an amoeboid olivine inclusion aoi in ck3 nwa 1559 comparison to aois in cv3 allende and the origin of aois in ck and cv chondrites an amoeboid olivine inclusion in ck3 nwa 1559 0 54 1 3 mm consists of a diopside rich interior approximately 35 vol and an olivine rich rim approximately 65 vol it is the first aoi to be described in ck chondrites the apparent paucity of these inclusions is due to extensive parent body recrystallization the aoi interior contains irregular 3 15 m sized al bearing diopside grains approximately 70 vol 2 20 m sized pores approximately 30 vol and traces of approximately 2 m plagioclase grains the 75 160 m thick rim contains 20 130 m sized ferroan olivine grains some with 120o triple junctions a few coarse 25 50 m sized patches of plagioclase with 2 18 m thick diopside rinds occur in several places just beneath the rim the occurrence of olivine rims around aoi 1 and around many aois in cv3 allende suggests that ck and cv aois formed by the acquisition of porous forsteritic rims around fine grained rimless cais that consisted of diopside anorthite melilite and spinel individual aois in carbonaceous chondrites may have formed after transient heating events melted their olivine rims as well as portions of the underlying interiors in aoi 1 coarse plagioclase grains with diopside rinds crystallized immediately below the olivine rim secondary parent body alteration transformed forsterite in the rims of cv and ck aois into more ferroan olivine some of the abundant pores in the interior of aoi 1 may have formed during aqueous alteration after fine grained melilite and anorthite were leached out chondrite groups with large chondrules tend to have large aois aois that formed in dust rich nebular regions where cv and ck chondrites later accreted tend to be larger than aois from less dusty regions

the age of the solar system redefined by the oldest pb pb age of a meteoritic inclusion the age of the solar system is defined by the formation of the first solid grains in the solar nebula pb pb age dating of these solids which were later trapped in a meteorite indicates that the solar system is 0 34 1 91 million years older than previously thought the age of the solar system can be defined as the time of formation of the first solid grains in the nebular disc surrounding the proto sun this age is estimated by dating calcium aluminium rich inclusions in meteorites these inclusions are considered as the earliest formed solids in the solar nebula their formation marks the beginning for several long and short lived radiogenic clocks that are used to precisely define the timescales of solar system events such as the formation and evolution of planetary bodies1 2 3 here we present the 207pb 206pb isotope systematics in a calcium aluminium rich inclusion from the northwest africa 2364 cv3 group chondritic meteorite which indicate that the inclusion formed 4 568 2 million years ago this age is between 0 3 refs 4 5 and 1 9 refs 1 6 million years older than previous estimates and is the oldest age obtained for any solar system object so far we also determined the 26al 26mg model age of this inclusion and find that it is identical to its absolute pb pb age implying that the short lived radionuclide 26al was homogeneously distributed in the nebular disc surrounding the proto sun from the consistently old ages in the studied inclusion we conclude that the proto sun and the nebular disc formed earlier than previously thought

16 o rich melilite in co3 0 chondrites possible formation of common 16 o poor melilite by aqueous alteration a problem of long standing is the origin of the high 17o 17o 0 52 18o values of melilite in the refractory inclusions of carbonaceous chondrites the spinel and usually also the diopside in the inclusions have primitive 17o 20 but in the widely studied cv3 chondrite allende the melilite commonly has a 17o of about 4 2 recent studies of oxygen diffusion coefficients in melilite and spinel have shown that the traditional model for altering the melilite diffusive exchange with the gas in the solar nebula cannot occur under plausible nebular scenarios because of increasing evidence for aqueous alteration of allende and other carbonaceous chondrites we tested the hypothesis that melilite alteration might occur during aqueous alteration by studying melilite in co chondrites showing variable degrees of alteration our results show that almost all melilite in co3 2 kainsaz and co3 3 ornans has 17o 15 whereas in co3 0 colony and inclusions in co3 0 yamato 81020 studied by itoh et al 2000 17o in the melilite is 20 with the exception of one unusual inclusion that has undergone two melting episodes we suggest that the o isotopic composition of the melilite is reset by dissolution of the primitive melilite and reprecipitation in the presence of h2o having a high 17o value similar to that inferred from studies of cv magnetite choi et al 1997 choi et al 2000 although alteration of melilite can produce phases such as nepheline andradite and hedenbergite it appears that depending on the composition of the microenvironment melilite present in a high energy state because of fine grain size dislocations other defects can dissolve and reprecipitate with an o isotopic composition intermediate between the initial composition and that of the h2o a possible implication of our study is that the slope 0 9 arrays observed in the minerals of refractory inclusions of many carbonaceous chondrites could be mainly the result of aqueous alteration

osmium isotopic homogeneity in the ck carbonaceous chondrites abstract variable proportions of isotopically diverse presolar components are known to account for nucleosynthetic isotopic anomalies for a variety of elements e g ca ti cr ni sr zr mo ru pd ba nd and sm in both bulk chondrites and achondrites however although large os isotopic anomalies have been measured in acid leachates and residues of unequilibrated chondrites bulk chondrites of various groups iron meteorites and pallasites exhibit os isotopic compositions that are indistinguishable from terrestrial or bulk solar isotopic abundances since the magnitude of nucleosynthetic anomalies is typically largest in the carbonaceous chondrites this study reports high precision os isotopic compositions and highly siderophile element hse concentrations for ten ck chondrites the isotope dilution concentration data for hse and high precision os isotope ratios were determined on the same digestion aliquots to precisely correct for radiogenic contributions to 186os and 187os while acid leached bulk unequilibrated carbonaceous chondrites show deficits of s process os components to the same extent as revealed by unequilibrated enstatite ordinary and rumuruti chondrites equilibrated bulk ck chondrites exhibit no resolvable os isotopic anomalies these observations support the idea that acid resistant carbon rich presolar grains such as silicon carbide sic or graphite are major carriers for nucleosynthetic isotopic anomalies of os the destruction of these presolar grains which are omnipresent in unequilibrated meteorites must have occurred during aqueous alteration and thermal metamorphism early in the ck chondrite parent body history the dispersal of ck chondrites along the iiiab iron meteorite isochron on a 187os 188os versus 187re 188os diagram with re os ratios from 0 032 to 0 083 in combination with the observed redistribution of other hse e g pt pd highlights the influence of parent body processes overprinted by effects of recent terrestrial alteration under the oxidizing conditions prevalent on the ck parent body evident from high abundances of magnetite and limited fe ni metal in ck chondrites these parent body processes made all isotopically anomalous os originally hosted in reduced presolar grains accessible the absence of os isotopic anomalies in ordinary enstatite and now also carbonaceous chondrites implies that the carriers of s and r process os must have been effectively homogenized across the region of chondrite formation and possibly even the entire solar protoplanetary nebula as suggested by the os isotopic compositions of iron meteorites and non anomalous ureilites except for a limited number of ureilites the relative proportions of presolar s and r process carriers of os and other elements such as w in chondrites and most other planetary bodies must have remained constant during all subsequent nebular and planetary processes which appears not to have been the case for other siderophile elements including mo ru and pd the existence of mo ru pd and other siderophile element isotopic anomalies thus appears to be in part controlled by the chemical properties of these elements e g volatility their host phase s e g sic graphite metal sulfides and the nature of the nebular or planetary processes experienced in the early solar system

a plagioclase olivine spinel magnetite inclusion from maralinga ck evidence for sequential condensation and solid gas exchange abstract we report a detailed petrography mineral chemistry and trace element study of matroc a large calcium aluminum rich inclusion cai 5 2 5 mm of irregular triangular shape the inclusion has a zonal structure the core consists of a porous plagioclase olivine ca rich pyroxene intergrowth with subordinate apatite its texture is meta gabbro like similar to other plagioclase olivine inclusions pois the mantle has variable thickness 0 1 1 5 mm and consists of a compact symplectitic intergrowth of spinel hercynite and plagioclase with abundant dispersed magnetite subordinate ca rich pyroxene and traces of sulfides the thin 5 50 m discontinuous crust of matroc consists mainly of plagioclase with some olivine and magnetite the mg fe phases of matroc are fe rich olivine has fa33 2 and high nio content similar to that in the host rock ca rich pyroxene has much lower tio2 and cr2o3 contents than that of the host chondrite and plagioclase is an55 an74 magnetites have variable compositions are poorer in al2o3 and cr2o3 and richer in nio than those in the host spinels have also variable compositions rich in feo nio and zno despite their different mineralogy both core and mantle have bulk trace element abundances similar to those in average group ii cais however the mantle is richer in nb and u and poorer in eu be b sr and li than the core all minerals have high trace element contents minerals in the core show signs of incomplete equilibration of trace elements within and between them mantle minerals are far from equilibrium with each other and the bulk system spinel and anorthite carry the trace element signature of their precursor melilite or hibonite and magnetite contains large amounts of a heterogeneously distributed remnant extremely rich in trace elements obscurite possibly of a former perovskite inclusion matroc has a complex history the poi core probably formed by reaction of an unknown precursor s of condensation origin with a vapor to form olivine plagioclase clinopyroxene apatite and an unknown phase s that vanished leaving abundant void space the spinel rich mantle is also a secondary mineral assemblage that formed by breakdown of and solid vapor reactions with a precursor or precursors possibly melilite or hibonite the abundant magnetite formed by reaction of perovskite with an oxidizing vapor and by precipitation from such a vapor all phases of the inclusion experienced the metasomatic addition of fe ni and moderately volatile elements such as v be li cr and mn similar to all other constituents of the maralinga ck chondrite phases in matroc and in the host rock are close to equilibrium in the distribution of fe mg ni and mn but far from equilibrium in the distribution of m 3 and m 4 ions the minor and trace element abundances in the magnetite of the host rock and of matroc preclude an origin by oxidation of a metal precursor

