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

Ophiolitic blocks, rep re sented by metagabbro and ser pen tin ite con tain ing rel ict pyroxene, ol iv ine, baddeleyite, zirconolite, Ni-py rite and pyrrhotite, were found as ex otic blocks in an olistostrome in the Magura Nappe, Outer West ern Carpathians. The geo chem i cal and iso to pic fea tures of the blocks sug gest they rep re sent man tle-de rived rocks, with within-plate geochem is try sig na tures, mod i fied by subduction, with lithospheric man tle in put. A U-Pb ap a tite cool ing age (614 +/- 3 Ma) is within age un cer tainty of a pub lished U-Pb zir con mag matic crys tal li za tion age (-614 Ma) im ply ing rapid post-crys tal li za tion 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 mod el ling al low the in ter pre ta tion that the per va sive ocean-floor meta mor phism is the al ter ation in these meta-mafic rocks. These ophiolitic frag ments can be linked to the Neoproterozoic break up of Rodinia/Pannotia.