the role of sediment subduction and crustal growth in hercynian plutonism isotopic and trace element evidence from the sardinia corsica batholith

what is the actual structure of samarskite y a tem investigation of metamict samarskite from the garnet codera dike pegmatite central italian alps we investigated by scanning and transmission electron microscopy sem tem wavelength and energy dispersive spectroscopy wds eds and electron diffraction tomography edt several y ree u th nb ta ti oxides from the garnet codera dike pegmatite central italian alps these oxides have compositions in the samarskite y field and yield an amorphous response from the single crystal x ray diffractometer backscattered electron images reveal that the samples are zoned with major substitutions involving u th with respect to y ree at the tem scale the samples show a continuous range of variability both in terms of composition and in radiation damage and the amount of radiation damage is directly correlated with the u content areas with high u content and highly damaged show crystalline randomly oriented nanoparticles that are interpreted as decomposition products of the metamictization process on the other hand areas with lower u content and radiation dose contained within 0 7 10 16 event mg although severely damaged still preserve single crystal appearance such areas noticeably consisting of relicts of the original samarskite structure were deeply investigated by electron diffraction techniques surprisingly the retrieved crystal structure of untreated samarskite is consistent with aeschynite and not with ixiolite or columbite as believed so far after x ray diffraction experiments on annealed samples in particular the resolved structure is a niobioaeschynite y with pnma space group cell parameters a 10 804 1 b 7 680 1 c 5 103 1 a and composition y 0 53 fe 0 22 ca 0 10 u 0 09 mn 0 07 1 nb 1 07 ti 0 47 fe 0 34 ta 0 07 w 0 06 2 o 6 if this finding can be confirmed and extended to the other members of the group namely samarskite yb calciosamarskite and ishikawaite then the samarskite mineral group should be considered no longer as an independent mineral group but as part of the aeschynite group of minerals it is finally suggested that the rare crystalline sub micrometric ixiolite domains occasionally spotted in the sample by tem or the nanoparticles detected in highly metamict areas interpreted as decomposition product of the metamictization process which may have in fact the ixiolite structure act as seeds during annealing leading to the detection of ixiolite peaks in the x ray powder diffractograms

age geodynamic setting and mantle enrichment processes of a k rich intrusion from the meissen massif northern bohemian massif and implications for related occurrences from the mid european hercynian the plutonic complex of the meissen massif northern margin of the bohemian massif comprises dioritic to mainly monzonitic and granitic rocks the diorite to monzonite intrusions show major and trace element patterns typical for shoshonitic series the chemical signatures of less crustally contaminated diorites are similar to arc related shoshonitic rocks derived from continental lithospheric mantle clm sources previously enriched by subduction of altered oceanic crust laser step heating 40ar 39ar analyses on actinolitic to edenitic amphiboles from geographically different occurrences of the monzonitic intrusion yielded concordant plateau ages as well as total gas ages ranging from 329 1 1 4 to 330 4 1 4 ma and from 330 4 2 1 to 330 6 1 8 ma respectively these cooling ages are indistinguishable from sensitive highresolution ion microprobe shrimp 238u 206pb intrusion ages measured on magmatic zircon rims from the monzonite nasdala et al submitted this shows that the monzonite intrusion is probably not related temporally to active subduction because it postdates eclogites of the adjacent saxonian erzgebirge by approximately 20 ma the shoshonitic magmas intruded during strike slip tectonism along the elbe valley zone the enrichment of their mantle sources may be of upper devonian lower carboniferous age or older intrusions of shoshonitic to ultra potassic k rich rocks during the upper visean namurian are widespread in the moldanubian zone based on similar ages and structural relationships a similar post collisional setting to the meissen shoshonitic rocks can be demonstrated most of these occurrences cut high grade nappe units which were subducted during the upper devonian lower carboniferous in contrast to the meissen massif at least the ultra potassic members of the central and the south bohemian batholiths were derived from clm sources enriched by fluids or melts released from subducted oceanic crust and by greater portions of crustal material despite the similar post collisional geodynamic setting of the k rich intrusions different enrichment processes generated mid european hercynian clm sources with heterogeneous major and trace element and isotopic signatures

seismic reflection character analysis of stratigraphic traps in cretaceous cardium formation alberta canada the cretaceous cardium formation alberta canada produces oil and gas from thin sandstone stratigraphic traps the formation can be subdivided into the cardium sand and overlying cardium zone over a 4 000 mi2 10 000 km2 study area the cardium zone decreases in thickness from 80 120 ft 24 36 m in the northwest to about 40 ft 12 m in the east sandstone beds some of which are stratigraphic traps are interbedded with shale in the thicker northwest section sandstone beds are absent toward the east the underlying cardium sand increases in thickness from about 40 ft 12 m in the west to 160 ft 48 m in the east this increase in thickness corresponds to an increase in shale and decrease in thick bedded sandstones an analysis of 97 seismic lines in the study area indicates that two major seismic reflection patterns comprise the cardium formation seismic interval one pattern consists of two seismic reflections spaced 20 40 msec apart and the other pattern consists of a single reflection these two patterns can be mapped across a large area the areal distribution of the double seismic reflection pattern corresponds approximately to the occurrence of sandstone beds in the cardium zone reflection patterns of 26 synthetic seismograms generated from sonic logs are comparable to the reflection patterns observed on the field seismic data this relationship allows interpretation of the field seismic records in terms of stratigraphic characteristics thickness of the cardium zone and distribution of sandstone beds in the cardium zone control the seismic reflection patterns the double reflection pattern occurs where the cardium zone is greater than 80 ft 24 m thick and contains sandstone beds one reflection is generated at the interface of the cardium zone and an overlying shale whereas the other reflection is generated at the interface of the cardium zone and cardium sand the single reflection pattern occurs where the cardium zone is less than 80 ft 24 m thick and lacks sandstones because the seismic reflection patterns are regionally mappable units seismic reflection character analysis can be used to highgrade areas for prospect generation and to depict the trend of potential stratigraphic traps this study further demonstrates that sandstone stratigraphic traps and associated facies can be more accurately mapped using a combination of well logs and field seismic records than by using well control along

