evidence for early asteroidal collisions prior to 4 15 ga from basaltic eucrite phosphate u pb chronology abstract the late heavy bombardment lhb hypothesis wherein the terrestrial planets are thought to have suffered intense collisions ca 3 9 billion years ago is under debate coupled with new dynamical calculations re examination of geochronological data seem to support an earlier solar system instability and a smooth monotonic decline in impacts as opposed to a cataclysm to better understand this collisional history records from the asteroidal meteorites are required here we report a uranium lead u pb chronological dataset for eucrite meteorites thought to originate from the asteroid 4 vesta this dataset indicates to a continuous history of collisions prior to 4 15 ga our 207pb 206pb model ages of apatite ca5 po4 3 f cl oh and merrillite ca9namg po4 7 from three brecciated basaltic eucrites juvinas 4150 3 11 6 million years ago ma merrillite only camel donga disturbed around 4570 4370 ma and stannern 4143 0 12 5 ma record multiple thermal metamorphic events during the period of 4 4 4 15 ga we interpret this to mean that vesta or the vestoid cluster underwent multiple impacts and moderate high temperature reheating during this time the ages of 4 4 4 15 ga are distinctly younger than the initial magmatic process on vesta 4 5 ga but are significantly older than a later impact peak based on some interpretations of 40ar 39ar chronologies 3 9 3 5 ga the intense collisions prior to 4 15 ga on vesta are at odds with the conventional lhb hypothesis but not inconsistent with the much earlier bombardment and monotonic decline scenario different radiometric chronologies of the asteroid likely represent the different stages of a continual collisional process conversely the model 207pb 206pb ages of apatite in the unbrecciated basaltic eucrite agoult returned an age of 4524 8 9 6 ma this may represent slow cooling from an earlier global reheating of the crust on vesta at 4 55 ga as documented by other radiometric chronologies the apatite in juvinas recorded a coincident timing of 4516 9 10 4 ma which could be due to either slow crustal cooling or impact

factors controlling geochemical and mineralogical compositions of coals preserved within marine carbonate successions a case study from the heshan coalfield southern china abstract the late permian coals in the heshan coalfield of southern china are preserved within marine carbonate successions and characterized by super high organic sulfur 5 13 10 82 minerals identified in the coals include quartz kaolinite illite mixed layer illite smectite albite pyrite marcasite calcite and dolomite along with trace amounts of smectite fluorite strontianite rey bearing carbonate minerals jarosite and water bearing fe oxysulfate the coals are very rich in trace elements including f up to 3362 g g v up to 270 g g se up to 24 4 g g mo up to 142 g g u up to 111 g g and to a lesser extent sr y zr nb cd cs heavy rare earth elements hf ta w hg and th previous studies attributed the high organic sulfur and elevated trace elements to the seawater influence or the formation of soil horizons before the accumulation of peat in the basin however mineralogical and geochemical data presented in this study have shown that the sediment source region and multi stage hydrothermal fluids are the dominant influences on the mineralogical composition and elevated trace elements in the coal although seawater influence also contributed to the composition of the mineral matter for example a large proportion of the quartz and clay minerals as well as almost all the albite in both the coal benches and the parting mudstones were derived from detrital materials of terrigenous origin in the yunkai upland high concentrations of lithophile trace elements were also derived from the sediment source region minerals including fluorite calcite dolomite strontianite and rey bearing carbonate minerals were derived from multi stage hydrothermal activities high concentrations of v mo and u that occur through the coal seam sections were probably derived from hydrothermal solutions during peat accumulation or at the early diagenetic stages the hydrothermal fluids also corroded the syngenetically formed minerals quartz albite and pyrite and caused re distribution of lithophile elements from partings to the underlying coal benches resulting in higher key element ratios yb la nb ta and zr hf and more abundant heavy rare earth elements in the coal benches than in the immediately overlying partings

in situ sims u pb dating of phanerozoic apatite with low u and high common pb abstract apatite is a common accessory mineral in various igneous metamorphic and sedimentary rocks it has strong potential to provide important information for geochronology and petrogenesis however precise u th pb dating of apatite especially young samples is difficult due to low abundances of u and less radiogenic pb posing significant challenges for accurate common pb correction an additional issue is the lack of suitable apatite to serve as a standard for in situ analyses here we present both analytical and data reduction protocols for sims in situ u pb analyses on apatite with low u and high common lead with nw 1 apatite as the u pb age standard which was separated from 1160 ma carbonatite in the prairie lake complex in canada apatites from the kovdor carbonatite in the kola peninsula which contains low u mostly 2 5 ppm and high common pb 20 80 yielded weighted average 207pb corrected u pb ages of 375 13 ma kv 8 and kv 18 and 377 11 ma kv a respectively apatites from the quruqtagh ultramafic intrusion in nw china containing low u 2 3 ppm and high common pb 70 yield 207pb corrected u pb age of 805 21 ma the cenozoic durango apatite was dated at 31 2 ma all these new apatite u pb ages are indistinguishable from independently known age constraints to within 2 4 our results demonstrate that a u pb age can be accurately and precisely measured for apatite with low u 50 by sims with a suitable standard and a careful choice of common pb composition

isotopic evidence for trapped fissiogenic ree and nucleogenic pu in apatite and pb evolution at the oklo natural reactor abstract a part of the boundary layer of reactor zone 10 at the oklo natural reactor shows a unique petrologic texture which contains high grade uraninite and massive apatite concretions in order to study distribution behavior of fission products around the boundary between the reactor zone and the wall rock and to clarify the relation of migration mechanisms of fission products with geochemical factors in situ isotopic analyses of nd sm gd pb and u in uraninite and apatite from the sample were performed by sensitive high resolution ion microprobe shrimp sm and gd isotopic ratios of uraninite and apatite show evidence of neutron irradiation with fluence between 4 4 6 8 10 19 n cm 2 judging from the isotopic anomalies of nd and u the apatite coexisting with the uraninite plays an important role in trapping fissiogenic lree and nucleogenic 239 pu into the structure systematic pb isotopic data from apatite uraninite galena and minium suggest the following chronological interpretations 1 the apatite formed 1 92 0 01 ga ago and trapped fissiogenic light ree and nucleogenic 239 pu that migrated from the reactor during the criticality 2 the uraninite around the boundary between reactor and sandstone dissolved once 1 1 1 2 ga ago 3 galena grains were formed by u pb mobilization in association with the intrusion of dolerite dyke 0 45 0 83 ga ago 4 minium was derived from recent dissolution of galena under locally oxidizing conditions

in situ la icp ms u pb dating of metavolcanics of norrbotten sweden records of extended geological histories in complex titanite grains in situ u pb dating of a variety of mineral phases is an important goal in petrology this study reports data chiefly from titanite but also from rutile and apatite obtained using the laser ablation la icp ms methodology on polished thick sections in order to retain as much petrologic information as possible and allowing trace element analyses from adjacent areas to the u pb analyses the samples analysed come from svecofennian intermediate to acid volcanic rocks of the porphyry group within the major iron ore province of norrbotten northern sweden where titanite is a common phase associated with the mineralisation using a laser beam of 30 45 m in diameter accurate and relatively precise 2 3 2 on 206pb 238u ratios data can be obtained on titanite similar precision on pb u ratios can be obtained in rutile but accuracy cannot be assessed because of the lack of well characterised standards however the data are a priori accurate as they are geologically reasonable apatite shows reverse discordance which could be explained by a number of scenarios however the 207pb 206pb ages are fairly precise 1 3 2 and the calculated age is geologically reasonable suggesting that the data may be accurate the titanite grains studied show complex internal structures rare earth element ree analysis by la icp ms demonstrates that the core and rim zones are distinct and supports a model for two stage evolution in two out of three samples with the rims in these samples being enriched in total ree and particularly in lree in one sample and displaying a positive y anomaly in contrast to the cores in situ u pb analysis reveals that core zones from all samples retain distinct older ages of c 2050 ma whereas the reworked rims have either distinct younger or strongly reset ages the older cores are interpreted as representing the first alteration metamorphism of the volcanic pile titanite rims record a u pb age of 1870 24 ma 2 at luossavaara and 1826 15 ma 2 at the smaller fe oxide apatite body at gruvberget in both cases the ages are consistent with previous age determinations from the fe oxide apatite deposits a sample from malmberget records a slightly different scenario where u pb ages spread along concordia from c 1920 to 1708 ma we attribute this pattern to metamorphic reworking of primary metasomatic titanite rutile ages from inclusions within the core of gruvberget titanite essentially mimic the ages obtained from the surrounding titanite and suggest that they have undergone the same history apatite inclusions within titanite at malmberget record a younger age of 1584 12 ma 2 which we attribute to later events known to have affected the area these data indicate that the porphyry group volcanics must be at least c 2050 ma in age in contrast to previous age determinations from zircon which suggested a deposition age of c 1960 to 1880 ma the large grain size of the titanites studied coupled with the ability for the first time to obtain in situ u pb ages from small areas has allowed probing of this hitherto unrecognised event smaller zircon grain size coupled with extremely saline hot pressurised high p t metasomatic fluids relating to regional magnetite apatite mineralisation in the period 1900 to 1800 ma may have resulted in resetting of zircon u pb systematics 2007 elsevier b v all rights reserved

occurrence of minerals within fractures and matrix of selected bowen and ruhr basin coals abstract late permian age samples of black coal from the coeval bandanna formation and baralaba coal measures of queensland s bowen basin as well as carboniferous coal from germany s ruhr basin were investigated this paper presents scanning electron microscope sem analysis of the mode of occurrence of minerals within these coals and characterisation of the natural fractures present within the samples the coal samples located proximal to orogenic fronts in both basins are structurally complex with multiple generations of mineralisation evident stable isotope analyses of carbonates from selected samples indicate that methanogenesis related co2 reduction has occurred at two of the bowen basin sampling locations ankerite precipitated from a magmatic fluid or basinal brine is associated with significant sulphide mineralisation within brecciated ruhr coal proximal to major fault intersections with anticlines and has been meteorically altered to ferroan calcite and sulphates in coal from immediately below the carboniferous cretaceous unconformity similar alteration has occurred within a bowen basin coal sample close to the present day land surface variation of mineralisation within both the cleats and the coal matrix occurs on a fine scale with crystals of multiple mineral species often being present within micrometres of each other

