country rock contamination of marginal mafic granulites bordering the nain plutonic suite implications for mobilization of sr during high grade contact metamorphism the marginal mafic granulites that locally border the nain plutonic suite nps have a range of initial nd isotope ratios that overlap with that of the nps anorthosites and associated nain dykes the similarity in nd isotope data suggests that gneissic archaean country rocks have contaminated all the anorthosites marginal mafic granulites and dykes sr isotope data for the mafic granulites and dykes support a country rock contamination scenario but preclude wholesale assimilation of rocks such as the host archaean tonalite gneisses as the sole contaminant initial epsilonsr values of 10 to 403 and 0 9 to 242 for the mafic granulites and dykes respectively are significantly higher than values for nps country rocks examined thus far the elevated initial esr values are therefore interpreted to result from the introduction of radiogenic sr into the granulites and dykes via sr rich fluids generated by the breakdown of rb rich mineral phases such as biotite in the country rocks during nps

the late crystallization stages of low ti low fe tholeiitic magmas insights from evolved antarctic and tasmanian rocks abstract examples of the latest stages of crystallization in evolved tholeiitic rocks can be found in the low ti low p ferrar magmatic province in antarctica e g thern promontory and archambault ridge and tasmania e g the red hill intrusion and mount wellington sill evolved rocks of this magmatic province include a rocks of basaltic andesite composition containing plagioclase augite pigeonite and interstitial fe ti oxides b rocks of andesitic composition with plagioclase as a liquidus phase a single fe rich subcalcic clinopyroxene and fe ti oxides and c rocks of dacitic composition displaying granophyric texture containing sodic plagioclase alkali feldspar ferrohedenbergite fayalite fe ti oxides quartz and accessory phases the latest crystallization stages are thus characterized by the striking chemical convergence of subcalcic fe augite and fe pigeonite followed by more evolved rocks that preserve quartz alkali feldspar cotectic granophyric relationships lack subcalcic clinopyroxene and contain coexisting olivine and calcium rich clinopyroxene these features are consistent with crystallization at or below the quartz fayalite magnetite oxygen buffer at temperatures close to 800 c the trace element geochemistry of coexisting pyroxenes feldspar and fe ti oxides are entirely consistent with magmatic evolution caused by fractional crystallization of the observed phases similarities and differences with other silicic volcanic rocks elsewhere are also described there is no evidence for liquid immiscibility

crystallization experiments on a gusev adirondack basalt composition until recently the snc meteorites represented the only source of information about the chemistry and petrology of the martian surface and mantle the mars exploration rovers have now analyzed rocks on the martian surface giving additional insight into the petrology and geochemistry of the planet the adirondack basalts analyzed by the mer spirit in gusev crater are olivine phyric basaltic rocks which have been suggested to represent liquids and might therefore provide new insights into the chemistry of the martian mantle experiments have been conducted on a synthetic humphrey composition at upper mantle and crustal conditions to investigate whether this composition might represent a primary mantle derived melt the humphrey composition is multiply saturated at 12 5 kbar and 1375 c with olivine and pigeonite a primary anhydrous melt derived from a chondritic mantle would be expected to be saturated in orthopyroxene not pigeonite in addition the olivine and pigeonite present at the multiple saturation are too ferroan to have been from a martian mantle as is understood now therefore it seems likely that the humphrey composition does not represent a primary anhydrous melt from the martian mantle but was affected by mineral melt fractionations at lower crustal pressures

estimating the lunar mantle water budget from phosphates complications associated with silicate liquid immiscibility abstract the discovery of water within the lunar mantle has broad implications for the formation of the earth moon system differentiation of the moon and the magmatic evolution of lunar basalts as well as the highland rocks recently there has been considerable interest in using combined water abundances and h isotope systematics of lunar apatites from mare basalts to quantify the origin and extent of water within the moon s mantle however the petrologic and geochemical conditions that govern apatite crystallization are not well constrained especially for high feo basaltic melts that crystallize at fo2 values below the iron wustite buffer apatites are typically located within the late stage interstitial regions in this contribution we present detailed textural descriptions of late stage inter cumulus residual liquid pockets i e mesostasis pockets in order to understand the petrogenesis of lunar apatite results from five mare basalts demonstrate that the majority of the residual liquids in mesostasis regions have undergone silicate liquid immiscibility sli splitting into si k rich felsic and fe rich fe basaltic conjugate liquids we demonstrate the complexity of these residual liquids by documenting a wide range of water contents for apatites in several mesostasis pockets within a single mare basalt a complexity common to many basalts these data illustrate that individual apatite hosting mesostasis pockets behave as independent sub systems even within a single rock furthermore we present water concentrations for another phosphate phase merrillite indicating additional uncertainties during considerations of water partitioning into apatite fractional crystallization trends have been used in order to assess the conditions under which magmas are likely to undergo sli predicted liquid lines of descent indicate that it is the late stage residual liquids of lunar basalts with relatively low mg e g 50 may not intersect the two liquid field depending upon the fractionation trends in the late stage mesostasis pockets for samples that undergo sli the apatite melt partition coefficients required for back calculating water abundances of the parental melts are compromised by the generation of two populations of apatites merrillites from conjugate immiscible liquids this process highlights an important complexity inherent to all water back calculations that use apatite as this requires an additional set of partition coefficients we emphasize that the complex petrologic nature and common development of sli of apatite bearing late stage mesostasis pockets have not been considered in published apatite volatile data these factors in additional to other considerations illustrate why water back calculations to model the primary melts from such data must be viewed with caution