petrography and oxygen isotopic compositions in refractory inclusions from co chondrites fine grained ca al rich inclusions fgis in yamato 81020 co3 0 and kainsaz co3 1 co3 2 chondrites have been studied by secondary ion mass spectrometry the fgis from yamato 81020 consist of aggregates of hibonite spinel melilite anorthite diopside and olivine grains with no petrographic evidence of alteration in contrast the fgis from kainsaz commonly contain alteration products such as nepheline from replacement textures and chemical compositions of altered and unaltered fgis we conclude that the alteration products formed by decomposition of melilite and anorthite all phases in the yamato 81020 fgis are enriched in 16o with 17 18o 40 except for one fgi that experienced melting oxygen isotopic compositions of melilite anorthite some spinel and diopside in kainsaz fgis changed from 17 18o 40 toward 0 by aqueous alteration alteration products in fgis are depleted in 16o relative to primary phases with 17 18o 0 these results show that fgis in co chondrites commonly had 16o rich compositions in the solar nebula the original 16o rich fgis were modified to 16o poor compositions during aqueous alteration in the parent body

tectonic interpretations of holocene marine terraces east coast of coastal range taiwan abstract the east coast of the coastal range in taiwan is well known for its multiple holocene marine terraces and their very rapid uplift the study area extends from hualien to taitung over ca 150 km of coastline here we present some new data on the age and height of holocene marine terraces and we discuss their significance for holocene coastal tectonics the holocene marine terrace sequence is subdivided into a maximum of 10 steps the highest and oldest terrace mostly underlain by transgressive deposits represents the sea level position of the culmination of holocene sea level rise and reaches up to ca 80 m above sea level transgressive deposits are radiocarbon dated at several sites back to ca 13 000 yr bp the lower terraces are mostly erosional ones overlain by thin coral beds in situ less than 1 m thick and indicate successive lowering of relative sea level during the late holocene the uplift rate of the coast is very high ranging from 5 to 15 m ka three tectonic subregions a c are identified based on the pattern of marine terrace features and uplift rate the presence of many steps during holocene time implies that intermittent uplifts associated with large earthquakes at intervals of one thousand to several hundred years have repeatedly occurred in this coastal area but with different time and amount at each subregion the uplift of subregion a resulted from an onshore active fault milun fault causative faults for the uplift of the subregions b and c are not identified offshore active faults striking obliquely to the coastline appear to be causative faults

a geophysical study of the manila trench luzon philippines 1 crustal structure gravity and regional tectonic evolution the manila trench subduction zone is an active convergent plate margin between the south china sea and the northern philippines the trench trends northerly and is associated with a volcanic arc an east dipping benioff zone beneath luzon and a well developed fore arc basin system the luzon trough fore arc basins lie landward of the manila trench and contain up to 4 5 km of cenozoic sediments offscraping and accretion of turbidite sediments deposited in the manila trench have resulted in the upbuilding and outbuilding of an accretionary prism which forms the seaward margin of the fore arc basin system the uplifted zambales ophiolite and its offshore extension form the landward side of the fore arc basin multichannel seismic reflection profiles reveal that folding and thrust faulting of trench strata occur at the base of the trench slope the major structural decollement at the manila trench usually forms near the unconformity separating the hemipelagic sediments from the turbidite sediments subduction and perhaps underplating of the basal hemipelagic trench sediments accompany the deformation and accretion of the overlying clastic deposits faulting and uplift occur within a narrow zone of the fore arc where seamounts associated with the relict spreading center of the south china sea basin have presumably been subducted north of lingayan gulf the fore arc is disrupted by active fault systems that trend north and northwest offshore from the luzon central valley and from the southern cordillera central based on regional geological and tectonic observations we infer that subduction probably began at the manila trench in late oligocene to middle miocene time the long term average convergence rate at the manila trench is estimated to be between 10 and 20 mm yr and may be slowing in the north owing to the collision of taiwan with eurasia

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

evidence of large prehistoric offshore earthquakes deduced from uplifted holocene marine terraces in pangasinan province luzon island philippines abstract uplifted holocene marine terraces in pangasinan province westernmost luzon island philippines are reported here for the first time as geomorphic evidence of large prehistoric offshore earthquakes we recognized up to three holocene terrace steps elevations of shoreline angles are ti 1 to 5 m tii 2 to 7 m and tiii 4 to 11 m above mean sea level amsl the lateral variation in the elevation of terrace steps indicates differential uplift along the coast the staircase topography characterized by horizontal abrasion platforms meter scale terrace risers and wave cut notches suggests that these geomorphic features were formed by large coseismic uplift events terrace morphology and radiocarbon ages further suggest that at least three coseismic coastal uplift events have occurred since the culmination of the post glacial sea level rise 6000 years ago we interpret tiii to be the holocene transgressive surface 6000 ybp and estimated a maximum uplift rate of 1 7 mm yr which is almost the same as the late pleistocene uplift rate of 1 3 mm yr we infer that proximity to offshore seismic sources has contributed to the deformation pattern of holocene terraces and variation in the number of terrace steps uplift patterns of marine terraces also suggest that the magnitude and location of prehistoric earthquakes may have varied between individual coseismic uplift events we conducted simple elastic dislocation modeling to evaluate the source parameters of the causative faults our preliminary models show that a landward dipping offshore reverse fault located at the base of a steep slope separating the fore arc basin and continental shelf could be responsible for coastal uplift along the western pangasinan peninsula

hydrothermal experiments on alteration of ca al rich inclusions cais in carbonaceous chondrites implication for aqueous alteration in parent asteroids carbonaceous chondrites contain ca al rich inclusions cais which consist mainly of refractory minerals including gehlenite spinel perovskite and hibonite which are predicted to be the first phases formed from early solar nebula on the basis of thermodynamic calculations however many cais contain secondary minerals such as nepheline calcite and phyllosilicates the formation process of secondary minerals in cais is still controversial whether they were produced by the reaction with solar nebula or by aqueous alteration in parent asteroids we performed hydrothermal experiments on gehlenite spinel and diopside which are common in cais in carbonaceous chondrites to study aqueous alteration in parent asteroids mixtures of gehlenite with sio2 and or al2o3 and those of sio2 with al2o3 were also employed to study products of these systems which have a close relationship to crystallization of secondary minerals in cais in fluid in parent asteroids hydrogrossular calcite and amorphous al si were obtained from gehlenite by hydrothermal experiments whereas both spinel and diopside escaped alteration suggesting that gehlenite is the weakest mineral among these refractory minerals against alteration this result is consistent with observation of cais analcime nepheline hydrate and tobermorite were obtained from the runs for mixtures of gehlenite with sio2 whereas the products from mixtures of al2o3 with sio2 were analcime nepheline hydrate and hydrosodalite these results suggest that the alteration process of gehlenite is as follows 1 gehlenite was dissolved by fluid in chondrite parent asteroids to release ca al and si from the surface 2 co32 in fluid reacted with ca to crystallize calcite 3 na al and si in fluid crystallized nepheline hydrate hydrosodalite and or analcime 4 ca al and si in fluid crystallized hydrogrossular without co32 and excess ca and si crystallized ca si hydrate such as tobermorite heating experiments on several minerals obtained through hydrothermal experiments were also performed to study thermal metamorphism in parent asteroids hydrogrossular was converted into hydrogrossular with a lower h2o content and analcime and nepheline hydrate were converted into nepheline tobermorite is known to be converted into wollastonite with increasing temperature the results of experimental studies suggest that most secondary minerals found in cais in carbonaceous chondrites were produced from gehlenite by aqueous alteration and the subsequent thermal metamorphism in parent asteroids

u series dates of pleistocene corals and their implications to the paleo sea levels and the vertical displacement in the central philippines abstract results of high precision alpha spectrometric 230th 234u dating of hermatypic corals in palawan in western philippines and cebu bohol and panglao islands in the central philippines confirm the presence of mis 5e reef terraces at 2 to 13 m above the present mean sea level similar to stable regions this suggests the relative vertical stability of the islands since the last interglacial period in panglao island the elevation of the 5e terrace increases to the northeast indicating tilting of the island to the southwest the continued sense of uplift since at least the last interglacial is indicated by the similarity in the spatial variation of middle holocene tidal notch a 5c terrace though less developed is also recognized in panglao island along the san isidro coast the inner margins of 5c and 5e terraces are at elevations of 5 and 7 1 8 m respectively and the difference in altitude between the terraces is only ca 2 3 m assuming that the sea level during mis 5e was 3 6 m above the present sea level sea level at mis 5c is estimated to be equal to or slightly higher than the present mean sea level

