syntectonic development of a strain independent steady state grain size during mylonitization abstract michibayashi k 1993 syntectonic development of a strain independent steady state grain size during mylonitization tectonophysics 222 151 164 for a distance of greater than 50 km along the median tectonic line japan syntectonic recrystallization of quartz has resulted in the development of a strain independent steady state grain size within the core of the kashio shear zone that is also independent of rock type the mean grain size of quartz in recrystallized aggregates progressively decreases towards the shear zone core becoming stable at around approximately 37 m even though the strain increases within more strongly mylonitized rocks some variation of mean grain sizes may result from secondary effects due to hydrothermal activity associated with the median tectonic line despite the development of a steady state mean grain size individual grains were not stable as revealed by log normal grain size distributions consequently dynamic recrystallization and grain growth were competing processes that achieved a balance and hence resulted in the development of the steady state grain size the actual grain size that resulted probably depended on both the water content and strain rate as well as the flow stress approaching the centre of the shear zone mylonitic fabrics e g s c fabrics mica fish were established well before a steady state grain size was reached a steady state grain shape shape orientation and crystallographic fabrics may not be developed until even more mylonitization had occurred variable grain sizes result from heterogeneous deformation as a consequence of deformation partitioning even under a stable stress prior to the development of a steady state grain size consequently it should be determined whether a steady state grain size has been achieved within a shear zone before the grain size is used as a paleopiezometer

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

tem and xrd determination of crystallite size and lattice strain as a function of illite crystallinity in pelitic rocks average crystallite size and mean square strain of illite in rock specimens and clay separates were measured independently in tem images and by single line fourier voigt method profile analysis of the c 1 nm peak of xrd patterns for a prograde sequence of pelitic rocks illite crystallinity indices 0 17 0 58 d2h from the gaspepeninsula quebec the tem determined crystallite sizes in clay separates approxi mate those determined by fourier profile analyses and those calculated from illite crystallinity indices by the scherrer equation with the exception of the diagenetic sample the crystallite sizes and mean square strains of illite in rock samples exhibit a trend similar to that determined by profile analyses but the average crystallite sizes are up to five times larger than those measured for clay separates tem images show that all rock samples have a wide range of crystallite sizes and the proportions of larger crystallites increase with metamorphic grade the diagenetic illite is defect rich fine grained mean thickness by volume c 70 nm 1m d material anchizonal illite tends to occur as separate aggregates of small 1m d and larger 2m 1 crystals c 200 nm comprising arrays of subparallel coalescing packets the epizone sample has thick c 400 nm defect free crystals of muscovite occurring in stacks of parallel layers or subhedral crystals intergrown with large angle boundaries cleaved crystals that are free of intracrystalline layer terminations are dominant in clay separates of all samples having ranges of smaller sizes with volume average thicknesses of c 43 43 and 81 nm c 14 28 67 nm by the voigt method respectively for the three zones the results suggest that illite crystallinity indices do not provide a direct measure of a single microstruc tural state of illite in rocks although they yield consistent limits for average crystallite sizes for the anchizone 23 48 nm here therefore they serve as a general parameter of the degree of recrystallization on a relative basis in part because the contributions of all peak broadening variables mixed layering size and strain decrease regularly with prograde regional metamorphism of pelites the microstructural changes caused by rock disaggregation are probably a function of those variables as well the data collectively demonstrate a trend from metastable defect rich small crystals towards a stable assemblage of larger defect free crystals through dissolution of strained crystals and neocrystallization consistent with the ostwald step rule

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

40ar 39ar illite dating of late caledonian acadian metamorphism and cooling of k bentonites and slates from the welsh basin u k the vacuum encapsulation laser 40ar39ar technique allows extremely small 10 6 g samples of fine grained materials such as diagenetic clays to be dated here we show that the method can be extended to higher grade clay minerals the integration of transmission electron microscopic tem characterization with 40ar39ar dating of vacuum encapsulated samples permits the resolution of the timing of metamorphic growth cooling from the time of diagenesis we have applied this technique to well characterized lower paleozoic slates and k bentonites from the welsh basin which span the transition from anchizonal to epizonal grade which had been previously studied using rbsr and smnd dating tem observations of epizonal k bentonites and slate showed that illite in these samples is of 2m1 polytype of muscovite like composition and oriented parallel to cleavage suggesting that they are of metamorphic origin total gas ages equivalent to conventional kar ages for encapsulated epizonal k bentonites and slate 340 408 ma are considerably variable the ar retention ages calculated from 39ar and 40ar atoms retained in the sample after irradiation are more consistent 383 411 ma the 39ar recoil losses are minor for illites from whole rock samples of epizonal k bentonites but very significant for clay separates of epizonal slate plateaus in age spectra were observed in epizonal k bentonites and slate the plateau ages 414 421 ma and retention ages 383 411 ma can be correlated with the onset of acadian metamorphism and culmination of uplift and inversion of the welsh basin respectively these ages are significantly younger than the 450 ma ages previously reported for diagenetic clays using the same method suggesting that diagenetic history has been lost in these epizonal k bentonites and slate tem observations of anchizonal slates showed that there are two modes of illite the first mode is similar to that observed in epizonal samples suggesting a metamorphic origin the second mode consists of the 1md polytype has typical diagenetic illite composition and is oriented parallel to bedding suggesting a diagenetic origin total gas ages for encapsulated anchizonal slates vary considerably 361 422 ma the retention ages are more consistent 413 432 ma than the total gas ages the 39ar recoil losses are more significant than those for epizonal k bentonites and slate plateaus in age spectra are generally not observed however the consistent retention ages for the anchizonal slates correspond to the plateau ages for the epizonal samples and are inferred to represent the onset of acadian metamorphism these data when combined with our previously published results for diagenetic shales suggest that thermal conditions near the boundary of anchizonal and epizonal grades are necessary to completely reset ar systems in shales and slates

sediment flux dynamics over the shallow 25 m depth shelf of the mediterranean sea along the israeli coast abstract in order to study the dynamics of sediment fluxes at the northern end of the nile littoral cell sediment traps were deployed for one year over the shallow shelf of the mediterranean sea offshore israel the sediment traps replaced monthly were suspended on a mooring line two kilometers offshore of the hadera power station 10 m above a 25 m deep seafloor sea state conditions near the traps were measured by an acoustic doppler profiler that provided the bottom water temperature wave heights and current s velocities and direction the measured sediment fluxes greatly varied between sampling periods with a minimum value of 1 8 g m 2 d 1 in autumn and a maximum value of 83 g m 2 d 1 in winter this variation was mostly effected by wave induced resuspension of sediment a strong correlation r2 0 97 was found between integrated wave heights that exceeded 1 5 m and the measured sediment fluxes based on the sea state conditions and sediment trap data we conclude that the direction of sand transport at the study area was strictly northwards and that almost all of the annual sand transport occurred during several high energy events in the winter fine particles that consisted the majority of the mass flux were absent in the underlying 25 m deep seafloor suggesting that they are very effectively winnowed off beyond the sand strip

