the fine grained matrix of the semarkona ll3 0 ordinary chondrite an induced thermoluminescence study to investigate the nature origin and history of the fine grained matrix in semarkona and develop techniques suitable for small samples we have measured the induced thermoluminescence properties of six matrix samples 10 m to 400 m in size the samples had tl sensitivities comparable with 4 mg of bulk samples of type 3 2 3 4 ordinary chondrites which is very high relative to bulk semarkona the other induced tl properties of these samples tl peak temperatures and tl peak widths distinguish them from other ordinary chondrite samples where the tl is caused by feldspar cathodoluminescence images and other data suggest that the cause of the luminescence in the semarkona fine grained matrix is forsterite in some respects the matrix tl data resemble that of semarkona chondrules in which the phosphor is forsterite and terrestrial forsterites from a variety of igneous and metamorphic environments however differences in the tl peak temperature versus tl peak width relationship between the matrix samples and the other forsterites suggest a fundamentally different formation mechanism we also note that forsterite appears to be a major component in many primitive materials such as nebulae cometary dust and stardust particles

187re 187os systematics highly siderophile element s se te abundances in the components of unequilibrated l chondrites abstract the 187re 187os systematics abundances of highly siderophile elements hse re platinum group elements and au te se and s as well as major and minor elements were determined in separated components of two unequilibrated l chondrites que 97008 l3 05 and ceniceros l3 7 the 187re 187os systematics are disturbed in the components of both meteorites most likely due to open system behavior of re during terrestrial weathering of que 97008 and alteration on the l chondrite parent body as indicated by an internal errorchron generated for components of ceniceros the hse abundance patterns suggest that the bulk rock abundances were mainly controlled by two different end members non magnetic fractions display lower re os and hse ir than ci chondrites chondrules metal troilite spherules and fine magnetic fractions are depleted in refractory hse and show higher rh ir pd ir and au ir than in ci chondrites the different hse compositions indicate the presence of unequilibrated alloys and loss of refractory hse rich carrier phases from the precursors of some l chondrite components gold is decoupled from other hse in magnetic fractions and shows chalcophile affinities with a grain size dependent variation similar to s and se presumably inherited from preaccretionary processes tellurium is depleted in all components compared to other analysed siderophile elements and its abundance was most likely controlled by fractional condensation and different geochemical affinities the volatility dependent depletion of te requires different physical and chemical conditions than typical for the canonical condensation sequence as represented by carbonaceous chondrites tellurium also shows variable geochemical behavior siderophile in ceniceros predominantly chalcophile in que 97008 these differences may have been inherited from element partitioning during chondrule formation selenium and s on the other hand are almost unfractionated from each other and only show complementary s se in a few components presumably due to the effects of volatility or metal silicate partitioning during chondrule formation terrestrial weathering had negligible effects on the s se and te systematics

oxygen isotopic heterogeneities their petrological correlations and implications for melt origins of chondrules in unequilibrated ordinary chondrites abstract ten whole chondrules separated from the dhajala h3 4 hallingeberg l3 and semarkona ll3 chondrites were individually analyzed for bulk element composition by instrumental neutron activation with half of each chondrule subsequently sacrificed for oxygen isotopic analysis and half retained for petrographic and electron microprobe analysis on a three isotope plot 17 o vs 18 o the chondrules neither cluster near their respective chondrite hosts nor in the vicinities of previously recognized chondrite group averages instead they define a trend resolvable into mixing and fractionation components but dominated by mixing in a manner similar to that previously observed for clasts from the ll3 chondrite alha76004 covariations of chondrule isotopic mixing and fractionation parameters with petrological parameters were sought by two variable linear least squares regression analyses however the only two isotopic petrological correlations significant at the 95 confidence level were 17 o vs total bulk fe r 0 68 and mixing parameter m 18 vs bulk weight ratio cao al 2 o 3 mgo r 0 67 other correlations of apparent statistical significance were found by treating the chondrules as separate porphyritic 3 porphyritic olivine pyroxene 1 porphyritic olivine 1 barred olivine and non porphyritic 4 radial pyroxene 1 granular pyroxene cryptocrystalline textural subgroups the reliability of the trends based on so few samples is not clear but the results at least indicate that possible existence of distinct isotopic petrological subgroups of chondrules should be further investigated absence of certain isotopic petrological trends expected as condensation effects argues against direct nebular condensation as the dominant process of chondrule formation instead a model involving melting of heterogeneous solids followed by various degrees of liquid gas exchange is favored in any case chondrule oxygen isotopic evolution was dominated by two component mixing fractional vaporization was at most a second order effect in addition to chondrules parent bodies of unequilibrated ordinary chondrites must have also incorporated a 16 o rich component which might have been fine grained matrix

chondrules in h3 chondrites textures compositions and origins major and minor element bulk compositions of 90 individual chondrules and 16 compound chondrule sets in unequilibrated type 3 h group chondrites were determined in polished thin sections by broad beam electron probe analysis and the chondrules were classified petrographically into six textural types barred olivine porphyritic olivine porphyritic pyroxene barred pyroxene radiating pyroxene fine grained although analyses of individual chondrules scatter widely the mean composition of each textural type except barred pyroxene is rather distinct as verified by discriminant function analysis al2o3 tio2 and na3o are correlated in chondrules but al2o3 and cao do not correlate compound chondrule sets were found to consist almost entirely of chondrules or partial chondrules of similar texture and composition the data suggest that composition played a conspicuous role in producing the observed textures of chondrules though other factors such as cooling rates and degrees of supercooling prior to nucleation were also important if compound chondrules formed and joined when they were still molten or plastic then the data suggest that chondrules of each textural type could have formed together in space or time the correlation of al2o3 and tio2 with na2o and not with cao appears to rule out formation of chondrules by direct equilibrium condensation from the nebula we conclude that the most reasonable model for formation of the majority of chondrules is that they originated from mixtures of differing fractions of high intermediate and low temperature nebular condensates that underwent melting in space a small percentage of chondrules might have formed by impacts in meteorite parent body regoliths

al rich objects in ordinary chondrites related origin of carbonaceous and ordinary chondrites and their constituents ca al rich inclusions cais common constituents of carbonaceous chondrites have been studied extensively because they contain refractory high temperature minerals suggesting that they formed at high temperatures during the early history of the solar system few cais have previously been discovered in ordinary chondrites here we describe 169 al rich objects arbitrarily defined as having 10 wt al2o3 from 24 types 3 and 4 ordinary chondrites five regolith breccias containing unequilibrated material the unique meteorite kakangari and a few types 5 and 6 ordinary chondrites based on shape and texture we divide al rich objects into chondrules round with igneous textures irregularly shaped inclusions similar to type f and spinel rich complex cais and fragments probably fragments of al rich chondrules and inclusions for descriptive purposes we further subdivide al rich chondrules into compositional subgroups although they are entirely transitional conclusions 1 a al rich chondrules and irregularly shaped inclusions and fragments are wide spread albeit rare constituents of ordinary chondrites and are similar to cais except the coarse grained ones in carbonaceous chondrites thus providing strong support for a related origin of ordinary and carbonaceous chondrites and their constituents 2 b al rich chondrules formed as independent freely floating molten droplets and cooled rather rapidly 3 c al rich chondrules like the common mg fe rich chondrules formed by melting of millimeter to submillimeter sized dust balls in the case of al rich chondrules the dust balls consisted largely of mixtures of variable amounts of at least two solid precursor materials one refractory rich and the other volatile rich phases which we interpret as unmelted relicts in some of these objects support this model 4 d the wide ranges in bulk compositions of al rich chondrules from refractory rich to volatile rich ones yet complete transition between them and the existence of chondrules transitional in composition between the al rich and common mg fe rich chondrules of ordinary chondrites suggest that all chondrules formed by related processes differences in bulk composition result from mixing of different proportions of refractory volatile and mg fe rich and other solid precursor materials into dust balls which were then melted 5 e most irregularly shaped inclusions show no indication of a once molten origin secondary alteration has probably changed the original mineral assemblage mainly volatile rich materials entered the refractory objects as a gas reacted with the constituents and produced secondary phases rims probably formed both by decomposition and reaction with solar gas as well as by accretion 6 f coarse grained inclusions as found in allende were not observed in ordinary chondrites

intra cone plumbing system and eruptive dynamics of small volume basaltic volcanoes a case study in the calatrava volcanic field abstract the manoteras volcano tortonian to pleistocene calatrava volcanic field spain is composed of a scoria and spatter cone surrounded by a field of pahoehoe lava the volcanic cone is made essentially of vitreous lapilli tuffs with intercalations of vitreous tuffs and spatter deposits without any intercalations of lava flows erosion has uncovered an intra cone plumbing system formed by coherent dykes and pyroclastic dykes mixed type dykes this dyke swarm reflects processes of intrusion at the end of the eruption or even post eruption all the volcanic products are nephelinitic in composition the main dyke is up to 3 4 m thick and has an exposed length of 1000 m it is composed mostly of coherent nephelinite with some pyroclastic sections at its northern extremity this dyke is regarded as a feeder dyke of the volcano although the upper parts of the dike have been eroded which prevents the observation of the characteristics and nature of the possible overlying vent s mixed type dykes could also have acted as small linear vents and indicate that the magma fragmentation level during final waning stages of the eruption was located inside the volcanic cone the pyroclastic deposits that make up the volcanic cone at the current exposure level were probably developed during a major phase of violent strombolian style that formed the scoria cone followed by a hawaiian phase that formed the summital intracrater spatter deposit three central type vents have been identified one at the highest point of the remnant volcanic cone summital vent from where the earlier explosive eruptions took place and the other two at the fringe of the cone base from where emissions were only effusive the lava flows were emitted from these boccas through the scoria cone feeding the lava field the results obtained based on careful field observations add substantial complexity to the proposed eruptive models for small volume basaltic volcanoes as it appears evident that there may exist and evolution through time from central conduit settings to fissure eruptions moreover it is shown that intracone plumbing systems can integrate coherent and clastic dykes of variable thicknesses which in some cases could represent feeder dykes

volcanology history and myths of the lake albano maar colli albani volcano italy abstract the polygenetic albano maar is the most recent centre of the colli albani volcano located just few kilometres to the south east of roma presently the maar hosts a 167 5 m deep crater lake the deepest in europe the maar is to be considered quiescent as phreatic activity is documented throughout the holocene this paper illustrates the close relationships between the activity of the maar and the history of settlement in the roman region as recorded in the geology archaeology history and legends of the area severe fluctuations of the groundwater table and catastrophic overflows of the lake albano from the maar rim had occurred prior to and after the early prehistoric settlements dated in the maar area at the eneolithic times ca iii millennium b c repeated lahars occurred along the northwestern slope of the maar filling in the paleodrainage network and forming a vast plain paleohydraulic analyses on fluvial and lahar deposits originated from the holocene phreatic activity of the albano maar indicate sediment water flows in excess of hundreds of cubic metres per second absolute age determinations of the paleosoil underlying one of the most recent deposits of the lahar succession at 5800 100 yr b p 14 c cal are in perfect agreement with the age of the overlying eneolithic age settlements the last catastrophic overflow is described in the roman literature as a consequence of the anger of poseidon against the romans in 398 b c for their war against the etruscans in 394 b c the romans decided to prevent the repetition of such events by the excavation through the maar crater wall of a 1 5 km long drain tunnel which is still operational keeping the lake 70 m below the lowest point of the maar rim this tunnel drain may be regarded as the first prevention device for volcanic hazard in history and shows an unprecedented development of the engineering technology under the pressure of hazard perception the surprising and still largely unknown results of this study are very important to redefine the hazard of the roman region

