an evaluation of the barotropic and internal tides in a high resolution global ocean circulation model 1 global comparisons of barotropic and internal tides generated in an eddy resolving ocean circulation model are made with tidal estimates obtained from altimetric sea surface heights and an altimetry constrained tide model as far as we know our hybrid coordinate ocean model hycom simulations shown here and in an earlier paper are the only published high resolution global simulations to contain barotropic tides internal tides the general circulation and mesoscale eddies concurrently comparing the model barotropic tide with a global data assimilative shallow water tide model shows that the global tidal elevation differences are approximately evenly split between discrepancies in tidal amplitude and phase both the model and observations show strong generation of internal tides at a limited number of hot spot regions with propagation of beams of energy for thousands of kilometers away from the sources the model internal tidal amplitudes compare well with observations near these energetic tidal regions averaged over these regions the model and observation internal tide amplitude estimates agree to approximately 15 for the four largest semidiurnal constituents and 23 for the four largest diurnal constituents away from the hot spots the comparison between the model and altimetric amplitude is not as good due in part to two problems errors in the model barotropic tides and overestimation of the altimetric tides in regions of strong mesoscale eddy activity examining the general energy distribution of the simulated internal tide is an important first step in the evaluation of internal tides in hycom

numerical simulation of diffusion controlled nucleation and growth of porphyroblasts this article presents the conceptual basis for a new numerical model of diffusion controlled nucleation and growth of porphyroblasts describes its implementation and illustrates the range of crystallization behaviours encompassed by it the model differs from previous efforts principally in its ability to track explicitly the evolution in time and space of the chemical affinity for reaction in the intergranular medium which provides a more accurate characterization of nucleation suppression in the vicinity of pre existing crystals and of growth suppression due to competition for nutrients among neighbouring crystals critical new features of these numerical simulations include maintenance of local equilibrium for fluid in contact with reactants or products persistence of reactants until they are eliminated by dissolution due to reaction progress and local diffusive flux nucleation rates that vary as the local reaction affinity evolves complex initial distributions of reactants if desired and the flexibility to encompass any porphyroblast forming reaction for which changes in free energy as a function of time and temperature are specified model results reveal that radial growth rates remain proportional to the square root of time in diffusion systems buffered by persistent reactants they document the interchangeable effects of diffusivity porosity and solubility on material fluxes and thus growth rates and they illustrate the offsetting textural effects of rates of diffusion nucleation and heating the initial distribution of reactants is found to exert a first order effect on crystal size distributions confirming their limited utility for diagnosing crystallization mechanisms these numerical simulations yield novel and rigorous confirmation of the textural effects of nucleation site saturation and variation in interconnected porosity and reproduce with high fidelity much of the textural and chemical information gathered from natural specimens

strain rates from snowball garnet spiral inclusion trails in garnet porphyroblasts are likely to have formed due to simultaneous growth and rotation of the crystals during syn metamorphic deformation thus they contain information on the strain rate of the rock strain rates may be interpreted from such inclusion trails if two functions are known 1 the relationship between rotation rate and shear strain rate 2 the growth rate of the crystal we have investigated details of both functions using a garnetiferous mica schist from the eastern european alps as an example the rotation rate of garnet porphyroblasts was determined using finite element modelling of the geometrical arrangement of the crystals in the rock the growth rate of the porphyroblasts was determined by using the major and trace element distributions in garnet crystals thermodynamic pseudosections and information on the grain size distribution for the largest porphyroblast size fraction size l 12 mm we constrain a growth interval between 540 and 590 c during the prograde evolution of the rock assuming a reasonable heating rate and using the angular geometry of the spiral inclusion trails we are able to suggest that the mean strain rate during crystal growth was of the order of 6 6 10 14 s 1 these estimates are consistent with independent estimates for the strain rates during the evolution of this part of the alpine orogen

the global mesoscale eddy available potential energy field in models and observations global maps of the mesoscale eddy available potential energy eape field at a depth of 500m are created using potential density anomalies in a high resolution 112 5 global ocean model maps made from both a free running simulation and a data assimilative reanalysis of the hybrid coordinate ocean model hycom are compared with maps made by other researchers from density anomalies in argo profiles the hycom and argo maps display similar features especially in the dominance of western boundary currents the reanalysis maps match the argo maps more closely demonstrating the added value of data assimilation global averages of the simulation reanalysis and argo eape all agree to within about 10 the model and argo eape fields are compared to eape computed from temperature anomalies in a dataset of moored historical observations mho in conjunction with buoyancy frequencies computed from a global climatology the mho dataset allows for an estimate of the eape in high frequency motions that is aliased into the argo eape values at mho locations 15 32 of the eape in the argo estimates is due to aliased motions having periods of 10 days or less spatial averages of eape in hycom argo and mho data agree to within 50 at mho locations with both model estimates lying within error bars observations analysis of the eape field in an idealized model in conjunction with published theory suggests that much of the scatter seen in comparisons of different eape estimates is to be expected given the chaotic unpredictable nature of mesoscale eddies

internal waves across the pacific 1 the long range propagation of the semidiurnal internal tide northward from the hawaiian ridge and its susceptibility to parametric subharmonic instability psi at the critical latitude c 28 8 n were examined in spring 2006 with intensive shipboard and moored observations spanning 25 37 n along a tidal beam velocity and shear at c were dominated by intense vertically standing inertially rotating bands of several hundred meters vertical wavelength these occurred in bursts following spring tide contrasting sharply with the downward propagating wind generated features seen at other latitudes these marginally stable layers which have inverse 16 meter richardson number ri16 1 0 7 are interpreted as the inertial waves resulting from psi of the internal tide elevated near inertial energy and parameterized diapycnal diffusivity and reduced asymmetry in upgoing downgoing energy were also observed at and equatorward of c yet simultaneous moored measurements of semidiurnal energy flux and 1 km deep velocity sections measured from the ship indicate that the internal tide propagates at least to 37 n with no detectable energy loss or phase discontinuity at c our observations indicate that psi occurs in the ocean with sufficient intensity to substantially alter the inertial shear field at and equatorward of c but that it does not appreciably disrupt the propagation of the tide at our location

