Mineralogical and geodynamical conditions of transformation of peridotites from ophiolites in the Marmarosh zone roc
Journal Title: Геодинаміка - Year 2016, Vol 21, Issue 2
Abstract
Purpose. The purpose of our research is to reconstruct geodynamic condition of transformation of Marmaroch zone peridotites. This investigation is based on the study of rock petrography, chemical composition of minerals and recognizing of thermodynamic condition of mineral formation. Methodology. The occurrences of peridotites bodies in the basin of Mala Ugolka and Velyka Ugolka river have been studied. Laboratory study includes petrographic microscopic observations and analysis of mineral composition by using scanning electron microscope equipped with an energy dispersive spectrometer. Results. Ophiolites of the Marmaroch zone rocks are represented by cataclastic varieties of lherzolites and harzburgites. Rocks are characterized by the following minerals: olivine, orthopyroxene, clinopyroxene, amphibole, talc, chlorite, serpentine, magnetite, spinel. Based on microanalitycal data, the new varieties of spinel in peridotites have been recognized for the first time. According to Pavlov’s diagram (Pavlov, 1949), the first group of spinel can be attributed to pycotite, the second one to chrom-pycotite. Two equilibrium mineral association in ophiolite peridotites were originally distinguished: first – olivine+spinel+ orthopyroxene+clinopyroxene, second – spinel +amphibole+talc. In the context of temperature and pressure of mineral transformation, some mineral association have been analysed. For spinel and olivine-spinel geothermometer P-T parameters for first mineral association are estimated in a range – 900–1290 °С, ~ 15 kbar; for second mineral association – 430–450 °С, 4,0–4,5 kbar. Thermodynamic conditions of transformation of peridotites are displayed in the degree of partial melting and spreading velocity. First mineral association shows melting degree not exceed 14 %, that is the characteristic of slow-spreading peridotites; second mineral association shows 25 %, that is the characteristic of high-spreading peridotites. First stage of peridotite formation can be related to the slow-spreading condition in spinel peridotite zone of oceanic crust. On the second stage, peridotites are changed in above-subduction zone under condition of back-arc spreading. Scientific novelty. Application of scanning electron microscope equipped with an energy dispersive spectrometer enabled to specify the mineral content and petrotypes of peridotites, to distinguish two equilibrium mineral association, to determine thermodynamic conditions of formation and transformation of peridotites from Marmaroch rocks zone. Original model of multistage formation of peridotites in the Ukrainian Carpathians is proposed. Practical meaning. The study of substantial and geodynamic features of peridotite evolution is topical from point of view of problems, that concern Earth crust formation and formation of folded region lithosphere (based on the example of the Ukrainian Carpathians). The obtained results can be bused to forecast estimation of ore potential, related to the studied peridotite complexes
Authors and Affiliations
N. Bilyk, l. Generalova, I. Yatsenko, V. Stepanov
Keywords
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