Argon 40-argon 39 chronology of lithic clasts from the Kapoeta howardite

⁴⁰Ar-³⁹Ar age spectra have been measured on plagioclase separates from three basaltic clasts (A, B, C), a pyroxene separate from clast B, and a total sample of a fourth basaltic clast (ρ) from the Kapoeta achondritic meteorite. The Ar data show that three of the four clasts crystallized ≥4.5 AE ago. Xe measurements indicate all four formed within a 0.1 AE period (Huneke, et al., 1977, Lunar Science VIII, pp. 484–486). Three clasts have suffered various degrees of ⁴⁰Ar loss since that time. The times of ⁴⁰Ar degassing do not cluster about a single time analogous to the lunar cataclysm. The survival of ≥4.5 AE ages contrasts with the general absence of ages ≥4.0 AE on the moon.The Ar retention age of clast B of ≥4.57 AE is atypically older than the Rb-Sr age of 3.6 AE (Papanastassiouet al., 1974, Lunar Science V, p. 583). The 3.5 AE Ar age of clast A is distinctly younger than the Rb-Sr age of 3.9 AE (Papanastassiou et al., 1974). The K-Ar and Rb-Sr systems are clearly not equivalent dating techniques in these instances.The combined evidence of Ar, Xe and Rb-Sr studies suggests the period of volcanism on the Kapoeta parent planet was restricted to the first ~0.2 AE of solar system history. The subsequent thermal metamorphic histories recorded in each of the four clasts after formation are distinctly different. The clasts must have existed as independent fragments at least as recently as 3.5 AE ago. The cosmic ray exposure ages of all the four clasts are similar (~ 3 Myr), and are not significantly different from that of the bulk meteorite. The clasts spent essentially all of the time prior to the formation of Kapoeta at depths greater than a few meters.     

GALLIUM-BEARING SPHALERITE IN A METAL-SULFIDE NODULE OF THE QINGZHEN (EH3) CHONDRITE

The Qingzhen (EH3) chondrite contains a population of spheroidal metal-sulfide nodules, which display textural evidence of reheating and melting. Evidence of metal sulfuration is also present, suggesting replacement of metal by sulfide during melting. This process has led to the nucleation of perryite along metal-sulfide interfaces. Gallium-bearing sphalerite and a Cu-sulfide of composition intermediate between chalcopyrite and cubanite occur as inclusions within the metal of some nodules. Other phases present are: kamacite, troilite, Ga-free sphalerite, niningerite, perryite, schreibersite, oldhamite, Cr-sulfide (minerals A and B), djerfisherite, SiO₂, albite and enstatite. The Ga-bearing sphalerite may have formed by injection of molten sulfide droplets into the metal followed by subsolidus diffusion of Ga from the metal into the sulfide. The latter may occur because of Ga supersaturation in the metal during progressive sulfuration and its decreased affinity for the metal phase during cooling below the taenite-kamacite transition point.     

Development of probability distributions for urban hydrologic model parameters and a Monte Carlo analysis of model sensitivity

This paper proposes an approach to estimating the uncertainty related to EPA Storm Water Management Model model parameters, percentage routed (P_R) and saturated hydraulic conductivity (K_sat), which are used to calculate stormwater runoff volumes. The methodology proposed in this paper addresses uncertainty through the development of probability distributions for urban hydrologic parameters through extensive calibration to observed flow data in the Philadelphia collection system. The established probability distributions are then applied to the Philadelphia Southeast district model through a Monte Carlo approach to estimate the uncertainty in prediction of combined sewer overflow volumes as related to hydrologic model parameter estimation. Understanding urban hydrology is critical to defining urban water resource problems. A variety of land use types within Philadelphia coupled with a history of cut and fill have resulted in a patchwork of urban fill and native soils. The complexity of urban hydrology can make model parameter estimation and defining model uncertainty a difficult task. The development of probability distributions for hydrologic parameters applied through Monte Carlo simulations provided a significant improvement in estimating model uncertainty over traditional model sensitivity analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

