mobilization of gold as a polymetallic melt during pelite anatexis at the challenger deposit south australia a metamorphosed archean gold deposit the challenger gold deposit in south australia is hosted by pelitic migmatites that underwent peak metamorphism at 7 5 1 5 kbars and at least 800 c nd model ages suggest a protolith age of 2900 ma zircon u pb and garnet sm nd dating indicates that peak metamorphism occurred at 2440 ma and that garnet was present during this event at this time in situ vapor absent melting affected the pelitic host rock indicating that peak metamorphism occurred without introduction of a foreign fluid or melt thus evidence indicating the presence of ore minerals during peak metamorphism implies a prepeak mineralization event this evidence includes the occurrence of invisible gold in lollingite but not in adjacent arsenopyrite and the presence of spherical gold sulfide inclusions in peak metamorphic garnet and other silicates textures developed between pyrrhotite lollingite arsenopyrite and gold the lack of silicate alteration minerals supports this conclusion experimental evidence is presented to support our interpretation that a gold rich polymetallic melt was mobilized into leucosomes synchronously with silicate melt during peak metamorphism visible gold is restricted to migmatitic leucosomes and to a lesser extent melanosomes large inclusions of gold with coexisting arsenopyrite pyrrhotite and bismuth are hosted within peak metamorphic silicate minerals and at grain boundaries trails of micrometric spherical inclusions of predominantly gold and bismuth propagate along annealed fractures from these larger inclusions we show that these gold sulfide inclusions represent the crystallized products of an immiscible polymetallic melt metamorphism of the challenger deposit resulted in partial melting of the pelitic host rock and formation of this gold rich melt these two melts were synchronously redistributed to accumulate as leucosomes during development of a stromatic migmatite formation of a polymetallic melt thereby enabled extensive mobilization of gold producing leucosomes enriched in gold this occurred because the immiscible metallic melt was physically entrained rather than chemically dissolved within the silicate melt gold rich shoots at challenger parallel the plunge of ptygmatically folded leucosomes that are shown to be parasitic to a larger scale fold geometry which appears to be structurally related to the ore shoots it is interpreted that concurrent migration of polymetallic and silicate melt allowed concentration of gold into a series of dilational structures which developed within the larger scale fold geometry challenger represents a new deposit type other deposits around the world such as renco and griffins find are hosted in granulite facies rocks but challenger is the first reported example of leucosome hosted gold in migmatites

zn isotopic evidence for fluid assisted ore remobilization at the balmat zinc mine ny abstract shear zone hosted ore bodies at the balmat ny zinc deposit were remobilized at the kilometer scale during amphibolite facies metamorphism ca 1180 ma despite there being little evidence for interaction of hydrous fluids with ores during deformation such translocation distances are considered unlikely without the assistance of fluids measurements of zn isotopic composition of sphalerite from six balmat ore bodies that originated from the same stratigraphic level upper marble unit 6 reveal variation between ore bodies as well as intra orebody trends of isotopic lightening down plunge in general increasing distance of remobilization correlates with decreasing 66zn the syn tectonic isotopic fractionation recorded in balmat sphalerite is interpreted to have resulted from the interaction between the ore and sulfide melts that were fluxed by h2s localized primarily in upper marble unit 7 fetid dolomite lighter isotopes of zn were enriched in the melt leaving the residual ore enriched in heavier zn isotopes these observations support previous petrographic evidence for the presence of anatectic melts at balmat and help to explain the unusual scale of translocation at balmat by means of fluid assisted remobilization during which intergranular melts decreased rock competency

an improved method of determining sedimentation rates by the use of artificial radionuclides the use of radionuclide activity profiles to determine estuarine sedimentation rates aston stanners 1979 has been improved by the application of statistical tests a method is outlined for the use of regression analysis and test of best fit for applying nuclear waste discharge data to the quantitative determination of net sedimentation rates the methodology also allows the measurement of apparent diffusion of radionuclides in sediments and the lag time from discharge point to sediment deposition the technique has been applied to sediment cores from the ravenglass estuary near windscale england the range of sedimentation rates was 0 25 to 71 mm year 1 with a lag time of 1 5 year for radiocaesium

