Petrography and Rb-Sr mineral age of mafic dyke rock from Niban Iwa, Lützow-Holm Complex, East Antarctica

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  • MIYAMOTO Tomoharu
    Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University
  • YAMASHITA Katsuyuki
    Department of Earth Sciences, School of Science, Okayama University
  • DUNKLEY Daniel J.
    Department of Polar and Marine Research, Institute of Geophysics, Polish Academy of Sciences
  • TSUNOGAE Toshiaki
    Faculty of Life and Environmental Sciences, University of Tsukuba Department of Geology, University of Johannesburg
  • KATO Mutsumi
    Nittetsu Mining Consultants Co., Ltd.

Description

<p>A WNW-ESE-trending mafic dyke intruding across major structures in high-grade metamorphic rocks was found at Niban Iwa (translated as ‘Number Two Rock’) in the Proterozoic Lützow-Holm Complex of East Antarctica. It is holocrystalline and aphyric, and comprises biotite, hornblende, plagioclase, orthoclase, quartz, apatite, and titanite. Chemically the dyke rock is alkali basalt with high K2O/Na2O and total Fe contents, and low Cr and Ni contents, indicating that it was formed by the differentiation of olivine from a primary alkali basaltic magma derived from the subcontinental mantle. The Rb-Sr mineral isochron age was obtained of 487 ± 15 Ma with SrIR = 0.70486 ± 0.00007. Considering that the metamorphic age of the gneisses at Niban Iwa was estimated to be 532 Ma, the dyke probably intruded after metamorphism as part of the post-orogenic igneous activity following the collision of East and West Gondwana.</p>

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