vegetation climate and environmental history of the last 4500 years at lake shkodra albania montenegro three parallel overlapping cores have been taken in the albanian side of lake shkodra albania montenegro the chronological frame of the record spanning approximately the last 4500 years has been assessed using four radiocarbon dates and four well known tephra layers of italian volcanoes multidisciplinary analyses turned out to be decisive to understand environmental climatic changes and human impact here we focus on palynology the humidity at shkodra was always enough to allow the developing of a luxuriant arboreal vegetation the pollen percentage diagram does not record important changes in terrestrial plants percentages arboreal pollen ap shows only a rather slight decrease with natural forests replaced by intensive cultivation of chestnut and walnut in the last seven eight centuries the rather minimal changes in composition and dominance are because of the fact that the pollen rain comes from different vegetation belts from the mediterranean to the alpine one two major periods of hu

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

discontinuous grain growth of quartz in metacherts the influence of mica on a microstructural transition abstract the microstructure of quartz in metacherts of the ryoke metamorphic belt in central japan develops from polygonal through duplex to irregular with increasing metamorphic grade the polygonal microstructure is composed of small mostly 90 160 m equant equigranular polygonal quartz grains whereas the irregular microstructure is characterized by large 300 m grains with irregular grain boundaries the duplex microstructure is a mixture of small polygonal and large irregular grains the development of these microstructures is interpreted as being due to secondary recrystallization the size of polygonal grains is greatly influenced by the presence of second phase minerals such as mica whereas that of large irregular grains is unaffected by second phase minerals there seems to be a critical grain size for quartz to occur as polygonal aggregates no polygonal aggregates occur in rocks with larger than the critical grain size the size about 140 m decreases slightly with increasing volume fraction of mica the mean grain sizes of polygonal quartz d and coexisting mica d in the duplex microstructure are systematically related to the volume fraction of mica f by d 0 728d 1 f 0 629

geoarchaeology confirms location of the ancient harbour basin of ostia italy abstract to the northwest of the ancient city of ostia the analysis of cores revealed a stratigraphic sequence which we interpret as the filling of a harbour basin this basin located at the west of the so called palazzo imperiale presents seven characteristics 1 the maximum depth is 6 m below the roman sea level this depth allowed any type of ship even heavy tonnage to access the harbour 2 a chronostratigraphic gap at 6 m below roman sea level suggests digging operations in the basin or subsequent dredging that have caused the loss of sedimentary archives 3 the filling consists of dark clays typical of a quiet environment but open to marine and river influences 4 the dates at the base of this sequence give a range between the 4th and the 2nd century bc 5 in the harbour sequence a facies change at 2 5 m under the roman sea level involves a change in the processes of sedimentation and or operation 6 no later than the beginning of the 1st century ad the thickness of the water column in the basin is less than 50 cm and seems to be caused by a massive siltation following a succession of floods of the tiber 7 this basin was thus already abandoned during the start up of portus

grain boundary migration of quartz during annealing experiments at high temperatures and pressures with implications for metamorphic geology annealing experiments on agate quartz schist and metachert at 800 1000 c confining pressures of 400 and 800 mpa and annealing times of 6 0 10 3 6 105s revealed normal grain growth of quartz in the agate grain size increasing with time but the rate of grain growth decreasing with increasing grain size the boundaries of agate with quartz schist and metachert migrated into the agate at the expense of fine grained quartz in the agate the driving force for the migration appears to be the reduction of surface energy associated with removal of fine grained quartz in the agate assuming the activation energy as qm 11 kcal mol 1 a general expression for the relationship between velocity of boundary migration v and driving force p is where is the specific surface energy of quartz r is the gas constant and t is the absolute temperature the velocity is relatively fast at high temperatures on a geological time scale the expression assists a quantitative understanding of the microstructural development of quartz at metamorphic conditions

relationship between the sr and o isotope compositions of hydrothermal fluids and the spreading and magma supply rates at oceanic spreading centers we find a first order correlation between the sr and o isotope compositions of hydrothermal fluids and spreading rate at oceanic spreading centers the isotope signatures of hydrothermal fluids at slow spreading ridges are more rock dominated than those at fast spreading ridges implying that they have undergone a greater extent of sr and o exchange with the crust the local spatial and temporal variability in sr and o isotope signatures within individual hydrothermal sites can be attributed to short term variations in the hydrothermal system in response to magmatic or tectonic events phase separation at depth and mixing with seawater in the upwelling zone however these processes cannot explain the systematic global relationship of an increasing rock signature in hydrothermal fluids with decreasing spreading rate a greater extent of sr and o exchange between rocks and the circulating fluids can be achieved by 1 a longer fluid flow pathway through the oceanic lithosphere 2 more fractured rock that exposes a greater reaction area 3 an increased residence time of the fluid due to slower hydrothermal circulation or 4 a combination of all three our preferred interpretation is that fluid flow paths are longer and depths of penetration are likely greater at slow spreading ridges

the tiber river delta plain central italy coastal evolution and implications for the ancient ostia roman settlement geomorphologic stratigraphic faunistic palynological and carbon isotope analyses were carried out in the area of the tiber river mouth the results depict a complex palaeoenvironmental evolution

geochemical investigation of a sediment core from the trajan basin at portus the harbor of ancient rome a journal published by elsevier the attached copy is furnished to the author for internal non commercial research and education use including for instruction at the authors institution and sharing with colleagues other uses including reproduction and distribution or selling or licensing copies or posting to personal institutional or third party websites are prohibited in most cases authors are permitted to post their version of the article e g in word or tex form to their personal website or institutional repository authors requiring further information regarding elsevier s archiving and manuscript policies are encouraged to visit a b s t r a c t from the 1st century ad and for the duration of the roman empire the portus complex was the main harbor of rome its location on the tiber delta next to the tyrrhenian sea produced rapid environmental changes that together with historical vicissitudes largely determined the fate of the harbor we have assembled data on the mineralogy sedimentology geochemistry and ostracod populations of a sediment core drilled in the access channel of the hexagonal basin of trajan with the expectation that such a combined data set will shed new light on how the connections of the inland trajan basin with the tiber river the earlier claudius harbor on the nearby shoreline and the sea evolved through the centuries the data define four distinct periods which geochemistry characterizes by different conditions of salinity and oxygenation these in turn can be related to historical periods and events by means of 14

development of microstructure during deformation of carnallite and bischofite in transmitted light during deformation of 5 5 0 1 mm samples of carnallite and bischofite in transmitted light the development of the microstructure was followed by time lapse photography in dry samples carnallite deforms by mechanical twinning intracrystalline slip and by cataclastic processes the addition of brine strongly enhances dynamic recrystallization by progressive misorientation of subgrains and by grain boundary migration bischofite shows similar behaviour in agreement with results from samples deformed in a triaxial apparatus important microstructural processes during dynamic recrystallization of wet bischofite are grain coalescence grain dissection and grain migration the oscillatory motion of grain boundaries and sudden large changes in grain boundary migration rate were important features

vent fluid chemistry of the rainbow hydrothermal system 36 n mar phase equilibria and in situ ph controls on subseafloor alteration processes abstract the rainbow hydrothermal field is located at 36 13 8 n 33 54 15 w at 2300 m depth on the western flank of a non volcanic ridge between the south amar and amar segments of the mid atlantic ridge the hydrothermal field consists of 10 15 active chimneys that emit high temperature 365 c fluid in july 2008 vent fluids were sampled during cruise knox18rr providing a rich dataset that extends in time information on subseafloor chemical and physical processes controlling vent fluid chemistry at rainbow data suggest that the mg concentration of the hydrothermal end member is not zero but rather 1 5 2 mmol kg this surprising result may be caused by a combination of factors including moderately low dissolved silica low ph and elevated chloride of the hydrothermal fluid combining end member mg data with analogous data for dissolved fe si al ca and h2 permits calculation of mineral saturation states for minerals thought appropriate for ultramafic hosted hydrothermal systems at temperatures and pressures in keeping with constraints imposed by field observations these data indicate that chlorite solid solution talc and magnetite achieve saturation in rainbow vent fluid at a similar ph t p 400 c 500 bar of approximately 4 95 while higher ph values are indicated for serpentine suggesting that serpentine may not coexist with the former assemblage at depth at rainbow the high fe mg ratio of the rainbow vent fluid notwithstanding the mole fraction of clinochlore and chamosite components of chlorite solid solution at depth are predicted to be 0 78 and 0 22 respectively in situ ph measurements made at rainbow vents are in good agreement with ph t p values estimated from mineral solubility calculations when the in situ ph data are adjusted for temperature and pressure calculations further indicate that ph t p and dissolved h2 are extremely sensitive to changes in dissolved silica owing to constraints imposed by chlorite solid solution fluid equilibria indeed the predicted correlation between dissolved silica and h2 defines a trend that is in good agreement with vent fluid data from rainbow and other high temperature ultramafic hosted hydrothermal systems we speculate that the moderate concentrations of dissolved silica in vent fluids from these systems result from hydrothermal alteration of plagioclase and olivine in the form of subsurface gabbroic intrusions which in turn are variably replaced by chlorite magnetite talc tremolite with important implications for ph lowering dissolved sulfide concentrations and metal mobility

effect of paleoseawater composition on hydrothermal exchange in midocean ridges variations in the mg ca sr and so4 concentrations of paleoseawater can affect the chemical exchange between seawater and oceanic basalt in hydrothermal systems at midocean ridges mor we present a model for evaluating the nature and magnitude of these previously unappreciated effects using available estimates of paleoseawater composition over phanerozoic time as inputs and 87sr 86sr of ophiolite epidosites and epidote quartz veins as constraints the results suggest that modern hydrothermal fluids are not typical due to low ca and sr relative to mg and so4 in modern seawater at other times during the last 500 million years particularly during the cretaceous and ordovician hydrothermal fluids had more seawater derived sr and ca a prediction that is supported by sr isotope data the predicted 87sr 86sr of vent fluids varies cyclically in concert with ocean chemistry with some values much higher than the modern value of 0 7037 the seawater chemistry effects can be expressed in terms of the transfer efficiency of basaltic ca and sr to seawater in hydrothermal systems which varies by a factor of 1 6 over the phanerozoic with minima when seawater mg and so4 are low this effect provides a modest negative feedback on seawater composition and 87sr 86sr changes for the mid cretaceous the low 87sr 86sr of seawater requires either exceptionally large amounts of low temperature exchange with oceanic crust or that the weathering flux of continentally derived sr was especially small the model also has implications for mor hydrothermal systems in the precambrian when low seawater so4 could help explain low seawater 87sr 86sr

the ancient harbour parasequence anthropogenic forcing of the stratigraphic highstand record abstract unique chronostratigraphic similarities are observed in recent geoscience literature on ancient mediterranean harbours from these empirical port data a clear pattern of millennial anthropogenic forcing marked by a fining up sequence can be discerned in coastal stratigraphy the stratigraphic peculiarity of this artificial or human modified parasequence leads us to define a new working model the ancient harbour parasequence

