首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Abstract— The Yarle Lakes 001 meteorite was a single stone of 913 g found approximately 20 km north of Watson, South Australia, in 1990 October. It consists of olivine (Fa18.7 ± 0.4, n = 30), low-Ca pyroxene (Fs16.6 ± 0.2 Wo 12 + 0.4, n = 15). feldspar, high-Ca pyroxene, metallic Fe-Ni and troilite. Based on texture and mineral chemistry, Yarle Lakes 001 is classified as a H5 chondrite of shock stage S3.  相似文献   

2.
Abstract We report a new chondrite that fell in Hashima City in central Japan sometime during the period 1868–1912. The chondrite weighs 1110.64 g and exhibits distinct chondritic structure. Chondrules occupy 24 vol% of the stone and consist of olivine (average Fa17,8), low-Ca pyroxene (average Fs15,8 Wo0.9), devitrified glass and lesser amounts of oligoclase (ca. Ab80Or4), kamacite, taenite, troilite and chromian spinel. Matrix occupying 76 vol% of the stone consists of olivine, low-Ca pyroxene, kamacite, taenite, troilite, cryptocrystalline minerals and lesser amounts of chromian spinel and chlorapatite. Matrix minerals have the same compositions as those in chondrules. Mineral chemistry, bulk chemistry and magnetic properties indicate that Hashima is an H-group chondrite. Well-defined chondrules, scarcely recrystallized oligoclase and relatively small variations of olivine and low-Ca pyroxene compositions indicate that Hashima is of petrologic type 4.  相似文献   

3.
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   

4.
Abstract— A search of active deflation basins near Jal, Lea County, New Mexico resulted in the discovery of two meteorites, Lea County 001 and 002. Lea County 001 has mean olivine and low-Ca pyroxene compositions of Fa19 and Fs17, respectively. These and all other mineralogical and petrological data collected indicate a classification of H5 for this stone. Lea County 002 has mean olivine and low-Ca pyroxene compositions of Fa2 and Fs4, and is unequilibrated. Although it is mineralogically most similar to Kakangari and chondritic clasts within Cumberland Falls, the high modal amount of forsterite makes Lea County a unique type 3 chondrite. Oxygen isotope data for Lea County 002 fall on an 16O-mixing line through those of the enstatite meteorites and IAB irons, a feature shared by Kakangari.  相似文献   

5.
Abstract— An H5 chondrite was found near the village of Rumanová, Slovakia. dominant minerals of the meteorite are enstatite, olivine, kamacite, taenite and troilite. The minor minerals are oligoclase, augite, pigeonite, accessory chromite, whitlockite and chlorapatite. The composition of olivine (Fa19.0) and low-Ca orthopyroxene (Fs17.0), and the density and chemical composition of the meteorite correspond to those of an H chondrite. Normal zoning of Ni in metal grains and parallel planar fractures in olivine suggest weak shock metamorphism of stage S3. Due to moderate oxidation of metal, iron hydroxides were formed corresponding to weathering stage W2.  相似文献   

6.
The Kramer Creek, Colorado, chondrite was found in 1966 and identified as a meteorite in 1972. Bulk chemical analysis, particularly the total iron content (20.36%) and the ratio of Fetotal/SiO2 (0.52), as well as the compositions of olivine (Fa21.7) and orthopyroxene (Fs18.3) place the meteorite into the L-group of chondrites. The well-defined chondritic texture of the meteorite, the presence of igneous glass in the chondrules and of low-Ca clinopyroxene, as well as the slight variations in FeO contents of olivine (2.4% MD) and orthopyroxene (5.6% MD) indicate that the chondrite belongs to the type 4 petrologic class.  相似文献   

7.
Abstract— A new meteorite, the Juancheng chondrite, fell recently in Juancheng County, Shandong Province, China. It is classified as an H5 (S2) chondrite on the basis of the compositions of olivine (Fa 19.2, σFa 0.46), low-Ca pyroxene (Fs 16.9, σFs 0.4) and Co contents of kamacite (0.36–0.47 wt%). Plagioclase is compositionally heterogeneous.  相似文献   

