Kinematic analysis of rock flow in ductile shear zones using three-dimensional study of natural and experimental porphyroclasts.

The research deals with the kinematics in ductile shear zones and focuses on the problem of distinguishing the major flow types (monoclinic, triclinic, and more complicated flows) in natural shear zones. Aim of the research is to develop tools for recognizing the flow patterns which could be applicable in the field and laboratory studies. The approach to solution is the 3D study of mantled porphyroclasts, since these structures preserve the information about the flow in matrix and the deformation history. Methods of investigation include the field, laboratory, and experimental studies. Natural porphyroclasts will be studied using the accurate parallel-sectioning technique and the OPTIMAS image analysis system, that will be followed by the 3D reconstruction of their shapes. The field areas are the monoclinic Vochelarabina shear zone (north-eastern Baltic shield, Kola peninsula, Russia) and the triclinic Mylonite Zone (Sveconorwegian Province, Sweden). The experimental study focuses on 3D simulation of the development of porphyroclast systems in transpressionalranstensional ductile shear regimes. The experiments will be carried out using a planar shear machine and a ring shear machine. A transparent model material will be used, that allows a 3D monitoring. The scientific significance and urgency of the research are caused by the actual controversy on the problem which was inspired by the recent discovery of triclinic; shear zones. Shear zones have been commonly interpreted as plane-strain or monoclinic structures. If they are triclinic, then all the data must be reviewed and new shear direction indicators are to be established. That would mean enormous amount of work which is needless if they are monoclinic. The obtained criteria would allow recongition of the situations when the data revision is urgent. Natural porphyroclasts have not been studied yet in 3D, and this is a pioneering research. Experimental 3D study was initiated earlier, but it only begins to develop. The results are expected to be widely applied in the studies bounded up with kinematics of ductile defamation, including regional and theoretical studies as well as mineral exploration.

The research deals with ductile deformation of rocks. Rotation of large rigid mineral grains (porphyroclasts) records the history and geometry of the deformation. It was studied in three dimensions in natural rock samples and experiments.