sulfide and silicate anatexis in the balmat zinc deposit new york usa and its implications for ore remobilization abstract the cross cutting zone of the fowler ore body is one of the many ore bodies of the balmat ny massive sulfide zinc deposit that underwent remobilization during upper amphibolite metamorphism and associated deformation the kilometer scale remobilization is difficult to reconcile with purely solid state processes given that other polymetallic ores of similar metamorphic grade have been shown to have undergone varying degrees of anatexis sem eds micro petrographic analysis of ores was undertaken to determine if melts were present in balmat ores during metamorphism and deformation low melting temperature micro inclusions of sulfosalt and sulfide assemblages occur predominantly in qtz py and kfs py domains that cross cut peak metamorphic assemblages these results indicate that localized anatexis occurred on the prograde path producing low volumes of melts of varying composition polymetallic sulfide melts were initiated by the prograde breakdown of minor phases containing low melting temperature chalcophile elements including as sb pb and cu alkaline silicate carbonate sulfide melts were fluxed by halogens sulfur and other volatile components released during metamorphism of evaporitic and organic rich horizons in the marble dominated host sequence these low volume melts and residual fluids would have wetted grain boundaries affecting the rheology of the bulk ore and facilitating remobilization of the ores through a combination of solid and liquid state processes

an iberian stegosaurs paradise the villar del arzobispo formation tithonian berriasian in teruel spain since 2002 a number of sites containing stegosaurian remains bones and tracks have been discovered in the villar del arzobispo formation tithonian berriasian in the province of teruel spain mostly in the areas of el castellar and riodeva the material from the latter consists of the postcranial remains of the axial pelvic and appendicular skeleton of several different sized specimens related to the genus dacentrurus the footprints made by a stegosaurian at el castellar site reflect a new type of medium gauge trackway deltapodus ibericus isp nov the presence of these tracks near abundant bones related to dacentrurus highlights this geological formation as a window through which to examine the systematics behaviour and palaeoecology of these thyreophoran dinosaurs since these fossil bones were discovered next to those of other sauropods and ornithopods turiasaurus and ornithopoda indet where there has been virtually no transport of the remains and since stegosaurian tracks have been found in ichnoassociations with the same groups they may have coexisted in the wetlands of restricted tidal environments during the tithonian berriasian the presence of common or at least phylogenetically closely related taxa and ichnotaxa in western europe north america and africa indicates that sea level fall episodes may have occurred during which the fauna of each area may have reached the emerged regions of the others during the late jurassic

the possibility of a zns bearing sulfide melt at 600 c evidence from the rajpura dariba deposit india supported by laboratory melting experiment abstract inclusions of euhedral pyrite crystals are seen within sphalerite occupying veins and fractures in the rajpura dariba zn pb cu sulfide deposit in rajasthan india sphalerite in the deposit shows wide variation in composition and contains high sulfur with fe s zn varying from 0 49 to 1 06 indicating that a portion of the fe in sphalerite could be expressed as a pyrite fes 2 component and that the pyrite inclusions within sphalerite in the vein ore could have formed due to exsolution we have conducted experiments by the evacuated silica tube method at 600 c pertinent to the peak metamorphic conditions of the rajpura dariba deposit our experiments were aimed at exploring the possibility of a zns bearing sulfide partial melt that could precipitate sufficiently s rich sphalerite which in turn might exsolve pyrite the starting mixture comprised synthetic fes zns pbs cu 2 s and s in the molar proportions of 40 33 9 9 and 9 respectively which approximately corresponded to molar proportions of 27 fes 40 zns 11 pbs and 22 cufes 2 electron probe micro analysis epma of the resulting run product showed the presence of a cu fe zn pb s melt containing 4 61 mol zns in the coexisting sphalerite the estimated fes 2 component was 9 07 mol the eutectic temperature was determined to be 595 c with a melt containing 22 44 mol fes 31 24 mol cu 2 s 5 37 mol zns 35 81 mol pbs and 5 14 mol fes 2 the sphalerite that was in equilibrium with the eutectic melt contained 6 72 mol fes 2 our experimental results suggest that a zns bearing sulfide melt containing as high as 5 mol zns was produced during metamorphism at rajpura dariba by partial melting of the preexisting ore further experiments confirmed that a minimum sulfur fugacity of 2 46 log units is required for initiating melting pyrite and sphalerite containing fe and stoichiometrically excess s are the solidus phases present in all melt bearing experimental run products except one with much higher zns suggesting that these two minerals at rajpura dariba could have simultaneously crystallized from a sulfide partial melt giving rise to the observed poikilitic textural relation between the two