8.
Abstract— A stony meteorite fell near the Fuc Bin village, Vietnam, in July, 1971. Based on optical microscopy, scanning electron microscopy and electron probe microanalysis, the meteorite is classified as an L5 chondrite that contains olivine (Fa23.6), low-Ca pyroxene (Fs20.3 Wo1.3), high-Ca pyroxene (Fs7.5 Wo44.2), plagioclase (Ab83.8 Or5), chlorapatite, merrillite and opaque minerals: chromite, troilite, kamacite, taenite, tetrataenite and native copper.  相似文献   

9.
Al Huwaysah 010 is an ungrouped achondrite meteorite, recently referred to as a brachinite-like meteorite. This meteorite, showing a fine-grained assemblage of low-Ca pyroxene and opaque phases, is strongly reduced in comparison to other reduced brachinites. The occurrence of some tiny plates of graphite and oldhamite in this meteorite suggests that a partial melt residue has experienced a further reduction process. Olivine, the most abundant phase, is compositionally homogeneous (Fo83.3) as well as the clinopyroxene (En45.5Fs10.8Wo43.7) and the plagioclase (Ab69.5). Orthopyroxene (En85.4Fs13.9Wo0.7) also occurs but only in a fine intergrowth. Other accessory phases are Fe metal grains (Ni-free or Cr-bearing Fe-Ni alloy), troilite, chlorapatite, pentlandite (as inclusions in chromite). The sample shows two different closure temperatures: the highest (≈900°C) is determined via the olivine–chromite intercrystalline geothermometer and the lowest temperature (≈520°C) is determined via the pyroxene-based intracrystalline geothermometer. These temperatures may represent, respectively, the closure temperature associated with the formation and a subsequent impact event excavating the sample from the parental body. The visible to near-infrared (VNIR) reflectance spectra of Al Huwaysah 010 exhibit low reflectance, consistent with the presence of darkening components, and weak absorptions indicative of olivine and pyroxene. Comparing the spectral parameters of Al Huwaysah 010 to potential parent bodies characterized by olivine–pyroxene mineralogy, we find that it falls within the field previously attributed to the SIII type asteroids. These results lead us to classify the Al Huwaysah 010 meteorite as the most reduced brachinite, whose VNIR spectral features show strong affinities with those of SIII asteroids.  相似文献   

10.
Abstract Melnikovo is a relatively unweathered 545.6-g LL6 chondrite that was found in 1983. Only a few poorly defined chondrules are discernable in the examined sections; two of these are enriched in chromite. The meteorite contains olivine (Fa27,8), low-Ca pyroxene (Fs24,4), plagioclase, rare clinopyroxene, chlorapatite, merrillite and opaque minerals, which have a modal abundance (in wt%) of troilite (3.9%), kamacite (0.4%), taenite plus tetrataenite (0.7%), chromite (0.8%), and trace amounts of ilmenite and Mn-ilmenite. The meteorite appears unbrecciated on a centimeter scale.  相似文献   

11.
Abstract— The LEW 88774 ureilite is extraordinarily rich in Ca, Al, and Cr, and mineralogically quite different from other ureilites in that it consists mainly of exsolved pyroxene, olivine, Cr-rich spinel, and C. The presence of coarse exsolved pyroxene in LEW 88774 is unique because pyroxene in most other ureilites is not exsolved. The pyroxene has bulk Wo contents of 15–20 mol% and has coarse exsolution lamellae of augite and low-Ca pyroxene, 50 μm in width. The compositions of the exsolved augite (Ca33.7Mg52.8Fe13.5) and host low-Ca pyroxene (Ca4.4Mg75Fe20.6) show that these exsolution lamellae were equilibrated at 1280 °C. A computer simulation of the cooling rate, obtained by solving the diffusion equation for reproducing the diffusion profile of CaO across the lamellae, suggests that the pyroxene was cooled at 0.01 °C/year until the temperature reached 1160 °C. This cooling rate corresponds to a depth of at least 1 km in the parent body, assuming it was covered by a rock-like material. Therefore, LEW 88774 was held at this high temperature for 1.2 × 104years. The proposed cooling history is consistent with that of other ureilites with coarsegrained unexsolved pigeonites. Lewis Cliff 88774 includes abundant Cr-rich spinel in comparison with other ureilites. The range of FeO content of spinels in LEW 88774 is from 1.3 wt% to 21 wt% [Fe/(Fe + Mg) = 0.04–0.6]. The Cr-rich and Fe-poor spinel in LEW 88774 has less Fe (FeO, 1.3 wt%) than spinels in other achondrites. We classify this spinel as an Fe, Al-bearing picrochromite. Most ureilites are depleted in Ca and Al, but this meteorite has high-Ca and Al concentrations. In this respect, as well as mineral assemblage and the presence of coarse exsolution lamellae in pyroxene, LEW 88774 is a unique ureilite. Most differentiated meteorites are poor in volatile elements such as Zn, but the LEW 88774 spinels contain abundant Zn (up to 0.6 wt%). We note that such a high Zn concentration in spinel has been observed in the carbonaceous chondrites and recrystallized chondrites. This unusual ureilite has more primitive characteristics than most other ureilites.  相似文献   

