Martian basalt (shergottite) Queen Alexandra Range 94201 and lunar basalt 15555: A tale of two pyroxenes

Abstract— We present here ion microprobe analyses of rare earth and other selected trace and minor elements in pyroxenes of shergottite Queen Alexandra Range 94201 and lunar basalt 15555. Pyroxene zonation patterns record the crystallization histories of these two basaltic samples from Mars and the Moon, respectively, and allow a comparison of mafic melt evolution on these two planetary bodies. Elemental abundances and trends in pyroxenes of these two rocks indicate that their minerals formed by continuous, closed system fractional crystallization of their respective parent melts. This further supports the idea that QUE 94201 closely represents the composition of a true Martian basaltic melt (McSween et al., 1996). The main differences in pyroxene elemental zonation patterns in these two objects are attributed to earlier crystallization of whitlockite in QUE 94201 (i.e., before the Fe-rich pyroxenes) than in 15555 (after the Fe-rich pyroxenes). The size of Eu anomalies in pyroxenes of QUE 94201 is intermediate between that in pyroxenes of 15555 and the other shergottites and may imply that fO₂ conditions during crystallization of this Martian basalt were significantly more reducing than for other shergottites, although not quite as reducing as for lunar basalts. Cerium anomalies appear to be less prevalent in pyroxenes of QUE 94201 than other Antarctic shergottites and could be indicative of lesser degree of weathering in the Antarctic.     

High-resolution bispectrum speckle interferometry and two-dimensional radiative transfer modeling of the Red Rectangle

We present the first diffraction-limited K-band image of the Red Rectangle with 76 mas resolution, an H-band image with 75 mas resolution, and an RG 715 filter image ( 800 nm wavelength) with 78 mas resolution (corresponding to 25 AU for a distance of 330 pc). The H and K images were reconstructed from 6 m telescope speckle data and the RG 715 image from 2.2 m telescope data using the speckle masking bispectrum method. At all wavelengths the images show a compact, highly symmetric bipolar nebula, suggesting a toroidal density distribution of the circumstellar material. No direct light from the central binary can be seen as it is obscured by a dust disk or circumbinary torus. Our first high-resolution H−K color image of the nebula shows a broad red plateau of H−K≈ 2^m in the bright inner regions.The optical and near-infrared images and the available photometric continuum observations in a wide range of ultraviolet to centimeter wavelengths enabled us to model the Red Rectangle in detail using a two-dimensional radiative transfer code. Our model matches both the high-resolution images and the spectral energy distribution of this object very well, making the following picture much more certain. The central close binary system with a total luminosity of 3000 L is embedded in a very dense, compact circumbinary torus which has an average number density n_H ≈5×10¹² cm⁻³, an outer radius of the dense inner region of R≈30 AU (91 mas), and a ρ∝r⁻² density distribution. The full opening angle of the bipolar outflow cavities in our model is 70°. By comparing the observed and theoretical images, we derived an inclination angle of the torus to the line of sight of 7°±1°.The radiative transfer calculations show that the dust properties in the Red Rectangle are spatially inhomogeneous. The modeling confirms that the idea of large grains in the long-lived disk around the Red Rectangle (Jura et al., 1997 [ApJ, 474, 741]) is quantitatively consistent with the observations. In our models, unusually large, approximately millimeter-sized grains dominate the emission of the compact, massive torus. Models with smaller average grain sizes can possibly be found in future studies, for instance, if it turns out that the radio spectrum is not mainly caused by continuum dust emission. Therefore, the large grains suggested by our models require further confirmation by both new observations and radiative transfer calculations. Assuming a dust-to-gas ratio ρ_d/ρ_g of 0.005, the dense torus mass is 0.25 M. The model gives a lower limit of 0.0018 M, for the mass of the large particles, which produce a gray extinction of A≈ 28^m, towards the center. A much smaller mass of submicron-sized dust grains is presumably located in the polar outflow cavities, their conical surface layers, and in the outer low-density parts of the torus (where ρ∝r⁻⁴, in the region of 30 AUr 2000 AU corresponding to 0.^′′09–6^′′).     

Sapphirine-bearing granulites and related high-temperature metamorphic rocks from the Higo metamorphic terrane, west-central Kyushu, Japan

