PPS22-01

Room:A02

Time:May 28 09:00-09:30

Formation ages and places of hydrated chondrite parent bodies
FUJIYA, Wataru1∗
1

Max Planck Institute

When and where hydrated chondrite parent bodies accreted is a key question to understand the origin of chondritic water andthe dynamical processes of the solar system evolution.
The ages of aqueous alteration can be inferred from 53 Mn-53 Cr systematics of aqueously-formed secondary minerals (carbonates in CM, CI, and CR chondrites and fayalite in CV, CO, and ordinary chondrites). The 53 Mn-53 Cr ages of carbonates andfayalite in carbonaceous chondrites (CCs) are similar, 3.5 ‒ 5 Myr after the birth of the solar system (represented by CAIs inCVs) (Fujiya et al., 2013; Doyle et al., submitted). Fayalite in ordinary chondrites (OCs) seems to have formed slightly earlier(∼1 Myr) than that in CCs. These observations are consistent with 26 Al-26 Mg ages of chondrules (e.g., Kita and Ushikubo,2012). The 53 Mn-53 Cr ages of aqueous alteration indicate that water activity on CC and OC parent bodies started almost contemporaneously, and that the dominant heat source for aqueous alteration is the decay energy of 26 Al (half-life: 0.7 Myr). Basedon these ages, numerical simulations of the thermal history of CC and OC parent bodies suggest that they accreted 2.5 ‒ 4 Myr
after CAIs (Sugiura and Fujiya, 2014).
The formation places of chondrite parent bodies in the protoplanetary disk are more difficult to be inferred. The estimated water(ice) to rock mass ratios of CCs and OCs (<0.6) (e.g., Clayton and Mayeda, 1999), significantly lower than the solar value (1.2)(Lodders, 2003), suggest that CC and OC parent bodies accreted near from the snow line. The inferred D/H ratios and O isotopic
compositions of water in CCs are likely to be significantly different from those of primordial (molecular cloud) water and/or mostOort-cloud comets measured so far, indicating that they must have recorded various degrees of isotopic re-equilibration between
primordial water and nebular gas (Alexander et al., 2012; Krot et al., 2013). Model predictions on the location of the snow line
2.5 ‒ 4 Myr after CAIs (e.g., Ciesla and Cuzzi; 2006) and both the temporal and the spatial distribution of H and O isotopic
ratios of water in the protoplanetary disk (e.g., Yang et al., 2011, 2013) suggest that hydrated chondrite parent bodies accreted in
the main asteroid belt. I am currently trying to constrain the contribution of C from cometary inorganic ice to the C inventory inCCs. Carbon isotopic ratios of carbonates in Murchison (CM) suggest that C reservoirs in primitive aqueous fluids were highly
enriched in 13 C with δ 13 C >70 ‰, which provides no evidence for C contribution from cometary ice (Fujiya et al., submitted).
Keywords: Hydrated chondrites, Formation ages, Formation places, Compositions of stable isotopes

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PPS22-02

Room:A02

Time:May 28 09:30-09:45

Aqueously altered clasts in the NWA1232 CO3 carbonaceous chondrite
MATSUMOTO, Megumi1∗ ; TOMEOKA, Kazushige2 ; SETO, Yusuke2 ; MIYAKE, Akira3 ; KIRIISHI, Miho2 ;UMEHARA, Mariko2 ; YAMAMOTO, Yukiko2 ; HAMANE, Daisuke4
1

CSREA, Kobe Univ., 2 Graduate School of Science, Kobe Univ., 3 Graduate School of Science, Kyoto Univ., 4 ISSP, Tokyo Univ.

CO parent bodies are generally believed to have escaped significant degree of brecciation. However, Northwest Africa 1232
(NWA1232) CO3 chondrite is a breccia consisting of three distinct lithologies (A, B, and C) that have experienced different
degrees of thermal metamorphism [1,2] . Recently, we found that lithology A, which is the host lithology of NWA1232, contains
numerous small clasts (100-1800 µm in diameter) of different metamorphic grades [3,4] . Most of the clasts show little evidenceof thermal metamorphism and contain significant amounts of hydrous minerals. These characteristics have not been known inother CO3 chondrites and potentially provide new insights into the formation of CO3 chondrites. Here, we report the resultsof detailed mineralogical and petrographic study of the hydrous clasts in NWA 1232. We used SEM-EDS, TEM (STEM)-EDS,
EPMA-WDS, and SR-XRD.
Small clasts occur abundantly throughout lithology A. Among them, hydrous clasts are most abundant and comprise ˜2 vol.%of lithology A. Each of the clasts typically consists of one chondrule surrounded by a fine grained matrix, exhibiting the appearance of a chondrule with a rim. Some clasts contain multiple chondrules and CAIs embedded in a matrix.
Most chondrules in the clasts are Mg-rich Type I, and their olivine phenocrysts have homogeneous low Fe compositions (˜Fa1 )and show almost no Fe-Mg zoning; these are similar to those in CO3.0 chondrites. Enstatite phenocrysts and mesostasis werepartially replaced by fine grains (10-20 nm) of phyllosilicates and an Fe-Si-Mg-rich amorphous material. The amorphous material contains small amounts of fine olivine grains (<100 nm). High-resolution TEM observations reveal that the most abundantphyllosilicate exhibits ˜0.7 nm basal spacing; thus, it is serpentine. Minor amounts of smectite with 1.0-1.1 nm basal spacing,were also observed. These phyllosilicates are compositionally indistinguishable from the amorphous material.
The rim-like matrix surrounding the chondrules mainly consists of an Fe-Si-Mg rich amorphous material, and contains relatively coarse grains (1-2 µm) of magnetite, forsteritic olivine, enstatite, fine grains (100-500 nm) of olivine, troilite, and finer
grains (10-20 nm) of serpentine. The amorphous material is compositionally indistinguishable from the serpentine and mineralogically and compositionally similar to that within the chondrules.
Our results suggest that the clasts have experienced weak aqueous alteration in the meteorite parent body. However, theevidence of aqueous alteration was not observed in the outside of the clasts. These suggest that the clasts were formed andtransported from a region in the parent body that was different from the region where the meteorite was finally lithified, andsubsequently they were incorporated into lithology A. We note that the mineralogical and compositional characteristics of chondrules and matrix in the clasts are similar to those in the primitive CO3.0 chondrite ALHA77307 [5] .
References: [1] Kiriishi and Tomeoka (2008), JMPS, 103, 161-165. [2] Umehara et al. (2009), JAMS Annual Meeting (abstract). [3] Kiriishi et al. (2009), JAMS Annual Meeting (abstract). [4] Matsumoto et al. (2014), JpGU Meeting (abstract). [5]Brearley (1993), GCA, 57, 1521-1550.

Keywords: CO chondrite, clast, brecciation, aqueous alteration, TEM, SR-XRD

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PPS22-03

Room:A02

Time:May 28 09:45-10:00

Hydrothermal alteration experiments of MgO-SiO2 amorphous silicates
TAKAHASHI, Ryohei1 ; TSUCHIYAMA, Akira1∗ ; MIYAKE, Akira1 ; KAWAMURA, Katsuyuki2
1

Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, 2 Graduate School of Environmental
and life Science, Okayama University
Hydrothermal alteration is one of the important processes for solid evolution in the early solar system. So far, many experiments have focused on reaction between aqueous fluids and meteorite itself or crystalline silicates, such as olivine and pyroxene(e.g., [1, 2]). Reaction with amorphous silicates is also important because interstellar dust as original building blocks of planetesimals is mostly amorphous [3] and primitive amorphous silicates are present in cometary dust as GEMS (e.g., [4]) and somecarbonaceous chondrites (e.g., [5]). Hydrothermal alteration experiments with amorphous silicates were also carried out using
natural GEMS [6] and synthetic materials with CI composition [7]. However, any experiments using amorphous silicates ina simple system have not been made. In this study, hydrothermal alteration experiments of amorphous silicates in the system
MgO-SiO2 -H2O were carried out to understand basic features of hydrous layer silicate formation.
Nanoparticles of amorphous silicates ˜10 nm in size with nearly enstatite and forsterite compositions (E and F: Mg/Si = 1.15
and 2.02) were synthesized by the induction thermal plasma method as starting materials. Intermediate compositions were also
prepared by mixing E and F (ME, M and MF: Mg/Si=1.25, 1.5 and 1.75). Three types of experiments were made. (1) Synthetic experiments: Starting materials and pure water (water/rock ratio: W/R=5.0) were sealed and heated at 50, 100, 150 and
200o C or held at room temperature for 0 to 1344 hrs. The run products were dried in vacuum and examined by powder X-ray
diffraction (XRD) and SEM/EDX. (2) In-site experiments: Starting materials mixed with pure water (W/R=5.0) were exposed inwater-saturated atmosphere at 60o C and repeatedly measured by in-situ powder XRD (total duration: 9-292.5 hrs.). The final run
products were dried in vacuum and measured again by powder XRD. (3) Swelling experiments: some dried run products were
immersed in ethylene glycol, glycerol or water and measured by powder XRD to check swelling.
Layer silicates formed in all the run products even at room temperature. Brucite and sometimes magnesite were formed in runs
using F. XRD reflection peaks of the layer silicates are week and broad particularly for the (001) peak suggesting that they are thinand have low crystallinity. The (001) lattice spacing and the chemical compositions of the run products together with the resultsof the swelling experiments indicate that the layer silicates are disordered mixed layer minerals of stevensite (Mg-smectite) orvermiculite, serpentine and talc. The (001) peak becomes sharper to some extent and shift to higher 2θ (smaller lattice spacing)with increasing run duration or temperature except for runs using E. The crystallinity and degree of mixing order also changedby drying process. The experimental results can be explained by that aqueous solutions of high degree of supersaturation withrespect to layer silicate minerals formed by instantaneous dissolution of metastable amorphous silicate nanoparticles with highreactivity, and disordered mixed layer minerals metastably formed from these solutions. The presence of disordered mixed layer
minerals in some carbonaceous chondrites, such as in CI [8], indicates that they formed from amorphous silicates. It should also
be noted that we could not discuss hydrothermal conditions based on the present features of layer silicate minerals in meteorites,as they could be different from those during hydrothermal alteration.
[1] Jones and Brearley (2006) GCA, 70: 1040. [2] Ohnishi and Tomeoka (2007) MAPS, 42: 49. [3] Kemper et al. (2004) ApJ.
609: 826. [4] Bradley et al. (1994) GCA, 58: 2123. [5] Greshake (1997) GCA, 61: 437. [6] Nakamura et al. (2005) MAPS, 40:
A110. [7] Noguchi et al. (2008) MAPS. 43: A177. [8] Tomeoka and Buseck (1988) GCA, 52: 1627.
Keywords: hydrous layer silicate, hydrous alteration, carbonaceous chondrites, induction thermal plasma method, disordered
mixed layer minerals

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PPS22-04

Room:A02

Time:May 28 10:00-10:15

Hydrothermal and heating experiments: Implications for formation process of nephelinein carbonaceous chondrite
ICHIMURA, Shun1∗ ; SETO, Yusuke1 ; TOMEOKA, Kazushige1 ; OHI, Shugo2
1

