geothermobarometry of basaltic glasses from the tamu massif shatsky rise oceanic plateau 1 we present the results of a petrological study of core samples from tamu massif site u1347 recovered during the shatsky rise integrated ocean drilling program iodp expedition 324 the basaltic glasses from site u1347 are evolved tholeiitic basalts containing 5 2 6 8 wt mgo and are principally located within the compositional field of mid ocean ridge basalts morbs but they have systematically higher feo lower al2o3 sio2 and na2o concentrations and the cao al2o3 ratios are among the highest known for morbs in this sense glasses from site u1347 more closely resemble basaltic magmas from the ontong java plateau ojp although they still have lower sio2 concentrations in contrast to morb and similar to ojp our fractionation corrected values of na2o and cao al2o3 indicate more than 20 of partial melting of the mantle during the generation of the parental magmas of tamu massif the water contents in the glasses determined by midinfrared fourier transform infrared ftir spectroscopy are morb like and vary between 0 18 and 0 6 wt h2o the calculated pressure p temperature t conditions at which the natural glasses represent cotectic olivine plagioclase clinopyroxene compositions range from 0 1 to 240 mpa and 1100 to 1150 c reflecting magma storage at shallow depth the variation of the glass compositions and the modeled p t conditions in correlation with the relative ages indicate that there were at least two different magmatic cycles characterized by variations in eruptive styles massive flows or pillow lavas chemical compositions volatile contents and preeruptive p t conditions each magmatic cycle represents the progressive differentiation in course of polybaric crystallization after the injection of a more primitive magma batch magma crystallization and eruption episodes are followed by magmatic inactivity reflected in the core sequence by a sedimentary layer our data for tamu massif demonstrate that similar to ontong java ocean plateau the crystallization beneath shatsky rise occurs at different crustal levels

double flood basalts and plume head separation at the 660 kilometer discontinuity several of the world s flood basalt provinces display two distinct times of major eruptions separated by between 20 million and 90 million years these double flood basalts may occur because a starting mantle plume head can separate from its trailing conduit upon passing the interface between the upper mantle and the lower mantle this detached plume head eventually triggers the first flood basalt event the remaining conduit forms a new plume head which causes the second eruptive event the second plume head is predicted to arrive at the lithosphere at least 10 million years after the first plume head in general agreement with observations regarding double flood basalts

reconciling heterogeneity in crystal zoning data an application of shared characteristic diagrams at chaos crags lassen volcanic center california isotope trace element and textural crystal zoning patterns record heterogeneity in magmatic systems not resolved by whole rock analyses these zoning data are used to infer crystal residence times magma mixing and other magmatic processes in many magmatic systems we present the shared characteristic diagram scd as an organizational framework for crystal zoning data that compares information from different phases and chemical tracers in a common framework an example from chaos crags in the cascade arc produces three main results 1 anorthite zoning profiles in plagioclase have fewer shared characteristics in mafic inclusions than in the host rhyodacite 2 single crystal 87sr 86sr data from previous studies tepley et al 1999 are consistent with more shared history between crystals than in anorthite profiles this difference reflects a more homogeneous distribution of 87sr 86sr than the intensive parameters controlling plagioclase composition 3 the chaos crags system exhibits a layer of heterogeneity in crystal populations that is not represented in whole rock analyses that indicate only simple binary mixing the inconsistency between 87sr 86sr and anorthite zoning data highlights decoupling between compositionally controlled and temperature water controlled zoning in plagioclase from chaos crags

partition coefficients for calcic plagioclase implications for archean anorthosites by the use of a multiple aliquot technique combined with statistical calculations to overcome effects of alteration and contamination we have determined partition coefficients d s for rare earth elements rees between natural high ca plagioclase megacrysts and their basaltic matrices some of the basalts that we investigated are shown experimentally to crystallize only high ca plagioclase over approximately a 20 30 c temperature interval below the liquidus the ree d s agree well with experimentally determined values and predict equilibrium melts for archean anorthosites that agree well with coeval basaltic flows and dikes furthermore the d s appear to be valid for both tholeiitic and alkali basalts over a range of mg numbers 34 58 and ree concentrations la from 3 50 ppm similarly calculated d s for co sc cr rb sr cs ba hf ta and th also predict equilibrium melts for anorthosites that agree reasonably well with coeval basaltic flows and dikes the apparent values for co sc and ta seem good to better than 50 whereas the standard deviations for rb and th are equal to their means making the d s of questionable value the others are useful probably to within a factor of 2 experimental studies of the d for total fe as feot indicate a value of about 04 at an oxygen fugacity slightly below that of the qfm buffer a by product of the feot experiments was the experimental d s for mgo tio2 and k2o which could be compared with the d s from natural assemblages from the d s that were determined we suggest that plagioclase megacrysts in the bad vermilion lake anorthosite were in equilibrium with melts having the composition of tholeiitic basalts at an oxygen fugacity slightly below the qfm buffer the predicted melts have an feot content of about 13 k2o of about 15 tio2 of about 1 3 a chondrite normalized ree pattern that is nearly flat at 10 to 20 chondrites with a slight depletion of lrees other incompatible trace elements at 10 to 20 chondrites and cr and co at 0 01 to 0 1 chondrites this range of compositions is essentially identical to the tholeiitic flows and dikes in archean greenstone belts we therefore suggest that the moderately fe rich tholeiites that are hosts to plagioclase megacrysts in greenstone belts form the parental melts for megacrysts which make up the bad vermilion lake anorthositic complex and probably other similar archean anorthositic complexes

meteorite accumulations on mars abstract we have modeled single body meteoroid atmospheric entry speeds at mars and the effect of drag and ablation and identify a narrow range of small masses 10 50 g that should impact mars at survivable speeds the rate of oxidative weathering is much lower than that on earth so this small flux of meteorites could give rise to significant accumulations ca 5 10 2 to 5 10 5 meteorites greater than 10 g in mass per square kilometer given that extremely large numbers of meteorites may be present on mars future sample return missions should consider the real possibility that they may recover meteoritic material due to the low weathering rate meteorites may survive on the surface of mars for more than 10 9 years preserving a record of the temporal variability of the meteoroid flux and the compositional evolution of the meteoroid complex intact carbonaceous chondrites may also preserve organic compounds from degradation by ultraviolet radiation terrestrial meteorites may be present but would probably be sterile

evidence for a widespread mafic cover sequence and its implications for continental growth in the northeastern superior province abstract archean greenstone belts of the northeastern superior province nesp were emplaced over a 160 ma period 2 88 2 72 ga spanning a major episode of crustal reworking in which early tonalite trondhjemite plutonism evolved to dominant granite granodiorite and pyroxene bearing felsic plutonism the numerous greenstone belts that crop up across the craton contain lavas belonging to three mafic volcanic suites 1 mg tholeiites that have chemical compositions typical of many archean basalts with 4 10 wt mgo 9 15 wt fe2o3t 0 4 1 2 wt tio2 and la sm ratios between 1 and 3 2 fe tholeiites that have similar mgo contents and la sm ratios but markedly higher fe2o3t 11 20 wt tio2 1 0 2 6 wt and gd yb ratios that may reflect derivation from a distinct garnet bearing mantle source 3 light rare earth element lree enriched rocks that have the chemical characteristics typical of calc alkaline mafic magmas with higher sio2 al2o3 and la sm ratios but lower fe2o3t and tio2 than the tholeiitic suites at a given mgo content the presence of unconformities within single greenstone belts numerous inheritance ages in volcanic rocks replicating those of older volcanic plutonic assemblages and the recognition of widespread geographically separate yet coeval 2 78 ga extrusive assemblages containing the distinctive fe tholeiites do not support a plate tectonic model for a large portion of the nesp the correlations in composition and ages of greenstone belts are more consistent with a model in which they represent the remnants of an extensive autochthonous mafic cover sequence nd isotopic evidence for the presence of evolved crust in some syn volcanic felsic plutons and volcaniclastic rocks imply that this mafic cover sequence was erupted onto an older granitoid crust the amalgamation of two isotopically distinct terranes at ca 2 76 2 74 ga created a proto cratonic mass that consisted of a composite tonalite trondhjemite greenstone crust underplating by mafic mantle melts and widespread insulation after 2 75 ga increased temperatures sufficiently to produce extensive melting of this crust to generate pyroxene bearing felsic rocks and granodiorite to granite partial melts the isotopically enriched character of mantle derived magmas after 2 75 ga may reflect more extensive contamination by a felsic crust affected by widespread partial melting furthermore a decrease of nb th ratios in the lree enriched mafic rocks younger than 2 75 ga reflects a change in the nature of the crustal contaminant from tonalite trondhjemite prior to 2 75 ga to granite granodiorite afterwards

a new mesozoic isochron chart of the northwestern pacific ocean paleomagnetic and tectonic implications a new mesozoic isochron chart of the northwestern pacific ocean has been completed by utilizing all the currently available data from 357 cruises our chart provides the first whole view of the mesozoic magnetic anomaly lineations in the northwestern pacific ocean and yields essential information for understanding the problems of the mesozoic magnetostratigraphic time scale and the evolutional history of the pacific plate the mesozoic magnetostratigraphic time scale must be recalibrated using not only the hawaiian lineation set but also other mesozoic lineation sets the lack of lineation m0 in the lineation sets other than the hawaiian lineation set indicates that a reorganization of the ridges except the pacific farallon ridge occurred between chrons m1 and m0 nearly 120 ma the eruption rate of the shatsky hotspot seems to be comparable to that of the reunion hotspot at their initial stage the growth of the pacific plate began in a small triangular region at about 190 ma

hydrogeochemical cycling and chemical denudation in the fort river watershed central massachusetts an appraisal of mass balance studies the fort river watershed in central massachusetts receives precipitation with a composition similar to that in hubbard brook new hampshire yet the average stream water chemistry is substantially different showing higher ph and tds this is largely a function of bedrock and surficial geology and chemical differences among small streams within the fort river watershed are apparently controlled by the composition and thickness of the prevailing surficial cover the surficial deposits determine groundwater and surface water flow paths thereby affecting the resultant contact time with mineral matter and the chemistry of the runoff despite the rural setting over 95 of the annual sodium and chloride in the streams comes from road salt after correcting for this factor cation denudation rates are about equal to those at hubbard brook however silica removal is occurring at a rate more than 30 greater in the fort river when climatic conditions in hubbard brook and fort river are normalized weathering rates appear consistently higher in the fort river reflecting differences in weathering processes i e cation exchange and silicate breakdown and hydrogeology because of uncertainties in mechanisms of cation removal from watersheds the silica denudation rate may be a better index of weathering intensity

implications for magmatic processes at ontong java plateau from volatile and major element contents of cretaceous basalt glasses 1 major elements cl co2 and h2o were determined in unaltered tholeiitic basalt glasses from drilling program sites 803d and 807c on ontong java plateau ojp and sites 462a in nauru basin nb and 802a in east mariana basin emb glasses are moderately evolved mg 53 60 with low na2o indicating they formed by large extents of melting extent of melting is less for glasses from ojp than from emb requiring faster or more focused mantle upwelling or a longer period of activity for ojp glasses within each hole define 1 3 different compositional types each compositional type is made up of many glass bounded flow units whose chemistry is identical within analytical uncertainty suggesting that each compositional type formed during a single eruptive episode with multiple magma surges the lack of diversity within each type also suggests that the magmatic system was large and well buffered major element chemistry also requires that significant shallow crystallization occurred during plateau formation and limits the amount of deep crystallization that might be responsible for the thick crust of the plateau chlorine contents are constant within each compositional type and are 580 ppm in type a and 850 ppm in types c g from hole 807c and 360 ppm in glasses from hole 803d glasses from 802a and 462a have 240 ppm and 1975 ppm cl respectively cl k ratios range from 0 2 to 2 33 well above mid ocean ridge basalt morb mantle values 0 07 suggesting that most liquids assimilated hydrothermally altered material as they ascended and crystallized high cl k ratios also suggest that abundant hydrothermal activity may have accompanied plateau formation low dissolved co2 i e co32 contents in one ojp compositional type 54 ppm in 807c type a are similar to those on shallow sections of the mid ocean ridge and are consistent with a maximum depth of eruption of 1320 250 m in contrast to the greater eruption depths inferred from fossils in the overlying sediments our proposed eruption depth falls in the morb field on a plot of depth versus na8 0 supporting a ridge or near ridge origin the shallow depth estimate allows for more postformation subsidence and diminishes the importance but does noteliminate the need for additional processes such as prolonged underplating to account for ojp s shallow depth higher co2 in other glasses including types c g from hole 807c suggests that some liquids were oversaturated with co2 when emplaced and therefore did not travel far from their point of eruption h2o contents are similar to morb and range from 0 13 wt for nb to 0 25 wt 807c types c g to 0 49 wt 807c type a ratios of h2o to rare earth elements ree are slightly higher than most morb and are similar to those from northern mid atlantic ridge mar which has distinctively high h2o h2o ce constant in depleted through enriched morb ranges from 200 to 400 compared to 220 380 for northern mar glasses and 150 250 for morb elsewhere and 500 for arc related glasses the slightly higher h2o contents in the ojp mantle source could have contributed very little to the extensive melting that built the plateau so a substantial temperature anomaly is still required