volcanic stratigraphy of the quaternary la garrotxa volcanic field north east iberian peninsula this study was partially funded by the beca ciutat d olot and the european commission ft7 theme env 2011 1 3 3 1 grant 282759 vuelco

al rich chondrules from the ybbsitz h4 chondrite evidence for formation by collision and splashing three al rich chondrules al2o3 10 wt from the h4 chondrite ybbsitz were chemically and mineralogically studied all three clearly crystallized from molten droplets as individual objects they consist predominantly of olivine spinel and a feldspar rich mesostasis the three al rich chondrules have high concentrations of incompatible elements the rare earth element patterns are fractionated with enrichment of light rare earths and a strong positive eu anomaly this type of fractionated refractory element pattern is indicative of igneous processes ca al rich inclusions from carbonaceous chondrites also show high enrichments in refractory elements their patterns are however either flat or fractionated according to variable volatilities of refractory elements in the solar nebula e g yb anomaly the high level of refractory siderophiles observed in ca al rich inclusions from carbonaceous chondrites is not found in the al rich chondrules we therefore conclude that the al rich ybbsitz chondrules formed by different processes than the ca al rich inclusions from carbonaceous chondrites melting of inhomogeneous precursors generally assumed for the formation of ferromagnesian chondrules is also unlikely to produce such extreme compositions the possibility that metamorphism is the cause of the high content of incompatible elements can be excluded we therefore propose a new model for the formation of the al rich chondrules they may have formed by collisions of partly molten ferromagnesian chondrules with other objects chondrules during this process al rich melt fractions residual liquids may be ejected and form independent al rich chondrules this model explains the high enrichment and the fractionated patterns of incompatible elements in al rich chondrules as well as their generally much smaller sizes compared with ferromagnesian chondrules the eu anomaly is probably due to diffusive exchange of eu between matrix and the al rich chondrules eu is decoupled from the other ree in many ferromagnesian chondrules of equilibrated ordinary chondrites including three ferromagnesian chondrules from ybbsitz analyzed in this study

cenozoic magmatism of the valencia trough western mediterranean relationship between structural evolution and volcanism abstract the cenozoic magmatism of the valencia trough is characterized by the existence of two volcanic cycles the first cycle early miocene middle miocene comprises calc alkaline rocks which have been recognized in the central to eastern offshore areas and in mallorca the second cycle middle miocene to recent is represented mainly by poorly differentiated alkaline rocks which are predominantly distributed along the iberian margin of the valencia trough in accordance with the inferred structural evolution of the valencia trough petrological and geochemical data as well as volcanological evidence we suggest that two different geodynamic environments existed during these magmatic cycles the early to middle miocene calc alkaline volcanism developed under compressive tectonic conditions and seems to be associated with the northwestern dipping subduction of the african plate in contrast the middle miocene to recent alkaline volcanism is associated with extensional tectonics and can be explained within the framework of a low volcanicity rift model three zones catalan valencian and columbretes each located at different parts of the rift structure can be distinguished in the middle miocene to recent volcanism this intraplate volcanism results from partial melting due to extension driven decompression with the largest degrees of melting in the centre of the valencia trough columbretes volcanic zone in the catalan volcanic zone a progressive increase in the extension rate from the first to the last volcanic episode has occurred favouring the interaction of two mantle sources

volcanic stratigraphy a review abstract volcanic stratigraphy is a fundamental component of geological mapping in volcanic areas as it yields the basic criteria and essential data for identifying the spatial and temporal relationships between volcanic products and intra inter eruptive processes earth surface tectonic and climatic which in turn provides greater understanding of the geological evolution of a region establishing precise stratigraphic relationships in volcanic successions is not only essential for understanding the past behaviour of volcanoes and for predicting how they might behave in the future but is also critical for establishing guidelines for exploring economic and energy resources associated with volcanic systems or for reconstructing the evolution of sedimentary basins in which volcanism has played a significant role like classical stratigraphy volcanic stratigraphy should also be defined using a systematic methodology that can provide an organised and comprehensive description of the temporal and spatial evolution of volcanic terrain this review explores different methods employed in studies of volcanic stratigraphy examines four case studies that use differing stratigraphic approaches and recommends methods for using systematic volcanic stratigraphy based on the application of the concepts of traditional stratigraphy but adapted to the needs of volcanological environment

phyllosilicates in the matrix of the unique carbonaceous chondrite lewis cliff 85332 and possible implications for the aqueous alteration of ci chondrites abstract the fine grained matrix of the unique unequilibrated carbonaceous chondrite lewis cliff lew 85332 has been studied by scanning electron microscopy sem electron probe microanalysis epma and transmission electron microscopy tem compositionally lew 85332 has a matrix that is more fe rich than typical ci chondrites but has elemental abundance ratios that appear to be closer to ci matrices than to cm or cr chondrites the mineralogy of the matrix is dominated by phyllosilicate phases that are predominantly interlayered fe rich serpentine saponite anhydrous silicate phases such as olivine and pyroxene are rare minor magnetite troilite and ferrihydrite also occur associated with the phyllosilicates despite the high degree of weathering in lew 85332 the phyllosilicates appear to have an extraterrestrial origin but the highly variable mg fe ratios of saponite may be the result of partial terrestrial oxidation of fe rich saponite to a more mg rich saponite and ferrihydrite alternatively some of the ferrihydrite may have formed as a result of terrestrial weathering of fe ni metal the compositional and mineralogical data suggest that the matrix of lew 85332 may represent a very early stage in the type of aqueous alteration experienced by the ci chondrites although it is improbable that lew 85332 was a precursor to the ci chondrites because of its high abundance of chondrules the absence of carbonates the high fe content of the matrix and phyllosilicate phases and relatively low abundance of magnetite all indicate that the degree of oxidation and leaching of lew 85332 matrix was significantly less than that experienced by the ci chondrites the absence of clear evidence for alteration of chondrules suggests that either the formation of the hydrous phases in the matrix occurred prior to accretion or that alteration occurred on a parent body and involved limited amounts of fluid such that the reactions took place preferentially and exclusively within the fine grained anhydrous matrix materials

complex interaction between strombolian and phreatomagmatic eruptions in the quaternary monogenetic volcanism of the catalan volcanic zone ne of spain the catalan volcanic zone cvz at the ne of the iberian peninsula is one of the quaternary alkaline volcanic provinces of the european rifts system the cvz has been active during the last 12 ma despite the fact that this volcanism is significant in extension and volume and that eruptions have also occurred in holocene times it is mostly unknown compared to the contemporaneous alkaline volcanism in other parts of western and central europe volcanism younger than 0 5 ma is mostly concentrated in an area of about 100 km2 located between the main cities of olot and girona this basaltic volcanic field comprises more than 50 monogenetic cones including scoria cones lava flows tuff rings and maars magmatic eruptions range from hawaiian to violent strombolian phreatomagmatism is also common and has contributed to the construction of more than a half of these volcanic edifices frequently associated with the strombolian activity but also independently giving rise to a large variety of eruptive sequences we describe the main characteristics of this volcanism and analyse in particular the successions of deposits that form some of these volcanoes and discuss the potential causes of such a wide diversity of eruptive sequences we find that the main cause of such complex eruptive behaviour resides in the stratigraphic structural and hydrogeological characteristics of the substrate above which the volcanoes were emplaced rather than on the compositional characteristics of the erupting magma as they do not show significant variations among the different volcanoes studied

refractory precursor components of semarkona chondrules and the fractionation of refractory elements among chondrites abstract chondrules from the semarkona ll3 0 chondrite show refractory and common lithophile fractionation trends similar to those observed among the chondrite groups it appears that chondrules are mixtures of a small number of pre existing solid components and we infer that chondrule precursor materials were related to the nebular components involved in the lithophile element fractionations recognized in ordinary chondrites compositional trends among the chondrules can be used to deduce the compositions of these components we use instrumental neutron activation analysis to measure many 20 of the lithophile elements in 30 chondrules the amounts of oxidized iron were calculated from other compositional parameters concentrations of si were estimated using mass balance considerations the data were corrected for the diluting effects of non lithophile constituents plots of lithophile elements versus a reference refractory element such as al show that there were two major chondrule silicate precursor components a refractory olivine rich feo free one and a non refractory sio 2 feo rich one the refractory component probably forms from olivine enriched condensates formed above the condensation temperature of enstatite the non refractory component must have formed from fine grained materials that were able to equilibrate down to lower nebular temperatures chondrite matrix may have had an origin similar to that of the non refractory material and constitutes a third lithophile bearing component that took part in chondrite fractionation processes the low abundance of refractories and mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element mg ratio than that in the refractory component of chondrules

olivine in terminal particles of stardust aerogel tracks and analogous grains in chondrite matrix abstract the dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the wild 2 samples we present 68 analyses of olivine fa 0 97 in the coarse grained terminal particles of stardust aerogel tracks and a comprehensive dataset 10 3 analyses of analogous olivine grains 5 30 m isolated in ci cm cr ch co cv3 oxidized cv3 reduced c3 ungrouped acfer 094 and ningqiang l ll 3 0 4 eh3 and kakangari chondrite matrix these compositions reveal that wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite forming regions the wild 2 olivine includes amoeboid olivine aggregates aoas refractory forsterite type i and type ii chondrule fragments and or microchondrules and rare relict grain compositions in addition we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low temperature aqueous processing in the kuiper belt the generally low cr content of feo rich olivine in the stardust samples indicates that they underwent mild thermal metamorphism akin to a petrologic grade of 3 05 3 15

thin crust and active upper mantle beneath the southern sierra nevada in the western united states abstract analysis of seismic refraction wide angle reflection travel time and seismic amplitude data collected during the 1993 southern sierra nevada continental dynamics sscd project resolves a small crustal root 40 42 km thick centered 80 km west of the sierran topographic crest the sscd experiment consisted of a west east profile across the sierra nevada at approximately 36 5 n and a north south profile extending the length of owens valley located eastward of the sierran topographic crest two dimensional finite difference travel time inversion of p g and p n arrivals resolves upper crustal velocities of 6 0 to 6 4 km s 1 within the sierran batholith and basin and range an upper crustal west dipping wedge of higher velocities 6 8 7 2 km s 1 consistent with ophiolitic material underlying the great valley sedimentary sequence and higher velocities in the lower crust beneath the basin and range 6 8 7 0 km s 1 than those beneath the sierran batholith 6 6 km s 1 low average p n velocities 7 6 7 9 km s 1 and a laminated transitional moho imaged beneath the sierran batholith also differ from the higher p n velocities 7 9 8 0 km s 1 and sharp first order moho observed beneath the basin and range the crust decreases in thickness both westward of the root to 28 34 km beneath the great valley and eastward to 35 km beneath the highest sierran topography and decreases further to 27 30 km beneath the basin and range crustal thickness also appears to increase southeast to northwest from 29 30 km beneath the garlock fault in the south to 38 40 km beneath the north end of chalfant valley juxtaposition of the crustal model with previous p wave tomography models of the south ernmost sierra nevada upper mantle reveal that the thickest sierran crust on the west east profile overlies a pronounced upper mantle high velocity anomaly 5 whereas the region of laminated moho overlies a flanking upper mantle low velocity region 3 the upper mantle velocity anomalies relatively low p n and relatively flat moho observed beneath the sierran crest suggest that the recent uplift of the sierra nevada is due to asthenospheric flow and or lithospheric thinning beneath the southeastern sierra nevada and basin and range

