Magnetite lamellae in olivine and clinohumite from Dabie UHP ultramafic rocks, central China

Zhang, Ru Y.; Shu, Jiang; Mao, Ho Kwang; Liou, J. G.

doi:10.2138/am-1999-0410

Cited by 81 publications

(32 citation statements)

References 32 publications

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“…In contrast, magnetite generally forms as a secondary phase (Janecky and Seyfried, 1986;Toft et al, 1990;Nazarova, 1994;Zhang et al, 1999;Hwang et al, 2008) resulting from interaction with oxidizing fluids or melts through one or more magnetization processes (section 7).…”

Section: Reason 2 Magnetic Minerals In Upper Mantle Rocksmentioning

confidence: 99%

Eight good reasons why the uppermost mantle could be magnetic

et al. 2014

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Wasilewski et al. (1979) concluded that no magnetic remanence existed in the uppermost mantle and that even if present, such sources would be at temperatures too high to contribute to long wavelength magnetic anomalies (LWMA). However, new collections of unaltered mantle xenoliths indicate that the uppermost mantle could contain ferromagnetic minerals. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2/39This is most easily explained as a thermoremanent magnetization acquired by pre-existing ferromagnetic minerals as xenoliths cool rapidly at the Earth's surface from magmatic temperatures, acquired during ascent. 7. Modern experimental data suggest that the wüstite-magnetite oxygen buffer and the fayalite-magnetite-quartz oxygen buffer extend several tens of km within the uppermost mantle. 8. The magnetic properties of mantle xenoliths vary consistently across tectonic settings. In conclusion, the model of a uniformly non-magnetic mantle should be revisited.

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Section: Reason 2 Magnetic Minerals In Upper Mantle Rocksmentioning

confidence: 99%

Eight good reasons why the uppermost mantle could be magnetic

et al. 2014

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“…The energy dispersive single-crystal technique was developed originally at the beamline X17C of the National Synchrotron Light Source for high-pressure diamondcell investigations. The technique has been used for studying 10-m-sized single crystals of hydrogen at high pressure (28,29), 220-nm-diameter single-crystal fiber in glass capillaries (30), and submicrometer-thick magnetite lamellae in olivine phenocrysts from ultrahigh-pressure rocks (31). It was used in the present work for studying the same two coesite inclusions in diamond (Fig.…”

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confidence: 99%

Fossilized high pressure from the Earth's deep interior: The coesite-in-diamond barometer

Sobolev

Fursenko

Goryaĭnov

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

148

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Mineral inclusions in diamonds provide an important source of information about the composition of the continental lithosphere at depths exceeding 120 -150 km, i.e., within the diamond stability field. Fossilized high pressures in coesite inclusions from a Venezuela diamond have been identified and measured by using laser Raman and synchrotron x-ray microanalytical techniques. MicroRaman measurements on an intact inclusion of remnant vibrational band shifts give a high confining pressure of 3.62 (؎0.18) GPa. Synchrotron single-crystal diffraction measurements of the volume compression are in accord with the Raman results and also revealed direct structural information on the state of the inclusion. In contrast to olivine and garnet inclusions, the thermoelasticity of coesite favors accurate identification of pressure preservation. Owing to the unique combination of physical properties of coesite and diamond, this ''coesite-in-diamond'' geobarometer is virtually independent of temperature, allowing an estimation of the initial pressure of Venezuela diamond formation of 5.5 (؎0.5) GPa.S pecimens of Earth materials from great depths often contain mineralogical or textural clues, such as metastable highpressure polymorphs or characteristic mineral assemblages implicating their high-pressure genealogy (1-3). The actual pressure, however, is seldom preserved and observed. For such observations, the sample must be retained in a strong container with appropriate relative thermoelastic properties, and nondestructive analytical techniques must be developed to probe the fossilized pressure condition in situ in the container. Diamond is the strongest possible container. Infrared absorption spectroscopy has been used as the probe for fluid inclusions in diamond (4), and high residual pressures have been reported on the basis of infrared spectra of quartz and CO 2 inclusions in the material (5, 6). In these studies, bulk spectra of diamond and numerous microscopic inclusions were measured; pressures and phases of different inclusions were not determined individually. Herein, we present direct measurements of pressures up to 3.6 GPa in individual coesite inclusions in diamond, a thermoelastic couple most favorable for pressure preservation. We use micro-Ramanand micro-single-crystal x-ray diffraction techniques to probe the pressure of each inclusion separately and precisely. Application to coesite inclusions in diamond from Venezuela provides a determination of the pressure-temperature (P-T) conditions of its formation.Diamond and its inclusions contain rich information about the petrogenesis and geochemistry of the Earth's deep interior (7,8). Although coesite-and diamond-bearing rocks (9-12) undoubtedly have a high-pressure origin, individually, coesite and diamond cover a wide P-T domain of stability (13, 14) that precludes their use as a precise and accurate geobarometer, because they give only a lower bound on the pressure of formation. In many cases, much higher pressures are suggested (15) based on mineral equilibria d...

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“…We assume monticellite accommodates only Fe 2? in its structure, based on 57 Fe Mössbauer studies of olivine group minerals (Canil and O'Neill 1996;Dyar 2003;Pieters et al 2008;Treiman et al 2007;Zhang et al 1999). With increased fO 2 in kimberlite magmas, the redox equilibrium for Fe in the melt:…”

Section: Introductionmentioning

confidence: 99%

Iron in monticellite as an oxygen barometer for kimberlite magmas

Pioufle

Canil

2011

Contrib Mineral Petrol

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Monticellite is a common magmatic mineral in the groundmass of kimberlites. A new oxygen barometer for kimberlite magmas is calibrated based on the Fe content of monticellite, CaMgSiO 4 , in equilibrium with kimberlite liquids in experiments at 100 kPa from 1,230 to 1,350°C and at logfO 2 from NNO-4.1 to NNO?5.3 (where NNO is the nickel-nickel oxide buffer). The XFe Mtc /XFe liq was found to decrease with increasing fO 2 , consistent with only Fe 2? entering the monticellite structure. Although the XFein-monticellite varies with temperature and composition, these dependencies are small compared to that with fO 2 . The experimental data were fitted by weighted least square regression to the following relationship:DNNO ¼ log 0:858ðAE0:021Þ X Liq Fe X Mtc Fe h i À0:139ðAE0:022Þ n o 0:193ðAE0:004Þwhere DNNO is the fO 2 relative to that of the Nickel-bunsenite (NNO) buffer and XFe liq /XFe Mtc is the ratio of mole fraction of Fe in liquid and Fe-in-monticellite (uncertainties at 2r). The application of this oxygen barometer to natural kimberlites from both the literature and our own investigations, assuming the bulk rock FeO is that of their liquid FeO, revealed a range in fO 2 from NNO-3.5 to NNO?1.7. A range of Mg/(Mg ? Fe 2? ) (Mg#) for kimberlite melts of 0.46-0.88 was derived from the application of the experimentally determined monticelliteliquid Kd Fe 2? -Mg to natural monticellites. The range in Mg# is broader and less ultramafic than previous estimates of kimberlites, suggesting an evolution under a wide range of petrologic conditions.

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Magnetite lamellae in olivine and clinohumite from Dabie UHP ultramafic rocks, central China

Cited by 81 publications

References 32 publications

Eight good reasons why the uppermost mantle could be magnetic

Eight good reasons why the uppermost mantle could be magnetic

Fossilized high pressure from the Earth's deep interior: The coesite-in-diamond barometer

Iron in monticellite as an oxygen barometer for kimberlite magmas

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