late miocene coesite eclogite exhumed in the woodlark rift late miocene pliocene eclogites were exhumed in the woodlark rift of eastern papua new guinea an actively extending region west of the woodlark basin seafl oor spreading center we report the discovery of coesite in late miocene eclogite from the lower plate of one of the d entrecasteaux islands metamorphic core complexes within the woodlark rift zircon crys tallization temperatures 650 675 c and 238 u 206 pb age ca 8 ma and rutile thermometry 695 743 c combined with garnet pyroxene thermometry 600 760 c and garnet pyroxene phengite barometry 18 27 kbar indicate that the coesite eclogite was exhumed from mantle depths 90 km to the earth s surface at plate tectonic rates cm yr 1 this late miocene coesite eclogite is the youngest exhumed ultrahigh pressure uhp rock on earth and its preservation ahead of the westward propagating seafl oor spreading center forces reevaluation of models for uhp exhumation as well as the geologic and tectonic evolution of the woodlark rift

recent progress in snow and ice research a review of snow and ice research in 1987 1990 is presented focusing on the effects of layers in seasonal snow covers ice mechanics on fresh water and sea ice and remote sensig of polar ice sheets these topics provide useful examples of general needs in snow and ice research applicable to most areas such as better representation in models of detailed processes controlled laboratory experiments to quantify processes and field studies to provide the appropriate context for interpretation of processes from remote sensing

brittle failure of ice ice exhibits either ductile or brittle behavior depending upon the conditions under which it is loaded glaciers for instance are loaded by gravity under deviatoric stresses of 0 1 mpa or lower at temperatures of interest they flow through dislocation creep at strain rates of the order of 10 9 s 1 or lower patterson 1994 sheets of sea ice another terrestrially important ice feature are loaded predominantly by wind under global compressive stresses similar in magnitude to the shear stresses within glaciers richter menge and elder 1998 these bodies deform through a combination of creep and fracture the latter process manifested by oriented leads or open cracks and by compressive shear faults which often form as conjugate sets that traverse a large fraction of the arctic basin kwok 1999 schulson 2002 the cold icy crust of europa an extraterrestrial feature which may shield an ocean beneath within which a form of life may exist or may once have existed reynolds et al 1987 hoppa et al 1999 pappalardo et al 1999 greenberg et al 2000 kargel et al 2000 is loaded by the motion of diurnal tides and by non synchronous rotation greenberg and weidenschilling 1984 the crust deforms in a brittle manner as evident from the networks of cracks that lace through it greeley et al 2000 of the two kinds of ice deformation creep is probably the better known by readers of the geological and geophysical literature and is certainly the more fully explored and better understood the interested reader may wish to consult a number of excellent reviews of the subject e g see duval et al 1983 weertman 1983 durham and stern 2001 fracture in comparison has only recently been systematically examined the motivation with respect to terrestrial mechanics schulson 2001 comes largely

high temperature deformation during continental margin subduction exhumation the ultrahigh pressure western gneiss region of norway abstract a new dataset for the high pressure to ultrahigh pressure western gneiss region allows the definition of distinct structural and petrological domains much of the study area is an e dipping homocline with e plunging lineations that exposes progressively deeper more strongly deformed more eclogite rich structural levels westward although eclogites crop out across the wgr scandian deformation is weak and earlier structures are well preserved in the southeastern half of the study area the scandian reworking increases westward culminating in strong scandian fabrics with only isolated pockets of older structures the dominant scandian deformation was coaxial e w stretching the sinistrally sheared more trondelag fault complex and nordfjord mylonitic shear zone bound these rocks to the north and south there was moderate top e amphibolite facies deformation associated with translation of the allochthons over the basement along its eastern edge and the nordfjord sogn detachment zone underwent strong lower amphibolite facies to greenschist facies top w shearing a northwestward increase in exhumation related melting is indicated by leucosomes with hornblende plagioclase and scandian sphene in the western 2 3 of the study area exhumation related amphibolite facies symplectite formation in quartzofeldspathic gneiss postdated most scandian deformation further deformation was restricted to slip along biotite rich foliation planes and minor local folding that the western gneiss region quartzofeldspathic gneiss exhibits a strong gradient in degree of deformation implies that continental crust in general need not undergo pervasive deformation during subduction

eclogites and eclogites in the western gneiss region norwegian caledonides the western gneiss region wgr marks the outcrop of a composite terrane consisting of variably re worked proterozoic basement and parautochthonous or autochthonous cover units the wgr exhibits a gross structural petrographic and thermobarometric zonation from southeast to northwest reflecting an increasing intensity of scandian late palaeozoic

partial transformation of gabbro to coesite bearing eclogite from yangkou the sulu terrane eastern china an ultra high pressure uhp metamorphic slab at yangkou beach near qingdao in the sulu region of china consists of blocks of eclogite facies metagabbro metagranitoid ultramafic rock and mylonitic orthogneisses enclosed in granitic gneiss a gradational sequence from incipiently metamorphosed gabbro to completely recrystallized coesite eclogite formed at ultra high pressures was identified in a single 30 m block metagabbro is preserved in the core whereas coesite eclogite occurs along the block margins the metagabbro contains an igneous assemblage of pl aug opx qtz bt ilm ti mag it shows relict magmatic textures and reaction coronas fine grained garnet developed along boundaries between plagioclase and other phases primary plagioclase broke down to ab ky ms zo grt amp augite is rimmed by sodic augite or omphacite whereas orthopyroxene is rimmed by a corona of cum act and omp qtz layers or only omp qtz in transitional rocks augite and orthopyroxene are totally replaced by omphacite and the lower pressure assemblage ab ky phn zo grt coexists with domains of omp jd70 73 ky phn in pseudomorphs after plagioclase both massive and weakly deformed coesite bearing eclogites contain omp ky grt phn coe qtz rt and preserve a faint gabbroic texture coesite inclusions in garnet and omphacite exhibit limited conversion to palisade quartz some intergranular coesite and quartz pseudomorphs after coesite also occur assemblages of the coronal stage transitional and uhp peak occurred at about 540 50 c at c 13 kbar 600 800 c at 15 25 kbar and 800 850 c at 30 kbar respectively garnet from the coronal through the transitional to the eclogite stage rocks show a decrease in almandine and an increase in grossular pyrope components garnet in low grade rocks contains higher mno and lower pyrope components the growth textures of garnet within pseudomorphs after plagioclase or along grain boundaries between plagioclase and other phases are complex the application of garnet zoning to estimate p t should be carried out with caution some garnet enclosing quartz aggregates as inclusions shows radial growth boundaries these quartz aggregates as well as other primary and low p phases persisted metastably at uhp conditions due to sluggish reactions resulting from the lack of fluid during prograde and retrograde p t evolution

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

ultrahigh pressure macro diamonds from copeton new south wales australia based on raman spectroscopy of inclusions abstract mining of cenozoic alluvial deposits at copeton and bingara eastern australia has produced two million macrodiamonds 0 25 ct median size raman spectroscopy is used to identify included minerals within uncut copeton diamonds with sealed chamber remnant pressures of 31 7 to 35 6 kbar for coesite 13 6 and 22 7 kbar for clinopyroxene and 7 6 kbar for grossular garnet assuming elastic behaviour these values generate inclusion entrapment pt loci which intersect restricting diamond formation conditions from 250 c 43 kbar to 800 c 52 kbar larger than error 100 c and 4 kbar this range shows a systematic variation in inclusion composition with diamond zoning and n properties published research shows 1 copeton and bingara diamonds are unique and 2 modern alluvium in the bingara district carries mantle formed garnet captured by post tectonic alkali basalt from an extensive diamondiferous ultrahigh pressure uhp terrane that stalled at depth because it is dominated by mafic eclogite the combined raman and geological results indicate two sets of subduction uhp diamond formation conditions protolith are required firstly cooler oceanic slab and secondly including higher temperature continental crust the copeton and bingara stones are uhp macrodiamonds and carboniferous 40 ar 39 ar age dates on clinopyroxene inclusions should be interpreted as ages of crystallisation representing the termination of subduction the characteristic features of ruptured inclusions and etched percussion marks on copeton and bingara diamond indicate volcanic delivery to the earth s surface alluvial deposits elsewhere in eastern australia may carry similar diamond along with diamond of different origin

coesite eclogites from the roberts victor kimberlite south africa abstract coesite or pseudomorphic quartz is more common than previously recognized in the eclogite xenolith suite from the roberts victor mine south africa all coesite eclogites in this study 18 samples are classified as group i and have mineral compositions that span virtually the entire compositional range of group i eclogites described from this locality most of the roberts victor group i eclogite suite may be in equilibrium with free silica thus weakening the case for these rocks representing residues of partial melting oxygen isotope compositions of garnets from 15 samples are in the range 5 32 6 95 similar to other roberts victor group i eclogites these observations are consistent with a model in which protoliths of these rocks were oceanic basalts and intrusive rocks that underwent exchange with seawater at relatively low temperatures to variable extents prior to subduction and metamorphism to eclogite facies without suffering significant partial melting during or following subduction

controls on platinum group elemental distributions of podiform chromitites a case study of high cr and high al chromitites from chinese orogenic belts abstract a study of podiform chromite deposits from the asiatic orogenic belt and the qilian qiangling kunlun himalaya tectonic domain provides new insights into the geochemistry of the pges in podiform chromite deposits and the genesis of the deposits themselves the bulk of deposits which occur in mantle peridotites of ophiolites have typical ophiolitic pge patterns that are depleted in pt and pd relative to the average upper mantle and have negatively sloping distributions on mantle normalized diagrams type i high cr chromitites have higher os ir ru and rh contents than type ii high al chromitites although both have similar pd and pt most of the type i and ii chromite deposits have lower pd and pt contents than the upper mantle peridotites in which they occur podiform chromitites are essentially products of melt rock interaction in the upper mantle their cr and pges were contributed by not only the invading magmas but also by the upper mantle host the chromite deposits are in part metasomatic replacement bodies the type i high cr chromitite pge patterns were produced by interaction between s undersaturated boninitic magmas and depleted harzburgites whereas the type ii high al chromitite pge patterns were formed by interaction between initially s saturated tholeiitic magmas and depleted harzburgites the low to very low pd and pt contents of both type i and type ii chromitites require that the mantle assemblage in which the chromite deposits were formed had lost their sulfides and hence pd and pt prior to formation of the chromite deposits in addition no or little pd and pt were deposited by the invading magma which either remained s undersaturated boninite or became morb s undersaturated due to interaction with the s depleted harzburgitic mantle it is suggested that the very low ir os and ru contents of boninites in general might be due to loss of ir during the formation of podiform chromitites it is suggested that podiform chromitites with type i pge patterns were formed in an island arc environment whereas those with type ii pge patterns were formed in a back arc setting

