The Burnwell,Kentucky, low iron oxide chondrite fall: Description,classification and origin

Abstract— The Burnwell, Kentucky, meteorite fell as a single stone on 1990 September 4. The Burnwell meteorite has lower Fa in olivine (15.8 mol%), Fs in orthopyroxene (13.4 mol%), Co in kamacite (0.36 wt%), FeO from bulk chemical analysis (9.43 wt%), and Δ¹⁷O (0.51 ± 0.02%), and higher Fe, Ni, Co metal (19.75 wt% from bulk wet chemical analysis) than observed in H chondrites. The Burnwell meteorite plots on extensions of H-L-LL chondrite trends for each of these properties towards more reducing compositions than in H chondrites. Extensions of this trend have been previously suggested in the case of other low-FeO chondrites or silicate inclusions in the HE iron Netschaëvo, but interpretation of the evidence in these meteorites is complicated by terrestrial weathering, chemical disequilibrium or reduction. In contrast, the Burn-well meteorite is an equilibrated fall that exhibits no evidence for reduction. As such, it provides the first definitive evidence for extension of the H-L-LL ordinary chondrite trend beyond typical H values towards more reducing compositions.     

BETWEEN A REFUGE AND A BATTLEGROUND: BEIRUT'S DISCREPANT COSMOPOLITANISMS*

Beirut has experienced cosmopolitanism and its opposite. It is a site of multicultural encounters and communal entrenchment: a refuge and a battleground. How and where does Beirut's cosmopolitan project turn into violence? The notion of “discrepant cosmopolitanism” provides two answers, blurring accepted distinctions between multicultural openness and communitarian entrenchment. First, openness and closure are not opposed but part of discrepant cosmopolitanisms immanent in urban space. Second, these discrepant cosmopolitanisms originate in Lebanon's encounter with colonial modernity. The making of the Lebanese nation‐state has revolved around the sectarian spatiality of the ta'ifa (religious community), which produced contested but coexisting discourses and practices of rivalry and harmony. The rise of Beirut's international hotels in the 1960s, their destruction, and their role in contemporary urban redevelopment are treated here as embodiments of discrepant cosmopolitanisms. Within Beirut's recurrent tensions, a renegotiation of its cosmopolitan project could stem from a different relationship between the urban and national policies.     

The landslide hazard and human vulnerability in La Paz City, Bolivia

Landslides in the city of La Paz, Bolivia are complex in space and time. Their distribution within the city is differentiated by geographical variations in slope gradient, the nature of overlying surface deposits, and drainage density patterns. When mapped, the distribution of the most landslide-prone locations in the city coincides with the most mobile surface deposits on the higher and steeper slopes of the city. The timing of landslides is triggered when slope materials become saturated with moisture by rainfall, stream water, water seepage from high surrounding water tables, and from domestic sources. Landslide frequencies over the last 40 years show the role of inter-annual variations in summer rainfalls, especially the late summer period (Jan–Mar), and rising water tables connected to Lake Titicaca. Associations with ENSO events, both warm (El Nino) and cold (La Nina), prove negative, pointing to the importance of moisture sources from the north, south and east (Amazon) but not from the west (Pacific). The most vulnerable group exposed to the landslide hazard comprise the inhabitants of the self-built informal housing areas who occupy the more elevated steeper slopes of the northern part of the city. But societal vulnerability to earth movement in the city is widespread and interconnected. Higher income groups in the southern part of the city are affected by slower, if less dramatic, forms of land failure, and rich housing in downstream areas of the city are impacted by flash flooding encouraged by deforestation on the northern hill slopes where the poor live. Two case studies highlight the vulnerability and plight of the inhabitants of the self-built settlements in the aftermath of a major landslide, and a brief discussion of hazard mitigation and the importance of building hazard resilient communities concludes the paper.     

Mineral chemistry and geothermobarometry of Moshirabad pluton,Qorveh, Kurdistan,western Iran

The Moshirabad pluton is located southwest of the Sanandaj–Sirjan Metamorphic Belt, Qorveh, western Iran. The pluton is composed of diorite, monzodiorite, quartz diorite, quartz monzodiorite, tonalite, granodiorite, granite, aplite, and pegmatite. In this study 31 samples from various rocks were chosen for whole‐rock analyses and 15 samples from different lithologies were chosen for mineral chemical studies. The compositions of minerals are used to describe the nature of magma and estimate the pressure and temperature at which the Moshirabad pluton was emplaced. Feldspar compositions are near the binary systems in which plagioclase compositions range from An₅ to An₅₃ and alkali‐feldspar compositions range from Or₉₁ to Or₉₇. Mafic minerals in the plutonic rocks are biotite and hornblende. Based on the composition of biotites and whole‐rock chemistry, the Moshirabad pluton formed from a calc‐alkaline magma. Amphiboles are calcic amphiboles (magnesio‐hornblende or edenite). Temperatures of crystallization, calculated with the hornblende–plagioclase thermometer, range 550–750°C. These temperatures indicate that plutonic rocks have undergone some retrogressive changes in their mineral compositions. Aluminum‐in‐hornblende geobarometry indicates that the Moshirabad pluton was emplaced at pressures of 2.3–6.0 kbar, equal to depths of 7–20 km, but with consideration of regional geology, lower pressures than the above pressure range are more probable. Alteration of amphiboles can be the reason for some overestimation of pressures.     

Stromatolite reef crusts,Early Cretaceous,Spain: bacterial origin of in situ‐precipitated peloid microspar?

Peloidal crusts are significant components of Early Cretaceous (Aptian) reef carbonates in eastern Spain. The crusts form steep-sided laminated deposits on coral and other skeletal surfaces. Their microfabric consists almost entirely of silt-sized peloids in fenestral microspar matrix. This microfabric contrasts with more poorly sorted and generally finer grained detrital wackestone–packstone fabrics of the adjacent reef matrix. Scarcity of incorporated grains indicates that the crusts did not trap many particles. It is proposed that the crusts are stromatolites and that peloids and inter-peloid space were created concurrently by bacterial degradation of organic matter. As they developed, inter-peloid voids were protected from infiltration of extraneous sediment by the organic-rich exterior surface of the stromatolite. Even spacing of the peloids within microspar may reflect self-organization of bacterial colonies in the decaying organic matrix. Compressed and partly amalgamated peloids marginal to burrows in the stromatolites suggest that the peloid fabrics were initially only partially lithified. The grainstone-like peloid fabric is therefore interpreted as having formed in situ by very early diagenetic processes driven by heterotrophic bacteria.     

Dynamics of Difference

In this paper, I outline the empowerment methodologies used in workshops with Balinese women and men and discuss the different dynamics and responses they generated. I also evaluate the methodologies and offer some reflections on their applicability to future feminist research in geography.     

Presolar silicon carbide from the Indarch (EH4) meteorite: Comparison with silicon carbide populations from other meteorite classes

Abstract— Presolar SiC from the Indarch (EH4) meteorite was studied by scanning electron microscopy (SEM), by ion probe analysis for C and Si isotopic compositions, and by static source mass spectrometry for noble gas and C isotopic compositions. The data obtained are compared to SiC data from other meteorites, especially from Murchison (CM2), for which there is the most information available. The isotopic compositions of the major elements in SiC from Indarch and Murchison are similar. Stepped combustion data suggest a mean δ¹³C for SiC from both meteorites of ～+1430%o. Silicon isotopes in Indarch and Murchison SiC also compare well. In some other important respects, however, SiC in the two meteorites are different. Morphologically, SiC from Indarch appears finer grained than SiC from Murchison and is entirely composed of submicron grains. The finer-grained nature of Indarch SiC is confirmed by its noble gas characteristics. The mean Ne-E/Xe-S ratio for bulk Indarch SiC is significantly lower than the same ratio in Murchison (625 ± 47 vs. ～3500) but is similar to that of the finest grain-size fractions (<1 μm) in Murchison. A comparison of noble gas data from SiC from several different meteorites suggests that it might be Murchison SiC, rather than Indarch SiC, that is unusual. The grain-size disparities in SiC between meteorites are difficult to explain by residue processing differences or differing parent body processing. Instead, we speculate that a grain-size sorting mechanism for SiC may have operated in the solar nebula.