feo ratios in morbs suggest that such a temperature oxygen fugacity path may be typical of tholeiitic magma differentiation calculations of the temperature density paths of the experimental liquids indicate that at all possible oxygen fugacities the density must have decreased abruptly after fe ti oxide saturation accordingly liquids replenishing the intrusion after fe ti oxide saturation should pond at the bottom of the chamber quenching against older cumulates field observation at the newark island intrusion confirm this prediction the similarities in the fractionation paths of several other layered intrusions to that of the newark island intrusion suggest that the density of the liquids in these intrusions also decreased after fe ti oxide saturation experiments on a suggested initial skaergaard liquid are consistent with this model

dissolution origin and syn entrapment compositional change of melt inclusion in plagioclase abstract in the system di ab an h 2 o melt inclusions in plagioclase were reproducibly formed in a series of partial dissolution experiments and the compositional differences from the surrounding matrix melt were evaluated at 200 mpa and 1050 1150 c a seed crystal of an 59 was partially dissolved into the matrix melt which was in equilibrium with more calcic plagioclase than the seed the reaction proceeded inward from the crystal surface by a dissolution and recrystallization process to form a reaction zone composed of melt channels and recrystallized calcic plagioclase the melt channels were choked necked off by the recrystallized plagioclase at the crystal surface to create melt inclusions the experimentally formed inclusions having square and zigzag shapes up to a few tens of micrometers in size are similar in texture to some common types of natural melt inclusion since the partial dissolution of phenocrysts can occur during various magma mixing processes it should be taken into consideration as one of the inclusion formation mechanisms when trying to interpret information from natural melt inclusions especially for those in hydrous arc magmas the chemical composition of the reproduced melt inclusions deviates from the matrix melt basically along the plagioclase liquidus isotherm the molar ratio of ca ca na and the mgo concentration in the synthesized melt inclusion are up to 17 and 61 relative lower than those in the matrix melt respectively this compositional difference is caused by a combination of factors 1 supersaturation with dissolved plagioclase component 2 insufficient diffusive homogenization in the melt channels due to rapid dissolution of plagioclase and 3 the choking off effect on the basis of the experimental results a model for diffusion in a growing melt channel in dissolving plagioclase was constructed which revealed that the concentration of incompatible elements with low diffusivities can be significantly lower in the melt inclusions than that in the matrix melt these results demonstrate the importance of petrography for interpretation of inclusion data and of more experimental studies on melt inclusion origin

increasing seasonal upwelling in the subtropical south atlantic over the past 700 000 yrs evidence from deep living planktonic foraminifera abstract the distribution and character of deep living planktonic foraminifera such asgloborotalia truncatulinoides andg hirsuta are particularly sensitive to the structure of the upper ocean because of the wide range of water depths over which their life cycles extend like other planktonic foraminifera the deep living species begin growing in shallow surface waters but unlike the other species they continue growing while sinking into much deeper water their reproduction is synchronized with the seasonal deep mixing and upwelling of nutrient rich waters that precedes spring bloom where deep mixing is curtailed the abundances of the deeper dwelling species g hirsuta the deeper dwelling varieties e g left coilingg truncatulinoides and the larger presumably faster sinking shells are reduced leading to an apparent acceleration in shell development these changes are observed today in transects from the seasonally deep mixed subtropical gyres to the seasonally stable surface waters equatorward of the subtropical convergences past changes in the abundance and character of these deep living planktonic foraminifera have been measured in a late pleistocene record from the subtropical western south atlantic ocean over the past 700 kyrs abundances of these species have increased g truncatulinoides has changed from the predominantly shallower dwelling right coiling to the deeper dwelling left coiling variety and the accelerated shell development characteristic of shallow mixing has shifted toward the rates normally associated with deep mixing all this indicates that the structure of the upper ocean in the subtropical south atlantic before 700 kyrs ago was more like that nearer the equator today where mixing is limited to the upper 100 200 m since that time the scale of mixing has gradually increased to more than 400 m this implies a gradual increase through the late pleistocene in the seasonal upwelling of nutrients in the subtropical south atlantic and consequently in the intensity of the seasonal maximum in organic productivity

