2022/01/28 更新

写真a

フェイガン ティモシー ジェイ
フェイガン ティモシー ジェイ
所属
教育・総合科学学術院 教育学部
職名
教授

兼担

  • 理工学術院   大学院創造理工学研究科

学内研究所等

  • 2020年
    -
    2022年

    理工学術院総合研究所   兼任研究員

学位

  • ニューハンプシャ大学 (USA)   M.S.

  • カリフオニア大学 (USA)   Ph.D.

所属学協会

  •  
     
     

    ザ ミテオリティカル ソサイティ

  •  
     
     

    ジオラジカル ソサイティ アブ アメリカ

  •  
     
     

    ミネララジカル ソサイティ アブ アメリカ

  •  
     
     

    アメリカン ジオフイジカル ユニョン

 

研究キーワード

  • 同位体地球化学

論文

  • An active X-ray spectrometer for the SELENE-2 rover

    Kim K.J, Amano Y, Boynton W.V, Klingelhofer G, Bruckner J, Hasebe N, Hamara D, Starr R.D, Lim L.F, Ju G, Fagan T.J, Ohta R, Shibamura E

    Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan   12 ( 29 ) 35 - 42  2014年11月

  • Case study of magmatic differentiation trends on the Moon based on lunar meteorite Northwest Africa 773 and comparison with Apollo 15 quartz monzodiorite

    Timothy J. Fagan, Daiju Kashima, Yuki Wakabayashi, Akiko Suginohara

    GEOCHIMICA ET COSMOCHIMICA ACTA   133   97 - 127  2014年05月  [査読有り]

     概要を見る

    Pyroxene and feldspar compositions indicate that most clasts from the Northwest Africa 773 (NWA 773) lunar meteorite breccia crystallized from a common very low-Ti (VLT) mare basalt parental magma on the Moon. An olivine cumulate (OC), with low-Ca and high-Ca pyroxenes and plagioclase feldspar formed during early stages of crystallization, followed by pyroxene gabbro, which is characterized by zoned pyroxene (Fe# = molar Fe/(Fe + Mg) x 100 from similar to 35 to 90; Ti# = molar Ti/(Ti + Cr) x 100 from similar to 20 to 99) and feldspar (similar to Lambda n(90-95)Lambda b(05-10) to Lambda n(80-85 Lambda)b(10-16)). Late stage lithologies include alkali-poor symplectite consisting of fayalite, hedenbergitic pyroxene and silica, and alkaline-phase-ferroan clasts characterized by K-rich glass and/or K, Ba-feldspar with fayalite and/or pyroxene. Igneous silica only occurs with the alkaline-phase-ferroan clasts. This sequence of clasts represents stages of magmatic evolution along a ferroan-titanian trend characterized by correlated Fe# and Ti# in pyroxene, and a wide range of increase in Fe# and Ti# prior to crystallization of igneous silica.
    Clasts of Apollo 15 quartz monzodiorite (QMD) also have pyroxene co-existing with silica, but the QMD pyroxene has more moderate Fe# (similar to 70). Thus, in AFM components (A = Na2O+ K2O, M = MgO, F = FeO), the QMD clasts are similar to the terrestrial calc-alkaline trend (silica-enrichment at moderate Fe#), whereas the ferroan-titanian trend is similar to the terrestrial tholeiitic trend (silica-enrichment only after strong increase in Fe#). However, the variations in SiO2-contents of QMD clasts are due to variable mixing of SiO2-rich and FeO-rich immiscible liquids (i.e., not a progressive increase in SiO2). Immiscibility occurred after fractionation of a KREEP-rich parent liquid.
    A third trend is based on zoning relations within the NWA 773 OC, where pyroxene Ti# increases at constant Fe# with proximity to intercumulus, incompatible element-rich pockets rich in K, Ba-feldspar and Ca-phosphates. This type of fractionation (increasing refractory trace elements at constant Fe#) in a cumulate parent rock may have been important for generating lunar rocks that combine low Fe# with high incompatible trace element concentrations, such as KREEP basalts and the magnesian suite.
    MELTS (Ghiorso and Sack, 1995; Asimow and Ghiorso, 1998) models of one VLT, one low-Ti and two high-Ti mare basalts and oneKREEPbasalt all show evolution from low to high Fe# residual liquids during fractional crystallization; however strong enrichments in FeO-concentrations are limited to the VLT and low-Ti liquids. In the high-Ti liquids, crystallization of Fe-Tioxides prevents enrichment in FeO, and the increases in Fe# are due to depletion of MgO. Fe-Ti-oxide fractionation results in steady silica-enrichment in the high-Ti mare compositions. Intervals of FeO-enrichment on the VLT and low-Ti mare liquid lines of descent are linked to shifts from olivine to pyroxene crystallization. The onset of plagioclase feldspar crystallization limits the depletion of FeO during crystallization of one high-Ti mare basalt and of the KREEP basalt composition modeled. (C) 2014 Elsevier Ltd. All rights reserved.

    DOI

  • Identification of silicate and carbonaceous presolar grains by SIMS in the type-3 enstatite chondrite ALHA81189

    Shingo Ebata, Timothy J. Fagan, Hisayoshi Yurimoto

    APPLIED SURFACE SCIENCE   255 ( 4 ) 1468 - 1471  2008年12月

     概要を見る

    An isotope ratio imaging technique using the HokuDai isotope microscope system has been applied to in situ survey for presolar grains in the type-3 enstatite chondrite ALHA81189. Rastered and static ion beam were used for primary beam. Lateral resolution of the isotope image was achieved to be 0.4 mu m for static ion beam mode and to be 0.6 mu m for rastered ion beam mode. As a result, the abundances of presolar grains are 150-200% larger under the static ion beam mode than under the rastered ion beam mode. Development of image processing introducing isotopography of (32)S, (24)Mg(16)O and (56)Fe succeeded to increase efficiency of presolar grain characterization. Using the static ion beam and introducing appropriate isotopography were very useful methods of in situ characterization of presolar grains in meteorites. (C) 2008 Elsevier B. V. All rights reserved.

