Dark Inclusions Research Articles

Arcuate band texture in a dark inclusion from the Vigarano CV3 chondrite: Possible evidence for early sedimentary processes

Abstract— A dark inclusion in the Vigarano CV3 carbonaceous chondrite consists almost exclusively of small (<5 μm in diameter) grains of Fe‐rich olivine and is devoid of chondrules, Ca‐Al‐rich inclusions (CAIs) and their pseudomorphs. In backscattered electron images, this dark inclusion shows an unusual texture comprising a network of arcuate bands. Two or more bands occur roughly parallel, forming a set of succesive parallel bands, some crosscutting one another. The bands contain slightly higher amounts of relatively small (<1 μm) olivine grains and so are more densely packed than other areas. The olivine grains in the bands are slightly more Fe‐rich than those in other areas. The bands commonly show gradation on the concave side due to a decrease in the abundance of the small Fe‐rich olivine grains. Texturally, the arcuate bands closely resemble “dish structures” that are commonly observed in siltstones and sandstones on Earth. Dish structures are characterized by thin, dark‐colored, subhorizontal to concave‐upward laminations that are rich in relatively fine‐grained material. On Earth, dish structures form during compaction and dewatering of unconsolidated fine‐grained sediments; they are one of the characteristic sedimentary structures formed through fluidization of fine grains. The dark inclusion in Vigarano, therefore, provides the first evidence that sedimentary processes due to water migration may have taken place within planetesimals and further suggests that fluidization may have played a significant role in the formation of the carbonaceous chondrites.

Two Spectral Types of Retinal Light Damage Occur in Albino as well as in Pigmented Rat: No Essential Role for Melanin

Earlier we showed that two spectral types of retinal damage occur in the pigmented rat. In the present study we investigated whether the same is true for albino rats. When investigating this issue we implicitly investigated the role of melanin in both damage types.An albinotic (Wistar) and a pigmented (Long Evans) strain of rats were used. Under anesthesia, a small part of the retina was irradiated at either 380 nm or at 470 nm. Three days later, the retina was analysed by funduscopy and prepared for light microscopy. Funduscopy showed no signs of damage in the albinotic retina. In the pigmented retina a decoloration of the fundus was noticed after irradiations starting from retinal doses of 0.6±0.1 J cm-2at 380 nm, and from 489±71 J cm-2at 470 nm. By light microscopy, retinal damage was found in the albino retina. The histologic manifestations at 380 nm differed from those at 470 nm. Irradiation at 380 nm at a dose of 0.5–0.9 J cm-2damaged a few scattered photoreceptor cells. At doses of 1.2–1.6 J cm-2all rods were damaged, while the other retinal layers showed no changes. These findings were similar to those found at 380 nm in the pigmented rat. At 470 nm, damage was found most prominently in the retinal pigment epithelium. These cells showed swelling and an increased number of dark inclusions. Threshold damage occurred at doses of 250–500 J cm-2. Again, the pathology in the pigmented rat was highly similar to that in the albino rat.The results show that both spectral damage types occur in albino as well as in pigmented retina. Therefore, melanin plays no crucial role in these light damage types.

Petrology of Allende dark inclusions

Bulk compositions acquired by neutron activation analysis are reported for eight Allende dark inclusions (DIs) and compared with compositions of five DIs previously reported in the literature. Enrichments of the elements Na, K, Br, Ba, Au, and As are generally correlated with increased proportions of porous aggregates predominantly composed of fine-grained, platy to fibrous olivine. These aggregates have been interpreted by some workers as chondrules and inclusions that first were exposed to aqueous alteration, converting anhydrous silicates to phyllosilicates, and later were dehydrated by thermal metamorphism, converting phyllosilicates to olivine. Our data support this interpretation and suggest that the aqueous alteration was open system in character. Feldspathoid grains intergrown with platy to fibrous olivines in porous, olivine-rich aggregates and inclusions of sodalite, nepheline, pentlandite, ilmenite, and spinel in these olivines suggest that phyllosilicates produced during aqueous alteration could accommodate Na, K, Ni, S, etc and are most consistent with a mixture of both saponite and serpentine. Dehydration of saponite would require that the temperature of thermal metamorphism was higher than previously suggested and may have been as high as 800°–900°C. Nonporous rims containing Ca-rich minerals (andradite, hedenbergite) surrounding dark inclusions containing highest proportions of porous, olivine-rich aggregates and slight to moderate depletions of these clasts in Ca relative to bulk Allende suggest that these rims were also the result of redistribution of some elements during dehydration of these clasts caused by thermal metamorphism.

