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

condensation and aggregation of solar corundum and corundum hibonite grains forty three corundum grains 1 11 m in size and 5 corundum hibonite grains with corundum overgrown by hibonite 47 m in size were found in the matrix of the mineralogically pristine ungrouped carbonaceous chondrite acfer 094 by using cathodoluminescence imaging some of the corundum and corundum hibonite grains occur as aggregates of 2 to 6 grains having similar sizes the oxygen isotopic compositions of some of the corundum bearing grains suggest their solar nebula origin 26al 26mg systematics of one corundum grain showed the canonical initial 26al 27al ratio also suggesting a solar nebula origin quantitative evaluation of condensation and accretion processes made based on the homogeneous nucleation of corundum diffusion controlled hibonite formation collisions of grains in the nebula and critical velocity for sticking indicates that in contrast to the hibonite bearing aggregates of corundum grains the hibonite free corundum aggregates could not have formed in the slowly cooling nebular region with solar composition we suggest instead that such aggregates formed near the protosun either in a region that stayed above the condensation temperature of hibonite for a long time or in a chemically fractionated ca depleted region and were subsequently physically removed from this hot region e g by disk wind

sedimentology of early pliocene sandstones in the south western taiwan foreland implications for basin physiography in the early stages of collision abstract this work presents sedimentological observations and interpretations on three detailed sections of the pliocene yutengping ailiaochiao formations deposited in the early stages of collision in taiwan seven facies associations record paleoenvironments of deposition ranging from nearshore to lower offshore with a strong influence of tidal reworking even in shelfal sub tidal environments and a pro delta setting characterized by mass flows the association of shallow facies of the upper offshore to lower shoreface with pro delta turbidite facies sourced in the orogen to the east suggests a peculiar setting in which turbidite deposition occurred below wave base but on the shelf in water depths of probably less than 100 m this adds to the examples of shallow turbidites increasingly commonly found in foreland basins and challenges the classical view of a deep early underfilled foreland basin time series analysis on tidal rhythmites allow us to identify a yearly signal in the form of periodic changes of sand supply energy and bioturbation that suggests a marked seasonality possibly affecting precipitation and sediment delivery as well as temperature the taiwan foreland basin may also present a potentially high resolution record in shallow sediments of the early installation of monsoonal circulation patterns in east asia we confirm partly the paleogeography during the early stages of collision in taiwan the chinese margin displayed a pronounced non cylindrical geometry with a large basement promontory to the west in place of the modern taiwan mountain range collision in taiwan may have happened at once along the whole length of the modern mountain range instead of progressively from north to south as classically considered

thrust related river terrace development in relation to the 1999 chi chi earthquake rupture western foothills central taiwan abstract the 21 september 1999 earthquake mw 7 6 produced a surface rupture that extended for 100 km in a general north south direction in front of the western foothills central taiwan the study area located in a segment of the fold thrust belt of central taiwan provides an important natural laboratory to study the relationship between active thrust deformation and fluvial terrace development we recognize from west to east three subparallel thrusts the sanyi houli and shihkang faults in the northern part of the earthquake disaster area the 1999 earthquake rupture occurred only along the shihkang fault whereas the other two faults were inactive along the tachia river in the hanging wall of the shihkang fault eight well developed terrace levels are observed and can be subdivided into lateritic lt5 lt1 and non lateritic terraces ft3 ft1 five levels of lateritic terrace lt5 lt1 are located in the hanging wall of the houli fault and a lateritic terrace lt5 is present in the hanging wall of the sanyi fault stratigraphic and elevation correlations between these well developed fluvial terraces in relationship to nearby geologic structures show that the sanyi fault is the oldest structure lateritic terraces of at least 10 000 yr bp for example overlie the sanyi fault but correlative terraces associated with the houli fault are offset these types of terrace correlations allow us to define the progressive development of the thrust system within the western foothills

back arc extension in the okinawa trough the okinawa trough lying to the east of china is a back arc basin formed by extension within continental lithosphere behind the ryukyu trench arc system middle to late miocene uplift associated with normal faulting of the initially adjacent ryukyu nonvolcanic arc and the taiwan sinzi folded belt corresponds to the first rifting phase the timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern okinawa trough the rifting occurred after a major early miocene change in the motion of the philippine plate with respect to eurasia and ceased during the pliocene a second rifting phase started about 2 m y ago at the plio pleistocene boundary and has continued until the present time it has proceeded to a more advanced stage in the middle and southern okinawa trough than it has farther north detailed bathymetric sea beam seismic reflection and magnetics data collected during the pop 1 cruise of the r v jean charcot reveal the principal features of the extensional processes the back arc spreading phase started very recently in the southern and middle okinawa trough as exemplified by several en echelon and in some cases overlapping active central graben oriented n70 e n80 e some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies transform faults between these en echelon active rifts are not obvious we suggest that the major part of the southern okinawa trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern okinawa trough the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough the system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of okinawa island whereas active volcanoes in the ryukyu arc occur only north of okinawa island we refer to this transition between active arc and back arc volcanism as the volcanic arc rift migration phenomenon vamp globally back arc volcanism propagated from the southern okinawa trough to the okinawa vamp area rifting continues to occur in the northern okinawa trough but is not yet accompanied by associated volcanism the okinawa vamp area is characterized by a series of parallel basaltic ridges oriented n75 e with associated linear magnetic anomalies characteristic of dyke intrusions we suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending n75 e and that this zone presently ends at the southern extremity of the active volcanic chain the initial phase of formation of back arc basin oceanic crust is non steady state and is characterized by the lack of a developed fracture zone pattern the termination of the vamp area in the direction of the volcanic zone of the arc is consistent with the suggestion of molnar and atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs apparently back arc extension initially occurred within the continental lithosphere located westward of the ryukyu arc along its whole length but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward this migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc it is this transfer of volcanism that we call the vamp process thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc this interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence since the plate motion in the phillippine sea is oblique to the trench at least in the southern part of the okinawa trough we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc the motion of the ryukyu platelet with respect to eurasia is consequently an extensional strike slip motion trending roughly parallel to the okinawa trough

