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41.
Addi BISCHOFF Miha JERSEK Thomas GRAU Breda MIRTIC Ulrich OTT Jan KUČERA Marian HORSTMANN Matthias LAUBENSTEIN Siegfried HERRMANN Zdeněk ŘANDA Marc WEBER Gerd HEUSSER 《Meteoritics & planetary science》2011,46(6):793-804
Abstract– On April 9, 2009, at 3:00 CEST, a very bright fireball appeared over Carinthia and the Karavanke Mountains. The meteoroid entered the atmosphere at a very steep angle and disintegrated into a large number of objects. Two main objects were seen as separate fireballs up to an altitude of approximately 5 km, and witnesses reported loud explosions. Three stones were found with a total weight of approximately 3.611 kg. The measured activity of short‐lived cosmogenic radionuclides clearly indicates that two specimens result from a very recent meteorite fall. All cosmogenic radionuclide concentrations suggest a rather small preatmospheric radius of <20 cm; a nominal cosmic‐ray exposure age based on 21Ne is approximately 4 Ma, but the noble gas and radionuclide results in combination indicate a complex irradiation. Jesenice is a highly recrystallized rock with only a few relic chondrules visible in hand specimen and thin section. The texture, the large grain size of plagioclase, and the homogeneous compositions of olivines and pyroxenes clearly indicate that Jesenice is a L6 chondrite. The bulk composition of Jesenice is very close to the published average element concentration for L ordinary chondrites. The chondrite is weakly shocked (S3) as indicated by the undulatory extinction in olivine and plagioclase and the presence of planar fractures in olivine. Being weakly shocked and with gas retention ages of >1.7 Ga (4He) and approximately 4.3 Ga (40Ar), Jesenice seems not to have been strongly affected by the catastrophic disruption of the L‐chondrite parent body approximately 500 Ma ago. 相似文献
42.
T. Dahm D. Becker M. Bischoff S. Cesca B. Dost R. Fritschen S. Hainzl C. D. Klose D. K��hn S. Lasocki Th. Meier M. Ohrnberger E. Rivalta U. Wegler Stephan Husen 《Journal of Seismology》2013,17(1):197-202
Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community. Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology. 相似文献
43.
Limestones in the Palmers Oakey District, N.S.W., range in age from Middle Silurian to Early Devonian. They occur as sheet‐like, bioclastic beds and/or isolated clasts in three facies: a volcaniclastic facies, a mudstone‐limestone facies, and a limestone‐mudstone breccia facies. Multielement conodont taxa, not previously reported from Australia, include Kockelella absidata, Kockelella stauros, Ozarkodina asymmetrica, Ozarkodina stygia, Ozarkodina transitans, Pseudooneotodus bicornis, and Pseudooneotodus tricornis. 相似文献
44.
Abstract— NWA 2526 is a coarse‐grained, achondritic rock dominated by equigranular grains of polysynthetically twinned enstatite (?85 vol%) with frequent 120° triple junctions and ?10–15 vol% of kamacite + terrestrial weathering products. All other phases including troilite, daubreelite, schreibersite, and silica‐normative melt areas make up 1 vol% of the rock Oxygen isotopic analyses are well within the range of those for enstatite chondrites and aubrites. We show that the “enstatite achondrite” (Russell et al. 2005) Northwest Africa (NWA) 2526 is actually a partial melt residue of an enstatite chondrite‐like lithology that experienced ?20 vol% partial melting. We suggest that the heat source was internal to the parent body. The FeS‐Fe,Ni and plagioclase‐enstatite partial melts were removed from the parent lithology, leaving NWA 2526 as a residue highly depleted in troilite and lacking plagioclase. Sub‐solidus slow cooling and annealing is responsible for the coarsegrained, recrystallized texture of the rock. We also suggest that the parent lithology of NWA 2526, prior to partial melting, experienced a shock event which formed the curvilinear trails of blebs of minor troilite and rare metal that are enclosed in enstatite crystals; thus, these represent relicts. After partial melting and annealing, NWA 2526 experienced a second, relatively mild impact event (20 GPa) that caused formation of the polysynthetic twinning in the enstatite. We suggest that the meteorite Zaklodzie, which has been referred to as a “primitive enstatite achondrite” (Przylibski et al. 2005), did not form from a magma of internal origin, but that it is an impact‐melt breccia of enstatite chondrite‐like parentage, as previously discussed by Burbine et al. (2000) and Keil (2007). Finally, the “metal‐rich enstatite meteorite with achondritic texture” Itqiy (Patzer et al. 2001) formed by processes very similar to those responsible for formation of NWA 2526 and is also the residue of ?20 vol% partial melting of an enstatite chondrite‐like parent lithology, with the FeS‐Fe,Ni and plagioclase‐enstatite partial melts having been removed from the residue. It also experienced an impact event after partial melting that was responsible for the formation of the mixed Mg‐Mn‐Fe‐sulfides and the shock stage S3 features of the enstatite. These similarities indicate that NWA 2526 and Itqiy may have formed on the same parent body. This body was different from the EH, EL, Shallowater and aubrite parent bodies, and NWA 2526 and Itqiy may represent samples from yet another, fifth enstatite meteorite parent body. 相似文献
45.
