diffusion kinetics of fe2 and mg in aluminous spinel experimental determination and applications the diffusion coefficients of fe2 and mg in aluminous spinel at 20 kb 950 to 1325 c and at 30 kb 1125 c have been determined via diffusion couple experiments and numerical modeling of the induced diffusion profiles the oxygen fugacity fo2 was constrained by graphite encapsulating materials the retrieved self diffusion coefficients of fe2 and mg at 20 kb 950 to 1325 c fit well the arrhenian relation d d0exp q rt where q is the activation energy with d0 fe 1 8 2 8 10 5 d0 mg 1 9 1 4 10 5 cm2 s q fe 198 19 and q mg 202 8 kj mol comparison with the data at 30 kb suggests an activation volume of 5 cm3 mol from analysis of compositional zoning in natural olivine spinel assemblages in ultramafic rocks previous reports concluded that d fe mg in spinel with cr cr al 0 5 is 10 times that in olivine the diffusion data in spinel and olivine have been applied to the problems of preservation of mg isotopic inhomogeneity in spinel within the plagioclase olivine inclusions in allende meteorite and cooling rates of terrestrial ultramafic rocks

diffusion closure temperature and age of a mineral with arbitrary extent of diffusion theoretical formulation and applications the commonly used expression of the closure temperature tc of a diffusing species in a mineral as derived by m h dodson contrib mineral petrol 40 1973 259 264 is applicable only to systems which have undergone sufficient diffusion so that even the composition at the center of individual grains is significantly removed from that established at the onset of cooling we have extended dodson s formulation to include cases with arbitrarily small amount of diffusion and applied it to calculate tc and age profiles which would develop in single crystals of different geometries these results permit evaluation of the extent of resetting of mineral age and of ion exchange geothermometers during cooling the measured age profile of a mineral can also be used to constrain its cooling rate these applications have been illustrated for the cases of garnet biotite fe mg exchange geothermometer and the cooling age and closure temperatures of the sm nd and lu hf decay systems in garnet

eruption mechanism as inferred from geomagnetic changes with special attention to the 1989 1990 activity of aso volcano abstract geomagnetic changes associated with the volcanic activity of aso volcano were detected with a dense network of continuously recording proton precession magnetometers during the period from june 1989 to june 1990 magnetic date clearly indicate that changes in the magnetization within the volcano are most probably caused by temperature changes this activity can be divided into five stages which are characterized by magnetization and demagnetization of the volcano these magnetic changes with durations of a few months are definitely correlated with some typical volcanic events at the crater as well as the volcanic tremor activity the demagnetization stage appears when the vent is covered by a water pool or the volcanic activity is enhanced the magnetization stage follows the opening of a vent and several large explosions which make the vent permeable the source of magnetic changes lies at a depth of about 200 m below the crater rim in the southwestern part of the active crater magnetic moments responsible for observed magnetic changes at stages 1 2 and 4 are 3 4 5 2 and 2 2 wbm respectively the corresponding source volume is estimated as a single sphere of radius 40 50 m or a spherical shell of 100 m or so an effective mechanism of rapid heating cooling exists which is ascribed to the interaction of groundwater and superheated vapor i e a shallow hydrothermal system this hydrothermal system driven by the surface cap of the vent controls every feature of the eruptions at the final outlet of aso volcano

potassium diffusion in melilite experimental studies and constraints on the thermal history and size of planetesimals hosting cais among the calcium aluminum rich inclusions cais excess 41 k 41 k which was produced by the decay of the short lived radionuclide 41 ca t1 2 0 1 myr has so far been detected in fassaite and in two grains of melilites these observations could be used to provide important constraints on the thermal history and size of the planetesimals into which the cais were incorporated provided the diffusion kinetic properties of k in these minerals are known thus we have experimentally determined k diffusion kinetics in the melilite end members akermanite and gehlenite as a function of temperature 900 1200 c and crystallographic orientation at 1 bar pressure the closure temperature of k diffusion in melilite tc k mel for the observed grain size of melilite in the cais and cooling rate of 10 100 c myr as calculated from our diffusion data is much higher than that of mg in anorthite the latter was calculated from the available mg diffusion data in anorthite assuming that the planetesimals were heated by the decay of 26 al and 60 fe we have calculated the size of a planetesimal as a function of the accretion time tf such that the peak temperature at a specified radial distance rc equals tc k mel the ratio rc r 3 defines the planetesimal volume fraction within which 41 k in melilite grains would be at least partly disturbed if these were randomly distributed within a planetesimal a similar calculation was also carried out to define r versus tf relation such that 26 mg was lost from 50 of randomly distributed anorthite grains as seems to be suggested by the observational data these calculations suggest that 60 of melilite grains should retain 41 k if 50 of anorthite grains had retained 26 mg assuming that tf was not smaller than the time of chondrule formation our calculations yield minimum planetesimal radius of 20 30 km depending on the choice of planetesimal surface temperature and initial abundance of the heat producing isotope 60 fe

volcanomagnetic effects observed on piton de la fournaise volcano reunion island 1985 1987 a permanent network of four to six telemetered magnetic stations has been installed on piton de la fournaise volcano in october 1985 and 1986 eight eruptive sequences have occurred since then some of which affected only the summit whereas others affected the whole massif volcanomagnetic variations are observed with each of these volcanic events the geomagnetic field intensity is measured simultaneously every minute at each station with a precision of 0 25 nt nanotesla the main results are the following volcanomagnetic variations observed with eruptions have amplitudes of several nanoteslas to more than 10 nt with characteristic time durations ranging from l min or less to several months a good correlation between the magnetic variations recorded at the different stations is observed spatial and temporal properties of the volcanomagnetic field appear to be controlled by the features of the eruptions several days before the beginning of the december 1985 march july november december 1986 and january 1987 eruptions changes in the intensity differences are observed with amplitudes of a few nanoteslas up to 5 nt at stations located close to the active part of the rift zone variations are also observed in the most remote stations for larger eruptions in march 1986 november december 1986 and january 1987 correlations between magnetic variations ground deformations and seismic activity have been observed for the december 1985 march 1986 november december 1986 and january 1987 events three main mechanisms could account for the observed volcanomagnetic variations piezomagnetic effects electrokinetic effects and electrical resistivity changes since variations in the stress field in the surroundings can modify the induced and natural magnetizations of magnetized rocks the circulation of water through the interconnected pore network microcracks faults aquifers and also the electrical resistivity of geological structures through the modification of the properties of the pore network

