velocity modeling of a complex deep crustal structure across the mesoproterozoic south delhi fold belt nw india from joint interpretation of coincident seismic wide angle and near offset reflection data an approach using unusual reflections in wide angle records 1 seismic wide angle record sections from favorably placed source and limited aperture recording spreads particularly across collision boundaries reveal bright unusual high velocity contrast reflections of limited lateral coherence the arrival times of the unusual reflections for recording updip of the reflecting plane align as high apparent velocity phases at wide angle offsets coincident near offset reflection images from similar structural features provide additional control for modeling the unusual phases on the wide angle record sections we propose an approach for joint interpretation of these coincident seismic data sets and modeling the unusual phases on the processed wide angle records to delineate both the velocity stratification and the geometry of the deep crustal structures consistent with the near offset reflection images processed and migrated near offset reflection images reveal several steeply dipping isolated reflections on the western margin of the south delhi fold belt dfb nw india interpreted as the south delhi thrust fault coincident limited aperture wide angle records reveal bright unusual reflections which are also found to be associated with the same thrust fault observations of similar dipping reflection patterns in various other regions lend support to consider them as genuine in plane reflections resulting from a structural fabric imprinted on horizontally oriented geological structures we use the reflectivity structural model from the near offset data set that provides necessary constraints for modeling and simulating the travel times and amplitudes of the unusual reflections recognized in the wide angle records the unusual reflections are effectively used as part of the wide angle data set for gaussian beam synthetic seismogram modeling thus delineating for the first time a complex 2 d model of the seismic velocity structure of the deep crust and uppermost mantle across the marwar basin mb and the dfb the dipping events revealed in the wide angle data set are successfully modeled and interpreted as reflections from the thrust fault consistent with the near offset reflection image the 2 d velocity model parameterized as a stack of isolated dipping reflectors embedded in deep crustal layers is successively refined by including the structural features recognizable both in the near offset reflection image and in the wide angle records the unusual reflections are modeled as a set of discrete reflectors representing local velocity variations imprinted on the background of a deep crustal velocity structure the lamellar structure revealed by short isolated dipping and the subhorizontal middle to lower crustal reflections suggests heterogeneities at scale lengths on the order of at least the fresnel zone diameter as resolved here the local velocity variations in the deep crust can be considered analogous on a different scale to the models in which velocity heterogeneities on scale lengths of the seismic wavelength constitute a medium of random distribution of scatterers the crustal scale south delhi thrust fault on the western margin of the dfb delineated as the stack of reflectors dipping 25 30 se probably developed during the mesoproterozoic collisional episode related to the delhi orogeny contemporaneous with the formation of rodinia it is concluded that complex structural features developed during collisional episodes can survive through geological periods longer than generally expected depending on the accretionary characteristics at the time of orogenic evolution the 2 d velocity model further reveals significant variations of crustal seismic structure with a relatively sharp and shallow moho at 39 40 km in the mb and a deeper moho at 45 47 km underlying a 12 km thick subhorizontal lamella of high velocity 6 9 7 5 km s layers in the dfb regions

coesite bearing eclogites from the dabie mountains central china petrogenesis p t paths and implications for regional tectonics coesite and kyanite bearing eclogites are abundant in the southern part of the dabie mountains southern dabie terrane sdt two types of eclogites from the sdt types iii and iv were selected for detailed paragenetic study type iii eclogites most abundant in the northern part of the sdt occur as blocks in gneisses and marble and contain eclogitic assemblages of omphacite garnet phengite epidote coesite kyanite carbonate rutile ilmenite these minerals exhibit weak compositional zoning and contain few mineral inclusions type iv eclogites mostly in the southern part of the sdt occur as coherent layers interbedded with gneisses and amphibolites and have assemblages of omphacite garnet glaucophane kyanite epidote phengite quartz rutile ilmenite garnets of type iv eclogites exhibit a prograde compositional zoning and have mineral inclusions of paragonite phengite epidote quartz and rutile in the core and omphacite barroisite and mg katophorite in the rim prograd

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

preservation of primary lake signatures in alkaline earth carbonates of the eocene green river wilkins peak laney member transition zone abstract significant changes in carbonate mineralogy texture and stable isotope composition occur at the transition from the wilkins peak member to the laney member in the eocene green river formation bridger basin wyoming which reflect evolution of inflow waters lake waters and paleoenvironments the top of the wilkins peak member contains heterogeneous laminae of calcite and dolomite evaporites associated with these layers suggest deposition in hypersaline lakes diagenetic carbonate mineral textures include euhedral cement overgrowths and interlocking mosaics of calcite and dolomite crystals 20 70 m in size electron microprobe analyses indicate diagenetic overgrowth of fe rich dolomite on cloudy fe poor cores 18o values of carbonate laminae in the upper wilkins peak member vary by 6 with no depth dependent or mineralogic trends which also suggests diagenetic overprinting alternating organic rich and primary aragonite calcite and dolomite laminae were identified from the lower laney member primary lacustrine aragonite consists of well sorted prismatic crystals 5 10 m in length with micro lamination defined by crystal size variation primary precipitated calcite and dolomite laminae are monominerallic with well sorted polyhedral crystals 10 m in size primary mineralogy of the lower laney member changes from calcite to aragonite and dolomite stratigraphically upward along the same 15 m thick stratigraphic interval 18o values decrease upward by 3 all of which suggests 1 lake waters underwent evaporative concentration which together with calcite precipitation increased the lake water mg ca ratios and led to formation of aragonite and dolomite 2 source waters became lower in 18o possibly as inflow changed to higher altitude foreland rivers the results from this study show that understanding the primary lacustrine versus diagenetic origin of green river carbonate minerals is essential for paleoenvironmental and paleoclimate interpretations

ultrahigh pressure metamorphism in the magnesite aragonite stability field evidence from two impure marbles from the dabie sulu uhpm belt two magnesite bearing impure dolomitic marbles from the dabie sulu ultrahigh pressure uhp region have been investigated to clarify if they had actually attained p t conditions outside the dolomite stability field limited by the reaction dolomite aragonite magnesite and to test their potential for recording u hp conditions in both cases the silicate mineral assemblage records conditions around the terminal amphibole breakdown reaction amphibole aragonite quartz clinopyrox ene talc which is a good geobarometer between at least 2 0 and 2 6 gpa at higher pressures the terminal breakdown of talc to clinopyroxene coesite is the last p t milestone below 4 gpa recordable by the silicate assemblage but evidence of former coesite is ambiguous the dolomite dissociation curve becomes strongly divariant in fe bearing marbles and may thus be attainable during cold subduction near the 5 ck m 1 geotherm at least one of the samples from xinyan village near taihu dabie shan preserved relicts of both magnesite and aragonite and most likely attained conditions within the aragonite magnesite stability field for the second sample from sanqingge village in the sulu terrane no certain evidence has been found in this study impure dolomitic marbles have considerable potential to preserve ultra high pressure relicts particularly massive impure marbles that have not been pervasively infiltrated by fluids during exhumation are considered to preserve high pressure relicts better than metapelites paragneisses and orthogneisses and perhaps almost as well as eclogites or metaperidotites the inconspicuous mineral assemblage clinopyroxene talc or quartz after former coesite may in fact record uhp conditions

holocene coastal environments and processes in subantarctic temperate cold tierra del fuego argentina chile fil bujalesky gustavo gabriel consejo nacional de investigaciones cientificas y tecnicas centro austral de investigaciones cientificas argentina

ultra high pressure metamorphism of carbonate rocks in the dabie mountains central china abstract widespread ultra high p assemblages including coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite in marble gneiss and phengite schist are present in the dabie mountains eclogite terrane these assemblages indicate that the ultra high p metamorphic event occurred on a regional scale during triassic collision between the sino korean and yangtze cratons marble in the dabie mountains is interlayered with coesite bearing eclogite and gneiss and as blocks of various size within gneiss discontinuous boudins of eclogite occur within marble layers marble contains an ultra high p assemblage of calcite aragonite dolomite clinopyroxene garnet phengite epidote rutile and quartz coesite coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite occur as fine grained inclusions in garnet and omphacite phengites contain about 3 6 si atoms per formula unit based on 11 oxygens similar to the coesite bearing eclogite marble exhibits retrograde recrystallization under amphibolite greenschist facies conditions generated during uplift of the ultra high p metamorphic terrane retrograde minerals are fine grained and replace coarse grained peak metamorphic phases the most typical replacements are symplectic pargasitic hornblende epidote after garnet diopside plagioclase an18 after omphacite and fibrous phlogopite after phengite ferroan pargasite plagioclase and actinolite formed along grain boundaries between garnet and calcite and calcite and quartz respectively the estimated peak p t conditions for marble are comparable to those for eclogite garnet clinopyroxene geothermometry yields temperatures of 630 760 c the garnet phengite thermometer gives somewhat lower temperatures the minimum pressure of peak metamorphism is 27 kbar based on the occurrence of coesite such estimates of ultra high p conditions are consistent with the coexistence of grossular rich garnet rutile and the high jadeite content of omphacite in marble the fluid for the peak metamorphism was calculated to have a very low xco2 0 03 the p t conditions for retrograde metamorphism were estimated to be 475 550 c at 7 kbar

