Phase Relations in the Model System SiO2–MgO–Cr2O3: Evidence from the Results of Experiments in Petrologically Significant Sections at 12–24 GPa and 1600°C


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The new results of an experimental study of the majorite MgSiO3–magnesiochromite MgCr2O4 model section are discussed, and general topology of the SiO2–MgO–Cr2O3 system is analyzed. Despite the absence of some petrogenic components (CaO, FeO, Al2O3, Na2O, K2O, and others) in this system, our study, performed in wide pressure range (10–24 GPa), allows us to consider all of the most important phase transformations (in this case, magnesium silicates and oxides) in the upper mantle, transition zone, and uppermost lower mantle. Addition of Cr shows the influence of a minor element on the phase transition parameters. New data on the solubility of Cr in deep minerals (garnet, olivine, wadsleyite, ringwoodite, and bridgmanite) were obtained, which allowed us to determine the influence of Cr on the structural patterns of the major mantle phases. It is shown that addition of 1 wt % Cr2O3 shifts the boundaries of phase transformations by 50 km (olivine/wadsleyite) and 10 km (wadsleyite/ringwoodite) to a lower-pressure domain in comparison with Cr-free systems. In a first approximation, the results of experimental study of phase relations in pseudobinary sections of the SiO2–MgO–Cr2O3 system simulate the phase composition of the restitic part of the upper mantle, transition zone, and uppermost lower mantle under partial melting conditions. It is shown that the Cr concentration in mantle phases is significantly controlled by the Cr/Al ratio in the protolith.

作者简介

E. Matrosova

Vernadsky Institute of Geochemistry and Analytical Chemistry,
Russian Academy of Sciences

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Email: ekaterina.a.sirotkina@gmail.com
俄罗斯联邦, ul. Kosygina 19, Moscow, 119991

A. Bobrov

Vernadsky Institute of Geochemistry and Analytical Chemistry,
Russian Academy of Sciences; Geological Faculty, Moscow State University; Institute of Experimental Mineralogy, Russian Academy of Sciences

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Email: archi@geol.msu.ru
俄罗斯联邦, ul. Kosygina 19, Moscow, 119991; Moscow, 119991; ul. Akademika Osip’yana 4, Chernogolovka, Moscow oblast, 142432

L. Bindi

Dipartimento di Scienze della Terra, Università di Firenze; CNR—Istituto di Geoscienze e Georisorse, sezione di Firenze

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Email: luca.bindi@unifi.it
意大利, Via La Pira 4, Florence, 50121; Via La Pira 4, Florence, 50121

T. Irifune

Geodynamics Research Center, Ehime University; Earth Life Science Institute, Tokyo Institute of Technology

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Email: irifune@dpc.ehime-u.ac.jp
日本, Matsuyama, 7908577; Tokyo, 1528550

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