timing of arc construction and metamorphism in the slate creek complex northern sierra nevada california late paleozoic to early mesozoic rocks in the sierra nevada and klamath mountains western united states preserve a record of lateral growth of continental crust by incorporation of ophiolites volcanic arcs and associated sedimentary rocks deciphering the timing of arc construction and metamorphism is critical for elucidating tectonic and thermal evolution during this type of crustal growth but is difficult in complex accretionary terranes in this study we address the timing of arc construction and regional metamorphism in the slate creek complex a volcano plutonic terrane in the central part of the northern sierra nevada new 40 ar 39 ar ages from relict volcanic hornblende demonstrate that the youngest volcanic unit in the slate creek complex is ca 170 ma at least 30 m y younger than previous estimates of ca 200 ma for metaplutonic rocks in the lower part of the complex consequently the slate creek complex is polygenetic with two distinct episodes of arc magmatism the distribution of mineral assemblages and textures indicates that greenschist and epidote amphibolite facies metamorphism is younger than 170 ma and is associated with crosscutting plutons that yield cooling ages of 150 ma and younger amphiboles from foliated rocks in the slate creek complex yield plateau ages of 156 1 0 6 and 152 0 0 7 ma that date cooling subsequent to or dynamic recrystallization during the metamorphic event age and lithologic similarities suggest that the lower parts of the slate creek complex correlate with plutons ca 200 ma and the volcanic cover sequence of the rattlesnake creek terrane in the klamath mountains the uppermost volcanic unit correlates with the ca 170 ma western hayfork terrane that structurally overlies the rattlesnake creek terrane metamorphism in the slate creek complex correlates broadly with a similar late metamorphic event in the klamath mountains

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

low grade metamorphism of mafic rocks through most of this past century metamorphic petrologists in the united states have paid their greatest attention to high grade rocks especially those which constitute the core zones of exhumed mountain belts the pioneering studies of the 50 s through the 80 s those which applied the principles of thermodynamics to metamorphic rocks focused almost exclusively on high temperature systems for which equilibrium processes could be demonstrated by the 1980 s metamorphic petrologists had developed the methodologies for deciphering the thermal and baric histories of mountain belts through the study of high grade rocks of course low grade metamorphic rocks here defined as those which form at pressures and temperatures up to and including the greenschist facies had been well known and described as well initially through the efforts of alpine and circum pacific geologists who recognized that they constituted an integral and contiguous portion of mountain belts and that they underlay large portions of accreted terranes many of oceanic origins but until the mid 80 s much of the effort in studying low grade rocks for a comprehensive review of the literature to that point see frey 1987 had been concentrated on mudstones volcanoclastic rocks and associated lithologies common to continental mountain belts and arcs in the mid 80 s results of the deep sea drilling project dsdp rather dramatically mitigated a shift in the study of low grade metamorphic rocks

macro and micro factors affecting coal seam quality and distribution in southern africa with particular reference to the no 2 seam witbank coalfield south africa abstract petrographical and palynological coal quality investigations relating to variations in one of the best known and well researched coalfields in africa the witbank coalfield and one of the most commercially important seams within this coalfield the no 2 seam are highlighted in this paper the investigations were based on 14 channel samples covering a 40 20 km 2 area in the witbank coalfield the results indicate that the coals in the no 2 seam were formed at the stage of major change over from dwyka to ecca floras as illustrated by the progressive dying out of dwyka pollens and spores and the introduction of ecca floral elements this also suggests a rapid amelioration of climate over the period of peat accumulation following a period of continental glaciation furthermore it is proposed that the in seam horizons reflect fluctuating of cyclic environments probably due to changing water level and plant communities due to changing growth environments saccate pollens appear to occur in association with vitrinite rich microlithotypes trilete spores with inertodetrite and carbominerite rich microlithotypes and plicates with inertite semifusite inertodetrite microlithotypes acritarchs nonspinose are present in parts of the seam where inertodetrite is common and in association with unusual suites of trace and major elements possibly indicating changing geochemical environments in high groundwater conditions petrographic results indicate that the coals are medium rank hypobituminous and show wide variations in maceral mineral and microlithotype compositions both vertically and laterally on the basis of microlithotype and mineral group analyses investigations were undertaken to establish vertical subdivisions by the study of historical patterns and possible lateral correlations of these subdivisions in the area under investigation these methods were then compared with distribution of selected chemical and geochemical parameters the evidence suggests that a common sequence of major events and some minor events occurred during the accumulation of the no 2 seam as manifested by petrographic and palynological facies three major periods or zones are recognized these tepresent periods of relatively stability quiescence separated by major in seam disruptive events namely flood deposits bearing high proportions of detrital organic material or minor clastic sedimentation these zones are subdivided into several subzones representing periods of reworking local flooding or rise in ground water levels and or changing geochemical environments these events can be recognized throughout the area under investigation but the manifestation of these events varies from area to area depending upon topographic situation proximity to river channels valley flanks or palaeoshorelines degree of subsidence and compaction geochemical environment and length of time under a specific set of conditions thus channels in close proximity to one another or in similar positions relative to valley flanks or axes appear to be remarkably similar to one another direct correlation of stratigraphic zones and sub zones from sample site of sample site was therefore possible although the methods to achieve this are complex and require the support of several supplementary complementary interpretative techniques coal quality variations and distribution within the original seam are therefore explicable in terms of the detailed factors listed above

the smartville intrusive complex sierra nevada california the core of a rifted volcanic arc the smartville complex is a jurassic volcanic and plutonic arc in the northwestern sierra nevada that was deformed during the late jurassic nevadan orogeny we interpret the smartville intrusive complex to have formed during the incipient rifting of an active volcanic arc this interpretation is supported by the close relationship between volcanism and plutonism and by the close association between sheeted dikes and the younger plutonic rocks further support is found in the similarities that exist between the smartville complex and modern arcs that developed on oceanic crust either at a continental margin or in the ocean basins smartville volcanic rocks consist of a lower unit of tholeiitic submarine flows and pillowed flows that grades upward into an upper unit of calc alkaline pyroclastic and volcaniclastic deposits intrusive rocks include older units of metamorphosed gabbro and massive diabase which are intruded by a unit of 100 mafic and felsic sheeted and unsheeted dikes biotite hornblende tonalite and granophyric hornblende tonalite plutons are coeval with the dike complex and both rock types occur locally as dikes within the dike unit continuously and reversely zoned gabbro diorite plutons are also coeval with the dike complex granodiorite plutons are the youngest intrusive unit and may be related to the sierra nevada batholith relative age relations suggest that the smartville complex formed in a single volcanic plutonic system of pre nevadan age the dike complex intrudes and is intruded by both the tonalite and zoned gabbro diorite plutons both the upper and lower volcanic units are intruded by all of the plutonic and hypabyssal units and were deformed prior to the intrusion of the sheeted dike complex clasts of plutonic and hypabyssal rocks resembling the younger intrusives however occur locally in some of the youngest volcaniclastic rocks suggesting that shallow plutonism and volcanism could be broadly coeval early nevadan thrust faults juxtapose volcanic and older plutonic rocks of the smartville complex and mesozoic chert argillite broken formation to the east the younger plutons and the dike complex in the smartville are deformed by steep late nevadan faults and do not intrude chert argillite broken formation the youngest granodiorite plutons in the area truncate nevadan faults intrude the chert argillite formation and appear to be unrelated to the smartville complex the smartville volcanic arc underwent pre nevadan intra arc extension the sheeted dike complex is the primary manifestation of the rifting event the elongate shapes of the younger plutons which are coeval with the dike complex reflect extensional control on their emplacement volcanic rocks in the western and southern smartville complex were deformed prior to the intrusion of the dike complex

structure and tectonics of the northern sierra nevada recent detailed mapping suggests a new working hypothesis for the structure of the northern sierra nevada we propose that pre cretaceous rocks are deformed by a series of eastward directed over thrusts modified by west directed folds and faults the highest and westernmost tectonic unit is the jurassic smartville complex structurally below it there are imbricate thrust slices of jurassic and older ophiolitic and oceanic sedimentary rocks in the central belt and of paleozoic to jurassic sedimentary and volcanic rocks in the eastern belt the paleozoic feather river peridotite separates the eastern and central belts and our hypothesis suggests that both of its margins may be important thrust faults the east directed faults and folds are deformed by northwest trending upright and west vergent folds and reverse faults that control the present outcrop pattern these later structures have so modified the earlier east directed structures that the latter have been recognized only recently an important key to understanding the structure has been the recognition of ophiolitic complexes that can be correlated across major faults and that contain a pseudostratigraphy useful in determining local structures the events recorded by both the east and west directed deformations occurred during callovian through kimmeridgian time and represent the nevadan orogeny our hypothesis of early east directed overthrusts followed by west directed back folding and faulting implies shortening and thickening of the crust during the nevadan orogeny and is consistent with the idea that the northern sierra nevada is the result of a crustal collisional process

the pumpellyite actinolite and contiguous facies in part of the phyllite quartzite series central northern peloponnesus greece variations in assemblage and composition of the constituent minerals in basic and intermediate metavolcanics encountered in the zarouchla group of the phyllite quartzite series are consistent with a progressive sequence corresponding to temperature conditions estimated at 290 380 c minimum values under a total pressure greater than 3 5kbar and possibly as high as 5 kbar in the absence of more critical evidence the parageneses recorded in the metavolcanic rocks are interpreted as belonging to a prograde facies series from the lawsonite albitechlorite facies through the pumpellyite actinolite facies to the greenschist facies the present distribution of mineral assemblages does not show a simple increase of metamorphic grade in a given direction but is apparently related to the tectonic evolution of the metamorphic sequence

hypautochthonous allochthonous coal deposition in the permian south african witbank basin no 2 seam a combined approach using sedimentology coal petrology and palaeontology abstract a suite of techniques including coal petrology micropalynology mesofossil analysis and macroscopic appearance has been used to examine the early permian south african witbank basin no 2 seam from a sample locality near ogies this coal appears to be similar in its palynological and petrographic composition to other coals of this interval from this basin however its accumulation appears to have been largely hypautochthonous or allochthonous evidenced by erosive contacts small scale cross laminations and fine lenticular bodies being recognised within the coal seam profile this ex situ deposition probably in part relates to frequent wildfire activity which may have promoted subsequent run off and erosion and led to the numerous mineral rich horizons observed in the sample seam profile in addition to the sedimentological characters described above the petrology of the seam and its mesofossils most particularly megaspores from a lycopsid parent vegetation indicate saturated peat forming conditions however examination of charred mesofossil fragments indicates periods of low humidity and even drying of the peat itself rendering it liable to combustion these contradictory characters may indicate seasonality and suggest a coldness of the climate at least for part of the year that could account for the retardation of peat decay during these drier intervals these characters can be reconciled with deposition during an interglacial phase as the dwyka glaciation terminates as has previously been proposed for the witbank basin no 2 seam

kinematics of franciscan complex exhumation new insights from the geology of mount diablo california three major lithotectonic units of an ancient arc trench system are present in western california in ascending structural order they include the franciscan complex a remnant accretionary prism partly including high pressure blueschist facies metamorphic rocks in a subduction melange the relatively unmetamorphosed coast range ophiolite and the great valley group forearc sediments in the mount diablo study area east of san francisco the subduction complex and ophiolite are juxtaposed across the coast range fault and together they represent a structurally attenuated section through the ancestral forearc crust exposed by uplift and folding of the late cenozoic mount diablo anticline the coast range fault is locally associated with a sheared zone in the lower part of the attenuated ophiolite shear sense indicators in the serpentinite such as s c fabrics rotated clasts and slick enfibers record the deformation kinematics and consistently indicate that the ophiolite moved down in a normal sense relative to the franciscan rocks in the modern reference frame based on these kinematic relations and metamorphic facies contrasts between the franciscan and the coast range ophiolite as much as 6 18 km structural attenuation has occurred along the coast range fault after restoration of vertical axis rotation and late cenozoic fold deformation the coast range fault dips at a low angle toward the northeast and shear sense data restore to top to the northeast motion on the coast range fault implying normal displacement of the ophiolite with respect to the structurally underlying franciscan complex these relations are consistent with the hypothesis that the franciscan rocks were exhumed by crustal attenuation along a low angle fault system these data suggest that the coast range fault dominantly accommodated normal displacement and ductile thinning and that these processes were primarily responsible for the structural exhumation of high pressure assemblages in the franciscan complex relative to the structurally overlying forearc crust

the georges bank basin a quantitative basin analysis study using a one dimensional 1d fluid flow compaction model applied to wells of the georges bank basin east coast usa has enabled a simulation to be made of the history of the sedimentation basement subsidence tectonic activity geoheat flux evolution maturation of organic matter hydrocarbon generation and migration tendency based on the analysis of the basement tectonic activity the basin s development is related to the formation and the evolution of the east edge of the north american plate through the simulation of geoheat flux variation maturation of organic material and hydrocarbon generation at different positions in the basin at different time periods are analysed additionally from the modelling of excess fluid pressure porosity and permeability variations in the strata the potential hydrocarbon migration tendency and stratigraphic traps in the basin are discussed

distribution of selected trace elements in density fractionated waterberg coals from south africa abstract the waterberg coalfield located in the limpopo province north western area of south africa contains a significant proportion of the south african coal resource this permian coalfield typically contains high vitrinite high ash coals in the kungurian grootegeluk formation and high inertinite low ash coals in the artinskian vryheid formation four run of mine coals and density fractioned samples were analysed to determine their trace element content the concentrations of most trace elements in the run of mine coals exceed the global averages and certain global ranges and generally exceed values reported for other south african coalfields specifically hg concentrations are high to very high in all the coals up to 2 43 ppm in a sample from the vryheid formation cd and se concentrations are comparable to or lower than global averages and as is very low in the vryheid formation 1 57 ppm a sample from the grootegeluk formation is enriched in siderophile elements and a sample from the vryheid formation is depleted in chalcophile elements studies of the density fractionated samples indicate that cd exhibits an organic affinity in the grootegeluk formation samples and possibly a pyritic or sulphide affinity in the vryheid formation sample selenium has a greater affinity for the middle clay rich density fractions in all samples arsenic reports to the mineral rich sink fractions specifically the fractions enriched in pyrite mercury reports to both the float and sink fractions indicating an organic and inorganic affinity in these coals although there is more enrichment in the sink fractions in the grootegeluk formation samples and a definite organic correlation in the vryheid formation sample

determination of paleoheat flux from vitrinite reflectance data a method is presented for determining paleoheat flux from the reflectance of vitrinite collected from wells the maturation of vitrinite is modeled using a time temperature integral that assumes pseudo first order kinetics in testing the numerical algorithm it was necessary to introduce a critical temperature of 295 k below which vitrinite does not mature this result is consistent with the latest findings of independent researchers the degree of consistency obtained from a number of wells is not perfect much of the inconsistency can be attributed to large uncertainties in the vitrinite reflectance readings to test the method heat flow history was determined for the north sea basin and the national petroleum reserve of alaska quantitative results were obtained detailing the increase and or decrease of heat flux with time and were consistent with the qualitative behavior inferred for paleoheat flow from current geologic models

fluid mineral equilibria in prehnite pumpellyite to greenschist facies metabasites near flin flon manitoba canada implications for petrogenetic grids a sequence of regional metamorphic isograds indicating a range from prehnite pumpellyite to lower amphibolite facies was mapped in metabasites near flin flon manitoba the lowest grade rocks contain prehnite pumpellyite and are cut by younger brittle faults containing epidote chlorite calcite isobaric temperature xco2 and pressure temperature constant xco2 diagrams were calculated to quantify the effects of co2 in the metamorphic fluid on the stability of prehnite pumpellyite facies minerals in metabasites containing excess quartz and chlorite prehnite and to a lesser extent pumpellyite are stable only in fluids with xco2 0 002 epidote chlorite calcite assemblages are stable our calculated phase relations are consistent with regional metamorphism in the flin flon area in the presence of an h2o rich fluid and a more co2 rich fluid in the later fault zones we believe that the potential effects of small amounts of co2 in the metamorphic fluid should be assessed when considering the pressure temperature implications of mineral assemblages in low grade metabasites