faults and folds fact and fiction abstract after reviewing the microscopic and macroscopic texture of fault zones the localisation of rupture and creep is described and the reduced strength of fault zones is investigated simple strength and viscosity models for the whole lithosphere play a major role for the geometry of fault zones compressional faults thrusts show ramp and flat structures often soling in a weak detachment zone extensional faults prefer a listric shape often turning subhorizontal and being invisible in the seismic lamellae of the ductile lower crust which according to the models is also a broad zone of detachment and decoupling faults in the lower crust are rare and restricted to strain hardened fault rocks or intrinsically rigid rocks like oceanic mafic ultramafic rocks of suture zones transient faults in the lower crust are created by rupture processes of large earthquakes some deep faults moderately dipping or flat are again observed in the rather rigid uppermost mantle the observation of folding inside the crust seems to be connected with an intermediate viscosity range and with a broad vertical transition zone where rigid reactions and ductile processes are mixed various methods of detecting faults by seismic studies are critically reviewed and some sequence of reliability is suggested impedance contrasts polarity dip thickness and multiple fault strings have to be deciphered by wavefront modelling origin and survival of faults are considered to be a consequence of tectonic and thermal evolution under specific stress systems

ultrahigh pressure metamorphism in western tianshan china part i evidence from inclusions of coesite pseudomorphs in garnet and from quartz exsolution lamellae in omphacite in eclogites inclusions of coesite pseudomorphs in garnets have been found in type i eclogites interlayered with mafic blueschists and carbonate eclogites and quartz exsolution lamellae in omphacites have been recognized in type ii eclogites with pillow structure in western tianshan china based on mineralogy and petrology the metamorphic evolution of western tianshan eclogites can be divided into three stages 1 pre peak ultrahigh pressure uhp eclogite facies stage 356 443 c 8 10 kb 2 uhp eclogite facies stage 496 598 c 25 7 26 7 1 kbar and 3 retrograde epidote blueschist facies stage 500 530 c 10 12 kbar consequently the eclogites from the western tianshan region of china have undergone unambiguous uhp metamorphism

correlation and dating of quaternary littoral zones along the patagonian coast argentina six areas of the patagonian coast argentina were investigated in order to determine the number characteristics geomorphology and development of quaternary littoral zones it became apparent that utilizing dl ratios of aspartic acid and leucine of various molluscan species would be the most useful in correlation relative age dating and estimating the ages of these zones the oldest littoral zone is found at elevations between 24 and 41 m above mean sea level and is judged to be older than oxygen isotope substage 5e in age based on relatively high amino acid ratios and extrapolated from non linear kinetic models an intermediate aged littoral zone may be present at some locations based upon beach ridges or platforms varying in elevation between 16 and 28 m above mean sea level dl ratios are generally lower than those for the oldest zone but show a greater variation this zone may represent the substage 5e sea level stand well defined young beach ridges 8 12 m above mean sea level are found in most locations and have been 14c dated and verified by amino acid ratios as being holocene the presence of quaternary aged emerged littoral zones at roughly the same elevation suggest that the glacio eustatic contribution is the primary cause of the high sea level stands whereas secondary variations are attributed to other factors

carbon recycled into deep earth evidence from dolomite dissociation in subduction zone rocks comment and reply reply i appreciate the interest that hermann has shown in our study of carbon recycled into deep earth zhu and ogasawara 2002a 1 the work reported in that paper was accomplished in ogasawara s laboratory at waseda university all samples were collected by ogasawara and the first author

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

reflections from mantle fault zones around the british isles british institutions reflection profiling syndicate birps deep seismic reflection surveys show that the upper mantle around the british isles is reflective exhibiting discrete isolated reflecting zones within an otherwise seismically transparent mantle there are 20 known occurrences of reflectors within the upper mantle across the continental shelf of the british isles many delimited by intersecting or closely spaced profiles most of the mantle reflectors have similar reflection characteristics they dip 10 degree to 30 degree and are thin approximately 0 5 s approximately 2 km and discrete the geologic history of the continental shelf around the british isles an area 1000 x 1000 km is complex and the tectonic settings of these reflectors very each mantel reflector is associated with a major zone of deformation in the crust this association the dips of the reflectors and their high reflectivity all indicate a structural origin the birps mantle reflectors include probable early paleozoic thrusts and mesozoic normal faults in contrast to birps data deep reflection profiles in other areas of the world in a variety of geologic settings have only rarely imaged reflectors within the upper mantle

cannibalisation of holocene gravel beach ridge plains northern tierra del fuego argentina abstract gravel beach ridge plains form where there is sufficient availability of gravels and wave energy competent to transport the gravel even though beach ridge plains are formed on coasts where sea level has risen during the holocene they occur extensively on stable or emergent coasts unfortunately the holocene evolution of these plains is hard to decipher because of the lack of datable material and their reworked character minimum age the rollover of barriers is expected on submerging coasts on falling sea level coasts the beach ridge plains are in a punctuated process of progradation cannibalisation is common in both settings that is sediment is eroded to maintain longshore growth we present morphological and sedimentological data from three gravel beach ridge plains san sebastian rio chico and cabo penas of the northern coast of tierra del fuego these beach complexes occupy embayments that were infilled during the last 5000 yr under different environmental conditions depth flooded area local oceanographic processes and sediment availability in the evolution of bahia san sebastian a strong control was imposed by high waves originating within the bay due to the strong westerlies the rio chico beach ridge plain evolved during different stages of beach progradation cannibalisation spit growth and saltmarsh development the cabo penas beach ridge plain evolved in opposite directions due to wave refraction caused by rocky reefs and cannibalisation also took place

unusual sub moho events near bornholm baltic sea modelling of babel seismic wide angle data and a tectonic interpretation summary from the babel near vertical record sections a sporadically strong sub moho event ne of bornholm dipping 20 30 to the ne along line was observed over a distance of about 70km 4 to 5s two way traveltime twt below the moho the same reflection from the uppermost mantle rum was observed in the piggy back wide angle records of station 10 bornholm about 2 to 3 s twt later than the moho event p p slant ray paths at offsets of 100 to 150 km a nearby station station 11 recorded similar although much weaker rum signals our preferred model inferred from ample computations of synthetic seismograms is a n to ne dipping reflector of limited thickness below a low velocity zone studies of similar slightly dipping events around great britain and elsewherealthough mostly not confirmed by wide angle studies indicate the presence of faults or shear zones in a rigid uppermost mantle listric faults in the upper crust merging with the zone of unusually high reflectivity of the lower crust which acted as a transfer zone seem to be connected with still deeper faulting the wide angle information of rum provides additional evidence for faulting processes in the uppermost mantle most probably connected with the alpine orogeny

deep structure of the scottish caledonides revealed by the moist reflection profile the moine and outer isles seismic traverse moist is a deep crustal reflection profile shot at sea off the north coast of scotland in 1981 spectacular reflections are observed from the moho and from thrust zones within the caledonian fold belt and foreland deep reflection profiling of the continental crust of the united states under the direction of the cocorp group has amply demonstrated the value of this technique when applied to suitable geological problems see for example refs 1 2 a similar group the british institutes reflection profiling syndicate birps has now been set up in the uk to organize such projects funds are provided by the natural environment research council nerc through the core group based at cambridge university however a preliminary experiment of which moist is the result was organized through the institute of geological sciences igs

