Neoproterozoic ophiolite exotic blocks in the Outer Western Carpathians, southern Poland: a record of the fast ocean-floor cooling and alterations

Abstract

Ophiolitic blocks, represented by metagabbro and serpentinite containing relict pyroxene, olivine, baddeleyite, zirconolite, Ni-pyrite and pyrrhotite, were found as exotic blocks in an olistostrome in the Magura Nappe, Outer Western Carpathians. The geochemical and isotopic features of the blocks suggest they represent mantle-derived rocks, with within-plate geochemistry signatures, modified by subduction, with lithospheric mantle input. A U-Pb apatite cooling age (614 ±3 Ma) is within age uncertainty of a published U-Pb zircon magmatic crystallization age (~614 Ma) implying rapid post-crystallization cooling. Pervasive alteration with replacement of primary minerals by low-temperature assemblages is observed in all rock fragments and is interpreted as contemporaneous with shearing. The secondary mineral assemblages and temperature modelling allow the interpretation that the pervasive ocean-floor metamorphism is the alteration in these meta-mafic rocks. These ophiolitic fragments can be linked to the Neoproterozoic break up of Rodinia/Pannotia.