deformation and seismic precursors to dome collapse and fountain collapse nuees ardentes at merapi volcano java indonesia 1994 1998 abstract following the eruption of january 1992 episodes of lava dome growth accompanied by generation of dome collapse nuees ardentes occurred in 1994 1998 in addition nuees ardentes were generated by fountain collapse in january 1997 and the 1998 events also suggest an explosive component significant tilt and seismic precursors on varying time scales preceded these events deformation about the summit has been detected by electronic tiltmeters since november 1992 with inflation corresponding generally to lava dome growth and deflation or decreased inflation corresponding to loss of dome mass strong short term days to weeks accelerations in tilt rate and seismicity occurred prior to the major nuees ardentes episodes apart from those of 22 november 1994 which were preceded by steadily increasing tilt for over 200 days but lacked short term precursors because of the combination of populated hazardous areas and the lack of an issued warning about 100 casualties occurred in 1994 in contrast the strong precursors in 1997 and 1998 provided advance warning to observatory scientists enabled the stepped raising of alert levels and aided hazard management as a result of these factors but also the fortunate fact that the large nuees ardentes did not quite descend into populated areas no casualties occurred the nuee ardente episode of 1994 is interpreted as purely due to gravitational collapse whereas those of 1997 and 1998 were influenced by gas pressurization of the lava dome

basal tuffs and contemporaneity of the chattisgarh and khariar basins based on new dates and geochemistry abstracttime bracketing of thousands of meters thick unmetamorphosed fossil free sedimentary successions is a long standing challenge in indian proterozoic stratigraphy limited geochronologic ages from either the basal or the upper part of the successions prevent workers from constraining the precise age interval for individual basin fill leaving aside the issue of correlatability between different basin sequences this article deals with silicic tuff units from the basal part of two areally separated proterozoic sedimentary successions of central india the singhora group of the chattisgarh supergroup and the khariar group the singhora tuff is enriched in large ion lithophile rb ba th etc elements and light rare earth elements and in a discrimination diagram falls within the volcanic arc granite field u th pb electron probe microanalyzer geochronology of monazite and zircon grains from the singhora tuff revealed several age data clusters namely 2500 2100 1800 1500 and 1000 ma in c

el nino induced onshore transport in the california current during 1982 1983 persistent 9 month large scale positive temperature 3 4 c negative salinity 0 1 0 3 and positive dissolved oxygen 0 5 1 ml l subsurface anomalies characterize the el nino induced onshore transport in the california current during 1982 83 these anomalies characteristic diagrams and sign reversals in the salinity and oxygen anomalies are consistent only with enhanced onshore transport of subarctic water from the offshore california current onshore transport excludes poleward propagating kelvin waves as a generation mechanism for the 1982 83 californian el nino the data however support the conclusion simpson 1983 that an anomalous basinwide atmospheric circulation produced the californian el nino

signals recorded by demeter satellite over active volcanoes during the period 2004 august 2007 december more than 1500 volcanoes can potentially enter into eruption but only some tens of them are equipped with monitoring networks most of volcanic eruptions can be predicted by the integration of continuous real time observations data processing and analysing in the electromagnetic field em a long history of ground observations shows that electric magnetic and electromagnetic signals may precede and accompany volcanic eruptions the possibility that volcanic eruptions may also be preceded by transient electromagnetic anomalies in the ionosphere can be analysed on the basis of demeter mission this microsatellite launched by cnes in 2004 covers 14 orbits per day over seismic and volcanic regions of the earth two complementary and systematic studies are presented over the time period 2004 august 2007 december the first study shows that three types of electric and or magnetic anomalies can be observed in the time window of 30 d preceding an eruption and 15 d after on the 74 eruptions occurring on 50 volcanoes under consideration 48 anomalies are recognised along 30 eruptions 41 per cent of the eruptions were accompanied by em signals on board of the satellite 81 per cent of the anomalies are observed before the eruptions for the period 30 d 15 d and 69 per cent for the period 15 d 15 d in the second study the anomalies above three nearby volcanoes lopevi ambrym and aoba are systematically looked for all orbits between 2004 august and 2006 december anomalies are only observed during periods of larger activity on each of them taking into account that no anomaly is observed a long time before an eruption on can allocate the anomalies to each volcano although the database is still limited the study shows that volcanic activity may be preceded by em perturbations of the ionosphere

concurrent fractional and equilibrium crystallisation abstract this paper proposes the concept of concurrent fractional and equilibrium crystallisation cfec in a multi phase magmatic system in light of experimental results on diffusivities of elements and other species in minerals and melts a group of equations are presented to describe how the concentrations of an element or isotope change in fractionated solid equilibrated solid melt liquid and gas phases as well as in magma as a function of distribution coefficients and mass fractions during the cfec process cfec model is a generalised and unified formulation that is valid not only for pure fractional crystallisation fc and perfect equilibrium crystallisation ec singly as two of its limiting end member cases but also for the geologically more important process of concurrent fractional and equilibrium crystallisation the concept that both fractional and equilibrium crystallisation can operate concurrently in a magmatic system for a given element among different minerals and even within different sized crystal grains of the very same mineral phase is of fundamental importance in deepening our current understanding of magmatic differentiation processes cfec probably occurs more frequently in the natural world than either pure fractional or perfect equilibrium crystallisation alone as a result of the interplay of varying diffusivities of elements under diverse physicochemical conditions different residence time and growth rates of mineral phases in magmas and varying grain sizes within each phase and among different phases the marked systematic variations in trace element concentrations in the melts of the bishop tuff have long been perplexing and difficult to reconcile with existing models of differentiation cfec which is able to better explain the scatter trends in a systematic way than fractional crystallisation is considered to be the cause

present status of the geochronology of the precambrian rocks of rajasthan abstract age determinations mostly by rb sr analyses of the precambrian rocks of rajasthan by us and by others are summarized and discussed broad periods of acid magmatism at 1 3000 2900 m y 2 2600 2500 m y 3 2000 1900 m y 4 1700 1500 m y and 5 850 750 m y were identified the oldest rocks in the area are the yet undated banded gneisses bgc east of udaipur intruded by the untala granite dated at 2950 m y and hence of mid archean age the basal status hitherto attributed to the berach granite dated at 2600 m y is no longer tenable the radiometric control on the beginning and duration of the overlying aravalli supergroup is not yet satisfactory though a lower limit at 2000 m y is indicated heron s original delhi rocks have recorded two magmatic events widely separate in space and time while the earliest granitic activity at 1600 m y is recorded only in the alwar basin in the northeast the younger activity between 850 750 m y is widespread as shown by the nearly concordant ages of erinpura type granites along the aravalli mountain range and the malani rhyolites in the western plains of the aravalli range

merapi volcano central java indonesia a case study of radionuclide behavior in volcanic gases and its implications for magma dynamics at andesitic volcanoes for more than 20 years volcanic gases have been regularly collected at merapi volcano indonesia and have been subsequently analyzed for their 210pb 210bi and 210po activities and so2 contents these new results show the high volatility of the three radionuclides in andesitic gases although their emanation coefficients 0 94 3 5 and 53 for 210pb 210bi and 210po respectively are significantly lower than those observed at basaltic volcanoes this emphasizes the major role of magma temperature on the degassing of these metals which are mainly transported in volcanic gases as pb chloride compounds and as bi and po metallic species radioactive disequilibria between 210pb 210bi and 210po in the gas phase are characteristic of degassing processes and gas paths within the edifice gases released at both gendol and woro fumarolic fields are of magmatic origin but their radionuclide content is strongly altered by secondary processes chemical reactions with surrounding brines and deposition of sublimates in the ground high temperature gases collected in the summit gas plume are of pure primary magmatic origin and are likely directly tapped in the degassing reservoir gases arising from the growing domes are strongly depleted in the most volatile isotopes and gas species this suggests that magma mostly degasses at depth in open system explaining why the volcano usually undergoes no explosive eruptions the gas flux at merapi is sustained by a deep magma supply which is twice the extrusion rate of lava unerupted degassed magma thus progressively accumulates beneath the summit yielding an overpressure which can trigger dome collapse without precursor

diffusion kinetics of cr in olivine and 53mn 53cr thermochronology of early solar system objects we have determined the diffusion coefficient of cr in olivine as function of temperature oxygen fugacity fo2 and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short lived 53 mn 53 cr decay system in olivine during cooling within meteorite parent body the diffusion of cr in olivine was found to be anisotropic and effectively indepen dent of fo2 between wustite iron buffer and two orders of magnitude above this buffer the diffusion data were used to calculate the spatially averaged mean closure temperature of the 53 mn 53 cr decay system in olivine as function of the initial temperature cooling rate and grain size and also the closure age profile of this system in olivine single crystal as function of radial distance and a dimensionless parameter that incorporates the effects of various parameters that affect the closure age we also present a thermochronolgic formulation that permits retrieval of cooling rates from the extent of resetting of the bulk 53 mn 53 cr closure age of olivine during cooling this method was applied to determine the cooling rate of the pallasite omolon which showed 53 mn 53 cr bulk age of olivine that is 10 myr younger than the age of the solar system the calculated cooling rate which is 20 40 c myr at 985 1000 c is in good agreement with the metallographic cooling rate at 500 c when the two results are considered in terms of a cooling model in which the reciprocal temperature increases linearly with time the inferred cooling rate of omolon which seems to be a sample from the core mantle boun dary yields a burial depth of 30 km in a parent body of at least 100 km radius

manganese chromium formation intervals for chondrules from the bishunpur and chainpur meteorites whole chondrule mn cr isochrons are presented for chondrules separated from the chainpur ll3 4 and bishunpur ll3 1 meteorites the chondrules were initially surveyed by instrumental neutron activation analysis ll chondrite normalized mn cr mn fe and sc fe served to identify chondrules with unusually high or low mn cr ratios and to correlate the abundances of other elements to sc the most refractory element measured a subset of chondrules from each chondrite was chosen for analysis by a scanning electron microscope equipped with an energy dispersive x ray spectrometer prior to high precision cr isotopic analyses 53cr 52cr correlates with 55mn 52cr to give initial 53mn 55mn i 9 4 1 7 10 6 for chainpur chondrules and 53mn 55mn i 9 5 3 1 10 6 for bishunpur chondrules the corresponding chondrule formation intervals are respectively tlew 10 1 ma for chainpur and 10 2 ma for bishunpur relative to the time of igneous crystallization of the lewis cliff lew 86010 angrite because mn sc correlates positively with mn cr for both the chainpur and bishunpur chondrules indicating dependence of the mn cr ratio on the relative volatility of the elements we identify the event dated by the isochrons as volatility driven elemental fractionation for chondrule precursors in the solar nebula thus our data suggest that the precursors to ll chondrules condensed from the nebula 5 8 2 7 ma after the time when initial 53mn 55mn i 2 8 0 3 10 5 for calcium aluminum rich inclusions cais our preferred value determined from data for a mineral separates of type b allende cai br1 b spinels from efremovka cai e38 and c bulk chondrites mn cr formation intervals for meteorites are presented relative to average i mn 53mn 55mn ch 9 46 10 6 for chondrules mn cr ratios for radiogenic growth of 53cr in the solar nebula and later reservoirs are calculated relative to average i mn 53cr i 9 46 0 08 10 6 0 23 0 08 for chondrules inferred values of mn cr lie within expected ranges thus it appears that evolution of the cr isotopic composition can be traced from condensation of cais via condensation of the ferromagnesian precursors of chondrules to basalt generation on differentiated asteroids measured values of 53cr for individual chondrules exhibit the entire range of values that has been observed as initial 53cr values for samples from various planetary objects and which has been attributed to radial heterogeneity in initial 53mn 55mn in the early solar system estimated 55mn 52cr 0 42 0 05 for the bulk earth combined with 53cr 0 for the earth plots very close to the chondrule isochrons so that the earth appears to have the mn cr systematics of a refractory chondrule thus the earth apparently formed from material that had been depleted in mn relative to cr contemporaneously with condensation of chondrule precursors if as seems likely the earth s core formed after complete decay of 53mn there must have been little differential partitioning of mn and cr at that time

