Relation of lava compositions to volcano size and structure in El Salvador

Most of the lavas at the nine volcanic centers along the volcanic front of El Salvador are basalts, basaltic andesites and andesites. The compositional variation within and among these centers can be explained by fractionation processes within the crust. Cognate gabbroic inclusions found in the lavas have appropriate mineralogy (plagioclase, olivine, magnetite and augite) to be cumulates formed by fractional crystallization. Two main variation trends occur, depending on the proportion of plagioclase removal. The more common, or normal, trend has a high (> 55%) proportion of plagioclase being removed. A less common, Al-rich, trend has a low (40%) proportion of plagioclase being removed. The Al-rich trend is found only at volcanoes that lack large negative Bouguer gravity anomalies. These volcanoes are unlikely to have large shallow magma chambers and fractionation probably occurs deeper in the crust where plagioclase removal is inhibited.The incompatible element (Na₂O, K₂O, Rb, Ba) contents of lavas vary systematically with the volume of the volcanic centers. At the same level of SiO₂, large volcanic centers have higher incompatible element contents than small volcanic centers. This suggests that open system fractionation in a periodically refilled chamber is the controlling factor. The large difference in Ba contents of lavas between eastern (low) and western (high) El Salvador suggests a difference in the mantle source region.     

Generation and dispersal of fine ash and dust by volcanic eruptions

The volcanic eruptions which generate the greatest quantities of fine ash and dust are those of ignimbrite-forming, plinian, vulcanian and phreatomagmatic types; these are also the eruptions which produce the widest dispersal of this material, attributed to the superior height attained by their eruptive columns. However, much of the fine ash and dust may be rapidly flushed out of the eruptive plume by water, particularly in phreatomagmatic eruptions. Recent studies made on the dispersal and grain-size of pyroclastic deposits produced by examples of plinian and phreatomagmatic types, have yielded estimates of the quantities of material generated in each grain-size class, besides the extent of their dispersal. Not all of the fine volcanic particles are produced by fragmentation at the eruptive vent; in ignimbrite eruptions, there is good evidence for their large-scale generation in and loss from the moving ash flows.     

Cenozoic latitudinal shift of the Hawaiian hotspot and its implications for true polar wander

Pacific plate equatorial sediment facies provide estimates of the northward motion of the Pacific plate that are independent of paleomagnetic data and hotspot tracks. Analyses of equatorial sediment facies consistently indicate less northward motion than analyses of the dated volcanic edifices of the Hawaiian-Emperor chain. The discrepancy is largest 60–70 Ma B.P.; the 60- to 70-Ma equatorial sediment facies data agree with recent paleomagnetic results from deep-sea drilling on Suiko seamount [1] and from a northern Pacific piston core [2]. Equatorial sediment facies data and paleomagnetic data, combined with K-Ar age dates along the Emperor chain [3], indicate a position of the spin axis at 65 Ma B.P. of 82°N, 205°E in the reference frame in which the Pacific Ocean hotspots are fixed. This pole agrees well with the position of the spin axis in the reference frame in which the Atlantic Ocean hotspots and the Indian Ocean hotspots are fixed [4,5], supporting the joint hypotheses that (1) the Pacific Ocean hotspots are fixed with respect to the hotspots in other oceans, (2) the hotspots have shifted coherently with respect to the spin axis, and (3) the time average of the earth's magnetic field 65 Ma B.P. was an axial geocentric dipole. Global Neogene paleomagnetic data suggest that a shift of the mantle relative to the spin axis has been occurring during the Neogene in the same direction as the shift between 65 Ma B.P. and the present. All data are consistent with a model in which the hotspots (and by inference the mantle) have shifted with respect to the spin axis about a fixed Euler pole at a constant rate of rotation for the last 65 Ma.     

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.     

Effects of petroleum on estuarine bacteria

The effects of petroleum on the natural microbial flora of a given environment, that is, on the bacteria, yeasts, filamentous fungi, and achlorophyllous algae, have largely been ignored. This paper represents the first recorded investigation of the impact of petroleum on ecologically important groups of bacteria.     

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.     

Radiocarbon dating the Devensian Lateglacial in Britain: New evidence from Llanilid,South Wales

Radiocarbon dates are described from a section through Lateglacial and early Flandrian sediments at Llanilid, Mid-Glamorgan, South Wales. Comparisons between age determinations on the alkali soluble (humic) and alkali insoluble (humin) organic fractions from 12 biostratigraphic horizons reveal the extent of contamination by both older and younger carbon residues. The Llanilid time-scale suggests that for the Lateglacial, the earliest organic sediments date from around 13 200 yr BP, the early Interstadial Juniperus maximum occurred at ca. 12 400-12 500 yr BP with a marked decline some 200 years later, the main Betula phase lasted only from ca. 11 700 to 11 400 yr BP and the end of the Interstadial occurred around 11 100 yr BP. The beginning of the Flandrian dates from ca. 10 000 yr BP, the Juniperus maximum occurred approximately 200 years later, the expansion of birch woodland began around 9600 yr BP, while the first hazel arrived in the area at ca. 9300 yr BP. These age determinations are discussed in the context of radiocarbon dates from comparable biostratigraphic horizons in western Britain and the dating of Lateglacial events in the ocean core records from the North Atlantic.