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Input Site U13811

R.N. Harris, A. Sakaguchi, K. Petronotis, A.T. Baxter, R. Berg, A. Burkett, D. Charpentier, J. Choi, P. Diz Ferreiro, M. Hamahashi, Y. Hashimoto, K. Heydolph, L. Jovane, M. Kastner, W. Kurz, S.O. Kutterolf, Y. Li, A. Malinverno, K.M. Martin, C. Millan, D.B. Nascimento, S. Saito, M.I. Sandoval Gutierrez, E.J. Screaton, C.E. Smith-Duque, E.A. Solomon, S.M. Straub, W. Tanikawa, M.E. Torres, H. Uchimura, P. Vannucchi, Y. Yamamoto, Q. Yan, and X. Zhao2

Background and objectives

The primary objective of Integrated Ocean Drilling Program (IODP) Expedition 344 was to sample and quantify the material comprising the seismogenic zone of an erosive subduction margin. Fundamental to this objective is an understanding of the nature of the sediment and oceanic crust entering the seismogenic zone, the hydrologic system, and the thermal state of the igneous oceanic crust. Site U1381 serves as a reference site on the subducting aseismic Cocos Ridge.

Site U1381 is located on seismic Line BGR99-7 at common midpoint 5740 (Fig. F1) and is ~4.5 km seaward of the deformation front offshore the Osa Peninsula and Caño Island (Fig. F2). This site was chosen for multiple reasons. First, it is located on a local basement high. Basement relief often focuses fluid flow, so data from this site are likely to document the vigor of fluid flow in this area. Second, a clear seismic record of the plate stratigraphy is present at this site. The seismic section shows a 100 m thick sediment section resting on reflective basement interpreted as Cocos Ridge igneous crust. The sedimentary section is composed of pelagic and hemipelagic sediments (Expedition 334 Scientists, 2012). Sediment thickness along the seismic transect (southwest–northeast) is variable and reflects the relief of the Cocos Ridge basement. Third, Site U1381 is far enough from the frontal thrust that it is expected to be reasonably free from the influence of downslope debris flows that might emanate from the convergent margin slope. Finally, Site U1381 is located on the same seismic line as Sites U1412, U1380, and U1379. Paleomagnetic data constrain the age of this portion of Cocos Ridge to 14 Ma (Barckhausen et al., 2001).

During IODP Expedition 334, Site U1381 was cored using the rotary core barrel (RCB) system because the primary objective was recovery of oceanic crust and time constraints precluded advanced piston corer (APC) drilling through the sediment section (Expedition 334 Scientists, 2012). However, a disadvantage of the RCB system is that recovered sediments are highly disturbed. Thus, a primary goal for revisiting this site was to core the sediment section with the APC to obtain more pristine samples. As a result of APC coring, we recovered the uppermost 13 m of sediment that was not recovered during Expedition 334, identified a sediment hiatus of ~9–11 m.y. (see “Paleontology and biostratigraphy”), recovered 84 tephra layers (see “Lithostratigraphy and petrology”), and identified fractures and veins (see “Structural geology”).

1 Harris, R.N., Sakaguchi, A., Petronotis, K., Baxter, A.T., Berg, R., Burkett, A., Charpentier, D., Choi, J., Diz Ferreiro, P., Hamahashi, M., Hashimoto, Y., Heydolph, K., Jovane, L., Kastner, M., Kurz, W., Kutterolf, S.O., Li, Y., Malinverno, A., Martin, K.M., Millan, C., Nascimento, D.B., Saito, S., Sandoval Gutierrez, M.I., Screaton, E.J., Smith-Duque, C.E., Solomon, E.A., Straub, S.M., Tanikawa, W., Torres, M.E., Uchimura, H., Vannucchi, P., Yamamoto, Y., Yan, Q., and Zhao, X., 2013. Input Site U1381. In Harris, R.N., Sakaguchi, A., Petronotis, K., and the Expedition 344 Scientists, Proc. IODP, 344: College Station, TX (Integrated Ocean Drilling Program). doi:10.2204/iodp.proc.344.103.2013

2Expedition 344 Scientists’ addresses.

Publication: 11 December 2013
MS 344-103