in situ x ray observation of the reaction dolomite aragonite magnesite at 900 1300 k to determine the reaction boundary dolomite aragonite magnesite in situ x ray experiments on dolomite decomposition and synthesis were carried out in the temperature range 900 to 1300 k dolomite decomposition experiments were conducted with increasing pressure at constant temperature and the boundary was determined to be 5 3 5 9 gpa in the temperature range 800 1200 k and 5 9 6 3 gpa at 1300 k dolomite synthesis experiments were carried out with decreasing pressure at constant temperature or with increasing temperature at constant press load the dolomite synthesis boundary was determined to be 6 7 6 9 gpa at 1300 k 3 7 4 4 gpa at 1100 k and 2 3 gpa at 800 k except at 1300k the synthesis boundary is much lower in pressure and has a steeper d p d t slope than the decomposition boundary the difference in the reaction boundary reflects the different kinetics between decomposition and synthesis reactions and the former may be closer to the equilibrium phase boundary the experimental results show that the phase boundary between dolomite and aragonite magnesite is located at 6 4 gpa at 1300 k and has a d p d t slope of 0 001 0 001 gpa k in the temperature range 900 to 1200 k

comments on crystal melt equilibria involving potassium bearing clinopyroxene as indicator of mantle derived ultrahigh potassic liquids an analytical review by l l perchuk o g safonov v o yapaskurt and j m barton jr lithos 60 2002 89 111 k feldspar in metamorphic clinopyroxene from exsolution to potassium replacement

two feldspar geothermometry a review and revision for slowly cooled rocks recent improvements in the experimental and thermodynamic basis of two feldspar geothermometry allow one to recover temperatures of coexistence more reliably some problems however persist 1 the experimental solvi by seck 1971a and elkins and grove 1990 differ from each other 2 it is not known to what extent na k ca exchange equilibrium is approached 3 both solvi are probably metastable with regard to al si order 4 it is difficult to judge how closely high temperature natural feldspars compare to this situation 5 the thermodynamic treatment neglects phase transformations 6 the temperature dependence of the margules parameters used to model non ideal mixing behaviour may not be linear 7 it is not clear which expressions should be used to describe ideal activities with these caveats in mind we treat the problem of retrograde resetting in high grade metamorphic rocks that were slowly cooled under essentially dry conditions coexisting feldspars from such rocks commonly do not plot on a common isotherm thus temperatures derived from such pairs using any of the proposed two feldspar geothermometers will necessarily be in error we suggest that the non equilibrium compositions result from retrograde intercrystalline k na exchange this exchange continues after the plagioclase and alkali feldspar have already become essentially closed systems with respect to al si exchange which is a prerequisite for na k ca exchange we use a modified version of the fuhrman and lindsley 1988 programme to reverse the k na exchange and derive concordant temperatures

storm response and beach rotation on a gravel beach slapton sands u k abstract continuous argus video data and fortnightly measurements of subaerial morphology were obtained over a 3 year period from a steep macrotidal gravel beach on the southwest coast of the u k concurrent wave and water level data were also collected enabling the correlation of the observed morphological changes to the hydrodynamic forcing wave conditions are generally low h s 0 5 1 m but the beach is affected by frequent storm wave activity c 15 storms per year with h s 2 4 m with waves either approaching from the south swell waves or from the east wind waves an assessment of the three dimensional morphological response of the beach to the two typical storm types was carried out by analysing the impact of 27 storms that occurred from april 2007 to april 2009 southerly storms cause accretion of the supratidal zone and erosion of the intertidal zone and a significant loss in overall beach volume easterly storms on the other hand induce supratidal erosion and intertidal accretion and a significant gain in overall beach volume during the intervening calm periods a small supratidal berm is constructed and a modest gain in overall beach volume occurs wave modelling indicated that opposing longshore energy fluxes occur for the different storm types with a northerly energy flux during southerly storms and a southerly flux during easterly storms weekly shorelines derived from the argus images revealed that the northern end of the beach widened by c 30 m and the middle beach receded by c 40 m over a relatively brief period a few months the occurrence of this beach rotation event is attributed to a higher frequency of southerly storms and or a lower frequency of easterly storms over this period thus the development and stability of the beach on annual time scales depend on the relative contributions of the two storm types and their sequencing longshore sediment transport lst rates derived from the data on beach morphological change were compared with several littoral drift formulae previously applied to gravel beaches the cerc equation with a proportionality factor k between littoral drift rate i l and longshore wave energy flux p l of k 0 054 yielded the best results

experimental determination of the reaction aragonite magnesite dolomite at 5 to 9 gpa martinez et al bracketed the decomposition reaction of dolomite to aragonite magnesite between 5 0 and 5 5 gpa at 600 c using in situ xrd in a multi anvil apparatus they then extrapolated their results using the available thermodynamic data such that the breakdown reaction occurs at 1 000 c at 6 gpa if correct this extrapolation has implications for the type s of stable carbonate s in the mantle for example the reaction magnesite diopside dolomite enstatite would be metastable at p 7 gpa relative to the aragonite containing analog and thus aragonite rather than dolomite might be stable near the solidus of lherzolite this extrapolation would also imply that aragonite and magnesite would be stable in garnet clinopyroxene assemblages at pressures in the stability field of diamond to test this extrapolation experiments were conducted at higher temperatures in a multiple anvil apparatus results of initial experiments were consistent with the results of martinez et al at higher temperatures however the reaction occurs at higher pressures than predicted by martinez et al requiring significant curvature to the reaction boundary this curvature increasing dp dt with increasing t is consistent with increasing disorder in the dolomite with increasing temperature increasing the stability of dolomite relative to aragonite plus magnesite the experimental results restrict aragonite magnesite bearing assemblages to low temperature aragonite will not be present in near solidus lherzolite and can be present in orthopyroxene free eclogites and pyroxenites only at low temperature

subantarctic macrotidal flats cheniers and beaches in san sebastian bay tierra del fuego argentina abstract san sebastian bay is a large semicircular coastal embayment situated on the atlantic coast of tierra del fuego argentina it is a high energy subantarctic environment with a tidal range of 10 4 m influenced by large waves of atlantic and local origin and swept by constant strong westerly winds a 17 km long gravel spit protects the northern part of the bay giving rise to a gradient in sedimentary processes from south to north are seven distinct sedimentary environments coastal sedimentation started at least 5200 years before present bp and a rapid progradation related to a relative sea level drop has infilled about 6 kilometres of the bay with a sedimentary sequence 10 11 m thick 14 c dating of unabraded shells in the chenier ridges of the relict part of the complex allows for a precise reconstruction of the stages of the progradation that has slowed from 2 35 m year at 5000 years bp to 0 6 m year at present the possible causes of the sea level drop are discussed

high pressure phase transformations of carbonates in the system caomgosio2co2 the phase behaviour of the carbonates in the system mgocaosio2co2 have been studied in a diamond anvil press employing yag laser heating from about 40 to 260 kbar at 1000 c it is already known that at the caco3mgco3 join calcite caco3 is stable only at relatively low pressures 30 kbar that aragonite caco3 is stable between 30 and 400 kbar and that magnesite mgco3 is stable between 7 and 550 kbar at 1000 c in the present study it has been found that the intermediate mineral dolomite caco3 mgco3 decomposes into the mixture aragonite magnesite in the pressure range 60 70 kbar at 1000 c another intermediate mineral huntite caco3 3mgco3 transforms to a new phase at pressures below 40 kbar and then decomposes to the mixture dolomite magnesite at pressures greater than 60 kbar the new phase with the huntite composition possesses an orthorhombic cell with ao 9 933 0 002 bo 6 712 0 001 and co 24 06 0 02 a at ambient conditions there are only two well known silicate carbonate minerals in the caosio2co2 system these are spurrite and tilleyite both were found to decompose into their component silicates and carbonates at pressures below 40 kbar at 1000 c on the basis of the present study it can be concluded that aragonite and magnesite are the only two carbonates in the entire caomgosio2co2 system which are stable at pressures greater than about 70 kbar at 1000 c if no interaction occurs between carbonates and silicates at still higher pressures

seismic reflection coefficients from mantle fault zones summary several bright reflections from structures within the mantle can be seen on birps deep seismic reflection profiles we have calculated apparent reflection coefficients for the brightest of these events and obtain values around 0 1 it is not possible to produce such large reflections by either compositional layering or seismic anisotropy if olivine and pyroxene are the only significant minerals in the mantle these large reflections can be produced by a mafic layer or a partially hydrated layer within normal peridotite the brightest reflections seem to be best explained as major faults or shear zones within the mantle

