Basalt magmatism along the passive continental margin of SE Brazil (Campos basin)

The SE-Brazil passive continental margin is characterized by tholeiitic magmatism that is particularly widespread in the marginal Campos basin, facing the inland flood basalts of the adjacent Paranà basin. Campos magmatism is represented by Early Cretaceous (EC; 134–122 Ma) flood basalts and minor Upper Cretaceous-Early Tertiary basalt flows and intrusives, which were emplaced in a basin with attenuated crustal thickness (20 km). Petrography, mineral chemistry, wholerock geochemistry and Sr–Nd isotope composition emphasize that the EC-Campos basalts have suffered extensive seawater interaction which caused enrichment in MgO, FeO total, K₂O, Rb and Ba, and depletion in SiO₂ and CaO, while Zr, Nb, Y and REE remained virtually constant in samples with loss-on-ignition values less than 4 wt%. In general, Campos basalts have bulkrock chemistry similar to those of the inland Parana tholeiites (140–130 Ma) with relatively low concentrations of incompatible elements and TiO₂ (<2 wt%). Batch-melting calculations suggest that Campos basalt genesis requires a garnet-peridotite source and variable degree of melting (9–25%) in order to explain the rare-earth-element (REE) patterns with chondrite normalised La/Yb_(N) ratio ranging from 0.9–1.0 to 4.4–7.1. The Sr–Nd isotopic data for the slightly altered Campos basalts, of both Early Cretaceous and Upper Cretaceous-Early Tertiary age, plot close to bulk earth, or in the enriched quadrant of the mantle array. Inter-element (La, Zr, Nb, Ba) ratios preclude for the Campos (and Paranà) basalt genesis any significant participation of N-type (Zr/Nb>16) MORB (mid-ocean-ridge basalt) mantle in simple binary mixing models. On the whole, the Early Cretaceous Campos basalts appear as an easterly, younger extension of the northern Paranà volcanism and probably erupted during early stages of the major riftingprocesses which caused continental thinning. It is notable that in the Campos marginal basin both the basalt magmatism contemporaneous with the continental break-up, as well as that which occurred after the S. America-Africa separation, appears substantially related to subcontinental lithosphere and a Dupal-like OIB (ocean-island basalt) (e.g. Tristan da Cunha) source components.     

Correcting for crystal tilt in HRTEM images of minerals: the case of orthopyroxene

High-resolution transmission electron microscopy (HRTEM) is a powerful technique for crystal structure imaging and real structure analysis. It is theoretically possible to resolve inter-atomic distances with modern high resolution microscopes. In practice, however, the effects of sample and lens parameters such as crystal tilt and phase contrast transfer function (CTF) distort the images, reduce the resolution offered, and make image interpretation difficult. We have analyzed to what extent it is possible to reconstruct interpretable images of a tilted mineral by image processing.HRTEM images of orthopyroxene were simulated for a series of crystal tilts and thicknesses under Scherzer defocus condition using the parameters of a 400 kV microscope. The tilted images were reconstructed by crystallographic image processing. After correcting for crystal tilt, the images were as good as electron density maps calculated from X-ray diffraction structure factors.     

通过对调查数据的趋势和多变量分析确定宏观场

通过多变(相关分析)和趋势分析等统计方法对宏观调查数据进行了解释.这种方法使我们通过评定不同宏观效应叠加的程度、估计调查数据的不确定性更客观地评定烈度.通过滤波确定烈度场的区域分量,使我们消除观测中的局部变化.给出了选取适当滤波参数的准则.本文应用这一方法对发生在意大利的一次地震的调查数据进行了处理.     

The volcano of Capelinhos (Azores), the solar activity and the earth-tide

Bulletin of Volcanology - Correlations on the eruptive behaviour of the volcano of Capelinhos (Fayal island) in 1957–58, with (a) solar activity, and (b) earth-tide amplitudes, by way of a...     

The submarine volcano of Capelinhos and the tectonics of the Azores

Bulletin of Volcanology - In another paper of the author, a picture of the tectonics of the Azores was presented. The morphological analysis showed evidence of a folded and faulted structure and...     

On the propagation of Love waves in a non-homogeneous isotropic layer of finite depth lying on an infinite non-isotropic layer

Summary This paper deals with the propagation of Love waves in a non-homogeneous isotropic layer of finite depth standing on an infinite non-isotropic layer when there a parabolic irregular zone exists at the interface of the two media.     

Wave propagation through ionospheric plasma in presence of time-varying random irregularities

Summary The dielectric tensor of a time-varying anisotropic electron-plasma has been studied with the consideration of the effect of collision. The tripple splitting of the electromagnetic waves is obtained from the dispersion relation which gives the two usual magnetoionic modes in the limiting case. The randomness of electron number density has been evaluated by the help of field variables and also by the nature of fluctuation of dielectric tensor.     

Finite strain theory of love waves

Summary The propagation of Love waves is discussed on the basis of finite strain theory. The primary Love wave is found to be associated with a secondary Rayleigh wave and a tertiary Love wave. Numerical calculations are presented for two values of the wave-velocity; the results show that the theory of Love waves based on infinitesimal strain, is not applicable to short period waves.     

A method of estimating the excess electron density in random irregularities embedded in the ionosphere

Summary Wave propagation through the ionospheric plasma containing irregularities has been studied. The excess electron number density due to the presence of irregularities has been calculated in a way which may be suitably used for practical purposes.