Cykeltänkandet Och Granitproblemen

Abstract

Cycle concept and the granite problems. Discusses the relationships between orogenesis and plutonism in the Precambrian of Sweden. In 1936, Wahl introduced the terms primorogenic and serorogenic for different relations in this respect. Some aspects of the problem are here considered, especially in the light of scientific development in other regions. A review is given of the Cretaceous plutonism in the Cordilleran orogen of the Americas, including reference to an important paper by Gilluly (1963), as this plutonism gives an illustration of geologically contemporaneous primorogenic intrusions, similar in their magmatic development but with different relations to the structure of the invaded formations. Reference is also made to a paper on the “Main Donegal” granite by Pichter & Read (1958). Then the primorogenic granites of Central Sweden are discussed. Of the serorogenic granite types, the Lina granite of northernmost Sweden and northern Finland is especially considered. It shows a characteristic development over an extensive region. The writer maintains that this granite, which is migmatitizing, cannot derive from remelting of the older geological units known in these parts, and that all its various batholiths must stem from a common deep-seated magma chamber. The phenomena observed to be associated with it are not palingenic, but illustrate the effects of a serorogenic, presumably palingenic granite on the formations into which it is intruded. Similarly, in Central Sweden the mobilization of salic material which has taken place during the serorogenic phase, was not caused by heating due to depression to deeper levels in the crust, but by heat and material brought up from below the level where it can now be studied. In one district, dikes associated with the Lina granite show boudinage in a relation to linear structure in their wall rock, wholly similar to what has later been described from Donegal by Pitcher and Read (Geijer 1930, Pitcher & Read 1958).