nucleation dominated crystallization of forsterite in the ubehebe peak contact aureole california the morphology and number of forsterite crystals in the ubehebe peak california contact aureole vary systematically as a function of metamorphic grade from their first appearance to as close as 150 m from the intrusive contact forsterite crystals are large 5 20 mm and have a tabular habit a c b in contrast forsterite near the contact is equigranular and much smaller 1 mm in diameter the number of crystals per mole of forsterite increases from 3 5 104 at the forsterite in isograd to more than 1 5 108 near the contact this trend is interpreted to result from an increase in the ratio of nucleation rates with respect to growth rates with proximity to the intrusion the change in morphology from tabular to equigranular is explained by kinetic surface roughening the nucleation and growth information gained from this study highlights the important role of nucleation kinetics in the crystallization of forsterite at the ubehebe peak aureole

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

westward propagation of north anatolian fault into the northern aegean timing and kinematics comment and reply based on stratigraphical and structural evidence armijo et al 1999 1 considered that the north anatolian fault has 70 85 km total offset in the marmara region of northwest turkey they also suggested that the fault reached the marmara region 7 5 ma their main stratigraphic evidence is a

distinguishing climatic and tectonic signals in the sedimentary successions of marginal basins using sr isotopes an example from the messinian salinity crisis eastern mediterranean the evolution of oceanic 87 sr 86 sr through the tertiary has been sufficiently well documented to provide a useful stratigraphic tool for carbonate rich marine sediments which were deposited in basins connected to the global oceans in isolated basins sea water 87 sr 86 sr will diverge from coeval oceanic values thus if independent age information exists the geochemical signature can constrain the timing of isolation in marginal basins formed in tectonically active settings the timing of isolation is critical to the assessment of the relative importance of climate or tectonic controls on that event previously isolation has been assumed to coincide with the last occurrence of open marine fauna however in an example from the eastern mediterranean 87 sr 86 sr data challenge that assumption and can be interpreted as indicating a protracted period of isolation c 3 ma during which time marine conditions prevailed prior to the messinian salinity crisis at the end of the miocene this allows tectonic and climatic signals to be distinguished since although convergence of africa with eurasia was responsible for isolation of this part of the mediterranean it is more likely that later climatic change triggered desiccation

toward an understanding of disequilibrium dihedral angles in mafic rocks the median dihedral angle at clinopyroxene plagioclase plagioclase junctions in mafic rocks cpp is generally lower than equilibrium 109 plus minus 2 observation of a wide range of mafic bodies demonstrates that previous work on systematic variations of cpp is incorrect in several important respects firstly the spatial distribution of plagioclase compositional zoning demonstrates that the final geometry of three grain junctions and hence cpp is formed during solidification the igneous process sub solidus textural modification in most dolerites and gabbros previously thought to be the dominant control on cpp is insignificant cpp is governed by mass transport constraints the inhibiting effects of small pore size on crystallization and variation in relative growth rates of pyroxene and plagioclase during rapid cooling pyroxene preferentially fills wider pores while the narrower pores remain melt filled resulting in an initial value of cpp of 78 rather than 60 which would be expected if all melt filled pores were filled with pyroxene lower cooling rates create a higher initial cpp due to changes in relative growth rates of the two minerals at the nascent three grain junction low cpp associated with cuspate clinopyroxene grains at triple junctions can also be diagnostic of infiltration of previously melt free rocks by late stage evolved liquids the metasomatic process modification of cpp by sub solidus textural equilibration the metamorphic process is only important for fine grained mafic rocks such as chilled margins and intra plutonic chill zones in coarse grained gabbros from shallow crustal intrusions the metamorphic process occurs only in the centres of oikocrysts associated with rounding of chadacrysts

tectonics and sequence stratigraphy in messinian basins sicily constraints on the initiation and termination of the mediterranean salinity crisis deposits within the caltanissetta basin of central sicily have been important for developing the desiccating deep basin model for the messinian salinity crisis in the mediterranean linked structural and stratigraphic studies show that the sicilian depocenters are synclines related to underlying thrust structures of the frontal part of the maghrebian chain prior to the salinity crisis these basins were hydrodynamically linked through the foredeep to the mediterranean the precursor sediments terravecchia formation formed a delta sourced from the north early messinian regression acted on a range of paleobathymetries shallow in the north and progressively deeper in the south locally complicated by active thrust structures initial draw down of mediterranean base level is marked across the thrust belt by first cycle carbonates and evaporites on the structural highs and lows respectively vast accumulations of halite and potassium salts up to 1200 m are restricted to growing thrust synclines the different evaporite signatures may be related to different water conditions reflecting various meteoric and marine circulations across various subbasins with cyclicity reflecting high frequency variations in sea level a sequence stratigraphic model is developed to explain fractionation of evaporite facies between different paleobathymetric settings and to predict the temporal evolution of the successions in different subbasins thrusting provides accommodation space for evaporites and also controls the water pathways into the desiccating basins the intra messinian unconformity separating first and second cycle evaporites is a type 1 sequence boundary related to the forced regression associated with the acme of mediterranean desiccation an interpretation supported by local ravinement and incised valley fills the overlying second cycle evaporites are a combination of detrital reworked first cycle material and primary gypsum formed under brackish water regional onlap relationships and bed continuity suggest that this water body was of regional extent with a systematically rising base level these interpretations have several implications for messinian correlations in the mediterranean the deep basin evaporites correlate with an intra messinian unconformity that separates the two cycles on sicily and postdate the first cycle deposits regional base level was largely restored before the end of the salinity crisis

the rates and extent of textural equilibration in high temperature fluid bearing systems abstract the geometry of fluid filled pores in texturally equilibrated aggregates can in theory be uniquely determined given the porosity and the equilibrium dihedral angle for all possible orientations and combinations of the constituent solid phases while it is useful to be able to do this one should also ask whether and to what extent textural equilibrium is actually attained during fluid present intervals in high temperature rocks in fact textural equilibrium may be only rarely attained during melting of crustal rocks and equilibration under mid ocean ridges is possibly incomplete to depths as great as the garnet stability zone there is very little published information on the rates of attainment of textural equilibrium in fluid bearing geological environments the available experimental data for the rates of growth of equilibrated domains are consistent with a power law relationship between domain size and equilibration time with an exponent between 2 and 3 a simplified theoretical treatment of pore shape change governed by the gibbs thompson relationship demonstrates that an exponent of 3 is to be expected for equilibration by diffusion within the fluid phase with an effective diffusivity consistent with the available data

the traigh bhan na sgurra sill isle of mull flow localization in a major magma conduit field evidence points to localization of magma flowing in a tertiary doleritic sill on the isle of mull inner hebrides scotland regions of the sill in which flow was short lived have chilled margins a narrow or absent metamorphic aureole and alignment of plagioclase crystals resulting in pronounced flow parallel lineations on fracture surfaces type i regions prolonged flow resulted in blocky coarse grained dolerite with no chilled margins and an extensive metamorphic aureole type ii regions the distribution of type i and type ii regions shows no spatial pattern with stagnant solidifying sections immediately adjacent to sections with contemporaneous active and sustained flow the transition between type i and type ii regions occurs as the sill thickness exceeds 3 5 m our observation that sustained flow was only possible in regions of the sill thicker than 3 5 m is consistent with previously published theoretical models which predict a critical sill thickness in the range 2 2 5 m regions of the sill narrower than this experienced a single injection of magma simple models to determine flow duration from the width of the metamorphic aureole demonstrate that progressive focusing of flow into wider parts of the conduit created discrete channels active for up to 5 months

a new chronology for the middle to late miocene continental record in spain abstract the first detailed chronology for the middle to late miocene continental record in spain is presented based on high resolution magnetostratigraphic data of mammal bearing sections which were studied in several basins calatayud daroca teruel valles penedes duero and jucar cabriel our results indicate that these sections compose an almost complete magnetostratigraphic succession from the lower aragonian mn4 to the middle turolian mn12 seven successive mammal neogene mn zone boundaries are directly dated in these sections which often contain faunas of two successive zones in superposition the three oldest boundaries are dated in the aragonian type area calatayud daroca basin the mn4 mn5 boundary vargas section occurs in chron c5cr o with a corresponding age of 17 26 0 01 ma the mn5 mn6 boundary aragon section in chron c5acn 0 8 with an age of 13 75 0 03 ma and the mn6 mn7 8 boundary aragon section in the interval c5ar 1n c5ar 3r with an age of 12 75 0 25 ma the mn7 8 mn9 aragonian vallesian boundary occurring in chron c5r 1n at 11 1 ma and the mn9 mn10 boundary in chron c4ar 3r at 9 7 0 1 ma are recorded in the valles penedes basin vallesian type area and are supported by the results from the duero basin torremormojon section in the turolian type area teruel basin the mn10 mn11 vallesian turolian boundary la gloria section occurs in chron c4an y at 8 7 0 1 ma taking into account the pre existing data from the jucar cabriel basin the mn11 mn12 boundary cabriel valley section is recalibrated to c4n 1n at an age of 7 5 0 1 ma

messinian crisis what happened around the northeastern aegean abstract the effects of the severing of the atlantic mediterranean connection during the 400 000 year messinian event are also observed around the northern aegean during this time a sea of brackish water character developed between paratethys in the north and the mediterranean in the south this sea is named here egemar this basin was principally fed by surrounding rivers and by paratethyan waters that entered egemar via a connection through the sea of marmara which was then a bay of the paratethys the sedimentary sequence deposited in egemar is principally composed of limestones containing brackish water fauna paratethyan however there are some intercalations containing mediterranean species five intercalations of mediterranean character are found within the sedimentary sequence of egemar indicating the re establishment of an atlantic mediterranean connection from time to time and thus replenishment of marine waters the turolian is represented by continental clastics which interdigitate with the brackish water cycles implying a number of regressions egemar eventually became part of the eastern mediterranean due to a major transgression during the early pliocene

disequilibrium dihedral angles in layered intrusions a microstructural record of fractionation the dihedral angle formed at junctions between two plagioclase grains and a grain of augite is only very rarely in textural equilibrium in gabbros from kilometre scale crustal layered intrusions the median of a population of these disequilibrium angles cpp varies systematically within a single layered intrusion remaining constant over large stretches of stratigraphy with significant increases and decreases associated with the addition or reduction respectively of the number of phases on the liquidus of the bulk magma the stepwise changes in cpp are present in the upper zone of the bushveld complex the megacyclic unit i of the sept iles intrusion and the layered series of the skaergaard intrusion the plagioclase bearing cumulates of rum have a bimodal distribution of cpp dependent on whether the cumulus assemblage includes clinopyroxene the presence of the stepwise changes is independent of the order of arrival of cumulus phases and of the composition of either the cumulus phases or the inferred composition of the interstitial liquid the only parameter that behaves in an exactly analogous manner to cpp is the rate of change in enthalpy with temperature h t during crystallization both h t and cpp increase with the addition of a liquidus phase and decrease with the removal of a liquidus phase the replacement of one phase by another has little effect on h t and no discernible effect on cpp an increase of h t results in an increase in the fraction of the total enthalpy budget that is the latent heat of crystallization the fractional latent heat it also increases the mass crystallized in each incremental temperature drop the crystal productivity these increases of both fractional latent heat and crystal productivity are likely to cause an increase in the time taken to form three grain junctions in the mush via thermal buffering of a thickened mushy layer we suggest these are the underlying causes of stepwise increases in cpp stepwise changes in the geometry of three grain junctions in fully solidified gabbros thus provide a clear microstructural marker for the progress of fractionation down the liquid line of descent in layered intrusions