Graduate School of Science, Kobe University, 2 Graduate School of Science, kyoto University

Nepheline (NaAlSiO4 ) and sodalite (Na4 Al3 Si3 O12 Cl) are widely distributed in chondrules and matrices of CO/CV chondrites(Kimura et al. 2014; Matsumoto et al. 2014). Because of the low condensation temperatures of such Na-rich minerals, these
are likely not primary phases condensed from the solar nebula, but are secondary phases altered from melilite or plagioclase.
According to previous petrographic studies (e.g. Russell et al., 1998; Tomeoka and Itoh, 2004), nepheline and sodalite are considered to form by hydrothermal processes on their parent body. Because of the high volatility and high mobility, Na element
is potentially a powerful indicator reflecting aqueous environments of the chondrite parent bodies. In this study, we performedhydrothermal alteration experiments to understand the formation process of Na-rich minerals in chondrite parent bodies.
We used i) synthetic melilite (gehlenite, Ca2 Al2 SiO7 ) + SiO2 , and ii) natural plagioclase (An48 ) as starting materials. Fourreaction solutions of 1N (mol/l)-NaOH (pH 0), H2 O (pH 7), 0.1N-NaOH (pH 13) and 1N-NaOH (pH 14) were reacted with threedifferent water/rock ratios (10, 100 and 1000). Na+ concentration in all solutions was maintained at 1 mol/l by addition of NaCl.
Hydrothermal alteration experiments were performed with a PTFE reaction vessel loaded into steel autoclave and were carriedout at temperature at 200 ℃ and pressure of 1.5 MPa for run duration time of 168 hours. The recovered samples were analyzed
by XRD, SEM, TEM, and TG-DTA.
In the experiments using melilite+SiO2 with W/R = 100 and pH 7-14 solutions, hydrogrossulor (Ca3 Al2 [SiO4 ]1.6 [O4 H4 ]1.3 )formed as a secondary phase with low SiO2 contents, while analcime (NaAlSi2 O6 H2 O), nepheline-hydrate (NaAlSiO4 H2 O),
basic-cancrinite (Na8 Al6 Si6 O24 [OH]2 •2H2 O) and tobermorite (Ca5 Si6 O16 [OH]2 •4H2 O) formed with high SiO2 contents. Although no secondary phase was observed at high W/R (=1000), analcime and basic-cancrinite occurred at low W/R (=10). Under
the pH 0 solution, melilite was dissolved and no secondary phases formed. In the experiments using plagioclase with W/R = 100
and pH 0-7 solutions, no secondary phases formed. On the other hand, under pH 13-14 solutions, analcime and nepheline-hydrate
formed with W/R = 10 and 100.
A TG-DTA of nepheline-hydrate at heating rate 5 ℃/min in air showed that the dehydration started at ˜100 ℃ and finishedat ˜800 ℃. From the DTA and XRD data of this condition, nepheline-hydrate is considered to be transformed into nepheline at
˜800 ℃. From the TG-DTAs of nepheline-hydrate with different heating rates, we estimated that nepheline-hydrate could alter tonepheline for at least ˜103 years at 400 ℃. A TG-DTA of analcime at heating rate 2 ℃/min in air showed that dehydration started
at ˜120 ℃ and finished at ˜500 ℃. The XRD data showed analcime is transformed into nepheline and amorphous material below
1000 ℃, although we failed to estimate the required time of the transformation because of the DTA curves of analcime were toocomplicated.
The present results show melilite and plagioclase are easily altered into hydrous minerals like nepheline-hydrate and analcime
in Na+ -rich high alkali solutions. Because the experimental condition demonstrated in the present study seems to be comparable
to actual carbonaceous chondrite parent body, we infer that nepheline in carbonaceous chondrite formed initially as intermediate
products like nepheline-hydrate and analcime during aqueous alteration, and these hydrous minerals was subsequently dehydrated to nepheline.
Keywords: nepheline, melilite, aqueous alteration, hydrothermal experiments, dehydration heating experiments, carbonaceouschondrite

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PPS22-05

Room:A02

Time:May 28 10:15-10:30

Microtextures in the MAC 88107 carbonaceous chondrite: Is this meteorite really a primary accretionary rock?
SAKAI, Midori1∗ ; TOMEOKA, Kazushige1 ; SETO, Yusuke1 ; MIYAKE, Akira2
1

Department of Earth and Planetary Sciences, Faculty of Science, Kobe University, 2 Department of Geology and Mineralogy,
Graduate School of Science, Kyoto University
MAC 88107 is an ungrouped carbonaceous chondrite having intermediate properties between the CM and CO groups [1] .
Carbonaceous chondrites generally consist of chondrules and inclusions embedded in a fine-grained matrix, which constitutes>30 vol.% of the meteorites. In contrast, MAC 88107 virtually has no matrix and consists mainly of chondrules and inclusions
surrounded by rims. The rims are thought to have formed by accretion of dust onto the surface of chondrules and inclusions while
floating in the solar nebula [2] . Thus, meteorites like MAC 88107 are thought to be “primary accretionary rocks” , which formed
directly from the solar nebular [2] . However, recent studies of chondrules/rims in the Mokoia CV chondrite show abundant evidence for rim formation within the meteorite parent body [3,4] . Based on the model proposed by [3, 4], the rims are remnants offormer matrix adhering to chondrules and inclusions.
To reevaluate the formation processes of MAC 88107, we performed detailed observation and analyses of this meteorite using
SEM-EDS, STEM-EDS, and SR-XRD.
The rims in MAC 88107 mainly consist of extremely fine-grained material (<1µm) with small fragments (1-10 µm) of
forsterite, enstatite, and magnetite-fayalite-hedenbergite aggregates. Our STEM observations and SR-XRD measurements reveal that the extremely fine-grained material consists mostly of an amorphous material with minor amounts of phyllosilicate,olivine, pyroxene, pentlandite, and magnetite.
Many rims in MAC 88107 contain characteristic veins (˜10 µm in width) consisting of coarse grains (1-15 µm) of magnetite,
fayalite, and hedenbergite. Krot et al. (2000) [1] suggested that these veins were formed during fluid-assisted oxidation of metalsulfide nodules in chondrule peripheries. The oxidation was associated with a volume increase, induced high stresses in adjacentrims, and eventually broke to form fractures, which were subsequently filled with growing magnetite. However this model cannot explain the presence of veins in rims around CAIs which have no opaque nodules. If the veins were originated from cracks
formed by brecciation of the present meteorite lithology, there should have been veins penetrating multiple chondrules/rims.
However such vein is absent. These facts suggest that the veins were formed from cracks that resulted from brecciation of aprecursor lithology of the chondrules/rims.
Characteristic layers, 5-30 µm in width, occur between neighboring rims. These layers consist of relatively coarse-grained
magnetite, fayalite, and hedenbergite. Krot et al. (2000) [1] termed them “inter-rim layers” . The mineralogy and texture ofinter-rim layers resemble to those of veins in the rims.
We found several clasts which contain multiple chondrules in MAC 88107. These clasts are 150-500 µm in diameter and haveround shapes. They contact with adjacent chondrules or rims directly or through inter-rim layers. The chondrules in the clasts
have no rims. The matrices of the clasts have mineralogy and texture similar to the chondrule rims in the outside of the clasts.
These observations suggest that the chondrules/rims are actually clasts that resulted from brecciation of a precursor lithology andsubsequent transportation and abrasion.
From these results, we suggest that MAC 88107 was formed through the following processes: (1) formation of chondrule/rim
clasts by brecciation of a precursor lithology, (2) transportation and abrasion, and (3) accumulation and lithification of thoseclasts.
References:[1] Krot et al. (2000) MAPS 35, 1365?1386. [2] Metzler et al. (1992), GCA 56, 2873?2897. [3] Tomeoka and Ohnishi (2010),
GCA 74, 4438?4453. [4] Tomeoka and Ohnishi (2014), GCA 137, 18?34.
Keywords: MAC 88107, Primary accretionary rock, Carbonaceous chondrite, Brecciation, Aqueous alteration, Chondrule rims

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PPS22-06

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Time:May 28 10:30-10:45

Estimation of the equilibrium form of olivine from negative crystals in an equilibratedchondrite
NAKAMURA, Ryuta1∗ ; TSUCHIYAMA, Akira1 ; MIYAKE, Akira1 ; MATSUMOTO, Toru1 ; OHI, Shugo1 ;TAKIGAWA, Aki1 ; UESUGI, Kentaro2
1

Division of Earth and Planetary Sciences, Kyoto University, 2 Japan Synchrotron Radiation Research Institute

Olivine is one of the most common minerals both in the solar system and the interstellar and circumstellar environments.
Adsorption of hydrogen atoms and water molecules onto the olivine surfaces may play a significant role in the formation ofhydrogen molecules in the interstellar medium and the origin of water in the earth [2,3]. The crystal orientations of the olivinesurfaces may affect adsorption efficiency and reaction rates, and thus it is important to understand crystal forms of olivine.
Although the equilibrium form of olivine has been investigated based on the surface energies of olivine obtained by Ab initio
calculations [1], it has not been confirmed by observations of naturally occurred olivine.
Many voids with facets (negative crystals) several um in size have been identified within olivine grains in HAYABUSA samples
and equilibrated chondrites [4]. These negative crystals appear to be the equilibrium form because equilibrated chondrites haveexperienced thermal metamorphism at ˜800o C. In this study, we analyze the three-dimensional shapes of negative crystals in an
olivine grain to obtain the equilibrium form of olivine using micro-sampling with focused ion beam (FIB) and micro-tomography[5]. The results are compared with the estimated equilibrium form by the Ab initio calculations.
A thin section of Tuxtuac meteorite (LL5) was used in this study. A negative-crystal-rich region of an olivine grain was
identified by an optical microscope. The 30x30x60 um3 sized micro-sample was prepared by an FIB technique (FEI Quanta 200
3DS). X-ray microtomography was performed at the SPring-8 BL47XU beamline at (7 keV, 70.5 nm/voxel). Negative crystals
were extracted three-dimensionally by binarization of the CT images. The orientation of the host olivine crystal was determinedwith an FE-SEM/EBSD (JEOL 7001F/HKL CHANNEL5) and face angles of the negative crystals were measured using the
3D-CT images. Crystal plane indices of negative crystals were determined from the obtained crystal orientation and face angles.
We identified seven negative crystals 2-4 um in size. They aligned in the same plane within the olivine crystal suggestingthat they are a healed crack as well as those in the HAYABUSA samples [5]. All negative crystals have developed facets of thesame crystal orientations and have similar morphology, and some edges were rounded, which indicate that the morphology of thenegative crystals almost represents the equilibrium form of olivine. The (100), (001), and (011) facets were observed and (100)facet was most well-developed. The other facets seem to be (001), (102), and (343) planes although these facets were small withrespect to the spatial resolution of the micro-tomography.
Forsterite surface energies determined by Ab initio calculation increase in order of (010), (120), (001), (101), (111), (021),
and (110) [1]. The observed (010), (120), and (001) planes have low surface energies while the surface energy of the (100)plane is high [6] and those of (011), (102), and (343) are probably high as well. The possible interpretations of unexpected
facet planes with high energies are (1) changing surface energy due to adsorption of molecules onto the crystal surface, (2)temperature dependence of the surface free energy, and (3) kinetic effect. If surface energies change due to adsorption ofmolecules, anisotropy of the surface structures would play an important role for surface stability. Evaporation rate of forsterite
along the a-axis in hydrogen gas at less than 1400o C is smaller than those along the b- and c-axes [7], which is consistent withthis study.
[1] Bruno et al, 2014, J. Phys. Chem. C, 118, 2498.
[2] Vattuone et al, 2013, Phil. Trans. R. Soc, A371, 20110585.
[3] Navaro-Ruiz et al, 2014, PCCP, DOI:10, 1039/c4cp00819g.
[4] Tsuchiyama et al, 2014, MAPS, 49, 172.
[5] Tsuchiyama et al, 2014, MAPS, 49, 404.
[6] Takahashi, Personal communication,[7] Takigawa et al, 2009, ApJ, 707, 97.