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

deep mantle diamonds from south australia a record of pacific subduction at the gondwanan margin diamonds from jurassic kimberlites at eurelia south australia contain coexisting inclusions of ferropericlase and mgsi perovskite that provide evidence for their deep 670 km lower mantle origin eurelia diamonds formed from mixed carbon sources likely including subducted carbonate as indicated by a trend toward isotopically heavy carbon compositions 13 c 0 and low nitrogen concentrations

elongation and migration of sand dunes two distinct processes are known to act on dynamic dunes the process of migration by erosion on the windward side and deposition on the lee side typical for transverse dunes and the process of elongation typical for linear dunes these two processes are determined by wind direction relative to the dune alignment this article reviews the assertion that linear dunes experience lateral displacement in addition to elongation fieldwork on vegetated linear dunes vlds and gis work on seif dunes indicates no lateral migration for these dunes linear dunes can shift laterally only when a slip face formed on the lee side reaches the plinth of the dune the winds from both sides of the seif dune are never symmetric usually winds from one direction are more dominant and effective the outcome is the formation of peaks and saddles along the dune the strongest winds create a slip face on the lee side of the peak segments of the dune oblique to the dune alignment which reaches the base of the dune and displaces the peak downwind along the dune alignment the internal structure of the seif dune is formed mostly by this dominant wind direction and gives the impression that the dune has shifted laterally on the other hand there are cases in which the wind directions relative to dune alignment fall between those of transverse and seif dunes in such cases both processes act on the dune which subsequently experiences migration as well as elongation

genesis of diamond a mantle saga a model for the genesis of natural diamond is presented based on the physical chemical and mineralogical properties and features of diamond optical studies suggest that individual diamonds have had complex growth histories in which growth and dissolution may have occurred growth was not always continuous nor did diamonds grow in necessarily similar chemical environments evidence for this is provided by variation in the nitrogen and trace element contents in diamonds as well as information from studies of the minerals included in diamond isotopic data suggest that diamonds formed from carbon whose sources varied isotopically the possibility exists that some diamonds may be products of recycled subducted carbon whereas others have formed from primordial material either through magmatic or metasomatic processes it is also likely that most diamonds formed in the archaean or proterozoic the cognate host rocks for diamond in the mantle were several but can be broadly grouped into eclogitic and ultramafic peridotitic however in mineralogic and chemical detail these rocks are quite diverse although diamond is commonly found in kimberlite and in lamproite at the earth s surface these two rocks are not genetically related to diamond formation instead they are the transporting vehicles in which diamond ascended rapidly from mantle depths to the crust

ultrahigh pressure minerals and metamorphic terranes the view from china abstract ultrahigh pressure uhp metamorphism refers to mineralogical modifications of continental and oceanic crustal protoliths associated mafic ultramafic rocks initially formed or emplaced in shallow levels of the lithosphere but which subsequently have experienced p t conditions within or above the coesite stability field 2 7 gpa 700 c typical products include eclogite garnet peridotite and uhp varieties of metapelite quartzite marble paragneiss and orthogneiss uhp metamorphic assemblages require relatively cold lithospheric subduction to mantle depths some recrystallization even occurs under forbidden p t conditions characterized by a geotherm of the current explosion of research on continental uhp terranes reflects their significance for mantle dynamics and the tectonics of continental subduction collision exhumation mantle slab interactions and geochemical recycling a further characterization of uhp phases and positive identification of uhp minerals requires new experimental studies coupled with state of the art analyses for example the very rare occurrence of microdiamond inclusions in zircons from dabie sulu uhp rocks may reflect high f o 2 attending recrystallization inasmuch as epidote is rather common rutile needles within garnets from sulu uhp eclogitic rocks may not be the result of exsolution so in such cases the apparent uhp pressure may have been over estimated hadean igneous microdiamond inclusions in jack hills detrital zircons could have originated from mantle xenoliths whereas abundant detrital phanerozoic diamonds containing inclusions of coesite and other eclogitic minerals from new south wales might have been derived from unexposed uhp metamorphic terranes micro mineral intergrowth and nano size minerals may hold important key to deciphering the actual p t paths of subduction and mantle return flow although most exhumed terranes have returned surfaceward relatively rapidly after short time of uhp condition the long duration of storage at great depth and slow exhumation for the largest uhp terranes remain as major problems

localized surface ice weakness on a glacial ice runway following construction of a glacial ice runway on the ross ice shelf antarctica and prior to flight operations the runway was proof rolled the proof exercise was designed to simulate typical heavy aircraft initial testing produced numerous brittle surface failures in the runway ice thin sections of ice cores taken from the failed areas showed large crystals c axis vertical of clear blue ice with long vertical bubbles indicative ofice formed directly from meltwater uniaxial unconfined compression tests on core samples were used to compare runway ice strength with published data for polycrystalline laboratory ice since the frequent failure of surface ice had not been expected it was critical to understand the formation and mechanical properties of the weak ice to prevent its occurrence in the future and to strengthen the existing problem areas we discuss the likely scenarios for development of weak ice on the airstrip and the physical properties of this type of ice also the procedure used to repair successfully the runway surface is described which culminated in test flights followed by full flight operations

exhumation mechanisms of melt bearing ultrahigh pressure crustal rocks during collision of spontaneously moving plates a series of 2d petrological thermomechanical numerical experiments was conducted to i characterize the variability of exhumation mechanisms of ultrahigh pressure metamorphic uhpm rocks during collision of spontaneously moving plates and ii study the possible geodynamic effects of melting at ultrahigh pressure conditions for the exhumation of high temperature ultrahigh pressure metamorphic ht uhpm rocks to this end the models include fluid and melt induced weakening of rocks five distinct modes of exhumation of u hpm rocks associated with changes in several parameters in the models of plate collision and continent subduction are identified as follows vertical crustal extrusion large scale crustal stacking shallow crustal delamination trans lithospheric diapirism and channel flow the variation in exhumation mechanisms for u hpm rocks in numerical models of collision driven by spontaneously moving plates contrasts with the domination of the channel flow mode of exhumation in a majority of the published results from numerical models of collision that used a prescribed plate convergence velocity and or did not include fluid and melt induced weakening of rocks this difference in the range of exhumation mechanisms suggests that the prescribed convergence velocity condition and the neglect of fluid and melt related weakening effects in the earlier models may inhibit development of several important collisional processes found in our experiments such as slab breakoff vertical crustal extrusion large scale stacking shallow crustal delamination and relamination and eduction of the continental plate consequently the significance of channel flow for the exhumation of uhpm rocks may have been overstated based on the results of the earlier numerical experiments in addition the results from this study extend over a larger proportion of the high temperature range of p t conditions documented from uhpm rocks including those retrieved from ht uhpm rocks than the results of experiments from previous numerical models in particular the highest peak metamorphic temperatures up to 1000 degrees c are recorded in the case of the vertical crustal extrusion model in which subducted continental crust is subjected to a period of prolonged heating by asthenospheric mantle abutting the continental side of the vertically hanging slab nonetheless some extreme temperature conditions which have been suggested for the kokchetav and bohemian massifs perhaps up to 1100 1200 degrees c are still to be achieved in experiments using numerical models

a potential method to confirm the previous existence of lawsonite in eclogite the mass imbalance of sr and lrees in multistage epidote ganghe dabie uhp terrane lawsonite is an important hydrous mineral that is stable at low temperature lt and high to ultrahigh pressure hp uhp conditions in subducted slabs the occurrence absence of lawsonite in eclogite is a significant constraint for the construction of the metamorphic tectonic and fluid melt evolution histories of an hp uhp terrane however lawsonite is very rarely preserved in natural eclogites and accurate judgment of its former existence is a significant challenge for petrologists at present whether lawsonite has ever existed in lawsonite absent eclogite is mainly judged by i pseudomorphs after lawsonite and ii phase equilibria modelling in this study major element and trace element distributions in multistage minerals were examined in the ganghe lawsonite absent uhp eclogite in the dabie uhp terrane eastern china this work demonstrates that the whole rock sr and light rare earth elements lrees are mainly dominated by epidote other minerals garnet omphacite quartz kyanite barroisite phengite and accessory minerals play a very limited role in the sr and lrees budgets two stages of epidote which have noticeably different sr and lrees contents were recognized in the eclogite i epidote porphyroblasts ep p core which are suspected to be the pseudomorphic mineral after lawsonite contain significantly high sr 7200 10 300 ppm and lrees 160 1300 ppm for la ii an earlier stage epidote ep in core occurs as inclusions in matrix omphacite or in omphacite inclusions in the suspected pseudomorphic minerals after lawsonite spmal this early epidote has significantly lower sr 990 1890 ppm average 1495 ppm n 17 and lrees contents 60 110 ppm for la average 91 ppm n 17 all of the existing early stage minerals predating the spmal have very low contents of sr and lrees and the total amounts of these elements in the early stage minerals do not balance those in the spmal this indicates that a missing ca al sr and lree rich mineral which was previously in equilibrium with the early stage minerals likely existed in the ganghe eclogite on the basis of the mineral geochemistry and phase equilibria modelling we confirm that the missing mineral cannot be anything but lawsonite this study indicates that examining the mass im balance of sr and lrees between multistage hp uhp epidote can be used as a potential method to confirm the previous existence of lawsonite in lawsonite absent eclogite