oriented chromite diopside symplectic inclusions in olivine from lunar regolith delivered by luna 24 mission abstract calcium chromium rich lamellae in olivine grain no 1611 from the luna 24 regolith were studied with feg empa and tem the lamellae consist of a worm like intergrowth of fecr 2 o 4 chromite chr and camgsi 2 o 6 diopside di with a chr di modal proportion of 1 3 the linear extension of the lamellae and crystallographic orientation relationships among the symplectite phases and the olivine suggest that the lamellae nucleated at deformation defects in the olivine host calcium depletion haloes surrounding the lamellae amount to about 75 m and indicate that the chromite diopside lamellae were formed by segregation of calcium and chromium from the host olivine into the lamellae without addition of calcium and or chromium from outside the olivine the segregation of calcium and chromium and consequently the growth of the symplectic lamellae were diffusion controlled the segregation of a calcium chromium component from the host olivine was associated with oxidation of divalent to trivalent chromium oxidation was facilitated by dehydrogenation which was driven by decompression and or a change in redox potential hydrogen point defects in the original olivine with h substituting for divalent cations on the m sites provided the necessary electron acceptors for the oxidation of chromium and after electron transfer left olivine as molecular h 2 the internal microstructure of the lamellae suggests that exsolution of the calcium chromium rich lamellae from the host olivine and formation of the chromite diopside symplectic intergrowth occurred simultaneously the time scale derived from diffusion modeling of the calcium depletion haloes around the lamellae indicates a thermal event on the order of several months to several hundred years at most symplectic inclusions found in olivine from lunar martian and terrestrial rocks are similar with respect to their shape crystallographic orientation relationships and internal microstructure of the spinel clinopyroxene intergrowth these features are inconsistent with dry olivine oxidation that is by the uptake of oxygen dehydrogenation of oh bearing precursor olivine is suggested as a general mechanism of oxidation accompanied by chemical segregation and phase separation resulting in symplectite formation

installation of a doppler radar monitoring system at merapi volcano indonesia merapi volcano indonesia is one of the most active dome building volcanoes worldwide instabilities at the growing dome cause rockfalls and hot block and ash flows which can reach run out distances of several kilometers therefore merapi has been monitored extensively for many years however direct visual observation of the dome is often impossible due to cloud coverage of the summit in october 2001 a first prototype doppler radar system was installed to overcome this shortcoming the system is able to penetrate clouds and observe material movements at the dome giving valuable information about dynamic processes in the dome area the system also allows detection of rainfall in several distance intervals for precise positioning of the beam the system was equipped with an electromechanical mounting in 2003 a charge coupled device ccd camera attached to the radar mirror documents the radar beam position and provides visual observation of the dome recorded data camera images and status information are telemetered to the merapi volcano observatory where they can be processed and interpreted status information is also sent via short message service via a global system for mobile communications gsm modem by processing the doppler radar data we are able to discriminate between three different types of instability events sliding dome material dome material gravitationally breaking off the dome and explosive outbursts of dome material due to expansion of volcanic gas in order to independently verify our observations we compared rockfall events detected by the radar system to seismic recordings and found a good correlation

magnetic measurements on la soufriere volcano guadeloupe lesser antilles 1976 1984 a re examination of the volcanomagnetic effects observed during the volcanic crisis of 1976 1977 abstract during the seismovolcanic crisis of 1976 1977 at la soufriere on guadeloupe a magnetic network of 12 reference markers was set up measurements of the intensity of the earth s magnetic field carried out up to once a day at each marker showed volcano magnetic variations of several nanoteslas nt the variations at certain markers were more or less concealed by transient magnetic variations due to anomalies in conductivity as early as 1978 measurements were resumed and a telemetering network was coupled with the network of reference markers to which 4 new markers were added a detailed study of conductivity anomalies was carried out on the entire volcano contrasts in conductivity linked to the existence of a superficial conducting surface on a ssw nne axis located south of the volcano caused a great lack of homogeneity in the field variations measured at the surface variations greater than about 10 nt appeared in the difference in intensity of the earth s magnetic field between two stations no long term magnetic variation was observed between 1978 and 1984 on the network of markers the accuracy of measurements of volcanic effects was at best 2 nt measurements carried out on the telemetering network during the night refined these results since their accuracy was 1 nt the only significant volcanic crisis between 1978 and 1984 5 7 january 1981 seems to be observed by telemetering stations all the measurements carried out in periods of volcanic inactivity make it possible to re examine the crisis of 1976 1977 though volcanomagnetic effects over short periods cannot be accurately determined variations with a time constant of several weeks were present over the entire volcano these variations were as high as 7 8 nt in remote stations and they can be linked to the three major phases of eruptive activity at la soufriere during the crisis of 1976 1977

morphological analysis of olivine grains annealed in an iron nickel matrix experimental constraints on the origin of pallasites and on the thermal history of their parent bodies two types of pallasites can be distinguished on the basis of the grain shape of olivine rounded or angular it has been suggested that these two types of textures resulted from different degrees of annealing at high temperature in the parent body in order to characterize the kinetics of rounding of olivine grains in an fe ni matrix we carried out a series of annealing experiments using a mixture of olivine and fe ni powder we were able to reproduce at a miniature scale the range of textures in pallasites the rate of rounding was rapid enough to be observed and measured at the scale of a few micrometers to 20 m even though the experiments were performed below the solidus of the fe ni metal for instance grains 14 m in diameter became nearly spherical within 7 days at 1400 oc for the morphological analysis of olivine grains we used two independent techniques the critical diameter method and the gaussian diffusion resample method a new technique specially developed for our study both techniques indicate that the rounding time scale is proportional to the cube of the grain size and that morphological adjustments in our experiments occurred by volume diffusion in the olivine lattice not by surface diffusion along the olivine metal boundaries we used our experimental data to estimate the time scales required for the development of olivine metal textures in natural pallasites we determined that small scale rounding of olivine grains in a solid metal matrix can be produced within relatively short time intervals 100 years to produce rounded olivine grains 0 1 mm in radius at 1300 1400oc

176lu 176hf and 147sm 143nd ages of the martian shergottites evaluation of the shock resetting hypothesis through diffusion kinetic experiments and modeling and petrological observations abstract we address the age controversy of the shergottite suite of martian meteorites 200 ma dates determined by 176lu 176hf 147sm 143nd and various other decay systems as opposed to a 4 ga whole rock pb pb date by calculating the timescales needed to reset hf and nd isotopes in clinopyroxene which is the primary host of rare earth elements amongst the minerals used to compose the 176lu 176hf and 147sm 143nd isochrons at the peak and post shock p t conditions likely to have been experienced by the shergottites it is concluded that impact heating is highly unlikely to have significantly reset the 176lu 176hf and or 147sm 143nd mineral isochrons of these meteorites this conclusion is bolstered by the nature of measured concentration profiles of cr and fe across olivine maskelynite boundaries and ti profiles across clinopyroxene maskelynite melt interfaces in the shergottite rbt 04262 the lack of any evidence of diffusion in the measured concentration profiles coupled with the qualitative incompatibility of the measured crystal melt fractionation trends at these interfaces with the nature of fractionation expected from equilibrium partitioning provides strong evidence that no substantial chemical exchange took place between the solid and melt phases during peak shock p t conditions furthermore we find that the compositional profiles of major elements in coexisting augite and pigeonite are homogenous and reflect a magmatic temperature of 1143 9 c we argue that the pyroxene compositions and consequently the 176lu 176hf and 147sm 143nd geochronometers were highly unlikely to have been reset by the thermal effect of a shock event x ray mapping of a selected section of rbt 04262 shows no evidence of enhanced grain boundary diffusion we thus conclude that the 200 ma dates recorded by the 176lu 176hf and 147sm 143nd geochronometers most likely record the crystallization age of the shergottites

