world s highest tides hypertidal coastal systems in north america south america and europe abstract hypertidal systems can be defined as areas where spring tides have ranges greater than 6 m these very high tidal ranges results in unique patterns of sedimentation within hypertidal estuaries such systems are not common but they do occur on a number of continents this report will discuss six areas that have the highest tides in the world north america hypertidal systems occur within cook inlet in alaska usa leaf basin in ungava bay quebec province canada and the bay of fundy nova scotia and new brunswick canada in south america the straits of magellan and associated atlantic coastal settings exhibit hypertidal conditions european hypertidal systems include bristol channel and severn estuary in southwest england and the gulf of st malo in normandy france these six areas have the highest tides in the world and spring tidal ranges that regularly exceed 10 m all the six areas can be divided into intertidal sedimentological zones zone 1 is the outermost zone and contains longitudinal bars zone 2 exhibits laterally extensive sand flats zone 3 includes the innermost extent of tides and estuarine point bars annual and neap spring cycles have been documented in zone 3 and are probably the most indicative features of hypertidal systems the north american systems occur in high latitude cold climates where winter ice can have a minor or major impact on the development of sedimentary facies conversely the european and patagonia systems have climates minimal ice formation

characterization of an early metamorphic stage through inclusions in zircon of a diamondiferous quartzofeldspathic rock from the erzgebirge germany about 1000 zircon grains from a diamondiferous quartzofeldspathic rock of the saxonian erzgebirge were investigated for inclusions using optical microscopy and confocal laser raman spectroscopy cathodoluminescence imagery was applied to characterize the growth zone of zircon where the inclusions occurred the most abundant inclusion minerals are microdiamonds coesite was not detected however garnet and jadeite occur as rare inclusions in zircon cores where diamonds are lacking jadeite was detected for the first time in quartzofeldspathic rocks from the crystalline complex of the erzgebirge the compositions of the pristine garnets in the zircons are similar to those of core areas of millimeter sized garnets but the original garnet composition of the early metamorphic stage is only preserved in zircon intracrystalline diffusion at temperatures as high as 1000 c resulted for instance in higher ti concentrations in garnet cores compared with garnet enclosed in zircon rutile quartz and the compositions of jadeite and garnet inclusions in zircon and of phengite inclusions in cores of large garnets were applied for geothermobarometry the results related to an early metamorphic stage are 650 c and 18 kbar which represent conditions at the base of a thickened continental crust before deeper subduction

perpotassic granulites from southern bohemia garnetiferous perpotassic granulites associated with voluminous felsic calc alkaline garnet kyanite granulites in the blansk les massif are described as a new rock type a k2o content near 13 wt zr content ranging from 17 to 5877 ppm primary ca mg fe garnet pyrope up to 33 mol and the absence of primary plagioclase and quartz characterize the new type of granulite calcium is incorporated only in garnet and apatite owing to the content of garnet the bulk syenitic compositions are metaaluminous to peraluminous the perpotassic granulites are accompanied by subordinated melanocratic perpotassic granulite and alkali feldspar melanocratic granulite containing up to 20 vol quartz these rock types also contain highly variable amounts of zircon high pressure noneutectic partial melting of crustal rocks and crystallization under upper mantle conditions is suggested as the main process in generation of perpotassic granulites a polyphase ductile to brittle deformation and recrystallization in pyroxene granulite and later in amphibolite facies accompanied obduction of the granulite massif which carries numerous enclaves of pyrope peridotite euhedral equant zircon crystals up to 4 mm long enclosed in large garnet crystals and in the alkali feldspar matrix of perpotassic granulite represent a uniform high temperature population with a nearly concordant u pb system aftalion et al 1989 the hercynian age of this zircon indicates the role of the hercynian anatexis of crustal rocks under upper mantle conditions in generation of granulites in the moldanubian zone of the bohemian massif

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

the geochemistry of carbonate replacement pb zn ag mineralization in the lavrion district attica greece fluid inclusion stable isotope and rare earth element studies strata bound carbonate replacement pb zn ag deposits in the lavrion district greece are spatially related to a late miocene granodiorite intrusion 7 10 ma and various sills and dikes of mafic to felsic composition the plaka granodiorite contains porphyry molybdenum mineralization and is locally associated with a ca fe skarn carbonate replacement deposits occur predominantly in marbles upper and lower marble of the basal unit kaesariani schists and along a major detachment fault that separates the basal unit from the upper unit orebodies are mainly strata bound carbonate replacement although sulfides also occur in veins the mineralogy of carbonate replacement deposits is dominated by base metal sulfides and sulfosalts of ag bi sn sb as and pb particularly at plaka and kamariza carbonates are intergrown with earlier formed sulfides and sulfosalts but are more abundant late in the paragenetic sequence with fluorite and barite fluid inclusion studies of sphalerite fluorite calcite and quartz in carbonate replacement deposits suggest that they were deposited from 132 to 365 c from co2 poor low to high salinity fluids 1 20 wt nacl equiv carbon and oxygen isotope compositions of calcite 13c 15 6 to 1 5 and 18o 9 2 to 17 3 intergrown with sulfides reflect variable exchange of the ore bearing fluid with the upper and lower marbles and proximity to the plaka granodiorite post archean australian shale paas normalized rare earth and yttrium patterns of the upper and lower marbles and calcite intergrown with sulfides show positive eu and negative ce anomalies as well as y ho ratios between 40 and 80 normalized rare earth and yttrium patterns of fluorite also have positive eu and negative ce anomalies such anomalies for both the carbonates and fluorite reflect the high ph or high f o2 conditions of the late stage hydrothermal fluids and the likely derivation of calcium from marine carbonates precursors of the upper and lower marbles the range of sulfur isotope compositions for sulfides 34s 4 9 to 5 3 with one outlier of 9 4 in carbonate replacement and vein deposits is due likely to a magmatic sulfur source with a contribution of reduced seawater sulfate sulfur isotope compositions of barite from carbonate replacement range from 34s 17 2 to 23 7 per mil and reflect miocene seawater sulfate values if a magmatic source of sulfur is assumed along with an average temperature of 250 c for the ore forming fluids as based on fluid inclusion studies sulfides in carbonate replacement deposits were deposited at values of log f o2 41 to 36 and a ph 5 8 to 9 1 however the range of sulfur isotope values does not rule out the possibility that sulfur in sulfides could have been produced by the reduction of seawater sulfate with no contribution from a magmatic source the carbonate replacement deposits resemble manto type sulfide deposits in mexico central colorado south korea nevada and northern greece

interface coupled dissolution reprecipitation in garnet from subducted granulites and ultrahigh pressure rocks revealed by phosphorous sodium and titanium zonation garnet zonation provides an unparalleled record of the pressure temperature time fluid evolution of metamorphic rocks at extreme temperature conditions 900 c however most elements preserve little zonation due to intracrystalline diffusional relaxation under these conditions slowly diffusing trace elements including p na and ti have the best chance of recording metamorphic histories here we map dramatic zoning patterns of these elements in subducted high pressure felsic granulite saxon granulite massif and ultrahigh pressure diamondiferous saidenbachite saxonian erzgebirge bohemian massif the results show that garnet replacement via interface coupled dissolution reprecipitation can strongly affect garnet compositions in subduction zones and that p na and ti record burial and exhumation histories that are otherwise lost to diffusion in these samples p diffuses the slowest and ti the fastest

the effect of fluid and deformation on zoning and inclusion patterns in poly metamorphic garnets within the bergen arcs of w norway caledonian eclogite facies assemblages t 650 c p 15 kbar have formed from grenvillian granulites t 800 900 c p 10 kbar along shear zones and fluid pathways garnets in the granulites grti pyr56 40 alm45 25gro19 14 are unzoned or display a weak ca 1 wt feo over 1000 m zoning the eclogite facies rocks contain garnets inherited from their granulite facies protoliths these relict garnets have certain areas with compositions identical to the garnets in their nearby granulite but can be crosscut by bands of a more almrich composition grtii pyr31 41alm40 47gro17 21 formed during the eclogite facies event these bands orientated preferentially parallel or perpendicular to the eclogite foliation may contain mineral filled veins or trails of eclogite facies minerals omphacite amphibole white mica kyanite quartz and dolomite steep compositional gradients up to 9 wt feo over 40 m separate the two generations of garnets indicating limited volume diffusion the bands are interpreted as fluid rich channels where element mobility must have been infinitely greater than it was for the temperature controlled volume diffusion at mineral interfaces in the granulites the re equilibration of granulite facies garnets during the eclogite facies event must therefore be a function of fracture density deformation and fluid availability the results cast doubts on modern petrological and geochronological methods that assume pure temperature controlled chemical re equilibration of garnets

grain scale pressure variations and chemical equilibrium in high grade metamorphic rocks in the classical view of metamorphic microstructures fast viscous relaxation and so constant pres sure is assumed with diffusion being the limiting factor in equilibration this contribution is focused on the only other possible scenario fast diffusion and slow viscous relaxation and brings an alter native interpretation of microstructures typical of high grade metamorphic rocks in contrast to the pressure vessel mechanical model applied to pressure variation associated with coesite inclusions in various host minerals a multi anvil mechanical model is proposed in which strong single crystals and weak grain boundaries can maintain pressure variation at geological time scales in a polycrystalline material in such a mechanical context exsolution lamellae in feldspar are used to show that feldspar can sustain large differential stresses 10 kbar at geological time scales furthermore it is argued that the existence of grain scale pressure gradients combined with diffusional equilibrium may explain chemical zoning preserved in reaction rims assuming zero net flux across the microstructure an equilibrium thermodynamic method is introduced for inferring pressure variation corresponding to the chemical zoning this new barometric method is applied to plagioclase rims around kyanite in fel sic granulite bohemian massif czech republic yielding a grain scale pressure variation of 8 kbar in this approach kinetic factors are not invoked to account for mineral composition zoning preserved in rocks metamorphosed at high grade

stability limits of hydrous minerals in sediment and mid ocean ridge basalt compositions implications for water transport in subduction zones phase relationships in hydrated natural sediment and mid ocean ridge basalt morb compositions were investigated experimentally from 6 to 15 gpa and 700 c to 1400 c in order to determine the stability of hydrous phases in subducting slabs and to constrain reactions resulting in the release of water from subduction zones to the mantle phengite and hydrous aluminum silicates topaz oh and phase egg are stable in the sediment composition at depths greater than 150 km and constitute h2o reservoirs similarly lawsonite is an h2o reservoir in morb composition at depths greater than 150 km according to mass balance calculations based on experimental run products the weight proportions of phengite and h2o at 6 gpa in the sediment are about 50 and 2 respectively at pressures from 8 to 12 gpa topaz oh al2sio4 oh 2 appears as the hydrous mineral and the sediment retains about 0 5 0 7 wt h2o at higher pressures phase egg alsio3 oh appears as the hydrous phase with a large stability field the h2o content in the sediment is about 0 5 wt at pressures greater than 12 gpa in natural morb compositions lawsonite is the hydrous phase at pressures lower than 10 gpa about 1 wt h2o in the morb composition is retained by lawsonite at 6 gpa and 800 c above 6 gpa a lawsonite out reaction is controlled by compositional changes of garnet and clinopyroxene if the oceanic crust descends with an overlying sediment layer water can be carried down into the transition zone by the sediment the amount of transported water is controlled by the chemical compositions of the subducting sediments water in the morb layer can be stored to 300 km in lawsonite for a cold subduction zone geotherm water release at depths greater than 200 km through progressive lawsonite breakdown can hydrate the overlying mantle causing the generation of a peridotite region including hydrous phases chondrodite clinohumite phase a and phase e if this hydrous peridotite is dragged down by the descending oceanic crust water can be transported into the transition zone by the subduction process the amount of transported water is controlled by the thermal state of the slab and the chemical composition of morb

alpe arami a peridotite massif from depths of more than 300 kilometers the abundance of fetio 3 and chromite precipitates in olivine of the alpe arami peridotite massif switzerland requires a much higher solubility for highly charged cations than is found in mantle xenoliths from depths of 250 kilometers three previously unknown crystal structures of fetio 3 were identified that indicate that the originally exsolved phase was the high pressure perovskite polymorph of ilmenite implying a minimum depth of origin of 300 kilometers these observations coupled with the unique lattice preferred orientation of olivine further suggest that the original composition of olivine may reflect that of a precursor phase perhaps wadsleyite that is stable only at depths greater than 400 kilometers

high p granulites of the songshugou area qinling orogen east central china petrography phase relations and u pb zircon geochronology high pressure hp granulites provide telling records of mineral reactions at upper mantle to lower crustal levels and key information on the fate of material in subduction systems the latter especially applies when they abut eclogite and mantle dunite because such rock associations are crucial for understanding the incompletely known processes at the interface of converging plates a continental arc active c 520 395 ma ago formed an enigmatic example of such a rock association in the songshugou area qinling orogen to unravel the juxtaposition of the distinct rocks this study combines petrography phase equilibria modelling conventional thermobarometry and zircon u th pb ti ree analysis two mafic hp granulites which contain the mineral assemblages garnet clinopyroxene plagioclase rutile mesoperthite quartz and garnet clinopyroxene plagioclase rutile experienced peak metamorphic conditions of 1 4 gpa 860 c and 1 3 gpa 910 c respectively during decompression and cooling at 489 4 ma amphibole lamellae unmixed from a clinopyroxene solid solution and orthopyroxene in part replaced garnet a felsic hp granulite shows equilibration of garnet perthite antiperthite kyanite quartz and rutile at 810 860 c 1 2 gpa sillimanite growth during decompression and upper amphibolite facies cooling at 510 4 ma though the thermobarometric data are just within the methodological errors the u pb zircon ages imply the hp granulites did not evolve coherently the hp granulites either represent foundered lower arc crust or originated from subduction erosion because their geochemistry is indistinguishable from that of the hanging wall plate published and new pressure temperature time deformation paths converge at 710 c 0 9 gpa and 470 ma implying exhumation tectonics juxtaposed the hp granulites with a melange of eclogite and mantle dunite at lower crustal levels this study highlights that lower arc crust can comprise material of diverse evolution

microdiamond daughter crystals precipitated from supercritical coh silicate fluids included in garnet erzgebirge germany microdiamonds associated with phlogopite quartz paragonite phengite apatite and rutile are found as regular constituents of minute polyphase inclusions in garnet of ultrahigh pressure p metamorphic gneiss lenses within migmatites of the gneiss eclogite unit erzgebirge germany these aggregates are interpreted to represent original inclusions of a supercritical dense coh fluid rich in k na and sio 2 from this fluid diamond was precipitated as a daughter crystal due to cooling at ultrahigh p conditions brittle failure of the garnet host due to overpressure during release of confining pressure is demonstrated by healed radial cracks during further cooling the silicate phase assemblage of the inclusions crystallized at reduced internal pressures outside the stability field of diamond as indicated by the presence of quartz paragonite and plagioclase it is proposed that the mica dominated mineral assemblage of the inclusions formed by reaction between the fluid and the garnet host the previously formed diamond daughter crystals being preserved metastably these diamond bearing inclusions provide an unequivocal record of dense supercritical coh fluids rich in alkalies and silica within subducted continental crust during ultrahigh p metamorphism

sub critical fracture and associated retrogression of garnet during mylonitic deformation garnets from the alpine fault mylonites are fractured most fractures have a retrogressive fracture fill a small number have garnet fill a detailed sem study has been carried out to elucidate the mechanisms of fracture and associated retrogression wide fracture zones contain free floating islands of garnet in a retrogressive matrix electron channelling patterns show that segments of garnet across such fracture zones rarely show any relative rotations where rotations are observed they are small and systematic some large fractures show clearly that fracture and retrogression occurs by a replacement process fracture surface morphologies are indicative of surface dissolution a model is established where crack tips advance by a process of dissolution at a high stress crack tip whilst precipitation occurs as the tip and its associated stress field advance precipitation of retrogressive fracture fill occurs if fracture occurs out of the field of stability of garnet

calcium depletion halos and fe mn mg zoning around faceted plagioclase inclusions in garnet from a high grade pelitic gneiss

macrotidal subarctic environment of turnagain and knik arms upper cook inlet alaska sedimentology of the intertidal zone abstract an extensive sheet of silty sand crossed by tidal channels is exposed at low tide in turnagain and knik arms alaska transportation and deposition of sediment composing this sheet is the result of strong tidal currents due to the maximum spring tidal range of approximately 11 4 m in turnagain and knik arms the initiation of the floodtide is accompanied by the occurrence of a tidal bore that travels at a speed of 4 m sec or more up the tidal channels in intertidal environments in many parts of the world physical processes of sedimentation are typically influenced by surface fauna sedimentary structures in some zones are altered or obliterated by the activities of the infauna however in turnagain and knik arms virtually no macrofauna exist and so the area provides an opportunity to study depositional processes and sedimentary structures without the masking effects of bioturbation suspended sediment values for turnagain and knik arms are greatest in the summer months and nearest low tide stages ice floes form during winter months and in combination with the freezing of intertidal sediment to several meters of depth have a significant effect on sediment dispersal and on the deepening and increased stability of the tidal channels the intertidal sediment is mainly very well sorted medium to very fine sand and coarse silt with a notable paucity of gravel coarse sand and clay sediment accumulates in sandbars oriented parallel to the axis of the estuary textural and facies patterns reflect decreasing current energy first as a function of distance from the mouth of the estuary and second as a function of topographic elevation on the sandbars the intertidal deposits in turnagain arm contain a transitional upward fining sequence which is analogous to point bar and channel bar successions described by other workers the base of the sequence contains parallel laminated sand that is overlain by mixed parallel and cross laminated silty sand overlain by cross laminated silty sand at the top of the sequence is a unit of organically rich parallel laminated silt and sandy silt this suite of sedimentary features and textures indicates changing current velocities and directions as bars emerge or are modified during ebb tide and the vertical sequences could potentially be used to record intertidal bar erosion and aggradation by point and channel bar migration a process carried out primarily by bed load currents

precipitation of rutile and ilmenite needles in garnet implications for extreme metamorphic conditions in the acadian orogen u s a we report the discovery of oriented needles of rutile and ilmenite in garnet crystals from granulite facies metapelitic rocks of the merrimack synclinorium connecticut and present a precipitation model for their origin the rocks were strongly metamorphosed and deformed during the devonian acadian orogeny the needles are primarily elongated parallel to in garnet rutile has anomalous extinction angles as great as 35 cf griffin et al 1971 rutile and ilmenite needles are typically a few hundred nanometers to several micrometers in diameter and are several tens of micrometers to nearly a millimeter long other oxide inclusions that may be present include submicrometer to micrometer scale twinned rutile bicrystals as well as srilankite and a crichtonite group mineral some garnet cores have unusual box shaped quartz inclusions which coexist with ti fe oxide needles and commonly contain micrometer scale rods of f oh cl apatite negative garnet crystal pores are also widespread ti fe oxide needles are restricted to garnet core regions rims have a distinctly different inclusion population dominated by granulite facies minerals including sillimanite spinel cordierite and k feldspar consequently the garnet core regions represent an earlier distinct period of growth relative to the rims garnet cores contain 25 35 pyrope and a host of minor and trace constituents including tio2 0 07 0 6 wt cr2o3 0 01 0 10 wt na2o 0 01 0 03 wt p2o5 0 01 0 09 wt and zro2 up to 150 ppm na2o and zro2 correlate positively with tio2 titanium zoning is preserved in some garnets zoning profiles and two dimensional chemical mapping show that ti and to a lesser degree cr are depleted around ti fe oxide inclusions therefore we conclude that the needles are precipitates that formed from ti bearing garnet during exhumation and cooling garnet contained sufficient ti to form precipitates no ti source external to garnet was necessary titanium bearing garnets that contain oriented ti fe oxide needles are known primarily from ultrahigh pressure metamorphic rocks mantle peridotites and pyroxenites and high pressure granulites thus the presence of needle bearing garnets in connecticut strongly suggests that a previously unrecognized domain of extreme pressure and or temperature metamorphism exists in the acadian orogen

comment and reply on metasomatic origin for fe ti rich multiphase inclusions in olivine from kimberlite xenoliths comment richard l hervig center for solid state science arizona state university tempe arizona 85287 1704 drury and van roermund 1988 reported the observation by trans mission electron microscopy of fe ti rich multiphase microinclusions in olivines from hot deformed garnet iherzolites found in kimberlite they suggested that this is caused by infiltration metasomatism and that micro probe analyses of these olivines which show high trace element contents are not indicating the solid solution components in olivine in equilibrium with coexisting orthopyroxene clinopyroxene and garnet it is agreed that trace element enrichment probably resulted from an enrichment event s and that the observed chemistry is probably not representative of the upper mantle however the chemistry of these olivines represents an equilibrium relation with the other phases thus the textures observed by drury and van roermund 1988 are best explained as exsolution phenomena that occurred some time after enrichment and homogenizatio the phasesn of a compilation of trace element chemistry as determined by electron and ion probe microbeam analytical techniques in several types of mantle derived nodules was given in hervig et al 1986 they showed that the olivines from hot deformed hd garnet iherzolites generally stand out from other upper mantle olivines among the hd samples are the highest ai2o3 v2o3 and na20 contents of any olivine and they commonly show the highest concentrations of ti cr sc and li i empha size that this increase is not arbitrary from sample to sample but is in consonance with the chemistry of coexisting phases the electron and ion probe analyses were made on 20 30 ij m spots and most likely over lapped on the multiphase microinclusions these inclusions show a bimo dal size distribution 0 05 m and 0 2 1 m drury and van roermund 1988 the microbeam analyses presumably represent a random mixture of olivine and inclusions iron contents the iron content of phases from hd garnet iherzolites is generally higher than in undeformed cooler garnet iherzolites however the fe mg relations between the hd minerals are those expected for an equilibrium assemblage and a geothermometer based on fe mg exchange between olivine and garnet gives temperatures in general agreement with the more commonly used two pyroxene geothermometer see review by finnerty and boyd 1984 sodium chromium aluminum vanadium and scandium a metasomatic event might not add enough iron to change signifi cantly the composition of the minerals in garnet lherzolite so it is more revealing to study the trace element composition of these phases not only is the na content of hd olivine high up to 400 ppm na20 but also the orthopyroxenes show up to 0 4 wt na20 significantl higher thay n typi cal low temperature garnet lherzolite orthopyroxene hervig and smith 1980 discovered that the logarithm of the molar ratio na20

crystallographic orientation relationships in host inclusion systems new insights from large ebsd data sets crystallographic orientation relationships cors between mineral inclusions and their hosts could potentially deliver information about inclusion formation processes and conditions most previous studies are based on small numbers of analyses this paper uses ebsd to study host inclusion cors in an inclusion rich permian metapegmatite garnet koralpe region eastern alps austria demonstrating the importance of large data sets and of ebsd in particular for the analysis of cors the distribution of measured orientations reflects host garnet point group symmetry for 89 of inclusions analyzed total n 530 each inclusion phase rutile corundum and ilmenite shows at least three different cors to host garnet statistical cors are introduced to describe distributions of inclusion orientations that have one or two degrees of freedom with respect to the host but still reflect host crystal symmetry two end member characteristics of statistical cors are distinguished rotation and dispersion most statistical cors observed show a mixture of both each inclusion phase shows at least one statistical cor multiple coexisting cors and statistical cors are not restricted to rutile re examination of previous garnet rutile cor studies in light of the new results indicates that cor information may have been overlooked when using small data sets variation in cor parameters correlates with broad differences in assumed metamorphic conditions for new and literature samples suggesting that petrogenetic information may be available if cor formation can be understood the favorability of the detected cors cannot be explained by a simple model involving minimization of misfit between lattice planes implying that other interface properties or the inclusion formation mechanism are important controls on cor development

garnet yield strength at high pressures and implications for upper mantle and transition zone rheology 1 garnet helps control the mechanical behavior of the earth s crust mantle and transition zone here measurements are presented suggesting that garnet long considered to be a high viscosity phase is actually weaker than the other dominant components in the transition zone the mechanical behavior of garnet at high pressures was examined using radial diffraction techniques in the diamond anvil cell the yield strength of grossular garnet was inferred from synchrotron x ray measurements of differential lattice strains the differential stress was found to increase from 1 3 0 6 gpa at a hydrostatic pressure 5 8 1 1 gpa to 4 1 0 4 gpa at 15 7 1 0 gpa where it was level to 19 gpa the strength results are consistent with inferred strength values for majorite garnet from measurements in the diamond cell normal geometry bolstering the idea that garnet structured materials may all have similar strengths in this low temperature high differential stress regime garnet is shown to be significantly weaker than anhydrous ringwoodite and to have a strength similar to hydrous ringwoodite this result suggests that the presence of water in the transition zone may not be required to explain a weak rheology and therefore models of transition zone behavior built assuming that garnet is the high strength phase may need to be revised