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

hadean diamonds in zircon from jack hills western australia this paper reports the discovery of micro diamond inclusions in zircon from the jack hills western australia which is up to 4 252 million years old and includes the oldest known diamonds found in terrestrial rocks the spread of ages indicates that either the conditions required for diamond formation were repeated several times during early earth history or that there was significant recycling of ancient diamond

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

deep subduction of continental crust in accretionary orogen evidence from u pb dating on diamond bearing zircons from the qinling orogen central china abstract accretionary orogenic belts are considered the most important sites for the generation of continental crust however it is still not very clear whether in such settings the continental crust has been significantly transported back to the mantle accompanied with its lateral growth continental uhp rocks the best indicators of the recycling of the continental crust have rarely been discovered in accretionary orogenic belts which hinder the exploration of this essential process the possible occurrence of early paleozoic uhp metamorphism in the qinling orogen provides an excellent opportunity to address this question this article reports an integrated study of u pb age trace element and mineral inclusion of zircon from an amphibolite sample in the qinling orogen the zircon crystals show typical metamorphic growth zoning low th u ratios flat hree patterns and insignificant eu anomalies they give a weighted mean u pb age of 490 4 5 8 ma most importantly an in situ diamond inclusion was identified from one of the zircon crystals therefore the obtained 490 4 5 8 ma age was taken as registering the peak uhp metamorphism the discovery of in situ diamond inclusion provides important evidence for the uhp metamorphism of the qinling orogen and indicates that the north qinling microcontinent was subducted to mantle depths of 120 km when it collided with the erlangping arc attached to the southern margin of the north china block combining with previous results we suggested that the north qinling uhp terrane underwent fast exhumation from 120 km to ca 30 km within 10 myr intervals as a few examples of uhp metamorphism have been discovered in some accretionary orogens more attention needs to be paid to the occurrence of continental uhp metamorphism during accretionary orogenic process furthermore evident crustal growth has been documented in the north qinling orogen during the early paleozoic it is inferred that the accretionary orogenic belts may play important roles in recycling of continental crust into the mantle besides generation of continental crust

qusongite wc a new mineral an unusual group of mantle minerals including about 70 80 species has been recovered from podiform chromitites of the luobusa ophiolite qusong county tibet china all of the minerals were hand picked from heavy mineral separates of the chromitite the minerals include diamond coesite moissanite wustite intermetallic compounds os ir alloys with diamond inclusions fe silicides and a new mineral qusongite qusongite is associated with chromian chlorite calcite w ti c and ti w c alloys and chromite it occurs as angular grains generally 4 8 m in diameter but some are as large as 0 2 0 3 0 25 mm the grains are opaque and steel gray with a metallic luster and grayish yellow reflection the empirical formula based on 2 atoms is w 1 006 cr 0 02 c 0 992 and the simplified formula is wc qusongite has a hexagonal structure and belongs to space group p 6 m 2 with a 2 902 1 a c 2 831 1 a c a 0 9775 v 20 05 1 a 3 z 1

dynamic processes acting on a longitudinal seif sand dune abstract field measurements were made on a longitudinal dune in the sinai desert in order to understand its morphology and dynamics the field measurements contradicted the wind structure indicated by the helicoidal flow theory rather it was found that winds coming from two basically different directions at different times and striking the dune obliquely were responsible for sand transport and erosion or deposition along the lee flank the essence of this mechanism is the deflection of the wind airflow on the lee flank of the dune to a direction parallel to the crest line the occurrence of erosion or deposition depends upon the angle of incidence between the wind and the crest line when this angle is 40 the velocity of the deflected wind drops and deposition takes place on the lee flank the angle of incidence in each wind storm is changed intermittently between 30 and 100 along the dune because the dune meanders and because of the sinuous outline of the crest line in this manner sand transport and erosion or deposition occurs along the lee flank depending on the angle of incidence between the wind and the crest line as a result of the deflection of the wind the dune elongates at an average rate of more than 1 m per month peaks and saddles along the crest line advance at an average rate of 0 7 m per month the lack of uniformity in the effects of the wind on both sides of the dune creates a lack of uniformity in the rate of erosion and deposition this can explain the formation of peaks along the crest line of the dune

formation and exhumation of ultra high pressure rocks during continental collision role of detachment in the subduction channel 1 uhp rocks commonly form and exhume during the transition from oceanic subduction to continental collision their exhumation in subduction channels depends on the balance between down channel shear traction and up channel buoyancy thermal mechanical upper mantle scale numerical models are used to investigate how variations in material properties of the subducting continental margin affect this balance changes in shear traction leading to crustal decoupling detachment are investigated by varying the onset of strain weakening thermal parameters and convergence velocity variations in buoyancy force are investigated by modifying subducted material density and volume the model results are interpreted in terms of the exhumation number e which expresses the role of the pressure gradient channel thickness effective viscosity and subduction velocity peak metamorphic conditions exhumation velocity and timing of exhumation are temporally and spatially variable and are sensitive to the evolution of e the models reproduce natural ptt constraints and indicate that neither slab breakoff nor surface erosion is required for uhp exhumation

the origin and significance of crustal minerals in ophiolitic chromitites and peridotites abstract various combinations of zircon quartz corundum k feldspar plagioclase apatite amphibole rutile titanite almandine garnet kyanite andalusite and coesite have been recovered from podiform chromitites of the luobusa and dongqiao ophiolites in tibet the oman ophiolite and the ray iz ophiolite in the polar urals russia chromitites in all four ophiolites also contain moissanite and the luobusa and ray iz ophiolites contain in situ diamonds most of the recovered zircons are sub rounded grains with complex internal structures indicating polyphase growth trace element contents and a low pressure inclusion assemblage quartz muscovite k feldspar apatite ilmenite rutile indicate a continental crustal origin for the zircons they have sims u pb ages that are generally much older than the host body total range 90 to 2500 ma the presence of numerous crustal minerals particularly zircon suggests derivation from metasedimentary rocks subducted into the mantle their preservation in chromitites and peridotites implies effective isolation from the mafic melts that formed the ophiolites we suggest that most of these minerals were derived from the crustal parts of subducted slabs and were encapsulated into chromite grains precipitated from rising asthenospheric and suprasubduction magmas the chromite grains were carried in melt channels to shallow levels in suprasubduction mantle wedges and then deposited as podiform chromitites near the moho the rise of asthenospheric peridotites into suprasubduction zones was facilitated by subduction initiation and possibly by slab tear allowing mixing of the uhp highly reduced minerals and crustal minerals now found in ophiolitic chromitites and peridotites

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

flume experiments on the alignment of transverse oblique and longitudinal dunes in directionally varying flows for more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow whereas others are parallel or oblique to flow this problem of bedform alignment was studied experimentally using subaqueous dunes on a 3 6 m diameter sand covered turntable on the floor of a 4 m wide flume in each experiment two flow directions relative to the bed were produced by alternating the turntable between two orientations the turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms the resulting bedforms were in equilibrium with the time averaged conditions of the bimodal flows dune alignment was studied for five divergence angles the angle between the two flow directions 45 67 5 90 112 5 and 135 the flow depth during all experiments was approximately 30 cm mean velocity was approximately 50 cm s 1 and mean grain diameter was 0 6 mm each experiment continued for 30 75 min during which time the flume flow was steady and the turntable position changed every 2 min at the end of each experiment water was slowly drained from the flume and dune alignment was measured transverse dunes defined relative to the resultant transport direction were created when the divergence angle was 45 and 67 5 and longitudinal dunes were created when the divergence angle was 135 at intermediate divergence angles dunes with both orientations were produced but transverse dunes were dominant at 90 and longitudinal dunes were dominant at 112 5 one experiment was conducted with a divergence angle of 135 and with unequal amounts of transport in the two flow directions this was achieved by changing the orientation of the turntable at unequal time intervals thereby causing the amount of transport to be unequal in the two directions the dunes formed during this experiment were oblique to the resultant transport direction these experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments in both sets of experiments the bedforms developed with the orientation having the maximum gross bedform normal transport the orientation at which the sum of the bedform normal components of the two transport vectors reaches its maximum value in other words the bedforms develop with an orientation that is as transverse as possible to the two flows in those cases where the two flows diverge by more than 90 and transport equal amounts of sand bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors although such bedforms have been defined by previous work as longitudinal bedforms they are intrinsically the same kind of bedform as transverse bedforms

the fracture of ice on scales large and small arctic leads and wing cracks from observations and calculations of crack patterns in ice it is suggested that a similar mechanism may account for cracking over a wide range of scales