apatite composition tracing petrogenetic processes in transhimalayan granitoids apatites crystallized from different types of igneous rocks show significant variations in the abundances of some minor and trace elements in this study electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry were used to determine the concentrations of 25 minor and trace elements in apatite separated from three principal rock types of thetranshimalayan igneous plutonic suite s type granites the i type gangdese batholith and postcollisional adakites f mn sr and rare earth elements ree in apatite vary systematically with the composition of the host magma and thus have high potential as petrogenetic tracers more specifically the f and mn contents of apatite can be used as an indicator of magma aluminosity or differentiation index combined with sr and ree data which show significant variations in apatite from different rock types these elements are useful for constructing discrimination diagrams this study also reveals that apatite has the capacity to retain geochemical information about the host magma through the course of magmatic evolution systematic variations of sr and ree in apatite with bulk rock aluminosity are the results of partition competition with pre existing and coexisting major and accessory minerals in silicate melts and thus are useful for more detailed investigations of petrogenetic processes such as fractional crystallization and magma mixing which is signaled by inconsistent eu anomalies sr abundances and ree patterns relative to bulkrock compositions

disrupted coal and carbonate facies within two pennsylvanian cyclothems southern illinois basin united states two cyclothems contain an unusual suite of disrupted fabrics this study9s interdisciplinary integration of coal maceral and sedimentological information offers significant new interpretations of coal limestone interchange both depositionally and diagenetically disrupted fabrics within the herrin coal and providence limestone are interpreted as representing previously undocumented interactive processes between coals and limestones the herrin coal contains brecciated beds that are the result of marine transgression over a coastal plain mire representing high energy conditions at the swamp beach interface this interface has rarely been documented in detail peat is inherently unstable prior to its conversion to coal and we document this by interpreting conglomeratic beds in overlying strata differential compaction of herrin peats generated subaqueous debris flows in the overlying providence limestone this mechanism for syndiagenetic and early diagenetic sediment deformation has not been previously recognized in addition near surface and surface processes produced other disrupted fabrics in the providence limestone such as in situ mosaic breccias nodular fabrics and calcrete horizons this study also documents that stratigraphically adjacent alkaline carbonate sediments were further altered by undersaturated acidic pore waters derived from compacting peats during early diagenesis our interdisciplinary approach to distinguishing and interpreting all of these disrupted fabrics led to a new appraisal of the importance of depositional and postdepositional interactions between coal and limestone the presence of mire deposits can have a significant influence on the thickness distribution and fabrics in overlying strata in cyclothems climatic and eustatic changes may control overall depositional patterns but peat compaction may determine certain facies

fluid migration and associated diagenesis in the greater reelfoot rift region midcontinent united states the sources and pathways of basinal fluid flow on the north american craton have been the subjects of intense debate regional dolomitization and the distribution of petroleum and sulfide mineralization on the southern midcontinent are believed to be related to migration of warm basinal fluids from and within the arkoma and illinois basins because of its hydrologic connection with these two basins the reelfoot rift has been postulated as a potential source and or conduit for one or more of these fluids cathodoluminescence petrography has revealed nine distinct carbonate cement microstratigraphies in the reelfoot rift and on its adjacent carbonate platforms in missouri western platform and tennessee eastern platform temporal geochemical trends within each of the three areas are distinct eastern platform carbonate cements and their fluid inclusions exhibit decreasing 13c 18o homogenization temperatures t h and last ice melting t m values with decreasing age reelfoot rift dolomite and calcite cement and their fluid inclusions define a trend of decreasing 13c and 18o values and increasing t h and t m values western platform dolomite cements including those in the nearby southeast missouri mississippi valley type mineral district display a paragenetic trend of increasing 13c and 18o values followed by a return to lower values during the final stage of cement deposition distinct geochemical patterns indicate that stratigraphically controlled fluid flow through carbonate aquifers in the reelfoot rift was restricted within individual fault blocks that had limited communication with the adjacent carbonate platforms lateral fluid migration between fault blocks and vertical migration within fault blocks in the reelfoot rift likely was restricted by faults stratigraphic offset and impermeable units if significant fluid movement occurred from the reelfoot rift onto the adjacent western carbonate platform it likely occurred along northwest striking strike slip faults

the geology and palynology of lower and middle pennsylvanian strata in the western kentucky coal field abstract the western kentucky coal field is the southern tip of the eastern interior or illinois basin pennsylvanian rocks in this area which include conglomerate sandstone siltstone shale limestone and coal were deposited primarily in coastal deltaic settings at a time when western kentucky was located close to the equator this paper discusses temporal changes in regional sedimentation patterns and coal forming floras of lower and middle pennsylvanian strata in the western kentucky coal field lower pennsylvanian strata of the caseyville formation are characterized by paleovalley filling sedimentation patterns and extabasinal quartz pebbles caseyville formation coals are characteristically thin and discontinuous and were strongly influenced by subsidence within underlying paleovalleys and the dissected lower pennsylvanian paleotopography caseyville coals are commonly dominated by lycospora but can also have variable palynofloras which probably reflects variable edaphic conditions and edge effects within small patchy paleomires tradewater formation strata show increased marine influences and tidal estuarine sedimentation especially in the middle and upper parts coal beds in the lower part of the tradewater typically are thin and discontinuous although some economically important beds are present coals become thicker more abundant and more laterally persistent towards the top of the formation palynologically lower and middle tradewater formation coals are dominated by lycospora but begin to show increased amounts of tree fern spores middle and upper tradewater coals are thicker and more continuous and contain high percentages of tree fern spores in addition cordaite pollen is locally abundant in this interval carbondale and shelburn desmoinesian strata are much more laterally continuous and occur within classic cyclothems that can be traced across the coal field cyclothems have long been interpreted as being eustatically driven and glacio eustacy controlled not only sedimentation but also the formation of desmoinesian paleomires palynologically carbondale and shelburn coals are either dominated by lycospora or have heterogeneous palynofloras palynologic and coal quality data suggest that hydrologic base level may have been the primary control on desmoinesian paleomires rather than paleoclimate as the coals display rheotrophic rather than ombrotrophic characteristics

direct ion microprobe u pb dating of fossil tooth of a permian shark abstract we report here direct ion microprobe dating of fossil tooth dentine of a permian fresh water shark orthacanthus senckenbergianus using the shrimp instrument recently installed at hiroshima university fifteen spots on the small sample approximately 2 mm 1 mm indicate a 238 u 206 pb isochron age of 266 18 ma and a tera wasserburg concordia intercept age of 266 24 ma in a three dimensional 238 u 206 pb 207 pb 206 pb 204 pb 206 pb diagram these permian ages are consistent with a 235 u 207 pb age of 453 170 ma and a 232 th 208 pb age of 235 310 ma suggesting indistinguishable depositional and early diagenetic ages of the fossil in its sedimentary sequences the success of the method depends on the chemical fractionation of uranium from lead in a specimen a few hundred microns in size and the consequent variations in lead isotopic compositions due to radioactive decay

the occurrence of buddingtonite in super high organic sulphur coals from the yishan coalfield guangxi southern china abstract this paper discusses the identification abundance modes of occurrence and origin of buddingtonite and associated minerals in three lopingian coals from the yishan coalfield guangxi province southern china the coals of this coalfield are preserved within carbonate successions and are characterized by super high organic sulphur contents mostly 6 9 three different types of feldspars have been identified in these coals buddingtonite albite and minor k feldspar both the albite and k feldspar in the coal were largely derived from detrital materials of terrigenous origin although some were authigenically deposited they were subsequently subjected to corrosion dissolution by percolating fluids buddingtonite was derived largely from k feldspar via diffusion mechanisms through the substitution of k by nh4 the latter coming from decomposition of organic matter in the coal or from changes in the organic matter with rank advance a small proportion of the buddingtonite was also derived from albite through the replacement of na by nh4

high closure temperatures of the u pb system in large apatites from the tin mountain pegmatite black hills south dakota usa abstract the cores of several large 1 2 cm apatites from the early proterozoic tin mountain pegmatite black hills south dakota have concordant u pb ages the age uncertainties of these samples are less than 5 ma the lead isotopic compositions of muscovite and k feldspar coexisting with the apatites were used for initial lead isotopic corrections the resulting u pb concordia ages agree well with u pb and pb pb isochron ages based solely on multiple fragments from single apatites this agreement justifies the use of coexisting muscovite and k feldspar for initial lead corrections the precision of these u pb ages is comparable to those of the u pb systems of more commonly analyzed minerals such as zircon monazite and sphene the estimated u pb closure temperature t c of these apatites is about 620 c this t c is in close agreement with the t c calculated for 0 5 cm diffusion radii and published data for diffusivity and activation energy of lead diffusion in apatite apatite can therefore yield high precision u pb ages that are close to its crystallization age in igneous rocks

the oldest zircons in the solar system abstract here we report the occurrence chemistry and u th pb isotopic systematics of three meteoritic zircon assemblages two from the vaca muerta mesosiderite and one from the simmern h5 chondrite one of the vaca muerta zircons occurs in the mesosiderite proper the other in a eucritic clast associated with chromite ilmenite and tridymite whereas the simmern zircon occurs in a chondrule composed predominantly of chromite and feldspar like terrestrial zircons the meteoritic zircons are enriched in the heavy rare earth elements but unlike terrestrial zircons they do not show a positive ce anomaly this feature is also absent in one lunar zircon analyzed and probably reflects the oxidation state of the formation environment under oxidising conditions ce4 which can substitute for zr4 in the zircon structure is stabilized whereas under relatively reducing conditions ce3 is stable the zircon from simmern has depletions in the relative abundances of tm and yb a characteristic of volatility fractionation of the ree the u concentrations of the two vaca muerta zircons are quite different at 1 and 50 ppm respectively both zircons have extremely low initial lead and give radiogenic ages that are the same albeit with relatively large errors on vm 1 zircon because of its much lower u concentration and hence radiogenic pb concentration the mean of the two analyses made on vm 2 zircon is concordant with a207pb 206pb age of 4563 15 ma 2 the simmern zircon has an exceptionally low u concentration of around 180 ppb and only a poorly constrained 207pb 206pb age of 4100 700 ma could be obtained

