Downhole temperature measurements at NanTroSEIZE input Sites and their implications

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Author(s): Henry, P.; Kanamatsu, T.; Marcaillou, B.; Matsubayashi, O.; Lee, Y.; Underwood, M.; Moe, K.
Integrated Ocean Drilling Program, Expedition 333 Scientists
Author Affiliation(s): Primary:
Aix-Marseille University, Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement, Aix-En-Provence, France
Japan Agency for Marine-Earth Science and Technology, Japan
Universite des Antilles et de la Guyane-Ponte a Pitre, France
National Institute of Advances Industrial Science and Technology, Japan
Korea Institute of Geoscience and Mineral Resources, South Korea
University of Missouri, United States
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: Short heat flow probe data available in the Nankai Trough display a wide range of variation from 80 to 150 mW/m2. Accurate determination of heat flow at depths was needed to better constrain the seaward boundary condition in thermal models of subduction, and as an input parameter for models of diagenesis and fluid-rock interaction in the sediment and oceanic crust. One objective of NanTroSEIZE expedition 333 was to perform bottom-hole measurements of temperature with APCT-3 at two sites located on the seaward side of Nankai Trough. Site C0011 is located on the flank of the Kashinosaki Knoll where sediment thickness is ≈1 km and Site C0012 is located near its summit where sediment thickness is 520 m. These two sites had been partly cored during NanTroSEIZE Exp. 322, which revealed contrasting trends in pore fluid chemistry with depth. Chlorinity decreasing with depth at Site C0011 was interpreted as a consequence of smectite-illite reaction. Chorinity increasing with depth at Site C0012 could result from alteration of volcanic material in the sediment and from diffusional exchange with the basaltic basement. Exp. 333 documented a major change of physical properties associated with a sharp decrease in dissolved silica concentration at ≈250 mbsf at Site C0011 and tentatively identified a similar transition between 60 and 80 mbsf at Site C0012. From an analogy with results obtained after ODP Leg 190 (Spinelli et al., 2007), it can be proposed that the process responsible for an anomalously high porosity of the sediment above this boundary is cementation by opal-CT and opal dissolution with precipitation of quartz below the boundary. Heat flow measured during Expedition 333 is 90 mW/m2 at Site C0011 and 140 mW/m2 at Site C0012. The measurement at site C0011 is consistent with the heat flow expected from conductive cooling of a 20 Ma lithosphere after correction for the thermal impact of the sedimentation. At site C0012 the measurement is 30% higher than expected. The temperatures extrapolated to basement are, respectively, ≈80° and ≈65°C at Sites C0011 and C0012. Preliminary conclusions follow. (1) Sedimentation rate variations and thermal convection in the oceanic basement could account for the heat flow contrast between sites and be the main factors behind heat flow variability in Nankai Trough. (2) The current temperature of the opal-quartz diagenetic front is unusually low (25°C at Site C0011, as opposed to 55°C at ODP Site 1173), suggesting either strong variations of heat flow with time or an influence of other factors. (3) The temperature conditions in the lowermost sediments at Site C0011 are within the temperature window for the onset of the smectite-illite reaction (∼55°-90°C) and illitization should continue into the trench where the Shikoku Basin sediments are buried to greater depths. As proposed after Exp. 322, the contrasting chlorinity trends observed at Site C0011 and C0012 could thus result primarily from diffusional exchange with the lower part of the sedimentary column and also, at site C0012, with basement.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Basement; Boundary conditions; Concentration; Crust; Diagenesis; Heat flow; IODP Site C0011; IODP Site C0012; Integrated Ocean Drilling Program; Lithosphere; Measurement; Models; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Oceanic crust; Pacific Ocean; Plate tectonics; Sediments; Shikoku Basin; Silica; Solutes; Subduction; Temperature; Thermal anomalies; Water-rock interaction; West Pacific
Coordinates: N324944 N324945 E1365256 E1365254
N324453 N324453 E1365501 E1365501
Record ID: 2015100784
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