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1

Dynamic crystallization study of barred olivine chondrules  

SciTech Connect

Chondrules, which comprise the bulk of most chondrites, formed very early in the solar system, and understanding their formation will elucidate early nebular processes. Barred olivine (BO) chondrules make up approximately 10% of chondrules and because of their unique dendritic textures represent a restricted set of crystal growth conditions and, thus, formation conditions. BO textures have been replicated using dynamic crystallization techniques on olivine-rich chondrule starting compositions in an attempt to determine these formation conditions. One composition was modeled after the average BO chondrule composition in L-chondrites determined by Weisberg (1987) in a survey of BO chondrules. Chondrule droplets are presumed to form by the melting of crystalline material. BO textures developed best if the crystalline precursor was melted slightly above to tens of degrees above the liquidus temperature eliminating all ready nuclei. Crystalline material (embryos) of subcritical nuclei size in the melts provide the nuclei when they reach critical nucleus size at degrees of supercooling which stabilize the plate dendritic crystal form of olivine. The plate dendrite is the basic crystal unit of the BO texture. Multiple-plate dendrites are the common texture in experimentally produced chondrules; the classic, single-plate-dendrite BO chondrule has not been reproduced in the experiments.

Lofgren, G. (NASA Johnson Space Center, Houston, TX (USA)); Lanier, A.B. (Lockheed Engineering and Science Company, Houston, TX (USA))

1990-12-01

2

Alkali (Rb/K) abundances in Allende barred-olivine chondrules - Implications for the melting conditions of chondrules  

SciTech Connect

Twenty five petrographically characterized chondrules, including 18 barred olivine (BO) chondrules from the Allende (CV3) meteorite, were analyzed for alkalis (K and Rb) and alkaline earths (Sr, Ba, Ca and Mg) by mass spectrometric isotope dilution. Most BO chondrules with higher alkalis (greater than the CI level) have nearly CI-chondritic Rb/K ratios, while those with lower alkalis clearly show higher Rb/K ratios than the CI-chondritic. In general, BO chondrules with higher Rb/K exhibit more depletion of alkalis relative to Ca. The mean olivine Fa for individual chondrules positively correlates with bulk alkali concentrations in BO type but not in porphyritic type chondrules. These observations suggest that some BO chondrules formed from more reducing assemblages of precursor minerals, which experienced more intensive vaporization losses of alkalis, accompanied by Rb/K fractionation, during the chondrule-formation melting. 30 refs.

Matsuda, Hitoshi; Nakamura, Noboru; Noda, Shinji (Kobe Univ. (Japan))

1990-06-01

3

The primary liquid condensation model and the origin of barred olivine chondrules  

NASA Astrophysics Data System (ADS)

Barred olivine (BO) chondrules are some of the most striking objects in chondrites. Their ubiquitous presence and peculiar texture caught the attention of researchers and, as a consequence, considerable effort has been expensed on unraveling their origin(s). Here we report on a detailed study of two types of chondrules: the Classic and the Multiple-Plate Type of BO chondrules from the Essebi (CM2), Bishunpur (LL3.1), Acfer 214 (CH3) and DAG 055 (C3-UNGR) chondrites, and discuss the petrographic and chemical data of their major mineral phases and glasses. Glasses occur as mesostasis or as glass inclusions, the latter either enclosed inside the olivine bars (plates) or still connected to the mesostasis. The chemical composition of all glasses, characterized by being Si-Al-Ca-rich and free of alkali elements, is similar to those of the constituents (the building blocks, such as chondrules, aggregates, inclusions, mineral fragments, etc.) of CR and CV3 chondrites. They all have high trace element contents ( ˜10×CI) with unfractionated CI-normalized abundances of refractory trace elements and depletions in moderately volatile and volatile elements with respect to the refractory trace elements. The presence of alkali elements (Na + K + Rb) is coupled with a low Ca content and is only observed in those glasses that have behaved as open systems. This result supports the previous finding that Ca was replaced by alkalis (e.g., Na-Ca exchange), presumably through a vapor-solid reaction. The glasses apparently are the quenched liquid from which the olivine plates crystallized. However, they do not show any chemical fractionation that could have resulted from the crystallization of the olivines, but rather have a constant chemical compositions throughout the formation of the chondrule. In a previous contribution we were able to demonstrate the role of these liquids in supporting crystal growth directly from the vapor. Here we extend application of the primary liquid condensation model to formulate a new model for the origin of BO chondrules. The primary liquid condensation model is based on the ability of dust-enriched solar-nebula gas to directly condense into a liquid, provided the gas/dust ratio is sufficiently low. Thus, we propose that chondrules can be formed by condensation of a liquid droplet directly from the solar nebula. The extensive variability in chemical composition of BO chondrules, which ranges from alkali-poor to alkali-rich, can be explained by elemental exchange reactions with the cooling nebula. We calculate the chemical composition of the initial liquid droplet from which BO chondrules could have formed and speculate about the physical and chemical conditions that prevail in the specific regions of the solar nebula that can promote creation of these objects.

Varela, M. E.; Kurat, G.; Zinner, E.

2006-10-01

4

Formation conditions of pyroxene-olivine and magnesian olivine chondrules  

SciTech Connect

Dynamic crystallization experiments performed on a Type I and an intermediate Type II/III composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei. This factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time. Glassy and excentroradial textures form from superheated melts with no nuclei, and barred textures form with initial temperatures near the olivine disappearance temperature. Porphyritic and granular textures form with initial temperatures below the liquidus with abundant nuclei. Comparison of zoning characteristics of experimental olivines with those in natural porphyritic olivine chondrules indicates cooling rates of 100 to 1000{degree}C/h, whereas olivine morphology indicates barred olivines cooled at rates of 250 to 1,000{degree}C/h. Texture/composition relationships suggest chondrules experienced initial temperatures below 1,750{degree}C. These observations are consistent with the idea that chondrules formed by transient heating in dust-rich regions (i.e., in the midplane) of the solar nebula.

Radomsky, P.M.; Hewins, R.H. (Rutgers Univ., New Brunswick, NJ (USA))

1990-12-01

5

Laboratory Experiments Bearing on the Origin and Evolution of Olivine-rich Chondrules  

SciTech Connect

Evaporation rates of K2O, Na2O, and FeO from chondrule-like liquids and the associated potassium isotopic fractionation of the evaporation residues were measured to help understand the processes and conditions that affected the chemical and isotopic compositions of olivine-rich Type IA and Type IIA chondrules from Semarkona. Both types of chondrules show evidence of having been significantly or totally molten. However, these chondrules do not have large or systematic potassium isotopic fractionation of the sort found in the laboratory evaporation experiments. The experimental results reported here provide new data regarding the evaporation kinetics of sodium and potassium from a chondrule-like melt and the potassium isotopic fractionation of evaporation residues run under various conditions ranging from high vacuum to pressures of one bar of H2+CO2, or H2, or helium. The lack of systematic isotopic fractionation of potassium in the Type IIA and Type IA chondrules compared with what is found in the vacuum and one-bar evaporation residues is interpreted as indicating that they evolved in a partially closed system where the residence time of the surrounding gas was sufficiently long for it to have become saturated in the evaporating species and for isotopic equilibration between the gas and the melt. A diffusion couple experiment juxtaposing chondrule-like melts with different potassium concentrations showed that the diffusivity of potassium is sufficiently fast at liquidus temperatures (DK>2-10-4cm2/s at 1650-C) that diffusion-limited evaporation cannot explain why, despite their having been molten, the Type IIA and Type IA chondrules show no systematic potassium isotopic fractionation.

Richter, Frank M.; Mendybaev, Ruslan A.; Christensen, John N.; Ebel, Denton; Gaffney, Amy

2011-06-24

6

Granoblastic olivine aggregates as precursors of Type I chondrules: An experimental test  

NASA Astrophysics Data System (ADS)

Chondrule formation models involving precursors of granoblastic olivine aggregates (GOA) of either planetesimal or nebular origin have recently been proposed. We have therefore conducted chondrule simulation experiments using mixtures of 100 h-thermally annealed GOA and An + En to test the viability of GOA as predecessors of porphyritic olivine (PO) chondrules. Isothermal runs of less than 5 min at 1350-1550 °C result in GOA disaggregation and Fe-Mg exchange; runs of 0.5-4 h show textures superficially similar to granular and PO chondrules, but with reversely zoned olivine. Charges isothermally heated at 1550 °C for 1 and 4 h before being cooled at 10 and 100 °C/h undergo olivine crystallization and yield classical PO textures. Although most evidence of origin from GOA is erased, the cores of normally zoned euhedral crystals are relict. As 'phenocrysts' in Type I chondrules can be relict such chondrules could have experienced similar peak temperatures to those of Type II chondrules. Chondrules containing GOA with olivine triple junctions resemble experimental charges heated for minutes at temperatures between 1350 and 1450 °C and Type I chondrules with subhedral to anhedral olivine plus GOA relicts resemble charges heated at the same temperatures but for longer duration. Type I chondrules with a mass of granular olivine or irregular, anhedral olivine grains in the center, and much glass nearer the margin, on the other hand, require limited heating at high temperature (1550 °C) while Type I chondrules with euhedral olivines, resemble charges heated at 1550 °C for 4 h. The majority of Type I chondrules in CV chondrites display evidence of derivation from GOA. Many finer-grained chondrules in CR and UOC on the other hand, could not have been derived from such coarse-grained precursors, but could have formed from fine-grained dustballs as stipulated in the standard paradigm. Thus, both GOA and dustballs represent viable chondrule precursors of coarser and finer-grained Type I PO chondrules, respectively.

Whattam, Scott A.; Hewins, Roger H.

2009-09-01

7

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

SciTech Connect

Melts of the same composition as has been defined for porphyritic olivine chondrules have been crystallized under controlled cooling conditions, dynamic crystallization. The full range of textures observed in such chondrules has been duplicated in the experimentally produced analogs. The primary controlling factor in producing this range of textures is the heterogeneous nucleation behavior. In general, if nuclei are present when cooling begins, growth starts immediately at low degrees of supercooling and porphyritic textures result. The shapes of the phenocrysts depend on the growth rate, which in turn depends on the cooling rate. The shapes of the crystals depend on the degree of supercooling when growth is initiated and on the subsequent cooling rate. The resulting textures vary from plate dendrites to randomly oriented, elongated, skeletal crystals as the degree of supercooling and cooling rates decrease. The results of a matrix of experiments set limits on the maximum melting temperatures of chondrule forming materials and the subsequent cooling rates. Based primarily on crystal shape, the porphyritic textures develop best for this composition at melting temperatures less than 1,590{degree}C and cooling rates near 100{degree}C/hr and definitely less than 1,000{degree}C/hr. At cooling rates significantly less than 100{degree}C/hr, the phenocrysts are generally larger than observed in chondrules, and as cooling rates approach 1,000{degree}C/hr, they become more skeletal. Barred olivine chondrule textures form best from materials melted at higher temperatures and cooling rates in the range 1,000 to 3,000{degree}C/hr.

Lofgren, G. (NASA Johnson Space Center, Houston, TX (USA))

1989-02-01

8

Relict olivine, chondrule recycling, and the evolution of nebular oxygen reservoirs  

NASA Astrophysics Data System (ADS)

Chondrules often contain relict olivine grains that did not crystallize in situ, providing opportunities to decipher how chondrule components evolved. We studied olivine in the Sahara-97210 (LL3.2), Wells (LL3.3) and Chainpur (LL3.4) chondrites using SEM, EMPA, and SIMS techniques. Oxygen isotopes were analyzed in 16 objects from all three meteorites, and trace elements were analyzed in Sahara-97210 and Chainpur. Two groups of olivine are identified based on oxygen isotope compositions. One group is enriched in 16O (? 17O ˜ - 8 to - 4‰) and falls close to the CCAM mixing line; it includes forsterite and Mg-rich olivine present as relict grains in Type II (ferrous) chondrules and the forsteritic cores of some isolated grains. These low-? 17O grains are poor in MnO (< 0.2 wt.%) and are usually enriched in CaO (˜ 0.3-0.65 wt.%). The other group is less enriched in 16O (? 17O ˜ - 3 to + 4 ‰); it includes normal (non-relict) ferrous olivine in type II chondrules, normal (non-relict) Mg-rich olivine in Type I (magnesian) chondrules, dusty olivine relict grains in Type I chondrules, and Mg-rich olivine relicts in a Type II and a Type I chondrule. These high-? 17O grains have variable CaO (0-0.95 wt.%) and MnO (˜ 0-0.45 wt.%) contents, with the more calcic and Mn-poor compositions associated with forsteritic olivine. Trace-element data show that forsteritic olivine grains in both oxygen groups are similarly enriched in refractory elements (Al, Sc, Y, Ca, Ti, V) and depleted in volatile elements (Cr, Mn, P, Rb, sometimes K and Na) compared to normal ferrous olivine, suggesting that variations in chemical composition reflect the extent of thermal processing (greater for magnesian olivine). The data are consistent with a model in which nebular reservoirs became less enriched in 16O with time. An earlier episode of chondrule formation produced Type I chondrules and isolated forsterites in carbonaceous chondrites, and forsteritic grains that were incorporated into ordinary chondrites as relict grains in chondrules and as isolated grains. Later episodes of chondrule formation produced both Type I and Type II chondrules in ordinary chondrites under a variety of thermal and redox conditions.

Ruzicka, A.; Hiyagon, H.; Hutson, M.; Floss, C.

2007-05-01

9

Relict olivine grains, chondrule recycling, and implications for the chemical, thermal, and mechanical processing of nebular materials  

NASA Astrophysics Data System (ADS)

Chondrules and isolated forsterites in five low-subtype ordinary chondrites [NWA 3127 (LL3.1), Sahara 97210 (LL3.2), Wells (LL3.3), Chainpur (LL3.4), and Sahara 98175 (LL3.5)] were studied using petrographic, EMPA, and SIMS techniques to better constrain the origin of chondrules and the olivine grains within them. Our results imply that igneous crystallization, vapor fractionation, redox effects, and open-system behavior were important processes. All olivine grains, including normal, relict, and isolated forsterite grains, show evidence for igneous fractionation under disequilibrium conditions, with olivine crystallizing during rapid cooling (closer to 2000 °C/h than to 100 °C/h). Vapor fractionation is manifested by anti-correlated abundances between refractory elements (Al, Sc, Y, Ti, Ca, V) and volatile elements (Cr, Mn, P, Rb, Fe) in olivine. Redox effects are evidenced in various ways, and imply that Fe, Co, Ni, and P were partitioned more into metal, and V was partitioned more into olivine, under reducing conditions in the most FeO-poor melts. There is no obvious evidence for systematic variations in olivine composition according to meteorite subtype, but shock melting in Sahara 97210 resulted in the injection of glass-derived melt into olivine, resulting in artificially high abundances of Ba, Sr, Na, Ti, and some other incompatible elements in olivine. Terrestrial weathering in a hot desert environment may have mobilized Ba and Sr in some glasses. Our data suggest that chondrules in ordinary chondrites experienced repeated thermal, chemical, and mechanical processing during a "recycling" process over an extended time period, which involved multiple episodes of melting under fluctuating redox and heating conditions, and multiple episodes of chondrule break-up in some cases. Forsterite grains, including normal grains in forsterite-bearing type I chondrules, the cores of isolated forsterites, and relict forsterite in type II chondrules, all crystallized from similar, refractory melts under reducing conditions; relict Mg-olivine and isolated forsterite grains were thus derived from type I chondrules. Olivine in type II chondrules, including normal grains and ferroan overgrowths on relict Mg-olivine, crystallized from more volatile-rich, oxidized, and relatively unfractionated melts. Relict dusty olivine grains in type I chondrules were derived from type II chondrules during incomplete melting episodes involving reduction and some vaporization, with clear (non-dusty) grains in dusty olivine-bearing chondrules crystallizing from the reduced and partly vaporized melts. Melt compositions parental to normal olivine grains in type I and II chondrules are systematically enriched in refractory elements compared to bulk chondrule compositions, implying that chondrules often experienced open-system exchange with more volatile-rich surroundings after some olivine had crystallized, possibly while the chondrules were still partly molten. Type II chondrules could have been derived from type I chondrules by the addition of relatively volatile-rich material, followed by re-melting and little evaporation under oxidizing conditions. In contrast, type I chondrules could have been derived from type II chondrules by re-melting involving more-or-less evaporation under reducing conditions. Chemical, oxygen isotope, and petrographic data are best accommodated by a model in which there were several (>2-3, sometimes ?4-5) melting episodes for most chondrules in ordinary chondrites.

Ruzicka, Alex; Floss, Christine; Hutson, Melinda

2008-11-01

10

Amoeboid olivine aggregates with low-Ca pyroxenes: a genetic link between refractory inclusions and chondrules?  

NASA Astrophysics Data System (ADS)

Amoeboid olivine aggregates (AOAs) in primitive (unmetamorphosed and unaltered) carbonaceous chondrites are uniformly 16O-enriched (? 17O ˜ -20‰) and consist of forsterite (Fa <2), FeNi-metal, and a refractory component (individual CAIs and fine-grained minerals interspersed with forsterite grains) composed of Al-diopside, anorthite, ±spinel, and exceptionally rare melilite (Åk <15); some CAIs in AOAs have compact, igneous textures. Melilite in AOAs is replaced by a fine-grained mixture of spinel, Al-diopside, and anorthite. Spinel is corroded by anorthite or by Al-diopside. In ˜10% of > 500 AOAs studied in the CR, CV, CM, CO, CH, CB, and ungrouped carbonaceous chondrites Acfer 094, Adelaide, and LEW85332, forsterite is replaced to a various degree by low-Ca pyroxene. There are three major textural occurrences of low-Ca pyroxene in AOAs: (i) thin (<10 ?m) discontinuous layers around forsterite grains or along forsterite grain boundaries in AOA peripheries; (ii) haloes and subhedral grains around FeNi-metal nodules in AOA peripheries, and (iii) thick (up to 70 ?m) continuous layers with abundant tiny inclusions of FeNi-metal grains around AOAs. AOAs with low-Ca pyroxene appear to have experienced melting of various degrees. In the most extensively melted AOA in the CV chondrite Leoville, only spinel grains are relict; forsterite, anorthite and Al-diopside were melted. This AOA has an igneous rim of low-Ca pyroxene with abundant FeNi-metal nodules and is texturally similar to Type I chondrules. Based on these observations and thermodynamic analysis, we conclude that AOAs are aggregates of relatively low temperature solar nebular condensates originated in 16O-rich gaseous reservoir(s), probably CAI-forming region(s). Some of the CAIs were melted before aggregation into AOAs. Many AOAs must have also experienced melting, but of a much smaller degree than chondrules. Before and possibly after aggregation, melilite and spinel reacted with the gaseous SiO and Mg to form Ca-Tschermakite (CaAl 2SiO 6)-diopside (CaMgSi 2O 6) solid solution and anorthite. Solid or incipiently melted olivine in some AOAs reacted with gaseous SiO in the CAI- or chondrule-forming regions to form low-Ca pyroxene: Mg 2SiO 4 + SiO (g) + H 2O (g) = Mg 2Si 2O 6 + H 2(g). Some low-Ca pyroxenes in AOAs may have formed by oxidation of Si-bearing FeNi-metal: Mg 2SiO 4 + Si (in FeNi) + 2H 2O (g) = Mg 2Si 2O 6 + 2H 2(g) and by direct gas-solid condensation: Mg (g) + SiO (g) +H 2O (g) = Mg 2Si 2O 6(s) + H 2(g) from fractionated (Mg/Si ratio < solar) nebular gas. Although bulk compositions of AOAs are rather similar to those of Type I chondrules, on the projection from spinel onto the plane Ca 2SiO 4-Mg 2SiO 4-Al 2O 3, these objects plot on different sides of the anorthite-forsterite thermal divide, suggesting that Type I chondrules cannot be produced from AOAs by an igneous fractionation. Formation of low-Ca pyroxene by reaction of AOAs with gaseous SiO and by melting of silica-rich dust accreted around AOAs moves bulk compositions of the AOAs towards chondrules, and provide possible mechanisms of transformation of refractory materials into chondrules or chondrule precursors. The rare occurrences of low-Ca pyroxene in AOAs may indicate that either AOAs were isolated from the hot nebular gas before condensation of low-Ca pyroxene or that condensation of low-Ca pyroxene by reaction between forsterite and gaseous SiO was kinetically inhibited. If the latter is correct, then the common occurrences of pyroxene-rich Type I chondrules may require either direct condensation of low-Ca pyroxenes or SiO 2 from fractionated nebular gas or condensation of gaseous SiO into chondrule melts.

Krot, Alexander N.; Petaev, Michail I.; Yurimoto, Hisayoshi

2004-04-01

11

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

12

Chromite and olivine in type 2 chondrules in carbonaceous and ordinary chondrites: Implications for thermal histories and group differences  

SciTech Connect

Analyses of chromite and olivine in type 2 chondrules in CM, CO, CV, CR, H, L, LL, and two ungrouped chondrites indicate that chromites are extremely sensitive indicators of thermal metamorphism. Chromite-olivine pairs in chondrites of petrographic types {le}3.0 have iron-magnesium partitioning characteristic of phsases which crystallized from silicate melts at temperatures > 1,400C; paris in chondrites of types > 3.0 have partitioning characteristic of reequilibration at lower temperatures. With the possible exception of the CR group, chondrite chemical groups underwent either substantial aqueous alteration (CM) or sufficient heating to reset type 2 chromites, but not both. The CR parent body may have been heated following aqueous alteration, although our data are insufficient to support a firm conclusion. Chromite and olivine compositions differ systematically among three of the chondrite groups, which suggest that type 2 melts differed in composition. Whether differences existed among the other groups is uncertain.

Johnson, C.A.; Prinz, M. (American Museum of Natural History, New York, NY (United States))

1991-03-01

13

Evidence for fractional crystallization of wadsleyite and ringwoodite from olivine melts in chondrules entrained in shock-melt veins  

PubMed Central

Peace River is one of the few shocked members of the L-chondrites clan that contains both high-pressure polymorphs of olivine, ringwoodite and wadsleyite, in diverse textures and settings in fragments entrained in shock-melt veins. Among these settings are complete olivine porphyritic chondrules. We encountered few squeezed and flattened olivine porphyritic chondrules entrained in shock-melt veins of this meteorite with novel textures and composition. The former chemically unzoned (Fa24–26) olivine porphyritic crystals are heavily flattened and display a concentric intergrowth with Mg-rich wadsleyite of a very narrow compositional range (Fa6–Fa10) in the core. Wadsleyite core is surrounded by a Mg-poor and chemically stark zoned ringwoodite (Fa28–Fa38) belt. The wadsleyite–ringwoodite interface denotes a compositional gap of up to 32 mol % fayalite. A transmission electron microscopy study of focused ion beam slices in both regions indicates that the wadsleyite core and ringwoodite belt consist of granoblastic-like intergrowth of polygonal crystallites of both ringwoodite and wadsleyite, with wadsleyite crystallites dominating in the core and ringwoodite crystallites dominating in the belt. Texture and compositions of both high-pressure polymorphs are strongly suggestive of formation by a fractional crystallization of the olivine melt of a narrow composition (Fa24–26), starting with Mg-rich wadsleyite followed by the Mg-poor ringwoodite from a shock-induced melt of olivine composition (Fa24–26). Our findings could erase the possibility of the resulting unrealistic time scales of the high-pressure regime reported recently from other shocked L-6 chondrites.

Miyahara, Masaaki; El Goresy, Ahmed; Ohtani, Eiji; Nagase, Toshiro; Nishijima, Masahiko; Vashaei, Zahra; Ferroir, Tristan; Gillet, Philippe; Dubrovinsky, Leonid; Simionovici, Alexandre

2008-01-01

14

26Al26Mg systematics of Ca-Alrich inclusions, amoeboid olivine aggregates, and chondrules from the ungrouped carbonaceous chondrite Acfer 094  

Microsoft Academic Search

We report in situ magnesium isotope measurements of 7 porphyritic magnesium-rich (type I) chondrules, 1 aluminum-rich chondrule, and 16 refractory inclusions (14 Ca-Al-rich inclusions [CAIs] and 2 amoeboid olivine aggregates [AOAs]) from the ungrouped carbonaceous chondrite Acfer 094 using a Cameca IMS 6f ion microprobe. Both AOAs and 9 CAIs show radiogenic 26Mg excesses corresponding to initial 26Al\\/27Al ratios between

Naoji Sugiura; A. N. Krot

2007-01-01

15

Experimental reproduction of textures of chondrules  

NASA Astrophysics Data System (ADS)

The textures of chondrules have been reproduced by crystallizing melts of three different compositions at 1 atm with cooling rates from 400 to 20 C/min. A porphyritic olivine texture has been formed from a melt of olivine-rich composition (SIO2 = 45 wt.%), a barred-olivine texture from melt of intermediate composition (SiO2 = 47 wt.%), and radial-olivine texture from melt of pyroxene-rich composition (SiO2 = 57 wt.%). The cooling rate for producing barred olivine is most restricted; the rate ranges from 120 to 50 C/min. The results of the experiments indicate that some of the major types of textures of chondrules can be formed with cooling rate of about 100 C/min, and that the texture varies depending on the composition of melt.

Tsuchiyama, A.; Nagahara, H.; Kushiro, I.

1980-06-01

16

Demonstration of REE fractionation among individual chondrules from the allende (CV3) chondrite  

SciTech Connect

Abundances of REE, Ba, Sr, Rb, K, Mg and Ca were determined by precise mass spectrometric isotope dilution techniques for 24 chondrules from the Allende (CV3) chondrite. The REE abundances are 2.5-10 {times} CI for barred olivine chondrules, 2-8 {times} CI for porphyritic and nonporphyritic pyroxene chondrules, 0.15-4 {times} CI for porphyritic olivine and porphyritic olivine-pyroxene chondrules and are more or less similarly fractionated. General REE fractionations and large (up to 170%) anomalies of Ce, Eu and Yb occur in all chondrule types, particularly for barred olivine and pyroxene-rich chondrules. Positive correlations of REE with the moderately volatile elements, K and Rb, as well as other refractory elements, Ca, Sr and Ba, are independent of textural type and major chemical compositions. Each type of chondrule has large and systematic abundance variations of K and Rb, but shows a constant K/Rb ratio close to that of CIs. From the these results, the following constraints on the chemical characteristics of precursors and chondrule-forming events are suggested: (1) vaporization loss of alkalis accompanied by K/Rb fractionation did not occur during chondrule-formation melting events, (2) elemental abundances were basically established prior to melting events by accretion of alkali-free component(s) and alkali-bearing refractory precursors with fractionated REE, (3) gas/solid (or liquid) processes yielding REE fractionations took place during the formation of refractory precursors.

Misawa, K; Nakamura, N. (Kobe Univ. (Japan))

1988-06-01

17

Trace Element Microdistribution in Carbonaceous Chondrite Chondrules  

NASA Astrophysics Data System (ADS)

We present LA-ICP-MS analyses of silicate phases in chondrules of CR and CV chondrites. Olivine/mesostasis REE partitioning approach equilibrium for the coarser-grained chondrules. Pyroxene data offer further evidence of gas-melt interaction.

Jacquet, E.; Gounelle, M.; Alard, O.

2012-03-01

18

Oxygen isotope systematics of chondrule phenocrysts from the CO3.0 chondrite Yamato 81020: Evidence for two distinct oxygen isotope reservoirs  

NASA Astrophysics Data System (ADS)

High-precision oxygen three-isotope measurements of olivine and pyroxene were performed on 33 chondrules in the Yamato 81020 CO3.0 chondrite by secondary ion mass spectrometry. In chondrules where oxygen isotopes were measured in both olivine and pyroxene, the majority of grains have similar values, indicating co-magmatic crystallization. However, many chondrules contain relict grains with unique oxygen isotope ratios. A striking feature of Yamato 81020 chondrules is a bimodal distribution of oxygen isotope ratios, as those with Mg# >97 phenocrysts range in ?17O from ?4.8‰ to ?6.5‰ ("?5.5‰" group), and those with Mg# 96–36 phenocrysts have ?17O values of ?2.1‰ to ?3.0‰ ("?2.5‰" group). A single Mg# 99.6 barred olivine chondrule has a ?17O of ?3.3‰. We discuss that ?17O ˜?5.5‰ chondrules are derivative of a reservoir with limited dust enrichment (100× Solar System), which yielded a relatively reduced chondrule-forming environment. In contrast, the ?17O ˜?2.5‰ chondrules may have been influenced by 16O-poor H2O ice that sublimed and then homogenized with precursor material. The addition of H2O, when combined with high dust enrichment (1000× Solar System) and greater bulk Fe content, could have induced an oxidized environment at high temperatures, forming Mg# 96–36 chondrules. Among the 33 chondrules studied, the Al–Mg relative ages of 20 had been obtained previously. Comparing the oxygen isotope ratios and the 26Al ages of these chondrules, it is likely that the "?5.5‰" and "?2.5‰" oxygen isotope reservoirs existed contemporaneously. This implies that the snow line was spatially fixed during chondrule formation, and separated the CO chondrite accretion region into two distinct volumes of precursors.

Tenner, Travis J.; Ushikubo, Takayuki; Kurahashi, Erika; Kita, Noriko T.; Nagahara, Hiroko

2013-02-01

19

Retention of sodium during chondrule melting  

NASA Astrophysics Data System (ADS)

Using published data, the differences in Na concentrations in different groups of porphyritic olivine chondrules are analyzed. The results show that Na was incorporated into type II chondrule precursors as albite and was not significantly lost during melting. Type I chondrules, which contain very low concentrations of Na, were also not depleted in Na during melting, as indicated by the lack of correlation between the Na/Al ratios and the liquidus temperatures in type I chondrules. It is concluded that the difference in Na concentration is caused by the abundance of precursor albite in type II chondrules, rather than the loss of Na from the melt.

Hewins, R. H.

1991-04-01

20

Kosmochloric Ca-rich pyroxenes and FeO-rich olivines (Kool grains) and associated phases in Stardust tracks and chondritic porous interplanetary dust particles: Possible precursors to FeO-rich type II chondrules in ordinary chondrites.  

NASA Astrophysics Data System (ADS)

Terminal particles and mineral fragments from comet 81P/Wild 2 were studied in 16 aerogel tracks by transmission and secondary electron microscopy. In eight tracks clinopyroxenes with correlated Na2O and Cr2O3 contents as high as 6.0 wt% and 13.0 wt%, respectively, were found. Kosmochloric (Ko) clinopyroxenes were also observed in 4 chondritic interplanetary dust particles (IDPs). The Ko clinopyroxenes were often associated with FeO-rich olivine ± Cr-rich spinel ± aluminosilicate glass or albitic feldspar, assemblages referred to as Kool grains (Ko = kosmochloric Ca-rich pyroxene, ol = olivine). Fine-grained (submicron) Kool fragments have textures suggestive of crystallization from melts while coarse-grained (>1 µm) Kool fragments are often glass-free and may have formed by thermal metamorphism in the nebula. Average major and minor element distributions between clinopyroxenes and coexisting FeO-rich olivines are consistent with these phases forming at or near equilibrium. In glass-bearing fine-grained Kool fragments, high concentrations of Na in the clinopyroxenes are inconsistent with existing experimentally determined partition coefficients at equilibrium. We speculate that the availability of Cr in the melt increased the clinopyroxene Na partition coefficient via a coupled substitution thereby enhancing this phase with the kosmochlor component. The high temperature minerals, fine-grain sizes, bulk compositions and common occurrence in the SD tracks and IDPs support the idea that Kool grains could have been precursors to type II chondrules in ordinary chondrites. These grains, however, have not been observed in these meteorites suggesting that they were destroyed during chondrule formation and recycling or were not present in the nebula at the time and location where meteoritic chondrules formed.

Joswiak, D. J.; Brownlee, D. E.; Matrajt, G.; Westphal, A. J.; Snead, C. J.

2009-11-01

21

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

22

An olivine-microchondrule-bearing clast in the Krymka meteorite  

SciTech Connect

A small (150 x 200-micron-size) clast consisting of 20 vol pct olivine microchondrules (with barred and granular textures) and 80 vol pct recrystallized silicate matrix material occurs in Krymka (LL3.1). This is the fourth microchondrule-bearing clast to be described. The chondrules are zoned in FeO with concentrations increasing toward the surface. The clast most closely resembles a previously described radial-pyroxene-microchondrule-bearing clast in Piancaldoli (LL3.4). 8 refs.

Rubin, A.E. (California Univ., Los Angeles (USA))

1989-09-01

23

Mineralogical and isotopic constraints on chondrule formation from shock wave thermal histories  

NASA Astrophysics Data System (ADS)

When a shock wave passes through a nebular gas, increasing water enrichment leads to higher temperatures and post-shock P, but lower cooling rates. A kinetic evaporation model is developed for tracking the chemical and isotopic changes that would occur in a clump of chondrule precursor dust surrounded by nebular gas in a closed system traversed by a nebular shock wave, taking into account effects of non-equilibrium melting and fractional crystallization on the liquid composition and the temperature difference between the gas and the droplet. A range of shock wave temperature-pressure histories computed for systems enriched relative to solar composition by factors of 550 in water, to achieve the redox state of chondrules, and 600 in dust, to retard evaporation, are employed, and redox changes are assumed to occur on the time-scale of heating and cooling in each. Two different system compositions are assumed, with the mean Fe/Si ratios of Types I and II chondrules. Two different textural outcomes are modeled, PO, in which nuclei are preserved and olivine crystallization begins immediately upon reaching saturation, and BO, in which no nuclei are preserved and olivine crystallization begins only after 300-400 K of supersaturation. In all cases, all iron evaporates, regardless of its oxidation state, as well as alkalis and smaller fractions of Mg and Si. In most cases, recondensation occurs on the time-scale of cooling, resulting in droplets whose bulk compositions have small isotopic anomalies in Mg, Si and Fe, comparable to those seen in bulk chondrules. Because fractional crystallization of olivine occurs before recondensation is complete, however, large isotopic variations, especially for iron, would have been recorded both within olivine crystals and between olivine and glass within these objects. Even after diffusive relaxation during crystal growth and cooling, variations in ?25Mg of several tenths of a ‰ to several ‰, in ?29Si of 0.1‰ to several ‰ and in ?56Fe of several ‰ would be measurable within large grains that grew throughout the olivine crystallization interval in many cases, and olivine-glass differences of ?several tenths of a ‰ in ?29Si, and of several ‰ in ?56Fe would be preserved. Such internal isotopic heterogeneities have not yet been observed in chondrules, suggesting that the latter did not form in these shock wave thermal histories. Suppression of production of internal isotopic variations requires heating times that are shorter by a factor of 100, combined with dust enrichments ? 6 × 104 and/or P?10-2 bar. Together with relatively high f, these constraints suggest that chondrules formed in clouds of liquid and vapor generated by impact on ice-rich planetesimals.

Fedkin, Alexei V.; Grossman, Lawrence; Ciesla, Fred J.; Simon, Steven B.

2012-06-01

24

Partitioning of Na between olivine and melt: An experimental study with application to the formation of meteoritic Na 2O-rich chondrule glass and refractory forsterite grains  

Microsoft Academic Search

We report experimentally determined 1atm olivine\\/melt DNa partitioning data for low fO2, a variety of melt compositions and a temperature range of 1325–1522°C. We demonstrated that high-current electron microprobe analyses (EPMA, I=500nA, 600s on the peak) allow quantitative determination of Na2O in olivine down to ?10?g\\/g. The mean olivine\\/melt DNa from 12 experimental runs is 0.0031±0.0007 (1?). This is the

Alexander Borisov; Andreas Pack; Andreas Kropf; Herbert Palme

2008-01-01

25

Tetrad effects in REE abundance patterns of chondrules from CM meteorites: Implications for aqueous alteration on the CM parent asteroid  

NASA Astrophysics Data System (ADS)

Lanthanide tetrad effect in bulk chondrules from two moderately altered CM chondrites, Murchison and Yamato-793321 (Y-793321), are reported for the first time. Twenty-three chondrules were petrographically characterized and analyzed for 10 rare earth elements (REE) and other trace and major elements (Ba, Sr, Rb, K, Ca, Mg and Fe) using the precise isotope dilution technique. The results indicate systematic depletion (several times) of alkali and alkaline earths compared to CV and CO chondrules. Most of the porphyritic olivine (8 PO) and olivine-pyroxene (4 POP), porphyritic and radial pyroxene (2 PP, 1 RP), and granular olivine (1 GO) chondrules show a light-REE (L-REE) depleted, heavy-REE (H-REE) smoothly fractionated pattern composed of four (upward convex) segments possessing a relatively large negative Eu anomaly (CI-normalized La/Sm, Lu/Er and Eu/Eu* ratios = 0.3-1: Eu*, normal value). On the other hand, all barred-olivine (5 BO) chondrules, a few PO and POP indicate almost a flat L-REE pattern. In addition, regardless of their textural types, nearly half of the chondrules have a variable degree of Ce and Yb anomalies, and/or L/H-REE discontinuity, which is similar to CV and CO chondrules. The observed L- and H-convex REE patterns accompanied with the negative Eu anomaly is the first known case for chondrules as well as meteoritic materials, but have been previously reported for geological samples such as sedimentary rocks, late stage igneous and metamorphic rocks, and are explained as the lanthanide tetrad effect, which plausibly results from fluid-rock interaction. We suggest that the marked REE fractionations occurred by the selective incorporation of L-, H-REEs and Eu into alteration products in the matrix during alteration processes on the CM parent body, but that the gas/solid REE fractionation characteristics established in the nebula have basically remained unchanged. We suggest that the tetrad effects observed here represent a new index of physico-chemical conditions of fluid-rock interactions prevalent on the CM parent body.

Inoue, Mutsuo; Nakamura, Noboru; Kimura, Makoto

2009-09-01

26

The relative formation ages of ferromagnesian chondrules inferred from their initial aluminum-26\\/aluminum-27 ratios  

Microsoft Academic Search

We performed a systematic high precision SIMS 26Al-26Mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite Bishunpur (LL3.1). The chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and\\/or glass. The chemical compositions of the chondrules vary from FeO-poor to FeO-rich. Eight chondrules show resolvable 26Mg-excesses with a maximum ?26Mg of

Smail Mostefaoui; Noriko T. Kita; Shigeko Togashi; Shogo Tachibana; Hiroko Nagahara; Yuichi Morishita

2002-01-01

27

Chondrules and other components in C, O, and E chondrites Similarities in their properties and origins  

NASA Astrophysics Data System (ADS)

Three types of chondrules are described that are common to H3, LL3, CM2, CO3, and CV3 chondrites. Low- and high-FeO, porphyritic olivine chondrules contain olivine with Fa0.3-8 and Fa5-50 respectively, and can easily be distinguished petrographically. Poikilitic pyroxene chondrules have 1-20 vol pct olivine (Fa0.2-8) enclosed by low-Ca pyroxene (Fs0.5-7), and also occur in E chondrites. These three types formed in separate nebular regions which had dimensions and spacings such that a few percent of the chondrules that collided to form compound chondrules were of different types. Sorting of chondrule precursor material and mixing of chondrule types probably account for most variations in bulk and mineral chemistry among chondrite groups. Metallic Fe,Ni grains containing 0.1-1 percent Cr, Si, and P are present in low-FeO olivine chondrules from all type 2 and least metamorphosed type 3 chondrites. Metal compositions reflect reduction during chondrule formation in the nebula, not nebular condensation. Opaque matrices in type 3 ordinary and carbonaceous chondrites are somewhat similar in composition and mineralogy, and probably have related origins. It is concluded that chondrules in all known chondrite groups share similar nebular origins.

Scott, E. R. D.; Taylor, G. J.

1983-11-01

28

A Critical Examination of the X-wind Model for Chondrule and Calcium-rich, Aluminum-rich Inclusion Formation and Radionuclide Production  

NASA Astrophysics Data System (ADS)

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.; Connolly, H. C., Jr.; Boss, Alan P.

2010-12-01

29

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

30

Retention of sodium during chondrule melting  

SciTech Connect

Type I chondrules in unequilibrated ordinary and carbonaceous chondrites tend to be enriched in refractory elements and depleted in volatiles relative to bulk CI. Type II chondrules show chondritic concentrations of major and minor lithophile elements with Na, in particular, at or slightly above the appropriate bulk-rock values. Element ratio diagrams for chondrule bulk compositions show that Type II chondrules plot on a mixing line between forsterite and a Na phase, with Na/Al 1:1, whereas Type I compositions can be explained by mixing forsterite with melilite or CAI or other refractory component with little Na. If their bulk compositions are manipulated, subtracting Ca is diopside and Fe + Mg as olivine, the residue is 90{percent} albite and 10{percent} silica. Albite was incorporated into the precursors of Type II chondrules, which clearly have not been depleted in Na although their initial temperatures overlap with those of Type I. There is no (negative) correlation between Type I liquidus temperatures (1450-1900{degree}C) and Na/Al ratios and hence no indication of Na loss from the melt. If Type I precursors contained albite, the most aluminous chondrules would have suffered the most extreme Na loss, but these have the lowest liquidus temperatures. Their precursors were Na depleted, whereas those of Type II were Na enriched, as a function of the abundance of albite. The simplest way to obtain the bulk compositions of chondrules is to assemble condensates into precursors at different temperatures, and concentration of solids in the nebula or exceptionally rapid heating is required to preserve Na in chondrules after melting. Substantial exchange of Na occurred between chondrules and chondrite matrix during parent-body metamorphism to petrologic type 3.6.

Hewins, R.H. (Rutgers Univ., New Brunswick, NJ (USA))

1991-04-01

31

Kinetics of Melting and Applications to Chondrules  

NASA Astrophysics Data System (ADS)

The congruent melting kinetics of Amelia albite were experimentally determined at 1125o C,/ 1150o C,/ 1175o C, and 1200o C. It was determined that congruent melting is a heterogeneous process. Melting is initiated at external surfaces and cleavage planes. Melting kinetics of albite are best described using a normal growth model. Congruent melting of albite was found to be interface controlled, and rates of melting are directly proportional to the amount of superheat, and inversely proportional to viscosity. Comparison of the results obtained here with previous studies of melting kinetics on other materials (oxides and silicates) finds that the normal growth model can be used to predict melting rates within an order of magnitude. The normal growth model was used to predict congruent melting rates of forsterite and enstatite as well as other minerals which may have been present in the chondrule forming region of the solar nebula. Constraints on the peak temperatures of chondrule formation are thus obtained. Specifically, chondrules containing relict grains of forsteritic olivine and enstatitic pyroxene could not have been heated above 1901o C and 1577o C, respectively, for more than a few seconds. Reanalyses of Na-Al-rich chondrule glasses by EPMA have found that previous EPMA work resulted in loss of Na from the activated volume due to migration in an electrical potential gradient. The Na-Al-rich chondrules have Na/Al ratios of unity, suggesting that they did not lose alkalis during flash heating. Experiments reproduced the chondrule glasses and determined the formational constraints of these chondrules. Specifically, the chondrules needed to have been cooled at low rates (<6o C/hr) at the lower temperature end of chondrule formation.

Greenwood, James Paul

1997-12-01

32

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

33

High precision SIMS oxygen three isotope study of chondrules in LL3 chondrites: Role of ambient gas during chondrule formation  

NASA Astrophysics Data System (ADS)

We report high precision SIMS oxygen three isotope analyses of 36 chondrules from some of the least equilibrated LL3 chondrites, and find systematic variations in oxygen isotope ratios with chondrule types. FeO-poor (type I) chondrules generally plot along a mass dependent fractionation line (? 17O ˜ 0.7‰), with ? 18O values lower in olivine-rich (IA) than pyroxene-rich (IB) chondrules. Data from FeO-rich (type II) chondrules show a limited range of ? 18O and ? 17O values at ? 18O = 4.5‰, ? 17O = 2.9‰, and ? 17O = 0.5‰, which is slightly 16O-enriched relative to bulk LL chondrites (? 17O ˜ 1.3‰). Data from four chondrules show 16O-rich oxygen isotope ratios that plot near the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line. Glass analyses in selected chondrules are systematically higher than co-existing minerals in both ? 18O and ? 17O values, whereas high-Ca pyroxene data in the same chondrule are similar to those in olivine and pyroxene phenocrysts. Our results suggest that the LL chondrite chondrule-forming region contained two kinds of solid precursors, (1) 16O-poor precursors with ? 17O > 1.6‰ and (2) 16O-rich solid precursors derived from the same oxygen isotope reservoir as carbonaceous chondrites. Oxygen isotopes exhibited open system behavior during chondrule formation, and the interaction between the solid and ambient gas might occur as described in the following model. Significant evaporation and recondensation of solid precursors caused a large mass-dependent fractionation due to either kinetic or equilibrium isotope exchange between gas and solid to form type IA chondrules with higher bulk Mg/Si ratios. Type II chondrules formed under elevated dust/gas ratios and with water ice in the precursors, in which the ambient H 2O gas homogenized chondrule melts by isotope exchange. Low temperature oxygen isotope exchange may have occurred between chondrule glasses and aqueous fluids with high ? 17O (˜5‰) in LL the parent body. According to our model, oxygen isotope ratios of chondrules were strongly influenced by the local solid precursors in the proto-planetary disk and the ambient gas during chondrule melting events.

Kita, Noriko T.; Nagahara, Hiroko; Tachibana, Shogo; Tomomura, Shin; Spicuzza, Michael J.; Fournelle, John H.; Valley, John W.

2010-11-01

34

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

35

Chondrules and matrix in the ornans CO/sub 3/ meteorite: possible precursor components  

SciTech Connect

Bulk compositions of 17 chondrules and one sample of matrix from CO3 Ornans were determined by instrumental neutron activation analysis. Chondrule precursor components deduced from chondrule compositions are characterized by: (1) common and lightly volatile siderophiles, Cr and chalcophiles, (2) refractory lithophiles and Na, (3) Mn, Si and modal pyroxene, and (4) FeO and olivine. Component 4 may be closely related to matrix material. Precursor components have now been inferred for OC, EH, CV, CM and CO chondrules. A Mn- and Si-rich component occurs exclusively among carbonaceous chondrite chondrules. Although there are significant intergroup differences, common to chondrules in all chondrite groups are refractory-lithophile-rich, common-siderophile-rich, and (with the exception of EH) common-lithophile-rich components. This indicates that the siderophile/lithophile and refractory lithophile/common lithophile fractionations recorded in chondrite whole-rocks were established prior to chondrule formation at all nebular locations.

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

1988-02-01

36

Origin of plagioclase-olivine inclusions in carbonaceous chondrites  

Microsoft Academic Search

Plagioclase-Olivine Inclusions (POIs) are an abundant group of chondrule-like objects with igneous textures found in carbonaceous chondrites. POIs consist of plagioclase, olivine, pyroxene, and spinel, and cover a wide range of compositions between Type C Ca-Al-rich Inclusions (CAIs) and ferromagnesian chondrules. POIs are distinguished from CAIs by the absence of melilite, lack of refractory siderophile-rich opaque assemblages, more sodic plagioclase,

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

1991-01-01

37

Chondrules Formed Through Cementation of Mineral Clusters by Feldspathic Melts  

NASA Astrophysics Data System (ADS)

Several rare chondrules with an unusual combination of phenocryst minerals and mesostases have been found in the Semarkona chondrite. Chondrules SC-28-1, SC-16-2, and SC-16-6 are all POP in texture with unusual CL properties. Their mesostases are greenish yellow in CL, and enclose mineral grains with no CL. The extremely high CaO contents (>17.2 wt%) of the mesostases resemble those of group A1 chondrules. However, the FeO-rich silicates (Fa(sub)>17.0%, FS(sub)>17.0%) are typical of group B1 chondrules (Lu et al., 1991; Sears et al., 1992). Such an unusual combination of melt and phenocrysts is apparent in Fig. 1, in which the CaO/MgO molar ratios in the olivines are plotted against the same ratios for the coexisting mesostasis. Most of the chondrules cluster in a well-defined region that shows a positive correlation between olivine and mesostasis CaO/MgO, suggesting that the phenocrysts were formed in situ. The three unusual chondrules, however, plot outside of this region and have unusually high CaO/MgO ratios for their mesostases. A close examination of the largest chondrule (SC-28-1) reveals that the olivines are either poikilitically enclosed in pyroxenes or form discrete clusters. All the olivines have resorbed and rounded edges. The textures are those expected from incomplete melting of pre-existing mineral clusters. Unlike the strongly zoned olivines in group B1 chondrules, olivines in this chondrule are rather uniform in composition. The pyroxenes are highly FeO-rich (Fs(sub)17.4Wo(sub)1.9) and have high-Ca pyroxene rims (Fs(sub)12.4Wo(sub)38.9) when they are in contact with the mesostasis. The mesostases of these chondrules are highly anorthitic (normative An > 80 wt%). More importantly, a sightly MgO-rich relic pyroxene core (Fs(sub)13.8Wo(sub)0.4) was found inside the FeO-rich pyroxene, which also encloses some poikilitic olivines (Fig. 2). The olivines and pyroxenes are closely associated and have Fs/Fa ratios close to one. However, the pyroxenes are not at equilibrium with the coexisting mesostases. Although the olivine compositions and textures are similar to the relic grains described by Nagahara (1983), the association of "incompatible" phenocrysts and melts in these unusual chondrules suggests that they were formed through cementation of unmelted mineral clusters by non-cogenetic melts. Considering the high CaO contents of group A1 and A2 chondrules, the viscosity of the melts must be much lower than the SiO(sub)2-rich melts of group B1 chondrules. It is therefore possible that some of these low viscosity melts may spin off from their host droplets and cement the FeO-rich mineral clusters in the vicinity. The presence of these unusual chondrules suggests that chondrule-forming processes were very dynamic and that while most chondrules were formed through in situ melting of pre-existing solid material, possibly accompanied by reduction and volatilization, some chondrules could have been formed through cementation of unmelted mineral clusters by feldspathic melts. Lu J., Sears D.W.G., Benoit P.H., Prinz M. and Weisberg M.K. (1991) Meteoritics 26, 367. Sears D.W.G., Lu J., Benoit P.H., DeHart J.M. and Lofgren G.E. (1992) Nature, in press. Nagahara H. (1983) Chondrules and Their Origins (ed. King E.A.), Lunar and Planet. Inst., Houston, 211-222. Figure 1, which in the hard copy appears here, shows CaO/MgO (molar) in olivine vs. CaO/MgO (molar) in mesostasis for Semarkona chondrules. Figure 2, which in the hard copy appears here, shows a BSE image of a fragment of chondrule SC-28-1 chiseled from Semarkona. ol = olivine, py = pyroxene (gray), rpy = relic pyroxene (dark gray), m = mesostasis.