antarctic intermediate water circulation and variability in a coupled climate model the variability of antarctic intermediate water aaiw in a long term natural integration of a coupled climate model is examined the mean state of the climate model includes a realistic representation of aaiw which appears centered on the su 5 27 2 kg m23 density surface hereinafter s 27 2 both in observations and the model an assessment of ventilation rates on the s 27 2 surface suggests that this particular climate model forms aaiw in a mostly circumpolar fashion with a significant contribution from antarctic surface water this motivates the assessment of oceanic variability along this core aaiw isopycnal surface complex empirical orthogonal function analyses decompose the variability into three dominant modes showing circumpolar patterns of zonal wavenumber 1 2 and 3 on the s 27 2 density surface the modes contain eastward propagating signals at interannual to centennial time scales mechanisms forcing this variability are investigated using heat and salt budget analyses at the wintertime outcrop of the s 27 2 surface such an approach ignores the mechanism of aaiw variability sourced by subantarctic mode water variations which has been examined previously and is for the most part beyond the present study variability in meltwater rates and atmospheric heat and freshwater fluxes are found to dominate the intermediate water variability at the outcrop region in contrast northward ekman transport of heat and salt plays a significant but localized role in aaiw temperature salinity variability there is also an important contribution from the antarctic circumpolar current to the variability at the outcrop region via zonal transport of heat and salt while the magnitude of aaiw natural variability can be large near the outcrop of the salinity minimum layer recent observations of cooling and freshening at depth are suggested to be beyond that of the unperturbed system

magmatic inclusions and felsic clasts in the dar al gani 319 polymict ureilite magmatic inclusions occur in type ii ureilite clasts olivine orthopyroxene augite assemblages with essentially no carbon and in a large isolated plagioclase clast in the dar al gani dag 319 polymict ureilite type i ureilite clasts olivine pigeonite assemblages with carbon as well as other lithic and mineral clasts in this meteorite are described in ikeda et al 2000 the magmatic inclusions in the type ii ureilite clasts consist mainly of magnesian augite and glass they metastably crystallized euhedral pyroxenes resulting in feldspar component enriched glass on the other hand the magmatic inclusions in the large plagioclase clast consist mainly of pyroxene and plagioclase with a mesostasis they crystallized with a composition along the cotectic line between the pyroxene and plagioclase liquidus fields dag 319 also contains felsic lithic clasts that represent various types of igneous lithologies these are the rare components not found in the common monomict ureilites porphyritic felsic clasts the main type contain phenocrysts of plagioclase and pyroxene and their groundmass consists mainly of plagioclase pyroxene and minor phosphate ilmenite chromite and or glass crystallization of these porphyritic clasts took place along the cotectic line between the pyroxene and plagioclase fields pilotaxitic felsic clasts crystallized plagioclase laths and minor interstitial pyroxene under metastable conditions and the mesostasis is extremely enriched in plagioclase component in spite of the ubiquitous crystallization of plagioclase laths in the clasts we suggest that there are two crystallization trends pyroxene metal and pyroxene plagioclase trends for the magmatic inclusions and felsic lithic clasts in dag 319 the pyroxene metal crystallization trend corresponds to the magmatic inclusions in the type ii ureilite clasts and the pilotaxitic felsic clasts where crystallization took place under reducing and metastable conditions suppressing precipitation of plagioclase the pyroxene plagioclase crystallization trend corresponds to the magmatic inclusions in the isolated plagioclase clast and the porphyritic felsic clasts this trend developed under oxidizing conditions in magma chambers within the ureilite parent body the felsic clasts may have formed mainly from albite component rich silicate melts produced by fractional partial melting of chondritic precursors the common monomict ureilites type i ureilites may have formed by the fractional partial melting of alkali bearing chondritic precursors however type ii ureilites may have formed as cumulates from a basaltic melt

large silica rich igneous textured inclusions in the buzzard coulee chondrite condensates differentiates or impact melts we studied three large 2 4 mm diameter igneous textured inclusions in the buzzard coulee h4 chondrite using microanalytical techniques olm sem empa sims to better elucidate the origins of igneous inclusions in ordinary chondrites the inclusions are clasts that come in two varieties 1 white inclusions bz 1 and bz 2 represent a nearly holocrystalline assemblage of low ca and high ca pyroxene 63 66 area and cristobalite 33 36 and 2 tan inclusion bz 3 is glass rich approximately 60 with low ca and high ca pyroxene phenocrysts the bulk compositions of the inclusions determined by modal reconstruction are all sio2 rich approximately 67 wt for bz 1 and bz 2 approximately 62 for bz 3 but bz 3 is enriched in incompatible elements e g ree approximately 4 5 ci abundances whereas bz 2 and bz 1 are depleted in those elements that are most incompatible in pyroxene e g la ho approximately 0 15 0 4 ci abundances these bulk compositions do not resemble what one would expect for partial or complete shock melting of a chondritic precursor and show no evidence for overall volatility control we infer that the inclusions originated through igneous differentiation and feo reduction with bz 3 forming as an andesitic partial melt approximately 30 40 partial melting of an h chondrite precursor and bz 1 and bz 2 forming as pyroxene cristobalite cumulates from an si rich melt we suggest that both types of melts experienced a period of transit through a cold low pressure space environment in which cooling feo reduction and interaction with a vapor occurred melts may have been lofted into space by excavation or splashing during collisions or by pyroclastic volcanism our results indicate intriguing similarities between the inclusions in buzzard coulee and the silicates in some iron iie type and stony iron iva type meteorites suggesting a genetic relationship