3 d x ray tomography of diamondiferous mantle eclogite xenoliths siberia a review abstract diamonds form over billions of years hundreds of kilometers beneath the earth s surface and in combination with inclusions trapped within provide important constraints on the evolution of the mantle over geological time diamonds are generally studied as individual crystals sourced from highly explosive kimberlite pipes which entrain and subsequently disaggregate mantle fragments xenoliths en route to the surface this has resulted in a general absence of robust textural descriptions of diamonds relative to their hosting mantle protolith the textural associations of diamonds within their mantle host rocks are reviewed here on the basis of a compilation of x ray tomographic data for 17 diamondiferous eclogite xenoliths from siberian kimberlites this review represents a comprehensive description of diamonds relative to their host silicates the lack of such descriptions in previous studies is largely due to the rarity of these xenoliths the difficulty in preparing petrographic thin sections containing diamonds and their high monetary value high resolution computed x ray tomography hrcxt produces up to 1200 sequential 2 d slices through individual xenoliths each of which represents a pseudo thin section with a resolution on the order of 5 20 m the improved resolution of x ray imaging in recent studies allows for the identification of not only primary minerals but metasomatic minerals assemblages including spongy textured clinopyroxene phlogopite k richterite and hercynitic spinel allowing for the delineation of distinct metasomatic pathways through the xenoliths and their relationship to diamonds diamonds are observed in three distinct textural settings potentially representing several temporally distinct diamond growth events these setting includes 1 diamonds completely enclosed in garnet 2 diamonds associated with highly embayed silicate grain boundaries and 3 diamonds contained within distinct metasomatic plumbing systems diamonds observed completely enclosed in garnets suggest an early diamond forming event prior to major re crystallization and eclogite formation during subduction the occurrence of diamond in association with embayed garnets suggests that diamond grew at the expense of the hosting silicate protolith in addition the spatial relationships of diamonds with metasomatic pathways which are generally interpreted to result from late stage proto kimberlitic fluid percolation indicate a period of diamond growth occurring close to but prior to the time of kimberlite emplacement furthermore the paragenesis of sulfides within eclogite xenoliths are described using 3 d models for entire xenoliths volumes providing important constraints of the timing of sulfide mobilization within the mantle three d animations created using x ray tomography data for ten of the xenoliths can be viewed at the following link http eps utk edu faculty taylor tomography php

coesite and clinopyroxene exsolution lamellae in chromites in situ ultrahigh pressure evidence from podiform chromitites in the luobusa ophiolite southern tibet abstract we report in situ petrological evidence of deep mantle origin from podiform chromitites in the luobusa ophiolite southern tibet analytical transmission electron microscopy measurements reveal that chromites in podiform chromitites from the luobusa ophiolite have numerous exsolution lamellae of diopsidic clinopyroxene and coesite which indicate an ultrahigh pressure origin of over 3 gpa 100 km deep the presence of these lamellae coupled with abundant micro inclusions of clinopyroxene requires high solubility of sio2 and cao in the host chromite and suggests a precursor of chromite a cafe2o4 structured high pressure polymorph stable at pressures over 12 5 gpa 380 km deep these nano scale observations and geological occurrence indicate that the mantle peridotite under the tibetan mid ocean ridge was transported from the deep mantle at least 100 km probably more than 380 km deep by the mantle convection it implies that the root of mantle upwelling has a much deeper origin than previously believed

continental plate collision p t t z conditions and unstable vs stable plate dynamics insights from thermo mechanical modelling there was much debate recently on the mechanisms of continental convergence and related pressure temperature p t conditions both in modeling and petrologic community depending on the mechanisms of convergence subduction collision folding or rt instability one can argue about the possibility of large scale deviations of pressure and temperature in the accretion prism and below it from reference i e lithostatic conditions commonly used for petrologic reconstructions of evolution of exhumed metamorphic rocks these deviations can be caused for example by tectonic overpressure that as suggested in some studies may be responsible for formation of uhp ultra high pressure rocks however overpressure in exhumation zones can be built only in specific collision scenarios associated with plate coupling pure shear folding in this study we analyze conditions that define various mechanisms of convergence and consequently of exhumation these mechanisms can be represented as a superposition of 1 simple shear subduction 2 pure shear collision 3 folding and 4 rayleigh taylor instability we study these scenarios using a thermo mechanical model that accounts for brittle elastic ductile rheology surface processes and metamorphic changes it appears that stable oceanic type subduction may occur in the case of cold lithospheres tmohob550 c and relatively high convergence rates n3 5 cm yr depending on the lower crustal rheology strong or weak either the whole upper and lower crust or only the lower crust can be involved in subduction in case of weak metamorphic rheologies phase changes improve chances for stable subduction pure shear becomes a dominant mechanism when tmohon550 c or convergence rates are lower than 3 cm yr large scale folding is favored in case of tmoho 500 650 c and is more effective in the case of mechanical coupling between crust and mantle e g strong lower crust gravitational rayleigh taylor instabilities overcome other mechanisms for very high values of tmoho n800 c and may lead to development of subvertical cold spots however it is reasonable to assume that in most cases continental collision is initiated at oceanic subduction rate which is rarely slower than 5 cm yr this rate is sufficient to drive continental subduction during the first several myr of collision in this case the subduction channel is characterized by nearly lithostatic pressure conditions large scale zones of tectonic overpressure may be built outside the channel but do not affect the exhumed rocks overpressure may be built inside the channel in the short moment of its closure we suggest that most continental orogenic belts could have started their formation from continental subduction this evokes small tectonic overpressures and thus deep origin of the uhp rocks that may be brought to the surface via the suggested multi level mechanism of exhumation

transient hot channels perpetrating and regurgitating ultrahigh pressure high temperature crust mantle associations in collision belts abstract two dimensional numerical modeling of early continental collision associated with subduction of the lithospheric mantle shows that the formation and exhumation of coesite and diamond bearing rocks metamorphosed at 700 to 900 c in the presence of dense supercritical silicate fluids and melts may be explained by a transient hot channel effect anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper crustal rocks especially sediments of passive margin origin and mantle rocks heating is associated with partial melting of crustal rocks caused by pervasive flow of aqueous fluids relieved by rapid dehydration deserpentinization of the overriding mantle lithosphere that has been hydrated during earlier subduction stages the channel penetrates the plate interface to the bottom of the lithosphere of the overriding plate 150 200 km and is characterized by metamorphic temperatures reaching 700 to 900 c low effective viscosity of rocks subsequent to increased temperature partial melting and fluid infiltration permits profound mixing of hydrated mantle and crustal rocks the hot channel exists only during early collision but rapidly produces large amounts of ultrahigh pressure high temperature rocks further collision closes the channel by squeezing rheologically weak partially molten buoyant rocks between the strong lithospheric mantles of the two colliding plates assemblages of complicated p t paths with repetitive loops characterize exhumation of ultrahigh pressure rocks in the convoluted flow pattern of the hot channel

overview of the meso to neoproterozoic evolution of the vindhyan basin central india abstract despite its origin in a stable intracratonic basin the vindhyan supergroup central india embodies tectonic driven depositional cycles of various orders a marked change in sedimentation pattern was coupled with a transient plate margin compression in the otherwise extensional regime an unconformity laterally correlatable with a conformity that divides the supergroup in two sequences arose in consequence maximum flooding surfaces mfs within the sequences can generally be correlated with intrabasinal volcanism that drastically diminished through the initial rift to later sag stage of basin evolution concomitantly with the change in tectonic milieu paleoseismic deformation structures and related deposits also became drastically reduced in scale nevertheless metre and decametre scale depositional cycles correlate well with the subtle record of paleoseismicity intermittent tilting of the depositional substratum is demonstrable in systematic bed dip changes in metre scale fining upward depositional cycles in the rift stage in the sag stage it is reflected merely in consistent deflection of paleocurrent directions at the top of the decametre scale parasequence sets towards the top of the supergroup progressive thickening and decreasing frequency of parasequences indicates a declining rate of basin subsidence progradation despite punctuation thus resulted in basin filling

first record of k cymrite in north qaidam uhp eclogite western china inclusions of polycrystalline k feldspar aggregates after k cymrite kalsi 3 o 8 nh 2 o were discovered in garnet from a dulan eclogite in the qaidam ultrahigh pressure uhp terrane western china the eclogite consists of garnet alm 56 grs 23 prp 20 sps 01 omphacite jd 35 aeg 6 aug 59 and minor rutile and apatite the 20 to 200 m inclusions vary in shape from prismatic hexagonal to rounded and exhibit palisade and mosaic textures host garnets show radial fractures similar to those surrounding quartz pseudomorphs after coesite some inclusions consist of almost end member k feldspar or 99 100 ab 0 1 polycrystalline aggregates whereas others are composed of 90 vol k feldspar or 96 99 ab 1 4 with minor secondary albite occurring along the margins of the inclusions raman spectra of k feldspar crystalline aggregates vary slightly reflecting various degrees of si al ordering and show a raman peak at 390 395 cm 1 typical for cymrite structure these characteristics of the k feldspar polycrystalline inclusions imply the presence of former k cymrite in the dulan eclogite formed at 3 gpa at 720 c the occurrence of k cymrite in uhp eclogite is significant because of its potential as an important carrier of crustal k and h 2 o to the upper mantle

coesite in clinopyroxene in the caledonides and its implications for geodynamics coesite is reported for the first time from the caledonide orogen it occurs as inclusions in clinopyroxene in the dolomite eclogite at grytting norway and provides valuable new evidence to support the hypothesis of extremely high pressure 30 kbar in certain norwegian eclogites this finding has implications for the geodynamics and kinetics of the concepts of microscale intracrystalline tectonic overpressure and of macroscale local or regional tectonic overpressure and for the hypotheses of subduction and obduction involving a more than 100km vertical component of transport

