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1.
2.
We have determined the quenched cation ordering states of five orthopyroxene crystals collected from the marginal border
group and the lower zone a and b of the Skaergaard intrusion, and modeled these data to retrieve their closure temperatures
(T
c) of Fe–Mg ordering and cooling rates. According to existing thermal models for the Skaergaard pluton, conductive cooling
dominated the high and low temperature regimes, which were separated by an intermediate temperature regime in which the cooling
was controlled primarily by convective fluid circulation. The cooling rates retrieved from the quenched cation ordering states
of the orthopyroxene crystals strictly apply to temperatures around the closure temperatures of the ordering states, ∼340–400° C, which fall at the transition from convective to the lower temperature conductive cooling. The cooling rates obtained from
the cation ordering states of orthopyroxene vary from ∼1 to 270 K/ka. These results agree well with a thermal model calculated
using an assumed average permeability of 10-12 cm2 for the pluton, but not completely with a model calculated on the basis of an average permeability of 10-13 cm2, although both values produced shifts of δ18O that are comparable to those observed in the pluton.
Received: 27 February 1995/Accepted: 20 July 1995 相似文献
3.
Lineament extraction approach allowed mapping of larger number of lineaments in a classical manner in tectonic and structural studies. In the present study, various techniques were adopted to extract lineaments using Landsat ETM+ images. To remove the biasness of the images, some pre-processing techniques like stream ordering, band differencing, colour texturing were employed to enhance the edges of the structural features. Extracted lineaments and its distribution and orientation were mapped using ArcGIS Spatial analyst tool. Results of the study showed maximum number of lineaments were oriented in the ENE–SWS direction with 63° overall inclination. Accuracy assessment and validation were made with respect to visual interpretation and overlaying the lineament on Digital Topographic Model as well as with respect to an existing geological lineament map of the study site. The result of accuracy assessment indicates higher compatibility of Central Indian Suture with the geological map of the study area. 相似文献
4.
The Upper Cretaceous Bagh Beds yield many biota of which ammonoids are particularly well known. Previously Bagh ammonoids were grouped into many genera and species within several families. The present study, however, shows that failure to recognize dimorphism and a wide range of interspecific variation within the single genus Placenticeras perhaps results in taxonomic oversplitting. Specific dimorphism in P. mintoi has been established. 相似文献
5.
Jibamitra Ganguly Weiji Cheng Sumit Chakraborty 《Contributions to Mineralogy and Petrology》1998,131(2-3):171-180
Diffusion couples made from homogeneous gem quality natural pyrope and almandine garnets were annealed within graphite capsules
under anhydrous conditions at 22–40 kbar, 1057–1400 °C in a piston-cylinder apparatus. The concentration profiles that developed
in each couple were modeled to retrieve the self diffusion coefficients [D(I)] of the divalent cations Fe, Mg, Mn and Ca.
Because of their usually low concentrations and lack of sufficient compositional change across the interface of the diffusion
couples, only a few reliable data can be obtained for D(Ca) and D(Mn) from these experiments. However, nine sets of D(Fe)
and D(Mg) data were retrieved in the above P-T range, and cast in the form of Arrhenian relation, D=D
0exp{−[Q(1 bar)+PΔV
+]/RT}. The values of the activation energy (Q) and activation volume (ΔV
+) depend on whether f
O2 is constrained by graphite in the system C-O or held constant. For the first case, we have for Fe:Q(1 bar)=65,532±10,111 cal/mol, D
0=3.50 (±2.30)×10−5 cm2/s, ΔV
+=5.6(±2.9) cm3/mol, and for Mg:Q(1 bar)=60,760±8,257 cal/mol, D
0=4.66 (±2.48)×10−5 cm2/s, ΔV
+=5.3(±3.0) cm3/mol. Here the ΔV
+ values have been taken from Chakraborty and Ganguly (1992). For the condition of constant f
O2, the Q values are ∼9 kcal lower and ΔV
+ values are ∼4.9 cm3/mol larger than the above values. Lower temperature extrapolation of the Arrhenian relation for D(Mg) is in good agreement
with the Mg tracer diffusion data (D
*
Mg) of Chakraborty and Rubie (1996) and Cygan and Lasaga (1985) at 1 bar, 750–900 °C, when all data are normalized to the same
pressure and to f
O2 defined by graphite in the system C-O. The D
*
Mg data of Schwandt et al. (1995), on the other hand, are lower by more than an order of magnitude than the low temperature
extrapolation of the present data, when all data are normalized to the same pressure and to f
O2 defined by the graphite buffer. Comparison of the D(Fe), D(Mg) and D(Mn) data in the pyrope-almandine diffusion couple with
those in the spessartine-almandine diffusion couple of Chakraborty and Ganguly (1992) shows that the self diffusion of Fe
and Mn are significantly enhanced with the increase in Mn/Mg ratio; the enhancement effect on D(Mg) is, however, relatively
small. Proper application of the self diffusion data to calculate interdiffusion coefficient or D matrix elements for the purpose of modeling of diffusion processes in natural garnets must take into account these compositional
effects on D(I) along with the effects of thermodynamic nonideality, f
O2, and pressure.
