Environmental Magnetism Research Of C0011B Core Of IODP Expedition322

Integrated Ocean Drilling Program (IODP) Expedition322is part of the NankaiTrough Seismogenic Zone Experiment (NanTroSEIZE) and was designed todocument characteristics of incoming sedimentary strata and igneous basement in theShikoku Basin of northern Philippine Sea prior to their arrival beneath the Eurasianplate. Site C0011is located on the northwest flank of the Kashinosaki Knoll at thesubduction front, is from7.6to14Ma in age and extends from340mbsf to876mbsf(without coring from782to844mbsf), the totall core recovery is70%and can bedivided into five lithologic units.A detailed environmental magnetism and rock magnetism research was carriedout on503samples in the II、III and IV lithologic units. The Hole C0011B can bedivided into three sections based on the variation characteristics of all environmentalmagnetism parameters and their ratios. Section A is located at II lithologic unit, themiddle Shikoku Basin facies which is first established; III lithologic unit is dividedinto two sections at the boundary of Section B and C, which is the drop of the rate ofhemipelagic sedimentation at the Shikoku Basin in10.8Ma. Section A and B, ischaracterized by the higher concentration of ferromagnetic minerals and fineferromagnetic minerals than Section C. Isothermal remanent magnetization (IRM) andremanence coercivity (Bcr) acquisition analysis implied that ferrimagnetic mineral oflow-coercivity is a principal magnetic mineral. The dependence of the x with SIRMindicate that titanomagnetite is a principal magnetic mineral in Section A andparamagnetic mineral in Section B and C. Thermal magnetic experiments indicate thatprincipal magnetic mineral may be titanomagnetite mineral, Section A has a highercontent of titanomagnetite minerals than Section B and C. Hysteresis parameters aresummarized in a typical Day plot and indicate that principal magnetic mineral is PSD,the grain size of the magnetic carriers is more coarse and/or the content of MD-grainis higher in Section C than that in Section A and B. As a result, the magneticproperties of Section A and C is completely different and Section B possesses themagnetic characteristics of the two.The previous studies show that the sediment source of Section C is the SW Japanand Section A is the Izu-Bonin Arc. As a result, magnetic properties of the Section Bindicate the transition of the sediment source, is more sensitive than lithologic. So,sedimentary evolution of the region of the C0011B core is: before10.8Ma (the Section C), the sediment source is the SW Japan.10.8～9.1Ma (the Section B),provenance from the two, which mainly in southwestern Japan, Izu-Bonin Arc,supplemented.9.1～7.6Ma (the Section A), primary and secondary relationship ofthe two provenances is reverse.The boundary of Section B and C is the drop of the rate of hemipelagicsedimentation at the Shikoku Basin in10.8Ma. The accretionary complex of the SWJapan was rapidly uplifted and denudation during the early period of subduction ofShikoku Basin, so the change may corresponds to the cessation of this tectonic event.