thermal history modeling of the georges bank u s a thermal inversion of transmittance color index tci and vitrinite reflectance vr data abstract using a one dimensional basin analysis model for the cost g 2 well in the georges bank area offshore east coast u s a thermal inversion of measured vitrinite reflectance vr data and of the transmittance color index tci converted to an equivalent vr value yielded essentially identical paleoheat flux variations with time the paleoheat flux showed two peaks at 175 ma bp and at 125 75 ma bp the earlier event corresponds to continental breakup and the beginning of the rift phase the latter event corresponds to continued drifting of the continents and formation of new oceanic basement beside answering some important tectonic questions the observations corroborated the theoretical and empirical connections between tci and vr found for the g 2 well and for other wells in different geological settings this fact together with the fact that tci measurements on physically amorphous organic material can be made on rocks devoid of vitrinite or spores and pollen carbonates pre late silurian rocks and siliceous black shales should promote the utility of tci as an effective geothermal history indicator

geochemistry and sedimentology of coal seams from the permian witbank coalfield south africa a means of identification abstract sedimentological investigations of the coal bearing vryheid formation karoo sequence in the witbank coalfield have revealed that coal peat deposition was associated with both marine and non marine palaeodepositional events at the terminal stage of peat accumulation swamps were inundated by marine transgressions which deposited mud and silt above the peat coal and these overlying sediments contain typical marine features glauconite associated with marine ichnofossil assemblages in similar stratigraphic positions elsewhere in the basin the peat swamps were invaded by basinward prograding non marine fluvial systems which deposited coarse sand and gravel over the peat these overlying sediments are coarse grained arkosic strata geochemical analysis of the no 2 no 4 and no 5 coal seems in the region were undertaken using instrumental neutron activation analysis inaa and x ray fluorescence spectrometry xrfs these analyses show that the geochemistry of the coal compliments the sedimentological interpretations elements which tend to be more concentrated in marine derived sediments e g boron chlorine lithium and bromine occur in greater concentrations in the top of coals overlain by marine strata than in coals overlain by non marine fluvial sequences the latter do not show enrichments of these elements trace element composition of the coal seams was further utilized as means of identifying the seams using multivariant discriminant analysis each coal seam plot in a specific field thereby permitting its identification based on the trace element content if unknown areas of the coalfield are being explored a knowledge of the palaeodepositional stratigraphic sequences together with quantitative geochemical analyses could permit rapid identification of the coals concerned

epidote group minerals in low medium pressure metamorphic terranes epidote group minerals are common in metamorphosed mafic to intermediate igneous rocks quartzofeldspathic sediments and calc alumina silicate marl rocks of higher grade zeolite to medium grade amphibolite facies of low medium pressure contact and regional metamorphic terranes i e pressure and temperature conditions below the calcite to aragonite transition within any one rock epidote composition in terms of fe3 fe3 al can be variable but in general is limited by whole rock composition such that epidote group minerals in metabasite lithologies are more fe rich than those in marls that tend to be more al rich and typically include zoisite because of their wide range of p t stability epidote group minerals of variable composition may form in a single rock during several stages of metamorphic re equilibration slow rates of intra crystalline fe3 al exchange especially at low temperatures preserve complex zonation patterns in individual grains that can serve as a tape recorder providing evidence for continuous or discontinuous prograde and retrograde reactions and the p t fluid redox conditions of metamorphism thus relic lower grade epidote typically fe rich often form cores over which new typically less fe rich higher grade epidote rims form in such a case the boundary between the two generations of epidote may be sharp or gradational depending on the temperature history of the rock and fe3 al diffusivity often compositional differences are blurred across the boundary in addition to zoning is the spread of individual epidote grain compositions within a rock even on a thin section scale this is related to variation in the composition of coexisting phases or reactants e g quartz ca al silicates such as plagioclase margarite lawsonite mafic silicates such as chlorite pumpellyite amphiboles other ca fe3 silicates such as prehnite andraditic garnet carbonates fe oxides relict volcanic glass which serve as compositional micro domains in which epidote may form

stochastic modelling of coalbed methane resources a case study in southeast qinshui basin china this paper presents a stochastic analysis of coalbed methane cbm resources for a coal seam in southeast qinshui basin china log and laboratory data are used to predict the coal thickness coal ash content and coal gas content using reservoir modelling the distributions of the karst collapse column kcc coal seam thickness coal quality and coal gas content are generated the convergent interpolation and sequential gaussian simulation methods are used to model the surface and structure of the coal seam the structural models are determined by the surface structure and coal seam thickness based on the structural models the coal and kcc are converted to two facies and their distributions are obtained using object modelling the coal density distributions are simulated based on each facies model using the sequential gaussian simulation finally different realisations are used to study cbm resources the results show that the heterogeneities in coal seam thickness and coal quality lead to significant uncertainty in estimating cbm resources a model with lower heterogeneity gives a greater cbm resource the distributions of kcc coal seam thickness coal quality and gas content are the main sources for uncertainty in cbm resource estimation the density variogram and top structure contribute less to the uncertainty in cbm resources

low grade metamorphism and geotectonic setting of the macuchi formation western cordillera of ecuador the cretaceous eocene basic to intermediate marine volcanic rocks of the mucuchi formation constitute the western cordillera in northern ecuador their chemical features mostly correspond to those of tholeiitic basalts with some calc alkaline affinities and suggest an oceanic island arc setting the macuchi rocks are affected by low grade non deformative metamorphism characterized by zeolite prehnite pumpellyite and lower greenschist facies assemblages depth zonation is suggested by the downward mineral sequence i laumontite pistacitic epidote pumpellyite prehnite ii pumpellyite prehnite pistacitic epidote iii actinolite biotite pistacitic epidote chlorite this broad zonation and the chemistry of individual minerals point to an interaction between the volcanic rocks and sea water under a moderate to high thermal gradient 75 c km alteration appears to have been dependent primarily on fluid control volume pressure composition temperature and reaction kinetics which together partly overshadow the role of load pressure compositional variations of a mineral species at the scale of a contiguous flow or even at the scale of a thin section show that intensity of alteration was spatially uneven depending on rock permeability and consequently metastable equilibrium commonly exists however a progressive approximation to equilibrium as a result of p t control is shown by the mineralogy a high fo2 of the fluid phase is evident from the mineral chemistry the metamorphism of the macuchi volcanics is similar to the hydrothermal burial type produced during the development of a volcanic arc where lavas and volcanoclastics accumulated in a shallow marine environment however some of its characteristics point to a transition toward systems defined by a higher t p ratio such as those found in ocean floor metamorphism a model is proposed in which the macuchi volcanics are assigned to an oceanic island arc generated contemporaneously with a marginal basin which has opened as the outcome of progressive north south attenuation of the continental crust due to mantle diapirism

synthesis of fe pumpellyite and its stability relations with epidote hydrothermal synthesis of fe pum pellyites was conducted using high pressure cold seal apparatus and solid oxygen buffering techniques at temperatures between 250 c and 550 c and 2 0 9 1 kbar pfluid fe pumpellyites were synthesized from partially crystalline gel mixtures of compositions 4cao 2 1al2o3 1 5feo 0 3mgo 6sio2 ii and 3cao 1 5 al2o3 2 7feo 0 3mgo 6sio2 iii in the presence of excess h2o at pfluid of 5 9 1 kbar temperatures between 275 c and 325 c and fo2 defined by the qfm and hm buffers for both of these compositions ii and iii the condensed synthetic run products included minor 7a chlorite garnet fe oxide the cell dimensions and aggregate refractive index a 19 13 2 a b 5 940 4 a c 8 847 5 a 97 37 6 and n 1 702 2 of the pum pellyite synthesized from the bulk composition ii mix are compatible with those of natural pumpellyites containing similar total fe contents attempts at synthesizing fe pumpellyites from a mg free bulk composition were not successful these results are consistent with the total absence of natural mg free pumpellyites the higher temperature higher oxygen fugacity assemblages of the equivalent bulk compositions ii and iii consist of epidote minor amounts of chlorite garnet quartz hematite and magnetite the results of these synthesis experiments accord with the mineral parageneses observed in low grade metabasites which imply that fe pumpellyites are replaced by epidote with increasing temperature and or fo2 and that fe3 is preferentially partitioned into epidote with respect to coexisting pum pellyite in addition these synthesis experiments indicate that fe bearing pumpellyites crystallize at and are stable to lower temperatures than more aluminous pumpellyites a result also consistent with natural systems