the distribution of gamma emitting radionuclides in surface subtidal sediments near the sellafield plant abstract detailed distributions of total gamma activity 137 cs 106 ru and 95 zr 95 nb in surface seabed sediments near the sellafield plant are presented the results are derived from a towed seabed gamma ray spectrometer survey in september 1982 all the distributions are similar with contours of equal activity parallel to the coast defining a ridge of higher activity which is displaced northwards relative to the outfall this pattern appears to be largely a response to the transport of particle associated radioeffluent modified in places by the type of seabed sediment present at greater distance from sellafield the uptake of nuclides from solution seems to be more important nuclide concentrations decrease with increasing distance from sellafield rates of decrease being in the order zr nb ru cs this can be related to the levels of the nuclides discharged their sorption characteristics and their half lives the pattern of seabed activity seems to have been fairly stable over the period 1978 1985 but there is evidence of a small northward shift concentrations of 137 cs and 106 ru in 1985 were considerably lower than in 1978 or 1982 this is explicable in terms of the fall in discharge levels allied in the case of ru to its short half life and for cs the desorption observed in laboratory experiments nuclide ratios in sediment samples yield apparent transit times for the transport of nuclides in the survey area of 1 7 3 7 years these times are generally greater than those obtained from sediments in the more distant solway firth and ravenglass estuary it is suggested that they reflect fairly intense bioturbation causing mixing of relatively recent effluent with that from earlier discharges this is supported by structures observed in x radiographs of box cores an abundant burrowing benthos and by interpretations of nuclide profiles and radiocarbon dating of sediment cores by other workers a lag effect of up to two years across the survey area appears to be superimposed on that due to mixing

textural evidence for extensive melting of the broken hill orebody galena pyrrhotite and chalcopyrite in samples of zn rich ore from the broken hill orebody show textures similar to those in partially melted metamorphic rocks including strings of low melting phases separating lithons of minerals likely to be restite low dihedral angles between low melting temperature minerals and restitic minerals and enlargement of these dihedral angles due to partial annealing analysis of existing experimental work from the system fe pb zn s indicates that at 1 bar galena and sphalerite coexisting with pyrrhotite of the compositions found at broken hill would have been partially melted at temperatures of about 750 c at 5 kbars this melting would occur at 780 c this temperature is well within the range of metamorphic temperatures reported from the area from these data we conclude that the broken hill orebody was partially molten at peak metamorphism with much of the pb cu ag sb and as in the melt and fe and zn residing mostly in the restite differentiation during cooling enriched the residual melt in sb as ag and other low melting temperature chalcophile elements the main sulfide melt froze after the last penetrative deformation to affect the orebody at temperatures below 720 c and possibly as low as 650 c sulfosalts crystallized out of the remaining melt at temperatures of 600 to 450 c and the final melt crystallized native bismuth at ca 250 c