controls on facies and sequence stratigraphy of an upper miocene carbonate ramp and platform melilla basin ne morocco abstract upwelling of cool seawater paleoceanographic circulation paleoclimate local tectonics and relative sea level change controlled the lithofacies and sequence stratigraphy of a carbonate ramp and overlying platform that are part of a temporally well constrained carbonate complex in the melilla basin northeastern morocco at melilla from oldest to youngest a third order depositional sequence within the carbonate complex contains 1 a retrogradational transgressive warm temperate type rhodalgal ramp 2 an early highstand progradational bioclastic platform composed mainly of a temperate type bivalve rich molechfor facies and 3 late highstand progradational to downstepping subtropical tropical type chlorozoan fringing porites reefs the change from rhodalgal ramp to molechfor platform occurred at 7 0 0 14 ma near the tortonian messinian boundary during a late stage in the development of the bioclastic platform a transition from temperate type molechfor facies to subtropical tropical type chlorozoan facies occurred and is bracketed by chron 3an 2n 6 3 6 6 ma comparison to a well dated carbonate complex in southeastern spain at cabo de gata suggests that upwelling of cool seawater influenced production of temperate type limestone within the ramp and platform at melilla during postulated late tortonian early messinian subtropical tropical paleoclimatic conditions in the western paleo mediterranean region the upwelling of cool seawater across the bioclastic platform at melilla could be related to the beginning of siphoning of deep cold atlantic waters into the paleo mediterranean sea at 7 17 ma the facies change within the bioclastic platform from molechfor to chlorozoan facies may be coincident with a reduction of the siphoning of atlantic waters and the end of upwelling at melilla during chron 3an 2n the ramp contains one retrogradational parasequence and the bioclastic platform three progradational parasequences minor erosional surfaces that bound the upper surface of the ramp and upper surface of the oldest platform parasequence are related to relative falls in sea level induced by local volcanism and associated tectonic uplift these local relative falls had little influence on a broader scale rise to stillstand in relative sea level that controlled development of the transgressive and early highstand systems tracts represented in the ramp and platform respectively

eustatic implications of late miocene depositional sequences in the melilla basin northeastern morocco abstract the age 5 78 ma or lower chron c3r of the major drawdown of the paleo mediterranean sea during the messinian salinity crisis has been established by combining results from stratigraphy paleontology magnetostratigraphy and argon dating for a late miocene sedimentary succession in the melilla basin ne morocco this event is inferred from a marine to continental series of carbonate and siliciclastic rocks that record the end of messinian marine deposition in the melilla basin and presumably marks the final isolation of the paleo mediterranean sea the evidence from the melilla basin is approximately coeval with an increase in benthic foraminiferal 18 o values from a deep marine section in the bou regreg valley nw morocco hodell et al 1994 this increase suggests that a glacio eustatic lowering of sea level at least contributed to the final closure of the mediterranean during the messinian salinity crisis the marine to continental succession onlaps a carbonate complex that contains evidence for multiple relative sea level changes leading up to the main drawdown from bottom to top the carbonate complex is composed of 1 an onlapping ramp 2 a prograding bioclastic platform 3 a prograding and locally downstepping porites reef complex and 4 a topography draping sequence composed of grainstones porites reefs and stromatolites terminal carbonate complex of esteban 1979 the transgressive ramp correlates to relatively low values of benthic foraminiferal 18 o values from a tortonian to lower messinian section at bou regreg hodell et al 1994 this correlation indicates at least in part a link between rising sea level and a reduction in global ice volume during deposition of the ramp a major fall in relative sea level 60 m occurred near the demise of the reef complex during chron c3n 1n at 5 95 0 10 ma this signals the initiation of drawdown and changing environmental conditions in the melilla basin a marginal basin and perhaps the entire paleo mediterranean sea a megabreccia interpreted as forming by solution collapse of evaporites on the basin margin of the reef complex occurs at the base of the terminal carbonate complex updip a major subaerial unconformity separates the reef complex and terminal carbonate complex evaporite deposition likely occurred during this exposure event and has been dated at 5 82 0 02 ma near the base of chron c3r we contend that these evaporites restricted to the shallow melilla basin are related to the continuation of the initial stage of the major drawdown of the paleo mediterranean sea

grain scale melt distribution in two contact aureole rocks implications for controls on melt localization and deformation the grain scale spatial arrangement of melt in layer parallel leucosomes in two anatectic rocks from two different contact aureoles located in central maine usa is documented and used to constrain the controls on grain scale melt localization the spatial distribution of grain scale melt is inferred from microstructural criteria for recognition of mineral pseudomorphs after melt and mineral grains of the solid matrix that hosted the melt in both rocks feldspar mimics the grain scale distribution of melt and quartz is the major constituent of the solid matrix the feldspar pockets consist of individual feldspar grains or aggregates of feldspar grains that show cuspate outlines they have low average width length ratios 0 54 and 0 55 respectively and are interstitial between more rounded and equant width length ratios 0 65 for both samples quartz grains in two dimensions the feldspar pockets extend over distances equivalent to multiple quartz grain diameters possibly forming a connected three dimensional intergranular network both samples show similar mesoscopic structural elements and in both samples the feldspar pockets have a shape preferred orientation in one sample feldspar inferred to replace melt is aligned subparallel to the shape preferred orientation of quartz indicating that pre or syn anatectic strain controlled the grain scale distribution of melt in the other sample the preferred orientation of feldspar inferred to replace melt is different from the orientations of all other mesoscopic or microscopic structures in the rock indicating that differential stress controlled grain scale melt localization this is probably facilitated by conditions of higher differential stress which may have promoted microfracturing grain scale melt distribution and inferred melt localization controls give insight into possible grain scale deformation mechanisms in melt bearing rocks application of these results to the interpretation of deep crustal anatectic rocks suggests that grain scale melt distribution should be controlled primarily by pre or syn anatectic deformation feedback relations between melt localization and deformation are to be expected with important implications for deformation and tectonic evolution of melt bearing rocks

tectonic evolution of the marmara sea and its surroundings abstract the basins in the marmara sea are the products of a superimposed evolutionary history defined by two different aged fault systems the early miocene early pliocene thrace eskisehir fault zone and its branches and the late pliocene recent north anatolian fault and its branches the thrace eskisehir fault and its westward branching secondary fault systems define the early neotectonic signature in the region the late neotectonic period started at the end of the early pliocene when the north anatolian fault divided the thrace eskisehir fault into four parts during the late neotectonic period the north anatolian fault extended westward as a number of splays by joining with the ganos bandirma behramkale and manyas edremit fault zones the branches of the north anatolian fault zone nafz caused the evolution of a number of basins which differ in character depending on the trend and past characteristics of the older branches that became connected since the northern branch of the north anatolian fault is connected to the n80 e trending ganos fault zone gfz in the west a single buried fault has developed in the marmara sea causing the well known troughs and ridges superimposed onto the negative flower structure formed by the gfz in the early neotectonic period the middle strand which extends from iznik lake to bandirma is oriented east west up to the n60 e trending bandirma behramkale fault zone then turns southward in the vicinity of bandirma forming a region dominated by compressional tectonics this bending caused n30 e trending tension in addition to the strike slip motion between the eastern part of gemlik bay and bandirma bay the southern branch of the nafz on the other hand produced three pull apart basins with different characteristics along the yenisehir bursa and manyas segments the southern branch of the nafz connected to the manyas edremit fault zone which is oriented n45 e to the south of manyas and the associated bending and rotation caused a n15 e trending extension in addition to the strike slip regime between manyas and uluabat the branches of north anatolian fault cut through the thrace eskisehir fault at three places the east marmara sea region in gemlik bay and to the east of bursa giving lateral offsets of 58 59 7 8 and 10 11 km respectively the cumulative motion is 75 78 km corresponding to the total lateral offset of the north anatolian fault in the region the correlation of these offsets with global positioning system slip vectors and with stratigraphic results implies that the north anatolian fault reached into the marmara sea region about 3 5 million yr ago tectonic processes forming the marmara sea and its environs were initiated by the thrace eskisehir fault and its splays have been most recently controlled by the north anatolian fault and its splays during the last 3 5 million yr

the monte del casino section northern apennines italy a potential tortonian messinian boundary stratotype abstract results are presented from a high resolution integrated stratigraphic study of the monte del casino section which is considered as a candidate boundary stratotype section for the tortonian messinian t m boundary the section yields a good to excellent cyclostratigraphy tephrastratigraphy and planktonic foraminiferal and nannofossil biostratigraphy it can be correlated in detail to other mediterranean sections using cyclostratigraphic patterns in combination with the planktonic foraminiferal biostratigraphy these correlations indicate that the succession of the monte del casino composite section is continuous in the t m boundary interval and that all sedimentary cycles volcanic ash layers and bio events can be accurately dated by tuning the sedimentary cycles to astronomical target curves the quality of the paleomagnetic signal varies considerably throughout the section a reliable magnetostratigraphy cannot be established for the t m boundary interval because of a secondary magnetisation carried by iron sulphides cyclostratigraphic correlations indicate that discrepancies exist between the position of the reversals recorded here and those found in earlier magnetostratigraphic studies comparison of 40 ar 39 ar ages of ash layers with their astronomical ages show that biotite ages give a good approximation of the age of the section but are not suitable for high resolution chronology despite these short comings the monte del casino section remains a candidate to define the t m boundary but its qualities should be critically weighted against those of other sections

differentiation and compaction in the skaergaard intrusion igneous differentiation processes are constrained from bulk compositions densities and mineral modes of 116 cumulate gabbro samples in a new reference profile through the layered series of the skaergaard intrusion east greenland the stratigraphic distribution of p u and rb in cumulates and residual magma modeled by rayleigh fractionation constrains the final porosities or trapped liquid contents to 30 52 in lza troctolites decreasing to 4 12 at the top of lzb olivine gabbros and remaining low 1 13 4 middle dot 6 on average in the oxide gabbros of lzc mz and uz local variations in trapped liquid content are associated with modal layering leucocratic low density rocks have higher proportions of trapped melt than adjacent melanocratic high density rocks these observations are explained by varying degrees of compaction compaction was most important after the onset of fe ti oxide crystallization because of the high densities of the crystal matrix here computed rates of compaction exceed the rate of crystal accumulation in layers that are metres to a few tens of metres thick in the basal section lza the crystal pile was too thin and the density of the crystal matrix too low to drive the rate of compaction above the high rate of crystal accumulation promoted by initial cooling through the intrusion floor in the overlying section lzb the efficiency of compaction gradually increased as a result of thickening of the crystal pile and lowering of the rate of crystal accumulation the modeling constrains the p2o5 content of the residual magma to 1 middle dot 7 wt at the level of apatite in suggesting that the magma contained 49 wt sio2 and followed a trend of iron enrichment compaction of the uppermost metres to tens of metres of crystal mush at the top of the cumulate pile was an efficient means of differentiation and resulted in layers with variable final porosities and trace element contents depending on the mineralogy and density of the crystal matrix

experimental investigation of melt topology in partially molten quartzo feldspathic aggregates under hydrostatic and non hydrostatic stress continental collision results in deep burial of crustal rocks and their subsequent partial melting field relations of melt along zones of intense deformation suggest that partially molten rocks may play an important role in regional tectonics however subsequent deformation may erase the microstructures produced by the earlier deformation mechanisms inhibiting our understanding of the rheology of partially molten crustal rocks thus in this paper we report the results of an experimental study of the distribution of 2 5 vol melt in quartzo feldspathic aggregates of various grain sizes 2 5 5 10 10 16 and 26 31 m three types of samples were examined all with the composition of 60 wt albite 25 wt potassium feldspar 10 wt quartz and 5 wt biotite the first group included mineral powders annealed at 1000 c 1 0 gpa for c 100 h the second group included commercially hot pressed mineral powders which yielded c 25 vol glass cores of this material were also annealed at 1000 c 1 0 gpa for c 100 h the third group included cores of hot pressed material that were annealed at 1000 c 1 0 gpa for c 45 h then deformed all samples were quenched rapidly in order to examine the melt distribution wetting angles are very similar in both the hydrostatically annealed and the deformed samples analysis of melt pool orientations reveal that melt migrates away from grain boundaries normal to the maximum compressive stress direction in response to the applied non hydrostatic stress this response is easily seen in the coarser grained samples in which melt pools elongated parallel to the maximum compressive stress direction formed during deformation if these results extrapolate to naturally deformed rocks it will be important to consider the orientation of the state of stress in a region during syn magmatic deformation because of its effect on the melt distribution