discovery of metamorphic diamonds in central china an indication of a 4000 km long zone of deep subduction resulting from multiple continental collisions the central orogenic belt cob of china is a major continental collision zone that contains extensive outcrops of deeply subducted and exhumed rocks at both the eastern and the western end of the belt here we report discovery of microdiamonds from both eclogites and felsic gneisses in the north qinling zone in the central portion of the cob this discovery demonstrates that the country rocks of continental affinity shared in the ultra high pressure metamorphic uhpm event and provides a bridge connecting the two previously recognized uhpm terranes thereby establishing the existence of a uhpm belt extending more than 4000 km geochronological dating yields early palaeozoic ages in the west and early mesozoic ages in the east recording two separate continental collisions overprinted within the cob occurrence of uhp metamorphism during recurrent continental collision here and in the alps suggests that deep subduction of continental material during such collisions is probably common rather than exceptional with significant implications for processes of plate tectonic reorganization and mantle mixing over time

why deposits of longitudinal dunes are rarely recognized in the geologic record dunes that are morphologically of linear type many of which are probably of longitudinal type in a morphodynamic sense are common in modern deserts but their deposits are rarely identified in aeolian sandstones one reason for non recognition of such dunes is that they can migrate laterally when they are not exactly parallel to the long term sand transport direction thereby depositing cross strata that have unimodal cross bed dip directions and consequently resemble deposits of transverse dunes dune parallel components of sand transport can be recognized in ancient aeolian sands by examining compound crossbedding formed by small dunes that migrated across the lee slopes of large dunes and documenting that the small dunes migrated with a component in a preferred along crest direction over the large dunes

very low temperature record of the subduction process a review of worldwide lawsonite eclogites abstract lawsonite eclogites preserve a record of very low temperature conditions in subduction zones all occur at active margin settings typically characterized by accretionary complexes lithologies and as tectonic blocks within serpentinite matrix melange peak lawsonite eclogite facies mineral assemblages garnet omphacite lawsonite rutile typically occur in prograde zoned garnet porphyroblasts their matrix is commonly overprinted by higher temperature epidote bearing assemblages greenschist or amphibolite facies conditions erase former lawsonite eclogite relics various pseudomorphs after lawsonite occur particularly in some blueschist eclogite transitional facies rocks coesite bearing lawsonite eclogite xenoliths in kimberlitic pipes and lawsonite pseudomorphs in some relatively low temperature ultrahigh pressure eclogites are known using inclusion assemblages in garnet lawsonite eclogites can be classified into two types l type such as those from guatemala and british columbia contain garnet porphyroblasts that grew only within the lawsonite stability field and e type such as from the dominican republic record maximum temperature in the epidote stability field formation and preservation of lawsonite eclogites requires cold subduction to mantle depths and rapid exhumation the earliest occurrences of lawsonite eclogite facies mineral assemblages are early paleozoic in spitsbergen and the new england fold belt of australia this suggests that since the phanerozoic secular cooling of earth and subduction zone thermal structures evolved the necessary high pressure temperature conditions buoyancy of serpentinite and oblique convergence with a major strike slip component may facilitate the exhumation of lawsonite eclogites from mantle depths

water transport into the deep mantle and formation of a hydrous transition zone abstract the phase relations in the peridotite water system to the top of the lower mantle reveal that a certain amount of water can be transported and stored in the transition zone by various hydrous minerals resulting in formation of a hydrous transition zone results of preliminary experiments to clarify the effect of water on kinetics of the olivine wadsleyite transformation are given and show that water enhances the transformation kinetics significantly there are potential dehydration sites in the deep mantle four sites along the descending slabs depending on their temperature profiles i e the mantle wedge of the subduction zone mantle transition zone top of the lower mantle where hydrous ringwoodite and superhydrous phase b decompose and deep in the lower mantle around 1200 1500 km depth where decomposition of phase d g occurs we also expect one site of dehydration melting at the base of the upper mantle where the hot mantle plume hydrated in the transition zone can be dehydrated the transition zone can serve as a water absorber for the mantle scale water circulation system some of the recent seismic works including the p wave tomography images reveal the existence of low velocity anomalies in the transition zone suggesting possibly a wet transition zone elevation of the 410 km discontinuity and lack of clear evidence for a metastable olivine wedge in cold slabs may be consistent with the equilibrium phase transformation from olivine to wadsleyite in cold and wet slabs on the basis of our kinetic study of the transformation under wet conditions

oxygen isotopes in subducted oceanic crust a new perspective from siberian diamondiferous eclogites 1 there are three methods of investigating the oxygen isotope composition of oceanic crust 1 data from drilling obtained samples 2 study of obducted ophiolites and 3 from crustal derived xenoliths however each approach has limitations drilling capabilities are limited to the upper 1 3 km of the oceanic crust ophiolites are segments of oceanic crust and underlying mantle exposed at the earth s surface but their origin and emplacement are still debated nonetheless the study of ophiolite sequences has enabled many of the fundamental observations regarding ancient oceanic crust and the oxygen isotope signature of the upper mantle analyses of ophiolite sequences e g samail reveal 18o variations ranging from isotopically enriched in relation to morb 18o morb to isotopically depleted low 18o morb interpreted to show the effects of seawater interaction at different temperatures mantle derived xenoliths also display compelling geochemical evidence suggesting they are remnants of subducted ocean crust and may in fact be more representative samples some kimberlite hosted diamondiferous eclogite xenoliths with crustal protoliths reveal a marked oxygen isotope disparity between oceanic crust and the upper mantle i e a bimodal distribution of both mantle like 18o 5 6 and isotopically enriched oxygen 18o 6 8 the isotopically high 18o values are often observed in eclogite xenoliths with ultramafic protoliths which form beyond the low temperature alteration zone this finding is in contrast to traditional oxygen isotope versus depth curves of ophiolite sequences here we present a compiled data set from siberian eclogites and pyroxenites that illustrates this bimodality using magnesium number mg as a depth proxy and investigate the conditions that could potentially result in the observed abnormal oxygen isotope variations

mineral inclusions and geochemical characteristics of microdiamonds from the do27 a154 a21 a418 do18 dd17 and ranch lake kimberlites at lac de gras slave craton canada a mineral inclusion carbon isotope nitrogen content nitrogen aggregation state and morphological study of 576 microdiamonds from the do27 a154 a21 a418 do18 dd17 and ranch lake kimberlites at lac de gras slave craton was conducted mineral inclusion data show the diamonds are largely eclogitic 64 followed by peridotitic 25 and ultradeep 11 the paragenetic abundances are similar to macrodiamonds from the do27 kimberlite davies r m griffin w l o reilly s y 1999 diamonds from the deep pipe do27 slave craton canada in gurney j j gurney j l pascoe m d richardson s h eds the j b dawson vol proc 7th internat kimberlite conf red roof designs cape town pp 148 155 but differ to diamonds from nearby kimberlites at ekati e g lithos 2004 tappert r stachel t harris j w brey g p 2004 mineral inclusions in diamonds from the panda kimberlite s p canada 8th international kimberlite conference extended abstracts and snap lake to the south dokl earth sci 380 7 2001 806 that are dominated by peridotitic stones eclogitic diamonds with variable inclusion compositions and temperatures of formation 1040 1300 c crystallised at variable lithospheric depths sometimes in changing chemical environments a large range to very 13c depleted c isotope compositions 13c 35 8 to 2 2 and an nmorb bulk composition calculated from trace elements in garnet and clinopyroxene inclusions are consistent with an origin from subducted oceanic crust and sediments carbon isotopes in the peridotitic diamonds have mantle compositions 13c mode 4 0 mineral inclusion compositions are largely harzburgitic variable temperatures of formation garnet tni 800 1300 c suggest the peridotitic diamonds originate from the shallow ultra depleted and deeper less depleted layers of the central slave lithosphere carbon isotopes 13c av 5 1 and mineral inclusions in the ultradeep diamonds suggest they formed in peridotitic mantle 670 km the diamonds may have been entrained in a plume and subcreted to the base of the central slave lithosphere poorly aggregated nitrogen iaa without platelets in a large number of eclogitic 67 and peridotitic 32 diamonds with similar nitrogen contents indicates the diamonds were stored in the mantle at low temperatures 1060 1100 c following crystallisation in the archean type iaa diamonds have largely cubo octahedral growth forms and type ii and type iaab diamonds with higher nitrogen aggregation states mostly have octahedral morphologies however no correlation between these groups and their mineral inclusion compositions c isotopes and n contents rules out the possibility of unique source origins and suggests eclogitic and peridotitic diamonds experienced variable mantle thermal states variation in mineral inclusion chemistries in single diamonds possible overgrowths of 13c depleted eclogitic diamond on diamonds with peridotitic and ultradeep inclusions and type i ultradeep diamond with low n aggregation is consistent with diamond growth over time in changing chemical environments