petrogenesis and tectonic implications of the late carboniferous calc alkaline and shoshonitic magmatic rocks in the awulale mountain western tianshan abstract the widespread late carboniferous calc alkaline and shoshonitic magmatic rocks in the awulale mountain provide crucial constraints on the tectonic evolution of the western tianshan here we perform detailed petrological investigations as well as zircon u pb chronological whole rock geochemical and sr nd isotopic analyses on these magmatic rocks from two geological sections along the duku road magmatic rocks in the section i with zircon shrimp u pb ages of 306 8 ma and 306 4 ma are composed of medium k calc alkaline to shoshonitic basalt trachy andesite and trachyte while those in the section ii consist of shoshonitic trachy andesite trachyte with a u pb age of 308 1 ma and monzonite with a u pb age of 309 6 ma all these magmatic rocks are characterized by strong enrichments in large iron lithophile elements with depletions of nb ta and ti indicating the origination from subduction modified lithospheric mantle the end t values of the rock samples collected from the section i 2 80 5 45 and section ii 3 34 5 37 are generally higher than those of the devonian to early carboniferous arc type magmatic rocks in the yili central tianshan suggesting that depleted asthenosphere might also be involved in their generation based on these geochemical data and petrological observations we suggest that the early stage 308 1 309 6 ma shoshonitic monzonite trachy andesite and trachyte in the section ii were generated by mixing between mafic magmas and trachytic melts while the late stage 306 4 306 8 ma medium k calc alkaline to shoshonitic basalt trachy andesite and trachyte in the section i were produced by partial melting of depleted asthenospheric and metasomatized lithospheric mantle followed by the processes of fractional crystallization and crustal contamination taking into account the available regional geological data the subduction of south tianshan ocean was probably ceased at 310 ma and these calc alkaline and shoshonitic magmatic rocks in the awulale mountain formed in a post collisional setting subsequent to slab break off

geochemistry and age of ultrahigh pressure metamorphic rocks from the kokchetav massif northern kazakhstan isotopic and geochemical data of the zerenda series metamorphic rocks from the kokchetav massif are reported some of these rocks contain microdiamond inclusions in garnets and other indicators of ultrahigh pressure metamorphism p 40 kbar t 900 1000 c the diamond bearing rocks exhibit distinctive geochemical characteristics compared to typical crustal rocks the ree patterns range from lree depleted to slightly lree enriched chondrite normalized la yb n 0 1 5 4 with a negative eu anomaly they are depleted in incompatible elements e g sr ba u th with respect to the upper crust in contrast non diamondiferous rocks of the zerenda series exhibit normal crustal geochemistry all rocks of the zerenda series have very radiogenic lead isotopes the measured values 238u 204pb compared with those calculated for the interval between crust formation and ultrahigh pressure uhp metamorphism suggest a decrease by factors of up to 200 during the uhp metamorphism the sm nd mineral isochrons from the diamond bearing rocks and other rock types of the zerenda series give a middle cambrian 524 535 ma age of metamorphism the nd model ages show that crust formation occurred about 2 3 ga ago significant fractionation of sm and nd and loss of incompatible elements may be due to partial melting of the protoliths the ar ar age determinations of secondary biotite and muscovite from the diamond bearing rocks yield an age of 517 5 ma this cooling age requires a short time interval between uhp metamorphism and uplift to a crustal level ultrahigh pressure metamorphism might be a significant source of pb for the mantle we propose that the radiogenic pb of the oceanic array is the contamination traces of numerous uhp events beside the geological aspect we demonstrate a method of dating a high grade metamorphic terrain using nd isotopes we compare whole rock isochrons and mineral isochrons and in this way get some insight into the behaviour of the sm nd system during very high grade metamorphic events

depositional model for a chenier plain gulf of carpentaria australia the southern coast of the gulf of carpentaria northern australia consists of a broad chenier plain which is comparable in size and morphology to those reported on the coasts of surinam and south western louisiana the carpentaria chenier plain has at some locations prograded over 30 km since the middle holocene by deposition of low tide muds over subtidal muds during periods of increased sediment input by the rivers chenier ridges are formed during periods of reduced sediment flux by wave induced sorting and redistribution processes an alternation of increased and decreased sediment flux from fluvial sources has occurred several times during the upper holocene such variation in sediment supply is believed to be related to temporal fluctuations in rainfall over the drainage basin which surrounds the southern and eastern gulf

the mineralogy of the kokchetav lamproite implications for the magma evolution abstract kokchetav lamproite occurs in the east end of kokchetav massif and consists of phenocryst mainly clinopyroxene and matrix mainly feldspar the compositions of clinopyroxene magnetite and biotite phenocryst were determined using wavelength dispersive spectrometry on a jeol super probe 8900 electron microprobe for the purpose of revealing the process of magma evolution analyses revealed a core rim variation which is consistent with three stages of magmatic evolution mg rich clinopyroxene cores diopside and biotite cores phlogopite crystallized in a deep magma chamber stage i fe rich clinopyroxene rim salite and biotite rim crystallized at low pressure in a shallow magma chamber stage ii magnetite phenocryst core also crystallized in a shallow magma chamber and co exists with fe rich clinopyroxene rim and biotite rim the magnetite rims probably formed during magma eruption at the same time when groundmass crystallized stage iii the calculated temperatures for ilmenite magnetite pair range from 679 to 887 c log f o 2 values range from 11 1 to 14 9 log units these values represent the latest conditions of magma as ilmenite exsolution in magnetite probably occurred during magma eruption from the shallow chamber to surface

holocene sea level changes along the strait of magellan and beagle channel southernmost south america abstract radiocarbon dated marine sediments from five coastal sites along the strait of magellan and beagle channel in southernmost chile permit construction of a curve of relative sea level fluctuations during the holocene morphologic and stratigraphic data point to coastal submergence during the early holocene as the sea rose to a maximum level at least 3 5 m higher than present about 5000 yr ago progressive emergence then followed during the late holocene data from widely separated localities define a smooth curve the form of which is explainable in terms of isostatic and hydroisostatic deformation of the crust resulting from changing ice and water loads apparently anomalous data from one site located more than 100 km behind the outer limit of the last glaciation may reflect isostatic response to deglaciation the sea level curve resembles one derived by clark and bloom 1979 in proceedings of the 1978 international symposium on coastal evolution in the quaternary sao paulo brasil pp 41 60 sao paulo using a spherical earth model both in amplitude and in the timing of the maximum submergence

zircon response to diamond pressure metamorphism in the kokchetav massif ussr ultrahigh pressure metamorphism of the diamond bearing gneisses in the kokchetav massif ussr has been dated at 530 7 ma 2 sgr by shrimp ion microprobe analysis of metamorphic zircons zircon xenocrysts as old as 2000 ma have retained original isotopic compositions through the extreme metamorphic conditions and indicate that the protolith that was buried to diamond forming pressures included early proterozoic components highly variable reset ting of u pb isotopic systems in zircon xenocrysts at the time of metamorphism suggests that diffusive lead loss had commenced but was incomplete a disequilibrium observation consistent with relatively transient exposure of the rocks to extreme crustal depths

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

evidence for early proterozoic plate tectonics from seismic reflection profiles in the baltic shield plate tectonics provides the linking framework for all tectonic and magmatic activity seen today but it is not known when plate tectonics first developed on earth new deep seismic reflection and

caledonian and proterozoic terrane accretion in the southwest baltic sea abstract a marine seismic reflection survey was carried out in 1996 by dekorp potsdam and bgr hannover in the sw baltic sea several tectonic lineaments were crossed nearly perpendicularly for example the caledonian deformation front which is assumed to mark the northern boundary of the terrane avalonia which accreted to baltica ca 400 ma here a bivergent collision is clearly observed confirming early ideas from the babel survey the ne dipping reflections in the uppermost mantle are interpreted as signs of the subducted tornquist ocean a similar tectonic style of compression and indentation is observed in the proterozoic crust northeast of bornholm where in addition a remarkable crustal thickening and a strong increase of reflection power is observed the three dekorp lines in this area provide a certain three dimensional control and allows extension of similar observations from the babel line a southward this proterozoic terrane accretion seems to be connected to major tectonic lineaments in southern sweden either to the gothian thrust or the sveconorwegian front

lithosphere rheology a note of caution abstract it has become common practice to use laboratory determined low temperature frictional sliding data together with power law equations for steady state creep of rocks at high temperatures to construct inferred profiles of rock strength and mode of failure with depth in the lithosphere in some cases this may involve unwarranted extrapolation of rock mechanics behaviour beyond the region of its validity the form of transition from frictional behaviour to intracrystalline plastic flow in the earth is much more complex than is suggested by the above model within the regime of plastic flow substantial changes in flow strength and mode of failure whether flow becomes localized into shear zones may accompany microstructural changes developed over large strains when deformation is accompanied by metamorphic changes existing flow laws for rocks are likely to be wholly inapplicable until a clearer understanding has emerged of the full range of expression of the rheological behaviour of rocks existing models of lithosphere rheology should be treated with caution

ordering in double carbonates and implications for processes at subduction zones we have studied cation ordering in dolomite in situ as a function of pressure temperature and experimental time using the multi anvil apparatus and synchrotron radiation starting with ordered dolomite we observe the onset of disordering taking place at 950 c while complete disordering is achieved at 1 070 20 c for pressures ranging between 3 37 and 4 05 gpa pressure does not appear to have significant effect on the order disorder transition over the investigated range we find that dolomite can reach its equilibrium ordering state above 900 c within duration of laboratory experiment few hours both from disordered state and from ordered state in addition we have reversed the dolomite breakdown reaction magnesite aragonite dolomite between 4 5 and 5 5 gpa by monitoring diffraction peak intensity we also have determined that dolomite is stable up to 7 4 gpa at 1 100 c we confirm some earlier studies where a change in slope dp dt has been observed but we find a non zero slope in the low pressure range combining the values of entropy obtained from dolomite degree of ordering with enthalpy values deduced from our bracketing of magnesite aragonite dolomite equilibrium we model the location of dolomite breakdown in the p t space as a function of cation ordering by comparing previous conflicting studies we show that although kinetics of order disorder is fast disequilibrium dolomite breakdown is possible our modeling shows that subducted disordered dolomite present in carbonated sediments could be decomposed to magnesite aragonite at lower pressure 3 5 gpa than usually considered 5 gpa this 2 gpa 60 km difference is valid on a fast subduction path and is possible if disorder inherited from sedimentation is preserved on a slow subduction path however dolomite breakdown is encountered at about 250 km depth which is 100 km deeper than currently considered

garnet pyroxene equilibria in the system cao mgo al 2 o 3 sio 2 cmas prospects for simplified t independent lherzolite barometry and an eclogite barometer new experimental data on compositions of garnets in two pyroxene garnet assemblages in the system cao mgo al2o3 sio2 cmas are presented for conditions between 1 100 and 1 570 c and 30 to 50 kb garnets in these assemblages become less calcic with increasing pressure garnet orthopyroxene barometry al solubility barometry pertinent to geobarometry for garnet lherzolites has been evaluated with a set of experimental data covering the range 900 to 1 570 c and 15 to 100 kb various formulations of this barometer work well to 75 kb phase equilibria are not sufficient to positively verify the thermodynamic validity of any of such models empirical garnet orthopyroxene barometry at least in the system cmas can be formulated to obtain a pressure estimate without previous temperature estimation p kb 34 4 19 175 1n x al m1 17 702 1n x ca m2 the potential application of an analogous garnetclinopyroxene equilibrium is limited because the amount of ca tschermaks in natural clinopyroxenes is usually quite small in garnet lherzolites and many eclogites the ca mg exchange between garnet and clinopyroxene appears however sufficiently sensitive to pressure to allow calibration of a cmas barometer the reaction 3camgsi2o6 mg3al2si3o12 3mg2si2o6 ca3al2si3o12 has a v o of 3 5 cm3 the total pressure dependency of this reaction is however closer to a theoretical v o of about 5 cm3 when excess volume properties of the phases involved are taken into account we have calibrated such a barometer mean error of estimate 2 8 kb for assemblages with pyrope rich py 80 garnets and orthopyroxenes this may provide the basis for a geobarometer for eclogites from kimberlites

upper mantle reflectors modelling of seismic wavefield characteristics and tectonic implications summary deep seismic experiments on continental lithosphere generally reveal marked reflectivity from structures in the crust and a significant decrease in reflectivity from the upper mantle however reflected and refracted energy from mantle lithosphere are observed in both near normal incidence and wide angle data the origin of the reflective structures is a matter of debate hypotheses include remnant subduction zones shear zones fluids and seismic anisotropy through analytical and numerical modelling studies including full wavefield modelling we investigate seismic characteristic signatures generated from a variety of geologically plausible models we have found that both upper mantle shear zones of reduced velocity and density and remnant subduction slabs containing high density eclogites may contain sufficient seismic impedance contrasts to normal mantle peridotites to generate near normal incidence reflectivity wide angle energy originates from subduction slabs containing either high or lowvelocity eclogites whereas intermediate velocity eclogites are unlikely to produce significant wide angle phases in general energy of seismic phases originating from upper mantle zones of anomalous seismic velocities and densities is significantly increased if homogeneous zones are replaced by zones of inhomogeneous petrophysical properties resulting from constructive interference maximum wavefield anomalies are generated from sub moho dipping slabs of incomplete transformation of low velocity low density crustal material to high velocity highdensity eclogites localized shear zones generated in mantle peridotite generally do not produce significant wide angle energy only if highly inhomogeneous structures containing material of marked ca 10 per cent velocity and density reduction are present may shear zones be observed in wide angle data analyses of two specific deep seismic data sets mona lisa data from the north sea and babel data from the baltic sea show good agreement between observations and modelling results for dipping remnant subduction slabs containing small scale inhomogeneities associated with incomplete transformation our modelling results improve our possibilities of distinguishing between two often contrasting tectonic interpretations for dipping upper mantle seismic reflectors the remnant subduction and shear zone models

pressure dependence and anisotropy of p wave velocities in ultrahigh pressure metamorphic rocks from the dabie sulu orogenic belt china implications for seismic properties of subducted slabs and origin of mantle reflections the compressional wave velocities vp pressure derivatives vpv and anisotropy a of three types of eclogites and country rocks from the dabie sulu ultrahigh pressure uhp metamorphic belt china have been measured under confining pressures up to 800 mpa type 1 eclogites which are coarse grained and subjected to almost no retrograde metamorphism experienced recovery accommodated dislocation creep at peak metamorphic conditions in the diamond stability field type 2 eclogites are fine grained reworked type 1 materials that experienced recrystallizationaccommodated dislocation creep under quartz coesite boundary conditions during the early stage of exhumation type 3 eclogites are retrogressed samples that were overprinted by significant amphibolite facies metamorphism during a late stage of exhumation within the crust type 1 eclogites are richer in al2o3 and mgo but poorer in sio2 and na2o than type 2 and type 3 eclogites anisotropy of type 1 and type 2 eclogites is generally low b4 because volumetrically important garnet is elastically quasi isotropic while type 3 eclogites can exhibit high anisotropy n10 due to the presence of strongly anisotropic retrograde minerals such as amphibole plagioclase and mica the transition of the pressure dependence of velocity from the poroelastic to elastic regimes occurs at a critical pressure pc which depends mainly on the density and distribution of microcracks and in turn on the exhumation history of rocks the vp pressure relationship can be expressed by vp a lnp 2 blnp c pvpc and vp v0 dp pzpc where p is the confining

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

depositional controls on a hypertidal barrier spit system architecture and evolution pointe du banc spit north western france physical stratigraphy architecture and evolution of barrier systems in hypertidal environments tidal range above 6 m are understudied and depositional controls are poorly understood compared with wave dominated barrier systems and barrier spits in microtidal mesotidal and macrotidal settings based on vibracores ground penetrating radar radiocarbon and optically stimulated luminescence age data the formation and evolution of the hypertidal barrier system of pointe du banc north western france has been reconstructed the study shows that the barrier spit has a complex composite sedimentary architecture consisting of wave dominated and tide dominated sedimentary bodies a morpho sedimentary model is presented that demonstrates how barrier spit progradation resulting from littoral drift was the main manner of spit elongation whereas sediment convergence caused by landward migration of swash bars and seaward migration of tidal dunes caused the spit terminus to grow in height and width these results suggest that long term accretion rates varied considerably in response to changes in sediment supply variations in storminess together with the large scale topography of the coast controlled the sediment supply and thus the evolution of the barrier system during latest holocene despite architectural complexity hypertidal barrier systems preserve records of past climate changes

