multi stage exhumation of young uhp hp rocks timescales of melt crystallization in the d entrecasteaux islands southeastern papua new guinea abstract on the d entrecasteaux islands southeastern papua new guinea png a series of domes expose the youngest known ultrahigh pressure uhp to high pressure eclogites and associated gneisses abundant evidence of partial melting is preserved throughout the d entrecasteaux domes in the form of variably deformed leucosomes dikes and plutonic bodies in order to understand 1 the timing of melt emplacement relative to the uhp metamorphism and 2 the complete exhumation and deformational history of the eclogites and surrounding gneisses a series of leucosomes dikes and eclogites from the mailolo dome in western fergusson island were analyzed by u pb id tims zircon geochronology zircons extracted from the eclogite at the uhp locality yield 206pb 238u tims dates from 5 60 0 22 to 4 61 0 18 ma zircons from three foliation parallel leucosomes are interpreted to record melt crystallization from 3 49 0 01 ma to 2 98 0 02 ma in comparison weakly deformed granitic granodioritic dikes that cut the leucosomes yield zircon 206pb 238u dates of 2 48 0 01 ma 2 420 0 002 ma based on these new and previously published results the eclogites may have undergone uhp metamorphism for several million years from 7 1 0 7 ma to 4 61 0 18 ma based on tims dates alone a more restricted interval of 5 6 4 6 ma is proposed following uhp metamorphism the eclogite and gneisses were exhumed to lower crustal depths intruded by foliation parallel leucosomes by ca 3 5 3 0 ma and by ca 2 45 ma late discordant dikes multiple generations of leucosomes and dikes allow a timeline for the exhumation of the png uhp terrane to be constructed mantle 100 km depths to the base of the crust in 1 my storage in the lower crust for 1 my and final emplacement into the shallow crust 1 my later

phlogopite and quartz lamellae in diamond bearing diopside from marbles of the kokchetav massif kazakhstan exsolution or replacement reaction exsolution lamellae of pyroxene in garnet grt coesite in titanite and omphacite from uhpm terranes are widely accepted as products of decompression however interpretation of oriented lamellae of phyllosilicates framework silicates and oxides as a product of decompression of pyroxene is very often under debate results are presented here of fib tem feg emp and synchrotron assisted infrared ir spectroscopy studies of phlogopite phlog and phlogopite quartz qtz lamellae in diamond bearing clinopyroxene cpx from ultra high pressure uhp marble these techniques allowed collection of three dimensional information from the grain boundaries of both the single phlogopite two phase lamellae phlogopite quartz and fluid inclusions inside of diamond included in k rich cpx and understanding their relationships and mechanisms of formation the cpx grains contain in their cores lamellae i which are represented by topotactically oriented extremely thin lamellae of phlogopite that generally are two units cell wide but locally can be seen to be somewhat broader and microdiamond the core composition is ca sub 0 94 k sub 0 04 na sub 0 02 al sub 0 06 fe sub 0 08 mg sub 0 88 si sub 1 98 al sub 0 02 o sub 6 00 fluid inclusions rich in k and si are recognized in the core of the cpx having no visible connections to the lamellae i lamellar ii inclusions consist of micron size single laths of phlogopite and lens like quartzmore or slightly elongated phlogopite quartz intergrowths all are situated in the rim zone of the cpx the composition of the rim is ca sub 0 95 fe sub 0 03 na sub 0 02 al sub 0 05 fe sub 0 05 mg sub 0 90 si sub 2 o sub 6 and the rim contains more ca mg than the core with no k there such chemical tests support our microstructural observations and conclusion that the phlogopite lamellae i are exsolved from the k rich cpx precursor during decompression it is assumed that cpx precursor was also enriched in h sub 2 o because diamond included in the core of this cpx contains fluid inclusions the synchrotron ir spectra of such diamond record the presence of oh sup stretching and h sub 2 o bending motion regions lamellar ii inclusions are interpreted as forming partly because of modification of the lamellae i in the presence of fluid enriched in k fe and si during deformation of the host diopside the latter is probably related to the shallower stage of exhumation of the uhp marble this study emphasizes that in each case to understand the mechanism of lamellar inclusion formation more detailed studies are needed combining both compositional structural and three dimensional textural features of lamellar inclusions and their host less

crystallization environment of kazakhstan microdiamond evidence from nanometric inclusions and mineral associations nanometric solid inclusions in diamond incorporated in garnet and zircon from felsic gneiss of the kokchetav massif kazakhstan have been examined utilizing electron microscopy and focused ion beam techniques host garnet and zircon contain numerous pockets of multiple inclusions which consist of 1 3 diamond crystals intergrown with quartz phengite phlogopite albite k feldspar rutile apatite titanite biotite chlorite and graphite in various combinations recalculation of the average chemical composition of the entrapped fluid represented by multiple inclusion pockets indicates that such fluid contained a low wt of sio2 suggesting a relatively low temperature fluid rather than a melt transmission electron microscopy revealed that the diamond contains abundant nanocrystalline inclusions of oxides rare carbonates and silicates within the 15 diamond crystals studied abundant inclusions were found of sio2 tio2 f e xoy c r 2o3 zrsio4 and single grains of thxoy baso4 mgco3 fecr2o4 and a stoichiometric fe rich pyroxene the diversity of trace elements within inclusions of essentially the same stoichiometry suggests that the kokchetav diamond crystallized from a fluid containing variable amounts of si fe ti cr zr ba mg and th and other minor components such as k na p s pb zn nb al ca cl most of the components in crystals included in diamond appear to have their origin in the subducted metasediments but some of them probably originate from the mantle it is concluded that kokchetav diamond most likely crystallized from a coh rich multicomponent supercritical fluid at a relatively low temperature hence the apparently low content of rock forming elements and that the diversity of major and minor components suggests interactions between subducted metasediments and mantle components

high temperature overprint in u hpm rocks exhumed from subduction zones a product of isothermal decompression or a consequence of slab break off slab rollback abstract this paper presents and discusses petrological observations from high to ultrahigh pressure u hp metamorphic terrains in relation to existing geophysical and numerical models for subduction and exhumation processes in orogenic belts the interpretations are mostly based on observations from gneiss terrains bearing abundant bodies mafic meta eclogite and ultramafic garnet peridotite and pyroxenite exposed in collisional orogens the inclusions and compositional zoning of minerals are considered to be first order information that is needed to constrain pt paths of hp uhp rocks and reconstruct the related geodynamic models for subduction and exhumation of crustal and mantle rocks the bohemian massif of the european variscides is used as the basis for a model example to explain these processes but u hp rocks from various other terrains are taken into consideration to discuss available pt paths in relation to proposed subduction and exhumation rates of u hp rocks based on geophysical and geochronological data primarily information used in this respect include textural relations and preserved prograde zoning in minerals from many u hp rocks which reveal that a relatively cool geothermal gradient typical of subduction zones tended to prevail during the prograde and peak pressure segments of pt paths prior to initiation of exhumation and may have continued even with cooling if exhumation rates were rapid the commonly applied interpretation of isothermal decompression during exhumation is critically appraised considering whether a simple thermal relaxation and radiogenic heating during exhumation is responsible for formation of post peak pressure retrograde mineral assemblages and textures observed in u hp rocks we go on to consider whether this can satisfactorily explain the often pervasive medium pressure high temperature metamorphic re equilibration of u hp rocks or whether an additional external source of heat is a better explanation we conclude that the commonly observed high temperature metamorphic overprint exhibited by u hp rocks occurs mostly after rocks have been exhumed from the subduction channel and have reached normal crustal positions when mantle upwelling resulting from slab breakoff delamination or slab rollback takes place at the onset of continent continent collision we also explore contrasting pt trajectories for mantle rocks that have been entrained into crustal material during their subduction or exhumation pt paths of mantle and subducted crustal rocks tend to converge as mantle rocks impinge upon the cooler subduction zone and once entrained share a common evolution that depends on the exhumation mechanism and rate considering all of the data presented in this work we conclude that the diverse polyphase metamorphic evolution exhibited by u hp terrains embodied in the pt paths of hp and uhp rocks has important consequences for reconstructing their changing thermal regimes and provides important constraints for geodynamic models involving subduction and the transition to collision

nanometric inclusions of carbonates in kokchetav diamonds from kazakhstan a new constraint for the depth of metamorphic diamond crystallization abstract previous studies have revealed that microdiamonds from the kokchetav ultra high pressure metamorphic terrane of kazakhstan contain nanometric scale inclusions of si fe ti and cr oxides because the structure of sio 2 inclusions was not confirmed to be coesite or stishovite due to their very small size such diamonds formerly served only as an indicator of a minimum pressure ca 4 gpa geothermobarometry applied to kokchetav diamond bearing rocks yielded a wide range of conditions t 700 c 1250 c and p 4 9 gpa our paper presents transmission electron microscopy studies with focused ion beam assistance that indicate that diamonds from marbles contain inclusions of aragonite caco 3 and magnesite mgco 3 and that aragonite and nitrogen bearing nanometric particles are associated with dislocations reflecting diamond growth at relatively high temperature conditions we determined the boundary of dolomite stability using the reaction camg co 3 2 dolomite caco 3 aragonite mgco 3 this allowed us to utilize available experimental data to evaluate the pressure at which diamond was crystallized taking into consideration uncertainties existing between experimental data produced in different laboratories we propose the pressure for kokchetav diamond crystallization to be 6 to 9 gpa this evaluation is based on the assumption that temperature was determined correctly as 980 c minimum and 1250 c maximum for diamond grade dolomitic marbles our data provide strong evidence that the metasedimentary rocks of the kokchetav massif containing diamonds were subducted to the depth of 190 280 km

deformation maps in grain size stress space as a tool to investigate mantle rheology abstract deformation maps have found widespread use in the study of the rheology of earth materials the usual procedure is to construct a map in stress temperature space from which predominant creep mechanisms strain rates and viscosities can be determined for a given grain size the rheology of polycrystals however depends strongly on grain size and consequently a fuller description would entail the construction of three dimensional stress grain size temperature diagrams as these do not display clearly the parameters of interest it is proposed to use deformation maps in stress grain size space at a given temperature in several situations of geodynamic interest grain size is a more critical parameter than temperature furthermore stress grain size maps have the advantages of simplicity and clarity for instance the boundaries between nabarro herring coble and power law creep are straight lines and so are constant strain rate and constant viscosity contours the triple point at which the three boundaries converge is under reasonable assumptions a function of temperature only and the slopes of the boundaries are independent of temperature it is therefore possible to project on a single map data for various temperatures the coordinates of the triple point contain all the necessary information for a synoptic representation of the rheology as an example deformation maps in stress grain size space are presented for olivine under laboratory and upper mantle conditions

