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1

Multiple melting in a four-layered barred-olivine chondrule with compositionally heterogeneous glass from LL3.0 Semarkona  

NASA Astrophysics Data System (ADS)

Chondrule K7p from LL3.0 Semarkona consists of four nested barred-olivine (BO) chondrules. The innermost BO chondrule (chondrule 1) formed by complete melting of an olivine-rich dustball. After formation, the chondrule was incorporated into another olivine-rich dustball. A second heating event caused this second dustball to melt; the mesostasis and some of the olivine in chondrule 1 were probably also melted at this time, but the chondrule 1 structure remained largely intact. At this stage, the object was an enveloping compound BO chondrule. This two-step process of melting and dustball enshrouding repeated two more times. The different proportions of olivine and glass in chondrules 1-4 suggest that the individual precursor dustballs differed in the amounts of chondrule fragments they contained and the mineral proportions in those fragments. The final dustball (which ultimately formed chondrule 4) was somewhat more ferroan; after melting, crystallizing, and quenching, chondrule 4 contained olivine and glass with higher FeO and MnO contents than those of the earlier formed chondrules. Subsequent aqueous alteration on the LL parent body transformed the abundant metal blebs and stringers at the chondrule surface into carbide, iron oxide, and minor Ni-rich metal. Portions of the mesostasis underwent dissolution, producing holes and adjacent blades of more resistant material. Much of the glass in the chondrule remained isotropic, even after minor hydration and leaching. The sharp, moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution.

Rubin, Alan E.

2013-03-01

2

Experimental Reproduction of Olivine rich Type-I Chondrules  

NASA Technical Reports Server (NTRS)

Ordinary chondritic meteorites are an abundant type of stony meteorite characterized by the presence of chondrules. Chondrules are small spheres consisting of silicate, metal, and sulfide minerals that experienced melting in the nebula before incorporation into chondritic meteorite parent bodies. Therefore, chondrules record a variety of processes that occurred in the early solar nebula. Two common types of unequilibrated chondrules with porphyritic textures include FeO-poor (type I) and FeO-rich (type II) each subdivided into an A (SiO2-poor) and B (SiO2-rich) series. Type IA chondrules include those with high proportions of olivine phenocrysts (>80% olivine) and type IB chondrules include those with high proportions of pyroxene phenocrysts (<20% olivine). An intermediate composition, type IAB chondrules include those chondrules in which the proportion of olivine phenocrysts is between 20-80%. We conducted high-temperature laboratory experiments (melting at 1550 C) to produce type I chondrules from average unequilibrated ordinary chondrite (UOC) material mixed with small amounts of additional olivine. The experiments were conducted by adding forsteritic rich olivine (San Carlos olivine, Fo 91) to UOC material (GRO 95544) in a 30/70 ratio, respectively. Results of these high temperature experiments suggest that we have replicated type IA chondrule textures and compositions with dynamic crystallization experiments in which a heterogeneous mixture of UOC (GRO 95544) and olivine (San Carlos olivine) were melted at 1550 C for 1 hr. and cooled at 5-1000 C/hr using graphite crucibles in evacuated silica tubes to provide a reducing environment.

Smith, Robert K.

2005-01-01

3

Crystal Size Distributions from Porphyritic Olivine Chondrules: Insights into Formation Conditions  

NASA Technical Reports Server (NTRS)

Most chondrules preserve, in their texture, a record of their precursor material and the nature and intensity of the nebular events in which they were formed. We have used crystal size distributions (CSDs) together with crystallization experiments to explore the textures of natural chondrules and their relationships to natural formation conditions. Many careful experimental studies have demonstrated fundamental relationships between the texture of a chondrule and its precursor material, melting intensity, and cooling rate. However, until recently most studies have focused on distinctions between textural types (e.g., barred, radial, porphyritic). Previous work has shown that CSDs provide precise, reproducible characterizations of chondrule-scale textures, and can be used together with crystallization experiments to estimate chondrule formation conditions. Here, we expand this study to investigate the link between texture and formation conditions for a range of natural porphyritic olivine (PO) chondrules.

Zieg, M. J.; Lofgren, G. E.

2003-01-01

4

Dynamic crystallization of chondrule melts of porphyritic olivine composition - Textures experimental and natural  

NASA Astrophysics Data System (ADS)

A full range of textures characteristic for porphyritic olivine chondrules was reproduced in melts of the same composition, crystallized under dynamic crystallization conditions (under controlled cooling), as determined by electron microprobe analyses. The primary differences between the natural and experimentally produced porphyritic olivine textures were the nature and the extent of matrix crystallization, which reflected the subsolidus or low-temperature cooling history. The most confining limits on the chondrule-forming process were found to be the presence of crystalline precursors for the chondrule melts and the upper temperature limit of melting.

Lofgren, G.

1989-02-01

5

Olivine-rich rims surrounding chondrules in the Mokoia CV3 carbonaceous chondrite: Further evidence for parent-body processes  

NASA Astrophysics Data System (ADS)

Fine-grained rims surrounding chondrules and inclusions in the Mokoia CV3 carbonaceous chondrite can be divided into phyllosilicate-rich and olivine-rich types. We present a petrographic and electron microscopic study of the olivine-rich rims and their host objects (referred to as chondrules/olivine-rich rims). The olivine-rich rims consist mainly of Fe-rich olivine and very minor phyllosilicate (saponite). Their host chondrules contain minor saponite and phlogopite, which resulted from aqueous alteration of anhydrous silicates. Mineralogical and compositional characteristics of the chondrules/olivine-rich rims suggest that they experienced mild thermal metamorphic effects. The rims commonly contain veins of coarse-grained Fe-rich olivine, magnetite, and Fe-(Ni) sulfides. The chondrules show abundant evidence of alteration along their peripheries, and the alteration textures suggest a mechanism for rim formation by replacement of the chondrules. Initially, enstatite and opaque nodules preferentially reacted to form coarse, platy, Fe-rich olivine crystals, which were subsequently divided into finer grains. Forsterite was also replaced by Fe-rich olivine. As the alteration advanced, these Fe-rich olivines were disaggregated, mixed with simultaneously produced saponite, and formed rims. In contrast, the surrounding matrix shows no evidence of such alteration and metamorphism. These observations indicate that the chondrules/olivine-rich rims did not experience these secondary processes in their present setting. The results suggest that the chondrules/olivine-rich rims experienced extensive replacement reactions in an environment in which aqueous fluids existed but only in minor amounts. They have probably also undergone simultaneous and/or subsequent mild thermal metamorphism. We suggest that the chondrules/olivine-rich rims are actually clasts transported from a relatively dry region in the parent body that was different from the region where Mokoia was finally lithified.

Tomeoka, Kazushige; Ohnishi, Ichiro

2014-07-01

6

Experimental Replication of Relict "Dusty" Olivine in Type 1B Chondrules  

NASA Technical Reports Server (NTRS)

Introduction: Relict "dusty" olivine is considered to be a remnants of previous chondrule forming events based on petrographic and chemical evidence. Dynamic crystallization experiments confirm that dusty olivine can be produced by reduction of FeO-rich olivine in Unequilibrated Ordinary Chondrite (UOC) material. The results of these experiments compliment those of who also produced dusty olivine, but from synthetic starting materials. Techniques: Dynamic crystallization experiments were conducted in which UOC material was reduced in presence of graphite. Starting material was coarsely ground GR095554 or WSG95300 that contained olivine of Fo 65-98. Approximately 75 mg. of UOC material was placed in a graphite crucible and sealed in an evacuated silica tube. The tube was suspended in a gas-mixing furnace operated at 1 log unit below the IW buffer. The experiments were as brief as 1.5 hrs up to 121 hrs. Results: Dusty olivine was produced readily in experiments melted at 1400 C for I hr. and cooled between 5 and 100 C/hr or melted at 1300-1400 C for 24 hours. Fe-rich olivine (dusty olivine precursors) that have been partially reduced were common in the experiments melted at 1400 C and cooled at 1000 C/hr or melted at 1200 C for 24 hrs. Relict olivine is absent in experiments melted at 1400 for 24 hrs, melted above 1400 C, or cooled more slowly than 10 C/hr. Relict olivine in the experiments has minimum Fo value of 83 . Thus even in the shortest experiments the most Fe-rich olivine has been altered significantly. The precursor olivine disappears in a few to many hours depending on temperature. The experiments show Fe-rich olivine in all stages of transition to the new dusty form. The olivine is reduced to form dusty olivine in a matter of a few hours at temperatures less than 1400 C and in minutes at higher temperatures. The reduction appears to proceed from the rim of the crystal inward with time. The reduction appears initially rectilinear as if controlled by crystallography, but with time Fe-metal blebs are randomly distributed throughout the olivine. In a given experiment, dusty olivine can be found in varying stages of development, but in the longest experiments, the Fe-metal blebs are dominant and they appear to be migrating out of the olivine. The composition of the dusty olivine ranges from Fo 94-99. The Cr, Mn, and Ca content of the newly formed, dusty olivine is slightly less on average that the precursor olivine, but is till with the range of type 1 olivine. Chadacrysts in the low Ca pyroxene are most common in the higher temperature, more slowly cooled experiments and range in composition from Fo 90-99. Application to chondrule formation: These experiments place time-temperature limits on the preservation of Fe-rich olivine and the production of dusty olivine during chondrule forming events. The reduction process proceeds in a few hours at temperatures above 1400 C and in 10's of hours at temperature between 1200 and 1300 C. This result further confirms th at chondrules form in a few hours to days as suggested earlier. The experiments also confirm that dusty olivine can form from typical Fe-rich olivine in UOC material during the recycling of such olivine in the chondrule forming process.

Lofgren, Gary E.; Le, L.

2002-01-01

7

An experimental study of trace element partitioning between olivine, orthopyroxene and melt in chondrules - Equilibrium values and kinetic effects  

NASA Technical Reports Server (NTRS)

Mineral/melt partition coefficients were measured using an ion microprobe for 32 elements in orthopyroxene and olivine in equilibrium and dynamic crystallization experiments on compositions corresponding to chondrules. The mineral/melt partition coefficients calculated from the measured concentrations for both olivine and orthopyroxene show very little change between equilibrium experiments and dynamic experiments with cooling rates of up to 100 C/h. The results provide a self-consistent set of partition coefficients that can be used in thermodynamic models of equilibrium and kinetic partitioning between olivine, orthopyroxene, and melt. These data can be used in models of partial melting and crystal fractionation in olivine- and orthopyroxene-rich systems, such as chondrules. The results may also be applicable to mantle peridotites, komatiitic and picritic lavas, and ultramafic intrusions.

Kennedy, A. K.; Lofgren, G. E.; Wasserburg, G. J.

1993-01-01

8

Chromite and olivine in type II chondrules in carbonaceous and ordinary chondrites - Implications for thermal histories and group differences  

NASA Astrophysics Data System (ADS)

Unequilibrated chromite and olivine margin compositions in type II chondrules are noted to differ systematically among three of the chondrite groups, suggesting that type II liquids differed in composition among the groups. These differences may be interpreted as indicators of different chemical compositions of the precursor solids which underwent melting, or, perhaps, as differences in the extent to which immiscible metal sulfide droplets were lost during chondrule formation. Because zinc is detectable only in type II chromites which have undergone reequilibration, the high zinc contents reported for chondritic chromites in other studies probably reflect redistribution during thermal metamorphism.

Johnson, C. A.; Prinz, M.

1991-03-01

9

Oxygen Isotopes of Fayalite, Magnetite and Chondrule Olivine in the CO (Y-81020, EET 90043) and CO-Like (MAC 88107) Chondrites  

NASA Astrophysics Data System (ADS)

O-isotope compositions of fayalite (fa) and magnetite (mgt) in three CO chondrites are in isotopic disequilibrium with chondrule olivine phenocrysts, consistent with low-temperature formation of fa and mgt during aqueous alteration on the CO parent body.

Doyle, P. M.; Krot, A. N.; Nagashima, K.

2013-09-01

10

A New Estimate of the Chondrule Cooling Rate Deduced from an Analysis of Compositional Zoning of Relict Olivine  

NASA Astrophysics Data System (ADS)

Compositional zoning in chondrule phenocrysts records the crystallization environments in the early solar nebula. We modeled the growth of olivine phenocrysts from a silicate melt and proposed a new fractional crystallization model that provides a relation between the zoning profile and the cooling rate. In our model, we took elemental partitioning at a growing solid-liquid interface and time-dependent solute diffusion in the liquid into consideration. We assumed a local equilibrium condition, namely, that the compositions at the interface are equal to the equilibrium ones at a given temperature. We carried out numerical simulations of the fractional crystallization in one-dimensional planar geometry. The simulations revealed that under a constant cooling rate the growth velocity increases exponentially with time and a linear zoning profile forms in the solid as a result. We derived analytic formulae of the zoning profile, which reproduced the numerical results for wide ranges of crystallization conditions. The formulae provide a useful tool to estimate the cooling rate from the compositional zoning. Applying the formulae to low-FeO relict olivine grains in type II porphyritic chondrules observed by Wasson & Rubin, we estimate the cooling rate to be ~200-2000 K s-1, which is greater than that expected from furnace-based experiments by orders of magnitude. Appropriate solar nebula environments for such rapid cooling conditions are discussed.

Miura, H.; Yamamoto, T.

2014-03-01

11

Constraints on Chondrule Origins  

NASA Astrophysics Data System (ADS)

The origin of chondrules continues to be a problem resistant to detailed solution. Each passing year brings important new facts, but the small size of most chondrules (a 200- micrometer-diameter chondrule has a nominal mass of 12 micrograms) leads to difficulties for some kinds of studies, and the small size also makes the chondrules particularly vulnerable to alteration by metamorphism, even the mild reheating experienced by the least metamorphosed, type 3.0 chondrites. There is now a consensus within the community that the vast majority of chondrules formed in the solar nebula rather than in presolar or planetary processes. I therefore limit my discussion to nebular processes. Although one can find exceptions to all generalizations, the following features are general enough to require explanation by any successful model: (1) Chondrules have generally chondritic compositions; as an example, most chondrules have unfractionated rare-earth-element patterns and roughly constant Cr/Si and Mg/Si ratios. (2) Chondrules have variable compositions inconsistent with formation from a fine-grained, homogeneous precursor but consistent with precursors consisting of mixtures of cosmochemically plausible nebular components such as common silicates, refractory silicates, etc. (3) Chondrules were molten or partly molten for very brief periods. Depending on composition, chondrules are completely molten in the range 1400 to 1750 K; at these temperatures in a low-pressure (pH(sub)2 < 10^-3 atm) not only the volatile but also the common elements such as Mg, Si, and Fe would evaporate, yet most chondrules show no evidence for the loss of elements as volatile as Na and S. It follows that the period spent at the peak temperature was extremely brief, of order 1 s. (4) Many, perhaps most, chondrules were partly molten; the common porphyritic chondrules contain mineral fragments that survived the chondrule-producing heating events. The magnitude of the individual thermal events was only marginally sufficient to form chondrules. (5) Chondrule- forming events were relatively common; statistics based on compound barred-olivine chondrules indicate that most chondrules experienced two heating events of sufficient magnitude to melt a sizable fraction of the chondrule. (6) Coarse-grained rims on chondrules testify to additional brief heating events prior to particle agglomeration and thus removal of the chondrule from contact with the nebula. The evidence points to a series of flash heating events that occurred in a nebular region having a high dust/gas ratio. Impact heating seems implausible because the required interparticle velocities are too high. Large-scale heat sources such a shock fronts seem unable to provide the short durations of maximum heating. Magnetic field reconnection is only efficient at altitudes where vanishingly small amounts of dust are expected. Lightning powered by the differential rotation between the nebular gas and the thin (100-km) dusty midplane seems to be the most plausible heating mechanism, but the detailed physics is yet to be worked out.

Wasson, J. T.

1992-07-01

12

Relict grains in chondrules: Evidence for chondrule recycling  

NASA Technical Reports Server (NTRS)

The presence of relict grains in chondrules, which offers some insight into the degree to which chondrule material was recycled in the chondrule-forming region, is discussed in this report. Relics are grains that clearly did not crystallize in situ in the host chondrule. They represent coarse-grained precursor material that did not melt during chondrule formation, and provide the only tangible record of chondrule precursor grains. Relics are commonly identified by a large difference in size, textural differences, and/or significant compositional differences compared with normal grains in the host chondrule. Two important types of relics are: (1) 'dusty,' metal-bearing grains of olivine and pyroxene; and (2) forsterite (Mg-rich olivine) grains present in FeO-rich chondrules.

Jones, R. H.

1994-01-01

13

The Vaguries of Pyroxene Nucleation and the Resulting Chondrule Textures  

NASA Technical Reports Server (NTRS)

Pyroxene is a major phase in chondrules, but often follows olivine in the crystallization sequence and depending on the melting temperature and time may not nucleate readily upon cooling. Dynamic crystallization experiments based on total or near total melting were used to study PO (porphyritic olivine) and PP (Porphyritic pyroxene) compositions as defined by. The experiments showed that pyroxene nucleated only at subliquidus temperatures in the PP melts and rarely in the PO melts. Porphyritic chondrules with phenocrysts of both olivine and pyroxene (POP chondrules) were not easily produced in the experiments. POP chondrules are common and it is important for deciphering their formation that we understand pyroxene nucleation properties of chondrule melts.

Lofgren, G. E.; Le, L.

2004-01-01

14

Cooling Rates of Chondrules  

NASA Astrophysics Data System (ADS)

Cooling rates for chondrules are among many aspects of chondrule forming events currently under debate and estimates by different authors vary considerably. Calculations based on radiation from isolated chondrules yield an extremely high cooling rate of ~10^5 degrees C/hr [1]. The cooling rates derived from previous petrological and experimental studies are much lower but inconsistent, ranging from 5 - 100 degrees C/hr [2] to ~1000 degrees C/hr [3]. Since cooling rates bear important information about the chondrule-forming environment, they need to be more tightly constrained. Here we re-evaluate the chondrule cooling rates based on the results of our recent flash heating experiments, mainly the volatile loss data, as well as textures, and olivine zoning profiles of the chondrule analog materials. Linear cooling vs. cooling curves. Many previous studies either assumed or used linear cooling rates for chondrules [2,3]. In reality, even with simple radiative cooling, the cooling rates should have followed a non-linear path, according to the Stefan- Boltzmann law. We used non-linear cooling rates throughout our experiments, and our observations show that the initial cooling rate at the high temperature end of a specific cooling curve affects chondrule properties most. Volatile loss results. Our Na and S loss experiments [4] have shown that to reproduce the very high Na contents [5,6] and primary sulfide [7] found in some natural chondrules, heating has to be brief, but fast cooling and relatively high fO2 are also essential. With an fO2 of ~10^(-10) atm, for a type II chondrule flash heated to its liquidus temperature, cooling curves beginning at ~2500 degrees C/hr are necessary to retain >90% of its original Na content or part of its S, unless the ambient gas is very enriched in these elements [8]. Under lower fO2, or for type I chondrule composition, even higher cooling rates are required. Textures and olivine zoning with ~10^1 - ~10^3 degrees C/hr initial cooling rates. Depending on temperature and starting composition, the charges cooled under such cooling rates exhibit either total glass, BO, PO, POP, or relict olivine texture, consistent with previous linear cooling experiments [2,3,9]. For type IIAB chondrule charges with PO, olivine zoning produced by initially cooling between 500 degrees C/hr and 5000 degrees C/hr is very similar to that of Semarkona chondrules [2]. In this cooling rate range, higher cooling rates enhance the zoning. Charges cooled between 10 degrees C/hr and 100 degrees C/hr show very limited olivine zoning. Textures and olivine zoning with ~10^5 degrees C/hr initial cooling rates. A cooling rate this high can only be achieved by quenching the charge in air immediately after the desired temperature is reached. The final charges are composed of glass and numerous small olivine crystals with grain sizes seldom exceeding 20 fm. Repeated heating/quenching cycles at lower temperature slowly coarsen the olivine crystals: 100 heating/quenching cycles can double the size of olivine, but the final olivine crystals are somewhat rounded and have curved embayments. Very limited olivine zoning is produced: the core/rim difference in FeO rarely exceeds 5%. Discussion. Under flash heating conditions, cooling rates of 10 - 100 degrees C/hr will cause extensive volatile loss except with an unusual ambient gas, and produce limited olivine zoning. Cooling rates of as high as 105 degrees C/hr certainly can preserve high volatile contents, but the crystals grown are too small. Repeated heating/extremely fast cooling cycles can coarsen the olivine grains, but not enough, and do not reproduce porphyritic chondrule textures well. In addition, the heating mechanism to heat chondrules hundreds of times with peak temperatures always constrained within a narrow window is unrealistic. The initial cooling rates of the chondrule cooling curves are more likely between these two extremes, and from our volatile loss results, they are probably in the range of several thousand degrees per hour, especially for type II chondrules.

Yu, Y.; Hewins, R. H.; Eiben, B. A.

1995-09-01

15

Experimental Constraints on Chondrule Reduction  

NASA Astrophysics Data System (ADS)

Whether or not chondritic metal results from equilibrium condensation in the nebula [1], or reflects reduction during chondrule formation [2] is still a matter of debate. Tiny metal globules are found both in matrix of primitive meteorites and in olivine-pyroxene bearing chondrules, suggesting that reduction reactions could have been established either before or during chondrule formation. The causes of reduction processes are also controversial, either controlled by the reduced protosolar atmosphere or due to the presence of reduced carbon in the chondrule precursors [3]. These issues are of fundamental importance in understanding chondrule formation processes and conditions. In addition, because chondrules are the raw material for the Earth accretion, the understanding of the processes controlling the formation of metal (and its compositions) might be also essential for the understanding of the early differentiation of the Earth. In order to shed light on metal formation in chondrules, a series of reduction experiments were carried out to establish 1. the timing of the reduction 2. the compositional effects of reduction and 3. the causes of the reduction. San Carlos olivines, Fa16 with trace amounts of Ni, Co, P, Mn, were used as starting material, this composition being close to that of chondrules on average. Olivines were ground to 50-100 m in order to be comparable to chondrule precursors. Experiments were run in a 1 atmosphere vertical furnace, in the temperature range 1550 to 1650 C and under different oxygen fugacities (IW-1 to C-CO buffer). These reduced atmospheres were imposed by a flux of different proportions of gases (CO, CO2, H2 and Ar) or by using graphite capsules with a flux of pure CO gas. For a given T and fO2, experiments were performed with time scales of 5 mn to 8 hours, and terminated by quenching the run products in dry conditions at 500 C/sec. Each experiment produced an assemblage of olivines (Fo-rich), silicate glass and metal globules (Fe-Ni) either as tiny blebs (< 1m) included in olivine or as globules (1 to 50 m) located in the silicate melt at the olivine grain boundaries. The textural features are very similar to those observed in natural unequilibrated ordinary chondrules. Indeed, olivines may or may not show a dusty appearance, with or without preferential alignment of metal blebs in the same run products. Owing to these experiments, it is also possible to specify unambiguously the mechanism for the reduction reaction: Olivine (Fa 16) > Olivine (< Fa16) + Si-glass + Fe metal + O2. In term of composition, olivine, Fe metal and glass are drastically dependent on the imposed oxygen fugacity, run duration and temperature. Within the experimental conditions, olivines vary from Fa 16 to Fa 0.15, Fe metal from 60 wt% Ni to 2 wt% Ni, and glass from silica-poor and iron-rich composition to silica-rich and iron-poor composition. In general, olivine becomes more forsteritic as oxygen fugacity decreases and run duration increases, and for a fixed oxygen fugacity, the Ni content of metal phases shows a drastic decrease as run duration increases. Moreover, these data show that the rate of this reduction process is strongly sensitive to the temperature and the nature of the reducing agent. In the light of these textural and compositional data, this study suggests that metal in chondrules can be produced on a time scale relevant for chondrule formation by reduction reactions and that these processes could also explain the main textural and compositional features of olivine and metal observed in natural chondrules. References: [1] Grossman L. and Olsen E. (1974) GCA, 38, 173-187. [2] Scott E. R. D and Taylor G. J. (1983) Proc. LPSC 14th, in JGR, 88, B275-B286. [3] Connolly H. C. Jr. et al. (1994) Nature, 371, 136-139.

Libourel, G.; Chaussidon, M.

1995-09-01

16

Constraints on the oxidation state of chondrule precursors from titanium XANES analysis of Semarkona Chondrules  

SciTech Connect

The valence of Ti is not easily reset during chondrule formation. To investigate the oxidation state of chondrule precursors, we measured the valence of Ti in olivine, pyroxene and mesostasis in a type I and a type II chondrule in Semarkona. Chondrules are very important because they formed in the solar nebula and are a major component of chondrites, the most common type of meteorite. In unequilibrated chondrites, the ferromagnesian silicates in chondrules exhibit wide ranges of fe (Fe/(Mg + Fe)). On this basis, chondrules can be divided into type I (fe < 0.1) and type II (fe > 0.1). Because a metal must be oxidized to enter a silicate, mafic silicates with low fe's are inferred to have formed in environments where little oxidized iron was available, implying reducing conditions. Therefore, type I and type II chondrules record different oxidation states. A fundamental question in the study of chondrules is whether this difference was established during chondrule formation, or if it reflects differences in their precursors. Last year, we reported the presence of trivalent Ti in refractory forsterite found in the dense fraction of the Tagish Lake CM chondrite. In addition, in the corresponding oral presentation, we reported high Ti{sup 3+}/Ti{sup 4+} in refractory forsterite containing 0.4-0.7 wt% FeO, present in a type I chondrule. Even these low FeO contents reflect a much higher fO{sub 2} than that at which pyroxene with equivalent Ti{sup 3+}/Ti{sup 4+} would be stable. This suggests that either: the equilibrium Ti{sup 3+}/Ti{sup 4+} is higher in olivine than in pyroxene for a given fO{sub 2}; or the grains formed under highly reducing conditions and the valence of Ti in chondrule olivine is a robust recorder of the oxidation state of chondrule precursors, not easily reset during chondrule formation. To improve our understanding of the origin of chondrules we have used XANES (X-ray absorption near edge structure) spectroscopy to measure the valence state of Ti in a type I and a type II chondrule in Semarkona (LL3.0). If olivine from type I chondrules contains Ti{sup 3+} and that from type II chondrules does not, that would tell us that either their precursors formed under different conditions, or that type IIs were more strongly oxidized during formation. If olivine in type II chondrules contains Ti{sup 3+}, that would probably mean that the precursors of these chondrules were originally reduced and that oxidation occurred during chondrule formation.

Simon, S.B.; Sutton, S.R.; Grossman, L. (UofC)

2008-04-28

17

Textural evidence bearing on the origin of isolated olivine crystals in C2 carbonaceous chondrites  

NASA Technical Reports Server (NTRS)

In some cases the mechanical competence of chondrules in carbonaceous chondrites has been reduced by alteration of their mesostasis glass to friable phyllosilicate, providing a mechanism by which euhedral olivines can be separated from chondrules. Morphological features of isolate olivine grains found in carbonaceous chondrites are similar to those of olivine phenocrysts in chondrules. These observations suggest that the isolated olivine grains formed in chondrules, by crystallization from a liquid, rather than by condensation from a vapor.

Richardson, S. M.; Mcsween, H. Y., Jr.

1978-01-01

18

Chondrule formation, metamorphism, brecciation, an important new primary chondrule group, and the classification of chondrules  

NASA Technical Reports Server (NTRS)

The recently proposed compositional classification scheme for meteoritic chondrules divides the chondrules into groups depending on the composition of their two major phases, olivine (or pyroxene) and the mesostasis, both of which are genetically important. The scheme is here applied to discussions of three topics: the petrographic classification of Roosevelt County 075 (the least-metamorphosed H chondrite known), brecciation (an extremely important and ubiquitous process probably experienced by greater than 40% of all unequilibrated ordinary chondrites), and the group A5 chondrules in the least metamorphosed ordinary chondrites which have many similarities to chondrules in the highly metamorphosed 'equilibrated' chondrites. Since composition provides insights into both primary formation properties of the chondruies and the effects of metamorphism on the entire assemblage it is possible to determine the petrographic type of RC075 as 3.1 with unique certainty. Similarly, the near scheme can be applied to individual chondrules without knowledge of the petrographic type of the host chondrite, which makes it especially suitable for studying breccias. Finally, the new scheme has revealed the existence of chondrules not identified by previous techniques and which appear to be extremely important. Like group A1 and A2 chondrules (but unlike group B1 chondrules) the primitive group A5 chondruies did not supercool during formation, but unlike group A1 and A2 chondrules (and like group B1 chondrules) they did not suffer volatile loss and reduction during formation. It is concluded that the compositional classification scheme provides important new insights into the formation and history of chondrules and chondrites which would be overlooked by previous schemes.

Sears, Derek W. G.; Shaoxiong, Huang; Benoit, Paul H.

1995-01-01

19

Major element chemical compositions of chondrules in unequilibrated chondrites  

NASA Technical Reports Server (NTRS)

The chemical compositions (except for metals and sulfides in chondrules) of more than 500 chondrules from unequilibrated E, H, L, LL, and C chondrites were measured using a broad beam of an electron-probe microanalyzer. The compositions of chondrules can be represented by various mixtures of normative compositions of olivine, low-Ca pyroxene, plagioclase, and high-Ca pyroxene with minor amounts of spinel, feldspathoid, SiO2-minerals, etc., indicating that the chondrule precursor materials consisted of aggregates of these minerals. The Al, Na, and K contents of most chondrules reflect the compositions of the ternary feldspar (An-Ab-Kf) of the chondrule precursor materials, and chemical types of chondrules (KF, SP, IP, and CP) are defined on the basis of the atomic proportion of Al, Na, and K.

Ikeda, Y.

1984-01-01

20

A CRITICAL EXAMINATION OF THE X-WIND MODEL FOR CHONDRULE AND CALCIUM-RICH, ALUMINUM-RICH INCLUSION FORMATION AND RADIONUCLIDE PRODUCTION  

SciTech Connect

Meteoritic data, especially regarding chondrules and calcium-rich, aluminum-rich inclusions (CAIs), and isotopic evidence for short-lived radionuclides (SLRs) in the solar nebula, potentially can constrain how planetary systems form. Interpretation of these data demands an astrophysical model, and the 'X-wind' model of Shu et al. and collaborators has been advanced to explain the origin of chondrules, CAIs, and SLRs. It posits that chondrules and CAIs were thermally processed <0.1 AU from the protostar, then flung by a magnetocentrifugal outflow to the 2-3 AU region to be incorporated into chondrites. Here we critically examine key assumptions and predictions of the X-wind model. We find a number of internal inconsistencies: theory and observation show no solid material exists at 0.1 AU; particles at 0.1 AU cannot escape being accreted into the star; particles at 0.1 AU will collide at speeds high enough to destroy them; thermal sputtering will prevent growth of particles; and launching of particles in magnetocentrifugal outflows is not modeled, and may not be possible. We also identify a number of incorrect predictions of the X-wind model: the oxygen fugacity where CAIs form is orders of magnitude too oxidizing, chondrule cooling rates are orders of magnitude lower than those experienced by barred olivine chondrules, chondrule-matrix complementarity is not predicted, and the SLRs are not produced in their observed proportions. We conclude that the X-wind model is not relevant to chondrule and CAI formation and SLR production. We discuss more plausible models for chondrule and CAI formation and SLR production.

Desch, S. J.; Morris, M. A. [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States); Connolly, H. C. [Kingsborough Community College and the Graduate Center of the City University of New York, 2001 Oriental Boulevard, Brooklyn, NY 11235-2398 (United States); Boss, Alan P., E-mail: steve.desch@asu.ed [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015-1305 (United States)

2010-12-10

21

Evaporation of olivine - Low pressure phase relations of the olivine system and its implication for the origin of chondritic components in the solar nebula  

Microsoft Academic Search

Vapor pressures and the mode of evaporation of forsterite and fayalite and the low-pressure phase relations of the olivine solid solution system were studied using the Knudsen method. The results are applied to evaluate the genetic relationships among type IA chondrules, type II chondrules, and matrix olivine of chondrites.

Hiroko Nagahara; Bjorn O. Mysen; Ikuo Kushiro

1994-01-01

22

Constraints on chondrule origins  

NASA Astrophysics Data System (ADS)

Textures and composition variations were studied in a group of compound chondrules and constraints on chondrule formation were derived from the results obtained. Common chondrule textures and petrological-chemical studies of separated chondrules are discussed. Relic grains and cooling rates are considered and observations of compound chondrules are described. Results indicate that the size range of chondrules is limited and that while chondrules show well resolved differences in chemical and isotopic composition, almost all contain relict grains. Chondrule composition is distinct from igneous rock and volatile phases are common in their interiors. It is suggested that chondrules are formed by turbulence generated lightning at the interface between the dusty midplane and the gas-rich portion of the nebula.

Wasson, J. T.

1993-03-01

23

Non-spherical lobate chondrules in CO3.0 Y-81020: General implications for the formation of low-FeO porphyritic chondrules in CO chondrites  

NASA Astrophysics Data System (ADS)

Non-spherical chondrules (arbitrarily defined as having aspect ratios ?1.20) in CO3.0 chondrites comprise multi-lobate, distended, and highly irregular objects with rounded margins; they constitute 70% of the type-I (low-FeO) porphyritic chondrules in Y-81020, 75% of such chondrules in ALHA77307, and 60% of those in Colony. Although the proportion of non-spherical type-I chondrules in LL3.0 Semarkona is comparable (60%), multi-lobate OC porphyritic chondrules (with lobe heights equivalent to a significant fraction of the mean chondrule diameter) are rare. If the non-spherical type-I chondrules in CO chondrites had formed from totally molten droplets, calculations indicate that they would have collapsed into spheres within 10 -3 s, too little time for their 20-? m-size olivine phenocrysts to have grown from the melt. These olivine grains must therefore be relicts from an earlier chondrule generation; the final heating episode experienced by the non-spherical chondrules involved only minor amounts of melting and crystallization. The immediate precursors of the individual non-spherical chondrules may have been irregularly shaped chondrule fragments whose fracture surfaces were rounded during melting. Because non-spherical chondrules and "circular" chondrules form a continuum in shape and have similar grain sizes, mineral and mesostasis compositions, and modal abundances of non-opaque phases, they must have formed by related processes. We conclude that a large majority of low-FeO chondrules in CO3 chondrites experienced a late, low-degree melting event. Previous studies have shown that essentially all type-II (high-FeO) porphyritic chondrules in Y-81020 formed by repeated episodes of low-degree melting. It thus appears that the type-I and type-II porphyritic chondrules in Y-81020 (and, presumably, all CO3 chondrites) experienced analogous formation histories. Because these two types constitute 95% of all CO chondrules, it is clear that chondrule recycling was the rule in the CO chondrule-formation region and that most melting events produced only low degrees of melting. The rarity of significantly non-spherical, multi-lobate chondrules in Semarkona may reflect more-intense heating of chondrule precursors in the ordinary-chondrite region of the solar nebula.

Rubin, Alan E.; Wasson, John T.

2005-01-01

24

Oxygen Isotope Systematics of Chondrules from the Least Equilibrated H Chondrite  

NASA Technical Reports Server (NTRS)

Oxygen isotope compositions of bulk chondrules and their mineral separates in type 3 ordinary chondrites (UOC) show several % variability in the oxygen three isotope diagram with slope of approx.0.7 [1]. In contrast, ion microprobe analyses of olivine and pyroxene phenocrysts in ferromagnesian chondrules from LL 3.0-3.1 chondrites show mass dependent isotopic fractionation as large as 5% among type I (FeO-poor) chondrules, while type II (FeO-rich) chondrules show a narrow range (less than or equal to 1%) of compositions [2]. The .Delta(exp 17)O (=delta(exp 17)O-0.52xdelta(exp 18)O) values of olivine and pyroxene in these chondrules show a peak at approx.0.7% that are systematically lower than those of bulk chondrule analyses as well as the bulk LL chondrites [2]. Further analyses of glass in Semarkona chondrules show .17O values as high as +5% with highly fractionated d18O (max +18%), implying O-16-poor glass in chondrules were altered as a result of hydration in the parent body at low temperature [3]. Thus, chondrules in LL3.0-3.1 chondrites do not provide any direct evidence of oxygen isotope exchange between solid precursor and O-16-depleted gas during chondrule melting events. To compare the difference and/or similarity between chondrules from LL and H chondrites, we initiated systematic investigations of oxygen isotopes in chondrules from Yamato 793408 (H3.2), one of the least equilibrated H chondrite [4]. In our preliminary study of 4 chondrules, we reported distinct oxygen isotope ratios from dusty olivine and refractory forsterite (RF) grains compared to their host chondrules and confirmed their relict origins [5].

Kita, N. T.; Kimura, M.; Ushikubo, T.; Valley, J. W.; Nyquist, L. E.

2008-01-01

25

Tomographic study of shapes and metal abundances of Renazzo chondrules  

SciTech Connect

Analysis of 3-dimensional tomographic data for 3 Renazzo chondrules shows that 2-D thin section methods are inadequate to quantify 'convolution index', grain sizes and distributions, or modal metal abundance, but 3-D methods are more promising. The origin of metal in the metalrich, highly primitive, CR2 chondrites is vigorously debated. In some Renazzo chondrules, metal has an approximately solar Ni:Co ratio which led to suggest that it is a product of solar nebula condensation. Additionally, in many chondrules, metal occurs in two locations: as one or two large metal grains in the chondrule interior and as numerous smaller metal grains along the chondrule rim. In other chondrules, metal is more evenly dispersed in smaller grains. Interior metal generally has higher concentrations of the more refractory siderophile elements than metal in the rim, which tends to be enriched in volatile metals. This difference may be due to (1) partial evaporation and rapid recondensation of metal; (2) condensation of core metal at higher temperatures, suggesting accretionary growth of the chondrules as temperature decreased; or (3) late Fe addition to the metal on the chondrule rims due to FeO reduction from the adjoining silicates. [4] analyzed PGE distribution in CR chondrite metal and argued that rim metal may have formed by a reaction with the surrounding silicates at the time of chondrule formation. [5] showed that Ni and Co concentrations in the metal grains of the least circular, finest-grained chondrules do not follow a condensation trend. This implies that the relative amounts of Ni and Co in the interior grains were gradually established during chondrule melting due to Fe oxidation or reduction. More recently, observed that chondrules that appear more circular in thin section outline also have coarser metal and silicate grains and a more clearly defined compositional differentiation between rim and core metal grains. These textures were interpreted as reflecting a higher degree of partial melting and 'maturation' of the chondrules, as measured by lower fayalite content in olivine and higher P and Ni concentrations of interior metal. To quantify the degree of melting of chondrules, measured a convolution index (CVI) for each chondrule. The CVI, ranging from 1 to 2, is defined as the ratio of the measured perimeter of the chondrule to the perimeter of a circle with the same area as that measured for the chondrule. Correlation of the CVI with chemical data led to conclude that Renazzo chondrules formed 'by aggregation of numerous droplets in a dust-rich environment'.

Hertz, J.; Ebel, Denton; Weisberg, W.K. (Columbia Preparatory School); (AMNH); (Kingsborough College)

2003-05-19

26

The lack of potassium-isotopic fractionation in Bishunpur chondrules  

NASA Astrophysics Data System (ADS)

In a search for evidence of evaporation during chondrule formation, the mesostases of eleven Bishunpur chondrules, and melt inclusions in olivine phenocrysts in seven of them have been analyzed for their alkali element abundances and K isotopic compositions. Except for six points, all areas of the chondrules that were analyzed had ?41K compositions that were normal within error (typically +/-i3, 2?). The six 'anomalous' points are probably all artifacts. Experiments have shown that free evaporation of K leads to large 41K enrichments in the evaporation residues, consistent with Rayleigh fractionation. Under Rayleigh conditions, a 3 enrichment in ?41K is produced by about a 12% loss of K. The range of L-chondrite normalized K/Al ratios (a measure of the K elemental fractionation) in the areas analyzed vary by almost three orders of magnitude. If all chondrules started out with L-chondrite-like K abundances and the K loss occurred via Rayleigh fractionation, the most K depleted chondrules would have had compositions of up to ?41K 200 deg. Clearly, K fractionation did not occur by evaporation under Rayleigh conditions. Yet experiments and modeling indicate that K should have been lost during chondrule formation under currently accepted formation conditions (peak temperature, cooling rate, etc.). Invoking precursors with variable alkali abundances to produce the range of K/Al fractionation in chondrules does not explain the K isotopic data because any K that was present should still have experienced sufficient loss during melting for there to have been a measurable isotopic fractionation. If K loss and isotopic fractionation was inevitable during chondrule formation, the absence of K isotopic fractionation in Bishunpur chondrules requires that they exchanged K with an isotopically normal reservoir during or after formation. There is evidence for alkali exchange between chondrules and rim/matrix in all UOCs. However, melt inclusions can have alkali abundances that are much lower than the mesostases of the host chondrules, suggesting that they at least remained closed since formation. If it is correct that some or all melt inclusions remained closed since formation, the absence of K isotopic fractionation in them requires that the K isotopic exchange took place during chondrule formation, which would probably require gas-chondrule exchange. Potassium evaporated from fine grained dust and chondrules during chondrule formation may have produced sufficient K vapor pressure for gas-chondrule isotopic exchange to be complete on the timescales of chondrule formation. Alternatively, our understanding of chondrule formation conditions based on synthesis experiments needs some re-evaluation.

Alexander, C. M. O'd.; Grossman, J. N.; Wang, J.; Zanda, B.; Bourot-Denise, M.; Hewins, R. H.

2000-07-01

27

Vesicles in Experimental Chondrules as Clues to Chondrule Precursors  

NASA Astrophysics Data System (ADS)

The processing of chondrule precursors during melting is so extensive that there are few unambiguous indicators of their mineralogical composition. The specific combination of peak temperature and heating time, i.e., the heating mechanism, is also unknown. The general absence of vesicles in chondrules is a potential constraint on both questions. Meteor ablation spherules, whose origins are well understood, differ from chondrules in having abundant vesicles [1]. Chondrules simulated experimentally in a variety of ways have vesicles in many cases, but it has been suggested that the presence of vesicles rules out flash heating [2]. We therefore examine in detail the formation of vesicles in synthetic chondrules. Vesicles have been produced in experiments with long heating times [3] as well as short [2]. They are most prominent in charges that experienced low degrees of melting, probably because of surface tension effects that trap bubbles between relict grains, aided by high melt viscosity. The gas could be derived from air trapped when the powdered sample is prepared, binding agents (acetone, water), or volatiles in the starting minerals (Na, H2O). We have conducted experiments to determine the source of vesicles in synthetic chondrules initially heated slightly below the liquidus and cooled at 500 degrees C/hr. Runs made in pairs included charges with and without acetone binder and charges baked out at 200 degrees C for different lengths of time. Charges with acetone produced more vesicles, which could be avoided to some extent by preliminary baking. Charges with no binder had very few vesicles if baked for 1/2 hour. Vesicles are more prominent when using a well-sorted fine-grained powder than with an unsorted more uniform size distribution. Pulling a vacuum on pellets had no effect on subsequent vesicle development. Vesicles are unlikely to be due to loss of Na from the charge, because vesicles are equally prevalent in flash-heated charges, which retain most of their Na, and earlier experiments that spent longer times at temperature. Experiments with serpentine in the starting materials resulted in a popcorn vesicle texture with voids as large as 3 mm, like some ablation spherules [1]. Trapped air and binding agents cause most vesicles in experimental charges. Chondrule precursors must have consisted of olivine, etc., with no hydrous minerals, assembled at low pressure, or they would have generated vesicles. The absence of vesicles in chondrules does not rule out flash heating mechanisms. References: [1] Brownlee D. E. et al. (1983) In Chondrules and Their Origin (E. A. King, ed.), 10-25, LPI, Houston. [2] Wdowiak T. J. (1983) In Chondrules and Their Origin (E. A. King, ed.), 279-283, LPI, Houston. [3] Radomsky P. M. and Hewins R. H. (1990) GCA, 54, 3475-3490.

Maharaj, S. V.; Hewins, R. H.

1993-07-01

28

Chondrule magnetic properties  

NASA Technical Reports Server (NTRS)

The topics discussed include the following: chondrule magnetic properties; chondrules from the same meteorite; and REM values (the ratio for remanence initially measured to saturation remanence in 1 Tesla field). The preliminary field estimates for chondrules magnetizing environments range from minimal to a least several mT. These estimates are based on REM values and the characteristics of the remanence initially measured (natural remanence) thermal demagnetization compared to the saturation remanence in 1 Tesla field demagnetization.

Wasilewski, P. J.; Obryan, M. V.

1994-01-01

29

Metal and Sulfide in Semarkona Chondrules and Rims: Evidence for Reduction, Evaporation, and Recondensation During Chondrule Formation  

NASA Astrophysics Data System (ADS)

The fact that many chondrules in UOCs contain metal associated with sulfide has been attributed to either low temperature of formation (<680 K) and lack of subsequent heating sufficient to cause evaporation [1] or metamorphism after chondrule formation [2]. We have examined the metal and sulfide in group A and B chondrule interiors and rims in the most primitive ordinary chondrite, Semarkona, in order to further explore these options. Most group A1 chondrules contain abundant metal(3-4 wt%), which is mainly as rounded grains of kamacite (< 1 micrometer~60 micrometers) usually situated in the mesostasis near chondrule edge. For the 37 group A1 chondrules investigated, only five contain sulfide and in only one was it abundant. Usually the sulfides were found associated with metal near the chondrule surfaces, and in a few cases, the metal grains were enclosed in sulfides. The "dusty metal" [3] is common in group A1 chondrules, but is not found in group B chondrules, and the host olivine is often embayed by metal-free pyroxene, which has lower Fe/Fe+Mg ratio than the coexisting olivine. In contrast, metal in group B1 chondrules is much less abundant (generally less than 1 wt%) and occurs as both kamacite and taenite. It is often associated with sulfide, with the sulfide being more abundant than metal. Metal in group A1 chondrules is generally poorer in Ni than the metal in group B1 chondrules (Fig. 1). A similar observation was made for type IA and II chondrules [4,5], which are subsets of group A and B respectively. Additionally, metal in chondrules with Fe-poor olivine contains lower abundance of Ni and Co than metal in chondrules with Fe-rich olivine (Fig. 1) [6]. Group A1 chondrules are more frequently rimmed than group B1 chondrules (~70% by number, compared with ~30% ) and seem to have higher ratios of rim thickness to chondrule diameter (Fig. 2). Most group A1 chondrule rims contain ultra-fine-grained metal- and sulfide-rich materials, which are not observed in chondrites of higher petrographic grades. In contrast, group B1 chondrule rims, when present, contain fine-grained matrix-like materials with dispersed or massive sulfide and metal, which, in contrast to the ultra-fine sulfides/metal-rich rims in group A chondrules, are also observed in higher petrographic types [7]. These results can best be explained by reduction of ferrous olivine and loss of FeS by evaporation during group A1 chondrule formation with the recondensation of FeS and/or reactions between recondensed metal and H2S in the nebular gas at lower temperatures. Thermoluminescence, cathodoluminescence, and compositional zoning in several Semarkona group A1 chondrules has also been interpreted in terms of recondensation of major volatile elements like Na and Mn [8,9]. References: [1] Grossman J. N and Wasson J. T. (1983) In Chondrules and their Origins (E. K. King, ed.), 88-121. [2] Wood J. A. (1993) personal communication; see also Grossman J. N. (1988) In Meteorites and the Early Solar System (J. F. Kerridge and M. S. Matthews, eds.), 680-696. [3] Rambaldi E. R. and Wasson J. T. (1982) GCA, 46, 929-939. [4] Jones R. H. and Scott E. R. D. (1989) LPS XIX, 523-536. [5] Jones R. H. (1990) GCA, 54, 1785- 1802. [6] Snellenburg J. (1978) Ph.D. Thesis, State University of New York at Stony Brook. [7] Allen J. S. et al. (1980) GCA, 44, 1161-1176. [8] DeHart J. M. (1989) Ph.D. Thesis, University of Arkansas. [9] Matsunami S. et al (1992) GCA (in press). Fig. 1, which appears here in the hard copy, shows chondrule melt compositions (data from [4,6,8]). Fig. 2, which appears here in the hard copy, shows rim thickness against chondrule diameter with regression lines.

Huang, S.; Benoit, P. H.; Sears, D. W. G.

1993-07-01

30

Terminal particle from Stardust track 130: Probable Al-rich chondrule fragment from comet Wild 2  

NASA Astrophysics Data System (ADS)

A 4 6 ?m terminal particle from Stardust track 130, named Bidi, is composed of a refractory assemblage of Fo97 olivine, Al- and Ti-bearing clinopyroxene and anorthite feldspar (An97). Mineralogically, Bidi resembles a number of components found in primitive chondritic meteorites including Al-rich chondrules, plagioclase-bearing type I ferromagnesian chondrules and amoeboid olivine aggregates (AOAs). Measured widths of augite/pigeonite lamellae in the clinopyroxene indicate fast cooling rates suggesting that Bidi is more likely to be a chondrule fragment than an AOA. Bulk element concentrations, including an Al2O3 content of 10.2 wt%, further suggests that Bidi is more akin to Al-rich rather than ferromagnesian chondrules. This is supported by high anorthite content of the plagioclase feldspar, overall bulk composition and petrogenetic analysis using a cosmochemical Al2O3-Ca2SiO4-Mg2SiO4 phase diagram. Measured minor element abundances of individual minerals in Bidi generally support an Al-rich chondrule origin but are not definitive between any of the object types. Oxygen isotope ratios obtained from olivine (+minor high-Ca pyroxene)fall between the TF and CCAM lines and overlap similar minerals from chondrules in primitive chondrites but are generally distinct from pristine AOA minerals. Oxygen isotope ratios are similar to some minerals from both Al-rich and type I ferromagnesian chondrules in unequilibrated carbonaceous, enstatite and ordinary chondrites. Although no single piece of evidence uniquely identifies Bidi as a particular object type, the preponderance of data, including mineral assemblage, bulk composition, mineral chemistry, inferred cooling rates and oxygen isotope ratios, suggest that Bidi is more closely matched to Al-rich chondrules than AOAs or plagioclase-bearing type I ferromagnesian chondrules and likely originated in a chondrule-forming region in the inner solar system.

Joswiak, D. J.; Nakashima, D.; Brownlee, D. E.; Matrajt, G.; Ushikubo, T.; Kita, N. T.; Messenger, S.; Ito, M.

2014-11-01

31

A RELICT Spinel Grain in an Allende Ferromagnesian Chondrule  

NASA Astrophysics Data System (ADS)

It is suggested that one of the refractory lithophile precursors in CV-CO chondrules was a hightemperature condensate from the nebular gas and was related to Ca,Al-rich inclusions (CAIs) [1-3]. However, little is known about refractory siderophile precursors in chondrules [4]. Allende barred olivine chondrule R-11 consists mainly of olivine (Fa(sub)7- 18), pyroxene (En(sub)93Fs(sub)1Wo(sub)6, En(sub)66Fs(sub)1Wo(sub)33), plagioclase (An(sub)80), Fe-poor spinel, and alkali-rich glass. The CI- chondrite normalized REE pattern of the chondrule, excluding a spinel grain, are fractionated, HREEdepleted (4.6-7.8 x CI) with a large positive Yb anomaly. The REE abundances are hump-shaped functions of elemental volatility, moderately refractory REE-enriched, suggesting that the refractory lithophile precursor component of R-11 could be a condensate from the nebular gas and related to Group 11 CAIs [1,2]. An interior portion of spinel is almost Fe-free, but in an outer zone (2040 micrometers in width) FeO contents increase rapidly. TiO(sub)2, Cr(sub)2O(sub)3, and V(sub)2O(sub)3 contents in core spinel are less than 0.5%, which is different from the V-rich nature of spinel in fluffy Type A CAIs [5]. The Fe-Mg zoning of spinel may have been generated by diffusional emplacement of Mg and Fe during chondrule-forming events. The spinel contains silicate inclusions and tiny metallic grains. The largest silicate inclusion is composed of Al,Ti-rich pyroxene and Ak 40 melilite. One of the submicrometersized grains was analyzed by SEM-EDS and found to be composed of refractory Pt-group metals with minor amounts of Fe and Ni. This is the first occurrence of refractory Pt-group metal nuggets in a ferromagnesian chondrule from the Allende meteorite. Tungsten, Os, Ir, Mo, and Ru are enriched 2-6 x 10^5 relative to CIs, and abundances of Pt and Rh decrease 2-10 x 10^4 with increasing volatility. In addition, abundances of Fe and Ni in the nugget are equal to or less than that CI chondrites. A depletion of Mo relative to other refractory metals may have resulted from high- temperature oxidation [6]. Chondrule R-11 exhibits both similarities (spinel and plagioclase chemistry; Group II REE pattern) and differences (fassaite chemistry; existence of refractory Pt-group metal nuggets and melilite) with respect to POIs [3] carrying isotopically fractionated Mg. Refractory Pt-group metal nuggets in CAIs are considered to have been produced during high-temperature events (at least 1300 degrees C) before total condensation of Fe in the early solar nebula [8-10]. In analogy with the formation history with CAIs, we suggest that one of the refractory siderophile precursor components of Allende chondrules is a high-temperature condensate from the nebular gas and is associated with refractory oxide and silicates. References: [1] Misawa K. and Nakamura N. (1988) GCA, 52, 1669. [2] Misawa K. and Nakamura N. (1988) Nature, 334, 47. [3] Sheng Y. J. et al. (1991) GCA, 55, 581. [4] Grossman J. N. et al. (1988) In Meteorites and the Early Solar System (J. F. Kerridge and M. S. Matthews, eds.), 619, Univ. of Arizona. [5] MacPherson G. J. and Grossman L. (1984) GCA, 48, 29. [6] Fegley B. Jr. and Palme H. (1985) EPSL, 72, 311. [7] Wark D. A. and Lovering J. F. (1976) LS VII, 912. [8] Palme H. and Wlotzka F. (1976) EPSL, 33, 45. [9] El Goresy A. et al. (1978) Proc. LPSC 9th, 1279. [10] Blander M. and Fuchs L. H. (1980) Proc. LPSC 11th, 929.

Misawa, K.; Fujita, T.; Kitamura, M.; Nakamura, N.; Yurimoto, H.

1993-07-01

32

EH3 matrix mineralogy with major and trace element composition compared to chondrules  

NASA Astrophysics Data System (ADS)

We investigated the matrix mineralogy in primitive EH3 chondrites Sahara 97072, ALH 84170, and LAR 06252 with transmission electron microscopy; measured the trace and major element compositions of Sahara 97072 matrix and ferromagnesian chondrules with laser-ablation, inductively coupled, plasma mass spectrometry (LA-ICPMS); and analyzed the bulk composition of Sahara 97072 with LA-ICPMS, solution ICPMS, and inductively coupled plasma atomic emission spectroscopy. The fine-grained matrix of EH3 chondrites is unlike that in other chondrite groups, consisting primarily of enstatite, cristobalite, troilite, and kamacite with a notable absence of olivine. Matrix and pyroxene-rich chondrule compositions differ from one another and are distinct from the bulk meteorite. Refractory lithophile elements are enriched by a factor of 1.5-3 in chondrules relative to matrix, whereas the matrix is enriched in moderately volatile elements. The compositional relation between the chondrules and matrix is reminiscent of the difference between EH3 pyroxene-rich chondrules and EH3 Si-rich, highly sulfidized chondrules. Similar refractory element ratios between the matrix and the pyroxene-rich chondrules suggest the fine-grained material primarily consists of the shattered, sulfidized remains of the formerly pyroxene-rich chondrules with the minor addition of metal clasts. The matrix, chondrule, and metal-sulfide nodule compositions are probably complementary, suggesting all the components of the EH3 chondrites came from the same nebular reservoir.

Lehner, S. W.; McDonough, W. F.; Nmeth, P.

2014-11-01

33

Chondrule rims and interchondrule matrix in UOC  

NASA Technical Reports Server (NTRS)

Opaque rims around chondrules and clasts were distinguished from opaque, interchondrule matrix apparently unrelated spatially to chondrules and clasts. Microprobe and electron microscope techniques were used. The mean chemical composition for dark rim and matrix in Bishunpur and Tieschitz are similar to the opaque matrix of Huss, et al. However, the mean dark rim compositions in Bishunpur have significantly higher Fe, and lower Na, K, Al and Si than opaque interchondrule matrix. The opaque matrix of Huss, et al, essentially lies between these compositions. In Tieschitz only rim material was observed. In Tieschitz the rims are Si-poor and dominated by normative olivine (Fo50). Again there is an Na, K, Al component but is often nepheline normative rather than albitic. It too is probably present as glass, Ashworth (pers.comm.). In Bishunpur rims as well as the silicate-FeS, FeNi layering described by Allen, et al, discontinuous layering was observed within the silicate portion. This is apparently due to variations in the proportions of the components, particularly in the glassy phase. In Bishunpur there is a strong genetic link between matrix and rims, although rims seem to have formed under different, possibly more oxidizing, conditions. Also the presence of the same component in rims, matrix chondrules, and clasts suggests a common source.

Alexander, C.; Hutchison, R.; Barber, D. J.

1984-01-01

34

An Impact Origin for Chondrules  

NASA Astrophysics Data System (ADS)

Impact jetting from planetesimal surfaces during low velocity impacts can eject a mass of chondrule-sized melt droplets comparable to the mass of the asteroid belt. Radiative cooling rates of such droplets match those of observed chondrules.

Melosh, H. J.; Johnson, B. C.; Minton, D. M.; Zuber, M. T.

2014-09-01

35

Thermoluminescence and compositional zoning in the mesostasis of a Semarkona group A1 chondrule and new insights into the chondrule-forming process  

NASA Astrophysics Data System (ADS)

A large, group A1, porphyritic olivine chondrule in the Semarkona chondrite with induced thermoluminescence (TL) and compositional zoning in its mesostasis has been discovered. The chondrule has Ca-rich and Fe-poor olivine and its mesostasis is highly anorthite-normative. The chondrule shows an intense induced TL peak at about 300 C with a half-width of about 180 C. The induced TL in the 40-440 C range increases monotonically by a factor of about 6 from center to rim, while SiO2, Na2O, and MnO increase by factors of about 1.1, about 3.6, and about 6, respectively. The spectrum of the induced TL over the 200-350 C range and the Mn-TL correlation suggest Mn-activated plagioclase is an important constituent of the refractory mesostases in group A1 chondrules. The zoning may reflect fractional crystallization, Soret diffusion, transport of volatiles into the chondrule by aqueous alteration, a zoned precursor, reduction of precursor dust aggregate, or recondensation of volatiles lost during chondrule formation.

Matsunami, S.; Ninagawa, K.; Nishimura, S.; Kubono, N.; Yamamoto, I.; Kohata, M.; Wada, T.; Yamashita, Y.; Lu, J.; Sears, D. W. G.; Nishimura, H.