naturally occurring ferric iron sanidine from the leucite hills lamproite sanidine crystals precipitating from lamproitic magmas characteristically contain appreciable amounts of feh sanidine grains from the leucite hills lamproites wyoming have compositions in which up to 70 mol of the kaisi30gmolecule is replaced by kfehsi30g thus constituting a new natural feldspar component sanidine is among the last phases to crystallize in the groundmass of leucite hills lamproites and rarely exceeds 150 lmin length nearly all grains are zoned in fe ranging from 2 5 wt fez03in the cores to 19 6 wt fez03at rims adjacent to quenched glass the fe rich rims are relatively narrow on 010 crystal faces in comparison with 001 faces maximum width 10 lm probably reflecting faster 001 and slower growing 010 crystallographic directions a near perfect correlation is obtained by combining ti mg and excess si cations with feh in tetrahedral substitution for ai insufficient numbers of r2 cations exist to balance the high concentrations of mg through an r2 mg2 r r substitution suggestingthe exchangemg2 si4 ai i in 2kalsi30g analogousto that found in synthetic leucite and kalsilite selected area electron diffraction and convergent beam electron diffraction show that the fe rich sanidine rims have a c2 m structure with cell dimensions of a 8 68 t 0 15 b 13 14 t 0 23 c 7 31 t 0 15 a ex 90 0 t 0 54 j 116 0 t 0 46 y 90 0 t 0 33 and a calculated cell volume of 747 t 21 a3 these crystallographic data are in very close agreement to those obtained previously for synthetic kfehsi30g the unusually high concentrations of feh ti and mg in the sanidine rims are likely the consequence of rapid crystallization during quenching of an unusually siand k rich yet ai deficient residual magma

lithic taphonomy in desert environments contributions from fuego patagonia southern south america abstract this paper focuses on the contributions of taphonomic approaches to the study of lithic assemblages based on actualistic and archaeological case studies from fuego patagonia south america here i summarize some of the main taphonomic issues identified for the regional lithic record which are of relevance for the archaeological research in other desert environments specifically distributional patterns in lithic assemblages produced by wind are highlighted and main guidelines for pseudoartifact study are presented and discussed actualistic data show lithic artifacts up to 50 mm in size or weighting 13 g can be moved by winds blowing at 90 km h finally a methodological exercise banyai s zoom is proposed for lithic mimic recognition

seismic profiling the continental lithosphere deep seismic reflection profiling is successfully being used worldwide to study the structure of the continental crust1 7 the moist8 profile recorded by birps british institutions reflection profiling syndicate was the first to show that the structure of the upper mantle could also be imaged given a powerful source and long recording times birps has recently acquired an ultra deep seismic reflection line drum deep reflections from the upper mantle the drum line was designed specifically to investigate the reflectivity of the lower continental lithosphere and was therefore recorded to a two way time twt of 30 s giving a depth of penetration into the lithosphere of 110 km this profile has now revealed strong reflections which are unequivocally from the lower lithosphere well below the base of the crust and which are as far as we are aware the deepest and most continuous structures imaged in the upper mantle by multi channel seismic reflection profiling

gravel drift and wind effects on the macrotidal san sebastian bay tierra del fuego argentina abstract in northeastern tierra del fuego the holocene mean sea level msl fluctuation reworked much pre wisconsin glacial drift into sand gravel beaches and spits and sand mud tidal flats for the last 7000 years sea level has been falling a southwards wave induced longshore transport of sand and gravel has constructed the 17 km long el paramo spit which partly encloses the wide san sebastian bay semidiurnal tides with a range of up to 10 m enter the bay from the south causing a dominance of flood currents and wave action in the southern part of the bay ebb currents predominate in the north this segregation of flows conditioned sedimentation and is thus responsible for the south north transition of welded gravel ridges sand flats mixed flats and mud flats on the southern coast of the bay wave action constructed discrete sets of gravel ridges which diverted the san mar in river inlet northwards over the tidal flats north of this inlet where gravels are not yet available storms produce chenier systems discrete deposits of shells and sands the lengths of which progressively shortened as the inlet of the bay became narrower and the bay infilled because storms affect both the bay and the atlantic beach washover fans cut these cheniers and the gravel ridges on the narrower part of the spit the fossil gravel ridges in the northern and southern parts of san sebastian bay are not the only supratidal environments fossil and active marshes evolve conditioned by the strong and persistent wind action seasonal ponds are produced by intense deflation salicornia marsh occurs as circular structures 2 3 m diameter clustered over the supratidal flats on the intertidal mud flats wind causes deflation during neap tides and silting during spring tides north of the bay the eastward migration of straight tidal channels or rills is conditioned by winds the effects of strong and persistent winds from the pacific influence not only the tidal flats but also the gravel spit if ocean waves induce a southward drift of gravels within the bay the wind induced gravel drift is to the north during winter there are no aeolian effects over the iced tidal flats

holocene raised beaches along the northern coast of the beagle channel tierra del fuego argentina abstract raised beaches developed during holocene times along the northern beagle channel coast these deposits contain a rich marine fauna especially shelled organisms such as mollusks four holocene marine sites along the northern coast of the beagle channel have been analysed from west to east they are bahia ensenada playa larga bahia brown and cutalataca airfield they were studied in relation to relative altitude sediment type faunal composition and radiocarbon dates the area is characterized by several discontinuous terraces with elevations varying from about 1 5 to 10 m above sea level their possible origin 1 due to tectonic uplifting in comparison with raised beaches of the northern part of tierra del fuego and 2 resulting from glacio isostatic recovery taking into account the ice retreat is discussed seventeen species of mollusks eight bivalves nine gastropods were collected from the study sites all of them are living species from the beagle channel and have been interpreted as representative of holocene paleocommunities in this channel these species show no evidence of substantial climatic changes during the holocene although minor temperature fluctuations cannot be ruled out yet

observations of seismic reflectors in the lower lithosphere beneath the skagerrak the lithosphere the rigid outer shell of the earth includes both the crust and the upper mantle in the past decade the complex continental crust and underlying shallower mantle lithosphere have been extensively studied using reflection seismology but the lower lithosphere has not been successfully imaged here we report the observation of continuous and virtually horizontal reflectors in the lower continental lithosphere down to depths of 100 110 km below the skagerrak scandinavia these are apparently not structurally associated with the crust whereas previously reported mantle reflectors such as those observed by the birps group around the british isles1 2 are often located near large faults in the overlying crust like the crust the mantle lithosphere shows a seismically transparent upper and a reflective lower part thus the processes that form seismic reflectors seem to have an affinity for ductile rheological environments in the mantle as well as in the crust our observations are consistent with a model consisting of a mechanically strong upper lithosphere underlain by a thermal boundary layer which separates it from the convecting asthenosphere

holocene sea level fluctuation in the southern hemisphere abstract if rising sea levels dominate in the northern hemisphere nh falling or fluctuating sea levels predominate in the southern hemisphere sh endogenic processes tectonics isostasy or geoidal changes could explain local or regional mean sea level msl fluctuations but not an hemispherical one evidence from south america africa antarctica australia and the pacific and indian oceans suggest that the holocene transgression rose above the present msl in higher latitudes before the tropics by plotting latitude against the age of msl arrival at present coasts good correlation is observed oceanic salinity mixing has been already proposed to explain this mid holocene sea level fluctuation climate could be the only factor responsible for this hemisphere wide behavior of msl it has been suggested previously that the climate of the sh precedes that of the nh by 3000 years the climatic optimum or maximum warmth occurred predominantly about 6000 bp in the nh but about 10 9000 bp in the sh short term climatic effects on the sea level monsoons southern oscillation el nino phenomena should have significant occurrences during the past in the windiest oceanic hemisphere this latitudinal trend in former msl should be considered when using shorelines as reference points for measuring vertical crustal movements

coesite inclusions in dolomite from eclogite in the southern dabie mountains china the significance of carbonate minerals in uhpm rocks coesite inclusions have been discovered in dolomite from carbonate bearing eclogite in the dabie uhp terrane the eclogite boudins are enclosed in calc silicate rocks that contain quartz aggregatesafter coesite in the matrix the carbonate bearing eclogite is composed of garnet coesite or quartz dolomite magnesite omphacite rutile tminor phengite apatite and zircon and was formed at 760 dc 28 kbar and 0 01 100 km