alpine and pacific styles of phanerozoic mountain building subduction zone petrogenesis of continental crust a broad continuum exists between two distinct end member types of mountain building alpine type orogenic belts develop during subduction of an ocean basin between two continental blocks resulting in collision they are characterized by an imbricate sequence of oceanward verging nappes some alpine belts exhibit superimposed late stage backthrusting sediments are chiefly platform carbonates and siliciclastics in some cases associated with minor amounts of bimodal volcanics pre existing granitic gneisses and related continental rocks constitute an autochthonous parautochthonous basement metamorphism of deeply subducted portions of the orogen ranges from relatively high pressure hp to ultrahigh pressure uhp calcalkaline volcanic plutonic rocks are rare and have peraluminous s type bulk compositions in contrast pacific type orogens develop within and landward from long sustained oceanic subduction zones they consist of an outboard oceanic trench accretionary prism and an inboard continental margin island arc the oceanic assemblage consists of first cycle in part melanged volcaniclastics and minor but widespread cherts deep water carbonates intimately mixed with disaggregated ophiolites the section recrystallized under hp conditions recumbent fold vergence is oceanward a massive slightly older to coeval calcalkaline arc is sited landward from the trench complex on the stable non subducted plate it consists of abundant dominantly intermediate metaluminous i type volcanics resting on old crust both assemblages are thrown into open folds intruded by comagmatic i type granitoids and metamorphosed locally to regionally under high t low p conditions in the subduction channel of collisional and outboard circumpacific terranes combined extension above and subduction below allows buoyancy driven ascent of ductile thin aspect ratio slices of hp uhp complexes to midcrustal levels where most closely approached neutral buoyancy exposure of rising sheets caused by erosion and gravitational collapse results in moderate amounts of sedimentary debris because exhumed sialic slivers are of modest volume at massive sialic buildups associated with convergent plate cusps syntaxes tectonic aneurysms may help transport hp uhp complexes from mid to upper crustal levels the closure of relatively small ocean basins that typify many intracratonic suture zones provides only limited production of intermediate and silicic melts so volcanic plutonic belts are poorly developed in alpine orogens compared with circumpacific convergent plate junctions generation of a calcalkaline arc mainly depends on volatile evolution at the depth of magma generation phase equilibrium studies show that under typical subduction zone p t trajectories clinoamphibole ca al hydrous silicates constitute the major hydroxyl bearing phases in deep seated metamorphic rocks of morb composition other hydrous minerals are of minor abundance ca and na clinoamphiboles dehydrate at pressures of above approximately 2 gpa but low temperature devolatilization may be delayed by pressure overstepping thus metabasaltic blueschists and amphibolites expel h2o at melt generation depths and commonly achieve stable eclogitic assemblages partly serpentinized mantle beneath the oceanic crust dehydrates at roughly comparable conditions for reasonable subduction zone geothermal gradients however white micas biotites remain stable to pressures 3 gpa accordingly attending descent to depths of 100 km mica rich quartzofeldspathic lithologies that constitute much of the continental crust fail to evolve substantial amounts of h2o and transform incompletely to stable eclogite facies assemblages underflow of amphibolitized oceanic lithosphere thus generates most of the deep seated volatile flux and the consequent partial melting to produce the calcalkaline suite along and above a subduction zone where large volumes of micaceous intermediate and felsic crustal materials are carried down to great depths volatile flux severely diminishes thus continental collision in general does not produce a volcanic plutonic arc whereas in contrast the long continued contemporaneous underflow of oceanic lithosphere does

reply to comments by y zhu k feldspar in clinopyroxene from grt cpx silicate rocks of the kokchetav massif

size and exhumation rate of ultrahigh pressure terranes linked to orogenic stage abstract a growing set of data indicates a stark contrast between the evolution of two types of ultrahigh pressure uhp terranes large terranes that evolved slowly over 10 30 myr and small terranes that formed and were exhumed on timescales of

experimental evidence for diamond facies metamorphism in the dora maira massif the peak metamorphic conditions of subducted continental crust in the dora maira massif western alps have been revised by combining experimental results in the kcmash system with petrologic information from whiteschists textural observations in whiteschists suggest that the peak metamorphic assemblage garnet phengite kyanite coesite talc originates from the reaction kyanite talc garnet coesite liquid in the experimentally determined petrogenetic grid this reaction occurs above 45 kbar at 730 c at lower pressures talc reacts either to orthopyroxene and coesite or together with phengite to biotite coesite and kyanite the liberated liquid contains probably similar amounts of h2o and dissolved granitic components the composition of the liquid in the whiteschists at peak metamorphic conditions a major unknown in earlier studies was probably very similar to the liquid composition produced in the experiments therefore the experimentally determined petrogenetic grid represents a good model for the estimation of the peak metamorphic conditions in whiteschists experimentally determined si isopleths for phengite further constrain peak pressures to 43 kbar for the measured si 3 60 of phengite in the natural whiteschists all these data provide evidence that the whiteschists reached diamond facies conditions the fluid absent equilibrium 4 kyanite 3 celadonite 4 coesite 3 muscovite pyrope has been calibrated on the basis of garnet and phengite compositions in the experiments and serves as a geothermobarometer for ultra high pressure uhp metapelites for graphite bearing metapelites and kyanite phengite eclogites forming the country rocks of the whiteschists peak metamorphic pressures of about 44 3 kbar were calculated from this barometer for temperatures of 750 c estimated from garnet phengite thermometry therefore the whole ultra high pressure unit of the dora maira massif most likely experienced peak metamorphic conditions in the diamond stability field while graphite is common in the metapelites diamond has not been found so far the absence of metamorphic microdiamonds might be explained by the low temperature of metamorphism the absence of a free fluid phase in the metapelites and a short residence time in diamond facies conditions resulting in kinetic problems in the conversion of graphite to diamond

supersilicic clinopyroxene and silica exsolution in uhpm eclogite and pelitic gneiss from the kokchetav massif kazakhstan abundant exsolved quartz rods occur in matrix clinopyroxene of eclogite from the kokchetav massif kazakhstan these rocks are diamond grade ultrahigh pressure uhp metamorphic rocks that recrystallized at p 6 gpa and t 1000 c zircon is an excellent container which effectively protects peak uhp metamorphic phases from retrogression therefore to ascertain the pre exsolution composition of the clinopyroxene we analyzed clinopyroxene inclusions in zircon of the eclogite and a diamond bearing biotite gneiss clinopyroxene in zircon has an excess of fe 3 vi al over iv al na k and calculated cation totals significantly less than 4 0 per six o atoms the stoichiometry of these pyroxenes can be reconciled if the ca eskola end member ca 0 5 0 5 alsi 2 o 6 is considered the zircon hosted clinopyroxene in the eclogite contains up to 9 6 mol of the ca eskola component and in the biotite gneiss up to 18 2 mol whereas the matrix clinopyroxene contains much less 1 3 mol on average recalculation of the composition of the matrix clinopyroxene prior to exsolution of quartz rods yields 6 8 mol ca eskola component which is consistent with the composition of the clinopyroxene inclusions in zircon we conclude that the ca eskola component in the peak metamorphic clinopyroxenes broke down by a retrograde reaction 2 ca 0 5 square 0 5 alsi 2 o 6 rightarrow caal 2 sio 6 3 sio 2 resulting in exsolution of the quartz rods in the matrix clinopyroxene subducted crustal and supracrustal rocks form the ca eskola clinopyroxene at high pressures and temperatures the vacancy containing clinopyroxene may have an important bearing on the physico chemical properties of the subducted slab at upper mantle depth

boron cycling by subducted lithosphere insights from diamondiferous tourmaline from the kokchetav ultrahigh pressure metamorphic belt abstract subduction of lithosphere involving surficial materials into the deep mantle is fundamental to the chemical evolution of the earth however the chemical evolution of the lithosphere during subduction to depth remains equivocal in order to identify materials subjected to geological processes near the surface and at depths in subduction zones we examined b and li isotopes behavior in a unique diamondiferous k rich tourmaline k tourmaline from the kokchetav ultrahigh pressure metamorphic belt the k tourmaline which includes microdiamonds in its core is enriched in 11b relative to 10b 11b 1 2 to 7 7 and 7li relative to 6li 7li 1 1 to 3 1 it is suggested that the k tourmaline crystallized at high pressure in the diamond stability field from a silicate melt generated at high pressure and temperature conditions of the kokchetav peak metamorphism the heavy isotope signature of this k tourmaline differs from that of ordinary na tourmalines in crustal rocks enriched in the light b isotope 11b 16 6 to 2 3 which experienced isotope fractionation through metamorphic dehydration reactions a possible source of the heavy b isotope signature is serpentine in the subducted lithospheric mantle serpentinization of the lithospheric mantle with enrichment of heavy b isotope can be produced by normal faulting at trench outer rise or trench slope regions followed by penetration of seawater into the lithospheric mantle serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy b isotope signature which was acquired during the serpentinization prior to subduction the fluids could ascend and cause partial melting of the overlying crustal layer and the resultant silicate melt could inherit the heavy b isotope signature the subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle

water content in natural eclogite and implication for water transport into the deep upper mantle abstract infrared spectroscopy and ion micro probe measurements showed that the major constituent minerals of eclogites from the kokchetav massif which have been subducted to 180 km depths contain significant amounts of water up to 870 ppm h 2 o by weight in omphacite 130 ppm h 2 o in garnet and 740 ppm h 2 o in rutile omphacite shows three hydroxyl absorption bands at 3440 3460 3500 3530 and 3600 3625 cm 1 garnet has a single band at 3580 3630 cm 1 and rutile has a single sharp band at 3280 cm 1 the hydroxyl absorbance at these wavenumbers changes with the crystal orientation in polarized infrared radiation indicating that the water is structurally incorporated in these minerals the water contents in omphacite and garnet increase systematically with the metamorphic pressure of the host eclogites the partitioning coefficient of the water content between coexisting garnet and omphacite is similar in different eclogites d grt omp 0 1 0 2 but decreases slightly at high pressure based on the mineral proportions of the eclogites we estimate bulk rock water content in the eclogites ranging from 3070 to 300 ppm h 2 o by weight although hydrous minerals are absent in the diamond grade eclogite 60 kbar and 1000 c trace amounts of water are incorporated in the nominally anhydrous minerals such as omphacite and garnet the presence of significant water in these minerals implies that the subducting oceanic crust can transport considerable amounts of water into the deep upper mantle beyond the stability of hydrous minerals such water may be stored in the deep upper mantle and have an important influence on dynamics in the earth s interior