    DOI

  • Al-Mg isotopic evidence for episodic alteration of Ca-Al-rich inclusions from Allende

    T. J. Fagan, Y. Guan, G. J. MacPherson

    Meteoritics and Planetary Science   42 ( 7-8 ) 1221 - 1240  2007年

     概要を見る

    Textures, mineral assemblages, and Al-Mg isotope systematics indicate a protracted, episodic secondary mineralization history for Allende Ca-Al-rich inclusions (CAIs). Detailed observations from one type B1 CAI, one B2, one compact type A (CTA), and one fluffy type A (FTA) indicate that these diverse types of CAls are characterized by two distinct textural and mineralogic types of secondary mineralization: (1) grossular-rich domains, concentrated along melilite grain boundaries in CAI interiors, and (2) feldspathoid-bearing domains, confined mostly to CAI margins just interior to the Wark-Lovering rim sequence. The Al-Mg isotopic compositions of most secondary minerals in the type B1 CAI, and some secondary minerals in the other CAIs, show no resolvable excesses of 26Mg, whereas the primary CAI phases mostly yield correlated excesses of 26Mg with increasing Al/Mg corresponding to "canonical" initial 26Al/27Al ∼ 4.5-5 × 10-5. These secondary minerals formed at least 3 Ma after the primary CAI minerals. All but two analyses of secondary minerals from the fluffy type-A CAI define a correlated increase in 26Mg/24Mg with increasing Al/Mg, yielding (26Al/27 Al)0 = (4.9 ± 2.8) × 10-6. The secondary minerals in this CAI formed 1.8-3.2 Ma after the primary CAI minerals. In both cases, the timing of secondary alteration is consistent with, but does not necessarily require, alteration in an asteroidal setting. One grossular from the type B2 CAI, and several grossular and secondary feldspar analyses from the compact type A CAI, have excesses of 26Mg consistent with initial 26Al/27Al ∼ 4.5 × 10-5. Especially in the compact type A CAI, where 26Mg/24Mg in grossular correlates with increasing Al/Mg, these 26Mg excesses are almost certainly due to in situ decay of 26Al. They indicate a nebular setting for formation of the grossular. The preservation of these diverse isotopic patterns indicates that heating on the Allende parent body was not pervasive enough to reset isotopic systematics of fine-grained secondary minerals. Secondary mineralization clearly was not restricted to a short time interval, and at least some alteration occurred coincident with CAI formation and melting events (chondrule formation) in the nebula. This observation supports the possibility that alteration followed by melting affected the compositional evolution of CAIs. © The Meteoritical Society, 2007.

    DOI

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

    AN Krot, TJ Fagan, K Nagashima, MI Petaev, H Yurimoto

    GEOCHIMICA ET COSMOCHIMICA ACTA   69 ( 7 ) 1873 - 1881  2005年04月  [査読有り]

     概要を見る

    Amoeboid olivine aggregates (AOAs) in primitive carbonaceous chondrites consist of forsterite (Fa(< 2)), Fe,Ni-metal, spinel, Al-diopside, anorthite, and rare gehlenitic melilite (angstrom k(< 15)) similar to 10% of AOAs contain low-Ca pyroxene (Fs(1-3)Wo(1-5)) that is in corrosion relationship with forsterite, and is found in three major textural occurrences: (i) thin (< 15 mu m) discontinuous layers around forsterite grains or along forsterite grain boundaries in AOA peripheries; (ii) 5-10-mu m-thick haloes and subhedral grains around Fe,Ni-metal nodules in AOA peripheries, and (iii) shells of variable thickness (up to 70 mu m), commonly with abundant tiny (3-5 mu m) inclusions of Fe,Ni-metal grains, around AOAs. AOAs with the low-Ca pyroxene shells are compact and contain euhedral grains of Al-diopside surrounded by anorthite, suggesting small (10%-20%) degree of melting. AOAs with other textural occurrences of low-Ca pyroxene are rather porous. Forsterite grains in AOAs with low-Ca pyroxene have generally O-16-rich isotopic compositions (Delta(17)O < -20%). Low-Ca pyroxenes of the textural occurrences (i) and (ii) are O-16-enriched (Delta(17)O < -20%), whereas those of (iii) are O-16-depleted (Delta(17)O = -6% to -4%). One of the extensively melted (> 50%) objects is texturally and mineralogically intermediate between AOAs and Al-rich chondrules. It consists of euhedral forsterite grains, pigeonite, augite, anorthitic mesostasis, abundant anhedral spinel grains, and minor Fe,Ni-metal; it is surrounded by a coarse-grained igneous rim largely composed of low-Ca pyroxene with abundant Fe,Ni-metal-sulfide nodules. The mineralogical observations suggest that only spinel grains in this igneous object were not melted. The spinel is O-16-rich (Delta(17)O similar to -22%), whereas the neighboring plagioclase mesostasis is O-16-depleted (Delta(17)O similar to -11%).
    We conclude that AOAs are aggregates of solar nebular condensates (forsterite, Fe,Ni-metal, and CAls composed of Al-diopside, anorthite, spinel, and +/- melilite) formed in an O-16-rich gaseous reservoir, probably CAI-forming region(s). Solid or incipiently melted forsterite, in some AOAs reacted with gaseous SiO in the same nebular region to form low-Ca pyroxene. Some other AOAs appear to have accreted O-16-poor pyroxene-normative dust and experienced varying degrees of melting, most likely in chondrule-forming region(s). The most extensively melted AOAs experienced oxygen isotope exchange with O-16-poor nebular gas and may have been transformed into chondrules. The original O-16-rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains. Copyright (c) 2005 Elsevier Ltd.