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

evolution of the blueschist and greenschist facies rocks of sifnos cyclades greece the metamorphism on the island of sifnos is characterized by the eocene development of a coherent highpressure blueschist terrane and an early miocene greenschist facies overprint this study documents the metamorphic evolution of the blueschist assemblages still preserved in the northern parts of the island and their subsequent transformation into greenschists in the central and southern parts the oxygen isotope geothermometry is based on calibrations for quartz pyroxenes and magnetite matthews et al 1983a augmented by revised calibrations for the minerals muscovite qz mu 1 55 106 t 2 epidote qz ep 1 56 1 92 ps 106 t 2 and rutile qz ru 4 54 106 t 2 oxygen isotope analyses of minerals from the blueschist unit of northern sifnos give consistent fractionations which are independent of rock type an average temperature of 455 c was obtained although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred the minerals and whole rocks of the greenschists of central sifnos are systematically enriched in 18o relative to the blueschist assemblages chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of ca2 and co2 the petrologic isotopic and chemical evidence favour a metamorphism governed by the infiltration of 18o co2 enriched aqueous solutions it is reasonable to assume that this is connected with the miocene magmatic activity observed throughout the cyclades the marbles separating the blueschist from the greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation the pressure of the blueschist metamorphism is estimated at 14 2 kbar corresponding to a depth of ca 50 km the structural style and stratigraphy of sifnos are suggestive of the subduction of a continental margin sequence it is clear that the considerable tectonic depression may be associated with continental collision and underthrusting

the influence of kinetics on the oxygen isotope composition of calcium carbonate paleotemperature reconstructions rely on knowledge of the equilibrium separation of oxygen isotopes between aqueous solution and calcium carbonate although oxygen isotope separation is expected on theoretical grounds the temperature dependence remains uncertain because other factors such as slow exchange of isotopes between dissolved co2 species and water can obscure the temperature signal this is problematic for crystal growth experiments on laboratory timescales and for interpreting the oxygen isotope composition of crystals formed in natural settings we present results from experiments in which inorganic calcite is precipitated in the presence of 0 25 m dissolved bovine carbonic anhydrase ca the presence of dissolved ca accelerates oxygen isotope equilibration between the dissolved carbon species co2 h2co3 hco3 co32 and water thereby eliminating this source of isotopic disequilibrium during calcite growth the experimental results allow us to isolate for the first time kinetic oxygen isotope effects occurring at the calcite water interface we present a framework of ion by ion growth of calcite that reconciles our new measurements with measurements of natural cave calcites that are the best candidate for having precipitated under near equilibrium conditions our findings suggest that isotopic equilibrium between calcite and water is unlikely to have been established in laboratory experiments or in many natural settings the use of ca in carbonate precipitation experiments offers new opportunities to refine oxygen isotope based geothermometers and to interrogate environmental variables other than temperature that influence calcite growth rates

some garnet microstructures an illustration of the potential of orientation maps and misorientation analysis in microstructural studies the microstructures of two contrasting garnet grains are mapped using automated electron backscatter diffraction in both cases there is a very strong crystallographic preferred orientation with measurements clustered round a single dominant orientation each garnet grain is divided into domains with similar orientations limited by boundaries with misorientations of 2 or more in both samples most of misorientation angles measured across orientation domain boundaries are significantly lower than those measured between random pairs of orientation domains one sample is a deformed garnet that shows considerable distortion within the domains lines of orientation measurements within domains and across domain boundaries show small circle dispersions around rational crystallographic axes the domain boundaries are likely to be subgrain boundaries formed by dislocation creep and recovery the second sample is a porphyroblast in which the domains have no internal distortion and the orientation domain boundaries have random misorientation axes these boundaries probably formed by coalescence of originally separate garnets we suggest that misorientations across these boundaries were reduced by physical relative rotations driven by boundary energy the data illustrate the potential of orientation maps and misorientation analysis in microstructural studies of any crystalline material

deformation of crystalline materials in thin section a method applicable to weak low melting point model materials permits observation through a petrographic microscope of large simple shearing deformation of samples as thin as ordinary thin sections examples of ductile brittle and intermediate behavior can be studied the method lends itself to teaching and may also prove valuable in research

stable calcium isotopic composition of meteorites and rocky planets abstract new measurements of mass dependent calcium isotope effects in meteorites lunar and terrestrial samples show that earth moon mars and differentiated asteroids e g 4 vesta and the angrite and aubrite parent bodies are indistinguishable from primitive ordinary chondritic meteorites at our current analytical resolution 0 07 sd for the 44 ca 40 ca ratio in contrast enstatite chondritic meteorites are slightly enriched in heavier calcium isotopes ca 0 5 and primitive carbonaceous chondritic meteorites are depleted in heavier calcium isotopes ca 0 5 the calcium isotope effects cannot be easily ascribed to evaporation or intraplanetary differentiation processes the isotopic variations probably survive from the earliest stages of nebular condensation and indicate that condensation occurred under non equilibrium undercooled nebular gas conditions some of this early high temperature calcium isotope heterogeneity is recorded by refractory inclusions niederer and papanastassiou 1984 and survived in planetesimals but virtually none of it survived through terrestrial planet accretion the new calcium isotope data suggest that ordinary chondrites are representative of the bulk of the refractory materials that formed the terrestrial planets enstatite and carbonaceous chondrites are not the enrichment of light calcium isotopes in bulk carbonaceous chondrites implies that their compositions are not fully representative of the solar nebula condensable fraction

tracing the evolution of hydrothermal fluids in the upper oceanic crust sr isotopic constraints from dsdp odp holes 504b and 896a

the sediments of the stagno di maccarese marsh tiber river delta central italy a late holocene record of natural and human induced environmental changes the environmental evolution inferred from the sedimentary sequence that has occurred during the last three millennia in a drained coastal marsh in the tiber delta is presented the stratigraphy o

post deformational annealing of calcite rocks abstract the evolution of microstructure and crystallographic preferred orientation cpo during post deformational annealing was studied on three calcite rock types differing in purity and grain size carrara marble 98 calcite mean grain size of 115 m solnhofen limestone 96 5 m and synthetic calcite aggregates 99 7 m samples were first deformed in torsion at 727 c at a shear strain rate of 3 10 4 s 1 to a shear strain of 5 and subsequently heat treated at 727 c for various durations between 0 and 24 h microstructures and cpos were analysed by optical microscopy image analysis and electron backscatter diffraction ebsd all rock types deformed in the dislocation creep field at the same applied conditions but their microstructures and cpos after deformation and after annealing differed depending on starting grain size and material composition in carrara marble and in the synthetic calcite aggregate a strong cpo developed during deformation accompanied by dynamic recrystallisation with significant changes in grain size during annealing widespread grain growth and subtle changes of cpo occurred and equilibrated foam microstructures were approached after long annealing times the cpo is the only feature in annealed samples indicating an earlier deformation phase although it is not always identical to the cpo formed during deformation in the more impure solnhofen limestone secondary phases on grain boundaries suppressed grain boundary mobility and prevented both the formation of a recrystallisation cpo during deformation and grain size modification during deformation and annealing

reconstructing the oxygen isotope composition of late cambrian and cretaceous hydrothermal vent fluid oxygen isotope analyses 18o of 16 quartz epidote pairs from late cambrian betts cove and mings bight newfoundland ordovician thetford mines quebec canada and cretaceous troodos cyprus ophiolites are used to calculate the 18o of the hydrothermal fluids from which they crystallized we combine these with 3 quartz fluid inclusion measurements and 3 quartz magnetite measurements from the cambrian ophiolites to explore how the range in the 18o of submarine hydrothermal vent fluid has varied between the late cambrian cretaceous and today the range of calculated 18o values of vent fluid 4 to 7 4 is larger than that of modern seafloor hydrothermal vent fluid 0 to 4 we employ two numerical models to ascertain whether this range is most consistent with changes in paleo seawater 18o or with changes in the reactive flow path in ancient hydrothermal systems a static calculation of the vent fluid oxygen isotope composition as a function of the water rock ratio suggests that in an ocean with a lower 18o than today the range of vent fluid 18o should be larger our data however show little evidence that the 18o of the ocean was much lower than the global ice free value of 1 2 a dual porosity model for reactive flow through fractured and porous media is used to model the relative evolution of the 87sr 86sr and 18o of vent fluid in contact with rock our 87sr 86sr and 18o for cretaceous epidotes suggest the strontium concentration of the cretaceous oceans may have been much higher than at present the 87sr 86sr and 18o data from cambrian epidotes are strikingly different from the younger samples and are difficult to model unless fluid rock interaction in the cambrian hydrothermal systems was substantially different it is also possible that some of the quartz epidote veins have been reset by obduction related metamorphism our data suggest that the high calcium to sulfate ratio in early and cretaceous seawater may have affected the degree of strontium isotope exchange causing hydrothermal fluids to have 87sr 86sr closer to that of seawater than in modern systems