arsenic bearing pyrite and marcasite in the fire clay coal bed middle pennsylvanian breathitt formation eastern kentucky abstract arsenic concentrations determined on 11 lithotype samples from the middle pennsylvanian breathitt group fire clay coal bed leslie county ky range from 1 to 418 ppm whole coal basis the 11 lithotype samples which vary in thickness from 4 to 18 cm were sampled from a continuous 1 38 m channel sample and were selected based on megascopic appearance vitrain rich versus attrital rich a lithotype that contains 418 ppm as is located near the top of the coal bed and is composed of 10 5 cm of bright clarain bands containing fusain that within short distances grade laterally into fe sulfide bands to determine the mode of occurrence of as in this lithotype the coal was examined with scanning electron microscopy and analyzed by energy dispersive x ray fluorescence massive framboidal cell filling cell wall replacement and radiating forms of fe sulfide were observed in the high as lithotype many of the radiating fe sulfide forms and one of the cell wall replacements contained as examination of the grains with optical light microscopy shows that the majority of radiating morphologies are pyrite the remainder are marcasite selected fe sulfide grains were also analyzed by electron microprobe microscopy arsenic concentrations within individual grains range from 0 0 wt to approximately 3 5 wt on the basis of morphology these fe sulfides are presumed to be of syngenetic origin and would probably be removed from the coal during physical coal cleaning thus eliminating a potential source of as from the coal combustion process however because the grains are radiating and have high surface area dissolution and release of as could occur if the pyrite is oxidized in refuse ponds

transition from the zeolite to prehnite pumpellyite facies in the karmutsen metabasites vancouver island british columbia

titaniferous accessory minerals in very low grade metamorphic rocks keweenaw peninsula michigan usa abstract titanite tio 2 and pseudorutile are associated with primary igneous fe oxide grains in basalt and rhyolite clasts from the keweenaw peninsula michigan usa which were metamorphosed to the prehnite pumpellyite facies pseudorutile occurs with titanite tio 2 in broad lamellae within titaniferous magnetites it also occurs as intergrowths with titanite and fe oxide in embayments within primary oxide grains and in composite fe oxide titanite grains that appear to represent nearly complete replacement of original ti bearing fe oxides thin 111 lamellae in titaniferous magnetite grains contain titanite titanite tio 2 and titanite tio 2 fe oxide tio 2 also occurs by itself in networks of closely spaced small elongated lenses in fe ti oxides concentrations of caalsio 4 f caalsio 4 oh in titanite range from 0 to 30 the large variation in titanite compositions suggests that equilibrium was not achieved except on a very local scale a conclusion also supported by local variations in the assemblages of ti bearing secondary minerals textures and mineral assemblages indicate that ulvospinel lamellae were altered to titanite and or tio 2 polymorphs while ilmenite was altered to pseudorutile and titanite tio 2 the relative proportions of tio 2 and titanite appear to reflect local variations in the composition of the metamorphic fluid phase that may be linked to the degree of interaction with a hydrothermal fluid titanite rich regions may indicate a greater degree of fluid flushing than tio 2 rich regions textures and mineral assemblages cannot distinguish between models in which pseudorutile and a tio 2 polymorph formed during weathering or diagenesis followed by conversion of tio 2 to titanite during metamorphism and models in which pseudorutile formed together with titanite and tio 2 during metamorphism in either case pseudorutile was able to persist through prehnite pumpellyite metamorphism suggesting that it can be a significant ti rich accessory mineral in very low grade metamorphic rocks

actinolite forming reaction at low pressure and the role of fe 2 mg substitution the 6km thick karmutsen metabasites exposed over much of vancouver island were thermally metamorphosed by intrusions of jurassic granodiorite and granite observation of about 800 thin sections shows that the metabasites provide a complete succession of mineral assemblages ranging from the zeolite to pyroxene hornfels facies around the intrusion the reaction leading to the appearance of actinolite which is the facies boundary between prehnite pumpellyite and prehnite actinolite facies was examined using calcite free karmutsen metabasites collected from the route along the elk river in the prehnite pumpellyite facies xfe3 fe3 fe3 al in prehnite pumpellyite and epidote buffered by the four phase assemblage prehnite pumpellyite epidote chlorite systematically decreases with increasing metamorphic grade such a trend is the reverse of that proposed by cho et al 1986 this may be related to the higher f o 2 in the mt menzies area the actinolite forming reaction depends on the value of xfe3 in pumpellyite if using a low value of fe3 3 89 pr 0 06 0 48 ep 0 26 0 60 chl h2o 2 10 pm 0 08 0 17 act 0 88 qz is delineated the number in parentheses stands for the xfe3 value in ca al silicates on the other hand replacing the xfe3 of 0 08 in pumpellyite with a higher xfe3 value 0 24 changes the reaction to 0 41 pm 0 02 chl 0 42 qz 0 11 pr 0 62 ep 0 10 act h2o the first hydration reaction forms pumpellyite and actinolite on the high temperature side whereas the second dehydration reaction consumes pumpellyite to form prehnite epidote and actinolite the former reaction seems to explain the textural relationship of ca al silicates in the study area however actinolite forming reaction changes to a different reaction depending on the compositions of the participating minerals although in the other area even physical conditions may be similar to those in the study area chemographic analysis of phase relations in the pra facies indicates that the appearance of prehnite depends strongly on the bulk feo mgo ratio this may explain the rarity of prehnite in common metabasites in spite of the expected dominant occurrence in the conventional pseudo quaternary ca al fe3 fm system an increasing feo mgo ratio stabilizes the pr act assemblage and reduces the stability of the pm act one therefore the definition of pumpellyite actinolite facies should include not only pm act but also the absence of pr act assemblages in addition to the possible role of high x co 2 cho and liou 1987 and or high f o 2 to mask the appearance of prehnite the effect of the feo mgo ratio is emphasized

prehnite as an indicator mineral in the wadi nasb uralitized gabbro south sinai egypt abstract we report the first finding of prehnite in the southern sinai peninsula in a uralitized gabbro developed at the contact of the appinitic gabbro of the wadi nasb mafic intrusion wnmi with younger granitic intrusions subsolidus reactions with hydrothermal fluids caused the gabbro to gain al2o3 and cao while losing sio2 fe2o3 tio2 p2o5 ba nb zr and y uralitization proceeded through two stages of alteration and mineral replacement the early stage includes uralitization of pyroxene formation of new biotite as aggregates of small flakes transformation of primary amphiboles into actinolite and actinolitic hornblende and saussuritization of plagioclase the late stage of alteration is characterized by chloritization of mafic minerals apparent crystallization temperatures of the primary relics of pyroxene hornblende and biotite range from 800 1000 c 865 925 c and 700 c respectively suggesting partial resetting of the biotite exchange thermometer the early biotite forming alteration occurred at moderate temperature 300 450 c while the late chlorite forming alteration occurred at low temperature

