three dimensional imaging of ordinary chondrite microporosity at 2 6 μm resolution abstract we show that high resolution 2 6 m voxel synchrotron x ray microtomography ct scans are able to observe the majority of microporosity in ordinary chondrites this porosity is present in the form of microcracks and voids among and between mineral grains we examined in total seven small 6 12 mm 3 chips of the ordinary chondrites baszkowka l5 s1 alh a77258 h5 s2 moorleah l6 s3 and kyushu l6 s5 these four samples were chosen because of their variable impact histories using ct and various digital isolation and visualization techniques we found that the structure of microporosity varies with the degree of compaction and shock loading experienced by the materials the microporosity in the compacted and more strongly shock samples moorleah and kyushu is visible as sheet like fractures within brittle silicates as well as in discontinuous distributed voids sometimes associated with chondrule rims and grain boundaries in samples that have experienced less shock and only mild compaction we found few if any microcracks in the silicate grains of the materials microporosity in the baszkowka and alh a77258 samples is largely represented by intergranular voids with occasional intragranular voids being present regardless of degree of shock loading ductile fe ni or fes grains give no evidence of shock related internal fractures contributing to porosity

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

the wood lake ontario h4 ordinary chondrite a new canadian meteorite1 the wood lake meteorite was found in the muskoka region of ontario in july 2003 we examine the mineralogy physical properties shock and weathering state of this recently reported canadian meteo

visualisation and quantification of cv chondrite petrography using micro tomography abstract micro computed tomography is a non destructive technique that allows the study of 3d meteorite petrography the technique produces a unique and instructive visualisation of the meteorite for quantifying its components we studied the overall petrography of the two cv chondrites allende and mokoia to constrain their formation histories a set of movies and stereographic images detail the 3d petrography component modal abundances agree with previous reports and modal abundance differences between allende and mokoia support the chondrule matrix complementarity and that chondrules and matrix formed from the same chemical reservoir we identified two types of chondrules a normal type and one where a normal type i or ii chondrule is almost completely encapsulated by an opaque rich layer this layer was probably acquired during a late stage condensation process the appearance of opaques in chondrules and matrix is different not supporting a genetic relationships between these low abundances of compound chondrules 1 75 vol in allende and 2 50 vol in mokoia indicate low chondrule densities and or low relative component velocities in chondrule formation regions porosities on a scale

development of a shear flow test apparatus and determination of coupled properties for a single rock joint abstract a new laboratory technique for coupled shear flow tests of rock joints was developed and used to investigate the coupled effect of joint shear deformation and dilatancy on hydraulic conductivity of rock joints this technique was used to carry out coupled shear flow tests with an artificial created granite joint sample under constant normal loads and up to residual shear deformations of 20 mm the hydraulic conductivity was estimated by using a finite difference method and an approximate equation assuming the cubic law the shear flow testing results revealed that the change of hydraulic conductivity is approximately similar to that of the dilatancy of a joint the hydraulic conductivity increases rapidly by about 1 2 1 6 orders of magnitude for the first 5 mm of shear displacement after passing the residual shear stress the hydraulic conductivity becomes gradually a constant value with increasing shear displacement on the other hand the hydraulic conductivity after shearing is about one order of magnitude larger than that prior to shearing shear flow coupling characteristics obtained from these tests have a consistent trend with barton s model prediction during the initial shear process however increasing deviation between measured and predicted hydraulic conductivity of rock joint samples has been observed with increasing shear displacement

incompletely compacted equilibrated ordinary chondrites we document the size distributions and locations of voids present within five highly porous equilibrated ordinary chondrites using high resolution synchrotron x ray microtomography ct and helium pycnometry we found total porosities ranging from 10 to 20 within these chondrites and with ct we show that up to 64 of the void space is located within intergranular voids within the rock given the low s1 s2 shock stages of the samples and the large voids between mineral grains we conclude that these samples experienced unusually low amounts of compaction and shock loading throughout their entire post accretionary history with fe metal and fes metal abundances and grain size distributions we show that these chondrites formed naturally with greater than average porosities prior to parent body metamorphism these materials were not fluffed on their parent body by impact related regolith gardening or events caused by seismic vibrations samples of all three chemical types of ordinary chondrites ll l h are represented in this study and we conclude that incomplete compaction is common within the asteroid belt

laboratory investigation of nonlinear flow characteristics in rough fractures during shear process abstract to understand the influence of shear behavior on the transporting properties of fluid through a single fracture splitting fractures were made in the laboratory and shear flow tests were carried out under constant normal load conditions the applied normal stress is in the range of 0 5 3 0 mpa before the physical test the fracture s morphology is measured for identification of the roughness at each shear step we performed 5 8 high precise hydraulic tests with different hydraulic gradient the relationship between pressure gradient and volume flow rate demonstrates to be nonlinear and fits very well with forchheimer s and izbash s laws the linear and nonlinear coefficients in forchheimer s law are quite sensitive to shear deformation closure or dilation experienced 1 2 and 1 3 orders of magnitude reduction during shear respectively an empirical equation is proposed to quantify the relationship between linear coefficient and nonlinear coefficient based on the experimental observations the two coefficients in izbash s law are quantified the m value is in the range between 1 06 and 1 41 and the value experiences a reduction of 1 2 orders of magnitude during shear in addition the studied critical reynolds number exhibits a decreasing and increasing variation corresponding to shear contraction and shear dilation of rock fracture for all the cases in this study the critical reynolds number ranges between 1 5 and 13 0

plagioclase rich chondrules in the reduced cv chondrites evidence for complex formation history and genetic links between calcium aluminum rich inclusions and ferromagnesian chondrules plagioclase rich chondrules prcs in the reduced cv chondrites efremovka leoville vigarano and grosvenor mountains gro 94329 consist of magnesian low ca pyroxene al ti cr rich pigeonite and augite forsterite anorthitic plagioclase feni metal sulfide nodules and crystalline mesostasis composed of silica anorthitic plagioclase and al ti cr rich augite the silica grains in the mesostases of the cv prcs are typically replaced by hedenbergitic pyroxenes whereas anorthitic plagioclase is replaced by feldspathoids nepheline and minor sodalite some of the prcs contain regions that are texturally and mineralogically similar to type i chondrules and consist of forsterite low ca pyroxene and abundant feni metal nodules several prcs are surrounded by igneous rims or form independent compound objects twelve prcs contain relic calcium aluminum rich inclusions cais composed of anorthite spinel high ca pyroxene forsterite and al rich low ca pyroxene anorthite of these cais is generally more heavily replaced by feldspathoids than anorthitic plagioclase of the host chondrules this suggests that either the alteration predated formation of the prcs or that anorthite of the relic cais was more susceptible to the alteration than anorthitic plagioclase of the host chondrules these observations and the presence of igneous rims around prcs and independent compound prcs suggest that the cv prcs may have had a complex multistage formation history compared to a more simple formation history of the cr prcs relatively high abundances of moderately volatile elements such as cr mn and si in the prcs suggests that these chondrules could not have been produced by volatilization of ferromagnesian chondrule precursors or by melting of refractory materials only we infer instead that prcs in carbonaceous chondrites formed by melting of the reduced chondrule precursors magnesian olivine and pyroxene feni metal mixed with refractory materials relic cais composed of anorthite spinel high ca pyroxene and forsterite the mineralogical chemical and textural similarities of the prcs in several carbonaceous chondrite groups cv co ch cr and common presence of relic cais in these chondrules suggest that prcs may have formed in the region s intermediate between the regions where cais and ferromagnesian chondrules originated

