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1.
The Kamiomi, Sashima-gun (Iwai-shi), Ibaraki-ken, Japan, chondrite (observed to fall in spring, during the period 1913–6), consists of olivine, orthopyroxene, nickel-iron and troilite with minor amount of plagioclase, clinopyroxene, apatite and chromite. The average molar composition of olivine (Fa19) and orthopyroxene (Fs17) indicates that Kamiomi is a typical olivine bronzite chondrite. From the well-recrystallized texture, the presence of poorly-definable chondrules, homogeneous composition of olivine and absence of glass, this chondrite could be classified in petrologic type 5. The bulk chemical composition, especially, total Fe (27.33%) and metallic Fe (17.00%) as well as Fetotal/SiO2(0.72), Femetal/Fetotal (0–633) and SiO2/MgO (1.59) support the above conclusion. Coexistence of heavily-shocked olivine grains in the matrix composed of olivines and pyroxenes which suffered from light to moderate shock effect suggest that impacting phenomena, small-scaled but locally strong, occurred on the Kamiomi parent body.  相似文献   

2.
A mineralogical and chemical analysis has been performed on a slice of the Mills, New Mexico, chondrite, which was found in August 1970. The mineralogical composition is olivine Fa19.5, bronzite, Fs17.4, plagioclase, nickel-iron, troilite and ilmenite. The chemical analysis confirms that Mills is a typical bronzite, H5 chondrite, with considerable degree of weathering, as indicated by the presence of large amounts of Fe2O3. A comparison with other stones found in the same New Mexico region by Nininger may show a possible relation between Mills and previous finds.  相似文献   

3.
The Putinga, Rio Grande do Sul, chondrite (fall, August 16, 1937), consists of major olivine (Fa24.8), orthopyroxene (Fs21.3), and metallic nickel-iron (kamacite, taenite, and plessite); minor maskelynite (Ab81.0An12.4Or6.6) and troilite; and accessory chromite (Cm79.0Uv8.2Pc1.8Sp11.0) and whitlockite. Mineral compositions, particularly of olivine and orthorhombic pyroxene, as well as the bulk chemical composition, particularly the ratios of Fe°/Ni° (5.24), Fetotal/SiO2 (0.58), and Fe°/Fetotal (0.27), and the contents of Fetotal (22.42%) and total metallic nickel-iron (7.25%) classify the meteorite as an L-group chondrite. The highly recrystallized texture of the stone, with well-indurated, poorly discernible chondrules; xenomorphic, well-crystallized groundmass olivine and pyroxene; and the occurrence of poikilitic intergrowth of olivine in orthopyroxene suggest that Putinga belongs to petrologic type 6. Maskelynite of oligoclase composition was formed by solid state shock transformation of previously existing well-crystallized plagioclase at estimated shock pressures of about 250–350 kbar. Thus, recrystallization (i.e., formation of well-crystallized oligoclase) must have preceded shock transformation into maskelynite.  相似文献   

4.
Inman (find, 1966) is a single, relatively unweathered stone of 7.25 kg that contains fresh metal and only few weathering products away from fractures. It has a pronounced chondritic texture, with 38 vol % of the meteorite being made up of chondrules of virtually all textural types. The recalculated bulk analysis, particularly the ratios of Fetotal/SiO2 (0.46), Fe°/Fetotal (0.35), and Fe°/Ni° (6.67) and the contents of Fetotal (19.45%) and metallic nickel-iron (7.94%), indicate that Inman is an L-group chondrite. The pronounced chondritic texture; the compositional variabilities of olivine, pyroxene, chromite, and ilmenite; the presence of a fine-grained, nearly opaque matrix, glass and twinned monoclinic low-Ca pyroxene indicate that the chondrite belongs to petrologic type 3.  相似文献   

