Activated release of alkalis during the vesiculation of molten basalts under high vacuum: implications for lunar volcanism

Knudsen cell-quadrupole mass spectrometry was used to study the high-temperature vaporization of Hawaiian basalts, plagioclase, tektites, and samples from the Allende meteorite. Procedures are described by which mass loss rates and vapor pressures of Na and K were measured quantitatively.Gas-rich glassy basalts were observed to vesiculate under vacuum over the 900–1000°C region and simultaneously evaporate alkalis in nonequilibrium fashion at rates (units of μg/g/hr) of approximately 200–300 Na and 75–250 K. Degassed residues of the same basalts demonstrated equilibrium evaporation rates (over the same temperature range) of 60–120 Na and 30–60 K. The gas-deficient plagioclase and tektite sample showed only equilibrium vaporization with rates of 60 Na, 10 K (plagioclase) and 10 Na, 5K (tektites) at 900–1000°C. The Allende meteorite vaporized at rates of 2400 Na and 200 K at 900–1000°C, possibly by the reaction of Na₂O and K₂O with C or S₂, or by the thermal decomposition of nepheline or sodalite.The nonequilibrium vaporization of alkalis from the gas-rich basalts is attributed to vigorous agitation of the melt during its vesiculation by a gas phase composed principally of SO₂, CO₂, H₂O, CO, and H₂S. The major gases released from the Allende meteorite at 900–1000°C are, in order of decreasing abundance, CO, S₂, CO₂, H₂O, SO₂, and H₂S.It is proposed that nonequilibrium vaporization of alkalis during the vesiculation of lunar lavas was responsible for the production of alkali-rich vapors which subsequently deposited plagioclase crystals in the vugs of lunar rocks. The vesiculative, nonequilibrium vaporization of Na and K during a lunar volcanic eruption should be expected to occur at a high rate upon initial extrusion of the lava into vacuum but then decrease by a factor of approximately three when degassing is nearing completion. Vaporization losses remain inadequate to explain the uniformly low alkali concentrations in lunar basalts.     

Greatlakean Substage: A replacement for Valderan Substage in the Lake Michigan basin

New evidence from recent field and seismic investigations in the Lake Michigan basin and in the type areas of the Valders, Two Creeks and Two Rivers deposits necessitates revision of late-glacial ice-front positions, rock- and time-stratigraphic nomenclature and climatic interpretations and deglaciation patterns for the period ca. 14,000–7,000 radiocarbon years B.P. The previously reported and long accepted pattern of deglaciation for the Lake Michigan basin started with a regular retreat from the Lake Border Morainic System, with a minor oscillation marked by the Port Huron moraine(s) and then an extensive Twocreekan deglaciation followed by a major (320 km) post-Twocreekan advance (Valders). However, we now record a major retreat between the times of the Lake Border and Port Huron moraines, followed by a gradual retreat from the Port Huron limit and interrupted by a minor standstill (deposition of Manitowoc Till), a retreat (Twocreekan) and a readvance (Two Rivers Till). No Woodfordian or younger readvance was as extensive as had been the preceding one. This sequence argues for a normal, climatically controlled, progressive deglaciation rather than one interrupted by a major post-Twocreekan (formerly Valderan) surge. This revision appears finally to harmonize the geologic evidence and the palynological record for the Great Lakes region. Our investigations show that Valders Till from which the Valderan Substage was named is late-Woodfordian in age. We propose the term “Greatlakean” as a replacement for the now misleading time-stratigraphic term “Valderan”. The type section and the definition of the upper and lower boundaries of the Greatlakean Substage remain the same as those originally proposed for the Valderan Substage but the name is changed.     

Baseline levels of benzo(a)pyrene in southern California mussels

Marine mussels accumulate the carcinogen benzo(a)pyrene from contaminated environments. Baseline studies in California indicate that levels of the carcinogen in mussels are at or near zero, except in areas of human activity. This finding runs counter to previous suggestions that benzo(a)pyrene is widely distributed in marine organisms.     

Geophysical transitions across the northwest Atlantic magnetic quiet-zone border

Deep and surface magnetic measurements, gravity and subbottom seismic profiling data have been gathered across a part of the northwest Atlantic smooth-rough magnetic border. These data indicate that the transition involves only a change in the magnetic field, without associated gravity or subbottom topographic signature. Model studies suggest that a change in basement magnetization from 0.010 emu/cm³ to 0.005 emu/cm³ could account for the magnetic field change across the boundary from the rough to the smooth sectors. Various theories previously proposed to explain this magnetic boundary are discussed with respect to these newer data; reduction of basement magnetization by weathering of the proto-Atlantic Ocean floor as described by Drake et al. (1968) is the preferred explanation.     

Mercury in tissues of mussel off southern California

Total mercury content has been determined in three tissues of the intertidal mussel Mytilus californianus collected at locations along the southern California coast and at island control stations. The apparent influence of certain harbours and municipal wastewater outfalls was reflected by the relatively higher levels of mercury in all tissues of mussels from these areas. In general, the concentrations reported here are lower than those in mussels on west European coasts.     