    DOI

  • Amoeboid olivine aggregates and related objects in carbonaceous chondrites: records of nebular and asteroid processes

    AN Krot, MI Petaev, SS Russell, S Itoh, TJ Fagan, H Yurimoto, L Chizmadia, MK Weisberg, M Komatsu, AA Ulyanov, K Keil

    CHEMIE DER ERDE-GEOCHEMISTRY   64 ( 3 ) 185 - 239  2004年09月  [査読有り]

     概要を見る

    Amoeboid olivine aggregates (AOAs) are the most common type of refractory inclusions in CM, CR, CH, CV, CO, and ungrouped carbonaceous chondrites Acfer 094 and Adelaide; only one AOA was found in the CBb chondrite Hammadah al Hamra 237 and none were observed in the CB, chondrites Bencubbin, Gujba, and Weatherford. In primitive (unaltered and unmetamorphosed) carbonaceous chondrites, AOAs consist of forsterite (Fa(<2)), Fe, Ni-metal (5-12 wt% Ni), and Ca, Al-rich inclusions (CAIs) composed of Al-diopside, spinel, anorthite, and very rare melilite. Melilite is typically replaced by a fine-grained mixture of spinel, Aldiopside, and +/- anorthite; spinel is replaced by anorthite. About 10% of AOAs contain low-Ca pyroxene replacing forsterite. Forsterite and spinel are always O-16-rich (delta(17,18)O-40parts per thousand to -50parts per thousand), whereas melilite, anorthite, and diopside could be either similarly O-16-rich or O-16- depleted to varying degrees; the latter is common in AOAs from altered and metamorphosed carbonaceous chondrites such as some CVs and COs. Low-Ca pyroxene is either O-16-rich (delta(17,18)O-40parts per thousand) or O-16-poor (delta(17,18)Osimilar to0parts per thousand). Most AOAs in CV chondrites have unfractionated (similar to2-10 x CI) rare-earth element patterns. AOAs have similar textures, mineralogy and oxygen isotopic compositions to those of forsterite-rich accretionary rims surrounding different types of CAIs (compact and fluffy Type A, Type B, and fine-grained, spinel-rich) in CV and CR chondrites. AOAs in primitive carbonaceous chondrites show no evidence for alteration and thermal metamorphism. Secondary minerals in AOAs from CR, CM, and CO, and CV chondrites are similar to those in chondrules, CAIs, and matrices of their host meteorites and include phyllosilicates, magnetite, carbonates, nepheline, sodalite, grossular, wollastonite, hedenbergite, andradite, and ferrous olivine.
    Our observations and a thermodynamic analysis suggest that AOAs and forsterite-rich accretionary rims formed in O-16-rich gaseous reservoirs, probably in the CAI-forming region(s), as aggregates of solar nebular condensates originally composed of forsterite, Fe, Ni-metal, and CAIs. Some of the CAIs were melted prior to aggregation into AOAs and experienced formation of Wark-Lovering rims. Before and possibly after the aggregation, melilite and spinel in CAIs reacted with SiO and Mg of the solar nebula gas enriched in O-16 to form Al-diopside and anorthite. Forsterite in some AOAs reacted with O-16-enriched SiO gas to form low-Ca pyroxene. Some other AOAs were either reheated in O-16-poor gaseous reservoirs or coated by O-16-depleted pyroxene-rich dust and melted to varying degrees, possibly during chondrule formation. The most extensively melted AOAs experienced oxygen isotope exchange with O-16- poor nebular gas and may have been transformed into magnesian (Type I) chondrules. Secondary mineralization and at least some of the oxygen isotope exchange in AOAs from altered and metamorphosed chondrites must have resulted from alteration in the presence of aqueous solutions after aggregation and lithification of the chondrite parent asteroids. (C) 2004 Elsevier GrnbH. All rights reserved.

    DOI

  • Oxygen isotopic alteration in Ca-Al-rich inclusions from Efremovka: Nebular or parent body setting?

    TJ Fagan, AN Krot, K Keil, H Yurimoto

    METEORITICS & PLANETARY SCIENCE   39 ( 8 ) 1257 - 1272  2004年08月  [査読有り]

     概要を見る

    In situ SIMS oxygen isotope data were collected from a coarse-grained type B1 Ca-Al-rich inclusion (CAT) and an adjacent fine-grained CAI in the reduced CV3 Efremovka to evaluate the timing of isotopic alteration of these two objects. The coarse-grained CAI (CGI-10) is a sub-spherical object composed of elongate, euhedral, normally-zoned melilite crystals ranging up to several hundreds of mum in length, coarse-grained anorthite and Al, Ti-diopside (fassaite), all with fine-grained (similar to10 mum across) inclusions of spinet. Similar to many previously examined coarse-grained CAIs from CV chondrites, spinet and fassaite are (16)O-rich and melilite is (16)O-poor, but in contrast to many previous results, anorthite is (16)O-rich. Isotopic composition does not vary with textural setting in the CAI: analyses of melilite from the core and mantle and analyses from a variety of major element compositions yield consistent (16)O-poor compositions. CGI-10 originated in an (16)O-rich environment, and subsequent alteration resulted in complete isotopic exchange in melilite. The fine-grained CAI (FGI-12) also preserves evidence of a 1st-generation origin in an (16)O-rich setting but underwent less severe isotopic alteration. FGI-12 is composed of spinel +/- melilite nodules linked by a mass of Al-diopside and minor forsterite along the CAI rim. All minerals are very fine-grained (<5 mum) with no apparent igneous textures or zoning. Spinet, Al-diopside, and forsterite are (16)O-rich, while melilite is variably depleted in (16)O (delta(17), (18)O from similar to-40parts per thousand to -5parts per thousand).
    The contrast in isotopic distributions in CGI-10 and FGI-12 is opposite to the pattern that would result from simultaneous alteration: the object with finer-grained melilite and a greater surface area/volume has undergone less isotopic exchange than the coarser-grained object. Thus, the two CAN were altered in different settings. As the CAIs are adjacent to each other in the meteorite, isotopic exchange in CGI-10 must have preceded incorporation of this CAI in the Efremovka parent body. This supports a nebular setting for isotopic alteration of the commonly observed (16)O-poor melilite in coarse-grained CAls from CV chondrites.