the architecture eruptive history and evolution of the table rock complex oregon from a surtseyan to an energetic maar eruption abstract the table rock complex trc pliocene pleistocene first documented and described by heiken heiken g h 1971 tuff rings examples from the fort rock christmas lake valley basin south central oregon j geophy res 76 5615 5626 is a large and well exposed mafic phreatomagmatic complex in the fort rock christmas lake valley basin south central oregon it spans an area of approximately 40 km2 and consists of a large tuff cone in the south trc1 and a large tuff ring in the northeast trc2 at least seven additional smaller explosion craters were formed along the flanks of the complex in the time between the two main eruptions the first period of activity trc1 initiated with a surtseyan style eruption through a 60 70 m deep lake the trc1 deposits are dominated by multiple 1 2 m thick fining upward sequences of massive to diffusely stratified lapilli tuff with intermittent zones of reverse grading followed by a finely laminated cap of fine grained sediment the massive deposits are interpreted as the result of eruption fed subaqueous turbidity current deposits whereas the finely laminated cap likely resulted from fallout of suspended fine grained material through a water column other common features are erosive channel scour and fill deposits massive tuff breccias and abundant soft sediment deformation due to rapid sediment loading subaerial trc1 deposits are exposed only proximal to the edifice and consist of cross stratified base surge deposits the eruption built a large tuff cone above the lake surface ending with an effusive stage which produced a lava lake in the crater 365 m above the lake floor a significant repose period occurred between the trc1 and trc2 eruptions evidenced by up to 50 cm of diatomitic lake sediments at the contact between the two tuff sequences the trc2 eruption was the last and most energetic in the complex general edifice morphology and a high percentage of accidental material suggest eruption through saturated trc1 deposits and or playa lake sediments trc2 deposits are dominated by three dimensional dune features with wavelengths 200 500 m perpendicular to the flow and 20 200 m parallel to the direction of flow depending on distance from source large u shaped channels 10 32 m deep run up features over obstacles tens of meters high and a large 13 m chute and pool feature are also identified the trc2 deposits are interpreted as the products of multiple erosive highly inflated pyroclastic surges resulting from collapse of an unusually high eruption column relative to previously documented mafic phreatomagmatic eruptions

alkali basalts and leucitites in an extensional intracontinental plate setting the late cenozoic calatrava volcanic province central spain the calatrava volcanic province cvp of central spain is characterised by a intracontinental plate magmatic association of leucitites melilitites nephelinites and olivine basalts extruded during the late miocene to quaternary most of the rocks represent relatively primitive magmas and less than 45 have experienced small degrees 25 of crystal fractionation melilitites nephelinites and olivine basalts form a suite generated by variable degrees of partial melting f 5 17 of a nearly homogeneous enriched up to x18 chondritic values for the highly incompatible elements and 3 for the moderately incompatible mantle source composed of ol opx cpx gt phl the leucitites appear to be derived by low degrees of partial melting 4 from a different mantle source characterized by higher rb ba k and 87sr enrichment and the presence of residual apatite phlogopite contributed to the leucititic liquids in a higher proportion than in the basaltic suite whereas clinopyroxene participated in lower amounts the geochemical characteristics of the primary liquids suggest a contribution from two source components 1 a subcontinental lithospheric component which appears to be a strongly enriched garnet lherzolite with phlogopite apatite and 2 an asthenospheric diapir component with characteristics similar to the himu reservoir these conclusions combined with geophysical observations indicate that the cvp magmatism could develop in two stages in a first stage a himu like mantle diapir would trigger magma generation in the overlying subcontinental lithosphere by melting of pervasive enriched streaks or veins with phlogopite apatite giving rise to small amounts of leucititic liquids and to initial extension of the upper crust in subsequent steps the extension developed the lithosphere becomes stripped of its enriched components and the asthenospheric diapir starts to melt giving rise to the basaltic liquids which are virtually oib like magmas this model is also supported by the available k ar radiometric ages as the leucitites were extruded first 7 6 ma followed by the basaltic suite 4 6 1 75 ma this volcanic region is linked with the rift system which developed from late miocene to quaternary times in western central europe and shows strong geochemical similarities with this volcanism in which both lithospheric and asthenospheric components have been detected

compositional evidence regarding the origins of rims on semarkona chondrules abstract the compositions of the interiors and abraded surfaces of 7 chondrules from semarkona ll3 0 were measured by neutron activation analysis for nonvolatile elements the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors siderophile and chalcophile concentrations are much higher in the surfaces whereas lithophile concentrations are similar in both fractions most of the similarities in lithophile patterns and some of the similarities in siderophile patterns between surfaces and interiors may reflect incomplete separation of the fractions in the laboratory but for 3 or 4 chondrules the siderophile resemblance is inherent implying that the surface and interior metal formed from a single precursor assemblage metal and sulfide rich chondrule rims probably formed when droplets of these phases that migrated to the chondrule surface during melting were reheated and incorporated into matrix like material that had accreted onto the surface the moderately volatile to volatile elements k as and zn tend to be enriched in the surfaces compared with other elements of similar mineral affinity both enrichments and depletions are observed for other moderately volatile elements a small fraction of chondrules experienced fractional evaporation while they were molten

mineralogy of fine grained material in the krymka ll3 1 chondrite two dark lithic fragments and matrix of the krymka ll3 1 chondrite were mineralogically and chemically studied in detail these objects are characterised by the following chemical and mineralogical characteristics which distinguish them from the host chondrite krymka 1 bulk chemical analyses revealed low totals systematically lower than 94 wt due to high porosity 2 enrichment in feo and depletion in s mgo and sio2 due to a high abundance of fe rich silicates and low sulfide abundance 3 fine grained almost chondrule free texture with predominance of a porous cryptocrystalline groundmass and fine grains 4 occurrence of a small amount of once molten material microchondrules enclosed in fine grained materials 5 occurrence of accretionary features especially unique accretionary spherules 6 high abundance of small calcium aluminium rich inclusions cais in one of the fine grained fragments it is suggested that the abundance of cais in this fragment is one of the highest ever found in an ordinary chondrite accretionary fine grained spherules within one of the fragments bear fundamental information about the initial stages of accretion as well as on the evolution of the clast its incorporation and history within the bulk rock of krymka the differences in porosity bulk composition and mineralogy of cores and rims of the fine grained spherulitic objects allow us to speculate on the following processes 1 low velocity accretion of tiny silicate grains onto the surface of coarse metal or silicate grains in a dusty region of the nebula is the beginning of the formation of accretionary porous fluffy silicate spherules 2 within a dusty environment with decreasing silicate metal sulfide ratio the porous spherules collected abundant metal and sulfide particles together with silicate dust which formed an accretionary rim variations of the silicate sulfide metal ratio in the dusty nebular environment result in the formation of multi layered rims on the surface of the silicate rich spherules 3 soft accretion and lithification of rimmed fluffy spherules fine grained silicate rich dust metal sulfide particles cais silicate rich microchondrules and coarse silicate grains and fragments followed 4 after low temperature processing of the primary accretionary rock collisional fragmentation occurred the fragments were subsequently coated by fine grained material which was highly oxidized and depleted in sulfides 5 in a final stage this accretionary dusty rock was incorporated as a fragment within the krymka host

characterizing earthquake location uncertainty in north america using source receiver reciprocity and usarray abstract the comprehensive nuclear test ban treaty community often uses calibration events with well determined origins to improve absolute locations of nearby seismic events by accounting for the biasing effects of unknown velocity structure but the number of these ground truth events is limited to provide additional constraints source receiver reciprocity allows us to use seismic stations as calibration events with known locations the dense and uniform spacing of the usarray transportable array stations makes them ideal to measure the spatial coherence of mislocation vectors across north america and hence to assess how close calibration events or stations need to be to target events to improve locations for a given region we use a grid search approach for the station relocations using both teleseismic earthquakes and simulated regional events our results show that the mislocation vectors are spatially coherent for scales up to 500 km in many regions but that in some places such as regions that can be associated with strong velocity anomalies in the upper mantle mislocation vectors exhibit large changes over short distances online material figures showing station location and dislocations and travel time residuals

microstructural analysis of wark lovering rims in the allende and axtell cv3 chondrites implications for high temperature nebular processes a coordinated electron backscatter diffraction ebsd and transmission electron microscope tem study was undertaken to obtain information on the origin of rims on refractory inclusions in the allende and axtell cv3 chondrites these measurements were supported by theoretical modeling using density functional theory crystal orientation analysis of wark lovering rims via ebsd revealed pyroxene grains with similar crystallographic orientations to one another in both inclusions an epitaxial relationship between grains within the diopside and anorthite rim layers was observed in allende tem examination of the rims of both samples also revealed oriented crystals at depth the microstructural data on the rims suggest that grain clusters grew in the form of three dimensional islands density functional theory calculations confirm that formation of oriented grain islands is the result of energy minimization at high temperature the results point toward condensation as the mode of origin for the rims studied here

building and testing an a priori geophysical model for western eurasia and north africa we construct and evaluate a new three dimensional model of crust and upper mantle structure in western eurasia and north africa wena extending to 700 km depth and having 1 parameterization the model is compiled in an a priori fashion entirely from existing geophysical literature specifically combining two regionalized crustal models with a high resolution global sediment model and a global upper mantle model the resulting wena1 0 model consists of 24 layers water three sediment layers upper middle and lower crust uppermost mantle and 16 additional upper mantle layers each of the layers is specified by its depth compressional and shear velocity density and attenuation quality factors q p and q s the model is tested by comparing the model predictions with geophysical observations including crustal thickness surface wave group and phase velocities upper mantle n velocities receiver functions p wave travel times waveform characteristics regional 1 d velocities and bouguer gravity we find generally good agreement between wena1 0 model predictions and empirical observations for a wide variety of independent data sets we believe this model is representative of our current knowledge of crust and upper mantle structure in the wena region and can successfully be used to model the propagation characteristics of regional seismic waveform data the wena1 0 model will continue to evolve as new data are incorporated into future validations and any new deficiencies in the model are identified eventually this a priori model will serve as the initial starting model for a multiple data set tomographic inversion for structure of the eurasian continent

oxygen isotopes in asteroidal materials measurement of the variation of the 17o 16o and 18o 16o ratios of extraterrestrial materials has proven to be a key tool in understanding the formation and evolution of the solar system this chapter attempts to collate the huge data set of oxygen isotopic measurements of asteroidal material as sampled by meteorites in order to understand some of the processes involved in the formation of these primitive bodies and how such events have affected the oxygen isotopic ratios ultimately offering a window back to the very origin of solar system and its primordialoxygen isotopic heterogeneity oxygen is generally a major element in the gas liquid and solid phases that have interacted throughout the evolution of the solar system its chemical properties ensuring that there is abundant opportunity for reactions and exchange the details of which can be recorded in the isotopic ratios of the products such processes can be crudely subdivided into the following six categories early solar nebular isotopic heterogeneity high temperature modifi cation of nebular components metamorphism and melting in asteroids aqueous alteration in asteroids mixing of components brecciation terrestrial weathering it is clear from the isotopic variation in the earliest formed nebular components such as refractory inclusions and chondrules that there was considerable oxygen isotopic heterogeneity in the early solar nebula spanning over 50 and perhaps much greater in both 17o and 18o the origin of this variation is discussed elsewhere in this volume however isotopic exchange between the 16o rich solids and 17o and 18o rich gas phase s resulted in a wide range of isotopic variation in these early formed components offering insight into the conditions of these processes and the evolution of the reservoirs with time and or space once accreted onto the early planetisemals much of the primitive nebular components experienced considerable modification the metamorphism and melting experienced by some of these bodies most probably the result of heating from the decay of short lived radionuclides e g 26al resulted in progressive homogenization within individual bodies of any original isotopic heterogeneity complete homogenization appears to have been achieved in the hed parent body indicating very high levels of melting and the development of a large magma ocean the carbonaceous and ordinary chondrite parent bodies experienced more modest heating sufficient to mobilize water ice that accreted along with the more refractory materials the subsequent reactions between the liquid and solid phases at low temperature imparted large isotopic fractionations which record some of the conditions of this alteration such as water rock ratio temperature and isotopic signature and thus potentially the origin of the water ice the evolution of the asteroidal bodies has been far from simple and an important use of oxygen isotope measurements has been in the identifi cation of the components present in some meteorites the result of breakup reassembly and mixing of different bodies during impact processing the final oxygen isotopic signatures imparted into meteorite samples are those associated with terrestrial weathering the isotopic compositions of the weathering products depend on location primarily latitude while the magnitude of the weathering is dependent on many factors with some meteorites e g highly reduced enstatite chondrites and the matrix rich co3s particularly susceptible to such effects