the meteoritical bulletin no 82 1998 july abstract meteoritical bulletin no 82 lists information for 974 new meteorites including 521 finds from antarctica 401 finds from the sahara 21 finds from the nullarbor region of australia and 7 falls ban rong du burnwell fermo jalanash juancheng monahans 1998 and silao many rare types of meteorites are reported counting pairing groups as one these include one cr chondrite two ck chondrites two co chondrites four cv chondrites one ch chondrite or bencubbin like six c2 unclassified chondrites two eh chondrites two el chondrites three r chondrites thirty unequilibrated ordinary chondrites one un grouped chondrite three eucrites six howardites one diogenite eleven ureilites nine iron meteorites one mesosiderite two brachinites one lodranite one winonaite and two lunar meteorites dar al gani 400 and eet 96008 all italicized abbreviations refer to addresses tabulated at the end of this document

anorthite spinel rich inclusions in the ningqiang carbonaceous chondrite genetic links with type a and c inclusions many ca al rich inclusions cais were molten once and the question of what their precursors consisted of is controversial in this paper we report a new type of anorthite spinel rich inclusion asi in the ningqiang carbonaceous chondrite the modal and bulk compositions of the asis are similar to those of type c inclusions but with nonmolten textures the asis are proposed to be the precursors of type c inclusions the asis show alteration textures with melilite being replaced by anorthite and ca pyroxene furthermore compositions of the melilites and the calculated modal and bulk compositions of the possible precursors of the asis are close to those of the spinel rich type a inclusions in the ningqiang meteorite which suggests that asis formed by alteration of the latter in the solar nebula petrography and mineral chemistry of one type c inclusion in ningqiang are also reported

late orogenic extension in mountain belts insights from the basin and range and the late paleozoic variscan belt from two examples of orogenic domains some general mechanisms significant of late orogenic tectonic processes in mountain belts are characterized the basin and range province and the variscan belt in the french massif central have both suffered important compressional orogenic crustal thickening and the results of late orogenic processes can be observed in the field both areas are covered by deep seismic profiling providing constraints on the geometry of a crust which has been restored to a normal thickness late orogenic features from the two domains are compared at different scales and their tectonic significance for extension mechanisms is discussed at the scale of the orogenic domains the most prominent tectonic features are the metamorphic core complexes mcc which expose deformed rocks from the middle crust generally affected by high temperature low to medium pressure metamorphism partial melting and widespread granite emplacement in these mcc large scale extensional shear zones present an intense mylonitic deformation characterized by low dipping foliations and pervasive stretching lineations they show a complete evolution from early deep seated ductile deformation generally achieved under high temperature low to medium pressure metamorphism to a late shallow brittle stage characterized by cataclastic deformation the late detachment stage generally controls the development of asymmetrical extensional sedimentary basins filled by continental deposits two main geometries of mcc are defined that are characterized by differing geometry and kinematics of low angle shear zones in the first case two low angle shear zones with opposite vergence develop along the flanks of a roughly symmetrical mcc often one system is dominant over the other the second geometry characterizes asymmetrical mcc bounded by a single normal shear zone which is upwarped during uplift and doming of the core caused by tectonic denudation detailed strain analysis performed in several extensional shear zones shows that the deformation regime is heterogeneous and results from general noncoaxial flow deformation along the shear zones evolves progressively from slight homogeneous pure shear strain to intense heterogeneous noncoaxial shear strain strain distribution within the lower crust is less well constrained by field observation however analogies between cocorp and ecors deep seismic reflection profiles give important constraints on crustal structure wide zones of highly subhorizontally layered lower crust and a flat high amplitude reflection moho characterize both evolved orogenic domains suggesting that major deformations and flow occur within the lower crust during extension a kinematic model involving heterogeneous crustal deformation and regional scale flow fits relatively well with late orogenic structures observed in continental domains a weak hot upper mantle allows large scale flow of lower crust material from zones of deep ductile extension to uplifted domains of upper crustal denudation heterogeneous strain is accommodated by low angle extensional shear zones from localized zones of extension in the brittle crust to ductile lower crust combined pure and simple shear occurs along localized shear zones whereas at the scale of the whole lithosphere deformation nearly corresponds to a vertical pure shear such deformation processes which affect a thick and hot crust seem to be common in both compared domains suggesting that late orogenic extensional processes are slightly dependent of the type of contractional tectonics thus as much in the andean type west american cordilleran belt as in the collision type variscan belt late orogenic processes produced similar extensional features

opening of the okinawa basin and collision in taiwan a retreating trench model with lateral anchoring using a two dimensional finite element model with an elasto plastic behavior we show that the opening of the okinawa basin behind the ryukyu trench since about 6 ma can be explained by a retreating trench model with lateral anchoring due to the collision in taiwan we assume that a suction force is applied to the edge of the overriding plate this force corresponds to the difference between the mean lithospheric pressure in the overriding lithosphere and the normal pressure applied to its edge it results in an outward motion of the edge of the continental margin retreating trench and in the opening of the okinawa basin if on the contrary no suction force is applied the collision in taiwan does not result in any extension in the okinawa area on both extremities of the ryukyu trench this outward motion is locked by the collision in taiwan and the buoyant subduction of the palau kyushu ridge it results in the arcuate shape of the ryukyu arc in order to explain the actual amount of extension in the okinawa basin it is however necessary to take into account the presence of the miocene volcanic arc which results in a weakened lithosphere in our model this weak zone is simulated by a lower yield condition finally the dissymmetry of the ryukyu arc and okinawa basin can be explained by a lateral variation of the suction force related to the variation of the length of the subducting slab thus of the slab pull force

tsunami deposits and recurrence on a typhoon prone coast of northern taiwan from the last millennium abstract widely known for its hazardous history taiwan holds valuable records of nw pacific tsunamis and typhoons despite the similarity between tsunami and typhoon deposits historical accounts enabled the identification of the 1867 tsunami deposit on the northern coast through matching with the record setting inundation however the identification of prehistoric tsunami deposits has been hindered by severe sediment reworking and post depositional changes produced by the typhoon prone tropical and humid climate in this study we investigated the upper holocene facies and their sediment sources and radiocarbon ages on distal floodplains and rocky backshores of the northern coast where sediment reworking is less intense four decimetre thick gravelly layers were identified intercalated with fluvial mud and colluvium the gravelly layers are composed of beach derived quartz rich sand and rounded gravels of the sedimentary basement rocks longshore drift andesite and stranded pumice the remarkable layer thickness gravel size and quartz richness were determined to have endured post depositional changes the event layers are sharp based matrix supported and poorly sorted and have recorded scouring sediment entrainment and rapid fallout of suspension rich turbulent flows that probably originated with tsunamis the event layers occur 0 5 0 8 km inland and 3 11 5 m above sea level matching the 1867 tsunami inundation and wave height respectively radiocarbon dating tied the event layers to the 1867 tsunami and three prehistoric events that occurred in the periods 1545 to 1810 1293 to 1414 and 1090 to 1235 representing a recurrence interval of 83 436 years over the last millennium

