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1.
A meteorite which fell at Lahrauli, district Basti, U.P. (India) in 1955 has been examined for mineralogical, chemical and cosmogenic characteristics. It contains pigeonite Wo7.7Fs18 (with Cr2O3 = 1.2% and Al2O3 = 0.4%), olivine Fo79 (with CaO = 0.3% and Cr2O3 = 0.7%) and diamond. The basic similarities of this meteorite to Goalpara, Dyalpur, Havero and Novo Urei indicate that it is a ureilite. Cosmic ray tracks have been measured in the olivine and pyroxene grains. Track density of 2.3 × 106 per cm2 in olivines and VVH/VH ratio of 10?3 is similar to that observed in other meteorites.  相似文献   

2.
The Kyle, Texas, U.S.A., chondrite was identified in 1965. Electron microprobe analyses and microscopic examination show the following mineralogy: olivine (Fa 26.2 mole %), orthopyroxene (Fs 21.0 mole %), clinopyroxene, plagioclase (An 10.3 mole %), chlorapatite, whitlockite, kamacite, taenite, troilite, chromite, and an iron-bearing terrestrial weathering product. Eutectic intergrowths of metaltroilite and a brecciated matrix indicate that the Kyle chondrite was shocked. Recrystallization and shock have obliterated chondrule-matrix boundaries. A chemical analysis of the meteorite shows the following results (in weight %): Fe 0.38, Ni 1.22, Co 0.05, FeS 5.98, SiO2 38.41, TiO2 0.11, Al2O3 2.13, Cr2O3 0.55, Fe2O3 8.02, FeO 14.83, MnO 0.31, MgO 23.10, CaO 1.60, Na2O 0.74, K2O 0.08, P2O5 0.19, H2O+ 1.73, H2O? 0.37, C 0.03, Sum 99.83. On the basis of bulk chemistry, composition of olivine and orthopyroxene, and the recrystallized matrix, the Kyle meteorite is classified as an L6 chondrite.  相似文献   

3.
The Oro Grande, New Mexico, U.S.A., chondrite was found in 1971. Electron microprobe analyses and microscopic examination show the following mineralogy: olivine (Fa 19.3 mole percent), orthopyroxene (Fs 16.2 mole percent), diopside, feldspar (An 13.6 mole percent), chlorapatite, whitlockite, kamacite, taenite, troilite, chromite, and an iron-bearing terrestrial weathering product. A bulk chemical analysis of the meteorite shows the following results (weight percent): Fe 0.84, Ni 1.46, Co 0.07, FeS 3.62, SiO2 34.18, TiO2 0.14, Al2O3 1.83, Cr2O3 0.55, Fe2O3 21.25, FeO 9.13, MnO 0.31, MgO 21.52, CaO 1.72, Na2O 0.70, K2O 0.08, P2O5 0.25, H2O+ 2.14, H2O- 0.40, C 0.22, Sum 100.41. On the basis of composition and texture, the Oro Grande meteorite is classified as an H5 chondrite. A large lithic fragment (～5 mm long) with a very fine-grained texture different from that of the host meteorite was analyzed for bulk composition using the broad beam of an electron microprobe, and was found to be enriched in Ca, Al, Na, and K, and depleted in Mg and Fe relative to the bulk composition of the host meteorite. Its mineral compositions, however, are very similar to those of the host. It is suggested that the fragment is not a xenolith of a previously undescribed type of achondrite, but is probably an impact-produced partial melt of the host chondrite or a fragment of an unusually large chondrule.  相似文献   

4.
A new analysis of the Johnstown meteorite, a hypersthene achondrite, gives the following results (weight percent): SiO2 53.48, TiO2 0.12, Al2O3 1.43, Cr2O3 0.83, FeO 15.63, MnO 0.54, MgO 25.87, CaO 1.40, Na2O 0.04, K2O 0.00, P2O5 0.00, H2O+ <0.1, H2O- 0.05, Ni <0.05, Co <0.01, FeS 1.18, sum 100.57. Published and unpublished data on minor and trace elements in the bulk meteorite and in the pyroxene are presented in tabular form.  相似文献   

