the source region and melting mineralogy of high titanium and low titanium lunar basalts deduced from lu hf isotope data five high ti basalts from the apollo 11 and 17 landing sites have been analyzed for their hafnium isotope composition these data serve to better constrain the hafnium isotope variation of the moon s mantle variations in initial hf and nd values of low and high ti basalts imply that the source region mineral assemblages of these lunar magma types are distinct low ti basalts have higher initial hf values at a given nd value than high ti basalts the differences in the hafnium and neodymium isotopic composition of low and high ti basalts reflect the fact that the source of low ti basalts had a lu hf n ratio approximately four times greater than its sm nd n ratio in contrast the high ti source region had subequal lu hf n and sm nd n ratios if it is assumed that mare basalts are partial melts of the moon s cumulate mantle the differences between low and high ti basalts can only be explained by these mare magma types being generated from melting sources with distinctly different mineral assemblages the large lu hf fractionations relative to sm nd fractionations of low ti basalts can best be produced by an assemblage of olivine and orthopyroxene with trace amount of clinopyroxene that crystallized early in the history of the lunar magma ocean lmo the subequal lu hf n and sm nd n fractionations of high ti basalts can be produced from a variety of ilmenite bearing mineral assemblages low and high ti basalts have similar lu hf ratios approximately 0 6 times chondrite the low lu hf ratios measured for these mare magmas contrast sharply with the high lu hf ratios greater than chondritic calculated for their sources from initial hf values and an assumed chondritic bulk moon initial hf value the difference between the measured lu hf of a lava vs the calculated lu hf of its source implies that during partial melting lu was preferentially retained in the residual source relative to hf in order to explain the extreme fractionation of measured lu hf ratios we suggest mare basalts can best be explained using a polybaric melting model initial melting of a garnet bearing source followed by continued melting in the spinel stability field can produce the required lu hf fractionations and produce a liquid that last equilibrated with a residuum of olivine and orthopyroxene

samarium neodymium and rubidium strontium systematics of nakhlite governador valadares abstract the sm nd systematics of whole rock and mineral separate samples from nakhlite governador valadares define a good 147sm 143nd mineral isochron age of 1 37 0 02 ga this age is in excellent agreement with the 39ar 40ar and rb sr ages obtained previously for this meteorite however the rb sr isotopic data for our sample show that the isotopic system is disturbed the lack of isotopic equilibrium is probably caused by the weathering of the sample as indicated by the presence of secondary alteration phases the whole rock and acid washed mineral data yield a rb sr age of 1 20 0 05 ga which probably represents a lower limit to the crystallization age of the rock the petrographic evidence indicates that this meteorite is a clinopyroxene cumulate that probably crystallized in a subsurface sill mcsween 1994 thus the sm nd isotopic age probably represents the age of such a magmatic event the initial e143nd value determined for the rock at 1 37 ga is 17 1 indicating that the parent magma of the rock came from a light rare earth element depleted source of 147sm 144nd 0 237 based on a simple two stage evolution model results of the same model calculation for the initial 87sr 86sr ratio of the rock suggest that its source material was depleted in 87rb 86sr by 50 relative to the estimated martian value at 1 37 ga both the high sm nd and low rb sr values support a clinopyroxene rich cumulate source for the genesis of the nakhlite governador valadares furthermore our sm nd age and e143nd data and the previously published e142nd datum for the rock harper et al 1995 are consistent with early differentiation of the parent planet formation of cumulate sources 4 56 ga ago and late melting of the sources and formation of the rock 1 37 ga ago the good agreement of isotopic ages and petrographic features among governador valadares nakhla and lafayette strongly suggests that all three nakhlites have undergone similar evolutionary histories the nakhlite age data suggest that isotopic heterogeneity in the martian mantle sources existed up to 1 37 ga ago and early mantle structures probably have not been disturbed for a significant portion of martian history

remnant colloform pyrite at the haile gold deposit south carolina a textural key to genesis auriferous iron sulfide bearing deposits of the carolina slate belt have distinctive mineralogical and textural features traits that provide a basis to construct models of ore deposition our identification of paragenetically early types of pyrite especially remnant colloform crustiform and layered growth textures of pyrite containing electrum and pyrrhotite establishes unequivocally that gold mineralization was coeval with deposition of host rocks and not solely related to paleozoic tectonic events ore horizons at the haile deposit south carolina contain many remnants of early pyrite 1 fine grained cubic pyrite disseminated along bedding 2 fine grained spongy rounded masses of pyrite that may envelop or drape over pyrite cubes 3 fragments of botryoidally and crustiform layered pyrite and 4 pyritic infilling of vesicles and pumice detailed mineral chemistry by petrography microprobe sem and eds analysis of replaced pumice and colloform structures containing both arsenic compositional banding and electrum points to coeval deposition of gold and the volcanic host rocks and thus confirms a syngenetic origin for the gold deposits early pyrite textures are present in other major deposits of the carolina slate belt such as ridgeway and barite hill and these provide strong evidence for models whereby the sulfide ores formed prior to tectonism the role of paleozoic metamorphism was to remobilize and concentrate gold and other minerals in structurally prepared sites recognizing the significance of paragenetically early pyrite and gold textures can play an important role in distinguishing sulfide ores that form in volcanic and sedimentary environments from those formed solely by metamorphic processes exploration strategies applied to the carolina slate belt and correlative rocks in the eastern united states in the avalonian basement will benefit from using syngenetic models for gold mineralization

a petrogenetic model for the origin and compositional variation of the martian basaltic meteorites the major element trace element and isotopic compositional ranges of the martian basaltic meteorite source regions have been modeled assuming that planetary differentiation resulted from crystallization of a magma ocean the models are based on low to high pressure phase relationships estimated from experimental runs and estimates of the composition of silicate mars from the literature these models attempt to constrain the mechanisms by which the martian meteorites obtained their superchondritic cao al2o3 ratios and their source regions obtained their parent daughter 87 rb 86 sr 147 sm 144 nd and 176 lu 177 hf ratios calculated from the initial sr nd and hf isotopic compositions of the meteorites high pressure experiments suggest that majoritic garnet is the liquidus phase for mars relevant compositions at or above 12 gpa early crystallization of this phase from a martian magma ocean yields a liquid characterized by an elevated cao al2o3 ratio and a high mg olivine pyroxene garnet dominated cumulates that crystallize subsequently will also be characterized by superchondritic cao al2o3 ratios melting of these cumulates yields liquids with major element compositions that are similar to calculated parental melts of the martian meteorites furthermore crystallization models demonstrate that some of these cumulates have parent daughter ratios that are similar to those calculated for the most incompatible element depleted source region i e that of the meteorite queen alexandra que 94201 the incompatible element abundances of the most depleted que 94201 like source region have also been calculated and provide an estimate of the composition of depleted martian mantle the incompatible element pattern of depleted martian mantle calculated here is very similar to the pattern estimated for depleted earth s mantle melting the depleted martian mantle composition reproduces the abundances of many incompatible elements in the parental melt of que 94201 e g ba th k p hf zr and heavy rare earth elements fairly well but does not reproduce the abundances of rb u ta and light rare earth elements the source regions for meteorites such as shergotty are successfully modeled as mixtures of depleted martian mantle and a late stage liquid trapped in the magma ocean cumulate pile melting of this hybrid source yields liquids with major element abundances and incompatible element patterns that are very similar to the shergotty bulk rock

two stage plume melting a possible mechanism for the origin of martian magmatism abstract the origin of martian magmatism is investigated by geochemical modeling based on the isotopic and rare earth element ree compositions of the shergottite nakhlite and chassignite snc meteorites the model proposed in this study consists of three processes early mantle differentiation in the deepest mantle to produce a plume source region composed of hydrated ringwoodite and majorite first stage dehydration melting of the plume to produce nakhlite and chassignite magmas in the deep mantle and finally second stage decompression melting of the residual plume to produce shergottite magmas in the uppermost mantle the production of light ree enriched nakhlite and chassignite magmas can be explained by the persistence of residual garnet through first stage melting and the depleted isotopic composition of the nakhlite and chassignite meteorites can be reasonably attributed to the presence of majorite in the plume source region the strongly depleted ree and isotopic composition of the primitive shergottites can similarly be explained by the existence of majorite in the plume source region coupled with extraction of the nakhlite melt from the depleted source the proposed two stage plume melting model therefore reproduces the chemical and isotopic variations of the martian magmas well suggesting a genetic relationship among the snc magmas

chronology and petrogenesis of young achondrites shergotty zagami and alha77005 late magmatism on a geologically active planet a study was undertaken to determine the chronology petrogenesis and relationships among the shergottites shergotty and zagami and the unique achondrite alha77005 these meteorites are the product of a variety of complex processes petrogenesis chondrite normalized abundance patterns of shergotty and zagami are very similar and show pronounced depletions of both the light ree la nd and heavy ree dy lu relative to sm gd these characteristic depletions are even more pronounced for alha77005 the light ree depletion is qualitatively consistent with the presence of cumulus pyroxene and or olivine in these meteorites but trace element models show that the parental magmas of all three meteorites were probably also light ree depleted both trace element model calculations and combined rb sr and sm nd isotopic systematics show that the meteorites could not have been co magmatic nor can alha77005 be representative of the source material of the shergottites light ree depletion of the parental magmas also implies light ree depletion of the source material the sm nd systematics of the shergottites require a time averaged sub chondritic light ree enriched sm nd ratio since 4 6 ae ago the sm nd systematics of alha77005 permit a time averaged super chondritic light ree depleted sm nd ratio if its crystallization age is less than tice 0 72 ae chronology rb sr internal isochrons for all three meteorites and a sm nd internal isochron for zagami are concordant at 180 myr 39ar 40ar plateau ages of shergotty and zagami maskelynite are 250 260 myr these ages apparently reflect resetting of these isotopic systems by shock metamorphism which converted the feldspar to maskelynite the concordance of these ages suggests a single shock event during which the meteorites were in close physical proximity the time of this event is most precisely given by the rb sr age of 180 4 myr for zagami the crystallization ages of the meteorites were not precisely determined extreme upper limits are determined by sm nd model ages relative to an eucrite initial 143nd144nd 0 505835 at 4 6 ae ago these model ages for shergotty zagami and alha77005 are 3600 3500 and 2850 myr respectively the sm nd whole rock age of 1340 60 myr for the three meteorites gives the crystallization age if the sm nd ratios of the precursor materials were always the same we consider this 1340 myr age as a best estimate upper limit best estimate lower limits for shergotty and zagami are taken from the average 39ar 40ar ages of 1200 and 900 myr of pyroxene separates the average 39ar 40ar age of a whole rock sample of alha77005 was 1600 myr and can be partitioned between a low temperature feldspar phase and a high temperature olivine pyroxene inclusions phase the average apparent 39ar 40ar age of the low temperature phase is 1050 myr which is chosen as the best estimate lower limit to the age the crystallization ages of shergotty zagami and alha77005 probably lie within the ranges of 1200 1300 900 1300 and 1000 1300 myr respectively the rb sr whole rock age of 4400 400 myr and single stage babi model ages of 4800 5100 myr are interpreted as reflecting differentiation of the parent body at 4600 myr ago the complex geochemical and isotopic evolution recorded by these meteorites suggests a geologically active parent body capable of sustaining melting at two or more epochs in its history