crust mantle boundaries in the taiwan luzon arc continent collision system determined from local earthquake tomography and 1d models implications for the mode of subduction polarity reversal abstract in order to better understand the mode of subduction polarity reversal in the taiwan luzon arc continent collision zone we mapped its crust mantle boundaries using local earthquake tomography by contouring surfaces of constant vp 7 5 km s 1 we identified three moho discontinuities and the plate interface that juxtaposes eurasian lower crust against mantle lithosphere of the philippine sea plate the plate interface dips to the east under southeastern taiwan and steepens progressively towards north until it becomes vertical at 23 7 n from there it continues northward in a vertical orientation until the limit of the tomographic model inhibited further mapping for the moho additional depth constraints were derived from 1d models using p wave arrivals of local earthquakes the mohos of the eurasian and philippine sea plates are disconnected across the plate interface beneath southern taiwan the eurasian moho dips to the east at 50 60 following the orientation of the plate boundary and continuous with the benioff zone towards north the eurasian moho steepens into subvertical again together with the plate boundary the philippine sea plate moho exhibits a synform like crustal root interpreted as the base of the magmatic luzon arc towards the north this root deepens from 30 to 70 km underneath the ryukyu trench in northernmost taiwan the hinge of the vertically subducting eurasian slab steps westward out of the thrust belt leaving the deformation front to the east inactive and giving way to the north dipping philippine sea plate a subhorizontal moho at 30 35 km depth overlies the north dipping philippine sea slab and is interpreted as a newly formed moho established after westward rollback and delamination of the subducting eurasian slab in combination these data support a model of progressive subduction polarity reversal in which a tear within the eurasian lithosphere propagated southwestward deactivating the deformation front

feo rich silicates in the sahara 97159 eh3 enstatite chondrite mineralogy oxygen isotopic compositions and origin we report the mineralogy and oxygen isotopic compositions of feo rich silicates in the sahara 97159 eh3 chondrite this component is referred to as feo rich because it contains substantially more feo than the characteristic feo poor silicates in the highly reduced enstatite meteorites these feo rich silicates are mostly low ca pyroxene fs535 and their compositions suggest an origin under more oxidizing conditions like those for the ordinary chondrites however the mafic silicates in ordinary and carbonaceous chondrites are dominantly olivine and the feo rich silicates in the e chondrites are less commonly olivine the oxygen isotopic compositions of the feo rich silicates are indistinguishable from those of feo poor silicates in sahara 97159 these observations suggest that both the feo rich silicates and the feo poor silicates in eh chondrites formed from the same oxygen reservoir where redox conditions varied widely

the nature and origin of type b1 and b2 caal rich inclusions in the allende meteorite abstract the type b ca al rich inclusions in the allende carbonaceous chondrite form a continuous range from the mineralogically concentrically zoned b1 subtype to the unzoned b2 subtype these subtypes differ in i structure texture grain size and shape ii mineralogical proportions and compositions iii accessory mineralogy iv relative abundance of spinel framboids v rim layering vi major element chemistry and vii degree of secondary alteration these differences together with observations on the crystallization of synthetic melts suggest that the b1 inclusions crystallised relatively rapidly from molten parental material while b2 types crystallised relatively slowly close to the solidus from material that had not been completely melted the same data are used to construct an evaporative residue model for the origin of the parental type b materials in the model dust in the protosolar nebula was heated with removal of more volatile elements leaving completely melted type b1 residues at the highest temperatures and incompletely melted less highly evaporated type b2 residues at lower temperatures

the blue angel i the mineralogy and petrogenesis of a hibonite inclusion from the murchison meteorite a detailed mineralogie chemical and petrologic study of the blue angel a relatively large 1 5 mm hibonite containing inclusion from the murchison meteorite was performed in an attempt to understand the mechanisms of formation and modification of hibonite rich inclusions the blue angel inclusion is composed of roughly equal amounts of hibonite and calcite with minor amounts of spinel perovskite diopside and an fe rich silicate the inclusion can be divided into three roughly concentric zones a hibonite rich core a calcite rich mantle and a spinel rich layered rim the mineral chemistry and petrography of the blue angel are consistent with a three stage formation history 1 an early stage of nebular condensation which produced the hibonite perovskite and spinel 2 a moderate temperature stage of aqueous alteration and metamorphism occurring on a small planetary body containing co 2 and h 2o during which calcite was formed in the inclusion and 3 the final emplacement of the blue angel into its present position in murchison the study of the blue angel indicates that extensive alteration of ca al rich inclusions cai may have occurred by aqueous alteration and thermal metamorphism followed by explosive mixing processes on a parent body such metamorphic reactions may involve formation and destruction of phases such as melilite and diopside which have been previously thought to be primary condensates the mechanisms proposed for the formation and modification of the blue angel help to explain the secondary phases and oxygen isotope anomalies found in many cai and eliminate the need for invoking kinetically complicated back reactions at very low pressures with a cool part of the solar nebula the contribution of planetary metamorphism in the formation and alteration of cai must be considered along with nebular processes in order to understand the formation of carbonaceous chondrites

oxygen isotopes in calcium aluminum rich inclusions from enstatite chondrites new evidence for a single cai source in the solar nebula calcium aluminum rich inclusions cais from enstatite chondrites have large 16o excesses similar to cais in carbonaceous and ordinary chondrites and are also similar in morphology mineralogy and al mg isotopic systematics these similarities provide new evidence that most cais might have formed in a single restricted nebular locale and were then distributed unevenly throughout the various chondrite accretion regions