Origin of fayalitic olivine rims and lath‐shaped matrix olivine in the CV3 chondrite Allende and its dark inclusions

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.

Abee and related EH chondrite impact-melt breccias

The Abee EH chondrite is an impact-melt breccia. About 80–90% of the chondrules were melted; many of those that remain have been partly resorbed. Euhedral enstatite phenocrysts are abundant; many have nucleated on the surfaces of relict chondrules and now protrude into kamacite globules. Euhedral laths of graphite, essentially identical to those produced magmatically on Earth, occur throughout the rock. Abee experienced two episodes of impact melting with an intervening period of brecciation. The first impact-melting event produced a relatively homogeneous rock with abundant melt. Upon cooling, the rock was shattered by bombarding meteoroids; igneous oldhamite-rich dark inclusions were introduced at this time. A second impact event produced melt which engulfed the Abee fragments and dark inclusions, primarily digesting the small ones; heat lost to the surrounding clastic debris caused the groundmass melt to quench. Previously described diamonds in Abee containing typical solar-system isotopic compositions of N and Xe were probably produced from graphite by shock. Several other EH chondrites may also be impact-melt breccias. The most extensively melted of these is Adhi Kot, which contains shocked, but largely unmelted, chondrule-rich clasts as well as chondrule-free sulfide- and silica-rich clasts that also appear to be impact products.

Multiple phases of hydrocarbon generation and migration in the Tazhong petroleum system of the Tarim Basin, People's Republic of China

Organic petrology, organic geochemical analysis and fluid inclusion methods were employed to investigate a series of core samples from the Tazhong Uplift. Bitumens and organic inclusions were found to occur widely in Paleozoic rocks, especially carbonates, and both can be subdivided into three groups. The reflectance ranges of the three bitumen groups are: 1.30-1.60% (I); 0.50-0.80% (II); and 0.15-0.40% (III), respectively, and the corresponding organic inclusion groups are: dark yellow fluorescence organic inclusions with a homogenization temperature of 200–240°C; blue-green fluorescence organic inclusions with a temperature of 160–200°C; and the strong yellow fluorescent organic inclusions with a temperature of 80–130°C. The wide occurrence of the three group bitumens and organic inclusions in the Tazhong Uplift reveals that there were three periods of large-scale oil migration and accumulation in this area. The analysis of hydrocarbon-generating history based on paleotemperature and burial history of source rocks shows that they underwent three oil-generating peaks, in Early Ordovician, Triassic and Cenozoic, respectively, which led to three phases of hydrocarbon generation and migration. It is believed that the Tazhong Uplift is an old uplift rich in oil and gas, and has been fed with oil and gas from nearby source areas during a long geological history, and also that it has great hydrocarbon potential.