5.
The Homewood meteorite is a slightly weathered find of 325 grams discovered in 1970 about 64 km southwest of Winnipeg, Manitoba. It consists of olivine (Fa25.4; 43.8 normative wt. percent), orthopyroxene (Fs23.3; 28.5 percent), kamacite and taenite (7.5 percent), troilite (5.6 percent), maskelynite (8.3 percent), chromite (1.0 percent), whitlockite (0.7 percent) and minor patchy Ca pyroxene. Bulk chemical analysis yielded Fetotal 21.60 wt. percent, Fe/SiO20.55, SiO2/MgO 1.53 and FeO/Fetotal 0.29. Barred olivine, radiating pyroxene and porphyritic chondrules, all with ill-defined outlines, occur in the meteorite. Most chemical and mineralogical features characterize the Homewood meteorite as an L6 (hypersthene) chondrite. The presence of maskelynite, the undulatory extinction, extensive fracturing and pervasive mosaicism of olivine, and the poor definition of chondrule outlines suggest that the Homewood meteorite has been shocked in the range of 300–350 kbar.  相似文献   

6.
On June 12, 2004, a meteorite passed through Earth's atmosphere and landed under the television in the living room of a house in Auckland, New Zealand. Textural characteristics, the chemistry of olivine (Fa23–24) and orthopyroxene (Fs20.7), and the bulk rock triple oxygen isotopes (δ17O + 3.1; δ18O + 4.2‰) from the interior of the completely unweathered (W0) 1.3 kg meteorite, hereafter referred to as Auckland, suggest it to be a strongly metamorphosed fragment from the interior of a low iron ordinary chondrite (L6) parent asteroid. The occurrence of maskelynite but shock fracturing of olivine and pyroxene indicates Auckland experienced extreme shock metamorphism (S5), likely during Ordovician fragmentation of the asteroid parent. The fusion crust consists of three zones: (1) an innermost zone containing narrow Fe-Ni-S-bearing veins that migrated along pre-existing shock fractures in olivine and pyroxene; (2) a middle zone in which the meteorite partially melted to form a silicate glass and immiscible blebs of metal and troilite, and is accompanied by unmelted silicate minerals; and (3) an approximately 0.1 mm wide vesicular-rich outermost layer that largely melted, volatilizing sulfides, before quenching to form glass and olivine. Oxygen isotope values of the bulk rock and/or maskelynite of melted rim and modified substrate are 2–3‰ greater than the meteorite interior and indicate that up to 19% of terrestrial atmospheric O2 was incorporated into the fusion crust during the formation. The fusion crust migrated inwards as ablation occurred, enabling melting, migration, and re-precipitation ± loss of sulfide and metal components, with the prominent glassy rim therefore forming from an already chemically modified zone.  相似文献   

