HR: 0830h
AN: T11C-0406    [PDF]
TI: Calculating Upper Mantle Heat Flow Values Using Xenolith P-T Data and Temperature-Dependent Thermal Conductivity Estimates
AU: * Morgan, P
EM: Paul.Morgan@nau.edu
AF: Northern Arizona University, Dept. Geology, Box 4099, Flagstaff, AZ 86004 United States
AU: * Morgan, P
EM: Paul.Morgan@nau.edu
AF: ARC National Key Centre, Geochemical Evolution and Metallogeny of Continents, Dept. Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109 Australia
AU: O'Reilly, S Y
EM: sue.oreilly@mq.edu.au
AF: ARC National Key Centre, Geochemical Evolution and Metallogeny of Continents, Dept. Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109 Australia
AB: Lithosphere properties and dynamics are controlled primarily by composition (including fluid content) and temperature. Temperatures may be extrapolated to depth in stable lithosphere from near-surface heat-flow data, but these extrapolated values become increasingly uncertain with depth because of lack of knowledge of depth variations in thermal conductivity and radiogenic heat production. Most heat production, and thus its variability, is concentrated in the continental crust. However, variations in thermal conductivity of rocks that are likely candidates to form a bulk of the middle and lower crust are relatively minor and are relatively temperature insensitive. For oceanic crust the structure and composition are relatively well known and their thermal parameters may be reasonably estimated. At mantle depths, where the extrapolations become more uncertain, heat production is generally very low (although it may be significant over a depth range of 100 km or more), but experimental data suggest that ultramafic compositions dominated by olivine are strongly temperature dependant. Uncertainly in extrapolation of heat flow to depth, and problems in converting this heat flow to temperature because of uncertainties in thermal conductivity, make desirable another method of determining mantle-lithosphere temperatures and heat flow. Mantle xenoliths, pieces of the mantle lithosphere entrained in magmas and brought to the surface by volcanism, generally retain mineral equilibria representative of their pressure (depth) and temperature of origin. Some of these equilibria may be used to estimate these pressures and temperatures allowing the depths and temperatures, the geotherm, from which the xenoliths were extracted to be estimated. Using experimental data, a temperature-dependent relation for the conductivity of olivine has been determined. A new transformation has been developed between the xenolith temperatures and the temperature-dependent thermal conductivity that allows heat flow to be calculated from the slope of the transformed temperature vs. depth data, thus allowing the xenolith data to be used both to provide mantle-lithosphere temperatures and mantle-lithosphere heat flow with temperature-dependent conductivities.
DE: 5134 Thermal properties
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8130 Heat generation and transport
DE: 8147 Planetary interiors (5430, 5724)
DE: 8149 Planetary tectonics (5475)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting