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

the summit erosion surfaces of the inner betic cordillera their value as tools for reconstructing the chronology of topographic growth in southern spain erosion surfaces at the top of mountain ranges have suggested to geomorphologists that the earth s crust can undergo rapid pulses of uplift during which rates of denudation fail to balance with rates of crustal uplift thereby preserving much of the initial plateau topography as it rises to greater elevations here we analyze a regionally extensive population of mappable planar surfaces which crown several major tectonically active sierras of the inner south eastern betic cordillera se spain based on a synthesis of long term landscape evolution involving landform reconnaissance dem based morphometric analysis structural geology sediment provenance analysis and field stratigraphy we conclude that the summit surfaces are a mosaic of discrete post orogenic erosion surfaces that each developed in relation to mediterranean marine base levels at a time when the sierras formed a series of low elevation islands they are not therefore fragments of a once regionally continuous paleoplain the summit surfaces were partly the result of shallow angle detachment faulting during the middle miocene in response to lithospheric slab detachment where evidence exists that the resulting low relief topography was reworked by marine abrasion during the tortonian sea level rise the terminal age of the surfaces is latest miocene age bracketing based on stratigraphic correlations among the many depocentres of the region and on published thermochronological data indicates that some erosion surfaces locally formed in less than 3 million years 8 ma 5 7 ma they were subsequently uplifted to their current elevations 1 7 to 2 km by pliocene to quaternary neotectonics in at least two major pulses

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

pre eruptive crystallization conditions of mafic and silicic magmas at the plat pays volcanic complex dominica lesser antilles andesitic to dacitic magmas of the plat pays volcanic complex dominica lesser antilles that erupted during the last not vert similar100 ka equilibrated at temperatures of 800 880 c and total pressures of 1 1 2 3 kbar magmatic conditions were moderately oxidizing fo2 not vert similar1 5 0 3 log units above fmq and estimated melt water contents vary from 5 2 to 6 5 wt the crystal rich nature of the samples the relatively narrow bulk rock compositional range and the similarity of the intensive crystallization parameters throughout the sample suite are consistent with the presence of a long lived highly crystallized magma reservoir further crystallization during ascent produced highly evolved rhyolitic glass compositions the silicic magma reservoir was occasionally invaded by more mafic melts of basaltic andesitic to basaltic composition these were rarely erupted but they mixed with the silicic magmas and were frequently incorporated as mafic enclaves the mafic magmas record temperatures of not vert similar1060 c at fo2 1 6 2 0 log units above fmq the similarities in mineralogy petrology and inferred magma storage conditions of the plat pays volcanic complex with the soufriere hills volcano montserrat and montagne pelee martinique can serve as a useful guide for forecasting and evaluation of possible future eruptions

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

magma mixing in alkaline series an example from sancy volcano mont dore massif central france three magmatic units grande cascade pyroclastic deposits grande cascade lava flow durbise nuee ardente deposits from the quaternary volcano sancy mont dore area auvergne france show textural evidences of magma mixing between a silica undersaturated basic magma alkali basalt and hawaiite and an acid magma quartz bearing trachyte three kinds of mixed rock types are described basic inclusions within an acid host emulsified rocks showing infracentimetric basic globules disseminated within an acid groundmass and banded rocks in which elongated acid and basic zones alternate the chemical compositions of mixed rocks plot systematically onto linear trends in petrographic diagrams microprobe analyses of the groundmass show similar linear variations between basic and acid end members the mineralogical associations of these mixed rocks are highly complex and present many disequilibrium features olivine is stable in the basic component and becomes rimmed by orthopyroxene in the acid one zoning patterns of feldspars are complex clinopyroxene kaersutite and phlogopite phenocrysts have increasing component mg contents from core to rim both in the basic and the acid titanomagnetite and hemoilmenite phenocrysts were equilibrated at 900 800 c under high oxygen fugacities mixing results primarily from a mechanical disintegration of partly liquid basic inclusions within their acid host and also from a mechanical transfer of phenocrysts from one component to the other in which they often remain surrounded by a coating of their original groundmass chemical data on the groundmass indicates that some true hybridization between coexisting acid and basic liquids may also have occurred the extent of mixing is controlled by the type of emplacement for pyroclastic deposits a chemical gap exists between basic inclusions and their acid hosts in contrast mechanical mixing was enhanced during the emplacement of the viscous grande cascade lava flow and complete transitions occur between basic and acid components the two end members are genetically associated the latter deriving from the former by crystal fractionation mixing appears as a late stage phenomenon in the petrogenetic history of the mont dore series in the case of the grande cascade lava flow its extent is primarily dependent on emplacement modalities

microcrystalline textures resulting from rapid crystallization in a pseudotachylite melt in a meta anorthosite the very fine grained 1 m polygonal microcrystalline texture occurring in the groundmass of pseudotachylite veins in the harris meta anorthosite and its variation with position are described and an origin by crystallization from a melt at very large undercooling suggested the intrusive nature of the veins is shown by their geometry and internal structures clasts which are almost always only plagioclase are generally concentrated towards the centres of veins flow of tens of millimetres can account for this concentration in millimetre thick veins as a result of the bagnold effect the veins are generally thin 5 m to 5 mm or more are frequently zoned and always contain transparent granules of high relief probably al rich pyroxene and opaque granules of magnetite up to a few micrometres in size the granules are either uniformly distributed in microcrystalline textures or concentrated locally giving cellular textures in some veins spherulitic or bow tie textures occur the coarsest textures are found in the centres of the thickest veins the groundmass of the pseudotachylite is never completely isotropic but consists of a mosaic of transparent plagioclase crystals decreasing in size from the centres of thick veins to less than 1 m in thin veins or in the margins of thicker veins this fine microcrystalline texture was studied by both scanning and transmission electron microscopy and consists of polyhedral crystals of regular size in the range 0 2 1 5 m which show little sign of deformation the local composition of the pseudotachylites varies little from the average compositions of the rocks in optically homogeneous veins the variation being within the compositional space defined by the minerals of the host rock this shows that homogenization of the pseudotachylite has occurred in cellular veinsdifferentiation has occurred as the compositions of the cell centres lie outside those of the minerals of the host rock this was produced by segregation of the granules pyroxene being absent from the host rock the plagioclase in the pseudotachylite is more disordered than that in the host rock all the microtextures described are absent from the associated cataclasites and cannot be due to recrystallization of a fine grained and intensely strained rock powder the physical state on and after intrusion was that of a melt and injection was followed by crystallization the melt was produced by more or less total fusion of the host rock minerals at shallow depth by heat produced during local faulting and perhaps during crack propagation the fine microcrystalline texture very closely resembles that produced during hypercooling of molten metals and alloys it thus possibly formed not by devitrification but from a melt at much greater degrees of undercooling than the spherulitic and bow tie textures

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

petrogenesis of contrasting hercynian granitoids from the calabrian arc southern italy abstract the granitoids of the southern calabrian arc have been investigated for whole rock and phase chemistry zircon typology ree sr and nd isotopes two distinct granitoid associations which are related in time and partly in space are present a calc alkaline one and a peraluminous one the prevailing calc alkaline association is compositionally expanded sio2 48 70 and biotite dominated with tonalites and granodiorites as predominant rock types the peraluminous association is compositionally restricted sio2 67 76 and contains two mica al silicates distinct peraluminous typologies occur also as core facies within the calc alkaline types all granitoids are ilmenite bearing the cittanova cn villa s giovanni vsg and capo rasocolmo cr peraluminous granites display zircon typology ree patterns srt 51 to 113 and ndt values 8 5 to 4 6 at 290 ma suggesting a dominantly quartzofeldspathic metasedimentary source in more detail the cn types and the cr vsg types require heterogeneous and different sources the calc alkaline granitoids display very variable ree patterns cen 25 227 and ybn 3 5 18 5 in the tonalites granodiorites and variable age corrected ndt values 8 5 to 0 25 whereas sr values vary little 82 to 93 thus in terms of ndt srt covariation the data points define a vertical array which is inconsistent with a model involving crustal contamination by mantle derivatives a more viable mechanism seems to be the melting of hydrous and heterogeneous mafic lower crust and or basic underplate producing distinct magma batches evolving independently crustal contamination mingling and fractionation processes may all have contributed to the observed geochemical variations within the granitoids the peraluminous granodiorites occurring within the serre and capo vaticano multipulse calc alkaline plutons exhibit isotopic ratios ndt 6 11 to 0 33 and srt 93 to 97 which are similar to those of the calc alkaline host rocks suggesting a possible genetic link geologic and geochemical data indicate a continental collision setting for this plutonic activity the magmas were produced during late thickening to exhumation phases following collision and moderate crustal overthickening and were emplaced subsequently during a short time span a mantle contribution should have favoured melting which affected various sectors of the continental crust

role of large flank collapse events on magma evolution of volcanoes insights from the lesser antilles arc flank collapse events are now recognized as common processes of destruction of volcanoes they may occur several times on a volcanic edifice pulling out varying volumes of material from km3 to thousands of km3 in the lesser antilles arc a large number of flank collapse events were identified here we show that some of the largest events are correlated to significant variations in erupted magma compositions and eruptive styles on montagne pelee martinique magma production rate has been sustained during several thousand years following a 32 ka old flank collapse event basic and dense magmas were emitted through open vent eruptions that generated abundant scoria flows while significantly more acidic magmas were produced before the flank collapse the rapid building of a new cone increased the load on magma bodies at depth and the density threshold magma production rate decreased and composition of the erupted products changed to more acidic compared to the preceding period of activity these low density magma generated plinian and dome forming eruptions up to the present in contrast at soufriere volcanic centre of st lucia and at pitons du carbet in martinique the flank collapses have an opposite effect in both cases the acidic magmas erupted immediately after the flank collapses these magmas are highly porphyritic up to 60 phenocrysts and much more viscous than the magmas erupted before the flank collapses they have been generally emplaced as voluminous and uptight lava domes called the pitons such magmas could not ascent without a significant decrease of the threshold effect produced by the volcanic edifice loading before the flank collapse

magmatology of mt pelee martinique f w i i magma mixing and triggering of the 1902 and 1929 pelean nuees ardentes abstract at mt pelee martinique f w i the 1902 and 1929 nuees ardentes occurred before the final emplacement of the dome at an early phase during the eruption the first 1902 nuees ardentes on may 8 and may 20 were also the most destructive corresponding products present heterogeneous textures with the occurrence of mafic enclaves banded and emulsified lavas the terminal dome is andesitic and texturally homogeneous these features are compatible with 1 co eruption of two contrasted magmas basalt and dacite 2 interaction between the two magmas which led to intermediate andesitic compositions 3 a predominantly mechanical magma mixing process the evolution of which could be observed during the eruption a similar evolution appeared in the 1929 sequence mineralogical evidence depends essentially on phenocryst transfers between basaltic and dacitic magmas and their paragenetic implications frequent disequilibrium features wide compositional ranges polymodal distribution of plagioclase and strong zoning of phenocrysts all these features occur in the mingled hybrids as well as in blended mixtures the chemical compositions of the juvenile magma of nuees ardentes range from basalt or basaltic andesite mafic enclaves to dacite clear host lavas with all intermediate and predominant andesite composition the terminal dome is andesitic and from major and trace element data it is interpreted as the result of a basalt dacite mixing nevertheless a fractional crystallization process is necessary to generate the acid component from the basic one we suggest a model comprising a double magma chamber with a shallow reservoir dacitic in composition and a deep reservoir where the mafic magma is stored the rising mafic magma intersects the superficial chamber inducing magma mixing and rapidly triggering an explosive pelean eruption the early eruptive activity associated with a deep seated mafic injection intersecting a differentiated shallow chamber immediately reaches a climax we emphasize the necessity for quick detection of such a rising mafic magma since the superficial chamber has a relatively short time lag before an explosive and dangerous eruption

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

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

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

cummingtonite and the evolution of the mount st helens washington magma system an experimental study hydrothermal experiments have been conducted on the 3 5 ka cummingtonite bearing yn tephra from mount st helens washington to determine the stability field of cummingtonite in volcanic rocks and to gather additional data on the evolutionary history of the mount st helens magmatic system cummingtonite is not stable in experiments conducted at or above 810 c at pressures 2 o analyses of melt inclusions that yield preeruption melt h 2 o contents of 6 4 wt the yn tephra belongs to a series of cummingtonite bearing dacites that erupted early in the history of mount st helens these early dacites have relatively homogeneous compositions and are characterized by low temperature 800 c high water pressure and high oxygen fugacity nno 1 phenocryst crystallization silicic magmas that erupted after eruption of basaltic andesite at mount st helens 2 3 ka are more heterogeneous in composition and last equilibrated under higher temperatures 900 c lower water pressures and lower oxygen fugacities than the early dacites these changes in the magma chamber conditions appear to have been related to the intrusion of mafic magma into an upper crustal dacitic magma chamber