intra tooth isotope variations in late miocene bovid enamel from afghanistan paleobiological taphonomic and climatic implications abstract the rich mid turolian site of molayan afghanistan has yielded more than 100 mandibles from the bovid tragoportax afghanicus in this study we document different aspects of the paleobiology and paleoecology of this fossil bovid by examining patterns of inter and intra tooth carbon and oxygen isotopic analyses in m1 to m3 molars from five specimens accurate paleoecological and paleoclimatic inferences based on carbon and oxygen isotope analyses in fossil enamel are directly dependent upon the way in which teeth are sampled as well as taphonomic processes which are responsible for fossil accumulation because this sampling methodology provides a unique opportunity to detect seasonal changes in diet and environment during tooth formation it also offers the possibility of testing between catastrophic and progressive deposition at this site preservation of 13c and 18o values is shown to be good and permits inter individual comparisons of isotopic trends to be made timing of molar crown formation and enamel growth rate were deduced from the pattern of intra tooth carbon and oxygen isotope variation the pattern of 18o variation found in the first and second molars is similar in all the individuals which suggests that a single birth season occurred probably before the hot dry season large differences in average 18o values 2 5 are found within a single cohort and indicate that fossil accumulation was progressive rather than catastrophic the hypothesis that t afghanicus evolved in an open environment is supported by high 13c values in a c3 context increasing temperature and or aridity eastward along the greco irano afghan biogeographic province is strongly suggested by increasing 18o values between greece and afghanistan

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

a statistical analysis of the distribution of cordierite and biotite in hornfels from the bugaboo contact aureole implications for the kinetics of porphyroblast crystallization

correlation of plio pleistocene tephra in ethiopian and kenyan rift basins temporal calibration of geological features and hominid fossil records abstract the 200 m thick fossiliferous konso formation and overlying terrace deposits which crop out at the end of the southern sector of the main ethiopian rift mer contain more than 30 distal tephra layers local and regional tephra correlations of more than 20 tephra units were established using major and trace element data of discrete and purified bulk glass samples within the konso study area eleven correlative marker tuffs were recognized in stratigraphic sections of both the konso formation and the omo turkana basin sediments in southern ethiopia and northern kenya the turoha hope ivory bright white and boleshe tuffs in the konso formation and the upper white tuff in the overlying terrace deposits are securely correlated with the kbs akait lokapetamoi chari lower nariokotome and silbo tuffs of the omo turkana basin using least mobile major elements cao fe2o3 and tio2 and geochronology preliminary correlations are also suggested between the konso formation distal tephra and proximal units of the quaternary caldera forming silicic centers in the central sector of the mer the strongly peralkaline tuffs of the konso formation are compositionally similar to proximal eruptions mostly located along the quaternary axial rift zone of the southern central and northern sectors of the mer the tephra correlation provides information about the temporal and spatial features of the volcanic and tectonic processes recorded in the evolving basins thickness and sedimentation rate were determined for both the konso formation and the omo turkana basin sections measured between the turoha kbs 1 91 0 03 ma and the bright white chari 1 40 0 02 ma tuffs although the lithostratigraphic sequence at the konso study area is younger sedimentation rate within the konso formation was comparable to that of the koobi fora formation higher in the nachukui formation and lower in the shungura formation local and regional differences in thickness and sedimentation rates within the plio pleistocene deposits of the konso shungura nachukui and koobi fora formations may be attributed to erosion associated with increased topographic gradients maintained by continued subsidence mostly along axial fault zones of basins and uplift along the margins of the broadly rifted zone of the omo turkana basin and the southern sector of the mer

feeding ecology of tragelaphini bovidae from the shungura formation omo valley ethiopia contribution of dental wear analyses abstract to better understand the environmental conditions that prevailed in the plio pleistocene shungura formation lower omo valley ethiopia we analyze the feeding preferences of tragelaphini the third most common tribe of shungura bovids molar mesowear and dental microwear texture analyses were applied to three species tragelaphus rastafari t nakuae and t gaudryi and body mass estimates were calculated for the t rastafari nakuae lineage to test whether dietary shifts were linked to body mass changes we compare our results with previous work on stable carbon isotopes 13c of enamel which indicated that tragelaphins from the shungura formation possessed dietary flexibility we found that the both the t rastafari nakuae lineage and t gaudryi maintained a mixed feeding dietary niche with varying proportions of c3 versus c4 inputs from 3 6 to 2 ma our results show that t rastafari consumed more browse than its descendant t nakuae which was a mixed feeder consuming a greater proportion of c4 dicots 2 8 ma the t rastafari t nakuae dietary shift may reflect environmental changes in the shungura formation during this time but appears to be offset from body mass increases in this lineage which occurred gradually through the plio pleistocene this study highlights the importance of a multi proxy approach to precisely determine the dietary ecologies of extinct bovids and points to how each proxy offers a slightly different perspective on the ecology of fossil organisms

chronostratigraphy of the miocene pliocene sagantole formation middle awash valley afar rift ethiopia the sagantole formation comprises more than 200 m of lacustrine alluvial and volcaniclastic sediments plus compositionally bimodal tephras and basaltic lavas exposed in a domelike horst named the central awash complex in the southwestern afar rift of ethiopia the sagantole formation is widely known for abundant vertebrate faunas including the 4 4 ma primitive hominid ardipithecus ramidus new lithostratigraphic data are used to subdivide the sagantole formation into the kuseralee gawto haradaso aramis beidareem adgantole and belohdelie members in ascending order the members are defined on the basis of lithologic differences and laterally continuous bounding tephras 40 ar 39 ar dating of 12 intercalated volcanic units firmly establishes the age of the sagantole formation to be 5 6 to 3 9 ma significantly older than previous proposals based on erroneous correlations magnetostratigraphic data reveal eight paleomagnetic polarity zones which can be correlated unambiguously with the thvera sidufjall nunivak and cochiti subchrons of the gilbert chron thus by reference to the geomagnetic polarity time scale seven additional chronological datums can be placed in the sagantole formation with a total of 19 such datums the age resolution anywhere in the sagantole formation is better than 100 k y making this the best dated miocene pliocene succession in africa

