The degree of oxidation of iron in synthetic iron-magnesian biotites

Tikhomirova, V. I.; Konilov, A. N.; Koshemchuk, S. K.

doi:10.1007/bf01164809

Cited by 7 publications

(2 citation statements)

References 11 publications

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“…(e.g., Vedder and Wilkins 1969;Sanz et al 1983;Tikhomirova et al 1989). This reaction generates a vacancy in the hydroxyl site, unstable in a closest packed site, and therefore leads to the breakdown of biotite and the development of reaction rims.…”

Section: Discussionmentioning

confidence: 99%

Ferric-ferrous ratios, H 2 O contents and D/H ratios of phlogopite and biotite from lavas of different tectonic regimes

Feldstein

Lange

Vennemann

et al. 1996

Contributions to Mineralogy and Petrology

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Complete chemical analyses, including ferric and ferrous iron, H 2 O contents and dD values for 16 phlogopite and biotite and 2 hornblende separates are presented. Samples were obtained from volcanic rocks from four localities: (1) phlogopite phenocrysts from minette lavas from the western Mexico continental arc, (2) biotite and hornblende phenocrysts from andesite lavas from Mono Basin, California, (3) phlogopite and biotite from clinopyroxenite nodules entrained in potassic lavas from the East African Rift, Uganda, and (4) phlogopite phenocrysts from a wyomingite lava in the Leucite Hills, Wyoming. The Fe 2 O 3 contents in the micas range from 0.8 to 10.5 wt%, corresponding to 0.09 to 1.15 Fe 3ϩ per formula unit (pfu). Water contents vary from 1.6 to 3.0 wt%, corresponding to 1.58 to 3.04 OH pfu, significantly less than would be expected for a site fully occupied by hydroxyl. Cation-and anion-based normalization procedures provide accurate mineral formulae with respect to most cations and anions, but are unable to generate accurate estimates of Fe 3ϩ ͞Fe T , and overestimate OH at the expense of O on the hydroxyl site. These inaccuracies are present despite acceptable adjusted totals and stoichiometric calculated site occupancies. The phlogopite and biotite phenocrysts in arc-related lavas from western Mexico and eastern California have the highest Fe 3ϩ ͞Fe T ratios (56-87%), reflecting high magmatic oxygen fugacities (DNNO ϭ ϩ2 to ϩ5), in contrast to those from Uganda (25-40%) and the Leucite Hills (23%). There is no correlation between the OH content and the Fe 3ϩ ͞Fe T ratio in the micas. Values of K Mg͞Fe 2ϩ D (+ 2s errors) were calculated for three phlogopite-olivine pairs (0.12 + 0.12, 0.26 + 0.14, 0.09 + 0.12), two biotite-hornblende pairs (0.73 + 0.08 and 1.22 + 0.10) and a single phlogopite-augite pair (1.15 + 0.12). Values of K F͞OH D for two biotite and hornblende pairs could not be determined without significant error because of the extremely low F contents (Ͻ 0.2 wt%) of the four phases. The dD values obtained in this study encompass a large range (Ϫ137 to Ϫ43‰). The phlogopite and biotite separates from Uganda have dD values of Ϫ70 to Ϫ49‰, which overlap those believed to represent "primary" mantle. There is a larger range in dD values (Ϫ137 to Ϫ43‰) for phlogopite phenocrysts from western Mexico minette lavas, although their range in d 18 O values (5.2-6.2‰) is consistent with "normal" mantle. It is unlikely, therefore, that the variable dD values reflect heterogeneity in the mantle source region of the minette magmas. Nor can the extremely low dD values reflect degassing of H 2 or H 2 O since almost 100% loss of dissolved water in the magma is required, an unrealistic scenario given the stability of the hydrous phenocrysts. The very low dD values of the Mascota minette phlogopites require that the hydrogen be introduced from an external source (e.g., meteoric water). Whatever the process responsible for the observed hydrogen isotope composition, it had no effect on the d 18 O value, f O 2 , a H...