magma reservoir systems inferred from tilt patterns inflation patterns based on water tube tiltmeter and levelling observation show different features for krafla volcano in iceland and kilauea volcano in hawaii monotonous sawtooth shape inflation is observed at krafla while inflation curves at kileauea are more or less complicated the difference was attributed to differences in the system of magma reservoir for the two volcanoes by using the electrical equivalent of a magma reservoir and volcanic conduit as a capacitor and a resistor an electrical oseillator was considered to be a possible model for a magma reservoir system in the case of krafla the magma reservoir system is replaced with one electric oscillator called single system or icelandic type system

seismic monitoring and modeling of an active volcano for prediction we describe seismic monitoring and modeling of an active volcano for the purpose of predicting the magma transport process in real time we selected the piton de la fournaise which has been monitored by an observatory since the early 1980s and is active with 28 eruptions from 1980 until august 1992 it erupted on march 9 1998 after an unusually long quiet period the eruption lasted until september 21 1998 before the march eruption we completed the initial construction of a model of a magma system based primarily on long period lp events and coda localization we found that lp events are associated with the lateral movement of magma to the rift zone and not with the vertical movement to the summit we also found that the source of 2 hz lp events is located below that of 1 hz lp events the coda localization is a newly discovered phenomenon that helped to locate a magma body this model was used for interpreting the incoming information from the precursory seismic crisis and the eruption tremor during the 6 months of the eruption the simultaneous monitoring and modeling of an active volcano led us to a quantitative simulation of the eruption process computing excess pressure and flow rate in a system of reservoirs connected by channels

rare earth element partition coefficients from enstatite melt synthesis experiments enstatite en80fs19wo01 was synthesized from a hypersthene normative basaltic melt doped at the same time with la ce nd sm eu dy er yb and lu the rare earth element concentrations were measured in both the basaltic glass by empa and the enstatite by sims rare earth element concentrations in the glass were determined by electron microprobe analysis with uncertainties less than two percent relative rare earth element concentrations in enstatite were determined by secondary ion mass spectrometry with uncertainties less than five percent relative the resulting rare earth element partition signature for enstatite is similar to previous calculated and composite low ca pigeonite signatures but is better defined and differs in several details first the enstatite lree signature is steeper than for pigeonite second the signature has a negative eu anomaly which relates to oxygen fugacity and third the dependence of the partition coefficients on alumina content is linked to crystal structural constraints

the age of the martian meteorite northwest africa 1195 and the differentiation history of the shergottites samarium neodymium isotopic analyses of unleached and acid leached mineral fractions from the recently identified olivine bearing shergottite northwest africa 1195 yield a crystallization age of 347 13 ma and an end143 value of 40 1 0 9 maskelynite fractions do not lie on the sm nd isochron and appear to contain a martian surface component with low 147sm 144nd and 143nd 144nd ratios that was added during shock the rb sr system is disturbed and does not yield an isochron terrestrial sr appears to have affected all of the mineral fractions although a maximum initial 87sr 86sr ratio of 0 7016 is estimated by passing a 347 ma reference line through the maskelynite fraction that is least affected by contamination the high initial end143 value and the low initial 87sr 86sr ratio combined with the geologically young crystallization age indicate that northwest africa 1195 is derived from a source region characterized by a long term incompatible element depletion the age and initial sr and nd isotopic compositions of northwest africa 1195 are very similar to those of queen alexandra range 94201 indicating these samples were derived from source regions with similar sr nd isotopic systematics these similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano the meteorites yamato 980459 dar al gani 476 sayh al uhaymir 005 008 and dhofar 019 also have relatively old ages between 474 and 575 ma and trace element and or isotopic systematics that are indicative of derivation from incompatible element depleted sources this suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible element depleted sources closed system fractional crystallization of this suite of meteorites is modeled with the melts algorithm using the bulk composition of yamato 980459 as a parent these models reproduce many of the major element and mineralogical variations observed in the suite in addition the rare earth element systematics of these meteorites are reproduced by fractional crystallization using the proportions of phases and extents of crystallization that are calculated by melts other shergottites that demonstrate enrichments in incompatible elements and have evolved sr and nd isotopic systematics have some geochemical systematics that are similar to those observed in the depleted group most notably although they exhibit a very limited range of incompatible trace element and isotopic compositions they have highly variable major element compositions this is also consistent with evolution from a common mantle source region by variable amounts of fractional crystallization if this scenario is correct it suggests that the combined effects of source composition and fractional crystallization are likely to account for the major element trace element and isotopic diversity of all shergottites