Keywords: equilibrium form, negative crystal, equilibrated chondrite, olivine, Ab initio, surface energy

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PPS22-07

Room:A02

Time:May 28 11:00-11:15

An experimental study on the formation of the type I chondrules
IMAE, Naoya1∗ ; ISOBE, Hiroshi2
1

National Institute of Polar Research, 2 Kumamoto University

Introduction: Chondrules have been reproduced at 1 bar under the IW-0.5 oxygen pressure, where FeO-rich, type II chondrules
are produced. Although type I chondrules have been experimentally examined by Cohen and Hewins (2004), the charge wasquenched and dissimilar to natural chondrules. In the present study, chondrules were reproduced under the condition of the IW-3
to -5 with the various cooling rates mainly of 100 oC/h, where FeO-poor, type I chondrules are produced.
Experiments: Three kinds of sintered pellets of homogenized powders with chondritic compositions were prepared as starting
materials of the present experiments; (1) Allende CV3.2, (2) NWA 1465 (a carbonaceous chondrite), and (3) powder mixtures
including iron, olivine, enstatite, anorthite, and diopside. The peak temperatures of the runs 1200-1550 oC and the cooling rates
80-10000 oC/h. Two cases were considered in the use of silica powder as Si-rich gas source and in the absent of the silica powder.
The furnace was low pressure type controlling below the atmospheric pressure under the reduced condition, whose pressure wascontrolled to be mainly 100 Pa. The capsule made of alumina has an orifice (1 mm) on the top and the charge is held using
the Mo-wire of 0.2 mm in diameter in the capsule. Silica was put on the bottom of the capsule for its use The vapor pressure
from the charge and silica in the capsule is about 1 Pa at ˜1450 oC of the peak temperature. When the furnace total pressure iscontrolled to be 100 Pa using the hydrogen gas, the hydrogen gas enters into the capsule balancing the outside of the capsule.
The oxygen pressure is IW-3 in the case of the existence of silica powder, and IW-4 in the absence of the silica powder at 1450
oC. The starting materials (1) and (2) correspond to the metallic iron poor starting materials and the runs of 53 times were carriedout (23 times with Si-rich gas and 30 times without Si-rich gas). The starting material (3) corresponds to the metallic iron richstarting materials and the runs of 21 times were carried out (11 times with Si-rich gas and 10 times without Si-rich gas). The
polished sections were made from the run produces, and observed and analyzed using an electron probe micro analyzer (EPMA,
JXA-8200).
Results and discussion: Poikilitically enclosed rounded forsteritic olivines in porphyritic enstatites formed from metallic ironpoor starting materials at the peak temperature of 1450 oC and the cooling rate of 100 oC/h, which is similar to type I chondrules.
The rounded olivines are relict phase, dusty olivines and forsterites, common in chondrules. The texture of the runs with Si-richgas source is similar to the type I chondrules. Although kamacite droplets enclosed in olivines and pyroxenes are usually abundantin type I chondrules, they are not common in the run products. The iron content of the run products decreased. Since the volumeof the absorption of iron into the Mo wire is much less than the volume of compositional change, the significant of the iron oxide
component directly evaporated but not the reduction into metallic iron.
Metallic iron melt tends to aggregate into a clump at the peak temperature more than 1500 oC from metallic iron rich starting
materials. The metallic iron was dispersed in the charge due to the low melting degree at the peak temperature less than 1500 oC,
but the iron was deficient on the charge surface, suggesting the evaporation of iron. The textures are not similar to chondrules.
Considering the present experimental results, we may prefer the metal-deficient precursors for the type I chondrules rather
than metal-bearing precursors. However, the origin of kamacite droplets enclosed in Mg-rich olivine and pyroxenes in type
I chondrules is still unclear. They may be originated from the injection during the chodnrule melting or the iron vapor was
saturated during the chondrule melting.
Reference: Cohen B. A. and Hewins R. H. 2004. GCA, 68, 1677-1689.
Keywords: chondrule, type I, chondrule formation, reproduction, experimental study

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PPS22-08

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Time:May 28 11:15-11:30

Cosmic-ray exposure age and heliocentric distance of the parent body of the rumuruti
chondrite PRE 95410
OBASE, Tomoya1∗ ; NAKASHIMA, Daisuke1 ; NAKAMURA, Tomoki1 ; NAGAO, Keisuke2
1

Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, 2 Geochemical ResearchCenter, Graduate School of Science, University of Tokyo
We measured concentrations and isotopic ratios of noble gases in the rumuruti (R) chondrite Mt. Prestrud (PRE) 95410. Thismeteorite contains high concentrations of solar and cosmogenic noble gases, from which solar gas implantation rate (concentrations of solar noble gases implanted per unit time) can be estimated. By comparing the solar gas implantation rates between PRE
95410 and lunar regolith samples, the parent-body heliocentric distance of the meteorite can be obtained, as solar wind flux isinversely related to the square of heliocentric distance. Based on the exposure model of solar noble gases and galactic cosmic
rays, we calculated the exposure age on its parent body (15.4±5.2 Ma), exposure age in space after ejection from the parent body
(9.5±1.3 Ma), and heliocentric distance of the parent body (1.3±0.2 AU) . The calculated exposure age in space is consistent
with the peak of space exposure age distribution of other R chondrites. The derived heliocentric distance suggests the locationof parent body when constituents of the PRE 95410 meteorite were exposed to the solar wind. From the previous studies ofmineralogy and chemistry, R chondrites might have formed between the regions where ordinary and carbonaceous chondrites
formed (2-4 AU). Hence the heliocentric distance of the PRE 95410 parent body studied in this work is not consistent with theformation region. This may imply that the parent body of the PRE 95410 migrated from the R chondrite formation region to theinner area where irradiated by solar wind before the ejection of the meteorite (9.5±1.3 Ma). Kr isotopic ratios show excessesof 80Kr and 82Kr produced by neutron capture reaction on Br during space exposure. The minimum radius of the PRE 95410
meteoroid was calculated as 53 cm from the abundances of neutron-induced Kr.
Keywords: Rumuruti chondrite, noble gas analysis, cosmic-ray exposure age, heliocentric distance

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PPS22-09

Room:A02

Time:May 28 11:30-11:45

Nucleosynthetic Strontium Isotope Anomalies in Carbonaceous Chondrites
YOKOYAMA, Tetsuya1∗ ; FUKAMI, Yusuke1 ; OKUI, Wataru1 ; ITO, Nobuaki1 ; YAMAZAKI, Hiroshi1
1Department of Earth and Planetary Sciences, Tokyo Institute of Technology

We present precise Sr isotopic compositions in samples from sequential acid leaching experiments for three carbonaceouschondrites, Allende, Murchison, and Tagish Lake, together with those in the bulk aliquots of these meteorites. The chondritic
acid leachates and residues were characterized by Sr isotope anomalies with variable µ84 Sr values (106 relative deviation froma standard material) ranging from +120 to -4700 ppm, documenting multiple nucleosynthetic sources within a single meteorite.
In addition, the µ84 Sr patterns across leaching samples for individual chondrites differed from one another. The highest µ84 Srvalues were observed for leaching Step 3 (HCl+H2 O, 75 ℃) for Allende and Murchison likely because of the incorporation of
calcium and aluminum-rich inclusions (CAIs). In contrast, extremely low µ84 Sr values were observed in the later fractions (Steps
6 and 7) for Murchison and Tagish Lake, suggesting the existence of s-process-enriched presolar SiC grains derived from AGB
stars.
A µ84 Sr-²54 Cr diagram was prepared with the CAIs and bulk aliquots of carbonaceous chondrites and other meteorites (noncarbonaceous) that were plotted separately; however, they still formed a global positive correlation. CAIs presented the highestµ84 Sr and ²54 Cr values, whereas carbonaceous chondrites and noncarbonaceous meteorites had intermediate and the lowestµ84 Sr and ²54 Cr values, respectively. The positive trend was interpreted as resulting from global thermal processing in which
sublimation of high µ84 Sr and ²54 Cr carriers generated the excess µ84 Sr and ²54 Cr signatures in CAIs, while noncarbonaceousplanetesimals accreted from materials that underwent significant thermal processing and thus had relatively low µ84 Sr and ²54 Cr
values. Apart from the global trend, the carbonaceous chondrites and noncarbonaceous meteorites both exhibited intrinsic variations that highlight an isotopic dichotomy similar to that observed in other isotope combinations (e.g., ²54 Cr-²50 Ti, ²54 Cr-417 O).
A plausible scenario for creation of the intrinsic variations involves local thermal processing (e.g., flash heating for chondrule
formation) caused by additional selective destruction of presolar grains different than that caused by global thermal processing.
The existence of such a global positive trend and local variations for two meteorite groups suggests a complicated dynamic history for the dust grains with respect to thermal processing, material transportation, and mixing in the protoplanetary disk prior toplanetesimal formation.
Keywords: Sr isotopes, presolar grains, acid leaching, chondrites, nucleosynthesis, thermal processing

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PPS22-10

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Time:May 28 11:45-12:00

High precision neodymium isotopic analysis of chondrites with complete sample digestion
FUKAI, Ryota1∗ ; YOKOYAMA, Tetsuya1 ; KAGAMI, Saya1
1

