Observations of the inner F and K coronas below λ2220

The inner coronal continuum has been observed and measured below 2220 on the slitless spectra obtained by Speer et al. (1970) at the 7 March 1970 eclipse. These observations set some constraints on the brightness of the inner F corona and hence on the scattering efficiency of the inner interplanetary dust cloud particles in the far ultraviolet. They neither confirm nor reject the possibility that the inner dust cloud has the same sharp upturn in scattering efficiency below 2000 observed in the zodiacal light and in the interstellar medium.On leave from Imperial College, London.This work was supported in part by NASA grant NGL 12-001-011. An I.A.U. travelgrant to one of us (R.J.S.) is gratefully acknowledged.     

The detection of HCN on Jupiter

We report the detection of HCN on Jupiter. Three R-branch lines of the ν₂ fundamental of HCN near 13.5 μm were observed in absorption, from which the HCN column density is inferred to be 5 × 10^?3 cm-am with an uncertainty of a factor of 2. If emission from the stratosphere exists, then the derived column density is only a lowe limit. We suggest that the Jovian HCN most likely originates from the photolysis of CH₄ and NH₃ in the lower stratosphere and upper troposphere. In addition, an upper limit of 2.5 × 10^?2 cm-am was established for the column density of HCN on Saturn.     

Modification Of The Standard ∈-Equation For The Stable Abl Through Enforced Consistency With Monin–Obukhov Similarity Theory

A condition is derived for consistency of the standard-equation with Monin–Obukhov (MO) similarity theory of thestably-stratified surface layer. The condition is derivedby extending the procedure used to derive the analogous condition forneutral theory to stable stratification. It is shown that consistencywith MO theory requires a function of flux Richardson number, Ri_f, to be absorbed into either of two closure parameters, c ₁ or c ₂.Inconsistency, on the other hand, results if constant values of these are maintained for all Ri_f, as is done in standardapplication of the equation, and the large overpredictions ofturbulence found in such application to the one-dimensionalstable atmospheric boundary layer (1D-SBL) are traced to thisinconsistency. Guided by this, we formulate a MO-consistent-equation by absorbing the aforementioned function intoc ₁, and combine this with a Level-2.5 second-orderclosure model for vertical eddy viscosity and diffusivities.Numerical predictions of the 1D-SBL by the modified model converge to a quasi-steady state, rectifying the predictive failure of the standard -equation for the case.Quasi-steady predictions of non-dimensional variables agree stronglywith Nieuwstadt's theory. Qualitative accuracy of predictionsis inferred from comparisons to field data, large-eddy simulationresults and Rossby-number similarity relationships.     

A methodology to estimate renewal time scales in estuaries: the Tagus Estuary case

High-resolution hydrodynamic models are a common tool to simulate water dynamics in estuaries. Results from these models are, however, difficult to interpret without the aid of additional parameters to integrate the information. In this paper a methodology to understand the transport patterns in the Tagus Estuary is proposed. It is based on the computation of two renewal time scales: residence time and integrated water fraction. This last parameter is used to build a dependency matrix that gives the integrated influence of each region of the estuary at a selected point. The parameters are computed using a Lagrangian transport model coupled to the hydrodynamic model. Results show that Tagus Estuary has two different types of regions: the central part of the estuary, with low renewal efficiency, and three regions with higher renewal efficiency. Renewal mechanisms are, however, different for each region as shown by the dependency matrix. Comparison of renewal time scales with results from a water-quality model revealed that residence time is not a limiting parameter for primary production in the Tagus Estuary.Responsible Editor: Hans Burchard     

Mineral-scale Sr-isotope constraints on magma evolution and chamber dynamics in the Rum layered intrusion,Scotland

