Lithium isotopic evidence for deep-seated fluids from Kumano mud volcano in Nankai accretionary prism

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Author(s): Nishio, Y.; Ijiri, A.; Toki, T.; Morono, Y.; Inagaki, F.
Author Affiliation(s): Primary:
Japan Agency for Marine-Earth Science and Technology, Kochi Institute, Nankoku, Japan
University of Ryukyus, Faculty of Science, Nishihara, Japan
Volume Title: AGU 2011 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2011; American Geophysical Union 2011 fall meeting, San Francisco, CA, Dec. 5-9, 2011. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Deep-seated fluids in the accretionary prism play an important role in the occurrence of earthquakes near trench. Knowledge of expelled fluids associated with mud volcanoes activity helps to delineate possible fluid origins and/or sediment-water interactions at depth within the accretionary prisms. It is, however, difficult to research deep-seated fluids from pore water samples using traditional hydrogen and oxygen isotopic compositions owing to contamination from seawater. Lithium (Li) is relatively unsusceptible to contamination from seawater because the Li content of deep-seated fluid is significantly higher than that of seawater. The amount of Li leached from sediment to fluid increases dramatically with temperature, and the leached Li is retained in the fluid as it cools. Lithium has two stable isotopes, 7Li and 6Li, with respective relative abundances of 92.5% and 7.5%, and 7Li/6Li ratios may provide further insight into the origin of deep-seated fluids. To provide new constraint on the origin of forearc mud volcano fluid, we analyzed Li isotopic compositions of pore fluids in Kumano mud volcano in Nankai accretionary prism. Analyzed samples, C9004 and C9005 were recovered from center and margin of mud volcano, respectively, using deep sea drilling vessel "Chikyu" in March, 2009. The results show that δ7Li values of analyzed Kumano mud volcano fluid vary from +5.5 ppm to +10.6 ppm (δ7Li = [[7Li/6Li]sample/[7Li/6Li]L-SVEC standard - 1] × 1000). It has already reported that the δ7Li values of decollement fluid in Nankai subduction zone range from +18 ppm to +20 ppm (You et al., 1995. Geology 23, 37-40). Judging from the Cl/Li ratios are significantly lower than seawater value, the Li isotopic difference between Kumano mud volcano fluids and Nankai decollement fluids are not due to seawater contamination (Fig. 1). Our Li isotopic data suggest that the Li in Kumano mud volcano fluids are originated from deeper (higher temperature) than those in the Nankai decollement fluids.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Accretion; Alkali metals; Fluid dynamics; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Kumano Basin; Li-7/Li-6; Lithium; Metals; Mud volcanoes; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Ocean floors; Pacific Ocean; Pore water; Stable isotopes; Subduction zones; West Pacific
Record ID: 2015077231
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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