volcanic rock hosted gold and base metal mineralization associated with neoproterozoic early paleozoic back arc extension in the carolina terrane southern appalachian piedmont volcanogenic mineral deposits in the carolina terrane southern appalachian piedmont include kuroko type polymetallic massive sulfide deposits and disseminated gold pyrite deposits associated with propylitic silicic argillic and advanced argillic alteration host rocks are metavolcaniclastic and metaepiclastic rocks of a neoproterozoic early cambrian magmatic arc the favorable gold horizon is the transition from a lower succession of andesitic and rhyolitic pyroclastic rocks with basal mafic lavas to an upper sequence of epiclastic sedimentary units and minor lava and ash flows kuroko type deposits are associated with mafic to bimodal volcanic rocks in the upper sequence whole rock oxygen isotope analyses indicate that gold mineralization is associated with a transition from hydrothermal systems dominated by isotopically relatively light 18o 6 to 10 waters typical of high latitude subaerial systems to seawater 18o 0 plots of 18o vs sio2 of the host rocks show a compositional gap associated with mineralization at the subaerial to submarine transition values of 18o for the hydrothermal waters lithostratigraphic analyses and tectonic models of the carolina terrane demonstrate that mineralization coincided with extension in a rifted arc

u pb zircon ages and pb isotope geochemistry of gold deposits in the carolina slate belt of south carolina volcanic rocks of the persimmon fork formation host the largest known gold mines of the carolina slate belt u pb shrimp zircon ages have been obtained from rocks closely associated with pyrite enargite gold deposits at brewer quartz topaz rhyolite breccia from the argillic alteration zone in the brewer pit and felsic ash flow tuff from the quartz sericite alteration zone from the disseminated and semimassive pyrite gold deposits at haile crystal lithic rhyolitic ash flow tuffs from the champion pit and from the ridgeway deposit felsic ash flow tuff from the stratigraphic host of the north pit gold deposit generally the zircons are fine grained fractured and contain crystal imperfections corrosion inclusions and pits 206 pb 238 u zircon spot ages for all deposits span a wide range mostly from 400 to 760 ma inclusions and cores indicative of inherited domains in the zircons were not found and only a few analyses range from 1 1 to 1 8 ga a distinct xenocrystic zircon population was not identified the 206 pb 238 u weighted age averages of zircon indicate the following crystallization dates for the volcanic and volcaniclastic rocks closely associated with the gold deposits 550 3 ma for brewer 553 2 ma for haile and 556 2 ma for the ridgeway deposit these zircon crystallization ages represent close estimates of the age of the original gold mineralizing events younger zircon spot ages can be attributed to the effects of paleozoic regional metamorphism pb isotope compositions of sulfide minerals galena pyrite enargite sphalerite chalcopyrite and molybdenite and silicate minerals k feldspar and sericite in the gold deposits help to constrain the sources of fluids and metals during the mineralizing events the deposits are pyrite rich containing multiple generations of pyrite including early crystallized pyrite that is closely associated with the original gold mineralizing event as well as recrystallized pyrite formed in response to paleozoic metamorphism pb isotope compositions of pyrite span a wide range including the most radiogenic values for the sulfides galena and k feldspar are not abundant but where present they are typically the least radiogenic minerals galena has a limited range of pb isotope compositions that are representative of the gold deposits as a group 206 pb 204 pb 18 020 18 326 207 pb 204 pb 15 550 15 639 208 pb 204 pb 37 605 38 286 values of 207 pb 204 pb straddle the average crustal pb growth curve consistent with contributions involving the mantle and continental crust whole rock pb isotope compositions of volcanic and volcaniclastic rocks of the persimmon fork formation nearly match the range for sulfides in the gold deposits subtle regional contrasts in pb isotope compositions exist among the deposits sulfide minerals from barite hill e g galena 206 pb 204 pb 206 pb 204 pb 18 169 haile 206 pb 204 pb 18 233 and brewer 206 pb 204 pb 18 311 in northern south carolina because pb isotope compositions of basement rocks from grenville massifs in the southern appalachians and sulfide minerals from the gold deposits do not match a direct genetic connection cannot be established diversity in values of 206 pb 204 pb and the relatively high values of 207 pb 204 pb suggest that the deposits evolved adjacent to or closely related to continental blocks perhaps linked to a back arc tectonic setting among potential younger analogues of the slate belt gold deposits are the sulfide deposits of the okinawa trough in the western pacific mantle derived isotopic contributions were more important at barite hill in southern south carolina the least radiogenic among the deposits where oceanic crust had developed than at brewer haile and ridgeway in northern south carolina where rifting thinned the continental crust

regional 18o depletion of neoproterozoic igneous rocks from avalonia cape breton island and southern new brunswick canada neoproterozoic igneous rocks of the avalonian mira terrane cape breton island and caledonia terrane southern new brunswick have experienced regional 18 o depletion the majority of these rocks have 18 o wr values between 1 and 6 markedly different from igneous rocks of the inboard ganderian terranes which have normal high 18 o wr values of 7 to 12 the 18 o depletion of these avalonian terranes resulted from pervasive hydrothermal alteration all of the igneous rocks contain classic propylitic alteration assemblages of turbid feldspar chlorite epidote sericite and calcite and host multiple generations of veins containing the same phases the 18 o values of the rock forming minerals show strong disequilibrium with qtz fs ranging from 2 5 to 11 0 and kfs plg from 0 5 to 1 0 such values are indicative of post magmatic hydrothermal alteration the hydrothermal alteration occurred at ca 560 550 ma during initial transcurrent rifting of avalonia at the gondwanan margin the development of rift wrench basins with associated bimodal volcanism allowed large volumes of hydrothermal fluids to penetrate and circulate within mira and caledonia terrane crust before its submergence in the early cambrian ca 540 530 ma the hydrothermal fluids were predominantly meteoric although the presence of a significant seawater component cannot be ruled out the almost ubiquitous 18 o depletion exhibited by the neoproterozoic rocks in these avalonian terranes is absent in the associated ganderian terranes suggesting that avalonia remained separate from ganderia until at least the cambrian ordovician this 18 o depletion provides an additional geochemical tool for identification of avalonian crust in other areas of the appalachians and europe

rare earth elements in minerals of the alha77005 shergottite and implications for its parent magma and crystallization history abstract rare earth element ree and selected trace element abundances were measured in individual grains of pyroxenes whitlockite maskelynite and olivine of the alha77005 shergottite minor 1 whitlockite which displays a negative eu anomaly indicative of co crystallization with plagioclase dominates the bulk rock ree pattern detectable ce anomalies in 20 of the pyroxene grains analyzed appear to be the result of weathering in the antarctic environment and indicate that pyroxene is particularly susceptible to element remobilization mineral compositions and textural observations suggest that alha77005 is a cumulate with 50 cumulus material olivine chromite olivine re equilibrated with intercumulus liquid on cooling the intercumulus liquid then crystallized as a closed system to form successively poikilitic low ca and high ca pyroxene followed by interstitial pyroxenes plagioclase whitlockite and other minor phases and reacted with cumulus crystals to form rims of different composition this crystallization sequence provides a constraint on the shergottite source region composition the alha77005 and shergotty intercumulus liquids had similar ree compositions however as opposed to shergotty if alha77005 was formed during the last 0 72 ga its parent melt was not contaminated by lree enriched material

experimental study of polybaric ree partitioning between olivine pyroxene and melt of the yamato 980459 composition insights into the petrogenesis of depleted shergottites abstract a synthetic composition representing the yamato 980459 martian basalt shergottite has been used to carry out phase relation and rare earth element ree olivine and pyroxene partitioning experiments yamato 980459 is a sample of primitive basalt derived from a reduced end member among martian mantle sources experiments carried out between 1 2 gpa and 1350 1650 c simulate the estimated pressure temperature conditions of basaltic melt generation in the martian mantle olivine melt and orthopyroxene melt partition coefficients for la nd sm eu gd and yb d ree values were determined by la icpms and are similar to the published values for terrestrial basaltic systems we have not detected significant variation in d values with pressure over the range investigated and by comparison with previous studies carried out at lower pressure we apply the experimentally obtained olivine melt and orthopyroxene melt d ree values to fractional crystallization and partial melting models to develop a three stage geochemical model for the evolution of martian meteorites in our model we propose two ancient 4 535 ga sources the nakhlite source located in the shallow mantle and the deep mantle source located close to the martian core mantle boundary these two sources evolved distinctly on the e 143 nd evolution curve due to their different sm nd ratios by partially melting the nakhlite source at 1 3 ga we are able to produce a slightly depleted residue nakhlite residue the nakhlite residue is left undisturbed until 500 ma at which point the depleted deep mantle source is brought up by a plume mechanism carrying with it high heat flow melts and isotopic signatures of the deep mantle e g e 182 w e 142 nd etc the plume derived deep mantle source combines with the nakhlite residue producing a mixture that becomes a mantle source herein referred to as the y98 source for yamato 980459 and the other depleted shergottites with the characteristic range of sm nd ratios of these meteorites the same hot plume provides a heat source for the formation of enriched and intermediate shergottites our model reproduces the ree patterns of nakhlites and depleted shergottites and can explain high e 143 nd in depleted shergottites furthermore the model results can be used to interpret whole rock rb sr and sm nd ages of shergottites

defining the mechanisms that disturb the sm nd isotopic systematics of the martian meteorites examples from dar al gani 476 and allan hills 77005 microbeam studies of martian meteorites dar al gani dag 476 and allan hills alh 77005 have been conducted to identify potential causes of disequilibrium exhibited in their sm nd isotopic systematics olivine and maskelynite mineral fractions on the dag 476 isochron are displaced relative to their positions as dictated by measured mineral compositions the olivine mineral fractions from alh 77005 not only have a relatively low sm nd ratio but appear to contain an unradiogenic component that shifts the olivine mineral fraction off the isochron defined by the pyroxene and maskelynite mineral fractions trace components such as melt inclusions impact melt high si mesostasis and altered olivine were analyzed using scanning electron microscopy quantitative electron microscopy and secondary ion mass spectrometry to determine their potential for disturbing the isotopic systematics of the mineral fractions assuming that the mineral fractions were not completely pure mixing models indicate that the presence of melt inclusions in the dag 476 olivine mineral fraction lowered its sm nd ratio the maskelynite mineral fraction contains a related but more evolved mesostasis component that raised the sm nd ratio of the fraction the position of two olivine mineral fractions below the alh 77005 isochron is interpreted to reflect small additions of impact melt with a light rare earth element enriched pattern and a non indigenous unradiogenic nd component furthermore the presence of rare earth elements in olivine and maskelynite from both igneous and non igneous components such as melt inclusions mesostasis and impact melt is observed on a fine 30 m scale despite the addition of this material the sm nd ages are not affected this study demonstrates that detailed mineral separation procedures as employed by modern geochronology laboratories permit reliable ages to be derived from shocked and altered samples

geochemistry and tectonic significance of the stony mountain gabbro north carolina implications for the early paleozoic evolution of carolinia abstract carolinia comprises a collection of neoproterozoic early paleozoic magmatic arc and sedimentary terranes that were amalgamated and accreted to laurentia in the early to middle paleozoic in central north carolina mafic rocks of the stony mountain gabbro intrude sub aqueous volcanic and sedimentary rocks and submarine epiclastic sedimentary rocks of the albemarle group the age of the stony mountain gabbro is constrained to the early cambrian middle ordovician field relations indicate that the gabbro represents the final phase of magmatism following the eruption and deposition of the neoproterozoic earliest cambrian albemarle group yet the gabbro pre dates regional metamorphism and tectonism related to the late ordovician accretion of carolinia to laurentia the stony mountain gabbro has a sub alkaline basaltic composition variable tio 2 mgo and ni cr values the rocks have a geochemical signature typical of island arcs the degree of lree enrichment prominent negative nb anomalies and nb th ratios are all features of low k to medium k tholeiitic basalts in modern island arc subduction related lavas isotope data are dominated by juvenile compositions that are consistent with derivation from lithospheric and asthenospheric sources during decompression melting of the mantle the stony mountain gabbro records subduction zone magmatism in a rifted island arc setting and can be modeled as the product of 10 15 hydrous partial melting of variable mixtures of morb and oib like mantle sources overprinted by a minor subducted slab derived hydrous fluid component by analogy with modern settings the rocks of the stony mountain gabbro are comparable to morb like to oib type enriched rocks from the lau island and sumisu rift and are interpreted to have formed within an evolving early paleozoic island arc back arc rift basin system the presence of an early cambrian arc back arc rift system in carolinia is broadly coeval with arc back arc volcanism in other peri gondwanan blocks of the appalachians and may be related to the early paleozoic opening of the rheic ocean

martian mantle mineralogy investigated by the 176lu 176hf and 147sm 143nd systematics of shergottites abstract chemical heterogeneities in the martian mantle are believed to result from the crystallization of a magma ocean in the first 100 million years of its history shergottite meteorites from mars are thought to retain a compositional record of such early differentiation and the resulting mineralogy at different depths the coupled 176 lu 176 hf and 147 sm 143 nd isotope systematics in 9 shergottites are used here to investigate these issues three compositional groups in the shergottites display distinct isotope systematics one group commonly termed as depleted is characterized by positive 176 hf i from 46 2 to 50 4 and 143 nd i from 36 2 to 39 1 another termed as enriched has negative 176 hf i 16 5 to 13 2 and 143 nd i 7 0 to 6 5 the third group is intermediate between the depleted and enriched groups with positive 176 hf i 30 0 to 33 4 and 143 nd i 16 9 together they describe mixing curves between 176 hf 177 hf 143 nd 144 nd lu hf and sm nd implying that they sample two distinct sources in the martian mantle all shergottites are characterized by sm nd source sample but lu hf source lu hf sample this decoupling can be explained by two successive partial melting episodes in the depleted shergottite source and localized in the martian upper mantle the genesis of shergottites can be modeled using non modal equilibrium partial melting in a source initially composed of 60 olivine 21 clinopyroxene 9 orthopyroxene and 10 garnet with degrees of partial melting of 8 8 and 3 9 respectively for the two successive events the enriched end member of the shergottite mixing curve is best modeled by late stage quenched residual melt resulting from the crystallization of a magma ocean the depleted shergottite source may be modeled as a mixture of cumulates and residual melt as convection in the martian magma ocean is expected to reduce the incompatible trace element heterogeneity in the final solidified layers consequently equilibrium crystallization is preferred to model the crystallization of the martian magma ocean the models that best explain the shergottite data are those where the magma ocean is at a depth of at least 1350 km in mars

the age of dar al gani 476 and the differentiation history of the martian meteorites inferred from their radiogenic isotopic systematics samarium neodymium isotopic analysis of the martian meteorite dar al gani 476 yields a crystallization age of 474 11 ma and an initial end143 value of 36 6 0 8 although the rb sr isotopic system has been disturbed by terrestrial weathering and therefore yields no age information an initial 87sr 86sr ratio of 0 701249 33 has been estimated using the rb sr isotopic composition of the maskelynite mineral fraction and the sm nd age the sr and nd isotopic systematics of dar al gani 476 like those of the basaltic shergottite que94201 are consistent with derivation from a source region that was strongly depleted in incompatible elements early in the history of the solar system nevertheless dar al gani 476 is derived from a source region that has a slightly greater incompatible enrichment than the que94201 source region this is not consistent with the fact that the parental magma of dar al gani 476 is significantly more mafic than the parental magma of que94201 and underscores a decoupling between the major element and trace element isotopic systematics observed in the martian meteorite suite combining the end142 end143 isotopic systematics of the martian meteorites yields a model age for planetary differentiation of 4 513 0 033 0 027 ga using this age the parent daughter ratios of martian mantle sources are calculated assuming a two stage evolutionary history the calculated sources have very large ranges of parent daughter ratios 87rb 86sr 0 037 0 374 147sm 144nd 0 182 0 285 176lu 177hf 0 028 0 048 these ranges exceed the ranges estimated for terrestrial basalt source regions but are very similar to those estimated for the sources of lunar mare basalts in fact the range of parent daughter ratios calculated for the martian meteorite sources can be produced by mixing between end members with compositions similar to lunar mare basalt sources two of the sources have compositions that are similar to olivine and pyroxene rich mafic cumulates with variable proportions of a rb enriched phase such as amphibole whereas the third source has the composition of liquid trapped in the cumulate pile i e similar to kreep after 99 crystallization correlation between the proportion of trapped liquid in the meteorite source regions and estimates of fo2 suggest that the kreep like component may be hydrous the success of these models in reproducing the martian meteorite source compositions suggests that the variations in trace element and isotopic compositions observed in the martian meteorites primarily reflect melting of the crystallization products of an ancient magma ocean and that assimilation of evolved crust by mantle derived magmas is not required furthermore the decoupling of major element and trace element isotopic systematics in the martian meteorite suite may reflect the fact that trace element and isotopic systematics are inherited from the magma source regions whereas the major element abundances are limited by eutectic melting processes at the time of magma formation differences in major element abundances of parental magma therefore result primarily from fractional crystallization after leaving their source regions

altering avalonia oxygen isotopes and terrane distinction in the appalachian peri gondwanan realmlaboratory for stable isotope science lsis the university of western ontario contribution 236 distinct 18o depletion is characteristic of a large majority of the 620 550 ma felsic igneous rocks of avalonia in the northern appalachian orogen neoproterozoic rocks in the boston avalon terrane have the lowest 18owr values 3 1 followed by the mira terrane in cape breton island and the caledonia terrane in new brunswick 1 2 the avalon terrane in newfoundland 2 8 and the antigonish highlands in nova scotia 5 3 in contrast this depletion of 18o is observed in very few of the paleozoic felsic igneous rocks from these avalonian terranes and also in very few of the neoproterozoic and paleozoic felsic igneous rocks from the inboard ganderian terranes the low 18o character of the neoproterozoic igneous rocks is related to regional pervasive post magmatic alteration by predominantly meteoric hydrothermal fluids 18oh2o 6 to 4 at 200 450 c the alteration likely occurred during late neoproterozoic transtensional extension of avalonia large scale fluid infiltration and circu

synchronous deformation and hydrothermal activity in the shear zone hosted high sulphidation au cu deposit at peak hill nsw australia altered and mineralised rocks at peak hill are confined to a 300 500 m wide north south striking steeply dipping shear zone that is flanked by the mingelo volcanics along its western side and cotton formation siltstones along its eastern side this shear zone is defined by extensive zones of cataclasite and strongly foliated micaceous schists in marked contrast to the largely undeformed nature of the adjacent rocks advanced argillic assemblages quartz kaolinite pyrite alunite illite occur throughout the core of the peak hill deposit propylitic assemblages including albite quartz interlayered chlorite smectite illite and ankerite and a narrow discontinuous zone of argillic quartz illite pyrite alteration are developed in the mingelo volcanics along the western side of the deposit propylitic argillic and advanced argillic assemblages are overprinted by an internally zoned phase of phyllosilicate alteration that grades inwards from a peripheral sericite clay chlorite assemblage through phyllic assemblages muscovite illite pyrite paragonite to a pyrophyllite pyrite diaspore andalusite altered core au cu mineralisation is hosted by barite pyrite veins that cut the advanced argillic assemblage but pre date the phyllosilicate dominated alteration native au lacking ag calaverite te rich tennantite tetrahedrite goldfieldite chalcopyrite covellite and chalcocite occur in the barite pyrite veins no ore bearing minerals were detected in any of the alteration assemblages the total gold content of the peak hill deposit is currently 720 k ounces and this includes 100 k ounces of unmined reserves within the shear zone phyllosilicate minerals are developed in strain shadows and partly define the stretching lineation associated with dip slip movement the zonation within the phyllosilicate assemblages mimics the geometry of bends in the shear zone and minor internal structures these textures indicate that the phyllosilicate alteration developed synchronous with movement on the shear zone earlier advanced argillic alteration and mineralisation are developed in rocks derived from both sides of the shear zone hydrothermal activity associated with the earlier advanced argillic alteration was therefore either synchronous with juxtaposition of these distinct rock units or occurred during a later phase of movement on the shear zone cross cutting fibrous textures in the auriferous barite pyrite veins indicate that repeated fracturing of the advanced argillic altered rocks accompanied development of successive generations of auriferous veins concentrations of auriferous veins are localised in steeply plunging shoots that are oriented parallel to the stretching lineation in the shear zone these features all indicate movement on the host shear zone accompanied each phase of hydrothermal activity in the peak hill deposit the location alteration zonation and distribution of mineralised veins within the deposit are intimately controlled by deformation on the host shear zone synchronous with hydrothermal activity the development of high sulphidation hydrothermal systems synchronous with deformation along brittle ductile shear zones is a predictable consequence of intrusive activity during deformation in areas characterised by a high geothermal gradient the close relationship between tectonism and hydrothermal activity indicates that these deposits are likely to be located in the vicinity of regional scale shear zones deposits are likely to be aligned parallel to the regional scale structural grain and restricted to areas of conspicuous deformation as is the case at peak hill and temora nsw aluminous alteration zones concentrated in the vicinity of regional scale structures in the carolina slate belt may be a further example of this style of hydrothermal activity