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

fluid rock interactions in the lower oceanic crust thermodynamic models of hydrothermal alteration rocks from the lower oceanic crust show both petrologic and isotopic evidence for extensive alteration by circulating hydrothermal fluids derived from seawater deeply circulating fluids may have a substantial but as yet largely undetermined impact on the thermal regime of spreading centers magmatic processes at mid ocean ridges and elemental fluxes at ridge hydrothermal systems in the present study the consequences of water rock interactions during the penetration of seawater into hot lower oceanic crust were investigated using thermodynamic reaction path models alteration assemblages predicted for reaction of an evolving seawater with olivine gabbro gabbronorite and troctolite during heating from 300 to 900 c closely resemble alteration assemblages observed in rock samples from the lower oceanic crust these assemblages include sodic plagioclase actinolite diopsidic clinopyroxene epidote chlorite prehnite analcime quartz at lower temperatures 300 500 c and plagioclase hornblende diopside chlorite trace magnetite at intermediate temperatures 500 700 c the relative abundances of these alteration products show much greater variation with temperature than with water rock w r ratio indicating that variations in the amounts of hydrated minerals such as amphiboles may not be an accurate indication of the w r ratio experienced by rocks in the lower crust since the same amount of fluid may produce widely differing amounts of amphibole at slightly different temperatures depending on the temperature of interaction some rocks in the lower oceanic crust may have experienced much higher w r ratios than has previously been proposed based on the amount of amphibole present at higher temperatures 750 900 c the models predict that very little alteration occurs before the fluid equilibrates with the rock producing only trace amounts of amphibole as an alteration phase with the remainder of the rock retaining its igneous mineral composition essentially unchanged this result suggests that extensive penetration of rocks by aqueous fluids may occur in the lower ocean crust at temperatures 700 c and leave very little conspicuous petrologic evidence for their presence such cryptic alteration is consistent with isotopic evidence for hydrothermal alteration of oxygen and sr isotopes by seawater in lower ocean crust rock samples which otherwise retain their igneous compositions and textures taken together the model results allow for much more extensive circulation of fluids in the lower oceanic crust and at much higher temperatures than has been proposed by previous studies based on petrologic interpretations

oxygen and magnesium isotope compositions of calcium aluminum rich inclusions from rumuruti r chondrites abstract we report oxygen and magnesium isotope compositions of ca al rich inclusions cais from several rumuruti r chondrites measured in situ using a cameca ims 1280 ion microprobe on a three isotope oxygen diagram 17o vs 18o compositions of individual minerals in most r cais analyzed fall along a slope 1 line based on the variations of 17o values 17o 17o 0 52 18o within individual inclusions the r cais are divided into i 16o rich 17o 23 26 ii uniformly 16o depleted 17o 2 and iii isotopically heterogeneous 17o ranges from 25 to 5 one of the hibonite rich cais h030 l has an intermediate 17o value of 12 and a highly fractionated composition 18o 47 we infer that like most cais in other chondrite groups the r cais formed in an 16o rich gaseous reservoir the uniformly 16o depleted and isotopically heterogeneous cais subsequently experienced oxygen isotope exchange during remelting in an 16o depleted nebular gas possibly during r chondrite chondrule formation and or during fluid assisted thermal metamorphism on the r chondrite parent asteroid three hibonite bearing cais and one spinel plagioclase rich inclusion were analyzed for magnesium isotope compositions the cai with the highly fractionated oxygen isotopes h030 l shows a resolvable excess of 26mg 26mg corresponding to an initial 26al 27al ratio of 7 10 7 three other cais show no resolvable excess of 26mg 26mg the absence of 26mg in the spinel plagioclase rich cai from a metamorphosed r chondrite nwa 753 r3 9 could have resulted from metamorphic resetting two other hibonite bearing cais occur in the r chondrites nwa 1476 and nwa 2446 which appear to have experienced only minor degrees of thermal metamorphism these inclusions could have formed from precursors with lower than canonical 26al 27al ratio

type c ca al rich inclusions from allende evidence for multistage formation abstract the coarse grained igneous anorthite rich type c cais from allende studied 100 160 6 1 72 3529 40 cg5 abc ts26 and 93 have diverse textures and mineralogies suggesting complex nebular and asteroidal formation histories cais 100 160 6 1 72 and 3529 40 consist of al ti diopside fassaite 13 23 wt al 2 o 3 2 14 wt tio 2 na bearing akermanitic melilite 0 1 0 4 wt na 2 o ak 30 75 spinel and fine grained 5 10 m anorthite groundmass most of the fassaite and melilite grains have lacy textures characterized by the presence of abundant rounded and prismatic inclusions of anorthite 5 10 m in size lacy melilite is pseudomorphed to varying degrees by grossular monticellite and pure forsterite or wollastonite cai 6 1 72 contains a relict type b cai like portion composed of polycrystalline gehlenitic melilite ak 10 40 fassaite spinel perovskite and platinum group element nuggets the type b like material is overgrown by lacy melilite and fassaite some melilite and fassaite grains in cais 100 and 160 are texturally similar to those in the type b portion of 6 1 72 cais abc and ts26 contain relict chondrule fragments composed of forsteritic olivine and low ca pyroxene cai 93 is overgrown by a coarse grained igneous rim of pigeonite augite and anorthitic plagioclase these three cais contain very sodium rich akermanitic melilite 0 4 0 6 wt na 2 o ak 63 74 and cr bearing al ti diopside up to 1 6 wt cr 2 o 3 1 23 wt al 2 o 0 5 7 wt tio 2 melilite and anorthite in the allende type c cai peripheries are replaced by nepheline and sodalite which are crosscut by andradite bearing veins spinel is enriched in feo the cai fragment cg5 is texturally and mineralogically distinct from other allende type cs it is anorthite poor and very rich in spinel poikilitically enclosed by na free gehlenitic melilite ak 20 30 fassaite and anorthite neither melilite nor pyroxene have lacy textures secondary minerals are absent the al rich chondrules 3655b 2 and 3510 7 contain aluminum rich and ferromagnesian portions the al rich portions consist of anorthitic plagioclase al rich low ca pyroxene and cr bearing spinel the ferromagnesium portions consist of fosteritic olivine low ca pyroxene and opaque nodules we conclude that type c cais 100 160 6 1 72 and 3529 40 formed by melting of coarse grained type b like cais which experienced either extensive replacement of melilite and spinel mainly by anorthite and diopside traces of secondary na bearing minerals e g nepheline or sodalite might have formed as well or addition of silica and sodium during the melting event cg5 could have formed by melting of fine grained spinel melilite cai with melilite and spinel partially replaced anorthite and diopside cais abc 93 and ts 26 experienced melting in the chondrule forming regions with addition of chondrule like material such as forsteritic olivine low ca pyroxene and high ca pyroxene anorthite rich chondrules formed by melting of the al rich type c cai like precursors mixed with ferromagnesian type i chondrule like precursors the allende type c cais and al rich chondrules experienced fluid assisted thermal metamorphism which resulted in pseudomorphic replacement of melilite and anorthite by grossular monticellite and forsterite 100 160 6 1 72 3592 40 or by grossular monticellite and wollastonite abc 93 ts 26 the pseudomorphic replacement was followed or accompanied by iron alkali metasomatic alteration resulting in replacement of melilite and anorthite by nepheline and sodalite enrichment of spinel in feo and precipitation of salite hedenbergite pyroxenes wollastonite and andradite in fractures and pores in and around cais

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

silicate darkening in the kobe ck chondrite evidence for shock metamorphism at high temperature the kobe ck4 chondrite like most metamorphosed ck chondrites exhibits pronounced silicate darkening of matrix and chondrule mesostases our petrographic and scanning electron microscopic study reveals that the matrix of kobe consists mostly of intermixtures of two types of fine grained olivine one forms subhedral to anhedral normal crystals the other fills interstices of the subhedral to anhedral olivine crystals exhibiting a complex network of veinlets the latter type of olivine contains high densities of small spherical vesicles 0 05 3 m in diameter and grains 0 05 5 m of magnetite and pentlandite as well as round to anhedral grains 1 10 m of plagioclase low ca pyroxene diopside and chlorapatite the vesicular olivine is particularly abundant in regions of matrix that exhibit a relatively high degree of darkening and commonly fills chondrule mesostases the vesicular olivine is clearly the principal cause of the silicate darkening in kobe the internal texture of the vesicular olivine closely resembles those of local melts produced from the matrices of experimentally and naturally shocked carbonaceous chondrites the occurrence and texture of the vesicular olivine suggest that it resulted from recrystallization of partially melted matrix olivine by shock kobe exhibits light shock effects in olivine that are consistent with shock stage s2 that is too low to explain the occurrence of olivine melting we suggest that the vesicular olivine in kobe was produced by shock metamorphism at a relatively mild shock pressure 600 c thus it is probable that the shock effects in olivine manifest as fracturing and deformation were relatively minor but heating was strong enough to cause partial melting of matrix olivine

an isotopic and petrologic study of calcium aluminum rich inclusions from co3 meteorites we have studied the mineralogy and petrology of 229 calcium aluminum rich inclusions cais from ten co3 meteorites of petrologic types 3 0 3 7 subsets of these inclusions were measured by ion probe for magnesium calcium and titanium isotopes and ree abundances most cais from co3 meteorites fall into three major types 1 melilite rich inclusions which also contain spinel hercynite perovskite and occasionally hibonite 2 spinel pyroxene inclusions and 3 hibonite hercynite inclusions in addition several isolated hibonite grains two grossite caal 4o 7 bearing cais two hibonite fassaite microspherules and one anorthite spinel pyroxene inclusion were found cais from co3 meteorites exhibit all of the ree patterns commonly seen in inclusions from cv3 and cm2 chondrites most exhibit evidence of 26 ai and many have inferred 26 ai 27 ai o 5 10 5 the relative abundances of different types of cais in co3 chondrites differ from those in cv3 and cm2 chondrites cais in co3 chondrites have experienced considerable secondary alteration both before and after accretion signatures of nebular alteration include wark lovering rims and the high fe contents in spinels from all hibonite hercynite inclusions occasionally melilite and anorthite show evidence of nebular alteration to feldspathoids and pyroxene the magnesium aluminum systematics of some melilite rich inclusions were apparently disturbed prior to final accretion of the parent body parent body alteration is indicated by correlations between cai characteristics and the petrologic type of the host meteorite spinel in melilite rich and coarse grained spinel pyroxene inclusions becomes more fe rich with the development of relatively homogeneous hercynitic spinel 50 60 mol in cais from metamorphic grades 3 4 perovskite has been converted to ilmenite in types 3 4 melilite rich inclusions are abundant in co3 0 3 3 meteorites rare in 3 4 meteorites and absent meteorites of types 3 5 3 7 melilite rich cais are probably replaced by inclusions rich in feldspathoids pyroxene and fe rich spinel isotopic disturbance of the magnesium aluminum systematics may be more severe in higher petrologic types hibonite seems to be unaffected by this level of metamorphism three isotopically unusual inclusions were found one single crystal hibonite isna sp16 has a ree pattern strongly depleted in ce and y 26 ai 27 ai o 2 4 0 3 10 5 and mass fractionated calcium f ca 12 2 amu but no resolvable nuclear anomalies in neutron rich calcium isotopes the ree pattern which is thought to reflect nebular conditions and mass fractionated calcium indicative of evaporation are similar to those of the fun inclusion hal and related hibonites indicating similar formation conditions the absence in isna sp16 of the nuclear anomalies observed in hal and the difference in 26 ai 27 ai o between hal and isna sp16 indicate that the processes that produced hal type hibonites operated on diverse materials two hibonite bearing microspherules colony sp1 and alh82101 sp15 exhibit nearly flat ree patterns with negative europium anomalies and slightly negative 26 mg alh82101 sp15 has resolved excesses of 48 ca and 50 ti these characteristics are similar to those of previously described microspherules from murchison and lance implying that the microspherules formed via a single process from related but not identical source materials