distinct 238 u 235 u ratios and ree patterns in plutonic and volcanic angrites geochronologic implications and evidence for u isotope fractionation during magmatic processes angrites are differentiated meteorites that formed between 4 and 11 myr after solar systemformation when several short lived nuclides e g 26 al 26 mg 53 mn 53 cr 182 hf 182 w were still alive as such angrites are prime anchors to tie the relative chronology inferred from these short lived radionuclides to the absolute pb pb clock the discovery of variable u isotopic composition at the sub permil level calls for a revision of pb pb ages calculated using an assumed constant 238 u 235 u ratio i e pb pb ages published before 2009 2010 in this paper we report high precision u isotope measurement for six angrite samples nwa 4590 nwa 4801 nwa 6291 angra dos reis d orbigny and sahara 99555 using multi collector inductively coupled plasma mass spectrometry and the irmm 3636 u double spike the age corrections range from 0 17 to 1 20 myr depending on the samples after correction concordance between the revised pb pb and hf w and mn cr ages of plutonic and quenched angrites is good and the initial 53 mn 55 mn 0 ratio in the early solar system ess is recalculated as being 7 1 10 6 at the formation of the solar system the error bar incorporates uncertainty in the absolute age of calcium aluminum rich inclusions cais an uncertainty remains as to whether the al mg and pb pb systems agree in large part due to uncertainties in the pb pb age of cais a systematic difference is found in the u isotopic compositions of quenched and plutonic angrites of 0 17 a difference is also found between the rare earth element ree patterns of these two angrite subgroups the 238 u values are consistent with fractionationduring magmatic evolution of the angrite parent melt stable u isotope fractionation due to a change in the coordination environment of u during incorporation into pyroxene could be responsible for such a fractionation in this context pb pb ages derived from pyroxenes fraction should be corrected using the u isotope composition measured in the same pyroxene fraction

combined fe mg chemical and isotopic zoning in olivine constraining magma mixing to eruption timescales for the continental arc volcano irazu costa rica and cr diffusion in olivine

olivine spinel geospeedometry analysis of diffusion controlled mg fe2 exchange subsolidus mg fe2 exchange between olivine and spinel is governed by mg fe2 interdiffusion incomplete exchange results in mg fe2 heterogeneity in both olivine and spinel which provides information on the thermal histories of the host rocks a composite sphere model has been developed to obtain quantitative cooling rates or heating duration from the mg fe2 heterogeneity the model assumes that a spherical core of spinel and a surrounding semi infinite spherical shell of olivine interact by diffusion controlled exchange of mg and fe2 the differential equations describing the model are solved numerically by finite difference approximations the numerical solution reveals that cooling rates or heating duration can be estimated from the relationship between the grain size of spinel and temperature calculated from the chemical compositions of the core of a spinel grain and of olivine far away from it the calculated temperature is employed in place of mg mg fe2 at the center of spinel to obtain the absolute temperature of thermal events this olivine spinel geospeedometer has been applied to peridotites gabbro and picrites from some ophiolite complexes in japan to estimate their cooling rates the estimated cooling rates for the peridotites range from 10 4 to 10 1 c yr and those for the picrites from 103 to 104 c yr the geospeedometer has been extended to estimate the heating duration of lherzolite xenoliths in basalt from the ichinomegata crater northeast japan the estimated heating duration of the xenoliths is less than one day

in situ observation of dome instabilities at merapi volcano indonesia a new tool for volcanic hazard mitigation understanding the mechanism and repetition frequency of dome instability events at high risk dome building volcanoes located near densely populated areas is one crucial piece of information when dealing with volcanic hazard mitigation although some visual in situ observations of such processes have been made at unzen volcano and on montserrat continuous monitoring of dome activity has been severely hampered by weather conditions such as cloud coverage using a newly designed microwave doppler system we are able to continuously monitor in situ processes at active dome systems with our instrument we can determine the velocity of material breaking off an active dome as well as the approximate amount of material passing through the radar beam allowing us to continuously identify different types of dome instabilities a data set collected during a highly active period at the end of oct early nov 2001 at merapi volcano indicates two different instability types a purely gravitational instabilities and b gravitational instabilities that are followed immediately by an explosion such information continuously collected allows tight constrains on the activity status of dome building volcanoes and is an important information for hazard mitigation the number of instabilities detected by the radar during the observational period is larger than the number of rockfall events detected by the seismic network operated at merapi during that time

magnetic monitoring at merapi volcano indonesia abstract merapi volcano located 30 km north of the heavily populated city of yogjakarta java is one of the most active of the 129 volcanoes in indonesia about every 2 years a new phase of activity is observed depending on the past activity the unrest gives rise either to an endogenous dome which partly collapses in the southwest direction or to pyroclastic flows which travel as far as 15 km the 1990 1997 period has involved a plume emission on 30 august 1990 an extrusion on 20 january 1992 and a pyroclastic eruption on 22 november 1994 the intensity of the earth magnetic field has been measured simultaneously and digitally recorded at four stations since 1990 two overhauser magnetometers with resolution of 0 01 nt have been installed in the summit area to strengthen the volcano monitoring outstanding magnetic changes appear to correlate with volcanic activity three types of volcanomagnetic signals can be identified long term trends up to 15 nt with period 10 years medium term cyclic variations at most 3 nt in amplitude and with 1 2 years period and small events reaching 1 5 nt lasting a few months and associated with any remarkable volcanic activity merapi volcano began a new cycle of activity in 1995 leading to a dome growth in july 1996 and accompanied by 27 nuees ardentes in august the comparison between magnetic data seismicity and surface phenomena suggests that some long term trends of decade periods could be of thermomagnetic origin while mid term volcanomagnetic variations associated with the cycles of merapi activity could be of piezomagnetic origin short term variations of a few weeks duration less than 1 5 nt are well correlated with the 1995 1996 seismic activity

late archaean to proterozoic tectonothermal events in napier complex east antarctica correlation with east gondwana fragments