processes active in mafic magma chambers the example of kilauea iki lava lake hawaii abstract kilauea iki lava lake formed in 1959 as a closed chamber of 40 million m 3 of picritic magma repeated drilling and sampling of the lake allows recognition of processes of magmatic differentiation and places time restrictions on the periods when they operated this paper focuses on evidence for the occurrence of lateral convection in the olivine depleted layer and constraints on the timing of this process as documented by chemical petrographic and thermal data on drill core from the lake lateral convection appears to have occurred in two distinct layers within the most olivine poor part of the lake created a slightly olivine enriched septum in the center of the olivine depleted section a critical marker for this process is the occurrence of loose clusters of augite microphenocrysts which are confined to the upper half of the olivine poor zone this process which took place between late 1962 and mid 1964 is inferred to be double diffusive convection both this convection and a process of buoyant upwelling of minimum density liquid from deep within the lake helz r t kirschenbaum h and marinenko j w 1989 diapiric melt transfer a quick efficient process of igneous differentiation geological society of america bulletin v 101 578 594 result from the fact that melt density in kilauea iki compositions decreases as olivine and augite crystallize above the incoming of plagioclase the resulting density vs depth profile creates 1 a region of gravitationally stable melt at the top of the chamber the locus of double diffusive convection and 2 a region of gravitationally unstable melt at the base of the melt column the source of upwelling minimum density melt helz r t kirschenbaum h and marinenko j w 1989 diapiric melt transfer a quick efficient process of igneous differentiation geological society of america bulletin v 101 578 594 by contrast the variation of melt density with temperature for the 1965 makaopuhi lava lake does not show a decrease in density as temperature decreases so neither process should have occurred in that lava lake because many mafic magmas crystallize significant olivine and or pyroxene before they begin to crystallize plagioclase the density relations observed for kilauea iki and the processes that result from them may be relevant to crystallization in other mafic magma chambers the results for the 1965 makaopuhi lava lake emphasize the role of bulk composition as a critical control on magmatic processes

chemical evolution of intercumulus liquid as recorded in plagioclase overgrowth rims from the skaergaard intrusion the intercumulus liquid of a crystal mush fills pore spaces and typically solidifies to form overgrowths on cumulus grains and poikilitic post cumulus minerals if the liquid is immobile solidification produces zoned intercumulus minerals as a result of progressive fractionation of the residual liquid convection within the mush results in buffering of the liquid composition and thus limits mineral zonation for fully solidified cumulates fossil changes in liquid composition or porosity are difficult to identify however detailed study of immobile minor components of plagioclase overgrowth rims can provide information about the progressive solidification of intercumulus material ti contents of plagioclase overgrowths in samples from the lowermost parts of the skaergaard intrusion show strong variations with anorthite content with decreasing xan ti concentrations first rise and then fall consistent with changing tio2 contents of the intercumulus liquid during solidification tio2 in plagioclase decreases sharply at an55 reflecting local saturation of fe ti oxides ti in clinopyroxene oikocrysts also falls rimward but zoning in faster diffusing species fe mg is limited other than slight reverse zones that may occur on the plagioclase margins xan falls continuously during crystallization the reverse zoning is interpreted as the result of compaction driven dissolution and reprecipitation of plagioclase the continual decrease in xan is exploited together with back scattered electron images of the cumulates to produce calibrated images showing regions of progressive crystallization this allows the regions crystallizing at each stage of solidification to be visualized these images show that the final remnants of interstitial melt were present in triangular pockets and as thin grain boundary melt films this approach can provide information about the progressive reduction of porosity during cumulate solidification

silicate liquid immiscibility within the crystal mush late stage magmatic microstructures in the skaergaard intrusion east greenland late stage microstructures developed during the last stages of solidification of the skaergaard intrusion comprise a wide array of reactive and non reactive intergrowths reactive microstructures ascribed to open system behaviour include serrated grain boundaries between pyroxene and plagioclase primocrysts fish hook pyroxenes and mafic symplectites they form by the addition of fe and ca and removal of alkalis and silica other microstructures include those formed by internally generated redox reactions between olivine fe ti oxides and pyroxene non reactive microstructures include closely spatially associated granophyric intergrowths and previously undescribed ilmenite rich intergrowths that are interpreted as a consequence of crystallization of separated conjugate immiscible liquids the open system reactive microstructures occur predominantly in the cumulates on the chamber floor appearing in lzb and disappearing to be replaced by a granophyre ilmenite rich intergrowth association in the upper zone they are not common in the marginal border series their distribution mirrors that of efficient expulsion of trapped liquid and can be attributed to the gravitationally driven loss of a si rich immiscible component from the interstitial liquid the loss of the si rich component causes the remaining fe rich liquid to react with the primocrysts bulk rock major element data are consistent with little or no preferential loss of the si rich liquid from the mush but the resolution of the available data is not sufficient to assess the effect of this relative movement on the liquid line of descent of the bulk magma the first appearance of the paired conjugate non reactive intergrowths in mz marginal border series points to the early onset of immiscibility in the bulk liquid

on the identification of textural equilibrium in rocks using dihedral angle measurements three dimensional numerical simulations have been constructed to investigate the distributions of apparent dihedral angles expected in unequilibrated rock textures for comparison with those expected in equilibrated rock textures for unequilibrated fully crystallized monomineralic rocks the simulation shows that the distribution of apparent dihedral angles is nonrandom and similar to that expected from an equilibrated rock and is largely independent of crystal shape and crystal nuclei distribution this new distribution together with the one previously derived for an equilibrated texture defines a pair of apparent dihedral angle curves which encompass curves corresponding to any degree of textural equilibrium within a monomineralic rock the location of a measured curve within this range allows a quantitative assessment of the degree of textural equilibrium within that rock the simulations also show that unequilibrated partially crystallized rocks generate apparent dihedral angle distributions for closed triangular pores that depending on crystal shape may mimic equilibrated dihedral angle distributions they also indicate that unless a rock is in complete equilibrium different dihedral angle distributions are produced by measuring the apparent dihedral angles of closed triangular or open nontriangular pores an important conclusion of this work is that apparent dihedral angle curves for unequilibrated textures are similar to those for equilibrated textures therefore care must be taken when interpreting textural equilibrium from apparent dihedral angle curves

palaeogeographical evolution of the thrace neogene basin and the tethys paratethys relations at northwestern turkey thrace abstract the thrace neogene basin situated in northwestern turkey was initiated by strike slip faulting that was active from the early miocene until the end of the pliocene during the early miocene it began to form under the control of the thrace eskisehir fault zone initiated by continental collision in northwestern anatolia late oligocene early miocene during the late early miocene the basin was a site of mainly fluviatile and limnic sedimentation to the west and marine sedimentation via the paratethyan transgression in the north with the onset of the middle miocene the thrace block started to rotate in a counterclockwise sense and escaped westward with respect to the strandja istanbul block owing to rejuvenation of fossil fault systems within it in this period warm marine conditions were also established around the gulf of saros through a mediterranean originated transgression during the middle late miocene fluviatile and limnic conditions were created over the western thrace by the westerly propagation of the thrace eskisehir fault zone one of the principal results of the early middle miocene tectonics is the tilting of the strandja istanbul block to the south severing the tethys and the paratethys during the latest miocene early pliocene period the thrace eskisehir fault zone was deactivated because of the evolution of the north anatolian fault zone to the south the resurrected ganos fault zone situated on the dissected fossil suture zone in the sea of marmara also joined the north anatolian fault zone uplifting the gelibolu peninsula and thus severing the connection that existed between the sea of marmara and the paratethys the sea of marmara eventually became an endemic basin by the activity of the north anatolian fault zone

the thickness of the crystal mush on the floor of the bushveld magma chamber the thickness of the crystal mush on magma chamber floors can be constrained using the offset between the step change in the median value of dihedral angles formed at the junctions between two grains of plagioclase and a grain of another phase typically clinopyroxene but also orthopyroxene and olivine and the first appearance or disappearance of the liquidus phase associated with the step change in median dihedral angle we determined the mush thickness in the rustenburg layered suite of the bushveld complex at clinopyroxene in in lower main zone and magnetite in in upper zone we also examined an intermittent appearance of cumulus apatite in upper zone using both the appearance and disappearance of cumulus apatite in all cases the mush thickness does not exceed 4 m these values are consistent with field observations of a mechanically rigid mush at the bases of both magnetitite and chromitite layers overlying anorthosite mush thickness of the order of a few metres suggests that neither gravitationally driven compaction nor compositional convection within the mush layer is likely to have been important processes during solidification adcumulates in the bushveld are most likely to have formed at the top of the mush during primary crystallisation similarly it is unlikely either that migration of reactive liquids occurs through large stretches of stratigraphy or that layering is formed by mechanisms other than primary accumulation

textural analysis of magmatic enclaves from the kameni islands santorini greece abstract the kameni islands have been the focus of historic volcanic activity on santorini greece the islands comprise a series of dacite lavas the erupted compositions of which have remained approximately constant for the last 2200 years the dacite lava flows of nea kameni contain a variety of mafic enclaves distinguished by differences in texture composition and mechanical behaviour the mafic enclaves represent chilled fragments of mafic magma that crystallised rapidly on contact with the cooler more silicic host magma the absence of chilled margins on the enclaves suggests that the replenishing magma initially formed a dense layer at the base of the chamber groundmass textures are interpreted as an indication of the degree of undercooling between the enclaves and the host groundmass textural information obtained from the enclaves has been used to determine the relative volumes of replenishing magmas injected into the host magma before eruption which indicates that the volume of erupted magma is directly proportional to the volume of replenishing magma emplaced in the chamber prior to eruption which thus may act as a potential eruption trigger the variety of replenishing magmas implies the existence of a complex conduit and chamber system beneath santorini volcano andesitic enclaves with linear crystal size distributions are thought to have originated as an aphyric andesitic melt expelled from a crystal mush by filter pressing disequilibrium phenocryst assemblages in the lavas and phenocryst bearing enclaves provide evidence for the entrainment and recycling of older phenocryst populations

on the pseudomorphing of melt filled pores during the crystallization of migmatites pseudomorphs of melt filled pores recognized by their generally cuspate shape are used as diagnostic for the former presence of partial melt they are commonly observed in migmatites from the mid to deep crust although they occur in the smaller pores in migmatites from shallower levels 1 2 kbar the pseudomorphing of meltfilled pores is controlled by the kinetics of nucleation and is a consequence of the greater supersaturation required for nucleation in a small pore compared with a larger one we examine three migmatites in detail a contact metamorphosed cherty band from an iron formation an archaean regional granulite from an accretionary prism and an amphibolite facies sample from the roots of an archaean mountain chain the greater undercooling required for nucleation in progressively smaller pores is recorded by the composition of plagioclase pseudomorphs a study of dihedral angles at the corners of pseudomorphed pores demonstrates that melt solid textural equilibrium was probably attained only in the contact aureole the regional granulite preserves an almost unmodified reaction controlled melt distribution with little evidence for either melt solid textural equilibration or solid solid re equilibration whereas the reactioncontrolled melt distribution in the regional amphibolite facies example has been modified by a partial approach to solid solid textural equilibrium it is not clear whether the differences in dihedral angle population are due to differences in uplift and exhumation rates or due to the presence of h2o on grain boundaries

