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ROLE OF METASOMATIC PROCESSES IN RUBY-BEARING MARBLES FORMATION OF THE SOUTHERN URAL MOUNTAINS
2017, 24(3):
257-262.
Rubybearing marbles of the Southern Ural Mountains are developed in the metamorphic perimeter of granitesgneisses domes where high grade metamorphic granitization and diaphthoresis have occurred. Geological research into the development and occurrence of rubybearing marbles indicate that they formed as a result of repeated transformation. Their substrate consisted of an organogenous marine limestone containing Visean faunal remains. Intensive Mg metasomatism of limestone during early progressive stages of metamorphism resulted in a substrate of dolomite composition containing faunal remains with a calcite composition. Increased temperature and pressure resulted in metamorphism of early Mg metasomatites, turning them into finegrained marble containing Visean faunal remains. Tensional stresses near the intrusive domes resulted in dedolomitization of early Mg metasomatites, giving rise to light, coarsegrained calcite marbles having polygonalgrained structure. Such carbonaceous marbles became metamorphosed around the perimeter of granitegneiss massifs. Their rheological properties allowed for plastic flow in these marbles into areas of tectonic neutrality, forming bodies of rheomorphic marbles, sometimes even among marbled limestone. Relict bodies of Mg metasomatites underwent boudinage and rotation. Flow cleavage occurred in axial blocks of interdome structures and in their steep walls. Therefore platy jointing (banding, pseudolamination) formed in the marbles. Thickness of the plates is from several millimeters to 23 m. Calcite underwent recrystallization with extension of grain size in the central parts of plates, sometimes amounting to 1525 cm in crosssection. Rubybearing marbles consist of Mgcalcite. The rock is coarsegrained, with a panidiomorphic texture. Schistosity is often observed in the plane of cleavage. Mgcalcite marble occurs among and grades into background calcite marbles, which are controlled by cleavage of flowing. It is supposed that the rubybearing Mgcalcite marbles bodies are elongated in the direction of dip. Their formation is caused by recrystallization under the action of rising metamorphogenic fluids at high temperatures and higher pressures (amphibolitic and epidoteamphibolitic facies). Rubybearing marbles formed at the end of the prograde stage of metamorphism. The early retrograde stage of metamorphism is defined by a new wave of Mg metasomatism and formation of calcitedolomitic marbles with a poikiloblastic texture from calcite or Mgcalcite marbles. Usually the boundaries of the bodies are clear, planar, and controlled by cleavage. Studies of small bodies have shown that they are elongated in the direction of dip. Usually they contain pink corundum and/or pink spinel; red corundum is replaced by red spinel. Thus the initial marine limestones were transformed into various marbles and completely lost their primary composition and bedding as a result of metamorphism, deformation, and metasomatic transformation. Rubyspinel mineralization in marbles is controlled by cleavage.
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