EFFECTS OF STRESS IN THE EVOLUTION OF LARGE SILICIC MAGMATIC SYSTEMS: AN EXAMPLE FROM THE MIOCENE FELSIC VOLCANIC FIELD AT KII PENINSULA, SW HONSHU, JAPAN

Abstract

Miocene felsic volcanic field at the Kii Peninsula (MFVK) in southwest Japan allows us to reveal temporal and spatial change of a large felsic volcanic system in response to changes in the local and regional stress field. The MFVK was active episodically ejecting more than a few hundred cubic kilometers of magma in a span of hundred thousand to million years. Remnant of this large-scale volcanism is characterized by a broad area of deeply incised and complex cluster of collapse calderas in the Kii Peninsula. Major conduits for ash–flow tuff eruptions lie on the margins of the MFVK. Paleostress orientation of the σHmax was inferred from lithologic distribution and structure in rocks in the MFVK. The optimal tectonic stress orientation at the time of the MFVK formation was NNE–SSW to the present azimuth. Approximately 1500 km³ of magma were erupted from the MFVK during a duration of 0.1 million to 1.6 Myr. This suggests an area normalized eruption rate of 10–2 to 10–3 km³/ka km². This long-term eruption rate of the MFVK is at the high end of rates for other large felsic volcanic fields (LFVFs), and ranks as one of the larger rates of LFVF worldwide.