Lu, J.

1992-07-01

38

Composition of chondrule silicates in LL3-5 chondrites and implications for their nebular history and parent body metamorphism  

SciTech Connect

The authors petrologic studies of 75 type 1A and type 2 porphyritic olivine chondrules in nine selected LL group chondrites of type 3.3 to type 5 and comparisons with published studies of chondrules in Semarkona (LL3.0) show that compositions of silicates and bulk chondrules, but not overall chondrule textures, vary systematically with the petrologic type of the condrite. These compositional trends are due to diffusive exchange between chondrule silicates and other phases (e.g., matrix), such as those now preserved in Semarkona, during which olivines in both chondrule types gained Fe{sup 2+} and Mn{sup 2+} and lost Mg{sup 2+}, Cr{sup 3+}, and Ca{sup 2+}. In a given LL4-5 chondrite, the olivines from the two chondrule types are identical in composition. Enrichments of Fe{sup 2+} in olivine are particularly noticeable in type 1A chondrules from type 3.3-3.6 chondrites, especially near grain edges, chondrule rims, grain boundaries, and what appear to be annealed cracks. Compositional changes in low-Ca pyroxene lag behind those in coexisting olivine, consistent with its lower diffusion rates. With increasing petrologic type, low-Ca pyroxenes in type 1A chondrules become enriched in Fe{sup 2+} and Mn{sup 2+} and depleted in Mg{sup 2+}, Cr{sup 3+}, and Al{sub 3+}. These compositional changes are entirely consistent with mineral equilibration in chondritic material during metamorphism. From these compositional data alone they cannot exclude the possibility that chondritic material was metamorphosed to some degree in the nebula, but they see no evidence favoring nebula over asteroidal metamorphism, nor evidence that the chondrule reacted with nebular gases after crystallization.

McCoy, T.J. (Univ. of Hawaii, Honolulu (USA) Univ. of New Mexico, Albuquerque (USA)); Scott, E.R.D.; Keil, K.; Taylor, G.J. (Univ. of Hawaii, Honolulu (USA)); Jones, R.H. (Univ. of New Mexico, Albuquerque (USA))

1991-02-01

39

Three Unusual Chondrules in the Bovedy (L3) Chondrite  

NASA Astrophysics Data System (ADS)

The Bovedy (L3) chondrite [1] has recently been studied petrographically using SEM and EMPA as part of a general review of the Irish meteorites. The following chondrules are notable: Chondrule 1. A covered thin-section of the Bovedy (Sprucefield) meteorite contains a very highly-strained, ellipsoidal, radiating pyroxene chondrule with a semi-major axis of 2mm. The elongation ratio, 2.6 x, is higher than values published elsewhere [2]. Chondrule 2. A slab of Bovedy (~48 cm^2) contains an exceptionally large, ellipsoidal, porphyritic olivine chondrule (semi-major axis = 1.4 cm, minor axis = 0.8 cm). This is among the largest droplet chondrule on record [2]. The chondrule is texturally identical to other PO chondrules in the meteorite. Chondrule 3. A polished thin-section, prepared from the above slab, contains an ellipsoidal-to-irregular shaped glassy chondrule (Fig. 1). SEM and EMPA confirm a composition of pyroxenitic glass (brown) with globular and elongate inclusions of silica glass (colorless). Representative EMPA of the brown glass (in wt%) is: SiO2 57.49, Al2O3 0.93, Cr2O3 0.38, FeO 14.22, MnO 0.63, MgO 23.32, CaO 2.69, Na2O 1.03 (no other elements detected). This can be recast as a pyroxene with formula Ca(sub)0.10 Na(sub)0.07 Fe(sub)0.43Mg(sub)1.26Al(sub)0.04 Cr(sub)0.01Mn(sub)0.02Si(sub)2.08O(sub)6. The composition corresponds closely with that reported by [3] for a silica pyroxenite clast from the same meteorite. It suggests that the chondrule was derived by rapid melting of the material represented by the clast, which has been interpreted as an igneous fractionate formed in a planetary environment. References: [1] Graham A. L. et al. (1976) GCA, 40, 529-535. [2] Grossman J. N. et al. (1988) In Meteorites and the Early Solar System (J. F. Kerridge and M. S. Matthews, eds.), 619-659, Univ. Arizona. [3] Ruzicka A. and Boynton W. V. (1992) Meteoritics, 27, 283. Fig. 1, which appears here in the hard copy, shows a photograph of chondrule 3 photographed in plane polarized light. Darker areas within chondrule boundary are pyroxenitic glass. The (white) globular and elongate inclusions are silica glass. The width of the image is 1.7 mm across.

Hill, H. G. M.

1993-07-01

40

Conditions for growth of chondrules and their precursors  

NASA Astrophysics Data System (ADS)

New plots of published data from 17 of the Chainpur meterorite's chondrules suggest that fractionation loss of metal was liked to transport of sulfur due to a Fe-S-O melt, a rapid change of the abundances of the volatiles Na, K, Fe, and Ga near the onset of lithophile refractory (LR) increases, and a competition between the growth of LRs and Mg-rich chondrules. Mg is argued to be special among the LRs in that it tends to be retained in the refractory olivine and pyroxene major phases.

Kenknight, Charles E.

1997-03-01

41

Carbon, CAIs and chondrules  

NASA Astrophysics Data System (ADS)

It has been shown that C is present in CAI's and chondrules. It can be distinguished from matrix C both by its thermal stability and isotopic composition, which implies that it was not introduced after parent body accretion. It is concluded that C must have been present in the chondrule and CAI precursor material. Therefore any models of chondrule and CAI formation and inferences drawn about solar system conditions during these events must take into account the consequences of the presence of C on inclusion chemistry, mineralogy, and oxidation state.

Ash, R. D.; Russell, S. S.

42

Deformation and thermal histories of chondrules in the Chainpur (LL3. 4) chondrite  

SciTech Connect

The results of optical and TEM studies of chondrules in the Chainpur (LL3.4) chondrite are presented. Results were obtained, using a microprobe, from quantitative microchemical analyses for Mg, Fe, Si, and Ca for the chondrule olivine and pyroxene, showing that chondrules in the Chainpur chondrite experienced varied degrees of annealing and deformation. It is suggested that Chainpur may be an agglomerate of a breccia that experienced little overall deformation or heating during and after the final accumulation and compaction of its constituents. 75 refs.

Ruzicka, A. (Arizona Univ., Tucson (USA))

1990-06-01

43

Towards a Novel Classification of Chondrules: Examples From the L4 Ordinary Chondrite Saratov  

NASA Astrophysics Data System (ADS)

In order to classify and thoroughly investigate the origin of chondrites, the most primitive class of meteorites, exhaustive and systematic textural and mineralogical observations of chondrules are required. Long-standing mineralogical-textural classifications for chondrules obscure relevant data. Accepted classification schemes place chondrules in relatively few categories (e.g. radiating, cryptocrystalline, granular, porphyritic, barred) but ignore abundant micron-scale features within chondrules (relict crystals, overgrowths, zonations, quench textures) that provide invaluable evidence of chondrule history. Chondrule mineralogy and textures in polished thin sections and slabs of Saratov (L4) have been recorded using a scanning electron microscope (SEM). The most detailed work so far, on a single section, has mapped the size, sorting, packing, mineralogy and textures of 370 chondrules greater than 100 microns in diameter. Using back-scatter electron (BSE) images, a photomosaic of the entire thin section was created, and overlain with a grid system to locate and map specific chondrules. Textures and mineral phases were documented with BSE images, energy-dispersive spectrometry (EDS) and cathodoluminescence (CL). Chondrule textures are akin to those of igneous and metamorphic Earth rocks, and the processes forming them can be likewise interpreted. Many different heating, cooling and annealing histories, for chondrules now found associated in the same chondrite, are implied. Groups of chondrules with similar provenance, different from other groups, may be recognized by their analogous textural histories. Each chondrule has had at least a two-stage origin. Many show the effects of multi-stage processing. We anticipate that our conclusions will contribute to a new comprehensive classification scheme for chondrules and chondrites, and encourage others to examine the petrology of these complex and fascinating rocks.

Herd, R. K.; Dixon, L.; Samson, C.; Hunt, P. A.

2009-05-01

44

Experimental investigation of the nebular formation of chondrule rims and the formation of chondrite parent bodies  

NASA Astrophysics Data System (ADS)

We developed an experimental setup to test the hypothesis that accretionary rims around chondrules formed in the solar nebula by accretion of dust on the surfaces of hot chondrules. Our experimental method allows us to form dust rims around chondrule analogs while levitated in an inert-gas flow. We used micrometer-sized powdered San Carlos olivine to accrete individual dust particles onto the chondrule analogs at room temperature (20 °C) and at 1100 °C. The resulting dust rims were analyzed by means of two different techniques: non-destructive micro computer tomography, and scanning electron microscopy. Both methods give very similar results for the dust rim structure and a mean dust rim porosity of 60% for the hot coated samples, demonstrating that both methods are equally well suited for sample analysis. The chondrule analog's bulk composition has no measurable impact on the accretion efficiency of the dust. We measured the chemical composition of chondrule analog and dust rim to check whether elemental exchange between the two components occurred. Such a reaction zone was not found; thus, we can experimentally confirm the sharp border between chondrules and dust rims described in the literature. We adopted a simple model to derive the degree of post-accretionary compaction for different carbonaceous chondrites. Moreover, we measured the rim porosity of a fragment of Murchison meteorite, analyzed it with micro-CT and found rim porosities with this technique that are comparable to those described in the literature.

Beitz, E.; Blum, J.; Mathieu, R.; Pack, A.; Hezel, D. C.

2013-09-01

45

The formation of chondrules by open-system melting of nebular condensates  

NASA Astrophysics Data System (ADS)

Experiments were conducted under canonical nebular conditions to see whether the chemical compositions of the various chondrule types can be derived from a single CI-like starting material by open-system melting and evaporation. Experimental charges, produced at 1580 °C and P H2 of 1.31×10 -5 atm over 1 to 18 hours, consisted of only two phases, porphyritic olivine crystals in glass. Sulfur, metallic-iron and alkalis were completely evaporated in the first minutes of the experiments and subsequently the main evaporating liquid oxides were FeO and SiO 2. Olivines from short runs (2-4 hours) have compositions of Fo 83-Fo 89, as in Type IIA chondrules, while longer experimental runs (12-18 hours) produce ˜Fo 99 olivine, similar to Type IA chondrules. The concentration of CaO in both olivine (up to 0.6 wt.%) and glass, and their Mg#, increased with increasing heating duration. Natural chondrules also show increasing CaO with decreasing S, alkalis, FeO and SiO 2. The similarities in bulk chemistry, mineralogy and textures between Type IIA and IA chondrules and the experimental charges demonstrate that these chondrules could have formed by the evaporation of CI precursors. The formation of silica-rich chondrules (IIB and IB) by evaporation requires a more pyroxene-rich precursor. Based on the FeO evaporation rates measured here, Type IIA and IA chondrules, were heated for at least ˜0.5 and ˜3.5 h, respectively, if formed at 1580 °C and P H2 of 1.31×10 -5 atm. Type II chondrules may have experienced higher cooling-rates and less evaporation than Type I. The experimental charges experienced free evaporation and exhibited heavy isotopic enrichments in silicon, as well as zero concentrations of S, Na and K, which are not observed in natural chondrules. However, experiments on potassium-rich melts at the same pressure but in closed capsules showed less evaporation of K, and less K isotopic mass fractionation, than expected as a function of decreasing cooling rate. Thus the environment in which chondrules formed is as important as the kinetic processes they experienced. If chondrule formation occurred under conditions in which evaporated gases remained in the vicinity of the residual melts, the extent of evaporation would be reduced and back reaction between the gas and the melt could contribute to the suppression of isotopic mass fractionation. Hence chondrule formation could have involved evaporative loss without Rayleigh fractionation. Volatile-rich Type II and volatile-poor Type I chondrules may have formed in domains with high and low chondrule concentrations, and high partial pressures of lithophile elements, respectively.

Cohen, Bosmat A.; Hewins, Roger H.; Alexander, Conel M. O.'D.

2004-04-01

46

Chronology of the early Solar System from chondrule-bearing calcium-aluminium-rich inclusions.  

PubMed

Chondrules and Ca-Al-rich inclusions (CAIs) are high-temperature components of meteorites that formed during transient heating events in the early Solar System. A major unresolved issue is the relative timing of CAI and chondrule formation. From the presence of chondrule fragments in an igneous CAI, it was concluded that some chondrules formed before CAIs (ref. 5). This conclusion is contrary to the presence of relict CAIs inside chondrules, as well as to the higher abundance of 26Al in CAIs; both observations indicate that CAIs pre-date chondrules by 1-3 million years (Myr). Here we report that relict chondrule material in the Allende meteorite, composed of olivine and low-calcium pyroxene, occurs in the outer portions of two CAIs and is 16O-poor (Delta17O approximately -1 per thousand to -5 per thousand). Spinel and diopside in the CAI cores are 16O-rich (Delta17O up to -20 per thousand), whereas diopside in their outer zones, as well as melilite and anorthite, are 16O-depleted (Delta17O = -8 per thousand to 2 per thousand). Both chondrule-bearing CAIs are 26Al-poor with initial 26Al/27Al ratios of (4.7 +/- 1.4) x 10(-6) and <1.2 x 10(-6). We conclude that these CAIs had chondrule material added to them during a re-melting episode approximately 2 Myr after formation of CAIs with the canonical 26Al/27Al ratio of 5 x 10(-5). PMID:15846340

Krot, Alexander N; Yurimoto, Hisayoshi; Hutcheon, Ian D; MacPherson, Glenn J

2005-04-21

47

The Origin of Chondrules and Chondrites  

NASA Astrophysics Data System (ADS)

1. Historical introduction; 2. Potential meteorite parent bodies; 3. Chondrites and their main properties; 4. Chondrules and their main properties; 5. Theories for the origin of chondrules; 6. Discussion of theories for the origin of chondrules; 7. Making the chondrites: chondrule sorting and metal-silicate fractionation; 8. So how far have we come and where do we go next?

Sears, Derek W. G.

2011-11-01

48

A chondrule-like object captured by space-exposed aerogel on the international space station  

NASA Astrophysics Data System (ADS)

Here we report on the mineralogy, petrography, and oxygen-isotope compositions of a micrometeoroid captured on the international space station. This micrometeoroid has the texture of a porphyritic olivine chondrule. Because hydrated phases were not identified in the micrometeoroid and because Ni-rich sulfide in it does not show exsolution of pentlandite on the TEM scale, the micrometeoroid probably escaped low temperature events such as aqueous alteration on its parent body. However, the mean value and standard deviation of Cr 2O 3 wt.% in olivine in the micrometeoroid suggest that the micrometeoroid experienced weak thermal metamorphism. Oxygen isotope ratios of pyroxene and olivine in the micrometeoroid are similar to those of chondrule-like objects in comet 81P/Wild2 and coarse-grained crystalline micrometeorites as well as those in chondrules in major types of carbonaceous chondrites. These data suggest that the micrometeoroid is a fragment of a chondrule-like object that was derived from a primitive parent body that experienced thermal metamorphism.

Noguchi, T.; Nakamura, T.; Ushikubo, T.; Kita, N. T.; Valley, J. W.; Yamanaka, R.; Kimoto, Y.; Kitazawa, Y.

2011-09-01

49

Origin of plagioclase-olivine inclusions in carbonaceous chondrites  

SciTech Connect

Plagioclase-Olivine Inclusions (POIs) are an abundant group of chondrule-like objects with igneous textures found in carbonaceous chondrites. POIs consist of plagioclase, olivine, pyroxene, and spinel, and cover a wide range of compositions between Type C Ca-Al-rich Inclusions (CAIs) and ferromagnesian chondrules. POIs are distinguished from CAIs by the absence of melilite, lack of refractory siderophile-rich opaque assemblages, more sodic plagioclase, and abundance of olivine and aluminousenstatite. Rare accessory minerals including armalcolite, zirconolite, rutile, and sapphirine are found in several POIs. The petrographic and chemical properties of POIs indicate that they are not condensates or evaporative residues but formed by melting or partial melting of pre-existing solids. Seven of fourteen POIs contain isotopically fractionated Mg, and despite their textures these POIs are not isotopically homogeneous. A comparison of the essential characteristics of POIs and CAIs suggests that the major processes leading to formation of POIs - including condensation, dust/gas fractionation, aggregation of chemically and isotopically disparate materials, and partial melting - are common to most CAIs and chondrules. We present a scenario for the formulation of these objects and conclude that the homogeneity of the final assemblage - CAI, POI, or chondrule - is primarily a reflection of the thermal history rather than the nature of precursor materials.

Sheng, Y.J.; Hutcheon, I.D.; Wasserburg, G.J. (California Inst. of Tech., Pasadena (USA))

1991-02-01

50

Classifying Chondrules Based on Cathodoluminesence  

NASA Astrophysics Data System (ADS)

Sears et al. (1991) proposed a scheme to classify chondrules based on cathodoluminesence color and electron microprobe analysis. This research evaluates that scheme and criticisms received from Grossman and Brearley (2005).

Cristarela, T. C.; Sears, D. W.

2011-03-01

51

Little Chondrules and Giant Impacts  

NASA Astrophysics Data System (ADS)

Alexander (Sasha) Krot (University of Hawaii), Yuri Amelin (University of Toronto), Pat Cassen (SETI Institute), and Anders Meibom (Museum National d'Histoire Naturelle, Paris) studied and then extracted frozen droplets of molten silicate (chondrules) from unusual meteorites rich in metallic iron-nickel. Called CB (Bencubbin-like) chondrites, these rare but fascinating meteorites contain chondrules with different properties than those in other types of chondrites. Most notably, the chondrules contain very small concentrations of volatile elements and variable concentrations of refractory elements. (Volatile elements condense from a gas at a relatively low temperature, or are boiled out of solids or liquids at relatively low temperature. Refractory elements are the opposite.) Some of the metal grains in CB chondrites are chemically zoned, indicating that they formed by condensation in a vapor cloud. The most intriguing feature of chondrules in CB chondrites is their relatively young age. Lead-lead isotopic dating of chondrules separated from two CB chondrites show that they formed 5 million years after formation of the first solids in the solar system (calcium-aluminum-rich inclusions), which is about at least two million years after formation of other chondrules, and after energetic events in the solar nebula stopped. Krot and his colleagues suggest that the CB chondrules formed as the result of an impact between Moon- to Mars-sized protoplanets. Such impacts were so energetic that huge amounts of material were vaporized and then condensed as chondrules or chemically zoned metal grains. This event enriched refractory elements and depleted volatile elements. Such large impacts appear to play important roles in planet formation, including the formation of the Moon.

Taylor, G. J.

2005-10-01

52

A model of the thermal processing of particles in solar nebula shocks: Application to the cooling rates of chondrules  

NASA Astrophysics Data System (ADS)

We present a model for the thermal processing of particles in shock waves typical of the solar nebula. This shock model improves on existing models in that the dissociation and recombination of H2 and the evaporation of particles are accounted for in their effects on the mass, momentum and energy fluxes. Also, besides thermal exchange with the gas and gas-drag heating, particles can be heated by absorbing the thermal radiation emitted by other particles. The flow of radiation is calculated using the equations of radiative transfer in a slab geometry. We compute the thermal histories of particles as they encounter and pass through the shock. We apply this shock model to the melting and cooling of chondrules in the solar nebula. We constrain the combinations of shock speed and gas density needed for chondrules to reach melting temperatures, and show that these are consistent with shock waves generated by gravitational instabilities in the protoplanetary disk. After their melting, cooling rates of chondrules in the range 10-1000 K h-1 are naturally reproduced by the shock model. Chondrules are kept warm by the reservoir of hot shocked gas, which cools only as fast as the dust grains and chondrules themselves can radiate away the gas's energy. We predict a positive correlation between the concentration of chondrules in a region and the cooling rates of chondrules in that region. This correlation is supported by the unusually high frequency of (rapidly cooled) barred chondrules among compound chondrules, which must have collided preferentially in regions of high chondrule density. We discuss these and other compelling consistencies between the meteoritic record and the shock wave model of chondrule formation.

Desch, S. J.; Connolly, H. C., Jr.

2002-02-01

53

The Fayalite Content of Chondritic Olivine: Obstacle to Understanding the Condensation of Rocky Material  

Microsoft Academic Search

Solar gas is too reducing for the equilibrium XFa in condensate olivine to reach the minimum XFa of the precursors of chondrules in unequilibrated ordinary chondrites (UOCs), 0.145, at temperatures above those where Fe-Mg interdiffusion in olivine stops. Vaporization of a region enriched in dust relative to gas compared to solar composition yields higher fO2, and condensate grains with higher

A. V. Fedkin; L. Grossman

2006-01-01

54

Magnesium Isotope Evidence for Single Stage Formation of CB Chondrules by Colliding Planetesimals  

NASA Astrophysics Data System (ADS)

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 27Al/24Mg ratios of individual chondrules are positively correlated to their stable Mg-isotope composition (?25Mg), indicating that the correlated variability was imparted by a volatility-controlled process (evaporation/condensation). The mass-independent 26Mg composition (?26Mg*) of chondrules is consistent with single stage formation from an initially homogeneous magnesium reservoir if the observed ?25Mg 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 27Al/24Mg 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 ?26Mg* 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 26Al-free component.

Olsen, Mia B.; Schiller, Martin; Krot, Alexander N.; Bizzarro, Martin

2013-10-01

55

Comment on "Cosmogenic neon in grains separated from individual chondrules: Evidence of precompaction exposure in chondrules" by J. P. Das, J. N. Goswami, O. V. Pravdivtseva, A. P. Meshik, and C. M. Hohenberg  

NASA Astrophysics Data System (ADS)

Das et al. (2012) claim that in several cases nominal cosmic ray exposure ages derived from concentrations of cosmogenic Ne in individual olivine grains separated from chondrules substantially exceed exposure ages of matrix samples. Some grains were also reported to show larger apparent exposure ages than other grains from the same chondrule. The authors conclude that the excesses were caused by an exposure of chondrules to high fluences of solar energetic particles and suggest that their data provide direct evidence for a highly active phase of the early Sun, similar to what is observed in X-ray emissions of recent naked T-Tauri stars. Here, we show that the production rates of cosmogenic Ne used by Das et al. (2012) to derive nominal cosmic ray exposure ages of their olivine grains are often much too low, as the reported major element concentrations in many cases sum up to considerably less than 100% even if converted to oxides. In contrast, adopted element concentrations for matrix samples are basically self-consistent. A precompaction exposure of chondrules to a very high flux of solar energetic particles is thus not supported by the data presented by Das et al. (2012). Das et al. (2012) claim that in several cases nominal cosmic ray exposure ages derived from concentrations of cosmogenic Ne in individual olivine grains separated from chondrules substantially exceed exposure ages of matrix samples. Some grains were also reported to show larger apparent exposure ages than other grains from the same chondrule. The authors conclude that the excesses were caused by an exposure of chondrules to high fluences of solar energetic particles and suggest that their data provide direct evidence for a highly active phase of the early Sun, similar to what is observed in X-ray emissions of recent naked T-Tauri stars. Here, we show that the production rates of cosmogenic Ne used by Das et al. (2012) to derive nominal cosmic ray exposure ages of their olivine grains are often much too low, as the reported major element concentrations in many cases sum up to considerably less than 100% even if converted to oxides. In contrast, adopted element concentrations for matrix samples are basically self-consistent. A precompaction exposure of chondrules to a very high flux of solar energetic particles is thus not supported by the data presented by Das et al. (2012).

Ott, U.; Wieler, R.; Huber, L.

2013-08-01

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

RELICT Olivines in Micrometeorites from Greenland and Antarctica  

NASA Astrophysics Data System (ADS)

Previously, [1] studied the bulk chemistry and texture of 223 micrometeorites from Greenland (size: 100-200 micrometers): 82% spherical, 6% porous, and 12% monomineralic particles or particles with unique textures and from Antarctica (size: 50-100 micrometers): 24% spheres, 62% porous, and 14% particles with unique textures. In order to obtain information about the origin of micrometeorites we have studied minerals within these particles that escaped melting during atmospheric heating. Relict olivine grains occur in 27 spheres, 3 porous particles, and 11 particles with unique textures. Relict olivines (mostly > 5 micrometers in apparent size) can be distinguished from secondary crystallized (subsequent to atmospheric melting) olivines by their grain size, morphology, composition, and/or the presence of Fe/Ni-metal inclusions in olivine. Previously, [2] studied 26 Mg-rich olivines from Antarctic micrometeorites and [3] investigated about 70 olivines in micrometeorites from Antarctica and Greenland. Within the 41 micrometeorites containing such grains, 98 relict olivines were analyzed by electron microprobe, representing a much wider range of compositions than reported by [2]. In most micrometeorites, only one or two relict olivines occur and were large enough to be analyzed. In some particles, however the Fa-contents of several relict olivines were obtained (Fig. 1). Relict olivines with Fa-contents below 5.2 mol% Fe are abundant (Fig. 1). One forsterite within a porous particle is manganese- enriched and similar in composition to LIME olivines known from IDPs and primitive meteorites [4]. Comparing olivines from chondrites with those in micrometeorites, Fa-poor olivines occur in Type I chondrules from carbonaceous chondrites [5] and as isolated olivines in the matrix of C2, C3, and unequilibrated ordinary chondrites [2]. Between Fa(sub)5.2 and Fa(sub)~12 a gap exists in the distribution of the Fa-contents (Fig. 1). Relict olivines, however, with about 12 and 30 mol% Fa occur. These Fa- contents are similar to those of equilibrated H, L, and LL chondrites and may indicate that many particles are related to ordinary chondrites. In addition, several other micrometeorites contain olivines with Fa-contents exceeding those of olivines in ordinary chondrites. Considering chondrites as potential material of their origin, they may be related to matrix olivines in Type III carbonaceous chondrites and to olivines in Type II chondrules [5]. In six micrometeorites relict olivines with highly variable compositions were analyzed, indicating that the precursor was unequilibrated prior to thermal processing during atmospheric entry. Comparing all data, it appears that the larger-sized particles from Greenland may contain a slightly higher abundance of forsteritic relict olivines than the small particles from Antarctica. However, we cannot rule out that this observation is a result of insufficient data. References: [1] Beckerling W. et al. (1992) Meteoritics, 27, 200- 201. [2] Steele I. M. (1992) GCA, 56, 2923-2929. [3] Christophe Michel-Levy M. and Bourot-Denise M.(1992) Meteoritics, 27, 73-80. [4] Klock W. et al. (1989) Nature, 339, 126-128. [5] McSween H. Y. (1977) GCA, 41, 477-491.

Beckerling, W.; Klock, W.; Bischoff, A.

1993-07-01

59

Chondrule Precursors and Cooling Paths: The Sulfur Evidence.  

National Technical Information Service (NTIS)

The behavior of moderately volatile elements (Na and S) is controversial but critical in understanding chondrule precursors and heating processes. Sulfide appeared to be present in most chondrules, but S should have been vaporized during chondrule formati...

B. Zanda Y. Yu M. Bourot-denise R. H. Hewins H. C. Connolly

1994-01-01

60

The formation conditions of chondrules and chondrites  

USGS Publications Warehouse

Chondrules, which are roughly millimeter-sized silicate-rich spherules, dominate the most primitive meteorites, the chondrites. They formed as molten droplets and, judging from their abundances in chondrites, are the products of one of the most energetic processes that operated in the early inner solar system. The conditions and mechanism of chondrule formation remain poorly understood. Here we show that the abundance of the volatile element sodium remained relatively constant during chondrule formation. Prevention of the evaporation of sodium requires that chondrules formed in regions with much higher solid densities than predicted by known nebular concentration mechanisms. These regions would probably have been self-gravitating. Our model explains many other chemical characteristics of chondrules and also implies that chondrule and planetesimal formation were linked.

Alexander, C. M. O'D.; Grossman, J. N.; Ebel, D. S.; Ciesla, F. J.

2008-01-01

61

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

SciTech Connect

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% 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, A.E. (Univ. of California, Los Angeles (USA)); Pernicka, E. (Max-Planck-Institute fuer Kernphysik, Heidelberg (West Germany))

1989-01-01

62

Amoeboid olivine aggregates (AOAs) in the Efremovka, Leoville and Vigarano (CV3) chondrites: A record of condensate evolution in the solar nebula  

NASA Astrophysics Data System (ADS)

Amoeboid olivine aggregates (AOAs) in the Efremovka, Leoville, and Vigarano CV3 chondrites were studied using petrographic and microanalytical techniques to evaluate the origins of these inclusions and their relationships to other chondrite components. Our data support the idea that the inclusions formed by dust growth in the solar nebula as condensates and that they preserve a record of mineralogical and chemical evolution. Spinel-rich nodules and ribbons in AOAs often show Group II trace element patterns and formed either by fractional condensation or by condensation following partial vaporization. The dominant olivine component in AOAs can be explained as a condensate produced in the same way, but with fractionation occurring at a lower temperature. Other spinel-rich material in AOAs appears to be a vaporization residue. Ca-rich pyroxene + anorthite patches in AOAs show chemical signatures similar to those observed for spinel- or melilite-bearing regions but with lower refractory element and higher Mg and Si contents, supporting the idea that the patches formed by reaction between CAI-like material and Mg-Si-rich gas. Different trace element patterns (Group II and non-Group II refractory) are sometimes found for Al-rich regions (Ca-pyroxene + anorthite, or melilite-bearing) in a given AOA, suggesting that AOAs agglomerated from materials that formed under different conditions and that they did not subsequently homogenize. AOAs appear to have originated in a system with near-canonical solar composition and a low pressure gas (˜10-6-10-4 bar) over a range of temperatures (mainly ˜1200-1384 K) under somewhat non-equilibrium conditions. Relative to predicted equilibrium condensates, most AOAs show an apparent paucity of metal, possibly reflecting differential, density-dependent sorting between olivine and metal grains during aggregate formation. Trace element data are consistent with a simple model involving melting and igneous fractionation of AOA-like olivine to produce Type I chondrule olivine, but other data suggest that open-system melting of chondrules occurred in a different gaseous environment than that which produced AOAs.

Ruzicka, Alex; Floss, Christine; Hutson, Melinda

2012-02-01

63

Li Diffusion in Olivine  

NASA Astrophysics Data System (ADS)

We have carried out experiments to study the diffusion of Li along the [001] direction of oriented, polished single crystals of San Carlos olivine at 800 °C and atmospheric pressure under a controlled fO2 of 10- 17 bars (~ WM buffer). Cubes of the crystals were annealed surrounded by a powder mix of the same olivine and 6Li enriched lithium silicate. After the experiments, the crystals were sectioned parallel to the diffusion direction and concentration profiles were measured using a Cameca IMS4f ion microprobe in the step scanning mode. The concentration profiles show (i) complex shapes with plateaus in between that are not amenable to treatment using standard solutions to the diffusion equation, and (ii) isotopic fractionation. The shapes of the profiles clearly indicate that at least two different species of Li are involved in the diffusion process. However, a time series of anneals (10 min, 5 h, 10 h, 40 h and 100 h) demonstrate that the shapes are reproducible and evolve systematically with time. We find that the concentration evolution can be described by the following set of processes: (i) incorporation of Li in olivine primarily in octahedral metal sites, (ii) a fast, homogeneous reaction involving metal vacancies (V''Me) that partitions Li between the octahedral site (Li'Me) and interstitial positions (Li\\bulleti): Li'Me = V''Me + Li\\bulleti, and (iii) diffusion of total Li as Li'Me as well as Li\\bulleti, at very different rates. The concentration of Li'Me is at least 10 times higher than the concentration of Li\\bulleti but the diffusion rate of Li\\bulleti is about two orders of magnitude faster than of Li'Me. At the experimental conditions, we can fit the profiles using known values of metal vacancy diffusion coefficients in olivine D(V''Me) = 10-14 m2/s, D(Li'Me) = 10-15 m2/s and D(Li\\bulleti) = 2.5 · 10-13 m2/s. Once these parameters are obtained by fitting any one profile, calculated profiles for any other run duration are an excellent fit to the observed profile shapes, confirming the inferred mechanism. Experiments are in progress to study the temperature dependence of these processes.

Dohmen, R.; Kasemann, S.; Coogan, L.; Chakraborty, S.

2007-12-01

64

Oxygen isotopic compositions of chondrules from the metal-rich chondrites Isheyevo (CH/CB b), MAC 02675 (CB b) and QUE 94627 (CB b)  

NASA Astrophysics Data System (ADS)

It has been recently suggested that (1) CH chondrites and the CB b/CH-like chondrite Isheyevo contain two populations of chondrules formed by different processes: (i) magnesian non-porphyritic (cryptocrystalline and barred) chondrules, which are similar to those in the CB chondrites and formed in an impact-generated plume of melt and gas resulted from large-scale asteroidal collision, and (ii) porphyritic chondrules formed by melting of solid precursors in the solar nebula. (2) Porphyritic chondrules in Isheyevo and CH chondrites are different from porphyritic chondrules in other carbonaceous chondrites ( Krot et al., 2005, 2008a,b). In order to test these hypotheses, we measured in situ oxygen isotopic compositions of porphyritic (magnesian, Type I and ferroan, Type II) and non-porphyritic (magnesian and ferroan cryptocrystalline) chondrules from Isheyevo and CB b chondrites MAC 02675 and QUE 94627, paired with QUE 94611, using a Cameca ims-1280 ion microprobe. On a three-isotope oxygen diagram ( ?17O vs. ?18O), compositions of chondrules measured follow approximately slope-1 line. Data for 19 magnesian cryptocrystalline chondrules from Isheyevo, 24 magnesian cryptocrystalline chondrules and 6 magnesian cryptocrystalline silicate inclusions inside chemically-zoned Fe,Ni-metal condensates from CB b chondrites have nearly identical compositions: ?17O = -2.2 ± 0.9‰, -2.3 ± 0.6‰ and -2.2 ± 1.0‰ (2 ?), respectively. These observations and isotopically light magnesium compositions of cryptocrystalline magnesian chondrules in CB b chondrites ( Gounelle et al., 2007) are consistent with their single-stage origin, possibly as gas-melt condensates in an impact-generated plume. In contrast, ?17O values for 11 Type I and 9 Type II chondrules from Isheyevo range from -5‰ to +4‰ and from -17‰ to +3‰, respectively. In contrast to typical chondrules from carbonaceous chondrites, seven out of 11 Type I chondrules from Isheyevo plot above the terrestrial fractionation line. We conclude that (i) porphyritic chondrules in Isheyevo belong to a unique population of objects, suggesting formation either in a different nebular region or at a different time than chondrules from other carbonaceous chondrites; (ii) Isheyevo, CB and CH chondrites are genetically related meteorites: they contain non-porphyritic chondrules produced during the same highly-energetic event, probably large-scale asteroidal collision; (iii) the differences in mineralogy, petrography, chemical and whole-rock oxygen isotopic compositions between CH and CB chondrites are due to various proportions of the nebular and the impact-produced materials.

Krot, Alexander N.; Nagashima, Kazuhide; Yoshitake, Miwa; Yurimoto, Hisayoshi

2010-04-01

65

Mineralogy, Petrography, and Oxygen-Isotope Compositions of Carbonates and Olivines in Sutter"s Mill, CM Chondrite Breccia  

NASA Astrophysics Data System (ADS)

Sutter's Mill sample we studied has two CM-like lithologies, CM2.0 and CM2.1. O-isotope compositions of chondrule and AOA olivines plot along CCAM line. Dolomites and calcites plot below TF line. Calcites show a spread in ?18O values, +13 to +39‰.

Nagashima, K.; Yin, Q.-Z.; Krot, A. N.; Ogliore, R. C.

2012-09-01

66

A compositional classification scheme for meteoritic chondrules  

NASA Astrophysics Data System (ADS)

A compositionally based classification scheme for chondrules is proposed that will help in systematizing the wealth of data available and disentangling the effects of nebular and subsequent processes. The classification is not by texture or the composition of a single phase, or a mixture of these two, but rather is a comprehensive, systematic approach which uses the composition of the two main chondrule components. This scheme is applicable to over 95 percent of the chondrules and is easily applied using an electron microprobe. It stresses the original diversity of the chondrules and the complex yet facile way in which they respond to parent-body metamorphism. Results using this classification scheme suggest that arguments against an important role of chondrules in determining the compositional trends of the chondrites have been premature.

Sears, Derek W. G.; Jie, Lu; Benoit, Paul H.; Dehart, John M.; Lofgren, Gary E.

1992-05-01

67

The conditions of chondrule formation, Part I: Closed system  

NASA Astrophysics Data System (ADS)

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

Hezel, Dominik C.; Palme, Herbert

2007-08-01

68

Pb isotopic age of the Allende chondrules  

NASA Astrophysics Data System (ADS)

We have studied Pb-isotope systematics of chondrules from the oxidized CV3 carbonaceous chondrite Allende. The chondrules contain variably radiogenic Pb with a 206Pb/204Pb ratio between 19.5-268. Pb-Pb isochron regression for eight most radiogenic analyses yielded the date of 4566.2 ± 2.5 Ma. Internal residue-leachate isochrons for eight chondrule fractions yielded consistent dates with a weighted average of 4566.6 ± 1.0 Ma, our best estimate for an average age of Allende chondrule formation. This Pb-Pb age is consistent with the range of model 26Al-26Mg ages of bulk Allende chondrules reported by Bizzarro et al. (2004) and is indistinguishable from Pb-Pb ages of Ca-Al-rich inclusions (CAIs) from CV chondrites (4567.2 ± 0.6 Ma) (Amelin et al. 2002) and the oldest basaltic meteorites. We infer that chondrule formation started contemporaneously with or shortly after formation of CV CAIs and overlapped in time with formation of the basaltic crust and iron cores of differentiated asteroids. The entire period of chondrule formation lasted from 4566.6 ± 1.0 Ma (Allende) to 4564.7 ± 0.6 Ma (CR chondrite Acfer 059) to 4562.7 ± 0.5 Ma (CB chondrite Gujba) and was either continuous or consisted of at least three discrete episodes. Since chondrules in CB chondrites appear to have formed from a vapor-melt plume produced by a giant impact between planetary embryos after dust in the protoplanetary disk had largely dissipated (Krot et al. 2005), there were possibly a variety of processes in the early solar system occurring over at least 4-5 Myr that we now combine under the umbrella name of "chondrule formation."

Amelin, Yuri; Krot, Alexander

2007-08-01

69

Stardust to Planetesimals: A Chondrule Connection.  

National Technical Information Service (NTIS)

The unique nature of chondrules has been known for nearly two centuries. Modern techniques of analysis have shown that these millimeter sized silicate objects are among the oldest objects in our solar system. Researchers have devised textural and chemical...

J. Paque T. Bunch

1997-01-01

70

The Protostellar Jet Model of Chondrule Formation  

Microsoft Academic Search

A chondrule formation theory is presented where the chondrule formation zone\\u000ais located within 0.1 AU of the protosun. This hot, optically thick, inner zone\\u000aof the solar accretion disk is coincident with the formation region of the\\u000aprotosolar jet.\\u000a The model assumes that particles, ranging in diameter from 1 micron to 1 cm,\\u000acan be ejected from the inner-accretion

Kurt Liffman; Michael J. I. Brown

2006-01-01

71

Metal Precursors and Reduction in Renazzo Chondrules  

NASA Astrophysics Data System (ADS)

The positive Co-Ni correlation and Cr, P contents of metal in CR chondrites have generally been taken to indicate their primitive nature, probably inherited from condensation [1,2]. Si in the metal of primitive chondrites has also been reported and interpreted as a condensation heritage [3,4]. However, Cr, P, and Si (dissolved or in the form of inclusions) in metal of any CR chondrule generally fall within a +-10% range, though large interchondrule variations exist [5]. We have shown that Cr and Si in metal are in equilibrium with Fo and En in silicates, due to the reducing conditions that prevailed during chondrule formation [6]. In the present paper, we show that the Co-Ni trend was also established during chondrule formation out of heterogeneous precursor material with a variable Co/Ni ratio. Chondrules in Renazzo are classified as highly molten (HM), in which metal has been expelled to form a mantle outside the chondrule, medium molten (MM), with metal inside and at the periphery, and with evidence for grain coalescence, and little melted (LM), in which metal is only present in the form of small blebs dispersed among the silicates. In HM chondrules, Ni and Co concentrations are extremely homogeneous, comparatively low and in the cosmic ratio. In LM chondrules, quite the opposite: Ni and Co spread over a large range and the amount of scatter increases with decreasing degree of melting of the chondrule. In addition, they do not correlate along the cosmic ratio, but show a negative correlation if any. This heterogeneity is present not only from grain to grain in these chondrules, but also in individual metal grains. Such a heterogeneity is also exhibited in Cr and P abundances that span a much larger range than the +-10% found in the other chondrules. These results indicate that chondrule formation is responsible for the homogenization of Co and Ni contents of metal grains through coalescence and mixing. The less melted objects give an idea of the nature of metal in chondrule precursors, extremely heterogeneous and fine grained (each small heterogeneous metal bleb might be the result of partial melting of one or of coalescence and imperfect mixing of a few such grains). Co and Ni in these individual grains were not in the cosmic ratio, but wide sampling of dust in each chondrule precursor insured that this ratio was attained after mixing and homogenization, as seen in HM chondrule metal grains and from mean values of Co and Ni in LM chondrules. In MM chondrules, scatter of Ni and Co data are, as expected, intermediate between those of HM and LM chondrules, but Co and Ni are close to the cosmic ratio. The scatter is mostly due to addition of variable quantities of iron in the reduction during chondrule formation, which is responsible for Cr and Si integration into metal. Further evidence of such a process can be found in the less molten of these objects, in which metal grain coalescence is limited and peripheral grains are still different from inside grains. In these cases, Co and Ni distributions are clearly bimodal, high in inside grains, low in peripheral grains. Co/Ni in these two populations are somewhat scattered around the cosmic ratio, but their means (Ni: 7.75 = +- 0.24, Co: 0.36 +- 0.04, and Ni: 4.39 +- 0.34, Co: 0.23 +- 0.02, e.g., in the case of chondrule AL1) are very close to the cosmic ratio. This is in good agreement with the low values found in the homogeneous mantle grains of HM chondrules and, as noted by Lee et al. [7], indicates that the reducing agent was external to the chondrule. Cr abundances of these peripheral metal grains, however, match Cr abundances of the interior ones in these chondrules. This indicates that the redox state of all these grains was attained simultaneously and controlled by equilibrium with chondrule silicates. Slightly more extensive reduction of the latter close to the chondrule surface that added more Fe to peripheral metal grains resulted in only a minor variation of the Cr partition coefficient: it consequently also induced Cr addition, the Cr/Fe ratio varying only marg

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

1993-07-01

72

Aristarchus Olivine in Context with Circum-Imbrium Olivine Deposits  

NASA Astrophysics Data System (ADS)

We investigate the origin of olivine-bearing deposits in Aristarchus Crater ejecta. Given that spectrally similar olivine is found circum Imbrium, olivine in Aristarchus may represent reexposed Imbrium ejecta or other impact transported deposits.

Wiseman, S. M.; Donaldson Hanna, K. L.; Mustard, J. F.; Isaacson, P. J.; Pieters, C. M.; Jolliff, B. L.

2012-07-01

73

Compositional and Mineralogical Trends in Fine-Grained Chondrule Rims in CO Chondrites  

NASA Astrophysics Data System (ADS)

The compositions and mineralogy of fine-grained chondrule rims in 6 CO chondrites, spanning the range of petrologic subtypes from petrologic types 3.0 to 3.7, have been determined by electron microprobe analysis and TEM. Based on individual electron microprobe analyses, Fe, Mg and Mn are uncorrelated and somewhat heterogeneous in rims in ALH A77307 (3.0), but rapidly become tightly clustered and develop strong positive correlations by petrologic type 3.2 (Felix). In contrast the minor elements Cr, Ti and Al are relatively homogeneous in low petrologic type CO chondrites, but become progressively more heterogeneous as the petrologic subtype increases. These changes are strongly correlated with changes in the mineralogy and mineral chemistry of the fine-grained rim materials. Olivine-Cr-spinel geothermometry from coexisting olivine and spinel grains in the rims suggest equilibration temperatures of ~600 degrees C for Ornans and 1000 degrees C for Warrenton.

Brearley, A. J.

1996-03-01

74

Cooling rate of chondrules in ordinary chondrites revisited by a new geospeedometer based on the compensation rule  

NASA Astrophysics Data System (ADS)

For several decades efforts to constrain chondrite cooling rates from diffusion zoning in olivine gave rise to a range of values from 5 to 8400 K/h (Desch, S.J., Connolly Jr., H.C., 2002. A model for the thermal processing of particles in solar nebula shocks: application to cooling rates of chondrules. Meteorit. Planet. Sci. 37, 183-208; Greeney, S., Ruzicka, A., 2004. Relict forsterite in chondrules: implications for cooling rates. Lunar Planet. Sci. XXXV, abstract # 1246.). Such large uncertainties directly reflect the variability of diffusion data. Alternatively, from this variability results a compensation rule, log D0 = a + bE (diffusion coefficients are written D = D0 exp(- E/ RT)). We test a new geospeemetry approach, based on this rule, on cooling of chondrules in chondrites, Sahara-97210 LL 3.2 and Wells LL 3.3. Greeney and Ruzicka (2004) matched Fe-Mg diffusion profiles in olivine from these chondrites with cooling rates between 200 and 6000 K/h. In our geospeedometry model, the use of the compensation rule greatly reduces the uncertainties by avoiding the choice of one diffusion coefficient among many. The cooling rates we found are between 700 and 3600 K/h for Sahara and 700-1600 K/h for Wells. Finally, we discuss the influence of our analytical model parameters on our cooling rate estimates.

Béjina, Frédéric; Sautter, Violaine; Jaoul, Olivier

2009-01-01

75

Compositional trends in chondrules from unequilibrated enstatite chondrite, Parsa  

NASA Astrophysics Data System (ADS)

Multielemental analysis of chondrules from the unequilibrated E3 chondrite Parsa shows that the lithophile elements, both refractory and volatile, are enriched and siderophiles are depleted relative to C1 abundances. This behaviour is generally similar to chondrules from unequilibrated ordinary chondrites (UOC). A detailed comparison of compositional trends in chondrules from E3 chondrites (Parsa and Quingzhen) with UOC's indicates that some of the precursor components of chondrules of E3's are different from those of UOC's.

Shukla, P. N.; Bhandari, N.

76

An experimental investigation of olivine morphology  

Microsoft Academic Search

Olivine crystals can adopt ten types of shape. Experimental crystallization of eight rock melts shows that there is a systematic change from polyhedral or granular olivines --> hopper olivines --> branching olivines --> randomly oriented chain olivines --> parallel-growth chain olivines --> chain+lattice olivines --> plate or feather olivines, with increase in cooling rate and with increase in degree of

Colin H. Donaldson

1976-01-01

77

An experimental investigation of olivine morphology  

Microsoft Academic Search

Olivine crystals can adopt ten types of shape. Experimental crystallization of eight rock melts shows that there is a systematic change from polyhedral or granular olivines ? hopper olivines ? branching olivines ? randomly oriented chain olivines ? parallel-growth chain olivines ? chain+lattice olivines ? plate or feather olivines, with increase in cooling rate and with increase in degree of

Colin H. Donaldson

1976-01-01

78

The Origin of Chondrules and Refractory Inclusions in Chondritic Meteorites  

Microsoft Academic Search

Examples of calcium-aluminum-rich inclusions (CAIs) surrounded by thick chondrule mantles have been found in chondritic meteorites and cast doubt on the conventional belief that CAIs and chondrules possessed different spacetime origins in the primitive solar nebula. We study specific processes by which such objects, and the more common ordinary CAIs and chondrules, might have formed by flare heating of primitive

Hsien Shang; Matthieu Gounelle; Alfred E. Glassgold; Typhoon Lee

2001-01-01

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

On the origin of porphyritic chondrules  

NASA Astrophysics Data System (ADS)

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 1A and 2 porphyritic chondrules at two different temperatures at any pressure between 10-2 and 1 (or possibly 10-3 to 5) atm. The different types of chondrules (types 1, 2, 3) 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 improbable heating mechanism.

Blander, M.; Unger, L.; Pelton, A.; Ericksson, G.

81

A precise olivine-augite Mg-Fe-exchange geothermometer  

Microsoft Academic Search

Olivine and augite that were experimentally equilibrated in the temperature interval 1175–1080°C at 1 bar in natural basaltic\\u000a and andesitic bulk compositions are used to calibrate an Mg-Fe2+ cation-exchange geothermometer. Within its temperature interval of experimental calibration, and over a broad range in olivine\\u000a Mg\\/Fe ratio, the geothermometer has a standard error of ±6°C. In compositionally simpler synthetic systems, the

Robert R. Loucks

1996-01-01

82

A New Astrophysical Setting for Chondrule Formation  

NASA Astrophysics Data System (ADS)

Chondrules in the metal-rich meteorites Hammadah al Hamra 237 and QUE 94411 have recorded highly energetic thermal events that resulted in complete vaporization of a dusty region of the solar nebula (dust/gas ratio of about 10 to 50 times solar). These chondrules formed under oxidizing conditions before condensation of iron-nickel metal, at temperatures greater than or equal to 1500 K, and were isolated from the cooling gas before condensation of moderately volatile elements such as manganese, sodium, potassium, and sulfur. This astrophysical environment is fundamentally different from conventional models for chondrule formation by localized, brief, repetitive heating events that resulted in incomplete melting of solid precursors initially residing at ambient temperatures below approximately 650 K.