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

replacement textures in cai and implications regarding planetary metamorphism textural and chemical features of five coarse grained calcium aluminum rich inclusions from the allende meteorite indicate that some of the melilite in these inclusions was formed by a secondary metamorphic event and not by primary crystallization from a melt or by a sequential nebular condensation process these inclusions contain embayed pyroxene surrounded by melilite physically separated pyroxene crystals are often in optical continuity indicating that they were once part of larger single crystals that have been partly replaced by melilite other evidences of metamorphism include reaction textures between melilite and spinel and metamorphic textures such as kink band like features lobate sutured grain boundaries and 120 triple points this type of metamorphic process requires the addition of ca which we propose came from calcite or by introduction of a fluid phase we believe that the most likely environment for this metamorphic process is on a small planetary body and not in the solar nebula the results of this study are compatible with oxygen isotopic heterogeneities within cai and provide a mechanism for producing lower temperature alteration phases and the rim phases found in these inclusions we conclude that planetary processes must thus be considered in the formation history of cai and that it is necessary to reconsider the classification system of these objects in light of the replacement process proposed here

origin of zoned fine grained inclusions in the allende meteorite many fine grained ca al rich inclusions in the allende meteorite show a consistent pattern of mineralogic and textural zonation the center zone a consists mostly of spinel nepheline al diopside and salite with minor amounts of olivine sodalite grossular anorthite perovskite and ilmenite in most inclusions these minerals occur as loosely packed discrete anhedral to subhedral grains with only minor intergrowth between phases in the others zone a is made of 5 to 30 m sized spinel centered multi rimmed objects and of finer grained loosely packed interstitial material the intermediate zone b is characterized by the presence of hedenbergite and andradite in addition to the minerals which occur in zone a partially filling voids one type of outer zone c consists mostly of intergrown olivine and nepheline with small ilmenite grains enclosed the other type of zone c consists of symplectic texture with spinel rimmed by nepheline or anorthite rimmed by al diopside the textural and mineralogical similarity of zone a except for the rimmed spinel objects to altered areas of coarsegrained melilite rich cais suggests that a similar open system alteration affected the fine grained inclusions and that zone a s contained melilite before being completely altered to anorthite grossular nepheline and sodalite by comparing the mineralogies before and after the alteration some ca must have evaporated from and si fe na and cl condensed onto the inclusions under conditions of low temperatures 1000 k and or at ho ratios lower than the cosmic abundance ca is more volatile than si due to the formation of gaseous ca hydroxides the thermodynamic stability of minerals in zones a and b also indicates alteration at temperatures less than 1000 k the mode of occurrence of hedenbergite and andradite in zone b implies that they are condensates deposited on the edge of zone a it is likely that the ca migrating out of the center of the inclusions and the si and fe migrating inward from the surrounding nebular gas coprecipitated according to the thermodynamic stability of these minerals zone c on the other hand most likely existed even before alteration surrounding what is now zone a however the mineralogy of zone c appears to have changed by alteration the zone c consisting of olivine nepheline and ilmenite was probably a spinel rich belt mantling the inclusion

chondrules in ck carbonaceous chondrites and thermal history of the cv ck parent body ck chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6 it is commonly reported than 15 vol of ck4 6 samples are composed of chondrules the modal abundance of chondrules estimated here for 18 ck3 6 including 5 ck3s ranges from zero totally recrystallized to 50 5 although almost all chemically re equilibrated with the host matrix we recognized in ck3s and tanezrouft tnz 057 ck4 up to 85 of chondrules as former type i chondrules mean diameters of chondrules range from 0 22 to 1 05 mm for karoonda ck4 and tnz 057 ck4 respectively up to 60 of chondrules in ck3 4 are surrounded by igneous rims from 20 m to 2 mm width zoned olivines were found in unequilibrated chondrules from dag 431 ck3 an nwa 4724 ck3 8 nwa 4423 ck3 9 and tnz 057 ck4 we modeled fe mg interdiffusion profiles measured in zoned olivines to evaluate the peak metamorphic temperatures and time scales of the ck parent body metamorphism and proposed a two stage diffusion process in order to account for the position of inflection points situated within chondrules time scales inferred from fe mg interdiffusion in olivine from unequilibrated chondrules are on the order of tens to a hundred of thousand years from 50 to 70 000 years for peak metamorphic temperatures of 1140 and 920 k respectively these durations are longer than what is commonly accepted for shock metamorphism and shorter than what is required for nuclide decay using the concept of a continuous cv ck metamorphic series which is reinforced by this study we estimated peak metamorphic temperatures 850 k for cv 850 920 k for ck3 and 920 1140 k for ck4 6 chondrites considering a duration of 70 000 years

the fractal geometry of the surface ruptures of the 1999 chi chi earthquake taiwan summary the 1999 september 20 chi chi earthquake is the largest seismic event which occurred in the island during the twentieth century available seismic data relative to this earthquake are of high quality and surface ruptures identified as features associated to the chelungpu fault can be clearly observed at the surface and precisely mapped we calculated the fractal dimension d and b value of gutenberg richter law for 6 month aftershocks of the chi chi earthquake for the fault area and find that the surface ruptures exhibit self similar geometry only within specific ruler intervals the d values of the surface ruptures reflect the fault slip and geometry at depth more importantly the small size aftershocks seem more likely to occur within high d value and high b value areas whereas small d value and small b value areas have a high potential for medium and large size aftershocks

the identification of group ii inclusions in carbonaceous chondrites by electron probe microanalysis of perovskite abstract group ii ca al rich inclusions cais which are relatively depleted in super refractory lithophile trace elements sre e g er lu sc zr y hf formed from nebular or interstellar reservoirs depleted in sre enriched dust their unusual chemistry preserves a record of widespread but incompletely understood fractionation processes in the primitive solar nebula we demonstrate that because group ii inclusions have anomalously high ti sre ratios they can be identified by electron probe microanalysis epma of perovskite a host for ti and several sre perovskites in group ii allende cais generally contain 0 25 wt zro2 the y content of perovskite also can be used to identify group ii inclusions by this technique inclusions with zr y poor perovskite in principle need not be depleted in sre if they contain other phases suitably enriched in sre but an analysis of sre carriers in allende inclusions and bulk compositions of cais shows that in practice this factor does not invalidate the epma technique for identifying group ii cais epma of perovskite in eight allende inclusions demonstrates that 75 of fine grained cais i e spinel rich complex cais are group ii inclusions in agreement with their abundance as determined by bulk trace element analyses of 24 cais a spinel rich nodule in a rimmed olivine aggregate contains zr y poor perovskites evidence that similar nodules which occur in 25 of olivine rich allende inclusions are the group ii ree carrier in olivine rich inclusions that have highly fractionated trace element patterns i e fractionated aoas

magnetite in the unequilibrated ck chondrites implications for metamorphism and new insights into the relationship between the cv and ck chondrites bulk isotopic and elemental compositions of cv and ck chondrites have led to the suggestion that both originate from the same asteroid it has been argued that magnetite compositions also support this model however magnetite has been studied almost exclusively in the equilibrated type 4 6 cks magnetite in seven unequilibrated cks analyzed here is enriched in mgo tio2 and al2o3 relative to the equilibrated cks suggesting that magnetite compositions are affected by metamorphism magnetite in cks is compositionally distinct from cvs particularly in abundances of cr2o3 nio and tio2 although there are minor similarities between cv and equilibrated ck chondrite magnetite this is contrary to what we would expect if the cvs and cks represent a single metamorphic sequence cv magnetite should resemble ck3 magnetite as both were metamorphosed to type 3 conditions oxygen fugacities and temperatures of cvox and ck chondrites are also difficult to reconcile using existing cv ck parent body models mineral chemistries which eliminate issues of bulk sample heterogeneity provide a reliable alternative to techniques that involve a small amount of sample material cv and ck chondrite magnetite has distinct compositional differences that cannot be explained by metamorphism