crystal size distribution and composition of garnets in eclogites from the dabie orogen central china crystal size and spatial distributions of minerals in metamorphic rocks provide insight into their nucleation growth environment and the metamorphic evolution of their host rocks episodic nucleation and growth histories for garnets in eclogites from the dabie orogen are revealed by variations in crystal size geochemical zoning and mineralogy of inclusions in garnets the studied garnets show pseudo lognormal crystal size distributions csds prograde chemical zoning patterns indexed by mineral inclusions and are mainly distributed at random constant growth rate for each episode is proposed based on the mineralogy of inclusions in garnets and the chemical zoning patterns the csd shapes were evaluated in terms of a size dependent proportionate growth model and a thermally accelerated diffusion controlled model but neither is consistent with the geochemical data and the concordant occurrence of mineral inclusions in garnet initial increasing nucleation rate followed by a subsequent medial stage of nearly constant growth and finally declining nucleation rate is inferred from the csd data this study suggests that linking chemical analysis with textural analysis is crucial to avoid misleading interpretation solely through csd shapes of minerals in metamorphic rocks

ontong java and kerguelen plateaux cretaceous icelands together with iceland the two giant oceanic plateaux ontong java in the western pacific and kerguelen broken ridge in the indian ocean are accumulations of mafic igneous rock which were not formed by normal seafloor spreading we compare published geochronological crustal structure and subsidence results with tectonic fabric highlighted in new satellite derived free air gravity data from the three igneous provinces and conclude that existing evidence weighs lightly against the ontong java and kerguelen plateaux originating at a seafloor spreading centre

the geology of darwin crater western tasmania australia abstract darwin glass is a siliceous impact glass found in a 400 km 2 strewn field near mt darwin western tasmania australia it has been dated by ar ar methods at 816 7 ka a 1 2 km diameter circular depression named darwin crater 42 18 39 s 145 39 41 e is the assumed source crater for the glass darwin crater is situated in a remote rain forested valley developed within siluro devonian quartzite and slate eldon group earlier geophysical investigations demonstrated that the structure is an almost circular bowl shaped sediment filled basin this paper provides the first detailed description of the geology of darwin crater the centre of the crater has been penetrated by two drill cores the deeper to a maximum depth of 230 m the drill cores intersected fine grained lacustrine sediments 60 m thick overlying poorly sorted coarser crater fill deposits the pre lacustrine crater fill stratigraphy comprises an uppermost polymict breccia 40 m thick of angular quartz and country rock which contains very rare 1 fresh glass fragments crater fill facies a beneath the polymict breccia facies the drill core intersected monomict sandy breccias of angular quartz crater fill facies b and a complicated package of deformed slate clasts crater fill facies c quartz grains in the crater fill samples contain abundant irregular fractures in some of the most deformed quartz grains sub planar fractures define zones of alternating extinction that superficially resemble twinning kinked micas are also present while the deformation observed in clasts of the crater fill facies is far greater than in rocks cropping out around the crater no diagnostic shock indicators such as planar deformation features pdf s in quartz were observed if the crater is of impact origin as seems likely due to the close association with darwin glass this is another example of a simple crater where diagnostic shock indicators appear to be absent preventing confirmation of an impact origin by petrographic analysis of crater fill samples alone

the genesis of refractory melts in the formation of oceanic crust refractory primary liquids arising in various oceanic plate tectonic settings are characterized by high mgo sio2 ca na low tio2 and generally low incompatible element abundances relative to primary liquids parental to morb we propose that the former melts segregate from upper mantle peridotite which has earlier been depleted by extraction of picritic melts which were parental to morb a compositional range in the second stage melts is expected depending on the extent of previous depletion of the peridotite the temperature and pressure of melt segregation and the possible influence of volatile phases c h o present during melting

partitioning of strontium between plagioclase and melt a comment abstract the origin of the partition coefficient d for sr in plagioclase is ascribed by blundy and wood 1991 mainly to the chemistry of the crystal rather than that of the liquid however a major data set used to support this conclusion also demonstrates an important correlation of d with the augite content of the liquid one truth cannot be used to deny another from the same data set moreover it appears that d has a limiting value of 1 0 in the system an ab confirming the importance of liquid composition the data base of natural magmas said to justify the conclusions of the paper omits the important troctolitic and noritic low augite varieties for which the augite effect was specifically claimed and therefore cannot be used to discount the effect the data base is skewed toward silicic igneous rocks for which a high value of d is experimentally known the attempt to rationalize the data from the kiglapait intrusion by supposing the escape of low sr material ignores the evidence of the chilled margin which matches the sr budget of the cumulates and neglects to mention that the vented mass would have to be equal to that of the entire intrusion to account for the small variation in sr observed much work remains to be done but it is clear that the liquid plays a much more important role in this partitioning effect than allowed by the authors

phreatomagmatic eruptions on the ontong java plateau chemical and isotopic relationship to ontong java plateau basalts the compositions of glass clasts in volcaniclastic rocks recovered from drilling at site 1184 on the eastern salient of the ontong java plateau ojp are investigated using microbeam analytical methods for major minor and trace elements these data are com pared with whole rock elemental and isotopic data for bulk tuff samples and with data from basalts on the high plateau of the ojp three subunits of hole 1184a contain blocky glass clasts thought to represent the juvenile magmatic component of the phreatomagmatic eruptions that generated the volcaniclastic rocks the glass clasts have unaltered centres and are all basaltic low k tholeiites with flat chondrite normalized rare earth element ree patterns their elemental compositions are very similar to the kwaimbaita type and kroenke type basalts sampled on the high plateau each subunit has a distinct glass com position and there is no intermixing of glass compositions between subunits indicating that each subunit is the result of one eruptive phase and that the volcaniclastic sequence has not experienced reworking the relative heterogeneity preserved at site 1184 contrasts with the uniformity of compositions recovered from individual sites on the high plateau and suggests that the eastern salient of the ojp had a different type of magma plumbing system our data support the hypothesis that the voluminous subaerially erupted volcani clastic rocks at site 1184 belong to the same magmatic event as the construction of the main ontong java plateau thus the ojp would have been responsible for volatile fluxes into the atmosphere in addition to chemical fluxes into the oceans and these factors may have influenced the contemporaneous oceanic anoxic event

experimental study of a kiglapait marginal rock and implications for trace element partitioning in layered intrusions abstract experiments on a chilled marginal rock from the kiglapait intrusion labrador have been performed in order to constrain the partitioning behaviour of major and trace elements during formation of kiglapait lower zone lz cumulates at 0 1 mpa and f o 2 close to fmq the liquidus is bracketed between 1225 and 1212 c and the only liquidus phases are plagioclase an 73 74 and olivine fo 82 85 in contrast lz troctolites contain fo 67 5 olivine and an 63 4 plagioclase plagioclase melt partition coefficients d s for li ti rb sr y zr ba la and eu determined by ion microprobe analysis of run products are similar to those for other basaltic systems but differ systematically from apparent d s calculated from bulk analyses of lz plagioclases and modelled liquid compositions obtained by summation the discrepancies in d s and phase compositions are inconsistent with diffusion controlled boundary layer growth crystallisation of trapped intercumulus liquid is quantitatively plausible however a the volume of liquid required to reconcile experimental and model d s 20 1 is larger than that estimated from observed proportions of intercumulus phases 11 2 and b this mechanism alone cannot reduce x an in lz plagioclases due to very slow al si interdiffusion the discrepancy between experiment and model is best resolved if the parental melt to lz cumulates was more evolved higher fe mg na ca ree and alkalis lower sr than the summed bulk composition in accord with a recent revision of the kiglapait fe mg based on olivine compositions

geochemistry of darwin glass and target rocks from darwin crater tasmania australia darwin glass formed about 800 000 years ago in western tasmania australia target rocks at darwin crater are quartzites and slates siluro devonian eldon group analyses show 2 groups of glass average group 1 is composed of sio2 85 al2o3 7 3 tio2 0 05 feo 2 2 mgo 0 9 and k2o 1 8 group 2 has lower average sio2 81 1 and higher average al2o3 8 2 group 2 is enriched in feo 1 5 mgo 1 3 and ni co and cr average ni 416 ppm co 31 ppm and cr 162 ppm in group 2 are beyond the range of sedimentary rocks glass and target rocks have concordant ree patterns la lu 5 910 eu eu 0 55 0 65 and overlapping trace element abundances 87sr 86sr ratios for the glasses 0 80778 0 81605 fall in the range 0 76481 1 1212 defined by the rock samples e nd results range from 13 57 to 15 86 nd model ages range from 1 2 1 9 ga chur and the glasses 1 2 1 5 ga fall within the range defined by the target samples the 87sr 86sr versus 87rb 86sr regression age 411 42 ma and initial ratio 0 725 0 016 and the initial 43nd 144nd ratio 0 51153 0 00011 and regression age 451 140 ma indicate that the glasses have an inherited isotopic signal from the target rocks at darwin crater mixing models using target rock compositions successfully model the glass for all elements except feo mgo ni co and cr in group 2 mixing models using terrestrial ultramafic rocks fail to match the glass compositions and these enrichments may be related to the projectile

kiglapait geochemistry iii potassium and rubidium abstract the regular geometry and completeness of the kiglapait intrusion permit its bulk composition to be obtained by summation and the composition of successive liquids to be obtained by subtraction the summations for k and rb give 1806 and 1 08 ppm yielding r frsol k rb 1670 for the intrusion taken as equal to the parent magma r increases slightly from this initial value to 2000 at the end of crystallization where mgo approaches zero in the rocks k and rb are therefore closely coherent and their distribution coefficients can differ only by a small amount in the kiglapait system apparent feldspar liquid distribution coefficients d f l can be estimated from detailed plots of feldspar and liquid compositions against f l the kiglapait data imply that these coefficients are linear 1 1 functions of plagioclase composition within experimental error having values given by d k f l 1 42 x an d rb f l 1 13 x an with minimum values of 0 75 and 0 49 respectively the ratio r f r l lies in the range of 1 53 0 03 for the plagioclase composition range x an 0 34 to 0 67 showing that high r rocks such as anorthosite crystallized from high r liquids the apparent feldspar distribution coefficients are much closer to 1 0 than common literature values they can be reduced by assuming that the cumulate pile was continuously recharged by the circulating magma until an advanced stage of differentiation was reached and assuming that alkalies were exchanged to the feldspars from the magma when such an aquifer recharge model is calibrated using olivine liquid equilibria as a time marker for the liquid the inferred minimum equilibrium values of the distribution coefficients are d k f l 0 42 d rb f l 0 25 at the base of the intrusion their variation is given by d k f l 1 66 1 88x an d rb f l 1 17 1 41x an the equilibrium values are considered to be appropriate for deducing liquid compositions in plutonic bodies where alkali exchange can be shown or inferred to have been inhibited such as in small intrusions the apparent values are considered to be appropriate even though they may be artificial for large intrusions similar to the kiglapait the bulk k and rb concentrations in the kiglapait intrusion are consistent with a plagioclase rich abyssal tholeiite magma clinopyroxene and olivine fractionation in the mantle may contribute to the production of such high r magmas

zoned orthopyroxenes in the ni co sulfide ore bearing xiarihamu mafic ultramafic intrusion in northern tibetan plateau china implications for multiple magma replenishments abstract the xiarihamu mafic ultramafic intrusion is situated in the east kunlun orogenic belt e kob northern tibetan plateau china with ni co sulfide mineralization mainly in orthopyroxenite and olivine orthopyroxenite whole rock and mineral compositions show cyclic variations in drill hole intersections through the xiarihamu mafic ultramafic intrusion microbeam x ray fluorescence xrf mapping shows reverse zoning cr poor core cr rich rim and oscillatory zoning cr poor core cr rich mantle and cr poor rim in orthopyroxene of olivine orthopyroxenite and orthopyroxenite zoned orthopyroxenes are euhedral or subhedral and there are relatively sharp interfaces between zones with distinct cr contents crystal size distribution csd curves of orthopyroxenes in olivine orthopyroxenite show concave upward curvature at size larger than 3 0 mm and larger orthopyroxenes commonly display zoning implying a secondary recrystallization and grain growth of larger orthopyroxenes quantitative analyses show that cr and enstatite contents of cores are relatively lower but incompatible element e g ti zr ga and sr contents of cores are higher than rims in reverse zoned orthopyroxenes and chemical profiles of unzoned orthopyroxenes resemble those of rims but different from those of cores in reverse zoned orthopyroxenes chemical profiles of orthopyroxenes indicate that cr zoning is not due to the change in cr partitioning behavior between orthopyroxene and silicate melt which shows significant temperature and redox dependence textural feature and crystal size distribution of orthopyroxenes suggest the formation of cr rich zones attests to the multi stage growth in the process of magma replenishment rather than a reactive liquid flow model or in situ trapped liquid overgrowth orthopyroxene zoning together with compositional variation and intrusive relationship between olivine orthopyroxenite and orthopyroxenite imply that the xiarihamu mafic ultramafic intrusion was formed by multiple magma replenishments with magma varying roughly from a more evolved to a more primitive composition

