Oxygen isotopic variations in soil quartz developed on rhyolite residuum from Kiso,central Japan |
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| Institution: | 1. Institute of Geology and Paleontology, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Sendai, 980-8578, Japan;2. Faculty of Education, Gifu University, 1-1 Yanagido, Gifu, 501-1193, Japan;3. Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan;1. Department of Pharmacology, College of Medicine, University of Arizona, Tucson, AZ 85724, USA;2. Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN, USA;3. Department of Psychiatry, Indiana University School of Medicine, Indianapolis, IN, USA;4. Graduate Interdisciplinary Program in Neuroscience, College of Medicine, University of Arizona, Tucson, AZ, USA;5. The Center for Innovation in Brain Sciences, The University of Arizona Health Sciences, Tucson, AZ 85724, USA;1. Consiglio Nazionale delle Ricerche, Istituto di Scienze Marine (CNR-ISMAR), 00133, Rome, Italy;2. National Institute for Space Research, INPE, Av. dos Astronautas, 1758 - 12227-010, São José dos Campos, SP, Brazil;3. Scripps Institution of Oceanography, University of California SanDiego, 8810 Shellback Way, La Jolla, CA, USA;4. Instituto de Biologia and SAGE/COPPE, Universidade Federal do Rio de Janeiro, 21941-902, Rio de Janeiro, RJ, Brazil;5. Department of Oceanography, Universidade Federal do Espirito Santo, Av. Fernando Ferrari 514, Vitoria, ES, Brazil |
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| Abstract: | Positive identification of the origin of fine-grained quartz in highly weathered soils is not proven by routine microscopic examination. The oxygen isotope composition (δ18O vs SMOW) of quartz was determined in the albic horizon of three soils developed on the Cretaceous Nohhi rhyolite from Kiso, central Japan. Differences in the isotopic composition of quartz as a function of particle size were observed and attributed to the degree of hydrothermal alteration. One soil sample developed nearby hornblende porphyrite intrusion showed systematic increases in the δ18O values with increasing particle size, from +3.6‰ (1–10 μm) to +9.5‰ (500–2000 μm). Such a trend is indicative of the higher contribution of secondary quartz precipitated from hydrothermal meteoric fluids in fine size fractions in contrast to primary magmatic quartz in coarse size fractions. Hydrothermal activity was inferred for another soil where no lateral intrusion is mapped. The variation in the oxygen isotopic composition of quartz in different particle sizes precludes both eolian and authigenic origins for the soils. The stable isotope technology provides the only rationale for positive identification of the origin of fine-grained quartz in soils. |
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