1993-05-01

36

Origin of Chondrules and Matrix in Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

We have recently shown that in Allende, chondrules and matrix are complementary in composition. Chondrules have low Fe/Cr ratios and matrix has high Fe/Cr ratios; the bulk meteorite has the CI ratio. Chondrules on the average have Ca/Al ratios below the solar system ratio of 1.10, which is also the bulk Allende ratio; matrix and related dark inclusions have ratios above 1.10. It was therefore concluded that chondrules and matrix formed from a single reservoir characteristic of the bulk Allende composition [1,2]. Recent reports on the CV meteorite Y-86751 [3,4] indicated the opposite relationship, with high Ca/Al ratios in chondrules and low ratios in matrix. Different compositions of individual components of Y-86751 and of Allende but similar bulk compositions of both meteorites may reveal important details on the preaccretionary evolution of the carbonaceous chondrites. We have therefore begun chemical analyses of the bulk of Y-86751 and its individual lithic components, chondrules, matrix, amoeboid olivine inclusions, Ca,Al-rich inclusions, etc. Results of the bulk analysis of Y-86751 show that this meteorite has (within the accuracy of the analysis) the same bulk composition as Allende. In particular, the Ca/Al ratio is within 3% of the average solar system ratio of 1.1 (by weight). The only statistically resolvable difference is the 50% higher content of Zn in Y-86751. Major-element INA analyses indicate a Ca/Al ratio above the chondritic ratio for several chondrules and opposite to that of average Allende chondrules [1]. Matrix samples have a tendency for low Ca/Al ratios, confirming EMP-matrix analyses [4]. The separates are presently analyzed for a large number of trace elements. After the analyses, separates will be investigated petrographically. The apparent disequilibrium among Allende components and the strong compositional zoning of olivine grains constrain the thermal history of the Allende parent body [e.g., 5]. Any metamorphic redistribution of Ca or Al between chondrules and matrix can be virtually excluded. Therefore, the complementary relationship in the distribution of Ca and Al between matrix and chondrules must be of nebular origin and must reflect conditions of formation of chondrules and matrix. Early condensation and separation of spinel may be responsible for the high Ca/Al in Y-86751 chondrules. The early separated spinel grains were later collected with the matrix and are responsible for the low Ca/Al ratio in Y-86751 matrix [3,4]. A different evolution, where chondrules incorporated less Ca than Al, must have occurred for Allende. Perhaps conditions were more oxidizing and some Ca remained as Ca(OH)(sub)2 in the gas before matrix was formed, as suggested by Hashimoto [6]. Allende dark inclusions representing matrix have excess Ca while all other refractory elements occur in CI proportions, suggesting a unique behavior of Ca [7]. A different nebular history for two members of the same group (CV) would indicate strong local differences in formation conditions for chondrules and matrix from two identical nebular reservoirs. In addition, if both meteorites come from the same parent body there could only be limited mixing on the parent body to retain the different signatures. References: [1] Palme H. et al. (1992) LPS XXIII, 1021-1022. [2] Palme H. (1992) 17th Symp. Antarc. Met., Tokyo, 71-1-3. [3] Murakami T. et al. (1992) 17th Symp. Antarc. Met., Tokyo, 11-1-2. [4] Murakami T. and Ikeda Y. (1993) in preparation. [5] Weinbruch S. et al. (1990) Meteoritics, 25, 115-125. [6] Hashimoto A. (1992) GCA, 56, 511-532. [7] Palme H. et al. (1989) Z. Naturforsch., 44a, 1005-1014.

Palme, H.; Spettel, B.; Ikeda, Y.

1993-07-01

37

Zoned chondrules in Semarkona: Evidence for high-and low-temperature processing  

USGS Publications Warehouse

At least 15% of the low-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 micropobe 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 of volatile 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 chondrules 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 of low- and high-Ca pyroxene played some role in Ti, Cr, Mn, Si, Al, and some Ca zoning. But direct condensation of elements into hot chondrules, secondary melting of late condensates into the outer portions of chondrules, and subsolidus diffusion of elements into warm chondrules cannot account for the sub-parallel zoning profiles of many elements, the presence of H2O, or elemental abundance patterns. Zoning of moderately volatile elements and Ca may have been produced by hydration of chondrule 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, low-FeO chondrules appear to have fully altered mesostasis.

Grossman, J.N.; Alexander, C.M. O'D.; Wang, J.; Brearley, A.J.

2002-01-01

38

Evidence for primitive nebular components in chondrules from the Chainpur chondrite  

NASA Astrophysics Data System (ADS)

In view of the fact that the least equilibrated ordinary chondrites contain chondrules that have changed little since the time of their formation in the early solar system, and are therefore excellent indicators of the physical and chemical nature of the solar nebula, 36 chondrules were separated from the Chainpur chondrite and analyzed for 20 elements and petrographic properties. The dominant nebular components found are: (1) a mixture of metal and sulfide whose composition is similar to whole rock metal and sulfide, (2) Ir-rich metal, (3) olivine-rich silicates, (4) pyroxene-rich silicates, and possibly (5) a component containing the more volatile lithophiles. Although etching experiments confirm that chondrule rims are enriched in metal, troilite and moderately volatile elements relative to the bulk chondrules, a large fraction of the volatiles remains in the unetched interior.

Grossman, J. N.; Wasson, J. T.

1982-06-01

39

Origins of Al-rich chondrules: Clues from a compound Al-rich chondrule in the Dar al Gani 978 carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

Aluminum-rich chondrules are one of the most interesting components of primitive chondrites, because they have characteristics that are similar to both Ca, Al-rich inclusions (CAIs) and ferromagnesian chondrules. However, their precursor and formation history remain poorly constrained, especially with respect to their oxygen isotopic distributions. In this study, we report on the petrography, mineralogy, oxygen isotope ratios, and rare-earth-element compositions of a sapphirine-bearing Al-rich chondrule (SARC) in the ungrouped chondrite Dar al Gani (DaG) 978. The SARC has a complex core-mantle-rim texture; while both the core and the mantle are mainly composed of Al-rich enstatite and anorthite with minor amounts of mesostasis, these regions are distinguished by the presence of Fe-rich spinel and sapphirine in the core and their absence in the mantle. The rim of the SARC consists mainly of Fe-rich olivine, enstatite, and Fe-Ni metal. Spinel and some olivine grains in the SARC are 16O-rich, with ?17O values down to -20 and -23, respectively. Enstatite, sapphirine, and most olivine grains have similar ?17O values (? -7), which are lower than those of anorthite and the mesostasis (including augite therein) (?17O: ? -3). Mesostasis from both the core and mantle have Group II rare-earth-element (REE) patterns; however, the core mesostasis has higher REE concentrations than the mantle mesostasis. These observations provide a strong indication that the SARC formed by the melting and crystallization of a mixture of materials from Group II CAIs and ferromagnesian chondrules. Both spinel and olivine with 16O-rich features could be of relict origin. The 16O-poor isotopic compositions of most components in Al-rich chondrules can be explained by oxygen isotopic exchange between the melt and 16O-poor nebular gas (?17O: ? -7) during melting in chondrule-forming regions; whereas the anorthite and mesostasis could have experienced further oxygen isotopic exchange with a relatively 16O-poor reservoir (?17O: ? -3) on the parent body, likely during fluid-assisted thermal metamorphism. During the same thermal metamorphism event, spinel, olivine, some enstatite, and the mesostasis experienced Mg-Fe exchange to various extents. The 16O-rich spinel and olivine in the SARC are of relict origin. The high bulk Al2O3 contents, the presence of relict spinel, and the characteristic Group II REE composition in mesostasis strongly indicate that the precursor of the Al-rich portion of the SARC is a mixture of materials from CAIs and ferromagnesian chondrules. The Al-rich portion of the SARC experienced melt-gas oxygen isotope exchange in the chondrule-forming region, which could well explain why the oxygen isotopic compositions of most Al-rich chondrules are similar to those of ferromagnesian chondrules. The presence of 16O-rich olivine indicates that AOAs contributed in some manner to the formation of ferromagnesian chondrules. After accretion onto the parent body of DaG 978, components in the SARC experienced oxygen and Fe-Mg exchange to various degrees, likely during fluid-assisted thermal metamorphism.

Zhang, Ai-Cheng; Itoh, Shoichi; Sakamoto, Naoya; Wang, Ru-Cheng; Yurimoto, Hisayoshi

2014-04-01

40

Sibling and Independent Compound Chondrules  

NASA Astrophysics Data System (ADS)

We studied compound chondrules in 79 cm2 of ordinary chondrite (OC) thin sections. Compound chondrules consist of a primary that solidified first and one or more secondaries attached to the primary. Sibling compound chondrules have very similar textures and compositions; most, perhaps all, seem to consist of chondrules melted in the same heating event. About 1.4% of all chondrules are the primaries of sibling compound chondrules. A smaller fraction, 1.0%, of all chondrules are the primaries of independent chondrules, the members of which were melted in separate heating events. Independent chondrules show appreciable differences in texture and/or composition. We propose that sibling chondrules originated when numerous chondrules were created from one large, more-or-less homogeneous, precursor assemblage that was flash-melted to produce a large set (perhaps 100-1000) of chondrules; some of these collided while molten, probably within several centimeters of the production site. We envision that small radial velocities were imparted to the members of the set, with small differences in velocity causing collisions among those few in intersecting trajectories. If all chondrules were produced this way, the collision efficiency was 1.4%; if only 10% were produced in this fashion, the efficiency rises to 14%. The original Gooding-Keil model of independent compound chondrule formation calls for random collisions to occur while the secondaries were molten. This appears improbable because the mean period between collisions in the dusty midplane of the nebula is estimated to be hours (or days), orders of magnitude longer than the period during which chondrules could have retained low viscosities following a flash-heating event in a cool (<700 K) nebula. We suggest that most independent compound chondrules formed by the mechanism that accounts for chondrules with relict grains and for chondrules with coarse- grained rims: the primary chondrule was embedded in a porous dust assemblage at the time of the second heating event; it experienced minimal melting because melting efficiency increases with increasing surface/volume ratio. There is a minor tendency for the FeO/(FeO+MgO) ratio in independent secondaries to be higher than in primaries, as expected if this ratio increased with time in the nebular dust. However, Monte Carlo calculations confirm that the compositions of independent secondaries are not randomly distributed, but related to those of primaries. Some exchange probably occurred during the fusion of the two chondrules, but this mechanism seems unable to account for the general similarity of independent primary/secondary compositions. This suggests that, in the environment where, at any one time, chondrules were forming (perhaps the interface between the gaseous nebula and the dusty midplane), the dust composition was more uniform than it was in the central midplane at a later time when agglomeration occurred.

Wasson, J. T.; Krot, A. N.; Rubin, A. E.

1993-07-01

41

Chondrule Formation in Lightning Discharges  

Microsoft Academic Search

Chondrules represent a significant mass fraction of primitive meteorites. These millimeter-sized glassy droplets appear to be the products of intensive transient heating events. Their size distribution, chemical and mineral composition, texture, and isotope composition suggest that chondrules were produced as a result of short duration melting followed by rapid cooling of solid precursor particles. Gas dynamic heating, magnetic reconnection, and

M. Hornyi; G. Morfill; C. K. Goertz; E. H. Levy

1995-01-01

42

A Parent Magma for the Nakhla Martian Meteorite: Reconciliation of Estimates from 1-Bar Experiments, Magmatic Inclusions in Olivine, and Magmatic Inclusions in Augite  

NASA Technical Reports Server (NTRS)

The composition of the parent magma for the Nakhla (martian) meteorite has been estimated from mineral-melt partitioning and from magmatic inclusions in olivine and in augite. These independent lines of evidence have converged on small range of likely compositions. Additional information is contained in the original extended abstract.

Treiman, Allan H.; Goodrich, Cyrena Anne

2001-01-01

43

Producing chondrules by recycling and volatile loss  

NASA Technical Reports Server (NTRS)

Interelement correlations observed in bulk chondrule INAA data, particularly between the refractory lithophiles, have led to the now generally accepted conclusion that the chondrule precursors were nebular condensates. However, it has been recently suggested that random sampling of fragments from a previous generation of chondrules could reproduce much of the observed range of bulk chondrule composition.

Alexander, C. M. O.

1994-01-01

44

Iodine-xenon, chemical, and petrographic studies of Semarkona chondrules - Evidence for the timing of aqueous alteration  

NASA Technical Reports Server (NTRS)

The relationship of the I-Xe system of the Semarkona meteorite to other measured properties is investigated via INAA, petrographic, and noble-gas analyses on 17 chondrules from the meteorite. A range of not less than 10 Ma in apparent I-Xe ages is observed. The three latest apparent ages fall in a cluster, suggesting the possibility of a common event. It is argued that the initial I-129/I-127 ratio (R0) is related to chondrule type and/or mineralogy, with nonporphyritic and pyroxene-rich chondrules showing evidence for lower R0s than porphyritic and olivine-rich chondrules. Chondrules with sulfides on or near the surface have lower R0s than other chondrules. The He-129/Xe-132 ratio in the trapped Xe component anticorrelates with R0, consistent with the evolution of a chronometer in a closed system or in multiple systems. It is concluded that the variations in R0 represent variations in ages, and that later events, possibly aqueous alteration, preferentially affected chondrules with nonporphyritic textures and/or sulfide-rich exteriors about 10 Ma after the formation of the chondrules.

Swindle, T. D.; Grossman, J. N.; Olinger, C. T.; Garrison, D. H.

1991-01-01

45

Iodine-xenon, chemical, and petrographie studies of Semarkona chondrules: Evidence for the timing of aqueous alteration  

USGS Publications Warehouse

We have performed INAA, petrographie, and noble gas analyses on seventeen chondrules from the Semarkona meteorite (LL3.0) primarily to study the relationship of the I-Xe system to other measured properties. We observe a range of ???10 Ma in apparent I-Xe ages. The three latest apparent ages fall in a cluster, suggesting the possibility of a common event. The initial 129I/127I ratio (R0) is apparently related to chondrule type and/or mineralogy, with nonporphyritic and pyroxene-rich chondrules showing evidence for lower R0'S (later apparent I-Xe ages) than porphyritic and olivine-rich chondrules. In addition, chondrules with sulfides on or near the surface have lower R0S than other chondrules. The 129Xe/132Xe ratio in the trapped Xe component anticorrelates with R0, consistent with evolution of a chronometer in a closed system or in multiple similar systems. On the basis of these correlations, we conclude that the variations in R0 represent variations in ages, and that later event(s), possibly aqueous alteration, preferentially affected chondrules with nonporphyritic textures and/or sulfide-rich exteriors about 10 Ma after the formation of the chondrules. ?? 1991.

Swindle, T.D.; Grossman, J.N.; Olinger, C.T.; Garrison, D.H.

1991-01-01

46

Semarkona: Lessons for chondrule and chondrite formation  

E-print Network

We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona's parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.

Hubbard, Alexander

2014-01-01

47

Olivine Thermometry  

NSDL National Science Digital Library

This assignment is ostensibly about geothermometry, but is also part of a sequence of assignments where students learn about mineral components â what they represent (in regards to solid solution phenomena especially), and how they calculated. I begin with olivine because its components are simple, and reasonably good thermometers do not require long equations. I also use this assignment to teach about binary solid solutions and phase diagrams, though the interpretations of such are based within other assignments. This is part of a sequence of assignments where students learn about mineral components â what they represent (in regards to solid solution phenomena especially), and how they calculated. Though students will not use a binary solid solution diagram per se, I use this HW assignment to re-emphasize such concepts. This assignment also allows students to begin tests of equilibrium, so they must understand the concept and use of an equilibrium constant.

Putirka, Keith

48

Strain Measurements of Chondrules and Refraction Inclusion in Allende  

NASA Technical Reports Server (NTRS)

This study uses traditional strain measurement techniques, combined with X-ray computerized tomography (CT), to evaluate petrographic evidence in the Allende CV3 chondrite for preferred orientation and to measure strain in three dimensions. The existence of petrofabrics and lineations was first observed in carbonaceous meteorites in the 1960's. Yet, fifty years later only a few studies have reported that meteorites record such features. Impacts are often cited as the mechanism for this feature, although plastic deformation from overburden and nebular imbrication have also been proposed. Previous work conducted on the Leoville CV3 and the Parnallee LL3 chondrites, exhibited a minimum uniaxial shortening of 33% and 21%, respectively. Petrofabrics in Allende CV3 have been looked at before; previous workers using Electron Back Scatter Diffraction (EBSD) found a major-axis alignment of olivine inside dark inclusions and an "augen"-like preferred orientation of olivine grains around more competent chondrules

Tait, Alastair W.; Fisher, Kent R.; Simon, Justin I.

2013-01-01

49

Evidence in CO3.0 Chondrules for a drift in the O Isotopic Composition of the Solar Nebula  

NASA Technical Reports Server (NTRS)

Several recent studies have shown that materials such as magnetite that formed in asteroids tend to have higher Delta O-17 (=delta O-17 -0.52 delta O-18) values than those recorded in unaltered chondrules. Other recent studies have shown that, in sets of chondrules from carbonaceous chondrites, Delta O-17 tends to increase as the FeO contents of the silicates increase. We report a comparison of the O isotopic composition of olivine phenocrysts in low-FeO (Fal5) type II porphyritic chondrules in the highly primitive C03.0 chondrite Yamato-81020. In agreement with a similar study of chondrules in C03.0 ALH A77307 by Jones et al., Delta O-17 tends to increase with increasing FeO. We find that Delta O-17 values are resolved (but only marginally) between the two sets of olivine phenocrysts. In two of the high-FeO chondrules, the difference between Delta O-17 of the late-formed, high-FeO phenocryst olivine and those in the low-FeO cores of relict grains is well-resolved (although one of the relicts is interpreted to be a partly melted amoeboid olivine inclusion by Yurimoto and Wasson). It appears that, during much of the chondrule-forming period, there was a small upward drift in the Delta O-17 of nebular solids and that relict cores preserve the record of a different (and earlier) nebular environment.

Wasson, John T.; Rubin, Alan E.; Yurimoto, Hisayoshi

2006-01-01

50

Conference on Chondrules and Their Origins  

NASA Technical Reports Server (NTRS)

Chondrule parent materials, chondrule formation, and post-formational history are addressed. Contributions involving mineralogy petrology, geochemistry, geochronology, isotopic measurements, physical measurements, experimental studies, and theoretical studies are included.

Hrametz, K.

1983-01-01

51

Chronicle of a Chondrule's Travels  

NASA Astrophysics Data System (ADS)

Cometary particles returned in 2006 by NASA's Stardust spacecraft provide crucial information not only about the mission's target, comet 81P/Wild 2, but also about the dynamics in the solar nebula that brought the comet's materials together. Ryan Ogliore (University of Hawaii) and colleagues from the universities of Hawaii, California, and Washington, and the Lawrence Berkeley National Laboratory have focused attention on a tiny chondrule fragment from one of the Wild 2 particles. Using petrology, oxygen isotopes, and aluminum-magnesium isotopic measurements, they determined this chondrule formed relatively late (as chondrules go) in the inner solar nebula and moved out to the comet-forming region before Jupiter could have blocked its way. The timing implies Jupiter formed more than three million years after the formation of the first solids in our Solar System.

Martel, L. M. V.

2012-02-01

52

MAGNESIUM ISOTOPE EVIDENCE FOR SINGLE STAGE FORMATION OF CB CHONDRULES BY COLLIDING PLANETESIMALS  

SciTech Connect

Chondrules are igneous spherical objects preserved in chondritic meteorites and believed to have formed during transient heating events in the solar protoplanetary disk. Chondrules present in the metal-rich CB chondrites show unusual chemical and petrologic features not observed in other chondrite groups, implying a markedly distinct formation mechanism. Here, we report high-precision Mg-isotope data for 10 skeletal olivine chondrules from the Hammadah al Hamra 237 (HH237) chondrite to probe the formation history of CB chondrules. The {sup 27}Al/{sup 24}Mg ratios of individual chondrules are positively correlated to their stable Mg-isotope composition (?{sup 25}Mg), indicating that the correlated variability was imparted by a volatility-controlled process (evaporation/condensation). The mass-independent {sup 26}Mg composition (?{sup 26}Mg*) of chondrules is consistent with single stage formation from an initially homogeneous magnesium reservoir if the observed ?{sup 25}Mg variability was generated by non-ideal Rayleigh-type evaporative fractionation characterized by a ? value of 0.5142, in agreement with experimental work. The magnitude of the mass-dependent fractionation (?300 ppm) is significantly lower than that suggested by the increase in {sup 27}Al/{sup 24}Mg values, indicating substantial suppression of isotopic fractionation during evaporative loss of Mg, possibly due to evaporation at high Mg partial pressure. Thus, the Mg-isotope data of skeletal chondrules from HH237 are consistent with their origin as melts produced in the impact-generated plume of colliding planetesimals. The inferred ?{sup 26}Mg* value of 3.87 0.93 ppm for the CB parent body is significantly lower than the bulk solar system value of 4.5 1.1 ppm inferred from CI chondrites, suggesting that CB chondrites accreted material comprising an early formed {sup 26}Al-free component.

Olsen, Mia B.; Schiller, Martin; Krot, Alexander N.; Bizzarro, Martin [Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350 (Denmark)] [Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350 (Denmark)

2013-10-10

53

Impact-Induced Chondrule Deformation and Aqueous Alteration of CM2 Murchison  

NASA Technical Reports Server (NTRS)

Deformed chondrules in CM2 Murchison have been found to define a prominent foliation [1,2] and lineation [3] in 3D using X-ray computed tomography (XCT). It has been hypothesized that chondrules in foliated chondrites deform by "squeezing" into surrounding pore space [4,5], a process that also likely removes primary porosity [6]. However, shock stage classification based on olivine extinction in Murchison is consistently low (S1-S2) [4-5,7] implying that significant intracrystalline plastic deformation of olivine has not occurred. One objective of our study is therefore to determine the microstructural mechanisms and phases that are accommodating the impact stress and resulting in relative displacements within the chondrules. Another question regarding impact deformation in Murchison is whether it facilitated aqueous alteration as has been proposed for the CMs which generally show a positive correlation between degree of alteration and petrofabric strength [7,2]. As pointed out by [2], CM Murchison represents a unique counterpoint to this correlation: it has a strong petrofabric but a relatively low degree of aqueous alteration. However, Murchison may not represent an inconsistency to the proposed causal relationship between impact and alteration, if it can be established that the incipient aqueous alteration post-dated chondrule deformation. Methods: Two thin sections from Murchison sample USNM 5487 were cut approximately perpendicular to the foliation and parallel to lineation determined by XCT [1,3] and one section was additionally polished for EBSD. Using a combination of optical petrography, SEM, EDS, and EBSD several chondrules were characterized in detail to: determine phases, find microstructures indicative of strain, document the geometric relationships between grain-scale microstructures and the foliation and lineation direction, and look for textural relationships of alteration minerals (tochilinite and Mg-Fe serpentine) that indicate timing of their formation relative to deformation event(s). Preliminary Results: Deformed chondrules are dominated by forsterite and clinoenstatite with lesser amounts of Fe-Mg serpentine, sulfides, and low calcium pyroxene. Olivine grains are commonly fractured but generally show sharp optical extinction. The pyroxene, in contrast, is not only fractured but also often displays undulose extinction. In addition, the clinoenstatite is frequently twinned but it is unclear whether the twins are the result of mechanical deformation or inversion from protoenstatite [8]. EBSD work is currently ongoing to determine if areas of higher crystallographic strain can be imaged and mapped, and to determine the pyroxene twin orientations. In regards to alteration, we have found evidence for post-deformation formation of tochilinite and Mg-Fe serpentine indicating that aqueous alteration has indeed post-dated the deformation of the chondrules.

Hanna, R. D.; Zolensky, M.; Ketcham, R. A.; Behr, W. M.; Martinez, J. E.

2014-01-01

54

Oxygen isotopes in chondrules and coarse-grained chondrule rims from the Allende meteorite  

NASA Astrophysics Data System (ADS)

The relationship between the porphyritic chondrules and coase-grained chondrule rims of the Allende CV chondrite are examined. The oxygen isotopic compositions of seven chondrule-rim pairs and a large rimless refractory chondrule from Allende are determined. The results suggest that, to account for the O-isotopic compositions of the CV chondrules and rims, three solid precursor components are required: a high-temperature, refractory-, alkali, and (O-16)-rich component; a low-temperature, FeO-rich, refractory, and (O-16)-poor component, and an additional component to explain the composition of BO chondrules.

Rubin, A. E..; Wasson, J. T.; Clayton, R. N.; Mayeda, T. K.

1990-01-01

55

Not All Refractory Spherules in CM2S are Chondrules  

NASA Astrophysics Data System (ADS)

Refractory spherules in CM2 meteorites are small, <300 micrometers in diameter, inclusions composed predominantly of spinel, with accessory hibonite and perovskite (Macdougall 1981). On the basis of their chondrule-like morphology, and the inward-radiating habit of hibonite in some inclusions, it has been suggested that refractory spherules formed from liquid droplets (Macdougall 1981; MacPherson et al. 1983). Since many spherules are composed purely of spinel, Macdougall (1981) estimated that their 1-atm melting temperature might have been as high as 2135 degrees C. Melt temperatures in excess of 1550 degrees C were estimated by MacPherson et al. (1983) for the spinel-hibonite spherule BB1. Refractory spherules are a minor component of the Ca-Al rich inclusions (CAIs) found in CM2s. Of 345 CAIs located in the CM2 Cold Bokkeveld only 4 are refractory spherules (study in collaboration with M. Lee, University of Essex). Textural evidence from Cold Bokkeveld demonstrates that CAIs in CM2s are highly fragmented and must have been derived by disruption of larger objects (Greenwood et al. 1991). That this is also the case for refractory spherules is clearly demonstrated by MSP1, an anhedral, spinel-bearing inclusion (300 mmicrometer longest dimension) located in situ in Murchison (CM2). It comprises a rounded core (110 micrometers in diameter) of Fe-free spinel (V2O3 0.5wt%) surrounded by a rim of pyroxene (15-25 micrometers thick), in turn enclosed by a zone of olivine (Fo 99.7) and Mg-rich phyllosilicate. The spinel core contains 15% void space (estimated). The pyroxene rim is zoned outwards from fassaite to diopside. Blocky crystals of olivine <20 micrometers in diameter form a discontinuous rim to pyroxene and occur as isolated grains enclosed by Mg-phyllosilicate. The inclusion has an irregular outline and a sharp contact with surrounding matrix, indicating that it is a fragment of a larger, now disrupted CAI. In CV3 meteorites refractory spinel-rich spherules, similar to the Murchison example, occur within a number of different inclusion-types. Nodules, 5-300 micrometers in diameter, composed of spinel, melilite, perovskite, and pyroxene are common constituents of amoeboid olivine aggregates (Hashimoto and Grossman 1987). Melilite is also present in some Murchison spherules (MacPherson et al. 1983), and prior to aqueous alteration may have been an important constituent in many of these objects. Spherical clumps of spinel crystals, termed "framboids" by El Goresy et al. (1979) are common constituents of type B2 coarse-grained CAIs (Wark and Lovering 1982). One B2 CAI in Vigarano contains a 160-micrometer-diameter framboid with a 10-20-micrometer-thick rim of spinel enclosing a touching framework of rounded grains (5-15 micrometers in diameter). Melilite, present in the bulk inclusion, forms an outer rind to the framboid 5-10 micrometers thick and may be contiguous with crystals (angstrom k(sub)16.5) interstitial to spinel within the framboid. Individually rimmed spinel nodules, up to 300 micrometers in diameter, are also an important component of "fluffy" type A inclusions (MacPherson and Grossman 1984). The structure of the Murchison inclusion MSP1 indicates that at least some CM2 refractory spherules were components of larger inclusions. In CV3s, experimental evidence suggests that spinel spherules represent residual solid material that acquired a rounded form during partial melting (Wark and Lovering 1982). The comparison made between chondrules and spherules may therefore be misleading and results in erroneously high estimates of the temperatures experienced by these objects. El Goresy A., Nagel K., and Ramdohr P. (1979) Proc. Lunar Planet. Sci. Conf. 10th, 833-850. Greenwood R.C., Hutchison R., and Cressey G. (1991) Meteoritics (abstract) 26, 340. Hashimoto A. and Grossman L. (1987) Geochim. Cosmochim. Acta 51, 1685-1704. Macdougall J.D. (1981) Geophys. Res. Lett. 8, 966-969. MacPherson G.J. and Grossman, L. (1984) Geochim. Cosmochim. Acta 48, 29-46. MacPherson G.J., Bar-Matthews M., Tanak

Greenwood, R. C.

1992-07-01

56

Petrology, trace element abundances and oxygen isotopic compositions of a compound CAI-chondrule object from Allende  

NASA Astrophysics Data System (ADS)

We report the petrology, trace element abundances and oxygen isotopic characteristics of a compound CAI-chondrule object, WI-025, found in the Allende CV3 chondrite. The WI-025 is an irregularly shaped inclusion consisting of three texturally and chemically distinct portions: the interior portion, the igneous rim and the intermediate zone located between these two portions. The interior portion consists of anorthite, spinel, olivine and Al-bearing low-Ca pyroxene. The major element chemistry of the interior portion corresponds to that of Al-rich chondrules and is of intermediate character between fine-grained spinel-rich CAIs and ferromagnesian chondrules. The interior portion has abundant 16O-rich spinel (?17O = -14.2 to -24.7) and displays a group II CAI-like REE composition. These observations indicate that the interior portion contains a CAI component formed by fractional condensation. The major and trace element chemistry of the interior portion indicate that the CAI had subsequently assimilated chondrule materials through partial melting. The maximum heating temperature of the partial melting is estimated at approximately 1400 C, similar to the maximum heating temperature of Type-B CAIs. The oxygen isotopic compositions of the olivine and low-Ca pyroxene (?17O = -6.3) in the interior portion indicate that the partial melting and chondrule assimilation took place under a moderately 16O-poor nebular gas. The igneous rim is texturally and chemically similar to ferromagnesian chondrules and entirely surrounds the interior portion. The oxygen isotopic compositions of the olivine and low-Ca pyroxene in the igneous rim are indistinguishable from those of the interior olivine and Al-bearing low-Ca pyroxenes. These observations indicate that a chondrule material, which was melted in the same nebular gas as the interior portion, was accreted to the interior portion. The intermediate zone represents a reaction zone accompanying the igneous rim formation. The formation history of WI-025 can be summarized by the following processes: (1) original CAI formation, (2) partial melting and chondrule assimilation, (3) igneous rim formation and (4) secondary alteration on the parent body.

Wakaki, S.; Itoh, S.; Tanaka, T.; Yurimoto, H.

2013-02-01

57

Magnetite-Pentlandite Chondrules in CK Chondrites  

NASA Astrophysics Data System (ADS)

Opaque-mineral-rich chondrules are among the least common chondrule types and have received scant attention since their discovery by Gustav Rose in 1864. This category includes chondrules comprised principally of metallic Fe-Ni (Tschermak, 1885; Gooding and Keil, 1981) or chrome-spinel (Ramdohr, 1967; Krot et al., 1992). Here I report the occurrence of seven magnetite-pentlandite chondrules in Karoonda (CK4), PCA82500 (CK4/5) and EET90007 (CK5). The chondrules range in size from 225x255 micrometers to 440x570 micrometers and have ellipsoidal or spheroidal morphologies. All are concentrically layered: five of the chondrules have 20-60-micrometer-thick magnetite rims surrounding pentlandite-rich cores or mantles; two of the chondrules have thin pentlandite rims surrounding magnetite-rich cores and mantles. One chondrule from Karoonda has four distinct alternating layers of magnetite and pentlandite. Accessory phases, which occur in one or more of the chondrules, include pyrrhotite, chlorapatite, ilmenite, and chalcopyrite. The chondrules have finely to coarsely granular textures; in the center of one chondrule from PCA82500 there is a 25x100 micrometers subhedral crystal of pentlandite. All of the chondrules appear to be recrystallized, presumably due to metamorphism of their host rocks. The magnetite-pentlandite chondrules are very similar to the magnetite-pentlandite-rich nodules within mafic silicate chondrules in CK chondrites. I examined four nodules that range in size from 58x64 micrometers to 400x670 micrometers and have ellipsoidal or spheroidal morphologies. All but one are concentrically layered; one nodule from a Karoonda chondrule has four concentric layers of magnetite+-pentlandite. The nodules probably formed from immiscible sulfide-oxide droplets within their molten silicate chondrule hosts during chondrule formation. Upon cooling, magnetite and monosulfide solid solution (Mss) precipitated during cotectic crystallization; the Mss transformed into pentlandite after cooling below 610 degrees C. Dense immiscible liquid droplets tend to get expelled from the equators of their spinning molten spheroidal hosts if they do not happen to be located in the molten spheroids' centers where the centrifugal forces are minimal. This phenomenon also affected the four magnetite-pentlandite nodules: one nodule is near the margin and three are at the centers of their host silicate chondrules. The similarities in size, shape, mineralogy, and texture between the magnetite-pentlandite chondrules and nodules indicate that these chondrules constitute the set of immiscible nodule droplets that were lost to their mafic silicate chondrule hosts after melting. The occurrence of magnetite-pentlandite chondrules and nodules has important implications for the timing of CK chondrite oxidation. If oxidation had occurred after agglomeration and transformed metallic Fe-Ni into magnetite, the large (factor of 2) increase in molar volume would have disrupted the nodules and chondrules and destroyed the evidence for rhythmic layering. The intactness of the chondrules and nodules implies that the oxidation of fine-grained metallic Fe-Ni into magnetite probably occurred before agglomeration, either during chondrule formation in a region of high fo(sub)2 or within porous chondrule-precursor dust clumps after nebular temperatures cooled below ~130 degrees C. Hence, the pervasive silicate darkening of CK chondrites (Kallemeyn et al., 1991; Rubin, 1992) was caused by the shock mobilization of magnetite and pentlandite, not metallic Fe-Ni and troilite as in shock-darkened ordinary chondrites. References: Gooding J.L. and Keil K. (1981) Meteoritics 16, 17- 43; Kallemeyn G.W., Rubin A.E. and Wasson J.T. (1991) Geochim. Cosmochim. Acta 55, 881-892; Krot A., Ivanova M.A. and Wasson J.T. (1992) Earth Planet. Sci. Lett., submitted; Ramdohr P. (1967) Geochim. Cosmochim. Acta 31, 1961-1967; Rubin A.E. (1992) Geochim. Cosmochim. Acta 56, 1705-1714; Tschermak G. (1885) Die Mikroskopische Beschaffenheit der Meteoriten. Schweizerbart'sche Verlagshandlung, Stuttga

Rubin, A. E.

1992-07-01

58

The Compositional Classification of Chondrules and the Petrologic Type of an Especially Primitive H Chondrite  

NASA Astrophysics Data System (ADS)

While LL chondrites of petrologic type <3.4 are relatively common, it has been only recently that a few H chondrites of type <3.4 have been reported. One of them is the heavily weathered Roosevelt County 075 [1]. Weathering and the lack of equilibration make classification uncertain, but it is probably an H chondrite. Weathering also makes it very difficult to assign a petrologic type. For example, removal of the weathering products by acid washing increased the TL sensitivity of RC075 by a factor of ~7, equivalent to a change in petrologic type estimate from 3.0 to 3.3, a major difference. The compositional classification scheme for chondrules [2,3] summarizes considerably more information than previous schemes [4-6], not least being that it tracks metamorphic effects as well as more thoroughly monitoring primary chondrule differences. It is also very easy to apply and almost 100% of the chondrules can be classified. As an example of its utility, we here show that application of the scheme to the chondrules in RC075 provides the best means of determining the petrologic type of this highly weathered, but very important, unequilibrated chondrite. The compositional classification scheme for chondrules divides them into eight classes (A1, A2, A3, A4, A5, B1, B2, B3) on the basis of the composition of the two major phases (phenocrysts and mesostasis) [2,3]. Among the changes that occur during metamorphism, olivines lose CaO and acquire uniform FeO, while the mesostases acquire oligoclase compositions having originally included compositions that were SiO2 rich (the B series), CaO rich (the A series), and Na2O rich (A5). These changes give rise to CL properties that can be used as an alternative to microprobe analysis and which, like microprobe data, are insensitive to weathering. Thus we were able to assign all of the almost 100 chondrules present in a 7 x 5-mm section of RC075 to compositional classes. The results are shown in Fig. 1, along with similar data from [3]. The relative abundance and classes of chondrules present provides an excellent method of assigning petrographic type. The relative abundance of group B chondrules in RC075 is less than Semarkona (3.0), and comparable with the higher types, while the abundance of A5 chondrules is comparable to that in Krymka (3.1) and intermediate between that in Semarkona and Chainpur (3.4). Most significantly, the fraction of A1 chondrules is very large and comparable (within error) to that of Semarkona, while the large number of group A3 chondrules is comparable only to Krymka. Apparently, RC075 is intermediate to Semarkona and Chainpur and comparable to Krymka in its petrologic type. McCoy et al. [1] report means ranging from 0.07 to 7.2 mol% Fa and 0.11 to 0.36 wt% CaO for olivine in six type-IA chondrules and 12.3-20.2 mol% Fa for five type-II chondrules in RC075 [1]. Four of the type IA chondrules resembled those of Semarkona in olivine composition (<2 mol% Fa). Unlike the compositional classification scheme, which leads fairly simply to unambiguous petrologic type assignment, it seems difficult to assign RC075 to a petrologic type on the basis of olivine compositions and texture alone. Other advantages of the new scheme are (1) that it applies to individual chondrules and makes no assumptions about average response of chondrules to metamorphism; (2) it is insensitive to brecciation, which is common in UOC [7]; and (3) it is quantitative, and does not require subjective evaluations of texture, although textural descriptions may be used with the compositional class (just as they are for chondrites). The compositional classification scheme is certainly subject to improvement(e.g. class A5, both in type 3 and higher types). However, as it currently stands the scheme clearly provides the best way of not only describing individual chondrules, but of assessing primary chondrule properties and the extent of changes experienced during metamorphism. Thus it provides the best method for assigning the weathered and highly unequilibrated RC075 meteorite to a petrologic ty

Sears, D. W. G.; Huang, S.; Benoit, P. H.

1993-07-01

59

Spatially resolved NRM of the Bishunpur LL3.1 chondrite measured by scanning SQUID microscopy: implications for chondrule formation  

NASA Astrophysics Data System (ADS)

Chondrites represent the building blocks of the solar system and the factors controlling their formation have implications for processes within the protoplanetary disk and interactions between the solar nebula and the early Sun. However, the source of the flash heating that formed the constituent chondrules is a subject of debate, with proposed mechanisms including various forms of convection drawing nebular dust towards and ejecting it away from the Sun, or alternatively extra-nebular energy pulses that require no interaction with the young star. Because the Sun was strongly magnetic early in its life, paleointensity measurements of chondrules can be used to determine the distance at which they cooled through their Curie temperature, providing evidence about which formation mechanism caused their melting and potentially shedding light on accretionary processes within the protoplanetary disk. The Bishunpur LL3.1 meteorite is among the most pristine ordinary chondrites, having both limited thermal and aqueous alteration and a known (magnetic) history on Earth. As such, its chondrules have the potential to preserve primary remanence from their formation if the recorders are capable of maintaining a stable magnetic state over timescales greater than 4.6 Ga. Previous work has shown that dusty olivineiron nanoparticle-bearing silicate that constitutes a proportion of the chondrules of Bishunpuris an stable recorder over these timescales even at temperatures approaching the Curie temperature of iron. In bulk measurements, however, the paleointensity signal from the chondrules is masked by magnetic phases on chondrule rims and in the matrix, necessitating a technique that allows the contribution of different signals to be distinguished. Scanning SQUID microscopy presents an ideal solution as it produces a map of magnetic field measurements with a spatial resolution of 10s of ?m from which the absolute magnetization can be calculated, allowing the paleointensity and demagnetization behavior of the chondrules to be directly observed. This work presents the demagnetization sequence of a thin section of Bishunpur as well as rock magnetic measurements acquired on the scanning SQUID microscope and a bulk moment magnetometer. Bulk measurements of the NRM are dominated by signal from the matrix and chondrule rim, but the sensitivity of the scanning SQUID technique allows weak signals from individual chondrules to be identified which are stable in alternating-field demagnetization through 290 mT. These signals can be modeled as single dipoles, which means the magnetization of dusty olivine regions can be quantitatively measured. Calibration curves from synthetic analogues will permit the paleointensity of these regions to be determined and combined with SEM observations of the microstructure, used to provide a unique line of evidence about chondrule formation and the process of accretion in the solar nebula.

Church, N. S.; Andrade Lima, E.; Lappe, S. L.; Russell, S.; Weiss, B. P.; Harrison, R. J.

2012-12-01

60

MAGNESIUM ISOTOPIC COMPOSITION OF CAIs AND CHONDRULES FROM CR CHONDRITES. B. , M. Gounelle1  

E-print Network

MAGNESIUM ISOTOPIC COMPOSITION OF CAIs AND CHONDRULES FROM CR CHONDRITES. B. Mimoun1 , M. Gounelle1. Introduction: The magnesium isotopic composi- tion of primitive extraterrestrial materials is worth measuring.g. 10]. Figure 1: The magnesium isotopic composition of CAIs in CR chondrites. Error bars are 1

Technische Universiteit Delft

61

Chondrules in the Sharps H3 chondrite - Evidence for intergroup compositional differences among ordinary chondrite chondrules  

NASA Technical Reports Server (NTRS)

Bulk compositions of 19 chondrules and one matrix-rich sample from H3.4 Sharps were determined by instrumental neutron activation analysis. Samples were characterized petrographically, and mineral compositions were determined by electron microprobe analysis. There is constancy among ordinary chondrite (OC) groups in the compositional interrelationships of different chondrule types; e.g., in H3 as well as L3 and LL3 chondrites, porphyritic chondrules are more refractory than nonporphyritic chondrules. Precursor components of H3 chondrules are closely related to those of LL3 chondrules. The mean Ir/Ni, Ir/Co, and Ir/Au ratios of H3 chondrules differ from the corresponding ratios of LL3 chondrules at the 99, 90, and 79 percent confidence levels, respectively. The ratios in H3 chondrules exceed those in LL3 chondrules by amounts similar to those by which H whole-rocks exceed LL whole-rocks. These data suggest that there are primary systematic differences in bulk composition between H and LL chondrules. These differences support the inference that chondrule formation occurred after major nebular fractionation events had established the observed bulk compositional differences among OC groups.

Rubin, Alan E.; Pernicka, Ernst

1989-01-01

62

Chemical production of chondrule oxygen isotopic composition  

NASA Technical Reports Server (NTRS)

Defining the source of observed meteoritic O isotopic anomalies remains a fundamental challenge. The O isotopic composition of chondrules are particularly striking. There are at least three types of chemical processes that produce the isotopic compositions observed in chondrules and Ca-Al-rich inclusions (CAI's). The processes are rather general, viz, they require no specialized processes and the processes associated with chondrule production are likely to produce the observed compositions.

Thiemens, M. H.

1994-01-01

63

Spinel-bearing, Al-rich chondrules in two chondrite finds from Roosevelt County, New Mexico - Indicators of nebular and parent body processes  

NASA Astrophysics Data System (ADS)

Two rare spinel-bearing Al-rich chondrules are identified in chondrite finds from Roosevelt County, New Mexico-RC 071 (L4) and RC 072 (L5). These chondrules have unusual mineralogies dominated by highly and asymmetrically zoned Al-Cr-rich spinels. Two alternatives exist to explain the origin of this zoning-fractional crystallization or metamorphism. Fractional crystallization formed the zoning of the trivalent cations and caused a localized depletion in chromites around the large Al-Cr-rich spinels. Diffusive exchange and partitioning of Fe and Mg between olivine and spinel during parent-body metamorphism can explain the asymmetric zoning of these elements. The bulk compositions of the chondrules suggest affinities with the Na-Al-Cr-rich chondrules, as would be expected from the abundance of Al-Cr-rich spinels. The most important factors are the temperature to which the molten chondrule was heated and the cooling rate during crystallization. These two chondrules cooled rapidly from near the liquidus, as indicated by the zoning, occurrence and sizes of spinels, radiating chondrule textures and localized chromite depletions.

McCoy, Timothy J.; Pun, Aurora; Keil, Klaus

1991-12-01

64

Spinel-bearing, Al-rich chondrules in two chondrite finds from Roosevelt County, New Mexico - Indicators of nebular and parent body processes  

NASA Technical Reports Server (NTRS)

Two rare spinel-bearing Al-rich chondrules are identified in chondrite finds from Roosevelt County, New Mexico-RC 071 (L4) and RC 072 (L5). These chondrules have unusual mineralogies dominated by highly and asymmetrically zoned Al-Cr-rich spinels. Two alternatives exist to explain the origin of this zoning-fractional crystallization or metamorphism. Fractional crystallization formed the zoning of the trivalent cations and caused a localized depletion in chromites around the large Al-Cr-rich spinels. Diffusive exchange and partitioning of Fe and Mg between olivine and spinel during parent-body metamorphism can explain the asymmetric zoning of these elements. The bulk compositions of the chondrules suggest affinities with the Na-Al-Cr-rich chondrules, as would be expected from the abundance of Al-Cr-rich spinels. The most important factors are the temperature to which the molten chondrule was heated and the cooling rate during crystallization. These two chondrules cooled rapidly from near the liquidus, as indicated by the zoning, occurrence and sizes of spinels, radiating chondrule textures and localized chromite depletions.

Mccoy, Timothy J.; Pun, Aurora; Keil, Klaus

1991-01-01

65

Chondrule destruction in nebular shocks  

E-print Network

Chondrules are millimeter-sized silicate spherules ubiquitous in primitive meteorites, but whose origin remains mysterious. One of the main proposed mechanisms for producing them is melting of solids in shock waves in the gaseous protoplanetary disk. However, evidence is mounting that chondrule-forming regions were enriched in solids well above solar abundances. Given the high velocities involved in shock models destructive collisions would be expected between differently sized grains after passage of the shock front as a result of differential drag. We investigate the probability and outcome of collisions of particles behind a 1D shock using analytic methods as well as a full integration of the coupled mass, momentum, energy and radiation equations. Destruction of protochondrules seems unavoidable for solid/gas ratios $\\epsilon \\gtrsim 0.1$, and possibly even for solar abundances because of "sandblasting" by finer dust. A flow with $\\epsilon \\gtrsim 10$ requires much smaller shock velocities ($\\sim 2$ vs 8 k...

Jacquet, Emmanuel

2014-01-01

66

CONDENSATION OF CHONDRULES: CONDITIONS FOR "FIERY RAIN".  

E-print Network

little Na condenses above the solidus, and Na2O contents of most chondrules plot above Na2O-FeO trajectories of calculated con- densates. A much more difficult constraint to satisfy comes from recent work was condensed at near-liquidus temperatures. In the context of melting chondrule precursors, we showed that Na

Grossman, Lawrence

67

Mn-Cr isotopic systematics of individual Chainpur chondrules. [Abstract only  

NASA Technical Reports Server (NTRS)

Twenty-eight chondrules separated from Chainpur (LL3.4) were surveyed for abundances of Mn, Cr, Na, Fe, Sc, Hf, Ir, and Zn by Instrumental Neutron Activation Analysis (INAA). Six, weighting 0.6-1.5 mg each, were chosen for Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray (EDX) and high-precision Ce-isotopic studies. LL-chondrite-normalized (Mn/Fe)(sub LL) and (Sc/Fe)(sub LL) were found to be useful in categorizing them. Five chondrules (CH-16, -17, -18, -23, and -28) were in the range 0.5 less than (Mn/Fe)(sub LL) less than 1. 4 and 0.5 less than (Sc/Fe)(sub LL) less than 1.4. The sixth (CH-25) had (Mn/Fe)(sub LL) and (Sc/Fe)(sub LL) ratios of 0.40 and 8.1, respectively, and was enriched in the refractory lithophile elements Sc and Hf and the refractory siderophile element Ir by 2.7 and 4.4x LL abundances respectively. SEM/EDX of exterior surfaces of the chondrules showed they consisted of varying proportions of low- and high-Ca pyroxenes, olivine, glass, kamacite/taenite, and Fe-sulfides. Chromium-53/chromium-52 for the six chondrules and bulk Chainpur (WR) are presented. Chromium-54/chromium-52 is close to terrestrial and does not correlate with Mn/Cr. We provisionally ignore the possibility of initial Cr isotopic heterogeneities among the chondrules. Omitting both the CH-25 and WR data, a linear regression gives initial (Mn-53/Mn-55)(sub I) = 8 +/- 4 x 10(exp -6), corresponding to chondrule formation at Delta(t)(sub LEW) = -9 +/- 4 Ma prior to igneous crystallization of the LEW 86010 angrite. If initial (Mn-53/Mn-55)(sub 0) in the solar system were as high as approximately 4.4 x 10(exp -5) when Allende CAI formed, our data suggest Chainpur chondrules formed approximately 9 Ma later, in qualitative agreement with 'late' I-Xe formation ages for most Chainpur chondrules.

Nyquist, L.; Lindstrom, D.; Wiesmann, H.; Martinez, R.; Bansal, B.; Mittlefehldt, D.; Shih, C.-Y.; Wentworth, S.

1994-01-01

68

Opaque Mineral Assemblages at Chondrule Boundaries in the Vigarano CV Chondrite: Evidence for Gas-Solid Reactions Following Chondrule Formation  

NASA Technical Reports Server (NTRS)

Recent studies of opaque minerals in primitive ordinary chondrites suggest that metal grains exposed at chondrule boundaries were corroded when volatile elements recondensed after the transient heating event responsible for chondrule formation. Metal grains at chondrule boundaries in the Bishunpur (LL3.1) chondrite are rimmed by troilite and fayalite. If these layers formed by gas solid reaction, then the composition of the corrosion products can provide information on the chondrule formation environment. Given the broad similarities among chondrules from different chondrite groups, similar scale layers should occur on chondrules in other primitive meteorite groups. Here I report on metal grains at chondrule boundaries in Vigarano (CV3).

Lauretta, Dante S.

2004-01-01

69

Relationships Among Intrinsic Properties of Ordinary Chondrites: Oxidation State, Bulk Chemistry, Oxygen-isotopic Composition, Petrologic Type, and Chondrule Size  

NASA Technical Reports Server (NTRS)

The properties of ordinary chondrites (OC) reflect both nebular and asteroidal processes. OC are modeled here as having acquired nebular water, probably contained within phyllosilicates, during agglomeration. This component had high Ai70 and acted like an oxidizing agent during thermal metamorphism. The nebular origin of this component is consistent with negative correlations in H, L, and LL chondrites between oxidation state (represented by olivine Fa) and bulk concentration ratios of elements involved in the metal-silicate fractionation (e.g., NdSi, Ir/Si, Ir/Mn, Ir/Cr, Ir/Mg, Ni/Mg, As/Mg, Ga/Mg). LL chondrites acquired the greatest abundance of phyllosilicates with high (delta)O-17 among OC (and thus became the most oxidized group and the one with the heaviest O isotopes); H chondrites acquired the lowest abundance, becoming the most reduced OC group with the lightest O isotopes. Chondrule precursors may have grown larger and more ferroan with time in each OC agglomeration zone. Nebular turbulence may have controlled the sizes of chondrule precursors. H-chondrite chondrules (which are the smallest among OC) formed from the smallest precursors. In each OC region, low-FeO chondrules formed before high-FeO chondrules during repeated episodes of chondrule formation. During thermal metamorphism, phyllosilicates were dehydrated; the liberated water oxidized metallic Fe-Ni. This caused correlated changes with petrologic type including decreases in the modal abundance of metal, increases in olivine Fa and low-Ca pyroxene Fs, increases in the olivine/pyroxene ratio, and increases in the kamacite Co and Ni contents. As water (with its heavy 0 isotopes) was lost during metamorphism, inverse correlations between bulk (delta)O-18 and bulk (delta)O-17 with petrologic type were produced. The H5 chondrites that were ejected from their parent body approx.7.5 Ma ago during a major impact event probably had been within a few kilometers of each other since they accreted approx.4.5 Ga ago. There are significant differences in the olivine compositional distributions among these rocks; these reflect stochastic nebular sampling of the oxidant (Le., phyllosilicates with high (delta)O-17) on a 0.1-1 km scale during agglomeration.

Rubin, Alan E.

2006-01-01

70

Genetic Relationships Between Chondrules, Rims and Matrix  

NASA Technical Reports Server (NTRS)

The most primitive chondrites are composed of chondrules and chondrule fragments, various types of inclusions, discrete mineral grains, metal, sulfides, and fine-grained materials that occur as interchondrule matrix and as chondrule/inclusion rims. Understanding how these components are related is essential for understanding how chondrites and their constituents formed and were processed in the solar nebula. For example, were the first generations of chondrules formed by melting of matrix or matrix precursors? Did chondrule formation result in appreciable transfer of chondrule material into the matrix? Here, we consider three types of data: 1) compositional data for bulk chondrites and matrix, 2) mineralogical and textural information, and 3) the abundances and characteristics of presolar materials that reside in the matrix and rims. We use these data to evaluate the roles of evaporation and condensation, chondrule formation, mixing of different nebular components, and secondary processing both in the nebula and on the parent bodies. Our goal is to identify the things that are reasonably well established and to point out the areas that need additional work.

Huss, G. R.; Alexander, C. M. OD.; Palme, H.; Bland, P. A.; Wasson, J. T.

2004-01-01

71

Photophoretic Strength on Chondrules. 1. Modeling  

NASA Astrophysics Data System (ADS)

Photophoresis is a physical process that transports particles in optically thin parts of protoplanetary disks, especially at the inner edge and at the optical surface. To model the transport and resulting effects in detail, it is necessary to quantify the strength of photophoresis for different particle classes as a fundamental input. Here, we explore photophoresis for a set of chondrules. The composition and surface morphology of these chondrules were measured by X-ray tomography. Based on the three-dimensional models, heat transfer through illuminated chondrules was calculated. The resulting surface temperature map was then used to calculate the photophoretic strength. We found that irregularities in particle shape and variations in composition induce variations in the photophoretic force. These depend on the orientation of a particle with respect to the light source. The variation of the absolute value of the photophoretic force on average over all chondrules is 4.17%. The deviation between the direction of the photophoretic force and illumination is 3.0 1.5. The average photophoretic force can be well approximated and calculated analytically assuming a homogeneous sphere with a volume equivalent mean radius and an effective thermal conductivity. We found an analytic expression for the effective thermal conductivity. The expression depends on the two main phases of a chondrule and decreases with the amount of fine-grained devitrified, plagioclase-normative mesostasis up to factor of three. For the chondrule sample studied (Bjurble chondrite), we found a dependence of the photophoretic force on chondrule size.

Loesche, Christoph; Wurm, Gerhard; Teiser, Jens; Friedrich, Jon M.; Bischoff, Addi

2013-12-01

72

Microbial Weathering of Olivine  

NASA Astrophysics Data System (ADS)

Controlled microbial weathering of olivine experiments displays a unique style of nanoetching caused by biofilm attachment to mineral surfaces. We are investigating whether the morphology of biotic nanoetching can be used as a biosignature.

Longazo, T. G.; Wentworth, S. J.; Southam, G.; McKay, D. S.

2002-03-01

73

Olivine-liquid equilibrium  

Microsoft Academic Search

A number of experiments have been conducted in order to study the equilibria between olivine and basaltic liquids and to try and understand the conditions under which olivine will crystallize. These experiments were conducted with several basaltic compositions over a range of temperature (11501300 C) and oxygen fugacity (10-0.6810-12 atm.) at one atmosphere total pressure. The phases in these experimental

P. L. Roeder; R. F. Emslie

1970-01-01

74

Reappraisal of Planetary Collision as a Mechanism for Chondrule Formation  

NASA Astrophysics Data System (ADS)

Planetary models for chondrule formation are not widely favored [1]. During the past decade, however, the importance of planetary impacts in the early solar system has featured prominantly in the fashionable "single large impactor" hypothesis for the origin of the Moon. If the Moon was, indeed, born out of the rapidly re-accreted debris of a planetary collision, then it may be supposed that other, smaller bodies (such as the chondrite parent bodies) could have been formed in a similar way, albeit on a more modest scale. The recent discovery in Bovedy (L3) of an immiscible glassy chondrule that formed from a silica pyroxenite precursor (a fractionated planetary rock) argues strongly in favor of this concept [2]. When the Bovedy evidence is placed alongside the considerations listed below, a general case for chondrule formation by early planetary collision seems attractive. 1. Radiogenic 26Mg began to accumulate in Ste. Marguerite about 5 Ma after it was first trapped in Allende CAIs [3]. Assuming uniform distribution of 26Al, planetesimals of 100 km radius or more formed during the first 2 Ma of this 5- Ma interval would have overheated and melted [4]. Collisions between such bodies would have discharged showers of molten silicate and metal into space, some of it escaping from the solar system altogether, some of it re-accreting sooner or later into new planetesimals (or onto existing ones) where it would again become ingested as melt. Through time, planetesimals would become fewer and larger, and their mutual collisions more energetic. Between about 4 and 5 Ma, with 26Al radioactivity now mostly spent, the bodies would have begun to cool and fractionate into a carapace of volcanic igneous rock (mixed with heterogeneous ejecta) overlying residual silicate melt, crystal cumulates, and molten metal/sulphide. Collision at this stage would yield droplets and rock fragments broadly comparable to those seen in chondritic meteorites. The accreted debris would be insufficiently radioactive to melt. 2. Alternative models involving remelting of dust in the nebula [1] require the fortuitous aggregation of precursor material into discrete (e.g., olivine-rich, pyroxene-rich, and metal-rich) compositional clusters before melting. 3. Collisions would produce enormous numbers of incandescent droplets simultaneously, sufficient to retard radiative heat loss and yield the relatively slow cooling rates implied by chondrule textures [5]. Also, volatile elements like Na may have remained close at hand as vapor, and later recondensed onto the cooling chondrule surfaces [6]. 4. Prior to collision, each planetesimal would have been surrounded by an orbiting torus of infalling debris, including primary interstellar dust. Mixing of the incandescent spray with the orbiting dust could explain a number of chondritic features, including accretionary chondrule rims, a source of nuclei to initiate crystallization, and the presence of unheated interstellar dust in the matrix of some meteorites. Also, re-integration of the disrupted planetesimal materials and intermingling of interstellar dust and other debris would help to maintain the primitive chemistry of chondrites and to provide an appropriate variety of chondrules and clasts. 5. The presence of more than one example of a very unusual and distinctive kind of chondrule in a particular meteorite (e.g., silica pyroxenite in Bovedy) suggests that accretion occurred near to the chondrule source, and was probably therefore rapid. In this case, hot accretion rather than metamorphic reheating is a plausible scenario. Besides, heating by 26Al decay is only possible during a short and specific time interval [4]. References: [1] Grossman J. N. (1988) in Meteorites and the Early Solar Sytem (J. F. Kerridge and M. S. Matthews, eds.), 680-696, Univ. of Arizona. [2] Hill H. G. M., this volume. [3] Zinner E. and Gopel C. (1992) Meteoritics, 27, 311. [4] Morden S. J. (1992) Meteoritics, 27, 263-264. [4] Radomsky P. M. and Hewins R. H. (1990) GCA, 54, 3475-3490. [6] Matsunami S. et al. (1992) Meteoritics, 2

Sanders, I. S.

1993-07-01

75

Trace elements in rims and interiors of Chainpur chondrules  

NASA Astrophysics Data System (ADS)

Trace elements were measured in the rims and interiors of nine chondrules separated from the Chainpur LL-3 chondrite. Whole rock samples of Chainpur and samples of separated rims were also measured. Chondrule rims are moderately enriched in siderophile and volatile elements relative to the chondrule interiors. The enriched volatile elements include the lithophilic volatile element Zn. The moderate enrichment of volatiles in chondrule rims and the lack of severe depletion in chondrules can account for the complete volatile inventory in Chainpur. These results support a three-component model of chondrite formation in which metal plus sulfide, chondrules plus rims and matrix silicates are mixed to form chondrites.

Wilkening, L. L.; Boynton, W. V.; Hill, D. H.

1984-05-01

76

Chondrules in the bishunpur L13 chondrite  

NASA Technical Reports Server (NTRS)

Twenty-six chondrules, chondrule fragments or clasts were analyzed. An automated wavelength dispersive instrument with a 90 micrometer beam integrated a series of analyses in traverses across each object. Depending on the size of the cross-sectional area, from 1 to 21 analyses were performed for each bulk analysis. Si, Ti, Al, Cr, Fe, Ni, Mn, Mg, Ca, Na, K and S were determined, and an analyzed augite was used as a secondary standard before and after each set of analyses. The work is part of a study of chondrule rims, interchondrule matrix, chondrules and clasts in unequilibrated ordinary chondrites. Only two of the twenty-six objects analyzed have Ca/Al atomic ratios greater than the ordinary chondritic average of 0.74. The bulk meteorite has a normal Ca/Al ratio, so presumably a Ca-rich, Al-poor component must be present to compensate for chondrules and chlasts. This component is unlikely to be rim or matrix, but may be phosphate associated with metal or sulphide. Na/Al ratios range from 1 to almost zero, but there is no hiatus as in a suite of Manych chondrules and glasses.