stress tensor analysis in the taiwan area from focal mechanisms of earthquakes abstract we produce a map of the stress pattern in and around taiwan based on 200 earthquake focal mechanism solutions these solutions were determined by using data from taiwan telemetered seismographic network microearthquake surveys and wwssn the stresses are derived through a minimization of angles between the slip vector and the shear stress on each nodal plane considered as a fault employing appropriate weighting factors the whole set of focal mechanisms is divided into several groups mainly according to apparent clustering of the event locations the results show that the direction of maximum principal stress in taiwan area is nearly horizontal and se nw on average this is in good agreement with the direction of relative motion between the philippine sea plate and the eurasian plate in western taiwan the fan shaped distribution of the maximum principal stress is consistent with the direction of philippine sea eurasian plate convergence through a simple model of viscous material indented by a rigid wedge in the northeastern part of taiwan a nearly horizontal minimum principal stress oriented n s is found for shallow depths it occurs in a region of low seismic velocities probably related to the back arc activity of the okinawa trough down dip compressional and down dip extensional stresses have been identified in different depth ranges within the subducting slab of the philippine sea plate in the northern taiwan this may reflect the slab characteristics in this area a complex stress pattern prevails in the hualien area at the junction between the ryukyu subduction system and the taiwan collision zone

calcium aluminum rich inclusions in enstatite chondrites i mineralogy and textures abstract like calcium aluminum rich inclusions cais from carbonaceous and ordinary chondrites enstatite chondrite cais are composed of refractory minerals such as spinel perovskite al ti diopside melilite hibonite and anorthitic plagioclase which may be partially to completely surrounded by halos of na cl rich minerals porous aggregate and compact textures of the refractory cores in enstatite chondrite cais and rare wark lovering rims are also similar to cais from other chondrite groups however the small size 100 m low abundance 1 by mode in thin section occurrence of only spinel or hibonite rich types and presence of primary ti v oxides and secondary geikelite and ti fe sulfides distinguish the assemblage of enstatite chondrite cais from other groups the primary mineral assemblage in enstatite chondrite cais is devoid of indicators e g oldhamite osbornite of low o fugacities thus high temperature processing of the cais did not occur under the reducing conditions characteristic of enstatite chondrites implying that either 1 the cais are foreign to enstatite chondrite forming regions or 2 o fugacities fluctuated within the enstatite chondrite forming region in contrast secondary geikelite and ti fe sulfide which replace perovskite indicate that alteration of perovskite occurred under reducing conditions distinct from cais in the other chondrite groups we have not ascertained whether the reduced alteration of enstatite chondrite cais occurred in a nebular or parent body setting we conclude that each chondrite group is correlated with a unique assemblage of cais indicating spatial or temporal variations in physical conditions during production or dispersal of cais

crustal scale seismic profiles across the manila subduction zone the transition from intraoceanic subduction to incipient collision 1 we use offshore multichannel seismic mcs reflection and wide angle seismic data sets to model the velocity structure of the incipient arc continent collision along two trench perpendicular transects in the bashi strait between taiwan and luzon this area represents a transition from a tectonic regime dominated by subduction of oceanic crust of the south china sea west of the philippines to one dominated by subduction and eventual collision of rifted chinese continental crust with the luzon volcanic arc culminating in the taiwan orogeny the new seismic velocity models show evidence for extended to hyperextended continental crust 10 15 km thick subducting along the manila trench at 20 5 n along transect t1 as well as evidence indicating that this thinned continental crust is being structurally underplated to the accretionary prism at 21 5 n along transect t2 but not along t1 to the south coincident mcs reflection imaging shows highly stretched and faulted crust west of the trench along both transects and what appears to be a midcrustal detachment along transect t2 a potential zone of weakness that may be exploited by accretionary processes during subduction an additional seismic reflection transect south of t1 shows subduction of normal ocean crust at the manila trench

calcium aluminum rich inclusions in enstatite chondrites ii oxygen isotopes abstract ln situ ion microprobe analyses of spinel in refractory calcium aluminium rich inclusions cais from type 3 eh chondrites yield 160 rich compositions dl80 and 6170 about 40 0 spinel and feldspar in a cai from an el3 chondrite have significantly heavier isotopic compositions dl80 and 6170 about 5 0 a regression through the data results in a line with slope 1 o on a three isotope plot similar to isotopic results from unaltered minerals in cais from carbonaceous chondrites the existence of cais with 160 rich and 16o poor compositions in carbonaceous as well as enstatite chondrites indicates that cais formed in at least two temporally or spatially distinct oxygen reservoirs general similarities in oxygen isotopic compositions of cais from enstatite carbonaceous and ordinary chondrites indicate a common nebular mechanism or locale for the production of most cais introduction refractory calcium aluminium rich inclusions cais in chondritic meteorites preserve a record of high temperature processing in the early solar nebula including condensation evaporation and melting macpherson

lanthanide and actinide chemistry at high c o ratios in the solar nebula abstract chemical equilibrium calculations were performed to study the condensation chemistry of the ree and actinides under the highly reducing conditions which are necessary for the formation of the enstatite chondrites 1 2 our calculations confirm that the ree and actinides condensed into oldhamite cas the major ree and actinide host phase in enstatite chondrites at a carbon oxygen co ratio 1 in an otherwise solar gas five basic types of ree abundance patterns several of which are analogous to ree abundance patterns observed in the ca al rich inclusions cais in carbonaceous chondrites are predicted to occur in meteoritic oldhamites all of the reported ree patterns in oldhamites in enstatite chondrites can be interpreted in terms of our condensation calculations the observed patterns fall into 3 of the 5 predicted categories the reported th and u enrichments and ratios in meteoritic oldhamites are also consistent with predictions of the condensation calculations finally pure ree sulfides are predicted to condense in the 10 6 to 10 9 bar range and may be found in enstatite chondrites if they formed in this pressure range

fluffy type a ca al rich inclusions in the allende meteorite abstract allende fluffy type a s fta s are a distinct sub group of ca al rich inclusions whose primary mineral assemblage consists of al rich melilite ak 0 33 spinel that is commonly very v rich perovskite and frequently hibonite some contain relatively coarse grained melilite up to 1 5 mm that is intensely kink banded and commonly reversely zoned hibonite and v rich spinel others contain much finer grained and strain free melilite 50 m and have not been found to contain hibonite or v rich spinel some fta s contain both coarser and finer grained melilite and textural relationships indicate that the latter is replacing the former fta s are characterized by extremely irregular shapes and 60 75 volume per cent of fine grained secondary alteration products many are aggregates of innumerable nodules each of which is surrounded by a wark lovering type rim sequence these nodules are frequently separated from one another by matrix like clastic rim material other fta s do not have nodular structure structural and mineralogical characteristics of their wark lovering rims suggest that fta s did not achieve their shapes by deformation of a liquid or a hot plastic solid in contrast to those in type b inclusions formation of reverse zoning in the coarser grained melilite crystals in fta s cannot be understood in terms of crystallization from a liquid but are readily explainable by condensation from a solar nebular gas during a period of falling pressure further evidence against a liquid origin is the wide range of spinel compositions within individual coarser grained fta s the fact that the reversely zoned melilite crystals cannot have been produced in any kind of sublimation or distillation process precludes formation of these inclusions as volatilization residues fta s are aggregates in some of which are preserved vapor solid condensate grains that formed at high temperature in the solar nebula

