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Deep Sea Drilling Project geothermal measurements: A review
Author(s) -
Hyndman R. D.,
Langseth M. G.,
Von Herzen R. P.
Publication year - 1987
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg025i008p01563
Subject(s) - borehole , scientific drilling , drilling , geothermal gradient , geology , heat flux , heat flow , crust , deep sea , geothermal energy , sedimentary rock , arctic , geophysics , thermal , petrology , oceanography , heat transfer , geotechnical engineering , paleontology , meteorology , mechanics , mechanical engineering , physics , engineering
In this article the geothermal measurements made from the scientific drilling ship Glomar Challenger are evaluated, edited, and reviewed. For a number of sites the heat flow values given in the Initial Reports of the Deep Sea Drilling Project have been revised; less than half of the boreholes in which thermal measurements were attempted gave reliable data. By the end of the Deep Sea Drilling Project (DSDP) in 1983, reliable borehole heat flow measurements had been obtained at some 80 sites in all of the world oceans except the Arctic. The reliable values are considered to represent the deeper heat flux to within 20%; for a few the accuracy is within 5%. Most temperature measurements have been obtained using probes penetrating the undisturbed sediments at the bottom of the hole at subbottom depths of between 75 m and 250 m, although some data have been obtained at depths less than 30 and over 1000 m. Temperatures have been obtained a significant distance into the crust in eight holes. The main general conclusions are as follows: (1) There are no large or systematic differences between borehole heat flow values and oceanographic probe values obtained nearby. Such a test of shallow‐penetration oceanographic probe measurements was one of the first objectives of the DSDP heat flow program. (2) There are very few clear, smooth changes of borehole heat flow with depth in areas with thick sedimentary sections that are indicative of either long‐term bottom water temperature changes (tens to thousands of years) or large heat production in the sediments. Vertical migration of sediment interstitial pore water is suggested by nonlinear temperature‐depth profiles at a few sites, particularly where the sediment is relatively thin and the temperature gradient is high. (3) Temperatures in the crustal parts of deep‐sea drill holes exhibit a wide range of behavior, generally indicating hydrothermal circulation in the upper crust. At five sites, seawater is inferred to be moving down the holes into the crust, indicating low formation pressures and very high permeability in the upper crust. In two deep holes, however, such flow is limited to above several hundred meters into the crust, and heat fluxes close to theoretical cooling lithosphere values for the age of the crust (6 and 7 Ma) are found at greater depth. These sites suggest that hydrothermal circulation may be concentrated at shallow depths in the crust. Summary tables are presented of the heat flow data considered to be reliable after review and revision, and an appendix provides detailed comments on all the measurements for which data are available. Geothermal measurements are continuing on the new Ocean Drilling Program ship JOIDES Resolution .