  • Oxygen isotopic evolution of amoeboid olivine aggregates in the reduced CV3 chondrites Efremovka, Vigarano, and Leoville

    TJ Fagan, AN Krot, K Keil, H Yurimoto

    GEOCHIMICA ET COSMOCHIMICA ACTA   68 ( 11 ) 2591 - 2611  2004年06月  [査読有り]

     概要を見る

    Amoeboid olivine aggregates (AOAs) from the reduced CV chondrites Efremovka, Vigarano, and Leoville consist of forsteritic olivine, FeNi-metal and a refractory component composed of spinel, Al-diopside, +/- anorthite. Secondary ferrous olivine and alkali-rich minerals (nepheline and sodalite), commonly observed in the oxidized CVs, are rare. Mineralogy and chemical compositions of AOAs are similar to those predicted by equilibrium thermodynamic condensation models, suggesting that AOAs formed primarily by gas-solid condensation over a narrow temperature range, slightly below the temperatures over which most Ca-Al-rich inclusions (CAIs) formed. AOAs in the reduced CVs preserve a 1(st)-generation (16)O-rich signal (delta(17,18)O similar to -40parts per thousand) similar to that observed in many CAls, suggesting that these refractory objects originated from a common source in the solar nebula. In fact AOAs and many fine-grained CAls may have formed by the same processes, but at slightly different temperatures, and can be considered a single class of refractory objects.
    Alteration of the AOAs is manifested by differing extents of (16)O-depletion in original AOA minerals, FeO-enrichment in olivine, and formation of interstitial very fine grained Na-bearing phases. From the six AOAs and one fine-grained, melilite-pyroxene-rich CAI examined in this study, five distinct patterns of alteration were identified. (1) One unaltered AOA from Vigarano is characterized by (16)O-rich forsterite without FeO-rich rims and interstitial Na-bearing phases. (2) Weak alteration in the melilite-pyroxene-rich CAI is characterized by incomplete (16)O-depletion in some melilite and precipitation of Na-bearing phases near the CAI rim. (3) Oxygen isotopic composition and mineralogy are correlated in two AOAs from Leoville with (16)O-rich olivine, (16)O-poor anorthite and a range of intermediate compositions in Al-diopside. This pattern is consistent with model diffusion between original grains and a (16)O-poor reservoir during a relatively short-term ( < 60 yr), high-temperature (900-1100degreesC) event. (4) Original forsterite has been enriched in FeO, but remained (16)O-rich in one AOA from Vigarano. This result is consistent with the slower rate of diffusion of O than Fe and Mg in olivine. At least some interstitial phases are (16)O-rich, and Na-bearing phases are abundant in this AOA. (5) In contrast, oxygen isotopic composition and Fo-content are correlated in two AOAs from Eftemovka. The olivine in these AOAs tends to have forsteritic (16)O-rich cores and FeO-rich (16)O-depleted rims. The general correlation between oxygen isotopic composition and Fo-content is difficult to model by diffusion, and may have formed instead by aqueous dissolution and precipitation along the margins of preexisting olivine grains.
    Independent evidence for aqueous alteration of the Eftemovka AOAs is provided by OH-rich signals detected during ion beam sputtering of some of the (16)O-poor olivine. Elevated (16)OH-count rates and order of magnitude increases in (16)OH detected during single analyses reflect trapping of an aqueous phase in (16)O-depleted olivine. An elevated (16)OH signal was also detected in one analysis of relatively (16)O-poor melilite in the melilite-pyroxene CAI from Vigarano, suggesting that this object also was altered by aqueous fluid. Copyright (C) 2004 Elsevier Ltd.

    DOI

  • Ca,Al-rich inclusions, amoeboid olivine aggregates, and Al-rich chondrules from the unique carbonaceous chondrite Acfer 094: I. Mineralogy and petrology

    AN Krot, TJ Fagan, K Keil, KD McKeegan, S Sahijpal, ID Hutcheon, MI Petaev, H Yurimoto

    GEOCHIMICA ET COSMOCHIMICA ACTA   68 ( 9 ) 2167 - 2184  2004年05月  [査読有り]