Oxygen- and magnesium-isotope compositions of calcium-aluminum-rich inclusions from Rumuruti (R) chondrites 总被引:1,自引:0,他引:1
We report oxygen- and magnesium-isotope compositions of Ca,Al-rich inclusions (CAIs) from several Rumuruti (R) chondrites measured in situ using a Cameca ims-1280 ion microprobe. On a three-isotope oxygen diagram, δ17O vs. δ18O, compositions of individual minerals in most R CAIs analyzed fall along a slope-1 line. Based on the variations of Δ17O values (Δ17O = δ17O − 0.52 × δ18O) within individual inclusions, the R CAIs are divided into (i) 16O-rich (Δ17O ∼ −23-26‰), (ii) uniformly 16O-depleted (Δ17O ∼ −2‰), and (iii) isotopically heterogeneous (Δ17O ranges from −25‰ to +5‰). One of the hibonite-rich CAIs, H030/L, has an intermediate Δ17O value of −12‰ and a highly fractionated composition (δ18O ∼ +47‰). We infer that like most CAIs in other chondrite groups, the R CAIs formed in an 16O-rich gaseous reservoir. The uniformly 16O-depleted and isotopically heterogeneous CAIs subsequently experienced oxygen-isotope exchange during remelting in an 16O-depleted nebular gas, possibly during R chondrite chondrule formation, and/or during fluid-assisted thermal metamorphism on the R chondrite parent asteroid.Three hibonite-bearing CAIs and one spinel-plagioclase-rich inclusion were analyzed for magnesium-isotope compositions. The CAI with the highly fractionated oxygen isotopes, H030/L, shows a resolvable excess of 26Mg (26Mg∗) corresponding to an initial 26Al/27Al ratio of ∼7 × 10−7. Three other CAIs show no resolvable excess of 26Mg (26Mg∗). The absence of 26Mg∗ in the spinel-plagioclase-rich CAI from a metamorphosed R chondrite NWA 753 (R3.9) could have resulted from metamorphic resetting. Two other hibonite-bearing CAIs occur in the R chondrites (NWA 1476 and NWA 2446), which appear to have experienced only minor degrees of thermal metamorphism. These inclusions could have formed from precursors with lower than canonical 26Al/27Al ratio. 相似文献
46.
47.
A. Bischoff T. Geiger H. Palme B. Spettel L. Schultz P. Scherer J. Schlüter J. Lkhamsuren 《Meteoritics & planetary science》1993,28(4):570-578
Abstract— Adzhi-Bogdo is an ordinary chondrite regolith breccia (LL3–6) which fell on 1949 October 30 in Gobi Altay, Mongolia. The rock consists of submm- to cm-sized fragments embedded in a fine-grained clastic matrix. The polymict breccia contains various types of clasts, some of which must be of foreign origin. Components of the breccia include chondrules, melt rock clasts (some of which are K-rich), highly recrystallized rock fragments (“granulites”), breccia clasts, pyroxene-rich fragments with achondritic textures, and alkali-granitoids. The composition of olivine in most fragments is in the range of LL-chondrites. However, olivine in some components has significantly lower fayalite contents, characteristic of L-chondrites. The bulk meteorite is very weakly shocked (S2). Based on the bulk chemical composition, Adzhi-Bogdo is an ordinary chondrite. The concentrations of Fe and Ni are somewhat intermediate between L- and LL-chondrites. The contents of solar gases indicate that Adzhi-Bogdo is a regolith breccia. Most of the solar He and probably a part of the solar Ne of Adzhi-Bogdo has been lost. It is suggested that Adzhi-Bogdo experienced an (impact-induced) thermal event early in its history, because most of the radiogenic 40Ar is retained. 相似文献
48.