a fundamental dispute a discussion of on some fundamentals of igneous petrology by bruce d marsh contributions to mineralogy and petrology 2013 166 665 690 marsh contrib miner petrol 166 665 690 2013 again claims that crystal free basalt magmas are unable to differentiate in crustal magma chambers and regards layered intrusions as primarily due to the repeated emplacement of crystal suspensions he ignores an earlier critique of his unconventional inferences latypov j petrol 50 1047 1069 2009 as well as a wealth of petrographic geochemical and experimental evidence supporting the dominant role of fractional crystallization in the solidification of layered intrusions most tellingly the cryptic variations preserved in the skaergaard and many other basaltic layered intrusions would require an exceedingly implausible sequence of phenocrystic magmas but are wholly consistent with in situ fractional crystallization a major flaw in marsh s hypothesis is that it dismisses progressive fractional crystallization within any magma chamber and hence prohibits the formation of crystal slurries with phenocrysts and melts that change systematically in composition in any feeder system this inherent attribute of the hypothesis excludes the formation of layered intrusions anywhere

estimates of ice thickness in the conamara chaos region of europa europa the second galilean moon outward from jupiter is similar in size to earth s moon but has an outer water ice layer on the order of 100 km thick images acquired by the galileo spacecraft reveal domical features and iceberg like blocks in some areas that suggest the ice was regionally thin at the time the features formed this paper applies buoyancy and flexural models to some of the features to estimate ice thickness assuming that the ice blocks were floating in a liquid sublayer the buoyancy model suggests an ice layer 0 2 3 0 km thick also the flexural models suggest that only the upper 0 1 0 5 km of that ice layer responded elastically to stresses acting as an elastic lithosphere

mineralogy of silicate inclusions of the colomera iie iron and crystallization of cr diopside and alkali feldspar from a partial melt we studied the mineralogy mineral chemistry and compositions of 48 interior silicate inclusions and a large k rich surface inclusion from the colomera he iron meteorite common minerals in the interior silicate inclusions are cr diopside and na plagioclase albite they are often enclosed by or coexist with albitic glasses with excess silica and minor fe mg components this mineral assemblage is similar to the andesitic material found in the caddo county iab iron meteorite for which a partial melt origin has been proposed the fairly uniform compositions of cr diopside ca44mg46fe10 and na plagioclase or 2 5 ab 90 0 an 7 5 to or 3 5 ab 96 1 an 0 4 in colomera interior inclusions and the angular boundaries between minerals and metal suggest that diopside and plagioclase partially crystallized under near equilibrium conditions from a common melt before emplacement into molten metal the melt crystal assemblage has been called crystal mush the bulk compositions of the individual composite inclusions form an array between the most diopside rich inclusion and plagioclase this is consistent only with a simple mechanical mixing relationship not a magmatic evolution series we propose a model in which partly molten metal and crystal mush were mixed together by impact on the he parent body other models involving impact melting of the chondritic source material followed by growth of diopside and plagioclase do not easily explain near equilibrium growth of diopside and na plagioclase followed by rapid cooling in the k rich surface inclusion k feldspar orthopyroxene and olivine were found together with diopside for the first time k feldspar sanidine or 92 7 ab 7 2 an 0 1 to or 87 3 ab 11 0 an 1 7 occurs in an irregular veinlike region in contact with large orthopyroxene crystals of nearly uniform composition ca1 3mg80 5fe17 8 to ca3 1mg78 1fe18 9 and intruding into a relict olivine with deformed oval shape silica and subrounded cr diopside are present within such k feldspar regions some enrichments of the albite component have been detected at the end of curved elongated nodules of k feldspar intruded into the mafic silicates the textural relationships suggest that a k rich melt was present a k rich melt is neither the first melt of a chondritic system nor a differentiation product of a na rich partial melt of chondritic material the k rich material may have originated as a fluid phase that leached k from surrounding materials and segregated by a mechanism similar to that proposed for the na rich inclusions copyright c 2003 elsevier science ltd

fractional melting and smelting on the ureilite parent body we investigate petrologic and physical aspects of melt extraction on the parent asteroid of the ureilite meteorites upb we first develop a petrologic model for simultaneous melting and smelting reduction of feo by c at various depths for a model starting composition determined from petrologic constraints to have been cv like except for elevated ca al 2 5 ci we determine 1 degree of melting 2 the evolution of mg 3 production of co co2 gas and 4 the evolution of mineralogy in the residue as a function of temperature and pressure we then use these relationships to examine implications of fractional vs batch melt extraction in the shallowest source regions 30 bars melting and smelting begin simultaneously at 1050 c so that mg and the abundance of low ca pyroxene initially pigeonite ultimately pigeonite orthopyroxene begin to increase immediately however in the deepest source regions 100 bars smelting does not begin until 1200 c so that mg begins to increase and low ca pyroxene pigeonite appears only after 21 melting the final residues in these two cases obtained just after the demise of augite match the end members of the ureilite mg range 94 76 in pyroxene abundance and type in all source regions production of co co2 by smelting varies over the course of melting the onset of smelting results in a burst of gas production and very high incremental gas melt ratios up to 2 5 by mass after a few s melting however these values drastically decline to 0 05 in the final increments physical modelling based on these relationships indicates that melts would begin to migrate upwards after only 1 2 melting and thereafter would migrate continuously fractionally and rapidly reaching the surface in a year in a network of veins dikes all melts produced during the smelting stage in each source region have gas contents sufficient to cause them to erupt explosively and be lost however since in all but the shallowest source regions part of the melting sequence occurs without smelting fractional melting implies that a significant fraction of upb melts may have erupted more placidly to form a thin crust 3 3 km thick for a 100 km radius body our calculations suggest that melt extraction was so rapid that equilibrium trace element partitioning may not have been attained we present a model for disequilibrium fractional melting in which ree partitioning is limited by diffusion on the upb and demonstrate that it produces a good match to the ureilite data the disequilibrium model may also apply to trace siderophile elements and might help explain the overabundance of these elements in ureilites relative to predictions from the smelting model our results suggest that melt extraction on the upb was a rapid fractional process which can explain the preservation of a primitive oxygen isotopic signature on the upb