seismotectonics of northeastern united states and adjacent canada data for local earthquakes recorded by a network of stations in northeastern united states and adjacent canada were analyzed to study the seismicity the relationship between earthquakes and known faults the state of stress and crustal and upper mantle velocity structure in addition portable seismographs were deployed in the field to study aftershocks as a result accurate locations for about 364 local earthquakes 2 mb 5 and 22 focal mechanism solutions were determined a comparison of the spatial distribution of these events 1970 1979 with historical earthquakes 1534 1959 reveals that seismic activity in the northeast is relatively stationary in space those areas that have had little or no seismicity historically are relatively aseismic today whereas the historically active areas are also active today the instrumental locations historical seismicity and focal mechanism solutions show an internal consistency that help us distinguish two distinct seismogenic provinces 1 the adirondack western quebec province is a northwesterly trending zone of seismic activity about 200 km wide and at least 500 km long extending from the se adirondacks into western quebec canada thrust faulting on planes striking nnw to nw appears to predominate and the inferred axis of maximum horizontal compression is largely uniform and trends wsw nearly parallel to the calculated absolute plate motion of north america little or no seismicity is found where anorthosite outcrops at the surface correlations between gravity anomalies and earthquake locations suggest that seismic activity in this zone is localized to regions of steep ne or sw gradient in bouguer anomalies this zone does not appear to extend southeastward to boston as proposed by some workers 2 the appalachian province is a northeasterly trending zone of seismic activity extending from northern virginia to new brunswick canada highangle reverse or thrust faulting on n to ne trending planes appears to predominate the western margin of this province however appears to be relatively aseismic we attribute this relative lack of activity to one or more of the following the presence of igneous activity postdating rifting of africa from north america the occurrence of intense metamorphism during the acadian orogeny which may have annealed preexisting faults and the predominance of ductile as opposed to brittle deformation in the geologic past the inferred axis of maximum horizontal compression along the eastern margin of the appalachians is rather uniform and trends w wnw almost perpendicular to the magnetic lineations offshore we suggest that this w wnw compression reflects the gravitational force arising from horizontal density variations in the oceanic lithosphere as it cools and moves away from spreading centers

diversity of potassium bearing tourmalines in diamondiferous kokchetav uhp metamorphic rocks a geochemical recorder from peak to retrograde metamorphic stages abstract chemical variations and inclusion mineralogy of tourmaline in diamond bearing ultrahigh pressure uhp gneisses and related siliceous rocks from the kokchetav massif kazakhstan are extensively investigated in conjunction with a review of previously discovered k bearing tourmaline with microdiamond inclusions tourmalines in these kokchetav uhp rocks have a wide compositional range dravite potassium oxy dravite schorl uvite feruvite foitite and some of their oxy variants with potassium content ranging from 0 to 0 576 atoms per formula unit apfu based on y z t cations 15 or 0 2 76 wt k 2 o and decreasing from core to rim the variation in potassium is spatially related to the inclusion mineralogy and is attributed to changes in metamorphic grade four stages of tourmaline growth in the kokchetav uhp rocks are recognized based on the potassium contents and occurrences in order of decreasing p and t 1 k dominant tourmaline k na ca and x vacancy with microdiamond and high si ti phengite inclusions and without quartz inclusions 2 k rich tourmaline k 0 2 0 05 apfu with graphite phengite kyanite and quartz inclusions 3 k poor tourmaline k 0 05 0 01 apfu with matrix quartz and biotite and 4 k free anhedral or overgrown tourmaline associated with low p t minerals such as amphibole or chlorite several lines of evidence also suggest that k dominant tourmaline crystallized in the diamond stability field tourmalines in the kokchetav uhp rocks recorded multi stage growth history from peak uhp conditions through a granulite facies overprint event including partial melting and ultimately to the latest retrograde metamorphism during exhumation

evolution of host inclusion systems a visco elastic model a visco elastic model is suggested to recover the p t t paths of spherically symmetrical host inclusion systems from residual pressure patterns for a coesite garnet aragonite garnet and diamond garnet system with partial transition of high pressure polymorphs to low pressure ones the model predicts that the exhumation history of ultra high pressure metamorphic rocks from depths below 90 km began with pressure decrease to 1 gpa 40 km depth while the temperature remained high 800 c then the system cooled and decompressed to ambient conditions non spherical inclusion shapes in the 3 d model lead to heterogeneities in residual pressure and shear stress distributions as well as to significant gradients of shear stress which may affect the kinetics and thermodynamics of phase transformation in the inclusions

diamond graphite relationships in ultrahigh pressure metamorphic rocks from the kokchetav massif northern kazakhstan graphite inclusions in diamond k bearing clinopyroxene garnet and kyanite and graphite coatings around microdiamonds from the ultrahigh pressure kokchetav massif northern kazakhstan were investigated by means of scanning electron microscopy laser raman spectroscopy and x ray diffraction important observations include the increasing size of the graphite crystals from the diamond graphite interface to the external part of the graphite coatings the high volume fraction of graphite in the graphite coatings the presence of composite crystals of successively formed diamond core graphite mantle zone diamond rim external graphite coating the spherulitic texture of the graphite coatings the formation of both ordered and disordered graphite and the absence of any fluid associated with the graphite inclusions in diamond and other ultrahigh pressure metamorphic uhpm minerals these features combined with the presence of oriented graphite flakes in k bearing clinopyroxene and in diamond bearing garnet and kyanite and the presence of intergranular diamonds without graphite coatings in the quartzo feldspathic matrix require reconsideration of the generally accepted diamond graphitization model for interpreting the formation of graphite in uhpm rocks metastable growth of graphite within the diamond stability field is suggested and the following crystallization scheme for the c polymorph is proposed graphite was the first c polymorph formed in the diamond stability field followed by diamond the graphite coatings around diamond formed during the final stage of uhpm conditions

the kokchetav massif kazakhstan type locality of diamond bearing uhp metamorphic rocks abstract after the discovery of metamorphic coesite in crustal rocks from the western alps italy and the western gneiss region norway in the mid 1980s of the last century metamorphic diamond was observed only a few years later in situ in the kokchetav massif kazakhstan findings of such coesite and diamond bearing ultrahigh pressure metamorphic uhp rocks with protoliths formed or embedded in crustal levels and subsequently experienced pt conditions within or even higher than the coesite stability field have dramatically changed our geodynamic view of orogenetic processes these occurrences provide evidence that crustal rocks were subducted into mantle depths and exhumed to the surface recent studies even suggest continental subduction to depths exceeding 300 km these rocks have been extensively studied and many new and important observations have been made thus far more than 350 papers have been published on various aspects of kokchetav uhp rocks the kokchetav massif of northern kazakhstan is part of one of the largest suture zones in central asia and contains slices of hp and uhp metamorphic rocks classical uhp rocks mainly occur in the kumdy kol barchi kol and kulet areas and include a large variety of lithologies such as calcsilicate rocks eclogite gneisses schists marbles of various compositions garnet pyroxene quartz rocks and garnet peridotite most of them contain microdiamonds some of which reach a grain size of 200 m most diamond grains show cuboid shapes but in rare cases diamonds within clinozoisite gneiss from barchi kol occur as octahhedral form microdiamonds contain highly potassic fluid inclusions as well as solid inclusions like carbonates silicates and metal sulfides which favour the idea of diamond formation from a c o h bearing fluid nitrogen isotope data and negative 13c values of kokchetav diamonds indicate a metasedimentary origin pt estimates of kokchetav uhp rocks yield peak metamorphic conditions of at least 43 kbar at temperatures of about 950 1000 c some zircon separates show inherited proterozoic cores and 537 530 ma uhp metamorphic mantle zones several ar ar ages on micas scatter around 529 528 and 521 517 ma and reflect different stages of the exhumation history migmatization occurred during exhumation at about 526 520 ma isotopic studies on calcsilicate rocks confirm a metasedimentary origin 18o values of garnet and clinopyroxene of a layered calcsilicate rock rule out the possibility having a primitive mantle protolith similar studies on eclogites indicate their basaltic protolith having experienced water rock interaction prior to uhp metamorphism a number of unique mineralogical findings have been made on kokchetav uhp rocks k feldspar exsolutions in clinopyroxene demonstrate that potassium can be incorporated into the cpx structure under upper mantle pressures other significant observations are coesite exsolutions in titanite quartz rods in cpx the discovery of k tourmaline as well as new minerals like kokchetavite a hexagonal polymorph of k feldspar and kumdykolite an orthorhombic polymorph of albite the kokchetav uhp rocks represent a unique and challenging stomping ground for geoscientists of various disciplines from crystallography petrology and geochemistry to geophysics and geodynamics geotectonics it concerns all who are interested in the diverse metamorphic processes under upper mantle conditions

an experimental investigation of hydroxyl solubility in jadeite and na rich clinopyroxenes the solubility and incorporation mechanisms of water in synthetic water saturated jadeite and na rich clinopyroxenes have been experimentally investigated infrared spectra for water saturated jadeite synthesised from 2 0 to 10 gpa show two prominent sharp peaks at 3 373 and 3 613 cm 1 together with several weaker features in the oh stretching region indicating that there are at least 5 distinct modes of hydrogen incorporation in the structure water solubility in pure jadeite reaches a maximum of about 450 ppm by weight at 2 gpa and slowly decreases with increasing pressure to about 100 ppm at 10 gpa solubility can be described by the function coh a fh2o0 5 exp p vsolid rt where coh is water solubility in ppm h2o by weight a is 7 144 ppm bar0 5 fh2o is water fugacity and vsolid 8 019 cm3 mol is the volume change of the clinopyroxene upon incorporation of oh jadeite provides a good model for understanding hydrogen incorporation mechanisms in more complex omphacite compositions assignment of absorption bands in ir spectra verifies the importance of cation vacancies on the m2 site in providing mechanisms for hydrogen incorporation however results also suggest that substitution of lower valency cations onto the m1 site may also be important solid solution of jadeite with diopside and in particular with ca eskola component leads to a drastic increase of water solubility and the bulk composition has a more important effect on the capacity of omphacite to store water than pressure and temperature omphacite is expected to be the major carrier of water in a subducted eclogite after the breakdown of hydrous minerals

viscoelastic membrane tectonics the theory of membrane tectonics proposed by turcotte and oxburgh 1973 to explain intraplate tensional features and earthquakes and developed by turcotte 1974 for an elastic lithospheric membrane is extended to the case of a viscoelastic lithosphere such an extension may be expected to seriously modify the theory since for all lithospheric viscosities except the very highest the time scale for viscous relaxation is comparable to the time scale for changes in plate curvature it is found that for most viscosities considered the membrane stresses generated by changes in plate curvature do not exceed 10 bars we conclude that either the effective viscosity of the lithosphere is much higher than indicated by most studies or membrane tectonic stresses play a secondary role in the generation of intraplate features and earthquakes

geochronology petrogenesis and tectonic settings of pre and syn ore granites from the w mo deposits east kounrad zhanet and akshatau central kazakhstan abstract there is significant debate regarding the mineralization ages of the east kounrad zhanet and akshatau w mo deposits of central kazakhstan and the petrogenesis and tectono magmatic evolution of the granites associated with these deposits to address these issues we present molybdenite re os dating zircon u pb dating whole rock geochemistry as well as sr nd pb and zircon o hf isotopic analyses on the pre mineralization and ore forming granites u pb dating of zircons from pre mineralization granitic rocks yield late carboniferous ages of 320 309 ma whereas ore forming granites have early permian ages of 298 285 ma molybdenite re os isotopic data indicate a mineralization age of 296 ma at east kounrad 294 ma at akshatau and 285 ma at zhanet the pre ore and ore forming granites are high k calc alkaline metaluminous to slightly peraluminous i type granites the pre mineralization granites are relatively unfractionated whereas the ore forming granites are highly fractionated the fractionating mineral phases are probably k feldspar apatite ti bearing phases and minor plagioclase the pre mineralization and ore forming rocks are characterized by similar sr nd pb hf o isotopic compositions 87 sr 86 sr i 0 70308 0 70501 e nd t 0 5 to 2 8 207 pb 204 pb 15 60 15 82 zircon e hf t 1 2 to 15 6 and 18 o 4 6 to 10 3 whole rock t dm c nd 840 1120 ma and zircon t dm c hf 320 1240 ma the isotopic characteristics are consistent with a hybrid magma source caused by 10 30 assimilation of ancient crust by juvenile lower crust the geochronology and geochemistry of these granites show that the late carboniferous pre mineralization granitic rocks formed during subduction whereas the early permian ore forming highly fractionated granite probably underwent significant fractionation with a restite assemblage of k feldspar apatite ti bearing phases and minor plagioclase and developed during collision between the yili and kazakhstan terranes commenced at the latest late carboniferous