H. Schulze A. Bischoff H. Palme B. Spettel G. Dreibus J. Otto 《Meteoritics & planetary science》1994,29(2):275-286
Abstract— The Rumuruti meteorite shower fell in Rumuruti, Kenya, on 1934 January 28 at 10:43 p.m. Rumuruti is an olivine-rich chondritic breccia with light-dark structure. Based on the coexistence of highly recrystallized fragments and unequilibrated components, Rumuruti is classified as a type 3–6 chondrite breccia. The most abundant phase of Rumuruti is olivine (mostly Fa~39) with about 70 vol%. Feldspar (~14 vol%; mainly plagioclase), Ca-pyroxene (5 vol%), pyrrhotite (4.4 vol%), and pentlandite (3.6 vol%) are major constituents. All other phases have abundances below 1 vol%, including low-Ca pyroxene, chrome spinels, phosphates (chlorapatite and whitlockite), chalcopyrite, ilmenite, tridymite, Ni-rich and Ge-containing metals, kamacite, and various particles enriched in noble metals like Pt, Ir, arid Au. The chemical composition of Rumuruti is chondritic. The depletion in refractory elements (Sc, REE, etc.) and the comparatively high Mn, Na, and K contents are characteristic of ordinary chondrites and distinguish Rumuruti from carbonaceous chondrites. However, S, Se, and Zn contents in Rumuruti are significantly above the level expected for ordinary chondrites. The oxygen isotope composition of Rumuruti is high in δ17O (5.52 ‰) and δ18O (5.07 ‰). Previously, a small number of chondritic meteorites with strong similarities to Rumuruti were described. They were called Carlisle Lakes-type chondrites and they comprise: Carlisle Lakes, ALH85151, Y-75302, Y-793575, Y-82002, Acfer 217, PCA91002, and PCA91241, as well as clasts in the Weatherford chondrite. All these meteorites are finds from hot and cold deserts having experienced various degrees of weathering. With Rumuruti, the first meteorite fall has been recognized that preserves the primary mineralogical and chemical characteristics of a new group of meteorites. Comparing all chondrites, the characteristic features can be summarized as follows: (a) basically chondritic chemistry with ordinary chondrite element patterns of refractory and moderately volatile lithophiles but higher abundances of S, Se, and Zn; (b) high degree of oxidation (37–41 mol% Fa in olivine, only traces of Fe, Ni-metals, occurrence of chalcopyrite); (c) exceptionally high Δ17O values of about 2.7 for bulk samples; (d) high modal abundance of olivine (~70 vol%); (e) Ti-Fe3+?rich chromite (~5.5 wt% TiO2); (f) occurrence of various noble metal-rich particles; (g) abundant chondritic breccias consisting of equilibrated clasts and unequilibrated lithologies. With Rumuruti, nine meteorite samples exist that are chemically and mineralogically very similar. These meteorites are attributed to at least eight different fall events. It is proposed in this paper to call this group R chondrites (rumurutiites) after the first and only fall among these meteorites. These meteorites have a close relationship to ordinary chondrites. However, they are more oxidized than any of the existing groups of ordinary chondrites. Small, but significant differences in chemical composition and in oxygen isotopes between R chondrites and ordinary chondrites exclude formation of R chondrites from ordinary chondrites by oxidation. This implies a separate, independent R chondrite parent body. 相似文献
49.
Abstract— The Portales Valley meteorite provides an opportunity to investigate and compare the microstructure in Fe‐Ni metal of the metallic particles in the chondritic portion and in the metal veins. The low‐temperature phase decomposition of Fe‐Ni metal was investigated using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The microstructure is formed as the Portales Valley meteorite cooled from high temperatures and includes the outer taenite rim, the cloudy zone, clear taenite, and martensite. Martensite in turn decomposes into a fine admixture of fcc rods in a bcc matrix. The width of the island phase of the cloudy zone in the metal particles of the chondritic portion and the metal veins can be used to estimate a low‐temperature cooling rate. The microstructural evidence indicates that the chondritic portions and the metal veins in the Portales Valley meteorite cooled together as a mixture with a cooling rate of roughly 6.5 K/Ma. 相似文献
50.
Josep M. Trigo‐Rodríguez Jordi Llorca Mona Weyrauch Addi Bischoff Carles E. Moyano‐Cambero Klaus Keil Matthias Laubenstein Andreas Pack José María Madiedo Jacinto Alonso‐Azcárate My Riebe Rainer Wieler Uli Ott Mar Tapia Narcís Mestres 《Meteoritics & planetary science》2014,49(8):1475-1484
We report and describe an L6 ordinary chondrite fall that occurred in Ardón, León province, Spain (longitude 5.5605°W, latitude 42.4364°N) on July 9th, 1931. The 5.5 g single stone was kept hidden for 83 yr by Rosa González Pérez, at the time an 11 yr old who had observed the fall and had recovered the meteorite. According to various newspaper reports, the event was widely observed in Northern Spain. Ardón is a very well‐preserved, fresh, strongly metamorphosed (petrologic type 6), and weakly shocked (S3) ordinary chondrite with well‐equilibrated and recrystallized minerals. The mineral compositions (olivine Fa23.7±0.3, low‐Ca pyroxene Fs20.4±0.2Wo1.5±0.2, plagioclase An10.3±0.5Ab84.3±1.2), magnetic susceptibility (log χ = 4.95 ± 0.05 × 10?9 m3 kg?1), bulk density (3.49 ± 0.05 g cm?3), grain density (3.58 ± 0.05 g cm?3), and porosity (2.5 vol%) are typical for L6 chondrites. Short‐lived radionuclides confirm that the meteorite constitutes a recent fall. The 21Ne and 38Ar cosmic ray exposure ages are both about 20–30 Ma, similar to values for many other L chondrites. The cosmogenic 22Ne/21Ne ratio indicates that preatmospheric Ardón was a relatively large body. The fact that the meteorite was hidden in private hands for 83 yr makes one wonder if other meteorite falls may have experienced the same fate, thus possibly explaining the anomalously low number of falls reported in continental Spain in the 20th century. 相似文献