12.
The Ragland, New Mexico chondrite was found in 1978, and consists of a single stone of 12.16 kg that broke into three pieces. The stone is moderately weathered and has a pronounced chondritic texture. Bulk composition favors an LL classification, and modal analysis and oxygen isotopic composition are consistent with this. The thermoluminescence sensitivity of 0.056 ± 0.020 normalized to Dhajala, compositional variability of olivine (mean Fa 18.3, σ = 10.1) and low-Ca pyroxene (mean Fs 14.6, σ = 6.7), and Ca concentrations in olivine indicate metamorphic subtype 3.4 ± 0.1. The isotopically heavy oxygen composition, which is characteristic of subtypes 3.0–3.1, may be a primary characteristic and not a result of weathering. Low concentrations of radiogenic 40Ar and planetary 36Ar suggest noble gas loss.  相似文献   

13.
Abstract— The Julesburg chondrite, a single stone weighing 57.9 kg, was found in 1983 in Sedgewick County, Colorado, USA. It contains abundant chondrules and chondrule fragments but little fine-grained matrix. The olivine composition ranges from Fa1 to Fa25 but a frequency plot of olivine compositions is strongly peaked at Fa23. The low-Ca pyroxenes range from Fs3 to Fs28 and show no dominant composition. The abundance of clearly defined chondrules, the heterogeneity of the silicates and the presence of glass within chondrules indicate a type 3 chondrite, refined by thermoluminescence data to 3.6. The total iron content of 20.46% is indicative of an L-group stone. The low noble gas retention ages indicate that this meteorite was outgassed late in its history. This is supported by petrographic evidence of brecciation and shock. Aluminum-rich spinels within chondrules and inclusions contain up to 2.6% ZnO which suggests that they formed in a volatile-rich environment.  相似文献   

14.
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   

15.
Abstract— Approximately 275 mineral species have been identified in meteorites, reflecting diverse redox environments, and, in some cases, unusual nebular formation conditions. Anhydrous ordinary, carbonaceous and R chondrites contain major olivine, pyroxene and plagioclase; major opaque phases include metallic Fe-Ni, troilite and chromite. Primitive achondrites are mineralogically similar. The highly reduced enstatite chondrites and achondrites contain major enstatite, plagioclase, free silica and kamacite as well as nitrides, a silicide and Ca-, Mg-, Mn-, Na-, Cr-, K- and Ti-rich sulfides. Aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates, complex organic compounds, magnetite, various sulfates and sulfides, and carbonates. In addition to kamacite and taenite, iron meteorites contain carbides, elemental C, nitrides, phosphates, phosphides, chromite and sulfides. Silicate inclusions in IAB/IIICD and IIE iron meteorites consist of mafic silicates, plagioclase and various sulfides, oxides and phosphates. Eucrites, howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides. Ureilites are made up mainly of calcic, chromian olivine and low-Ca clinopyroxene embedded in a carbonaceous matrix; accessory phases include the C polymorphs graphite, diamond, lonsdaleite and chaoite as well as metallic Fe-Ni, troilite and halides. Angrites are achondrites rich in fassaitic pyroxene (i.e., Al-Ti diopside); minor olivine with included magnesian kirschsteinite is also present. Martian meteorites comprise basalts, lherzolites, a dunite and an orthopyroxenite. Major phases include various pyroxenes and olivine; minor to accessory phases include various sulfides, magnetite, chromite and Ca-phosphates. Lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase. Several meteoritic phases were formed by shock metamorphism. Martensite (α2-Fe,Ni) has a distorted body-centered-cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling. The C polymorphs diamond, lonsdaleite and chaoite formed by shock from graphite. Suessite formed in the North Haig ureilite by reduction of Fe and Si (possibly from olivine) via reaction with carbonaceous matrix material. Ringwoodite, the spinel form of (Mg,Fe)2SiO4, and majorite, a polymorph of (Mg,Fe)SiO3 with the garnet structure, formed inside shock veins in highly shocked ordinary chondrites. Secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic Fe-Ni by oxidation, phosphates formed by the alteration of schreibersite, and sulfates formed by alteration of troilite.  相似文献   