residence time of diffuse waves in the crust as a physical interpretation of coda q application to seismograms recorded in mexico summary we consider a simple model for elastic wave propagation in the earth s litho sphere consisting of a heterogeneous and scattering crust overlying a homogeneous mantle that is we neglect backscattering from the upper mantle this rough condition is not strictly valid everywhere but this model allows us to investigate the effects of variations of diffracting properties between crust and mantle on the coda decay the free parameters describing the wave propagation are the mean free path of the waves and the intrinsic absorption in the crust in the framework of the radiative transfer theory we treat accurately jumps in s wave speed and the mean free path at the moho without intrinsic absorption this configuration yields a synthetic coda decay 1 texp 2 ft qc a form similar to that proposed by aki chouet 1975 to parametrize the observations the exponential decay in our purely elastic model is due to the partial leakage of diffuse energy into the mantle in order to test the applicability of our model we have determined the coda q parameter qc in the 1 15 hz frequency band from data recorded at four stations in mexico in the low frequency regime around 1 hz we suggest that the energy leakage significantly affects coda q whilst at higher frequencies around 10 hz the anelastic attenuation dominates a weak intrinsic absorption expressed by a frequency independent parameter qi of about 1000 accounts satisfactorily for the observed qc values in the whole frequency range our very simple model has only two free parameters and offers an attractive alternative physical interpretation of coda q in mexico this model is sufficient to interpret the coda observations according to our model in regions where the mean free path is much larger than the crustal thickness weakly heterogeneous crust the leakage effect should be small and the observed qc will mainly be due to the intrinsic absorption on the other hand when the mean free path is of the order of the crustal thickness strongly heterogeneous crust we predict a strong sensitivity of the decay rate of the coda to the crustal thickness this dependence may be important for the interpretation of the regional variations of coda q we propose introducing a new parameter d the residence time of diffuse energy in the crust which is physically more meaningful than a quality factor to quantify the leakage effect

caledonian deformation upon southwest baltica and its tectonic implications alternatives and consequences the continuation of the basement of the southwestern baltic shield toward the sw is of major interest for the caledonian evolution in the southwestern baltic sea and northern germany a reinterpretation of various marine seismic data suggests a reconsideration of the caledonian collision pattern the sorgenfrei tornquist zone forming the northwestern extension of the tornquist zone is regarded as the northeasterly boundary fault and the elbe lineament is regarded as the southwestern limit of an area which suffered from the docking of east avalonia to baltica it shows many northwestsoutheast striking structures anomalies and fault patterns from our studies two alternative models emerge one which considers the caledonian deformation front as the northeastern limit of east avalonia and a zone of major transpression collision and subduction of the tornquist sea another model considers the elbe lineament in schleswig holstein nw germany as a major dextral strike slip fault which is interpreted as the northeasterly limit of east avalonia and the southwest boundary of the baltic shield along the elbe lineament the tornquist sea plus rotating avalonia were displaced to the northwest a large part of the area to be studied might have developed into a passive margin toward the upper ordovician a decision which of the two models is to be prefered has to be the major goal of future geophysical experiments

flat mantle reflectors in eastern china possible evidence of lithospheric thinning abstract recent 24 s deep seismic reflection records revealed five flat reflectors in the lithospheric mantle in eastern china with increasing depth they are named m1 to m5 and can be seen on both field single shot and stacked records reflector m1 corresponds to the moho discontinuity whereas m5 may be the reflection from the bottom of the current lithosphere which is about 78 km deep according to geothermal measurements the other three reflectors seem peculiar and might result from interactions between the lithosphere and deeper mantle based on lithological and geochemical data it is suggested that the lithosphere has been thinned from about 150 km to about 60 km in the late mesozoic and then has been thickened to about 78 km during the cenozoic the thinning process produced a granulite layer in the old lower crust caused by magmatic underplating whereas an eclogite layer formed beneath owing to the subduction of the paleo tethys and yangtze craton during the permian and early mesozoic reflector m2 at about 12 s two way traveltime twt might result from the paleozoic moho which represents the boundary between the previous granulite and eclogite facies reflector m3 at about 14 s might correspond to the bottom of the eclogite layer beneath which the old lithospheric mantle remained the old and the newly developed mantle may have different compositions resulting in reflector m4 the multi layered mantle reflectors demonstrate a mantle structure that possibly correlates with the lithospheric thinning process that occurred in eastern china during the late mesozoic the discovery of multi layered mantle reflectors in the studied areas indicates a high heterogeneity of the upper mantle reflection seismology with improved technology together with velocity and resistivity imaging and rock physics measurements can provide more details of the heterogeneity and related dynamic processes that occurred in the lithospheric mantle

saltation on gravel beaches tierra del fuego argentina abstract saltation is a common phenomenon on gravel beaches sediment traps across two beaches of the el paramo spit tierra del fuego argentina yielded different results on mean grain size sorting saltating load shape and height above the bed mean clast size increases with height above the bed to an altitude where the saltating size diminishes the sorting of the saltating populations also increases until an altitude where it begins to diminish spheres are preferentially set into saltation although the bed is dominated by platy bladed and elongated gravels much of the behavior of the saltation population is related to local wave dynamics beach steepness and stage of the tide the processes of gravel segregation size and shape on beaches obey to particular phenomena not considered in present day sediment transport equations but of much importance in relation to coastal defense improvements as dynamic revetments

energetics of calcium rich dolomite abstract the enthalpy of formation of sedimentary ca rich dolomite has been determined by oxide melt calorimetry the results show that ca rich dolomite is energetically different from well ordered stoichiometric dolomite the enthalpy of formation from calcite and magnesite becomes strongly more endothermic with increasing excess ca content this supports the idea that the substitution of ca in the mg layer of dolomite is energetically unfavorable ca rich dolomite is unstable relative to well ordered stoichiometric dolomite and calcite the enthalpy behavior for excess ca substitution in dolomite is different from that of mg substitution in calcite the enthalpy change is much larger in magnitude in dolomite and is more strongly dependent on composition differences in cation order as well as the presence of a modulated structure and low symmetry domains in ca rich dolomite cannot be discerned from the enthalpy data the findings confirm that the growth and occurrence of ca rich dolomite in sedimentary environments must be attributed to kinetic factors rather than to equilibrium

clinopyroxene phenocrysts with green salite cores in trachybasalts implications for two magma chambers under the kokchetav uhp massif north kazakhstan abstract clinopyroxene phenocrysts in the kokchetav trachybasalts are variable in composition and textures two distinctive cores are recognized diopside cores and green salite cores the diopside cores with mg of 80 90 are mantled by colorless salite rims with mg of 70 80 the green salite cores have especially low mg

experimental investigation on dolomite dissociation into aragonite magnesite up to 8 5 gpa we carried out high pressure and high temperature experiments on the composition camg co3 2 to determine the equilibrium boundary of dolomite aragonite magnesite up to 8 5 gpa and 1200 c using a 6 8 type multianvil high pressure apparatus employing a quenching technique dolomite dissociates into aragonite and magnesite under high p t conditions and the phase boundary of dissociation is described by a linear equation p gpa 1 75 0 0061t c at p 6 3 gpa and t 800 c the equilibrium boundary was established by reverse and backward experiments to grow dolomite from mixtures of caco3 and mgco3 with or without dolomite respectively this study suggests that the equilibrium line of the dolomite aragonite magnesite reaction could be very useful in addition to phase transformation of quartz coesite and graphite diamond to constrain p t conditions for the metamorphism of dolomite bearing ultrahigh pressure rocks

taphonomic and archaeological perspectives from northern tierra del fuego argentina this paper focuses on late holocene coastal occupations of hunter gatherers that inhabited the northern steppes of grande island of tierra del fuego available archaeological data produced by our previous research in the argentine portion of the island located north of san sebastian cape is discussed from a regional taphonomy perspective our approach is based on the characterization of the main taphonomic modes recognized in the region preservational and other patterns for bones and lithics are presented and discussed based on the comparative study of isotaphonomic assemblages general trends in human coastal occupations are discussed

quaternary of tierra del fuego southernmost south america an updated review abstract the quaternary of tierra del fuego is represented by glacial glaciofluvial glaciolacustrine marine and aeolian deposits six drift units have been described the oldest dating from the late pliocene these are starting from the oldest the rio grande sierra de los frailes cabo virgenes punta delgada primera angostura and segunda angostura drifts neoglacial and little ice age events are represented in cirques and higher mountain valleys marine deposits and raised beaches were formed during middle pleistocene late pleistocene and holocene interglacial stages after the definitive ice retreat 10 ka ago vegetation changed from tundra and cold steppe to subantarctic forest environments marine deposits reflect also colder conditions than the present ones aeolian processes prevailed in northern tierra del fuego where semiarid conditions and the frequent westerlies favoured the retransportation of finer materials coming from pre existing deposits before the opening of the magellan straits earliest human colonization occurred in northern tierra del fuego ca 11 ka bp in tundra like environmental conditions pedestrian hunters of camelids and foxes co existed with pleistocene fauna that became extinct during late glacial earliest holocene times the steppe area inland and atlantic coast was successively occupied since then until recent times on the other hand the beagle channel coasts were occupied since 6 ka bp by hunter gatherer groups adapted to maritime littoral conditions finally the easternmost area of the island was inhabited at least since 1 5 ka bp the human settlements in these latter areas occurred under environmental conditions similar to the present ones when the fuegian forest was definitively established