the subsolidus segregation of layer parallel quartz feldspar veins in greenschist to upper amphibolite facies metasediments layer parallel i e parallel to foliation or bedding vein formation in the graywackes and pelites of the quetico metasedi mentary belt occurred during synchronous prograde metamorphism and regional dj com pression in a traverse across metasediments which change in metamorphic grade from green schist to upper amphibolite migmatite facies layer parallel veins show the following trends 1 an increase in thickness and internal corn plexity the latter due to successive boudinage 2 low grade veins are parallel to planes of anisotropy due to the original sedimentary fabric of the host rocks but at higher grades other sites are also used and 3 a systematic increase in plagioclase quartz ratio in the veins towards higher grade adjacent mafic selvedges first exhibit quartz depletion then in the amphibolite facies plagioclase depletion mineralogical zoning is often preserved in a single vein older parts are more quartz rich than younger mass balance calculations and whole rock geochemistry based on veins mafic selvedges and country rock are consistent with a closed system subsolidus segregation origin the layer parallel veins are syntectonic and migration of the mobile components required to form their mineralogy is a stress induced mass transfer the source of these components appears to be dominantly pressure solution of the same minerals in the host rocks although metamor phic reactions may also have contributed veins nucleated first at those sites where initial sedimentary heterogeneites such as fine scale graded bedding provided gradients of normal stress across grain boundaries and hence of chemical potential necessary to drive the sub solidus segregation process the earliest veins are thus parallel to bedding later nucleation of the veins could also occur along more randomly distributed sites within the metasediments and these veins grew parallel to the schistosity rather than bedding if the two were distinct once formed the veins themselves which are more competent than the surrounding rock provide the stress heterogeneity required for their further growth the increasing plagioclase quartz ratio in the veins may be due to a tem perature dependent increase in plagioclase com ponent mobility relative to quartz alterna tively the increasing transfer distances for silica resulting from prior quartz depletion in the inner parts of the mafic selvedge may increase the relative mobility of plagioclase component

on the initiation of metamorphic sulfide anatexis mineral assemblages in common sulfide ore deposits are examined together with phase relations to 1 investigate the pressure temperature conditions required for the onset of metamorphically induced partial melting involving economic minerals and 2 place constraints on the amount of melt produced deposits that contain sulfosalt or telluride minerals may start to melt at conditions ranging from lowest greenschist facies to amphibolite facies deposits lacking sulfosalt and or telluride minerals may begin to melt once p t conditions reach the upper amphibolite facies if galena is present or well into the granulite facies if galena is absent the result is two broad melting domains a lowto medium temperature low melt volume domain involving melting of volumetrically minor sulfosalt and or telluride minerals and a high temperature potentially higher melt volume domain involving partial melting of the major sulfide minerals epithermal gold deposits which are especially rich in sulfosalt minerals are predicted to commence melting at the lowest temperatures of all sulfide deposit types massive pb zn cu deposits may start to melt in the lower to middle amphibolite facies if pyrite and arsenopyrite coexist at these conditions and in the upper amphibolite facies if they do not excepting sulfosalt bearing occurrences massive ni cu pge platinum group element deposits will show little to no melting under common crustal metamorphic conditions whereas disseminated cu deposits are typically incapable of generating melt until the granulite facies is reached when partial melting commences in bornite bearing rocks the volume of polymetallic melt that can be generated in most deposit types is therefore largely a function of the abundance of sulfosalt minerals even at granulite facies conditions this volume is usually less than 0 5 the exception is massive pb zn deposits where melt volumes significantly exceeding 0 5 vol may be segregated into sulfide magma dykes allowing mobilization over large distances

seasonal changes in surface level of a salt marsh creek nineteen surveys were carried out over a two year period to determine the surface height of a salt marsh creek located on the north side of the river esk cumbria england an aga 112 electromagnetic distance measurer mounted on a wild ti theodolite was used in conjunction with acrylic reflectors to follow the form of the ground the results showed that there were no significant net trends in surface level although seasonal variations of the order of 2 cm occurred vegetated areas responded in similar fashion to bare surfaces it is thought that the elevational changes were attributable to the swelling of clay particles during the winter months rather than the effects of erosion and accretion