morphology internal structure and mechanics of small longitudinal seif dunes in an aeolian horizon of the proterozoic dhandraul quartzite india the excellently preserved metre scale linear bedforms in an aeolian horizon of the proterozoic dhandraul quartzite india show oppositely dipping strata arranged in a zigzag pattern the strata are dominantly of translatent type deposited by along crest migrating ripples preserved on the flanks of dunes the bedforms thus may be interpreted in a morphodynamic sense as longitudinal seif dunes in order to determine the regional palaeoflow pattern the migration directions of ripples preserved at the top of sheet sandstones that are associated with the dune cross strata and internally show subhorizontal translatent strata were measured a directionally varying flow with a mean direction nearly parallel to the mean axial trend of the dunes is indicated the kinematics of the dunes were thus largely the result of alternate operation of two oblique flow components each of which was deflected at a dune crest into an along crest flow on the downwind flank of the dune the deflected flow formed along crest migrating ripples which in turn deposited climbing ripple strata alternate deposition on the two opposite flanks resulted in near vertical accretion of the dunes as is indicated by the zigzag pattern of stratal arrangement

proterozoic platform sequences of peninsular india implications towards basin evolution and supercontinent assembly abstract a group of less disturbed and unmetamorphosed proterozoic platformal sediment package lying over deformed and metamorphosed archean to paleoproterozoic basement in several parts of peninsular india is informally termed as purana basins in indian stratigraphy the trend shift in the understanding of these basin fills in last two decades often supported by international collaborations has made significant advancements in respect to unconformity and sequence development relationship with accretion and break up of the supercontinents initiation and evolution of the basins in different tectonic set ups nature of sediment provenance paleoclimate and paleo weathering patterns and basin water chemistry geophysical backups encompassing the basins occasionally extending up to the craton and adjacent mobile belts helped in refining the understanding on the basement structure and tectonic forcings the present paper is an attempt towards the collation of the database generated in last two decades in order to present the status of current understanding on different purana basins with regard to interactions of physical chemical and biological parameters of the proterozoic earth

a crustal mineral in a mantle diamond recent studies of diamonds inclusions in diamonds and rock fragments from the earth s mantle have shown the presence of minerals and rocks with a chemical composition that suggests a previous origin in the crust presumably this crustal material was transported into the mantle at a subduction zone the chemical evidence of previous residence of mantle materials in the crust has come principally from determinations of the proportions of the isotopes of oxygen1 2 sulphur3 4 lead4 5 and carbon6 which typically show a much wider range of composition in the crust than in material of purely mantle origin here we report a less subtle crustal signature in a mantle derived diamond an inclusion of the mineral staurolite staurolite has never previously been found in mantle diamonds or rocks but is a common mineral in metamorphic rocks in the crust the characteristics of the staurolite suggest not only the probability that it formed in rocks with a crustal bulk composition but also the possibility that it formed by metamorphism in the crust or in a subduction zone before being incorporated in the mantle and eventually in a growing diamond

extreme crustal oxygen isotope signatures preserved in coesite in diamond the anomalously high and low oxygen isotope values observed in eclogite xenoliths from the upper mantle beneath cratons have been interpreted as indicating that the parent rock of the eclogites experienced alteration on the ancient sea floor1 recognition of this genetic lineage has provided the foundation for a model of the evolution of the continents whereby imbricated slabs of oceanic lithosphere underpin and promote stabilization of early cratons2 early crustal growth is thought to have been enhanced by the addition of slab derived magmas leaving an eclogite residuum in the upper mantle beneath the cratons3 but the oxygen isotope anomalies observed in eclogite xenoliths are small relative to those in altered ocean floor basalt and intermediate stage subduction zone eclogites and this has hindered acceptance of the hypothesis that the eclogite xenoliths represent subducted and metamorphosed ocean floor basalts we present here the oxygen isotope composition of eclogitic mineral inclusions analysed in situ in diamonds using an ion microprobe secondary ion mass spectrometer the oxygen isotope values of coesite a polymorph of sio2 inclusions are substantially higher than previously reported for xenoliths from the subcratonic mantle but are typical of subduction zone meta basalts and accordingly provide strong support for the link between altered ocean floor basalts and mantle eclogite xenoliths

recycling of crustal materials through study of ultrahigh pressure minerals in collisional orogens ophiolites and mantle xenoliths a review abstract newly recognized occurrences of ultrahigh pressure uh p minerals including diamonds in ultrahigh temperature uh t felsic granulites of orogenic belts in chromitites associated with ophiolitic complexes and in mantle xenoliths suggest the recycling of crustal materials through deep subduction mantle upwelling and return to the earth s surface this circulation process is supported by crust derived mineral inclusions in deep seated zircons chromites and diamonds from collision type orogens from eclogitic xenoliths in kimberlites and from chromitities of several alpine himalayan and polar ural ophiolites some of these minerals contain low atomic number elements typified by crustal isotopic signatures ophiolite type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone in addition to ringwoodite and inferred stishovite a number of nanometric minerals have been identified as inclusions employing state of the art analytical tools reconstitution of now exsolved precursor uh p phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier uh p conditions for example tibetan chromites containing exsolution lamellae of coesite diopside suggest that the original chromitites formed at p 9 10 gpa at depths of 250 300 km the precursor phase most likely had a ca ferrite or a ca titanite structure both are polymorphs of chromite and at 2000 c would have formed at minimum pressures of p 12 5 or 20 gpa respectively some podiform chromitites and host peridotites contain rare minerals of undoubted crustal origin including zircon feldspars garnet kyanite andalusite quartz and rutile the zircons possess much older u pb ages than the time of ophiolite formation these uh p mineral bearing chromitite hosts evidently had a deep seated evolution prior to extensional mantle upwelling and partial melting at shallow depths to form the overlying ophiolite complexes these new findings together with stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere recycling of surface organic carbon into the lower mantle and ascent to the earth s surface through mantle upwelling intensified study of uh p granulite facies lower crustal basement and ophiolitic chromitites should allow a better understanding of the geodynamics of subduction and crustal cycling

thermobarometry and geotectonic significance of high pressure granulites examples from the moldanubian zone of the bohemian massif in lower austria

origin and sequence stratigraphic implications of high alumina glauconite within the lower quartzite vindhyan supergroup abstract an integrated field petrographical and geochemical investigation reveals a shallow marine dys oxic depositional setting for the glauconite at the top of the mesoproterozoic lower quartzite member of the vindhyan supergroup a thorough facies and paleogeographic analysis indicates a storm influenced shallow subtidal depositional condition for the glauconitic sandstone occupying the mid level of a transgressive systems tract tst deposit which is capped by the maximum flooding zone mfz the x ray diffractional parameters confirm the evolved character of the glauconite the mineral chemical analysis indicates the glauconite is enriched in k2o mgo and al2o3 and depleted in fe2o3 total compared to the phanerozoic variety it formed by the pseudomorphic replacement of the k feldspar by the addition of fe2o3 at consistently high content of k2o unlike most phanerozoic examples the elevated level of h3sio4 cl k na mg and fe possibly derived by the continental weathering and or contemporary volcanism facilitated the glauconitization process the high content of mg in the glauconite corresponds to the mg rich mesoproterozoic seawater a dys oxic depositional condition associated with a major marine flooding surface favoured the formation of glauconite while the onset of anoxic regime caused the disappearance of glauconite and the deposition of pyritiferous and carbonaceous shale in the overlying condensed zone deposits

diamond and coesite discovered in saxony type granulite solution to the variscan garnet peridotite enigma diamond and coesite were discovered in situ as inclusions in garnet kyanite and zircon in high pressure granulites from northern bohemian massif these continental crustal rocks were therefore subducted to depths of c 140 km which also explains their common association with mantle garnet bearing peridotites models involving crustal thickening for these high pressure granulites need to be significantly modified whole variscan belt with numerous hp granulite occurrences can represent a large ultrahigh pressure terrain

diagenesis of quartz in the upper proterozoic kaimur sandstones son valley central india abstract the upper proterozoic kaimur sandstones in central india are quartz sublithic and lithic arenites cemented by quartz illite and hematite diagenetic quartz occurs in five modes syntaxial overgrowths fracture healings aggregates of small euhedral crystals quartz resulting from the alteration of detrital silicates and from the recrystallization of quartz intergranular pressure dissolution is suggested as the main source of silica with smaller contribution from other sources such as silica dissolved in meteoric waters stylolitization clay mineral diagenesis and the alteration of detrital silicates studies on the fluid inclusions and oxygen isotopes of diagenetic quartz suggest that meteoric water modified by diagenetic reactions has mediated the quartz cementation

nature of diamonds in yakutian eclogites views from eclogite tomography and mineral inclusions in diamonds abstract we have performed dissections of two diamondiferous eclogites ux 1 and u33 1 from the udachnaya kimberlite yakutia in order to understand the nature of diamond formation and the relationship between the diamonds their mineral inclusions and host eclogite minerals diamonds were carefully recovered from each xenolith based upon high resolution x ray tomography images and three dimensional models the nature and physical properties of minerals in direct contact with diamonds were investigated at the time of diamond extraction polished sections of the eclogites were made containing the mould areas of the diamonds to further investigate the chemical compositions of the host minerals and the phases that were in contact with diamonds major and minor element compositions of silicate and sulfide mineral inclusions in diamonds show variations among each other and from those in the host eclogites oxygen isotope compositions of one garnet and five clinopyroxene inclusions in diamonds from another udachnaya eclogite u51 span the entire range recorded for eclogite xenoliths from udachnaya in addition the reported compositions of almost all clinopyroxene inclusions in u51 diamonds exhibit positive eu anomaly this feature together with the oxygen isotopic characteristics is consistent with the well established hypothesis of subduction origin for udachnaya eclogite xenoliths it is intuitive to expect that all eclogite xenoliths in a particular kimberlite should have common heritage at least with respect to their included diamonds however the variation in the composition of multiple inclusions within diamonds and among diamonds from the same eclogite indicates the involvement of complex processes in diamond genesis at least in the eclogite xenoliths from yakutia that we have studied

nanocrystalline diamond from the earth s mantle underneath hawaii abstract melt inclusions in a mantle derived garnet pyroxenite xenolith from salt lake crater hawaiian island of oahu have been analysed by means of transmission electron microscopy including energy dispersive x ray analysis electron energy loss spectroscopy and electron diffraction the melt inclusions represent trapped low degree melt that metasomatised the hawaiian mantle lithosphere before the eruption of the host magma the inclusions consist of a c cl s rich glass of basaltic composition an exsolved gas fluid phase mainly co2 with minor amounts of co h2o and some unidentified c h and h s species and or carbonate diamond is the major phase in the glass ranging in size between a few and several hundred nanometres two varieties of nanocrystalline diamonds are identified polycrystalline aggregates of nanometre size diamonds are tentatively explained as pseudomorphs after carbonate while single crystals are suggested to have crystallised from the melt other nanocrystalline phases include native fe and cu fes fes2 zns ags and several ti nb zr ir in pd rich phases of unknown composition overall the observed mineral assemblage suggests that the melt was highly reduced and strongly enriched in volatiles and trace elements of contrasting geochemical affinity our findings are the first evidence for a metasomatic impregnation of the hawaiian mantle by low degree melts here we report the first occurrence of diamond in the modern oceanic mantle

