graphitization of carbonaceous matter during metamorphism with references to carbonate and pelitic rocks of contact and regional metamorphisms japan this study is an attempt to correlate the graphitization process of carbonaceous matter during metamorphism with metamorphic grade graphitization can be parameterized using crystal structure and chemical and isotopic compositions the extent of graphitization could be characterized mainly by temperature duration of metamorphism and rock composition we compared the graphitization trends for two metamorphic terrains a contact aureole of the kasuga area and a regional metamorphic terrain of high temperature low pressure type of the ryoke metamorphic terrain in northern kiso area central japan and for two different lithologies carbonate and pelite using x ray diffractogram dta tg analysis and chemical and stable isotope analyses during contact metamorphism graphitization and carbon isotopic exchange reactions proceeded simultaneously in pelitic and carbonate rocks the decreases in basal spacing d 002 of the carbonaceous matter in carbonate rocks is greatly accelerated at temperatures higher than about 400 c furthermore carbon isotopic ratios of graphite in carbonate rocks also change to 13c enriched values implying exchange with carbonates the beginning of this enrichment of 13c in the carbonaceous matter coincides with an abrupt increase of the graphitization processes carbon isotopic shifting up to 5 in pelites could be observed as metamorphic temperature increased probably by about 400 c carbonaceous matter in pelitic rocks is sometimes a mixture of poorly crystallized organic matter and well crystallized graphite detritus dta tg analysis is an effective tool for the distinction of detrital graphitic material two sources for the original carbon isotopic composition of carbonaceous matter in pelites in the kasuga contact aureole can be distinguished about 28 and 24 regardless of the presence of detrital graphite and were mainly controlled by depositional environment of the sediments graphitization in limestones and pelitic rocks in regional metamorphism proceeds further than in a contact aureole in the low temperature range the differences in extent of graphitization between the two metamorphic regions is large however at temperatures higher than 600 c the extent of graphitization in both regions is indistinguishable the degree of graphitization is different in limestones and pelitic rocks from the ryoke metamorphic terrain we demonstrate that the graphitization involves a progressive re construction process of the crystal structure the sequence of the first appearance of crystal inter planar spacing correlates with the metamorphic grade and indicates the crystal growth of three dimensional structured graphite

tectonic stacking of hp lt metamorphic rocks in accretionary wedges and the role of shallowing slab mantle decoupling hp lt chloritoid bearing micaschists crop out widely in the central part of northern turkey and represent deep seated subduction accretionary complexes three peak metamorphic assemblages are identified in the area studied 1 garnet chloritoid glaucophane with pseudomorphs after lawsonite 2 chloritoid with pseudomorphs after glaucophane and 3 chloritoid with pseudomorphs after jadeite in addition to phengite paragonite quartz chlorite rutile and apatite the latter is interpreted as transformation of a chloritoid glaucophane assemblage to chloritoid jadeite with increasing pressure pt modeling indicates 17 and 22 25 kbars for the two peak parageneses the diversity of peak metamorphic assemblages and the pt estimates suggest that basal accretion occurred at different depths within the wedge the depth of the basal accretion is possibly controlled by the slab mantle decoupling depth stretching and thinning of the lithospheric forearc induced by the slab roll back possibly caused shallowing of the slab mantle decoupling depth which limited depth of the basal accretion from 70 80 km to 55 km within the subduction channel a slab mantle coupling depth controlled basal accretion may also explain the scarcity of eclogite and high grade blueschist facies metamorphic rocks in active intra oceanic subduction zones because the overriding plate is young and hot in intra oceanic subductions the slab and mantle are coupled at a relatively shallow depth before eclogitization of the oceanic crust this prevents accretion and exhumation of eclogite along the subduction channel

deformation fabrics and strain localization mechanisms in graphitic carbon bearing rocks from the ailaoshan red river strike slip fault zone abstract graphitic carbon bearing rocks generally occur in low to high grade metamorphic units in many brittle faults graphitic carbon is often associated with gouge or low grade metamorphic rocks whereas in ductile faults graphitic carbon commonly occurs in marble schist or gneiss carbonaceous material gradually transforms from an amorphous into an ordered crystalline structure by increasing thermal metamorphism the degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock in this contribution based on detailed field observations the variably deformed and metamorphosed graphitic gneisses to phyllites located within the footwall and hangingwall unit of the cenozoic ailaoshan red river strike slip shear zone are studied according to lithological features and temperatures determined by raman spectra of carbonaceous material these graphitic rocks and deformation fabrics are divided into three types type i is represented by medium grade metamorphism and strongly deformed rocks with an average temperature of 509 c and a maximum temperature of 604 c type ii is affected by low grade metamorphism and deformed rocks with an average temperature of 420 c type iii is affected by lower grade metamorphism and occurs in weakly deformed undeformed rocks with an average temperature of 350 c slip localized micro shear zones and laterally continuous or discontinuous slip planes constituted by graphitic carbon aggregates are developed in types i and ii the electron back scattered diffraction ebsd lattice preferred orientation lpo patterns of graphitic carbon grains were firstly observed in comparison with lpo patterns of quartz and switch from basal rhomb to prism slip systems which indicate increasing deformation temperatures comparison of quartz and graphite lpos indicates that graphite lpos show higher temperature conditions according to the graphitic slip planes micro shear zones with grain size reduction and mylonitic foliation constituted by graphitic carbon minerals we also propose that the development of fine grained amorphous carbon plays an important role in rheological weakening of the whole rock during progressive ductile shearing

thermal and structural evolution of the external western alps insights from u th sm he thermochronology and rscm thermometry in the aiguilles rouges mont blanc massifs in the western alps the external crystalline massifs ecm are key places to investigate the kinematics and thermal structure of a collisional crustal wedge as their paleo brittle ductile transition is now exhumed at the surface new u th sm he data on zircon and new raman spectroscopy on carbonaceous material rscm data from the aiguilles rouges and the mont blanc massifs coupled to hefty thermal modeling constrain the thermal evolution and exhumation of the massifs in the cover of the aiguilles rouges massif we found that the maximal temperature was about 320 c 25 c close to the maximal temperature reached in the cover of the mont blanc massif 350 c 25 c we show that after a fast heating period the thermal peak lasted 10 15 myrs in the mont blanc massif and probably 5 10 myrs in the aiguilles rouges massif this thermal peak is synchronous with crustal shortening documented in the basement u th sm he data and thermal modeling point toward a coeval cooling of both massifs like other ecm at around 18 ma 1 ma this cooling was related to an exhumation due to the initiation of frontal crustal ramps below the ecm quite synchronously along the western alps arc

late wisconsin landform distribution and glacier bed conditions in wisconsin abstract the late wisconsin laurentide ice sheet advanced across permafrost and reached its maximum extent in wisconsin between about 18 000 and 15 000 years ago deep permafrost persisted in southern wisconsin until about 14 000 years ago and in northern wisconsin until about 13 000 years ago we suggest that during maximum glaciation a zone about 5 km wide in the south and 20 km wide in the north along the margin of the late wisconsin glacier was frozen to its bed meltwater from farther behind the margin where the bed was at least locally thawed cut a series of closely spaced tunnel channels through the frozen bed zone these channels most likely formed episodically and they were the source for much of the meltwater stream sediment deposited in broad outwash plains beyond the ice margin frozen bed conditions near the margin also likely contributed to increased upward shearing of sediment and the accumulation of thicl supraglacial sediment in northern areas up ice from the frozen bed zone the glacier bed was at least locally thawed in a zone about 75 km wide extensive drumlin fields formed in the area of the bed that was thawed by about 13 000 years ago permafrost melted in northern wisconsin and thawed bed conditions probably extended to the ice margin throughout wisconsin and adjacent areas after about 13 000 years ago in northern wisconsin the glacier was sliding on its bed and forming drumlins out to the ice margin and thick supraglacial sediment no longer accumulated

the continental margin of the mesozoic tethys in the western alps abstract most of the structural units of the western alps were derived from the european continental margin of the ligurian ocean a segment of the mesozoic tethys ocean their mesozoic palaeotectonic and stratigraphic evolution bears witness of the following main stages 1 deposition of the triassic platform carbonates essentially prerift but nevertheless bearing the imprint of some extensional movements 2 the liassic middle jurassic rifting corresponds to the creation of a horst and graben system with especially tilted blocks and hence a shoal and basin palaeogeography but without a preliminary doming event 3 the late jurassic early cretaceous opening and spreading of the ligurian ocean began with a general collapse of the continental margin thermal subsidence latest middle jurassic and earliest late jurassic in this paper emphasis is given to the refting derived structures more especially to the major tilted crustal blocks a few tens of kilometres wide which can be either reconstructed or directly observed the rifting stage lasted roughly 40 m y with the alternation of extensional tectonic phases and of relatively quiet periods during the extensional phases movements along fault planes and related episodes of tilting were followed by sudden and rapid episodes of subsidence the latter may be interpreted as resulting from the isostatic and thermal readjustment that follows a phase of stretching of the crust and of the lithosphere the tectonic evolution of the margin continued but decreased during the late jurassic early cretaceous oceanspreading stage tectonic activity resumed in the late cretaceous this probably resulting from the beginning of contraction of both the ocean and the continental margin leading progressively to the continental collision in the tertiary

reviewing the puzzling intracontinental termination of the aracuai west congo orogenic belt and its implications for orogenic development abstract palinspastic reconstructions suggest that the late proterozoic cambrian brasiliano pan african orogenic belt in southeast brazil and west congo terminated northwards into an embayment within the sao francisco congo cratonic unit the orogenic shortening that created the aracuai west congo orogen in this embayment has been explained by tightening of the horseshoe shaped sao francisco congo craton in a fashion referred to as nutcracker tectonics we show that this model is incompatible with the general orogenic evolution proposed in recent literature which involves 1 50 m y of subduction of oceanic crust and associated arc formation followed by 2 collisional orogeny and crustal thickening quantitative considerations show that the original nutcracker model is too rigid to explain even the second crustal thickening part let alone any long pre collisional history to soften the model we suggest that the so called sao francisco congo bridge was broken by a 150 km wide orogenic corridor along the current african atlantic margin this corridor adds sufficient mobility to the system to explain the orogenic thickening of the crust to 60 65 km however even with this additional softening the confined nature of this orogen is incompatible with prolonged arc development we therefore suggest that oceanic crust was nonexistent or very limited in the macaubas basin and reject the widely published model involving 50 m y of subduction of oceanic crust and related arc development instead we find strong support for a hot intracontinental orogen model in the currently available p t geochronologic petrographic and structural data in this model extensive melting and flow of the middle crust is likely to have caused spreading of the upper crust in an orogenic setting that was created by collisions along the n w and s margins of the sao francisco craton from 630 ma

raman geothermometry of carbonaceous material in the basal ediacaran doushantuo cap dolostone the thermal history of extremely negative δ13c signatures in the aftermath of the terminal cryogenian snowball earth glaciation abstract extremely negative 13 c values as low as 48 of blocky calcite cements filling cavities sheet cracks and fractures in the basal ediacaran cap dolostone of the doushantuo formation in south china have been considered as evidence for methane release possibly associated with gas hydrate destabilization in the aftermath of the terminal cryogenian snowball earth glaciation alternatively these extremely negative 13 c values may have resulted from oxidation of thermogenic methane derived from localized hydrothermal activity long after the deposition of the doushantuo cap dolostone the latter interpretation was based on carbonate clumped isotope thermometry suggesting that the precipitation of extremely 13 c depleted calcite occurred at temperatures up to 476 c mean 378 c n 4 whereas carbonate fabrics with moderately negative 13 c values generally 10 were formed at much lower temperatures mean 112 c n 4 to assess these competing hypotheses we systematically investigated the petrography carbonate carbon and oxygen isotopes and carbonaceous material cm raman spectroscopy of the doushantuo cap carbonate raman geothermometry suggests that cm associated with different microfabrics and 13 c signatures including sedimentary fabrics with moderately negative 13 c values e g peloids stromatolite laminae microbial mat fragments diagenetic fabrics with moderately negative 13 c values e g some void filling or crack filling cements and diagenetic fabrics with extremely negative 13 c values e g void filling or crack filling blocky and bladed calcites experienced temperatures generally 13 c signatures and paleotemperatures whereas the origins of these extremely negative 13 c values remain unresolved the raman geothermometric data challenge the previous interpretation that they were derived from thermogenic methane related to localized hydrothermal activity at temperatures up to almost 500 c that only affected the thermal history of the calcite with extremely negative 13 c values instead the new data suggest that the analyzed microfabrics experienced the same peak temperatures

carbon spherules in ni cu pge sulphide deposits in the sudbury impact structure canada abstract the formation of sudbury s economically important magmatic ni cu pge sulphide deposits is attributed to superheating of crustal rocks following meteorite impact at 1 85 ga crustal contamination of magmatic sulphide deposits is thought to be important in the mineralization process and this paper documents the first occurrence of sedimentary carbon in the sudbury ni cu pge sulphides near the base of the sudbury igneous complex sic spherules of graphitic and more disordered carbon inclusions were found in chalcopyrite crystals suggesting that carbon has behaved as a chalcophilic element in the impact melt samples from the impact structure have been subjected to carbon isotopic analysis and raman microspectroscopy in order to investigate the relationship between carbonaceous strata of the huronian basement the crater fill impact breccias and the mineral deposits associated with the sudbury impact carbonaceous material occurs in the impact breccias of the onaping formation and this study presents stratigraphically constrained carbon isotopic analysis of the impact breccias sulphides from the hydrothermal zn pb cu vermilion errington deposits 1 5 km above the sic were found to contain both carbon spherules and larger irregular carbonaceous flakes suggesting a genetic link between the ni cu pge deposits and the hydrothermal zn pb cu mineralization a shared source of carbon for the vermilion errington mineralization and the cross cutting anthraxolite veins 100m above the deposits in post impact carbonaceous shales of the onwatin formation is indicated by the similarity in their raman spectra this is considered to be carbon remobilized by metamorphic hydrothermal fluids preferentially scavenging disordered carbon from within the onaping formation breccias the occurrence of carbon in the sudbury ni cu pge massive sulphide deposits indicates that carbon from the target rocks played a role in the mineralization process hitherto unrecognized

textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone alpine fault new zealand graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization we examine processes of graphitic carbon emplacement and deformation in the active alpine fault zone new zealand by analysing samples obtained from deep fault drilling project dfdp boreholes optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain raman spectroscopy allowed interpretation of the degree of graphite crystallinity which reflects both thermal and mechanical processes in the amphibolite facies alpine schist highly crystalline graphite indicating peak metamorphic temperatures up to 640 c occurs mainly on grain boundaries within quartzo feldspathic domains the subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions 500 600 c resulting in clustered in protomylonites and foliation aligned graphite in mylonites in cataclasites derived from the mylonitized schists graphite is most abundant 50 as opposed to 10 elsewhere and has two different habits inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon tectonic hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences the increasing abundance of graphite towards the fault zone core may be a significant source of strain localization allowing fault weakening

extending the applicability of the raman carbonaceous material geothermometer using data from contact metamorphic rocks the degree of graphitization of carbonaceous material cm has been widely used as an indicator of metamorphic grade previous work has demonstrated that peak metamorphic temperature t o f regional metamorphic rocks can be estimated by an area ratio r2 of peaks recognized in raman spectra of cm the applicability of this method to low pressure 50 that adequately reflects the range of sample heterogeneity using this procedure with 532 nm laser and adapting our new calibration the errors of the raman cm geothermometer for contact metamorphic rocks decrease to 30 c

the role of serpentinization in exhumation of high to ultra high pressure metamorphic rocks abstract analysis of physical processes involved in serpentinization show that it can lead to a significant reduction in density huge volume increase and generate giant pressure within serpentinizing rocks combined together these factors make the serpentinization process a very important one for the start and support of exhumation of high and ultra high pressure rocks serpentinization can generate a significant buoyancy force as well as forces capable of horizontal displacing of an exhuming block exhumation of high grade rocks to the surface requires the presence of an external force and it cannot be accomplished by buoyancy alone intimate relationships between exhumation and serpentinization serpentinized peridotites and hp lt uhp lt rocks and co existence of eclogites and blueschists with thrusts and nappes containing peridotites serpentinites or ophiolites point to the significant role of serpentinization in exhumation formal analysis of the viscous properties of the lithosphere illustrates that exhumation within the continental crust is extremely slow that its velocity increases with an increase of slab size and that the velocity value during the subduction process should be greater than during exhumation generated by serpentinization process pressure can play an important role in both forcing an exhuming block up and or detaching the upper part of the subducting slab from its bottom part an absence of serpentinites of the archean age proves that serpentinization cannot play a significant role in exhumation of high grade rocks in the archean

continuous metamorphic gradient documented by graphitization and k ar age southeast otago new zealand the chrystalls beach brighton coastal section southwest of dunedin new zealand exposes otago schist including the weakly metamorphosed triassic accretionary melange of the chrystalls beach complex and higher grade rocks of a largely felsic arc derived provenance melange zones contain pelagic sediments some of which are manganiferous and metabasites the grade of metamorphism increases progressively from southwest to northeast four mineral zones are recognized largely on the basis of mineral assemblages in psammitic and semipelitic rocks pumpellyite chlorite pumpellyite actinolite epidote actinolite and biotite d 002 data for carbonaceous material b 0 values for phengite and metamorphic phengite k ar ages are reported for 32 pelitic and semipelitic samples remarkably tight correlations are revealed between d 002 for progressively graphitized carbonaceous material k ar ages that range from 184 6 to 138 7 ma and linear distance along the section both the d 002 values and the k ar ages decrease progressively toward the northeast through the four mineral zones and with progressive textural changes all rocks cropping out in the section have undergone a coherent episode of progressive metamorphism associated with terrane collision and have not been disturbed by any later major displacements a convex trend for phengite b 0 values plotted against advancing graphitization suggests p t conditions during metamorphism as in the high pressure intermediate facies series the age of the metamorphic peak is inferred to be 175 155 ma middle to late jurassic with cooling to the mica closure temperature at 155 135 ma late jurassic to early cretaceous unloading denudation and cooling were accompanied by localized hydrothermal events the oldest covering strata were deposited at ca 100 ma and denudation was completed by ca 75 80 ma middle triassic radiolarian nodules in melange zones are dated as preceding the metamorphic peak by about 65 ma associated turbidites contain suspected late middle to early late triassic tube fossils

nanodiamonds and silicate minerals in ordinary chondrites as determined by micro raman spectroscopy we present here the raman spectroscopic study of silicate and carbonaceous minerals in three ordinary chondrites with the aim to improve our understanding the impact process including the peak metamorphic pressures present in carbon bearing ordinary chondites the characteristic raman vibrational peaks of olivines pyroxenes and plagioclase have been determined on three ordinary chondrites from india dergaon h5 mahadevpur h4 5 and kamargaon l6 the raman spectra of these meteorite samples show the presence of nanodiamonds at 1334 1345 cm 1 and 1591 1619 cm 1 the full width at half maximum fwhm of raman peaks for mahadevpur and dergaon reflect the nature of shock metamorphism in these meteorites the frequency shift in raman spectra might be because of shock effects during the formation of the diamond graphite grains

first finding of microdiamond coesite and other uhp phases in felsic granulites in the moldanubian zone implications for deep subduction and a revised geodynamic model for variscan orogeny in the bohemian massif abstract heavy mineral fractions and polished thin sections from felsic granulites from the moldanubian zone of the bohemian massif were thoroughly studied by means of raman microspectroscopy combined with optical microscopy and scanning electron microscopy the following phases were identified among others as inclusions in robust minerals such as garnet and zircon diamond characterized by an intense narrow peak at 1332 cm 1 was found in two inclusions in zircon they have a size of 5 m coesite identified by its very characteristic peak at 520 cm 1 was found in an inclusion in garnet together with quartz coesite has been almost completely transformed into quartz only minor coesite nano domains remain kumdykolite the orthorhombic polymorph of naalsi 3 o 8 characterized by strong peaks at 220 456 and 492 cm 1 occurs either as single crystals or as a part of multiphase inclusions in garnet and in zircon along with other mineral phases such as k feldspar phengite rutile moissanite sic exhibiting the characteristic raman bands at 767 788 and 969 cm 1 occurs as inclusions in garnet diamond and coesite are considered to have formed at the peak ultrahigh pressure metamorphic uhpm conditions kumdykolite has been proposed to be a metastable phase formed during rapid cooling from high temperature moissanite points to extremely reduced conditions during subduction to great depths the finding of uhp phases in felsic granulites in the moldanubian zone is clear evidence for subduction of crustal materials to mantle depths the garnet hosting the uhp phase inclusions usually preserves prograde compositional zoning this in combination with the uhpm mineral inclusions suggests that the felsic material should have passed uhp metamorphism at a low temperature gradient isothermal decompression the commonly accepted model at temperatures of 850 950 c would have substantially modified and homogenized the garnet composition eliminating any compositional zoning therefore the uhpm felsic rocks could have experienced only a short term granulite facies metamorphism after they were exhumed to crustal levels

the origin and hydrothermal mobilization of carbonaceous matter associated with paleoproterozoic orogenic type gold deposits of west africa abstract the chemical and physical properties of carbonaceous matter cm were studied in paleoproterozoic metasediment hosted orogenic type gold deposits in burkina faso the inata deposit in mali the syama deposit and in ghana the obuashi and bogoso deposits two types of cm occur in all the studied deposits metamorphosed and hydrothermal metamorphosed cm prevails in all the deposits hydrothermal cm occurs in small veinlets in hydrothermally altered rocks and in quartz veins or forms irregular accumulations parallel or sub parallel to c type cleavage within the shear zones the origin of hydrothermal cm which occurs in paragenesis with au bearing arsenopyrite or pyrite seems to have been due to supersaturation of hydrothermal fluids with carbon at the deeper or middle crustal levels the isotopic composition of carbon in bulk cm 33 1 to 26 2 vpdb indicates its biogenic origin the isotopic composition of carbon in hydrothermal carbonates ranges from 14 5 to 4 4 vpdb which suggest mixing of carbon derived from a deep seated source with carbon derived from an organic source the interaction of hydrothermal fluids with metamorphosed cm could be one of the causes of the reduction of hydrothermal fluids and formation of the respective mineralization the optical properties and raman spectra of the metamorphosed cm particles in the individual studied mineral deposits differ considerably the temperatures calculated on the basis of the raman spectra of metamorphosed cm vary between 280 and 440 c depending on the thermometer used and correspond to temperatures of metamorphism of upper sub grenschist and greenschist facies the temperatures calculated for hydrothermal cm at the individual deposits are only slightly lower compared to the metamorphosed cm at the same deposits which indicates approximately the same temperature of the metamorphic and hydrothermal processes

ftir microspectroscopy of ediacaran phosphatized microfossils from the doushantuo formation weng an south china abstract phosphatized microfossils from ca 580 ma from the doushantuo formation in the weng an region of south china were analyzed by fourier transform infrared ftir microspectroscopy for their chemical characterization two morpho types of phosphatized embryo like fossils megasphaera and megaclonophycus were analyzed together with algal fossils transmission ir spectra of the microfossils have absorption bands of around 2960 cm 1 and 2925 cm 1 indicating the presence of aliphatic hydrocarbon anti symmetric aliphatic ch 3 and aliphatic ch 2 and have an additional band of around 1595 cm 1 probably derived from aromatic moieties aromatic c c in addition ir microscopic mapping shows that aliphatic hydrocarbon and aromatics are distributed inside the embryo like fossils the embryo like fossils appear to show three types of ch 3 ch 2 peak height ratios r 3 2 and aromatic c c ch 2 peak height ratios r c c 2 values 1 high r 3 2 low r c c 2 type r 3 2 0 2 1 0 and r c c 2 0 2 2 low r 3 2 medium r c c 2 type r 3 2 0 2 0 6 and r c c 2 1 4 and 3 low r 3 2 high r c c 2 type r 3 2 0 2 0 6 and r c c 2 1 8 all three types are contained in both megasphaera and megaclonophycus raman spectra for the carbonaceous matter within the rock sample show a similar degree of thermal alteration indicating that the organics were embedded in situ prior to thermal maturation the ir spectroscopic differences might reflect differences in original organic compositions of microorganisms and or immediate post mortem alteration this suggests that the origins of phosphatized embryo like fossils are more diverse than was previously recognized on the basis of their morphology a comparison of r 3 2 and r c c 2 values in the embryo like fossils with those of the algal fossils and the extant microorganisms indicates the possible interpretation that some of the embryo like fossils belong to animal embryo others are algae but none of them originate from bacteria

exceptional preservation of fossil plant spores in high pressure metamorphic rocks it is commonly believed that high grade metamorphism erases all traces of fossils and more generally of biogenicity in rocks to address this issue we report in this study x ray spectromicroscopy raman microspectroscopy and electron microscopy observations at the nm scale of fossil lycophytes megaspores found in triassic metasedimentary rocks from the french alps these rocks have undergone high pressure metamorphic conditions not vert similar 14 kbar not vert similar 360 c during the alpine orogeny corresponding to a burial of not vert similar 35 km during subduction despite such metamorphism the fossil megaspores are remarkably well preserved texturally an unusual mineralogical zonation consisting of magnetite ankerite and calcite is superposed on the structures of the spore walls in parallel chemical heterogeneities of the organic matter om composing the spore walls were detected we discuss different interpretations for our observations in particular a scenario in which these features are remnants of the original structural heterogeneities in the spores and provide insights on the fossilization processes under high grade metamorphic conditions whatever the processes leading to such heterogeneities our observations oppose the usual assumption that high grade metamorphism erases all indications of biogenicity in rocks and open new avenues for investigation at the nm scale of the evolution of organic matter during diagenesis and metamorphism

vitrinite reflectance and shear induced graphitization in orogenic belts a case study from the kandersteg area helvetic alps switzerland vitrinite reflectance vr is an important indicator of incipient metamorphism and it is generally assumed that temperature and to a lesser degree time are the two main variables the role of stress in vr is controversial and will be addressed in this study in the kandersteg area north of lake oeschinen four different helvetic tectonic units are present comprising mainly limestones marls and greywackes of mesozoic and lower tertiary age vr rr rmax rmin and illite crystallinity ic were determined from a very steep section at elevations between 1700 and 2900 m a s l in general rr rmax and ic increase from tectonically higher to lower units i e from upper diagenetic 2 3 to 4 5 rr to upper anchizonal conditions 3 4 to 5 6 rmax several samples contain in addition to coaly fragments abundant semigraphitized and graphitized particles that are believed to be of authigenic origin transitional matter showsrmax values ranging from 7 to about 11 and rmin of 1 3 3 4 optical graphite showsrmax of about 15 16 and rmin of 1 6 1 8 there is good textural evidence that tectonic deformation has played a major role in the development of these strongly coalified particles the first tiny needle like crystals of graphitic material occur within narrow shear zones transecting the rock matrix the beginning of graphite formation parallels the onset of plastic deformation and dynamic recrystallization of quartz elevated vitrinite reflectance rmax and bireflectance values are found near thrust planes where simple optical observation on quartz grain morphology indicates an increase in strain intensity it appears that frictional heating associated with thin shear zones may have been responsible for the formation of authigenic graphite in the kandersteg samples

thermal metamorphism of the arunachal himalaya india raman thermometry and thermochronological constraints on the tectono thermal evolution determination of the peak thermal condition is vital in order to understand tectono thermal evolution of the himalayan belt the lesser himalayan sequence lhs in the western arunachal pradesh being rich in carbonaceous material cm facilitates the determination of peak metamorphic temperature based on raman spectroscopy of carbonaceous material rscm in this study we have used rscm method of beyssac et al j metamorph geol 20 859 871 2002a and rahl et al earth planet sci lett 240 339 354 2005 to estimate the thermal history of lhs and siwalik foreland from the western arunachal pradesh the study indicates that the temperature of 700 800 c in the greater himalayan sequence ghs decreases to 650 700 c in the main central thrust zone mctz and decreases further to 600 and 12 km than the upper siwalik sediments to its south at depths 8 km before they were exhumed the 40ar 39ar ages suggest that the upper zones of se la evolved 13 15 ma the middle zone exhumed at 11 ma and lower zone close to 8 ma indicating erosional unroofing of the mct sheet the footwall of mctz cooled between 6 and 8 ma analyses of p t path imply that lhs between mct and u mbt zone falls within the kyanite stability field with near isobaric condition at higher structural level the temperatures increase gradually with p t conditions in the sillimanite stability field the near isothermal 700 800 c condition in the ghs isobaric condition in the mctz together with t t path evidence of ghs that experienced relatively longer duration of near peak temperatures and rapid cooling towards mctz compares the evolution of ghs and inverted metamorphic gradient closely to channel flow predictions

significance of graphite occurrences in the aracena metamorphic belt iberian massif the significance of syngenetic and epigenetic graphite occurrences from the variscan high temperature low pressure aracena metamorphic belt is discussed in the framework of the tectono thermal evolution of this southern zone of the iberian massif syngenetic graphite is associated with both low to medium grade metamorphic rocks la umbria series precambrian in age and high grade granulite facies rocks the precambrian fuente del oro series and a cambrian calc silicate series epigenetic fluid deposited occurrences correspond to overgrowths on existing metamorphic graphite grains and vein type mineralization two types of graphitized particles with remarkable differences in reflectance anisotropy and size can be distinguished in the precambrian metapelites of the la umbria series large 150 m length platy crystals with high reflectance and anisotropy are interpreted as detrital and are considered indirect evidence of an old orogenic cycle prior to the cadomian orogeny during which metamorphism exceeded greenschist facies the coexistence of two types of particles explains the scattering of values of the c parameter of graphite determined by xrd c 6 72 6 74 a and the anomalously high temperatures of the dta exothermic peak close to 600 c of graphite with respect to that inferred from mineral assemblages in these rocks the presence of graphite rich quartzites and gneisses within the fuente del oro series and the calc silicate series is evidence of sedimentation under reducing conditions in a continental shelf the characteristics of graphite reflect the high grade metamorphic conditions attained in the southern area of the aracena metamorphic belt pervasive flow of fluids related to a major variscan extensional event resulted in overgrowths on the pre existing graphite in the gneisses and quartzites of the calc silicate series as evidenced by the heterogeneous isotopic composition of graphite single crystals in these rocks a later stage of graphite precipitation is represented by scarce vein type occurrences in mafic granulites that document channelled flow of fluids

graphitization of organic matter and fluid deposited graphite in palaeoproterozoic birimian black shales of the kaya goren greenstone belt burkina faso west africa palaeoproterozoic black shales form an essential part of the birimian volcanosedimentary belt in burkina faso west africa the mean rmax values and the atomic h c values of the bulk carbonaceous matter bcm together with rock structures and mineral assemblages indicate that these carbon rich rocks were metamorphosed to sub greenschist and low grade greenschist facies x ray diffraction reveals that the 002 graphite peak width in half maximum fwhm ranges from 0 43 to 0 71 2 in sub greenschist facies and from 0 27 to 0 41 2 in greenschist facies rocks but the d 002 values in both groups of rocks are approximately the same 3 35 a the bcm of individual samples is composed of particles with very variable shape reflectance and raman spectra type i particles that predominate in sub greenschist facies are fine grained irregular or elongate bodies 1 to 3 m in size their maximum reflectance rmax ranges between 2 5 and 8 2 and raman parameters r1 and r2 range from 0 5 to 1 4 and 0 5 to 0 8 respectively type ii particles are lath shaped up to 40 m large bodies commonly arranged parallel to white mica flakes the number of these particles increases from sub greenschist to greenschist facies maximum reflectance varies between 6 and 11 2 and r1 and r2 raman parameters range from 0 05 to 0 7 and from 0 1 to 0 5 respectively type iii particles occur in hydrothermally altered and sheared rocks these are nodular aggregates composed of grains up to 10 m in size this type of particles has very high reflectance rmax 11 15 and its raman spectra indicate a very high degree of structural ordering corresponding to well ordered graphite type i particles represent original organic matter in the metasediments type ii particles are believed to have been formed either in situ by solid state transformation of type i particles or by crystallization from metamorphic fluids gradual graphitization of the type i organic particles and the growth of lath shaped type ii particles from a fluid phase is assumed to have taken place under the peak metamorphic conditions associated with the burial of birimian sediments during thrust tectonism progressive tectonic accretion and crustal thickening during the d1 event of the eburnean orogeny the growth of equant high reflectance postkinematic nodular aggregates of type iii particles is ascribed to the reduction of co2 rich fluids during a hydrothermal event associated with late eburnean d2 exhumation and strike slip movements type i carbonaceous particles were only slightly affected by high temperature low pressure contact metamorphism during intrusion of late eburnean magmatic bodies whereas formation of type ii or iii particles was not recorded in contact metamorphosed rocks at all

multiple generations of carbonaceous material deposited in apex chert by basin scale pervasive hydrothermal fluid flow abstract the pilbara craton in western australia contains the best preserved and most complete record of archean rocks in the world as such they are some of the most studied rocks in the world paleontologists isotopic geochemists geologists and geobiologists have all investigated these rocks for clues about the early biosphere and atmosphere here we show using high resolution transmission electron microscopy that the carbonaceous material found in the apex chert and potentially in other associated units was formed by multiple processes such as abiotic catalytic synthesis and or biological synthesis we use these data as well as the geological history of the craton to demonstrate that when the rocks of the pilbara craton experienced a high degree of post depositional hydrothermal alteration carbonaceous material could have been remobilized and redeposited as the carbonaceous material within the apex chert samples was formed over nearly a billion years bulk chemistry even at the micron level will be unable to unambiguously delineate the presence of life in these ancient rocks although nanoscale observations may provide a way forward in the search for ancient life

organic geochemistry of precambrian shales and schists bohemian massif central europe abstract the composition and the structure of kerogens and subgraphitic materials from upper proteroic regionally metamorphosed black shales were investigated by different physico chemical method the isotopic composition of carbon changes with the intensity of the regional metamorphism kerogens from low grade metasediments have averaged 13 c values 35 kerogens from chlorite and biotite zones 31 samples display high diversity of primary sedimentary materialos details were obtained using transmission electron microscopy tem crystalline order improves with the intensity of the regional metamorophism turbostratic carbonacveous matter is described from low grade metasediments graphite occurs at the end of the biotite zone however both metallogenetic and contact metamorphic processes can be involved in some samples the second form of graphite has been identified probably of detrital origin inherited from some high grade metamorphic area existing at the time of sedimentation of primary rocks

multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks pyritized plant tissues with well preserved morphology were studied in rocks from vanoise western alps france that experienced high pressure low temperature metamorphic conditions in the blueschist facies during the alpine orogeny organic and inorganic phases composing these fossils were characterized down to the nanometer scale by raman microspectroscopy scanning transmission x ray microscopy and transmission electron microscopy the graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and or thermal degradation during metamorphism various mineral phases are closely associated with this organic matter including sulphides such as pyrite and pyrrhotite carbonates such as ankerite and calcite and iron oxides a tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed the absence of traces of organic matter sulphurization the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional diagenetic environment of these metasediments was likely rich in reactive iron fe sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism in contrast iron oxides which form rims of 100 nm in thickness at the interface between organic matter and fe sulphides may result from metamorphic processes this study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism

fossil biomass preserved as graphitic carbon in a late paleoproterozoic banded iron formation metamorphosed at more than 550 c metamorphism is thought to destroy microfossils partly through devolatilization and graphitization of biogenic organic matter however the extent to which there is a loss of molecular elemental and isotope signatures from biomass during high temperature metamorphism is not clearly established we report on graphitic structures inside and coating apatite grains from the c 1850 ma michigamme silicate banded iron formation from michigan metamorphosed above 550 c traces of n s o h ca and fe are preserved in this graphitic carbon and x ray spectra show traces of aliphatic groups graphitic carbon has an expanded lattice around 3 6 a forms microscopic concentrically layered and radiating polygonal flakes and has homogeneous 13c values around 22 identical to bulk analyses graphitic carbon inside apatite is associated with nanometre size ammoniated phyllosilicate precursors of these metamorphic minerals and graphitic carbon originated from ferruginous clay rich sediments with biomass we conclude that graphite coatings and inclusions in apatite grains indicate fluid remobilization during amphibolite facies metamorphism of precursor biomass this new evidence fills in observational gaps of metamorphosed biomass into graphite and supports the existence of biosignatures in the highly metamorphosed iron formation from the eoarchean akilia association which dates from the beginning of the sedimentary rock record supplementary material figures illustrating the petrography and analytical results are available at https doi org 10 6084 m9 figshare c 4430609

graphitization in a high pressure low temperature metamorphic gradient a raman microspectroscopy and hrtem study the graphitization of carbonaceous material cm in a high pressure metamorphic gradient is characterized along a cross section in the schistes lustres formation western alps along this 25 km cross section both the cm precursor and the host rock lithology are homogeneous and the prograde evolution of the pressure temperature metamorphic conditions from the lower blueschist facies 13 kbar 330 c to the eclogite facies 20 kbar 500 c is tightly constrained by literature data raman microspectroscopy shows that at the micrometre scale this process is progressive and continuous with increasing metamorphic grade and that the structure of cm is very sensitive to temperature variations at the nanometre scale hrtem the cm is composed of a mixture of a microporous phase and an onion ring like phase both known as non graphitizing under the effect of temperature at ambient pressure the hp lt graphitization produces structurally and microtexturally heterogeneous cm with increasing metamorphic grade the graphitization of the two types of cm proceeds up to the triperiodic graphite stage because of microtextural and structural changes that are specific to each type of cm the microporous material is progressively transformed into graphite through a macroporous transitional stage in this case graphitization mainly occurs on the pore walls as a result of pore growth in the case of concentric onion ring like material graphitization occurs in the regions with the largest radius of curvature i e on the outer part of the ring in comparison with 1 bar experiments pressure seems to induce microtextural changes which allows the subsequent structural modifications of the starting material