paleoenvironmental reconstruction of jurassic dinosaur habitats of the vega formation asturias spain jurassic aged strata of asturias spain contain trace fossils including sauropod theropod and ornithopod dinosaur footprints but their paleoenvironmental context has been relatively unstudied a coastally exposed continuous section at playa de vega shows a clear transition from the marine middle jurassic rodiles formation to the terrestrial upper jurassic vega formation within the 100 m of vega formation stratigraphy that was logged there four distinct types of paleosols were identified 1 entisols 2 inceptisols 3 vertisols and 4 composite or cumulative paleosols the paleosol types and their features indicate a floodplain depositional setting with short stature shrubby vegetation theropod and ornithopod tracks have been identified at the base of the section indicating that a dinosaurian fauna was present at playa de vega during the jurassic results from well characterized climofunctions based on modern soils and paleosol b horizon chemical composition of the inceptisols and vertisols yield mean annual precipitation estimates of 400 980 mm yr 1 and mean annual temperature estimates of 8 15 c the presence of vertisols with both evidence for shrink and swell behavior and dispersed pedogenic carbonate is consistent with a strongly seasonal precipitation regime the 13 c analyses of pedogenic carbonates yield values that range from 7 09 to 8 88 relative to vienna peedee belemnite vpdb and indicate carbon dioxide levels about six times pre industrial levels consistent with previous results the asturian vertebrate track assemblage is remarkably similar to that of the morrison formation western united states but it has greater overall richness the pattern is reversed for body fossils the reconstructed paleoenvironmental and paleoclimatic conditions indicate similar depositional settings in both places but with a cooler wetter more seasonal environment in asturias the greater seasonality indicated by the vega formation relative to the morrison formation may explain the observed differences in richness

on the presence of allosaurus fragilis theropoda carnosauria in the upper jurassic of portugal first evidence of an intercontinental dinosaur species the species allosaurus fragilis from the morrison formation of north america kimmeridgian tithonian upper jurassic is one of the best known members of the theropoda the group including all predatory non avian dinosaurs and birds here we report on the first diagnostic theropod remains discovered from the jurassic of the iberian peninsula the specimen is the first evidence of a fragilis outside north america thus this taxon represents the first dinosaur species found on two different continents and suggests the existence of a land bridge between north america and europe during the late jurassic

first american record of the jurassic ichnospecies deltapodus brodricki and a review of the fossil record of stegosaurian footprints abstract we describe the first american stegosaur track of the ichnospecies deltapodus brodricki collected in the upper jurassic morrison formation of san juan county southeastern utah united states the track is preserved as a natural cast on the underside of a slab of fluvial sandstone and consists of a well preserved pes track and the eroded remains of a manus track previously deltapodus was known only from the middle jurassic yorkshire coast of england and the upper jurassic of portugal and spain the new discovery thus substantially extends the geographic record of this ichnospecies and highlights the similarities between the late jurassic dinosaur faunas of north america and those of western europe

age and provenance of grenville supergroup rocks trans adirondack basin constrained by detrital zircons detrital zircons from quartzites constrain the timing of deposition provenance and basin evolution of the grenville supergroup in the adirondack lowlands three samples from the stratigraphic succession yield maximum depositional ages of 1284 16 ma to 1257 6 16 ma shifts in provenance from rifting unimodal volcanic carbonate platform laurentian interior deep water clastics southern adirondack arc to final basin fill laurentian interior are documented the trans adirondack backarc basin is one of several that opened at ca 1 30 ga filled with thick carbonate dominated sequences and closed during the elzevirian orogeny ca 1245 1220 ma terminating widespread extension across the leading edge of southeast laurentia

new dinosaur track occurrences from the upper jurassic salt wash member morrison formation of southeastern utah implications for thyreophoran trackmaker distribution and diversity abstract recent construction at the moab giants dinosaur museum property 10 miles 16 km north of moab in grand county utah in 2014 2015 revealed a number of moderately well preserved dinosaur tracks from the upper jurassic salt wash member of the morrison formation the best specimens were preserved as natural casts on the underside of massive sandstone beds many containing dense assemblages of invertebrate traces here we describe several tridactyl theropod tracks an ornithischian manus attributable to ichnogenus stegopodus and an ornithischian pes track attributed to ichnogenus deltapodus variably preserved deltapodus have now been reported from the tidwell salt wash and brushy basin members of the morrison formation from garfield grand and san juan counties respectively suggesting a wide distribution in space and time the salt wash specimen is considered to be the most representative of deltapodus morphologies reported from large samples in other regions notably in spain portugal western china and north africa differences between stegopodus and deltapodus are reviewed deltapodus is reported from europe and asia as well as north america in the middle jurassic through late cretaceous and is often represented by abundant trackways stegopodus is presently reported from the jurassic where it occurs in the late jurassic of north america as isolated tracks and with some debate as trackways and isolated tracks from europe a middle jurassic occurrence from morocco is also reported