Distribution and source of tar on the Pacific Ocean

Petroleum residues, or tar lumps, are concentrated in the northwestern portion of the Pacific Ocean, particularly in the Kuroshio current system. The source of the tar appears to be tank washings from tankers on the very large Middle East to Japan route. Tar pollutants apparently are discharged by tankers south of Japan, become entrained in the Kuroshio current, and create a plume of contamination which extends downstream for 7000 km across the Pacific.     

On eddy convection velocity in the atmospheric boundary layer

Lumley's model is extended to predict the effect of convection velocity fluctuations on eddy convection velocity for the high-frequency region of the longitudinal, transverse and scalar phase spectra in the atmospheric boundary layer. The resulting model predicts that the eddy convection velocity will be higher than the mean wind speed. The increase over the mean wind speed is largest for the longitudinal spectrum.     

Nappe displacement in the Scandinavian Caledonides

Large areas of the Scandinavian Caledonides are eroded to the level of the basement/cover contact. Relationships between the Precambrian crystalline basement (largely Svecofennian-Dalslandian, 1800-1000 m.y.) and cover sequences are exposed both in transverse profiles through the mountain belt and along the belt in the various windows. These relationships provide an unique opportunity for studying the basement configuration, character of basement involvement and general nappe geometry. Major allochthonous units of the central part of the Scandinavian Caledonides — the Offerdal, Särv and Seve-Köli Nappe Complex — have been shown to wedge out westwards, having been displaced eastwards from environments along and west of the present Norwegian coast. Recent investigations have shown that these units (the Offerdal, Särv and Seve) reappear in western Norway as major pinch-and-swell structures, the lenses reaching thicknesses in the order of 2 km and with long axes of several tens of kilometres. Within the western parts of the Swedish Caledonides the thicker parts of the lenses approximately coincide with the axes of the late synforms which fold basement and cover together. Further west, in Norway, the tensing appears to be unrelated to the geometry of these major folds.This evidence increases estimates of nappe displacement distance (now thought to be in the order of at least 1000 km). At the same time it emphasizes that translation may account for only about half of this amount, the rest being achieved by stretching of the nappes. Apparently, a nappe sequence built up in the west which subsequently collapsed, leading to continued displacement eastwards on to the Baltoscandian Platform. Whereas basement shortening is of the order of several tens to perhaps hundreds of kilometres in the western part of the central Scandes, it is of lesser importance from central Trøndelag eastwards, a distance of about two hundred kilometres, to the Caledonian Front.Biostratigraphic evidence from the late-orogenic intramontane basins, taken in relation to the youngest units involved in the nappes, requires nappe translation into western Norway to have occurred after the Llandoverian (Köli Supergroup) and prior to the (Ludlovian?) Downtonian (Hitra Formation) deposition in the intramontane basins. The nappes contain sequences derived from a variety of probable oceanic and continental margin environments, and this translation may greatly exceed the minimum estimate of five hundred kilometres. Further displacement eastwards occurred during uplift of seaboard Norway and accompanied sedimentation both in the intra- and extramontane basins. The latter were not finally influenced by the décollement tectonics until after the Early Devonian.This evidence suggests that a compressive regime dominated the early phases of orogenesis during basement shortening, build up of the nappe pile and translation of these denser units on to the western margin of the Baltoscandian Platform. This compression subsequently gave way to a gravity regime, collapse and stretching of the nappes dominating the late phases of displacement on to the Baltoscandian Platform.     

Submergence avoidance behavior in the periwinkleLittorina irrorata is not due to threat of drowning

An attempt to establish an LD₅₀ for submergence onLittorina irrorata casts strong doubt on the hypothesis that submergence avoidance behavior is due to the threat of drowning. Predator avoidance is offered as a more plausable hypothesis. Respiration rates of 2.73×10^?3 ml O₂/g body wt./min. for submerged snails and 2.70×10^?2 ml O₂/g body wt./min. for controls were determined.     

A post-Transvaal age for the Marydale Formation,Kheis Group,Southern Africa

The metabasic Marydale Formation of the Kheis Group occupies a zone of contact between the Sanama and Kaapvaal structural provinces of South Africa. Stratigraphic relationships between the two provinces are not well understood. Whilst the well-known Kaapvaal basement and supracrustal succession yield radiometric ages older than 1900 m.y., Sanama Province ages reflect a Kibaran(1200 ± 200m.y.) tectogenetic cycle. The age of the Marydale, stratigraphically the oldest Sanama formation, has been variously estimated at2500m.y., about 2000 m.y., or Kibaran, based on controversial field interpretations or on available radiometric data.Rb-Sr data are presented for Marydale samples from a nappe-like body which, having been thrust over the Kaapvaal basement, was shielded from metamorphism. Two types of alteration are described and possible causes of isotopic homogenisation are discussed. It is concluded that an isochron age of 1899± 57m.y. (I = 0.7040 ± 0.0003) represents the age of extrusion of the Marydale volcanics.The stratigraphic controversy is thus resolved, Kheis Group formations being approximately coeval with the Matsap, the youngest formation of the Kaapvaal Precambrian succession. The implications of this and other recent work to theories of crustal evolution are considered. It is suggested that the continental crust of Sanama Province originated partly during the Eburnian(2000 ± 100m.y.) period of African orogeny and partly during the Kibaran tectogenetic cycle during which the province became cratonised and was added to the Southern African cratonic block.