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

the onset of major northern hemisphere glaciations and their impact on dinoflagellate cysts and acritarchs from the singa section calabria southern italy and dsdp holes 607 607a north atlantic abstract the climatic deterioration related to the onset of northern hemisphere glaciations circa 2 52 ma b p must have lead to reorganization and relocation of species associations and may have enhanced species turnover the present study investigates how this deterioration affects the dinoflagellate cyst and acritarch assemblages from two locations dsdp site 607 north atlantic and the singa section southern italy the records from these locations cover the interval from 2 8 to 2 2 ma with at least a 5 ka resolution and they have been correlated to the milankovitch periodicities on a cycle to cycle basis by means of integrated high resolution stable isotope calcium carbonate foraminiferal palynological and magnetostratigraphical datasets in the present study this high resolution stratigraphic framework is used for a detailed correlation of events occurring in each of the depositional sequences it also enables further assessment of the palaeoenvironmental preferences of some dinoflagellate cyst forms comparison of the two palynological records reveals a close correspondence in the timing of major assemblage changes and extinction events confirming their milankovitch cycle based correlation a close link between periods of northern hemisphere cooling at oxygen isotope stages 110 104 and 100 96 and increased dinoflagellate cyst turnover appears to be present for both dsdp site 607 and the singa section the turnover events can also be recognized in the records of planktic foraminifera and calcareous nannoplankton comparison of the singa section with site 607 and with other time equivalent marine palynological data sets shows that some oceanic taxa respond similarly over a large area the biostratigraphical implications are discussed notably the last occurrence of invertocysta lacrymosa appears to be a valuable marker for isotope stage 110 in the mediterranean and north atlantic

palaeoceanography of the last deglaciation in the alboran sea western mediterranean stable isotopes and planktonic foraminiferal records abstract oxygen isotope changes of the foraminiferal species globigerina bulloides and uvigerina peregrina eleven radiocarbon dates on the sediment fraction above 50 m and 13 biostratigraphical events allow us to correlate and to date the sediment record of the last climatic cycle in four cores from the alboran sea nine ecozones are recognized which differ from those previously established for atlantic sediments cored immediately west of gibraltar these ecozones can be grouped into two broad phases from the last glacial maximum up to near 9 500 yr b p cold north atlantic microfaunas are the major component of the assemblages during this interval dominant species replace each other according to the varying temperature and density stratification of the water masses from 9 500 yr b p up to the present time subtropical forms from the central atlantic dominate the northern atlantic forms an abrupt increase in the percentages of g inflata occurred near 7 000 b p this event was diachronous within the mediterranean during the last glacial g inflata was endemic inside the mediterranean and its abrupt increase near the end of the deglaciation did not result from replenishment from the atlantic between 4 000 and 5 000 yr b p percentages of g bulloides also increased abruptly warming conditions associated with the onset of a seasonal thermal stratification and a contrasting winter vertical convection are strongly suggested

age of the plio pleistocene boundary in the vrica section southern italy new palaeomagnetic data from the proposed plio pleistocene boundary stratotype section vrica section southern italy are presented here in order to improve the correlation of these sediments to the magnetic polarity time scale if the interpretation preferred here is correct the boundary falls above the olduvai normal subchron at approximately 1 6 myr

