STRUCTURE-FORMING ROLE OF ALTERNATING MOVEMENTS IN THE ZONES OF SHEAR, TRANSPRESSION AND TRANSTENSION AS APPLIED TO LOCALIZATION CONDITIONS OF DIAMONDIFEROUS KIMBERLITES (PHYSICAL MODELING RESULTS)

Purpose. The work is aimed at studying the faulting dynamics and the types of disjunctive structural traps for ore solutions under alternating movements in the zones of shear, transpression and transtension. Methods. Physical modeling was performed in the Laboratory of Tectonophysics, Institute of the Earth's Crust SB RAS on the Fault Installation, which allowed to set up both the direction and two speeds of stamp (plate) movement (10^-4 and 10^-5 m/s). The studies were carried out on the basis of the experiments of physical modeling with the use of an equivalent material in the form of an aqueous suspension of montmorilonite clay (viscosity of 10⁶-10⁷ PA∙s). Each experiment included two stages. Stage I reproduced the conditions that correspond to shear, shear with tension (transtension) or shear with compression (transpression). Stage II included the simulation of structure forming under reverse movement of experimental installation stamps, i.e. under alternating shear of transtension or transpression. Results. The parageneses of fractures with the emphasis on extensional structures that can be favorable for kimberlite body location have been studied in the series of 8 experiments. The formation patterns of disjunctives are examined in terms of shear zone paragenesis formation in the models of known discontinuities. The extensional structures favorable for ore deposition are more characteristic of the experiments performed at slow speed. Another factor affecting the formation of the internal structure of fault zones is the vector of relative movement of stamps (plates), on which the dynamic conditions of the first and second stages depend. Consideration is also given to the combinations of right- and left-lateral shearing, transtension-transpression, and transpression-transtension. Conclusion. The physical modeling experiments have shown that the deformation rate has a significant influence on structure formation. In case of alternating movements in fault zones the deformation rate is the factor that affects the width of the fault zone and the distance between the fault systems as well as the specific set of elements in structural paragenesis. Extensional structure of the different types characterized by the highest tension amplitudes occur near the major joints of disjunction, where the dilatancy is the highest. The dilatancy is manifested most clearly in the fault zones which are formed in transpression conditions at the stage I and under transtension conditions at the stage II. The largest disjunctive structural traps associated with е-, R- and Y-fractures are observed in such fault zones.

modeling, equivalent material, faulting, alternating movements, transpression, transtension, shear zones

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