7.
At 9:20 A.M. on August 18, 1974, a stony meteorite of approximately 3200 grams struck the roof of a secondary school at Naragh, Central Iran, (51°30′E, 33°45′N). The ellipsoidal dark-gray meteorite was 17 × 15 × 13 cm (density 3.62 gr/cm3). XRF and wet chemical analysis yields the bulk composition of the meteorite as follows in weight percent: Fe 11.95, Ni 1.05, Co 0.07, FeS 5.49, SiO2 37.15, TiO2 0.15, Al2O3 2.43, Cr2O30.62, FeO 14.25, MnO 0.23, MgO 23.79, CaO 1.61, Na2O 0.92, K2O 0.08, P2O5 0.26. Modal mineral contents (in volume percent) are olivine 40, orthopyroxene 25, clinopyroxene 3, plagioclase 10.5, chromite 0.80, phosphate 0.70, troilite 6, metal phases 14. The meteorite is fine-grained, with average grain size about 0.4–0.6 mm and contains numerous recrystallized glassy chondrules. Olivine occurs as laths and radiating crystals in chondrules and as coarse-grained phenocrysts and interstitial microcrystalline grains in the matrix. These olivines have relatively uniform composition (Fo80–82Fa20–18). Fine-grained skeletal orthopyroxenes of average composition (En16Fs82Wo01) are inter-grown with olivine in both chondrules and matrix. Clinopyroxene and plagioclase of average composition (En6.5Fs48Wo45.5) and (Ab82An12Or06) respectively, are evenly distributed in the matrix, together with kamacite (Fe92–95), plessite (Fe69.6–82.2) and taenite (Fe46.7–66.1), troilite (Ni-free) and chromite grains. The high ratios of total Fe to SiO2 of 0.71, metallic Fe to total Fe of 0.54, and SiO2 to MgO of 1.56 in the bulk composition, the Fa component of olivine grains of 17.5–19.6, and the high Ca content of orthopyroxenes between 0.53 and 0.87 wt % suggest that the Naragh meteorite belongs to the H-group and petrologic type 6 of Van Schmus and Wood (1967) classification. In addition, the occurrence of fine-grained clear sodic plagioclase, the presence of numerous recrystallized chondrules with homogeneous silicate minerals, and the absence of Ni in the sulfide phase indicate that the Naragh meteorite has been metamorphosed after the initial crystallization in the parental body.  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.
The Colony meteorite is an accretionary breccia containing several millimeter-to centimeter-size chondritic clasts embedded in a chondritic host. Colony is one of the least equilibrated CO3 chondrites; it has an unrecrystallized texture and contains compositionally heterogeneous olivine and low-Ca pyroxene, kamacite with low Ni and Co and high Cr, amoeboid inclusions with low FeO and MnO, a fine-grained silicate matrix with very high FeO, and numerous small chondrules with clear pink glass. However, Colony differs from normal CO chondrites in several respects: Although Al, Sc, V, Cr, Ir, Fe, Au and Ga abundances are consistent with a CO chondrite classification, certain lithophiles (Mg and Mn), siderophiles (Ni and Co) and chalcophiles (Se and Zn) are depleted by factors of 10–40%. The shape of Colony's thermoluminescence (TL) glow curve is similar to that of Allan Hills A77307 (another unequilibrated chondrite with CO3 petrological characteristics) and different from those of normal CO chondrites. [ALHA77307 also resembles Colony in having low Mg, Mn, Ni and Co, compared to normal CO chondrites, but it possesses CO-CV levels of Se and Zn and nearly CV levels of Cd.] Colony is badly weathered; it contains 22.7 wt.% Fe2O3 and 5.7 wt.% H2O. Recalculating the analysis on an H2O-free basis with all Fe2O3, NiO and CoO converted to metal, yields an inferred original metallic Fe, Ni abundance of ～ 19 wt.%. This is similar to that of Kainsaz (an unweathered CO3 fall), but much higher than that of all other CO3 chondrites (< 6.3 wt.%). Although it is possible that Colony and either ALHA77307 or Kainsaz constitute distinct CO3 chemical subgroups, the weathered nature of Colony and ALHA77307 preclude the drawing of firm conclusions. Nevertheless, it is clear that CO3 chondrites vary more in compositional and petrological properties than was previously recognized.  相似文献   