the diamond bearing kokchetav uhp massif in northern kazakhstan exhumation structure in the kokchetav ultrahigh pressure uhp massif in northern kazakhstan diamond bearing uhp rocks occur exclusively in a western rhomb shaped domain that differs from an eastern transpressional domain with coesite bearing remnants indicating highest uhp conditions different mechanisms may have contributed to the early ascent of the uhp kokchetav massif the geometry and structure of the diamond bearing domain are interpreted as a sheath like fold coeval with early stage melting in contrast the coesite bearing domain has a sheet like geometry at mid crustal level this early difference in the ascending uhp wedge is reflected in a western rhomb horst and an eastern transpression structure respectively the latter extends to the east borovoye where the uppermost sequences of the uhp massif were defined by others sheath folding is postulated as a suitable mechanism contributing to the early buoyancy driven ascent of the subducted rocks and explains the selective spatial distribution of diamond and coesite bearing sequences preserved in the wedge

multiple breakdown and chemical equilibrium of silicic clinopyroxene under extreme metamorphic conditions in the kontum massif central vietnam clinopyroxene in ultrahigh temperature mafic granulites from the kontum massif in central vietnam records multiple metamorphic stages manifested as exsolution textures quartz rods and orthopyroxene hornblende plagioclase needles and as symplectitic intergrowths involving clinopyroxene plagioclase these textures suggest a metamorphic evolution characterized by decompression and subsequent cooling from eclogite facies to amphibolite facies conditions through ultrahigh temperature conditions quartz rods in clinopyroxene and clinopyroxene plagioclase symplectites were formed under eclogite conditions prior to ultrahigh temperature metamorphism the orthopyroxene hornblende plagioclase needles in clinopyroxene are regarded as cooling products after ultrahightemperature metamorphism recalculated compositions of precursor clinopyroxene show supersilicic composition during the metamorphic evolution the chemical composition varies from silicic ca eskola rich via sodic jadeite rich to aluminous ca tschermak rich compositions presence of supersilicic clinopyroxene suggests that the granulite decompressed from possible ultrahigh pressure conditions ca 800 900 c at 2 3 gpa preceding the ultrahigh temperature stage 1050 c at 1 3 gpa which provide strong constraints on the tectonic evolution of the indochina region and it also provides insights on crustal exhumation at a continental collision zone another significant aspect of this study is that the breakdown textures of clinopyroxene and its chemical variations may provide important information in establishing pre and post peak evolution especially for extremely high temperature or high pressure metamorphic rocks

microseismicity in the mid st lawrence valley charlevoix zone quebec abstract previous seismicity studies of the charlevoix zone of the mid st lawrence valley have defined the extent of the active zone continued monitoring of this zone has yielded more hypocenters that together with the previous data give a more detailed picture of the hypocentral distribution of the microactivity a more definite correlation can now be made with the known structure in this region and the faults of the st lawrence valley in general the cumulative data permit a definition of lateral boundaries of the seismic activity range of focal depths and anomalous nonseismic zones it is also possible to make a correlation with the normal faults that were probably associated with the paleorifting of the st lawrence valley but are now under compression in this seismically active region part of these preexisting partially sealed faults were most likely weakened again at the time of formation of the charlevoix impact structure

uppermantle anisotropy and the oceanic lithosphere rayleigh wave and love wave dispersion data for oceanic paths cannot be satisfied by an isotropic uppermantle and it is incorrect to invert these two datasets independently for separate isotropic structures available phase and group velocity data are inverted for oceanic structure as a function of age taking into account anelastic dispersion sphericity and anisotropy the resulting models are quite different from previous results which ignore the above effects and the extra parameters involved in proper anisotropic inversion the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age and an anisotropic low velocity zone with an age dependent anisotropy the lid or seismic lithosphere reaches a maximum thickness of 50 km which is about one half the thickness obtained in previous isotropic or pseudo isotropic inversions the seismic lithosphere therefore may be comparable in thickness to the elastic or flexural lithosphere raising the possibility that both are controlled by effects other than temperature stress and time such as mineralogy crystal orientation or partial melting the velocities in the low velocity zone are higher than inferred by previous surface wave studies

analysis of states of stress between provinces of constant stress recent studies have indicated the existence of crustal provinces or domains within which the state of stress shows little apparent horizontal variation between provinces the state of stress may undergo substantial changes often over remarkably short distances as analyzed here the transition in stress state between adjacent domains is caused by shear tractions acting on the base of the elastic brittle layer and is mediated by a stress field within a zone between the provinces that can be determined by solving the equations of force equilibrium and stress compatibility the component of horizontal stress oriented perpendicular to the provincial boundary changes smoothly across the transition zone from one province to the other whereas the horizontal stress oriented parallel to the boundary shows smaller but discontinuous changes the horizontal component of shear stress is unlikely to change from one province to another because of the implausible nature of the required basal traction thus in this regard states of stress in adjacent domains appear to be coupled the coincidence of a number of stress transition zones with boundaries defined by heat flow suggests that in many cases the basal tractions are the result of thermally induced mass transport below the elastic brittle layer in the direction of increasing horizontal compressive stress this analysis provides a quantitative relationship between changes in the stress field measured in the upper portion of the crust and shear stresses acting on the base of the elastic brittle layer

low pressure and low temperature k bearing kosmochloric diopside from the osayama serpentinite melange sw japan kosmochloric diopside with high k content up to 0 56 wt 0 026 k atom per formula unit was discovered from the osayama serpentinite melange in the chugoku mountains sw japan k bearing clinopyroxene fills microcracks 5 150 m in wide together with uvarovite within albite vein of a tremolite rock compositions of analyzed clinopyroxene consist mainly ofkosmochlor augite 92 98 mol ko 1 9 3 8 aug 5 6 7 6 components and minor amounts of jadeite 0 6 mol aegirine 0 5 mol ca tschermak 0 3 mol and k kosmochlor 0 2 mol although the k content in clinopyroxene is also variable and heterogeneous even in a single vein clinopyroxene with higher k content occurs in ko rich part higher magnification secondary electron images confirmed that exsolution and inclusion are essentially absent in the analyzed clinopyroxenes the good negative correlation between cr na k and ca mg fe 2 indicates the cr incorporation into the octahedral site furthermore k correlates with na and cr indicating a simultaneous enrichment of k for na and cr during pyroxene growth textual relations and parageneses and compositions of minerals suggest that the k cpx precipitated together with uvarovite in brittle microcracks directly from a ca and cr rich hydrothermal fluid at approximately p 4 gpa environment permits to host relatively large k cation into the clinopyroxene structure our finding indicates that the incorporation of k into the kosmochlor diopside series solid solution with at least 0 2 cr cation p f u is possible even at low p conditions

late paleozoic magmatic record of east junggar nw china and its significance implication from zircon u pb dating and hf isotope abstract late paleozoic magmatic rocks including basic dykes basaltic andesite rhyolite keratophyre and syenite porphyry with minor tuff are widespread in the western margin of the east junggar terrane in situ zircon u pb dating and hf isotope analyses were carried out for these magmatic rocks from the baijiangou and zhangpenggou localities of east junggar integrating with geochemical data to investigate their tectonic evolution as well as crustal accretionary process of this region in the late paleozoic inherited zircons from basic dykes range in age from 435 ma to 300 ma the zhangpenggou rhyolite and keratophyre have typical arc like geochemical signatures and were formed in the early carboniferous 332 ma and 336 ma respectively suggesting they are products of subduction related magmatism the baijiangou rhyolites were formed in the late carboniferous 315 ma and 323 ma and their formation ages are similar to those of the syenite porphyries 307 ma and 312 ma the hf model ages and the formation ages of zircons from these magmatic rocks are alike with positive e hf t values vary from 0 7 to 16 6 implying that voluminous growth of juvenile crust happened in the east junggar terrane during the late paleozoic the absence of precambrian inherited zircons in basic dykes indicates the lack of precambrian basement beneath the east junggar terrane taking geochronological studies on regional ophiolites into account the east junggar terrane is considered as a devonian carboniferous oceanic island arc which has been continuously accreted to the southern active margin of the siberian craton since the early carboniferous

raman spectroscopic and microscopic criteria for the distinction of microdiamonds in ultrahigh pressure metamorphic rocks from diamonds in sample preparation materials natural diamond from three ultrahigh pressure metamorphic uhpm terranes erzgebirge massif germany kokchetav massif northern kazakhstan rhodope metamorphic province greece and synthetic diamond from cutting and polishing materials paste spray saw blade were studied by means of optical microscopy and raman microspectroscopy to constitute a new petrographic and spectroscopic data set that might be a useful tool for identifying and characterizing metamorphic diamond several criteria are established for distinguishing natural microdiamond identified in a rock thin section from the externally introduced ones i e diamond as residual particles contaminants from the cutting and polishing material such as the diamond size the presence of inclusions coatings or coexistent phases and two diamond raman band parameters i e the raman shift and the full width at half maximum height fwhm

paleozoic crustal growth and metallogeny of central asia evidence from magmatic hydrothermal ore systems of central kazakhstan abstract the ore deposit spectrum of central kazakhstan reflects a range of lithospheric magmatism controlled by the polycyclic geodynamic evolution of an active continental margin which develops from back arc oceanic settings volcanic hosted massive sulphide cu au ore deposits to subduction controlled calcalkaline magmatism copper porphyries with subsequent stages of crust differentiation of low degree partial melting and extended intramagmatic fractionation molybdenum porphyries on to continental rifting peralkaline ree zr nb rich systems mesothermal gold deposits mark transcrustal shear zone controlled fluid conduits formed during arc slicing and thermal relaxation in a post orogenic setting the ore deposits characterize successive and spatially overlapping stages of crustal growth and consolidation the general subduction setting of this range of ore deposits is reflected by calc alkaline trends in the associated subalkaline high k felsic rocks with a wide range in silica contents the predominant metal spectrum of au cu and mo indicates relatively oxidized magmatic hydrothermal systems in accordance with the metaluminous i type nature of their igneous host rocks i e oxidized igneous precursor material despite of presumably highly variable ratios of mantle crust components in individual magmatic systems gabbros to leucogranites most rocks have very similar positive initial e nd values of 0 to 5 5 and depleted mantle model ages in the range of 500 800 ma the ubiquitous relatively young mantle extraction age is likely to characterize the lower crust of central kazakhstan this basement is interpreted as back arc oceanic crust that formed behind oceanwards drifting continental margin slivers during the initial stages of the active continental margin evolution of the late precambrian angara baltica supercontinent the early back arc oceanic crust was transformed into the present lower crust during the paleozoic orogenic evolution in which the back arc crust was buried by magmatic arc and sedimentary material and recurrently affected by high grade metamorphism basaltic melt injection underplating and granitic melt extraction anorogenic rift related permian peralkaline riebeckite granites with ree zr nb mineralization have very high positive e nd of 5 to 8 which is probably inherited from young subcrustal lithosphere at the mantle crust boundary that was affected by partial remelting due to asthenospheric upwelling during rifting