implications of sedimentological and hydrological processes on the distribution of radionuclides the example of a salt marsh near ravenglass cumbria this paper summarizes sedimentological and hydrological studies at a salt marsh site on the north bank of the river esk near ravenglass which have a bearing on the fate of the low level radioactive effluent from the reprocessing facility at sellafield cumbria a range of techniques has been used including electromagnetic distance measurement edm and pore water pressure studies the results show that 1 a over a two year period there were no significant net changes in salt marsh creek level although shorter term probably seasonal fluctuations of the order of 2 cm occurred these were attributed to expansion of clay particles during the winter months nearby however there were vertical changes of the order of 1 m due to erosion 2 b pore water pressures indicated a dynamic situation with very rapid responses both to tidal fluctuations and to rainfall during neap tides there was clear evidence for water seeping upwards from the underlying clay sand interface shortlived radionuclides 95zr95nb and 106ru were detected in this zone 3 c soil polygons once initiated by desiccation thereafter provide preferential routes for water and radionuclides to the sub surface sediment these and other results are discussed in the context of previous studies it is concluded that the complexity of the estuarine environment results in most data being site specific

local variability in the distribution of windscale fission products in estuarine sediments the local variations of fission product activites 144ce 106ru 137cs and 134cs in surface sediments from a location in the ravenglass estuary north west england have been studied the sediments are contaminated by the radioactive effluents discharged to the eastern irish sea by the windscale nuclear fuel reprocessing facility the results indicate that significant activity variations occur for surface samples taken from small scale sedimentary features of the estuarine environment and that sediment grain size characteristics and radioactive decay exert controls on fission product distributions the assessment of radiation exposure of the public by external gamma doses from contaminated sediments should take intt account the variability of radionuclide distributions over small scale features as well as the broader surveying of estuarine areas

carbon isotope thermometry in marbles of the adirondack mountains new york carbon isotope thermometry has been applied to coexisting calcite and graphite in marbles from throughout the adirondack mountains new york eighty nine calcite graphite pairs from the amphibolite grade nw adirondacks change systematically in temperature north westwards from 680 to 640 to 670 c over a 30 km distance reflecting transitions from amphibolite facies towards granulite facies to the north west and to the south east temperature contours based on calcite graphite thermometry in the nw adirondacks parallel mineral isograds with the orthopyroxene isograd falling above 675 c and indicate that regional metamorphic temperatures were up to 75 c higher than temperatures inferred from isotherms based on cation and solvus thermometry bohlen et al 1985 fifty five calcite graphite pairs from granulite grade marbles of the central adirondacks give regional metamorphic temperatures of 670 780 c in general agreement with cation and solvus thermometry data for amphibolite and granulite grade marbles show a 12 oo range in 13ccal and 13cgr a strong correlation between carbon isotopic composition and the abundance of graphite cgr crock indicates that the large spread in isotopic compositions results largely from exchange between calcite and graphite during closed system metamorphism the trends seen in 13c vs cgr crock and 13ccal vs 13cgr could not have been preserved if significant amounts of co2 rich fluid had pervasively infiltrated the adirondacks at any time the close fit between natural data and calculated trends of 13c vs cgr crock indicates a biogenic origin for adirondack graphites even though low 13c values are not preserved in marble delamination of 17 graphite flakes perpendicular to the c axis reveals isotopic zonation with higher 13c cores these isotopic gradients are consistent with new graphite growth or recrystallization during a period of decreasing temperature and could not have been produced by exchange with calcite on cooling due to the sluggish rate of diffusion in graphite samples located 2km from anorthosite show a decrease of 0 5 0 8 oo in the outer 100 of the grains while samples at distances over 8 km show smaller core to rim decreases of c 0 2 oo correlation between the degree of zonation and distance to anorthosite suggests that the isotopic profiles reflect partial overprinting of higher temperature contact metamorphism by later granulite facies metamorphism core graphite compositions indicate contact metamorphic temperatures were 860 890 c within 1 km of the marcy anorthosite massif if samples with a significant contact metamorphic effect cal gr 3 2 oo are not included then the remaining 38 granulite facies samples define the relation 13c cal gr 3 56 106t 2 k