paleodepositional environments and tectonosedimentary controls of the postglacial permian coals karoo basin south africa abstract coal deposits of the karoo basin in south africa are contained within an 80 250 m thick clastic sequence designated the vryheid formation this formation constitutes part of the ecca group of the karoo sequence and contains several mineable bituminuos coal and anthracite beds and sporadic coking coal seams the sedimentary succession was deposited during the early permian following the late carboniferous dwyka ice age paleoclimate initially influenced the paleodepositional environments which for the lowermost stages comprised glaciofluvinal outwash braided plain deposits overlying minor deltaic and glaciolacustrine fill the early permian floral assemblages attest to a cool temperature climatic regime in the extreme northern parts of the basin the lowermost coals frequently directly overlie dwyka diamictite or pre karoo basement paleodepositional systems associated with the coals above the glaciogenic succession consisted predominantly of regressive fluviodeltaic facies assemblages in the northern regions regressive deltaic lobes prograded rapidly basinward across the relatively shallow intracratonic platform in the northeast areas greater subsidence rates were accompanied by multiple stacking of regressive deltaic cycles in several areas of the coalfields peat accumulation was associated with the bed load braided fluvial systems these subsequently modified the underlying deltaic deposits by intense and deep erosion that removed portions of the underlying stratigraphy smaller scale syndepositional anastomosed rivers which were contemporaneous with certain peat swamps locally controlled seam distribution and adversely affected coal seam quality coal distribution was directly controlled a the tectonic setting b the nature of the pre karoo basement lithologies c the basement paleotopography and d the paleodepositional systems associated with and following peat formation the coalfields are restricted to a relatively small area in the northern and northeastern parts of the karoo basin where a stable intracratonic shelf provided a suitable tectonic setting for peat accumulation resistant basement lithologies orthoquartzite and felzite produced positive topographic relief while easily weatehred archean granite basement terrain left residual topographic depressions that were later extensively filled by sediment differential compaction of fine sediment mud and silt deposited over the diverse basement topography provided further subtle controls on coal seam thickness sediments and coal overlying basement highs compacted significantly causing thinning and a draping effect of the sedimentary cover in contrast paleovalleys contained substantial thickness of sediment and host some of the thickest seams these coals can however thin and shale out against the adjacent elevated valley flanks the paleovalley coals were further affected by multiple seam splits produced by fluvial channels that contemporaneously occupied the lowland areas

compositional controls on coexisting prehnite actinolite and prehnite pumpellyite facies assemblages in the tal y fan metabasite intrusion north wales implications for caledonian metamorphic field gradients the tal y fan intrusion is a 110 m thick sub concordant metabasite sheet intruded into volcaniclastic and pyroclastic rocks of ordovician age in north wales despite low grade metamorphism primary textural zones resulting from initial cooling of the sheet are preserved and retain primary mineralogical and chemical variations which influenced the nature and extent of metamorphic recrystallization this has resulted in a vertical sequence of secondary mineral assemblages through the intrusion during early hydrothermal alteration k feldspar replaced plagioclase micropheno crysts in the marginal and contact zones and olivine in the central zone was replaced by saponite subsequent regional metamorphism resulted in the development of metastable prehnite pumpellyite epidote assemblages in two sub zones characterized by high fe2o3 elsewhere the assemblage prehnite actinolite epidote developed except in the contact and marginal zones where activity of co2 suppressed both prehnite and pumpellyite both assemblages contain excess albite quartz and chlorite and on the basis of uniform mineral compositions over the area of an individual thin section are considered to represent buffered equilibrium assemblages indicative of prehnite pumpellyite and prehnite actinolite facies conditions a metamorphic temperature of 310 c at 1 85 kbar is obtained using the p t x grid of liou maruyama cho 1985 which implies a field gradient of 44 c km 1 assuming that metamorphism relates to burial an overburden thickness of 7 km is indicated total maximum thicknesses however of ordovician silurian and lower devonian strata in the area do not exceed 6 km indicating a field gradient of 52 c km 1 these relatively high gradients may possibly be related to concealed late caledonian intrusions or alternatively may result from high heat flow as a consequence of crustal thinning rapid sedimentation and intense magmatic activity in a marginal basin setting

metamorphism of a late jurassic volcano plutonic arc northern california usa the metamorphic history of the middle to upper jurassic volcanic and hypabyssal rocks exposed in the klamath mountains and sierra nevada of california is related in part to the rifting of a volcano plutonic arc the callovian to kimmeridgian rocks exposed in the region consist of from north west to south east a back arc ophiolite a rifted volcanic arc and a volcanic arc complex all of these units have been metamorphosed and contain various combinations of the phases chlorite amphibole epidote prehnite and pumpellyite projection of coexisting phases onto the composition plane mgo mgo feo and al2o3 fe2o3 0 75 cao na2o through quartz water albite and epidote results in consistent mineralogical compatibilities within each region but crossing tie lines between regions this suggests that the volcanic and hypabyssal rocks from each region have equilibrated under different intensive conditions the back arc ophiolite in the north has suffered subseafloor high t p hydrothermal metamorphism with geothermal gradients on the order of 100 c km 1 the rifted volcanic arc has undergone synchronous burial hydrothermal and contact metamorphism metamorphic field gradients in the region pass through the prehnite pumpellyite and greenschist facies suggesting geothermal gradients on the order of 30 c km 1 the southernmost volcanic arc complexes contain metavolcanics of the pumpellyiteactinolite and greenschist facies suggesting moderate to high p t metamorphism and geothermal gradients on the order of 20 c km 1 the apparent increase in rifting and calculated geothermal gradients from south east to north west suggest that the observed very low and low grade metamorphism may be a response to enhanced thermal gradients during extension of the volcanic arc this correlation between the extent of rifting and metamorphism is consistent with a model of diastathermal metamorphism of a propagating rift along the western margin of north america during the late jurassic the plate tectonic setting may be analogous to the present day andaman sea region

sedimentology of fraser river delta peat deposits a modern analogue for some deltaic coals abstract on the recent lobe of the fraser river delta peat accumulation has actively occurred on the distal lower dilta plain the transition between upper and lower delta plains and the alluvial plain distal lower delta plain peats developed from widespread salt and brackish marshes and were not influenced appreciably by fluvial activity lateral development of the marsh facies were controlled by compaction and eustatic sea level rise the resulting thin discontinuous peat network contains numerous silty clay partings and high concentrations of sulphur freshwater marsh facies formed but were later in part eroded and altered by transgressing marine waters the peats overlie a thin fluvial fining upward sequence which in turn overlies a thick coarsening upward prodelta delta front succession lower delta plain upper delta plain peats initially developed from interdistributary brackish marshes and were later fluvially influenced as the delta prograded the thickest peats occur in areas where distributary channels were abandoned earliest sphagnum biofacies replace sedge grass dominated communities except along active channel margins where the sedge grass facies is intercalated with overbank and splay deposits the peats are underlain by a relatively thin sequence of fluvial deposits which in turn is underlain by a major coarsening upward delta front and pro delta sequence alluvial plain peats accumulated in back swamp environments of the flood plain earliest sedge clay and gyttjae peats developed over thin fining upward fluvial cycles or are interlaminated with fine grained flood deposits thickest accumulations occur where peat fills small avulsed flood channels overlying sedge grass and sphagnum biofacies are horizontally stratified and commonly have sharp boundaries with fine grained flood sediments at active channel margins however sedge grass peats are intercalated with natural levee deposits consisting of silty clay these levees reduce both the number and size of crevasse splay deposits coal originating from peats of the different environments of the fraser delta would vary markedly in character peats of the lower delta plain will form thin lenticular coal seams with numerous splits and have a high ash and sulphur content peats from the lower to upper delta plain will be laterally extensive and of variable thickness and quality basal portions of the seams will contain numerous splits and have a high sulphur content whereas upper portions will be of higher quality peats from the upper delta plain alluvial plain will form thick isolated and laterally restricted coal seams characterized by low ash and sulphur contents

facies evolution and cyclicity of alluvial coal deposits in the lower permian of east africa tanzania the ruhuhu basin in sw tanzania contains several small coal basins i e mchuchuma ngaka north mbalawala lumecha consisting of fault controlled half grabens submitted to several stages of tectonic activation all basins underwent fragmentation in the middle jurassic and late miocene to pliocene palaeotopography of pre karoo basement was partly responsible for the development of coal seam thickness distribution facies characteristics of the lower middle and upper mchuchuma formation and the scarp sandstone of the overlying ketewaka formation exhibit synsedimentary basin subsidence vitrinite reflectance data suggest similar temperature gradients and burial history for the mchuchuma and ngaka subbasins