Hutchison, R.; Alexander, C.; Barber, D. J.

1984-01-01

77

An Evaluation of Microcomputer-Based Strain Analysis Techniques on Meteoritic Chondrules  

NASA Astrophysics Data System (ADS)

Introduction: Chondrule flattening and distinct foliation are preserved in certain chondrites [1] and have been interpreted, by some, as evidence of shock-induced pressure through hypervelocity impacts on parent bodies [2]. Recently, mean aspect ratios of naturally and artificially shocked chondrules, in the Allende (CV3) chondrite, have been correlated with shock intensity [3] using established shock stage criteria [4]. Clearly, quantification of chondrule deformation and appropriate petrographic criteria can be useful tools for constraining parent body shock history and, possibly, post-shock heating [3]. Here, strain analysis techniques (R(sub)(f)/phi and Fry) normally employed in structural geology, have been adapted and evaluated [5], for measuring mean chondrule strain, and orientation. In addition, the possible use of such strain data for partial shock stage classification is considered. R(sub)(f)/phi and Fry Analysis: The relationship between displacement and shape changes in rocks is known as strain [6] and assumes that an initial circle with a unit radius is deformed to form an ellipse, the finite strain ellipse (Rf). The strain ratio (Rs) is an expression of the change of shape. The orientation of the strain ellipse (phi) is the angle subtended between the semi-major axes and the direction of a fixed point of reference. Generally, log mean Rf ~ Rs and, therefore, the approximation Rf = Rs is valid. For chondrules, this is reasonable as they were originally molten, or partially-molten, droplets [7]. Fry's 'center-to-center' geological strain analysis technique [8] is based on the principle that the distribution of particle centers in rocks can sometimes be used to determine the state of finite strain (Rf). Experimental Techniques: The Bovedy (L3) chondrite was chosen for investigation as it contains abundant, oriented, elliptical chondrules [5]. Hardware employed consisted of a Macintosh microcomputer and a flat-bed scanner. Chondrule outlines, obtained from macrophotographic tracings of four complete thin-sections (total area 8.2 cm2) and a sawn slab (49.45cm2), were digitally scanned using application Ofoto v. 1.0.0^(TM). Chondrule outline (pict) files were then exported to a fabric analysis program, Image v. 1.44, and Rf values obtained thereafter exported to a spreadsheet environment for manipulation. Fry analysis was undertaken with an interactive program, Fry v. 5.0 [9] using the same pict files as before. Chondrule central points were manually inserted and center-to-center distances, when calculated, were displayed on screen in a way which echoes mean chondrule strain and orientation. Results and Conclusion. 364 chondrule outlines (three thin-sections and a sawn slab) were analysed by R(sub)(f)/phi and Fry techniques. In its present form, the Fry technique was judged to be unsuited to chondrule shape analysis as it is too dependant on grain size, i.e. the smallest grain, and the need for a planar homogenous sample bearing several hundred grains [8]. Recent developments in the Fry technique [10] may make it more suitable for chondrule analysis. Representative strain (Rf) data obtained for parallel thin-sections Bovedy M5385b and M5385c (total of 158 chondrules) were 1.49 and 1.41 respectively. Corresponding phi values were 115.0 degrees and 114.6 degrees respectively (with respect to a fixed reference point). Rf data together with petrographic shock features noted, mostly in olivine (e.g. planar fractures, undulatory extinction and weak mosaicism), were suggestive of shock stage S3 [4]. The degree of chondrule flattening and the nature of the (S3) shock effects observed are comparable with artifically flattened chondrules belonging to the same shock stage [3, 11]. The R(sub)(f)/phi technique evaluated was found to be more precise and quantitative than other methods previously employed for measuring maximum and minimum chondrule axes and orientation. Furthermore, it can provide reliable strain (axial, orientation) data for material subjected to very low grades of shock which would otherwise be difficult to

Hill, H. G. M.

1995-09-01

78

Use of a CO2 laser to prepare chondrule-like spherules from supercooled molten oxide and silicate droplets.  

NASA Technical Reports Server (NTRS)

Chondrule-like spherules were formed from individual freely falling subcooled droplets of alumina, enstatite, forsterite, enstatite-albite and forsterite-albite mixtures that had been melted with a focused continuous CO2 laser beam. Their textures (rimmed, excentro-radial, barred, glassy) are strikingly similar to those of many meteoritic chondrules. It is suggested that the phenomena associated with rapid crystallization from the supercooled melt are responsible for the various textures observed in the artificial spherules as well as in similar meteoritic chondrules. It is suggested that the textures observed would also result from rapid crystallization of relatively slowly cooling molten droplets that may have been produced in larger scale events, including condensation from a nebula of solar composition and solidification in an ambient medium of high temperature.

Nelson, L. S.; Blander, M.; Keil, K.; Skaggs, S. R.

1972-01-01

79

On the origin of porphyritic chondrules  

SciTech Connect

A computer program for the complex equilibria in a cooling nebular gas was used to explore a possible origin of porphyritic chondrules, the major class of chondrules in chondritic meteorites. It uses a method of accurately calculating the thermodynamic properties of molten multicomponent aluminosilicates, which deduces the silicate condensates vs temperature and pressure of a nebular gas. This program is coupled with a chemical equilibrium algorithm for systems with at least 1000 chemical species; it has a data base of over 5000 solid, liquid, and gaseous species. Results are metastable subcooled liquid aluminoscilicates with compositions resembling types IA and II porphyritic chondrules at two different temperatures at any pressure between 10{sup {minus}2} and 1 (or possibly 10{sup {minus}3} to 5) atm. The different types of chondrules (types I, II, III) could have been produced from the same gas and do not need a different gas for each apparent oxidation state; thus, the difficulty of current models for making porphyritic chondrules by reheating different solids to just below their liquidus temperatures in different locations is not necessary. Initiation of a stage of crystallization just below liquidus is part of the natural crystallization (recalescence) process from metastable subcooled liquidus and does not require an improbably heating mechanism. 2 tabs.

Blander, M. [Argonne National Lab., IL (United States); Unger, L. [Purdue Univ., Westville, IN (United States); Pelton, A.; Ericksson, G. [Ecole Polytechnique, Montreal, PQ (Canada)

1994-05-01

80

Sintering of olivine and olivine-basalt aggregates  

Microsoft Academic Search

The sintering behavior of olivine and olivine-basalt aggregates has been examined at temperatures near 1,300 C. Experimental factors contributing to rapid sintering kinetics and high-density, fine-grained specimens include: (i) the uniform dispersion of basalt throughout the specimen, (ii) a very fine, uniform particle size for the olivine powder, (iii) oxygen fugacities near the high PO2 end of the olivine stability

R. F. Cooper; D. L. Kohlstedt

1984-01-01

81

Exogenous Olivine on Vesta  

NASA Astrophysics Data System (ADS)

Vesta has conserved an early status of planetary evolution, demonstrated by the global coverage of HED lithology on its surface. Being sufficiently large to retain some material from slow projectiles, but small enough to prevent its complete evaporation during the impacts, this unique environment is ideal for distinction and identification of exogenous material. In particular, the distribution, concentration, and geological context of olivine exposures are poorly consistent with a Vestan mantle origin. Similar arguments are valid for the areas of dark carbonaceous chondrite-like lithology, and a few other features with unusual visual spectral slopes. Most olivine is found close to the large impact craters Bellicia, Arruntia, and Pomponia in the northern hemisphere, whose ejecta sheet is characterized by a mixing trend from an HED lithology to S- or A-type asteroid material. The olivine has diagnostic significance for the extent and duration of differentiation during the early accretion of parent bodies in the asteroid region. Sources for exogenous olivine are available in Vestas environment among A- and S-type asteroids. It is not clear, however, if it is derived mainly from achondritic or chondritic sources. On the other hand, the lack of evidence for Vestas mantle material implies constraints on its inner structure, e.g. the depth of the crust.

Hoffmann, Martin; Nathues, Andreas; Schfer, Michael; Thangjam, Guneshwar; Le Corre, Lucille; Vishnu, Reddy; Christensen, Ulrich; Mengel, Kurt; Sierks, Holger; Vincent, Jean-Baptist; Cloutis, Edward A.; Russell, Christopher T.; Schfer, Tanja; Gutierrez-Marques, Pablo; Hall, Ian; Ripken, Joachim; Bttner, Irene

2014-11-01

82

Olivine Crystal Structure  

NSDL National Science Digital Library

This exercise is based on recent crystallographic research on the olivine crystal structure published by Redfern et al. (2000). The authors of this study synthesized Fa50 olivine olivine (MgFeSiO4) in an experimental apparatus at temperatures ranging from 100 to 1250 °C, quenched the experiments, and used in situ neutron powder diffraction techniques to investigate changes in the synthesized olivines as a function of temperature. While this study reports cutting-edge materials research carried out with the latest crystallographic techniques, the results are educationally instructive and illustrate important concepts normally covered in an undergraduate mineralogy course. In this exercise, students are guided into the American Mineralogist Crystal Structure Database to retrieve and download published crystal structure data for viewing in either the CrystalMaker or XtalDraw visualization software packages. The students are instructed on how to manipulate the structures and are asked to plot some of the crystallographic data from this study on graphs using a spreadsheet program such as Excel.

Ratajeski, Kent

83

Microbial Weathering of Olivine  

NASA Technical Reports Server (NTRS)

Controlled microbial weathering of olivine experiments displays a unique style of nanoetching caused by biofilm attachment to mineral surfaces. We are investigating whether the morphology of biotic nanoetching can be used as a biosignature. Additional information is contained in the original extended abstract.

McKay, D. S.; Longazo, T. G.; Wentworth, S. J.; Southam, G.

2002-01-01

84

Cosmochemical Studies: Meteorites, Asteroidal Processes, Chondrules  

NASA Technical Reports Server (NTRS)

Our research mainly concerned the asteroidal processes involved in the formation of meteorites and meteoritic chondrules. We continued to generate large amounts of instrumental-neutron-activation analysis (INAA) data, both for irons, chondrites and primitive achondrites. Major themes of our chondrule research were: (1) the temperature and crystallization history of individual chondrules, and (2) the evolution of the solar nebula during the period within which chondrule formation occurred. Much of our chondrule research was focused on the highly primitive CO3 chondrites. We initiated a study of the cooling history of high-FeO chondrules by characterizing the overgrowth layers on relict grains.. We also continued our studies of the composition and the formation of iron meteorites and the evolution of their parent planets. The large data sets that we have generated at UCLA allows systematic comparisons of the large magmatic groups both in terms of fractional crystallization (including rough estimates of non-metal contents of the parental melts) and in terms of the effects of variable contents of trapped melt. We have completed a preliminary study of group IIIAB in which we developed a trapped-melt model and more detailed studies of group IVA and the main-group pallasites. By comparing these large groups and modeling them by a combination of crystallization and melt trapping, we are able to better define both the formation processes and the nature of the solid/liquid elemental partitioning. We helped maintain the excellent neutron-activation facilities at UCLA, a major resource for the cosmochemical community.

Wasson, John T.

2002-01-01

85

Partitioning of Trace Elements Between Pyroxene and Liquid in a Porphyritic Pyroxene Chondrule in Semarkona  

NASA Astrophysics Data System (ADS)

The unequilibrated chondrite Semarkona (LL3.0) enables us to investigate primary properties of chondrules that have not been overprinted by secondary processes. Electron microprobe studies of the compositions and zoning properties of silicate phases in these chondrules have helped to interpret crystallization behavior and, hence, offer important insights into formation conditions [e.g., 1,2]. However, the behavior of trace elements in these systems has not been investigated, largely because of the difficulties encountered in analyzing such elements in chondrule silicates. Here we report preliminary ion microprobe data obtained on coexisting pyroxene and glass phases from a pyroxene-rich chondrule in Semarkona. Trace elements analyzed are REE (La, Ce, Nd, Sm, Eu, Dy, Er, Yb), Sr, Y, and Zr. The chondrule studied is a typical example of textural type IAB [2]. It contains phenocrysts of olivine (Fa(sub)3) and clinoenstatite and a glassy mesostasis occupying approximately 15 vol% of the chondrule. Augite (Fs(sub)3, Wo(sub)44) occurs as narrow (10-micrometer) rims on clinoenstatite phenocrysts. Clinoenstatite is FeO-poor (Fs(sub)3, Wo(sub)0.4) and shows little zoning in major and minor elements. Trace-element analyses have been carried out on clinoenstatite, augite, and glass in this chondrule. REE contents in clinoenstatite are extremely low, lying in the range 0.01-0.1 x CI, and show a smooth increase in abundance from La to Yb. REE abundances are enriched in both augite and glass at levels approximately 4-10 x CI, with a small negative Eu anomaly in augite and a small positive Eu anomaly in glass. Olivine is likely to contain REE abundances similar to low-Ca pyroxene [3]. These relative abundances are consistent with closed-system crystallization of the chondrule, assuming that its bulk composition has chondritic abundances of REE [4]. Trace-element partition coefficients (Ds) for the two pyroxene phases are shown in Fig. 1. Clinoenstatite Ds vary smoothly, increasing from 0.0006 (La) to 0.02 (Yb). These data are broadly consistent with equilibrium D values obtained experimentally [3]. However, chondrule Ds for the LREE and Sr are consistently higher than equilibrium experimental values. This could be attributed to the effect of rapid cooling in chondrules [3]. Values for D(sub)Y and D(sub)Zr are also consistent with the experimental data. For augite, the Ds we determined are approximately flat, at values around 1, with a decrease in the LREE and a negative Eu anomaly. The chondrule data are consistently higher than equilibrium experimental data for pyroxenes of composition Wo(sub)40 [5]. This may also be attributable to the effect of rapid cooling rate. However, the partitioning behavior of REE in Ca-rich pyroxene as a function of melt composition is not fully understood. D(sub)Sr, D(sub)Y, and D(sub)Zr are comparable with REE values, consistent with the data of [6]. In summary, trace-element partitioning among chondrule silicate phases appears to be entirely consistent with closed-system crystallization of the chondrule. Data such as these will be valuable in assessing the origins of, and relationships between, various chondritic components. They may also provide a valuable tool for studying metamorphism in ordinary chondrites. This work is supported by NASA grant NAGW-3347 (J. J. Papike). SIMS analyses were performed at the UNM/SNL Ion Microprobe Facility, a joint operation of the Institute of Meteoritics, UNM, and Sandia National Laboratories. References: [1] Jones R. H. (1990) GCA, 54, 1785-1802. [2] Jones R. H. (1992) LPS XXIII, 631-632. [3] Kennedy A. K. et al. (1993) EPSL, 115, 177-195. [4] Grossman J. N. et al. (1988) In Meteorites and the Early Solar System, 619- 659. [5] McKay G. et al. (1986) GCA, 50, 927-937. [6] Hart S. R. and Dunn T. (1993) CMP, 113, 1-8. Fig. 1 appears here in the hard copy.

Jones, R. H.; Layne, G. D.

1993-07-01

86

Experimental Reproduction of Type 1B Chondrules  

NASA Technical Reports Server (NTRS)

We have replicated type 1B chondrule textures and compositions with crystallization experiments in which UOC material was melted at 1400 deg.C and cooled at 5-1000 deg.C/hr using graphite crucibles in evacuated silica tubes to provide a reducing environment. Additional information is contained in the original extended abstract.

Lofgren, G. E.; Le, L.

2002-01-01

87

Revisiting Jovian-resonance Induced Chondrule Formation  

NASA Astrophysics Data System (ADS)

It is proposed that planetesimals perturbed by Jovian mean-motion resonances are the source of shock waves that form chondrules. It is considered that this shock-induced chondrule formation requires the velocity of the planetesimal relative to the gas disk to be on the order of >~ 7 km s-1 at 1 AU. In previous studies on planetesimal excitation, the effects of Jovian mean-motion resonance together with the gas drag were investigated, but the velocities obtained were at most 8 km s-1 in the asteroid belt, which is insufficient to account for the ubiquitous existence of chondrules. In this paper, we reexamine the effect of Jovian resonances and take into account the secular resonance in the asteroid belt caused by the gravity of the gas disk. We find that the velocities relative to the gas disk of planetesimals a few hundred kilometers in size exceed 12 km s-1, and that this is achieved around the 3:1 mean-motion resonance. The heating region is restricted to a relatively narrowband between 1.5 AU and 3.5 AU. Our results suggest that chondrules were produced effectively in the asteroid region after Jovian formation. We also find that many planetesimals are scattered far beyond Neptune. Our findings can explain the presence of crystalline silicate in comets if the scattered planetesimals include silicate dust processed by shock heating.

Nagasawa, M.; Tanaka, K. K.; Tanaka, H.; Nakamoto, T.; Miura, H.; Yamamoto, T.

2014-10-01

88

Electrical conduction in olivine  

Microsoft Academic Search

This paper reports detailed measurements of electrical conductivitysigma and thermoelectric effect \\/ital S\\/ in the mineral olivine and in syntheticforsterite as functions of temperature in the range from 1000\\/degree\\/ to1500 \\/degree\\/C and oxygen partial pressure in the range from 10\\/sup \\/minus\\/10\\/ to10⁴ Pa. The two most striking observations are strong conductivityanisotropy in forsterite and a sign change in \\/ital S\\/

Robert N. Schock; Alfred G. Duba; Thomas J. Shankland

1989-01-01

89

Electrical Conductivity of Olivine  

Microsoft Academic Search

The electrical conductivity a of single crystals of olivine of 0, 7.7, 8.2, 9.4, and 26.4 mole % fayalite has been measured up to 1200C and 7.5 kb. Samples from different localities with approximately the same fayalite content and impurity levels have electrical conductivities that differ by 2-3 orders of magnitude. It is proposed that the oxidation state of the

Al Duba

1972-01-01

90

Evaporation of nebular fines during chondrule formation  

NASA Astrophysics Data System (ADS)

Studies of matrix in primitive chondrites provide our only detailed information about the fine fraction (diameter <2 ?m) of solids in the solar nebula. A minor fraction of the fines, the presolar grains, offers information about the kinds of materials present in the molecular cloud that spawned the Solar System. Although some researchers have argued that chondritic matrix is relatively unaltered presolar matter, meteoritic chondrules bear witness to multiple high-temperature events each of which would have evaporated those fines that were inside the high-temperature fluid. Because heat is mainly transferred into the interior of chondrules by conduction, the surface temperatures of chondrules were probably at or above 2000 K. In contrast, the evaporation of mafic silicates in a canonical solar nebula occurs at around 1300 K and FeO-rich, amorphous, fine matrix evaporates at still lower temperatures, perhaps near 1200 K. Thus, during chondrule formation, the temperature of the placental bath was probably >700 K higher than the evaporation temperatures of nebular fines. The scale of chondrule forming events is not known. The currently popular shock models have typical scales of about 10 km. The scale of nebular lightning is less well defined, but is certainly much smaller, perhaps in the range 1 to 1000 m. In both cases the temperature pulses were long enough to evaporate submicrometer nebular fines. This interpretation disagrees with common views that meteoritic matrix is largely presolar in character and CI-chondrite-like in composition. It is inevitable that presolar grains (both those recognized by their anomalous isotopic compositions and those having solar-like compositions) that were within the hot fluid would also have evaporated. Chondrule formation appears to have continued down to the temperatures at which planetesimals formed, possibly around 250 K. At temperatures >600 K, the main form of C is gaseous CO. Although the conversion of CO to CH 4 at lower temperatures is kinetically inhibited, radiation associated with chondrule formation would have accelerated the conversion. There is now evidence that an appreciable fraction of the nanodiamonds previously held to be presolar were actually formed in the solar nebula. Industrial condensation of diamonds from mixtures of CH 4 and H 2 implies that high nebular CH 4/CO ratios favored nanodiamond formation. A large fraction of chondritic insoluble organic matter may have formed in related processes. At low nebular temperatures appreciable water should have been incorporated into the smoke that condensed following dust (and some chondrule) evaporation. If chondrule formation continued down to temperatures as low as 250 K this process could account for the water concentration observed in primitive chondrites such as LL3.0 and CO3.0 chondrites. Higher H 2O contents in CM and CI chondrites may reflect asteroidal redistribution. In some chondrite groups (e.g., CR) the Mg/Si ratio of matrix material is appreciably (30%) lower than that of chondrules but the bulk Mg/Si ratio is roughly similar to the CI or solar ratio. This has been interpreted as a kind of closed-system behavior sometimes called "complementarity." This leads to the conclusion that nebular fines were efficiently agglomerated. Its importance, however is obscured by the observation that bulk Mg/Si ratios in ordinary and enstatite chondrites are much lower than those in carbonaceous chondrites, and thus that complementarity did not hold throughout the solar nebula.

Wasson, John T.

2008-06-01

91

Origin of plagioclase-olivine inclusions in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

The origin of plagioclase-olivine inclusions (POIs) from three CV chondrites and one ungrouped chondrite was investigated by examining the chemical, mineralogical, and isotopic characteristics of a group of POIs from these chondrites. Results of these analyses demonstrate that the mixing and the partial melting processes in these inclusions were superimposed on more ancient isotopically heterogeneous material. A comparison of the essential characteristics of POIs and CAIs suggests that the major processes leading to the formation of POIs (such as condensation, dust/gas fractionation, aggregation of chemically and isotopically disparate materials, and partial melting) are common to most CAIs and chondrules. A scenario for the origin of POIs is proposed, showing that the homogeneity of the final assemblage (whether a POI, a CAI, or a chondrite) is primarily a reflection of the thermal history rather than the nature of precursor materials.

Sheng, Y. J.; Hutcheon, I. D.; Wasserburg, G. J.

1991-02-01

92

Alkali elemental and potassium isotopic compositions of Semarkona chondrules  

USGS Publications Warehouse

We report measurements of K isotope ratios in 28 Semarkona chondrules with a wide range of petrologic types and bulk compositions as well as the compositions of CPX-mesostasis pairs in 17 type I Semarkona chondrules, including two chondrules with radial alkali zonation and 19 type II chondrules. Despite the wide range in K/Al ratios, no systematic variations in K isotopic compositions were found. Semarkona chondrules do not record a simple history of Rayleigh-type loss of K. Experimentally determined evaporation rates suggest that considerable alkali evaporation would have occurred during chondrule formation. Nevertheless, based on Na CPX-mesostasis distribution coefficients, the alkali contents of the cores of most chondrules in Semarkona were probably established at the time of final crystallization. However, Na CPX-mesostasis distribution coefficients also show that alkali zonation in type I Semarkona chondrules was produced by entry of alkalis after solidification, probably during parent body alteration. This alkali metasomatism may have gone to completion in some chondrules. Our preferred explanation for the lack of systematic isotopic enrichments, even in alkali depleted type I chondrule cores, is that they exchanged with the ambient gas as they cooled. ?? The Meteoritical Society, 2005.

Alexander, C.M. O'D.; Grossman, J.N.

2005-01-01

93

Partitioning of Moderately Siderophile Elements Among Olivine, Silicate Melt, and Sulfide Melt: Constraints on Core Formation in the Earth and Mars  

NASA Technical Reports Server (NTRS)

This study investigates the effects of Variations in the fugacities of oxygen and sulfur on the partitioning of first series transition metals (V, Cr, Mn, Fe, Co, Ni. and Cu) and W among coexisting sulfide melt, silicate melt, and olivine. Experiments were performed at 1 atm pressure, 1350 C, with the fugacities of oxygen and sulfur controlled by mixing CO2, CO, and SO2 gases. Starting compositions consisted of a CaO-MgO-Al2O3-SiO2-FeO-Na2O analog for a barred olivine chondrule from an ordinary chondrite and a synthetic komatiite. The f(sub O2)/f(sub S2), conditions ranged from log of f(sub O2) = -7.9 to - 10.6, with log of f(sub S2) values ranging from - 1.0 to -2.5. Our experimental results demonstrate that the f(sub O2)/f(sub S2) dependencies of sulfide melt/silicate melt partition coefficients for the first series transition metals arc proportional to their valence states. The f(sub O2)/f(sub S2) dependencies for the partitioning of Fe, Co, Ni, and Cu are weaker than predicted on the basis of their valence states. Variations in conditions have no significant effect on olivine/melt partitioning other than those resulting from f(sub O2)-induced changes in the valence state of a given element. The strong f(sub O2)/f(sub S2) dependence for the olivine/silicate melt partitioning of V is attributable to a change of valence state, from 4+ to 3+, with decreasing f(sub O2). Our experimentally determined partition coefficients are used to develop models for the segregation of sulfide and metal from the silicate portion of the early Earth and the Shergottite parent body (Mars). We find that the influence of S is not sufficient to explain the overabundance of siderophile and chalcophile elements that remained in the mantle of the Earth following core formation. Important constraints on core formation in Mars are provided by our experimental determination of the partitioning of Cu between silicate and sulfide melts. When combined with existing estimates for siderophile element abundances in the Martian mantle and a mass balance constraint from Fe, the experiments allow a determination of the mass of the Martian core (approx. 17 to 22 wt% of the planet) and its S content (approx.0.4 wt%). These modeling results indicate that Mars is depleted in S, and that its core is solid.

Gaetani, Glenn A.; Grove, Timothy L.

1997-01-01

94

Applicability of Henry's Law to helium solubility in olivine  

NASA Astrophysics Data System (ADS)

Applicability of Henry's Law to helium solubility in olivine We have experimentally determined helium solubility in San Carlos olivine across a range of helium partial pressures (PHe) with the goal of quantifying how noble gases behave during partial melting of peridotite. Helium solubility in olivine correlates linearly with PHe between 55 and 1680 bar. This linear relationship suggests Henry's Law is applicable to helium dissolution into olivine up to 1680 bar PHe, providing a basis for extrapolation of solubility relationships determined at high PHe to natural systems. This is the first demonstration of Henry's Law for helium dissolution into olivine. Averaging all the data of the PHe series yields a Henry's coefficient of 3.8(3.1)10-12 mol g-1 bar-1. However, the population of Henry's coefficients shows a positive skew (skewness = 1.17), i.e. the data are skewed to higher values. This skew is reflected in the large standard deviation of the population of Henry's coefficients. Averaging the median values from each experiment yields a lower Henry's coefficient and standard deviation: 3.2( 2.3)10-12 mol g-1 bar-1. Combining the presently determined helium Henry's coefficient for olivine with previous determinations of helium Henry's coefficients for basaltic melts (e.g. 1) yields a partition coefficient of ~10-4. This value is similar to previous determinations obtained at higher PHe (2). The applicability of Henry's Law here suggests helium is incorporated onto relatively abundant sites within olivine that are not saturated by 1680 bar PHe or ~510-9 mol g-1. Large radius vacancies, i.e. oxygen vacancies, are energetically favorable sites for noble gas dissolution (3). However, oxygen vacancies are not abundant enough in San Carlos olivine to account for this solubility (e.g. 4), suggesting the 3x10-12 mol g-1 bar-1 Henry's coefficient is associated with interstitial dissolution of helium. Helium was dissolved into olivine using an externally heated pressure vessel (Brown University). The starting materials were prepared by cutting gem-quality San Carlos olivine (~Fo90) into small blocks (~421 mm) using a diamond wafering blade saw and polishing with alumina slurries and colloidal silica. Analysis was completed by laser ablation-mass spectrometry using a 193 nm excimer laser and a MAP 215-50 specifically tuned for He (Open University, UK). Laser ablation pit depth varied from 2 to 40 ?m, and no correlation between pit depth and [He] is observed after accounting for variations PHe across the different experiments. This lack of correlation indicates a close approach to equilibrium was achieved over the experimental durations. Two analyses yielded spuriously high [He] (>3 std. dev. from the population mean, n = 85), and these analyses were not used to calculate Henry's coefficients. The two spuriously high analyses, in combination with the right skew of Henry's coefficients calculated from individual data points, suggests gem-quality San Carlos olivine contains volumes with anomalously high helium solubility. The nature of these volumes is currently under investigation. However, despite their presence, helium is still highly incompatible in olivine during partial melting. [1] Lux GCA 1987 [2] Heber et al. GCA 2007 [3] Shcheka & Keppler Nature 2012 [4] Walker et al. PEPI 2009

Jackson, C.; Parman, S. W.; Kelley, S. P.; Cooper, R. F.

2013-12-01

95

Relict Forsterite in Chondrules: Implications for Cooling Rates  

NASA Technical Reports Server (NTRS)

Forsterite (Fo(sub 99-100)) is often present in chondrules as relict grains that did not crystallize in situ and as isolated grains outside of chondrules; both are surrounded by ferrous overgrowths which clearly formed at a later time, probably during chondrule formation. We performed microprobe analyses across forsterite-overgrowth interfaces in 12 chondrules and 4 isolated grains in the Sahara-97210 LL3.2 (Sahara), Wells LL3.3, and Chainpur LL3.4 chondrites and modelled diffusional exchange between forsterite and overgrowths, with the goal of constraining the thermal histories during chondrule formation. The cooling rates experienced by chondrules provide an important constraint on the origin and setting of these objects.

Greeney, S.; Ruzicka, A.

2004-01-01

96

Helium Diffusion in Olivine  

NASA Astrophysics Data System (ADS)

Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950C: D = 3.91x10-6exp(-159 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm experiments, indicating that the results reported here can be reasonably applied to modeling He transport in the upper mantle. The insensitivity of He diffusion to pressure over the investigated range of conditions suggests that compression of the mineral lattice is not sufficient to significantly influence migration of the relatively small helium atoms, which likely diffuse via crystal interstices. The He diffusivities in this work are generally consistent with results from the study of Futagami et al. (1993), who measured He diffusion in natural olivine by outgassing 4He implanted samples, and with the diffusivities measured by bulk-release of 4He and 3He by Shuster et al. (2003), but are about 2 orders of magnitude slower than the recent findings of Tolstikhin et al. (2010) and Blard et al. (2008) . An up-temperature extrapolation of our data also show reasonable agreement with the higher-temperature measurements of Hart (1984). Blard et al. (2008) GCA 72, 3788-3803; Futagami et al. (1993) GCA 57, 3177-3194; Hart (1984) EPSL 70, 297-302; Shuster et al.( 2003) EPSL 217, 19-32; Tolstikhin et al. (2010) GCA 74, 1436-1447

Cherniak, D. J.; Watson, E. B.

2011-12-01

97

In Situ Investigation of Preirradiated Olivines in CM Chondrites  

NASA Astrophysics Data System (ADS)

Most CM chondrites are breccias that contain fragments of primary rock representing densely packed agglomerates of chondrules, CAIs, etc., all of which are mantled by thick layers of fine-grained mineral dust [1]. These dust mantles seem to be the result of dust sampling by the various components during their isolated existence in the solar nebula prior to the formation of the CM parent body [1]. Metzler et al. [1] concluded that these rock fragments are well-preserved remnants of the freshly accreted CM parent body(ies). There is an opposing hypothesis that favors an origin of the dust mantles in an active regolith on the CM parent body [e.g., 2]. A list of arguments against the latter view is given by Metzler et al. [1], including a hint at the absence of solar-wind-implanted gases in dust mantles and in fragments of primary rock. In analogy to brecciated ordinary chondrites and lunar breccias, the most probable residence of the solar gases in CM chondrites is their clastic matrix. The same holds for track-rich olivines that were observed in CM chondrites. The occurrence of these grains in the clastic matrix and their absence in the primary rock would give an additional argument for the idea of a dust mantle origin in the solar nebula rather than in a planetary regolith. To answer this important question, mosaics of backscattered electron images of several large polished thin sections of Murchison and Cold Bokkeveld were prepared. The thin sections (1.5-5 cm^2 each) were etched in a WN solution [3] for about 4 hr to reveal the heavy ion tracks in olivines. Results: The background GCR track density produced during meteoroid transit is on the order of 10^4 tracks/cm^2, as was previously observed by [4]. Following the definition given by Goswami and Lal [4], olivines with track densities >10^5 tracks/cm^2 were classified as preirradiated grains and were found in both meteorites in a very small quantity. In both meteorites, 39 preirradiated isolated olivine grains were found in the clastic matrix, whereas the investigated fragments of primary rock do not contain preirradiated olivines. In Murchison about 1.8% (15 out of 850 investigated grains) of the isolated olivines in the clastic matrix show high track densities in the range between 1.9 x 10^6 and >5 x 10^7, comparable to the results of Goswami and co-workers [4,5]. Both Fe-poor and Fe-rich olivines with grain sizes between 40 and 710 micrometers were found to be preirradiated. Track gradients were found in 33% of these olivines, which is very similar to the values obtained by Goswami and Lal [4] and identical to those obtained by MacDougall and Phinney [6]. About 0.4% (2 out of 530) of the investigated olivine-bearing chondrules and chondrule fragments are preirradiated. In the case of Cold Bokkeveld, 3.7% (24 out of 650) of the isolated olivines show high track densities. Thirteen of these 24 grains were found to be concentrated in a distinct inclusion (1 x 4 mm) that is characterized by its elongated appearence and clastic fabric. The track densities of its preirradiated olivines show a very narrow range, indicating a common irradiation history of these grains. The petrography of this inclusion is currently under investigation. Conclusions: Track-rich (preirradiated) olivines in CM chondrites occur exclusively in the clastic matrix of these meteorites, comparable to observations in brecciated ordinary chondrites. Fragments of primary rock in CM chondrites do not contain solar-wind-implanted gases [1] or preirradiated grains. This confirms the view that the dust mantles around various components of these rocks are the products of dust accretion in the solar nebula rather than of regolith processes on the parent body surface. References: [1] Metzler K. et al. (1992) GCA, 56, 2873. [2] Kerridge J. (1992) personal communication. [3] Krishnaswami S. et al. (1971) Science, 174, 287. [4] Goswami J. N. and Lal D.(1979) Icarus, 40, 510. [5] Goswami J. N. and MacDougall J. D. (1983) Proc. LPSC 13th, in JGR, 88, A755. [6] MacDougall J. D. and Phinney D. (1977) Proc. LS

Metzler, K.

1993-07-01

98

A constraint on impact theories of chondrule formation  

NASA Technical Reports Server (NTRS)

The association between agglutinates and chondrule-like spherules, which characterizes the assemblage of impact-derived melt products in lunar regolith samples and some gas-rich achondrites, is not found in primitive chondrites. This observation suggests that impacts into a parent-body regolith are unlikely to have produced the chondrules. We believe that if chondrules were formed from impact melt, it was probably generated by jetting during particle-to-particle collisions, presumably in the nebula.

Kerridge, J. F.; Kieffer, S. W.

1977-01-01

99

Magnesium isotopic fractionation in chondrules from the Murchison and Murray CM2 carbonaceous chondrites  

E-print Network

Magnesium isotopic fractionation in chondrules from the Murchison and Murray CM2 carbonaceous. Investigation of the magnesium isotopic compositions of chondrules can place stringent constraints on the timing

Grossman, Lawrence

100

Olivine in terminal particles of Stardust aerogel tracks and analogous grains in chondrite matrix  

NASA Astrophysics Data System (ADS)

The dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the Wild 2 samples. We present 68 analyses of olivine (Fa0-97) in the coarse-grained terminal particles of Stardust aerogel tracks and a comprehensive dataset (>103 analyses) of analogous olivine grains (5-30 ?m) isolated in CI, CM, CR, CH, CO, CV3-oxidized, CV3-reduced, C3-ungrouped (Acfer 094 and Ningqiang), L/LL 3.0-4, EH3, and Kakangari chondrite matrix. These compositions reveal that Wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite-forming regions. The Wild 2 olivine includes amoeboid olivine aggregates (AOAs), refractory forsterite, type I and type II chondrule fragments and/or microchondrules, and rare relict grain compositions. In addition, we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low-temperature, aqueous processing in the Kuiper Belt. The generally low Cr content of FeO-rich olivine in the Stardust samples indicates that they underwent mild thermal metamorphism, akin to a petrologic grade of 3.05-3.15.

Frank, David R.; Zolensky, Michael E.; Le, Loan

2014-10-01

101

A short duration of chondrule formation in the solar nebula: evidence from 26Al in Semarkona ferromagnesian chondrules  

Microsoft Academic Search

The 26Al26Mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite Semarkona (LL3.0) were studied using a secondary ion mass spectrometer. Their glass or plagioclase portions contain excesses of 26Mg, and in two chondrules the 26Mg excesses are well correlated with 27Al\\/24Mg, which demonstrates the in-situ decay of 26Al. The initial 26Al\\/27Al ratios in these chondrules obtained from

Noriko T. Kita; Hiroko Nagahara; Shigeko Togashi; Yuichi Morishita

2000-01-01

102

Revisiting Jovian-Resonance Induced Chondrule Formation  

E-print Network

It is proposed that planetesimals perturbed by Jovian mean-motion resonances are the source of shock waves that form chondrules. It is considered that this shock-induced chondrule formation requires the velocity of the planetesimal relative to the gas disk to be on the order of > 7 km/s at 1 AU. In previous studies on planetesimal excitation, the effects of Jovian mean-motion resonance together with the gas drag were investigated, but the velocities obtained were at most 8 km/s in the asteroid belt, which is insufficient to account for the ubiquitous existence of chondrules. In this paper, we reexamine the effect of Jovian resonances and take into account the secular resonance in the asteroid belt caused by the gravity of the gas disk. We find that the velocities relative to the gas disk of planetesimals a few hundred kilometers in size exceed 12 km/s, and that this is achieved around the 3:1 mean-motion resonance. The heating region is restricted to a relatively narrow band between 1.5 AU and 3.5 AU. Our res...

Nagasawa, M; Tanaka, H; Nakamoto, T; Miura, H; Yamamoto, T

2014-01-01

103

Chondrules from the Earth and Moon: A Review  

NASA Astrophysics Data System (ADS)

Since chondrules are arguably the most important constituent of chondritic meteorites, deciphering their origin would constitute a major step towards understanding early solar system processes. We here draw attention to proposed chondrules found in lunar and terrestrial samples since their existence on these parent bodies would seriously constrain theories for the origin of meteoritic chondrules. Terrestrial chondrules. Graup has reported lithic chondrules in the crater suevite and both fluid drop and lithic chondrules in the fall-out suevite of the Ries Crater [1, see also 2]. He observed 115 fluid drop and 44 lithic chondrules (as well as 10 glass spherules). Fourteen were shown in figures. He argued that textures and sizes, and thus modes of formation, are very similar to those of meteoritic chondrules. The Ries chondrules often have fine-grained rims similar to those found on meteoritic chondrules and similar origins have been proposed for both kinds of rim [1. 3, 4]. There is little available data beyond Graup's initial descriptions and these objects require further study. Lunar chondrules. Chondrules have been found in Apollo 11, 14, 15, 16 and Luna 16 soils and breccias [5-11]. Both fluid drop and lithic chondrules have been reported, many with fine-grained rims. Again, because of the similarity in texture, similar formation details to those of meteoritic chondrules have been proposed for both the chondrules and their rims. Most lunar chondrules have ANT compositions, as opposed to basaltic compositions, either because nucleation of these compositions is favored or because of the more intense impact history of the lunar highlands [e.g. 11]. Lunar agglutinates, which constitute 50 vol% of some soil samples, have histories involving reduction and evaporation similar to those of group A meteoritic chondrules [12]. They differ from the chondrules mainly in size, shape, the presence of unmelted dust particles and abundant vesicles [12]. At the moment there appear to be only two significant differences hetween lunar, terrestrial and meteoritic chondrules, their compositions and their place of origin. Further study, especially of the terrestrial chandrules, is required to confirm this. In many respects, size, texture, the presence of rims and the existence of both droplet and lithic forms, they resemble each other and are distinguishable from simple melt spherules which are relatively common on the Moon. The occurrence of true chondrules on three planetary bodies, especially when associated with impact, and differing only in that their compositions, would suggest that the meteoritic chondrules are impact in origin. The differences in chondrule abundance on the meteorite bodies and other planetary objects could reflect differences in parent body size, impact mechanics, surface processes, and selection effects surrounding the transfer of meteorites to earth and their passage through the atmosphere. References: [1] Graup G. (1981) EPSL, 55, 407-418. [2] Newsom H. E. (1990) GSA Spec. Paper 247, 195-206. [3] Hewins R. H. (1989) Symp. Antarc. Meteorites, 2, 200-220. [4] Huang S. et al. (1995) Icarus, submitted. [5] Fredriksson K. et al. (1970) Science, 167, 664-666. [6] Kurat G. et al. (1972) Proc. LSC 3rd, 707-721. [7] King E. A. et al. (1972) Science, 175, 59-60. [8] King E. A. et al. (1972) Proc. LSC 3rd, 673-686. [9] Bunch T. E. et al. (1972) Nature, 239, 57-59. [10] Holder J. and Ryder G. (1995) Lunar News, 58, 7. [11] Keil K. et al. (1972) EPSL, 13, 243-256. [12] McKay D. S. et al. (1991) in Lunar Sourcebook (Heiken G. H. et al., eds.), 285-356, Cambridge Univ.

Sears, D. W. G.; Huang, S.; Benoit, P.

1995-09-01

104

Noble Gas Partitioning Between Olivine and Melt to 2 GPa  

NASA Astrophysics Data System (ADS)

We have extended our experimental measurements of noble gas partition coefficients to 2 GPa in the piston-cylinder device. The experimental set-up involves surrounding wafers of gem quality San Carlos olivine (250-1000 microns thick, 3-4 mm diameter) with diamond powder or vitreous carbon spheres. A layer of melt is placed at the bottom of the capsule which infiltrates the porous media and touches the olivine. This allows the original surface of the crystal to be identified and large coherent pieces of olivine to be recovered intact. The inner capsule is graphite and the outer capsule is Pt. Up to 60 bars of HeNeAr were preloaded into the Pt capsule before it was welded shut. This method combines a number of desireable qualities: 1) it avoids producing melt inclusions in the olivine, 2) it yields large areas of olivine to analyze by laser-ablation and 3) it has both melt and crystals present and in contact. The experimental glasses and olivine wafers were analyzed by laser-ablation noble gas mass spectrometry at the Open University, UK. Both depth profiles and cross-sections were analyzed on the olivine wafers. Equilibrium (flat) concentration profiles were only obtained for He in our experiments (up to 20 hr run durations). These yield olivine-melt partition coefficients (D) between 0.0007 and 0.002 at 1-2 GPa and at 1450. These values are within the range of measurements at low pressures (100 MPa or less), suggesting a minimal pressure effect on noble gas partitioning in the upper mantle. Henrys Law behavior is maintained over 4 orders of magnitude variation in He concentration in the olivine (0.0001 to 1 ppm He). High near-surface concentrations of He (21ppm), Ne (36ppm) and Ar (4,360ppm) were observed in the olivine. The thickness of the enriched layer (5 microns) was the same for all three noble gases. We do not know the origin of the high near-surface concentrations, but if they were due to lattice diffusion of the noble gases, the thickness of the high concentration layer should decrease with the diffusivity of the noble gas from He to Ne to Ar. Thus we speculate that the high near-surface concentrations are due to a change in the material properties of the olivine.

Parman, S. W.; Kelley, S. P.; Ballentine, C. J.; van Orman, J. A.; Holland, G.

2009-12-01

105

The origin of non-porphyritic pyroxene chondrules in UOCs: Liquid solar nebula condensates?  

NASA Astrophysics Data System (ADS)

A total of 56 non-porphyritic pyroxene and pyroxene/olivine micro-objects from different unequilibrated ordinary chondrites were selected for detailed studies to test the existing formation models. Our studies imply that the non-porphyritic objects represent quickly quenched liquids with each object reflecting a very complex and unique evolutionary history. Bulk major element analyses, obtained with EMPA and ASEM, as well as bulk lithophile trace element analyses, determined by LA-ICP-MS, resulted in unfractionated (solar-like) ratios of CaO/Al 2O 3, Yb/Ce as well as Sc/Yb in many of the studied objects and mostly unfractionated refractory lithophile trace element (RLTE) abundance patterns. These features support an origin by direct condensation from a gas of solar nebula composition. Full equilibrium condensation calculations show that it is theoretically possible that pyroxene-dominated non-porphyritic chondrules with flat REE patterns could have been formed as droplet liquid condensates directly from a nebular gas strongly depleted in olivine. Thus, it is possible to have enstatite as the stable liquidus phase in a 800 Cl dust-enriched nebular gas at a p of 10 -3 atm, if about 72% of the original Mg is removed (as forsterite?) from the system. Condensation of liquids from vapor (primary liquid condensation) could be considered as a possible formation process of the pyroxene-dominated non-porphyritic objects. This process can produce a large spectrum of chemical compositions, which always have unfractionated RLTE abundances. Late stage and subsolidus metasomatic events appear to have furthered the compositional diversity of chondrules and related objects by addition of moderately volatile and volatile elements to these objects by exchange reactions with the chondritic reservoir (e.g., V, Cr, Mn, FeO as well as K and Na). The strong fractionation displayed by the volatile lithophile elements could be indicative of a variable efficiency of metasomatic processes occurring during and/or after chondrule formation. Histories of individual objects differ in detail from each other and clearly indicate individual formation and subsequent processing.

Engler, Almut; Varela, Maria Eugenia; Kurat, Gero; Ebel, Denton; Sylvester, Paul

2007-12-01

106

Fractionation of B and Li in the Solar Nebula or in Chondrules: Insight from Chondrule Formation Experiments  

NASA Technical Reports Server (NTRS)

Chondrule formation experiments suggest that the B/Li ratios of synthesized chondrules are always lower than that of the starting material, and that the B/Li ratios systematically decrease with decreasing cooling rates at constant temperature. Additional information is contained in the original extended abstract.

Xiong, Y.-L.; Hewins, R. H.; Cetiner, Z.; Wood, S. A.

2002-01-01

107

Fe/Mn in olivine of carbonaceous meteorites  

NASA Technical Reports Server (NTRS)

Olivines in primitive meteorites show a range of Fe/Mn both within one grain and among grains suggesting that they have recorded changing conditions during or after growth. Because olivine should be an early forming phase, Fe/Mn is used here to infer these earliest conditions. Initial Fe/Mn in cores of isolated, euhedral forsterite in both C2 and C3 meteorites ranges from 25 to 35 but differs at grain edge. Murchison (C2) forsterites show Fe/Mn approaching 1.0 at the grain edge while Ornans Fe/Mn is near 60 at grain edge. These values are lower than the matrix Fe/Mn for both meteorites and the distinct difference in zoning profile indicates different processes operating during and after grain growth. The Fe/Mn of bulk samples from a particular source such as the Moon is nearly constant. Individual samples show variation suggesting that there is some fractionation of Mn from Fe. Minerals have their individual ranges of Fe/Mn which has been used to recognize different types of olivine within one meteorite. Extreme values of Fe/Mn below 1.0 occur in forsterite from some IDP's, UOC matrix, and C1 meteorites. There are apparently no detailed studies of Fe/Mn variation within single olivine grains. Forsterite grains in C2 and C3 carbonaceous chondrites show complex zoning, and the nearly pure forsterites (Fo greater than approximately 99.5) have high levels of some minor elements including Ti, Al, V, and Sc. There is disagreement on the original source of these grains and both chondrule and vapor growth have been proposed. In addition, there is clear evidence that diffusion has affected the outer margins but in some cases the whole grain. Within the cores, the FeO range is limited, and if growing under constant conditions, the Fe/Mn should be near constant as there is little fractionation of Mn from Fe by forsterite. Additionally, there are apparently no co-crystallizing phases as evidenced by a lack of common inclusions in the forsterites. These observations are now followed by analyses of isolated olivine grains in C2 and C3 meteorites.

Steele, Ian M.

1993-01-01

108

Chondrules and Isolated Grains in the Fountain Hills Bencubbinite  

NASA Technical Reports Server (NTRS)

The Fountain Hills (FH) meteorite was recently classified as a Bencubbin-like (CB(sub a)) chondrite, which are part of the CR clan [1]. The FH O-isotopic composition is indistinguishable from CB(sub a) chondrites. Metal and silicate compositions are consistent with the CB(sub a) classification. Significant differences between FH and the other CB(sub a) chondrites were noted. These include abundant porphyritic chondrules and complete lack of sulfide minerals. We are furthering this investigation by analyzing silicate chondrules and isolated grains in FH to determine more about its composition, thermal history, and implications for chondrule formation in the early solar system.

LaBlue, A. R.; Lauretta, D. S.; Killgore, M.

2004-01-01

109

Chondrule Formation: Nebular Gas Confinement of Impact Splashes  

NASA Astrophysics Data System (ADS)

We show that the impact debris from a high-speed collision between two planetesimals during the first few million years would sweep up the nebular gas as a snow plow, leading to deceleration and compression of the debris into a thin shell. This shell breaks up into dense bullets through the Rayleigh-Taylor instability. As a result of the compression by the gas, these bullets will have super-Roche densities and thus will gravitationally collapse to form new planetesimals. Chondrules that may have formed from impact melting would thus rapidly be reaccreted into planetesimals. These dense environments are ideal for forming compound chondrules. The hydrodynamic interaction with the nebular gas could lead to mixing between the newly formed chondrules and surviving pre-impact material. Volatiles can be exchanged between these components in the dense bullets, allowing for chemical complementarity. We believe that this scenario may have some advantages over earlier impact scenarios for chondrule formation.

Dullemond, Cornelis Petrus; Johansen, Anders

2013-07-01

110

Irradiation Histories of CAIs and LL3/CB Chondrules  

NASA Astrophysics Data System (ADS)

Spallogenic 40K anomalies in LL3 chondrules and CV3 CAIs suggest that they experienced irradiating conditions prior to accretion on their respective parent bodies, arguing against midplane dead zone storage for the entirety of their nebular storage.

Wielandt, D.; Bizzarro, M.

2014-09-01

111

Mineralogy and Petrology of Amoeboid Olivine Inclusions in CO3 Chondrites: Relationship to Parent-Body Aqueous Alteration  

NASA Technical Reports Server (NTRS)

Petrographic and mineralogic studies of amoeboid olivine inclusions (AOIs) in CO3 carbonaceous chondrites reveal that they are sensitive indicators of parent-body aqueous and thermal alteration. As the petrologic subtype increases from 3.0 to 3.8, forsteritic olivine (Fa(sub 0-1)) is systematically converted into ferroan olivine (Fa(sub 60-75)). We infer that the Fe, Si and O entered the assemblage along grain boundaries, forming ferroan olivine that filled fractures and voids. As temperatures increased, Fe(+2) from the new olivine exchanged with Mg(+2) from the original AOI to form diffusive haloes around low-FeO cores. Cations of Mn(+2), Ca(+2) and Cr(+3) were also mobilized. The systematic changes in AOI textures and olivine compositional distributions can be used to refine the classification of CO3 chondrites into subtypes. In subtype 3.0, olivine occurs as small forsterite grains (Fa(sub 0-1)), free of ferroan olivine. In petrologic subtype 3.2, narrow veins of FeO-rich olivine have formed at forsterite grain boundaries. With increasing alteration, these veins thicken to form zones of ferroan olivine at the outside AOI margin and within the AOI interior. By subtype 3.7, there is a fairly broad olivine compositional distribution in the range Fa(sub 63-70), and by subtype 3.8, no forsterite remains and the high-Fa peak has narrowed, Fa(sub 64-67). Even at this stage, there is incomplete equilibration in the chondrite as a whole (e.g., data for coarse olivine grains in Isna (CO3.8) chondrules and lithic clasts show a peak at Fa(sub39)). We infer that the mineral changes in A01 identified in the low petrologic types required aqueous or hydrothermal fluids whereas those in subtypes greater than or equal to 3.3 largely reflect diffusive exchange within and between mineral grains without the aid of fluids.

Chizmadia, Lysa J.; Rubin, Alan E.; Wasson, John T.

2003-01-01

112

Origin of olivine at Copernicus  

NASA Technical Reports Server (NTRS)

The central peaks of Copernicus are among the few lunar areas where near-infrared telescopic reflectance spectra indicate extensive exposures of olivine. Other parts of Copernicus crater and ejecta, which were derived from highland units in the upper parts of the target site, contain only low-Ca pyroxene as a mafic mineral. The exposure of compositionally distinct layers including the presence of extensive olivine may result from penetration to an anomalously deep layer of the crust or to the lunar mantle. It is suggested that the Procellarum basin and the younger, superposed Insularum basin have provided access to these normally deep-seated crustal or mantle materials by thinning the upper crustal material early in lunar history. The occurrences of olivine in portions of the compositionally heterogeneous Aristarchus Region, in a related geologic setting, may be due to the same sequence of early events.

Pieters, C. M.; Wilhelms, D. E.

1985-01-01

113

A critical analysis of shock models for chondrule formation  

NASA Astrophysics Data System (ADS)

In recent years many models of chondrule formation have been proposed. One of those models is the processing of dust in shock waves in protoplanetary disks. In this model, the dust and the chondrule precursors are overrun by shock waves, which heat them up by frictional heating and thermal exchange with the gas. In this paper we reanalyze the nebular shock model of chondrule formation and focus on the downstream boundary condition. We show that for large-scale plane-parallel chondrule-melting shocks the postshock equilibrium temperature is too high to avoid volatile loss. Even if we include radiative cooling in lateral directions out of the disk plane into our model (thereby breaking strict plane-parallel geometry) we find that for a realistic vertical extent of the solar nebula disk the temperature decline is not fast enough. On the other hand, if we assume that the shock is entirely optically thin so that particles can radiate freely, the cooling rates are too high to produce the observed chondrules textures. Global nebular shocks are therefore problematic as the primary sources of chondrules.

Stammler, Sebastian M.; Dullemond, Cornelis P.

2014-11-01

114

Rock magnetic properties of dusty olivine: a potential carrier of pre-accretionary remanence in unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

The mechanism of chondrule formation is an important outstanding question in cosmochemistry. Magnetic signals recorded by Fe-Ni nanoparticles in chondrules could carry clues to their origin. Recently, research in this area has focused on 'dusty olivine' grains within ordinary chondrites as potential carriers of pre-accretionary remanence. Dusty olivine is characterised by the presence of sub-micron Fe-Ni inclusions within the olivine host. These metal particles form via subsolidus reduction of the olivine during chondrule formation and are thought to be protected from subsequent chemical and thermal alteration by the host olivine. Three sets of synthetic dusty olivines have been produced, using natural Icelandic olivine (average Ni-content of 0.3 wt%), synthetic Ni-containing olivine (0.1wt% Ni) and synthetic Ni-free olivine as starting materials. The starting materials were ground to powders, packed into a 2-3 mm3 graphite crucible, heated up to 1350 C under a pure CO gas flow and kept at this temperature for 10 minutes. After this the samples were held in a fixed orientation and quenched into water in a range of known magnetic fields, ranging from 0.2 mT to 1.5 mT. First-order reversal curve (FORC) diagrams contain a central ridge with a broad coercivity distribution extending to 600 mT, attributed to non-interacting single-domain (SD) particles. A braod vertically spread positive peak is centred on Hc = 56 14 mT and Hu = -114 41 mT, and is accompanied by a broad horizontaly spread negative peak at Hc = 183 30 mT, just underneath the central ridge. The combination of positive and negative peaks can be attributed to the presence of single-vortex (SV) states. Average SV nucleation and annihilation fields of 58 55 mT and 170 55 mT, respectively, were extracted from the FORC diagrams, indicating that demagnetization to >>170 mT would be required to isolate the stable SD signal. Single-vortex states are likely to be important remanence carriers in dusty olivine. Accounting for their presence will be essential in interpreting the remanence of natural samples. All samples showed uni-directional, single-component demagnetization behaviour. Even after applying the highest possible AF-field of 150 mT it was not possible to fully demagnetize the samples. The REM ratio (NRM/SIRM) shows non-linear behaviour as a function of applied field, saturating at a value of ~0.3. Saturation of REM at a value < 1 is explained by the presence of particles that can adopt either stable SV or metastable SD states depending on the field. Such particles are likely to adopt low-remanence SV states during TRM acquisition and high-remanence SD states after appication of a saturating field, hence artificially lowering the REM value. A calibration factor f = 3000 ?T, relating paleofield to the REM value, was derived from the low-field region of the data, which matches well with literature values. A range of more sophisticated normalisation techniques are assessed for use in paleointensity determination from meteorties, including the newly proposed method based on Preisach analysis of FORC diagrams.

Lappe, S. L.; Harrison, R. J.; Feinberg, J. M.

2011-12-01

115

The Formation of Chondrules at High Gas Pressures in the Solar Nebula  

Microsoft Academic Search

High-precision magnesium isotope measurements of whole chondrules from the Allende carbonaceous chondrite meteorite show that some aluminum-rich Allende chondrules formed at or near the time of formation of calcium-aluminum-rich inclusions and that some others formed later and incorporated precursors previously enriched in magnesium-26. Chondrule magnesium-25\\/magnesium-24 correlates with [magnesium]\\/[aluminum] and size, the aluminum-rich, smaller chondrules being the most enriched in the

Albert Galy; Edward D. Young; Richard D. Ash; R. Keith O'Nions

2000-01-01

116

EXTREME CONDITIONS REQUIRED FOR SUPPRESSION OF ALKALI EVAPORATION DURING CHONDRULE FORMATION. A. V. Fedkin1  

E-print Network

times have also been stressed [2, 4]. Retention of Na at levels neces- sary to account for the Na in order to oxidize Fe to levels appropri- ate for chondrules, at rates assumed to occur on the time necessary for retention of Na and K during chondrule formation. Method: The assumed chondrule precursor has

Grossman, Lawrence

117

Chondrule Glass Alteration in Type IIA Chondrules in the CR2 Chondrites EET 87770 and EET 92105: Insights into Elemental Exchange Between Chondrules and Matrices  

NASA Technical Reports Server (NTRS)

CR2 carbonaceous chondrites are a primitive group of meteorites that preserve evidence of a variety of processes that occurred in the solar nebula as well as on asteroidal parent bodies. CR2 chondrites are distinct from other carbonaceous chondrites by (among other properties) their relatively high abundance of chondrules (50-60 vol. %) and Fe,Ni metal (5-8 vol. %) [1]. Like the CM2 chondrites, the CRs have been affected by aqueous alteration and according to [2] show a range of degrees of alteration. In weakly- altered CR chondrites, fine-grained matrices and chondrule rims have been partially altered and chondrule mesostases show evidence of incipient aqueous alteration. In these meteorites, glassy mesostasis is still common. However, some CR chondrites, (e.g. Renazzo and Al Rais) show evidence of much more extensive alteration with complete replacement of chondrule mesostasis [2] by chlorite and serpentine. Although the general characteristics of alteration of the CR chondrites have been described, the details of alteration reactions in these meteorites remain unclear. In addition, the setting for aqueous alteration is poorly understood: both asteroidal and preaccretionary alteration scenarios have been proposed [2].

Burger, Paul V.; Brearley, Adrian J.

2004-01-01

118

Compositional evidence regarding the origins of rims on Semarkona chondrules  

USGS Publications Warehouse

The compositions of the interiors and abraded surfaces of 7 chondrules from Semarkona (LL3.0) were measured by neutron activation analysis. For nonvolatile elements, the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors. Siderophile and chalcophile concentrations are much higher in the surfaces, whereas lithophile concentrations are similar in both fractions. Most of the similarities in lithophile patterns and some of the similarities in siderophile patterns between surfaces and interiors may reflect incomplete separation of the fractions in the laboratory, but for 3 or 4 chondrules the siderophile resemblance is inherent, implying that the surface and interior metal formed from a single precursor assemblage. Metal and sulfide-rich chondrule rims probably formed when droplets of these phases that migrated to the chondrule surface during melting were reheated and incorporated into matrix-like material that had accreted onto the surface. The moderately-volatile to volatile elements K, As and Zn tend to be enriched in the surfaces compared with other elements of similar mineral affinity; both enrichments and depletions are observed for other moderately volatile elements. A small fraction of chondrules experienced fractional evaporation while they were molten. ?? 1987.

Grossman, J.N.; Wasson, J.T.

1987-01-01

119

Noble-gas-rich chondrules in an enstatite meteorite.  