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

experimental and numerical study of the geometrical and hydraulic characteristics of a single rock fracture during shear abstract coupled shear flow tests were conducted on two artificial rock fractures with natural rock fracture characteristics under constant normal loading boundary conditions numerical simulations using the 3 d navier stokes equations taking account of the inertial effects of fluid were conducted using the void space geometry models obtained from the coupled shear flow tests the test and numerical simulation results show that the evolutions of geometrical and hydraulic characteristics of rock fracture exhibit a three stage behavior transmissivity of a certain void space geometry within a fracture is related to the reynolds number of fluid flow due to the inertial effects of fluid which can be represented by the navier stokes equations but cannot be represented by some simplified equations such as the cubic law the reynolds equation or the stokes equations the mechanical aperture is usually larger than the hydraulic aperture back calculated from measured flow rate and the difference between them is found strongly related to the geometrical characteristics of the fractures a mathematical equation is proposed to describe the relation between hydraulic aperture and mechanical aperture by means of the ratio of the standard deviation of local mechanical aperture to its mean value the standard deviation of local slope of fracture surface and reynolds number

modal mineralogy of cv3 chondrites by x ray diffraction psd xrd abstract using position sensitive detector x ray diffraction psd xrd we determine a complete modal mineralogy for all phases present in abundances greater than 1 wt in vigarano efremovka mokoia grosnaja kaba and allende reduced cv3 samples are comprised of vol olivine 83 85 enstatite 6 5 8 1 anorthite 1 1 1 2 magnetite 1 4 1 8 sulphide 2 4 5 1 fe ni metal 2 2 2 the oxidized samples are comprised of olivine 76 3 83 9 enstatite 4 8 7 8 anorthite 1 1 1 7 magnetite 0 3 6 1 sulphide 2 9 8 1 fe ni metal 0 2 1 1 fe oxide 0 2 7 and phyllosilicate 1 9 4 2 when our modal data is used to calculate a bulk chemistry that is compared to literature data a near 1 1 correlation is observed psd xrd data indicates that olivine compositions may span almost the entire fe mg solid solution series in all cv samples and that these contain a component 4 13 of fine grained olivine that is more fe rich fa 60 than is typically reported modal mineralogy shows that there are mineralogic differences between cv3 samples classified as oxidized and reduced but that these sub classes are most clearly distinguished by the relative abundance of metal and ni content of sulphide rather than abundance of magnetite the most significant difference in modal mineralogy observed is the relative absence of phyllosilicate in reduced cv that essentially escaped aqueous alteration fayalite ferrous olivine and magnetite are typically considered secondary alteration products the abundances of these minerals overlap in oxidized and reduced samples and correlate positively supporting common conditions of formation in a relatively oxidizing environment the abundances of fayalite ferrous olivine and magnetite show no relationship to petrographic type and if these abundances were used as a proxy for alteration allende would be the least altered cv contrary to all previous data the implication is that thermal metamorphism on the parent body was de coupled from formation of fe rich secondary minerals low temperature fluid assisted metamorphism can also not easily explain the origin of fayalite ferrous olivine and magnetite since the reduced cvs appear to be largely unaffected by this process parent body models require an anhydrous low temperature mechanism of secondary alteration the alternative is that these phases formed prior to accretion of the final cv parent body

self propping and fluid flow in slightly offset joints at high effective pressures we have made laboratory measurements of joint closure and permeability of both well and poorly mated laboratory produced joints in westerly granite under joint normal stresses to 160 mpa appropriate to midcrustal depths we have also made detailed topographic measurements of the joint surfaces both before and after pressure testing the purpose of the study was to characterize and understand the hydraulic behavior of joints under conditions where fluid migration under natural settings is known to occur but where physical conditions namely high lithostatic load suggest that the presence of open fluid conducting joints might be improbable normal stress was applied by hydrostatic confinement of cylindrical samples each containing a single axial tensile fracture experiments were performed at room temperature under conditions designed to minimize chemical effects of dissolution or precipitation we found that while a mated joint can be completely closed by the application of high normal stresses the same joint laterally offset by 0 53 mm remains open and many orders of magnitude more hydraulically conductive than the mated joint even at highest stresses detailed topographic observations are consistent with self propping of the offset joint permanent damage to the surfaces of the offset joint is not widespread but occurs at isolated locales covering about 10 of the surface damage is confined to regions of negative convex upward curvature such as summits and the edges of plateaus approximately 20 of the joint surface is in wall to wall contact at 160 mpa and the flow tortuosity thus induced is probably the cause of the breakdown of the parallel plate approximation for fluid flow in the offset joint

influence of fracture geometry on shear behavior abstract laboratory research during the past 10 years has explained many critical links between the geometrical characteristics of fractures and their hydraulic and mechanical behavior one of the remaining research challenges is to directly link fracture geometry with shear behavior including behavior in response to changes in normal stress and shear direction this paper describes results from a series of shear tests performed on identical copies replicas of a natural granite fracture based on these tests we developed a method using image processing techniques to identify and quantify damage that occurs during shearing we find that there is a strong relationship between the fracture s geometry and its mechanical behavior under shear stress and the resulting damage using a three dimensional geostatistical model of the fracture surfaces we analyze the dependence of the size and location of damage zones on the local geometry and propose an algorithm for predicting areas that are most likely to be damaged during shearing in a given direction

shock compaction heating and collisional processes in the production of type 3 ordinary chondrites lessons from the nearly unique l3 chondrite melt breccia northwest africa 8709

quantifying the error of 2d bulk chondrule analyses using a computer model to simulate chondrules simchon bulk chondrule compositions are important to many questions in cosmochemistry however the number of available bulk chondrule data sets is still small a main reason for this is the difficulties of determining bulk chondrule compositions a commonly used technique is to obtain 2d bulk chondrule compositions from meteorite sections this technique has an error that we quantify here for the first time using a mathematical model of a chondrule called simchon the theoretically calculated errors are compared to errors that we determined from serial sectioning of eight efremovka chondrules the errors obtained from both approaches are in excellent agreement proving that our mathematical model produces reliable errors that can be assigned to 2d bulk chondrule compositions these errors allow a much better interpretation of 2d bulk chondrule data we provide a table that contains typical errors for 2d bulk compositions of porphyritic chondrules the errors are in the range of 1 30 relative this should be acceptable for many problems in cosmochemistry the effect of a chemical layering inside chondrules and the occurrence of a rim around them as well as the occurrence of opaque and other accessory phases have been studied a spreadsheet is provided that enables the calculation of errors for any desired chondrule mineral composition bo chondrules have a negligible error but it is impossible to provide reasonable error estimates for bo chondrules with an igneous rim radial pyroxene chondrules have negligible errors

the texture of a fine grained calcium aluminium rich inclusion cai in three dimensions and implications for early solar system condensation abstract a 16 mm fine grained spinel rich calcium aluminium rich inclusion cai from the allende cv3 meteorite was analysed using nano computed tomography and scanning electron microscopy on uncoated chips and a polished thin section the cai is composed of spinel nodules surrounded by anorthite and al rich diopside rims minor secondary minerals including hedenbergite and nepheline are also present the uncoated chips contain abundant wollastonite needles that are only rarely observed in the thin section nano computed tomography shows that the structure of the cai is a branching interconnected network of nodules most of which are attached to each other in three dimensions however some nodules are unattached to the rest of the cai the texture suggests that the cai formed by condensation from a gas and condensation and aggregation of nodules occurred contemporaneously implying a high density of newly formed dust one portion of the cai is compact and rich in melilite with a composition and texture dissimilar to the bulk of the inclusion we infer that this is a melilite rich mantle of the same cai that has experienced melting on one side

synchrotron x ray computed microtomography studies on vesiculated basaltic rocks synchrotron x ray computed microtomography cmt was applied to five basalt samples from different locations in order to determine the microgeometrical structures and physical properties of vesicles two vesiculated basaltic lavas and one calcite filled vesiculated basaltic lava were collected from the lesotho highland south africa and two basaltic scoria tephra were taken from the lungkuan volcano group in northeast china they were examined with cmt on the x27c beam line of the brookhaven national synchrotron light source the voxel size varied from 10 to 20 m depending on the chosen field of view of the tomographic instrument a fast filtered back transform ffbt algorithm was employed in the tomographic reconstruction a 3d image geometry analysis package was used to measure the vesicularity specific surface area and interconnectivity of the vesicles the results of the analyses showed that the bubbles have roughly spheroidal forms of different sizes vesicularity ranged from 45 for lavas to 80 for scoria at least 90 of the vesicles are interconnected specific surface area was determined both by counting voxel faces and by use of two point correlation functions