ion microprobe u th pb dating and ree analyses of phosphates in the nakhlites lafayette and yamato 000593 000749 u th and pb isotopes and rare earth elements rees in individual phosphate grains from martian meteorites lafayette and yamato 000593 000749 were measured using a sensitive highresolution ion microprobe shrimp observed u pb data of 12 apatite grains from yamato y 000593 000749 are well represented by linear regressions in both conventional 2d isochron plots and the 3d u pb plot total pb u isochron indicating that the formation age of this meteorite is 1 53 0 46 ga 2 on the other hand the data of nine apatite grains from lafayette are well represented by planar regression rather than linear regression indicating that its formation age is 1 15 0 34 ga 2 and that a secondary alteration process slightly disturbed its u pb systematics as discussed in the literature regarding nakhla the observed ree abundance patterns of the apatites in lafayette and yamato 000749 normalized to ci chondrites are characterized by a progressive depletion of heavy rees hrees a negative eu anomaly similarity to each other and consistency with previously reported data for nakhla considering the extensive data from other radiometric systems such as sm nd rb sr ar ar and trace elements our results suggest that the parent magmas of the nakhlites including the newly found y 000593 000749 are similar and that their crystallization ages are 1 3 ga

geochronology of the belmont lake metavolcanic complex and implications for crustal development in the central metasedimentary belt grenville province ontario u pb analyses of zircon and titanite were carried out on eight rocks from the belmont lake metavolcanic complex a volcano sedimentary sequence in the central metasedimentary belt of the grenville province of southeastern ontario the ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position the youngest volcanic age is from a rhyolite near the base of the sequence the oldest age is from a dacite in the middle this is overlain by a rhyolite in age a rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 ma old the complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age tectonic emplacement of these segments was most likely along previously unrecognized thrust faults the supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism the earliest event was probably associated with thrusting t

ion microprobe u pb dating of apatite abstract to illustrate in situ sensitive high resolution ion microprobe shrimp analysis of apatites pb isotopes and pb u ratios of five apatite samples with different ages have been measured using shrimp ii ion microprobe at hiroshima university the prap apatite from a carbonatite complex at prairie lake ontario with a 207 pb 206 pb age of 1156 45 ma 2 was used as the standard for 206 pb 238 u 238 u 16 o 238 u calibration apatites from the poohbah lake alkaline complex give 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages of 2726 145 ma 2 and 2701 86 ma 2 in agreement with a conventional tims 207 pb 206 pb age of 2667 10 ma 2 and a k ar isochron age of 2706 46 ma 2 for the remaining three apatite samples the 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages obtained by shrimp are consistent with radiometric and geological ages in the literature

ragged edge of the herrin no 11 coal western kentucky abstract the herrin no 11 coal in western kentucky is normally a bright banded high vitrinite high sulfur coal three sites have been found where the coal deviates from the expected appearance in union county a site known only from a literature description the upper two thirds of the coal was described as a cannel in ohio county a thin truncated section of the herrin coal has a greater abundance of liptinite and inertinite rich microlithotypes towards the top of the seam the various microlithotypes were frequently found in brecciated assemblages in hopkins county the herrin coal was found to be largely a coarse breccia of oxidized macerals cemented by calcite a marine limestone was present as a parting within the coal each occurrence represents the edge of the coal the sites varied in the energy of the environment and perhaps also in proximity to marine waters

analysis origin and significance of mineral matter in coal an updated review abstract the material classed as mineral matter in coal embraces crystalline mineral materials as well as a range of inorganic elements that occur in non crystalline form this review outlines the methods that may be used to evaluate the percentage of mineral matter for a coal sample as opposed to the ash yield and to identify the minerals their individual percentages and their modes of occurrence within the coal the principal techniques include low temperature oxygen plasma ashing quantitative evaluation of x ray diffraction data observation using optical microscopy and a combination of observation chemical analysis and in some cases mapping based on scanning electron microscopy and related methods a range of other techniques may also be used to provide additional information on particular mineral matter components processes responsible for mineral matter formation include detrital input biogenic activity and authigenic precipitation at different stages of the coal s depositional and post depositional history differential migration of non mineral inorganic elements may also occur in lower rank coals and expulsion of non mineral inorganics may take place with rank advance knowledge of the mineral matter may be of assistance in understanding the modes of trace element occurrence with implications for assessing possible environmental impacts and also the potential for recovery of economic products from coal the behaviour of different mineral matter components at high temperatures is also discussed as well as methods for mineralogical analysis of ashes and other coal utilization products information from mineral matter studies may provide an improved basis for understanding coal formation and for evaluating the response of particular coals to different combustion gasification and coking processes

u th pb systematics of individual perovskite grains from the allende and murchison carbonaceous chondrites ion microprobe u th pb isotopic measurements have been made of individual perovskite grains from the allende cv3 and murchison cm2 chondrites these are the first chronological data reported for murchison refractory inclusions several generations of perovskite were identified in polished thin sections of fluffy type a inclusions 3529 44 and 4691 from allende of which only the largest anhedral perovskites 20 m were analysed with the ion microprobe the allende perovskites are characterised by low u typically 3 ppm but ranging up to 12 ppm in grain 7 1 from 3529 44 and th u of around 4 in 3529 44 and 10 in 4691 the204pb concentrations in the allende perovskites range from 6 to 140 ppb a precise age measurement could be obtained on grain 7 1 only the u pb systematics of this grain are concordant with a207pb 206pb age of 4565 34 2 ma two of the murchison perovskites occurred as individual 20 m inclusions in spinel grains 7 309 7 a52 while the third perovskite bearing inclusion was a spherule dominated by perovskite with interstitial spinel 7 396 u concentrations range from 3 6 to 15 ppm with th u less than 0 5 and204pb concentrations ranging from 61 to 369 ppb all analyses of the murchison perovskites are consistent with a single formation age of 4569 26ma the ages determined by ion microprobe from these perovskites show good agreement with previous age estimates of allende refractory inclusions measured by conventional mass spectrometric techniques there is no evidence in the u pb systematics of allende and murchison refractory inclusions for material that substantially predates the formation of the solar system

ion microprobe u th pb dating of phosphates in martian meteorite alh 84001 phosphates in martian meteorites are important carriers of trace elements although they are volumetrically minor minerals po4 also has potential as a biomarker for life on mars here we report measurements of the u th pb systematics of phosphates in the martian meteorite alh 84001 using the sensitive high resolution ion microprobe shrimp installed at hiroshima university japan eleven analyses of whitlockites and 1 analysis of apatite resulted in a total pb u isochron age of 4018 81 ma in the 238u 206pb 207pb 206pb 204pb 206pb 3 d space and a 232th 208pb age of 3971 860 ma these ages are consistent within a 95 confidence limit this result is in agreement with the previously published ar ar shock age of 4 0 0 1 ga from maskelynite and other results of 3 8 4 3 ga but are significantly different from the sm nd age of 4 50 0 13 ga based on the whole rock and pyroxene taking into account recent studies on textural and chemical evidence of phosphate our result suggests that the shock metamorphic event defines the phosphate formation age of 4018 81 ma and that since then alh 84001 has not experienced a long duration thermal metamorphism which would reset the u pb system in phosphates

mineral occurrence and its impact on fracture generation in selected qinshui basin coals an experimental perspective abstract the effect of mineral matter on the fracture evolution was investigated for lower permian and upper pennsylvanian coal samples from the qinshui basin of china optical microscopy scanning electron microscopy with energy dispersive x ray spectrometry sem eds and x ray computed tomography x ray ct were used to investigate the composition and modes of occurrence of minerals within the coals and to characterize the natural and induced fractures present within the samples the spatial distribution of mineral matter investigated by x ray ct demonstrates that the variation of mineralization within the cleats fractures occurred at fine scales and most of minerals were scattered in coal core samples the original fractures normally were present as two sets one set was almost parallel to the bedding plane and the other was almost perpendicular to the bedding plane for created fractures the difference in density between the matrix and mineral matter may weaken the cohesion of coals and it could explain why the created fractures propagate along the junction of minerals and organic coal matrix the internal fracture porosities varied from 0 06 to 20 69 which indicates a strong internal heterogeneity of the coals after a stress is applied the inclination of the main shear fractures ranges from 55 to 95 using energy analysis the fracture energy appears to represent nearly half of the total dissipated energy which can be correlated with the fracture density and orientation the formation and distribution of shear fractures is related to the spatial distribution of mineral matter and the overall mineral content these investigations serve to characterize hydro fracturing and pulverized coal generation during coalbed methane development

predicted equilibrium constants for solid and aqueous selenium species to 300 c applications to selenium rich mineral deposits abstract in this study an attempt has been made to assess aqueous speciation of selenium and solubility product constants of common selenides at elevated temperatures up to 300 c by using various extrapolation methods this study predicts that reduced selenium species are dominant species in many geological processes even under relatively oxidized conditions such as those dictated by the magnetite hematite buffer on the basis of extrapolated equilibrium constants and solubility product constants for common se bearing mineral phases critical se s ratios molal ratios in mineralizing fluids are proposed for independent selenium mineralization the minimum se s ratios in mineralizing fluids for independent selenium mineralization should be at least 10 6 10 5 and 10 4 at 100 200 and 300 c respectively for giant independent selenium deposits such as the la erma and qiongmo au se deposits in the western qingling mountains and yutangba se deposits in hubei province china the mineralizing fluids have reached much higher se s ratios ranging from 10 1 to 10 3 at 200 c this study also suggests that the equilibrium assemblage of pyrite ferroselite among the common ore minerals requires the highest se s ratios in mineralizing fluids followed in decreasing order by the assemblages of stibnite antimonselite galena clausthalite cinnabar tiemannite and acanthite argentite naumannite the assemblage of pyrite ferroselite can also be formed under relatively oxidizing conditions where h 2 se h 2 s ratios can be high enough for the formation of independent ferroselite

an 40ar 39ar geochronological study of the elzevir batholith and its bearing on the tectonothermal history of the southwestern grenville province canada results of 40ar 39ar step heating for muscovite potassium feldspar and plagioclase from the ca 1240 ma elzevir trondhjemite in the central metasedimentary belt of the canadian grenville province have been combined with earlier data and used to deduce a thermal history for the eastern elzevir terrane following the ottawan orogeny 1050 950 ma muscovite yielded precise plateau dates of ca 900 ma whereas the potassium feldspar displayed disturbed age spectra with ca 730 760 ma dates for broad plateau regions this age difference could be explained by slow cooling or by thermal overprinting at 760 800 ma that has updated the microcline the plagioclase spectra provide evidence for a low temperature hydrothermal event ca 380 ma ago that has generated sericite in saussurite and has caused partial argon loss from the microcline this result agrees with the other plagioclase thermochronometry and paleomagnetism on the cordova gabbro 25 km to the west but provides a lower estimate for the upper age brac