PubMed

Chondrules are silicate spherules that are found in abundance in the most primitive class of meteorites, the chondrites. Chondrules are believed to have formed by rapid cooling of silicate melt early in the history of the Solar System, and their properties should reflect the composition of (and physical conditions in) the solar nebula at the time when the Sun and planets were forming. It is usually believed that chondrules lost all their noble gases at the time of melting. Here we report the discovery of significant amounts of trapped noble gases in chondrules in the enstatite chondrite Yamato-791790, which consists of highly reduced minerals. The elemental ratios 36Ar/132Xe and 84Kr/132Xe are similar to those of 'subsolar' gas, which has the highest 36Ar/132Xe ratio after that of solar-type noble gases. The most plausible explanation for the high noble-gas concentration and the characteristic elemental ratios is that solar gases were implanted into the chondrule precursor material, followed by incomplete loss of the implanted gases through diffusion over time. PMID:11518959

Okazaki, R; Takaoka, N; Nagao, K; Sekiya, M; Nakamura, T

2001-08-23

120

THERMAL HISTORIES OF CHONDRULES IN SOLAR NEBULA SHOCKS  

SciTech Connect

Chondrules are important early Solar System materials that can provide a wealth of information on conditions in the solar nebula, if their formation mechanism can be understood. The theory most consistent with observational constraints, especially thermal histories, is the so-called shock model, in which chondrules were melted in solar nebula shocks. However, several problems have been identified with previous shock models. These problems all pertained to the treatment of the radiation field, namely, the input boundary condition to the radiation field, the proper treatment of the opacity of solids, and the proper treatment of molecular line cooling. In this paper, we present the results of our updated shock model, which corrects for the problems listed above. Our new hydrodynamic shock code includes a complete treatment of molecular line cooling due to H{sub 2}O. Previously, shock models including line cooling predicted chondrule cooling rates exceeding 10{sup 5} K hr{sup -1}. Contrary to these expectations, we have found that the effect of line cooling is minimal; after the inclusion of line cooling, the cooling rates of chondrules are 10-1000 K hr{sup -1}. The reduction in the otherwise rapid cooling rates attributable to line cooling is due to a combination of factors, including buffering due to hydrogen recombination/dissociation, high column densities of water, and backwarming. Our model demonstrates that the shock model for chondrule formation remains consistent with observational constraints.

Morris, M. A.; Desch, S. J., E-mail: melissa.a.morris@asu.ed [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States)

2010-10-20

121

A critical analysis of shock models for chondrule formation  

E-print Network

In recent years many models of chondrule formation have been proposed. One of those models is the processing of dust in shock waves in protoplanetary disks. In this model, the dust and the chondrule precursors are overrun by shock waves, which heat them up by frictional heating and thermal exchange with the gas. In this paper we reanalyze the nebular shock model of chondrule formation and focus on the downstream boundary condition. We show that for large-scale plane-parallel chondrule-melting shocks the postshock equilibrium temperature is too high to avoid volatile loss. Even if we include radiative cooling in lateral directions out of the disk plane into our model (thereby breaking strict plane-parallel geometry) we find that for a realistic vertical extent of the solar nebula disk the temperature decline is not fast enough. On the other hand, if we assume that the shock is entirely optically thin so that particles can radiate freely, the cooling rates are too high to produce the observed chondrules texture...

Stammler, Sebastian M

2014-01-01

122

Forming Chondrules in Impact Splashes. I. Radiative Cooling Model  

NASA Astrophysics Data System (ADS)

The formation of chondrules is one of the oldest unsolved mysteries in meteoritics and planet formation. Recently an old idea has been revived: the idea that chondrules form as a result of collisions between planetesimals in which the ejected molten material forms small droplets that solidify to become chondrules. Pre-melting of the planetesimals by radioactive decay of 26Al would help produce sprays of melt even at relatively low impact velocity. In this paper we study the radiative cooling of a ballistically expanding spherical cloud of chondrule droplets ejected from the impact site. We present results from numerical radiative transfer models as well as analytic approximate solutions. We find that the temperature after the start of the expansion of the cloud remains constant for a time t cool and then drops with time t approximately as T ~= T 0[(3/5)t/t cool + 2/5]-5/3 for t > t cool. The time at which this temperature drop starts t cool depends via an analytical formula on the mass of the cloud, the expansion velocity, and the size of the chondrule. During the early isothermal expansion phase the density is still so high that we expect the vapor of volatile elements to saturate so that no large volatile losses are expected.

Dullemond, Cornelis Petrus; Stammler, Sebastian Markus; Johansen, Anders

2014-10-01

123

Rock magnetic properties of dusty olivine: a potential carrier of pre-accretionary remanence in unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

The mechanism of chondrule formation is an important outstanding question in cosmochemistry. Magnetic signals recorded by Fe-Ni nanoparticles in chondrules could carry clues to their origin. Recently, research in this area has focused on 'dusty olivine' grains within ordinary chondrites as potential carriers of pre-accretionary remanence. Dusty olivine is characterised by the presence of sub-micron Fe-Ni inclusions within the olivine host. These metal particles form via subsolidus reduction of the olivine during chondrule formation and are thought to be protected from subsequent chemical and thermal alteration by the host olivine. Three sets of synthetic dusty olivines have been produced, using natural olivine (average Ni-content of 0.3 wt%), synthetic Ni-containing olivine (0.1wt% Ni) and synthetic Ni-free olivine as starting materials. The starting materials were ground to powders, packed into a 2-3 mm3 graphite crucible, heated up to 1350 C under a pure CO gas flow and kept at this temperature for 10 minutes. After this the samples were held in a fixed orientation and quenched into water in a range of known magnetic fields, ranging from 0.2 mT to 1.5 mT. We present here for the first time an analysis of a new FORC-based method of paleointensity determination applied to metallic Fe-bearing samples [1, 2]. The method uses a first-order reversal curve (FORC) diagram to generate a Preisach distribution of coercivities and interaction fields within the sample and then physically models the acquisition of TRM as a function of magnetic field, temperature and time using thermal relaxation theory. The comparison of observed and calculated NRM demagnetisation spectra is adversely effected by a large population of particles in the single-vortex state. Comparison of observed and calculated REM' curves, however, yields much closer agreement in the high-coercivity SD-dominated range. Calculated values of the average REM' ratio show excellent agreement with the experimental values - including the observed non-linearity of the remanence acquisition curve - suggesting that this method has the potential to reduce the uncertainties in non-heating paleointensity methods for extraterrestrial samples. [1] AR Muxworthy and D Heslop(2011) A Preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements: 1. Theoretical framework. Journal of Geophysical Research, 116, B04102, doi:10.1029/2010JB007843. [2] AR Muxworthy, D Heslop, GA Paterson, and D Michalk. A Preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements: 2. Experimental testing. Journal of Geophysical Research, 116, B04103, doi:10.1029/2010JB007844.

Lappe, S. C. L. L.; Harrison, R. J.; Feinberg, J. M.

2012-04-01

124

A chondrule-forming scenario compatible with chondrite metamorphism  

NASA Astrophysics Data System (ADS)

Chondrules evidently formed by the flash melting of precursor solids in the dusty midplane of the solar nebula. Since chondrule production probably overlapped in time with accretion of the earliest planetesimals, possible genetic links between chondrules and accretion have been explored. Primitive bodies that accreted less than 1 m.y. after the solar system began were rapidly heated to melting by the decay of short-lived radioactive isotopes. Subsequent collisions yielded copious volumes of incandescent spray that stuck to, irradiated, sintered, and even melted dust and coarser fragments in the local toroidal 'nebula' already orbiting each planetesimal. In this way various kinds of additional chondrules were produced. Because impact velocity was low, much of the collisional debris fell back to the growing planetesimal surface. The planetesimal interior was still molten, so a steep thermal gradient quickly developed through the insulating blanket of chondritic debris, and metamorphism ensued. This scenario seems reconcilable with most, possibly all, petrographic, chemical, and isotopic constraints imposed by observations in chondrites. The collision scenario is consistent with three important constraints. It yields chondrules with high efficiency, in sufficient quantities to retard radiative heat loss, and with a restricted range of subliquidus temperatures. Total disruption of the smaller molten body would tend to re-mix segregated metal and silicate and restore primitive chemistry on a small scale. The metal core of the larger body would tend not to re-mix. An attractive feature of the model is that a single heat source, namely radiogenic heat stored as thermal energy inside planetesimals, accounts both for chondrule formation and for later metamorphism. The model simplifies the metamorphic regime; it circumvents the narrow time window during which in-situ radioactive decay would be effective, and it can accommodate either hot or cold accretion.

Sanders, I. S.

1994-07-01

125

The formation of chondrules at high gas pressures in the solar nebula.  

PubMed

High-precision magnesium isotope measurements of whole chondrules from the Allende carbonaceous chondrite meteorite show that some aluminum-rich Allende chondrules formed at or near the time of formation of calcium-aluminum-rich inclusions and that some others formed later and incorporated precursors previously enriched in magnesium-26. Chondrule magnesium-25/magnesium-24 correlates with [magnesium]/[aluminum] and size, the aluminum-rich, smaller chondrules being the most enriched in the heavy isotopes of magnesium. These relations imply that high gas pressures prevailed during chondrule formation in the solar nebula. PMID:11099410

Galy, A; Young, E D; Ash, R D; O'Nions, R K

2000-12-01

126

Shape, metal abundance, chemistry, and origin of chondrules in the Renazzo (CR) chondrite  

SciTech Connect

We used synchrotron X-ray microtomography to image in 3-dimensions (3D) eight whole chondrules in a {approx}1 cm{sup 3} piece of the Renazzo (CR) chondrite at {approx}17 {micro}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.

Ebel, D.S.; Weisberg, M.K.; Hertz, J.; Campbell, A.J. (AMNH)

2009-03-31

127

Papers presented to the Conference on Chondrules and the Protoplanetary Disk  

NASA Technical Reports Server (NTRS)

The following topics are covered in the presented papers: (1) producing chondrules; (2) carbons, CAI's, and chondrules; (3) large scale processes in the solar nebula; (4) chondrule-matrix relationships in chondritic meteorites; (5) overview of nebula models; (6) constraints placed on the nature of chondrule precursors; (7) turbulent diffusion and concentration of chondrules in the protoplanetary nebula; (8) heating and cooling in the solar nebula; (9) crystallization trends of precursor pyroxene in ordinary chondrites; (10) precipitation induced vertical lightning in the protoplanetary nebula; (11) the role of chondrules in nebular fractionations of volatiles and other elements; (12) astronomical observations of phenomena in disks; (13) experimental constraints on models for origins of chondrules, and various other topics.

1994-01-01

128

Amoeboid olivine aggregates from CH carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Amoeboid olivine aggregates (AOAs) in CH carbonaceous chondrites are texturally and mineralogically similar to those in other carbonaceous chondrite groups. They show no evidence for alteration and thermal metamorphism in an asteroidal setting and consist of nearly pure forsterite (Fa<3; in wt%, CaO = 0.1-0.8, Cr2O3 = 0.04-0.48; MnO < 0.5), anorthite, Al-diopside (in wt%, Al2O3 = 0.7-8.1; TiO2 < 1), Fe,Ni-metal, spinel, and, occasionally, low-Ca pyroxene (Fs1Wo2-3), and calcium-aluminum-rich inclusions (CAIs). The CAIs inside AOAs are composed of hibonite, grossite, melilite (k13-44), spinel, perovskite, Al,Ti-diopside (in wt%, Al2O3 up to 19.6; TiO2 up to 13.9), and anorthite. The CH AOAs, including CAIs within AOAs, have isotopically uniform 16O-rich compositions (average ?17O = -23.4 2.3, 2SD) and on a three-isotope oxygen diagram plot along ?slope-1 line. The only exception is a low-Ca pyroxene-bearing AOA 1-103 that shows a range of ?17O values, from -24 to -13. Melilite, grossite, and hibonite in four CAIs within AOAs show no evidence for radiogenic 26Mg excess (?26Mg). In contrast, anorthite in five out of six AOAs measured has ?26Mg corresponding to the inferred initial 26Al/27Al ratio of (4.3 0.7) 10-5, (4.2 0.6) 10-5, (4.0 0.3) 10-5, (1.7 0.2) 10-5, and (3.0 2.6) 10-6. Anorthite in another AOA shows no resolvable ?26Mg excess; an upper limit on the initial 26Al/27Al ratio is 5 10-6. We infer that CH AOAs formed by gas-solid condensation and aggregation of the solar nebula condensates (forsterite and Fe,Ni-metal) mixed with the previously formed CAIs. Subsequently they experienced thermal annealing and possibly melting to a small degree in a 16O-rich gaseous reservoir during a brief epoch of CAI formation. The low-Ca pyroxene-bearing AOA 1-103 may have experienced incomplete melting and isotope exchange in an 16O-poor gaseous reservoir. The lack of resolvable ?26Mg excess in melilite, grossite, and hibonite in CAIs within AOAs reflects heterogeneous distribution of 26Al in the solar nebula during this epoch. The observed variations of the inferred initial 26Al/27Al ratios in anorthite of the mineralogically pristine and uniformly 16O-rich CH AOAs could have recorded (i) admixing of 26Al in the protoplanetary disk during the earliest stages of its evolution and/or (ii) closed-system Mg-isotope exchange between anorthite and Mg-rich minerals (spinel, forsterite, and Al-diopside) during subsequent prolonged (days-to-weeks) thermal annealing at high temperature (?1100 C) and slow cooling rates (?0.01 K h-1) that has not affected their O-isotope systematics. The proposed thermal annealing may have occurred in an impact-generated plume invoked for the origin of non-porphyritic magnesian chondrules and Fe,Ni-metal grains in CH and CB carbonaceous chondrites about 5 Myr after formation of CV CAIs.

Krot, Alexander N.; Park, Changkun; Nagashima, Kazuhide

2014-08-01

129

Bar Fight Bar  

E-print Network

dressed up like those suckers. A bar here in Nanjing, China has come up with a new method of attracting clientele: it lets them beat up the staff. Clients ask the staff to dress up like the person they wish to muscle up on most. As of now, China lags...

Hacker, Randi; Tsutsui, William

2006-11-29

130

The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways during serpentinization  

NASA Astrophysics Data System (ADS)

Crystal-plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow. Although crystal-plastic deformation and serpentinization are spatio-temporally decoupled, we identified compositional readjustments expressed on the micrometric level as a striped Fe-enriched ( bar{X}_{text{Fe}} = 0.24 0.02 (zones); 0.12 0.02 (bulk)) or Fe-depleted ( bar{X}_{text{Fe}} = 0.10 0.01 (zones); 0.13 0.01 (bulk)) zoning in partly serpentinized olivine grains from two upper mantle sections in Norway. Focused ion beam sample preparation combined with transmission electron microscopy (TEM) and aberration-corrected scanning TEM, enabling atomic-level resolved electron energy-loss spectroscopic line profiling, reveals that every zone is immediately associated with a subgrain boundary. We infer that the zonings are a result of the environmental Fe2+Mg-1 exchange potential during antigorite serpentinization of olivine and the drive toward element exchange equilibrium. This is facilitated by enhanced solid-state diffusion along subgrain boundaries in a system, which otherwise re-equilibrates via dissolution-reprecipitation. Fe enrichment or depletion is controlled by the silica activity imposed on the system by the local olivine/orthopyroxene mass ratio, temperature and the effect of magnetite stability. The Fe-Mg exchange coefficients K_{text{D}}^{{{text{Atg}}/{text{Ol}}}} between both types of zoning and antigorite display coalescence toward exchange equilibrium. With both types of zoning, Mn is enriched and Ni depleted compared with the unaffected bulk composition. Nanometer-sized, heterogeneously distributed antigorite precipitates along olivine subgrain boundaries suggest that water was able to ingress along them. Crystallographic orientation relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along olivine subgrain boundaries.

Plmper, Oliver; King, Helen E.; Vollmer, Christian; Ramasse, Quentin; Jung, Haemyeong; Austrheim, Hkon

2012-04-01

131

Sulfur Isotope Composition of Putative Primary Troilite in Chondrules  

NASA Technical Reports Server (NTRS)

Sulfur isotope compositions of putative primary troilites in chondrules from Bishunpur were measured by ion probe. These primary troilites have the same S isotope compositions as matrix troilites and thus appear to be isotopically unfractionated. Additional information is contained in the original extended abstract.

Tachibana, Shogo; Huss, Gary R.

2002-01-01

132

Electrical Discharge Heating of Chondrules in the Solar Nebula  

Microsoft Academic Search

We present a rudimentary theoretical assessment of electrical discharge heating as a candidate mechanism for the formation of chondrules in the solar nebula. The discharge model combines estimates of the properties of the nebula, a mechanism for terrestrial thunderstorm electrification, and some fundamental electrical properties of gases. Large uncertainties in the model inputs limit these calculations to order-of-magnitude accuracy. Despite

Stanley G. Love; Klaus Keil; Edward R. D. Scott

1995-01-01

133

Magnetic Properties of Avanhandava H4 Meteorite Chondrules  

NASA Astrophysics Data System (ADS)

The magnetic properties of twenty individual chondrules from Avanhandava chondritic (H4) meteorite fall were studied. Magnetic hysteresis measurements and isothermal remanent magnetization (IRM) acquisition experiments reveal two populations of chondrules with different magnetic properties within the meteorite. The first group shows magnetically hard behavior with coercivities (Hc) ranging between 20 and 60 mT and IRM acquisition curves displaying two distinct coercivity components. The low coercivity component is acquired at fields < 250 mT, while the high coercivity component is acquired mostly between 400 and 1200 mT. This high coercivity component is also apparent in first order reversal curve (FORC) diagrams. The median destructive field (MDF) for samples' saturation isothermal remanent magnetization (SIRM) was 160 mT. The second group shows magnetically soft behavior, with Hc values below 5 mT and IRM acquisition curves showing only a single low coercivity component acquired at fields < 250 mT. Additionally, there are no high coercivity components observed in the FORC diagrams of these chondrules, and MDFs are generally lower than those of the first group. The natural remanent magnetization (NRM) of the chondrules is weak ( 10-2 - 10-1 mAm2/kg). Surprisingly, there is no correlation between the stability of the NRM and the presence of the high coercivity component. The NRM directions of individual chondrules define a random distribution. Alternating field demagnetization reveals one or two stable components. Some chondrules display erratic variations in intensity during demagnetization, which can be caused by the presence of multi-domain grains. While the low coercivity component is likely related to the presence of multi-domain kamacite, the mineralogy of the high coercivity fraction is uncertain. Experiments are underway to identify the magnetic carriers of the two coercivity fractions. This information will be essential for isolating the NRM component held by the high coercivity carriers, which may be related to processes such as original chondrule formation, subsequent coalescence into a parent meteorite body, and/or shock events.

Kohout, T.; Pesonen, L.; Feinberg, J.

2009-05-01

134

Constraints for chondrule formation from Ca-Al distribution in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Chondritic meteorites and their components formed in the protoplanetary disk surrounding the nascent sun. We show here that the two volumetrically dominating components of carbonaceous chondrites, chondrules and matrix did not form independently. They must have been derived from a single, common source. We analyzed Ca and Al in chondrules and matrix of the CV type carbonaceous chondrites Allende and Y-86751. The Ca/Al-ratios of chondrules and matrix of both chondrites are complementary, but in case of Allende chondrules have sub-chondritic and matrix super-chondritic Ca/Al-ratios and in case of Y-86751 chondrules have super-chondritic and matrix sub-chondritic Ca/Al-ratios. This rules out the redistribution of Ca between chondrules and matrix during parent body alteration. Tiny spinel grains in the matrix produce the high Al in the matrix of Y-86751. In Allende these spinels were most probably included in chondrules. The most plausible explanation for this Ca- and Al-distribution in the same type of chondrite is that both chondrules and matrix formed from the same chemical reservoir. Tiny differences in nebular conditions during formation of these two meteorites must have led to the observed differences. These are severe constraints for all models of chondrule formation. Any model involving separate formation of chondrules and matrix, such as the X-wind model can be excluded.

Hezel, D. C.; Palme, H.

2008-01-01

135

Chondrule size and related physical properties: a compilation and evaluation of current data across all meteorite groups  

E-print Network

The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. We include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. We also compile and review current literature data for other astrophysically-relevant p...

Friedrich, Jon M; Ebel, Denton S; Biltz, Alison E; Corbett, Bernadette M; Iotzov, Ivan V; Khan, Wajiha S; Wolman, Matthew D

2014-01-01

136

Contemporaneous formation of chondrules and refractory inclusions in the early Solar System.  

PubMed

Chondrules and calcium-aluminium-rich inclusions (CAIs) are preserved materials from the early history of the Solar System, where they resulted from thermal processing of pre-existing solids during various flash heating episodes which lasted for several million years. CAIs are believed to have formed about two million years before the chondrules. Here we report the discovery of a chondrule fragment embedded in a CAI. The chondrule's composition is poor in 16O, while the CAI has a 16O-poor melilite (Ca, Mg, Al-Silicate) core surrounded by a 16O-rich igneous mantle. These observations, when combined with the previously reported CAI-bearing chondrules, strongly suggest that the formation of chondrules and CAIs overlapped in time and space, and that there were large fluctuations in the oxygen isotopic compositions in the solar nebula probably synchronizing astrophysical pulses. PMID:12802328

Itoh, Shoichi; Yurimoto, Hisayoshi

2003-06-12

137

Shock-Wave Heating Model for Chondrule Formation: Prevention of Isotopic Fractionation  

E-print Network

Chondrules are considered to have much information on dust particles and processes in the solar nebula. It is naturally expected that protoplanetary disks observed in present star forming regions have similar dust particles and processes, so study of chondrule formation may provide us great information on the formation of the planetary systems. Evaporation during chondrule melting may have resulted in depletion of volatile elements in chondrules. However, no evidence for a large degree of heavy-isotope enrichment has been reported in chondrules. In order to meet this observed constraint, the rapid heating rate at temperatures below the silicate solidus is required to suppress the isotopic fractionation. We have developed a new shock-wave heating model taking into account the radiative transfer of the dust thermal continuum emission and the line emission of gas molecules and calculated the thermal history of chondrules. We have found that optically-thin shock waves for the thermal continuum emission from dust ...

Miura, H; Miura, Hitoshi; Nakamoto, Taishi

2006-01-01

138

Formation of accretionary dust mantles in the solar nebula: Evidence from preirradiated olivines in CM chondrites  

NASA Astrophysics Data System (ADS)

CM chondrites are regolith breccias consisting of lithic clasts embedded in a fine-grained clastic matrix. The majority of these lithic clasts belongs to a texturally well-defined rock type (primary rock) that can be described as an agglomerate of chondrules and other coarse-grained components, most of which are surrounded by fine-grained rims (dust mantles). Metzler et al. (1992) explain these textures as the result of accretionary processes in the solar nebula, while an alternative model explains them to be the result of regolith processes on the parent body (Sears et al. 1993). The main intention of the present study is to discern between both models by investigating the occurrence, frequency, spatial distribution, and textural setting of preirradiated (track-rich) olivines in CM chondrites. Track-rich olivines were studied in situ in six polished thin sections from 4 different CM chondrites (Cold Bokkeveld, Mighei, Murchison, Nogoya) by optical and scanning electron microscopy (SEM). It was found that their occurrence is restricted to the clastic matrix of these meteorites. The primary rock seems to have formed in an environment shielded from cosmic radiation, since fragments of this rock are free of track-rich grains and solar noble gases. This finding supports the solar nebula model for the formation of dust mantles around chondrules and other coarse-grained components, and points against a regolith origin. In Cold Bokkeveld, a small breccia-in-breccia clast was found, which has been irradiated as an entity within the uppermost millimeters to meters of its parent body for at least about 3 Ma. This clast seems to represent a compacted subsurface layer that was later excavated by impact and admixed to the host breccia. Furthermore, the results of this study may affect the interpretation of compaction ages obtained by fission track methods, since these ages may be mixtures of different contact ages between finegrained, U-rich dust and U-poor olivines. In some cases, they may date the formation of dust mantles in the solar nebula, while in other cases the lithification of the host breccias may be dated.

Metzler, Knut

2004-08-01

139

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  

NASA Astrophysics Data System (ADS)

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 120 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.

Rubin, Alan E.

2013-03-01

140

Turbulent Concentration of Chondrules: Size Distribution and Multifractal Scaling  

NASA Technical Reports Server (NTRS)

Size-selective concentration of particles in 3D turbulence may be related to collection of chondrules and other constituents into primitive bodies in a weakly turbulent protoplanetary nebula. In the terrestrial planet region, both the characteristic size and narrow size distribution of chondrules are explained, whereas "fluffier" particles would be concentrated in lower density, or more intensely turbulent, regions of the nebula. The spatial distribution of concentrated particle density obeys multifractal scaling, suggesting a dose tie to the turbulent cascade process. This scaling behavior allows predictions of the concentration probabilities to be made in the protoplanetary nebula, which are so large (> 10(exp 3) - 10(exp 4)) that further studies must be made of the role of mass loading.

Cuzzi, Jeffrey N.; Hogan, Robert C.; Paque, Julie M.; Dobrovolskis, Anthony R.

1999-01-01

141

Magnetocentrifugal jets and chondrule formation in protostellar disks  

NASA Astrophysics Data System (ADS)

Chondrite meteorites are the building blocks of the solar nebula, out of which our Solar System formed. They are a mixture of silicate and oxide objects (chondrules and refractory inclusions) that experienced very high temperatures, set in a matrix that remained cold. Their prevalence suggests that they formed through a very general process, closely related to stellar and planet formation. However the nature and properties of the responsible mechanism have remained unclear. The evidence for a hot solar nebula provided by this material seems at odds with astrophysical observations of forming stars. These indicate that the typical temperatures of protostellar disks are too low to melt and vapourise silicate minerals at the radial distances sampled by chondrule-bearing meteorites. Here, we show that processing of precursors in a protostellar outflow at radial distances of about 1 - 3 AU can heat them to their melting points and explain their basic properties, while retaining association with the colder matrix.

Salmeron, Raquel; Ireland, Trevor

2014-01-01

142

Not All Refractory Spherules in CM2S are Chondrules  

Microsoft Academic Search

Refractory spherules in CM2 meteorites are small, <300 micrometers in diameter, inclusions composed predominantly of spinel, with accessory hibonite and perovskite (Macdougall 1981). On the basis of their chondrule-like morphology, and the inward-radiating habit of hibonite in some inclusions, it has been suggested that refractory spherules formed from liquid droplets (Macdougall 1981; MacPherson et al. 1983). Since many spherules are

R. C. Greenwood

1992-01-01

143

Olivine-dominated asteroids: Mineralogy and origin  

NASA Astrophysics Data System (ADS)

Olivine-dominated asteroids are a rare type of objects formed either in nebular processes or through magmatic differentiation. The analysis of meteorite samples suggest that at least 100 parent bodies in the main belt experienced partial or complete melting and differentiation before being disrupted. However, only a few olivine-dominated asteroids, representative of the mantle of disrupted differentiated bodies, are known to exist. Due to the paucity of these objects in the main belt their origin and evolution have been a matter of great debate over the years. In this work we present a detailed mineralogical analysis of twelve olivine-dominated asteroids. We have obtained near-infrared (NIR) spectra (0.7-2.4 ?m) of asteroids (246) Asporina, (289) Nenetta, (446) Aeternitas, (863) Benkoela, (4125) Lew Allen and (4490) Bamberry. Observations were conducted with the Infrared Telescope Facility (IRTF) on Mauna Kea, Hawai'i. This sample was complemented with spectra of six other olivine-dominated asteroids including (354) Eleonora, (984) Gretia, (1951) Lick, (2501) Lohja, (3819) Robinson and (5261) Eureka obtained by previous workers. Within our sample we distinguish two classes, one that we call monomineralic-olivine asteroids, which are those whose spectra only exhibit the 1 ?m feature, and another referred to as olivine-rich asteroids, whose spectra exhibit the 1 ?m feature and a weak (Band II depth 4%) 2 ?m feature. For the monomineralic-olivine asteroids the olivine chemistry was found to range from Fo49 to Fo70, consistent with the values measured for brachinites and R chondrites. In the case of the olivine-rich asteroids we determined their olivine and low-Ca pyroxene abundance using a new set of spectral calibrations derived from the analysis of R chondrites spectra. We found that the olivine abundance for these asteroids varies from 0.68 to 0.93, while the fraction of low-Ca pyroxene to total pyroxene ranges from 0.6 to 0.9. A search for dynamical connections between the olivine-dominated asteroids and asteroid families found no genetic link (of the type core-mantel-crust) between these objects.

Sanchez, Juan A.; Reddy, Vishnu; Kelley, Michael S.; Cloutis, Edward A.; Bottke, William F.; Nesvorn, David; Lucas, Michael P.; Hardersen, Paul S.; Gaffey, Michael J.; Abell, Paul A.; Corre, Lucille Le

2014-01-01

144

Clear Evidence for Fe-60 in Silicate from a Semarkona Chondrule  

NASA Technical Reports Server (NTRS)

Fe-60 (t(sub 1/2) = 1.5 Ma) is key to understanding the sources of short-lived radionuclides in the early solar system because it is the only one among those known from meteoritic material that is produced only in stars [1]. Within the last year, it has become clear that Fe-60 was present in sulfides from primitive ordinary and enstatite chondrites in amounts sufficient to require a recent stellar input [2-5]. The sulfide data indicate an initial Fe-60/Fe-56 ratio for the early solar system of between approx. 3 10(exp -7) and approx. 1.6 10(exp -6) [2-4]. However, iron (and nickel?) in sulfides is easily mobilized by very mild heating [e.g., 6], so there is considerable uncertainty over the true initial ratio. To resolve this uncertainty, we have begun a search for evidence of Fe-60 in silicates from primitive chondrites. In olivine from type 3.0-3.1 ordinary chondrites, diffusive exchange of iron and magnesium has not occurred to any significant degree, and diffusive exchange in pyroxene is slower [7]. However, the relatively small elemental fractionation of iron from nickel in silicates, coupled with the fact that the daughter nuclide, Ni-60, makes up approx. 26 % of normal nickel, make detection of excesses of radiogenic Ni-60 very difficult. Fortunately, we have found a fine-grained radiating-pyroxene chondrule in Semarkona (LL3.0) with a very high Fe/Ni ratio that gives clear evidence of Fe-60.

Huss, G. R.; Tachibana, S.

2004-01-01

145

Extremely NA and CL Rich Chondrule AL3509 from the Allende Meteorite  

SciTech Connect

We report on the mineralogy, petrology, chemistry, oxygen isotopes, {sup 26}Al-{sup 26}Mg and {sup 36}Cl-{sup 36}S isotope systematics of the Allende chondrule Al3509 discovered and described by [1] and [2]. This spherical object ({approx}1cm {phi}) contains {approx}10% Na and 1% Cl, and nearly pure {sup 129}Xe [({sup 129}Xe/{sup 127}I) = 1.1 x 10{sup -4} (3)]. This high enrichment in halogens makes it of interest in searching for radiogenic {sup 36}S from {sup 36}Cl (t{sub 1/2} {approx} 0.3 Ma) decay. While there is strong evidence for the presence of {sup 36}Cl in sodalite and wadalite in CV CAIs [4,5], some sodalites show no evidence for excesses of {sup 36}S ({sup 36}S*). In contrast, high inferred initial {sup 36}Cl/{sup 35}Cl = 2 x 10{sup -5} has been found in wadalite from the Allende CAI AJEF [5]. The observed {sup 36}S excesses in sodalite are not correlated with radiogenic {sup 26}Mg, decay product of {sup 26}Al (t{sub 1/2} {approx} 0.72 Ma) [4]. From the inferred initial {sup 36}Cl/{sup 35}Cl ratios and consideration of both AGB and SNe stellar sources, {sup 36}Cl must be the product of charged particle irradiation within the early solar system. However, neither the specific nuclear production mechanism nor the irradiation site have been identified. Both sodalite and wadalite are found as late stage alteration products of CAIs together with grossular, monticellite, Al-rich pyroxene, wollastonite, nepheline, ferroan olivine, and ferroan pyroxenes. This late-stage alteration has been found to extensively change some CAIs in Allende, but clear residues of spinel, hibonite and Wark-Lovering rims are recognizable remnants of the original CAIs. The nature of the widespread volatile alteration process as well as that of the fluid phase remain controversial.

Wasserburg, G J; Hutcheon, I D; Aleon, J; Ramon, E C; Krot, A N; Nagashima, K; Brearley, A J

2011-04-07

146

Exsolved Ferromagnesian Olivine: Why Only in Divnoe?  

NASA Astrophysics Data System (ADS)

Recently Petaev and Brearley [1] showed that lamellar structure in olivine grains in the Divnoe meteorite was produced by the low-temperature exsolution of primary homogeneous grains. Exsolved olivine in Divnoe is in accordance with the thermodynamic model of olivine solid solution of [2], which predicts a miscibility gap in ferromagnesian olivines below ~340 degrees C within a compositional range that widens with decreasing temperature. Experiments on the coexistence of olivines having a range of compositions with aqueous solutions of (Fe,Mg)Cl2 [3] suggest that exsolution in ferromagnesian olivines could occur even at temperatures as high as ~400 - 450 degrees C. However, [1] remains the only observation of exsolution in natural olivines so far. This means either that (1) the exsolution in Divnoe olivine is unique, or (2) olivine grains in other slowly cooled coarse-grained rocks has not been studied closely enough to detect them. This work attempts to clarify the issue. Olivine grains from selected meteorites (Springwater pallasite, Lowitz mesosiderite, ALHA 84025 brachinite, Gorlovka H3-4 chondrite and Krymka L3 chondrite, and the Calcalong Creek lunar meteorite) and terrestrial rocks (San Carlos forsterite and Rockport fayalite) were studied by EPMA using the same equipment and technique as in [1]. Among meteorites, pallasites and mesosiderites are known to have slowest cooling rates at low temperatures. Olivines in the Springwater pallasite (Fa18) [4] and the Lowitz mesosiderite (Fa15-37) [5] are compositionally comparable with that of Divnoe (Fa23-29) [1], and it was expected that exsolved olivine grains would be found there. Olivines from other samples were studied for comparison. No lamellar structure was observed in BSE images of the olivine grains studied. The variations of Fa contents in olivine grains from all samples but Springwater and Lowitz meteorites display no regular pattern, and are basically within the 2sigma uncertainty range (+/-0.2 mole % Fa). As expected, olivines from the Lowitz mesosiderite and, especially, from the Springwater pallasite display somewhat larger variations, within the ranges of 20.1 - 21.0 and 15.8 -17.7 mole % Fa, respectively. The olivine in Springwater shows a surprisingly regular pattern of minima spaced at ~ 16 micrometers. For reasons that are unclear all 'minima' analyses have low totals (90.47-94.31 wt.%), whereas most other analyses have totals > 97%. However, stoichiometry of all analyses is perfect; cation totals per 4 oxygens are 3.00+/-0.01, with very minor excess of Si over Mg+Fe in the 'minima' analyses. The results obtained so far suggest that lamellar structure of olivine grains in the Divnoe meteorite is unique. While chemical variability is found in the Springwater and Lowitz olivines, there is no lamellar structure, and the magnitude of the variations is 1.5 - 2 times smaller than it is in Divnoe olivines. Since olivine compositions in Divnoe, Lowitz and Springwater are similar, the structural differences among them must be due to different thermal histories. The lack of lamellar structure in the Lowitz olivine implies that even the slowest cooling down to 250 degrees C recorded in mesosiderites [6] does not result in olivine exsolution. It is possible that Divnoe experienced secondary reheating followed by prolonged low-temperature annealing. This would also account for the lack of shock features in the Divnoe opaque minerals [7] and the difference in distributions of cosmic-ray track lengths and densities between olivine and pyroxene [8]. References: [1] Petaev M. I. and Brearley A. J. (1994) Science, 266, 1545-1547. [2] Sack R. O. and Ghiorso M. S. (1989) Contrib. Mineral. Petrol., 102, 41-68. [3] Schulien S. (1980) Contrib. Mineral. Petrol., 74, 85-91. [4] Buseck P. R. (1977) GCA, 41, 711-740. [5] Delaney J. S. et al. (1980) Proc. LPSC 11th, 1073-1087. [6] Ganguly J. et al. (1994) GCA, 58, 2711-2723. [7] Petaev M. I. et al. (1994) Meteoritics, 29, 182-199. [8] Petaev M. I. et al. (1990) LPS XXI, 950-951.

Petaev, M. I.

1995-09-01

147

Unusual olivine zoning --- Evidence for complex physico-chemical changes during the evolution of olivine melilitite and kimberlite magmas  

Microsoft Academic Search

Olivine melilitites from Namaqualand, South Africa are characterized by a broad range in olivine compositions on the scale of individual hand specimens. It is possible to distinguish four petrographically and chemically distinct olivine populations in both the northern and southern pipe clusters studied: (a) Scarce anhedral or subhedral olivines that display marked disequilibrium features with the surrounding matrix, and which

A. E. Moore; A. J. Erlank

1979-01-01

148

Olivine dissolution in sulphuric acid at elevated temperaturesimplications for the olivine process, an alternative waste acid neutralizing process  

Microsoft Academic Search

A kinetic model for the dissolution of olivine in sulphuric acid at elevated temperatures is presented. Such a model is essential for the design of an industrial process for the neutralization of waste acids by olivine, or for the production of precipitated silica from olivine. The effects of temperature, grainsize fraction and olivine amount on the neutralization rate have been

R. C. L. Jonckbloedt

1998-01-01

149

Chemical and petrographic constraints on the origin of chondrules and inclusions in carbonaceous chondrites  

NASA Technical Reports Server (NTRS)

Bulk chemical compositions of the various petrographic types of chondrules and inclusions in Type 3 carbonaceous chondrites (excluding those affected by metamorphism) have been determined by microprobe defocused-beam analysis. Inclusion compositions follow approximately the theoretical compositional trajectory for equlibrium condensation. Chondrules occurring in the same meteorites have higher silica contents and show only slight overlap with inclusion compositions. Dust fusion is apparently an inadequate mechanism for producing the wide chemical variations observed among chondrules. Impact-melting models require sampling of complex target rocks which are unknown as components of meteorites; this mechanism also demands efficient mechanical processing of chondrules before accretion. A genetic relationship between chondrules and inclusions in carbonaceous chondrites is suggested by the compositional continuum between these objects. A condensation sequence which dips into the liquid stability field at lower temperatures is advocated for the production of both inclusions and chondrules. Textural relationships between intergrown chondrules and inclusions support such a sequence. This model suggests that the assembled components (inclusions and chondrules) of carbonaceous chondrites are related by a common process.

Mcsween, H. Y., Jr.

1977-01-01

150

Gas dynamic heating of chondrule precursor grains in the solar nebula  

Microsoft Academic Search

In the present investigation of solar nebula gasdynamic processes which may account for the melting of chondrule precursor grains, both drag heating due to grain relative motion and heating due to collisions with gas molecules in thermal motion are considered in conjunction with the effect of thermally emitted radiation on grain heating and cooling. The melting of chondrule-sized grains is

L. L. Hood; M. Horanyi

1991-01-01

151

Metamorphism of the H-group chondrites - Implications from compositional and textural trends in chondrules  

NASA Technical Reports Server (NTRS)

The paper discusses element bulk compositions of 373 chondrules from 18 H3 to H6 chondrites determined by broad-beam electron probe analysis. Bulk chondrule FeO and Al2O3 amounts increase and TiO2 and Cr2O3 decrease with increasing petrologic type; normative faylite, albite, and plagioclase amounts increase through the petrologic sequence. Chondrule diameters correlate with phenocryst sizes in porphyritic chondrules of type 3 chondrites, but this correlation is diminished in the higher petrologic types. The compositional trends in chondrules through the petrologic sequence are attributed to diffusion and equilibration among chondrules, and between chondrules and matrix in response to increasing degrees of thermal metamorphism. It is suggested that H-group chondrites are formed by accretion of high-temperature (chondrules) and low-temperature (matrix) materials. Internal reheating of the parent materials to different temperatures caused compositional equilibration, grain coarsening, and reduction of FeO to Fe(0) by carbon.

Lux, G.; Keil, K.; Taylor, G. J.

1980-01-01

152

Atom Probe Tomography of Olivine  

NASA Astrophysics Data System (ADS)

Here we present atom probe tomographic (APT) analyses of natural olivine. APT provides three-dimensional trace element and isotopic analysis with sub-nanometer spatial resolution. It has been used for many years in engineering and materials science, but has not been applied to geological materials because traditional APT can only be used on conducting (usually metal) samples. The recent development of laser assisted APT has changed this situation, and now semi-conductors and insulators can be analyzed (Marquis et al., 2009, Kelly et al 2007). Potentially, this opens APT to extensive use in geoscience as many Fe-bearing silicates are semi-conductors. In this study, we explore the capability of the new class of APT instrumentation to analyze geological materials. APT involves the controlled evaporation of small, cylindrical specimens (100's nm in diameter) within an electric field. Specimens are typically prepared using in-situ focused-ion-beam (FIB) liftout and shaping techniques. Evaporated atoms are accelerated to a detector plate that records the position of the atom with sub-nm precision. Evaporated atoms are measured using time-of-flight mass spectrometry, allowing both elemental and isotopic determination. Since the method progressively ablates into the needle, the final analytical result is a nm-scale 3-dimensional image in which the position and identity of each detected atom is known. Typical mass resolution is between 200 and 1200 (full-width at half maximum) and typical concentration detection limits are 10 ppm. The number of potential applications of APT to igneous, metamorphic and sedimentary materials is large, ranging from studies of mineral and melt inclusions, to fine scale layering in minerals, to reaction surfaces and diffusion profiles. Much recent progress in the geochemical and petrologic fields has been driven by the increasing spatial resolution of the ion probe and laser ablation ICPMS. The ability of APT to provide atom-scale mass spectrometry should continue this trend. The main limitations to atom probe analysis of geological materials are the ability to control heat flow during laser pulsing and the associated ability to control clustering during field evaporation. Both of these factors can be controlled through specimen preparation and varying the atom probe experimental factors. Olivine specimens were properly analyzed using laser pulsed APT through the use of shallow (nominally 1mm) FIB liftouts and wide shank angle specimen apices. APT settings were found to give the best mass resolution using low specimen temperatures, 0.2 nJ laser energy, and 50 kHz pulse repetition rate. Increasing any of these values increases the amount of thermal tails due to excessive heat buildup, reducing the mass spectrum resolution, and ultimately affecting the spatial resolution of the reconstruction. Marquis EA, Miller MK, Blavette D, Ringer SP, Sudbrack CK and Smith DW (2009). MRS Bulletin 34: 725-730. Thomas F. Kelly, David J. Larson, Keith Thompson, Roger L. Alvis, Joseph H. Bunton, Jesse D. Olson, Brian P. Gorman, Ann. Rev. Mat. Res. 37: 681-727.

Parman, S. W.; Gorman, B.; Jackson, C.; Cooper, R. F.; Jaeger, D.

2010-12-01

153

Pb-Pb Isotopic and X-ray Tomographic Constraints on the Origin of Chondrules  

NASA Astrophysics Data System (ADS)

207Pb*/206Pb* chronometry was used to obtain the ages of Ca,Al-rich inclusions (CAIs) and chondrules found in ancient meteorites. Assuming a 238U/235U=137.88, Pb/Pb ages of chondrules in NWA801 (a CR2 meteorite) are 4564.6+/-1.0 Ma, chondrules in Mokoia (a CV3 chondrite) are 4564.2+/-1.1Ma, and CAIs in Mokoia are 4567.9+/-5.4 Ma. The Pb/Pb age of NWA801 chondrules is concordant with 26Al/ 26Mg ages of CR chondrules. However if a 238U/ 235U<137.88 is used, the age for NWA801 chondrules becomes younger by 1Ma and discordant with26Al/26Mg ages of CR chondrules. This suggests either a discrepancy with the U compositions or the initial Mg isotopic compositions of NWA801 chondrules. The shapes of NWA801 chondrules, and blebs of FeNi metal in the meteorite matrix, were further studied by 3D X-ray micro-computed tomography (CT). Most chondrules (92%) were 'armoured' with one discontinuous layer of FeNi metal. Two layers of FeNi metal (one on the exterior and one concentric through the interior separated by silicate) were rare <8%. Chondrules and matrix blebs occur as oblates, prolate, spheres and triaxial spheroids. It is proposed that the shapes were made free-floating in the nebula likely by ash-melting precursors into molten droplets that were vibrating as harmonic oscillators that 'froze-in' their shapes during cooling. Parent-body metamorphism and shock are not likely processes affecting the matrix-bleb and chondrule shapes. Chondrules with?2 FeNi metal layers were likely formed by mergers and not by successive deposition and annealing of metal in multiple ash-melting events. Attempts to obtain 207Pb*/206Pb* ages from chondrules and CAIs by thermal extraction (TE)-TIMS were unsuccessful. However LA-ICP-MS was shown to be useful for rapidly determining Pb isotopic trends in meteorites and unknown objects. In particular, it was shown that 137La (T1/2=60ky) should be detectable in recently fallen meteorites using LaF-4 to suppress the 137Ba isobar during tandem accelerator mass spectrometry combined with a novel instrumental technique for isobar separation.

Charles, Christopher R. J.

154

The origin and history of the metal and sulfide components of chondrules  

NASA Astrophysics Data System (ADS)

Instrumental and radiochemical neutron activation analysis is used to determine the concentrations of 14 siderophile and other nonlithophilic elements in 31 chondrules from the extremely unequilibrated chondrite Semarkona. The results are presented in tables and graphs, characterized in detail, and compared with the results obtained for lithophile elements in the same samples by Grossman and Wasson (1983). The elements studied are found to be significantly more fractionated than the lithophile elements, with variations in chondrule/whole-rock abundances of up to a factor of 1000, a mean ratio of 0.2, and differences between Ni-rich and Ni-depleted chondrules. It is argued that the metal and sulfides in the chondrules represent the composition of the solar nebula before chondrule formation and already contained the siderophile and chalcophile elements, although some Fe was contained in silicates along with Ni, Co, Au, Ge and Se. The segregation of metals during a molten stage is considered of minor importance.

Grossman, J. N.; Wasson, J. T.

1985-04-01

155

The origin and history of the metal and sulfide components of chondrules  

NASA Technical Reports Server (NTRS)

Instrumental and radiochemical neutron activation analysis is used to determine the concentrations of 14 siderophile and other nonlithophilic elements in 31 chondrules from the extremely unequilibrated chondrite Semarkona. The results are presented in tables and graphs, characterized in detail, and compared with the results obtained for lithophile elements in the same samples by Grossman and Wasson (1983). The elements studied are found to be significantly more fractionated than the lithophile elements, with variations in chondrule/whole-rock abundances of up to a factor of 1000, a mean ratio of 0.2, and differences between Ni-rich and Ni-depleted chondrules. It is argued that the metal and sulfides in the chondrules represent the composition of the solar nebula before chondrule formation and already contained the siderophile and chalcophile elements, although some Fe was contained in silicates along with Ni, Co, Au, Ge and Se. The segregation of metals during a molten stage is considered of minor importance.

Grossman, J. N.; Wasson, J. T.

1985-01-01

156

The origin of chondrules and chondrites: Debris from low-velocity impacts between molten planetesimals?  

NASA Astrophysics Data System (ADS)

We investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin-shelled, largely molten planetesimals collided at low speed during accretion. This scenario, here dubbed "splashing," stems from evidence that such planetesimals, intensely heated by 26Al, were abundant in the protoplanetary disk when chondrules were being formed approximately 2 Myr after calcium-aluminum-rich inclusions (CAIs), and that chondrites, far from sampling the earliest planetesimals, are made from material that accreted later, when 26Al could no longer induce melting. We show how "splashing" is reconcilable with many features of chondrules, including their ages, chemistry, peak temperatures, abundances, sizes, cooling rates, indented shapes, "relict" grains, igneous rims, and metal blebs, and is also reconcilable with features that challenge the conventional view that chondrules are flash-melted dust-clumps, particularly the high concentrations of Na and FeO in chondrules, but also including chondrule diversity, large phenocrysts, macrochondrules, scarcity of dust-clumps, and heating. We speculate that type I (FeO-poor) chondrules come from planetesimals that accreted early in the reduced, partially condensed, hot inner nebula, and that type II (FeO-rich) chondrules come from planetesimals that accreted in a later, or more distal, cool nebular setting where incorporation of water-ice with high ?17O aided oxidation during heating. We propose that multiple collisions and repeated re-accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties, and led to so-called "complementarity" and metal depletion in chondrites. We suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation.

Sanders, Ian S.; Scott, Edward R. D.

2012-12-01

157

Effect of fO2 on the incorporation and diffusivity of Li in olivine  

NASA Astrophysics Data System (ADS)

Over the last decade the geochemical behaviour of Li has become of special interest since it was speculated that Li stable isotopes could be a promising tracer for subduction zone processes. However, there have been many studies of natural samples but our experimental and theoretical basis for interpreting these data is still lacking. Two diffusion mechanisms were identified for Li in olivine [1]. Their contribution to the net flux of Li in olivine depends on the vacancy concentration on the metal sites, which is sensitive to the fO2. Therefore we have studied the effect of fO2 on Li solubility and diffusion in olivine. Experimental approach: thin plates of crushed, natural olivine single crystals were embedded into two different kind of powders, ground plagioclase with about 2.5 ppm Li or a pre-annealed powder mixture of San Carlos olivine and isotopically enriched Li. All runs were performed in a gas-mixing furnace with fO2 controlled by flowing CO/CO2 mixture. In each run we simultaneously annealed about 100 micrometer-sized samples of Pakistan olivine and San Carlos olivine. In addition we have added to each run a mm sized crystallographically oriented parallelepiped of San Carlos olivine. For each powder reservoir we have performed a set of three anneals at 1200 C and different fO2. Cross sections of the run products were polished and analyzed with LA-ICP-MS. Results: In all cases the Li isotopes and concentrations were homogeneous in the 100 micrometer sized grains with one exception, the experiment at 1.e-10 bar with the highly enriched Li reservoir. The final Li concentration was slightly lower in the Pakistan than San Carlos olivine and was much lower in general if buffered by the plagioclase powder. Most importantly, the Li concentration increased systematically with increasing oxygen fugacity, indicating that the incorporation of Li in olivine is fO2 dependent. The mm-sized, oriented crystal was in most cases zoned and the extent of zoning depends on the diffusion direction. In addition the profiles became systematically longer with decreasing fugacity and at the most reducing conditions the crystal was almost homogenous. However, the isotopes were in all cases completely homogenized and equilibrated with the isotopically enriched reservoir. Thermodynamic model: We extended the quantitative point defect model for olivine [2] and reproduced the effect of fO2 on the solubility of Li when we assume it is mainly on the metal site and charge balanced by the formation of Fe3+ on the metal site. Conclusions: Our results strongly indicate that incorporation of Li is dependent on the fO2, less dependent on the trace element content. Diffusion of Li in olivine is anisotropic and dependent on fO2. Our quantitative point defect model for olivine underpins the experimental results. This will allow us to develop a multi-component diffusion model considering relevant point defects, e.g. Fe3+ and metal vacancies. Such a model will hopefully help us to simulate diffusion of Li at various natural circumstances including fO2 as a critical parameter. References: [1] Dohmen et al. (2010) Geochim Cosmochim Acta 74, 274-292; [2] Dohmen and Chakraborty (2007), Phys Chem Minerals 34, 597- 598.

Dohmen, R.; Coogan, L. A.

2012-12-01

158

Raman spectra of shocked minerals. I - Olivine  

NASA Technical Reports Server (NTRS)

The Raman spectra of olivine contained in a chip of the Twin Sisters Peak (Washington) dunite shocked to 22.2 GPa is shown to be identical to that of unshocked olivine in the same rock. The Raman spectra of powder of the rock shocked to 20.1 GPa and of chips shocked to 59.5 GPa and 60.7 GPa display strong and broad low-frequency features with crests at 475/cm, 556/cm, and 572/cm, and broad high-frequency features near 1100/cm. It is suggested that these features are due to the formation of olivine glass with a considerable degree of three-dimensional Si-O-Si linkage having scattered domains of greatly variable grain size, internal structure, and chemical composition.

Heymann, D.; Celucci, T. A.

1988-01-01

159

Possible Clues to the Physical Nature of Chondrule Precursors: an Experimental Study Using Flash Melting Conditions  

NASA Astrophysics Data System (ADS)

In a continuing series of experiments to assess how flash melting conditions can reproduce chondrule textures we have investigated how the initial grain size of the starting material can affect chondrule textures. A previous series of experiments [1] has been carried out using an Fa analog composition (T(sub)L 1211 degrees C) with initial grain size ranges from 23-45 micrometers, 45-63 micrometers, 63-125 micrometers, and 125-250 micrometers. New experiments ([2], this research) use an average Type IIA chondrule composition (TL 1550 degrees C) with initial grain size ranges of 23-45 micrometers and 125-250 micrometers. All experiments utilized the flash melting techniques of [1,2]. Experiments performed with the finer grain fractions (<125 micrometers) of these composition for flash melting conditions less than 50 degrees C above their respective TL yield microporphyritic textures typical of Type IA chondrules [3]. Higher initial flash melting temperatures generate textures typical of Type IIA chondrules (i.e., PO,BO). However, the same experimental conditions that produced Type IA textures produced porphyritic textures typical of Type IIA chondrules [4] with starting grain size of 125-250 micrometers. Experiments with 125- 250-micrometer grain size produced only the typical Type IIA chondrule textures from initial flash melting temperatures ranging to 125 degrees C above TL. These charges also had a high number of large (100-200 micrometers) relict grains indicating that melting was not very extensive. Fewer nucleation sites survived the melting process allowing larger crystals to grow in the Type IIA textured charges than charges that produced Type LA textures. From our experiments it is clear that for the flash melting conditions used we cannot produce the microporphyritic textures typical of Type IA chondrules from precursors with an initial grain size of 125-250 micrometers with our compositions. If chondrules were produced by flash melting conditions similar to our experimental conditions it is clear that Type IA chondrules had precursors with a relatively homogeneous grain size that is less than 125 micrometers. Based on our experiments, in order to obtain the high nucleation density needed after melting to produce textures truly analogous to Type IA chondrules a grain size of 45 micrometers or less is favored. Therefore, Type IA chondrules could not have experienced high degrees of melting, either due to a relatively short, high-temperature melting event (i.e. flash melting) or a longer, lower-temperature (subTL) melting event(s). The presence of BO textures and large phenocrysts within PO textures of Type IIA group indicates that melting was more extensive, thus fewer nucleation sites survived, for Type IIA than for Type IA chondrules. Relict grains produced from flash melting with 125250-micrometer precursor material in the lab may be analogous to relict grains found in Type IIA chondrules. However, these experiments cannot rule out the possibility that Type IIA chondrules were totally melted and their texture is a function of the number of nucleation sites caused by collisions with dust and the temperatures at which those collisions occur. Type IA chondrules were made by partial melting of fine grained precursor dust. Type IIA chondrules could either have been made by partial melting of coarse grained precursor dust or they could have been totally melted precursor dust (with any size characteristics) provided dust of any size range collided with molten chondrules during their formation to act as nucleation sites. References: [1] Connolly H. C. Jr. et al. (1991) Meteoritics, 26, 329. [2] Connolly H. C. Jr. et al. (1993) LPSC XXIV, 329-330. [3] Jones R. H. and Scott E. R. D. (1989) Proc. LPSC 14th, 559-566. [4] Jones R. H. (1990) GCA, 54, 1784-1802.

Connolly, H. C., Jr.; Hewins, R. H.; Lofgren, G. E.

1993-07-01

160

Chondrule-like objects and brown glasses in howardites  

NASA Technical Reports Server (NTRS)

Chondrulelike objects and brown glasses were analyzed in the howardites, Bununu, Malvern, Monticello, Pavlovka, and Yamato 7308. The objects are very similar to chondrules in ordinary and carbonaceous chondrites. Like the brown glasses, the chondrulelike objects could have been produced by impact melting that left some crystalline nuclei, followed by a slower cooling rate than for the glasses. Alternatively, these objects are chondrules implanted from chondrite impactors. They are, however, without rims or any adhering matrix. The brown glasses appear to represent melting of average regolithic surface material, except for Monticello and Y7308, both of which have some siliceous glasses. The siliceous glasses could not have been produced by vapor fractionation but by melting of differentiated lithologies such as fayalitic granites. Impact mechanics indicates that howardites with abundant brown glasses came from an asteroid larger than Vesta (greater than 400 km radius), upon which impacts occurred at relative velocities of up to 5 km/s. Howardites with little or no brown glasses came from a smaller parent body. It is concluded that at least two parent bodies are likely sources for the basaltic achondrites.

Olsen, Edward J.; Fredriksson, Kurt; Rajan, Sundar; Noonan, Albert

1990-01-01

161

Bar Graph  

NSDL National Science Digital Library

In this activity, students use preset data or input their own data to be represented by a bar graph. This activity allows students to explore bar graphs and how changing scales will alter how their data is represented. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

2010-01-01

162

Constraints to the Formation of Matrix Reduced Olivine in Yamato-691 (EH3) Chondrite: Implications for the Evolution of EH Chondrites  

NASA Astrophysics Data System (ADS)

In order to understand the origin of oxidized components in enstatite chondrites, matrix reduced olivine (RO) (<~60 micrometers in diameter) in Yamato-691 (EH3) chondrite has been examined in detail using EPMA. It commonly shows a lamellar structure, composed of alternation (with the spacing of about 1 micrometer) of "reduced olivine," which is a mixture of forsterite, metallic Fe, and probably unreacted olivine (relict), and sub-grain boundaries (SB) partly filled with decomposition products (Fe-metal, troilite, enstatite, and siliceous melt) due to reduction, strongly suggesting that the reduction of high-FeO olivine took place along SB (Boland and Duba, 1986). The presence of RO with bended SB is also suggestive of plastic deformation of the olivine before reduction. We estimated the rate of reduction of (Mg,Fe)-olivine as a function of temperature, composition of olivine (X(sub)Fe) and PO(sub)2 of reducing gas. We assumed that PO(sub)2 of the reducing gas was buffered by Si-bearing Fe-Ni metal + quartz assemblage. A mean Si- and Ni-contents of kamacite in Y-691 (Si=2.09 wt%; Ni=2.90 wt%) was adopted (El Goresy et al., 1988). To form RO with the SB spacing of 1 micrometer within 10^6-7 yr, which is a typical time-scale of thermal metamorphism at shallow parts of meteorite parent bodies (Wood, 1979), the temperature during reduction must have exceeded 700 K. From these results, the formational history of matrix RO and other coexisting phases in Y-691 could be summarized as follows: (1) High-FeO chondrule olivines crystallized in chondrule melts enriched in oxidized components. (2a) A severe impact process deformed them plastically and generated numerous dislocations (>10^9/cm^2) in them. (2b) Post-shock high-T (>~1100 K) annealing process formed SB in them due to dislocation climb. (3) The olivine grains were then mixed with E-chondritic materials containing at least both Si-bearing Fe- Ni metals and silica. (4) During metamorphism and/or impact heating process (T>~700 K), reduction of the olivine proceeded along SB to precipitate reduction products. (5) After reduction, the ROs were comminuted to grain sizes less than ~60 micrometers. (6) Finally, the fine- grained ROs were assembled with other E-chondritic components (e.g., sulfides) to form Y-691 chondrite at temperatures lower than ~500 degrees C (Nagel, 1991). Boland J.N. and Duba A.G. (1986) Jour. Geophys. Res. 91, 4711- 4722. El Goresy A. et al. (1988) Proc. NIPR Symp. Antarct. Meteorites 13th, 65-101. Nagel H.-J. (1991) Ph.D. Thesis, Univ. of Heidelberg, 117 pp. Wood J.A. (1979) In Asteroids (ed. T. Gehrels), pp. 849-891. Univ. Arizona Press, Tucson, Arizona.

Matsunami, S.; El Goresy, A.