Krot, Alexander N.; Meibom, Anders; Russell, Sara S.; O'D. Alexander, Conel M.; Jeffries, Timothy E.; Keil, Klaus

2001-03-01

83

International conference: Chondrules and the protoplanetary disk  

NASA Astrophysics Data System (ADS)

This book is the first comprehensive review of chondrules and their origins since a consensus developed that they were made in the disk of gas and solids that formed the Sun and planets 4.5 billion years ago. Fifty scientists from assorted disciplines have collaborated to review how chondrules could have formed in the protoplanetary disk. When and where in the disk did they form? What were they made from and how fast were they heated and cooled? What provided the energy to melt chondrules--nebular shock waves, lightning discharges, protostellar jets? Following an exciting international conference in Albuquerque, New Mexico, the latest answers to these questions are presented in thirty-four articles, which will appeal to researchers in planetary science and meteoritics.

Hewins, Roger H.; Jones, Rhian H.; Scott, Ed R. D.

1996-06-01

84

A new astrophysical setting for chondrule formation.  

PubMed

Chondrules in the metal-rich meteorites Hammadah al Hamra 237 and QUE 94411 have recorded highly energetic thermal events that resulted in complete vaporization of a dusty region of the solar nebula (dust/gas ratio of about 10 to 50 times solar). These chondrules formed under oxidizing conditions before condensation of iron-nickel metal, at temperatures greater than or equal to 1500 K, and were isolated from the cooling gas before condensation of moderately volatile elements such as manganese, sodium, potassium, and sulfur. This astrophysical environment is fundamentally different from conventional models for chondrule formation by localized, brief, repetitive heating events that resulted in incomplete melting of solid precursors initially residing at ambient temperatures below approximately 650 K. PMID:11230691

Krot, A N; Meibom, A; Russell, S S; Alexander, C M; Jeffries, T E; Keil, K

2001-03-01

85

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 (1150–1300° C) and oxygen fugacity (10-0.68–10-12 atm.) at one atmosphere total pressure. The phases in these experimental

P. L. Roeder; R. F. Emslie

1970-01-01

86

REE Diffusion in Olivine  

NASA Astrophysics Data System (ADS)

Diffusion of rare earth elements has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. The source of diffusant was a mixture of REE aluminate garnet powder and synthetic forsterite powder in 3:1 proportions. Experiments were prepared by enclosing source material and polished forsterite in platinum capsules, which were crimped shut. For experiments on natural olivine, samples were placed with the source in AgPd capsules, which were sealed under vacuum in silica glass ampoules with a solid buffer to buffer at NNO. Prepared capsules were then annealed in 1 atm furnaces for times ranging from an hour to several weeks, at temperatures from 850 to 1300°C. REE distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for Dy diffusion in forsterite: D = 2.3x10-10 exp(-273 kJ mol-1/RT) m2sec-1. Diffusivities of Yb and La in forsterite appear similar, and preliminary results for Dy diffusion in natural olivine also suggest similar diffusivities. REE diffusivities in forsterite are about an order of magnitude faster than those of REE+3 in enstatite (Cherniak and Liang, 2007). However, if the Arrhenius relation above is extrapolated up to 1450C, it yields diffusivities about three orders of magnitude smaller than those determined for REE diffusion in olivine by Spandler et al. (2007). Work is currently underway in further characterizing diffusion in Fe-bearing olivine. If an Arrhenius relation similar to that for forsterite is found to apply, timescales for preservation of REE signatures in olivine-hosted melt inclusions may be relatively long. Cherniak and Liang (2007) GCA 71, 1324-1340; Spandler et al. (2007) Nature 447, 303-306.

Cherniak, D. J.

2007-12-01

87

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

88

New Evidence for 26Al in CAI and Chondrules from Type 3 Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

We have known since 1976 that 26A1 (tl/2 = 7.2 x 105 yrs) was alive in the early solar system, at a level of (26Al/27Al)o z 5 x 10-5 in calcium-aluminum inclusions (CAI). However, several outstanding questions remain. Little evidence for 26A1 has been found in other chondritic material, and none has been found in differentiated meteorites. These results might imply that 26A1 was heterogeneously distributed in the nebula or by mineralogic site in nebular dust, or they might reflect differences in time of formation. There are strict limitations on finding evidence of 26A1 in normal chondrules with bulk Al/Mg ~ 0.1, since even quenched, perfectly preserved, late-stage glasses would have low Al/Mg. Primary plagioclase crystals provide the only possibility, but these only crystallize rarely in melts within the compositional range of normal chondrules. Also, metamorphism can erase the evidence in high-AI/Mg phases. To address these issues, we have conducted a search for chondrules and CAI with high-Al/Mg phases suitable for ion-probe measurement in type 3 ordinary chondrites. Previous work has revealed evidence for 26Al in a plagioclase bearing, olivine-pyroxene class from Semarkona (LL3.0; (26Al/27Al)o = 7.7+/-2.1 x 10-6)), a plagioclase-rich object from Bovedy (L3.7?; 2.5+/-1.2 x 10-7), in separated plagioclase from St. Marguerite (H4; 2.0+/-0.6 x 10-7), an isolated hibonite grain from Dhajala (H3.8; 8.4+0.5 x 10-6), and in Al2O3 and hibonite grains ((26Al/27Al)o = 2-5 x 10-5; [GRH, unpublished]) from acid residues of Semarkona, Bishunpur (LL3.1), and Krymka (LL3.1). We have identified and measured Al-Mg isotope systematics in two CAI and seven chondrules from ordinary chondrites of low metamorphic grade and have found clear evidence for 26A1 in both CAI and in two chondrules.

Srinivasan, G.; Russell, S. S.; MacPherson, G. J.; Huss, G. R.; Wasserburg, G. J.

1996-03-01

89

The crystalline lunar spherules: Their formation and implications for the origin of meteoritic chondrules  

NASA Astrophysics Data System (ADS)

Crystalline lunar spherules (CLS) from three thin sections of Apollo 14 regolith breccias (14318,6; 14318,48 and 14315,20) have been examined. The objects have been classified and their abundances, size distributions, bulk compositions, and (where possible) plagioclase compositions determined. By number, 64% consist predominantly of very fine-grained equant plagioclase grains, but can also contain larger (~50 mm) feldspar crystals (type X), while 22% contain plagioclase lathes in a fine-grained mafic mesostasis (type Y). Plagioclase in both spherule types displays bright yellow cathodoluminescence which is conspicuous among the blue CL of the normal feldspar of the breccias. Type Z spherules (5%) contain feldspar with blue CL and minor amounts of olivine and pyroxene. Type Q spherules (4%) contain feldspar with yellow CL but in a luminescent mesostasis (of quartz or feldspar?). A few spherules are mixtures of type Y and type X textures. Most type X spherules, and a few type Y spherules, have fine-grained opaque rims. Compound objects were also found and consist of two or more CLS that appear to have collided while still plastic or molten. The CLS are thought to be impact spherules that crystallized in free flight, their coarse textures suggesting fairly slow cooling rates (roughly <1(C/s). The abundance of the CLS resembles that of chondrules in the CM chondrite Murchison, and their cumulative size-frequency distributions are very similar to those of the chondrules in several meteorite classes. The bulk compositions of the CLS do not resemble regoliths at any of the Apollo sites, including Apollo 14, or any of the common impact glasses, but they do resemble the bulk compositions of several lunar meteorites and the impact glasses they contain. The Apollo 14 site is located on a region containing Imbrium ejecta and we suggest that the CLS derive from the Imbrium impact. Ballistic calculations indicate that only impact events of this size on the moon are capable of producing melt spherules with the required free flight times and slow cooling rates. Smaller impacts produce glassy spherules and agglutinates. As has been pointed out many times, the CLS have many properties in common with meteoritic chondrules. While much remains unclear, difficulties with a nebular origin and new developments in chondrule chronology, studies of asteroid surfaces and impact ejecta behavior, and the present observations indicate that meteoritic chondrules could have formed by impact.

Symes, Steven J. K.; Sears, Derek W. G.; Taunton, Anne; Akridge, D. Glen; Huang, Shaoxiong; Benoit, Paul H.

1998-01-01

90

Combined Fe- and Si-Isotope Measurements of CV Chondrite Chondrules and CAIs  

NASA Astrophysics Data System (ADS)

Chondrules have variable Fe-isotopic, but similar Si-isotopic compositions. 3D tomography revealed 1-7 vol% sulfide/metal in Allende. We conclude that isotopic and chemical variabilites among chondrules were established during chondrule formation.

Hezel, D. C.; Armytage, R. M. G.; Georg, R. B.; Keren, E.; Russell, S. S.

2009-03-01

91

The Origin of Silica-Rich Chondrules and Clasts in Ordinary and Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

Chondrules and clasts containing a silica mineral or a silica glass are a minor but important constituent in many ordinary (Planner, 1983; Brigham et al., 1986) and some carbonaceous (Olsen, 1983) chondrites, and have been considered somewhat enigmatic. The recent discovery of a large, silica-rich igneous clast in the Bovedy (L3) chondrite (Ruzicka and Boynton, 1992) sheds light on the possible origin of other silica-rich objects. As discussed in Ruzicka and Boynton (1992), the Bovedy clast probably crystallized from an Lchondrite silicate magma in a relatively large magma body that had previously undergone olivine fractionation. The existence of similar fractionating magmas can also account for the origin of other silica-rich objects, as shown below. Pyroxene-silica objects. Chondrules (drop-formed objects) and clasts (irregularly shaped objects) consisting essentially of a mixture of orthopyroxene (opx) and a silica mineral (SiO2) have been found in various ordinary chondrites (Brigham et al., 1986). Brigham and coworkers (1986) proposed that these objects could be condensates. However, fractional crystallization of a liquid similar in composition to the Bovedy clast (Ruzicka and Boynton, 1992) will produce (Morse, 1980) the following solids: (a) orthopyroxenite, (b) an opx + SiO2 rock, and (c) a feldspar, SiO2 and pyroxene rock. Brecciation or remelting of rock (b), which lies on the opx-SiO2 join in the cristobalite primary crystallization field, could have produced the pyroxene-silica objects of Brigham et al. (1986) and Planner (1983). Fayalite-silica clasts. These clasts consist of SiO2, olivine (ol, Fa(sub)63-96), and highly variable amounts of opx and clinopyroxene (Brigham et al., 1986). Brigham et al. (1986) discussed various origins for these objects and concluded that none were entirely satisfactory, but that an accidental mixture of the various phases in them was probably the best hypothesis. However, a rock mainly containing SiO2 and fayalitic ol (Fa(sub)>59) can form as a late-stage differentiate of a melt of any ol + opx or opx + SiO2 mixture (Bowen and Schairer, 1935). The presence of some opx in these objects suggests disequilibrium and incomplete removal of opx from the fractionating liquids. The absence of appreciable feldspar in the fayalite-silica objects may indicate that the parent melt formed from an opx or opx + SiO2 cumulate. Murchison chondrules. Olsen (1983) described two chondrules in Murchison that contain opx (En(sub)99-97Wo(sub)O.5-0.7) set in a groundmass of feldspar or feldspathic glasses, Mgclinopyroxene, and pods of silica glass. Cr-bearing metal also occurs in the chondrules. Olsen (1983) proposed that the two chondrules experienced a nearly equilibrium cooling history from a melt composition projecting in the opx primary crystallization field. These melt compositions are best explained as the result of ol and opx fractionation from a magma of CM-like composition. CM-chondrites have a high bulk CaAl2Si2O7:SiO2 ratio compared to L-chondrites, and this can account for the more feldspathic compositions of the Murchison chondrules compared to that of the Bovedy clast (Ruzicka and Boynton, 1992). Remelting of the differentiate produced by ol and opx fractionation could have formed the two objects. Their Mg-rich pyroxene compositions imply either that the initial magmatic or that the chondrule-forming event was accompanied by reduction. References Bowen N.L. and Schairer J.F. (1935) The system MgO-FeO-SiO2. Am. J. Sci., 5th ser., 29, 151-217. Brigham C.A., H. Yabuki, Z. Ouyang, M.T. Murrell, A. El Goresy and D.S. Burnett (1986) Silica-bearing chondrules and clasts in ordinary chondrites. Geochim. Cosmochim. Acta. 50, 1655-1666. Morse S.A. (1980) Basalts and Phase Diagrams. An Introduction to the Quantitative Use of Phase Diagrams in Igneous Petrology. Springer-Verlag. 493 pp. Olsen E.J. (1983) SiO2-bearing chondrules in the Murchison meteorite. In Chondrules and Their Origins (ed. E.A. King), pp. 223-234. Lunar and Planetary Institute, Houston. Planner H.N. (1983) Phase separation in

Ruzicka, A.; Boynton, W. V.

1992-07-01

92

The conditions of chondrule formation, Part I: Closed system  

Microsoft Academic Search

Mixing was an important process in the early solar nebula and is often used as an argument to explain the compositional scatter among chondrules—mm-sized, once molten silicate spherules in chondritic meteorites. If it is hypothesized that chondrules only acted as closed systems and the scatter in chondrule bulk chemical compositions is only the result of mixing heterogeneous precursor grains—the basic

Dominik C. Hezel; Herbert Palme

2007-01-01

93

Magnetic characteristics of CV chondrules with paleointensity implications  

NASA Astrophysics Data System (ADS)

We have conducted a detailed magnetic study on 45 chondrules from two carbonaceous chondrites of the CV type: (1) Mokoia and (2) Allende. Allende has been previously extensively studied and is thought to have a high potential of retaining an extra-terrestrial paleofield. Few paleomagnetic studies of Mokoia have previously been undertaken. We report a range of magnetic measurements including hysteresis, first-order reversal curve analysis (FORCs), demagnetization characteristics, and isothermal remanent (IRM) acquisition behavior on both Mokoia and Allende chondrules. The Mokoia chondrules displayed more single domain-like behavior than the Allende chondrules, suggesting smaller grain sizes and higher magnetic stability. The Mokoia chondrules also had higher average concentrations of magnetic minerals and a larger range of magnetic characteristics than the Allende chondrules. IRM acquisition analysis found that both sets of chondrules have the same dominant magnetic mineral, likely to be a FeNi phase (taenite, kamacite, and/or awaruite) contributing to 48% of the Mokoia chondrules and 42% of the Allende chondrule characteristics. FORC analysis revealed that generally the Allende chondrules displayed low-field coercivity distributions with little interactions, and the Mokoia chondrules show clear single-domain like distributions. Paleointensity estimates for the two meteorites using the REMc and Preisach methods yielded estimates between 13 and 60 ?T and 3-56 ?T, respectively, for Allende and 3-140 ?T and 1-110 ?T, respectively, for Mokoia. From the data, we suggest that Mokoia chondrules carry a non-primary remagnetization, and while Allende is more likely than Mokoia to retain its primary magnetization, it also displays signs of post accretionary magnetization.

Emmerton, Stacey; Muxworthy, Adrian R.; Hezel, Dominik C.; Bland, Philip A.

2011-12-01

94

A condensation model for the formation of chondrules in enstatite chondrites  

NASA Astrophysics Data System (ADS)

It is proposed that the chondrules in enstatite chondrites formed near the Sun from rain-like supercooled liquid silicate droplets and condensed Fe-Ni alloys in thermodynamic equilibrium with a slowly cooling nebula. FeO formed and dissolved in the droplets in an initial stage when the nucleation of iron was blocked, and was later mostly reduced to unalloyed Fe. At high temperatures, the silicate droplets contained high concentrations of the less volatile components CaO and Al2O3. At somewhat lower temperatures the equilibrium MgO content of the droplets was relatively high. As cooling progressed, some droplets gravitated toward the Sun, and moved in other directions, depleting the region in CaO, Al2O3, and MgO and accounting for the relatively low observed CaO/SiO2, Al2O3/ SiO2, and MgO/SiO2 ratios in enstatite chondrites. At approximately 1400 K, the remaining supercooled silicate droplets crystallized to form MgSiO3 (enstatite) with small amounts of olivine and a high-SiO2 liquid phase which became the mesostases. The high enstatite content is the result of the supercooled chondrules crystallizing at a relatively low temperature and relatively high total pressure. Finally, FeS formed at temperatures below 680 K by reaction of the condensed Fe with H2S. All calculations were performed with the evaluated optimized thermodynamic databases of the FactSage thermodynamic computer system. The thermodynamic properties of compounds and solutions in these databases were optimized completely independently of any meteoritic data. Agreement of the model with observed bulk and phase compositions of enstatite chondrules is very good and is generally within experimental error limits for all components and phases.

Blander, M.; Pelton, A. D.; Jung, I.-H.

2009-05-01

95

Constraints on chondrule origin from petrology of isotopically characterized chondrules in the Allende meteorite  

SciTech Connect

The petrologic and chemical properties of the ferromagnesian chondrules in the Allende carbonaceous chondrite were examined in terms of the isotopic composition and the correlations between isotopic patterns. Areas of thin sections were studied with a SEM and bulk chemical fractions of 12 constituents were quantified to calculate correlations with petrologic features. A possible correlation between (CaO + Al2O2)/MgO and oxygen isotopes imply the formation of oxygen isotopic compositions in the chondrules by exchanges between isotopically heavy nebular gases and O-16 enriched solids. Different rates of gaseous exchange occurred with the various types of chondrules. Factors which may have controlled the exchanges are discussed. 21 references.

Mcsween, H.Y. Jr.

1985-09-01

96

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

97

An experimental study of the formation of metallic iron in chondrules1  

Microsoft Academic Search

The abundance of metallic iron is highly variable in different kinds of chondrites. The precise mechanism by which metal fractionation occurred and its place in time relative to chondrule formation are unknown. As metallic iron is abundant in most Type I (FeO-poor) chondrules, determining under what conditions metal could form in chondrules is of great interest. Assuming chondrules were formed

BOSMAT A. COHEN; ROGER H. HEWINS

2004-01-01

98

Implications of Textural Distributions for Chondrule Formation: A Survey of CR Chondrules  

NASA Astrophysics Data System (ADS)

The common (>95% low-FeO) chondrules in CR chondrites have two main textures: round shapes with minimal interior metal, and irregular shapes with abundant, small, interior metal. These reflect large differences in degree of melting, and thus in mean maxim

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

2007-03-01

99

CHONDRULE FORMATION IN BOW SHOCKS AROUND ECCENTRIC PLANETARY EMBRYOS  

SciTech Connect

Recent isotopic studies of Martian meteorites by Dauphas and Pourmand have established that large ({approx}3000 km radius) planetary embryos existed in the solar nebula at the same time that chondrules-millimeter-sized igneous inclusions found in meteorites-were forming. We model the formation of chondrules by passage through bow shocks around such a planetary embryo on an eccentric orbit. We numerically model the hydrodynamics of the flow and find that such large bodies retain an atmosphere with Kelvin-Helmholtz instabilities allowing mixing of this atmosphere with the gas and particles flowing past the embryo. We calculate the trajectories of chondrules flowing past the body and find that they are not accreted by the protoplanet, but may instead flow through volatiles outgassed from the planet's magma ocean. In contrast, chondrules are accreted onto smaller planetesimals. We calculate the thermal histories of chondrules passing through the bow shock. We find that peak temperatures and cooling rates are consistent with the formation of the dominant, porphyritic texture of most chondrules, assuming a modest enhancement above the likely solar nebula average value of chondrule densities (by a factor of 10), attributable to settling of chondrule precursors to the midplane of the disk or turbulent concentration. We calculate the rate at which a planetary embryo's eccentricity is damped and conclude that a single planetary embryo scattered into an eccentric orbit can, over {approx}10{sup 5} years, produce {approx}10{sup 24} g of chondrules. In principle, a small number (1-10) of eccentric planetary embryos can melt the observed mass of chondrules in a manner consistent with all known constraints.

Morris, Melissa A.; Desch, Steven J.; Athanassiadou, Themis [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States); Boley, Aaron C., E-mail: melissa.a.morris@asu.edu [Department of Astronomy University of Florida, Gainesville, FL 32611 (United States)

2012-06-10

100

Accretion, dispersal, and reaccumulation of the Bishunpur (LL3.1) brecciated chondrite - Evidence from troilite-silicate-metal inclusions and chondrule rims  

NASA Astrophysics Data System (ADS)

A set of troilite-silicate-metal (TSM) inclusions and chondrule rims in the Bishunpur (LL3.1) chondrite provide information regarding impact brecciation of small bodies in the early solar system. The TSM inclusions and chondrule rims consist of numerous angular to subrounded silicate grains that are individually enclosed by fine networks of troilite. FeNi metal also occurs in the troilite matrix. The silicates include olivine (Fo 55-98), low-Ca pyroxene (En 78-98), and high-Ca pyroxene (En 48-68Wo 11-32). Al- and Si-rich glass coexists with the silicates. Relatively coarse silicate grains are apparently fragments of chondrules typical of petrologic type-3 chondrites. Troilite fills all available cracks and pores in the silicate grains. Some of the TSM inclusions and rims are themselves surrounded by fine-grained silicate-rich rims (FGR). The TSM inclusions and rims texturally resemble the troilite-rich regions in the Smyer H-chondrite breccia. They probably formed by shock-induced mobilization of troilite during an impact event on a primitive asteroidal body. Because silicates in the TSM inclusions and rims have highly unequilibrated compositions, their precursor was presumably type-3 chondritic material like Bishunpur itself. The TSM inclusions and the chondrules with the TSM rims were fragmented and dispersed after the impact-induced compaction, then reaccreted onto the Bishunpur parent body. FGR probably formed around the TSM inclusions and rims, as well as around some chondrules, during the reaccumulation process. Components of most type-2 and 3 chondrites probably experienced similar processing, i.e., dispersal of unconsolidated materials and subsequent reaccumulation.

Kojima, Tomoko; Lauretta, Dante S.; Buseck, Peter R.

2003-08-01

101

Mineral Magnetism of Dusty Olivine: A Potential Carrier of Pre-Accretionary Remanence?  

NASA Astrophysics Data System (ADS)

The mechanism and location of chondrule formation is an important question in cosmochemistry. The remanent magnetisation of chondrules may provide clues to their formation environment, but requires magnetic carriers with extraordinary thermal and magnetic stability. Recently, the search for a suitable magnetic carrier has focussed on ‘dusty olivine’: relict grains that survived the chondrule heating event without fully melting. Dusty olivine grains contain submicron inclusions of metallic Fe-Ni, formed by sub-solidus reduction of the Fe-bearing olivine during heating. The Fe inclusions within dusty olivine potentially possess the ideal magnetic characteristics for acquiring and maintaining primary remanence. Here we describe a mineral magnetic characterisation of synthetic dusty olivine formed by laboratory reduction of terrestrial olivine. Crushed olivine grains were packed in a graphite crucible and reduced in a CO atmosphere at 1350°C for 10 minutes, before quenching into water. Samples were characterised by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), temperature-dependent magnetic susceptibility (?-T), and first-order-reveral-curve (FORC) diagrams. The results demonstrate the potential, as well as the pitfalls, of using dusty olivine for paleomagnetism. Microscopy reveals abundant Fe-Ni particles with sizes ranging from > 1 ?m to < 20 nm. ?-T reveals the presence of both a bcc-Fe phase with Tc = 770°C and bcc/fcc Fe-Ni phases with varying Ni content. The presence of Ni complicates the magnetic properties due to the effect of the bcc-fcc martensitic transition. Evidence for Fe-Ni redistribution within the particles at high temperature is found in the ?-T measurements, which leads to the formation of a ferromagnetic Ni-rich alloy with fcc structure and Tc = 200°C. Further complications arise due to the formation of magnetite above 300°C, and its subsequent transformation to wustite above 580 °C. EBSD analysis reveals the presence of magnetite rims on the surface of some large Fe inclusions that have been exposed to air. FORC analysis demonstrates the presence of MD signals associated with > 1 ?m Fe particles, as well as an SD-like signal with broad coercivity distribution (extending to over 500 mT in some cases) and a narrow vertical spread. Comparison with TEM observations indicates that the coercivity distribution is consistent with SD particles dominated by shape anisotropy. This work highlights the combination of high magnetic stability and thermal stability that make dusty olivine a potential carrier of pre-accretionary remanence. It also demonstrates that a thorough characterisation of the Fe particles within natural dusty olivine and a detailed understanding of the mineral magnetic phase relations is necessary in order to design an effective paleointensity protocol capable of extracting the value of the paleofield.

Harrison, R. J.; Lappe, S.; Feinberg, J. M.; Russell, S.; Bromiley, G.; Bastos da Silva Fanta, A.; Dunin-Borkowski, R.

2009-12-01

102

Silica-Fayalite-bearing Chondrules in Ordinary Chondrites: Evidence of Oxidation in the Solar Nebula  

NASA Astrophysics Data System (ADS)

Most ordinary chondrite (OC) chondrules have compositions similar to those of bulk OC in terms of lithophile-element abundances. There are only a few rare chondrule classes that deviate significantly from OC-like compositions; these include Al-rich chondrules, chromitic and chromite-bearing silicate chondrules, and silica-rich chondrules. We studied 41 thin sections of unequilibrated OC and found 82 silica-bearing chondrules that can be divided into two major categories: silica-pyroxene chondrules and silica-fayalite- pyroxene chondrules. These chondrules are more common in H (>3/cm^2) than in L and LL chondrites (<1/cm^2). Silica-pyroxene chondrules consist mainly of low-Ca pyroxene and silica and have radial and porphyritic textures. Silica-bearing radial pyroxene (RP) chondrules contain 5-10 vol% silica grains; the low-Ca pyroxene is uniform in individual chondrules but varies from one chondrule to another (Fs(sub)10.2- Fs(sub)31.5). Silica-bearing porphyritic pyroxene (PP) chondrules contain 15- 40 vol% silica; the low-Ca pyroxene varies in composition within individual PP chondrules and tends to be more magnesian than in the silica-bearing RP chondrules (Fs(sub)5.0-Fs(sub)21.1). Petrographic observations suggest that some PP chondrules were not completely molten; they appear to have cooled more slowly than the silica-bearing RP chondrules. Silica-fayalite-pyroxene chondrules consist of silica, fayalite, and low-Ca pyroxene; accessory high-Ca pyroxene, plagioclase mesostasis, troilite, and metallic Fe-Ni are also present. Based on texture and the modal abundances of pyroxene and silica these chondrules can be divided into two types: (1) radial or porphyritic silica-fayalite-pyroxene chondrules containing 5-40 vol% silica and (2) granular silica-fayalite-pyroxene chondrules consisting almost entirely (90-95 vol%) of silica. Silica-fayalite-bearing pyroxene chondrules are texturally and compositionally similar to the silica-bearing pyroxene chondrules described above; the principal difference between them is the presence of fayalite-forming veins within or rims around the silica grains. The continuum between these chondrule categories implies that they are genetically related: We infer that the fayalite veins and rims formed by nebular alteration of the silica grains. Fayalite forms veins along the silica grain boundaries in granular silica-fayalite-bearing chondrules. Fragments of granular silica chondrules occur as relict clasts within two pyroxene chondrules in Sharps. These fragments were altered after chondrule solidification. Conclusions: (1) Silica-bearing chondrules have similar textures to common mafic silicate chondrules and were formed by melting silica-rich precursor material that possibly formed by nonequilibrium condensation. (2) The higher abundance of silica-bearing chondrules in H than in L and LL chondrites may indicate a greater degree of silica condensation in the H-formation region. (3) Silica-fayalite-bearing chondrules formed by alteration of silica-bearing chondrules. The common occurrence of both categories within the same chondrite suggests that oxidation and fayalite formation by nebular gas was an inefficient process.

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

1993-07-01

103

Kimberlite Ascent: Insights from Olivine  

NASA Astrophysics Data System (ADS)

Olivine is ubiquitous in both extrusive and intrusive kimberlite deposits worldwide. Within kimberlite, it is mainly present as xenocrysts derived from the disaggregation of mantle-derived peridotitic xenoliths. Many textural and chemical features within the mantle-derived olivine xenocrysts result from post entrainment processes. On that basis, these features record physical and chemical changes attending kimberlite ascent and can be used to elucidate the transport and eruption of kimberlite magma. Our textural study of kimberlitic olivine is based on intrusive and pyroclastic kimberlite from the Diavik kimberlite cluster and from the Igwisi Hills kimberlitic lava flows. Based on these observations and the physical and chemical properties of olivine we derive a relative sequence of textural events. Textural features include: sealed cracks, healed cracks, phases trapping in cracks, rounded grains, overgrowths and phase trapping in overgrowths. These features record processes that operate in kimberlite during ascent, and from these features we create a summary model for kimberlite ascent: -- Olivine is incorporated into kimberlitic melts in peridotitic mantle xenoliths continuously during ascent. Xenolith incorporation is focused at the crack tip where the stress regime is highest. -- Shortly after the incorporation of these xenocrysts the tensile strength of the xenoliths is reached at a maximum of 2 km from its source. Disaggregation of mantle xenoliths (producing xenocrysts) is facilitated by expansion of the minerals within the xenoliths causing intra-crystal slip (i.e. along grain boundaries). -- Continued decompression causes olivine to also break in tension approximately 20 km from source. The void space produced by the failure of the crystals (inter-crystal cracks) is filled with melt and crystals consisting of primary carbonate (high-Sr), chromite and spinel crystals. The carbonate later crystallizes to produce sealed fractures. -- Mechanical rounding of the xenocrysts occurs during pressure release (ascent) events characterized by phase separated (fluid at top: liquid at bottom) flow. Turbulent and fluidized flow heads the propagation whereas kimberlite melt state follows. -- Settling of olivine crystals into the melt state occurs when crack propagation halts. At these points, cracks that are not totally sealed begin to heal, and are ultimately present as healed fractures in olivine in the end deposit. -- Saturation of olivine produces rounded overgrowths on large xenocrysts, euhedral overgrowths on smaller xenocrysts, and a volumetrically minor population of olivine phenocrysts. Olivine growth traps fluid, solid and melt inclusions. Calculations based on these relationships suggest that the melt saturates with olivine at a maximum depth of 20 km and a minimum depth of 7 km.

Brett, C.; Russell, K.

2009-05-01

104

Oxygen Isotope Microanalysis of Enveloping Compound Chondrules in CV3 and LL3 Chondrites  

NASA Astrophysics Data System (ADS)

SIMS data for enveloping compound chondrules in CV3 and LL3 chondrites indicate that they were formed by multiple heating events during which the O-isotope compositions of chondrules and nebular gas reservoirs have not changed significantly.

Akaki, T.; Nakamura, T.

2005-03-01

105

Possible Role of Elemental Carbon in the Formation of Reduced Chondrules.  

National Technical Information Service (NTIS)

Recent experiments have been designed to produce chondrule textures via flash melting while simultaneously studying the nature of chondrule precursors. However, these experiments have only been concerned with silicate starting material. This is a prelimin...

H. C. Connolly R. H. Hewins R. D. Ash G. E. Lofgren B. Zanda

1994-01-01

106

Iron isotope signatures within chondrules from Allende and Chainpur as indicators of thermal history  

Microsoft Academic Search

Introduction: We have studied the petrography and Fe-isotope composition of seven chondrules, four from Allende (CV3) and three from Chainpur (LL3.4). A range of textural-chemical chondrule types are represented, allowing us to examine the Fe-isotope signature in material with different thermal histories, with a view to constraing the chondrule forming process and elucidating the nature of chondrule precursor material. Analytical

E. Mullane; S. S. Russell; M. Gounelle; T. F. D. Mason

2003-01-01

107

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

108

Oxygen Isotopes of Chondrules in the Queen Alexandra Range 99177 CR3 Chondrite: Further Evidence for Systematic Relationships Between Chondrule Mg# and ?^1^7O and the Role of Ice During Chondrule Formation  

NASA Astrophysics Data System (ADS)

QUE 99177 chondrules steadily rise in ?^1^7O (-5 to -1 ‰) as Mg# decreases (99 to 97). Addition of +?1^7O H_2O ice to dry precursors could reduce chondrule Mg# (by oxidation during formation) while increasing ?^1^7O. Estimated H_2O ice ?^1^7O is 0.5 to 6‰.

Tenner, T. J.; Nakashima, D.; Ushikubo, T.; Kita, N. T.; Weisberg, M. K.

2012-03-01

109

Chondrule Tieschitz XII Revisited: Reading a Very Old Logbook  

NASA Astrophysics Data System (ADS)

Chondrule Tieschitz XII (Tie XII) was recently re-investigated with an ion micro-probe. Tie XII perfectly fit the PLC model (Varela and Kurat, 2009) and the theoretical predictions of phase condensation in a non-canonical solar nebula [Ebel 2006].

Kurat, G.; Varela, M. E.; Zinner, E.

2010-03-01

110

Rb-Sr Ages of Chondrules and Carbonaceous Chondrites  

Microsoft Academic Search

Determinations of Rb, Sr, and K contents and isotopic compositions of Sr are reported for the carbonaceous chondrites Orgueil, Murray, Mokoia, and Lance, the hypersthene chondrite Peace River, and four chondrules from the Peace River meteorite. In accordance with previous work, the abundances of Rb and K in type I is greater than in type III; 8r is relatively constant.

V. Rama Murthy; W. Compston

1965-01-01

111

A Suggestion as to the Origin of Chondrules.  

National Technical Information Service (NTIS)

Consideration is given to the possibility of chondrule formation in the primeval dust atmospheres that would probably be present in the proximity of asteroids during their formation from a Laplace-type nebula. It is proposed that lightning may have functi...

F. L. Whipple

1966-01-01

112

PIXE analyses of olivine grains in Semarkona - Microdistribution and correlation of trace elements  

NASA Astrophysics Data System (ADS)

Results are reported from proton-induced X-ray emission (PIXE) studies of trace elements (20-100 ppm) in isolated and chondrule olivines (IOs and COs) from the Semarkona chondrite (LL3.0). The experimental procedures are described, and the results are presented in extensive tables, graphs, and micrographs and discussed in detail. The absolute concentrations of Ca, Ti, V, Cr, Mn, Fe, and Ni in small IOs are found to be similar to those in Fe-rich COs, whereas those in large IOs are between those of Fe-rich and Fe-poor COs. It is inferred that the large IOs were briefly exposed to high temperatures and ambient gas pressures.

Bajt, S.; Pernicka, E.; Traxel, K.

113

Supernova olivine from cometary dust.  

PubMed

An interplanetary dust particle contains a submicrometer crystalline silicate aggregate of probable supernova origin. The grain has a pronounced enrichment in 18O/16O (13 times the solar value) and depletions in 17O/16O (one-third solar) and 29Si/28Si (<0.8 times solar), indicative of formation from a type II supernova. The aggregate contains olivine (forsterite 83) grains <100 nanometers in size, with microstructures that are consistent with minimal thermal alteration. This unusually iron-rich olivine grain could have formed by equilibrium condensation from cooling supernova ejecta if several different nucleosynthetic zones mixed in the proper proportions. The supernova grain is also partially encased in nitrogen-15-rich organic matter that likely formed in a presolar cold molecular cloud. PMID:15994379

Messenger, Scott; Keller, Lindsay P; Lauretta, Dante S

2005-06-30

114

Serpentinization of oceanic peridotites: 2. Kinetics and processes of San Carlos olivine hydrothermal alteration  

NASA Astrophysics Data System (ADS)

The kinetics of the reaction (Mg,Fe)-olivine + H2O ? serpentine + magnetite + brucite + H2 were investigated at 500 bars in the 250-350°C range using natural olivine (San Carlos; Fo91) with grain sizes between 1 and 150 ?m and for run durations up to 514 d. The amount of magnetite produced, which directly relates to reaction progress, was accurately monitored using up to 24 time-resolved magnetic measurements per experiment. Eighty percent of serpentinization was achieved after 60 d for olivine grain sizes of 5-15?m and after 500 d for grain sizes of 50-63 ?m. Serpentinization kinetics were found to be inversely proportional to the geometrical surface area of the starting olivine grains. They were one or two orders of magnitude slower than serpentinization kinetics commonly used for modeling serpentinization-related processes. The nature of the serpentine mineral product depended on the initial olivine grain size (IGS); for IGS in the 5-150?m range lizardite formed, and olivine dissolution was the rate-limiting process. At IGS below 5?m, chrysotile crystallized instead of lizardite, and the relationship between olivine surface area and reaction kinetics no longer held. We infer that for such small olivine grain sizes dissolution is no longer the rate-limiting process. Serpentinization in our experiments was associated with the creation of new reactive surface area according to two cooperative processes: etch pits formation associated with dissolution and grain fracturing for IGS above 20?m. Interestingly, fractures and etch pits with similar geometry and sizes were also observed for residual olivine (with a typical grain size of 50 ?m) in serpentinized peridotite samples from the Southwest Indian Ridge. This suggests that the processes governing olivine serpentinization kinetics in our experiments are similar to those prevailing in natural systems. We therefore suggest that the new kinetic data set that we present here, which encompasses a range of olivine grain sizes and reaction temperatures, is relevant to the serpentinization of olivine in the oceanic crust insofar as water is available.

Malvoisin, Benjamin; Brunet, Fabrice; Carlut, Julie; RouméJon, StéPhane; Cannat, Mathilde

2012-04-01

115

Surface destabilization and laboratory-induced non-stoichiometry in San Carlos olivine  

Microsoft Academic Search

Annealing experiments on natural olivine (Mg1-xFex)2SiO4 (with x˜0.11) crystals (San Carlos, Arizona, spinel-lherzolite context) have been performed between T=1,100° C and 1,500° C for oxygen partial pressures pO2=10-3 to 10-13 bar and times of 1 to 140 h in CO\\/CO2 or H2\\/H2O gas mixtures. Even specimens annealed within the T-pO2theoretical stability field (TSF) calculated for stoichiometric olivine (Nitsan 1974) show

O. Jaoul; B. Houlier; M. Cheraghmakani; R. Pichon; R. C. Liebermann

1987-01-01

116

First-Order Reversal Curve (FORC) analysis of chondrule magnetism  

NASA Astrophysics Data System (ADS)

We report a rock magnetic study of the magnetic properties of chondrules from the Allende and Mokoia carbonaceous chondritic meteorites. To characterise the magnetic carriers, we have made detailed magnetic hysteresis analysis including FORC measurements. We have also conducted isothermal acquisition unmixing analysis. We have determined the ancient magnetic field intensities (paleointensities) recorded by the two meteorites. As these chondrules are highly susceptible to chemical alteration on heating, we have employed two non-heating methods of determining the ancient field intensity: (1) the calibrated REM method and (2) the newly developed Preisach-based approach that determines absolute paleointensities. Allende has been extensively studied but this is the first paleointensity estimate for the Mokoia meteorite.

Emmerton, S.; Muxworthy, A. R.

2009-12-01

117

Petrology, Rare Earth Element Composition and Oxygen Isotopic Composition of a Compound CAI-Chondrule Inclusion from Allende  

Microsoft Academic Search

A compound CAI-chondrule inclusion from Allende represents a mixture of partially melted CAI and chondrule materials that have underwent multiple heating processes under nebula gases with different 16O enrichments.

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

2010-01-01

118

Gravitational Instabilities, Chondrule Formation, and the FU Orionis Phenomenon  

NASA Astrophysics Data System (ADS)

Using analytic arguments and numerical simulations, we examine whether chondrule formation and the FU Orionis phenomenon can be caused by the burstlike onset of gravitational instabilities (GIs) in dead zones. At least two scenarios for bursting dead zones can work, in principle. If the disk is on the verge of fragmentation, GI activation near r~4-5 AU can produce chondrule-forming shocks, at least under extreme conditions. Mass fluxes are also high enough during the onset of GIs to suggest that the outburst is related to an FU Orionis phenomenon. This situation is demonstrated by numerical simulations. In contrast, as supported by analytic arguments, if the burst takes place close to r~1 AU, then even low pitch angle spiral waves can create chondrule-producing shocks and outbursts. We also study the stability of the massive disks in our simulations against fragmentation and find that although disk evolution is sensitive to changes in opacity, the disks we study do not fragment, even at high resolution and even for extreme assumptions.

Boley, Aaron C.; Durisen, Richard H.

2008-10-01

119

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

120

Oxygen isotopic compositions of chondrules: Implications for evolution of oxygen isotopic reservoirs in the inner solar nebula  

Microsoft Academic Search

We review the oxygen isotopic compositions of minerals in chondrules and compound objects composed of a chondrule and a refractory inclusion, and bulk oxygen isotopic compositions of chondrules in unequilibrated ordinary, carbonaceous, enstatite, and Kakangari-like chondrites, focusing on data acquired using secondary ion mass-spectrometry and laser fluorination coupled with mass-spectrometry over the last decade. Most ferromagnesian chondrules from primitive (unmetamorphosed)

Alexander N. Krot; Hisayoshi Yurimoto; Kevin D. McKeegan; Laurie Leshin; Marc Chaussidon; Guy Libourel; Miwa Yoshitake; Gary R. Huss; Yunbin Guan; Brigitte Zanda

2006-01-01

121

Formation conditions of plagioclase-bearing type I chondrules in CO chondrites: A study of natural samples and experimental analogs  

NASA Astrophysics Data System (ADS)

About ten percent of type I, FeO-poor chondrules in unequilibrated CO chondrites contain plagioclase that appears to be igneous in origin, crystallizing at a late stage of solidification of host chondrule melts. We have studied plagioclase-bearing chondrules in detail, and compared them with plagioclase-free chondrules, in order to determine the formation conditions of plagioclase and the constraints that the presence of plagioclase places on the conditions of chondrule formation. Plagioclase-bearing chondrules have similar textures, mineral compositions and bulk compositions to plagioclase-free chondrules. The only possible chemical difference that might control the presence or absence of plagioclase in a given chondrule is that most plagioclase-bearing chondrules have a slightly higher bulk Al/Ca ratio than plagioclase-free chondrules. We carried out dynamic cooling experiments on a type IAB chondrule analog in order to investigate chondrule formation conditions. Our experiments at slow cooling rates, <25 °C/hr, reproduce natural type I chondrule textures as well as mineral and glass compositions very closely. We attempted to facilitate nucleation and growth of plagioclase by optimizing several parameters, including using a bulk composition for our experiments comparable to natural plagioclase-bearing chondrules, using slow cooling rates, quenching from low temperatures, seeding the experiments with anorthite crystals, and maintaining a Na-rich atmosphere around the experimental charges. Of all these parameters, we only succeeded in growing plagioclase in the slowest cooled experiment, which included multiple linear cooling steps with a final cooling stage of 1 °C/hr between 1000 and 800 °C. Our experiments indicate that type I chondrules can plausibly be formed at slow cooling rates, and slow cooling rates may actually be a requirement for production of plagioclase. The cooling histories we examined are very similar to those predicted in recent shock wave models for chondrule formation.

Wick, Molly J.; Jones, Rhian H.

2012-12-01

122

Crystallography and magnetic domain states of dusty olivine observed by electron holography: implications for recording of magnetic fields in the proto-planetary disc  

NASA Astrophysics Data System (ADS)

Dusty olivines are chondrules found in some L and LL chondrites which contain iron-nickel nanoparticles that are believed to have exsolved from the host olivine in a brief heating event shortly after chondrule formation. Geochemical analyses indicate that the iron particles have not equilibrated with the surrounding material, suggesting that they have the potential to record the magnetic field of the early solar system and hence evaluate proposed mechanisms for the heating event and the chondrules' proximity to the strongly magnetic young sun. However, the ability of these particles to preserve primary magnetic signals over timescales on the order of the age of the solar system is dependent on their crystallography and the domain states of the magnetic carriers. We employ the transmission electron microscopy technique of electron holography to directly observe the magnetic domain states in the iron-nickel particles in synthetic dusty olivine and examine if they have the characteristics required for stable magnetic recording. Particles exhibiting pseudo-single domain (PSD) vortex states are common, but uniformly magnetised single domain (SD) behaviour is observed in elongated particles with a wide range of sizes. These observations of domain state allow the determination of the PSD-SD boundary in iron as a function of particle size and elongation and the location of the boundary as observed in experiments is broadly consistent with theoretical predictions. The holography technique also provides quantitative measurements of the magnetic moment which can be used to accurately calculate the volume of nanoparticles and infer the particle shape in three dimensions from a single measurement. Combining the volume information with constraints on coercivity, the thermal relaxation characteristics of the particles can be calculated and we demonstrate that the high-coercivity component of remanence would remain stable for 4.6 Ga, even at temperatures approaching the Curie temperature of pure iron. The high coercivity of the particles, together with the chemical protection offered by the surrounding olivine, is likely to make them resistant to shock remagnetization, isothermal remagnetization and terrestrial weathering, making dusty olivine a credible recorder of pre-accretionary magnetic fields.

Church, N. S.; Lappe, S. C. L. L.; Kasama, T.; da Silva Fanta, A. B.; Dunin-Borkowski, R. E.; Feinberg, J. M.; Russell, S.; Harrison, R. J.

2012-04-01

123

Questions, questions: Can the contradictions between the petrologic, isotopic, thermodynamic, and astrophysical constraints on chondrule formation be resolved?  

NASA Astrophysics Data System (ADS)

Here, we show that several geochemical indicators point to number densities during chondrule formation that were far higher than can be accounted for by known nebula processes. The number densities implied by compound chondrules and nonspherical chondrules are shown to be significantly higher than estimated in previous studies. At the implied chondrule number densities, if a chondrule formation region survived a formation event it would have been gravitationally bound and would have collapsed quite rapidly to form an asteroidal-sized body. The diversity of chondrule compositions and textures in a chondrite group could have formed in a single event in subvolumes of a formation region that were chemically isolated from one another because of slow diffusion in the gas. Within these subvolumes, equilibration between chondrules with different compositions would have been fairly rapid, although small isotopic mass fractionations in elements like Fe, Si, Mg, and O may persist. This could explain the existence of the small isotopic mass fractionations in these elements that have been observed in chondrules. However, the evidence for recycling of chondrules requires that there was more than one chondrule formation event prior to formation of a parent asteroid. Finally, we argue that OC and CO chondrule Mg-Al systematics are both consistent with single ages or narrow ranges of ages, and that the CO, and possibly the OC, ages date parent body alteration. This would resolve the conundrum of needing to preserve in a turbulent nebula physically and chemically distinct CO and OC chondrule populations for 1-2 Myr.

Alexander, Conel M. O'D.; Ebel, Denton S.

2012-07-01

124

Evaporative Loss and Degree of Melting in Semarkona Type I Chondrules  

NASA Astrophysics Data System (ADS)

Bulk compositions have been determined by broad beam techniques for Semarkona type I (FeO-poor) chondrules. The finest grained (least melted) approach CI in composition, and abundances of moderately volatile elements (K, Na, Fe, Ni, P, S) decrease as grain size (degree of melting) increases. This is unequivocal evidence of evaporative loss during chondrule formation.

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

1996-03-01

125

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

Microsoft Academic Search

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

D. C. Hezel; H. Palme

2008-01-01

126

Chemical Composition of Matrix and Chondrules in Carbonaceous Chondrites: Implications for Disk Transport  

NASA Astrophysics Data System (ADS)

LA-ICP-MS analyses of unaltered matrix, chondrules, and bulk CM and CR chondrites show that the preaccretionary matrix had a CI composition. Chondrules could have formed in the inner disk and been transported to be embedded in matrix further out.

Zanda, B.; Humayun, M.; Hewins, R. H.

2012-03-01

127

Experimental Production of Matrix Lumps within Chondrules: Evidence of Post-Formational Processes.  

National Technical Information Service (NTIS)

The processes that acted upon chondrules after their formation are as important clues to the nature of the early solar nebula as are the exact processes that formed the chondrules. Recent experiments have studied the rim forming processes and the effects ...

H. C. Connolly R. H. Hewins

1993-01-01

128

Meteorite Ablation Rinds as Analogs for the Origin of Rims on Chondrules  

Microsoft Academic Search

Conventional wisdom holds that UOC chondrule rims were formed in the nebula by dust accretion. Following the accretion stage, some investigators suggest that these porous rims were subjected to thermal alteration that ranged from sintering to melting [e. g., 1-3]. To understand the evolutionary history of chondrules we need to ask: (1) What nebular mechanism(s) concentrated the dust for rapid

T. Bunch; J. M. Paque; R. Reynolds; M. Podolak; D. Prialnik

1993-01-01

129

Water-Induced Fabric Transitions in Olivine  

Microsoft Academic Search

The interpretation of seismic anisotropy in Earth's upper mantle has traditionally been based on the fabrics (lattice-preferred orientation) of relatively water-poor olivine. Here we show that when a large amount of water is added to olivine, the relation between flow geometry and seismic anisotropy undergoes marked changes. Some of the puzzling observations of seismic anisotropy in the upper mantle, including

Haemyeong Jung; Shun-ichiro Karato

2001-01-01

130

Ultrarapid chondrite formation by hot chondrule accretion? Evidence from unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

Unequilibrated ordinary chondrites (UOCs) of all groups (H, L, LL) contain unique chondrite clasts, which are characterized by a close-fit texture of deformed and indented chondrules. These clasts, termed "cluster chondrites," occur in 41% of the investigated samples with modal abundances between 5 and 90 vol% and size variations between <1 mm and 10 cm. They show the highest chondrule abundances compared with all chondrite classes (82-92 vol%) and only low amounts of fine-grained interchondrule matrix and rims (3-9 vol%). The mean degree of chondrule deformation varies between 11% and 17%, compared to 5% in the clastic portions of their host breccias and to values of 3-5% found in UOC literature, respectively. The maximum deformation of individual chondrules is about 50%, a value which seemingly cannot be exceeded due to geometric limitations. Both viscous and brittle chondrule deformation is observed. A model for cluster chondrite formation is proposed where hot and deformable chondrules together with only small amounts of co-accreting matrix formed a planetesimal or reached the surface of an already existing body within hours to a few days after chondrule formation. They deformed in a hot stage, possibly due to collisional compression by accreting material. Later, the resulting rocks were brecciated by impact processes. Thus, cluster chondrite clasts are interpreted as relicts of primary accretionary rocks of unknown original dimensions. If correct, this places a severe constraint on chondrule-forming conditions. Cluster chondrites would document local chondrule formation, where chondrule-forming heating events and the accretion of chondritic bodies were closely linked in time and space.

