Kinematic analysis of ultrahigh-pressure-high-pressure metamorphic rocks in the Chaglinka-Kulet area of the Kokchetav Massif, Kazakhstan

The central part of the Kokchetav Massif is exposed in the Chaglinka-Kulet area, northern Kazakhstan. The ultrahigh-pressure-high-pressure (UHP-HP) me tamorphic belt in this area is composed of four subhorizontal lithological units (Unit I-IV) metamorphosed under different pressure-temperature (P-T) conditions. The coesite- and diamond-bearing Unit II, which consists mainly of whiteschist and eclogite blocks, is tectonically sandwiched between the amphibolite-dominant Unit I on the bottom and the orthogneiss-dominant Uni t III on the top. Total combined thickness of these units is less than 2 km . The rocks of the UHP-HP metamorphic belt are affected by at least four de formational events post-dating peak metamorphism: (i) The earliest penetrat ive deformation is characterized by non-coaxial ductile flow in a NW-SE dir ection. The shear sense indicators in oriented samples from Unit I provide consistent top-to-the-northwest motions and those from Unit III provide top -to-the-southeast, south or south-west motions; (ii) Upright folds with sub horizontal enveloping surface refold earlier foliations including shear-ind icators throughout the metamorphic belt; (iii) The third stage of deformati on is denoted by large-scale bending around a subvertical axis; and (iv) La te localized fault (or shear) zones cut all earlier structures. The fault z ones have subvertical shear planes and their displacements are essentially strike-slip in manner. The subhorizontal structure and opposite shear direc tions between Unit I and Unit III during the earlier deformation stage sugg est north-westward extrusion of UHP Unit II.