plutonium in intertidal coastal and estuarine sediments in the northern irish sea abstract surface intertidal sediments from 35 sites in the irish sea have been analysed for their 238 pu and 239 240 pu activities together with an intensive study of plutonium in sediments of the esk estuary nw england the range of plutonium activities for the whole survey were 0 14 4118 and 1 3 16 026 bq kg 1 for 238 pu and 239 240 pu respectively the levels of pu activity derived from the sellafield nuclear fuel reprocessing effluents in sediments are controlled by lithological factors and the influence of transport and post depositional processes grain size distribution is particularly important the major part of plutonium activity being in the mud fraction of all sediments the data suggest that over the irish sea coastline dynamic mixing of sediment grains by reworking and resuspension and or by dispersion in tidal currents are important in determining plutonium distributions the exponential decrease in sediment plutonium activities away from the sellafield source is attributed to the progressive mixing with older contaminated and uncontaminated sediments

sulfide melt inclusions as evidence for the existence of a sulfide partial melt at broken hill australia polyphase sulfide melt inclusions are hosted within garnetite rocks and quartz veins in garnetite surrounding droppers and large masses of the orebody at broken hill australia and record the presence of a former sulfide melt sulfide melt inclusions are either primary or occur along healed fractures in both garnets and quartz veins common daughter minerals in the inclusions are galena sphalerite arsenopyrite chalcopyrite tetrahedrite tennantite and minor amounts of argentite bornite dyscrasite ag3sb and gudmundite fesbs the inclusions exhibit a strong enrichment in low melting point chalcophile elements compared to the main orebody experimental reequilibration of sulfide melt inclusions shows homogenous melt at temperatures as low as 720 10 c and 5 kbars well below that of peak metamorphism at broken hill 800 10 c and 5 kbars thus these inclusions are interpreted to represent a trapped sulfide melt formed during peak metamorphism at broken hill australia

three orders of regional sea level changes control facies and stacking patterns of shallow platform carbonates in the maestrat basin tithonian berriasian ne spain middle tithonian berriasian shallow platform carbonates of the maestrat basin salzedella and montanejos sections ne spain are stacked in sequence stratigraphic units of different orders higher order sequences parasequences and subunits have a shallowing or deepening shallowing evolution they have been related to the short term eccentricity and precession cycles major facies changes and stacking pattern of parasequences reveal the presence of two 2nd order sequences the lower sequence is middle tithonian mid early berriasian in age the upper sequence extends up to the mid late berriasian it is suggested that local subsidence changes along with regional sea level changes controlled the long term evolution of accommodation in the maestrat basin facies evolution stacking pattern and sharp lithological changes have allowed the definition of five 3rd order sequences in the lower sequence in montanejos the transgressive deposits are characterised by the progressive absence of the restricted lagoon facies and the presence of deepening upward intervals in the parasequences the highstand deposits display an increase in siliciclastics and a progressive predominance of restricted lagoon facies some of the 3rd order sequence boundaries match the sequence boundaries identified in other european basins and may be related to sea level falls induced by the long term eccentricity cycle enhanced during periods of long term loss of accommodation