a finfoot from the late miocene of toros menalla chad africa palaeobiogeographical and palaeoecological implications a fossil humerus from the hominid fossiliferous area of toros menalla ca 7 ma chad africa belongs to the heliornithidae aves gruiformes it is the second documented fossil record for the family and the first in the old world it is compared with all the living species the sungrebe heliornis fulica the masked finfoot heliopais personata and the african finfoot podica senegalensis it belongs to the genus heliopais and is very similar to the only species h personata the masked finfoot appears to have evolved little morphologically since the miocene this poorly known and threatened genus and species is today confined to tropical south east asia its presence in the late miocene of chad is a further asian element in the late neogene african avifaunas today the distribution of heliopais is highly relictual and some heliornithidae will certainly be encountered in the paleogene and the miocene deposits of the palearctic region the african finfoot is today the heliornithidae geographically the closest to the site area and occurs in forested regions south of the sahelian area apparently this genus was already absent further north where the asian genus was present in the late neogene palaeoecologically the presence of this heliornithidae is indicative for toros menalla of a freshwater body with thick overhanging vegetation and partly forested edges this kind of precise indication about a component of the palaeoenvironment is critical for the study of hominid sites and early hominid evolution a growing number of fossil birds from african hominid localities is yielding important clues regarding biogeography and environment

diffusion limited ree uptake by eclogite garnets and its consequences for lu hf and sm nd geochronology garnets from the zermatt saas fee eclogites contain narrow central peaks for lu yb tm er and at least one additional small peak towards the rim the ree sm eu gd tb dy are depleted in the cores but show one prominent peak close to the rim these patterns cannot be modeled using rayleigh fractionation accompanied by mineral breakdown reactions instead the patterns are well explained using a transient matrix diffusion model where ree uptake is limited by diffusion in the matrix surrounding the porphyroblast observed profiles are well matched if a roughly linear radius growth rate is used the secondary peaks in the garnet profiles are interpreted to reflect thermally activated diffusion due to temperature increase during prograde metamorphism the model predicts anomalously low 176lu 177hf and 147sm 144nd ratios in garnets where growth rates are fast compared to diffusion of the ree and these results have important implications for lu hf and sm nd geochronology using garnet

geology and palaeontology of the late miocene middle awash valley afar rift ethiopia the middle awash study area of ethiopia s afar rift has yielded abundant vertebrate fossils 10 000 including several hominid taxa1 2 3 4 the study area contains a long sedimentary record spanning late miocene 5 3 11 2 myr ago to holocene times exposed in a unique tectonic and volcanic transition zone between the main ethiopian rift mer and the afar rift sediments along the western afar rift margin in the middle awash provide a unique window on the late miocene of ethiopia these deposits have now yielded the earliest hominids described in an accompanying paper5 and dated here to between 5 54 and 5 77 myr these geological and palaeobiological data from the middle awash provide fresh perspectives on hominid origins and early evolution here we show that these earliest hominids derive from relatively wet and wooded environments that were modulated by tectonic volcanic climatic and geomorphic processes a similar wooded habitat also has been suggested for the 6 0 myr hominoid fossils recently recovered from lukeino kenya6 these findings require fundamental reassessment of models that invoke a significant role for global climatic change and or savannah habitat in the origin of hominids

space time scales of shear in the north pacific abstractthe spatial temporal and directional characteristics of shear are examined in the upper 1400 m of the north pacific during late spring with an array of five profiling moorings deployed from 25 to 37 n 1330 km and simultaneous shipboard transects past them the array extended from a regime of moderate wind generation at the north to south of the critical latitude 28 8 n where parametric subharmonic instability psi can transfer energy from semidiurnal tides to near inertial motions analyses are done in an isopycnal following frame to minimize contamination by doppler shifting approximately 60 of rms shear at vertical scales 20m and 80 for vertical scales 80 m is contained in near inertial motions an inertial back rotation technique is used to index shipboard observations to a common time and to compute integral time scales of the shear layers persistence times are o 7 days at most moorings but o 25 days at the critical latitude simultaneous shipboard transects show that these sh

the clustered nucleation and growth processes of garnet in regional metamorphic rocks from north west connecticut usa serial sectioning and imaging with a flatbed scanner yielded the three dimensional size and spatial distribution of garnet porphyroblasts in two garnet schists and one staurolite bearing schist from the everett formation north west connecticut the dominant garnet producing reaction in all samples was chlorite quartz garnet h2o the appearance of staurolite and additional garnet growth in the staurolite bearing sample was due to the reaction chloritoid garnet staurolite chlorite statistical measures of garnet spatial distributions using the pair correlation function pcf indicate that garnet crystals are weakly to strongly clustered at length scales between 2 and 10 mm such clustered nucleation may reflect minor bulk compositional variations covariance measures between garnet size and nearest neighbour distance using the mark covariance function mcf suggest a very weak correlation between crystal size and nearest neighbour distance for length scales of 2 mm or less these statistical data suggest that if diffusional gradients were present around growing garnet crystals they did not influence nucleation and growth patterns at length scales greater than c 2 mm compositional maps through the garnet centres show that the smaller crystals have lower mn core compositions relative to larger crystals consistent with progressive nucleation during pro grade metamorphism radius rate plots calculated from compositional x ray maps show similar growth rates for garnet crystals of different size consistent with an interface controlled growth model for garnet the presence of minor diffusional gradients around growing garnet cannot be entirely dismissed but the lack of observable reaction rims the clustered spatial distribution and the radius rate data are most consistent with an interface controlled garnet growth model

long period tides in an atmospherically driven stratified ocean abstractlong period tides lpt are studied using a stratified primitive equation model on a global domain and in the presence of a fully developed atmospherically forced ocean general circulation the major lpt constituents from termensual to nodal 18 6 yr periods are examined ocean circulation variability can overwhelm the longest tide signals and make inferring lpt from data difficult but model results suggest that bottom pressure offers cleaner signal to noise ratios than sea level particularly at low latitudes where atmospherically driven variability is substantially stronger at the surface than at the bottom most tides exhibit a significant large scale dynamic response with the tendency for weaker nonequilibrium signals in the atlantic compared to the pacific as seen in previous studies however across most tidal lines the largest dynamic signals tend to occur in the arctic and nordic seas and also in hudson bay bathymetry and coastal geometry contribute to the modeled nonequilibrium b

evolution of grasses and grassland ecosystems the evolution and subsequent ecological expansion of grasses poaceae since the late cretaceous have resulted in the establishment of one of earth s dominant biomes the temperate and tropical grasslands at the expense of forests in the past decades several new approaches have been applied to the fossil record of grasses to elucidate the patterns and processes of this ecosystem transformation the data indicate that the development of grassland ecosystems on most continents was a multistage process involving the paleogene appearance of c3 and c4 open habitat grasses the mid late cenozoic spread of c3 grass dominated habitats and finally the late neogene expansion of c4 grasses at tropical subtropical latitudes the evolution of herbivores adapted to grasslands did not necessarily coincide with the spread of open habitat grasses in addition the timing of these evolutionary and ecological events varied between regions consequently region by region investigations using both direct plant fossil

diatom phytolith and pollen records from a 10be 9be dated lacustrine succession in the chad basin insight on the miocene pliocene paleoenvironmental changes in central africa abstract a discontinuous 200 m long borehole drilled in the bol archipelago 13 n lake chad provided 25 samples which were dated using the 10 be 9 be method and analyzed for their micro biological content the dating provided ages ranging from 6 3 0 1 to 2 6 0 1 ma a period contemporaneous with the pliocene fossil localities located in the current djurab desert of chad 16 17 n well preserved diatom assemblages first occurred at 4 7 0 1 ma and were dominated by the freshwater planktonic genera aulacoseira and stephanodiscus until the end of the pliocene this supports the recurrence of lacustrine conditions at bol during all the pliocene the presence of pelite and argillaceous deposits in the core before 4 7 0 1 ma however suggests that the lake settled earlier at least since 6 3 0 1 ma the abundance of afromontane pollen taxa at 4 2 0 1 ma and the occurrence of trapeziform polylobate phytoliths throughout the sequence suggest significant vegetation inputs from the southern highlands while the importance of kaolinite in the clay sediments indicates a water supply predominantly from the south during the pliocene phytolith assemblages are all dominated by lobate grass silica short cells and by blocky and elongate types which attest to the presence of herbaceous dominated vegetation around bol and or in the southern drainage basin during the pliocene this result is also supported by the pollen assemblage described at 4 2 0 1 ma which shows highest affinity for the savanna biome moreover low values for the xerophytic grass phytolith index indicate the presence of humid loving mesophytic and aquatic grass communities in this vegetation at last significant variations in the abundance of blocky and elongate phytoliths are indicative of local alternations of fully lacustrine and marshy conditions at bol particularly between 3 6 and 2 7 ma the abundance of silicified bulliform cells combined with the absence of diatoms support a significant lacustrine reduction at bol favoring the increasing of local marshy vegetation

dental mesowear analysis of the late miocene bovidae from toros menalla chad and early hominid habitats in central africa this study aimed to reconstruct the environmental conditions that prevailed in the chadian palaeo lake basin ca 7 ma ago based on the feeding preferences of late miocene bovidae from toros menalla chad this is a key issue for understanding the circumstances regional landscapes under which the earliest known hominid sahelanthropus tchadensis evolved a dental mesowear analysis was applied to 117 specimens of bovids representing the four tribes present in the anthracotheriid unit localities hippotragini reduncini antilopini and bovini all these bovids fed on grasses at least partially previous analyses and the present results indicate the presence of a mosaic like environment containing various habitats from grasslands to woodlands in the surroundings of the chadian lake basin indeed our data support the availability of grass or grass like plants and therefore open patches in the vicinity of the chadian palaeo lake shores

getting the inside story using computed x ray tomography to study inclusion trails in garnet porphyroblasts this study demonstrates how high resolution x ray computed tomography can be used to determine the geometry of curved inclusion trails in garnet porphyroblasts for the first time the three dimensional geometry of these features is shown as an animation a stereo pair a vrml model and two dimensional sections the spatial resolution of the data in this study approximately 10 m is high enough to resolve inclusions and finer resolutions are possible comparisons of scan imagery with thin section and microprobe data demonstrate that many typical inclusion phases in garnet porphyroblasts can be clearly distinguished including quartz ilmenite and monazite a sodium metatungstate solution with a density of 1 19 g cm3 was used for a wedge calibration during scanning reducing artifacts to a minimum and allowing maximum image contrast the overall conclusion of this study is that high resolution x ray computed tomography is a quick non destructive technique that is invaluable in the study of porphyroblast microstructure the three dimensional data generated by this technique can be compared with geometries predicted by the varying theoretical models for the formation of curved inclusion trails in garnet porphyroblasts they can also be analyzed to determine the three dimensional orientation of curvature axes in individual porphyroblasts which has not been possible until now

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

quantitative textural analysis of packings of elongate crystals the spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush and in turn is controlled by the rate of crystal growth and accumulation a predominant non spherical habit for igneous minerals brings into question the use of spherical particles in reference packings used for quantification of spatial distribution furthermore variations of crystal clustering ordering with length scale require spatial statistics which take into account the distribution of particles beyond nearest neighbours using random close packings of spherocylinders we demonstrate the importance of aspect ratio for the aggregation index usually known as r and show that packings of spherical particles have more structure than packings of rods the spatial distribution functions demonstrate that the plagioclase grains in the colonnade from the holyoke basalt are clustered on a length scale of 0 5 mm understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques to well understood environments

garnet polycrystals and the significance of clustered crystallization polycrystalline garnets are common in metamorphic rocks and may form as a result of close spacing of nuclei if clustering is early or impingement of larger grains if clustering occurs later in the growth history the timing of clustering relative to garnet growth is relevant to understanding the formation and evolution of porphyroblasts and evaluating the significance if any of clustering electron backscattered diffraction ebsd analysis of garnet bearing metamorphic rocks reveals the presence of polycrystalline garnet in nine localities examined in this study the northern appalachians vermont maine new york usa north american cordillera north cascades range washington snake range nevada usa western rocky mountains british columbia canada southern menderes massif turkey santander massif colombia and the sanandaj sirjan zone hamadan iran in some samples polycrystals comprise 20 30 of garnets analyzed and chemical and textural evidence suggests that early coalescence of garnet polycrystals is common some early coalescing polycrystals exhibit growth zoning that is concentric about the geometric center of the polycrystal in thin section these garnets may be undetectable as polycrystals based on morphology or zoning in some polycrystals zoning is unrelated to the location of internal grain boundaries in others fe mn mg zoning has a different pattern than that of ca zoning patterns may vary on the scale of a single thin section in addition some polycrystals are characterized by high angle misorientation boundaries that may be in special non random orientations an observation that indicates that these polycrystals are not random clusters of grains the presence of internal grain boundaries may affect diffusion pathways and length scales and may facilitate communication of porphyroblast interiors with matrix phases thereby influencing reaction history of the rock and the composition zoning of garnet

seasonality in transition scale from balanced to unbalanced motions in the world ocean abstractthe transition scale lt from balanced geostrophic motions to unbalanced wave motions including near inertial flows internal tides and inertia gravity wave continuum is explored using the output from a global 1 48 horizontal resolution massachusetts institute of technology general circulation model mitgcm simulation defined as the wavelength with equal balanced and unbalanced motion kinetic energy ke spectral density lt is detected to be geographically highly inhomogeneous it falls below 40 km in the western boundary current and antarctic circumpolar current regions increases to 40 100 km in the interior subtropical and subpolar gyres and exceeds in general 200 km in the tropical oceans with the exception of the pacific and indian sectors of the southern ocean the seasonal ke fluctuations of the surface balanced and unbalanced motions are out of phase because of the occurrence of mixed layer instability in winter and trapping of unbalanced motion ke in shallow mixed layer in summe

long range propagation of the semidiurnal internal tide from the hawaiian ridge abstract the northeastward progression of the semidiurnal internal tide from french frigate shoals ffs hawaii is studied with an array of six simultaneous profiling moorings spanning 25 5 37 1 n 1400 km and 13 yr long ocean topography experiment topex poseidon t p altimeter data processed by a new technique the moorings have excellent temporal and vertical resolutions while the altimeter offers broad spatial coverage of the surface manifestation of the internal tide s coherent portion together these two approaches provide a unique view of the internal tide s long range propagation in a complex ocean environment the moored observations reveal a rich time variable and multimodal internal tide field with higher mode motions contributing significantly to velocity displacement and energy in spite of these contributions the coherent mode 1 internal tide dominates the northeastward energy flux and is detectable in both moored and altimetric data over the entire array phase and group prop

the late miocene climate of northeastern africa unravelling the signals in the sedimentary succession examination of the depositional profile of the miocene plio pleistocene succession at two locations in the gulf of suez and seven locations in the red sea leads to the conclusion that the messinian zeit formation and equivalent sedimentary rocks were deposited at a rate greater than other units of the miocene plio pleistocene in these areas the zeit formation contains a significantly higher clastic content than the underlying south gharib formation these two aspects of the stratigraphy are taken to indicate that the messinian was a time of high rainfall and high sediment yield rates this period named the zeit wet phase stands in marked contrast to the arid conditions of the preceding tortonian stage the latter stage is represented in the gulf of suez and red sea area by the halite bearing south gharib formation and its equivalents physical evidence for a humid messinian is provided by five lines of evidence involving four sites around the red sea and two sites offshore it is suggested that the zeit wet phase was marked by high monsoonal activity as demonstrated by drilling sites of the ocean drilling program it is probable that the wet phase peaked in the late messinian at the time of the low stand of the mediterranean during the messinian salinity crisis

crystallization processes in migmatites an important prerequisite for interpreting microstructures in plutonic and metamorphic rocks is understanding crystallization processes this study uses crystal size distribution csd and grain shape parameters to investigate mineral reaction controlled crystal growth and melt solidification in migmatites of the bayerische wald variscan orogeny germany partially molten rocks were studied because they allow the simultaneous investigation of crystallization of a melt and the growth of solid products of a metamorphic reaction csd and shape factors were obtained for three different minerals 1 cordierite in a diatexite where the melt remained in the system 2 k feldspar in a segregated k feldspar quartz leucosome and 3 plagioclase from a segregated plagioclase quartz leucosome cordierite crystals exhibit a nearly linear csd pattern and subeuhedral crystal shapes k feldspar grains display an approximately linear csd except for a marked increase at large crystal size classes k feldspar grains are characterized by strongly lobate grain boundaries the csd of plagioclase crystals is nearly linear with a slight decrease at small crystal size classes plagioclase shape factors also indicate lobate grain boundaries however with lower values than k feldspar cordierite csd and shape data are consistent with interface controlled crystallization the csd indicates that nucleation and growth is the rate limiting step during the cordierite producing reaction in contrast to porphyroblast growth in solid rocks where mass transfer is typically rate limiting csd combined with information on the duration of crystallization yields growth rates of 10 17 to 10 18 m s the plagioclase data are consistent with magmatic crystallization and are well described by the communicating neighbor theory the k feldspar data also indicate magmatic crystallization the overproduction of large grains of k feldspar reflects the interplay between nucleation and growth rates at the initial stage of crystallization because of different environments between solid and anatectic rocks the csd may help to decipher metamorphic from anatectic migmatites