geochemical characterization of rocky mountain northern great plains and interior province coals abstract statistical summaries of proximate and ultimate analyses heat of combustion and content of 36 major minor and trace elements were calculated for 37 eocene 470 paleocene and 419 cretaceous coal samples from 31 coal fields or areas in the rocky mountain and northern great plains coal provinces and for 503 pennsylvanian coal samples from 14 areas in the interior coal province these analyses show that coals within an age group have similar ranges in composition and that each group has its own distinctive compositional characteristics most variability in element content can be related to changes in rank and differences in ash and total sulfur contents mean contents of ca mg na ba and sr are related to rank and decrease as apparent coal rank increases from lignite a to high volatile b bituminous coal mean contents of si al k ti ga li sc th v y and yb increase as the mean ash content increases correlation coefficients 0 6 suggesting that these elements are present as aluminosilicates stable oxides or phosphate mineral phases mean contents of fe as cd co cu mo ni pb sb and zn show high correlation with total sulfur contents of these elements are low in paleocene 0 6 sulfur and cretaceous 0 7 sulfur coals higher in eocene 1 8 sulfur coals and generally highest in pennsylvanian 3 9 sulfur coals the mean contents of b be cr f hg mn nb se u and zr show no direct relationships to changes in rank or ash and total sulfur contents decrease in element content with increased rank probably is related to loss o functional groups that act as cation exchange sites on organic matter ash and sulfur contents are dependent on ph controlled levels of bacterial activity in ancestral peat swamps end of article last page 447

distribution and significance of crystalline perlitic and vesicular textures in the ordovician garth tuff wales diverse spherulitic and granular crystalline fabrics perlitic textures and fabrics related to the growth and migration of vesicles occur in the garth tuff a largely welded ordovician ignimbrite defining the distribution of such textures helps to constrain the ignimbrite s cooling and degassing history suites of spherulitic and perlitic textures closely reflect variation in cooling rates seven facies are defined based on the style and intensity of crystallisation 1 a medium to coarsely crystalline equigranular facies 2 an intensely spherulitic facies 3 a sparsely spherulitic facies 4 a pectinate facies 5 a microcrystalline to cryptocrystalline equigranular facies 6 a lithophysal facies and 7 a transitional perlite pectinate facies textural changes from facies 1 to 5 reflect progressively higher cooling rates facies 1 occurs in proximal settings in the ignimbrite s core facies 2 to 5 successively envelop facies 1 with facies 2 becoming the dominant fabric in the ignimbrite s core in medial settings facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite s welded margins crystallisation under hydrous conditions is reflected by second boiling textures in the sporadically developed lithophysal facies the seventh facies reflects a subtle interplay between cooling hydration and crystallisation which locally prevented perlitic fracturing the distribution of amygdales reflects patterns of volatile migration and entrapment in the lower levels of the ignimbrite amygdales occur in irregular concentrations or rare subvertical pipe like structures pipe like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state amygdales are widespread and evenly distributed in the upper levels of the ignimbrite however the top of the welding profile is characterised by a thin poorly vesiculated originally vitrophyric horizon that abruptly caps an intense concentration of amygdales ductile and brittle fabrics developed during the upward migration of gas microscopic drag folds occur around some amygdales jigsaw fit to clast rotated breccias originated through both late stage pneumatic fracturing and autobrecciation vaporisation of water at the flow base provided a significant source of volatiles in addition to gas released during cooling and crystallisation secondary alteration has enhanced or modified some fabrics perlitic zones were susceptible to patchy chlorite sericite carbonate diagenetic alteration diagenesis and metamorphism have contributed to the infilling of vesicles

phase relations of pumpellyite actinolite facies metabasites in the sanbagawa metamorphic belt in central shikoku japan abstract sanbagawa metabasites metamorphosed at conditions near the upper limit of the pumpellytic actinolite facies were examined in terms of phase equilibria in the five component system al2o3 fe2o3 cao mgo feo the fe3 content of epidote measured as x ep fe fe fe al of epidote in the assemblage epidote chlorite actinolite pumpellyite decreases gradually towards the higher grade pumpellyite free areas the progressive change in xfeep can be detected within one metabasite bed 200 meters thick near the upper limit of the pumpellyite actinolite facies the mg fe2 substitution as expressed by variation of fe fe mg in chlorite 0 40 0 55 has little effect on the fe3 al ratios of epidote and pumpellyite in the above mentioned assemblage the lowet xfeep in the pumpellite bearing assemblage is 0 15 and hence the upper limit of the pumpellyite actinolite facies is defined by the appearance of an epidote chlorite actinolite assemblage with x ep fc c 15

coal seams of the walbrzych formation intrasudetic basin poland inferences on changing depositional environment abstract the petrological composition of coal seams of the walbrzych fm was studied and depositional conditions were reconstructed on the basis of both coal and clastic sediment analysis coal of this formation is of medium to low volatile bituminous rank vitrinite reflectance r o max ranges from 0 8 to 2 0 and volatile matter content from 29 to 16 the coal seams of the walbrzych formation contain mainly banded coal bright and dull lithotypes occur sporadically the amount of banded and banded dull coals increases towards the top of the formation at the expense of banded bright coal consequently vitrinite and vitrite content tends to decrease upwards peat deposition in the lower part of the walbrzych formation occurred predominantly in a telmatic forest zone the mires were located between interdistributary channels on a delta plain and they were probably ombrotrophic in the upper part of the walbrzych formation swamps were the primary sites of peat deposition abandoned channels were favoured as peat deposition sites for seams where increases in seam thickness are associated with increases in coarse clastic content below seams continuous peat deposition in overbank zones is postulated for seams wherein decreases in seam thickness are associated with increases in coarse clastic content where no relationship between seam thickness and coarse clastic content beneath the seam exists the swamp may have encroached into overbank and channel zones rapidly changes in the environment of peat deposition may be related to tectonic activity along the basin margins during the namurian

reactions leading to the formation and breakdown of stilpnomelane in the otago schist new zealand semi pelitic rocks ranging in grade from the prehnite pumpellyite to the greenschist facies from south eastern otago new zealand have been investigated in order to evaluate the reactions leading to formation and breakdown of stilpnomelane detrital grains of mica and chlorite along with fine grained authigenic illite and chlorite occur in lower grade rocks with compactional fabric parallel to bedding at higher grades detrital grains have undergone dissolution and metamorphic phyllosilicates have crys tallized with preferred orientation sub parallel to bedding leading to slaty cleavage stilpnomelane is found in metapelites of the pumpellyite actinolite facies and the chlorite zone of the greenschist facies but only rarely in the biotite zone of the greenschist facies illite or phengite is ubiquitous whereas chlorite occurs only rarely with stilpnomelane upgrade of the pumpellyite out isograd chemical and textural relationships suggest that stilpnomelane formed from chlorite phengite quartz k feldspar and iron oxides stilpnomelane was produced by grain boundary replacement of chlorite and by precipitation from solution overprinting earlier textures some relict 14 achlorite layers are observed by tem to be in the process of transforming to 12 astilpnomelane layers the aem analyses show that fe is strongly partitioned over mg into stilpnomelane relative to chlorite k d 2 5 and into chlorite relative to phengite k d 1 9 modified aaefm diagrams projected from the measured phengite composition rather than from ideal kal 3 si 3 o 10 oh 2 are used to elucidate reactions among chlorite stilpnomelane phengite and biotite in addition to pressure temperature and bulk rock composition the stilpnomelane in isograd is controlled by variations in k fe3 fe2 o oh and h 2 o contents and the locus of the isograd is expected to vary in rocks of diverent oxidation states and permeabilities biotite quartz and less phengitic muscovite form from stilpnomelane chlorite and phengite in the biotite zone projection of bulk rock compositions from phengite naalo 2 sio 2 and h 2 o reveals that they lie close to the polyhedra defined by the aaefm minerals and albite other extended aaefm diagrams such as one projected from phengite naalo 2 caal 2 o 4 sio 2 and h 2 o may prove useful in the evaluation of other low grade assemblages