volatiles in submarine basaltic glasses from the northern kerguelen plateau odp site 1140 implications for source region compositions magmatic processes and plateau subsidence submarine pillow basalts 34 ma recovered from the northern introduction kerguelen plateau at odp site 1140 contain abundant unaltered the kerguelen plateau and broken ridge formed mostly glass providing the first opportunity to measure the volatile contents during the cretaceous as a single giant oceanic plateau of tholeiitic basaltic magmas related to the kerguelen mantle plume that is interpreted to represent voluminous magmatism the glasses have la sm and nb zr ratios that vary from values associated with emplacement of a mantle plume head similar to southeast indian ridge seir morb unit 1 to below young indian ocean lithosphere duncan slightly more enriched unit 6 to values transitional between storey 1992 weis et al 1992 during ocean drilling seir morb and basaltic magmas formed by melting of the program odp leg 183 igneous basement rock and kerguelen plume units 2 and 3 volatile contents for glasses in sediment cores were obtained from five sites on the units 1 and 6 are similar to depleted mid ocean ridge basalt kerguelen plateau and two on broken ridge fig 1 the morb values 0 25 0 27 wt h2o 1240 1450 ppm s results combined with subsequent radiometric dating 42 54 ppm cl in contrast h2o contents are higher for the demonstrate that from south to north the age of the enriched glasses unit 2 0 44 wt h2o unit 3 0 69 wt uppermost crust decreases from 120 110 ma in the as are s 1500 ppm and cl 146 206 ppm cl k ratios southern kerguelen plateau to 110 to 95 ma in the for all glasses are relatively low 0 03 0 04 indicating that central kerguelen plateau broken ridge and elan bank assimilation of hydrothermally altered material did not occur during to 35 ma in the northern kerguelen plateau coffin shallow level crystallization h2o ce for the enriched glasses et al 2000 pringle duncan 2000 duncan 2002 at units 2 and 3 is significantly lower than pacific and south six of seven basement sites as well as at four sites drilled atlantic morb values suggesting that low h2o ce may be an on earlier odp cruises subaerially erupted basalt flows inherent characteristic of the kerguelen plume source vapor saturation were recovered indicating that the growth rate of the pressures calculated using the h2o and co2 contents of the glasses kerguelen large igneous province lip was sufficient to indicate that 1700 m of subsidence has occurred on this part of form a subaerial landmass however a sequence of the plateau since eruption of the basalts at 34 ma subsidence submarine erupted pillow basalt flows of 90 m thickness estimates for site 1140 and other odp drill sites indicate that the was drilled at site 1140 on the northern kerguelen various parts of the kerguelen plateau subsided at a rate comparable plateau coffin et al 2000 with that for normal indian ocean lithosphere the site 1140 submarine glasses provide the first

the effects of feo on the system cmas at low pressure and implications for basalt crystallization processes the common occurrence of olivine clinopyroxene and plagioclase in natural basalts may suggest that crystallization of these phases exerts important controls on the evolution of natural basalts at low pressure in order to understand the effects of such an assemblage on the evolution of basalt an experimental study of the divariant assemblage 1 an cpx ol in the system cmas feo was undertaken at 1 bar and under very reducing conditions experiments have been performed along three isothernal sections detailed electron microprobe data have been collected on all the coexisting phases combining these data with available data in the system cmas the compositions of all the coexisting phases have been described as functions of temperature and cao content in the melt by applying a multiple linear regression method this allows a quantitative characterization of the divariant assemblage 1 an epx ol in the system cmas feo from 1275 c to 1160 c with liquid compositions ranging from mg 1 to mg 0 28 knowing the composition temperature relationships the basic t x configuration of the assemblage 1 an cpx ol has been analysed and mass balance calculations have been performed to examine the feo effect on different crystallization processes addition of feo to the system cmas transforms the thermal divide in the assemblage 1 an cpx ol to a thermal ridge and shifts the spine of the thermal ridge towards sio2 poor compositions with decreasing temperature this indicates that tholeiitic basalts can be relatively silica poor and evolve towards slightly more silica poor compositions with increasing feo content pigeonite replaces ortheonstatite as a crystallizing phase along the silica rich boundary of the assemblage 1 an cpx ol in some iron and silica rich composition olivine possibly terminates its crystallization or even starts resorption prior to pigeonite precipitation this suppresses silica enrichment in the melt crystallization paths of the assemblage 1 an cpx ol are determined by the detailed t x relations of the thermal ridge with the melt evolving away from the spine the liquid evolution trend depends strongly on the initial compositions a tholeiitic liquid can follow a moderate silica enrichment path at the same very reducing condition of there is a high modal proportion of olivine a fenner mechanism therefore is at work at the same place as a bowen mechanism

structure and dynamics of the laacher see magma chamber eifel germany from major and trace element zoning in sanidine a cathodoluminescence and electron microprobe study microtextures and zoning patterns in sanidine phenocrysts from the phonolitic laacher see tephra germany were investigated in order to constrain processes occurring in the magma chamber before eruption the laacher see tephra unit is chemically zoned and has been inferred to represent the product of eruption of an inverted layered magma chamber samples from various levels in the deposit were investigated we used a combination of textural studies optical microscopy and back scattered electron bse imaging electron microprobe emp analysis of major minor and trace elements ca na k al si ba sr fe and ti and element mapping the samples studied contain two feldspar phases and the ternary composition of the sanidine thus constrains the temperature of crystallization whereas its trace element content reflects the melt composition the large diversity in textures found in the sanidine crystals can be classified into three types composite c type pseudooscillatory po type and resorbed patchy r type trace elementpoor lamellar composite alkali feldspars c type are found in samples inferred to represent the top and the middle part of the magma chamber they grew as composite crystals from the melt at temperatures as low as 650 c in a highly differentiated and volatilerich boundary layer at the magma chamber roof or wall pseudooscillatory zoning with resorption surfaces po type is found in sanidinesfromsamplesinferredtorepresentthemiddlepartandthebase of the magma chamber repeated large an variations 1 4 mol reflect temperature variations of 100 300 ca ssociated with changes in water content variations of minor and trace elements ba sr and ti in sanidine decoupled from the pseudo oscillations of the major elements reflect chemical changes in the melt and are damped by chemicaldiffusioninthemelt bothmajorandminorelementvariations inpo typecrystalsareinterpretedastheprogressiveinfluenceofamore mafic hotter melt this may be partly explained by the settling of crystals through the thermal and chemical gradient existing in the magma chamber however the additional role of magma recharge may be required to explain the large temperature variations resorbed patchy zoned crystals r type found mainly in samples corresponding to the middle part of the magma chamber reflect early growth in a differentiated boundary layer followed by resorption and overgrowthinthemainmagmabody manyofthelaacherseesanidine crystals did not crystallize for the most part in the melt in which they were erupted in the presence of preserved major and trace element zonation in the magma this observation indicates crystal dispersion within a layered magma chamber without large scale mixing and overturn

trace element and textural evidence favoring lunar not terrestrial origin of the mini granite in apollo sample 14321 abstract the 14321 lunar granite 14321g has recently been reinterpreted bellucci et al 2019 as a piece of the hadean earth impact transported to the moon in principle samples of such derivation may afford important insights into the nature of earth s hadean crust we have tested the terrestrial provenance hypothesis by comparing trace element data from 14321g versus other lunar evolved rocks and a large data base for terrestrial granites volatile trace metals zn ga and ge are depleted in 14321g below the terrestrial granite ranges and relative to the terrestrial granite averages by factors of 27 2 0 and 18 respectively evidence from shocked chondrites martian meteorites and impact shock studies in general indicates that such major depletions are unlikely to develop without near complete shock melting which clearly did not occur in the mostly still crystalline 14321g moreover other aspects of compositional disparity between 14321g and terrestrial granites involve exclusively refractory trace elements compared to terrestrial granites of similarly high ba content 14321 is enriched in ta by a factor of 10 and the few terrestrial granites that are as ta rich as 14321 have 10 times lower ba the refractory element ratio lu sm is also close to 10 times higher in 14321g than in terrestrial granites of similarly high ba content other highly evolved lunar rocks felsites strongly resemble 14321g in all these respects we conclude that 14321g is probably of wholly lunar derivation this finding stands in contradiction to a recent inference from ti in quartz modeling bellucci et al 2019 that 14321g crystallized at a pressure of 0 69 gpa the geodynamically limited moon was presumably never capable of forming or burying such a highly granitic material 100 km below the base of its crust nor of excavating material from such a depth to the surface

sr nd and pb isotopes in proterozoic intrusives astride the grenville front in labrador implications for crustal contamination and basement mapping abstract we report sr nd and pb isotopic compositions of mid proterozoic anorthosites and related rocks 1 45 1 65 ga and of younger olivine diabase dikes 1 4 ga from two complexes on either side of the grenville front in labrador anorthositic or diabasic samples from the mealy mountains grenville province and harp lake nain churchill provinces complexes have very similar major minor and trace element compositions but distinctly different isotopic signatures all mealy mountains samples have isr 0 7025 0 7033 end 0 6 to 5 6 and pb isotopic compositions consistent with derivation from a mantle source depleted with respect to nd sm and rb sr pb isotopic compositions for the mealy mountains samples are slightly more radiogenic than model mantle compositions all harp lake samples have isr 0 7032 0 7066 end 0 3 to 4 4 and variable but generally unradiogenic 207pb 204pb and 206pb 204pb compared to model mantle suggesting mixing between a mantle derived component and a u depleted crustal contaminant crustal contaminants are probably a variety of archean high grade quartzofeldspathic gneisses with low u pb ratios and include a component that must be isotopically similar to the early archean 3 6 ga uivak gneisses of labrador or the amitsoq gneisses of west greenland this would imply that the ancient gneiss complex of coastal labrador and greenland is larger than indicated by present surface exposure and may extend in the subsurface as far west as the labrador trough if harp lake and mealy mountains samples were subjected to the same degree of contamination as suggested by their chemical similarities then the mealy contaminants must be much younger probably early or middle proterozoic in age the labrador segment of the grenville front therefore appears to coincide with the southern margin of the archean north atlantic craton and may represent a pre mid proterozoic suture

reequilibration of olivine with trapped liquid in the duluth complex minnesota a 525 m long drill core ddh 221 through the partridge river intrusion in northeastern minnesota consists of mesocumulates and or orthocumulates of troctolite olivine gabbro and olivine gabbronorite the cumulus olivine whose composition fo 31 to fo 71 is a function of the amount of intercumulus liquid followed an equilibrium crystallization path with this liquid estimates of the primary magmatic compositions of the olivine are fo 57 to fo 79 none of the olivine in the drill core samples has retained an original cumulus composition i e one that was in equilibrium with the parental magma the plagioclase is strongly zoned and the cumulus cores an 59 to an 73 are thought to record crystallization from the parental magma

rummaging through earth s attic for remains of ancient life abstract we explore the likelihood that early remains of earth mars and venus have been preserved on the moon in high enough concentrations to motivate a search mission during the late heavy bombardment the inner planets experienced frequent large impacts material ejected by these impacts near the escape velocity would have had the potential to land and be preserved on the surface of the moon such ejecta could yield information on the geochemical and biological state of early earth mars and venus to determine whether the moon has preserved enough ejecta to justify a search mission we calculate the amount of terran material incident on the moon over its history by considering the distribution of ejecta launched from the earth by large impacts in addition we make analogous estimates for mars and venus we find for a well mixed regolith that the median surface abundance of terran material is roughly 7 ppm corresponding to a mass of approximately 20 000 kg of terran material over a 10 10 square km area over the same area the amount of material transferred from venus is 1 30 kg and material from mars as much as 180 kg given that the amount of terran material is substantial we estimate the fraction of this material surviving impact with intact geochemical and biological tracers