16.
On February 13, 2023, a huge fireball was visible over Western Europe (fireball event 2023 CX1). After the possible strewn field was calculated, the first of several recovered samples, with a mass of about 100 g, was discovered just 2 days after the fireball event on the ground of the village of Saint-Pierre-le-Viger. Meanwhile, more than 60 samples with a total mass of more than 1 kg were recovered and a piece of one of these is studied here. The fall occurred 220 years after the historic meteorite fall of L'Aigle on April 26, 1803, <120 km south. L'Aigle is the closest meteorite fall to Saint-Pierre-le-Viger and belongs to the same chondrite group. Both meteorites are breccias containing only clasts of high metamorphic degree (type 5 and type 6). Since only 20% of the L chondrites are breccias this coincidence is remarkable. As just mentioned, both samples studied from these rocks in this work are ordinary chondrite breccias and consist of equilibrated and recrystallized lithologies of petrologic type 6. The brecciated texture in L'Aigle, resulting in a remarkable light–dark structure, is more pronounced than the brecciated features in Saint-Pierre-le-Viger, from which also type 5 fragments have been reported. The compositions of low-Ca pyroxene and olivine grains in Saint-Pierre-le-Viger (Fs21.2 and Fa23.4, respectively) clearly require an L-group classification. L'Aigle was classified as an L6 breccia in the past, and this has now been confirmed by new data on low-Ca pyroxene and olivine (Fs20.7 and Fa23.8, respectively). Saint-Pierre-le-Viger contains local thin shock veins, and both meteorites are moderately shocked. Most olivines in the studied samples have planar fractures, but the estimated abundance of mosaicized olivines of 30%–40% among the large grains require a S4 shock classification. Oxygen isotope and bulk chemical data of Saint-Pierre-le-Viger certainly support the L chondrite classification. Bulk spectral data of Saint-Pierre-le-Viger are dominated by silicate minerals, that is, Fe-bearing low-Ca pyroxene, olivine, and plagioclase. Isotopic, chemical, and spectral data of the L'Aigle meteorite are shown for comparison and are very similar, providing additional circumstantial evidence of Saint-Pierre-le-Viger's L chondritic nature.  相似文献   

