Uwagi o wulkanitach permskich w okolicach Tłumaczowa (wschodnia część depresji śródsudeckiej)

Abstract

 Na podstawie wyników badań terenowych w okolicach Tłumaczowa w depresji śródsudeckiej dokonano reinterpretacji następstwa zjawisk wulkanizmu autuńskiego. Relacje przestrzenne między wulkanitami permskimi i skałami osłony pozwoliły stwierdzić intruzywny charakter andezytów i związanych z nimi skal piroklastycznych (brekcje intruzyjne). Subwulkaniczny etap aktywności andezytowej poprzedzony był eksplozywną działalnością wulkaniczną, w wyniku której powstały tufy ryolitowe.

SOME REMARKS ON PERMIAN VOLCANIC ROCKS IN THE VICINITIES OF TŁUMACZÓW (EASTERN PART OF THE CENTRAL SUDETIC DEPRESSION)

The paper presents results of geological studies on Autunian sedimentary and volcanic rocks occurring in the vicinities of Tłumaczów. Sedimentary rocks forming upper part of the section represent a monotonous complex of fine detrital deposits. Middle part of that complex displays pyroclastics rocks and volcanic lavas. According to S. Kozłowski (1958, 1963), the development of Autunian volcanism proceeded in three stages in this area. Each of these stages began with extrusions of andesite lavas which were followed by those of rhyolite lavas. Andesite tuffs represent facies equivalents of andesites, and the rhyolite – of rhyolites.

My studies showed that the first stage of volcanic activity in this area was connected with deposition of rhyolite tuffs. The tuffs were originating in time of sedimentation of the Zagórzyn building sandstone member. The stage of acid volcanism was followed by that of andesite activity, resulting in origin of lenticular andesite bodies. The bodies were presumably stopped in cover rocks, not penetrating them. Andesite magma was migrating upwards along tensional fissures formed in the basement of the Central Sudetic Depression in time of subsidence of its floor. Pyroclastic material related to andesite magma was also unable to penetrate through the cover of sedimentary rocks. That is why pyroclastic andesite rocks may represent breccia of the intrusive type – tuffisite (K. Dziedzic, 1980a, b, 1981).

An important problem rised in this paper is that of the age and chronology of the volcanic phenomena.

Assuming surface nature of the volcanism, the eruptive complex may be interpreted as coeval with rocks in which the volcanites occur. Subvolcanic model makes plausible wider interpretation of time interval of the volcanic activity. Centres of the rhyolite-type eruptive volcanism have undoubtedly been active in time of sedimentation of the Zagórzyn building sandstone member. The activity of andesite magma has been subsequent in relation to the origin of acid volcanic rocks. Therefore, it appears that Permian volcanism was developing in two stages in the vicinities of Tłumaczów.