redox effect on the partitioning of nickel in olivine abstract the fractionation of nickel by olivine in the lower zone of the kiglapait intrusion in company with the olivine compositions compared to estimated liquid compositions places stringent limits on the value of the olivine liquid partition coefficient for ni estimated at 4 0 0 8 at the base of the lower zone data from a strong ni mgo correlation in mauna loa picrites also require a low value of d estimated at 5 8 0 4 these values are much lower than usually considered normal for mafic magmas and the effect is ascribed to the low oxygen fugacity of the magmas estimated independently for the kiglapait case to be near the wustite magnetite buffer at this redox state a significant amount in this case about half of the ni in the melt is dissolved as ni 0 which inflates the liquid concentration without entering the olivine because the analyzed values reflect only total ni rather than the species the partition coefficient decreases with reduction as shown by recent experimental studies the mauna loa data imply a reduced condition for that magma as well knowledge of the redox regime governing the partition coefficient is vitally important in modelling fractional crystallization and in discussing early planetary history conversely knowledge of the ni fractionation in a magma series can specify the redox regime of the magma as at mauna loa

sedimentary environments and mechanisms of organic matter enrichment in the mesoproterozoic hongshuizhuang formation of northern china abstract the mesoproterozoic hongshuizhuang formation in jixian northern china is a hydrocarbon source unit containing abundant organic matter we investigated the mechanisms controlling this organic matter accumulation by analyzing the sedimentology and geochemistry of the qinghe section in the kuancheng region of northern china trace element geochemistry suggests that organic matter accumulation was controlled primarily by marine productivity which was the main determinant of redox conditions elevated marine productivity and consequent anoxic sulfidic bottom water conditions were coincident with accumulation of the organic rich toc 1 0 lower part of the hongshuizhuang formation deposition of the organic lean upper hongshuizhuang formation appears to have been coeval with diminished productivity and a transition to oxic suboxic redox conditions enhanced organic matter accumulation in the lower hongshuizhuang formation was promoted by a warm humid paleoclimate and submarine hydrothermal activity average rb sr ratios 3 42 and negative carbon isotope excursion reflect a warm climate likely caused by the release of volcanogenic co 2 warm conditions would have promoted continental weathering and increased the flux of nutrients into the oceans enhancing marine productivity an increased supply of nutrients and enhanced marine productivity would have depleted oxygen in the bottom water environment and favored the proliferation of sulfate reducing bacteria leading to anoxic sulfidic conditions the relative stability of 13 c carb values suggests that organic matter enrichment in the hongshuizhuang formation reflects changes in surface water productivity and redox conditions caused by climate induced sea level fluctuations shale normalized rare earth element ree distributions show a depletion in light rees and enrichment in heavy rees positive eu anomalies and mean y ho and ba sr ratios of 33 2 and 9 91 respectively suggesting that deposition of the hangshuizhuang formation was accompanied by submarine hydrothermal activity

impact origin for the greater ontong java plateau abstract the 120 ma ontong java plateau and neighboring contemporaneous nauru east mariana and probably pigafetta basin flood basalts in the western equatorial pacific ocean comprise the earth s largest flood basalt province geophysical geochemical and geodynamic evidence from the province are difficult to reconcile with mantle plume models absence of an obvious hotspot source or track minor crustal uplift associated with emplacement minor total subsidence compared with normal oceanic crust or other oceanic plateaus and submarine ridges high degrees of melting at shallow upper mantle depths low water contents of basalts enrichment of platinum group elements in basalts and a 300 km deep seismically slow mantle root are more consistent with the consequences of an impacting bolide an object 20 km in diameter impacting relatively young 20 myr pacific lithosphere and penetrating into the uppermost asthenosphere would have initiated massive decompression melting in the upper mantle and may have resulted in emplacement of the greater ontong java plateau

magma mixing recharge and eruption histories recorded in plagioclase phenocrysts from el chichon volcano mexico operative throughout the 200 ky history of the el chichon magma consistent core to rim decreases of sr sr ratios and coincident system increases in sr concentrations in plagioclase phenocrysts of varying size 1 cm to 2 mm are reported from samples of the 1982 and pre 1982 200 ka eruptions of el chichon volcano maximum sr sr ratios of 0 7054 significantly higher than the wholerock isotopic ratios 0 7040 0 7045 are found in the cores

experimental study of liquid evolution in an fe rich layered mafic intrusion constraints of fe ti oxide precipitation on the t f o 2 and t ϱ paths of tholeiitic magmas the newark island layered intrusion a composite intrusion displaying a similar fractionation sequence to the skaergaard has both dikes which preserved liquids fed into the intrusion and chilled pillows of liquids resident in the chamber this study reports experimentally determined one atmosphere liquid lines of descent of these compositions as a function of oxygen fugacity which varies from qfm quartz fayalite magnetite to 0 5 log10 units above iw iron wustite these experiments reveal a strong oxygen fugacity dependence on the order of appearance and relative abundances of the fe ti oxide minerals titanomagnetite saturates prior to ilmenite at qfm but the order is reversed at lower oxygen fugacities in the layered series of the newark island intrusion ilmenite arrives shortly before titanomagnetite and the titanomagnetite ilmenite ratio decreases monotonically after the cumulus appearance of titanomagnetite comparison of the crystallization sequence in the intrusion with that of the experiments requires that the oxygen fugacity in the intrusion increased relative to qfm before titanomagnetite saturation and decreased afterward but always remained between the qfm and iw buffers similar trends in the modes of the fe ti oxides ilmenite and titanomagnetite in the skaergaard kiglapait and somerset dam intrusions along with fe2o3 feo ratios in morbs suggest that such a temperature oxygen fugacity path may be typical of tholeiitic magma differentiation calculations of the temperature density paths of the experimental liquids indicate that at all possible oxygen fugacities the density must have decreased abruptly after fe ti oxide saturation accordingly liquids replenishing the intrusion after fe ti oxide saturation should pond at the bottom of the chamber quenching against older cumulates field observation at the newark island intrusion confirm this prediction the similarities in the fractionation paths of several other layered intrusions to that of the newark island intrusion suggest that the density of the liquids in these intrusions also decreased after fe ti oxide saturation experiments on a suggested initial skaergaard liquid are consistent with this model

origin of strongly reversed rims on plagioclase in cumulates abstract narrow reversed rims on plagioclase are ubiquitous in troctolites and olivine gabbros of the kiglapait intrusion and may be a common feature of all such cumulates the rims occur at plag plag plag ol and less strongly at plag aug grain boundaries they are optically obvious at an and can reach an 32 mol or more in parallel k na drops sharply although ubiquitous from sample to sample the reversed rims are only locally present at grain boundaries even for the same pair of crystals in contact they are prominent in linear networks suggesting the last trace of intercumulus liquid a subsolidus origin is ruled out by the absence of reactants at plag plag and plag ol boundaries and by the local rather than pervasive development of rims the rims are required to grow from intercumulus liquid in which the partition of an component between crystals and liquid increases with the trapped augite component of the liquid calculations from published experimental data show that an 30 can easily be achieved by such a process it is also probable that the trapped liquid is part of an an rich boundary layer generated by solute rejection during adcumulus growth the ability of the rims to sustain steep k na gradients despite a long subsolidus cooling history proves that the k na exchange rate is vanishingly small over a geologic time scale in an rich feldspar suggesting that at low k content the potassium is site bound to the tetrahedral al si distribution reversed rims therefore provide important information on diffusion limits as well as on the late stage solidification history of plagioclase rich cumulates moreover they demonstrate that plagioclase geothermometry cannot be divorced from effects of liquid composition and structure as monitored for example by augite content

the effect of pressure on dsr plag melt and dcr opx melt implications for anorthosite petrogenesis the crystal liquid partition coefficients for sr and cr dsr and dcr have been determined from electron microprobe analyses of plagioclase liquid and orthopyroxene liquid pairs produced in melting experiments run at pressures from 1 bar to 27 kbar on two compositions relevant to anorthosite petrogenesis one is a primitive jotunite hypersthene monzodiorite tj the other is a sample of an anorthositic dyke 500b results indicate that dsr plag liq remains nearly constant with increasing pressure tj 1 7 to 2 6 500b 0 9 to 1 4 this modest variation apparently results from the combined and opposing effects of crystal chemistry and pressure dsr increases with the albite content of plagioclase which itself increases with pressure along a composition s liquidus so pressure must have an intrinsic negative effect the two models for dsr j blundy b wood geochim cosmochim acta 55 1991 193 209 i bindeman a davis m drake geochim cosmochim acta 62 1998 1175 1193 that take into account the strong correlation between dsr and plagioclase composition overestimate dsr at high pressure whereas the two models that ignore plagioclase composition s morse geochim cosmochim acta 56 1992 1735 1738 r nielsen comput geosci 18 1992 773 788 underestimate it moreover since none of these models takes into account any pressure effect the discrepancies between predicted and observed dsr increase with pressure for all models the new results also show that dcr opx liq increases significantly with pressure dcr 2 at 1 atm and 14 2 at 10 kbar these new data confirm earlier less precise determinations of dcr that were used to infer a high pressure origin for al and cr rich orthopyroxene megacrysts the calculated sr and cr concentrations of liquids in equilibrium at 10 kbar with plagioclase and orthopyroxene megacrysts from anorthosite massifs sr 370 to 610 ppm and cr 20 to 130 ppm are in the range of what is observed in high al gabbros and primitive jotunites the inferred parent magmas of massive anorthosites fl 2000 published by elsevier science b v all rights reserved

subsidence and growth of pacific cretaceous plateaus abstract the ontong java manihiki and shatsky oceanic plateaus are among the earth s largest igneous provinces and are commonly believed to have erupted rapidly during the surfacing of giant heads of initiating mantle plumes we investigate this hypothesis by using sediment descriptions of deep sea drilling project dsdp and ocean drilling program odp drill cores to constrain plateau subsidence histories which reflect mantle thermal and crustal accretionary processes we find that total plateau subsidence is comparable to that expected of normal seafloor but less than predictions of thermal models of hotspot affected lithosphere if crustal emplacement was rapid then uncertainties in paleo water depths allow for the anomalous subsidence predicted for plumes with only moderate temperature anomalies and volumes comparable to the sources of modern day hotspots such as hawaii and iceland rapid emplacement over a plume head of high temperature and volume however is difficult to reconcile with the subsidence reconstructions an alternative possibility that reconciles low subsidence over a high temperature high volume plume source is a scenario in which plateau subsidence is the superposition of 1 subsidence due to the cooling of the plume source and 2 uplift due to prolonged crustal growth in the form of magmatic underplating this prolonged crustal growth and uplift scenario may explain the low and thus submarine relief during plume initiation the late stage eruptions found on ontong java 90 ma and manihiki 70 ma a large portion of the high seismic velocity lower crust and the widespread normal faults observed throughout and along the margins of the three plateaus such late stage underplating may have occurred continuously or in discrete stages over 30 m y and implies lower magmatic fluxes than previously estimated

modeling the ries steinheim impact event and the formation of the moldavite strewn field using detailed geological petrographic geochemical and geographical constraints we have performed numerical modeling studies that relate the steinheim crater apparent diameter da 3 8 km the ries crater da 24 km in southern germany and the moldavite tektite strewn field in bohemia and moravia czech republic lusatia east germany and lower austria the moldavite strewn field extends from 200 to 450 km from the center of the ries to the east northeast forming a fan with an angle of 57 an oblique impact of a binary asteroid from a west southwest direction appears to explain the locations of the craters and the formation and distribution of the moldavites the impactor must have been a binary asteroid with two widely separated components some 1 5 and 0 15 km in diameter respectively we carried out a series of three dimensional hydrocode simulations of a ries type impact the results confirm previous results suggesting that impacts around 30 50 from the horizontal are the most favorable angles for near surface melting and consequently for the formation of tektites finally modeling of the motion of impact produced tektite particles through the atmosphere produces in the downrange direction a narrow angle distribution of the moldavites tektites in a fan like field with an angle of 75 an additional result of modeling the motion of melt inside and outside the crater is the preferred flow of melt from the main melt zone of the crystalline basement downrange towards the east northeast rim this explains perfectly the occurrence of coherent impact melt bodies some tens of meters in size in a restricted zone of the downrange rim of the ries crater the origin of these melt bodies which represent chemically a mixture of crystalline basement rocks similar to the main melt mass contained as melt particles 0 5 m in size in the suevite do not occur at any other portion of the ries crater rim and remained enigmatic until now although the calculated distribution of moldavites still deviates to some degree from the known distribution our results represent an important step toward a better understanding of the origin and distribution of the high velocity surface melts and the low velocity deep seated melt resulting from an oblique impact on a stratified target

