calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

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

magmatic epidote and its petrologic significance epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the mesozoic accreted terranes between northern california and southeastern alaska textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase the observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure plutonic rocks bearing magmatic epidote must have formed under moderately high pressures corresponding to lower crustal depths under fairly oxidizing conditions

epidote in calcalkaline magmas an experimental study of stability phase relationships and the role of epidote in magmatic evolution experiments on tonalite and granodiorite were performed at conditions ranging from 2 1 to 18 kbar and 550 to 850 c to establish the magmatic stability field of epidote as a function of p t and f02 at water saturated conditions and f02 buffered by nno epidote has a wide magmatic stability field in tonalite at 13 kbar this field extends from the wet solidus at 630 to 790 0c the low pressure intersection of the magmatic epidote crystallization reaction and the h20 saturated tonalite solidus and hence the minimum pressure for magmatic epidote occurs at about 5 kbar the clapeyron slopes of epidote melting reactions are moderately positive in p t space at pressures below the intersection of the epidote melting and the gamet in reactions at 13 kbar 790 c at this intersection epidote reaches its maximal thermal stability 790 c in tonalite h20 in the presence of garnet that is above 14 kbar epidote melting reactions have steep negative clapeyron slopes in p t space at p t conditions near the low pressure intersection of the epidote melting reaction with the water saturated solidus experiments were also performed with f02 buffered by hm at these oxidizing conditions the magmatic stability field of epidote is enlarged down to a pressure of about 3 kbar in granodiorite the stability of epidote has been investigated at pressures from 7 5 to 18 kbar with respect to the tonalite the epidote out reaction is located almost at the same p t conditions at 10 kbar but the maximum thermal stability is about 50 c lower toward higher pressures although few experiments indicate that epidote stability does not increase dramatically with decreasing water activity at present state it is not possible to predict melting and crystallization behavior of epidote at waterundersaturated conditions modal abundances of epidote are low 05 vol in the presence of major 40 vol melt fractions thus epidote in calc alkaline magmatic rocks is not likely to affect major elements strongly by fractional crystallization

factors controlling high yield coalbed methane vertical wells in the fanzhuang block southern qinshui basin abstract whether a coalbed methane cbm well achieves high yield is controlled by various factors structural and hydrological control models of cbm productivity in vertical wells were built using a combined investigation of basic tectonic settings and hydrological conditions as well as drainage parameters of the coal reservoir in the fanzhuang block southern qinshui basin this study indicates that gas water production differs significantly among wells with different structural settings or hydrogeological conditions low and unstable gas production rates in individual wells are the primary problem for the cbm development in the fanzhuang block the impacts of some geologic and engineering factors on gas production were analyzed and estimated based on comparative analysis quantitative analysis and gray system theory the results indicate that the critical reservoir ratio crr liquid column height lch and gas content are the most important factors in determining well productivity followed by the equivalent drainage radius edr the volume of frac sand and the decline rate of working fluid levels during initial production high yield wells in the fanzhuang block always have the following conditions gas content 20 m 3 t burial depth of 500 700 m crr 0 7 lch 400 m volume of frac sand 40 m 3 edr of 30 60 m and a decline rate of working fluid level lower than 2 m day during the initial production stage

geochronological and mineralogical constraints on depth of emplacement and ascencion rates of epidote bearing magmas from northeastern brazil calc alkalic to high k calc alkalic granitoid plutons in the borborema province northeastern brazil have been studied to constrain depth of emplacement by mineralogical and geological methods and to estimate upward magma transport rate based on partial dissolution of magmatic epidote laser probe incremental heating 40ar 39ar dating of biotite and hornblende single crystals from the neoproterozoic tavares and brejinho high k calc alkalic magmatic epidote mep bearing plutons reveals age differences of around 60 m y between these two minerals in each of these two intrusions these data suggest solidification at relatively great depth followed by prolonged cooling interval between the closure temperatures of biotite and hornblende al in hornblende barometry indicates that hornblende in several mep bearing plutons in the transversal domain of the borborema province solidified at 5 to 7 kbar whereas in the serido and macurure terranes solidification pressures range from 3 to 4 kbar partial dissolution of epidote indicates very rapid upward transport partial corrosion occurred during 15 35 years cachoerinha salgueiro terrane 10 30 years alto pajeu 15 years serido and 10 years macurure corresponding to upward transport rates of 450 1300 650 1050 1200 and 1800 m year respectively in these four terranes rapid upward magma migration in most cases was probably facilitated by diking simultaneous with regional shearing

lithoprobe seismic reflection structure of the southeastern canadian cordillera initial results nearly 270 km of crustal seismic reflection data obtained by lithoprobe in the southern canadian cordillera provide a geometric link between the rocky mountain foreland thrust and fold belt the purcell anticlinorium and the extensional regime superimposed on the crystalline core zone autochthonous north american basement and its overlying deformed and transported cover can be traced from the thrust and fold belt beneath the rocky mountain trench to 20 km depth beneath the central part of the purcell anticlinorium the purcell anticlinorium is cored by foreshortened proterozoic supracrustal rocks that were carried northeastward on a series of west dipping imbricate thrust faults these faults crop out within and east of the anticlinorium and converge downward with subhorizontal detachments above the autochthonous north american basement beneath the western purcell anticlinorium and kootenay arc reflections associated with the purcell stratigraphy and its underlying crystalline basement terminate at about 20 km depth and may be truncated against the east dipping eocene slocan lake fault zone the slocan lake fault zone is clearly imaged from the surface to about 12 km depth and can probably be followed discontinuously to about 25 km depth a west dipping high amplitude reflection from beneath the valhalla gneiss complex outlines the domal geometry of the complex and is probably related to an east verging compressional shear zone

evidence of early cretaceous transpression in the sulu orogenic belt eastern china abstract recent studies have documented marine turbidites with syn sedimentary deformation features in the central sulu orogenic belt of eastern china these units preserve essential information on the late mesozoic evolution of the sulu orogenic belt referred to as the baxiandun formation the turbidites exhibit similar lithologic characteristics to nearby units such as the lingshandao formation that have been well studied even though precise geochronologic constraints are lacking for a more precise correlation this study reports detrital zircon u pb age data that correlate the baxiandun formation turbidites of the central sulu orogenic belt to the early cretaceous lingshandao formation we also report al in hornblende emplacement depth estimates for granitic intrusions of the sulu orogenic belt s laoshan mountain a sharp contact between the laoshan granites and the marine baxiandun formation indicates that the baxiandun basin rapidly subsided to the emplacement depth of the laoshan plutons lateral correlation among the marine turbidites the lingshandao and baxiandun formations combined with information established by previous studies indicates initiation of transpressional tectonics at 122 121 ma transpression ceased with the emplacement of the laoshan granites whose a1 type composition indicates a return to extensional tectonics at ca 111 ma

hornblende geobarometry of the nelson batholith southeastern british columbia tectonic implications hornblende geobarometry has been applied to granitic rocks of the middle jurassic nelson batholith british columbia locally containing magmatic epidote geobarometry suggests equilibration pressu

eocene structural development of the valhalla complex southeastern british columbia the valhalla complex a cordilleran metamorphic core complex is a 100 km by 30 km structural culmination within the omineca belt of southeastern british columbia it comprises sheets of granitic orthogneiss ranging in age from 100 to 59 ma with intervening paragneiss of uncertain age and stratigraphic correlation the complex is roofed by the ductile valkyr shear zone and the ductile brittle slocan lake fault zone the upper plate comprises lower grade metasedimentary rocks intruded by middle jurassic plutons the valkyr shear zone and the slocan lake fault zone deform 62 and 59 ma granitic sheets in their footwalls the easterly directed valkyr shear zone is a 2 to 3 km thick zone of distributed ductile strain which is arched over the complex and is exposed around the periphery on the northern western and southern margins the shear zone was active between 59 and 54 ma under amphibolite facies conditions the juxtaposition of upper and lower plates with different structural and metamorphic histories indicates that the valkyr shear zone is a significant structure with large displacement there is evidence to support an easterly rooting direction consistent with an extensional origin its surface breakaway is suggested to be west of the valhalla complex the slocan lake fault zone on the eastern side of the complex is a gently 30 easterly dipping ductile brittle normal fault which roots to the east it was active between 54 and approximately 45 ma and truncates the valkyr shear zone timing and structural relationships indicate that the valkyr shear zone and the slocan lake fault zone are genetically related movement on the ductile valkyr shear zone arching of the complex and displacement on the slocan lake fault zone occurred as a continuum in early to middle eocene time this paper documents the presence of significant eocene ductile strain in the valhalla complex and suggests that the role of extension in this region is more profound than had been previously recognized

the irish variscides a fold belt developed within a major surge zone an arcuate fold belt characterizes the irish variscides south of the dingle dungarvan line the folds are cross cut by numerous faults which tend to be sinistral in the west and dextral in the east clockwise transection of major fold axes by minor folds and by cleavage has been recorded in the east while anticlockwise transections are common in the west these and other features suggest that north south dextral and sinistral shearing occurred in the east and west respectively this is considered to be a consequence of the morphology of the munster basin which allowed the development of a surge zone in the centre of the fold belt the variscan sole thrust is believed to lie at the base of or within the old red sandstone however to the east thinning of the upper palaeozoic cover sequence forces the sole thrust to cut down laterally stratigraphic section into lower palaeozoic basement in the depocentre the sole thrust surged ahead by propagating along bedding surfaces or possibly a devonian carboniferous extensional detachment beneath the basin while to the east and offshore to the west its propagation was inhibited by the absence of easy decollement horizons within the basement consequently the tip line became strongly arcuate and the thrust developed into a surge zone the sole thrust propagated northwards by stick slip processes much of the deformation within the cover sequence occurred during sticking events particularly fold tightening and accommodation faulting