large trends in french topsoil characteristics are revealed by spatially constrained multivariate analysis spatially constrained multivariate analysis methods multispati pca and classical principal component analysis are applied for the entire country of france to study the main soil characteristics of topsoil and to assess if their multivariate spatial pattern can provide insight on their extent and origin the results of the multspati pca provided evidence of strong spatial structures attributed to different natural processes the first axis was interpreted as an axis of global soil richness in clay content axis 2 reflected the influence of some parent materials on the geochemical content of k and al axis 3 showed a very large gradient of relative content in coarse silt axis 4 was driven by gradients of maritime influence we show that multispati pca allows better than classical pca to detect and map large regional trends in the distribution of topsoil characteristics the two first axes were expected and the maps obtained by both methods were consistent interestingly the other gradients were not expected and were better shown by multispati pca than by classical pca

the loess and coversands of northern france and southern england loess and coversands are widespread on either side of the english channel in southern england loess is generally thin and discontinuous but locally reaches thickness of about 4 m in east kent coversands occur mainly in areas well north of the channel such as parts of east anglia and the southern side of the bristol channel most of the loess and coversand deposits in southern england date from the late devensian cold stage marine oxygen isotope stage mois 2 but there are also a few localised patches of older mainly mois 6 and 12 loess which are the dissected remnants of originally more extensive covers in france loess is widespread and locally very thick up to 12 m especially in northern and northeastern france in normandy and in the somme basin some long records indicate that accumulation began at the end of the lower pleistocene at about 900 ka nevertheless the main accumulations of typical calcareous loess are related to the upper weichselian and upper saalian stages mois 2 and end of mois 3 and mois 6 indeed before about 160 170 ka loess deposition was generally restricted to special sediment traps such as fluvial and marine terraces exposed to the east or northeast these older deposits are characterised by more sandy facies derived from local fluvial sources mainly by northwest to north northwest winds coversands occur locally along the coast of the mont saint michel bay and over the northern part of the seine estuary near le havre the main differences in thickness and extent of the loess deposits between southern england and northern france are linked to their location in relation to the source areas channel and north sea to ice sheets and to the main wind directions northwest to north northwest in france and western england but northeast in eastern england copyright 2003 john wiley sons ltd

the pleistocene of northern france a table of stratigraphic correlation has been established between the different provinces of the quaternary paleogeographic regions of northern france extending from brittany to alsace and from the welshbelgium basin to the paris basin initially based on loess and slope deposits in the framework of the aeolian periglacial zone of northwestern europe paepe and sornme 1970 lautridouand sornme 1974 these correlations not only include data from brittany but also provide sequences from achenheim alsace to enable correlation with more continental european areas

tectonic evolution of the european variscan belt constrained by palaeomagnetic structural and anisotropy of magnetic susceptibility data from the northern vosges magmatic arc eastern france geochronology structural and anisotropy of magnetic susceptibility data from the northern vosges batholith which belongs to the northern vosges mid german crystalline rise arc show contrasting emplacement modes of southern granodiorites and northern granites the ene wsw trending fabrics of granodiorites 346 334 ma are parallel to the metamorphic cleavage affecting the host rocks developed during regional compression the nnw sse trending fabrics of younger granitoids c 330 ma reveal an extensional emplacement mode associated with a normal shear zone separating the two magmatic suites palaeomagnetism shows that the switch from a compressive to an extensional regime coincides with a regional counterclockwise rotation the 330 325 ma extension is further supported by palaeomagnetic and seismic data indicating southeastward tilt of the whole batholith finally the system is rotated clockwise without any structural overprint data from the early carboniferous northern vosges magmatic arc and remote bohemian massif suggest that this evolution is valid for the whole eastern branch of the european variscan belt for which the following model is proposed 1 late devonian early carboniferous east west shortening of the variscides above the rhenohercynian subduction zone 2 axial nnw sse shortening of the assembled variscan orogen associated with 3 internal sinistral rotation of inherited rhenohercynian transform faults and shortening of intervening blocks 4 east west extension and dextral external rotation of blocks between dextrally reactivated transforms supplementary materials analytical procedures for geochronology magnetism anisotropy of magnetic susceptibility and palaeomagnetism are available at www geolsoc org uk sup18635

magma mixing in the subvolcanic environment petrology of the gerena interaction zone near seville spain the mechanisms by which felsic and mafic magmas interact and approach a uniform hybrid composition through the processes of mingling and mixing have been studied in a high level subvolcanic setting in the spanish hercynian at gerena near seville the compositions involved are calc alkaline and the situation is one of tonalite quartz diorite synplutonic dykes injected into a granitic magma chamber the resulting hybrids include dykes pillows and globules of tonalite with chilled margins which are variously disrupted and homogenised with the host granite the present investigation is based on field and petrographic observations of hybridization textures the identification of different stages in the crystallisation history of the tonalite through mineral textures and the characterization of mineral compositions at these various stages proportions of the end member magmas involved were obtained by major oxide mixing models and tested satisfactorily with trace elements a mechanistic model is presented to account for these observations which involves the early quenching of the tonalite when it was emplaced into the granite magma chamber after high temperature crystallization had occurred the two magmas attained thermal equilibrium and disruption of the tonalite in the high energy regime of this subvolcanic complex resulted in dispersion of fragments and crystals through the granite giving rise to hybrid granodiorite compositions it is argued that such high energy flow conditions are a necessary requirement for effective hybridization in this environment in contrast to most large scale magma chamber settings where mixing is driven by thermal and buoyancy contrasts