Indicators of aqueous alteration and thermal metamorphism on the CV parent body: Microtextures of a dark inclusion from Allende

An unusual dark clast in the Allende CV3 chondrite (termed Allende-AF), which was previously interpreted as a primary aggregate formed in the solar nebula (Kurat et al., 1989; Palme et al., 1989), was re-examined. Our study reveals abundant evidence suggesting that it probably experienced extensive aqueous alteration and subsequent thermal metamorphism on the meteorite parent body. Allende-AF contains numerous rounded to oval-shaped inclusions embedded in a dark matrix. The inclusions, consisting predominantly of fine grains of Fe-rich olivine, have internal textures suggesting that they are pseudomorphs after chondrules. Several inclusions appear to be replaced CAIs. Veins filled with fibrous olivine grains occur abundantly in both inclusions and matrix; some veins (up to 4 mm in length) penetrate several inclusions, providing strong evidence that aqueous alteration occurred after accretion. The fibrous morphology of olivine in veins and inclusions suggests that the olivine was produced by dehydration and thermal transformation of phyllosilicate that had been formed by aqueous alteration. Olivine grains in the matrix contain numerous micro-inclusions of FeNi sulfide, which were probably incorporated during transformation from phyllosilicate. Allende-AF is probably related to the fine-grained variety of dark inclusions reported from CV3 chondrites that has been described as the type containing abundant porous aggregates of Fe-rich olivine by Johnson et al. (1990). Many dark inclusions previously described appear to be similar in texture and mineralogy to Allende-AF, and probably experienced similar secondary process on the meteorite parent body. The wide variation in texture of dark inclusions can be explained by different degrees of aqueous alteration that preceded thermal metamorphism. The size distribution of chondrule pseudomorphs and the abundance of CAI pseudomorphs suggest that the precursor of Allende-AF is a CV type chondrite, probably Allende itself. Oxygen isotopic and chemical compositions are consistent with this interpretation. The CV parent body has been commonly thought to have escaped major secondary processing. However, Allende-AF provides evidence that extensive aqueous alteration and thermal metamorphism have occurred locally on the CV parent body.

Oxygen isotope studies of achondrites

Oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites. Among the differentiated achondrites, three isotopic groups are recognized: (l ) SNC (Mars), (2) Earth and Moon, and (3) HED (howardites, eucrites, diogenites). The HED group also contains the mesosiderites, main-group pallasites, and silicates from IIIAB irons. The angrites may be marginally resolvable from the HED group. Within each of these groups, internal geologic processes give rise to isotopic variations along a slope- 1 2 fractionation line, as is well known for terrestrial materials. Variations of Δ 17O from one planet to another are inherited from the inhomogeneities in the solar nebula, as illustrated by the isotopic compositions of chondrites and their constituents. Among the undifferentiated achondrites, five isotopic groups are found: (1) aubrites, (2) winonaites and IAB-IIICD irons, (3) brachinites, (4) acapulcoites and lodranites, and (5) ureilites. The isotopic compositions of aubrites coincide with the Earth and Moon, and also with the enstatite chondrites. These bodies apparently were derived from a. common reservoir, the isotopic composition of which was established at the chondrule scale by nebular processes. Isotopic similarities between chondrites and achondrites are seen only for the following instances: (1) enstatite chondrites and aubrites, (2) H chondrites and HE irons, and (3) L or LL chondrites and IVA irons. The isotopic data also support the following genetic associations: (1) winonaites and IAB-IIICD irons, (2) acapulcoites and lodranites, and (3) ureilites and dark inclusions of C3 chondrites. An attempt to reconcile the whole-planet isotopic compositions of Earth, Mars, and the eucrite parent body with mixing models of their chemical compositions failed. It is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive Solar System components.

Mineralogical and chemical modification of components in CV3 chondrites: Nebular or asteroidal processing?

Abstract— Calcium‐ and aluminum‐rich inclusions (CAIs), chondrules, dark inclusions and matrices in certain CV3 carbonaceous chondrites appear to have been modified by different degrees of late‐stage alteration processes that caused significant variations in mineralogy and chemistry. Some chondrules and CAIs are rimmed with fayalitic olivine. Metal in all components may be oxidized and sulphidized to magnetite, Ni‐rich metal and sulfides. Silicates in all components are aqueously altered to different degrees to phyllosilicates. Primary minerals in some CAIs experienced Fe‐alkali‐halogen metasomatism forming nepheline, sodalite, wollastonite, hedenbergite and other secondary minerals. In CV3 chondrites with metasomatized CAIs, nepheline, sodalite, etc. are also present in chondrule mesostases and in matrices. McSween's (1977b) reduced subgroup of CV3 chondrites generally shows minimal alteration of all components and may represent the unaltered precursors for the oxidized CV3 chondrites, which generally show major alteration. Most studies have been focused on specific components in CV3 chondrites and have not considered possible relationships between alteration processes. We infer from the correlated occurrences of the alteration features that they were closely related in time and space and review nebular and asteroidal models for their origins. We prefer an asteroidal model.