magnetotelluric observations along the lithoprobe southeastern canadian cordilleran transect as part of the lithoprobe southern cordilleran transect investigations twenty seven wideband magnetotelluric mt responses were obtained along 150 km of the reflection seismic lines the mt profile begins to the east on the rocky mountain trench above autochthonous north american basement traverses across the purcell anticlinorium the kootenay arc the nelson batholith and ends on the east side of the valhalla gneiss complex sites near kootenay lake respond to a major near surface conductivity anomaly that is probably due to either graphitic schists or to an extension of the silver bearing mineralization found further north the short period 1 s data are highly complex and exhibit 3d regional features inversions of the data from the two sites on the valhalla complex yield 1d models with interfaces in electrical conductivity at depths that agree with an increase in the number of reflectors at 9 km the base of layered reflections at 22 km and the mono at 35 km of major significance to our understanding of the current composition and state of the lower continental crust is that although for the valhalla complex there are few reflections below 22 km the mt responses indicate that the zone is conducting this is the only location known to the authors where the lower crust is seismically transparent but electrically conductive

middle jurassic exhumation along the western flank of the selkirk fan structure thermobarometric and thermochronometric constraints from the illecillewaet synclinorium southeastern british columbia new thermobarometric and thermochronometric data from the illecillewaet synclinorium a broad regional southwest verging structure in the western flank of the selkirk fan structure indicate that accretion of the intermontane superterrane resulted in deep burial 20 25 km of the outer margin of ancestral north america and that subsequent southwest verging folding and thrusting were accompanied by rapid exhumation southwest verging folding of lower paleozoic rocks in the illecillewaet synclinorium was initiated during regional peak metamorphic conditions at 6 7 kbar crystallization of late synkinematic granitoid plutons that intrude the illecillewaet synclinorium also occurred at pressures of 6 7 kbar however equilibration of the contact aureoles of the plutons occurred at 3 3 5 kbar during the latter stages of the southwest verging deformation evidently a decompression on the order of 3 kbar occurred concurrently with southwest verging folding and thrusting in the illecillewaet synclinorium thermochronometric analyses further indicate that plutonic rocks from the illecillewaet synclinorium cooled rapidly between times of crystallization and times of ar closure in biotite regional relationships indicate that the accretion of the intermontane superterrane to the edge of the north american margin in southeastern british columbia occurred between 187 and 173 ma toarcian bajocian subsequent southwest verging deformation occurred approximately between 173 and 168 ma bajocian bathonian thus the removal of at least 10 km of rocks from above the illecillewaet synclinorium inferred from thermobarometric data occurred approximately between 173 and 168 ma rapid denudation of the selkirk fan structure was probably the result of synorogenic extension or extensional collapse contemporaneous with the development of southwest verging structures at deeper levels of the orogen the data presented here indicate that all significant deformation and most of the exhumation along the western flank of the selkirk fan structure were complete by late middle jurassic time after the middle jurassic the selkirk fan structure must have been transported passively northeastward along the basal decollement of the cordilleran foreland thrust and fold belt together with the intermontane superterrane as the fold and thrust belt tectonically overrode the margin of the north american craton

differentiation conditions of a basaltic magma from santorini and its bearing on the production of andesite in arc settings santorini volcano in the aegean region greece is characterized by andesitic to silicic dominated explosive activity and caldera forming eruptions sourced from magmatic reservoirs located at various structural levels beneath the volcano there is a good understanding of the silica rich magmatism of the island whereas the andesite dominated volcanism and the petrogenesis of the parental mafic magmas are still poorly understood to fill this gap we have performed crystallization experiments on a representative basalt from santorini with the aim of determining the conditions of differentiation pressure temperature volatile fugacities and the parental magma relationship with the andesitic eruptive rocks experiments were carried out between 975 and 1040 c in the pressure range 100 400 mpa fo2 from qfm to nno 3 5 where qfm is quartz fayalite magnetite and nno is nickel nickel oxide with h2omelt contents varying from saturation to nominally dry conditions the results show that basalt phenocrysts within the basalt crystallized at around 1040 c in a magma storage reservoir located at a depth equivalent to 200 400 mpa pressure with 3 5 wt dissolved h2o and fo2 around qfm comparison with the xenocryst and phenocryst assemblages of the upper scoria 1 andesite shows that andesitic liquids are produced by fractionation of a similar basalt at 1000 c and 400 mpa following 60 80 wt crystallization of an ol cpx plag ti mag opx 6 pig ilm assemblage with melt water contents around 4 6 wt at santorini the andesitic low viscosity and water rich residual liquids produced at these depths segregate from the parent basaltic mush and feed the shallow magma reservoirs eventually erupting upon mixing with resident magma changes in prevailing oxygen fugacity may control the tholeiitic calc alkaline character of santorini magmas explaining the compositional and mineralogical differences observed between the recent thyra and old eruptive products from akrotiri

kinematic history of the narragansett basin massachusetts and rhode island constraints on late paleozoic plate reconstructions the formation of the narragansett basin of rhode island and massachusetts and the polyphase deformation geometry of the pennsylvanian age basin sediments can be explained by collision and strike slip interactions between an avalonian microcontinent the european north american plate and the african plate during the late paleozoic sinistral movement between an avalonian microcontinent and the european north american plate resulted in formation of pull apart basins subsequently africa moved toward north america along an east west trending dextral megashear zone and collided with the eastern margin of southern north america the narragansett basin is located on the avalonian microcontinent near the suture with the north american continent and in the transition zone between the megashear and the collision tectonic regimes the basin shape stratigraphy and sedimentary relationships can be explained by the coalescence of two composite grabens which formed at different times the thicker northern graben is only affected by one deformation whereas the southern graben shows evidence of four distinct phases of postrifting deformation the first two coaxial folding deformations of the basin sediments are attributed to the closure of the basin complex during collision of africa and north america the third and fourth deformations are interpreted as sinistral r riedal and dextral shears respectively associated with the east west trending megashear system a prograde barrovian metamorphic front started in the western portion of the southern graben slightly after the first deformation and migrated northward and eastward where it is synchronous with the second deformation

geological and hydrological controls on water coproduced with coalbed methane in liulin eastern ordos basin china significant amounts of water are currently being extracted from coalbed methane cbm wells in permian carboniferous coal in the liulin area of the eastern ordos basin china waters coproduced with cbm have common chemical characteristics that can be an important exploration tool because they relate to the coal depositional environment and hydrodynamic maturation of groundwater and can be used to guide cbm development strategies the cbm production targets of the no 3 and 4 coal seams from sandstone in the shanxi formation and no 8 9 and 10 coal seams in the karst of the taiyuan formation were deposited in fluvial deltaic and epicontinental sea environments respectively this paper combines cbm geology hydrogeology cbm recovery and laboratory data to define mechanisms of cbm preservation including the important influence of groundwater relevant indices include fluid inclusions as an indicator of the hydraulic connection between the coal seam reservoir and the overlaying strata and the ensemble characteristics of total dissolved solids tds contents of water water production rates and reservoir temperatures as an indication of the current hydraulic connection the tds contents of waters from the no 3 and 4 and no 9 and 10 coal seams are double those from the subjacent karst no 8 coal seam indicating the important control of fast flow in karst low salinity fluid inclusions from the roof of the subjacent karst no 8 coal seam also indicate an enduring hydraulic connection with overlaying strata during its burial history relatively low current temperatures in the no 8 subjacent karst coal seam also infer a strong hydraulic connection and active flow regime deuterium concentrations are elevated in the mudstone bounded no 9 and 10 coal seams further confirming low rates of fluid transmission the gas contents of coal seams from the taiyuan formation are higher than those from the sandstone bounded coal seams in shanxi formation also correlating with low rates of water transmission and low permeability conceptual models for these fluvial deltaic and epicontinental sea environments that are consistent with geology gas content and gas and water production rate histories are of gas pressure sealing for the shanxi formation and hydrostatic pressure sealing for the taiyuan formation these results confirm the important controls of hydrogeological conditions on the preservation of cbm and the utility of hydrogeological indicators in prospecting for cbm

timing of intrusion of the narragansett pier granite relative to deformation in the southwestern narragansett basin rhode island the pennsylvanian sediments of the narragansett basin rhode island were deformed during the al leghanian orogeny and record the effects of alleghanian deformation in southeast new england without the complication of earlier structures during this deformation the basin was intruded at its southwestern corner by the narragansett pier granite which has a crystallization age of 273 ma mapping of basin metasediments along the narragansett bay shore in the southwestern portion of the basin reveals features formed by several episodes of deformation two generations of isoclinal folds along north trending axes f1a and f1b are the earliest structures in the area followed by a set of small closed folds f2 also on north trending axes the fla f1b and f2 folds are the result of east west closure of the basin minor sinistral and more significant dextral motion on faults within the beaverhead shear zone produced local east trending crenulations s3 and open folds with north trending axes f4 in the study