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

pumpellyite in low grade metamorphic rocks from ligurian and lucanian apennines maritime alps and calabria italy in the ligurian apennines and the brianzonese area of the maritime alps northern italy and in the lucanian apennines and calabria southern italy pumpellyite formed during the alpine metamorphism is widespread in terranes of late paleozoic to miocene age particularly in mafic ophiolites tethyan ophiolites of jurassic early cretaceous age pumpellyite developed under variable metamorphic conditions which include zeolite prehnite pumpellyite pumpellyite actinolite lawsonite albite and blueschist facies pumpellyite from rocks belonging to all these facies was studied in 30 specimens of different chemistry derived mostly from ophiolitic basalt and gabbro but also from gneiss amphibolite and greywacke protoliths microprobe data give evidence of strong compositional variations of pumpellyite the ranges are extreme for al and fetot al2o3 18 74 30 91 feotot 0 46 12 71 to a lesser extent for mg mgo 0 58 4 00 with a reciprocal variation of al and fetot which suggests that most fe is fe3 pumpellyite compositions can be related with the metamorphic conditions particularly an increase of the al fetot ratio with increasing pressure but larger compositional variation for each facies in the al fetot mg diagram than those previously described was recognized particularly the compositions of pumpellyite from the pumpellyite actinolite and blueschist fades assemblages extend towards higher fetot contents moreover pumpellyites of the lawsonite albite facies rocks result to be more aluminous than in blueschist facies such relations appear to be inconsistent with that expected by the effects of pressure on the al content as the rocks are generally incompletely re equilibrated their bulk chemistry is not an important factor of pumpellyite composition in fact the correlations of al fetot and mg are low the local environment of crystallization more evidently the composition of the precursor minerals seems to be a major controlling factor the observed topologic relations indicate that either the nature of the precursor mineral or the presence of relict phases have a great influence on the pumpellyite composition the observed variations within individual specimens as well as the interspecimen ones can be explained by small scale inhomogeneities and in some cases by differences in the activity of o2 it can be therefore concluded that the composition of pumpellyite often reflects disequilibrium crystallization and cannot be generally used as an indicator of metamorphic conditions

the franciscan complex california usa the model case for return flow in a subduction channel put to the test the model of return flow in a subduction channel rfsc is put to the test by opposing key assumptions of the model to an integrated review of field data petrology geochronology and structures of high p melanges of the franciscan subduction complex fsc to which rfsc has been first applied key assumptions are i the subduction channel sc is a low viscosity zone of finite width restrained by the rigid subducted and overriding plates ii forced return flow in the sc is associated with formation and km scale displacements of small tectonic blocks 1 km in a highly deformable matrix iii this results in apparently random distributions and close associations of blocks exhumed from different depths hence the block in matrix structures and exotic blocks in high p melanges would reflect the structural state at depth of the sc on the basis of the predictions ensuing from the key assumptions of the rfsc model on the rock record it is detailed why the actual record of the high p melanges of the fsc does not comply with this perception the record rather reflects recurring subduction underplating associated decollement erosion and mingling of high p rocks by sedimentary processes in the trench all occurring in an 80 m y lasting period distributed deformation of the melange matrix is unrelated to formation of apparently chaotic block in matrix structures since i creation subduction ascent and cooling of exotic blocks on counterclockwise p t paths predates deposition of the bulk of the metasediments constituting the matrix by 20 40 m y ii deformation of the matrix occurs during a second loop of high p metamorphism postdating creation and ascent of the exotic blocks by at least 20 40 m y iii the magnitudes of distributed deformation of the matrix are too low to cause juxtaposition of blocks different in p t paths against each other from km scale vertical distances instead narrow few tens of metres wide fault shear and decollement zones formed at locally high pore fluid pressures accumulate the major tectonic transport during high p metamorphism they bound several 100s of metres wide tabular tectonic bodies that are coherent sedimentary processes at the active continental margin formed the bulk of the melanges tectonically formed block in matrix structures within the shear and decollement zones are unrelated to juxtaposition of exotic blocks universal diagnostic criteria are developed to identify return rfsc as a mechanism that potentially amalgamates heterogeneous metamorphic terrains by using field data petrology and geochronology

palaeoenvironmental control on coal formation distribution and quality in the permian vryheid formation east witbank coalfield south africa abstract the no 1 and no 2 coal seams from the permian vryheid formation in the east witbank coalfield south africa are described with respect to their distribution thickness and quality these two coal seams accumulated in a postglacial climatic environment and peat accumulation was closely associated with and influenced by deposition in a braided river system the fluvial channels that were syndepositional with peat accumulation have resulted in thinning of coal below and above channel axes and pinch out of coal adjacent to channel margins low ash coal originated from peat which accumulated in areas away from the influence of clastic sedimentation in contrast higher ash coals are situated adjacent and parallel to channel margins where interbedded channel sand and silt contaminated the peat the lower no 1 seam peat originated under near optimum conditions in a lacustrine swamp which blanketed an underlying platform of glaciofluvial braided river sediment this peat swamp was not subjected to syndepositional clastic contamination and as a result is of superior quality lower ash higher calorific value and volatile matter than the overlying no 2 coal seam the no 2 seam is split by a clastic parting produced by a braided fluvial channel which transected the swamp midway through peat accumulation this fluvial clastic parting deleteriously affected coal thickness and quality a comparison of the gondwanan permian peat forming conditions with those from carboniferous northern hemisphere counterparts suggests that the differences in coal characteristics between these two regions are probably related to different palaeoclimatic conditions and basin tectonics cool temperate climatic conditions which prevailed over the permian peat swamps resulted in less species diversification of vegetation at these high latitude settings than the diverse floral assemblages of the carboniferous swamps a stable intracronic basin platform caused lateral dispersion of sedimentary facies rather than the stacking of vertical facies which occurred in rapidly subsiding depositories partial exposure of the permian peat swamps during peat accumulation may account for the relatively higher inertinite content of the coals

water input and water release from the subducting nazca plate along southern central chile 33 s 46 s the age of the subducting nazca plate off chile increases northward from 0 ma at the chile triple junction 46 s to 37 ma at the latitude of valparaiso 32 s age related variations in the thermal state of the subducting plate impact on a the water influx to the subduction zone as well as on b the volumes of water that are released under the continental fore arc or alternatively carried beyond the arc southern central chile is an ideal setting to study this effect because other factors for the subduction zone water budget appear constant we determine the water influx by calculating the crustal water uptake and by modeling the upper mantle serpentinization at the outer rise of the chile trench the water release under fore arc and arc is determined by coupling fem thermal models of the subducting plate with stability fields of water releasing mineral reactions for upper and lower crust and hydrated mantle results show that both the influx of water stored in and the outflux of water released from upper crust lower crust and mantle vary drastically over segment boundaries in particular the oldest and coldest segments carry roughly twice as much water into the subduction zone as the youngest and hottest segments but their release flux to the fore arc is only about one fourth of the latter this high variability over a subduction zone of 1500 km length shows that it is insufficient to consider subduction zones as uniform entities in global estimates of subduction zone fluxes

low grade blueschist facies metamorphism of metagreywackes franciscan complex northern california metagreywackes in the eastern belt of the franciscan complex contain the assemblage qtz ab lws chl ph pmp fgl hem cal arg or compatible subassemblages blue amphibole first appears in the westernmost part of the belt and pumpellyite is absent in the eastern part the compositions of the coexisting minerals and the nature of the continuous reactions in these low grade blueschists suggest that the distribution of blue amphibole and pumpellyite in the eastern belt of the franciscan complex reflects differences of effective bulk composition rather than differences in physical conditions of metamorphism in rocks lacking pumpellyite white mica may be essential to the growth of blue amphibole but carbonate plays only a limited role the continuous reaction that limits the appearance of blue amphibole and the disappearance of coexisting pumpellyite has the general form pmp chl ab qtz hem h2o femg 1 fgl lws this reaction requires significant hydration as pressure increases in order to produce blue amphibole most of the eastern belt of the franciscan complex formed in limited ranges of temperature and pressure which are estimated to be 240 280 c 6 5 7 5 kbar pressures in the westernmost part of the area were about 1 kbar lower than in the east pressures of about 8 5 10 kbar are estimated for tectonic blocks that contain sodic clinopyroxene

