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121.
In this paper, we show that supercritical fluids have a greater significance in the generation of pegmatites,and for ore-forming processes related to granites than is usually assumed. We show that the supercritical melt or fluid is a silicate phase in which volatiles; principally H_2O are completely miscible in all proportions at magmatic temperatures and pressures. This phase evolves from felsic melts and changes into hydrothermal fluids, and its unique properties are particularly important in sequestering and concentrating low abundance elements, such as metals. In our past research, we have focused on processes observed at upper crustal levels, however extensive work by us and other researchers have demonstrated that supercritical melt/fluids should be abundant in melting zones at deep-crustal levels too. We propose that these fluids may provide a connecting link between lower and upper crustal magmas,and a highly efficient transport mechanism for usually melt incompatible elements. In this paper, we explore the unique features of this fluid which allow the partitioning of variouselements and compounds, potentially up to extreme levels,and may explain various features both of mineralization and the magmas that produced them. 相似文献
122.
ABSTRACT Basic shallowing-upward cycles (shu-cycles) and five-bundled megacycles in the Latemar platform have been widely regarded as a model example for precessional and eccentricity forcing in the Mesozoic. Based on bio-/chronostratigraphic data, recent studies questioned this particular type of Milankovitch forcing on the Latemar cyclic series. We present an integrated model that incorporates (i) new cyclostratigraphic data, (ii) new and existing bio-/chronostratigraphic data and (iii) new spectral analyses. The basic shu-cycles in the Latemar reflect sub-Milankovitch control. Cycle bundles of 1 : 4–5 (megacycles : shu-cycles) indicate precessional forcing. They do not reflect eccentricity superimposed on precessional forcing. Spectral analyses reveal highly significant ratios in the large-scale cycle bundlings. Stacking patterns of 1 : 9.9 and 1 : 24.0 shu-cycles represent obliquity and short eccentricity forcing. Both sub-Milankovitch and Milankovitch forcing potentially controlled shallow subtidal carbonate deposition in Mesozoic greenhouse times. Cyclostratigraphic models require an integrated approach including bio- and chronostratigraphic data. 相似文献
123.
A review of water column processes influencing hypoxia in the northern Gulf of Mexico 总被引:1,自引:0,他引:1
Michael J. Dagg James W. Ammerman Rainer M. W. Amon Wayne S. Gardner Rebecca E. Green Steven E. Lohrenz 《Estuaries and Coasts》2007,30(5):735-752
In this review, we use data from field measurements of biogeochemical processes and cycles in the Mississippi River plume
and in other shelf regions of the northern Gulf of Mexico to determine plume contributions to coastal hypoxia. We briefly
review pertinent findings from these process studies, review recent mechanistic models that synthesize these processes to
address hypoxia-related issues, and reinterpret current understanding in the context of these mechanistic models. Some of
our conclusions are that both nitrogen and phosphorus are sometimes limiting to phytoplankton growth; respiration is the main
fate of fixed carbon in the plume, implying that recycling is the main fate of nitrogen; decreasing the river nitrate loading
results in less than a 1:1 decrease in organic matter sinking from the plume; and sedimenting organic matter from the Mississippi
River plume can only fuel about 23% of observed coastal hypoxia, suggesting significant contributions from the Atchafalaya
River and, possibly, coastal wetlands. We also identify gaps in our knowledge about controls on hypoxia, and indicate that
some reinterpretation of our basic assumptions about this system is required. There are clear needs for improved information
on the sources, rates, and locations of organic matter sedimentation; for further investigation of internal biogeochemical
processes and cycling; for improved understanding of the rates of oxygen diffusion across the pycnocline; for identification
and quantification of other sources of organic matter fueling hypoxia or other mechanisms by which Mississippi River derived
organic matter fuels hypoxia; and for the development of a fully coupled physical-biogeochemical model. 相似文献
124.
125.
Frank?M.?FlockeEmail author Andrew?J.?Weinheimer Aaron?L.?Swanson James?M.?Roberts Rainer?Schmitt Stephen?Shertz 《Journal of Atmospheric Chemistry》2005,52(1):19-43
A fast, automated, gas chromatographic system for the airborne measurement of PAN and a series of its homologues is described
and its performance is evaluated. Response factors for PAN, PPN, APAN, PiBN, and MPAN have been determined and are discussed
with regard to ECD response and to potential losses in the analytical system. Calibration methods used for these tasks are
described and compared. The results from this work should help investigators who are employing the widely used GC/ECD method
for the measurement of peroxyacyl nitrates to evaluate peaks of PAN homologues that cannot be calibrated for by using the
reported response factors. 相似文献
126.
We have developed a computer code that solves numerically the 1D heat transport equation for small planetary bodies consisting of silicate material and heated by 26Al. At the same time the bodies' accretion (with a size from 1 km—or smaller—to several hundred kilometers) is taken into account as radial growth. We find that the consideration of accretion is inevitable as it affects the thermal evolution resulting from heating by radioisotopes. Significant changes in thermal behavior are shown to occur in comparison with calculations that assume instantaneous accretion. 相似文献
127.
A global positioning system (GPS)-based online control and alarm system (GOCA) for monitoring of three-dimensional movements
has been developed at the Karlsruhe University of Technology. The GOCA hardware consists of an array of GPS sensors and communication
units to be placed in the monitoring area. The hardware-dependent control software communicates with the GPS sensors and provides
the GPS baseline data and covariance information to the GOCA deformation analysis software. The GOCA center, which comprises
both the control software and the GOCA software, may be linked – for example, over a long distance – to another personal computer
(PC) that serves as a remote control station. GOCA is able to provide the full capabilities of classical deformation analysis
online (with stations grouped into stable points and moving object points). Both types of points may be occupied either continuously
or over short periods at different times. The object points are determined with respect to the stable points. A network adjustment
is performed for each interval of data collection, and the coordinate and covariance information may optionally be transformed
into a specific reference system (e. g., the building system). Unstable reference points are to be detected by statistical
tests. The estimated object point time series are filtered with respect to gross errors using robust estimation techniques.
Online filters are used to smooth the time series data of critical displacements and to predict other deformation functions.
The time series data, as well as prediction results, are displayed graphically for each object point. An example concerning
the online monitoring of a slag heap in a coal-mining area is included. ? 2000 John Wiley & Sons, Inc. 相似文献
128.
Abstract— We present Ne data from plagioclase separates from the solar noble‐gas‐rich meteorite Kapoeta, obtained mainly by in vacuo etching. samples rich in solar gases contain an excess of cosmogenic ne compared to solar‐gas‐poor samples, testifying to an exposure to cosmic rays in the parent body regolith. The 21Ne/22Ne ratio of the excess component is slightly lower than that of the Ne acquired during the meteoroid flight. Model calculations indicate that the observed isotopic composition of the excess Ne can be produced by galactic cosmic rays at a reasonable mean shielding of around a hundred to a few hundred grams per square centimeter. No substantial contribution from Ne produced by solar cosmic rays is needed to explain the data. We therefore conclude that they do not offer evidence for a substantially enhanced flux of solar energetic particles early in solar history, contrary to other claims. This conclusion is in agreement with solar flare track data. 相似文献
129.
130.