Effect of an ocean ridge model on geomagnetic variations

Duba, A.; Lilley, F. E. M.

doi:10.1029/jb077i035p07100

Cited by 16 publications

(3 citation statements)

References 21 publications

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“…The upper mantle is thought to be composed of peridotite (Ringwood 1969), the most conductive constituent of which is olivine, and the exponential decrease of olivine resistivity with temperature could provide an explanation. Combining the temperature-depth profile of MacDonald (1965) with the compilation of experimental conductivity-temperature results for 10 per cent fayalite olivine, (Duba & Lilley 1972), it is seen that by a depth of order 150 km and deeper the resistivity of olivine might be expected to decrease to about 10ohm-m. me pr-po.edmod/Ii-/ii. reasom~i agceemeflt ma &m& 1 he general conductivity section, then, appears consistent with that found in a number of other continental magnetotelluric soundings (Keller 1971).…”

Section: Discussionmentioning

confidence: 95%

A Magnetotelluric Traverse in Southern Australia

Tammemagi

Lilley

1973

Geophysical Journal International

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Telluric potentials were recorded at nine sites stretching 1000 km from east of Wilcannia (N.S.W.) to west of Coober Pedy (S.A.) in south central Australia. These were combined with data obtained from a simultaneous magnetic variometer study, and analysed to yield magnetotelluric impedance tensors. The estimation of probable errors for the impedance tensors was an important part of the calculations. Numerical calculations for two-dimensional models showed that the observed data could be explained by a conductive-resistive-conductive layering. The top conductive (10 ohm-m) layer is approximately 5 km deep and the ensuing resistive section (1000ohm-m) continues to a depth of about 230km. This is underlain by an indeterminably thick conductive layer. Embedded in this general structure is an extremely good conductor (0.1 ohm-m) which strikes north-south. The detection of this good conductor is the main result of this work. The good conductor lies just east of the Adelaide Geosyncline at a depth of a few kilometres, and is of minimum thickness 10 km. It is thought to be related to the accretion of the eastern portion of the Australian continent on to the stable western Precambrian platform by tectonic processes. The strong anisotropy present in the magnetotelluric data at all sites could not be explained by induction in conductive sediments, and is thought to be caused by localized conductivity inhomogeneities distorting current flow.

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Section: Discussionmentioning

confidence: 95%

A Magnetotelluric Traverse in Southern Australia

Tammemagi

Lilley

1973

Geophysical Journal International

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“…It is now generally accepted that the major phase in the earth's upper mantle is olivine with an approximate composition Mgx.sFe0.•.SiO4 [Fujisawa, 1968]. Published values of electrical conductivity a of olivine of this composition (either single crystal or polycrystalline) at high temperatures show very poor agreement [Duba and Lilley, 1972]. In many instances the difference can be attributed either to trace cation impurities or to different FeS+/Fe 2+ ratios [Duba, 1972].…”

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confidence: 99%

Electrical conductivity of olivine at high pressure and under controlled oxygen fugacity

Duba¹,

Heard²,

Schock³

1974

J. Geophys. Res.

166

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Electrical conductivity σ in the [100] direction has been determined for the Red Sea olivine (Fo 91) to 1440°C and 8 kbar in argon. No systematic variation of σ with pressure was observed. The effect of an 8‐kbar variation in pressure over the 1270°–1440°C range is equivalent to a temperature uncertainty of ±5°C. We have also determined σ on the same sample up to 1660°C with controlled oxygen fugacity ƒo2 at 1 bar of total pressure. By using published σ‐depth profiles and assuming olivine as the major phase in the earth's upper mantle with ƒ o 2 = 10 −6 ‐10 −3 bar, temperatures of the upper mantle are calculated as a function of depth. The temperature uncertainty due to possible pressure effects is 2–5 times smaller than that resulting from the ambiguity in published σ‐depth profiles.

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“…7) and the requirement that it form a lateral conductivity contrast with the sub-continental conductivity profiles. (Assuming the conductivity of the partial melt could approach that of molten basalt above 120O0C, the bulk conductivity could rise to values of order 1 (ohm-m)-' (Duba & Lilley 1972). This is an interesting possibility from a tectonic viewpoint, since under stable oceanic basins, surface wave dispersion data (Brune 1969;Kanamori & Press 1970) and oceanic heat flow (Sclater & Francheteau 1970;Sclater 1972) suggest low-Q partial melt zones may not lie at depths shallower than about 60 km.…”

Section: Geological Interpretationmentioning

confidence: 99%

Electrical conductivity structure in the southeast Australian region

Bennett

Lilley

1974

Geoexploration

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An array of variometers across south-east Australia has recorded natural magnetic variations having power in a frequency band of 0.04-10 cycles/hr. The set data have outlined two major regions of high terrestrial electrical conductivity (c); the first beneath the sea floor off the Australian southeast coast; the second in the vicinity of the most recent eruptive centres of the ' Newer Volcanics ' in western Victoria. Both regions may indicate low Q upper mantle zones. Daily variation data provide significant control on permissible conductivity models.

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Effect of an ocean ridge model on geomagnetic variations

Cited by 16 publications

References 21 publications

A Magnetotelluric Traverse in Southern Australia

A Magnetotelluric Traverse in Southern Australia

Electrical conductivity of olivine at high pressure and under controlled oxygen fugacity

Electrical conductivity structure in the southeast Australian region

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