temporal association of ductile deformation and granitic plutonism rb sr and 40 ar 39 ar isotopic evidence from roof pendants above the central bohemian pluton czech republic the stare sedlo gneiss complex occurs as a roof pendant in the early carboniferous central bohemian pluton mylonitic tonalitic gneiss and amphibolite in the complex share a common foliation which is discordant to the margins of the granitoid masses of the enclosing pluton hornblende 40 ar 39 ar and biotite whole rock biotite plagioclase rb sr isotopic data give closely corresponding early carboniferous cooling ages for hornblende 500 c and biotite 300 c in amphibolite and mylonitic tonalitic gneiss respectively ages of 338 pm 2 5 335 pm 2 and 331 pm 2 5 ma biotite whole rock and biotite plagioclase rb sr and 332 3 pm 3 0 332 2 pm 3 1 and 331 7 pm 3 0 ma hornblende 40 ar 39 ar are interpreted as representing times of closure of isotopie systems associated with rapid cooling during the final stages of ductile deformation and metamorphism in a thrust regime they overlap the time of emplacement of at least early intrusions that show some foliati

sr nd isotopic constraints on the petrogenesis of the central bohemian pluton czech republic the sr nd isotopic data for selected granitoids of the central bohemian pluton show a broad negative correlation with the total range of 87sr 86sr 330 0 7051 0 7129 and nd330 0 2 to 8 9 the older intrusions have more depleted sr nd compositions and calc alkaline geochemistry sazava suite whereas the younger intrusions shift towards k rich calc alkaline blatna suite and shoshonitic rocks icany and certovo b emeno suites with more evolved isotopic signatures the distribution of the data is interpreted as reflecting a diversity of sources and processes rather than a single progressive crustal contamination trend the sazava suite could have originated by partial melting of metabasites or of a mantle source with an isotopic composition close to bulk earth or by hybridization of crustally derived tonalitic and mantle derived magmas variation within the blatna suite is modelled by mixing between a moderately enriched 87sr 86sr 330 0 708 nd330 3 mantle component with either an isotopically evolved metasedimentary component or with more evolved magmas of the suite the icany suite was most probably produced by partial melting of peraluminous lithologies possibly of the adjacent moldanubian unit the certovo b emeno suite evolved from strongly enriched mantle derived magmas 87sr 86sr 330 0 7128 end330 7 either through closed system fractional crystallization or interaction with magma corresponding to leucogranites of the central bohemian pluton

scale of spatial dependence between chemical properties of topsoil and subsoil over a geologically contrasted area massif central france this study investigates scale spatial specific dependence of some major and trace element contents in topsoil horizons and in alterite type horizons subsoil horizons over a weakly contaminated area the study seeks also to compare the spatial distributions of chemical elements at both depths to the spatial variability of the alterite type in order to examine the effect of the parent material the probability of occurrence of alterite type was estimated using indicator kriging ik factorial kriging analysis fka was used to analyze spatial variability in some soil chemical properties ca mg k fe cr and co measured at two depths over a geologically contrasted area of 10 ha in central of france the coefficients of the coregionalization matrix at different spatial scales reveal the dominant long range autocorrelation and cross correlation in all chemical elements in both depths except for trace elements co and cr where the short range structure dominates the cross correlation the resulting structural correlation coefficients showed strong correlations between variables changing as a function of spatial scale these relationships between chemical properties at different spatial scales were not revealed by the linear correlation coefficients a principal component analysis was performed on the coregionalization matrices at each depth to summarize the relationships among the variables at the different spatial scales cokriging allowed mapping each spatial component for both depths these maps were then compared with the probability map of alterite type estimated using indicator kriging this comparison revealed that the spatial pattern of chemical elements in the subsoil horizons is almost certainly due to the alterite type effect whereas the alterite type effect on the spatial pattern of chemical properties in the topsoil horizons was partly hidden by human activities and erosion

tectonic evolution of a continental magmatic arc from transpression in the upper crust to exhumation of mid crustal orogenic root recorded by episodically emplaced plutons the central bohemian plutonic complex bohemian massif the central bohemian plutonic complex cbpc consists of episodically emplaced plutons the internal fabrics of which recorded tectonic evolution of a continental magmatic arc the 354 350 ma calc alkaline plutons were emplaced by multiple processes into the upper crustal tepla barrandian unit and their magmatic fabrics recorded increments of regional transpression multiple fabrics of the younger 346 ma blatna pluton recorded both regional transpression and the onset of exhumation of mid crustal orogenic root moldanubian unit continuous exhumation related deformation during pluton cooling resulted in the development of a wide zone of sub solidus deformation along the se margin of the cbpc finally syn exhumation tabular durbachitic pluton of ultrapotassic composition was emplaced atop the intrusive sequence at 343 340 ma and the ultrapotassic tabor pluton intruded after exhumation of the orogenic root 337 ma we suggest that the emplacement of plutons during regional transpression in the upper crust produced thermally softened domain which then accommodated the exhumation of the mid crustal orogenic root and that the complex nature of the tepla barrandian moldanubian boundary is a result of regional transpression in the upper crust the enhancement of regional deformation in overlapping structural aureoles the subsequent exhumation of the orogenic root domain and post emplacement brittle faulting

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

multiple magmatic fabrics in plutons an overlooked tool for exploring interactions between magmatic processes and regional deformation this paper elaborates on the concept of multiple magmatic fabrics in plutons after a general overview of various types of multiple fabrics that may develop in magmatic rocks two case examples of porphyritic granite and melasyenite plutons in the bohemian massif are examined in the jizera granite complex variations in k feldspar phenocryst shape fabric revealed by image analysis of a 200 m long section of an underground tunnel are in contrast with homogeneously oriented magnetic ams fabric carried by coaxial contributions of biotite magnetite and maghemite in the kni eci stolec melasyenite pluton emplacement related margin parallel feldspar foliation was overprinted by flat lying foliation the latter is interpreted to record regional tectonic strain at the two stations examined in detail the crystallographic preferred orientation of biotite and amphibole in the inter phenocryst matrix measured using electron back scatter diffraction ebsd differed from both feldspar fabric and also from the ams principal directions multiple magmatic fabrics in these two plutons are interpreted in terms of fabric superposition where late weak strain is superposed onto a high strength phenocryst framework but is accommodated preferentially by small mineral grains biotite magnetite in the melt bearing matrix this mechanism may explain the discrepancy between mesoscopic feldspar fabric and ams we conclude that multiple magmatic fabrics in plutons may thus result from accumulated strain caused by different processes during final crystallization and as such may serve as a sensitive indicator of the evolving interactions between magmatic and tectonic processes in the earth s crust