the natural and cultural landscape of naples southern italy during the graeco roman and late antique periods the landscape around the graeco roman town of neapolis was reconstructed through morphostratigraphic methods and pollen analysis of the sediments filling the bay hosting the ancient harbor this was discovered in 2004 thanks to excavations for two new lines of the naples metro network the harbor s sedimentary record spans the period between the late 4th century bc and the 6th century ad the main changes occurring in the marine and terrestrial landscape surrounding the ancient town are highlighted through the reconstruction of a detailed geological cross section and four 3d palaeogeographic models pollen analysis suggested the presence of mixed oak woods on the slopes surrounding the town and of vegetable gardens around the harbor area the tree crops mainly consisted of walnut and to a lesser extent chestnut and grapevines the horticultural varieties were dominated by brassicaceae most likely representing cabbage cultivation which was rather common in roman times comparison with reference pollen material reinforces this hypothesis during the 3rd century ad a drastic decrease in horticultural activity in concurrence with an increase in wild vegetation and tree crops suggest reduced maintenance due to a phase of abandonment historical data imply for the same period a phase of economic and social decline which involved the whole empire from the end of the 3rd century ad the growth of a spit bar at the port entrance gave rise to the establishment of a lagoon and then to the final closure of the bay

palaeoenvironmental reconstruction of the ancient harbors of rome claudius and trajan s marine harbors on the tiber delta during the first and second centuries ad emperor claudius and then emperor trajan successively ordered the construction of two large harbors on the tyrrhenian coast research resulted in advances in understanding the palaeoenvironments of the portus from a bathymetric point of view the drillings indicate a 7 8 m depth for the main basins different sedimentary behaviors were observed claudius basin shows sand accretion whereas the access channel to trajan s basin shows mud accumulation trajan built the second hexagonal basin because claudius harbor did not protect the ships from the wind and swell and not because it was prone to rapid silting in terms of chronology the channel between both basins worked between the end of the 2nd century and the beginning of the 5th century when it became completely clogged this means that after the beginning of the 5th century only the junction channel canale traverso remained to provide an access to the tiber and to the sea

plagioclase and epidote buffering of cation ratios in mid ocean ridge hydrothermal fluids experimental results in and near the supercritical region abstract experiments have been performed with na ca k cl fluids of seawater chlorinity and diabase basalt and plagioclase bearing mineral mixtures at 350 425 c and 250 400 bars to help constrain hydrothermal alteration processes at mid ocean ridges dissolved ca na and ph for all experiments responded systematically to differences in dissolved sio2 concentrations and the compositions of plagioclase reactants diabase alteration at low fluid rock mass ratios 0 5 to 1 produces fluids undersaturated with respect to quartz during hydration of primary olivine and orthopyroxene whereas basalt alteration under similar conditions yields fluids slightly supersaturated with respect to quartz during breakdown of glass to smectite and amphibole fluid chemistry in all experiments appears to approach a partial equilibrium state with the albite and anorthite components in plagioclase and approaches a ph consistent with plagioclase alteration to epidote trace element data from vent fluids specifically b and sr together with major element chemistry ca na sio2 ph provides evidence that the reaction zone for black smoker fluids at mid ocean ridges is composed of only slightly altered diabase and is characterized by small amounts of epidote nearly fresh plagioclase and clinopyroxene and partially to completely hydrated olivine and orthopyroxene fluids reacting with this rock may be undersaturated with respect to quartz so pressure estimates based on the quartz geobarometer should be regarded as minimums using equilibrium between plagioclase the dominant reactant and epidote the dominant reaction product in experiments we estimate that temperatures in reaction zones are in excess of 375 c for most vent systems these temperatures are higher than measured vent temperatures suggesting that hotspring fluids commonly loose heat during ascent to the seafloor

intragranular dynamic recrystallization in naturally deformed calcite marble diffusion accommodated grain boundary sliding as a result of subgrain rotation recrystallization abstract intragranular microshear zones within a greenschist facies calcite marble were studied to try to constrain better the processes of dynamic recrystallization as well as the deformation processes that occur within newly recrystallized grains intragranular recrystallized grains within large twinned calcite porphyroclasts can be related to the host from which they have recrystallized and are the focus of an electron backscatter diffraction study lattice distortions low angle boundaries and some high angle boundaries 15 in the microshears within a porphyroclast have the same misorientation axes suggesting that deformation occurred by climb accommodated dislocation creep involving subgrain rotation recrystallization changes in the ratio of host and twin domain as the deformation zone is entered show that twin boundary migration also occurred recrystallized grains have similar sizes 10 60 m to subgrains suggesting that they formed by subgrain rotation however within the intragranular microshear zones the misorientations between recrystallized grains and porphyroclasts are considerably larger than 15 and misorientation axes are randomly oriented moreover recrystallized grain orientations average around the porphyroclast orientation we suggest that the recrystallized grains once formed are able to deform partly by diffusion accommodated grain boundary sliding which is consistent with predictions made from lab flow laws

an oxygen isotopic profile through the upper kilometer of the oceanic crust dsdp hole 504b dsdp hole 504b is the deepest basement hole in the oceanic crust penetrating through a 571 5 m pillow section a 209 m lithologic transition zone and 295 m into a sheeted dike complex an oxygen isotopic profile through the upper crust at site 504 is similar to that in many ophiolite complexes where the extrusive section is enriched in18o relative to unaltered basalts and the dike section is variably depleted and enriched basalts in the pillow section at site 504 have 18o values generally ranging from 6 1 to 8 5 smow mean 7 0 although minor zeolite rich samples range up to 12 7 rocks depleted in18o appear abruptly at 624 m sub basement in the lithologic transition from 100 pillows to 100 dikes coinciding with the appearance of greenschist facies minerals in the rocks whole rock values range to as low as 3 6 but the mean values for the lithologic transition zone and dike section are 5 8 and 5 4 respectively oxygen and carbon isotopic data for secondary vein minerals combined with the whole rock data provide evidence for the former presence of two distinct circulation systems separated by a relatively sharp boundary at the top of the lithologic transition zone the pillow section reacted with seawater at low temperatures near 0 c up to a maximum of around 150 c and relatively high water rock mass ratios 10 100 water rock ratios were greater and conditions were more oxidizing during submarine weathering of the uppermost 320 m than deeper in the pillow section the transition zone and dikes were altered at much higher temperatures up to about 350 c and generally low water rock mass ratios 1 and hydrothermal fluids probably contained mantle derived co2 mixing of axial hydrothermal fluids upwelling through the dike section with cooler seawater circulating in the overlying pillow section resulted in a steep temperature gradient 2 5 c m across a 70 m interval at the top of the lithologic transition zone progressive reaction during axial hydrothermal metamorphism and later off axis alteration led to the formation of albite and ca zeolite rich alteration halos around fractures this enhanced the effects of cooling and18o enrichment of fluids resulting in local increases in 18o of rocks which had been previously depleted in18o during prior axial metamorphism

geometry conditions and timing of off axis hydrothermal metamorphism and ore deposition in the solea graben the recent discovery of fossil spreading axes along the northern margin of the troodos ophiolite1 provides a unique opportunity to compare a fossil seawater hydrothermal system with systems of modern oceanic spreading centres2 6 whereas previous accounts of ophiolite hydrothermal systems7 13 including troodos14 16have elucidated many aspects of sea floor hydrothermal metamorphism earlier workers have not placed ophiolite hydrothermal features within any specific spreading centre structural framework most ophiolites exhibit complex histories of post accretion deformation that mask or obliterate early structures related to seafloor spreading the troodos ophiolite is apparently still in the process of being emplaced 17 and most structural elements at troodos appear to have originated beneath a cretaceous sea floor1 we have discovered an extensive area of intense seawater hydrothermal alteration within the sheeted dyke complex of the solea graben fig 1 the metamorphic petrology and oxygen isotope geochemistry of 100 dyke samples from this graben reveal the size and three dimensional geometry of the hydrothermal system and yield estimates of temperature salinity oxygen isotope composition and recharge discharge geometry for fluids that transported the constituents of massive sulfide orebodies geometric discordance between the trends of the hydrothermally altered area and of earlier seafloor spreading structures compels us to consider a post spreading off axis origin for the orebodies of the solea graben

the holocene record of environmental changes in the stagno di maccarese marsh tiber river delta central italy the stratigraphic study of the stagno di maccarese carried out on the sediments exposed in about 7 km of trenches excavated in an area of approximately 1 5 km2 has shown that in the course of the holocene many environmental variations have taken place the complex evolution of the marsh is demonstrated by the variations in water salinity and the presence of erosion surfaces and soils between the sediments in the early holocene the area studied was an isolated marsh with water having variable salinity and it was only about 6000 cal yr bp that it was encompassed in the system of inner delta marshes in the delta environment the water of the marsh was oligohaline until about 9th 8th centuries bc brackish from 9th 8th centuries bc to about 600 yr bp and later oligohaline until the 19th century drainage a number of environmental variations are connected with local phenomena such as erosion of the beach ridges and tiber floods but the others can be correlated chronologically with climatic events rec