Metzler, Knut

2012-12-01

131

Dissolution of olivine during natural weathering  

NASA Astrophysics Data System (ADS)

Naturally weathered olivine occurring as phenocrysts in Hawai'ian volcanic rocks from several volcanic centers and regolith/outcrop settings, and as tectonized olivines from several metadunite bodies in the southern Appalachian Blue Ridge, are all similarly corroded by natural weathering. Conical (funnel-shaped) etch pits occur as individual pits, base-to-base pairs of cone-shaped pits, or en echelon arrays. Etch-pit shapes and orientations in the smallest etch-pit arrays visible in conventional scanning electron microscopy resemble even smaller features previously reported from transmission electron microscope investigations of olivine weathering. Etch pits occur in samples with chemical and/or mineralogical evidence of weathering, and/or are associated with, or proximal or directly connected to, fractures or exposed outcrop surface, and therefore are formed by weathering and not inherited from pre-weathering aqueous alteration (e.g., serpentinization, iddingsitization) of these parent rocks. Many etch pits are devoid of weathering products. Natural weathering of olivine is surface-reaction-limited. Similarity of corrosion forms from naturally weathered olivine from multiple igneous and metamorphic parent-rock bodies suggests that olivine weathers in the same manner regardless of its specific crystallization/recrystallization history, eruption/weathering/exposure ages of the olivine's host rock, and the local regolith history.

Velbel, Michael A.

2009-10-01

132

Ca-Fe-Mg olivines: phase relations and a solution model  

Microsoft Academic Search

Reversed phase equilibrium experiments in the system (Ca, Mg, Fe)2SiO4 provide four tielines at P?1 bar and 1 kbar and 800 C–1,100 C. These tielines have been used to model the solution properties\\u000a of the olivine quadrilateral following the methods described by Davidson et al. (1981) for quadrilateral clinopyroxenes. The\\u000a discrepancy between the calculated phase relations and the experimentally determined

Paula M. Davidson; Dilip K. Mukhopadhyay

1984-01-01

133

Chondrule formation in particle-rich nebular regions at least hundreds of kilometres across.  

PubMed

Chondrules are millimetre-sized spherules (mostly silicate) that dominate the texture of primitive meteorites. Their formation mechanism is debated, but their sheer abundance suggests that the mechanism was both energetic and ubiquitous in the early inner Solar System. The processes suggested--such as shock waves, solar flares or nebula lightning--operate on different length scales that have been hard to relate directly to chondrule properties. Chondrules are depleted in volatile elements, but surprisingly they show little evidence for the associated loss of lighter isotopes one would expect. Here we report a model in which molten chondrules come to equilibrium with the gas that was evaporated from other chondrules, and which explains the observations in a natural way. The regions within which the chondrules formed must have been larger than 150-6,000 km in radius, and must have had a precursor number density of at least 10 m(-3). These constraints probably exclude nebula lightning, and also make formation far from the nebula midplane problematic. The wide range of chondrule compositions may be the result of different combinations of the local concentrations of precursors and the local abundance of water ice or vapour. PMID:16724060

Cuzzi, Jeffrey N; Alexander, Conel M O'D

2006-05-25

134

Primary trapped melt inclusions in olivine in the olivine-augite-orthopyroxene ureilite Hughes 009  

Microsoft Academic Search

We describe the first known occurrence of primary melt inclusions in a ureilite. The ureilite is Hughes 009, one of a small number of ureilites whose primary mineralogy is olivine-augite-orthopyroxene, rather than olivine-pigeonite. Hughes 009 has a coarse-grained, equilibrated texture typical of ureilites, and homogeneous primary mineral compositions: olivine — mg 87.3; augite — mg 89.2, Wo 37.0, Al2O3 =

Cyrena Anne Goodrich; Anna Maria Fioretti; Mario Tribaudino; Gianmario Molin

2001-01-01

135

Water in Olivine - not a Simple Question  

NASA Astrophysics Data System (ADS)

How much "water" is present in olivine is of great interest for the upper mantle. Thermodynamics mandates that small amounts of H2O become structurally incorporated, when olivine crystallizes in an H2O-laden environment. It is widely believed that the formation of hydroxyl (OH- or Si-OH) is the end point of the H2O dissolution mechanism. Therefore it is also believed that quantitative solute H2O contents can be obtained by measuring the O-H stretching bands in olivine crystals by infrared (IR) spectroscopy. However, we can take olivine crystals, which are devoid of OH- according to the IR criteria, and fracture them in front of a mass spectrometer. Instantly upon fracture, H2 molecules evolve from the freshly formed surfaces, followed by H2O and then again by H2. This observation indicates that an apparently "dry" olivine can contain dissolved H2O, though not in form of IR-recognizable OH- or Si-OH. When we measure the effective dielectric constant \\epsiloneff at the limit of 0 Hz, we observe that \\epsiloneff changes reversibly in two steps, around 200°C and 400°C. At about 400°C the olivine turns into a p-type semiconductor. Our observations point (i) at the conversion of hydroxyl, probably Si-OH pairs, into H2 plus peroxy links, Si-OO-Si, (ii) at a two-step dissociation of the peroxy links. We conclude that, to determine the amount of solute "water" in olivine, it is not enough to measure its hydroxyl content by IR spectroscopy. Other methods have to be used or developed to provide information about the number of H2 molecules and peroxy links in the olivine matrix.

Bansal, S. A.; Dickinson, J. T.; Freund, F.

2004-12-01

136

Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions.  

PubMed

The lead-lead isochron age of chondrules in the CR chondrite Acfer 059 is 4564.7 +/- 0.6 million years ago (Ma), whereas the lead isotopic age of calcium-aluminum-rich inclusions (CAIs) in the CV chondrite Efremovka is 4567.2 +/- 0.6 Ma. This gives an interval of 2.5 +/- 1.2 million years (My) between formation of the CV CAIs and the CR chondrules and indicates that CAI- and chondrule-forming events lasted for at least 1.3 My. This time interval is consistent with a 2- to 3-My age difference between CR CAIs and chondrules inferred from the differences in their initial 26Al/27Al ratios and supports the chronological significance of the 26Al-26Mg systematics. PMID:12215641

Amelin, Yuri; Krot, Alexander N; Hutcheon, Ian D; Ulyanov, Alexander A

2002-09-01

137

Composition of Chondrules and the Assessment of Chondritic Abundances: A Planetary Perspective  

NASA Astrophysics Data System (ADS)

We have measured refractory trace-element ratios in chondrules from enstatite, ordinary and carbonaceous chondrites and find a high intrameteorite variability that has consequences for the modeling of planetary compositions.

McDonough, W. F.; Ash, R. D.; Puchtel, V.

2011-03-01

138

Trace Element Distribution Among Matrix, Chondrules, Metal, and Sulfides in Sahara 97072 EH3  

NASA Astrophysics Data System (ADS)

Trace- and major-element data is presented for Sahara 97072, a primitive EH3 chondrite. The results indicate that the silicate proportion of the matrix must have formed from material more depleted in refractory elements than the chondrule precursors.

Lehner, S. W.; Buseck, P. B.; McDonough, W. F.

2011-03-01

139

A Critical Examination of the X Wind Model for the Formation of Chondrules and CAIs  

NASA Astrophysics Data System (ADS)

We critically examine the "X wind model" for chondrule and CAI formation and radionuclide production. We identify internal inconsistencies and predictions at odds with observations that lead us to reject it.

Desch, S. J.; Morris, M. A.; Connolly, H. C.

2010-03-01

140

Homogeneous distribution of 26Al in the solar system from the Mg isotopic composition of chondrules.  

PubMed

The timing of the formation of the first solids in the solar system remains poorly constrained. Micrometer-scale, high-precision magnesium (Mg) isotopic analyses demonstrate that Earth, refractory inclusions, and chondrules from primitive meteorites formed from a reservoir in which short-lived aluminum-26 (26Al) and Mg isotopes were homogeneously distributed at +/-10%. This level of homogeneity validates the use of 26Al as a precise chronometer for early solar system events. High-precision chondrule 26Al isochrons show that several distinct chondrule melting events took place from approximately 1.2 million years (My) to approximately 4 My after the first solids condensed from the solar nebula, with peaks between approximately 1.5 and approximately 3 My, and that chondrule precursors formed as early as 0.87(-0.16)(+0.19) My after. PMID:19696348

Villeneuve, Johan; Chaussidon, Marc; Libourel, Guy

2009-08-21

141

Incompatible Trace Element Abundances in Hawaiian Olivines  

NASA Astrophysics Data System (ADS)

Our understanding of trace elements partitioning between olivine and silicate melt is clouded by large variations in values of partition coefficients presented in the literature. In general, partition coefficients from phenocryst-matrix results are higher than those from experimental equilibration and in-situ measurements (such as LA-ICP-MS and Ion-probe) (Blard and Farley, 2008; Lee et al., 2007). This discrepancy is possibly caused by the presence of melt or micromineral inclusions in the analyzed phenocrysts, or contamination of grain boundaries by enriched glasses or accessory phases or uranium pick up from alteration of olivines. To further investigate why analysis of natural phenocrysts usually results in relative high apparent D’s for incompatible trace elements, six aliquots of olivine grains from a single sediment sample of Waimea river watershed, on the western side of the island of Kauai, Hawaii, were analyzed by solution ICP-MS at Harvard University for trace element concentrations. Two aliquots of olivines were leached in 1% oxalic acid for 45-60 min at 90 OC before dissolution. Leached and unleached olivines mostly show positive linear correlations in plots of incompatible trace elements versus La, which possibly indicates mixing lines between olivine and one end-member with higher incompatible element concentration (possibly melt inclusion). Assuming La concentration in olivine is zero, we estimate concentration of other incompatible elements in olivines using intercepts of these mixing lines. We obtain that U and Th concentration in the olivines to be about 1 ppb and 0.1 ppb respectively, corresponding to apparent DUol/melt and DThol/melt of 0.003 and 0.0001 if host lave has U of 0.3 ppm and Th of 1ppm (Gayer et al.,2008). Recently, helium isotopic measurements were made in these olivines (Gayer et al., 2008) and the results yield a basin-wide average erosion rate of 0.056 mma-1 for Waimea river watershed. Gayer et al. (2008) argued that radiogenic 4He in these ~4.5 Ma old olivines is negligible using DUol/melt=2×10-5 and DThol/melt=5×10-5 (Beattie 1993; Kennedy et al., 1993) and 0.3 ppm U and 1 ppm Th for host lavas. This assumption has been challenged by Blard and Farley (2008), who argued that radiogenic 4He in these olivines are significant and could affect the calculated erosion rate by a factor of 10-100. They used apparent DUol/melt and DThol/melt ranging between 0.03 and 0.1, which were obtained from analyses of whole natural phenocrysts and host lava (Blard and Farley, 2008). In contrast, using our measured U and Th contents in the Kauai olivines suggest revisions to erosion rates on order of only 15%. Therefore, Blard and Farley (2008)’s apparent D values may not be representative of Kauai olivines and their assertion that Gayer et al. (2008)’s erosion rates from Hawaii require revision by more than a factore of 10 is incorrect.

Yu, G.; Huang, S.; Mukhopadhyay, S.; Jacobsen, S. B.

2009-12-01

142

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

143

Micrometeorite craters discovered on chondrule-like objects from kapoeta meteorite.  

PubMed

Craters attributable to hypervelocity impacts of micrometeorites have been discovered on rare chondrule-like objects from the gas-rich meteorite Kapoeta. These chondrule-like objects, probably generated by impacts themselves, provide further evidence for the regolith origin of Kapoeta. The micrometeorite flux at the time of formation of the meteorites was probably an order of magnitude higher than the present flux, but the solar luminosity could not have been higher than 1.7 times its present value. PMID:17733113

Brownlee, D E; Rajan, R S

1973-12-28

144

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

145

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

146

Can a chondrule precursor survive a shock wave?  

NASA Astrophysics Data System (ADS)

In a shock-wave heating model, a chondrule is formed due to frictional heating between its precursor and gas. If the tensile stress inside the precursor derived from the gas dynamic pressure, is greater than the tensile strength of the precursor, the precursor is broken into smaller pieces. The yield (onset of plastic deformation) and breaking (onset of fracturing) strengths of the precursor when sintering is taken into account was calculated. The timescale of sintering is estimated. The model in Sirono & Greenberg (2000, Icarus 145, 230), in which agrain aggregate is assumed to comprise chains of spherical grains of uniform size was used. The critical packing fraction above which anaggregate can survive ashock wave is obtained. If the degree of sintering is low, the breaking strength of the aggregate decreases due to sintering. When sintering has sufficiently occurred, the aggregate can avoid breaking up. Sintering can proceed upstream of the shock wave before the passage of the shock wave.

Sirono, S.

2006-08-01

147

Constraints on the Origin of Chondrules and CAIs from Short-Lived and Long-Lived Radionuclides  

SciTech Connect

The high time resolution Pb-Pb ages and short-lived nuclide based relative ages for CAIs and chondrules are reviewed. The solar system started at 4567.2 {+-} 0.6Ma inferred from the high precision Pb-Pb ages of CAIs. Time scales of CAIs ({le}0.1Myr), chondrules (1-3Myr), and early asteroidal differentiation ({ge}3Myr) inferred from {sup 26}Al relative ages are comparable to the time scale estimated from astronomical observations of young star; proto star, classical T Tauri star and week-lined T Tauri star, respectively. Pb-Pb ages of chondrules also indicate chondrule formation occur within 1-3 Myr after CAIs. Mn-Cr isochron ages of chondrules are similar to or within 2 Myr after CAI formation. Chondrules from different classes of chondrites show the same range of {sup 26}Al ages in spite of their different oxygen isotopes, indicating that chondrule formed in the localized environment. The {sup 26}Al ages of chondrules in each chondrite class show a hint of correlation with their chemical compositions, which implies the process of elemental fractionation during chondrule formation events.

Kita, N T; Huss, G R; Tachibana, S; Amelin, Y; Nyquist, L E; Hutcheon, I D

2005-10-24

148

Macrochondrules in chondrites—Formation by melting of mega-sized dust aggregates and/or by rapid collisions at high temperatures?  

NASA Astrophysics Data System (ADS)

Seventy-four macrochondrules with sizes >3 mm were studied. Considering the extraordinary size of the chondrules (occasionally achieving a mass of 1000 times (and more) the mass of a normal-sized chondrule), the conditions in the formation process must have been somewhat different compared with the conditions for the formation of the common chondrules. Macrochondrules are typically rich in olivine and texturally similar to specific chondrule types (barred, radial, porphyritic, and cryptocrystalline) of normal-sized chondrules. However, our studies show that most of the macrochondrules are fine-grained or have elongated crystals (mostly BO, RP, and C), which lead to the assumption that they were once totally molten and cooled quite rapidly. Porphyritic chondrules belong to the least abundant types of macrochondrules. This distribution of chondrule types is highly unusual and just a reverse of the distribution of chondrule types among the typical-sized chondrules in most chondrite groups except for the CH and CB chondrites. New chondrule subtypes (like radial-olivine [RO] or multi-radial [MR] chondrules) are defined to better describe the textures of certain large chondrules. Macrochondrules may have formed due to melting of huge precursor dust aggregates or due to rapid collisions of superheated melt droplets, which led to the growth of large molten spherules in regions with high dust densities and high electrostatic attraction.

Weyrauch, Mona; Bischoff, Addi

2012-12-01

149

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

150

Effect of a Si-rich layer on olivine carbonation under in-situ conditions  

NASA Astrophysics Data System (ADS)

Mineral carbonation, a geochemical reaction between Mg-, Fe-, and Ca-silicate minerals and dissolved carbon dioxide (CO2), results in the long-term, stable storage of CO2 as carbonate minerals. Although the reaction is thermodynamically favored and occurs naturally, the kinetics are typically slow at temperatures < 100°C and thus limit industrial applications of the process. This study presents the results of a series of batch reactions designed to further understand the kinetics and mechanism of olivine carbonation in a three-phase system (water, solid, and supercritical CO2) at conditions relevant to in-situ¬ carbonation (60°C, 100 bar CO2 pressure, water:solid of 20:1 to 50:1, pH 3-6 ). Twin Sisters (OR) olivine ((Mg0.85 Fe0.15)2SiO4) was chosen as the reactive silicate mineral because olivines are abundant and undergo carbonation in nature. The carbonation of olivine in the presence of water and supercritical CO2 proceeds via dissolution of the starting mineral and CO2, followed by precipitation of secondary phases. Two secondary phases are relevant to this study. The first is Mg-carbonate (magnesite, MgCO3), the desired reaction product because it sequesters CO2 for geologic time scales. The second is amorphous silica (SiO2), a side-product that increases the total volume of solids in the system but does not interact with CO2. Because the solubility of silica is much less than that of Mg-carbonate at <100°C, silica reaches thermodynamic saturation first. The present study shows that the rate of olivine dissolution depends on the saturation state of amorphous silica and decreases by up to two orders of magnitude (from 10-11 to 10-13 mol cm-2 s-1) as saturation is approached. This observed effect is likely due to formation of a Si-rich layer on olivine grain surfaces after exposure to acidic solution, observed by x-ray photoelectron spectroscopy. The initial olivine dissolution is incongruent over the timeframe of several hours as shown by solution compositions determined by ICP-AES, but becomes congruent over longer periods. This behavior has been noted by others. We hypothesize that when in contact with an aqueous solution at saturation with respect to silica, the Si-rich layer will significantly lower Mg diffusion as well as the dissolution rate of olivine. The net effect is thus an apparent olivine dissolution rate of near zero for time periods ranging from 1 to 20 days. After this period the measured olivine dissolution rate increases, indicating that the Si-rich layer is no longer plays a role in passivating the surface. We hypothesize that as the surface area of secondary silica increases, there is an increasing movement of SiO2 from the olivine surface layer to physically separate secondary silica particles. We conclude that the rate of olivine carbonation under the conditions of our experiments depends strongly on SiO2 saturation and that this effect must be mitigated for a commercially viable Mg-silicate carbonation process.

Johnson, N. C.; Thomas, B.; Rosenbauer, R. J.; Maher, K.; Brown, G. E.

2011-12-01

151

A search for olivine activation volume  

NASA Astrophysics Data System (ADS)

Knowledge of the rheological properties of mantle materials is critical in modeling the dynamics of the Earth. The flow law of olivine defined at mantle pressure and temperature is especially important since the pressure dependence of rheology may affect our estimation for the strength of olivine in the Earth's interior. Conventional deformation methods in defining the flow law of olivine have to face factors of large uncertainties of differential stress measurements and/or limited confining pressure for deformation. In this study, high-temperature (up to 1473 K) deformation experiments of polycrystalline olivine (average grain size < 5 micron) at pressure up to 6.5(0.2) GPa were conducted in-situ using large-volume high-pressure apparatus (Deformation DIA) and synchrotron x-ray radiation. More than 30% strain was generated during the uniaxial compression. The sample lengths during the deformation process were monitored by x-ray radiography. The strain rate was derived with precision up to 10-6. Macroscopic differential stress was measured at constant strain rate (˜ 10-5 s-1) using a multi-element solid-state detector combined with a conical slit. The new data, measured at 1473 and 1273K at 6.5 and 3GPa, fits well an empirical power-law creep flow law under the condition that the activation energy is 520(20) kJ/mol and the activation volume is less than 3 cm^3/mol. Consistent with TEM observations on recovered samples, tests for grain size dependence of flow, and the empirical power law exponent, we conclude that power-law creep is the dominant flow mechanism for dry olivine at upper mantle conditions. The success of defining the flow law for olivine in this study also symbolizes a huge opening for defining the rheological flow law for other materials in the Earth's interior.

Li, L.; Weidner, D.; Mei, S.; Raterron, P.; Chen, J.; Durham, W.

2003-04-01

152

OH point defects in olivine from Pakistan  

NASA Astrophysics Data System (ADS)

The infrared (IR) spectra of gem-quality olivine crystals from Pakistan, formed in serpentinised dunitic rocks, are characterised by strongly pleochroic absorption bands at 3,613, 3,597, 3,580 and 3,566 cm-1. These bands are assigned to O-H stretching vibrations of OH point defects corresponding to H2O concentrations of about 35 wt ppm. Unlike other olivine spectra, the dominating bands are strongly polarised parallel to the b-axis. The unusual spectra type, excludes the presence of planar defects. This finding is supported by transmission electron microscopy. The 3,613 cm-1 band is related to vacant Si sites, the slightly lower energetic bands preferentially to vacant M2 sites. The exclusive presence of these bands is not only a characteristic feature of olivines treated under high P,T conditions equivalent to mantle environment, the presence of these bands in untreated natural olivine also indicates formation conditions equivalent to crustal rocks.

Gose, Jürgen; Schmädicke, Esther; Markowitz, Margit; Beran, Anton

2010-05-01

153

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

154

Cations in olivine, Part 1: Calcium partitioning and calcium-magnesium distribution between olivines and coexisting melts, with petrologic applications  

Microsoft Academic Search

As part of a study of kinetic and equilibrium aspects of magmatic olivines (Jurewicz 1986; Jurewicz and Watson 1988), calcium distribution and partitioning sys- tematics have been experimentally determined for olivine\\/ melt pairs under a wide variety of temperatures, pressures and oxygen fugacities. The calcium content of an equilibrated olivine depends upon (1) the concentration of calcium in the melt

Amy J. G. Jurewicz; E. Bruce Watson

1988-01-01

155

Aqueous alteration of chondrules in the CM carbonaceous chondrite, Allan Hills 81002: implications for parent body alteration  

Microsoft Academic Search

ALH 81002 is a CM carbonaceous chondrite that has petrographic characteristics suggesting that it experienced a high degree of aqueous alteration, but has entirely escaped parent body brecciation. In this study, we report the results of a systematic investigation of the alteration of more than 35 chondrules in ALH 81002 that belong to specific well-defined chondrule types. Our results show

Nicolaus P Hanowski; Adrian J Brearley

2001-01-01

156

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

157

Iodine-xenon studies of petrographically and chemically characterized Chainpur chondrules  

NASA Astrophysics Data System (ADS)

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.

1991-03-01

158

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°-290°C (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

159

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

160

Shock-produced olivine glass: First observation  

USGS Publications Warehouse

Transmission electron microscope (TEM) observations of an experimentally shock-deformed single crystal of natural peridot, (Mg0.88Fe 0.12SiO4 recovered from peak pressures of about 56 ?? 109 pascals revealed the presence of amorphous zones located within crystalline regions with a high density of tangled dislocations. This is the first reported observation ofolivine glass. The shocked sample exhibits a wide variation in the degree of shock deformation on a small scale, and the glass appears to be intimately associated with the highest density of dislocations. This study suggests that olivine glass may be formed as a result of shock at pressures above about 50 to 55 ?? 109 pascals and that further TEM observations of naturally shocked olivines may demonstrate the presence of glass.

Jeanloz, R.; Ahrens, T. J.; Lally, J. S.; Nord, Jr. , G. L.; Christie, J. M.; Heuer, A. H.

1977-01-01

161

Olivine-rich patches observed by OMEGA  

NASA Astrophysics Data System (ADS)

Several small regions with very intense and broad 1 ?m absorption have been observed by OMEGA. They are mostly located in the dark, older highland plateaus of the southern hemisphere, in particular Terra Tyrrhena and Noachis Terra. The band starts at 0.9 ?m, presents a steep absorption front located up to 1.6 ?m, 20% in strengh, and is accompanied in some cases by a subdued feature at ~0.5 ?m. Such broad signatures, when they appear alone, are matched only by olivines with high Fe content (fayalite endmember). The observed patches are typically on the kilometer scale, and are located in otherwise pyroxene-rich areas. In at least one occurrence, an enhanced olivine feature is located in the rim and ejecta blanket of a crater, suggesting excavated material. Some of them could correspond to areas tentatively detected by TES (Hoefen & Clark 2001).

Erard, S.; Langevin, Y.; Forni, O.; Poulet, F.; Bibring, J.-P.

162

Mechanisms and Timescales for Reequilibration of Water in Olivine-Hosted Melt Inclusions  

NASA Astrophysics Data System (ADS)

Water solubility in silicate melts drops substantially with decreasing pressure. A magma containing several weight % dissolved H2O in the shallow crust is left with only a few thousand ppm following eruption. Olivine-hosted melt inclusions provide information on the pre-eruptive H2O contents of degassed magmas because the strength of the host crystal protects the melt inclusion from the decompression experienced by the entraining magma. The principal uncertainty involved with interpreting pre-eruptive H2O concentrations from melt inclusions is the potential for diffusive loss or gain of H+ (protons) through the host olivine. It has been proposed that Fe redox reactions severely limit the proton flux, and that episodes of H2O loss/gain are easily identifiable through changes in oxidation state of the inclusion [1,2]. Results from hydration and dehydration experiments carried out on natural inclusion-bearing olivines and analyzed by SIMS confirm that H2O re-equilibratrion occurs rapidly via proton diffusion through the host olivine, and demonstrate that re-equilibration of oxygen fugacity within the inclusions occurs on comparable timescales via diffusion of point defects. Therefore, an olivine-hosted melt inclusion only provides a reliable record for the H2O content of the external melt with which it most recently equilibrated. Hydration experiments were performed on olivines from Puu Wahi, a scoria cone on the NE rift zone of Mauna Loa volcano. Melt inclusions initially containing 0.36±0.05 wt% H2O were held at 1 GPa and 1250°C in water enriched in 18O (18O/?O = 0.977) and D (2H/?H = 0.998) to map the transport of protons and oxygen during equilibration of melt inclusions with an external fluid. Dehydration experiments were carried out for 1 to 18 hrs at 1 bar and 1250 °C on inclusion-bearing olivines in scoria erupted from Cerro Negro volcano, Nicaragua, in 1999. The initial concentration of H2O in these melt inclusions is uniformly high (3.6±0.6 wt%). All run products were analyzed by SIMS on the Cameca 1280 ion microprobe at WHOI. Results from our experiments confirm that the mechanism for loss or gain of H2O from olivine-hosted melt inclusions is lattice diffusion of protons. This process leaves behind an O2- for every 2 protons lost, and scavenges an O2- for every 2 protons gained, producing an increase or decrease, respectively, of the fugacity of oxygen within the inclusion. However, H2O loss/gain for olivine-hosted melt inclusions is coupled with point defect-mediated oxygen fugacity re-equilibration. Therefore, Fe redox reactions do not limit either the amount or rate of water loss or gain by the inclusion. The H2O concentration of an olivine-hosted melt inclusion can change rapidly, and that change is not recorded by the oxygen fugacity of the melt. References: [1] A. V. Sobolev, L. V. Danyushevsky, J Petrol 35, 1183 (1994); [2] L. V. Danyushevsky, A. W. McNeill, A. V. Sobolev, Chem Geol 183, 5 (2002).

Gaetani, G. A.; O'Leary, J. A.; Shimizu, N.

2009-12-01

163

Dislocation creep of fine-grained olivine  

Microsoft Academic Search

Deformation experiments conducted in a gas medium apparatus at temperatures from 1200 to 1350°C with a fine-grained, solution-gelation derived Fe-bearing olivine show a stress dependence of the strain rate at stresses above ?150 MPa, which is much stronger than previously reported for polycrystalline samples. The data can be fit by a power law with $\\\\dot {\\\\epsilon }$$\\\\propto$?n with n ?

U. H. Faul; J. D. Fitz Gerald; R. J. M. Farla; R. Ahlefeldt; I. Jackson

2011-01-01

164

Free collisions in a microgravity many-particle experiment - II: The collision dynamics of dust-coated chondrules  

NASA Astrophysics Data System (ADS)

The formation of planetesimals in the early Solar System is hardly understood, and in particular the growth of dust aggregates above millimeter sizes has recently turned out to be a difficult task in our understanding (Zsom, A., Ormel, C.W., Güttler, C., Blum, J., Dullemond, C.P. [2010]. Astron. Astrophys., 513, A57). Laboratory experiments have shown that dust aggregates of these sizes stick to one another only at unreasonably low velocities. However, in the protoplanetary disk, millimeter-sized particles are known to have been ubiquitous. One can find relics of them in the form of solid chondrules as the main constituent of chondrites. Most of these chondrules were found to feature a fine-grained rim, which is hypothesized to have formed from accreting dust grains in the solar nebula. To study the influence of these dust-coated chondrules on the formation of chondrites and possibly planetesimals, we conducted collision experiments between millimeter-sized, dust-coated chondrule analogs at velocities of a few cm s-1. For 2 and 3 mm diameter chondrule analogs covered by dusty rims of a volume filling factor of 0.18 and 0.35-0.58, we found sticking velocities of a few cm s-1. This velocity is higher than the sticking velocity of dust aggregates of the same size. We therefore conclude that chondrules may be an important step towards a deeper understanding of the collisional growth of larger bodies. Moreover, we analyzed the collision behavior in an ensemble of dust aggregates and non-coated chondrule analogs. While neither the dust aggregates nor the solid chondrule analogs show sticking in collisions among their species, we found an enhanced sicking efficiency in collisions between the two constituents, which leads us to the conjecture that chondrules might act as "catalyzers" for the growth of larger bodies in the young Solar System.

Beitz, E.; Güttler, C.; Weidling, R.; Blum, J.

2012-03-01

165

Sushi Bar  

NSDL National Science Digital Library

An innovative website where customers order from a realistic sushi bar menu to learn about international fisheries resources and impacts. Select shrimp, tuna, squid, octopus, or sea urchin to learn where resources are harvested, current fisheries methods, population status and concerns. This on-line activity also demonstrates how global our use of resources has become, with a single country dependent on seafood imports from around the world. The site also contains lesson plans on natural resources and resource management. Appropriate for grades 6 and up.

2010-12-02

166

Refractory Inclusions and Aluminum-rich Chondrules in the CB/CH-like Carbonaceous Chondrite Isheyevo  

NASA Astrophysics Data System (ADS)

The CAIs and Al-rich chondrules in Isheyevo are texturally and mineralogically similar to those in other previously studied CH chondrites and to a lesser degree to those in the CB chondrites and different from those in CO, CM, CR, and CV chondrites.

Krot, A. N.; Ulyanov, A. A.; Ivanova, M. A.

2006-03-01

167

Two forgotten pioneers of meteoritics - The discoverers of chondrules and etching figures in meteorites  

NASA Astrophysics Data System (ADS)

A survey of the historical data shows that chondrules were discovered by John Lloyd Williams in 1799, as a result of the study of the Benares meteorite. The discovery of Widmanstatten structure by William Thompson (first publication on this subject in 1804) is also discussed.

Eremeeva, A. I.

168

Two forgotten pioneers of meteoritics - The discoverers of chondrules and etching figures in meteorites  

Microsoft Academic Search

A survey of the historical data shows that chondrules were discovered by John Lloyd Williams in 1799, as a result of the study of the Benares meteorite. The discovery of Widmanstatten structure by William Thompson (first publication on this subject in 1804) is also discussed.

A. I. Eremeeva

1988-01-01

169

Chemical energy in cold-cloud aggregates - The origin of meteoritic chondrules  

Microsoft Academic Search

If interstellar particles and molecules accumulate into larger particles during the collapse of a cold cloud, the resulting aggregates contain a large store of internal chemical energy. It is here proposed that subsequent warming of these accumulates leads to a thermal runaway when exothermic chemical reactions begin within the aggregate. These, after cooling, are the crystalline chondrules found so abundantly

D. D. Clayton

1980-01-01

170

Boron and lithium isotopic composition in chondrules from the mokoia meteorite  

Microsoft Academic Search

Introduction: Large Boron isotopic variations have been reported in individual chondrules from several meteorites [1, 2]. These variations were interpreted as resulting from the incomplete mixing of two isotopically distinct sources of Boron. Spallation is the only known nucleosynthetic process that can yield Boron in substantial amounts at the scale of the Universe. Therefore it has been proposed that the

F. Robert; M. Chaussidon

2003-01-01

171

Electrical conductivity of synthetic iron-bearing olivine  

Microsoft Academic Search

The electrical conduction in synthetic, dry polycrystalline, iron-bearing olivine (Fo90) was investigated as a first-order approach to the electrical conductivity in the upper mantle. This fundamental study is\\u000a of great importance to better understand the charge-transport mechanisms seen in olivine. Conduction processes in synthetic\\u000a samples are not influenced by a complex geological history in contrast to conductivity in natural olivine.

Robert J. M. Farla; C. J. Peach; S. M. ten Grotenhuis

2010-01-01

172

Search for olivine spectral signatures on the surface of Vesta  

NASA Astrophysics Data System (ADS)

The occurrence of olivines on Vesta were first postulated from traditional petrogenetic models which suggest the formation of olivine as lower crustal cumulates. An indirect confirmation is given by their presence as a minor component in some samples of diogenite meteorites, the harzburgitic diogenites and the dunitic diogenites, and as olivine mineral clasts in howardites. Another indication for this mineral was given by interpretations of ground-based and Hubble Space Telescope observations that suggested the presence of local olivine-bearing units on the surface of Vesta. The VIR instrument onboard the DAWN mission has been mapping Vesta since July 2011. VIR acquired hyperspectral images of Vesta's surface in the wavelength range from 0.25 to 5.1 µm during Approach, Survey and High Altitude Mapping (HAMO) orbits that allowed a 2/3 of the entire asteroid surface to be mapped. The VIR operative spectral interval, resolution and coverage is suitable for the detection and mapping of any olivine rich regions that may occur on the Vesta surface. The abundance of olivine in diogenites is typically lower than 10% but some samples richer in olivine are known. However, we do not expect to have extensive exposures of olivine-rich material on Vesta. Moreover, the partial overlap of olivine and pyroxene spectral signatures will make olivine difficult to detect. Different spectral parameters have been used to map olivine on extraterrestrial bodies, and here we discuss the different approaches used, and develop new ones specifically for Vesta. Our new methods are based on combinations of the spectral parameters relative to the 1 and 2 micron bands (the most prominent spectral features of Vesta surface in the visible and the infrared), such as band center locations, band depths, band areas, band area ratios. Before the direct application to the VIR data, the efficiency of each approach is evaluated by means of analysis of laboratory spectra of HED meteorites, pyroxenes, olivines and their mixtures.

Palomba, E.; De Sanctis, M. C.; Ammannito, E.; Capaccioni, F.; Capria, M. T.; Farina, M.; Frigeri, A.; Longobardo, A.; Tosi, F.; Zambon, F.; McSween, H. Y.; Mittlefehldt, D. W.; Russell, C. T.; Raymond, C. A.; Sunshine, J.; McCord, T. B.

2012-04-01

173

Non-equilibrium concepts lead to a unified explanation of the formation of chondrules and chondrites  

NASA Astrophysics Data System (ADS)

Calculations of the formation of seven types of chondrules in Semarkona from a gas of solar composition were performed with the Fact computer program to predict the chemistries of oxides, including silicates, developed by the authors and their colleagues. The constrained equilibrium theory was used in the calculations with two nucleation constraints suggested by nucleation theory. The first constraint was the blocking of Fe and other metal gaseous atoms from condensing to form solids or liquids because of the very high surface free energies and high surface tensions of the solid and liquid metals, respectively. The second constraint was the blocking of the condensation of solids and the formation of metastable liquid oxides (including silicates) well below their liquidus temperatures. Our laboratory experiments suggested subcooling of type IIA chondrule compositions of 400 degrees or more below the liquidus temperature. The blocking of iron leads to a supersaturation of Fe atoms, so that the partial pressure of Fe (pFe) is larger than the partial pressure at equilibrium (pFe(eq)). The supersaturation ratio S = pFe/pFe(eq) becomes larger than 1 and increases rapidly with a decrease in temperature. This drives the reaction Fe + H2O ??H2 + FeO to the right. With S = 100, the activity of FeO in the liquid droplet is 100 times as large as the value at equilibrium. The FeO activities are a function of temperature and provide relative average temperatures of the crystallization of chondrules. Our calculations for the LL3.0 chondrite Semarkona and our study of some non-equilibrium effects lead to accurate representations of the compositions of chondrules of types IA, IAB, IB, IIA, IIAB, IIB, and CC. Our concepts readily explain both the variety of FeO concentrations in the different chondrule types and the entire process of chondrule formation. Our theory is unified and could possibly explain the formation of chondrules in all chondritic meteorites as well as provide a simple explanation for the complex chemistries of chondrites, especially type 3 chondrites.

Blander, Milton; Pelton, Arthur D.; Jung, In-Ho; Weber, Richard

2004-12-01

174

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 -10.6±5.7‰, ?18O -7.5±2.5‰ and ?17O +1.4±4.3‰, ?18O -6.5±1.6‰ (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

175

Experimental simulation of oxygen isotopic exchange in olivine and implication for the formation of metamorphosed carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

We have conducted hydration-dehydration experiments on terrestrial olivine to investigate the behavior of oxygen isotopic fractionation to test the hypothesis that multiple cycles of aqueous and thermal processing on a parent asteroid comprise a genetic relationship between CM2s and metamorphosed carbonaceous chondrites (MCCs). Two experiments were undertaken. In the first experiment, serpentine was obtained by hydrating terrestrial olivine (Fo90.9) in the laboratory. During this experiment, olivine was reacted with isotopically heavy water (?18O 21.5‰) at T = 300 °C, PH2O = 300 bar, for 100 days. The oxygen isotopic composition of the experimental serpentine was enriched in 18O (by 10 ‰ in ?18O) due to exchange of oxygen isotopes between olivine and the 18O-rich water. Dehydrated serpentine was then produced during laboratory heating experiment in vacuum, at T = 930 °C, for 1 h. The oxygen isotopic composition of the dehydrated serpentine was enriched in 18O by a further 7 ‰. The net result of the hydration-dehydration process was an enrichment of 18O in the final material by approximately 17‰. The new experimental results suggest that the oxygen isotopic compositions of MCCs of the Belgica-like group, including Dhofar 225 and Dhofar 725, could be derived from those of typical CM2 chondrites via several cycles of hydration-dehydration caused by aqueous alteration and subsequent thermal metamorphism within their parent asteroids.

Ivanova, Marina A.; Lorenz, Cyril A.; Franchi, Ian A.; Bychkov, Andrei Y.; Post, Jeffrey E.

2013-09-01

176

Olivine-based heat storage refractories  

NASA Astrophysics Data System (ADS)

The processing properties and performance of special refractory shapes produced from olivine for prototype evaluations in heat storage furnaces are investigated. Heat storage furnaces and related consumer owned thermal storage units are energy conversion/storage devices of the sensible heat type. Their primary purpose is to permit electrical load leveling of large generating/distributing systems. Load-leveling enables power generating plants to operate more efficiency thus contributing to better overall energy utilization. The principal application for these ceramic thermal energy reservoirs is in home or business heating (furnaces, space heaters).

Gay, B. M.; Palmour, H., III; Cochrane, R. L.

1981-03-01

177

Effect of Water on Olivine Metastability in Subducting Lithosphere  

NASA Astrophysics Data System (ADS)

The roles of metastably persisting olivine in subducting lithosphere has been investigated in light of mineralogical and thermal structures, plate velocities, and deep seismogenesis. Many different variables have been used in these examinations: latent heat feedback, kinetic models, and thermal conductivity models, to name a few. In all these models, however, the olivine has been anhydrous, though the presence of H2O in the (Mg,Fe)2SiO4 system is well-known to enhance the rates of phase transformation. Diedrich et al. [2005] recently determined growth rates for olivine with low (300 wt ppm) water content and found that, compared with dry samples, hydrous olivine has growth rates 1.7 orders faster at 1100°C. Using these kinetic data, we modeled 25 subducting slabs with thermal parameters (?) ranging from 3400-17000 km to see the effect of water on olivine metastability. Except within the coldest, fastest slabs, (? > 10000 km) all olivine had transformed to wadsleyite or ringwoodite within 1-2 km of the equilibrium phase boundary, resulting in regions of metastability only 5-10% in size as compared with slabs with dry olivine. Wedges of metastable olivine did form in slabs moving at velocities ?14 cm/yr, yet these were only 4-5% in size with respect to their anhydrous counterparts. Metastable olivine only reached maximum depths of ~360 km, compared with 500-550 km for dry slabs, 5-15 km down-dip of the equilibrium phase boundary. These results suggest that, given small amounts of water, subducting slabs will exhibit near-equilibrium mineralogical structures. Therefore, in consequence, explanations of deep seismogenesis that rely on the persistence of metastable olivine would seem unlikely for hydrous lithosphere. In addition, any decrease in subduction velocity due to the existence of a low-density wedge of metastable olivine (the parachute effect) in dry slabs would not be evident in hydrous ones.

Marton, F. C.; Diedrich, T.; Sharp, T. G.

2006-12-01

178

Olivine Annealing in Molten Iron-Sulfide. A Tool to Interpret the Origin of Pallasites  

NASA Astrophysics Data System (ADS)

Annealing of olivine in molten Fe-S was performed in order to decipher the origin of rounded olivine group pallasite meteorites. Growth mechanism and growth rate of olivine was obtained and a variety of formation models are critically discussed.

Solferino, G. F. D.; Muir, S. L.

2013-09-01

179

Possible Xenolith and Xenocrysts of Olivine in the Asuka-881371 Angrite Collected from Antarctica  

NASA Astrophysics Data System (ADS)

Angrite is the oldest aged rock in all meteorites. Asuka-881371 angrite include some xenolith-xenocrysts like olivine aggragate and/ or large olivine grains. They are differ from any olivine in host for their occurrences, texture and compositions.

Yanai, K.

2003-03-01

180

Fe/Mn in Olivine of Carbonaceous Meteorites.  

National Technical Information Service (NTIS)

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 thes...

I. M. Steele

1993-01-01

181

Effect of Water on Olivine Metastability in Subducting Lithosphere  

Microsoft Academic Search

The roles of metastably persisting olivine in subducting lithosphere has been investigated in light of mineralogical and thermal structures, plate velocities, and deep seismogenesis. Many different variables have been used in these examinations: latent heat feedback, kinetic models, and thermal conductivity models, to name a few. In all these models, however, the olivine has been anhydrous, though the presence of

F. C. Marton; T. Diedrich; T. G. Sharp

2006-01-01

182

Ceramic Bar-on-Bar Impact Experiments.  

National Technical Information Service (NTIS)

Ceramic bar-on-bar (uniaxial stress) experiments are performed to extend uniaxial strain deformation states imposed in flyer plate impact experiments. The major objective of these experiments is to generate a variety of multi axial deformation states for ...

N. S. Brar

2003-01-01

183

Ringwoodite lamellae in olivine: Clues to olivine-ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs  

PubMed Central

The first natural occurrence of ringwoodite lamellae was found in the olivine grains inside and in areas adjacent to the shock veins of a chondritic meteorite, and these lamellae show distinct growth mechanism. Inside the veins where pressure and temperature were higher than elsewhere, ringwoodite lamellae formed parallel to the {101} planes of olivine, whereas outside they lie parallel to the (100) plane of olivine. The lamellae replaced the host olivine from a few percent to complete. Formation of these lamellae relates to a diffusion-controlled growth of ringwoodite along shear-induced planar defects in olivine. The planar defects and ringwoodite lamellae parallel to the {101} planes of olivine should have been produced in higher shear stress and temperature region than that parallel to the (100) plane of olivine. This study suggests that the time duration of high pressure and temperature for the growth of ringwoodite lamellae might have lasted at least for several seconds, and that an intracrystalline transformation mechanism of ringwoodite in olivine could favorably operate in the subducting lithospheric slabs in the deep Earth.

Chen, Ming; Goresy, Ahmed El; Gillet, Philippe

2004-01-01

184

Ringwoodite lamellae in olivine: Clues to olivine-ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs.  

PubMed

The first natural occurrence of ringwoodite lamellae was found in the olivine grains inside and in areas adjacent to the shock veins of a chondritic meteorite, and these lamellae show distinct growth mechanism. Inside the veins where pressure and temperature were higher than elsewhere, ringwoodite lamellae formed parallel to the [101] planes of olivine, whereas outside they lie parallel to the (100) plane of olivine. The lamellae replaced the host olivine from a few percent to complete. Formation of these lamellae relates to a diffusion-controlled growth of ringwoodite along shear-induced planar defects in olivine. The planar defects and ringwoodite lamellae parallel to the [101] planes of olivine should have been produced in higher shear stress and temperature region than that parallel to the (100) plane of olivine. This study suggests that the time duration of high pressure and temperature for the growth of ringwoodite lamellae might have lasted at least for several seconds, and that an intracrystalline transformation mechanism of ringwoodite in olivine could favorably operate in the subducting lithospheric slabs in the deep Earth. PMID:15479764

Chen, Ming; El Goresy, Ahmed; Gillet, Philippe

2004-10-12

185

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

186

Boron and lithium isotopic composition in chondrules from the mokoia meteorite  

NASA Astrophysics Data System (ADS)

Introduction: Large Boron isotopic variations have been reported in individual chondrules from several meteorites [1, 2]. These variations were interpreted as resulting from the incomplete mixing of two isotopically distinct sources of Boron. Spallation is the only known nucleosynthetic process that can yield Boron in substantial amounts at the scale of the Universe. Therefore it has been proposed that the two sources observed in chondrules correspond to two different types of spallation reactions, namely at high and low energies. Indeed, in the case of Boron, the 11B/10B ratio is sensitive to the energy at which the spallation reaction takes place. Since this report of large B isotopic variations in chondrules, two observations have allowed to identify the natural conditions under which at least one of such spallation reactions may have taken place in the early solar system. First, X-ray observations of T-Tauri stars have revealed daily outbursts which mimic the present day solar activity during the emission of flares [3]. Second, the decay product (i.e. 10B) of the short lived radio-isotope 10Be was discovered in Calcium-Aluminum-rich inclusions (CAIs) [4]. This is an indication that spallation did occurr in the solar system, shortly (i.e. less than a few million years) before the formation of the CAIs. In addition the possible occurrence of 7Be in CAIs suggests that this duration can be as short as a few months [5]. Sampling and Results: In the 8 chondrules from Mokoia, the ?11B values range between -39±6.8 ppm and -0.6±7.8 ppm (2 sigma). In one Boron depleted area of one chondrule, the ?11B value was found to be as low as -68.5 ppm and -61.5 ppm (±29; 2 sigma). In one chondrule from Mokoia the ?11B values range between -33.7±5.4 ppm and -3.8±5.4 ppm. These data confirm with a resolution of ? ±6 ppm the presence of a significant Boron isotopic heterogeneity,.The ?^7Li were also measured along with the ^delta11B. They range from -53.7±2.4 and -0.15±1.6 ppm (2 sigma) in the 8 chondrules of the Mokoia meteorite. Therefore the heterogeneity in B has its counterpart for Li. Interpretation: A two end member mixing model members can be proposed : ?11B ?0 ppm and ?11B<= -70 ppm. The value of 0 ppm is still significantly different from the matrix value reported by [6] (+19.2 ppm) and thus the possible contamination of the chondrule by their surrounding matrix is highly unlikely. The second end member should have ?11B and ?^7Li values le-70 ppm and le-50 ppm, respectively, resulting from Li and B produced at high energy by spallation reactions (E >= 100 MeV/nucleon, ?11B =-375 ?^7Li = -830 ppm). References: [1] Chaussidon M., Robert F. (1995) Nature 374, 337-339. [2] Chaussidon M. and Robert F. (1998) Earth Planet Sci. Lett. 164, 577-589. [3] Montmerle T. (1999) MPE Report : Astronomy with Radioactivities, 225-236. [4] McKeegan K., Chaussidon M., Robert F. (2000) Science 289, 1334-1337. [5] Chaussidon M., Robert F. McKeegan K. (2002) Abst. 33th LPSC #1563 [6] Hoppe et al., (2001) MAPS, 36, 1331-1343. [7] Zhai M et al., (1996) Geochim. Cosmochim. Acta 60, 4877-4881.

Robert, F.; Chaussidon, M.

2003-04-01

187

Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites  

Microsoft Academic Search

The degree of compositional variation of fine-grained minerals displayed by the members within any carbonaceous chondrite group (i.e., CI, CM, CV, CR) is a direct reflection of the range of aqueous alteration assemblages present. Matrix and fine-grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another, but not necessarily similar in bulk elemental composition, even

M. Zolensky; R. Barrett; L. Browning

1993-01-01

188

Constraining early processes that lead to planet formation: CAIs and Chondrules  

Microsoft Academic Search

If it were not for the ubiquitous presence of chondrules and CAIs (Ca-Al-rich inclusions) in chondritic meteorites, astophysical theories for the origin of our solar system would not predict their existence. After fine dust was concentrated relative to gas, it was then melted by some unknown high-temperature energetic process within our protoplanetary nebula to produce mm to cm-sized silicate spheres

H. C. Connolly Jr.; D. S. Burnett

2000-01-01

189

Experiments on the consolidation of chondrites and the formation of dense rims around chondrules  

NASA Astrophysics Data System (ADS)

It is generally accepted, that chondrites are formed by coagulation of chondrules and the matrix dust. Such pre-chondrites can be formed in low-velocity collisions and would therefore be more porous than the typical chondrites are. Those chondrites have volume filling factors (porosity) ranging from ?=0.3 (70%) to ?=0.6 (40%). We will present impact experiments into mixtures of chondrule analogs and dust materials to determine the dynamic pressure range under which these can be compacted to achieve porosities found in chondritic meteorites. The second objective of the experiment was to test whether or not fine-grained dust rims around chondrules can be formed due to the dynamic compaction process. In our experiments, aluminum cylinders were used as projectiles to compact the chondrite-analog samples in a velocity range between 165 m/s and 1200 m/s. The resulting impact pressures in the samples fall between ~90 and ~2400 MPa. To measure the achieved porosities of our samples, 25 samples were analyzed using computer-aided tomography. We found volume filling factors to be between ?= 0.70 and ?= 0.99. Additionally, we determined the mean pressure range in which CM chondrites were likely to be compacted and found values between 60 and 150 MPa. As for the high-density rims found around chondrules, we can show that these do not form in dynamic compaction processes. Moreover, we found that for a collision between two pre-chondritic bodies of 0.4< ? < 0.5, the collision velocity for a pressure range of 0.05 GPa to 2 GPa falls between 100 m/s and 2000 m/s, which is within the typical velocity range of the of planetary growth models and agrees with a formation distance of chondrites between 2 and 3 AU at given orbital eccentricities of 0.02 and 0.1 for the pre-chondrites.

