NEW DATA ON THE MINERALOGY OF SUPRA-SUBDUCTION OPHIOLITES OF THE TEKTURMAS MOUNTAINS (CENTRAL KAZAKHSTAN)
Stepanets V.G. Levin V.L. Togizov K.S. Silachyov I.Yu. Zheltov D.А.
2022National Academy of Sciences of the Republic of Kazakhstan
News of the National Academy of Sciences of the Republic of Kazakhstan, Series of Geology and Technical Sciences
2022#2022Issue 5219 - 237 pp.
The article is devoted to one of the typical problems of the geology of plutonic ophiolites of Central Kazakhstan. For the first time, mineralogical and geochemical studies of peridotites of the Tekturmas mountains have been carried out using precision methods of analysis, which gave grounds to substantiate their supra-subduction environment of formation. The electron-probe method showed that peridotite chips, obtained from heavy mineral concentrate (earlier, source of zircon), contain orthopyroxene, olivine-chrome spinel and olivine-magnetite aggregates, which allowed not only to determine the chemical composition of the minerals but also to calculate such important parameters of chrome spinel as Cr-number (Cr#), Mg-number (Mg#) and iron oxidation level (Fe+3#=Fe+3/(Fe+3/Fe+2)). Chromospinelides in peridotites are in their majority related to subferrialumochromite (Cr#=0.63-0.75, Mg#=0.23-0.33, Fe+3#=0.222-0.333), rarely to alumochromite (Cr#=0.54-0.69, Mg#=0.27-0.46, Fe+3#=0.165-0.279); extremely rare are ferrialumochromite (Cr#=0.64-0.76, Mg#=0.16-0.24, Fe+3#=0.394-0.434), ferrichromite (Cr#=0.78, Mg#=0.29, Fe+3#=0.248) and chromite (Cr#=0.85, Mg#=0.26, Fe+3#=0.174). Secondary magnetite contains impurities of NiO =0.01-0.28 wt%, Cr2 O3 =0.10-0.21 wt% typical for chromespinelides, which it replaces. The primary magnetite does not contain such impurities. Along with the presence of polyform chromite in the pre-arc peridotites, extensive development of secondary magnetite masses was identified. The secondary nature of the harzburgites was established based on the presence of secondary orthopyroxene in the dunite. They contain high-magnesium olivine (Fo=90.25-92.47), high-magnesium orthopyroxene (En=89-91) and have low concentrations of CaO (0.01-0.50 wt%), Al2 O3 (0.35-2.47 wt%) and high-chromium chromespinelides, which is typical for pre-arc peridotites of supra-subduction zones. This is not contradicted by high concentrations of REE harzburgites, reflecting their high degree of refertilisation (secondary enrichment) resulting from the melt-rock interactions.
Central Kazakhstan , chromite , forearc peridotites , olivine , serpentinite , Tekturmas
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Astra Mining Kazakhstan, London, United Kingdom
Institute of Geological sciences named after K.I. Satpayev, Almaty, Kazakhstan
RSE «Institute of Nuclear Physics», Almaty, Kazakhstan
Astra Mining Kazakhstan
Institute of Geological sciences named after K.I. Satpayev
RSE «Institute of Nuclear Physics»
10 лет помогаем публиковать статьи Международный издатель
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