Preliminary magnetostratigraphy of cores collected during IODP Expedition 344 (CRISP-A2) offshore Costa Rica

Integrated Ocean Drilling Program (IODP) Expedition 344 (CRISP-A2 - Costa Rica Seismogenesis Project, Program A Stage 2) investigated the tectonic and oceanographic evolution of the pacific erosive subduction margin west of Costa Rica, in front of Osa Peninsula. One objective of this expedition is to establish the course of volcanic activity in relation to anomalous subduction zone geometries and to analyze the impact of these changes on the regional and local paleoceanographic evolution for the last ~20 Ma. Expedition 344 drilled 5 sites which complement the 2011 Expedition 334 (CRISP-A1) that recovered volcaniclastics from the same area. Initial shipboard paleomagnetic results demonstrate that sediments and igneous basement from the drill sites of Exp. 344 contain both reversely and normally magnetized samples. Flux-jumps and anomalous events in the measurements with the cryogenic magnetometer have been experienced, imposing an overprint on the natural remanent magnetization (NRM). Preliminary interpretations of shipboard biostratigraphic data at these sites also indicate that the fossils needed to anchor the biostratigraphy are available. Our post-expedition study involves detailed alternating field and thermal demagnetization analysis of discrete samples. Stable characteristic remanent magnetization (ChRM) components are observed throughout the studied cores, following removal of a low stability drilling-induced remanence. Inclination values of ChRM are moderate downward or upward, consistent with the expected inclination for the sites. In order to examine the origin of the ChRM, supportive rock magnetic experiments on the same samples that used for magnetostratigraphy were also conducted. The new magnetic results from this study should help refine the temporal evolution of the sedimentation processes and tectonic activities above and within the Costa Rica seismogenic zone.