Numerical calculations of the longevity of impact oases on Titan

A promising setting for the formation of interesting prebiotic molecules on Titan is the transient liquid water environment formed by a comet impact, as originally suggested by Thompson and Sagan (1992, in: Symposium on Titan, ESA SP, vol. 338, p. 167). The impact melt (water or a water-ammonia mixture) generated in such an event can react with the abundant photochemical hydrocarbons and nitriles deposited on the surface of Titan to form more complex molecules such as purines and amino acids. We use a finite-difference thermal conduction code to calculate how long it takes for realistic liquid deposits in crater floors to freeze in the Titan environment. Our results suggest that 15 km diameter craters can sustain liquid water or water-ammonia environments for ∼¹⁰²-10³ yr and 150 km craters can sustain them for ∼¹⁰³-10⁴ yr. We discuss the implications of these timescales for organic chemistry on Titan.     

THE INMAN,McPHERSON COUNTY,KANSAS METEORITE

Inman (find, 1966) is a single, relatively unweathered stone of 7.25 kg that contains fresh metal and only few weathering products away from fractures. It has a pronounced chondritic texture, with 38 vol % of the meteorite being made up of chondrules of virtually all textural types. The recalculated bulk analysis, particularly the ratios of Fe_total/SiO₂ (0.46), Fe°/Fe_total (0.35), and Fe°/Ni° (6.67) and the contents of Fe_total (19.45%) and metallic nickel-iron (7.94%), indicate that Inman is an L-group chondrite. The pronounced chondritic texture; the compositional variabilities of olivine, pyroxene, chromite, and ilmenite; the presence of a fine-grained, nearly opaque matrix, glass and twinned monoclinic low-Ca pyroxene indicate that the chondrite belongs to petrologic type 3.     

THE DEL RIO ATAXITE,TEXAS

Del Rio is a new ataxite from Texas that is not related to either Monahans or Nordheim, the only previously known ataxites from Texas. Del Rio has a nickel content of approximately 12.9 weight percent, apparently has been shocked prior to its fall, and contains minor inclusions of daubreelite, schreibersite and troilite.     

Origin and history of chondrite regolith,fragmental and impact-melt breccias from Spain

Abstract— Six ordinary chondrite breccias from the Museo Nacional de Ciencias Naturales, Madrid (Spain), are described and classified as follows: the solar gas-rich regolith breccia Oviedo (H5); the pre-metamorphic fragmental breccias Cabezo de Mayo (type 6, L-LL), and Sevilla (LL4); the fragmental breccias Cañellas (H4) and Gerona (H5); and the impact melt breccia, Madrid (L6). We confirm that chondrites with typical light-dark structures and petrographic properties typical of regolith breccias may (Oviedo) or may not (Cañellas) be solar gas-rich. Cabezo de Mayo and Sevilla show convincing evidence that they were assembled prior to peak metamorphism and were equilibrated during subsequent reheating. These meteorites contain small melt rock clasts that were incorporated into the host chondrite while still molten and/or plastic and cooled rapidly and, yet, are totally equilibrated with their hosts. Compositions of olivine and low-Ca pyroxene in host chondrite and breccia clasts in Cabezo de Mayo are transitional between groups L and LL. It is suggested, based on mineralogic and oxygen isotopic compositions of host and clasts, that the rock formed on the L parent body by mixing, prior to peak metamorphism. This was followed by partial equilibration of two different materials: the indigenous L chondrite host and exotic LL melt rock clasts.     

