Index Geophysics

eng PLAGIOGRANITES FROM THE OPHIOLITE COMPLEXES OF DINARIDES AND VARDAR ZONE

hrv PLAGIOGRANITI IZ OFIOLITNIH KOMPLEKSA ZONE DINARIDA I VARDARA

eng Geochemical dana of plagiogranites associated with ophiolite conplexes of Central Dinaride Ophiolite Belt (CDOB) and Vardar Zone Ophiolite Belt (VZOB) are presented. Plagiogranites occur as dikes or small intrusive bodies in the upper part of the gabbrodolerite or diabase section in the ophiolite sequence. On the basis of normative An-Ab-Or diagram most of studied plagiogranites are classified as trondhjemites. They are typically low in K2O, Rb and MgO and contain low to moderate Al2O3, but light SiO2 and Na2O. Their ocean ridge granite normalized patterns of trace elements displaying low contents of HFS and high contents of LIL elements are very similar to those of the volcanic arc granites. But assuming that in trace element pattern elevated K2O and Rb contents are result of alteration, the studied plagiogranites have also strong similarity with typical Troodos supra-subduction ocean ridge granite. The using of Peacock indeks reveals that they are characterized by calcic character what is typical for supra-subduction ocean ridge granite. The studied plagiogranites are probably formed in extensional conditions above a subduction zone and in terms of their origin the most probably related to crystal-liquid differentiation process.

hrv Prikazani su geokemijski podaci plagiogranita koji se nalaze u ofiolitnim kompleksima Centralne ofiolitne zone Dinarida (CDOB) i Vardarske ofiolitne zone (VZOB). Plagiograniti se pojavljuju kao dajkovi ili mala intruzivna tijela u gornjem dijelu gabro-doleritne ili dijabazne jedinice ofiolitne sekvence. Na temelju normativnog An-Ab-Or dijagrama većina proučavanih plagiogranita je klasificirana kao trondhjemiti. Oni tipično imaju niske sadržaje K2O, FeO i MgO, niski do srednji sadržaj Al2O3, ali visoke sadržaje SiO2 i Na2O. Usporedba elemenata u tragovima u plagiogranitima s onima tipičnim za granite oceanskog grebena pokazuje da plagiograniti imaju viši sadržaj elemenata velikog radijusa (LIL elementi), a niži sadržaj elemenata malog radijusa i visokog naboja (HFS elementi). Slično ponašanje elemenata u tragovima pokazuju i graniti vulkanskog luka uspoređeni s onima u granitima oceanskog grebena. Međutim, ako se pretpostavi da je povišeni sadržaj K2O i Rb u proučavanim plagiogranitima rezultat alteracije, tada oni imaju također veliku sličnost s Trodos granitom koji je tipični predstavnik granita suptra-subdukcijskih oceanskih grebena. Upotreba Peacock indeksa polazuje da su plagiograniti karakterizirani kalcijskim karakterom što je tipično za granite supra-subdukcijskih oceanskih grebena. Proučavani plagiograniti su vjerovatno formirani u ekstenzijskim uvjetima iznad subdukcijske zone, a njihov postanak je najvjerovatnije vezan za procese kristalno-likvidne diferencijacije.

Majer, Vladimir

Garašić, Vesnica

eng Plagiogranite;Ophiolite;CDOB;VZOB;Supra-subduction ocean ridge granite;Volcanic arc granite;Crystal-liquid differentiation process

hrv Plagiogranit, Ofiolit;CDOB;VZOB;Graniti suprasubdukcijskog vulkanskog luka;Proces kristalno-likvidne diferencijacije

Faculty of Mining, Geology and Petroleum Engineering University of Zagreb

2001

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Rudarsko-geološko-naftni zbornik

ISSN 1849-0409 (Online)

Volume 13

Issue 1

eng

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