Beitz, Eike; Güttler, Carsten; Nakamura, Akiko; Blum, Jürgen

2013-07-01

190

Size distributions and the mass equivalence of chondrules and metal grains in Bjurbole  

NASA Astrophysics Data System (ADS)

Chondrules from four thin sections of the Bjurbole meteorite were measured in reflected light, and a four-gram sample of the meteorite was examined at 100-micron resolution via X-ray tomography in order to give attention to the metal grains. The densities and proportions of Fe-Ni metal and troilite were used to ascertain the mass of the average grain present in Bjurbole; results are presented in tabular form.

Kuebler, Karla E.; McSween, Harry Y.; Carlson, William D.

1997-03-01

191

The Lunar Devitrified Glass Spherules: Implications for the Origin of Meteoritic Chondrules  

NASA Astrophysics Data System (ADS)

Devitrified glass spherules (DGS) from three thin sections of Apollo 14 regolith breccias (14318, 6; 14318, 46 and 14315, 20) have been classified (type X, equant plagioclase, and type Y, plagioclase lathes both in a devitrified mafic mesostasis), the abundance and size distributions determined and their bulk compositions and the compositions of plagioclase and mesostasis in type Y have been determined. The abundance and size distributions of the DGS resembled those of chondrules in the CM chondrite Murchison. Their coarse textures suggest fairly slow cooling (<1 degree C/s). The bulk compositions of the DGS do not resemble any of the regoliths of the Apollo sites, including Apollo 14, or any of the common impact glasses, but resemble those of impact spherules from the lunar meteorites. It is suggested that the DGS are ejecta from the Imbrium impact and that only impact events of this size are capable of producing melt spherules with sufficiently slow cooling rates and the long free flight times required on the moon. Smaller impacts produce glassy spherules and agglutinates. While much remains unclear, difficulties with a nebula origin and new developments in chondrule chronology, asteroid surfaces and impact ejecta behavior, mean that the formation of meteoritic chondrules by impact is a reasonable possibility to explore.

Sears, D. W. G.; Symes, S.; Taunton, A.; Akridge, G.; Huang, S.; Benoit, P.

1996-03-01

192

Minor and trace element partitioning between pyroxene and melt in rapidly cooled chondrules  

SciTech Connect

We present minor and trace element (REE, Sr, Y, and Zr) data for pyroxenes and mesostases in four porphyritic chondrules from the Semarkona ordinary chondrite. Apparent partition coefficients for clinoenstatite, orthoenstatite, pigeonite, and augite are compared with experimental and petrologic data from the literature, and the effects on apparent partition coefficients of the rapid cooling rates at which chondrules crystallized are evaluated. For most elements, the effects of cooling at rates of hundreds of degrees per hour cannot be distinguished from variations in equilibrium data resulting from differences in temperature or composition. However, for LREE apparent partition coefficients are significantly higher than comparable equilibrium data, and the ratio of HREE/LREE partition coefficients is lower, particularly for Ca-poor pyroxene. We attribute this flattening of REE patterns to the effect of rapid cooling. Apparent partition coefficients of all REE and Y in augite are higher than equilibrium data, particularly in one chondrule with a high ALO, content. We suggest that this may be attributed to an increase in the uptake of trivalent trace element cations in the pyroxene crystal structure as a result of charge-balanced substitutions with API cations. 32 refs., 6 figs., 3 tabs.

Jones, R.H. [Univ. of New Mexico, Albuquerque, NM (United States); Layne, G.D. [Univ. of New Mexico, Albuquerque, NM (United States)]|[Woods Hole Oceanographic Institution, MA (United States)

1997-05-01

193

The case for a cognate, polybaric origin for kimberlitic olivines  

NASA Astrophysics Data System (ADS)

Kimberlitic olivines typically show a continuous range in size and texture rather than two discrete populations. The cores of small euhedral olivines commonly provide the template for the final crystal shape, which in turn closely matches morphologies produced by crystallization from a moderately under-cooled magma. Cores and edges of the majority of all olivines define a continuous compositional field, which can be interpreted in terms of Raleigh crystallization. Marked chemical gradients at the olivine margins are linked to rapid physico-chemical changes to the magma associated with loss of volatiles during the late stages of emplacement. Thus, rapid crystallization of groundmass olivines would deplete the magma in Ni, but increase Ca activity. The latter would be enhanced by decreasing pressure coupled with loss of CO2 from the carbonate-bearing kimberlite magma.For mantle olivines and the most refractory olivines in kimberlites (~ Fo94) to be in equilibrium with bulk rock compositions matching those of Mg-rich macrocrystic and aphanitic kimberlites (Mg# ~ 88) requires a mineral-melt Mg-Fe distribution coefficient of 0.47. This is well within the experimentally determined range for this distribution coefficient in carbonate-bearing systems. In southern African post-Gondwana alkaline pipe clusters, the average bulk rock Mg# and composition of the associated most Mg-rich olivine both decrease sympathetically from the interior to the continental margin, which is also consistent with a cognate origin for the olivines.A kimberlite magma following a plausible P-T trajectory relative to the CO2/H2O peridotite solidus would initially experience superheating, resulting in partial resorption of early-formed olivines that crystallized on the cool conduit walls. It would become supersaturated as it crossed the carbonated peridotite "ledge", resulting in tabular and hopper growth forms typical of euhedral olivine cores. With further ascent, the magma would once again become superheated, resulting in partial resorption of these cores. Thus, apparently complex textures and internal zonation patterns of kimberlitic olivines are predicted by a plausible magma P-T trajectory.

Moore, Andy E.

2012-01-01

194

Origin of three-dimensional shapes of chondrules. I. Hydrodynamics simulations of rotating droplet exposed to high-velocity rarefied gas flow  

NASA Astrophysics Data System (ADS)

The origin of three-dimensional shapes of chondrules is an important information to identify their formation mechanism in the early solar nebula. The measurement of their shapes by using X-ray computed topography suggested that they are usually close to perfect spheres, however, some of them have rugby-ball-like (prolate) shapes [Tsuchiyama, A., Shigeyoshi, R., Kawabata, T., Nakano, T., Uesugi, K., Shirono, S., 2003. Lunar Planet. Sci. 34, 1271-1272]. We considered that the prolate shapes reflect the deformations of chondrule precursor dust particles when they are heated and melted in the high velocity gas flow. In order to reveal the origin of chondrule shapes, we carried out the three-dimensional hydrodynamics simulations of a rotating molten chondrule exposed to the gas flow in the framework of the shock-wave heating model for chondrule formation. We adopted the gas ram pressure acting on the chondrule surface of p=10 dyncm in a typical shock wave. Considering that the chondrule precursor dust particle has an irregular shape before melting, the ram pressure causes a net torque to rotate the particle. The estimated angular velocity is ?=140 rads for the precursor radius of r=1 mm, though it has a different value depending on the irregularity of the shape. In addition, the rotation axis is likely to be perpendicular to the direction of the gas flow. Our calculations showed that the rotating molten chondrule elongates along the rotation axis, in contrast, shrinks perpendicularly to it. It is a prolate shape. The reason why the molten chondrule is deformed to a prolate shape was clearly discussed. Our study gives a complementary constraint for chondrule formation mechanisms, comparing with conventional chemical analyses and dynamic crystallization experiments that have mainly constrained the thermal evolutions of chondrules.

Miura, Hitoshi; Nakamoto, Taishi; Doi, Masao

2008-09-01

195

Olivines from Kimberlites and Diamonds: Problem of Origin  

NASA Astrophysics Data System (ADS)

Mg-rich olivine Fo [100Mg/(Mg + Fe)] 85-94 is the principal mineral of kimberlites, peridotite xenoliths and diamond inclusions. It is completely altered in common kimberlites, however, it is absolutely fresh in a huge block from Udachnaya-East kimberlite in Yakutia (Russia). Pioneering studies of this unaltered kimberlite resulted in a discovery of high role of a mantle chlorine along with very low water content (Kamenetsky et al., 2004, Geology, 32: 845-848). Two olivine populations are distinguished, which are represented by oval-rounded unzoned or partly zoned xenocrysts of olivine I (more than 1 mm) and well defined zoned phenocrysts ( 0.05-1.0 mm) of olivine II (e.g. Kamenetsky et al., 2008, J.Petrol., 49: 823-839). The cores of olivine II are compositionally similar to olivine I with Mg# 86-94, but rims of olivine II and partly preserved rims of olivine I have constant Fo values about 89-90. We report here the results of major and minor elements analyses by EPMA of more than 300 grains of olivine I and olivine II, both of cores and rims by high precision approach (Sobolev et al., 2007, Science, 316: 412-417) to minor elements including Ti, Al, Cr, Ca, Mn, Ni, Co using the high sample current and high counting time, which was found optimal to obtain limit of detection about 10 ppm. Several grains of analyzed olivines contain clinopyroxene (cpx) and pyrope (prp) inclusions confirming their high pressure origin. One large olivine I grain contains clusters of cpx ( 33 grains) and prp ( 6 grains) inclusions., having a range in Cr2O3 (1.52- 2.36 wt%) , Al2O3 (0.99-5.53 wt%) and Na2O (1.45-5.96 wt%) for cpx and Cr2O3 (3.51-4.42 wt%) and CaO (5.64-6.61 wt%) for prp, showing disequilibrium in olivine I core, containing 200 ppm Ti. This is completely different from any peridotite xenoliths, confirming the uniqueness of this assemblage. The systematic high Ti ( more than 150 ppm) of all studied cores of olivine grains containing low T (Ca# 43.3-48) cpx and prp inclusions confirm the listed differences from all olivines from peridotites and diamonds (e.g. Sobolev et al., 2009, Lithos, 112S: 701-713.). Earlier, similar Ti abundance was reported only for olivines from dunite nodules in Greenland kimberlites (e.g. Arndt et al., 2010, J. Petrol., 51: 573-602).We suggest that Ti-bearing olivine, represented more that 70% of studied samples, is a part of high pressure pyrope lherzolite assemblage, which was formed and grew during the formation and early evolution of kimberlites

Sobolev, N. V.; Sobolev, A. V.; Tomilenko, A. A.; Kovyazin, S. V.; Kuzmin, D. V.

2011-12-01

196

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

SciTech Connect

CO{sub 2} sequestration via carbonation of widely available low-cost minerals, such as olivine, can permanently dispose of CO{sub 2} in an environmentally benign and a geologically stable form. The paper reports 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 NaHCO{sub 3} at T {approx} 185{sup o}C and P{sub CO{sub 2}} {approx} 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 the observation that carbonation increases dramatically with solid particle concentration in stirred experiments. Multiphase hydrodynamic calculations are combined with experiment to 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 SiO{sub 2} structure that can permit diffusion of key reactants. Mitigating passivating layer effectiveness is critical to enhancing carbonation and lowering sequestration process cost. 30 refs., 7 figs.

Hamdallah Bearat; Michael J. McKelvy; Andrew V.G. Chizmeshya; Deirdre Gormley; Ryan Nunez; R.W. Carpenter; Kyle Squires; George H. Wolf [Arizona State University, Tempe, AZ (United States). Center for Solid State Science, Science and Engineering of Materials Graduate Program, Departments of Mechanical and Aerospace Engineering and Chemistry and Biochemistry

2006-08-01

197

Multiple Olivine Phase Transitions in the Shocked Martian Meteorite Tissint  

NASA Astrophysics Data System (ADS)

In some melt regions of Tissint olivine dissociated into silicate perovskite + magnesiowüstite while in others it transformed into ringwoodite. These different reactions and reaction mechanisms can be explained by local temperature variations.

Sharp, T. G.; Hu, J.; Walton, E. L.

2013-09-01

198

Olivine diogenites: The mantle of the eucrite parent body  

SciTech Connect

Two olivine-rich Antarctic diogenites (ALH A77256 and ALH 84001) of the howardite-eucritediogenite (HED) meteorite association have olivine/pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites. Based on chemical data and petrological analysis, these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body (EPB). Mineral assemblages in these olivine-rich diogenites record a continuum in thermal histories from initial partial melting (1150-1200{degree}C) to subsolidus re-equilibration (795 {plus minus} 55{degree}C). The small number of olivine-rich diogenites known hints that only the outer portion of the EPB has been sampled.

Sack, R.O.; Azeredo, W.J.; Lipschutz, M.E. (Purdue Univ., IN (USA))

1991-04-01

199

A Natural Example of Olivine LPO Variation With Shear Strain  

NASA Astrophysics Data System (ADS)

Understanding mantle rheology, seismic anisotropy, and strain localization requires knowledge of the evolution of olivine lattice preferred orientations (LPOs) as a function of strain and melt content. The Josephine Peridotite in southwest Oregon is ideal for analysis of the interaction of deformation and melt, due to the presence of shear zones with associated melt migration structures. We present results on the variation of olivine LPO with shear strain in these shear zones. The LPO evolution with proximity to the shear zone center provides a link between experimental data and LPO evolution models, which can be applied to the interpretation of mantle seismic anisotropy and to models of melt extraction at mid-ocean ridges. Results for harzburgites from the largest Josephine shear zone, which is 100m wide and contains syn-deformational dunite, indicate that the olivine LPO rotates in the shear zone so that the [100] maxima lies parallel to the shear direction. Outside of the shear zone, the harzburgites have a pre-existing LPO. Shear strain for the Josephine samples is calculated from the deflection angle of the regional pyroxene foliation. By ~100% shear strain, the olivine LPO evolves so that the [100] axis is aligned with the flow direction. These results on olivine LPO evolution during shear agree with the experimental data of Zhang and Karato (1995). They extend observations of olivine LPO to much higher strains and lower stresses. At face value, the Josephine shear zone data also agree with predictions from polycrystal plasticity models that incorporate the effects of dynamic recrystallization (Ribe and Yu, 1991; Wenk and Tomé, 1999). The variation of olivine LPO during simple shear is important for correctly interpreting seismic anisotropy. Our results indicate how much strain is necessary for olivine LPO to align in the flow direction. In conjunction with modelling studies, this information can be used to interpret the kinematics of deformation in regions where mantle anisotropy varies spatially.

Warren, J. M.; Hirth, G.

2005-12-01

200

Petrogenesis of olivine-phyric shergottite Yamato 980459, revisited  

Microsoft Academic Search

Primitive magmas provide critical information on mantle sources, but most Martian meteorites crystallized from fractionated melts. An olivine-phyric shergottite, Yamato 980459 (Y-980459), has been interpreted to represent a primary melt, because its olivine megacrysts have magnesian cores (Fo84–86) that appear to be in equilibrium with the Y-980459 whole-rock composition based on Fe–Mg partitioning. However, crystal size distribution (CSD) plots for

Tomohiro Usui; Harry Y. McSween Jr.; Christine Floss

2008-01-01

201

Waveform effects of a metastable olivine tongue in subducting slabs  

Microsoft Academic Search

We constructed velocity models of subducting slabs with a kinetically-depressed olivine ? ?- and ?-spinel transition, and examined the effect that such structures would have on teleseismic P waveforms using a full-wave finite-difference method. These two-dimensional calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge-shaped, low-velocity metastable olivine tongue (MOTO) to

John E. Vidale; Quentin Williams; Heidi Houston

1991-01-01

202

Waveform effects of a metastable olivine tongue in subducting slabs  

Microsoft Academic Search

Velocity models of subducting slabs with a kinetically-depressed olivine to beta- and gamma-spinel transition are constructed, and the effect that such structures would have on teleseismic P waveforms are examined using a full-wave finite-difference method. These 2D calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge-shaped, low-velocity metastable olivine tongue (MOTO)

John E. Vidale; Quentin Williams; Heidi Houston

1991-01-01

203

Spatial and Compositional Variations of Olivine in Terra Tyrrhena, Mars  

Microsoft Academic Search

Global modeling of thermal and VIS\\/NIR spectra of the Martian highlands reveal that many materials contain 10 - 20% olivine that spans a relatively large range of Mg\\/Fe contents (forsterite numbers 100 - 35). We examine the olivine-bearing locales in Terra Tyrrhena using TES-derived mineralogies, spectral variation maps made from THEMIS IR images, THEMIS and MOC visible images, MOLA topographic

W. C. Koeppen; V. E. Hamilton

2007-01-01

204

Dislocation recovery in fine-grained polycrystalline olivine  

Microsoft Academic Search

The rate of static dislocation recovery in Fo90 olivine has been studied under conditions of high temperature and controlled atmosphere in compressively deformed polycrystals\\u000a hot-pressed from synthetic (sol–gel) and natural (San Carlos) precursor powders. The sol–gel olivine, containing a small fraction\\u000a of orthopyroxene, was deformed to a final strain of 19% with a maximum differential stress of 266 MPa whereas the

R. J. M. Farla; H. Kokkonen; J. D. Fitz Gerald; A. Barnhoorn; U. H. Faul; I. Jackson

2011-01-01

205

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 128°C 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

206

Olivine Instability: An Experimental View of Mechanism of Deep Earthquakes  

NASA Astrophysics Data System (ADS)

Olivine (¦Á-(Mg,Fe)2SiO4) is the major constituent of the upper mantle and the ocean lithosphere. In subduction zone, where the earthquakes happen, the rheology of slab is mainly controlled by that of olivine. Several different mechanisms for deep focus earthquakes have been suggested, which include olivine instability (Bridgman, 1936; Orowan, 1960; Post, 1977; Ogawa, 1987; Hobbs and Ord, 1988; Kao and Chen, 1995), shear-induced melting (Griggs, 1954, 1972; Griggs and Handin, 1960; Griggs and Baker, 1969), phase transformation (Bridgman, 1945; Benioff, 1963; Meade and Jeanloz, 1989), dehydration of hydrous specimens (Meade and Jeanloz, 1991), and olivine metastability-induced anticrack (Green and Houston, 1995). Since the low temperature of the ¡°cold¡± slab, which can be as low as 600¡ãC in transition zone, olivine may still exist there and thus its shear instability may still be the possible mechanism for the deep-focus earthquakes. In our experimental study on deformation of San Carlos olivine at subduction zone conditions carried out on a D-DIA apparatus, Sam85 at X17B2, NSLS, we observed that the transitional temperature between regimes of insensitive to temperature and sensitive to temperature can be as high as 900¡ãC or even higher for the annealed polycrystal olivine sample, while that for unannealed sample can be as low as 450¡ãC. Our results for the unannealed sample are consistent to the result of Raterron et al (2004), which is concluded from the relaxation experiments. The annealed and unannealed olivine can be present the natural olivine in non-fault systems and that in pre-existing fault systems in subduction zone, respectively. We therefore propose a new olivine instability model with a ¡°sandwich¡± formation for the deep focus earthquakes: In this model the pre-existing fault system is surrounded by the no-fault systems. When the slab dives down, the olivine in both systems undergoes a stress- build-up process and can hold very high stress in both cases. However, as it keeps diving to the transition zone, the slab is heated and its temperature arrives at the boundary temperature from the insensitive temperature regime to the sensitive to temperature regime for the olivine in pre-existing fault system. As a result, while the olivine in non-fault system is still in regime of insensitive to temperature and can still hold the built high stress, the olivine in pre-existing fault system can not hold the built stress any more and gives a stress release. The pre- existing fault is re-active and heat from the re-active fault accelerates the ongoing process. Earthquake happens.

Long, H.; Weidner, D.; Li, L.; Chen, J.; Wang, L.

2007-12-01

207

Tow Bar for Aircraft.  

National Technical Information Service (NTIS)

The tow bar includes a rigid, elongated beam having a hitch located at each of its opposite ends for accommodating a coupling of the tow bar between a gear truck and a towing vehicle. Interposed between the center mass of the tow bar and the end thereof t...

P. Baldridge

1978-01-01

208

I-Xe dating of chondrules from the Qingzhen unequilibrated enstatite chondrite  

NASA Astrophysics Data System (ADS)

It is shown that in Qingzhen, the I-Xe chronometer is decoupled from, and more stable than, both Ar-Ar and Rb-Sr chronometers, which were reset by unknown processes in the 1.4-2.8 Ga period. Because the range of I-Xe ages obtained are comparable to those observed in most unequilibrated ordinary chondrite chondrules, the enstatite chondrite region of the nebula was subject to the same processes at the same time as more oxidized regions of the nebula.

Ash, R. D.; Gilmour, J. D.; Whitby, J.; Prinz, M.; Turner, G.

1997-03-01

209

A Method for the Flux Growth of Intermediate Composition Olivine  

NASA Astrophysics Data System (ADS)

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 and olivine compositions are wide ranging. Unfortunately, the amount of samples from the Moon and Mars is extremely limited; with only Apollo and Luna mission samples, lunar meteorites, and Martian meteorites available for direct mineralogic and petrologic characterization. These characterizations have provided a useful basis for many spectroscopic and modeling interpretations, but many fundamental questions remain and may only be answerable through either direct observation of rocks or by analog experimentation. The motivation for our work on growth of intermediate olivine crystals, therefore, is to create realistic starting material for use in Mars and Moon analog experiments. A variety of crystal growth methods have been previously used to synthesize olivine, including: the Czochralski-pulling (CZ) method, the floating-zone image furnace (FZ) method, and sol-gel processing techniques. Both the CZ and FZ methods have the advantage of producing large crystals, but the growth apparatus and regulation of reduced atmospheric conditions during growth can make these techniques both time and cost intensive. Sol-gel processing to produces olivine fibers is a useful chemical technique, but obtaining larger grain sizes can be difficult. An alternative method for crystal growth is through the use a flux, which can grow crystals relatively quickly and inexpensively. We have grown synthetic crystals of intermediate composition (Fo30-Fo70) olivine using a lithium borate (B5Li3O9) flux. The starting material was a mixture of magnesite (MgCO3), siderite (FeCO3), and quartz (SiO2) powder in a 1:1:1 ratio. The advantage of using siderite is that the iron is already present in the ferrous form. Upon heating and decarbonation, this mixture represents a bulk composition of Fo50 (FeMgSiO4) olivine. Flux was then added to the starting material mixture so that the final mixture was 50% starting material and 50% flux by weight. This final mix was then placed in a platinum crucible that was heated to 1100 °C in a vacuum furnace for three days. The use of a vacuum furnace ensured that conditions remained reducing during crystal growth. The result was growth of olivine crystals that are generally small (< 1 mm in length) and have euhedral crystal form. These crystals have been analyzed by electron microprobe, and are systematically zoned from core to rim with Mg-rich cores (˜Fo70) transitioning to Fe-rich rims (˜Fo30). This zoning represents an expected heterogeneity due to olivine growth from a finite reservoir of starting material. The flux growth of this intermediate composition olivine was primarily a 'proof of concept' experiment, and showed that olivine crystals can be grown using a flux under sub-solidus conditions. Additional crystal growth experiments would be useful to gauge the response of olivine to changes in temperature, duration, and composition of the flux + starting material mixture.

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

2009-05-01

210

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

211

B-type Olivine Fabric induced by Grain Boundary Sliding  

NASA Astrophysics Data System (ADS)

Olivine fabric, or Lattice Preferred Orientation (LPO), in naturally deformed peridotite largely contributes to the seismic anisotropy of the upper mantle. LPO usually results from motion of intra-crystalline dislocations during dislocation creep. In this case, experimental and numerical data indicate that the degree of mineral alignment (fabric strength) increases with increasing finite strain. Here, we show an opposite trend suggesting that olivine fabric can also result from a different deformation mechanism. Based on documentation of olivine LPOs in peridotites of a kilometer-scale mantle shear zone in the Ronda massif (Spain), we highlight a transition from a flow-parallel [a]- axis LPO (A-type fabric) to a flow-normal [a]-axis LPO (B-type fabric). While dislocation sub-structures indicate that A-type fabric results from dislocation motion, we conclude that the B-type fabric does not originate from dislocation creep, but instead from grain boundary sliding (GBS) because: (1) dislocation sub-structures remain consistent with the A-type slip system in all samples; (2) the fabric transition from A-type to B-type correlates with decreasing fabric strength despite increasing finite strain; and (3) our observations are supported by experiments that document B-type fabric in olivine aggregates where deformation involves a component of GBS. The B-type olivine fabric has a specific signature in term of seismic anisotropy, and hence, our results may have important implications for interpreting upper mantle structures and deformation processes via seismic observations.

Précigout, Jacques; Hirth, Greg

2013-04-01

212

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

213

Petrology and mineralogy of the Yamato-86751 CV3 chondrite  

NASA Astrophysics Data System (ADS)

The Y-86751 chondrite (CV3) consists of fine-grained Ca- and Al-rich inclusions (CAIs), amoeboid olivine inclusions (AOIs), spinel-rich inclusions, chondrules with and without dark rims, dark inclusions, isolated minerals, metal-sulfide aggregates, and matrix. Olivines in chondrules without dark rims and AOIs coexist with magnetite and show strong zoning from a magnesian core to a ferroan rim. Spinels in spinel-rich inclusions show similar zoning. This zoning seems to be caused by exchange reaction of olivine and spinel with an oxidized nebular gas prior to the accretion onto the parent body, and the Mg/Fe diffusion in olivines and spinels took place at a temperature of about 830-860 K. At the same time, enstatite in chondrules without dark rims was replaced by ferroan olivine at the grain boundaries. This feature sugests that chondrules without dark rims, fine-grained CAIs, spinel-rich inclusions, and AOIs have experienced oxidation in an oxidizing nebular gas. The oxygen fugacity of the oxidized nebular gas was greater than 10-27.3 bars at about 830 K, being more than 104x larger than that of the canonical nebular gas. Magnetite occurs in the Y-86751 matrix in close association with Ni-rich taenite and Co-rich metal, and it was produced under a condition with the oxygen fugacity of approx. 10-38 bars at a temperature of about 620-650 K. On the other hand, olivines in chondrules with dark rims and dark inclusions are magnesian and rich in MnO. They do not show such strong zoning. Probably they were in equilibrium with a nebular gas under a redox condition different from the oxidized nebular gas that produced the zoned olivines in chondrules without dark rims.

Murakami, Toshio; Ikeda, Yukio

1994-05-01

214

Dislocation recovery in fine-grained polycrystalline olivine  

NASA Astrophysics Data System (ADS)

The rate of static dislocation recovery in Fo90 olivine has been studied under conditions of high temperature and controlled atmosphere in compressively deformed polycrystals hot-pressed from synthetic (sol-gel) and natural (San Carlos) precursor powders. The sol-gel olivine, containing a small fraction of orthopyroxene, was deformed to a final strain of 19% with a maximum differential stress of 266 MPa whereas the San Carlos specimen was deformed to 15% strain and 260 MPa differential stress. Small samples cut from these deformed materials were annealed under high-temperature, controlled atmosphere conditions, for different durations to allow partial recovery of the dislocation sub-structures. Oxidative-decoration of the microstructural features, followed by backscattered electron imaging at 5 kV and image analysis, was used to determine dislocation density. The variation of dislocation density ? with time t at absolute temperature T was fitted to a second-order rate equation, in integral form, 1/?( t) - 1/?(0) = kt with k = k 0 exp(- E a/RT). The activation energy E a of the recovery process is 240 ± 43 and 355 ± 81 kJ mol-1 for sol-gel and San Carlos olivine polycrystals, respectively. The measured rates are one to two orders of magnitude lower than those reported in previous studies on natural single crystal olivine. The difference may be explained by several factors such as high dislocation densities measurable from large areas at high magnification for the SEM and the technique used to estimate dislocation densities. Comparison between fine-grained sol-gel olivine and the coarser-grained San Carlos olivine aggregate did not indicate that grain boundaries play an important role in dislocation recovery, but the absence of grain boundaries might also have contributed to the high dislocation recovery rates previously measured for single crystals.

Farla, R. J. M.; Kokkonen, H.; Fitz Gerald, J. D.; Barnhoorn, A.; Faul, U. H.; Jackson, I.

2011-05-01

215

Dislocation recovery in fine-grained polycrystalline olivine  

NASA Astrophysics Data System (ADS)

The rate of static dislocation recovery in Fo90 olivine has been studied under conditions of high temperature and controlled atmosphere in compressively deformed polycrystals hot-pressed from synthetic (sol-gel) and natural (San Carlos) precursor powders. The sol-gel olivine, containing a small fraction of orthopyroxene, was deformed to a final strain of 19% with a maximum differential stress of 266 MPa whereas the San Carlos specimen was deformed to 15% strain and 260 MPa differential stress. Small samples cut from these deformed materials were annealed under high-temperature, controlled atmosphere conditions, for different durations to allow partial recovery of the dislocation sub-structures. Oxidative-decoration of the microstructural features, followed by backscattered electron imaging at 5 kV and image analysis, was used to determine dislocation density. The variation of dislocation density ? with time t at absolute temperature T was fitted to a second-order rate equation, in integral form, 1/?(t) - 1/?(0) = kt with k = k 0 exp(-E a/RT). The activation energy E a of the recovery process is 240 ± 43 and 355 ± 81 kJ mol-1 for sol-gel and San Carlos olivine polycrystals, respectively. The measured rates are one to two orders of magnitude lower than those reported in previous studies on natural single crystal olivine. The difference may be explained by several factors such as high dislocation densities measurable from large areas at high magnification for the SEM and the technique used to estimate dislocation densities. Comparison between fine-grained sol-gel olivine and the coarser-grained San Carlos olivine aggregate did not indicate that grain boundaries play an important role in dislocation recovery, but the absence of grain boundaries might also have contributed to the high dislocation recovery rates previously measured for single crystals.

Farla, R. J. M.; Kokkonen, H.; Fitz Gerald, J. D.; Barnhoorn, A.; Faul, U. H.; Jackson, I.

2010-12-01

216

Rheology of olivine at high temperature and high pressure  

NASA Astrophysics Data System (ADS)

Two major contributions were accomplished in this dissertation. From the scientific aspect, the rheological properties of olivine at mantle condition were investigated by defining the flow mechanism and quantifying the high-pressure and high temperature flow law for olivine. From the technical development aspect, a breakthrough to measure macroscopic differential stress and strain rate in situ under mantle pressure and temperature condition was recorded in this dissertation. Conventional deformation methods in defining the flow law of olivine have to face factors of large uncertainties of differential stress measurements and/or limited confining pressure for deformation. These two difficulties were overcome by conducting high-temperature (up to 1473 K) deformation experiments of polycrystalline olivine (average grain size <5 micron) at pressure up to 8 GPa using large-volume high-pressure apparatus and synchrotron x-ray radiation. Strain rates of the deformation from x-ray radiograph of the sample itself were measured. Image analysis software for strain rate measurement was developed. Macroscopic differential stress of olivine was measured by monitoring the elastic strain of lattice spacing. The algorithms and programs were developed to convert the elastic strain of samples deformed under uniaxial compression into the macroscopic differential stress. In summary, the flow law for olivine at high temperature and high pressure has been defined as dislocation creep, assisted by dynamic recrystallization. The activation volume is characterized as 0˜5 cm3/mol. The technology developed in the course of this dissertation research opens new possibilities for rheological studies in the future. The accuracy of the results is comparable to the best rheological studies that are carried out in any system at the present.

Li, Li

217

Grinding methods to enhance the reactivity of olivine  

SciTech Connect

The Albany Research Center (ARC) conducted studies of mechanical activation by conventional and ultra-fine grinding techniques to enhance olivine reactivity in mineral carbonation reactions. Activated olivine is one of several solid feed materials used at ARC in reactions with carbon dioxide to form carbonate minerals. This paper compares grinding techniques via energy demand data and product characteristics, including particle size distributions, surface areas, full width at half maximum (FWHM) XRD analyses, and particle morphology by SEM analyses. Reactivity was gauged by percent conversion to carbonate in subsequent carbonation tests.

Summers, Cathy A.; Dahlin, David C.; Rush, Gilbert E.; O'Connor, William K.; Gerdemann, Stephen J.

2004-01-01

218

Search for extinct 36Cl: Vigarano CAIs, the Pink Angel from Allende, and a Ningqiang chondrule  

NASA Astrophysics Data System (ADS)

We have searched for excesses of 36S derived from the decay of extinct 36Cl in sodalite, a secondary Cl-rich mineral, in Ca-Al-rich inclusions (CAIs) from the Vigarano and Allende CV3 chondrites and in a chondrule from the Ningqiang carbonaceous chondrite. The presence of sodalite in two CAIs from Vigarano and its absence from surrounding CAI fragments suggests sodalite formation after CAI fragmentation. As for sodalite in the Allende Pink Angel CAI, oxygen isotopic compositions have been interpreted as indicative of high temperature interactions, thus suggesting formation prior to accretion to the parent body, probably in a nebular setting. Sodalite in the Ningqiang chondrule is considered to have formed via alkali-Ca exchange, which is believed to have occurred before accretion to the parent body. Sodalites in the Vigarano CAIs and in the Ningqiang chondrule show no clear evidence for the presence of radiogenic 36S. The inferred 2 ? upper limits for 36Cl/ 35Cl at the time of sodalite formation are 1.6 × 10 -6 (Vigarano CAIs) and 3.3 × 10 -6 (Ningqiang chondrule), respectively. In the Pink Angel CAI sodalite exhibits small 36S excesses which weakly correlate with 35Cl/ 34S ratios. The inferred 36Cl/ 35Cl ratio of (1.8 ± 2.2) × 10 -6 (2 ? error) is lower than that found by Hsu et al. [Hsu, W., Guan, Y., Leshin, L. A., Ushikubo, T. and Wasserburg, G. J. (2006) A late episode of irradiation in the early solar system: Evidence from extinct 36Cl and 26Al in meteorites. Astrophys. J. 640, 525-529], thus indicative of heterogeneous distribution of 36Cl in this CAI. Spallation reactions induced by energetic particles from the young Sun are suggested for the origin of 36Cl, similar to the case of 10Be. While 10Be appears to be present in roughly equal abundance in all studied CAIs, our study indicates the level of 36Cl abundances to be variable so that there seems to be no simple relationship between 10Be and 36Cl. This would be expected if trapped cosmic rays rather than Early Solar System spallation were the dominant source of 10Be in the Early Solar System, since their contribution to 36Cl would have been tiny. If the variability of 36Cl abundances is caused by temporal differences in the alteration that formed sodalite, sodalite in the Vigarano CAIs and in the Ningqiang chondrule may have formed ?0.5 and ?0.2 Ma after formation of the sodalite in the Ningqiang CAI analyzed by Lin et al. [Lin, Y., Guan, Y., Leshin, L. A., Ouyang, Z. and Wang, D. (2005) Short-lived chlorine-36 in a Ca- and Al-rich inclusion from the Ningqiang carbonaceous chondrite. Proc. Natl. Acad. Sci. USA 102, 1306-1311]. The Pink Angel sodalite that we analyzed may have formed ˜0.3 Ma after formation of the sodalite in the Pink Angel analyzed by Hsu et al. [Hsu, W., Guan, Y., Leshin, L. A., Ushikubo, T. and Wasserburg G. J. (2006) A late episode of irradiation in the early solar system: Evidence from extinct 36Cl and 26Al in meteorites. Astrophys. J. 640, 525-529]. The estimated temporal differences suggest that alteration extended over at least 0.5 Ma. If previous works showing very low initial 36Cl/ 35Cl in the Allende CAIs and a H3 chondrite CAI are also considered, then alteration processes may have been more than 1.7 Ma.

Nakashima, Daisuke; Ott, Ulrich; Hoppe, Peter; El Goresy, Ahmed

2008-12-01

219

Laboratory spectra of amorphous and crystalline olivine: An application to comet Halley IR spectrum.  

National Technical Information Service (NTIS)

Among the various silicates proposed as components of cosmic dust grains, olivine is considered one of the most likely materials. In this work we present the infrared spectra of three different types of olivine grains: crystalline, amorphous, and syntheti...

A. Blanco V. Orofino E. Bussoletti S. Fonti L. Colangeli

1990-01-01

220

Ringwoodite Rims Around Olivine Fragments in Melt Vein of Antarctic Chondrite GRV 022321: Transformation Kinetics  

NASA Astrophysics Data System (ADS)

Ringwoodite rims around olivine in shocked veins of chondrites GRV 022321 were investigated by electron microscopes to elucidate mechanisms of transformation and Mg-Fe diffusion of olivine to ringwoodite, and estimate shock duration using kinetics.

Xie, Z.; Li, X.; Sharp, T. G.; DeCarli, P. S.

2013-09-01

221

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

NASA Astrophysics Data System (ADS)

We have examined the relationships between T112 particle and amoeboid olivine aggregates. Slight enrichment of Fe in olivine rim and associated chromites suggest that T112 may have experienced a minor degree of metamorphism.

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

2012-03-01

222

Bar Code Labels  

NASA Astrophysics Data System (ADS)

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

223

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

Microsoft Academic Search

The Baffin Island picrites are highly magnesian (<=22 wt% 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

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

2004-01-01

224

Search for olivine in the Vesta surface from the Dawn-VIR hyperspectral data  

NASA Astrophysics Data System (ADS)

We study the possibility to discern the infrared spectral signature of olivine in pyroxene based multimineralic mixtures. Different spectral indexes are selected and tested onto laboratory controlled spectral set of mixtures. The best index able to detect even low amount of olivines, will be applied to the VIR-Dawn dataset to search for olivine on the surface of Vesta.

Palomba, E.; Longobardo, A.; De Sanctis, M. C.; Ammannito, E.; Capaccioni, F.; Capria, M. T.; Farina, M.; Frigeri, A.; Tosi, F.; Zambon, F.; McSween, H. Y.; Mittlefehldt, D. H.; Russell, C. T.; Beck, A.; Toplis, M. J.; McFadden, L.; Cloutis, E.

2012-09-01

225

Hydroxide in olivine: A quantitative determination of the absolute amount and calibration of the IR spectrum  

Microsoft Academic Search

Olivine is an important host of hydrogen in the Earth's upper mantle, and the OH abundance in this mineral determines many important physical properties of the planet's interior. To date, natural and experimentally hydrated olivines have been analyzed by uncalibrated spectroscopic methods with large (±100%) uncertainties in accuracy. We determined the hydrogen contents of three natural olivines by 15N nuclear

David R. Bell; George R. Rossman; Joachim Maldener; Denis Endisch; Friedel Rauch

2003-01-01

226

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 Köhler; Jens Hartmann; Dieter A. Wolf-Gladrow

2010-01-01

227

Hydroxyl in mantle olivine xenocrysts from the Udachnaya kimberlite pipe  

Microsoft Academic Search

The incorporation of hydrogen in mantle olivine xenocrysts from the Udachnaya kimberlite pipe was investigated by Fourier-transform infrared spectroscopy and secondary ion mass spectrometry (SIMS). IR spectra were collected in the OH stretching region on oriented single crystals using a conventional IR source at ambient conditions and in situ at temperatures down to ?180°C as well as with IR synchrotron

Monika Koch-Müller; Stanislav S. Matsyuk; Dieter Rhede; Richard Wirth; Natasha Khisina

2006-01-01

228

Surface modification of olivine by H + and He + bombardment  

Microsoft Academic Search

Laboratory simulations of solar wind irradiation of olivine, a constituent of ordinary chondritic meteorites and S-type asteroids, show a dramatic chemical reduction of surface iron and, to a lesser extent, silicon. Earth's atmosphere oxidizes any reduced iron instantaneously, whereas irradiated material on the surface of an asteroid would remain reduced. Changes in optical reflectance, due to metallization of the surface,

C. A. Dukes; R. A. Baragiola; L. A. McFadden

1999-01-01

229

Investigating Asteroids on the Olivine-to-Pyroxene Continuum  

NASA Astrophysics Data System (ADS)

The spectral characteristics of asteroids having a strong 1 um absorption feature are attributed to the presence of pyroxene, olivine, or both. Distinguishing between pyroxene and olivine requires measuring the strength of an additional absorption band centered near 2 um. Accurate measurements of both bands are now possible using SpeX, a new generation low- to medium-resolution infrared spectrograph in operation as a facility instrument at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Visible-wavelength surveys such as SMASSII (Bus 1999; Ph. D. thesis) show a continuum of properties in terms of spectral slope and the depth of the 1 um band, as measured over the wavelength interval 0.4-1.0 um. With SpeX, we are now examining whether this apparent continuum is also evident within spectra extending out to 2.5 um. Taking advantage of our ability to infer mineralogy based on near-infrared spectral information, we are also seeking to understand the extent to which this spectral continuum is rooted in a smooth gradient in olivine-pyroxene mineralogy. We are estimating olivine-pyroxene ratios using the Modified Gaussian Model (MGM) of Sunshine et al. (1990, JGR 95, 6955).

Bus, S. J.; Sunshine, J. M.; Binzel, R. P.; Burbine, T. H.

2001-11-01

230

Challenges in detecting olivine on the surface of 4 Vesta  

NASA Astrophysics Data System (ADS)

Identifying and mapping olivine on asteroid 4 Vesta are important components to understanding differentiation on that body, which is one of the objectives of the Dawn mission. Harzburgitic diogenites are the main olivine-bearing lithology in the howardite-eucrite-diogenite (HED) meteorites, a group of samples thought to originate from Vesta. Here, we examine all the Antarctic harzburgites and estimate that, on scales resolvable by Dawn, olivine abundances in putative harzburgite exposures on the surface of Vesta are likely at best in the 10-30% range, but probably lower due to impact mixing. We examine the visible/near-infrared spectra of two harzburgitic diogenites representative of the 10-30% olivine range and demonstrate that they are spectrally indistinguishable from orthopyroxenitic diogenites, the dominant diogenitic lithology in the HED group. This suggests that the visible/near-infrared spectrometer onboard Dawn (VIR) will be unable to resolve harzburgites from orthopyroxenites on the surface of Vesta, which may explain the current lack of identification of harzburgitic diogenite on Vesta.

Beck, Andrew W.; McCoy, Timothy J.; Sunshine, Jessica M.; Viviano, Christina E.; Corrigan, Catherine M.; Hiroi, Takahiro; Mayne, Rhiannon G.

2013-07-01

231

Micromechanical modeling of the viscoplastic behavior of olivine  

NASA Astrophysics Data System (ADS)

Efforts to couple mantle flow models with rheological theories of mineral deformation typically ignore the effect of texture development on flow evolution. The fact that there are only three easy slip systems for dislocation glide in olivine crystals leads to strong mechanical interactions between the grains as the deformation proceeds, and subsequent development of large viscoplastic anisotropy in polycrystals exhibiting pronounced Lattice Preferred Orientations. Using full-field simulations for creep in dry polycrystalline olivine at high temperature and low pressure, it is shown that very large stress and strain rate intragranular heterogeneities can build up with deformation, which increase dramatically with the strength of the hard slip system (included for the purpose of enabling general deformations). Compared with earlier nonlinear extensions of the Self-Consistent mean-field theory to simulate polycrystal deformation, the "Second-Order" method is the only one capable of accurately describing the effect of intraphase stress heterogeneities on the macroscopic flow stress, as well as on the local stress- and strain rate fluctuations in the material. In particular, this approach correctly predicts that olivine polycrystals can deform with only four independent slip systems. The resistance of the fourth system (or accommodation mechanism), which is likely provided by dislocation climb or grain boundary processes as has been observed experimentally, may essentially determine the flow stress of olivine polycrystals. We further show that the "tangent" model, which had been used extensively in prior geophysical studies of the mantle, departs significantly from the full-field reference solutions.

Castelnau, O.; Blackman, D. K.; Lebensohn, R. A.; Ponte CastañEda, P.

2008-09-01

232

Deformation of olivine in torsion under hydrous conditions  

NASA Astrophysics Data System (ADS)

We performed torsional deformation experiments on pre-hydrated fine-grained olivine aggregates using an innovative experimental assembly to investigate water weakening in mantle rocks at high shear strains. San Carlos olivine powder was cold-pressed and then hot-pressed under hydrous conditions, producing aggregates with average grain sizes of 7 or 15 ?m. Deformation experiments were performed in a high-resolution gas-medium apparatus equipped with a torsional actuator, under a confining pressure of 300 MPa, a temperature of 1200 °C, and constant shear strain rates ranging from 8 × 10-5 to 1.4 × 10-4 s-1. Maximum shear stresses range from 150 to 195 MPa. These values are 30% lower relative to those determined in previous torsion experiments on dry, fined-grained dunites under similar conditions. Textures and microstructures of the starting and deformed specimens were characterized by scanning and transmission electron microscopy. All deformed aggregates exhibit a shape-preferred orientation marking a foliation and lineation, as well as a reduction in mean grain size from 15 ?m down to 3-4 ?m due to dynamic recrystallization. Olivine crystallographic fabrics developed rapidly (? < 0.1), but their strength, characterized by the J-index, is low compared to naturally deformed peridotites or to polycrystalline olivine deformed at similar finite shear strains under dry conditions. The crystallographic fabrics are consistent with deformation by a dislocation accommodated creep mechanism with activation of multiple {0 k l}[1 0 0] systems, among which the (0 1 0)[1 0 0] slip system is dominant, and minor participation of the (0 1 0)[0 0 1] slip system. Transmission electron microscopy confirmed the occurrence of dislocations with [1 0 0] and [0 0 1] Burgers vectors in most grains. Analysis of unpolarized infrared spectra indicates that hydrogen concentration in the olivine lattice is below the saturation level of 18 ppm wt H2O, which is similar to those typically observed in spinel-bearing peridotite xenoliths, and also provide evidence for water-rich inter-granular material trapped in pores and grain boundaries. Seismic properties computed from the CPO observations correspond to those most commonly observed in naturally deformed mantle peridotites with fast P-wave propagation and S-wave polarization subparallel to the shear direction. These torsion experiments on fine-grained olivine polycrystals under hydrous conditions indicate that water weakening under lithospheric conditions is linked to various defects with hydrogen in the olivine structure, as well as with water-derived species in grain boundaries or pores.

Demouchy, Sylvie; Tommasi, Andréa; Barou, Fabrice; Mainprice, David; Cordier, Patrick

2012-08-01

233

Activities of olivine slip systems in the upper mantle  

NASA Astrophysics Data System (ADS)

We investigated the effect of pressure (P) on olivine [1 0 0](0 0 1) and [0 0 1](1 0 0) dislocation slip systems by carrying out deformation experiments in the Deformation-DIA apparatus (D-DIA) on single crystals of Mg2SiO4 forsterite (Fo100) and San Carlos (SC) olivine (Fo89), at P ranging from 5.7 to 9.7 GPa, temperature T = 1473 and 1673 K, differential stress ? in the range 140-1500 MPa, and in water-poor conditions. Specimens were deformed in axisymmetry compression along the so-called [1 0 1]c crystallographic direction, which promotes the dual slip of [1 0 0] dislocations in (0 0 1) plane and [0 0 1] dislocations in (1 0 0) plane. Constant ? and specimen strain rates (??) were monitored in situ by synchrotron X-ray diffraction and radiography, respectively. Comparison of the obtained high-P rheological data with room-P data, previously reported by Darot and Gueguen (1981) for Fo100 and Bai et al. (1991) for SC olivine, allowed quantifying the activation volume V* in classical creep power laws. We obtain V* = 9.1 ± 1.6 cm3/mol for Fo100. For SC olivine, we obtain V* = 10.7 ± 5.0 cm3/mol taking into account the oxygen-fugacity uncertainty during the high-P runs. These results, combined with previous reports, provide complete sets of parameters for quantifying the activities of olivine dislocation slip systems. Extrapolation of the rheological laws obtained for SC olivine crystals to conditions representative of natural deformations show that [1 0 0](0 1 0) slip largely dominates deformation in the shallow upper mantle. At depths greater than ˜65 km along a 20-Ma oceanic geotherm or ˜155 km along a continental geotherm, the dual activity of [1 0 0](0 0 1) and [0 0 1](1 0 0) slips becomes comparable to that of [1 0 0](0 1 0) slip. At depths greater than ˜240 km, [0 0 1](0 1 0) slip becomes dominant over all other investigated slip systems. Such changes in olivine dislocation-slips relative activity provide a straightforward explanation for the seismic anisotropy contrast and attenuation with depth observed in the Earth's upper mantle.

Raterron, Paul; Girard, Jennifer; Chen, Jiuhua

2012-06-01

234

Open-system degassing, gas fluxing, and the growth and entrainment of olivine during small volume mafic eruptions: A case study of Volcan Jorullo, central Mexico  

NASA Astrophysics Data System (ADS)

Olivine-hosted melt inclusions from mafic arc volcanoes commonly contain highly variable H2O and CO2 contents that are best explained by olivine crystallization over a wide range of depths during ascent and degassing. An excellent example of this is found in deposits from the 1759-1774 eruption of Jorullo volcano in the subduction-related Trans-Mexican Volcanic Belt. Jorullo's earliest lavas are primitive (9.3 wt% MgO, Fo86-91 olivine), and lava compositions evolved over time as a result of crystal fractionation (Luhr and Carmichael, 1985). We analyzed melt inclusions in Mg-rich olivine from a 5-meter-thick proximal ash fall sequence. Melt inclusions from the basal tephra have variable H2O (<1-5.2 wt%) and CO2 (44-900 ppm), corresponding to crystallization pressures of <100 bars to 4.2 kb. This indicates that olivine crystallized over a range of depths extending from the mid-crust to very shallow levels beneath the volcano. Relations between H2O and incompatible K, Ti, and P, and comparison to experimental phase equilibria demonstrates that olivine crystallization is driven primarily by the effects of H2O loss from the melt during ascent. A puzzling feature of the H2O and CO2 data at Jorullo and other mafic arc volcanoes is that CO2 concentrations do not decrease as rapidly with degassing as is predicted by degassing models. A likely explanation involves open-system degassing in which relatively CO2-rich vapor fluxes upwards through the conduit. This vapor is probably released by crystallizing and degassing magma at greater depths within the system. Melt inclusions from the upper part of the tephra section at Jorullo have lower H2O (0.2-1.4 wt%) than inclusions from the basal tephra and no detectable CO2, suggesting shallow crystallization of degassed magma toward the end of the violent-Strombolian-style eruptions. The change in olivine crystallization depths over time probably results from evolution of the conduit system. During the early, pre-eruption stage, as magma fractures its way upward and creates a conduit system, olivine crystallizes over a wide range of depths, trapping variably degassed melts. These crystals are probably stored in the complex dike and sill network that is growing beneath the volcano. When magma finally breaks out at the surface, initiating the eruption, magma flux increases, and magma moving upward through the conduit system entrains olivine crystals stored in the dike and sill network. Over time, the conduit system becomes localized, so early-formed olivine from greater depths are no longer entrained, and crystallization occurs mainly at shallow depths beneath the volcano. Such a model may have general applicability to many mafic eruptions and helps to explain how olivine crystals formed at diverse depths and of sometimes diverse compositions become incorporated into a batch of erupting magma.