pressure temperature and time indicators in mafic schist their application to reconstructing the polymetamorphic history of vermont mineral chemistry and overgrowth relationships in mafic schist from vermont are shown to be sensitive indicators of pressure temperature and relative time and to be good chronicles of the paleozoic history of this polymetamorphic terrane within the common assemblage amphibole chlorite epidote plagioclase quartz ti phase carbonate k mica fe 3 oxide electron microprobe analyses show that increasing metamorphic grade as defined by intercalated pelitic schist is recorded by an increase in the edenite glaucophane and tschermakite contents of amphibole in the anorthite content of plagioclase and in the substitution of al vi f 2 ti al iv for fe 2 mg mn si in biotite chlorite and muscovite with increasing pressure the glaucophane component of amphibole increases for medium pressure metamorphism the albite oligoclase gap is in the garnet zone where amphibole has between 1 2 and 1 8 formula proportion al iv and al vi fe 3 ti cr this gap is below the garnet isograd in low pressure mafic schist where al iv and al vi fe 3 ti cr in the amphibole are both less than 0 6 mineral growth periods observed are characterized by metamorphic grade and facies series and are assigned to two ordovician taconic and two devonian acadian events silurian devonian mafic schist in northeastern vermont records two periods of low pressure devonian metamorphism these events are expressed by medium pressure and low pressure metamorphism in the cambrian and ordovician rocks to the west and south in the pre silurian rocks high pressure and medium pressure metamorphism is assigned to the ordovician the observed high pressure metamorphism is confined to a 110 by 40 km area along the green mountain anticlinorium axis in north central vermont

subsidence in late paleozoic basins in the northern appalachians during the interval between continental collision in the devonian and continental breakup in the triassic the northern appalachians became the site of a wide plate boundary zone of dominantly right lateral strike slip as is typical of intracontinental transforms tectonism was both diachronous and rapidly variable along strike through regimes of pure strike slip transpressional deformation and rapid subsidence of extensional basins up to 9 km of mainly nonmarine clastic sediments accumulated in these local depocenters which subsided episodically in two stages 1 an initial phase of stretching and thinning of the lithosphere when subsidence was rapid fault controlled and often accompanied by volcanism and 2 a subsequent phase of gradual thermal subsidence during which the depositional basins expanded to bury the earlier border faults and progressively younger sedimentary units onlapped basement the largest depocenter the magdalen basin opened as a pull apart between strike slip faults in newfoundland and new brunswick from late devonian to early carboniferous subsequent thermal subsidence affected a large area during medial and late carboniferous a phenomenon that is well recorded to the north and west where no later tectonism occurred in areas to the south and east of the basin strike slip on other faults continued into the time of thermal subsidence introducing complications such as localized transpressional deformation and rapid subsidence in smaller pull aparts

late mesozoic post collisional intermediate to silicic magmatism in the badjal area far east of russia abstract the late cretaceous badjal intrusive suite at the far east of russia includes a spectrum of rocks having emplaced successively in four phases from i diorite and quartz diorite to ii granodiorite iii granite and iv high silica granite various facies being distinguished within the phases the generation of these rocks took place after the collision of a number of island arcs and a terrane now locally preserved in sikhote alin region with the asian continent that had happened in the end of early to the beginning of late cretaceous the massifs intrude in early mesozoic sedimentary and volcanic sedimentary rocks topping the basement and in comagmatic volcanic rocks chemically the granitoid rocks have high k calc alkaline character and form continuous and regular trends of most of major oxides and trace elements with the sio2 contents ranging from 55 to 77 wt that favors the concept of crystal fractionation major oxides and ree have a break at 70 wt sio2 pointing to a change of precipitating mineral assemblage such change is also documented by the negative eu anomaly we believe that the fractionation of mafic minerals had to take place at the first stage of fractionation whereas plagioclase and possibly biotite began precipitating later as supposed by abrupt decrease of ba this hypothesis is in accordance with the mass balance calculations diorite magma compositionally similar to the first intrusive phase rocks should be taken for parental for the entire badjal suite small volume of these oldest rocks makes us suggest that the parental magma was a mixture of silicic liquid and restite mineral phases that would result from the partial melting of a heterogeneous metapelite basaltic or metapelite amphibolitic protolith almost total absence of basalt and gabbro of close age in the area makes a suggestion of crustal silicic contamination of a mantle produced basic magma unlikely after the melting the differentiation of the derived magmatic mixture during ascent and the separation of mineral phases acquired from the protolith restite phases and of newly formed ones are believed to produce the entire range of rocks of the badjal intrusive suite provided the progressive succession of emplacement from less to more silicic species

fission track evidence for cenozoic uplift of the nelson batholith southeastern british columbia apatite and zircon fission track data from the nelson batholith in southeastern british columbia reveal that a significant amount of uplift has occurred since paleocene time including an episode of rapid uplift during eocene time age versus elevation curves for apatite and zircon combined with a calculated present depth to the 105 c apatite annealing isotherm suggest that some 6 km of apparent uplift has occurred in the vicinity of the nelson batholith since paleocene time a period of rapid cooling and uplift occurred from 59 to 45 ma when the bounding faults of the adjacent valhalla gneiss dome the valkyr shear zone and the slocan lake fault zone were active the rapid uplift is interpreted as being related to eocene extension and the rise of the adjacent valhalla gneiss dome during eocene time

a tale of two plutons petrographic and mineralogic constraints on the petrogenesis of the red lake and eagle peak plutons central sierra nevada california the red lake and eagle peak plutons are similar in age k ar 87 89 m y and range in composition from granodiorite to granite the red lake pluton is equigranular has a locally greisened marginal zone and shows only minor mineralogical and chemical zoning whereas the eagle peak pluton is mineralogically compositionally and texturally zoned with an equigranular margin and a porphyritic core modal and normative trends within each pluton are consistent with separation of plagioclase and mafic minerals leading to a residual liquid enriched in quartz and alkali feldspar the formation of the prominent alkali feldspar megacrysts in the eagle peak core was promoted by plagioclase separation h 2 o undersaturation and a slower cooling rate relative to the red lake magma early loss of volatiles and a resulting increase in magma melt crystals viscosity inhibited crystal segregation within the red lake pluton and prevented the development of zoning late stage aplites associated with both plutons f

magma reservoir conditions beneath tsurumi volcano sw japan evidence from amphibole thermobarometry and seismicity abstract calcic amphibole phenocrysts in the tsurumidake summit ts lava which was produced during the most recent eruption at tsurumi volcano sw japan at around 7 5 10 5 ka have been analyzed to determine the pre eruptive conditions such as temperature t pressure p oxygen fugacity fo2 sio2 content sio2melt and feo mgo ratio feo mgomelt of coexisting silicate melts in the magma reservoir beneath the volcano although most of the amphibole phenocrysts have been completely decomposed to a fine grained opaque symplectite 6 of the grains remain intact the degree of amphibole breakdown dab defined as the ratio of the area of symplectite to the area of symplectite plus relict amphibole in each phenocryst varies from 20 to 100 compositional zoning was not observed in the amphibole grains however two distinct groups of amphibole phenocrysts have been identified based on their chemical compositions group i amphiboles which are relatively si poor and 6 al rich and have a relatively high mg 100mg mg fe2 and group ii amphiboles which are si rich and 6 al poor and have a relatively low mg empirical equations for geothermobarometry oxygen barometry and chemometry that exclusively rely on the amphibole composition were applied to estimate the t p fo2 sio2melt feo mgomelt conditions of the silicate melts with which the amphibole crystals equilibrated the results show that group i and group ii amphiboles equilibrated with andesitic melts group i melts and dacitic rhyolitic melts group ii melts respectively the t p fo2 conditions of group i melts were estimated as 374 483 mpa 13 9 17 9 km depth 950 c and nno 1 3 respectively and those of group ii melts were 93 242 mpa 3 4 9 0 km depth 824 913 c and nno 0 6 1 7 respectively the estimated t p fo2 sio2melt feo mgomelt conditions were almost constant for group i melts whereas the t nno and feo mgomelt values of group ii melts decreased with increasing sio2melt the dab decreased as the temperature increased low dab grains are absent in group ii amphiboles our results suggest that 1 a deeper reservoir at a depth of 16 km stored an andesitic melt coexisting with group i amphiboles at 950 c 2 a chemically zoned reservoir at shallower depth 6 4 km was filled with dacitic rhyolitic melts that coexisted with group ii amphiboles at 824 913 c 3 the ts lava was the product of magma mixing of at least three components including the andesitic melt derived from the deeper reservoir the dacitic and rhyolitic melts from the shallower reservoir and a mafic magma derived from the lower crust and or upper mantle and 4 the ts lava eruption occurred within a month or less of the magma mixing

