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Granity "zimne" i "gorące"-charakterystyka i optymalizowanie metod datowania cyrkonów

100%

Klimas K.

tom Vol. 57, nr 7

567-568

A petrogenetic comparative study of zircons rom the mylonites of the Niemcza Shear Zone and the gneisses of the Góry Sowie Block (SW Poland)

51%

Klimas K. , Kryza R. , Mazur S. , Jendrzejaczyk M.

Geologia Sudetica

2003

tom Vol. 35

1-12

The morphological features and typological distributions of zircon in the mylonites of the Niemcza Shear Zone (NZ) and in the gneisses and migmatites of the Góry Sowie Block (GSB), in the NE part of the Bohemian Massif, SW Poland, provide important petrogenetic indicators in the strongly deformed metamorphic rocks. The observed similarities between the zircon populations (combined with other field and petrographic evidence) strongly suggest that at least a part of the mylonites developed at the expense of rocks similar to the GSB gneisses and migmatites. The protoliths of the gneisses and migmatites (both in the GSB and within the NZ) were predominantly of sedimentary character, but the zircons suggest that crustal-type granites (in the case of the NZ gneiss and mylonite protoliths) and hybrid mantle/crustal-type granites (in the case of the GSB migmatite protoliths) could have been important sources for the original, mostly detrital (?) material. The large proportion of zircon grains in the NZ mylonites, showing effects of disintegration, can result from sedimentary abrasion of detrital material, and this apparently corroborates the hypotheses that a part of the NZ mylonites derived from protoliths other (more strongly reworked by sedimentary processes?) than those typical of the gneisses and migmatites of the GSB. However, there is also evidence that mylonitization could have influenced the morphometric features of the zircon crystals, generally increasing the proportion of fractured and broken crystals and, most spectacularly, reducing the mean size of the zircon grains in the mylonites. The controversy remains open and to find better constraints would require further detailed petrological studiem

Gneiss protolith ages and tectonic boundaries in the NE part of the Bohemian Massif (Fore-Sudetic Block, SWPoland

45%

Oberc-Dziedzic T. , Kryza R. , Klimas K. , Fanning M. C. , Madej S.

2005

tom Vol. 49, No. 4

363--378

Published geochronological data, petrology, geochemistry and geological context of orthogneisses in the Strzelin and the Stachów complexes (NE-part of the Fore-Sudetic Block), together with structural observations help to locate the northern extension of the boundary between the East and West Sudetes within the poorly exposed NE margin of the Bohemian Massif. The Strzelin complex, in the east, comprises the Strzelin gneiss, with zircon ages of 600š7 and 568š7Ma, and the Nowolesie gneiss with a mean zircon age of 1020_ 1Ma. The Stachów complex to the west, which forms several tectonic klippen in the Strzelin Massif and in the Lipowe Hills Massif, contains the Gościęcice gneiss and pale Stachów gneiss, both yielding Late Cambrian zircon ages (~500š5 Ma). The orthogneisses in both complexes correspond to peraluminous S-type granites, but have different inherited zircon ages and display contrasting trace element characteristics, indicating different sources and petrogenetic histories. Based on the ages, petrology and overall geological context, the Strzelin orthogneiss is similar to the Keprník orthogneiss of the East Sudetes, whereas the orthogneisses of the Stachów complex correspond to rocks known from theWest Sudetes (e.g. the Izera and Śnieżnik orthogneisses). The Stachów and the Strzelin complexes are separated by the Strzelin Thrust, which may be interpreted as the northern extension of the boundary between the East and West Sudetes, i.e. part of the boundary between the Brunovistulian and Moldanubian terranes of the NE part of the Bohemian Massif.