radar enabled recovery of the sutter s mill meteorite a carbonaceous chondrite regolith breccia doppler weather radar imaging enabled the rapid recovery of the sutter s mill meteorite after a rare 4 kiloton of tnt equivalent asteroid impact over the foothills of the sierra nevada in northern california the recovered meteorites survived a record high speed entry of 28 6 kilometers per second from an orbit close to that of jupiter family comets tisserand s parameter 2 8 0 3 sutter s mill is a regolith breccia composed of cm mighei type carbonaceous chondrite and highly reduced xenolithic materials it exhibits considerable diversity of mineralogy petrography and isotope and organic chemistry resulting from a complex formation history of the parent body surface that diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to c class asteroids are interpreted

ascent and eruption of a lunar high titanium magma as inferred from the petrology of the 74001 2 drill core abstract an analysis of the orange glasses and crystallized beads from the 68 cm deep 74001 2 core has been conducted to understand the processes occurring during ascent and eruption of the apollo 17 orange glass magma equilibrium between melt and metal blebs fe85ni14co1 within the core along with cr contents in olivine phenocrysts suggest there was an oxidation of c and a reduction of the melt at an o fugacity of iw 1 3 and 1320 c to form co gas at 200 bars or 4 km depth this was followed by development of more oxidized conditions during ascent also during ascent there was formation of euhedral homogeneous fo81 olivine crystals and spinel crystals with higher al and mg contents than the smaller spinels in the crystallized beads both the metal blebs and al rich spinels were trapped inside the fo81 olivine phenocrysts as they grew prior to eruption the composition of the orange glasses are homogeneous throughout the core except for a few distinct glasses at the top that appear to have been mixed in by micrometeorite reworking a few glassy melt inclusions of orange glass composition trapped in the fo81 phenocrysts contain 600 100 ppm s and 50 ppm cl compared to the 200 ppm s and 50 ppm cl in the orange glass melt when quenched these inclusions therefore document the addition of 400 ppm s to the co rich volcanic gas during the eruption the size and distribution of different volcanic beads in the apollo 17 deposit indicate a mode of eruption in which the orange glasses and partially crystallized beads formed further away from the volcanic vent where cooling rates were faster progressively larger and more numerous crystals in the black beads reflect slower cooling rates at higher optical densities in the volcanic plume the development of a brown texture in the orange glasses at the bottom of the core where the black beads dominate is interpreted to result from devitrification by subsolidus heating either as the orange glasses fell back through the hot plume or after deposition on the surface the change from domination by orange glasses to black beads in the core probably reflects a decrease in gas content over time which consequently would increase the plume optical density and favor slower cooling rates

applications of x ray computed tomography in the geosciences x ray computed tomography ct is a technique that allows non destructive imaging and quantification of internal features of objects it was originally developed as a medical imaging technique but it is now also becoming widely used for the study of materials in engineering and the geosciences x ray ct reveals differences in density and atomic composition and can therefore be used for the study of porosity the relative distribution of contrasting solid phases and the penetration of injected solutions as a non destructive technique it is ideally suited for monitoring of processes such as the movement of solutions and the behaviour of materials under compression because large numbers of parallel two dimensional cross sections can be obtained three dimensional representations of selected features can be created in this book various applications of x ray ct in the geosciences are illustrated by papers covering a wide range of disciplines including petrology soil science petroleum geology geomechanics and sedimentology

experimental study of the hydro mechanical behavior of rock joints using a parallel plate model containing contact areas and artificial fractures in recent years geological disposal of radioactive wastes is considered to be the most promising option which requires the understanding of the coupled mechanical hydraulic and thermal properties of the host rock masses and rock fractures the hydro mechanical behavior and properties of rock fractures are usually determined by laboratory experiments on fracture specimens that serve as the basic building block of the constitutive models of fractured rock masses laboratory testing of rock fractures involve a number of technical issues that may have significant impacts on the reliability and applicability of the testing results chief among them are the quantitative estimation of the evolutions of hydraulic transmissivity fields of fractures during shear under different normal constraint conditions and the sealing techniques when fluid flow during shear is involved in this study a new shear flow testing apparatus with specially designed fluid sealing techniques for rock fractures were developed under constant normal load cnl or constant normal stiffness cns constraint the topographical data of all fracture specimens were measured before testing to constitute the geometrical models for simulating the change of mechanical aperture distributions during shearing a number of shear flow coupling tests were carried out on three kinds of rock fracture specimens to evaluate the influence of morphological properties of rock fractures on their hydro mechanical behaviour some empirical relations were proposed to evaluate the effects of contact area and surface roughness on the behavior of fluid flow through rock fractures

shear enhanced nonlinear flow in rough walled rock fractures abstract nonlinear flow in 3d rough walled rock fractures is simulated by solving the navier stokes equations the emphasis is on the impact of shear caused aperture changes variable apertures and asperity contacts and flow conditions inertial term upon nonlinear flow behavior in order to compare shear effects two 3d fracture models with and without shear were established with identical initial rough walled surfaces topographies of a realistic rock sample five groups of simulations with different inflow boundary conditions of flowrates reynolds numbers re were conducted to demonstrate shear enhanced nonlinearity of flow fields and limitations of local cubic law lcl approach the flow results clearly show channeling flow along the preferential paths transverse flow around the contact spots and eddy flows behind contact spots with increasing re which cannot be observed in 2d models the effective transmissivity of the 3d fracture model was calculated from the modeling results of velocity and pressure fields the results showed that the effective transmissivity is a function of local apertures with important uncertainties even when re is small i e re 0 4 in this study thus the validity of the transmissivity evaluation using lcl approach for nonlinear flow in 3d rough walled rock fractures is questionable

chondrules in the qingzhen type 3 enstatite chondrite possible precursor components and comparison to ordinary chondrite chondrules abstract the qingzhen eh3 fall appears to be the least equilibrated enstatite chondrite mineral compositions vary widely from chondrule to chondrule and in some cases from grain to grain within individual chondrules as in ordinary chondrite oc chondrules most elements show appreciable ranges in concentration porphyritic olivine pyroxene pop chondrules are richer than porphyritic pyroxene pp and radial pyroxene rp chondrules in refractory lithophiles and siderophiles unlike oc chondrules qingzhen s rp and pp chondrules have similar bulk compositions elements in each of the following sets intercorrelate significantly probably because these elements were present in the same nebular components 1 1 fe co ni ir au 2 2 ca eu se 3 3 al sc hf 4 4 na ree 5 5 cl br several additional elements show no correlations set 1 elements were probably derived from a metal component as in oc chondrules set 3 elements which occur in higher concentrations in olivine bearing pop chondrules suggest the existence of a refractory lithophile rich olivine rich component similar to the one previously inferred for oc chondrules set 2 elements suggest a precursor component rich in oldhamite and set 4 elements suggest another refractory bearing component components 2 and 4 were not precursors of oc chondrules for some chondrules interelement ratios of refractory lithophiles such as ca al ti sc and ree are similar to ci ratios this indicates that these elements were probably derived from silicates we suggest that the earliest solid phases were refractory silicates that were sulfurized before chondrule formation some of these sulfurized components e g one rich in oldhamite were abundant in the region where the qingzhen chondrules formed