The infection process ofFusarium oxysporum in cotton root tips

Conidia ofFusarium oxysporum f. sp.vasinfectum started to germinate on the roots of cotton (Gossypium barbadense L.) 6 h after inoculation and formed a compact mycelium covering the root surface. 18 h later, penetration hyphae branched off and infected the root. The number of penetration hyphae increased with the number of conidia used for inoculation. The optimal temperature for penetration was between 28 and 30 °C. The highest numbers of penetration hyphae were found in the meristematic zone, 40 percent less in the elongation and root hair zones, and none in the lateral root zone. The fine structure of the infection process was studied in protodermal cells of the meristematic zone and in rhizodermal cells of the elongation zone. The penetration hyphae were well preserved after freeze substitution and showed a Golgi equivalent consisting of three populations of smooth cisternae. Plant reactions were found already during fungal growth on the root surface. In the meristematic zone, a thickening of the plant cell wall due to an apposition of dark and lightly staining material below the hyphae occurred. This wall apposition increased in size around the hypha invading the plant cell and led to the formation of a prominent wall apposition with finger-like projections into the host cytoplasm. In the elongation zone, the deposits around the penetration hypha appeared less thick and the dark inclusions were less pronounced. High pressure freezing of infected cells revealed, thatF. oxysporum penetrates and grows within the host cells without inducing damages such as plasmolysis, cell degeneration or even host necrosis. We suggest thatF. oxysporum has an endophytic or biotrophic phase during colonization of the root tips.

Sequential deposition of plant glycoproteins and polysaccharides at the host-parasite interface ofUromyces vignae andVigna sinensis

Monokaryotic haustoria (M-haustoria) ofUromyces vignae inVigna sinensis cells are surrounded by an extrahaustorial matrix (ema) and the invaginated host plasmalemma, the extrahaustorial membrane (ehrn). The ema was characterized with antibodies against components of the plant cell wall; the ema contained hydroxyproline-rich glycoproteins and arabinogalactans/arabinogalactan proteins, both at a higher concentration close to the ehm. Haustoria with large vacuoles had the ema encased by additional layers. An electron-translucent inner layer deposited on top of the ema contained arabinogalactans/arabinogalactan proteins, hydroxyproline-rich glycoproteins, and callose. The inner layer was surrounded by an electron-translucent middle layer with numerous dark inclusions, rich in pectin and fucose bound to xyloglucans. Finally, a more electron-dense outer layer containing arabinogalactans/arabinogalactan proteins and hydroxyproline-rich glycoproteins encased the whole structure. These polysaccharides, with the exception of callose and un-esterified pectin, were also found in the plant Golgi apparatus. The polysaccharides were synthesized in the trans Golgi cisternae and secreted into the host-parasite interface. The secretory events seem to be coupled to endocytosis since numerous coated pits were found on the ehm too. The pits were elongated, sometimes formed tubules and the coat reacted with an antibody against plant clathrin. Our results suggest intensive membrane recycling around haustoria, together with the secretion of cell wall material, which in the case of more or less vacuolated haustoria seems to be responsible for encasement

Deep penetration of sedimentary fluids in basement rocks from southern Norway: Evidence from hydrocarbon and brine inclusions in quartz veins

