Młodopaleozoiczny wulkanizm południowo-wschodnich okolic Wałbrzycha

Abstract

YOUNG PALAEOZOIC VOLCANISM IN AN AREA SE OF WAŁBRZYCHThe present paper is based on geological material obtained from bore-holes and mining operations in an area lying east of Wałbrzych, within the Inner-Sudeten basin (fig. 1). The prospecting drillings have penetrated the section of Lower Carboniferous coal measures (fig. 3). The here described layers are Wałbrzych beds containing coal seams, Biały Kamień beds consisting of sandstones and conglomerates (chart 1) and Żacler beds made up mainly of arkose sandstones. Over the Żacler (Westphalian) beds the occurrence is noted locally of porphyritic tuffites, indicating pre-Permian volcanic activity. Strongest volcanic phenomena are here associated with the eruptive stage of the Rotliegendes. The volcanic cycle of the Rotliegendes begins with basic lavas of the meIaphyric type and their tuffs, passing into progressively more acid lavas. The terminal members of this cycle consist of lavas and corresponding effusive rocks of the quartz-parphyry group. Within the Niedźwiadki hills lying E of Wałbrzych (fig. 2) porphyries and their tuffs merge with the silI introduced between variously resistant layers in the Wałbrzych beds (fig. 3). Effusive rocks (lapilla tuffs, volcanic breccias, tuff agglomerates and tuffites) are grouped around volcanic necks. Porphyries and their effusives are dissected by a melaphyre dyke with a narrow belt of basic tuffs suggesting for the basic eruptive rocks a younger age than that of the more acid effusive constituents. The age of the porphyries may be established as bordering on the upper Westphalian and the Stephanian. Subsurface sub-volcanic breccias caused by violently ascending steam, gases and lava have been yielded by bore-hole Y. The thick porphyry sill (fig. 4) is a magmatic rock. Some subvolcanic breccias contain porphyry material, others lack it. The breccias primarily consist of sandstones, shales and conglomerates from the Biały Kamień beds. Plate LIV, fig. 1 shows thin zigzag coal seams whose argillaceous constituents have been crushed and bent owing to mechanical shifting and bending. These breccias display similarities with mud volcano breccias. Steam and gases owed their origin to the cooling porphyry sill. During expansion they crumbled up the adjacent rocks so that mud and the ascending rock fragments filled the free spaces there. Sub-volcanic breccias which pierce coal seams are a hindrance to mining operations. In literature they are commonly referred to as ,,Riegel". So far they have been regarded as volcanic neck breccias, explosive pipes (ExplosiverØhre) and directly associated with volcanic activity. The ancient opinions considered them as "StrudellØcher" or "Reibungsbreccien".