structural characterization of kerogen in 3 4 ga archaean cherts from the pilbara craton western australia hydrogen lean kerogen atomic h c 0 46 isolated from the 3 4 ga strelley pool chert in the north pole area pilbara craton western australia were studied by vibrational spectroscopy fourier transform infrared ftir spectroscopy and raman spectroscopy nuclear magnetic resonance spectroscopy solid state 13 c nmr spectroscopy catalytic hydropyrolysis followed by gas chromatography mass spectrometry hypy gc ms and isotope ratio mass spectrometry irms the kerogen occurs in sedimentary rocks as clasts and clots deposited together with other detrital materials that are finely disseminated throughout a chert matrix the bulk kerogen 13 c values range from 28 3 to 35 8 solid state 13 c nmr spectroscopy and ftir spectroscopy reveals that the kerogen is highly aromatic fa varying from 0 90 to 0 92 and contains only minor aliphatic carbon or carbon oxygenated c o functionalities the raman carbon first order spectra for the isolated kerogens are typical of spectra obtained from disordered sp 2 carbons with low 2 d ordering biperiodic structure the implications of the raman results show low 2 d ordering throughout the carbonaceous network indicate the incorrect usage of the term graphite in the literature to describe the kerogen or carbonaceous material in the warrawoona cherts hydropyrolysates contain aromatic compounds consisting of 1 ring to 7 ring polycyclic aromatic hydrocarbons which were covalently bound into the kerogen as well as alkanes linear branched and cyclic which were most probably trapped in the microporous network of the kerogen these pahs have mainly c1 and c2 alkylation while c3 substitued aromatics are low in abundance and do not show a high degree of branched alkylation for the first time we have shown a correlation between elemental analysis h c atomic ratios raman spectroscopic parameters id1 ig id1 id1 ig and la and the degree of alkylation of bound polyaromatic molecular constituents generated from hypy for archaean kerogens similarities in molecular

reconstruction of a 200 ma multi stage five element bi co ni fe as s system in the penninic alps switzerland abstract hydrothermal five element veins ag co ni bi as are mineral successions of native metals encapsulated by fe co ni arsenides and carbonates recent studies focused on the evolution from ordinary base metal systems sulfide rich to five element veins sulfide poor and revealed the importance of hydrocarbon dominated fluids as essential redox agent in these systems although mineral successions reveal the natural subdivision into native as native ag bi or arsenide dominated vein types and suggested processes explain the mineralogical variation to a certain degree the ni co fe variations among the arsenides are not well understood yet this is the first case study explaining compositional mineralogical and textural features of five element veins by changing metal contents arsenic sulfur activities ph and temperatures applied to a multi stage vein mineralization in the penninic alps switzerland textural relationships mineral chemistry fluid inclusion compositions microthermometry and raman spectroscopy stable s isotopes and in situ u pb age dating of carbonates magnetite and multi mineral isochrons were investigated u pb ages of paragenetic mineral fractions constrain a primary formation of lollingite skutterudite dolomite dominated ores at 233 10 ma and niccolite gersdorffite skutterudite ankerite dominated ores at 188 32 ma which links their formation to crustal thinning caused by the breakup of the meliata ocean and alpine tethys as secondary processes during the alpine orogeny a in situ remobilization of the ores occurred as mostly ternary fe co ni sulfarsenides at 73 24 ma due to continent continent collision and neoformations of safflorite cobaltite skutterudite dominated ores at 29 16 ma due to transtensional strike slip tectonics ore textures indicate that the dissolution of primary siderite oxidation of ferrous iron and its precipitation as magnetite was the redox couple to precipitate native bi arsenides and sulfarsenides bi0 as3 and as 1 from their oxidized aqueous species bi3 cl4 and as3 oh 3 at temperatures between 200 and 300 c ni and co signatures of the arsenides sulfarsenides show increasing mobilization from the host rocks during the successive evolution of the hydrothermal system in the triassic jurassic and during the alpine orogeny stable s isotopes and as s signatures of the sulfarsenides indicate an increasing mobilization of host rock sulfides i e fahlbands from the primary to the secondary ores fluid inclusions and stable s isotopes suggest involvement of fluid modification by water rock interactions i e cover rocks carbonate sulfate and halite dissolution basement rocks albitisation of plagioclase during fluid descent

polymetallic mineralization at the browns deposit rum jungle mineral field northern territory australia the rum jungle mineral field northern territory australia forms part of the paleoproterozoic pine creek orogen the geology of the area comprises two archean granitic basement domes overlain by a paleoproterozoic sequence of metasedimentary and subordinate metavolcanic rocks the rocks have been deformed and metamorphosed to greenschist facies during the 1880 ma barramundi orogeny but the original stratigraphic succession has been preserved the browns deposit browns and its extension browns east hosted within black carbonaceous pelites of the paleoproterozoic whites formation is the largest base metal deposit found to date in the pine creek orogen present resource estimates are 39 million metric tons mt at 0 44 percent cu 3 61 percent pb 0 11 percent co and 0 09 percent ni browns and 31 mt at 1 29 percent cu 1 28 percent pb 0 13 percent co and 0 13 percent ni browns east major sulfide minerals in the ore zone are galena sphalerite chalcopyrite pyrite and the main carrier of ni and co siegenite ni co 3 s 4 digenite group minerals and bornite ca bearing plumbogummite pbal 3 po 4 2 oh 5 h 2 o arsenopyrite and gersdorffite are present in minor quantities ore minerals occur as fine grained wisps parallel to the main bedding parallel foliation and as coarse grained mono and polyminerallic aggregates that crosscut the foliation total noncarbonate carbon contents of unaltered rocks range from 1 07 to 7 51 wt percent total sulfur contents range from 2 13 to 6 14 wt percent petrographic studies and raman spectroscopy identify three varieties of carbonaceous matter primary syngenetic premetamorphic epigenetic grain coating and postmetamorphic epigenetic uraniferous migrated altered rocks are rarely encountered values of 34 s for sulfides range from 5 to 15 per mil and are interpreted to reflect a combination of inorganic thermochemical reduction of seawater and bacterial activity no specific sulfur isotope patterns for individual minerals can be established indicating nonequilibrium conditions homogeneous lead isotope signatures of galena 206 pb 204 pb 16 20 16 22 207 pb 206 pb 15 48 15 51 208 pb 207 pb 35 86 35 92 suggest that all pb was derived from a single crustal source and paragenetically late crosscutting galena appears to have been remobilized from bedding parallel galena despite the occurrence of uranium in similar rocks nearby uranium is quantitatively insignificant in the browns deposit and is not genetically related to base metal mineralization instead it is linked to brittle deformation in the waning stages of orogenesis the browns deposit differs from other well known sediment hosted stratiform ore deposits both the zambian copperbelt and the polish kupferschiefer deposits are copper dominant and hosted in sedimentary sequences with significant psammitic components the pb zn ag deposits of the proterozoic australian zinc province also have significant carbonate in their host rocks e g carbonaceous dolomitic and siltstone at mcarthur river and lack economically interesting cu co and ni the nearby woodcutters pb zn ag deposit in rocks of similar age also differs in structural setting veins dominant metals and pb isotopes from the browns deposit

metamorphism of carbonaceous material in the tono contact aureole kitakami mountains japan abstract optical and x ray studies of carbonaceous material in the tono contact metamorphic aureole kitakami mountains northeast japan have revealed that metamorphic graphitization proceeded through two discontinuous changes first optically anisotropic domains develop within the coaly phytoclast forming transitional material and then ordered graphite crystallizes by the decomposition of pre existing carbonaceous materials coaly material disappears in the uppermost chlorite zone transitional material appears in the middle of the lower chlorite zone graphite appears in the upper chlorite zone and its modal abundance increases across the andalusite iso grad to the cordierite isograd where all the carbonaceous materials have converted to graphite the apparently continuous variation in the crystallographic parameters of the bulk carbonaceous material during graphitization is largely due to variation in the modal proportions of three types of carbonaceous materials the temperature of graphitization in the present area is at least 100 c higher than the temperature in the sanbagawa and new caledonia high pressure metamorphic terrains probably due to the slow reaction rate of metamorphic graphitization and to the short duration of contact metamorphism

vitrinite and vitrinite like solid bitumen reflectance in thermal maturity studies correlations from diagenesis to incipient metamorphism in different geodynamic settings abstract vitrinite reflectance vr is a useful and reliable parameter to monitor the level of organic matter maturation from the immature stage to graphite additionally vr is a useful and essential tool in modelling the temperature maturation time path huminite vitrinite bearing sedimentary and meta sedimentary rocks can be used to reconstruct the thermal history of basins or orogenic terranes throughout their geological history the usefulness of vr evidently depends on the presence of huminite vitrinite phytoclasts however pre upper silurian rocks and many organic rich marine rocks e g sapropelic sediments lack of huminite vitrinite particles furthermore vitrinite is sparse in carbonate sediments however the presence of bitumen in rocks lacking type iii kerogen provides a valuable aid via its reflectance vitrinite like solid bitumen reflectance vlbr and or solid bitumen reflectance br to fulfil the above described tasks that vr enables this study presents basically a relationship between br vlbr and vr for various types of geodynamic settings and over the largest possible range of maturation levels so that vlbr may be used as a substitute for vr whereas the effort to correlate vr with br is not novel it is the first time that the vr br correlation is re judged discriminating bitumen from vlb moreover for the first time the correlation is established for various geodynamic settings the investigated geological contexts are 1 sedimentary basins e g the saar ruhr ohio west virginia and petrosani basins 2 metasedimentary terranes occurring as inverted basins in orogenic belts e g from the subalpine molasse helvetic austroalpine and danubian nappe systems and having suffered from very low to low grade metamorphism from anchizone to greenschist facies 3 metasedimentary terranes e g slates and schists from the franciscan and alpine belts that were subducted at anchizone to blueschist facies conditions and 4 metasedimentary rocks affected by contact metamorphism together the frequent geological settings are referred and most of the earth geothermal conditions and heat fluxes considered despite temperature pressure and heating time also heat flow gradient dependences cannot be ignored