5.
Maralinga,a metamorphosed carbonaceous chondrite found in Australia   总被引：1，自引：0，他引：1  
Abstract— The Maralinga meteorite was found near the village of Maralinga, South Australia (30°18′S, 131°16′E) in 1974, but was not recognized as a meteorite until 1989. One weathered individual was recovered with a total mass of 3.38 kg. The bulk composition and petrography of Maralinga indicate that it is a metamorphosed (petrographic type 4) carbonaceous chondrite with major similarities to the Vigarano-subtype. However, recent trace element data from the literature suggest that Maralinga should be included with the CK (Karoonda-type) carbonaceous chondrites. We classify Maralinga as an anomalous CK4 chondrite because of its abundant chondrules and refractory inclusions relative to other known members of the CK group. Maralinga contains homogeneous silicates, including Ni-bearing olivines (Fa34), high-Ca clinopyroxene, and rare orthopyroxene. Plagioclase is chemically heterogeneous and falls into two distinct compositional groups one of ～ An20 and an ～ An80 group. Highly oxidizing conditions during metamorphism of Maralinga are indicated by the abundance of magnetite and the paucity of Fe-Ni metal.  相似文献   

6.
The mineralogical and chemical compositions of meteorites from the Motta di Conti, Vercelli, Italy, shower (February 29, 1868) have been determined. Microprobe analyses, of olivine (Fa19,6) and orthopyroxene (Fs17,8), as well as the bulk chemical composition, particularly the ratios of SiO2/MgO (1.50), Fe°/Ni° (11.03), Fetotal/SiO2 (0.81), Fe°/Fetotal (0.70) and the content of Fetotal (28.60%) classify the meteorite as an H-group chondrite. The percentage of total metallic nickel-iron (22.06%) is somewhat higher than the average in H-group chondrites. The texture of our stone shows evidence of metamorphism. The integration between matrix and chondrules is advanced and may suggest a high petrographic grade, but the identification of several microscopic features (e.g. small grains of monoclinic twinned pyroxene, FeNi-FeS intergrowths, globules and mosaic) leads to the conclusion that a variety of petrographic types (4–6) are present. Metamorphic equilibration in chondrites is discussed and a preliminary hypothesis for H4–6 chondrites is suggested.  相似文献   

7.
The Conquista chondrite consists of major olivine, low-Ca pyroxene (both ortho- and twinned clino-), troilite and metallic nickel-iron; minor glassy to microcrystalline material and pigeonite; and accessory chromite, high-Ca clinopyroxene and hydrous ferric oxides that formed by terrestrial weathering of metallic nickel-iron. Results of microscopic, electron microprobe, and bulk chemical studies, particularly the compositions of olivine (Fa17.2) and low-Ca pyroxene (Fs15.4); the contents of metallic nickel-iron (18.5%) and total iron (25.83%); and the ratios of Fe°/Fetotal (0.64), Fe°/Ni° (9.59) and Fetotal/SiO2 (0.69) indicate H-group classification. The pronounced, well-developed chondritic texture; the slight compositional variations in constituent phases; the high Ca contents of pyroxene and the presence of pigeonite, glassy to microcrystalline interstitial material rich in alkalis and SiO2, and of twinned low-Ca clinopyroxene suggest that Conquista is of petrologic type 4.  相似文献   

8.
Twelve stones, ranging up to 504 g (total weight 2.92 kg), of a very fresh eucrite have been collected from a 1 km2 area on the Nullarbor Plain in Western Australia. The location is approximately 75 km N6°E from Nurina Siding on the Trans-Australian Railway; coordinates 30°19′S, 126°37′E. This eucrite consists almost entirely of pyroxene (mean composition Wo 16 Fs 49) and plagioclase (mean composition An 85) in approximate proportions 3: 2, with 2% almost pure Fe metal and accessory amounts of troilite, ilmenite, and an SiO2 phase. Gabbroic and doleritic clasts are present in a groundmass of comminuted pyroxene and plagioclase. The chemical composition (weight per cent) is: SiO2 49.53, TiO2 0.74, Al2O3 12.49, Cr2O3 0.33, FeO 16.07, MnO 0.56, MgO 6.31, CaO 10.41, Na2O 0.49, K2O 0.04, P2O5 < 0.01, H2O + < 0.1, H2O — 0.07, Fe metal 2.07, Ni < 0.01, Co < 0.01, FeS 0.19, C 0.03, sum 99.33.  相似文献   

