Dokąd zmierza współczesna geotektonika?

Stefan Cwojdziński



The developments in geotectonics in the XIX and this century well illustrate the Imre Lakatos (36, 40) methodological concept of so-called scientific research programmes in operation. The analysis of research programmes of the geotectonics makes it possible to formulate some prognoses of further developments in global tectonics. All the hitherto proposed geotectonic theories fall within frames of four models of the Earth as a planet, i.e.: shrinking Earth, the Earth with dimensions constant throughout its geological evolution, expanding Earth and that of pulsating Earth. Bach of these models forms a core of a separate scientific programme, the history of which is shown in Fig. 1. In the last two or three decades, i.e. after abandonment of the contracting Barth programme and crisis in that of pulsating Barth, we may speak about continuation and developments in two programmes only. Within the frame of the programme of the Barth with constant dimensiotis there appeared two series of theories: a mobilistic one, assuming horizontal movements of major geostructures, and a stabilistic one, assuming permanent nature of the geostructures. The expanding Earth programme was developing independently of the former (one could even say that out of the way of the main stream of recent geotectonics), giving rise to its own series of theories.
Figure 2 shows schematically evolution of the above mentioned three major modern series of geotectonic theories as a response to new findings and discoveries and their interrelations and mutual influences. Within the frame of the mobilistic series there successively originated concepts of continental drift, convection hypotheses and, in connection with supply of new data on oceanic areas - hypotheses of sea-floor spreading and plate tectonics theory, which became the predominating geotectonic idea in the middle seventies.
Within the frame of the plate tectonics, there were worked out concepts of plate tectogenesis and (for explanation of interplate phenomena) those of hot spots and mantle plumes. Attempts to adjust the plate tectonics theory to results of further studies resulted in origin of a number of its modifications such as the concepts of oblique collision, thin-skin tectonics, soft-plate tectonics, microplate tectonics, hypothesis of induced arcs and lithosphere delamination, etc. Despite of steadily increasing number of its modifications, the plate tectonics theory is facing steadily increasing difficulties in explanation of data gathered in the course of further studies and there are growing sings of crisis in the scientific programme of mobilism which is based on the Barth model assuming dimensions constant throughout the geological history.
As it was mentioned above, the stabilistic programme has been developing independently of the mobilistic. Within its frame there have been worked out theories of vertical tectonics, explaining tectogenic phenomena in terms of vertical displacements of masses in the Earth crust and mantle and secondary character of gravity deformations ( oscillatory, undational, radiomigration, astenolith and other theories). The Byeloussov oceanization and van Bemmelen internal differentiation theories may be treated as a reaction to the supply of new data on geological structure of oceanic floor, paleomagnetic data, etc. Despite of some unquestionable achievements (for example, working out of the idea of orogenic diapirism and gravity tectonics), the stabilistic programme appears conservative in character and without much chances for further development.
The scientific programme assuming expansion of the Barth originated in the 1920' s as an alternative explanation of the same set of data as in the case of the mobilistic programme. Two groups of hypotheses originated in the course of its evolution: that of limited expansion - and another, assuming large expansion. The former looks for explanations and evidence for expansion of the Barth in extraterrestial, cosmic processes (30 - 32, 46), showing small (up to 5%) increase in the Barth radius from the Cambrian till the present.
The second group of hypotheses assumes large expansion of the Barth due to intraplanetary phase processes (22, 25-27, 11, 12, 18, 19, and others). The results of geological and geophysical studies from the last years give a firm data base for these hypotheses. Within the frame of that programme it is very easy to explain such facts as sea-floor spreading, relative youth of oceans, connections of structure of continents and basement in the Barth mantle down to 700 km depth, lack of compensation of spreading around Antarctica and Africa, tensional nature of frame of the Pacific, elongation of mid-oceanic ridges, evident paleogeographic and paleobiogeographic connections of America and areas of the Tethys, China and Asiatic continent, the lack of undisputable oceanie sediments in the Paleozoic and Precambrian, and many, many others. Orogenic processes are explained in this programme with reference to ideas worked out in other ones, using some concepts of vertical tectonics, geoundations, hot spots, etc. The expanding Barth programme may be nowadays treated as an example of a progressive, dynamic programme in the Lakatos scheme. However, its wide acceptation would require a real revolution of concepts and a break-through in the mode of thinking of geologists.

Pełny tekst: