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Detrital tourmaline as an indicator of source rock lithology : an example from the Ropianka and Menilite formations (Skole Nappe, Polish Flysch Carpathians)

Salata D.

Geological Quarterly

2014

Vol. 58, No. 1

19--30

Tourmaline populations studied from the Campanian-Maastrichtian part of the Ropianka (Upper Cretaceous-Paleocene) and Menilite (Oligocene) formations of the Polish Carpathians, represent a mixture of first-cycle and polycyclic grains. The tourmalines of the deposits studied display very strong resemblance in terms of optical features and chemical composition. They belong mostly to the schorl-dravite series with a minor contribution of tourmalines of foititic or Mg-foititic composition. Euhedral tourmalines originated from metasedimentary rocks, while the rounded grains crystallised in Li-poorgranitic rocks or in pegmatites, Al-poor and Al-rich metasedimentary rocks. Most of the tourmalines studied crystallised during a single igneous or metamorphic event. However, tourmal ines form ng in evolving chemical conditions as well as polymetamorphic grains (having a metamorphic detrital core and metamorphic overgrowths) are also present. The chemical composition of the metamorphic tourmalines studied indicates theirformation in medium-grade metamorphic conditions. This is supported by the crystallisation temperature of the garnet-biotite inclusion present in one of rounded metamorphic tourma l ines from the Ropianka Formation. The euhedral grains derive from metasediments, directly from a massif located close to the Skole Basin. The scarcity of euhedral grains in the tourmaline populations studied suggests that their source rocks were poor in these minerals. The direct sources of rounded tourmalines (most probably polycyclic grains), may have been Paleozoic and Mesozoic sedimentary rocks of the Skole Basin foreland or crystalline rocks of remote source areas. The initial igneous and metamorphic host rocks of the tourma l ines may have been crystall ine domains of the Bohemian Massif and/or the crystalline basement of Brunovistulicum.

Source rocks for heavy minerals in lower part of Menilite Formation of Skole Nappe (Polish Flysch Carpathians), based on study of detrital garnet and tourmaline

Salata D.

Annales Societatis Geologorum Poloniae

2013

Vol. 83, No. 1

1--17

The study focused on the chemistry of detrital garnet and tourmaline from sediments of the Boryslav and Kliva Sandstone types in the Oligocene part of the Menilite Formation of the Skole Nappe (Western Outer Carpathians, Poland), with regard to provenance. Almandine and almandine-pyrope compositional varieties are the most common garnets, with minor almandine-pyrope-grossular garnet. Scarce garnet grains, with grossular and spessartine as the dominant end-members, are also present. The tourmaline belongs to the alkali tourmaline principal group and represents the schörl-dravite series. The detrital garnet and tourmaline display strong, compositional similarities to minerals, occurring in igneous and metamorphic rocks of the Bohemian Massif, as well as to detrital grains, deposited within the internal basins of the massif. This suggests that the primary rocks for the garnet and tourmaline may be crystalline complexes of the Bohemian Massif. However, other uplifted areas, similar to the complexes of the Bohemian Massif, cannot be ruled out. Such hypothetical areas could be located in the northern foreland of the Carpathian basins. Euhedral tourmaline and other minerals, occurring in the heavy- mineral assemblages studied, most probably were derived from eroded and presently not exposed, crystalline complexes, originally situated in the Skole Basin foreland or within the basin.