a counterclockwise p t path for anatectic pelites south central massachusetts pelitic gneisses cordierite garnet bearing pegmatites and leucocratic garnetiferous melt segregations garnet leucosomes from within the acadian 360 ma granulite facies of south central massachusetts were investigated to further understand the counterclockwise p t evolution of the merrimack synclinorium the rocks were investigated with specific reference to phase equilibria in the system na2o k2o feo mgo al2o3 sio2 h2o nakfmash in the context of the petrogenetic grid proposed by spear et al 1999 an early low pressure history is suggested by the widespread occurrence of sillimanite pseudomorphs after andalusite as well as abundant matrix k feldspar in both gneisses and partial melts biotite consuming fluid absent melting of pelitic gneisses produced cordierite garnet bearing pegmatites and garnet cordierite leucosomes at conditions of 700 750 c and 4 5 kbar the major reaction is qtz sil bt kfs crd grt melt kfmash magnesian gneisses melted to form cordierite garnet bearing pegmatites and iron richer gneisses melted to form garnet cordierite bearing leucosomes previous studies of the quartz plagioclase k feldspar sillimanite biotite garnet cordierite assemblages in the gneisses suggest peak metamorphism at 700 750 c and 6 7 kbar retrograde reactions are essentially the reverse of prograde reactions and produced intergrowths of pale green biotite sillimanite quartz on cordierite and or garnet grain boundaries within the melt products as well as late muscovite water dissolved in the melt during prograde metamorphism was available for retrogression as the melts cooled the rocks investigated record part of a counterclockwise p t path

on the origin of oriented rutile needles in garnet from uhp eclogites although oriented rutile needles in garnet have been reported from several ultrahigh pressure uhp rocks and considered to be important uhp indicators their crystallographic features including growth habit and lattice correspondences with garnet host have never been properly characterized this paper presents a detailed analytical electron microscopic aem study on evenly distributed oriented rutile needles in garnet of two eclogitic rocks from sulu some garnet in one uhp diamondiferous quartzofeldspathic rock from the saxonian erzgebirge and in one high pressure hp felsic granulite from bohemia also contain a few unevenly distributed oriented rutile needles they have also been studied for the purpose of comparison despite different distribution patterns aem revealed that all rutile needles are oriented along the 111 directions of garnet with their lateral sides surrounded by the 110 planes of garnet and that the growth directions of most needles are close to the normal of the 101 planes of rutile no other specific crystallographic orientation relationships between rutile and garnet host were observed and there is no pyroxene associated with rutile as necessitated by the precipitation reaction of rutile in garnet as previously proposed a simple solid state precipitation scenario for the formation of the rutile needles in garnet in these two eclogitic rocks is not justified three alternative mechanisms are considered for the formation of oriented rutile needles i the rutile needles may be inherited from precursor minerals ii the rutile needles may be formed by a dissolution reprecipitation mechanism and iii the rutile needles may be formed by cleaving and healing of garnet with rutile deposition none of these mechanisms can fully explain the observations although the first one is less likely and the third one is preferred this study presents an example where the presence of oriented aligned inclusions in minerals does not necessarily imply a precipitation origin

a tem study of the oriented orthopyroxene and forsterite inclusions in garnet from otroy garnet peridotite wgr norway new insights on crystallographic characteristics and growth energetics of exsolved pyroxene in relict majoritic garnet regularly oriented orthopyroxene opx and forsterite fo inclusions occur as opx rutile rt or fo rt inclusion domains in garnet grt from otroy peridotite electron diffraction characterization shows that forsterite inclusions do not have any specific crystallographic orientation relationships cor with the garnet host in contrast orthopyroxene inclusions have two sets of cor that is cor i grt opx and 110 grt 100 opx 13 off and cor ii grt opx and 110 grt 100 opx 14 off in four garnet grains analysed both variants of orthopyroxene have a blade like habit with one pair of broad crystal faces parallel sub parallel to 110 grt plane and the long axis of the crystal opx for cor i and opx for cor ii along grt direction whereas the lack of specific cor between forsterite and garnet along with the presence of abundant infiltrating trails veinlets decorated by fo rt at garnet edges provide compelling evidence for the formation of forsterite inclusions in garnet through the sequential cleaving infiltrating precipitating healing process at low temperatures the origin of the epitaxial orthopyroxene inclusions in garnet is not so obvious in this connection the reported cor the crystal habit and the crystal growth energetics of the exsolved orthopyroxene in relict majoritic garnet were reviewed clarified the exsolved ortho pyroxene in a relict majoritic garnet follows cor iii 112 grt 100 opx and grt opx based on the detailed trace analysis on published sem images these exsolved orthopyroxene inclusions are shown to have the crystal habit with one pair of broad crystal faces parallel to 112 grt 100 opx and the long crystal axis along grt opx such a crystal habit can be rationalized by the differences in oxygen sub lattices of both structures and represents the energetically favoured crystal shape of orthopyroxene inclusions in garnet formed by solid state exsolution mechanism considering the very different cor crystal habit as well as crystal growth direction the orthopyroxene inclusions in garnet of the present sample most likely had been formed by mechanism s other than solid state exsolution regardless of their regularly oriented appearance in garnet and the cor specification between orthopyroxene and garnet in fact the crystallographic characteristics of orthopyroxene and the similar chemical compositions of garnet at opx rt inclusion domains fo rt inclusion domains trails and garnet rim suggest that the orthopyroxene inclusions in the garnet are most likely formed by similar cleaving infiltration process as forsterite inclusions though probably at an earlier stage of metamorphism this work demonstrates that the oriented inclusions in host minerals with or without specific cor can arise from mechanism s other than solid state exsolution caution is thus needed in the interpretation of such cor so that an erroneous identification of exhumation from uhp depths would not be made

decrepitated uhp fluid inclusions about diverse phase assemblages and extreme decompression rates erzgebirge germany minute polyphase inclusions in garnet of quartzofeldspathic rocks saidenbachite from the saxonian erzgebirge germany contain microdiamond or graphite phlogopite quartz paragonite phengite and other minerals in minor amounts these inclusions are interpreted to represent an original dense coh silicate fluid trapped in crystallizing garnet at depths of 150 km inspection of the inclusion population in a single garnet by sem reveals two characteristic features i the shape of most inclusions indicates healed radial cracks in the host garnet and thus the buildup of a significant differential pressure p i e a contrast in pressure between the inclusion pi and the host mineral pe the mineral assemblages sealing the cracks and showing an equilibrated microstructure indicate temperatures of 750 50 c and pressures below 2 5 gpa ii the diverse types of inclusions appear to be randomly distributed in the garnet host thus the variable phase assemblages do not reflect a compositional evolution of the fluid trapped in the garnet combining observations i and ii we propose that the diversity of the phase assemblage in the inclusions is the result of decrepitation at different times and thus of distinct histories of pi as p at decrepitation is primarily controlled by inclusion size and shape applying a flow law for dislocation creep of garnet a low strength of garnet at 750 50 c for low geological strain rates is predicted thus differential pressure should have been kept low i e pi pe by continuous stretching of the inclusion for typical exhumation rates of metamorphic rocks to attain the differential pressure pi pe required for catastrophic brittle failure of the garnet host the decompression rate must have been extremely high as a robust lower bound a minimum exhumation rate on the order of 100 m year 1 is suggested which corresponds to ascent rates of magma

pressure temperature reaction history of metapelitic rocks from the maryland piedmont on the basis of correlated garnet zoning and plagioclase inclusion composition regional structural interpretation thermobarometry and gibbs method calculations were combined to determine an approximate p t path for kyanite grade metapelitic rocks of the baltimore gneiss terrane garnet growth along the estimated p t path was modeled using the computer program diffgibbs models were evaluated by comparing calculated profiles of garnet components with measured profiles of a large garnet rich in plagioclase inclusions in a kyanite bearing sample from the area modifications in the p t path constrained by changes in garnet components along critical portions of the profile resulted in a very satisfactory match between measured and model garnet profiles in the most successful model garnet growth began at 550 c and 6500 bars in the assemblage chlorite biotite garnet muscovite plagioclase quartz with increasing temperature and with decreasing and then constant pressure at 570 c and 5724 bars staurolite was added to the assemblage and some garnet was consumed in the model garnet growth resumed after chlorite was consumed along a path having a substantial increase in pressure the region near the rim with low measured grossular content was reproduced by cessation of garnet growth as temperature increased at constant pressure to a maximum of 615 c at 6474 bars after kyanite was added to the assemblage grossular increased to the constant rim value only if temperature decreased and pressure increased cooling and decompression affected garnet zoning only very near the rim measured compositions of the rims of plagioclase inclusions in the garnet are consistent with plagioclase compositions predicted by the model this study demonstrates that complex garnet zoning can be modeled successfully even when the reaction history includes episodes of garnet consumption over a path that is consistent with geologic evidence details of garnet zoning provide surprisingly tight constraints on the p t path

the lavrion pb zn ag rich vein and breccia detachment related deposits greece involvement of evaporated seawater and meteoric fluids during postorogenic exhumation

modeling of radial microcracks at corners of inclusions in garnet using fracture mechanics radial microcracks around inclusions in garnet are important indicators of ultrahigh pressure metamorphism and have been used to interpret changes in pressure as a function of temperature during decompression of metamorphic terrains we investigate the growth of microcracks from inclusion corners using a two dimensional fracture mechanics based boundary element method code and propose that microcracks emanating from inclusions are primarily controlled by inclusion shape and size and do not require high confining lithostatic pressure or significant decompression to initiate results suggest that inclusions 100 m diameter develop microcracks during modest decompression the magnitude of decompression required to initiate microcracks decreases with increased degree of faceting and increased inclusion size the potential for crack growth at each corner depends on the corner sharpness and the overall shape of the inclusion we integrate model results with petrographic observations to understand mechanisms and conditions of garnet microcracking during regional metamorphism

textural and compositional characterization of recent sediments along a paraglacial estuarine coastline maine usa abstract textural and mineralogical characteristics of bottom sediments collected from the lower kennebec river estuary maine and adjacent nearshore region were used to differentiate subtidal sedimentary environments five depositional environments defined on the basis of bottom morphology bathymetry and dominant sedimentary processes estuarine channel channel margin outer bar shoreface and offshore possess distinct sedimentological characteristics trends in textural characteristics of these environments and those along the adjacent barrier beach include 1 systematic decrease in mean grain size from the estuarine channel to the offshore facies 2 similarity between the outer bar and estuarine channel sands 3 increase in sediment sorting from the channel margin and offshore to shoreface facies and 4 fining of the low tide terrace beachface and berm samples away from the bar welding region the fine grained nature of the offshore facies is the result of deposition of suspended sediment delivered to the coast during large flood events whereas the coarse fraction is contributed through the attrition of carbonate tests of the local macrofauna results of compositional analyses reveal 1 a decrease in shell fragments from the estuarine channel 50 to the offshore

soft sediment deformation produced by tides in a meizoseismic area turnagain arm alaska turnagain arm is a semidiurnal hypertidal estuary in southeastern alaska with a recorded tidal range of 9 m contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the mw 9 2 great alaskan earthquake of 1964 horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas although many types of soft sediment deformation structures can be formed by earthquakes observations of sedimentation on tidal flats in the inner parts of turnagain arm in the summers of 2003 and 2004 show that a wide range of soft sediment deformation structures similar to those inferred to have been formed by earthquakes can form in macrotidal estuaries in the absence of seismic shock during sedimentation rate measurements in 2004 soft sediment deformation structures were recorded that formed during one day s tide either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1 8 m tidal bore structures consisted of flow rolls dish structures flames and small dewatering pipes in a bed 17 cm thick in the future if the flow rolls in turnagain arm were found in isolated outcrops across an area 11 km in length in an estuary known to have been influenced by large magnitude earthquakes would they be interpreted as seismites these examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms tidal flux tidal bores slumping flooding that can cause deformation in rapidly deposited unconsolidated silts and sands are orders of magnitude more common than great earthquakes