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

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

mg ca ratios of two globigerinoides ruber white morphotypes implications for reconstructing past tropical subtropical surface water conditions 1 tests of the planktonic foraminifer globigerinoides ruber white d orbigny have become a standard tool for reconstructing past oceanic environments paleoceanographers often utilize the mg ca ratios of the foraminiferal tests for reconstructing low latitude ocean glacial interglacial changes in sea surface temperatures sst we report herein a comparison of mg ca measurements on sample pairs n 20 of two g ruber white morphotypes g ruber sensu stricto s s and g ruber sensu lato s l from surface and downcore samples of the western pacific and indian oceans g ruber s s refers to specimens with spherical chambers sitting symmetrically over previous sutures with a wide high arched aperture whereas g ruber s l refers to a more compact test with a diminutive final chamber and small aperture the g ruber s s specimens generally show significantly higher mg ca ratios compared to g ruber s l our results from the mg ca ratio analysis suggest that g ruber s l specimens precipitated their shells in slightly colder surface waters than g ruber s s specimens this conclusion is supported by the differences in 18o and 13c values between the two morphotypes although it is still unclear if these two morphotypes represent phenotypic variants or sibling species our findings seem to support the hypothesis of depth and or seasonal allopatry within a single morphospecies

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

enhanced carbon export to the abyssal depths driven by atmosphere dynamics long term biogeochemical observations are critical to understand the natural ability of the oceans to fix co2 into organic carbon and export it to the deep as sinking particles here we present results from a 3 year 2010 2013 sediment trap deployment that allowed detecting interannual variations of carbon fluxes beyond 4000 m depth in the eastern mediterranean sea anomalous atmospheric conditions triggering strong heat losses in winter spring 2012 resulted in convective mixing nutrient uplifting and a diatom dominated bloom southeast of crete phytoplankton growth reinforced by the arrival of nutrients from airborne etna volcano ash was the highest in the last decade satellite derived chl a concentrations up to 1 9 mg m 3 this situation caused carbon export to increase by 2 orders of magnitude 12 2 mg m 2 d 1 with respect to typical values which demonstrates how pulses of sinking fresh phytodetritus linked to rare atmospheric processes can episodically impact one of the most oligotrophic environments in the world ocean

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

sedimentation processes in the eastern mediterranean sea during the late glacial and holocene revealed by end member modelling of the terrigenous fraction in marine sediments we present grain size distributions of the terrigenous fraction of two sediment cores from the southeast levantine sea sl112 and the northern aegean sea sl148 spanning the time interval from the late glacial to the present end member modelling of the grain size distribution allows discriminating between aeolian and fluvial transport of the sediments and helps to infer palaeoenvironmental conditions in the source areas sedimentary and depositional processes during the late glacial and holocene were controlled by climatic variations of both the northern high latitudes and the african climate system the sedimentation at site sl112 off israel is dominated by the suspension load of the river nile and aeolian dust from the sahara variations in grain size reflect the early to mid holocene climate transition from the african humid period to recent arid conditions this climate change was gradual in contrast to the abrupt humidity change documented in western saharan records this implies a successive decrease in nile river sediment supply due to a step wise aridification of the headwaters the grain size data of sl112 show a humidity maximum at 5 kyr bp coincident with a regionally restricted wet phase in the levantine sea the sediments at the north aegean site sl148 consist of riverine particles and low amounts of aeolian dust probably derived from south european sources and with probably minor saharan influence the sedimentation processes are controlled by climate conditions being characterized by enhanced deposition of dust during the cold and dry glacial period and by decreased aeolian influx during the temperate and humid holocene

microstructural development of fine grained quartz aggregates by syntectonic recrystallization abstract experimental study of syntectonic recrystallization of fine grained quartz aggregates was carried out in order to simulate the development of some natural microstructures of quartz tectonites and to understand their formation condition agate was axially compressed with a constant strain rate apparatus experiments were conducted at 4 kbar solid confining pressure 700 1000 c and 10 4 10 6 sec 1 to 10 45 strain in all runs deformation has proceeded under wet condition caused by dehydration of pyrophyllite used as pressure medium two different types of microstructure were distinguished in the deformed specimens one is p type which is characterized by equant equidimensional and polygonal grains the other is s type which is characterized by the highly oblate grains with the largest dimension perpendicular to the compression axis the p type microstructure is developed at higher temperatures and slower strain rates while the s type developed at lower temperatures and faster strain rates the transition between the s and p types is found to be very sharp

systematic change of foraminiferal mg ca ratios across a strong salinity gradient abstract the mg ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures used in conjunction with 18 o of foraminiferal calcite it allows deconvolution of temperature and ice volume signals to infer past ocean temperatures and salinities assuming the relationship between seawater 18 o and salinity is known such work assumes that temperature is the only or at least the dominant environmental controller of foraminiferal mg ca the semi enclosed mediterranean sea where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 c to 8 c provides a relevant setting to test this assumption outside the laboratory in this study planktonic foraminifera o universa g siphonifera g bulloides and g ruber white and pink were picked from 11 box core tops spanning the mediterranean salinity gradient and analysed for their trace element concentrations mg ca ratios are higher for the associated calcification temperatures than in other regions where calibrations have been conducted and correlate poorly with calcification temperature mg ca ratios are particularly high for samples from the eastern mediterranean where salinity is unusually high correlations of mg ca with the calcification salinity are statistically significant with mg ca changing by 15 59 per psu suggesting that salinity may act as a control on mg ca ratios in addition to the dominant temperature control we show that contamination by non carbonate material and diagenetic high mg carbonate overgrowths cannot account for the observed trend of increasing mg ca with salinity a relationship between mg ca and salinity is also suggested by re analysis of calibrations from open ocean settings these new mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the mg ca palaeothermometer should be considered even in open ocean settings particularly where large salinity changes occurred in the past

evidence for syntectonic crystallization for the mudstone to slate transition at lehigh gap pennsylvania u s a data primarily for phyllosilicates have been obtained for the continuous transitional sequence from mudstone to slate with well developed slaty cleavage at lehigh gap pennsylvania and for slates from quarries in the same area samples were studied by optical microscopy powder x ray diffraction and electron microprobe analysis with emphasis on transmission and analytical electron microscopy mineral grains are virtually free of deformation induced strain concomitant with the gradual development of cleavage normal to bedding the following changes are observed or confirmed 1 the orientation of phyllosilicate grains changes discontinuously from being preferentially parallel to bedding to being parallel to cleavage 2 crystal imperfections as expressed in layer terminations low angle grain boundary like features and other defects decrease in density 3 complex mixed layering is replaced by homogeneous packets of layers of single phases and 4 illite transforms to muscovite with increase in k a1 and change from a lmd to 2m polytype slaty cleavage apparently develops due in part to pressure solution of phyllosilicates oriented parallel to bedding mass transport of components and crystallization to form new grains parallel to cleavage it reflects transitions from imperfect metastable phases toward ordered stable phases in a low temperature 225 c metamorphic environment