Wallace, P. J.; Johnson, E. R.; Delgado Granados, H.

2005-12-01

235

Olivine as a key to unlocking Kilauea's magmatic history  

NASA Astrophysics Data System (ADS)

Olivine is a ubiquitous mineral in Hawaiian basalts. It is on the liquidus at pressures <0.5 GPa and has the potential to record numerous petrologic processes including the histories of parental magma composition changes, crystal fractionation, magma mixing and crustal contamination. These processes are recorded in olivine composition (major and trace elements, and isotopes) and by melt inclusions trapped within olivine. Here we focus on Kilauea's historical lavas (1820-present) to evaluate the magmatic history one of world's most active volcanoes. Kilauea has shown dramatic variations in it eruptive rate and style (from vigorous, quiescent effusion in 1820 to infrequent explosive activity in 1924 and then to its highest effusion during the last decade). Eruption rates correlate with whole-rock compositional and isotopic variations (P-G 1999). Most Kilauea lavas have normally zoned olivine in equilibrium with whole-rock compositions which belies complex magma chamber processes. Parental magma composition changed rapidly based on the heterogeneity of melt inclusion compositions in higher Mg olivine (>86 forsterite). Melt inclusions from single eruptions show wider variation in ratios of Ca/Al and Nb/Y than observed in lavas for the historical period. Thus, the mantle source is heterogeneous on a small scale and small batches of compositionally distinct melt are frequently delivered to the volcano. These magma batches undergo mixing, fractionation and after caldera collapses (e.g.1924), crustal contamination in the summit reservoir. This work demonstrates that an Ernstonian approach, using minerals to understand petrologic processes, is key to unlocking Kilauea's magmatic processes. Pietruszka, A.P. and Garcia, M.O., 1999, J. Petrol. 40, 1321-1342.

Garcia, M. O.; Norman, M. D.

2011-12-01

236

Rheological studies of olivine under high pressure and temperature  

NASA Astrophysics Data System (ADS)

The rheological properties of San Carlos olivine and forsterite were studied under simultaneous high pressure and temperature conditions on the cubic anvil high-pressure apparatus. Using the synchrotron x-ray diffraction method, elastic strain, stress and strain rate information were extracted, and the flow laws on olivine were derived by fitting the experimental data. The microstructures of samples quenched under high pressure at different temperatures were observed using transmission electron microscopy (TEM). The rheology of lab-dry San Carlos olivine was studied up to 9 GPa and 800°C. Our results show that lab-dry San Carlos olivine reaches yield point around 5.4 GPa differential stress at room temperature. The yield stress increases with the loading pressure and decreases with the increasing temperature. A dramatic decrease in strength occurs around 430--500°C that reflects a change of the flow mechanism. Two different flow laws at 9 GPa at different temperature regimes have been derived based on the experimental data. A 3? -sigma-T deformation map was constructed using the derived flow laws. TEM observations reveal that c dislocation glide and recrystallization are the active deformation processes responsible for the stress instability above 400°C. It is believed that this stress instability can provide experimental constraints for the possible existence of a run-away plastic instability process that may be the cause of the deep earthquakes. The variation of the differential stress with temperature and pressure was studied on both lab-dry and dehydrated forsterite samples up to 9 GPa confining pressure and 1000°C. Lab-dry forsterite exhibits identical rheological behaviors at similar pressure and temperature conditions as that of San Carlos olivine. The dehydrated forsterite sample behaves quite similarly to the lab-dry sample at room temperature, and appears to be stronger at high temperature. The water content in the sample can affect the critical temperature where the stress instability would be operative.

Wu, Yujun

2000-10-01

237

Kamacite and olivine in ordinary chondrites: Intergroup and intragroup relationships  

SciTech Connect

The three principal groups of ordinary chondrites (OCs), H (high total Fe), L (low total Fe), and LL (low total Fe, low metallic Fe), constitute {approximately}80% of all meteorites observed to fall. In going from H to L to LL chondrites, the abundances of siderophile elements decrease and the degree of oxidation increases. The proportion of oxidized Fe (i.e., FeO in silicates) increases at the expense of metallic Fe. Because Fe is more readily oxidized than Ni or Co, bulk metal becomes increasingly rich in Ni and Co (e.g., Prior, 1916). Equilibrated LL chondrites are thus characterized by high FeO/(FeO + MgO) ratios in olivine and low-Ca pyroxene, high taenite/kamacite ratios, and the occurrence of Co-rich kamacite. The present study reports high-precision electron microprobe analyses of olivine and kamacite in a large suite of OCs. The purpose of the study was sixfold: (1) rigorously define the compositional ranges of these phases for each OC group, (2) identify anomalous OCs whose olivine and/or kamacite compositions lie outside the established ranges, and hence may not belong to the three main OC groups, (3) characterize the phases in the chondritic clasts of the Netschaevo iron meteorite and determine how closely related Netschaevo is to OCs, (4) determine if there are intragroup variations of olivine and kamacite compositions with petrologic type, (5) identify those OCs as fragmental breccias that contain some olivine and/or kamacite grains with aberrant compositions, and (6) search for new metallic Fe-Ni phases with extreme compositions. An expected by-product of this investigation was that a few meteorites that previously had not been well-characterized would be reclassified.

Rubin, A.E. (Univ. of California, Los Angeles (USA))

1990-05-01

238

Reaction-induced weakening of plagioclase olivine composites  

NASA Astrophysics Data System (ADS)

The localisation of strain into natural ductile shear zones is often associated with the occurrence of metamorphic reactions. In order to study the effects of solid solid mineral reactions on plastic deformation of rocks, we have investigated the shear deformation of plagioclase olivine composites during the reaction plagioclase + olivine ? orthopyroxene + clinopyroxene + spinel (± garnet). Microstructures of plagioclase olivine composites were studied after shear deformation experiments in a Griggs apparatus. Experiments were performed on anorthite forsterite (An Fo) and labradorite forsterite (Lab Fo) composites at 900 °C, confining pressures between 1000 1600 MPa and with constant shear strain rates of ˜5 × 10-5 s-1. In absence of reaction, Lab Fo composites are stronger than pure olivine and labradorite end-members that deform with a high temperature plasticity mechanism. Lab Fo composites strain harden due to the inhibition of extensive recrystallisation by interphase boundaries. In An Fo composites, the reaction induces strain weakening by a switch from dislocation creep to grain size sensitive deformation mechanisms through the development of fine-grained (size < 0.5 ?m) polyphase reaction products. Interconnecting layers of reaction products accommodate most of the applied strain by grain size sensitive creep. Recovery processes are pronounced during syndeformational reaction: original anorthite and olivine dynamically recrystallise by subgrain rotation and bulging recrystallisation. Presumably, the dynamic recrystallisation is caused by reduced stress conditions and partitioning of strain and strain rates between the new reaction products and the relict An Fo grains. The results of our experiments are in good agreement with natural observations of shear localisation in the lower crust and upper mantle, and imply that anhydrous mineral reactions can be important causes for localisation of deformation.

de Ronde, A. A.; Stünitz, H.; Tullis, J.; Heilbronner, R.

2005-11-01

239

Geoengineering potential of artificially enhanced silicate weathering of olivine  

PubMed Central

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 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 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.

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

2010-01-01

240

Bar Graph Sorter  

NSDL National Science Digital Library

In this activity, students make bar graphs by sorting shapes either by shape or by color. This activity allows students to explore how to sort data to make bar graphs. 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

241

Ring Bar Grizzly.  

National Technical Information Service (NTIS)

The patent application relates to a ring bar grizzly used as a materials handling device to enable the jam-free transfer of loose rocks or other materials at the discharge end of a generally horizontal conveyor. Normally, this ring bar grizzly is used in ...

A. T. Fisk

1980-01-01

242

Multi Bar Graph  

NSDL National Science Digital Library

In this activity, students enter in data to be represented in a double bar graph. Multi bar graphs allow the student to compare multiple characteristics of different subjects like population for different continents over time. 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

243

Oskri Recalls “Coconut Bar Dark Chocolate”, “Coconut Bar ...  

Center for Food Safety and Applied Nutrition (CFSAN)

... of Lake Mills, WI is recalling “Coconut Bar Dark Chocolate”, “Coconut Bar Dark Chocolate Minis”, “Fig Dark Chocolate Bars” and “Almond Dark ... More results from www.fda.gov/food/recallsoutbreaksemergencies/recalls

244

Phase separation in a chondrule fragment from the Piancaldoli (LL3) chondrite  

SciTech Connect

A chondrule fragment has been found in the Piancaldoli (LL3) chondrite that contains prolate silica spheroids embedded in a matrix with an approximate low-Ca pyroxene (Fs14) composition. Although compositional and textural evidence supports metastable coexistence of two liquid phases, neither phase is preserved as glass. The matrix has a fan-spherulitic texture, and many of the silica spheroids contain dendritic cristobalite. Silica interdendrite voids near the two-phase interface do not modify the smooth curvilinear outline of the interface, indicating that the iron magnesium silicate matrix had congealed prior to cristobalite crystallization from the silica-rich phase. Available data suggest that this immiscibility is formed upon cooling from the melt. A temperature near 1275/sup 0/-1300/sup 0/C, based on phase composition, is thought to be the temperature at which these coexisting liquids last approached metastable equilibrium.

Planner, H.N.

1985-01-01

245

Controls on helium solubility in olivine at low pressures  

NASA Astrophysics Data System (ADS)

Experiments on the solubility of helium in olivine have been conducted over a range of conditions to evaluate the thermodynamic controls on helium partitioning during melting. The experiments were performed at 1 to 150 atm. total pressure at temperatures between 1350 and 1550° C. Helium partial pressures ranged from 0.5 to 150 atm. The effect of oxygen fugacity was examined by running experiments at both the QFM and Ni-NiO buffer, and by using both Fe-bearing and Fe-free olivines. Temperature: Experiments at 1350, 1450 and 1550° C (Ni-NiO buffer) show a clear decreasing solubility of helium with temperature, as expected for a gas dissolving in a solid. In contrast, previous experiments on basaltic melts show little change of helium solubility with temperature. Therefore the olivine-melt D value decreases steadily with temperature. Linear regression yields the equation DHe=-8.8e-6T+ 0.014 (with R2 > 0.999), where T is in degrees C. Using the van't Hoff equation, this implies an enthalpy of solution of -2.0 kJ/mole and an entropy of solution of -1.97 J/mole K. Pressure: Experiments on powdered samples at helium partial pressures of 0.5 and 150 atmospheres suggest a Henry's law constant between 1e-6 and 3e-6 STP cc/g/atm. This value is around 2 orders of magnitude lower than the Henry's law constant for basaltic melts, consistent with the higher density of olivine. Note that these values should be taken as preliminary as only two helium partial pressures have been studied so far and there are large uncertainties in analyzing powdered samples. Oxygen Fugacity: Experiments on Fe-bearing and Fe-free olivine as well as at varying oxygen fugacity indicate that at least some He is located in vacancies associated with Fe3+ in the olivine crystal lattice. A single experiment at the QFM buffer suggests a DHe at 1 atm. of ~0.001, a factor of 2-3 lower than at Ni-NiO. Assuming that the measured Henry's law constant is valid at high pressure, that mantle melting takes place between temperatures of 1200 and 1450° C and that fO2 conditions are near the QFM buffer, our experiments suggest D values during mantle melting of 0.001 to 0.002.

Parman, S. W.; Kurz, M. D.; Hart, S. R.; Grove, T. L.

2005-12-01

246

Magmatic versus metamorphic origin of olivine-plagioclase coronas  

NASA Astrophysics Data System (ADS)

An SEM, REE, and mineral Sm-Nd isotope study on olivine-plagioclase coronas in the Vestre Dale gabbro, Norway, was carried out in order to solve the temporal relationships within these coronas. It is demonstrated that in contrast to common models, corona formation is a multistage, late-magmatic process, starting with the formation of orthopyroxene by (partial) dissolution of olivine, followed by the nucleation and rapid outward growth of orthopyroxene+spinel symplectites at its outer margin, and concluded by replacement of this precursory outer shell by calcic amphibole. Isotopic equilibrium between inner shell orthopyroxene and the magmatic assemblage, and the REE contents of orthopyroxene and outer shell amphibole also provide strong arguments for a magmatic origin, with the local availability of fractionated magma acting as a limiting factor. The absence of replacement of intercumulus clinopyroxene by amphibole also favours a late stage magmatic rather than a metamorphic origin for corona amphibole.

de Haas, Geert-Jan; Nijland, Timo; Valbracht, Peter; Maijer, Cees; Verschure, Rob; Andersen, Tom

2002-05-01

247

Grinding methods to enhance the reactivity of olivine  

SciTech Connect

The Albany Research Center (ARC) conducted studies of mechanical activation by conventional and ultrafine grinding techniques to enhance olivine reactivity in mineral carbonation reactions. Activated olivine is one of several solid feed materials used at ARC in reactions with carbon dioxide to form carbonate minerals. This paper compares grinding techniques via energy demand data and product characteristics, including particle size distributions, surface areas, full-width-at-half-maximum (FWHM) XRD analyses, and particle morphology by SEM analyses. Reactivity was calculated by percent conversion to carbonate in subsequent carbonation tests. Particle size reduction has the greatest impact on reactivity, and wet grinding is more energy efficient than dry grinding. Large additional inputs of energy to increase surface area or reduce crystallinity do not result in proportional improvements in reactivity.

Summers, Cathy A.; Dahlin, David C.; Rush, Gilbert E.; O'Connor, William K.; Gerdemann, Stephen J.

2005-08-01

248

Visualizing frozen point defect tracks in Fe-containing olivines  

NASA Astrophysics Data System (ADS)

Using a combination of first-principles calculations and Monte Carlo simulations, we show that Fe-containing silicates such as olivines naturally offer a way for visualizing tracks left by diffusing vacancies. Fe in its 2+ and 3+ valency states prefers two distinct cation sites in the olivine structure. Vacancies formed at the cationic M sites, cause neighboring Fe ions in their normally occurring Fe2+ state to change valency to Fe3+, compensating for the charge imbalance and reducing energy costs, consequently altering the local site preference of Fe. Once the vacancy diffuses away, Fe atoms remain stuck in their metastable location producing a microscopic record of the vacancy's trajectory. Our results may be verified using high-resolution transmission electron microscopy, combined with electron energy-loss spectroscopy.

Chatterjee, S.; Saha-Dasgupta, T.; Sengupta, S.

2012-04-01

249

Olivine and pyroxene-rich deposits in Holden Crater, Mars  

NASA Astrophysics Data System (ADS)

Holden crater is a ~150 km diameter crater centered at 326 E, 26S breached in the south by Uzboi Vallis. Holden has been proposed as a possible landing site for the Mars Science Laboratory (MSL) rover and has been the subject of intense scrutiny due to its potential as a paleolake basin. Near the region where Uzboi Vallis breaches the southern Holden Crater wall are layered rocks that have been suggested to be aqeously deposited. Additionally, fan-shaped deposits originate in the southern and western crater walls that have been interpreted as alluvial fans and fan deltas. New analyses of THEMIS and TES data indicate that both the basement and layered rocks - those interpreted to have been deposited in an aqueous environment - near the breach point of Holden crater are olivine and pyoxene- rich. Based on THEMIS IR imagery, these units have a higher thermal inertia than the surrounding terrain. The higher-TI units correspond with lighter-toned layered units seen in THEMIS Vis and MOC imagery that also have a distinct mafic signature in THEMIS daytime IR false-color decorrelation stretch images. The fan deposit in western Holden Crater, which has been proposed as a specific landing site for MSL may also have an elevated olivine abundance based on TES data. High olivine and pyroxene abundances in the sedimentary units of Holden crater do not preclude the presence of water in the history of the crater. However, based on analysis of TES and THEMIS data over the region, there is no evidence for extended chemical weathering present at the surface. Olivine-rich bedrock is likely to be a regional property as it is also present in chaos terrain to the northeast of Holden which is the source of the Landon Vallis outflow channel. These regions should be considered high priority targets for future investigations by OMEGA and CRISM.

Glotch, T. D.

2006-12-01

250

Nickeliferous sulfides in xenoliths, olivine megacrysts and basaltic glass  

Microsoft Academic Search

The composition of olivine and nickeliferous sulfide inclusions from a selection of mafic and ultramafre rocks, xenoliths and megacrysts, including picritic basalts from Kilauea Volcano, Hawaii, kimberlite from Fayette County, Pennsylvania, and megacrysts from Mount Shasta, California are compared with the mean experimental value of the distribution coefficient for Ni\\/Fe exchange (KD3=32). Only nine of the forty five olivipe\\/bulk-sulfide pairs

Michael E. Fleet; William E. Stone

1990-01-01

251

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 µm 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 µm 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

252

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

253

Bar Code Label Requirements  

Center for Biologics Evaluation and Research (CBER)

... Blood and blood components must be labeled with with specific machine-readable bar code information by April 26th, 2006. ... More results from www.fda.gov/biologicsbloodvaccines/developmentapprovalprocess/advertisinglabelingpromotionalmaterials

254

Experimental deformation of olivine single crystals at lithospheric temperatures  

NASA Astrophysics Data System (ADS)

Rheological properties of mantle minerals and rocks at temperatures (T) appropriate to much of Earth's lithosphere have remained poorly constrained, even though past experimental studies on olivine single crystals and polycrystalline aggregates have quantified the high-temperature creep mechanisms (T > 1200°C). Consequently, we have performed deformation experiments on crystals of San Carlos olivine at lower temperatures, from 900° to 1200°C, in triaxial compression along the [101]c direction. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at differential stresses of 100 to 500 MPa. Several samples were deformed at constant displacement rate and others at constant load, in order to provide insight into possible effects of work-hardening. Under the deformation conditions investigated, little evidence of work-hardening was observed. The data follow a power-law dependence on stress, as in previous high-temperature deformation studies. The samples were, however, considerably weaker than predicted by the experimentally determined high-temperature constitutive equation for olivine crystals of this orientation from the study of Bai et al. (1991). The mechanical behavior correlates instead with the weaker of the two mechanisms (flow laws) that contribute to the high-temperature constitutive equation. Thus, our experiments demonstrate that published high-temperature constitutive equations overestimate the strength of lithospheric mantle and that the transition to low-temperature creep occurs at lower temperatures than previously inferred.

Demouchy, Sylvie; Schneider, Stephen E.; Mackwell, Stephen J.; Zimmerman, Mark E.; Kohlstedt, David L.

2009-02-01

255

The effect of water on the electrical conductivity of olivine.  

PubMed

It is well known that water (as a source of hydrogen) affects the physical and chemical properties of minerals--for example, plastic deformation and melting temperature--and accordingly plays an important role in the dynamics and geochemical evolution of the Earth. Estimating the water content of the Earth's mantle by direct sampling provides only a limited data set from shallow regions (<200 km depth). Geophysical observations such as electrical conductivity are considered to be sensitive to water content, but there has been no experimental study to determine the effect of water on the electrical conductivity of olivine, the most abundant mineral in the Earth's mantle. Here we report a laboratory study of the dependence of the electrical conductivity of olivine aggregates on water content at high temperature and pressure. The electrical conductivity of synthetic polycrystalline olivine was determined from a.c. impedance measurements at a pressure of 4 GPa for a temperature range of 873-1,273 K for water contents of 0.01-0.08 wt%. The results show that the electrical conductivity is strongly dependent on water content but depends only modestly on temperature. The water content dependence of conductivity is best explained by a model in which electrical conduction is due to the motion of free protons. A comparison of the laboratory data with geophysical observations suggests that the typical oceanic asthenosphere contains approximately 10(-2) wt% water, whereas the water content in the continental upper mantle is less than approximately 10(-3) wt%. PMID:17066032

Wang, Duojun; Mookherjee, Mainak; Xu, Yousheng; Karato, Shun-ichiro

2006-10-26

256

Olivine crystals align during diffusion creep of Earth's upper mantle.  

PubMed

The crystallographic preferred orientation (CPO) of olivine produced during dislocation creep is considered to be the primary cause of elastic anisotropy in Earth's upper mantle and is often used to determine the direction of mantle flow. A fundamental question remains, however, as to whether the alignment of olivine crystals is uniquely produced by dislocation creep. Here we report the development of CPO in iron-free olivine (that is, forsterite) during diffusion creep; the intensity and pattern of CPO depend on temperature and the presence of melt, which control the appearance of crystallographic planes on grain boundaries. Grain boundary sliding on these crystallography-controlled boundaries accommodated by diffusion contributes to grain rotation, resulting in a CPO. We show that strong radial anisotropy is anticipated at temperatures corresponding to depths where melting initiates to depths where strongly anisotropic and low seismic velocities are detected. Conversely, weak anisotropy is anticipated at temperatures corresponding to depths where almost isotropic mantle is found. We propose diffusion creep to be the primary means of mantle flow. PMID:24132289

Miyazaki, Tomonori; Sueyoshi, Kenta; Hiraga, Takehiko

2013-10-17

257

Rheology of olivine and the strength of the lithosphere  

SciTech Connect

In order to throw some light on the rheological behavior of the upper mantle of the Earth, a detailed series of high-temperature deformation experiments has been performed on olivine single crystals at 1 atm pressure under highly controlled thermodynamic conditions. The effects of stress, temperature, oxygen fugacity and orthopyroxene activity on the deformation rate of olivine have been carefully measured for the major high-temperature slip systems. These experimental results have been extrapolated to the pressures and strain rates of the upper mantle to provide new insight into the mechanical behavior of the mantle and a better constrained approach to extrapolation of laboratory deformation data to the conditions present in the upper mantle. The authors suggest that extrapolations in stress provide the most reliable means for extending laboratory creep data to upper mantle strain rates. They also predict that, in the dislocation creep field, the bulk of the strain in olivine in the upper mantle is accommodated by the (010)(100) slip system. In addition, true mantle strengths are probably most accurately modeled using the experimental data for samples oriented favoring the (010)(001) slip system. However, the reliable prediction of mantle strengths requires highly accurate temperature versus depth relationships and good indications of the local oxygen fugacity in the mantle.

Mackwell, S.J. (Pennsylvania State Univ. (USA)); Bai, Q.; Kohlstedt, D.L. (Cornell Univ. (USA))

1990-01-01

258

Iron Currency-Bars  

Microsoft Academic Search

IN NATURE of May 19, p. 372, reference is made to iron currency-bars and ``early British water-clocks.'' The discovery of the true nature of the currency-bars is not, as is implied, a recent one, but was made in 1905 by Mr. Reginald Smith (see his paper, Proceedings of the Society of Antiquaries, vol. xx., pp. 179-94). Similarly, the ``early British

O. G. S. Crawford

1921-01-01

259

{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

260

LA-ICP-MS mapping of olivine from the Brahin and Brenham meteorites: Complex elemental distributions in the pallasite olivine precursor  

NASA Astrophysics Data System (ADS)

To investigate the early history of olivine from the Main-Group pallasites Brahin and Brenham, we have spatially mapped their trace-element distributions using laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICP-MS). Brahin olivine interiors contain ˜100-200 ?m patches enriched in Cr, Al, Ti, V, Sc and Ga, separated by linear enrichments of P; these structures bear no relation to current crystal morphologies. Rather, cross-cutting relationships suggest they predate olivine-metal mixing. Brenham olivine also has internal variations for these elements. By contrast, Ni and Co concentrations in olivine from both meteorites decrease near crystal margins, as expected for freezing-in of profiles formed during diffusive re-equilibration with metal during cooling. Brenham olivine also has decreasing Al, Cr and Ti near the margin. Correlations between concentrations of Cr and Al exist for individual Brahin olivine grains, but do not hold over multiple grains, indicating a heterogeneous precursor. Al and Ti are correlated over multiple grains in Brahin, interpreted as Ti cations decorating pre-existing Al-defects. In Brenham olivine, similar geochemical trends exist, but the Cr-Al relationship probably represents both grain margin effects and pre-existing internal heterogeneity. The preservation of structure for elements which are normally fast diffusers in olivine hinges on coupled substitutions involving Al, which along with P diffuses much more slowly than most other elements under some conditions. Al concentrations in olivine are low and variable (3-33 ppm) which is inconsistent with crystallisation from a normal silicate melt; Al-in-olivine thermometers indicate that pallasite olivine was formed in a low-temperature environment. Following its delivery to the magma ocean/core-mantle boundary, Al-P systematics were not substantially modified. Assuming diffusivities for Al and P that are similar to Si (since they reside in the same crystallographic site) and temperatures of 1600-1650 K (from the melting point of the metal and the absence of orthopyroxene in pallasites) an upper limit on the residence time of pallasite olivine of ˜1 Ma can be inferred by the persistence of trace element detail over scales of 100 ?m. Following the olivine-metal mixing event, homogeneous Ni and Co distributions were modified by diffusion; Cr and V were partially modified; Al and P were essentially unchanged.

McKibbin, Seann J.; O'Neill, Hugh St. C.; Mallmann, Guilherme; Halfpenny, Angela

2013-10-01

261

Effects of organic ligands and temperature variations on the kinetics of olivine carbonation and the formation of associated secondary phases  

NASA Astrophysics Data System (ADS)

The slow dissolution kinetics of Mg-rich silicates has become a critical issue for the geologic CO2 sequestration in basic rocks. Previous batch carbonation studies on San Carlos olivine [1] performed in CO2 saturated water (at 90°C and P CO2 = 280 bar) have focused on the role that secondary phases, such as amorphous silica layers (SiO2 (am)), have on the transport of reactants from and to the reactive surfaces. The fluid composition remained roughly constant over the duration of the experiment, close to saturation with respect to amorphous silica and with a [Mg2+]/[SiO2 (aq)] ratio close to stoechiometric release, suggesting a passivation of the olivine surface by the silica layer. In order to accelerate the dissolution process, organic ligands such as citrate and acetate were added to the solutions and tested at 1M and 0.1M concentrations in similar batch experiments. An intrinsic increase of the dissolution rate of olivine was expected [2], [3] prior to the formation of a passivating silica layer. Preliminary results confirm this idea since Mg was released in non-stoechimoetric proportions with respect to SiO2 (aq) (found to be in equilibrium with SiO2 (am)). Similarly, a slight increase of temperature (from 90°C to 120°C) accelerated the reaction kinetics as well, possibly impacting the textural properties of SiO2 (am). Current TEM investigations are directed to confirming a possible link between the observed increase of the rate and textural properties of secondary phases. In addition, because carbonate minerals have a retrograde solubility, thermodynamical modelling suggests that this temperature increase should allow the fluid to reach saturation with respect to carbonates before reaching saturation with respect to SiO2 (am). Enough Mg can therefore be released to initiate the formation of carbonates before the silica precipitates and passivates the olivine surface. [1] Daval et al (2011), Chemical Geology, v.284, p.193-209 [2] Grandstaff, D.E. (1986) In: Colman, S.M., Dethier, D.P. Eds., Rates of Chemical Weathering of Rocks and Minerals. 41-57. [3] Krevor and Lackner (2009) Energy Procedia v 1, 4867-4871.

Sissmann, O.; Daval, D.; Martinez, I.; Brunet, F.; Verlaguet, A.; Pinquier, Y.; Guyot, F. J.

2011-12-01

262

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

263

Petrogenesis and Nd-, Pb-, Sr-isotope geochemistry of the Cenozoic olivine melilitites and olivine nephelinites ("ankaratrites") in Madagascar  

NASA Astrophysics Data System (ADS)

The Cenozoic ankaratrites of the Alaotra, Takarindoha-Vatomandry and Votovorona (NE Ankaratra) volcanic fields, Madagascar, range from olivine (± monticellite) melilitites, through olivine-melilite nephelinites to olivine (± leucite) nephelinites. The rocks show significant compositional ranges in their coexisting magmatic minerals (olivine-group minerals, melilite, clinopyroxene, nepheline, leucite, Ba-phlogopite, perovskite, ilmenite, spinels, apatite), and evidence of distinct parental magmas, often in different facies of the same vent. Primitive compositions (high Mg#, Cr and Ni concentrations) are found in each volcanic district, and a few lavas contain mantle xenoliths or xenocrysts. The rocks show enrichment in the most strongly incompatible elements (e.g., Ba and Nb up to 200 times primitive mantle, La/Ybn = 24 to 40), with troughs at K and smooth, decreasing patterns towards the least incompatible elements in mantle-normalized diagrams. The Nd-Pb-Sr isotope geochemistry indicates a marked heterogeneity of the mantle sources of the various districts (e.g., 206Pb/204Pb = 18.68-18.77, 87Sr/86Sr = 0.704011-0.704207 for the Alaotra-Votovorona districts; 206Pb/204Pb = 19.04-19.14, 87Sr/86Sr = 0.703544-0.704017 for the Takarindoha-Vatomandry districts), with significant differences to other Cenozoic mafic volcanic rocks of northern Madagascar. The genesis of the Madagascan ankaratrites is related to rifting events which triggered low-degree partial melting of a garnet peridotite enriched in dolomite and incompatible-element-rich phases, in the lowermost lithosphere. Despite marked geochemical similarities, the source of the Madagascan melilitites bears no isotopic similarity to the HIMU-related sources of melilitites of eastern and southern Africa.

Melluso, Leone; Le Roex, Anton P.; Morra, Vincenzo

2011-12-01

264

Partition of Ni between olivine and sulfide and its application to Ni-Cu sulfide deposits  

Microsoft Academic Search

Equilibration of natural olivine with (Fe, Ni)S in sealed silica glass tubes yields a value for the distribution constant for Ni\\/Fe exchange (KD3) of 27.7±3.5, for 1,200° C, product olivine and sulfide compositions in the ranges 96 to 97 mol% Fo and 15 to 70 mol% NiS, respectively, and run durations of 28 days. Electron microprobe analysis of product olivine

M. E. Fleet; N. D. MacRae

1983-01-01

265

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

Microsoft Academic Search

The Baffin Island picrites are highly magnesian (?22 wt% 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

266

Rheology of San Carlos Olivine at High Pressure and Low Temperature  

Microsoft Academic Search

Olivine, alpha -(Mg,Fe)2SiO4, represents a large fraction of the cold lithospheric material sinking into the mantle in subduction zones. The low-temperature (typically T<800\\\\deg C) olivine rheology, thus, must control the rheology of subducting slabs. Despite its importance, olivine low-temperature rheology is still poorly documented, mainly because of the experimental complications resulting from the high differential yield stress (sigma m) of

P. Raterron; Y. Wu; D. J. Weidner

2001-01-01

267

Phosphorus zoning in olivine of Kilauea Iki lava lake, Hawaii  

NASA Astrophysics Data System (ADS)

Kilauea Iki lava lake was formed when the lavas of the 1959 summit eruption of Kilauea volcano ponded in Kilauea Iki pit crater, as described by [1]. The main chamber of this lake has been drilled repeatedly from 1960 to 1981 as the lake has cooled and crystallized and partial descriptions of core can be found in [2-7]. The bulk of the core consists of a gray, olivine-phyric basalt matrix [3]. Rapid diffusion of divalent cations through olivine at magmatic temperatures can delete information on early-formed zoning and thus information on early magmatic history, recorded in olivine during its growth, is often largely lost [8-11]. In the last years many studies [8-11] have shown that natural olivine, terrestrial and extraterrestrial, from several localities and rock types can preserve a complex zoning in P (sometimes associated with Cr and Al). Simple crystallization experiments conducted by [10] and [11] were able to replicate these features (i.e., sector and oscillatory zoning). Here, we describe P, Cr and Al zoning in olivine from the 1981 drilling of Kilauea Iki lava lake hole #1 (KI81-1) [6]. K? X-ray intensity maps and major and minor element quantitative analyses were obtained using the Caltech JEOL JXA-8200 electron microprobe. We acquired P, Cr, Al, Fe and Ti X-ray maps simultaneously at 15 kV and 400 nA, a beam diameter of 1 ?m, pixel spacing of 1-2 ?m, and count times of 420-1500 msec/step were used depending on the dimension of the crystal. 15 kV and 40 nA with a beam diameter of 1 ?m were used to collect quantitative analyses. P2O5 contents of the Iki olivines range from below detection limit to 0.30 wt%. Zoning in phosphorus, based on X-ray intensity maps, was observed in all olivines we examined. The P zoning patterns of the olivines display several styles. P shows oscillatory zoning comparable to that seen in terrestrial and extraterrestrial igneous olivines and in experimentally grown olivine [8-11]; high P regions, inside the crystals, outline low P chambers and P enriched zones were also observed; near the margins of the crystals is possible to find the presence of discontinuous sets of P-enriched bands that generally outline euhedral crystal forms; some crystals are characterized by P-enriched ghosts of relict crystals in their interior that are associated with probable undercooling and/or with an initial pulse of rapid crystal growth [8, 10]. Phenocrysts and microphenocrysts are frequently unzoned in major and minor divalent cations (Fe, Mg, Mn, Ca, Ni), but all are zoned in P. Variations in Cr and Al correlate spatially with P but are much fainter or absents, in some crystal the P-enriched bands are superimposed with small crystals of chromite (?1 ?m) aligned along the P zoning. Probably these chromites were formed by precipitation from the original Cr and Al bands. In no case was observed Ti zoning. [1] Richter D.H. et al. (1970) US Geol Surv Prof Pap 537-E, 73 p. [2] Richter D.H., Moore J.G. (1966) US Geol Surv Prof Pap 537-B, 26 p. [3] Helz R.T. (1980) Bull Volcanol 43-4, 675-701. [4] Helz R.T. et al. (1984) US Geol Surv Open File Rep 84-484, 72 p. [5] Hardee H.C. et al. (1981) Geophys Res Lett 8, 1211-1214. [6] Helz R.T., Wright T.L. (1983) US Geol Surv Open File Rep 83-326, 66 p. [7] Helz R.T. (1987) Geochem Soc Spec Pub 1, 241-258. [8] Beckett J.R. et al. (2008) LPSC abs. 1726. [9] Mccanta M.C. et al. (2008) LPSC abs. 1807. [10] Milmann-Barris M.S. et al. (2008) CMP 155, 739-765. [11] Mccanta M.C. et al. (2008) GCA 72-12, S1, A610.

Fabbrizio, Alessandro; Beckett, John R.; Baker, Michael B.; Stolper, Edward M.

2010-05-01

268

Olivine/Fe-metal equilibrium under high pressure: an ATEM investigation  

NASA Astrophysics Data System (ADS)

San Carlos olivine samples enclosed in soft iron capsules were annealed in an uniaxial split-sphere apparatus, at pressures ranging from 4.6 to 9.0 GPa and temperature ranging from 1310º to 1595 ºC. We estimated the annealing fO2, theoretically controlled by the olivine/Fe-metal equilibrium, to be 1 to 2 log units above the fO2 of the iron/wustite buffer. Samples were investigated by analytical transmission electron microscopy (ATEM) in order to verify that olivine and Fe capsule did equilibrate during the annealings. TEM imaging of the olivine bulk shows a and c dislocations confined in the (010) plane, and small (0.5 µm) spatially coupled precipitates of (1) Al-rich spinel and (2) enstatite (volumic proportion of precipitates =60 ppm). These coupled precipitates are surrounded by split c dislocation loops. Olivine composition profiles, determined by ATEM near the Fe-capsule/olivine contact, reveal a weak loss of Ni from the olivine matrix toward the capsule, as expected in such reducing conditions. These profiles also reveal a marked incorporation of Fe from the capsule into the olivine matrix. These observations, and their interpretation in terms of olivine point defect chemistry, lead to the following conclusions: (1) the starting olivine contained a high concentration of vacancies on octahedral sites (>=1000 ppm per site); such a high vacancy concentration is expected in San Carlos olivine which equilibrated in nature at relatively high fO2; (2) the olivine/Fe-metal equilibrium did control fO2 during the annealings, that resulted in a rapid re-equilibration of olivine at the beginning of the runs to the lower fO2 imposed by the Fe capsule; this led to a strong decrease of the octahedral vacancy concentration in olivine. (3) Such a fO2 decrease promoted in olivine the coupled precipitation of both types of Al-rich spinel and enstatite precipitates. These observations show that the use of Fe-capsule in high pressure experiments is an efficient method for controlling fO2 when studying olivine, and more generally Fe-bearing silicates.

Raterron, P.; Béjina, F.; Doukhan, J. C.; Jaoul, O.; Liebermann, R. C.

269

Thermochemical stability of low-iron, manganese-enriched olivine in astrophysical environments  

NASA Astrophysics Data System (ADS)

Low-iron, manganese-enriched (LIME) olivine grains are found in cometary samples returned by the Stardust mission from comet 81P/Wild 2. Similar grains are found in primitive meteoritic clasts and unequilibrated meteorite matrix. LIME olivine is thermodynamically stable in a vapor of solar composition at high temperature at total pressures of a millibar to a microbar, but enrichment of solar composition vapor in a dust of chondritic composition causes the FeO/MnO ratio of olivine to increase. The compositions of LIME olivines in primitive materials indicate oxygen fugacities close to those of a very reducing vapor of solar composition. The compositional zoning of LIME olivines in amoeboid olivine aggregates is consistent with equilibration with nebular vapor in the stability field of olivine, without re-equilibration at lower temperatures. A similar history is likely for LIME olivines found in comet samples and in interplanetary dust particles. LIME olivine is not likely to persist in nebular conditions in which silicate liquids are stable.

Ebel, Denton S.; Weisberg, Michael K.; Beckett, John R.

2012-04-01

270

Dependence of Water Solubility in Mantle Olivine on the Silica Activity  

NASA Astrophysics Data System (ADS)

Trace amount of hydrogen stored in nominally anhydrous minerals in the Earth's mantle plays an important role in the dynamics of solid state processes. It may change mineral physical properties such as strength, diffusion and creep rates, electrical conductivity, and transformation kinetics. There have been tremendous efforts to study the incorporation of hydrogen in mantle minerals. However, answers to problems such as incorporation mechanism and solubility of hydrogen in olivine, the most abundant mineral in the upper mantle, remain controversial and somewhat illusive. We present here the results from experimental studies of dependence of hydrogen solubility in olivine on the silica activities, which in turn help our understanding of the incorporation mechanism of hydrogen. Off-line high-pressure experiments were performed on SAM85 press equipped with a DIA module at beamline X17B2 of NSLS at 5-10 GPa and 800 - 1200C. Durations range from one to four hours. Standard cell assembly for DIA was used, each consisting pressure medium of amorphous boron mixed with epoxy, graphite heater, and BN sample capsule. San Carlos olivine was used as starting material. Three layers of sample separated by Pt foil were packed into the capsule, with a fine powder of olivine, a mixture of olivine and orthopyroxene, and a mixture of olivine and periclase in each layer. Several larger grains of olivine (few hundred microns) were embedded in each powder sample. Volatiles were provided by the decomposition of epoxy at high temperature. After experiments samples were cut and double-polished for FTIR analyses, which were conducted at beamline U2A of NSLS. Both powder and single crystal FTIR data revealed the following trend for water solubility in olivine in three samples: olivine + MgO >> olivine > olivine + opx. Water content in olivine in low silica environment (i.e., in sample olivine + MgO) is al least an order of magnitude higher than that equilibrated with high silica activity (i.e., in sample olivine + opx). However, no significant difference among IR patterns in terms of hydroxyl stretching bands for different samples was found, in contrary to findings in some earlier studies. Our results suggest the silica activity may be the dominant factor for water solubility in mantle olivine, and that hydrogen could prefer to enter Si vacancies in olivine.

Allen, K.; Wang, L.; Chen, J.; Weidner, D. J.; Liu, Z.

2004-12-01

271

Origin of graphitic carbon and pentlandite in matrix olivines in the Allende meteorite.  

PubMed

Matrix olivines in the Allende carbonaceous chondrite are believed to have formed by condensation processes in the primitive solar nebula. However, transmission electron microscope observations of numerous matrix olivines show that they contain abundant, previously unrecognized, nanometer-sized inclusions of pentlandite and poorly graphitized carbon. Neither of these phases would have been stable at the high-temperature conditions required to condense iron-rich olivine in the solar nebula. The presence of these inclusions is consistent with formation of the olivines by parent body processes that involved overgrowth of fine-grained organic materials and sulfides in the precursor matrix materials. PMID:10464092

Brearley, A J

1999-08-27

272

Deformation of Olivine at Mantle Pressure using D-DIA  

SciTech Connect

Knowledge of the rheological properties of mantle materials is critical in modeling the dynamics of the Earth. The high-temperature flow law of olivine defined at mantle conditions is especially important since the pressure dependence of rheology may affect our estimation of the strength of olivine in the Earth's interior. In this study, steady-state high-temperature (up to 1473 K) deformation experiments of polycrystalline olivine (average grain size ? 10 ?m) at pressure up to 9.6 GPa, were conducted using a Deformation-DIA (D-DIA) high-pressure apparatus and synchrotron X-ray radiation. The oxygen fugacity (fo2) during the runs was in-between the iron-wustite and the Ni/NiO buffers' fo2. The water content of the polycrystalline samples was generally about 150 to 200 wt. ppm but was as low as 35 wt ppm. Typically, 30 % strain was generated during the uniaxial compression. Sample lengths during the deformation process as well as the differential stresses were monitored in situ by X-ray radiography and diffraction, respectively. The strain rate was derived with an accuracy of 10?6 s?1. Differential stress was measured at constant strain rate (?10?5 s?1) using a multi-element solid-state detector combined with a conical slit. Recovered specimens were investigated by optical and transmission electron microscopy (TEM). TEM shows that dislocation glide was the dominant deformation mechanism throughout the experiment. Evidence of dislocation climb and cross-slip as active mechanisms are also reported. Deformation data show little or no dependence of the dislocation creep flow with pressure, yielding to an activation volume V* of 0 {+-} 5 cm3/mol. These new data are consistent with the high-temperature rheological laws at lower pressures, as reported previously.

Li,L.

2006-01-01

273

Serpentinization of sintered olivine during seawater percolation experiments  

NASA Astrophysics Data System (ADS)

The mantle exposed at slow to ultra-slow spreading ridges is pervasively and variably serpentinized down to depth of 4-8km according to available geophysical data. The onset and durability of this hydration process require efficient penetration and renewal of fluids at the mineral-fluid interface. Moreover, serpentinization is exovolumic if a mass-conservative system is assumed, or chemical elements have to be 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 coupled 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-hosted, hydrothermal systems. The percolation-reaction experiment was carried out at 19 MPa and 190°C; the initial water flow was set at 0.2 mL/h then decreased down to 0.06 mL/h after 8 days. During experiment, 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 expanse of olivine. Mass balance calculations indicate that, ca. 8 wt. % olivine was dissolved while the same mass of serpentine (+/- brucite) was formed finally resulting in a porosity decrease 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. We observed that the outlet fluid composition is not modified by changes in the fluid flow. These experimental results are used better understand the scale and efficiency of serpentinization at the onset of the alteration reactions (effective reaction rates in porous/fractured media).

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

2012-04-01

274

Experimental constraints of the olivine crystals compaction in cumulus layer  

NASA Astrophysics Data System (ADS)

The layered intrusions are the result of magma crystallization and differentiation in a form of lateral structures, which are often observed in magmatic chambers. They are markers of processes occurring during a prolonged cooling stage (several tens of thousands years for bodies 1 km in size). There is no unique explication for the mechanism of layering during the intrusion formation. The most plausible mechanism proposed to explain the observed layering includes the coupled crystal settling and residual liquid advection. In the layers containing a large crystal fraction (> 66 vol%) and a small percentage of the residual liquid, the compaction mechanism and the decrease of cumulate layer porosity due to the diffusion adjustment of grain boundaries could effectively occur. In this study, the compaction mechanisms of crystals settling in magma chambers have been modelled with the use of a high temperature centrifuge. The suspensions of olivine crystals and a basaltic melt (33 vol% and 67 vol%, respectively) were centrifuged at the melting temperature of basalt (temperature range of 1270-1280°C). The experiments were conducted at 200-1500 g under a pressure between 0.8-1.1 GPa. During centrifugation run olivine grains are compacted because of the x-time enhanced centrifugation force which is equivalent to x-time larger volume of crystals compacting from above. After crystals have reached a maximum compaction concentration due to this accelerated piling from above, their locations and porosity in cumulates change under the influence of the solution - recrystallisation process. The concentration of crystals in a cumulate layer increases much slower than during their sedimentation. The solution-precipitation and recrystallisation process is a diffusion type mechanism of compaction and has not been addressed experimentally before. Evidences of the precipitation - recrystallisation process of olivine grains in centrifuged samples with TEM analyses are revealed. In fact, knowing that Ca is characteristic only for MORB-melt, the first feature is the presence of Ca at the interface of two adjacent Ol-grains even when the melt phase is escaped. Another evidence of the diffusion compaction is the presence of some small melt inclusions at the growing Ol-boundaries of compacting Ol-grains. Finally, the precipitation - recrystallisation process of olivine grains during the cumulus compaction stems from the observation that the new boundary between two Ol-grains is distinct and not fully crystallized as the interior of grains. This indicates some MORB melt elements (for example, enrichment in Ca) prevent to recrystallize Ol in a fully crystalline structure.

Forien, M.; Bagdassarov, N.; Schmidt, M. W.

2009-12-01

275

Mechanical properties of weightlifting bars.  

PubMed

Weightlifting training and competition involves lifting a revolving shaft bar loaded with weights. The design of a bar and the location of the weights result in bar deformation during lifting tasks. Because there are many manufacturers of weightlifting bars, the actual deformation of a bar may vary, depending on the steel alloys used. A modified 4-point static bending test was used to assess deformation of 8 weightlifting bars and 1 general purpose weight training bar. The apparent stiffness of the bars was determined by plotting bending moment vs. bar deformation (the vertical height difference between the center vs. ends of the bar). All bars tested had an absence of hysteresis during cyclic loading and unloading in 50-kg increments (up to 220-kg total barbell weight), demonstrating pure elastic properties. At maximum loading, bar deformation was 4-5 cm. A large range existed for apparent stiffness. Based on apparent stiffness calculations, recommendations are made for which bars are suitable for weightlifting training and competition. The deformable nature of weightlifting and weight training bars should be considered before their use in exercise, sport, or research. PMID:20683350

Chiu, Loren Z F

2010-09-01

276

Rheology of San Carlos Olivine at High Pressure and Low Temperature  

NASA Astrophysics Data System (ADS)

Olivine, ? -(Mg,Fe)2SiO4, represents a large fraction of the cold lithospheric material sinking into the mantle in subduction zones. The low-temperature (typically T<800\\deg C) olivine rheology, thus, must control the rheology of subducting slabs. Despite its importance, olivine low-temperature rheology is still poorly documented, mainly because of the experimental complications resulting from the high differential yield stress (? m) of olivine in this range of temperature (e.g., ? m > 5 GPa at T>100 \\deg C, e.g., Evans and Goetze, 1979). At low temperature and low pressure (typically P<300 MPa) only indentation measurements can be performed without breaking apart the specimen. Although several attempts have been made to study the olivine rheology at high pressure, they were until recently either limited to room temperature measurements or inaccurate in the determination of specimen yield stresses and/or strain rates. We report here new results using a new experimental method (see Weidner, 1998) for investigating the low-temperature olivine rheology. San-Carlos olivine rheological properties were studied at high pressure, during relaxation experiments carried out in a large-volume cubic-anvil (SAM85, DIA-type) press, by using in-situ synchrotron X-ray diffraction at the NSLS (Brookhaven, NY) and APS (Argonne, IL) facilities. The olivine elastic strain and strain rate were measured from the broadening of the olivine diffraction peaks. The stress in olivine was deduced from the elastic strain using the olivine elastic constants. Assuming a constant total strain (sum of both the elastic and the plastic strains), a classic assumption for relaxation experiments for which the loading pressure is maintained constant, the olivine plastic strain rate was deduced from the elastic strain rate, ultimately leading to the olivine rheological law at low temperature. The run products were investigated by transmission electron microscopy (TEM) in order to interpret the rheological data in terms of olivine microstructures. We will present these results with particular attention to highlighting the future prospects regarding these new techniques which today allow accurate rheological measurements at high pressure. Evans, B., and Goetze, C. (1979) The temperature variation of hardness of olivine and its implication for polycrystalline Yield stress, J. Geophys. Res., 84: 5,505-5,524. Weidner (1998) Rheological studies at high pressure, in "Ultrahigh-pressure mineralogy: Physics and chemistry of the Earth's deep interior", R. J. Hemley Ed., Reviews in Mineralogy, vol.37, Mineralogical Society of America, Washington D.C., pp.493-524.

Raterron, P.; Wu, Y.; Weidner, D. J.

