Radiative thermal conductivity in obsidian and estimates of heat transfer in magma bodies

Journal Article · Sun May 10 00:00:00 EDT 1981 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB086iB05p03684· OSTI ID:6289837

Stein, J; Shankland, T J; Nitsan, U

The optical transmission spectra of four ryholitic obsidian samples were measured in order to determine the importance of radiative heat transfer in granite magmas. The spectra, obtained in the temperature range 20-800/sup 0/C, show that the radiative spectral window in these samples is limited by a charge transfer band in the UV (400 nm) and Si-O stretching overtone in the IR (4500 nm). Within this window the main obstacles to radiative transfer, in order of decreasing importance, are background scattering, a water band centered at 2800 nm, and an Fe/sup 2 +/ crystal field band at 1100 nm. Unlike crystalline silicates the absorption bands in obsidian do not broaden significantly as temperature increases. As a result, the temperature dependence of the calculated radiative thermal conductivity K/sub R/ is dominated by the T/sup ..beta../ term. Actual values of K/sub R/ increase from 9 x 10/sup -5/ to 1 x 1/sup -3/ cal cm/sup -1/ s/sup -1/ deg/sup -1/ between 300/sup 0/ and 800/sup 0/C, the high-temperature value being comparable to the lattice thermal conductivity in obsidian and a lower limit for K/sub R/ in granitic melts. As the scattering coefficient in melts is probably significantly lower than in obsidian, the radiative conductivity in active plutons is likely to be much higher. As an example, if scattering and the water band are removed from the observed spectra of the obsidian samples, calculated values of K/sub R/ could increase by a factor of 5, to about 5 x 10/sup -3/ cal cm/sup -1/ s/sup -1/ deg/sup -1/ at 1000/sup 0/C.

• Research Organization: Geophysics Group, Los Alamos Scientific Laboratory, Los Alamos, New Mexico 87545
• OSTI ID: 6289837
• Journal Information: J. Geophys. Res.; (United States), Vol. 86:B5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
MAGMA
ABSORPTION SPECTRA
HEAT TRANSFER
RHYOLITES
THERMAL CONDUCTIVITY
EARTH CRUST
GLASS
HIGH TEMPERATURE
MEDIUM TEMPERATURE
PHOTON TRANSPORT
SILICATES
TEMPERATURE DEPENDENCE
ENERGY TRANSFER
IGNEOUS ROCKS
NEUTRAL-PARTICLE TRANSPORT
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RADIATION TRANSPORT
ROCKS
SILICON COMPOUNDS
SPECTRA
THERMODYNAMIC PROPERTIES
VOLCANIC ROCKS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)