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61.
Storage and interaction of compositionally heterogeneous magmas from the 1986 eruption of Augustine Volcano, Alaska 总被引:2,自引:0,他引:2
Diana C. Roman Katharine V. Cashman Cynthia A. Gardner Paul J. Wallace John J. Donovan 《Bulletin of Volcanology》2006,68(3):240-254
Compositional heterogeneity (56–64 wt% SiO2 whole-rock) in samples of tephra and lava from the 1986 eruption of Augustine Volcano, Alaska, raises questions about the
physical nature of magma storage and interaction beneath this young and frequently active volcano. To determine conditions
of magma storage and evolutionary histories of compositionally distinct magmas, we investigate physical and chemical characteristics
of andesitic and dacitic magmas feeding the 1986 eruption. We calculate equilibrium temperatures and oxygen fugacities from
Fe-Ti oxide compositions and find a continuous range in temperature from 877 to 947°C and high oxygen fugacities (ΔNNO=1–2)
for all magmas. Melt inclusions in pyroxene phenocrysts analyzed by Fourier-transform infrared spectroscopy and electron probe
microanalysis are dacitic to rhyolitic and have water contents ranging from <1 to ∼7 wt%. Matrix glass compositions are rhyolitic
and remarkably similar (∼75.9–76.6 wt% SiO2) in all samples. All samples have ∼25% phenocrysts, but lower-silica samples have much higher microlite contents than higher-silica
samples. Continuous ranges in temperature and whole-rock composition, as well as linear trends in Harker diagrams and disequilibrium
mineral textures, indicate that the 1986 magmas are the product of mixing between dacitic magma and a hotter, more mafic magma.
The dacitic endmember is probably residual magma from the previous (1976) eruption of Augustine, and we interpret the mafic
endmember to have been intruded from depth. Mixing appears to have continued as magmas ascended towards the vent. We suggest
that the physical structure of the magma storage system beneath Augustine contributed to the sustained compositional heterogeneity
of this eruption, which is best explained by magma storage and interaction in a vertically extensive system of interconnected
dikes rather than a single coherent magma chamber and/or conduit. The typically short repose period (∼10 years) between Augustine's
recent eruptive pulses may also inhibit homogenization, as short repose periods and chemically heterogeneous magmas are observed
at several volcanoes in the Cook Inlet region of Alaska. 相似文献
62.
Kenneth W. Able Kenneth L. Heck Michael P. Fahay Charles T. Roman 《Estuaries and Coasts》1988,11(2):83-86
The habitats utilized by small juvenile (<40 mm carapace length, CL) lobsters (Homarus americanus) are poorly known. We discovered and studied an undescribed juvenile lobster habitat in Nauset Marsh, Cape Cod. Juvenile lobsters (X=26.7 mm carapace length, 6 to 72 mm, n=38) were collected from suction samples primarily 0144 01 in “peat reef” habitats during the period from August 1985 through October 1986. The reefs consisted of large blocks ofSpartina alterniflora peat that had separated from the marsh surface and fallen into adjacent subtidal marsh channels. The smallest lobsters (6 to 7 mm CL) were collected from peat reefs in October 1985, and April and July 1986. In these habitats, juvenile lobster density averaged 2.5 individuals m?2 (range 0–5.7) in suction samples. Peat reef habitats occur in other salt marshes in the northeastern United States and may be an important nursery habitat for small juvenile lobsters. 相似文献
63.