This paper presents evidence for fluid flow and fluid-rock interaction at upper crustal levels within the crystalline basement of southern Norway. In the high-grade Modum Complex postmetamorphic veins of quartz occur in association with albitisation of metagabbros and metasediments. Pressure-temperature conditions for the formation of these veins are in the range 250–300°C and ca. 1–2 kbar. Primary and pseudosecondary fluid inclusions in the quartz veins show two fluids: (1) hydrocarbon ± C0 2 inclusions and (2) aqueous inclusions with variable salinities. Dark carbonaceous solid inclusions are also present. The hydrocarbon inclusions are methane dominated (ca. 80–100 mot%), and the presence of higher, complex hydrocarbons is demonstrated. The aqueous inclusions in the metagabbro-hosted veins show more saline compositions than the metasediment-hosted veins. A salinity range of ca. 23-0 wt% NaCl eq is found. Some of the aqueous inclusions may contain NaHCO 3. Crush-leach analyses of inclusion fluids show Na-Ca-K-CI dominated compositions, with Na⪢Ca>K. Hydrocarbon-poor concentrates yield Br/Cl ratios close to seawater, while hydrocarbon-rich concentrates show higher values. The types and chemistry of the hydrocarbons in these veins indicate a biogenic origin of the hydrocarbon fluids. The inclusion fluids are interpreted as derived from an overlying sedimentary basin in late Precambrian or Permian times. The veining is interpreted as the deep expression of the percolation of basinal fluids into the metamorphic basement during crustal extension.

Petrology and mineralogy of the Yamato‐86751 CV3 chondrite

Abstract— The Y‐86751 chondrite (CV3) consists of fine‐grained Ca‐ and Al‐rich inclusions (CAIs), amoeboid olivine inclusions (AOIs), spinel‐rich inclusions, chondrules with and without dark rims, dark inclusions, isolated minerals, metal‐sulfide aggregates, and matrix. Olivines in chondrules without dark rims and AOIs coexist with magnetite and show strong zoning from a magnesian core to a ferroan rim. Spinels in spinel‐rich inclusions show similar zoning. This zoning seems to be caused by exchange reaction of olivine and spinel with an oxidized nebular gas prior to the accretion onto the parent body, and the Mg/Fe diffusion in olivines and spinels took place at a temperature of about 830–860 K. At the same time, enstatite in chondrules without dark rims was replaced by ferroan olivine at the grain boundaries. This feature suggests that chondrules without dark rims, fine‐grained CAIs, spinel‐rich inclusions, and AOIs have experienced oxidation in an oxidizing nebular gas. The oxygen fugacity of the oxidized nebular gas was >10−27.3 bars at about 830 K, being more than 104x larger than that of the canonical nebular gas. Magnetite occurs in the Y‐86751 matrix in close association with Ni‐rich taenite and Co‐rich metal, and it was produced under a condition with the oxygen fugacity of ∼10−38 bars at a temperature of about 620–650 K. On the other hand, olivines in chondrules with dark rims and dark inclusions are magnesian and rich in MnO. They do not show such strong zoning. Probably they were in equilibrium with a nebular gas under a redox condition different from the oxidized nebular gas that produced the zoned olivines in chondrules without dark rims.

Origin of dark clasts in the Acfer 059/El Djouf 001 CR2 chondrite

Abstract— The ten specimens of the paired Acfer 059/El Djouf 001 CR2 chondrite contain abundant lithic fragments which we refer to as dark clasts. Petrological and mineralogical studies reveal that they are not related to the CR2 host meteorite but are similar to dark clasts in other CR2 chondrites. Dark clasts consist of chondrule and mineral fragments, phyllosilicate fragments and clusters, magnetite, sulfides and accessory phases, embedded into a very fine‐grained, phyllosilicate‐rich matrix. Magnetite has morphologies known from CI chondrites: spherules, framboids and platelets. Average abundances of major elements in the dark clasts are mostly in the range of both CR and CV chondrites, but strong depletions in Na and S are apparent. Oxygen isotopic compositions of two dark clasts suggest relationships to type 3 carbonaceous chondrites and dark inclusions in Allende. The dark clasts are clearly different in texture and mineralogical composition from the host matrix of Acfer 059/El Djouf 001. Therefore, these dark clasts are xenoliths and are quite unlike the Acfer 059/El Djouf 001 CR2 host meteorite. We suggest that dark clasts accreted at the same time with all other components during the formation of Acfer 059/El Djouf 001 whole rock.