high temperature kinetic isotope fractionation of calcium in epidosites from modern and ancient seafloor hydrothermal systems abstract calcium isotope ratios in epidote from epidosites in ophiolites of varying phanerozoic ages have 44ca 40ca ratios that are lower by 0 1 to 0 6 relative to typical mid ocean ridge hydrothermal fluids epidosites are inferred to form in high temperature parts of seafloor hydrothermal systems at temperatures above 300 c and where fluid fluxes are high so the ca isotopic composition of the epidote is likely to reflect fractionation during growth of crystals from aqueous solution available ca isotope data from mor hydrothermal vent fluids and mantle peridotites constrain the 44 ca of likely modern hydrothermal fluids to a narrow range at 44 ca 0 05 0 1 a reactive transport model is used to evaluate whether the 44 ca of hydrothermal fluids might have been higher during the cretaceous and late cambrian the ages of the troodos oman and betts cove ophiolites from which we have data for these calculations we use the epidosite 87sr 86sr as a guide to the extent of ca isotopic exchange that affected the ancient hydrothermal fluids which were derived from seawater with higher ca and sr and lower sulfate concentration than modern seawater the calculations suggest that the ancient hydrothermal fluid 44 ca values were not much different from modern values with the possible exception of the late cambrian example we infer that the epidote fluid ca isotope fractionation averaging 44 ca 0 2 to 0 6 is most likely due to kinetic isotope fractionation during mineral precipitation there is evidence from the literature that hydrothermal epidote may commonly form from oversaturated solutions which makes the kinetic isotope interpretation plausible the equilibrium epidote fluid ca isotope fractionation is estimated to be 44 ca eq 0 based on recently reported dft calculations our results suggest that kinetic calcium isotope fractionation can affect hydrothermal silicate minerals and may be only slightly smaller in magnitude than the effects observed in ca bearing minerals at low temperature kinetic isotope effects during mineral growth could provide new insights into the formation mechanisms of hydrothermal silicate minerals

strontium alteration in the troodos ophiolite implications for fluid fluxes and geochemical transport in mid ocean ridge hydrothermal systems new and published strontium isotope analyses from the troodos ophiolite constrain fluid solid exchange processes and the magnitude and circulation paths of the hydrothermal fluids the87sr 86sr profile reflects alteration in the recharge zone of an evolving hydrothermal system fluid rock strontium isotope exchange in the upper 1 5 km of extrusive lavas was kinetically limited and seawater derived fluids emitted from the base of this zone were buffered to87sr 86sr ratios between 0 7047 and 0 7059 in contrast over the next 1 km depth interval of sheeted dykes and the uppermost plutonics 87sr 86sr values cluster about0 7054 7 2 and fluid flow is inferred to have been pervasive with near equilibrium fluid rock exchange quartz chlorite and epidosite zones the probable pathways of the concentrated high temperature upwelling fluids have identical87sr 86sr ratios to adjacent diabase dykes on troodos a time integrated fluid flux in excess of2 9 107 kg m 2 is required to transport the strontium isotope composition of 0 7054 set in the kinetically controlled exchange zone through the 1 km of sheeted dykes and into the zones of concentrated upwelling the uniformity of the87sr 86sr ratios in the diabase sheeted dykes and high temperature epidosite and quartz chlorite rocks indicate that the strontium isotopic alteration took place during the high temperature phase of hydrothermal circulation the inferred minimum time integrated fluid flux of2 9 107 kg m 2 substantially exceeds that of 5 106 kg m 2 inferred from thermal models of high temperature circulation but is comparable with estimates of the hydrothermal flux from oceanic budgets of3he mg and87sr the high flux estimate for troodos is consistent with the ophiolite venting fluids with87sr 86sr elevated significantly above rock values which contrasts with the near morb87sr 86sr ratios of fluids from active high temperature vents at mid ocean ridges and the87sr 86sr profile in dsdp hole 504b this requires that either the modern systems are immature and there is a protracted phase of lower temperature circulation or that circulation in the troodos ophiolite differed from that in normal mid ocean ridges and oceanic strontium budgets are balanced by another source the lack of very elevated87sr 86sr values in the vent fluids precludes significant channelling in the recharge zones of the active systems

discontinuous grain growth in recrystallised vein quartz implications for grain boundary structure grain boundary mobility crystallographic preferred orientation and stress history abstract grain growth is a process driven by the reduction of interfacial free energy leading to an increase in grain size and a reduction of the number of grains in a given volume of a single phase polycrystalline material discontinuous grain growth dcgg as opposed to normal grain growth ngg involves just a few grains blasts growing at the expense of a matrix that itself undergoes much slower modification in grain size hence producing a bimodal grain size distribution as a transient state prior to impingement of the blasts such a transient state has been found in a quartz layer in metamorphic rocks of the sesia zone western alps there large strain free quartz grains occur that reveal concave outward grain boundaries against a matrix of small grains with a pronounced crystallographic and a weak dimensional preferred orientation the misorientation of the blasts with respect to the matrix grains systematically exceeds 30 this finding suggests that the mobility of high angle grain boundaries in a natural quartzite depends on the degree of their misorientation among other factors as known for metals and alloys the width of the grain boundaries must be sufficiently small to allow for this effect dcgg is promoted by a pronounced crystallographic preferred orientation cpo that leaves only a few grain boundaries with sufficient misorientation to be mobile in contrast to ngg dcgg wipes out any pre existing cpo and information on activated glide systems or kinematics during the preceding stage of flow is lost after dcgg has gone to completion a complementary new cpo could even develop that could be difficult to interpret with respect to tectonic history interfacial free energy driven grain growth reflects a period of low stress annealing and thus constitutes a first order signal

dredging and canal gate technologies in portus the ancient harbour of rome reconstructed from event stratigraphy and multi proxy sediment analysis ancient harbours are rich archives of human environment interaction however dating harbour deposits and correlating their stratigraphy is a major challenge because of typically high sedimentation rates over short periods and possible curative dredging events portus the maritime harbour of rome at the height of the roman empire was a port complex composed of basins and canals connecting the commercial harbour to rome via the tiber river sediment core cps1 in the narrowest of these canals canale traverso is located centrally in what was the capital city s commercial hub and contains a continuous harbour depositional record with average sedimentation rates greater than 1 cm per year here we use piston coring high resolution core scanning and a multi proxy sediment analysis including for the first time paleo and rock magnetism and bulk and clay mineralogy in order to overcome the problems of dating harbour deposits and correlating their stratigraphy the method allowed precise identification of major reworked events including a dredged deposit and a hyperpycnal deposit which improve the chronostratigraphy and water depth reconstruction and sheds light on harbour technologies at the height of the roman empire a debris layer with abundant ceramic fragments and rocks marks the decommissioning of canale traverso and provides a new chronostratigraphic marker at portus multi proxy riverine input signatures point to the possible use of canal gate technology for water flow management

grain coarsening in contact metamorphic carbonates effects of second phase particles fluid flow and thermal perturbations under contact metamorphic conditions carbonate rocks in the direct vicinity of the adamello pluton reflect a temperature induced grain coarsening despite this large scale trend a considerable grain size scatter occurs on the outcrop scale indicating local influence of second order effects such as thermal perturbations fluid flow and second phase particles second phase particles whose sizes range from nano to the micron scale induce the most pronounced data scatter resulting in grain sizes too small by up to a factor of 10 compared with theoretical grain growth in a pure system such values are restricted to relatively impure samples consisting of up to 10 vol micron scale second phase particles or to samples containing a large number of nano scale particles the obtained data set suggests that the second phases induce a temperature controlled reduction on calcite grain growth the mean calcite grain size can therefore be expressed in the form d 1 4 c2 eq rt dp fp m where c2 is a constant q is an activation energy t the temperature and m the exponent of the ratio dp fp i e of the average size of the second phases divided by their volume fraction however more data are needed to obtain reliable values for c2 and q besides variations in the average grain size the presence of second phase particles generates crystal size distribution csd shapes characterized by lognormal distributions which differ from the gaussian type distributions of the pure samples in contrast fluid enhanced grain growth does not change the shape of the csds but due to enhanced transport properties the average grain sizes increase by a factor of 2 and the variance of the distribution increases stable d18o and d13c isotope ratios in fluid affected zones only deviate slightly from the host rock values suggesting low fluid rock ratios grain growth modelling indicates that the fluid induced grain size variations can develop within several ka as inferred from a combination of thermal and grain growth modelling dykes with widths of up to 1 m have only a restricted influence on grain size deviations smaller than a factor of 1 1 to summarize considerable grain size variations of up to one order of magnitude can locally result from second order effects such effects require special attention when comparing experimentally derived grain growth kinetics with field studies

syndeformational grain growth microstructures and kinetics abstract grain growth can be an important high temperature process in fine grained polycrystalline materials we studied its effect on texture during deformation using a two dimensional computer model and a see through experiment with octachloropropane syndeformational grain growth in geological materials can slow down the development of a grain shape preferred orientation or even obliterate it important processes are preferentially oriented deformation induced neighbour switches the presence of a grain shape preferred orientation slows down the increase in grain size due to grain growth

palynology and ostracodology at the roman port of ancient ostia rome italy new detailed palynological and ostracodological analyses together with texture data from a sediment core drilled in ostia antica confirm the existence of the ancient ostia harbour and its location by the tiber river using the different proxies analysed in this work and chronologically framing the sediment record with three ams radiocarbon dates four phases have been singled out pre harbour harbour bay under fluvial influence more protected harbour basin and post harbour phase ostracodology is used to reconstruct the marine versus freshwater influence in the basin palynology is used to reconstruct the plant landscape and the surrounding environment phases with low pollen concentration and expansions of npps suggest soil erosion and are alternated with quieter ones where human impact was very clear deciduous oaks typical of coastal plain forests are the main taxon during the harbour phases the occurrence of riparian trees increases in periods with low pollen concentration high npps and very high pine percentages these should be the periods in which important sediment inputs inside the harbour basin arrived and could be the expression of intense flooding phases the comparison between the ostracod assemblages recovered in the two cores and has led to speculate a complex harbour structure a separation could explain the micropalaeontological differences between the cores thus we suggest that a pier must have been built in order to protect the inner harbour from the marine influence and to unload the goods transported by the big ships