chemical zoning of olivine in several pallasites chemical zoning profiles of olivines in the esquel imilac and yamato 8451 pallasites were measured by using an electron probe microanalyzer in order to study their cooling histories pallasite olivines are considered to be compositionally uniform but show faint zoning for fe mg cao al2o3 cr2o3 and mno within a few hundred micrometers from the rim the cao al2o3 and cr2o3 contents of olivines in pallasites decrease gradually toward the rim the fe mg zoning and the mno enrichment in olivine rims of pallasite olivines may reflect a redox process on the basis of diffusion calculations to estimate the cooling rate by using chemical zoning of pallasite olivine the formation process of chemical zoning was discussed similar cooling rates obtained for the fe mg cao and mno profiles of an olivine imply that these zoning patterns formed during the same event

sm nd dating of spatially controlled domains of garnet single crystals a new method of high temperature thermochronology ganguly and tirone meteorit planet sci 36 2001 167 175 recently presented a method of determining the cooling rates of rocks from the difference between the core and bulk ages of a crystal as determined by a single decay system here we present the first application of the method using the core and bulk ages of garnet single crystals according to the sm nd decay system in two rock samples with contrasting cooling rates which can be constrained independently the samples belong to the metamorphic core complex valhalla british columbia and the mid crustal magmatic arc exposure of the salinian terrane california we have micro sampled the garnet crystals over specific radial dimensions and measured the nd isotopes of these small sample masses as ndo via solid source mass spectrometry to determine the sm nd age difference between the core and bulk crystals using a peak metamorphic p t condition of 8 1 kbar 820 30 c spear and parrish j petrol 37 1996 733 765 the core 67 3 2 3 ma and bulk 60 9 2 1 ma ages of the british columbian garnet sample yield a cooling rate of 2 13 c myr which is in very good agreement with the cooling rates that we have derived by modeling the retrograde fe mg zoning in the same garnet and assuming the same peak metamorphic p t condition considering earlier cooling rate data derived from closure temperature vs age relation of multiple geochronological systems spear and parrish j petrol 37 1996 733 765 a cooling rate of v15 20 c myr seems most reasonable for the valhalla complex diffusion kinetic analysis shows that the sm nd core age of the selected garnet crystal could not have been disturbed during cooling consequently the core age of the garnet crystal 67 3 2 3 ma corresponds to the peak metamorphic age of the valhalla complex the salinian sample on the other hand yields indistinguishable core 78 2 2 7 ma and bulk 77 9 2 9 ma ages as expected from its fast cooling history which can be constrained by the results of earlier studies the sm nd decay system in garnet has relatively high closure temperature usually s 650 c therefore the technique developed in this paper fills an important gap in thermochronology since the commonly used thermochronometers are applicable only at lower temperatures simultaneous modeling of the retrograde fe mg zoning in garnet spatially resolved sm nd ages of garnet single crystals and resetting of the bulk garnet sm nd age

an overview of the seismicity of merapi volcano java indonesia 1983 1994 abstract from 1982 to 1995 merapi volcano java indonesia experienced two main eruptive cycles from 1984 to 1986 and from 1992 to 1994 each cycle had a duration slightly larger than 2 years four major eruptive events occurred in 1984 1986 1992 and 1994 these eruptions were monitored by a telemetered seismic network we present an overview of the seismicity observed between 1983 and 1995 from seismological observations several types of characteristic events are recognised volcanotectonic earthquakes are standard microearthquakes either shallow an aseismic zone is situated between two seismic zones at a depth between 1 5 and 2 5 km below the summit we postulate that it is a small shallow magma reservoir where magma injected from below can be stored temporarily we try to relate seismic observations during both eruptive cycles to the initial injection of deep magma to the superficial magma system the first eruption in each case seems to involve magma enriched in gas that extrudes the content of the conduit and explodes the old dome a regular outflow of magma follows the initial explosion and gradually a dome is building up then it stops and a period of repose is observed later a second episode of dome growth occurs the height of the dome reaches a maximum corresponding to a state of lithostatic equilibrium the time delay of more than 2 years between the beginning and the end of a cycle may result from crystallisation in a volatile rich magma and from the building up of pressure in the superficial magma pocket some important events like the collapse of the dome on 22 november 1994 are not preceded by any seismic precursor when it reaches a large volume the dome is not stable and is likely to collapse by gravity for instance after the sudden influx of matter or gas or after a heavy rain on merapi tremors are observed but do not always precede a dangerous event

volcanomagnetic signals associated with the quasi continuous activity of the andesitic merapi volcano indonesia 1990 1995 abstract merapi volcano in java island indonesia is an andesitic stratovolcano which presents long periods of effusive activity during which an endogeneous dome is continuously growing the viscous lava dome gives rise to unstable blocks which collapse or turn into pyroclastic flows when the volcano does not exhibit any surface activity the overpressure within the volcano slowly increases depending on the quietness duration the unrest of the volcano can start with an explosive phase during which the former dome is partly destroyed magnetic variations of different time constant are observed during the 1990 1995 period which includes one gas plume emission on august 26 1990 and two eruptions on january 20 1992 and on november 22 1994 compared with other types of active volcanoes the observed volcanomagnetic variations are very small at the most a few nanoteslas nt to discriminate the variations associated with the global activity from the signals correlated with each unrest phase one has to dissociate the different time constant variations over the six year time span when long term trends are removed from the magnetic field in each station of the network an outstanding correlation between all the magnetic differences is emphasised the midterm variations point out 2 cycles of activity which fit the stress field evolution within the edifice leading to the 1992 and 1994 eruptions a new cycle has started in may 1995 in every identified cycle rapid volcanomagnetic signals are well associated with stress field changes may 1991 september 1991 february 1993 december 1993 some of the volcanomagnetic variations are short term precursory signals as the three months decrease up to 1 3 nt preceding the 1992 eruption the comparison between magnetic data seismicity and surface phenomena implies that the midterm volcanomagnetic variations associated with the cycles of merapi activity are of piezomagnetic origin