The kinematics of gouge deformation

The methods and first results of a new approach to examining fault gouge are described. Samples of undisturbed fault gouge from the exhumed Lopez fault zone in the San Gabriel Mountains, California were impregnated with low viscosity epoxy resin and sectioned to produce microscope slides. The slides were photographed using optical and electron microscopy with magnifications ranging in factors of 2 from 12.5 to 1600. At all scales, the particles appeared angular with planar faces, suggesting tensile failure. No shear zones were discernable. The particle size distribution was studied. At each magnification the particles were sorted by diameter into four classes, differing in mean diameter by factors of 2. The numbers in each class were then scaled by the characteristic class dimension. The process revealed a remarkable degree of self-similarity. Over the range examined, the fractal dimension was within 5% of 2.60.On the basis of the observations, a new model for the mechanical processes that generate gouge is offered. It is argued that self-similarity results from repeated tensile splitting of grains. Unlike earlier models that consider splitting probability to be either independent of particle size or due to the preexisting distribution of defects, we propose that failure probability depends largely on the relative size of nearest neighbors. If nearest neighbors of the same size are preferentially broken, any initial distribution of particles will tend toward a self-similar distribution having a fractal dimension of 2.58.The model allows us to outline a procedure whereby the observed comminution in a fault zone can be related to the shear strain that the zone has accommodated and propose a theoretical frequency magnitude relation for the seismic energy emitted by the fracture process.     

The neotectonics of the Aegean: An alternative view

Flow directions are estimated from the measurement of the magnetic fabric of 106 samples, collected at 18 sites in four welded tuff units in the central San Juan Mountains of southern Colorado. The estimates assume that the tuffs generally flowed directly away from the extrusive vents and that the lineations of magnetic grains within the tuffs represent the flow direction at individual sites. Errors in the estimation may arise from topographic variation, rheomorphism (post-emplacement mass flow) within the tuff, and other factors. Magnetic lineation is defined as the site mean anisotropy of magnetic susceptibility maximum azimuth. A test on the flow directions for individual units is based on the projection of lineation azimuths and their intersection within or near the known source caldera for the tuff. This test is positive for the four units examined. Paleomagnetic results for these tuffs are probably reliable indicators of the geomagnetic field direction in southwest Colorado, during the time (28.2–26.5 Ma) of emplacement.     

The Campania-Lucania (southern Italy) earthquake of 23 November 1980

We present the main seismological results of our study of the Campania-Lucania earthquake of 23 November 1980. A complete set of far field and local data has been analysed. From long-period body waves data we determine the fault plane solution (φ₁ = 140°,δ₁ = 60°,φ₂ = 75°,δ₂ = 54°), a depth of 15 km and calculate a seismic moment of 6 × 10²⁵ dyne cm and a source duration of 6 s. From data of a local network deployed immediately after the event we determine aftershock locations: they are aligned in a direction NW-SE that fit extremely well with the focal solution determined above. We can choose as fault plane the plane striking 140° and dipping at 60° and the event is a normal event with a large component of left-lateral strike slip. The source area evaluated from this aftershock distribution 14 km × 40 km is quite suitable for an earthquake of a seismic moment of 6 × 10²⁵ dyne cm.     

Long-Term Ground Water Quality Impacts from the Use of Hexazinone for the Commercial Production of Lowbush Blueberries

Lowbush blueberries, native to eastern Canada and Maine, are an important economic crop in these areas. Herbicides containing the active ingredient hexazinone are commonly applied to blueberry fields, and there is a high frequency of detection of relatively low concentrations of hexazinone in domestic wells located close to areas of lowbush blueberry production. The objective of this study was to determine the long-term impacts from hexazinone-based herbicide use on ground water quality in the immediate growing areas.
Physical and chemical hydrogeologic data were collected for an outwash sand and gravel aquifer in southwestern New Brunswick, Canada. The majority of the land overlying the aquifer is devoted to lowbush blueberry production. Twenty-one nested monitoring wells were sampled for hexazinone and hexazinone metabolites over a four-year period. Hexazinone was consistently detected at values of 1 to 8 parts per billion (ppb) in all but two of these wells, one that is upgradient of herbicide applications, and one that is downgradient with anoxic conditions. Hexazinone metabolites B and A1 were also detected in all but two of the 21 wells at values ranging from 0.5 to 2.5 ppb. The hexazinone and metabolite data suggest both aerobic and anaerobic degradation of hexazinone. Complete degradation of hexazinone appears to occur only in the one downgradient well exhibiting anoxic ground water conditions. Concentrations of hexazinone and its metabolites in the ground water were essentially constant over the four-year period.