origin and chronology of chondritic components a review abstract mineralogical observations chemical and oxygen isotope compositions absolute 207pb 206pb ages and short lived isotope systematics 7be 7li 10be 10b 26al 26mg 36cl 36s 41ca 41k 53mn 53cr 60fe 60ni 182hf 182w of refractory inclusions ca al rich inclusions cais and amoeboid olivine aggregates aoas chondrules and matrices from primitive unmetamorphosed chondrites are reviewed in an attempt to test i the x wind model vs the shock wave model of the origin of chondritic components and ii irradiation vs stellar origin of short lived radionuclides the data reviewed are consistent with an external stellar origin for most short lived radionuclides 7be 10be and 36cl are important exceptions and a shock wave model for chondrule formation and provide a sound basis for early solar system chronology they are inconsistent with the x wind model for the origin of chondritic components and a local irradiation origin of 26al 41ca and 53mn 10be is heterogeneously distributed among cais indicating its formation by local irradiation and precluding its use for the early solar system chronology 41ca 41k and 60fe 60ni systematics are important for understanding the astrophysical setting of solar system formation and origin of short lived radionuclides but so far have limited implications for the chronology of chondritic components the chronological significance of oxygen isotope compositions of chondritic components is limited the following general picture of formation of chondritic components is inferred cais and aoas were the first solids formed in the solar nebula 4567 4568 myr ago possibly within a period of 10 and have 26al 27al 0 similar to those in chondrules 5 nebular gas the majority of chondrules within a chondrite group may have formed over a much shorter period of time

petrogenesis of a mid proterozoic anorthosite mangerite charnockite granite amcg complex isotopic and chemical evidence from the nain plutonic suite the nain plutonic suite nps about 1 30 ga underlies some 19 000 km intruding the boundary between middle to late archean rocks in the east nain province and late archean and early proterozoic rocks in the west churchill province nd isotopic compositions in most igneous units of the nps reflect their geographic position relative to the inferred boundary between the nain and churchill provinces rare exceptions are local intrusions of olivine bearing basic rocks with highest epsilon nd 1 3 ga near 3 0 present in both eastern and western sectors of the nps anorthositic rocks have variable and significant contributions of crustal nd but notably lower i sr than granitoid rocks ferrodiorites are similar isotopically to the anorthositic group and have chemical and mineral compositions more akin to the anorthositic group than the granitoids aluminous orthopyroxene megacrysts in nps anorthositic rocks indicate crystallization pressures of 6 2 to 11 0 kbar consistent with lower cru

are ureilites residues from partial melting of chondritic material the answer from magpox calculations performed using magpox show that no bulk compositions having chondritic ca al ratio and within the range of chondritic si mg ratios can produce the olivine pigeonite ureilites which constitute 65 of those for which modal abundances are known as residues of single stage equilibrium partial melting calcium aluminum ratios of 2 3 5 ci are required in addition all the ureilites could not have formed from a single composition at various degrees of reduction because they show no correlation between pigeonite olivine ratio and mg ratio materials with various al mg ratios ranging from subchondritic to superchondritic are required if these materials are primitive i e created by nebular processes rather than planetary igneous processes they are unknown in the meteorite record excess accretion relative to chondrites of 5 10 mol of a high temperature condensate component which was itself almost completely depleted in corundum due to early fractionation could create the necessary compositions the plausibility that such processes occurred on a parent body sized scale is difficult to assess in contrast lodranites can be produced as residues of 3 30 equilibrium partial melting of an average ordinary chondritic composition at the appropriate level of reduction although many features of ureilites suggest that they are relatively primitive residues produced by low degrees of melting of chondritic materials and thus resemble lodranites and other groups of primitive achondrites their predominantly pigeonite olivine mineralogy remains difficult to explain within this simple scenario

petrography mineral chemistry and petrogenesis of antarctic shergottite lew88516 abstract lew88516 lew like its near twin alh77005 alh is a maskelynite bearing harzburgite and a member of the snc family of achondrites lew is texturally heterogenous exhibiting both poikilitic pyroxene oikocrysts enclosing subhedral olivine and euhedral chromite and non poikilitic cumulus framework of olivine and minor pyroxene with interstitial maskelynite and secondary minerals textures pyroxenes in lew appear to be slightly more iron rich and more varied in composition than those in alh lew olivines have distinctly higher fe contents most of the olivine grains in lew have compositions more iron rich than any alh olivine observed lew olivine in non poikilitic areas is substantially more iron rich than olivine armored by pyroxene trace element and minor element patterns of lew and alh minerals are essentially identical and are consistent with closed system large volume crystallization of the major phases followed by development of later phases after assembly of the crystal pile major element compositions show the effects of moderate near solidus re equilibration in both meteorites the compositions of possible lew parent magmas calculated from mass balance methods using the components of magmatic inclusions in large olivine grains are very similar to those proposed earlier for alh and the eeta79001 shergottite while the subtle differences between lew and alh suggest they are not part of the same fall it is likely that they are derived from the same igneous processes

