Kinematic analysis of ultrahigh-pressure–high-pressure metamorphic rocks in the Chaglinka–Kulet area of the Kokchetav Massif, Kazakhstan |
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Authors: | Hiroshi Yamamoto,Masahiro Ishikawa,Ryo Anma and,Yoshiyuki Kaneko &dagger |
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Affiliation: | Department of Earth and Environmental Sciences, Kagoshima University, Korimoto 1-21-35, Kagoshima 890-0065, Japan (email:;), Department of Environmental Sciences, Faculty of Education and Human Sciences, Yokohama National University, Yokohama 240-8501, Japan,;Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan |
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Abstract: | Abstract 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. |
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Keywords: | deformation history Kokchetav shear sense ultrahigh-pressure |
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