10.
A total chemical analysis of the Isna, Egypt, meteorite is similar to analyses for chondrites of type C3, Ornans sub-type; however, comparison with one group of chemical data indicates that Isna is intermediate between the C3(O)'s and C3(V)'s in terms of total Fe. On the basis of atom ratios of Fe, Ca, Al, and Ti to Si, Isna can also be placed into a chemical group which includes types C1 and C2, as well as C3(O). Thin sections show a variety of small, closely-packed chondrules, fragments, and aggregate-like masses in a poorly translucent matrix. Olivine + clinoenstatite inclusions rich in metal and troilite, and olivine-rich inclusions are abundant and show evidence of shock. Ca-Al-Ti-rich inclusions, of probable high-temperature origin, contain olivine, spinel, Ca-rich nepheline, gehlenite, diopside, augite, enstatite, and anorthite. Kamacite and taenite from various occurrences in the meteorite have rather uniform Ni and Co contents, and Ni/Co for kamacite is close to that for several C3(O)'s.  相似文献   

11.
The fall occurred near Piancaldoli, Florence, Italy, at 19.14 U.T. on the 10th August 1968. The fireball broke up in the atmosphere producing a cloud like a balloon. The trajectory and the terminal point were calculated, leading to the recovery of three small meteoritic fragments, found on the roof of a house. Chemical analysis gave the following results: SiO2 40.80; TiO2 0.15; Al2O3 2. 70; Cr2O3 0.47; FeO 17.20; MnO 0.07; MgO 25.18; CaO 1.95; Na2O 0.64; K2O 0.07; P2O5 0.20; NiS 0.93; FeS 6.24; Fe° 2.40; Ni° 0.40; Co 0.05; sum 99.45. In the lithic portion of the meteorite the following minerals were found: both clino and orthopyroxenes (En = 76 to 98%), olivines (Fo = 66 to 98%), troilite, pyrrhotite, pentlandite, kamacite, ilmenite, apatite, merillite, schreibersite, chromite and Henderson phase. From all the mineralogical and petrological data, we conclude that the Piancaldoli meteorite is an “unequilibrated ordinary chondrite,” LL3. The microbrecciated structure of the rock and some shock features were observed, while the rock as a whole is unshocked, suggesting that these features were caused by impact events which took place during the accretion of the parent body.  相似文献   

12.
Abstract— The mineralogical and chemical characteristics of the Didwana‐Rajod chondrite are described. The mean mineral composition is found to be olivine (Fo83.2) and pyroxene (En83.5Wo0.7Fs15.8), and feldspar is mainly oligoclase. Oxygen isotopic analysis shows δ18O = +3.8%0 and δ17O = +2.59%0. The nitrogen content of Didwana‐Rajod is ～2 ppm with δ15N ? 3.4%0. Based on microscopic, chemical, isotopic and electron probe microanalysis, the meteorite is classified as an H5 chondrite. Cosmogenic tracks, radionuclides and the isotopic composition of rare gases were also measured in this meteorite. The track density in olivines varies in a narrow range with an average value of (6.5 ± 0.5) × 105/cm2 for four spot samples taken at the four corners of the stone. The cosmic‐ray exposure age based on neon and argon is 9.8 Ma. 22Na/26Al ? 0.94 is lower than the solar‐cycle average value of ～1.5 and is consistent with irradiation of the meteoroid to lower galactic cosmic‐ray fluxes as expected at the solar maximum. The track density, rare gas isotopic ratios, 60Co activity and other radionuclide data are consistent with a preatmospheric radius of ～15 cm, corresponding to a mass of ～50 kg. The cosmogenic properties are consistent with a simple exposure history in interplanetary space.  相似文献   

