%0 Journal Article
%T Geochemistry, petrology and tectonomagmatic significance of basaltic rocks from the ophiolite m¨¦lange at the NW External-Internal Dinarides junction (Croatia)
%A Damir Slovenec
%A Bo ko Lugovi
%A Irena Vlahovi
%J Geologica Carpathica
%@ 1336-8052
%D 2010
%I 
%R 10.2478/v10096-010-0016-1
%X At the NW inflexion of the Sava-Vardar Suture Zone ophiolite m¨¦langes, known as the Kalnik Unit, form the surface of the slopes of several Pannonian inselbergs in the SW Zagorje-Mid-Transdanubian Zone. The Mt Samoborska Gora ophiolite m¨¦lange, thought to be a part of the Kalnik Unit, forms a separate sector obducted directly onto Dinaric Triassic carbonate sediments. Basaltic rocks, the only magmatic rocks incorporated in the m¨¦lange, include Middle-Triassic (Illyrian-Fassanian) alkali within-plate basalts and Middle Jurassic (uppermost Bathonian-Lower Callovian) tholeiitic basalts. The latter sporadically constitute composite olistoliths, and are geochemically divided into N-MORB-like (high-Ti basalts) and transitional MORB/IAT (medium-Ti basalts). These geochemically different rocks suggest crystallization at various tectonomagmatic settings, which is also indicated by the rock paragenesis and host clinopyroxene compositions. Alkali basalts reflect melts derived from an OIB-type enriched mantle source [Ti/V= 62.2-82.4; (La/Lu)cn= 6.4-12.8] with Nd-Sr isotope signatures close resembling the Bulk Earth [¦ÅNd(T=235 Ma)= + 1.6 to + 2.5]. They are recognized as preophiolite continental rift basin volcanic rocks that closely predate the opening of the Repno oceanic domain (ROD) of the Meliata-Maliac ocean system. The high-Ti and medium-Ti basalts from composite blocks derived from a similar depleted mantle source (¦ÅNd(T=165 Ma) = + 6.01 vs. + 6.35) succesively metasomatized by expulsion of fluids from a subducting slab leading to a more pronounced subduction signature in the latter [Ti/V=31.6-44.8 and (Nb/La)n=0.67-0.90 vs. Ti/V=21.5-33.9 and (Nb/La)n=0.32-0.49]. These composite blocks indicate crust formation in an extensional basin spreading over the still active subducting ridge. The majority of high-Ti basalts may represent the fragments of older crust formed at a spreading ridge and incorporated in the m¨¦lange of the accretionary wedge formed in the proto-arc-fore-arc region. The Mt Samoborska Gora ophiolite m¨¦lange represents the trailing edge of the Kalnik Unit as a discrete sector that records the shortest stage of tectonomagmatic evolution related to intraoceanic subduction in the ROD.
%K Triassic-Jurassic
%K Croatia
%K Samoborska Gora Mts
%K proto-arc extension
%K back-arc spreading
%K alkali within-plate basalts
%K tholeiitic basalts
%K ophiolite m¨¦lange
%U http://versita.metapress.com/content/u408328n87394851/?p=acc84d9a5d49493a9edeab935502cb75&pi=1