Accretion process of sediments below Kumano basin by analyzing cuttings from IODP Exp.319, the first riser drilling

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Author(s): Kawabata, K.; Sakaguchi, A.; Kitamura, Y.; Saito, S.
Author Affiliation(s): Primary:
National Central University, Institute of Geophysics, Taoyuan, Taiwan
Japan Agency for Marine-Earth Science and Technology, IFREE, Yokohama, Japan
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The structure, stress condition and rock properties of accreted sediments in the Nankai Trough have been studied by reflection seismology and deep sea drillings. Accretion processes have been suggested by onland geological studies that the sediments are circulated with undergoing lithification and deformation along thrusts in shallow subduction zone driven by the plate motion. However the process in the modern Nankai Trough has yet to be elucidated. We discuss the accretion process of the shallow Nankai Trough accretionary prism below Kumano basin by clarifying thermal structure and materials by vitrinite measurement and whole rock chemical analyses, respectively, using cuttings samples from IODP The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) the first scientific riser drilling Expedition 319 at Site C0009. Cuttings were collected with an interval of every 5 m from 703.9 to 1604 m and cores were recovered from 1509.7 m to 1593.9 m below sea floor (mbsf). Due to poor consolidation of drilled sediments, cuttings samples typically consist of sand and silt floating in a matrix of mixed sedimentary and drilling muds, and solid rock chips were not retrieved above 802.7 mbsf. Visual description based on macro- and microscopic observation, XRD and XRF analysis, rocks properties and the age of washed cuttings (i.e. grains without mud) were made throughout the hole, which allowed to establish some indexes to estimate lithology. Four lithologic units (Unit I - IV) were defined at Site C0009 based on compositional and textural variations of cuttings samples, which are believed to closely reflect lithologic changes of drilled sequences, and show good consistency with logging data. Unit IV is believed to be accreted sediment by mainly age and the textural change of sediments. Dissoluble component ratios (TiO2/P2O5) and clay content ratios in the samples analyzed by XRF and XRD are different from that in basin sediment, which might support Unit IV are accreted materials. Paleop-maximum Temperature (i.e. highest temperature rock experienced) of drilled sediments is estimated by vitrinite reflectance measurement in cuttings and core samples. Vitrinite is common in all units and the results show 0.2 - 0.3% in reflectance which are indicative of 50 - 60 degree C when considering sedimentary age. The reflectance (temperature) slightly increases depth-ward. There is no large temperature difference between the units including unconformity, which suggests that the temperature distribution is similar to the past or present geothermal gradient and that the accreted sediments (Unit IV) have not subducted, accordingly. Our attempt further connects to the detailed discussion on ongoing accretion processes when we reach to the greater depth in the planned future expeditions of NanTroSEIZE.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Accretionary wedges; Cores; Drilling; Expedition 319; IODP Site C0009; Integrated Ocean Drilling Program; Marine sediments; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Pacific Ocean; Plate tectonics; Sediments; West Pacific
Coordinates: N332728 N332728 E1363209 E1363209
Record ID: 2014082039
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