Department of Earth and Planetary Sciences, Tokyo Institute of Technology

A variety of isotope anomalies have been discovered in bulk chondrites and differentiated meteorites (e.g., Cr, Mo [1, 2]).
These results point to the existence of planetary-scale isotope heterogeneities for refractory heavy elements, which are most
likely due to the heterogeneous distribution of presolar grains (e.g., SiC, graphite) in the protosolar nebula before the onset ofplanetesimal formation.
High precision Nd isotope analyses in meteorites have been the center of interest in recent cosmochemistry community. One of
the most remarkable results is that chondrites possess 142 Nd/144 Nd ratios ∼20 ppm lower than those in terrestrial rocks [3]. The
anomaly was interpreted to be caused by the Sm-Nd fractionation via early differentiation of the terrestrial mantle. On the other
hand, variations in stable Nd isotopes (e.g., 148,150 Nd/144 Nd) have been documented in chondrites [4]. Although the authors
concluded that the observed variation was due to incomplete digestion of presolar grain-bearing samples, the existence of Nd
isotope anomalies in bulk aliquots of chondrites remains unclear unless high precision Nd isotope data with complete sample
digestion become available.
In this study, we revisit high precision Nd isotope analysis of chondrites coupled with a new sample digestion technique that
confirms complete dissolution of acid resistant presolar grains. We also develop a modified dynamic multicollection method
using TIMS to improve the analytical reproducibilities.
We investigated two carbonaceous chondrites (Murchison, CM2; Allende, CV3), five ordinary chondrites (Kesen, H4; Chergach, H5; Saratov, L4; Hamlet, LL4; St.Severlin, LL6). The ordinary and Rumuruti chondrites with a petrologic grade greaterthan 3 were dissolved by a conventional acid digestion method using HNO3 + HF + HClO4 [5]. For carbonaceous chondrites,
each sample was digested using a high-pressure digestion system (DAB-2, Berghof) with HF + HNO3 + H2 SO4 to completely
dissolve acid resistant presolar grains [6].
The Nd isotope compositions were measured by TIMS (Triton-plus, Tokyo Tech). In previous studies, Nd isotope compositions of bulk meteorites have been commonly measured in the “static-multicollection” mode, which may be affected by thetime-related deterioration of Faraday cups [7]. In contrast, the “multi-static” [8] or “dynamic-multicollection” methods can reduce the effect of cup deterioration by acquiring Nd isotopes with multiple lines of different cup configurations within a single
analytical cycle. In this study, we developed a modified “dynamic-multicollection” method.
In contrast to the static mode, the dynamic method achieved improved reproducibilities as follows; 142 Nd/144 Nd: 2.8 ppm,
148
Nd/144 Nd: 4.5 ppm, and 150 Nd/144 Nd: 9.2 ppm. It should be noted that improvements of reproducibilities are evident for148
Nd/144 Nd and 150 Nd/144 Nd ratios even compared to those obtained in the multi-static method (6 ppm and 19 ppm, respectively) conducted in [8].
All samples have µ142 Nd values 20 ‒ 30 ppm lower than the terrestrial value. In contrast, all but one sample (Allende) have148
µ Nd values indistinguishable from the terrestrial value. Likewise, µ150 Nd values in chondrites are generally within the rangeof the terrestrial component. Although the data points are limited, this study suggests that stable Nd isotopes were homogenously
distributed in the protosolar nebula, at least for carbonaceous, ordinary, and Rumuruti chondrites.
References: [1] Trinquier, A. et al. (2007) ApJ , 655 , 1179. [2] Burkhardt, C. et al. (2011) EPSL , 312 , 390. [3] Boyet, M.
and Carlson, R. (2005) Science , 309 , 576. [4] Carlson, R. et al. (2007) Science , 316 , 1175. [5] T. Yokoyama et al. (1999)
Chem Geol. , 157 , 175. [6] T. Yokoyama et al. (2015) EPSL , in press . [7] Brandon, A. et al. (2009) GCA , 73 , 6421. [8] Caro,
G. et al. (2006) Geochim , 70 , 164.
Keywords: isotopic heterogeneity, isotopic anomaly, chondrite, neodymium, TIMS, presolar grain

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PPS22-11

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Time:May 28 12:00-12:15

Chemical composition of a precursor material of an Allende F(UN) CAI estimated froma mass dependent fractionation
FUKUDA, Kohei1∗ ; HIYAGON, Hajime1 ; TAKAHATA, Naoto2 ; SANO, Yuji2 ; HASHIMOTO, Akihiko3
1

Department of Earth and Planetary Science, The Univ. of Tokyo, 2 AORI, The Univ. of Tokyo, 3 Department of Cosmosciences,
Hokkaido University
Calcium-aluminum-rich inclusions (CAIs) are considered to be the oldest solid materials in the solar system [e.g., 1, 2]. Some
CAIs show mineralogy, texture, and isotopic signature that have experienced melting, evaporation and recrystallization [e.g.,3, 4]. These CAIs have lost primordial chemical compositions caused by evaporative loss of less refractory elements such as
magnesium and silicon from the melt. Hence, in order to understand the origin and evolution of such ‘igneous’ and isotopicallyfractionated CAIs, estimations of primordial compositions of these CAIs are required.
Estimations of primordial compositions of ‘normal’ igneous CAIs have been conducted by determination of mass dependentisotopic fractionation degrees in Mg and Si [5, 6], but those of igneous CAIs with F ractionation and U nknown N uclear effects(FUN [e.g., 7]) have been poorly carried out. FUN CAIs are amongst solar system materials with extreme mass dependentisotopic fractionations in Mg, O, and Si. The origin of FUN CAIs is still not well understood, but they must have information
about an earliest stage of the solar system evolution. Here we report chemical and Si isotopic compositions of a CAI from
Allende, called AL1B-F. AL1B-F is a forsterite-bearing CAI which shows large mass dependent isotopic fractionations in oxygenand magnesium [8]. These fractionation signatures indicate that AL1B-F is related to FUN CAIs.
FEG-EPMA (JEOL JXA-8530F, the Univ. of Tokyo) was used for petrologic studies. Silicon isotopic compositions have beenmeasured by the NanoSIMS installed at Atmosphere and Ocean Research Institute, the Univ. of Tokyo.
AL1B-F is composed of two parts, a forsterite-rich core and a spinel-rich mantle. Among these two parts are filled with
abundant secondary minerals (e.g., sodalite and nepheline). Silicon isotopes of forsterites and Al-Ti-rich pyroxenes in AL1B-F
show a large mass dependent isotopic fractionation of up to ∼22 ‰/amu.
In order to estimate the primordial composition of AL1B-F, we combined Si and previously measured Mg and O isotopic
data [8]. If we assume that mass dependent isotopic fractionations in AL1B-F were resulted from simple one-stage evaporation
event, ∼80% of Mg and ∼75% of Si must have been lost (evaporated) from the molten precursor of AL1B-F based on theexperimentally determined isotopic fractionation factors [9]. Because of the presence of abundant secondary minerals, it is notpossible to precisely determine the bulk chemical composition of the present AL1B-F. If we assume, however, that secondary
minerals in AL1B-F are alteration products of primary melilites with Ak mole% of, e.g., ∼89, which is a composition of melilites
in the Vigarano forsterite-bearing FUN CAI 1623-5 [10], the estimated precursor composition for AL1B-F would be ∼34 wt%
MgO and ∼50 wt% SiO2 . The result suggests that the precursor of AL1B-F also have a Mg- and Si-rich composition like C1,
1623-5, and CMS-1 FUN CAIs [9, 11].
References: [1] Bouvier A. and Wadhwa H. (2010) Nat. Geosci, 3, 637-641. [2] Connelly et al. (2012) Science, 338, 651-655.
[3] MacPherson G. J. and Davis A. M. (1993) GCA, 57, 231-243. [4] MacPherson G. J. et al. (2012) EPSL, 331-332, 43-54. [5]Grossman L. et al. (2008) GCA, 72, 3001-3021. [6] Bullock E. S. et al. (2013) MAPS, 48, 1440-1458. [7] Clayton R. N. andMayeda T. K. (1977) GRL, 4, 295-298. [8] Hiyagon H. and Hashimoto A. (2008) MAPS, #5128. [9] Mendybaev R. A. et al.
(2013) GCA, 123, 368-384. [10] Davis A. M. et al. (1991) GCA, 55, 621-637. [11] Williams C. D. et al. (2014) LPS XXXXV,#2146.

Keywords: FUN CAI, mass dependent isotopic fractionation, silicon isotopes, ion microprobe

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PPS22-12

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Time:May 28 12:15-12:30

Oxygen isotopic distribution of Type B1 CAI from the Vigarano
YAMAMOTO, Yoshihiro1∗ ; KAWASAKI, Noriyuki1 ; SAKAMOTO, Naoya1 ; YURIMOTO, Hisayoshi1
1

Hokkaido University

Ca-Al-rich inclusions (CAIs) in meteorites are the oldest objects in the Solar System. Heterogeneous oxygen isotope distributions among inter- and intra-crystals have been observed for CAIs (e.g., Yurimoto et al., 1998). The heterogeneous oxygenisotope distributions of CAI minerals are interpreted to be the result of thermal processes in the solar nebular with different oxygen isotopic compositions, which are multiple melting, condensation, and solid-state diffusion processes, as well as aqueous andthermal metamorphism/alteration on the parent body (Yurimoto et al., 2008). However, most efficient processes to form oxygenisotopic compositions were different at each mineral and each CAI. In this study, we have conducted systematic oxygen isotope
measurements for a large area in a CAI and compared with the petrography, in order to understand the processes to form theheterogeneous oxygen isotope distributions.
A type B1 CAI from the Vigarano was examined. FE-SEM-EDS system (JEOL JSM-7000F; Oxford X-Max 150) was used
for petrographic observations. Oxygen isotopic compositions were measured using SIMS of Hokkaido University (Cameca ims1280HR). Secondary ions (16 O− , 17 O− , and 18 O− ) were measured simultaneously in a multicollection mode. We selected three
regions with sizes of 1 x 1 mm and measured oxygen isotopes of 40 x 40 points every 25 micrometers. Measurement time foreach spot was 55 seconds including 10 seconds of ion counting time, pre-sputtering, and stage moving.
The CAI is 6.5 x 3 mm and has an irregular and a wrinkled surface. The CAI has a core-mantle structure. The core consistsof spinel, melilite, anorthite, and Al-Ti-rich augite, while the mantle is composed mainly of melilite. The Wark-Lovering rim
surrounds the CAI. The CAI is a fragment and an entire shape is unclear. A bulk chemical composition corresponds to those fortypical Type B1 CAIs (Grossman, 1975). Crystallization sequences from a melt of the CAI composition were spinel, melilite,
anorthite, and fassaite (Stolper, 1982).
The oxygen isotopic compositions of minerals in the CAI are distributed along the CCAM line in a three oxygen isotope
diagram. Spinel shows a 16 O-rich composition (δ 18 O ∼ -45 permil), while melilite shows a 16 O-poor composition (δ 18 O ∼ 11
permil). Anorthite has bimodal distributions of oxygen isotopic compositions. Fassaite shows mainly a 16 O-rich compositionand less spots having a 16 O-poor composition.
The oxygen isotopic compositions of mineral measured are not readily explained by crystallization sequences from the melt,
indicating that the heterogeneous oxygen isotope distributions are the results of either multiple re-melting events or any otherprocesses except for the melting event.