Roman Magda 《Geotechnical and Geological Engineering》1985,3(4):271-293
Summary The basic foundations of an integrational method of modelling and estimating the economic effectiveness of a deep coal mine production process is presented. The method is founded on the concept of integration of smaller structural elements into larger ones in order to obtain a representational model of the whole mine production process. It involves analysis of the spatial, engineering and time structures of the mining process. The basic structural unit of the production process is the elementary time interval,T, together with a linear function of the approximate intensity of financial outlays or effects. The repeated integration of these elementary time intervals within the spatial, engineering and time structures of the mine production process can be extended to model the whole mine or discrete spatial structure elements.The model may be used to investigate the trends of financial outlays and effects, and their current values updated for arbitrarily assumed updating moments. The model can also be used as an investigation tool for analysing the economical effectiveness of the mine production process. 相似文献
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Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the
100 – 4000 MHz range (type I – V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them
occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely
absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to
have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100 MHz were accompanied
by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5
generally emit coherent radio waves when observed radially above the source. 相似文献
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Roman Tomaschitz 《Astrophysics and Space Science》2000,271(2):181-203
A pre-relativistic cosmological approach to electromagnetism and gravitation is explored that leads to a cosmic time variation
of the fundamental constants. Space itself is supposed to have physical substance, which manifests by its permeability. The
scale factors of the permeability tensor induce a time variation of the fundamental constants. Atomic radii, periods, and
energy levels scale in cosmic time, which results in dispersionless redshifts without invoking a space expansion. Hubble constant
and deceleration parameter are reviewed in this context. The time variation of the gravitational constant at the present epoch
can be expressed in terms of these quantities. This provides a completely new way to restrain the deceleration parameter from
laboratory bounds on the time variation of the gravitational constant. This variation also affects the redshift dependence
of angular diameters and the surface brightness, and we study in some detail the redshift scaling of the linear sizes of radio
sources. The effect of the varying constants on source counts is discussed, and an estimate on the curvature radius of the
hyperbolic3-space is inferred from the peak in the quasar distribution. The background radiation in this dispersionless, permeable
space-time stays perfectly Planckian. Cosmic time is discussed in terms of atomic and gravitational clocks, as well as cosmological
age dating, in particular how the age of the Universe relates to the age of the Galaxy in a permeable space-time.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
70.
Multiple re‐advances of a Lake Vättern outlet glacier during Fennoscandian Ice Sheet retreat,south‐central Sweden 下载免费PDF全文
Sarah L. Greenwood Matt O'Regan Henrik Swärd Tom Flodén Roman Ananyev Denis Chernykh Martin Jakobsson 《Boreas: An International Journal of Quaternary Research》2015,44(4):619-637
Lake Vättern represents a critical region geographically and dynamically in the deglaciation of the Fennoscandian Ice Sheet. The outlet glacier that occupied the basin and its behaviour during ice‐sheet retreat were key to the development and drainage of the Baltic Ice Lake, dammed just west of the basin, yet its geometry, extent, thickness, margin dynamics, timing and sensitivity to regional retreat forcing are rather poorly known. The submerged sediment archives of Lake Vättern represent a missing component of the regional Swedish deglaciation history. Newly collected geophysical data, including high‐resolution multibeam bathymetry of the lake floor and seismic reflection profiles of southern Lake Vättern, are used here together with a unique 74‐m sediment record recently acquired by drill coring, and with onshore LiDAR‐based geomorphological analysis, to investigate the deglacial environments and dynamics in the basin and its terrestrial environs. Five stratigraphical units comprise a thick subglacial package attributed to the last glacial period (and probably earlier), and an overlying >120‐m deglacial sequence. Three distinct retreat–re‐advance episodes occurred in southern Lake Vättern between the initial deglaciation and the Younger Dryas. In the most recent of these, ice overrode proglacial lake sediments and re‐advanced from north of Visingsö to the southern reaches of the lake, where ice up to 400 m thick encroached on land in a lobate fashion, moulding crag‐and‐tail lineations and depositing till above earlier glacifluvial sediments. This event precedes the Younger Dryas, which our data reveal was probably restricted to north‐central sectors of the basin. These dynamics, and their position within the regional retreat chronology, indicate a highly active ice margin during deglaciation, with retreat rates on average 175 m a?1. The pronounced topography of the Vättern basin and its deep proglacial‐dammed lake are likely to have encouraged the dynamic behaviour of this major Fennoscandian outlet glacier. 相似文献