garnets as open systems during regional metamorphism if a garnet fractures during metamorphism its interior will be in chemical communication with matrix phases solids and fluids and may participate in late prograde or retrograde metamorphic reactions the core of a growth zoned garnet is unlikely to be in equilibrium with matrix phases and may react locally in the vicinity of fractures or extensively resulting in dissolution and reprecipitation of the garnet interior and or production of new phases the results of petrologic techniques such as thermobarometry pressure temperature path calculations and geochronometry may be misinterpreted if sites of garnet and mineral inclusion compositional modification are not identified brittle fracturing of garnet during regional metamorphism may be facilitated by the presence of mineral inclusions the conditions at which differential expansion of an inclusion relative to its host garnet are sufficient to cause radial cracking around the inclusion vary as a function of peak pressure retrograde pressure temperature path and thermoelastic properties of the inclusion and garnet inclusion induced fracturing is favored by nearly isothermal decompression a common metamorphic pressure temperature path other fractures may form as a result of propagation of an inclusion host boundary or by mechanisms external to the garnet

plastic deformation of garnets systematics and implications for the rheology of the mantle transition zone abstract plastic properties of materials with garnet structure have been studied under wide temperature conditions ranging from room temperature to 95 of the melting temperatures using uniaxial compression and hot microhardness tests garnets studied include single crystals of oxide garnets y 3 al 5 o 12 gd 3 ga 5 o 12 and y 3 fe 5 o 12 and silicate garnets various solid solutions including grossular almandine andradite pyrope spessartine and uvarovite both uniaxial compression and hot hardness tests indicate that there is a general trend in the plasticity of garnets when the data are compared at normalized conditions t t m and and that the resistance to plastic deformation in garnets is significantly higher than most of the other minerals in the earth s mantle based on both stress dip tests and microstructural observations it is proposed that the creep strength of garnet is largely controlled by the resistance to dislocation glide rather than by recovery processes this conclusion is consistent with the high peierls stress inferred from the hot hardness tests the high peierls stress in garnets is presumably due to the large unit cell i e long burgers vectors and or the bcc packing which are common to all garnets we postulate therefore that the present results can be applied to the strength of high pressure garnet majorite and suggest that garnet rich layers in the earth such as subducted oceanic crust in the transition zone or a possibly garnet rich bottom part of the transition zone will be considerably stronger than surrounding regions

behaviour of apatite during partial melting of metapelites and consequences for prograde suprasolidus monazite growth abstract the suprasolidus behaviour of apatite and monazite is examined for an average metapelite composition using phase equilibria modelling coupled with solubility equations of these minerals both closed and open system scenarios are considered partial melting above the solidus requires apatite and monazite breakdown in order to saturate the anatectic melt in phosphorus and the light rare earth elements in general melt loss is predicted to increase the stability of apatite and monazite at high temperature most apatite is predicted to survive up to ultrahigh temperature conditions except for rocks with low bulk phosphorus concentrations by contrast most monazite is expected to be consumed by uht conditions thorium substitution in monazite is expected to increase the stability of monazite to higher temperatures the presence of lree rich apatite decreases the stability of monazite above the solidus but the breakdown of this apatite during anatexis may generate prograde monazite at the apatite melt interface in local pockets of melt oversaturation however prograde suprasolidus monazite along grain boundaries is expected to be consumed during further partial melting or during melt homogenization when an interconnected melt network develops anatectic melts are predicted to be saturated with respect to apatite except at uht conditions and for rocks with low initial p2o5 bulk concentrations

first application of the revised ti in zircon geothermometer to paleoproterozoic ultrahigh temperature granulites of tuguiwula inner mongolia north china craton the revised titanium in zircon geothermometer was applied to paleoproterozoic ultrahigh temperature uht granulites at tuguiwula inner mongolia north china craton the tuguiwula granulites contain diagnostic uht mineral assemblages such as sapphirine quartz and high alumina orthopyroxene sillimanite quartz suggesting formation under temperatures of ca 1 000 c and pressures of up to 10 kbar here we report detailed petrographic studies and icp ms data on titanium concentration in zircons associated with the uht assemblages the zircons associated with sapphirine spinel sillimanite magnetite assemblages have the highest ti concentration of up to 57 ppm yielding a temperature of 941 c and suggesting that the growth of zircons occurred under ultrahigh temperature conditions the maximum temperatures obtained by the revised ti in zircon geothermometer is lower than the equilibrium temperature of sapphirine quartz indicating an interval of cooling history of the granulites from uht condition to ca 940 c many of the zircons have ti concentrations ranging from 10 to 33 ppm indicating their growth or recrystallization under lower temperatures of ca 745 870 c these zircons are interpreted to have recrystallized during the retrograde stage indicated by microstructures such as cordierite rim or corona between spinel and quartz and orthopyroxene cordierite symplectite around garnet previous geochronological study on the zircons of the tuguiwula uht granulites gave a mean u pb shrimp age of 1 92 ga however based on the ti in zircon geothermometer results reported in this work and considering the relatively slow thermal relaxation of these rocks we infer that the timing of peak uht metamorphism in the tuguiwula area could be slightly older than 1 92 ga

microdiamond in high grade metamorphic rocks of the western gneiss region norway three grains of microdiamond were recovered from high grade gneiss exposed in the western gneiss region norway identification and characterization of the diamond grains by raman and infrared spectroscopy indicate the presence of substitutional impurities of h and n primary fluid inclusions in garnet and quartz in the diamond bearing rock demonstrate the evolution of metamorphic volatile fluids from reduced n 2 co 2 compositions during the peak phase of metamorphism to n 2 ch 4 h 2 o bearing compositions during retrograde metamorphism compatible geologic petrologic and fluid composition data imply a metamorphic origin for the microdiamonds if so the metamorphic and fluid conditions recorded by the microdiamonds and gneissic host may be applicable to microdiamond investigations in other high pressure regionally metamorphosed orogens

dissolution reprecipitation metasomatism and growth of zircon within phosphatic garnet in metapelites from western massachusetts highly restitic garnet kyanite phlogopite metapelitic schists from the goshen dome of western massachusetts contain a population of prograde monocrystalline megacrystic garnet some with significant p in substitution for si precipitates of hydroxylapatite and rutile and 5 mm 3 the unusual p content and the abundant internal precipitate suite are similar to features reported in garnet from ultrahigh pressure uhp and mantle settings suggesting a potential u hp origin for the garnet megacrysts zircon included in megacrysts is surrounded by radial fractures indicating in situ volumetric expansion or new growth cores display rare earth element ree profiles and cathodoluminescence cl zoning consistent with magmatic growth and yield only paleozoic dates 447 404 ma the embayed core rim boundary is marked by a several micrometers wide band of cl dark zircon enriched in y p u and th that is interpreted as the accumulation of redistributed xenotime component from the original zircon rim during metamorphism outside of this band the rim has elevated hf th u 1 and steep heavy ree profiles the metamorphic rims yield concordant dates from 400 to 381 ma matrix zircon grains have magmatic cores 1726 415 ma with similar core rim boundaries enriched in y p u and th metamorphic rims on matrix zircon yield slightly younger dates 393 365 ma and are compositionally heterogeneous the difference between the youngest core and oldest rim indicates a short interval ca 4 ma between deposition of detrital zircon and the onset of metamorphism in the earliest acadian the oldest zircon rim dates are found within phosphatic garnet megacrysts of possible very high pressure origin the compositional uniformity of these rims indicates equilibrium with a single source the anomalous composition suggests a combination of dissolution reprecipitation and new growth of zircon that is derived from garnet the range in both composition and dates indicates that matrix zircon rims formed in response to local changes in mineralogy and fluid melt composition and or availability new growth of zircon on these grains cannot be confirmed suggesting that dissolution reprecipitation reactions during continued metamorphism may be the dominant mechanism that formed these rims the data collectively suggest that dissolution reprecipitation may be a common mechanism for producing metamorphic rims on zircon that does not require additional zr and hf which are limited within most metamorphic settings

texturally early fluid inclusions in garnets evidence of the prograde metamorphic path well formed texturally early fluid inclusions in garnets from the archean pikwitonei granulite domain manitoba canada have been analyzed using microthermometric methods the mean co2 homogenization temperature to liquid for inclusions in 12 of 13 samples from the cauchon lake nelson river area is 15 2 c n 125 2 8 2 c corresponding to a co2 density of 0 82 g cm3 inclusions in the remaining sample have somewhat lower co2 homogenization temperatures mean 5 4 c n 24 the studied inclusions contain an estimated 10 to 20 vol percent h2o with minor amounts of other fluid species such as ch4 n2 and or h2s the fluid inclusions were probably trapped during early garnet growth at relatively low pressures 5 kbar if at 750 c and appear to have undergone only limited or possibly no subsequent re equilibration this interpretation is consistent with the anti clock wise p t t path heating before loading determined for the pikwitonei region by other workers for such a prograde path inclusions entrapped early at high temperatures but at relatively low pressures would experience internal underpressures during most of the subsequent prograde and retrograde phases of metamorphism the texturally early fluid inclusions in garnets from the pikwitonei region therefore cannot be used to provide direct information about the highest metamorphic temperature and pressure conditions 750 c and 7 kbar however the results obtained in this study suggest that texturally early fluid inclusions in garnets may in some cases retain evidence of the prograde metamorphic path

a terracing operator for physical property mapping with potential field data the terracing operator works iteratively on gravity or magnetic data using the sense of the measured field s local curvature to produce a field comprised of uniform domains separated by abrupt domain boundaries the result is crudely proportional to a physical property function defined in one profile case or two map case horizontal dimensions this result can be extended to a physical property model if its behavior in the third vertical dimension is defined either arbitrarily or on the basis of the local geologic situation the terracing algorithm is computationally fast and appropriate to use with very large digital data sets where gravity and magnetic data are both available terracing provides an effective means by which the two data sets can be compared directly results of the terracing operation somewhat resemble those of conventional susceptibility or density mapping in contrast with conventional susceptibility mapping however the terraced function is a true step function which cannot be depicted by means of contour lines magnetic or gravity fields calculated from the physical property model do not in general produce an exact fit to the observed data by intent the terraced map is more closely analogous to a geologic map in that domains are separated by hard edged domain boundaries and minor within domain variation is neglected the terracing operator was applied separately to aeromagnetic and gravity data from a 136 km x 123 km area in eastern kansas results provide a reasonably good physical representation of both the gravity and the aeromagnetic data superposition of the results from the two data sets shows many areas of agreement that can be referenced to geologic features within the buried precambrian crystalline basement the emerging picture of basement geology is much better resolved than that obtained either from the scanty available drill data or from interpretation of the geophysical data by inspection

petrogenetic relations among titanium rich minerals in an anatectic high p mafic granulite the petrogenetic relations among ti rich minerals in high grade metabasites is illuminated here through a detailed petrological investigation of an anatectic garnet clinopyroxene granulite from the grenville province ontario canada containing rutile titanite and ilmenite in distinct microtextural settings garnet porphyroblasts exhibit zoned ti concentrations up to 0 15 wt tio2 in their cores as well as a variety of rutile inclusion types including clusters of small variably elongate grains and thin 1 m oriented needles calcite inclusions in garnet commonly observed surrounding garnet cores containing quartz and clinozoisite indicate the presence of evolving c o h fluids during garnet growth and suggest that the rutile clusters may have formed from subsequent ti diffusion and rutile precipitation within existing fluid inclusions titanite forms large subhedral crystals and typically occurs where the primary garnet clinopyroxene assemblage is in contact with leucosome containing megacrystic hornblende silvialitic scapolite and calcic plagioclase many titanite crystals exhibit marginal subgrains that correspond with sharp changes in their major and trace element composition likely related to a dissolution precipitation or recrystallization process following primary crystallization clinopyroxene ilmenite symplectite coronas surround titanite in most locations likely forming from reaction with the hornblende plagioclase matrix fluids melt integration of multi equilibria thermobarometry and zr thermometry in rutile and titanite with phase equilibrium modelling allows definition of a clockwise p t path evolving to peak pressures of 1 5 gpa at 750 c during garnet and rutile growth followed by peak temperature conditions of 1 2 gpa and 820 880 c associated with melt present titanite growth and finally cooling and decompression to regional amphibolite facies conditions 1 0 gpa and 750 c associated with the formation of clinopyroxene ilmenite symplectites surrounding titanite p t pseudosections calculated for the pristine leucosome and titanite free metabasite bulk composition reproduce much of the prograde phase relations but predict rutile as the stable ti rich mineral at the peak thermal conditions associated with melt present titanite growth the p m cao and t m cao models show that bulk cao concentrations have a significant effect on the stability ranges of titanite and rutile increased bulk cao tends to stabilize titanite to higher pressure and temperature at the expense of rutile with a 15 increase in cao producing the observed titanite bearing assemblage at high p granulite facies conditions thus the model results are consistent with the textural observations which suggest that titanite stability is associated with a chemical exchange between the host metabasite and a ca rich melt

