Calc-alkaline magmatism in the south-west Ukraine occurred between 13.8 and 9.1 Ma and formed an integral part of the Neogene subduction-related post-collisional Carpathian volcanic arc. Eruptions occurred contemporaneously in two parallel arcs (here termed Outer Arc and Inner Arc) in the Ukrainian part of the Carpathians. Outer Arc rocks, mainly andesites, are characterized by LILE enrichment (e.g. K and Pb), Nb depletion, low compatible trace element abundances, high 87Sr/86Sr, high δ18O and low 143Nd/144Nd isotopic ratios (0.7085–0.7095, 7.01–8.53, 0.51230–0.51245, respectively). Inner Arc rocks are mostly dacites and rhyolites with some basaltic and andesitic lavas. They also show low compatible element abundances but have lower 87Sr/86Sr, δ18O and higher 143Nd/144Nd ratios (0.7060–0.7085, 6.15–6.64, 0.5125–0.5126, respectively) than Outer Arc rocks. Both high-Nb and low-Nb lithologies are present in the Inner Arc. Based on the LILE enrichment (especially Pb), a higher fluid flux is suggested for the Outer Arc magmas compared with those of the Inner Arc.
Combined trace element and Sr–Nd–O isotopic modelling suggests that the factors which controlled the generation and evolution of magmas were complex. Compositional differences between the Inner and Outer Arcs were produced by introduction of variable proportions of slab-derived sediments and fluids into a heterogeneous mantle wedge, and by different extents of upper crustal contamination. Degrees of magmatic fractionation also differed between the two arcs. The most primitive magmas belong to the Inner Arc. Isotopic modelling shows that they can be produced by adding 3–8% subducted terrigenous flysch sediments to the local mantle wedge source. Up to 5% upper crustal contamination has been modelled for fractionated products of the Inner Arc. The geochemical features of Outer Arc rocks suggest that they were generated from mantle wedge melts similar to the Inner Arc primitive magmas, but were strongly affected by both source enrichment and upper crustal contamination. Assimilation of 10–20% bulk upper crust is required in the AFC modelling, assuming an Inner Arc parental magma. We suggest that magmagenesis is closely related to the complex geotectonic evolution of the Carpathian area. Several tectonic and kinematic factors are significant: (1) hydration of the asthenosphere during subduction and plate rollback directly related to collisional processes; (2) thermal disturbance caused by ascent of hot asthenospheric mantle during the back-arc opening of the Pannonian Basin; (3) clockwise translational movements of the Intracarpathian terranes, which facilitated eruption of the magmas. 相似文献
The present paper deals with the pulsation period variability of the high-amplitude δ Scuti star GP Andromedae using a data
set covering a time base of 26.9 years. The possibility of a periodic component (reflecting the light-time effect induced
by a hypothetic binarity) in the O-C curve is inferred. The presence of this periodicity in the period variation of GP And leads to a diminution of the discrepancy
between predicted and observed relative period change rates. The hypothesis of the existence of an unseen companion is discussed.
The statistical analysis of the final O-C residuals distribution, indicates their normal or close to normal character.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Photoelectric observations of the asteroid 433 Eros were carried out with the 50-cm reflector of the Astronomical Observatory of the University of Cluj-Napoca on January 21 and February 4 and 5, 1975. 相似文献
We present a numerical scheme for reactive contaminant transport with nonequilibrium sorption in porous media. The mass conservative scheme is based on Euler implicit, mixed finite elements, and Newton method. We consider the case of a Freundlich-type sorption. In this case, the sorption isotherm is not Lipschitz but just Hölder continuous. To deal with this, we perform a regularization step. The convergence of the scheme is analyzed. An explicit order of convergence depending only on the regularization parameter, the time step, and the mesh size is derived. We give also a sufficient condition for the quadratic convergence of the Newton method. Finally, relevant numerical results are presented. 相似文献
A variability survey on the shape of the light curve of the classical Cepheid DL Cas has been performed on the basis of Johnson
V photometry data covering about 38 years. The input parameters (mean magnitude, pulsation frequency and period, light curve
amplitude, harmonics amplitudes, Fourier type structural parameters) for our study were determined through the Fourier decomposition
technique applied to each data set. The analysis of the outcoming time series, using different and complementary methods,
seems to indicate the constancy of these parameters within the precision limits of the available data, although the hypothesis
of the presence of a low level variability cannot be excluded. The only exception is the pulsation period, which displays
a possible increasing trend with a rate of 0.109 ± 0.037 s yr−1. This trend may be, at least partly, an effect of the unequal precision of pulsation period estimated values, corresponding
to each considered data set.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
A study of the orbital period variation of the W UMa system CK Bootis is made using an extended observational time base. The biperiodicity of the orbital period modulation is emphasized. Both detected periodicities (24.14 yr and 10.62 yr) cannot be explained through the light-time effect unless the companion would be a white dwarf as suggested by other authors, too. Moreover, we also argue that, nowadays at least, it seems that there is no causal relation between the orbital period variation and the recently discovered visual companion. Consequently, we infer that at least one of the two periodicities may be related to the magnetic activity cycles in the component stars of CK Boo, while the other periodicity could be related to the presence of a fourth companion in the system. 相似文献