cosmogenic nuclide dating of sahelanthropus tchadensis and australopithecus bahrelghazali mio pliocene hominids from chad ages were determined at two hominid localities from the chad basin in the djurab desert northern chad in the koro toro fossiliferous area kt 12 locality 16 00 n 18 53 e was the site of discovery of australopithecus bahrelghazali abel and in the toros menalla fossiliferous area tm 266 locality 16 15 n 17 29 e was the site of discovery of sahelanthropus tchadensis toumai at both localities the evolutive degree of the associated fossil mammal assemblages allowed a biochronological estimation of the hominid remains early pliocene 3 3 5 ma at kt 12 and late miocene 7 ma at tm 266 atmospheric 10be a cosmogenic nuclide was used to quasicontinuously date these sedimentary units the authigenic 10be 9be dating of a pelite relic within the sedimentary level containing abel yields an age of 3 58 0 27 ma that points to the contemporaneity of australopithecus bahrelghazali abel with australopithecus afarensis lucy the 28 10be 9be ages obtained within the anthracotheriid unit containing toumai bracket by absolute dating the age of sahelanthropus tchadensis to lie between 6 8 and 7 2 ma this chronological constraint is an important cornerstone both for establishing the earliest stages of hominid evolution and for new calibrations of the molecular clock

the effect of reaction overstep on garnet microtextures in metapelitic rocks of the ilesha schist belt sw nigeria garnet bearing assemblages of k rich and k poor metapelites from the ilesha schist belt sw nigeria are investigated k rich samples contain the assemblages a garnet staurolite muscovite chlorite magnetite b andalusite garnet staurolite muscovite chlorite magnetite and c sillimanite andalusite garnet muscovite chlorite magnetite k poor samples contain the assemblages d garnet staurolite cordierite chlorite and e garnet cordierite chlorite staurolite all assemblages contain quartz plagioclase biotite and ilmenite p t pseudosections calculated in the system cao na2o k2o tio2 mno feo mgo al2o3 sio2 h2o o2 suggest peak metamorphism at 590 20 c at 5 0 5 kbar followed by retrogression to 550 c at 3 0 kbar in agreement with field evidence domain assemblages mineral compositions modes and geothermobarometry the absence of compositional zonation shows that garnet in all investigated rocks nucleated and grew at constant p t x in equilibrium with associated minerals on the thin section scale however the garnet in reaction did not begin until the establishment of a significant temperature overstep of 80 c with consequent rapid dehydration of chloriteand muscovite bearing assemblages resulting in interface controlled garnet growth under locally hydrostatic pressure conditions garnet in rock types a and b formed with a characteristic pattern of biotite and quartz inclusions a house of cards texture additionally clusters and aggregates of unzoned garnet grains formed in rock types a and d garnet resorption in rock types a c resulted from prograde stauroliteand retrograde andalusite forming reactions

diffusion control of garnet growth harpswell neck maine usa a detailed analysis of chemical zoning in two garnet crystals from harpswell neck maine forms the basis of an interpretation of garnet nucleation and growth mechanisms garnet apparently nucleates initially on crenulations of mica and chlorite and quickly overgrows the entire crenulation giving rise to complex two dimensional zoning patterns depending on the orientation of the thin section cut contours of ca zoning cross those of mn fe and mg indicating a lack of equilibrium among these major garnet constituents zoning of fe mg and mn is interpreted to reflect equilibrium with the rock matrix whereas ca zoning is interpreted to be controlled by diffusive transport between the matrix and the growing crystal image analysis reveals that the growth of garnet is more rapid along triple grain intersections than along double grain boundaries moreover different minerals are replaced by garnet at different rates the relative rate of replacement by garnet along double grain boundaries is ordered as muscovite chlorite plagioclase quartz flux calculations reveal that replacement is limited by diffusion of si along double grain boundaries to or from the local reaction site it is concluded that multiple diffusive pathways control the bulk replacement of the rock matrix by garnet with si and al transport being rate limiting in these samples

the morton black hypothesis for the thinning of continental crust revisited in western afar abstract geological observations along the western margin of afar show that the morton black model in which thinning of upper continental crust at a nascent continental margin is accomplished through block faulting and tilting is not wholly applicable rather dikes are concentrated into swarms suggestive of important direct dilatation faults are concentrated into sets within which no block tilting steeper than 45g is observed therefore attenuation of the afar margins requires a significant role for processes other than block tilting and in some margin sectors the transition from continental to neo oceanic crust may be relatively abrupt

the late miocene paleoenvironment of afghanistan as inferred from dental microwear in artiodactyls abstract dental microwear of late miocene artiodactyls from afghanistan can yield information on paleodiet and thus inferences can be drawn about their paleoenvironment the molayan locality lies at the border between the greek iranian and siwalik bioprovinces knowledge of the paleoenvironment will further our understanding of the faunal exchanges between these two provinces during the late miocene ninety nine specimens of seven bovid and one giraffid species are considered the number and diversity of the samples provide objective data which enable the reconstruction of the paleoenvironment prostrepsiceros aff vinayaki and sporadotragus tadzhikistanicus have similar dental microwear pattern which suggests a meal by meal mixed feeding diet phronetragus aff secondus gazella sp and the giraffid palaeotragus cf rouenii can only be characterized as mixed feeders in a general sense dorcadoxa porrecticornis was an obligate grazer and the two species of tragoportax were variable grazers the analysis also brings out clear similarities between extinct grazers and equus przewalskii which is a c3 grazer isotopic evidence from previous studies supports the microwear data comparisons with data from the late miocene of the potwar plateau suggest strong environmental differences with the afghan locality when brought together this disparate evidence about diet suggests an open and dry environment composed mainly of c3 grasses and evergreen bushes during the late miocene in afghanistan

