Thermal conductivity of vesicular basalt from Hawaii

Abstract

Thermal conductivity measurements at 35°C under 30 bars uniaxial pressure were made on 61 samples of olivine‐bearing basalt with solidity γ (1 − ф, where ф is porosity) ranging from 2 to 98%.Two series of tests were made, one with air and the other with water in the pores. Conductivity varies with γ, the abundance of olivine phenocrysts, and the nature of the pore fluid. From the lowest to the highest γ, the observed conductivities range from 0.2 to 4.3×10−3 cal/cm s °C for samples with air in the pores and from 2.0 to 5.8×10−3 cal/cm s °C for samples with water in the pores. Differences in vesicle size in samples of the same total porosity do not affect the thermal conductivity. The measured conductivities were compared with values calculated on the basis of 11 theoretical models and combinations using conductivities of air and water and a reasonably well determined conductivity of fully solid basalt. For air‐saturated samples the values calculated by several models compare well with observed values for samples with solidity of <0.9. Samples with high solidity have measured conductivities appreciably less than the conductivity determined for fully solid rock; in olivine‐poor samples the difference is 40%. For water‐saturated samples the measured values also are less than the value for solid rock, 15% less for olivine‐poor samples. We postulate that the difference between observed and calculated conductivities for both air‐ and water‐saturated samples is due to the insulating effect of micropores and thin microfractures that were formed during initial cooling of the volcanic samples; these micropores and microfractures were not completely filled with water during our measurements of water‐saturated samples. In still‐cooling newly formed lava the microfractures will not yet have opened, and the conductivity of the lava may be higher than what would be predicted from our measurements. When empirical correction factors are used to account for the insulating effect of the microfractures and micropores, the conductivity of basalt can be predicted by two models. When the mean of the parallel and series models is used, the conductivity of both air‐ and water‐saturated samples can be predicted within 0.3×10−3 cal/cm s °C from the mineral and pore fluid compositions, conductivities, and proportions. With a quadratic model the values for the square root of conductivity form linear plots against solidity, requiring only the porosity and abundance of olivine phenocrysts of Hawaiian basalts to estimate conductivity within 0.2×10−3 cal/cm s °C.

Effects of Alteration on Physical Properties of Basalts from the Pigafetta and East Mariana Basins

“…Scatter in the data at high thermal conductivities may in part reflect determination of these values by extrapolation beyond the range of conductivities of the calibration standards (Lancelot, Larson, et al, 1990). The trend of the thermal conductivity data roughly follows the relationship derived by Robertson and Peck (1974), with a displacement toward higher conductivity values (Fig. 9).…”

“…The minute, devitrified glass inclusions in the phenocrysts are also slightly larger and commonly coalesce in the two more altered samples compared to those of the basal sample. The groundmass in Hyndman et al, 1984) between porosity (Φ) and thermal conductivity (K) for basalts with 7% olivine from Robertson and Peck (1974). the center and near top samples is almost completely reduced to remnants of skeletal plagioclase and clumps of dark-brown to black opaques (spinel and sphene surrounded by Fe-oxyhydroxides) floating in a matrix of clay and cloudy calcite.…”

The Physical Nature of Young Upper Oceanic Crust on the Mid-Atlantic Ridge, Deep Sea Drilling Project Hole 395A

“…The mean sample thermal conductivity is 1.77 W m~^K~1, the mean thermal diffusivity is 0.68 mm 2 s~ *, and the mean heat capacity is 0.91 J g~ l0 K~l, at an average porosity of 4.0% (Hyndman et al, this volume). A number of models have been proposed relating thermal conductivity to porosity Φ, but the most appropriate appears to be that of Robertson and Peck (1974), in which…”

Tables of room temperature electrical properties for selected rocks and minerals with dielectric permittivity statistics

“…Petrophysics Laboratory sample collection. Those with bracketed numbers beginning with "R" are from Robertson and Peck (1974). Those with other bracketed numbers are from Hunt and Salisbury (1976) and references therein.…”