     概要を見る

    Based on their mineralogy and petrography, similar to200 refractory inclusions studied in the unique carbonaceous chondrite, Acfer 094, can be divided into corundum-rich (0.5%), hibonite-rich (1.1%), grossite-rich (8.5%), compact and fluffy Type A (spinel-melilite-rich, 50.3%), pyroxene-anorthite-rich (7.4%), and Type C (pyroxeneanorthite-rich with igneous textures, 1.6%) Ca,Al-rich inclusions (CAIs), pyroxene-hibonite spherules (0.5%), and amoeboid olivine aggregates (AOAs, 30.2%). Melilite in some CAIs is replaced by spinel and Al-diopside and/or by anorthite. whereas spinel-pyroxene assemblages in CAIs and AOAs appear to be replaced by anorthite. Forsterite grains in several AOAs are replaced by low-Ca pyroxene. None of the CAN or AOAs show evidence for Fe-alkali metasomatic or aqueous alteration. The mineralogy, textures, and bulk chemistry of most Acfer 094 refractory inclusions are consistent with their origin by gas-solid condensation and may reflect continuous interaction with SiO and Mg of the cooling nebula gas. It appears that only a few CAls experienced subsequent melting. The Al-rich chondrules (ARCs; > 10 wt% bulk Al2O3) consist of forsteritic olivine and low-Ca pyroxene phenocrysts, pigeonite, augite, anorthitic plagioclase, +/- spinel, FeNi-metal, and crystalline mesostasis composed of plagioclase, augite and a silica phase. Most ARCs are spherical and mineralogically uniform, but some are irregular in shape and heterogeneous in mineralogy, with distinct ferromagnesian and aluminous domains. The ferromagnesian domains tend to form chondrule mantles, and are dominated by low-Ca pyroxene and forsteritic olivine, anorthitic mesostasis, and Fe,Ni-metal nodules. The aluminous domains are dominated by anorthite, high-Ca pyroxene and spinel, occasionally with inclusions of perovskite; have no or little FeNi-metal; and tend to form cores of the heterogeneous chondrules. The cores are enriched in bulk Ca and Al, and apparently formed from melting of CAI-like precursor material that did not mix completely with adjacent ferromagnesian melt. The inferred presence of CAI-like material among precursors for Al-rich chondrules is in apparent conflict with lack of evidence for melting of CAIs that occur outside chondrules, suggesting that these CAIs were largely absent from chondrule-forming region(s) at the time of chondrule formation. This may imply that there are several populations of CAIs in Acfer 094 and that mixing of "normal" CAIs that Occur outside chondrules and chondrules that accreted into the Acfer 094 parent asteroid took place after chondrule formation. Alternatively, there may have been an overlap in the CAI- and chondrule-forming regions, where the least refractory CAIs were mixed with Fe-Mg chondrule precursors. This hypothesis is difficult to reconcile with the lack of evidence of melting of AOAs which represent aggregates of the least refractory CAIs and forstefite grains. Copyright (C) 2004 Lsevier Ltd.

    DOI

  • Northwest Africa 773: Lunar origin and iron-enrichment trend

    TJ Fagan, GJ Taylor, K Keil, TL Hicks, M Killgore, TE Bunch, JH Wittke, DW Mittlefehldt, RN Clayton, TK Mayeda, O Eugster, S Lorenzetti, MD Norman

    METEORITICS & PLANETARY SCIENCE   38 ( 4 ) 529 - 554  2003年04月  [査読有り]

     概要を見る

    The meteorite Northwest Africa 773 (NWA 773) is a lunar sample with implications for the evolution of mafic magmas on the moon. A combination of key parameters including whole-rock oxygen isotopic composition, Fe/Mn ratios in mafic silicates, noble gas concentrations, a KREEP-like rare earth element pattern, and the presence of regolith agglutinate fragments indicate a lunar origin for NWA 773. Partial maskelynitization of feldspar and occasional twinning of pyroxene are attributed to shock deformation. Terrestrial weathering has caused fracturing and precipitation of Ca-rich carbonates and sulfates in the fractures, but lunar minerals appear fresh and unoxidized.
    The meteorite is composed of two distinct lithologies: a two-pyroxene olivine gabbro with cumulate texture, and a polymict, fragmental regolith breccia. The olivine gabbro is dominated by cumulate olivine with pigeonite, augite, and interstitial plagioclase feldspar. The breccia consists of several types of clasts but is dominated by clasts from the gabbro and more FeO-rich derivatives. Variations in clast mineral assemblage and pyroxene Mg/(Mg + Fe) and Ti/(Ti + Cr) record an igneous Fe-enrichment trend that culminated in crystallization of fayalite + silica + hedenbergite-bearing symplectites.
    The Fe-enrichment trend and cumulate textures observed in NWA 773 are similar to features of terrestrial ponded lava flows and shallow-level mafic intrusives, indicating that NWA 773 may be from a layered mafic intrusion or a thick, differentiated lava flow. NWA 773 and several other mafic lunar meteorites have LREE-enriched patters distinct from Apollo and Luna mare basalts, which tend to be LREE-depleted. This is somewhat surprising in light of remote sensing data that indicates that the Apollo and Luna missions sampled a portion of the moon that was enriched in incompatible heat-producing elements.

  • Northwest Africa 032: product of lunar volcanism

    TJ Fagan, GJ Taylor, K Keil, TE Bunch, JH Wittke, RL Korotev, BL Jolliff, JJ Gillis, LA Haskin, E Jarosewich, RN Clayton, TK Mayeda, VA Fernandes, R Burgess, G Turner, O Eugster, S Lorenzetti

    METEORITICS & PLANETARY SCIENCE   37 ( 3 ) 371 - 394  2002年03月  [査読有り]