exhumation of high pressure rocks of the kokchetav massif facts and models abstract the exhumation of ultrahigh pressure uhp metamorphic units from depths more than 100 120 km is one of the most intriguing questions in modern petrology and geodynamics we use the diamondiferous kumdy kol domain in the kokchetav massif to show that exhumation models should take into consideration initially high uplift velocities from 20 down to 6 cm year and the absence of the deformation of uhp assemblages the high rate of exhumation are indicated by ion microprobe shrimp dating of zircons from diamondiferous rocks and supported by the low degree of nitrogen aggregation in metamorphic diamonds diamondiferous rocks in the kumdy kol domain occur as steeply dipping 60 80 thin slices few hundred metres within granite gneiss using geological petrological and isotopic geochemical data we show that partial melting of diamondiferous metamorphic rocks occurred a very important factor which has not been taken into account in previous models deformation of diamondiferous rocks at kumdy kol is insignificant diamond inclusions in garnet are often intergrown with mica crystals carrying no traces of deformation all these facts could be explained by partial melting of metapelites and granitic rocks in the kumdy kol domain the presence of melt is responsible for an essential reduction of viscosity and a density difference between crustal rocks and mantle material and reduced friction between the upwelling crustal block the subducting and overriding plates besides the exhumation rate seems to depend on internal pressure in the subducting continental crustal block which can be regarded as a viscous layer between subducting continental lithosphere and surrounding mantle we construct different models for the three stages of exhumation a model similar to corner flow for the first superfast exhumation stage an intermediate stage of extension most important from structural point of view and a very low rate of exhumation in final diapir erosional uplift

dating of zircon from ti clinohumite bearing garnet peridotite implication for timing of mantle metasomatism garnet peridotites from the kokchetav ultrahigh pressure uhp massif contain abundant volatile and high field strength element hfse bearing minerals such as ti clinohumite and zircon these characteristics are interpreted to be related to fluid infiltrated mantle metasomatism from the oceanic lithosphere that had been subducted below the area the zircons from the peridotites were dated by using sensitive high resolution ion microprobe shrimp and yielded apparent u pb ages of 554 494 ma weighted mean age 528 ma that are mostly consistent with the timing of uhp metamorphism deduced from diamond bearing country rocks in this massif these zircons have an almost flat rare earth element ree pattern and very low ree concentrations these characteristics are similar to those observed in kimberlitic zircons inherited zircon cores although only rarely preserved yielded apparently proterozoic ages and have different trace element characteristics compared to the overgrowth rims these features indicate that the mantle metasomatic events and the recrystallization of ti clinohumite and zircon were due to hfse enriched fluid infiltration during the uhp metamorphism at great depths the metasomatized mantle may have been transported farther into the deep upper mantle and contributed to the source of intraplate magmas such as kimberlites and alkali basalts because these rocks have characteristically high volatile and hfse concentrations such as those of the ti clinohumite bearing garnet peridotites

upper crustal stresses and vertical stress migration in eastern canada diversified phenomena are contributing to our knowledge of various aspects of the stress field and the origin of the crustal stresses in eastern canada both in situ stress measurements to 2100 m and earthquake fault plane solutions in the upper crust 5 20 km indicate that the maximum horizontal stress is greater than the vertical absence of earthquakes in the lower crust 20 km implies a comparatively lower deviatoric horizontal stress in this layer stress directions as determined from both in situ measurements and earthquake fault plane solutions indicate an overprint confined to the ene octant which correlates with the direction predicted by modeling of plate tectonic stresses thus spreading mid atlantic ridge stress is considered to be one of the important contributors to the stress field in eastern canada viscoelastic relaxation of this stress is considered to enhance the deviatoric stress level in the upper crust while simultaneously reducing that in the lower crust the crust acts as a stress guide within which stresses in the upper crust that are lost through brittle failure i e earthquake stress drop can be replenished from the lower crust moreover the directionality predicted by modeling of spreading mid atlantic ridge stress is maintained incomplete postglacial rebound also contributes to deviatoric compression other possible contributors to the upper crustal stress field are basal drag and membrane stress but the relative contributions from these sources are not properly understood

p t t path of garnetites in south altyn tagh west china a complete record of the ultradeep subduction and exhumation of continental crust

oxygen isotope variations of garnets and clinopyroxenes in a layered diamondiferous calcsilicate rock from kokchetav massif kazakhstan a window into the geochemical nature of deeply subducted uhpm rocks calcsilicate and garnet pyroxene rocks with dolomite and mg calcite matrices occur with uhpm dia mondiferous biotite gneisses and schists of the kokchetav massif the calcsilicates are characterized by high dia mond grade k bearing diopside and very high mg garnets mg 77 with variable ca contents ca 42 5 80 a rare calcsilicate sample with alternating layers of different bulk compositions was selected for oxygen isotope and electron probe microanalysis of garnets and pyroxenes a grain of fresh garnet with a brownish yellow luminescent inner domain mg 94 and a non luminescent outer part mg 88 was selected for in situ analysis of d 18 o by ion microprobe 10 lm spot the profile demonstrates a d 18 o gradient of 1 5 200 lm from 11 3 rim to 12 8 core vsmow additional 2 mg samples of hand picked garnet and clinopyroxene fragments from different parts of the same sample selected by color and chemical differences were analyzed for d 18 o by laser fluorination yielding even larger differences in d 18 o 6 3 10 6 in garnets and 6 1 8 1 in clinopyroxenes the zonation in d 18 o among grains of the same mineral in different lithologies may in part reflect initial heterogeneities of the finely layered sedimentary precursors the d 18 o values for the garnets are among the highest observed for uhp origin both for crustal or mantle rocks confirming a sedimentary origin for these carbonate bearing rocks and ruling out a primi tive mantle derived protolith oxygen diffusion in garnet at peak metamorphism temperature 1 000c was arrested by rapid cooling

phase relations in the camgsi 2 o 6 kalsi 3 o 8 join at 6 and 3 5 gpa as a model for formation of some potassium bearing deep seated mineral assemblages the join camgsi2o6 kalsi3o8 has been studied at 6 gpa 890 1 500 c and 3 5 gpa 1 000 1 100 c k rich melts in the join produce assemblages cpx grt cpx opx cpx san and cpx grt san at 1 100 1 300 c at nsansystem 90 mol this explains a scarcity of san in mantle cpx rich assemblages and its association with high k aluminosilicate melt inclusions in diamonds in absence of san kcpx is the only host for potassium the k jadeite content in kcpx systematically increases with decreasing temperature and reaches 10 12 mol near the solidus however kcpx coexists with san at nsansystem 70 mol and 4 gpa to cpx san at p 4 gpa similar sequence of assemblages is observed in some eclogitic xenoliths from kimberlites and grt cpx rocks of the kokchetav complex northern kazakhstan

coesite inclusions and prograde compositional zonation of garnet in whiteschist of the hp uhpm kokchetav massif kazakhstan a record of progressive uhp metamorphism coarse grained whiteschist containing the assemblage garnet kyanite phengite talc quartz coesite is an abundant constituent of the ultrahigh pressure metamorphic uhpm belt in the kulet region of the kokchetav massif of kazakhstan garnet displays prograde compositional zonation with decreasing spessartine and increasing pyrope components from core to rim cores were recrystallized at t 380 c inner to 580 c outer at p 10 kbar garnet ilmenite geothermometry margarite quartz stability and mantles at t 720 760 c and ph20 34 36 kbar coesite graphite stability phengite geobarometer kfmash system reaction equilibria textural evidence indicates that rims grew during decompression and cooling within the qtz stability field silica inclusions quartz and or coesite of various textural types within garnets display a systematic zonal distribution cores contain abundant inclusions of euhedral quartz type 1 inclusions inner mantle regions contain inclusions of polycrystalline quartz pseudomorphs after coesite type 2 with minute dusty micro inclusions of chlorite and more rarely talc and kyanite in their cores intense radial and concentric fractures are well developed in the garnet intermediate mantle regions contain bimineralic inclusions with coesite cores and palisade quartz rims type 3 which are also surrounded by radial fractures subhedral inclusions of pure coesite without quartz overgrowths or radial fractures type 4 occur in the outer part of the mantle garnet rims are silica inclusion free type 1 inclusions in garnet cores represent the low p low t precursor stage to uhpm recrystallization and attest to the persistence of low p assemblages in the coesite stability field coesites in inclusion types 2 3 and 4 are interpreted to have sequentially crystallized by net transfer reaction kyanite talc garnet coesite h2o and were sequestered within the garnet with progressively decreasing amounts of intragranular aqueous fluid during the retrograde evolution of the rock all three inclusion types diverged from the host garnet p t path at the coesite quartz equilibrium and followed a trajectory parallel to the equilibrium boundary resulting in inclusion overpressure coesite in type 2 inclusions suffered rapid intragranular h2o catalysed transformation to quartz and ruptured the host garnet at about 600 c when inclusion p 27 kbar garnet host p 9 kbar instantaneous decompression to the host garnet p t path passed through the kyanite talc chlorite quartz reaction equilibrium resulting in the dusty micro assemblage in inclusion cores type 3 inclusions suffered a lower volumetric proportion transformation to quartz at the coesite quartz equilibrium and finally underwent rupture and decompression when t 400 c facilitating coesite preservation type 4 coesite inclusions are interpreted to have suffered minimal transformation to quartz and proceeded to surface temperature conditions along or near the coesite quartz equilibrium boundary

luminescence of diamonds from metamorphic rocks this study explores the effects of metamorphism on luminescence of diamond four diamond suites extracted from metamorphic rocks were characterized using optical cathodoluminescence ftir spectroscopy photoluminescence at the liquid nitrogen temperature and cathodoluminescence spectroscopy the studied diamonds are from sedimentary conglomerate and lamprophyric breccia metamorphosed to the greenschist facies wawa canada and from the ultrahigh pressure uhp terranes of kokchetav kazakhstan and erzgebirge germany the majority of studied diamonds that experienced metamorphism have distinct cathodoluminescence and photoluminescence when compared to diamonds from unmetamorphosed rocks i e kimberlites or placers diamonds in metamorphic rocks do not show the prevalent blue cathodoluminescence emittance at 415 440 and 480 490 nm typical of common kimberlite and placer diamonds ultrahigh pressure diamonds are mostly non luminescent whereas diamonds from greenschists display green yellow orange and red cathodoluminescent colors emitting light at 520 and 576 nm and between 586 and 664 nm the shift of cathodoluminescence in octahedrally grown type ia diamonds metamorphosed in the greenschist facies results from the presence of optical centers with zero phonon lines at 575 and 637 nm detected via photoluminescence spectroscopy the centers may have formed due to irradiation of diamonds in the upper crust followed by annealing at t 500 c this process creates vacancies that diffuse through the diamond lattice and get trapped at n sites creating nv o and nv optical centers the distinct luminescence of metamorphosed diamonds can persist for billions of years in the crust but is annealed in the mantle