9.
Nepheline and sodalite have been found in association with glass in a barred olivine chondrule from the Allende C3V meteorite. The major minerals of the chondrule are olivine (Fo80–88), bronzite (En85Fs12Wo3), and chromite. Olivine bars are separated by glass of nearly pure plagioclase composition (An81–99). Olivine composition is more Fe-rich than predicted by olivine-liquid equilibria (Fo96). Conditions of non-equilibrium are implied from this and the presence of plagioclase glass and small amounts of subcalcic diopside (En75Fs12Wo13) in the chondrule. The properties of this chondrule are consistent with liquid condensation, but melting of an amoeboid olivine aggregate or similar object could also have generated the chondrule-forming liquid. Nepheline and sodalite appear to have crystallized from this liquid under non-equilibrium conditions.  相似文献   

10.
Abstract– There are 31 proven impact structures in Fennoscandia—one of the most densely crater‐populated areas of the Earth. The recently discovered Keurusselkä impact structure (62°08′ N, 24°37′ E) is located within the Central Finland Granitoid Complex, which formed 1890–1860 Ma ago during the Svecofennian orogeny. It is a deeply eroded complex crater that yields in situ shatter cones with evidence of shock metamorphism, e.g., planar deformation features in quartz. New petrophysical and rock magnetic results of shocked and unshocked target rocks of various lithologies combined with paleomagnetic studies are presented. The suggested central uplift with shatter cones is characterized by increased magnetization and susceptibility. The presence of magnetite and pyrrhotite was observed as carriers for the remanent magnetization. Four different remanent magnetization directions were isolated: (1) a characteristic Svecofennian target rock component A with a mean direction of D = 334.8°, I = 45.6°, α95 = 14.9° yielding a pole (Plat = 51.1°, Plon = 241.9°, A95 = 15.1°), (2) component B, D = 42.4°, I = 64.1°, α95 = 8.4° yielding a pole (Plat = 61.0°, Plon = 129.1°, A95 = 10.6°), (3) component C (D = 159.5°, I = 65.4°, α95 = 10.7°) yielding a pole (Plat = 21.0°, Plon = 39.3°, A95 = 15.6°), and (4) component E (D = 275.5°, I = 62.0°, α95 = 14.4°) yielding a pole (Plat = 39.7°, Plon = 314.3°, A95 = 19.7°). Components C and E are considered much younger, possibly Neoproterozoic overprints, compared with the components A and B. The pole of component B corresponds with the 1120 Ma pole of Salla diabase dyke and is in agreement with the 40Ar/39Ar age of 1140 Ma from a pseudotachylitic breccia vein in a central part of the structure. Therefore, component B could be related to the impact, and thus represent the impact age.  相似文献   

11.
The new Brazilian chondrite, Lavras do Sul, was found in 1985 at Lavras do Sul, Rio Grande do Sul State-Brazil (33°30′48″S; 53°54′65″W). It consists of a single mass weighing about 1 kg, covered by a black fusion crust with grayish interior. Four polished thin sections were prepared from a slice weighing 67 g on deposit at the Museu Nacional/UFRJ. It consists mostly of chondrules and chondrule fragments dispersed in a recrystallized matrix. Most chondrules are poorly defined and range in size from 300 to 2,000 μm, although some of them show distinct outlines, particularly when viewed under cross-polarized transmitted and reflected light. The texture of chondrules varies from non-porphyritic (e.g., barred-olivine, radial-pyroxene) to porphyritic ones (e.g., granular olivine as well as olivine-pyroxene). The meteorite contains mainly olivine (Fa24.9), low-Ca pyroxene (Fs22.6) and metal phases, with minor amounts of plagioclase, chromite and magnetite. Mössbauer Spectroscopy studies indicate that the metal phase is kamacite, tetrataenite and antitaenite. Veins of secondary iddingsite crosscut the thin section and some ferromagnesian silicates. The chemical composition indicates that Lavras do Sul is a member of the low iron L chondrite group. The poorly delineated chondritic texture with few well-defined chondrules, the occurrence of rare clinopyroxene and plagioclase (and maskelynite) with apparent diameters ranging from 5 to 123 μm led us to classify Lavras do Sul as an equilibrated petrologic type 5. The shock features of some minerals suggest a shock stage S3, and the presence of a small amount of secondary minerals such as iddingsite and goethite, a degree of weathering W1. The meteorite name was approved by the Nomenclature Committee (Nom Com) of the Meteoritical Society (Meteoritic Bulletin Nº99).  相似文献   