strontium and oxygen isotopic variations in mesozoic and tertiary plutons of central idaho regional variations in initial 87sr 86sr ratios r i of mesozoic plutons in central idaho locate the edge of precambrian continental crust at the boundary between the late paleozoic mesozoic accreted terranes and precambrian sialic crust in western idaho the r i values increase abruptly but continuously from less than 0 704 in the accreted terranes to greater than 0 708 across a narrow 5 to 15 km zone characterized by elongate lens shaped highly deformed plutons and schistose metasedimentary and metavolcanic units the chemical and petrologic character of the plutons changes concomitantly from ocean arc type diorite tonalite trondhjemite units to a weakly peraluminous calcic to calcalkalic tonalite granodiorite granite suite the idaho batholith plutons in both suites yield late cretaceous ages but permian through early cretaceous bodies are confined to the accreted terranes and early tertiary intrusions are restricted to areas underlain by precambrian crust the two major terranes were juxtaposed between 75 and 130 m y ago probably between 80 and 95 m y oxygen and strontium isotopic ratios and rb and sr concentrations of the plutonic rocks document a significant upper crustal contribution to the magmas that intrude precambrian crust magmas intruding the arc terranes were derived from the upper mantle subducted oceanic lithosphere and may have been modified by anatexis of earlier island arc volcanic and sedimentary units plutons near the edge of precambrian sialic crust represent simple mixtures of the precambrian wall rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r i of 0 7035 rb sr varies linearly with r i producing pseudoisochrons with apparent ages close to the age of the wall rocks measured 18o values of the wall rocks are less than those required for the assimilated end member by sr o covariation in the plutons however indicating that wall rock 18o was reduced significantly by exchange with circulating fluids metasedimentary rocks of the belt supergroup are similarly affected near the batholith documenting a systematic depletion in 18o as much as 50 km from the margin of the batholith plutons of the bitterroot lobe of the idaho batholith are remote from the accreted terranes and represent mixtures of precambrian wall rocks with melts dominated by continental lower crust r i 0 708 rather than mantle pseudoisochrons resulting from these data are actually mixing lines that yield apparent ages less than the true age of the wall rocks and meaningless ri assimilation fractional crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region

contrast of metamorphic and structural histories across the work channel lineament coast plutonic complex british columbia a prominent topographic lineament along the western margin of the coast plutonic complex of southeast alaska and adjacent parts of british columbia separates terranes of contrasting metamorphic histories where it enters british columbia near prince rupert as the work channel lineament the western terrane preserves a regional medium high pressure metamorphic facies series increasing from chlorite grade in the west to kyanite muscovite migmatite near the lineament the metamorphic structural and age relations of the western terrane are consistent with a model of crustal thickening accompanied by westward transport of higher over lower grade metamorphic units during the jurassic this terrane was uplifted and cooled by cretaceous time 85 ma east of work channel lineament high temperature relatively low pressure assemblages are overprinted onto high pressure assemblages the low pressure metamorphic assemblages developed in the eocene during rapid uplift 2 mm yr of rocks which initially may have been metamorphosed at the same time and along the same pt gradient as those of the western terrane structures along the work channel lineament suggest vertical motion during uplift of the eastern terrane and after metamorphism of the western terrane because the metamorphic discontinuity across the lineament is 3 5 kbar at about 700 the lineament in the prince rupert area marks a major crustal break

silver lead zinc veins and crustal hydrology during eocene extension southeastern british columbia canada abstract the kokanee range southeastern british columbia canada contains more than 370 ag pb zn vein and replacement deposits hosted by the middle jurassic nelson batholith and surrounding cambrian to triassic metasedimentary rocks all deposits are in the hanging wall of the slocan lake fault an east dipping low angle normal fault that reaches the moho and along which the valhalla metamorphic core complex has been unroofed during the eocene fluid inclusions in sphalerite quartz or siderite indicate a temperature and pressure of trapping of approximately 300 c and 0 17 gpa the fluid inclusions display a large range of salinities from 0 to 18 wt nacl eq assuming lithostatic pressure at the time of mineralization the depth of mineralization was 6 3 km 34ssulfide values display a 20 range and a regional zonation that correlates with the distribution of sulfur isotopic compositions of host rocks in contrast gd13csiderite values are homogeneous 7 1 0 5 over an area of 1200 km2 it is concluded that s was derived from local country rocks whereas c was derived from mantle co2 degassing the 18osiderite and 18orock values display regional zonations revealing fluid flow paths of a large ancient hydrothermal system three different fluids are identified from salinity 18o and d values 1 1 a high salinity deep seated and isotopically crust equilibrated fluid 2 2 a low salinity upper crustal fluid of evolved meteoric origin 3 3 meteoric water mixing between thermally similar fluids having different salinities is proposed to have been the dominant mineralizing process regional isotopic zonations are controlled by the slocan lake fault which channelled deep seated hydrothermal fluids and mantle co2 to higher crustal levels where mixing occurred with upper crustal fluids that leached local sulfur meteoric water invaded the fracture network in the waning stages of the hydrothermal system

experimental data for a proposed empirical igneous geobarometer aluminum in hornblende at 10 kbar pressure knowledge of the depth of solidification of talc alkalic plutons is critical to understanding and unraveling the complex spatial temporal and chemical evolution of orogenic belts an empirical geobarometer has recently been proposed based on the total al content alt of near solidus calcic hornblendes in tonalite and granodiorite intrusive rocks in the pressure range 1 to 8 kbar pressures were estimated from mineral assemblages in associated metamorphic country rocks we report experimental data on newly crystallized near solidus amphiboles in partly melted vapor absent garnet tonalite at 10 kbar that provide some experimental support for the proposed geobarometer consistent with the extrapolated empirical result and confirm its limited applicability to specific multimineral assemblages

tectonic domains and exhumation history of the omineca belt in southeastern british columbia from 40ar 39ar thermochronology a large geochronological data set comprising 40ar 39ar and k ar hornblende muscovite biotite and k feldspar rb sr muscovite fission track zircon and apatite and u pb zircon and monazite

a multidisciplinary study of the emplacement mechanism of the qingyang jiuhua massif in southeast china and its tectonic bearings part ii amphibole geobarometry and gravity modeling abstract the late mesozoic geology of the lower yangtze area is characterized by extensional sedimentary basins numerous granitic plutons and several world class ore deposits regionaly the coeval tectonic and geodynamic framework remains inadequately investigated in order to provide a more comprehensive understanding of the regional tectonic context we performed a multidisciplinary study of the emplacement mechanism of the qingyang jiuhua massif it consists of the granodioritic qingyang and the monzogranitic jiuhua plutons u pb dated at 142 1 0 ma and 131 2 6 ma respectively biotite and amphibole cooling ages are 5 8 myr younger results deduced from field structural observation petrographic and magnetic fabrics paleomagnetism show that this massif was probably vertically emplaced by permissive intrusion coeval with weak regional extension however detailed information on the characteristics of this tectonic event and its emplacement depth was not documented therefore we carried out an investigation of amphibole geobarometry and gravity modeling in order to address the emplacement mode of the plutons within their regional tectonic framework amphibole data show that the qingyang jiuhua massif was emplaced in the upper crust at a depth between 5 and 12 km gravity modeling indicates that the massif is laccolithic it is characterized by several ne sw striking linear thickening zones that we interpret as the feeder roots of the massif these results led us to conclude that 1 the qingyang jiuhua massif was fed by vertical ne sw striking tension gashes 2 consequently the late early cretaceous tectonics in the study area was characterized by nw se extension

emplacement petrological and magnetic susceptibility characteristics of diverse magmatic epidote bearing granitoid rocks in brazil argentina and chile abstract magmatic epidote mep bearing granitoids from five neoproterozoic tectonostratigraphic terranes in northeastern ne brazil early palaeozoic calc alkalic granitoids in northwestern nw argentina and from three batholiths in chile have been studied the elongated shape of some of these plutons suggests that magmas filled fractures and that dyking was probably the major mechanism of emplacement textures reveal that in many cases epidote underwent partial dissolution by host magma and in these cases may have survived dissolution by relatively rapid upward transport by the host magma in plutons where such a mechanism is not evident unevenly distributed epidote at outcrop scale is armoured by biotite or near solidus k feldspar aggregates which probably grew much faster than epidote dissolution preventing complete resorption of epidote by the melt al in hornblende barometry indicates that in most cases amphibole crystallized at p 5 kbar kyanite bearing thermal aureoles surrounding plutons that intruded low grade metamorphic rocks in ne brazil support pluton emplacement at intermediate to high pressure mep show overall chemical variation from 20 to 30 mol mole percent pistacite ps and can be grouped into two compositional ranges ps20 24 and ps27 30 the highest ps contents are in epidotes of plutons in which hornblende solidified under p 3 0 10 3 si typical of magnetite series granitoids crystallized under higher oxygen fugacity in ne brazil argentina and chile it seems that mep is more common in precambrian to palaeozoic ilmenite series granitoids while its occurrence in magnetite series granitoids is more restricted to mesozoic to tertiary granitoids

the effects of stress and fracturing on permeability of coal abstract this paper examines the changes in structure and permeability of coal under the stress conditions experienced around longwall faces the effect of fracturing on permeability of coal is discussed and the stress permeability relationship for fractured coal is compared with that of non fractured coal an empirical relationship between stress and permeability for coal is derived from the experimental data which relates the stress permeability behaviour of coal to its rank through the compressibility of the coal itself

epidote phenocrysts in dacitic dikes boulder county colorado epidote ps21 crystallized early as elongate phenocrysts in late cretaceous rhyodacitic dikes in the vicinity of ward boulder county colorado other unusual phenocryst phases are garnet gr17 24 and muscovite in a xenolith containing kyanite corundum biotite and plagioclase magmatic garnet grew as a rim around xenocrystic pyrope rich py37 garnet the xenolith was derived from a granulite facies zone not represented at the present day erosion surface which is composed of upper amphibolite facies cordierite and sillimanite bearing gneisses the dike magmas were fed not from an immediately underlying batholith but from a magma chamber at a depth corresponding to a pressure of 8 13 kilobars phenocrysts cystallized in the temperature range 800 to 700 c under h2o and o2 activities greater than normal for silicic magmas this occurrence shows convincingly not only that epidote can be magmatic but that it is a possible early crystallization phase in silicic magmas

time space relationships among structural and metamorphic aureoles related to granite emplacement a case study from the serre massif southern italy tectonic and thermal perturbations related to emplacement of granodiorite in the upper continental crust have been investigated in the late hercynian basement exposed in southern calabria italy here the structural aureole is marked by the presence of a major rim fold adjacent to the intrusive contact for a length of at least 20 km geometrical analysis of the structural aureole and related foliations lineations and crenulations reveals that the perturbed zone is at least 3000 m wide and characterized by an open synform trending nearly parallel to the intrusive contact this pattern is compatible with a laccolith like mode of magma emplacement related to the accretion of the pluton that shouldered weak phyllitic and slaty wall rocks the metamorphic aureole about 1800 m wide is characterized by biotite cordierite and andalusite that appear sequentially in spotted schists and hornfelses approaching the intrusive contact the peak assemblage equilibrated between 535 and 590 c at pressures between 175 and 200 mpa confirmed by al in hornblende barometry on granodiorite microstructural analysis allowed the inference of a time lag between the thermal and tectonic perturbations with the aid of thermal modelling it was possible to quantify the time required to reach the peak temperature at a distance from the intrusive contact where cordierite spots and andalusite porphyroblasts clearly overprint crenulations this estimate represents the time limit to accomplish deformation in the inner portion of the aureole and thus indicates a minimum strain rate of 4 10 14 s 1 within the country rocks during granodiorite intrusion