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

clinopyroxenite from the sulu ultrahigh pressure terrane eastern china origin and evolution of garnet exsolution in clinopyroxene the rizhao garnet clinopyroxenite occurs as small mantle slices faulted into subducted continental crust in the sulu ultrahigh pressure uhp terrane china two representative garnet clinopyroxenites with exsolution microstructures were studied 1 a massive ilmenite rich specimen composed of coarse grained clinopyroxene containing abundant exsolution rods of grossular rich garnet 20 vol ilmenite 3 4 vol in a fine grained matrix of clinopyroxene garnet ilmenite and 2 megacrystic garnet bearing sample characterized by garnet containing inclusions of clinopyroxene and ilmenite the clinopyroxene inclusions show exsolution rods and blebs with variable amounts of garnet 1 15 vol and minor ilmenite both exsolved and matrix garnets have similar grossular rich compositions the aggregate composition of clinopyroxene garnet ilmenite intergrowth is similar to the whole rock composition we propose that the parental phase of exsolved garnet ilmenite lamellae and clinopyroxene host was either a homogeneous clinopyroxene hypothesis a or a majoritic garnet hypothesis b that experienced three discrete evolution stages if the parental phase was clinopyroxene abo3 with an si deficiency in the b site the rizhao garnet clinopyroxenite could have an initial assemblage clinopyroxene grt ilm formed at near solidus conditions 1400 c at 5 gpa in the upper mantle the second stage is defined by garnet exsolution from the primary clinopyroxene involving decreasing temperature and or increasing pressure related to continental subduction coexisting clinopyroxene host and garnet exsolution grtexs recrystallized at temperatures of 900 c at an assumed minimum p of 5 gpa the third stage is represented by recrystallization of exsolution phases to form the fine grained matrix of cpx grt ilm at 700 c and 3 gpa during the early exhumation of the uhp terrane the speculative hypothesis b implies that the proposed majoritic garnet was from the mantle transition zone 450 km depth this suggestion remains to be tested

ternary ca fe mg carbonates subsolidus phase relations at 3 5 gpa and a thermodynamic solid solution model including order disorder subduction carries atmospheric and crustal carbon hosted in the altered oceanic crystalline basement and in pelagic sediments back into the mantle reactions involving complex carbonate solid solutions s lead to the transfer of carbon into the mantle where it may be stored as graphite diamond in fluids or melts or in carbonates to constrain the thermodynamics and thus reactions of the ternary ca mg fe carbonate solid solution piston cylinder experiments have been performed in the system caco3 mgco3 feco3 at a pressure of 3 5 gpa and temperatures of 900 1 100 c at 900 c the system has two miscibility gaps the solvus dolomite calcite which closes at xmgco3 0 7 and the solvus dolomite magnesite which ranges from the mg to the fe side of the ternary with increasing temperature the two miscibility gaps become narrower until complete solid solutions between caco3 ca0 5mg0 5co3 is reached at 1 100 c and between caco3 feco3 at 1 000 c the solvi are characterized by strong compositional asymmetry and by an order disorder mechanism to deal with these features a solid solution model based on the van laar macroscopic formalism has been calculated for ternary carbonates this thermodynamic solid solution model is able to reproduce the experimentally constrained phase relations in the system caco3 mgco3 feco3 in a broad p t range to test our model calculated phase equilibria were compared with experiments performed in carbonated mafic protolithes demonstrating the reliability of our solid solution model at pressures up to 6 gpa in complex systems

a comparison of the evolution of diamondiferous quartz rich rocks from the saxonian erzgebirge and the kokchetav massif are so called diamondiferous gneisses magmatic rocks abstract the petrography and chemical composition of minerals of quartz rich diamondiferous rocks from the kokchetav massif especially the zonation of garnet were studied and compared with diamondiferous quartzofeldspathic rocks from the saxonian erzgebirge many compositional and textural features were found to be similar for instance microdiamonds are enclosed systematically in a specific intermediate growth zone of garnet in these rocks on the basis of experimental data a magmatic scenario was constructed to check if the quartz rich diamondiferous rocks are of magmatic origin by this the p t paths derived here for the kokchetav rocks and the textural observations it is concluded that the minerals of the diamondiferous rocks have crystallized from silicate melts these melts originated by anatexis of deeply submerged metasediments erzgebirge at t as high as 1200 c kokchetav massif at 50 100 c lower t and ascended from at least 200 km depth relics of the pre anatectic evolution are still present for instance as garnet cores after ascent and emplacement of the magma in deep portions of thickened continental crust kokchetav massif 45 50 km close to 800 c erzgebirge 55 60 km at 30 50 c lower t considerable quantities of white and or dark micas formed by peritectic reactions from melt for instance garnets could be resorbed at this stage and biotite grew instead after the magmatic stage retrogression took place much stronger in the kokchetav massif this was accompanied by deformation transforming broadly the magmatic texture of quartz rich diamondiferous rocks from the kokchetav massif to a gneissic texture

fluids in metamorphic rocks abstract basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated a major problem relates to the number of inclusions possibly formed on a wide range of p t conditions having also suffered in most cases extensive changes after initial trapping the interpretation of fluid inclusion data can only be done by comparison with independent p t estimates derived from coexisting minerals but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host the three essential steps in any fluid inclusion investigation are described observation measurements and interpretation observation with a conventional petrographic microscope leads to the identification and relative chronology of a limited number of fluid types same overall composition eventually changes in fluid density for the chronology the notion of gis group of synchronous inclusions is introduced it should serve as a systematic basis for the rest of the study microthermometry measurements completed by nondestructive analyses mostly micro raman specify the composition and density of the different fluid types the major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms allowing elimination of a great number of inclusions having suffered late perturbations finally the interpretation is based on the comparison between few isochores representative of the whole inclusion population and p t mineral data essential is a clear perception of the relative chronology between the different isochores when this is possible as illustrated by the complicated case of the granulites from central kola peninsula a good interpretation of the fluid inclusion data can be done if not fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur

high pressure metamorphism in the western cordillera of north america the skagit gneiss a major component of the crystalline core of the north cascades was metamorphosed during a mid cretaceous to early tertiary high p event driven by the collision of the insular and intermontane superterranes maximum pressures recorded by metapelitic rocks are 8 10 kbar at 650 725 c high pressures are also indicated by coexisting staurolite and hornblende in amphibolites in the skagit gneiss and adjacent cascade river schist mineral reactions continued during nearly isothermal decompression from 8 10 kbar to c 3 5 kbar early high p minerals e g kyanite are present as armoured relics in garnet in gneisses that contain sillimanite and cordierite in the groundmass skeletal relics of kyanite are also present in the groundmass of lower grade staurolite bearing schists that contain texturally later cordierite this matrix kyanite may have been preserved as a result of rapid uplift following initial decompression at high temperature these results represent a revision of the metamorphic history of the skagit gneiss which was formerly thought to have experienced only relatively low p barrovian metamorphism qualitative estimates of metamorphic conditions based on stable matrix mineral assemblages result in an underestimation of maximum pressures because mineral reactions continued during decompression geobarometric results for the skagit gneiss are interpreted as evidence for major crustal thickening in the north cascades recognition that pressures of c 9 kbar were attained supports a contractional model for north cascades orogenesis and requires that tectonic syntheses account for the burial of the skagit gneiss protoliths to a depth of c 25 30 km

the architecture of precambrian high energy tidal channel deposits an example from the lyell land group eleonore bay supergroup northeast greenland abstract within the 2 5 km thick late proterozoic lyell land group of the eleonore bay supergroup in east greenland numerous successions of stacked sheet sandstone bodies 10 70 m thick occur each succession consists of several 5 50 m thick multistorey sand sheets separated from each other by 0 2 2 m thick heterolithic mudstone or sandstone beds individual sand sheets are 0 2 3 0 m thick they have highly erosive lower contacts show a rough fining upward trend and are capped by a thin mudstone veneer containing desiccation cracks dominant sedimentary structures within the sand sheets are sets of planar cross bedding showing a range of characteristic tidal features such as successive bundles of foresets herringbone cross stratification ebb and flood caps and numerous reactivation surfaces horizontal lamination is abundant and may in some instances comprise more than half of the structures within a sand sheet the sand sheets represent high energy tidal channels with the multistorey sand sheets constituting larger tidal channel complexes the heterolithic beds represent mixed tidal flat sediment deposited during periods of tidal channel complex abandonment probably caused by channel aggradation and changing drainage patterns the tidal channels were wide shallow and very sandy with a very poorly developed channel morphology caused by lack of fine grained sediments and vegetation most likely they evolved within a meso to microtidal sandy back barrier setting where the channels migrated swiftly across tidal flats and reworked most interchannel sediment an architecture was developed consisting of stacked sand sheets interbedded with rare heterolithic mudstone beds the model presented incorporates sedimentary parameters and processes characteristic of a pre vegetative landscape and it has no direct modern analogue

diamond former coesite and supersilicic garnet in metasedimentary rocks from the greek rhodope a new ultrahigh pressure metamorphic province established abstract we report here the first discovery of ultrahigh pressure uhp indicator minerals and textures from the rhodope metamorphic province rmp northern greece in particular we document the exsolution of quartz rutile and apatite in sodic garnet from metapelites garnet biotite kyanite gneisses which attests to the presence of a si ti na p rich precursor garnet phase similar textures in garnet have been reported in the literature only once before for eclogites from the su lu uhp metamorphic province china we also document the presence of microdiamonds and multicrystalline quartz pseudomorphs after coesite included in garnet from both eclogites and metapelites we then argue that these rocks had once been transported to depths exceeding 220 km well into the upper mantle thus establishing the rmp as another important uhp metamorphic belt in the world

geology and structure of diamond bearing rocks of the kokchetav massif kazakhstan abstract two crustal settings for microdiamond formation have been described from eclogite bearing metamorphic areas 1 the economic concentration of microdiamonds in metasedimentary gneisses and calc silicate rocks northern kazakhstan and 2 microdiamonds recently found in eclogite garnet pyroxenite and jadeitite from dabie shan mountain eastern china the latter occurrence is interpreted to be the product of ultra high pressure metamorphism in a mesozoic collision zone there are however a number of discrepancies between the geological structural and geochemical data for kazakhstan microdiamond deposits and an interpretation in terms of a deep subduction zone model the geodynamic setting of the kokchetav massif can be defined as a continental rise prism environment related to a passive continental margin where rifting predominated during early palaeozoic orogeny the kumdikol microdiamond province is closely associated with a tectonic melange zone involved in ductile to semi ductile shearing abundant in graphite microdiamonds of the kumdikol area have a dual setting in the rocks they appear to be included not only in refractory garnet and zircon but also in almost all rock forming minerals as biotite phlogopite diopside quartz and secondary sericite chlorite and sericite chlorite calcite aggregates after garnet pyroxene and plagioclase and in spite of softness of the host phases microdiamonds are well preserved on the other hand the ore body extends along the shear zone and high concentrations of the microdiamonds within it are distributed without any lithological control along the local s c surfaces of the main kumdikol strike slip shear zone this duality of microdiamond settings in absence of practically all ultra high pressure minerals except diamond itself weakens the interpretation of this occurrence in terms of very deep subduction and very fast uplift and exhumation during 15 10 ma according to recent geochronological data these microdiamonds could have been formed metastably under anisotropic stress conditions in fact the available data from the kumdikol province provides certain support for either metastable and stable hypothesis