12.
Abstract— The Loxton meteorite is a single stone of 22 g found in South Australia in 1968. It has been classified as an L5 chondrite, shock facies ‘a,’ and contains olivine (Fa24), orthopyroxene (Fs21–22), clinopyroxene (Wo44.7En45.9Fs9.4), nickel-iron, troilite, chromite and chlorapatite.  相似文献   

13.
A new high‐pressure silicate, (Mg,Fe,Si)2(Si,□)O4 with a tetragonal spinelloid structure, was discovered within shock melt veins in the Tenham and Suizhou meteorites, two highly shocked L6 ordinary chondrites. Relative to ringwoodite, this phase exhibits an inversion of Si coupled with intrinsic vacancies and a consequent reduction of symmetry. Most notably, the spinelloid makes up about 30–40 vol% of the matrix of shock veins with the remainder composed of a vitrified (Mg,Fe)SiO3 phase (in Tenham) or (Mg,Fe)SiO3‐rich clinopyroxene (in Suizhou); these phase assemblages constitute the bulk of the matrix in the shock veins. Previous assessments of the melt matrices concluded that majorite and akimotoite were the major phases. Our contrasting result requires revision of inferred conditions during shock melt cooling of the Tenham and Suizhou meteorites, revealing in particular a much higher quench rate (at least 5 × 103 K s?1) for veins of 100–500 μm diameter, thus overriding formation of the stable phase assemblage majoritic garnet plus periclase.  相似文献   

14.
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15.
Abstract— The Carcote meteorite, detected in 1888 in the northern Chilean Andes, is a brecciated, weakly shocked H5 chondrite. It contains a few barred olivine chondrules and, even more rarely, fan-shaped or granular orthopyroxene chondrules. The chondrules are situated in a fine-grained matrix that consists predominantly of olivine and orthopyroxene with accessory clinopyroxene, troilite, chromite, merrillite, and plagioclase. The metal phase is mainly kamacite with subordinate taenite and traces of native Cu. In its bulk rock composition, Carcote compares well with other H5 chondrites so far analysed, except for a distinctly higher C content. Microprobe analyses revealed the following mineral compositions: olivine (Fa16.5–20), orthopyroxene (Fs14–17.5), diopsidic clinopyroxene (FS6–7), plagioclase (An15–20). Troilite is stoichimetric FeS with traces of Ni and Cr; chromite has Cr/(Cr + Al) of 0.86, Fe2+/(Fe2+ + Mg) of 0.80-0.88 and contains considerable amounts of Ti, Mn, and Zn. Merrillite is close to the theoretical formula Ca18(Mg, Fe)2Na2(PO4)14, although with a Na deficiency not compensated for by excess Ca; the Mg/(Mg + Fe2+) ratio of the Carcote merrilite is 0.93-0.95. Kamacite and taenite have Ni contents of 5.6–7.2 and 17.1–23.4 wt%, respectively. Native Cu contains about 3.1–3.3 wt% Fe and 1.6 wt% Ni. Application of different geothermometers to the Carcote H5 chondrite yielded apparently inconsistent results. The highest temperature range of 850–950 °C (at 1 bar) is derived from the Ca-in-opx thermometer. From the cpx-opx solvus geothermometers and the two-pyroxene Fe-Mg exchange geothermometer, a lower temperature range of 750–840 °C is estimated, whereas lower and more variable temperatures of 630–770 °C are obtained from the Ca-in-olivine geothermometer. Recent calibrations of the olivine-spinel geothermometer yielded a still lower temperature range of 570–670 °C, which fits well to the temperature information derived from the Ni distribution between kamacite and taenite. Judging from crystal chemical considerations, we assume that these different temperatures reflect the closure of different exchange equilibria during cooling of the meteorite parent body.  相似文献   