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

use of seismic stratigraphy for minnelusa exploration northeastern wyoming while minnelusa sands have yielded significant reserves in wyoming s powder river basin geologic complexities have made these sands an elusive target this paper briefly describes the development of a technique which was used successfully in the exploration of minnelusa sands this tehnique can be applied to many stratigraphic exploration programs sonic logs which are key logs in defining minnelusa sands in the c h field were used to construct synthetic seismograms these synthetics were then organized in cross section form to define whether a change in minnelusa sands would yield an identifiable change on the synthetics the idealized seismic response did show an obvious lateral change from upper sand to no upper sand conditions and a pilot seismic line was shot using a vibroseis source this line which was shot through the c h field successfully showed the updip limits of the upper minnelusa sands a subsequent seismic program was acquired and other leads and prospects were identified includi

inversion of the assimilation and fractional crystallization afc equations characterization of contaminants from isotope and trace element relationships in volcanic suites the assimilation and fractional crystallization afc equations of depaolo 1981 are inverted with the aim of characterizing the chemistry of contaminants involved in magma evolution from observed isotope and trace element relationships equations are derived for contours of the ratio of the rate of assimilation to the rate of fractional crystallization in the isotope or trace element region where the contaminant might be located even for volcanic suites in which afc is thought to have been the dominant process the characterization of the contaminant is poorly constrained although afc is likely to be a normal process it leaves a recognizable isotopic signature in volcanics only when magmas assimilate material derived from continental crust in subduction related volcanics this can be the case where the volcanic arc lies on or near continental crust

elevator tectonics and orogenic collapse of a tibetan style plateau in the european variscides the role of the bohemian shear zone variscan collision of peri gondwanan terranes led to a doubly vergent crustal wedge that was thicker than 55 km in the area of the bohemian massif this crustal thickness resulted in a highly elevated bohemian plateau with a topographic height 3 4 km the bohemian plateau was covered with unmetamorphic paleozoic strata all of which are today well preserved in the tepla barrandian unit because of crustal scale vertical slip along the bohemian shear zone bsz the bsz forms a subvertical ca 500 km long and up to 2 km wide belt of dip slip mylonites which show several 90 deflections in map view tepla barrandian down movements were active under retrograde metamorphic conditions starting with granulite and ceasing with greenschist facies conditions as slip along the bsz was largely vertical and led to a minimum throw of 10 km this type of crustal scale deformation is referred to as elevator tectonics the elevator style movements caused the juxtaposition of the supracrustal tepla barrandian lid the elevator against high grade rocks of the extruding orogenic root the bsz has further governed the foci of mantle derived plutonism new u pb zircon and monazite tims dating of six plutons suggest that emplacement of mantle derived melts along the bsz lasted for at least 20 m y starting with the emplacement of the klatovy granodiorite at 347 4 3 ma and ceasing with the emplacement of the drahotin pluton at 328 1 ma when taking into account the new ages of synkinematic plutons the simultaneous vertical slip along the individual segments of the bsz north west and central bohemian shear zone is bracketed to the period 343 337 ma elevator tectonics was probably controlled by delamination of thickened mantle lithosphere that caused a dramatic thermal turnover and heating up of the orogenic root the overheated lower crust was thermally softened by anatexis and diffusion creep resulting in channel flow vertical extrusion fast uplift and exhumation of the orogenic root

magmatic stoping as an important emplacement mechanism of variscan plutons evidence from roof pendants in the central bohemian plutonic complex bohemian massif the presence of numerous roof pendants stoped blocks and discordant intrusive contacts suggests that magmatic stoping was a widespread large scale process during the final construction of the central bohemian plutonic complex bohemian massif the measured total length of the discordant contacts that cut off the regional cleavage and were presumably formed by stoping corresponds to about half of all contacts with the upper crustal host rocks in addition at least some of the straight cleavage parallel intrusive contacts may also have recorded complex intrusive histories ending with piecemeal stoping of thin cleavage bounded host rock blocks into the magma chamber based on the above we argue that the fast strain rates required for emplacement of large plutons of the central bohemian plutonic complex into brittle upper crustal host rocks over relatively short time span could not have been accommodated entirely by slow ductile flow or slip along faults instead the emplacement was largely accommodated by much faster thermal cracking and extensive stoping independent of regional tectonic deformation finally we emphasize that magmatic stoping may significantly modify the preserved structural patterns around plutons may operate as an important mechanism of final construction of upper crustal plutons and thus may contribute to vertical recycling and downward transport of crustal material within the magma plumbing systems in the crust

y ree nb ta ti oxide ab2o6 minerals from rel ree euxenite subtype pegmatites of the třebic pluton czech republic substitutions and fractionation trends this paper describes subtitutions and fractionation trends in the y ree nb ta ti oxides aeschynite and euxenite group minerals from nyf euxenite subtype pegmatites of t ebic pluton

cryptic trace element variation as an indicator of reverse zoning in a granitic pluton the ricany granite czech republic cryptic variation recognized on the basis of trace element patterns shows the oieany granite in the northeastern part of the hercynian central bohemian pluton to be a reversely zoned high level intrusion unlike many other reversely zoned plutons there are no marked differences in modal composition between the margins and the centre of the intrusion the granite is generally peraluminous and geochemically evolved as demonstrated by its restricted and high sio 2 range and low k rb ratio coupled with a c two fold variation in ba and sr concentrations modelling shows that the geochemical variations can be most readily explained by k feldspar dominated fractionation in a magma chamber below the present level of exposure the reverse zoning is interpreted as the product of emplacement of an essentially single pulse of magma from a deeper level magma chamber in which fractionation has led to a vertical compositional gradient the least evolved magma was emplaced in the centre of the high level pluton with the more evolved magma around it recognition of cryptic reverse zoning in granites has major implications for granite petrogenesis in that the magmatic evolution of such bodies has to be established before assessing potential mechanisms of emplacement

submarine fan and slope facies of tonkawa missourian virgilian sandstone in deep anadarko basin the tonkawa sandstone missourian virgilian in the anadarko basin consists of upper middle and lower sandstone units separated by intervening shales the lower tonkawa sandstone consists of coarse to pebbly sandstones deposited in thick coarsening upward sequences the unit is up to 400 ft 120 m thick and the sandstones grade to shale from the southeast to the northwest gross sand isopachs outline northwest southeast oriented linear thicks that extend for tens of miles the middle tonkawa sandstone consists of thin and thick bedded fine grained sandstones displaying wavy and flaser bedding a convolute laminae and some small scale cross laminae these sandstones range in thickness from 100 ft 30 m to 400 ft 120 m the thicks in the middle tonkawa extend nly for a few miles and do not show a preferred directional orientation the upper tonkawa sandstone caps the entire sequence and is overlain by oolitic limestones we interpret the lower tonkawa sandstone to represent a submarine fan complex for the following reasons the regional setting indicates that the sandstones were deposited tens of miles from the shelf edge graded beds convolute laminae and load casts indicate transportation by sediment gravity flows the areal geometry of sandstones indicates channelized flows that coalesced to form an overall fanlike geometry the middle tonkawa sandstones are interpreted as a sequence deposited on the basin slope regional setting indicates that the unit is located immediately basinward of the shelf edge and that it progrades over the lower tonkawa sandstone deposition as sheets or aprons is suggested by lateral continuity at least for several miles of individual beds small scale cross laminae wavy and flaser bedding and sharp bed contacts suggest bottom current activity presence of short numerous channels is suggested by the thick beds of middle tonkawa sandstones that extend for only a few miles although the sedimentology and areal geometry of the upper tonkawa are not discussed in this paper the regional setting and lithologic character suggest shallow water nearshore deposition the entire tonkawa clastic sequence is capped by shallow water marine limestone the lower and middle tonkawa sandstones represent offshelf deposition in an interior basin setting the present study shows that the understanding of the geologic setting and the integration of all available data rather than sedimentologic data alone are required for proper identification the following formations in the anadarko basin also appear to contain fan and or slope facies springer morrow springerian morrowan red fork desmoinesian and cleveland marchand and cottage grove all missourian if the deep water sandstones in interior basins are indeed as common as they appear to be in the anadarko basin then it is crucial for stratigraphic exploration that we recognize and document such deposits in other interior basins as well

columbite solubility in granitic melts consequences for the enrichment and fractionation of nb and ta in the earth s crust the behaviour of niobium and tantalum in magmatic processes has been investigated by conducting mnnb2o6 and mnta2o6 solubility experiments in nominally dry to water saturated peralkaline aluminium saturation index a s i 0 64 to peraluminous a s i 1 22 granitic melts at 800 to 1035 c and 800 to 5000 bars the attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution crystallization mn doped and nb or ta doped experiments at the same pressure and temperature the solubility products of mnnb2o6 ksp nb and mnta2o6 ksp ta at 800 c and 2 kbar both increase dramatically with alkali contents in water saturated peralkaline melts they range from 1 2 10 4 and 2 6 10 4 mol2 kg2 respectively in subaluminous melt a s i 1 02 to 202 10 4 and 255 10 4 mol2 kg2 respectively in peralkaline melt a s i 0 64 this increase from the subaluminous composition can be explained by five non bridging oxygens being required for each excess atom of nb5 or ta5 that is dissolved into the melt the ksp nb and ksp ta also increase weakly with al content in peraluminous melts ranging up to 1 7 10 4 and 4 6 10 4 mol2 kg2 respectively in the a s i 1 22 composition columbite tantalite solubilities in subaluminous and peraluminous melts a s i 1 02 and 1 22 are strongly temperature dependent increasing by a factor of 10 to 20 from 800 to 1035 c by contrast columbite tantalite solubility in the peralkaline composition a s i 0 64 is only weakly temperature dependent increasing by a factor of less than 3 over the same temperature range similarly ksp nb and ksp ta increase by more than two orders of magnitude with the first 3 wt h2o added to the a s i 1 02 and 1 22 compositions whereas there is no detectable change in solubility for the a s i 0 64 composition over the same range of water contents solubilities are only slightly dependent on pressure over the range 800 to 5000 bars the data for water saturated sub and peraluminous granites have been extrapolated to 600 c conditions at which pegmatites and highly evolved granites may crystallize using a melt concentration of 0 05 wt mno 70 to 100 ppm nb or 500 to 1400 ppm ta are required for manganocolumbite and manganotantalite saturation respectively the solubility data are also used to model the fractionation of nb and ta between rutile and silicate melts predicted rutile melt partition coefficients increase by about two orders of magnitude from peralkaline to peraluminous granitic compositions it is demonstrated that the nb2o5 ta2o5 activity coefficient ratio in the melt phase depends on melt composition this ratio is estimated to decrease by a factor of 4 to 5 from andesitic to peraluminous granitic melt compositions accordingly all the relevant accessory phases in subaluminous to peraluminous granites are predicted to incorporate nb preferentially over ta this explains the enrichment of ta over nb observed in highly fractionated granitic rocks and in the continental crust in general