Carbonaceous chondrite clasts in the howardites Bholghati and EET87513

Abstract— Twenty‐two carbonaceous chondrite clasts from the two howardites Bholghati and EET87513 were analyzed. Clast N from EET87513 is a fragment classified as CM2 material on the basis of texture, bulk composition, mineralogy, and bulk O isotopic composition. Carbonaceous chondrite clasts from Bholghati, for which less data are available because of their small size, can be divided into two petrologic types: C1 and C2. C1 clasts are composed of opaque matrix with rare coarse‐grained silicates as individual mineral fragments; textures resemble CI meteorites and some dark inclusions from CR meteorites. Opaque matrix is predominantly composed of flaky saponite; unlike typical CI and CR meteorites, serpentine is absent in the samples we analyzed. C2 clasts contain chondrules, aggregates, and individual fragments of coarse‐grained silicates in an opaque matrix principally composed of saponite and anhydrous ferromagnesian silicates with flaky textures similar to phyllosilicates. These anhydrous ferromagnesian silicates are interpreted as the product of heating of pre‐existing serpentine. The carbonaceous chondrite clasts we have studied from these two howardites are, with one notable exception (clast N from EET87513), mineralogically distinct from typical carbonaceous chondrites. However, these clasts have very close affinities to carbonaceous chondrites and have also experienced thermal metamorphism and aqueous alteration, but to different degrees.

Unusual dark clasts in the Vigarano CV3 carbonaceous chondrite: Record of parent body process

Abstract— Two unusual dark clasts found in the Vigarano CV3 chondrite were examined using an optical microscope and a scanning electron microscope (SEM). Both clasts lack chondrules, Ca‐Al‐rich inclusions, and coarse‐grained mineral fragments; they, instead, contain abundant inclusions that consist of fine grains (<1 μm) of homogeneous Fe‐rich olivine, thus resembling the fine‐grained variety of dark inclusions in CV3 chondrites. The external shapes of inclusions in the clasts bear a close resemblance to those of chondrules and chondrule fragments; some of the inclusions are surrounded by dark rims similar to chondrule rims. Our SEM observations reveal the following unusual characteristics: 1) the inclusions are not mere random aggregates of olivine grains but have peculiar internal textures, that is, assemblages of round or oval shaped outlines, which are suggestive of pseudomorphs after porphyritic olivine chondrules; 2) one of thick inclusion rims contains a network of vein‐like strings of elongated olivine grains; 3) an Fe‐Ni metal aggregate in one of the clasts has an Fe‐, Ni‐, S‐rich halo suggesting a reaction between its precursor and the surrounding matrix; and 4) olivine in the clasts commonly shows a swirly, fibrous texture similar to that of phyllosilicate. These characteristics suggest that the dark clasts in Vigarano are not primary aggregates of dust in the solar nebula but were affected by aqueous alteration and subsequent dehydration by heating after accretion to the meteorite parent body. The fine olivine grains in these clasts were presumably produced by thermal transformation of phyllosilicate, as is the case with those in the two thermally metamorphosed Antarctic CM chondrites, Belgica‐7904 and Yamato‐86720. From textural and mineralogical similarities, some of the dark inclusions and clasts previously reported from CV3 chondrites and other types of meteorites may have origins common with these clasts in Vigarano.

