BIOSTRATIGRAPHIC COMPARISON OF TWO NEOTETHYAN OPHIOLITES BY RADIOLARIAN, WESTERN IRAN

Ophiolites of Alpine-Himalayan Orogenic belt are remnants of the Tethys Oceanic crust. The Bitlis-Zagros-Oman zone in the Alpine-Iranian sector of this orogenic belt contains a number of ophiolites (e.g., Samail in Oman, Neyriz and Kermanshah in Iran, Hatay in Turkey). Recent studies of the Khoy ophiolite, which is located in northwestern Iran, suggests that this complex is another ophiolite of the Bitlis-Zagros-Oman Zone which has been overlooked in previous tectonic models for the area (Ghazi and Hassanipak, 1999; Kariminia et al. 2001). The similarity of Radiolarian assemblage from volcanic member of the Khoy ophiolite (e.g., Dictyomitra torquata, Dictyomitra formosa, Pseudodictyomitra sp., Xitus sp., Petallula sp.) with those of Kermanshah and Samail ophiolites suggests all these three ophiolites are remnants of an oceanic crust with Coniacian age, which was located at the northern margin of the Arabian Plate. Field observations from the Khoy and the Kermanshah ophiolites show a vast stratified radiolarian chert succession for the Kermanshah Ophiolite, which except of a few small patches is completely absent in the Khoy Ophiolite. On the other hand the Khoy ophiolite contains one of the most extensive basaltic unit of any ophiolite in the region (with pillow and mega-pillow structures), representing a tremendous amount of submarine volcanism. The similarities in microfossil record together with the differences in lithologic record between the neighboring Khoy and Kermanshah ophiolites suggest a broad seaway or slow spreading for the Kermanshah ophiolite changing to a deep and narrow oceanic environment or fast spreading for the Khoy ophiolite.