compositions sources and depositional environments of organic matter from the middle jurassic clays of poland abstract the comprehensive biomarker characteristics from previously undescribed middle jurassic clays of poland are presented the molecular composition of the organic matter om derived from clays of aalenian to callovian age has not changed significantly through time high relative concentrations of many biomarkers typical for terrestrial material suggest a distinct dominance of om derived from land plants increasing concentrations of c29 diaster 13 17 enes towards the northern part of the basin indicate an increase in terrestrial input this terrestrial material would have originated from the enhanced transport of organic matter from land situated at the northern bank of the basin i e the fennoscandian shield the organic matter was deposited in an oxic to suboxic environment as indicated by relatively low concentrations of c33 c35 homohopanes moderate to high pr ph ratio values an absence of compounds characteristic for anoxia and water column stratification such as isorenieratane aryl isoprenoids and gammacerane as well as common benthic fauna and burrows 18o measurements from calcitic rostra of belemnites suggest that the mean value of the middle jurassic sea water temperature of the polish basin was 13 1 c it is suggested that this mirrored the temperature of the lower water column because belemnites are considered here to be necto benthic the organic matter from the middle jurassic basin of poland is immature this is clearly indicated by a large concentration of biomarkers with the biogenic configurations such as hopanes hop 13 18 enes hop 17 21 enes diasterenes and sterenes the identification of preserved unaltered biomolecules like ferruginol 6 7 dehydroferruginol and sugiol in protopodocarpoxylon wood samples from these sediments present particularly strong evidence for the presence of immature om in the middle jurassic sediments moreover the occurrence of these polar diterpenoids is important due to the fact that they are definitely the oldest known natural products detected in geological samples

geochemical characterisation of fika formation in the chad bornu basin northeastern nigeria implications for depositional environment and tectonic setting late cretaceous shales of the fika formation in the chad bornu basin northeastern nigeria were analysed to define paleoenvironment and source of the organic matter and their relation to tectonic setting the organic carbon and sulphur contents of fika shale samples are in the range of 0 51 2 13 and 0 31 1 65 wt respectively pointing that these shales were deposited in suboxic anoxic marine conditions the biomarker and chemical compositions provide evidence for a major contribution of aquatic algae and microorganisms with minor terrigenous organic matter input moderate salinity stratification and relatively anoxic suboxic bottom water conditions are also likely in the fika shales therefore stratified water column with moderate salinity and relatively anoxic suboxic bottom water conditions have contributed to organic matter om preservation in the fika shale layer fika shale samples are rich in sio2 54 80 wt followed by al2o3 23 75 wt and fe2o3 10 19 wt compared with average shale the analysed shale samples are obviously enriched in al2o3 23 75 wt tio2 1 34 wt and p2o5 0 30 wt indicating that these sediments are rich in clay minerals and represent a good possibility for enhanced organic matter production and enrichment plots of fika shale on bivariate discriminant function diagram suggest an active continental margin setting for the provenance the inferred tectonic setting for the late cretaceous shales of the fika formation of the chad bornu basin is in agreement with the tectonic evolutionary history of the west and central africa during the cretaceous period

near real time mapping of peak ground acceleration and peak ground velocity following a strong earthquake during a disastrous earthquake the early assessment and timely reporting of the peak ground acceleration pga and peak ground velocity pgv maps will be crucial in an effective emergency response operation in this study we first derive an empirical relationship between m l and m w the pga and pgv attenuation relationships are deduced with data from the taiwan strong motion instrumentation program tsmip and the taiwan rapid earthquake information release system treirs site corrections of the attenuation relationships for shallow and large earthquakes in taiwan region are also obtained peak values of earthquake strong ground motion can be well determined in taiwan as soon as the earthquake location is determined and magnitudes are calculated by the treirs this peak ground motion value information can be immediately turned into the calculated pga and pgv maps that can be issued within two minutes of the earthquake origin time during any disastrous earthquake these maps are found to be very useful for immediate seismic damage assessment and dispatching of emergency response missions manuscript received 1 december 2000

u pb monazite ages in amphibolite to granulite facies orthogneiss reflect hydrous mineral breakdown reactions sveconorwegian province of sw norway in the rogaland vest agder terrain of the sveconorwegian province of sw norway two main sveconorwegian metamorphic phases are reported a phase of regional metamorphism linked to orogenic thickening m1 and a phase of low pressure thermal metamorphism associated with the intrusion of the 931 2 ma anorthosite charnockite rogaland igneous complex m2 phase m1 reached granulite facies to the west of the terrane and m2 culminated locally at 800 850 c with the formation of dry osumilite bearing mineral associations monazite and titanite u pb geochronology was conducted on 17 amphibolite to granulite facies orthogneiss samples mainly from a suite of 1050 2 8 ma calc alkaline augen gneisses the feda suite in these rocks prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012 1006 ma in the feda suite and other charnockitic gneisses concordant to slightly discordant monazite at 1024 997 ma probably reflects breakdown of biotite during granulite facies m1 metamorphism a spread of monazite ages down to 970 ma in biotite hornblende samples possibly corresponds to the waning stage of this first event in the feda suite a well defined monazite growth episode at 930 925 ma in the amphibolite facies domain corresponds to major clinopyroxene formation at the expense of hornblende during m2 growth or resetting of monazite was extremely limited during this phase in the granulite facies domain up to the direct vicinity of the anorthosite complex the m2 event was shortly followed by cooling through ca 610 c as indicated by tightly grouped u pb ages of accessory titanite and titanite relict inclusions at 918 2 ma over the entire region a last generation of u poor monazite formed during regional cooling below 610 c in hornblende rich samples at 912 904 ma this study suggests 1 that monazite formed during the prograde path of high grade metamorphism may be preserved 2 that monazite ages reflect primary or secondary growth of monazite linked to metamorphic reactions involving redistribution of rees and th and or fluid mobilisation 3 that the u pb system in monazite is not affected by thermal events up to 800 850 c provided that conditions were dry during metamorphism

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

partial high grade alteration of monazite using alkali bearing fluids experiment and nature recent advances in the dating of monazite using the electron microprobe indicate that thsio 4 and or cath po 4 2 enriched intergrowths in monazite can give ages younger than the original monazite the morphology of the intergrowths suggests that the original monazite grain has been partly altered by a fluid in which th si and ca are mobile this hypothesis has been tested in the piston cylinder apparatus at 1000 mpa and 900 c utilizing a natural unzoned th and pb bearing monazite ce and na 2 si 2 o 5 h 2 o during the experiment a subset of the monazite grains acquired thsi0 4 enriched areas with sharp compositional boundaries devoid of pb and show evidence of being a pseudomorphic partial replacement of the monazite rather than an overgrowth of the monazite these experiments support the hypothesis that similar th enriched or th depleted patches with sharp compositional boundaries observed in natural monazite could be the result of fluid induced alteration via coupled dissolution reprecipitation if so such altered regions would yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of single or multiple metasomatic events assuming that all pre existing radiogenic pb is removed during alteration

a reappraisal of kerogen formation abstract comparative microscopical and chemical studies of recognizable entities in kerogen and their extant counterparts suggest a new and simple mechanism of kerogen formation which clarifies the interrelationships between extant biomass kerogen and fossil fuels

th diffusion in monazite abstract diffusion of th has been characterized in synthetic monazite under dry conditions the synthetic monazites either pure cepo4 ndpo4 or a mixed lree phosphate containing ce nd and sm were grown via a na2co3 moo3 flux method the sources of diffusant for the experiments were either synthesized thsio4 or cath po4 2 powders mixed with cepo4 experiments were performed by placing source and monazite in pt capsules and annealing capsules in 1 atm furnaces for times ranging from 3 weeks to a few hours at temperatures from 1350 to 1550 c the th distributions in the monazite were profiled by rutherford backscattering spectrometry rbs the following arrhenius relation was obtained for th diffusion in monazite d 6 7 10 1 exp 740 63 kj mol 1 r t m 2 s 1 the diffusivity of th was found to be similar for monazites containing a single ree ce or nd and the mixed lree phosphates th diffusion was also similar for experiments run using the th silicate and ca th phosphate sources suggesting that the substitutional mechanism for th in monazite i e th 4 si 4 ree 3 p 5 for the thsio4 source and th 4 ca 2 2ree 3 for the cath po4 2 source does not significantly affect th diffusivities and that th is likely the rate limiting species in diffusion th diffusion in monazite is about 3 orders of magnitude slower than pb diffusion cherniak d j watson e b grove m harrison t m 2004a pb diffusion in monazite a combined rbs sims study geochimica et cosmochimica acta 68 829 840 this contrasts with findings of gardes et al gardes e jaoul o montel j m seydoux guillaume a m wirth r 2006 pb diffusion in monazite an experimental study of pb2 th4 2nd3 interdiffusion geochimica et cosmochimica acta 70 2325 2336 who determined that diffusivities measured in pb th ree exchange which would under most circumstances be rate limited by the slowest diffusing species are comparable to those measured by cherniak et al cherniak d j watson e b grove m harrison t m 2004a pb diffusion in monazite a combined rbs sims study geochimica et cosmochimica acta 68 829 840 for pb th diffusion in zircon cherniak d j hanchar j m watson e b 1997 diffusion of tetravalent cations in zircon contributions to mineralogy and petrology 127 383 390 is about an order of magnitude slower than in monazite but with similar activation energy for diffusion the lower diffusivities in zircon may be a consequence of the larger disparity in size between th and the zr site in zircon as compared with th and the ree site in monazite nonetheless th is essentially immobile in monazite with respect to exchange by volume diffusion under most geologic conditions these findings may also have implications for containment of high level actinide based nuclear waste in monazite ceramic waste forms but it should be noted that mechanisms other than diffusive exchange e g recrystallization dissolution reprecipitation may be important to consider along with diffusion when evaluating the retentivity of monazite for th and other actinide elements

geochronology and geochemistry of multiple generations of monazite from the wepawaug schist connecticut usa implications for monazite stability in metamorphic rocks u pb isotope analyses rare earth and trace element analyses and petrographic observations are presented for monazites from the wepawaug schist in southern connecticut usa two samples of kyanite zone schist were collected less than a meter apart each sample contains a different variety of monazite with distinct morphology chemistry and pb isotopic composition one sample preserves a largely amphibolite facies mineralogy including kyanite staurolite garnet biotite and chlorite with little textural evidence of later shearing monazites from this sample are xenoblastic with about 1 wt tho2 0 3 wt cao and a more lree enriched pattern than monazites from the second sample these xenoblastic monazites preserve textural evidence of a retrograde reaction to apatite which involves chlorite indicating that these monazites became unstable during retrograde chloritization of biotite these monazites give strongly discordant u pb ages which fit a chord with an upper intercept age of 411 18 ma interpreted as the minimum growth age of these xenoblastic monazites perhaps during amphibolite facies metamorphism the second sample contains s c banding evidence of dynamic recrystallization and abundant retrograde chlorite this sample contains idioblastic monazites with about 3 wt tho2 0 8 wt cao and with less fractionated ree patterns these monazites give close to concordant u pb ages with a mean 207pb 206pb age of 388 2 ma this age is interpreted as probably representing the time of monazite growth during retrogression of the sample from an amphibolite to greenschist facies mineralogy

chemical characteristics of liptinite macerals in humic and sapropelic coals abstract according to previous studies alginite does not occur in humic coals however in coals from the saar district f r germany alginite was identified by fluorescencemicroscopy in addition high amounts of an undeterminable liptinite maceral were found and tentatively explained as an alteration product of alginite therefore organic geochemical methods were used to characterize and identify this unknown liptinite maceral organic geochemical parameters such as cpi pristane phytane ratio and methylphenanthrene index show not only a dependence from coal rank but also yield additional information about the type of organic matter input and the depositional environment of the coals a series of coals of different origins around 0 8 vitrinite reflectance were investigated to determine how far the geochemical parameters reflect change in facies the samples included cannel boghead and resinite rich coals as well as isolated durain bands with increasing amounts of alginite in the coal the cpi pristane phytane and c 4 naphthalene phenanthrene ratios of the extracts decrease as illustrated by two representatives samples some resinite and sporinite rich coals show a primarily naphthalene derived aromatic composition whereas some alginite rich coals of the same rank show phenanthrene and its derivatives to be dominant with respect to technological properties most coals from the saar district correspond with a higher rank than indicated by reflectance measurements those coals in general show lower values of the aforementioned ratios in comparison with ruhr coals of similar vitrinite reflectance values

chemical characteristics of upper cretaceous turonian jet of the gosau group of gams hieflau styria austria abstract jet and coaly sediments within the upper cretaceous gosau schoenleiten formation were collected from two outcrops near gams hieflau styria austria for comparison additional jet and coal samples from different gosau localities were included in the study the identification of jet as bituminous driftwood collotelinite has been provided by microscopical examination of organic matter kollmann h a and sachsenhofer r f mitt ref geol und palaont landesmuseum joanneum sh 2 1998 223 rock eval analyses revealed enhanced hi and lower t max values of jet compared with the coals and coaly shales the results reflect the higher contents of bituminous organic matter compared to vitrain rich coals of similar maturity in comparison with the coals and coaly shales high amounts of liberated hydrocarbons mg hc g c org are in contrast to generally lower yields of soluble organic matter during extraction with dichloromethane indicating that portions of the hydrocarbons are liberated from lipids loosely bound to kerogen during pyrolysis further differences in n alkane distribution patterns odd over even predominance pristane phytane and pristane n c 17 ratios exist between jet coals and coaly shales the microbial origin of short chain n alkanes presumably resulted from the degradation of the predominant odd numbered long chain n alkanes within the jet the occurrence of biological markers sesqui and diterpenoids within the sediments coaly shales coals and jet samples indicates the origin of terrestrial organic matter from conifers biomarker composition of jet samples indicates enhanced aromatisation of sesqui and diterpenoids these results correspond to enhanced aromatisation of steranes as reflected by generally higher relative contents of triaromatic steroids in the jet because of comparable maturation 0 5 0 6 r r of the coals coaly shales and the jet samples confirmed by the isomerisation of c 31 hopanes and c 29 steranes the increase in aromatisation in the jet is thought to reflect increased contribution of bacteria to organic matter degradation the lack of enrichment of the jet samples in hopanes relative to steranes suggests that enhanced biomarker aromatisation is caused by anaerobic rather than by aerobic bacteria

neocimmerian events in central and western afghanistan abstract the neocimmerian orogenic belt of afghanistan is about 350 wide and lies between a northern eocimmerican orogenic belt which resulted from the closure of the paleotethys to the north and the alpine himalayan orogenic belt which resulted from the closing of the neotethys to the south this neocimmerian orogenic belt resulted from the closure of the waras penjaw oceanic realm at some time between the neocomian and the cenomano turonian the waras penjaw oceanic realm opened during or shortly after the triassic breaking off from continental asia where the ascent of the northern eocimmerian orogenic belt had recently ended it was located behind an active tectonic and magmatic arc which resulted from the neotethyan subduction during this opening the adjacent continental blocks were subjected to extension at that time the entire region was of the same type as the present japanese archipelago sea of japan eastern continental asia system located behind the western pacific subduction zone when the waras penjaw oceanic realm began to close its southern margin was activated the subsequent collision affected a vast region particularly the remnants of the northern eocimmerian orogenic belt this collision continued to act on the region during the neotethyan subduction shortly after these neocimmerian events the region was of the same type as the present southern andean region located between the south american continent and the eastern pacific subduction zone

formation of monazite via prograde metamorphic reactions among common silicates implications for age determinations three lines of evidence from schists of the great smoky mountains nc indicate that isogradic monazite growth occurred at the staurolite in isograd at 600 c 1 monazite is virtually absent below the staurolite in isograd but is ubiquitous several hundred grains per thin section in staurolite and kyanite grade rocks 2 many monazite grains are spatially associated with biotite coronas around garnets formed via the reaction garnet chlorite muscovite biotite plagioclase staurolite h2o 3 garnets contain high y annuli that result from prograde dissolution of garnet via the staurolite in reaction followed by regrowth and rare monazite inclusions occur immediately outside the annulus and in the matrix but not in the garnet core larger monazite grains also exhibit quasi continuous th zoning with high th cores and low th rims consistent with monazite growth via a single reaction and fractional crystallization during prograde growth common silicates may host sufficient p and lrees that reactions among them can produce observable lree phosphate specifically phosphorus contents of garnet and plagioclase are hundreds of parts per million and dissolution of garnet and recrystallization of plagioclase could form thousands of phosphate grains several micrometers in diameter per thin section lrees may be more limiting but sheet silicates and plagioclase can contain tens to 100 ppm lree so recrystallization of these silicates to lower lree contents could produce hundreds of grains of monazite per thin section monazite ages determined via electron and ion microprobes are 400 ma directly linking prograde barrovian metamorphism of the western blue ridge with the acadian orogeny in contrast to previous interpretations that metamorphism was taconian 450 ma interpretation of ages from metamorphic monazite grains will require prior chemical characterization and identification of relevant monazite forming reactions including reactions previously viewed as involving solely common silicates

the composition and formation of miocene tholeiites in the central european cenozoic plume volcanism cecv tholeiites accompanying a majority of alkali basalts are restricted to the highly productive central part of the cecv plume activity in vogelsberg and hessian depression they mainly occur as quartz tholeiites which according to experiments of partial melting and material balances are products of olivine tholeiitic primary melts the differentiation from olivine to quartz tholeiitic melts took place in lower crustal magma chambers where olivine tholeiitic melt intruded due to a density comparable with that of the country rocks the fractionation due to separation of olivine and some clinopyroxene caused contamination of tholeiite magmas by tonalitic partial melts from the wall rocks of the magma chambers the latter process is indicated by relatively high rb k and pb and low nb concentrations and by nd sr and pb isotopes contaminating crustal melts which roughly attained a proportion of 10 contained very low 143nd 144nd ratios from a nd sm fractionation as old as 2 6 ga this is the first evidence from mafic rocks of this high age in the lower crust beneath central europe modelling with incompatible elements allows to recognize olivine tholeiites as products of about 1 partial melting of plume rocks consisting of 35 primitive and 65 depleted mantle materials the production of tholeiites other than alkali basalts is restricted to the highest plume activity and the largest fraction of morb type source rocks

analytical perils and progress in electron microprobe trace element analysis applied to geochronology background acquisition interferences and beam irradiation effects electron probe microanalysis epma of accessory minerals such as monazite xenotime and thorite for minor and trace element concentrations and geochronology requires consideration of beam irradiation effects increasing heat and charge as higher current densities and lengthy counting times are employed and requires careful detailed assessment of background intensities and interferences a carbon coat 250 a thickness is generally inadequate for prevention of absorbed current s uctuation and beam damage when using the high current densities applied for high precision e g 200 na focused beam beam irradiation effects include element mobility in monazite resulting in p loss relative to ree coating materials of higher electrical and thermal conductivity are indicated and use of gold 100 a is strongly suggested systematic compositional and therefore age variability can result simply from analytical effects requiring evaluation of all aspects of data acquisition the spectra relevant to measurement of y th pb and u are complex especially in ree bearing minerals acquisition of detailed spectral wavelength scans allows recognition of background and peak interferences as well as curvature background intensities can be extracted directly from scan data by regression x ray mapping allows delineation of domains guiding background acquisition and detailed quantitative analysis minor substitution or s uorescence of unexpected elements can compromise analyses one documented effect being the s uorescence of k in monazite adjacent to or hosted by k feldspar or micas this effect clearly evident within 10 micrometers from k feldspar can result in erroneous u concentrations leading to misinterpretation of rim ages as younger overgrowths absorption edges associated with th also become relevant to the measurement of u at high th concentrations because background intensity is sensitive to variation in average atomic number backgrounds must be acquired from each identi ed domain with particular attention being paid to th variation misapplication of background intensities can result in large age discrepancies for example application of backgrounds obtained from a high th domain in monazite to measurement of a low th domain 1 3 of the amount in the high th domain results in an overestimation of the um background intensity of 0 008 cps na and an overall increase in age of 70 m y

potential minerals for determining u th pb chemical age using electron microprobe abstract after a decade of studies and development it is now accepted that reliable u th total pb isochron ages can be calculated for monazite using an electron microprobe at m scale either directly on thin sections or on separated grains mounted in polished section the potential for determining u th pb chemical ages from other u and th enriched phases has been investigated compared to chemical monazite dating results for which individual spot age precisions of 20 to 100 ma can be achieved from individual spot analyses using isochron plots for monazite the age homogeneity of a given population of data can be assessed and depending upon the number of analyses n 50 a precision of 5 to 10 ma can be obtained the u content in xenotime widely varies from less than 0 1 wt up to 3 wt but th rarely exceeds 1 wt as a consequence the amount of radiogenic pb produced during a given period remains significantly lower for xenotime than for monazite leading to a lower precision 20 ma on the mean ages xenotime however appears to remain as a closed system but common pb must be carefully checked furthermore the electron microprobe technique epma allows controlling any age discrepancy on xenotime grains as small as 10 20 m that cannot be dated by other isotopic methods such xenotime ages can be useful when studying the monazite xenotime equilibrium the electron microprobe is not the most reliable method for dating zircon since u and th concentrations are generally low and common pb is not negligible nevertheless the spatial resolution of epma coupled with isotope methods allows conclusive in situ studies about radiogenic pb mobility and metamictization thorite does not seem suitable for dating with either isotope methods or epma because of continuous radiogenic pb loss conversely the oxide phases thorianite and baddeleyite are robust minerals with closed systems they are rather rare and seem to incorporate negligible common pb making epma a method of choice for dating them for thorianite the precision on the mean age can be similar as that obtained for monazite or even better while the precision for baddeleyite cannot be significantly better than 20 to 50 ma due to the limited amount of u 0 1 and the lack of th

a modified ground motion attenuation relationship for southern california that accounts for detailed site classification and a basin depth effect the attenuation relationship presented by boore et al 1997 has been evaluated and customized with respect to southern california strong motion data for peak ground acceleration pga and 0 3 1 0 and 3 0 sec period spectral acceleration this study was motivated by the recent availability of a new site classification map by wills et al 2000 which distinguishes seven different site categories for california based on the 1994 nehrp classification with few exceptions each of the five site types represented in the southern california strong motion database exhibit distinct amplification factors supporting use of the wills et al 2000 map for microzonation purposes following other studies a basin depth term was also found to be significant and therefore added to the relationship sites near the center of the la basin exhibit shaking levels up to a factor of 2 greater on average than otherwise equivalent sites near the edge relative to boore et al 1997 the other primary difference here is that pga exhibits less variation among the wills et al 2000 site types in fact the pga amplification implied by the basin depth effect is greater than that implied by site classification the model does not explicitly account for nonlinear sediment effects which if important will most likely influence rock site pga predictions the most evidence for a magnitude dependent variability or prediction uncertainty is also found and included as an option

the okinawa trough genesis of a back arc basin developing along a continental margin abstract the okinawa trough is the only example of a marginal back arc basin type at a young stage of evolution that developed along a continental margin the first phase of crustal stretching and subsidence occurred during late miocene early pliocene times a second major phase occurred after the latest pliocene or early pleistocene with en echelon rift axes along the axes of the okinawa trough oblique to the general trend of the arc and trench crustal separation and active spreading has occurred in the central and southern okinawa trough but the north okinawa trough is only in a rifting stage the development of the basin has several correlations with the general tectonism of the arc system 1 1 there was a synchronism between opening and subsidence of the okinawa trough and tilting and subsidence of the fore arc terrace 2 2 back arc rifting was initiated in the volcanic arc and propagated along it during the neogene remnants of a volcanic arc are found on the continental side of the basin the beginning of the back arc spreading observed in the central and southern okinawa trough correspond to a relative minimum in the activity of the volcanic arc 3 3 the timing and kinematic evolution of the taiwan collision and the south okinawa trough opening suggest a connection between these two events such a collision lateral back arc opening model could explain the initiation of the opening of back arc basins but additional phenomena such as thermal convection retreating trench model or anchored slab model are indispensable to maintain extension in the back arc basin

near source attenuation of peak horizontal acceleration strong motion data recorded within 50 km of the rupture zone were used to study near source attenuation characteristics of horizontal peak ground acceleration for worldwide earthquakes of magnitudes 5 0 to 7 7 the data base consisted of 229 horizontal components of peak acceleration recorded from 27 earthquakes including the 15 october 1979 imperial valley earthquake these data were found to be adequately represented by the functional relationship pga a exp b m r c m d where pga represents the mean of the peak values scaled from the two horizontal components of each recording m is richter magnitude and r is distance from the fault rupture zone peak acceleration was found to be lognormally distributed with a standard error representing a 45 per cent increase in the median estimate the regression analysis statistically confirmed the results of earthquake simulation studies that have predicted peak acceleration to become independent of magnitude and distance in the near field an extensive sensitivity study showed that predictions based on our attenuation relationships are stable with respect to reasonable model and parameter variations an analysis of residuals was used to investigate the behavior of peak acceleration with respect to various earthquake site and recording parameters the more significant findings being 1 a similarity in the level of acceleration recorded on soil or rock 2 larger than average accelerations recorded at sites located on shallow soils or in areas of steep topography 3 larger than average accelerations associated with earthquakes having reverse fault mechanisms and 4 lower than average accelerations recorded in large embedded structures

metamorphic evolution of the precambrian south badakhshan block based on mineral reactions in metapelites and metabasites associated with whiteschists from sare sang western hindu kush afghanistan abstract textural relations and metamorphic fabrics of metapelites and associated metabasites from the precambrian sare sang series which is known to contain lapis lazuli deposits and whiteschists indicate an increase in metamorphic pressures and temperatures to the transition of eclogite amphibolite facies boundary and a subsequent retrograde p t trajectory to amphibolite facies conditions the metapelites are characterized by the presence of garnet biotite plagioclase k feldspar and al2sio5 phases showing the p t path involved change by compression from sillimanite to kyanite stability fields and subsequent decompression along an overall clockwise loop the metabasites contain garnet hornblende and plagioclase biotite and clinopyroxene plagioclase symplectites that might represent a replacement product after omphacite maximum p t conditions of 12 13 kbar at 700 750 c were deduced from thermobarometric calculations peak metamorphism was accompanied by dehydration melting of muscovite but not biotite followed by minor back reaction of garnet k feldspar h2o al2sio5 biotite plagioclase retrograde phases in metapelites and metabasites are muscovite calcite and fluorine and or chlorine rich amphiboles and biotite which probably resulted from infiltration of fluid that had equilibrated with surrounding metacarbonates and metaevaporites