On the role of a supernova in the formation of the solar system

We consider four possible scenarios relating the proto-solar cloud to the “last-minute” supernova presumed responsible for the isotopic anomalies in Allende and other meteorites. The probability that a chance supernova occurred close enough to an already-collapsing proto-solar cloud to inject sufficient matter is extremely small, even if the Sun formed in a region of enhanced supernova activity such as Orion OB1. The ambient level of ²⁶Al inside a molecular cloud in Orion is also apparently too low to account for the meteorite data, unless the supernova ejecta accumulates at the edges of the cloud and star formation occurs there preferentially. Two modes of supernova-induced star formation are discussed. In one, the supernova shock collapses a preexisting cloud; in the other, stars form within the snowplow shell of the supernova. Canis Major R1 and Monoceros R1 are possible present-day examples of such star formation regions.     

The variation of cosmogenic Kr and Xe in a core from Estherville mesosiderite: direct evidence that the lunar131Xe anomaly is a depth effect

Kr and Xe were measured by a stepwise heating technique in three samples of a drill core in the “Minnesota” fragment of the Estherville mesosiderite. The cosmogenic⁷⁸Kr/⁸³Kr decreased from the “top” sample to the “bottom” sample(“top” = 0.163 ± 0.005, “bottom” = 0.151 ± 0.005) while the cosmogenic¹³¹Xe/¹²⁶Xe ratio increased(“top” = 5.58 ± 0.35, “bottom” = 6.92 ± 0.17). Cosmic-ray track studies have shown that the “top” sample was indeed closer to the preatmospheric surface than the “bottom” sample by ～ 10 cm. This is the first direct evidence, in a sample of known geometry, that the cosmogenic¹³¹Xe/¹²⁶Xe ratio increases as a function of depth, and as such, confirms the hypothesis that the lunar¹³¹Xe anomaly is a bona fide depth effect due to resonance neutron capture in¹³⁰Ba.     

Results from the Geoacoustic Inversion Techniques Workshop using modal inverse methods

This paper presents the results of a perturbative inverse approach applied to the range-dependent acoustic data provided as part of the Geoacoustic Inversion Techniques Workshop. The method is based on the Hankel transform relationship between complex-pressure field data measured on a horizontal array and the depth-dependent Green's function for a horizontally stratified medium. The input data to the inversion algorithm are discrete values of horizontal wavenumbers estimated for locally range-independent subapertures of the acoustic data. Inversion results are presented with emphasis placed on inverting for compressional wave speed as a function of both range and depth in the bottom.     

ROEDDERITE IN THE QINGZHEN (EH3) CHONDRITE

The rare mineral roedderite, (Na_1.09 K_0.89 Ca_0.02)_2.00 (Mg_4.71 Fe_0.27)_4.98 (Si_11.80 Al_0.09)_11.89 O₃₀ has been found in accessory amounts in the highly unequilibrated enstatite chondrite, Qingzhen. It occurs in association with minor amounts of albite and SiO₂ as inclusions within the metal or sulfide phases of metal-sulfide assemblages. The roedderite crystals are connected through oxide and silicate veins to the surrounding matrix. The presence of glass coated vesicles on the surface of the assemblages strongly suggests that roedderite originated in the presence of a fluid phase, presumably during post-accretional planetary processes.     

The 1024 channel digital correlator receiver of the Gauribidanur radioheliograph

A low frequency (40–150 MHz) radioheliograph for observations of the solar corona is in operation for the last few years at the Gauribidanur radio observatory, about 100 km north of Bangalore. The array has 32 antenna groups and a 1-bit digital correlator system consisting of 1024 channels is used as the back-end receiver. This paper describes the latter and results of the associated system tests.     

Seismic imaging of Paleogene sediments of Kachchh Shelf (western Indian margin) and their correlation with sea-level fluctuations

The sedimentary history of Kachchh offshore (central western Indian margin), especially since the eruption of the Deccan Traps (∼65 Ma), has remained scantily studied despite an area with promising resource potential. Of late, new marine surveys combined with industrial drilling along the Kachchh shelf are beginning to elucidate the depositional history of this region. Here, we attempt to synthesize interpretation of new offshore seismic data, along with borehole information and long-term sea-level variations to provide a coherent sedimentological and lithostratigraphic framework over the past ∼65 Ma in this area.