ion and electron microprobe study of troctolites norite and anorthosites from apollo 14 evidence for urkreep assimilation during petrogenesis of apollo 14 mg suite rocks abstract most of the moon s highland crust formed during the period 4 65 4 45 ga ago from a vast magma ocean up to 800 km deep hess and parmentier 1995 this early lunar crust comprises fe rich anorthosites with calcic plagioclase compositions subsequent evolution of the highland crust was dominated by troctolites anorthosites and norites of the mg suite this plutonic series is characterized by calcic plagioclase and mafic minerals with high mg 100 mg mg fe these rocks evidently formed by partial melting of ultramafic rocks of the lunar mantle but their bulk rock incompatible element characteristics are too enriched to represent such a primitive source previous studies have suggested that this enrichment in incompatible trace elements is the result of metasomatism of the crust by fluids rich in ree and p the products of this suggested metasomatic event are ree rich phosphates typically whitlockite deposited interstitially alternatively the incompatible element rich nature of these plutonic rocks may represent a characteristic of their parent magma acquired prior to crystallization of the plutons in an effort to distinguish the origin of this important lunar rock series we have analyzed the ree content of primary cumulus phases in ten mg suite cumulates using sims along with their major and minor element compositions by electron microprobe analysis nine of these samples have high mg s consistent with their formation from the most primitive parent melts of the mg suite the data presented here show that mg suite troctolites and anorthosites preserve major and trace element characteristics acquired during their formation as igneous cumulate rocks and that these characteristics can be used to reconstruct related aspects of the parent magma composition our data show that primitive cumulates of the mg suite crystallized from magmas with ree contents similar to high k kreep in both concentration and relative abundance the highly enriched nature of this parent magma contrasts with its primitive major element characteristics as pointed out by previous workers this enigma is best explained by the mixing of residual magma ocean urkreep melts with ultramagnesian komatiitic partial melts from the deep lunar interior the data do not support earlier models that invoke crustal metasomatism to enrich the mg suite cumulates after formation or models which call for a superkreep parent for the troctolites and anorthosites

petrogenesis of silicate inclusions in the weekeroo station iie iron meteorite differentiation remelting and dynamic mixing the weekeroo station iie iron meteorite contains a variety of felsic and mafic inclusions enclosed in an feni metal host petrographic emp and sims data suggest that the petrogenesis of the silicates was complex and included differentiation remelting feo reduction and dynamic mixing of phases differentiation produced a variety of olivine free inclusion assemblages ranging from pyroxene 1 plagioclase 1 tridymite with peritectic compositions to coarse orthopyroxene to plagioclase 1 tridymite and its glassy equivalent individual phases have similar trace element abundances and patterns despite large variations in inclusion textures modes and bulk compositions probably as a result of mechanical separation of pre existing phases in an impact event that dynamically mixed silicates with the metallic host trace element data imply that augite and plagioclase grains in different inclusions crystallized from the same precursor melt characterized by relatively unfractionated ree abundances of 20 30 3 ci chondrites except for a negative eu anomaly such a precursor melt could have been produced by 2 5 equilibrium partial melting of an h chondrite silicate protolith or by higher degrees of partial melting involving subsequent fractional crystallization glass appears to have formed by the remelting of pre existing plagio clase and orthopyroxene in a process that involved either disequilibrium or substantial melting of these phases during remelting silicate melt reacted with the feni metal host and feo was reduced to fe metal following remelting and metal silicate mixing inclusions apparently cooled at different rates in a near surface setting on the parent body glass or pigeonite bearing inclusions cooled more rapidly 2 5 c hr between 1000 850 c than pigeonite free largely crystalline inclusions the results of this study point to two likely models for forming iie iron meteorites both involving collision between an feni metal impactor and either a differentiated or undifferentiated silicate rich target of h chondrite affinity each model has difficulties and it is possible that both are required to explain the diverse iie group copyright 1999 elsevier science ltd

generation and polybaric differentiation of east greenland early tertiary flood basalts major element trace element isotope and petrographic studies of magma diverentiation mantle melting the basal volcanics in the kangerdlugssuaq fjord region of the east greenland margin provide constraints on the generation and subsequent diverentiation and contamination histories of magmas during the early stage of continental rifting creating the north atlantic ocean basin most primitive lavas of the succession are introduction shown to have accumulated olivine corrections for crystal ac the distinctive geochemical features of continental flood cumulation yield estimates for erupted primitive liquids with mgo basalts cfbs are strongly controlled by the composition contents between 9 and 13 wt the occurrence of suspended and structure of the continental lithosphere and underfo88 olivine phenocrysts further requires the existence of parental lying mantle significant controversy remains concerning magmas with mgo contents up to 17 wt and feo contents up the balance of contributions from the lithosphere and to 14 wt quantitative modeling of fractionation indicates the mantle and the mechanisms by which the various that kangerdlugssuaq magmas primarily diverentiated at moderate source components contribute to basalt petrogenesis pressures 8 kbar to form dunitic and wehrlitic cumulates at how are basalt compositions influenced by generation depths of 25 km evolved east greenland flood basalts from the in anomalous regions in the deep mantle plumes by scoresby sund region record a more complex fractionation history interaction between rising magmas and the continental involving olivine clinopyroxene fractionation in the lower crust lithospheric mantle and by contamination with conas found for the lower basalts followed by olivine plagioclase tinental crust how are the diverentiation con clinopyroxene fractionation at shallow crustal levels cor tamination magma mixing and storage histories of cfbs relations between sio2 incompatible elements and sr nd isotopic controlled by the structure of the continental lithosphere ratios for the lower basalts are consistent with bulk assimilation and how do the thermal and chemical features of the of up to 15 20 archean leucogneiss with unradiogenic sr and mantle and the extensional history of the continental nd isotopic ratios characteristic of lewisian type lower crust lithosphere avect mantle melting and compositions of comparisons between inferred magma types for lower basalts and primary liquids estimated primary liquids from elsewhere in the north atlantic these questions are best addressed in the context of show complex relationships among feo mgo tio2 contents a geologically and geochemically well constrained cfb and cao al2o3 ratios that relate to regional and temporal changes province such as the north atlantic tertiary province in mantle temperatures lithospheric thickness and involvement of separation of east greenland from northern europe in at least two end member mantle sources we postulate that the the early tertiary at 60 myr ago was accompanied by lower basalts of east greenland were derived from iron poor voluminous volcanic activity the blosseville coast of mantle depleted by prior melt extraction and distinct from morb east greenland extending from kangerdlugssuaq fjord source mantle that was enriched in tio2 and lrees by a to scoresby sund fig 1 contains spectacularly exposed metasomatic event shortly before early tertiary magmatism we sections of lavas these sections begin at the basal contact associate this depleted mantle source with the ancestral iceland of the lavas with underlying cretaceous tertiary sediments and archean basement and continue to the plume anomaly