hydraulic properties of 3d rough walled fractures during shearing an experimental study abstract this study experimentally analyzed the influence of shear processes on nonlinear flow behavior through 3d rough walled rock fractures a high precision apparatus was developed to perform stress dependent fluid flow tests of fractured rocks then water flow tests on rough walled fractures with different mechanical displacements were conducted at each shear level the hydraulic pressure ranged from 0 to 0 6 mpa and the normal load varied from 7 to 35 kn the results show that i the relationship between the volumetric flow rate and hydraulic gradient of rough walled fractures can be well fit using forchheimer s law notably both the linear and nonlinear coefficients in forchheimer s law decrease during shearing ii a sixth order polynomial function is used to evaluate the transmissivity based on the reynolds number of fractures during shearing the transmissivity exhibits a decreasing trend as the reynolds number increases and an increasing trend as the shear displacement increases iii the critical hydraulic gradient critical reynolds number and equivalent hydraulic aperture of the rock fractures all increase as the shear displacement increases when the shear displacement varies from 0 to 15 mm the critical hydraulic gradient ranges from 0 3 to 2 2 for a normal load of 7 kn and increases to 1 8 8 6 for a normal load of 35 kn and iv the forchheimer law results are evaluated by plotting the normalized transmissivity of the fractures during shearing against the reynolds number an increase in the normal load shifts the fitted curves downward additionally the forchheimer coefficient decreases with the shear displacement but increases with the applied normal load

itqiy a metal rich enstatite meteorite with achondritic texture itqiy is a unique coarse grained metal rich enstatite meteorite that was found in the western sahara and consists of two rocks together weighing 4 72 kg which are both completely coated with fusion crust we report results from our electron microprobe and instrumental neutron activation analysis techniques itqiy consists of subhedral equigranular millimeter sized enstatite 25 vol of millimeter sized kamacite and a few tiny intergrowths of sulfides and kamacite relic chondrules are absent pyroxene fs0 2 is chemically similar to enstatite in el chondrites but the metal is closer in composition to that in eh chondrites sulfides resemble those in e chondrites but their compositions are distinct from those in both el and eh chondrites itqiy clearly formed under very reducing conditions but it does not appear to have formed from eh or el chondrites two thermal events can be distinguished silicate compositions including rare earth element abundances indicate loss of partial melt and slow cooling heterogeneous sulfides indicate a subsequent reheating and quenching event which may have been due to shock as many enstatite grains show shock stage s3 features

analysis of vesicular basalts and lava emplacement processes for application as a paleobarometer paleoaltimeter abstract we have developed a method for determining paleoelevations of highland areas on the basis of the vesicularity of lava flows vesicular lavas preserve a record of paleopressure at the time and place of emplacement because the difference in internal pressure in bubbles at the base and top of a lava flow depends on atmospheric pressure and lava flow thickness at the top of the flow the pressure is simply atmospheric pressure while at the base there is an additional contribution of hydrostatic lava overburden thus the modal size of the vesicle bubble population is larger at the top than at the bottom this leads directly to paleoatmospheric pressure because the thickness of the flow can easily be measured in the field and the vesicle sizes can now be accurately measured in the lab because our recently developed technique measures paleoatmospheric pressure it is not subject to uncertainties stemming from the use of climate sensitive proxies although like all measurements it has its own sou

a petrographic chemical and isotopic study of calcium aluminum rich inclusions and aluminum rich chondrules from the axtell cv3 chondrite petrographic compositional and isotopic characteristics were studied for three calcium aluminum rich inclusions cais and four plagioclase bearing chondrules three of them al rich from the axtell cv3 chondrite all seven objects have analogues in allende cv3 and other primitive chondrites yet axtell like most other chondrites contains a distinctive suite of cais and chondrules in common with allende cais cais in axtell exhibit initial 26 al 27 al ratios 26 al 27 al 0 ranging from 5 10 5 to 2 ma after the first cais as in other cv3 chondrites some objects in axtell show evidence of isotopic disturbance axtell has experienced only mild thermal metamorphism 600 c probably not enough to disturb the al mg systematics its cais and chondrules have suffered extensive metasomatism probably prior to final accretion these data indicate that cais and chondrules in axtell and other meteorites had an extended history of several million years before their incorporation into the axtell parent body these long time periods appear to require a mechanism in the early solar system to prevent cais and chondrules from falling into the sun via gas drag for several million years before final accretion we also examined the compositional relationships among the four plagioclase bearing chondrules two with large anorthite laths and two barred olivine chondrules and between the chondrules and cais three processes were examined 1 igneous differentiation 2 assimilation of a cai by average nebular material and 3 evaporation of volatile elements from average nebular material we find no evidence that igneous differentiation played a role in producing the chondrule compositions although the barred olivine compositions can be related by addition or subtraction of olivine methods 2 and 3 could have produced the composition of one chondrule axch 1471 but neither process explains the other compositions our study indicates that plagioclase bearing objects originated through a variety of processes

oxidation states and ascent history of the apollo 17 volcanic beads as inferred from metal glass equilibria abstract the composition mode of occurrence and relationships of metal blebs in the apollo 17 74001 2 core have been examined to provide insight into variations in oxidation states during ascent and eruption of the lunar volcanic glasses the 74001 2 core is composed of 99 orange volcanic glasses and their crystallized equivalents black beads with olivine phenocrysts metal blebs and in the upper 8 cm of the core lithic fragments composing the remaining 1 in an analysis of this core twenty nine metal blebs larger than 4 m in size were discovered in thin sections taken along the length of the 68 cm deep core these blebs are classified into three types on the basis of their shape composition and distribution fourteen of the metal blebs were found trapped inside or between olivine phenocrysts type i blebs microprobe analyses showed that these spherical blebs have a homogeneous composition of 85 fe 14 ni and 1 1 co from core to rim six type ii rounded blebs were discovered trapped inside volcanic beads their core compositions are similar to the type i but near the rim these blebs have a sharp decrease in fe and increase in ni content in the lower half of the 74001 2 core where the beads are predominantly black many contain 5 m amoeba shaped type iii metal blebs type iii blebs are composed of fe with trace amounts of ni two angular metal fragments could not be classified into any of the three types we propose that the type i blebs formed initially at 4 0 km depth and 1 3 log units below iw at a pressure of 200 bars and a temperature of 1320 c by the formation of c o gas during graphite oxidation once trapped by olivine phenocrysts the blebs were buffered from further reactions with the melt the type ii blebs remained in contact with the melt during ascent and experienced loss of fe to the surrounding melt phase by oxidation reactions which range from 1 3 to 0 9 log below iw finally type iii blebs formed either by exsolution of fe during crystallization in the fire fountain or by loss of volatiles originally coordinated with fe to the volcanic gas phase under the reduced conditions in the fountain

anisotropy of flow in a fracture undergoing shear and its relationship to the direction of shearing and injection pressure abstract the work presented deal with the effects of shear direction and injection flow rate on the directional anisotropy of the flow for a given normal stress also is related to these effects the evolution of the intrinsic transmissivity of the fracture in relation to the shear direction and tangenital displacements particularly for small displacements tests are performed on mortar replicas of a natural fracture so that the fracture roughness and void space geometry are the same for each test three shear directions are defined these tests results show that the evolution of the intrinsic transmissivity of a fracture depends on the shear direction particularly for small displacements less than 0 5 mm and that shearing induces noticeable modifications in flow direction

the conditions of chondrule formation part i closed system abstract mixing was an important process in the early solar nebula and is often used as an argument to explain the compositional scatter among chondrules mm sized once molten silicate spherules in chondritic meteorites if it is hypothesized that chondrules only acted as closed systems and the scatter in chondrule bulk chemical compositions is only the result of mixing heterogeneous precursor grains the basic components of chondrules it is in turn possible to determine the sizes of the precursor grains using statistical calculations in order to reproduce the observed compositional scatter in chondrules not more than 10 precursor grains should contribute to a single chondrule each with a diameter of several 100 m this finding has important implications for the conditions of chondrule formation and replaces the so far widely accepted model that chondrules formed from fine grained dust balls chondrules rather formed from coarse grained precursor aggregates with variable amounts of m fine matrix material as a consequence only chondrite matrix or interstellar material winnows as precursor material large grains of variable composition serving as precursor grains must have been formed prior to chondrule formation chondrules probably have not been their immediate precursors as only 1 2 chondrule recycling steps would have homogenized bulk chondrule compositions chondrule recycling can therefore only have occurred to a limited extent chondrule formation needed at least three steps 1 production of large and heterogeneous chondrule precursor grains 2 agglomeration of large precursor grains and fine grained precursors into aggregates 3 formation of chondrules during transient heating events al rich chondrules can in this context be explained by the admixture of cais to either chondrule precursors or a population of existing chondrules