Sr isotopic zoning within single plagioclase crystals from rocks from Unit 9 of the Rum layered intrusion is used to infer events during crystal growth in a magma undergoing contamination. The ⁸⁷Sr/⁸⁶Sr diversity among minerals and between cores and rims of plagioclase crystals increases as the boundary between unit 9 and the overlying Unit 10 peridotite is approached. Models of near-solidus interaction of the cumulate with a fluid or melt, or large scale textural re-equilibration, cannot easily account for the systematic differences in ⁸⁷Sr/⁸⁶Sr between small crystals and the rims of larger crystals.We propose a simple interpretation in which crystal growth is concentrated along the cool margins of the reservoir. Crystals are subsequently advected to a site of accumulation at the base of the reservoir, probably by episodic plume-like dense downwellings allowing mixing of isotopically zoned and unzoned crystals.If the core-rim isotope variations are inherited from primary magmatic growth, then the small distances over which they are now preserved (1–2 mm) place constraints on the minimum cooling rate of the intrusion. Although the length scale of diffusive equilibration is influenced by a number of poorly-constrained variables (starting temperature, feldspar composition, temperature-time path) cooling was clearly very rapid with cooling to effective closure (~1,000 °C) within a few thousand years.Editorial responsibility: I. Parsons     

Adakite-like signature of Late Miocene intrusions at the Los Pelambres giant porphyry copper deposit in the Andes of central Chile: metallogenic implications

Adakite-like features are recognized in the Late Miocene (~10 Ma) porphyritic intrusions of the Los Pelambres giant porphyry copper deposit, central Chile (32°S). Located within the southern portion of the flat-slab segment (28–33°S) of the Chilean Andes, the Al- and Na-rich porphyries of Los Pelambres display distinctly higher Sr/Y (~100–300) and La_N/Yb_N (~25–60) ratios than contemporaneous and barren magmatic units (e.g., La Gloria pluton, Cerro Aconcagua volcanic rocks) of the same Andean magmatic belt. Strong fractionation of heavy rare earth elements (HREE), absence of Eu anomalies, high Sr/Y and Zr/Sm and low Nb/Ta ratios suggest melt extraction from a garnet-amphibolite source. The Late-Miocene adakite-like porphyritic intrusions at Los Pelambres formed closely related in time and space to the subduction of the Juan Fernández Ridge (JFR) hotspot chain along the Chilean margin. Current tectonic reconstructions reveal that, at the time of formation of the Los Pelambres rocks, a W-E segment of the JFR started to subduct beneath them, producing a slow-down of a previously rapid southward migration of a NE-ridge—trench collision. These particular tectonic conditions are favorable for the origin of the Los Pelambres porphyry suite by melting of subducting young hotspot rocks under flat-slab conditions. The incorporation of crustal components into the oceanic lithopheric magma source by subduction erosion is evidenced by the Sr-Nd isotope composition of the Los Pelambres rocks different from the MORB signatures of true adakites. A close relationship apparently exists between the origin of this adakite-like magmatism and the source of the mineralization in the Los Pelambres porphyry copper deposit.Editorial handling: R.J. Goldfarb     

Regional-scale hydrothermal alteration in the Central Blake River Group,western Abitibi subprovince,Canada: implications for VMS prospectivity

The Late Archean Blake River Group is a thick succession of predominantly mafic volcanic rocks within the southern zone of the Abitibi greenstone belt. It contains a number of silicic volcanic centers of different size, including the large Noranda volcanic complex, which is host to 17 past-producing volcanogenic massive sulfide deposits. The Noranda complex consists of a 7- to 9-km-thick succession of bimodal mafic and felsic volcanic rocks erupted during five major cycles of volcanism. Massive sulfide formation coincided with a period of intense magmatic activity (cycle III) and the formation of the Noranda cauldron. Hydrothermal alteration in these rocks is interpreted to reflect large-scale hydrothermal fluid flow associated with rapid crustal extension and rifting of the volcanic complex. The alteration includes abundant albite, chlorite, epidote and quartz (silicification), which exhibit broad stratigraphic and structural control and correlate with previously mapped whole-rock oxygen isotope zonation. The Mine Sequence volcanic rocks are characterized by abundant iron-rich chlorite (Fe/Fe+Mg >0.5), hydrothermal amphibole (ferroactinolite) and coarse-grained epidote of clinozoisite composition (<10 wt% Fe ₂O ₃). Volcanic rocks of the pre-cauldron sequences, which contain only subeconomic stringer mineralization, are characterized by less abundant chlorite and mainly fine-grained epidote (>10 wt% Fe ₂O ₃) lacking the clinozoisite solid solution. Alteration in the Mine Sequence volcanic rocks persists along strike well beyond the limits of the main ore deposits (as far as several tens of kilometers) and can be readily distinguished from greenschist facies metamorphic assemblages at a regional scale. The lack of similar alteration in the pre-cauldron sequences is consistent with limited ¹⁸O-depletion and suggests that the early history of the volcanic complex did not support large-scale, high-temperature fluid flow in these rocks. Comparisons with a much smaller, barren volcanic complex in nearby Ben Nevis township reveal important differences in the alteration mineralogy between volcanoes of different size, with implications for area selection during regional-scale mineral exploration. The Ben Nevis Complex consists of a 3- to 4-km-thick succession of mafic, intermediate and felsic volcanic rocks centered on a small subvolcanic intrusion. Alteration of the volcanic rocks comprises mainly low-temperature assemblages of prehnite, pumpellyite, magnesium-rich chlorite (Fe/Fe+Mg <0.5), iron-rich epidote (>10 wt% Fe ₂O ₃) and calcite. Actinolite ± magnetite alteration occurs proximal to the intrusive core of the complex, but the limited extent of this alteration indicates only local high-temperature fluid circulation adjacent to the intrusion. A distal zone of carbonate alteration is located 4–6 km from the center of the volcano. Although iron-bearing carbonates are present locally within this zone, the absence of siderite argues against a high-temperature origin for this alteration. These observations do not offer positive encouragement for the existence of a fossil geothermal system of sufficient size or intensity to have produced a large massive sulfide deposit.     