petrology and oxygen isotope compositions of chondrules in e3 chondrites chondrules in e3 chondrites differ from those in other chondrite groups many contain near pure endmember enstatite fs 1 some contain si bearing feni metal cr bearing troilite and in some cases mg mn and ca sulfides olivine and more feo rich pyroxene grains are present but much less common than in ordinary or carbonaceous chondrite chondrules in some cases the feo rich grains contain dusty inclusions of metal the oxygen three isotope ratios 18o 17o of olivine and pyroxene in chondrules from e3 chondrites which are measured using a multi collection sims show a wide range of values most enstatite data plots on the terrestrial fractionation tf line near whole rock values and some plot near the ordinary chondrite region on the 3 isotope diagram pyroxene with higher feo contents 2 10 wt feo generally plots on the tf line similar to enstatite suggesting it formed locally in the ec enstatite chondrite region and that oxidation reduction conditions varied within the e3 chondrite chondrule forming region olivine shows a wide range of correlated 18o and 17o values and data from two olivine bearing chondrules form a slope 1 mixing line which is approximately parallel to but distinct from the ccam carbonaceous chondrite anhydrous mixing line we refer to this as the ecm enstatite chondrite mixing line but it also may coincide with a line defined by chondrules from acfer 094 referred to as the pcm primitive chondrite mineral line ushikubo et al 2011 the range of o isotope compositions and mixing behavior in e3 chondrules is similar to that in o and c chondrite groups indicating similar chondrule forming processes solid gas mixing and possibly similar 16o rich precursors solids however e3 chondrules formed in a distinct oxygen reservoir internal oxygen isotope heterogeneity was found among minerals from some of the chondrules in e3 chondrites suggesting incomplete melting of the chondrules survival of minerals from previous generations of chondrules and chondrule recycling olivine possibly a relict grain in one chondrule has an r chondrite like oxygen isotope composition and may indicate limited mixing of materials from other reservoirs calcium aluminum rich inclusions cais in e3 chondrites have petrologic characteristics and oxygen isotope ratios similar to those in other chondrite groups however chondrules from e3 chondrites differ markedly from those in other chondrite groups from this we conclude that chondrule formation was a local event but cais may have all formed in one distinct place and time and were later redistributed to the various chondrule forming and parent body accretion regions this also implies that transport mechanisms were less active at the time of and following chondrule formation

two unusual type b refractory inclusions in the ningqiang carbonaceous chondrite evidence for relicts xenoliths and multi heating abstract two type b refractory inclusions consisting mainly of melilite fassaite and spinel anorthite were found in the anomalous ningqiang carbonaceous chondrite the composition of melilite varies from ak4 15 near the diopside rims to ak80 90 in the centers of these inclusions in addition melilite exhibits intergrowths with fassaite and or anorthite in the centers of the inclusions these observations suggest that both inclusions were once molten the na2o content of melilite is positively correlated with the ak content for ak beyond crystallization from melts the ningqiang type b refractory inclusions contain possible relict fassaite fragments these fragments are embedded in gehlenitic melilite and have corroded outlines surrounded by highly tio2 enriched fringes as distinguished from the fassaites intergrown with melilite in the centers of the inclusions in inclusion nqj331 most grains of anorthite occur as irregular coarse grained fragments distinct from those intergrown with melilite toward these anorthite fragments melilite shows a steep decrease in ak content we propose that these anorthite fragments are xenoliths and were probably injected into the host while the latter was crystallizing palisades occur only in nqj331 and are probably relicts too distinctly low v2o3 concentrations of the spinels from the palisade bodies and the presence of palisade bodies consisting of one or more corroded crystals of fassaite anorthite are new lines of the evidence for a relict origin of palisades the other type b refractory inclusion nqj354 contains a spherule consisting of a grossite core and a spinel mantle enclosing laths of hibonite the modal abundance and mineral chemistry of the spinel hibonite spherule are distinctly different from the host inclusion we propose that the spinel hibonite spherule crystallized from a sio2 poor melt at a very high temperature and was injected into the type b host before the latter was completely solidified this grossite bearing spinel hibonite spherule may be related to the spinel hibonite spherules in cm2 chondrites

plagioclase rich inclusions in carbonaceous chondrite meteorites liquid condensates plagioclase rich inclusions in carbonaceous chondrites are of two types 1 mm cm sized ca al rich inclusions cais with 30 60 vol anorthite and up to 35 vol each of ti al pyroxene tpx melilite and spinel and 2 smaller 3 mm ca chondrules similar to those found in ordinary chondrites containing more sodic plagioclase pyroxene olivine and spinel the cais which were formerly named type i and thought to be intermediate between type a and type b cais are shown to be an independent type renamed type c with distinctive chemical and mineralogical compositions type c cais have group i or group ii trace element patterns low initial 26al27al ratios of 5 10 6 typical ak 35 55 melilite tpx with 2 12 tio2 and opaque grains osirrumopt alloy nuggets and fremdlinge smaller than 10 m the textures sequence of crystallization and concentric zonation indicate that they crystallized from melt droplets the texture of the anorthite ranges from coarse laths to a fine grained groundmass reflecting increasing retardation of its nucleation the few cais with the coarse laths cooled slowly 2 5 h from below the liquidus but the majority cooled faster from completely molten material as the elemental abundances in type c s are dominated by volatility the melts were not formed by planetary magmatic processes evaporative residues and remelted solid condensates are also ruled out because the compositions of naturally occurring experimentally produced and thermodynamically calculated residues and solid condensates differ from those of type c cais type c cais have compositions similar to those calculated for liquid condensates under high solar gas pressure 1 atm or in dust rich environments and are probably liquid condensates the few type c cais that crystallized from incompletely molten materials may have been reheated liquid condensates or mixed liquidsolid condensates