quantifying the three dimensional shapes of spheroidal objects in rocks imaged by tomography abstract the shapes of objects in rocks are sometimes measured through tomographic sections either physical sections or virtual x ray computed tomography approximation of these objects as ellipsoids is often sufficient in these analyses here we present an easily implemented algorithm to best fit an ellipsoid to a set of n points n 9 distributed on the surface of a spheroidal object observed in tomographic sections the method is demonstrated on x ray computed tomography data of 90 chondrules in a cr2 chondrite by averaging the ellipsoids for all the objects measured in a rock one can then readily describe its fabric by an average ellipsoid and if that average ellipsoid is interpreted as a strain ellipsoid and assuming all objects have undergone the same strain each object can be retro deformed and the inferred initial population of objects studied

physical characterization of a suite of buzzard coulee h4 chondrite fragments on november 20 2008 the buzzard coulee h4 chondrite fell to earth outside of lloydminster alberta canada eighteen fresh samples obtained by the national meteorite collection of canada ranging from 8 80 to 109 14 g were investigated in this study physical properties of the samples were first obtained using a suite of nondestructive techniques the bulk density archimedean bead method 3 48 0 04 g cm 3 3 d laser imaging 3 46 0 03 g cm 3 micro computed tomography 3 44 0 03 g cm 3 porosity 6 2 0 1 bulk magnetic susceptibility log 5 364 0 056 10 9 m3 kg 1 at 825 hz 5 329 0 052 10 9 m3 kg 1 at 19 000 hz and other derived magnetic properties frequency dependence 8 7 6 2 degree of anisotropy a 22 0 2 0 ellipsoid shape b 18 7 8 7 are typical of h chondrites the coefficient of variation associated with the properties measured directly was low 0 10 1 15 indicating that the samples are homogenous at the interfragment scale the study then proceeded with detailed analyses at the intrafragment scale visual inspection of micro computed tomographic images allowed the identification of an anomalous large clast with low metal content in a fragment another fragment exhibited macroscopic shock veins that warranted further examination these fragments were cut and polished thin sections prepared for petrological analysis by optical and scanning electron microscopy based on mineralogical and textural similarities with several chondrules the large clast was interpreted to be a macrochondrule in a larger context this study proposes a protocol for the systematic investigation of extraterrestrial material that can be exported to other new meteorite falls and finds and specimens from sample return mission

crystallization of the basaltic shergottites insights from crystal size distribution csd analysis of pyroxenes quantitative petrographic analysis using the crystal size distribution csd method provides a novel approach for examining the crystallization histories of basaltic shergottites grain number densities at different sizes are plotted against grain size and the resulting curve relates to the geologic processes involved with the crystallization of the grain population most basaltic shergottites are dominated by pigeonite and augite and because plagioclase is primarily interstitial and therefore constrained in its growth by the surrounding pyroxenes we limited our size measurements to the pyroxene phases the groundmasses of elephant moraine eet a79001 lithology a and dar al gani dag 476 are fine grained with cumulus pyroxene and interstitial plagioclase glass their simple linear csd plots record a single stage of pyroxene crystallization under steady state conditions of continuous nucleation and growth the textures of queen alexandra range que 94201 and eeta79001 lithology b are quite different from the other shergottites with intergrown pyroxene and plagioclase likewise their csd plots are also distinct with curved trends that suggest a lack of large grains most likely because of interference between simultaneously growing silicate phases however the csd plot shapes are smooth also implying a single stage of growth shergotty and zagami with coarser cumulus textures display csd plots that are generally linear over most grain sizes this implies that conditions of nucleation and growth were dominant during formation of the pyroxene populations both plots however also display kinks implying multiple stages of growth a similar kink is also visible in a csd plot of only the mg rich cores of shergotty pyroxenes which suggests the feature represents changes in conditions during core crystallization rather than an event coincident with the change in composition to the fe rich rims the plot may be interpreted as representing two stages of core growth with an intervening short hiatus of nucleation with continued crystallization associated with ascent of the magma eruption onto the surface probably triggered the compositional change to fe rich rims the csd analysis of products from a controlled crystallization study agree with experimental and petrologic estimates that cooling rates for zagami were on the order of a few tenths of a degree per hour growth rates derived from these cooling rates suggest crystallization of shergotty and zagami pyroxenes occurred over a period of a few weeks to months

meteorite 3 d synchrotron microtomography methods and applications methods of synchrotron x ray computed microtomography xrcmt are described which allow nondestructive high spatial and contrast resolution imaging of the density structures of meteorites and their components in three dimensions images of bulk chondrites to one cubic centimeter in size reveal compound chondrules chondrule matrix volumetric ratios metal and sulfide distribution petrofabrics and 3 d chondrule and calcium aluminum inclusion cai sizes and shapes images of separated chondrules and cais reveal void spaces mineral intergrowth textures and the true locations of crystal rims and cores at resolutions to 8 cubic micron volume element images of achondrites reveal mineral fabrics and crystal zoning lunar glass spherules can be searched for phenocrysts bearing deeply sourced melt inclusions a companion dvd and url contain images for classroom and research use numerical techniques for quantification of x ray computed microtomography xrcmt data and its potential applications are discussed three dimensional x ray images of meteorites provide a way to discover components of interest and to precisely slice samples to expose these components with minimal damage and loss of material three dimensional studies of petrographic features size shape texture and modal abundance of chondrites and their components as well as other meteorites have definite advantages over standard 2 d studies using randomly sliced thin sections

nondestructive high resolution visualization and measurement of anisotropic effective porosity in complex lithologies using high resolution x ray computed tomography abstract new methods are presented that allow high resolution x ray computed tomography hrxct to be utilized for imaging and measuring the effective porosity field of mineralogically complex specimens at resolutions in the 5 100 m range these methods extend previous established approaches by allowing sample displacement between successive imaging runs and eliminating the need for a highly attenuating tracer a highly detailed map of partial porosity can be generated by scanning a sample in a dry state and infiltrated by distilled water and performing a three dimensional alignment of the two data sets this map can then be used to obtain a number of quantitative analyses such as the frequency distribution of partial porosity and directional analysis to infer flow anisotropy it can also be used for petrographic study of the relationship of porosity to evolving mineralogy in a dynamic system these methods are demonstrated on a series of altered volcanic rocks from a deep sea hydrothermal field

non destructive observation of meteorite chips using quantitative analysis of optimized x ray micro computed tomography abstract a method for the non destructive observation of extraterrestrial materials using x ray computed tomography ct is discussed this method allows to image texture of objects in meteorites without destructive methods of sample preparation quantitative analysis of x ray ct data was achieved by measuring x ray linear attenuation coefficients lacs the histogram of the lac value provides information regarding the meteorite structure such as the internal components and their chemical composition the change of the signal to noise ratio s n ratio of ct data is investigated by optimizing the ct measurement conditions these results form an important baseline for the initial analysis of extraterrestrial materials

an autocorrelation method for three dimensional strain analysis abstract we present a method of finite strain estimation using the autocorrelation properties of deformed rock autocorrelation is the correlation of an image with itself as a function of an offset or lag in two and three dimensions the lag has both distance and direction many geologic materials are initially isotropic which means that the autocorrelation function acf will be initially isotropic as well deformation imposes an anisotropic distortion which can be measured using the ramsay and fry strain methods for example but can also be estimated from the acf x ray tomography now provides a rapid way to measure the three dimensional acf of a geologic sample strain parameters are estimated by using a non linear best fit method to minimize the anisotropy in the acf the acf method works best for materials where the objects are internally uniform and contrast strongly with the matrix and other grains