Application of matrix analysis in delineating sinkhole risk areas along highway (I-70 near Frederick,Maryland)

Sinkhole collapse in the area of Maryland Interstate 70 (I-70) and nearby roadways south of Frederick, Maryland, has been posing a threat to the safety of the highway operation as well as other structures. The occurrence of sinkholes is associated with intensive land development. However, the geological conditions that have been developing over the past 200 million years in the Frederick Valley control the locations of the sinkholes. Within an area of approximately 8 km², 138 sinkholes are recorded and their spatial distribution is irregular, but clustered. The clustering indicates the existence of an interaction between the sinkholes. The point pattern of sinkholes is considered to be a sample of a Gibbsian point process from which the hard-core Strauss Model is developed. The radius of influence is calculated for the recorded sinkholes which are most likely to occur within 30 m of an existing sinkhole. The stochastic analysis of the existing sinkholes is biased toward the areas with intensive land use. This bias is adjusted by considering (1) topography, (2) proximity to topographic depressions, (3) interpreted rock formation, (4) soil type, (5) geophysical anomalies, (6) proximity to geologic structures, and (7) thickness of overburden. Based on the properties of each factor, a scoring system is developed and the average relative risk score for individual 30-m segments of the study area is calculated. The areas designated by higher risk levels would have greater risk of a sinkhole collapse than the areas designated by lower risk levels. This risk assessment approach can be updated as more information becomes available.     

Tectonic and sedimentary basin evolution of the eastern Bangong–Nujiang zone (Tibet): a Reading cycle

The ophiolite-bearing Bangong-Nujiang zone (BNZ) traversing central Tibet from east to west separates the Qiangtang block in the north from the Lhasa block in the south. Their stratigraphic development indicates that both blocks once formed a continuous continental platform until the Late Triassic. Following Late Paleozoic-Triassic rifting, ocean crust formed between both blocks during the Late Triassic creating the Dongqiao-Naqu basin (DNB) among other basins (Yu et al. 1991). The analysis of the rift flank sequences reveals that rifting was dominated by transtension. The basin was shortened by post-Mid-Cretaceous transpression. Thus, the overall basin evolution represents a Reading cycle despite some active margin processes which gave this cycle a special imprint. Major basin parts were preserved despite transpressional shortening suggesting that the eastern BNZ represents a remnant basin. Our understanding of the DNB solves the prior problem of viewing the BNZ as a Mid-Late Jurassic collisional suture although typical collision-related deformation, thickening, mountain building, as well as related molasse formation are lacking. Our model also explains the scattered linear ophiolite distribution by local transpression of remnant oceanic basin floor without having to consider problematic long range ophiolite thrusting.     

A review of mortality maps included in the annual reports on vital statistics for Ireland, 1864-1998

Since 1864, some 135 reports have been produced examining marriages, birth and deaths for Ireland. The reports produced during the period prior to World War I are notable for the maps and charts that are included and the level of detail provided. Recent reports have failed to include mortality maps, while those produced since 1950 generally show a declining level of detail.