petrogenesis of picritic mare magmas constraints on the extent of early lunar differentiation calculations of isobaric batch polybaric batch and polybaric fractional melting have been carried out on a variety of proposed lunar and terrestrial source region compositions results show that magmas with a generally tholeiitic character plagioclase and high ca pyroxene crystallize before low ca pyroxene reflecting relatively high al2o3 concentrations 12 wt are the inevitable consequence of anhydrous partial melting of source regions composed primarily of olivine and two pyroxenes with an aluminous phase on the solidus low al2o3 magmas 10 wt as typified by the green picritic glasses in the lunar maria require deep 700 1000 km low al2o3 source regions without an aluminous phase the difference between primitive and depleted mantle beneath mid ocean ridges amounts to less than 0 1 wt al2o3 whereas formation of the green glass source region requires a net loss of between 1 5 and 2 5 wt al2o3 basalt extraction cannot account for fractionations of this magnitude accumulation of olivine and pyroxene at the base of a crystallizing magma ocean is however an effective method for producing the necessary al2o3 depletions both olivine rich and pyroxene rich source regions can produce the picritic magmas but mixing calculations show that both types of source region are likely to be hybrids consisting of an early to intermediate stage cumulate olivine plus enstatite and a later stage cumulate assemblage mass balance calculations show that refractory element enriched bulk moon compositions contain too much al2o3 to allow for the deep low al2o3 source regions even after extraction of an al2o3 rich 26 30 wt crust between 50 and 70 km thick

the parent magma of the nakhlite meteorites clues from melt inclusions abstract several forms of trapped liquid found within nakhlite meteorites have been examined including interstitial melt and magmatic inclusions within the cores of large olivine grains differences in the mineralogy and texture between two types of trapped melt inclusions and between these inclusions and the mesostasis indicate that vitrophyric inclusions are most appropriate for estimating the composition of a nakhlite parental magma in equilibrium with early forming olivine and augite parent liquids were calculated from the mineralogy of large inclusions in nakhla and governador valadares using a system of mass balance equations solved by linear regression methods the chosen parental liquids were cosaturated in olivine and augite and had mg fe values consistent with measured augite liquid kd s these parental magma compositions are similar to other published compositions for nakhla chassigny and shergotty parental melts and may correspond to a significant magma type on mars

petrology of the yamato nakhlites the yamato nakhlites y 000593 y 000749 and y 000802 were recovered in 2000 from the bare icefield around the yamato mountains in antarctica consisting of three independent specimens with black fusion crusts they are paired cumulate clinopyroxenites we obtained the intercumulus melt composition of the yamato nakhlites and here call it the yamato intercumulus melt yim the yim crystallized to form the augite rims the olivine rims and the mesostasis phases in the cumulates the augite rims consist of two layers inner and outer the crystallization of the inner rim drove the interstitial melt into the plagioclase liquidus field subsequently the residual melt crystallized pigeonites and plagioclase to form the outer rims and the mesostasis three types of inclusions were identified in olivine phenocrysts rounded vitrophyric angular vitrophyric and monomineralic augite inclusions the monomineralic augite inclusions are common and may have been captured by growing olivine phenocrysts the rounded vitrophyric inclusions are rare and may represent the composition of middle stage melts whereas the angular vitrophyric inclusions seem to have been derived from fractionated late stage melts glass inclusions occur in close association with titanomagnetite and ferroan augite halo in phenocryst core augites and the assemblages may be magmatic inclusions in augites we compared the yim with compositions of magmatic inclusions in olivine and augite the composition of magmatic inclusions in augite is similar to the yim phenocrystic olivines contain exsolution lamellae augite magnetite aggregates and symplectites in the cores the symplectites often occur at the boundaries between olivine and augite grains the aggregates symplectite and lamellae formed by exsolution from the host olivine at magmatic temperatures we present a formational scenario for nakhlites as follows 1 accumulation of augite olivine and titanomagnetite phenocrysts took place on the floor of a magma chamber 2 olivine exsolved augite and magnetite as augite magnetite aggregates symplectites and lamellae 3 the overgrowth on olivine phenocrysts formed their rims and the inner rims crystallized on augite phenocryst cores and finally 4 the outer rim formed surrounding the inner rims of augite phenocrysts and plagioclase and minor minerals crystallized to form mesostasis under a rapid cooling condition probably in a lava flow or a sill