sulfur isotopic profile through the oceanic crust sulfur mobility and seawater crustal sulfur exchange during hydrothermal alteration measurements of the abundance of anhydrite and pyrite veins and the distribution of alteration types in oceanic basement enable estimates of global mass and isotopic fluxes of sulfur during hydrothermal alteration of oceanic crust fluxes of 2 5 10 12 g yr s 34 s 2 7 from the volcanic section to seawater and 2 1 10 12 g yr of seawater s 21 into the crust result in an insignificant change in the s content of altered ocean crust these are clearly second order fluxes compared to the riverine input of s to the oceans and the output of sedimentary pyrite most of the anhydrite that forms in the high temperature axial convection cell must later be dissolved at lower temperatures during off axis circulation the mean 34 s of altered oceanic basement is 0 9 only slightly changed from the primary value of 0 1 unless s is preferentially mobilized from 34 s rich sulfide deposits or mineralized zones subduction of altered basaltic crust is unlikely to be the source of high 34 s values of arc volcanic rocks 4 but could contribute to isotopic heterogeneities of s in the mantle

physical and chemical properties of the epidote minerals an introduction epidote minerals are known since the 18th century but at that time the greenish to dark colored varieties were termed actinolite or schorl and not distinguished from the minerals to which these names apply today hauy defined the mineral species and introduced the name epidote in 1801 whereas werner in 1805 used the term pistacite quoted from hintze 1897 epidote is derived from greek epidosis to increase because the base of the rhombohedral prism has one side larger than the other and pistacite refers to its green color all references for names after luschen 1979 blackburn and dennen 1997 weinschenk 1896 proposed the name clinozoisite from its monoclinic symmetry and zoisite like composition for those monoclinic members of the epidote family that are fe poor optically positive and have low refractive indices and birefringence zoisite was probably confused with tremolite until the beginning of the 19th century in 1804 siegmund zois baron von edelstein 1747 1819 an austrian sponsor of mineral collections found and described a new mineral in a handspecimen from the saualpe mountains in carinthia that was named zoisite by werner hauy 1822 interpreted zoisite as a variety of epidote and included it in his epidote spezies weiss 1820 presented a theory of the epidote system and also discussed crystal morphological features of the epidote minerals weiss 1828 rammelsberg 1856 studied the relationship between epidote and zoisite and presented a compilation of chemical analyses of zoisite he already noticed that the relative concentrations of di tri and tetravalent cations are identical in zoisite and epidote but that the fe content in zoisite about 2 3 5 wt fe2o3 is generally less than in epidote about 9 12 wt fe2o3 piemontite see bonazzi and menchetti 2004 was probably first described in 1758 by cronstedt

effect of confining pressure on dilatation recrystallization and flow of rock salt at 150 c microstructural evidence for fluid assisted dynamic recrystallization fadrx is widespread in naturally deformed rock salt however the principal experimental evidence for fadrx in salt has been obtained from stress relaxation experiments and it is unclear whether the process occurs during steady state dislocation creep and what its effect might be here we report deformation experiments performed on natural rock salt at a constant strain rate of 3 5 10 7 s 1 150 c and confining pressures pc of 3 30 mpa samples deformed at pc 3 mpa showed continuous work hardening and minor dilatation microstructurally they exhibited intergranular cracking plus slip band and subgrain structures indicative of dislocation glide creep electron backscatter diffraction analysis revealed a high frequency of boundaries with low angle misorientations in the range 5 10 in contrast samples deformed at pc 6 5 mpa showed work hardening followed by steady state flow at strains 6 7 these samples compacted slightly and crystal plastic deformation was accompanied by extensive fadrx with a predominance of high angle boundaries 30 50 over low angle boundaries we infer that fadrx is suppressed by dilatation at low pressures as a result of grain boundary disruption at pressures high enough to prevent dilatation however fadrx acts as a recovery mechanism counteracting work hardening the results offer a possible explanation for rheological variability seen in previous experiments conducted at pressures up to 30 mpa a simple rate model for diffusion and interface controlled fadrx indicates that fadrx should become increasingly important toward natural halokinetic conditions although the effect on flow stresses is likely to be small

human impact at lago di mezzano central italy during the bronze age a multidisciplinary approach abstract the purpose of this contribution is to disentangle climate forcing and human influence in the catchment of lago di mezzano through the interfingering of data obtained by means of archaeological geomorphological sedimentological and palynological approaches a systematic archaeological survey has been undertaken and three submerged settlement areas with piles pottery and metal tools have so far been found the artifacts indicate that the site was inhabited although not continuously during the bronze age geomorphological investigations and observations in some trenches dug out on the lake shore indicate that great variations in the lake s size and strong changes in the catchment lake surface area ratio occurred during the second half of the holocene palynological micro charcoal sedimentological and geochemical analyses carried out on long cores taken from the lake centre have indicated environmental changes due to either climatic influence or human impact even if human presence in the area has been detected during the whole bronze age period the human populations caused a strong impact only in two periods centred around 3600 and 3200 cal years bp when they settled along the lake shore and around 3400 cal years bp when they caused an increase in erosion leading to the beginning of the deposition of turbidites

microstructural evolution during initial stages of static recovery and recrystallization new insights from in situ heating experiments combined with electron backscatter diffraction analysis we present in situ observations performed using electron backscatter diffraction of static recovery and recrystallization processes occurring in a plastically deformed geological material namely rocksalt static heating experiments carried out in a scanning electron microscope at temperatures of up to 450 c allowed direct detailed observations of grain boundary migration between substructured grains in deformed polycrystalline samples contrary to expectations crystallographic orientation maps reveal that behind slowly migrating grain boundaries new subgrain boundaries form while pre existing subgrain boundaries are sometimes inherited moreover the crystallographic character especially the preferred orientation of misorientation axes of the new substructures reflects the character of the previous deformation history these results imply that substructural features such as subgrain misorientation distributions may be relatively robust indicators of deformation mechanisms and conditions even in tectonites that have undergone late static recrystallization in addition our observations suggest that the process of static grain boundary migration does not necessarily reset earlier deformation microstructures as commonly assumed the kinematic observations of boundary migrations are inconsistent with simple models in which migration is achieved by single atoms jumping across the boundary

the petrological significance of misorientations between grains misorientation analysis quantifies microstructural features in tectonites metamorphic and igneous rocks and allows hypotheses on their formation to be tested the misorientation between two lattices can be expressed by a rotation axis and rotation angle for lattices with symmetry it is conventional to take the minimum angle that enables one lattice to be rotated into the other for a group of lattice measurements two types of misorientation distribution can be calculated selecting random pairs of grains gives the random pair misorientation distribution selecting neighbouring pairs gives the neighbour pair misorientation distribution the forms of both distributions are visualised using histograms or cumulative frequency diagrams they are strongly influenced by any overall crystallographic preferred orientation and by intrinsic crystal symmetry in many rocks the random pair misorientation distribution and neighbour pair misorientation distribution are statistically significantly different quantified using the kolmogorov smirnov test differences between the random pair misorientation distribution and neighbour pair misorientation distribution imply that adjacent grains have physically interacted or are inherited from a precursor microstructure interactions include 1 reduction in surface energy by lattice alignment we show this may have occurred in garnet clusters in schist and olivine in a cumulate it is well known in metals and may be a common geological process 2 nucleation where those nuclei have influenced the orientation of adjacent nuclei 3 mechanical rotations of facetted grains in compacting crystal mushes so that faces become parallel 4 growth twinning inheritance includes 1 subgrain rotation recrystallisation in tectonites deforming by crystal plastic processes 2 mechanical and transformation related twinning 3 domainal microstructures e g where grains have formed from a few large original grains may give rise to spurious correlations when the orientation data cover more than one domain with this proviso misorientation analysis can be used to investigate many important microstructural processes

dislocation density stress relationships in natural and synthetic sodium chloride abstract to determine the relationship between applied stress and dislocation density creep experiments have been carried out on single crystals of natural and synthetic sodium chloride with differential stresses between 2 0 and 20 0 mpa at temperatures in the range 20 to 600 c dislocation densities were measured on etched cleavage surfaces using a scanning electron microscope the dislocation density is proportional to the differential stress to approximately the 1 3 power at a given differential stress the density of edge dislocations is larger and the density of screw dislocations smaller in natural crystals than in synthetic samples the mean dislocation density was unaffected this difference in the dislocation densities between natural and synthetic crystals is related to differences in the concentrations of impurities natural salt samples from a lansing n y salt mine were collected from locations in close proximity to excavation openings dislocation densities in the natural samples when compared to our experimentally derived stress dislocation density curve indicate that the samples were deformed at in situ stresses of 10 to 30 mpa

climatic interpretation of carbon isotope content of mid holocene archaeological charcoals from eastern anatolia abstract the 13c 12c ratio of juniper charcoals from the archaeological site of arslantepe malatya turkey was analysed for the mid holocene period spanning from 3350 to 2000 years bc in addition modern juniper and deciduous oak specimens were collected during a botanical survey around arslantepe in august 2008 after the evaluation of weather parameters the modern 13c 12c ratio was compared with the archaeological one to infer past seasonal precipitation relative magnitude patterns 13c values obtained from these samples suggest that the present day climate is on average drier than that recorded in the past comparing the 13c juniper record with the already published curve for archaeological charcoals of deciduous oaks from arslantepe it appears that the two curves show similar trends in the short period between ca 2850 and 2500 bc in which the curves are substantially parallel and the 13c difference between them is quite reduced but they are shifted by ca 50 150 years in the rest of the record for the interpretation of the arboreal curves however it was necessary to consider the autoecology of modern plants and the source of the water used for photosynthesis as the two selected trees show 13c curves with rather different patterns overall 13c 12c contrasting ratios in juniper and deciduous oaks suggest that seasonality in rainfall distribution and aquifer recharge played a complex role thus a consistent seasonal contrast in precipitation similar to the one in recent times took place at ca 3350 3100 and 2300 bc indicating that semi arid conditions have occurred in the past in alternation with periods characterised by minor differences in the distribution of annual precipitation in particular the period between ca 2850 and 2500 bc may suggest more humid conditions in late winter early spring the combination of the two records suggests that 1 two periods of drought are found at ca 3350 3100 and at ca 2300 2200 bc and 2 that at present winter precipitation is lower than that recorded during the period 3350 2000 bc and summer aridity less or equal to that recorded ca 2200 bc changes in precipitation seasonality and the complex and the peculiar hydrogeological situation hindered the interpretation of the isotope records the use of two taxa having different autoecology and different growing season allows interpretation of the data in terms of changes in precipitation seasonality and of specific habitat in this complex and peculiar hydrological setting