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

unusual micro and nano inclusions in diamonds from the juina area brazil abstract a series of uncommon micro and nano inclusions has been identified in diamonds from the rio soriso placer deposit in mato grosso state brazil the micro inclusions are variable in size from 1 to 300 m usually they are polymineralic being formed predominantly by intergrowths of carbonates silicates and other minerals carbonates are represented mostly by dolomite and occasionally by calcite silicates found are coesite wollastonite ii cuspidine and monticellite sulphides and ilmenite form micro inclusions as well nano inclusions are different from micro inclusions not only in size not exceeding 200 nm they are usually included in micro inclusions among nano inclusions halides nacl kcl cacl2 and pbcl2 anhydrite spinel phlogopite pbo2 tio2 with an pbo2 structure native fe and other phases are identified all these minerals are of the eclogitic association they are either associated with coesite or are included in a diamond with a light organic carbon isotopic composition with 13c from 14 to 25 pdb this confirms our earlier conclusion that diamonds from the juina area may have formed as a result of subduction of the crustal material to depths of at least the lower transition zone or even the lower mantle the pressure estimates for the investigated diamonds vary in a range from 3 to 10 gpa an interesting assemblage of calcite cuspidine wollastonite monticellite fluid identified in one of the studied diamonds is considered as a product of a reaction of wollastonite fluid forming cuspidine monticellite the presence of numerous pores cavities and bubbles in mineral inclusions and identification of an association of volatile containing mineral inclusions such as halides nacl kcl cacl2 and pbcl2 fluorine containing silicate cuspidine and phlogopite emphasize the important role of volatiles particularly chlorine and fluorine in the formation of the diamonds

raman confirmation of microdiamond in the svartberget fe ti type garnet peridotite western gneiss region western norway introductionvestiges of ultra high pressure meta morphism uhpm havebeenfoundincontinental and oceanic rocks of dif ferentorogensworldwide smith 1988 coleman and wang 1995 carswelland compagnoni 2003 indirectuhpmevidencecomesfromtheappli cation of geothermobarometric tech niques lappin and smith 1978 ravna krogh and paquin 2003 ap plied to uhpm mineral assemblagesand directly from mineralogical indi cators such as coesite diamond andmajoritic garnet chopin 1984 smith 1984 sobolev and shatsky 1990 do brzhinetskaya et al 1995 van roer mund and drury 1998 nasdala andmassonne 2000 mposkos andkosto poulos 2001 van roermund et al 2002 godard et al 2003 neverthe less the mechanisms responsible forthe formation preservation and exhu mation of uhpm rocksin orogens arestill not fully understood the volume and spatial distributionof uhpm rocks within uhpm terr anes including the observed contrastin metamorphic grade between rocksthat contain uhpm minerals andadjacent country rocks that do notcontain them have led to di erentexplanations concerning the origin emplacement and preservation ofthese rocks to explain the occur rence volume and areal extent ofuhpm rocks in the western gneissregion wgr the following mecha nisms that assume a continental sub duction scenario have been proposed a the existence of major and orminor post uhpm tectonic contactssuch as nappes and or tectonic mel anges e g lappin and smith 1978 smith 1984 1988 wain 1997 cuth bert et al 2000 terry and robinson 2003 2004 or b the presence of uids and or deformation leading todi erential prograde or retrogradereactions and di erences in reaction kinetics between rock types austr heim et al 1997 cuthbert et al 2000 wain et al 2001 carswell andcuthbert 2003 cuthbert and car swell 2003 hypotheses that do notnecessarily involve continental sub duction may involve local regional tectonic overpressure in rocks smith 1984 mancktelow 1993 petrini and podladchikov 2000 it isconsidered here that the volume andareal extent of uhpm domains withina single metamorphic terrain are thusimportant parameters to determine asthey can modify or identify the loca tions of inferred or observed tectoniccontacts the relations between uidsand uhpm and or the scales atwhich continental crust subductionor tectonic overpressure might act here we report raman data thatcon rm the previously reported butnot proven presence of microdia monds at the svartberget uhpmlocality in the wgr of norway vrijmoed et al 2006 micro diamond con rmation is consistentwith the results of vrijmoed et al 2006 that the volume and arealextent of the northern uhpm domainof the wgr fig 1 are considerablyexpanded eastwards and followingthe reasoning in the paragraph above the new microdiamond nding willput important constraints on themodels described above ultra high pressure metamorphismin the western gneiss regionthe wgr represents a window inthe scandinavian caledonides wherescandian reworked high grade gneis sic rocks of proterozoic age presum ably belonging to the baltic plate are exposed in addition variableamounts of metadolerites amphi abstract

imbricate structure of the luobusa ophiolite and surrounding rock units southern tibet abstract the cretaceous luobusa ophiolite is a tectonic slice less than 1 2 km thick the structurally underlying unit is the tertiary luobusa formation and the overlying unit is composed of feebly metamorphosed triassic sedimentary rocks the top and bottom contacts of the ophiolite dip gently to the south the major part of the luobusa ophiolite is mantle peridotite including podiform chromitite this chromitite has received much attention because it contains an unusual mineral assemblage which includes diamond and moissanite a serpentinite melange zone including clasts of basaltic and sedimentary rocks occurs underneath the mantle peridotite mesoscopic microscopic structures were observed in the sheared rocks shear indicating structures c type shear bands and type porphyroclasts in the rocks near the top and bottom boundaries of the luobusa ophiolite show consistent top to the north or northeast reverse displacement the results reveal that the luobusa ophiolite was overturned and intercalated into an imbricate structure the thrust faults on the top and bottom of the ophiolite can be correlated with north vergent back thrusting which was associated with crustal shortening along the main central thrust due to the continued northward movement of india after the welding of india to asia

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

into the forbidden zone very low temperatures at high pressures have long been believed to constitute a forbidden zone not realized in earth however recent studies of ultrahigh pressure uhp terranes indicate that these rocks have experienced such forbidden zone conditions liou et al discuss the implications of these observations for plate tectonics

triaxial experiments on iceberg and glacier ice triaxial experiments at confining pressures in the range 0 13 79 mpa have been performed on glacial ice collected from four icebergs and one glacier tests were conducted at strain rates in the range of 5 10 5 to 5 10 2 s 1 and at four temperatures in the range of 1 to 16 c depending on test conditions the ice failed by one of four possible modes ductile deformation due to extensive non interacting microcracks fracture along a shear plane followed by continuous or stick slip sliding large scale brittle fracture and combined ductile and shear plane fracture and slip the strength increased with decreasing temperature increasing strain rate up to 5 10 3 s 1 and increasing confining pressure at the lower temperatures the strength at 5 10 2 s 1 was lower than at 5 10 s 1 probably because extension and interaction of microcracks is enhanced at the higher rate for higher confining pressures at 1 c the strength decreased due to freezing point depression the ice from the different sources exhibited different mean uniaxial compressive strengths the mean number of air bubbles per unit volume correlated with the mean uniaxial compressive strengths and this may be the dominant factor distinguishing the strengths of the various ice types

