Nature and origin of the sedimentary pile subducting in the Nankai Through

Author(s): Chauvel, Catherine; Garcon, Marion; Yobregat, Elsa; Chipoulet, Clara; Labanieh, S.
Author Affiliation(s): Primary:
Institut des Sciences de la Terre, Grenoble, France
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Nd-Hf isotopes and trace and major element concentrations were measured on bulk sediments recovered at Site C0012 during IODP Expedition 322 and 333 in the Shikoku basin. We analyzed the composition of different lithologies such as clay, claystone, sand, sandstone, and ash layers, all through the sedimentary pile, from the surface to the sediment-basalt interface, in order to identify compositional trends and source variations with depth. Major and trace element contents of the background sediments (hemipelagic mudstone) are very homogenous and span a relatively small range of values throughout the entire sedimentary pile. Their composition resembles that of the average upper continental crust of Rudnick and Gao (2003, Treatise on Geochemistry, Vol.3, p. 1-64). Nd and Hf isotopes are more variable, relatively unradiogenic (-8 < εNd < -3 ; -4 < εHf < +5) but display no systematic variations with depth (Fig. 1). Such isotopic compositions indicate that the background sedimentation of the Shikoku basin may consist of volcaniclastic material from the Izu-Bonin and/or Ryukyu arcs, detrital material eroded from SW Japan and relatively high amount of an evolved continental-derived component, probably Chinese loess as already suggested by Mahomet (2005, Sediment. Geol., 182, p.183-199). Compared to the background sedimentation, volcanic ash layers and volcaniclastic sandstones have very different trace element patterns and more radiogenic Nd-Hf isotopic signature (Fig. 1). Our results allow us to distinguish at least two different volcanic sources for these deposits. At the bottom of the sedimentary pile, siliciclastic sandstones with a mid-Miocene age are present; they have remarkably low εNd and εHf values (i.e. εNd < -8 and εHf < -5). Such isotopic compositions clearly demonstrate that their source cannot be the Japanese mainland, as suggested by previous studies (e.g. Underwood et al, 2009, Exp.322 PR ; Fergusson, 2003, Proc. ODP, Sci. Results 190/196). These sandstones are also too coarse to result from an accumulation of Chinese loess transported by wind (particles usually finer than 40 µm). Given the location of the Shikoku basin at 15 Ma, we suggest that the siliciclastic sandstones mainly consists of detrital materials transported by Chinese rivers up to the sea in the Shikoku basin.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Expedition 322; Expedition 333; IODP Site C0012; Integrated Ocean Drilling Program; Mineral composition; NanTroSEIZE; North Pacific; Northwest Pacific; Pacific Ocean; Shikoku Basin; Subduction zones; West Pacific
Coordinates: N324453 N324453 E1365501 E1365501
Record ID: 2015031158
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