the thermometry of enstatite chondrites a brief review and update due to the discoveries in antarctica the number of known enstatite chondrites has doubled in the last few years and many rare or previously unknown types have been collected most notably many el3 and eh3 chondrites we have applied the five major enstatite chondrite thermometers to the new and previously known enstatite chondrites the thermometers being 1 kamacite quartz enstatite oldhamite troilite kqeot 2 oldhamite 3 alabandite niningerite 4 sphalerite and 5 phosphide metal measured temperatures based on the kqeot and oldhamite systems are 800 c 1000 c with the type 3 enstatite chondrites having values similar to those of type 4 6 it seems likely that these temperatures relate to events prior to parent body metamorphism such as nebula condensation or chondrule formation and were not significantly reset by later events measured temperatures for alabandite niningerite metal phosphide and sphalerite in eh chondrites increase from 300 c 400 c to 600 c 800 c with petrographic indications of increasing metamorphism in contrast measured temperatures for all el chondrites including the most heavily metamorphosed are generally 400 c apparently el chondrites cooled more slowly than the eh chondrites regardless of metamorphism experienced measured temperatures for the alabandite niningerite metal phosphide and sphalerite are actually closure temperatures for the last thermal event suffered by the meteorite and the fast cooling rates indicated are most consistent with processes occurring in thick regoliths

a comparative study of opaque phases in qingzhen eh3 and macalpine hills 88136 el3 representatives of eh and el parent bodies opaque minerals in the qingzhen eh3 and macalpine hills mac 88136 el3 enstatite chondrites were studied and compared with other eh and el chondrites all opaque minerals usually occur in multi sulfide metal clasts and nodules in the matrix between chondrules el goresy et al 1988 the higher abundance of opaque minerals the occurrence of niningerite and various alkali sulfides e g caswellsilverite phases a and b djerfisherite are diagnostic criteria for eh chondrites while alabandite is characteristic for el chondrites in addition eh chondrites are characterized by enrichments of si in both kamacite and perryite and alkali elements in sphalerite and chalcopyrite the mn contents of daubreelite and sphalerite are lower in eh than in el chondrites these are consistent with lower oxygen fugacity and higher h2s fugacity of eh than el chondrites in contrast the discovery of sphalerite and zn rich daubreelite in mac 88136 indicates that their absence in el6 chondrites is probably related to thermal metamorphism in the parent body schreibersite microspherules are commonly enclosed in most sulfides in qingzhen but are absent in mac 88136 they were once molten and probably predated all sulfide host phases the petrographic setting and chemical compositions of the sulfide hosts of the schreibersite microspherules in eh3 chondrites are consistent with formation by condensation the earliest sulfide condensates oldhamite and niningerite occupy the interiors of the clasts and nodules whereas the rims consist of troilite and djerfisherite in addition in qingzhen some other troilite djerfisherite and sphalerite assemblages coexist with perryite they were produced by sulfurization of metallic fe ni in the nebula in mac 88136 sulfurization of si bearing fe ni metal is less pronounced and it produced troilite schreibersite and less abundant perryite two kinds of normal zoning and a reverse zoning trends of niningerite and both normal and reverse zoning of sphalerite were found in clasts and nodules in qingzhen the coexistence of normal and reverse zoning profiles in niningerite grains in the same meteorite strongly suggests that they formed before accretion in the parent body because an asteroidal metamorphic or an impact event in the parent body would have erased these contrasting profiles and destroyed the textural settings in contrast alabandite in mac 88136 shows only normal zoning with the fes content decreasing to 9 3 mol toward troilite indicating very slow cooling at low temperature

yamato 792947 793408 and 82038 the most primitive h chondrites with abundant refractory inclusions in this paper we report petrological and chemical data of the unusual chondritic meteorites yamato y 792947 y 93408 and y 82038 the three meteorites are very similar in texture and chemical composition suggesting that they are pieces of a single fall the whole rock oxygen isotopes and the chemical compositions are indicative ofh chondrites in addition the mineralogy and the abundances of chondrule types opaque minerals and matrices suggest that these meteorites are h3 chondrites they were hardly affected by thermal and shock metamorphism the degree of weathering is very low we conclude that these are the most primitive h chondrites h3 2 3 4 si known to date on the other hand these chondrites contain extraordinarily high amounts of refractory inclusions intermediate between those of ordinary and carbonaceous chondrites the distribution of the inclusions may have been highly heterogeneous in the primitive solar nebula the mineralogy chemistry and oxygen isotopic compositions of inclusions studied here are similar to those in co and e chondrites

extensional collapse of the northern taiwan mountain belt as an active collision zone between the luzon arc and the china continental margin the taiwan mountain belt particularly its south central part is undergoing crustal shortening and rapid uplift the northern part of the orogen is however subjected to crustal stretching and rifting as a result of flipping of subduction from the northwest facing luzon arc system to the south facing ryukyu arc system taiwan and its neighboring southern ryukyu used to be part of the rifted china continental margin before the collision started in late miocene time engineered by the northwest movement of the philippine sea plate in the past 5 m y the north south trending luzon arc obliquely overrode the northeast southwest trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from northeast to southwest following the southwest propagating collision the north dipping philippine sea plate which was subducting beneath the ryukyu arc also extended westward and caused flipping of subduction in the northern part of the collision orogen in consequence the orogen lost the compressive support by the colliding plates and became subjected to lithospheric stretching induced by the trench suction the collision orogen collapsed as a result of crustal thinning and its central part foundered into a deep submerged basin a whole spectrum of active tectonic scenarios ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence can be readily observed in the taiwan ryukyu area and provides a vivid example for the process of orogenic collapse

petrographic comparison of refractory inclusions from different chemical groups of chondrites twenty four refractory inclusions 40 230 m with average of 86 40 m were found by x ray mapping of 18 ordinary chondrites all inclusions are heavily altered consisting of finegrained feldspathoids spinel and ca pyroxene with minor ilmenite the presence of feldspathoids and lack of melilite are due to alteration that took place under oxidizing conditions as indicated by feo zno rich spinel and ilmenite the pre altered mineral assemblages are dominated by two types one rich in melilite referred to as type a like and the other rich in spinel referred to as spinel pyroxene inclusions this study and previous data show similar type and size distributions of refractory inclusions in ordinary and enstatite chondrites a survey of refractory inclusions was also conducted on allende and murchison in order to make unbiased comparison with their counterparts in other chondrites the predominant inclusions are type a and spinel pyroxene with average sizes of 170 130 m except for two mm sized inclusions in allende and 150 100 m in murchison the relatively larger sizes are partially due to common conglomerating of smaller nodules in both chondrites the survey reveals closely similar type and size distributions of refractory inclusions in various chondrites consistent with our previous data of other carbonaceous chondrites the petrographic observations suggest that refractory inclusions in various groups of chondrites had primarily formed under similar processes and conditions and were transported to different chondrite accreting regions heterogeneous abundance and distinct alteration assemblages of refractory inclusions from various chondrites could be contributed to transporting processes and secondary reactions under different conditions

ca al rich inclusions from the ningqiang meteorite continuous assemblages of nebular condensates and genetic link to type b inclusions the petrography and mineral chemistry of 110 ca al rich inclusions cais and 9 ca and or al rich amoeboid olivine aggregates aoas from the ningqiang carbonaceous chondrite are reported these cais are referred to as hibonite bearing and hibonite free melilite spinel rich type a and spinel pyroxene inclusions melilite is more gehlenitic in the hibonite bearing type as than in the other two types and all of them vary within a range of ak0 30 modal compositions of the three types of cais overlap with each other and make up a continuum with wide ranges of melilite spinel diopside the diopside occurs as rims on the cais or their individual concentric objects the 9 aoas contain spinel diopside anorthite in the centers of the aggregates the spinel grains rimmed by diopside in the centers are similar to the spinel pyroxene inclusions bulk compositions of these cais vary along the condensation trajectory with the hibonite bearing type as plotting at the beginning followed by hibonite free type as then by spinel pyroxene inclusions as temperature decreases bulk compositions of the aoas are close to the lowest temperature condensation trajectory except for a few with compact textures most of the type as and spinel pyroxene inclusions are fluffy aggregates probably pristine vapor solid condensates of the nebula the bulk compositions of the type as appear to overlap with the range of most melilite ti al clinopyroxene rich type b inclusions hence crystallization of liquids produced by melting the type as can form type b inclusions without significant evaporative loss of mgo or sio2 a few type bs have bulk compositions deviating from the range of their proposed precursors and may have suffered significant evaporation as suggested in previous studies

geology and tectonics of the ryukyu islands abstract the ryukyu islands are divided morphologically and geologically into three island groups north central and south ryukyus north central ryukyu represents the geological continuation of the outer belt of southwest japan composed of mesozoic eocene sedimentary sequences whereas south ryukyu is characterized by high pressure metamorphic rocks eocene volcanics and limestone and lower miocene sediments the geological and structural contrasts between north central and south ryukyus are conspicuous before the late miocene transgression covered the whole area the ryukyu islands have been established since then the successive developments of the goto tunghai senkaku basins since the paleogene of the okinawa trough since the miocene and of the grabens near the island group since the pliocene signify a southeastward shift of the basins in relation to the activity in the granite diapir zones accompanied by volcanism

using fossil leaves as paleoprecipitation indicators an eocene example estimates of past precipitation are of broad interest for many areas of inquiry including reconstructions of past environments and topography climate modeling and ocean circulation studies the shapes and sizes of living leaves are highly sensitive to moisture conditions and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations however when tested on extant forests this method has consistently overestimated precipitation we present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set the significant relationship that results in addition to having value for paleoclimatic reconstruction refines understanding of the long observed positive relationship between leaf area and precipitation seven precipitation estimates for the eocene of the western united states are revised as lower than previously published but remain far wetter than the same areas today abundant moisture may have been an important factor in maintaining warm frost free conditions in the eocene because of the major role of water vapor in retaining and transporting atmospheric heat

tectonic setting of western pacific marginal basins abstract global kinematics as well as magnetic anomalies of marginal basins with continental geology and paleomagnetic data as additional constraints are used to present a set of reconstructions of the western pacific marginal basins between 56 ma and the present at key periods 56 43 32 20 12 and 3 ma our model accounts for the rapid motion of exotic terranes along the whole of the western pacific convergent zone marginal basins appear to open in a great variety of tectonic settings the two extreme examples being the mariana trough where trench suction may be the predominant driving force and the south china sea where intracontinental deformation appears to be the major mechanism the study of marginal basins is a 3 d problem which must take into account the whole tectonic context subduction related tectonics in cross section and upper plate deformation in map view and not only a 2 d problem the classical trench arc back arc problem

plate collision and paleostress trajectories in a fold thrust belt the foothills of taiwan abstract field analyses of compressional faulting and folding in the foothills of western taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events two main compressional events have contributed to the present structure of the fold thrust belt stratigraphic data show that these events are plio pliocene in age older normal faulting indicates nnw sse extension across the chinesse passive continental margin during the neogene the two main compressional events of the taiwan collision correspond to similar fan shaped distributions of maximum compressive stress trajectories with a counterclockwise shift of 30 50 between the two events using the relationship between recent stress trajectories and the direction of recent plate motion as a guide we reconstruct the direction of plate convergence for the older event we suspect that the relative motion philippine sea plate eurasia has rotated counterclockwise of at least 35 45 in taiwan during collision this conclusion is in agreement with independent plate tectonic reconstructions several problems provide objectives to further tectonic and paleomagnetic studies including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost taiwan

the origin of type c inclusions from carbonaceous chondrites type c inclusions are plagioclase rich ca al rich inclusions found in carbonaceous chondrites they formed as solid condensates which were later melted in an event that destroyed the original condensate grains neither the melting event nor secondary alteration had a significant effect on bulk composition two stages in the condensation history can be discerned on the basis of major element bulk compositions as in type a inclusions the condensate phase assemblage originally consisted of melilite spinel perovskite hibonite type c s were however significantly enriched in spinel relative to unaltered portions of most type a s in contrast to type a s condensate grains of spinel and melilite in type c s reacted partially with a coexisting gas to produce anorthite diopside one half to two thirds of the silica now in type c inclusions was introduced by this process the reactions involving melilite and spinel that are predicted by equilibrium condensation calculations for a cooling gas of solar composition did not occur probably due to kinetic constraints type c s may be related to al rich chondrules in ordinary chondrites by the addition of olivine and albite bulk compositions of al rich chondrules in enstatite chondrites are consistent with the addition of orthopyroxene and albite to type c inclusions thus types a and c inclusions and al rich chondrules could represent sequences of condensates removed from interaction with the primitive solar nebula at progressively lower temperatures if al rich chondrules represent the high temperature component in chondritic material then type c inclusions rather than the more common subgroups of cais could be the true parents of chondrites

