Publication Date:
2022-05-26
Description:
Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Lithos 109 (2009): 131-143, doi:10.1016/j.lithos.2008.10.014.
Description:
Can mineral physics and mixing theories explain field observations of seismic velocity
and electrical conductivity, and is there an advantage to combining seismological and
electromagnetic techniques? These two questions are at the heart of this paper. Using
phenomologically-derived state equations for individual minerals coupled with multi-phase,
Hashin-Shtrikman extremal-bound theory we derive the likely shear and compressional
velocities and electrical conductivity at three depths, 100 km, 150 km and 200 km, beneath
the central part of the Slave craton and beneath the Kimberley region of the Kaapvaal craton
based on known petrologically-observed mineral abundances and magnesium numbers,
combined with estimates of temperatures and pressures. We demonstrate that there are
measurable differences between the physical properties of the two lithospheres for the upper
depths, primarily due to the different ambient temperature, but that differences in velocity are
negligibly small at 200 km. We also show that there is an advantage to combining seismic and
electromagnetic data, given that conductivity is exponentially dependent on temperature
whereas the shear and bulk moduli have only a linear dependence in cratonic lithospheric
rocks.
Focussing on a known discontinuity between harzburgite-dominated and lherzolitic
mantle in the Slave craton at a depth of about 160 km, we demonstrate that the amplitude of
compressional (P) wave to shear (S) wave conversions would be very weak, and so
explanations for the seismological (receiver function) observations must either appeal to
effects we have not considered (perhaps anisotropy), or imply that the laboratory data require
further refinement.
Keywords:
Archean lithosphere
;
Seismic velocity
;
Electrical conductivity
;
Mineral physics
;
Extremal bounds
;
Velocity-conductivity relationship
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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