using earthquake doublets to study inner core rotation and seismicity catalog precision 1 we report our search for doublets in the south sandwich islands ssi region among 906 earthquakes from january 1982 to december 1998 event pairs with source separation less than 40 km which was calculated using pde locations were checked using vertical component short period and broadband digital records cross correlation coefficients of p or pkp waveforms were computed for similarity comparison whole waveforms of those event pairs with correlation coefficients larger than 0 8 were checked by eye by this process 17 doublets were found some of which form multiplets however only one doublet event pair 14 august 1995 and 28 march 1987 has clear pkp df phases on both records at college alaska col the pkp df travel time change measured by cross correlation is a decrease by 0 15 s with standard deviation 0 02 s over a time period of about 8 years this result strongly supports differential rotation of the earth s inner core relative to the mantle and the crust the estimated rotation rate ranges from 0 4 to 1 per year eastward the special case of a locked inner core can then be ruled out we also checked the precision of pde and isc locations using the 17 doublets results show that both catalogs have relatively high location precision standard deviations in latitude longitude and depth are less than 4 km 6 km and 10 km respectively supporting prior claims of detection of inner core rotation song and richards 1996

fabric asymmetry and shear sense in movement zones asymmetry between lattice preferred orientation and shape fabrics is commonly observed in microstructural studies of many deformed mineral aggregates e g ice carbonate rocks peridotites and quartzites theoretical predictions are limited by the nature of the models available and more can be gained by discussion of the mechanisms which give rise to such asymmetry in specific natural and experimental situations

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

influence of volcanic shards on foraminiferal mg ca in a core from the galapagos region 1 variability in the mg fe al mn and u to ca composition of the planktonic foraminifera g ruber in core tr163 22 an 8 8 m long piston core from just northwest of the galapagos islands reveals distinct patterns of downcore behavior mg ca data follow a general climatic trend with lower values during cold intervals i e marine isotope stages mis 2 4 and higher values during warm intervals i e mis 1 and 5 fe ca and al ca data reveal distinct intervals in which concentrations are elevated tenfold or more over baseline values with highly variable elemental ratios in these intervals the mg ca data are highly correlated with the fe ca and al ca data in these intervals with slopes of 1 13 0 03 and 0 66 0 07 mole mole respectively examination of the sediments from these intervals reveals that they are rich in volcanic debris that is likely derived from galapagos volcanic rocks the presence of small amounts of this volcanic debris can bias shell mg ca to elevated values attempts to use enhanced cleaning to remove the volcanic particles were largely unsuccessful the most successful strategy is to use the fe ca and al ca from the shell digests along with the fe to mg ratio of the volcanic debris to correct the mg ca data for al silicate contamination in which case the corrected data more clearly reveal the primary climatological patterns mn ca and u ca data are characterized by cycles of 20 200 cm length with mn ca having a distinct trend toward higher values between the core top and 200 cm these trends appear to be related to diagenetic coatings on the foraminifera shells most likely in the form of mn carbonates

a method for precise analysis of trace element calcium ratios in carbonate samples using quadrupole inductively coupled plasma mass spectrometry an improved method has been developed using a quadrupole inductively coupled plasma mass spectrometer q icp ms to analyze carbonate samples for multiple trace element to calcium ratios problems alleviating shorter term drift have been overcome by manipulating the instrument to bracket each trace metal measurement with a calcium measurement while longer term drift is corrected by bracketing each sample analysis with external matrix matched standards of typical foram composition our method is optimized for measuring the ratios sr ca mg ca zn ca cd ca ba ca mn ca and u ca from a single carbonate sample but could be adapted to include a range of alternative ratios evaluation has shown the method to be extremely precise at less than 1 rsd 1 for 3 trace metal to calcium ratios we have achieved comparable precision to a sector field icp ms instrument and an advance over previous methods using the q icp ms instrument precision rsd for each ratio based on 96 sample analyses in 5 batches made over a period of 9 months using a 100 mg l ca standard is 2 2 for u ca 1 7 for cd ca 1 9 for zn ca 1 1 for ba ca 0 7 for mn ca and 0 7 and 0 6 for sr ca and mg ca respectively accuracy of the method is confirmed by comparing standard ratios with those obtained from an icp aes instrument and by comparing sample analyses of neap4b material from the north atlantic with data measured using thermal ionization mass spectrometry tims and flame atomic absorption spectroscopy faas

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

reorientation mechanisms of phyllosilicates in the mudstone to slate transition at lehigh gap pennsylvania abstract the mudstone to slate transition of the martinsburg formation at lehigh gap pennsylvania was re examined using a new transmission mode x ray texture goniometer supplemented by sem xrd and optical studies three mesoscopic zones are recognized in the outcrop i mudstone ii transition and iii slate zone in the mudstone zone the mica basal planes are parallel to bedding whereas the preferred orientation of the chlorite basal planes is up to 30 shallower than bedding the angular difference between chlorite and mica decreases towards the transition zone becoming subparallel at ca 50 m from the contact with the overlying shawangunk formation in the transition zone the preferred orientations of both mica and chlorite are intermediate to bedding and cleavage orientations which is consistent with mechanical reorientation of phyllosilicates this is supported by a decrease in march strain with a minimum at ca 95 m from the contact for both mica and chlorite sem observations similarly show the importance of grain rotation in large detrital grains in the slate zone both chlorite and mica orientations are parallel to cleavage chlorite and mica in the cleavage orientation of the slate zone have high fe contents whereas low fe mica and mg fe chlorite dominate in the mudstone and transition zone which indicates that dissolution neocrystallization is the dominant mechanism in the slate zone thus mechanical rotation of large detrital grains is important in the early stages of cleavage development with dissolution neocrystallization occurring at all stages and becoming dominant in the more evolved stages