     概要を見る

    Mineralogy, major element compositions of minerals, and elemental and oxygen isotopic compositions of the whole rock attest to a lunar origin of the meteorite Northwest Africa (NWA) 032, an unbrecciated basalt found in October 1999. The rock consists predominantly of olivine, pyroxene and chromite phenocrysts, set in a crystalline groundmass of feldspar, pyroxene, ilmenite, troilite and trace metal. Whole-rock shock veins comprise a minor, but ubiquitous portion of the rock. Undulatory to mosaic extinction in olivine and pyroxene phenocrysts and micro-faults in groundmass and phenocrysts also are attributed to shock.
    Several geochemical signatures taken together indicate unambiguously that NWA 032 originated from the Moon. The most diagnostic criteria include whole-rock oxygen isotopic composition and ratios of Fe/Mn in the whole rock, olivine, and pyroxene. A lunar origin is documented further by the presence of Fe-metal, troilite, and ilmenite; zoning to extremely Fe-rich compositions in pyroxene; the ferrous oxidation state of all Fe in pyroxene; and the rare earth element (REE) pattern with a well-defined negative europium anomaly. This rock is similar in major element chemistry to basalts from Apollo 12 and 15, but is enriched in light REE and has an unusually high Th/Sm ratio. Some Apollo 14 basalts yield a closer match to NWA 032 in REE patterns, but have higher concentrations of Al(2)O(3). Ar-Ar step release results are complex, but yield a whole-rock age of similar to2.8 Ga, suggesting that NWA 032 was extruded at 2.8 Ga or earlier. This rock may be the youngest sample of mare basalt collected to date. Noble gas concentrations combined with previously collected radionuclide data indicate that the meteorite exposure history is distinct from currently recognized lunar meteorites. In short, the geochemical and petrographic features of NWA 032 are not matched by Apollo or Luna samples, nor by previously identified lunar meteorites, indicating that it originates from a previously unsampled mare deposit.
    Detailed assessment of petrographic features, olivine zoning, and thermodynamic modelling indicate a relatively simple cooling and crystallization history for NWA 032. Chromite-spinel, olivine, and pyroxene crystallized as phenocrysts while the magma cooled no faster than 2 degreesC/h based on the polyhedral morphology of olivine. Comparison of olivine size with crystal growth rates and preserved Fe-Mg diffusion profiles in olivine phenocrysts suggest that olivine was immersed in the melt for no more than 40 days. Plumose textures in groundmass pyroxene, feldspar, and ilmenite, and Fe-rich rims on the phenocrysts formed during rapid crystallization (cooling rates similar to20 to 60 degreesC/h) after eruption.

  • Refractory calcium-aluminum-rich inclusions and aluminum-diopside-rich chondrules in the metal-rich chondrites Hammadah al Hamra 237 and Queen Alexandra Range 94411

    AN Krot, KD McKeegan, SS Russell, A Meibom, MK Weisberg, J Zipfel, TV Krot, TJ Fagan, K Keil

    METEORITICS & PLANETARY SCIENCE   36 ( 9 ) 1189 - 1216  2001年09月  [査読有り]

     概要を見る

    The metal-rich chondrites Hammadah al Hamra (HH) 237 and Queen Alexandra Range (QUE) 94411, paired with QUE 94627, contain relatively rare (<1 vol%) calcium-aluminum-rich inclusions (CAIs) and Al-diopside-rich chondrules. Forty CAIs and CAI fragments and seven Al-diopside-rich chondrules were identified in HH 237 and QUE 94411/94627. The CAIs, <similar to>50-400 mum in apparent diameter, include (a) 22 (56%) pyroxene-spinel +/- melilite (+forsterite rim), (b) 11 (28%) forsterite-bearing, pyroxene-spinel +/- melilite +/- anorthite (+forsterite rim) (c) 2 (5%) grossite-rich (+spinel-melilite-pyroxene rim), (d) 2 (5%) hibonite-melilite (+spinel-pyroxene +/- forsterite rim), (e) 1 (2%) hibonite-bearing, spinel-perovskite (+melilite-pyroxene rim), (f) 1 (2%) spinel-melilite-pyroxene-anorthite, and (g) 1 (2%) amoeboid olivine aggregate. Each type of CAI is known to exist in other chondrite groups, but the high abundance of pyroxene-spinel melilite CAIs with igneous textures and surrounded by a forsterite rim are unique features of HH 237 and QUE 94411/94627. Additionally, oxygen isotopes consistently show relatively heavy compositions with Delta O-17 ranging from -6 parts per thousand to -10 parts per thousand (1 sigma = 1.3 parts per thousand) for all analyzed CAI minerals (grossite, hibonite, melilite, pyroxene, spinel). This suggests that the CAIs formed in a reservoir isotopically distinct from the reservoir(s) where "normal", O-16-rich (Delta O-17 < -20<parts per thousand>) CAIs in most other chondritic meteorites formed.
    The Al-diopside-rich chondrules, which have previously been observed in CH chondrites and the unique carbonaceous chondrite Adelaide, contain Al-diopside grains enclosing oriented inclusions of forsterite, and interstitial anorthitic mesostasis and Al-rich, Ca-poor pyroxene, occasionally enclosing spinel and forsterite. These chondrules are mineralogically similar to the Al-rich barred-olivine chondrules in HH 237 and QUE 94411/94627, but have lower Cr concentrations than the latter, indicating that they may have formed during the same chondrule-forming event, but at slightly different ambient nebular temperatures. Aluminum-diopside grains from two Al-diopside-rich chondrules have O-isotopic compositions (Delta O-17 approximate to -7 +/- 1.1 parts per thousand) similar to CAI minerals, suggesting that they formed from an isotopically similar reservoir. The oxygen-isotopic composition of one Ca, Al-poor cryptocrystalline chondrule in QUE 94411/94627 was analyzed and found to have Delta O-17 approximate to -3 +/- 1.4 parts per thousand.
    The characteristics of the CAIs in HH 237 and QUE 94411/94627 are inconsistent with an impact origin of these metal-rich meteorites. Instead they suggest that the components in CB chondrites are pristine products of large-scale, high-temperature processes in the solar nebula and should be considered bonafide chondrites.