diversity and paleoecology of greek late miocene mammalian faunas abstract the late miocene of macedonia has yielded several rich faunal assemblages ranging from late vallesian to late turolian they may be compared to the classical localities of pikermi samos and maragheh taxonomic comparisons based upon updated faunal lists allowed us to compute faunal similarity indices which were submitted to principal component and cluster analysis on the graphs ravin de la pluie is always remote from the other macedonian fossil mammal localities it can only be explained by its vallesian age the other macedonian sites cluster next demonstrating some provinciality of this area during the turolian comparisons of the frequencies of the various taxonomic groups support the installation of a more forested environment in the latest faunal set dytiko the indices of diversity and the rank abundance curves seem also to reflect a change of the ecological conditions during the turolian the fauna of ravin de la pluie and of the vathylakkos prochoma ravin des zouaves group is marked by the predominance of 1 or 2 species while the species frequency of the dytiko set is more balanced suggesting warmer climate and less contrasted climatic conditions another way of evaluating the ecological significance of the fossil assemblages is the analysis of the distribution of the body weight of each category of mammals in each fauna when possible we used the cenogram method or a multivariate analysis of the number of species in each weight class excluding small mammals which are very rare in macedonia we have analysed in this way 25 fossil and 23 recent localities we show that although all the fossil localities are separated from the recent ones it is possible to deduce an open environment in ravin de la pluie and a more forested one in dytiko

spectral decomposition of internal gravity wave sea surface height in global models two global ocean models ranging in horizontal resolution from 1 12 to 1 48 are used to study the space and time scales of sea surface height ssh signals associated with internal gravity waves igws frequency horizontal wavenumber ssh spectral densities are computed over seven regions of the world ocean from three simulations of the hybrid coordinate ocean model hycom and two simulations of the massachusetts institute of technology general circulation model mitgcm high wavenumber high frequency ssh variance follows the predicted igw linear dispersion curves the realism of high frequency motions 0 87cpd in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest resolution runs of each model 1 25 hycom and 1 48 mitgcm with dynamic height variance frequency spectral density computed from 9 in situ profiling instruments these high frequency motions are of particular interest because of their contributions to the small scale ssh variability that will be observed on a global scale in the upcoming surface water and ocean topography swot satellite altimetry mission the variance at supertidal frequencies can be comparable to the tidal and low frequency variance for high wavenumbers length scales smaller than 50km especially in the higher resolution simulations in the highest resolution simulations the high frequency variance can be greater than the low frequency variance at these scales

sustained full water column observations of internal waves and mixing near mendocino escarpment abstract the relative strength and spatiotemporal structure of near inertial waves niw and internal tides it are examined in the context of recent moored observations made 19 km south of mendocino escarpment an abrupt ridge step feature in the eastern pacific in addition to strong internal tide generation steps and ridges give rise to the possibility of shadowing wherein near inertial energy is prevented from reaching depths beneath a characteristic intersecting the ridge top a combination of two moored profilers and a long range acoustic doppler current profiler adcp yielded velocity and shear measurements from 100 to 3640 m 60 m above bottom and isopycnal depth strain and overturn inferred turbulence dissipation rate from 1000 to 3640 m sampling intervals 20 min in the upper 1000 m and 1 5 h below that were fast enough to minimize aliasing of higher frequency internal wave motions the 67 day long record is easily sufficient to isolate niw and it via bandpass filtering and to capture

geology and palaeontology of the upper miocene toros menalla hominid locality chad all six known specimens of the early hominid sahelanthropus tchadensis come from toros menalla site 266 tm 266 a single locality in the djurab desert northern chad central africa here we present a preliminary analysis of the palaeontological and palaeoecological context of these finds the rich fauna from tm 266 includes a significant aquatic component such as fish crocodiles and amphibious mammals alongside animals associated with gallery forest and savannah such as primates rodents elephants equids and bovids the fauna suggests a biochronological age between 6 and 7 million years taken together with the sedimentological evidence the fauna suggests that s tchadensis lived close to a lake but not far from a sandy desert perhaps the oldest record of desert conditions in the neogene of northern central africa

shape size spatial distribution and composition of garnet crystals in highly deformed gneiss of the otter lake area quebec and a model for garnet crystallization garnet biotite sillimanite gneiss 700 c 7 kbar of the otter lake area in the western grenville province canadian shield occurs as granitic gneiss group 4 that forms a large part of the otter complex and as widely distributed more heterogenous metasedimentary gneiss group 2 in one sample of group 4 gneiss qtz25 pl34 kfs28 bt10 grt2 5 sil1 the true diameter determined by serial grinding of subhedral garnet crystals ranges from 0 2 to 3 0 mm with a mode at 1 0 mm nearest neighbour measurements in this sample and in surfaces of nine additional samples all 5 garnet confirm that garnet crystals are distributed mainly at random slight clustering was detected in two samples in one sample of group 4 gneiss microprobe analyses on sections through crystal centres obtained by serial slicing reveal that small crystals and margins to large crystals contain more fe and mn and less mg than the broad central regions of large crystals based on these and previous results together with theoretical considerations a crystallization model is proposed in which i garnet was produced by the continuous reaction ms bt qtz grt kfs h2o ii nucleation occurred by the random selection of randomly distributed ms bt qtz triple junctions iii the rate of linear growth remained constant and iv as temperature increased the rate of nucleation first increased slowly then remained nearly constant and finally declined within population compositional homogenization was followed on cooling by local fe mg mn exchange with biotite