calcium isotope record of phanerozoic oceans implications for chemical evolution of seawater and its causative mechanisms a total of 280 brachiopods of ordovician to cretaceous age complemented by published data from belemnites and planktonic foraminifera are used to reconstruct the evolution of calcium isotope composition of seawater 44 40casw over the phanerozoic the compiled 44 40casw record shows a general increase from 1 3 nist srm 915a at the beginning of the ordovician to 2 at present superimposed on this trend is a major long term positive excursion from the early carboniferous to early permian as well as several short term mostly negative oscillations a numerical model of the global cycles of calcium carbon magnesium and strontium was used to estimate whether the recorded 44 40casw variations can be explained by varying magnitudes of input and output fluxes of calcium to the oceans the model uses the record of marine 87sr 86sr ratios as proxy for seafloor spreading rates a record of oceanic mg ca ratios to estimate rates of dolomite formation and reconstructed atmospheric co2 discharge and erosion rates to estimate continental weathering fluxes the model results indicate that varying magnitudes of the calcium input and output fluxes cannot explain the observed 44 40casw trends suggesting that the isotope signatures of these fluxes must also have changed as a possible mechanism we suggest variable isotope fractionation in the sedimentary output flux controlled by the dominant mineralogy in marine carbonate deposits i e the oscillating calcite aragonite seas the ultimate control of the calcium isotope budget of the phanerozoic oceans appears to have been tectonic processes specifically variable rates of oceanic crust production that modulated the hydrothermal calcium flux and the oceanic mg ca ratio which in turn controlled the dominant mineralogy of marine carbonates hence the 44 40casw as to the causes of the short term oscillations recorded in the secular 44 40casw trend we tentatively propose that these are related to variable rates of dolomite formation and or to changing chemical composition of the riverine flux in particular and ratios induced by variable proportions of silicate vs carbonate weathering rates on the continents

late quaternary sea level changes along the tyrrhenian coast near orbetello tuscany central italy palaeoenvironmental reconstruction using ostracods abstract a multidisciplinary study has been carried out on a 51 m long core drilled on coastal lowlands near the albegna river tuscany central italy both sedimentological and faunal analyses ostracods and molluscs indicate a coastal lagoon environment repeatedly influenced both by the rising holocene sea and the albegna river alluvial inflow 13c 18o mg ca sr ca and 87sr 86sr analyses were performed on cyprideis torosa shells in order to detail the influence of albegna river freshwater on the coastal lagoon water the analytical data illustrate the difficulties of using geochemical proxies in marginal marine settings four radiocarbon dates provide a chronostratigraphy for the early holocene part of the core the data are used to reconstruct late pleistocene to early holocene palaeoenvironments along this part of the coast and show the development of freshwater environments followed by a coastal brackish lagoon formed in response to the initial holocene rapid rise in relative sea level an attempt is made to relate sediments and age data from the core to the relative sea level curve for the tyrrhenian sea

temperature dependent grain boundary migration in deformed then annealed material observations from experimentally deformed synthetic rocksalt abstract grain boundary migration between strained substructured grains and newly appearing strain free grains has been observed during static in situ annealing of pre deformed rocksalt in the sem with increasing temperature t the migration velocity increases and the character of grain boundary migration changes as temperature increases there is an increase in the length of individual migrating boundary segments that move at similar rates in addition the frequency of migrating boundaries that form traces of a 100 boundary plane of at least one of the crystals involved increases and moving grain boundaries between new and old grains change from highly irregular to smooth straight boundaries at the same time there is a decrease in the influence of the substructure of pre existing strained grains on the grain boundary movement resultant microstructures reflect these changes at 325 350 c the deformed then annealed microstructure is characterized by very irregular grain boundaries a high abundance of 5 50 m scale remnants of old substructured grains within new grains giving a poikilitic microstructure at 350 400 c grain boundaries often exhibit elongate embayments into the strained grains and most remnants of old strained grains are located at former grain boundaries at 400 c grain boundaries between new and old strained grains are straight to smoothly curved the grain boundary velocity observations are explained by the effect of temperature on mobility coupled with local driving force variations additionally at low annealing temperature impurity solute drag and driving force variations are influential while at high temperature the anisotropy in grain boundary energy with crystallographic orientation becomes more important transferring the knowledge from our experiments to geological samples enables us to recognize and interpret similar microstructures in rocks thereby making it is possible to relate microstructural characteristics to the pre annealing and post deformational annealing history

channelling of hydrothermal fluids during the accretion and evolution of the upper oceanic crust sr isotope evidence from odp hole 1256d abstract odp hole 1256d in the eastern equatorial pacific is the first penetration of a complete section of fast spread ocean crust down to the dike gabbro transition and only the second borehole to sample in situ sheeted dikes after dsdp hole 504b here a high spatial resolution record of whole rock and mineral strontium isotopic compositions from site 1256 is combined with core observations and downhole wireline geophysical measurements to determine the extent of basalt hydrothermal fluid reaction and to identify fluid pathways at different levels in the upper ocean crust the volcanic sequence at site 1256 is dominated by sheet and massive lava flows but the sr isotope profile shows only limited exchange with seawater however the upper margins of two anomalously thick 25 m massive flow sequences are strongly hydrothermally altered with elevated sr isotope ratios and appear to be conduits of lateral low temperature off axis fluid flow elsewhere in the lavas high 87 sr 86 sr are restricted to breccia horizons mineralised hyaloclastic breccias in the lava dike transition are strongly altered to mg saponite silica and pyrite indicating alteration by mixed seawater and cooled hydrothermal fluids in the sheeted dike complex 87 sr 86 sr ratios are pervasively shifted towards hydrothermal fluid values 0 705 dike chilled margins display secondary mineral assemblages formed during both axial recharge and discharge and have higher 87 sr 86 sr than dike cores indicating preferential fluid flow along dike margins localised increases in 87 sr 86 sr in the dike gabbro transition indicates the channelling of fluids along the sub horizontal intrusive boundaries of the 25 to 50 m thick gabbroic intrusions with only minor increases in 87 sr 86 sr within the cores of the gabbro bodies when compared to the pillow lava dominated section from hole 504b the sr isotope measurements from site 1256 suggest that the extent of hydrothermal circulation in the upper ocean crust may be strongly dependent on the eruption style sheet and massive flow dominated lava sequences typical of fast spreading ridges may experience relatively restricted circulation but there may be much more widespread circulation through pillow lava dominated sections in addition the hole 1256d sheeted dikes display a much greater extent of sr isotopic exchange compared to dikes from hole 504b because seawater derived hydrothermal fluids must transit the dikes during their evolution to black smoker type fluids the different sr isotope profiles for holes 504b and 1256d suggest there are significant variations in mid ocean ridge hydrothermal systems at fast and intermediate spreading ridges which may impact geochemical cycles of elements mobilised by fluid rock exchange at different temperatures

metal depleted root zones of the troodos ore forming hydrothermal systems cyprus the cupriferous pyrite deposits of cyprus were precipitated from hydrothermal solutions derived by interaction of contemporaneous seawater with hot mafic rock at the ancient troodos spreading centre here we identify the zones in which this interaction took place the zones occur in the lower part of the sheeted dyke complex and within them 30 50 of the rock is made up of epidosite an epidote quartz rock replacing the dykes as sheets and pipes the epidosites contain abundant fluid inclusions which give trapping temperatures of 350 400 c or even higher and contain water normally near seawater in salinity zones of epidosite are elongate parallel to the strike of the sheeted dykes and are up to 1 km wide the rocks throughout these zones are strongly depleted in cu and zn and the metals removed are sufficient to supply the ore deposits in fact several large ore deposits lie along strike from zones of epidosite all of these features support the identification of the epidosites as the hydrothermal reaction zones the location of the epidosite zones immediately above the gabbros of the plutonic complex supports the hypothesis that the heat to drive the ore forming systems came from the underlying magma as is also likely for modern black smoker springs

molecular simulations of kinetic stable calcium isotope fractionation at the calcite aqueous interface abstract the measurement of calcium stable isotope fractionation during crystal growth can provide insights into the dominant pathways and mechanisms of crystal growth but these interpretations require a detailed understanding of mass dependent reaction rates and free energy states at the molecular scale here we report the results of free energy calculations used to determine the rate limiting step controlling kinetic stable isotope fractionation during calcium ion attachment to active growth sites kink sites at the calcite surface the free energy profile for attachment is combined with ion coordination states to reconstruct the multi step molecular pathway for the ion attachment process dissociative desolvation of a water molecule coordinating the calcium ion approaching the kink is identified as the rate limiting step with a free energy barrier of 18 kj mol which is equal to the energetic cost of water molecule leaving ca2 coordination shell in the aqueous phase molecular dynamics simulations were used to investigate the dependence of this desolvation step on calcium ion mass both brute force md and an analysis of mass dependent water exchange coefficients kwex give identical kinetic stable isotope fractionation factor values f44 40 0 992 which corresponds to 44 40ca of 8 originating from a mass dependent transition frequency for the ca bound solvation water at the kink this value is significantly higher than the fractionation factor associated with water exchange dynamics around ca2 in bulk aqueous solution determined here f44 40 0 999 our results confirm that the growing calcite surface should be depleted in 44ca with respect to the aqueous phase due to kinetically preferred desolvation of the lighter isotope we conclude that the maximum kinetic stable isotope fractionation associated with calcium attachment to surfaces is not constant but can vary due to changes in the interfacial environment that affect local solvent dynamics during desolvation

the use of ostracods from marginal marine brackish waters as bioindicators of modern and quaternary environmental change abstract ostracoda microscopic aquatic crustacea from brackish waters have a great potential for ecological monitoring and palaeoenvironmental analyses in highly variable environments this has been proven in many articles during recent decades but their potential has yet to be fully developed or utilised the analysis of ostracod assemblage composition species distributions eco phenotypic variability and the analysis of stable isotopes and trace elements in ostracod shells provide valuable information on present and past water salinity temperature and chemistry hydrodynamic conditions substrate characteristics climate sea level variations oxygen and nutrient availability this article provides an overview on the application of ostracods from brackish waters for palaeoenvironmental reconstruction in the quaternary and for environmental studies in present day environments