implications of deflation inflation event models on kīlauea volcano hawaiʻi abstract surface deformation of volcanic areas can reveal information about subsurface magma reservoirs and how magma is transported between them which is an important part of volcano monitoring for hazard mitigation one prominent style of deformation observed at k lauea volcano hawai i is episodic deflation inflation di events which are recorded in surface deformation data and characterized by deflation of the summit region over hours to days followed by rapid re inflation the exact cause of di events is unknown however a commonly proposed explanation is that a temporary blockage occurs in the conduit connecting the south caldera magma reservoir to the shallower halema uma u reservoir thus interrupting the influx of magma this model is investigated by testing the hypothesis that during the deflationary phase of a di event the volume of magma blocked from reaching the halema uma u reservoir is added to the south caldera reservoir using a mass balance approach and deformation modeling the expected deformation tilt pattern was predicted for the reservoirs and compared to tilt observations from 16 large 4 rad magnitude di events between 2010 and 2012 while the predicted tilts due to inflation from the south caldera reservoir are strong enough to be detected this signal is not seen in the tilt observations we also explore the possibility that the blockage occurs below the south caldera reservoir as well as alternative configurations that include a direct connection between the south caldera reservoir and the eruption site none of the simple two reservoir models we test are able to adequately satisfy the observations selected di events show that tilt vectors change in both magnitude and azimuthal direction over the course of deflation we conclude that the portion of the summit storage and plumbing system active during these di events is more complicated than two connected chambers and that it is more likely that these summit reservoirs have their own source conduits connecting in some complex way to the deep magma source

rb sr sm nd and ar ar isotopic systematics of martian dunite chassigny abstract isotopic analysis of the martian meteorite chassigny yields a rb sr age of 1406 14 ma with an initial 87 sr 86 sr ratio of 0 702251 0 000034 a sm nd age of 1386 28 ma with an initial e 143nd value of 16 9 0 3 and an 39 ar 40 ar age of 1360 40 20 ma the concordance of these ages and the rb sr and sm nd initial isotopic signatures suggest that chassigny crystallized from low rb sr light rare earth element depleted source materials 1390 ma ago the ages and e 143nd values of chassigny and the nakhlites governador valadares and lafayette overlap suggesting that they could have come from very similar mantle sources nakhla northwest africa 998 and yamato 000593 appear to be from similar but distinct sources chassigny and all nakhlites so far studied have undergone similar evolution histories that is chassignites nakhlites were derived from a region where volcanism lasted at least 50 ma and crystallized from different lava flows or subsurface sills they probably were launched from mars by a single impact event the trapped martian atmospheric 40 ar 36 ar ratios in chassigny nakhlites and shergottite impact glass are similar and possibly indicate minimal change in this ratio over the past 600 ma

clinopyroxene ree distribution coefficients for shergottites the ree content of the shergotty melt abstract ree distribution coefficients were measured between synthetic pyroxenes and melts similar in composition to the inferred shergotty intercumulus liquid by in situ analysis with the electron microprobe using samples doped to per cent concentration levels these coefficients exhibit a strong positive correlation with pyroxene wollastonite content recommended values for augites similar in composition to the shergotty cumulus augite cores wo32en48 are d la 0 023 d ce 0 039 d nd 0 10 d sm 0 17 d eu 0 16 d gd 0 20 d yb 0 29 and d lu 0 30 recommended values for pigeonites similar in composition to the shergotty cumulus pigeonite cores wo12en58 are d la 0 002 d ce 0 004 d nd 0 019 d sm 0 031 d yb 0 13 and d lu 0 13 these values resemble distribution coefficients measured for terrestrial basalts of higher mg fe than the shergotty melt rather than those of more evolved siliceous rocks of similar mg fe to the shergotty melt thus it appears that mg fe is considerably less important than other factors in determining distribution coefficient values for pyroxenes ree abundances were computed for the shergotty intercumulus melt using distribution coefficients measured for the natural phase compositions these computed abundances display lree depletion such lree depleted abundance patterns cannot be generated by simple partial melting of a mafic mineral assemblage having the lree enriched patterns required for a two stage sm nd evolution history this result implies that either 1 the melting process was complex e g continuous melting 2 the source region had a more complex history than that of the simple 2 stage model or 3 shergotty does not satisfy the closed system assumption of the calculation and has suffered post magmatic lree enrichment

trace and minor elements in minerals of nakhlites and chassigny clues to their petrogenesis abstract ion microprobe measurements of ree rare earth element and other selected trace and minor element concentrations were made in clinopyroxene olivine feldspar and chlorapatite in chassigny and the three nakhlites nakhla governador valadares and lafayette in chassigny we have found pigeonite occurring in a poikilitic habit it is the first reported occurrence of this mineral in this meteorite the most significant implication of this finding is that estimates of the major element composition of the chassigny parent melt will have to accommodate pigeonite as a primary mineral crystallizing before plagioclase chlorapatite contains the highest ree abundances in all meteorites studied here the ree patterns of chlorapatite plagioclase and augite in nakhlites and chassigny are similar although the downward trends of ree patterns are somewhat steeper for these minerals in chassigny than in the nakhlites pyroxenes in nakhlites and chassigny are extensively zoned in rees and other trace and minor elements such as y zr ti and al which appear to be resistant to diffusive reequilibration thus primary igneous zoning of these elements has been preserved in the pyroxenes of these meteorites and can be used to infer their crystallization histories the calculated ree patterns of the parent melts of nakhlites and chassigny are lree enriched and parallel to their whole rock ree patterns indicating that once crystal accumulation occurred the intercumulus trapped melt fractionally crystallized in an essentially closed system and that infiltration i e metasomatism by lree enriched magmas need not be invoked to explain the lree enrichment in bulk samples of these meteorites fractional crystallization model calculations for nakhla also confirm these conclusions the distributions of trace and minor elements in augites in nakhlites and chassigny suggest that all three nakhlites could be samples from different horizons of the same lithologic unit but that chassigny was not comagmatic with the nakhlites