metasomatic origin for fe ti rich multiphase inclusions in olivine from kimberlite xenoliths because solid solution trace elements in olivine have significant influence on upper mantle rheology it is important to establish whether inclusions in olivine are exsolved from an intrinsic solid solution or are introduced by metasomatism in a study of olivine in hot deformed peridotite xenoliths from kimberlites we have found a new type of multiphase inclusion that contains fe ti rich and si fe al rich phases microstructural relations indicate that these inclusions form by a process involving metasomatic fluid infiltration along a fine network of cracks shortly before entrainment of the xenoliths followed by crack healing during xenolith transport in the magma the high trace element content of ti ca al and na found in fe ti rich hot deformed olivine is related to metasomatic enrichment that occurred shortly before kimberlite eruption assessment of the effects of the fe ti metasomatism indicates that the cr c rich inclusions found in olivine from other hot deformed xenoliths are formed by precipitation from an intrinsic solid solution in olivine that has not been affected by fe ti rich metasomatism

genesis of ilmenite rods and palisades along humite type defects in olivine from alpe arami rod shaped ilmenite inclusions in olivine have been observed in numerous peridotite lenses of the adula cima lunga unit central alps the rods are elongated parallel to 010 ol and identical in size shape and concentration to those reported from garnet peridotite at alpe arami aa tem investigation of the rods at aa cima di gagnone cdg and monte duria md demonstrates that the titanate inclusions correspond to a mg bearing ilmenite with exclusively a trigonal crystal structure no other fetio3 polymorphs have been identified the shape of the ilmenite inclusions concurs with minimum topotactic misfits between the lattices of olivine and mg bearing ilmenite optical microscopy reveals that the ilmenite rods are not randomly distributed within olivine but have at all localities a preferred alignment parallel to 001 ol forming palisades tem images of the ilmenite palisades at aa and cdg show that they are controlled by the presence of 001 planar defects in olivine along which the rods nucleated the defects have been characterised by high resolution tem and identified as 4 4 a wide humite type layers i e mg2sio4 mg oh f 2 intergrown within olivine in such layers substitution of up to 50 mol mgh2 by ti4 is possible assuming ti saturated humite slabs the maximum density of 001 faults observed at aa approximately 1900 mm 1 can accommodate about 170 ppm tio2 in olivine this represents about half the values obtained by uv laser ablation icp ms and empa analysis evidence for annealing of the defects however suggests that only parts of the defects are still preserved the formation of ilmenite rods is considered to be a consequence of the breakdown of isolated humite layers in olivine the apparent tio2 content in olivine at aa cdg and md is regarded as a function of the ti humite defect density

tio2 exsolution from garnet by open system precipitation evidence from crystallographic and shape preferred orientation of rutile inclusions we investigated rutile needles with a clear shape preferred orientation in garnet from ultra high pressure metapelites from the kimi complex of the greek rhodope by electron microprobe electron backscatter diffraction and tem techniques a definite though complex crystallographic orientation relationship between the garnet host and rutile was identified in that rt 001 is either parallel to grt or describes cones with opening angle 27 6 around grt each rt 001 small circle representing a cone on the pole figure displays six maxima in the density plots this evidence together with microchemical observations in tem when compared to various possible mechanisms of formation corroborates a precipitate origin a review of exchange vectors for ti substitution in garnet indicates that rutile formation from garnet cannot occur in a closed system it requires that components are exchanged between the garnet interior and the rock matrix by solid state diffusion a process we refer to as open system precipitation osp the kinetically most feasible reaction of this type will dominate the overall process the perhaps most efficient reaction involves internal oxidation of fe2 to fe3 and transfer from the dodecahedral to the octahedral site just vacated by text ti 4 6 text m 2 3 text tial left text alsi 2 right text o 1 2 6 text m 2 2 5 text tialsi 3 text o 1 2 10 text m 2 3 0 text al 1 8 text fe 0 2 text si 3 text o 1 2 text m 2 2 text e 1 2 text tio 2 osp is likely to occur at conditions where the transition of natural systems to open system behaviour becomes apparent as in the granulite and high temperature eclogite facies

hydrodynamic analysis of a mediterranean aquifer system with the use of hydrochemical and isotopical analysis as supporting tools the management of groundwater resources in coastal environments within the mediterranean basin has become of paramount importance especially in the light of global changes a typical example of such a hydrosystem is the lavrio basin in greece this research site involves two aquifer types granular and karstic formations that are hydraulically interconnected furthermore the proximity to the sea and the abstractions for irrigation and drinking water supply have led to the phenomenon of seawater intrusion the present study aims at analyzing the hydraulic hydrological and hydrogeological conditions of the area by means of hydrochemical and isotopical data interpretation as supporting tools which will inform and support the development of an integrated conceptual hydrogeological model of the area field investigations were conducted in order to collect piezometric and chemical data and use them to retrieve the quantitative and qualitative status of the local aquifer units new interpretation of an older dataset gave an insight into how the karstic aquifer behaves in terms of hydraulics the results have also demonstrated that there is a hydraulic connection between the different aquifers and the mediterranean sea while natural recharge was quantified for both aquifer types

analysis of potential field anomalies in lavrion mining area greece mining activities in lavrion began during the first millennium b c after the decline of ancient athens and then restarted more deliberately during the nineteenth century aeromagnetic data from a 1967 survey of the mining area was recompiled processed and interpreted for the present study the original flight lines were digitized and leveled and the international geomagnetic reference field igrf was removed the data were inverted by means of a terracing technique that defines separate domains of uniform distribution of physical properties that cause the magnetic anomalies the log power spectrum was computed along with the results of terracing it suggested the existence of two sources of the magnetic anomaly the long wavelength anomaly reflects a large concealed body that is most probably a granitic intrusion consistent with local geological evidence the source of the short wavelength anomaly is a strongly magnetized body attributed to the net effect of various thin magnetite bearing sulfide zones the anomalies were then separated in the wavenumber domain magnetic susceptibility measurements were made in situ on the exposed parts of the local formations three dimensional models whose effect simulates the observed anomalies were calculated results of the modeling show that the large magnetic body is buried at 0 68 km depth the small relatively shallow body is about 0 035 km thick and buried at 0 6 km depth the bodies do not show any corresponding gravity anomaly on the regional bouguer gravity anomaly map

topotaxial reactions during the genesis of oriented rutile hematite intergrowths from mwinilunga zambia oriented rutile hematite intergrowths from mwinilunga in zambia were investigated by electron microscopy methods in order to resolve the complex sequence of topotaxial reactions the specimens are composed of up to several centimeter large euhedral hematite crystals covered by epitaxially grown reticulated rutile networks following a top down analytical approach the samples were studied from their macroscopic crystallographic features down to subnanometer scale analysis of phase compositions and occurring interfaces already a simple morphological analysis indicates that rutile and hematite are met near the left langle 0 10 right rangle r left 10 1 right r left langle 00 1 right rangle h left 1 10 right h orientation relationship however a more detailed structural analysis of rutile hematite interfaces using electron diffraction and high resolution transmission electron microscopy hrtem has shown that the actual relationship between the rutile and hosting hematite is in fact left langle 0 10 right rangle r left 40 1 right r left langle 00 1 right rangle h left 1 70 right h the intergrowth is dictated by the formation of left 1 70 right h left 40 1 right r equilibrium interfaces leading to 12 possible directions of rutile exsolution within a hematite matrix and 144 different incidences between the intergrown rutile crystals analyzing the potential rutile rutile interfaces these could be classified into four classes 1 non crystallographic contacts at 60 and 120 2 101 twins with incidence angles of 114 44 and their complementaries at 65 56 3 301 twins at 54 44 with complementaries at 125 56 and 4 low angle tilt boundaries at 174 44 and 5 56 except for non crystallographic contacts all other rutile rutile interfaces were confirmed in mwinilunga samples using a hrtem and high angle annular dark field scanning tem methods combined with energy dispersive x ray spectroscopy we identified remnants of ilmenite lamellae in the vicinity of rutile exsolutions which were an important indication of the high t formation of the primary ferrian ilmenite crystals another type of exsolution process was observed in rutile crystals where hematite precipitates topotaxially exsolved from fe rich parts of rutile through intermediate guinier preston zones characterized by tripling the 101 rutile reflections unlike rutile exsolutions in hematite hematite exsolutions in rutile form left 30 1 right r left 0 30 right h equilibrium interfaces the overall composition of our samples indicates that the ratio between ilmenite and hematite in parent ferrian ilmenite crystals was close to ilm67hem33 typical for fe ti rich differentiates of mafic magma the presence of ilmenite lamellae indicates that the primary solid solution passed the miscibility gap at 900 c subsequent exsolution processes were triggered by surface oxidation of ferrous iron and remobilization of cations within the common oxygen sublattice based on nanostructural analysis of the samples we identified three successive exsolution processes 1 exsolution of ilmenite lamellae from the primary ferrian ilmenite crystals 2 exsolution of rutile lamellae from ilmenite and 3 exsolution of hematite precipitates from fe rich rutile lamellae all observed topotaxial reactions appear to be a combined function of temperature and oxygen fugacity fo2

p t evolution of a variscan lower crustal segment a study of granulites from the schwarzwald germany pressure temperature time p t t paths of orogenic granulites introduction provide important information on the thermal and chemical structure general background of the lower continental crust through time and constraints on tectonic granulites are typical rocks of the earth s middle to processes we present the first detailed petrological investigation of lower crust under high temperature conditions they are granulites from the variscan schwarzwald pelitic granulites from the found as xenoliths in basaltic volcanic rocks mainly central schwarzwald gneiss complex csgc are characterized by within continental rifts but most granulites occur as the peak assemblage garnet rutile kyanite antiperthite complexes or terranes in orogenic settings orogenic quartz felsic to intermediate granulites from the southern granulites display a wide compositional range harley schwarzwald gneiss complex ssgc exhibit different peak as1989 1998 and are known from a variety of collisional semblages with clinopyroxene orthopyroxene ternary feldspar garnet belts that formed during different episodes since the quartz and sillimanite and manifold retrograde reaction textures archaean e g harley 1998 clarke et al 2000 moller peak p t conditions were calculated by two feldspar thermometry et al 2000 determination of bulk rock and mineral garnet orthopyroxene thermometry and various geobarometers minicompositions calculation of peak equilibration conmum estimates for peak conditions are 950 1010 c and 1 4 1 8 ditions and dating of orogenic granulites thus provide us gpa for the granulites of the csgc which followed a clockwise with important constraints on the thermal and chemical p t path the retrograde path is characterized by initial isothermal structure of the earth s continental crust at different decompression associated with partial melting followed by isobaric geological times cooling peak conditions for the ssgc are 1015 c and 1 5 gpa harley 1989 showed that equilibration conditions minimum temperature maximum pressure no prograde relics are deduced from natural orogenic granulites cover a wide preserved and isothermal decompression was less pronounced than range in particular pressures are highly variable and in the csgc other variscan hp ht granulites from central the granulite field may be divided into a low pressure europe show similar lithologies equilibration temperatures and lp a medium pressure mp and a high pressure hp ages 340 335 ma the heat for widespread high temperature facies according to green ringwood 1967 peak metamorphism in the variscan lower crust could have been supplied temperatures of many granulite terranes scatter around by repeated intrusion of subduction related basic magmas rapid 800 c bohlen 1987 but an increasing number of near isothermal decompression of the granulites may have been ultra high temperature uht granulite complexes facilitated by considerable volumes of partial melt and by orogenic extension 900 1100 c and 0 7 1 3 gpa harley 1998 are being recognized e g harley hensen 1990 dasgupta et al 1995 klemd brocker 1999 hokada 2001 regarding retrograde p t paths harley 1989 distinguished two

titanium solubility in coexisting garnet and clinopyroxene at very high pressure the significance of exsolved rutile in garnet exsolution microstructures including ilmenite garnet in clinopyroxene and rutile in garnet are common in clinopyroxenite and eclogite from the sulu ultrahigh pressure uhp terrane in order to understand the phase relations and ti solubility in both garnet and clinopyroxene in a natural tio2 bearing system several experiments at 5 15 gpa 1000 1400 c were carried out using the multianvil high pressure apparatus the hujianlin ilmenite rich garnet clinopyroxenite showing exsolution microstructure was selected as starting material because it closely approaches a composition lying in the tio2 cao mgo feo al2o3 sio2 system except for minor melt in one experiment at 1400 c and 5 gpa other run products contain majoritic garnet clinopyroxene ilmenite or rutile and exhibit neoblastic texture with increasing pressure ti and ca mg and si contents of neoblastic garnet increase with decreasing al the principal coupled substitutions are ca2 ti4 2al3 and si4 mg2 2al3 responding to majorite component increase titanium solubility 0 8 4 5 wt as tio2 in garnet and grtti cpxti ratio have a pronounced positive correlation with pressure between 5 and 15 gpa on the other hand the coexisting clinopyroxene contains low ti 0 17 0 53 wt as tio2 and shows no significant pressure effect rutile exsolution in garnet is coupled to that of pyroxene exsolution both are exsolved from majoritic garnet on decompression therefore the amount of such exsolved lamellae is a potential indicator of high pressure metamorphism in exhumed rocks whereas the tio2 content of clinopyroxene coexisting with garnet is not sensitive to pressure change