Received: 8 May 1997 / Accepted: 2 October 1997 相似文献
6.
An extensive series of incoherent scatter studies of the ionospheric D-region was carried out at the Arecibo radar facility during 1978 and 1979. They included several full-day sequences of electron density measurements over a range of altitudes, and also included a sequence during the serendipitous occurrence of a large solar flare. For the solar flare event simultaneous data on solar X-ray fluxes in several wavelength bands were available from the GOES-2 and ISEE-3 satellites.
In the course of development of a large ionospheric computer model at Los Alamos we have used the solar flare data as a reality check. The solar X-ray flux data were used as inputs for computing ionization rates. The model computer includes 999 chemical reactions, and also includes diffusion and transport processes. In the course of the flare studies we used the data comparisons to adjust the values of three chemical rate coefficients that were poorly known. With those adjustments the model computations fitted the data quite well.
Subsequent to the flare analysis we have been using the same model with some minor updates to compute the expected diurnal variations of the ambient D-region under conditions chosen to match those existing at the times of the incoherent scatter measurements. Comparisons of the computations and the data will be shown, and the relative importance of the several separate ionization processes will be discussed. We also compare model results with experimental data on concentrations of NO. 相似文献
7.
Haimanti Biswas Mitali Dey Dipnarayan Ganguly Tarun K. De Sandip Ghosh Tapan K. Jana 《Estuaries and Coasts》2010,33(2):395-398
Inter-annual variations of phytoplankton abundance and community organization were observed over a two-decade period along
with the ancillary parameters at the land–ocean boundary associated with the Sundarban mangrove forest (21°32′ and 22°40′
N and 88°05′ and 89° E), along the NE Coast of the Bay of Bengal. The number of definable Bacillariophyceae species exceeded Dinophyceae taxa, and the total number of bloom-forming species declined from a maximum of ten in 2000 and a minimum of two in 2007.
Blooms of the diatom Coscinodiscus radiatus were common in 2000 and 2007. Tide cycles and the onset of the monsoon season played important roles in diurnal and seasonal
variability of phytoplankton. Phytoplankton biovolume showed seasonality, with the highest levels during post-monsoon periods
and lowest levels during the monsoon period. Phytoplankton abundance was correlated to rainfall patterns, which may be altered
by long-term changes in climate. 相似文献
8.
A multivariate statistical analysis was carried out with log-transformed values of Cu, Ni, Co, Pb, Zn, Ag, Cr, Mn, Ca, and Sr in several sets of samples collected across the mineralized base metal zone in sheared soda granite, feldspathic schist, and chlorite schist from the central section of Mosaboni Mine of the famous Singhbhum Copper Belt of eastern India. Linear correlation coefficient matrices of two sets of ore samples (>0.5% Cu)—one from levels 18 and 21 and the other from levels 25 and 28—indicate two well-defined and distinct clusters comprising Cu, Ni, Co, Pb, and Zn on one hand and Ca, Sr, and Mn on the other. Varimax-rotatedR-mode factor analysis of two above-noted sample sets, taken along with available geologic information, indicates that over 80% of the variability in data matrices for 9–10 elements can be accounted for by four distinct processes: (a) an early phase of copper mineralization which apparently replaced Mn, Ca, and Sr in the host rock; (b) a silicate-cum-oxide phase of crystallization/recrystallization of host rock; (c) remobilization of sulfide-forming ore elements (Cu, Ni, Co, Pb, and Zn); and (d) a phase of mineralization of Ag which appears to have replaced Cr, Ca and Cu. Process (c) was quantitatively most important. Factor score studies are suggestive of preferred introduction of Ni, Co, Pb, and Zn along central parts of preexisting copper-mineralized zones. 相似文献
9.
Two theoretical models, spherical and cylindrical, of propagation of shockwaves with varying energy in a rotating, magneto-radiative,self-gravitating non-uniform atmosphere have been developed. Subsequently,a comparison between the two models has been drawn with the aid ofvariation of flow variables with distance graphically. Significant is thedifference between two models, when one observes the variations of radialvelocity, pressure, mass, radiation flux, magnetic field and energy withdistance. Also, the respective influences of radiation flux, magneticfield and rotational velocity on the variations of the flow variables havebeen studied. 相似文献
10.