high silica rhyolites of niijima volcano in the northern izu bonin arc japan petrological and geochemical constraints on magma generation and supply abstract niijima volcano in the northern part of the quaternary izu bonin volcanic arc japan consists predominantly of rhyolitic volcanic units associated with minor basaltic and andesitic units most of the rhyolites are characterized by a phenocryst assemblage of orthopyroxene opx cummingtonite cum biotite bt and hornblende which are classified into four types opx cum cum cum bt and bt in eruption order the major element compositions of the rhyolites are typified by high sio2 73 78 wt and k2o 1 5 3 3 wt contents and the trace elements are indicative of a highly differentiated nature which differs significantly from rhyolites at other sites in the izu bonin arc the presence of cummingtonite phenocrysts and mineralogical and whole rock chemical compositions of the rhyolite lavas clearly indicate that these magmas were produced under low temperatures 13 units in a shallow magma system at the same time and at deeper levels basaltic and rhyolitic parental magmas mixed to produce andesitic magmas between the basaltic and rhyolitic parental magmas in some cases basaltic and andesitic magmas in deeper level ascended and mingled with shallow rhyolitic magmas before eruption the eruption of rhyolitic magmas from shallow levels might have been triggered by the injection of basaltic and andesitic magmas from deeper levels the complex magmatic system beneath niijima volcano formed within a relatively thick crustal sequence on the rear arc side of the izu bonin volcanic arc

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

geothermometry and geobarometry of a cummingtonite bearing dacite from martinique lesser antilles a dacite sample from a nuee ardente deposit at pitons du carbet martinique contained cummingtonite orthopyroxene quartz magnetite and ilmenite as phenocrysts and thus was suitable for evaluation of the t f text o text 2 p text total p text h text 2 text o conditions of crystallization of nuee ardente materials according to the method of ewart et al 1971 the estimations were obtained with the aid of a fortran iv program which permitted the operation of all the arrangements between the available microprobe analyses the results indicated that the phenocrystic association crystallized at moderate temperatures ca 750 c under high oxygen fugacities nno and total pressures 2 3 4 5 kb with a maximal density of points at about 3 5 kb and water pressures approximating total pressures the groundmass fe ti oxides equilibrated at lower temperatures and under relatively increasing oxygen fugacities the variation of which is tentatively ascribed to the aerial emplacement of the nuee ardente materials the phenocryst data imply that in the case studied the high fluid pressures characterizing the nuee ardente eruptions were not acquired at a shallow level because of the deep intratelluric stage of crystallization of these differentiated calcalkalic magmas

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

oligocene shoshonitic rocks of the rogozna mts central balkan peninsula evidence of petrogenetic links to the formation of pb zn ag ore deposits article this study focuses on age and evolution of the oligocene quartz latite of the rogozna mts central balkan peninsula in order to better understand the link between magmatism and formation of pb zn ag min eralization new 40 ar 39 ar biotite and amphibole plateau ages sugg est that the rogozna mts quartz latite originated through a continuous volcanic episode from 27 3 0 1 to 29 5 0 1 ma which was immediate ly followed by a hydrothermal phase the quartz latites are hypocrystalline porphyritic with phenocrysts and microphenocrysts 60 vol of plagioclase an37 49 biotite mg 100 mg mg fetot b 50 cal cic amphibole quartz sanidine clinopyroxene and phlogopite mg 79 to 84 the rocks display nu merous disequilibrium textures such as sieved plagioclase phenocrysts dissolution effects on quartz phlogopitized biotite and amphibole crystals and phlogopite microphenocrysts showing effects of incomplete growth or dissolution and biotitization the rogozna mts quartz latites are shoshonitic in character with na2o k2ob 1 high lile hfse ratios strong depletions at nb and ti and k pb and u peaks on primitive mantle normalized diagrams they are similar to other potassic ultrapotassic rocks in this region in particular to those of veliki majdan and rudnik west serbia which are also related to pb zn deposits the evolution of the rogozna mts quartz latite is modeled using a trace element bina ry mixing model adopting a lamproite magma and a dacite like calc alkaline melt as end members the model implies that a fractionating magma chamber 4 5 9 5 km undergoes cooling in the range of 850 c 720 c and injection of lamproite like melts the injection causes an increase of temperature and a decrease of viscosity of the resulting hybrid magma facilitating its upwelling and triggering pyro clastic eruptions the addition of new volatiles by lamproitic melts most probably established the condi tions for a hydrothermal phase above the magma chamber that was previously degassed explosively this implies that magma mixing processes can be of great importance for the formation of pb zn deposits similar processes are likely to have occurred in other areas with economically significant pb zn ag other metal mineralization in the region of the central balkan peninsula veliki majdan rudnik golija kopaonik avala etc

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

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

petrology of basaltic xenoliths in andesitic to dacitic host lavas from martinique lesser antilles evidence for magma mixing some recent calc alkaline andesites and dacites from southern and central martinique contain basic xenoliths belonging to two main petrographic types the most frequent one has a hyalodoleritic texture h type with hornblende plagioclase fe ti oxides set in an abundant glassy and vacuolar groundmass the other one exhibits a typical porphyritic basaltic texture b type and mineralogy olivine plagioclase orthopyroxene clinopyroxene fe ti oxides and scarce or absent hornblende

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