1992-07-01

163

Serpentinization of sintered olivine during seawater percolation experiments  

NASA Astrophysics Data System (ADS)

Hydration of the mantle lithosphere exposed along detachment faults at slow-spreading ridges leads to strong modification of rock rheological, geophysical and geochemical properties, and to the emission of large amounts of H2 and CH4, and of complex carbon molecules that support primitive ecosystems. The sustainability and efficiency of this hydration process, serpentinisation, and of associated reactions, requires penetration and renewal of fluids at the mineral-fluid interface. However, precipitation of material along flow paths will affect porosity and permeability that, in turn, will have feedbacks effects on the reactions. It is thus necessary to investigate the sustainability of flow paths, and the evolution of reaction rates for a dynamic system under representative conditions. We investigate these processes by percolation experiments carried out under P, T representative conditions, using the ICARE Microlab experimental bench. We present the preliminary results of seawater percolation within samples of sintered San Carlos olivine. The experiments were carried out under a confined pressure of 190 bars and a temperature of 190 C and water flow was set at a constant specific discharge of 0.06 ml/h.. The experiments were performed at very slow flow rate to be more representative of natural systems. ICARE Microlab allows measuring continuously the permeability changes during the percolation experiment and sampling the brine at the outlet of the sample. After 20 days of experiments, poorly crystallized serpentine and iron oxide formed within the micro-cracks while permeability strongly decreases. Such rapid precipitation of serpentine results in clogging of fluid paths. The chemical composition of the outlet fluid is dominated by Si and is depleted in Mg relative to stoechiometric dissolution of olivine during the whole experiment suggesting that brucite possibly formed. SEM and AEM/TEM are used to characterize the reactive interfaces and the neoformed materials.

Luquot, Linda; Andreani, Muriel; Godard, Marguerite; Gouze, Philippe; Gibert, Benoit

2010-05-01

164

A Chemical Model of Micrometeorite Impact into Olivine  

NASA Technical Reports Server (NTRS)

Laboratory simulations of space weathering using laser irradiation have been successful in reproducing space weathering characteristics such as the reduction of olivine to form nanophase iron particles. However, the chemistry of the reduction of Fe2+ in olivine to Fe metal has not been fully explored. We present a thermodynamic model of olivine undergoing post-impact cooling and decompression.

Sheffer, A. A.; Melosh, H. J.

2005-01-01

165

Mineralogy of Stardust Track 112 Particle: Relation to Amoeboid Olivine Aggregates  

NASA Technical Reports Server (NTRS)

The successful analysis of comet 81P/Wild 2 particles returned by the Stardust mission has revealed that the Wild 2 dust contains abundant silicate grains that are much larger than interstellar grains and appear to have formed in the inner regions of the solar nebula [1]. Wild 2 particles include minerals which are isotopically and mineralogically similar to CAIs [e.g., 2, 3] and chondrules [e.g., 4] in chondrites. In addition, particles similar to amoeboid olivine aggregates (AOAs) also have been discovered [5, 6,7]. C2067,2,112,1 is a terminal particle recovered from track #112 (T112). Nakamura-Messenger et al. [7] showed that the forsterite grain in T112 has O-16 enrichment of approximately 40 0/00 (vs. SMOW) and possibly formed together with AOAs. In this study, we have examined the mineralogy of the T112 particle and compared the possible relationships between T112 and AOAs in primitive meteorites.

Komatsu, M.; Fagan, T.; Mikouchi, T.; Miyamoto, M.; Zolensky, M.; Ohsumi, K.

2012-01-01

166

Origin of low-Ca pyroxene in amoeboid olivine aggregates: Evidence from oxygen isotopic compositions  

NASA Astrophysics Data System (ADS)

Amoeboid olivine aggregates (AOAs) in primitive carbonaceous chondrites consist of forsterite (Fa <2), Fe,Ni-metal, spinel, Al-diopside, anorthite, and rare gehlenitic melilite (k <15). 10% of AOAs contain low-Ca pyroxene (Fs 1-3Wo 1-5) that is in corrosion relationship with forsterite and is found in three major textural occurrences: ( i) thin (<15 ?m) discontinuous layers around forsterite grains or along forsterite grain boundaries in AOA peripheries; ( ii) 5-10-?m-thick haloes and subhedral grains around Fe,Ni-metal nodules in AOA peripheries, and ( iii) shells of variable thickness (up to 70 ?m), commonly with abundant tiny (3-5 ?m) inclusions of Fe,Ni-metal grains, around AOAs. AOAs with the low-Ca pyroxene shells are compact and contain euhedral grains of Al-diopside surrounded by anorthite, suggesting small (10%-20%) degree of melting. AOAs with other textural occurrences of low-Ca pyroxene are rather porous. Forsterite grains in AOAs with low-Ca pyroxene have generally 16O-rich isotopic compositions (? 17O < -20). Low-Ca pyroxenes of the textural occurrences ( i) and ( ii) are 16O-enriched (? 17O < -20), whereas those of ( iii) are 16O-depleted (? 17O = -6 to -4). One of the extensively melted (>50%) objects is texturally and mineralogically intermediate between AOAs and Al-rich chondrules. It consists of euhedral forsterite grains, pigeonite, augite, anorthitic mesostasis, abundant anhedral spinel grains, and minor Fe,Ni-metal; it is surrounded by a coarse-grained igneous rim largely composed of low-Ca pyroxene with abundant Fe,Ni-metal-sulfide nodules. The mineralogical observations suggest that only spinel grains in this igneous object were not melted. The spinel is 16O-rich (? 17O -22), whereas the neighboring plagioclase mesostasis is 16O-depleted (? 17O -11). We conclude that AOAs are aggregates of solar nebular condensates (forsterite, Fe,Ni-metal, and CAIs composed of Al-diopside, anorthite, spinel, and melilite) formed in an 16O-rich gaseous reservoir, probably CAI-forming region(s). Solid or incipiently melted forsterite in some AOAs reacted with gaseous SiO in the same nebular region to form low-Ca pyroxene. Some other AOAs appear to have accreted 16O-poor pyroxene-normative dust and experienced varying degrees of melting, most likely in chondrule-forming region(s). The most extensively melted AOAs experienced oxygen isotope exchange with 16O-poor nebular gas and may have been transformed into chondrules. The original 16O-rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains.

Krot, Alexander N.; Fagan, Timothy J.; Nagashima, Kazuhide; Petaev, Michael I.; Yurimoto, Hisayoshi

2005-04-01

167

Origin of spinel-rich chondrules and inclusions in carbonaceous and ordinary chondrites  

NASA Technical Reports Server (NTRS)

The evaluation of three models of the origin of spinel-rich chondrules and inclusions presented here includes new calculations of the major-element refractory mineral condensation sequence from a gas of solar composition over a wide pressure interval. Condensation calculations show that spinel-rich chondrules did not crystallize from metastable liquid condensates, and that spinel-rich inclusions are not aggregates of refractory nebular condensates. It is proposed that spinel-rich objects are fractionated distillation residues of small aggregates of primitive dust that lost Ca, Si-rich partial melts by evaporation, ablation, or splashing during collisions. This model also explains why spinel-rich chondrules and inclusions (1) are usually smaller than melilite-rich chondrules and inclusions; (2) often have highly fractionated trace-element compositions; and (3) usually do not contain Pt-metal nuggets even when they are more enriched in the Pt-group metals than nugget-bearing melilite-rich objects.

Kornacki, A. S.; Fegley, B., Jr.

1984-01-01

168

Al-rich chondrules from the Ybbsitz H4-chondrite - Evidence for formation by collision and splashing  

NASA Astrophysics Data System (ADS)

A chemical and mineralogical study of three Al-rich chondrules from the H4-chondrite Ybbsitz is presented. These chondrules are found to have a high concentration of incompatible elements, to be fractionated, and to be enriched in light rare earths. The results indicate that the Al-rich Ybbsitz chondrules formed by different processes than the Ca-Al-rich inclusions from carbonaceous chondrites. A model is proposed in which partly molten ferromagnesian chondrules collided with other objects, and Al-melt fractions were ejected to form independent Al-rich chondrules. It is suggested that the strong positive Eu anomaly noted may be due to diffusive exchange of Eu between the matrix and the Al-rich chondrules.

Bischoff, A.; Palme, H.; Spettel, B.

1989-06-01

169

Magnetite-sulfide chondrules and nodules in CK carbonaceous chondrites - Implications for the timing of CK oxidation  

NASA Astrophysics Data System (ADS)

CK carbonaceous chondrites contain rare (about 0.1 vol pct) magnetite-sulfide chondrules that range from about 240 to 500 microns in apparent diameter and have ellipsoidal to spheroidal morphologies, granular textures, and concentric layering. They resemble the magnetite-sulfide nodules occurring inside mafic silicate chondrules in CK chondrites. It seems likely that the magnetite-sulfide chondrules constitute the subset of magnetite-sulfide nodules that escaped as immiscible droplets from their molten silicate chondrule hosts during chondrule formation. The intactness of the magnetite-sulfide chondrules and nodules implies that oxidation of CK metal occurred before agglomeration. Hence, the pervasive silicate darkening of CK chondrites was caused by the shock mobilization of magnetite and sulfide, not metallic Fe-Ni and sulfide as in shock-darkened ordinary chondrites.

Rubin, A. E.

1993-03-01

170

Water loss from olivine hosted melt inclusions  

NASA Astrophysics Data System (ADS)

Water content in melt inclusions has long been used as an important index for the water content of the hosting magma. However, many studies have shown that post-entrapment diffusive re-equilibration can affect the water content of melt inclusions. This process must be considered when using melt inclusions to infer water content of the hosting magma. Theoretical model on the diffusive re-equilibration between melt inclusions and external melts showed that the re-equilibration rate depends on the diffusivity of the re-equilibrating species in the host mineral, the partition coefficient of this species between the host mineral and melt, and the geometry of the melt inclusion and host mineral. The water diffusivity in olivine and water partition coefficient between melt and olivine have been measured by recent studies, therefore the diffusive re-equilibration model can be tested by experiments. In this study, we carried out in-situ Fourier transform infrared spectroscopy (FTIR) measurements on the water content of olivine hosted melt inclusions at high temperatures. Initial water content of the melt inclusions is about 4 wt%. A heating stage system is combined with a microscope FTIR and the absorption spectrum through the olivine and melt inclusion is repeatedly measured. Although the absorption band at around 3540 cm-1 has not be calibrated at high temperatures, it is assumed that the absorbance is linearly related to the total water concentration in the melt inclusion, and the relative water content can be inferred. Cautions have been exercised to maintain a consistent measurement spot such that the thickness of the melt inclusion within the beam path did not change significantly during each experiment. Oxygen fugacity in the heating stage is controlled by Zr purified Ar gas to be about 7 logarithm units below the QFM buffer and about 1 logarithm unit above the QIF buffer at 1473 K. Preliminary results showed that at 1430 and 1581 K, the total water content of the melt inclusion decreased by 80% within about 7 and 1 hours, respectively. This rapid decrease of water content agrees with previous observations. Applying the model and water partition coefficient between olivine and melt by a previous study yields water diffusivities in olivine as 5E-12 and 3E-11 m2/s at 1430 and 1581 K, respectively. These numbers are consistent with the diffusivities measured by a previous study. Due to some experimental difficulties, it is unclear whether bubble existed during the experiments and affected the apparent water content change. Oxygen fugacity may also play a role in water re-equilibration. Further efforts will be made to investigate these aspects and better understand the water re-equilibration process.

Chen, Y.; Provost, A.; Schiano, P.; Cluzel, N.

2009-12-01

171

Nd Isotope Composition in Single Chondrules from the Tieschitz (H3) Chondrite  

NASA Astrophysics Data System (ADS)

Larger-than-average sized chondrules, separated from the Tieschitz (H3) chondrite (sample no. C793), were cleaned ultrasonically several times in double distilled ethanol, then rinsed in ultra clean water, dried, and weighed. The chondrules were then dissolved in a mixture of five parts HF and one part HClO4. An aliquot of 1/10 of the solution was spiked with a Nd tracer. A second aliquot of 2/10 of the solution was put aside. Nd and Sr were separated from the remaining solution by ion-exchange chromatography. The Nd isotopic composition was measured with a single collector thermal ionization mass spectrometer, utilizing NdO^+ ions. After correction for oxygen, the isotopic ratios were normalized to ^146Nd/^144Nd = 0.7219. The results are summarized in Table 1. So far we succeeded in measuring the contents and isotopic ratios of Nd in two individual chondrules. Both yielded a total of about 10 ng Nd each. The ^143Nd/^144Nd ratio of the two chondrules, however, differs from each other with one being close to the chondritic ratio and the second being non-chondritic with remarkably non-radiogenic Nd. In addition, the abundance of ^142Nd is also significantly different in each of these two chondrules. This may indicate the presence of live ^146Sm (half-life = 1.03*10^8 a) during the formation of the solid components, which aggregated into proto-chondrules.

Krestina, N.; Jagoutz, E.; Kurat, G.

1995-09-01

172

I-Xe Dating: The Time Line of Chondrule Formation and Metamorphism in LL Chondrites  

NASA Technical Reports Server (NTRS)

Refractory inclusions, considered to be the oldest solids formed in the solar nebula. (4567.2 0.6 Ma) [1], are common in many carbonaceous and in some ordinary and enstatite chondrites. High-precision Pb- Pb ages for CAI s and chondrules (from different meteorites) suggested that chondrule formation appeared to have started about 2 Ma later than that of CAIs [1]. However, recent 26Al/26Mg data suggest simultaneous formation of CAI s and chondrules in Allende [2]. The I-Xe ages of CAI s in Allende are about 2 Ma younger than the I-Xe ages of Allende chondrules [3] but, like all chronometers, the I-Xe system records closure time of its particular host phase. In the case of Allende CAI s, the major iodine-bearing phase is sodalite, a secondary phase presumably formed by aqueous alteration, so I-Xe reflects the post-formational processes in these objects. In chondrules the iodine host phases vary and can reflect formation and/or alteration but, to put chondrule ages on a quantative basis, some problems should first be addressed.

Pravdivtseva, O. V.; Hohenberg, C. M.; Meshik, A. P.

2005-01-01

173

Shock-Wave Heating Model for Chondrule Formation: Prevention of Isotopic Fractionation  

E-print Network

Chondrules are considered to have much information on dust particles and processes in the solar nebula. It is naturally expected that protoplanetary disks observed in present star forming regions have similar dust particles and processes, so study of chondrule formation may provide us great information on the formation of the planetary systems. Evaporation during chondrule melting may have resulted in depletion of volatile elements in chondrules. However, no evidence for a large degree of heavy-isotope enrichment has been reported in chondrules. In order to meet this observed constraint, the rapid heating rate at temperatures below the silicate solidus is required to suppress the isotopic fractionation. We have developed a new shock-wave heating model taking into account the radiative transfer of the dust thermal continuum emission and the line emission of gas molecules and calculated the thermal history of chondrules. We have found that optically-thin shock waves for the thermal continuum emission from dust particles can meet the rapid heating constraint, because the dust thermal emission does not keep the dust particles high temperature for a long time in the pre-shock region and dust particles are abruptly heated by the gas drag heating in the post-shock region. We have also derived the upper limit of optical depth of the pre-shock region using the radiative diffusion approximation, above which the rapid heating constraint is not satisfied. It is about 1 - 10.

Hitoshi Miura; Taishi Nakamoto

2006-07-03

174

Dissolution of Olivine Promoted by Ion Irradiation  

NASA Astrophysics Data System (ADS)

Recent laboratory simulations of ion irradiation effects on planetary minerals show changes in the surface composition of surfaces that are different depending on whether the analysis is done in-situ (without removing the sample from vacuum) or ex-situ using an electron microscope. We found that olivine samples that have been irradiated by keV ions show preferential loss of magnesium when exposed to water. Irradiations were done with 4 keV argon ions to fluences between 1015 and 1018 ions/cm2. Soak times in high purity water ranged from minutes to days, and exhibit the same degree of Mg depletion, independent of soak time. The concentration of magnesium on the surface of irradiated natural olivine decreases by 40% upon contact with water, as measured with x-ray photoelectron spectroscopy. This finding is important for laboratory simulations of regolith processes and for establishing procedures for the handling of irradiated samples, including those from sample return missions.

Cantando, E. D.; Dukes, C. A.; Baragiola, R. A.

2006-12-01

175

Magnesium isotopic systematics of chondrules and CAIs from Allende, Murchison, Murray and Bjurbole. F.-, M. Wadhwa1,  

E-print Network

Magnesium isotopic systematics of chondrules and CAIs from Allende, Murchison, Murray and Bjurbole: Magnesium isotopic analyses were performed at the Isotope Geochemistry Labora- tory of the Field Museum

Grossman, Lawrence

176

Manganese olivine II: point defect relaxation  

Microsoft Academic Search

To investigate the point defect chemistry and the kinetic properties of manganese olivine Mn2SiO4, the point defect relaxation time (tau) characterizing the rate of re-equilibration of electrical conductivity following a change in oxygen fugacity was measured for single crystals oriented for electrical conduction along the [010] direction. The experiments were carried out at temperatures T = 1173-1473 K and oxygen

Q. Bai; Z.-C. Wang; D. L. Kohlstedt

1998-01-01

177

Manganese olivine II: point defect relaxation  

Microsoft Academic Search

To investigate the point defect chemistry and the kinetic properties of manganese olivine Mn2SiO4, the point defect relaxation time (?) characterizing the rate of re-equilibration of electrical conductivity following a\\u000a change in oxygen fugacity was measured for single crystals oriented for electrical conduction along the [010] direction. The\\u000a experiments were carried out at temperatures T?=?11731473?K and oxygen fugacities with the

Q. Bai; Z.-C. Wang; D. L. Kohlstedt

1998-01-01

178

Mechanisms of electrical conductivity in olivine  

SciTech Connect

Data on the electrical conductivity and the thermoelectric effect in single crystals indicate that the charge conduction mechanism in pure magnesium forsterite is electrons. The concentration of electrons can be varied by controlling the number of oxygen vacancies through manipulation of the oxygen pressure. For iron bearing olivine, the conduction mechanism is by electron holes localized on an iron ion. Since iron strongly affects the creep process as well, oxidation of iron is probably accompanied by the production of magnesium vacancies. 15 references.

Schock, R.N.; Duba, A.G.; Shankland, T.J.

1984-01-01

179

Bleached chondrules: Evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites  

USGS Publications Warehouse

We present the first detailed study of a population of texturally distinct chondrules previously described by Kurat (1969), Christophe Michel-Levy (1976), and Skinner et al. (1989) that are sharply depleted in alkalis and Al in their outer portions. These 'bleached' chondrules, which are exclusively radial pyroxene and cryptocrystalline in texture, have porous outer zones where mesostasis has been lost. Bleached chondrules are present in all type 3 ordinary chondrites and are present in lower abundances in types 4-6. They are most abundant in the L and LL groups, apparently less common in H chondrites, and absent in enstatite chondrites. We used x-ray mapping and traditional electron microprobe techniques to characterize bleached chondrules in a cross section of ordinary chondrites. We studied bleached chondrules from Semarkona by ion microprobe for trace elements and H isotopes, and by transmission electron microscopy. Chondrule bleaching was the result of low-temperature alteration by aqueous fluids flowing through fine-grained chondrite matrix prior to thermal metamorphism. During aqueous alteration, interstitial glass dissolved and was partially replaced by phyllosilicates, troilite was altered to pentlandite, but pyroxene was completely unaffected. Calcium-rich zones formed at the inner margins of the bleached zones, either as the result of the early stages of metamorphism or because of fluid-chondrule reaction. The mineralogy of bleached chondrules is extremely sensitive to thermal metamorphism in type 3 ordinary chondrites, and bleached zones provide a favorable location for the growth of metamorphic minerals in higher petrologic types. The ubiquitous presence of bleached chondrules in ordinary chondrites implies that they all experienced aqueous alteration early in their asteroidal histories, but there is no relationship between the degree of alteration and metamorphic grade. A correlation between the oxidation state of chondrite groups and their degree of aqueous alteration is consistent with the source of water being either accreted ices or water released during oxidation of organic matter. Ordinary chondrites were probably open systems after accretion, and aqueous fluids may have carried volatile elements with them during dehydration. Individual radial pyroxene and cryptocrystalline chondrules were certainly open systems in all chondrites that experienced aqueous alteration leading to bleaching.

Grossman, J.N.; Alexander, C.M. O'D.; Wang, J.; Brearley, A.J.

2000-01-01

180

Vapor pressures and evaporation coefficients for melts of ferromagnesian chondrule-like compositions  

NASA Astrophysics Data System (ADS)

To determine evaporation coefficients for the major gaseous species that evaporate from silicate melts, the Hertz-Knudsen equation was used to model the compositions of residues of chondrule analogs produced by evaporation in vacuum by Hashimoto [Hashimoto A. (1983) Evaporation metamorphism in the early solar nebula-evaporation experiments on the melt FeO-MgO-SiO 2-CaO-Al 2O 3 and chemical fractionations of primitive materials. Geochem. J. 17, 111-145] and Wang et al. [Wang J., Davis A. M., Clayton R. N., Mayeda T. K., Hashimoto A. (2001) Chemical and isotopic fractionation during the evaporation of the FeO-MgO-SiO 2-CaO-Al 2O 3-TiO 2 rare earth element melt system. Geochim. Cosmochim. Acta 65, 479-494], in vacuum and in H 2 by Yu et al. [Yu Y., Hewins R. H., Alexander C. M. O'D., Wang J. (2003) Experimental study of evaporation and isotopic mass fractionation of potassium in silicate melts. Geochim. Cosmochim. Acta 67, 773-786], and in H 2 by Cohen et al. [Cohen B. A., Hewins R. H., Alexander C. M. O'D. (2004) The formation of chondrules by open-system melting of nebular condensates. Geochim. Cosmochim. Acta 68, 1661-1675]. Vapor pressures were calculated using the thermodynamic model of Ghiorso and Sack [Ghiorso M. S., Sack R. O. (1995) Chemical mass transfer in magmatic processes IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures. Contrib. Mineral. Petrol. 119, 197-212], except for the late, FeO-free stages of the Wang et al. (2001) and Cohen et al. (2004) experiments, where the CMAS activity model of Berman [Berman R. G. (1983) A thermodynamic model for multicomponent melts, with application to the system CaO-MgO-Al 2O 3-SiO 2. Ph.D. thesis, University of British Columbia] was used. From these vapor pressures, evaporation coefficients ( ?) were obtained that give the best fits to the time variation of the residue compositions. Evaporation coefficients derived for Fe (g), Mg (g), and SiO (g) from the Hashimoto (1983) experiments are similar to those found by Alexander [Alexander C. M. O'D. (2004) Erratum. Meteoritics Planet. Sci. 39, 163] in his EQR treatment of the same data and also adequately describe the FeO-bearing stages of the Wang et al. (2001) experiments. From the Yu et al. (2003) experiments at 1723 K, ?Na = 0.26 0.05, and ?K = 0.13 0.02 in vacuum, and ?Na = 0.042 0.020, and ?K = 0.017 0.002 in 9 10 -5 bar H 2. In the FeO-free stages of the Wang et al. (2001) experiments, ?Mg and ?SiO are significantly different from their respective values in the FeO-bearing portions of the same experiments and from the vacuum values obtained at the same temperature by Richter [Richter F. M., Davis A. M., Ebel D. S., Hashimoto A. (2002) Elemental and isotopic fractionation of Type B calcium-, aluminum-rich inclusions: experiments, theoretical considerations, and constraints on their thermal evolution. Geochim. Cosmochim. Acta 66, 521-540] for CMAS compositions much lower in MgO. When corrected for temperature, the values of ?Mg and ?SiO that best describe the FeO-free stages of the Wang et al. (2001) experiments also adequately describe the FeO-free stage of the Cohen et al. (2004) H 2 experiments, but ?Fe that best describes the FeO-bearing stage of the latter experiment differs significantly from the temperature-corrected value derived from the Hashimoto (1983) vacuum data.

Fedkin, A. V.; Grossman, L.; Ghiorso, M. S.

2006-01-01

181

Turbulent Size Selection and Concentration of Chondrule-Sized Objects: Reynolds Number Invariance and Implications  

NASA Technical Reports Server (NTRS)

It is generally agreed that individual chondrules formed as entities in a gaseous nebula prior to being accumulated into a meteorite parent body, within which they incur various forms of modification before arriving in our labs. While there are major unanswered questions about the properties of the nebula environment in which chondrules formed, the process by which the most primitive meteorites are formed overwhelmingly from chondrules must then be an aspect of "nebula processing". Textures in certain fragments of primitive meteorites might be summarized as being primarily chondrules and clastic, chondrule-sized, fragments of other minerals, each covered with a rim of fine dust with physical and chemical properties which are essentially independent of the composition and mineralogy of the underlying chondrule. This (unfortunately rather rare) texture was called "primary accretionary texture" to reflect their belief that it precedes subsequent stages in which fragmentation, comminution, mixing, heating, and other forms of alteration occur on the parent body(-ies). The size distribution of these chondrules and fragments, and the properties of their dusty rims, are key clues regarding the primary nebula accretion process. Even in the much more abundant meteorites which have clearly suffered internal mixing, abrasion, grinding, and even mineralogical alteration or replacement (due presumably to the collisional growth and heating process itself), key chondrule properties such as mean size and density remain relatively well defined, and well defined rims persist in many cases. It has been our goal to infer the key nebula processes indirectly from the properties of these very earliest primitive meteorites by making use of a theoretical framework in which the nebula possesses a plausible level of isotropic turbulence. We have shown that turbulence has the property of concentrating one particular particle size by orders of magnitude, where the preferentially concentrated size depends primarily on the intensity of the turbulent kinetic energy (represented by the Reynolds number of the nebula). Specifically, the preferentially concentrated particle is that which has a stopping time equal to the turnover time of the smallest eddy. The intensity level of turbulence implied by chondrule sizes can be maintained by even a small fraction of the energy released by the radially evolving disk (it must be noted that the details of how this transfer of energy actually occurs remain obscure, however).

Cuzzi, J. N.; Hogan, R.; Dobrovolskis, A.; Paque, J.

2006-01-01

182

Water and Carbon Dioxide Adsorption at Olivine Surfaces  

SciTech Connect

Plane-wave density functional theory (DFT) calculations were performed to simulate water and carbon dioxide adsorption at the (010) surface of five olivine minerals, namely, forsterite (Mg2SiO4), calcio-olivine (Ca2SiO4), tephroite (Mn2SiO4), fayalite (Fe2SiO4), and Co-olivine (Co2SiO4). Adsorption energies per water molecule obtained from energy minimizations varied from -78 kJ mol-1 for fayalite to -128 kJ mol-1 for calcio-olivine at sub-monolayer coverage and became less exothermic as coverage increased. In contrast, carbon dioxide adsorption energies at sub-monolayer coverage ranged from -20 kJ mol-1 for fayalite to -59 kJ mol-1 for calcio-olivine. Therefore, the DFT calculations show a strong driving force for carbon dioxide displacement by water at the surface of all olivine minerals in a competitive adsorption scenario. Additionally, adsorption energies for both water and carbon dioxide were found to be more exothermic for the alkaline-earth (AE) olivines than for the transition-metal (TM) olivines and to not correlate with the solvation enthalpies of the corresponding divalent cations. However, a correlation was obtained with the charge of the surface divalent cation indicating that the more ionic character of the AE cations in the olivine structure relative to the TM cations leads to greater interactions with adsorbed water and carbon dioxide molecules at the surface and thus more exothermic adsorption energies for the AE olivines. For calcio-olivine, which exhibits the highest divalent cation charge of the five olivines, ab initio molecular dynamics simulations showed that this effect leads both water and carbon dioxide to react with the surface and form hydroxyl groups and a carbonate-like species, respectively.

Kerisit, Sebastien N.; Bylaska, Eric J.; Felmy, Andrew R.

2013-11-14

183

Young chondrules in CB chondrites from a giant impact in the early Solar System.  

PubMed

Chondrules, which are the major constituent of chondritic meteorites, are believed to have formed during brief, localized, repetitive melting of dust (probably caused by shock waves) in the protoplanetary disk around the early Sun. The ages of primitive chondrules in chondritic meteorites indicate that their formation started shortly after that of the calcium-aluminium-rich inclusions (4,567.2 +/- 0.7 Myr ago) and lasted for about 3 Myr, which is consistent with the dissipation timescale for protoplanetary disks around young solar-mass stars. Here we report the 207Pb-206Pb ages of chondrules in the metal-rich CB (Bencubbin-like) carbonaceous chondrites Gujba (4,562.7 +/- 0.5 Myr) and Hammadah al Hamra 237 (4,562.8 +/- 0.9 Myr), which formed during a single-stage, highly energetic event. Both the relatively young ages and the single-stage formation of the CB chondrules are inconsistent with formation during a nebular shock wave. We conclude that chondrules and metal grains in the CB chondrites formed from a vapour-melt plume produced by a giant impact between planetary embryos after dust in the protoplanetary disk had largely dissipated. These findings therefore provide evidence for planet-sized objects in the earliest asteroid belt, as required by current numerical simulations of planet formation in the inner Solar System. PMID:16107841

Krot, Alexander N; Amelin, Yuri; Cassen, Patrick; Meibom, Anders

2005-08-18

184

Experimental Determination of Scattering Matrices of Olivine  

NASA Astrophysics Data System (ADS)

Mid- and far-infrared spectra have provided striking evidence for the presence of crystalline olivine in comets, circumstellar envelopes and planetary nebulae. In many cases the light scattering properties of these particles are required for the interpretation of observations of these objects. Since many data on the scattering behaviour of irregular mineral particles in general, and of crystalline olivine in particular, are lacking in the literature, we have measured the whole scattering matrix as a function of the scattering angle of a sample of Olivine (Mg2yFe_{2-2y}SiO4 y=0.9) at two wavelengths (633nm and 442nm). In our experimental setup we use a laser as a light source. This light is scattered by randomly oriented particles located in a jet stream. We employ polarization modulation in combination with lock-in detection to obtain all elements of the four-by-four Mueller matrix (Fij), which describes the scattering process. The elements depend on the wavelength of the laser light, the scattering angle as well as size, shape and complex refractive index of the particles. The sample has been prepared so that the measurements have been repeated for three different size distributions: d=6, 32 and 100 microns respectively, where d is the median diameter for volume equivalent spheres. One of the interesting results pertains to the element ratio -F21/F11, which equals the degree of linear polarization for unpolarized incident light. This shows negative values at angles close to the backward direction for the three size distributions and at both wavelengths. Such negative polarization has been observed for many objects in the Solar System. We intend to compare the measured matrix elements with calculated elements using the T-matrix method.

Munoz, O.; Volten, H.; Vermeulen, K.; de Haan, J. F.; Vassen, W.; Hovenier, J. W.

1999-09-01

185

Discovery of Olivine in the Nili Fossae Region of Mars  

USGS Publications Warehouse

We have detected a 30,000-square-kilometer area rich in olivine in the Nili Fossae region of Mars. Nili Fossae has been interpreted as a complex of grabens and fractures related to the formation of the Isidis impact basin. We propose that post-impact faulting of this area has exposed subsurface layers rich in olivine. Linear mixture analysis of Thermal Emission Spectrometer spectra shows surface exposures of 30% olivine, where the composition of the olivine ranges from Fo30 to Fo70.

Hoefen, T.M.; Clark, R.N.; Bandfield, J.L.; Smith, M.D.; Pearl, J.C.; Christensen, P.R.

2003-01-01

186

A scanning electron microscope study of olivine crystal surfaces  

NASA Technical Reports Server (NTRS)

SEM photographs were taken of euhedral olivine grains from the Murchison C2 chondrite and several terrestrial and lunar occurrences. In general, the crystal faces of the meteorite grains are rough and uneven, with irregular growth patterns. They are very similar to crystal faces on terrestrial olivine grains that formed by sublimation from a vapor phase. They are very different from the relatively smooth and featureless surfaces of magmatic olivine crystals that precipitated from igneous melts. Qualitatively, the surface morphology of the crystal supports the contention that many euhedral crystals of olivine in C2 meteorites condensed from a gas phase.

Olsen, E. J.; Grossman, L.

1974-01-01

187

2D Size Distribution of Chondrules and Chondritic Fragments of an Ordinary Chondrite from Lut Desert (Iran)  

NASA Astrophysics Data System (ADS)

2D size measurement of chondrules and chondiritic fragments of a meteorite from Lut desert of Iran is conducted. Chondrules exhibit a size range of 551800 m (average 437 m). Chondiritic fragments show a size range of 461220 m (average 261 m).

Pourkhorsandi, H.; Mirnejad, H.

2014-09-01

188

February 21, 2012 ---Isotopic measurements of a chondrule in a Comet Wild 2 grain tell the story of  

E-print Network

of outward migration of solar nebula solids, helping to set the formation age of Jupiter. Written by Linda M, but also about the dynamics in the solar nebula that brought the comet's materials together. Ryan Ogliore, they determined this chondrule formed relatively late (as chondrules go) in the inner solar nebula and moved out

189

VAPOR PRESSURES AND EVAPORATION COEFFICIENTS OF FE, NA AND K OVER CHONDRULE COMPOSITION MELTS. A. V. Fedkin1  

E-print Network

VAPOR PRESSURES AND EVAPORATION COEFFICIENTS OF FE, NA AND K OVER CHONDRULE COMPOSITION MELTS. A. V and isotopic evidence of significant evaporative losses from chondrules is rare. The free evaporation flux and evaporation coefficient of species x, resp., R is the gas constant and T is the temperature. Thus, computation

Grossman, Lawrence

190

S1. Modal olivine abundances of diogenites Most diogenites contain some olivine, usually <5 vol%31  

E-print Network

of such areas vary for the two scenarios. Multispectral images obtained with Hubble Space Telescope (HST) have rotational spectral variations observed with ground-based telescopes3 and two possible maps of the major hemisphere and dominated by more diogenitic minerals. S3. Exogenic source Delivery of olivine by impacts

Cai, Long

191

Mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions.  

PubMed

Primitive or undifferentiated meteorites (chondrites) date back to the origin of the Solar System, and thus preserve a record of the physical and chemical processes that occurred during the earliest evolution of the accretion disk surrounding the young Sun. The oldest Solar System materials present within these meteorites are millimetre- to centimetre-sized calcium-aluminium-rich inclusions (CAIs) and ferromagnesian silicate spherules (chondrules), which probably originated by thermal processing of pre-existing nebula solids. Chondrules are currently believed to have formed approximately 2-3 million years (Myr) after CAIs (refs 5-10)--a timescale inconsistent with the dynamical lifespan of small particles in the early Solar System. Here, we report the presence of excess (26)Mg resulting from in situ decay of the short-lived (26)Al nuclide in CAIs and chondrules from the Allende meteorite. Six CAIs define an isochron corresponding to an initial (26)Al/(27)Al ratio of (5.25 +/- 0.10) x 10(-5), and individual model ages with uncertainties as low as +/- 30,000 years, suggesting that these objects possibly formed over a period as short as 50,000 years. In contrast, the chondrules record a range of initial (26)Al/(27)Al ratios from (5.66 +/- 0.80) to (1.36 +/- 0.52) x 10(-5), indicating that Allende chondrule formation began contemporaneously with the formation of CAIs, and continued for at least 1.4 Myr. Chondrule formation processes recorded by Allende and other chondrites may have persisted for at least 2-3 Myr in the young Solar System. PMID:15372023

Bizzarro, Martin; Baker, Joel A; Haack, Henning

2004-09-16

192

Geobarometry of ultramafic xenoliths from Loihi Seamount, Hawaii, on the basis of CO2 inclusions in olivine  

USGS Publications Warehouse

Abundant fluid inclusions in olivine of dunite xenoliths (???1-3 cm) in basalt dredged from the young Loihi Seamount, 30 km southeast of Hawaii, are evidence for three coexisting immiscible fluid phases-silicate melt (now glass), sulfide melt (now solid), and dense supercritical CO2 (now liquid + gas)-during growth and later fracturing of some of these olivine crystals. Some olivine xenocrysts, probably from disaggregation of xenoliths, contain similar inclusions. Most of the inclusions (2-10 ??m) are on secondary planes, trapped during healing of fractures after the original crystal growth. Some such planes end abruptly within single crystals and are termed pseudosecondary, because they formed during the growth of the host olivine crystals. The "vapor" bubble in a few large (20-60 ??m), isolated, and hence primary, silicate melt inclusions is too large to be the result of simple differential shrinkage. Under correct viewing conditions, these bubbles are seen to consist of CO2 liquid and gas, with an aggregate ??{variant} = ??? 0.5-0.75 g cm-3, and represent trapped globules of dense supercritical CO2 (i.e., incipient "vesiculation" at depth). Some spinel crystals enclosed within olivine have attached CO2 blebs. Spherical sulfide blebs having widely variable volume ratios to CO2 and silicate glass are found in both primary and pseudosecondary inclusions, demonstrating that an immiscible sulfide melt was also present. Assuming olivine growth at ??? 1200??C and hydrostatic pressure from a liquid lava column, extrapolation of CO2 P-V-T data indicates that the primary inclusions were trapped at ??? 220-470 MPa (2200-4700 bars), or ??? 8-17 km depth in basalt magma of ??{variant} = 2.7 g cm-3. Because the temperature cannot change much during the rise to eruption, the range of CO2 densities reveals the change in pressure from that during original olivine growth to later deformation and rise to eruption on the sea floor. The presence of numerous decrepitated inclusions indicates that the inclusion sample studied is biased by the loss of higher-density inclusions and suggests that some part of these olivine xenoliths formed at greater depths. ?? 1983.

Roedder, E.

1983-01-01

193

Chondrules with peculiar REE patterns: implications for solar nebular condensation at high C/O.  

PubMed

Rare earth element (REE) data from two ordinary chondrite chondrules show distinct negative chondrite-normalized concentration anomalies of samarium, europium, and ytterbium. The peculiar patterns may be the result of REE gas/solid fractionation at an oxygen fugacity lower than has been assumed for the canonical solar nebula. We suggest that the two ordinary chondrite chondrules acquired the fractionated REE patterns by incorporation of highly reduced, ultrarefractory condensates in their precursors. This interpretation implies that high-temperature condensation processes occurred in nebular environments with a strong deficit in oxygen, such as regions with an enhanced carbon/oxygen ratio. PMID:14963326

Pack, Andreas; Shelley, J Michael G; Palme, Herbert

2004-02-13

194

A proposed origin for chondrule-forming shocks in the solar nebula  

E-print Network

We propose that the nebular shocks currently favored as a model to form chondrules and other annealed silicates in the solar nebula originate in the dynamical activity present in the envelope of forming Jovian planets. In contrast to the classic `core accretion model', our 3D hydrodynamic simulations show that this envelope is not a 1D hydrostatic structure but is instead vigorously active and contains densities and temperatures that appear similar in magnitude and spatial extent to those thought to be responsible for the production of chondrules.

Andrew F. Nelson; Maximilian Ruffert

2005-10-13

195

Iodine-xenon studies of petrographically and chemically characterized Chainpur chondrules  

NASA Technical Reports Server (NTRS)

INAA, noble gas, and petrographic studies conducted on samples of 18 chondrules and matric material from the Chainpur (LL3) indicate that the I-129/I-127 ratio, R(0), varies by a factor of more than 10 among the chondrules. This corresponds to a greater-than-50 Ma span in apparent I-Xe ages. Models which invoke either gas-dust mixing or nebular heterogeneity cannot satisfactorily explain these data, any more than can hypotheses which attribute the variations to differences in formation age, metamorphic rate, or time of aqueous alteration. It is alternatively suggested that the variations represent periods of low-grade shock events.

Swindle, T. D.; Caffee, M. W.; Hohenberg, C. M.; Lindstrom, M. M.; Taylor, G. J.

1991-01-01

196

The origin of chromitic chondrules and the volatility of Cr under a range of nebular conditions  

NASA Technical Reports Server (NTRS)

We characterize ten chromatic chondrules, two spinelian chondrules andd one spinel-bearing chondrule and summarize data for 120 chromitic inclusions discovered in an extensive survey of ordinary chondrites. Compositional and petrographic evidence suggests that chromitic chondrules and inclusions are closely related. The Cr/(Cr + Al) ratios in the spinal of these objects range from 0.5 to 0.9 and bulk Al2O3 contents are uniformly high (greater than 10 wt%, except for one with 8 wt%). No other elements having comparable solar abundances are so stongly enriched, and alkali feldspar and merrillite are more common than in normal chondrules. The Cr/Mg ratios in chromitic chondrules are 180-750 times the ratios in the bulk chondrite. With the possible exception of magnetic clumping of chromite in the presolar cloud, mechanical processes cannot account for this enrichment. Examination of nebular equilibrium processes shows that 50%-condensation temperatures of Cr at pH2/pH2O of 1500 are several tens of degrees below those of Mg as Mg2SiO4; the condensation of Cr is primarily as MgCr2O4 dissolved in MgAl2O4 at nebular pressures of 10(exp -4) atm or below. At pH2 = 10(exp -3) atm condesation as Cr in Fe-Ni is favored. Making the nebula much more oxidizing reduces the difference in condensation temperatures but Mg remains more refractory. We conclude that nebular equilibrium processes are not responsible for the enhanced Cr/Mg ratios. We propose that both Cr and Al became enriched in residues formed by incomplete evaporation of presolar lumps. We suggest that spinals remained as solid phases when the bulk of the silicates were incorporated into the evaporating melt; vaporization of Al and Cr were inhibited by the slow kinetics of diffusion. Subsequent melting and crystallization of these residues fractionated Cr from Al. The resulting materials constituted major components in the precursors of chromitic chondrules. Our model implies that chromitic chondrules and inclusions preserve the Cr isotopic record of presolar sources.

Krot, Alexander; Ivanova, Marina A.; Wasson, John T.

1993-01-01

197

Mn-Cr isotopic systematics of Chainpur chondrules and bulk ordinary chondrites  

NASA Technical Reports Server (NTRS)

We report on ongoing study of the Mn-Cr systematics of individual Chainpur (LL3.4) chondrules and compare the results to those for bulk ordinary chondrites. Twenty-eight chondrules were surveyed for abundances of Mn, Cr, Na, Fe, Sc, Hf, Ir, and Zn by INAA. Twelve were chosen for SEM/EDX and high-precision Cr-isotopic studies on the basis of LL-chondrite-normalized Mn(LL), Sc(LL), (Mn/Fe)(LL), and (Sc/Fe)(LL) as well as their Mn/Cr ratios. Classification into textural types follows from SEM/EDX examination of interior surfaces.

Nyquist, L.; Lindstrom, D.; Wiesmann, H.; Bansal, B.; Shih, C.-Y.; Mittlefehldt, D.; Martinez, R.; Wentworth, S.

1994-01-01

198

A secondary origin of chondrule magnetization in the Allende CV carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

Magnetic fields in the solar nebula may have played a key role in the radial transport of angular momentum and mass during the early accretional phase of the solar system. Chondrules and many calcium aluminum inclusions (CAIs), millimeter sized silicate objects found in most chondritic meteorites, were heated to high temperatures and cooled in the nebula and therefore may have recorded a thermoremanent magnetization (TRM) from the nebula field. Additionally, primitive magnetization in chondrules and CAIs may yield constraints about their mode of formation. However, any such primary magnetization may have been significantly altered during subsequent metamorphism and aqueous alteration on the parent asteroid. We performed two tests to determine the nebular origins of remanent magnetization in chondrules and refractory inclusions in the Allende CV3 carbonaceous chondrite: 1) a classic paleomagnetic conglomerate test to identify post-accretional remagnetization events and 2) a unidirectionality test of subsamples taken from individual chondrules and CAIs. We conducted individual measurements of mutually oriented chondrules, CAIs, and matrix as well as SQUID microscope maps of the magnetic fields of 30 ?m thin sections. All samples and thin sections were mutually oriented to within 5. Our results confirm previous findings that all subsamples of the meteorite carry a unidirectional overprint blocked up to 260-290C (MT component). Chondrules and CAIs also carry a higher temperature (HT) remanence oriented in scattered directions unrelated to the direction of the MT overprint. We have confirmed that this HT magnetization is not an artifact of the demagnetization procedure but is a preterrestrial component. Measurements of subsamples of single chondrules and CAIs show that the HT magnetization is not unidirectional within each inclusion. Petrographic data suggests that most magnetic minerals in Allende were the product of parent body alteration. These facts suggest that the magnetization in Allende chondrules and CAIs is not a preaccretional TRM and is unlikely to record the nebular field. We suggest that preaccretional remanence in Allende material was destroyed by aqueous alteration and metasomatism, which was followed or coincident with metamorphism that introduced the MT overprint. The HT component we detect may represent a chemical remanent magnetization (CRM) acquired during aqueous alteration.

Carporzen, L.; Fu, R.; Andrade Lima, E.; Weiss, B. P.

2011-12-01

199

Olivine in an unexpected location on Vesta's surface.  

PubMed

Olivine is a major component of the mantle of differentiated bodies, including Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta, which is the lone surviving, large, differentiated, basaltic rocky protoplanet in the Solar System. Only a few of these meteorites, the orthopyroxene-rich diogenites, contain olivine, typically with a concentration of less than 25 per cent by volume. Olivine was tentatively identified on Vesta, on the basis of spectral and colour data, but other observations did not confirm its presence. Here we report that olivine is indeed present locally on Vesta's surface but that, unexpectedly, it has not been found within the deep, south-pole basins, which are thought to be excavated mantle rocks. Instead, it occurs as near-surface materials in the northern hemisphere. Unlike the meteorites, the olivine-rich (more than 50 per cent by volume) material is not associated with diogenite but seems to be mixed with howardite, the most common surface material. Olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the olivine exposures and the absence of associated diogenite favour a mantle source, but the exposures are located far from the deep impact basins. The amount and distribution of observed olivine-rich material suggest a complex evolutionary history for Vesta. PMID:24196707

Ammannito, E; De Sanctis, M C; Palomba, E; Longobardo, A; Mittlefehldt, D W; McSween, H Y; Marchi, S; Capria, M T; Capaccioni, F; Frigeri, A; Pieters, C M; Ruesch, O; Tosi, F; Zambon, F; Carraro, F; Fonte, S; Hiesinger, H; Magni, G; McFadden, L A; Raymond, C A; Russell, C T; Sunshine, J M

2013-12-01

200

Olivine in the Southern Isidis Basin  

NASA Technical Reports Server (NTRS)

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) took this observation of the transition region between Libya Montes and the Isidis Basin on Mars at 17:16 UTC (12:16 p.m. EST) on January 2, 2007, near 3.6 degrees north latitude, 84.1 degrees east longitude. The image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 18 meters (60 feet) across. The image is about 11 kilometers (7 miles) wide at its narrowest point.

The Isidis Basin resulted from of a gigantic impact on the surface of Mars early in the planet's history. The southern rim, where this target is located, is a region of complex geology and part of the planetary dichotomy boundary that separates the older southern highlands from the lower, younger northern plains. The image on the left was constructed from three visible wavelengths (RGB: 0.71, 0.60, 0.53 microns) and is a close approximation of how the surface would appear to the human eye. The image on the right was constructed from three infrared wavelengths (RGB: 2.49, 1.52, 1.08 microns) chosen to highlight variations in the mineralogy of the area. Of interest is that features in this image not only differ in color, but also in texture and morphology. The gray areas absorb similarly at all wavelengths used in this image, but display absorptions at other wavelengths related to the iron- and magesium-rich mineral pyroxene. The reddest areas absorb strongly at the wavelengths used for green and blue, which is attributable to another iron- and magesium-rich mineral, olivine. The brownish areas show subdued mineral absorptions and could represent some type of mixture between the other two materials. The presence of the mineral olivine is particularly interesting because olivine easily weathers to other minerals; thus, its presence indicates either the lack of weathering in this region or relatively recent exposure.

CRISM's mission: Find the spectral fingerprints of aqueous and hydrothermal deposits and map the geology, composition and stratigraphy of surface features. The instrument will also watch the seasonal variations in Martian dust and ice aerosols, and water content in surface materials -- leading to new understanding of the climate.

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.

2007-01-01

201

Did Ordinary Chondrite Impactors Deliver Olivine to Vesta?  

NASA Astrophysics Data System (ADS)

Ground-based and Hubble Space Telescope observations of asteroid Vesta suggested the presence of olivine. However, subsequent analysis of data from NASAs Dawn mission proved that this olivine-bearing unit, identified as Oppia crater and its ejecta blanket, was composed of HED impact melt rather than olivine. The lack of widespread olivine in the 19 km deep Rheasilvia basin on the South Pole suggests that the crust-mantle boundary was not breached during the formation of the basin, and that Vestas crust is thicker than originally anticipated. Recently, local-scale olivine units have been reported in the walls and ejecta of two craters, Arruntia and Bellicia, located in the northern hemisphere of Vesta, 350-430 km from the Rheasilvia basin (Ammannito et al., 2013). These units were interpreted as exposed plutons by Clenet et al. (2014) rather than of mantle origin excavated during the formation of the Rheasilvia basin. We explored alternative sources for these olivine-rich units by reanalyzing the data published by Ammannito et al. (2013). Our mineralogical analysis gives olivine abundance between 70-80 vol.% consistent with those obtained previously (>60%). The pyroxene ferrosilite content and olivine abundance of the olivine-rich units are similar to ordinary chondrites. Meteoritic evidence suggests contamination of HEDs by several ordinary chondrite impactors including H, L and LL chondrites. This includes howardite JaH 556, which contains ~20 vol.% H chondrite material mixed with HED impact melt. Based on the non-diagnostic curve match and detailed mineralogical analysis using diagnostic spectral band parameters, we conclude that the olivine units in the northern hemisphere of Vesta could be explained by the delivery of exogenic H/L chondrite material rather than being a product of planetary differentiation.

Le Corre, Lucille; Reddy, Vishnu; Sanchez, Juan A.; Cloutis, Edward A.; Izawa, Matthew R.; Mann, Paul

2014-11-01

202

Cotectic proportions of olivine and spinel in olivine-tholeiitic basalt and evaluation of pre-eruptive processes  

USGS Publications Warehouse

The volume %, distribution, texture and composition of coexisting olivine, Cr-spinel and glass has been determined in quenched lava samples from Hawaii, Iceland and mid-oceanic ridges. The volume ratio of olivine to spinel varies from 60 to 2800 and samples with >0.02% spinel have a volume ratio of olivine to spinel of approximately 100. A plot of wt % MgO vs ppm Cr for natural and experimental basaltic glasses suggests that the general trend of the glasses can be explained by the crystallization of a cotectic ratio of olivine to spinel of about 100. One group of samples has an olivine to spinel ratio of approximately 100, with skeletal olivine phenocrysts and small (100 ??m) spinel crystals that show evidence of two stages of growth, and a volume ratio of olivine to spinel of 100 to well over 1000. The olivine and spinel in this group have crystallized more slowly with little physical interaction, and show evidence that they have accumulated in a magma chamber. ?? 2006 Oxford University Press.

Roeder, P.; Gofton, E.; Thornber, C.

2006-01-01

203

Volatile fractionation in the early solar system and chondrule matrix complementarity  

E-print Network

. Although volatile depletion was the most fundamental chemical process affecting the inner solar nebula Carbonaceous chondrites were first recognized as primitive samples of the early solar nebula in the 1960s, whenVolatile fractionation in the early solar system and chondrule matrix complementarity Philip A

Demouchy, Sylvie

204

THE FORMATION OF PHYLLOSILICATES IN CHONDRULE FORMING SHOCK WAVES. F. J. Ciesla,1  

E-print Network

that forms chondrules in an icy portion of the solar nebula. As the ice particles evaporate, we track, is stable below 225 K in the canonical solar nebula [5]. However, kinetic considerations suggest that the rate of serpentine formation is too slow to occur within the lifetime of the solar nebula under

Cohen, Barbara Anne

205

Non-nebular origin of dark mantles around chondrules and inclusions in CM chondrites  

Microsoft Academic Search

Our examination of nine CM chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in CM chondrites are not discrete fine-grained rims acquired in the solar nebula as modeled by Metzler et al. [Accretionary dust mantles in CM chondrites: evidence for solar nebula processes. Geochim. Cosmochim. Acta56, 1992, 2873

Josep M. Trigo-Rodriguez; Alan E. Rubin; John T. Wasson

2006-01-01

206

Vapor pressures and evaporation coefficients for melts of ferromagnesian chondrule-like compositions  

E-print Network

Vapor pressures and evaporation coefficients for melts of ferromagnesian chondrule in revised form 17 August 2005 Abstract To determine evaporation coefficients for the major gaseous species that evaporate from silicate melts, the Hertz­Knudsen equation was used to model the compositions of residues

Grossman, Lawrence

207

MODEL EVAPORATION OF CHONDRULE PRECURSORS IN NEBULAR SHOCKS. A. V. Fedkin1 Grossman1,2  

E-print Network

MODEL EVAPORATION OF CHONDRULE PRECURSORS IN NEBULAR SHOCKS. A. V. Fedkin1 , L. Grossman1,2 and M, Seattle, WA 98115. Introduction: It is widely accepted that evaporation of such elements as S, Na, K, Fe evaporation [2]; re-introduction of nearly completely volatilized elements either by back- reaction

Grossman, Lawrence

208

Chondrule Precursors: The Nature of the S- and Ni-bearing Phases(s)  

Microsoft Academic Search

Lauretta and Fegley showed that troilite made by S condensation on kamacite should include a significant amount of Ni, but they reported being unsuccessful in their search for Ni-bearing troilite in chondrites. We show the various opaque associations (OAs) found in veneers around chondrules in primitive and less primitive chondrites to be the result of parent body decomposition under different

B. Zanda; M. Bourot-Denise; R. H. Hewins

1996-01-01

209

The evolution of enstatite and chondrules in unequilibrated enstatite chondrites: Evidence from iron-rich pyroxene  

NASA Technical Reports Server (NTRS)

FeO-rich (Fs(sub 6)-34) pyroxene lacking cathodoluminescence (CL), hereafter black pyroxene, is a major constituent of some of the chondrules and fragments in unequilibrated (type 3) enstatite chondrites (UECs). It contains structurally oriented zones of Cr-, Mn-, V-rich, FeO-poor enstatite with red CL, associated with mm-sized blebs of low-Ni, Fe-metal and, in some cases, silica. These occurrences represent clear evidence of pyroxene reduction. The black pyroxene is nearly always rimmed by minor element (Cr, Mn, V)-poor enstatite having a blue CL. More commonly, red and blue enstatites, unassociated with black pyroxene, occur as larger grains in chondrules and fragments, and these constitute the major silicate phases in UECs. The rare earth element (REE) abundance patterns of the black pyroxene are LREE-depleted. The blue enstatite rims, however, have a near-flat to LREE-enriched pattern, approx. 0.5-4x chondritic. The petrologic and trace element data indicate that the black pyroxene is from an earlier generation of chondrules that formed in a nebular region that was more oxidizing than that of the enstatite chondrites. Following solidification, these chondrules experienced a more reducing nebular environment and underwent reduction. Some, perhaps most, of the red enstatite that is common throughout the UECs may be the product of solid-state reduction of black pyroxene. The blue enstatite rims grew onto the surfaces of the black pyroxene and red enstatite as a result of condensation from a nebular gas. The evolutionary history of some of the enstatite and chondrules in enstatite chondrites can be expressed in a four-stage model that includes: Stage 1. Formation of chondrules in an oxidizing nebular environment. Stage 2. Solid-state reduction of the more oxidized chondrules and fragments to red enstatite in a more reducing nebular environment. Stage 3. Formation of blue enstatite rims on the black pyroxene as well as on the red enstatite. Stage 4. Reprocessing, by various degrees of melting, of many of the earlier-formed materials.

Weisberg, Michael K.; Prinz, Martin; Fogel, Robert A.

1994-01-01

210

Chondrule fragments from Comet Wild2: Evidence for high temperature processing in the outer Solar System  

NASA Astrophysics Data System (ADS)

Terminal grains from C2063,1,154,1,0 (Track 154) and C2061,1,113,5 (Track 113) from the Stardust collection of Comet Wild2's coma have been studied by TEM and NanoSIMS. Terminal grain 2 of C2063,1,154,1,0 consists of an Al-rich diopside (En 97-99%, Al2O3 9-11 wt%), pigeonite (En 85% Wo 15% with TiO2 and Al2O3 contents of 0.5 and 5.2 wt%) and minor forsterite and enstatite. The mineral assemblage and Al-rich, Ti-poor composition of the grain are consistent with being a fragment of an Al-rich chondrule, similar to those present in carbonaceous chondrites. The oxygen isotopic composition of the C2063,1,154,1,0 grain was determined by NanoSIMS analyses and found to be ?17O -10.65.7, ?18O -7.52.5 and ?17O +1.44.3, ?18O -6.51.6 (1? errors) for the two sections. These figures are distinct from CAIs and consistent with an origin as Al-rich chondrule fragments. Terminal grain 5 of C2061,1,113,5 consists of low Ca pyroxene En 86-87% Fs 10-11% Wo 3-4% and ?2 wt% Al2O3 and in one section 5-10% of a Na-rich silicate phase. This assemblage may be a fragment of a low-Ca pyroxene-bearing chondrule and mesostasis. The original chondrule diameter for the C2063,1,154,1,0 and C2061,1,113,5 samples, by analogy with carbonaceous chondrite chondrules, might have been in the range 0.2-1.0 mm. If they were of that size, then the presence of large grains of high temperature material (e.g. ?1500 K for such refractory assemblages) could be explained through commonly invoked models of radial drift from inner to outer Solar System, but only if the chondrules were first fragmented to dust within the inner Solar System. An alternative scenario is that some chondrule formation was associated with high temperature processing and planetesimals in the outer Solar System.

Bridges, J. C.; Changela, H. G.; Nayakshin, S.; Starkey, N. A.; Franchi, I. A.

2012-08-01

211

The evolution of enstatite and chondrules in unequilibrated enstatite chondrites: Evidence from iron-rich pyroxene  

NASA Astrophysics Data System (ADS)

FeO-rich (Fs6-34) pyroxene lacking cathodoluminescence (CL), hereafter black pyroxene, is a major constituent of some of the chondrules and fragments in unequilibrated (type 3) enstatite chondrites (UECs). It contains structurally oriented zones of Cr-, Mn-, V-rich, FeO-poor enstatite with red CL, associated with mm-sized blebs of low-Ni, Fe-metal and, in some cases, silica. These occurrences represent clear evidence of pyroxene reduction. The black pyroxene is nearly always rimmed by minor element (Cr, Mn, V)-poor enstatite having a blue CL. More commonly, red and blue enstatites, unassociated with black pyroxene, occur as larger grains in chondrules and fragments, and these constitute the major silicate phases in UECs. The rare earth element (REE) abundance patterns of the black pyroxene are LREE-depleted. The blue enstatite rims, however, have a near-flat to LREE-enriched pattern, approx. 0.5-4x chondritic. The petrologic and trace element data indicate that the black pyroxene is from an earlier generation of chondrules that formed in a nebular region that was more oxidizing than that of the enstatite chondrites. Following solidification, these chondrules experienced a more reducing nebular environment and underwent reduction. Some, perhaps most, of the red enstatite that is common throughout the UECs may be the product of solid-state reduction of black pyroxene. The blue enstatite rims grew onto the surfaces of the black pyroxene and red enstatite as a result of condensation from a nebular gas. The evolutionary history of some of the enstatite and chondrules in enstatite chondrites can be expressed in a four-stage model that includes: Stage 1. Formation of chondrules in an oxidizing nebular environment. Stage 2. Solid-state reduction of the more oxidized chondrules and fragments to red enstatite in a more reducing nebular environment. Stage 3. Formation of blue enstatite rims on the black pyroxene as well as on the red enstatite. Stage 4.

Weisberg, Michael K.; Prinz, Martin; Fogel, Robert A.

1994-05-01

212

Olivine Weathering: Abiotic Versus Biotic Processes as Possible Biosignatures  

NASA Technical Reports Server (NTRS)

A preliminary study to determine how abiotic versus biotic processes affect the weathering of olivine crystals. Perhaps the differences between these weathering processes could be used as biosignatures. Additional information is contained in the original extended abstract.

Longazo, T. G.; Wentworth, S. J.; McKay, D. S.; Southam, G.; Clemett, S. J.

