Wgłębne podłoże Karpat

Piotr Karnkowski

Abstrakt


DEEP-SEATED BASEMENT OF THE CARPATHIANS

Summary
During the last 20 years about 90 boreholes 2500 to 5500 m deep were drilled in the area of the Carpathians. Twenty five of these boreholes penetrated folded Flysch, Miocene, Mesozoic as well as Paleozoic deposits of the platform type and entered weakly metamorphosed and strongly folded Precambrian phyllites and crystalline rocks (Figs. 1-2; Table 1). Crystalline rocks were not found in the area of the Carpathian Forefield, except for those pierced by the borehole Puńców 1 which may be explained by the thickness of phyllites greater than beneath the Carpathians. Precambrian metamorphic and crystalline rocks were found beneath Mesozoic or Paleozoic rocks or directly beneath Flysch series in the basement of the Flysch Carpathians, along the section from Przemyśl to Cieszyn (Figs. 1-2). Folded Precambrian phyllites were recently found directly beneath the Flysch (Lower Cretaceous Spaskie Beds) in two boreholes at the depths of 4050-4098 m (Fig. 4). In the Carpathians, the Cambrian deposits with guide trilobites were penetrated by the borehole at Goczałkowice. End parts of the columns of boreholes Borzęta IG-1 and Dobczyce 8, represented by almost black siltstones and claystones with a shade of violet and strongly diagenesed but without any traces of metamorphism were tentatively assigned to the Cambrian. In the basement of the Carpathian Mts the Silurian rocks were penetrated by 3 boreholes. They are represented by polymictic conglomerates consisting of well-rounded fragments of igneous and sedimentary rocks. The Devonian and Carboniferous rocks were recently penetrated by over a dozen boreholes whilst the Permian was found in a few boreholes only. The deposits assigned to the Permian are very thick (1370 m thick) close to the margins of the Carpathians and they may partly belong to the Triassic. The Triassic was found in 5 boreholes situated at the extension of the Nida Basin beneath the Carpathian overthrust in the area of the Carpathian Przedgórze. Its thickness rapidly decreases towards the south. Jurassic rocks are discordantly overlying strongly faulted and denuded post-Variscan surface. They were found in the Carpathian basement in several boreholes, in the area from the Robczyce meridian on the east to the Cracow meridian of the west. The borehole Jastrzębia 1 (at the depth of 4022 m) is here the most southern locality of Oxfordian limestones. Jurassic rocks were penetrated by numerous boreholes in the Carpathian basement. Upper Cretaceous (Cenomanian, Turonian and Sanonian) rocks were found in several boreholes at the extension of the Nida Basin, beneath the Carpathians. Sandy Cenomanian deposits and Malm limestones are oil and gas collections. Flysch deposits are thrusted over the Miocene (Lower Badenian) deposits represented by siltstones intercalated by siltstone sandstones, claystones and polymictic conglomerates interpreted as equivalents of Dębowiec conglomerates overlying clay-siltstone sub-Dębowiec series. The Flysch Carpathians are thrusted over the Neogene deposits. The drilling works have shown that the Flysch is thrust over the Lower Carpathian, Badenian and Sarmatian deposits along 50 km distance. The thrusting of the Flysch Carpathians over their forefield proceeded gradually from the Early Miocene till the Early Sarmatian. The subduction of the forefield beneath the Carpathian Mts resulted in the fact that its basement descended so deeply that it underwent partial melting. This assumption is in agreement with the results of recent studies and is here illustrated by schematic sections through the Carpathians (Figs. 3-4).

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