high pressure high temperature raman spectroscopy of kerogen relevance to subducted organic carbon the amount of insoluble macromolecular organic matter in the earth s crust commonly referred to as kerogen far exceeds the mass of living organic matter the fraction of kerogen in sediments subducted into the mantle remains poorly constrained and will vary depending on the physical chemical properties of kerogen along different slab geotherms we studied the pressure temperature evolution of carbon vibrational frequencies in isolated kerogen previously not subjected to metamorphism using raman spectroscopy in a sapphire optical cell up to 3 2 gpa and 450 c corresponding to colder subduction geotherms for blue green laser excitation we find optical irradiance exceeding 3 kw cm 2 induces changes in spectral features of the primary graphitic g band and two main disordered modes d1 and d2 that might otherwise be mistaken for thermal maturation whereas previous in situ studies have investigated the changes in these molecular vibrations of kerogen at high temperature or high pressure we collected raman spectra of isolated kerogen at simultaneous high p t conditions although instantaneous and irreversible changes in band ratios of isolated kerogen were observed above 350 c at room pressure long duration 2 8 h heating experiments at 450 c and 2 7 3 0 gpa reveal no permanent change in band structure the reduction in vibrational frequencies of the disordered carbon modes with temperature d d t at pressures 1 gpa is slightly less than found at room pressure further indicating that pressure effectively increases the thermal stability of kerogen our results suggest that kerogen reaching depths of 60 km where the temperature is below 450 c may subduct into the mantle providing a potential source for the organic rich component of carbon recently detected in certain lower mantle diamonds

peak temperature patterns of polyphase metamorphism resulting from accretion subduction and collision eastern tauern window european alps a study with raman microspectroscopy on carbonaceous material rscm raman microspectroscopy on carbonaceous material rscm from the eastern tauern window indicates contrasting peak temperature patterns in three different fabric domains each of which underwent a poly metamorphic orogenic evolution domain 1 in the northeastern tauern window preserves oceanic units glockner nappe system matrei zone that attained peak temperatures tp of 350 480 c following late cretaceous to palaeogene nappe stacking in an accretionary wedge domain 2 in the central tauern window experienced tp of 500 535 c that was attained either within an exhumed palaeogene subduction channel or during oligocene barrovian type thermal overprinting within the alpine collisional orogen domain 3 in the eastern tauern subdome has a peaktemperature pattern that resulted from eo oligocene nappe stacking of continental units derived from the distal european margin this pattern acquired its presently concentric pattern in miocene time due to post nappe doming and extensional shearing along the katschberg shear zone system kszs tp values in the largest hochalm dome range from 612 c in its core to 440 c at its rim the maximum peak temperature gradient 70 c km 1 occurs along the eastern margin of this dome where mylonitic shearing of the katschberg normal fault knf significantly thinned the subpenninic and penninic nappe pile including the pre existing peak temperature gradient

characteristics of molecular nitrogen generation from overmature black shales in south china preliminary implications from pyrolysis experiments abstract high content of molecular nitrogen n2 is one of the natural gas exploration risks in petroliferous basins where black shales act as source rocks of either hydrocarbon gas or molecular nitrogen in this study two overmature and one low maturity shale samples and their kerogens were investigated to determine the generation characteristics of molecular nitrogen as well as methane and the differences in the release processes of inorganic nitrogen fixed in ammonium bearing minerals and organic nitrogen bound in kerogen the results illustrate that with increasing pyrolysis temperature the yield of methane first increases and then decreases with an inflection temperature of 650 c eqvro 3 4 whereas the yield of molecular nitrogen shows a continuous increase throughout the pyrolysis experiment the molecular nitrogen during the stage of methane generation i e eqvro 3 4 the results also reveal that at the experimental maxima of thermal maturity eqvro 4 9 the generation potential of inorganic molecular nitrogen mg g ninorg is much lower than that of organic molecular nitrogen mg g norg indicating that in our experiments the organic nitrogen in kerogen is more easily to be converted into molecular nitrogen than the inorganic nitrogen in ammonium bearing minerals all these results indicate that molecular nitrogen content in shale gas may change dramatically during thermal evolution and source rocks with exceptionally high maturity and high abundance of organic nitrogen likely lead to a high molecular nitrogen risk particularly in regions of poor preservation conditions of shale gas which may be the main reasons for the high molecular nitrogen content in the lower cambrian shale gas in south china

evidence for biogenic graphite in early archaean isua metasedimentary rocks the archaean rocks of isua west greenland contain graphite but its origins are debated geochemical and microscopic analyses suggest that the graphite was formed from biologically formed carbon that was deposited at least 3 7 billion years ago

3 d assessment of peak metamorphic conditions by raman spectroscopy of carbonaceous material an example from the margin of the lepontine dome swiss central alps this study monitors regional changes in the crystallinity of carbonaceous matter cm by applying micro raman spectroscopy to a total of 214 metasediment samples largely so called bundnerschiefer dominantly metamorphosed under blueschist to amphibolite facies conditions they were collected within the northeastern margin of the lepontine dome and easterly adjacent areas of the swiss central alps three dimensional mapping of isotemperature contours in map and profile views shows that the isotemperature contours associated with the miocene barrow type lepontine metamorphic event cut across refolded nappe contacts both along and across strike within the northeastern margin of the lepontine dome and adjacent areas further to the northeast the isotemperature contours reflect temperatures reached during the late eocene subduction related blueschist facies event and or during subsequent near isothermal decompression these contours appear folded by younger large scale post nappe stacking folds a substantial jump in the recorded maximum temperatures across the tectonic contact between the frontal adula nappe complex and surrounding metasediments indicates that this contact accommodated differential tectonic movement of the adula nappe with respect to the enveloping bundnerschiefer after maximum temperatures were reached within the northern adula nappe i e after late eocene time

the association of poorly ordered graphite coke and bitumens in greenschist facies rocks of the ponikla group lugicum czech republic the result of graphitization of various types of carbonaceous matter greenschist facies rocks of the ponikla group ordovician silurian czech republic contain several types of carbonaceous matter that differ in their morphology texture reflectance and raman characteristics the first type consists of large up to 3 mm irregularly bound particles of low reflectance romin 0 9 romax 5 6 the area ratio of the 1585 cm 1 to 1350 cm 1 raman peaks 1 08 1 17 indicates an intermediate degree of graphitization the formation of this type of highly porous particle displaying a texture reminiscent of regular or needle coke is attributed to the thermal alteration of the amorphous structureless kerogen of the precursor sediments the second type consists of lamellar particles up to 30 m thick which can be associated with the latter or can occur independently in white mica rich laminae this type is characterized by high bireflectance romin 0 6 romax 11 9 and by lower ratios 0 70 0 82 of the raman peak areas these particles are interpreted as the product of solid state diffusion controlled graphitization of a chemically homogeneous organic material e g of graptolite periderms the third type consists of isometric up to 2 mm large commonly fractured grains and fragments which mainly occur in quartz rich laminae in reflected light the texture is either homogeneous or consists of various types of anisotropic mozaics the raman peak area ratios 0 75 1 14 indicate a highly variable degree of structural ordering these particles are considered as the remains of metamorphosed bitumens accumulated in the sandy laminae of the original sediments the fourth type consists of small particles of carbonaceous matter maximum length 25 m thickness 1 2 m which occur adjacent to crystal faces of white micas this type is probably the product of epitaxial growth of graphite from the gaseous phase the results of this work indicate that the differences in the degree of graphitization of the carbonaceous matter in low grade metamorphosed rocks can be mainly related to the initial nature of the sedimentary organic matter and to its premetamorphic history

conversion of carbonaceous material to graphite within the greywacke zone of the eastern alps morphology and reflectance of carbonaceous material cm in late carboniferous metasediments of the eastern greywacke zone eastern alps indicate a mixture of vitrinite grainy textured and lamellar shaped particles as imaged by high resolution atomic force microscopy vitrinite and the grainy textured particles show mesophase structures which can be described as facetted nanocrystals within the carbon matrix high resolution transmission electron microscopy has revealed two types of microtextures representing different degrees of graphitization the first type is characterized by elongated ring shaped microtextures whereas the second type is characterized by graphite lamellae and polygonal flakes with long range ordered aromatic layers in spite of the heterogeneity of the cms the geographical distribution of quantitative metamorphic parameter raman spectra parameter x ray diffraction pattern microscopic reflectance suggests a graphitization process which is promoted by advective heat transport during post collisional processes in a tentative pressure time path late cretaceous thrusting results in a turbostratic ordering of the aromatic layer ordering to long range ordered aromatic layers was achieved during the late cretaceous paleogene exhumation of mid crustal rocks beneath the eastern greywacke zone

raman spectrum of carbonaceous material a possible metamorphic grade indicator for low grade metamorphic rocks raman spectral analyses of carbonaceous material cm extracted from pelitic samples along two sections traversing the metamorphic belt of taiwan were carried out in the present study the results show similar spectral variations of cm with metamorphic grade as those documented in the literature however continuous sampling from zeolite facies through prehnite pumpellyite facies to greenschist facies metamorphic rocks in the present study does reveal some interesting features on the raman spectra of cm that were not noted before both the raman d disordered o ordered peak area i e integrated intensity ratio and the d o peak width i e full width at half maximum fwhm ratio of the cm decrease with progressive metamorphism but the most prominent change in the d o peak area ratio occurs in samples of lower greenschist facies metamorphic grade while the most significant decrease in the d o peak width ratio occurs in samples near the boundary of prehnite pumpellyite facies and greenschist facies this phenomenon is interpreted as a result of the decoupling of the changing rates of in plane crystallite size and degree of defects of cm with progressive metamorphism it is postulated that the raman spectrum of cm can serve as a metamorphic grade indicator to distinguish samples of prehnite pumpellyite facies metamorphic grade from those of greenschist facies metamorphic grade