massive volcanism at the permian triassic boundary and its impact on the isotopic composition of the ocean and atmosphere abstract bulk carbonate and conodonts from three permian triassic p t boundary sections at guryul ravine kashmir abadeh central iran and pufels bula bulla italy were investigated for 13 c and 18 o carbon isotope data highlight environmental changes across the p t boundary and show the following features 1 a gradual decrease of 4 to more than 7 starting in the late permian changhsingian c bachmanni zone with two superimposed transient positive excursions in the c meishanensis h praeparvus and the m ultima s mostleri zones 2 two 13 c minima the first at the p t boundary and a higher occasionally double minimum in the lower i isarcica zone it is unlikely that the short lived phenomena such as a breakdown in biological productivity due to catastrophic mass extinction a sudden release of oceanic methane hydrates or meteorite impact s could have been the main control on the latest permian carbon isotope curve because of its prolonged 0 5 ma duration gradual decrease and the existence of a 1 positive shift at the main extinction horizon the p t boundary 13 c trend matches in time and magnitude the eruption of the siberian traps and other contemporaneous volcanism suggesting that volcanogenic effects such as outgassed co 2 from volcanism and even more thermal metamorphism of organic rich sediments as the likely cause of the negative trend

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

metamorphic diamonds mechanism of growth and inclusion of oxides we report a detailed series of electron microscope observations of metamorphic microdiamonds included in and separated from garnets and zircons from a single specimen of garnet biotite feldspar gneiss from the kokchetav massif kazakhstan the morphology of the diamonds ranges from skeletal forms composed of thin 111 plates through cuboid and octahedral forms included within the diamonds is a diverse suite of nanometric oxides suggesting that the c o h fluid from which the diamonds grew may have carried chemical components derived from both the sediments and the mantle the spectrum of morphologies and their abundant tiny inclusions can all be explained by a simple model based on the ratio of the rate at which 111 plates grow and the rate of random nucleation of new plates at their edges

the thickness of the lithosphere from the dispersion of surface waves summary the inversion of regional rayleigh and love wave dispersion data in the period range 30 200 or 250 s leads to an inference that high s wave velocities in the mantle are to be found to depths of the order of 300 km or greater under the ancient precambrian shields of the world under the other parts of the world a low s wave velocity channel is found at depths up to 100 km below the surface the depth to the onset of the low velocity channel is consistent with the onset of partial melting of a mantle of peridotitic composition under the shields there is no evidence for partial melting to depths of the order of 300km no statement can be made from these data about the presence or absence of a low velocity channel in subduction zones if the lithosphere is defined to be that region of the mantle that moves with the same velocity of flow as the surface above it then the pacific and nazca plates have uniform thicknesses of only 100 km for all the other major plates of the world two models can be proposed that cannot be resolved with the present data in the first model all the other major plates including their oceanic parts have uniform thicknesses of at least 300 km and may have thicknesses as great as 700 km in the second model all the other major plates have deep roots under the ancient precambrian shields and an eddy of flow around these roots begins at a depth of about 100 km

kokchetavite a new potassium feldspar polymorph from the kokchetav ultrahigh pressure terrane kokchetavite a new polymorph of k feldspar kalsi3o8 has been identified as micrometer size inclusions in clinopyroxene and garnet in a garnet pyroxene rock from the kokchetav ultrahigh pressure terrane kazakhstan kokchetavite has a hexagonal structure with a 5 27 1 a c 7 82 1 a v 188 09 a 3 z 1 and is found to be associated with phengite a b cristobalite or quartz siliceous glass phlogopite titanite calcite zircon occurring as multi phase inclusions in clinopyroxene and garnet it is concluded that kokchetavite could not be an exsolution phase in host minerals instead it might be metastably precipitated from an infiltrated k rich melt during rock exhumation alternatively although less likely kokche tavite might be derived from dehydration of k cymrite which in turn was formed at high pressures in either case kokchetavite is a metastable polymorph of k feldspar

geochemistry of garnetiferous ti clinohumite rock and talc kyanite phengite almandine schist from the kokchetav uhp terrane kazakhstan an insight to possible origins of some chemically unusual uhp rocks abstract major element trace element and o isotope analyses were carried out for garnetiferous ti clinohumite rocks and eclogites from the kumdy kol area as well as talc kyanite phengite almandine schists previously named as whiteschists and eclogites from the kulet area of the kokchetav ultrahigh pressure uhp terrane to explore their possible origins both garnetiferous ti clinohumite rocks and talc kyanite phengite almandine schists are possibly genetically related to eclogites as they occur in close association with eclogites enclosed within gneiss metapelite in these two areas most eclogites from the kumdy kol and the kulet areas exhibit chemical characteristics similar to that of ocean floor basalt although a few show arc affinity with slight ta and nb depletions garnetiferous ti clinohumite rocks from the kumdy kol region are characterized by very high mg low si ca na and k contents compared with eclogites they also exhibit lree depleted patterns with negative eu anomalies their o isotope compositions are less than 5 6 on the other hand the rocks show comparable al ni cr co and hree contents as eclogites the mg enrichment of these garnetiferous ti clinohumite rocks is suggested to have originated from their mafic protoliths that had been subjected to mafic rock ultramafic rock fluid interactions talc kyanite phengite almandine schists from the kulet area are typically low in ca and na but high in mg k rb ba cs th u and o isotope compositions 6 to 10 relative to eclogites this peculiar chemical composition can be accounted for if the basaltic protoliths had been subjected to sequential high temperature enrichment of mg and low temperature enrichment of k rb ba cs th u and o isotope compositions seawater basalt interactions one talc kyanite phengite almandine schist sample klw 7 is distinctly high in si and k but low in mg and fe which can be attributed to more severe low temperature hydrothermal alterations however except for mg the enrichment of rb ba cs th u and o isotope compositions in these schist samples could also be enhanced by or otherwise be interpreted as a result of fluid influx sourced from enclosing metapelite during subduction

isostasy and the ambient state of stress in the oceanic lithosphere two conditions are normally considered to be characteristic of the state of stress in a system in local isostatic equilibrium the first is that the stress is hydrostatic below some depth the level of compensation and the second is that above that depth there are no vertical shear stresses in the case of a planar two dimensional mid ocean ridge these two conditions suffice to determine the stress completely except for the normal component parallel to the ridge but to determine that component an additional assumption is required it is proposed here that an appropriate additional assumption is that in unflexed regions where the stress is due only to the elevation of mid ocean ridges the deviatoric stress in the oceanic lithosphere is a minimum the unique state of deviatoric stress consistent with this assumption is horizontally compressive in a direction perpendicular to the axes of mid ocean ridges with a magnitude in old ocean basins of a few hundred bars in agreement with oceanic intraplate earthquake mechanisms at any given distance from the ridge the stress is maximum at the seafloor and it decreases with depth at about the same rate as the cooling of the lithosphere so that the entire thermal boundary layer may be regarded as acting to support the global square root of age topography of the oceans

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

metamorphic evolution of diamond bearing and associated rocks from the kokchetav massif northern kazakhstan representative diamond bearing gneisses and dolomitic marble eclogite and ti clinohumite bearing garnet peridotite from unit i at kumdy kol and whiteschist from unit ii at kulet eastern kokchetav massif northern kazakhstan were studied diamond bearing gneisses contain variable assemblages including grt bt qtz pl kfs zo chl tur cal and minor ap rt and zrn abundant inclusions of diamond graphite chlorite or calcite phengite clinopyroxene k feldspar biotite rutile titanite calcite and zircon occur in garnet diamond bearing dolomitic marbles consist of dol di grt phl inclusions of diamond dolomite graphite biotite and clinopyroxene were identified in garnet whiteschists carry the assemblage ky tlc grt rt garnet shows compositional zoning and contains abundant inclusions of talc kyanite and rutile with minor phlogopite chlorite margarite and zoisite inclusions and zoning patterns of garnet delineate the prograde p t path inclusions of quartz pseudomorphs after coesite were identified in garnet from both eclogite and gneiss other ultrahigh pressure uhp indicators include na bearing garnet up to 0 14 wt na2o with omphacitic cpx in eclogite occurrence of high k diopside up to 1 56 wt k2o and phlogopite in diamond bearing dolomitic marble and cr bearing kyanite in whiteschist these uhp rocks exhibit at least three stages of metamorphic recrystallization the fe mg partitioning between clinopyroxene and garnet yields a peak temperature of 800 1000 c at p 40 kbar for diamond bearing rocks and about 740 780 c at 28 35 kbar for eclogite whiteschist and ti bearing garnet peridotite the formation of symplectitic plagioclase amphibole after clinopyroxene and replacement of garnet by biotite amphibole or plagioclase mark retrograde amphibolite facies recrystallization at 650 680 c and pressure less than about 10 kbar the exsolution of calcite from dolomite and development of matrix chlorite and actinolite imply an even lower grade greenschist facies overprint at c 420 c and 2 3 kbar a clockwise p t path suggests that supracrustal sediments together with basaltic and ultramafic lenses apparently were subjected to uhp subduction zone metamorphism within the diamond stability field tectonic mixing may have occurred prior to uhp metamorphism at mantle depths during subsequent exhumation and juxtaposition of many other tectonic units intense deformation chaotically mixed and mylonitized these lithotectonic assemblages

phase transition of zircon at high p t conditions in situ observations of the zircon reidite transition in zrsio4 were carried out using a multianvil high pressure apparatus and synchrotron radiation the phase boundary between zircon and reidite was determined to be p gpa 8 5 0 0017 t 1200 k for temperatures between 1100 1900 k when subducted slabs including igneous rocks and sediments descend into the upper mantle the zircon in the subducted slab transforms into reidite at pressures of about 9 gpa corresponding to a depth of 270 km reidite found in an upper eocene impact ejecta layer in marine sediments is thought to have been transformed from zircon by a shock event the peak pressure generated by the shock event in this occurrence is estimated to be higher than 8 gpa