hydrothermal alteration of monazite ce and chevkinite ce from the sin quyen fe cu lree au deposit northwestern vietnam the sin quyen deposit in northwestern vietnam is composed of fe cu lree au ore bodies hosted in proterozoic metapelite there are massive and banded replacement ores with variable amounts of monazite ce and chevkinite ce crystals which have undergone fluid induced alteration monazite ce and chevkinite ce were deposited from high temperature fluids in the early ore forming stage but became thermodynamically unstable and thus were altered to other phases in later ore forming stages the alteration of monazite ce formed a three layered corona texture which commonly has relict monazite ce in the core newly formed fluorapatite in the mantle and newly formed allanite ce in the rim in some cases the original monazite ce was completely consumed forming a core of polygonal fluorapatite crystals rimmed by allanite ce crystals the formation of allanite ce and fluorapatite at the expense of monazite ce indicates that the later stage fluids had high ca na ratios and relatively low temperatures chevkinite ce was variably replaced by an assemblage of allanite ce aeschynite ce bastnasite ce columbite fe ilmenite the replacement of chevkinite ce by mainly allanite ce and aeschynite ce required low temperature ca lree and nb rich metasomatic fluids probably with relatively low f o 2 mass balance calculations were made to investigate the hydrothermal element mobility it is assumed that th was immobile during the alteration process of monazite ce light and middle ree from la to tb u as and ge were variably lost relative to th while heavy ree from dy to lu hfse e g nb ta zr and hf and sr were variably gained relative to th regarding the alteration of chevkinite ce some major elements in chevkinite ce such as ti la and ce were obviously removed from the system during alteration whereas ca al nb u and hree were needed to be variably supplied by the metasomatic fluids concerning the hydrothermal mobility of trace elements previous studies demonstrated that ree and hfse can be commonly reserved in the system during alteration consistent with the traditionally assumed immobile nature of these elements in contrast this study shows that ree and hfse can be mobilized on at least the hundreds of micrometers scale this may be related to the high flux and strong chemical reactivity of the metasomatic fluids

modelling diverse processes in the petrogenesis of a composite batholith the central bohemian pluton central european hercynides the multiple intrusions making up the central bohemian pluton in the central european hercynides have petrographic and geochemical features consistent with the presence of four main granitoid suites major element trace element and sr nd isotopic compositions are used to model their petrogenesis partial melting of metabasic locks or of a chur like mantle source are interpreted to have produced melts parental to the most primitive calc alkaline sazava suite interaction of basic with more acidic magmas followed by extensive amphibole plagioclase dominated fractionation accounts for the production of trondhjemites alternatively the trondhjemites correspond to small degree melts of a metabasic source afc assimilation fractional crystallization modelling with a paragneiss as a contaminant and increasing d nd values simulates the characteristics of the blatna suite closed system fractionation of strongly enriched mantle derived magmas or their interaction with leucogranitic melts is deduced for the petrogenesis of the shoshonitic certovo bremeno suite partial melting of a metasedimentary source followed by k feldspar dominated fractionation accounts for the granites of rite ricany suite the progression from relatively primitive calc alkaline granitoids towards evolved k rich calc alkaline and shoshonitic rocks is interpreted to reflect the increasing enriched mantle input in the petrogenesis of the later suites the evidence for hercynian subduction is equivocal and the mantle enrichment could have been significantly older

the relationship between ree y nb th minerals and the evolution of an a type granite wentworth pluton nova scotia the wentworth pluton in the eastern cobequid highlands consists principally of metaluminous to peralkaline a type granite 362 ma a large part of which was remelted by a major gabbro intrusion 357 ma magmatic minerals like allanite ce chevkinite ce zircon and hingganite y and post magmatic mineral phases such as ree bearing epidote samarskite y aeschynite y fersmite thorite like phases and hydroxylbastnasite ce were identified the presence of fluorine in the parental magma indicated by whole rock geochemical data and the presence of fluorite increased the solubility of monazite and xenotime and thus facilitated retainment of rare metals in the magmatic system fractionation of allanite ce and chevkinite ce led to a melt enriched in heavy rare earth elements hree from which hingganite y crystallized during late magmatic stages the remelting of the early granite led to fluorine and sulfur release in volatile phases which circulated with hydrothermal fluids thus mobilizing the ree and other rare metals reduction of fluorine activity during the late to post solidus crystallization resulted in the precipitation of hree and rare metals in samarskite y thereby enriching the residual hydrothermal fluids in light rare earth elements lree post magmatic lree minerals such as hydroxylbastnasite ce either replaced earlier minerals or precipitated from these hydrothermal fluids carbonate fluids involved in a late regional hydrothermal circulation event along the cobequid chedabucto fault 320 315 ma promoted ti mobility and the formation of tio 2 minerals and probably of aeschynite y this mineralogical diversity in addition to the complex geological history of the pluton provides a unique opportunity to correlate the formation of individual rare metal minerals to different stages of pluton evolution and thus provide an insight to the formation conditions of these minerals

exploration for oil accumulations in entrada sandstone san juan basin new mexico recent exploration activity in the san juan basin of northwestern new mexico has resulted in the discovery of new oil fields in the entrada sandstone of jurassic age the major trapping element is provided by topographic relief in excess of 100 ft 30 m on top of the entrada preliminary analyses indicate that the topographic relief was created by preserved eolian sand dunes which were formed in a topographic basin which then became the sight of a large lake in which limestones and anhydrites of the todilto formation were deposited over the entrada sands the organic rich limestones of the todilto provide the most likely source for the oil found in the underlying entrada analysis of stratigraphy oil shows source rock potential and porosity distribution led to the selection of an initial exploration area located along the southeastern flank of the san juan basin seismic model studies confirmed by an experimental seismic program indicated that the topographic relief on top of the entrada could be mapped seismically an extensive seismic and drilling program has resulted in the discovery of six new oil pools in addition to the topographic relief on top of the entrada other factors which control the oil accumulations include local structural conditions hydrodynamics source rock and oil migration history and porosity permeability relations in the entrada the knowledge gained from this exploration program should aid in future exploration for entrada oil fields in the san juan basin and encourage exploration for similar stratigraphic traps in other basins