2001-01-01

213

Aluminum speeds up the hydrothermal alteration of olivine  

NASA Astrophysics Data System (ADS)

The reactivity of ultramafic rocks toward hydrothermal fluids controls chemical fluxes at the interface between the internal and external reservoirs of silicate planets. On Earth, hydration of ultramafic rocks is ubiquitous and operates from deep subduction zones to shallow lithospheric environments where it considerably affects the physical and chemical properties of rocks and can interact with the biosphere. This process also has key emerging societal implications, such as the production of hydrogen as a source of carbon-free energy. To date, the chemical model systems used to reproduce olivine hydrothermal alteration lead to the formation of serpentine with sluggish reaction rates. Although aluminum is common in geological environments and in hydrothermal systems in particular, its role in serpentinization or olivine dissolution has not been investigated under hydrothermal conditions. Nevertheless, abundant Al supply is expected in fluids released from dehydration of metapelites in subduction zones as well as during the hydrothermal alteration of gabbros at mid-ocean ridges. Aluminum was also abundant in primitive environments of both the Earth and Mars, stored in either Al-rich minerals like plagioclase or Al-enriched ultramafic lavas. We have investigated the role of Al on the hydrothermal alteration of olivine in a series of experiments performed in a low-pressure diamond anvil cell while following the reaction progress in situ by optical imaging and Raman spectroscopy. Experiments were run for 4.5 to 7.5 days with two olivine grains reacted in saline water (0.5 molal NaCl) at 200C and 300C, and P=200 MPa. After two days, olivine crystals were fully transformed to an aluminous serpentine, also enriched in iron. The presence of Al in the hydrothermal fluid increases the rate of olivine serpentinization by more than one order of magnitude by enhancing olivine solubility and serpentine precipitation. The mechanism responsible for this increased solubility has to be further investigated but this result motivates a re-evaluation of the natural rates of olivine serpentinization and of olivine hydrolysis in general in a wide range of settings where olivines or peridotites are intimately associated with Al-providers. Such a fast reaction rate may affect the contribution of reaction-enhanced processes at the micrometer-scale, such as reaction-driven cracking, already proposed for enhancing serpentinization or carbonation of olivine. The effect of Al on lower crust and upper mantle metasomatism is expected to be even stronger at higher pressure in subduction zones where those reactions control the rheology and physical properties of the subducting plate and mantle wedge.

Andreani, Muriel; Daniel, Isabelle; Pollet-Villard, Marion

2014-05-01

214

Carbon sequestration via aqueous olivine mineral carbonation: role of passivating layer formation.  

PubMed

CO2 sequestration via carbonation of widely available low-cost minerals, such as olivine, can permanently dispose of CO2 in an environmentally benign and a geologically stable form. We report the results of studies of the mechanisms that limit aqueous olivine carbonation reactivity under the optimum sequestration reaction conditions observed to date: 1 M NaCl + 0.64 M NaHCO3 at Te 185 degrees C and P(CO2) approximately equal to 135 bar. A reaction limiting silica-rich passivating layer (PL) forms on the feedstock grains, slowing carbonate formation and raising process cost. The morphology and composition of the passivating layers are investigated using scanning and transmission electron microscopy and atomic level modeling. Postreaction analysis of feedstock particles, recovered from stirred autoclave experiments at 1500 rpm, provides unequivocal evidence of local mechanical removal (chipping) of PL material, suggesting particle abrasion. This is corroborated by our observation that carbonation increases dramatically with solid particle concentration in stirred experiments. Multiphase hydrodynamic calculations are combined with experimentto better understand the associated slurry-flow effects. Large-scale atomic-level simulations of the reaction zone suggest that the PL possesses a "glassy" but highly defective SiO2 structure that can permit diffusion of key reactants. Mitigating passivating layer effectiveness is critical to enhancing carbonation and lowering sequestration process cost. PMID:16913142

Barat, Hamdallah; McKelvy, Michael J; Chizmeshya, Andrew V G; Gormley, Deirdre; Nunez, Ryan; Carpenter, R W; Squires, Kyle; Wolf, George H

2006-08-01

215

Chondrites: The Compaction of Fine Matrix and Matrix-like Chondrule Rims  

NASA Astrophysics Data System (ADS)

Primitive chondritic meteorites mainly consist of chondrules, sulfide+/-metal, and fine-grained matrix. The most unequilibrated chondrites preserve in their phase compositions and, to a lesser degree, their textures, many details about processes that occurred in the solar nebula. On the other hand, much of the textural evidence records processes that occurred in or on the parent body. I suggest that the low-porosity of chondrule matrix and matrix-like rims reflects compaction processes that occurred in asteroid-size bodies, and that neither matrix lumps nor compact matrix-like rims on chondrules could have achieved their observed low porosities in the solar nebula. Recent theoretical studies by Donn and Meakin (1) and Chokshi et al. (2) have concluded that grain-grain sticking in the solar nebula mainly produces fluffy structures having very high porosities (probably >>50%). If these structures grow large enough, they can provide an aerogel-like matrix that can trap chondrules as well as metal and sulfide grains, and thus form suitable precursors of chondritic meteorites. However, the strength of any such structure formed in the solar nebula must be a trivial fraction of that required to survive passage through the Earth's atmosphere in order to fall as a meteorite. The best evidence of accretionary structures appears to be that reported by Metzler et al. (3). They made SEM images of entire thin sections of CM chondrites, and showed that, in the best preserved chondrites, rims are present on all entitities--on chondrules, chondrule fragments, refractory inclusions, etc. A study by Krot and Wasson (4) shows a more complex situation in ordinary chondrites. Although matrix is common, a sizable fraction of chondrules are not surrounded by matrix-like rims. As summarized by Rubin and Krot (1995), there are reports of small textural and compositional differences between matrix lumps and mean matrix-like chondrule rims, but there is so much overlap in properties between these two classes that I will assume that they can be treated as parts of a single statistical population. Published SEM images of matrix lumps and matrix-like rims show them to be relatively compact. Although some porosity is surely present as indicated by broad-beam electron-probe analysis totals <100%, it never reaches values comparable to those expected from low-velocity collisions in the solar nebula. Most chondrite researchers seem to hold that the low porosities reflect efficient packing of each grain as it accreted to the assemblage (i.e., as micrometer-size grains gradually covered the surface of a chondrule to form the matrix-like rim). I find this process very difficult to envision. If the velocities are low, the fluffy structures of Dodd and Meakin (1) should result; if the velocities are high, then rim erosion would seem to be more probable than growth. A possible scenario that avoids this dilemma is to form cm to m-size fluffy structures in low-turbulence regions of the nebular midplane. During accretion of these larger objects these experienced enough compaction to form tough, low-porosity (but unequilibrated) chondrites. If no chondrules were in a region, matrix lumps formed; if chondrules were widely separated, a matrix-like rim resulted. And, if chondrules were close to other chondrules or chondrule fragments, only small amounts of intervening fine-grained materials now separate them from their neighbors. During the compaction event, gas and dust migration occurred, and matrix filled all interstices, as now observed in the most primitive chondrites. According to this picture there could have been more diversity in the fine-grained nebular component before compaction occurred. These differences would be best preserved in matrix-like rims and matrix lumps. Much of the interchondrule matrix should consist of homogenized dust that was mixed during compaction-induced transport. References: [1] Donn B. and Meakin P. (1989) Proc. LPSC 19th, 577-580. [2] Chokshi A. et al. (1993) Astrophys. J., 407, 806-819. [3] Metzler K. et al. (1992) GCA,

Wasson, J. T.

1995-09-01

216

Dissolution of olivine in basaltic liquids: experimental observations and applications.  

USGS Publications Warehouse

Rates of olivine dissolution in synthetic lunar basalt 77115 and a silica-enriched 77115 composition (Sil-77115) at superliquidus temperatures have been determined. Dissolution-rate data have been applied to the problem of the thermal history of fragment-laden impact-melt rocks of the lunar highlands. Textural and chemical criteria are discussed for the recognition of olivine resorption (and growth) phenomena in igneous rocks. -J.A.Z.

Thornber, C.R.; Huebner, J.S.

1985-01-01

217

A Method for the Flux Growth of Intermediate Composition Olivine  

Microsoft Academic Search

Though solid solution of iron and magnesium between forsterite (Mg2SiO4) and fayalite (Fe2SiO4) is possible in the olivine crystal structure, the high oxygen fugacity condition of the terrestrial mantle inhibits the widespread crystallization of intermediate (Fo40-Fo60) composition olivine. This limitation is not the same for some other inner solar system bodies (e.g. the Moon and Mars), where conditions are reducing

M. T. Deangelis; L. M. Anovitz; T. C. Labotka; D. A. Frederick

2009-01-01

218

Mechanically Activated Olivine as Feedstock for Ex-situ Carbon Dioxide Sequestration: Preliminary Experiments  

NASA Astrophysics Data System (ADS)

Fossil fuel power plants need sequestration to significantly lower CO2 emissions. In nature, Mg- and Ca- rich silicates react with CO2(aq) and perform a natural sequestration by dissolution of silicates and a later precipitation of carbonates. This type of sequestration is environmentally friendly and stable. One severe problem with adopting this method for industrial processes is the slow reaction rate. For mineral carbonation to be an alternative, reaction rates have to be increased. Pretreatment methods involving mechanical, chemical or physical treatment can increase the rate. Resources of suitable minerals are also acquired. One abundant Mg-rich silicate mineral is olivine. Forsterite is olivine containing only Mg. An experimental study of an aqueous flow-through process was done with olivine(Fo93) reacted at 128C and 150 bars in fluid flow of 0.15 ml/min CO2 and 0.75 ml/min H2O. The total duration of the experiments varied between 19 and 71h. With a total of 2,22 mol % CO2 in the mixture, the fluid had two phases and 1,68 mol % CO2 dissolved in the H2O phase. The chosen pretreatment was mechanical activation (energy intensive milling). Influence of activation can not solely be explained by the decreased particle size. Mechanical activation also disturbs the crystal lattice, leading to amorphization. Distorted bonds in the crystal lattice due to deformation and micro fractures are also important features. The activation was done in a Fritsch mono planetary mill for 0-60 minutes, 20 grams of olivine, and 2ml DI H2O added to some samples. An observed effect was non-stochiometric dissolution in the first 20-60 minutes, with max Mg:Si = 10.5 (material molar ratio=1.86). After the initial reactions, Mg:Si stabilized near stochiometric values (1.73-1.94). Geochemical modeling of the reference material indicates subsaturation of forsterite (log Q/K ? -11), serpentine (log Q/K ? -177), and magnesite (log Q/K ? -1.4).

Haug, A.; Munz, I. A.; Kihle, J.

2006-12-01

219

Calcio-olivine ?-Ca2SiO4: I. Rietveld refinement of the crystal structure  

NASA Astrophysics Data System (ADS)

The structure of the natural mineral calcio-olivine (?-Ca2SiO4) found in skarn xenoliths in the region of the Lakargi Mountain (North Caucasus, Kabardino-Balkaria, Russia) is refined by the Rietveld method [ a = 5.07389(7) , b = 11.21128(14) , c = 6.75340(9) , V = 384.170(5) 3, Z = 4, ?calcd = 2.98 g/cm3, space group Pbnm]. The X-ray diffraction pattern of a powdered sample is recorded on a STOE STADI MP diffractometer [?Cu K ?1; Ge(111) primary monochromator; 6.00 < 2? < 100.88; step width, 2.5 in 2?; number of reflections, 224]. All calculations are performed with the WYRIET (version 3.3) software package. The structural model is refined in the anisotropic approximation to R p = 6.44, R wp = 8.52, R exp = 5.85, R B = 4.98, R F = 6.90, and s = 1.46. It is shown that the sample under investigation is a mixture of several mineral phases, among which calcio-olivine (the natural analogue of the ?-Ca2SiO4 compound) (83%), hillebrandite (13%), and wadalite (4%) are dominant. Only the scale factors and the unit cell parameters are refined for hillebrandite Ca2SiO3(OH)2 [ a = 3.63472(16) , b = 16.4140(10) , c = 11.7914(8) , space group Cmc21, Z = 6] and wadalite Ca6Al5Si2O16Cl3 ( a = 12.0088 , space group, I bar 4 3 d Z = 4). The results of the structure refinement of the main component of the sample confirm that the mineral calcio-olivine is isostructural to the synthetic compound ?-Ca2SiO4. The structure of this compound is formed by the heteropolyhedral framework composed of Ca octahedra joined together into olivine-like ribbons and isolated Si tetrahedra.

Gobechiya, E. R.; Yamnova, N. A.; Zadov, A. E.; Gazeev, V. M.

2008-05-01

220

Exposing metal and silicate charges to electrical discharges: Did chondrules form by nebular lightning?  

E-print Network

In order to investigate the hypothesis that dust aggregates were transformed to meteoritic chondrules by nebular lightning, we exposed silicatic and metallic dust samples to electric discharges with energies of 120 to 500 J in air at pressures between 10 and 10^5 Pa. The target charges consisted of powders of micrometer-sized particles and had dimensions of mm. The dust samples generally fragmented leaving the major fraction thermally unprocessed. A minor part formed sintered aggregates of 50 to 500 micrometer. In a few experiments melt spherules having sizes smaller than 180 micrometer in diameter (and, generally, interior voids) were formed; the highest spherule fraction was obtained with metallic Ni. Our experiments indicate that chondrule formation by electric current or by particle bombardment inside a discharge channel is unlikely.

C. Gttler; T. Poppe; J. T. Wasson; J. Blum

2007-12-04

221

A transmission electron microscope study of pyroxene chondrules in equilibrated L-group chondrites  

NASA Astrophysics Data System (ADS)

Analytical electron microscopy is used to investigate the fine structures and chemical compositions of pyroxenes in ion-thinned specimens of rock chips from the L chondrites Allan Hills 77252, Fukutomi, and Satsuma. The results are presented graphically and characterized in detail. The differences noted between the pyroxenes of L3 and those of L3-4 and L4-5 chondrules are interpreted as evidence for more rapid cooling in L3, while shock deformations obscure the original thermal history of L6. The similar periodicities of the spinodal decomposition textures in the Ca-rich pyroxenes of the L3, L3-4, and L4-5 chondrules are attributed to the lack of a significant reheating event in the equilibrated chondrites.

Watanabe, S.; Kitamura, M.; Morimoto, N.

1985-01-01

222

Anisotropy of magnetic susceptibility in natural olivine single crystals  

NASA Astrophysics Data System (ADS)

flow dynamics can cause preferential alignment of olivine crystals that results in anisotropy of physical properties. To interpret anisotropy in mantle rocks, it is necessary to understand the anisotropy of olivine single crystals. We determined anisotropy of magnetic susceptibility (AMS) for natural olivine crystals. High-field AMS allows for the isolation of the anisotropy due to olivine alone. The orientations of the principal susceptibility axes are related to the olivine's crystallographic structure as soon as it contains >3 wt % FeO. The maximum susceptibility is parallel to the c axis both at room temperature (RT) and at 77 K. The orientation of the minimum axis at RT depends on iron content; it is generally parallel to the a axis in crystals with 3-5 wt % FeO, and along b in samples with 6-10 wt % FeO. The AMS ellipsoid is prolate and the standard deviatoric susceptibility, k', is on the order of 8*10-10 m3/kg for the samples with <1wt % FeO, and ranges from 3.1*10-9 m3/kg to 5.7*10-9 m3/kg for samples with 3-10 wt % FeO. At 77 K, the minimum susceptibility is along b, independent of iron content. The shape of the AMS ellipsoid is prolate for samples with <5 wt % FeO, but can be prolate or oblate for higher iron content. The degree of anisotropy increases at 77 K with p'77 = 7.1 0.5. The results from this study will allow AMS fabrics to be used as a proxy for olivine texture in ultramafic rocks with high olivine content.

Biedermann, Andrea R.; Pettke, Thomas; Reusser, Eric; Hirt, Ann M.

2014-07-01

223

Non-nebular origin of dark mantles around chondrules and inclusions in CM chondrites  

Microsoft Academic Search

Our examination of nine CM chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in CM chondrites are not discrete fine-grained rims acquired in the solar nebula as modeled by Metzler et al. [Accretionary dust mantles in CM chondrites: evidence for solar nebula processes. Geochim. Cosmochim. Acta56, 1992, 28732897].

Josep M. Trigo-Rodriguez; Alan E. Rubin; John T. Wasson

2006-01-01

224

Volatile fractionation in the early solar system and chondrule/matrix complementarity.  

PubMed

Bulk chondritic meteorites and terrestrial planets show a monotonic depletion in moderately volatile and volatile elements relative to the Sun's photosphere and CI carbonaceous chondrites. Although volatile depletion was the most fundamental chemical process affecting the inner solar nebula, debate continues as to its cause. Carbonaceous chondrites are the most primitive rocks available to us, and fine-grained, volatile-rich matrix is the most primitive component in these rocks. Several volatile depletion models posit a pristine matrix, with uniform CI-like chemistry across the different chondrite groups. To understand the nature of volatile fractionation, we studied minor and trace element abundances in fine-grained matrices of a variety of carbonaceous chondrites. We find that matrix trace element abundances are characteristic for a given chondrite group; they are depleted relative to CI chondrites, but are enriched relative to bulk compositions of their parent meteorites, particularly in volatile siderophile and chalcophile elements. This enrichment produces a highly nonmonotonic trace element pattern that requires a complementary depletion in chondrule compositions to achieve a monotonic bulk. We infer that carbonaceous chondrite matrices are not pristine: they formed from a material reservoir that was already depleted in volatile and moderately volatile elements. Additional thermal processing occurred during chondrule formation, with exchange of volatile siderophile and chalcophile elements between chondrules and matrix. This chemical complementarity shows that these chondritic components formed in the same nebula region. PMID:16174733

Bland, Philip A; Alard, Olivier; Benedix, Gretchen K; Kearsley, Anton T; Menzies, Olwyn N; Watt, Lauren E; Rogers, Nick W

2005-09-27

225

Extraction of in situ cosmogenic 14C from olivine  

USGS Publications Warehouse

Chemical pretreatment and extraction techniques have been developed previously to extract in situ cosmogenic radiocarbon (in situ 14C) from quartz and carbonate. These minerals can be found in most environments on Earth, but are usually absent from mafic terrains. To fill this gap, we conducted numerous experiments aimed at extracting in situ 14C from olivine ((Fe,Mg)2SiO4). We were able to extract a stable and reproducible in situ 14C component from olivine using stepped heating and a lithium metaborate (LiBO2) flux, following treatment with dilute HNO3 over a variety of experimental conditions. However, measured concentrations for samples from the Tabernacle Hill basalt flow (17.3 ?? 0.3 ka4) in central Utah and the McCarty's basalt flow (3.0 ?? 0.2 ka) in western New Mexico were significantly lower than expected based on exposure of olivine in our samples to cosmic rays at each site. The source of the discrepancy is not clear. We speculate that in situ 14C atoms may not have been released from Mg-rich crystal lattices (the olivine composition at both sites was ~Fo65Fa35). Alternatively, a portion of the 14C atoms released from the olivine grains may have become trapped in synthetic spinel-like minerals that were created in the olivine-flux mixture during the extraction process, or were simply retained in the mixture itself. Regardless, the magnitude of the discrepancy appears to be inversely proportional to the Fe/(Fe+Mg) ratio of the olivine separates. If we apply a simple correction factor based on the chemical composition of the separates, then corrected in situ 14C concentrations are similar to theoretical values at both sites. At this time, we do not know if this agreement is fortuitous or real. Future research should include measurement of in situ 14C concentrations in olivine from known-age basalt flows with different chemical compositions (i.e. more Fe-rich) to determine if this correction is robust for all olivine-bearing rocks. ?? 2010 by the Arizona Board of Regents on behalf of the University of Arizona.

Pigati, J.S.; Lifton, N.A.; Timothy, Jull A.J.; Quade, J.

2010-01-01

226

Olivine Composite Cathode Materials for Improved Lithium Ion Battery Performance  

SciTech Connect

Composite cathode materials in lithium ion batteries have become the subject of a great amount of research recently as cost and safety issues related to LiCoO2 and other layered structures have been discovered. Alternatives to these layered materials include materials with the spinel and olivine structures, but these present different problems, e.g. spinels have low capacities and cycle poorly at elevated temperatures, and olivines exhibit extremely low intrinsic conductivity. Previous work has shown that composite structures containing spinel and layered materials have shown improved electrochemical properties. These types of composite structures have been studied in order to evaluate their performance and safety characteristics necessary for use in lithium ion batteries in portable electronic devices, particularly hybrid-electric vehicles. In this study, we extended that work to layered-olivine and spinel-olivine composites. These materials were synthesized from precursor salts using three methods: direct reaction, ball-milling, and a coreshell synthesis method. X-ray diffraction spectra and electrochemical cycling data show that the core-shell method was the most successful in forming the desired products. The electrochemical performance of the cells containing the composite cathodes varied dramatically, but the low overpotential and reasonable capacities of the spinel-olivine composites make them a promising class for the next generation of lithium ion battery cathodes.

Ward, R.M.; Vaughey, J.T.

2006-01-01

227

Textural evolution of polyhedral olivine experiencing rapid cooling rates  

NASA Astrophysics Data System (ADS)

Dynamic crystallization experiments in the CaO MgO Al2O3 SiO2 (CMAS) system have been used to investigate the change in crystal shape when pre-existing polyhedral olivine crystals are cooled rapidly (1,639 2,182C/h). Polyhedral olivines are crystallized initially in a first step using a slow cooling rate (2C/h), then skeletal and dendritic overgrowths develop on the polyhedral crystals during a subsequent fast cooling event. During this second episode small dendritic olivines also nucleate within the liquid phase. Observation of the experimental sample by optical microscopy shows that the polyhedral olivine shape progressively changes to a skeletal and then to a dendritic morphology in the following sequence: polyhedral ? hopper polyhedral ? dendritic polyhedral. This evolutional sequence is discussed in terms of changes in the crystal growth conditions during cooling and a general relation between these olivine dynamic crystallization experiments and the integrated model of crystal growth by Sunagawa (Bull Minr 104:81 87, 1981, Morphology of crystals, Terra Scientific Publishing Company, 1987) is proposed.

Faure, Franois; Schiano, Pierre; Trolliard, Gilles; Nicollet, Christian; Soulestin, Bernard

2007-04-01

228

Early crystallization history of alkali olivine basalts, Diamond Craters, Oregon  

NASA Astrophysics Data System (ADS)

Basaltic lavas form the isolated Quaternary volcanic centers of Diamond Craters and occur at Cow Lakes in S.E. Oregon. The exposed rocks are olivine and plagioclase phyric alkali olivine basalts. The holocrystalline groundmasses contain plagioclase, titanaugite, olivine, Fe-Ti oxides and minor apatite, and occur in the high-alumina (greater than 17%) petrographic province of the northwestern Great Basin. The whole rock and phenocryst compositions provide enough information to define the equilibrium state of the magmas. The solutions to the thermodynamic equations are valid for systems of known bulk composition and can be used to evaluate whether rock compositions are close to magma compositions. Two of the lavas from Diamond Craters have whole rock and phenocryst compositions consistent with their being natural melts. Rock compositions that reflect the effects of crystal separation (open systems) are recognized by significant differences in predicted versus observed phenocryst modes. The P-T conditions of phenocryst saturation and the crystallization history of the magmas can be inferred from petrologic data combined with thermodynamic modelling and mass balance constraints. The initial melts are inferred to have equilibrated at 0.8-1.0 GPa and 1210-1240C. The majority of the lavas from Diamond Craters have compositions that reflect olivine and plagioclase crystal separation. These lavas can be related to two possible parent rock compositions by small amounts (2-8% by weight) of olivine and plagioclase separation.

Russell, J. K.; Nicholls, J.

1987-01-01

229

Bar Graph Mania  

NSDL National Science Digital Library

Use these activities to build and interpret data on bar graphs. Catch all the bugs in the system and put them in the correct column of the bar graph. Answer the questions about the bugs in the graph. Catch bugs in six rooms. Bugs in the system Do these bar graphing activities. You don\\'t have to do the last question ...

Thurlow, Ms.

2005-10-26

230

Exotic Olivine in Antarctic Angrites LEW 87051 and Asuka 881371  

NASA Astrophysics Data System (ADS)

Angrites are basaltic meteorites with very early formation ages [e.g., 1] suggesting magrnatic activity on their parent body shortly after accretion. To constrain the nature of this magmatism, it is necessary to determine the composition of the melts parental to the angrite meteorites so that these melts can be compared with known phase relationships. Of the four known angrites, Angra dos Reis is highly differentiated and has had a complex history [e.g.,2]. LEW 86010 is probably a low-temperature partial melt containing minor accumulated plagioclase [3]. LEW 87051 (LEW 87) contains porphyritic olivine in a fine-grained groundmass, and the olivine crystals have variously been interpreted as phenocrysts [e.g., 4], xenocrysts [e.g., 5], and compound crystals in which exotic xenocryst cores have been overgrown by olivine that crystallized from the melt [e.g 6]. Asuka 881371 (Asuka 88) contains large olivine crystals in a medium-grained groundmass [7 and these large olivines are unambiguously xenocrysts that are not directly related to the melt in which they now reside [9], and may shed light on the olivines in LEW 87. Several lines of evidence point towards the exotic nature of the large olivines in Asuka 88. Despite being internally homogeneous, these crystals show large variations in composition from one crystal to another. Such variations are shown for Ca and Mg/Mg+Fe in Fig. 1, but are also observed for Cr, Al, and Y. Moreover, the concentrations of these elements in the large olivines are different from the concentrations in the cores of the groundmass olivines that were obviously the first minerals to crystallize from the Asuka 88 melt (Fig 1). Thus the large olivines could not have been in equilibrium with one another nor with the host melt. Furthermore, along healed fractures the the large olivines have been altered towards the groundmass olivine composition either through physical invasion of melt or by enhanced surface diffusion along the fractures. However, despite the clear exotic relationship to the Asuka 88 melt, the O isotopic composition of one olivine xenocryst falls within the angrite group [9], so the xenocrysts are probably not completely exotic to the angrite parent body. By analogy with Asuka 88, we infer that the Mg-rich cores of some porphyritic olivines in LEW 87 are xenocrysts (Fig. 1), but the main portions of these crystals surrounding the cores (labeled LEW 87 phenos in Fig. 1) grew from the LEW 87 melt. Agreement in minor elements between the main portions of LEW 87 olivines and synthetic olivines from LEW 87 experiments supports this interpretation (Fig. 1). We plan to use elemental mapping to locate more cores in LEW 87, to look for core-to-core variation and to measure additional profiles to test for diffusive equilibration between xenocrysts and the outer part of the olivine or groundmass. Using the compositions of first olivines to crystallize from the parent melts of both meteorites and K(sub)(DFe/Mg) of 0.29 from LEW 87 crystallization experiments, we calculate that the bulk compositions reported for Asuka 88 by [9] and LEW 87 by [12] have about 11% and 20% excess olivine (exotic or accumulated) of Fo(sub)83 and Fo(sub)81 respectively. References: [1] Nyquist L. et al. (1994) Meteoritics, 29, 872-885. [2] Mittlefehldt D. and Lindstrom M. (1990) GCA, 54, 3209-3218. [3] McKay G. et al. (1988) LPS XIX, 762-763. [4] McKay G. et al. (1990) LPS XXI, 771-772. [5] Prinz et al. (1990) LPS XXI, 979. [6] Mikouchi T. et al. (1995) LPS XXVI, 973-974. [7] Yanai K. (1994) Proc. NIPR Symp. Antarc. Meteorites, 7, 30-41. [8] McKay G. et al. (1995) Antarc. Meteorites, XX, 155-158. [9] Warren P. et al. (1995) Antarc. Meteorites, XX, 261-264. [10] Warren P. and Kallemeyn G. (1990) LPS XXI, 1295-1296.

McKay, G.; Crozaz, G.; Mikouchi, T.; Miyamoto, M.

1995-09-01

231

An olivine-free mantle source of Hawaiian shield basalts.  

PubMed

More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations. PMID:15800614

Sobolev, Alexander V; Hofmann, Albrecht W; Sobolev, Stephan V; Nikogosian, Igor K

2005-03-31

232

Electrical Conductivity of Hydrous Single Crystal San Carlos Olivine  

NASA Astrophysics Data System (ADS)

The electrical conductivity of anhydrous San Carlos olivine is too low to explain the observed electrical conductivity of Earth's upper mantle. Although the solubility of hydrogen in olivine is relatively low at mantle P and T conditions, it has been estimated that even at concentrations of less than 1000 ppm, electrical conductivity is enhanced by as much as a factor of one hundred, based on a conduction mechanism involving hydrogen diffusion (Karato, Nature 347, 272-273, 1990). In this study we have measured the electrical conductivity of hydrated San Carlos olivine single crystals, oriented along (100), (010) and (001). SCO single crystals were first oriented, machined into 2 mm diameter cylinders, and then sandwiched between layers of a talc+brucite mix in sealed Pt capsules for hydration runs at pressures up to 8 GPa and 1200C in a multianvil apparatus. Recovered samples were then cut into wafers ranging from 0.2 to 0.6 mm in thickness for subsequent complex impedance measurements to determine electrical conductivity, also carried out at high pressure. For the electrical measurements, temperatures were limited to about 700C in order to minimize loss of water from the sample. FTIR spectroscopy was used to determine water content of samples both before and after the electrical measurements. Preliminary results indicate that at concentrations of a few hundred ppm water, conductivities are several orders of magnitude higher than for dry olivine. Activation energies decrease with increasing water content, indicating that extrapolation of conductivities to higher temperatures leads to a smaller overall effect. However, based on these results, at upper mantle conditions, the presence of minor amounts of hydrogen in olivine is sufficient to bridge the gap between the conductivity of dry olivine and that of the mantle.

Poe, B.; Romano, C.; Nestola, F.; Rubie, D.

2005-12-01

233

Grain Boundary Structurally-Bonded Water in Olivine Aggregates  

NASA Astrophysics Data System (ADS)

Water storage capacity of nominally anhydrous olivine has been extensively investigated because of its numerous geophysical and geochemical implications for the Earth's dynamic mantle. However, all previous experimental research has been concentrated on the water solubility in single crystals of olivine. Grain boundary as potential storage sites for water in the mantle has not been experimentally studied, in part because solubility experiments were always performed under water-saturated condition, rendering the examination of grain boundaries nearly impossible due to the presence of free water. In the present study we have conducted annealing experiments on forsterite at 5 - 6 GPa and 1200 C and at water- undersaturated condition. Duration was typically 2 - 3 hours. A small amount of enstatite or periclase was added to the starting forsterite powder (including a few large olivine grains) to buffer the silica activity, while oxygen fugacity was controlled by using various capsule materials (Re, Fe, or BN). FTIR analyses were performed on both single crystal and polycrystalline olivine in doubly-polished thin section of each experimental charge. The results are as follows: (1) single crystal and polycrystalline olivine in the same charge always yielded similar IR pattern, indicating all absorption peaks are due to similar structurally-bonded water (i.e., hydroxyl); (2) water content of periclase-buffered (i.e., low silica activity) sample is at least one order of magnitude higher than those of enstatite-buffered and unbuffered (pure forsterite) samples; (3) under reducing environment (Fe or BN capsule), water content of polycrystalline olivine is always higher than that of single crystal by at lease a factor of 5, regardless of silica activity buffering. We therefore infer that large amount of structurally-bonded water is stored at grain boundaries; (4) with decreasing oxygen fugacity, IR spectra of olivine are increasingly dominated by an absorption peak centered around 3600 cm-1, indicating a gradual change in dominant water incorporation mechanism in olivine. These results strongly suggest that grain boundaries could be significant storage sites for water in the Earth's mantle, especially at locations where oxygen fugacity and silica activity are low.

Wang, L.

2008-12-01

234

BROWN AND CLEAR OLIVINE IN CHASSIGNITE NWA 2737: WATER AND DEFORMATION. A.H. , M. McCanta1  

E-print Network

section plane show interfingering bands and flame-shaped patches of vc olivine traversing the brown chemical composition and orientations in the host brown olivine. VC olivine has the same bulk chemical chemical transformation. The differences in color and

Hiroi, Takahiro

235

Trace Element Compositions of Pallasite Olivine Grains and Pallasite Origin  

NASA Technical Reports Server (NTRS)

Pallasites are mixtures of metal with magnesian olivine. Most have similar metal compositions and olivine oxygen isotopic compositions; these are the main-group pallasites (PMG). The Eagle Station grouplet of pallasites (PES) have distinctive metal and olivine compositions and oxygen isotopic compositions. Pallasites are thought to have formed at the core-mantle boundary of their parent asteroids by mixing molten metal with solid olivine of either cumulatic or restitic origin. We have continued our investigation of pallasite olivines by doing in situ trace element analyses in order to further constrain their origin. We determined Al, P, Ca, Ga and first row transition element contents of olivine grains from suite of PMG and PES by LA-ICP-MS at JSC. Included in the PMG suite are some that have anomalous metal compositions (PMG-am) and atypically ferroan olivines (PMG-as). Our EMPA work has shown that there are unanticipated variations in olivine Fe/Mn, even within those PMG that have uni-form Fe/Mg. Manganese is homologous with Fe2+, and thus can be used the same way to investigate magmatic fractionation processes. It has an advantage for pallasite studies in that it is unaffected by redox exchange with the metal. PMG can be divided into three clusters on the basis of Mn/Mg; low, medium and high that can be thought of as less, typically and more fractionated in an igneous sense. The majority of PMG have medium Mn/Mg ratios. PMG-am occur in all three clusters; there does not seem to be any relationship between putative olivine igneous fractionation and metal composition. The PMG-as and one PMG-am make up the high Mn/Mg cluster; no PMG are in this cluster. The high Mn/Mg cluster ought to be the most fractionated (equivalent to the most Fe-rich in igneous suites), yet they have among the lowest contents of incompatible lithophile elements Al and Ti and the two PMG-as in this cluster also have low Ca and Sc contents. This is inconsistent with simple igneous fractionation on a single, initially homogeneous parent asteroid. For Al and Ti, the low and high Mn/Mg clusters have generally uniform contents, while the medium cluster has wide ranges. This is also true of analyses of duplicate grains from the medium cluster pallasites which can have very different Al and Ti contents. Those from the low and high clusters do not. These observations suggest that pallasite olivines are not cumulates, but rather are restites from high degrees of melting. The moderately siderophile elements P and Ga show wide ranges in the high Mn/Mg cluster, but very uniform compositions in the medium cluster, opposite the case for Al and Ti. There is no correlation of P or Ga and Fe/Mn as might be expected if redox processes controlled the contents of moderately siderophile elements in the olivines. The lack of correlation of P could reflect equilibration with phosphates, although there is no correlation of Ca with P as might be expected

Mittlefehldt, David W.; Herrin, J. S.

2010-01-01

236

Metal-olivine associations and Ni-Co contents in two Apollo 12 mare basalts  

NASA Technical Reports Server (NTRS)

Olivine crystals in mare basalts 12004,8 and 12022,12 are normally zoned with Cr-poor rims. The Ni content of rare 2- to 10-micron metal inclusions in olivine decreases markedly as Fe/Mg in their immediate olivine hosts increases. Each metal grain appears to have been enclosed by late olivine almost immediately after it crystallized. The fractionation trend for the olivine and metal contrasts with the subsolidus equilibration trend for pallasites. For the basalts, not even local equilibrium of Fe, Ni and Co at metal/olivine interfaces can be detected by microprobe. Ni and Co concentrations range from about 300 ppm in olivine cores to about 70 ppm in rims. The limits of detection, at 95% confidence, are 36 ppm (Ni) and 25 ppm (Co). The distribution of Ni and Co in olivine, like that of Mg and Cr, records the depletion of these elements in the melt.

Hewins, R. H.; Goldstein, J. I.

1974-01-01

237

The electrical conductivity of an isotropic olivine mantle  

Microsoft Academic Search

In order to extend the useful temperature range of interpretation of olivine electrical conductivity sigma, the nonlinear iterative Marquardt technique is used to fit experimental data over the range 720-1500 C to a parametric form. The model describes conduction by migration of two different thermally activated defect populations with activation energies A1 and A2, and preexponential terms sigma (1) and

Steven Constable; Thomas J. Shankland; Al Duba

1992-01-01

238

Effect of secondary phase formation on the carbonation of olivine.  

PubMed

Large-scale olivine carbonation has been proposed as a potential method for sequestering CO(2) emissions. For in situ carbonation techniques, understanding the relationship between the formation of carbonate and other phases is important to predict the impact of possible passivating layers on the reaction. Therefore, we have conducted reactions of olivine with carbonated saline solutions in unstirred batch reactors. Altering the reaction conditions changed the Mg-carbonate morphology. We propose that this corresponded to changes in the ability of the system to precipitate hydromagnesite or magnesite. During high-temperature reactions (200 degrees C), an amorphous silica-enriched phase was precipitated that was transformed to lizardite as the reaction progressed. Hematite was also precipitated in the initial stages of these reactions but dissolved as the reaction proceeded. Comparison of the experimental observations with reaction models indicates that the reactions are governed by the interfacial fluid composition. The presence of a new Mg-silicate phase and the formation of secondary products at the olivine surface are likely to limit the extent of olivine to carbonate conversion. PMID:20704252

King, Helen E; Plmper, Oliver; Putnis, Andrew

2010-08-15

239

The geoengineering potential of artificially enhanced silicate weathering of olivine  

Microsoft Academic Search

Geoengineering is a proposed action to manipulate Earth's climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate in more detail the potential of a specific geoengineering technique, the carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification,

Peter Khler; Jens Hartmann; Dieter A. Wolf-Gladrow

2010-01-01

240

How robust are melt inclusions in olivine for mantle study?  

NASA Astrophysics Data System (ADS)

Melt inclusions in olivine are commonly used to address composition of mantle sources and processes of mantle melting. Here I will assess basic assumption of such studies: ability of melt inclusions to preserve chemical characteristics of parental melts formed in the mantle. Using published and new data I will demonstrate that olivines generally trap their melt inclusions during shallow crystallization in the crust by fast growth in the thermal boundary layers of mixing magma batches. Whether such trapped melts represent parental melts or they were modified by reaction on route could be recognized by chemical evidence of shallow equilibrium with plagioclase or pyroxene. Some inclusions reveal post-trapping modification of heaviest REE and H2O by volume diffusion through host olivine as predicted by the high diffusion coefficients for these elements in olivine (e.g . Spandler et al, Nature 2007 and Portnyagin et al, EPSL 2008). However, the contents of the middle and light REE and those of all highly incompatible trace elements are fully preserved. I conclude that (1) time scales in the magmatic system are short enough to preserve the abundances of highly and moderately incompatible elements inherited from primary melts, and (2) there is no evidence that wall-rock interaction has contributed significantly to the incompatible-element composition of Hawaiian melt inclusions.

Sobolev, A. V.

2008-12-01

241

The effect of mineral paragenesis on Al diffusion in olivine  

NASA Astrophysics Data System (ADS)

Al is the most abundant trivalent impurity of olivine and is particularly important because its concentration in olivine is temperature dependant, and it therefore has potential as a geothermometer (Wan, et al. 2008). Furthermore recent studies show that the incorporation of water into the olivine lattice is affected by the presents of trivalent cations such as Al3+ (Berry, et al. 2007; Hauri, et al. 2006). The Al distribution in olivines from volcanic rocks is often zoned and mantle olivines may also show an inhomogeneous distribution of Al, whereas the majority of other trace elements homogenized by diffusion (Mallmann, et al. 2009; McKibbin, et al.). However, there are no quantitative experimental data for Al diffusion in olivine, probably because the combination of low concentration rate and low diffusion rate make measurement difficult. We investigated the effect of silica activity on the diffusion rate of Al in forsterite at varying temperatures using solid-state buffer assemblages. Our study aimed to quantify the effect of major cation activities on the diffusion and concentration of Al in forsterite and also provide insights into the mechanism of Al substitution into the olivine lattice. The activities of SiO2, MgO and Al2O3 were buffered in each experiment by four different mineral associations: forsterite + periclase + spinel (fo+per+sp); forsterite + spinel + sapphirine (fo+sp+spr); forsterite + sapphirine + cordierite (fo+spr+cor); forsterite + cordierite + enstatite (fo+cor+en). Iron oxide in proportion of FeO/(FeO+MgO) = 0.1 was added to mixtures for San Carlos olivine experiments. Diffusion experiments were performed at the one-atmosphere vertical tube furnaces modified to control the fO2 by CO-CO2 gas mixing or in a box furnace in air for 10 - 28 days at temperatures from 1100 to 1500oC and logfO2 -0.7 and -5.7. The experiment with the San Carlos olivine was performed at 1300oC and at logfO2 = -5.7. In order to obtain equilibrium concentrations of the point defects we performed some experiments with pre-annealing. Diffusion profiles were measured by LA-ICP-MS in a traverse mode. The Al content of forsterite decreases with temperature dependence, increasing the potential of Al in olivine as a geothermometer. We obtain the activation energy of 379 kJ/mol for the high aSiO2 experiments, which is close within error of the value of 364 kJ/mol for the low aSiO2 experiments implying a common diffusion mechanism. The pre-exponential factor, however, increases by 5 orders of magnitude from low aSiO2 (fo+per+sp buffer) to high aSiO2 (fo+cor+en buffer). The much higher diffusivity at high aSiO2 indicates that Al diffusion occurs through octahedral cation site vacancies.

Zhukova, Irina; O'Neill, Hugh; Capbell, Ian

2014-05-01

242

Oxygen isotope heterogeneity and disequilibria of olivine crystals in large volume Holocene basalts from Iceland: Evidence  

E-print Network

and compositional zoning in selected grains, and subtle to severe D18 O (melt-olivine) and D18 O (plagioclase isotope laser fluorination analyses of 55 individual and bulk olivine crystals, coexisting individual different lavas, and variable core-to-rim oxygen isotopic zoning is present in selected olivine grains. Many

Bindeman, Ilya N.

243

Effect of water and stress on the lattice-preferred orientation of olivine  

E-print Network

) of olivine aggregates was investigated through large strain, shear deformation experiments at high pressures are hot-pressed synthetic olivine aggregates or single crystals of olivine. Water was supplied to the sample by decomposition of a mixture of talc and brucite. Deformation experiments were conducted up

Jung, Haemyeong

244

Evidence for equilibrium conditions during the partitioning of nickel between olivine and komatiite liquids.  

USGS Publications Warehouse

Olivine-liquid partition coefficients for Ni(DNi), calculated from Ni vs MgO abundance variations in komatiite series basalts, compare favourably with experimentally determined values, if Ni variations in olivine-controlled basalts can be modelled with an equation that assumes equilibrium between the entire olivine crystal and its coexisting liquid.-J.A.Z.

Budahn, J. R.

1986-01-01

245

Geoengineering potential of artificially enhanced silicate weathering of olivine.  

PubMed

Geoengineering is a proposed action to manipulate Earth's climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO(2) sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1-5 Pg of C per year for the 21st century by this technique. PMID:21059941

Khler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A

2010-11-23

246

Geoengineering potential of artificially enhanced silicate weathering of olivine  

PubMed Central

Geoengineering is a proposed action to manipulate Earths climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO2 sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 15Pg of C per year for the 21st century by this technique. PMID:21059941

Kohler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A.

2010-01-01

247

Bar Code Labels  

NASA Technical Reports Server (NTRS)

American Bar Codes, Inc. developed special bar code labels for inventory control of space shuttle parts and other space system components. ABC labels are made in a company-developed anodizing aluminum process and consecutively marketed with bar code symbology and human readable numbers. They offer extreme abrasion resistance and indefinite resistance to ultraviolet radiation, capable of withstanding 700 degree temperatures without deterioration and up to 1400 degrees with special designs. They offer high resistance to salt spray, cleaning fluids and mild acids. ABC is now producing these bar code labels commercially or industrial customers who also need labels to resist harsh environments.

1988-01-01

248

Interactive WSN-Bar  

NASA Astrophysics Data System (ADS)

Based on the concept of ambient intelligence, we utilized wireless sensor network (WSN) and vision-based tracking technologies to create an interactive WSN-Bar. WSN-Bar is an interactive and innovative creation which has two modules: Garden of Light and Vivacious Bushes. It refers the variety of natural environmental factors and focuses on the relationship between human and nature. WSN-Bar can also detect the changes of brightness, temperature, CO2 density outdoors and the movement of people inside the building. Besides, WSN-Bar is an interactive installation art which creates the opportunity to reduce the estranged gape among the participants.

Lin, Jiun-Shian; Hsu, Su-Chu; Chen, Ying-Chung

249

Low temperature annealing and cathodoluminescence studies of type 1 chondrule compositions  

NASA Technical Reports Server (NTRS)

Preliminary results indicate that the yellow luminescing mesostases in type I chondrules can be altered by the effects of the low level thermal metamorphism. Although heat alone was insufficient to alter the CL, reheating for geologically relevant periods could have the same results as we obtained in a second series of experiments with water present. It is known that both water and solutions of sodium metasilicate greatly accelerate the devitrification of glasses. The results of the experiments that will be repeated should further clarify how the CL changes with increased thermal alteration.

Dehart, John M.; Lofgren, Gary E.

1991-01-01

250

Lattice preferred orientations of olivine in the schistosed antigorite serpentinite  

NASA Astrophysics Data System (ADS)

The lattice preferred orientation (LPO) of the schistosed antigorite serpentinite is considered as causes of the seismic anisotropy observed at the subduction zones (Katayama et al., 2009; Jung, 2011) and the natural examples are reported by several researchers (Bezacier et al., 2010; Hirauchi et al., 2010; Soda and Takagi, 2010). Formation process of the antigorite LPO is unclear, especially at primary serpentinized stage. To understand the development of micro-structures of antigorite serpentinite, we made structural analyses of serpentinite schist and the former peridotite fabric. Samples were taken from lenticular serpentinite bodies (< 1km) stack in Jurassic accretionary complex, Toba area, Southwest Japan. The serpentinite consist of olivine, antigorite, meta-clinopyroxene and Cr-spinel. The foliation and lineation of serpentinite is defined by parallel alignment of elongated olivine grain and antigorite blades, which make up mylonitic textures, such as a porphyroclast system and composite planar fabric. Antigorite blades show syn-kinematic growth in pressure shadows and pull-apart of olivine porphyroclast. In the less serpentinized part, antigorite blades are crystallized along the grain boundary of olivine. We measure the LPOs of coarse olivine grains in the serpentinite schist using a u-stage. The X, Y and Z directions represent directions of lineation, normal to lineation within the foliation and normal to foliation, respectively. The LPOs of olivine show point maximum or partial girdle distribution, and these concentrated crystal axes are incongruous with X, Y and Z direction. The a[100] axes of olivine are parallel to the serpentinite foliation, and form a point maximum several degrees away from the Y direction. The b[010] axes and the c[001] axes are concentrated Z and X direction forming a partial girdle normal to Y direction, respectively. Boudier et al. (2010) have reported the topotactic relationship between olivine and antigorite. They show that the (100)ol is parallel to the (001)atg or the (010)ol is parallel to the (001)atg. And, the a[100] axes of olivine are normal to serpentinite foliation with point maximum in the thin section scale. However, in the case of this study, the simple topotactic relationship does not connect the fabric in the thin section scale of serpentinite schist. Although, more detail analysis need to discuss the formation of antigorite LPO, the other mechanisms, such as crystal plastic deformation or diffusion-precipitation, might cause rearrangement of antigorite fabric. References Bezacier, L. et al., 2010, Earth and Planetary Science Letters, 289, 198-208. Boudier, F. et al., 2010, Journal of Petrology 51, 495-512. Hirauchi et al., 2010, Earth and Planetary Science Letters, 299, 196-206. Jung, H., 2011, Earth and Planetary Science Letters, 307, 535-543. Katayama, I., et al., 2009, Nature, 461, 1114-1118. Soda, Y. and Takagi, H., 2010, Journal of Structural Geology, 32, 792-802.

Soda, Y.; Ando, J.; Mizukami, T.; Morishita, T.

2011-12-01

251

The role of Fe and redox conditions in olivine carbonation rates: An experimental study of the rate limiting reactions at 90 and 150 C in open and closed systems  

NASA Astrophysics Data System (ADS)

The mechanisms and rates of olivine carbonation reactions have been the object of a number of studies, but the thermodynamic limitations and the kinetics of the elementary processes that control the overall reaction are still poorly understood and characterized. The main objective of this study is to probe the effect of Fe on the measured rates of olivine carbonation and its role in the formation of Si-rich surface layers, which can significantly inhibit olivine dissolution and limit the extent of the carbonation reaction. A series of batch and flow-through reactor experiments was conducted in pure water at 90 and 150 C and under a CO2 partial pressure of 100 and 200 bar, using both a natural sample of Fe-bearing olivine (Fo88) and a synthetic sample of pure forsterite (Fo100). Experimental results show that Fe plays an ambivalent role in the carbonation rates of olivine. On one hand, the presence of Fe favors the formation of Fe-Si-rich protective layers at the interface between olivine and aqueous solution, slowing down the dissolution reaction and limiting the extent of carbonation, whereas pure silica coatings have little to no inhibiting effect on measured carbonation rates. On the other hand, Fe enhances olivine to carbonate conversion rates at low degrees of supersaturation, by promoting the formation of fast precipitating Mg-Fe carbonate solid solutions. The passivating properties of Fe-Si-rich layers originate from the strong Fe(III)-Si interaction and are linked to the permanence of oxidizing conditions in the aqueous fluid. As a consequence, under reducing conditions, olivine carbonation rates can be significantly increased by higher extents of dissolution and by the formation of ferroan magnesites (Mg,Fe)CO3, which nucleate faster than the pure Mg end-member. Forsterite and olivine carbonation reactions can be hindered by the formation of secondary Mg sheet-silicates but, at the conditions studied, the formation of such silicate phases was observed to be transitional and not affecting significantly the rates of carbonation at the end of one-month long experimental runs. This work presents new measurements of olivine carbonation rates and delivers relevant information that suggest new reference criteria for the assessment of the sequestration potential of CO2 repositories and the optimization of the mineral carbonation process in mafic and ultramafic rocks.

Saldi, Giuseppe D.; Daval, Damien; Morvan, Gilles; Knauss, Kevin G.

2013-10-01

252

Chemical variation and zoning of olivine in lunar dunite 72415 - Near-surface accumulation  

NASA Technical Reports Server (NTRS)

Electron microprobe remeasurements have been used to reevaluate the range of olivine compositions, including CaO, in lunar dunite sample 72415 and compare that range with olivines in established plutonic rocks. Olivines from ferroan anorthosite 62237 and samples from the Stillwater intrusion were analyzed; literature data for other lunar and terrestrial plutonic samples were used for comparisons. The analyses show that the lunar dunite 72415 contains a range of olivine compositions, that the olivines are zoned, and that they have CaO abundances that are consistent with shallow hypabyssal rather than deep plutonic accumulation.

Ryder, Graham

1992-01-01

253

Building Brilliant Bar Graphs  

NSDL National Science Digital Library

In this series of three lesson plans, students create bar graphs, double bar graphs, and determine appropriate intervals for scale. Each lesson incorporates teacher modeling, student practice (students have an opportunity to label and create the scale for their own graphs), assessment (including rubrics), and reteaching or extension options.

Bower, Briana; Miller, Mary

2005-01-01

254

High-temperature elasticity of iron-bearing olivines  

NASA Astrophysics Data System (ADS)

The first high-temperature data on the nine adiabatic elastic moduli for iron-bearing olivine are reported. These measurements are on two single-crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 K. The two specimens contain 8 and 9 modal percent fayalite, which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability. The rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of CO and CO2 gas. A small increase (1-2 GPa) in the adiabatic bulk modulus of each specimen, over that of end-member forsterite, was found. The data are high quality to extreme temperatures, with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens. Neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli, which is in contrast to published forsterite data. The temperature derivatives of the isotropic bulk modulus KS are (-1.69, -1.80) 10-2 GPa K-1 for the two olivine specimens, and the shear modulus G derivatives are (-1.38, -1.36) 10-2 GPa K-1. These derivatives are only slightly larger in magnitude than |(?KS/?T)P| = 1.56 10-2 and |(?G/?T)P| = 1.30 10-2 GPa K-1 found previously for iron-bearing olivine over a very small temperature range. There are also no significant differences between the temperature derivatives found here and the average derivatives of end-member forsterite from data retrieved over a slightly larger temperature range. Several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high-pressure phases in Earth's transition zone. One result from these systematics related to the seismic velocities in the Earth, and especially the shear wave velocities, is that an olivine content of less than 50% is implied at the 400-km discontinuity if Earth's upper mantle is isochemical. Furthermore, the substitution of almost 10% iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature.

Isaak, Donald G.

1992-02-01

255

Olivine separates from Murchison and Cold Bokkeveld - Particle tracks and noble gases  

NASA Technical Reports Server (NTRS)

Olivine separates from Murchison and Cold Bokkeveld were analyzed for particle tracks and noble gases. The matrix remaining after olivine separation was also analyzed for noble gases. The olivines from both meteorites have comparable fractions of solar-flare-irradiated grains, but the highest track densities in Murchison are an order of magnitude greater than those in Cold Bokkeveld. Solar Ne content in Murchison olivines follows this trend, being at least an order of magnitude higher than that in Cold Bokkeveld. Track gradients in Cold Bokkeveld olivines are flatter than those in Murchison or recently exposed lunar crystals. Relative to the matrix, olivine separates in both meteorites have small enrichments at the heavy and light Xe isotopes and smaller Ar-36/Ar-38 ratios. These noble-gas effects may be related to a chromite impurity in the olivine separates.

Macdougall, J. D.; Phinney, D.

1977-01-01

256

The Anatomy of Altered Chondrules and FGRs Covering them in a CM Chondrite by FIB-TEM/STEM  

NASA Astrophysics Data System (ADS)

Altered chondrules covered by fine-grained rims (FGRs) in Cold Bokkeveld CM chondrite were anatomized by FIB-TEM/STEM to clarify aqueous alteration record. FIB-TEM/STEM analyses could reveal aqueous alteration by Fe- and Mg-rich fluid.

Miyahara, M.; Uehara, S.; Ohtani, E.; Nagase, T.; Nishijima, M.; Vashaei, Z.; Kitagawa, R.

2008-03-01

257

I-Xe System of Hammadah al Hamra 237 CB Chondrule: Supporting Evidence for Late High-Energy Forming Event  

NASA Astrophysics Data System (ADS)

Simultaneous closure of I-Xe system in different mineral phases within the same Hammadah al Hamra 237 CB chondrule at 4562.0 - 0.4 Ma supports formation due to highly-energetic event and following rapid cooling in a late-stage protoplanetary disk.

Pravdivtseva, O.; Meshik, A.; Hohenberg, C. M.; Krot, A. N.

2014-09-01

258

First-principles studies of native defects in olivine phosphates  

NASA Astrophysics Data System (ADS)

Olivine phosphates LiMPO4 (M=Mn, Fe, Co, Ni) are promising candidates for rechargeable Li-ion battery electrodes because of their energy storage capacity and electrochemical and thermal stability. It is known that native defects have strong effects on the performance of olivine phosphates. Yet, the formation and migration of these defects are not fully understood, and we expect that once such understanding has been established, one can envisage a solution for improving the materials' performance. In this talk, we present our first-principles density-functional theory studies of native point defects and defect complexes in LiMPO4, and discuss the implications of these defects on the performance of the materials. Our results also provide guidelines for obtaining different native defects in experiments.

Hoang, Khang; Johannes, Michelle

2011-03-01

259

The solubility of olivine in basaltic liquids - An ionic model  

NASA Technical Reports Server (NTRS)

A model is presented which enables the temperature at which olivine is in equilibrium with any alkali-depleted basaltic compound to be calculated to within + or - 30 C. It is noted that the error increases substantially when applied to terrestrial basalts which contain several weight percent alkalis. In addition the model predicts and quantifies the reduced activity of SiO4(4-) monomers due to increasing SiO2 concentrations in the melt. It is shown that the coordination of alumina in melts which precipitate olivine only appears to be dominantly octahedral, while titanium acts as a polmerizing agent by interconnecting previously isolated SiO4(4-) monomers. It is concluded that the model is sufficiently sensitive to show that there are small repulsive forces between Mg(2+) and calcium ions which are in association with normative diopside in the melt.

Herzberg, C. T.

1979-01-01

260

Electrical conductivity of olivine single crystals at high temperature  

Microsoft Academic Search

The electrical conductivity in three single crystal specimens of olivine (fayalite mole %; 7.4, 8.4 and 12.6) is measured along the three crystallographic orientations in the temperature range of 600 to 1200K. There are two different mechanisms with different activation energy for electrical conduction; presumably the impurity (Fe) conduction is predominant above 800K and extrinsic conduction is predominant below 800K.

Yoji Kobayashi; Hiroshi Maruyama

1971-01-01

261

Space Weathering Evolution on Airless Bodies - Laboratory Simulations with Olivine  

NASA Astrophysics Data System (ADS)

Lunar-type space weathering of airless bodies is associated with nanophase iron (npFe0) production in Fe bearing silicate minerals that is often responsible for observable changes of its reflectance spectra. A new method of controlled npFe0 production on olivine grains was developed in order to quantitatively evaluate spectral changes related to space weathering and presence of npFe0. Through a two-step thermal treatment a series of olivine samples with increasing concentration of iron nanoparticles on the grain surfaces was prepared. The grain size of the npFe0 particles was kept in the same range 5-20 nm). Magnetic methods were used to estimate npFe0 concentration. Compared to fresh olivine, treated samples exhibit the spectral characteristics of lunar type space weathering (darkening, shallowing of 1 m olivine absorption band, and reddening) related to increasing presence of npFe0. From quantitative point of view, a logarithmic trend was found between spectral changes and npFe0 concentration. One sample with additional population of larger ~50 nm npFe0 particles follows the darkening and the 1 m band shallowing trend, but does not fully follow the reddening trend. This is due to fact that the larger 40 50 nm sized) npFe0 particles do not contribute to the spectral slope change. The observed logarithmic trend between the spectral changes and the npFe0 concentration give constrains on time evolution of space weathering. In the case of constant micro impact, solar wind and cosmic radiation on a regolith, the npFe0 concentration increases linearly with time while spectral changes related to space weathering evolve logarithmically with time.

Kohout, Tomas; Cuda, J.; Bradley, T.; Britt, D.; Filip, J.; Tucek, J.; Malina, O.; Kaslik, J.; Siskova, K.; Kletetschka, G.; Zboril, R.

2013-10-01

262

Polaron formation and transport in olivine cathode materials  

NASA Astrophysics Data System (ADS)

One of the critical factors limiting Li ion battery performance is electronic conduction through the cathode material. In the olivine structure type materials, such as LiFePO4, the parent materials are insulators with a gap of approximately 4 (or more) eV. The withdrawal of an electron results not in a band-type hole state, but rather a localized polaronic state. Transport then occurs via hopping of the polaron through the crystal. The measured electronic conduction in olivine materials depends on the transition metal cation type. In this study, we use density functional theory to compare formation of polarons in olivine materials with different transition metal cations: Mn, Fe, Co, and Ni. We show that the underlying electronic structure of the fully lithiated material (or fully delithiated material) essentially determines whether or not polaron formation is possible in localized d-states or whether the holes that result from adding or removing an electron reside in oxygen-derived states. We also investigate the facility of polaronic hopping by calculating the barrier between adjacent polaron sites in each of the four materials.