13.
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   

14.
The Jezersko meteorite is a newly confirmed stony meteorite found in 1992 in the Karavanke mountains, Slovenia. The meteorite is moderately weathered (W2), indicating short terrestrial residence time. Chondrules in partially recrystallized matrix are clearly discernible but often fragmented and have mean diameter of 0.73 mm. The meteorite consists of homogeneous olivine (Fa19.4) and low‐Ca pyroxenes (Fs16.7Wo1.2), of which 34% are monoclinic, and minor plagioclase (Ab83An11Or6) and Ca‐pyroxene (Fs6Wo45.8). Troilite, kamacite, zoned taenite, tetrataenite, chromite, and metallic copper comprise about 16.5 vol% of the meteorite. Phosphates are represented by merrillite and minor chlorapatite. Undulatory extinction in some olivine grains and other shock indicators suggests weak shock metamorphism between stages S2 and S3. The bulk chemical composition generally corresponds to the mean H chondrite composition. Low siderophile element contents indicate the oxidized character of the Jezersko parent body. The temperatures recorded by two‐pyroxene, olivine‐chromite, and olivine‐orthopyroxene geothermometers are 854 °C, 737–787 °C, and 750 °C, respectively. Mg concentration profiles across orthopyroxenes and clinopyroxenes indicate relatively fast cooling at temperatures above 700 °C. A low cooling rate of 10 °C Myr?1 was obtained from metallographic data. Considering physical, chemical, and mineralogical properties, meteorite Jezersko was classified as an H4 S2(3) ordinary chondrite.  相似文献   

15.
The evolution and variability of atmospheric ozone over geological time   总被引：1，自引：0，他引：1  
The rise of atmospheric O3 as a function of the evolution of O2 has been investigated using a one-dimensional steady-state photochemical model based on the chemistry and photochemistry of Ox(O3, O, O(1D)), N2O, NOx(NO, NO2, HNO3), H2O, and HOx(H, OH, HO2, H2O2) including the effect of vertical eddy transport on the species distribution. The total O3 column density was found to maximize for an O2 level of 10?1 present atmospheric level (PAL) and exceeded the present total O3 column by about 40%. For that level of O2, surface and tropospheric O3 densities exceeded those of the present atmosphere by about an order of magnitude. Surface and tropospheric OH densities of the paleoatmosphere exceeded those of the present atmosphere by orders of magnitude. We also found that in the O2-deficient paleoatmosphere, N2O (even at present atmospheric levels) produces much less NOx than it does in the present atmosphere.  相似文献   

16.
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17.
We report an occurrence of hexagonal CaAl2Si2O8 (dmisteinbergite) in a compact type A calcium‐aluminum‐rich inclusion (CAI) from the CV3 (Vigarano‐like) carbonaceous chondrite Northwest Africa 2086. Dmisteinbergite occurs as approximately 10 μm long and few micrometer‐thick lath‐shaped crystal aggregates in altered parts of the CAI, and is associated with secondary nepheline, sodalite, Ti‐poor Al‐diopside, grossular, and Fe‐rich spinel. Spinel is the only primary CAI mineral that retained its original O‐isotope composition (Δ17O ~ ?24‰); Δ17O values of melilite, perovskite, and Al,Ti‐diopside range from ?3 to ?11‰, suggesting postcrystallization isotope exchange. Dmisteinbergite, anorthite, Ti‐poor Al‐diopside, and ferroan olivine have 16O‐poor compositions (Δ17O ~ ?3‰). We infer that dmisteinbergite, together with the other secondary minerals, formed by replacement of melilite as a result of fluid‐assisted thermal metamorphism experienced by the CV chondrite parent asteroid. Based on the textural appearance of dmisteinbergite in NWA 2086 and petrographic observations of altered CAIs from the Allende meteorite, we suggest that dmisteinbergite is a common secondary mineral in CAIs from the oxidized Allende‐like CV3 chondrites that has been previously misidentified as a secondary anorthite.  相似文献   