Acfer 182 and paired samples, an iron-rich carbonaceous chondrite: Similarities with ALH85085 and relationship to CR chondrites

Three samples of a new, Fe-rich chondrite were found in the Sahara in 1990 and 1991 (Acfer 182, Acfer 207, Acfer 214). The samples are paired and the meteorite will be designated as Acfer 182. The chondrite is chemically, texturally, and mineralogically similar to the Allan Hills meteorite ALH85085. One important difference between the two meteorites is the smaller average chondrule size in ALH85085. The major components of Acfer 182 (in decreasing abundance) are 1. (1) highly altered (by terrestrial weathering) matrix 2. (2) mineral and polymineralic silicate fragments and aggregates 3. (3) chondrule fragments 4. (4) chondrules 5. (5) metal 6. (6) fine-grained, dark inclusions. The abundance of chondrules is lower and the average chondrule size ( $ ̃ 90 μm) smaller than in most other chondrites. Chondrule fragments are often so large that they cannot be derived from the present chondrule population. Apparently, size sorting has prevented accumulation of the larger parent chondrules. Several spectacular Ca,Al-rich inclusions were found, rich in Ca-dialuminate, hibonite, or Zr-, Y-, Sc-bearing phases. The chemical composition of Acfer 182 and of ALH85085 are almost indistinguishable. Major chemical signatures are 1. (1) uniform enrichment of Fe and other nonvolatile metals relative to CI-chondrites by about 70% 2. (2) absence of enrichment in refractory lithophiles, characteristic of most type 2 and 3 carbonaceous chondrites 3. (3) strong depletion of volatile and moderately volatile elements. Based on the oxygen isotopic composition, the chemical composition, and the abundances of chondrules and matrix, Acfer 182 should be classified as a carbonaceous chondrite. Considering their affinity to carbonaceous chondrites and their high bulk iron content the two meteorites, Acfer 182 and ALH85085, are designated as CH-chondrites. There are mineralogical and chemical similarities among Acfer 182, ALH85085, and CR chondrites which distinguish these meteorites from other types of carbonaceous chondrites: 1. (1) low FeO contents of olivine and pyroxene and correspondingly high metal contents 2. (2) high Cr-content in olivine 3. (3) abundant fine-grained dark inclusions 4. (4) abundant Ca-dialuminate (CaAl 4O 7) in CAIs 5. (5) similarities in oxygen isotopic composition 6. (6) low contents of moderately volatile elements 7. (7) low refractory element contents 8. (8) presence of a unique component of subsolar rare gases. These observations suggest similar conditions of formation for the components of these meteorites. A single common parent body is unlikely in view of the differences in chemical composition and in the size distribution of individual components.

The CR (Renazzo-type) carbonaceous chondrite group and its implications

A petrologic, geochemical and oxygen isotopic study of eight meteorites, identified as CR (Renazzo-type) chondrites, reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms CR as a carbonaceous chondrite group. Characteristics of the CR group include 1. (1) abundant large multilayered, Fe.Ni metal-rich, type I chondrules, 2. (2) abundant matrix and dark inclusions (DI) that contain microchondrules, microfragments and magnetite framboids and platelets, 3. (3) unique assemblages of serpentine- and chlorite-rich phyllosilicates and Ca-carbonates, 4. (4) Ca-carbonate rims on chondrules, 5. (5) abundant Fe,Ni metal with a positive Ni vs. Co trend and a solar Ni:Co ratio, 6. (6) low abundance of refractory-rich inclusions, 7. (7) amoeboid olivine aggregates (AOA) with Mn-rich and Mn-poor forsterite and 8. (8) oxygen isotopic compositions that form a unique mixing line. The CR chondrites are breccias consisting of two major components: the large layered chondrules and the matrix (+ dark inclusions). Al Rais is an anomalous member in having a higher abundance of the dark inclusion component (>70 vol.%) and this accounts for its having a higher volatile content than other members of the group. The conditions that prevailed during aqueous alteration of the CR chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the CI and CM chondrites. The CR chondrite components (chondrules, matrix, dark inclusions, etc.) experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite. The overall degree of hydration in CR chondrites varies among meteorites, with Al Rais being the most hydrated. The oxygen isotopic variation of the whole rocks, chondrules and matrices may be related to degree of hydration, indicating that CR chondrites interacted with a water-rich component having heavy oxygen and that was the same as CI and CM water.