the origin and formation of metamorphic microdiamonds from the kokchetav massif kazakhstan a nitrogen and carbon isotopic study abstract this study reports 13c 15n and n content values for microdiamonds from ultrahigh pressure metamorphic rocks of the kokchetav massif in kazakhstan both alluvial diamonds and in situ diamonds from a garnet clinopyroxene rock and a marble i e a garnet pyroxene dolomitic rock were investigated in situ diamonds were analysed in batches because of their small size average 40 m whereas the larger alluvial diamonds were analysed individually the latter group has 13c values ranging from 15 92 to 10 57 15n from 1 8 to 1 1 and n contents from 2300 to 3650 ppm diamonds from the garnet clinopyroxene rock yield mean values of 10 50 for 13c 5 9 for 15n and a high average nitrogen content of 11 150 ppm values for diamonds in marble are 10 19 8 5 and 2650 ppm respectively for diamonds from garnet clinopyroxene rock and marble there is more nitrogen released by bulk combustion than estimated by infrared ir spectroscopy the differences being of about 7000 and 1500 ppm respectively these differences suggest that a significant quantity of nitrogen is ir inactive and may be present as fluid inclusions their carbon and nitrogen isotopic compositions are compatible with an in situ crystallisation of diamond from dominantly metasedimentary sources suggesting that sedimentary nitrogen can be subducted to very high pressures carbon isotopic fractionation between coexisting carbonate and diamond suggests crystallisation temperatures before the peak of metamorphism at temperatures probably below 700 c and deduced pressures of 3 gpa relative to the isotopic data reported for sediments metasediments and in situ diamonds the slightly 15n depleted compositions of alluvial diamonds is striking these values suggest that the contribution of any metasedimentary source is unlikely and may point toward a mafic ultramafic protolith

higher harmonic effects of the earth s gravitational field from post glacial rebound as observed by lageos recently long term orbital data from the artificial satellite lageos have been analyzed to determine the rate of post glacial rebound rubincam has compared the observed values against values derived from two realistic earth models wu peltier l1 l2 working with the second harmonic mode of excitation the data support model l1 with a uniform mantle viscosity of 1022 poise over l2 with a lower mantle viscosity of 1023 poise we find the higher degree harmonic contributions are significant and considerably strengthen the support for model l1 we perform such calculations using the same parameter values for glaciation as rubincam and also values due to peltier and coworkers we also show that a similar analysis of data from the satellite starlette is less likely to be as definitive as analysis of lageos data since there are significant contributions from very high harmonics indicating that the behavior of the earth must be known in much greater detail

characteristics of the western quebec seismic zone a comparison of geological data shows that most of the earthquakes of western quebec lie within or near the eastern and western boundaries of a grenville ca 1000 ma central metasedimentary belt and in the area of the younger fault zone along the ottawa river although most of the earthquakes have occurred within terrain of grenville age or older the younger rift zone is characterized by the larger earthquakes temiskaming m6 2 1935 cornwall massena m5 7 1944 the earthquakes also correlate with gradient zones around two prominent anomalies in the smoothed bouguer gravity field the pattern of aeromagnetic anomalies and drainage channels reflects preeambrian structural trends and indicates the central metasedimentary belt continues beneath paleozoic sediments to lake ontario the strikes of magnetic gravity and drainage features north of lake ontario are parallel to features mapped to the south of the lake geological data and geophysical trends suggest that a cataclastic zone is continuous alon

oriented kokchetavite compound rods in clinopyroxene of kokchetav ultrahigh pressure rocks abstract two microdiamond bearing samples a dolomite marble and a garnet clinopyroxene rock from the kokchetav ultrahigh pressure metamorphic terrane were selected in the present study to explore the possible origin of kalsi3o8 rod inclusions oriented along the c axis of clinopyroxene host the kalsi3o8 rod inclusions at clinopyroxene cores where k2o content is high in the range of 0 5 1 0 wt are mostly fine grained with a rod width less than 1 m aem studies showed that the kalsi3o8 phase in most rod inclusions is kokchetavite k feldspar is present only in a few cases probably the result of phase transformation recrystallization from kokchetavite during rock exhumation electron diffractions further showed that kokchetavite rods are oriented parallel to clinopyroxene 0 0 1 direction and they exhibit the same epitaxial relation with the clinopyroxene host in both samples with the al si o4 tetrahedra chains along the hexagonal a axis of kokchetavite parallel to the single sio4 chain along the c axis of clinopyroxene i e 1 2 1 0 ko 0 0 1 cpx and 0 0 0 1 ko 1 0 0 cpx it is interesting to note that kokchetavite is always in association with phengite tremolite cristobalite si rich al k ca bearing low crystallinity phase si ca cl as phase calcite apatite lollingite feas2 forming compound rods furthermore all these phases are also present within submicron scale polyphase inclusion pockets in garnet within garnet clinopyroxene rock sample these kokchetavite compound rods are therefore most likely to have resulted from melt fluid clinopyroxene interactions leading to epitaxial deposition rather than exsolution sensu stricto from the clinopyroxene host the suggested melt fluid would have an external and or an internal origin related to rock partial melting involving phengite breakdown discrete phlogopite and phengite needle like inclusions with a needle width less than 1 m as well as phlogopite phengite and kokchetavite mica intergrowth needles are also not uncommon in clinopyroxene cores there are specific crystallographic orientation relationships among phases these micas might have formed earlier than kokchetavite and have exsolved from clinopyroxene host although the mass balance issue during exsolution and the temporal relation between phlogopite and phengite needles remain to be settled clinopyroxene rims generally contain mica needles only domains near fractures with coarse grained kokchetavite compound rods or with coarse grained phlogopite quartz needles are not uncommon these clinopyroxene rims domains are low in k2o

hydroxyl in clinopyroxene from the deep subducted crust evidence for h2o transport into the mantle clinopyroxenes in eclogites from the deep subducted crust in the kokchetav kazakhstan ultrahigh pressure metamorphic terrane were found by infrared spectroscopy to contain up to 3020 ppm oh these rocks were recrystallized at pressures over 60 kbar and temperatures over 1000 c where no hydrous minerals are stable infrared spectra of the clinopyroxenes show three hydroxyl absorption bands in the regions 3440 3460 cm 1 3500 3530 cm 1 and 3600 3625 cm 1 the hydroxyl absorbance increases with recrystallization pressure of the eclogites and with vacancy concentration in the pyroxene structure ca eskola component clinopyroxenes represent about 40 50 vol of eclogites such that the bulk eclogites contain approximately 1300 ppm hydroxyl at depths greater than 150 km thus subducted oceanic crust can transport trace amounts of h2o into the upper mantle even in the absence of nominally hydrous minerals

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

experimental constraints on phase relations in subducted continental crust synthesis piston cylinder experiments were carried out in the range 2 0 4 5 gpa and 680 1 050 c to investigate phase relations in subducted continental crust a model composition kcmash has been used because all major ultrahigh pressure uhp minerals of the whole range of rock types typical for continental crust can be reproduced within this system the combination of experimental results with phase petrologic constraints permits construction of a uhp petrogenetic grid the phase relations demonstrate that the most important uhp paragenesis consists of coesite kyanite phengite clinopyroxene and garnet in subducted continental crust below 700 c talc is stable instead of garnet as most of these minerals are also stable at much lower pressure and temperature conditions it is thus not easy to recognize uhp metamorphism in subducted crust a general feature however is the absence of feldspars at h2o saturated conditions plagioclase is never stable at uhp conditions but k feldspar can occur in h2o undersaturated rocks mineral compositions in the experiments are fully buffered by coexisting phases the si content of phengite and biotite increase with increasing pressure at 4 0 gpa 780 c biotite contains 3 28 si per formula unit which is most probably caused by solid solution of biotite with talc above 800 c the caal2sio6 component in clinopyroxene buffered with kyanite coesite and a mg phase increases with increasing temperature providing a tool to distinguish between cold and hot eclogites up to 10 ca eskolaite ca0 5 0 5alsi2o6 in clinopyroxene has been found at the highest temperature and pressure investigated 900 c 4 5 gpa garnet buffered with coesite kyanite and clinopyroxene displays an increase of grossular component with increasing pressure for a given temperature although the investigated system represents a simplification with respect to natural rocks it helps to constrain general features of subducted continental crust the observed phase relations and phase compositions demonstrate that at pressures 3 0 gpa and temperatures 800 c continental crust can retain significant amounts of h2o 1 wt whereas k free mafic or ultramafic rocks are dry at these conditions uhp parageneses are only preserved if the whole exhumation path is situated within the stability field of phengite i e if there is cooling during exhumation or if the whole exhumation occurred at t 700 c in contrast break down of phengite and concomitant partial melting in terranes that show isothermal decompression may lead to a complete recrystallization of the subducted crust during exhumation the density of uhp rocks can be estimated on the basis of the established phase relations pelitic rocks are likely to have a density close to mantle rocks 3 3 g cm3 because of significant amounts of dense garnet and kyanite whereas granitic rocks are less dense 3 0 g cm3 hence subducted average continental crust is most probably buoyant with respect to mantle rocks and tends to get exhumed as soon as it is detached from the down going slab electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00410 001 0336 3

oxygen carbon and strontium isotope geochemistry of diamond bearing carbonate rocks from kumdy kol kokchetav massif kazakhstan abstract diamond bearing carbonate rocks from kumdy kol kokchetav massif kazakhstan were strongly altered by fluids flowing through fractures and infiltrating along grain boundaries during exhumation alteration includes retrogradation of high grade silicate assemblages by hydrous minerals replacement of diamond by graphite and of dolomite by calcite diamond bearing carbonate rocks are among the most intensely altered isotopically with 18 o vsmow values as low as 9 13 c vpdb 9 and 87 sr 86 sr as high as 0 8050 evidence of isotopic equilibration between coexisting dolomite and high mg calcite during ultrahigh pressure metamorphism uhpm is preserved only rarely in samples isolated from infiltrating fluids by distance from fractures isotopic heterogeneity and isotopic disequilibrium are widespread on a hand specimen scale because of this lack of homogeneity bulk analyses cannot provide definitive measurements of 13 c 12 c fractionation between coexisting diamond and carbonate our study adequately documents alteration on a scale commensurate with observed vein structures but testing the hypothesis of metamorphic origin of microdiamonds has not fully succeeded because our analytical spatial resolution limited to 0 5 mm is not small enough to measure individual dolomite inclusions or individual diamond crystals

kyanite deformation in whiteschist of the ultrahigh pressure metamorphic kokchetav massif kazakhstan microstructures in minerals from ultrahigh pressure metamorphic uhpm terranes are keys to understanding the rheological properties and the exhumation mechanisms of rocks from subduction zones kyanite bearing whiteschist associated with eclogite lenses is part of uhpm unit ii located south west of lake zheltau in the kulet region of the kokchetav massif the equilibrium assemblage is kyanite garnet talc phengite coesite quartz previously reported peak pressure temperature p t conditions are 3 5 gpa at 750 c a strong foliation is defined by the talc and phengite with a corresponding weak shape preferred alignment of kyanite crystallographic orientation maps and analysis of kyanite blades were performed using electron backscatter diffraction methods the data are consistent with a 100 001 slip system for the formation of undulose extinction and kink bands in kyanite rotations measured across individual kink bands are 10 50 about and rotations along kyanite with undulose extinction are up to 50 about with variations between adjacent points typically 2 the undulose extinction is interpreted to have developed through crystal plastic deformation by dislocation creep kink bands mark the development of high angle grain boundaries by dislocation climb the deformation of kyanite occurred in the fault bounded terrane during the exhumation of the kokchetav massif