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

contact metamorphism hydrothermal alteration of tertiary basalts from the isle of skye northwest scotland alkali olivine basalts from skye were simultaneously contact metamorphosed by tertiary gabbro and granite intrusions and altered by the hydrothermal convection system that the plutons induced four metamorphic zones were mapped around the plutons furthest from the intrusions in the primary olivine zone metabasalts are composed of combinations of igneous olivine augite plagioclase titaniferous magnetite ilmenite zeolites gyrolite sulfides and chlorite smectite intergrowths closer to the plutons in the smectite zone saponite and carbonate appear primary olivine and gyrolite disappear and zeolites decrease dramatically in abundance still closer to the plutons in the amphibole zone actinolite edenite chlorite sphene epidote andradite and quartz appear and saponite and chlorite smectite intergrowths disappear along parts of the contact between gabbro and basalt in the orthopyroxeneolivine zone orthopyroxene metamorphic olivine and biotite appear and amphibole chlorite sphene epidote andradite carbonate and quartz disappear whole rock chemical data indicate only minor change in the major element chemical composition of the metabasalts during progressive metamorphism hydrothermal alteration two pyroxene eothermometry and various mineral fluid equilibria suggest the range of peak temperatures attained in the metamorphic zones orthopyroxene olivine zone 900 1 030 c amphibole zone 400 900 c smectite and primary olivine zones 5 smow mineralogically more altered basalts from the smectite zone have whole rock 18o 2 to 5 still more mineralogically altered basalts from the amphibole zone with one exception have 18o 2 completely recrystallized hornfelses from the orthopyroxene olivine zone have 18o 0 the principal mechanism of isotope exchange between basalt and metamorphic hydrothermal fluid probably was heterogeneous mineralfluid reaction

plagioclase in the skaergaard intrusion part 1 core and rim compositions in the layered series the anorthite content of plagioclase grains xan in 12 rocks from the layered series of the skaergaard intrusion has been studied by electron microprobe typically 30 core and 70 rim analyses per thin section mean core compositions vary continuously from an66 at the base of the layered series lza to an32 30 at the top on the other hand crystal rims are of approximately constant composition an50 1 from the lza to the lower middle zone mz above the mz core and rim compositions generally overlap profiles across individual plagioclase grains from the lower zone show that most crystals have an external zone buffered at xan 50 1 the simplest explanation for these features is that during postcumulus crystallization in the lower zone interstitial liquids passed through a density maximum this interpretation is consistent with proposed liquid lines of descent that predict silica enrichment of the liquid associated with the appearance of cumulus magnetite

an experimental study of ostwald ripening of olivine and plagioclase in silicate melts implications for the growth and size of crystals in magmas we carried out an experimental study to characterize the kinetics of ostwald ripening in the forsterite basalt system and in the plagioclase an65 andesite system eight experiments were done in each system to monitor the evolution of mean grain size and crystal size distribution csd with time t the experiments were performed in a 1 atmosphere quench furnace at 1 250 c for plagioclase and 1 300 c for olivine very contrasted coarsening kinetics were observed in the two series in the plagioclase series the mean grain size increased as log t from 3 m to only 8 7 m in 336 h the kinetic law in log t means that ostwald ripening was rate limited by surface nucleation at plagioclase liquid interfaces in the olivine series the mean grain size increased as t1 3 from 3 m to 23 2 m in 496 h a kinetic law in t1 3 is expected when ostwald ripening is rate limited either by diffusion in the liquid or by grain growth dissolution controlled by a screw dislocation mechanism the shape of olivine csds in particular their positive skewness indicates that grain coarsening in the olivine experiments was controlled by a screw dislocation mechanism not by diffusion as the degrees of undercooling t or supersaturation involved in ostwald ripening are essentially 1 c the mechanisms of crystal growth identified in our experiments are expected to be those prevailing during the slow crystallisation of large magma chambers we extrapolated our experimental data to geological time scales to estimate the effect of ostwald ripening on the size of crystals in magmas in the case of plagioclase ostwald ripening is only efficient for mean grain sizes of a few microns to 20 m even for a time scale of 105 years it can however result in a significant decrease of the number of small crystals per unit volume and contribute to the development of convex upwards csds for olivine the mean grain size increases from 2 3 m to 70 m in 1 year and 700 m in 103 years a mean grain size of 3 mm is reached in 105 years accordingly the rate of grain size dependent processes such as compaction of olivine rich cumulates or melt extraction from partially molten peridotites may significantly be enhanced by textural coarsening

an ocean ridge type magma chamber at a passive volcanic continental margin the kap edvard holm layered gabbro complex east greenland the gabbros of the tertiary kap edvard holm layered serieshave a stratigraphic thickness of more than 5000 m earlier work has shown that the range in cumulus mineral compositions is restricted plagioclase an 81 an 51 olivine fo 85 fo 66 pyroxenes ca 43 mg 46 fe 11 to ca 43 mg 37 fe 20 field evidence of magma injections is common which together with the restricted range in mineral chemistry suggests that the magma chamber was frequently replenished by a less fractionated magma a detailed study of a 600 m section 900 1500 m in the lower layered series reveals a period of crystallization when the magma chamber behaved as a closed system 900 1300 m the rocks formed during this periodare well laminated olivine gabbros 900 110 m which evolved to well laminated oxide gabbros 1100 1300 m compositional trends in the cumulusminerals are towards more evolved compositions plagioclase an 64 an 58 pyroxene mg from 80 to 76 with stratigraphic height from 1300 m to 1500 m granular olivine gabbros dominate with moreprimitive mineral compositions plagioclase an 67 an 76 pyroxene mg from 78 to 82 the transition olivine gabbro to oxide gabbro at 1100m is a consequence of fractional crystallization and it is shown how changes in activities of feo and fe 2 0 3 in the magma are reflected in the total iron content of plagioclases the transition from oxide gabbro to olivine gabbro at 1300 m results from replenishment by less evolved basaltic magma on the basis of calcic pyroxene chemistry and the mineral crystallization sequence it is concluded that the kap edvard holm layered series crystallized from a tholeiitic magma similar to morb melanogabbroic units occur throughout the intrusion as discordant to subconcordant sill like bodies 0 2 2 0 m thick the melanogabbroic units consist of cr rich augite olivine plagioclase heteradcumulates and contain deformed mica crystals of pre emplacement origin these units crystallized from a wet mgo rich magma which was injected into the layered host gabbros after the formation of the cumulus pile but before the magma was completely solidified the kap edvard holm layered series has several parallels with the plutonic part of ophiolite sequences these include cumulus mineral assemblage compositions of the minerals and the restricted range in compositions with stratigraphic height field evidence of repeated replenishment of basaltic magma dyke swarms overlying the roof zone of the magma chamber and the existence of a late intrusive suite of wet mgo rich magma these parallels suggest that the processes involved in the formation of the kap edvard holm layered series were similar to those involved in the formation of the crustalpart of many ophiolites and beneath present day spreading ridges the kap edvard holm layered series is therefore believed to represent a shallow level magma chamber which acted as a reservoir for basaltic flows at the continental margin during the opening of the north atlantic ocean

asynchronous marine terrestrial signals of the last deglacial warming in east asia associated with low and high latitude climate changes a high resolution multiproxy record including pollen foraminifera and alkenone paleothermometry obtained from a single core dg9603 from the okinawa trough east china sea ecs provided unambiguous evidence for asynchronous climate change between the land and ocean over the past 40 ka on land the deglacial stage was characterized by rapid warming as reflected by paleovegetation and it began ca 15 kabp consistent with the timing of the last deglacial warming in greenland however sea surface temperature estimates from foraminifera and alkenone paleothermometry increased around 20 19 kabp as in the western pacific warm pool wpwp sea surface temperatures in the okinawa trough were influenced mainly by heat transport from the tropical western pacific ocean by the kuroshio current but the epicontinental vegetation of the ecs was influenced by atmospheric circulation linked to the northern high latitude climate asynchronous terrestrial and marine signals of the last deglacial warming in east asia were thus clearly related to ocean currents and atmospheric circulation we argue that i early warming seawater of the wpwp driven by low latitude insolation and trade winds moved northward via the kuroshio current and triggered marine warming along the ecs around 20 19 kabp similar to that in the wpwp and ii an almost complete shutdown of the atlantic meridional overturning circulation ca 18 15 kabp was associated with cold heinrich stadial 1 and delayed terrestrial warming during the last deglacial warming until ca 15 kabp at northern high latitudes and hence in east asia terrestrial deglacial warming therefore lagged behind marine changes by ca 3 4 ka

timing and progression of climatic tectonic and glacioeustatic influences on the messinian salinity crisis abstract new palynological analysis of the continuous upper neogene sequence from the rifian corridor at sale morocco permits the deconvolution of climatic tectonic and eustatic control on the messinian salinity crisis via two indices 1 a distance from shore index based on dinoflagellate cyst versus pollen distribution and 2 a land climate index based on detailed pollen analysis this new pollen analysis indicates that the messinian salinity crisis 6 8 ma to 5 3 ma was not associated with major climate change detailed analyses of dinoflagellate cyst ecology at sale correlated to the sale 18o record show that initial shoaling of the rifian corridor after 7 3 ma primarily resulted from tectonic uplift however from 6 5 ma to 5 4 ma the rifian corridor was sufficiently shallow to have experienced significant restriction of atlantic inflow during at least four small amplitude glacioeustatic lowstands at 5 4 ma abrupt increase in the ratio of continental versus marine derived palynomorphs indicates that restriction intensified as tectonic uplift significantly outpaced gradual glacioeustatic rise despite eustatic rise at 5 32 ma the sale palynological data show that the rifian corridor experienced a second major drop in relative sea level tectonic uplift or increased sedimentation therefore termination of the messinian salinity crisis was probably associated with a breach elsewhere along the gibraltar arc

short paper textures of forsterite calcite marbles from the beinn an dubhaich aureole skye and implications for the structure of metamorphic porosity in the aureole of the beinn an dubhaich granite forsterite grew with dihedral angles of less than 110 against calcite but was progressively and variably annealed towards the equilibrium dihedral angle of 165 new experimental estimates of calcite calcite fluid dihedral angles are presented ranging from 50 90 the early low angles may be due to rapid olivine growth into a fluid filled porosity the preservation of a range of textural states in the beinn an dubhaich aureole has the potential to provide information on the kinetics of grain boundary readjustments in metamorphic rocks which control pore geometry and permeability

thinking about lips a brief history of ideas in large igneous province research abstract large igneous provinces lips are extraordinary igneous and tectonic events that have influenced the planet in profound ways including the major turnovers in the history of life the lip concept definitions and terminology first nucleated in a 1990 workshop jointly arranged by joint oceanographic institutions and u s science support program subsequently presented in a series of seminal papers by millard f coffin and olav eldholm in the early 1990 s they combined existing data and information from continental flood basalts with the emerging geophysical understanding of oceanic plateaus and rifted continental margins the new terminology had major implications within the geosciences and beyond however when investigating how geoscientists described and interpreted these vast provinces prior to the 1990 s we are left with a series of questions who first realized that lips represent extraordinary events in the history of the earth what terminology was used and why were geologists interested in this type of events here we discuss some of the key developments in lip research including mapping projects expeditions international programs correlations across continents and the history of the terminology we focus our discussion on four cases the karoo lip the siberian traps the north atlantic igneous province and the ontong java plateau comprising key examples of lips with long histories of study and exploration we conclude that the past 150 years of lip related research and endeavor was largely driven by a need to understand fundamental aspects of earth evolution including continental drift plate tectonic reconstructions the origin of basalt mantle processes and plumes and the role of volcanism in driving mass extinctions and climatic changes

kinetics of crystallization of igneous rocks the geochemistry of igneous rocks is discussed with the primary objectives of bringing together the theories underlying the kinetics of crystallization of igneous rocks and illustrating the use of these theories in understanding experimental and observational data the primary purpose of the chapter is to introduce current thinking about the kinetics of igneous rocks and to provide a basis for understanding other work a basic assumption made in the discussion is that the rate of any chemical reaction including the crystallization of igneous rocks is zero at equilibrium and proceeds at a finite rate only at a finite deviation from equilibrium as such an understanding of the processes operating in igneous rocks requires an understanding of how deviation from equilibrium affects the rates and mechanisms of the processes occurring during crystallization these processes are detailed with special emphasis given to nucleation and crystal growth jmt

