Ancient age of zircons and problems of dunits genesis from gabbro-hyperbasez complexes of folded areas and central type platform massives

• Main Authors: Vsevolod N. Anfilogov, Artur A. Krasnobaev, Vyacheslav M. Ryzhkov
• Format: Article
• Language: English
• Published: A.N. Zavaritsky Institute of Geology and Geochemistry 2018-10-01
• Series: Литосфера
• Subjects: дунит; циркон; возраст; фазовые равновесия; бадделеит; рестит; генезис; dunite material; zircon; age; phase relations; ultrabasite; origin
• Online Access: https://www.lithosphere.ru/jour/article/view/249
• ISSN: 1681-9004; 2500-302X

Some problems appeared after determinations of the old age of dunite material in the ultrabasite massifs of the folded regions and zonal massifs on the continental plateaus: 1) the problem of equilibrium of zircon and olivine + pyroxene composition in ultrabasite; 2) the problem of different age of zircon in every massif of ultrabasite and the way of the zonal zircon crystal formation; 3) the problem of the origin of the most old dunite material in ultrabasite massives; 4) the problem of formation of zonal zircon crystals in dunite. Experimental investigation of phase equilibrium in MgO-SiO2-ZrO2 system showed that zircon able to crystallize coincidentally with olivine and pyroxene. It was found that zircon in dunite is stable to 1450°C. Zircon is replaced to baddeleite at more high temperature. It is shown that the zonal zircon crystal can be formed by its transformation to baddeleite and the inverse process. The mechanism of dunite material accumulation at partial melting of mantle peridotite and possible way of transport of the residue dunite to the surface in diaper form are considered. The difference between ultrabasite of the Platinum belt of the Urals and Alpine type of ultrabasite is discussed. It is proposed that massifs of the Alpine type ultrabasite were intruded сlose to the surface where they interacted with porous water. The interaction of hyperbasites with the pore fluid will lead to their intensive serpentinization, the redistribution of chromium and its concentration in the form of ore bodies.