engleski

MORB-type vs. BARB-type ophiolites of the Dinarides: geologic and geochemical data

The Dinaridic Alpine ophiolites can be divided into two groups: 1) those of the Jurassic Dinaride Ophiolite Zone (DOZ) and 2) those of the Cretaceous-Early Paleogene (1) Sava-Vardar Zone (SVZ). However geologically and petrologically they have so far been treated as a whole, and their geotectonic setting has not been reliably established. We have investigated ophiolite terranes from both regions in order to determine their tectonic setting. Our comparison is based on trace element data and characteristic elemental ratios correlated with ophiolite settings in recent oceans. We show that the DOZ tectonite peridotites are enriched in LREE and have high TIIV ratios (up to 23), whereas the SVZ mantle rocks are LREE-depleted and have low Tl/V ratios (1-4). The DOZ cumu1ate gabbros and peridotites are characterized by increased Ni content and high Ba/Sr ratio, positive Eu anomaJies and lower Cr# of spinels, comparable with MORB cumu1ates. The SVZ cumu1ates do not showa positive Eu anomaly and are characterized byhigher concentrations of V, zr and Y, and higher K/Nb, TJ/ZI ; Zr/Sm ratios, which correlate with those from some recent back-arc settings. Essential differences between DOZ and SVZ basa!tic rocks are as follows: high-TI vs. low-TI ophioJites: TIIV = 20-50 vs. <20 ; higher Mg#, Ni, C Nb and Th. vs. higher Rb and Ba ; elementa! ratios of Sr/ZJ ; TJ/ZI ; Y/Nb, Zr/Nb, Th/Nb, Th/Th., La/Nb, La/lli and Sm/Hf are similar to those from recent back-arc settings. These geochemical data confirm the earJier geologic model of Pamić et al. (2002). These contrasting geochemical signatures are the resu1t of different geochemical processes taking place in two different settings: a) MORB along an accretionary plate margin under1ain by oceanic upper mantle, and b) BARB along a supra-subduction zone characterized by an obducting upper mantle wedge under1ain by subducted oceanic crust, which was a source of fluids.

Dinaride Ophiolote Zone; Sava-Vardar Zone; ophiolites

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