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

disequilibrium dihedral angles in dolerite sills a new proxy for cooling rate the geometry of clinopyroxene plagioclase plagioclase junctions in mafic rocks measured by the median dihedral angle cpp is created during solidification in the solidifying kilauea iki hawaii lava lake the wider junctions between plagioclase grains are the first to be filled by pyroxene followed by the narrower junctions the final cpp attained when all clinopyroxene plagioclase plagioclase junctions are formed is 78 in the upper crust of the lake and 85 in the lower solidification front cpp in the 3 5 m thick traigh bhan na sgurra sill inner hebrides is everywhere 78 in the whin sill northern england 38 m thick and the portal peak sill antarctica 129 m thick cpp varies symmetrically with the lowest values at the margins the 266 m thick basement sill antarctica has asymmetric variation of cpp attributed to a complex filling history the chilled margins of the basement sill are partially texturally equilibrated with high cpp the plagioclase grain size in the two widest sills varies asymmetrically with the coarsest rocks found in the upper third both cpp and average grain size are functions of model crystallization times cpp increases from 78 to a maximum of 100 as the crystallization time increases from 1 to 500 yr because the use of grain size as a measure of crystallization time is dependent on an estimate of crystal growth rates dihedral angles provide a more direct proxy for cooling rates in dolerites

origin of strongly reversed rims on plagioclase in cumulates abstract narrow reversed rims on plagioclase are ubiquitous in troctolites and olivine gabbros of the kiglapait intrusion and may be a common feature of all such cumulates the rims occur at plag plag plag ol and less strongly at plag aug grain boundaries they are optically obvious at an and can reach an 32 mol or more in parallel k na drops sharply although ubiquitous from sample to sample the reversed rims are only locally present at grain boundaries even for the same pair of crystals in contact they are prominent in linear networks suggesting the last trace of intercumulus liquid a subsolidus origin is ruled out by the absence of reactants at plag plag and plag ol boundaries and by the local rather than pervasive development of rims the rims are required to grow from intercumulus liquid in which the partition of an component between crystals and liquid increases with the trapped augite component of the liquid calculations from published experimental data show that an 30 can easily be achieved by such a process it is also probable that the trapped liquid is part of an an rich boundary layer generated by solute rejection during adcumulus growth the ability of the rims to sustain steep k na gradients despite a long subsolidus cooling history proves that the k na exchange rate is vanishingly small over a geologic time scale in an rich feldspar suggesting that at low k content the potassium is site bound to the tetrahedral al si distribution reversed rims therefore provide important information on diffusion limits as well as on the late stage solidification history of plagioclase rich cumulates moreover they demonstrate that plagioclase geothermometry cannot be divorced from effects of liquid composition and structure as monitored for example by augite content

tectonic elements controlling the evolution of the gulf of saros northeastern aegean sea turkey abstract tectonic elements controlling the evolution of the gulf of saros have been studied based upon the high resolution shallow seismic data integrated with the geological field observations evolution of the gulf of saros started in the middle to late miocene due to the nw se compression caused by the counterclockwise movement of the thrace and biga peninsulas along the thrace fault zone hence the north anatolian fault zone is not an active structural element responsible for the starting of the evolution of the gulf of saros the compression caused by the rotational movement was compensated by tectonic escape along the pre existing ganos fault system two most significant controllers of this deformation are the sinistral ganos fault and the dextral northern saros fault zone both extending along the gulf of saros the most important evidences of this movement are the left and right oriented shear deformations which are correlated with structural elements observed on the land and on the high resolution shallow seismic records at the sea another important line of evidence supporting the evolution of this deformation is that the transgression started in the early late miocene and turned as a result of regional uplift into a regression on the gelibolu peninsula during the turolian and in the north of the saros trough during the early pliocene the deformation on the gelibolu peninsula continued effectively until the pleistocene taking into account the fact that this deformation affected the late pleistocene units of the marmara formation the graben formation of the gulf of saros is interpreted as a recent event however at least a small amount of compression on the gelibolu peninsula is observed it is also evident that compression ceased at the northern shelf area of the gulf of saros

messinian reef building assemblages of the salento peninsula southern italy palaeobathymetric and palaeoclimatic significance abstract this paper mainly addresses the description and interpretation of different reef building assemblages recognised within an early messinian reef complex recently discovered along the eastern margin of the apulia platform salento peninsula southern italy it is the first late miocene reef recorded for the adriatic region and its location partly changes boundaries of coral reef distribution during this time in the mediterranean the messinian reef complex novaglie formation is interpreted as a succession of fringing reefs accommodated in palaeo reentrances or palaeo embayments of the original messinian rocky shore and overlying discordantly the underlying cretaceous to oligocene units it consists of a discontinuous reef tract and associated clinostratified fore reef slope relatively precise dating of the reef complex has been achieved using benthic foraminifera and ostracods associations three main different reef building assemblages have been recognised 1 halimeda bioherms 2 porites reef and 3 vermetid microbial trottoirs each assemblage is described in detail according to its architecture and structure setting shape quantitative estimation of the framework density biotic components taxonomic composition and relative abundance of the reef builders growth form associated fauna and intra reef sediment texture and fabric palaeoecologic analysis based on physical observation within the margin slope of the reef complex and in comparison with present day analogues and their ecological demands indicates that distribution and vertical succession of the three different reef assemblages are strictly depth related suggesting an ecological replacement consequent on small relative sea level changes fourth order closely comparable with those already indicated for the early messinian special attention is given to the remarkable abundance of vermetids that together with microbial crusts formed scattered trottoirs along the shoreline vermetid occurrences have been extensively cited in the literature for the late miocene of the mediterranean but poorly studied in detail here their palaeoecologic significance is emphasised indicating that these organisms can be used as reliable palaeobathymetric and palaeoclimatic indicators regarding the miocene of the mediterranean development of vermetid microbial reefs so far recorded for the messinian is preferentially associated with low diversity coral reefs and is interpreted as being mainly controlled by climatic constraints

the magma body at kilauea iki lava lake potential insights into mid ocean ridge magma chambers although geological and geophysical measurements at active ridges have provided indirect samples and remote images and ophiolites have provided fossil evidence the lack of direct sampling of in situ physical and chemical properties severly hinders our understanding of subsurface magmatic systems at mid ocean ridges in contrast with the ridge setting substantial information has been gained from direct sampling of kilauea iki lava lake we reanalyze time series physical and petrological data from both in situ sampling and remote seismic and electromagnetic imaging of this lava lake in order to gain insights into the evolution of an enclosed basaltic magma body with many characteristics similar to a mid ocean ridge magma chamber although the analogy is imperfect our analysis of observations from kilauea iki suggests that at a mid ocean ridge 1 a fine structure exists at the top of the magma body in the form of horizontal segregation veins i e sills 2 sustained convection within the magma chamber is highly unlikely 3 a dry out zone above the magma body and below the deepest penetration of hydrothermal circulation may exist 4 with high magma supply e g the east pacific rise where quasi steady state melt zones are present the magma chamber must be completely replenished very frequently at least every 300 600 years and 5 the onset of rigid behavior of the basaltic partial melt does not happen at a unique critical crystal fraction these results also show that significant differences may occur in interpretation of the rheology of a magmatic system depending upon the type of petrologic seismic or drilling data analyzed

calibrating the duration and timing of the messinian salinity crisis in the mediterranean linked tectonoclimatic signals in thrust top basins of sicily the messinian 9salinity crisis9 which affected the mediterranean represents one of the most dramatic examples of base level fluctuation known in the geological record an amplitude of perhaps 2 km within a stage with a duration of less than 2 ma deposits within the caltanissetta basin of central sicily are used to calibrate the duration and timing of these fluctuations two successions of evaporites termed 9first cycle9 and 9second cycle9 are separated by an inter regional unconformity the first cycle is regionally regressive while the second is transgressive chronostratigraphic calibration of these deposits has been provided by a linked magnetostratigraphic structural and sedimentological study the regression was protracted the earliest evaporites in our study accumulated early in chron c3ar pre 6 88 ma and the youngest accumulated late in chron c3an post 6 0 ma during this interval the basinward shift in coastline was 70 km and in vertical section implies a relative fall in sea level at 0 3 0 4 m ka 1 lowstand probably finally occurred at 5 8 5 5 ma transgression marked by accumulation of the 9second cycle9 deposits which all record reversed magnetizations c3r apparently occurred far more rapidly 200 ka prior to the return to 9normal9 marine conditions in the central mediterranean late in chron c3r local rates of tectonic deformation are relatively slow within the thrust belt which underlies the caltanissetta basin therefore it is likely that the timing and rates of the messinian 9salinity crisis9 on sicily are generally applicable to other basins in the region and help to underpin rates of climate change within this part of the neogene

origin of the strait of canakkale dardanelles regional tectonics and the mediterranean marmara incursion abstract the regional tectonics and the mid to late quaternary seismic stratigraphy of the strait of canakkale dardanelles and its opening towards the aegean sea were interpreted by using shallow seismic profiles this strait is a narrow valley that resulted from regional uplift of the gelibolu and biga peninsulas in the pliocene as a consequence of compressional events generated by strike slip faulting activity of the ganos fault a northern strand of the north anatolian fault a nne ssw trending fault system between eceabat and canakkale believed to result from the left lateral displacement of the ganos fault on the gelibolu peninsula cut this valley into different segments the connection between the marmara basin and the aegean sea has been achieved after flooding of the connected valleys during the mid to late pleistocene three major sea level lowstands 130 150 m during this period 600 kyear bp interrupted the sea water connection at least twice three main seismic unconformities detected in the sediments of the strait of canakkale represent these lowstands minor sea level lowstands could have induced narrowing of the strait and erosion of depositional units the recent geological history of the strait of canakkale appears as deduced from the gelibolu peninsula and its western regions strongly related to escape tectonics influenced by the compressional forcing of the anatolian block in addition it also shows a morphological evolution which carries the effects of the global sea level variations

coupled caal nasi diffusion in plagioclase feldspar experiments and applications to cooling rate speedometry abstract the rate of caal nasi interdiffusion in plagioclase feldspar was determined under 1 atm anhydrous conditions over the temperature range 1400 to 1000 c in calcic plagioclase an80 81 by homogenizing coherent exsolution lamellae the dependence of the average interdiffusion coefficient on temperature is given by the expression d 10 99 cm 2 sec exp 123 4 kcal mol rt t in k this value is for diffusion perpendicular to the 03 1 interface of the lamellae caal nasi interdiffusion is 4 to 5 orders of magnitude slower than oxygen diffusion in the temperature range 1400 to 1200 c and possibly 10 orders of magnitude slower at subsolidus temperatures the large differences in diffusion rates explain the apparent contradiction posed by the plagioclases of large layered intrusions e g the skaergaard which retain delicate ca na compositional zoning profiles on the micron scale but have undergone complete oxygen isotopic exchange with heated meteoric groundwater from the surrounding wall rocks caal nasi diffusion is slow the closure temperature is high within the solidus liquidus interval and ca na zoning is preserved oxygen diffusion is faster the closure temperature is lower 350 400 c and the feldspars exchange oxygen with the low temperature hydrothermal fluids the complex micron scale oscillatory zones in plagioclase can also be used as cooling rate speedometers for volcanic and plutonic plagioclase cooling histories typical of large mafic intrusions e g the stillwater are slow begin at high initial temperatures 1200 c and result in homogenization of oscillatory zones on the scale of 10 microns the oscillatory zones found in the plagioclase of granodioritic plutons are preserved because cooling is initiated at a lower temperature 1000 c limiting diffusion to submicron length scales despite the slow cooling rate of the intrusion