microstructural chemical and textural records during growth of snowball garnet the growth history of two populations of snowball garnet from the lukmanier pass area central swiss alps was examined through a detailed analysis of three dimensional geometry chemical zoning and crystallographic orientation the first population collected in the hinge of a chevron type fold shows an apparent rotation of 360 the first 270 are characterized by spiral shaped inclusion trails gradual and concentric mn zoning and a single crystallographic orientation whereas in the last 90 crenulated inclusion trails and secondary mn maxima centred on distinct crystallographic garnet domains are observed microstructural geochemical and textural data indicate a radical change in growth regime between the two growth sequences in the first 270 growth occurred under rotational non coaxial flow whereas in the last 90 garnet grew under a non rotational shortening regime the second population collected in the limb of the same chevron type fold structure is characterized by a spiral geometry that does not exceed 270 of apparent rotation these garnet microstructures do not record any evidence for a modification of the stress field during garnet growth concentric mn zoning as well as a single crystallographic orientation are observed for the entire spiral electron backscatter diffraction data indicate that nearly all central domains in the snowball garnet are characterized by one 001 axis oriented sub parallel to the symmetry axis and by another 001 axis oriented sub parallel to the orientation of the internal foliation these features suggest that the crystallographic orientation across the garnet spiral is not random and that a relation exists among the symmetry axis the internal foliation and the crystallographic orientation

formation of garnet polycrystals during metamorphic crystallization garnet polycrystals may form throughout the metamorphic history of a rock starting at the earliest stages of garnet growth when closely spaced nuclei coalesce in mica schist from townshend dam vt electron back scattered diffraction ebsd analysis shows that garnet polycrystals possess two or more distinct lattice orientations separated by high angle boundaries 28 61 the minimum rotational displacements required to bring these lattice orientations into concordance with each other are commonly normal to the same low energy planes that occur as crystal faces of euhedral garnet there is no evidence for intracrystalline deformation and the polycrystals therefore probably represent individual garnet crystals that coalesced during growth the boundaries cross cut growth zoning and inclusion trails of the polycrystals indicating that early formed polycrystals once coalesced behave chemically and physically as single crystals statistical analysis of a 3d high resolution x ray computed tomographic data set of a large sample 912 cm3 of a townshend dam schist combined with microprobe and ebsd analyses of garnet are consistent with a high degree of clustering at all stages of garnet growth the formation and prevalence of polycrystals implies that garnet nuclei impinged on each other and coalesced and that coalescence was a common feature throughout garnet growth in the rock

scales of disequilibrium and rates of equilibration during metamorphism mounting evidence suggests that partial disequilibrium meaning disequilibrium for some elements but not for others may be a common but rarely detected phenomenon during metamorphic mineral growth even in ordinary prograde reactions that progress to completion detailed examination of compositional variations in garnet crystals over a range of metamorphic grade suggests distinctly different scales of equilibration for common elements with strong temperature dependence under lower greenschist facies conditions fe and mg may equilibrate at hand sample scale whereas mn and ca may not equilibrate even at millimeter scale although mn may achieve hand sample scale equilibration under upper greenschist facies conditions ca and many trivalent cations e g rees may not do so until temperatures exceed those of the middle amphibolite facies even in the lower granulite facies some elements e g y yb show indications of disequilibrium at sub centimeter scales during garnet growth analysis and numerical modeling of undisputed disequilibrium textures demonstrate that the most common impediment to equilibration during metamorphism is the sluggishness of intergranular diffusion the same mechanism known to govern porphyroblast crystallization in many metamorphic environments despite this importance to petrology few quantitative determinations exist of inter granular diffusion rates under metamorphic conditions using numerical simulations of coupled intergranular and intracrystalline diffusion processes in coronal textures around partially resorbed garnet crystals from the llano uplift u s a a very precise and relatively accurate estimate is obtained for the rate of intergranular diffusion of al in fluid undersaturated systems this result and an earlier estimate for fluid saturated systems provide bracketing values for al diffusivity during metamorphism

the initiation and development of metamorphic foliation in the otago schist part 1 competitive oriented growth of white mica the 3d shape size and orientation data for white mica grains sampled along two transects of increasing metamorphic grade in the otago schist new zealand reveal that metamorphic foliation as defined by mica shape preferred orientation spo developed rapidly at sub greenschist facies conditions early in the deformation history the onset of penetrative strain metamorphism is marked by the rapid elimination of poorly oriented large clastic mica in favour of numerous new smaller grains of contrasting composition higher aspect ratios and a strong preferred orientation the metamorphic mica is blade shaped with long axes defining the linear aspect of the foliation and intermediate axes a partial girdle about the lineation once initiated foliation progressively intensified by an increase in the aspect ratio size and alignment of grains although highest grade samples within the chlorite zone record a decrease in aspect ratio and reduction in spo strength despite continued increase in grain size these trends are interpreted in terms of progressive competitive anisotropic growth of blade shaped grains so that the fastest growth directions and blade lengths tend to parallel the extension direction during deformation the competitive nature of mica growth is indicated by the progressive increase in size and resultant decrease in number of metamorphic mica with increasing grade from c 1000 relatively small mica grains per square millimetre of thin section at lower grades to c 100 relatively large grains per square millimetre in higher grade samples reversal of spo intensity and grain aspect ratio trends in higher grade samples may reflect a reduction in the strain rate or reduction in the deviatoric component of the stress field

melt producing versus melt consuming reactions in pelitic xenoliths and migmatites abstract melt producing reactions have operated both in pelitic xenoliths and in pelitic migmatites but melt consuming reactions related to in situ melt crystallization are largely restricted to migmatites hence xenolith reaction textures may provide clues on the relative roles of both reaction types in migmatites a comparison of xenoliths and migmatites results in a catalogue of textural and chemical features some of which are argued to be diagnostic the results have implications for the identification of restite in igneous rocks and for the relative importance of prograde and retrograde processes in different domains of layered migmatites