oman diopsidites a new lithology diagnostic of very high temperature hydrothermal circulation in mantle peridotite below oceanic spreading centres abstract mafic ultramafic dykes scattered in the mantle section of ophiolites are generally crystallisation products from common silicate melts in the frame of a global survey of these melt migration relics in the oman mantle harzburgites we discovered a peculiar lithology made essentially of pure diopside 0 95 m g m g f e total 1 whose characteristics do not match a magmatic or mantle origin arguments against a magmatic or mantle origin for these diopsidites combine compositional and textural evidence in spite of their refractory composition they are strongly depleted in cr cr2o3 0 2 wt by the same way other minor elements al ti na and rare earth elements have peculiarly low abundances and plot away from magmatic differentiation trends in a few samples the paragenetic association includes pure anorthite an up to 0 99 minor amounts of forsterite fo 0 95 or traces of andradite when not deformed the diopsides are automorphic and their texture points to metamorphic growth in a matrix composed of antigorite and or carbonate diopsidites have textures reminiscent to that of skarns developing in contact metamorphic halos or that of rodingite frequently present in the serpentine bodies of the ophiolitic crust they frequently appear as dykes former cracks with a few mm to few tens of cm wide transitional zones which contain high amounts of hydrous minerals between the diopsidite facies and its host rock the diopsidites are not randomly distributed in the oman ophiolite being more abundant near former asthenospheric diapirs emplaced at shallow depth in the lithosphere we interpret the diopsidites as the footprint of very high temperature circulation of seawater and carbonated fluids 800 c which may have leached plagioclase rich lithologies before penetrating the mantle as shown by a well developed positive eu anomaly our data confirm the prediction of mccollom and shock t m mccollom e l shock fluid rock interactions in the lower oceanic crust thermodynamic models of hydrothermal alteration j geophys res 103 b1 1998 547 575 who proposed that common anhydrous minerals like pyroxene plagioclase and olivine may crystallise from high temperature fluids intermediate between silicate melts and supercritical water this confirms that there is no clear cut thermal and chemical boundary between the fields of magmatic and hydrothermal crystallisations

aluminian low ca pyroxene in a ca al rich chondrule from the semarkona meteorite a ca al rich chondrule labeled g7 from the semarkona ll3 0 ordinary chondrite oc consists of 73 vol glassy mesostasis 22 vol skeletal forsterite 3 vol fassaite i e al ti diopside and 2 vol al rich low ca pyroxene the latter phase which contains up to 16 3 wt al 2 o 3 is among the most al rich low ca pyroxene grains ever reported it is inferred that 20 of the tetrahedral sites and 13 of the octahedral sites in this grain are occupied by al approximately parallel optical extinction implies that the al rich low ca pyroxene grains are probably orthorhombic consistent with literature data that show that al 2 o 3 stabilizes the orthoenstatite structure relative to protoenstatite at low pressure the order of crystallization in the chondrule was forsterite al rich low ca pyroxene and fassaite the residual liquid vitrified during chondrule quenching phase relationships indicate that for a g7 composition liquid at equilibrium spinel and anorthite should crystallize early and orthopyroxene should not crystallize at all the presence of al rich orthopyroxene in g7 is due mainly to the kinetic failure of anorthite to crystallize this failure was caused by quenching of the g7 precursor droplet aluminum preferentially enters the relatively large b tetrahedra of orthopyroxene because only one tetrahedral size occurs in fassaite this phase contains higher mean concentrations of al 2 o 3 than the al rich orthopyroxene 17 8 and 14 7 wt respectively chondrule g7 may have formed by remelting an amoeboid olivine inclusion that entered the oc region of the solar nebula during an episode of chondrule formation

determination of the petrologic type of cv3 chondrites by raman spectroscopy of included organic matter abstract this paper reports the first reliable quantitative determination of the thermal metamorphism grade of a series of nine cv3 chondrites allende axtell bali mokoia grosnaja efremovka vigarano leoville and kaba the maturity of the organic matter in matrix determined by raman spectroscopy has been used as a powerful metamorphic tracer independent of the mineralogical context and extent of aqueous alteration this tracer has been used along with other metamorphic tracers such as fe zoning in type i chondrules of olivine phenocrysts presolar grain abundance and noble gas abundance bulk and p3 component the study shows that the petrologic types determined earlier by induced thermoluminescence were underestimated and suggests the following values pt allende axtell 3 6 pt bali mokoia grosnaja 3 6 pt efremovka leoville vigarano 3 1 3 4 pt kaba 3 1 the most commonly studied cv3 allende is also the most metamorphosed bali is a breccia containing clasts of different petrologic types the attribution suggested by this study is that of clasts of the highest petrologic types as pointed out by iom maturity and noble gas bulk abundance cv3 chondrites have complex asteroidal backgrounds with various degrees of aqueous alteration and or thermal metamorphism leading to complex mineralogical and petrologic patterns fe mg chemical zoning in olivine phenocrysts on the borders of type i chondrules of porphyritic olivine and pyroxene rich textural types has been found to correlate with the metamorphism grade this suggests that chemical zoning in some chondrules often interpreted as exchanges between chondrules and nebular gas may well have an asteroidal origin furthermore the compositional range of olivine matrix is controlled both by thermal metamorphism and aqueous alteration this does not support evidence of a nebular origin and does not necessarily mirror the metamorphism grade through fe mg equilibration on the other hand it may provide clues on the degree of aqueous alteration vs thermal metamorphism and on the timing of both processes in particular mokoia experienced significant aqueous alteration after the metamorphism peak whereas grosnaja which has similar metamorphism grade did not

calcium aluminum rich inclusions and amoeboid olivine aggregates from the cr carbonaceous chondrites calcium aluminum rich refractory inclusions cais in cr chondrites are rare 1 vol fairly small 500 m and irregularly shaped and most of them are fragmented based on the mineralogy and petrography they can be divided into grossite hibonite rich melilite rich and pyroxene anorthite rich cais other types of refractory objects include fine grained spinel melilite pyroxene aggregates and amoeboid olivine aggregates aoas some of the pyroxene anorthite rich cais have igneous textures and most melilite rich cais share similarities to both the fluffy and compact type a cais found in cv chondrites one major difference between these cais and those in cv cm and co chondrites is that secondary mineral phases are rare in situ ion microprobe analyses of oxygen isotopic compositions of 27 cais and aoas from seven cr chondrites demonstrate that most of the cais are 16o rich 17o of hibonite melilite spinel pyroxene and anorthite 22 and isotopically homogeneous within 3 4 likewise forsterite spinel anorthite and pyroxene in aoas have nearly identical 16o rich compositions 24 17o 20 deg in contrast objects which show petrographic evidence for extensive melting are not as 16o rich 17o less than 18 o secondary alteration minerals replacing 16o rich melilite in melilite rich cais plot along the terrestrial fractionation line most cr cais and aoas are mineralogically pristine objects that largely escaped thermal metamorphism and secondary alteration processes which is reflected in their relatively homogeneous 16o rich compositions it is likely that these objects or their precursors condensed in an 16o rich gaseous reservoir in the solar nebula in contrast several igneous cais are not very enriched in 16o probably as a result of their having melted in the presence of a relatively 16o poor nebular gas if the precursors of these cais were as 16o rich as other cr cais this implies either temporal excursions in the isotopic composition of the gas in the cai forming regions and or radial transport of some cai precursors into an 16o poor gas the absence of oxygen isotope heterogeneity in the primary minerals of melilite rich cais containing alteration products suggests that mineralogical alteration in cr chondrites did not affect oxygen isotopic compositions of their cais

shock metamorphism of carbonaceous chondrites abstract we have studied shock effects in carbonaceous chondrites using optical microscopy of thin sections and find that our petrographic classification of progressive shock metamorphism in ordinary chondrites can also be applied to carbonaceous chondrites we find that sixty nine carbonaceous chondrites can be assigned to four shock stages si to s4 largely on the basis of shock effects in olivine the least shocked chondrite groups are cm2 and co3 thirty six out of thirty eight members are classified as shock stage s1 differences between the mean shock levels of certain groups of chondrites e g co3 and cv3 are probably due to stochastic differences in the sampling of their parent bodies however there is an overall tendency for the mean shock level of carbonaceous chondrites and ordinary chondrites to increase with increasing petrologic type that may reflect real differences in the shock level of near surface materials on their parent bodies caused by intrinsic variations in the chemical and physical properties of these materials petrologic type 2 and 3 chondrites are more porous and richer in volatiles than types 4 to 6 the greater porosity of types 2 3 causes higher post shock temperatures and melting at lower pressures and the higher volatile contents ensure that strongly shocked material is more readily dispersed on release from high pressure we suggest that type 2 3 material shocked above 20 30 gpa normally escapes from the parent asteroids and forms particles that are too small to survive as meteorites in the cv3 group there is a correlation between the degree of chondrule flattening and the intensity of shock metamorphism analogous to that discovered in ordinary chondrites by sneyd et al 1988 suggesting that shock rather than static overburden pressure is responsible for chondrule flattening we infer that the correlations are due to collapse of pores under shock pressures of at least 5 10 gpa and that shock is an important process affecting many physical properties of type 2 4 chondrites

alteration of al rich inclusions inside amoeboid olivine aggregates in the allende meteorite lightly altered al rich inclusions in amoeboid olivine aggregates have cores containing primary melilite fassaite spinel perovskite and no secondary alteration products in moderately altered inclusions whose cores now contain only fassaite spinel perovskite melilite was replaced by a fine grained mixture of grossular anorthite feldspathoids and perovskite was partially replaced by ilmenite in heavily altered inclusions fassaite has been replaced by a mixture of phyllosilicates ilmenite and the remaining primary phases are spinel perovskite in very heavily altered inclusions no primary phases remain the spinel having reacted to form either phyllosilicates or a mixture of olivine feldspathoids this sequence of alteration reactions may reflect successively lower solar nebular equilibration temperatures during alteration sio2 na2o k2o feo cr2o3 h2o and cl were introduced into the inclusions and cao was lost mgo may have been lost during the melilite reaction and added during formation of phyllosilicates electron microprobe analyses indicate that the phyllosilicates are a mixture of na rich phlogopite and chlorite or alrich serpentine thermodynamic calculations suggest that at a solar nebular water fugacity of 10 6 na rich phlogopite could have formed from fassaite at 470 k and chlorite from na rich phlogopite at 328 k olivine mantling al rich inclusions is not serpentinized suggesting that these objects stopped equilibrating with the nebular gas above 274 k