the mediterranean water body in the late messinian interpreting the record from marginal basins on sicily the stratigraphic record of climatic and palaeoceanographic changes in the mediterranean during the late messinian is controversial on sicily sedimentary facies show a steady transgression suggesting that sub basins were hydrodynamically linked to a larger water body here we test this hypothesis using strontium isotope studies from messinian materials collected from a range of sites in the caltanissetta basin of central sicily the strata include a regionally regressive first cycle of early mid messinian age and a younger transgressive second cycle these cycles are separated by an inter regional unconformity which may be correlated with base level low stand in the mediterranean 87 sr 86 sr ratios for all first cycle gypsum fall within the expected global marine composition 0 70891 0 70897 all second cycle analyses fall within a grouping of significantly lower values 0 70868 0 70878 a surprisingly tight but discrepant grouping for data collected from shells of a brackish water fauna and from gypsum analyses from these different second cycle materials are statistically indistinguishable these results indicate that the strontium isotopic composition of waters from different sub basins on sicily are indistinguishable regardless of salinity during the late messinian therefore these basins must have mixed with a larger homogenized reservoir which we infer was the ancestral mediterranean thus circum mediterranean basins may indeed chart regional palaeoceanographic and climatic events by the end of messinian times the base level of the mediterranean was within the range of the world9s oceans but the water body probably had a distinctly different but internally homogeneous strontium isotopic composition

silicate liquid immiscibility within the crystal mush evidence from ti in plagioclase from the skaergaard intrusion a key target in the study of layered intrusions is to constrain the liquid line of descent of the magma however the evolution of the interstitial liquid is rarely considered and its liquid line of descent is often assumed to be equivalent to that of the bulk magma because of extensive sub solidus and diffusional changes that occur in slowly cooled rocks clues to the composition of the interstitial liquid can only be obtained using very slowly diffusing trace elements and components this study uses the ti concentrations and anorthite contents of interstitial plagioclase to consider the compositional evolution of the interstitial liquid in the skaergaard intrusion ti xan zoning of interstitial plagioclase does not follow the same cryptic variations that develop in plagioclase primocrysts as a function of stratigraphic height demonstrating that the bulk and interstitial liquid lines of descent are not equivalent after fe ti oxides start to crystallize ti concentrations decrease in both primocryst and interstitial plagioclase as a result of decreasing melt ti however in the interstitial plagioclase within a single thin section divergent trends develop adjacent to fine grained interstitial pockets containing diverse mineral assemblages which are interpreted to represent the crystallized products of late stage immiscible liquids these trends vary systematically as a function of stratigraphic height and spatial location within the intrusion the distribution and compositions of these plagioclase zoning trends are used to comment on the spatial distribution and differential movement of interstitial immiscible liquids within the intrusion the author 2010 published by oxford university press all rights reserved

insights into the behaviour of s f and cl at santiaguito volcano guatemala from apatite and glass abstract the mineral apatite can incorporate all of the major magmatic volatile species into its structure where melt inclusions are not available magmatic apatite may therefore represent an opportunity to quantify volatile concentrations in the pre eruptive melt we analysed apatites and matrix glasses from andesites and dacites erupted from santiaguito volcano guatemala between the 1920s and 2002 x ray mapping shows complex zoning of sulphur in the apatite grains but typically with sulphur rich cores and sulphur poor rims apatite microphenocrysts are enriched in f and depleted in cl relative to inclusions matrix glasses are dacite to rhyolite and contain low f but up to 2400 ppm cl overall the data are consistent with progressive depletion of cl in the most evolved melts due to crystallisation and degassing in the absence of pristine melt inclusions we used apatite together with published partitioning data to reconstruct the likely volatile contents of the pre eruptive melt and hence estimate long term average gas emissions of so 2 hf and hcl for the ongoing eruption the data indicate time averaged so 2 emissions of up to 157 tonnes day hcl of 74 1382 tonnes day and up to 196 tonnes day hf apatite may provide a useful measure of long term volatile emissions at volcanoes where direct emissions measurements are unavailable or for comparison with intermittent gas sampling methods however significant uncertainty remains regarding volatile distribution coefficients for apatite and their variations with temperature and pressure

the unit 12 allivalite eastern layered intrusion isle of rum a textural and geochemical study of an open system magma chamber the eastern layered intrusion of the rum central complex nw scotland comprises 16 macro units broadly defined by a basal peridotite body overlain by gabbros and troctolites the local term for the upper plagioclase bearing cumulates is allivalite the unit 12 allivalite contains five subsidiary peridotite horizons each continuous on the kilometre scale field textural and geochemical evidence points to the unit 12 allivalite forming by progressive accumulation of crystals from up to seven separate magma batches varying from picrite to basalt the thickness of the magma lens in the sill like chamber was as low as 30 m during a significant part of the development of the unit 12 allivalite and evidence supports one eruption from the chamber during its accumulation

infiltration metasomatism of cumulates by intrusive magma replenishment the wavy horizon isle of rum scotland the eastern layered intrusion of the rum layered suite comprises paired peridotite and allivalite troctolite and gabbro layers forming 16 macro rhythmic units whereas the majority of these macro units are believed to have formed by a process of crystal liquid differentiation involving successive accumulation of crystals from multiple picritic replenishments of the chamber the unit 9 peridotite is interpreted as a layer parallel picrite intrusion closely correlated with this discontinuous peridotite body is a distinctive feature generally known as thewavy horizon which divides the overlying allivalite into a lower troctolite and an upper gabbro along a well defined undulating contact we propose that the wavy horizon is a metasomatic feature formed consequent to the removal of clinopyroxene from an original gabbroic mush foundering of the mush into the picritic sill resulted in the replacement of the original interstitial liquid by one saturated only in olivine plagioclase progressive through flow of this liquid resulted in the stripping out of clinopyroxene from the lower parts of the allivalite we interpret thewavy horizon as a reaction front representing the point at which the invading liquid became saturated in clinopyroxene the distinctive pyroxene enriched zone immediately above thewavy horizon could have formed when mixing of the interstitial liquids on either side of the reaction front formed a supercooled liquid oversaturated in pyroxene as a result of the curvature of the olivine plagioclase clinopyroxene cotectic the presence of many such approximately layer parallel features defined by differences in pyroxene content in the eastern layered intrusion of rum suggests that such an infiltration reaction process was not unique to unit 9

the campsite dykes a window into the early post solidification history of the skaergaard intrusion east greenland the skaergaard intrusion of east greenland is cut by several generations of dykes the earliest of which is thought to have intruded shortly after solidification of the skaergaard two 6 m wide doleritic dykes from the earliest generation are exposed in the campsite area near homestead bay of the skaergaard peninsula one of the dykes the campsite dyke locally contains abundant xenoliths of troctolitic cumulate the other the plagioclase phyric dyke contains abundant large plagioclase phenocrysts cross cutting relationships between the two dykes are not exposed the median clinopyroxene plagioclase plagioclase dihedral angle cpp in the campsite dyke is 88 89 5 whereas that of the plagioclase phyric dyke is 79 using an empirical relationship between cpp and the duration of crystallisation derived from dolerite sills the observed cpp suggests that the campsite dyke is the older of the two intruding the skaergaard when it had cooled to 920 970 c the plagioclase phyric dyke intruded later once the skaergaard had cooled below 670 c the troctolitic xenoliths divide into two separate groups type a xenoliths have microstructures similar to those of the skaergaard layered series although mineral compositions are generally more primitive than those of the exposed cumulates this type of xenolith is likely to have been derived from either deeper levels in the skaergaard intrusion or from a closely related underlying magma chamber one type a xenolith has mineral compositions and cpp consistent with an origin in lzb of the layered series this xenolith contains partially inverted pigeonite suggesting that inversion of low ca pyroxene in the lower part of the layered series took place after the intrusion had completely solidified type b xenoliths are characterized by plagioclase containing large and abundant melt inclusions comparison with the microstructures of glassy crystalline nodules from iceland points to a multi stage cooling history for type b xenoliths consistent with step wise entrainment of partially crystallised material from a deep chamber type b xenoliths are very unlikely to have been derived from deeper levels in the skaergaard chamber

the equilibration of high angle grain boundaries in dynamically recrystallized quartz the effect of crystallography and temperature abstract dynamically recrystallized and sutured quartz grains from metamorphic rocks with different strain intensities and temperature conditions ranging from ca 350 c to ca 700 c have been studied universal stage measurements on quartz quartz high angle grain boundaries show that they are never curved but always consist of straight segments which preferentially occupy specific crystallographic orientations in relation to both neighboring crystals with increasing temperature the segments preferentially concentrate in a decreasing number of orientations mainly near the rhombohedral 1011 planes the crystallographic data and the observations on grain boundary geometries suggest that i grain boundary orientations are strongly crystallographically controlled ii this control is the main factor on the textural equilibration of quartz quartz grain boundaries in metamorphic rocks and iii grain boundaries from dynamically recrystallized quartz should be regarded as annealed and equilibrated fabrics that are stable against subsequent annealing as long as the material is not re deformed

textural immaturity of cumulates as an indicator of magma chamber processes infiltration and crystal accumulation in the rum eastern layered intrusion textural maturity describes the extent to which rocks have approached textural equilibrium for igneous rocks this is a function of the time integrated thermal history in the sub solidus which for cumulate rocks generally translates to the cooling history via the rate of solidification of the accumulating crystal mush the most straightforward way to quantify the textural maturity of orthocumulates sensu lato is to measure the angle subtended at the corners of interstitial grains texturally mature cumulates have angle populations with median values of c 120 whereas texturally immature cumulates have lower medians inherited by the interstitial phase which infills either an impingement texture in the accumulating mush or a texturally equilibrated pore topology textural observations of allivalites from the rum layered suite demonstrate that stratigraphically localized excursions towards textural immaturity are the result of either transient relatively rapid solidification rates perhaps a result of the arrival of cold crystal laden bodies of fluid on the chamber floor or late stage infiltration of fully solidified cumulates by evolved liquids expelled upwards by compaction of underlying horizons these two processes have distinct textural and compositional signatures

crystallographic control on the development of foam textures in quartz plagioclase and analogue material the shape pattern and crystallographic orientation of grain boundaries represent important characteristics of crystalline material and contain information about its deformation and annealing history the present study includes measurements of grain boundaries from experimentally annealed analogue material as well as natural foam texture of quartz and plagioclase the main subject is the relation between the development of a foam texture and the crystallographic orientation of its grain boundaries and their geometry 1 during annealing grain sizes stabilize at certain values on a statistical basis these values can be applied as a geothermometer 2 on the light microscope scale the grain boundaries in foam textures commonly consist of two or several planar facets they are preferentially oriented along specific crystallographic planes namely in relation to both neighbouring crystals for quartz they tend to be rhombohedral 3 even highly misoriented facets and dihedral angles largely deviating from the equilibrium angle of 120 may be stable over long periods of annealing 4 parts of single boundaries may migrate whereas other parts are stationary during annealing the results of the present study suggest that the anisotropy of surface energy has a considerable influence on the development of foam textures and that modelling of texture development should include the influence of the crystallographic orientation of grain boundaries

rapid crystallization of precious metal mineralized layers in mafic magmatic systems the solidified remnants of mafic magmatic systems host the greatest concentrations of platinum group metals in the earth s crust our understanding of precious metal mineralization in these intrusive bodies is underpinned by a traditional view of magma chamber processes and crystal mush solidification however considerable uncertainty remains regarding the physical and temporal controls on concentrating these critical metals despite their importance to modern society we present high precision 87sr 86sr analyses of plagioclase and clinopyroxene from within centimetre thick precious metal enriched layers in the palaeogene open system rum layered intrusion northwest scotland isotopic heterogeneity is present between plagioclase crystals between clinopyroxene and plagioclase and within plagioclase crystals throughout the studied section on the basis of these observations we demonstrate that platinum group element mineralization formed by repeated small volume reactive melt percolation events the preservation of strontium isotope heterogeneities at 10 100 m length scales implies cooling of the melts that formed the precious metal rich layers occurred at rates greater than 1 c per year and cooling to diffusive closure within tens to hundreds of years our data highlight the importance of cyclic dissolution recrystallization events within the crystal mush and raise the prospect that precious metal bearing mafic intrusions may form by repeated self intrusion during cooling and solidification mineralization of platinum group elements in mafic intrusions occurs due to repeated self intrusion of magma according to strontium isotope heterogeneities preserved in the rum layered intrusion scotland

