Compositions of Formosan basalts and aspects of their petrogeneses

Twenty-three basalts from northwestern Formosa were analyzed for Si, Ti, Al, Fe, Mg, Ca, Na, K, Rb, Sr, Hf, Co, Sc, Cr, Th, and 7 REE. Formosan alkalic basalts are generally similar to most alkalic basalts, and Formosan tholeiites are somewhat similar to island arc and continental tholeiites in terms of trends in K/Rb, Rb/Sr, K/Sr, and Ca/Sr ratios. Compared to most submarine tholeiites, Formosan tholeiites are enriched in Rb relative to K and Sr, and enriched in Sr relative to K and Ca. Both types of Formosan basalts show, relative to chondritic proportions, enrichments in light REE which smoothly decrease through the heavy REE. Their REE patterns are similar to those observed in Dogo-Oki alkalic basalts, Hawaiian basalts, and Deccan Plateau basalt, but differ strikingly from those of Japanese tholeiites and oceanic ridge basalts. These relationships and contrasts suggest that Formosan basalts originated in a plagioclase-free portion of the upper mantle and at greater depths that did Japanese tholeiites and oceanic ridge basalts.     

Some constraints on the origin of phonolites from the Gregory Rift,Kenya, and inferences concerning basaltic magmas in the Rift System

Plateau-type phonolites of the Gregory Rift represent magmas with densities of about 2.3 g/cm³. These magmas must have erupted soon after their formation. The average depth of the bases of the approximately 100 to 300 magma chambers from which they erupted was between about 10 and about 24 km. The average vertical extent of the magma chambers was between about 3 and about 8 km. The aggregate volume of phonolitic magma formed beneath the Rift in Miocene times probably lies in the range of 0.5 to 1×10⁵ km³. Both the crystal fractionation model and the anatectic model for formation of this volume of phonolitic magma require the presence of a large reservoir of basaltic magma, probably picritic in character, with a volume of at least 5×10⁵ km³ and perhaps as much as 20×10⁵ km³. This reservoir presumably is now part of the dense basic intrusive complex along the Rift axis. The Miocene and Pliocene episodes of basaltic volcanism in this region may be related to eruption of evolved liquids from this reservoir.     

The spatial context of manpower policy: Implications of current Canadian policy on regional development and planning

Macro government policies are often considered outside the context of their spatial impact. Following recent discussions of the problem, this paper is concerned with a critical review of Canadian Manpower policy in the context of national efficiency, regional equity and their interaction. Thus Manpower policy is analysed with respect to its implications concerning regional development as well as implicit regional policy. It is contended that many of the problems of Manpower policy in the spatial context can be traced back to the implicit theoretical background of Manpower policy; Human Capital theory. A radical critique of Human Capital theory is presented and a brief discussion of the ‘functional’ relationship between regional inequality and national macro-planning is also noted. In general the paper concludes that Manpower and regional policies in Canada tend to be contradictory although more research is needed to analyse the spatial impact of macro-policy which may overwhelm spatial policy and significantly influence the future of the spatial economy.     

Generation of homologous porphyrins under simulated geochemical conditions

Crude oils generally contain at least one symmetrical homologous series of porphyrins, which is usually centered at m/e 476 (DPEP) or m/e 478 (etioporphyrin). Simulated geochemical conditions in the present study resulted in decarboxylations and alkylations which ultimately led to the synthesis of homologous porphyrins from a single porphyrin. In several series of closed tube experiments, mesoporphyrin IX dimethylester (MPDME) was mixed with a variety of constituents including benzene, acetic acid, propionic acid, water and clay; the experiments were performed at temperatures between 135°C and 400°C at time intervals up to 80 days. Dealkylation, alkylation, hydrolysis, decarboxylation and metallation products were observed. An unsymmetrical homologous series of porphyrins was produced from MPDME. The dominant mass was m/e 478 (corresponding to a double deoarboxylation). Dealkylation products in multiples of 14 amu below the m/e 478 peak comprised the other members of the series. Cu-MPDME also produced homologous porphyrins. These, however, exhibited symmetry about the dominant members, similar to the symmetry found for the porphyrins of most petroleums and oil shales.     

Glacier fluctuations in the southern Peruvian Andes during the late‐glacial period,constrained with cosmogenic 3He

The occurrence of pronounced climate reversals during the last glacial termination has long been recognised in palaeoclimate records from both hemispheres and from high to low latitudes. Accurate constraint of both the timing and magnitude of events, such as the Younger Dryas and Antarctic Cold Reversal, is vital in order to test different hypotheses for the causes and propagation of abrupt climate change. However, in contrast to higher‐latitude regions, well‐dated records from the Tropics are rare and the structure of late‐glacial tropical climate remains uncertain. As a step toward addressing this problem, we present an in situ cosmogenic ³He surface exposure chronology from Nevado Coropuna, southern Peru, documenting a significant fluctuation of the ice margin during the late‐glacial period. Ten tightly clustered ages from a pair of moraines located halfway between the modern glacier and the Last Glacial Maximum terminus range from 11.9 to 13.9 ka and give an arithmetic mean age of 12.8 ± 0.7 ka (1σ). These data constitute direct evidence for a readvance, or prolonged stillstand, of glaciers in the arid Andes of southwestern Peru. Copyright © 2011 John Wiley & Sons, Ltd.     

