Regional metamorphism of some Dalradian pelites in the Buchan area,N.E. Scotland     

Neil F. C. Hudson 《Contributions to Mineralogy and Petrology》1980,73(1):39-51

Regional metamorphic zones, based on mineral assemblages in pelites, are presented for the Dalradian rocks of Aberdeenshire and Banffshire, in the type area of Buchan metamorphism; electron microprobe analyses of cordierite (C), staurolite (S), chlorite (Chl), biotite (B) and white mica (Ms) are reported for rocks from the classic sections of the Banffshire coast and the valley of the Ythan.A low grade biotite zone, separates two NE-SW trending sets of higher grade zones, in which the sequence s defined by the entry of cordierite, andalusite (A) and (in the west only) staurolite. The zones are characterised by the assemblages (with quartz and muscovite) B-Chl, C-B-Chl, A-C-B and S-A-B.The western sequence contains a transition towards higher pressure, Barrovian type, metamorphism. The isograds arise from continuous reactions affecting rocks of restricted bulk composition (M/FM). With increasing grade, there is a regular trend towards more magnesian ranges of composition for the assemblages C-B-Chl, A-C-B and finally (as P increases in the west), S-A-B. The isograds form when these assemblages intersect the most Fe⁺⁺-rich rock compositions present which occurs in each case when the biotite M/FM=40. A complex of divariant equilibria, derived for the system KFMASH, is used to model the natural reactions.  相似文献   

Josephinite: Crystal structures and phase relations of the metals     

William A. Bassett  John M. Bird  Maura S. Weathers  D.L. Kohlstedt 《Physics of the Earth and Planetary Interiors》1980,23(4):255-261

Josephinite, a complex, metal-bearing rock from the region of the Josephine Peridotite in southwest Oregon, contains FeNiCo metal alloy phases having exsolution textures. Scanning and transmission electron microscopy have revealed Widmanstaetten patterns in which the lamellae are polysynthetically twinned, ordered, face-centered-cubic FeNi₃ surrounded by untwinned, ordered, face-centered-cubic FeNi₃ and body-centered-cubic FeCo. These exsolution textures require a temperature in excess of 500°C for their formation. This is consistent with a mantle derivation of josephinite prior to obduction of the peridotite in one of the Klamath ophiolites.  相似文献   

The measurement of dissolved organic carbon released by phytoplankton     

Neil S. Shifrin 《Estuaries and Coasts》1980,3(3):230-233

The effects of applied filtration vacuum and incubation time on the release of dissolved organic carbon (DOC) by natural phytoplankton populations dominated by diatoms were examined. The rate of primary production and release of DOC remained reasonably constant during a 5 hour incubation period. The measured release of DOC was found to be quite sensitive to the applied filtration vacuum, ranging from near 2 percent of fixed carbon (neglecting respiration) for gravity-filtered samples to 36 percent for samples filtered at 40 cm Hg vacuum.  相似文献   

Hydrogen and oxygen isotope exchange reactions between clay minerals and water   总被引：1，自引：0，他引：1  

James R O&#x;Neil  Yousif K Kharaka 《Geochimica et cosmochimica acta》1976,40(2):241-246

The extent of hydrogen and oxygen isotope exchange between clay minerals and water has been measured in the temperature range 100–350° for bomb runs of up to almost 2 years. Hydrogen isotope exchange between water and the clays was demonstrable at 100°. Exchange rates were 3–5 times greater for montmorillonite than for kaolinite or illite and this is attributed to the presence of interlayer water in the montmorillonite structure.Negligible oxygen isotope exchange occurred at these low temperatures. The great disparity in D and O¹⁸ exchange rates observed in every experiment demonstrates that hydrogen isotope exchange occurred by a mechanism of proton exchange independent of the slower process of O¹⁸ exchange.At 350° kaolinite reacted to form pyrophyllite and diaspore. This was accompanied by essentially complete D exchange but minor O¹⁸ exchange and implies that intact structural units in the pyrophyllite were inherited from the kaolinite precursor.  相似文献   

The decay of the mean solar magnetic field     

Neil R. Sheeley Jr.  C. Richard DeVore 《Solar physics》1986,103(2):203-224

We have analyzed the effects that differential rotation and a hypothetical meridional flow would have on the evolution of the Sun's mean line-of-sight magnetic field as seen from Earth. By winding the large-scale field into strips of alternating positive and negative polarity, differential rotation causes the mean-field amplitude to decay and the mean-field rotation period to acquire the value corresponding to the latitude of the surviving unwound magnetic flux. For a latitudinally broad two-sector initial field such as a horizontal dipole, the decay is rapid for about 5 rotations and slow with a t ^–1/2 dependence thereafter. If a poleward meridional flow is present, it will accelerate the decay by carrying the residual flux to high latitudes where the line-of-sight components are small. The resulting decay is exponential with an e-folding time of 0.75 yr (10 rotations) for an assumed 15 m s^–1 peak meridional flow speed.E.O. Hulburt Center for Space Research.Laboratory for Computational Physics.  相似文献   

Sedimentological,geomorphological and dynamic context of debris-mantled glaciers,Mount Everest (Sagarmatha) region,Nepal     

Michael J. Hambrey  Duncan J. Quincey  Neil F. Glasser  John M. Reynolds  Shaun J. Richardson  Samuel Clemmens 《Quaternary Science Reviews》2009,28(11-12):1084

This paper presents the sediment, landform and dynamic context of four avalanche-fed valley glaciers (Khumbu, Imja, Lhotse and Chukhung) in the Mount Everest (Sagarmatha) region of Nepal. All four glaciers have a mantle of debris dominated by sandy boulder-gravel that suppresses melting to an increasing degree towards the snout, leading to a progressive reduction in the overall slope of their longitudinal profile. Prominent lateral–terminal moraine complexes, also comprising sandy bouldergravel, enclose the glaciers. These terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin, probably by folding and thrusting when the glaciers were more dynamic during the Little Ice Age. The four glaciers are in various stages of recession, and demonstrate a range of scenarios from down-wasting of the glacier tongue, through morainedammed lake development, to post-moraine-dam breaching. Khumbu Glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake, although one is likely to develop behind its >250 m high composite terminal moraine. Imja Glacier terminates in a substantial body of water behind a partially ice-cored moraine dam (as determined from geophysical surveys), but morphologically appears unlikely to be an immediate threat. Chukhung Glacier already has a breached moraine and a connected debris fan, and therefore no longer poses a threat. Lhotse Glacier has an inclined, free-draining tongue that precludes hazardous lake development. From the data assembled, a conceptual model, applicable to other Himalayan glaciers, is proposed to explain the development of large, lateral-terminal moraine complexes and associated potentially hazardous moraine dams. – 2008 Elsevier Ltd. All rights reserved.  相似文献   

The origin of the 28- to 29-day recurrent patterns of the solar magnetic field     

Neil R. Sheeley Jr.  C. Richard DeVore 《Solar physics》1986,104(2):425-429

Numerical simulations of the Sun's mean line-of-sight magnetic field suggest an origin for the 28-to 29-day recurrent patterns of the field and its associated interplanetary phenomena. The patterns are caused by longitudinal fluctuations in the eruption of new magnetic flux, the transport of this flux to mid latitudes by supergranular diffusion and meridional flow, and the slow rotation of the resulting flux distributions at the 28- to 29-day periods characteristic of those latitudes.E. O. Hulburt Center for Space Research.Laboratory for Computational Physics.  相似文献   

Broad-band X-ray spectrum of the newly discovered broad-line radio galaxy IGR J21247+5058     

M. Molina  M. Giroletti  A. Malizia  R. Landi  L. Bassani  A. J. Bird  A. J. Dean  A. De Rosa  M. Fiocchi  F. Panessa 《Monthly notices of the Royal Astronomical Society》2007,382(2):937-943

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Comments on “Japan's Direct Manufacturing Investment”     

Neil Reid 《The Professional geographer》1990,42(2):223-226

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Similarity of new palaeomagnetic data from the Santa Rosa Mountains with those from Steens Mountain gives wide regional evidence for a two-stage process of geomagnetic field reversal     

Neil Roberts  Mike Fuller 《Geophysical Journal International》1990,100(3):521-526

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