the mineral chemistry and origin of inclusion matrix and meteorite matrix in the allende cv3 chondrite the two textural varieties of olivine rich allende inclusions rimmed and unrimmed olivine aggregates consist primarily of a porous fine grained mafic constituent inclusion matrix that differs from the opaque meteorite matrix of cv3 chondrites by being relatively depleted in sulfides metal grains and perhaps carbonaceous material olivine is the most abundant mineral in allende inclusion matrix clinopyroxene nepheline sodalite and ti al pyroxene occur in lesser amounts olivine in unrimmed olivine aggregates type 1a inclusions is ferrous and has a narrow compositional range fo50 65 olivine in rimmed olivine aggregates type 1b inclusions is on average more magnesian with a wider compositional range fo53 96 olivine grains in the granular rims of type 1b inclusions are zoned with magnesian cores fo 80 and ferrous rinds fo 70 ferrous olivines fo 65 in both varieties of inclusions commonly contain significant amounts of al2o3 as much as 0 7 wt cao as much as 0 4 wt and tio2 as much as 0 2 wt refractory elements that probably occur in submicroscopic inclusions of ca al ti rich glass rather than in the olivine crystal structure defocussed beam analyses of allende matrix materials demonstrate that 1 inclusion matrix in type 1a inclusions is more enriched in olivine and feo than inclusion matrix in the cores of type 1b inclusions 2 opaque matrix materials are depleted in feldspathoids and enriched in sulfides and metal grains relative to inclusion matrix 3 the bulk compositions of type 1a and type 1b inclusions overlap and 4 excluding sulfides and metal the bulk compositions of allende matrix materials cluster in a complementary pattern around the bulk composition of c1 chondrites inclusion matrix and meteorite matrix in allende and other cv3 chondrites are probably relatively primitive nebular material but a careful evaluation of the equilibrium condensation model suggests that these matrix materials do not consist of crystalline phases that formed under equilibrium conditions in a relatively cool gas of solar composition allende inclusion matrix is interpreted as an aggregate of condensates that formed under relatively oxidizing non equilibrium conditions from supercooled supersaturated vapors produced during the vaporization of interstellar dust by aerodynamic drag heating in the solar nebula cv3 meteorite matrix contains in addition a proportion of interstellar material that was heated but not vaporized in the nebula granular olivine in rimmed olivine aggregates may have formed during the recrystallization and incipient melting of aggregates of inclusion matrix in the nebula the mineral chemistry of matrix olivine in allende seems to have been established by three different processes non equilibrium vapor solid condensation recrystallization and partial melting in the nebula and femg equilibration without textural homogenization in the meteorite parent body

the origin and nebular history of the metal phase of ordinary chondrites abstract we present new inaa results for bulk metal from h and ll chondrites both have characteristic elemental patterns similar to l chondrite metal in particular increasing abundances of w and ga from unequilibrated to equilibrated chondrites but a reverse variation of v and cr abundances these characteristics indicate that metal in ordinary chondrites formed by melting and reduction of highly oxidized material the similarities of melting features and the complementary nature of compositions between metal and chondrules suggest that these two components were derived from a common precursor similar to ci or cm material in redox state and compositionally related to the matrix of highly unequilibrated ordinary chondrites co ni abundance ratios are similarly low for bulk metal in the least metamorphosed ordinary chondrites of all three chemical groups this suggests that metal in ordinary chondrites initially had the same composition and formed under the same melting conditions the chondrites that accreted earliest have preserved their melting characteristics while those that accreted later reequilibrated with the ambient gas at different temperatures the differences in redox state between equilibrated and unequilibrated chondrites show that formation of chondritic metal and chondrules by melting occurred during the accretion of ordinary chondrite parent bodies the initial metal composition established during the melting stage 13 wt ni co ni 0 031 is inferred from the metal in highly unequilibrated chondrites the accretion temperatures of about 600 k for ordinary chondrites are calculated from the reequilibration reaction h chondrites were accreted at the highest temperature and are most reduced among the three ordinary chondrite groups ll chondrites were accreted at the lowest temperature and are most oxidized compositionally the metal component that would account for the fe si fractionation among h l and ll chondrites is different from the metal formed by melting indicating that the different fe s ratios of h l and ll chondrites were established before their accretion

matrix material in type 3 chondrites occurrence heterogeneity and relationship with chondrules abstract matrix material in type 3 chondrites forms rims on chondrules metal sulfide aggregates ca al rich inclusions and chondritic clasts it also forms lumps up to a millimeter in size which may contain coarser silicates chondrules of all types were found with internal matrix lumps that appear to have entered the chondrules before the latter had crystallized mean concentrations of mg na al and ca in matrix occurrences show up to fivefold variations in a single chondrite variations between mean matrix compositions of individual type 3 ordinary chondrites are almost as large and partly reflect systematic differences between h l and ll matrices such variations are probably a result of nebular separation of feldspathic material and ferromagnesian silicates compositions of chondrules and their matrix rims are normally unrelated although rim compositions are correlated with those of matrix lumps inside chondrules a single chondrule was found with a composition nearly identical to that of its internal matrix lump suggesting that some chondrules may have formed from matrix material matrix lumps are as heterogeneous as chondrules but mean chondrule and matrix compositions differ even allowing for possible loss of metallic fe ni during chondrule formation since bulk compositions of matrix lumps and rims have probably not changed significantly since their formation except for fe mg exchange our matrix samples cannot represent typical chondrule precursor materials

cenozoic intra plate volcanism related to extensional tectonics at calatrava central iberia the calatrava volcanic province is characterized by an intra plate alkaline undersaturated magmatic association of melilitites nephelinites alkali olivine basalts and leucitites that were extruded in the central iberian peninsula spain during late miocene quaternary time this volcanism can be related to the following two stage scenario 1 an initial mantle diapir stage during which magma generation would have occurred at the lithosphere asthenosphere boundary triggering minor accumulation processes at the crust mantle interface and consequent weakening extension of the upper crust and 2 a final indentation stage related to disruption effects caused by the tectonic welding of the prebetic arc onto the iberian foreland

trace element contents of chondrule rims and interchondrule matrix in ordinary chondrites abstract the abundances of forty elements have been measured in the rims and matrices of the unequilibrated ordinary chondrites semarkona bishunpur chainpur and krymka the rims appear to be mixtures of matrix like material and material that was volatilized during chondrule formation iron silicon manganese and copper all appear to have behaved as volatiles during chondrule formation and their enrichments are generally confined to the rims suggesting recondensation of these elements was rapid and localized this is supported by petrologic observations that show many chondrules were still partially molten or plastic when the rims accreted some rims also exhibit a decrease in both their feo content and the degree of mineral re equilibration away from the chondrule the alkali metals are enriched in both the rims and matrices the alkalis may have recondensed onto the matrix as well as the rims but their mobility is such that they have probably undergone extensive redistribution after accretion some na may even have been able to diffuse back into chondrules either during chondrule cooling or during metamorphism alteration most refractory lithophiles are depleted with respect to a1 in the rims and matrices in all four uocs these depletions are probably due to postaccretional redistribution of these elements into phosphates and other secondary minerals that form in and around metal sulfide grains the matrix is probably composed of chondrule fragments and processed nebular dust but the presence of carbonaceous presolar grains in the matrix indicates that there must be unprocessed presolar silicates present too on average the presolar silicates presumably have a ci like composition but a ci like signature is not seen in the matrix compositions simple estimates suggest that the abundances of carbonaceous presolar grains are consistent with there being at most 10 wt o presolar silicates present in uoc matrix which would be hard to detect in this study

seismic event location calibration using the eastern turkey broadband seismic network analysis of the agri dam explosion a 12 ton controlled source explosion took place in eastern turkey on 5 june 2001 and was recorded by 18 stations of the eastern turkey seismic experiment etse passcal broadband network this is a unique recording obtained for the first time in this region due to the blasting type and extremely high lg and sn attenuation in eastern turkey the blast is only observed out to a distance of about 300 km we have used travel time data from this explosion to obtain average crustal structure and site correction terms for the stations the explosion was located using two new regional velocity models and the iasp91 velocity model to test the location capabilities of the etse network we found that for surface focus events the etse network is able to locate events to within 1 2 km of the true epicenter

the transition of spatter to lava like body in lava fountain deposits features and examples from the cabezo segura volcano calatrava spain abstract the cabezo segura ii volcanic cone calatrava volcanic province iberian microplate comprises proximal wall deposits with a well defined crater wall unconformity and crater fill deposits the complex volcanic succession that shows evidence of several eruptive episodes was built by magmatic and hydrovolcanic explosions of different styles strombolian hawaiian sub plinian and phreato strombolian generated from a multiple feeder ultrabasic dyke intra crater rock units at the volcano summit include spatter deposits together with up to 10 m thick and more than 200 m long lava like bodies geological logs for the main lava like bodies define a characteristic facies model that involves a central lava like mass which grades vertically into a transition zone of apparently coherent spatter then dense spatter and finally into vuggy spatter deposits these units are inferred to have formed during pulsating lava fountain type explosive eruptions the depicted facies distribution being the result of progressive increase in welding grade and densification of the spatter in response to variations in the accumulation rate their field features may be used as a guide for the precise identification of vent sites in deposits of hawaiian eruptions also structures like those here recognised that might have survived in lava like flows could be of help to identify when lava producing eruptions represented an explosive hawaiian event lava fountains and not a purely effusive event

k ar ages of pleistocene lava dams in the grand canyon in arizona at least 13 times during the pleistocene epoch lava flowed into the inner gorge of the grand canyon and formed lava dams as high as 600 m that temporarily blocked the flow of the colorado river k ar ages on these lava dams indicate that the seven youngest formed within a short period of time between about 0 6 and 0 4 mega annum ma the physiography of the lava dam remnants within the canyon shows that each dam was destroyed by erosion the colorado river rapidly reaching its pre existing grade level before the next dam was emplaced by new eruptions the total time for emplacement and destruction for an individual lava dam was probably as little as 0 01 0 02 million years the k ar ages of the two oldest dams the lava butte dam 0 577 0 054 ma and the prospect dam 0 684 0 051 ma are somewhat younger than the physiography of their remnants suggest

primitive ultrafine matrix in ordinary chondrites abstract ultrafine matrix material has been concentrated by sieving and filtering disaggregated samples of six ordinary chondrites of different classes this component s holy smoke hs is enriched in both volatile e g na k zn sb and pb as well as refractory elements e g w and ree however the element ratios vary greatly among the different chondrites sem studies show that hs contains fragile crystals differing in composition and apparently in gross disequilibrium not only among themselves but also with the major mineral phases and consequently thermodynamic equilibration did not occur thus hs must have originated from impacting bodies and or was inherent in the primitive regolith subsequent impact brecciation and reheating appears to have altered to varying degrees the original composition of this ultrafine matrix material recent cosmic dust studies may indicate that hs still exists in the solar system survival of such delicate material must be considered in all theories for the origin of chondrites