18.
Abstract– The Grove Mountains (GRV) 021663 meteorite was collected from the Grove Mountains region of Antarctica. The meteorite is composed primarily of olivine (Fa5.4), orthopyroxene (Fs4.7Wo3.0), chromian diopside (En53.6Fs2.4Wo44), troilite, kamacite, and plagioclase (Ab74.5Or4An21.5). Minor phases include schreibersite and K‐feldspar. The meteorite is highly weathered (W3) and weakly shocked (S2). We determine a whole rock oxygen isotopic composition of δ18O = 7.50‰, δ17O = 3.52‰. Comparisons of these data with other primitive achondrites have resulted in the reclassification of this meteorite as a member of the winonaite group. The occurrences of troilite, metal, and schreibersite in GRV 021663 indicate that these minerals were once completely molten. Euhedral inclusions of pyroxene within plagioclase further suggest that these may have crystallized from a silicate melt, while the depletion of plagioclase, metal, and troilite indicates that GRV 021663 could represent a residuum following partial melting on its parent asteroid. Trace element distributions in silicate minerals do not, however, confirm this scenario. As with other winonaite meteorites, the formation of GRV 021663 probably relates to brecciation and mixing of heterogeneous lithologies, followed by varying degrees of thermal metamorphism on the parent body asteroid. Peak metamorphic conditions may have resulted in localized partial melting of metal and silicate mineralogies, but our data are not conclusive.  相似文献   

19.
Abstract— A stony meteorite fell at Itawa Bhopji, Rajasthan, India on 2000 May 30. This is the fifth recorded fall in a small area of Rajasthan during the past decade. The meteorite is an ordinary chondrite with light clasts in a dark matrix, consisting of a mixture of equilibrated (mainly type 5) and unequilibrated components. Olivine is Fa24–26 and pyroxene Fs20–22 but, within the unequilibrated components, olivine (Fa5–29) and low calcium pyroxene (Fs5–37) are highly variable. Based on petrographic studies and chemical analyses, it is classified as L(3–5) regolith breccia. Studies of various cosmogenic records, including several gamma‐emitting radionuclides varying in half‐life from 5.6 day 52Mn to 0.73 Ma 26Al, tracks and rare gases have been carried out. The exposure age of the meteorite is estimated from cosmogenic components of rare gases to be 19.6 Ma. The track density varies by a factor of ?3 (from 4 to 12 times 106/cm2) within the meteorite, indicating a preatmospheric body of ?9 cm radius (corresponding to a meteoroid mass of ?11 kg) and small ablation (1.5 to 3.6 cm). Trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite. Large excess of neutron‐produced 82Kr and 128Xe in both the light and the dark lithology but very low 60Co, indicating low neutron fluxes received by the meteoroid in the interplanetary space, are clear signatures of an additional irradiation on the parent body.  相似文献   

20.
Models are presented for the height distribution of various photochemically active gases in Venus' upper atmosphere. Attention is directed to the chemistry and vertical transport of odd hydrogen (H, OH, HO2, H2O2), odd oxygen (O, O3), free chlorine (Cl, ClO, ClOO, Cl2), CO, O2, H2 and H2O. Supply of O2 may play a limiting role in the formation of a possible H2SO4 cloud on Venus. The supply rate is influenced by both chemical and dynamical processes in the stratosphere, and an analysis of recent spectroscopic data for O2 implies a lower limit to the appropriate eddy coefficient of about 3 × 105 cm2/sec. The abundances of thermospheric O and CO are determined largely by vertical mixing, and an analysis of Mariner 10 measurements of Venus' Lyman α airglow suggests that the eddy coefficient in the lower thermosphere may be as large as 5 × 107cm2sec. The corresponding values for the mixing ratios of O and CO at the ionospheric peak are approximately 1 per cent. The Lyman α data could be reconciled with larger values for thermospheric O, and smaller values for the vertical eddy coefficient, if non-thermal loss processes were to play a dominant role in hydrogen escape, and if the corresponding flux were to exceed 107 atoms/cm2/sec. A sink of this magnitude would imply major depletion of Venus' atmospheric water over geologic time, and would appear to require mixing ratios of H2O in the lower atmosphere in excess of 4 × 10?4. The extensive component to the Lyman α emission measured by Mariner 5 may be due to resonance scattering of sunlight by hot atoms formed by charge transfer with O+. The H scale height, therefore, may reflect the temperature of positive ions in Venus' topside ionosphere.  相似文献   

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