Petrology of the Yugu peridotites in the Gyeonggi Massif, South Korea

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harzburgite (K100) dunite (K39) websterite (KC8) Ol Opx Sp Ol Sp Opx Cpx Sp SiO2 41.19 58.41 0.03 41.61 0.02 54.81 51.37 0.00 TiO2 0.00 0.03 0.01 0.01 0.25 0.02 0.07 0.00 Al2O3 0.00 0.96 23.03 0.00 27.79 5.13 5.65 54.58 Cr2O3 0.00 0.16 42.92 0.00 41.02 0.72 1.54 13.97 FeO* 7.87 5.03 23.00 9.05 18.95 7.14 2.10 12.53 MnO 0.12 0.18 0.20 0.07 0.33 0.13 0.11 0.19 MgO 50.64 35.93 10.59 50.75 12.75 32.53 15.97 17.64 NiO nd nd nd 0.31 nd nd nd nd CaO 0.05 0.20 0.00 0.00 0.01 0.28 23.09 0.03 Na2O 0.00 0.00 0.00 0.06 0.04 0.05 0.69 0.07 K2O 0.00 0.02 0.02 0.05 0.05 0.02 0.02 0.03 Total 99.87 100.92 99.80 101.91 101.21 100.83 100.61 99.04 Mg# 0.920 0.927 0.493 0.909 0.572 0.890 0.931 0.703 Cr# 0.556 0.498 0.147 Mg/(YCr) 0.924 0.532 0.000 0.886 0.473 0.147 Fe*/(YAl) 0.073 0.426 0.109 0.035 0.853 Ca/(YFe) 0.004 0.042 0.005 0.492 0.000 Peridotites from Yugu, Korea 491 FeO*, total iron as FeO; Mg, Fe*, Ca, atomic fractions of Mg, total Fe and Ca, respectively, over (Mg + total Fe + Ca) of pyroxenes. YCr, YAl, YFe, cationic fractions of Cr, Al and Fe3+ , respectively, over (Cr + Al + Fe3+ ) in chromian spinel. Ol, olivine; Opx, orthopyroxene; Cpx, clinopyroxene; Sp, chromian spinel; Amph, amphibole; suffixes 1 and 2, porphyroclasts and neoblasts, respectively; c and r, cores and rims, respectively; inc, inclusions. © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Asia Pty Ltd
492 S. Arai et al. Cr/(Cr + Al) spinel 1 0.5 OSMA Bibong ocean floor & arc Yugu lherzolite harzburgite dunite Baekdong 0 95 90 Fo olivine 85 Fig. 4 Relationships between the Fo content of olivines and Cr/(Cr + Al) atomic ratio of spinels in the Yugu peridotites. Representative pairs were determined for individual samples by averaging microprobe analyses of porphyroclast phases. OMSA, olivine–spinel mantle array as a spinel peridotite residual trend (Arai 1994). Typical residual trend (thick gray line) for abyssal and Japan-arc peridotites (Arai 1994) is shown for comparison. Note that the Yugu peridotite trend is almost equivalent to that for abyssal and Japan-arc peridotites. Fields for the Bibong and Baekdong peridotites (Seo et al. 2005) are shown for comparison. porphyroclast cores than in neoblasts/porphyroclast rims. The Na2O content of clinopyroxenes is relatively low even in the porphyroclast cores, up to 0.3 to 0.5 wt% in the most fertile lherzolite that contains chromian spinels with Cr# of 0.1 (No. K82 of Table 1). Pyroxenes of websterites are similar in chemistry to those of porphyroclasts in lherzolites (Table 1). Neoblasts of amphiboles exhibit a wide compositional range from tremolite to hornblende [magnesiohornblende to pargasite after Leake et al. (1997)]. They sometimes show chemical zoning from hornblende in the core to tremolite in the rim (Fig. 6). Hornblendes are characterized by relatively low contents of TiO2 (
Page 2 and 3: Island Arc (2008) 17, 485-501 Thema
Page 4 and 5: 1989). Several isolated ultramafic
Page 6 and 7: colorless Al-rich spinels, which ha
Page 10 and 11: Fig. 5 Elemental distribution maps
Page 12 and 13: Mineral/Chondrite Mineral/Chondrite
Page 14 and 15: is possibly ascribed to its small d
Page 16 and 17: DICK H. J. B. & BULLEN T. 1984. Chr
Page 18: WELLS P. R. A. 1977. Pyroxene therm

Petrology of the Yugu peridotites in the Gyeonggi Massif, South Korea

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