Et funn av pseudotachylitt i S. Trøndelag, og en teori for dannelsen.

Abstract

(forkortet) A new locality of pseudotachylite, and a theory of formation: A new locality of pseudotachylite, in southern Trøndelag, southern Norway is described. The geology of the area in which it occurs has been described earlier (Bryn, 1959). The pseudotachylite was found in the Stuedal schist. Optical and chemical data are given. The formation of pseudotachylite, which the author has tried to explain as a result of hot spots, has earlier been discussed. Experiments, e.g. those carried out by Bowden, Stone and Tudor (1947), show that by friction between sliding polished surfaces, visible hot spots may be developed even when the sliding speed is as slow as one or two feet pr. second and the load is about 1000 g. If the load or speed was increased, the spots become brighter and whiter, indicating higher temperatures. In general, the maximum temperature is limited by the melting-point of the solid. The speed used in the experiments varied from 50 to 450 cm\/sec., and the load beetween the surface could be varied between 1 and 10 kg. These experiments show that even along small faults or slips, high temperatures may be reached. To melt rock, the circumstances must be such that the heat energy is not conducted away too fast. This is most likely along a zone of movement surrounded by solid rock.