merapi central java indonesia an outline of the structural and magmatological evolution with a special emphasis to the major pyroclastic events abstract merapi volcano in the central part of java is regarded as the most active and most dangerous volcano in indonesia on the basis of field studies and geochronological data its history is divided into four periods ancient middle recent and modern merapi according to our preliminary age data the ancient period may have begun around 40 000 y bp and lasted until 14 000 y bp when the middle period begun the recent period begun around 2200 y bp and was replaced by the modern period after the eruption of 1786 during the middle merapi stage a mount st helens type edifice collapse occurred our data suggest that his event is younger than 6700 y bp and older than 2200 y bp during the recent merapi stage violent magmatic to phreatomagmatic eruptions twice interrupted the growth of the volcano the older gumuk phreatoplinian deposits cover the entire cone charcoal found within these deposits gave 14c ages of 2200 and 1470 y bp the overlying sambisari ash deposits were emplaced by violent pyroclastic surges directed towards the south i e to the present location of the town of yogyakarta they buried the shivaitic temple of sambisari at the start of the 15th century modern merapi is characterised by the persistent growth of a summit dome periodically interrupted by partial or total collapse of the dome to generate frequent merapi type nuees ardentes blocks and ash flows and associated surges or more exceptionally fall back st vincent type nuees ardentes scoria flows in contrast previous stages were characterised by effusion of long lava flows alternating with violent explosive phases generating essentially st vincent type nuees ardentes merapi lavas are calc alkaline with a compositional range between 49 5 and 60 5 wt sio2 moreover high k basaltic andesites represent about 90 of merapi lavas disequilibrium features are common in the mineralogical assemblage plagioclase orthopyroxene clinopyroxene olivine amphibole titanomagnetite scarce alkali feldspar macroscopic and microscopic textural heterogeneities are related to magma mixing that may have buffered the compositions of lavas and caused the restricted range of compositions our studies of past activity at merapi provide some insights into future activity and to related volcanic hazards it is clear that merapi has the potential of eruptions much more powerful than observed during the historic period

merapi volcano java indonesia and merapi type nuee ardente a particular nuee ardente type merapi type avalanche nuee has been defined at the merapi volcano because of its prominent role in the recent activity of the volcano gravity plays a significant role during the eruption

pallasite paleomagnetism quiescence of a core dynamo recent paleomagnetic studies of two main group pallasites the imilac and esquel have found evidence for a strong late stage magnetic field on the parent body it has been hypothesized that this magnetic field was generated by a core dynamo driven by compositional convection during core solidification cooling models suggest that the onset of core solidification occurred 200 ma after planetary accretion prior to core solidification a core dynamo may have been generated by thermal convection however a thermal dynamo is predicted to be short lived with a duration of 10 ma to 40 ma after planetary accretion these models predict therefore a period of quiescence between the thermally driven dynamo and the compositionally driven dynamo when no core dynamo should be active to test this hypothesis we have measured the magnetic remanence recorded by the marjalahti and brenham pallasites which based on cooling rate data locked in any magnetic field signals present 95 ma to 135 ma after planetary accretion before core solidification began the cloudy zone a region of nanoscale tetrataenite islands within a fe rich matrix was imaged using x ray photoemission electron microscopy the recovered distribution of magnetisation within the cloudy zone suggests that the marjalahti and brenham experienced a very weak magnetic field which may have been induced by a crustal remanence consistent with the predicted lack of an active core dynamo at this time we show that the transition from a quiescent period to an active compositionally driven dynamo has a distinctive paleomagnetic signature which may be a crucial tool for constraining the time of core solidification on differentiated bodies including earth

piezomagnetic fields due to an inclined rectangular fault in a viscoelastic half space an application to the 2002 2003 etna eruption summary time dependent piezomagnetic fields due to inclined rectangular faults embedded in a viscoelastic homogeneous half space were investigated a viscoelastic rheology of the surrounding medium was assumed to relate piezomagnetic changes at the surface to the stress field at depth the viscosity of the medium strongly influences time dependent stress changes especially in volcanic areas rocks near magmatic sources are considerably heated the presence of higher temperatures produces a lower effective viscosity in the crust making it necessary to consider its inelastic properties rocks no longer behave in a purely elastic manner but permanently deform because the viscosity is significantly lowered to determine the time dependent piezomagnetic fields in a viscoelastic medium we applied the correspondence principle to the analytical elastic solutions for dislocation sources among all the possible rheological models we investigated three cases in which the bulk modulus is purely elastic and the shear modulus relaxes as for i a maxwell solid ii a standard linear solid sls and iii a kelvin solid the piezomagnetic field completely vanishes after the relaxation process for a maxwell rheology whereas it is found to decrease over time and reach some finite offset values for sls and kelvin rheologies a real case study concerning the magnetic anomalies observed during the 2002 2003 mt etna eruption is also investigated post eruptive magnetic variations were in general agreement with a viscoelastic relaxation process of a sls rheology undergoing in the volcano edifice

relationship between cooling rate and cooling age of a mineral theory and applications to meteorites we reviewed here the recent development on the mathematical formulation of closure temperature of a cooling geochronological system which permits direct retrieval of cooling rate from cooling age when the diffusion parameters grain size and initial temperature are known this formulation is used to show how the cooling rate can be retrieved by comparing the core and bulk age of a mineral determined by a single decay system the cooling rates of seven h chondrites of the metamorphic types h4 h5 and h6 were retrieved from the available data on the pb pb model ages of the phosphates and the diffusion kinetic data of pb in apatite the results are in excellent agreement with the metallographic cooling rates and show an inverse relation with the metamorphic grade of these chondrites we also addressed the problem of 90 ma younger sm nd mineral isochron age defined by orthopyroxene phosphate and plagioclase of the morristown mesosiderite compared to the pb pb age of the estherville mesosiderite it is shown that this younger age could have been a consequence of resetting during cooling instead of an impulsive heating event as suggested earlier

rare earth diffusion kinetics in garnet experimental studies and applications abstract we determined the diffusion coefficient of sm in almandine garnet as function of temperature at 1 bar and fo 2 corresponding to that of wustite iron buffer and to a limited extent that of a few other selected rare earth elements in almandine and pyrope garnets both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields the experimental diffusion profiles were analyzed by secondary ion mass spectrometry and in addition by rutherford back scattering spectroscopy for two samples transmission electron microscopic study of an almandine crystal that was diffusion annealed did not reveal any near surface fast diffusion path using reasonable approximations and theoretical analysis of vacancy diffusion the experimental data were used to develop an expression of rare earth element ree diffusion coefficient in garnet as a function of temperature pressure fo 2 ionic radius and matrix composition calculation of the closure temperature for the sm nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently modeling of the ree evolution in melt and residual garnet suggests that for dry melting condition the ree pattern in the melt should commonly conform closely to that expected for equilibrium melting however for much lower solidus temperatures that would prevail in the presence of a h 2 o co 2 fluid the concentration of light ree in the melt could be significantly lower than that under equilibrium melting condition a reported core and rim differences in the ree content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the ree zoning was a consequence of entrapment in a magma derived from an external source for 32 000 yr before the eruption