Paired Renazzo-type (CR) carbonaceous chondrites from the Sahara

Ten chondrites with chemical and mineralogical similarities to the carbonaceous chondrite Renazzo were recovered at two locations of the Sahara: Acfer 059, 087, 097, 114, 139, 186, 187, 209, 270 and El Djouf 001. Although the El Djouf location is more than 500 km away from the Acfer location, all samples appear to result from a single fall based on chemical and petrographic similarities and supported by light element stable isotope geochemistry, noble gas record, and similar 26Al contents. The Acfer-El Djouf meteorite is classified as a CR (Renazzo-type) carbonaceous chondrite. This group presently comprises three non-Antarctic members (Al Rais, Renazzo, Acfer-El Djouf) and five Antarctic meteorites. The major lithological components of the Acfer-El Djouf meteorite are large chondrules (up to 1 cm in size; mean diameter: 1.0 ± 0.6 mm), chondrule and mineral fragments, Ca,Al-rich inclusions, FeNi-metal (about 8–10 vol%) and dark inclusions embedded in a fine-grained fragment-bearing groundmass. Mineral compositions of the ten Acfer-El Djouf samples are similar to those of other CR chondrites. Most of the Ca,Al-rich inclusions are below 300 μm in size and rich in melilite and spinel. In some CAIs the rare phase CaAl 4O 7 is dominant. Fo-rich, Cr-bearing olivine (Fa 0–4) and enstatite (Fs 0–4) are the major phases of the chondrite. The meteorite is mildly shocked with a shock stage of S2 indicating a peak shock pressure of 5–10 GPa for the bulk meteorite. The oxygen isotopic compositions and carbon and nitrogen stable isotope geochemistry of the Acfer-El Djouf samples are very similar to those of the other CR-type chondrites. The major element composition of the Acfer-El Djouf meteorite is indistinguishable from CR chondrites. When compared to Renazzo the Acfer-El Djouf samples, however, have systematically lower contents of the moderately volatile elements Zn, Ga, As, Au, Sb, and Se and the highly volatile elements Br, C, and N. This is thought to reflect primary differences between Renazzo and the Acfer-El Djouf meteorite.

Ocular-chondrodysplasia in Labrador Retriever dogs: A morphometric and electron microscopical analysis

Ocular-chondrodysplasia in Labrador Retriever dogs is characterized by short-limbed dwarfism and ocular abnormalities. The purposes of the present study were to develop morphological criteria to define the matrix and/or chondrocytic abnormalities associated with this chondrodysplasia, and to test the hypothesis that ineffective matrix-directed cellular swelling was associated with the decreased longitudinal bone growth in these animals. The proximal and distal radial growth plates were collected from four affected animals of the same litter. Stereological techniques were used to analyze both cellular shapes and cellular volume changes in the hypertrophic zone. The pathological changes seen in these growth plates varied between animals and included disorganization of cellular columns with abnormal extent of calcification. Chondrocytes of all zones contained two types of abnormal cellular inclusions classified as light and dark, based on the intensity of eosinophilic staining. Both types of inclusions contained material that resembled the surrounding extracellular matrix, varying only in the apparent hydration of the contents. It could be demonstrated that light inclusions were located in the peripheral cytoplasm and connected to the extracellular matrix through narrow channels. By contrast, dark inclusions were membrane bound and perinuclear. Chondrocytes with multiple, large inclusions appeared to be undergoing degenerative changes. Although the final volume achieved by hypertrophic chondrocytes was consistent with that of normal growth plates, there was a high level of variability of chondrocytic shape and evidence of premature cellular condensation in the maturation zone. The severity of the dwarfism correlated both with the extent of chondrocytic changes and the severity of the ocular lesions.(ABSTRACT TRUNCATED AT 250 WORDS)