Implications of measured thermal gradients for water movement through the Northeast Japan accretionary prism

Online Access: Get full text
doi: 10.1029/JB092iB05p03683
Author(s): Reck, Brian H.
Author Affiliation(s): Primary:
Univ. Tex. at Austin, Dep. Geol. Sci., Austin, TX, United States
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 92(B5), p.3683-3690. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 40 refs.; illus. incl. 3 tables
Summary: Thermal gradients of 24°-36°C/km have been found in the slope cover sediments of the accretionary prism off northeast Japan (Deep Sea Drilling Project (DSDP) sites 438A, 439, and 440). These gradients lead to the prediction of temperatures in excess of 400°C at depths of 15 km using an increase in thermal conductivity with depth due to the decrease in porosity. Such temperatures conflict with the predictions of temperatures of 150°C at even greater depths from conductive thermal models and petrologic studies of low-temperature blueschists at similar ancient margins. One-dimensional, steady state conduction and advection via Darcian water flow, of heat, up through the prism was simulated numerically. The measured thermal gradients can be reconciled with temperatures less than 125°C at the prism base by water flowing upward at rates of the order of 10-10 m/s. Such velocities imply that the total volume of water available from compaction of sediments subducted beneath the northeast Japan prism would flow up through a <10 km width of the prism (perpendicular to the trench) and would require the DSDP sites to have been located fortuitously over the localized zone(s) of water flow. Smaller velocities will reproduce the measured gradients, and thus greater widths through which water flow occurs are predicted, if the temperature at the prism base is higher and/or if the prism is thinner and a subduction channel several kilometers high separates the accreted sediments from the descending plate. Where water flow is significant, as likely wherever abundant, water-rich sediments are subducted, thermal gradients below a few kilometers in accretionary prisms may be much lower than near-surface values. This has profound implications for the thermal structure of the prism off northeast Japan and elsewhere.
Year of Publication: 1987
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Accretion; Accretionary wedges; Advection; Asia; DSDP 439; DSDP 440; DSDP Site 438; Deep Sea Drilling Project; Far East; Geothermal gradient; Heat flow; IPOD; Japan; Leg 57; Marine sediments; Measurement; Movement; North Pacific; Northeastern Japan; Northwest Pacific; Pacific Ocean; Plate tectonics; Pore water; Sediments; Subduction zones; Tectonophysics; Temperature; Thermal conductivity; Trenches; West Pacific
Coordinates: N370000 N420000 E1450000 E1400000
Record ID: 1987049580
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.