response spectral attenuation relations for shallow crustal earthquakes in taiwan article i nfo attenuation relationship crustal earthquakes strong ground motion peak ground acceleration spectral acceleration hanging wall effect in this study a local set of response spectral attenuation equations developed for seismic hazard analysis in taiwan are introduced as an example for determining the local strong motion attenuation relationship for a region strong ground motion data for shallow crustal earthquakes are obtained from the taiwan strong motion instrumentation program tsmip these data are used to establish peak ground acceleration pga and response spectral acceleration sa attenuation equations taking into consideration both hanging wall effects and site conditions the obtained results show that the local set of attenuation equations gives significantly lower values of pga and sa for structural periods shorter than 0 3 s as compared to a set of global relations obtained from international data the sas obtained for structural periods longer than 0 3 s are similar to those obtained for global sets this indicates that developing a local set of ground motion attenuation equations is necessary for more accurate prediction of ground motion values

geochemical characterisation of early cretaceous lacustrine sediments of bima formation yola sub basin northern benue trough ne nigeria organic matter input preservation paleoenvironment and palaeoclimatic conditions the bima formation is the oldest lithogenetic unit occupying the base of the cretaceous successions in the yola sub basin of the northern benue trough it is differentiated into lower b1 middle b2 and upper b3 bima members integrated organic and inorganic geochemical studies were applied on the lacustrine sediments of the bima formation with the aim of reconstructing the palaeodepositional environment and organic matter input in response to climate and tectonism the analysed sediments were deposited in a freshwater lacustrine environment with a low salinity stratified water column and suboxic to relatively anoxic conditions as indicated by the bulk geochemical parameters the biomarkers provide evidence for a contribution of aquatic algae and microorganisms with a significant amount of terrigenous organic matter input the preservation of the organic matter is possibly attributed to the stratified water column with low salinity and suboxic to relatively anoxic conditions based on the geochemistry of major and trace elements the sediments were deposited during semi arid climatic conditions within passive continental margin setting this agrees with the tectonic events in the west and central african rift system wcars during the early cretaceous period

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

the chi chi earthquake sequence active out of sequence thrust faulting in taiwan we combined precise focal depths and fault plane solutions of more than 40 events from the 20 september 1999 chi chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central taiwan is a moderately dipping 20 to 30 thrust fault away from the deformation front a second subparallel seismic zone lies about 15 kilometers below the main thrust these seismic zones differ from previous models indicating that both the basal decollement and relic normal faults are aseismic

monazite paragenesis and u pb systematics in rocks of the eastern mojave desert california u s a implications for thermochronometry abstract studies of the paragenesis and u pb systematics of monazite in rocks from the eastern mojave desert california corroborate its potential usefulness as a prograde thermochronometer and in dating granite inheritance unmetamorphosed latham shale and its equivalents at grades ranging from greenschist to upper amphibolite facies are virtually identical in composition monazite is absent in the shale and low grade schists but it is abundant in schists at staurolite and higher grades lower grade schists instead include minute th and ce oxides and unidentified ce poor lree phosphates that apparently are lower temperature precursors to monazite thus monazite originates when the pelite passes through lower amphibolite facies conditions monazites from three upper cretaceous granites yield ages that are strongly discordant upper intercepts of 1 6 1 7 ga are similar to those defined by u pb data for coexisting zircons and coincide with a period of copious magmatism in the mojave crust as the host upper cretaceous granitic magmas were all above 700 c effective closure of the restitic monazites to pb loss must be well in excess of this temperature u pb compositions of monazite from proterozoic granitoids and schist also indicate high pb retentivity taken together these studies support the suggestion that monazite can be an effective prograde thermochronometer at least in pelites it is not usually retained as a detrital mineral but rather forms during moderate temperature metamorphism its u pb system should not be reset by subsequent higher grade metamorphism

oil shale formation in the upper cretaceous nenjiang formation of the songliao basin ne china implications from organic and inorganic geochemical analyses abstract two oil shale layers are present in the upper cretaceous nenjiang formation of the songliao basin representing excellent hydrocarbon source rocks their biomarker compositions provide evidence for a major contribution by aquatic organisms within the photic zone of the water column phytoplankton blooms were promoted by warm humid climate and lake eutrophication salinity stratification and anoxic bottom water conditions are indicated in the lower oil shale layer whereas decreased salinity and partial oxygenation of the water column are evident in the upper oil shale layer moreover an increase in sizes of alginite from the lower to the upper oil shale layer and enhanced telalginite concentrations is detected therefore a stratified water column with high salinity and anoxic bottom water conditions contributes to organic matter om preservation in the lower oil shale layer in contrast high bioproductivity in combination with om preservation favored by enhanced algae sizes and telalginite concentrations are suggested as the om enrichment mechanisms in the upper oil shale layer in addition factors such as clay minerals microbial activity and detrital matter input cannot be ignored for their influence on om enrichment in this study a preservation model within the lower oil shale layer and a productivity model within the upper oil shale layer are established the models imply that excellent preservation is the major controlling factor for om enrichment in the lower oil shale layer whereas the high bioproductivity is the major controlling factor for om enrichment in the upper oil shale layer however the combination of both factors for oil shale deposition must be considered

cyclic terpenoids of contemporary resinous plant detritus and of fossil woods ambers and coals abstract cyclic terpenoids present in the solvent extractable material of fossil woods ambers and brown coals have been analyzed the sample series chosen consisted of wood remains preserved in holocene to jurassic sediments and a set of of ambers from the philippines copalite israel canada and dominican republic the brown coals selected were from the fortuna garsdorf mine and miocene formations on fiji the fossil wood extracts contained dominant diterpenoid or sesquiterpenoid skeletons and aromatized species were present at high concentrations with a major amount of two ring aromatic compounds tricyclic diterpenoids were the predominant compounds in the ambers aromatized derivatives were the major components consisting of one or two aromatic ring species with the abietane and occasionally pimarane skeletons the saturated structures were comprised primarily of the abietane and pimarane skeletons having from three to five carbon c1 c2 etc substituents kaurane and phyllocladane isomers were present in only minor amounts bicyclic sesquiterpenoids as saturated and partial or fully aromatized forms were also common in these samples but only traces of sesterterpenoids and triterpenoid derivatives were found the brown coal extracts were composed of major amounts of one and two ring aromatized terpenoids with a greater proportion of triterpenoid derivatives than in the case of the woods and ambers this was especially noticeable for the german coal where the triterpenoids were predominant open c ring aromatized structures were also present in this coal steroid compounds were not detectable but some hopanes were found as minor components in the german brown coal an overview of the skeletal structure classes identified in each sample as well as the general mass spectrometric characteristics of the unknown compounds are included in the present paper it can be concluded from these structural distributions that aromatization is the main process for the transformation of terrestrial cyclic terpenoids during diagenesis constituting a general pathway for all terpenoids

electron microprobe dating of monazite because monazite is extremely rich in u and th radiogenic pb pb accumulates very quickly and reaches in about 100 ma a level where it is possible to analyse it with the electron probe assuming that common pb is negligible and that partial loss of pb has not occurred the simultaneous measurement of u th and pb allows to obtain a geologically meaningful age from a single electron probe analysis here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method a specific statistical method to deal with the large number of data which can be obtained on a single sample is described and several guidelines illustrated by examples are suggested to optimize the method electron probe measurements carried out on samples of known age from 200 ma to 3 1 ga yield ages that always fall inside the confidence interval of the isotopically determined age demonstrating that this method is reliable the younger age limit is approximately 100 ma although it can be younger in some favourable cases in old monazites extremely high pb contents have been found up to 5 wt indicating that monazite can tolerate high radiation doses without experiencing lead loss the final precision on the age for a normal monazite is 30 50 ma for a total counting time of 600 s a complete dating procedure can be completed in less than 1 h first results indicate that old ages can be preserved in monazite either in small relict cores in crystals or by the coexistence of several generations of monazites in a sample this method has all the advantages of the electron probe it is non destructive has an excellent spatial resolution monazites as small as 5 i m can be dated and because it is possible to work on normal polished thin sections the petrographical position of the dated crystal is known this method offers a large number of geologists access to an in situ dating technique at moderate cost

five generations of monazite in langtang gneisses implications for chronology of the himalayan metamorphic core monazite grains from greater himalayan sequence gneisses langtang valley nepal were chemically mapped and then dated in situ via th pb ion microprobe analysis correlation of ages and chemistry reveals at least five different generations of monazite ranging from c 9 to 300 ma petrological models of monazite chemistry provide a link between these generations and the thermal evolution of these rocks yielding an age for the melting of greater himalayan rocks within the main central thrust sheet c 16 ma and for the timing of thrust sheet emplacement that are younger than commonly viewed chemical characterization of monazite is vital prior to chronological microanalysis and many ages previously reported for monazite from the greater himalayan sequence are interpretationally ambiguous

