Shigeru Sueoka

and 9 more

Arc-arc collision plays an important role in the formation and evolution of continents (e.g., Yamamoto et al., 2009; Tamura et al., 2010). The Izu collision zone central Japan, an active collision zone between the Honshu Arc and the Izu-Bonin Arc since the middle Miocene (Matsuda, 1978; Amano, 1991; Kano, 2002; Hirata et al., 2010), provides an excellent setting for reconstructing the earliest stages of continent formation. Multi-system geo-thermochronometry was applied to different domains of the Izu collision zone, together with some previously published data, in order to reveal mountain formation processes, i.e., vertical crustal movements. For this study nine granitic samples yielded zircon U–Pb ages of 10.2–5.8 Ma (n = 2), apatite (U–Th)/He ages of 42.8–2.6 Ma (n = 7), and apatite fission-track (AFT) ages of 44.1–3.0 Ma (n = 9). Thermal history inversion modelling based on the AFT data using HeFTy ver. 1.9.3 (Ketcham, 2005), suggests rapid cooling events confined to the study region at ~5 Ma and ~1 Ma. The Kanto Mountains are thought to be uplifted domally in association with collision of the Tanzawa Block at ~5 Ma. But this uplift may have slowed down following migration of the plate boundary and late Pliocene termination of the Tanzawa collision. The Minobu Mountains and possibly adjacent mountains may have been uplifted by collision of the Izu Block at ~1 Ma. Mountain formation in the Izu collision zone was mainly controlled by collisions of the Tanzawa and Izu Blocks and motional change of the Philippine Sea plate at ~3 Ma (Takahashi, 2006). Earlier collisions of the Kushigatayama Block at ~13 Ma and Misaka Block at ~10 Ma appear to have had little effect on mountain formation. Together with ~90° clockwise rotation of the Kanto Mountains at 12-6 Ma (Takahashi & Saito, 1997), these observations suggest that horizontal deformation predominated during the earlier stage of arc-arc collision, whereas vertical movements due to buoyancy resulting from crustal shortening and thickening developed at a later stage. References: Amano, K., 1991, Modern Geol., 15, 315-329; Hirata, D. et al., 2010, J. Geogr., 119, 1125-1160; Kano, K., 2002, Bull. EQ Res. Inst. Univ. Tokyo, 77, 231-248; Ketcham, R.A., 2005, Rev. Min. Geochem., 58, 275-314; Matsuda, T., 1978, J. Phys. Earth, 56, S409-S421; Takahashi, M., 2006, J. Geogr., 115, 116-123; Takahashi, M. & Saito, K., 1997, Isl. Arc, 6, 168-182; Tamura et al., 2010, J. Petrol., 51, 823, doi:10.1093/petrology/egq002; Yamamoto, S. et al., 2009, Gond. Res., 15, 443-453.