Environmental Magnetism Research On The Prism Sediments At The Nankai Trough

Subduction zone earthquakes release energy accounted for90%of energy released by global seismicity (Lay,2005), and the earthquake and tsunami generated by the earthquake activity have the disastrous effects to densely populated areas. Therefore, the study of subduction zone area is becoming a hot spot of earth science research, the Nankai Trough Seismogenic Zone Experiment is a comprehensive multidisciplinary program, and it research the basic characteristics of rocks, sediments and fluid of subduction zone area to better understand the evolution rule of subduction zones and its causes of the earthquake (Margins Steering Committee,2004). Hole C0004and C0008A of Integrated Ocean Drilling Program (IODP) Expedition316is located at at the shallow portion of the accretionary prismof the Nankai Trough where the megasplay fault system branches and approaches the surface.In order to explore magnetic characteristics of the sediment coming from different tectonic position and provide information for tectonic and environmental evolution of the Nankai Trough, in this paper, the trough of the south China sea voyage316Sites C0004, C0008A stance columnar samples was studied by means of system of environmental magnetism. Environmental magnetism study shows the environment of the hole of C0004, C0008A are reductive environment, magnetic minerals are mainly iron sulfide (pyrite, greigite, pyrrhotite) and coarse grain of magnetite. Sulfate-methane conversion interface identified using magnetism parameters: the top boundary of the SMT of hole C0004is at2m CSF, the bottom boundary is at20m CSF, and the SMT of hole C0008A is between3to15m CSF. Magnetic characteristics of sediment have a good response to the tectonic evolution of the accretionary wedge. Affected by fluid the pyritization of sediment of Hold C0004is complete.