[SSS04-P03] Comparison of volcanic glasses from tephra deposits frontal prism and incoming sediments
Keywords:tephra, Core-Log-Seismic Investigation at Sea, Nankai Trough
At Site C0007 of NanTroSEIZE transect in off-Kumano region, present decollement lies in between Pliocene Shikoku Basin facies composed of mudstone and volcanic ash (Unit III) and Pleistocene Trench wedge/Axial channel facies (Unit IV). The sedimentary age of the bottom of Unit III (~5.32 Ma) is equivalent to that of the boundary of Unit IA and IB at C0011, Upper Shikoku Basin sediments. The Upper Shikoku Basin sediments include many tephra layers (e.g. Azuki (0.85 Ma), Pink (1.05 Ma), Habutaki (2.85 Ma), and Ohta (4.0 Ma) ashes). For better age constraint of Site C0007, we determine major and trace element compositions of volcanic glasses included in the tephra layers using LA-ICPMS. In this presentation, we report preliminary results of tephrachlonology and compare the results to that of the input sediments (Site C0011). The results will also be integrated to biostratigraphy, paleomagnetism, and detrital zircon U-Pb dating results (Clift et al., 2013). Updated high-resolution stratigraphic comparison has a potential to reconstruct the faulting/sedimentational history of the prism toe, where very-low-frequency earthquakes and slow-slip events occurs.