Keywords: CAI, meteorite, oxygen isotope, SIMS

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PPS22-13

Room:A02

Time:May 28 12:30-12:45

Al-Mg chronology and oxygen isotope distributions of multiple melting for a Type C CAI
from the Allende
KAWASAKI, Noriyuki1∗ ; KATO, Chizu2 ; ITOH, Shoichi3 ; WAKAKI, Shigeyuki4 ; ITO, Motoo4 ;YURIMOTO, Hisayoshi1
1

Hokkaido University, 2 IPGP, 3 Kyoto University, 4 JAMSTEC

Ca-Al-rich inclusions (CAIs) in meteorites have undergone multiple melting processes in the early solar nebula, which indicates that transient heating events repeatedly occurred in the early Solar System (e.g., Yurimoto et al., 1998). A relative
chronometer with Al-Mg systematics for the CAIs could be applied to determine the time interval of heating events. To determine the time interval of heating events for the CAIs, detailed histories of multiple melting events in the CAIs should be wellunderstood. We have carried out a coordinated study of detailed petrographic observations and in-situ oxygen and Al-Mg isotope
measurements for a Type C CAI, EK1-04-2, from Allende CV3. Precise petrographic observations and oxygen isotopic measurements were performed to understand the individual melting processes that occurred in the CAI. Investigation of the Al-Mg
systematics was performed for minerals formed by different melting and recrystallization processes to determine the age differences of individual CAI melting events.
The CAI consists mainly of spinel, anorthite, olivine, and pyroxene, and has a core and mantle structure. Petrography of thecore suggests that the crystallization sequences of the core minerals are spinel, anorthite, olivine, and pyroxene. The mantle has
the same mineral assemblages as the core, and shows incomplete melting and solidification textures.
Oxygen isotopic compositions of the minerals are distributed along with a carbonaceous chondrite anhydrous mineral (CCAM)
line (δ 18 O = -44 to +9 ‰), which indicates to preserve a chemical disequilibrium status in the CAI. Spinel shows 16 O-rich signature (δ 18 O ˜-43 ‰), while anorthite shows 16 O-poor signature (δ 18 O ˜+8 ‰). Olivine and pyroxene in the core have the same
oxygen isotopic composition (δ 18 O ˜-15 ‰), which indicates their equilibrium. Olivine and pyroxene in the mantle have variableoxygen isotopic compositions and are slightly depleted in 16 O (δ 18 O = -13 to -4 ‰) compared with the same minerals in thecore. The 26 Al-Mg systematics is consistent with the disequilibrium status observed according to the petrography and oxygenisotopes. Spinel is plotted on a line of (26 Al/27 Al)0 = (3.5±0.2) x 10−5 , anorthite is (-1±5) x 10−7 , and olivine and pyroxene in
the core are (-1±7) x 10−6 . Plots of olivine and pyroxene in the mantle are scattered below the isochron of these minerals in thecore.
The coordinated study of the oxygen and magnesium isotopes and the petrography indicates that the EK1-04-2 Type C CAI
underwent multiple heating events after a precursor CAI formation. The precursor CAI was formed at 0.43 Myr after the formation of the Solar System defined by canonical CAI formation. At least 1.6 Myr after the precursor CAI formation, the CAI
was partially melted and the partial melting melt exchanged oxygen isotopes with surrounding 16 O-poor nebular gas. 16 O-poor
olivine and pyroxene in the core were recrystallized from the partial melting melt. Subsequently, Al-rich chondrules accreted
on the CAI, and the CAI experienced partial melting again and recrystallized to form the mantle. The oxygen and magnesium
isotopes in anorthite were redistributed during thermal metamorphism in the Allende parent body. Our study reveals that the CAI
had been retained in the solar nebula for at least 1.6 Myr and underwent multiple melting events in the nebula, and oxygen and26
Al-Mg systematics has been partially disturbed depending on crystal sizes by metamorphism on the parent body.

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PPS22-14

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Time:May 28 14:15-14:45

Mixing of exogenic impactor materials on the surface of asteroids: Disruption, penetration, and consolidation
NAKAMURA, Akiko1∗
1

Graduate School of Science, Kobe University

Dawn observation found dark materials on the surface of the hypothesized HED meteorites’ parent body, asteroid 4 Vesta.
The dark materials are interpreted to be fragments of carbonaceous chondrite impactors, while HED meteorites were known to
include carbonaceous chondrite clasts. Meteorite fall named Almahata Sitta, originally was an asteroid 2008 TC3 , is a polymict
ureilite with various foreign materials such as enstatite chondrites, ordinary chondrites, one carbonaceous chondrite, etc. Dust
particles returned from comet 81P/Wild 2, a Jupiter-Family Comet (JFC) contained materials condensed at high temperature
formed near the Sun. It shows that materials of different temperature histories were mixed into the comet at some point during its
formation and evolution. Mixing process of materials of different origins occurred ubiquitously or repeatedly on small bodies.
We performed impact experiments of simulated small bodies as targets using various impactors including rocks, metals, andporous sintered materials in order to examine the degree of disruption, penetration, and consolidation of impactors in relation
with the material properties and impact velocity for the purpose of understanding the mixing process of materials due to collsion.
We found that (1) degree of impactor’s disruption can be described by the ratio of initial pressure to dynamic strength of the
impactor, (2) penetration depth of silicate impactor is only up to 100 times of its size even when it collides with an icy bodyof 90% porosity, however, (3) impactor with large porosity can survive with larger fraction and can penetrate deeper, probably
because local microscopic collapse of pores inhibits growth of overall fracture, and (4) when impacted on fine regolith at highvelocity, mutual consolidation of impactor fragments and also with regolith particles occurs owing to temperature increase due
to compaction of pores in regolith.
We will summarize these results in relation with porosity, size of impacting body, and impact velocity and will discuss themin comparison with observational evidences, especially, of asteroids.

Keywords: asteroids, collision, laboratory experiments, meteorites, regolith

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PPS22-15

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Time:May 28 14:45-15:00

Experimental confirmation of ringwoodite crystallization from shock-induced melts
MUTOU, Daiki1 ; SEKINE, Toshimori1∗ ; KOBAYASHI, Takamichi2 ; MASHIMO, Tsutomu3 ; OHFUJI, Hiroaki4
1

Hiroshima University, 2 NIMS, 3 Kumamoto University, 4 Ehime University

Many high-pressure phases have been identified in meteorites that experienced heavy collisions. The presence of high-pressure
phase may provide an estimate of pressure condition. However, the dynamic formation conditions may not be equal to those atstatic pressures and there is no firm experimental report to indicate the ringwoodite formation at dynamic pressures, although there
are Hugoniot data and trials to synthesize ringwoodite by shock compressions. We tried to confirm the ringwoodite formation byhypervelocity impacts from two powdered mixtures of biotite and cristobalite (sample A) and phlogopite and cristobalite (sampleB) for Fe-rich and Mg-rich ringwoodites, respectively. When we used stainless steel containers for recovery, the container had
reacted with the biotite melt to form chromite spinels. No spinel phase was observed in sample B. When we used copper
containers for sample A, X-ray diffraction data on the recovered samples indicated a spinel phase (a =0.8257 nm). Because thelattice constant is greater than that of Fe2SiO4 (ahrensite) and significantly less than those of magnesioferrite and magnetite, thecomposition can be a Fe-rich ringwoodite. However, detailed scanning electron microscopy indicated no obvious crystals on thepolished surface where there were many spherical voids. Finally the Raman spectroscopy investigations detected spectra similar
to Fe-rich ringwoodite in the voids. We will try to investigate the spinel phase using analytical transmission electron microscopy.
The present experimental results confirm the formation of ringwoodite from shock-induced melts. Further studies need toprovide Mg-rich ringwoodite formation and the minimum dynamic pressures required to the formation. If such experiments areextended to the other high-pressure phases present in meteorites, the shock pressure estimation will be more powerful and helpful
than the present.

Keywords: ringwoodite, shock-induced melt, crystallization, recovery shots

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PPS22-16

Room:A02

Time:May 28 15:00-15:15

Formation of metastable lingunite
KONO, Mari1 ; KUBO, Tomoaki1∗ ; KATO, Takumi1 ; UEHARA, Seiichiro1 ; KONDO, Tadashi2 ;KIKEGAWA, Takumi3 ; HIGO, Yuji4 ; TANGE, Yoshinori4
1

Kyushu Univ., 2 Osaka Univ., 3 Photon Factory, 4 JASRI

Lingunite (hollandite-type NaAlSi3O8) has been frequently found in shocked meteorites with other high-pressure minerals(Liu and El Goresy, 2007). According to the laser-heated diamond anvil cell (LHDAC) experiment by Liu (1978), following thedecomposition of albite (NaAlSi3O8) into jadeite (NaAlSi2O6) plus silica (SiO2) at 2-3 GPa, these phases recombine to form
lingunite in the range of pressure between 21 and 24 GPa, and then it decomposes again into calcium ferrite-type NaAlSiO4 plus
stishovite at pressures above 24 GPa. Similarly, Tutti (2007) observed lingunite as a minor phase at 21-23 GPa and 2273K using
LHDAC. In contrast to these LHDAC studies, high-pressure experiments using multi-anvil type (MA) apparatus revealed thatthe maximum solubility of NaAlSi3O8 component in hollandite structure is limited to ˜50 mol% at 14-25 GPa and 1073-2673K(Yagi et al., 1994, Liu, 2006) and NaAlSi3O8 lingunite is not stable at least up to 2273K (Akaogi et al., 2010). This contradiction
has not been solved yet, which makes it dif?cult to understand the shock conditions for the presence of lingunite in shocked
meteorites.
To investigate the lingunite puzzle, we focused on the formation process of lingunite by conducting time-series experiments.
We performed high-pressure experiments at 18-27 GPa and 1073-2023K using both LHDAC and MA apparatus. Powders ofnatural albite, oligoclase and labradorite are used as starting materials. Existing phases were identified by X-ray diffraction
method.
The quenching experiments using MA apparatus revealed that lingunite does not form in 5 min, but forms in 60 min as a single
phase from oligoclase at 20 GPa and 1473K. In situ X-ray diffraction study indicated that oligoclase becomes amorphous withincreasing pressure and temperature. At 22 GPa and 1473K, lingunite first crystallizes from the complete amorphous oligoclase
in 100 sec, and it decomposes into stishovite and CAS phase in 60 min. These results suggest that lingunite forms as a metastablephase by solid-state reaction after the amorphization of oligoclase, which might have also occurred with maskelynite in shockedchondritic meteorites (Tomioka et al., 2000). In contrast, lingunite was not observed when albite and labradorite were used as
starting materials. The amorphization pressure increases with increasing albite component. The pressure condition for complete
amorphization of albite is higher than that for the lingunite formation. No lingunite observed from the albite sample in thisstudy implies that the complete amorphization is required for the metastable formation of lingunite by solid-state reaction. In thecase of labradorite, lingunite was not formed even after the complete amorphization. This is consistent with the observation that
lingunite with labradorite composition in martian shocked meteorites crystallized not by solid-state reaction but from plagioclase
melt (e.g., El Goresy et al., 2013).