zoned chondrules in semarkona evidence for high and low temperature processing at least 15 of the 10w feo chondrules in semarkona ll3 0 have mesostases that are concentrically zoned in na with enrichments near the outer margins we have studied zoned chondrules using electron microprobe methods x ray mapping plus quantitative analysis ion microprobe analysis for trace elements and hydrogen isotopes cathodoluminescence imaging and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved mesostases in these chondrules are strongly zoned in all moderately volatile elements and h interpreted as water calcium is depleted in areas ofvolatile enrichment titanium and cr generally decrease toward the chondrule surfaces whereas al and si may either increase or decrease generally in opposite directions to one another mn follows na in some chondru1es but not in others fe and mg are unzoned d h ratios increase in the water rich areas of zoned chondrules mesostasis shows cathodoluminescence zoning in most zoned chondrules with the brightest yellow color near the outside mesostasis in zoned chondrules appears to be glassy with no evidence for devitrification systematic variations in zoning patterns among pyroxene and olivine rich chondrules may indicate that fractionation oflow and high ca pyroxene played some role in ti cr mn si ai and some ca zoning but direct condensation ofelements into hot chondrules secondary melting oflate condensates into the outer portions of chondrules and subsolidus diffusion of elements into warm chondrules cannot account for the sub parallel zoning profiles ofmany elements the presence ofh20 or elemental abundance patterns zoning ofmoderately volatile elements and ca may have been produced by hydration ofchondrule glass without devitrification during aqueous alteration on the parent asteroid this could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material calcium was mainly lost during this process and other nonvolatile elements may have been mobile as well some unzoned 10w feo chondrules appear to have fully altered mesostasis

the origin and history of the metal and sulfide components of chondrules abstract fourteen siderophile and other non lithophile elements determined in 31 semarkona ll3 0 chondrules by neutron activation analysis are severely fractionated relative to lithophile elements their chondrule whole rock abundance ratios vary by factors of up to 1000 the mean ratio is 0 2 non refractory siderophile abundance patterns in ni rich chondrules are smooth functions of volatility and in ni poor chondrules patterns are more irregular refractory siderophile elements are often fractionated from ni they covary confirming the presence of a refractory metal component the chalcophile element se correlates with br and siderophile elements zinc is uniformly low and uncorrelated with other elements most metal and sulfide in chondrules was probably present in the solar nebula before chondrule formation most siderophile and chalcophile elements were in these materials some fe was also in silicates as were minor amounts of ni co au ge and possibly se the amount of metal formed by reduction during chondrule melting was minor the common metal component in chondrules is similar to and may be the same as the common component involved in the metal silicate fractionation of the ordinary chondrite groups chondrules are depleted in metal chiefly because they sampled metal poor precursor assemblages metal segregation during the molten period and subsequent loss was a minor process that may be responsible for most surface craters on chondrules

the paradox between low shock stage and evidence for compaction in cm carbonaceous chondrites explained by multiple low intensity impacts abstract petrographic analysis of eight cm carbonaceous chondrites eet 96029 lap 031166 lon 94101 met 01072 murchison murray sco 06043 que 93005 by electron imaging and diffraction and x ray computed tomography reveals that six of them have a petrofabric defined by shock flattened chondrules with the exception of murchison those cms that have a strong petrofabric also contain open or mineralized fractures indicating that tensional stresses accompanying the impacts were sufficient to locally exceed the yield strength of the meteorite matrix the cms studied span a wide range of petrologic subtypes and in common with rubin 2012 we find that the strength of their petrofabrics increases with their degree of aqueous alteration this correspondence suggests that impacts were responsible for enhancing alteration probably because the fracture networks they formed tapped fluid reservoirs elsewhere in the parent body two meteorites that do not fit this pattern are met 01072 and murchison both have a strong petrofabric but are relatively unaltered in the case of met 01072 impact deformation is likely to have postdated parent body aqueous activity the same may also be true for murchison but as this meteorite also lacks fractures and veins its chondrules were most likely flattened by multiple low intensity impacts multiphase deformation of murchison is also revealed by the microstructures of calcite grains and chondrule defined petrofabrics as revealed by x ray computed tomography the contradiction between the commonplace evidence for impact deformation of cms and their low shock stages most belong to s1 can be explained by most if not all having been exposed to multiple low intensity i e

permeability anisotropy induced by the shear displacement of rough fracture walls 1 the permeability anisotropy that results from a shear displacement between the complementary self affine walls of a rough fracture is investigated experiments in which a dyed fluid radially injected into a transparent fracture displaces a transparent one are presented a clear anisotropy is observed in the presence of shear displacements and allows us to estimate the ratio of the permeabilities for flows parallel and perpendicular to a simple model which accounts for the development of channels perpendicular to qualitatively explains these results and predicts a permeability decreasing increasing linearly with the variance of the aperture field for flow parallel perpendicular to the shear displacement these predictions are then compared to the results of numerical simulations performed using a lattice boltzmann technique and to the anisotropies measured in displacement experiments

estimating the relation between surface roughness and mechanical properties of rock joints discontinuities in rock masses have an important influence on deformational behaviour of blocky rock systems for a single rock joint the roughness of its surface is of paramount importance to its mechanical and hydraulic properties such as friction angle shear strength and dilatancy aperture many methods have been used to characterize the surface roughness of rock joints such as joint roughness coefficients jrc root mean square rms value structure function sf etc however most of these methods can only be used in the 2 d models in this study we carried out direct shear experiments on rock joints under both constant normal load cnl and constant normal stiffness cns conditions and measured the surfaces of rock joints before and after shearing using a 3 d laser scanning profilometer system by using a 3 d fractal evaluation method of roughness characterization the projective covering method pcm and a direct shear apparatus of high accuracy the relation between mechanical properties of rock joints under different boundary conditions and the change of their fractal dimensions in both 2 d and 3 d models have been examined which gives a new approach to accurately evaluate the evolution of roughness of rock joint surfaces and its influence on the hydro mechanical behaviours of rock joints

numerical investigation of geometrical and hydraulic properties in a single rock fracture during shear displacement with the navier stokes equations extensive research has shown that fluid flow through rock fractures is greatly influenced by surface roughness for a single rock fracture the roughness of the upper and bottom surfaces is the same in the initial condition and then its deformation occurs with normal stress and shear stress imposed on the natural rock previous researchers have paid considerable attention to describing the roughness of the single fracture and its effects on fluid flow however few studies have explained the fluid flow with shear displacement and the direction of the fluid flow velocity field in this work a more detailed 2d numerical model was developed using a laser scanner system with a spacing grid of 0 1 mm to investigate the influence of shear displacement accurately the comsol multiphase codes were applied by applying the navier stokes equations the results of the procedure for shear displacement simulation illustrate the distribution of the absolute velocity and pressure drop under the constant pressure gradient the velocities predicted at the vertical profiles of the inlet were similar to the parabolic velocity curve defined by the cubic laws the mean mechanical aperture was usually larger than the hydraulic aperture from the measured flow rates and a devised empirical equation was proposed to describe the relationship between the mechanical aperture and the hydraulic aperture values the recirculation zones observed in directional fluid flow during shear explain the anisotropy of roughness of a single fracture and the phenomenon argues the applicability of local cubic laws which overestimate the total fluid flow rate

the frequency of compound chondrules and implications for chondrule formation the properties of compound chondrules and the implications that they have for the conditions and environment in which chondrules formed are investigated formulae to calculate the probability of detecting compound chondrules in thin sections are derived and applied to previous studies this reinterpretation suggests that at least 5 of chondrules are compounds a value that agrees well with studies in which whole chondrules were removed from meteorites the observation that adhering compounds tend to have small contact arcs is strengthened by application of these formulae while it has been observed that the secondaries of compound chondrules are usually smaller than their primaries these same formulae suggest that this could be an observation bias it is more likely than not that thin section analyses will identify compounds with secondaries that are smaller than their primaries a new model for chondrule collisional evolution is also developed from this model it is inferred that chondrules would have formed on average in areas of the solar nebula that had solids concentrated at least 45 times over the canonical solar value