cenozoic and mesozoic metamorphism in the longmenshan orogen implications for geodynamic models of eastern tibet new zircon u pb and mica 40ar 39ar dating combined with structural studies in the longmenshan orogen confirm that most of the upper crustal deformation in the eastern margin of tibet is mesozoic however at lower structural levels apatite u pb and monazite electron microprobe dating reveals a previously unknown domain of cenozoic ca 65 ma barrovian type metamorphism and deformation this discovery shows that the crust in the eastern margin of tibet was already a substantial thickness around the time of the india asia collision associated deformation has a n s oriented stretching lineation implying that deformation was not driven by topographic gradients in the tibetan plateau the observed moderate amounts of distributed postmetamorphic e w shortening can probably explain the present thickness of the continental crust in the area these results do not support models of crustal thickening caused by solid state lateral flow of midcrustal metamorphic rocks

coal metamorphism in the upper portion of the pennsylvanian sturgis formation in western kentucky coals from the pennsylvanian upper sturgis formation missourian and virgilian were sampled from a borehole in union county western kentucky the coals exhibited two discrete levels of metamorphism the lower rank coals with vitrinite reflectances indicative of high volatile c bituminous were assumed to represent the normal level of metamorphism a second set of coals with vitrinite reflectances indicative of high volatile a bituminous was found to be associated with sphalerite chlorite and twinned calcite the latter mineral assemblages indicate that hydrothermal metamorphism was responsible for the anomalous high rank consideration of the sphalerite fluid inclusion temperatures from nearby ores and coals and the time temperature aspects of the coal metamorphism suggests that the hydrothermal metamorphic event was in the 150 to 200 c range for a brief time 10 5 10 6 yr as opposed to the longer term 25 50 m y 60 to 75 c ambient metamorphism

mineral chemistry and in situ upb geochronology of the mare basalt northwest africa 10597 implications for low ti mare volcanism around 3 0 ga abstract unbrecciated mare basalts are rare in the lunar meteorite collection found in 2015 northwest africa nwa 10597 is a medium grained low ti mare basalt with a subophitic texture the meteorite consists mostly of mm sized pyroxene and plagioclase with minor olivine spinel ilmenite phosphates silica and trace zr rich minerals such as baddeleyite zirconolite and tranquillityite a portion of plagioclase and silica has been transformed to their high pressure polymorphs due to shock metamorphism nwa 10597 has a low tio2 content 2 9 wt but is relatively enriched in rare earth elements ree laaverage 65 ci with an overall unfractionated pattern except for a negative eu anomaly calculated ree concentrations of parent melts in equilibrium with mg rich pyroxene and ca rich plagioclase suggest no significant assimilation of ree rich melts after the onset of pyroxene crystallization in situ u pb analyses of baddeleyite and apatite reveal a mutually consistent age of 3 0 ga which is also in excellent agreement with that of low ti mare basalts nwa 4734 and lapaz icefield lap 02205 dated with other independent techniques the concordance suggests no significant thermal disturbance in the u pb isotopic system of nwa 10597 although it was heavily shocked nwa 10597 closely resembles nwa 4734 in terms of petrographic texture mineral chemistry and geochronology indicating a pairing relationship

geochemistry of the pond creek coal bed eastern kentucky coalfield the pond creek coal bed middle pennsylvanian breathitt formation is an important low sulfur resource in pike and martin countries in the eastern kentucky coalfield the mined area is crossed by the n20 e trending belfry anticline the pond creek coal bed has a higher sulfur content on the west side of the anticline the vertical trends in the ash geochemistry also vary across the anticline the sites to the east of the anticline represent deposition of peat through periods of relative stability with slow deposition bright lithotypes interspersed with periods of relatively rapid clastic deposition dull lithotypes both generally removed from marine influence comparison of elemental trends between the lowest bright lithotype and the second bright lithotype suggest that the swamp became less acidic with time an upward decrease in minor element concentration may be related to the influx of clays and other silicates present in the bone lithotype this bone may have acted as a relatively low nutrient soil for the growth of the plants which contributed to the overlying bright lithotype the sites to the west of the anticline were subjected to a greater marine influence than the eastern sites high k2o al2o3 ratios at the bottom and top of the coal bed and a high tio2 zr dull clarain near the bottom of the coal point to clastic influences on the geochemistry the relatively high cao percentages in the middle third of the coal bed suggest deposition at near neutral ph the upper third of the coal bed was dominated by syngenetic and epigenetic pyrite emplacement

a provenance study of mineral matter in coal from appalachian basin coal mining regions and implications regarding the respirable health of underground coal workers a geochemical and nd isotope investigation abstract this study presents geochemical data produced from the analysis of coal and adjacent rock samples retrieved from coal mining regions in the u s to examine mineral matter provenance study sites included the northern appalachian basin where the units of interest were the lower kittanning coal bed the overlying columbiana shale and the underlying paleosol allegheny formation additional study sites were located in the central appalachian basin where sampling was conducted on strata associated with multiple coal beds of middle and lower pennsylvanian age the central appalachian basin rock and coal samples were much lower in overall mineral matter and contained very little carbonate calcite and siderite or pyrite mineralogy which was common at the northern appalachian basin sites elemental analysis of rock samples indicated a trend of enrichment in ca mg mn na and k cations in the immediate overburden compared to the underlying rock in the central appalachian basin a similar trend was observed in coal related strata from the northern appalachian basin which was attributed to epigenetic marine incursions rare earth element ree concentrations were determined in the samples and showed eu and ce anomalies when normalized by chondritic values the total ree content of the overburden is generally less than that of the underlying rock units neodymium isotopic analysis of the lower kittanning coal overburden and paleosol from the northern basin indicate partial resetting of the sm nd system close to the time of deposition the data indicate a common appalachian source for the clastic mineral matter in the overburden underclay and coal mineral matter the geochemical findings of this study may provide a viable method for distinguishing respirable dust sources in both appalachian basins there are potential applications for this research to aid in the respiratory health of underground coal miners

notes on the origin of altered macerals in the ragged edge of the pennsylvanian asturian herrin coalbed western kentucky the ragged edge of the herrin western kentucky no 11 coal bed has a variety of maceral textures and assemblages that do not fit in the conventional vitrinite and inertinite definitions as established by the international committee for coal organic petrology within a narrow zone at the marine margin of the coalbed the coal is brecciated and cemented by carbonate with some of the brecciated clasts metamorphosed to anthracite level vitrinite reflectances this is in contrast to the ambient high volatile c bituminous coal rank in the region low rank peat like textures are preserved in the clasts suggesting that the metamorphism took place soon after deposition of the peat geochemical and mineralogical evidences suggest that the increase in reflectance was the consequence of the channeling of hydrothermal fluids through the breccia the narrow zone of metamorphism and further the juxtaposition of breccia clasts of varying degrees of metamorphism suggest that the hydrothermal influx occurred at shallow depths of burial perhaps shortly following deposition of the peat

further examination of the ragged edge of the herrin coal bed webster county western kentucky coal field abstract the herrin western kentucky no 11 coal bed in the dixon 7 1 2 min quadrangle webster county kentucky displays another manifestation of the thinning margin of the coal bed previous studies in adjacent hopkins county have demonstrated that the coal is brecciated as the margin is approached the brecciated coal is not always thin 1 5 m of brecciated inertinite rich coal was previously described to the southeast of the present study area in general the brecciated coals are considerably thinner than the 1 5 2 m thick normal herrin coal both cores studied are thin 22 6 and 33 cm and display petrographic characteristics different from thicker herrin coals the cores described in the present study show some signs of brecciation in certain cases the fragmented macerals are cemented by exsudatinite multiple generations of pyrite mineralization were noted in one core with total sulfur exceeding 13 in the upper 8 48 cm lithotype overall the cores investigated in this study along with examples from previous studies illustrate the progression of the herrin coal from its absence either through nondeposition or erosion through thin brecciated coals to mineable coals no other economic coal in western kentucky shows as many examples of the depositional edge as does the herrin all of the examples studied are from cores emphasizing the need to study more than just the thick mineable coals if the total extent of the coal body is to be understood

porosity and permeability characterization of coal a micro computed tomography study abstract a unique contrast agent technique using x ray micro computed tomography micro ct was developed for studying micrometer sized features in coal the technique allows for the visualization of coal fractures not visible with conventional imaging methods a late permian medium volatile bituminous coal from moura coal mine was imaged and the resulting three dimensional coal cleat system was extracted for fluid flow simulations the results demonstrate a direct relationship between coal lithotype and permeability i e bright coals offer more permeability than dull coals however there was no direct relationship between porosity and permeability for any given lithotype scanning electron microscope and energy dispersive spectrometry sem eds together with x ray diffraction xrd methods were used for identifying mineral matter at high resolution after segmentation of the micro ct image mineral phase was removed from the segmented data and it was found that permeability was significantly improved by increasing cleat void space and connectivity suggesting that enhanced recovery methods could target de mineralization techniques overall only the epigenetic mineral phases in the bright band influenced permeability while lithotype had a stronger impact on permeability than porosity coal lithotype and mineralization are important evaluation criteria when considering coal seam gas development sites

ion microprobe u pb dating of quaternary zircon implication for magma cooling and residence time abstract an ion microprobe u pb dating method of quaternary zircon is developed using the sensitive high resolution ion microprobe shrimp and applied to igneous rocks from japan total pb u isochron age of 1 36 0 23 ma 95 confidence limit cl mswd 1 03 was obtained for zircons extracted from takidani granodiorite in central japan this may provide a constraint on magma cooling when coupled with fission track ages of the zircon as well as rb sr and k ar ages on co existing minerals the closure temperature determined by each method has lead to exponentially declining cooling history the history is consistent with a simple conductive cooling model of a small magma body 10 2 10 3 km 3 a pb u isochron age of 271 58 ka 95 cl mswd 0 85 has been determined for volcanic zircons from torihama dacite sw japan the age is significantly older than the 238 u 230 th ionium age of 145 33 ka and fission track age of 163 8 ka found in the literature suggesting either the magma residence time of 100 kyr or a rapid cooling rate of about 6 c kyr in contrast a tephrochronological estimate of 240 10 ka agrees well with the observed pb u age implying that the ionium and fission track ages are incorrect the pb u isochron age of 90 29 ka 95 cl mswd 1 04 is obtained for zircons in pyroclastic rocks from the unzen eruption in 1991 sw japan the age is again older than the eruptive age which suggests a magma residence time of 90 kyr in a shallow reservoir

