Naslov
Contrasting P-T-t paths from the basement of the Tisia Unit (Slavonian Mts., NE Croatia): application of quantitative phase diagrams and monazite age dating

Autori
Horváth, Péter ; Balen, Dražen ; Finger, Fritz ; Tomljenović, Bruno ; Krenn, Erwin

Izvornik
Lithos (0024-4937) 117 (2010); 269-282

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
micaschist; P-T-t paths; quantitative phase diagrams; monazite age dating; Tisia Unit; Croatia

Sažetak
Petrological investigations, quantitative phase diagram modelling and monazite dating were carried out on medium-grade metamorphic rocks from two outcrops in the Slavonian Mts., Tisia Unit (NE Croatia). Micaschists from the Kutjevo outcrop contain complexly zoned garnets with Mn-rich cores and Ca-rich rims. Mn decreases steadily from core to rim, but there is an abrupt increase of Ca between core and rim. In intercalated paragneisses and amphibolites a different kind of gradual garnet zoning was observed with a decrease of Ca from core to rim. Quantitative phase diagrams and garnet composition isopleths calculated from bulk rock analyses reveal that the Ca-poor garnet cores in the micaschists formed during an earlier event at 584-592 oC and 6.4-7.8 kbar. P-T conditions of 600-660 oC and 11-12 kbar were calculated for the garnet rim and the matrix assemblage of biotite, muscovite, plagioclase and quartz. Paragneiss and amphibolite from the Kutjevo outcrop provide a similar P-T information (P-T peak at ca. 650°C, 10-12 kbar), but do not preserve a record of the first metamorphic stage at ca. 7 kbar and 590 °C. Modelling shows that garnet was not stable in these rocks at these conditions. Staurolite mentioned previously in the literature was not observed in this study and the application of quantitative phase diagrams contoured for H2O mode isopleths supports our opinion that during the retrograde P-T path the analyzed rock did not cross staurolite-bearing fields. Micaschists from the Krndija outcrop contain zoned polyphase garnets. Phase diagram calculations reveal that Ca-rich garnet cores formed between 520 and 630 oC and 7-8 kbar. The rims of the garnets have a lower Ca content and formed at reduced pressures together with andalusite and staurolite. The conditions of this LP metamorphic stage were ca. 3-4 kbar and 530-570 oC. EMP monazite ages are generally Variscan (350 Ma) in the Krndija micaschists and around 440 Ma in the Kutjevo micaschists (pre- or early Variscan). We therefore propose that the metamorphic evolution of the Slavonian Mts. includes a pre-Variscan and a Variscan cycle.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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