Sulfide and oxide minerals from S-type and I-type granitic rocks |
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| Institution: | 1. Rigaku Industrial Corporation, 14-8, Akaoji-cho, Takatsuki-shi, Osaka 569, Japan;2. Hiruzen Research Institute, Okayama University of Science, 1-1, Ridai-cho, Okayama 700, Japan;1. Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS, Beijing 100037, China;4. Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia;1. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;2. Public Geological Survey Management Center of Anhui Province, Hefei 230091, China;3. CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei 230026, China;4. School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea;1. School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China;2. Nanjing Center, China Geological Survey, Nanjing 210016, China |
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| Abstract: | In the Ohmine I-type and S-type granitic rocks of Miocene age, Kii peninsula, central Japan, ilmenite, rutile, pyrrhotite, pyrite and chalcopyrite are common, but no magnetite is present. The primary paragenetic relations of these minerals are determined by their modes of occurrence as inclusions within major plagioclase, orthoclase, quartz, hornblende and biotite, although their parageneses changed during cooling. Significant subsolidus reactions for sulfide minerals took place in both the groundmass and the inclusions until the rocks cooled below 300°C. The loss of S and Cu through silicate crystals was too easy to preserve the chemistry of sulfides included in silicates. However, the removal of Ni through silicate crystals as well as along grain boundaries was restricted, as indicated by the fact that the distribution frequency of Ni-bearing pyrrhotite is higher in inclusions than in the groundmass, and significantly higher in I-type cognate enclaves than in host I-type rocks. Nickel-bearing pyrrhotite is common in I-type but rare in S-type rocks, sedimentary enclaves, restates and country rocks. This eliminates the possibility that the Ohmine S-type rocks were formed by interaction of I-type magma and sedimentary rocks or by mixing between I-type and an ideal S-type magmas, as interpreted from the chemistry of biotite and the chronology of these rocks.On the basis of mineralogy, and isotopic data for S, O, Sr, C, and rare gases, it was shown that I-type granitic rocks were derived from partial melting of intermediate igneous rocks containing hornblende and plagioclase and S-type, from partial melting of sedimentary rocks containing biotite and orthoclase. |
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