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PPS22-17

Room:A02

Time:May 28 15:15-15:30

Shock-metamorphosed zircons from the Jack Hills metaconglomerate in the Narryer Gneiss
Complex, Western Australia
YAMAMOTO, Shinji1∗ ; KOMIYA, Tsuyoshi1
1Department of Earth and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo

An intense flux of extraterrestrial bodies into inner solar system during ca. 3.8-4.1, called as Late Heavy Bombardment (LHB),
has been hypothesized originally from studies of the Moon. Extraterrestrial impacts by meteoritic bodies and comets on the early
Earth play a significant role for the initial state of crustal, atmospheric and biological evolution. Considering the planetary size,
the Earth should have suffered approximately 20 times the impact flux compared to the Moon. Ancient terrestrial evidence of
impact in the early Earth is, however, scarcely preserved due to surface erosion, sedimentary burial and tectonic destruction. To
date, the oldest impact structure on the Earth is the 2.02 Ga Vredefort Dome, South Africa, and another oldest evidence of impact
is 3.47-3.24 Ga spherule layers in the Barberton Greenstone Belt, South Africa. The impact chronology from these spherule
layers suggest that the impact flux was significantly higher 3.5 Ga than today, but there are no terrestrial evidence of impact prior
3.5 Ga.
Geological information during Hadean era (before 4.0 Ga) can be deduced from detrital zircons as old as 4.4 Ga preserved inmetasedimentary rocks at Jack Hills in the Narryer Gneiss Complex, Western Australia. Previous studies have reported that theJack Hills metasedimentary rocks contain detrital zircons with ages continuously spanning from ca. 3.0 up to 4.4 Ga, but evidenceof impact, such as shock-metamorphosed minerals, have not been confirmed. In the study we first report shock-metamorphosed
detrital zircons from the Jack Hills metaconglomerate, in the Narryer Gneiss complex, Western Australia. A total of 8993 detrital
zircons were investigated for the surface and internal structure using a scanning electron microscope and optical microscope
with/without acid treatment, and four types of shock-metamorphosed zircons were currently identified; (1) curvi-planar (nonplanar) feature (n = 6), (2) multiple sets of planar feature (n = 7), (3) partly granular (polycrystalline) texture (n = 2), and (4)fully granular texture (n = 10). Of these four, multiple sets of planar feature are proved for diagnostic evidence for impact origin,and now observed as annealed (decorated) planar feature, probably due to post-impact thermal heating or regional metamorphic
overprint. Coarse polycrystalline zircon represents several micro-meter sized crystallites in a glassy ZrSiO4 matrix that may
resulted from shock-induced amorphization and subsequent recrystallization. This grain shows abundant micro-vesicles and tiny
ThSiO4 phase suggesting incipient melting and degassing.
Shock-metamorphosed zircons are often utilized for impact-dating due to their partly or completely Pb-loss (age resetting).
Therefore, impact age determinations on shock-metamorphosed detrital zircons from the Jack Hills metaconglomerate would
provide significant clues not only for the deciphering the impact history on the early Earth but also for the verifying LHB hypothesis.

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PPS22-18

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Time:May 28 15:30-15:45

Shock P-T history of Martian meteorites as revelaed by electron microscopy of ”brown”
olivine
TAKENOUCHI, Atsushi1∗ ; MIKOUCHI, Takashi1 ; YAMAGUCHI, Akira2
1

Department of Earth and Planetary Science, The University of Tokyo, 2 National Institute of Polar Research

Introduction: Most Martian meteorites are heavily shocked and exhibit various shock features. Among these shock features,
olivine darkening (”brown” olivine) is unique in Martian meteorites. Detailed observation of brown olivine by TEM reveals that
olivine darkening is due to the presence of iron nano-particles (Fe metal and/or magnetite) ranging 5-20 nm in size in olivine.
Although nano-particles are considered to be formed by heavy shock metamorphism, their formation processes and conditions
are not well understood and there is a possibility to obtain new constraints on shock events on Mars. In this study, we observedand compared Martian meteorites containing brown olivine with those without brown olivine and heavily-shocked chondrite forrevealing their darkening processes and conditions and seeking singularities of planetary shock events on Mars.
Sample: Eight shergottites (NWA 1950, LAR 06319, LEW 88516, Y984028, NWA 1068, RBT 04261, LAR 12095 andTissint) and one L chondrite (NWA 4719) were observed in this study. Four shergottites (NWA 1950, LAR 06319, LEW 88516,
Y984028) contain darkened olivine. Olivine grains in other samples are almost colorless although they are certainly heavily
shocked.
Results and Discussion: Observation of brown olivine by optical microscopy reveals heterogeneous coloration on the scaleof tens of µm. In three shergottites (LAR 06319, LEW 88516, Y984028) olivine around shock melts is recrystallized and not
darkened.
The brown areas look brighter in BSE images and have fewer cracks and low crystallinity by EBSD compared to the colorlessareas. Observation at high magnifications reveals that some brighter areas of NWA 1950 are composed of abundant lenticularareas with submicron-sized Fe particles around them. Shergottites with brown olivine contain no high pressure minerals although
they show similar lamellar textures to olivine with high pressure polymorphs.
In contrast, shergottites without brown olivine contain high pressure minerals and also partially darkened areas in olivine
adjacent to shock melt veins. These darkened areas show similar microstructures to those of brown olivine, and therefore theirformation processes seem to be identical and olivine darkening (formation of iron nano-particles) requires high temperature
because darkened areas are present only near shock melts in these meteorites without brown olivine. It is conceivable that theheterogeneity of olivine darkening corresponds to temperature difference. Since temperature heterogeneity is vanished within
about <1 sec, iron nano-particles need to be formed in such a short time. The absence of Si-rich phases means that mechanismof nano-particle formation is similar to the initial process found in olivine reduction experiments whose rate is limited by atomic
diffusion rates. Atomic diffusion in olivine is too slow to reflect temperature heterogeneity to their color distribution in sucha short time, and therefore rapid diffusion, for example transformation to high pressure minerals, is needed. Lenticular areas
in brown olivine with low crystallinity may have been a high pressure mineral and, if that is the case, it seems easy to reflect
temperature heterogeneity to their coloration. Thus, Martian meteorites with brown olivine have undergone such a high pressuretemperature condition in a short time (˜a few ms) on which most olivine in the meteorites is transformed to high pressurepolymorphs. Temperature increase throughout meteorite induces a slow cooling of shock melt and it seems also related torecrystallization of olivine and back-transformation of high pressure minerals around shock melt.
This condition may be induced by an extremely strong shock event and meteorites with brown olivine have undergone suchstronger shock than those containing high pressure minerals and colorless olivine. Thus, the collisional events ejecting rocks
from Mars may be extremely strong compared to those affecting the other meteorites.

Keywords: Mars, Martian meteorite, High pressure mineral, shock, brown olivine

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PPS22-19

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Pressure dependence of cathodoluminescence spectra of shocked quartz.
CHANG, Yu1∗ ; KAYAMA, Masahiro2 ; TAJIKA, Eiichi3 ; SEKINE, Yasuhito1 ; SEKINE, Toshimori4 ;NISHIDO, Hirotsugu5 ; KOBAYASHI, Takamichi6
1

Earth & Planetary Sci., Univ. of Tokyo, 2 Earth & Planetary Sci., Kobe Univ., 3 Complexity Sci. & Eng., Univ. of Tokyo, 4 Earth& Planetary Sci., Hiroshima Univ., 5 Research Institute of Natural Science, Okayama Univ. of Science., 6 National Institute forMaterial Science (NIMS)
Impact cratering is a ubiquitous process on both terrestrial planets and small bodies in the solar system. Study on impact
craters on the Earth provides a unique opportunity to constrain planetary-scale impact phenomena. In particular, reconstructionof distribution and shock pressure recorded on the shock-metamorphosed minerals would provide vital information on partitionof the impact energy and cratering mechanism on Earth.
Quartz, which is one of the most abundant and widely distributed rock-forming minerals on the Earth, has been conventionally used to evaluate shock pressure on the minerals. However, the precious shock estimations using quartz, such as PDFs, arerather qualitative, hence it is required for more detailed evaluation of shock pressure to develop new advanced method. Recently,
cathodoluminescence (CL), emissions of photon from materials in ultraviolet to infrared wavelength regions, especially CL ofquartz is expected to be used as shock barometer because of change of luminescent properties with shock metamorphism, butsystematic study focused on pressure dependence of CL spectra have never been reported. In this study, we conducted a series ofsystematic shock recovery experiments of impact on quartz crystals and analyzed recovered samples to evaluate the CL spectralfeatures and their dependence on shock pressure.
The shock recovery experiments were performed on natural and synthesis quartz crystals in the National Institute for Material
Science (NIMS) using a one stage propellant gun. The velocity range of flyer plate was 0.5 to 1.8 km/s, which produces peak
shock pressure from 5 to 40 GPa. Recovered samples were polished to make thin sections, and then are coated by carbon for
CL analysis. CL measurements of grain by grain were conducted at Okayama University of Science using a SEM-CL (SEM
combined with a grating monochromator) instrument.
Based on CL measurements of over a hundred shock-recovered quartz grains, we found drastic change in spectral pattern withan increase in shock pressure. The starting material of synthetic and natural quartz has only one broad emission peak around 630
nm, but another broad peak around 450-460 nm (blue emission) appears from the shock-recovered samples at 10 to 20 GPa. At
higher pressure, the CL intensity of blue emission of shocked quartz increases drastically up to 100 times as large as that of thestarting materials. On the other hand, CL emission intensity around 630 nm changes less than 3 times in spite of the pressure
increase.
CL spectra of quartz with β-form (e.g., quartz from Goroku, Sendai) show extremely intense blue emission and unique luminescent properties depending on temperature (e.g. activation energy) similar to quartz from terrestrial impact craters, suggesting
probably relationship of the blue CL with defects associated with Daufine twins formed as a result of α-β transition. On theother hand, Daufine twins are also confirmed in the experimentally shocked quartz under TEM observation. Therefore, the riseof blue emission intensity in our measurements suggests generation and density increase of defects related to Daufine twins withascending shock pressure. Quantitative evaluation of this relationship presumably enables us to construct a new quantitative
pressure barometer or thermometer for shocked quartz grains.
Keywords: shock metamorphism, shocked quartz, cathodoluminescence

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PPS22-20

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Time:May 28 16:15-16:30

High-pressure polymorphs in Gujba CB type carbonaceous chondrite.
MIYAHARA, Masaaki1∗ ; OHTANI, Eiji2 ; YAMAGUCHI, Akira3
1

Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 2 Department of Earthand Planetary Materials Science, Graduate School of Science, Tohoku University, 3 National Institute of Polar Research
One of the most unambiguous evidences for shock metamorphism is a dense polymorph, high-pressure polymorph in andaround the shock-melt veins and/or melt-pockets of shocked meteorites. Now, the existences of high-pressure polymorphs havebeen reported from ordinary chondrite, enstatite chondrite, ureilite, eucrite, iron meteorite, lunar meteorite, Apollo sample andMartian meteorite (e.g., Ohtani et al., 2004; Miyahara et al., 2014). On the other hand, it is widely accepted that carbonaceous chondrites were less shocked than ordinary chondrites, implying that high-pressure polymorphs would not be included incarbonaceous chondrites. However, Hollister et al. (2014) identified ringwoodite and stishovite from Khatyrka CV type carbonaceous chondrite. Shock metamorphism in carbonaceous chondrites may be overlooked or underestimated. CB type carbonaceouschondrite is a unique grouplet because it consists mainly of metallic Fe-Ni and chondrtic fragment (Weisberg et al., 2001). Although the origin of CB type carbonaceous chondrite has been under debated, some previous studies propose that it may beformed through a planetesimal collision (Weisberg et al., 2010). In this study, we investigated a high-pressure polymorph in
CB type carbonaceous chondrite, Gujba to clarify its shock metamorphism history and origin using FEG-SEM, EPMA and laser
Raman spectroscope.
We prepared a polished Gujba sample for this study. Gujba studied here consists of metal and chondritic fragment. Shock-meltveins occur widely between the chondritic fragments and metals. The major constituent minerals of the chondritic fragments are
low-Ca pyroxene (Fs1−5 , En89−98 , Wo0−6 ), Mg-rich olivine (Fa1−18 , Fo82−99 ) and Ca pyroxene (Fs1−13 , En41−66 , Wo32−57 )based on EPMA analysis. Many mineral fragments and fine-grained chondritic fragments are entrained in the shock-melt veins.
We confirmed the existences of many kinds of high-pressure polymorphs from such fragments and chondritic fragments adjacentto the shock-melt veins. Raman spectroscopy analyses indicate that olivine entrained in the shock-melt veins transform into
wadsleyite. A small amount of ringwoodite is accompanied with some wadsleyite. Low-Ca pyroxene is replaced with akimotoite, majorite or probably bridgmanite. Minor Fe-rich olivine (Fa39−40 ) and albitic feldspar (Ab82 An13 Or5 ) are entrained in theshock-melt veins. Lamellar ringwoodite occurs in the Fe-rich olivine. The albitic feldspar is replaced with jadeite, lingunite or
maskelynite. We also clarified the distributions of these high-pressure polymorphs in Gujba studied here. High-pressure polymorphs occur ubiquitously in and around the shock-melt veins, indicating that the parent-body of Gujba was heavily shocked.
The metals, which consist of kamacite and minor FeS, show evidence for melting. Alternatively, we can also infer that Gujba is
a part of shock-met veins induced by a collision.
References
Miyahara et al. (2014) Discovery of coesite and stishovite in eucrite. Proceedings of the National Academy of Sciences
U.S.A., doi: 10.1073/pnas.1404247111.
Ohtani et al. (2004) Formation of high-pressure minerals in shocked L6 chondrite Yamato 791384: constraints on shock conditions and parent body size. Earth and Planetary Science Letters 227, 505-515.
Hollister L.S., et al. (2014) Impact-induced shock and the formation of natural quasicrystals in the early solar system. Nature
Communications, doi: 10.1038/ncomms5040.
Weisberg M.K. and Kimura M. (2010) Petrology and Raman spectroscopy of high pressure phases in the Gujba CB chondriteand the shock history of the CB parent body. Meteoritics & Planetary Science 45, 873-884.
Weisberg M.K. et al. (2001) A new metal-rich chondrite grouplet. Meteoritics & Planetary Science 36, 401-418.

Keywords: carbonaceous chondrite, high-pressure polymorph, shock metamorphism

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PPS22-21

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Symmetry of majorite garnet in shocked chondrites revisited: A TEM study
TOMIOKA, Naotaka1∗ ; MIYAHARA, Masaaki2 ; ITO, Motoo1
1

Kochi Institute for Core Sample Research, JAMSTEC, 2 Department of Earth and Planetary Systems Science, Graduate Schoolof Science, Hiroshima University
Majorite is a garnet-structured mineral with a composition on the join (Mg,Fe)SiO3 -(Mg,Fe)3 Al2 Si3 O12 , which contains Si
in the octahedral sites. Al-free majorite samples synthesized by Kawai-type multianvil apparatus are known to have a tetragonal
symmetry (space group I 41 /a ) [1]. However, all of natural Al-free majorite samples found in shocked chondrites have beenreported to be cubic (Ia -3d ) [2]. Single-crystal X-ray study of a synthetic MgSiO3 majorite clarified the tetragonal distortion ofmajorite is caused by Mg-Si ordering in the octahedral sites [3]. Subsequent microstructural observations of synthetic Al-freemajorite by TEM concluded that the tetragonal phase is formed from the cubic phase through the cation ordering even upon
rapid quenching (103 ℃/sec) and the symmetry reduction phase derives modulated and twinning structures [4]. On the contrary,
cubic (Mg,Fe)SiO3 majorite in shocked chondrites is inferred to have been preserved due to higher cooling rate than that in
high-pressure synthesis where the cation ordering is inhibited.
Due to very small tetragonal distortion from the cubic phase (c /a = 0.99) and very week extra reflections for the tetragonalphase, it is difficult to judge the symmetry of small amount of natural majorite samples by powder X-ray diffractometry. For
the symmetry analyses of submicron-sized grains, single-crystal electron diffraction is a suitable method, since the intensities
of weak reflections to diagnose the tetragonal symmetry are enhanced by the effect of dynamical diffraction. In this study, werevisit symmetries of majorite grains in shocked ordinary chondrites (Tenham; L6, Y-75100; H6) and also synthetic (Mg,Fe)SiO3
majorite by TEM. The intensity of {101} reflections, which appears only for the I 41 /a tetragonal phase, is under investigation
by selected are electron diffraction.
References:[1] e.g. Kato, T., and Kumazawa, M. (1985) Garnet phase of MgSiO3 filling the pyroxene-ilmenite gap at very high temperature. Nature , 316, 803-805.
[2] e.g. Smith, J.V., and Mason, B. (1970) Pyroxene-garnet transformation in Coorara meteorite. Science , 168, 832-833; Jeanloz, R. (1981) Majorite: Vibrational and compressional properties of a high-pressure phase. J. Geophys. Res. , 86, 6171-6179.
[3] Angel, R.J., Finger, L.W., Hazen, R.M., Kanzaki, M., Weidner, D.J., Liebermann, R.C., Veblen, D. R. (1989) Structure andtwinning of single-crystal MgSiO3 garnet synthesized at 17 GPa and 1800 ℃. Amer. Mineral. , 74, 509-512.
[4] e.g. Heinemann, S., Sharp, T.G., Seifert, F., and Rubie, D.C. (1997) The cubic-tetragonal phase transition in the system
majorite (Mg4 Si4 O12 ) - pyrope (Mg3 Al2 Si3 O12 ), and garnet symmetry in the Earth’s transition zone. Phys. Chem. Minerals ,24, 206-221.; Tomioka, N., Fujino, K., Ito, E., Katsura, T., Sharp, T., and Kato, T. (2002) Microstructures and structural phasetransition in (Mg,Fe)SiO3 majorite. Eur. J. Mineral. , 14, 7-14.
Keywords: majorite, shock metamorphism, high-pressure phase transition, TEM

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PPS22-22

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Basin forming event on Vesta: Petrologic evidence from a diogenite, NWA 5480
YAMAGUCHI, Akira1∗ ; BARRAT, Jean-alix2 ; SHIRAI, Naoki3 ; EBIHARA, Mitsuru3
1

National Institute of Polar Research, 2 Universite Europeenne de Bretagne, U.B.O.-I.U.E.M., 3 Tokyo Metropolitan University

The HED (Howardite, Eucrite, Diogenite) meteorites are the largest group of achondrites, and are derived from the regolithand crustal lithologies of asteroid 4-Vesta, which is the only surviving differentiated protoplanet in the Solar System. Diogenites
are considered to have been derived from intrusions from within the curst or from a deep global layer. Some of them display highlevels of platinum group element (PGE) concentrations that have been attributed to impact events on the parent body.
NWA 5480 is an unusual olivine diogenite. It has a heterogeneous crystalline texture. Irregular and subrounded clasts of duniteand fragments of olivine and chromite are set in an igneous matrix mainly composed of Low-Ca pyroxene. In some cases, large
dunite clasts are intersected by pyroxene matrix. Flow textures are observed near some clasts. Olivine, chromite, and pyroxene
show minor chemical zoning, implying relatively rapid cooling compared to typical diogenites. NWA 5480 contains a significant
amount of PGE (CI x ˜0.001 for Ir) with chondritic relative proportions. All these line of evidence support that NWA 5480 is an
impact melt breccia from a target composed of olivine and pyroxene-rich lithologies.
Upon heating of olivine diogenites, low-Ca pyroxene is the earliest phase to melt, and olivine and chromite are the last at>˜1600 C. The irregular and rounded shape resulted from resorption, and pyroxene veins and flow textures formed by violent
mixing during impact melting. The pyroxene matrix crystallized from impact melts. Cooling rates estimated from the shape of
Ca zoning of profiles near the rims in olivine fragments could be several tens of C/year, corresponding to burial depths less than a
few km in impact melt sheet. An impact crater with diameter >a few hundreds km would be needed to produce impact melt sheet>a few km in thickness. Thus, we suggest that NWA 5480 was derived from impact melts from a very large crater of Vesta. The
bulk chemical compositions indicate that the target was an area where olivine and orthopyroxene-rich rocks are largely exposed.
However, there are no such areas on Vesta except minor olivine spots. Thus, it is likely that NWA 5480 sampled a part of large
impact melt sheet (>a few km thick) formed by melting of deep crustal materials rich in olivine and orthopyroxene. One of thebest candidates is the Rheasilvia basin (˜500 km diameter), where orthopyroxene-rich materials were observed in the crater floor.
Keywords: diogenite, Vesta, impact melt breccia, impact crater

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PPS22-23

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147Sm-143Nd and 146Sm-142Nd chronology of a basaltic eucrite, NWA 7188
KAGAMI, Saya1∗ ; YOKOYAMA, Tetsuya1 ; USUI, Tomohiro1 ; FUKAI, Ryota1
1

