O strefie dyslokacyjnej Rozdroża Izerskiego w Górach Izerskich

Abstract

DISLOCATION ZONE OF ROZDROŻE IZERSKIE IN THE IZERSKIE MOUNTAINSSummaryIn West Sudetes, between Szklarska Poręba and Świeradów Zdrój, in the vicinities of Rozdroże Izerskie, quartz rocks occur so far reckoned as a vein formation, the presence of which has variously been interpreted. G. Berg (1926), for example, was of the opinion that here an old tectonic scar occur, but he thought that the quartz itself is of vein origin. Similar opinion was expressed by K. Smulikowski; however, this scientist did not explain the origin of the quartz considered. Other research workers maintained that the quartz from the Rozdroże Izerskie area represented a vein formation, however, the way of its intrusion was variously interpreted. On the basis of a versatile recognition of geological problems connected with the quartz occurrence in the Rozdroże Izerskie area, the present author decided to explain both petrogenetical character of the formation and mechanics or its origin. Petrogenetical analysis has demonstrated that the main quartz mass does not bear a vein character, but bas originated from mylonitized, hydrothermally and metasomatically altered rocks of tectonic zone. Alteration of these rocks was so strong and co-ordinated that it was responsible for the formation of a specific rock environment characterized by a series of petragraphical varieties strongly different from those of the rocks occurring beyond the dislocation zone. To these rocks belong hornfelses and various structural varieties of gneisses. Within the tectonic zone thin-laminated mylonitic gneisses, hornfels schists (strongly quartzous) and banded quartz rocks have been formed, among which a series of secondary varieties can be distinguished. Microstructural investigations allowed to trace a series of camroscopically invisible features proving a strong, mechanical remodelling of rocks in the narrow dislocation zone, leading also to a formation of new direction of lamination, almost perpendicular here to regional lamination. Three directions of lamination have been encountered in the area considered: 1 - relict lamination, which in relation to the formation of tectonic zone represents a pre-deformation lamination and has been preserved only in quartz as bands of microlites left after the incompletely etched primary minerals; 2 – syntectonic lamination being in accordance with the extension of tectonic zone; 3 - recrystallization lamination, almost perpendicular to the second lamination. Analysis of small structures found in a stone quarry, Izerskie Garby area, has shown the presence of foliation characterized by two directions, the first one of a NNE-SSW direction, dipping to ESE, the second one of a NE-SW direction, dipping to SE. Beyond the tectonic zone the foliation shows a general direction ESE-WNW, with a dip towards NE. The fissures reveal some interesting properties. The most important is that the tectonic zone reacted against tangential deformations as a completely separate and stiff rock mass characterized by a peculiar coordination scheme. Linear directions of the zone of dislocations are identical with the prevailing directions of linear structures in gneisses and hornfelses. This proves that they are younger than the time of formation of tectonic zone in the Rozdroże Izerskie area, since they could not suffer intense plastic deformations. Young tectonic deformations were responsible for the disintegration of the uninterrupted tectonic zone into blocks, through homogenous, related and series slides. This caused formation of a kind of shear fold with its front in the Izerskie Garby area. According to the present authors the tectonic zone of Rozdroże Izerskie may represent a type of deep fault developed on shear plane. Tectonic predisposition of this fault has enabled migration of solutions and vapours from deep zones of the earth crust, where geothermic degree and temperature increasing during friction of deformed rock masses could strongly change the products under discussion. In this way also greater masses of silica could have been moved, which passed then into solutions and, migrating upwards, hydrothermally changed rocks of the tectonic zone and even sedimented in the form of separate veins. Such active alterations might have increased during intrusion of the Karkonosze granite.