the relationship between ck and cv chondrites ck chondrites are highly oxidized meteorites containing abundant magnetite and trace amounts of fe ni metal although the group is predominately composed of equilibrated meteorites types 4 6 in recent years a significant number of new samples have been classified as being either ck3 or ck3 anomalous these unequilibrated cks often display a close affinity with members of the cv oxidized subgroup cks and cvs oxidized subgroup may therefore form a continuum and by implication could be derived from a single common parent body to investigate the relationship between these two groups a detailed study of the oxygen isotope composition opaque mineralogy and major and trace element geochemistry of a suite of cv and ck chondrites has been undertaken the results of oxygen isotope analysis confirm the close affinity between cv and ck chondrites while excluding the possibility of a linkage between the co and ck groups magnetites in both cv and ck chondrites show significant compositional similarities but high ti contents are a diagnostic feature of the latter group the results of major and trace element analysis demonstrate that both cv and ck chondrites show overlapping variation supporting evidence for a single common source for both groups comes from their similar cosmic ray exposure age distributions recent reflectance spectral analysis is consistent with both the cvs and cks being derived from eos family asteroids which are believed to have formed by the catastrophic disruption of a single large asteroid thus a range of evidence appears to be consistent with cv and ck chondrites representing samples from a single thermally stratified parent body in view of the close similarity between cv and ck chondrites some modification of the present classification scheme may be warranted possibly involving integration of the two groups one means of achieving this would be to reassigned ck chondrites to a subgroup of the oxidized cvs it is recognized that a full evaluation of this proposal may require further study of the still poorly understood ck3 chondrites

metamorphosed calcium aluminum rich inclusions in ck carbonaceous chondrites ck chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6 although cks are described as calcium aluminum rich inclusion cai poor objects the abundance of cais in the 18 ck3 6 we analyzed ranges from zero to approximately 16 4 during thermal metamorphism some of the fine grained cais recrystallized as irregular assemblages of plagioclase ca rich pyroxene olivine ca poor pyroxene magnetite coarse grained cais display zoned spinel fassaite destabilization and secondary grossular and spinel secondary anorthite grossular ca rich pyroxene and spinel derive from the destabilization of melilite which is lacking in all cais investigated the al mg isotopic systematics measured in fine and coarsegrained cais from tanezrouft tnz 057 was affected by mg redistribution the partial equilibration of al mg isotopic signatures obtained in the core of a coarse grained cai cg1 cai in tnz 057 may indicate a lower peak temperature for mg diffusion of approximately 540 580 c while grossular present in the core of this cai indicates a higher temperature of around 800 c for the metamorphic event on the parent body of tnz 057 excluding metamorphic features the similarity in nature and abundance of cais in ck and cv chondrites confirms that cvs and cks form a continuous metamorphic series from type 3 to 6

compositional and petrographic similarities of cv and ck chondrites a single group with variations in textures and volatile concentrations attributable to impact heating crushing and oxidation abstract greenwood et al 2010 gathered data on o isotopic and elemental compositions and reevaluated literature data for cv and ck chondrites they concluded that these two chondrite groups originated on the same parent asteroid with ck chondrites being metamorphosed cv chondrites which are otherwise missing types 4 through 6 to test this interpretation we have gathered new instrumental neutron activation analysis inaa data for cv and ck chondrites and reexamined their petrographic features the new inaa data like the older data show scatter attributable to weathering effects but we conclude that the refractory lithophile abundances are the same in cv and ck in agreement with the greenwood et al interpretation several volatile elements are significantly lower in ck than in cv chondrites among the elements we determine the greatest difference between cv and ck is found for br for which the cv ck ratio is 4 as and sb are about 20 lower in ck than cv and smaller differences are observed for zn ga and se it seems likely that volatiles were lost during impact heating events that also provided the heat responsible for metamorphic recrystallization within statistical uncertainty chondrules in cv and ck chondrites are the same size and have similar textural distributions a significant petrographic difference between ck and cv chondrites cited by kallemeyn et al 1991 was the much higher percentage of igneous rims around cv chondrules however we now recognize that many chondrules in ck3 8 nwa 1559 have igneous rims and in ck4 chondrites igneous rims are recognizable by their associated sulfide rich rings there are no quantifiable cv ck differences in igneous rim abundances we used ca and al maps to show that ck chondrites have cai abundances similar to those of cv chondrites it thus appears that there are no resolvable pre metamorphic petrographic differences between cv and ck chondrites we recommend that the ck designation be abandoned and that the cv group be acknowledged as spanning the range of petrologic types 3 6 we suggest that ck3 chondrites be designated cv3oxk most ck4 chondrites are highly fragmental collisional crushing appears to be much more common than in cv chondrites it seems likely that ck chondrites formed from reduced cv3 materials after the latter was impacted buried aqueously altered and annealed

amoeboid olivine aggregates aoas in the efremovka leoville and vigarano cv3 chondrites a record of condensate evolution in the solar nebula abstract amoeboid olivine aggregates aoas in the efremovka leoville and vigarano cv3 chondrites were studied using petrographic and microanalytical techniques to evaluate the origins of these inclusions and their relationships to other chondrite components our data support the idea that the inclusions formed by dust growth in the solar nebula as condensates and that they preserve a record of mineralogical and chemical evolution spinel rich nodules and ribbons in aoas often show group ii trace element patterns and formed either by fractional condensation or by condensation following partial vaporization the dominant olivine component in aoas can be explained as a condensate produced in the same way but with fractionation occurring at a lower temperature other spinel rich material in aoas appears to be a vaporization residue ca rich pyroxene anorthite patches in aoas show chemical signatures similar to those observed for spinel or melilite bearing regions but with lower refractory element and higher mg and si contents supporting the idea that the patches formed by reaction between cai like material and mg si rich gas different trace element patterns group ii and non group ii refractory are sometimes found for al rich regions ca pyroxene anorthite or melilite bearing in a given aoa suggesting that aoas agglomerated from materials that formed under different conditions and that they did not subsequently homogenize aoas appear to have originated in a system with near canonical solar composition and a low pressure gas 10 6 10 4 bar over a range of temperatures mainly 1200 1384 k under somewhat non equilibrium conditions relative to predicted equilibrium condensates most aoas show an apparent paucity of metal possibly reflecting differential density dependent sorting between olivine and metal grains during aggregate formation trace element data are consistent with a simple model involving melting and igneous fractionation of aoa like olivine to produce type i chondrule olivine but other data suggest that open system melting of chondrules occurred in a different gaseous environment than that which produced aoas

al mg isotopic evidence for episodic alteration of ca al rich inclusions from allende textures mineral assemblages and al mg isotope systematics indicate a protracted episodic secondary mineralization history for allende ca al rich inclusions cais detailed observations from one type b1 cai one b2 one compact type a cta and one fluffy type a fta indicate that these diverse types of cais are characterized by two distinct textural and mineralogic types of secondary mineralization 1 grossular rich domains concentrated along melilite grain boundaries in cai interiors and 2 feldspathoid bearing domains confined mostly to cai margins just interior to the wark lovering rim sequence the al mg isotopic compositions of most secondary minerals in the type b1 cai and some secondary minerals in the other cais show no resolvable excesses of 26mg whereas the primary cai phases mostly yield correlated excesses of 26mg with increasing al mg corresponding to canonical initial 26al 27al 4 55 10 5 these secondary minerals formed at least 3 ma after the primary cai minerals all but two analyses of secondary minerals from the fluffy type a cai define a correlated increase in 26mg 24mg with increasing al mg yielding 26al 27al 0 4 9 2 8 10 6 the secondary minerals in this cai formed 1 8 3 2 ma after the primary cai minerals in both cases the timing of secondary alteration is consistent with but does not necessarily require alteration in an asteroidal setting one grossular from the type b2 cai and several grossular and secondary feldspar analyses from the compact type a cai have excesses of 26mg consistent with initial 26al 27al 4 5 10 5 especially in the compact type a cai where 26mg 24mg in grossular correlates with increasing al mg these 26mg excesses are almost certainly due to in situ decay of 26al they indicate a nebular setting for formation of the grossular the preservation of these diverse isotopic patterns indicates that heating on the allende parent body was not pervasive enough to reset isotopic systematics of fine grained secondary minerals secondary mineralization clearly was not restricted to a short time interval and at least some alteration occurred coincident with cai formation and melting events chondrule formation in the nebula this observation supports the possibility that alteration followed by melting affected the compositional evolution of cais

chemical compositions and classifica tion of five thermally altered carbonaceous chondrites to establish the chemical group provenance of the five thermally altered carbonaceous chondrites asuka a 881551 asuka 882113 elephant moraine eet 96026 mulga west and northwest africa nwa 3133 we quantified 44 trace elements in each of them we also analyzed larkman nunatak lar 04318 ck4 miller range mil 090001 cr2 roberts massif rbt 03522 ck5 as reference samples as their chemical group affinity is already recognized we conclude that asuka 881551 asuka 882113 and mulga west are thermally metamorphosed ck chondrites compositionally elephant moraine 96026 most resembles the cv chondrites nwa 3133 is the most significantly thermally altered carbonaceous chondrite in our suite of samples it is completely recrystallized no chondrules or matrix remain but its bulk composition is consistent with a cv ck clan provenance the thermally labile element e g se te zn and bi depletion in nwa 3133 indicates a chemically open system during the heating episode it remains unclear if the heat necessary for its thermal alteration of nwa 3133 was due to the decay of 26al or was impact related finally we infer that mil 090001 mulga west and nwa 3133 show occasional compositional signatures indicative of terrestrial alteration the alteration is especially evident within the elements sr ba la ce th u and possibly sb despite the alteration we can still confidently place each of the altered chondrites within an established chemical group or clan

refractory inclusions with unusual chemical compositions from the vigarano carbonaceous chondrite abstract ten inclusions nine from vigarano and one from leoville both members of the reduced subgroup of c3v chondrites were analyzed for major and trace elements by neutron activation most have some refractory element characteristics that are common in refractory inclusions from allende a member of the oxidized subgroup of c3v chondrites for instance three leo 3537 2 vig 1623 8 vig 1623 11 are type b inclusions with group i or modified group i ree patterns three vig 1623 5 vig 1623 10 vig 1623 13 are olivine rich inclusions each of which is rather uniformly diluted in most refractory elements compared to group i inclusions and two vig 1623 14 vig 1623 16 are fine grained inclusions with group ii ree patterns six of the vigarano inclusions however have refractory element fractionations that are unusual in allende inclusions vig 1623 11 has cl chondrite normalized enrichment factors for th and refractory siderophiles that are lower than those for ree by 60 or more a positive mo anomaly mo ir 1 92 0 02 relative to cl chondrites and an unusually low zr hf ratio 0 67 0 06 relative to cl relative to cl chondrites the ir enrichment factor is 1 7 times greater than the mean enrichment factor for re os and ru in vig 1623 10 vig 1623 13 has one of the lowest ir sm ratios 0 00044 0 00007 relative to cl ever measured in an olivine chondrule vig 1623 16 has a modified group ii ree pattern which reflects removal of refractory rees from the nebular gas at unusually low temperatures vig 477 5 has a ree pattern with a small negative ce anomaly ce la 0 79 0 01 relative to cl a large negative yb anomaly yb lu 0 57 0 02 relative to cl and no eu anomaly this inclusion also has a positive mo anomaly mo ir 2 25 0 03 relative to cl and enrichment factors for zr and th that are lower than those for lu by about 65 vig 477 b has a ree pattern that may be a mixture of five parts of a component with an ultrarefractory ree pattern and ninety five parts of another with a modified group ii ree pattern vigarano apparently sampled a different population of refractory inclusions from allende presumably because refractory nebular materials were not well mixed where and when c3v chondrites accreted the vigarano and leoville coarse grained inclusions studied here like others analyzed previously tend to have lower concentrations of na and au than allende coarse grained inclusions but the two vigarano fine grained inclusions of this study have concentrations of these elements that are comparable to those of allende fine grained inclusions thus although coarse grained inclusions in the reduced subgroup of c3v chondrites were altered under different conditions from those in the oxidized subgroup some fine grained inclusions in the reduced subgroup were altered under similar conditions as some in the oxidized subgroup

sea level higher than present 3500 years ago on the northern main hawaiian islands new data from an emerged coastal bench and associated fossil beach on kapapa island oahu hawaii preserve a detailed history of middle to late holocene sea level these include 29 new calibrated radiocarbon ages and elevations indicating mean sea level reached a maximum position of 2 00 0 35 m ca 3500 yr b p these results correlate with additional evidence from hawaii and other pacific islands and provide constraints on oahu s long term uplift rate 0 03 0 07 mm yr previously based solely on pleistocene age shorelines our sea level reconstruction is consistent with geophysical model predictions of earth s geoid response to the last deglaciation and with observations of increased antarctic ice volume during the late holocene

fassaite composition trends during crystallization of allende type b refractory inclusion melts fassaite is a major phase in type b refractory inclusions and its wide compositional variability makes it an excellent recorder of crystallization induced changes in liquid composition traverses across zoned crystals with electron and ion microprobes show that ti v sc zr and hf decrease from core to rim while mg si rees and other trace elements increase fassaite liquid distribution coefficients derived from the compositions of early fassaite and calculated parent liquid compositions are higher than previously reported fassaite ds e g 0 2 0 8 vs 0 08 0 5 for the trivalent rees possibly due to the high ti and al contents of the fassaite we analyzed log log plots of concentrations of elements vs those of sc give linear relationships with slopes of dixl l 1 dscxl l 1 where dixl l is the bulk crystal liquid distribution coefficient for element i from this relationship we derive effective fassaite liquid ds of 2 8 for sc 1 5 for hf 1 1 for zr 0 52 for y 0 34 for ta 0 29 for nb and 0 31 0 48 for trivalent rees the effective ds are applicable to fassaite crystallizing from melts having the compositions and thermal histories of allende type b refractory inclusions and incorporate any equilibrium and kinetic effects that modify ds during the course of crystallization observed fassaite ree contents can be reproduced by a fractional crystallization model in which the effective ds are used ti3 is more compatible in fassaite than ti4 and without equilibration of the residual liquid with an external reducing gas ti3 titot ratios where titot ti3 ti4 should decrease from core to rim in fassaite crystals comparison of profiles of ti3 titot ratios in several crystals with those calculated for fractional crystallization suggests that the trend in one crystal was controlled by fractional crystallization alone but in two others the virtually constant ti3 titot ratios may imply that the liquids in these inclusions were able to maintain equilibrium with the solar nebular gas throughout crystallization attempts to determine the o2 of fassaite crystallization on the basis of ti3 titot ratios must be based on fassaite grains which are not zoned with respect to ti3 titot the range of observed ree abundances in subliquidus fassaite 7 800 cl for la and 30 2000 cl for lu now encompasses those in grains previously identified as relict removing a major reason for their identification as such rounded fassaite grains with fairly sharp mg rich rims and ti rich cores poikilitically enclosed in mantle melilite in ts34 are candidates for relict grains the grains are so scrich that they would require extreme prior crystallization of spinel and melilite which is inconsistent with their very low ree contents e g la at 3 7 cl we suggest that the cores of these grains are relict and were trapped with liquid during formation of the mantle

ca al rich inclusions in rumuruti r chondrites rumuruti chondrites r chondrites constitute a well characterized chondrite group different from carbonaceous ordinary and enstatite chondrites many of these meteorites are breccias containing primitive type 3 fragments as well as fragments of higher petrologic type ca al rich inclusions cais occur within all lithologies here we present the results of our search for and analysis of al rich objects in rumuruti chondrites we studied 20 r chondrites and found 126 ca al rich objects 101 cais 19 al rich chondrules and 6 spinel rich fragments based on mineralogical characterization and analysis by sem and electron microprobe the inclusions can be grouped into six different types 1 simple concentric spinel rich inclusions 42 2 fassaite rich spherules 3 complex spinel rich cais 53 4 complex diopside rich inclusions 5 al rich chondrules and 6 al rich spinel rich fragments the simple concentric and complex spinel rich cais have abundant spinel and based on the presence or absence of different major phases fassaite hibonite na al cl rich alteration products can be subdivided into several subgroups although there are some similarities between cais from r chondrites and inclusions from other chondrite groups with respect to their mineral assemblages abundance and size the overall assemblage of cais is distinct to the r chondrite group some ca al rich inclusions appear to be primitive e g low feo contents in spinel low abundances of na al cl rich alteration products abundant perovskite whereas others were highly altered by nebular and or parent body processes e g high concentrations of feo and zno in spinel ilmenite instead of perovskite abundant na al cl rich alteration products there is complete absence of grossite and melilite which are common in cais from most other groups cais from equilibrated r chondrite lithologies have abundant secondary ab rich plagioclase oligoclase and differ from those in unequilibrated type 3 lithologies which have nepheline and sodalite instead

a shock metamorphic model for silicate darkening and compositionally variable plagioclase in ck and ordinary chondrites abstract silicate darkening in ordinary chondrites oc is caused by tiny grains of metallic fe ni and troilite occurring mainly within curvilinear trails that traverse silicate interiors and decorate or in some cases cut across silicate grain boundaries highly shocked oc characterized by olivine grains with undulose to mosaic extinction tend to have greater degrees of silicate darkening than lightly shocked oc this indicates that silicate darkening is probably a result of shock metamorphism the low fe fes eutectic temperature 988 c renders metal and troilite susceptible to melting and mobilization during shock heating a few oc also contain thin melt veins of chromite this implies that localized shock temperatures reached 1635 c in these meteorites silicate darkening is also evident in ck carbonaceous chondrites where magnetite and pentlandite grains form analogous curvilinear trails it is possible that magnetite and pentlandite in ck chondrites were mobilized during shock metamorphism and dispersed through silicate interiors alternatively metal and troilite may have been dispersed and then transformed into magnetite and pentlandite during subsequent oxidation of these chondrites unshocked oc tend to have plagioclase with uniform compositions shocked oc tend to have plagioclase with more variable albeit still stoichiometric compositions the low impedance of plagioclase to shock compression makes it particularly susceptible to melting and mobilization this is consistent with the molten appearance of plagioclase in highly shocked oc e g rose city and paragould ck chondrites also have compositionally variable plagioclase the common association of silicate darkening with compositionally variable plagioclase is consistent with the hypothesis that both are products of shock metamorphism some ck and oc chondrites exhibit light shock effects in olivine that are consistent with equilibrium peak shock pressures that are too low to account for the silicate darkening or opaque shock veins in these meteorites therefore the olivine in these chondrites may have been annealed after intense shock produced these effects a few ck chondrites that contain olivine with undulose or mosaic extinction e g lew87009 and eet83311 may have been shocked again after annealing

