Previous   |    Next

doi:10.2204/iodp.proc.322.207.2013

Introduction

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) was designed to constrain in situ properties at seismogenic depths in an effort to understand fault zone behavior during earthquake nucleation and rupture propagation (Tobin and Kinoshita, 2006). Two sites were drilled during Integrated Ocean Drilling Program (IODP) Expeditions 322 and 333 on the subducting Philippine Sea plate to characterize the subducting materials before deformation. Site C0011, located on the northeast flank of a prominent bathymetric high (Kashinosaki Knoll), targeted a 1050 m sediment column (based on the seismic profile), of which we were able to recover 858 m. This section consists of sandy turbidite intervals within hemipelagic sediment (Figs. F1, F2). Site C0012 targeted a 526 m sedimentary section near the crest of the Kashinosaki Knoll (Fig. F1). Coring penetrated 23 m into igneous basement at 630.5 meters below seafloor (mbsf) (see the “Expedition 322 summary” chapter [Underwood et al., 2010]; Expedition 333 Scientists, 2012).

A fundamental component of our understanding of subduction inputs focuses on sampling sediments, fluids, and crustal rocks because fluids and associated diagenetic reactions affect hydrological parameters (e.g., permeability and pore pressure) and may regulate the mechanical state of the plate interface at depth. The isotopic composition of strontium (Sr) acts as a conservative tracer that does not undergo biological fractionation (Mook, 2001). Because of this property, ⁸⁷Sr/⁸⁶Sr has proved to be valuable in establishing fluid-rock reactions, sources, and fluid mixing (e.g., Torres et al., 2004; Teichert et al., 2005; Solomon et al., 2009; Joseph et al., 2012). Potential source materials responsible for the ⁸⁷Sr/⁸⁶Sr of interstitial waters in this region are continental detritus (⁸⁷Sr/⁸⁶Sr ~ 0.7119–0.7133), biogenic calcite (⁸⁷Sr/⁸⁶Sr ~ 0.7075–0.7092), volcanic ash (⁸⁷Sr/⁸⁶Sr ~ 0.706), and oceanic crust (⁸⁷Sr/⁸⁶Sr ~ 0.703) (Veizer, 1989). Here we report on the ⁸⁷Sr/⁸⁶Sr composition of fluids sampled from the sediment column prior to subduction.

Top of page   |    Previous   |    Next