the first deep sea mooring station in the eastern levantine basin deeplev outline and insights into regional sedimentological processes abstract the eastern levantine basin elb is an ultra oligotrophic warm and saline marine system significantly affected by climate change during the past several decades the deployment of the first moored station at the elb deeplev at 1500 m water depth 50 km offshore haifa israel aimed at enhancing synchronized measurements of physical and biogeochemical dynamics the station carries an array of sediment traps and sensors that measure physical chemical and biological attributes along the water column here we describe the station and present sediment flux data from the first 1 5 years of operation since november 2016 we show that despite deeplev s offshore location and the open sea characteristics of the water column lateral transport from the continental margin contributes the greatest fraction of particulate flux to the seafloor at this site this mostly occurs via intermediate nepheloid layer plumes entering the study area between depths of 180 and 800 m bottom currents are weak average sd 3 5 2 cm s 1 and are unlikely to cause significant resuspension based on sedimentation rates obtained from nearby sediment cores and sediment particle fluxes sampled in the traps calculated accumulation rates of total particulate matter and of particulate organic carbon at the seafloor were 95 108 g m 2 y 1 and 0 5 0 6 g m 2 y 1 respectively offshore changes in sedimentation rates and in surface sediment elemental ratios indicate that sediment originating from the continental margins is transported at least 100 km offshore

simulation of fabric development in recrystallizing aggregates i description of the model abstract a new computer simulation of the development of grain shape and crystallographic preferred orientations in dynamically recrystallizing aggregates is presented this model is based on a uniform array of points each of which represents a small area of crystal this model combines homogeneous strains simplified versions of the lattice rotations predicted by taylor bishop hill theory mobile grain boundaries and the nucleation of subgrains it allows the progressive development of the fabrics and microstructures to be followed the limitations of the simplifying assumptions used in this model are discussed

kinetics of grain growth in anorthite abstract we investigated the grain growth kinetics of synthetic pure anorthite aggregates the starting material was prepared from glass and has a homogeneous starting grain size of 3 4 m porosity was less than 1 and the dislocation density was less than 2 10 7 cm 2 the samples were subsequently annealed at temperatures between 1100 c and 1350 c in air from 10 min to 480 h grain size was determined optically we observed normal grain growth for anneals less than 24 h the grain growth exponent n varied between 2 5 2 7 for different temperatures we determined the activation energy for grain growth to be 365 25 kj mol microstructural observations show a decrease in aspect ratio of the grains from 2 8 to 1 7 with increasing annealing temperatures and duration

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part i meso and macro scopic scale there is considerable variability in the thickness structure and macroscopic deformation style within shale prone major thrust zones which also impacts the structural style in the overlying and sometimes the underlying section the properties and percentages of clay minerals and percentages of organic material quartz and calcite affect fault zone weakness and behaviour the distribution of competent units within a shale prone zone can also significantly affect fault zone architecture even over short strike distance of 10s to 100s of metres other influences include high pore fluid pressures and associated veins deformation of the fault zone may disrupt the original principal displacement zones and force them to relocate including switching lithologies calcite veins can become concentrated locally in the fault zone and become a focus of fault zone weakness we still need many more descriptions of shale prone fault zones to understand the potential variations in thrust sheet structural style caused by differences in shale detachment characteristics the variations in structural style in the hanging walls of shale detachments are broad and range between the sledge runner style in many appalachian examples and the extensive closely spaced imbricate style of the osen roa detachment southern norway such contrasts are related to several factors including thrust sheet mechanical stratigraphy thickness of the overburden lateral continuity of the detachment detachment mechanical properties composition pore fluid pressures presence absence of higher level detachments and strain rate in many structural locations and at many scales shale prone sequences will pile up to produce over thickened masses cleavage duplexes s c fabrics duplexes imbricates pseudo duplexes and vein formation can all contribute to the thickening at nested scales a mixture of brittle and solution diffusion processes overall cause the affected unit to exhibit flow like characteristics while the broad principles are now well established considerable work remains to be done understanding the full range of structural geometries associated with shale detachments what factors regarding the nature of the detachments affect overlying structural styles rates of deformation and the controls on deformation mechanisms within the thrust zones

deformation of chlorite in naturally deformed low grade rocks the intracrystalline deformation of chlorite in naturally deformed low grade rocks was investigated with transmission electron microscopy tem as in other phyllosilicates the deformation of chlorite is dominated by the 001 slip plane slip along this plane is very easy through the generation and movement of partial dislocations with burgers vector b 1 n uv0 after initial bending of the 001 planes through a flexural slip mechanism accommodated by slip along 001 the misorientation is concentrated in tiltwalls subnormal to 001 which are formed by partial dislocations with b 1 n uv0 tiltwalls subparallel to 001 are formed by arrays of dislocations with a total burgers vector 001 these boundaries are either initiated at the grain boundary and move inwards by dislocation climb or form by movement of free dislocations towards the tip of propagating boundaries by glide along planes inclined to 001 once a boundary is formed the increasing misfit is accommodated by climb of these dislocations along 001 due to the combination of very easy slip along 001 and the ability to form subgrain boundaries subparallel to 001 by dislocation climb and activation of hard slip systems chlorite deforms plastically even at temperatures below 300 c

interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data clay mineral crystallinity and crystallite domain size data determined by x ray diffraction xrd are methods extensively used in the characterization of very low grade metamorphic conditions however the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained a consequence of the different machine conditions measurement methods and sample preparations used during analysis a calibration approach to the standardization of data using rock chip standards is presented which allows data sets produced by different research groups to be directly and quantitatively compared a standardized scale the crystallinity index standard cis is proposed with illite crystallinity anchizonal boundary limits of 0 25d 2 and 0 42d 2 and equivalent illite crystallite sizes of 52 and 23 nm respectively determined by the warren averbach method calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments and should improve the accuracy and reliability of correlations made between xrd data and other indicators of very low grade metamorphism hence increasing the value of such clay mineral studies

variation of illite muscovite 40 ar 39 ar age spectra during progressive low grade metamorphism an example from the us cordillera 40ar 39ar step heating data were collected from micron to submicron grain sizes of correlative illite and muscovite rich cambrian pelitic rocks from the western united states that range in metamorphic grade from the shallow diagenetic zone zeolite facies to the epizone greenschist facies with increasing metamorphic grade maximum ages from 40ar 39ar release spectra decrease as do total gas ages and retention ages previous studies have explained similar results as arising dominantly or entirely from the dissolution of detrital muscovite and precipitation recrystallization of neo formed illite while recognizing the importance of these processes in evaluating our results we suggest that the inverse correlation between apparent age and metamorphic grade is controlled primarily by thermally activated volume diffusion analogous to the decrease in apparent ages with depth observed for many thermochronometers in borehole experiments our results suggest that complete resetting of the illite muscovite ar thermochronometer occurs between the high anchizone and epizone or at roughly 300 c this empirical result is in agreement with previous calculations based on muscovite diffusion parameters which indicate that muscovite grains with radii of 0 05 2 m should have closure temperatures between 250 and 350 c at high anchizone conditions we observe a reversal in the age grain size relationship the finest grain size produces the oldest apparent age which may mark the stage in prograde subgreenschist facies metamorphism of pelitic rocks at which neo formed illite muscovite crystallites typically surpass the size of detrital muscovite grains it is also approximately the stage at which neo formed illite muscovite crystallites develop sufficient ar retentivity to produce geologically meaningful 40ar 39ar ages results from our sampling transect of cambrian strata establish a framework for interpreting illite muscovite 40ar 39ar age spectra at different stages of low grade metamorphism and also illuminate the transformation of illite to muscovite at frenchman mtn nv where the cambrian bright angel formation is at zeolite facies conditions illite muscovite 40ar 39ar data suggest a detrital muscovite component with an apparent age 967 ma the correlative carrara fm is at anchizone conditions in the panamint and resting spring ranges of eastern california and in these locations illite muscovite 40ar 39ar data suggest an early permian episode of subgreenschist facies metamorphism the same type of data from equivalent strata at epizone conditions greenschist facies in the footwall of the bullfrog fluorspar canyon detachment in southern nevada reveals a period of slow to moderate late cretaceous cooling