petrology of types 4 6 carbonaceous chondrites we have studied the petrology of three type 4 carbonaceous chondrites coolidge karoonda and pecora escarpment 82500 which was previously classified as an ll6 chondrite and compared them to published descriptions of the other known metamorphosed c chondrites yamato 6903 and mulga west all except coolidge have abundant matrix typically 80 vol composed largely of homogeneous olivine fa 29 33 and surprisingly heterogeneous plagioclase mostly an 20 75 their opaque mineralogy indicates high oxygen fugacities during metamorphism metallic fe ni and troilite are rare and magnetite and pentlandite are abundant with accessory pyrrhotite chalcopyrite and pyrite possibly because of a lower matrix abundance coolidge has more reduced minerals metallic fe ni and olivine with fa 14 the properties of all c4 6 chondrites appear to be consistent with an origin by metamorphism of c3 like precursors by processes analogous to those operating in ordinary chondrite parent bodies or planetesimals however type 4 6 material was not well mixed with type 3 material in the cv3 parent body as it was in the ordinary chondrite parent bodies conceivably c4 6 chondrites come from one or more separate parent bodies

the geochemical behavior of refractory noble metals and lithophile trace elements in refractory inclusions in carbonaceous chondrites abstract recent models of ca al rich inclusion cai petrogenesis suggest that refractory inclusions may be residues of interstellar dust aggregates that were incompletely evaporated and partially melted in the solar nebula these models and the recent availability of new thermodynamic data have led us to re examine the traditional interpretation that lithophile refractory trace elements lrte condensed as oxides in solid solution in refractory major condensates while refractory noble metals rnm condensed as micron sized nuggets of pt metal alloys calculations of lrte rnm alloy stability fields under nebular oxygen fugacities and partitioning experiments lead us to conclude that 1 ti zr nb hf u and ta form stable alloys with rnm under nebular conditions 2 the observation that metallic zr nb and ta occur in some pt metal nuggets and grains is explained by the stability of these lrte rnm alloys under normal nebular oxygen fugacities 3 metallic ti hf and u may also occur in some nuggets 4 the lanthanides the other actinides th pu and y do not form stable alloys and thus probably do not occur alloyed with rnm and 5 the partitioning of u but not th pu or the ree into rnm is a novel actinide and ree actinide fractionation mechanism that is based on metal silicate fractionation rather than on the relative volatility of their oxides we propose that micron sized pt metal nuggets formed from smaller grains of rnm alloys and compounds during the evaporation and melting of primitive dust aggregates this process would have been enhanced by 1 the possibility that the rnm were present as compounds especially with as and s as well as metallic alloys in interstellar dust and in some primitive meteoritical material since they often exhibit non siderophile behavior and 2 the fluxing of volatiles through cai s during distillation microscopic nuggets are common in melilite chondrules indicating that residence in a slowly cooled silicate melt may have favored their formation cation diffusivity and variations in local f o 2 can explain why metallic lrte bearing nuggets are not common in cai s despite the relative stability of lrte rnm alloys we propose that the lithophile component of fremdlinge is enriched in super refractory elements and that group ii cai s formed from fremdlinge poor dust we interpret the group ii ree fractionation as a pre solar event and predict that nd sm dating will yield an age greater than the canonical age of the solar system if metal silicate fractionation in a cold solar nebula can explain group ii ree patterns the possibility that group ii cai s are also distillation residues cannot be excluded

higher than present holocene mean sea levels in ilocos palawan and samar philippines abstract holocene paleo mean sea levels along the coasts of ilocos palawan and samar in the philippines are established using estimates from emerged tidal notches and coral reef terraces age control is provided by 17 14 c and 22 230 th 234 u dates the notches and terraces with the oldest dating back to approximately 8 2 ky have elevations from 0 1 to 6 7 m above the present mean sea level in each of the study sites adjacent coastal areas show different paleosea level histories in both the level and number of relative stillstands due to local faulting in ilocos paleosea levels show greater elevation and number of recorded stillstands due to a significant thrust component along this segment of the philippine fault in samar a general increase in the elevation of paleosea level to the east indicates tilting of the island towards the philippine fault abrupt changes in the elevations of correlative paleosea level indicators and an overall northeast and southwest tilting respectively of northern and southern palawan suggest the presence of active faults in central palawan discrete double notches suggest two emergent stillstands occurring between 7 3 and 2 4 ky the lower and higher notches respectively correspond to earlier and later stillstand events possible across site variation in the duration and timing of initiation and termination of these stillstands can be due to differences in regional tectonics and crustal response to hydro isostasy or an artifact of sampling

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

mg diffusion in anorthite implications for the formation of early solar system planetesimals we have measured the self diffusion coefficients of mg ca and sr in anorthitic plagioclase in order to assess the potential of mg isotopic heterogeneities in early solar system planetesimals to survive thermal metamorphism diffusion couples were constructed from polished single crystals of natural anorthite and synthetic isotopically enriched anorthite glass couples were annealed at atmospheric pressure and 1200 1400 c and isotopic concentration profiles were measured with an ion microprobe the results show that mg diffusion in anorthite is surprisingly fast with d mg being over 2 orders of magnitude greater than d sr this indicates that the diffusion coefficient of mg in anorthite cannot be approximated with that for sr mg diffusion in the c direction is also slightly faster than in the b direction while ca and sr diffusion appear to be isotropic the results provide important constraints on the thermochronological history of anorthite bearing mineral assemblages that preserve radiogenic 26 mg excesses in a planetesimal heated by the decay of 26 al the temperature at any point depends on the planetesimal size time of formation thermal conductivity and depth within the planetesimal given sufficient heating 26 mg heterogeneities produced by the in situ decay of 26 al in ca al rich inclusions cais and chondrules will be erased by diffusive equilibration using the self diffusion coefficient for mg in anorthite measured in this study we show that the common occurrence of 26 mg excesses in these inclusions requires that they must be stored in small 15 km bodies or the outermost rims of larger bodies for the first 1 2 million years of the solar system s history for early formed bodies larger than 15 km most of the mass will have been heated sufficiently for any radiogenic 26 mg to have been diffusively homogenized in the mg rich planetary environment

new constraints on early solar system chronology from al mg and u pb isotope systematics in the unique basaltic achondrite northwest africa 2976 abstract we report elemental abundances and the isotopic systematics of the short lived 26 al 26 mg half life of 0 73 ma and long lived u pb radiochronometers in the ungrouped basaltic meteorite northwest africa nwa 2976 the bulk geochemical composition of nwa 2976 is clearly distinct from that of the eucrites and angrites but shows broad similarities to that of the paired nwa 001 and 2400 ungrouped achondrites indicating that it is likely to also be paired with these two samples the major and trace element abundances in nwa 2976 further indicate that it formed by extensive melting and magmatic fractionation processes on its parent body the al mg and pb pb isotope systematics indicate that this meteorite represents the earliest stages of crust formation on a differentiated parent body in the early solar system the absolute pb pb internal isochron age of nwa 2976 obtained from acid leaching residues of three whole rock samples and two pyroxene separates is 4562 89 0 59 ma mswd 0 02 this pb pb age is calculated using the measured 238 u 235 u ratio of a nwa 2976 whole rock of 137 751 0 018 2 which was determined relative to the recently revised value of 137 840 0 008 for the srm 950a u isotope standard the al mg systematics reveal the presence of 26 mg isotopic anomalies produced by the decay of 26 al with an 26 al 27 al 0 of 3 94 0 16 10 7 and indicate a time of formation of 0 26 0 18 ma after the d orbigny angrite using the revised pb pb age of 4563 36 0 34 ma for the d orbigny anchor corrected for its u isotopic composition we deduce an al mg model age of 4563 10 0 38 ma for nwa 2976 which is consistent with its pb pb internal isochron age the concordance of the pb pb and al mg chronometers when taking into account the differences in the u isotopic compositions of the d orbigny and nwa 2976 achondrites whose parent bodies likely formed in distinct regions of early solar system as indicated by their different oxygen isotopic compositions implies that 26 al was homogeneously distributed in the early solar system it also suggests that igneous processes on planetesimals as represented by the formation of various basaltic meteorite groups that likely originated on distinct parent bodies e g eucrites and angrites as well as ungrouped achondrites were widespread throughout the protoplanetary disk within the first 5 ma of the history of the solar system

petrography and classification of ca al rich and olivine rich inclusions in the allende cv3 chondrite a detailed systematic petrographic survey of all 189 ca al rich and olivine rich inclusions larger than 0 2 mm in diameter in 17 thin sections of allende was performed by optical and scanning electron microscopy most of these inclusions are aggregates containing varying proportions of three distinct constituents termed concentric objects chaotic material and inclusion matrix a new classification system for allende inclusions is proposed olivine rich inclusions occur in two textural varieties unrimmed olivine aggregates type 1a inclusions and rimmed olivine aggregates type 1b inclusions we classify ca al rich inclusions cai s on the basis of the size and abundance of their constituent concentric objects rather than their grain size into unrimmed complex cai s type 2 inclusions rimmed complex cai s type 3 inclusions and simple cai s type 4 inclusions several of the inclusion classes grade into each other some fundamental relationships among various types of allende inclusions are discussed we suggest that the term coarse grained even if used only in a relative sense is too restrictive for some members of one class of inclusion simple cai s and is inappropriate for most members of another class melilite rich complex cai s