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

re examining the role of chondrules in producing the elemental fractionations in chondrites the matrices of all primitive chondrites contain presolar materials circumstellar grains and interstellar organics in roughly ci abundances suggesting that all chondrites accreted matrix that is dominated by a ci like component the matrix normalized abundances of the more volatile elements condensation temperatures 750800 k in carbonaceous and ordinary chondrites are also at or slightly above ci levels the modest excesses may be due to low levels of these elements in chondrules and associated metal subtraction of a ci like matrix component from a bulk ordinary chondrite composition closely matches the average composition of chondrules determined by instrumental neutron activation analysis inaa if some fe metal is added to the chondrule composition measured matrix compositions are not ci like sampling bias and secondary redistribution of elements may have played a role but the best explanation is that 1030 of refractory rich volatile depleted material was added to matrix if most of the more volatile elements are in a ci dominated matrix the major and volatile element fractionations must be largely carried by chondrules there is both direct and indirect evidence for evaporation during chondrule formation type iia and type b chondrules could have formed from a mixture of ci material and material evaporated from type ia chondrules the mg si fe fractionations in the ordinary chondrites can be reproduced with the loss of type ia chondrule material and associated metal the loss of evaporated material from the chondrules could explain the volatile element fractionations mechanisms for how these fractionations occurred are necessarily speculative but two possibilities are briefly explored

diffusion in silicate minerals and glasses a data digest and guide to the literature the rates of diffusion of cations oxygen and hydrogen in silicates are of fundamental importance to a wide range of petrological and geochronological problems in order that the earth scientist may readily apply the available experimentally determined diffusion rates to such problems a compilation of data for diffusion in silicate minerals and glasses is presented along with a working guide for its use published data and experimental conditions are listed in tables and these are preceded by an outline of diffusion mechanisms terminology equations and units diffusion regimes factors controlling diffusion rates measurement techniques and diffusional behaviour

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

nature and origin of matrix in the unique type 3 chondrite kakangari the mineralogy and textural characteristics of fine grained matrix 1 m in the unique type 3 chondrite kakangari have been investigated by high resolution and analytical electron microscopy the matrix contains a diverse primary mineralogy dominated by enstatite and olivine with lesser amounts of albite anorthite cr spinel troilite and fe ni metal texturally the matrix is characterized by irregular clusters or aggregates of crystals which constitute distinct structural units within the matrix 2 8 m in diameter and frequently have distinct mineralogies enstatite in these clusters is an intergrowth of monoclinic and orthorhombic polymorphs with a microstructure indicative of an origin by high temperature inversion from protopyroxene during rapid cooling corroded inclusions of olivine frequently occur within enstatite suggesting that enstatite formed by reaction of olivine with a silica polymorph at high temperature the matrix mineralogy of kakangari formed by high temperature annealing and reaction of fine grained dust which probably consisted of amorphous or partially crystalline presolar or solar nebula condensates the constituents of kakangari matrix cannot therefore be considered as pristine unprocessed solar system material annealing probably occurred in a thermal event similar to that which formed the chondrules but the microstructures and textures of the matrix components suggest that melting did not occur chondrules in kakangari were probably formed from identical precursors to the matrix but reached temperatures sufficiently high to produce melting despite this high temperature processing the mineralogical clusters in the matrix preserve mineralogical and hence chemical heterogeneities in the precursor materials similar to those observed in interplanetary dust particles

progressive aqueous alteration of cm carbonaceous chondrites abstract cm chondrites are aqueously altered rocks that contain 9 wt h 2 o i e indigenous water bound in phyllosilicates also present are clumps of serpentine tochilinite intergrowths previously called poorly characterized phases or pcp pentlandite and ni bearing pyrrhotite we studied 11 cm chondrites that span the known range from least altered to most altered we used various petrologic properties many previously identified that provide information regarding the degree of aqueous alteration there are no known unaltered or slightly altered cm chondrites e g rocks containing numerous chondrules with primary igneous glass some cm properties result from processes associated with early and intermediate stages of the alteration sequence i e hydration of matrix alteration of chondrule glass and production of large pcp clumps other petrologic properties reflect processes active throughout the alteration sequence these include oxidation of metallic fe ni alteration of chondrule phenocrysts changes in pcp composition reflecting an increase in the phyllosilicate sulfide ratio and changes in carbonate mineralogy reflecting the development of dolomite and complex carbonates at the expense of ca carbonate on the basis of these parameters we propose a numerical alteration sequence for cm chondrites because there are no known cm samples that display only incipient alteration the least altered sample was arbitrarily assigned to subtype 2 6 the most altered cm chondrites currently classified cm1 are assigned to subtype 2 0 these highly altered rocks have essentially no mafic silicates they contain chondrule pseudomorphs composed mainly of phyllosilicate however their bulk compositions are cm like and they are closer in texture to other c2 chondrites than to ci1 chondrites which lack chondrule pseudomorphs using several diagnostic criteria we assigned petrologic subtypes 0 1 to every cm chondrite in our study que 97990 cm2 6 murchison cm2 5 kivesvaara cm2 5 murray cm2 4 2 5 y 791198 cm2 4 que 99355 cm2 3 nogoya cm2 2 cold bokkeveld cm2 2 que 93005 cm2 1 lap 02277 cm2 0 met 01070 cm2 0 the proposed cm numerical alteration sequence improves upon the existing scheme of browning et al 1996 in that it does not require a complicated algorithm applied to electron microprobe data to determine the average matrix phyllosilicate composition the new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values new neutron activation analyses of que 97990 que 93005 met 01070 murchison and crescent together with literature data confirm the compositional uniformity of the cm group different degrees of alteration among cm chondrites do not lead to resolvable bulk compositional differences this suggests that the textural differences among individual cm chondrites reflect progressive alteration of similar hypothetical cm3 0 starting materials in different regions of the same parent body with minimal aqueous transport of materials over appreciable e g meters distances

upper mantle models and the thickness of the continental lithosphere summary analysis of the early rise traveltimes in the united states shows that on several of the profiles there are features which can be interpreted as indicating a low velocity zone above 200km i e that the continental lithosphere thickness is less than 200 km the explosion data from the nevada test site gnome and early rise are all consistent with lehmann s suggestion that there is a discontinuity at a depth of about 200 km comparison of the observed data between 15 and 23 with model calculations shows that the major differences between the western and centraleastern united states upper mantles occur above 200 km it appears that the only reasonable explanation for the 200 km discontinuity is that it represents the termination of a zone of partial melting

oxygen isotope studies of ordinary chondrites several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components chondrules fragments clasts and matrix the whole rock isotopic compositions reflect the iron group of the meteorite h l or ll isotopic uniformity of h3 to h6 and l3 to l6 are consistent with closed system metamorphism within each parent body ll3 chondrites differ slightly from ll4 to ll6 implying a small degree of opensystem aqueous alteration and carbon reduction on the scale of individual chondrules the meteorites are isotopically heterogeneous allowing recognition of the solar nebular processes of chondrule formation chondrules for all classes of ordinary chondrites are derived from a common population which was separate from the population of chondrules in carbonaceous or enstatite chondrites chondrules define an isotopic mixing line dominated by exchange between 16o rich and 16o poor reservoirs the oxygen isotopic compositions of chondrites serve as fingerprints for identification of genetic association with other meteorite types achondrites and iron and for recognition of source materials in meteoritic breccias

trace elements in rims and interiors of chainpur chondrules trace elements were measured in the rims and interiors of nine chondrules separated from the chainpur ll 3 chondrite whole rock samples of chainpur and samples of separated rims were also measured chondrule rims are moderately enriched in siderophile and volatile elements relative to the chondrule interiors the enriched volatile elements include the lithophilic volatile element zn the moderate enrichment of volatiles in chondrule rims and the lack of severe depletion in chondrules can account for the complete volatile inventory in chainpur these results support a three component model of chondrite formation in which metal plus sulfide chondrules plus rims and matrix silicates are mixed to form chondrites

cinder cone clustering in the transmexican volcanic belt implications for structural and petrologic models cinder cone distributions have most often been characterized using univariate statistics here a new technique to volcano distribution studies cluster analysis is applied to cinder cone distribution in the central transmexican volcanic belt tmvb a total of 1016 cinder cones are identified over an area of approximately 60 000 km2 application of cluster analysis reveals structure in cinder cone distribution using a search radius parameter of 16 km 75 of the cinder cones within the central tmvb are found within eight clusters of 45 159 cones each these clusters are each 2000 to 5000 km2 in area only 22 cones are found within clusters of three or fewer cinder cones indicating that clustering is a pervasive phenomenon some petrologic variation is evident among clusters low mg alkaline cinder cones are found within a single cluster 360 400 km from the trench application of alignment analysis techniques including the two point azimuth method the hough transform and two dimensional fourier analysis demonstrates that cinder cone alignments have common orientations on a regional scale within three clusters all located in the southernmost part of the michoacan guanajuato volcanic field in the western portion of the study area these alignments consist of tens of cinder cones are 20 50 km long and are all oriented with azimuths of 020 040 parallel to the direction of plate convergence high mg lavas which last fractionated at pressures in excess of 8 kbar are only found associated with these alignments indicating that magma transport is significantly enhanced in these areas although local alignments of three to six cinder cones occur within mapped fault zones that transect the area regional cinder cone alignment patterns and the distribution of clusters themselves do not appear to be affected by the presence of these fault zones the cluster analysis the alignment analysis and some petrologic data support the hypothesis that the tmvb is segmented near 101 w

upper mantle shear structure beneath the colorado rocky mountains a tomographic inversion of teleseismic shear wave delays has been performed using data collected in the 1992 program for array seismic studies of the continental lithosphere rocky mountain front experiment the shear wave residuals used as data were corrected for known crustal sediment and topographic differences and thus were sensitive to mantle shear velocity variations beneath the colorado array large differences in shear wave travel time are observed across colorado and into western kansas with a maximum difference of near 5 sec between the central rockies in colorado and a station in western kansas the shear wave residuals were inverted for shear wave velocity variations in the upper 350 km of the mantle beneath colorado and kansas large differences in mantle shear velocity are found between the rockies and the kansas great plains the average shear velocity in the upper 200 km is about 9 greater beneath kansas than beneath the rockies at greater depths lateral variations are far smaller and not as well correlated with surface tectonics in a qualitative sense there appear to be three mantle structures present beneath the study area beneath the rockies the upper mantle is extremely slow both to the west and east of the rockies we find intermediate mantle shear velocity there is then an abrupt increase in mantle shear velocity near the colorado kansas border we interpret the abrupt increase in mantle shear velocity near the colorado kansas border to mark the boundary of cratonic lithosphere the slow velocity zone beneath the rockies appears to be upwelled asthenosphere as is seen beneath the rio grande rift to the south to match the seismic contrast between the mantle beneath kansas and the colorado rockies requires a temperature contrast of at least 350 c as well as partial melt beneath the rockies the hot mantle beneath the rockies implies that the mantle density is low and the high topography of the rockies is at least partially due to buoyant mantle

