engleski

A Tectono-magmatic correlation of basaltic rocks from ophiolite mélanges at the North-Eastern tip of the Sava-Vardar suture Zone, Northern Croatia, constrained by geochemistry and petrology

Ophiolite mélanges of Mts. Kalnik and Ivanščica form the northern sector of the Kalnik Unit and represent the northeasternmost surface tip of Sava-Vardar Suture Zone. Petrological, geochemical and isotopic characteristics of extrusive rock blocks incorporated in the mélanges, particularly of pillow basalts altered to spilite in association with radiolarian cherts, allow the rocks to be separated into five distinct groups. Each group has an age-marker based on the radiolarian assemblage in the associated cherts and/or on isotope dating which, along with previous published data on the Kalnik Unit, provide detailed analysis of the approximately 80 Ma long geodynamic evolution of the Repno Oceanic Domain - a part of Meliata-Maliak ocean system. The rock groups are: (1) Late Anisian alkali basalts [(La/Lu)cn=5.9-7.2 ; εNd(T)=+2.96 ; Cpx-TiO2=3-6 wt.%] related to a terminal phase of intracontinental rifting. (2) enriched E-MORB-type basalts [(La/Lu)cn=2.4-2.8 ; εNd(T)=+4.74 ; Cpx-TiO2=2.1-2.9 wt.%] and depleted E-MORB-type basalts [(La/Lu)cn~1.5 ; εNd(T)=+5.26 ; Cpx-TiO2=1.9-2.3 wt.%] which reflect successive proto-oceanic crust crystallized at the ridge during early Ladinian and late Ladinian, respectively. (3) middle Carnian T-MORB-type basalts [(La/Sm)cn=0.79-0.87 ; εNd(T)=+6.63 ; Cpx-TiO2=1.2-2.2 wt.%] representing crust from an evolved spreading center. (4) N-MORB-type basalts [(La/Sm)cn=0.67-0.87 ; εNd(T)=+6.58 ; Cpx-TiO2=0.6-1.9 wt.%] with inherited suprasubduction signatures that diminish from late Carnian basalts [(Nb/La)n=0.81] to the Bajocian basalts [(Nb/La)n=1.1], and middle Jurassic (Bathonian ?) N-MORB-type basalts with recurrent subduction related influence [Nb/La)n=0.72 ; (La/Sm)cn=0.76 ; εNd(T)=+6.23]. (5) late Bathonian medium-Ti [(Nb/La)n=0.24-0.72 ; εNd(T)=+6.30 ; Cpx-TiO2=0.6-1.1 wt.%] to late Oxfordian low-Ti IAT-type basalts [(Nb/La)n=0.12-0.22 ; εNd(T)=+6.31 ; Cpx-TiO2=0.2-0.6 wt.%] which reflect melts derived from metasomatized and successively depleted mantle wedge in an extensional proto-arc setting.

geochemistry; petrology; WPAB; E-MORB; T-MORB; N-MORB; IAT; ophiolite mélange; Sava-Vardar Suture Zone; Mts. Kalnik and Ivanščica; Croatia

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