18o 16o evidence for contrasting hydrothermal regimes involving magmatic and meteoric hydrothermal waters at the valhalla metamorphic core complex british columbia modeling of published oxygen isotope analyses of 115 whole rock quartz and feldspar samples from the valhalla metamorphic core complex provides evidence for three distinct stages of hydrothermal activity affecting the detachment faults and upper plate 1 lithostatically pressured aqueous fluids having 18o 10 per mil were expelled from the lower plate and moved upward into the upper plate through an oblique sinistral transfer zone between the southern terminus of the columbia river detachment fault and the northern terminus of the slocan lake detachment fault these fluids ascended through fractures and exchanged with slocan group shales and graywackes to produce the marked zonation of vein siderite 18o 11 4 18 4 observed in previous studies of the sandon group of ag pb zn lode deposits 2 later as brittle deformation along the slocan lake detachment fault became the dominant tectonic process these magmatic and or metamorphic fluids intermittently mixed with even larger quantities of downward circulating hydrostatically pressured meteoric hydrothermal fluids in the upper plate nelson granodiorite adjacent to the slocan lake detachment fault 18o values of quartz 8 9 11 9 and feldspar 5 0 to 9 6 define a steep array in space slope 25 suggesting that synextensional meteoric hydrothermal activity along the slocan lake detachment fault initial 18owater 15 and t 300 c was relatively short lived 106 yr but very intense with w ropen system 1 05 and fluid flux 0 1 to 3 m yr the 18o values of quartz 10 8 12 4 and feldspar 6 4 10 1 from lower plate greenschist mylonites indicate that small quantities of the low 18o meteoric hydrothermal fluids penetrated into the lower plate the systematic decrease in feldspar 18o toward the slocan lake detachment fault in both the upper and lower plates shows that these low 18o waters were channeled along the detachment fault 3 meteoric hydrothermal activity along the valkyr shear zone postdates ductile deformation and was associated with the emplacement of the coryell plutons in the upper plate the 18o values of quartz 7 6 11 0 and feldspar 0 0 8 6 from the valkyr shear zone define a much shallower array in space slope 2 3 than those at the slocan lake detachment fault indicating a higher temperature and or longer lived episode of hydrothermal activity the geographic distribution of pronounced disequilibrium 18o effects in coryell quartz 5 8 8 2 and feldspar 4 4 to 7 4 indicates that meteoric hydrothermal activity was most intense along inferred coeval extensional fracture zones that lie beneath arrow lake this modeling suggests that transfer zones that accommodate deformation between detachment faults may be a very attractive exploration setting for lode type mineral deposits

current status and geological conditions for the applicability of cbm drilling technologies in china a review abstract coalbed methane cbm drilling technology is critical in achieving efficient cbm development the geological conditions for cbm development in china are complex including special terrain high rank coal areas deep coal seams multiple superposed coal seams and coal measure gas symbiosis areas steeply inclined coal seam areas and tectonic coal seam areas therefore it is critical to apply the optimum drilling technology in each different area this paper first reviews the current cbm drilling technologies and gas production behaviors in china it is found that although vertical wells and cluster well groups are common well types for cbm development in china u v and l shaped horizontal wells and multilateral horizontal wells have been favored for cbm development in recent years the paper then discusses the applicability of different well types to geological conditions and proposes a modification method for well design in various geologic conditions this method uses the coal structure ro in situ stress and ratio of critical desorption pressure to the reservoir pressure as the main inputs

large lateral ramps in the eocene valkyr shear zone extensional ductile faulting controlled by plutonism in southern british columbia abstract a 2 5 km high s facing lateral ramp links northern and southern segments of the ductile eocene valkyr extensional shear zone which defines the upper and outer boundary of the valhalla core complex in southern british columbia canada the evolution of the valkyr shear zone and of the lateral ramp is strongly influenced by the setting and geometry of middle jurassic tonalitic plutons and of paleocene eocene leucogranite aplite and pegmatite middle jurassic plutons were emplaced in the region of the valhalla complex as a series of interconnected flatbottomed laccoliths with the basal surfaces of adjacent bodies at the same structural level however on a large scale the southern portion of the laccolithic complex is structurally 2 5 km lower than the northern portion the lower surface of the laccolithic complex formed the upper limit of injection of gently dipping paleocene eocene leucogranite sheets as a consequence the upper margin of leucogranite is 2 5 km structurally lower in the south than in the north during the eocene extensional shear zones propagated along the interface between the upper plate stiffened by the cool strong middle jurassic tonalite and the lower plate made weak and ductile by voluminous hot paleoceneeocene leucogranite sheets the northern and southern segments of the valkyr shear zone propagated at two different structural levels and a lateral ramp formed in the intervening zone the ramp was localized at a rheological change across a s dipping boundary between hot ductile paleocene eocene leucogranite and an adjacent strong middle jurassic pluton maximum displacement of 15 20 km occurs in the central portion of the northern segment of the valkyr shear zone the southern segment has only 1 3 km of displacement this has left the pre eocene geological relationships of the southern valhalla complex and its surrounding rocks nearly intact and it can be demonstrated that the valkyr shear zone formed with a gentle original dip

age and tectonic setting of the camaguey volcanic intrusive arc cuba late cretaceous extension and uplift in the western greater antilles abstract ar ar ages determined on rocks and minerals from the camaguey area in central cuba provide age constraints on events that accompanied the northward migration of cuba into the caribbean region and its subsequent collision with the bahamas bank whole rock samples from the camujiro and piragua formations part of the camaguey volcanic sequence yielded ar ar ages of 74 72 ma distinctly younger than the 100 80 ma ages indicated by fossils in interlayered sedimentary rocks syenite and granodiorite in the camaguey batholith which cut these volcanic rocks yield generally similar ar ar ages of 75 72 ma for hornblende biotite and feldspar these ages are interpreted to reflect relatively rapid uplift and cooling of most of the volcanic intrusive arc additional constraints on the timing of this uplift are provided by ar ar ages of 71 75 ma for rhyolite rhyodacite domes of the la sierra formation and 52 ma for andesitic basalt of la mulata formation which appear to have been emplaced onto erosion s

alleghanian polyphase deformation of the hope valley shear zone southeastern new england structural petrographical and rb sr isotopic studies in the highly deformed basement rocks of southern rhode island have allowed the identification of the southern continuation of the hope valley shear zone hvsz previous work recognized the hvsz as an alleghanian tectonic boundary separating the distinct late precambrian esmond dedham and hope valley terranes in southeastern new england two important components of the esmond dedham terrane the late precambrian ponaganset gneiss and the devonian scituate granite gneiss now have been traced with structural continuity into southern rhode island the distribution of these gneissic units and their structures shows that the southern segment of the hvsz has been strongly deformed abruptly deflecting it from a nw se orientation to a n s trend the deflection of the hvsz marks an abrupt structural boundary between two distinct regionally developed mineral lineation domains a northwestern domain with north to nnw trends characteristic of most of the hvsz and a southeastern domain with ne trends structural relations suggest that all mineral lineations were originally parallel along the hvsz with a north to nnw trend the deflection formed during a subsequent phase of ductile right lateral shear producing a clockwise rotation of both lineations and the hvsz in southern rhode island thus basement gneisses in southeastern new england have suffered polyphase alleghanian deformation at high metamorphic grades it has been argued that during the late paleozoic southern new england was located in a structural transition zone between convergent tectonics in the central and southern appalachians and wrench tectonics in the northern appalachians the structural link between these two distinct tectonic regimes is an e w right lateral transcurrent fault the late dextral shear deformation described in southern rhode island basement rocks appears to have resulted from right lateral movement at depth within this transcurrent fault zone

