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2 Acta Geologica Polonica

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High (ultrahigh) pressure metamorphic terrane rocks as the source of the detrital garnets from the Middle Jurassic sands and sandstones of the Cracow Region (Cracow-Wieluń Upland, Poland)

Meres S., Aubrecht R., Gradziński M., Sykora M.

Acta Geologica Polonica

2012

Vol. 62, no. 2

231-245

The Middle Jurassic (Upper Bathonian/Lower Callovian) sands and sandstones of the Cracow.Wieluń Upland contain detrital garnets with high contents of the pyrope molecule (30.73 mol %). The predominance of detrital pyrope garnets, and inclusions represented mainly by omphacite and kyanite, show that the garnets were derived from high (ultrahigh) pressure (H/UHP) metamorphic terrane rocks (garnet peridotites, eclogites and granulites). Their source is unknown. The Moldanubian Zone of the Bohemian Massif is closely comparable. However, the terranes between this zone and the Cracow-Wieluń Upland are dominated by almandine garnets. The relatively low proportion of almandine garnets in the examined samples indicates that transport of the detrital material could not have been from a far distant source as the garnet assemblage would otherwise be strongly dominated by almandine. A less distant possible source could have been the Góry Sowie Mts., which incorporate UHP/HP metamorphic rocks, but the exposed areal extent of these rocks is too small. It is possible that larger portions of these metamorphic rocks are buried beneath the Cenozoic cover and might have earlier represented a larger source area. Reworking of the entire heavy mineral spectra from older clastics is improbable because of the low maturity of the heavy mineral assemblages (higher proportion of less stable minerals). The source area therefore remains unknown. Most probably it was formed by primary crystalline complexes of lower crust to mantle origin, outcrops of which were not far distant from the area of deposition. Similar detrital garnet compositions were also recorded in the Outer Western Carpathians (Flysch Zone, Pieniny Klippen Belt), i.e. the crustal segments which formed the Silesian and Magura cordilleras; the Czorsztyn Swell was also formed by similar rocks.

The Eastern Sudetic Island in the Early-to-Middle Turonian : evidence from heavy minerals in the Jerzmanice sandstones, SW Poland

Biernacka J., Józefiak M.

Acta Geologica Polonica

2009

Vol. 59, no. 4

545-565

The Eastern Sudetic Island was an emerged area in the late Cretaceous shelf-sea of central Europe that delivered coarse siliciclastic material to adjacent basins. The extent of this land area during the Early-to-Middle Turonian has been reconstructed on the basis of a heavy-mineral analysis of the Jerzmanice sandstones from the North Sudetic Basin. The heavy minerals studied predominantly derive from medium to high grade metamorphic rocks, such as granulites and metabasites, calc-silicate rocks, mica schists and gneisses, and from garnet peridotites and pegmatites/granites. The interpretation of various heavy mineral species provides evidence that the major part of the detritus constituting the Jerzmanice sandstones was supplied from a relatively small area of the fore-Sudetic part of the Gory Sowie Massif and its immediate vicinity, approx. 50 km away from the depositional site. Heavy minerals and particularly the chemical characteristics of detrital garnets, Cr-spinels and tourmalines, have turned out to be excellent indicators of the provenance of these mature late cretaceous sandstones.