calcium diffusivity in alumino silicate garnets an experimental and atem study concentration gradients in calcium are common in metamorphic or magmatic garnets and can be used to determine the timescales of geological processes however the kinetics of ca diffusion in garnet is poorly constrained and experimental studies have to date yielded widely varying diffusion coefficients in this paper we describe a new method for generating diffusion profiles in garnet we incorporated polished and compositionally homogeneous garnet seeds in a finely ground powder of clinopyroxene and garnet during the experiments 1 3 gpa 1 050 1 250 c and o2 the graphite o2 buffer the mineral powder partially melted recrystallized and formed a 10 50 m wide overgrowth zone of compositionally distinct garnet around the seeds long duration experiments generated measurable relaxation profiles at these seed overgrowth interfaces we performed analytical transmission electron microscope traverses across the interfaces in each experiment thirteen usable compositional profiles were obtained with characteristic distances of diffusion ranging from 300 to 1 000 nm from these profiles ca fe mg interdiffusion coefficients were retrieved using an analytical solution for the diffusion equation and the data were cast in an arrhenius relation linear regression of the data yields an activation energy q ca fe mg equal to 188 48 kj mol 1 and a frequency factor d 0 equal to 6 6 10 14 m2 s 1 within the compositional range studied the composition of garnet has no major effect on the ca fe mg interdiffusion coefficient the very slow diffusion rate of ca is in agreement with natural observations indicating that ca diffuses more slowly than fe and mg the ca diffusion coefficients derived from this study are not model dependent and can be used to determine the durations of geological events from ca relaxation profiles in natural garnets

focal mechanism determination in taiwan by genetic algorithm we determined the focal mechanism solutions for earthquakes with mag nitude ml 4 0 that occurred in the taiwan region between 1991 and 2005 first motion polarities of p waves recorded at over 700 seismic stations in taiwan were used because of the large number of events and stations involved we implemented the genetic algorithm in a nonlinear global search for the focal mechanism solutions the algorithm was tuned and validated through synthetic tests we finally determined the focal mechanisms of 1635 events with good qualities among 4188 earthquakes focal mechanism solutions for a majority of the earthquakes display a dominant pat tern of thrust fault type reflecting the compressive stress field due to the plate colli sion normal fault events occurred at intermediate depths in subduction zones which is likely the result of the bending of the subducting slabs strike slip faults are also found within the eurasia plate around the peikang basement high and in collision zones near ilan where the geometry of the colliding plates is complex our study pro vides a database of focal mechanisms for studying seismogenic structures and plate tectonics this database can also be used by structural seismologists to compute syn thetics for waveform tomography studies

hercynian and eocimmerian events in afghanistan and adjoining regions abstract the area centered around afghanistan is a collage of continental blocks derived from gondwanaland this collage comprises among others 1 1 a hercynian orogenic belt widely represented in afghanistan and also by some sparse outcrops in the northern iran it is a subduction type orogen constructed at the margin between the paleotethys and the turan turkestan tarim block 2 2 a northern eocimmerian orogenic belt widely represented in afghanistan and the north of iran it is a collision type orogen constructed in the same place as the hercynian orogenic belt and resulted from the closure of the paleotethys and the collision of the central iran and central afghanistan blocks with the turan turkestan tarim block 3 3 a southern eocimmerian orogenic belt of which outcrops are now confined to southern iran but which may project beneath the neogene and quaternary formations of southern afghanistan it is a subduction type orogen constructed at the margin between the neotethys and the central iran central afghanistan block which itself was at that time subjected to regional extension this belt is now incorporated in the alpine himalayan orogen the geology of these belts suggests that the opening of the neotethys became effective only from the permian or triassic and was in a red sea type phase during the upper devonian its initial rifting possibly occurred during the lower paleozoic much like the paleotethys in which initial rifting also occurred in lower paleozoic time and whose opening became effective from the ordovician thus each of the oceanic realms in this region appears to have possibly resulted from the same extension of gondwanaland during the lower paleozoic after which they followed more or less different paths of evolution moreover the proposed geodynamic interpretation implies that during the permian and triassic there was in this region a certain coexistence of the vanishing paleotethys with the relatively young neotethys which was beginning to subduct

titaniferous magnetite ilmenite thermometry and titaniferous magnetite ilmenite orthopyroxene quartz oxygen barometry in granulite facies gneisses bamble sector se norway implications for the role of high grade co 2 rich fluids during granulite genesis oxygen fugacities have been estimated for a wide distribution of samples from the granulite facies terrane region c of the bamble sector se norway using both the titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers these oxygen fugacities are estimated using temperatures calculated from the titaniferous magnetite ilmenite thermometer of ghiorso and sack 1991 and are both internally consistent with each other as well with the thermometer in samples for which the estimated temperature is high the two oxygen barometers show good agreement whereas agreement is poor for low temperature samples in these low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably less than those estimated from orthopyroxene titaniferous magnetite quartz an increase in this discrepancy with decrease in temperature appears to reflect preferential resetting of the hematite component in the ilmenite grains without significant alteration of the more numerous titaniferous magnetite grains this is due in part to greater re equilibration of the ilmenite grains during retrograde interoxide resetting between the ilmenite grains and the titaniferous magnetite grains the mean temperature for the non reset samples 791 17 c 1 is in good agreement with temperatures obtained from garnet orthopyroxene kd exchange thermometry in the same region 785 795 c 1 harlov 1992 2000a most non reset oxygen fugacities range from log10 f o2 14 to 11 8 or approximately 0 5 1 5 log units above quartz fayalite magnetite at 7 5 kbar both these temperatures and the range of oxygen fugacities are in good agreement with those estimated using the titaniferous magnetite ilmenite thermometer oxygen barometer of andersen et al 1991 the quilp equilibrium quartz ulvospinel ilmenite pyroxene is used to project self consistent equilibrium temperatures and oxygen fugacities for samples reset due to hematite loss from the ilmenite grains these projected temperatures and oxygen fugacities agree reasonably well with the non reset samples the mean projected quilp temperature is 823 6 c 1 this result supports the conclusion that low titaniferous magnetite ilmenite temperatures down to 489 c and accompanying low oxygen fugacities are the result of hematite loss from the ilmenite grains non reset oxygen fugacities lie approximately 1 5 log10 units above the upper graphite stability curve indicating that the stable c o h fluid phase interacting with these gneisses whether regionally or locally was co2 this is borne out by the presence of numerous co2 rich fluid inclusions in these rocks

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

non ideal mixing in the phlogopite annite binary constraints from experimental data on mg fe partitioning and a reformulation of the biotite garnet geothermometer the existing experimental data ferry and spear 1978 perchuk and lavrent eva 1983 on mg fe partitioning between garnet and biotite are disparate the underlying assumption of ideal mg fe exchange between the minerals has been examined on the basis of recently available thermochemical data using the updated mixing parameters for the pyrope almandine asymmetric regular solution as inputs ganguly and saxena 1984 hackler and wood 1984 thermodynamic analysis points to non ideal mixing in the phlogopite annite binary in the temperature range of 550 c 950 c the non ideality can be approximated by a temperature independent one constant margules parameter the retrieved values for enthalpy of mixing for mg fe biotites and the standard state enthalpy and entropy changes of the exchange reaction were combined with existing thermochemical data on grossular pyrope and grossular almandine binaries to obtain geothermometric expressions for mg fe fractionation between biotite and garnet t in k begin gathered text t hw 20286 0 text 0193p 2080 x text mg text gt text text 2 text 6350 x text fe text gt text text 2 hfill text 13807 x text ca text gt text 1 x text mn text gt text 8540 x text fe text gt text x text mg text gt text 1 x text mn text gt text hfill text 4215 x text ca text gt text x text mg text gt text x text fe text gt text 4441 text 2x text mg text bt text 1 mathord left vphantom text 2x text mg text bt text 1 text 13 text 138 right kern nulldelimiterspace text 13 text 138 hfill text 8 text 3143 ink text d text 6 text 276 x text ca text gt text 1 x text mn text gt hfill text t gs 13538 0 text 0193p 837 x text mg text gt text 2 text 10460 x text fe text gt 2 hfill text 13807 x text ca text gt 1 text x text mn text gt text 19246 x text fe text gt text x text mg text gt text 1 x text mn text gt hfill text text 5649 x text ca text gt text x text mg text gt text x text fe text gt text 7972 2x text mg text bt text 1 mathord left vphantom text 5649 x text ca text gt text x text mg text gt text x text fe text gt text 7972 2x text mg text bt text 1 text 6 text 778 right kern nulldelimiterspace text 6 text 778 hfill text 8 text 3143ink text d text 6 text 276 x text ca text gt 1 text x text mn text gt hfill end gathered the reformulated geothermometer is an improvement over existing biotite garnet geothermometers because it reconciles the experimental data sets on fe mg partitioning between the two phases and is based on updated activity composition relationship in fe mg ca garnet solid solutions

the baganuur coal deposit mongolia depositional environments and paleoecology of a lower cretaceous coal bearing intermontane basin in eastern asia abstract the investigations involved geophysical sedimentological palynological chemical and mineralogical studies supported by field based infrared spectrometry the baganuur basin central mongolia is among the rift or pull apart basins which subsided at the boundary between the jurassic and the lower cretaceous in east asia during the berriasian peat accumulation began in the area under study in central mongolia the palynoflora is akin to the siberian palynological province based on the phytoclast assemblages and the ratios of total sulfur content to total organic content marine transgressions into this intermontane basin may be ruled out the coal interseam sediments were laid down prevalently under neutral to slightly alkaline conditions only in some carbonaceous sediments the ph of intrastratal solutions was lowered suboxic to anoxic conditions persisted during almost the entire lower cretaceous period in the baganuur basin based on the distribution of fining and coarsening upward sequences and the organic matter the basin fill has been subdivided into seven depositional units a fluvial swamp b fluvial lacustrine c deltaic fluvial d fluvial e fluvial deltaic lacustrine floodplain f lacustrine deltaic swamp g swamp fluvial a conspicuous change in the fluvial lacustrine regime and an increase in the sediment supply may be observed at the boundary between depositional units b and c a strong uplift triggered the onset of an intensive delta sedimentation lithoclasts heavy minerals e g apatite zircon garnet anatase brookite epidote sphene tourmaline and phyllosilicates e g kaolinite smectite mica chlorite attest to a mixing of detrital material one provenance area was abundant in acidic plutonic rocks as shown by the granitic lithoclasts the other in volcanic rocks which produced the vitroclastic debris deposited as tephra fallout post depositional alteration of the siliciclastic interseam sediments was favored by a distinctive facies association of transmissive and sealing horizons it led to a re deposition of ca u and sr in the siliciclastics post depositional alteration of the organic material converted it into lignite to subbituminous c coal

a short report of the investigations made on the facies of austrian coal deposits petrological studies on austrian coal deposits started in the 1940s during the last decade multi disciplinary investigations involving petrology geochemistry and palynology were performed to study the relationship between geodynamics coal forming environments and coal properties

molecular composition of a leaf and root bearing oligocene oxbow lake clay in the weisselster basin germany abstract a plant fossil bearing clay profile from the upper oligocene thierbach strata weisselster basin germany has been sectioned into horizons and the plant macrofossils of each section surface have been identified by morphological and anatomical studies in the upper half of the profile leaves from populus germanica and carpinus grandis and branchlets from the conifer taxodium balticum vel t dubium dominate the horizons while the lower part contains only root remains of unknown higher plants in the soxhlet extracted samples from each section n alkanes n alkanols n carboxylic acids and several terpenoids amyrin 24 25 dinoreleana 1 3 5 10 12 tetraene olean 12 en 3 one simonellite and hop 17 21 ene were identified by combined gas chromatography mass spectrometry the comparison of the extracted chemical compounds and the macrofossil record of the profile shows that simonellite occurs preferentially in the taxodium bearing horizons n alkanes n alkanols n carboxylic acids and amyrin were found in all sections but are enriched in the root containing part of the profile the distribution of hop 17 21 ene is independent of the input of higher plant remains

geochemical characteristics of crude oils their asphaltene and related organic matter source inputs from fula oilfields in the muglad basin sudan abstract bulk geochemical characteristics of crude oils coupled with geochemical analyses of reservoir oil asphaltenes from fula oilfields in the muglad basin have provided information on source organic matter input depositional environment and the correlation between these crude oils and their potential source rocks in the basin only one oil family is present within the fula oilfields as indicated by biomarker and non biomarker parameters the fula oils are characterized by moderate api gravity low sulphur and moderate trace metal ni v contents and high wax contents this suggested that the oils were generated from source rock that was deposited in a principally lacustrine environment this is supported by bulk geochemical characteristics and biomarker compositions a variety of biomarker specific parameters obtained from n alkanes regular isoprenoids terpanes and steranes indicate that the fula oils were generated predominantly from algae derived organic matter that was deposited in a lacustrine environment which then experienced a slight seawater influence under suboxic to relatively anoxic conditions these oils were generated from source rock with a wide range of thermal maturity ranging from early to peak oil window the biomarker characteristics of these oils are consistent with those of the early cretaceous abu gabra shales the oil source rock relationship is also demonstrated by similarities in the structural moieties of the fula oil asphaltene and the abu gabra shale kerogens the pyrolysis gc of the analyzed fula oil asphaltene indicates that the oils were derived from type i algal organic matter consistent with paraffinic high wax oils

summary and discussion of p t estimates from garnet pyroxene plagioclase quartz bearing granulite facies rocks from sri lanka abstract in granulite facies rocks of granitic to basic composition from the highland complex hc of sri lanka maximum p t estimates for about 115 locations have been obtained from core compositions of garnet orthopyroxene and plagioclase their distribution shows a decrease in pressure from the east and southeast where pressures exceed 9 kbar towards the west and southwest where pressures are about 5 kbar the accompanying temperature decrease in the order of about 200 c is less pronounced the regional distribution pattern of garnet quartz clinopyroxene reaction textures around orthopyroxene and plagioclase indicates that the lower crustal rocks of the eastern and southeastern parts of the hc have experienced an episode of near isobaric cooling subsequent uplift resulted in the breakdown of garnet and clinopyroxene to orthopyroxene plagioclase this reaction texture is found in all parts of the hc with the exception of the west and southwest where the higher crustal levels are exposed comparisons of the array of calculated maximum p t data with published continental geotherms for normal to elevated mantle heat flows 30 50 70 and 90 10 3 w m 2 at the base of a 36 km crust show that the depth versus temperature gradient is not a simple geothermal one the p t array in which the gradient is steeper than the geotherms would be consistent with magmatic heating this model would suggest a scenario in which intrusions that were generated in the lower crust were emplaced at higher crustal levels and heated up the surrounding rocks however since the number of known slightly pre to synmetamorphic intrusions in sri lanka is very limited other mechanisms of the heat supply seem to be required prior to uplift and exposure of this partial cross section through the lower to upper crust

thermodynamics of the amphiboles ca mg fe2 quadrilateral a thermodynamic model has been developed and calibrated for monoclinic and orthorhombic amphiboles compositionally contained within the ca mg fe 2 amphibole quadrilateral the model incorporates the energetic consequences of cation ordering of fe 2 and mg over nonequivalent sites in the crystal structure and accounts for the temperature pressure and compositional dependence of the orthorhombic monoclinic phase transition calibration is based on previously published work on the thermodynamic properties of fe 2 mg amphiboles and tremolite and experimental cation ordering data along with solvus width and tieline orientations of natural coexisting amphiboles in the quadrilateral among derived parameters is the enthalpy of formation of end member ferroactinolite 10534 966 kj mol a calculated femg 1 isopotential solvus at mid composition in the quadrangle agrees well with a revised calibration of experimental data from cameron 1975 the solvus is not strongly asymmetric and narrows with increasing fe mg ratio and temperature phase relations along the mg and fe sides of the quadrilateral are compared and contrasted cummingtonite anthophyllite phase relations are shown in the t x f e plane with and without coexisting calcic amphibole the breakdown reactions of quadrilateral amphiboles to assemblages of two pyroxenes olivine quartz and h 2 o are depicted as functions of temperature pressure composition h 2 o activity and oxygen fugacity some highlights of their relevance to metamorphic and igneous systems are discussed

geochemical characterization and depositional environment of source rocks of small fault basin in erlian basin northern china abstract a combined investigation of molecular geochemistry elements and carbon isotopic composition of carbonate distribution was carried out on the early cretaceous mudstones of the tengger formation in the erlian basin northern china to define source rock geochemical characteristics depositional environment and tectonic setting of small faulted basin the biomarkers of mudstone extracts are characterized by short to middle chain n alkanes high cpi values 1 12 a wide range of pr ph 0 4 1 94 relatively high concentrations of c 29 sterane and the presence of relatively low tricyclic terpanes and low gammacerane index values 0 01 0 25 which is consistent with a relatively oxic to anoxic depositional environment of fresh to brackish water conditions with a major contribution of terrigenous organic matter input and a low contribution of aquatic algal bacterial organic matter the oxic to anoxic depositional environment of small fault basins and a fresh and brackish water conditions are also confirmed by reduced sulphur organic carbon ratio and element distribution in these small fault basins the cross plots of 13 c carb and toc show that productivity has an obvious control on source rock development the differences in tectonic settings cause variations in productivity redox conditions and terrigenous organic matter input which account for the distinctly different geochemical characteristics and depositional environment of source rocks in small fault basins

