Applicability of palaeomagnetism of pyrrhotite to ore-genetic studies

Pyrrhotite has never before been used in palaeomagnetic investigations, being highly anisotropic magnetically. The aim of this paper is to show that fine-grained pyrrhotite aggregates of hydrothermal origin can be used for palaeomagnetic purposes. This has been proved with polymetallic Turkak veins from Kutná Hora in Central Bohemia as an example. It can be assumed that other localities with occurrence of hydrothermal pyrrhotite aggregates which contain directionless, uniformly scattered pyrrhotite grains and therefore forming a magnetically isotropic medium may be suitable for palaeomagnetic studies.

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Zusammenfassung Pyrrhotin, mit einem hohen Grad magnetischer Anisotropie, ist bisher für die paläomagnetische Datierung unbeachtet geblieben. Diese Arbeit will zeigen, daß feinkörnige Pyrrhotinaggregate hydrothermalen Ursprungs für paläomagnetische Untersuchungen geeignet sind, was am Beispiel polymetallischer Gänge von Turkak in Kutná Hora in Zentralböhmen dargestellt wird. Es ist anzunehmen, daß auch andere Vorkommen hydrothermaler Pyrrhotinaggregate in denen regelmäßig verteilte Körner richtungslos orientiert vorliegen und so ein magnetisch isotropes Medium bilden, sich für paläomagnetische Untersuchungen eignen.

     

The mean curvature of the external equipotential surface and the vertical gravity gradient as functions of stokes's constants

Summary The mean curvature of the equipotential surface and the vertical gradient of gravity are expressed in terms of a development into a series of spherical harmonics [1, 2, 4], neglecting terms of the order of 10^–8. The curvature anomalies have been computed using the satellite data [3]. The symbols used are the same as in [5].Dedicated to 90th Birthday of Professor Frantiek Fiala     

Recent movements of the earth's crust

Summary It has been shown that it is necessary to combine several methods to be able to describe and explain recent movements of the Earth's crust.Presented at the XV^th General Assembly of the IUGG, Moscow 1971.     

Vlf experiment with the interkosmos-5 satellite

Summary The Interkosmos5 VLF experiment consisted of a spectrum analyser with twelve narrow-band channels and broadband measurements between0.07 and20 kHz using an analogue telemetry with a tape recorder on board. The apparatus used in the experiment is shortly described, some examples ofVLF phenomena observed are given and a review of all analogue data recorded is shown in a graphical calendar.     

Peralkaline acid tendencies in Gran Canaria (Canary Islands)

The study of a volcanic series from the island of Gran Canaria (Canary Islands) in which alkaline and peralkaline, saturated and undersaturated rocks coexist, is reported here. Materials with high volatile content (ignimbritic trachytes) were first emitted and the series ended with the eruption of phonolitic lavas. The average peralkalinity index in these rocks is typically about 1.0 and, therefore, peralkaline rocks coexist with non-peralkaline ones. However, a maximum in peralkalinity is found in the ignimbritic rocks of the lower part of the series. In spite of the evident acid peralkaline tendencies of these rocks, it does not seem appropriate to classify them as pantellerites or comendites. Nor are they consistent with the genetic processes proposed for rocks of similar composition and oceanic environment.The crystallization of the feldspars controls the variation trends among the different magmas but the fractionation alone does not sufficiently explain the genesis of successive fluids. Various factors seem to point to the important role which a gas-transfer process causing a geochemical stratification inside the magmatic chamber may have played.The occurrence of peralkaline silicics at Gran Canaria, which is located for away from the active Mid-Atlantic ridge, is not related to transitional basalts. These rocks are a deviation from the main undersaturated alkalic trend which characterizes the volcanism of the Canary Islands, their genesis being related to the realization of favourable local volcanic conditions.     

Comment on the effect of a vorticity centre on a frontal boundary

Zusammenfassung Es wird der Einfluss des sogenannten Vorticity-Zentrums auf die Grenzfläche zweier Luftmassen der mittleren geographischen Breiten studiert. Zwecks Aufklärung der Rolle des Bewegungs- und Druckfeldes in diesem Prozesse wurde ein einfaches Modell konstruiert und numerisch gelöst. Die sich entwickelnde frontale Welle kann beziehungsweise als ein Anfangswert beim Lösen der mit der Stabilität der Wellen verbundenen Probleme mittels der Gleichungen, linearisiert durch die Methode der kleinen Störungen, dienen. Bei der Konstruktion des Modells wird ausser anderem von der Geometrie der Bewölkung ausgegangen, wie sie auf den Aufnahmen der meteorologischen Satelliten erfasst ist.     

Results of deep seismic soundings along international profile VII in Czechoslovakia and poland

Summary The paper deals with the results of DSS measurements along international profile VII, carried out by Czechoslovak and Polish geophysicists in 1970 – 71. The profile situation is shown in Fig. 1. By 1971 part of the profile in the region of the Bohemian Massif between points 1 and 3 and in Poland between points 5 and 7 had been surveyed (Fig. 2). The seismograms were used to construct the travel-time curves of the fundamental types of waves P^K, P^M, P_n (Fig. 4). The mean velocities were computed from the travel-time curves of the reflected waves (P^M and P^K) and the refracted waves (P_g). Isolines of the mean velocities could be constructed for the region of the Bohemian Massif (Fig. 6). The velocity data found were used for the depth interpretation of the travel-time curves of the principal types of waves and to construct a seismic section (Fig. 8). In the region of the Pre-Sudeten block the thickness of the crust was found to be 34–37 km, and in the Sudeten it increased to 40 km. Towards the south the thickness of the crust gradually reduces to 30 km in the system of the Luice faults. In the Bohemian Cretaceous the thickness of the crust is about 30 km. Further to the south, in the region of the Moldanubicum, the thickness of the Earth's crust increases rapidly, and at the southern border of the Central Bohemian pluton it reaches values of about 42 km.