geochemical comparison between minettes and kersantites from the western european hercynian orogen trace element and pbsrnd isotope constraints on their origin trace element and isotopic characteristics of late carboniferous to early permian minettes and kersantites have been determined these lamprophyres have been sampled throughout the western european hercynian orogen from brittany to the west to schwarzwald to the east in spite of sharp petrological differences reflected by mineralogy and major element geochemistry minettes and kersantites exhibit close identity with respect to trace element and isotopic features these features comprise enrichment in incompatible elements highcs rb and lowce pb ratios ta and ti relative depletion high abundance in transition elements and highni mg ratios pb isotope ratios are undistinguishable from those measured on hercynian continental crust initial143nd 144nd ratios are between0 5120 ei 5 and0 5122 ei 1 for minettes and kersantites whereas initial87sr 86sr ratios vary between 0 7055 0 710 for minettes and 0 707 0 708 for kersantites no simple mixing relations are visible on rbsr and smnd isochron diagrams the exceptional homogeneity of these geochemical characteristics along a 1000 km traverse does not allow for an hypothesis of enrichment through upper level assimilation and thus leads to propose that these rocks originated through melting of a mantle enriched by recycling of crustal material

late caledonian dyke swarms of northern britain spatial and temporal intimacy between lamprophyric and granitic magmatism around the ross of mull pluton inner hebrides numerous sheet intrusions in iona and western mull scotland range from basic calc alkaline lamprophyres 45 sio2 mg number 65 75 thornton tuttle differentiation index di 45 through intermediate microdioritic compositions malchites to microgranitic porphyries 70 sio2 di 85 well defined major element trends remarkably consistent normalized multielement patterns and strong linear correlations between homologous elements e g sc v fe ti mg ni cr suggest that these sheets form one cogenetic suite although rb sr systems have been disturbed by archaean country rock contamination isotopic signatures and field evidence suggest that sheet emplacement bracketed that of the 414 ma ross of mull granitoid pluton a few late sheets cut the pluton exceptionally well developed multiple and composite sheets provide clear evidence forsimultaneity of lamprophyric and granitic magmas and an early group of sheets appears to be metamorphosed by the pluton the composite sheets comprise lamprophyric borders around thicker microgranitic quartz feldspar porphyries each rock type carrying xenocrysts or xenoliths of the other mutual contacts mark wide discontinuities in major element composition and sites of local hybridisation yet close trace element similarities strongly imply the lamprophyres and porphyries are cogenetic least squares modelling further shows that fractionation of actual phenocrysts in one lamprophyric margin could reproduce the porphyry with which it is in intimate contact the most primitive mg 70 lamprophyres combine very high k rb th and ba with morb like contents of cr ni ti y and sc implying a substantial mantle derived component and in some cases near primary status but not precluding some crustal participation biotite and hornblende lamprophyres are locally heteromorphic discontinuities in some chemical trends field evidence and initial87sr 86sr ratios 0 706 imply more complex interactions of fractionation and hybridisation with lamprophyric parent magmas plus crustal contamination in the genesis of the intermediate and microgranitic rocks the association between lamprophyric and granitic magmatism in iona western mull is not therefore fortuitous but genetic the lamprophyres have an undoubted role in the genesis not merely of the microgranitic minor intrusions but probably of the granite pluton itself

accessory mineral fractionation of rare earth element ree abundances in granitoid rocks abstract accessory minerals with large distribution coefficients k d s for the ree have the potential to strongly affect the evolution of ree abundances during igneous differentiation e g crystallization melting assimilation a cogenetic suite of lavas basaltic andesites through high silica rhyolites from the batopilas area of mexico which preserve petrographic evidence for apatite and zircon saturation is used to illustrate and confirm an inverse geochemical approach to recognizing early liquidus accessory mineral saturation the transition in behavior of zr from an incompatible trace element in basaltic andesites and dacites to an essential structural constituent esc in high silica rhyolites marks the onset of zircon crystallization a previously published zircon saturation model provides liquidus temperatures that support the interpretation that three high silica rhyolites represent zircon saturated melts while one has excess zircon these results contradict the previous study in which zircon fractionation had been argued against the potential effect of zircon fractionation and accumulation on ree abundances in the samples is evaluated and contributes to an improved petrogenetic interpretation a cogenetic suite of granitoid samples from the saganaga tonalite minnesota ontario north america is characterized by apparently strongly compatible behavior of the ree apatite zircon and sphene are the observed high ree k d accessory minerals forward and inverse modelling approaches provide no evidence that accessory mineral fractionation contributed to the behavior of the ree during differentiation of the samples the data instead suggest that the ree characteristics of the samples were already established by other petrogenetic processes prior to the samples becoming saturated with the observed accessory minerals

post collisional variscan lamprophyres black forest germany 40ar 39ar phlogopite dating nd pb sr isotope and trace element characteristics abstract subsequent to high pressure and temperature metamorphism of the axial zone of the variscan foldbelt in central europe at ca 340 to 330 ma formation of lamprophyre dikes during transtensional tectonics may be viewed as the beginning of the post collisional stage of the orogeny we report the results of 40 ar 39 ar mica dating major and trace element data and isotope compositions for lamprophyre and rhyodacite samples from the southern black forest the chemical compositions of these rocks shed light on the upper mantle and crust at the end of the variscan orogeny 40 ar 39 ar plateau ages for four phlogopite biotite separates from lamprophyres indicate emplacement at 332 to 314 ma this event coincides with melting of the crust as indicated by 40 ar 39 ar biotite plateau ages of ca 332 ma for rhyodacite dikes which are probably related to coeval undeformed granites incompatible trace element patterns of the lamprophyre samples reveal the characteristics of evolved continental crust and are interpreted as evidence for melting of sediment in a subduction modified mantle nd sr and pb isotope compositions indicate an enriched mantle source with end values of 1 5 to 6 8 which is similar to variscan crust significant contamination of the lamprophyric melts by variscan crust can be ruled out as mantle derived phlogopite phenocrysts have similar end values as in the whole rock samples we propose that the isotope compositions and incompatible trace element characteristics of the lamprophyres were predominantly inherited from melted sediment the isotope compositions of variscan lamprophyres from western europe suggest that enriched upper mantle was only partly delaminated when ascending hot mantle triggered melting of the lower crust as has been invoked for the origin of post collisional granites the isotope compositions of tertiary basalts and mantle xenoliths indicate a depleted upper mantle under western europe implying that the enriched variscan material was efficiently removed and mixed into the convecting mantle