the typical structure of tornado proximity soundings an objective scheme based on empirical orthogonal function analysis to detect patterns in a single or multivariate data set is developed and applied to rawinsonde observations taken in the near tornado environment if only temperature data are considered two distinct categories differentiated chiefly by the tropopause height are found when moisture observations are included with the temperatures the separation between categories becomes less distinct however it is noted that within the near tornado environment there is an inverse relationship between the degree of observed convective and conditional instability analysis of only the winds shows that a low level veering with height is the rule however the strength of the veering can vary considerably when the temperature moisture and winds are treated in concert two categories again appear one group occurs with strong winds and a low tropopause while the other group features weak winds and a high tropopause these groups correspond to springtime and summertime synoptic situations respectively comparisons of the various analyses indicate that the near tornado environment typically features a balance between the strength of the veering of the winds and the amount of conditional instability present summer tornadoes feature strong conditional instability and weak winds while springtime tornadoes occur with stronger veering and convective instability the strongest tornadoes occur with springtime type conditions

tornadoes and downbursts in the context of generalized planetary scales abstract in order to cover a wide range of horizontal dimensions of airflow the author proposes a series of five scales maso meso miso to be read as my so moso and muso arranged in the order of the vowels a e 1 o u the dimensions decrease by two orders of magnitude per scale beginning with the planet s equator length chosen to be the maximum dimension of masoscale for each planet mesoscale highs and lows were described on the basis of mesoanalyses while sub mesoscale disturbances were depicted by cataloging over 20 000 photographs of wind effects taken from low flying aircraft during the past 15 years various motion thus classified into these scales led to a conclusion that extreme winds induced by thunderstorms are associated with misoscale and mososcale airflow spawned by the parent mesoscale disturbances

igneous rims on low feo and high feo chondrules in ordinary chondrites abstract many ordinary chondrite oc chondrules are surrounded by rims that show evidence of appreciable melting and can be called igneous these rims formed after the melting and solidification of the host chondrule we studied thirteen igneous rims on low feo chondrules fa or fs 10 mol in ordinary chondrites of petrographic type 3 5 by electron microprobe analysis and scanning electron microscopy in both sets olivine and pyroxene compositions of the rims are similar to or moderately higher in feo than those in the host igneous rims around low feo chondrules show evidence of large degree 80 melting including 1 resorbed chondrule surfaces 2 rounded metal troilite nodules and feldspathic mesostasis 3 euhedral and subhedral morphology of olivine and pyroxene and limited ranges in grain sizes and 4 a rarity of relict grains most low feo chondrules have olivine as their major phase but pyroxene is commonly the predominant phase in their rims rims on high feo chondrules generally have smaller grain sizes and exhibit lower degrees of melting than rims around low feo chondrules mg rich relict grains are observed in high feo rims most low feo chondrules have matrix like rims around the igneous rims but matrix like rims are rare around rims on high feo chondrules there is a continuum between igneous rims and enveloping secondaries of compound chondrules the existence of both sets of objects supports the view that in the oc region most mm size grain assemblages experienced more than one melting event the precursors melted to produce the igneous rims on low feo chondrules differ from those that comprise the rims on high feo chondrules a sizeable fraction of the precursors of low feo rims are from the host chondrule most high feo rims appear to consist largely of melted matrix like materials if the rim precursors are mainly independent the similar fa and fs contents in mafic minerals of rims and host chondrules indicate that 1 oc nebular subregions bounded in space and or in time were dominated by well mixed solids 2 many chondrules experienced multiple heating events during a short period and were then withdrawn from the chondrule forming region and 3 chondrules formed at different times were mixed before agglomeration to form chondrites if the host chondrules were the main source of the low feo rim materials the fact that pyroxene is generally more abundant than in the host suggests that sio 2 normative matrix was also an important ingredient and or that kinetics favored pyroxene crystallization in the rim rims around high feo chondrules were heated to lower temperatures than rims around low feo chondrules the rarity of matrix like rims around high feo igneous rims may indicate that the dust chondrule ratio was lower where they formed

zagami product of a two stage magmatic history abstract large specimens of the zagami shergottite show highly varied grain sizes and mineral abundances on a cm scale and preferred alignment of pyroxene laths we document the presence of whitlockite and of melt veins and pockets of shock origin pyroxene crystals have homogeneous mg rich pigeonite and augite cores overgrown by fe rich zoned pyroxene mostly pigeonite rims amphibole bearing magmatic melt inclusions occur exclusively in the cores we conclude that zagami experienced a twostage crystallization history the first stage occurred in a deep seated slowly cooling magma chamber there the homogeneous mg rich cores of the pyroxenes crystallized during relatively slow cooling the deep seated origin of the cores is also indicated by the presence of amphibole within them which requires pressures of formation equivalent to crystallization at depths 7 5 km on mars modest abundance of homogeneous mg rich cores 15 20 indicates that crystal settling did not play a significant role in this part of the magma chamber during the second stage the mg rich pyroxenes were entrained into a magma that either intruded to the near surface and cooled in a relatively thin dike or sill or extruded to the surface and crystallized in a lava flow 10 m thick again without indications for crystal settling this scenario is suggested by estimates of cooling rates of 0 1 0 5 c h based on sizes of the plagioclase maskelynite crystals and of 0 02 c h based on the width of pyroxene exsolution lamellae brearley 1991 irregular shapes of the mg rich cores result from resorption and possible solid state diffusion and the shapes and sizes of the pyroxenes after crystallization of fe rich pigeonite rims onto the cores were strongly controlled by the shapes and sizes of the cores the finer grained areas of the rock inherited smaller and more numerous mg rich pyroxene cores from the first stage than did the coarser grained areas crystallization of both augite and pigeonite cores at depth but mostly pigeonite rims in the nearsurface environment may be the result of a phase boundary shift and expansion of the pigeonite stability field at lower pressures the estimated depth of the magma chamber for zagami of 7 5 km and thickness of the putative lava flow of 10 m are consistent with calculations and observations of volcanic constructs and flows in the tharsis region of mars

determining chondrule size distributions from thin section measurements a method is described for correcting thin section derived chondrule sizes for three common sources of bias 1 the non equatorial sectioning of chondrules 2 the non zero thickness of thin sections and 3 the unequal probability of sectioning different size chondrules application of the correction procedure to chondrule data from co chondrites results in a reduction of mean and median chondrule diameters an increase in minimum diameters and transforms nearly log normal distributions to distributions that conform to a weibull probability function the weibull function form of co chondrule size distributions is similar to the form of chondrule distributions in ordinary chondrites obtained by disaggregation analyses

computed tomographic analysis of meteorite inclusions the discovery of isotopic anomalies in the calcium and aluminum rich inclusions of the allende meteorite has improved our knowledge of the origin of the solar system inability to find more inclusions without destroying the meteorite has hampered further study by using a fourth generation computed tomographic scanner with modifications to the software only the interior of heterogeneous materials such as allende can be nondestructively probed the regions of material with high and low atomic numbers are displayed quickly the object can then be cut to obtain for analysis just the areas of interest

three dimensional observation of carbonaceous chondrites by synchrotron radiation x ray ct quantitative analysis and developments for the future sample return missions abstract carbonaceous chondrites were observed by synchrotron radiation x ray computed tomography sr ct three dimensionally we analyzed the chemical composition of the components of the carbonaceous chondrites such as chondrules matrix and iron inclusions from the linear attenuation coefficient lac of x rays histograms of the lac were used for the analysis of chemical composition of the internal material and we could find a clear relation of the compositions between the chondrules and matrix we also analyzed the size distribution of low fe inclusions chondrules using image processing of ct images cumulative size distribution of chondrules shows power law distribution and slopes of the distribution changed for different chondrite classes results of these analyses show that the chondrule and matrix would have formed from the same precursor and were incorporated into the parent bodies without large scale mixing in the solar nebula the method will also provide important information for the analysis of future sample return missions our examinations demonstrate great potential of the quantitative determination of chondrite class nondestructively by sr ct