multiple bench architecture and interpretations of original mire phases examples from the middle pennsylvanian of the central appalachian basin usa abstract coal seams often exhibit lateral and vertical variability in composition when sampled as a whole seam this variability is masked but if a seam is subdivided into correlateable components this variability can be tested and better understood herein an architectural approach is used to divide seams into intra seam components clastic splits and mineral partings as well as persistent fusain and durain layers can be used as intra seam bounding units to subdivide a seam into subdivisions called benches regional examination of lower and middle pennsylvanian age coal seams shows that many contain laterally persistent bounding surfaces that can be used to define multiple benches of coal within each seam inter bench analyses from some of the most extensively mined seams in the central appalachian basin show that individual benches often have different spatial and quality trends hence some component of whole seam variability is a function of changes in the relative contribution of these different benches to the seam as a whole many coal benches also exhibit intra bench variation in coal parameters intra bench variation can be analyzed in terms of parameters such as sulfur content and ash yield in order to address changes in coal quality for regional resource evaluation intra bench variation can also be analyzed in terms of a combination of palynologic petrographic and geochemical parameters termed compositional groups in order to better understand the development of the original mire systems compositional groups are defined by ranges of multiple criteria which are inferred to owe their origin to the mire type in which they formed vertical changes in compositional groups within coal benches can be used to infer paleo edaphic conditions during peat accumulation if seam thickness is a product of bench configuration and trends in compositional groups occur in benches then trends in quality can be marginally predicted based upon seam thickness and inferred bench architecture additionally changes in inter bench and intra bench thickness and compositional profiles can be used to infer original depositional controls such as paleotopography syndepositional structural movement and syndepositional clastic influx for more accurate reserve estimates

south africa s coalfields a 2014 perspective abstract for well over a century and a half coal has played a vital role in south africa s economy and currently bituminous coal is the primary energy source for domestic electricity generation as well as being the feedstock for the production of a substantial percentage of the country s liquid fuels it furthermore provides a considerable source of foreign revenue from exports based on geographic considerations and variations in the sedimentation origin formation distribution and quality of the coals 19 coalfields are generally recognised in south africa this paper provides an updated review of their exploration and exploitation histories general geology coal seam nomenclature and coal qualities within the various coalfields autocyclic variability is the norm rather than the exception whereas allocyclic variability is much less so and allows for the correlation of genetically related sequences during the mid jurassic break up of gondwana most of the coal bearing successions were intruded by dolerite these intrusions are important as they may cause devolatilisation and burning of the coal create structural disturbances and related seam correlation problems and difficulties in mining operations whilst many of the coalfields have been extensively explored and exploited those in the north of the country have until recently received much less attention four coalfields occur partly or wholly within the limpopo province of south africa and these may contain as much as 70 of south africa s remaining coal resources these coalfields in particular have been the focus of recent exploration due to the presence of large coking and thermal coal resources as well as for their coal bed methane potential and these resources need to be unlocked with regards to creating maximum benefit and minimal environmental degradation south africa s coals have also been recently addressed as palaeoclimate archives recording gondwana s postglacial climate amelioration by major changes in land plant communities and proving high resolution palyno stratigraphy as a crucial tool to decipher climate change during the permo carboniferous this aspect of the coals of south africa is also reviewed

a new petrogenetic grid for low grade metabasites abstract we have used internally consistent thermodynamic data to present calculated phase equilibria for the system na2o cao mgo al2o3 sio2 h2o ncmash in the range 0 500 c and 0 1 10 kbar involving the phases anorthite glaucophane grossular heulandite jadeite laumontite lawsonite paragonite prehnite pumpellyite stilbite tremolite wairakite zoisite with excess albite clinochlore quartz and pure water average activity terms derived from published mineral chemical data were included for clinochlore glaucophane prehnite pumpellyite tremolite and zoisite the new petrogenetic grid delineates stability fields and parageneses of common index minerals in zeolite prehniteactinolite prehnite pumpellyite pumpellyite actinolite blueschist and greenschist facies metabasites the stability fields of mineral assemblages containing prehnite pumpellyite epidote actinolite albite chlorite quartz were analysed in some detail using activity data calculated from five specific samples for example the prehnite actinolite facies covers a p t field ranging from about 220 to 320 c at pressures below 4 5 kbar the transition from the prehnite actinolite and pumpellyite actinolite to greenschist facies occurs at about 250 300 c at 1 3 kbar and at about 250 350 c at 3 8 kbar p t fields of individual facies overlap considerably due to variations in chemical composition

an end member sensitivity analysis of vitrinite reflectance distributions for the cost g 2 well in the georges bank basin abstract vitrinite reflectance vr is one of the most popular thermal indicators in basin analysis studies with the mean values of the vr distribution data usually used for determining the thermal history of sediments abnormally high mean values and thus abnormally high vr derived paleoheat flux may be recorded when recycled or highly oxidized vitrinite macerals are mixed in situ with virgin vitrinite in this study end member sensitivity analysis methods are applied to vr distribution data measured in the cost g 2 well in georges bank basin u s a to investigate the mixing properties of the vr data the modified vr data obtained through a filtering procedure are then used to generate a modified thermal history a 1 d fluid flow compaction model is employed for the basin s burial and thermal history inversion relative to the thermal history derived from the mean vr distribution data the modified thermal history results in a lower paleoheat flux and paleotemperature and is consistent with other geological evidence and with the thermal history obtained from other thermal indicators such as transmittance color index and temperature alteration index

prehnite pumpellyite to greenschist facies transition smartville complex near auburn california the smartville complex is a late jurassic rifted volcanic arc in the northern sierra nevada california near auburn california it consists of a lower volcanic unit dominated by basaltic flows and an upper volcanic unit of andesitic volcaniclastic rocks both of which have been intruded by dykes and irregular bodies of diabase these rocks contain relict igneous minerals and the metamorphic minerals albite chlorite quartz pumpellyite prehnite epidote amphibole titanite garnet biotite k feldspar white mica calcite and sulphide and oxide minerals prehnite pumpellyite prp prehnite actinolite pra and greenschist gs zones have been identified the pumpellyite out isograd separates the prp and pra zones and the prehnite out isograd separates the pra and gs zones the minerals ab qtz mt tn are common to most assemblages in all three zones the mgo mgo feo ratio of the effective bulk composition has an important and systematic effect on the observed mineral assemblages in the prp zone prehnite bearing assemblages contain the additional minerals pmp amp ep chl in mgo rich rocks and either pmp ep chl or amp ep chl in less magnesian rocks subcalcic to calcic amphibole is common in the prp zone the mineral assemblage prh act ep chl without pmp characterizes the pra zone and the mineral assemblage act ep chl without prh or pmp characterizes the gs zone the disappearance of pumpellyite and prehnite occurred by continuous reactions the sequence of mineral assemblages was produced by burial metamorphism at p t conditions of 300 50 c at approximately 2 5 0 5 kbar during metamorphism the composition of the fluid phase was nearly 100 h2o and the oxygen fugacity was between the hematite magnetite and quartz fayalite magnetite buffers

impact of geological modeling processes on spatial coalbed methane resource estimation spatial coalbed methane cbm resource estimation is based on spatial distributions of coal coal adsorbed gas content and coal density however the spatial distribution of gas content can be generated via two different geological modeling processes 1 the gas content distribution is generated by geological modeling based on the interpreted gas content at boreholes 2 distributions of gas content related logs or coal properties are generated firstly then the gas content distribution is calculated based on the spatial distributions of logs or coal properties by the relationship between the gas content and logs or coal properties this paper presents a study to compare the impact of these two processes on cbm resource estimation for coal seam no 3 cs 3 in southeast qinshui basin china well logs from 22 wells laboratory data from five wells and well tops from 131 wells for cs 3 are used in log interpretation and geological modeling the simple kriging sk is used to build the structural model and the coal distribution weighted and unweighted omni directional variograms for structural residual and coal thickness are calculated using an in house program logs of gamma ray gr and density den or rhob are distributed in 3d by using sequential gaussian simulation sgs with sk algorithm artificial neural network ann is used to build the relationship of the measured raw gas content rgc gas content in raw coal basis with the logs of gr den and measured depth md then the rgc is distributed in 3d by the two geological modeling processes cbm resources are calculated in 3d based on the cells volume coal density and rgc results show that rgc increases with an increase in burial depth total cbm resources for the study area calculated by these two processes are similar for cs 3 but the distribution probability of high gas content is highly different which is important for locating wells