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

status report on stability of k rich phases at mantle conditions abstract experimental research on k rich phases and observations from diamond inclusions uhp metamorphic rocks and xenoliths provide insights about the hosts for potassium at mantle conditions k rich clinopyroxene kcpx km3 si2o6 can be an important component in clinopyroxenes at p 4 gpa dependent upon coexisting k bearing phases solid or liquid but not apparently upon temperature maximum kcpx content can reach 25 mol with 17 mol the highest reported in nature partitioning k d cpx liquid above 7 gpa 0 1 0 2 require ultrapotassic liquids to form highly potassic cpx or critical solid reactions e g between kspar and di phlogopite can be stable to about 8 gpa at 1250 c where either amphibole or liquid forms when fluorine is present it generally increases in phl upon increasing p and probably t to about 6 gpa but reactions forming amphibole and or kmgf3 limit f content between 6 and 8 gpa the perovskite kmgf3 is stable up to 10 gpa and 1400 c as subsolidus breakdown products of phlogopite upon increasing p m4 k substituted potassic richterite ideally k kca mg5si8o22 oh f 2 is produced in k rich peridotites above 6 gpa and in di phl from 6 to 13 gpa k content of amphibole is positively correlated with p al and f content decrease with p in the system 1kspar 1h2o k cymrite hydrous hexasanidine kalsi3o8 nh2o kcym is stable from 2 5 gpa at 400 to 1200 c and 9 gpa kcym can be a supersolidus phase formation of kcym is sensitive to water content not forming within experiments with h2o kspar phase x a potassium di magnesium acid disilicate k1 x n 2 mg1 nmn3 2si2o7h2x forms in mafic compositions at t 1150 1400 c and p 9 17 gpa and is a potential host for k and h2o at mantle conditions with a low t geotherm or in subducting slabs the composition of phase x is not fixed but actually represents a solid solution in the stoichiometries 2mg2si2o7h2 k mg2si2o7h k2mg2si2o7 vacancy apparently stable only near the central composition k hollandite kalsi3o8 is possibly the most important k rich phase at very high pressure as it appears to be stable to conditions near the core mantle boundary 95 gpa and 2300 c other k rich phases are considered

structural classification of chromite pods in southern new caledonia a structural classification of podiform chromite orebodies from southern new caledonia results in a division of deposits into three major types discordant subconcordant and concordant with penetrative structures foliation and lineation in the enclosing peridotite discordant deposits are very irregular in shape and clearly crosscut banding and foliation subconcordant deposits are generally tabular in shape and lie within 10 degrees to 25 degrees in strike and or dip to the foliation concordant deposits are also tabular and lie parallel to foliation in peridotite pyroxene lineation in host peridotite always indicates the elongation direction of these deposits within subconcordant and discordant deposits chromite lineations are often oblique to those in the surrounding rocks they follow local variations in the orebody shape and indicate possible deposit extensions at depth the classification of chromite bodies corresponds to three stages of increasing deformation as evidenced by chromite ore textures discordant deposits which are the least deformed are characterized by primary textures such as the nodular one the foam texture the chromite net and the occluded silicate texture within subconcordant and mainly concordant deposits massive disseminated and antinodular ores show evidence of strong deformation the lack of geochemical distinctions between the different deposit types supports such an hypothesis these chromite deposits in ophiolitic harzburgites are thought to have been formed beneath an oceanic spreading ridge if the discordant pods are considered as representative of the original situation it is proposed that the chromite has crystallized and has been dynamically concentrated along steep conduits traversing the enclosing harzburgite and feeding a magma chamber next the chromite enriched pipes are caught up by plastic deformation in the mantle and tectonically reoriented toward the foliation the chromite deposits in the massif du sud are located within a domain about 1 5 km thick in the harzburgites and dunite zones this domain is limited upward by the first cumulates and gabbros and downward by the transition to a different plastic flow regime in the harzburgites finally some guides to chromite prospecting and exploration are cited applicable at different geologic scales and based on lithologic and structural criteria

microdiamonds frontier of ultrahigh pressure metamorphism a review abstract this is a comprehensive review paper devoted to microdiamonds from ultrahigh pressure metamorphic uhpm terranes incorporated in orogenic belts formed at convergent plate boundaries in paleozoic mesozoic alpine time when in 1980 the first small diamonds were discovered within amphibolite granulate facies metamorphic rocks it came as a great surprise that buoyant continental crust could be subducted to depths of hundreds of kilometers and then subsequently exhumed since then much progress has been made in understanding the mechanism of these diamonds formation and the number of new diamond bearing uhpm terranes was significantly increased especially within european orogenes moreover new variations in tectonic settings in which uhp rocks can be formed and exhumed came to the attention of geologists simply due to the finding of diamonds in places previously forbidden for their formation e g oceanic islands ophiolites and forearc environments over the past decade the rapidly moving technological advancement has made it possible to examine microdiamonds in detail and to learn that part of them has a polycrystalline nature that they contain nanometric multiphase inclusions of crystalline and fluid phases and that they keep a crustal signature of carbon isotopes scanning and transmission electron microscopy focused ion beam techniques synchrotron infrared spectroscopy micro x ray diffraction and nano secondary ion mass spectrometry studies of these diamonds provide evidence that they keep traces of fluid originated from both crustal and mantle reservoirs and that they probably interacted with deep mantle plumes hypotheses proposed for diamond formation in subduction zones founded on both analytical and experimental studies are discussed the paper also emphasizes that the discovery of these microdiamonds as well as coesite triggered a major revision in the understanding of deep subduction processes leading to a clear realization of how continental materials can be recycled into the earth s mantle and geochemically rejuvenate it

first find of polycrystalline diamond in ultrahigh pressure metamorphic terrane of erzgebirge germany this article describes polycrystalline diamond from the erzgebirge ultrahigh pressure metamorphic uhpm terrane of the bohemian massif related to the variscan 340 ma continent continent collision the foils polycrystalline diamond included in zircon were prepared with focused ion beam fib and studied with transmission electron microscopy tem each domain of the polycrystalline diamond consisted of a series of diamond monocrystals from 1 to 4 up to 15 containing numerous nanometric fluid and crystalline inclusions of sio2 caco3 kcl and kalsi3o8 the integrated chemistry of the nanoinclusions suggests that the polycrystalline diamond was crystallized from a mixture of two end members which includes a carbon rich hydrous silicic fluid containing si al k and a hydrous saline fluid rich in cl k na traces of carbonate sulphate and phosphate coupled with the presence of metallic cations such as fe mg ti cr co zn zr pb as and hg found in the diamond are coherent with the local geochemical diversity of the host metasedimentary rocks the oxidation state of the diamond forming fluid was close to c co buffer for example fo2 6 log units which is at the upper limit of the diamond stability region the presence of dislocation arrays indicating low angle grain boundaries together with zig zag features or kinks at diamond grain boundaries reflects rapid crystallization of the polycrystalline diamond triangular fluid pockets with steps at the surface related to 110 and 111 planes of diamond could promote the formation of c h and c oh bonds that probably could facilitate the process of diamond graphitization the microstructural features of polycrystalline diamond from the erzgebirge uhpm terrane as well as their undisputed formation from crustal organic carbon can be used for better understanding of the origin of any polycrystalline diamond formation from both kimberlitic and alluvial sources including enigmatic polycrystalline black diamond commonly called carbonado

size frequency distribution of longitudinal dune rippled flank sands compared to that of slipface sands of various dune types rippled flanks of longitudinal dunes and the slip faces of various dune types can be distinguished granulometrically by comparing the top to bottom trend of changes of sorting in the sand population of each individual slope flank sands which are prone to sorting processes through migration of ripples alongslope are always better sorted upslope whereas slipface sands which are controlled by avalanche and grainfall of sands become better sorted downslope considering the absolute values of the bottom samples the sands of the slip faces are both better sorted and the size distribution more symmetrical than those of the rippled flanks applying this approach in investigating ancient sediments could improve palaeogeographical interpretations

unusual upper mantle beneath guaniamo guyana shield venezuela evidence from diamond inclusions the geochemistry of mineral inclusions in diamond is an important source of information about the composition of the continental lithospheric mantle at depths exceeding 120 150 km at these depths two main types of geochemical environment support diamond formation they are ultramafic or peridotitic u type and eclogitic e type environments as shown by minerals that occur as inclusions in diamonds in primary diamond bearing kimberlite or lamproite rock the ratio of diamonds from these two geochemical environments varies widely between localities the u type environment dominates for the majority of diamond occurrences worldwide whereas the e type environment dominates for a very limited number of localities in south africa north america and australia the present study shows that an uncommonly high percentage 99 4 of e type diamonds with extremely variable inclusion assemblages is found in kimberlites in the northwestern part of the guyana shield at guaniamo venezuela these variations range from previously unknown silica undersaturated corundum eclogite to abundant silica rich coesite eclogite assemblages representing 22 of all e type diamonds some of which contain syngenetic ilmenite and magnetite the compositional variations of garnet and omphacite inclusions are extremely broad the wide variability of the eclogitic source in which diamonds formed beneath the guyana shield indicates a broadly basaltic chemistry in this environment which may represent ancient subducted oceanic crust such specific features have not been reported for any other diamond occurrence and reflect an unusual composition of the deep lithospheric mantle in this area

ultrahigh ϵnd eclogites from an ultrahigh pressure metamorphic terrane of china the su lu ultrahigh pressure uhp metamorphic terrane is part of the qinling dabie suture zone formed by the collision between the sino korean and yangtze cratonic blocks geochemical and isotopic investigation of the uhp metamorphic rocks has revealed a spectacular history for some eclogitic rocks retrograded coesite bearing eclogites from the weihai area in the eastern end of the su lu terrane have recorded an extraordinary nd isotopic growth with a world record high nd value of 264 range 170 to 264 such isotopic characteristics are consistent with the observed extreme lree fractionation and very high sm nd ratios the sm nd isotopic data allow us to calculate the minimum age of protolith formation at 1 7 ga assuming their evolution from a depleted or a chondritic mantle geochemical data indicate that the eclogite protoliths were of basaltic compositions originally but underwent metasomatism water rock interaction at high pressures and temperatures leading to the present apparent andesitic composition and extreme lree depletion this process took place in the proterozoic 1 7 ga and was not related to the mesozoic continental collision and ultrahigh pressure metamorphism at 210 220 ma ago because of a protracted retrograde metamorphism garnet sm nd systems were not closed until 160 ma ago 50 ma after the peak eclogite metamorphism this implies that the exhumation history is significantly different in different parts of the dabie and su lu uhp metamorphic terranes from geochemical analyses and isotopic age determinations we argue that at least two ancient tectonic events in the middle and late proterozoic can be identified prior to the last mesozoic continental collision and accompanying uhp metamorphism in the su lu and dabie terrane