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Evolution of the Iron–Silicate and Carbon Material of Carbonaceous Chondrites A

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Evolution of the Iron–Silicate and Carbon Material of Carbonaceous Chondrites A ISSN 01458752, Moscow University Geology Bulletin, 2013, Vol. 68, No. 5, pp. 265–281. © Allerton Press, Inc., 2013. Original Russian Text © A.A. Marakushev, L.I. Glazovskaya, S.A. Marakushev, 2013, published in Vestnik Moskovskogo Universiteta. Geologiya, 2013, No. 5, pp. 3–17. Evolution of the Iron–Silicate and Carbon Material of Carbonaceous Chondrites A. A. Marakusheva, L. I. Glazovskayab, and S. A. Marakushevc aInstitute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia email: [email protected] bFaculty of Geology, Moscow State University, Moscow, 119234 Russia email: [email protected] cInstitute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia email: [email protected] Received February 18, 2013 Abstract—The observed consistence of the composition of chondrules and the matrix in chondrites is explained by their origin as a result of chondrule–matrix splitting of the material of primitive (not layered) planets. According to the composition of chondrites, two main stages in the evolution of chondritic planets (silicate–metallic and olivine) are distinguished. Chondritic planets of the silicate–metallic stage were ana logs of chondritic planets, whose layering resulted in the formation of the terrestrial planets. The iron–silicate evolution of chondritic matter is correlated with the evolution of carbon material in the following sequence: diamond ± moissanite → hydrocarbons → primitive organic compounds. Keywords: meteorite matter, carbonaceous chondrites, hydrocarbons DOI: 10.3103/S0145875213050074 INTRODUCTION 2003) in star–planet systems that are similar to the solar system, in which nearstar giant planets were still The occurrence of diamond in a stable paragenesis preserved and are distinguished under the name rapid with moissanite (SiC) in an ironrich matrix is a char Jupiters. Passage of the protoplanetary stage with the acteristic and the most interesting peculiarity of all formation of the dense cores by chondritic planets is types of chondrites. Diamond grains are overfilled also proven by other discoveries. This was directly con with hydrogen fluid to the extent that their bulk den 3 firmed in 1996, when the Galileo space probe pene sity decreases to 2.2–2.3 g/cm (Brearley and Jones, trated to the fluid envelope of Jupiter. This envelope 1998, p. 278; Besmen, Hoppe, and Ott, 2011) at a 3 was characterized by a high ratio of xenon isotopes density of diamond of 3.5 g/cm . (136Xe/134Xe = 1.04) equal to that in fluid inclusions in The presence of the moissanite–diamond paragen diamonds from carbonaceous chondrites (Kissin, esis provides direct evidence for the origin of chondrite 2003). In the solar wind this ratio is 0.8. matter in the cores of giant planets, which are the only Paragenesis of diamond with moissanite is typical objects in the solar system in which the huge fluid of the matrix of all types of chondrites, which allows us pressure may be found that is necessary for the forma to assume that all chondritic planets were formed and tion of this paragenesis. Small diamond grains dis developed under the huge pressure of the fluid enve persed in a chondrite matrix demonstrate the original lopes of their parental giant planets on orbits between ity of this process controlled by the extreme compres Mars and Jupiter. They became individual planets sion of hydrogen fluids: only after the complete loss of the fluid envelopes by H2 + CO = H2O + C (diamond) and 4H2 + 2CO their parental giant planets under the influence of the + SiO2 = 4H2O + C (diamond) + SiC (moissanite). Sun, but underwent explosive decomposition into The nearsolar planets that were lost by the solar asteroids; their belt is the source of chondrites that system under the influence of the Sun were the paren compose 87% of all meteorite falls (Vityazev, Pecher tal giant planets for the chondritic planets (which were nikova, and Safronov, 1990). destroyed with the formation of asteroids and chon Destruction was initiated by the accumulation of drites), as well as for the terrestrial planets. Their ana such condensed fluids in the cores of chondritic plan logs were discovered by astronomers (Charbonneau, ets that their expansion with the loss of total pressure 265 266 MARAKUSHEV et al. Fe chondrules (their fragments form CAI in carbon 1 aceous chondrites) were formed; then forsterite chon 2 ix drules originated. The age of CAI has been estimated r 3 0.82Fe + 0.18SiC t a 4 at 4567–4568 Ma (Krot et al., 2009); chondrules were m ordinary y 5 r formed later by 1–4 m. y. Later, enstatite primary a e m n 6 i s r chondrules were formed (Fig. 1). t p a t i 0.66Fe + 0.34SiC t The occurrence of diamonds accompanied by e moissanite in the primary chondrite matrix reflects the reduced character of matrix formation at an extremely high hydrogen pressure. A metallic chondrite matrix HH containing diamond and moissanite is formed under E H C these conditions. It contains native silicon, although c a L r less abundantly than moissanite. The following b LL o n sequence of chondrites (their average compositions a c e o are given in Table 1) occurs by enrichment in moisso u s nite: carbonaceous chondrites (C, enriched in Mg SiO MgSiO3 2 4 moissanite); enstatite chondrites (E); and ordinary Si Mg primary chondrules chondrites (HH, H, L, and LL) with negligible con tents of Si and SiC in the primary metallic matrix. Fig. 1. The systematics of chondrites based on correlations of their average compositions (data from Tables 1–6), the The primary metallic taenite–kamacite matrix of compositions of their primary chondrules (empty circles), carbonaceous chondrites was a unique formation, and the metallic matrix (ful circles). The tie lines connect because of the high concentrations of Ca, Al, and Ti. ing them correspond to the types of chondrites: (1–4) With an increase of the H2O/H2 ratio in fluids, they ordinary (HH–H–L–LL), (5) enstatite (E), and (6) car were oxidized first, which was the basis for the forma bonaceous. tion of relatively large calc–alumina chondrules in the matrix. These were ejected by chondrites with smaller had an explosive character. Indicators of the explosive forsterite chondrules formed later. CAIs consisting of formation of asteroids include the presence of impact calc–alumina minerals (melilite, hibonite, spinel, diopside, plagioclase, and others) are characterized by minerals (ringwoodite and others) in the newly formed 16 superposed glassy phase of the chondrites. Chondrites an extremely light oxygenisotope composition ( O). are heliocentric meteorites and their falls from the This peculiarity is also typical of primary forsterite (Si asteroid belt occurred during 4 billion years, judging 33.3; Mg 66.7 at %) that forms primary chondrules by the age of the oldest chondrites. Because of this, the (Fig. 1), which is characterized by the presence of modern weight of the asteroid belt is quite far from its inclusions of metallic nickel–iron drops. initial weight. The evolution of chondritic magmas is controlled Consequently, the protoplanetary (in the cores of by the introduction of isotopically heavy oxygen of the parental giant planets) and planetary evolutions of water. With the presence of silicon, this results in the chondrite matter are distinguished. Protoplanetary replacement of forsteritic chondrules by enstatitic evolution occurs during the selective loss of hydrogen ones, according to the reaction: by parental giant planets in the mode of a decrease of Mg2SiO4 + Si + 2H2O = 2MgSiO3+ 2H2. total pressure and an increase of the H2O/H2 ratio in This provides a completely different, primarily fluids. enstatitic type of chondritic magmatism, which is dif ferent from the formation of carbonaceous chondrites with primary forsterite and calc–alumina chondrules. SYSTEMATICS AND STAGES OF THE EVOLUTION OF CHONDRITE The chondrule–matrix interaction under the pres MATTER sure of the hydrogen component of fluids controlled the entire successive evolution of the iron–silicate Chondritic planets (parental in relation to asteroids matter of chondritic planets. The initial stage of the and chondrites) were primarily formed as metallic cores evolution is illustrated in a diagram (Fig. 1) with tie lines of nearsolar giant planets composed of iron, nickel, connecting the compositions of the primary matrix and many other elements (Si, Ca, Al, Mg, and others), and chondrules of the main types of chondrites. The average carbon. Selective loss of hydrogen by their parental compositions of differentiates of carbonaceous and giant planets and corresponding increase of the enstatitic chondrites, as well as the main types of ordi H2O/H2 ratio in their fluid envelopes were accompa nary chondrites (the sequence HH–H–L–LL corre nied by oxidation of metals starting from the most lates with increase of iron content in their silicates) plot refractory ones and the formation of chondrules in the on tie lines. The evolution of the enstatitic type of following sequence of parageneses of typical elements: chondritic magmatism is schematically characterized (Ca + Al + Si + Ti)–(Si + Mg). First, calc–alumina by the reaction: MOSCOW UNIVERSITY GEOLOGY BULLETIN Vol. 68 No. 5 2013 EVOLUTION OF THE IRON–SILICATE AND CARBON MATERIAL 267 Table 1. Comparison of the average bulk compositions of chondrites (at %) Elements LL (60) L (166) H (172) HH* C (31) E (7) Si 15.42 15.44 14.75 14.71 13.48 15.36 Ti 0.03 0.03 0.03 0.07 0.05 0.03 Al 1.22 1.15 1.13 0.97 1.48 1.34 Fe 8.65 9.59 12.52 16.61 11.03 14.23 Mn 0.11 0.11 0.10 0.13 0.09 0.10 Mg 14.99 15.06 14.75 13.31 14.69 12.39 Ca 0.76 0.76 0.73 0.80 0.97 0.56 Na 0.70 0.68 0.60 0.67 0.33 0.61 K 0.05 0.05 0.04 0.11 0.03 0.04 P 0.09 0.09 0.08 0.21 0.10 0.12 Cr 0.15 0.15 0.14 0.21 0.17 0.14 Ni 0.38 0.45 0.64 1.16 0.54 0.73 Co 0.01 0.02 0.02 0.05 0.02 0.03 S 1.63 1.76 1.71 1.15 2.34 4.34 O 55.81 54.66 52.75 49.84 54.69 49.99 The bulk compositions of meteorites are given after (Marakushev, Zinov’eva, and Granovsky, 2010).
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