major intrusive stages in afghanistan typology age and geodynamic setting afghanistan straddles the gondwana eurasia boundary most of its major structural areas comprise large plutonic belts based on some 700 major element analyses the typology of the eleven main plutonic belts has been determined these belts differ from each other on the whole they display a very broad range of petrographic types from nepheline syenites and gabbros to leucocratic muscovite tourmaline granites and a wide diversity of magmatic associations from cafemic or alumino cafemic associations of various types tholeiitic calc alkaline subalkaline i e monzonitic alkaline peralkaline to various aluminous ones taking into account the typology of the belts and chronological data four major intrusive stages have been recognized and related to the geodynamic evolution of afghanistan and central asia 1 aluminous lower palaeozoic ca 500 ma stage related to linear crustal thinning at the gondwana scale 2 cafemic and alumino cafemic triassic ca 230 ma stage related to southward dipping subduction of oceanic crust beneath an island arc involving a large continental strip detached from the southern asia margin 3 cafemic and alumino cafemic cretaceous ca 100 ma stage dominantly related to subduction of oceanic crust under marginal gondwana fragments 4 eocene oligocene stage ca 35 ma induced by the india eurasia collision including two quite different groups of intrusives a a cafemic and alumino cafemic group related to extensional phenomena dominantly associated with the westward extrusion of central afghanistan along the herat fault these phenomena occurred on both sides of the gondwana palaeozoic asia boundary b an aluminous group resulting from crustal thickening in marginal gondwana fragments

the origin type and preservation of organic matter of the barremian aptian organic rich shales in the muglad basin southern sudan and their relation to paleoenvironmental and paleoclimate conditions barremianeaptian organic rich shales from abu gabra formation in the muglad basin were analysed using geochemical and petrographic analyses these analyses were used to define the origin type of organic matters and the influencing factors of diagenesis including organic matter input and preservation and their relation to paleoenvironmental and paleoclimate conditions the bulk geochemical characteristics indicated that the organic rich shales were deposited in a lacustrine environment with seawater influence under suboxic conditions their pyrolysis hydrogen index hi data provide evidence for a major contribution by type i ii kerogen with hi values of 400 mg hc g toc and a minor type ii iii contribution with hi values 400 mg hc g toc this is confirmed by kerogen microscopy whereby the kerogen is characterized by large amounts of structured algae botryococcus and structureless amorphous with a minor terrigenous organic matter input an enhanced biological productivity within the photic zone of the water columns is also detected the increased biological productivity in the organicrich shales may be related to enhanced semi arid humid to humid warm climate conditions therefore a high bio productivity in combination with good organic matter preservation favoured by enhanced algae

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

mesozoic ophiolites sutures and arge scale tectonic movements in afghanistan abstract the tectonic history of afghanistan appears to be the result of successive accretion of fragments of gondwana to the active margin of laurasia since the end of the paleozoic the margin in afghanistan lies along the present herat and panjshir faults south of hindu kush swings around the central pamirs and can presumably be traced along the present western altyn tagh and kunlun faults in tibet north of this boundary paleozoic rocks have been deformed in the upper paleozoic whereas south of it there is no trace of the hercynian orogeny the first collision of gondwanian fragments with laurasia probably occurred in the early mesozoic along the hindu kush and kunlun to the south ophiolites along the panjao and pangong nu chiang sutures respectively in central afghanistan and central tibet testify for another suturing event in the upper jurassic or lower cretaceous the indus tsangpo suture between india and tibet corresponds in eastern afghanistan to two ophiolite subbelts near kabul and khost both ophiolite complexes have been emplaced between maestrichtian and lower eocene by choking of two northward dipping subduction zones after complete contact between the indian and asian continents was achieved presumably in the end of eocene the penetration of india into asia caused large scale intra continental shortening a large part of the shortening was accommodated by strike slip faulting along mesozoic and more ancient sutures central afghanistan in particular was extruded to the west along the herat suture by the protrusion of the pamir wedge it subsequently collided with the lut block

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

complexity in the behavior and recrystallization of monazite during high t metamorphism and fluid infiltration abstract a detailed study of monazite grains in silica undersaturated and quartz bearing mg al metapelite from the oygarden group of islands east antarctica reveals a complex history of growth and recrystallization during two separate events in the neoproterozoic and earliest cambrian monazite grains from garnet poor and garnet rich metapelite preserve core domains that have ages corresponding to growth and or recrystallization at granulite facies p 9 1 0 gpa t 850 900 c conditions during the rayner structural episode between 930 and 890 ma high th rims 22 wt tho 2 that are in textural equilibrium with sapphirine orthopyroxene symplectites formed after garnet during late rayner decompression occur on monazite grains in garnet rich assemblages and give electron microprobe ages 883 18 ma within error of core domains 903 14 ma these high th rim domains are interpreted to have formed through recrystallization of liberated inclusions via a process dominated by coupled dissolution reprecipitation reactions facilitated by transient fluid films on the large surface areas in the symplectite and not by new growth in garnet poor metapelite monazite grains that have grain boundaries in textural equilibrium with the granulite facies assemblage also show alteration to higher th compositions on rims and along vein like fractures this compositional shift is accompanied by partial to complete resetting of ages to 500 ma along with minor modification of core domain ages textures and patterns of chemical age resetting are interpreted to also be the result of a coupled dissolution reprecipitation reaction process but in contrast to garnet bearing assemblages this alteration occurred during a fluid influx at lower temperatures during regional pan african tectonism this study highlights the susceptibility of monazite to resetting with fluid present conditions dramatically increasing the potential for recrystallization

reducing marine and warm climate conditions during the late cretaceous and their influence on organic matter enrichment in the oil shale deposits of north jordan abstract late cretaceous oil shales located in the yarmouk sub basin north jordan were analysed using techniques of organic and inorganic geochemistry coupled with a microfossil study results of this study were used to reconstruct the paleoenvironmental and paleoclimatic conditions during the late cretaceous and to investigate their influence on organic matter enrichment of the oil shale deposits the analysed oil shales have high toc and s total content values in the ranges of 2 11 12 85 wt and 1 83 8 81 wt respectively the high s total content and its relation with toc values indicate that the sulfur is associated with organic matter and that the oil shales were deposited in a marine environment under reducing conditions this is shown by petrographic observation and supported by biomarker distributions the microscopic investigation indicated that the oil shales contain abundant liptinitic materials i e alginite and amorphous organic matter and planktonic foraminifera the presence of these sapropelic materials and planktonic foraminifera assemblages further suggests a marine origin biomarker distributions are also known to reflect dominantly marine plankton algal and microorganisms source input water column stratification and low oxygen reducing conditions are indicated by narrow pr ph values relatively high v ni elemental ratios and the presence of gammacerane reducing conditions contribute to preservation of organic matter warm water periods during the late cretaceous are also indicated by dominant occurrences of warm water index microfossil taxa the warm climate combined with elevated phosphorus p are the major causes of excessive algae growth and led to enhanced biological productivity within the photic zone of the water column during deposition of the oil shale deposits this increased bio productivity in combination with good preservation of organic matter are the main mechanisms of organic matter enrichment within the late cretaceous oil shales in the north jordan

near fault broadband ground motion simulations of the 2016 meinong taiwan earthquakenear fault broadband ground motion simulations of the 2016 meinong taiwan earthquake

terpenoid composition and botanical affinity of cretaceous resins from india and myanmar abstract fossil resins from the cretaceous sediments of meghalaya india and kachin myanmar burma were analysed using curie point pyrolysis gas chromatography mass spectrometry and thermochemolysis gas chromatography mass spectrometry to help elucidate their botanical source the major pyrolysis products and methyl esterified thermochemolysis products of both the resins were abietane and labdane type diterpenoids with minor amount of sesquiterpenoids the thermochemolysis products also included methyl 16 17 dinor callitrisate methyl 16 17 dinor dehydroabietate and methyl 8 pimaren 18 oate the latter two from just the myanmarese resin the exclusive presence of both labdane and abietane diterpenoids and the lack of phenolic terpenoids may suggest that the studied cretaceous resins were derived from pinaceae pine family conifers

evolution of the eastern karakoram metamorphic complex ladakh nw india and its relationship to magmatism and regional tectonics abstract the eastern karakoram terrane nw india records crustal evolution in the core of the himalayan tibetan orogen recent debate has centred on whether prograde metamorphism anatexis and leucogranite emplacement were the result of localised shear heating and magma advection within the karakoram fault zone kfz or instead predate the kfz and were the result of regional tectonometamophic events inclusions within andalusite porphyroblasts that grew during 15 7 ma leucogranite emplacement have fabrics that are random or discordant to the kfz matrix foliation indicating that the kfz initiated after this time therefore earlier anatexis and metamorphism are the result of regional metamorphic events amphibole plagioclase thermobarometry on a c 17 ma migmatite melanosome later exhumed within a transpressional zone of the kfz shows that melting occurred at 688 c and 522 mpa amphibolites record an older kyanite grade metamorphic event that occurred at 677 736 c and 875 1059 mpa metapelites also record a kyanite grade event which is constrained by ti in biotite thermometry to have occurred at 622 c and 650 mpa the tectonometamorphic history of the eastern karakoram correlates closely with that of the central karakoram away from the kfz this correlation supports the interpretation that metamorphism and anatexis were regional in extent and also indicates a limited offset of