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

plant landscape and environmental changes recorded in marginal marine environments the ancient roman harbour of portus rome italy abstract the interpretation of past environment changes in coastal marshes river mouths and drainage channels connecting fresh to salt water bodies is a difficult task since several factors must be considered such as the variable influence of climate sea level changes coastline variations and changes in the river discharge it is even more difficult if this attempt is carried out in basins and channels of an ancient harbour used for centuries connected to the sea and to a river this is the case of the ancient harbour of rome located in the tiber delta area which had a prominent role during the imperial age in the mediterranean a town named portus arose in the vicinity and although sacked many times by barbarians was still very important during medieval times the romans managed the harbour the city and the surroundings and the impact on the environment must have been very strong a multi proxy approach was used to characterize and date environment and landscape changes in the ancient port of rome area from the 1st century to the 15th century ad plant macrofossil results have been integrated not only with pollen and microcharcoal but also with the tiber river bi millennial record available in literature this integration used to improve the chronological framing of the cores was carried out using ostracod analyses micro crustaceans commonly occurring in marginal marine environments and widely used for palaeoenvironmental reconstructions in particular the ability of some species to live within specific salinity ranges has been a precious tool to identify the hydrological setting of the depositional environment the cores recovered allowed recognition of two different sedimentary sequences the older shows the silting of the harbour during the first centuries and the younger records the sedimentation that occurred between the 4th and the 15th century ad this multi proxy approach applied to the study of plant remains indicates that 1 the human impact was lower during the first centuries ad than during late antiquity and middle ages or that 2 clues of human presence were easier to detect in a closed marshy area than in an open harbour the correlations between macroremains pollen percentage and concentration freshwater brackish water and salt water ostracods and the frequencies of tiber river floods during a 1500 year time span link some environmental changes and the silting of the harbour to the variations in hydrological regime of the tiber river

dynamic recrystallization of wet synthetic polycrystalline halite dependence of grain size distribution on flow stress temperature and strain abstract it is often observed that dynamic recrystallization results in a recrystallized grain size distribution with a mean grain size that is inversely related to the flow stress however it is still open to discussion if theoretical models that underpin recrystallized grain size stress relations offer a satisfactorily microphysical basis the temperature dependence of recrystallized grain size predicted by most of these models is rarely observed possibly because it is usually not systematically investigated in this study samples of wet halite containing 10 ppm water by weight were deformed in axial compression at 50 mpa confining pressure the evolution of the recrystallized grain size distribution with strain was investigated using experiments achieving natural strains of 0 07 0 12 and 0 25 at a strain rate of 5 10 7 s 1 and a temperature of 125 c the stress and temperature dependence of recrystallized grain size was systematically investigated using experiments achieving fixed strains of 0 29 0 46 and one to a strain of 0 68 at constant strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c yielding stresses of 7 22 mpa the microstructures and full grain size distributions of all samples were analyzed the results showed that deformation occurred by a combination of dislocation creep and solution precipitation creep dynamic recrystallization occurred in all samples and was dominated by fluid assisted grain boundary migration during deformation grain boundary migration results in a competition between grain growth due to the removal of grains with high internal strain energy and grain size reduction due to grain dissection i e moving boundaries that crosscut or consume parts of neighbouring grains at steady state grain growth and grain size reduction processes balance yielding constant flow stress and recrystallized grain size that is inversely related to stress and temperature evaluation of the recrystallized grain size data against the different models for the development of mean steady state recrystallized grain size revealed that the data are best described by a model based on the hypothesis that recrystallized grain size organizes itself in the boundary between the grain size sensitive solution precipitation and grain size insensitive dislocation creep fields application of a piezometer calibrated using the recrystallized grain size data to natural halite rock revealed that paleostresses can vary significantly with temperature up to a factor of 2 5 for t 50 200 c and that the existing temperature independent recrystallized grain size stress piezometer may significantly underestimate flow stresses in natural halite rock

subseafloor phase equilibria in high temperature hydrothermal fluids of the lucky strike seamount mid atlantic ridge 37 17 n abstract as part of an integrated study conducted at the lucky strike seamount mid atlantic ridge 37 17 n in 2008 gas tight sampling devices were used to collect high temperature 300 c hydrothermal fluids issuing from sulfide structures distributed throughout the vent field located in the summit depression compared with previous observations from 1993 to 1997 the most substantial changes in vent fluid compositions are dramatically increased co2 concentrations 5 up to 133 mmol l and the observation of vent fluids enriched in dissolved chloride relative to seawater combined with an increase in 13 c co 2 values by 4 in 2008 the elevated co2 indicates replenishment of the magmatic heat source and may be indicative of a recent magmatic event the additional supporting fluid chemistry is however similar to that of the previous sampling intervals necessitating a reassessment of the subseafloor controls on vent fluid chemistry at lucky strike in the context of recently obtained geophysical data that provides the depth extent of a steady state magma chamber two phase behavior is indicated by the chloride variability in the vent fluids and comparison with experimental data for the associated chloride dependent partitioning of minor trace elements suggests the possibility of a similar source fluid for all the vent structures while limiting the likelihood of shallow phase separation and subseafloor mixing for the hydrothermal end members a recently calibrated fe mn geothermometer indicates minimum subseafloor equilibration temperatures of 350 385 c however constraints imposed by dissolved si cl in conjunction with geophysical observations are consistent with peak reaction conditions at temperatures of 430 475 c and pressures near the top of the axial magma chamber 410 480 bars where magmatic co2 becomes entrained in the circulating fluids the distance between the magma chamber and the seafloor at lucky strike is substantially greater than at most faster spreading ridges and we propose the resulting increased residence time in the up flow zone leads to the re equilibration of temperature sensitive transition metals at conditions less extreme than those associated with peak reaction agreement between experimental data thermodynamic model calculations and dissolved concentrations of fe cu zn h2 and h2s in the lucky strike fluids reinforce the hypothesis of ph redox equilibria for transition metals at relatively oxidizing conditions and temperatures predicted by the empirical fe mn geothermometer in situ ph measurements of the high temperature fluids exiting the seafloor are also consistent with the model calculations

the high temperature static recovery and recrystallization behaviour of cold worked carrara marble the static recovery and recrystallization behaviour of carrara marble has been investigated as a function of pre strain 8 27 and annealing temperature 500 700 c quantitative estimates of the rate of recovery were obtained by comparing the stress strain curves generated at a temperature of 426 c a confining pressure of 170 mpa and a strain rate of 3 10 4s 1 before and after a period of isostatic annealing curves of fractional recovery r as a function of log time t show a characteristic sigmoidal shape in which the rate of recovery dr d logt is initially small increases rapidly and finally becomes small again the acceleration of recovery occurs at shorter times both with increasing pre strain and with increasing annealing temperature microstructural examination of the annealed material shows that the acceleration of recovery corresponds to the onset of recrystallization and that prior to the onset of recrystallization recovery is controlled by the development of a subgrain structure whereas after recrystallization has gone to completion it is controlled by the intensification and growth of this substructure the results have been interpreted within the perspective of hart s state variable description of inelastic deformation this analysis shows that the decay of the mechanical state of the marble during annealing can be treated as a two stage static recovery process substructure formation substructure coarsening with the recrystallization marking the transition between these two stages

calcium isotope fractionation in calcite and aragonite abstract calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite precipitation temperatures ranged from 0 to 28 c calcium isotope fractionation shows a temperature dependence in accordance with previous observations 1000 ln cc 1 4 0 021 t c for calcite and 1000 ln ar 1 9 0 017 t c for aragonite within uncertainty the temperature slopes are identical for the two polymorphs however at all temperatures calcium isotopes are more fractionated in aragonite than in calcite the offset in 44 40 ca is about 0 6 the underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals or to different ca reaction behavior at the solid liquid interface recently the observed temperature dependence of the ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting lemarchand et al 2004 we show that this mechanism can in principle also be applied to caco 3 precipitation in natural environments in normal marine settings following this model ca isotope fractionation in marine ca carbonates is primarily controlled by precipitation rates on the other hand the larger ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates the rate control model of ca isotope fractionation predicts a strong dependence of the ca isotopic composition of carbonates on ambient co 3 2 concentration while this model is in general accordance with our observations in marine carbonates cultured specimens of the planktic foraminifer orbulina universa show no dependence of ca isotope fractionation on the ambient co 3 2 concentration the latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water

