COMPOSITION AND TECTONIC FORMATION HISTORY OF OPHIOLITES IN THE TATARKA-ISHIMBA SUTURE ZONE OF THE YENISEI RIDGE

We report results of geostructural, mineralogical, petrographic, geochemical and geochronological (40Ar/39Ar) investigations of ophiolites from the northern and southeastern fragments of the Tatarka-Ishimba suture zone of the Yenisei Ridge combined into the Rybnaya-Panimba belt. The ophiolites consist of massive and pillow-lava metabasalt, massive and layered metagabbro and metadolerite, and represent fragments of the upper part of the oceanic crust. They formed in a mid-ocean ridge or marginal sea setting from depleted mantle sources corresponding to components of the N-MORB and E-MORB geochemical types. We propose a model for the tectonic history of emplacement of the ophiolites in the Meso-Neoproterozoic time. At the Meso-Neoproterozoic boundary (Stenian–Tonian), 1051–916 Ma, a thrust system was formed and the oceanic crust fragments (ophiolites) were accreted to the passive margin of the Central Angara terrane (microcontinent). The subsequent convergence and collision of this microcontinent with the Siberian Craton (786–749 Ma) caused the formation of strike-slip/thrust deformation in the rocks of the TatarkaIshimba suture zone including the ophiolites. In the Cryogenian time (708–700 Ma), strikeslip and reverse fault deformations occurred in these rocks due to a new episode of tectonic activity caused by the transition between convergent settings – end of the collision and start of the active continental margin.