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A Carboniferous/Permian, calc-alkaline, I-type granodiorite from the Małopolska Block, Southern Poland: implications from geo chemi cal and U-Pb zircon age data

Żelaźniewicz A., Pańczyk M., Nawrocki J., Fanning M.

Geological Quarterly

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2008

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Vol. 52, No 4

301-301

EN

A granodiorite from bore hole WB-102A in the Dol ina Będkowska, the Małopolska Block (MB), South ern Po land, yielded a mean U-Pb zir con age of 300 š3 Ma with SHRIMP II. No in her ited older com po nent was de tected. Geo chemically, it is a K-rich, I-type, calc-al ka line granodiorite with su pra-subduction char ac ter is tics (neg a tive Nb and Ti anom a lies). Silicic ig ne ous rocks are abun dant at the MB mar gin along the Kraków-Lubliniec Fault Zone (KLFZ) across which it ad joins to the Up per Silesian Block (USB) where such rocks are scarce. Both blocks be long to the Variscan fore land. Gra nitic rocks can not, how ever, gen er ate at fore land set tings. Thus, the hy poth e sis is put for ward that the par ent melt for the silicic rocks was de rived from the thick ened lower crust of the Variscan orogenic belt ow ing to extensional de com pres sion melt ing, and trans ported away to wards pul-apart open ings de vel oped along the crustal-scale fault zone (KLFZ) that un der went a com plex strike-slip his tory around the Car bon if er ous/Perm ian bound ary.

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New Late Vendian palaeogeography of Baltica and the TESZ

Nawrocki J., Boguckyj A., Katinas V.

Geological Quarterly

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2004

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Vol. 48, No 4

309--316

EN

New palaeomagnetic poles obtained from the Vendian tuffs and basalts of western Ukraine indicate the necessity of a substantial revision of the Late Vendian-Early Cambrian palaeogeography of the Baltic plate. The palaeopole calculated for the most stable component isolated from the Vendian tuffs and basalts is far away from the Vendian-Cambrian apparent polar wander path (APWP), constructed on the basis of Scandinavian poles but is very close to the pole recently isolated from the Vendian sediments of the White Sea Region. Depending on the polarity of the newly-determined Late Vendian pole, two palaeogeographic models of the Baltic plate in the Late Vendian-Early Cambrian are possible. In our preferred model the Baltic plate moved at that time from the moderate southern latitudes to the equator rotating anticlockwise of ca. 120 degrees Celsius. This reconstruction explains the geological structures of the marginal zones of Baltica better than the previously proposed stationary model of the Late Vendian-Cambrian Baltica. According to the new late Vendian palaeogeographic scenario, the European, passive margin of Baltica was separated from an active, Avalonian margin of Gondwana. The Late Neoproterozoic tectonic structures of the Brunovistulian Terrane and the Małopolska Block were developed near the present day southwestern corner of Baltica that was tectonically active at that time. Alternative reconstruction shows the Baltic platemoving from the moderate northern latitudes in the Vendian, crossing palaeoequator in the latest Vendian, and reaching moderate southern palaeolatitudes in the Late Cambrian. This model, however, would have required exceptionally high plate velocity (ca. 33 cm/year).

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Gdzie była płyta bałtycka we wczesnym kambrze ?

Nawrocki J.

Przegląd Geologiczny

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2003

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Vol. 51, nr 9

744-747

PL

Najnowsze dane paleomagnetyczne wskazują, że na przełomie wendu i kambru płyta bałtycka mogła znajdować się w strefie równikowej. Orogen późnokadomski może być częściowo wynikiem konwergencji płyty bałtyckiej i Gondwany. We wczesnym kambrze terrany Brunovistulikum i Małopolski ulokowane były w brzeżnej części obszaru objętego wcześniej orogenezą kadomską, w pobliżu dzisiejszej południowej krawędzi płyty bałtyckiej. Terrany te znajdowały się tam już od środkowego proterozoiku zajmując skraj rozwiniętego miedzy płytą amazońską a bałtycką pasa grenwilskiego. Za taką interpretacją przemawia grenwilski wiek detrytycznych cyrkonów z osadów kambru terranu małopolskiego. Nie można jednak definitywnie wykluczyć, że terrany te będąc fragmentem północnego obrzeżenia Gondwany zostały stamtąd oderwane w ciągu kambru. Obydwa rozwiązania implikują późniejszy wielkoskalowy transport tych jednostek wzdłuż SW krawędzi płyty bałtyckiej do obecnej ich pozycji. Terran małopolski odbył tę wędrówkę przed dewonem lub nawet przed środkowym ordowikiem, na co wskazują dane paleomagnetyczne.

EN

New Early Cambrian geographic reconstruction locates the Baltic plate in the equatorial position. The late Cadomian orogen, developed between present eastern and southern margin of Baltic plate andNW margin ofGondwana, could be partly considered as a result of convergence of these plates. In the Early Cambrian the Małopolska and Brunovistulian terranes were located in the area of Cadomides, close to the present southern margin of Baltica. The Grenwilian ages of detrital zircons from the Małopolska terrane indicate that it could have been located there in the Middle Proterozoic as well. It is not be to excluded, however, that Małopolska and Brunovistulian terranes coupled the southern margin of Baltic plate in the Cambrian time after derivation from the northern margin of Gondwana. For both solutions the subsequent dextral tectonic transport of these units along the Baltic margin is required. The Małopolska terrane was moved into present position before the Devonian or even before the Middle Ordovician.