three dimensional petrography of metal phases in equilibrated l chondrites effects of shock loading and dynamic compaction abstract to examine the role of impacts in the evolution of asteroids as seen through their chondritic offspring we have performed a quantitative three dimensional 3d study of metal grains in a suite of increasingly shocked l chondrites with synchrotron x ray microtomography xmt our data allow rigorous quantification of size number distributions and collective morphology of fe ni metal phases in chondritic meteorites at the resolution of our xmt measurements 8 4 17 9 m voxel the number of metal particles increase with higher degrees of petrographically identified shock loading indicating a coalescing of fe ni metal at or below this scale our results demonstrate that collective degrees of metal grain preferred orientation increase with greater degrees of impact related compaction and shock loading ductile metal grains in l chondrites begin to show foliation at peak shock pressures

shape metal abundance chemistry and origin of chondrules in the renazzo cr chondrite we used synchrotron x ray microtomography to image in 3 dimensions 3d eight whole chondrules in a 1 cm 3 piece of the renazzo cr chondrite at 17 m per volume element voxel edge we report the first volumetric 3d measurement of metal silicate ratios in chondrules and quantify indices of chondrule sphericity volumetric metal abundances in whole chondrules range from 1 to 37 volume in 8 measured chondrules and by inspection in tomography data we show that metal abundances and metal grain locations in individual chondrules cannot be reliably obtained from single random 2d sections samples were physically cut to intersect representative chondrules multiple times and to verify 3d data detailed 2d chemical analysis combined with 3d data yield highly variable whole chondrule mg si ratios with a supra chondritic mean value yet the chemically diverse independently formed chondrules are mutually complementary in preserving chondritic solar fe si ratios in the aggregate cr chondrite these results are consistent with localized chondrule formation and rapid accretion resulting in chondrule matrix aggregates meteorite parent bodies that preserve the bulk chondritic composition of source regions

multiple impact events recorded in the nwa 7298 h chondrite breccia and the dynamical evolution of an ordinary chondrite asteroid abstract the major geologic process that has shaped the asteroids and led to development of their regoliths is impact petrofabrics in ordinary chondrites are undoubtedly the result of impact events on their asteroidal parent bodies and the foliation present in a chondrite serves as an enduring record of the magnitude of the most intense compacting event experienced by the material an overwhelming majority of chondrites have an internally consistent petrofabric contained within the spatial dimensions of the entire rock including across clasts or different petrographic domains this indicates that the magnitude of the most recent impact to have affected the assembled chondrite was significant enough to impart a foliation across all lithologies information of any previous impacts is largely lost because of the consistent realigned foliations we present x ray microtomography derived 3d petrofabric intensity and orientation data for three lithologies in the nwa 7298 breccia the internally inconsistent petrofabrics among differing lithologies indicate that the magnitude of the final impact event was smaller than previous ones this latter case preserves fabric information recorded during previous impacts and allows a more complete interpretation of the impact history of a local region of the asteroidal parent we used our data to infer the sequence and intensity of distinct impact events affecting the nwa 7298 parent asteroid we suggest a near surface impact debris zone on the h chondrite parent asteroid as an origin for nwa 7298 these observations yield new opportunities for investigating and interpreting the dynamic collisional evolution of asteroids

long lived magnetism on chondrite parent bodies abstract we present evidence for both early and late stage magnetic activity on the cv and l ll parent bodies respectively from chondrules in vigarano and bjurbole using micro ct scans to re orientate chondrules to their in situ positions we present a new micron scale protocol for the paleomagnetic conglomerate test the paleomagnetic conglomerate test determines at 95 confidence whether clasts within a conglomerate were magnetized before or after agglomeration i e for a chondritic meteorite whether the chondrules carry a pre or post accretionary remanent magnetization we found both meteorites passed the conglomerate test i e the chondrules had randomly orientated magnetizations vigarano s heterogeneous magnetization is likely of shock origin due to the 10 to 20 gpa impacts that brecciated its precursor material on the parent body and transported it to re accrete as the vigarano breccia the magnetization was likely acquired during the break up of the original body indicating a cv parent body dynamo was active 9 ma after solar system formation bjurbole s magnetization is due to tetrataenite which transformed from taenite as the parent body cooled to below 320 c when an ambient magnetic field imparted a remanence we argue either the high intrinsic anisotropy of tetrataenite or brecciation on the parent body manifests as a randomly orientated distribution and a l ll parent body dynamo must have been active at least 80 to 140 ma after peak metamorphism primitive chondrites did not originate from entirely primitive never molten and or differentiated parent bodies primitive chondrite parent bodies consisted of a differentiated interior sustaining a long lived magnetic dynamo encrusted by a layer of incrementally accreted primitive meteoritic material the different ages of carbonaceous and ordinary chondrite parent bodies might indicate a general difference between carbonaceous and ordinary chondrite parent bodies and or formation location in the protoplanetary disk

a 3 d study of mineral inclusions in chromite from ordinary chondrites using synchrotron radiation x ray tomographic microscopy method and applications abstract a method is described for imaging in 3 d the interiors of meteoritic chromite grains and their inclusions using synchrotron radiation x ray tomographic microscopy in ordinary chondrites chromite is the only common mineral that survives long term weathering on earth information about the silicate matrix of the original meteorite however can be derived from mineral inclusions preserved in the protecting chromite the inclusions are crucial in the classification of fossil meteorites as well as sediment dispersed chromite grains from decomposed meteorites and larger impacts as these are used for characterizing the past influx of material to earth but have previously been difficult to locate the method is non destructive and time efficient for locating inclusions the method allowed quantitative and morphological studies of both host chromite grains and inclusions in three dimensions the study of 385 chromite grains from eight chondrites h4 6 l4 6 ll4 ll6 reveals that inclusions are abundant and equally common in all samples almost two thirds of all chromite grains contain inclusions regardless of group and type the study also shows that the size of the inclusions and the host chromite grains as well as the number of inclusions within the host chromite grains vary with petrographic type thus the petrographic type of the host of a suite of chromite grains can be determined based solely on inclusion content the study also revealed that the amount of fractures in the host chromite can be correlated to previously assigned shock stages for the various chondrites the study has thus shown that the features and inclusions of fossil chromite grains can give similar information about a former host meteorite as do studies of an unweathered whole meteorite meaning that this technique is essential in the studies of ancient meteorite flux to earth

a novel three dimensional discrete fracture network model for investigating the role of aperture heterogeneity on fluid flow through fractured rock masses abstract effect of anisotropic aperture on the hydraulic properties of single rock fractures has been systematically investigated yet the aperture variability of individual fractures in 3d discrete fracture networks dfns is commonly negligible by using parallel plate fractures the present study proposed a 3d dfn model with fractures having heterogeneous apertures to estimate the influence of fracture variability on fluid flow in total a set of 1280 3d models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code the influences of aperture heterogeneity and network topology on the flow pattern and permeability of 3d dfns are estimated the results show that the network topology provides a first order frame of geometrical connectivity and the heterogeneous aperture further allows the flow to select some most transmissive channels within these connected fractures the dfn model with identical apertures generates a large number of medium flow rate regions whereas the dfn model with fractures having heterogeneous apertures results in extremely low and high flow rate regions the permeability ratio of the two models is widely spread in terms of a small variation in the average mechanical aperture as a result of strong dependence on the aperture distribution the average permeability ratio increases significantly first and then approaches to 1 0 with increasing the average mechanical aperture this allows for the definition of a critical mechanical aperture above which the permeability can be properly predicted using the dfn model with fractures having identical apertures and below which the permeability is much altered by the aperture variability and the dfn model with fractures having heterogeneous apertures should be employed