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

volcanism sedimentation interaction in the campo de calatrava volcanic field spain a magnetostratigraphic and geochronological study this work focuses on the influence of cenozoic volcanism of the campo de calatrava volcanic field on the sedimentation of two small continental basins in spain argamasilla and calzada moral basins the volcanism in this area was mainly monogenetic according to the small volume volcanic edifices of scoria cones that were generated and the occurrence of tuff rings and maars a sedimentological analysis of the volcaniclastic deposits led to the identification of facies close to the vents low density dilute pyroclastic surges secondary volcanic deposits and typical maar deposits whole rock k ar dating together with palaeomagnetic constraints yielded an age of 3 11 3 22 ma for the onset of maar formation the deposition finished in the late gauss early matuyana using both techniques and previous paleontological data allowed it to be inferred that the maar formation and the re sedimentation stage that occurred in argamasilla and calzada moral basins were roughly coeval the occurrence of syn eruption volcaniclastic deposits with small thicknesses that were separated by longer inter eruption periods where fluvial and lacustrine sedimentation was prevalent together with the presence of small volume volcanic edifices indicated that there were short periods of volcanic activity in this area the volcanic activity was strongly controlled by previous basement faults that favoured magma feeding and the faults also controlled the location of volcanoes themselves the occurrence of the volcanoes in the continental basins led to the creation of shallow lakes that were related to the maar formation and the modification of sedimentological intra basinal features specifically valley slope and sediment load

testing the chondrule rich accretion model for planetary embryos using calcium isotopes abstract understanding the composition of raw materials that formed the earth is a crucial step towards understanding the formation of terrestrial planets and their bulk composition calcium is the fifth most abundant element in terrestrial planets and therefore is a key element with which to trace planetary composition however in order to use ca isotopes as a tracer of earth s accretion history it is first necessary to understand the isotopic behavior of ca during the earliest stages of planetary formation chondrites are some of the oldest materials of the solar system and the study of their isotopic composition enables understanding of how and in what conditions the solar system formed here we present ca isotope data for a suite of bulk chondrites as well as allende cv chondrules we show that most groups of carbonaceous chondrites cv ci cr and cm are significantly enriched in the lighter ca isotopes 44 40 ca 0 1 to 0 93 compared with bulk silicate earth 44 40 ca 1 05 0 04 huang et al 2010 or mars while enstatite chondrites are indistinguishable from earth in ca isotope composition 44 40 ca 0 91 to 1 06 chondrules from allende are enriched in the heavier isotopes of ca compared to the bulk and the matrix of the meteorite 44 40 ca 1 00 to 1 21 this implies that earth and mars have ca isotope compositions that are distinct from most carbonaceous chondrites but that may be like chondrules this ca isotopic similarity between earth mars and chondrules is permissive of recent dynamical models of planetary formation that propose a chondrule rich accretion model for planetary embryos

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

matrix mineralogy of the orgueil ci carbonaceous chondrite a petrographic and transmission electron microscopic study of the orgueil ci carbonaceous chondrite shows that the matrix consists mainly of fe bearing mg rich serpentine and smectite saponite as well as a poorly crystallized fe rich material that contains minor variable s and ni the fe rich material is probably ferrihydrite a ferric hydroxide the ferrihydrite occurs in small particles 80 a in diameter and the s and ni are probably adsorbed on its surfaces the serpentine and saponite occur in poorly crystallized fine crystallites fine phyllosilicates that are intimately associated with the ferrihydrite coarsely crystallized phyllosilicates coarse phyllosilicates occur in clusters relatively free of ferrihydrite the ferrihydrite is a major matrix constitutent and probably accounts for most of the fe3 as well as the superparamagnetic fraction in the orgueil matrix the textures suggest that the fine phyllosilicates resulted from alteration of the coarse phyllosilicates the alteration probably involved a substantial amount of water and coincided with the period of sulfate vein formation during the aqueous alteration magnetite grains disaggregated from framboids and fe ni sulfides were replaced by ferrihydrite simultaneously aqueous solutions reacted with the coarse phyllosilicates and precipitated ferrihydrite producing intimate pervasive mixtures with the fine phyllosilicates the matrix mineralogy of the orgueil chondrite suggests that orgueil experienced considerably different alteration conditions from the cm chondrites the mineralogical and petrological differences between ci and cm chondrites can not simply be explained as the result of different degrees of aqueous alteration

locating and modeling regional earthquakes with two stations 1 we developed a new technique caploc to retrieve full source parameters of small seismic events from regional seismograms which include origin time epicenter location depth focal mechanism and moment magnitude despite rather complicated propagation effects at short periods a simple localized one dimensional model can well explain signals of periods 3 10 s if we break the three component records into different segments and allow differential time shifts among them these differential time shifts once established from a calibration process or a well determined tomographic map can be used together with p wave travel times to refine an event s location in this study we tested whether our new method could produce satisfactory results with as few as two stations so that we can improve source estimates of poorly monitored events with sparse waveform data we conducted the test on 28 events in the tibetan plateau the focal mechanisms and locations determined from only two stations agree well with those determined from a whole passcal array in particular our new method produces better locations than international seismological centre with the average mislocation error reduced from 16 to 5 km we also tested whether an event s depth and mechanism can be determined separately from its epicenter relocation in a two step approach we find that the two step approach does not always give the correct solution but the reliability of a solution can be evaluated using a reduced chi square value

the p wave upper mantle structure beneath an active spreading centre the gulf of california summary detailed analysis of short period travel time dt d and wave form data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km more than 1400 digital seismograms from earthquakes in mexico and central america recorded at scarlet yield 1753 travel times and 58 direct measurements of dt d as well as high quality stable waveforms the 29 events combine to form a continuous record section from 9 to 40 with an average station spacing of less than 5 km first the travel times are inverted using the tau method of bessonova et al the resultant model is adjusted to agree with the experimental p values further constraints arise from the observed relative amplitudes of mantle phases which are modelled by trial and error using wkbj synthetic seismograms chapman wiggins model gca which is appropriate for western mexico north of 20 latitude is similar to existing upper mantle models for shield tectonic continental and arc trench regimes below 400 km but differs significantly in the upper 350 km gca velocities are very low in this depth range the model catches up with the others with a very large velocity gradient from 225 to 390 km this well resolved feature is consistent with the shear wave model tna for western north america of grand helmberger the abundant data from 20 to 30 control the detailed shape of the 660 km discontinuity very large velocity gradients lie both above 620 660 km and below 661 680km a 2 8 per cent velocity change

titanium isotopic anomalies in chondrules from carbonaceous chondrites abstract isotopic analyses of ti from chondrules of carbonaceous chondrites reveal that ti anomalies are present anomalies are detected only at 50ti for a suite of eight allende chondrules four give well resolved anomalies which range from a 50ti deficit of two units to a 50ti excess of nine units no clear link is evident between the structure or composition of the chondrules and the ti anomalies however the chondrule with by far the largest ti isotopic anomaly is also al rich yet the absence of a strict correlation between the ca al ti contents and the ti anomalies together with the similarity of the 50ti excess for the one chondrule to that of most ca al rich inclusions cais indicate that the relation between degree of refractory enrichment and the magnitude of ti isotopic anomalies is not a simple one single chondrules from murchison kaidun and kakangari all fail to exhibit a well resolved anomaly although in the latter two the single analysis of each precludes resolving anomalies of less than three units these observations support the view that the ti isotopic diversity in chondrules is an inherited feature from their precursor assemblages of dust models which envision similar precursors for both chondrules and matrix are consistent with the ti isotopic data but at least two distinct solid matter reservoirs are required for the allende chondrules alone which underscores the diversity in the nebular dust these ti anomalies also caution that more than one dust isotopic component may be necessary to account fully for the oxygen isotopic variations in chondrules the ti anomalies in chondrules argue strongly against models which ascribe the ti anomalies in cais to unique features of their evolution instead heterogeneities were more common in the nebular dust

geological mapping of volcanic terrains discussion on concepts facies models scales and resolutions from new zealand perspective abstract geological mapping in volcanic terrains is a challenging task as there needs to be input from various geologists groups and only limited often ambiguous guidelines exist volcanoes and volcanic successions are in many ways viewed and treated differently than normal sedimentary successions volcanic systems are very much a part of the normal sedimentary environment and as such need to integrated into the stratigraphic framework of the enclosing deposits most volcanoes supply large volumes of material pyroclasts into the sedimentary system the type and style of eruption determines the time frame of the process while the type of volcano defines the interaction between volcano and background sedimentation e g monogenetic versus polygenetic volcanic systems a sound lithostratigraphic framework for mapping geological units in volcanic terrains should also adopt the latest developments in volcanology and understanding of volcanic systems the lithostratigraphic classification needs to define the mapping unit and apply it to the 1 proximal to distal volcanic facies 2 eruption styles and their temporal changes and 3 mode of pyroclast transportation i e fallout versus pyroclastic density current differentiation of syn and post eruption re sedimentation during either within or between eruptive phases will determine the most useful stratigraphic nomenclature system to apply to the volcanic units the approach to geological mapping in ancient and modern volcanic terrains can be different but the same basic stratigraphic principles and classification apply the purpose of the geological mapping project whether it be in ancient or modern volcanic systems will define the style and scale of mapping the type of output depends upon the objectives and available resources including the volcanological experience of the mapping team here we provide some insight from a new zealand perspective to geological mapping on active volcanic terrains in a convergent plate margin

fluvial response to holocene volcanic damming and breaching in the gediz and geren rivers western turkey this study discusses the complex late holocene evolution of the gediz river north of kula western turkey when a basaltic lava flow dammed and filled this river valley age control was obtained using established and novel feldspar luminescence techniques on fluvial sands below and on top of the flow this dating constrained the age of the lava flow to 3 0 2 6 ka two damming locations caused by the lava flow have been investigated the upstream dam caused lake formation and siltation of the upstream gediz the downstream dam blocked both the gediz and a tributary river the geren the associated lake was not silted up because the upstream dam already trapped all the gediz sediments backfillings of the downstream lake are found 1 5 km upstream into the geren valley the downstream dam breached first after which the upstream dam breached creating an outburst flood that imbricated boulders of 10 m3 size and created an epigenetic gorge the gediz has lowered its floodplain level at least 15 m since the time of damming triggering landslides some of which are active until present the lower reach of the geren has experienced fast base level lowering and changed regime from meandering to a straight channel complex response to base level change is still ongoing in the geren and gediz catchments these findings are summarized in a diagram conceptualizing lava damming and breaching events this study demonstrates that one lava flow filling a valley floor can block a river at several locations leading to different but interrelated fluvial responses of the same river system to the same lava flow

geomorphological evolution and chronology of the eruptive activity of the columba and cuevas volcanoes campo de calatrava volcanic field ciudad real central spain abstract in this study we analyze the geomorphological evolution and chronology of the eruptive phases of the columba and cuevas volcanoes campo de calatrava volcanic field central spain these are two cinder cones located at the margins of the jabalon river valley between the localities of granatula de calatrava and aldea del rey ciudad real in order to generate geomorphological map we conducted fieldwork and photointerpretation of aerial images in addition to morphometric and volcanostratigraphic analyses aimed at correlating the volcanic deposits and fluvial terraces of the jabalon river finally we applied osl optically stimulated luminescence dating to obtain the age of fluvial deposits affected by both volcanoes plus radiocarbon dating to the organic matter of a paleosoil located between the columba volcano deposits the results provide a maximum age of 75 16 4 9 ka for the formation of the cuevas volcano moreover the columba volcano began its activity with a strombolian phase around 33 9 2 36 ka bp followed by a long period of inactivity between 24 9 and 23 2 ka and 14 13 5 ka bp in which the aforementioned paleosoil formed subsequently the eruptive activity resumed with a phreatomagmatic phase followed by another strombolian phase in which a lava flow was emplaced crossing and damming the jabalon river thus forcing the deposition of a 9 m thick fluvial terrace above it at about 6 27 4 28 ka the columba volcano is a good example of polycyclic eruptive behavior in a monogenetic volcanic field whose last eruption occurred between 14 and 6 2 ka ago the interaction between volcanic and fluvial processes was responsible for the morphological evolution of the area the study of which has been crucial to determine the evolution of the eruptive activity its morphological results and the relative chronologies