nanosims u pb dating of fossil associated apatite crystals from ediacaran 570 ma doushantuo formation abstract sedimentary rocks record a wealth of information on the evolution of lithosphere hydrosphere atmosphere and biosphere however uncertainty about the age of many precambrian sequences makes it very difficult to establish the accurate temporal framework which can dramatically improve our understanding of the scale and duration of geological and biological events the neoproterozoic doushantuo formation south china preserve unique assemblages of early multicellular fossils and records valuable paleoenvironmental information the age of these formations is thus critical for understanding the important biological and climatic events that occurred towards the end of the proterozoic eon in this study we used nanosims to date samples from the doushantuo formations by apatite u pb geochronology fossil associated precipitated apatite grains were identified using optical microscope and raman spectrometer the resultant age is 305 26 ma high common pb and low u concentration in those apatite specimens limit the precision of age determination while the yielded age suggests that the doushantuo formation may have experience a post depositional hydrothermal event

organic petrology geochemistry gas content and gas composition of middle pennsylvanian age coal beds in the eastern interior illinois basin implications for cbm development and carbon sequestration abstract fifty four samples of coal and organic rich roof shale strata were collected as part of a coal bed methane exploration program following canister desorption to document gas contents the samples were analyzed by geochemical and petrographic methods coal samples were found to have moderate ash yields avg 13 5 dry basis and high total sulfur contents avg 4 3 dry basis the average gas content was 1 91 m3 ton petrographically the coals were dominated by vitrinite macerals avg 81 6 mmf especially telovitrinite by comparison liptinite avg 7 1 mmf and inertinite macerals avg 11 3 mmf were minor in occurrence coal samples ranged from high volatile c to high volatile a bituminous in rank avg ro maximum 0 76 shale samples had higher ash yields avg 76 1 dry basis though total sulfur contents were comparable to the coal samples avg 4 2 dry basis gas contents were lower than the corresponding coal samples avg 0 65 m3 ton petrographically the shale samples contained decreased amounts of vitrinite avg 25 6 mmf and higher amounts of liptinite avg 45 4 mmf and inertinite avg 29 0 mmf macerals relative to the coal samples gas obtained from coal and shale beds in the illinois basin was relatively pure high ch4 content limited data also indicated that illinois basin coals have the ability to adsorb fairly significant amounts of co2 this suggests that co2 injection to enhance methane production ecbm and or to sequester co2 may have some potential mineralization in the coals could negatively impact cbm production but it was found that the majority of the mineralization was present in the roof strata

brecciated and mineralized coals in union county western kentucky coal field abstract coals from the d 2 and d 3 boreholes in the grove center 7 1 2 min quadrangle union county ky have been found to be highly brecciated and mineralized the mineralization is dominated by a carbonate assemblage with minor sulfides and sulfates included among the secondary minerals is the lead selenide clausthalite overall the emplacement of secondary vein minerals was responsible for raising the rank of the coals from the 0 6 0 7 rmax range found in the area to as high as 0 95 0 99 rmax a 1 3 m thick coal found in one of the boreholes is unique among known western kentucky coals in having less than 50 vitrinite semifusinite and fusinite dominate the maceral assemblages the coal is also low in sulfur coal which is unusual for the illinois basin it has an ash yield of less than 10 much of it dominated by pervasive carbonate veining the age of the thick coal in core d 2 is similar to that of the elm lick coal bed found elsewhere in the western kentucky coalfield the coals in d 3 are younger having stephanian palynomorph assemblages

ion microprobe pb pb dating of carbonado polycrystalline diamond abstract we report in situ ion microprobe pb pb dating of quartz rutile and clay mineral inclusions and matrix part of polycrystalline diamonds carbonado derived from a proterozoic conglomerate in diamond bearing deposit of minas gerais in brazil together with u pb ages of zircons also extracted from the deposit thirty four spots on seven quartz grains located in the cavity of the gm01 carbonado yield 207pb 206pb isochron age of 3247 800 ma 2 mswd 0 75 and six spots on three rutile inclusions give the age of 3916 1300 ma 2 mswd 0 092 seven spots on three clay mineral inclusions of the do3 carbonado show common lead compositions while four spots on matrix define 207pb 206pb isochron age of 3811 1800 ma 2 mswd 0 012 seventy six spots on seventy zircon grains derived from the same conglomerate show three major u pb concordant ages of 2151 17 ma 2692 20 ma and 2931 22 ma with two concordant zircon outliers of 1726 58 ma and 3599 12 ma the youngest age is consistent with the formation age of 1750 1700 ma in the proterozoic conglomerate estimated by other workers the 3 6 ga zircon is the oldest record in the south american platform it may be detrital in origin and reflect the remnant of an archean craton the pb pb age of quartz and rutile inclusions in gm01 carbonado and that of do3 carbonado matrix are 3315 720 ma and 3811 1800 ma the matrix age is consistent with pb pb age of 2 6 3 8 ga of central african carbonados in the literature suggesting a close genetic relationship between brazilian and african carbonados

the age and pb loss behaviour of zircons from the isua supracrustal belt as determined by ion microprobe ion microprobe uthpb analyses of zircons from a conglomeratic metavolcanic unit in the isua supracrustal belt of west greenland show that their magmatic age is3807 1ma and failed to detect any older zircon cores or xenocrysts low u areas within zircons at a 30 m scale lost only small amounts of radiogenic pb and only in the recent past whereas high u areas within grains lost much greater proportions of their pb both recently and as early as the archaean some areas in the zircons have concordant upb and thpb ages the ion probe results agree with earlier determinations for the isua supracrustals and clarify minor discrepancies between previous multigrain and single crystal analyses

the role of high and low frequency dynamics in blocking formation time evolutions of prominent blocking flow configurations over the north pacific and europe are compared based upon composites for the 30 strongest events observed during 27 recent winter seasons fluctuations associated with synoptic scale migratory eddies have been filtered out before the compositing a quasi stationary wave train across the atlantic is evident during the blocking amplification over europe while no counterpart is found to the west of the amplifying blocking over the north pacific correlation between the tropopause level potential vorticity pv and meridional wind velocity associated with the amplifying blocking is found to be negative over europe in association with the anticyclonic evolution of the low pv center but it is almost zero over the north pacific feedback from the synoptic scale eddies as evaluated in the form of 250 mb geopotential height tendency due to the eddy vorticity flux convergence accounts for more than 75 of the observed amplification for the pacific blocking and less than 45 for the european blocking this difference is highlighted in two types of contour advection with surgery experiments in one of them pv contours observed four days before the peak blocking time were advected by composite time series of the low pass filtered observational wind and in the other experiment they were advected by the low pass filtered wind from which the transient eddy feedback evaluated as above had been removed at every time step hence the latter data should be dominated by low frequency dynamics for the european blocking both experiments can reproduce the anticyclonic evolution of low pv air within a blocking ridge as observed for the pacific blocking in contrast the observed intrusion of low pv air into the higher latitudes cannot be reproduced without the transient feedback furthermore in a barotropic model initialized with the composite 250 mb flow observed three days before the peak time a simulated blocking development over the north pacific is more sensitive to the insertion of the observed transient feedback than that over europe these results suggest that the incoming wave activity flux associated with a quasi stationary rossby wave train is of primary importance in the blocking formation over europe whereas the forcing by the synoptic scale transients is indispensable to that over the north pacific

diagenetic apatite character and in situ ion microprobe u pb age keeseville formation potsdam group new york state an occurrence of diagenetic fluorapatite cement is documented within the cambro ordovician keeseville formation potsdam group near chateaugay in new york state the fluorapatite cement occurs as stratiform layers within ephemeral fluvial quartz arenites which have been reworked by aeolian processes prior to burial the paragenetic sequence includes the following compaction of dust rimmed grains quartz cementation minor kaolinite fluorapatite cementation followed by secondary dissolution porosity and telogenetic hematite cementation mesogenetic illitization of kaolinite may have taken place prior to or following fluorapatite cementation the fluorapatite occurs as elongated bladed crystals that characteristically contain ladder like inclusion rich cores running parallel to crystal length surrounded by clearer rims and larger blocky crystals towards the middle of interstices in situ shrimp analyses of blocky fluorapatite crystals yield a u pb age of 486 29 ma indicating that the cement for

monazite and xenotime u th pb geochronology by ion microprobe dating highly fractionated granites at xihuashan tungsten mine se china zircon monazite and xenotime have proven to be valuable chronometers for various geological processes due to their commonly high u th and low common pb contents however zircons that have crystallized in highly fractionated granites often have such high u contents that radiation damage can lead to scattered u pb ages when measured with secondary ion mass spectrometry sims in this study monazite and xenotime were separated from a number of highly fractionated granites at the xihuashan tungsten mine southeast china for alternative dating methods by sims for monazite analysis obvious excess 204 pb signal mainly from interference of 232 th 144 nd 16 o 2 was observed in high th 2 wt monazite which hinders 204 pb based common pb correc tions a 207 pb based common pb correction method was used instead by employing power law relationships between pb u versus uo2 u p b th versus tho2 th and suitable exponentials monazites with tho2 contents in the range of 3 19 do not exhibit this matrix effect inde pendent sims u pb ages and th pb ages of three phases of xihuashan granite samples were consistent with each other and yielded dates of 158 7 0 7 158 0 0 7 and 156 9 0 7 ma respectively xenotime does show marked matrix effects due to variations of u th and y or total rare earth element ree referred as rree hereafter contents suitable correction factors require end member standards with extremely high or low u th and y or rree con tents no excess 204 pb was observed indicating that the 204 pb based common pb correction method is feasible independent 207 pb 206 pb ages can be obtained although multi collector mode is necessary to improve precision the main difficulties with dating xenotime are when high th u mineral inclusions are ablated we can identify when this occurs however by comparing the measured uo2 u and tho2 th with those in xenotime standards three xeno time samples from the first phase of xihuashan granite yielded a weighted mean 207 pb 206 pb date of 159 5 4 4 ma mswd 1 0 and a 206 pb 238 u date of 159 4 0 9 ma mswd 1 6 which are consistent with mona zite u pb and th pb ages from the same granites this study demonstrates that monazite and xenotime are better sims chronometers for highly fractionated granites than zircon which can yield doubtful ages due to high u contents