genesis of microdiamonds from melt and associated multiphase inclusions in garnet of ultrahigh pressure gneiss from erzgebirge germany abstract the common association of microdiamonds with the phase assemblage phlogopite apatite paragonite and quartz containing amorphous na al silicate inclusions as inclusions in garnets of quartzofeldspathic rocks from the saxonian erzgebirge germany was studied by analytical electron microscopy the assemblage implies a precedent melt which coexisted with the microdiamonds before and after entrapment in the garnet host and subsequently crystallized the formation of microdiamonds in this metamorphic rock could be explained by cotectic induced partial melting of a subducted continental slab at about 4 6 gpa and 1000 c as constrained by the occurrence of tio 2 with an pbo 2 type structure at the peak metamorphic conditions and by the catalytic effect of siderophile and chalcophile elements

tio2nanoparticle trails in garnet implications of inclusion pressure induced microcracks and spontaneous metamorphic reaction healing during exhumation a new mechanism of cleaving healing of garnet in metamorphic rocks during exhumation is reported almandine garnet with submicron multiple phase inclusions characteristic of the grail reaction garnet rutile kyanite ilmenite low quartz was found by analytical electron microscopy to have non epitaxial rutile nanoparticles distributed along internal 110 microcrack trails at the acute corner of submicron multiple phase inclusions defined by the intersecting 110 and 011 mould surfaces such garnet microcracks were formed during lithostatic decompression due to a relatively high compressibility of quartz in the inclusion pockets and stress concentration at the acute corner spontaneous healing with accompanied formation of non epitaxial rutile nanoparticles was activated predominantly via the grail reaction due to high surface tension at the tip of microcracks and to a lesser extent decreasing lithostatic pressure or increasing inclusion pressure upon exhumation this new mechanism of microcracking and healing involves stress build up fracture propagation mineral reaction transport of elements to the reaction site and lowering of reaction boundaries by capillarity effect all under the influence of thermodynamic and kinetic factors at the submicron scale thus tio2 nanoparticle trails in garnet provide additional information on the p t path and may shed light on exhumation rates mechanisms and metamorphic reactions processes careful scrutiny of host minerals on the submicron scale is required to tell whether there are other metamorphic reaction facilitated healing processes being overlooked by inappropriate techniques or being obliterated by the predominant healing processes of fluid infiltration and resorption zoning

oriented multiphase needles in garnet from ultrahigh temperature granulites connecticut u s a this study investigates distinctive oriented needle shaped multiphase inclusions found within cores of garnets from felsic granulites of the upper member of the bigelow brook formation and the brimfield schist northeastern connecticut u s a the rocks crop out in the southern end of the central maine terrane and thus are a part of the acadian neoacadian orogen the typical mineral assemblage is garnet sillimanite k feldspar plagioclase quartz cordierite biotite spinel the sillimanite is commonly pseudomorphous after kyanite the multiphase needle inclusions and associated exsolved needles of rutile and ilmenite are mostly oriented parallel to of garnet the multiphase needles contain various combinations of quartz micas chlorite rutile graphite a siliceous compositionally variable phase phase cv zn spinel apatite zircon and rare ilmenite we hypothesize that they represent inclusions of fluid that adhered to exsolving ti fe oxide needles mostly rutile or extended along zones of weakness in garnet this requires that multiphase needle formation occurred in response to cooling and or decompression the needles ultimately decrepitated during retrogression we note that micaceous needle shaped multiphase inclusions are rarely described the closest analogs of which we are aware are found in uhp garnets of the erzgebirge perchuk 2008 the brimfield schist in this area underwent ultrahigh temperature metamorphism uhtm of 1000 c at a minimum pressure of 1 gpa ague et al 2013 here we provide new temperature estimates for the adjacent upper member of the bigelow brook formation ternary feldspar reintegration using the activity model of benisek et al 2004 and zr in rutile thermometry tomkins et al 2007 give average temperatures of 990 and 1010 c respectively at 1 gpa for this unit therefore the recently discovered uht zone in the brimfield schist of northeastern connecticut extends to the east to include the upper member of the bigelow brook formation consequently the first confirmed regional uht locality in the united states is larger than initially recognized and is at least 25 km long and 5 10 km wide the oriented elongate multiphase inclusions and petrographically obvious oriented ti fe oxide needles may be useful indicators of extreme temperature and or pressure rocks in other field areas

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

footwall mineralization during late miocene extension along the west cycladic detachment system lavrion greece the west cycladic detachment system wcds has been mapped from the western cycladic islands to lavrion mainland greece where several top to ssw low angle normal faults at different structural levels are observed near the detachment horizon hydrothermal fluid flow originating from miocene intrusions lead to high temperature carbonate strata bound pb ag zn ore deposits zircon u th he cooling ages from the mineralized footwall are 7 1 0 6 to 7 9 0 6 ma carbon and o isotope analyses of the carbonate host indicate high water to rock ratios during brittle deformation induced metasomatism and that this interaction unrelated to proximity of the intrusions plays the dominant role in the mineralization the late miocene geology of lavrion is strikingly similar to serifos island on the se termination of the wcds both characterized by strong localization of detachment faulting and the interaction of brittle deformation with the injection of fluids related to granitoid intrusions

th u ratios in metamorphic zircon this is the peer reviewed version of the following article yakymchuk c kirkland c l clark c 2018 th u ratios in metamorphic zircon journal of metamorphic geology which has been published in final form at https doi org 10 1111 jmg 12307 this article may be used for non commercial purposes in accordance with wiley terms and conditions for self archiving

exsolution of rutile or apatite precipitates surrounding ruptured inclusions in garnet from uht and uhp rocks this study describes halos of rutile apatite needles and or plates centred on quartz inferred former coesite inclusions or multiphase inclusions in garnet both types of central inclusions are surrounded by cracks the multiphase inclusions contain mica or carbonate minerals and are interpreted to represent decrepitated fluid inclusions examples from two localities are examined i ultrahigh temperature uht metapelitic gneisses from the southern end of the central maine terrane in northeastern connecticut usa rutile only and ii ultrahigh pressure uhp diamondiferous saidenbachite from the saxonian erzgebirge rutile and apatite the needles of apatite or rutile are typically oriented in three directions within garnet chemical zonation in garnet shows clear ti or p depletion halos corresponding spatially with the rutile or apatite inclusion halos the radii of the inclusion halos when measured from the centre of the central inclusions are about two to several times the radii of the central inclusions we propose that the inclusion halos of rutile apatite formed by exsolution out of ti bearing and or p bearing garnet during retrogression because of its strength garnet can internally maintain higher pressures than the surrounding matrix nonetheless if the inclusion pressure is significantly greater than the confining lithostatic pressure then deformation of the host garnet can occur during exhumation high internal pressures relative to the matrix can result from retention of fluid entrapment pressure or a phase change with a large positive volume increase e g coesite quartz the differential stress imposed on the garnet adjacent to the central inclusion preceding and during mechanical failure would create dislocations and other crystalline defects which are ideal sites for exsolved precipitates to nucleate and grow the strain induced exsolution hypothesis is consistent with observations i the radii of the halos are roughly consistent with the pressure vessel model or the multi anvil model for an inclusion which predict that differential stress will drop off sharply away from the boundary of the central inclusion into the host garnet ii the rutile or apatite inclusions formed in ti or p bearing garnet adjacent to ruptured central inclusions rutile or apatite are rare or absent elsewhere in garnet even in areas of high ti or high p concentration in addition rutile is absent in areas surrounding the central inclusion that were depleted in ti prior to rupturing e g garnet rims that lost ti during retrogression thus both elevated ti p concentrations and proximity to inclusions which deformed the host garnet were necessary for halo formation iii reintegrated garnet ti or p contents in and adjacent to the halos obtained using wide beam electron probe microanalysis are consistent with local derivation of the ti or p necessary to form rutile and apatite from garnet elevated ti p concentrations in aluminous garnet are mostly found in uht hp uhp granulite and mantle environments consequently the phenomena described will most likely occur in such settings

ultradeep ultramafic mantle xenoliths transmission electron microscopy preliminary results abstract the defect microstructure of ultradeep garnets from the jagersfontein kimberlite pipe south africa was investigated by transmission electron microscopy these crystals exhibit a high density of dislocations most of which form well organized and regularly spaced subgrain boundaries free dislocations are also detected most of them have a burgers vector 1 2 111 shortest lattice repeat but a few 100 burgers vectors are also characterized especially in junctions small needle shaped pyroxene exsolutions are also detected they exsolved from the si rich garnets during assent to the earth s surface their nucleation and growth required bulk diffusion and this process may have affected the original dislocation microstructure it is believed however that the observed dislocation pattern still reflects the original deformation regime of garnets at very high pressure and temperature and this dislocation pattern strongly suggests that garnets were highly ductile finally a number of precipitates of a dense amorphous phase of pure carbon are also detected they might result from the amorphization of small diamonds exsolved from the garnet as the pressure was progressively released

ultradeep greater than 300 kilometers ultramafic upper mantle xenoliths geophysical discontinuities in earth s upper mantle and experimental data predict the structural transformation of pyroxene to garnet and the solid state dissolution of pyroxene into garnet with increasing depth these predictions are indirectly verified by omphacitic pyroxene exsolution in pyropic garnet bearing xenoliths from a diamondiferous kimberlite conditions for silicon in octahedral sites in the original garnets are met at pressures greater than 130 kilobars placing the origin of these xenoliths at depths of 300 to 400 kilometers these ultradeep xenoliths support the theory that the 400 km seismic discontinuity is marked by a transition from peridotite to eclogite

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

diamond inclusions in garnets from metamorphic rocks a new environment for diamond formation diamonds commonly occur in kimberlites lamproites and alluvial sediments derived from these rocks more recently diamonds or their graphite pseudomorphs have been discovered in ultramafic massifs1 and picrites2 here we report the occurrence of diamonds in situ in crustal rocks highly retrograded high pressure metamorphic garnet pyroxene and pyroxene carbonate garnet rocks biotite gneisses and schists from the kokchetav massif northern kazakhstan ussr the diamonds are cubo octahedral averaging 12 m in size and occur in zircons and with euhedral graphite as inclusions in unzoned garnets we believe that the zircon and garnet matrices protected these diamonds from retrogressive transformation to graphite mica rutile titanite clinopyroxene kyanite and zircon also occur as inclusions in garnet often intergrown with the diamonds equilibration relations of inclusions and host garnets indicate that both diamonds and graphite crystallized from a fluid phase under static conditions at pressures of 40 kbar and temperatures 900 1 000 c

analytical electron microscopy of a synthetic peridotite experimentally deformed in the β olivine stability field a synthetic harzburgite prepared by isostatic hot pressing of finely ground natural olivine admixed with 3 enstatite was deformed at high temperature and high pressure such that the olivine phase boundary was traversed both residual and new phases their grain sizes their deformation induced lattice defects and their compositions were then characterized by analytical electron microscopy owing to large heterogeneities in temperature pressure and deformation conditions contrasting microstructures were observed some areas consist essentially of untransformed olivine while the polymorph is the main constituent of other areas crystals of the polymorph are generally free of dislocations except at the grain boundaries of the larger grains where slip bands were nucleated probably induced by stress concentrations the activated glide systems are 021 100 the orthopyroxene grains have been transformed to very fine grained clinopyroxene and have reacted with chromite to form garnet with a majoritic component compared to olivine crystals of the phase contain significantly higher concentrations of fe and trivalent cations all crystals are free of inclusions confirming the conclusion from previous infrared spectroscopic analysis that the high oh concentration in this specimen is dissolved in the phase coupled with these previously measured oh concentrations our new measurements suggest that incorporation of hydrogen into the phase and substitution of trivalent cations into the octahedral sites may be coupled such increased complexity of mineral chemistry points to a need for detailed investigation of the spectrum of compositions stable in the structure and coexisting phases in order to better estimate the modal mineralogy of the transition zone