geochemistry and 40ar 39ar geochronology of the mafic metavolcanic rocks from the rýchory mountains complex west sudetes bohemian massif palaeotectonic significance the mafic metavolcanic rocks blueschists and greenschists of the r chory mountains crystalline complex west sudetes experienced sea floor hydrothermal alteration spilitization prior to regional metamorphism the metabasite geochemistry namely trace element and ree abundances indicates that the protolith was comparable in composition with 1 tholeiitic to transitional ocean floor basalts and 2 transitional and alkaline intra oceanic island basalts two main metamorphic events affected the r chory mountains metabasites in an earlier high pressure low temperature metamorphic event the rocks experienced blueschist facies metamorphism the results of 40 ar 39 ar geochronology studies on phengites from the mafic blueschists date the end of the earlier metamorphism to 360 ma the greenschist metamorphic overprint followed around 340 ma the elongated bodies of mafic metavolcanic rocks are situated within the prominent nne ssw leszczyniec shear zone following the trend of the r chory mountains and the rudawy janowickie mountains both the geochemical affinities and the blueschist facies metamorphism of the metabasites suggest that this shear zone evolved from the variscan suture dividing western and central terranes of the west sudetes according to the radiometric age for the end of the high pressure low temperature metamorphism the terranes accreted during the famennian a considerable time span between the formation of the metabasite protolith and the blueschist metamorphism may indicate long lasting subduction of a large oceanic plate between gondwana and laurussia possibly accompanied by terrane accretion prior to the variscan orogeny

chemical and isotopic systematics of the caledonian intrusions of scotland and northern england a guide to magma source region and magma crust interaction chemical and 0 sr nd and pb isotope relations for the british caledonian granitoids exhibit systematic variations that are attributed to derivation from both mantle and crustal sources the older more than ca 470 ma pre and syn tectonic granites were the product of local anatectic melting of late proterozoic metasedimentary upper crust 6180 i 8 to 14 87sr 86sr 0 710 206pb 204pb w 18 1 19 2 during the peak thermal conditions of the grampian orogeny the younger less than ca 440 ma post tectonic granitoids have a complex origin which in individual cases involved at least four different source regions i the upper mantle or subducted oceanic crust 6180 5 7 to 7 0 o 87sr 86sr w 0 7035 0 7040 206pb 204pb 17 9 to 18 1 and ii lower palaeozoic geosynclinal sedimentary upper crust 6180 11 to 14 o 87sr 6sr w 0 705 0 711 206pb 204pb 18 4 within the paratectonic caledonides in the scottish midland valley and southern uplands and in northern england or iii middle proterozoic mafic to intermediate granulitic lower crust 6180 w 8 to 10 o 87sr 86sr w 0 705 0 707 206pb 20pb 16 5 17 0 and iv middle to late proterozoic metasedimentary upper crust 6180 8 to 14 87sr 86sr 0 710 206pb 207pb w 18 1 19 2 in the scottish highlands mantle derived magmas or their direct derivatives were likely involved in the development of all of the younger granitoids either as end member components or as the source for a substantial part of the heat required for crustal melting and assimilation although the lower palaeozoic was a time during which a large amount of igneous material was introduced into the upper crust in britain it was not a major crust forming period because the caledonian granitoids are dominated by recycled continental crust

the quartz diorites of limousin elemental and isotopic evidence for devono carboniferous subduction in the hercynian belt of the french massif central a chain of late devonian early carboniferous intrusions on the western margin of the french massif central the limousin tonalite belt consists of quartz diorites which are unusual among french hercynian granitoids in their low silica contents 53 68 wt sio2 and abundant hornblende they represent the earliest and most primitive plutonism post dating the main phase of hercynian metamorphism and have chemical characteristics strongly resembling andesitic lavas of calc alkaline affinity they differ from other massif central hercynian granitoids in their low 87sr86sr360 0 7047 0 7059 and high nd360 0 7 to 1 8 their initial pb composition was rather homogeneous 206pb204pb360 18 15 18 38 207pb204pb360 15 57 15 62 208pb204pb360 38 06 38 26 and their 207pb204pbi values are significantly lower than those of other hercynian granitoids the limousin quartz diorites are considered to have originated from an enriched mantle with characteristics modified by subduction of oceanic crust and terrigenous sediments the primitive quartz dioritic magmas were then contaminated in the lower continental crust by an afc process involving acid metaigneous or metasedimentary lithologies the occurrence of such plutons in the earliest phase of hercynian plutonism in the massif central is probably related to minor subduction at an active continental margin

passive roof duplexes under the rocky mountain foreland basin alberta seismic reflection data in the central alberta foothills near edson reveal the presence of small passive roof duplexes in upper cretaceous rocks within the otherwise undeformed foreland basin as much as 40 km northeast of the mountain front monocline the tops and bottoms of the duplexes are defined by backthrusts and sole thrusts which follow bedding planes within upper cretaceous strata overlying the structures is an essentially uncontracted 1 8 km thick section of upper cretaceous and tertiary rocks which is passively uplifted over the thickened duplexes the underlying autochthonous sequence of mesozoic and paleozoic rocks exhibits some minor folding but is also uncontracted our interpretation extends both the upper and lower detachments of the widely accepted triangle zone model more than 30 km farther under the foreland basin than has previously been supposed the seismic data illustrate relatively clearly the form of the leading edge of the last phase of rocky mountain thrusting we expect that similar features will be observed elsewhere in the rocky mountain foothills and probably at other mountain fronts worldwide

petrogenesis of archaean trondhjemites tonalites and granodiorites from eastern finland major and trace element geochemistry