mediterranean neogene planktonic foraminifer biozonation and biochronology abstract planktonic foraminifera are widely used for biostratigraphy and correlation of mediterranean neogene marine sediments and are a fundamental component in the astronomical tuning of the neogene time scale recent developments in high resolution studies focused on the astronomical calibration of cyclically marine sediments cropping out in land based sections and recovered from deep sea successions increased the accuracy of stratigraphic ranges of planktonic foraminiferal species improving the biostratigraphic resolution and biochronology the large amount of data on planktonic foraminifera obtained through quantitative semiquantitative analyses published in the recent years allowed the revision of many biohorizons and their calibrations we incorporate these developments and emendments into the existing mediterranean planktonic foraminiferal biozonation therefore in this paper we present an emended standard mediterranean planktonic foraminiferal biozonation with a detailed description of zones and subzones within the framework of the astronomical tuned neogene time scale 2004 and 2012 atnts2004 atnts2012 and we provide the range chart of the most common planktonic foraminiferal taxa and the quantitative distribution pattern of selected marker species twenty two biozones and thirty one subzones that span the past 23 million years have been identified we distinguished them using the following code system mmi1 to mmi13 and ndz for the time interval related to the messinian salinity crisis mediterranean miocene biozones mpl1 to mpl6 mediterranean pliocene biozones according to the gelasian as the uppermost stage of the pliocene series epoch and mple1 to mple2 mediterranean pleistocene biozones according to the calabrian as the lowermost stage of the pleistocene series epoch we assembled 118 neogene planktonic foraminiferal biohorizons from multiple datasets and incorporated the calibration of these bioevents into a revised neogene planktonic foraminiferal biochronology the revised and recalibrated data provide a major progress in biostratigraphic and biochronologic resolution and a template for future progress of the neogene time scale unfortunately two main gaps of planktonic foraminiferal quantitative data occur in the late burdigalian between 16 12 ma and 17 23 ma and at aquitanian burdigalian boundary between 19 74 ma and 20 66 ma due to the absence of high resolution studies of these time intervals in the mediterranean

calcareous plankton biostratigraphy and biochronology of the pliocene lower pleistocene succession of the capo rossello area sicily abstract in the first part of this paper we present the calcareous nannofossil biostratigraphy of the capo rossello section sicily which suggests that a sedimentary gap exists at the contact between the trubi and the overlying monte narbone formation close to the top of the proposed zanclean stratotype this suggestion is supported by the planktonic foraminiferal results and field observations in contrast the transition from the trubi to the monte narbone formation is well exposed gradational and biostratigraphically continuous in the nearby section of punta piccola a composite of the capo rossello and punta piccola sections serves as a good biostratigraphic reference for the pliocene of the mediterranean in a second part of this paper we have attempted to update the mediterranean pliocene time framework by integrating all of the available biostratigraphic biochronologic chronostratigraphic paleomagnetic and radiometric data

trace element partitioning between high an plagioclase and basaltic to basaltic andesite melt at 1 atmosphere pressure we determined plagioclase melt partition coefficients for 18 elements by performing controlled cooling rate 1 atmosphere experiments using both natural and synthetic basaltic 51 wt sio2 and basaltic andesite 56 wt sio2 powders in a vertical quench furnace the experiments produced an69 to an87 composition plagioclase three starting powders were gorda ridge basalt synthetic diopside 40 albite 28 anorthite 32 mixture and arenal volcano costa rica basaltic andesite the gorda and synthetic powders were doped at both low concentrations 20 200 ppm and high concentration 200 5000 ppm whereas the arenal powder was doped only at high concentrations resulting in two doped gorda powders low np and high sdp two doped diopside albite anorthite powders low dad high sdd and one doped arenal powder high ar99 2 trace elements concentrations in both glass and plagioclase were measured by secondary ion mass spectrometry sims and or by laser ablation inductively coupled plasma mass spectrometry la icp ms results for the partitioning of trace elements between plagioclase and melt at different doping levels demonstrate both adherence to henry s law and good agreement between the different analytical techniques in general plagioclase melt partition coefficients determined in the an69 73 range are similar to other published values however some of those occurring for plagioclase compositions an75 are distinctly lower than those predicted by current regression formulations we applied a two lattice melt model to these data to account for differences in melt composition and temperature and found that there were no aberrations associated with partition coefficients a new set of regression formulations is determined involving the newly determined dataset for plagioclase with an contents between 75 and 87