  • Timing of arc construction and metamorphism in the Slate Creek Complex, northern Sierra Nevada, California

    TJ Fagan, HW Day, BR Hacker

    GEOLOGICAL SOCIETY OF AMERICA BULLETIN   113 ( 8 ) 1105 - 1118  2001年08月  [査読有り]

     概要を見る

    Late Paleozoic to early Mesozoic rocks in the Sierra Nevada and Klamath Mountains, western United States, preserve a record of lateral growth of continental crust by incorporation of ophiolites, volcanic arcs, and associated sedimentary rocks. Deciphering the timing of arc construction and metamorphism is critical for elucidating tectonic and thermal evolution during this type of crustal growth, but is difficult in complex accretionary terranes. In this study, we address the timing of arc construction and regional metamorphism in the Slate Creek Complex, a volcano-plutonic terrane in the central part of the northern Sierra Nevada.
    New (40)Ar-(39)Ar ages from relict volcanic hornblende demonstrate that the youngest volcanic unit in the Slate Creek Complex is ca. 170 Ma, at least 30 m.y, younger than previous estimates of ca. 200 Ma for metaplutonic rocks in the lower part of the complex. Consequently, the Slate Creek Complex is polygenetic, with two distinct episodes of arc magmatism. The distribution of mineral assemblages and textures indicates that greenschist and epidote-amphibolite facies metamorphism is younger than 170 Ma and is associated with crosscutting plutons that yield cooling ages of 150 Ma and younger. Amphiboles from foliated rocks in the Slate Creek Complex yield plateau ages of 156.1 +/- 0.6 and 152.0 +/- 0.7 Ma that date cooling subsequent to or dynamic recrystallization during the metamorphic event.
    Age and lithologic similarities suggest that the lower parts of the Slate Creek Complex correlate with plutons (ca. 200 Ma) and the volcanic cover sequence of the Rattlesnake Creek terrane in the Klamath Mountains. The uppermost volcanic unit correlates with the ca. 170 Ma Western Hayfork terrane that structurally overlies the Rattlesnake Creek terrane. Metamorphism in the Slate Creek Complex correlates broadly with a similar late metamorphic event in the Klamath Mountains.

  • Calcium-aluminum-rich inclusions in enstatite chondrites (II): Oxygen isotopes

    TJ Fagan, KD McKeegan, AN Krot, K Keil

    METEORITICS & PLANETARY SCIENCE   36 ( 2 ) 223 - 230  2001年02月  [査読有り]

     概要を見る

    In situ ion microprobe analyses of spinel in refractory calcium-aluminium-rich inclusions (CAIs) from type 3 EH chondrites yield O-16-rich compositions (delta O-18 and delta O-17 about -40 parts per thousand). Spinel and feldspar in a CAI from an EL3 chondrite have significantly heavier isotopic compositions (delta O-18 and delta O-17 about -5 parts per thousand). A regression through the data results in a line with slope 1.0 on a three-isotope plot, similar to isotopic results from unaltered minerals in CAIs from carbonaceous chondrites. The existence of CAIs with O-16-rich and O-16-poor compositions in carbonaceous as well as enstatite chondrites indicates that CAIs formed in at least two temporally or spatially distinct oxygen reservoirs. General similarities in oxygen isotopic compositions of CAIs from enstatite, carbonaceous, and ordinary chondrites indicate a common nebular mechanism or locale for the production of most CAIs.

  • Calcium-aluminum-rich inclusions in enstatite chondrites(I): Mineralogy and textures

    TJ Fagan, AN Krot, K Keil

    METEORITICS & PLANETARY SCIENCE   35 ( 4 ) 771 - 781  2000年07月  [査読有り]

     概要を見る

    Like calcium-aluminum-rich inclusions (CAIs) from carbonaceous and ordinary chondrites, enstatite chondrite CAIs are composed of refractory minerals such as spinel, perovskite, Al,Ti-diopside, melilite, hibonite, and anorthitic plagioclase, which may be partially to completely surrounded by halos of Na-(+/-Cl)-rich minerals. Porous, aggregate, and compact textures of the refractory cores in enstatite chondrite CAIs and rare Wark-Lovering rims are also similar to CAIs from other chondrite groups. However, the small size (<100 mu m), low abundance (<1% by mode in thin section), occurrence of only spinel or hibonite-rich types, and presence of primary Ti-(+/-V)-oxides, and secondary geikelite and Ti,Fe-sulfides distinguish the assemblage of enstatite chondrite CAIs from other groups.
    The primary mineral assemblage in enstatite chondrite CAIs is devoid of indicators (e.g., oldhamite, osbornite) of low O fugacities. Thus, high-temperature processing of the CAIs did not occur under the reducing conditions characteristic of enstatite chondrites, implying that either (1) the CAIs are foreign to enstatite-chondrite-forming regions or (2) O fugacities fluctuated within the enstatite-chondrite-forming region. In contrast, secondary geikelite and Ti-Fe-sulfide, which replace perovskite, indicate that alteration of perovskite occurred under reducing conditions distinct from CAIs in the other chondrite groups. We have not ascertained whether the reduced alteration of enstatite chondrite CAIs occurred in a nebular or parent-body setting. We conclude that each chondrite group is correlated with a unique assemblage of CAIs, indicating spatial or temporal variations in physical conditions during production or dispersal of CAIs.

  • Formation of feldspathic and metallic melts by shock in enstatite chondrite Reckling Peak A80259

    TJ Fagan, ERD Scott, K Keil, TF Cooney, SK Sharma

    METEORITICS & PLANETARY SCIENCE   35 ( 2 ) 319 - 329  2000年03月  [査読有り]

     概要を見る

    The enstatite chondrite Reckling Peak (RKP) A80259 contains feldspathic glass, kamacite, troilite, and unusual sets of parallel fine-grained enstatite prisms: that formed by rapid cooling of shock melts. Metallic Fe,Ni and troilite occur as spherical inclusions in feldspathic glass, reflecting the immiscible Fe-Ni-S and feldspathic melts generated during the impact. The Fe-Ni-S and feldspathic liquids were injected into fractures in coarse-grained enstatite and cooled rapidly, resulting in thin (less than or equal to 10 mu m) semicontinuous to discontinuous veins and inclusion trails in host enstatite. Whole-rock melt veins characteristic of heavily shocked ordinary chondrites are conspicuously absent. Raman spectroscopy shows that the feldspathic material is a glass. Elevated MgO and SiO2 contents of the glass indicate that some enstatite and silica were incorporated in the feldspathic melt. Metallic Fe,Ni globules are enclosed by sulfide and exhibit Ni-enrichment along their margins characteristic of rapid crystallization from a Fe-Ni-S liquid. Metal enclosed by sulfide is higher in Si and P than metal in feldspathic glass and enstatite, possibly indicating lower O fugacities in metal/sulfide than in silicate domains. Fine-grained, elongate enstatite prisms in troilite or feldspathic glass crystallized from local pyroxene melts that formed along precursor grain boundaries, but most of the enstatite in the target rock remained solid during the impact and occurs as deformed, coarse-grained crystals with lower CaO, Al2O3, and FeO than the fine-grained enstatite. Reckling Peak A80259 represents an intermediate stage of shock melting between unmelted E chondrites and whole-rock shock melts and melt breccias documented by previous workers. The shock petrogenesis of RKPA80259 reflects the extensive impact processing of the enstatite chondrite parent bodies relative to those of other chondrite types.