Johannes, Michelle; Hoang, Khang

2011-03-01

263

Si-rich layer formation on olivine surfaces during reaction with water and supercritical carbon dioxide under conditions relevant for geologic carbon storage  

NASA Astrophysics Data System (ADS)

The reaction of Mg-silicate minerals (i.e. olivine) with carbon dioxide (CO2) is a promising method for secure, long-term, geologic carbon storage. Several technical challenges must be overcome before implementing mineral carbonation technology on a large scale, one of which is slow reaction kinetics. This study probes surface reaction limitations of olivine carbonation, specifically the formation of a passivating, Si-rich layer on olivine surfaces upon exposure to water and CO2 under sequestration conditions (elevated temperature and pressure). A series of batch reactions were performed at 60C and 100 bar CO2 pressure in Dickson-style rocker bombs, varying the length of reaction and the amount of mixing (rocking). The initial aqueous phase was spiked with 29Si. Fluid samples were taken periodically and analyzed for cation content, alkalinity, and dissolved inorganic carbon. At the end of each experiment, the solid products were analyzed with a Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG) in order to measure the amount of 29Si incorporated into the Si-rich layer on reacted olivine grains. We also cut cross sections of reacted grains from each experiment using a Focused Ion Beam (FIB) which were thinned to <100nm and imaged using Transmission Electron Microscopy (TEM). SHRIMP-RG results show incorporation of 29Si on olivine grain surfaces reacted for 19 days with no mixing, and TEM images of olivine grains from the same experiment show an amorphous, Si-rich layer that is 30nm thick. Similarly, SHRIMP-RG results for olivine grains reacted for 19 days with mixing indicate 29SiO2 precipitation and TEM images reveal a Si-rich layer 60nm thick. In both experiments, EDS (energy dispersive spectroscopy) data show a step change in composition from the bulk rock to the surface layer in addition to the sharp crystalline/amorphous interface visible in the TEM images. Olivine from the unmixed experiment also has a slow decrease in Mg relative to Si before the step change, suggesting that, at least in this experiment, a Si-rich layer precipitated on top of a Mg-depleted layer that formed via a leaching process. SHRIMP-RG data also imply the presence of a precipitated Si-rich layer on top of a leached Si-rich layer, as the 29Si penetration depth is only 25-65% of the total Si-rich layer thickness. The combination of SHRIMP-RG and FIB/TEM analysis leads us to hypothesize that a Si-rich layer forms quickly on olivine surfaces due to preferential Mg removal from the surface (the traditional 'leached' layer), and as the reaction proceeds, amorphous silica reaches saturation in the fluid and precipitates on surfaces inside the reactor (including olivine grains).

Johnson, N. C.; Jackson, A.; Maher, K.; Bird, D. K.; Brown, G. E.

2013-12-01

264

Mass modeling for bars  

NASA Technical Reports Server (NTRS)

Methods of modeling mass for bars are surveyed. A method for extending John Archer's concept of consistent mass beyond just translational inertia effects is included. Recommendations are given for various types of modeling situations.

Butler, Thomas G.

1987-01-01

265

Annealing of deformed olivine single-crystals under 'dry' conditions  

NASA Astrophysics Data System (ADS)

Knowledge of rheological properties of Earth's materials is essential to understand geological processes. Open questions are the water content and crystallographic orientation dependences of dislocation creep rate, because the dominant slip system changes with increasing water content, which suggest different dislocations have different water content dependence. This project focuses on olivine, which is the most abundant mineral of the upper mantle. It is also considered to be the weakest phase and hence should control the rheology of the upper mantle. Several slip systems were reported for olivine, which are [100](010), [001](010), [001](100) and [100](001), each of which appear under different water content and stress conditions [1]. For this purpose we started to obtain data for 'dry' conditions, providing basic knowledge to understand the effect of water. Variation in dislocation creep rate according to change in physical conditions can be estimated by dislocation recovery experiments [2]. In this technique, deformed crystals are annealed, in which the dislocation density is expected to decrease due to coalescence of two dislocations. Dislocation densities are measured before and after the annealing. Dislocation mobility, which should be directly proportional to the dislocation creep rate, is estimated based on the change in dislocation density and duration of annealing. This technique has significant advantages partly because informations of strain rate and deviatoric stress, which are difficult to measure, are unnecessary, and partly because dislocation annealing is conducted under quasi-hydrostatic conditions, which allows wide ranges of P and T conditions. The first step of the experiments is to deform a single crystal of olivine. For this purpose, we developed an assembly, which deforms a single crystal in simple-shear geometry and prevent breakage, sub-grain formation and recrystallization of the crystal. Olivine single-crystals were placed in the high-pressure assembly so that a particular slip system is activated. The assemblies were compressed to 3 GPa. The shear deformation was conducted at 1600 K. EBSD measurements indicate that the recovered crystals are single crystals and sub-grain formation did not occur in most cases. The second step is to anneal the samples under the same P-T conditions as those of the deformation experiments. Annealing experiments are also performed at ambient pressures at 1600 K. Dislocation density was measured by means of the oxidation decoration technique [3]. The samples were firstly polished and then oxidized at 1200 K for 50 min. The dislocations are preferably oxidized, so that presence of dislocation can be observed using SEM. First Results indicate that the dislocation density decreased by annealing by 1/4 with an annealing period of 10 h for dislocations with b = [001]. References [1] H. Jung and S. I. Karato. Water-induced fabric transitions in olivine. Science, 293(5534):1460-1463, 2001. [2] S. I. Karato, D. C. Rubie, and H. Yan. Dislocation recovery in olivine under deep upper mantle conditions: Implications for creep and diffusion. Journal of Geophysical Research, 98(B6):9761-9768, 1993. [3] D. L. Kohlstedt, C. Goetze, W. B. Durham, and J. V. Sande. New technique for decorating dislocations in olivine. Science, 191(4231):1045-1046, March 1976.

Blaha, Stephan; Katsura, Tomoo

2013-04-01

266

Gray assist bar OPC  

Microsoft Academic Search

Assist bar Optical Proximity Correction (OPC) has been demonstrated to increase across pitch performance and depth-of-focus of semi-dense to isolated lines. As the sub-resolution assist feature (SRAF) or assist bar's size increases, so does its desired lithographic effect, as well as its undesired printability. In other words, when large assist features are required at isolated pitches, the assist features may

Neal V. Lafferty; Geert Vandenberghe; Bruce W. Smith; Matthew Lassiter; Patrick M. Martin

2004-01-01

267

A New Spinel-Olivine Oxybarometer: Near-Liquidus Partitioning of V between Olivine-Melt, Spinel-Melt, and Spinel-Olivine in Martian Basalt Composition Y980459 as a Function of Oxygen Fugacity  

NASA Technical Reports Server (NTRS)

Our research on valence state partitioning began in 2005 with a review of Cr, Fe, Ti, and V partitioning among crystallographic sites in olivine, pyroxene, and spinel [1]. That paper was followed by several on QUE94201 melt composition and specifically on Cr, V, and Eu partitioning between pyroxene and melt [2-5]. This paper represents the continuation of our examination of the partitioning of multivalent V between olivine, spinel, and melt in martian olivine-phyric basalts of Y980459 composition [6, 7]. Here we introduce a new, potentially powerful oxybarometer, V partitioning between spinel and olivine, which can be used when no melt is preserved in the meteorite. The bulk composition of QUE94201 was ideal for our study of martian pyroxene-phyric basalts and specifically the partitioning between pyroxene-melt for Cr, V, and Eu. Likewise, bulk composition Y980459 is ideal for the study of martian olivine-phyric basalts and specifically for olivine-melt, spinel-melt, and spinel-olivine partitioning of V as a function of oxygen fugacity.

Papike, J. J.; Le, L.; Burger, P. V.; Shearer, C. K.; Bell, A. S.; Jones, J.

2013-01-01

268

Magnetic Bar Field Model  

NSDL National Science Digital Library

The EJS Magnetic Bar Field Model shows the field of a bar magnet and has a movable compass that reports the magnetic field values. The bar magnet model is built by placing a group of magnetic dipoles along the bar magnet. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting Open Ejs Model from the pop-up menu item. The Magnetic Bar Field model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_MagneticBarField.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang; Franciscouembre; Cox, Anne

2009-09-18

269

Non-nebular origin of dark mantles around chondrules and inclusions in CM chondrites  

NASA Astrophysics Data System (ADS)

Our examination of nine CM chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in CM chondrites are not discrete fine-grained rims acquired in the solar nebula as modeled by Metzler et al. [Accretionary dust mantles in CM chondrites: evidence for solar nebula processes. Geochim. Cosmochim. Acta56, 1992, 2873-2897]. Nebular processes that lead to agglomeration produce materials with porosities far higher than those in the dark mantles. We infer that the mantles were produced from porous nebular materials on the CM parent asteroid by impact-compaction (a process that produces the lowest porosity adjacent to chondrules and inclusions). Compaction was followed by aqueous alteration that formed tochilinite, serpentine, Ni-bearing sulfide, and other secondary products in voids in the interchondrule regions. Metzler et al. reported a correlation between mantle thickness and the radius of the enclosed object. In Yamato 791198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation ( r2 = 0.44) if we limit consideration to central objects with radii >35 ?m; a moderate correlation is also found in QUE 97990. We suggest that impact-induced shear of a plum-pudding-like precursor produced the observed "mantles"; these were shielded from comminution during impact events by the adjacent stronger chondrules and inclusions. Some mantles in CM chondrites with low degrees of alteration show distinct layers that may largely reflect differences in porosity. Typically, a gray, uniform inner layer is surrounded by an outer layer consisting of darker silicates with BSE-bright speckles. The CM-chondrite objects characterized as "primary accretionary rocks" by Metzler et al. did not form in the nebula, but rather on the parent body. The absence of solar-flare particle tracks and solar-wind-implanted rare gases in these clasts reflect their lithified nature and low surface/volume ratios during the period when they resided in the regolith and were subject to irradiation by solar particles. The clasts are analogous to the light-colored metamorphosed clasts in ordinary-chondrite regolith breccias (which also lack solar-flare particle tracks and solar-wind gas).

Trigo-Rodriguez, Josep M.; Rubin, Alan E.; Wasson, John T.

2006-03-01

270

Calcio-olivine {gamma}-Ca{sub 2}SiO{sub 4}: I. Rietveld refinement of the crystal structure  

SciTech Connect

The structure of the natural mineral calcio-olivine ({gamma}-Ca{sub 2}SiO{sub 4}) found in skarn xenoliths in the region of the Lakargi Mountain (North Caucasus, Kabardino-Balkaria, Russia) is refined by the Rietveld method [a = 5.07389(7) A, b = 11.21128(14) A, c = 6.75340(9) A, V = 384.170(5) A{sup 3}, Z = 4, {rho}{sub calcd} = 2.98 g/cm{sup 3}, space group Pbnm]. The X-ray diffraction pattern of a powdered sample is recorded on a STOE STADI MP diffractometer [{lambda}CuK{sub {alpha}1}; Ge(111) primary monochromator; 6.00{sup o} < 2{theta} < 100.88{sup o}; step width, 2.5{sup o} in 2{theta}; number of reflections, 224]. All calculations are performed with the WYRIET (version 3.3) software package. The structural model is refined in the anisotropic approximation to R{sub p} = 6.44, R{sub wp} = 8.52, R{sub exp} = 5.85, R{sub B} = 4.98, R{sub F} = 6.90, and s = 1.46. It is shown that the sample under investigation is a mixture of several mineral phases, among which calcio-olivine (the natural analogue of the {gamma}-Ca{sub 2}SiO{sub 4} compound) (83%), hillebrandite (13%), and wadalite (4%) are dominant. Only the scale factors and the unit cell parameters are refined for hillebrandite Ca{sub 2}SiO{sub 3}(OH){sub 2} [a = 3.63472(16) A, b = 16.4140(10) A, c = 11.7914(8) A, space group Cmc2{sub 1}, Z = 6] and wadalite Ca{sub 6}Al{sub 5}Si{sub 2}O{sub 16}Cl{sub 3} (a = 12.0088 A, space group, I 4 bar 3d, Z = 4). The results of the structure refinement of the main component of the sample confirm that the mineral calcio-olivine is isostructural to the synthetic compound {gamma}-Ca{sub 2}SiO{sub 4}. The structure of this compound is formed by the heteropolyhedral framework composed of Ca octahedra joined together into olivine-like ribbons and isolated Si tetrahedra.

Gobechiya, E. R., E-mail: elgob@mail.ru; Yamnova, N. A. [Lomonosov Moscow State University (Russian Federation); Zadov, A. E. [Scientific and Production Enterprise OOO 'NPP Teplokhim,' (Russian Federation); Gazeev, V. M. [Russian Academy of Sciences, Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM) (Russian Federation)

2008-05-15

271

EXPERIMENTAL INVESTIGATION OF Ti and Fe VALENCE IN CHONDRULE-LIKE MELTS DURING COOLING UNDER CHANGING REDOX CONDITIONS AT LOW PARTIAL PRESSURES. S. B. Simon1  

E-print Network

(sbs8@uchicago.edu); 2 Div. Geol. Planet. Sci., Caltech, Pasadena, CA 91125, 3 CARS, Univ. of Chicago- ing environment, such as a solar gas, but that cooling following the chondrule melting event occurred

Grossman, Lawrence

272

Normalized Homologous Temperature of Olivine: Implications for the Effect of Iron Content on Mantle Deforamtio  

NASA Astrophysics Data System (ADS)

The flow laws and fabric transition of olivine under different thermal-mechanical conditions are generally obtained from HP-HT experiments on San Carlos olivine (Fo90), which hampers our understanding of the effect of iron content on the mantle flow and deforamtion. Because the melting temperature is related with the strength of the bonds binding a crystalline material together, the normalized homologous temperature T/Tm(P), is defined by the ratio between the absolute temperature of olivine and its melting point Tm at certain pressure P. Using the forsterite-fayalite melting loop at room pressure, the generalized mean is adopted to predict the dependence of Tm on pressure and iron content of olivine up to 7.5 GPa. Using T/Tm(P), we can evaluate the integreted effect of temperature and pressure on the deformation mechanisms of olivine. A new olivine fabric diagram is set up as a function T/Tm(P) and water content. The result indicates that the A-type olivine fabric becomes dominant at T/Tm(P) > 0.72, while the B- and C-type olivine fabrics are favorable at T/Tm(P) < 0.7, no matter their water content. Partial melting will produce resudies with higher Fo number in olivine, and consequently, a more rigid mantle with higher Tm. The relatively smaller T/Tm(P) of olivine beneath cratons can explain the long-term stability of the continental roots. In addition, a 2D profile of olivine T/Tm(P) for the oceanic lithosphere shows good correlation between T/Tm(P) and the distribution of earthquakes. Therefore T/Tm(P) of olivine can be used as a parameter to model the rheology of the upper manlte, especailly when taking into account of the compostional change in different tectonic processes.

Wang, Q.

2012-12-01

273

Origins of compositional heterogeneity in olivine-hosted melt inclusions from the Baffin Island picrites  

Microsoft Academic Search

The Baffin Island picrites are highly magnesian (?22wt% MgO) olivine tholeiites, erupted through felsic continental crust. Plots of most major and minor element oxides against MgO for the lavas define very tight trends consistent with modification of melts parental to the erupted suite by olivine fractionation or accumulation. However, melt inclusions trapped in primitive olivine phenocrysts in these lavas have

Gregory M. Yaxley; Vadim S. Kamenetsky; Maya Kamenetsky; Marc D. Norman; Don Francis

2004-01-01

274

Destabilization of olivine by 10kV electron irradiation  

NASA Astrophysics Data System (ADS)

Mineral phases in the interplanetary medium are subjected to the solar wind irradiation. Irradiation induces fractional volatilization of chemical elements in silicates; if large scale directional flow occurs, such as predicted by numerous models in the early solar system, then large scale chemical fractionnations occur. Electron irradiation experiments were performed using a 30 keV electron beam on single crystals of olivine in a scanning electron microscope (SEM) and in an electron microprobe (EMP) (Lemelle et al. 2003). Structural damage is caused to the irradiated surface of the iron-bearing olivines. The irradiated areas comprise spherules with sizes of hundreds of nanometers and micrometer-sized holes observed on Focused Ion Beam cuts. In the immediate vicinities of the irradiated areas, droplets with sizes of tens of nanometers and tracks are observed. With increasing total charge, the hundreds of nanometer-sized spherules become larger and more irregular in shape. The size and shape of the nanometer-sized droplets remain almost constant, but their surface density increases (in cm-2). Compared to the initial olivine, irradiated areas are slightly enriched in MgO, whereas the deposits are enriched in SiO_2. This destabilization of olivine results most probably from electrostatic discharges leading to the breakdown of the dielectric lattice. The possibility that such processes could be responsible for significant space weathering of interplanetary dust particles and regoliths of planetary surfaces should be taken into account. In the interplanetary medium, 10 keV-range electrons are carried by the solar wind, whereas at 1 AU from the Sun, the lifetime of cometary dust and the exposure time of lunar regolith are, at least, 10 to 100 times greater than the duration required to accumulate the damaging electronic doses applied in this study. Moreover, the comparison of the microstructures of samples irradiated in the present study with features of lunar regolith grains reveals several chemical and structural similarities. Interestingly, experiments carried out in transmission EM, with 100 keV-range electrons (Carrez et al. 2002) showed different mechanism of destabilization and chemical fractionation elemental loss from the silicate matrix. Lemelle et al. (2003) to be printed in Geochimica Cosmochimica Acta. Carrez P., Leroux H., Cordier P. and Guyot F. (2001) Philos. Mag. A 81, 2823-2840.

Lemelle, L.; Beaunier, L.; Borensztajn, S.; Fialin, M.; Guyot, F.

2003-04-01

275

Chromium valences in ureilite olivine and implications for ureilite petrogenesis  

NASA Astrophysics Data System (ADS)

Ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon-rich asteroid. They show a large variation in FeO content (olivine Fo values ranging from ?74 to 95) that cannot be due to igneous fractionation and suggests instead variation in oxidation state. The presence of chromite in only a few of the most ferroan (Fo 75-76) samples appears to support such a model. MicroXANES analyses were used in this study to determine the valence states of Cr (previously unknown) in olivine cores of 11 main group ureilites. The goal of this work was to use a method that is independent of Fo to determine the oxidation conditions under which ureilites formed, in order to evaluate whether the ureilite FeO-variation is correlated with oxidation state, and whether it is nebular or planetary in origin. Two of the analyzed samples, LEW 88774 (Fo 74.2) and NWA 766 (Fo 76.7) contain primary chromite; two others, LAP 03587 (Fo 74.4) and CMS 04048 (Fo 76.2) contain sub-micrometer-sized exsolutions of chromite + Ca-rich pyroxene in olivine; and one, EET 96328 (Fo 85.2) contains an unusual chromite grain of uncertain origin. No chromite has been observed in the remaining six samples (Fo 77.4-92.3). Chromium in olivine in all eleven samples was found to be dominated by the divalent species, with valences ranging from 2.10 0.02 (1?) to 2.46 0.04. The non-chromite-bearing ureilites have the most reduced Cr, with a weighted mean valence of 2.12 0.01, i.e., Cr2+/Cr3+ = 7.33. All low-Fo chromite-bearing ureilites have more oxidized Cr, with valences ranging from 2.22 0.03 to 2.46 0.04. EET 96328, whose chromite grain we interpret as a late-crystallizing phase, yielded a reduced Cr valence of 2.15 0.07, similar to the non-chromite-bearing samples. Based on the measured Cr valences, magmatic (1200-1300 C) oxygen fugacities (fO2) of the non-chromite-bearing samples were estimated to be in the range IW-1.9 to IW-2.8 (assuming basaltic melt composition), consistent with fO2 values obtained by assuming olivine-silica-iron metal (OSI) equilibrium. For the primary chromite-bearing-ureilites, the corresponding fO2 were estimated (again, assuming basaltic melt composition) to be ?IW to IW+1.0, i.e., several orders of magnitude more oxidizing than the conditions estimated for the chromite-free ureilites. In terms of Fo and Cr valence properties, ureilites appear to form two groups rather than a single Cr-valence (or fO2) vs. Fo trend. The chromite-bearing ureilites show little variation in Fo (?74-76) but significant variation in Cr valence, while the non-chromite-bearing ureilites show significant variation in Fo (?77-95) and little variation in Cr valence. These groups are unrelated to petrologic type (i.e., olivine-pigeonite, olivine-orthopyroxene, or augite-bearing). The chromite-bearing ureilites also have lower contents of Cr in olivine than most non-chromite-bearing ureilites, consistent with predictions based on Cr olivine/melt partitioning in spinel saturated vs. non-spinel-saturated systems. Under the assumption that at magmatic temperatures graphite-gas equilibria controlled fO2 at all depths on the ureilite parent body, we conclude: (1) that ureilite precursor materials having the Fo and Cr valence properties now observed in ureilites are unlikely to have been preserved during planetary processing; and (2) that the Fo and Cr valence properties now observed in ureilites are consistent with having been established by high-temperature carbon redox control over a range of depths on a plausible-sized ureilite parent body. The apparent limit on ureilite Fo values around 74-76 suggests that the precursor material(s) had bulk mg# ? that of LL chondrites.

Goodrich, C. A.; Sutton, S. R.; Wirick, S.; Jercinovic, M. J.

2013-12-01

276

Olivine-rich exposures at Bellicia and Arruntia craters on (4) Vesta from Dawn FC  

NASA Astrophysics Data System (ADS)

We present an analysis of olivine-rich exposures at Bellicia and Arruntia craters using Dawn Framing Camera (FC) color data. Our results confirm the existence of olivine-rich materials at these localities as described by Ammannito et al. using Visual Infrared Spectrometer (VIR) data. Analyzing laboratory spectra of various howardite-eucrite-diogenite meteorites, high-Ca pyroxenes, olivines, and olivine-orthopyroxene mixtures, we derive three FC spectral band parameters that are indicators of olivine-rich materials. Combining the three band parameters allows us, for the first time, to reliably identify sites showing modal olivine contents >40%. The olivine-rich exposures at Bellicia and Arruntia are mapped using higher spatial resolution FC data. The exposures are located on the slopes of outer/inner crater walls, on the floor of Arruntia, in the ejecta, as well as in nearby fresh small impact craters. The spatial extent of the exposures ranges from a few hundred meters to few kilometers. The olivine-rich exposures are in accordance with both the magma ocean and the serial magmatism model (e.g., Righter and Drake; Yamaguchi et al.). However, it remains unsolved why the olivine-rich materials are mainly concentrated in the northern hemisphere (approximately 36-42N, 46-74E) and are almost absent in the Rheasilvia basin.

Thangjam, Guneshwar; Nathues, Andreas; Mengel, Kurt; Hoffmann, Martin; Schfer, Michael; Reddy, Vishnu; Cloutis, Edward A.; Christensen, Ulrich; Sierks, Holger; Corre, Lucille Le; Vincent, Jean-Baptiste; Russell, Christopher T.

2014-10-01

277

Extremely Na and Cl-rich chondrule from the CV3 carbonaceous chondrite Allende  

Microsoft Academic Search

We report on a study of Al3509, a large Na- and Cl-rich, radially-zoned object from the oxidized CV carbonaceous chondrite Allende. Al3509 consists of fine-grained ferroan olivine, ferroan Al-diopside, nepheline, sodalite, and andradite, and is crosscut by numerous veins of nepheline, sodalite, and ferroan Al-diopside. Some poorly-characterized phases of fine-grained material are also present; these phases contain no significant H2O.

G. J. Wasserburg; I. D. Hutcheon; J. Alon; E. C. Ramon; A. N. Krot; K. Nagashima; A. J. Brearley

2011-01-01

278

Chondrule-Forming Shock Fronts in the Solar Nebula: A Possible Unified Scenario for Planet and Chondrite Formation  

E-print Network

Chondrules are mm-sized spherules found throughout primitive, chondritic meteorites. Flash heating by a shock front is the leading explanation of their formation. However, identifying a mechanism for creating shock fronts inside the solar nebula has been difficult. In a gaseous disk capable of forming Jupiter, the disk must have been marginally gravitationally unstable at and beyond Jupiter's orbit. We show that this instability can drive inward spiral shock fronts with shock speeds of up to about 10 km/s at asteroidal orbits, sufficient to account for chondrule formation. Mixing and transport of solids in such a disk, combined with the planet-forming tendencies of gravitational instabilities, results in a unified scenario linking chondrite production with gas giant planet formation.

A. P. Boss; R. H. Durisen

2005-01-26

279

Annealing behaviour of ion tracks in olivine, apatite and britholite  

NASA Astrophysics Data System (ADS)

Ion tracks were created in olivine from San Carlos, Arizona (95% Mg2SiO4), apatite (Ca5(PO4)3(F,Cl,O)) from Durango, Mexico, and synthetic silicates with the apatite structure: Nd8Sr2(SiO4)6O2 and Nd8Ca2(SiO4)6O2 using 1.6 and 2.2 GeV Au ions. The morphology and annealing behaviour of the tracks were investigated by means of synchrotron based small angle X-ray scattering in combination with ex situ annealing. Tracks in olivine annealed above ?400 C undergo a significant change in track radius due to recrystallisation of the damage tracks. At temperatures higher than 620 C, the scattering images indicate fragmentation of the track cylinders into smaller subsections. Ion tracks were annealed at elevated temperatures up to 400 C in the Durango and Ca-britholite, and up to 560 C in Sr-britholite. While there was a significant change in the track radii in the Durango apatite, tracks in the two synthetic samples remained almost unchanged.

Afra, B.; Lang, M.; Bierschenk, T.; Rodriguez, M. D.; Weber, W. J.; Trautmann, C.; Ewing, R. C.; Kirby, N.; Kluth, P.

2014-05-01

280

Extended solid solutions and coherent transformations in nanoscale olivine cathodes.  

PubMed

Nanoparticle LiFePO4, the basis for an entire class of high power Li-ion batteries, has recently been shown to exist in binary lithiated/delithiated states at intermediate states of charge. The Mn-bearing version, LiMn(y)Fe(1-y)PO4, exhibits even higher rate capability as a lithium battery cathode than LiFePO4 of comparable particle size. To gain insight into the cause(s) of this desirable performance, the electrochemically driven phase transformation during battery charge and discharge of nanoscale LiMn0.4Fe0.6PO4 of three different average particle sizes, 52, 106, and 152 nm, is investigated by operando synchrotron radiation powder X-ray diffraction. In stark contrast to the binary lithiation states of pure LiFePO4 revealed in recent investigations, the formations of metastable solid solutions covering a remarkable wide compositional range, including while in two-phase coexistence, are observed. Detailed analysis correlates this behavior with small elastic misfits between phases compared to either pure LiFePO4 or LiMnPO4. On the basis of time- and state-of-charge dependence of the olivine structure parameters, we propose a coherent transformation mechanism. These findings illustrate a second, completely different phase transformation mode for pure well-ordered nanoscale olivines compared to the well-studied case of LiFePO4. PMID:24548146

Ravnsbk, D B; Xiang, K; Xing, W; Borkiewicz, O J; Wiaderek, K M; Gionet, P; Chapman, K W; Chupas, P J; Chiang, Y-M

2014-03-12

281

Morphology and surface features of olivine in kimberlite: implications for ascent processes  

NASA Astrophysics Data System (ADS)

Most kimberlite rocks contain large proportions of ellipsoidal-shaped xenocrystic olivine grains that are derived mainly from disaggregation of peridotite. Here, we describe the shapes, sizes and surfaces of olivine grains recovered from kimberlite lavas erupted from the Quaternary Igwisi Hills volcano, Tanzania. The Igwisi Hills kimberlitic olivine grains are compared to phenocrystic olivine, liberated from picritic lavas, and mantle olivine, liberated from a fresh peridotite xenolith. Image analysis, scanning electron microscopy imagery and laser microscopy reveal significant differences in the morphologies and surface features of the three crystal populations. The kimberlitic olivine grains form smooth, rounded to ellipsoidal shapes and have rough flaky micro-surfaces that are populated by impact pits. Mantle olivine grains are characterised by flaked surfaces and indented shapes consistent with growth as a crystal aggregate. Phenocrystic olivine exhibit faceted, smooth-surfaced crystal faces. We suggest that the unique shape and surface properties of the Igwisi Hills kimberlitic olivine grains are products of the transport processes attending kimberlite ascent from mantle source to surface. We infer that the unique shapes and surfaces of kimberlitic olivine grains result from three distinct mechanical processes attending their rapid transport through the thick cratonic mantle lithosphere: (1) penetrative flaking from micro-tensile failure induced by rapid decompression; (2) sustained abrasion and attrition driven by particle-particle collisions between grains within a turbulent, volatile-rich flow regime; and (3) higher-energy particle-particle collisions producing impact cavities superimposed on decompression structures. The combination of these processes during the rapid ascent of kimberlite magmas is responsible for the distinctive ellipsoidal shape of olivine xenocrysts found in kimberlites worldwide.

Jones, T. J.; Russell, J. K.; Porritt, L. A.; Brown, R. J.

2014-05-01

282

Olivine-rich exposures in the South Pole-Aitken Basin  

NASA Astrophysics Data System (ADS)

The distribution and the geological context of the olivine-rich exposures in the South Pole-Aitken (SPA) Basin on the Moon were investigated based on the spectral data obtained from the Spectral Profiler (SP) and Multiband Imager (MI) onboard the Japanese lunar explorer Kaguya/SELENE. The olivine-rich exposures are found only in the peak rings or central peaks of the Schrdinger basin and Zeeman crater, which are located in the outer region of the SPA Basin and not in the center region. On a localized scale, the olivine-rich materials are exposed on landslide features on the crater walls or sloped wall of the central peaks or the peak rings. Another observational finding is the co-existence of olivine-rich and plagioclase-rich materials on a kilometer scale spanning most of the olivine-rich sites in the Schrdinger basin. Pyroxene-rich materials are found in fresh craters outside the peak rings or the central peaks with olivine-rich materials. Based on these results, the following scenario are proposed: (1) the impact to form the SPA Basin melted a large amount of the lunar upper mantle and crust, and distributed the melted materials to the outer region; (2) local differentiation of melted materials hid the olivine-rich materials in the center region of the SPA Basin; (3) later impacts that formed the Schrdinger and Zeeman craters excavated and exposed the olivine-rich materials to the surface again; and (4) space weathering and regolith gardening obscured the olivine-rich spectra at the exposure sites, but recent, small scale impacts or landslides on the sloped wall exposed fresh olivine-rich materials, allowing the identification of the olivine-rich exposures by spectral remote-sensing. This suggests that several, different scale events play an important role in forming the surface distributions of originally deep-seated materials on the Moon, as well as on other planetary bodies.

Yamamoto, Satoru; Nakamura, Ryosuke; Matsunaga, Tsuneo; Ogawa, Yoshiko; Ishihara, Yoshiaki; Morota, Tomokatsu; Hirata, Naru; Ohtake, Makiko; Hiroi, Takahiro; Yokota, Yasuhiro; Haruyama, Junichi

2012-03-01

283

Shock-wave heating model for chondrule formation: Hydrodynamic simulation of molten droplets exposed to gas flows  

NASA Astrophysics Data System (ADS)

Millimeter-sized, spherical silicate grains abundant in chondritic meteorites, which are called as chondrules, are considered to be a strong evidence of the melting event of the dust particles in the protoplanetary disk. One of the most plausible scenarios is that the chondrule precursor dust particles are heated and melt in the high-velocity gas flow (shock-wave heating model). We developed the non-linear, time-dependent, and three-dimensional hydrodynamic simulation code for analyzing the dynamics of molten droplets exposed to the gas flow. We confirmed that our simulation results showed a good agreement in a linear regime with the linear solution analytically derived by Sekyia et al. [Sekyia, M., Uesugi, M., Nakamoto, T., 2003. Prog. Theor. Phys. 109, 717-728]. We found that the non-linear terms in the hydrodynamical equations neglected by Sekiya et al. [Sekiya, M., Uesugi, M., Nakamoto, T., 2003. Prog. Theor. Phys. 109, 717-728] can cause the cavitation by producing negative pressure in the droplets. We discussed that the fragmentation through the cavitation is a new mechanism to determine the upper limit of chondrule sizes. We also succeeded to reproduce the fragmentation of droplets when the gas ram pressure is stronger than the effect of the surface tension. Finally, we compared the deformation of droplets in the shock-wave heating with the measured data of chondrules and suggested the importance of other effects to deform droplets, for example, the rotation of droplets. We believe that our new code is a very powerful tool to investigate the hydrodynamics of molten droplets in the framework of the shock-wave heating model and has many potentials to be applied to various problems.

Miura, Hitoshi; Nakamoto, Taishi

2007-05-01

284

The Iodine-Xenon System in Outer and Inner Portions of Chondrules from the Unnamed Antarctic LL3 Chondrite  

NASA Technical Reports Server (NTRS)

Alteration processes may affect I-Xe system in unequilibrated ordinary chondrites. It was shown that at the edges, where a contribution is made by matrix material around the rim, *Xe-129/Xe-128 values are generally lower (later apparent ages) than in the main chondrule mass. In this work we attempted to investigate whether thermal metamorphism can affect the I-Xe system in LL3 chondrites which did not experienced aqueous alteration.

Meshik, A. P.; Pravdivtseva, O. V.; Hohenberg, C. M.; Amelin, Y.

2004-01-01

285

Serpentinization of Olivine by Seawater: A Flow-Through Experiment  

NASA Astrophysics Data System (ADS)

The mantle exposed at slow spreading ridges is pervasively serpentinized, down to ca. 5km according to geophysical data. The onset and durability of this hydration process require efficient penetration and renewal of fluids at the mineral-fluid interface. However, the mechanisms of fluid penetration are still poorly understood. Moreover, serpentinization is exovolumic, if a mass-conservative system is assumed, or chemical elements are leached out to conserve rock volume. Thus, the extent of serpentinization depends of the system capacity to create space and/or to drive mass transfers. In order to investigate these hydrodynamic and chemical mechanisms, we did a laboratory experiment during which seawater was injected in a sintered San Carlos olivine sample at conditions representative of low temperature ultramafic hydrothermal systems. The percolation-reaction experiment was carried out at 19 MPa and 190C; the initial water flow was set at 0.2 mL/h then decreased down to 0.06 mL/h after 8 days. During the experiment (23 days), permeability decreased continuously. The composition of the outlet fluid varied strongly during the first 24h of the experiment, then reached equilibrium values. The high Si concentrations in outlet fluids indicated steady olivine dissolution, while their low Fe and Mg concentrations suggested precipitation of Fe- and Mg-rich mineral phases. The reacted sample acquired a reddish brown color, indicating oxidation reactions occurred. Optical observation and SEM imaging revealed the presence of a soft white material filling the pores of the reacted sample. It was identified as a poorly crystallized serpentine type material by AEM/TEM analyses. This proto-serpentine is intimately associated to <100 nm Fe-oxide patches (probably hematite) growing on the olivine surface. We interpret the precipitation of this proto-serpentine together with Fe-oxides throughout the sample as marking the early stages of serpentinization. The fluid composition not being modified by changes in fluid flow, we posit that olivine serpentinization is not controlled by elemental transport and/or by chemical kinetics, but takes place at-equilibrium; the reaction velocity is very fast and independent on the changes in the reaction surface area. Indeed, mass balance calculations indicate that more than 15 wt. % olivine was dissolved while the same mass of proto-serpentine was formed; concurrently, porosity decreased from 12% to 5 %. We infer that the structure of the newly formed proto-serpentine resulted in the clogging of fluid paths and explain the decrease of permeability during experiments. Yet the loose structure of the proto-serpentine allows maintaining a connected pore structure ensuring the perennial renewing (diffusion and/or advection) of the reactants at the reaction surfaces. These experimental results are used to constrain numerical reactive transport models and better understand the scale and efficiency of serpentinization reactions (effective reaction rates in porous/fractured media) at the scale of spreading ridges.

Gouze, P.; Luquot, L.; Andreani, M.; Godard, M.; Gibert, B.

2011-12-01

286

Toll Bar on Sea  

ERIC Educational Resources Information Center

In the summer of 2007 the United Kingdom experienced some of the heaviest rainfall since records began. Toll Bar in South Yorkshire featured prominently in media coverage as the village and the homes surrounding it began to flood. Many people lost everything: their homes, their furniture, their possessions. In an effort to come to terms with what

Hunter, Dave

2008-01-01

287

Bar-grid oscillators  

Microsoft Academic Search

Grid oscillators are an attractive way of obtaining high power levels from the solid-state devices, since potentially the output powers of thousands of individual devices can be combined. The active devices do not require an external locking signal, and the power combining is done in free space. Thirty-six transistors were mounted on parallel brass bars, which provide a stable bias

ZOYA BASTA POPOVIC; ROBERT M. WEIKLE; MOONIL KIM; KENT A. POTTER; DAVID B. RUTLEDGE

1990-01-01

288

Permanent Bar Magnets  

NSDL National Science Digital Library

This is an activity about the basic properties of magnets and magnetism. Learners explore concepts such as magnetic fields and polarity, which form the basic ingredients of a study of Earth's magnetic field and the technology of magnetometers. Materials needed include bar magnets and paper clips. This is Activity 1 of Exploring Magnetism: A Teacher's Magnetism Activity Guide.

289

Data Analysis: Bar Graphs  

NSDL National Science Digital Library

In this Bridges In Mathematics Supplement, two activities are presented in which primary students are introduced to bar graphs. In each activity students graph catagorical data that reflects their own opinions. Once the graphs are complete, students analyze the data as a class and make conclusions based on the data.

2009-01-01

290

{sup 60}Fe AND {sup 26}Al IN CHONDRULES FROM UNEQUILIBRATED CHONDRITES: IMPLICATIONS FOR EARLY SOLAR SYSTEM PROCESSES  

SciTech Connect

The presence of about a dozen short-lived nuclides in the early solar system, including {sup 60}Fe and {sup 26}Al, has been established from isotopic studies of meteorite samples. An accurate estimation of solar system initial abundance of {sup 60}Fe, a distinct product of stellar nucleosynthesis, is important to infer the stellar source of this nuclide. Previous studies in this regard suffered from the lack of exact knowledge of the time of formation of the analyzed meteorite samples. We present here results obtained from the first combined study of {sup 60}Fe and {sup 26}Al records in early solar system objects to remove this ambiguity. Chondrules from unequilibrated ordinary chondrites belonging to low petrologic grades were analyzed for their Fe-Ni and Al-Mg isotope systematics. The Al-Mg isotope data provide the time of formation of the analyzed chondrules relative to the first solar system solids, the Ca-Al-rich inclusions. The inferred initial {sup 60}Fe/{sup 56}Fe values of four chondrules, combined with their time of formation based on Al-Mg isotope data, yielded a weighted mean value of (6.3 {+-} 2) x 10{sup -7} for solar system initial {sup 60}Fe/{sup 56}Fe. This argues for a high-mass supernova as the source of {sup 60}Fe along with {sup 26}Al and several other short-lived nuclides present in the early solar system.

Mishra, R. K.; Goswami, J. N.; Rudraswami, N. G. [Physical Research Laboratory, Ahmedabad-380009 (India); Tachibana, S. [Department of Earth and Planetary Sciences, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033 (Japan); Huss, G. R., E-mail: goswami@prl.res.i [Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)

2010-05-10

291

The Planetesimal Bow Shock Model for Chondrule Formation: More Detailed Simulations in the Near Vicinity of the Planetesimal  

NASA Technical Reports Server (NTRS)

Gas dynamic shock waves in a low temperature nebula have been considered to be a leading candidate mechanism for providing the repetitive, short-duration heating events that are believed to have been responsible for the formation of chondrules in chondrites. It has been found, for example, that shocks with Mach numbers greater than 4 or 5 would be capable of rapidly melting 0.1-1 mm sized silicate particles as required by meteoritic data. Near the nebula midplane where chondrite parent bodies are believed to have formed, possible energy sources for generating multiple shocks include mass concentrations in a gravitationally unstable nebula, tidal interactions of proto-Jupiter with the nebula, and bow waves upstream of planetesimals scattered gravitationally into eccentric orbits by proto- Jupiter. In a recent study, we have found that chondrule precursors that are melted following passage through a planetesimal bow shock would likely cool at rates that are too rapid to be consistent with meteoritic evidence. However, that study was limited to the bowshock exterior to about 1.5 planetesimal radii (measured perpendicular to the symmetry axis) to avoid complications interior to this distance where large pressure gradients and lateral flow occur as the gas flows around the planetesimal. In this paper, we reconsider the planetesimal bow shock model and report more detailed numerical simulations of chondrule precursor heating, cooling, and dynamical histories in the near vicinity of a representative planetesimal.

Hood, Lon L.; Ciesla, Fred J.

2005-01-01

292

Resonances in barred galaxies  

NASA Astrophysics Data System (ADS)

The inner parts of many spiral galaxies are dominated by bars. These are strong non-axisymmetric features which significantly affect orbits of stars and dark matter particles. One of the main effects is the dynamical resonances between galactic material and the bar. We detect and characterize these resonances in N-body models of barred galaxies by measuring angular and radial frequencies of individual orbits. We found narrow peaks in the distribution of orbital frequencies with each peak corresponding to a specific resonance. We found five different resonances in the stellar disc and two in the dark matter. The corotation resonance (CR) and the inner and outer Lindblad resonances are the most populated. The spatial distributions of particles near resonances are wide. For example, the inner Lindblad resonance is not localized at a given radius. Particles near this resonance are mainly distributed along the bar and span a wide range of radii. On the other hand, particles near the CR are distributed in two broad areas around the two stable Lagrange points. The distribution resembles a wide ring at the corotation radius. Resonances capture disc and halo material in near-resonant orbits. Our analysis of orbits in both N-body simulations and simple analytical models indicates that resonances tend to prevent the dynamical evolution of this trapped material. Only if the bar evolves as a whole, resonances drift through the phase space. In this case particles anchored near resonant orbits track the resonance shift and evolve. The criteria to ensure a correct resonant behaviour discussed by Weinberg and Katz can be achieved with few millions particles because the regions of trapped orbits near resonances are large and evolving.

Ceverino, D.; Klypin, A.

2007-08-01

293

Nitrogen Isotopes in Olivine Separates from Volcanic Arcs, Hot Spots and Continental Mantle Xenoliths  

Microsoft Academic Search

We report the first nitrogen isotopic data of olivine separates from volcanic arcs (Cerro Negro, Nicaragua; Izalco, El Salvador; Turrialba, Costa Rica; Ichinomegata, Japan). In addition, we report nitrogen isotopic data of olivine separates from ocean islands (Hawaii, Reunion, Iceland) and continental mantle xenoliths (San Carlos, Arizona). Samples were processed by crushing and analyzed using a modified noble gas mass

T. P. Fischer; N. Takahata; Y. Sano; D. R. Hilton

2004-01-01

294

Cooling rates in the lower crust of the Oman ophiolite: Ca in olivine, revisited  

E-print Network

Cooling rates in the lower crust of the Oman ophiolite: Ca in olivine, revisited Jill A. Van crust of the Khafifah section in the Wadi Tayin massif of the Oman ophiolite. Additionally, very high B.V. All rights reserved. Keywords: calcium; olivine; oman; hydrothermal; cooling; crust 1

VanTongeren, Jill A.

295

High-temperature condensation of iron-rich olivine in the solar nebula  

Microsoft Academic Search

The origin of oxidized iron in chondritic meteorites is a fundamental problem in meteoritics. Conventional models of meteorite formation assume FeO incorporation into olivine and pyroxene at around 500 K. There is evidence that at least some fayalitic olivine in Allende must have formed by condensation. Thermodynamic equilibrium calculations presented here define the nebular conditions that would enable condensation of

Herbert Palme; Bruce Fegley Jr.

1990-01-01

296

BAR PACKAGES Standard Bar Package Price Liquor Beer/Wine  

E-print Network

BAR PACKAGES Standard Bar Package Price Liquor Beer/Wine 1-2 hours $21/ person Sobieski Vodka MGD 3 Select Wine Cutty Sark Scotch Cruzan Rum Premium Bar Package Price Liquor Beer/Wine 1-2 hours $24/person Brothers Brewing Co* Dewars Scotch Field Museum Select Wine Bacardi Rum Super Premium Package Price Liquor

Westneat, Mark W.

297

The importance of defining chemical potentials, substitution mechanisms and solubility in trace element diffusion studies: the case of Zr and Hf in olivine  

NASA Astrophysics Data System (ADS)

The diffusion, substitution mechanism and solubility limits of Zr and Hf in synthetic forsterite (Mg2SiO4) and San Carlos olivine (Mg0.9Fe0.1)2SiO4 have been investigated between 1,200 and 1,500 C as a function of the chemical potentials of the components in the system MgO(FeO)-SiO2-ZrO2(HfO2). The effect of oxygen fugacity and crystallographic orientation were also investigated. The solubilities of Zr in forsterite are highest and diffusion fastest when the coexisting three-phase source assemblage includes ZrSiO4 (zircon) or HfSiO4 (hafnon), and lower and slower, respectively, when the source assemblage includes MgO (periclase). This indicates that Zr and Hf substitute on the octahedral sites in olivine, charge balanced by magnesium vacancies. Diffusion is anisotropic, with rates along the crystal axes increasing in the order a < b < c. The generalized diffusion relationship as a function of chemical activity (as ), orientation and temperature is: where the values of log D 0 are -3.8(0.5), -3.4(0.5) and -3.1(0.5) along the a, b and c axes, respectively. Most experiments were conducted in air ( fO2 = 10-0.68 bars), but one at fO2 = 10-11.2 bars at 1,400 C shows no resolvable effect of oxygen fugacity on Zr diffusion. Hf is slightly more soluble in olivine than Zr, but diffuses slightly slower. Diffusivities of Zr in experiments in San Carlos olivine at 1,400 C, fO2 = 10-6.6 bars are similar to those in forsterite at the same conditions, showing that the controls on diffusivities are adequately captured by the simple system (nominally iron-free) experiments. Diffusivities are in good agreement with those measured by Spandler and O'Neill (Contrib Miner Petrol 159:791-818, 2010) in San Carlos olivine using silicate melt as the source at 1,300 C, and fall within the range of most measurements of Fe-Mg inter-diffusion in olivine at this temperature. Forsterite-melt partitioning experiments in the CaO-MgO-Al2O3-SiO2-ZrO2/HfO2 show that the interface concentrations from the diffusion experiments represent true equilibrium solubilities. Another test of internal consistency is that the ratios of the interface concentrations between experiments buffered by Mg2SiO4 + Mg2Si2O6 + ZrSiO4 or Mg2SiO4 + ZrSiO4 + ZrO2 (high silica activity) to those buffered by Mg2SiO4 + MgO + ZrO2 (low silica activity) agree well with the ratios calculated from thermodynamic data. This study highlights the importance of buffering chemical potentials in diffusion experiments to provide constraints on the interface diffusant concentrations and hence validate the assumption of interface equilibrium.

Jollands, Michael C.; O'Neill, Hugh St. C.; Hermann, Jrg

2014-09-01

298

Concentration and Mobility of Electrically-Conducting Defects in Olivine  

NASA Astrophysics Data System (ADS)

We have collected measurements of electrical conductivity and thermopower as a function of temperature and oxygen fugacity (f O2) on a sample of San Quintin dunite (95% olivine), and measurements of electrical conductivity equilibration after changes in f O2 on Mt.Porndon lherzolite (65% olivine). Both data sets have been analysed using nonlinear parameter inversion of mathematical models relating conductivity, thermopower, and diffusion kinetics to temperature, f O2, time, and defect concentration and mobility. From the dunite thermopower/conductivity data we are able to estimate the concentration and mobilities of electrically conducting defects. Our model allows electrons, small polarons (Fe+++ on Fe++ sites), and magnesium vacancies (V'' Mg) to contribute to conduction, but only polarons and V'' Mg are required by our data. Polarons dominate conduction below 1300~C; at this temperature conduction, is equal for the two defects at all f O2 tested. Thermopower measurements allow us to estimate defect concentration independently from mobility, and so we can back out polaron mobility as 12.2x 10-6 exp(-1.05~eV/kT) m2V-1s-1 and magnesium vacancy mobility as 2.72x 10-6 exp(-1.09~eV/kT) m2V-1s-1. Electrical conductivity of the lherzolite, measured as a function of time after changes in the oxygen fugacity of the surrounding CO2/CO atmosphere, is used to infer the diffusivity of the point defects associated with the oxidation reactions. An observed f O2 dependence in the time constants associated with equilibration implies two species of fixed diffusivity, each with f O2-dependent concentrations. Although the rate-limiting step may not necessarily be associated with conducting defects, when time constants are converted to mobilities, the magnitudes and activation energies agree extremely well with the model presented above for the dunite, after one free parameter (effective grain size) is fit at a plausible 1.6~mm diameter. Not only does this study represent one of the few direct measurements of polaron mobility, but the very good agreement between two independent measurement techniques (thermopower versus equilibration kinetics) and two independent samples (dunite versus lherzolite) provides some level of confidence in the results. We are currently extending these modeling techniques to study olivine defect mobility anisotropy.

Constable, S.; Roberts, J.; Duba, A.

2002-12-01

299

Termination and hydration of forsteritic olivine (0 1 0) surface  

NASA Astrophysics Data System (ADS)

Termination and hydration of the forsteritic (Fo90Fa10) olivine (0 1 0) surface have been investigated with high-resolution specular X-ray reflectivity and Atomic Force Microscopy. The surface was prepared by polishing a naturally grown {0 1 0} face, from which we found the polished surface in acidic (pH 3.5) alumina suspension exhibits regular steps while the basic (pH 9.5) silica polished surface is irregularly roughened, indicating there are two distinguishable mechanochemical processes for the surface dissolution. The quantitative interpretation of the regular steps from the alumina-polished surface suggests that the observed step heights correspond to multiples of crystallographic unit cell. Only this atomically terraced surface is investigated with the high-resolution X-ray reflectivity (HRXR) to determine the surface termination and hydration. The basic silica paste polished surface turned out too rough to measure with X-ray reflectivity. HRXR reveals that the alumina polished olivine (0 1 0) surface in pure water is terminated at a plane including half-occupied metal ion sites (M1), an oxygen vacancy site, and a silicate tetrahedral unit with one of its apices pointing outward with respect to the surface. An ideal termination with the oxygen vacancy would fulfill the stoichiometry of the formula unit; however, in the observation, the vacancy site is filled by an adsorbed water species and about a quarter of the remaining metal ions are further depleted. The terminating plane generates two distinct atomic layers in the laterally averaged electron density profile, on which two highly ordered adsorbed water layers are formed. The first layer formation is likely through the direct interaction with the M1 plane and the second layer is likely through the hydrogen bonding interaction with the first water layer. With this multilayered adsorbed water structure, the surface metal ion is partially hydrated by the vacancy-filling water species and adsorbed water molecules. The bulk water links to these distinct adsorbed water layers, with weak density oscillations that almost completely damp out after the first bulk water layer. The total thickness of the layered water structure including the two distinct adsorbed layers and the first layer of bulk water is slightly less than 1 nm, which corresponds to roughly three molecular layers of water. These results describe the steric constraints of the surface metal ion hydration and the iron redox environment during water-olivine interactions in this particular crystallographic orientation.

Yan, Hongping; Park, Changyong; Ahn, Gun; Hong, Seungbum; Keane, Denis T.; Kenney-Benson, Curtis; Chow, Paul; Xiao, Yuming; Shen, Guoyin

2014-11-01

300

The Mn-Fe negative correlation in olivines in ALHA 77257 ureilite  

NASA Astrophysics Data System (ADS)

An electron probe microanalyzer is used to measure the Mn, Fe, and oxygen zoning profiles of olivines in the ALHA 77257 ureilite. This is done to study the effects of reduction on the Mn-Fe value, as ureilite olivines exhibit thin reduced rims. Since the Mn content gradually increases toward the rim of ureilite olivines, while the Fa (= 100 x Fe/(Mg + Fe), mol percent) component decreases, the Mn-Fe content of olivine is likely related to redox conditions. The results of melting experiments suggest that the Mn-Fe positive correlation is related to temperature and that the negative correlation of Mn-Fe in olivine and low-Ca pyroxene is related to reduction.

Miyamoto, M.; Furuta, T.; Fujii, N.; McKay, D. S.; Lofgren, G. E.; Duke, M. B.

1993-03-01

301

The Mn-Fe negative correlation in olivines in ALHA 77257 ureilite  

NASA Technical Reports Server (NTRS)

An electron probe microanalyzer is used to measure the Mn, Fe, and oxygen zoning profiles of olivines in the ALHA 77257 ureilite. This is done to study the effects of reduction on the Mn-Fe value, as ureilite olivines exhibit thin reduced rims. Since the Mn content gradually increases toward the rim of ureilite olivines, while the Fa (= 100 x Fe/(Mg + Fe), mol percent) component decreases, the Mn-Fe content of olivine is likely related to redox conditions. The results of melting experiments suggest that the Mn-Fe positive correlation is related to temperature and that the negative correlation of Mn-Fe in olivine and low-Ca pyroxene is related to reduction.

Miyamoto, M.; Furuta, T.; Fujii, N.; Mckay, D. S.; Lofgren, G. E.; Duke, M. B.

1993-01-01

302

Measurements of vertical bar Vcb vertical bar and vertical bar Vub vertical bar at BaBar  

SciTech Connect

We report results from the BABAR Collaboration on the semileptonic B decays, highlighting the measurements of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix elements Vub and Vcb. We describe the techniques used to obtain the matrix element |Vcb| using the measurement of the inclusive B {yields} Xclv process and a large sample of exclusive B {yields} D*lv decays. The vertical bar Vub vertical bar matrix elements has been measured studying different kinematic variables of the B {yields} Xulv process, and also with the exclusive reconstruction of B {yields} {pi}({rho})lv decays.

Rotondo, M. [Dipartimento di Fisica Galileo Galilei, Via Marzolo 8, Padova 35131 (Italy)

2005-10-12

303

Extended planar defects and the rapid incorporation of Ti4+ into olivine  

NASA Astrophysics Data System (ADS)

The formation of extended planar defects in minerals such as olivine is related to high point defect concentration and can be driven by large gradients in chemical potential, where the energy of the system is lowered by the ordering of defects along specific planes in the crystal. The presence of extended defects has the potential to create the (apparently) anomalous ionic diffusion in olivine as reported recently (Spandler and O'Neill in Contrib Mineral Petrol 159(6):791-818, 2010). High-resolution transmission electron microscopy and energy-filtered imaging were done using experimental samples designed to examine the impact of a TiO2 and f O2 on the potential to form such defects in ferromagnesian olivine. Doped basalt (5 wt% TiO2)-olivine reaction couple experiments were run at 1 atm and 1,310 and 1,410 C for 50 h at various f O2, ranging from 102 below to 102 above the quartz-fayalite-magnetite buffer. Our results show that extended planar defects in olivine, parallel to {101}ol and occurring in ordered "clusters" with a prolate spheroid geometry 5-25 nm across and extending up to 150 nm into the olivine, are present near the olivine-glass interfaces in all of our experimental high-TiO2 basalt-olivine samples. Increased Ti content in the olivine is associated with the defects; ordering of Ti4+ and octahedral site vacancies leads to a two- or three-layer superstructure in the olivine. Defect nucleation and growth is driven by the large TiO2 chemical potential gradient across the phase boundary at the start of the experiments, which provides access to microstructures not otherwise present.

Burgess, Katherine D.; Cooper, Reid F.

2013-10-01

304

Mantle-crust interactions in the oceanic lithosphere: Constraints from minor and trace elements in olivine  

NASA Astrophysics Data System (ADS)

Minor and trace element compositions of olivines are used as probes into the melt-rock reaction processes occurring at the mantle-crust transition in the oceanic lithosphere. We studied mantle and lower crustal sections from the Alpine Jurassic ophiolites, where lithospheric remnants of a fossil slow-spreading ocean are exposed. Olivines from plagioclase-harzburgites and replacive dunites (Fo = 91-89 mol%) and from olivine-rich troctolites and troctolites (Fo = 88-84 mol%) were considered. Positive correlations among the concentrations of Mn, Ni, Co, Sc and V characterize the olivines from the dunites. These chemical variations are reconciled with formation by melts produced by a mixed source consisting of a depleted peridotite and a pyroxene-rich, garnet-bearing component melted under different pressure conditions. We thereby infer that the melts extracted through these dunites channels were not fully aggregated after their formation into the asthenospheric mantle. Olivines from the olivine-rich troctolites and the troctolites are distinct by those in the dunites by lower Ni and higher concentrations of Mn and incompatible trace elements (Ti, Zr, Y and HREE). Fractional crystallization cannot reproduce the chemical variations of the olivines from the olivine-rich troctolites and the troctolites. In these rock-types, the olivines commonly show heterogeneous Ti, Zr, Y and HREE compositions, which produce variable Ti/Y and Zr/Y values. We correlate these olivine characteristics with events of reactive melt migration occurred during the formation of the primitive lower oceanic crust. We propose that the migrating melts formed at the mantle-crust transition via interaction with mantle peridotites during periods of low melt supply.

Sanfilippo, Alessio; Tribuzio, Riccardo; Tiepolo, Massimo

2014-09-01

305

Phyllosilicate and Olivine around a Fracture in Nili Fossae  

NASA Technical Reports Server (NTRS)

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) took this observation of part of the Nili Fossae region at the western margin of the Isidis impact basin at 3:07 (UTC) on December 12, 2006, near 21.9 degrees north latitude, 78.2 degrees east longitude. The image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 18 meters (60 feet) across. The image is about 11 kilometers (7 miles) wide at its narrowest point.

The Isidis basin resulted from a gigantic impact on the surface of Mars early in the planet's history. The image of the Isidis basin at the top left is the colored elevation data from the Mars Orbiter Laser Altimeter (MOLA) overlain on a digital image mosaic from the Viking mission. Reds represent higher elevations, and blue lower elevations. The western rim of the Isidis basin has numerous, concentric troughs (or 'fossae') which may have formed during faulting associated with the impact event. Since then, the Nili Fossae region has since been heavily eroded, and is one of the most mineralogically diverse spots on Mars.

This CRISM image targets one of region's smaller fractures. The image is shown overlain on the Viking digital image mosaic at lower left. The lower right CRISM image was constructed from three visible wavelengths (0.71, 0.60 and 0.53 microns in the red, green and blue image planes, respectively) and is close to what the human eye would see. The blue on the right of the image is an artifact from light scattering in the atmosphere. The upper right image was constructed from three infrared channels (2.38, 1.80 and 1.15 microns in the red, green and blue image planes, respectively) to highlight the mineralogy of the area. The bright green areas are rich in 'phyllosilicates,' a category of minerals including clays. The purple material along the walls of the fracture likely contains small amounts of the iron- and magnesium-rich mineral pyroxene. The yellow-brown material contains the iron- and magnesium-rich mineral olivine. Olivine and pyroxene are minerals associated with igneous activity.

Overlaying CRISM data with images from the High-Resolution Imaging Science Experiment (HiRISE) camera shows that the phyllosilicates are in small, eroded outcrops of rock. The olivine is most abundant in sand dunes on the surface. The use of these two instruments together reveals more about the history of the region: Olivine sands covered the area shown in the image after the interaction of water and rock formed the phyllosilicates and after the fracture formed.

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.

2007-01-01

306

Serpentinization of Sintered Olivine during Seawater Percolation Experiments  

NASA Astrophysics Data System (ADS)

Hydration of the mantle lithosphere exposed at slow spreading ridges leads to significant changes of the rock rheological, geophysical, mineralogical and geochemical properties, and to the production of large amounts of H2 and CH4, and of complex carbon molecules that support primitive ecosystems. The onset and efficiency of these hydrothermal processes requires penetration and renewal of fluids at the mineral-fluid interface. However, the mechanisms and the depth of fluid penetration are still poorly understood. Moreover, serpentinization is exovolumic, if a mass-conservative system is assumed, or chemical elements are leached out to conserve rock volume. Thus, the durability and extent of serpentinisation depends of the system capacity to create space and/or to drive mass transfers. In order to investigate these hydrodynamic and chemical mechanisms, we did a series of laboratory experiments during which seawater was injected in sintered San Carlos olivine samples at conditions representative of low temperature ultramafic hydrothermal systems. The percolation-reaction experiments were carried out using the ICARE 2 experimental bench at a confined pressure of 19 MPa and a temperature of 190C; water flow was set at a constant specific discharge of 0.06 mL/h. During experiments (up to 23 days), permeability decreases continuously although the high Si concentrations in outlet fluids indicate steady olivine dissolution. Fluids are also depleted in Fe and Mg, suggesting precipitation of Fe- and Mg-rich mineral phases; SEM and AEM/TEM analyses of the reacted samples allowed to characterize hematite and poorly crystallized serpentine, both formed at the expense of olivine. Mass balance calculations indicate that, on average, 15 wt. % olivine was dissolved while the same mass of serpentine (+/- brucite) was formed; concurrently, porosity decreased from ~ 12% to 5 %. We infer that the structure of the newly formed serpentine resulted in the clogging of fluid paths and explain the decrease of permeability during experiments. Hematite (<1 wt.%) is also observed, indicating redox reactions. The estimated total hydrogen content of outlet fluids is 4.5 mmol/kg. Although these values are in the same range as those measured at the Lost City hydrothermal vent (e.g., Kelley et al, 2001), they are significantly lower than theoretical estimates of hydrogen composition of serpentinisation fluids (e.g., 21-170 mmol/kg, Wetzel & Shock, 2000). We infer that these differences result, in part, from poor fluid renewal at the mineral interface during experiments, and maybe also in natural systems. These experimental results are used to constrain numerical reactive transport models and better understand the scale and efficiency of serpentinization reactions (effective reaction rates in porous/fractured media) at the scale of spreading ridges. Ref.: Kelley et al., Nature, 412, 145-149, 2001; Wetzel & Shock, JGR, 105, 8319-8340, 2000.