calcium isotope δ 44 40 ca fractionation along hydrothermal pathways logatchev field mid atlantic ridge 14 45 n we investigate the logatchev hydrothermal field at the mid atlantic ridge 14 degrees 45 n to constrain the calcium isotope hydrothermal flux into the ocean during the transformation of seawater to a hydrothermal solution the ca concentration of pristine seawater ca sw increases from about 10 mm to about 32 mm in the hydrothermal fluid endmember ca hydend and thereby adopts a delta ca 44 40 hydend of 0 95 0 07 parts per thousand relative to seawater sw and a sr 87 sr 86 isotope ratio of 0 7034 4 we demonstrate that delta ca 44 40 hydend is higher than that of the bedrock at the logatchev field from mass balance calculations we deduce a delta ca 44 40 of 1 17 0 04 parts per thousand sw for the host rocks in the reaction zone and 1 45 0 057 parts per thousand sw for the isotopic composition of the entire hydrothermal cell of the logatchev field the values are isotopically lighter than the currently assumed delta ca 44 40 for bulk earth of 0 92 0 187 parts per thousand sw skulan j depaolo d j and owens t l 1997 biological control of calcium isotopic abundances in the global calcium cycle geochim cosmochim acta 61 12 2505 2510 and challenge previous assumptions of no ca isotope fractionation between hydrothermal fluid and the oceanic crust zhu p and macdougall j d 1998 calcium isotopes in the marine environment and the oceanic calcium cycle geochim cosmochim acta 62 10 1691 1698 schmitt a d chabeaux f and stille p 2003 the calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance earth planet sci lett 6731 1 16 here we propose that ca isotope fractionation along the fluid flow pathway of the logatchev field occurs during the precipitation of anhydrite two anhydrite samples from the logatchev hydrothermal field show an average fractionation of about delta 44 4c ca 0 57 parts per thousand relative to their assumed parental solutions ca isotope ratios in aragonites from carbonate veins from odp drill cores indicate aragonite precipitation directly from seawater at low temperatures with an average delta ca 44 40 of 1 54 0 08 parts per thousand sw the relatively large fractionation between the aragonite precipitates and seawater in combination with their frequent abundance in weathered mafic and ultramafic rocks suggest a reconsideration of the marine ca isotope budget in particular with regard to ocean crust alteration c 2008 elsevier ltd all rights reserved

in situ annealing experiments of octachloropropane as a rock analogue kinetics and energetics of grain growth abstract two dimensional in situ observation of the change of size of individual grains of octachloropropane ocp during post deformation annealing revealed that grain boundary migration occurred to reduce the grain boundary energy within the polycrystalline aggregate studied some grains show a cyclic change in grain size others have a stable grain size while most grains were consumed and disappeared in order that the mean grain size could increase during grain coarsening some grains were dissected then coalesced amalgamated with others and their centers migrated across the aggregate the average grain size d can be expressed by d k 0 exp q rt t n where k0 is a constant q is the activation energy r is the gas constant t is the temperature t is the annealing time and n is a constant we obtained n 0 1 0 2 and q 6 2 kcal mol the driving force p is the surface energy stored at grain boundaries the driving force can be expressed as p tm where m is the constant and hence the grain growth rate d can be expressed as d p n 1 m the value of n 1 m ranges from 4 to 10

seven types of subgrain boundaries in octachloropropane abstract subgrain boundaries in thin sheets of octachloropropane deformed at 0 7 0 8 t m on the stage of a microscope are seen to appear in the material in seven different ways type i boundaries show the classical evolution by polygonization of bent crystals type ii are essentially kink boundaries which migrate sideways during deformation to reach their present positions in the crystals type iii develop at the sites of former grain boundaries by reduction of misorientation of adjacent grains type iv and v originate by impingement of migrating grain boundaries or subgrain boundaries respectively type vi propagate in their own planes behind migrating grain boundaries to which they are attached type vii develop statically from optically strain free grains by a process probably otherwise similar to the type i process two thirds of the boundaries are types i or ii in view of the variety of subgrain boundary histories in ocp interpretation of similar features in minerals ought to be undertaken cautiously criteria are needed for telling the different types of subgrain boundaries apart in situations where only a final view of the structure is available as in optical and electron micrographs of rocks

the plant landscape of the imperial harbour of rome abstract the research concerns the tiber delta area about 3 km far from the present seacoast where the remains of the ancient harbour of rome are located in 42 ad claudius started the construction of the harbour and nero completed it in 64 ad then the emperor trajan went on to add a hexagonal basin to the former structure which had gradually silted up the imperial harbour was connected to the tiber river and ultimately to the city of rome through the trajan channel during the imperial period most of the supplies imported from the mediterranean provinces reached the city of rome through portus this study applies detailed pollen microcharcoal and ostracod analyses together with radiocarbon dating to the sediments recovered from two cores drilled in the area of the claudius harbour the objective of the drillings was to identify morphological and environmental features of the tiber delta dating back to the roman period and to characterize the landscape of the harbour the chronological framing of the records is based on stratigraphical criteria radiocarbon dates historical data and on the typology of pottery fragments pollen plant macroremains and ostracod assemblages indicate that the two cores record different periods of time the dock core shows the first phases of the harbour activities recording first a marine and then a brackish environment the plant landscape is typical of a coastal environment and appears rather preserved the human presence is clear but not of great impact the channel core records mainly a brackish water environment and a strong human impact related to the presence of portus the port town anthropic indicators such as cultivated and synanthropic taxa as well as strong fire use occurrence are evidence of a high human pressure increasing in the first centuries ad

deformation related recrystallization processes abstract recrystallization is a common microstructural transformation that occurs during deformation metamorphism and diagenesis of rocks studies on minerals and rock analogues have demonstrated that a wide range of recrystallization mechanisms can occur the range of mechanisms is related to the various ways in which two basic processes grain boundary migration and new grain boundary formation combine to transform the microstructure two recent papers drury et al 1985 urai et al 1986 have proposed different schemes for the description of recrystallization mechanisms the purpose of this paper is to provide a unified framework for the description of mechanisms recrystallization mechanisms are divided into three main types rotation mechanisms which principally involve the formation of new grain boundaries migration mechanisms which principally involve grain boundary migration and general mechanisms which involve both basic processes a further distinction is made on the basis of the continuity of the microstructural transformation with respect to time each of the three main types of mechanism can be divided into a number of sub types depending on whether the processes of grain boundary migration new grain boundary formation and new grain formation occur in a discontinuous or continuous manner with respect to time as the terms continuous and discontinuous have been used in the metallurgical literature to signify the spatial continuity of the microstructural transformation the terms discontinuai and continual are used to refer to the temporal continuity of the transformation it is recommended that the following aspects should be specified if possible in a general description of recrystallization mechanisms 1 1 how do the basic processes combine to transform the microstructure 2 2 if new grain development occurs what is the development mechanism and does new grain formation occur in a continual or discontinuai manner 3 3 if grain boundary migration is involved in the transformation what is the migration mechanism i e fast solute escape migration slow solute loaded migration fluid assisted migration etc and is migration a continual or discontinuai process the application of the unified scheme is illustrated by reviewing studies that have provided detailed information on the recrystallization mechanisms involved the complicating effects of solid solution impurities dispersed second phase particles and grain boundary fluid films are also considered and it is demonstrated that variations in content of these types of impurity can significantly effect the types of recrystallization that occur in a given material

calcium isotopes in the global biogeochemical ca cycle implications for development of a ca isotope proxy abstract at the earth s surface calcium ca is a critical element at a variety of scales it is soluble in natural waters a biological nutrient and a major constituent of the dominant mineral sink for carbon in the ocean caco3 there is a 4 variation in the ca isotopic composition 44ca 40ca expressed as 44ca of various ca reservoirs on earth suggesting ca isotopes as a promising tracer of ca cycling in both the present and the past fifteen years of high precision ca isotope measurements has revealed much about the behavior of ca isotopes in the earth surface environment but there remain fundamental questions concerning how ca isotopes are used to elucidate the marine and terrestrial ca cycles the current work presents a data compilation of over 70 published ca isotope studies totaling over 2600 measurements presented on a common delta scale that includes data on rivers and groundwater dust soils and soil pore fluids vegetation rainwater silicate minerals rocks and authigenic marine minerals carbonates sulfates and phosphates both modern and ancient the data compilation suggests that 1 there is a significant difference between carbonate 0 60 and silicate 44ca 0 94 2 riverine 44ca 0 88 does not simply reflect the compiled carbonate 44ca and 3 terrestrial vegetation exhibits the largest range of ca isotopic compositions 3 5 in the terrestrial setting we discuss these observations in the context of the global ca cycle exploring the extent to which seawater 44ca variability is feasible and how we can achieve accurate reconstructions of seawater 44ca over geologic time scales the current study presents simple mass balance models that quantify the leverage of inputs to change the ca isotopic composition of the ocean as this directly impacts the manner in which ca isotopes are interpreted although ca fractionates isotopically in the modern system during continental cycling the 44ca range of riverine inputs to the ocean is considerably smaller than the variability observed in putative seawater proxies such as nannofossil ooze and marine barite in the terrestrial realm plants exhibit a wide 44ca range and there is evidence that ca fluxes via biomass degradation are significant at the catchment scale we therefore assess the ability of the continental biosphere to influence riverine and consequently seawater 44ca a steady state biosphere has little leverage to alter riverine 44ca except in cases where the 44ca of the recycling flux is isotopically distinct from the 44ca of the uptake flux a non steady state biosphere can substantially impact both soil and riverine 44ca driving exchangeable ca either heavier or lighter depending on the magnitude of the recycling flux relative to the uptake flux based on estimates of the size of the global biosphere 1 5 1015 mol ca we suggest a decaying biosphere has the potential to impact riverine 44ca by tenths of a permil over time scales in the marine realm we evaluate the effect of a variable fractionation factor accompanying global removal of ca from the ocean on seawater 44ca and suggest methods by which such a mechanism can be recognized in the rock record experimental data suggest that there is considerable leverage