Application of nonlinear optimization technique to back analyses of deep excavation

This study presents a nonlinear optimization technique (NOT) for conducting the back analyses of geotechnical engineering problems based on the field observations. Additional auxiliary techniques are incorporated to enhance the convergence and stability of the NOT. The developed NOT and additional auxiliary techniques are incorporated into a finite element code and then applied to the back analysis of excavation-induced wall deflection. A number of hypothetical excavation cases with various scenarios of stratigraphy and two quality excavation case histories are used to validate the developed NOT, in which the dominant soil parameters are treated as target parameters. Results show that the wall deflections of all hypothetical and actual excavation cases at each stage can be accurately and efficiently back-figured. The developed NOT has a potential to be an useful tool for preventing the building damage through accurately and efficiently predicting the excavation-induced deformations at subsequent stages.     

The accumulation rate of meteorite falls at the Earth's surface: The view from Roosevelt County,New Mexico

Abstract— The discovery of 154 meteorite fragments within an 11 km² area of wind-excavated basins in Roosevelt County, New Mexico, permits a new calculation of the accumulation rate of meteorite falls at the Earth's surface. Thermoluminescence dating of the coversand unit comprising the prime recovery surface suggests the maximum terrestrial age of the meteorites to be about 16.0 ka. The 68 meteorite fragments subjected to petrological analyses represent a minimum of 49 individual falls. Collection bias has largely excluded carbonaceous chondrites and achondrites, requiring the accumulation rate derived from the recovered samples to be increased by a factor of 1.25. Terrestrial weathering destroying ordinary chondrites can be modelled as a first-order decay process with an estimated half-life of 3.5 ± 1.9 ka on the semiarid American High Plains. Having accounted for the age of the recovery surface, area of field searches, pairing of finds, collection bias and weathering half-life, we calculate an accumulation rate of 9.4 × 10² falls/a per 10⁶ km² for falls > 10 g total mass. This figure exceeds the best-constrained previous estimate by more than an order of magnitude. One possible reason for this disparity may be the extraordinary length of the fall record preserved in the surficial geology of Roosevelt County. The high accumulation rate determined for the past 16 ka may point to the existence of periods when the meteorite fall rate was significantly greater than at present.     

Hyperspectral mapping of alteration assemblages within a hydrothermal vug at the Haughton impact structure,Canada

Meteorite impacts on Earth and Mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization. We investigate a calcite–marcasite‐bearing vug at the ~23 km diameter Haughton impact structure, Devon Island, Nunavut, Canada, using imaging spectroscopy of the outcrop in the field (0.65–1.1 μm) and samples in the laboratory (0.4–2.5 μm), point spectroscopy (0.35–2.5 μm), major element chemistry, and X‐ray diffraction analyses. The mineral assemblages mapped at the outcrop include marcasite; marcasite with minor gypsum and jarosite; fibroferrite and copiapite with minor gypsum and melanterite; gypsum, Fe³⁺ oxides, and jarosite; and calcite, gypsum, clay, microcline, and quartz. Hyperspectral mapping of alteration phases shows spatial patterns that illuminate changes in alteration conditions and formation of specific mineral phases. Marcasite formed from the postimpact hydrothermal system under reducing conditions, while subsequent weathering oxidized the marcasite at low temperatures and water/rock ratios. The acidic fluids resulting from the oxidation collected on flat‐lying portions of the outcrop, precipitating fibroferrite + copiapite. That assemblage then likely dissolved, and the changing chemistry and pH resulting from interaction with the calcite‐rich host rock formed gypsum‐bearing red coatings. These results have implications for understanding water–rock interactions and habitabilities at this site and on Mars.     

Shock‐induced changes in density and porosity in shock‐metamorphosed crystalline rocks,Haughton impact structure,Canada

Abstract– Shock metamorphism can occur at transient pressures that reach tens of GPa and well over 1000 °C, altering the target material on both megascopic and microscopic scales. This study explores the effects of shock metamorphism on crystalline, quartzofeldspathic basement material from the Haughton impact structure on Devon Island, Arctic Canada. Shock levels were assigned to samples based on petrographic examination of main mineral phases. Conventional shock classification schemes proved to incompletely describe the Haughton samples so a modified shock classification system is presented. Fifty‐two crystalline bedrock samples from the clast‐rich impact melt rocks in the crater, and one reference site outside of the crater, were classified using this system. The shock levels range from 0 to 7 (according to the new shock stage classification proposed here, i.e., stages 0–IV after the Stöffler classification), indicating shock pressures ranging from 0 to approximately 80 GPa. The second aspect of this study involved measuring bulk physical characteristics of the shocked samples. The bulk density, grain density, and porosity were determined using a water displacement method, a bead displacement method, and a Hepycnometer. Results suggest a nonlinear, negative correlation between density and shock level such that densities of crystalline rocks with original densities of approximately 3 g cm^?3 are reduced to <1.0 g cm^?3 at high shock levels. The results also show a positive nonlinear correlation between porosity and shock level. These data illustrate the effect of shock on the bulk physical characteristics of crystalline rocks, and has implications for assessing the habitability of shocked rocks.