System organization of disjunctive tectonics in consolidated basement of Dnipro-Donets paleorift
Abstract
Formulation of the problem. The article is the second in trilogy, which exposes geological structure and geodynamic evolution of Proterozoic crystalline basement of Dnieper-Donets paleorift. Knowledge of strike-slip tectonics of intraplate geostructures with sedimentary basins belonging to them, such as Dnieper-Donets paleorift with cognominal hydrocarbon bearing basin within it, has important applied significance, owing to structure-froming and strcuture-controlling role of strike-slip faults, that cause spatial distribution of various tectono-magmatic centers, zones of fold uplifts series, structural-facial zones, salt-folds subbasins, etc., within which oil & gas fields are localised. The subject of the research is structural appearance of strike-slip tectonics in precambrian crystalline basement in the form of secondary deformed structures of rift evolution stage. The subject of studies has been structural-paleotectonic and peleogeodynamic conditions of Dnieper-Donets rift formation.
The purpose of the article. Purpose of the research has been study of structure-forming processes at the rifting stage, for which the following tasks have been resolved:
− study of territory expansion in the ancient rift zones of horizontal strike-slip dislocations;
− reconstruction of tectonical position of paleogeodynamic field’s main parameters in paleotensions of rift evolution stage;
− study of typical structural-kinematic paragenesis in identified zones of strike-slip dislocations;
− modelling of Dnieper-Donets rift formation kinematics.
Methods. Methodical approach in researches of rift stage tectonic evolution has been indentified by complexing of structural-kinematic and structural-paragenenetic methods of tectonophysical analysis for study and diagnostic of morphogenetic type of Precambrian basement dislocaion structures. Actual curvlinearity of basement faults has been converted to discrete assemblage of lineaments with overall number of 900 items, which filled output database for tectono-physics analysis of disjunctive systems.
Results. Spatial dislocation, paleotectonic position and paleogeodynamic conditions of ancient riftogenic fault systems formation has been studied. Modelling of rift formation kinematics has been carried-out based on reconstruction of main parameters of earth crust tension-deformation state at the stage of rifting. It has been shown that rifting was occurring in overall plate collision geodynamic environment under interference of local horizontal strike-slip field of paleotensions from tangential componental stretching. Under these geodynamic conditions in zones of dynamic influence of almost all regional systems of disjunctive faults, linear zones of concentration of horizontal strike-slip dislocations, creating within them typical ensembles of secondary deformed strike-slip structural-kinematic paragenesis, were forming. Elastic deformation with divergence of "cold" continental earth crust was grounded by the rifting mechanism. The main role in rifting mechanism was played by transforming faults formed following structural directions of transverse transregional fault systems. They served as unique tectonic “rails” by which opposite margins of megasegments – pull-apart basins were spreading, which consequently joined and tuned into one rift system.
Scientific novelty. The main factor and cause of continental rifting should be considered stretching deformations of earth crust in strike-slip field of geodynamic tesnsions, owing to that "embryo" subbasins, following mechanism of pull-apart basin was formed. They created "windows" for injection of mantle substance by newly built weaken zones in earth crust, and as a result they formed a steady-state "mantle window" in lithosphere, that served as distributary channel in the rift system of mantle fluids.
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References
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