2001-12-01

277

Mineral replacement rate of olivine by chrysotile and brucite under high alkaline conditions  

NASA Astrophysics Data System (ADS)

Olivine mineral replacement by serpentine is one major alteration reaction of oceanic hydrothermalism. In the present experimental study, olivine grains were replaced by chrysotile and brucite under high alkaline conditions. In our study, olivine replacement implied a spatial and temporal coupling of dissolution and precipitation reactions at the interface between olivine and chrysotile-brucite minerals. Coupled dissolution-precipitation led to the alteration of starting olivine grains (so-called primary or parent mineral) to a porous mineral assemblage of chrysotile and brucite with preservation of the initial olivine morphology. This mineral replacement reaction of olivine (serpentinization) has been characterized using XRD, FESEM and FTIR measurements. Moreover, a simple and novel method is here proposed to quantify the mineral replacement rate (or serpentinization rate) of olivine using thermogravimetric (TG) and differential TG (DTG) analyses. Serpentinization extent depends on the grain size: it is complete after 30 days of reaction for the smallest olivine grains (<30 ?m), after 90 days of reaction for the intermediate olivine grains (30 ?m-56 ?m). For the largest fraction (56-150 ?m), 55% of serpentinization extent was reached after 90 days. Based on the fitting of the serpentinization extent (?t) versus time (t) using a kinetic pseudo-second-order model, the serpentinization rates vary from 3.6×10-6 s-1 to 1.4×10-7 s-1 depending on the olivine grain size. An additional correlation between FTIR spectra analysis and TG measurements is proposed. The mineral replacement reactions frequently observed in natural alteration processes could be a powerful synthesis route to design new porous and/or nanostructured materials.

Lafay, Romain; Montes-Hernandez, German; Janots, Emilie; Chiriac, Rodica; Findling, Nathaniel; Toche, Francois

2012-05-01

278

Development of A-type olivine fabric in water-rich deep upper mantle  

NASA Astrophysics Data System (ADS)

Water controls the activity of slip systems in olivine resulting in various types of olivine crystallographic preferred orientation (i.e., fabric) in mantle rocks. The A-type olivine fabric is the most commonly observed olivine fabric in natural peridotites. Development of A-type olivine fabric (developed by the (010)[100] slip system) is known to be limited to the water-poor conditions of the shallow upper mantle (<200 km depth). We have performed simple-shear deformation experiments of olivine at 7.2-11.1 GPa and 1400-1770 K. Here we show that A-type olivine fabric was developed under water-rich conditions (>2130 ppm H/Si in olivine), while B-type fabric (by the (010)[001] slip system) was observed under moderately wet conditions (750-2130 ppm H/Si). Developments of C-type (by the (100)[001] slip system) fabric was limited to water-poor conditions (<220 ppm H/Si). We found that monotonic decrease in the seismic anisotropy VSH/VSV (the ratio of horizontally and vertically polarized shear waves) with depth in the global one-dimensional models is well explained by the olivine fabrics developed in the horizontal flow of a water-poor mantle. Only A-type olivine fabric can explain the vertical mantle flow which associates the seismic anisotropy of VSH/VSV<1 in the deep upper mantle (>200 km depth). A strong anomaly of VSH/VSV<1 observed in the deep upper mantle beneath the East Pacific Rise is well explained by the distribution of water-rich regions (in which A-type olivine fabric is dominantly developed) in the deep upper mantle and upwelling mantle flows.

Ohuchi, Tomohiro; Irifune, Tetsuo

2013-01-01

279

An experimental investigation into the metastable formation of phosphoran olivine and pyroxene  

NASA Astrophysics Data System (ADS)

The formation of phosphoran olivine by crystallization from a melt was investigated experimentally using a one atmosphere furnace, using San Carlos olivine [(Mg,Fe) 2SiO 4] mixed with either iron phosphide (FeP) or magnesium pyrophosphate (Mg 2P 2O 7). Both dynamic crystallization and isothermal experiments produced phosphoran olivine as zoned single crystals and as overgrowths surrounding normal, phosphorus-free olivine grains. The crystallization pathways that form phosphoran olivine were traced and confirm that it is a metastable phase that can crystallize from a phosphorus-rich melt over timescales of hours to days. Removal of the P and equilibration of the olivine however requires weeks to months in the presence of silicate melt. Phosphoran olivine with up to 27 wt% P 2O 5 was generated and up to 69% of the Si tetrahedral sites were replaced by P. The substitution of Si by P into olivine was confirmed as 4 VIM +2 + 2 IVSi +4 ? 3 VIM +2 + 2 IVP +5 + VI[]. Phosphoran olivine compositions that vary from (Mg,Fe) 2SiO 4 to (Mg,Fe) 1.65[] 0.35Si 0.3P 0.7O 4 have been produced in these experiments. Phosphoran pyroxene was also generated in a few experiments and forms when phosphoran olivine reacts with either tridymite or melt. It has compositions compatible with protopyroxene, orthopyroxene, pigeonite and sub-calcic augite, and can contain up to 31.5 wt% P 2O 5. Like phosphoran olivine, it is also a metastable phase. Phosphorus replaces Si in pyroxene by the following substitution methods: 8 IVSi +4 ? 3 IVSi +4 + 4 IVP +5 + IV[] with Al entering the structure by the exchange 2 IVSi +4 ? IVAl +3 + IVP +5. Phosphoran pyroxene compositions vary from (Mg,Fe) 8Si 8O 24 to (Mg,Fe) 8Si 3P 4[]O 24.

Boesenberg, Joseph S.; Hewins, Roger H.

2010-03-01

280

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

281

Candy Bar Earth  

NSDL National Science Digital Library

Students model Earth's interior and plate tectonics (movement at the boundaries) by manipulating taffy and a Milky Way candy bar. This is a worksheet-led activity to help students "visualize" the movement of the plates and to relate Earth's interior to objects they see on a regular basis.

Workshop, Rocks A.

2009-05-04

282

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

283

Partition of noble gases between olivine and basalt melt  

NASA Astrophysics Data System (ADS)

The distribution coefficients ( K i ) of noble gases were determined for synthesized olivine-basalt melt pairs. Seven samples (BH-series) were synthesized at 1370 ~ 1300°C under a one atmospheric pressure (~ 10 5 Pa) noble gas mixture, and four samples (HPP- and HPG-series) at 1360-1050°C at high pressures (0.2-1.5 GPa). The two different experiments gave consistent results with each other. Some BH-series olivine samples were apparently contaminated with gas-rich inclusions or the glass phase, and the effects of such interferences on the calculated distribution coefficients were evaluated. The possible ranges of the distribution coefficients of noble gases thus obtained are: K He 0.07, K Ne = 0.006-0.08, K Ar = 0.05-0.15, K Kr 0.15, and K Xe 0.3. These show remarkable features compared to solid element distribution coefficients: the distribution coefficients of noble gases are rather insensitive to, or even positively correlated with the atomic size of noble gases. The striking contrast between the partition of noble gases and that of solid elements may be attributed to the electrical neutrality of noble gases and the increasing electronic polarizability from He to Xe.

Hiyagon, H.; Ozima, M.

1986-09-01

284

The waveguide effect of metastable olivine in slabs  

NASA Astrophysics Data System (ADS)

We use a finite difference algorithm to compute P-SV synthetic seismograms for deep earthquakes recorded at regional seismic stations located above a subducting slab. We calculate synthetics for 2-D slab models in which the 410 km-discontinuity is uplifted, owing to the exothermic nature of the ? ? ? transition (the equilibrium model), and models in which the 410 km-discontinuity is depressed, owing to inhibited kinetics of the ? ? ? olivine transition (the metastable model). In the latter case the existence of the low-velocity wedge of metastable olivine has a profound influence on the waveforms of deep-focus earthquakes. The wedge acts as a geometrical waveguide, with the energy-focusing effect apparent even after the wavefront has traveled the several hundred kilometers from the wedge boundary to the Earth's surface. The guided energy is most pronounced for receivers located near the surface projection of the deep slab but is observable over a range of 300 km and so may provide a valuable diagnostic for discriminating between equilibrium and metastable models of subduction. A recent search for such guided energy, using regionally recorded P and S waves from deep events in Tonga, yielded negative results.

Koper, Keith D.; Wiens, Douglas A.

285

Olivine-spinel transition and the 400-km discontinuity  

NASA Astrophysics Data System (ADS)

The sequence of high-pressure phase transitions ?-olivine ? ?-modified spinel ? ?-spinel is commonly used as a model for upper mantle seismic velocity increases in the 200-650-km depth interval. The widths of seismic transition zones and the corresponding divariant (e.g., ?+? and ?+?) mineral stability fields are important criteria for correlating velocity variations with phase changes. Divariant mineral stability fields are poorly known for mantle molar Mg/(Mg+Fe) ratios (about 0.9), but C.R. Bina and B.J. Wood of the Department of Geological Sciences, Northwestern University (Evanston, Ill.), have demonstrated that these fields can be constrained by requiring the Mg2SiO4 -Fe2SiO4 phase diagram to be consistent with known thermochemical data. They have derived an internally consistent phase diagram (Figure 1) based on available calorimetric, thermoelastic, and synthetic data. They find that the divariant transition a ? ? + ? ? ? , which is generally regarded as occurring over a broad depth interval, is in fact extremely sharp. For mantle olivine compositions the transition takes place over a pressure interval of only about 2 kbar. The sharpness of this transition, claim the authors, is quite insensitive to uncertainties in the constraining thermodynamic data.

286

Increment Thresholds on Black Bars.  

National Technical Information Service (NTIS)

Under conditions that isolate rod vision, increment thresholds were measured on black bars of various widths, and compared to the increment threshold measured on a homogeneously illuminated field without the bar. Thresholds were found to be elevated in th...

D. Y. Teller

1968-01-01

287

Olivine-Hosted Melt Inclusions: Record of High-Pressure or Late-Stage Processes?  

Microsoft Academic Search

Melt inclusions in olivine have been thought to be high fidelity recorders of equilibrium melt compositions for incompatible trace elements because partition coefficients are very low, and incompatible elements are very large atoms that do not substitute in the olivine structure. This view has recently been shaken by the Spandler et al. (Nature, 2007) results on very fast REE diffusion

M. Laubier; C. H. Langmuir

2007-01-01

288

Evolution of olivine lattice preferred orientation during simple shear in the mantle  

Microsoft Academic Search

Understanding the variation of olivine lattice preferred orientation (LPO) as a function of shear strain is important for models that relate seismic anisotropy to the kinematics of deformation. We present results on the evolution of olivine orientation as a function of shear strain in samples from a shear zone in the Josephine Peridotite (southwest Oregon). We find that the LPO

Jessica M. Warren; Greg Hirth; Peter B. Kelemen

2008-01-01

289

Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere.  

PubMed

The oceanic asthenosphere is observed to have high electrical conductivity, which is highly anisotropic in some locations. In the directions parallel and normal to the plate motion, the conductivity is of the order of 10(-1) and 10(-2) S m(-1), respectively, which cannot be explained by the conductivity of anhydrous olivine. But because hydrogen can be incorporated in olivine at mantle pressures, this observation has been attributed to olivine hydration, which might cause anisotropically high conductivity by proton migration. To examine this hypothesis, here we report the effect of water on electrical conductivity and its anisotropy for hydrogen-doped and undoped olivine at 500-1,500 K and 3 GPa. The hydrous olivine has much higher conductivity and lower activation energy than anhydrous olivine in the investigated temperature range. Nevertheless, extrapolation of the experimental results suggests that conductivity of hydrous olivine at the top of the asthenosphere should be nearly isotropic and only of the order of 10(-2) S m(-1). Our data indicate that the hydration of olivine cannot account for the geophysical observations, which instead may be explained by the presence of partial melt elongated in the direction of plate motion. PMID:17066031

Yoshino, Takashi; Matsuzaki, Takuya; Yamashita, Shigeru; Katsura, Tomoo

2006-10-26

290

Catalytic decomposition of biomass tars: use of dolomite and untreated olivine  

Microsoft Academic Search

Although biomass is getting increased attention as a renewable energy source, one of the remaining problems still to be solved is the reduction of the high level of tar present in the product gas from gasification of biomass. The purpose of the present work is to study the activity of olivine and dolomite for tar destruction. Some researchers investigated olivine

Lopamudra Devi; Krzysztof J. Ptasinski; Frans J. J. G. Janssen; Sander V. B. van Paasen; Patrick C. A. Bergman; Jacob H. A. Kiel

2005-01-01

291

Effects of water and iron content on the rheological contrast between garnet and olivine  

NASA Astrophysics Data System (ADS)

The effects of water and iron content on the relative creep strengths of garnet and olivine were investigated by shear deformation experiments. Garnet and olivine samples were sandwiched together between alumina pistons in a simple shear geometry and were deformed at P = 1-2 GPa, T = 1473 K and strain rates ranging from 10 -5 to 10 -3 s -1 using a Griggs-type solid-medium apparatus. The stress- and strain-rate relation, as well as the deformation microstructures including lattice-preferred orientation and dynamic recrystallization, indicates that the deformation by dislocation creep. The creep tests show that the Fe-rich garnet (Alm 67Prp 29Grs 3) was slightly weaker than olivine (Fo90), whereas the Mg-rich garnet (Alm 19Prp 68Grs 12) was significantly stronger than olivine under dry conditions. The wet experiments show that the creep rate of the Mg-rich garnet is more sensitive to water than olivine; the water fugacity exponent on strain rate was estimated to be ˜2.4 for garnet and ˜1.2 for olivine, and the Mg-rich garnet becomes weaker than olivine in a water-rich environment. The experimental results show that the rheological contrast between garnet and olivine depends strongly on water content and to a lesser degree on Fe content. Consequently, the geodynamic behavior of geochemical reservoirs can be sensitive to their chemical environments in the upper mantle.

Katayama, Ikuo; Karato, Shun-Ichiro

2008-01-01

292

Remote Compositional Analyses of Lunar Olivine-rich Lithologies Using Moon Mineralogy Mapper (M3) Data  

Microsoft Academic Search

We have applied techniques developed for laboratory spectra of lunar olivines to spectra collected by M3. Our work suggests that the olivines analyzed to date are more Fe-rich than those in primitive Mg-suite rocks from the Apollo collection.

P. J. Isaacson; C. M. Pieters; R. N. Clark; J. W. Head; R. L. Klima; N. E. Petro; M. I. Staid; J. M. Sunshine; L. A. Taylor; K. G. Thaisen; S. Tompkins

2010-01-01

293

What's behind Orion's Bar?  

NASA Astrophysics Data System (ADS)

We propose to obtain deep spectra of the outer region of the Orion Nebula. The area of particular interest is SE of the Bar where archival Spitzer spectra have shown high signal-to-noise lines of [S IV] 10.5 and [Ne III] 15.6 microns. We were staggered with astonishment to see such S/N in high ionization species well beyond the Bright Bar, given the conventional view of the Bar as the boundary between ionized and photodissociated regions (PDR). Previous IR missions observed only the inner few arcmin, the so-called Huygens region. The extreme sensitivity of Spitzer's IRS short-high (SH) and long-high (LH) modules in the 10-37 micron spectral range will permit us to measure the above lines and many others of interest to much larger distances from the exciting star theta1 Ori C. Orion is the benchmark for studies of the interstellar medium, particularly for elemental abundances. In the case of the Orion Nebula, the best way to obtain abundances from observations has been through detailed photoionization modeling. These new Spitzer spectra will provide a unique, legacy dataset for new science, including improved current and future models of Orion. Indeed we will use our own modeling codes for this purpose, one of which self-consistently treats the H II region and the PDR. The Orion Bar is the defining interface by which all H+ - H0 - H2 regions are judged. Because there must be extra emission along this sight line, we need to understand this contribution and remove what is not physically a part of the Bar. Our program will permit a more reliable set of line emission that actually arises from the Bar that can rigorously be used to define the interface problem. Our spectra will be the deepest ever taken in these outer regions of Orion over the 10-37 micron range. Tracking the changes in ionization structure via the line emission to larger distances provides much more leverage for understanding the far less studied outer regions. The outer Veil is likely to provide a new, benchmark HIIR-PDR interface.

Rubin, Robert; Colgan, Sean; Erickson, Edwin; Ferland, Gary; O'Dell, C. Robert; Simpson, Janet

2008-03-01

294

FTIR spectroscopy of OH in olivine: A new tool in kimberlite exploration  

NASA Astrophysics Data System (ADS)

Our study of olivines from Canadian kimberlites shows that the application of FTIR spectroscopy significantly improves the reliability of olivine as a kimberlite indicator mineral (KIM). We have developed an algorithm that yields the water concentration and the normalized intensity of the OH IR absorption band at 3572 cm -1 from unpolished olivine grains of unknown thickness. For 80% of kimberlitic olivines these two parameters are significantly higher than those for olivines from non-kimberlitic magmas and consequently, olivines with water concentrations >60 ppm and a strong absorption band at 3572 cm -1 can be reliably classified as being kimberlitic. We have identified two major spectral features in the OH absorption bands of kimberlitic olivines that allow for a more detailed classification: (a) the presence of three types of high-requency OH absorption bands (Group 1A, 1B and 1C) and (b) the proportion of low-frequency OH absorption bands (Group 2) relative to high-frequency bands (Group 1). Comparison of our results with experimental studies suggests that differences within Group 1 OH absorption bands are due to different pressures of crystallization or hydrogenation. The three identified types of Group 1 OH absorption bands approximately correspond to high ( P > 2 GPa, Group 1A), moderate (2-1 GPa, Group 1B), and low (<1 GPa, Group 1C) pressures of hydrogenation. Group 2 OH IR absorption bands in olivines with NiO > 3500 ppm are interpreted to reflect olivine-orthopyroxene equilibria and hence are indicative of xenocrystic olivine derived from lherzolitic or harzburgitic mantle sources. Interaction of xenocrystic olivine with hydrous kimberlitic melts with low silica activity likely will cause a gradual increase in Group 1 absorption bands. Therefore, FTIR spectra of olivine can be used to obtain qualitative estimates of the duration of interaction between mantle material and a kimberlitic melt. In addition to applications in kimberlite and diamond exploration, FTIR spectra of olivine phenocrysts, combined with mineral chemical data, may also provide insights into kimberlite evolution. Our data suggest that in some instances the ascent of kimberlitic magmas could have been interrupted at or near the Moho, followed by olivine crystallization and exsolution of aqueous fluids.

Matveev, S.; Stachel, T.

2007-11-01

295

Systematics of Ni and Co partitioning between olivine and peridotitic liquids  

NASA Astrophysics Data System (ADS)

We have measured olivine/liquid partition coefficients (D) for Ni and Co in runs from 1550 to 2015° C and 1.5 to 6 GPa. D values (weight units) range from 7.2 to 1.4 for Ni and 2.0 to 0.9 for Co. The Ds correlate weakly with 1/T and P/T, but well with D/*(MgO) in accordance with the Jones'95 model (D/*MO = aD/*MgO +b, where D/* is the partition coefficient expressed in cation mole fraction, M is a divalent cation, and a and b are constants). Our experiments have D/*MgO in the range of 2.4 to 1.4. The model predicts that Ni and Co will become incompatible (D>1) for values of D/*MgO < 1.39 and 1.76, respectively, which correspond to peridotitic and komatiitic compositions. Calculations of the fractional crystallization of a lunar magma ocean with bulk composition similar to a degassed terrestrial upper mantle and an initial bottom pressure of 3.0 GPa show that both Ni and Co are initially incompatible, but that Ni becomes compatible after 10/% crystallization and Co after about 40/%. Ni in olivine has a prominent peak at intermediate fractions of crystallization; whereas Co in olivine in creases monotonically until the very latest stages. The patterns of Ni and Co concentration calculated in magma ocean olivine mimic patterns in observed in lunar rocks: olivines for the Mg-suite have the highest Mg/#s, but relatively low Ni; mare basalts have less magnesian olivine but much higher Ni in olivine, and ferroan anorthosites have olivines with lower Mg/# still, but also low Ni. Co is also low in the most magnesian olivines, but olivines from ferroan anorthosites have Co concentrations similar to olivine in mare basalts, so the overall pattern is a monotonic increase of Co as Mg/# decreases. Within the mare basalt series the expected pattern of Ni and Co concentrations in olivine decreasing as Mg/# decreases is observed. So the apparently anomalous behavior of Ni and Co can only be explained by crystallization of a magma ocean in which accumulation of the earliest olivines contributed to the formation of the Mg-suite source region, accumulation of intermediate olivine cumulates led to the formation of the mare basalts, and in the later stages ferroan anorthosites formed either directly in the magma ocean or their source regions did.

Longhi, J.; Walker, D.; Durand, S.

2006-12-01

296

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

297

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

298

Kolsky Bar Impact Test Facility  

SciTech Connect

Testing for the Kolsky Bar is conducted at Los Alamos National Laboratory, Los Alamos, New Mexico. The Kolsky bar is operated by the Dynamic testing team of NMT-11, (Nuclear Material Technology Division) to enable measurements of stress-strain characteristics for the MST-8 (Material Science and Technology) personnel. The Kolsky Bar is located at the Plutonium Facility at TA-55 (Tech Area).

Contreras, P.; Montoya, J.

1998-12-31

299

Remote compositional analysis of lunar olivine-rich lithologies with Moon Mineralogy Mapper (M3) spectra  

NASA Astrophysics Data System (ADS)

A systematic approach for deconvolving remotely sensed lunar olivine-rich visible to near-infrared (VNIR) reflectance spectra with the Modified Gaussian Model (MGM) is evaluated with Chandrayaan-1 Moon Mineralogy Mapper (M3) spectra. Whereas earlier studies of laboratory reflectance spectra focused only on complications due to chromite inclusions in lunar olivines, we develop a systematic approach for addressing (through continuum removal) the prominent continuum slopes common to remotely sensed reflectance spectra of planetary surfaces. We have validated our continuum removal on a suite of laboratory reflectance spectra. Suites of olivine-dominated reflectance spectra from a small crater near Mare Moscoviense, the Copernicus central peak, Aristarchus, and the crater Marius in the Marius Hills were analyzed. Spectral diversity was detected in visual evaluation of the spectra and was quantified using the MGM. The MGM-derived band positions are used to estimate the olivine's composition in a relative sense. Spectra of olivines from Moscoviense exhibit diversity in their absorption features, and this diversity suggests some variation in olivine Fe/Mg content. Olivines from Copernicus are observed to be spectrally homogeneous and thus are predicted to be more compositionally homogeneous than those at Moscoviense but are of broadly similar composition to the Moscoviense olivines. Olivines from Aristarchus and Marius exhibit clear spectral differences from those at Moscoviense and Copernicus but also exhibit features that suggest contributions from other phases. If the various precautions discussed here are weighed carefully, the methods presented here can be used to make general predictions of absolute olivine composition (Fe/Mg content).

Isaacson, Peter J.; Pieters, Carle M.; Besse, Sebastien; Clark, Roger N.; Head, James W.; Klima, Rachel L.; Mustard, John F.; Petro, Noah E.; Staid, Matthew I.; Sunshine, Jessica M.; Taylor, Lawrence A.; Thaisen, Kevin G.; Tompkins, Stefanie

2011-04-01

300

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

301

Fine-grained Chondrule Rims in the Murchison CM2 Chondrite: Compositional and Mineralogical Systematics  

NASA Astrophysics Data System (ADS)

The CM2 carbonaceous chondrites contain numerous chondrules, silicate grains, CAIs, etc, which are mantled by rims of fine- grained material [1]. These rims often consist of two or more layers that can be distinguished on chemical and textural criteria. The formation mechanisms of rims, and the timing and location (i.e., nebular vs planetary) of aqueous alteration of rim materials is the subject of some controversy. We are examining, in detail, the relationships between the mineralogy and bulk composition of individual rims in the Murchison CM2 chondrite in order to place constraints on their mechanisms of formation and alteration histories. We have carried out detailed SEM, electron microprobe and TEM studies of a number of rim sequences in Murchison. Our data provide further confirmation of some of the observations of [1]. For example, we have found that on any given chondrule, inner rims are almost invariably more Mg-rich than outer rims. However, when the entire population of rims is considered it is evident that the compositional field for inner rims overlaps that for outer rims in terms of Mg/Fe ratio. Na and K are also consistently enriched in inner rims, but all the other analyzed elements show variable behavior. Elemental ratio diagrams for rims show some variation in their shape, but in most cases are relatively flat. The elements that consistently show exceptions are Ca and S are frequently depleted relative to CI values in both inner and outer rims. We have also examined the interelement variations in inner and outer rims. One of the surprising results of this study is that some elements may be correlated in inner rims, but not in outer rims and vice versa. Fe and S show a strong positive correlation in outer rims, but have no correlation in inner rims. The reverse is true of Na and S. Our TEM studies of the fine-grained mineralogy of 5 rims have, so far, revealed consistent relationships between rim composition and mineralogy. All the inner rims studied consist dominantly of microcrystalline Mg-rich serpentine, rare platy cronstedtite crystals and poorly crystalline pentlandite and pyrrhotite. The sulfides are disseminated throughout the regions of microcrystalline serpentine. Tochilinite has not been found. The compositions of serpentine and cronstedtite in the different rims studied are very similar and define distinct, tightly clustered compositional groups on Si-Fe-Mg ternary diagrams. Outer rims are mineralogically distinct. For intermediate Mg/Fe ratios, outer rims are dominated by relatively coarse-grained platy cronstedtite, a minor amorphous component and sulfides, whereas the most Fe-rich outer rims contain tochilinite and minor cronstedtite. Our present data indicate clear relationships between bulk rim composition and mineralogy, which would appear to support a parent body location for aqueous alteration, rather than nebular. In addition, the evidence that some elements show variable correlations in inner and outer rims, indicates that there must be mineralogical controls on the major and minor element chemistry of rims. This may reflect variations in the mineralogy of the precursor components of rims, or the mineralogical constraints imposed on elemental mobility between rims and chondrules during alteration. The depletions in Ca and S in rims may be a reflection of the high mobility of these elements during alteration, as is certainly the case in CI chondrites. Finally the textural characteristics of inner rim materials appear to be inconsistent with alteration of a crystalline precursor, because there is no evidence of pseudomorphic replacement of phases. Many of the textures are similar to those produced during low temperature alteration of basaltic glass [2]. The possibility that the precursor was an amorphous material, perhaps of the type observed in ALH A77307 [3] and several of the least equilibrated ordinary chondrites [4], should be considered. Funded by NASA grant NAGW-3347 to J. J. Papike (P.I.). References: [1] Metzler K. et al. (1992) GCA, 65, 2873-2897. [2] Tazaki K. et al. (1989)

Brearley, A. J.; Geiger, T.

1993-07-01

302

Water under the BAR.  

PubMed

Many cellular processes require the generation of highly curved regions of cell membranes by interfacial membrane proteins. A number of such proteins are now known, and several mechanisms of curvature generation have been suggested, but so far a quantitative understanding of the importance of the various potential mechanisms remains elusive. Following previous theoretical work, we consider the electrostatic attraction that underlies the scaffold mechanism of membrane bending in the context of the N-BAR domain of amphiphysin. Analysis of atomistic molecular dynamics simulations reveals considerable water between the membrane and the positively charged concave face of the BAR, even when it is tightly bound to highly curved membranes. This results in significant screening of electrostatic interactions, suggesting that electrostatic attraction is not the main driving force behind curvature sensing, supporting recent experimental work. These results also emphasize the need for care when building coarse-grained models of protein-membrane interactions. These results are emphasized by simulations of oligomerized amphiphysin N-BARs at the atomistic and coarse-grained level. In the coarse-grained simulations, we find a strong dependence of the induced curvature on the dielectric screening. PMID:20858422

Lyman, Edward; Cui, Haosheng; Voth, Gregory A

2010-09-22

303

Water under the BAR  

PubMed Central

Many cellular processes require the generation of highly curved regions of cell membranes by interfacial membrane proteins. A number of such proteins are now known, and several mechanisms of curvature generation have been suggested, but so far a quantitative understanding of the importance of the various potential mechanisms remains elusive. Following previous theoretical work, we consider the electrostatic attraction that underlies the scaffold mechanism of membrane bending in the context of the N-BAR domain of amphiphysin. Analysis of atomistic molecular dynamics simulations reveals considerable water between the membrane and the positively charged concave face of the BAR, even when it is tightly bound to highly curved membranes. This results in significant screening of electrostatic interactions, suggesting that electrostatic attraction is not the main driving force behind curvature sensing, supporting recent experimental work. These results also emphasize the need for care when building coarse-grained models of protein-membrane interactions. These results are emphasized by simulations of oligomerized amphiphysin N-BARs at the atomistic and coarse-grained level. In the coarse-grained simulations, we find a strong dependence of the induced curvature on the dielectric screening.

Lyman, Edward; Cui, Haosheng; Voth, Gregory A.

2010-01-01

304

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

305

Hydrogen in the upper mantle: Diffusion and effects on olivine transformation kinetics  

NASA Astrophysics Data System (ADS)

Olivine is the most abundant mineral in Earth's upper mantle and can host significant amounts of hydrogen within its crystal structure. The presence of hydrogen affects many of olivine's physical properties such as electrical conductivity, viscosity, sound speed, transformation kinetics, phase equilibrium, and generally speaking the physics governing the interior of the earth. Understanding how hydrogen affects olivine is integral to understanding the Earth's interior. In this work olivine was experimentally hydrated and reacted at high pressure and temperature, to simulate upper mantle conditions. The physical properties measured in this work are used to understand seismic and magnetotelluric observations of the Earth. In the first project the effects of hydrogen on olivine transformation kinetics were examined. Growth rates for olivine's high pressure polymorphs, wadsleyite and ringwoodite, to determine if olivine can persist metastably inside cold subducting slabs in the mantle transition zone. Hydrogen significantly enhances the growth rates of olivine into ringwoodite. For olivine containing ˜75 (or higher) ppmw H2O At 18 GPa and 900°C the growth rate for ringwoodite rims is 1.0x10-9 m/s with activation enthalpy of 235 +/- 30 kJ/mol, which is too high for persistence of metastable olivine into the transition zone. Confirmation of the existence of metastable olivine by seismologists would constrain H2O contents at such locations to be < 75 ppmw H2O. In the second project deuterium-hydrogen interdiffusion coefficients were measured to help understand electrical conductivity, point defect populations, chemical transport, and defect dominated properties in olivine. For the fastest H-diffusing [100] orientation DD-H, [100] = 10(-5.04 +/- 1.43)*e(-137 +/- 31 kJ/mol)/(RT) m²/s at 2 GPa and 750--900°C. Comparison of DD-H to chemical diffusion coefficients allows us to calculate diffusivity of intrinsic defects. Olivine electrical conductivity is calculated from DD-H using the Nernst-Einstein relation. These results combined with geophysical electrical conductivity depth profiles permit first order calculations of H2O contents in the upper mantle and suggest that the hydrogen contribution to electrical conductivity is too small to account for high electrical conductivity anomalies in the asthenosphere.

Du Frane, Wyatt Louis

306

Shear Attenuation and Dispersion in Olivine + Orthopyroxene Aggregates (Synthetic Harzburgite)  

NASA Astrophysics Data System (ADS)

Low-frequency (10-2.25olivine (ol) and orthopyroxene (opx). The attenuation spectra reveal “high-temperature background” behavior where attenuation diminishes smoothly and mildly with increasing frequency (QG-1~f -0.3). At higher frequencies (f >10-0.5 Hz), the attenuation spectra reveal the onset of an apparent peak, likely due to elastically-accommodated grain boundary sliding. Most importantly, these experiments reveal a strong dependence of attenuation on the modal abundance of opx for constant frequency, temperature, grain size, and melt fraction: attenuation increases by roughly a factor of two as the modal abundance of opx rises from 6 to 54 vol%. Further addition of opx leads to diminished attenuation. These reciprocating torsion measurements were complemented by a series of unidirectional microcreep tests, which demonstrate that the variation in attenuation is complemented by both a lower shear viscosity and a drop in the activation energy as opx mode increases. The behavior suggests that: (1) phase boundaries are potent absorbers of mechanical energy, and (2) the background attenuation in dry, melt-free upper mantle may be larger than that predicted from experimental studies conducted on single-phase olivine aggregates. The implications of these results for understanding seismic signatures of mid-ocean ridges and subduction zones are discussed.

Sundberg, M. I.; Cooper, R. F.

2009-12-01

307

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

308

Electrical conductivity of olivine, a dunite, and the mantle  

SciTech Connect

Laboratory studies of the electrical conductivity of rocks and minerals are vital to the interpretation of electromagnetic soundings of the Earth's mantle. To date, the most reliable data have been collected from single crystals. The authors have extended these studies with electrical conductivity measurements on a dunite from North Carolina, in the temperature range of 600-1,200 C and under controlled oxygen fugacity. Observations of conductivity as a function of oxygen fugacity and temperature demonstrate that conduction in the dunite is indistinguishable from conduction in single olivine crystals. Thus the common practice of exaggerating the single-crystal conductivities to account for conduction by grain boundary phases in the mantle is unnecessary. Because the dunite conductivity is consistent with that published for single crystals under similar conditions, the authors have made a combined analysis of these data. Conductivity as a function of temperature between 600 and 1,450 C displays three conduction mechanisms whose activation energies may be recovered by nonlinear least squares fitting, yielding activation energies of 0.21 {plus minus} 2.56 {times} 10{sup {minus}19} J below 720 C, 2.56 {plus minus} 0.02 {times} 10{sup {minus}19} J between 720 C and 1,500 C and 11.46 {plus minus} 0.90 {times} 10{sup {minus}19} J above 1,500 C. The behavior of conductivity as a function of oxygen fugacity is well explained by a model in which an f{sub O{sub 2}}-independent population of charge carriers is supplemented at high oxygen fugacities with a population that is proportional to f{sub O{sub 2}}{sup 0.3}. This parametrization produces a clear correlation of the f{sub O{sub 2}} dependent term with iron content, which is otherwise obscured by variations in conductivity among olivines.

Constable, S. (Scripps Inst. of Oceanography, La Jolla, CA (United States)); Duba, A. (Lawrence Livermore National Lab., CA (United States))

1990-05-10

309

The Fidelity of Olivine-Hosted Melt Inclusions as Recorders of Pre-Eruptive Water Content and Oxygen Fugacity  

NASA Astrophysics Data System (ADS)

Olivine-hosted melt inclusions represent an important source of information on both the pre-eruptive H2O contents and oxygen fugacities of basaltic magmas [1]. The principal uncertainty involved with deriving pre-eruptive H2O concentrations from melt inclusions is the potential for diffusive loss or gain of H+ (protons) through the host olivine. Further, it has been proposed that the proton flux associated with H2O loss/gain affects the oxidation state of the inclusion [2,3]. Results from hydration and dehydration experiments carried out on natural inclusion-bearing olivines analyzed by SIMS and XANES confirm that H2O re-equilibratrion occurs rapidly via proton diffusion through the host olivine, and demonstrate that re-equilibration of oxygen fugacity within the inclusion occurs on comparable timescales via diffusion of point defects. Therefore, an olivine-hosted melt inclusion provides a reliable record of both the H2O content and oxygen fugacity of the external melt with which it most recently equilibrated. However, efficient re-equilibration of both H2O and oxygen fugacity limits the utility of olivine-hosted melt inclusions as indicators of mantle processes. Hydration experiments were performed on olivines from Puu Wahi, a scoria cone on the NE rift zone of Mauna Loa volcano. Melt inclusions initially containing 0.36±0.05 wt% H2O were held at 1 GPa and 1250° C in water enriched in 18O (18O/?O = 0.977) and D (2H/?H = 0.998) to map the transport of protons and oxygen during equilibration of melt inclusions with an external fluid. Dehydration experiments were carried out for 1 to 18 hrs at 1 bar and 1250 ° C on inclusion-bearing olivines in scoria erupted from Cerro Negro volcano, Nicaragua, in 1999. The initial concentration of H2O in these melt inclusions was uniformly high (3.6±0.6 wt%). All run products were analyzed for major elements by electron microprobe and for H2O by SIMS on the Cameca 1280 ion microprobe at WHOI. The oxidation state of Fe was determined by XANES at beamline 13-IDC of the Advanced Photon Source at Argonne National Laboratory. The D/H ratios of the melt inclusions from our hydration experiments range from 18.4-25.6, as compared to ~1.448 x 10-4 for mantle-derived basalt, indicating significant addition of deuterium. The 18O/17O ratios of melt inclusions are within uncertainty of natural ratios for mantle-derived materials. The H2O content of individual melt inclusions increased by as much as 3.9 wt %, while the oxidation state of Fe in the hydrated melt inclusions is not significantly different from the starting materials. The concentration of H2O in melt inclusions from the dehydration experiments ranges from 2.8 to 0.05 wt%, and dehydration is nearly complete after 18 hours. The ?D value of the melt inclusions increases significantly as dehydration progresses and is consistent with a calculated diffusive fractionation of hydrogen isotopes. Neither diffusive fractionation of H2O nor equilibrium fractionation via vapor loss is consistent with the isotopic enrichment observed in dehydrated melt inclusions. The oxidation state of Fe ranges from Fe3+/?Fe = 0.58±0.04 (NiNiO+4) for the starting materials to Fe3+/?Fe = 0.21±0.03 (NiNiO+0.6) for melt inclusions that were heated for 18 hours, and re-equilibrates on the same timescale as H2O. References: [1] K.A. Kelley, E. Cottrell, Science 325, 605 (2009); [2] A. V. Sobolev, L. V. Danyushevsky, J Petrol 35, 1183 (1994); [3] L. V. Danyushevsky, A. W. McNeill, A. V. Sobolev, Chem Geol 183, 5 (2002).

Gaetani, Glenn; O'Leary, Julie; Shimizu, Nobumichi

2010-05-01

310

Development of a composite boring bar  

Microsoft Academic Search

A composite boring bar, whose stability against chattering is superior to not only conventional steel bars but also cemented carbide bars, has recently been developed. The main material of this composite bar is pitch-based carbon fiber reinforced plastic. Carbon fibers aligned unidirectionally in the longitudinal direction of the bars give high bending stiffness. Four types of bar having different shaped

Shuzo Nagano; Takayuki Koizumi; Toru Fujii; Nobutaka Tsujiuchi; Hiroki Ueda; Kobe Steel

1997-01-01

311

Deformation of dry Olivine up to 11 GPa and 2100 K Using a Rotational Drickamer Apparatus  

NASA Astrophysics Data System (ADS)

Characterizing the pressure effects on plastic deformation of olivine is important for understanding mantle dynamics and evolution of the Earth. Although many experimental studies have been performed on olivine deformation, the magnitude of the pressure effects (activation volume, V*) remain controversial. We use the rotational Drickamer apparatus (RDA) to determine the pressure dependence of creep strength of olivine in the dislocation creep regime. Deformation experiments on dry hot-pressed polycrystalline San Carlos olivine have been conducted at 6-11 GPa, 1500-2100 K and strain rates of 0.9-7.4 × 10-5 s-1 using the RDA at X17B2, Brookhaven National Laboratory. Shear deformation experiments up to the strain of 0.45 were performed. Near steady-state deformation was observed after the shear strain of 0.04-0.24. The stress was measured from the dependence of lattice spacing on the orientation for (130), (131), (112), (122), (140), (211) and (241) planes, as well as dislocation densities. We found that (i) the strength of olivine at steady-state deformation at these pressures is much larger than those at lower pressures, (ii) the variation of stress values inferred from different lattice planes decreases with temperature. We conclude that the creep strength of olivine for dislocation creep increases significantly with pressure and that the plastic anisotropy in olivine decreases with temperature.

Kawazoe, T.; Otsuka, K.; Tinker, D.; Karato, S.; Nishihara, Y.; Jing, Z.; Mookherjee, M.

2007-12-01

312

Variable Olivine Detection in Soils at Meridiani Planum From Mars Express OMEGA and MER Opportunity Observations  

NASA Astrophysics Data System (ADS)

The Meridiani plains have been characterized spectrally using data collected on the ground by the Opportunity rover and from orbit by the Mars Express OMEGA instrument. Observations completed by the Opportunity rover show that the Meridiani plains are covered by aeolian deposits composed of basaltic sands, gray hematite spherules, and variable amounts of bright dust. Measurements made by the Mössbauer spectrometer (14.4keV) of the deposits imply subequal concentrations of iron contained in both olivine and pyroxene [Klingelhöfer et al., 2004] whereas Mini-TES (5-29?m) detects a higher abundance of pyroxene relative to olivine [Christensen et al., 2004]. Distinct spectral features attributable to olivine or pyroxene in the ~0.4-1?m range are not detectable in Pancam data [Bell et al., 2004]. Spectral reflectance data from OMEGA (in the ~0.92-2.69?m range) covering the Opportunity rover traverse regions show evidence for the presence of pyroxene but not olivine, although olivine has been detected several kilometers to the south [Arvidson et al., 2006]. The apparent discrepancy in the concentration of olivine detected by the various instruments at Meridiani suggests that olivine is masked by the presence of other phases in the VNIR.

Wiseman, S. M.; Arvidson, R. E.; Poulet, F.; Morris, R. V.; Ming, D. W.

2006-05-01

313

The influence of water on the Peierls stress of olivine at high pressures  

NASA Astrophysics Data System (ADS)

To investigate the influence of water on the low-temperature plasticity of olivine under lithospheric conditions, we carried out a series of creep experiments on polycrystalline olivine at high pressures (~6 GPa), relatively low temperatures (873 ? T ? 1173 K), and hydrous conditions using a deformation-DIA. Samples were fabricated from fine powdered San Carlos olivine under hydrous conditions. In the experiments, a sample column composed of a sample and alumina pistons was assembled with a talc sleeve and graphite resistance heater into a 6.2-mm edge length cubic pressure medium. Experiments were carried out at the National Synchrotron Light Source at Brookhaven National Laboratory. In a run, differential stress and sample displacement were monitored in-situ using synchrotron x-ray diffraction and radiography, respectively. The low-temperature plasticity of olivine under hydrous conditions is constrained by our data with a Peierls stress of 4.2 ± 0.3 GPa. This value is much lower than those reported the Peierls stress for olivine under anhydrous conditions (~ 6 - 15 GPa, Evans and Goetze, 1979; Raterron et al., 2004; Mei at al., 2010), indicating a significant influence of water on the low-temperature plasticity of olivine. The low-temperature flow behavior of olivine under hydrous conditions quantified in this study provides a necessary constraint for modeling the dynamic activities occurring within lithospheric mantle especially for those regions with the presence of water such as beneath a mid-ocean ridge and along a subducting slab.

Mei, S.; Suzuki, A. M.; Xu, L.; Kohlstedt, D. L.; Dixon, N. A.; Durham, W. B.

2012-04-01

314

Minor and trace elements in olivines as probes into early igneous and mantle melting processes  

NASA Astrophysics Data System (ADS)

The trace element composition of olivine is a rapidly growing research area that has several applications of great potential. Mantle olivines can be distinguished from volcanic olivines by lower concentrations of Ca (<700 ppm), Ti (<70 ppm), and often Cr. The melting of pyroxenites derived from recycled ocean crust can be recognized in volcanic olivines by correlations of Mn, Al, Sc and Co in addition to Ni. High Ni is characteristic of olivine derived from olivine-free source rocks, but alone it does not distinguish between recycling of ocean crust, continental crust, mantle wedge hybridization, and intra-mantle melt migration. Trace elements help to identify different types of non-peridotitic ultramafic rocks, including those not formed by ocean crust recycling. High Li may be caused by recycling of continental crust, as in Mediterranean post-collisional volcanics or by interaction with carbonatitic melts, and correlation with further elements such as Zn, Na, Ti and Ca will help to identify minerals in the source assemblages, such as phlogopite, spinel, garnet, amphiboles and carbonates, and thus the source of the olivine-free assemblages. Olivines often store the earliest chemical signals of melt loss in peridotites, but later absorb trace elements from passing melts, and are thus excellent monitors of the chemistry of metasomatic agents. Trace elements distinguish between Ti-enrichment by silicate melt metasomatism (high Ti, low Ca) and high-Ca signatures associated with plumes and rift regions that may be due to carbonate-silicate melts. Li may be enriched in olivine in the orogenic mantle, indicating the involvement of melted continental crustal material. Experimental data on element partitioning and diffusion currently partly conflicts with information from natural rocks.

Foley, Stephen F.; Prelevic, Dejan; Rehfeldt, Tatjana; Jacob, Dorrit E.

2013-02-01

315

Bar press and bar release as avoidance responses1  

PubMed Central

Two experiments were performed in which rats had to avoid shock by both pressing and releasing a bar within specified intervals. When the release-shock interval was held constant and the press-shock interval was increased, response rate decreased and bar holding increased. When the press-shock interval was held constant and the release-shock interval was increased, both response rate and bar holding decreased.

Meltzer, Donald; Tiller, James E.

1979-01-01

316

bar Knn Resonance bar Knn - ? yn Coupled Channel Faddeev Equation  

NASA Astrophysics Data System (ADS)

The three-body resonance of bar KNN system is investigated by using the bar KNN - ? YN coupled channels Faddeev equation. The resonance energy is determined from the pole of S-matrix on the unphysical sheet. It is found that the pole positions of the predicted amplitudes are significantly modified when the three-body dynamics is approximately treated by introducing the effective bar KN two-body interaction.

Sato, T.; Ikeda, Y.

317

Oriented chromite-diopside symplectic inclusions in olivine from lunar regolith delivered by "Luna-24" mission  

NASA Astrophysics Data System (ADS)

Calcium-chromium rich lamellae in olivine grain No. 1611 from the Luna-24 regolith were studied with FEG-EMPA and TEM. The lamellae consist of a worm-like intergrowth of FeCr2O4 chromite (Chr) and CaMgSi2O6 diopside (Di), with a Chr:Di modal proportion of 1:3. The linear extension of the lamellae and crystallographic orientation relationships among the symplectite phases and the olivine suggest that the lamellae nucleated at deformation defects in the olivine host. Calcium depletion haloes surrounding the lamellae amount to about 75 ?m and indicate that the chromite + diopside lamellae were formed by segregation of calcium and chromium from the host olivine into the lamellae without addition of calcium and/or chromium from outside the olivine. The segregation of calcium and chromium and, consequently, the growth of the symplectic lamellae were diffusion-controlled. The segregation of a calcium-chromium component from the host olivine was associated with oxidation of divalent to trivalent chromium. Oxidation was facilitated by dehydrogenation, which was driven by decompression and/or a change in redox potential. Hydrogen point defects in the original olivine with H+ substituting for divalent cations on the M-sites provided the necessary electron acceptors for the oxidation of chromium and after electron transfer left olivine as molecular H2. The internal microstructure of the lamellae suggests that exsolution of the calcium-chromium rich lamellae from the host olivine and formation of the chromite-diopside symplectic intergrowth occurred simultaneously. The time scale derived from diffusion modeling of the calcium depletion haloes around the lamellae indicates a thermal event on the order of several months to several hundred years at most. Symplectic inclusions found in olivine from lunar, martian and terrestrial rocks are similar with respect to their shape, crystallographic orientation relationships, and internal microstructure of the spinel-clinopyroxene intergrowth. These features are inconsistent with "dry" olivine oxidation that is by the uptake of oxygen. Dehydrogenation of OH-bearing precursor olivine is suggested as a general mechanism of oxidation accompanied by chemical segregation and phase separation resulting in symplectite formation.

Khisina, N. R.; Wirth, R.; Abart, R.; Rhede, D.; Heinrich, W.

2013-03-01

318

Olivines in the Kaba carbonaceous chondrite and constraints on their formation  

NASA Astrophysics Data System (ADS)

Kaba is unique in containing almost pure fayalitic olivine (Fo(sub 0.1)). Its coexistence with pure forsterite up to Fo(sub 99.6) and normal (Fo(sub 92) to Fo(sub 59)) and reversely (Fo(sub 0.4) to Fo(sub 4.7)) zoned olivines suggest that the Kaba olivines are in thermodynamic disequilibrium and experienced a complicated history. The fayalite is sufficiently pure that it is unlikely that it could have been produced by fractional crystallization. A gas-solid reaction under oxidizing conditions (H2O/H2 ratio approximately 10) is probably responsible for its formation.

Hua, X.; Buseck, P. R.

1993-03-01

319

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

320

Chondrites and their Components  

NASA Astrophysics Data System (ADS)

What are Chondrites?Chondrites are meteorites that provide the best% clues to the origin of the solar system. They are the oldest known rocks - their components formed during the birth of the solar system ca. 4,567 Ma - and their abundances of nonvolatile elements are close to those in the solar photosphere. Chondrites are broadly ultramafic in composition, consisting largely of iron, magnesium, silicon, and oxygen. The most abundant constituents of chondrites are chondrules, which are igneous particles that crystallized rapidly in minutes to hours. They are composed largely of olivine and pyroxene, commonly contain metallic Fe,Ni and are 0.01-10 mm in size. Some chondrules are rounded as they were once entirely molten but many are irregular in shape because they were only partly melted or because they accreted other particles as they solidified. Chondrites themselves were never molten. The definition of a chondrite has expanded recently with the discovery in Antarctica and the Sahara Desert of extraordinary meteorites with chondrules 10-100 ?m in size, and chondrites so rich in metallic Fe,Ni that they were initially classified as iron meteorites with silicate inclusions. Thus, in meteoritics, as in other fields of planetary science, new discoveries sometimes require definitions to be modified.Chondrites are so diverse in their mineralogical and textural characteristics that it is not possible to describe a typical chondrite. We show one with diversely textured chondrules including prominent, aesthetically pleasing, rounded chondrules (Figure 1(a)), and another with more uniformly textured chondrules (Figure 1(b)). Owing to the high abundance of rounded or droplet chondrules in the abundant, so-called "ordinary" chondrites ( Figure 1(a)), studies of the origin of chondrules have commonly been based on these chondrites. (7K)Figure 1. Maps showing magnesium concentrations in two chondrites: (a) PCA91082, a CR2 carbonaceous chondrite, and (b) Tieschitz, an H/L3.6 ordinary chondrite. In CR chondrites, as in most carbonaceous chondrites, nearly all chondrules have porphyritic textures and are composed largely of forsterite (white grains), enstatite (gray), and metallic Fe,Ni (black). The subscripts show type I chondrules, which are common, and type II, which are FeO-rich and rare in this chondrite. Tieschitz, like other ordinary chondrites, is composed of all kinds of chondrules with diverse FeO concentrations. Key to chondrule types: BO, barred olivine; C, cryptocrystalline, PO, porphyritic olivine; POP, porphyritic olivine-pyroxene; PP, porphyritic pyroxene; RP, radial pyroxene. These maps were made with an electron microprobe from Mg K? X-rays. Chondrites contain diverse proportions of three other components: refractory inclusions (0.01-10 vol.%), metallic Fe,Ni (<0.1-70%), and matrix material (1-80%). Refractory inclusions are tens of micrometers to centimeters in dimensions, lack volatile elements, and are the products of high-temperature processes including condensation, evaporation, and melting. Two types are recognized: calcium- and aluminum-rich inclusions or CAIs, and amoeboid olivine aggregates. CAIs are composed of minerals such as spinel, melilite, hibonite, perovskite and Al-Ti-diopside, which are absent in other chondritic components (see Chapter 1.08). Amoeboid olivine aggregates consist of fine-grained olivine, Fe,Ni metal, and a refractory component largely composed of aluminum-diopside, anorthite, spinel and rare melilite. Grains of metallic Fe,Ni occur inside and outside the chondrules as grains up to a millimeter in size and, like the chondrules and refractory inclusions, formed at high temperatures. Matrix material is volatile-rich, and fine-grained (5-10 ?m) and forms rims on other components and fills the interstices between them. Chondrite matrices have diverse mineralogies: most are disequilibrium mixtures of hydrated and anhydrous silicates, oxides, metallic Fe,Ni, sulfides, and organic material and contain rare presolar grains.