geochemical characterisation of tithonian berriasian chia gara organic rich rocks in northern iraq with an emphasis on organic matter enrichment and the relationship to the bioproductivity and anoxia conditions abstract tithonian berriasian chia gara organic rich rocks located in kurdistan northern iraq were analysed based on inorganic and organic geochemistry to define the origin type of organic matter and the influencing factors of organic matter om enrichment including the om input and preservation and their relationship to the paleoenvironment conditions the 13 c org values of the chia gara rocks range from 29 99 to 26 93 with average values of approximately 28 8 indicating that the organic matter has a predominantly marine origin enhanced biological productivity within the photic zone of the water column during deposition of the chia gara fm is indicated by consistently high organic carbon content in most samples average 3 wt as well as by bulk geochemical and biomarker characteristics major contributions by aquatic algae and microorganisms with a minor terrigenous organic matter contribution are indicated by the n alkane distribution patterns and the composition of the hopanoids steroids and tricyclic terpenoids strongly reducing bottom water is indicated by low pristane phytane ratios homohopane distribution patterns and the redox sensitive trace elements geochemistry salinity stratification with alkaline bottom waters is indicated by high sr ba ratios and the presence of gammacerane in the analysed chia gara samples these data indicate that om enrichment in the tithonian berriasian chia gara rocks results from the combination of enhanced biological productivity and salinity stratification with anoxic bottom water conditions which favoured om preservation

formation of authigenic monazite ce to monazite nd from upper carboniferous graywackes of the drahany upland roles of the chemical composition of host rock and burial temperature abstract irregular aggregates of monazite ce to monazite nd up to 150 m in diameter have been found in graywackes from the protivanov formation drahany upland czech republic monazite aggregates enclose a variety of detrital and authigenic minerals textural evidences suggest that they are of authigenic origin and grew during very low grade metamorphism at a maximum temperature 200 300 c in relation to a deep burial rarely they enclose relics of detrital monazite with a chemical composition typical for high grade monazite intensive fluid related ree remobilization occurred in relation to this very low grade metamorphism authigenic monazite appears to form only in ca poor rocks in ca rich graywackes which underwent the same low temperature metamorphic overprint authigenic synchysite ce or parisite ce are common instead in the overlaying rozstani and myslejovice formations t 150 200 c remobilization of rees was low and authigenic monazite did not form even in the ca poor graywackes authigenic monazite shows low concentrations of th u ca y hree and a low eu anomaly the central parts of the aggregates are enriched in nd mree whereas the outer parts are enriched in la and ce zoning pattern suggests an evolution in fluid chemistry during diagenesis very low grade metamorphism or it relates to different solubility of the individual ree phosphates the major source of rees in the pore fluids are probably detrital minerals mainly monazite other minor sources of rees probably include fe oxide hydroxide and or clay minerals which could have contributed to the nd mree rich cores in the authigenic monazite

sesqui and diterpenoid biomarkers preserved in taxodium rich oligocene oxbow lake clays weisselster basin germany several diterpenoids of the abietane pimarane and phyllocladane type and three cadalanetype sesquiterpenoids have been identified in the organic solvent extracts of lower oligocene clay sediments haselbach strata saxony germany the sediment contains needles and cone scales of a fossil taxodium species which represents the only conifer in the samples a clear correlation between the observed conifer biomarkers and taxodium is evident apart from diterpenoids detected previously in other sediments a new diaromatic totarane diterpenoid is reported in isolated fossil and recent taxodium needles and cone scales as well as in the haselbach clays a phenolic diterpenoid of the abietane type ferruginol has been identified the results indicate that the taxodium rich clay samples contain several diterpenoids which so far have been used as biomarkers for other conifer families and thus the chemotaxonomical use of diterpenoid biomarkers for the differentiation of fossil conifer families has to be revised

ground motion attenuation relationships for subduction zone earthquakes in northeastern taiwan subduction zone earthquakes have not been taken into special consid eration in most previous probabilistic seismic hazard analyses psha in taiwan however they may be critical to properly analyze the earthquake hazard in metro politan taipei so they need to be studied strong motion data from subduction zone earthquakes of both interface and intraslab types obtained by the tsmip and smart1 arrays in northeastern taiwan are used to establish the attenuation equa tions for peak ground acceleration pga and response spectral acceleration sa the resultant pga and sa attenuation equations include two site classes and two earth quake source types the ground motion values predicted by these attenuation equa tions are higher than those obtained from the crustal earthquake attenuation equations previously used in taiwan but are lower than those predicted by the attenuation equa tions for worldwide subduction zone earthquakes

characterization of organic matter and depositional environment of tertiary mudstones from the sylhet basin bangladesh abstract the sylhet basin of bangladesh is a sub basin of the bengal basin it contains a very thick up to 22 km tertiary stratigraphic succession consisting mainly of sandstones and mudstones the sylhet succession is divided into the jaintia paleocene late eocene barail late eocene early miocene surma middle late miocene tipam late miocene pliocene and dupitila groups pliocene pleistocene in ascending order the origin of the organic matter om and paleoenvironment of deposition have been evaluated on the basis of c n s elemental analysis rock eval pyrolysis and gas chromatography mass spectrometry gc ms analysis of 60 mudstone samples collected from drill core and surface outcrops total organic carbon toc content ranges from 0 11 to 1 56 sulfur content is low in most samples toc content in the sylhet succession varies systematically with sedimentation rate with low toc caused by clastic dilution produced by high sedimentation rates arising from rapid uplift and erosion of the himalaya the om in the succession is characterized by systematic variations in pristane phytane pr ph oleanane c30 hopane n c29 n c19 alkane tm ts 17 h 22 29 30 trisnorhopane 18 h 22 29 30 trisnorhopane and sterane c29 c27 c28 c29 ratios during the middle eocene to pleistocene based on biomarker proxies the depositional environment of the sylhet succession can be divided into three phases in the first middle eocene to early miocene deposition occurred completely in seawater dominated oxic conditions with abundant input of terrestrial higher plants including angiosperms the second phase middle to late miocene consisted of mainly freshwater anoxic conditions along with a small seawater influence according to eustasic sea level change with diluted om derived from phytoplankton and a lesser influence from terrestrial higher plants oxygen poor freshwater conditions prevailed in the third phase post late miocene planktonic om was relatively abundant in this stage while a high angiosperm influx prevailed at times tmax values of ca 450 c vitrinite reflectance ro of ca 0 66 and methylphenanthrene index mpi 3 of ca 1 indicate the om to be mature the lower part middle eocene to early miocene of the succession with moderate toc content and predominantly terrestrial om could have generated some condensates and oils in and around the study area

rates of fe mg mn and ca diffusion in garnet extraction of the thermal and chemical histories preserved by modified compositional zoning in garnet is compromised by large uncertainties in experimentally determined diffusion coefficients for principal divalent cations some of this uncertainty derives from long down temperature extrapolations but much of it arises from an inability to account accurately for large variations in diffusivity as a function of garnet composition numerical simulation of stranded diffusion profiles in partially resorbed natural garnets constrains diffusivities at low temperature and reveals a systematic dependence of diffusion rates on host garnet composition a comprehensive model incorporating a simple compositional dependence allows accurate prediction of diffusion rates for fe mg mn and ca for nearly all garnet compositions across the full range of geologically relevant temperatures pressures and oxygen fugacities

textural chemical and isotopic insights into the nature and behaviour of metamorphic monazite monazite is a mineral of choice for dating metamorphism in amphibolite and granulite grade metapelites however there exist a number of difficulties that complicate the interpretation of monazite geochronological data and prevent its application to many geological problems the two main obstacles addressed in this contribution are firstly the minor but significant e g 1 30 ma dispersal in duplicate isotope dilution thermal ionisation mass spectrometry id tims u pb age data commonly recorded from a single rock and secondly the difficulty of attaching monazite age data to pressure and temperature information through a multidisciplinary approach utilising tims and laser ablation multicollector inductively coupled plasma mass spectrometry la mc icpms isotope data quantitative and qualitative emp chemical analyses of monazite and textural studies we assess the significance of pb loss older components and continuous and episodic monazite growth in the generation of dispersed age data three samples from the canadian cordillera and one sample from the himalaya of pakistan are examined each sample exhibits an age dispersion of between 1 and 12 ma for single crystal and multi grain tims u pb monazite age determinations consideration of the closure temperature for pb diffusion in monazite and the metamorphic temperatures experienced by these samples suggests diffusive pb loss did not play a significant part in generating this age dispersal the la mc icpms study indicates that an older component 100 ma older than the tims ages contributed to the age dispersal in three of the four samples in all the samples however chemical analyses identified that the majority of monazites examined exhibited significant intra crystalline zoning in y content the la mc icpms analysis of one sample that was constrained to zones of distinct y content indicates that these zones are of distinct age we suggest that monazite grown before the appearance of garnet and during garnet breakdown is relatively rich in y whereas monazite grown after garnet is relatively poor in y a combination of these chemical data with textural observations suggests that once monazite had entered the mineral assemblage it grew or recrystallised episodically throughout the prograde and retrograde paths of the metamorphic event this behaviour contributes to and in one of the samples controls the observed age dispersal this recognition allows the generation of pressure temperature time points by combining textural and chemical information of monazite with in situ age determinations and pressure temperature information from garnet thus the episodic growth of compositionally distinct monazite throughout a metamorphic event provides the geochronologist with a very valuable chronological tool