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) metamorphic 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 Unit 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 deformational events post‐dating peak metamorphism: (i) The earliest penetrative deformation is characterized by non‐coaxial ductile flow in a NW–SE direction. 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 subhorizontal enveloping surface refold earlier foliations including shear‐indicators throughout the metamorphic belt; (iii) The third stage of deformation is denoted by large‐scale bending around a subvertical axis; and (iv) Late localized fault (or shear) zones cut all earlier structures. The fault zones have subvertical shear planes and their displacements are essentially strike‐slip in manner. The subhorizontal structure and opposite shear directions between Unit I and Unit III during the earlier deformation stage suggest north‐westward extrusion of UHP Unit II.