some phase equilibrium constraints on the origin of proterozoic massif anorthosites and related rocks experimental data in the range of 1 bar to 13 kbar enable us to introduction map the liquidus equilibria relevant to proterozoic massif anorthere is hardly a consensus on the petrogenesis of thosites and related mafic rocks massif anorthosites are widely proterozoic massif anorthosites but many investigators believed to have formed by accumulation of plagioclase into highbelieve in a petrogenetic scheme that involves at least al basaltic liquids mantle derived basaltic liquids fractionating two major stages 1 extensive crystallization asat pressures sufficiently high 10 13 kbar to crystallize the highly similation of a mantle derived magma ponded at or aluminous orthopyroxene megacrysts typically observed in anorthosite near the base of the crust that produces suspensions of massifs reach plagioclase saturation at low normative silica contents plagioclase in fe rich high al gabbroic liquids followed peritectic like equilibria e g liq opx plag cpx sp by 2 intrusion of these suspensions into the mid upper and a thermal divide on the plagioclase pyroxene liquidus surface crust where they form complex magma chambers e g ensure that mantle derived liquids become nepheline normative with duchesne 1984 emslie 1985 ashwal 1993 wiebe further crystallization and crustal assimilation at depth such 1994 a key component of the scheme is the presence liquids cannot produce the full range of troctolitic noritic to trocin most massifs of high al orthopyroxene megacrysts tolitic gabbroic mineral assemblages observed in anorthosite massifs haom emslie 1975 that appear to preserve a record without extensive low pressure granite assimilation conversely the of the high pressure stage maquil duchesne 1984 array of plausible anorthosite parental liquids not only lies along longhi et al 1993 the structures of massifs vary from the trace of the plagioclase two pyroxene cotectic from 10 to 13 those that are composites of multiple diapiric intrusions kbar but also straddles the thermal divide on the plagioclase harp lake emslie 1980 rogaland duchesne 1984 pyroxene liquidus surface this condition requires mafic source to intrusive bodies with well developed layering of regions such as lower continental crust or foundered mafic plutons leucocratic troctolites and leuconorites or leucogabbros for liquids parental to massif anorthosites and associated mafic overlain by masses of anorthosite michikamau emslie intrusions 1970 laramie frost et al 1993 so there may be

graphical analysis of the orthopyroxene pigeonite augite plagioclase equilibrium at liquidus temperatures and low pressure there are both natural and experimental observations of the coexistence of three pyroxenes orthopyroxene opx pigeonite pig augite aug with plagioclase pl commonly the assemblage occurs as an intermediate product in the following fractionation trend of a mafic magma opx aug pl opx aug pig pl aug pig pl to clarify the phase equilibria constraints on the existence of this mineral assemblage we have graphically analyzed the change in topology of an isobaric isoplethic section ol aug pl qtz with fe 25 50 where fe fe fe mg and an 50 arising from an increase in the fe value of silicate liquid the analysis shows that the stability field of the mineral assemblage opx aug pig pl is restricted and can onlycrystallize in the interval between two invariant points t 4 1 ol opx pig aug pl l and t 4 2 qtz opx pig aug pl l that emerge successively during expansion of a liquidus volume of pigeonite within the isobaric isoplethic section ol aug pl qtz at fe values lower than t 4 1 the 3 pyroxene assemblage cannot exist due to the absence of a contact surface between the primary volumes of plagioclase and pigeonite at fe values greater than t 4 2 the assemblage is unstable due to separation of the primary volumes of orthopyroxene and augite

a low viscosity lunar magma ocean forms a stratified anorthitic flotation crust with mafic poor and rich units much of the lunar crust is monomineralic comprising 98 plagioclase the prevailing model argues the crust accumulated as plagioclase floated to the surface of a solidifying lunar magma ocean lmo whether 98 pure anorthosites can form in a flotation scenario is debated an important determinant of the efficiency of plagioclase fractionation is the viscosity of the lmo liquid which was unconstrained here we present results from new experiments conducted on a late lmo relevant ferrobasaltic melt the liquid has an exceptionally low viscosity of 0 22 0 19 0 11 to 1 45 0 82 0 46 pa s at experimental conditions 1 300 1 600 c 0 1 4 4 gpa and can be modeled by an arrhenius relation extrapolating to lmo relevant temperatures our analysis suggests a low viscosity lmo would form a stratified flotation crust with the oldest units containing a mafic component and with very pure younger units old impure crust may have been buried by lower crustal diapirs of pure anorthosite in a serial magmatism scenario

anhydrous liquid line of descent of yamato 980459 and evolution of martian parental magmas we report the results of nominally anhydrous equilibrium and fractional crystallization experiments on a synthetic yamato 980459 y98 bulk composition at 0 5 gpa these experiments allow us to test a suggested fractional crystallization model calculated using melts by symes et al 2008 in which a y98 like initial liquid yielded a magma closely resembling the bulk composition of que 94201 although the two meteorites cannot be cogenetic owing to their age difference they are thought to represent bona fide magmatic liquids rather than products of crystal accumulation as are most martian basaltic meteorites hence understanding possible petrogenetic links between these types of liquids could be revealing about processes of melting and crystallization that formed the range of martian basalts we find that y98 can in fact generate a residual liquid closely resembling que but only after a very different crystallization process and different degree of crystallization than that modeled using melts in addition both the identity and sequence of crystallizing phases are very different between model and experiments our fractional crystallization experiments do not produce a que like liquid and the crystallizing phases are an even poorer match to the melts calculated compositions than in the equilibrium runs however residual liquids from our experiments define a liquid line of descent that encompasses bulk compositions of parental melts calculated for several martian basaltic meteorites suggesting that the known martian basaltic meteorites had their ultimate origin from the same or very similar source lithologies these are in turn similar to source rocks modeled by previous studies as products of extensive crystallization of an initial martian magma ocean