The Higo metamorphic unit in west-central Kyushu island, southwest Japan is an imbricated crustal section in which a sequence of units with increasing metamorphic grade from high (northern part) to low (southern part) structural levels is exposed. The basal part of the metamorphic sequence representing an original depth of 23–24  km consists mainly of garnet–cordierite–biotite gneiss, garnet–orthopyroxene gneiss, orthopyroxene-bearing amphibolite and orthopyroxene-bearing S-type tonalite. These metamorphic rocks underwent high amphibolite-facies up to granulite facies metamorphism with peak P – T  conditions of 720  MPa, 870  °C. In addition sapphirine-bearing granulites and related high-temperature metamorphic rocks also occur as tectonic blocks in a metamorphosed peridotite intrusion. The sapphirine-bearing granulites and their related high-temperature metamorphic rocks can be subdivided into five types of mineral assemblages reflecting their bulk chemical compositions as follows: (1) sapphirine–corundum–spinel–cordierite (2) corundum–spinel–cordierite (3) garnet–corundum–spinel–cordierite (4) garnet–spinel–gedrite–corundum, and (5) orthopyroxene–spinel–gedrite. These metamorphic rocks are characterized by unusually high Al₂O₃ and low SiO₂ contents, which could represent a restitic nature remaining after partial melting of pelitic granulite under the ultra high-temperature contact metamorphism at the peak metamorphic event of the Higo metamorphic unit. The metamorphic conditions are estimated to be about 800  MPa and above 950  °C which took place at about 250  Ma as a result of the thermal effect of the regional gabbroic rock intrusions.     

The electrification of flowing gases by mechanical abrasion of mineral surfaces

In the past, a number of workers have shown that both charged and neutral particles are released from inorganic materials during fracture and abrasion. In this work we show that charge can be transported by electrification of flowing gases over a surface undergoing abrasion. These results are relevant to possible mechanisms of a number of observed electrical phenomena associated with fault motion and earthquake activity. Received: 14 July 1997 / Revised, accepted: 2 January 1998     

A classification system for the assessment of slope stability of terrains along highway routes in Jordan

 The establishment of comprehensive development plans, in general, and the proper selection of highway routes, in particular, require an assessment of landslides or instability hazards in the project sites. The frequent landslides that occurred along the routes of major highways in Jordan, and particularly along the Amman-Na'ur-Dead Sea highway and Irbid-Jerash-Amman highway, have substantially increased the cost of construction and caused a considerable delay in the completion of work. The study of many landslides that occurred in the last 25 years along the highway routes and in the sites of some major civil engineering projects in Jordan has led to the recognition of major factors that affect the stability of slopes, and thus the safety and economics of these projects. The geological formation, structural features, topographic characteristics, geometry, and climatic conditions were adopted as the basis for the classification of terrains in terms of their stability. Each factor has been assigned a rating to indicate its relative contribution to the overall stability according to engineering judgment and past experience. The areas have been classified into 5 groups according to their total stability rate. The simplicity, comprehensiveness, and accuracy are the main characteristics of the proposed classification. Its significance stems from its helpfulness as a guide to the geotechnical and highway engineers in assessing the overall stability of the alternative routes of proposed highway projects. Received: 3 December 1996 · Accepted: 29 April 1997     

Clustering stochastic point process model for flood risk analysis

Since the introduction into flood risk analysis, the partial duration series method has gained increasing acceptance as an appealing alternative to the annual maximum series method. However, when the base flow is low, there is clustering in the flood peak or flow volume point process. In this case, the general stochastic point process model is not suitable to risk analysis. Therefore, two types of models for flood risk analysis are derived on the basis of clustering stochastic point process theory in this paper. The most remarkable characteristic of these models is that the flood risk is considered directly within the time domain. The acceptability of different models are also discussed with the combination of the flood peak counted process in twenty years at Yichang station on the Yangtze river. The result shows that the two kinds of models are suitable ones for flood risk analysis, which are more flexible compared with the traditional flood risk models derived on the basis of annual maximum series method or the general stochastic point process theory. Received: September 29, 1997     

Incoherent scatter radar observations of AGW/TID events generated by the moving solar terminator

Observations of traveling ionospheric disturbances (TIDs) associated with atmospheric gravity waves (AGWs) generated by the moving solar terminator have been made with the Millstone Hill incoherent scatter radar. Three experiments near 1995 fall equinox measured the AGW/TID velocity and direction of motion. Spectral and cross-correlation analysis of the ionospheric density observations indicates that ST-generated AGWs/TIDs were observed during each experiment, with the more-pronounced effect occurring at sunrise. The strongest oscillations in the ionospheric parameters have periods of 1.5 to 2 hours. The group and phase velocities have been determined and show that the disturbances propagate in the horizontal plane perpendicular to the terminator with the group velocity of 300–400 m s^–1 that corresponds to the ST speed at ionospheric heights. The high horizontal group velocity seems to contradict the accepted theory of AGW/TID propagation and indicates a need for additional investigation.     