variable gas content saturation and accumulation characteristics of weibei coalbed methane pilot production field in the southeastern ordos basin china using diverse geologic and geophysical data from recent exploration and development and experimental results of analysis of gas content gas capacity and gas composition this article discusses how geologic structural and hydrological factors determine the heterogeneous distribution of gas in the weibei coalbed methane cbm field the coal rank of the pennsylvanian no 5 coal seam is mainly low volatile bituminous and semianthracite the total gas content is 2 69 to 16 15 m3 t 95 00 570 33 scf t and gas saturation is 26 0 to 93 2 burial coalification followed by tectonically driven hydrothermal activity controls not only thermal maturity but also the quality and quantity of thermogenic gas generated from the coal gas composition indicates that the cbm is dry and of dominantly thermogenic origin the thermogenic gases have been altered by fractionation that may be related to subsurface water movement in the southern part of the study area three gas accumulation models are identified 1 gas diffusion and long distance migration of thermogenic gases to no flow boundaries for sorption and minor conventional trapping 2 hydrodynamic trapping of gas in structural lows and 3 gas loss by hydrodynamic flushing the first two models are applicable for the formation of two cbm enrichment areas in blocks b3 and b4 whereas the last model explains extremely low gas content and gas saturation in block b5 the variable gas content saturation and accumulation characteristics are mainly controlled by these gas accumulation models

the stability of amphibole in andesite and basalt at high pressures reinvestigation of earlier work on mt hood andesite and kilauea olivine tholeiite under n no conditions and with silver capsules the revised curve for the appearance of garnet is significantly lower in pressure no orthopyroxene appeared in the run products in contrast to the results of the earlier work the high temperature segment of the amphibole out curve for the tholeiite is at least as high as 1040 degrees c at 13 kbar and 1050 degrees c at 16 kbar and the high pressure part of this curve is at about 27 kbars about 6 kbar higher than in the earlier work amphibole is the sole silicate phase on the vapor saturated liquidus in the andesite at pressures below the garnet in curve 15 5 kbar revised phase relationships are consistent with the derivation of andesite by amphibole liquid equilibria in basaltic magma and reveal stability to depths of nearly 100 km the great depths to which amphiboles are stable make it probable that they are a source of h 2 o for martial melting in deeply subducted oceanic crust modified journal abstract

crust mantle interaction and craton destruction evidence from late mesozoic plutons in the north china craton late mesozoic granitoids widely distributed in the yanshan belt of the north china craton ncc are important markers of cratonic destruction and lithospheric thinning we report new petrological geochemical zircon u pb and lu hf isotopic data on two late mesozoic granitic plutons from the central ncc near the trans north china orogen we report zircon u pb emplacement ages of 162 156 ma and 132 ma from the siganding and fangshan plutons respectively indicating late jurassic early cretaceous magmatism the presence of a dusty zone and discontinuous zoning in plagioclase phenocrysts and the occurrence of mafic microgranular enclaves in both granitoid plutons suggest mingling and mixing of felsic and basic magmas the rocks investigated in this study show high na 2 o k 2 o and high mg mg mg fe mg and are metaluminous with enrichment in light rare earth elements and large ion lithophile elements rb ba u and sr and depletion in high strength field elements th u nb ta p and ti they also display negative ehf t values and high sr y ratios comparable with adakitic rocks suggesting that the felsic magmas of these intrusions were probably derived from the partial melting of the palaeoproterozoic two stage zircon hf depleted model ages between 2 5 and 1 9 ga thickened lower crust of the ncc whereas the mafic magma was probably derived from subcontinental lithospheric mantle we correlate the magmatism with lithospheric thinning beneath the ncc and associated crust mantle interaction it is inferred that lithospheric thinning was of limited extent in late jurassic 162 156 ma times the magma flare up at around 130 ma was produced by large scale melting of the enriched subcontinental lithospheric mantle with development of extensive intracontinental adakitic magmatic rocks derived from thickened ancient lower continental crust with variable involvement of subcontinental lithospheric mantle supplementary material mineral assemblages and abundance representative electron microprobe analyses la icp ms zircon u pb age data and la mc icp ms lu hf isotopic data are available at https doi org 10 6084 m9 figshare c 3815308

mantle derivation of archean amphibole bearing granitoid and associated mafic rocks evidence from the southern superior province canada amphibole bearing late archean 2 73 2 68 ga granitoids of the southern superior province are examined to constrain processes of crustal development the investigated plutons which range from tonalite and diorite to monzodiorite monzonite and syenite share textural mineralogical and geochemical attributes suggesting a common origin as juvenile magmas despite variation in modal mineralogy the plutons are geochemically characterized by normative quartz high al2o3 15 wt na rich fractionation trends mol na2o k2o 2 low to moderate rb generally 150 ppm are comagmatic with the evolved granitoids and indicate that the suites are mantle derived isotopic studies of archean monzodioritic rocks have shown lree enrichment and initial 143nd 144nd ratios indicating derivation from mantle sources enriched in large ion lithophile elements lile shortly before melting mineral assemblages record lower ph2o with increased alkali contents of the suites this evidence in conjunction with experimental studies suggests that increased alkali contents may reflect decreased ph2o during mantle melting these features indicate that 2 73 ga tonalitic rocks are derived from more hydrous mantle sources than 2 68 ga syenitic rocks and that the spectrum of late archean juvenile granitoid rocks is broader than previously recognized comparison with phanerozoic and recent plutonic suites suggests that these archean suites are subduction related

petrological constraints on crystallization conditions of mesoarchean sanukitoid rocks southeastern amazonian craton brazil we report petrological and geochemical data for the 2 87 ga rio maria sanukitoid granodiorite and associated rocks from mesoarchean granite greenstone terranes of the eastern amazonian craton brazil the dominant rocks have granodiorite to subordinate monzogranitic compositions with minor proportions of intermediate quartz diorites or quartz monzodiorites in addition to mafic endmembers occurring as layered rocks or as enclaves the mineral assemblage is dominated by amphibole plagioclase biotite and epidote minerals all of inferred magmatic origin pyroxenes being notably absent textural and compositional criteria indicate that amphibole is a principal mineral on the liquidus of all the rio maria rocks crystallization conditions have been derived from a comparison between natural phase assemblages proportions and compositions and experimental studies carried out on similar magma compositions the comparison shows that the parental magmas were water rich with more than 7 wt dissolved h2o with crystallization temperatures in the range 950 680 c the mg mg fe ratios of both amphibole and biotite indicate fo2 conditions in the range nno 0 5 to nno 2 5 where nno is nickel nickel oxide buffer therefore pointing to both water rich and oxidizing conditions for sanukitoid magmas amphibole compositions indicate emplacement at around 200 mpa and record a high pressure stage of magma crystallization around 600 900 mpa sanukitoid magmas share two of the principal characteristics of modern arc magmas elevated redox state and volatile contents which suggest that they may have formed in a geodynamic environment broadly similar to present day subduction zones

characteristics of natural fractures in the upper paleozoic coal bearing strata in the southern qinshui basin china implications for coalbed methane cbm development abstract natural fractures as the effective storage space and fluid flow pathway of hydrocarbons play a critical role in the exploration and development of unconventional gas resources in the coal bearing strata in the present study to reveal the effects of natural fractures on coalbed methane cbm preservation and development the types origins and development characteristics of natural fractures in the upper paleozoic permian shanxi formation in the southern qinshui basin were systematically described and analyzed based on outcrops cores borehole image logs thin sections and sem four types of natural fractures have been identified in the shanxi formation according to their geologic origins including the endogenic fractures cleats and exogenous fractures in the no 3 coal seam and tectonic fractures and diagenetic fractures in its roof and floor tectonic fractures can be further divided into small faults intraformational shear fractures intraformational open fractures and slip fractures while diagenetic fractures are mainly bed parallel fractures the statistical results show that the development and distribution characteristics of those types of fractures are significantly different which are mainly influenced by lithology layer thickness and geological structure further natural fractures with different types and distributions show different influences on cbm preservation and well productivity exogenous fractures can effectively improve the seepage capability of coal reservoirs and are conducive to cbm wells productivity whereas endogenic fractures have less contributions to coal permeability due to their poor effectiveness the intraformational open fractures in the fold axis zones and intraformational shear fractures and small faults in the fault zones are generally excessive developed those fractures may result in gas dissipation and external water supplement which have negative effects on cbm preservation and production however moderate developed intraformational shear fractures in the sandstone roof can favorably affect the pressure reduction of coal reservoir and improve the recovery potential of unconventional gas resources these investigations may serve as a geological basis for unconventional gas exploration and development of the upper paleozoic coal bearing strata in the southern qinshui basin

age and origin of late jurassic and paleocene granitoids nelson batholith southern british columbia in the middle jurassic nelson batholith southern british columbia young 40ar 39ar ages i e 50 60 ma and distorted isobaric surfaces in the batholith suggest the possibility of paleocene granitic plutonism we present the results of a study undertaken to evaluate this possibility geochemical criteria successfully distinguish a suite of granitoids within the nelson batholith that differ from nelson granites of similar sio2 content the granitoid suite is composed of 71 6 75 7 wt sio2 leucocratic biotite granite and quartz monzonite with strong enrichments in alkaline alkaline earth and rare earth elements nd and pb isotopic compositions suggest that biotite granite and quartz monzonite are not related biotite granite yields a u pb age of 158 9 0 6 ma concordant zircons quartz monzonite crystallized at 61 1 ma based on interpretation of titanite and zircon analyses zircons from this sample lie along a line from 61 to 160 ma and demonstrate the presence of middle jurassic inheritance ba

preliminary evaluation of the coalbed methane production potential and its geological controls in the weibei coalfield southeastern ordos basin china article i nfo the coalbed methane cbm geology resource and production potential in the weibei coalfield southeastern ordos basin are studied based on geological surveys and laboratory measurements the results showed that coal rank varies both laterally and vertically and changes from volatile bituminous coals in the margin to anthracites towards the basin 1 6 2 5 ro coals are composed of 60 85 vitrinite 15 40 inertinite and a trace amount of minerals methane isothermal adsorption measurements of 20 coal samples revealed that the maximum adsorption capacity on a dry and ash free basis of coals which are affected by coal rank coal maceral coal lithotype and especially to the moisture content varies from 13 91 to 29 54 m 3 t estimated gas contents range from 0 to 15 m