european cenozoic rift system abstract the european cenozoic rift system extends from the coast of the north sea to the mediterranean over a distance of some 1100 km it finds its southern prolongation in the valencia trough and a plio pleistocene volcanic chain crossing the atlas ranges development of this mega rift was paralleled by orogenic activity in the alps and pyrenees major rift domes accompanied by subsidence reversal of their axial grabens developed 20 40 ma after beginning of rifting uplift of the rhenish shield is related to progressive thermal lithospheric thinning the vosges black forest and the massif central domes are probably underlain by asthenoliths emplaced at the crust mantle boundary evolution of this rift system is thought to be governed by the interaction of the eurasian and african plates and by early phases of a plate boundary reorganization that may lead to the break up of the present continent assembly

chemical isotopic and mineralogical evidence for the origin of matrix in ordinary chondrites abstract we report the first combined chemical isotopic and mineralogical study of fine grained opaque matrix material from a type 3 ordinary chondrite allan hills a77299 h3 7 electron microprobe and instrumental neutron activation analysis of a large matrix lump show that it has a major element composition typical of matrix material in type 3 chondrites unlike chondrules it shows no siderophile element depletions and is remarkably unfractionated relative to ci chondrites suggesting that it is primitive solar system material the matrix lump has an unique oxygen isotopic composition which lies below the terrestrial fractionation line and differs markedly from the composition of fine grained matrix lumps and chondrule rims from semarkona grossman et al 1987 transmission electron microscope tem studies of microtomed samples of the fine grained fraction m of the matrix lump show that it consists of rare angular clastic grains 1 m of pyroxene and olivine embedded within a groundmass of rounded fine grained m olivines the mineralogy and textures of the matrix lump are typical of other occurrences of fine grained matrix studied by tem in other type 3 ordinary chondrites we conclude that the matrix lump in alha 77299 consists largely of material that formed by annealing of amorphous presolar dust or nebular condensates and could not have been derived from chondrules by any reasonable mechanism however the observed compositional differences between the matrix lump and chondrules in ordinary chondrites are consistent with the idea that some chondrules formed by melting of matrix like material accompanied by loss of siderophile and volatile elements

absolute location of 2019 ridgecrest seismicity reveals a shallow mw 7 1 hypocenter migrating and pulsing mw 7 1 foreshocks and duplex mw 6 4 ruptures

chondrules and other components in c o and e chondrites similarities in their properties and origins we describe three types of chondrules that are common to h3 ll3 cm2 co3 and cv3 chondrites low and high feo porphyritic olivine chondrules contain olivine with fa0 3 8 and fa5 50 respectively and can easily be distinguished petrographically poikilitic pyroxene chondrules have 1 20 vol olivine fa0 2 8 enclosed by low ca pyroxene fs0 5 7 and also occur in e chondrites these three types formed in separate nebular regions which had dimensions and spacings such that a few percent of the chondrules that collided to form compound chondrules were of different types sorting of chondrule precursor material and mixing of chondrule types probably account for most variations in bulk and mineral chemistry among chondrite groups metallic fe ni grains containing 0 1 1 cr si and p are present in low feo olivine chondrules from all type 2 and least metamorphosed type 3 chondrites metal compositions reflect reduction during chondrule formation in the nebula not nebular condensation opaque matrices in type 3 ordinary and carbonaceous chondrites are somewhat similar in composition and mineralogy and probably have related origins we conclude that chondrules in all known chondrite groups share similar nebular origins

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

matrices of type 3 ordinary chondrites primitive nebular records petrologic studies were made on the fine grained matrices of type 3 ordinary chondrites of the lowest petrologic subtype the matrix minerals in order of abundance are olivine fo99 to fo9 enstatite or bronzite augite or subcalcic augite albite fe ni metal troilite magnetite spinel mgal2o4 chromite and calcite fe and mg rich fluffy particles and albite like particles are also major constituents the chemical compositions of olivine and pyroxenes vary within and among the chondrites and are in gross disequilibrium showing that the matrix materials were hardly heated after their formation textural relationships indicate that magnesian olivine was formed after ca pyroxene followed by intermediate to iron rich olivine intermediate olivine was formed from enstatite and metallic iron under relatively oxidizing conditions the observations indicate that matrices of chondrites are neither the fragments of chondrules nor the precursors of chondrules they were mostly the products of condensation and reaction among solids and or between solids and the ambient gas mostly at low temperatures and thus they contain records of primitive processes in the nebula in order to explain the presence of olivines more iron rich than fo50 the presence of free sio2 or a high activity of sio2 in the gas is necessary which was not shown in previous thermochemical calculations mineral assemblages of matrix minerals of chondrites of different chemical groups differ systematically according to oxidation state of the parental meteorites indicating that they were formed at different oxygen fugacities the rims of chondrules and surrounding matrix materials must have accreted onto chondrules during turbulent movements of the nebula

upper mantle s velocity structure of north america we have inverted fundamental and higher mode rayleigh waveforms from 685 vertical component broadband seismograms with wave paths over north america to obtain an image of the upper mantle s velocity structure down to 660 km among the well resolved features of the new model are 1 a high velocity root beneath the north american craton which extends no deeper than 250 km except near the archean core of the craton where depths of 350 km are reached 2 a weak band of low velocity along the eastern margin of the north american craton which reaches into the transition zone 3 a low velocity slab window beneath the western united states down to a depth of 300 km 4 areas of low uppermost mantle velocity beneath the cascade volcanoes the yellowstone hotspot track the colorado plateau the sierra madre occidental and the grabens bordering the jalisco block and 5 a pronounced band of high velocities in the transition zone coinciding with the expected location of the subducted trailing fragments of the farallon plate we introduce several improvements to the method of partitioned waveform inversion which was used to compute the new model rather than to correct for an estimated depth to the mohorovicic discontinuity we leave the crustal thickness as a free though yet poorly resolved parameter in the inversion we also improve the windowing and filtering operator used to select uncontaminated waveforms

fayalitic olivine in matrix of the krymka ll3 1 chondrite vapor solid growth in the solar nebula fayalitic olivine fa54 94 is a ubiquitous component in the matrix of krymka ll3 1 as well as in other highly unequilibrated chondrites ordinary and carbonaceous in krymka the fayalitic olivine has an unusual anisotropic platy morphology that occurs in at least five types of textural settings that can be characterized as 1 isolated platelets 2 clusters of platelets 3 euhedral to subhedral crystals 4 overgrowths of platelets on forsteritic olivine and 5 fluffy porous aggregates from transmission electron microscope tem investigation the direction of elongation of the platy olivine overgrowths on forsteritic olivine substrates is along the c axis and in most cases it corresponds with the c axis of the substrate olivine which suggests that the fayalitic olivine grew in this unusual morphology and is not a replacement product of preexisting material the fayalitic olivine in the matrix of krymka is compositionally similar to olivine with platy morphology in the matrix of some cv3 chondrites and both have similar fe mn ratios but important morphological differences indicate that their relationship needs to be explored further textural and compositional data indicate that the fayalitic olivine in the matrix of krymka as well as in some other unequilibrated ordinary chondrites formed prior to final lithification of the meteorite and probably prior to parent body accretion we find that formation of the fayalitic olivine by vapor solid growth provides the best explanation for our observations and data and is the only feasible mechanism for the formation of fayalitic olivine in the matrix of krymka we propose that the fayalitic olivine formed by vaporization and recondensation of olivine rich dust during a period of enhanced dust gas ratio in the nebula

geology and eruptive history of unzen volcano shimabara peninsula kyushu sw japan abstract during the past 500 thousand years unzen volcano an active composite volcano in the southwest japan arc has erupted lavas and pyroclastic materials of andesite to dacite composition and has developed a volcanotectonic graben the volcano can be divided into the older and the younger unzen volcanoes the exposed rocks of the older unzen volcano are composed of thick lava flows and pyroclastic deposits dated around 200 300 ka drill cores recovered from the basal part of the older unzen volcano are dated at 400 500 ka the volcanic rocks of the older unzen exceed 120 km3 in volume the younger unzen volcano is composed of lava domes and pyroclastic deposits mostly younger than 100 ka this younger volcanic edifice comprises nodake myokendake fugendake and mayuyama volcanoes nodake myokendake and fugendake volcanoes are 100 70 ka 30 20 ka and

the influence of magma plumbing complexity on monogenetic eruptions jeju island korea terra nova 23 70 75 2011 abstract continuous pyroclastic successions from monogenetic volcanoes in the jeju island volcanic field korea were targeted for detailed geochemical investigations of juvenile ejecta to show that multiple distinct magma pulses may be erupted during a single monogenetic eruption deeply derived and possibly multiply sourced evolving magma pulses may erupt sequentially from the same vent and form generally uninterrupted depositional sequences with continuous chemical trends alternatively pulses can rise independently resulting in breccia horizons and truncation surfaces in depositional sequences and in stepped and mixed chemical trends we infer that uninterrupted eruptions result from clear plumbing systems in which a single large dyke system feeds an eruption and where differently sourced magmas are erupted independently congested plumbing systems consisting of dyke complexes give rise to vent shifts asymmetrical eruptive centres and composite depositional sequences integration of chemical variation and eruptive dynamics provides a powerful means of understanding monogenetic volcanoes

phase equilibrium constraints on angrite petrogenesis parameterizations of liquidus boundaries and solid solution in the cmas fe system shi 1992 have been employed to depict the liquidus equilibria relevant to the petrogenesis of angrites angrites are basaltic achondrites characterized by highly aluminous augite fassaite intermediate mg fe olivine and late stage cafe olivine kirschsteinite two important features of the equilibria on the olivine liquidus surface relevant to angrite petrogenesis are 1 the presence of a thermal divide on the ol aug plag liq boundary curve which separates the compositions of source materials that produce low silica angritic melts that crystallize highly aluminous augite from those that produce higher silica melts with tholeiitic to eucritic crystallization patterns and 2 the change in the pseudo invariant point on the low silica side of the thermal divide from a plagioclase peritectic involving spinel ol aug plag sp liq at high to intermediate mg mg mg fe to two pseudo eutectics involving kirschsteinite ol aug plag kir liq and ol kir plag sp liq at low mg the fassaitic aluminous augite pyroxene composition in angra dos reis ador the presence of minor green spinel and the absence of primary kirschsteinite prinz et al 1977 indicate that crystallization of the ador parental liquid was governed by the intermediate mg set of equilibria such that following crystallization of ol aug plag the plagioclase reacted completely at the plagioclase peritectic with the interstitial liquid which subsequently crystallized beyond the plagioclase peritectic onto the ol aug sp liquidus boundary curve the ador bulk composition is consistent with trapping 10 of the parental liquid in a cumulate with cotectic proportions of fassaite and olivine lewis cliff lew 86010 crystallized from a liquid with mg similar to that of ador but on the ol plag cotectic closer to the thermal divide such that the first pyroxene to crystallize had much lower al content than that of ador in the late stages of crystallization the 86010 residual liquid and that of lew87051 encountered the low mg set of equilibria involving kirschsteinite these relationships require either a higher degree of melting for the 86010 parent magma or source region different than ador s these relationships are also consistent with compositionally dependent ree partition coefficients between fassaite and the ador liquid being as much as 1 5 2 times higher than those for the 86010 liquid at the onset of pyroxene crystallization the combination of a trapped liquid component higher partition coefficients and smaller degrees of melting help to explain the observation that ador an apparent cumulate has ree concentrations twice as high as those in 86010 mittlefehdlt and lindstrom 1990 an apparent chilled liquid the absence of a strong negative eu anomaly in the ador parent liquid however requires relatively high degrees of partial melting to eliminate plagioclase in the source region resorption of plagioclase at the peritectic eliminates the eu anomaly that develops during crystallization so ultimately different source regions are required progressive iron loss from devolatilized primitive chondrites allende murchison produces source regions capable of producing a wide range of melt compositions with angritic to eucritic crystallization behavior the compositions of carbonaceous and ordinary chondrite provide a similar range of potential source region compositions however primitive chondrite fe source regions that produce angrite like melts have mg that is too low whereas chondrite fe sources that have mg sufficiently high to yield the mg in angrite minerals have too much silica or orthopyroxene component to yield angrite like liquids no single group of meteorites fe simultaneously satisfies the constraints of mg and silica component however mixtures of fe depleted chondrite plus a low silica component similar to ca al rich inclusions cais can satisfy the constraints the absence in angrites of 48ca and 50ti anomalies typical of cais lugmair and galer 1992 suggests that the low silica component was not simply an enrichment of cais but was the result of direct accretion of high temperature condensate grossman 1972 into sizable thermally shielded planetesimals thus angrites cryptically record mixing of planetesimal sized heterogeneities in the early solar system