comment on parent body depth pressure temperature relationships and the style of the ureilite anatexis by p h warren maps 47 209 227 ureilites are carbon rich ultramafic olivine dominantly low ca pyroxene achondrites with poorly understood petrogenesis one major problem concerns the origin of extensive variation in feo content olivine core fo values ranging from approximately 75 to 95 among the individual ureilites the two main competing hypotheses to explain this variation are 1 equilibrium smelting in which ureilite fo values were established by pressure dependent depth linked carbon redox reactions on the ureilite parent body during partial melting or 2 nebular inheritance in which the variation in feo contents was derived from ureilite precursors and was preserved during partial melting the paper parent body depth pressure temperature relationships and the style of the ureilite anatexis by warren 2012 discusses a series of topics related to ureilite petrogenesis in each case an argument is presented within the context of smelting versus nonsmelting models collectively these arguments create the impression that there are many valid arguments against smelting the purpose of this comment is to point out flaws in some of these arguments and or to show that the issues they address are independent of smelting versus nonsmelting models both equilibrium smelting and nebular inheritance simple anatexis models face challenges in explaining all the properties of ureilites but both remain viable

a partial melting study of an ordinary h chondrite composition with application to the unique achondrite graves nunataks 06128 and 06129 melting experiments of a synthesized alkali bearing h chondrite composition were conducted at ambient pressure with three distinct oxygen fugacity conditions iw 1 iw and iw 2 oxygen fugacity conditions significantly influence the compositions of partial melts partial melts at iw 1 are distinctly enriched in sio2 relative to those of iw and iw 2 melts the silica enriched reduced iw 1 melts are characterized by high alkali contents and have silica oversaturated compositions in contrast the silica depleted oxidized iw melts which are also enriched in alkali contents have distinctly silica undersaturated compositions these experimental results suggest that alkali rich felsic asteroidal crusts as represented by paired achondrites graves nunataks 06128 and 06129 should originate from a low degree relatively reduced partial melt from a parent body having near chondritic compositions based on recent chronological constraints and numerical considerations as well as our experimental results we propose that such felsic magmatism should have occurred in a parent body that is smaller in size and commenced accreting later than those highly differentiated asteroids having basaltic crusts and metallic cores

crystallization experiments of intercumulus melts for nakhlites under qfm 2 at 1 bar crystallization of parent melts for nakhlites was experimentally studied under qfm 2 at one bar isothermal experiments suggest that melts having parent magma composition for nakhlites crystallize both augites and titanomagnetites at liquidus temperatures of 11441154 c compositions of the augites are identical to those of phenocrystic core augites en36 38fs22 25wo39 40 in nakhlites no olivines crystallize from the isothermal runs and solidus temperature is about 1000 c linear cooling experiments were carried out at various cooling rates 117 c h ranging from liquidus to solidus temperatures under similar pressure conditions to the isothermal runs augites titanomagnetites and fayalites crystallized in the cooling runs but magnesian olivines never crystallized there magnesian core augite in the cooling runs has the same composition as those of nakhlites rims of augite crystals from the cooling runs of 1 4 c h consist of two layers ferroan augite inner rim and hedenbergite outer rim which are very similar to those in the miller range mil 03346 nakhlite small amounts of pyroxferroite crystallized in mesostasis and augite rims from two cooling runs titanomagnetites from cooling runs never accompany ilmenite lamellae as seen in nakhlites suggesting that the subsolidus cooling rate of the cooling runs was much more rapid than those of nakhlite intercumulus melts the cooling experiments reproduce the crystallization processes of pyroxenes and the compositional change of residual melt for a rapidly cooled magma such as mil 03346

magma traps and driving pressure consequences for pluton shape and emplacement in an extensional regime abstract the level of emplacement and final form of felsic and mafic igneous rocks of the wichita mountains igneous province southwestern oklahoma u s a are discussed in light of magma driving pressure lithostatic load and crustal magma traps deposition of voluminous a type rhyolites upon an eroded gabbroic substrate formed a subhorizontal strength anisotropy that acted as a crustal magma trap for subsequent rising felsic and mafic magma intruded along this crustal magma trap are the a type sheet granites length thickness 100 1 of the wichita granite group of which the mount scott granite sheet is typical and smaller plutons of biotite bearing roosevelt gabbro in marked contrast to the subhorizontal granite sheets the gabbro plutons form more equant stocks with flat roofs and steep side walls late diabase dikes cross cut all other units but accompanying basaltic flows are extremely rare in the volcanic pile based on magmastatic calculations we draw the following conclusions concerning the level of emplacement and the shape of these intrusions 1 magma can rise to a depth at which the magma driving pressure becomes negligible magma that maintains a positive driving pressure at the surface has the potential to erupt 2 magma ascent may be arrested at a deeper level in the crust by a subhorizontal strength anisotropy i e crustal magma trap if the magma driving pressure is greater than or equal to the lithostatic load at the depth of the subhorizontal strength anisotropy 3 subhorizontal sheet intrusions form along crustal magma traps when the magma driving pressure greatly exceeds the lithostatic load under such conditions the magma driving pressure is sufficent to lift the overburden to create the necessary space for the intrusion 4 thicker steep sided stocks or batholiths with flat roofs form at crustal magma traps when the magma driving pressure approximates that of the lithostatic load under these conditions the necessary space for the intrusion must be created by other mechanisms e g stoping 5 subvertical sheets i e dikes form when the magma driving pressure is less than the lithostatic load at the level of emplacement