Department of Earth and Planetary Sciences, Tokyo Institute of Technology

Eucrites are achondritic meteorites originating from the Vesta’s crust. They can be petrographically classified into basaltic
and cumulate eucrites. Determination of precise ages for eucrites will constrain the period of igneous activity and the following
thermal metamorphism of Vesta and may further provide insights into its differentiation and thermal history. We investigate
the long-lived 147 Sm-143 Nd (T1/2 = 1.06×1011 yr) and the short-lived 146 Sm-142 Nd (T1/2 = 6.8×107 yr [1]) systematics of abasaltic eucrite, NWA 7188 and compare the results with the ages obtained in previous chorological studies on cumulate andbasaltic eucrites. To obtain highly precise age data, we developed the techniques for determining Nd and Sm concentrations and
Nd isotope compositions in meteorite samples.
NWA 7188 was crushed and sieved into four sizes; G1) 500 ̶ 1700 µm, G2) 250 ̶ 500 µm, G3) 106 ̶ 250 µm, and G4)≤106 µm. G3 and G4 were separated into pyroxene and plagioclase grains by handpicking. We determined the 147 Sm-143 Nd
and 146 Sm-142 Nd ages of NWA 7188 using G1, G3-px, G4-px, G3-pl, and G4-pl. These were dissolved using a mixture ofconcentrated pure acids (HClO4 , HF, and HNO3 ). After the sample digestion, ~ 10% of the solution was removed and mixed
with 149 Sm- and 145 Nd-enriched spikes to determine the Sm and Nd concentrations by ID-ICP-MS (X-series Ⅱ, Thermo). The
remainder of the sample solution was used for highly precise Nd isotope analysis by TIMS (TRITON plus) with the dynamic
multicollection mode. Nd was separated by a three-step column chemistry procedure; 1) major elements were removed bypassing through a cation exchange resin, 2) Ce was removed using the LN resin (Eichrom) by oxidizing Ce3+ into Ce4+ using
KBrO3 [2] and 3) Nd was separated from Sm using the LN resin. We achieved Ce/Nd = ~ 3×10−5 and Sm/Nd = ~ 4×10−5
with ≥91% Nd recovery.
The 147 Sm-143 Nd mineral isochron of NWA 7188 yields an age of 4203±970 Ma. In contrast, we obtained a much older
146
Sm-142 Nd mineral isochron age of 4549±28 40 Ma when an initial solar system ratio of 146 Sm/144 Sm = 0.0094 at 4568 Ma
was applied [1]. It is presumed that thermal metamorphism on the Vesta has some effects on the 147 Sm-143 Nd age while the146
Sm-142 Nd age represents the timing of the last Sm-Nd isotopic closure. Therefore, we use the 146 Sm-142 Nd age of NWA
7188 in the following discussion.
The 146 Sm-142 Nd age (4549±28 40 Ma) for NWA 7188 is consistent with the 147 Sm-143 Nd age for cumulate eucrites (4546±8
Ma [3]) within analytical uncertainties. This suggests that the parent body processes associated with the last Sm-Nd isotopic
closure were contemporaneous for basaltic and cumulate eucrites. Likewise, the 146 Sm-142 Nd age of NWA 7188 is not resolvablefrom the metamorphic age of Agoult [4]. According to the 53 Mn-53 Cr systematics [5], the last global Mn/Cr fractionation in
the mantle of the Vesta occurred at 4564.8±0.9 Ma, the timing when basaltic magmas have formed in the mantle. This implies
that basaltic eucrites quenched rapidly on the surface of eucrite parent body, but thermal metamorphism may have affected both
Sm-Nd and U-Pb systematics. No apparent age difference between basaltic and cumulate eucrites implies that both types of
eucrites might have experienced similar cooling history as opposed to their petrographic distinction, or more likely that the timedifference is too subtle to be resolved by the 146 Sm-142 Nd system.
References: [1] Kinoshita, N. et al. (2012) Science, 335, 1614-1617. [2] Tazoe, H. et al. (2007) JAAS, 22, 616-622. [3] Boyet,
M. et al. (2010) EPSL, 291, 172-181. [4] Iizuka, T. et al. (2014) EPSL, 409, 182-192. [5] Lugmair, G.W. and Shukolyulov, A.
(1998) GCA, 62, 16, 2863-2886.

Keywords: basaltic eucrite, Sm-Nd chronology, NWA 7188

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Olivine petrofabric and chemical study of Divnoe ungrouped primitive achondrite
HASEGAWA, Hikari1∗ ; MIKOUCHI, Takashi1 ; YAMAGUCHI, Akira2 ; SHIRAI, Naoki3 ; EBIHARA, Mitsuru3
1

Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 2 National Institute of Polar
Research, 3 Tokyo Metropolitan University
Brachinite is a small group of achondrites mostly composed of olivine. Currently ˜30 meteorites belong to brachinite, however,what are called “brachinite-like” but classified as “ungrouped” exist (e.g., Day et al. 2012; Keil 2014). Such “brachinite-like” meteorites have a similar rock texture, oxygen isotopic compositions or trace elements abundance to brachinite but do not perfectly
match, and so they are classified as ungrouped. It is important to study these meteorites to understand the formation process ofbrachinite in general and their parental differentiated asteroid(s). Divnoe is one of such “brachinite-like” meteorite discovered in
Russia in 1981 (Graham 1983; Petaev et al. 1994) and recently some meteorites similar to Divnoe have been found from hot andcold deserts (e.g., RBT 04239 and Tafassasset). These findings may establish a new achondrite group (“Divnoeite” ) including
some of above “brachinite-like” meteorites (Gardner et al. 2007). In this study we analyzed Divnoe from mineralogical andchemical points of view to better understand its petrogenesis.
Divnoe is a medium- to coarse-grained achondrite (˜0.5-2.0 mm in grain size) dominated by olivine (Fo72−80 ) and apparent
shape preferred orientation (SPO) of olivine grains is observed by optical microscopic observation. It is known that dislocationcreep controlled flow of upper mantle materials develops crystallographic preferred orientation (CPO) of olivine and seismic
anisotropy in the Earth (Ohuchi 2013). Recently, Tkalcec et al. (2013) studied lattice preferred orientation (LPO) of olivine
in diogenite and proposed solid-state plastic deformation in the dynamic interior of 4Vesta. Our EBSD (Electron Back Scatter
Diffraction) analysis of Divnoe olivine grains shows that they are preferentially aligned along [001], which is parallel to elongation of olivine grains. The dimensions of [100] and [010] are randomly oriented. This observation indicates that CPO of Divnoe
olivine was achieved when olivine grains accumulated in magma rather than plastic deformation after solidification in the interiorof the parent body, which is consistent with previous study (Ando et al. 2003). Therefore, Divnoe is likely an olivine cumulate
rock. However, we found that its bulk chemical composition has high abundance of siderophile elements (Ir, Pt: ˜0.5 x CI),
which is unusual for an olivine cumulate. Such high abundance of siderophile elements may be derived from addition of an ironmeteorite component by impact. It is required to analyze other Divnoe-like meteorites to see whether (1) olivine SPO is present
or not and (2) such chemical signature (e.g., enrichment of siderophiles) is similarly seen.

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Crystallization and cooling conditions for the diogenite formation in the turbulent magma
ocean of the asteroid 4 Vesta
KAWABATA, Yusuke1∗ ; NAGAHARA, Hiroko1
1

Earth and Planetary Science, The University of Tokyo

The asteroid 4 Vesta has been completely differentiated to core and mantle despite its small size, of which surface materials arehowardite-eucrite-diogenite (HED) meteorites that we know the detailed petrology, and therefor, is a good target for understanding differentiation of terrestrial planets. A new differentiation model for crust formation was developed by taking magma ocean
fluid dynamics, chemical equilibrium, presence of 26 Al, and cooling into consideration with special care to crystal separation.
The role of crystal size, thickness of the conductive lib, and fO2 are evaluated as parameters. Large crystals (1cm) settle and forma km-thick cumulate layer of orthopyroxene with Mg# of 0.70-0.90 in 20 thousand years, which almost agrees with the Mg# of
diogenites, whereas thinner layers are formed if the grain size is smaller.
Keywords: magma ocean, Asteroid 4 Vesta, HED meteorites

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Time:May 28 17:45-18:00

A mineralogical and chemical study of primitive achondrite NWA 6704
HIBIYA, Yuki1∗ ; OZAWA, Kazuhito2 ; IIZUKA, Tsuyoshi3 ; YAMAGUCHI, Akira4
1

The University of Tokyo, 2 The University of Tokyo, 3 The University of Tokyo, 4 National Institute of Polar Research

Introduction: Primitive achondrites provide unique insights into the early stage of growth and differentiation of planetesimals.
Northwest Africa (NWA) 6704 is an ungrouped primitive achondrite found in Algeria in 2010. This meteorite is composed
mainly of low-Ca pyroxene, olivine, feldspar, chromite, awaruite, heazlewoodite, pentlandite, and whitlockite. The U-Pb datingof this meteorite shows the crystallization age of 4563.75 ± 0.41 Ma (1). To better understand the formation process of thisprimitive meteorite, we carried out a mineralogical and chemical study of NWA 6704 using SEM-EDS, EPMA and LA-ICP-MS.
Results & Discussion: Seven polished thin sections (TS-1˜7; 10×18mm; 10×20mm; 9×10mm; 10×12mm; 10×11mm;
15×28mm; 19×28mm) have been investigated. The texture is best characterized by the existence of many orthopyroxene (Opx)megacrysts up to 1.56 cm in length (Fs40−42 En53−57 Wo3−4 ). Olivine (Fa50−53 ) typically occur as interstices associated withfeldspar and have subhedral shapes, but locally occur as the vermicular olivine within the Opx. The vermicular olivine sharethe same optical extinction position under crossed-nicols and occurs only in one place near the center of each Opx crystal if
present. Feldspar (Ab91−93 An5−6 Or2−30 ) occurs in the Opx and the interstices as anhedral cuspate grains with extremely low
dihedral angles and sharing the same optical extinxtion position over up to 1cm, which implies that it’s pseudomorph of a meltfilled interstitial pore. Other phases include chromite (Cr# = 0.90-0.96) and awaruite (78-81 wt% Ni) also occur associated withfeldspar. We estimated fO2 of FMQ -2.6 using the Olv-Opx-Spl oxygen geobarometer (4).
The texture is properly represented by aggregate of large Opx hollow (skeletal) megacrysts with finer interstices. Other phasessuch as olivine are present in the hollow cores, and some of them are isolated from the interstices. The contiguity of feldspar in
the Opx megacrysts with or without olivine in three dimensions is clearly demonstrated by the fact that the same optical extinction
position are shared by feldspar isolated in the megacrysts and those present in the interstices. The distribution of the Opx hollow
crystal and the vermicular olivine are highly heterogeneous. In TS-1 and TS-6, Opx <6.2 mm across are dominant and more than
five of them include vermicular olivine; in TS-2˜5 and TS-7, Opx megacrysts up to 1.56cm across are common and only a few ofthem contain vermicular olivine. The vermicular olivine may be a decomposition product of the precursor pyroxene through theabrupt heating (>1400 ℃). There is a negative correlation between size of Opx and the number of vermicular-olivine bearing
Opx. Given this fact, a new scenario can be derived: this vermicular olivine and its host acted as nuclei for crystallization ofhollow Opx crystals, and the number of nuclei limits the size of Opx. Thus, more nuclei in a given area result in smaller grain size
as seen in TS-1,6. The abnormally large size of Opx and its hollow morphology indicates that the initial crystallization occurredunder rapid cooling. The SEM images, however, show that some pigeonite contain sub-micrometer-size augite (Fs17 En45 Wo39 )exsolution lamellae. We estimated equilibrium temperatures of 1050 ℃ using two-pyroxene geothermometry (3) and of 773℃ using Olv-Spl FeMg−1 exchange thermometry (4). The cooling rate between 1100-950 ℃ was estimated to be ˜0.02 ℃/hrfrom the thickness and wavelength of multiple exsolution lamellae (5), indicating significant decrease in cooling rate at a later
crystallization stage. The inferred thermal history suggests high internal temperature of the parent planetesimal due to 26 Al
decay, which was abruptly heated by impact followed by rapid cooling up to the ambient temperature to sustain slower cooling.
References: (1) Iizuka et al. (2013), (2) Warren et al. (2012), (3) Lindsley & Andersen (1983), (4) Ballhaus et al. (1991), (5)Jackson (1961)

Keywords: Primitive achondrite, NWA6704

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