  • Prevalence and origin of birefringence in 48 garnets from the pyrope-almandine-grossularite-spessartine quaternary

    Hofmeister A.M, Schaal R.B, Campbell K.R, Berry S.L, Fagan T.J

    American Mineralogist   83 ( 11-12 ) 1293 - 1301  1998年12月

  • Formation of amphibole after clinopyroxene by dehydration reactions: Implications for pseudomorphic replacement and mass fluxes

    TJ Fagan, HW Day

    GEOLOGY   25 ( 5 ) 395 - 398  1997年05月  [査読有り]

     概要を見る

    The replacement of anhydrous by hydrous minerals is commonly used to infer infiltration of a rack by H2O. However, our work indicates that the formation of pseudomorphic amphibole after clinopyroxene (uralitization) in low-grade metavolcanic rocks is a net dehydration process. In the ophiolitic Slate Creek complex, northern California, clinopyroxene exhibits four textural stages of alteration: (1) clinopyroxene, (2) clinopyroxene + chlorite +/- amphibole, (3) amphibole + chlorite, and (4) amphibole. This transformation occurs in subgreenschist to greenschist facies rocks with a common matrix assemblage: quartz, albite, chlorite, epidote, titanite, + amphibole, +/- white mica, +/- rare pumpellyite. A simple reaction space model based on these observations indicates that consumption of chlorite in the rock matrix releases more water than required to produce amphibole pseudomorphs of clinopyroxene. Thus, the net flux of H2O during uralitization of greenschist facies metavolcanic rocks is outward. These results imply that uralitization in metavolcanic rocks results from heating rather than whole-rock hydration, and that natural mass fluxes may be counter to fluxes inferred from textural evidence alone.

  • Single-crystal IR spectroscopy of pyrope-almandine garnets with minor amounts of Mn and Ca

    Hofmeister A.M, Fagan T.J, Campbel K.M, Schaal R.B

    American Mineralogist   81 ( 3-4 ) 418 - 429  1996年04月

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共同研究・競争的資金等の研究課題

  • Oxygen isotope systematics of amoeboid olivine aggregates from reduced CV chondrites

    研究期間:

    2001年
    -
    2003年
     

  • chondritic and lunar meteorites

    研究期間:

    1998年
    -
    2001年
     

  • metamorphism and tectonics in the northern Sierra Nevada, California

    研究期間:

    1994年
    -
    1997年
     

  • metamorphism and tectonics in southeastern New Hampshire, USA

    研究期間:

    1984年
    -
    1986年
     

  • 難揮発性包有物とエンスタタイトコンドライトの変質作用

     概要を見る

    本研究において,我々はエンスタタイトコンドライトとCVコンドライト中における粗粒難揮発性包有物(CAIs)において,次の4つについて調べた.(1)結晶化の初期条件,(2)変質と変成による再結晶化中に起きた元素変化,(3)再結晶化中に起きた化学反応,(4)変質発生の状態薄片の顕微鏡写真と電子顕微鏡による元素分析と,補足的に、カソードルミネツセンスのイメージ分析とレーザーラマン分光を行った.更に,同位体分析を他研究室の質量分析器を用いて共同で行った.CV3コンドライトのCAIsにおいて,次の4つのデータを得た.(1)アエンデ隕石の粗粒CAIs中の2次鉱物の判別,組成の特徴,構成鉱物の面積比率(2)アエンデとエフレモフ力隕石のCAIsにおけるスピネルとメリライトの組成変化(3)アエンデ隕石のCAIsの初期鉱物と2次鉱物のAl-Mg同位体組成(4)Acfer 094隕石のCAIsにおける組成と酸素同位体更に,様々な変成度を持つエンスタタイトコンドライトについて,次の3つのデータを得た.(1)コンドリユールの特徴と組成(2)シリカの存在と多形(3)橄欖石,輝石,金属鉄及びFeSの組成変化アエンデ隕石のCAIsの鉱物変質とエフレモフ力隕石のCAIsの元素変質は,CAI表面で大きく表面の変質度が大きいCAIsは内部も大きく変成している.故に,CAIsの変質は母体内で起こったとされそうである.しかし,メリライトにあるNaの微小な幅,灰長石のNaとMg,Al-Mg同位体組成は,変質が母体形成よりも先に起こったことを示し,Acfer094にある16Oが豊富なCAIの縁は星雲内で再結晶化して形成したと考えられる.また,コンドリュールの組成,シリカの多形,鉱物組成から,ALHA81189が最も始原的なエンスタタイトコンドライトであることが分かった.他のEH3コンドライトは,コンドリユール形成時により加熱されているようだ.鉄はEH3の変成時に珪酸塩鉱物から硫化物や金属に移動したのだが,珪酸塩,硫化物,金属鉱物は変成中において様々な再平衡を経験したようである

海外研究活動

  • Magmatic paths toward granitic rocks on the Moon

    2019年04月
    -
    2020年03月

    USA   Smithsonian Institution

 

現在担当している科目

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