Convection in the oceanic crust; simulation of observations from Deep Sea Drilling Project Hole 504B, Costa Rica Rift

Online Access: Get full text
doi: 10.1029/JB091iB05p04877
Author(s): Williams, Colin F.; Narasimhan, T. N.; Anderson, Roger N.; Zoback, Mark D.; Becker, Keir
Author Affiliation(s): Primary:
Lawrence Berkeley Lab., Earth Sci. Div., Berkeley, CA, United States
Lamont-Doherty Geol. Obs, United States
Stanford Univ., United States
Scripps Inst. Oceanogr., United States
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 91(B5), p.4877-4889. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 29 refs.; illus. incl. 2 tables, sketch map
Summary: Three-dimensional modeling of convection in the oceanic crust at Deep Sea Drilling Project site 504B using an integral finite difference model reasonably duplicates underpressures, surface heat flow, downhole temperature profiles, and fluid drawdown rates observed by in situ measurements in the borehole. The major constraint to produce such good fits is the permeability versus depth function, a quantity which was actually measured in the borehole. Pronounced "underpressuring" (fluid pressures less than hydrostatic) occurs throughout the convection cell if and only if a tight, nearly impermeable cap rock (chert) exists over the cell. The computed flow rates of water from the ocean through the borehole into the basalt agree closely with the measurements carried out 65, 720, and 1280 days after drilling. The model predicts an inflow rate of 50-60 L/h during the expected next occupation of the site by mid-1986. Numerical modeling has confirmed that an active hydrothermal convection cell exists in the region of hole 504B and that a very low permeability cap rock is necessary for the existence of the convection cell. Convective hydrothermal cells in the oceanic crust can explain observed periodic heat flow variations in suboceanic crust.
Year of Publication: 1986
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Convection; Convection currents; Costa Rica Rift; Crust; Currents; DSDP Site 504; Deep Sea Drilling Project; East Pacific; East Pacific Rise; Finite difference analysis; Galapagos Rift; Heat flow; Hydrothermal conditions; IPOD; Leg 111; Leg 137; Leg 140; Leg 148; Leg 69; Leg 70; Leg 83; Leg 92; Mathematical models; Ocean Drilling Program; Oceanic crust; Pacific Ocean; Simulation; Statistical analysis; Tectonophysics; Theoretical studies; Three-dimensional models
Coordinates: N000000 N040000 W0810000 W0870000
Record ID: 1986059407
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.