spatial constraints on magma chamber replenishment events from textural observations of cumulates the rum layered intrusion scotland the eastern layered series of the rum layered suite is formed of 16 macro units each comprising a lower peridotite and an overlying feldspar rich layer the local term is allivalite the origin of the peridotite layers is unresolved with two contrasting models the earlier of the two is based on repeated replenishment of an opensystem magma chamber with deposition of fractionated material on the chamber floor the second is based on the early formation of a troctolitic complex which is then repeatedly intruded by sills of replenishing picritic magma to form the peridotite horizons the lack of resolution of this fundamental problem is a consequence of the reliance of previously published studies on field observations i present evidence to show that the clinopyroxene in the allivalites preserves information about the distribution of the last melt to solidify permitting determination of not only the extent of supersolidus textural equilibration but also the sub solidus history of the allivalite horizons comparison of profiles of clinopyroxene plagioclase plagioclase median dihedral angle across allivalite units demonstrates that it is possible to distinguish between those that were intruded by later picrite sills and those adjacent to peridotite horizons formed by replenishment and subsequent deposition of fractionated crystals above the pre existing pile in the region studied only the main peridotite body of unit 9 was intruded into a pre existing allivalitic mush

partial melting of feldspathic quartzite around late caledonian minor intrusions in appin scotland granophyre patches on the sites of former sedimentary feldspars in the feldspathic appin quartzite show that partial melting took place in the inner parts of the aureoles of late caledonian minor intrusions mobilization of the melt and refractory quartz residue as a thixotropic suspension is shown to result in the formation of veins and breccias textures are related to the wetting of quartz quartz grain bounderies by the eutectic melt and the later growth of crystals during cooling from the presence of high quartz coexisting with melt minimum contact temperatures are estimated as 780 c showing that some convective circulation of magma took place

fluid dynamic and geochemical evolution of cyclic unit 10 rhum eastern layered series lithological major element trace element and sr isotope data from cyclic unit 10 of the rhum eastern layered series are presented the lower 65 metres of the unit are peridotite subdivided on textural and geochemical grounds into a lower homogeneous portion approximately 50 metres thick and an upper heterogeneous portion approximately 15 metres thick the uppermost 16 5 metres of the unit are allivalite there are steep geochemical gradients across the peridotite allivalite boundary in ni content of olivine and whole rock sr isotope composition calculations are presented on the geochemical evolution of a rhum picritic liquid undergoing olivine precipitation both when the olivines remain suspended in the residual liquid as they precipitate and when they are continuously fractionated quenched groundmass and olivine compositions from the rhum dykes and the unit 10 peridotite olivines show good agreement with the suspension model but are inconsistent with the fractionation model the rhum chamber is thought to have been replenished with a picritic liquid from which olivine crystallized while held in suspension however replenishment by a highly olivine phyric basalt is also possible the peridotite probably accumulated rapidly as olivines were dumped out of suspension onto the chamber floor the lower part of the peridotite is a poikilitic adcumulate it is suggested that this formed by convective circulation of melt in the pores of the pile of cumulus olivines in the latter stages of adcumulus growth more fe rich and isotopically contaminated magma entered the top of the cumulus pile causing cumulus olivines to re equilibrate and giving the intercumulus plagioclase a higher sr isotope ratio than lower down the olivines in the allivalite show steep stratigraphic gradients in major element composition but not in their ni content they also show substantial variation in major element composition laterally within the allivalite it is suggested that these features are a consequence of postcumulus re equilibration of olivine with migrating intercumulus magma

crystal settling and convection in the shiant isles main sill the 168 m thick shiant isles main sill is a composite body dominated by an early 24 m thick picrite sill formed by the intrusion of a highly olivine phyric magma and a later 135 m thick intrusion of olivine phyric magma that split the earlier picrite into a 22 m thick lower part and a 2 m thick upper part forming the picrodolerite crinanite unit pcu the high crystal load in the early picrite prevented effective settling of the olivine crystals which retain their initial stratigraphic distribution in contrast the position of the most evolved rocks of the pcu at a level 80 of its total height point to significant accumulation of crystals on the floor as evident by the high olivine mode at the base of the pcu crystal accumulation on the pcu floor occurred in two stages during the first most of the crystal load settled to the floor to form a modally and size sorted accumulation dominated by olivine leaving only the very smallest olivine grains still in suspension the second stage is recorded by the coarsening upwards of individual olivine grains in the picrodolerite and their amalgamation into clusters which become both larger and better sintered with increasing stratigraphic height large clusters of olivine are present at the roof forming a foreshortened mirror image of the coarsening upwards component of the floor accumulation the coarsening upwards sequence records the growth of olivine crystals while in suspension in a convecting magma and their aggregation into clusters followed by settling over a prolonged period with limited trapping at the roof as olivine was progressively lost from the convecting magma crystal accumulation on the contemporaneous floor of the pcu was increasingly dominated by plagioclase most likely forming clusters and aggregates with augite and olivine both of which form large poikilitic grains in the crinanite while the pcu is unusual in being underlain by an earlier still hot intrusion that would have enhanced any driving force for convection we conclude from comparison with microstructures in other sills that convection is likely in tabular bodies 100 m thickness

palaeoenvironmental and palaeoclimatic evolution of the serres basin n greece during the miocene abstract the palaeoenvironmental and palaeoclimatic evolution of the serres basin from the end of mid miocene to the end of the miocene is examined lignites were deposited over a thick sequence of conglomerates and sands fossils found in the lignites indicate a lacustrine environment with tropical subtropical climatic conditions the climate became progressively drier and only small lakes were reserved during the messinian salinity crisis deposition of lake sediments finally ended with the world wide pliocene marine transgression a correlation of the serres basin with other lacustrine basins in the aegean area is attempted

kinematics and evolution of the northern branch of the north anatolian fault ganos fault between the sea of marmara and the gulf of saros abstract the wsw ene trending ganos fault is a dextral strike slip fault running parallel to and southwest of the west marmara trough and south of the saros trough dextral structures started evolving in the early miocene and at this time the ganos fault system developed from a part of the thrace eskisehir fault system beginning in the late pliocene 3 5 ma the north anatolian transform fault propagated into the marmara region and captured the ganos fault subsequently this fault has accommodated the westward movement of the anatolian block because of the curvature of the microplate boundary in this area the ganos fault system has tended to rotate counterclockwise farther west in the gulf of saros the strike slip motion was accommodated by a new fault on the northern margin of the gulf rather than along the northern coast of the gelibolu peninsula as previously thought this interpretation differs from previous assessments of the position of the northern strand of the north anatolian fault marmara segment in the marmara sea and in the gulf of saros the role of the ganos fault proposed in this paper is considerably different from that proposed by earlier studies while the revised orientation of the north anatolian fault on land is about 7 different than specified by previous authors at sea it is different by 32 counterclockwise and 23 clockwise in the west marmara and saros submarine depressions respectively the revised position of the ganos fault in the marmara sea derived from shallow and conventional seismic reflection data calls into question the validity of evolutionary models previously used in kinematic and stress failure analyses in particular it is not possible to regard the marmara sea as a pull apart basin and the gulf of saros as a transtensional half graben furthermore palinspastic maps taking into account the revised position of the ganos fault and gps slip vectors support the idea that a dextral master fault is present to the north of the saros trough with a sinistral oblique fault dominated by normal offset gelibolu fault to its south the gelibolu fault is reactivated in a limited region

nanogranite and glassy inclusions the anatectic melt in migmatites and granulites using as a case study a granulite from the kerala khondalite belt india we show that a former anatectic melt can be preserved as tiny 25 m droplets within refractory minerals in this case garnet the melt is either fully crystallized as a qtz ab kfs bt cryptocrystalline aggregate nanogranite or completely glassy in inclusions 15 m both nanogranite and glassy inclusions have a peraluminous ultrapotassic granitic composition that in this case does not correspond to a minimum melt and points to high melting temperatures in agreement with the ultrahigh temperature origin of the rock this discovery indicates that peritectic minerals growing during incongruent melting reactions act as hosts for inclusions of anatectic melt and that in the general case of slow cooling of the crust these inclusions will occur as nanogranite exceptionally in the smallest inclusions glass may be present due to inhibition of crystallization our results extend the frontiers of petrological and geochemical research in crustal melting as the composition of natural anatectic melts can be directly analyzed rather than assumed

magma flow regimes in sills deduced from ar isotope systematics of host rocks the best place to seek evidence of the style of past magma flow through a conduit is in the country rock heat flow has been studied in country rock adjacent to two tertiary dolerite sills intruding the caledonian schists and quartzites on the isle of mull scotland radiogenic 40ar loss within mica grains in the thermal aureoles of the intrusions has been measured at high spatial resolution using the ultra violet laser ablation micro probe to discriminate between a history of prolonged magma flow a history of conductive cooling following laminar flow and instantaneous emplacement of the intrusions the 40ar 39ar mica data and thermal modeling suggest that a prolonged period of magma flow of 3 5 months resulted in extensive argon loss from the micas country rock melting and mineral breakdown adjacent to a 6 m sill these features were absent from the wall rocks of a smaller 2 7 m thick sill which exhibited even less argon loss than might have been predicted for an instantaneous intrusion if the heat loss from the 6 m sill observed in one locality had been repeated along its length it would have formed an important magma conduit to the mull volcano but dolerite is not a common flow composition on mull if on the other hand the heat loss from the sill varies along strike it constitutes strong evidence for channelling and heterogeneous flow within the sill

new experimental approach to understanding igneous texture thin sections containing a magma like mixture of three crystalline ammonium compounds and intercrystalline melt can be prepared and observed microscopically during crystallization melting and deformation the aim of such observations is to establish links between active processes in the crystal melt mixture and the textural signatures of the processes the hope is to improve the basis for process interpretation of textures in rocks although the value of the experimental system in this regard is still unknown three unexpected processes are seen creation of growth centers for later blocky grains by isothermal decomposition of early dendritic grains migration of grain boundaries early in the crystallization history and growth of porphyroblast like grains by phase boundary migration with abundant melt nearby textural metamorphism begins in this material well before its melt present history is complete

messinian evaporites in zakynthos greece abstract messinian gypsum deposits of central zakynthos consist of 10 15 m of gypsum turbidites intercalated in a terrigenous turbidite succession most of the turbidites are fine grained and thin bedded perhaps transported by dense briny underflows but one widespread 2 3 m thick bed of coarse gypsum crystals may have resulted from erosion in shallow water during a sea level fall the thickness of overlying terrigenous turbidite and pliocene shelf sediments shows that the gypsum turbidites accumulated in water depths of less than a few hundred metres pollen suggest cooling immediately prior to gypsum deposition and cool dry conditions on land during evaporite formation warmer wetter conditions returned immediately following gypsum deposition dinoflagellates provide no evidence for hypersaline marine conditions at the depositional site in contrast in eastern zakynthos the gypsum unit appears to have accumulated in shallow water and is unconformably overlain by shallow water pliocene sediments

successive episodes of reactive liquid flow through a layered intrusion unit 9 rum eastern layered intrusion scotland we present a detailed microstructural and geochemical study of reactive liquid flow in unit 9 of the rum eastern layered intrusion scotland unit 9 comprises an underlying lens like body of peridotite overlain by a sequence of troctolite and gabbro termed allivalite with some local and minor anorthosite the troctolite is separated from the overlying gabbro by a distinct sub horizontal undulose horizon the major wavy horizon higher in the stratigraphy is another similar horizon the minor wavy horizon that separates relatively clinopyroxene poor gabbro from an overlying gabbro to the north of the peridotite lens both troctolite and gabbro grade into poikilitic gabbro clinopyroxene habit in the allivalite varies from thin rims around olivine in troctolite to equigranular crystals in gabbro and to oikocrysts in poikilitic gabbro the poikilitic gabbros contain multiple generations of clinopyroxene with cr rich 1 1 wt cr2o3 anhedral cores with moderate ree concentrations core1 overgrown by an anhedral ree depleted second generation with moderate cr 0 7 wt cr2o3 core2 these composite cores are rimmed by cr poor 0 2 wt cr2o3 and ree poor to moderate clinopyroxene we interpret these microstructures as a consequence of two separate episodes of partial melting triggered by the intrusion of hot olivine phyric picrite to form the discontinuous lenses that comprise the unit 9 peridotite loss of clinopyroxene saturated partial melt from the lower part of the allivalite immediately following the early stages of sill intrusion resulted in the formation of clinopyroxene poor gabbro the spatial extent of clinopyroxene loss is marked by the minor wavy horizon a second partial melting event stripped out almost all clinopyroxene from the lowest allivalite to form a troctolite with the major wavy horizon marking the extent of melting during this episode the poikilitic gabbro formed from clinopyroxene saturated melt moving upwards and laterally through the remobilized cumulate pile and precipitating clinopyroxene en route this process called reactive liquid flow is potentially important in open magma chambers