16.
Abstract The Crestone Crater is an elliptical bowl measuring 355 feet by 246 feet with a mean depth of 23 feet. It lies in unconsolidated sand on the surface of an alluvial fan at the base of the Sangre de Cristo Mountain Range in the San Luis Valley, Colorado (37° 54′ N, 105° 39′ W). Aerial photographs show the crater as a striking feature in its setting on a gently undulating terrain. We examined the site in August 1963 to appraise the possibility that it was formed by meteorite or comet impact. The crater and its vicinity were mapped at two-foot contour intervals, and two lines of auger-hole samples, eight feet deep, were collected across the crater. Sand from the rim and floor is similar in grain size and composition to that several miles to the north and south. It is barren of meteoritic debris, nickel-iron spherules, rock flour, and impact glass. The crater is less than half as deep relative to its diameter as known meteorite explosion craters. Furthermore, topographic profiles indicate that the crater does not form a depression in the land surface. The crater rim is a positive feature enclosing a basin that has a floor approximately level with the surface of the alluvial fan on which it lies. In the absence of any mineralogic or topographic evidence of impact or explosion, we conclude that this landform is not meteoritic or cometary in origin.  相似文献   

17.
A mineralogical and chemical analysis has been performed on the largest mass (8750 g) of the Girgenti, Italy, meteorite, from the collection of the Smithsonian Institution, Washington, D.C. The mineralogical composition is olivine, Fa24–25; hypersthene, Fs21 –22; plagioclase, An12; maskelynite; whitlockite; nickel-iron; troilite; chromite and ilmenite. Girgenti is a severly metamorphosed stone, whose total iron content (23.5%) is somewhat higher than the average for hypersthene chondrites.  相似文献   

18.
The Beaver-Harrison, Utah chondrite (find July 24, 1979), a single, shock-veined stone of 925 grams, consists of major olivine (Fa25.0), low-Ca pyroxene (En77.3Fs21.1Wo1.6) and metallic nickel-iron; minor troilite and plagioclase (Ab82.6An11.1Or6.3), accessory high-Ca pyroxene (En47.0Fs8.5Wo44.5), chromite (Cm8.7Sp10.6Uv9.4Pc0.6Hc0.7), chlorapatite and whitlockite; and hydrous ferric oxide of terrestrial weathering origin. Mineral compositions indicate L-group classification, and homogeneity of minerals, highly recrystallized texture and presence of clear plagioclase suggest that the meteorite belongs to petrologic type 6.  相似文献   

19.
Abstract— Based on optical microscopy and electron microprobe analysis, Linum is classified as an L6b chondrite that contains olivine (Fa24), orthopyroxene (Fs20), clinopyroxene (Wo45En47Fs8), plagioclase (An10Ab84Or6), nickel-iron, troilite, chromite and accessory amounts of chlorapatite and whitlockite.  相似文献   

20.
The Galatia meteorite was found in August, 1971, approximately 7 km ENE of Galatia, Barton County, Kansas (98° 53′W., 38° 39.5′N). The single stone weighed 23.9 kg and is partially weathered. Olivine (Fa24.9) and pyroxene (Fs20.9) compositions indicate L-group classification, and textural observations indicate that the stone is of petrologic type 6. Galatia is similar in many respects to the Otis L6 chondrite (found 20 km to the west), but it does not have the brecciated structure of Otis and, thus, it is not part of the same fall.  相似文献   

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