paleo elevation and subsidence of 145ma shatsky rise inferred from co2 and h2o in fresh volcanic glass abstract shatsky rise a large mesozoic oceanic plateau in the northwest pacific consists of three massifs tamu ori and shirshov that formed near a mid ocean ridge triple junction published depth estimates imply that shatsky rise has not subsided normally like typical oceanic lithosphere we estimated paleo eruption depths of shatsky rise massifs on the basis of dissolved co2 and h2o in volcanic glass and descriptions of cores recovered from five sites of integrated ocean drilling program expedition 324 initial maximum elevations of shatsky rise are estimated to be 2500 3500 m above the surrounding seafloor and the ensuing subsidence of shatsky rise is estimated to be 2600 3400 m we did not observe the anomalously low subsidence that has been reported for both shatsky rise and the ontong java plateau although we could not resolve whether shatsky rise originated from a hot mantle plume or non plume fusible mantle uplift and subsidence histories of shatsky rise for the both cases are constrained based on the subsidence trend from the center of tamu massif 2600 m toward the flank of ori massif 3400 m in the case of a hot mantle plume origin shatsky rise may have formed on young 5 ma pre existing oceanic crust with a total crustal thickness of 20 km for this scenario the center of shatsky rise is subsequently uplifted by later prolonged crustal growth forming the observed 30 km thickness crust for a non plume origin shatsky rise may have formed at the spreading ridge center as initially thick crust 30 km thickness with later reduced subsidence caused by the emplacement of a buoyant mass perhaps a refractory mantle residuum beneath the center of shatsky rise

physical distribution trends in darwin glass darwin glass formed by impact melting probably during excavation of the 1 2 km diameter darwin crater tasmania australia the glass was ejected up to 20 km from the source crater and forms a strewn field of 400 km 2 there is at least 11 250 m 3 of glass in the strewn field and relative to the size of the crater this is the most abundant ejected impact glass on earth the glass population can be subdivided on the basis of shape 74 irregular 20 ropy 0 5 spheroid 6 droplet and 0 7 elongate and color 53 dark green 31 light green 11 black and 5 white the white glasses contain up to 92 wt sio2 and are formed from melting of quartzite black glasses contain a minimum of 76 wt sio2 and formed from melting of shale systematic variations in the proportion of glasses falling into each of the color and shape classes relative to distance from the crater show 1 a decrease in glass abundance away from the crater 2 the largest fragments of glass are found closest to the crater 3 small fragments 2 g dominate finds close to the crater 4 the proportion of white glass is greatest closest to the crater 5 the proportion of black glass increases with distance from the crater and 6 the proportion of splashform glasses increases with distance from the crater these distribution trends can only be explained by the molten glass having been ballistically ejected from darwin crater during impact and are related to 1 the depth of excavation from the target rock stratigraphy and or 2 viscosity contrasts between the high and low sio2 melt the high abundance and wide distribution of ejected melt is attributed to a volatile charged target stratigraphy produced by surface swamps that are indicated by the paleoclimate record

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

an unmetasomatized source for the malaitan alnoite solomon islands petrogenesis involving zone refining megacryst fractionation and assimilation of oceanic lithosphere the ma tan alnijite contains a rich and varied megacryst suite of unprecedented compositional range we have undertaken trace element and isotope modeling in order to formulate a petrogenetic scheme which links the host alniiite to its entrained megacrysts this requires that a proto alntiite magma is the product of zone refining initiated by diapiric upwelling where the initial melt passes through 200 times its volume of mantle isotopic evidence indicates the source of the proto alniiite contains a time integrated lree depleted signature 143nd 44nd 0 51274 impingement upon the rigid lithosphere halts or dramatically slows the upward progress of the mantle diapir at this point the magma cools and megacryst fractionation begins with augites crystallizingjirst followed by subcalcic diopsides and finally phlogopites garnet probably crystallizes over the entire range of clinopyroxene fractionation estimated proportions of fractionating phases are 30 augite 24 5 subcalcic diopside 27 garnet 12 9 phlogopite 5 bronzite 0 5 ilmenite and 0 1 zircon as this proto alnoite magma crystallizes it assimilates a subducted component of seawater altered basalt which underplates the ontong java plateau this is witnessed in the isotopic composition of the megacrysts and alnoite

paleo sedimentary environment in relation to enrichment of organic matter of early cambrian black rocks of niutitang formation from xiangxi area china abstract early cambrian organic rich black rocks are extensively distributed in the southern china in this study we have discussed the relation of paleo sedimentary environments with enrichment of organic matter based on toc data we divided the niutitang formation into three parts upper middle and lower the amount of total organic carbon in the lower 1 55 wt and the upper part 1 35 wt of niutitang formation is significantly smaller than the middle part 8 0 wt which suggest initial transgression and regression stages of the sea level respectively the middle part from both sections longbizui and sancha contains higher toc content which is a clue of intense transgression stage of sea level with high bio productivity kerogen type index kti using different macerals specify the organic matter in these black rock series is mainly type i with a minor amount of type ii1 moreover these black rocks were deposited in weak to moderately restricted hydrographic conditions the heterogenic mineral composition was also observed in these black rocks including quartz clay gypsum pyrite barite dolomite and plagioclase quartz content in the middle part is relatively higher than the upper and the lower part displays a strong positive relation with toc which suggests the main source of quartz during deposition of the middle part was biogenic quartz during early cambrian period due to extension between the yangtze and the cathaysian plate the hydrothermal fluids rich in uranium vanadium molybdenum zinc barium etc from the deeper part of the earth crust and entered the ocean basin through extensional remnant fissures and cracks and due to upwelling phenomena entered to the shelf area these nutrient rich deep crustal fluids at the surface of the sea enhanced the evolution and breeding of planktons and other marine life meanwhile it upsurges the bio productivity additionally it creates bottom water hypoxia which is favourable for the preservation of organic matter in the sedimentary rocks the main factors responsible for the enrichment of organic matter in these early cambrian black rock series of niutitang formation were a hydrographic restriction hydrothermal activities and paleo redox conditions respectively

impact origin of the chesapeake bay structure and the source of the north american tektites seismic profiles drill core samples and gravity data suggest that a complex impact crater 35 5 million years old and 90 kilometers in diameter is buried beneath the lower chesapeake bay the breccia that fills the structure contains evidence of shock metamorphism including impact melt breccias and multiple sets of planar deformation features shock lamellae in quartz and feldspar the age of the crater and the composition of some breccia clasts are consistent with the chesapeake bay impact structure being the source of the north american tektites

laser fusion argon 40 argon 39 ages of darwin impact glass three samples of darwin glass an impact glass found in tasmania australia at the edge of the australasian tektite strewn field were dated using the 40ar 39ar single grain laser fusion technique yielding isochron ages of 796 815 ka with an overall weighted mean of 816 7 ka these data are statistically indistinguishable from those recently reported for the australasian tektites from southeast asia and australia 761 816 ka with a mean weighted age of 803 3 ka however considering the compositional and textural differences and the disparity from the presumed impact crater area for australasian tektites darwin glass is more likely to have resulted from a distinct impact during the same period of time

boundary layer crystallization in a basaltic magma chamber evidence from rishiri volcano northern japan the evolution of basaltic magma by mushy boundary layer processes introduction in a magma chamber is documented for an alkali basalt kutsugata the evolution of magma chambers is of major petrologic lava from rishiri volcano northern japan on the basis of zoning interest and has been studied extensively experimental patterns of plagioclase phenocrysts and their spatial distribution in and theoretical studies that have investigated the cooling the lava plagioclase phenocrysts with complex zoning patterns can of magma chambers have demonstrated that a magma be divided into four types type 1 is characterized by an extremely chamber solidifies through formation of a mushy boundan rich core an71 90 which is commonly corroded and filled with ary layer composed of crystals and interstitial melt along sodic plagioclase type 2 has an ab rich core surrounded by a calcic the chamber walls e g brandeis jaupart 1986 turner mantle characteristic of partial dissolution type 3 is characterized by et al 1986 marsh 1988 tait jaupart 1992 layered igneous complexes e g morse 1969 shirley 1987 an ab rich core that is commonly surrounded by a reversely zoned mcbirney 1996 provide useful information on how slightly calcic mantle type 4 has an ab rich core without a calcic mafic magma chambers evolve and consolidate but they mantle the an rich cores of the type 1 plagioclase are too calcic do not offer much insight into the instantaneous state of to have crystallized from a liquid represented by any whole rock a chamber because those intrusions integrate processes composition at the estimated temperatures of the kutsugata magma that occurred over long solidification times mcbirney system the an rich cores are inferred to have been formed in a noyes 1979 tait 1988 volcanic products such as mushy boundary layer along the wall of a magma chamber where lava flows and tephra deposits can sample the inthe magma was relatively cool and rich in water because of significant stantaneous state of a magma chamber there are a few olivine fractionation and possibly because of addition of water studies along this line of approach tait 1988 de silva expelled from the chilled margin and or groundwater from the 1989 nakada et al 1994 these studies focused on surrounding crust the ab rich cores of types 2 4 plagioclase crystal aggregates in volcanic products and concluded phenocrysts are interpreted to have crystallized in the main magma that the crystal formation in a mushy boundary layer body of the reservoir the types 2 and 3 ab rich cores were brought plays a dominant role in magmatic evolution in a magma to the mushy layer by convection the temporal and spatial variations reservoir however these studies were mostly on silicic of zoning patterns of plagioclase phenocrysts in basaltic lava flows magmas and there are significant differences in physical give useful information on the evolution of mafic magma chambers and chemical features between silicic and mafic magma chambers in this paper the magmatic evolution of an alkali basalt kutsugata lava from rishiri volcano northern japan is studied the kutsugata lava is divided into three lava flows on the basis of whole rock chemical

hydrogeochemistry of the new jersey coastal plain 2 transport and deposition of iron aluminum dissolved organic matter and selected trace elements in stream ground and estuary water the geochemical controls on the transport and deposition of iron organic carbon and certain trace elements have been examined in bogs streams groundwater and estuaries of the new jersey coastal plain surface waters are unusually dilute total dissolved solids 25 ppm and acidic ph 4 5 and contain relatively high concentrations of organic c and fe liquid chromatographic analyses show that from 10 to 70 of total dissolved fe 0 2 m fe oxyhydroxide or oxyhydroxides admixed with insoluble organic material the proportion of organically complexed fe present varies seasonally with the doc content of the water these stream waters are near saturation with respect to amorphous fe oh 3 groundwaters are uniformly undersaturated with respect to amorphous fe oh3 both stream and groundwaters are near saturation with respect to halloysite slightly supersaturated with respect to gibbsite and highly supersaturated with respect to kaolinite bog iron deposits are common in streams and swamps where fe precipitation is catalyzed by iron oxidizing bacteria fe and al precipitate rapidly within both estuaries with ionic strength rather than increased ph exerting the prime control on estuarine deposition estuarine floccules contain very little or no organic matter suggesting that inorganic fe and al oxyhydroxides are the primary precipitates the high contents of dissolved 0 2 m fe and al suggest that both are either organically complexed or in the form of small 0 2 m oxyhydroxide colloids in the estuaries

organic geochemistry of impactites from the haughton impact structure devon island nunavut canada organic matter in impactites from the 24 km wide and 39 ma old haughton impact structure canadian high arctic is a mixture of fossil and modern biological components the fossil component represents a conventional oil that was generated from lower palaeozoic marine source material before impact and permeates bedrock dolomites biomarker maturity parameters record the thermal effect of the mid tertiary impact maturity influenced sterane rearranged hopanoid and triaromatic steroid ratios all increase towards the centre of the impact structure where thermal alteration was greatest the heating was probably dominated by an impact related hydrothermal system as such systems last long enough for kinetically based thermal alteration to occur kinetically related biomarker data suggest that the hydrothermal heating lasted for c 5000 years biomarkers are also preserved in dolomite clasts within impact melt breccia and indicate strong thermal alteration modern biological contamination of the rocks is responsible for the superposition of two geochemical signatures which could be cyanobacteria non marine algae or higher plant matter onto the fossil component but they can be recognized and distinguished the data show that the impact structure system holds a record of both the pre impact organic signature and the thermal signature of the impact and thereby indicates that organic geochemistry is a valuable tool in documenting the response of rocks to impacts

isotopic evidence for the origin of the manihiki and ontong java oceanic plateaus abstract pb nd and sr isotopic results for lavas of the cretaceous ontong java and manihiki oceanic plateaus fall well within the modern day oceanic island or hotspot field the data provide no evidence of old continental basements but indicate a major involvement of kerguelen type or em i like mantle in the sources of both plateaus which appear to have probably been formed at least in part by hotspots however the presently active hotspots that pacific plate reconstructions suggest might have been possible plateau sources lack kerguelen type isotopic compositions either these hotspots did not participate in the formation of the two plateaus or if they did kerguelen type material must have been volumetrically much more important early in their existence two hypotheses for the origins of these plateaus which involve hotspot sources are consistent with the sparse available geochemical geochronological and geophysical data the first holds that the plateaus formed cataclysmically in association with surfacing plume heads the second posits a relatively steady but robust hotspot at or near a ridge crest and requires a much longer period of formation a near ridge origin appears to be indicated by evidence that most of the pacific plateaus were built largely on relatively young ocean crust however we suggest that a near ridge origin is also compatible with the plume head concept in that plume heads appear very likely to become associated with spreading axes through their influence on rift propagation which should be substantially greater than for ordinary hotspots in either case the lack of hotspot tracks seamount chains attached to the two plateaus would be a consequence of ridge migration or rift propagation in a near ridge setting