dynamic variation effects of coal permeability during the coalbed methane development process in the qinshui basin china abstract the commercial exploitation of coalbed methane cbm has been achieved in the qinshui basin china however the productivity of wells varies greatly because of their different geological settings and production rules and the permeability damage to coal reservoirs caused during the development process is one of the most important factors affecting productivity in this study the patterns of permeability variation in coal seam no 3 and their influence on cbm recovery were analyzed and the degree of permeability damage caused by different factors was calculated the results show that the burial depth the bottom hole pressure and the dewatering rate affected the effective stress imposed on the coal reservoir which further induced changes in permeability and productivity the elastic modulus of the coal body reflects its ability to withstand compression the greater the elastic modulus is the less the permeability decreases when the pressure drops from 7 05 mpa to 0 20 mpa the relatively low elastic modulus of coal seam no 3 can cause a 10 decrease in permeability coals at different burial depths have different formation pressures and elastic moduli causing different levels of permeability damage during the development process calculations indicate that the absolute permeability will decrease by 5 5 and 14 3 at depths of 500 m and 1000 m respectively if the bottom hole pressure drops too fast or the dewatering rate is too high there will be a strong stress response resulting in decreasing permeability and productivity this study found that in high productivity wells a larger pressure drop approximately 0 022 mpa d and stroke 3 0 min are favorable in the early drainage period but a smaller pressure drop 0 002 mpa d and stroke 0 4 min should be applied when the gas peak appears

u pb geochronology of jurassic to early tertiary granitic intrusives from the nelson castlegar area southeastern british columbia canada eleven u pb zircon dates from seven intrusives in the nelson castlegar area provide new age constraints on the granitoid magmatism in southeastern british columbia four samples from the nelson batholith date three distinct intrusive phases spanning ca 10 ma one sample from the eastern porphyritic phase coffee creek yields the oldest age at 172 5 5 0 ma two samples from the central k feldspar megacrystic phase crescent bay give precise ages at 162 0 1 0 and 161 5 1 5 ma and possibly date the youngest phase of the batholith an intermediate age of emplacement at 166 0 3 0 ma is suggested for the southern tail of the batholith the new and published data suggest that the nelson batholith was emplaced in roughly concentric zones in contrast the southern quartz diorite phase and the northwestern granodiorite phase of the bonnington pluton were emplaced coevally during the middle jurassic at 167 4 2 0 and 165 0 3 0 ma respectively middle jurassic ages were also obtained for a sample of

crustal structure of the valhalla complex british columbia from lithoprobe seismic reflection and potential field data the valhalla complex situated in the omineca crystalline belt in southeastern british columbia is a cordilleran metamorphic core complex bordering the suture zone between quesnellia and north american rocks the region is tectonically interposed between a convergent plate margin along canada s west coast and the stable north american craton and is characterized by a crustal thickness of 35 km high surface heat flux and elevated lower crustal electrical conductivity in this study lithoprobe deep crustal seismic reflection data potential field data and geological constraints have been used to gain a better understanding of crustal structure in the vicinity of the valhalla complex analysis of bouguer gravity and total field aeromagnetic data indicates that mafic oceanic rocks and various syn and post accretionary granitoid plutonic rocks are not major constituents of the upper crust underlying the complex the seismic data reveal a moderately reflective upper crust and image several fault zones

in situ stress pore pressure and stress dependent permeability in the southern qinshui basin this study focuses on the in situ stress pore pressure and permeability in the southern qinshui basin one of largest coalbed methane basins in china well tests show that permeability in this basin is higher than other coalbed methane reservoirs this is because it is located in an extensional basin where the normal faulting stress regime is dominated this in situ stress regime is advantageous to keep coal cleats open hydraulic fracturing tests indicate that the fracture gradient or minimum horizontal stress is much lower than the shales in the gulf of mexico and other oil basins the minimum horizontal stress model is proposed with consideration of the stress coefficient based on the uniaxial strain method this model provides a fairly good prediction on the minimum stress permeability data show that the effective stress dependent permeability is pronounced in the coalbed methane reservoir this is significant for the dual porosity and dual permeability coal reservoirs which consist of coal porous matrices and cleats the reason is that a rapid increase in effective stress can induce the closure of cleats which may cause a permanent loss of permeability in the cleats this reduces the connectivity between the cleats and coal matrices hence the coal matrices cannot deliver gas pressure to the cleats for supporting the cleat space therefore slowing down the effective stress change during production e g slowing reservoir drawdown can decelerate the permeability reduction this is particularly important for the reservoir in which the pore pressure is not significantly overpressured such that in the southern qinshui basin

elastic and shear moduli of coal measure rocks derived from basic well logs using fractal statistics and radial basis functions abstract gamma ray density sonic and core logs obtained from two boreholes drilled over a longwall panel in southwestern sw pennsylvania were analyzed for formation boundaries log derived porosities and densities and for rock elastic properties from sonic transit times gamma ray gr and density logs dl were analyzed using univariate statistical techniques and fractal statistics for similarity and ordering of the log data in depth a fourier transformation with low pass filter was used as a noise elimination filtering technique from the original logs filtered data was tested using basic univariate and fractal statistics rescaled range r s and power spectrum ps analysis to compare the information characteristics of the filtered logs with the original data the randomness of log data in depth was analyzed for fractional gaussian noise fgn or fractional brownian motion fbm character a new prediction technique using radial basis function rbf networks was developed to calculate shear and young s moduli of the formations when sonic logs are not available for this approach the filtered logs were used as input to an rbf based upon a combination of supervised and unsupervised learning the network was trained and tested using rock elastic properties calculated from the sonic log of one of the boreholes the network was used to predict the elastic and shear moduli of the coal measure rocks over a longwall coal mine in sw pennsylvania this approach demonstrated that it could be used for prediction of elastic and shear moduli of coal measure rocks with reasonable accuracy

40ar 39ar age pattern associated with differential uplift along the eastern highlands shear zone cape breton island canadian appalachians abstract the eastern highlands shear zone in cape breton island is a crustal scale thrust it is characterized by an amphibolite facies deformation zone 5 km wide formed deep in the crust that is overprinted by a greenschist facies mylonite zone 1 km wide that formed at a more shallow level hornblende 40ar 39ar plateau ages on the hanging wall decrease towards the centre of the shear zone in the older zone over 7 8 km from the centre the ages are between 565 and 545 ma in the younger zone within 4 5 km of the centre they are between 425 and 415 ma and in the transitional zone in between they decrease abruptly from 545 to 425 ma pressures of crystallization of plutons in the hanging wall based on the al in hornblende barometer and corresponding to depth of emplacement increase towards the centre of the shear zone and indicate a differential uplift of up to 28 km associated with movement along the shear zone the age pattern is interpreted to have resulted from the differential uplift the pressure data show that rocks exposed in the younger zone were buried deep in the crust and did not cool through the hornblende ar blocking temperature 500 c until differential uplift occurred the 40ar 39ar ages in the zone 425 415 ma thus date shear zone movement or the last stage of it in contrast rocks in the older zone were more shallowly buried before differential uplift and cooled through the blocking temperature soon after the emplacement of 565 555 ma plutons in the area long before shear zone movement the transitional zone corresponds to the ar partial retention zone before differential uplift the 40ar 39ar age pattern thus reflects a neoproterozoic to silurian cooling profile that was exposed as a result of differential uplift related to movement along the shear zone a similar k ar age pattern has been reported for the alpine fault in new zealand it is suggested that such isotopic age patterns can be used to help constrain the ages kinematics displacements and depth of penetration of shear zones

crustal growth in south eastern australia evidence from lower crustal eclogitic and granulitic xenoliths mafic and ultramafic xenoliths in a basaltic cone at the anakies in south eastern australia are geochemically equivalent to continental basaltic magmas and cumulates the xenolith microstructures range from recognizably meta igneous for intrusive rocks to granoblastic for garnet pyroxenites contact relationships between different rock types within some xenoliths suggest a complex petrogenesis of multiple intrusive metamorphic and metasomatic events at the crust mantle boundary during the evolution of south eastern australia unaltered spinel lher zolite typical of the uppermost eastern australian mantle is interleaved with or veined by the metamorphosed intrusive rocks of basaltic composition geothermobarometry calculations by a variety of methods show a concordance of equilibration temperatures ranging from 880 c to 980 c and pressures of 12 to 18 kbar 1200 1800 mpa these physical conditions span the gabbro to granulite to eclogite transition boundaries the water vapour pressure during equilibration is estimated to be about 0 5 of the load pressure using amphibole breakdown data large fluid inclusions of pure co2 are abundant in the mineral phases in the xenoliths and it is suggested that flux of co2 from the mantle has been an important heat source and fluid medium during metamorphism of the mafic and ultramafic protoliths at the lower crust upper mantle boundary the calculated pressures and temperatures suggest that the south eastern australian crust has sustained a high geothermal gradient in addition the nature of the mineral assemblages and the contact relationships of granulitic rock with spinel lherzolite characteristic of mantle material suggest that the moho is not a discrete feature in this region but is represented by a transition zone approximately 20 km thick these inferences are in agreement with geophysical data including seismic heat flow and electrical resistivity data determined for south eastern australia underplating at the crust mantle boundary by continental basaltic magmas may be an important alternative or additional mechanism to the conventional andesite model for crustal accretion