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Section: Discussionmentioning

confidence: 99%

Ferric-ferrous ratios, H 2 O contents and D/H ratios of phlogopite and biotite from lavas of different tectonic regimes

Feldstein

Lange

Vennemann

et al. 1996

Contributions to Mineralogy and Petrology

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“…Different approaches have been undertaken to determine the amount of the ferric iron content including wet chemical analysis and indirect methods like variations in cell dimensions and refractive indices. Tikhomirova et al (1989) studied the amount of ferric iron in synthetic iron magnesium biotites using chemical and pyrolytical methods. They observed ferric iron ranging from 16% to 27%.…”

Section: Introductionmentioning

confidence: 99%

M�ssbauer spectroscopic and x-ray powder diffraction studies of synthetic micas on the join annite KFe3AlSi3O10(OH)2-phlogopite KMg3AlSi3O10(OH)2

1995

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Abstract. Micas of the composition K(Fe3_xMg~)A1Si 3 Olo(OH)2 (x=0.6, 1.2, 1.8, 2.4 and 3.0, corresponding to anns0phl20, ann6ophl4o, ann4oPhl6o, ann20phls0 and annophl~00) were synthesized hydrothermally under controlled oxygen fugacity conditions. Lattice parameters a o and b0 show a distinct linear decrease with increasing Mg content. With increasing ferric iron content a deviation from this linear trend is observed especially within iron rich samples. The tetrahedral rotation angle c~ increases smoothly from 0 ~ in annite to 9.1 ~ in phlogopite. M6ssbauer spectra show Fe a+ and Fe 3+ on the octahedral M1 and M2 sites and partially also Fe 3+ on the tetrahedral site. There is a smooth increase of the quadrupole splitting on both the M1 and the M2 site going from annite to phlogopite, probably due to changes in the lattice contribution to the electric field gradient, assuming a positive correlation between quadrupole splitting and distortion. Fe 3 + contents, as determined by M6ssbauer spectroscopy, versus oxygen fugacity shows that, depending on the composition of the micas, minimum amounts of Fe 3+ are present. For annsophl20 this minimum amount of Fe 3+ is about 8% decreasing to about 1-2% Fe 3+ for ann20phlso.The molar volume of each solid solution member has been estimated from the determined relations of the molar volume versus % Fe 3 + contents, extrapolated back to 0% Fe 3+. Plotting these volumes as a function of Xph 1 shows that negative excess volume occur in the annitephlogopite join, with the maximum deviation from ideality around Xph 1 = 0.3. Margules volume parameters have been constrained as:Wv, AnnPhl = 0.018 __ 0.016 J/(bar.mol) and Wv, PhlAnn = -0.391 + 0.025 J(bar.mol) (three site basis).

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Acid magmatism and related metallogenesis in the Erzgebirge

Tischendorf¹,

Förster

1990

Geological Journal

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In the Erzgebirge two post-collisional Hercynian granitoid complexes are developed: an older one, monzogranitic, moderately specialized, Sri =0.7064-68, &TNd = -1.8 to -6.2, lg f0, < -13 f 1, Ig fHF/fH20 = -3.9 f 0.2, S-type, 340-325Ma in age, and a younger one, monzo-to albitegranitic, highly specialized in Li, Rb, Cs, Sn, and W, Sri disturbed by strong autometasomatic influences, ET,, = -3.8 to -6.0, lg f02 < -17 f 1, lg MF/fH,O = -3 f 0.3, I-type, 310-295 Ma. Postplutonic volcanics (rhyolite, rhyodacite, latite, kersantite-minette) in each case complete the magmatic sequences.Muscovite-wolframite-molybdenite-pyrite-quartz association is locally related to the older complex, but numerous centres of cassiterite-wolframite-zinnwaldite (or muscovite) deposits are related to the younger one. Both mineralizations are of orthomagmatic origin and underwent strong physicochemical control. Thus, the granites genetically related to the tin-free older association are conditioned by medium f0, but low fHF/fH,O, the tin-bearing younger association, in contrast, is controlled by low f0, coupled with high MF/fH20.Vertical compositional zonation in magma chambers caused enrichment of compatible elements such as Zn, Pb, Mg, Ca, Ba, Sr, in deeper parts of the chamber and their transition into residual solutions which then may form base metal mineralization as cross-cutting veins. Mineralization events last up to the Triassic. Probably elements in the later stages were derived either from deep-originated residual solutions or, increasingly, by leaching of specialized magmatites. KEY WORDS Hercynian magmatites Leucocratic metallogenesis Melanocratic metallogenesis Tin mineralization

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The degree of oxidation of iron in synthetic iron-magnesian biotites

Cited by 7 publications

References 11 publications

Ferric-ferrous ratios, H 2 O contents and D/H ratios of phlogopite and biotite from lavas of different tectonic regimes

Ferric-ferrous ratios, H 2 O contents and D/H ratios of phlogopite and biotite from lavas of different tectonic regimes

M�ssbauer spectroscopic and x-ray powder diffraction studies of synthetic micas on the join annite KFe3AlSi3O10(OH)2-phlogopite KMg3AlSi3O10(OH)2

Acid magmatism and related metallogenesis in the Erzgebirge

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