dolomite cation order in the geological record abstract dolomite is a carbonate mineral frequently found in sedimentary rocks from proterozoic to holocene in the iberian peninsula dolomites appear in a wide number of geological formations and they can be considered as representative of dolomites crystallised in most post sedimentary environments on earth in this paper we present a first systematic study of the cation order of dolomites formed from neoproterozoic to late holocene we found that the lowest values of cation order quantified by measuring i01 5 i11 0 intensity ratios on diffractograms mainly correspond to dolomites formed in about the last 30 myr in contrast older dolomites usually reach maximum i01 5 i11 0 intensity ratios furthermore higher values of cation order seem to be related to higher values of the full width half maximum of 10 4 diffraction peaks fwhm10 4 assuming that a decrease in fwhm10 4 i e an increase in the crystallite size in sedimentary environments indicates mineral ripening our results show that mg ca ordering in dolomites might take place mainly by a dissolution re crystallisation ageing process operating over large geological periods

nature of crustal reflectivity along the dekorp profiles in germany in comparison with reflection patterns from different tectonic units worldwide a review reflectivity of the continental crust displays many different patterns the dekorp lines are used as a basis for comparing and reviewing reflectivity in different tectonic units the brittle upper crust generally exhibits only two types of reflectivity it is either rather transparent preferably in some extensional provinces or and it shows traces of thrust and shear zones of former or present ruptures as these zones have a low impedance interior with few exceptions their first reflection onsets have a negative polarity and evince strong but short signals which sometimes can be correlated over several kilometers the generally ductile lower crust displays a completely different reflectivity in warm extensional and thin crusts the lower part is full of reflecting lamellae it is suggested that this type of reflectivity has a thermo rheological origin the creation of lamellae must take place in a ductile material with contrasting impedance under extensional stresses it can be associated with mineral alignment and corresponding seismic anisotropy destruction of lamellae may take place by a cooling process transforming parts of the lower crust into a brittle regime small stresses might deform or break the lamellae and leave a certain dispersed reflectivity like that in some old and cold shields there are no observations of reflecting lamellae in the upper crust or in the upper mantle in all areas the moho is the last reflecting band reflection moho which most often is identical with the classical refraction moho there are isolated mostly dipping reflections in the uppermost mantle in zones where the last tectonic event a delamination or subduction was not succeeded by a heating process the uppermost mantle is brittle again in most areas and may keep the memory of a cold collision over billions of years

thermal stability and spectroscopic studies of zemkorite a carbonate from the venkatampalle kimberlite of southern india while characterizing the mineralogy of the kimberlite at venkatampalle andhra pradesh india lat 14 56 00 n long 77 22 15 e we found the second occurrence of zemkorite na k 2 ca co 3 2 which was first reported in 1989 in the udachnaya kimberlite in siberia we also report the first fourier transform infrared spectroscopic ftir scanning electron microscopic thermo gravimetric and high temperature heat capacity measurements on this rare carbonate powder x ray diffraction xrd patterns show 24 well resolved diffraction lines all of which can be indexed with a hexagonal cell with a 10 038 5 a and c 12 726 5 a the vibrational spectrum of zemkorite at room temperature exhibits 13 distinct absorption bands in the frequency range 2000 to 400 cm 1 the ir bands of zemkorite indicate a structural similarity with shortite but are quite distinct from other alkali carbonates such as nyerereite butschiite and fairchildite the heat capacity of zemkorite has been measured up to 700 k by differential scanning calorimetric techniques the temperature dependence of the heat capacity of zemkorite was fitted with the polynomial c p 140 2 8 584 10 2 t 2 458 10 6 t 2 the upper thermal stability of zemkorite is 700 k which is similar to shortite zemkorite may have formed during the late stages of kimberlite genesis possibly as a result of metasomatism or by the breakdown of metasomatic natrocarbonatitic minerals or glass that segregated on decompression melting in the upper mantle

carbon recycled into deep earth evidence from dolomite dissociation in subduction zone rocks comment and reply comment zhu and ogasawara 2002 1 interpret the textures and mineralogy of dolomitic marbles from the kokchetav massif in terms of pressure induced dissociation of dolomite dol to aragonite ara magnesite mag on the basis of this assumption they postulate a minimum metamorphic pressure of 7 85

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

timing and magnitude of holocene sea level changes along the middle and south patagonian atlantic coast derived from beach ridge systems littoral terraces and valley mouth terraces abstract geomorphologic and chronostratigraphic investigations in various coastal localities along the middle and south patagonian atlantic coast from bahia vera 44 s in the north to san julian 49 s in the south confirm a rich sequence of holocene beach ridge systems and littoral and valley mouth terraces beach ridges are present up to 10 m above current highest tide level htw and date to the early mid holocene transgression maximum beach ridge deposits represent high energy wave dominated coastal environments whereas valley mouth terraces and littoral terraces elevations of 5 5 6 5 m above htw developed in wave protected coastal environments the surface elevation of these littoral forms suggest that the middle and south patagonian atlantic coast is likely undergoing a slow glacio isostatic uplift on the order of 0 3 0 4 mm a since the mid holocene the early holocene sea level rise reached the modern coastline by 8100 14 c years ago c 8600 cal bp at the latest sea level at that time was most likely near its present position the holocene transgression maximum lasted from 6900 to at least 6200 14 c bp c 7400 to 6600 cal bp raising relative sea level to about 2 m to a maximum of 3 m above the present level after which sea level declined to the present level two significant sea level falls of at most 1 m occurred a between 6200 and 6000 14 c bp c 6600 to 6400 cal bp and b between 2600 and 2400 14 c bp c 2300 to 2050 cal bp we assume that both significant sea level falls were predominantly driven by eustatic changes of ocean volume whereas both thermo steric changes and changes of tides may also have contributed to these relatively strong sea level drops gravitational changes driven by greenland ice growth sensu mitrovica et al 2001 may also have amplified any eustatic portion of sea level fall the trend of a general sea level decline since the mid holocene transgression maximum seems to be predominantly glacio isostatically driven

terrane accumulation and collapse in central europe seismic and rheological constraints abstract an attempt is made to compare the tectonic units and their evolution in central europe with the deep seismic velocity structure and patterns of reflectivity caledonian and variscan terrane accretion and orogenic collapse dominate the tectonic development in central and western europe and have left their marks in a distinct velocity structure and crustal thickness as well as in the various reflectivity patterns whereas the memory of old collisional structures is still preserved in the rigid upper crust collapse processes have formed and modified the lower crust they have generally created rejuvenated thin crusts with shallow mohos in the variscan internides the center of collision and post orogenic heat pulses the lower crust developed strong and thick seismic lamellae the cooler externides show a thrust and shear pattern in the whole crust and the north german basin experienced large mafic intrusions in the lower crust and developed a high velocity structure with only very thin lamellae on top of the moho the various kinds of reflectivity patterns in the lithosphere can be explained by a thermo rheological model from terrane collision with crustal thickening to collapse in a hot post orogenic setting

graphite diamond relations in mantle rocks evidence from an eclogitic xenolith from the udachnaya kimberlite siberian craton relations of graphite and diamond have been studied in a garnet kyanite clinopyroxene sulfide coesite quartz diamond graphite eclogite xenolith from the udachnaya east kimberlite pipe in the yakutian diamond province euhedral crystals of diamond and graphite occur in the intra and intergranular space the equilibrium conditions of diamond formation reconstructed by geothermobarometry for the grt cpx ky coe mineral assemblage are 1020 40 c and 4 7 gpa raman imaging of graphite enclosed in diamond shows high ordering and a 9 cm 1 shift of the 1580 cm 1 band this raman shift of graphite as well as a 5 cm 1 shift of the 1332 cm 1 band of diamond indicate large residual stress in graphite and in diamond around the inclusion respectively according to ftir spectroscopy nitrogen in diamond is highly aggregated and exists mainly as the a centers while no other phases occur near graphite inclusions therefore diamond in the analyzed eclogite sample must be quite old it likely had crystallized long 1 byr before it became entrained with kimberlite melt new data show that graphite can stay in the upper mantle for billions of years without converting to diamond crystallization of various carbon polymorphs both in laboratory and natural systems remains poorly constrained graphite present in mantle and uhp rocks may be a metastable phase crystallized in the diamond stability field this fact should be taken into consideration when deducing petrological constrains and distinguishing diamond and graphite subfacies in upper mantle

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