j362d28 a new joint model of compressional and shear velocity in the earth s mantle summary the discrimination between chemical and thermal heterogeneity in the earth s mantle remains one of the most important and challenging questions to be answered by observational and theoretical geophysics to answer this question requires a thorough knowledge of the ratio between compressional and shear velocity anomalies we describe results of a joint inversion for compressional and shear velocity in the mantle using a large and diverse data set consisting of traveltimes complete waveforms and surface wave dispersion measurements a horizontal tessellation consisting of 362 spherical splines is used to parametrize the model which is approximately equivalent to a spherical harmonic of degree 18 in resolution the model contains peak variations from prem of up to 7 per cent in s velocity and 2 5 per cent in p velocity in the upper mantle these variations decrease to 1 5 and 0 6 per cent respectively at 1000 km depth and reach 2 5 and 1 0 per cent respectively in the d region the rms ratio of s to p velocity perturbations is fairly constant between 2 0 and 2 5 in the lower mantle but a local minimum in this ratio occurs at a depth of approximately 1700 km resolution tests show that the recovery of p and s velocity is not geographically uniform but also show that this amplitude ratio is well resolved between 670 and 2700 km depth we also observe a persistent negative correlation between bulk sound and shear velocity throughout the same region of the mantle in addition the model contains a minimum correlation between p and s velocity between 670 and 1100 km this feature is supported by both the favourable outcome of resolution experiments and the poor fit provided by the starting model from the inversion in which the p and s velocities are perfectly correlated to our data set of p wave traveltimes the power spectra of both p and s velocity heterogeneity are similar although we note a slightly larger dominance of degree two in the spectra for p velocity in the mid mantle where resolution is highest

application of 3 d crustal and upper mantle velocity model of north america for location of regional seismic events seismic event locations based on regional 1 d velocity depth sections can have bias errors caused by travel time variations within different tectonic provinces and due to ray paths crossing boundaries between tectonic provinces with different crustal and upper mantle velocity structures seismic event locations based on 3 d velocity models have the potential to overcome these limitations this paper summarizes preliminary results for calibration of ims for north america using 3 d velocity model a 3 d modeling software was used to compute source station specific corrections ssscs 3 d for pn travel times utilizing 3 d crustal and upper mantle velocity model for the region this research was performed within the framework of the united states russian federation joint program of seismic calibration of the international monitoring system ims in northern eurasia and north america an initial 3 d velocity model for north america was derived by combining and interpolating 1 d velocity depth sections for different tectonic units in areas where no information on 1 d velocity depth sections was available tectonic regionalization was used to extrapolate or interpolate a moho depth map was integrated this approach combines the information obtained from refraction profiles with information derived from local and regional network data the initial 3 d velocity model was tested against maps of pn travel time residuals for eight calibration explosions corrections to the 3 d model were made to fit the observed residuals our goal was to find a 3 d crustal and upper mantle velocity model capable predicting pn travel times with an accuracy of 1 0 1 5 seconds r m s the 3 d velocity model for north america that gave the best fit to the observed travel times was used to produce maps of ssscs 3 d for seismic stations the computed ssscs 3 d vary approximately from 5 seconds to 5 seconds for the western usa and the pre cambrian platform respectively these ssscs 3 d along with estimated modeling and measurement errors were used to relocate using regional data an independent set of large chemical explosions with known locations and origin times detonated within various tectonic provinces of north america utilization of the 3 d velocity model through application of the computed ssscs 3 d resulted in a substantial improvement in seismic event location accuracy and in a significant decrease of error ellipse area for all events analyzed in comparison both with locations based on the iaspei91 travel times and locations based on 1 d regional velocity models

metal phases of l chondrites their formation and evolution in the nebula and in the parent body abstract metal phases of six three equilibrated and three unequilibrated l chondrites were studied by inaa sem and mossbauer spectroscopy characteristics retained in the bulk metals of unequilibrated chondrites abundant carbon high contents of cr v mn and low contents of w mo and ga compared to metals of equilibrated chondrites less enrichment of w than mo and fractionation of co from ni demonstrate that chondrite metals are not nebular condensates all those characteristics can be well explained by melting chondrite metals are not melting remnants of previously condensed metals rather they were produced by reduction of ci or cm like material during the melting process the complementarity in composition and the similarity in melting feature suggest that chondritic metals and chondrules are the complementary components of the same melting event distribution of trace siderophile elements between taenite and bulk metal indicates that kamacite and taenite can only be the low temperature diffusion products and must have been developed in the chondrite parent body the difference in the taenite composition between equilibrated and unequilibrated chondrites reveals that the equilibrated chondrites were located near the surface while the unequilibrated chondrites were in the interior if they were derived from the common parent body thus while the exsolution of chondrite metal into kamacite and taenite was due to the internal thermal activity the crystallization of eoc silicates resulted from an external heating the internal metamorphism was mild 400 600 c and long whereas the external heating was intense with a maximum temperature in range of 800 950 c and short tetrataenite is present not only in uocs but also in eocs suggesting that the external heating occurred during the internal metamorphism i e within 100 myr of chondrite formation

numerical recognition of alignments in monogenetic volcanic areas examples from the michoacan guanajuato volcanic field in mexico and calatrava in spain abstract identification of geological lineaments using numerical methods is a useful tool to reveal structures that may not be evident to the naked eye in this sense monogenetic volcanic fields represent an especially suitable case for the application of such techniques since eruptive vents can be considered as point like features application of a two point azimuth method to the michoacan guanajuato volcanic field mexico and the calatrava volcanic province spain demonstrates that the main lineaments controlling the distributions of volcanic vents 322 in calatrava and 30 in michoacan approach the respective main compressional axes that dominate in the area i e the cocos north america plates convergence and the main betics compressional direction respectively considering the stress fields that are present in each volcanic area and their respective geodynamic history it seems that although volcanism may be a consequence of contemporaneous extensional regimes the distribution of the volcanic vents in these kinds of monogenetic fields is actually controlled by reactivation of older fractures which then become more favourable for producing space for magma ascent at near surface levels

sequential vein growth with fault displacement an example from the austin chalk formation texas to determine the opening and precipitation history and characteristics of vein forming fluids analyses of oxygen and carbon isotopes and trace elements were carried out on multilayered crack seal calcite veins in the austin chalk formation near san antonio texas the veins developed within the normal fault zones possessing unique chemical and textural characteristics which indicate sequential vein development they are composed of alternating millimeter to submillimeter thick calcite veinlets and host lithons occasionally crosscut by coarse equant grained secondary calcite veins regular changes in 18o e g 2 6 to 5 6 pee dee belemnite pdb of the calcite veinlets along the length of veins suggest that the individual calcite veinlets were sequentially developed a systematic 18o decrease in the vein opening direction primarily resulted from a continuous increase in temperature of the ascending fluids delivered to the austin chalk relatively constant 13c approximately 1 4 0 4 pdb for the multilayered veins and most secondary veins indicates that the composition of fluids from which the calcite veins precipitated was initially buffered by the bulk chalk there is no spatial variation in trace element composition of the calcite veinlets along the length of veins low sr concentrations in both calcite veinlets and secondary veins relative to those of the host chalk reflect a low partition coefficient of sr in calcite during vein formation normal faults in the cretaceous austin chalk were conduits to upwardly mobile vein forming fluids

basaltic ignimbrites in monogenetic volcanism the example of la garrotxa volcanic field ignimbrites are pyroclastic density current deposits common in explosive volcanism involving intermediate and silicic magmas and in less abundance in eruptions of basaltic central and shield volcanoes however they are not widely described in association with monogenetic volcanism where typical products include lava flows scoria and lapilli fall deposits as well as various kinds of pyroclastic density current deposits and explosion breccias in la garrotxa basaltic monogenetic volcanic field part of the neogene quaternary european rift system located in the northeast of the iberian peninsula we have identified a particular group of pyroclastic density current deposits that show similar textural characteristics to silicic ignimbrites indicating an overlap in transport and depositional processes these deposits can be clearly distinguished from other pyroclastic density current deposits generated during phreatomagmatic phases that typically correspond to thinly laminated units with planar to cross bedded stratification the monogenetic ignimbrite deposits correspond to a few meters to several tens of meters thick units rich in lithic and lapilli scoria fragments with an abundant ash matrix and internally massive structure emplaced along valleys and gullies with run out distances up to 6 km and individual volumes ranging from 106 to 1 5 107 m3 the presence of flattened scoria and columnar jointing in some of these deposits suggests relatively high emplacement temperatures coinciding with available paleomagnetic data that suggests an emplacement temperature around 450 500 c in this work we describe the main characteristics of these pyroclastic deposits that were generated by a number of phreatomagmatic episodes comparison with similar deposits from silicic eruptions and previous examples of ignimbrites associated with basaltic volcanism allows us to classify them as basaltic ignimbrites the recognition in monogenetic volcanism of such pyroclastic products which may extend several kilometres from source has an important consequence for hazard assessment in these volcanic fields which previously have been considered to present only minor hazards and risks

ages and composition of gas trapped in allan hills and byrd core ice gas is extracted from large 6 31 kg antarctic ice samples to obtain sufficient co2 for14c measurements with small low level proportional counters the14c ages of byrd core ice are in accord with glaciological estimates ranging from 2 2 1 1 1 4 103 yr at 271 m depth to more than 8 103 yr at 1071 m depth the co2 abundances in gas extracted from byrd core ice range from 0 0216 to 0 051 with below present day atmosphere co2 abundances for ice from 1068 and 1469 m depths the co2 abundance in gas from allan hills surface ice samples ranges between four and six times the atmospheric value and the co2 had a specific activity three times that of contemporary carbon a possible explanation for the anomalously high specific activity is surface melting with the incorporation into co2 of14c produced by cosmic ray spallation of oxygen in ice the co2 abundance in gas extracted from subsurface allan hills ice ranged from 0 030 to 0 065 and the specific activities are below contemporary carbon indicating ages greater than 5 103 yr the18o 16o ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the18o 16o ratio in the ice the o2 n2 and ar abundances and isotopic compositions are similar to those in contemporary air except for positive15n 14n ratios in a few samples

the semarkona meteorite first recorded occurrence of smectite in an ordinary chondrite and its implications abstract semarkona is an unshocked unequilibrated ordinary chondrite much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered analyses of altered materials and opaque matrix are presented ca and fe have been redistributed from primary anhydrous phases into calcite and na fe smectite respectively in semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites the low petrologic type previously assigned to semarkona is the result of retrograde metamorphism under aqueous conditions of a higher temperature mineral assemblage semarkona and possibly bishunpur should be assigned to petrologic type 2