Luquot, L.; Andreani, M.; Godard, M.; Gouze, P.; Gibert, B.; Lods, G.

2010-12-01

307

The distribution of olivine in the crater Copernicus  

NASA Technical Reports Server (NTRS)

Multispectral imaging in the visible and near-IR at four wavelengths (0.73, 0.96, 1.45, and 1.99 micron) of Copernicus crater has been used to map the distribution of olivine-rich, pyroxene-poor material known previously to occur in the central peak complex. Three additional portions of the crater exhibit spectral characteristics similar to those of the central peaks, strongly suggesting the presence of material similar to that exposed in the central peaks. These areas are a scarp forming a portion of the northern rim of Copernicus, and two slump blocks in the north wall which may have been derived from the same portion of the ejecta now exposed in the rim scarp. These occurrences decrease the minimum allowable depth for this unusual material in the Copernicus target site though still represent some of the deepest material exposed by Copernicus.

Lucey, Paul G.; Hawke, B. R.; Horton, Keith

1991-01-01

308

The x ray microprobe determination of chromium oxidation state in olivine from lunar basalt and kimberlitic diamonds  

NASA Technical Reports Server (NTRS)

The synchrotron x-ray microprobe is being used to obtain oxidation state information on planetary materials with high spatial resolution. Initial results on chromium in olivine from various sources including laboratory experiments, lunar basalt, and kimberlitic diamonds are reported. The lunar olivine was dominated by Cr(2+) whereas the diamond inclusions had Cr(2+/Cr(3+) ratios up to about 0.3. The simpliest interpretation is that the terrestrial olivine crystallized in a more oxidizing environment than the lunar olivine.

Sutton, S. R.; Bajt, S.; Rivers, M. L.; Smith, J. V.

1993-01-01

309

Olivine friction at the base of oceanic seismogenic zones  

USGS Publications Warehouse

We investigate the strength and frictional behavior of olivine aggregates at temperatures and effective confining pressures similar to those at the base of the seismogenic zone on a typical ridge transform fault. Triaxial compression tests were conducted on dry olivine powder (grain size ???60 ??m) at effective confining pressures between 50 and 300 MPa (using Argon as a pore fluid), temperatures between 600??C and 1000??C, and axial displacement rates from 0.06 to 60 ??m/s (axial strain rates from 3 ?? 10-6 to 3 ?? 10-3 s-1). Yielding shows a negative pressure dependence, consistent with predictions for shear enhanced compaction and with the observation that samples exhibit compaction during the initial stages of the experiments. A combination of mechanical data and microstructural observations demonstrate that deformation was accommodated by frictional processes. Sample strengths were pressure-dependent and nearly independent of temperature. Localized shear zones formed in initially homogeneous aggregates early in the experiments. The frictional response to changes in loading rate is well described by rate and state constitutive laws, with a transition from velocity-weakening to velocity-strengthening at 1000??C. Microstructural observations and physical models indicate that plastic yielding of asperities at high temperatures and low axial strain rates stabilizes frictional sliding. Extrapolation of our experimental data to geologic strain rates indicates that a transition from velocity weakening to velocity strengthening occurs at approximately 600??C, consistent with the focal depths of earthquakes in the oceanic lithosphere. Copyright 2007 by the American Geophysical Union.

Boettcher, M.S.; Hirth, G.; Evans, B.

2007-01-01

310

Breaking through the Bar  

ERIC Educational Resources Information Center

Howard University School of Law had a problem, and school officials knew it. Over a 20-year period, 40 percent of its graduates who took the Maryland bar exam failed it on their first try. During the next 24 months--the time frame required to determine its "eventual pass rate"--almost 90 percent of the students did pass. What they did not know was

Gray, Katti

2011-01-01

311

Bar coded retroreflective target  

DOEpatents

This small, inexpensive, non-contact laser sensor can detect the location of a retroreflective target in a relatively large volume and up to six degrees of position. The tracker's laser beam is formed into a plane of light which is swept across the space of interest. When the beam illuminates the retroreflector, some of the light returns to the tracker. The intensity, angle, and time of the return beam is measured to calculate the three dimensional location of the target. With three retroreflectors on the target, the locations of three points on the target are measured, enabling the calculation of all six degrees of target position. Until now, devices for three-dimensional tracking of objects in a large volume have been heavy, large, and very expensive. Because of the simplicity and unique characteristics of this tracker, it is capable of three-dimensional tracking of one to several objects in a large volume, yet it is compact, light-weight, and relatively inexpensive. Alternatively, a tracker produces a diverging laser beam which is directed towards a fixed position, and senses when a retroreflective target enters the fixed field of view. An optically bar coded target can be read by the tracker to provide information about the target. The target can be formed of a ball lens with a bar code on one end. As the target moves through the field, the ball lens causes the laser beam to scan across the bar code.

Vann, Charles S. (Fremont, CA)

2000-01-01

312

Martian Dunite NWA 2737: Petrographic Constraints on Geological History, Shock Events, and Olivine Color  

SciTech Connect

Meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine-rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of ?85% vol. olivine (Mg, molar Mg/(Mg + Fe), of 78.3 {+-} 0.4%), which is notable because it is black in hand sample and brown in thin section. Other minerals include chromite, pyroxenes (augite, pigeonite, orthopyroxene), and diaplectic glass of alkali-feldspar composition. Aqueous alteration is minimal and appears only as slight dissolution of glass. NWA 2737 formed by accumulation of olivine and chromite from a basaltic magma; the other minerals represent magma trapped among the cumulus grains. Minerals are compositionally homogeneous, consistent with chemical equilibration in late and postigneous cooling. Two-pyroxene thermometry gives equilibration temperatures 1150 C, implying a significant time spent at the basalt solidus. Olivine-spinel-pyroxene equilibria give ?825 C (possibly the T of mesostasis crystallization) at an oxidation state of QMF-1. This oxidation state is consistent with low Fe3+ in olivine (determined by EMP, Moessbauer spectra, and synchrotron micro-XANES spectroscopy) and with {approx}10% of the iron in pyroxene being Fe3+. NWA 2737 experienced two shock events. The first shock, to stage S5-S6, affected the olivine by producing in it planar deformation features, intense mosaicism and lattice strain, and abundant droplets of iron-nickel metal, 5-15 nm in diameter. At this stage the olivine became deeply colored, i.e., strongly absorbing at visible and near-infrared (NIR) wavelengths. This shock event and its thermal pulse probably occurred at {approx}170 Ma, the Ar-Ar age of NWA 2737. The colored olivine is cut by ribbons of coarser, uncolored olivine with long axes along [100] and shorter axes on {l_brace}021{r_brace} planes: These are consistent with the easy slip law for olivine [100]{l_brace}021{r_brace}, which is activated at moderate strain rate at high temperature. Within these ribbons the olivine was coarsened and the iron metal globules coalesced to micron-sized grains. The ribbons also are mosaicized and cut by planar fractures, which bespeak a second shock event, possibly that of ejection from Mars. The deeply colored olivine in NWA 2737 is unusual and represents a new 'ground truth' type for remote sensing of Mars. Understanding the occurrence of the brown color in olivine in NWA 2737 places important constraints on interpretation of optical measurements.

Treiman,A.; Dyar, M.; McCanta, M.; Noble, S.; Pieters, C.

2007-01-01

313

Phase equilibria controls on the chemistry of vent fluids from hydrothermal systems on slow spreading ridges: Reactivity of plagioclase and olivine solid solutions and the pH-silica connection  

NASA Astrophysics Data System (ADS)

Theoretical reaction path models were combined with experimental data to determine fluid-mineral equilibria controls on the chemistry of vent fluids issuing from ultramafic-hosted hydrothermal systems (e.g., Rainbow and Logatchev I) on the slow spreading Mid-Atlantic Ridge. The model involves the incremental reaction of Ca-bearing (evolved seawater) with a calcic-plagioclase and olivine-bearing mineral assemblage, and simulates aspects of an open geochemical system. Incipient reaction predicts Ca removal in exchange for Na, low silica, and high pH. With reaction progress, however, the Na for Ca exchange reaction reverses, while dissolved silica and pH increase and decrease, respectively. The combination of significant dissolved silica (8-9 mmol kg-1), together with elevated dissolved Ca concentrations (60-70 mmol kg-1) coexisting with secondary calc-silicate (tremolite) and Mg-chlorite mineralization, constitutes an important pH buffer. The inherently reducing nature (high H2) of the model system enhances Fe solubility, while low dissolved H2S contributes to elevated dissolved Cu, in keeping with compositional effects reported for Rainbow and Logatchev vent fluids. Data indicate that H2S is controlled at values more than 10 times lower than H2 owing to bornite-chalcocite-magnetite-fluid equilibria. Olivine is not unreactive in the silica-bearing fluid at 400-425C (500 bars) and is predicted to participate in the formation of calc-silicate, talc, and chlorite alteration phases. Model predictions, however, also indicate metastability of Fe-rich olivine. Experimental studies performed to examine olivine recrystallization reactions in silica bearing fluid indicate preferential dissolution of the forsterite component and precipitation of a more Fe-rich phase along with talc on the surface of the precursor olivine. Additional experimental data are required, however, to better determine the implications of this for the redox and pH evolution of vent fluids at slow spreading mid-ocean ridges.

Seyfried, W. E., Jr.; Pester, Nicholas; Fu, Qi

314

The composition of mesosiderite olivine clasts and implications for the origin of pallasites  

NASA Technical Reports Server (NTRS)

The composition of olivine clasts from the mesosiderites Emery, Mincy and Pinnaroo is investigated, and implications of the results for the origin of the pallasites, which, although chemically distinct, may be related to the diogenites, eucrites, howardites and mesosiderites, are discussed. Centimeter-sized olivines were analyzed by electron microprobe, and instrumental neutron activation analysis was performed on one olivine each from Emery and Pinnaroo and an olivine separate from the Brenham pallasite. The olivine compositions are found to range from Fa8 to Fa28, with Emery samples having values from Fa18 to Fa28, and to require essentially total melting of a source composition rich enough in FeO to produce basaltic clasts. It is argued that the mesosiderite olivines were formed in the outer few kilometers of their parent body, as were those of the pallasites, which have the same compositions as the mesosiderite olivines. A model is then developed for the origin of the pallasites as a by-product of igneous differentiation in the external heating of a chondritic parent body.

Mittlefehldt, D. W.

1980-01-01

315

Effect of Sulfur on Siderophile Element Partitioning Between Olivine and Martian Primary Melt  

NASA Technical Reports Server (NTRS)

Since olivine is a common early crystallizing phase in basaltic magmas that have produced planetary and asteroidal crusts, a number of experimental studies have investigated elemental partitioning between olivine and silicate melt [e.g., 1, 2, 3]. In particular, olivine/melt partition coefficients of Ni and Co (DNi and DCo) have been intensively studied because these elements are preferentially partitioned into olivine and thus provide a uniquely useful insight into the basalt petrogenesis [e.g., 4, 5]. However, none of these experimental studies are consistent with incompatible signatures of Co [e.g., 6, 7, 8] and Ni [7] in olivines from Martian meteorites. Chemical analyses of undegassed MORB samples suggest that S dissolved in silicate melts can reduce DNi up to 50 % compared to S-free experimental systems [9]. High S solubility (up to 4000 ppm) for primitive shergottite melts [10] implies that S might have significantly influenced the Ni and Co partitioning into shergottite olivines. This study conducts melting experiments on Martian magmatic conditions to investigate the effect of S on the partitioning of siderophile elements between olivine and Martian primary melt.

Usui, T.; Shearer, C. K.; Righter, K.; Jones, J. H.

2011-01-01

316

Detections and geologic context of local enrichments in olivine on Vesta with VIR/Dawn data  

NASA Astrophysics Data System (ADS)

magmatism characterizing the early history of the asteroid Vesta has long been investigated with the mafic and ultramafic meteorites howardite, eucrite, and diogenite (HED). The lack of geologic context for the meteorites, however, has limited its understanding. Here we use the visible to near-IR (VIR) orbital observations of Vesta's surface to detect relative enrichments in olivine and to study the associated geologic features. Because the near-IR signature of olivine on Vesta's surface is subtle relative to the widespread pyroxene absorption bands, a method was developed to distinguish olivine enrichments from admixture of pyroxenes with high Fe2+/M1, dark material, and potential Fe-bearing glass. Relative enrichment of olivine (~<50-60 vol %) is found in 2-5 km wide, morphologically fresh areas. Our global survey reveals a dozen of these areas clustering in the eastern hemisphere of Vesta. The hemispherical coincidence with a widespread, low enrichment in diogenite-like pyroxene suggests the presence of a distinct compositional terrain. On the central mound of the Rheasilvia impact basin, no olivine enrichment was found, suggesting the absence of an olivine-dominated mantle above the basin's excavation depth or, alternatively, a low amount of olivine homogeneously mixed with diogenite-like pyroxenes. Rare olivine-enriched areas in close proximity to diogenite-like pyroxene are found as part of material ejected by the Rheasilvia impact. Such cooccurrence is reminiscent of local, ultramafic lithologies within the crust. The possible formation of such lithologies on Vesta is supported by some HED meteorites dominated by olivine and orthopyroxene.

Ruesch, Ottaviano; Hiesinger, Harald; De Sanctis, Maria Cristina; Ammannito, Eleonora; Palomba, Ernesto; Longobardo, Andrea; Zambon, Francesca; Tosi, Federico; Capria, Maria Teresa; Capaccioni, Fabrizio; Frigeri, Alessandro; Fonte, Sergio; Magni, Gianfranco; Raymond, Carol A.; Russell, Christopher T.

2014-09-01

317

New insights into the formation of fayalitic olivine from Allende dark inclusions  

NASA Astrophysics Data System (ADS)

Although considerable progress has been made in unraveling the origin(s) of fayalitic olivines in dark inclusions (DIs), many questions remain still unresolved and/or controversial. We combine a chemical and petrographic study of the Allende dark inclusion 4884-2B (AMNH, New York) and ATEM studies of a fragment of the dark inclusion Allende AF (NHM, Vienna) and discuss an alternative way in which fayalitic olivines could have formed. Allende dark inclusion 4884-2B contains a few aggregates with variable proportions of transparent and feathery olivine. Two such objects (aggregates A and B) are the focus of this study as they preserve glasses that can help in deciphering the nature of the processes involved during olivine growth and subsequent olivine transformation. The petrographic and chemical characteristics of aggregates A and B indicate that the forsteritic stack olivines may be pseudomorphs of clear olivine crystals. The ATEM studies in All-AF suggest that fayalitic olivines may be the result of secondary processes (e.g., metasomatic exchange reactions) operating in the solar nebula. Transformation may have occurred through the mediation of a dry gas phase involving nonvolatile major elements, such as Mg and Fe (e.g., Dohmen et al. 1998). This mechanism could reveal olivine growth patterns (e.g., stacked platelets due to a rapid growth regime) and may have contributed to the development of their fibrous aspect while preserving the shape (i.e., volume) of the crystals. This highly selective process did completely or partially transform ferromagnesian minerals, but affected the fine-grained mesostasis only slightly.

Varela, Maria E.; Zinner, Ernst; Kurat, Gero; Chu, Hao-Tsu; Hoppe, Peter

2012-05-01

318

Global distribution, composition, and abundance of olivine on the surface of Mars from thermal infrared data  

NASA Astrophysics Data System (ADS)

We used spectral indexing and linear deconvolution to compare thermal infrared emission spectra of Fo91, Fo68, Fo53, Fo39, Fo18, and Fo1 olivine samples to Mars Global Surveyor Thermal Emission Spectrometer (TES) data over low-albedo regions of Mars. The Fo91, Fo68, Fo53, and Fo39 spectral end-members were confidently identified on Mars, a range of compositions wider than inferred from Martian meteorites. Small (less than hundreds of square kilometers) occurrences of the Fo91 spectral end-member are present in the rims of the Argyre and Hellas impact basins and may represent Martian mantle materials. The Fo68 spectral end-member is common throughout the highlands, chasmata, outflow channels, and Nili Fossae region. The Fo53 spectral end-member occurs in eastern Syrtis Major, the Nili Fossae region, and smooth-floored craters of the highlands. Although less abundant than Fo68 and Fo53, the distribution of the Fo39 spectral end-member suggests that some olivine on Mars is more Fe-rich than olivine in Martian meteorites. Global maps of olivine show that (1) materials containing 10-20% of olivine are common in the southern highlands of Mars, (2) olivine is most common near the topographic dichotomy boundary, and (3) olivine becomes uncommon near the poles suggesting that it may be influenced by topography and/or latitude (climate). Olivine is found in early Noachian to Amazonian terrains, some of which may be coeval with phyllosilicate and sulfate deposits detected by OMEGA implying that any early Noachian wet period of Mars' climate history may have been globally inhomogeneous or insufficient to weather the olivine that remains today.

Koeppen, William C.; Hamilton, Victoria E.

2008-05-01

319

H Diffusion in Olivine and Pyroxene from Peridotite Xenoliths and a Hawaiian Magma Speedometer  

NASA Technical Reports Server (NTRS)

Hydrogen is present as a trace element in olivine and pyroxene and its content distribution in the mantle results from melting and metasomatic processes. Here we examine how these H contents can be disturbed during decompression. Hydrogen was analyzed by FTIR in olivine and pyroxene of spinel peridotite xenoliths from Salt Lake Crater (SLC) nephelinites which are part of the rejuvenated volcanism at Oahu (Hawaii) [1,2]. H mobility in pyroxene resulting from spinel exsolution during mantle upwelling Most pyroxenes in SLC peridotites exhibit exsolutions, characterized by spinel inclusions. Pyroxene edges where no exsolution are present have less H then their core near the spinel. Given that H does not enter spinel [3], subsolidus requilibration may have concentrated H in the pyroxene adjacent to the spinel exsolution during mantle upwelling. H diffusion in olivine during xenolith transport by its host magma and host magma ascent rates Olivines have lower water contents at the edge and near fractures compared to at their core, while the concentrations of all other chemical elements appear homogeneous. This suggests that some of the initial water has diffused out of the olivine. Water loss from the olivine is thought to occur during host-magma ascent and xenolith transport to the surface [4-6]. Diffusion modeling matches best the data when the initial water content used is that measured at the core of the olivines, implying that mantle water contents are preserved at the core of the olivines. The 3225 cm(sup -1) OH band at times varies independantly of other OH bands, suggesting uneven H distribution in olivine defects likely acquired during mantle metasomatism just prior to eruption and unequilibrated. Diffusion times (1-48 hrs) combined with depths of peridotite equilibration or of magma start of degassing allow to calculate ascent rates for the host nephelinite of 0.1 to 27 m/s.

Peslier, A. H.; Bizimis, M.

2014-01-01

320

Cr, Mn, and Ca distributions for olivine in angritic systems: Constraints on the origins of Cr-rich and Ca-poor core olivine in angrite LEW87051  

NASA Technical Reports Server (NTRS)

Angrite meteorites are a type of basaltic achondrites that are noted for their very old cyrstallization ages (4.55 b.y.) and unusual chemical and mineralogical properties. In spite of great interest, only four angrites have been found. LEW87051 is the smallest one which weighs 0.6 g. It is a porphyritic rock with coarse subhedral to euhedral olivines set in a fine-grained groundmass which clearly represents a crystallized melt. The largest uncertainty about the petrogenesis of LEW87051 is the relationship between the large olivine crystals and the groundmass. Prinz et al. suggests that olivines are xenocrysts, while McKay et al. proposed a fractional cyrstallization model based on experimental studies. However, the crystals have Cr-rich and Ca-poor cores which do not match experimental olivines. Although Jurewicz and McKay tried to explaine the zoning of the rim by diffusion, some features are not explained. There also exists a definite composition boundary of Fe(2+) and MnO between the core and the rim. To clarify the origin of these olivines, we have performed experiments using LEW87051 analogs to measure the effects of oxygen fugacity on distribution coefficients of various elements in an angritic system.

Mikouchi, T.; Mckay, G.; Le, L.

1994-01-01

321

Fe-Mg-Mn relations of ureilite olivines and pyroxenes and the genesis of ureilites  

NASA Technical Reports Server (NTRS)

Microprobe analyses of ureilite and pigeonite cores are studied. The Fe/Mn-Fe/Mg relationship in the olivine core is examined. It is observed that magnetic processs such as fractional crystallization and partial melting, and FeO reduction contribute to the olivine core composition. The study of the Mg/Mn and Fe/Mn distributions reveals that these two distributions are not in equilibrium in the olivine and pigeonite cores. The effect of a reducing agent, carbon, on the ureilite genesis is investigated. It is concluded that fractional crystallization and FeO reduction are the major processes of ureilite genesis.

Mittlefehldt, D. W.

1986-01-01

322

Cellular Precipitates Of Iron Oxide in Olivine in a Stratospheric Interplanetary Dust Particle  

NASA Technical Reports Server (NTRS)

The petrology of a massive olivine-sulphide interplanetary dust particle shows melting of Fe,Ni-sulphide plus complete loss of sulphur and subsequent quenching to a mixture of iron-oxides and Fe,Ni-metal. Oxidation of the fayalite component in olivine produced maghemite discs and cellular intergrowths with olivine and rare andradite-rich garnet. Cellular reactions require no long-range solid-state diffusion and are kinetically favourable during pyrometamorphic oxidation. Local melting of the cellular intergrowths resulted in three dimensional symplectic textures. Dynamic pyrometamorphism of this asteroidal particle occurred at approx. 1100 C during atmospheric entry flash (5-15 s) heating.

Rietmeijer, Frans J. M.

1996-01-01

323

Water dissolved in olivine: A single-crystal infrared study  

NASA Astrophysics Data System (ADS)

Polarized infrared spectra of the hydrogen impurities in an olivine single crystal, approximately (Mg0.9Fe0.1)2SiO4, from the Zargabad Island, Red Sea, are reported in the range 4200-3000 cm-1. In the O-H stretching frequency region, two groups of IR absorption bands occur which show the same pleochroism and the same temperature-induced shift between room temperature and 80 K. Each of these IR groups is composed of three equidistant bands at 3614, 3591, 3567 m-1 and at 3576, 3530, 3485 cm-1 (80 K values). These distinct multiplets are assigned to the OH--compensated octahedral and tetrahedral vacancy defects [OHV?oct]' and [OHV'tetr]*, respectively. It is suggested that the reduced effective charge of the tetrahedral, i.e., Si-type, vacancy is due to Si entering a nearby nonideal site for partial charge compensation. The multiplet splitting, 23 and 45 cm-1, is due to the isomorphous substitution of Mg and Fe on the adjacent M1 and M2 positions to which the proton-bearing oxygen is bound. This leads to the combinations (Mg Mg Si), (Mg Fe Si), (Fe Fe Si) and (Mg Mg Mg), (Mg Mg Fe), (Mg Fe Fe) at the octahedral M2 and at the tetrahedral vacancy sites, respectively. An IR signal which would correspond to the fully OH--compensated divalent cation vacancy defect [OHV?octHO]* appears to be absent. Instead a weak absorption band is observed in the range of the H-H stretching frequency of molecular H2. By analogy to molecular H2 in MgO and CaO single crystals and in fused silica it is concluded that OH- pairs, associated with this type of defects, undergo a charge transfer conversion into (H2 + O22-). The H2 are loosely bound to the peroxy entities which probably form peroxy bridges between SiO4 tetrahedra, e.g., Si-O-O-Si. Outgassing of H2 would leave excess oxygen behind, shifting the stoichiometry of the olivine in a direction which has never been discussed before.

Freund, Friedemann; Oberheuser, Gert

1986-01-01

324

Number Line Bars--Fractions  

NSDL National Science Digital Library

Students use these virtual fraction bars to model fractional addition, subtraction, multiplication (of fractions by whole numbers), and division on a number line. Students can create bars in positive or negative fractional lengths; align, stack, or remove bars; and change the number line marks in increments between 1/2 and 1/15. Applet instructions and teaching ideas are included in the links at the top of the page.

2005-01-01

325

Charge Localization and Transport in Lithiated Olivine Phosphate Materials  

SciTech Connect

We report density functional theory (DFT) calculations for olivine-type LiTMPO4 and TMPO4 (TM=Mn, Fe, Co, Ni) structures, using GGA+U and the B3LYP hybrid density functional that includes nonlocal Fock exchange. TM is typically characterized in terms of the formal oxide states of 2+ or 3+, corresponding to TM with localized charge in LiTMPO4 and TMPO4 structures, respectively, in which electron transport would take place by thermally activated hopping of electrons strongly localized on the transition metal (small polarons). In this work, we assess the validity of the concept of formal TM oxidation states in these materials, and conclude that the valence depends in large part on the strength of d-p hybridization. Stable small polaron formation, i.e., mixed 2+ and 3+ valence states, appears to require that the ratio of differences in the metal and oxygen ionic charges (dQTM/dQO) of the two end member phases is larger than 2, corresponding to the mixed-valence TM system. If the ratio of dQTM/dQO is smaller than 2, excess electrons prefer delocalization and the system behaves more single-valence like with charge transport more akin to metallic conduction. The critical ratio emerging from our analysis may turn out to be relevant to other transition metal systems as well, as a criterion to discriminate single-valence or mixed-valence characteristics and hence the predominant conduction mechanism.

Yu, Jianguo; Rosso, Kevin M.; Liu, Jun

2011-11-10

326

Shallow crystallization of Kilauean olivines: Magma density and picritic eruptions  

SciTech Connect

Of 35 analyzed glass inclusions in olivine phenocrysts from the 1959 Kilauea Iki eruption, 23 formed at pressures less than 1 Kbar, 10 between 1 and 2 Kbar and 2 at pressures greater than 2 Kbar. The surprisingly topheavy distribution of formation pressures suggests that the 1959 magma rose rapidly to the upper parts of Kilauea's summit magma storage reservoir where cooling and crystallization dominantly occurred. The implication that the parental magma was buoyant relative to preexisting resident magma is consistent with an expected preeruptive bulk CO[sub 2] content of 0.3wt.% and petrographic evidence for turbulent mixing between parental and preexisting magma. That the 1959 magma was rich not only in crystals but also in gas, as evidenced by its high lava fountains, suggests that the storage time in the summit reservoir was too short for either crystals or gas to be lost. Therefore, the 1959 Kilauean magma probably is a near-parental magma that rose and formed a gas- and crystal-rich cap at the top of Kilauea's summit magma storage reservoir. Whether parental magma rises to the top or ponds at the base of the summit reservoir depends mainly on reservoir pressure and magma gas content. Consequently, it seems likely that the eruptive and degassing behavior of Kilauea is regulated in part by an interplay between the CO[sub 2] content of parental magma and the pressure at the base of the summit storage reservoir.

Anderson, A.T. Jr.; Brown, G.G. (Univ. of Chicago, IL (United States). Dept. of the Geophysical Sciences)

1992-01-01

327

Olivine-Orthopyroxene Equilibrium in Metal-rich Systems: Applications to Achondrites and Equilibrated Chondrites  

NASA Technical Reports Server (NTRS)

Olivine and orthopyroxene are major minerals in every type of stony meteorite. The majority of achondritic meteorites and silicate-bearing iron meteorites have experienced high temperatures. If these temperatures persisted for an extended period of time then the iron contents of olivine and orthopyroxene should be in equilibrium. In their study of ungrouped clasts and chondritic meteorites, suggested that the equilibrium compositions of olivine and orthopyroxene should fall on a mixing line between LL chondrites and aubrites. Here we show that this is not necessarily the case and that a range of FeO contents in olivine and orthopyroxene can be in equilibrium with each other. The key parameters that determine the equilibrium Fe content in these minerals are temperature, oxygen fugacity (fO2), and silica activity (aSiO2).

Lauretta, D. S.; Benedix, G. K.; McCoy, T. J.

2003-01-01

328

Relation of the spectroscopic reflectance of olivine to mineral chemistry and some remote sensing implications  

NASA Astrophysics Data System (ADS)

High-resolution visible and near-IR diffuse spectral reflectance are used to systematically investigate apparent wavelength shifts as a function of mineral chemistry in the Fe/Mg olivine series from Fo(11) to Fo(91). The study also shows that trace amounts of nickel can be spectrally detected in the olivine structure. Significant compositional information can only be extracted at relatively high resolution, because the overall spectral characteristics of the olivines change only subtly as a function of the Fe/Mg ratio. This laboratory study is expected to aid in the interpretation of remotely sensed data from both terrestrial and extraterrestrial bodies. Terrestrial applications may include the recognition of ultramafic, ultrabasic, and basaltic terrains which in themselves may have mineral potential. Among extraterrestrial applications, the asteroids are obvious candidates for further examination. Some permutations of Fe-Mg-Ni relations in olivines are discussed as they apply to the interpretation of asteroid surfaces and other extraterrestrial bodies.

King, Trude V. V.; Ridley, W. Ian

1987-10-01

329

Phase behavior and phase transformation kinetics during electrochemical cycling of lithium transition metal olivine compounds  

E-print Network

Olivine LiMPO4 (M = Fe, Mn, Co, Ni) compounds have received most attention from the battery research community as the cathodes for Li-ion batteries because of several advantages, including a high theoretical capacity, 170 ...

Meethong, Nonglak

2009-01-01

330

First-principles investigation of Li intercalation kinetics in phospho-olivines  

E-print Network

This thesis focuses broadly on characterizing and understanding the Li intercalation mechanism in phospho-olivines, namely LiFePO? and Li(Fe,Mn)PO?, using first-principles calculations. Currently Li-ion battery technology ...

Malik, Rahul

2013-01-01

331

Trace Element Distribution Between Olivine and Kirschsteinite in Angra Dos Reis  

NASA Technical Reports Server (NTRS)

The angrites are a small and enigmatic group of basaltic achondrites that possess unique mineralogical and chemical properties. The dominant mineralogy of the seven angrite members (Angra dos Reis, LEW 86010, LEW 87051, Asuka 881371, Sahara 99555, D Orbigny, and a new Moroccan member) is fassaite, olivine, and plagioclase. Angrites display a wide range of thermal histories, with Angra dos Reis (AdoR) exhibiting a cooling history different from that of the rapidly cooled members and from LEW86010, a more slowly cooled member. AdoR could represent either a cumulate or a porphyritic igneous rock that was later altered by metamorphism. We are re-examining the thermal history of AdoR in light of the more recently described angrite members. Our emphasis is a trace element study of low-Ca olivine, which we refer to as olivine, and high-Ca olivine, which we refer to as kirschsteinite, in AdoR.

Fittipaldo, M. M.; Jones, R. H.; Shearer, C. K.

2003-01-01

332

Raman spectroscopy of olivine in dunite experimentally shocked to pressures between 5 and 59 GPa  

NASA Astrophysics Data System (ADS)

Previous Raman investigations on experimentally shocked ingle-crystal olivine indicated that the olivine Raman bands seemingly shift to a higher wave number with increasing shock pressure. If this effect could be confirmed, Raman analysis of natural shock-metamorphosed minerals could potentially provide an important shock barometric tool. We carried out a Raman spectroscopic study on olivine in a series of natural dunite samples experimentally shocked to pressures between 5 and 59 GPa. In addition, we analyzed olivine grains in a sample of the Cold Bokkeveld C1 meteorite. We studied samples of several dunites with olivine of 90.64-92.00 mole% Fo to determine Raman effects in the region from 200 to 900 cm-1. Several olivine grains per sample/shock pressure stage were analyzed. Raman analysis, however, showed little or no shift with increasing shock pressure. The shifts to higher or lower frequencies observed were not specific for a given pressure stage, with some grains within a sample showing more shift than others. This finding is unrelated to the crystallographic orientation of analyzed grains and cannot be related systematically to the different degrees of optically determined shock metamorphism of the analyzed grains. We identified an increase in full width at half maximum (FWHM) for the 824 cm-1 band with increased shock pressure in the shocked heim samples above 45 GPa and, to a lesser extent, for the 856 cm-1 band. Evaluation of band broadening of olivine in the Cold Bokkeveld meteorite showed FWHM values that were much greater (9-20 cm-1) than those of olivine in the shocked dunite samples (7-12 cm-1). We concluded that these differences in FWHM are due to differences in chemical composition between the meteoritic and the experimentally shocked olivine. Therefore, using Raman spectroscopy to detect small shifts in wave numbers to higher frequencies with increased shock pressure does not yield consistent effects for polycrystalline dunite. An extra band at 650 cm-1 was identified in the Raman spectra of the unshocked Mooihoek dunite and the heim dunite samples shocked to 5, 29.3, and 59 GPa, as well as another at 696 cm-1 in all the spectra of the 59 GPa heim sample. The cause of these extra bands is not known. Comparison of these results with Raman spectra of olivine from the Cold Bokkeveld C1 meteorite did not allow us to determine shock pressures for the meteoritic olivine.

Farrell-Turner, S.; Reimold, W. U.; Nieuwoudt, M.; Erasmus, R. M.

2005-10-01

333

Electrical Conductivity of Olivine at High Pressure and Under Controlled Oxygen Fugacity  

Microsoft Academic Search

It is now generally accepted that the major phase in the earth's upper mantle is olivine with an approximate composi- tion Mgx.sFe0..SiO4 (Fujisawa, 1968). Published values of elec- trical conductivity a of olivine of this composition (either single crystal or polycrystalline) at high temperatures show very poor agreement (Duba and Lilley, 1972). In many in- stances the difference can be

A. Duba; H. C. Heard; R. N. Schock

1974-01-01

334

Effect of Water on the Rheological Behavior of Fe-rich Olivine  

Microsoft Academic Search

The influence of water content on the rheological properties of Fe-rich olivine was investigated in order to better understand the influence of hydrogen on the creep behavior of mantle rocks. Triaxial compressive creep experiments were performed on fine-grained samples of Fo50 and Fo50 + water. Samples were fabricated from a mixture of powders of San Carlos olivine, Fo90, and synthetic

Y. Zhao; M. E. Zimmerman; D. L. Kohlstedt

2003-01-01

335

Experimental and Natural Evidence for Rapid Water Exchange Between Melt Inclusions in Olivine and Host Magma  

NASA Astrophysics Data System (ADS)

We have carried an experimental study aimed at evaluating the ability of olivine to isolate chemically melt inclusions from the host magma after their entrapment. We demonstrate that nearly 'dry' (<0.5 wt% of water) melt inclusions from Galapagos Plateau basalt gain up to 2.5 wt% of water if they are placed for 2 days in a water-bearing melt at 200 MPa and 1140 C. Amount of structurally bound water in olivine crystals also increased, maintaining equilibrium with hydrous matrix melt (D olivine-melt ~ 0.002). Despite the complete re-equilibration of the system with respect to water, no or only partial re-equilibration was achieved with respect to major, volatile (S, Cl) and incompatible trace elements between matrix melt, olivines and melt inclusions. The apparent diffusion coefficient of water in olivine is found to be more or equal to 5E-12 m2/s at our experimental conditions that is as fast as proton-vacancy diffusion and at least 3-4 orders of magnitude faster than for other major (e.g., Fe and Mg) and trace elements at dry or hydrous conditions. These results indicate that inclusions in olivine can rapidly and selectively exchange water with matrix melt, probably, through combination of proton diffusion and molecular water transport along dislocations in olivine. The rapid re-equilibration of melt inclusions with matrix melt or atmosphere can explain the decoupling of water and incompatible trace elements (e.g, water vs. potassium) reported for suites of primitive inclusions from oceanic settings (43 N MAR, FAMOUS, Galapagos) and island arcs (Kamchatka, Central America, Cyprus). Rare cases of well preservation of initial water content in suites of co- genetic inclusions imply very short residence time (a few hours) of the olivine phenocrysts in magma with contrasting water content during fractionation and transport to the surface and rapid quenching upon eruption.

Portnyagin, M.; Almeev, R.; Matveev, S.; Mironov, N.; Holtz, F.

2008-12-01

336

Double Bars, Inner Disks, and Nuclear Rings in Barred Galaxies  

E-print Network

We present results of a high-resolution imaging survey of barred S0--Sa galaxies which demonstrate that the central regions of these galaxies are surprisingly complex. We see many inner bars --- small, secondary bars (typically less than a kiloparsec in radius) located inside of, and probably rotating faster than, the large primary bars. These are present in about one quarter to one third of all our sample. In contrast to some theoretical expectations, they do not seem to enhance AGN activity significantly. A third of barred S0's appear to host kiloparsec-scale disks within their bars; but the frequency of such inner disks is much lower in our S0/a and Sa galaxies. In addition, we find one example of a triple barred galaxy, and two cases of purely stellar nuclear rings --- probably the fossil remnants of past circumnuclear starbursts. We comment briefly on results from an ongoing analysis of known double-barred systems, extending to Hubble types as late as Sbc, and discuss their characteristic sizes and orientations.

Peter Erwin; Linda S. Sparke; Juan Carlos Vega Beltran; John Beckman

2001-07-07

337

Compositional controls on vent fluids from ultramafic-hosted hydrothermal systems at mid-ocean ridges: An experimental study at 400C, 500 bars  

Microsoft Academic Search

Olivine (Fo89), orthopyroxene (En85), and clinopyroxene (Di89) were reacted, individually and in combinations, with NaCl-MgCl2 at 400C, 500 bars to better assess alteration and mass transfer in ultramafic-hosted hydrothermal systems at mid-ocean ridges. Data indicate that temperature plays a key role in mineral solubility and kinetic processes, which influence the compositional evolution of the fluid. At the temperature and pressure

Douglas E. Allen; W. E. Seyfried

2003-01-01

338

Implementation of viscoelastic Hopkinson bars  

NASA Astrophysics Data System (ADS)

Knowledge of the properties of soft, viscoelastic materials at high strain rates are important in furthering our understanding of their role during blast or impact events. Testing these low impedance materials using a metallic split Hopkinson pressure bar setup results in poor signal to noise ratios due to impedance mismatching. These difficulties are overcome by using polymeric Hopkinson bars. Conventional Hopkinson bar analysis cannot be used on the polymeric bars due to the viscoelastic nature of the bar material. Implementing polymeric Hopkinson bars requires characterization of the viscoelastic properties of the material used. In this paper, 30 mm diameter Polymethyl Methacrylate bars are used as Hopkinson pressure bars. This testing technique is applied to polymeric foam called Divinycell H80 and H200. Although there is a large body of of literature containing compressive data, this rarely deals with strain rates above 250s-1 which becomes increasingly important when looking at the design of composite structures where energy absorption during impact events is high on the list of priorities. Testing of polymeric foams at high strain rates allows for the development of better constitutive models.

Curry, R.; Cloete, T.; Govender, R.

2012-08-01

339

Another bar in the Bulge  

E-print Network

A map of the projected density of the old stellar population of the Galactic Bulge region is reconstructed using 2MASS data. By making a combination of the H and K photometric bands, it is possible to overcome the effect of reddening, and thus penetrate the inner structure of the Galactic Bulge. The main structure in the map corresponds to the well documented peanut shaped bar which is formed by the inner parts of the Galactic disk as a result of dynamical instabilities. As suggested by numerical simulations, the projected Z profile of the bar, has an almost exponential shape. After subtracting the exponential profile associated with the bar, a large residual appear near the Galactic Center. This residual is elongated and asymmetrical, which suggest a bar structure. Thus we arrive at the conclusion that in addition to the main bar a smaller bar with a different orientation may exist in the central region of the Milky Way. This finding makes the Milky Way very similar to a large number of barred spiral Galaxies which show as well a smaller bar in their central regions.

C. Alard

2001-10-22

340

High-Temperature Microindentation Tests on Olivine and Clinopyroxene  

NASA Astrophysics Data System (ADS)

The perspectives of microindentation techniques for the investigation of the mechanical behaviour of minerals at high temperatures are explored. The technique offers the following advantages: (1) natural specimens with small grain size can be used, (2) preparation is simple, (3) a reasonable number of experiments can be performed within a short period of time. The strength of single crystals as a function of orientation and the activated glide systems are studied using scanning electron microscopy (SEM) combined with electron backscatter diffraction (EBSD) facilities. Furthermore, the effects of compositional variations on the flow strength of solid solutions are explored. The indentation hardness tests are performed on selected grains within natural polycrystalline aggregates. The surface of the specimen is polished mechanically and chemically. The orientation of the crystals is determined using EBSD. The indentation tests are performed with a diamond pyramid (Vickers indenter) at temperatures of 25 C to 900 C. Loading is done with a constant displacement rate up to a force of 0.5 N, followed by a creep period of 10 s at constant load. SEM is used to measure the size of the indents and to examine their morphology in detail. The microhardness obtained for olivine depends on crystal and indenter orientation and decreases slightly with temperature. Slip steps are observed on the surface around the indents. Their orientation with respect to the crystal orientation indicates that the predominant glide system activated in the indentation process is \\{110\\}[001]. The Schmid factors for this glide system correlate with the observed orientation dependence of the hardness. Indentation hardness of clinopyroxene solid solutions depends on composition with jadeite being stronger than diopside. This is inverse to what is expected for dislocation creep. The high yield stresses inferred from the hardness data and the weak dependence of hardness on temperature are consistent with plasticity being the deformation regime explored in indentation hardness tests.

Dorner, D.; Schellewald, M.; Stckhert, B.

2001-12-01

341

Olivine-type nanosheets for lithium ion battery cathodes.  

PubMed

Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li(+) to diffuse over a [010]-thickness of <5 nm (L) was calculated to be less than 25, 2.5, and 250 ?s for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L(2)/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets). PMID:23713414

Rui, Xianhong; Zhao, Xiaoxu; Lu, Ziyang; Tan, Huiteng; Sim, Daohao; Hng, Huey Hoon; Yazami, Rachid; Lim, Tuti Mariana; Yan, Qingyu

2013-06-25

342

Molecular Dynamics Simulations of Olivine-Silicate Melt Interfaces  

NASA Astrophysics Data System (ADS)

Partially molten rocks are important constituents of the Earth's crust and mantle. Their properties depend not only on the chemistry and mineralogy but also on the fraction and distribution of melt or fluid. Partially molten rocks strongly influence the chemical transport in the Earth and geodynamics. We model a partially molten rock on the atomic scale by confining a silicate melt of MgSiO3 composition between Mg2SiO4 olivine crystals. Molecular dynamics simulation is used to study the atomic scale structure and respective transport properties at the interfaces. To represent the atomic interaction, we use an advanced ionic model that accounts for anion polarization and shape deformations (Jahn and Madden, 2007). We construct interfaces between silicate melt layers of different thickness (1.85nm & 3.7nm) and mineral surfaces with different crystal orientations ((010), (001) and (100)). From the particle trajectories we derive various properties like charge density, cation coordination, connectivity of SiO4 tetrahedra and self diffusion coefficients. By adding some (Al, Ca) impurities to the system, the response to different chemical compositions is studied. To obtain a stable solid-melt interface, a temperature of 2000K is chosen. Simulations are performed at ambient pressure. We examine how the chemical composition and the self-diffusion coefficients vary across the interface. Our results indicate that with increase of surface energy, the self-diffusion coefficients of the various species decrease. This may be related to the stronger interaction of the crystal surface with the melt when the surface energy is high, which leads to more structured melt close to the interface. In conclusion, our simulations provide insight into the relation between atomic scale structure and transport properties in partially molten rocks. References S. Jahn and P.A. Madden (2007) Modeling Earth materials from crustal to lower mantle conditions: A transferable set of interaction potentials for the CMAS system. Phys. Earth Planet. Int. 162, 129-139.

Gurmani, Samia; Jahn, Sandro; Brasse, Heinrich; Schilling, Frank R.

2010-05-01

343

CO2-induced small water solubility in olivine and implications for properties of the shallow mantle  

NASA Astrophysics Data System (ADS)

H2O and CO2 are important components of fluids in the mantle at ?30-150 km depth, and may affect strongly water dissolution in nominally anhydrous olivine; however, available experimental hydrogenation of olivine has been nearly exclusively carried out in coexistence with H2O (CO2-free). In this study, the effect of CO2 on water solubility in olivine has been investigated by H-annealing natural olivine under peridotite- and fluid-saturated conditions. Experiments were conducted at 1.5-5 GPa and 1100-1300 C, with oxygen fugacity controlled by Ni-NiO and with either H2O or H2O-CO2 as buffering fluid. The olivine shows no change in composition during the experiments. The infrared spectra of the hydrated olivine are characterized by prominent OH bands from ?3650 to 3000 cm in all the runs, at both high frequency (>3450 cm) and low frequency (<3450 cm), and the H2O solubility is ?120-370 ppm for the olivine in coexisting with H2O, and ?65-180 ppm for the olivine in coexisting with H2O-CO2. When CO2 is present in the buffering fluid, the H2O solubility of olivine is reduced by a factor of ?2, due to effect on the partitioning of water between minerals and coexisting fluid, and the measured H2O solubility shows independence on fluid composition (the molar ratio of CO2 to CO2 + H2O at ?0.2-0.5) given pressure, temperature and oxygen fugacity. Olivine equilibrated in the shallow mantle is probably dominated by OH groups in the wavenumber ?3650-3000 cm, and the intensity of OH bands at low frequency may be higher than or comparable to those at higher frequencies. The storage capacity of water in the shallow mantle in previous estimates may have been overestimated by a factor of at least ?4 if the observed effect of CO2 on water solubility is correct. Our results have profound influence on understanding partial melting, electrical conductivity anomalies and metasomatism in the shallow mantle.

Yang, Xiaozhi; Liu, Dingding; Xia, Qunke

2014-10-01

344

Experimental Partitioning of Cr(3+) and Sc(3+) into Olivine: Mechanisms and Implications  

NASA Technical Reports Server (NTRS)

Olivine (Mg, Fe)Si2O4 does not, by stoichiometry, accept cations such as Sc(3+) or Cr(3+). However, the partition coefficients of Sc and Cr between olivine and liquid are significant 0.2-1.0. We have measured Cr(3+) partition coefficients of near unity and have grown olivines with nearly 3 wt.% Sc2O3. Therefore, there must be a simple means of charge balancing 3+ ions in a crystal structure that was obviously not designed to receive other than 2+ ions on the olivine M sites. The simplest explanation is that two 3+ ions enter the olivine structure by displacing three 2+ ions and creating an M site vacancy. Even this explanation has difficulties. For minor elements in our experiments (1 wt.%) the odds of a minor element 3+ ion finding a second 3+ for charge balance are of the order of 100:1 against. Because of the reducing conditions of our experiments, Fe(3+) will not suffice; and Al(3+) is not in sufficient quantity in olivine for charge balance. Therefore, Cr or Sc must, in effect, charge balance itself. For true trace elements, the problem is compounded many times. For an ion at the 10 ppm level the chances of finding a second (for example) Sc ion is approx.10(exp 5):1 against. Of course, any other 3+ ion would suffice but comparisons between percent level doping experiments and trace level partitioning indicate that Henry s law is obeyed. This implies that the same substitution mechanism occurs at both the percent and tens of ppm levels. There are two simple solutions to this problem: (i) The electrical conductivity of olivine is such that charge balance need not be local. This requires substantial domains within the olivine crystal in electrical contact by migration of vacancies or electronic defects. (ii) The 3+ cation brings along its own charge-balancing ion because it existed as a dimer in the silicate liquid. Olivine is not a true insulator but is actually a p-type semiconductor. Even so, electrical communication by this means is unlikely over the tens or hundreds of unit cells that would be required for charge balance to be local. Therefore, we cautiously favor the idea that melt speciation is the means by which 3+ ions enter the olivine structure. Possibly this model might be tested by in situ XAFS measurements or by molecular dynamical calculations.

Jones, John; Mackwell, S. J.

2006-01-01

345

Effect of water on compressibility of San Carlos olivine and its implications  

NASA Astrophysics Data System (ADS)

Water has been proved playing an important role in effecting physical properties of minerals. Previous studies have demonstrated that incorporating small amounts of water significantly reduce bulk moduli of wadsleyite and ringwoodite by 10% and 16% respectively (Yusa and Inoue, 1997; Inoue et al. 1998). Although olivine takes much smaller amount of water (10 times less) than wadsleyite and ringwoodite, rheology experiments have revealed that olivine is considerably weakened by water (Chen et al. 1998). Here we report a comparative study of effect of water on compressibility of San Carlos olivine, indicating a 5% reduction in bulk modulus. Hydrous olivine sample is prepared by annealing San Carlos olivine in presence of water at 12.5GPa and 1200C for an hour. Water content in the hydrous sample is about 0.1wt%, estimated according to water solubility in olivine at such P-T condition (Kohlstedt, Keppler and Rubie, 1996). Two small pieces of pressed hydrous and anhydrous sample are loaded in the same diamond anvil chamber; Ruby chips are placed between the two samples as a pressure marker. The specimens are compressed in solution of methanol and ethanol (4:1) pressure medium up to 11 GPa. Energy dispersive x-ray diffraction is conducted at the X17C beamline of the National Synchrotron Light Source. The diffraction data are processed using full spectrum Le Bail refinement method to derive accurate volumes of olivine. Fitting the experimental data to 3rd-order Birch-Murnaghan equation of state with fixed K0' = 4.29 (Abramson et al. 1997) yield bulk moduli of 130 4 GPa and 123 4 GPa for anhydrous and hydrous samples respectively. This result demonstrates that 0.1wt% of water reduces the bulk modulus of San Carlos olivine by 5%. As the hydrous sample is at water saturated condition, the 5% reduction represents the upper limit of water effect on the bulk modulus of olivine. Taking the effect of water on bulk moduli of both olivine and wadsleyite into account, if water presents at the boundary between upper mantle and transition zone, the amplitude of 410 km seismic discontinuity will be reduced, and therefore the mineral physics composition model will better agree with seismic observations - another evidence of presence of water in the mantle.

Chen, J.; Liu, H.; Yu, T.; Hu, J.

2005-12-01

346

Slip systems in wurtzite ZnO activated by Vickers indentation on {21bar1bar0} and {101bar0} surfaces at elevated temperatures  

NASA Astrophysics Data System (ADS)

Dislocations were introduced in wurtzite zinc oxide single crystals by Vickers indentations on {21bar1bar0} and {101bar0} surfaces at elevated temperatures, and their slip systems were determined by transmission electron microscopy combined with etch pit observations. The observed system for {21bar1bar0} indentations was {101bar1bar}<1bar21bar0> or (0001)<1bar21bar0>, while that for {101bar0} indentations was {101bar0}<1bar21bar0>. Activation of the slip systems was briefly discussed in terms of the Peierls stress and resolved shear stress acting on the slip systems.

Ohno, Y.; Koizumi, H.; Tokumoto, Y.; Kutsukake, K.; Taneichi, H.; Yonenaga, I.

2014-05-01

347

Galaxy Zoo: CANDELS Barred Disks and Bar Fractions  

E-print Network

The formation of bars in disk galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in disks decreases from the local Universe to z ~ 1, and by z > 1 simulations predict that bar features in dynamically mature disks should be extremely rare. Here we report the discovery of strong barred structures in massive disk galaxies at z ~ 1.5 in deep rest-frame optical images from CANDELS. From within a sample of 876 disk galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a sub-sample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5< z < 2 (f_bar = 10.7 +6.3 -3.5% after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disk galaxies have evolved over the last 11 bil...

Simmons, B D; Lintott, Chris; Masters, Karen L; Willett, Kyle W; Keel, William C; Smethurst, R J; Cheung, Edmond; Nichol, Robert C; Schawinski, Kevin; Rutkowski, Michael; Kartaltepe, Jeyhan S; Bell, Eric F; Casteels, Kevin R V; Conselice, Christopher J; Almaini, Omar; Ferguson, Henry C; Fortson, Lucy; Hartley, William; Kocevski, Dale; Koekemoer, Anton M; McIntosh, Daniel H; Mortlock, Alice; Newman, Jeffrey A; Ownsworth, Jamie; Bamford, Steven; Dahlen, Tomas; Faber, Sandra M; Finkelstein, Steven L; Fontana, Adriano; Galametz, Audrey; Grogin, N A; Grutzbauch, Ruth; Guo, Yicheng; Haussler, Boris; Jek, Kian J; Kaviraj, Sugata; Lucas, Ray A; Peth, Michael; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn

2014-01-01

348

Galaxy Zoo: CANDELS barred discs and bar fractions  

NASA Astrophysics Data System (ADS)

The formation of bars in disc galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in discs decreases from the local Universe to z 1, and by z > 1 simulations predict that bar features in dynamically mature discs should be extremely rare. Here, we report the discovery of strong barred structures in massive disc galaxies at z 1.5 in deep rest-frame optical images from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. From within a sample of 876 disc galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a subsample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5 ? z ? 2 ( f_{bar} = 10.7^{+6.3}_{-3.5} per cent after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disc galaxies have evolved over the last 11 billion years.

Simmons, B. D.; Melvin, Thomas; Lintott, Chris; Masters, Karen L.; Willett, Kyle W.; Keel, William C.; Smethurst, R. J.; Cheung, Edmond; Nichol, Robert C.; Schawinski, Kevin; Rutkowski, Michael; Kartaltepe, Jeyhan S.; Bell, Eric F.; Casteels, Kevin R. V.; Conselice, Christopher J.; Almaini, Omar; Ferguson, Henry C.; Fortson, Lucy; Hartley, William; Kocevski, Dale; Koekemoer, Anton M.; McIntosh, Daniel H.; Mortlock, Alice; Newman, Jeffrey A.; Ownsworth, Jamie; Bamford, Steven; Dahlen, Tomas; Faber, Sandra M.; Finkelstein, Steven L.; Fontana, Adriano; Galametz, Audrey; Grogin, N. A.; Grtzbauch, Ruth; Guo, Yicheng; Huler, Boris; Jek, Kian J.; Kaviraj, Sugata; Lucas, Ray A.; Peth, Michael; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn

2014-12-01

349

Effect of water and stress on the lattice-preferred orientation of olivine  

NASA Astrophysics Data System (ADS)

The influence of water and stress on the lattice-preferred orientation (LPO) of olivine aggregates was investigated through large strain, shear deformation experiments at high pressures and temperatures ( P = 0.5-2.1 GPa, T = 1470-1570 K) under both water-poor and water-rich conditions. The specimens are hot-pressed synthetic olivine aggregates or single crystals of olivine. Water was supplied to the sample by decomposition of a mixture of talc and brucite. Deformation experiments were conducted up to ? (shear strain) 6 using the Griggs apparatus where water fugacity was up to 13 GPa at the pressure of 2 GPa. The water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at P = 0.5-2 GPa was 400-1200 ppm H/Si. Several new types of LPO in olivine are found depending on water content and stress. Samples deformed in water-poor conditions show a conventional LPO of olivine where the olivine [100] axis is subparallel to the shear direction, the (010) plane subparallel to the shear plane (type-A). However, we identified three new types (type-B, C, and E) of LPO of olivine depending on the water content and stress. The type-B LPO of olivine which was found at relatively high stress and/or under moderate to high water content conditions is characterized by the olivine [001] axis subparallel to the shear direction, the (010) plane subparallel to the shear plane. The type-C LPO which was found at low stress and under water-rich conditions is characterized by the olivine [001] axis subparallel to the shear direction, the (100) plane subparallel to the shear plane. The type-E LPO which was found under low stress and moderate water content is characterized by the olivine [100] axis subparallel to the shear direction, the (001) plane subparallel to the shear plane. Observations by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) show that the dislocations in water-poor samples (type-A) are curved and both b = [100] and b = [001] dislocations have a similar population. Numerous subgrains are seen in water-poor samples in backscattered electron images. In contrast, water-rich samples (both type-B and type-C) contain mostly b = [001] dislocations and dislocations are straight and sub-grain boundaries are rare compared to those in water-poor samples. These observations suggest that (1) dominant slip systems in olivine change with water fugacity (and stress) and (2) grain boundary migration is enhanced in the presence of water. Seismic anisotropy corresponding to the fabrics under water-rich condition is significantly different from that under water-poor condition. Consequently, the relationship between seismic anisotropy and flow geometry in water-rich regions is expected to be different from that in water-poor regions in which type-A fabric dominates (i.e., the lithosphere). A few cases are discussed including anisotropy in the subduction zone and in the deep upper mantle.

Jung, H.; Katayama, I.; Jiang, Z.; Hiraga, T.; Karato, S.

2006-07-01

350

How Large Are the Bars in Barred Galaxies?  

E-print Network

I present a study of the sizes (semimajor axes) of bars in disc galaxies, combining a detailed study of 65 S0-Sb galaxies with measurements of 70 Sb-Sd galaxies from Martin (1995). As has been noted before with smaller samples, bars in early-type (S0-Sb) galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies; this is true both for relative sizes (bar length as fraction of isophotal radius R_25 or exponential disc scale length h) and absolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~3.3 kpc), ~0.2-0.8 R_25 (mean \\~0.38 R_25) and ~0.5-2.5 h (mean ~1.4 h). Late-type bars extend to only \\~0.5-3.5 kpc, 0.05-0.35 R_25 and 0.2-1.5 h; mean sizes are ~1.5 kpc, 0.14 R_25 and 0.6 h. Sb galaxies resemble earlier-type galaxies in terms of bar size relative to h; their smaller R_25-relative sizes may be a side effect of higher star formation, which increases R_25 but not h. For S0-Sbc galaxies, bar size correlates well with disc size (both R_25 and h); these correlations are stronger than the known correlation with M_B. All correlations appear to be weaker or absent for late-type galaxies; in particular, there seems to be no correlation between bar size and either h or M_B for Sc-Sd galaxies. I show that the bars detected in HST near-IR images at z ~ 1 by Sheth et al. (2003) have absolute sizes consistent with those in bright, nearby S0-Sb galaxies. I also compare the sizes of real bars with those produced in simulations, and discuss some possible implications for scenarios of secular evolution along the Hubble sequence. Simulations often produce bars as large as -- or larger than -- those seen in S0-Sb galaxies, but rarely any as small as those in Sc-Sd galaxies. (Abridged.)

Peter Erwin

2005-08-26

351

Influence of FeO and H on the electrical conductivity of olivine  

NASA Astrophysics Data System (ADS)

The influence of Fe (iron) and H (hydrogen) on the electrical conductivity of olivine was investigated. Synthetic olivine aggregates with the XFe = Fe/(Fe + Mg) (molar ratio) = 21-64% with the water content of 84-620 ppm wt (Paterson calibration) were prepared and their electrical conductivity was measured at P = 4 GPa and T = 873-1473 K. The impedance spectroscopy was used to calculate the DC electrical conductivity. We found that electrical conductivity of samples increases with increasing FeO content in both anhydrous and hydrous olivine. However, the way in which FeO enhances electrical conductivity is different between anhydrous and hydrous olivine. In anhydrous sample, the activation energy is reduced with FeO content and hence the effect of FeO content is large at low temperatures, but its effect is small at mantle temperatures. In contrast, FeO content does not affect the activation energy in hydrous olivine, and consequently, the magnitude of FeO effect is nearly independent of temperature.