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

impact of biomineralization processes on the mg content of foraminiferal shells a biological perspective the mg ca ratio in foraminiferal shells is widely used as a proxy for paleotemperatures nevertheless it seems that the basic mg content of foraminifera is determined by biological factors as can be concluded from the large inter species and intrashell variability and the frequent deviations from inorganic behavior this paper discusses three possible ways by which foraminifera can control or modify the mg content in their shell 1 involvement of organic matrix in the precipitation process that may alter the partition coefficient of mg in biogenic calcite 2 controlled conversion of transient amorphous phases to calcite and 3 modification of the mg concentration in the parent solution from which the crystals precipitate the first two mechanisms are probably responsible for the precipitation of high mg calcite phases whole shell or sublayers while the third mechanism leads to the formation of low mg calcite phases we propose a model adapted from epithelial cells that allows massive mg2 removal from the biomineralization site this model is especially relevant to the planktonic and deep benthic low mg foraminifera that are frequently used for paleotemperature reconstructions we discuss the possible biological roles of mg in the shell in terms of the calcite polymorph conservation the in vivo chemical stability of the shell the functions of mg as a stabilizer of transient phases and as a controlling agent of the precipitation process several temperature sensitive biological processes that may influence the mg ca ratio of the shell are suggested and a model that combines biogenic and inorganic considerations is presented the model uses mg heterogeneity in the shell together with temperature response biologic and inorganic of biomineralization processes to account for the deviation of planktonic foraminifera from inorganic calcite at equilibrium with seawater

climatic changes in the aegean sea influence the eastern mediterranean thermohaline circulation 1986 1997 recent changes of water mass characteristics in the south aegean sea have considerably influenced the eastern mediterranean thermohaline circulation a combination of salinity increase 1987 92 and temperature drop 1992 94 caused massive dense water formation and strong outflow towards the deep and bottom parts of the eastern mediterranean this climatic shift the most important since the existence of observations in the basin is a combined effect of extreme meteorological events superimposed on large scale trends it has initiated a series of modifications in the hydrology and dynamics of the entire eastern mediterranean with possible influence on the mediterranean outflow in the north atlantic ocean

dynamic recrystallization and fabric development during the simple shear deformation of ice abstract in situ observations of polycrystalline ice deformed in simple shear between 10 and 1 c are presented this study illustrates the processes responsible for the deformation the development of a preferred crystallographic orientation and the formation of a preferred dimensional orientation intracrystalline glide on the basal plane accompanying grain rotations and dynamic recrystallization helps to accommodate the large intragranular strains these are the most important mechanisms for crystallographic reorientation and produce a stable fabric that favours glide on the basal plane localized kinks developed in grains unfavourably oriented for easy glide are unstable and are overprinted by dynamic recrystallization dynamic recrystallization is a strain softening process with nucleation occurring in the form of equiaxed grains that grow subparallel to pre existing grain anisotropies and become elongate during deformation plots of grain axial ratio against orientation r indicate a weak shape fabric which does not correspond to the theoretical foliation and elongation for the appropriate increment of shear strain we argue that estimates of the strain magnitude made from orientation of elongate grains are unreliable in high temperature shear zones these results are applicable to both geological and glacial shear environments

new insights into the formation of diagenetic illite from tem studies diagenetic illite from the proterozoic chuanlinggou formation china has been investigated using the techniques of transmission electron microscopy tem selected area electron diffraction saed x ray diffraction xrd scanning electron microscopy sem and energy dispersive spectrometer eds polytypes of 1 m d and 1 m illite coexist in the diagenetic illite the 1 m d polymorph is predominant in the 0 2 m size fraction which has high al and low mg contents and irregular crystal shapes lattice fringe imaging and one dimensional structural imaging show abundant structure defects the 1 m d illite has both layer and sheet terminations caused by edge dislocations and layer displacements along c caused by screw dislocations these observations indicate that the disordered 1 m d structure of the diagenetic illite resulted from abundant dislocations the dislocation serves as nucleation sites for the illite nano particles to spontaneously nucleate in the initial stage of illite formation such a nucleation process obeys the ostwald ripening rule the illite only shows a 1 0 nm thickness for each layer in high resolution tem images which suggests that the illite crystals have no mixed smectite layer and the 1 m d illites are authigenic and not illitized from smectite or illite smectite heterogeneous nucleation led to directly crystallization of the 1 m d illite during the initial growth of illite in shale under a low temperature and tectonic stress free environment the results have implications for interpreting the distribution of 1 m d illite in sedimentary rocks

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

monte carlo simulation of normal grain growth in 2 and 3 dimensions the lattice model independent grain size distribution the phenomenon of normal grain growth in pure single phase systems is modeled with the monte carlo technique and a series of simulations are performed in 2 and 3 dimensions the results are compared with natural and experimental monomineralic rock samples in these simulations various lattice models with different anisotropic features in grain boundary energy are examined in order to check the universality of the simulation results the obtained microstructure varies with the artificial parameter t in each lattice model where t means scaled temperature and controls thermal fluctuation on grain boundary motion as t thermal fluctuation increases the boundary energy anisotropy characterizing each lattice model becomes less important for the evolution of the microstructure as a result the difference in the grain size distribution among the lattice models which is significantly large for low t is reduced with increasing t the distribution independent of both the lattice model and the dimension is obtained at sufficiently high t and is very close to the normal distribution when carrying out the weighting procedure with a weight of the square of each grain radius a comparison of the planar grain size distribution of the natural and experimental rock samples with the 3 d simulation results reveals that the simulations reproduce very well the distributions observed in the real rock samples although various factors such as the presence of secondary minerals and a fluid phase which are not included in the simulation modeling are generally considered to influence the real grain growth behavior the good agreement of the distribution indicates that the overall grain growth behavior in real rocks may still be described by the simplified model used in the present simulations thus the grain size distribution obtained from the present simulations is possessed of the universal form characterizing real normal grain growth of which the driving force is essentially grain boundary energy reduction through grain boundary migration