graphite thermometry in a low pressure contact aureole halifax nova scotia abstract intrusion of the late devonian south mountain batholith southern nova scotia produced a low pressure contact metamorphic aureole in its metasedimentary host rocks the effects of contact metamorphism are particularly well developed in pelitic rocks of the halifax group on the eastern margin of the batholith contact metamorphic isograds and mineral assemblages suggest low pressure metamorphism with p t conditions at the contact estimated at 2 5 3 0 kbar and ca 650 c in this study raman spectroscopy of carbonaceous material rscm was used to obtain temperatures from graphite which is common throughout the contact aureole temperature estimates range from ca 360 c just outside the cordierite in isograd to ca 640 c in the sillimanite k feldspar zone near the contact the latter consistent with the temperature estimated from the corresponding silicate mineral assemblage three different rscm calibrations produced very similar results except at the high temperature end of the observed range a thermal profile constructed from the rscm data was used to constrain a 2d numerical model for post intrusion conductive cooling of the batholith along its eastern margin comparison of rscm vs model thermal profiles suggest that observed differences between the thermal structure of the inner and outer aureole were controlled by the subsurface geometry of the pluton contact the model predicts that peak temperatures in country rocks within 1 km of the contact were reached within 50 ka of intrusion but that the outer part of the aureole took 250 500 ka to reach peak temperatures the results confirm the utility of rscm thermometry for acquiring temperature data over a range of metamorphic grades

the mesozoic along strike tectonometamorphic segmentation of longmen shan eastern tibetan plateau the longmen shan belt eastern border of the tibetan plateau constitutes a tectonically active region as demonstrated by the occurrence of the unexpected 2008 mw 7 9 wenchuan and 2013 mw 6 6 lushan earthquakes in the central and southern parts of the belt respectively these events revealed the necessity of a better understanding of the long term geological evolution of the belt and its effect on the present dynamics and crustal structure new structural and thermobarometric data offer a comprehensive dataset of the paleo temperatures across the belt and p t estimates for low grade metamorphic domains in the central longmen shan two metamorphic jumps of 150 200 c 5 6 kbar and 50 c 3 5 kbar acquired during the early mesozoic are observed across the wenchuan and beichuan faults respectively attesting to their thrusting movement and unrevealing a major decollement between the allochtonous songpan garze metasedimentary cover at t 500 c and the autochtonous units and the basement t 400 c in the southern longmen shan the only greenschist facies metamorphism is observed both in the basement 360 30 c 6 2 kbar and in the metasedimentary cover 350 30 c 3 1 kbar peak conditions were reached at c 80 60 ma in the basement and c 55 33 ma in the cover c 50 ma after the greenschist facies metamorphic overprint observed in the central longmen shan c 150 120 ma this along strike metamorphic segmentation coincides well with the present fault segmentation and reveals that the central and southern longmen shan experienced different tectono metamorphic histories since the mesozoic

exhumation of attica high pressure rocks in a subduction channel new metamorphic pt constraints from attica nw cyclades greece abstract the hymettus area in east attica contains predominantly greenschist facies schists and marbles blueschist facies key minerals are absent in the matrix however blueschist facies p t conditions are recorded in the phyllosilicate mineral chemistry we provide new integrated thermodynamic data from a lower tectonic unit indicating that the metamorphic path for both prograde and retrograde metamorphism was similar to that in other parts of the cycladic blueschist unit cbu new p t data from the hymettus area show that a peak pressure of 1 4 0 05 gpa was reached at 300 25 c followed by exhumation first with a significant temperature increase to 470 20 c at a pressure of 0 8 0 1 gpa followed by major cooling the mechanism that exhumed the hymettus rocks is interpreted to be wedge extrusion in a subduction channel accordingly the 15 km difference in pressure 0 5 gpa between the lower and upper tectonic units was eliminated by their juxtaposition during their exhumation in the extruded wedge which had a shallow dipping extensional fault at the top and a parallel thrust at the base retrogression of high to low pressure assemblages was a result of water infiltration from both sides of the wedge both these processes led to a typically symmetrical wedge structure with the relict hp rocks of the ltu in the centre and the utu lower pressure rocks in the upper margin

mineral templated growth of natural graphite films abstract organic material in sediments is progressively altered during diagenesis and metamorphism leading to the formation of kerogen and ultimately crystalline graphite bulk carbonaceous material in metamorphic terrains typically has attained an overall degree of structural order that is in line with peak metamorphic temperature on a micron to nano scale however carbonaceous material can display strong structural variation the main factor that drives this variation is the chemical and molecular heterogeneity of the precursor biologic material specific conditions during metamorphism however can also play a role in shaping the microstructure of carbonaceous material here we describe the structural variation of carbonaceous material in rocks of the 2 0 ga zaonega formation karelia russia raman spectroscopy indicates that bulk carbonaceous matter in these rocks has experienced peak temperatures between 350 and 400 c consistent with greenschist facies metamorphism on a nano scale however a strong structural heterogeneity is observed transmission electron microscopy tem reveals the occurrence of thin films of highly ordered graphitic carbon at mineral surfaces these graphite films consisting of 20 100 individual layers completely envelop quartz crystals and occur on specific crystal surfaces of chlorite it is proposed that minerals can act as templates for the parallel ordering of carbon crystallites causing enhanced graphitization within narrow zones at mineral surfaces alternatively oriented organic precursor molecules could have been adsorbed onto charged mineral surfaces leading to thin graphitic films during later metamorphic heating episodes overall the presented observations demonstrate that mineral surfaces can initiate and accelerate localized graphitization of sedimentary organic material during metamorphism and therefore cause distinct nano scale variation in structural order

thermal metamorphism in the lesser himalaya of nepal determined from raman spectroscopy of carbonaceous material the determination of metamorphic conditions is critical to the understanding of the formation of mountain belts however all collisional mountain belts contain large volumes of accreted sediments generally lacking metamorphic index minerals and are therefore not amenable to conventional petrologic investigations by contrast these units are often rich in carbonaceous material making it possible to determine thermal metamorphism through raman spectroscopy of carbonaceous material rscm method a technique that has been recently calibrated beyssac et al j metamorph geol 20 2002 859 871 the lesser himalaya lh is one of these problematic cases with a very poor mineralogy but a key structural position within the himalayan system that makes lh considered as diagnostic of the overall thermal behaviour of the orogen this work demonstrates the performance of the rscm technique and shows that this technique might thus be used to detect inter sample variations as small as 10 15 c but absolute temperatures can only be determined to 50 c due to the uncertainty on the calibration this study reveals that the lh has undergone a large scale thermal metamorphism with temperature decreasing progressively from about 540 c at the top to less than 330 c within the deepest exhumed structural levels

investigation of organo carbonate associations in carbonaceous chondrites by raman spectroscopy abstract carbonates record information regarding the timing nature and conditions of the fluids circulating through asteroid parent bodies during aqueous alteration events determining carbonate abundances and their relationships with organic matter improves our understanding of the genesis of major carbonaceous components in chondritic materials in this study five cm2 carbonaceous chondrites cm2 2 nogoya cm2 3 jbilet winselwan cm2 5 murchison cm2 santa cruz and cm2tii wisconsin range 91600 were studied with raman spectroscopy carbonates were identified in these meteorite samples by the distinctive raman band in the 1100 cm 1 region representing the symmetric stretching vibration mode 1 of the co 3 2 anion carbonates identified in the meteorite samples are all calcite with the exception of a single dolomite grain in nogoya the v 1 positions of the cm calcites are 2 3 cm 1 higher than in pure calcite which suggests that they contain significant impurity cations typical graphitic first order d and g bands were identified in the meteorite matrix as well as in 25 of the analyzed carbonate grains from the raman results we postulate that the carbonates might not have formed under equilibrium conditions from a single fluid the first generation of carbonate is interpreted to have formed from highly oxidized fluids that led to the oxidation of organic matter om and produced carbonates that are om barren the second generation of carbonate was formed from a more evolved aqueous fluid with the presence of om the raman parameters of the organics in carbonates clearly deviate from the matrix om which suggests that the carbonate organics contain very different carbonaceous components that are distinct from the typical amorphous om of the cm matrix the occurrence of different generations of carbonate in close proximity may be partly responsible for the wide range in estimated ages of carbonates in carbonaceous chondrites reported in previous studies

strain induced amorphization of graphite in fault zones of the hidaka metamorphic belt hokkaido japan abstract we report here on two distinct processes of deformation affecting graphite in fault zones of the hidaka metamorphic belt hokkaido japan one process involves the micrometer scale delamination mmd in the stacking of graphite and the other is the nanometer scale delamination nmd in the stacking plus pulverization p of carbon sheets to less than 10 nm graphite in mylonites mainly glide along the 002 planes and they exhibit layer separation kink banding and bending structures produced by mmd processes whereas nmd p processes induce a significant size reduction and amorphization of the graphitic structures in cataclasites ultracataclasites and pseudotachylytes the strain induced amorphization of graphite as inferred from xrd and micro raman spectroscopy corresponds well with nano to micro scale deformation structures observed under the hrtem suggesting a systematic increase of edge planes by interlayer delamination and pulverization of carbon sheets in addition the carbon isotopic compositions of the graphite in fault rocks have negative 13 c signatures indicating a sedimentary organic origin such graphite has a tendency to accumulate within the shear bands our data suggest that the graphitic structures record information on both the peak metamorphic temperatures and the deformation processes and they show the progressive amorphization with increasing brittle deformation