ion microprobe u pb dating of zircon with a 15 micrometer spatial resolution using nanosims abstract we developed a 238u 206pb and 207pb 206pb zircon dating method using a cameca nanosims ns50 ion microprobe a 7 to 9 na o primary beam was used to sputter a 15 m crater and secondary positive ions were extracted for mass analysis using the mattauch herzog geometry the multicollector system was modified to detect 90zr 204pb 206pb 238u16o and 238u16o2 ions simultaneously a mass resolution of about 4000 at 10 peak height and with a flat peak top was attained and the sensitivity of pb was about 4 cps na 1 ppm 1 a multicrystal zircon standard qgng from south australia with a u pb age of 1842 ma was used as a reference for pb uo uo2 uo calibration and on the basis of the positive correlation between these ratios we determined the sample 206pb 238u ratios 207pb 206pb ratios were measured by magnetic scanning in single collector mode the standard zircons 91500 from canada and sl13 from sri lanka were analyzed against qgng observed 238u 206pb and 207pb 206pb ages agreed well with published ages within experimental error then 16 zircon grains in a metamorphic rock from nagasaki japan were analyzed observed ages were compatible with shrimp ages suggesting that the nanosims with a 15 m probe diameter is suitable for ion microprobe u pb zircon dating

in situ u pb dating of monazite xenotime and zircon from the lantian black shales time constraints on provenances deposition and fluid flow events abstract the lantian formation located in eastern south china block scb forms the lower sequence of the ediacaran period at the transition from proterozoic to paleozoic the fossils of lantian formation have been proposed to predate the avalon biota about 579 565 ma the earliest known fossil assemblages with complex morphologies based largely on stratigraphy mineral chemistry and in situ u pb dating of monazites xenotimes and zircons from the black shale in fossil rich zone are studied for the first time to provide critical age constraints for provenance early diagenesis and fluid flow events detrital zircons and monazites give age populations similar to that of the doushantuo formation indicative of the same provenances for ediacaran basins throughout the scb the low y monazites formed during early diagenesis yield a weighted mean age of 612 29 ma n 9 mswd 3 1 age spectrum of analyzed monazites demonstrated that the sedimentation started from at least around 645 ma subsequently the overprinting events could be recorded by xenotimes and zircons precipitated from fluids during late diagenesis age results from xenotimes ranging from 441 ma and 585 ma were contemporaneous with the timing of collision of scb with gondwanaland and a weighted mean age of 394 8 3 7 ma n 23 mswd 2 8 obtained from diagenetic zircons could be correlated to the post tectonic granites widespread on the scb the pre existing monazites generally remain pristine and the multi staged fluids were locally interacted with the samples to form th rich domains in monazites

persistent anomaly forcing in a two level global circulation model abstract perpetual january data from a simple global two level model are used to diagnose the forcing of the model s low frequency lf large scale flow the forcing is considered within the context of a hypothetical low order model that resolves only the slowly varying planetary scale modes thus the forcing is partitioned into resolved components consisting of lf planetary scale i e autonomous processes and unresolved components that involve high frequency hf transient eddy and lf synoptic scale effects spatial patterns of the net tendencies of low pass filtered planetary scale barotropic streamfunction and vertically averaged temperature are compared with corresponding patterns of resolved and unresolved forcing during the onset maintenance and decay stages of composited persistent anomalies growth stages of positive and negative persistent anomalies that are found in both the atlantic atl and pacific pac regions are dominated by autonomous processes for positive anomalies the n

in situ ion microprobe u pb dating and ree abundances of a carboniferous conodont we report here in situ ion microprobe u pb dating of a conodont micro fossil using an ion microprobe method thirteen spots on the single fragment of the carboniferous conodont size approximately 800 m 100 m yield a 238u 206pb isochron age of 323 36 ma and a tera wasserburg concordia intercept age of 332 44 ma in a three dimensional 238u 206pb 207pb 206 pb 204pb 206pb diagram these ages are consistent with the depositional and early diagenetic ages of the fossil in its host mississippian sedimentary sequence within experimental error the success of the method depends on the chemical fractionation of u from pb within a hundred m length scale and the consequent variations in pb isotopic compositions due to radioactive decay shale normalized rare earth element ree abundances of two spots on the same sample show flat patterns from light ree to middle ree and decreases from middle ree to heavy ree with negative anomalies of both ce and eu the ree characteristics are significantly different from those of devonian conodonts reported by other workers suggesting discrepant redox states and or formation environments

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

bituminous coal seams from underground mines in the zonguldak basin nw turkey insights from mineralogy coal petrography rock eval pyrolysis and meso and microporosity abstract the zonguldak basin contains the main bituminous coal reserves of turkey ca 1 4 gt and several coal seams are mined in underground coal mines within the basin this study focuses on coal petrography mineralogy rock eval pyrolysis and the meso and microporosity characteristics of the coal samples collected from several late carboniferous pennsylvanian bituminous coal seams in the basin forty channel samples were collected from various coal seams in underground mines at the armutcuk zonguldak and amasra coalfields in the zonguldak basin the studied coal samples have low total moisture contents avg 2 3 on as received basis low total s contents avg 0 5 on dry basis and relatively high ash yields avg 21 2 on dry basis the random vitrinite reflectance values 0 69 1 21 and gross calorific values avg 33 0 mj kg on dry ash free basis indicate that the coal samples are of high volatile c bituminous to medium volatile bituminous coal minerals identified by xrd in bulk coal samples are clay minerals mainly kaolinite and rarely illite and chlorite quartz and carbonates calcite dolomite and siderite in a few samples pyrite and feldspar were also identified the sem edx analyses performed on the carbon coated polished blocks imply that the carbonate minerals are mainly epigenetic whereas the silicate minerals are generally syngenetic in origin the results of low pressure n2 adsorption analysis indicate that the bet surface areas 1 1 5 5 m2 g and mesopore volumes 0 003 0 011 cm3 g vary within a wide range the results of the low pressure co2 adsorption analyses show that micropores are abundant in the coal samples however the bet surface areas 10 41 78 11 m2 g and micropore volumes 0 010 0 049 cm3 g vary widely among the three coal mines and different coal seams our results suggest that variations in the mesopore characteristics are mainly controlled by mineral matter while microporosity is controlled by a combination of organic matter maceral compositions and coal rank of the studied coal seams

coal petrography mineralogy elemental compositions and palaeoenvironmental interpretation of late carboniferous coal seams in three wells from the kozlu coalfield zonguldak basin nw turkey abstract a number of coal seams of late carboniferous age in the coal bearing karadon kozlu and alacaagzi formations have been mined in several deep underground mines in the zonguldak basin nw turkey for this study a total of 154 coal core samples were collected from three research wells that were drilled in the tectonically complex settings of the kozlu coalfield all the coal samples were studied by means of coal petrography mineralogy and geochemistry special attention was given to the compositions and origins of fracture cleat filling minerals that were identified by sem edx on polished blocks the coal seams investigated are of bituminous rank they are characterized by low total sulphur contents 1 0 on dry basis and high gross calorific values 22 5 40 2 mj kg on dry ash free basis whereas ash yields and volatile matter contents are variable x ray powder diffraction data indicate that the mineralogical compositions of the studied coal seams are rather similar and clay minerals along with quartz and carbonate minerals were identified in almost all seams the statistical evaluations and sem data show that some elements such as mg ti zr nb and th are generally affiliated with silicate minerals whereas elements like cu zn mo and pb are mainly associated with sulphide minerals the silicate minerals are generally detrital and the majority of carbonate minerals are of epigenetic origin the epigenetic carbonate and sulphide minerals suggest that circulated solutions within coal seams were mainly derived from ca2 rich solutions leached from overlying formations such as cretaceous aged zonguldak formations and from hydrothermal solutions that likely were derived from andesitic dykes within the basin the regional tectonic activities during coalification seem to have deformed coal bearing formations and therefore intra basinal solutions could have penetrated into the studied coal seams the epigenetic mineralisation also resulted in elemental enrichments and elevated ash yields total sulphur and volatile matter contents in some coal seams thus deformation during coalification controlled some coal quality parameters in the studied wells the coal facies diagrams suggest that palaeomires mostly accumulated under limno telmatic conditions whereas a telmatic environment was more common in palaeomires of the kozlu formation coal petrography suggests that peat forming vegetation and water tables in palaeomires were changeable during the late carboniferous

ion microprobe u pb dating of phosphates in lunar basaltic breccia elephant moraine 87521 1 we report ion microprobe u pb dating of phosphates in lunar meteorite elephant moraine 87521 eet87521 which is a fragmental breccia consisting of very low ti vlt basaltic clasts and a small component of highland derived materials the observed pb pb age of phosphates in eet87521 is 3503 140 ma which is distinct from the results from previous chronological studies on vlt mare basalt of 3 2 3 3 ga for luna 24 this suggests that the vlt basalt volcanism appears to have been prolonged on the moon moreover the age is apparently different from those of other vlt meteorites 3 8 ga for que94281 and 4 0 4 4 ga for yamato793274 which are proposed to have been launched by a single impact event based on the similarity of launching ages mineralogical and geochemical signatures this evidence questions the validities of bulk age analyses for the yamato que meteorites in the literature and or the hypothesis of a single crater origin