simulation study on evolution of coalbed methane reservoir in qinshui basin china a dynamic equilibrium model has been proposed to describe the coalbed methane concentration dissipation evolution process in coal including its generation storage and migration the model developed with a computational program has been applied to the qinshui basin china which allows to evaluate features of coal seam of the basin including coal quality and burial palaeo geothermal field and coal organic material maturation evolution history the simulation study was focused on coalbed methane concentration dissipation evolution history of the upper and lower main coal seams in the basin the results indicate that the whole evolution process can be divided into three stages at the first stage i e the primary concentration stage gas generation quantity and gas content were lower and only weak diffusion took place the second stage can be called the active concentration dissipation stage during this period coal organic material was matured at a higher rate generating a large amount of gas because of abnormal high palaeo geothermal field in the middle and late yanshan epoch as a result gas content in coal reservoir was higher and gas could be lost in different ways including diffusion cap outburst and permeation the third stage can be defined as the absolute dissipation stage at which coal organic material no longer generates gas meanwhile much gas was lost mainly by diffusion and partly by permeation simulation results further show that although the high gas generation led to active dissipation in the coal reservoir there still remains comparatively high gas content on the south and north ends of the qinshui basin due to the preserving geological conditions this suggests that these regions are favorable for coalbed methane exploitation which has been confirmed by recent geological exploitations in qinshui basin c 2007 published by elsevier b v

production characteristics and the key factors in high rank coalbed methane fields a case study on the fanzhuang block southern qinshui basin china abstract the temporal and spatial production characteristics of coalbed methane cbm wells in the fanzhuang block of the southern qinshui basin the first commercial cbm producing basin in china were studied to determine the dominant factors the study indicates that gas production differs significantly in different wells adjacent to or located in different tectonic areas in combination with the production characteristics in the temporal and spatial variations the impact of seven factors burial depth thickness of coal gas content porosity permeability effect of fracturing structural setting and hydrogeological conditions on the gas production was analyzed based on bivariate correlation analysis and gray system theory which are suitable for solving the complex interrelationships between multiple factors and variables the results indicate that hydraulic fracturing is an effective guarantee of high production cbm wells in the first several months during a high rank cbm field development however the effect of hydraulic fracturing on enhancing the gas production of cbm wells decreases with time because the initial reservoir permeability lower than the hydraulic fracture permeability limits the adsorption diffusion and flow of cbm this limitation inevitably leads to a slow gas production rate when the adsorbed cbm from the initial reservoir becomes the main gas source instead of the fracturing affected zone gas content and permeability are two key factors that dominate cbm well productivity because they perform elementary roles in controlling the volume of gas sources and conductivity respectively the structural setting and hydrogeological condition are also two important factors that dominate cbm well productivity because they can influence the spatial distribution of permeability and gas content as well as other factors such as aquifers

comment on blundy and holland s 1990 calcic amphibole equilibria and a new amphibole plagioclase geothermometer

thermal history of the giant qulong cu mo deposit gangdese metallogenic belt tibet constraints on magmatic hydrothermal evolution and exhumation abstract a complete thermal history for the qulong porphyry cu mo deposit tibet is presented zircon u pb geochronology indicates that the mineralization at qulong resulted from brecciation veining events associated with the emplacement of a series of intermediate felsic intrusions combined with previously published ages our results reveal a whole intrusive history of the qulong composite pluton causative porphyries were emplaced at 16 0 ma as revealed by 40ar 39ar dating of hydrothermal biotite 15 7 0 2 ma and sericite 15 7 0 2 ma zircon and apatite u th he zhe and ahe dating of qulong revealed that both followed similar monotonic thermal trajectories from 900 c u pb ages 17 5 15 9 ma to 200 c zhe 15 7 14 0 ma and that the causative porphyries experienced faster cooling at a maximum rate of greater than 200 c myr the qulong deposit was exhumed between 13 6 ma and 12 4 ma ahe at an estimated rate of 0 16 0 24 mm y which is consistent with previous estimates for other gangdese miocene porphyry deposits our ahe thermochronology results suggest that neither the gangdese thrust system nor the yadong gulu graben affected or accelerated exhumation at the qulong deposit

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

the identification of granitic diapirs diapirism is a themomechanically viable ascent mechanism for granitic magmas however there is very little direct evidence of actual granite diapirs many of the characteristics we may expect to use to determine ascent mechanisms are destroyed by changes in the shapes of intrusions resulting from the interaction of buoyancy and tectonic forces during emplacement many features of ballooning plutons are identical to those we would expect for diapirs notably patterns of strain deduced from deformed xenoliths and concentric foliations cannot be used as unambiguous evidence for diapirism diapirism can only be proven beyond doubt where it is possible to demonstrate vertical uplift of country rocks in excess of the vertical thickness of the intrusion

mass balance and mass transfer in migmatites from the colorado front range metasomatic exchanges between the infiltrating fluids and wall rocks most likely initiated the formation of nine leucosomes in two large samples of the precambrian biotite quartz feldspar migmatites from the east central colorado front range the leucosomes 2 to 20 mm thick and enclosed in mafic salvages 1 to 10 mm thick are granitic to tonalitic in composition mass balance calculations suggest that each leucosome formed by local introduction of mass the net gains and losses calculated assuming that all such gains and losses were contained within the leucosome show that in general neither the gains nor the losses fit the composition of any silicate melt it is more likely that the components were transported in a fluid recalculated on constant al basis the most significant relative mass transfers were gain of k and losses of na and mg by the rocks the metasomatic reactions calculated are those for replacement of plagioclase by microcline and breakdown of biotite the reactions must have been the cause of incipient migmatization a mafic selvage formed from the paleosome by the loss of material whose composition is tonalitic to granodioritic varying systematically with the paleosome composition

a tectonic model for the late paleozoic of southeastern new england hornblende and biotite sup 40 ar sup 39 ar age spectra from rocks in south central connecticut help define a permian triassic cooling curve for the area together with petrologic and structural information a time temperature pressure strain path is established similar data for the narragansett basin in rhode island and massachusetts allow correlation of the late paleozoic histories of the two areas together these data suggest that in the late paleozoic south central new england was part of a fold thrust belt and the narragansett basin was a retroarc foreland basin nw se compression during the final assembly of pangaea resulted in se directed thrusting causing the development of clastic wedges in adjacent rhode island and massachusetts in the late carboniferous early permian a clockwise rotation of this deformation from nw to nne led to northward underthrusting and concomitant uplift of both eastern connecticut and rhode island in the permian and triassic

exhumation and tilting of the western metamorphic belt of the coast orogen in southern southeastern alaska the uplift history of the western metamorphic belt in southern southeastern alaska can be traced using emplacement depths and cooling ages of mid cretaceous plutons which intruded the metamorphic belt during the period 101 ma to 89 ma during the period 101 ma to 94 ma the rocks of the metamorphic belt now at the surface were buried to a depth of approximately 30 km pressure data indicate that by 89 ma the western portion of the metamorphic belt was at a shallower crustal level 23 km within the study area while the eastern side remained at a depth of approximately 30 km cooling curves constructed from minerals in mid cretaceous plutonic rocks indicate that the western side of the metamorphic belt cooled earlier than the eastern side an observation consistent with the inferred uplift history southwestward transport of metamorphic belt rocks within the hanging walls of thrust and high angle faults may have provided one mechanism for uplift during mid to late cretaceous time the eastern portion of the western metamorphic belt cooled rapidly at 55 ma probably in response to a period of rapid uplift the coast shear zone an early tertiary high angle fault with west side up displacement bounds the east side of the metamorphic belt we suggest tertiary uplift occurred by tilting of the metamorphic belt due to movement along this fault

evaluation of coal texture distributions in the southern qinshui basin north china investigation by a multiple geophysical logging method abstract coal texture is indicative of coal mechanical strength which is important not only for evaluating coalbed methane cbm reservoir permeability but also for evaluating the possibility of coal and gas outbursts in underground coal mining this paper begins with a foundation of a geophysical logging based coal texture evaluation method that compares the digital logging data with the results from 108 coring samples then the method was applied to the analyses of coal textures in 39 cbm wells the results of which are discussed in terms of the vertical distribution of coal textures in the study area finally a ternary diagram based on thickness proportions of coal textures was used to identify reservoir compartments in the zhengzhuang field of the southern qinshui basin the results show that undeformed coals are easily distinguished from cataclastic and granulated coals because of the high den and gr of undeformed coals meanwhile cataclastic coal has lower response values of ac and lld than granulated coal which can be used in identifying cataclastic from granulated coal a multiple geophysical logging method combining the log data of den gr ac and lld was provided for predication of the coal textures in the zhengzhuang field the predicated results show that the coal seam can be vertically divided into three to eight sub layers with a typical interbedded pattern of undeformed and cataclastic coals on the upper and lower parts and granulated coal in the middle at a relatively large thickness the study area is divided into four major regions and 11 sub regions based on the classification of coal texture types the undeformed coal dominated region is located in the southwestern part of the study area indicating a low permeability in the coal reservoir the granulated coal dominated region is mainly in the northern and eastern parts of the study area and has resulted from deep burial and multi period structural activities the cataclastic coal dominated region is in the middle of the study area the coal reservoir in this region is possibly the most favorable for cbm production