pressure conditions for the solidification of the skaergaard intrusion eruption of east greenland flood basalts in less than 300 000 years abstract primary granophyres are differentiated from olivine tholeiitic magma and occur interstitially throughout the cumulus stratigraphy of the skaergaard intrusion east greenland samples from the lower zones a c lza c the middle zone mz and the sandwich horizon sh are included in the present study together with granophyric accumulations in gabbroic pegmatite from lza c fluid inclusions in quartz and the mineral assemblage in the granophyres record the pressure under which the skaergaard intrusion crystallised pegmatitic granophyre from lza c consists mainly of quartz plagioclase an 4 7 and alkali feldspar or 40 80 enclosing an earlier formed assemblage of ferrohastingsitic and ferroedenitic hornblende fayalite fo 4 5 titanite biotite and fluor apatite granophyric quartz albite and alkali feldspar crystallised from water saturated granitic melts near eutectic minimum conditions between 680 and 660 c the pressure of granophyre crystallisation was modelled by the intercept between fluid inclusion isochores and the minimum melt solidus for granitic compositions pressures recalculated to the roof pendant of the intrusion are 0 7 0 5 for lza 2 0 0 2 for lzb c 2 3 0 8 for mz the triple group level and 3 3 1 3 kb for sh amphibole geobarometry independently confirm the pressure estimates for pegmatitic granophyres in lza c the granophyres formed as the intrusion cooled through the minimum melt solidus in lza lzb lzc mz and sh respectively the pressure increase from lza to sh granophyres is explained by progressive burial during cooling of the intrusion and contemporaneous outpouring of 5 3 6 3 2 7 km of flood basalts during the initial opening of the northeast atlantic ocean accordingly the skaergaard intrusion evolved from a subvolcanic magma chamber at emplacement to a more deep seated igneous system during terminal crystallization when the majority of the intercumulus phases formed the present cooling history suggests the intrusion cooled through the temperature of granophyre formation in less than 300 000 years the increase in the pressure of granophyre formation therefore implies that 5 3 6 3 2 7 km of flood basalts were emplaced within this time window

on the use of changes in dihedral angle to decode late stage textural evolution in cumulates the melt filled pore structure in the final stages of solidification of cumulates must lie somewhere between the two end members of impingement in which pore topology is controlled entirely by the juxtaposition of growth faces of adjacent grains and textural equilibrium in which pore topology is controlled by the minimization of internal energies the exact position between these two end members is controlled by the relative rates of crystal growth and textural equilibration for samples in which growth has stopped or is very slow textural equilibrium will prevail a close examination of dihedral angles in natural examples demonstrates that these two end member textures can be distinguished the impingement end member results in a population of apparent solid melt dihedral angles with a median of 60 and a standard deviation of 25 30 whereas the texturally equilibrated end member population has a median of 28 and a standard deviation of 14 for the specific case of cumulates in the rum layered intrusion residual porosity in troctolitic cumulates was close to the impingement end member whereas that in peridotites was close to melt bearing textural equilibrium suites of glass bearing samples from small or frequently disturbed magma systems show modification of initial impingement textures these modifications may be a consequence of textural equilibration or of diffusion limited growth during quenching distinction can be made between these two processes by a consideration of grain shape the geometry of interstitial phases in suites of fully solidified cumulates from the rum layered intrusion shows variable approach to sub solidus textural equilibrium from an initial state inherited by pseudmorphing of the last melt textural equilibration at pore corners occurs as a continuous process with a gradual movement of the entire dihedral angle population towards the equilibrium final state if the initial pseudomorphed state is one of disequilibrium i e a melt present impingement texture this change is accompanied by a reduction in the spread of the population if it is one of equilibrium the change is accompanied by an initial increase in the spread of the population followed by a decrease these observations demonstrate that previously published models of dihedral angle change involving the instantaneous establishment of the equilibrium angle in the immediate vicinity of the pore corner are incorrect

the earliest history of the skaergaard magma chamber a textural and geochemical study of the cambridge drill core ct and mh were supported by a royal society international joint project grant and by the carlsberg foundation ct was also supported by the danish council of independent research and the danish national research foundation the project was supported by the natural environment research council grant number ne f020325 1 on acknowledges support from magdalene college university of cambridge and the von humboldt foundation germany university of hannover

information about open system magma chambers derived from textures in magmatic enclaves the kameni islands santorini greece post caldera eruptions of santorini greece over the past 3000 years resulted in the formation of the kameni islands which comprise a series of compositionally similar dacitic lava flows each lava flow has a distinct population of partially crystalline mafic enclaves which we propose were derived from the break up of a layer of replenishing magma responsible for triggering the eruption five of the recent flows erupted in 1570 1939 1940 1941 and 1950 include enclaves of essentially identical andesitic bulk compositions which formed by crystallization of originally aphyric melts prior to eruption detailed examination of angles subtended at the junctions between pairs of plagioclase grains demonstrates that enclaves from each flow have a characteristic textural signature with distinct differences in the extent of quench related modification of the original population of dihedral angles formed by impingement of growing grains these variations suggest that the temperature difference between the host dacite and the replenishing andesite at the time of layer overturn and eruption differed between flows the uniformity of major element compositions of both the replenishing magma and the host dacitic lava flows demonstrates that the critical parameter in determining the timing of layer overturn is the pre eruptive h 2 o content of both host dacite and replenishing magma we suggest that the replenishing magma responsible for two of the three eruptions in the period 1939 1941 was significantly wetter than that responsible for the later 1950 eruption the enclaves with the least amount of quench related modification occur in the 1570 flow we suggest that in this case the intruding magma was relatively dry

textural maturity of cumulates a record of chamber filling liquidus assemblage cooling rate and large scale convection in mafic layered intrusions textural maturity describes the extent to which a rock has evolved from the initial reaction controlled texture towards textural equilibrium controlled by the minimization of interfacial energy solidification in a magma chamber results in the formation of an impingement texture by the random juxtaposition of planar sided grains orthocumulates in which the initial melt filled pores are pseudomorphed by later crystallizing phases have an ophitic or intersertal texture immediately after complete solidification which then evolves towards solid state equilibrium by rounding of initially planar grain boundaries and an increase in the median dihedral angle subtended at the junctions of two primocrystic grains with the interstitial phase the bulk of the increase in angle occurs just below the solidus temperature in kilometre scale mafic plutons quantification of textural maturity via measurement of dihedral angle populations in troctolitic and gabbroic cumulates from the rum eastern layered intrusion and the skaergaard intrusion demonstrates that the rocks preserve a record of thermal events related to magma chamber replenishment and the onset of chamber wide convection textural maturity is also a function of the liquidus phase assemblage for systems in which only olivine and plagioclase are liquidus i e cumulus phases in the main magma body above the crystal mush the texture is significantly less mature than that in systems in which clinopyroxene is an additional liquidus phase the difference in textural maturity reflects differences in the cooling and solidification rate and demonstrates directly that the liquidus phase assemblage plays a role in determining the thermal history of plutons

mediterranean messinian salinity crisis constraints from a coeval marginal basin sorbas southeastern spain abstract the extent timing and effects of late miocene desiccation and evaporite deposition in the mediterranean sea remain controversial marginal basins containing messinian 5 3 7 1 ma sequences now exposed onland supplement information from the deep mediterranean but have evaporites of a variety of ages some of these messinian evaporites pre date and others post date deep desiccation none appears to be exactly coeval with those of the deep mediterranean in the betic cordillera of southern spain basins e g granada basin far from the present day mediterranean lost connection with the mediterranean due to uplift 1 ma before the salinity crisis and have marine evaporites of early not late messinian age in contrast basins such as the sorbas basin in southeastern spain adjacent to the present day mediterranean record events directly reflecting the course of the salinity crisis the sorbas basin retained marine connection with the western mediterranean up until evaporative drawdown in the mid messinian and was rapidly reflooded immediately afterwards the sorbas messinian sequence is up to 320 m thick it is complete and normal marine except for an incised basinwide erosion surface overlain by a 130 m thick gypsum deposit we propose that this surface marks the interval of deep desiccation of the adjacent mediterranean basin erosion occurred shortly after 5 9 ma and the irregular unconformity has relief of at least 240 m confirming mediterranean drawdown significantly below the atlantic level sorbas gypsum deposits overlie the unconformity and are intercalated with marls estimated at 5 5 ma containing normal marine messinian biotas these gypsum deposits therefore post date deep desiccation and formed in a silled basin immediately following marine reflooding they mark the end of the salinity crisis and are overlain by 70 m of normal marine sediments containing unreworked foraminifers of latest messinian age this succession demonstrates that the salinity crisis occurred faster and was completed sooner than previously believed it took place within 0 4 ma time scale of berggren et al 1995b is 0 2 ma on the time scale of baksi 1993 and was completed before the end of the messinian this corrects previous views that the salinity crisis continued until the early pliocene there is no evidence in the sorbas basin for brackish lago mare conditions and the normal marine biotas that directly precede and follow drawdown rebut earlier suggestions of prolonged salinity effects

peridotite sills and metasomatic gabbros in the eastern layered series of the rhum complex mapping of the eastern layered series els of the rhum ultrabasic complex on the northern flank of hallival shows that peridotite and allivalite troctolite or gabbro layers are laterally discontinuous and vary both in thickness and lithology peridotite generally has sharp upper and lower contacts against the allivalites which sometimes cut across the layering in the allivalite reaction dissolution and hybridization effects between peridotite and allivalite are developed locally some troctolite layers terminate as isolated fingered blocks in peridotite there are many small peridotite bodies which are clearly intrusive into allivalite and have previously been identified as distinct peridotite sheets and plugs they are petrographically almost identical to the major stratiform peridotites and in some cases are apophyses from them we propose that many of the peridotite layers in the els formed as thick sills of picritic magma emplaced into a partly solidified layered troctolite complex the stratiform gabbros of the els are heterogeneous layered rocks that commonly contain relicts of troctolite and anorthosite wavy metre scale contacts between gabbro and troctolite cut across pre existing grain size modal and rhythmic layering with little disruption these metasomatic gabbros mimic the textures grain size and rhythmic layering of their troctolitic protoliths we propose that many of the els gabbros formed as a result of interaction between porous troctolites and a low temperature basaltic melt residual basaltic melt segregated from solidifying peridotite may have caused this metasomatism

sr isotope constraints on the mediterranean environment at the end of the messinian salinity crisis probably the most profound event that has affected the mediter ranean is the desiccation which occurred at the end of the miocene1 8 during this period there was a very rapid change from deep open marine conditions to environments of shallow water carbonate and massive evaporite deposition1 10 here we show that ostracod valves found in messinian lago mare lake sea sediments have a uniform but generally lower sr isotopic composition than contemporary sea water thus providing evidence that some of the major mediterranean basins for example balearic and levantine basins formed large lacustrine systems that were probably interconnected towards the end of the messinian salinity crisis1 3 after the major evaporites were deposited the most likely source of fresh water is from continental rivers flowing from the eastern european inland paratethys sea or perhaps the nile river in the lower part of the lago mare some ostracods have sr isotopic compositions identical to contemporary sea water indicating a transient influence of marine derived water sr compo sitions greater than that in contemporary sea water are only found in ostracods from onshore sediments in the sorbas basin4 5 of southeastern spain suggesting that this small basin adjacent to the straits of gibraltar became isolated after the deposition of the major evaporite sequences