trace elements in anorthite megacrysts from the kurile island arc a window to across arc geochemical variations in magma compositions abstract anorthite megacrysts from twelve volcanic centers of the kurile island arc were analyzed by the ion microprobe for concentrations of li be b f mg p cl k ti fe co rb sr y zr nb cs ba la ce pr nd sm eu and pb these 1 2 cm megacrysts are mainly found as early phenocrysts in basalts but are also present in andesites rhyolites and hybrid rocks from almost every studied volcanic center both subaerial and submarine electron and ion microprobe studies show that the cores of these megacrysts are homogeneous and unzoned whereas rims often result from overgrowth of sodium richer plagioclase in equilibrium with its host silica richer melt the cores of these megacrysts can be used to see back through fractional crystallization and magma mixing and serve as a window into an earlier basaltic stage of magmatic evolution petrological observations and numerical crystallization modeling indicate that highly anorthitic plagioclase is the first or second after olivine liquidus phase in high al basalts regardless of varying k2o contents across the arc given the narrow compositional range of anorthite megacrysts the across arc chemical variations are well displayed by direct comparison of trace element concentrations in the megacrysts across the arc the concentration of k in megacrysts increases linearly by a factor of 11 ba 13 sr eu 4 be ti p 3 li 2 ree 5 2 whereas concentrations of pb b and halogens and their ratios to hfse either remain constant or decrease with deepening of the benioff zone from 110 to 220 km we used ion microprobe derived plagioclase basalt partition coefficients to convert trace element concentrations in megacrysts to parental magmatic values the reconstructed concentrations of several key trace elements and their correlation with benioff zone depth are consistent with whole rock basalt data but all give systematically more primitive compositions therefore anorthite megacrysts are helpful for retrieving the chemistry of parental basalts which have subsequently suffered variable differentiation and mixing they can be used to assess delicate variations in primary basaltic magma chemistry as a function of benioff zone depth we also report new results for sr nd and pb isotopes for anorthite bearing rocks and other rocks from the same volcanoes across arc zoning with respect to trace element concentrations ratios and isotopic values is largely linear and requires superposition of several petrogenetic processes trace element transfer by fluids variation in degree of partial melting and progressive change of the melting source

crystallization and compositional convection in a porous medium with application to layered igneous intrusions growing crystals can provide a local source of buoyancy by depleting melt of certain chemical components and vigorous convective motions in the fluid can result we report a quantitative experimental study in which saturated aqueous solutions of cuso4 and na2so4 in porous media of either glass balls or cuso4 5h2o crystals were crystallized by cooling from below the crystals growing in the pore space released light chemically depleted solution which had the potential to convect out of the porous medium and be replaced by additional saturated solution from above we explore the physical and chemical effects of compositional convection during the complete solidification of the interstitial solution by varying the permeability of the porous medium the cooling rate and the initial composition of the solution this type of convection can form adcumulate rocks by enabling continuous circulation of melt from the main magma reservoir through the pores of a cumulus pile adcumulus growth can occur by this mechanism as long as the convective velocity in the porous medium is greater than the velocity of the solidification front we scale the experimental results to magmatic conditions and infer that this process should occur commonly in layered igneous intrusions when our porous media had a small permeability compositional convection enabled the adcumulate growth of a completely solid contact between melt and cumulate trapping of dynamically unstable melt beneath this impermeable layer of crystals also occurred in these experiments and may be important geologically small shallowly emplaced intrusions and the cumulate zones at the base of komatiites are probably cooled too rapidly for significant intercumulus convection to occur

velocity depth ambiguity and the seismic structure of large igneous provinces a case study from the ontong java plateau summary the seismic structure of large igneous provinces provides unique constraints on the nature of their parental mantle allowing us to investigate past mantle dynamics from present crustal structure to exploit this crust mantle connection however it is prerequisite to quantify the uncertainty of a crustal velocity model as it could suffer from considerable velocity depth ambiguity in this contribution a practical strategy is suggested to estimate the model uncertainty by explicitly exploring the degree of velocity depth ambiguity in the model space in addition wide angle seismic data collected over the ontong java plateau are revisited to provide a worked example of the new approach my analysis indicates that the crustal structure of this gigantic plateau is difficult to reconcile with the melting of a pyrolitic mantle pointing to the possibility of large scale compositional heterogeneity in the convecting mantle

crustal forensics in arc magmas abstract the geochemical characteristics of continental crust are present in nearly all arc magmas these characteristics may reflect a specific source process such as fluid fluxing common to both arc magmas and the continental crust and or may reflect the incorporation of continental crust into arc magmas either at source via subducted sediment or via contamination during differentiation resolving the relative mass contributions of juvenile mantle derived material versus that derived from pre existing crust of the upper plate and providing these estimates on an element by element basis is important because 1 we want to constrain crustal growth rates 2 we want to quantitatively track element cycling at convergent margins and 3 we want to determine the origin of economically important elements and compounds traditional geochemical approaches for determining the contributions of various components to arc magmas are particularly successful when applied on a comparative basis studies of suites from multiple magmatic systems along arcs for which differentiation effects can be individually constrained can be used to extrapolate to potential source compositions in the lesser antilles arc for example differentiation trends from individual volcanoes are consistent with open system evolution however such trends do not project back to a common primitive magma composition suggesting that differentiation modifies magmas that were derived from distinct mantle sources we propose that such approaches should now be complemented by petrographically constrained mineral scale isotope and trace element analysis to unravel the contributing components to arc magmas this innovative approach can 1 better constrain true end member compositions by returning wider ranges in geochemical compositions among constituent minerals than is found in whole rocks 2 better determine magmatic evolution processes from core rim isotopic or trace element profiles from the phases contained in magmas and 3 constrain rates of differentiation by applying diffusion controlled timescales to element profiles an example from nguaruhoe volcano new zealand underscores the importance of such a microsampling approach showing that mineral isotopic compositions encompass wide ranges that whole rock isotopic compositions are consequently simply element weighted averages of the heterogeneous crystal cargo and that open system evolution is proved by core rim variations in sr isotope ratios nguaruhoe is just one of many systems examined through microanalytical approaches the overwhelming conclusion of these studies is that crystal cargoes are not truly phenocrystic but are inherited from various sources the implication of this realization is that the interpretation of whole rock isotopic data including the currently popular u series needs careful evaluation in the context of petrographic observations

meteoric water basalt interactions ii a field study in n e iceland the compositions of rain snow melt spring and geothermal waters from the rift zone of n e iceland can be explained by seaspray addition chemical fractionation at the seawater air interface burning of fossil fuel farming activities purification by partial melting of snow and ice dissolution of basalts and buffering by alteration minerals the dissolution of the rocks appears to be incongruent during solute acquisition spring compositions move through the stability fields of kaolinite and smectite to the laumontite and illite fields all but four of the springs are undersaturated with respect to calcite silica concentrations are compatible with the solubility of basaltic glass the reactions reflected in the spring waters appear to have taken place sealed off from atmospheric co2 after initial saturation the geothermal waters which are recharged by the spring waters are depleted in mg and ca but enriched in carbon and sulfur with respect to dissolution of primary rocks expressions are derived relating dissolution rates of rocks age of groundwaters physical properties of groundwaters and mass transfer the characteristic rock particle radii in the cold water aquifers range from 0 2 to 2 cm and the characteristic crack openings are of the order 0 04 to 0 4 cm using laboratory studies on the icelandic lavas as a guide the residence times of the cold waters in the aquifers can be estimated at 60 days to 4 years the average active surface area of the aquifers enclosing 1000 g of spring water is of the order of 0 6 to 6 m2 and these 1000 g of water have reacted with 0 1 to 1 g of basaltic rocks the same mass of thermal water has interacted with 100 to 300 g of unaltered rocks

enigmatic tubular features in impact glass we describe the fi rst putative microbial trace fossils hosted in meteorite impact glass we conducted optical and scanning electron microscopy energy dispersive x ray spectroscopy and fourier transform infrared spectroscopy on postimpact tubular features hosted in impact glasses from the ries impact structure germany the morphologies of the tubules are inconsistent with known mineralogical crystallization mechanisms and combined with evidence of organic molecules suggest that these tubules cannot be formed through purely abiotic processes the simplest and most consistent explanation of the data is that biological activity played a role in the formation of the tubular textures in the ries glasses likely during postimpact hydrothermal activity as impact glass is a ubiquitous substrate on rocky bodies throughout the solar system and likely common on the early earth the preservation of biological activity in impact glass has signifi cant astrobiological implications for life on early earth as well as for the search for life on other planets

anomalous uplift and subsidence of the ontong java plateau inferred from co2 contents of submarine basaltic glasses the ontong java plateau in the western pacific is anomalous compared to other oceanic large igneous provinces in that it appears to have never formed a large subaerial plateau paleoeruption depths at 122 ma estimated from dissolved h2o and co2 in submarine basaltic glass pillow rims vary from 1100 m below sea level mbsl on the central part of the plateau to 2200 3000 mbsl on the northeastern edge our results suggest maximum initial uplift for the plateau of 2500 3600 m above the surrounding seafloor and 1500 400 m of postemplacement subsidence since 122 ma our estimates of uplift and subsidence for the plateau are significantly less than predictions from thermal models of oceanic lithosphere and thus our results are inconsistent with formation of the plateau by a high temperature mantle plume two controversial possibilities to explain the anomalous uplift and subsidence are that the plateau 1 formed as a result of a giant bolide impact or 2 formed from a mantle plume but has a lower crust of dense garnet granulite and or eclogite neither of these possibilities is fully consistent with all available geological geophysical and geochemical data the origin of the largest magmatic event on earth in the past 200 m y thus remains an enigma

biomass preservation in impact melt ejecta meteorites can have played a role in the delivery of the building blocks of life to earth only if organic compounds are able to survive the high pressures and temperatures of an impact event although experimental impact studies have reported the survival of organic compounds there are uncertainties in scaling experimental conditions to those of a meteorite impact on earth and organic matter has not been found in highly shocked impact materials in a natural setting impact glass linked to the 1 2 km diameter darwin crater in western tasmania is strewn over an area exceeding 400 km2 and is thought to have been ejected by a meteorite impact about 800 kyr ago into terrain consisting of rainforest and swamp here we use pyrolysis gas chromatography mass spectrometry to show that biomarkers representative of plant species in the local ecosystem including cellulose lignin aliphatic biopolymer and protein remnants survived the darwin impact we find that inside the impact glass the organic components are trapped in porous carbon spheres we propose that the organic material was captured within impact melt and preserved when the melt quenched to glass preventing organic decomposition since the impact we suggest that organic material can survive capture and transport in products of extreme impact processing at least for a darwin sized impact event

the preservation of fossil biomarkers during meteorite impact events experimental evidence from biomarker rich projectiles and target rocks a devonian siltstone from orkney scotland shows survival of biomarkers in high velocity impact experiments the biomarkers were detected in ejecta fragments from experiments involving normal incidence of steel projectiles at 5 6 km s 1 and in projectile fragments from impact experiments into sand and water at 2 5 km s 1 the associated peak shock pressures were calculated to be in the range of 110 147 gpa for impacts of the steel projectiles into the siltstone target and hydrocode simulations are used to show the variation of peak pressure with depth in the target and throughout the finite volume projectiles thermally sensitive biomarker ratios including ratios of hopanoids and steranes and the methylphenanthrene ratio showed an increase in thermal maturity in the ejecta and especially the projectile fragments measurement of absolute concentrations of selected biomarkers indicates that changes in biomarker ratios reflect synthesis of new material rather than selective destruction their presence in ejecta and projectile fragments suggests that fossil biomarkers may survive hypervelocity impacts and that experiments using biomarker rich rock have high potential for testing survival of organic matter in a range of impact scenarios