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

ion microprobe u pb dating of hydrothermal xenotime from an episyenite evidence for rift related reactivation abstract hydrothermally intergrown xenotime monazite from an episyenite in the bohus granite southwest sweden has been analyzed in situ by ion microprobe although the analysed xenotime crystals are extremely small sometimes less than the ion beam diameter 17 m they retain relatively undisturbed u pb systems which yielded a 206 pb 238 u age of 252 8 ma the evolution of this episyenite involved an initial stage of quartz dissolution accompanied by albitization followed by a second stage of vug infilling and replacement of igneous fe ti phases the obtained age shows that the second alteration stage during which xenotime was precipitated was coeval with the thermal anomaly associated with permo carboniferous crustal thinning and the development of the nearby oslo rift moreover the development of the permeable episyenite structure must be ascribed to a preceding high temperature event most likely the post magmatic cooling of the host granite at 920 ma this study shows that u pb dating of young xenotimes may address geochronological problems though further work is required to characterize possible matrix effects which presently limit the accuracy of the method

mineralogy and geochemistry of the no 6 coal pennsylvanian in the junger coalfield ordos basin china abstract this paper discusses the mineralogy and geochemistry of the no 6 coal pennsylvanian in the junger coalfield ordos basin china the results show that the vitrinite reflectance 0 58 is lowest and the proportions of inertinite and liptinite 37 4 and 7 1 respectively in the no 6 coal of the junger coalfield are highest among all of the late paleozoic coals in the ordos basin the no 6 coal may be divided vertically into four sections based on their mineral compositions and elemental concentrations a high boehmite content mean 6 1 was identified in the no 6 coal the minerals associated with the boehmite in the coal include goyazite rutile zircon and pb bearing minerals galena clausthalite and selenio galena the boehmite is derived from weathered and oxidized bauxite in the weathered crust of the underlying benxi formation pennsylvanian a high pb bearing mineral content of samples zg6 2 and zg6 3 is likely of hydrothermal origin the no 6 coal is enriched in ga 44 8 g g se 8 2 g g sr 423 g g zr 234 g g rees 193 3 g g hg 0 35 g g pb 35 7 g g and th 17 8 g g gallium and th in the no 6 coal mainly occur in boehmite and the pb bearing selenide and sulfide minerals contribute not only to se and pb contents in the coal but also probably to hg content a high zr content is attributed to the presence of zircon and sr is related to goyazite the rees in the coal are supplied from the sediment source region and the rees leached from the adjacent partings by groundwater

petrochronology based on ree minerals monazite allanite xenotime apatite ree minerals monazite xenotime and allanite are ree1 minerals sensu stricto because lanthanides la lu and yttrium are critical constituents in them apatite does not require ree but because it contains substantial ree in many rocks it is included in this review all four minerals also host unusually high radionuclide concentrations notably th and u forming the basis of their utility as geochronometers this quartet of accessory minerals is playing an increasingly important role in petrochronology because they provide ways to link robust spot ages to petrogenetic p t conditions so can lend petrogenetic context to chronology based on other minerals part i of this review assembles the basic requisites prior to integrative petrochronologic analysis individual characteristics of the four ree minerals are addressed first i e their crystal chemistry and stability relations thermobarometers and trace element geochemistry used for tracing petrogenesis are discussed next and finally their chronology is summarized part ii presents case studies to highlight the specific strengths of ree minerals used to resolve the dynamics of a broad range of processes from diagenetic to magmatic conditions finally a brief section at the end outlines a few of the current challenges and promising perspectives for future work to introduce the four ree minerals in style let us recall the origins of their names the three phosphates have well respected greek grandparents and allanite has solid scottish roots yet of all four of them show idiosyncracies in etymology or type material apatite had long puzzled naturalists as it shows great chemical and physical variability and can resemble other minerals once properly identified abraham gottlieb werner named it apatite his reasoning referred to the greek root and giving the precise latin translation decipio taken literally both mean i deceive or i mislead which sounds like an apt confession from this mineral for having fooled

mineralogy and geochemistry of a late permian coal in the dafang coalfield guizhou china influence from siliceous and iron rich calcic hydrothermal fluids abstract this paper describes the influence of siliceous and iron rich calcic low temperature hydrothermal fluids lthf on the mineralogy and geochemistry of the late permian no 11 coal anthracitic r r 2 85 in the dafang coalfield in northwestern guizhou province china the no 11 coal has high contents of vein ankerite 10 2 vol and vein quartz 11 4 vol with formation temperatures of 85 and 180 c respectively indicating that vein ankerite and vein quartz were derived from low temperature calcic and siliceous hydrothermal fluids in two epigenetic episodes the vein quartz appears to have formed earlier than vein ankerite did and at least three distinct stages of ankerite formation with different ca sr and fe mn ratios were observed the two types of mineral veins are sources of different suites of major and trace metals scanning electron microscope and sequential extraction studies show that in addition to fe mg and ca vein ankerite is the dominant source of mn cu ni pb and zn in the coal and the contents of these five elements are as high as 0 09 and 74 0 33 6 185 and 289 g g respectively in contrast vein quartz is the main carrier mineral for platinum group elements pges pd pt and ir in the coal and the contents of pd pt and ir are 1 57 0 15 and 0 007 g g respectively sequential extraction showed a high pge content in the silicate fraction up to 10 4 g g pd 1 23 g g pt and 0 05 g g ir respectively it is concluded that the formation of ankerite and quartz and the anomalous enrichment of trace elements in the no 11 coal in the dafang coalfield guizhou result from the influx of calcic and siliceous low temperature hydrothermal fluids

records of the moon forming impact and the 470 ma disruption of the l chondrite parent body in the asteroid belt from u pb apatite ages of novato l6 novato a newly observed fall in the san francisco bay area is a shocked and brecciated l6 ordinary chondrite containing dark and light lithologies we have investigated the u pb isotope systematics of coarse cl apatite grains of metamorphic origin in novato with a large geometry ion microprobe the u pb systematics of novato apatite reveals an upper intercept age of 4472 31 ma and lower intercept age of 473 38 ma the upper intercept age is within error identical to the u pb apatite age of 4452 21 ma measured in the chelyabinsk ll5 chondrite this age is interpreted to reflect a massive collisional resetting event due to a large impact associated with the peak arrival time at the primordial asteroid belt of ejecta debris from the moon forming giant impact on earth the lower intercept age is consistent with the most precisely dated ar ar ages of 470 6 ma of shocked l chondrites and the fossil meteorites and extraterrestrial chromite relicts found in ordovician limestones with an age of 467 3 1 6 ma in sweden and china the lower intercept age reflects a major disturbance related to the catastrophic disruption of the l chondrite parent body most likely associated with the gefion asteroid family which produced an initially intense meteorite bombardment of the earth in ordovician period and reset and degassed at least approximately 35 of the l chondrite falls today we predict that the 470 ma impact event is likely to be found on the moon and mars if not mercury

the saricicek howardite fall in turkey source crater of hed meteorites on vesta and impact risk of vestoids the saricicek howardite meteorite shower consisting of 343 documented stones occurred on september 2 2015 in turkey and is the first documented howardite fall cosmogenic isotopes show that sarici

uranium lead systematics of low ti basaltic meteorite dhofar 287a affinity to apollo 15 green glasses article i nfo dhofar 287 is a lunar meteorite found in oman in 2001 which consists of a major portion 95 of low ti mare basalt dho 287a and a minor attached part 5 of regolith breccia dho 287b here we report the u pb systematics of dho 287a using data collected with a sensitive high resolution ion microprobe shrimp in situ analyses of five merrillite and three apatite grains which are resistant to secondary petrologic events resulted in a total pb u isochron age of 3 34 0 20 ga in 238 u 206 pb 207 pb 206 pb 204 pb 206 pb 3 d space 95 confidence level the observed pb pb isochron of these eight phosphates coupled with four plagioclase grains alsoyieldeda 207 pb 206 pbageof3 35 0 13ga thisformationage whenconsideredasthecrystallizationageof

cryptomare magmatism 4 35 gyr ago recorded in lunar meteorite kalahari 009 the origin and evolution of the moon remain controversial one notable point of controversy being the timing of the beginning and end of basaltic volcanism in the lunar mares or plains lunar research over the past three decades has suggested that mare volcanism occurred mainly after the late heavy bombardment that ended 3 9 billion years ago because most of known mare basalts lunar meteorites and returned apollo and luna samples and remote sensing data indicate crystallization ages younger than 3 9 billion years but a new u pb dating of minerals in the lunar meteorite kalahari 009 gives an age of roughly 4 35 billion years for a lunar basalt this suggests that the volcanism started as early as 4 35 billion years ago relatively soon after lunar formation and differentiation and that kalahari 009 is our first sample of a cryptomare from the moon the result of u pb dating of minerals in a lunar meteorite kalahari 009 is reported analyses of five grains associated with basaltic clasts give an age of 4 35 0 15 billion years these are thought to represent the crystallization ages of parental basalt magma making kalahari 009 one of the oldest known mare basalt this suggests that mare basalt volcanism on the moon started as early as 4 35 billion years ago the origin and evolution of the moon remain controversial1 2 with one of the most important questions for lunar evolution being the timing and duration of basaltic mare magmatism1 3 4 5 6 7 8 here we report the result of ion microprobe u pb dating of phosphates in a lunar meteorite kalahari 009 which is classified as a very low ti mare basalt breccia in situ analyses of five phosphate grains associated with basaltic clasts give an age of 4 35 0 15 billion years these ancient phosphate ages are thought to represent the crystallization ages of parental basalt magma making kalahari 009 one of the oldest known mare basalts we suggest that mare basalt volcanism on the moon started as early as 4 35 gyr ago relatively soon after its formation and differentiation and preceding the bulk of lunar volcanism which ensued after the late heavy bombardment around 3 8 3 9 gyr refs 7 and 8 considering the extremely low abundances of incompatible elements such as thorium and the rare earth elements in kalahari 009 ref 9 and recent remote sensing observations illustrating that the cryptomaria tend to be of very low ti basalt type10 11 12 we conclude that kalahari 009 is our first sample of a very low ti cryptomare from the moon

geochronology of the martian meteorite zagami revealed by u pb ion probe dating of accessory minerals abstract the precise chronology of geological events on mars is hampered by the lack of absolute ages for the martian timescale and the significant uncertainties that result from the extrapolation of the lunar timescale to mars hartmann and neukum 2001 martian meteorites represent the only samples of mars currently available attempts to identify source craters for the meteorites have thus far proven inconclusive hamilton et al 2003 lang et al 2009 mouginis mark and boyce 2012 precluding their use in constraining the absolute martian timescale the majority of the known martian meteorites are basalts shergottites all dated shergottites have mineral separate rb sr or sm nd ages of borg et al 2005 here we report a 238u 206pb age of 182 7 6 9 ma by ion microprobe analysis of baddeleyite zro2 grains in the zagami shergottite there is no correlation between discordancy and baddeleyite grain location relative to shock metamorphism mineral petrography demonstrates that baddeleyite is the result of late stage igneous crystallization and raman spectroscopy shows that baddeleyite has not been transformed by shock into preservable high pressure polymorphs supported by an age of 153 81 ma for phosphate grains obtained using the same method we conclude that zagami crystallized at 180 ma in agreement with previous results from mineral separate geochronology therefore the shergottites represent igneous rocks preferentially ejected from young terrains on mars in a small number of ejection events

