Islandia w świetle tektoniki płyt

Abstract

ICELAND IN THE LIGHT OF PLATE TECTONICS Summary The author scientific journey Ito Iceland made possible analysis of the newest geological concepts of the genesis of that island, thanks to the courtesy of Professor S. Thorarinsson. The descriptive part of the paper is based on monographic literature and autopsy. lt is worth to note that the Pliocene/Pleistocene boundary is placed at 3 m. y. and 1,8 m. y. or less in Iceland and Europe, respectively. A special attention should be paid to Icelandic rift fissures open or filled with young lava, which clearly evidence tension conditions. The migration of rift zones in time is clearly marked. It may be noted that the zones were generally shifting eastwards in the area of the island during the last few millions years whilst their position was relatively constant in neighbouring oceanic areas. The frequency of eruptions of endogenic material is fairly stable and the interval between eruptions is 5 years long. Transform faults may be noted on both ends of the island. The majority of earthquake epicenters and some volcanos are situated along these faults. The island supplied some data for measuring the rate of spreading, estimated at 1cm per year in each direction. The genesis of acid lava beIong to the most controversial questions connected with Iceland. A lot of work has been done in order to identify processes responsible for seggregation of acid derivatives such as ryolite which are much more common than it wouId follow from earlier calculations. Iceland originated above “hot spot” as a product of eruption of lava from “mantle plume”. It was found that the lavas from eastern Greenland and Shetland ls., formed more than 55 m. y. ago, are identical in chemical composition as those from Iceland, differing in age only. The chemical composition of all the lavas is somewhat different from that of lavas from the mid-oceanic ridges, being typical “mantle plume” lavas. The question whether there was a single or more sources of the two types of lava is still open. The recent studies carried out by Soviet teams have given accurate refraction seismic profile from Iceland to Shetland Is. The interpretation of the profile has evidenced the presence of continental crust beneath Shetland Is. And Faeroe Is. and a ridge continuing further towards the shores of Iceland. A new concept of the tectonics of the Atlantic Ocean, presented here, takes into account the results of the seismic studies (Fig. 10). However, the comparison of the refraction seismic data with the model of the Mid-AtIantic Ridge presented by Talwani and others (1965) has shown that it is possible to accept another point of view (Fig. 10), that is that the crust of the lceland - Faeroe Ridge is anomalous oceanic crust. In this way the well-known tectonic image of this part of the Atlantic, that is that proposed by the supporters of the new plate tectonics, is revisited.