raman study of diamond based abrasives and possible artefacts in detecting uhp microdiamond abstract raman spectral characteristics of a range of diamond based abrasives powders and sprays and drilling and cutting tools originating from preparation laboratories worldwide are presented some abrasives show strong broadening of the main diamond band fwhm full width at half band maximum 5 cm 1 accompanied by strong band downshift 1316 1330 cm 1 others are characterised by moderate band broadening fwhm 1 8 5 cm 1 at rather regular band position 1331 1333 cm 1 in addition we found that a fresh abrasive and its used analogue may in some cases show vast differences in their raman spectra the raman parameters of diamond based abrasives overlap widely with raman parameters of uhp ultra high pressure microdiamond it is hence impossible to assign diamond detected in a geological specimen to either an introduced artefact or a genuine uhp relict from the raman spectrum alone raman is an excellent technique for the detection of minute amounts of diamond however it does not provide conclusive evidence for the identification of uhp microdiamond the latter requires thorough verification for instance by optical microscopy or if doubts cannot be dispelled transmission electron microscopy

the fate of subducted continental margins two stage exhumation of the high pressure to ultrahigh pressure western gneiss region norway thermobarometry suggests that ultrahigh pressure uhp to high pressure hp rocks across the western gneiss region ponded at the moho following as much as 100 km of exhumation through the mantle and before exhumation to the upper crust eclogite across the c 22 000 km 2 study area records minimum pressures of c 8 18 kbar and temperatures of c 650 780 c one orthopyroxene eclogite yields an uhp of c 28 5 kbar and evidence of former coesite has been found c 50 km farther east than previously known despite this widespread evidence of uhp to hp thermobarometry of metapelite and garnet amphibolite samples reveals a surprisingly uniform supra barrovian amphibolite facies overprint at c 11 kbar and c 650 750 c across the entire area chemical zoning analysis suggests that garnet in these samples grew during heating and decompression presumably during the amphibolite facies event these data indicate that the norwegian uhp hp province was exhumed from mantle depths of c 150 km to lower crustal depths where it stalled and underwent a profound high temperature overprint the ubiquity of late stage supra barrovian metamorphic overprints suggests that large scale collisional uhp terranes routinely stall at the continental moho where diminishing body forces are exceeded by boundary forces significant portions of the middle or lower crust worldwide may be formed from uhp terranes that were arrested at the moho and never underwent their final stage of exhumation

tracking the exhumation of a pliocene u hp terrane u pb and trace element constraints from zircon d entrecasteaux islands papua new guinea domal structures within the d entrecasteaux islands of eastern papua new guinea expose ultrahigh pressure uhp pliocene 5 6 4 6 ma eclogites and evidence for partial melting to better interpret the u hp exhumation history u pb geochronology and trace element abundances were determined in zircon from variably deformed host gneiss and crystallized melt leucosomes sills dikes and plutons from the goodenough and normanby domes by id tims isotope dilution thermal ionization mass spectrometry and icp ms inductively coupled plasma mass spectrometry respectively to constrain the timing of melt crystallization and deformation relative to uhp metamorphism zircons extracted from orthogneiss and deformed granodiorite sills of normanby dome located 40 km southeast of the uhp eclogite record hp metamorphism from 5 66 0 02 to 5 04 0 07 ma and melt crystallization at 4 1 ma strongly deformed layer parallel leucosomes from goodenough dome 20 km northwest of the uhp eclogite began to crystallize by 3 85 0 02 ma these dates indicate that melt crystallization began in the goodenough and normanby domes within 0 75 m y of u hp metamorphism the id tims dates from the orthogneiss and crystallized melt show that exhumation and cooling of the u hp rocks in the png terrane began first in the east within normanby dome then to the west in the goodenough dome 1 m y later and finally the middle dome rocks exposed within the mailolo dome cooled 2 m y after exhumation of normanby dome all domes reveal synchronous crystallization of late nondeformed melts and final extension driven exhumation by 1 82 0 03 ma

magnetotelluric interpretation of crustal and mantle structure in the grenville province summary accurate determinations of depths and conductivities of electrical structures in shield regions are often difficult because of the inhomogeneity of the uppermost crust a magnetotelluric mt station bat in the grenville province of the precambrian shield in eastern canada has been in operation since 1975 for time dependency studies of electrical resistivity changes related to earthquakes the mt response of the station displays low skew with small to moderate anisotropy one dimensional inversion of the apparent resistivity and phase reveals two well defined conductors in the crust one at 10 km and the second at the base of the crust the latter has a resistivity less than 50 m these results are substantiated by three additional mt stations located up to 40 km distant data from other new mt stations and from stations previously published in the literature are compared with two dimensional computer model results and with the three dimensional analogue scale model results of dosso et al while additional data for periods less than 100 s would be desirable the results from a number of the mt stations are not inconsistent with a widespread occurrence of a conducting zone at the base of the crust in the grenville the inversion analysis also indicates the existence of a conductor at some depth greater than 100 km with a resistivity less than 30 m this may coincide with a seismic low velocity zone observed in the mantle under the canadian shield

palaeozoic arc magmatism in the central asian orogenic belt of kazakhstan shrimp zircon ages and whole rock nd isotopic systematics abstract early palaeozoic tonalite to granodiorite intrusions in northern kazakhstan are associated with lode gold mineralization and have shrimp zircon ages of 457 3 6 6 ma aksu 452 9 5 6 ma and 447 4 5 4 ma both zholymbet the stepnyak intrusion contains large xenoliths with an age of 480 6 5 0 ma one early palaeozoic zircon from a porphyritic diorite at stepnyak has a core with a near concordant 207pb 206pb age of 3888 1 5 ma whereas other xenocrystic grains are between 983 and 2698 ma old the early archaean age is probably inherited from unexposed basement of the kokchetav massif and represents the oldest crustal material so far known from the asian continent it appears that the aksu zholimbet and stepnyak granitoids were emplaced in the late ordovician in an andean or japan type continental arc environment on the margin of the kokchetav massif late palaeozoic granitoids in central kazakhstan have devonian zircon ages of 407 1 3 9 381 1 3 1 and 369 2 4 9 ma whereas the youngest sample from the topar massif has a late carboniferous emplacement age of 314 1 5 1 ma initial end values range from 5 to 1 corresponding to nd model ages of 1 1 0 6 ga the isotopic data are similar to those of other phanerozoic granitoids of the central asian orogenic belt and corroborate melting of predominantly juvenile crustal protoliths our data also confirm that devonian and carboniferous arc magmatism in central kazakhstan assimilated older and already accreted island arc systems yet is derived from primitive sources probably in a subduction setting the range of end values with corresponding nd mean crustal residence ages in the range of 0 6 1 1 ga for most samples indicates variable recycling of late proterozoic largely juvenile continental crust in the formation of the palaeozoic magmatic arcs of central kazakhstan the orogenic evolution terminated with permian anorogenic rift related alkaline granite magmatism end 2 to 8 which reflects melting of juvenile mantle derived lower crust

stress relief buckles in the mcfarland quarry ottawa six quarry floor buckles in a west end ottawa bedrock quarry are described and a semi quantitative estimate of the stress field is inferred from them the maximum principal stress component is hori

subduction ultrahigh pressure metamorphism and regurgitation of buoyant crustal slices implications for arcs and continental growth abstract intracontinental collisional belts that retain mineralogic relics of phanerozoic ultrahigh pressure uhp metamorphism are increasingly being recognized adjacent regions generally lack evidence of coeval calcalkaline volcanism plutonism following consumption of intervening oceanic lithosphere each orogen marks the site of a deeply subducted microcontinental promontory fragments of which later returned to midcrustal levels mafic and ultramafic rocks are volumetrically minor pressures in uhp complexes approached or exceeded 2 8 gpa at 600 900 c subduction zones involve low t prograde gradients and constitute the only plate tectonic realm where such conditions exist although internal portions of descending plates may have even lower geothermal gradients crustal upper margins are typified by p t trajectories of 5 10 c km attending underflow clinoamphibole rich metabasaltic rocks dehydrate at pressures 2 2 2 5 gpa this accounts for the kinetically favorable solid state production of mafic eclogites and partial fusion of morbs to form hydrous andesitic melts devolatilization of partly serpentinized mantle lithosphere also introduces h 2 o to the magmagenic zone as large masses of continental crust enter deeper portions of subduction zones mineralogic transformations slow or cease because micas the major oh bearing phases in such rocks retain volatile contents to pressures 4 gpa persistence of hydroxyl bearing layer silicates may explain the metastable preservation of low density assemblages in continental crust subjected to uhp conditions and the dearth of calcalkaline magmatism in most collision belts exhumed uhp terranes are intensely deformed and disaggregated all consist dominantly of quartzofeldspathic compositions mafic eclogites garnet peridotites constitute only a few volume percent eventual decoupling of the relatively low density subducted crust promotes buoyancy propelled transport to shallow depths along the subduction channel with the hanging wall lithosphere acting as a stress guide extensional collapse and erosional unroofing of rising masses result in the continued ascent of deeply subducted but buoyant crustal material although equidimensional massifs must return surfaceward large volume to surface areas render the contained uhp phase assemblages virtually unquenchable surviving uhp terranes thus consist of relatively thin slabs of continental crust allochthons that retain uhp relics apparently lost heat by conduction across both upper normal fault and lower reverse fault contacts based on present exposures estimated thicknesses of uhp sheets are qinling dabie sulu belt 5 km kokchetav complex 1 3 km dora maira massif 1 2 km western gneiss region 1 km slices evidently rose to midcrustal levels at exhumation rates approaching 10 mm per year back reaction attending decompression in all cases was nearly complete where uhp mineral inclusions persisted retrogression apparently was limited by the relative impermeability of the rocks to catalytic aqueous fluids and by declining temperatures the coarse grain size of host phases also disfavored complete retrogression

coesite exsolution from supersilicic titanite in uhp marble from the kokchetav massif northern kazakhstan coesite exsolved from supersilicic titanite was discovered in an impure calcite marble at kumdy kol in the kokchetav uhp ultrahigh pressure metamorphic terrane northern kazakhstan this impure marble consists mainly of calcite k feldspar diopside and symplectites of diopside zoisite with minor amount of titanite phengite and garnet no diamond was found in the marble coesite and quartz which have needle or platy shapes measuring about 20 60 m in length occur as major exsolved phases in the cores and mantles of titanite crystals with minor calcite and apatite the strongest raman band for the coesite needles and plates was confirmed at about 524 cm 1 with a weak band at about 271 cm 1 to estimate the initial composition of the titanite before coesite exsolution exsolved phases were reintegrated by measuring their area fractions on digital images the highest excess si in titanite was thus determined to be 0 145 atoms per formula unit apfu this composition requires a pressure higher than 6 gpa on the basis of phase relations in the system catisio5 casi2o5 this pressure is consistent with other evidence of high pressure in the same marble such as 1 4 1 8 wt k2o and over 1000 ppm h2o in diopside supersilicic titanite and coesite exsolution also indicate that sio2 exsolution occurred in the coesite stability field during exhumation of the uhp metamorphic unit