Scott, E. R. D.; Krot, A. N.

2003-12-01

321

Stellar bar in NGC 1068  

SciTech Connect

High-resolution 2-micron mapping of the inner disk of NGC 1068 reveals a bar extending to + or - 16 arcsec from the nucleus at position angle 48 deg. The stellar mass distribution, presumably traced by the near-infrared light, is therefore strongly nonaxisymmetric with a contrast of approximately 3:1 between the major and minor axes of the bar. This large-scale galactic structure is probably responsible for the concentration of molecular clouds in a ring just outside the bar. The massive bar may also drive noncircular motions in the inner disk of the galaxy as possibly seen in the gaseous emission lines. 21 references.

Scoville, N.Z.; Matthews, K.; Carico, D.P.; Sanders, D.B.

1988-04-01

322

Measurement of Activation Volume of Dry Olivine at High Pressure  

NASA Astrophysics Data System (ADS)

Despite considerable effort to measure the activation volume V* of creep of olivine using a new generation of high-pressure deformation machines, namely the Rotational Drickamer Apparatus (RDA) and the Deformation- DIA (D-DIA) in conjunction with synchrotron x-ray sources, progress has been marred by a combination of an apparently weak signal (i.e., low V*) and measurement noise. The latter has a broad spectrum of causes, from inherent limitations of measurement systems (of stress, primarily) to limited time available for creep experiments at synchrotron sources to investigator-induced variations of sample state during measurement. We report here measurements following a significant advance in regulation of sample state: deforming polycrystalline olivine in a dry state under more uniform mechanical conditions gives us our first clear signal of a positive activation volume. The advance has been made possible by a choice of assembly materials that assures anhydrous conditions around the sample, and a technique for testing in the absence of a thermocouple within the sample assembly. The key to the anhydrous assembly is a self-gasketing D-DIA cube of hybrid composition: a sphere of mullite embedded in a cube of unfired pyrophyllite, where the diameter of the sphere matches the edge length of the cube (6-mm in our case). Unfired pyrophyllite is an excellent gasketing material, being soft and (in notable contrast with mullite) non-friable. Additionally, as a cube-filling "web" around the mullite sphere, the pyrophyllite is ideally configured for D-DIA self gasketing: maximum volume at the cube corners, minimum (zero) volume at cube faces. Thus the configuration under pressure is a bone-dry mullite pressure medium gasketed by pyrophyllite. Removal of the thermocouple from the deformation piston results in a demonstrably more symmetric deformation column within the assembly for the entire duration of the experiment, and the absence of the thermocouple is reliably compensated by off-line calibration of furnace power vs temperature. Results of creep experiments in the new cell indicate a value of V*/n (where n is the stress exponent) of 3 ± 1 × 10-6 m3/mol between 3 and 6 GPa. The value of n will be better resolved in future experiments, but if the deformation is in the dislocation creep regime (n ~ 3.5), then V* ~ 10 × 10-6 m3/mol.

Durham, W. B.; Kohlstedt, D. L.; Mei, S.; Dixon, D. A.; Wang, L.

2007-12-01

323

Titanium solubility in olivine in the system TiO2 MgO SiO2: no evidence for an ultra-deep origin of Ti-bearing olivine  

NASA Astrophysics Data System (ADS)

The finding of ilmenite rods in olivine from orogenic peridotites has sparked a discussion about the processes of incorporation and exsolution of titanium in olivine. We have experimentally investigated the solubility of Ti in olivine as a function of composition, temperature and pressure in the synthetic TiO2 MgO SiO2 system. Experiments at atmospheric pressure in the temperature range 1,200 1,500°C showed that the highest concentration of TiO2 is obtained when olivine coexists with spinel (Mg2TiO4). The amount of TiO2 in olivine in the assemblages olivine + spinel + periclase and olivine + spinel + ilmenite at 1,500°C was 1.25 wt.%. Changes in the coexisting phases and decreasing temperature result in a significant reduction of the Ti solubility. Olivine coexisting with pseudobrookite (MgTi2O5) and a Ti Si-rich melt at 1,500°C displays a fourfold lower TiO2 content than when buffered with spinel. A similar decrease in solubility is obtained by a decrease in temperature to 1,200°C. There is a negative correlation between Ti and Si and no correlation between Ti and Mg in Ti-bearing olivine. Together with the established phase relations this suggests that there is a direct substitution of Ti for Si at these temperatures, such that the substituting component has the stoichiometry Mg2TiO4. The unit cell volume of olivine increases systematically with increasing TiO2 content demonstrating that the measured TiO2 contents in olivine are not caused by micro-inclusions but by incorporation of Ti in the olivine structure. Least squares fitting of 20 olivine unit cell volumes against the Ti content yield the relation: V (Å3)=290.12(1) + 23.67(85) NTi. The partial molar volume of end-member Mg2TiO4 olivine (NTi=1) is thus 47.24±0.13 cm3. The change of the Ti solubilty in olivine coexistent with rutile and orthopyroxene with pressure was investigated by piston cylinder experiments at 1,400°C from 15 to 55 kbar. There is no increase in TiO2 contents with pressure and in all the experiments olivine contains ~0.2 wt.% TiO2. Moreover, a thermodynamic analysis indicates that Ti contents of olivine coexisting with rutile and orthopyroxene should decrease rather than increase with increasing pressure. These data indicate that the ilmenite exsolution observed in some natural olivine does not signify an ultra-deep origin of peridotite massifs.

Hermann, J.; O'Neill, H. S. C.; Berry, A. J.

2005-02-01

324

Optical constants of olivine particles between wavelengths of 7 and 200 microns  

SciTech Connect

Emission features are computed for spherical olivine particles of 0.03, 0.3, 3.0, and 30 micron radii, on the basis of laboratory determinations of the olivine particles' optical constants over the 7 to 200 micron range. It is noted that, while particles of radii smaller than 0.3 microns exhibit emission peaks at 16.3, 18.6, 23, 28, and 33.6 microns, together with a 10-micron region twin-peak structure, these readings weaken for particle radii of 3 microns or more. The appearance of the twin-peak feature in Comet P/Halley is accordingly judged to imply the presence of olivine particles smaller than 1 micron in radius; alternatively, such smaller olivines' enhancement may occur in the comet, which also exhibits a 10-micron silicate band twin-peak feature. 26 refs.

Mukai, Tadashi; Koike, Chiyoe (Kanazawa Institute of Technology (Japan) Kyoto Pharmaceutical Univ. (Japan))

1990-09-01

325

An Interactive Computer Program for Simulating the Effects of Olivine Fractionation from Basaltic and Ultrabasic Liquids.  

ERIC Educational Resources Information Center

|Describes interactive computer program (listing available from author) which simulates olivine fractionation from basaltic/ultrabasic liquid. The menu-driven nature of the program (for Apple II microcomputer) allows students to select ideal Rayleigh fractionation or equilibrium crystallization. (JN)|

Pearce, Thomas H.

1983-01-01

326

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.  

National Technical Information Service (NTIS)

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. That paper was followed by several on QUE94201 melt composition and specifically on Cr,...

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

2013-01-01

327

Investigation on deformation of olivine at high pressure and low temperature  

Microsoft Academic Search

Olivine is the dominant mineral in the upper mantle. Several deformation experiments of polycrystalline powdered San Carlos olivine at subduction zone conditions (pressures of 3-5 GPa and temperatures of 25-1100°C) have been performed on a deformation DIA (D-DIA) apparatus, SAM85, at X17B2, National Synchrotron Light Source (NSLS). Enstatite (MgSiO3) (3-5% total quality of sample) is used as buffer to control

Hongbo Long

2008-01-01

328

Fault Reactivation During the Olivine to Wadsleyite Transition: A Mechanism for Deep Focus Earthquakes  

Microsoft Academic Search

Slip plane orientations of some deep-focus earthquakes suggest that earthquakes can be triggered by reactivation of pre-existing faults in the transition zone. In order to test this theory, we have studied the effect of the olivine-wadsleyite transition on the remobilization of pre-existing olivine faults by performing axisymmetric deformation experiments in a multi-anvil apparatus. Experiments were performed on 3 mm long,

D. Dobson; A. de Ronde; F. Heidelbach; P. Meredith; S. Boon

2006-01-01

329

Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere  

Microsoft Academic Search

The oceanic asthenosphere is observed to have high electrical conductivity, which is highly anisotropic in some locations. In the directions parallel and normal to the plate motion, the conductivity is of the order of 10-1 and 10-2Sm-1, respectively, which cannot be explained by the conductivity of anhydrous olivine. But because hydrogen can be incorporated in olivine at mantle pressures, this

Takashi Yoshino; Takuya Matsuzaki; Shigeru Yamashita; Tomoo Katsura

2006-01-01

330

Combining [ 3He] cosmogenic dating with U–Th\\/He eruption ages using olivine in basalt  

Microsoft Academic Search

This paper presents new U–Th\\/He crystallization and 3He exposure ages on olivine for a suite of basalt samples from the Snake River Plain, Idaho. The results provide the first demonstration that U–Th\\/He geochronology can be successfully applied to Late Quaternary basalts using measurements of olivine phenocrysts as opposed to U-rich minerals. The approach employs abrasion to remove the outer rinds

Sarah M. Aciego; Donald J. DePaolo; B. M. Kennedy; Michael P. Lamb; Kenneth W. W. Sims; William E. Dietrich

2007-01-01

331

Experimental Study of the Effects of Dissolved Sulfur on Olivine-Liquid Ni Partitioning Behavior  

Microsoft Academic Search

The partitioning of Ni between olivine and a silicate melt is best described in terms of the Nernst partition coefficient, DNi which is equal to (wt % Ni)oliv \\/ (wt % Ni)melt. Ni in a silicate melt may partition into olivine according to the following reaction NiOmelt+ Fe2Si0.5O2oliv = Ni2Si0.5O2oliv + FeOmelt. In the presence of dissolved S, the oxide

J. G. Brophy; C. Li

2003-01-01

332

Cr-spinel\\/olivine and Cr-spinel\\/liquid nickel partition coefficients from natural samples  

Microsoft Academic Search

The Nernst partition coefficient of nickel (DNi) between Cr-spinel and silicate melt in natural systems has been investigated using mid-ocean ridge basalts (MORB) and other volcanic rocks. The Cr-spinel\\/olivine DNi values in volcanic rocks are between 1.2 and 0.3, indicating that the Cr-spinel\\/liquid DNi values vary from slightly higher to significantly lower than the olivine\\/liquid DNi values in natural systems.

Chusi Li; Edward M. Ripley; Yan Tao; Edmond A. Mathez

2008-01-01

333

The effect of S on the partitioning of Ni between olivine and silicate melt in MORB  

Microsoft Academic Search

The partitioning behavior of Ni between olivine and silicate melt in S-bearing systems has been investigated using mid-ocean ridge basalts (MORBs). The Nernst Ni partition coefficient between olivine and silicate melt (DNi) derived from the MORB samples varies between 4 and 9, values that are up to 50% lower than those derived from S-free experimental systems of similar composition. The

Chusi Li; E. M Ripley; E. A Mathez

2003-01-01

334

Lamellar pyroxene-spinel symplectites in lunar olivine from the Luna 24 regolith  

Microsoft Academic Search

Cr-Ca lamellae in a magnesian olivine grain (section 1611) from the Luna 24 regolith were investigated in detail by electron\\u000a microprobe analysis (EMPA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that\\u000a the lamellae are parallel to the (100) plane of oxygen closest packing in olivine and consist of regular vermicular intergrowths\\u000a of two phases, diopside

N. R. Khisina; R. Wirth; M. A. Nazarov

2011-01-01

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

Characterization and petrologic interpretation of olivine-rich basalts at Gusev Crater, Mars  

NASA Astrophysics Data System (ADS)

Rocks on the floor of Gusev crater are basalts of uniform composition and mineralogy. Olivine, the only mineral to have been identified or inferred from data by all instruments on the Spirit rover, is especially abundant in these rocks. These picritic basalts are similar in many respects to certain Martian meteorites (olivine-phyric shergottites). The olivine megacrysts in both have intermediate compositions, with modal abundances ranging up to 20-30%. Associated minerals in both include low-calcium and high-calcium pyroxenes, plagioclase of intermediate composition, iron-titanium-chromium oxides, and phosphate. These rocks also share minor element trends, reflected in their nickel-magnesium and chromium-magnesium ratios. Gusev basalts and shergottites appear to have formed from primitive magmas produced by melting an undepleted mantle at depth and erupted without significant fractionation. However, apparent differences between Gusev rocks and shergottites in their ages, plagioclase abundances, and volatile contents preclude direct correlation. Orbital determinations of global olivine distribution and compositions by thermal emission spectroscopy suggest that olivine-rich rocks may be widespread. Because weathering under acidic conditions preferentially attacks olivine and disguises such rocks beneath alteration rinds, picritic basalts formed from primitive magmas may even be a common component of the Martian crust formed during ancient and recent times.

McSween, H. Y.; Wyatt, M. B.; Gellert, R.; Bell, J. F.; Morris, R. V.; Herkenhoff, K. E.; Crumpler, L. S.; Milam, K. A.; Stockstill, K. R.; Tornabene, L. L.; Arvidson, R. E.; Bartlett, P.; Blaney, D.; Cabrol, N. A.; Christensen, P. R.; Clark, B. C.; Crisp, J. A.; Des Marais, D. J.; Economou, T.; Farmer, J. D.; Farrand, W.; Ghosh, A.; Golombek, M.; Gorevan, S.; Greeley, R.; Hamilton, V. E.; Johnson, J. R.; Joliff, B. L.; Klingelhöfer, G.; Knudson, A. T.; McLennan, S.; Ming, D.; Moersch, J. E.; Rieder, R.; Ruff, S. W.; Schröder, C.; de Souza, P. A.; Squyres, S. W.; Wänke, H.; Wang, A.; Yen, A.; Zipfel, J.

2006-01-01

337

Possible mantle origin of olivine around lunar impact basins detected by SELENE  

NASA Astrophysics Data System (ADS)

The composition, structure and evolution of the Moon's mantle is poorly constrained. The mineral olivine, one of the main constituents of Earth's mantle, has been identified by Earth-based telescopic observations at two craters on the near side of the Moon, Aristarchus and Copernicus. Global reflectance spectra in five discrete spectral bands produced by the spacecraft Clementine suggested several possible olivine-bearing sites, but one of the candidate occurrences of olivine was later re-classified, on the basis of continuous reflectance spectra over the entire 1?m band, as a mixture of plagioclase and pyroxene. Here we present a global survey of the lunar surface using the Spectral Profiler onboard the lunar explorer SELENE/Kaguya. We found many exposures of olivine on the Moon, located in concentric regions around the South Pole-Aitken, Imbrium and Moscoviense impact basins where the crust is relatively thin. We propose that these exposures of olivine can be attributed either to an excavation of the lunar mantle at the time of the impacts that formed the basins, or to magnesium-rich pluton in the Moon's lower crust. On the basis of radiative transfer modelling, we suggest that at least some of the olivine detected near impact basins originates from upper mantle of the Moon.

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

2010-08-01

338

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

339

High-temperature viscoelasticity of fine-grained polycrystalline olivine  

NASA Astrophysics Data System (ADS)

Torsional forced-oscillation and microcreep methods have been employed in a study of the viscoelastic behaviour of fine-grained polycrystalline olivine at high temperatures (to 1300°C), seismic frequencies and low strain amplitudes. The Fo90 specimens are of low porosity and low dislocation density. They vary in mean grain size from 8 to 150?m and contain only trace amounts (<<0.1vol%) of quenched melt glass. For T<=900°C, their behaviour is essentially elastic and the shear modulus G closely approaches that expected for a dense polycrystal from single-crystal elasticity data - confirming the suppression of thermal microcracking in this study. At higher temperatures, pronounced absorption-band dissipation and associated dispersion of the shear modulus provide evidence of linear viscoelastic behaviour. Both recoverable (anelastic) and permanent (viscous) strains are involved and the proportion of the latter increases with increasing temperature and decreasing frequency. Comparison of the results for the three specimens provides a clear indication that the viscoelastic behaviour, attributed to diffusional processes, is grain-size-sensitive with the dissipation and associated dispersion increasing with decreasing grain size. Both elastically accommodated and diffusionally accommodated grain-boundary sliding appear to be implicated.

Tan, B. H.; Jackson, I.; Fitz Gerald, J. D.

340

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

341

Properties of barred spiral galaxies  

NASA Astrophysics Data System (ADS)

Blue and near-infrared surface photometry of 15 barred spiral galaxies, combined with results from photometric and kinematic studies of barred galaxies, reveals that: (1) early Hubble types have flat bars with uniform intensities along their lengths and stellar spiral arms with amplitudes that decrease with radius, and (2) late Hubble types have bars with exponential-like intensity profiles and spiral arm amplitudes that increase or remain constant with radius. Relative bar luminosities are derived using Fourier decompositions of the bar azimuthal profiles. It is concluded that bars in early-type galaxies probably contain highly elongated stellar orbits out to the corotation vicinity and also stimulate stellar spiral structure either by continuously growing, in the case of a non-self-gravitating stellar disk, or by exciting a wave mode at a resonance, in the case of a strongly self-gravitating stellar disk. It is shown that bars in some late-type galaxies may extend out only to the inner Lindbald resonances and that they appear to be too short or too weak to drive prominent stellar spirals because the spirals in these galaxies are often irregular.

Elmegreen, B. G.; Elmegreen, D. M.

1985-01-01

342

Comparison of cosmic-ray exposure ages and trapped noble gases in chondrule and matrix samples of ordinary, enstatite, and carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

We performed a comprehensive study of the He, Ne, and Ar isotopic abundances and of the chemical composition of bulk material and components of the H chondrites Dhajala, Bath, Cullison, Grove Mountains 98004, Nadiabondi, Ogi, and Zag, of the L chondrites Grassland, Northwest Africa 055, Pavlograd, and Ladder Creek, of the E chondrite Indarch, and of the C chondrites Hammadah al Hamra 288, Acfer 059, and Allende. We discuss a procedure and necessary assumptions for the partitioning of measured data into cosmogenic, radiogenic, implanted, and indigenous noble gas components. For stone meteorites, we derive a cosmogenic ratio 20Ne/22Ne of 0.80 ± 0.03 and a trapped solar 4He/3He ratio of 3310 ± 130 using our own and literature data. Chondrules and matrix from nine meteorites were analyzed. Data from Dhajala chondrules suggest that some of these may have experienced precompaction irradiation by cosmic rays. The other chondrules and matrix samples yield consistent cosmic-ray exposure (CRE) ages within experimental errors. Some CRE ages of some of the investigated meteorites fall into clusters typically observed for the respective meteorite groups. Only Bath's CRE age falls on the 7 Ma double-peak of H chondrites, while Ogi's fits the 22 Ma peak. The studied chondrules contain trapped 20Ne and 36Ar concentrations in the range of 10-6-10-9 cm3 STP/g. In most chondrules, trapped Ar is of type Q (ordinary chondritic Ar), which suggests that this component is indigenous to the chondrule precursor material. The history of the Cullison chondrite is special in several respects: large fractions of both CR-produced 3He and of radiogenic 4He were lost during or after parent body breakup, in the latter case possibly by solar heating at small perihelion distances. Furthermore, one of the matrix samples contains constituents with a regolith history on the parent body before compaction. It also contains trapped Ne with a 20Ne/22Ne ratio of 15.5 ± 0.5, apparently fractionated solar Ne.

Eugster, Otto; Lorenzetti, Silvio; KräHenbühl, Urs; Marti, Kurt

2007-08-01

343

The planetesimal bow shock model for chondrule formation: A more quantitative assessment of the standard (fixed Jupiter) case  

NASA Astrophysics Data System (ADS)

One transient heating mechanism that can potentially explain the formation of most meteoritic chondrules 1-3 Myr after CAIs is shock waves produced by planetary embryos perturbed into eccentric orbits via resonances with Jupiter following its formation. The mechanism includes both bow shocks upstream of resonant bodies and impact vapor plume shocks produced by high-velocity collisions of the embryos with small nonresonant planetesimals. Here, we investigate the efficiency of both shock processes using an improved planetesimal accretion and orbital evolution code together with previous simulations of vapor plume expansion in the nebula. Only the standard version of the model (with Jupiter assumed to have its present semimajor axis and eccentricity) is considered. After several hundred thousand years of integration time, about 4-5% of remaining embryos have eccentricities greater than about 0.33 and shock velocities at 3 AU exceeding 6 km s-1, currently considered to be a minimum for melting submillimeter-sized silicate precursors in bow shocks. Most embryos perturbed into highly eccentric orbits are relatively large—half as large as the Moon or larger. Bodies of this size could yield chondrule-cooling rates during bow shock passage compatible with furnace experiment results. The cumulative area of the midplane that would be traversed by highly eccentric embryos and their associated bow shocks over a period of 1-2 Myr is <1% of the total area. However, future simulations that consider a radially migrating Jupiter and alternate initial distributions of the planetesimal swarm may yield higher efficiencies.

Hood, Lon L.; Weidenschilling, Stuart J.

2012-11-01

344

Barred Galaxies: Intrinsic or Extrinsic?  

NASA Astrophysics Data System (ADS)

A unified picture is presented of the formation of bar structures in disk galaxies of various morphological types. In order to discuss bar formation in the context of galactic disk formation, a simple analytic model is constructed of the growth of galactic disks by infall of primordial gas from halos and subsequent star formation in the disks. It is monitored during the course of disk growth whether or not the condition for spontaneous bar formation (i.e., bar instability) is fulfilled for the stellar disk component. It is found that the infall timescale is a key parameter that controls the dynamical property of the resulting stellar disk. Disks that grow fast by rapid infall experience gas-rich phases, in which massive gas clumps arising from gravitational instability in the gas disk heat the stellar disk component dynamically. When the disk has fully grown and becomes mostly stellar, it has already acquired enough random motions to suppress bar instability. On the other hand, when the gas infall from the halo region proceeds slowly, star formation (though less intense than in rapid infall cases) keeps gas mass in the disk low, leading to a dynamically cold stellar component due to lack of strong heating by massive gas clumps. Therefore, the stellar disk becomes unstable and forms a bar once its mass fraction relative to the total galaxy mass reaches a critical value. Based on this result, we propose that late-type barred galaxies, the disks of which are considered to have formed by slow accretion of the halo gas, have intrinsic origin, whereas the bars in early-type galaxies, whose disks are likely to have grown quickly, have been formed in tidal interactions with other galaxies. Numerical simulations have been carried out which show that the bars created by tidal perturbations tend to have a relatively flat density profile along the bar major axis with "shoulders" (abrupt steepening of the gradient) at the bar ends, whereas spontaneous bars have a steeper profile. The formation scenario described above, combined with this numerical result, can explain the observed dichotomy that early-type galaxies generally have a flat bar, while late-type galaxies have a bar of exponential type.

Noguchi, Masafumi

1996-10-01

345

How large are the bars in barred galaxies?  

NASA Astrophysics Data System (ADS)

I present a study of the sizes (semimajor axes) of bars in disc galaxies, combining a detailed R-band study of 65 S0-Sb galaxies with the B-band 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 R25 or exponential disc scalelength h) and absolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~ 3.3 kpc), ~0.2-0.8R25 (mean ~ 0.38R25) and ~0.5-2.5h (mean ~ 1.4h). Late-type bars extend to only ~0.5-3.5 kpc, ~0.05-0.35R25 and 0.2-1.5h their mean sizes are ~1.5 kpc, ~ 0.14R25 and ~0.6h. Sb galaxies resemble earlier-type galaxies in terms of bar size relative to h; their smaller R25-relative sizes may be a side effect of higher star formation, which increases R25 but not h. Sbc galaxies form a transition between the early- and late-type regimes. For S0-Sbc galaxies, bar size correlates well with disc size (both R25 and h); these correlations are stronger than the known correlation with MB. 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 MB for Sc-Sd galaxies. Because bar size scales with disc size and galaxy magnitude for most Hubble types, studies of bar evolution with redshift should select samples with similar distributions of disc size or magnitude (extrapolated to present-day values); otherwise, bar frequencies and sizes could be mis-estimated. Because early-type galaxies tend to have larger bars, resolution-limited studies will preferentially find bars in early-type galaxies (assuming no significant differential evolution in bar sizes). I show that the bars detected in Hubble Space Telescope (HST) near-infrared(IR) images at z~ 1 by Sheth et al. 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.

Erwin, Peter

2005-11-01

346

Reaction rim growth on olivine in silicic melts: Implications for magma mixing  

USGS Publications Warehouse

Finely crystalline amphibole or pyroxene rims that form during reaction between silicic host melt and cognate olivine xenocrysts, newly introduced during magma mixing events, can provide information about the timing between mixing and volcanic eruptions. We investigated rim growth experimentally by placing forsteritic olivine in rhyolitic and rhyodacitic melts for times between 25 and 622 h at 50 and 150 MPa, H2O-saturated, at the Ni-NiO buffer. Rims of orthopyroxene microlites formed from high-silica rhyolite and rhyodacite melts at 885??C and 50 MPa, and in the rhyolite at 150 MPa and 885??C. Rims of amphibole with lesser orthopyroxene formed in the rhyolite at 150 MPa and 800??C and in the rhyodacite at 150 MPa and 885??C. Irregular, convolute olivine edges and mass balance between olivine, melt, and rim phases show that olivine partly dissolved at all conditions. Iron-rich zones at the exteriors of olivines, which increased in width parabolically with time, show that Fe-Mg interdiffusion occurring in olivines was not outpaced by olivine dissolution. Linear increases of the square of rim widths with time suggest that diffusion within the melt is the rate-controlling process for olivine dissolution and rim growth. Rims grew one-half to one order-of-magnitude faster when melt water contents were doubled, unless conditions were far above the liquidus. Rim growth rate in rhyolite increases from 0.055 ?? 0.01 ??m2/h at 885 ??C and 50 MPa to 0.64 ?? 0.13 ??m2/h at 800 ??C and 150 MPa. Melt composition has a lesser effect on rim growth rates, with growth rate increasing as melt SiO2 content decreases. Pyroxene rims on olivines in andesite erupted from Arenal volcano (Costa Rica) grew at a rate of 3.0 ?? 0.2 ??m2/h over an eleven-year period. This rate is faster than those of the experiments due to lower melt viscosity and higher temperatures, and suggests that a magma mixing event preceded the start of the eruption by days.

Coombs, M. L.; Gardner, J. E.

2004-01-01

347

The rate of water loss from olivine-hosted melt inclusions  

NASA Astrophysics Data System (ADS)

Diffusive water loss from olivine-hosted melt inclusions has been reported previously. This process must be considered when interpreting melt inclusion data. This study measured the rate of water loss from olivine-hosted melt inclusions during heating-stage experiments to test a previous diffusive reequilibration model and the hydrogen diffusion mechanism that controls the rate. Olivine-hosted melt inclusions were heated to a constant temperature in reduced Ar gas in a heating stage for a few hours, and unpolarized Fourier transform infrared spectra were repeatedly measured through the inclusions. Water loss occurred rapidly in the experiments. Within a few hours, the water absorbance at 3,500 cm-1 wavenumber decreased by half. The observed water loss rate can be explained by the diffusive reequilibration model and hydrogen diffusion in olivine coupled with metal vacancy. The beginning of water loss was different in the low- and high-temperature experiments. At low temperatures (1,423 and 1,437 K), water loss did not occur in the initial 1 or 2 h. At high temperatures (1,471-1,561 K), water loss began immediately. The initial time period without water loss at low temperatures may be explained by a hydrogen fugacity barrier in the host olivine. At low temperatures, the internal pressure may be lower than the equilibrium pressure of melt inclusion and olivine, causing lower hydrogen fugacity in the melt inclusion than in the olivine, which will delay the water loss from the melt inclusion. The tested model and diffusivity were used to estimate the rate of water loss during homogenization experiments and magma eruption and cooling. For 1-h homogenization experiment, the model shows that large inclusions (50 ?m radius) in large olivines (500 ?m radius) are robust against water loss, while large or small inclusions (50-10 ?m radius) in small olivines (150 ?m radius) may suffer 30-100% water loss. For natural samples, the correlation between water concentration and melt inclusion and olivine sizes may be helpful to infer the initial water concentration, degree of diffusive reequilibration, and magma cooling rate.

Chen, Yang; Provost, Ariel; Schiano, Pierre; Cluzel, Nicolas

2011-09-01

348

Criminal careers behind bars.  

PubMed

In the criminal career literature, prison is usually viewed as an interruption of offending. Little research has applied the criminal career perspective to misconduct committed by prisoners. The current study used official data from a probability sample of 1,005 inmates from the southwestern United States to examine offending careers during incarceration. Descriptive and negative binomial regression analyses produced findings that suggest both similarities and dissimilarities between conventional and prison criminal careers. The incidence and prevalence of crime were inversely related to its seriousness but the magnitude of crime was higher in prison. One-third of inmates were never contacted for a prison violation and 74% were never contacted for a serious/violent violation. On the other hand, 40% of inmates were chronic or extreme career offenders even while incarcerated. A small cadre of inmates accounted for 100% of the murders, 75% of the rapes, 80% of the arsons, and 50% of the aggravated assaults occurring behind bars. Finally, prior criminality was the best predictor of prison offending, which is supportive of the importation model. While a significant number of inmates fully comply with prison rules, an even larger percentage of inmates continue to commit an array of crimes and rule violations despite the efforts of prison officials. PMID:14502694

DeLisi, Matt

2003-01-01

349

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

2013-05-30

350

Laboratory measurements of the viscous anisotropy of olivine aggregates.  

PubMed

A marked anisotropy in viscosity develops in Earth's mantle as deformation strongly aligns the crystallographic axes of the individual grains that comprise the rocks. On the basis of geodynamic simulations, processes significantly affected by viscous anisotropy include post-glacial rebound, foundering of lithosphere and melt production above subduction zones. However, an estimate of the magnitude of viscous anisotropy based on the results of deformation experiments on single crystals differs by three orders of magnitude from that obtained by grain-scale numerical models of deforming aggregates with strong crystallographic alignment. Complicating matters, recent experiments indicate that deformation of the uppermost mantle is dominated by dislocation-accommodated grain-boundary sliding, a mechanism not activated in experiments on single crystals and not included in numerical models. Here, using direct measurements of the viscous anisotropy of highly deformed polycrystalline olivine, we demonstrate a significant directional dependence of viscosity. Specifically, shear viscosities measured in high-strain torsion experiments are 15 times smaller than normal viscosities measured in subsequent tension tests performed parallel to the torsion axis. This anisotropy is approximately an order of magnitude larger than that predicted by grain-scale simulations. These results indicate that dislocation-accommodated grain-boundary sliding produces an appreciable anisotropy in rock viscosity. We propose that crystallographic alignment imparts viscous anisotropy because the rate of deformation is limited by the movement of dislocations through the interiors of the crystallographically aligned grains. The maximum degree of anisotropy is reached at geologically low shear strain (of about ten) such that deforming regions of the upper mantle will exhibit significant viscous anisotropy. PMID:23257885

Hansen, L N; Zimmerman, M E; Kohlstedt, D L

2012-12-20

351

Evolution of olivine lattice preferred orientation during simple shear in the mantle  

NASA Astrophysics Data System (ADS)

Understanding the variation of olivine lattice preferred orientation (LPO) as a function of shear strain is important for models that relate seismic anisotropy to the kinematics of deformation. We present results on the evolution of olivine orientation as a function of shear strain in samples from a shear zone in the Josephine Peridotite (southwest Oregon). We find that the LPO in harzburgites re-orients from a pre-existing LPO outside the shear zone to a new LPO with the olivine [100] maximum aligned sub-parallel to the shear direction between 168% and 258% shear strain. The strain at which [100] aligns with the shear plane is slightly higher than that observed in experimental samples, which do not have an initial LPO. While our observations broadly agree with the experimental observations, our results suggest that a pre-existing LPO influences the strain necessary for LPO alignment with the shear direction. In addition, olivine re-alignment appears to be dominated by slip on both (010)[100] and (001)[100], due to the orientation of the pre-existing LPO. Fabric strengths, quantified using both the J- and M-indices, do not increase with increasing shear strain. Unlike experimental observations, our natural samples do not have a secondary LPO peak. The lack of a secondary peak suggests that subgrain rotation recrystallization dominates over grain boundary migration during fabric re-alignment. Harzburgites exhibit girdle patterns among [010] and [001] axes, while a dunite has point maxima. Combined with the observation that harzburgites are finer grained than dunites, we speculate that additional phases (i.e., pyroxenes) limit olivine grain growth and promote grain boundary sliding. Grain boundary sliding may relax the requirement for slip on the hardest olivine system, enhancing activation of the two easiest olivine slip systems, resulting in the [010] and [001] girdle patterns. Overall, our results provide an improved framework for calibration of LPO evolution models.

Warren, Jessica M.; Hirth, Greg; Kelemen, Peter B.

2008-08-01

352

The Effect of Titanium on Water Incorporation and Rheology of Olivine  

NASA Astrophysics Data System (ADS)

While there is general agreement that water significantly affects the physical properties of rocks, the water incorporation mechanism, particularly in olivine, is still under debate. Experiments with synthetic, polycrystalline olivine allow the controlled addition of trace elements as well as water. To this end we have conducted hotpressing and deformation experiments with solution-gelation derived Fo90 olivine doped with Ca and Ti. While the addition of Ca does not change the behavior relative to trace element-free solgel, trace amounts of titanium have a significant effect both on water incorporation and the rheology. Infrared spectroscopy suggests that from the presence of titanium water is retained in olivine during prolonged firing in a controlled atmosphere furnace at 1400C, while it is lost in Ti- free olivine. The experimental infrared spectra have the same two prominent absorption bands at 3572 and 3525 cm-1 as spectra of olivine from xenoliths. These bands indicate that water (hydrogen) is incorporated in a titanium-clinohumite type point defect. This defect is stable and significantly affects the physical properties of mantle rocks at low water contents. Diffusion creep rates are increased by about one order of magnitude in Ti-doped olivine, even if water contents are below detection levels. Experiments with different capsule materials also highlight their importance for water retention in the absence of buffers. The potential significance of the relationship between Ti abundance, water content and rheology for natural systems is shown for example by the correlation between Ti content and hydrogen in titanium clinohumite defects in cratonic xenoliths.

Faul, U.; Farla, R. J.; Fitz Gerald, J. D.; Jackson, I.

2011-12-01

353

Experimental determination of Ni diffusion coefficients in olivine and their dependence on temperature, composition, oxygen fugacity, and crystallographic orientation  

Microsoft Academic Search

Diffusion couple experiments were carried out with San Carlos olivine (Fo90) and NiFe alloys (Ni100, Ni97Fe3, Ni90Fe10) or other olivine compositions (Fo100, Fo25) in order to determine the dependence on temperature, oxygen fugacity, composition and crystallographic orientation of Ni diffusion coefficient (DNi) in olivine. Experiments at 1 atmosphere total pressure cover a temperature range of 900–1445°C with run durations from

Christof Petry; Sumit Chakraborty; Herbert Palme

2004-01-01

354

Mineralogy and petrology of amoeboid olivine inclusions in CO3 chondrites: Relationship to parent-body aqueous alteration  

Microsoft Academic Search

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 (Fa0-1) is systematically converted into ferroan olivine (Fa60-75). We infer that the Fe, Si and O entered the assemblage along grain boundaries, forming ferroan

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

2002-01-01

355

Nickel, Cobalt and Chromium in early lunar magma ocean olivine: Constraints on the petrogenesis of the Mg-suite  

Microsoft Academic Search

The parental magmas of the lunar highlands Mg-suite cumulates had enigmatic chemical signatures. They co-crystallized Mg-rich olivine and Ca-rich plagioclase and had extremely evolved trace element signatures (KREEP). Most models of Mg-suite petrogenesis call upon early, Mg-rich, olivine dominated LMO cumulates as a source to explain the high Mg* of the parental magmas. The olivine in the Mg-suite, however, contains

S. M. Elardo; C. Shearer Jr.; D. S. Draper

2010-01-01

356

Male Bar Drinkers' Perspective on Female Bar Drinkers  

Microsoft Academic Search

Five focus group discussions were conducted with 34 male bar drinkers to obtain their perception of the character and risks for aggression among women they observe in bars. The majority of the men were European American (61.8%), 29.4% were African American, and 8.8% were from other ethnic groups. Their impressions of women were based on appearance, type and speed of

Kathleen A. Parks; Douglas M. Scheidt

2000-01-01

357

Compound chondrule formation in the shock-wave heating model: Three-dimensional hydrodynamics simulation of the disruption of a partially-molten dust particle  

NASA Astrophysics Data System (ADS)

We carried out three-dimensional hydrodynamics simulations of the disruption of a partially-molten dust particle exposed to high-speed gas flow to examine the compound chondrule formation due to mutual collisions between the fragments (fragment-collision model; [Miura, H., Yasuda, S., Nakamoto, T., 2008a. Icarus194, 811-821]). In the shock-wave heating model, which is one of the most plausible models for chondrule formation, the gas friction heats and melts the surface of the cm-sized dust particle (parent particle) and then the strong gas ram pressure causes the disruption of the molten surface layer. The hydrodynamics simulation shows details of the disruptive motion of the molten surface, production of many fragments and their trajectories parting from the parent particle, and mutual collisions among them. In our simulation, we identified 32 isolated fragments extracted from the parent particle. The size distribution of the fragments was similar to that obtained from the aerodynamic experiment in which a liquid layer was attached to a solid core and it was exposed to a gas flow. We detected 12 collisions between the fragments, which may result in the compound chondrule formation. We also analyzed the paths of all the fragments in detail and found the importance of the shadow effect in which a fragment extracted later blocks the gas flow toward a fragment extracted earlier. We examined the collision velocity and impact parameter of each collision and found that 11 collisions should result in coalescence. It means that the ratio of coalescent bodies to single bodies formed in this disruption of a parent particle is R=11/(32-11)=0.52. We concluded that compound chondrule formation can occur just after the disruption of a cm-sized molten dust particle in shock-wave heating.

Yasuda, Seiji; Miura, Hitoshi; Nakamoto, Taishi

2009-11-01

358

Impact of geoengineering with olivine dissolution on the carbon cycle and marine biology  

NASA Astrophysics Data System (ADS)

We investigate 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. If 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 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. These upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2 in examples for the rivers Amazon and Congo (Köhler et al., 2010). The secondary effects of the input of silicic acid connected with this approach leads in an ecosystem model (ReCOM2.0 in MITgcm) to species shifts aways from the calcifying species towards diatoms, thus altering the biological carbon pumps. Open ocean dissolution of olivine would sequestrate about 1 Pg CO2 per Pg olivine from which about 8% are caused by changes in the biological pumps (increase export of organic matter, decreased export of CaCO3). The chemical impact of open ocean dissolution of olivine (the increased alkalinity input) is therefore less efficient than dissolution on land, but leads due to different chemical impacts to a higher surface ocean pH enhancement to counteract ocean acidification. We finally investigate open ocean dissolution rates of up to 10 Pg olivine per year corresponding to geoengineering rates which might be of interest in the light of expected future emission (e.g. A2 scenario with emissions rising to 30 PgC/yr in 2100 AD). Those rates would still sequestrate only less than 20% of the emission until 2100, but would require that the nowadays available shipping capacity of tankers and bulk carriers is entirely used for olivine dissolution ten times a year. Reference Köhler, P.; Hartmann, J. and Wolf-Gladrow, D. A. (2010) Geoengineering potential of artificially enhanced silicate weathering of olivine, Proceedings of the National Academy of Science 107, 20228-20233, doi: 10.1073/pnas.1000545107.

Köhler, P.; Abrams, J.; Völker, C.; Wolf-Gladrow, D. A.; Hartmann, J.

2012-04-01

359

Boric Acid Reclamation System (BARS).  

National Technical Information Service (NTIS)

KLM Technologies' personnel have identified a Boric Acid Reclamation System (BARS) utilizing reverse osmosis and ultrafiltration to produce a recyclable grade of otherwise waste boric acid at PWRs, thus reducing a major source of low-level radwaste. The d...

B. G. Kniazewycz J. Markind

1986-01-01

360

Property Control through Bar Coding.  

ERIC Educational Resources Information Center

|A public utility company uses laser wands to read bar-coded labels on furniture and equipment. The system allows an 80 percent savings of the time required to create reports for inventory control. (MLF)|

Kingma, Gerben J.

1984-01-01

361

Effects of anneal, grain size and water content on deformation of olivine at subduction zone conditions  

NASA Astrophysics Data System (ADS)

Experimental study regarding to the effects of annealing process, grain size and water content on the deformation of polycrystalline San Carlos olivine has been performed at 3 GPa pressure with temperatures between 400 and 1000 C at a D-DIA facility at X17B2, NSLS. The total macroscopic strain is derived from the direct measurements of the images taken by X-ray radiograph technique. The differential stresses are deduced from elastic strains, which are calculated from olivine elastic properties. The experiments are preformed at constant strain rates of ~10-5-10-7s-1. Both annealed and unnannealed olivine samples exhibit a strain rate and temperature independent regime until a critical temperature where the olivine substantially softens. The annealed samples experience this softening process at temperatures as much as 370°C lower than the annealed samples. Grain size affects the rheological properties of olivine in the low temperature dislocation regime. Existence of water decreases the transition temperature of the boundary between the regimes of low temperature plasticity and power-law creep. The thermal softening of the unannealed samples could be the trigger of deep focus earthquakes in zones that were damaged by previous events.

Long, H.; Weidner, D. J.; Li, L.

2009-12-01

362

Sand bars in tidal channels. Part 1. Free bars  

NASA Astrophysics Data System (ADS)

We investigate the basic mechanism whereby bars form in tidal channels or estuaries. The channel is assumed to be long enough to allow neglect of the effects of end conditions on the process of bar formation. In this respect, the object of the present analysis differs from that of Schuttelaars & de Swart (1999) who considered bars of length scaling with the finite length of the tidal channel. The channel bottom is assumed to be cohesionless and consisting of uniform sediments. Bars are shown to arise from a mechanism of instability of the erodible bed subject to the propagation of a tidal wave. Sediment is assumed to be transported both as bedload and as suspended load. A fully three-dimensional model is employed both for the hydrodynamics and for sediment transport. At the leading order of approximation considered, the effects of channel convergence, local inertia and Coriolis forces on bar instability are shown to be negligible. Unlike fluvial free bars, in the absence of mean currents tidal free bars are found to be non-migrating features (in the mean). Instability arises for large enough values of the mean width to depth ratio of the channel, for given mean values of the Shields parameter and of the relative channel roughness. The role of suspended load is such as to stabilize bars in the large-wavenumber range and destabilize them for small wavenumbers. Hence, for large values of the mean Shields stress, it turns out that the first critical mode (the alternate bar mode) is characterized by a very small value of the critical width to depth ratio. Furthermore, the order-m mode being characterized by a critical value of the width to depth ratio equal to m times the critical value for the first mode, it follows that for large values of the mean Shields stress several unstable modes are simultaneously excited for relatively low values of the aspect ratio. This suggests that the actual bar pattern observed in nature may arise from an interesting nonlinear competition among different unstable modes.

Seminara, G.; Tubino, M.

2001-08-01

363

Valence State Partitioning of Vanadium Between Olivine-Melt in Olivine-Phyric Martian Basalts. Defining the fO2 of the Martian Mantle.  

NASA Astrophysics Data System (ADS)

Several recent studies have demonstrated that the fO2 in martian basalts varies by 2 to 3 log units and is correlated with geochemical parameters such as LREE/HREE, initial 87Sr/86Sr, and initial d. These correlations have been interpreted to indicate the presence of reduced, incompatible element-depleted and oxidized, incompatible element-enriched reservoirs that were produced during early stages of martian differentiation. Olivine-phyric basalts represent the closest approximation of primary martian basalts in the meteorite collection. Therefore, gaining a better understanding of the fO2 and incompatible element characteristics of the earliest phase (olivine) in these basalts may provide a clearer view into the martian mantle. Using the bulk composition of Yamato 980459 (an olivine-phyric basaltic melt composition), we conducted a series of near-liquidus experiments to determine the partitioning of V between olivine-melt at fO2 conditions between QFM and IW-1. XANES analyses of the glass indicate that the V4+/V3+ varies systematically with redox conditions of the experiments. SIMS analyses of V in glass and olivine indicated a systematic increase in DVol/melt from approximately 0.055 at QFM to approximately 0.5 at IW-1. This is consistent with the observed variation in V4+/V3+ measured in the glass by XANES and the crystal chemical preference of the olivine octahedral site for V3+ rather than V4+. Applying this oxybarometer calibration to well-defined lunar (IW-1) and terrestrial basaltic systems (QFM+0.2, Makaopuhi lava lake, Hawaii) indicate that it is vary robust over a wide range of planetary fO2 conditions. The determination of DVol/melt and incompatible element abundance using SIMS from martian olivine-phyric basalts indicate that they crystallized over a rather broad range in fO2 (IW+0.2 to IW+2) and from basaltic magmas with a range of incompatible element enrichments. These data indicate that correlations among these geochemical parameters are fundamental characteristics of the closest approximations of primary martian magmas. These signatures were not incorporated into the basaltic magmas during crystallization or involved late-stage processes. This suggests that if assimilation of martian crust by reduced, mantle derived magmas was an important mechanism for producing this array, assimilation occurred prior to the crystallization of any of the olivine now in these olivine-phyric shergottites. Thus the assimilation must have occurred at the base of the martian crust and all mineralogical evidence of assimilation was removed during transport to the martian surface. It appears more-likely that rather than assimilation, these arrays represent different mantle sources. This has substantial implications for the dynamics of a martian mantle that maintained two distinctly different reservoirs that were formed during initial martian differentiation at 4.5 Ga.

Shearer, C.; McKay, G.; Papike, J.; Karner, J.; Sutton, S.

2005-12-01

364

The olivine-wadsleyite phase transformation in mantle peridotite  

NASA Astrophysics Data System (ADS)

One of the most important goals in the study of the olivine (?) - wadsleyite (?) transformation is to understand the seismic discontinuity observed near the depth of 410 km in the Earth’s mantle. Although one school of thought attributes this discontinuity to radical chemical changes from lherzolite to picritic eclogite[1], the ?-? transformation in an isochemical peridotitic mantle has widely been accepted as the underlying cause. If the latter interpretation is valid, the composition and temperature can be inferred by the depth and magnitude of the discontinuity, providing useful information for understanding the present state of the Earth’s transition zone. In spite of extensive experimental investigations of this transformation, most studies were conducted in the simple system Mg2SiO4-Fe2SiO4 and/or using the quenching technique[2]. No efforts have been directed to study the kinetic barrier of the ?-? transformation under normal mantle conditions. In addition, recent studies have demonstrated increasing needs for the study of the ?-? transformation in multi-component systems relevant to the Earth’s mantle[3,4]. We choose the KLB-1 spinel lherzolite, a xenolith from Kilborne Hole Crater in New Mexico USA, as starting material because it represents one of the most undepleted mantle compositions. The high P-T x-ray diffraction experiments were conducted using a two-stage multi-anvil press on beamline 13-BM-D of Advanced Photon source, Argonne National Laboratory. Phase identifications were made by observing the first appearance of a phase that was absent in the starting sample and by closely monitoring complete disappearance of a low-pressure phase from the assembly. In the presence of both ? and ? phases, transformation direction was identified by observing a significant change in the relative intensity between the two phases. Our results demonstrate the experimental feasibility of studying ?-? transformation in complex systems and of resolving pressure differences of less than 0.4 GPa for the two-phase loop, even with the effect of kinetic barrier being taken into account. References: [1] Anderson and Bass, Nature 320, 321, 1986; [2] Katsura and Ito, J. Geophys. Res. 94, 15663, 1989; [3] Stixude, J. Geophys. Res. 102, 14835, 1997; [4] Irifune and Isshiki, Nature 392, 702, 1998.

Zhang, J.; Zhao, Y.; Wang, L.; Wang, Y.

2009-12-01

365

Trace-Element Analysis of Metal Nodules, Magnetic and Nonmagnetic Fractions, and Chondrules of the Qingzhen EH3 Chondrite  

NASA Astrophysics Data System (ADS)

The contents of Na, Sc, Cr, Mn, Fe, Co, Ni, Zn, Ga, As, Se, Br, Sb, W, Ir, and Au in metallic nodules, magnetic and nonmagnetic fractions, and chondrules of the Qingzhen EH3 chondrite have been determined by instrumental neutron activation analysis (INAA). Five of the largest separated chondrules (0.07- 5.77 mg) were selected for INAA. After extraction of the chondrules, the residual sample was gently ground to reduce the grain size and sieved into the following fractions: >500 micrometers, 200-500 micrometers, 100-200 micrometers, 50-100 micrometers, 15-50 micrometers, and <15 micrometers. All fractions were separated by a hand magnet into a nonmagnetic fraction, consisting mainly of silicates and sulfides (mainly troilite), and a magnetic fraction consisting of metal, sulfide, and minor sili