refractory inclusions in the prototypical cm chondrite mighei abstract refractory inclusions in the mighei cm2 meteorite are very abundant 35 being found in three thin sections of the meteorite the most common are pyroxene rimmed spinel rich inclusions that occur in a range of structural and textural types some inclusions are simple aggregates of crystals or rimmed crystals ranging from loose clusters of spinel grains to distended chains of pyroxene rimmed spinel knots others are more compact and may have experienced recrystallization or melting these include nodular spinel inclusions with polygonal granular textured spinel interiors and pyroxene rims ribbons of spinel in some cases with hibonite and or perovskite that are again rimmed by pyroxene and refractory spherules four inclusions are complex aggregates of several texturally distinct objects each collectively mighei inclusions are similar to those in murchison but appear to be somewhat more altered volatility fractionated and unfractionated trace element patterns similar to those found in refractory inclusions in other carbonaceous chondrites are represented in mighei inclusions and in addition some mighei inclusions have volatility fractionated pattern types not previously found in refractory inclusions in three of the complex aggregates fundamentally different trace element patterns are present within different portions of each inclusion meaning that these objects accreted from genetically different components that never equilibrated with one another subsequent to accretion bulk inclusion magnesium isotopic compositions show minor mass fractionation effects fmg values range from 2 3 to 7 5 but the average fmg value is indistinguishable from normal 1 8 1 2 there are no correlations between magnesium isotopic composition and textural type or trace element pattern type the diverse inclusion types in mighei represent a variety of origins and histories textures suggest that the nodular and banded inclusions may have experienced solid state recrystallization whereas the porous and chain like varieties and complex aggregates have not magnesium isotopic compositions and trace element abundances suggest that the mighei inclusions are unlikely to be evaporation residues and are more likely to be the products of condensation or recondensation processes

unusually abundant refractory inclusions from sahara 97159 eh3 a comparative study with other groups of chondrites abstract sixty eight refractory inclusions and fragments were found in two polished thin sections of the sahara 97159 eh3 chondrite indicative of the highest abundance of refractory inclusions 22 cm 2 or 0 06 vol in enstatite chondrites studied to date all of the inclusions are intensely altered mainly producing feldspathoids and albite cao depletion and minor ti rich compounds such as ti sulfides the alteration assemblages and feo poor spinel suggest that the reactions took place under reducing and sio 2 rich conditions this is consistent with the redox state of the host enstatite chondrite the presence of ti sulfides and low feo alteration phases distinguishes alteration of e chondrite refractory inclusions from that of carbonaceous and ordinary chondrites most of the inclusions are referred to as type a like 35 and spinel rich 26 respectively assuming melilite has been altered these inclusions could be analogues of individual concentrically zoned objects of fluffy melilite spinel rich type a and spinel pyroxene rich inclusions from carbonaceous chondrites such as the ningqiang cv anomalous and y 81020 co3 chondrites two inclusions consist mainly of ca pyroxene fine grained alteration products feldspathoids and albite and spinel they are probably altered fragments of ca pyroxene plagioclase rich type c inclusions assuming all plagioclase has been altered to produce the fine grained groundmass five other inclusions are hibonite and or corundum bearing similar to those reported in carbonaceous chondrites abundance ratios of various types of the inclusions from sahara 97159 are similar to those from ningqiang and y 81020 most of the observations including mineral assemblages mineral chemistry texture bulk compositions o isotopic compositions and ree patterns of the sahara inclusions suggest a common reservoir of refractory inclusions in enstatite ordinary and carbonaceous chondrites the apparent differences such as absence of melilite and anorthite rare wark lovering rim and small size can be explained by intense alteration due to large change of postformation environment of these inclusions size sorting and collision during transfer hence these differences are not inconsistent with the common reservoir model refractory inclusions in non carbonaceous chondrites may put additional constraints on origins of refractory inclusions and provide hints for a spatial relationship of their host meteorites

formation of orange hibonite as inferred from some allende inclusions we studied three fluffy type a refractory inclusions from allende that contain orange hibonite the melilite in the present samples is very al rich averaging ak6 ak14 and ak12 in the three samples studied hibonite in two inclusions unlike that in murchison has low rare earth element abundances of 10 ci in the other inclusion the hibonite melilite and perovskite have group ii like patterns the hibonite and melilite in all three inclusions studied have excess 26mg consistent with 26al 27al i 5 10 5 much of the hibonite and some of the spinel in these inclusions is corroded these phases are found enclosed in melilite but based on bulk compositions and phase equilibria hibonite should not be an early crystallizing phase in these inclusions we conclude that the hibonite and probably some of the spinel is relic reversely zoned melilite rounded spinel and isotopically heavy mg in the inclusions probably reflect reheating events that involved melting and evaporation alteration of the gehlenitic melilite gave rise to some rare phases including corundum and nearly pure cats pyroxene studies have shown that blue hibonite contains ti3 while orange hibonite does not ihinger and stolper 1986 beckett et al 1988 orange hibonite formed either under oxidizing conditions such as at oxygen fugacities at least seven orders of magnitude greater than that of a solar gas at 1700 k or under conditions reducing enough e g solar that it contained ti3 which was later oxidized in situ although v and ce oxides are volatile at the temperature and range of oxygen fugacities at which orange hibonite is known to be stable we find that a the hibonite is v rich 1 wt v2o3 and b there are no negative ce anomalies in allende hibonite this indicates that the hibonite did not form by condensation under oxidizing conditions in addition there are slight excesses of ti si cations relative to mg fe cations up to 0 1 of 0 8 cations per 19 oxygen anions probably reflecting the original presence of ti3 the results of this study strongly support the suggestion ihinger and stolper 1986 that allende hibonite originally formed under reducing conditions and was later oxidized oxygen fugacities within 2 3 orders of magnitude of that of a solar gas are implied otherwise strong ce and v depletions would be observed