raman micro spectroscopy on diamond graphite and other carbon polymorphs from the ultrahigh pressure metamorphic kimi complex of the rhodope metamorphic province ne greece raman micro spectroscopy was applied on carbon inclusions in garnet porphyroblasts from kyanite biotite garnet schists of the rhodope metamorphic province rmp ne greece diamond and cuboids of poorly to highly ordered graphite were identified either as single phase inclusions or as polyphase inclusions along with co2 and or carbonates calcite magnesian calcite questionable raman bands that may be assigned to other c phases nanodiamond lonsdaleite a different c polymorph have been observed the presence of diamond confirms beyond any doubt the ultrahigh pressure uhp metamorphism reported by mposkos and kostopoulos 1 e mposkos d kostopoulos diamond former coesite and supersilisic garnet in metasedimentary rocks from the greek rhodope a new ultrahigh pressure metamorphic province established earth planet sci lett 192 2001 497 506 in the rmp cuboid graphite showing variable degree of disordering most probably formed after diamond the possible involvement of co2 and or c o h fluids in the formation of diamond is discussed

raman spectroscopic study of polysulfanes h2s in natural fluid inclusions abstract sulfur bearing methane inclusions with up to 68 mol h2s in metamorphic quartzite from bastar craton india exhibit common 1 vibration modes of h2s and ch4 at 2609 cm 1 and 2919 cm 1 respectively associated with unknown raman bands at 2488 2503 2574 and 2899 cm 1 the fluid inclusions generate molecular hydrogen and surplus sulfur during irradiation with a 532 nm 25 mw laser thus indicating photolytic breakdown of polysulfanes h2sn quantum chemistry modeling based on the density functional theory was conducted to better understand the origin of the unusual raman bands in the sh stretching region vibrations of simple h2s h2s2 h2s3 h2s4 h2s5 s6 8 molecules were simulated together with selected complexes of n 1 4 polysulfanes with the crown shaped orthorhombic cycloocta sulfur identified in the fluid inclusions according to intense raman bands at 60 62 79 80 149 151 218 220 441 442 and 472 474 cm 1 theoretical calculations confirmed that the vibrations at 2488 2503 and 2574 cm 1 reflect symmetric and asymmetric h bonded and non h bonded h2s2 s8 h2s2 h2s2 s8 and h2s s8 h2s complexes in the crystallized sulfur melt a small band at 2899 cm 1 is tentatively attributed to ch3 s8 and or ch2 s8 bonds which also diminished during irradiation with green laser phantom bands occasionally occurring at 2580 cm 1 were identified as artificial bands resulting from an imprecise angle of incidence of laser beam to rotatable holographic grating another small 2579 1 cm 1 band in raman spectra recorded using longer acquisition times represents a combination band of host quartz rather than the a12 4 resonant vibration of ch4 located at the same frequency

rscm thermometry in the alpi apuane nw tuscany italy new constraints for the metamorphic and tectonic history of the inner northern apennines abstract in this study raman spectroscopy on carbonaceous material rscm is applied for the first time in the northern apennines with particular focus on the alpi apuane nw tuscany italy and surrounding areas in order to constrain peak metamorphic temperatures and their variability in the different continent derived units of the nappe stack peak temperatures in the range of 530 320 c were found in the alpi apuane whereas in the nearby metamorphic core of the monte pisano and punta bianca lower peak temperatures of 305 315 c and 350 c were found respectively the tuscan nappe in la spezia area west of alpi apuane shows temperatures in the range of 295 246 c whereas the same unit in the lima valley east of the alpi apuane shows temperatures lower than 230 c the collected data allowed refining the thermal architecture of the belt and the relationships between deformation early and late folds and low angle normal detachments and the metamorphic architecture of the alpi apuane core these results provide new contraints for the thermo mechanical evolution and exhumation history of the inner northern apennine and its geodynamic setting in particular our data support the interpretation of the alpi apuane as a cold metamorphic core complex in which the preserved paleothermal structure and part of the exhumation are related with crustal thickening while the final exhumation stages depth 15 km and at ambient crustal temperature 350 c are associated with crustal thinning still ongoing in the area

microstructure of graptolite periderm in silurian gas shales of northern poland abstract core samples of silurian graptolite shales from an exploration borehole within the baltic basin were examined by optical microscopy raman spectroscopy and high resolution transmission electron microscopy graptolite periderm is composed of poorly ordered carbonaceous material of mainly aromatic structures the dimension of the coherent domains is 1 2 nm they are composed of two to three stacked layers raman spectral parameters of graptolite periderm are correlated with the mean random rr and mean maximum rmax reflectance of graptolites the spectral id1 ig ratio predicts thermal maturity in a mean reflectance of graptolites rr range between 1 30 and 1 80 rmax 1 40 2 00 vitrinite reflectance equivalent vre 1 10 1 50 it is possible to calculate vreraman from the id1 ig ratio

the nappe des marbres unit of the basque cantabrian basin the tectono thermal evolution of a fossil hyperextended rift basin the architecture of the pyrenean cantabrian belt results from the inversion of a series of former cretaceous rift basins a ht lp metamorphic event dated at 105 to 85 ma ago is commonly associated with an albo cenomanian episode of hyperextension of the continental crust this metamorphism is well known in the eastern basque cantabrian basin within the nappe des marbres unit nmu that is preserved from intense compressional deformation during the pyrenean orogeny based on a structural study at the scale of the eastern basque cantabrian basin bcb and on a dense sampling for trscm estimates with the rscm method raman spectrometry on carbonaceous material we show following results 1 the nmu has recorded two major phases of deformation related to a localized extensional ductile foliation s1 during the cretaceous rifting and later by the regional n s shortening recorded by a regional cleavage s2 observed only in shale sediments 2 the nmu is affected by early salt tectonics related to several diapirs and salt walls fed by the upper triassic evaporitic layer 3 the nmu recorded maximum temperatures exceeding 550 c which represent some of the highest temperatures along the pyrenees these new data demonstrate that there is no e w lateral metamorphic gradient across the belt and that hyperextension rifting occurred consistently within a high thermal regime 4 metamorphic isograds are oblique in respect of the main structures suggesting that the metamorphic event postdates most of the early salt related deformations prior to or coeval with early stages of rifting as it represents one of the best preserved example of pre orogenic hyperextended basin the eastern bcb record may be used regionally to better understand the rift to orogen evolution of the pyrenean internal metamorphic zone but also more generally as an analog of salt bearing hyper extended rift record

evaluating raman spectra of carbonaceous matter by automated iterative curve fitting abstract raman spectroscopy of carbonaceous material rscm estimates the maximum metamorphic temperature of coal graphite and cm enclosed in metapelites however the evaluation of cm raman spectra is often biased by subjectivity which reduces the overall comparability of rscm results to decrease subjectivity an automated evaluation software is presented it is based on the iterative and simultaneous modeling of signal and baseline functions two new rscm parameters are introduced termed raman area ratio rar and scaled total area sta these parameters are tested on a sample suite of organic rich shales and slates of the teuschnitz syncline thuringia germany of well constrained very low to low metamorphic grade defined by illite crystallinty and vitrinite reflectance a correlation of both rscm parameters with vitrinite reflectance verifies that the rscm parameters reflect the metamorphic conditions this correlation prevails at different excitation wavelengths 488 nm 633 nm 785 nm used for the raman measurements

relationship between structure morphology and carbon isotopic composition of graphite in marbles implications for calcite graphite carbon isotope thermometry carbon isotope exchange between calcite and graphite is a useful and reliable geothermometer for medium to high grade marbles however in rare instances such as at naxos greece apparent disequilibrium carbon isotope fractionation between calcite and graphite has been previously reported in this study new results are presented on the morphological features x ray diffraction studies raman spectroscopic studies and carbon isotope studies of graphite three morphologically distinct graphite types are identified the first type is fine grained with distinct polygonal crystal aggregates having smooth pinacoid faces the second type consists of large botryoidal aggregates with typical crystal overgrowth features and the third type is normal large platy crystals associated with phlogopite graphite morphological features using an fe sem suggests that the botryoidal aggregates are composed of complexly intergrown and stacked graphite layers comprised of cone helix structures different types of graphite display distinct lc 002 and dg values as well as a sharp first order raman peak at 1580 cm 1 with disordered bands the presence of raman disordered bands in fine grained well crystallized graphite is attributed to edge effects carbon isotope analysis of graphite reveals that marble with fine grained well crystallized graphite show a consistent isotope fractionation with the calcite which perfectly match temperature estimates based on the mineral isograds in contrast coarse botryoidal graphite gives heterogeneous carbon isotope values about a few per mill and show anomalous carbon isotope fractionation between the calcite and graphite the graphite associated with phlogopite also shows variations in the carbon isotope values combining morphologic crystallographic and carbon isotopic data we conclude that the variations in carbon isotopic composition were caused by the overgrowth of graphite on the preexisting grain and that morphological observations and structural characterizations of graphite crystals is a key for predicting isotopic equilibration during metamorphism

carbonaceous material in the ryoke metamorphic rocks kinki district japan abstract carbonaceous material in the ryoke pelitic metamorphic rocks in the wazuka area kinki district japan has been studied by x ray diffraction xrd analysis detrital graphite in the lower grade rocks is recognized in both x ray diffractograms and transmission electron micrographs progressive graphitization is considered to have proceeded continuously on the basis of the xrd data of the bulk concentrates of carbonaceous material and a conspicuous asymmetric shape of xrd peaks in lower grade samples is ascribed to the mixture of carbonaceous materials with different crystallinities fully ordered graphite does not occur until the highest grade part of the chlorite biotite zone the variation of degree of crystallinity of carbonaceous materials inferred from xrd data is consistent with the prograde mineral zones the temperatures for the development of fully ordered graphite are estimated to be between 410 and 440 c in regional metamorphism through comparing the xrd data from low medium and high pressure types of metamorphic terrains