timing of anatexis in metapelites from the adirondack lowlands and southern highlands a manifestation of the shawinigan orogeny and subsequent anorthosite mangerite charnockite granite magmatism anatectic leucogranites are common in metapelites within both the highlands and lowlands terranes of the adirondack mountains of northern new york state the formation of these igneous bodies which are folded in the lowlands and commonly mylonitized in the highlands has been widely considered an event accompanying the ca 1050 ma ottawan orogeny during which metamorphic grade reached granulite facies in the highlands while the lowlands experienced amphibolite facies metamorphism sensitive high resolution ion microprobe shrimp analyses of zircons separated from leucosomes and melanosomes in both the southern highlands and the lowlands indicate that primary anatexis occurred ca 1180 1160 ma and is thus a manifestation of heating during the earlier shawinigan orogeny ca 1210 1160 ma and associated anorthosite mangerite charnockite granite amcg magmatism ca 1165 1150 ma the absence of ottawan overgrowths on shawinigan zircons in these leucosomes suggests that by ottawan time the rocks were too dry for further melting or zircon growth to occur however electron microprobe analyses of monazites from the southern highlands reveal multiple age zones including cores with ages of ca 1170 1180 ma consistent with primary growth during shawinigan orogenesis complex zones formed ca 1140 1155 ma during amcg magmatism and ca 1050 1020 ma formed during ottawan orogenesis and high grade metamorphism throughout the adirondacks leucosomes and melanosomes contain older ca 1320 ma zircons that are considered to be remnant detrital zircons derived from arc rocks of the elzevirian terrane the apparent absence of archean detrital zircons suggests that the protoliths of the metapelites were deposited in restricted basins that did not receive detritus from the superior craton

new information about the stratigraphic position and age of the sauropod aragosaurus ischiaticus from the early cretaceous of the iberian peninsula the sauropod aragosaurus ischiaticus sanz buscalioni casanovas santafe 1987 was the first dinosaur to be described in spain the holotype was recovered from the site of las zabacheras galve teruel province this site has traditionally been situated in the el castellar formation in the lower part of the wealden facies recently it has been proposed that the remains of aragosaurus stem from the villar del arzobispo formation late tithonian upper part of the early berriasian which would mean that the sauropod was almost 15 million years older than previously thought detailed field work has been carried out making it possible to pinpoint the position of the low angle unconformity between the villar del arzobispo formation and the el castellar formation this unconformity originated as a result of block tilting that occurred during the early stages of the early cretaceous rifting episode the upper levels of the jurassic sequence i e the villar del arzobispo formation were exposed to erosion and karstification leading to the formation of a discontinuous conglomeratic level this level has been locally preserved at the bottom of the wealden syn rift sequence i e the el castellar formation the results of our detailed mapping demonstrate that the aragosaurus holotype was found in the lower part of the el castellar formation moreover our revision of the existing datings suggests that the el castellar formation as a whole is valanginian early barremian in age given that aragosaurus was located in its lower part it is probably valanginian hauterivian in age

the use of reprocessing effluent radionuclides in the geochronology of recent sediments abstract over the last three decades artificial radionuclides have been introduced into the environment from the nuclear industry this paper discusses the use of such radionuclides for interpreting the geochronology of recent sedimentary deposits the discharges into the northeast irish sea from the windscale reprocessing plant u k provide a useful opportunity to study the transport and geochronology of sediments in this area a variety of different methods have been developed to study the behaviour of the local sediments and a number of examples are discussed illustrating the techniques used for dating the sediment deposits these involve the use of fission product radionuclides 134 cs 137 cs 106 ru and 144 ce transuranics 239 240 pu and 238 pu and the application of radionuclide concentration ratios in cores and surface samples the radionuclide activity profiles of the sediment cores and the concentration ratios of the surface samples were interpreted by comparison with the known discharge histories this provided information on net sedimentation rates apparent diffusion coefficients and lag times of transport the studies showed that post depositional redistribution of cs and especially pu nuclides within a sediment column are small apparent d 8 cm 2 s 1 net sedimentation rates varied in the range 16 71 mm yr 1 and lag times 0 0 75 yr from samples taken along a mud bank salt marsh transect correlations were shown between activities and sedimentary environment