Thermophysical properties of the Earth's crust; in situ measurements from continental and ocean drilling

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doi: 10.1029/JB095iB06p09209
Author(s): Williams, Colin F.; Anderson, Roger N.
Author Affiliation(s): Primary:
Lamont-Doherty Geol. Obs., Palisades, NY, United States
Volume Title: Special section on Logging and downhole measurements in Deep Sea Drilling Project/Ocean Drilling Program deep crustal holes
Source: Special section on Logging and downhole measurements in Deep Sea Drilling Project/Ocean Drilling Program deep crustal holes. Journal of Geophysical Research, 95(B6), p.9209-9236. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 110 refs.; illus. incl. 2 tables
Summary: Knowledge of the variation of thermal conductivity and heat production with depth is critical to understanding the thermal state of the crust. Continental and oceanic drill holes provide unique opportunities for the calibration of empirical and theoretical models relating crustal thermal properties to physical and chemical properties. These calibrations are based on more than 30,000 well log measurements of acoustic velocity (both compressional and shear), density, porosity, radioelement concentrations (K, U, Th), and major element chemistry (Al, Si, Ca, Fe, S, Mg + Na), in formations ranging in age from 5 to 620 Ma and in composition from granitic to gabbroic. The mineralogical data available from induced gamma ray spectroscopy logs, when combined with known mineral thermal conductivities in a model for the thermal conductivity of a crystalline aggregate, enable the in situ application of a laboratory estimation technique and yield continuous conductivity profiles. However, mineralogy-based conductivity models cannot account for the anisotropic conductivity observed in foliated metamorphic rocks. A phonon conduction model, which utilizes acoustic velocity and bulk density measurements, is accurate within ±15% in both isotropic and anisotropic formations of the upper continental crust and in oceanic crustal layers 2C and 3. In oceanic crustal layers 2A and 2B, however, the effects of fracturing on compressional and shear velocities lead to inaccurate results. The heat flow-heat production relationship, which provides one method of determining subsurface heat production, has well-documented limitations. Allis (1979) and Rybach and Buntebarth (1982, 1984), on the basis of laboratory measurements, have proposed quantitative relationships between heat production and rock compositional and physical properties. The well log K, U, and Th data indicate that heat production can be predicted from compositional data within a factor of 2 or 3. Predictions of heat production from acoustic velocity and bulk density measurements are only accurate to within an order of magnitude. Three factors account for these results: (1) the natural variability of velocity and density for a given rock composition, (2) the tendency of U and Th to associate with secondary rather than primary minerals, and (3) U and Th redistribution through fluid flow and metamorphism. Thus seismic velocity based heat production profiles can, at best, be taken as first-order estimates which may misrepresent the complexity of the continental crust. However, the correlation of formations of known heat production with subsurface structures, when combined with a suite of existing techniques for estimating heat production, may lead to more accurate results. Copyright 1990 by the American Geophysical Union.
Year of Publication: 1990
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Cajon Pass; California; Central Connecticut; Connecticut; Crust; DSDP Site 418; DSDP Site 504; Deep Sea Drilling Project; IPOD; In situ; Interpretation; Leg 102; Leg 111; Leg 118; Leg 137; Leg 140; Leg 148; Leg 52; Leg 53; Leg 69; Leg 70; Leg 83; Leg 92; Middlesex County Connecticut; Moodus Connecticut; New York; ODP Site 735; Ocean Drilling Program; Palisades New York; Properties; Rockland County New York; San Bernardino County California; Southeastern New York; Southern California; Tectonophysics; Thermomechanical properties; United States; Well-logging
Record ID: 1990053608
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.

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