ion microprobe uranium thorium lead dating of shergotty phosphates we report ion microprobe u th pb dating of shergotty phosphates by means of the sensitive high resolution ion microprobe shrimp recently installed at hiroshima university japan ten analyses of whitlockite merrillite and three analyses of apatite indicate a 238u 206pb isochron age of 225 200 ma and a tera wasserburg concordia constrained linear three dimensional isochron age of 217 110 ma in the 238u 206pb 207pb 206pb204pb 206pb diagram these ages agree well with the 232th 208pb age of 189 83 ma which suggests that primary crystallization or a shock metamorphic event defined the formation age of the phosphate minerals the average of the later two ages 204 68 ma is consistent with the previously published rb sr age of 165 11 ma and u th pb age of 200 ma these show marginal agreement with the 40ar 39ar age of 254 10 ma but are significantly different from the sm nd age of 360 16 ma taking into account the closure temperature of the u pb system in apatite we suggest the time that shergotty last experienced a temperature of 900 c was 204 68 ma

dynamics of low frequency variability barotropic mode the dynamics of low frequency variability is investigated in terms of sensitivity to the dependence of its relative zonal position of a single storm track in a simplified global circulation model a streamfunction tendency equation is derived that explicitly distinguishes between barotropic and baroclinic components one of the two low frequency patterns located in the center of the storm track grows barotropically and its decay is accomplished by low frequency eddy vorticity fluxes and the baroclinic contribution to the divergence term the growth and decay of the second pattern located at the downstream end of the storm track is dominated by nonlinear processes this indicates that the dynamical processes leading to growth and decay of low frequency patterns depend on the zonal position of the low frequency pattern relative to a storm track

lower and lower middle pennsylvanian coal palynofloras southwestern virginia copyright c 1996 elsevier science b v all rights reserved lower and lower middle pennsylvanian coals recovered from an exploratory drilling program in southwestern virginia were analyzed for their palynomorph content results show them to be dominated by spores produced by arboreous lycopsids lycospora pellucida and lycospora pusilla generally are the most common species with others namely lycospora granulata l micropapillata and lycospora orbicula being locally abundant densosporites cristatisporites radiizonates and cingulizonates representing small lycopsids and granulatisporites produced by small ferns and perhaps some pteridosperms typically are sub dominant taxa the recovered palynofloras are similar in overall composition making individual coal bed identification and correlation very difficult if not impossible however the introduction and extinction of a few forms do assist the correlation of packages of strata on both an intra and interbasinal scale dictyotriletes bireticulatus is first observed in basal lee formation strata at about the level of the cove creek coal bed radiizonates aligerans and r striatus also appear more abundantly at this level although some forms have been observed in older pocahontas formation coals this level essentially coincides with the namurian c westphalian a boundary based on plant megafossil evidence laevigatosporites minor l vulgaris endosporites globiformis e zonalis and granasporites medius are first seen consistently just above the sewell coal bed radiizonates aligerans r striatus and densosporites irregularis are last seen in the early middle pennsylvanian at about the level of the splash dam coal bed schulzospora rara occurs throughout early and early middle pennsylvanian strata and is last seen in the manchester coal the manchester is directly overlain by the betsie shale a widespread marine unit the base of the betsie marks the westphalian a b contact when compared with palynomorph assemblage zonations published for the western interior and eastern interior basins early and early middle pennsylvanian palynofloras from the central appalachian basin compare most favorably with early morrowan strata analysis of bench samples indicates that lycospora typically dominates basal and middle portions of early and early middle pennsylvanian coals more terminal layers often contain higher percentages of granulatisporites and related trilete sphaerotriangular genera e g lophotriletes acanthotriletes deltoidsporar and densosporites and related trilete crassicingulate genera e g cristatisporites cingulizonates radiizonatesr this temporal change is consistently observed and may primarily reflect a water table change within the paleomires from consistently high covered with water or at least water logged most of the timer to intermittently low occasional substrate exposurer

a metamorphic history from micron scale 207pb 206pb chronometry of archean monazite ion microprobe measurements of pb isotope ratios in monazites have been obtained in situ from thin sections using the cambridge isolab 120 molecular interferences are sufficiently resolved at an rp of 6500 to allow 2 7pb z 6pb dating of monazite with precisions as low as 4 5 ma 2 r the results presented here provide important information on the chronological history of the late archean metamorphism of the wind river range wyoming usa matrix monazites and monazite inclusions in garnets from a metapelite from the northern wind river range have been analysed by sims in a previous study peak metamorphic conditions t 800 c p 8 1 kb were estimated using inclusion assemblages in garnets from this same sample isolated monazite inclusions in garnet yield 2 7pb z 6pb age estimates of 2781 6 to 2809 10 ma those along fractures yield lower ages 2603 2687 ma which are similar to tims and sims ages of matrix monazites a single large 500 xm monazite grain locally preserves growth zoning but has a recrystallised core and a resorbed recrystallised rim age estimates for these three regions are 2788 9 ma 2663 4 and 2523 6 ma respectively thus the inclusion assemblages of sharp and essene may record peak metamorphic conditions at ca 2 8 ga and indicate a phase of metamorphism that predates by over 100 ma the emplacement of the bridget batholith the major lithologic component of the northern wind river range the analysed monazite grains appear to preserve ca 300 ma history even within a single grain monazite inclusions in garnet that are fully armoured may provide estimates for the time of garnet growth even in high grade terranes where most chronometers are reset the age pattern preserved by the large monazite grain cannot be simply related to diffusion controlled closure instead a chronology is preserved which can be related to the petrographic setting of individual grains through in situ analysis

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

ion microprobe u pb dating and ree analyses of phosphates in h4 chondrite yamato 74371 1 u and pb isotopes and rare earth elements rees in individual phosphate grains from h4 chondrites y 74371 were measured by using an ion microprobe nine analyses of whitlockite merrillite and five analyses of apatites indicate a total pb u isochron age of 4533 40 ma 2 sigma which are consistent with the results from previous using thermal ionization mass spectrometer tims the observed apatites age of 4525 30 ma 2 sigma however is younger than those of previous works on the other hand the time difference between the whitlockite age of 4601 94 ma 2 sigma and those of apatites are not observed because of the large uncertainties the ree abundance patterns of the whitlockites normalized to ci chondrite are characterized by an almost constant enrichment of 200 800 times ci abundance and a striking negative eu anomaly the ree abundances of the apatites are lower than those of whitlockite grains and vary appreciably among different grains the remarkable correlation between the eu anomaly eu eu and total concentration of ree is confirmed but significant correlation with eu anomaly and formation age of individual grains are not observed

coal rank trends in the western kentucky coalfield and relationship to hydrocarbon occurrence abstract vitrinite maximum reflectance trends for the middle pennsylvanian springfield no 9 coal bed in the western kentucky coalfield indicate that coal rank is high volatile a bituminous 0 70 0 85 rmax in portions of the webster syncline in webster and union counties south of the rough creek fault zone and is generally high volatile c bituminous 0 60 rmax in the remainder of the coalfield within the webster syncline the reflectance of the springfield coal does not vary significantly despite a difference in elevation of nearly 300 m reflectance gradients in the webster syncline are not well defined reflectances are generally highest in the baker no 13 coal bed and are lower in the underlying herrin no 11 and briar hill no 10 coals rank trends from the springfield data alone suggest pre tectonic coalification but the lack of well defined reflectance gradients complicates this interpretation hydrothermal alteration may have been a significant cause of the coalification in this region previous investigations of coals in fault blocks have considered the role of hydrothermal mineralization in coalification southern union and webster counties are adjacent to the fluorspar district a region of extensive hydrothermal metamorphism it is possible that convective heat transfer related to fluorspar district mineralization led to vertical heterogeneity in the temperature profile and consequent metamorphic history in henderson county north of the rough creek fault zone coal rank is significantly lower as low as 0 42 rmax for the springfield coal reflectance gradients are again poorly defined extensive oil and gas development has occurred in the high volatile c bituminous region to the north of the rough creek fault zone whereas fewer pools with lower production are known within the webster syncline to the south of the fault zone the rank of the middle pennsylvanian coals can be used to estimate the level of maturation of the devonian new albany shale a likely source rock for much of the oil and gas in the coalfield previous studies on the maturation of the new albany shale which lies about 1 km below the springfield coal indicate an equivalent medium volatile bituminous 1 0 1 2 rm rank in the fluorspar district new albany rank decreases to an equivalent high volatile b c 0 60 rm north of the rough creek fault zone the significance of the new albany reflectances is dependent on the level of suppression of vitrinite reflectance in organic rich shales the existence of reflectance suppression would imply that the shales could be more mature than studies to date have indicated it is possible that the episodes of basin dewatering which influenced the coal rank south of the rough creek fault zone also flushed the potential oil reservoirs in the same region

uranium lead systematics of phosphates in lunar basaltic regolith breccia meteorite hills 01210 chronological studies of brecciated lunar meteorites have proved difficult because they are mixtures of materials from various sources and the radiometric clocks are sometimes affected by the subsequent impact events on the moon here we report the in situ u pb dating of phosphates in lunar meteorite meteorite hills met 01210 which is a regolith breccia consisting of low ti mare basalt clasts and mineral fragments with a minor anorthositic component in situ analyses of four merrillite and four apatite grains in met 01210 which are resistant to secondary events resulted in a 207pb 206pb 204pb 206pb isochron age of 3904 85 ma 95 confidence limit this phosphate formation age when considered as the crystallisation age of this low ti basalt is similar to crystallization ages of 3 8 3 9 ga for unbrecciated low ti basalt meteorites asuka 881757 and yamato 793169 this result reinforces the hypothesis that all these three meteorites originated from the same area on the moon and were launched by a single impact event consistent with the similarity of launch ages mineralogical and geochemical signatures

palaeoproterozoic thermal events recorded in the 4 0 ga acasta gneiss canada evidence from shrimp u pb dating of apatite and zircon u pb isotopes of apatites and zircons extracted from a sample of the acasta gneisses that occurs along the western margin of the slave craton in northwest territories of canada have been measured using a shrimp ii ion microprobe eleven apatite analyses 30 m spot give 238u 204pb 206pb 204pb and 204pb 206pb 207pb 206pb isochron ages of 1905 86 ma 2 and 1936 28 ma 2 respectively analyses 20 m spot on the partly recrystallised central portions of fourteen zircons mostly define a mixing array on a 238u 206pb 207pb 206pb concordia plot with concordia intercepts at 4014 25 ma 2 and 1967 93 ma 2 the former agrees with 3 96 4 02 ga protolith ages obtained on the oldest components of the acasta gneisses by other workers the lower concordia intercept for the zircon data is consistent with the u pb age of apatites and may be related to a 500 c thermal event perhaps early in the palaeoproterozoic wopmay orogeny