sequence stratigraphy and carbonate siliciclastic mixing in a terminal proterozoic foreland basin urusis formation nama group namibia abstract superb three dimensional exposures of mixed carbonate and siliciclastic strata of the terminal proterozoic urusis formation in namibia make it possible to reconstruct cross basin facies relations and high resolution sequence stratigraphic architecture in a tectonically active foreland basin six siliciclastic facies associations are represented coastal plain upper shoreface middle shoreface lower shoreface storm influenced shelf and pebble conglomerate siliciclastic shoreface facies pass seaward into and interfinger with facies of an open carbonate shelf four carbonate facies associations are present mid shelf shelf crest outer shelf and slope facies are arranged hierarchically into three scales of unconformity bounded sequences small scale sequences are one to tens of meters thick and span a few thousand years they consist of shelf carbonate with or without shoreface siliciclastic facies near the bottom medium scale sequences are tens of meters thick and span a few hundred thousand years they consist of shoreface siliciclastic facies in their lower parts which grade upward and pass seaward into shelf carbonate large scale sequences are tens to hundreds of meters thick and span 1 to 2 million years they are identified by widespread surfaces of exposure abrupt seaward shifts in shoreface sandstone patterns of facies progradation and retrogradation and shoreline onlap by medium scale sequences patterns of carbonate siliciclastic mixing distinguish tectonic from eustatic controls on the evolution of large scale sequences characteristics of eustatically controlled large scale sequences include 1 basal unconformities and shoreface sandstone that extend across the shelf to the seaward margin 2 retrograde carbonate and siliciclastic facies belts that onlap the shoreline together symmetrically during transgression and 3 upper shoreface sandstone that progrades seaward during highstand in contrast tectonically controlled sequences feature 1 basal erosion surfaces and upper shoreface sandstone that are restricted to near the landward margin and pass seaward into zones of maximum flooding and 2 asymmetric stratigraphic development characterized by landward progradation of carbonate from the seaward margin coincident with backstepping and onlap of the shoreline by siliciclastic facies a two phase tectonic model is proposed to account for the stratigraphic asymmetry of tectonically controlled sequences increased flexural bending during periods of active thrust loading caused submergence of the seaward margin and uplift of the landward margin rebound between thrusting episodes flattened the basin gradient and submerged the landward margin causing expansion of carbonate facies from the seaward margin and simultaneous transgression of the landward margin although the two phase model should apply to single lithology successions deposited in active foreland basins the mixing of carbonate and siliciclastic facies provides a particularly sensitive record of tectonic forcing the sensitivity may be sufficient for medium and small scale sequences to record higher frequency variations in flexural warping

submicron polyphase inclusions in garnet from the tananao metamorphic complex taiwan a key to unravelling otherwise unrecognized metamorphic events kyanite and staurolite occur in the tananao metamorphic complex as submicron inclusions in almandine rich garnet from a metamorphosed palaeosol weathering horizon near hoping eastern taiwan quartz rutile brookite and zircon are also found as associated submicron inclusions in garnet employing the reaction ilmenite kyanite quartz almandine rutile and the breakdown of staurolite and quartz as thermobarometers these submicron scale minerals formed at 8 3 8 8 kbar and 660 690 c this p t estimate is different from that i e 5 7 kbar and 530 550 c derived from matrix minerals which include almandine rich garnet muscovite chlorite chloritoid plagioclase quartz and ilmenite these results suggest that submicron inclusions in garnet like materials may record portions of the otherwise undocumented prograde path or provide information about previous metamorphic events and thus yield new insights into orogenic belts

deformation of peridotite in the mantle and extraction by kimberlite a case history documented by fluid and solid precipitates in olivine abstract during an extensive study of the microstructure of peridotite xenoliths from kimberlite pipes coprecipitation of fluid and solid phases has been observed in olivine one specimen which displays these precipitates particularly well contains three generations of olivine 1 a original coarse grained highly deformed porphyroclasts 2 b dynamically recrystallized neoblasts 3 c statically recrystallized tablets all three generations display precipitates on virtually all dislocations indicating that exsolution occurred during transport to the surface analysis by a variety of analytical techniques has determined that the solid phase is chrome aluminum spinel and the fluid phase is probably co 2 the deformation and the exsolution microstructure allow construction of a detailed model of the p t path followed by the xenolith to the surface and further allow refinement of our earlier diapiric model of kimberlite genesis

the pressure path of solid inclusions in minerals the retention of coesite inclusions during uplift abstract an inclusion model allows calculation of the stresses in and around minerals included in other minerals during changes in pressure and temperature the equations are applied to illustrate cooling and uplift histories of quarzo feldspathic rocks from 500 c and various pressures to ambient conditions even in the absence of pore fluid pressure microfractures may open at external pressures of 200 400 mpa and temperatures of 200 400 c due to differential volume changes of the constituent minerals coesite included in garnet cannot have formed during progressive metamorphism from quartz at lithostatic pressures below the coesite stability field because of differential volume changes coesite inclusions are captured by their host minerals at ultra high pressures and they persist to lower pressures because of the large volume increase occurring at the coesite to quartz transition the pi t path followed by the sio2 inclusion traces the boundary between the stability fields of coesite and quartz until radial fractures develop in the host at low external pressure

evolution of metamorphic volatiles during exhumation of microdiamond bearing granulites in the western gneiss region norway fluid inclusions in garnet kyanite and quartz from microdiamond bearing granulites in the western gneiss region norway document a conspicuous fluid evolution as the rocks were exhumed following caledonian high and ultrahigh pressure hp uhp metamorphism the most important of the various fluid mixtures and daughter minerals in these rocks are n2 co2 magnesian calcite n2 co2 ch4 graphite magnesian calcite n2 ch4 n2 ch4 h2o co2 and h2o nacl cacl2 nahcolite rutile also occurs in the n2 co2 inclusions as a product of titanium diffusion from the garnet host into the fluid inclusions volatiles composed of n2 co2 magnesian calcite characterise the ambient metamorphic environment between hp uhp peak and early retrograde metamorphism during progressive decompression the mole fraction of n2 increased in the fluid mixtures as amphibolite facies conditions were reached ch4 and later h2o appeared in the fluids concomitant with the disappearance of co2 and magnesian calcite graphite is ubiquitous in the host lithologies and fluid inclusions thermodynamic modelling of the metamorphic volatiles in a graphite buffered c o h system demonstrates that the observed metamorphic volatile evolution was attainable only if the fo2 increased from c 3 5 0 3 to 0 8 0 3 log units relative to the fmq oxygen buffer external introduction of oxidising aqueous solutions along a system of interconnected ductile shear zones adequately explains the dramatic increase in the fo2 the oxidising fluids introduced during exhumation were likely derived from dehydration of oceanic crust and continental sediments previously subducted during an extended period of continental collision in conjunction with the caledonian orogeny

microstructures of melt inclusions in anatectic metasedimentary rocks the occurrence of crystallized and glassy melt inclusions mi in high grade partially melted metapelites and metagraywackes has opened up new possibilities to investigate anatectic processes the present study focuses on three case studies khondalites from the kerala khondalite belt india the ronda migmatites spain and the barun gneiss nepal himalaya the results of a detailed microstructural investigation are reported along with some new microchemical data on the bulk composition of mi these inclusions were trapped within peritectic garnet and ilmenite during crystal growth and are therefore primary inclusions they are generally isometric and very small in size mostly 15 m and only rarely reaching 30 m they occur in clusters in most cases inclusions are crystallized nanogranites and contain a granitic phase assemblage with quartz feldspar and one or two mica depending on the particular case study commonly with accessory phases mainly zircon apatite rutile in many cases the polycrystalline aggregates that make up the nanogranites show igneous microstructures e g granophyric intergrowths micrographic quartz in k feldspar and cuneiform rods of quartz in plagioclase further evidence for the former presence of melt within the investigated inclusions consists of melt pseudomorphs similar to those recognized at larger scale in the host migmatites moreover partially crystallized inclusions are locally abundant and together with very small 8 m glassy inclusions may occur in the same clusters both crystallized and partially crystallized inclusions often display a diffuse nanoporosity which may contain fluids depending on the case study after entrapment inclusions underwent limited microstructural modifications such as shape maturation local necking down processes and decrepitation mainly in the barun gneiss which did not influence their bulk composition re homogenized nanogranites and glassy inclusions show a leucogranitic and peraluminous composition consistent with the results of partial melting experiments on metapelites and metagraywackes anatectic mi should therefore be considered as a new and important opportunity to understand the partial melting processes

rapid resetting of an estuarine recorder of the 1964 alaska earthquake tides and plants have already restored much of a landscape that the 1964 alaska earthquake destroyed at the head of a macrotidal estuary near anchorage in the vicinity of portage subsidence during the earthquake changed meadows thickets and spruce groves into barren tidal flats tidal flat silt and sand soon buried the pre earthquake landscape while filling intertidal space that the subsidence had made the flats supported new meadows and thickets by 1973 and new spruce by 1980 three new findings confirm that the flats aggraded rapidly and that their vegetation is maturing 1 most of the postearthquake deposits at portage date from the first decade after the 1964 earthquake their thickness of 23 sites in a 0 5 km 2 area was 1 4 0 2 m in 1973 1 6 0 2 m in 1991 and 1 6 0 3 m in 1998 2 many of the deposits probably date from the first months after the earthquake the deposits contain sedimentary couplets in which coarse silt or very fine sand is capped by fine or medium silt about 100 such couplets make up the lowest 0 5 m or more of the postearthquake deposits in two outcrops these couplets thicken and thin rhythmically both as groups of 5 20 couplets and as pairs of successive couplets probably the groups of thick couplets represent the highest tides the groups of thin couplets represent some of the lesser high tides and the pairs record inequality between twice daily high tides 3 in the 1980s and 1990s thickets expanded and spruce multiplied the vegetation now resembles the fossil assemblage rooted in the buried landscape from 1964 had the 1964 alaska earthquake been repeated a decade later the two earthquakes would now be recorded by two superposed buried landscapes near portage much more than a decade is probably needed to reset similar recorders at mesotidal estuaries of the cascadia subduction zone

origin of rutile needles in star garnet and implications for interpretation of inclusion textures in ultrahigh pressure metamorphic rocks the asterism effect of star garnet has been attributed to the oriented distribution of needle like rutile inclusions rutile needles occur in garnet from a wide range of metamorphic settings and rock bulk compositions and their origin has been ascribed to different mechanisms such as exsolution and used to interpret petrological and tectonic processes results from an optical and transmission electron microscopy of idaho star garnet indicate a co precipitation origin it was found that rutile needles are predominantly oriented along the rt grt and rt grt directions following multiple crystallographic orientation relationships cors i e cor 1 2 2 3 4 and 5 in 6 ray star garnet and are oriented solely along the rt grt directions following exclusively cor 2 in 4 ray star garnet the sole presence of cor 2 grt needles in the common 4 ray star garnet in contrast to the presence of both grt and grt needles with multiple cors in the rare 6 ray star garnet suggests that the cor 2 grt needle probably is the energetically most favoured variant as is also supported by the coincidence site lattice considerations the unique crystallography controlled microstructures of 4 ray star garnet including the cloudy domains behind the 111 grt or 100 grt fronts with abundant inclusions of rutile needle rutile compound needle and multiple phase inclusion as well as the clear domains behind the 110 grt fronts with only a few above inclusions concentrated exclusively within the linear grt oriented continuous tube like domains further suggest that the cor 2 grt needles in 4 ray star garnet most likely have a growth in origin co precipitating with garnet at its growth fronts close to thermodynamic equilibrium conditions the 6 ray star garnet on the other hand most likely formed under far from equilibrium conditions thereby yielding a maximum of 99 crystallographic variants of rutile needles with multiple cors in a single crystal in the light of these findings along with the common occurrences of the sole cor in many inclusion host systems owing to the requirement to minimize the energy barrier in an exsolution process the presence of both rt grt and rt grt needles with multiple cors in garnet of sulu eclogite and erzegebirge quartzofeldspathic rock would therefore cast doubt on the assertion of an exsolution origin of rutile needles in garnet from these ultrahigh pressure rocks