hydrogeochemistry of the new jersey coastal plain abstract the new jersey coastal plain pine barrens is an extensive region where inorganic interactions between the soils and shallow groundwater are at a minimum this study compares the geochemistry of precipitation and surface water to analyze transport mechanisms of major elements and to evaluate hydrogeochemical balances in this relatively unusual system precipitation composition is controlled by proximity to the ocean and seasonal variability of storm movements total dissolved solids in precipitation are high 11 5 ppm but decrease inland na and cl are more abundant in winter precipitation whereas k so 2 4 ca 2 and no 3 exhibit greater concentrations during the summer months na and cl are derived from marine aerosols so 2 4 is a product of so 2 pollution in the atmosphere other ions have significant contributions from continental aerosols dissolved solids in rivers are low 20 ppm compared with average river water and ph is acidic 4 5 both reflect paucity of mineral water reactions in the uppermost aquifer cohansey formation quartz sand and gravel however regional variations in river water geochemistry suggest cross aquifer migration of deep groundwaters into the mullica river basin mass balances confirm that river water composition is controlled principally by precipitation however ca 2 po 3 4 and so 2 4 are depleted in river waters probably as a result of removal by biota or cedar swamp processes mg 2 shows an excess in the rivers suggesting a contribution from deep groundwater the poor chemical buffering in the waters of this region render them highly susceptible to contamination

mafic pegmatites intruding oceanic plateau gabbros and ultramafic cumulates from bolivar colombia evidence for a wet mantle plume

petrologic and geologic variations along the southern explorer ridge northeast pacific ocean mid ocean ridge basalts morb from the well defined southern explorer ridge segment ser in the northeast pacific ocean are moderately to strongly enriched in incompatible elements enriched morb were erupted at the highest and widest part of the segment culmination where the magma supply may be the greatest and also at the northern and southern ends of the ser variations in basalts incompatible element enrichment occur over short distances and suggest that the underlying mantle is heterogeneous on a small scale the variations also preclude the existence of a long lived well mixed magma chamber beneath the robust culmination instead magma chambers are probably temporally and spatially isolated as evidenced by the presence of highly differentiated lavas less enriched transitional morb were erupted along the central part of the ser 11 27 km south of the culmination and were supplied to the ridge separately from a less enriched pan of the mantle a more continuous magma chamber cannot be ruled out for this section on geochemical grounds all of the morb from the ser have undergone significant amounts of fractional crystallization unlike certain segments of the east pacific rise the most evolved morb were erupted near the culmination of the ridge segment aphyric lavas have been recovered only from the vicinity of the culmination while phyric lavas have erupted along the entire length of the ser there is no correlation between composition and total crystal abundances despite the requirement of multiple parental magmas most of the lavas from the culmination and the distal ends of the ridge fall on a common liquid line of descent indicating that they formed at similar depths and extents of partial melting the transitional morb from the central part of the ridge have probably formed by lesser extents of partial melting and separated from their mantle source at greater depths based on abundances of na and moderately incompatible elements such as sm and zr enriched high melt fraction lavas at the magma starved southern end of the ser closely resemble lavas from the culmination either the southernmost lavas have flowed laterally within the crust from near the culmination or there is another melting anomaly that supplies the southern end of the ser if the latter case is true correspondence between ridge morphology and mantle thermal state is poor

colloid mobilization in two atlantic coastal plain aquifers field studies the geochemical mechanisms leading to the mobilization of colloids in groundwater were investigated in the pine barrens of new jersey and in rural central delaware by sampling pairs of wells screened in oxic and anoxic groundwaters in the same geologic formations samples were carefully taken at very low flow rates 100 ml min 1 to avoid suspending immobilized particles the colloidal matter was characterized by light scattering photometry scanning electron microscopy energy dispersive x ray analysis microelectrophoresis and fe al si and organic carbon analyses the colloids composed primarily of clays were observed at high concentrations up to 60 mg colloids l in the anoxic groundwaters while the oxic groundwaters exhibited 1 mg colloids l colloidal organic carbon was present in all groundwaters but under anoxic conditions one third to one half of the total organic carbon was associated with the inorganic colloids the field evidence indicates that anoxic conditions cause the mobilization of soil colloids by dissolving the ferric oxyhydroxide coatings cementing the clay particles to the aquifer solids the depletion of oxidized iron on the surfaces of immobile particles and the addition of organic carbon coatings on the soil particles and colloids apparently stabilizes the colloidal suspension in the anoxic groundwaters

pin pricking the elephant evidence on the origin of the ontong java plateau from pb sr hf nd isotopic characteristics of odp leg 192 basalts age corrected pb sr and nd isotope ratios early aptian basalt from four widely separated sites on the ontong java plateau that were sampled during ocean drilling program leg 192 cluster within the small range reported for three earlier drill sites for outcrops in the solomon islands and for the nauru and east mariana basins hf isotope ratios also display only a small spread of values a vitric tuff with end t 4 5 that lies immediately above basement at site 1183 represents the only probable example from leg 192 of the singgalo magma type flows of which comprise the upper 46 750 m of sections in the solomon islands and at leg 130 site 807 on the northern flank of the plateau all of the leg 192 lavas including the high mgo 8 10 wt kroenke type basalts found at sites 1185 and 1187 have end t between 5 8 and 6 5 they are isotopically indistinguishable from the abundant kwaimbaita basalt type in the solomon islands and at previous plateau nauru basin and east mariana basin drill sites the little fractionated kroenke type flows thus indicate that the uniform isotopic signature of the more evolved kwaimbaita type basalt with 5 8 wt mgo is not simply a result of homogenization of isotopically variable magmas in extensive magma chambers but instead must reflect the signature of an inherently rather homogeneous relative to the scale of melting mantle source in the context of a plume head model the kwaimbaita type magmas previously have been inferred to represent mantle derived largely from the plume source region our isotopic modelling suggests that such mantle could correspond to originally primitive mantle that experienced a rather minor fractionation event e g a small amount of partial melting approximately 3 ga or earlier and subsequently evolved in nearly closed system fashion until being tapped by plateau magmatism in the early aptian these results are consistent with current models of a compositionally distinct lower mantle and a plume head origin for the plateau however several other key aspects of the plateau are not easily explained by the plume head model the plateau also poses significant challenges for asteroid impact icelandic type and plate separation perisphere models at present no simple model appears to account satisfactorily for all of the observed first order features of the ontong java plateau the geological society of london 2004

spectral properties of martian and other planetary glasses and their detection in remotely sensed data thirty silicate glasses were synthesized as realistic analogs to those expected to exist on mars the moon and mercury samples were measured using visible near infrared and mossbauer spectroscopy to determine the effects of varying bulk chemistry oxygen fugacity and temperature on spectral properties for martian glasses the fo2 during fusion strongly affects absorption band intensities in the spectra while bulk chemistry has noticeable secondary effects on absorption band positions titanium and iron content drive spectral changes in lunar glasses where fe3 is effectively absent iron free mercury analog glasses have much higher albedos than all other samples and their spectral shape is a close match to some pyroclastic deposits on mercury synthetic glass spectra were used as inputs into a spectral unmixing model applied to remote orbital datasets to test for the presence of glass the model is validated against physical laboratory mixture spectra as well as previous detections of glass rich pyroclastic deposits on the moon remote data were then used from suspected impact deposits and possible pyroclastic deposits on mars as a new application of the model the results reveal spatially coherent glass rich material and the strong spectral match of the synthetic glasses to these remotely sensed data gives new insights into the presence and character of glasses on the martian surface the large library of glass spectra generated here acquired from consistently synthesized and measured samples can serve as a resource for further studies of volcanic and impact processes on planetary bodies

the dynamics of kerguelen plateau magma evolution new insights from major element trace element and sr isotope microanalysis of plagioclase hosted in elan bank basalts abstract the kerguelen plateau and broken ridge in the southern indian ocean together represent one of the most voluminous large igneous provinces lips ever emplaced on earth a scientific objective of ocean drilling program odp leg 183 was to constrain the post melting magma evolution of kerguelen plateau magmas in an effort to better understand this evolution isotopic and trace element analysis of individual plagioclase crystals hosted within two kerguelen plateau basalts recovered from elan bank were undertaken previous whole rock studies established that the two host basalts investigated in this study are samples of crustally contaminated lower group and relatively uncontaminated upper group basalt plagioclase phenocrysts from the uncontaminated basalt are dominantly normal zoned and exhibit a 87sr 86sri range of 0 704845 0 704985 which overlaps uncontaminated group whole rock values previously reported plagioclase crystals from the contaminated basalt are dominantly reverse zoned and exhibit a 87sr 86sri range of 0 705510 0 705735 which all lie within contaminated group whole rock values previously reported there are no systematic within crystal core to rim variations in 87sr 86sri from either group with the exception that contaminated group crystal rims have overall less radiogenic 87sr 86sri than other zones these observations indicate that crustal assimilation occurred before the formation of unit 10 plagioclase phenocrysts which is supported by parent magma trace element abundance data inverted using carefully calculated partition coefficients trace element diffusion modeling indicates that the upper group basalt unit 4 experienced a more vigorous eruptive flux than the lower group basalt unit 10 we suggest that plagioclase phenocrysts in both the upper and lower group basalts originated from the shallowest section of what was likely a complex magma chamber system we contend that the magmatic system contained regions of extensive plagioclase dominated crystal mush crustal assimilation was not a significant ongoing process in this portion of the elan bank magmatic system both basalts exhibit compelling evidence for remobilization and partial resorption of crystalline debris e g reverse zoned crystals glomerocrysts we suggest unit 4 and 10 magmas ascended different sections of the elan bank magma system where the unit 10 magmas ascended a section of the magma system that penetrated a stranded fragment of continental crust

kiglapait geochemistry vii yttrium and the rare earth elements abstract based on 51 wholerock analyses by xrf and summation over the layered group the kiglapait intrusion contains 4 7 1 6 1 2 ppm y which resides principally in augite and apatite using liquid compositions calculated by summation the partition coefficient daug ly is 0 95 0 12 from 84 to 97 pcs percent solidified and 1 5 0 4 above 97 pcs for feldspar the most likely value for d is 0 028 0 02 n 6 ree analyses for 13 whole rocks were interpreted with the aid of yttrium models to yield trends for wholerocks and liquids vs pcs summations over the rocks of the layered group gave la 2 5 ce 5 8 nd 3 9 sm 1 0 eu 0 8 tb 0 17 yb 0 37 and lu 0 06 ppm with 2 s d errors near 30 all these elements are highly incompatible until the arrival of augite which affects chiefly the hree and apatite which affects all but more strongly the lree the net result is that after apatite arrival at 94 pcs the liquid compositions are nearly constant hence dwr lree 1 0 these results are compatible with the mineralogy of the intrusion and the estimated partition coefficients for feldspar olivine augite apatite and fe ti oxide minerals for pre apatite liquids dfsp lree vary regularly with the normative di content of the liquid and change by an order of magnitude hence the bulk liquid composition must be considered in any attempt to invert the compositions of feldspars to parent liquids the eu anomaly at first decreases in kiglapait liquids due to plagioclase fractionation but then increases due to removal of augite and apatite with negative eu anomalies the features dominantly responsible for eu partitioning are liquid structure and for monoclinic ternary feldspars crystal structure the former is best monitored by the augite or diopside content of the liquid and the latter by the k content of the feldspar the chondrite normalized ree pattern for the intrusion has lan 7 4 lun 1 6 ce yb n 3 6 and eu eu 2 4 indicating its feldspar rich nature the chilled margin of the nearby hettasch intrusion has a similar but more evolved pattern corresponding roughly to the kiglapait liquid at 70 pcs as with other data those for the ree suggest source differences for the two intrusions rather than a relationship due to fractionation

partition coefficients for iron between plagioclase and basalt as a function of oxygen fugacity implications for archean and lunar anorthosites abstract experimental studies were undertaken to determine d for feot between plagioclase and melt as a function of oxygen fugacity for a basaltic composition that occurs as matrices for plagioclase megacrysts that are similar to those in calcic anorthosites at liquidus conditions the d for feot between calcic plagioclase and tholeiitic basalt changes very little from 0 030 to 0 044 between the very low o 2 of the iron wustite buffer and that of the quartz fayalite magnetite qfm buffer at fugacities above qfm the value for d increases rapidly to 0 14 at the magnetite hematite buffer and 0 36 in air the increase in d results from the fact that nearly all of the fe is in the fe2 state at o 2 below qfm and the fe 3 fe 2 ratio in the melt increases rapidly above qfm causing more fe to enter the plagioclase which accepts fe3 more readily than fe2 there is essentially no change in values of d over cooling rates that vary by two orders of magnitude the d for feot of 0 030 at iron wustite is in good agreement with earlier studies at low o2 terrestrial calcic plagioclase matrix pairs display ds of about 0 043 in excellent agreement with the experimental value of 0 044 at qfm which is the accepted fugacity for terrestrial tholeiitic basalts application of the ds for feot and other components to terrestrial calcic anorthosites indicates that the anorthosites were in equilibrium with nearby coeval tholeiitic basalts at qfm as was expected lunar anorthosites however have anomalously low contents of feot as well as mgo and would be in equilibrium with melts that are several times lower in these components than expected the low values of feot and mgo in the plagioclase of lunar anorthosites are a result of subsolidus reequilibration with pyroxene olivine and other fe mg bearing phases during high temperature metamorphism as is the case in terrestrial anorthosites that have undergone granulite grade metamorphism the ds for k2o mgo and tio2 were determined as 0 21 0 044 and 0 033 respectively and show no variation with o 2 the value for k2o is in good agreement with natural assemblages the values for mgo and tio2 however are lower in natural assemblages but the high degree of mobility of mg and the very low contents of tio2 in plagioclase makes the reliability of the natural values rather low also the d for tio2 may be affected by rate of cooling attempts to determine the d for cr2o3 as a function of o 2 were made difficult by the low levels of cr2o3 300 to 500 ppm in the melt when saturation with a cr spinel occurred because the cr concentrations in plagioclase are nearly 100 times less than those in the melt it was not possible to obtain reliable analyses for plagioclase these uncertainties constrain the d for cr to be less than 0 07 at the qfm buffer