Spectral classification methods in monitoring small local events by the Israel seismic network

We use the dense Israel Seismic Network (ISN) to discriminate between low magnitude earthquakes and explosions in the Middle East region. This issue is important for CTBT monitoring, especially when considering small nuclear tests which may be conducted under evasive conditions. We explore the performance of efficient discriminants based on spectral features of seismograms using waveforms of 50 earthquakes and 114 quarry and underwater blasts with magnitudes 1.0–2.8, recorded by ISN short-period stations at distances up to 200 km. The single-station spectral ratio of the low and high-frequency seismic energy shows an overlap between explosions and earthquakes. After averaging over a subnet of stations, the resolving power is enhanced and the two classes of events are separated. Different frequency bands were tested; the (1–3 Hz)/(6–8 Hz) ratio provided the best discriminant performance. We also estimated normalized r.m.s. spectral amplitudes in several sequential equal frequency windows within the 1–12 Hz band and applied multiparametric automatic classification procedures (Linear Discrimination Function and Artificial Neural Network) to the amplitudes averaged over a subnetwork. A leave-one-out test showed a low rate of error for the multiparametric procedures. An innovative multi-station discriminant is proposed, based on spectral modulation associated with ripple-firing in quarry blasts and with the bubbling effect in underwater explosions. It utilizes a distinct azimuth-invariant coherency of spectral shapes for different stations in the frequency range (1–12 Hz). The coherency is measured by semblance statistics commonly used in seismic prospecting for phase correlation in the time domain. After modification, the statistics applied to the network spectra provided event separation. A new feature of all the above mentioned procedures is that they are based on smoothed (0.5 Hz window), instrument-corrected FFT spectra of the whole signal; they are robust to the accuracy of onset time estimation and, thus well suited to automatic event identification.     

Genesis of the Hussainiyat ironstone deposit, Western Desert, Iraq

The Hussainiyat ironstone deposit (Jurassic) is mainly pisolitic, intraclastic and concretionary in texture, associated with kaolinite mudstones and/or with quartzose sandstone. The ironstone consists mainly of goethite, hematite, kaolinite and quartz. The deposits were derived from a variety of parent rocks that included low- and medium-rank metamorphics, intermediate igneous rocks and pre-existing sediments of the Nubio-Arabian Shield. The source rocks suffered deep chemical weathering in the hinterland, and the products (Fe-oxyhydroxides, kaolinite and quartz) were later transported by rivers to the depositional site. Iron was mostly carried in association with the clay fraction and organic matter. Several genetic processes were involved in the ironstone formation. Iron concretions were mostly formed by bacterial build-up in swamps and marshes, and were subsequently embedded in kaolinitic mud. Large-scale development of groundwater laterite blanket (ferricrete) occurred later in the overbanks and floors of wadis, under oxidizing pedogenic conditions. During this stage iron was mobilized from the kaolinitic deposits and migrated upward in dry seasons and, to a lesser extent, downward in wet seasons. Pisolites and oolites grew in situ in the kaolinitic soil at the upper limit of the fluctuating water table. This ferricrete blanket had a wide and continuous extension within an elongated paleodepression. Seasonal heavy rain periods resulted in the flow of ephemeral streams and rivers, where major parts of this ferricrete was reworked and deposited with quartz sand and mud clasts as channel deposits. The original pisolitic-colloform ironstone was reworked continuously to form a semi-continuous sheet. In such wet seasons, additional Fe-enrichment took place as cementing materials or overgrowths. Received: 28 April 1995 / Accepted: 10 July 1997     

“Extreme boiling” model for variable salinity of the Hokko low-sulfidation epithermal Au prospect, southwestern Hokkaido, Japan

The Hokko prospect is located in the Minamikayabe area southwestern Hokkaido, Japan, where gold-bearing quartz veins of Pliocene age are exposed at the surface. The alteration mineral assemblage is typical of low-sulfidation epithermal systems, with the quartz veins associated with adularia alteration overprinted on Late Miocene propylitic alteration. Fluid inclusion studies of the vein quartz reveal mean homogenization temperatures of approximately 220 °C, and the co-existence of low-salinity (<2 wt.% NaCl equivalent) and moderate salinity (2 to 12 wt.% NaCl equivalent) fluid inclusions within the same veins. The moderate salinity fluid inclusions (2–12 wt.% NaCl equivalent) typically have relatively low homogenization temperatures between 150° to 200 °C. The results obtained from stable isotope analysis of  δ¹⁸O in quartz vein material showed a gradual decrease in  δ¹⁸O signatures with increasing depth. The majority of the samples have calculated fluid source signatures (δ¹⁸O_H2O) between −8.0 and −10.0‰, but there is a significant change in the composition above 185 m drill depth. The shallower samples in particular show a wide range of oxygen isotope signatures that are associated with the moderate salinity fluid inclusions. We interpret that low-salinity inclusions within the Hokko system represent the composition of the liquid phase of the fluid, before boiling, and that the moderate-salinity inclusions are representative of the residual liquid phase, after extensive non-adiabatic boiling and vapor loss in an open system. This mechanism resulted in the entrapment of fluids with variable salinities at the same time, and in close proximity to each other. This is also reflected in the  δ¹⁸O_H2O values which become more variable and heavier where the moderate-salinity inclusions occur. Deposition of ore minerals within the Hokko vein system also occurred at this time as a result of boiling and gas loss. Received: 30 May 1997 / Accepted: 6 January 1998