17.
Abstract— We have studied an Allende dark inclusion by optical microscopy, scanning electron microscopy, electron microprobe analysis and transmission electron microscopy. The inclusion consists of chondrules, isolated olivines and matrix, which, as in the Allende host, is mainly composed of 5–20 μm long lath-shaped fayalitic grains with a narrow compositional range (Fa42 ± 2) and nepheline. Olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5–10 μm wide fayalitic rims (Fa39 ± 2) and 100–1000 μm wide translucent zones, which consist of 5–20 μm long lath-shaped fayalitic grains (Fa41 ± 1) intergrown with nepheline. These fayalitic olivines, like those in the matrix of the dark inclusion, contain 10–20 nm sized inclusions of chromite, hercynite, and Fe-Ni sulfides. The fayalitic rims around remnant olivines are texturally and compositionally identical to those in Allende host, suggesting that they have similar origins. Chondrules are surrounded by opaque rims consisting of tiny lath-shaped fayalitic olivines (<1–3 μm long) intergrown with nepheline. As in the Allende host, fayalitic olivine veins may crosscut altered chondrules, fine-grained chondrule rims and extend into the matrix, indicating that alteration occurred after accretion. We infer that fayalitic olivine rims and lath-shaped fayalites in Allende and its dark inclusions formed from phyllosilicate intermediate phases. This explanation accounts for (1) the similarity of the replacement textures observed in the dark inclusion and Allende host to aqueous alteration textures in CM chondrites; (2) the anomalously high abundances of Al and Cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in Allende and Allende dark inclusions; (3) abundant voids and defects in lath-shaped fayalites in the Allende dark inclusion, which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed CM/CI chondrites. We conclude that the matrix and chondrule rims in Allende were largely converted to phyllosilicates and then completely dehydrated. The Allende dark inclusions experienced diverse degrees of aqueous/hydrothermal alteration prior to complete dehydration. The absence of low-Ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in Allende is consistent with the lower resistance of low-Ca pyroxene to aqueous alteration relative to forsteritic olivine. Hydro-thermal processing of Allende probably also accounts for the low abundance of planetary noble gases and interstellar grains, and the formation of nepheline, sodalite, salite-hedenbergite pyroxenes, wollastonite, kirschsteinite and andradite in chondrules and Ca,Al-rich inclusions.  相似文献   

18.
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   

19.
Abstract— The oxidized CV3 chondrites can be divided into two major subgroups or lithologies, Bali-like (CV3oxB) and Allende-like (CV3oxA), in which chondrules, calcium-aluminum-rich inclusions (CAIs) and matrices show characteristic alteration features (Weisberg et al, 1997; Krot et al, 1997d; Kimura and Ikeda, 1997). The CV3oxB lithology is present in Bali, Kaba, parts of the Mokoia breccia and, possibly, in Grosnaja and Allan Hills (ALH) 85006. It is characterized by the presence of the secondary low-Ca phyllosilicates (saponite and sodium phlogopite), magnetite, Ni-rich sulfides, fayalite (Fa>90), Ca-Fe-rich pyroxenes (Fs10–50Wo45–50) and andradite. Phyllosilicates replace primary Ca-rich minerals in chondrules and CAIs, which suggests mobilization of Ca during aqueous alteration. Magnetite nodules are replaced to various degrees by fayalite, Ca-Fe-rich pyroxenes and minor andradite. Fayalite veins crosscut fine-grained rims around chondrules and extend into the matrix. Thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures (<300 °C) in the presence of aqueous solutions. Oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large Δ18Ofayalite-magnetite fractionation (～20%). We infer that phyllosilicates, magnetite, fayalite, Ca-Fe-rich pyroxenes and andradite formed at relatively low temperatures (<300 °C) by fluid-rock interaction in an asteroidal environment. Secondary fayalite and phyllosilicates are virtually absent in chondrules and CAIs in the CV3oxA lithology, which is present in Allende and its dark inclusions, Axtell, ALHA81258, ALH 84028, Lewis Cliff (LEW) 86006, and parts of the Mokoia and Vigarano breccias. Instead secondary nepheline, sodalite, and fayalitic olivine are common. Fayalitic olivine in chondrules replaces low-Ca pyroxenes and rims and veins forsterite grains; it also forms coarse lath-shaped grains in matrix. Secondary Ca-Fe-rich pyroxenes are abundant. We infer that the CV3oxA lithology experienced alteration at higher temperatures than the CV3oxB lithology. The presence of the reduced and CV3oxA lithologies in the Vigarano breccia and CV3oxA and CV3oXB lithologies in the Mokoia breccia indicates that all CV3 chondrites came from one heterogeneously altered asteroid. The metamorphosed clasts in Mokoia (Krot and Hutcheon, 1997) may be rare samples of the hotter interior of the CV asteroid. We conclude that the alteration features observed in the oxidized CV3 chondrites resulted from the fluid-rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced CV3 chondrites.  相似文献   

20.
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   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号