marginal rocks resembling the estimated bulk composition of the kiglapait intrusion abstract the southern margin of the kiglapait intrusion labrador contains fine grained rocks 5 6 m above a contact with anorthosite of the nain complex and a laminated unit 3 m from the contact three fine grained samples and one of the laminated unit have a mean composition closely resembling that previously calculated by summation of the exposed layered group analyzed values agree closely with the earlier estimates for alkalies sr and y thus they support the mineral liquid partition coefficients previously calculated for these elements and for the rare earth elements based on new calculations the value for ferric oxide is revised to 1 04 from its original value of 1 91 the new samples are depleted in the incompatible elements titanium and phosphorus suggesting that they have lost some residual liquid by sidewall fractional crystallization and downward motion of rejected solute the marginal rocks provide no evidence for repeated injection of magma during lower zone time

geochemistry of tektites and impact glasses glass produced by melting during impact events is called impact glass or impactite although impact crate ring produces a great variety of shock metamorphosed rocks all of which are called impactites by various authors to a differing extent we restrict the use of this term here to material completely converted into glass the degree of metamorphism seen in different classes of impact materials starting with those showing simple shock effects shock lithification shatter cones diaplectic glasses coesite stishovite lechatelierite impact breccias glass depends on the peak pressure and temperature the rock has experienced as a result of mixing brecciation and similar processes impact glasses also tend to include fragments of less shocked or less homogeneous metamorphosed rocks we limit our discussion here however to the more homogeneous members of the terrestrial impactite family a discussion of lunar impact glasses was given by delano et al 1981 another group of natural glasses are tektites which at first glance are similar to obsidian most tektites are very homogeneous often aerodynam ically shaped spherically symmetric objects that are several centimeters in size and are found in various areas referred to as tektite strewn fields in reflected light they are usually black but in transmitted light they show variations of grey brown and green the surface features gouges furrows grooves pits striations clearly distinguish them from terrestrial volcanic glasses and have probably originated from solution etching and weathering effects on earth baker 1963 lamarche et a1 1984 and from surface stresses occurring during their cooling tektites found in geographically adjacent

variety and origin of magmas on shatsky rise northwest pacific ocean 1 shatsky rise consists of thick 30 km maximum basaltic crust with various geochemical compositions geochemistry data indicate that four magma types exist on the plateau namely normal low ti high nb and u1349 types the normal type is the most abundant in volume and appears on all three large edifices of the plateau tamu ori and shirshov massifs composition of the normal type is similar to normal mid ocean ridge basalt n morb composition but with slight relative enrichment of the more incompatible elements the low ti type is distinguished from the normal type basalt by slightly lower ti content at a given mgo composition of the high nb type is characterized by distinctively high contents of incompatible trace elements u1349 type basalts are composed of more primitive and depleted compositions compared with the others the normal type basalts constitute 94 of the lava units of the oldest tamu massif and non normal types i e the other three types basalts comprise 57 on the younger ori massif implying that geochemical compositions may have become heterogeneous with time petrological examination demonstrates that compositions of the normal low ti and high nb type basalts evolved through fractional crystallization of olivine plagioclase and augite in shallow magma chambers 200 mpa model calculations of immobile trace elements estimate that the normal type basalt can be formed by 15 melting of a depleted mantle source in the presence of residual garnet this degree of melting is similar to n morb but the larger effect of residual garnet during petrogenesis implies that a greater depth of melting

magma evolution revealed by anorthite rich plagioclase cumulate xenoliths from the ontong java plateau insights into lip magma dynamics and melt evolution abstract petrologic studies of igneous rocks often rely on whole rock analyses alone to deduce source and melting histories whole rock compositions represent a mixture of the processes responsible for the final texture and composition of the rock but do not emphasize the evolutionary processes that the rock may have experienced we examine the major minor and trace element compositions of plagioclase phenocrysts and plagioclase rich cumulate xenoliths from a sequence of kwaimbaita pillow basalt and massive flows recovered from ocean drilling program odp site 1183 on the expansive 122 ma ontong java plateau ojp and from subaerial outcrops on the island of malaita solomon islands these data are used to reconstruct equilibrium liquid compositions to understand magma dynamics magma evolution and the distribution basalt types across the ojp results reveal that crystals frequently are out of equilibrium with their host basalt two distinct compositional zones are present in plagioclase phenocrysts and xenolith crystals an80 86 and an65 79 equilibrium magma compositions derived from each of these zones are distinct in relative terms the following distinctions are made an80 86 sr y and eu richer ba and lree depleted higher sr ti lower ba sr and la y an65 79 sr y and eu poorer ba and lree enriched lower sr ti higher ba sr and la y we observed several an65 79 parent magmas with higher la y lower sr and higher lree than the majority of an65 79 zones which suggests that they grew from highly fractionated magmas the an80 86 zones of both xenolith crystals and phenocrysts appear to have crystallized relatively early and are attributed to growth in magmas more primitive than parent magmas of an65 79 zones or the host magma using melts modeling we demonstrate a significant role for h2o is not necessary to form an rich crystals from known ojp magma types these types of zones can instead form when relatively primitive ojp magmas ascend and partially crystallize at low pressures crystal mush layers are rheological elements of multiply saturated solidification fronts and conditions for extreme fractionation are met deep with thermally and mechanically insulated mush solidification fronts conditions in a homogenous magma body alone cannot generate the range of magma compositions and textures recorded in ojp plagioclase crystals we suggest that the ojp magma chamber system consisted of crystal mush dominated regions and liquid dominated regions in a laterally and vertically extensive system of interconnected dikes and sills solidification front disruption was common during magma recharge and transport which freed debris to mix with ojp magmas the volume of crystalline debris from disrupted solidification fronts was small relative to the overall magma volume which leads to little change of bulk magma chemistry this can explain the dominance of the kwaimbaita basalt type across the ojp evidence of solidification front disruption is best preserved as allochthonous crystals both more and less primitive than bulk magma chemistry both of which were observed in ojp basalts coincident with a zone of neutral buoyancy the shallow ojp magma chamber system existed at a depth of 0 7 km the ojp magma chamber system was thinner near the plateau margins which provided less density filtration of magmas this allowed more diverse magma types to reach the surface along the margins it is envisaged that as the ojp formed the zone of neutral buoyancy slowly migrated upward leading to slow yet pervasive assimilation of overlying seawater altered basalt at the base of the lava pile

intrabasement reflections of the ontong java plateau implications for plateau construction 1 the early cretaceous ontong java plateau ojp in the western equatorial pacific earth s most voluminous large igneous province lip is characterized by intrabasement seismic reflections to investigate the nature of such reflections we have analyzed new and all older multichannel seismic mcs reflection data from the ojp using an instantaneous phase velocity analysis technique and synthetic seismograms intrabasement reflections are most prevalent on the main ojp especially on its crest on mcs data the reflections 1 are semicontinuous and subparallel to the top of igneous basement 2 in places have the opposite phase of seafloor reflections and 3 have an average frequency of 20 hz we calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at ojp scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the mcs data alternatively to evaluate the possibility of sediment sedimentary rock interbeds causing the intrabasement reflections we use published early cretaceous sedimentation rates determined from ojp drill sites and published estimates for the duration of massive ojp volcanism to calculate a range of possible sedimentary interbed thicknesses the range proves to be below the detection limit of the mcs data therefore we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates both originating from vents and fissures on the ojp probably on its crest

steady state volcanism paleoeffusion rates and magma system volume inferred from plagioclase crystal size distributions in mafic lavas dome mountain nevada abstract the dome mountain dm lavas located in the moat of the timber mountain caldera of the sw nevada volcanic field cap a thick sequence of welded tuffs massive and bedded tuffs and mafic and rhyolitic lava flows these 10 9 m y old flows comprise a pile of some twenty flows with a total thickness of about 300 m individual flows range in thickness from 3 to 20 m and are characterized by a basal vesicular zone a massive central region and an upper vesicular region containing in most cases cooling fractures the flows dip gently away from the summit of dm a prominent topographic feature of the region with an elevation of 2065 m silica contents range from 48 8 wt at the base of the pile to 59 4 wt at the top although most of the flows are andesitic crystal size distributions csds for plagioclase in these comagmatic lavas have been determined to provide information on magma storage times these times when coupled with phase equilibria can be used to infer cooling rates which are indicative of the relative dimensions of magmatic bodies and the vigor of various magmatic cooling processes most of the csds show no sign of crystal fractionation or accumulation assuming a growth rate of 10 10 cm s calculated mean crystal residence times for most lavas cluster in the range of 1 5 to 4 years two of the lower lavas have residence times in the range of 4 to 9 years the residence times correlate inversely with nucleation density and broadly correlate inversely with silica content high residence time low silica lavas occur at the base of the pile whereas low residence time high silica lavas occur at the top of the pile one interpretation of the residence time data is that the lavas are from an open system of more or less constant residence time but varying spatially in system locations e g a magma chamber in which steady state recharge and eruption may have been reached alternatively these lavas may represent small samples closely spaced in time of a slowly cooling large batch or reservoir of magma the greater residence times associated with the lower flows may indicate the increased amount of time necessary to form the conduit of the magma volcano system by the oldest magma or simply that part of the system with the highest liquidus temperature a minimum volume of 1 4 to 2 5 km 3 for the magma chamber is estimated for the dm system using the estimated residence times in a simplified cooling model of a sheet of aspect ratio r the actual system volume depends on r which is strictly unknown and thus the actual system volume may be much larger e g 200 km 3 a mean paleoeffusion rate of 0 05 km 3 yr is obtained for the lavas by assuming that the residence time of each lava corresponds to the amount of time elapsed since the eruption of the underlying flow

the coagulation of dissolved239 240pu in estuaries as determined from a mixing experiment a mixing experiment using large volumes 100 l of filtered 1 m freshwater and seawater end members was performed to simulate and investigate the chemical reactivity of239 240pu during estuarine mixing an organic rich freshwater with a relatively high concentration 0 8 dpm 100 l of dissolved239 240pu was used as one end member buzzards bay seawater dissolved239 240pu 0 04dpm 100l was the other the results demonstrate that dissolved239 240pu in the freshwater undergoes extensive and rapid coagulation under simulated estuarine conditions there is a strong correlation between the amount of coagulation of dissolved239 240pu humic acids ha and fe the extent of coagulation of all three constituents increases with increasing salinity and the net extent of their removal is 53 57 and 100 for pu ha and fe respectively as has been documented for fe in freshwater dissolved239 240pu appears to be stabilized by naturally occurring humic substances to form negatively charged colloids which are then coagulated by seawater cations the extrapolation of these experimental results to real estuaries will require additional research

minor and trace element zoning in plagioclase implications for magma chamber processes at parinacota volcano northern chile textural and compositional zoning in plagioclase phenocrysts in a sample from parinacota volcano chile was investigated using backscattered electron images and electron microprobe analysis of major and trace elements large 2 mm oscillatory zoned crystals type i with resorption surfaces of moderate an discontinuities 10 an and decreasing trace element contents sr mg ti towards the rim reflect melt differentiation and turbulent convection in the main magma body early recharge with a low sr mafic magma is seen in the core small scale sr variations in the core indicate limited diffusion and thus residence and differentiation times of the magma shorter than a few thousand years smaller crystals type ii with low trace element an ratio reflect the influence of an h2o rich melt probably from a differentiated boundary layer closed system in situ crystallisation mafic magma recharge and the role of a water rich differentiated boundary layer can be distinguished from the an trace element relationships crystals apparently move relatively freely between different parts and regimes in the magma chamber evidence for convective crystal dispersion high sr type ii crystals indicate an earlier input of sr rich mafic magma recharge of two distinct mafic magma types is thus identified high sr and low sr which must have been present at increasing recharge rates with time in the plumbing system throughout the volcano s history