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Chemical composition of whole-rocks samples and volcanic glasses of the Miocene Tamateyama and Sekibutsu Tuffs in the area surrounding the Nara Basin

2010; The Meteorological Society of Japan; Volume: 116; Issue: 8 Linguagem: Inglês

10.5575/geosoc.116.447

1349-9963

Hironao Shinjoe, Hideki Iwano, Yutaka Wada, Yuji Orihashi, Tomoaki Sumii, Tohru Danhara,

earthquake and tectonic studies

We used XRF and INAA methods to analyze the chemical composition of whole-rock and volcanic glass samples from the Tamateyama and Sekibutsu Tuffs in the area surrounding the Nara Basin. Both tuffs have rhyolitic compositions with SiO2=73.6-75.0 wt.%, similar to that of the Muro Pyroclastic Flow Deposits (Muro PFD). The REE patterns of the tuffs are characterized by light REE enrichment, a pronounced negative Eu anomaly, and relatively constant chondrite-normalized middle to heavy REE abundances. These features are similar to those of S-type felsic rocks of the Outer Zone of southwest Japan. Our new petrochemical data provide additional constraints on correlations of the Tamateyama Tuff, Sekibutsu Tuff, and Muro PFD, and indicate that these units were derived from a large felsic igneous body in the Outer Zone of the Kii Peninsula.