phyllosilicates in very low grade metamorphism transformation to micas phyllosilicates produced mostly by weathering of magmatic metamorphic and sedimentary rocks are widespread in the surficial and near surface zones of the earth s crust these phyllosilicates display very fine grain sizes disordered crystal structures and greatly varying chemical compositions and they represent structurally and chemically metasable phases they are subjected to heat during diagenesis and concomitant metamorphism which provides a long life source of energy for transforming the metastable phases into thermodynamically more stable phases through a long series of partly continuous partly discontinuous reactions the present review summarizes some major mineralogical aspects of these processes with special reference to petrogenetic applications forty years have passed since the first petrogenetic application of the illite structural changes for characterizing diagenetic processes in sedimentary basins weaver 1960 weaver s sharpness ratio as well as kubler s 1964 1968 empirical illite crystallinity index have been easy to use x ray powder diffraction xrd measures of the manifold inter related changes that the hydrous mica like phyllosilicates experience during increasing burial in the first two decades after the introduction of the illite crystallinity concept it was applied to metamorphic petrogenetic studies in certain areas of europe especially to the external fold and thrust belts of the european alps variscides etc these studies were the starting point of important further developments which include awareness of the phyllosilicate transformations during deep burial in sedimentary basins hower et al 1976 inoue et al 1990 amouric and olives 1991 lanson and champion 1991 lindgreen and hansen 1991 eberl 1993 huang et al 1993 whitney and velde 1993 huggett 1995 elliott and matisoff 1996 nieto et al 1996 dong et al 1997 and recognition of the nature of interstratified clay minerals see reynolds and hower 1970 moreover using the theory of powder x ray powder diffraction e g

comparison of diagenetic and low grade metamorphic evolution of chlorite in associated metapelites and metabasites an integrated tem and xrd study chlorite is a common sheet silicate that occurs in various lithologies over a wide grade range involving diagenesis and low grade metamorphism thus the reaction progress of chlorite overs a unique oppor tunity for direct correlation of zonal classification of metasedimentary rocks based on illite crystallinity with metabasite mineral facies to provide such correlation chlorite crystallinity indices apparent mean crystallite sizes and lattice strains crystallite size distributions and compositions of chlorite from coexisting metapelites and metabasites were determined by x ray divraction xrd scanning electron microscopy sem transmission electron microscopy tem analytical electron microscopy aem and electron microprobe emp methods samples were from palaeozoic and mesozoic formations of the bukkium innermost western carpathians hungary that underwent alpine cretaceous orogenic metamorphism metapelites range in grade from late diagenesis to epizone whereas metabasites vary from prehnite pumpellyite through pumpellyite actinolite to greenschist facies despite significant diverences in composition mineral assemblages and textures reaction progress as measured in part by chlorite crystallinity in metapelites paralleled that in metabasites chlorite crystal linity and mean crystallite size increase and the proportion of mixed layers in chlorite decreases whereas the calculated lattice strain does not change significantly with increasing metamorphic grade similar trends but especially at higher grades significant diverences were found in mean crystallite size values using various methods for xrd line profile analyses the increase in crystallite size with increasing grade was demonstrated also by direct tem measurements on ion milled whole rock samples but with a larger scatter of data at higher grades in spite of the diverent kinds of mixed layering in chlorite mg rich smectitic mostly random local corrensite like units in metabasites and fe rich berthierine and diocta hedral smectite in metapelites xrd calculated and tem measured parameters were found to be reliable tools for measuring reaction progress and metamorphic grade of the same degree in both lithotypes

suspended sediment fluxes and transport processes in the gulf of lions submarine canyons the role of storms and dense water cascading contemporary suspended sediment transport was studied in seven submarine canyons of the gulf of lions gol current meters equipped with turbidity sensors were moored 4 m above bottom at 300 m depth in the canyon axis from november 2003 to may 2004 sediment transport events were monitored and studied in relation to forcing conditions there was a large flood in early december during which discharges from all of the coastal rivers increased by more than one order of magnitude a smaller flood of the rhone river occurred later in mid january followed by a persistent high river discharge that lasted until mid february there were also several e se storm events during the measurement period two of them causing large swell one in early december max hs 8 4 m coinciding with the major river flood andoneinlatefebruary maxhs 7m duringaperiodoflowerriverdischarge mostofthevariabilityindown canyoncurrentspeeds waslinkedtostrongdownwellinginducedbye sestormsandtocascadingofdenseshelfwaterinducedbynandnwwinds theintensity and timing of these processes strongly varied spatially eastern storms generated higher waves and induced stronger downwelling in the western than in the eastern sector of the gol shelf dense water cascading events were enhanced during eastern storms and they were also more intense in the western sector of the gol these events occurred frequently from january to may along the western canyons and from february to april along the eastern canyons from february to april they occurred simultaneously in all the canyons sediment transport was mainly down canyon and mostly concentrated during storm induced downwelling and dense water cascading events during the high river discharge season most of the newly supplied and resuspended sediment remained stored on theshelf however duringthelatefebruarystormandcascadingevent thestoredsedimentwasquicklyresuspendedandtransported mainly through the westernmost submarine canyon cap de creus following a flushing pattern later although minor storms and shelfdensewatercascadinghardlyincreasedsuspendedsedimentconcentrationswithinthecanyons theyinducedstrongnear bottom current velocities increasing down canyon sediment fluxes and generating small but significant sediment transport events most of the shelf canyon transfer took place during the late february storm and cascading event through the cap de creus canyon where the net suspended sediment flux was between one and two orders of magnitude higher than in the other canyons

effect of mica on the grain size of dynamically recrystallized quartz in a quartz muscovite mylonite abstract quartz ribbons in a quartz muscovite mylonite from the sunchang shear zone of south korea show a variation in the average size 25 107 m of dynamically recrystallized quartz depending on the fraction and dispersion of muscovite within the ribbons micas within the quartz ribbons occur both inside quartz grains and along their boundaries having a strong preferred orientation with the basal planes parallel to the mylonitic foliation micas or mica aggregates inside the quartz show a size range of 1 25 m whereas those along the quartz grain boundaries range from 2 to 98 m the average quartz grain size d calculated from three dimensional grain size distribution decreases drastically with increasing mica volume fraction f m up to f m 3 in the ribbons and further increases in the mica fractions above 3 result in only a little decrease with some fluctuation in the quartz grain size generating the equation of d 20 11 ln f m 9 64 with almost the same fraction of mica however the quartz ribbons with dispersed mica show a smaller quartz grain size than those with clustered mica indicating the importance of dispersion as well as fraction of second phase particles to the grain size of dynamically recrystallized quartz quartz c axes tend to have a random orientation with an f m 3 presumably due to the greater contribution to the total deformation of grain boundary sliding for quartz with a smaller grain size d

