RUSSIAN JOURNAL OF EARTH SCIENCES, VOL. 15, ES1003, doi:10.2205/2015ES000547, 2015

Table 2. Composition of Primary and Metamorphic Spinel and Magnetite in the Dunite
Sample NP06-20/1 NP06-51/2 NP06-51/2 NP06-51/2 NP06-32/1 NP06-26/2 NP06-26/2 NP06-54/2
Population Met3 Prim Met2 Mag Mag Met3 Mag Met3
Morphology Id Id Rim1 Rim2 Irr Id Rim Id
Anal. spot 3 3 3 3 2 5 3 3
$\mathrm{SiO_2}$ 0.07 0.05 0.06 0.06 0.06 0.06 0.06 0.08
$\mathrm{TiO_2}$ 0.80 0.25 0.31 0.01 0.60 1.30 0.13 0.33
$\mathrm{Al_2O_3}$ 0.25 11.95 2.49 0.02 0.01 0.17 0.02 0.08
FeO* 61.08 35.98 52.37 89.96 91.80 64.91 91.11 73.92
MnO 0.64 0.50 0.65 0.09 0.10 0.52 0.00 0.38
MgO 1.78 6.58 3.19 0.75 0.47 1.60 0.50 0.66
$\mathrm{Cr_2O_3}$ 31.04 42.07 37.10 2.45 0.73 26.57 1.28 18.80
NiO 0.21 0.10 0.18 0.36 0.09 0.24 0.16 0.20
$\mathrm{V_2O_3}$ 0.26 0.11 0.13 0.02 0.04 0.31 0.05 0.20
ZnO 0.20 0.47 0.20 0.00 0.00 0.25 0.12 0.13
Total 96.32 98.08 96.68 93.69 93.86 95.92 93.41 94.79
Total ** 99.93 99.55 99.57 100.43 100.68 99.88 100.19 99.68
YCr 0.472 0.570 0.601 0.037 0.011 0.412 0.019 0.287
YFe 0.522 0.189 0.403 0.962 0.971 0.584 0.980 0.711
$T_{C}$,° C 138 $-130$ 15 548 554 205 560 338
Sample NP06-43/4 NP06-43/4 NP06-54/3 NP06-54/3 NP06-57/2 NP06-57/2 NP06-57/2 NP06-57/2
Population Prim Met2 Prim Met2 Prim Met1 Met2 Mag
Morphology Id Rim Id Rim Id Vein Rim1 Rim2
Anal. spot 6 2 4 2 6 3 2 1
$\mathrm{SiO_2}$ 0.07 0.06 0.08 0.08 0.08 0.12 0.06 0.11
$\mathrm{TiO_2}$ 0.23 0.42 0.17 0.25 0.19 0.16 0.38 0.00
$\mathrm{Al_2O_3}$ 16.68 3.72 15.44 1.94 19.14 12.98 3.09 0.02
FeO* 37.78 60.01 33.41 55.48 34.05 41.54 57.12 92.62
MnO 0.41 0.43 0.43 0.52 0.40 0.60 0.57 0.08
MgO 7.09 2.18 7.92 2.43 7.13 4.24 1.93 0.29
$\mathrm{Cr_2O_3}$ 36.00 29.05 40.24 34.55 37.32 38.08 32.98 0.77
NiO 0.15 0.34 0.19 0.35 0.10 0.09 0.19 0.35
$\mathrm{V_2O_3}$ 0.16 0.22 0.10 0.10 0.17 0.16 0.20 0.04
ZnO 0.23 0.05 0.32 0.22 0.28 0.32 0.00 0.06
Total 98.79 96.48 98.30 95.93 98.88 98.28 96.53 94.34
Total ** 100.41 99.99 99.63 99.08 100.05 99.93 99.68 100.39
YCr 0.472 0.427 0.530 0.513 0.485 0.524 0.487 0.012
YFe 0.201 0.491 0.167 0.444 0.144 0.215 0.444 0.988
$T_{C}$, ° C $-127$ 105 $-135$ 55 $-136$ $-122$ 55 566
Sample NP06-20/2 NP06-23/3 NP06-46/2 NP06-49/2 NP06-49/2 NP06-53/2 NP06-53/2
Population Mag Met3 Prim Prim* Met1 Prim Met2
Morphology Irr Id Id Id Rim Id Rim
Anal. spot 2 6 6 5 3 6 4
$\mathrm{SiO_2}$ 0.07 0.07 0.06 0.07 0.07 0.07 0.09
$\mathrm{TiO_2}$ 0.06 0.76 0.26 0.22 0.57 0.39 0.57
$\mathrm{Al_2O_3}$ 0.01 0.34 25.67 20.17 8.22 23.30 1.99
FeO* 92.20 60.99 31.00 32.11 49.15 32.28 61.38
MnO 0.30 0.50 0.30 0.39 0.59 0.39 0.49
MgO 0.26 1.68 9.37 7.41 3.01 7.62 1.52
$\mathrm{Cr_2O_3}$ 0.23 31.83 31.13 37.81 34.89 34.70 30.46
NiO 0.10 0.16 0.17 0.11 0.16 0.11 0.03
$\mathrm{V_2O_3}$ 0.17 0.22 0.17 0.21 0.23 0.20 0.17
ZnO 0.00 0.22 0.22 0.42 0.22 0.34 0.14
Total 93.38 96.79 98.34 98.92 97.12 99.41 96.82
Total ** 100.26 100.34 99.41 99.91 99.48 100.37 100.37
YCr 0.003 0.481 0.390 0.489 0.501 0.442 0.455
YFe 0.996 0.511 0.131 0.123 0.323 0.116 0.501
$T_{C}$, ° C 571 126 $-136$ $-135$ $-56$ $-134$ 115
Note: Prim – primary Cr-spinel, Met – metamorphic Cr-spinel, (ferrite-chromite) of various populations, Mag – magnetite. Id – euhedral grains or their cores, Rim – homogeneous rim around euhedral grains, Rim1 – inner rim, Rim2 – outer rim, Irr – anhedral grains, Vein – veinlet cutting across the core of an euhedral grain. FeO* – all Fe in the form of FeO. Total** – total of oxides after recalculation of part of FeO* into Fe$_2$O$_3$ based on stoichiometric considerations for spinel (that is presumed to contain no structural vacancies). $\mathrm{YCr - Cr/(Cr+Al+V+Fe^{3+})}$, $\mathrm{YFe - Fe^{3+}/(Cr+Al+V+Fe^{3+}}$). Minerals were analyzed on a Cameca SX-100 microprobe at the Vernadsky Institute in polished petrographic thin sections in compliance with the conventionally used techniques [see Bazylev et al., 2013a for details of the analytical procedure]. $T_{C}$ – Curie temperature of spinel evaluated from its composition using the compositional dependence in [Ziemniak and Castelli, 2003]. The asterisk marks the spinel composition compiled from [Bazylev et al., 2013a].

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Citation: Popov K. V., B. A. Bazylev, V. P. Shcherbakov, V. A. Tsel'movich, N. N. Kononkova (2015), Thermomagnetic analysis of ultramafic rocks: A case study of dunite from the Pekul'ney Complex, Chukotka, NE Russia, Russ. J. Earth Sci., 15, ES1003, doi:10.2205/2015ES000547.
 

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