tafassasset evidence of early incipient differentiation on a metal rich chondritic parent body abstract tafassasset is a primitive meteorite the origin of which is still debated its possible relationship to either the cr chondrites considered among the most primitive meteorites or the brachinites complex primitive achondrites makes it an interesting sample for studying the initial stages of planetary accretion and differentiation in the early solar system here we report tungsten w isotope data for bulk rock samples as well as for mineral fractions from tafassasset along with micro computed tomography of a piece of the meteorite silicates show mass independent w isotope anomalies while the metal phase does not these nucleosynthetic anomalies are interpreted as reflecting the presence of sic presolar grains in the matrix of the meteorite carrying s process 184w after correction of the nucleosynthetic anomalies a correlation is observed between the 182w 184w isotope compositions and the hf w ratios of the different fractions a 182hf 182w age of ca 2 9 ma after cais is inferred from the 182hf 182w chronometer slightly older than other estimates based on the 53mn 53cr 26al 26mg and pb pb chronometers but consistent with the difference in closure temperatures of the different isotopic systems numerical modeling of the thermal evolution of tafassasset indicates accretion of a parent body less than 50 km in diameter 1 ma after the formation of cais at a time when short lived radio nuclides induced metal silicate separation and partial melting of the silicates with extraction of a basaltic component according to our new data tafassasset may represent an inner part of a cr like parent body with a differentiation history similar to but less severe than that of brachinites

formation of olivine textures in pallasites and thermal history of pallasites in their parent body an analysis of the textures of pallasites has been made using data concerning the kinetic and rheological properties of silicates and metals pallasites containing rounded olivines e g the springwater and brehnam pallasites have been heated to above the solidus temperature of the metallic iron phases 1270 k the rounded olivines of grain size 0 5 1 0 cm observed in the springwater pallasites were formed between 1270 and 1370 k on the other hand those of grain size 0 5 1 0 mm as found in the brehnam pallasites may have been heated to above 1370 k however the duration of heating at such high temperatures must have been less than 5 103 y pallasites containing angular olivines with microscopically rounded corners e g the eagle station dora pallasites have suffered shock events fracturing the olivine grains which may correspond to collisions during the accretional stage of the parent body and experienced successive annealing during cooling from a temperature between 1150 and 1270 k

53mn 53cr dating of fayalite formation in the cv3 chondrite mokoia evidence for asteroidal alteration fayalite grains in chondrules in the oxidized aqueously altered cv3 chondrite mokoia have large excesses of radiogenic chromium 53 these excesses indicate the in situ decay of short lived manganese 53 half life 3 7 million years and define an initial53mn 55mn ratio of 2 32 0 18 10 6 this ratio is comparable to values for carbonates in ci and cm chondrites and for several classes of differentiated meteorites mokoia fayalites formed 7 to 16 million years after allende calcium aluminum rich inclusions during hydrothermal activity on a geologically active asteroid after chondritic components had ceased forming in the solar nebula

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

a volcanomagnetic observation on mount st helens washington total magnetic fields were recorded at five sites on mt st helens between 23 october and 11 november 1981 an interval which included an extrusive dome building eruption of the volcano two of the magnetometers located in the volcano s crater measured reversible magnetic changes which correspond to fluctuations in tilt measured nearby however the relationship is highly nonlinear electric fields were measured on the east flank of the volcano near its summit to search for electrokinetic effects they show no correlation with the magnetic changes and in the long term are uncorrelated with eruptive activity our favored interpretation of the magnetic changes is that they result from stress induced changes in the magnetization of the volcano magnetic field values returned to pre anomaly values this reversibility rules out pressure induced magnetization as the dominant mechanism and places an upper limit of 300 bars on the stress changes the limited spatial extent of the magnetic anomaly field places the source of stress at shallow depth beneath the crater floor consistent with models based on strain data

intrinsic oxygen fugacity measurements on seven chondrites a pallasite and a tektite and the redox state of meteorite parent bodies abstract intrinsic oxygen fugacity fo2 measurements were made on five ordinary chondrites a carbonaceous chondrite an enstatite chondrite a pallasite and a tektite results are of the form of linear log f o 2 1 t plots except for the enstatite chondrite measured results agree well with calculated estimates by others the tektite produced fo2 values well below the range measured for terrestrial and lunar rocks the lowpressure atmospheric regime that is reported to follow large terrestrial explosions coupled with a very high temperature could produce glass with fo2 in the range measured the meteorite salta pallasite has low fo2 and lies close to hvittis e6 unlike the other samples results for salta do not parallel the iron wustite buffer but are close to the fayalite quartz iron buffer in slope minor reduction by graphite appears to have taken place during metamorphism of ordinary chondrites fo2 values of unequilibrated chondrites show large scatter during early heating suggesting that the constituent phases were exposed to a range of fo2 conditions the samples equilibrated with respect to fo2 in relatively short time on heating equilibration with respect to fo2 in ordinary chondrites takes place between grades 3 and 4 of metamorphism application of p t fo2 relations in the system c co co2 indicates that the ordinary chondrites were metamorphosed at pressures of 3 20 bars as it appears that they lay on the graphite surface a steep positive thermal gradient in a meteorite parent body lying at the graphite surface will produce thin reduced exterior an oxidized near surface layer and an interior that is increasingly reduced with depth a shallow thermal gradient will produce the reverse a body heated by accretion on the outside will have a reduced exterior and oxidized interior meteorites from the same parent body clearly are not required to have similar redox states

magnetic signatures associated with magma ascent and stagnation at popocatepetl volcano mexico during 2006 monitoring of real time magnetic signals at popocatepetl during 2006 has allowed discrimination of magma injection and dome growth magnetic signals correlated with seismic volcanotectonic events and harmonic tremor as well as number of small emissions spring water ph ash components and dome evolution helped define upward magma transport and yield a better understanding of the volcanic plumbing system magma ascent occurs mostly in periods of 7 3 days associated with harmonic tremor and decreasing magnetic signals between 21 1 and 215 nt followed by increasing signals linked to cooling of the domes and increased seismicity over periods of 1 to more than 3 months the dome clogs the vent after the negative magnetic anomaly harmonic tremor period associated with magma ascent and forces an explosive crater reopening explosion larger negative changes in the magnetic signals occurred in april 26 nt august 23 to 26 nt and october to december 25 to 215 nt associated with dome formation and growth negative magnetic anomalies preceded eruptions