the role of atmospheric deposition in the biogeochemistry of the mediterranean sea abstract estimates of atmospheric inputs to the mediterranean and some coastal areas are reviewed and uncertainities in these estimates considered both the magnitude and the mineralogical composition of atmospheric dust inputs indicate that eolian deposition is an important 50 or even dominant 80 contribution to sediments in the offshore waters of the entire mediterranean basin model data for trace metals and nutrients indicate that the atmosphere delivers more than half the lead and nitrogen one third of total phosphorus and 10 of the zinc entering the entire basin measured data in sub basins such as the north western mediterranean and northern adriatic indicate an even greater proportions of atmospheric versus riverine inputs when dissolved fluxes are compared the form most likely to impinge on surface water biogeochemical cycles the atmosphere is found to be 5 to 50 times more important than rivers for dissolved zinc and 15 to 30 times more important for lead fluxes neglecting co limitation by other nutrients new production supported by atmospheric nitrogen deposition ranges from 2 4 g c m 2 yr 1 whereas atmospheric phosphorus deposition appears to support less than 1 g c m 2 yr 1 in spite of the apparently small contribution of atmospheric deposition to overall production in the basin it has been suggested that certain episodic phytoplankton blooms are triggered by atmospheric deposition of n p or fe future studies are needed to clarify the extent and causal links between these episodic blooms and atmospheric oceanographic forcing functions a scientific program aimed at elucidating the possible biogeochemical effects of saharan outbreaks in the mediterranean through direct sampling of the ocean and atmosphere before and after such events is therefore highly recommended

the distinction between caledonian burial and regional metamorphism in metapelites from north wales an analysis of isocryst patterns in snowdonia and ll n three prograde stages in metapelites gwna group to wenlock are recognized stage i with white mica crystallinity values 0 43 2 stage ii 0 43 0 26 2 stage iii isocrysts at 0 03 2 intervals are drawn separately for pelites above and below the sub arenig unconformity approximately concordant isocryst patterns characterize the unconformity in the northwestern and southeastern limbs of the snowdonia syncline whereas discordant patterns are developed northwest of the aber dinlle fault and at the closure of the ynyscynhaiarn anticline the contrasting patterns are the result of a pre arenig burial metamorphism in post tremadoc pelites belts of steep metamorphic gradient coincide with belts of high strain and a broad area of higher grade caradoc pelites coincides with the core of the snowdonia syncline the later metamorphism is related to caledonian deformation rather than to burial pelite alteration adjacent to small intermediate to acid plutons suggests emplacement before the caledonian regional metamorphism a close correlation exists between metabasite zones and metapelite stages

a transmission electron microscope study of white mica crystallite size distribution in a mudstone to slate transitional sequence north wales uk high resolution transmission electron microscopy hrtem measurements of the thickness of white mica crystallites were made on three pelite samples that represented a prograde transition from diagenetic mudstone though anchizonal slate to epizonal slate crystallite thickness measured normal to 001 increases as grade increases whereas the xrd measured 10 a peak profile the kubler index decreases the mode of the tem measured size population can be correlated with the effective crystallite size n 001 determined by xrd the results indicate that the kubler index of white mica crystallinity measures changes in the crystallite size population that result from prograde increases in the size of coherent x ray scattering domains these changes conform to the scherrer relationship between xrd peak broadening and small crystallite size lattice strain broadening is relatively unimportant and is confined to white mica populations in the diagenetic mudstone rapid increases in crystallite size occur in the anchizone coincident with cleavage development changes in the distribution of crystallite thickness with advancing grade and cleavage development are characteristic of grain growth by ostwald ripening the kubler index rapidly loses sensitivity as an indicator of metapelitic grade within the epizone

simulation of fabric development in recrystallizing aggregates ii example model runs abstract this study investigates the role of the coupling of dynamic recrystallization and lattice rotations in fabric development a new two dimensional computer simulation of polycrystalline deformation is used which combines homogeneous straining internal lattice rotations and dynamic recrystallization processes five example runs of the simulation are described here which compare the progressive development of fabrics resulting from different recrystallization regimes and different straining geometries it is found that these fabrics can evolve significantly with progressive strain from one strong fabric pattern to another the effect of recrystallization is not only to create point maxima concentrations of c axes but also to modify and create girdle distributions correlations are made between the fabrics generated by this model and previously reported quartz and ice fabrics

diagenetic and low grade metamorphic terranes of gaspe peninsula related to the geological structure of the taconian and acadian orogenic belts quebec appalachians illite crystallinity ic measurements determination of the proportion of 2m mica polytypes and organic matter reflectance measurements establish regional diagenetic low grade metamorphic trends for the taconian and acadian belts of gaspe peninsula ic varies as a function of many factors besides maximum burial temperature and heating time correlation between ic and 2m illite polytypes for the fortin group and temiscouata formation suggests i that the amount of high grade detrital mica in the samples is low and ii that ic can be used with some confidence as an estimator of regional thermal maturation levels correlation of these parameters with available organic reflectance values further supports this assumption the illites of the temiscouata and western fortin groups are mostly phengitic in composition whereas in the eastern outcrop belt they are more mg and fe rich celadonitic but generally also of lower grade and lower 2m content the d 060 values for illites measured on the unorientated 2 m fraction of samples fall between 1 502 and 1 503 a range 1 500 1 504 a indicating relatively low octahedral occupancy by mg and fe between one fifth and one third of the available spaces pyrophyllite and paragonite were not detected chlorites are fe rich and ripidolitic the ic map for the acadian belt of the peninsula displays general congruence between ic contours 2200 sample points and structural trends for the 27 000 km2 area the highest grades anchimetamorphic are associated with the oldest rocks honorat and matapedia groups exposed in the cores of major anticlines anchimetamorphic grades associated with the western outcrop belt of the lower devonian fortin group require 7 8 km of subsidence to accommodate sufficient thickness of overlying younger rocks on top of 4 5 km of fortin group deep water clastics to explain the grades in terms of burial metamorphism assuming a geothermal gradient of 30 c km 1 the lowest grade diagenetic rocks occupy a large area in the northeastern part of the peninsula smaller areas in the northwestern part of the acadian belt in the centre of chaleurs bay synclinorium and in the ordovician mictaw group the contact between the taconian and acadian belt is marked by a distinct maturation discontinuity the grand pabos fault juxtaposes rocks of contrasting maturation levels matapedia group against fortin group in the west but shows no maturation offset further east in the honorat group the fault zone limiting the fortin group in the north is also associated with a major ic jump

a microstructural sequence of quartz schists in central shikoku south west japan abstract this paper describes a microstructural sequence of quartz schists metamorphosed chert in the asemi river region of the sambagawa metamorphic terrain in central shikoku southwest japan the asemi river region is divided into three areas on the basis of characteristics of microstructures of quartz schists observed under the optical microscope areas i ii and iii in ascending order of metamorphic grade microstructures in area i consist of finer equant equidimensional and polygonal quartz grains free from internal deformation features microstructures in area ii are characterized by oblate or elliptical grains with remarkable undulatory extinction surrounded by serrated grain boundaries microstructures in area iii consist mainly of coarser and equant grains without distinct internal deformation features the formation conditions of these microstructures are discussed in the light of recent experimental results

vertical distribution of mesozooplankton and its δ15n signature at a deep sea site in the levantine sea eastern mediterranean in april 1999 1 mesozooplankton samples were collected throughout the water column in the 4270 m deep ierapetra basin 30 nm se off crete in april 1999 information on trophic relationships within mesozooplankton size classes 0 5 0 5 1 1 2 and 2 5 mm and the sources of diet were obtained by measuring the composition of stable nitrogen isotopes of size fractionated zooplankton and particles collected by sediment traps compared to data from the arabian sea the 15n values of zooplankton were markedly lower in the levantine sea data from the upper 250 m 2 3 suggest that n2 from the atmosphere was used by diazotroph cyanophycea as a nitrogen source for primary production a loop system is hypothesized by which isotopically light nh4 is recycled and used by phytoplankton in the deep mesopelagic zone an increase in 15n with increasing depth was observed in the deep bathypelagic zone the 15n values were more or less stable and indicate a trophic level of 2 5 a first zooplankton analysis revealed that juveniles of the calanoid copepod lucicutia longiserrata one of the rare true deep sea species in the levantine basin were predominant in this zone the taxonomic composition as well as the vertical distribution of zooplankton in the large habitat zones resembled that in january 1987 before the onset of a hydrological shift in the eastern mediterranean we therefore suggest that the situation in april 1999 does not characterize the mode of nitrogen transfer during the emt

the relationship between shell size and mg ca sr ca δ18o and δ13c of species of planktonic foraminifera the relationship between shell size and mg ca sr ca 18o and 13c of planktonic foraminiferal calcite has been investigated using seventeen species in six different size fractions mg ca increases and sr ca decreases with increasing size except for two globorotaliid species which show the opposite trend the changes in mg ca broadly follow 18o calcification temperatures except that surface and near surface dwelling species show larger changes in mg ca than can be accounted for by differences in calcification temperature derived from 18o the increases in mg ca and decreases in sr ca vary linearly with the well established increase in 13c with size this is consistent with smaller individuals calcifying faster than larger individuals and larger individuals forming calcite that more closely reflects seawater temperature and composition it appears that variations in calcification rate affect mg and sr shell chemistry the observations may account for part of the temporal variability in foraminiferal sr ca within a single size fraction that has been attributed to changes in seawater sr ca

shearing during progressive retrogression in granitoids abrupt grain size reduction of quartz at the plastic brittle transition for feldspar the kashio shear zone chubu district japan affects the southeast margins of the ryoke granitic plutons as well as the ryoke metasedimentary rocks and is truncated by the median tectonic line near the shear zone centre coarse quartz grains within the granitic rocks have been dynamically recrystallized to quartz aggregates towards the pluton margins the grain size data show an abrupt reduction from various sizes 59 148 m to a steady state size around 35 m at approximately 400 m from the boundary of the granitic plutons without any tectonic boundary such as a fault being present this abrupt grain size reduction accompanies brittle deformation in feldspar that overprints earlier plastic deformation and develops strong mylonitic fabrics in contrast feldspar away from the pluton margins contains only weak microstructural evidence for plastic deformation and still locally preserves magmatic polycrystal structures amongst the inhomogeneously recrystallized quartz grains these features combined with an isochronological study suggest that the kashio shear zone began at high temperature 450 c as a ductile event that affected relatively wide regions in the ryoke granitic plutons before rapid cooling by ca 70 ma at this latter stage strong mylonitization at lower temperatures 300 c in a semiductile regime occurred in a narrow zone towards the shear zone centre here recrystallized quartz aggregates reached a steady state grain size by ca 60 ma that is cooling within the granitic plutons resulted in strain localization with the abrupt grain size reduction of quartz aggregates correlating with the plastic brittle transition of feldspar

calibration of the anchizone a critical comparison of illite crystallinity scales used for definition instrumental settings for determination of illite muscovite crystallinity half height width of the 10 a x ray diffraction peak and the limits of the anchimetamorphic zone adopted by various authors fall into several groups the variation in the limiting peak widths between the authors that have adopted kubler s neuch tel boundary values of 0 42 and 0 25 2 can be interpreted in terms of variation in the instrumental settings the choice of time constants higher than those given by the formula causes peak broadening this effect is particularly marked at high scan rates the peak broadening is by constant increments that are virtually independent of the absolute peak width the differences between the kubler neuch tel derived limiting values and some other scales are appreciably greater than can be accounted for by these differences in instrumental settings many of these scales are not equivalent in particular the limits adopted by dunoyer de segonzac 1969 and subsequent workers at strasbourg are too broad their anchizone represents a range of grades of metamorphism lower than that of kubler widely overlapping the latter s diagenetic zone those adopted by some other mainly french authors are too narrow the limits of the anchizone should be calibrated by inter laboratory standards and the instrumental settings should be specified in full

formation of corrensite chlorite and chlorite mica stacks by replacement of detrital biotite in low grade pelitic rocks transmission and scanning electron microscopy were utilized to investigate the nature and mechanisms of alteration of abundant detrital biotite of volcanic origin and progressive modification of phyllosilicate aggregates in a prograde sequence of pelitic rocks illite crystallinity index 0 19 0 58 a28 from the gasp6 peninsula in quebec detrital biotite has been diagenetically altered to form corrensite and chlorite through two mechanisms 1 layer by layer replacement gave rise to interstratification of packets of layers and complex mixed layering via several kinds of layer transitions between biotite and chlorite corrensite or smectite 2 dissolution transport precipitation resulted in the formation of relatively coarse grained aggregates of randomly orientated corrensite rich flakes and fine grained corrensite intergrown with chlorite and illite in the matrix the data show that stacks consisting of alternating packets of trioctahedral and dioctahedral phyllosilicates originated during early diagenesis when lenticular fissures in strained altering biotite were filled by dioctahedral clays subsequent prograde evolution of dioctahedral clays occurred through deformation dissolution and crystallization and overgrowth illite evolved to muscovite with k in part provided through biotite alteration and corrensite chlorite to homogeneous chlorite the alteration of detrital biotite is closely related to the formation of titanite and magnetite in diagenetic rocks and pyrite calcite and anatase or rutile in the higher grade rocks the observations demonstrate that detrital biotite of volcanic origin may be the principal precursor of chlorite in chlorite rich metapelites originating in marginal basins the mineral parageneses suggest that the transitions from corrensite to chlorite and illite to muscovite may be a function of local chemistry and time