Archaean cratonic roots, mantle shear zones and deep electrical anisotropy

Mareschal, Marianne; Kellett, Richard; Kurtz, R. D.; Ludden, John; Ji, Shaocheng; Bailey, R. C.

doi:10.1038/375134a0

Cited by 130 publications

(89 citation statements)

References 29 publications

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“…These high pressures are not appropriate for our study of lithospheric minerals, and we assume that pressure dependence is negligible. Karato (1990) suggested that hydrogen diffusion could be a significant contributor to electrical conductivity of normally anhydrous mantle minerals like olivine, and that indeed geophysical remote sensing methods could be used to determine the hydrogen distribution (Gaillard et al, 2003;Karato, 2006 (Mareschal et al, 1995;Ferguson et al, 2005;Frederiksen et al, 2006), although in at least one of these instances the anisotropy was inferred to be due to a graphite distribution resulting from internal deformation within the cratonic lithosphere.…”

Section: Pressure Effectsmentioning

confidence: 99%

Velocity–conductivity relationships for mantle mineral assemblages in Archean cratonic lithosphere based on a review of laboratory data and Hashin–Shtrikman extremal bounds

Jones

Evans

Eaton

2009

Lithos

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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. Jones et al.Velocity-conductivity relations of Archean lithospheric mantle

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Section: Pressure Effectsmentioning

confidence: 99%

Velocity–conductivity relationships for mantle mineral assemblages in Archean cratonic lithosphere based on a review of laboratory data and Hashin–Shtrikman extremal bounds

Jones

Evans

Eaton

2009

Lithos

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“…In the absence of magma, basin brines, or faultcontrolled fluid circulation, upper crustal anomalies of this magnitude are rarely observed. Where observed in tectonically stable regions, they are most commonly associated with graphitic films [e.g., Mareschal et al, 1995]. The only likely occurrence of graphite in upper crustal rocks of the region would be in upper Precambrian schists such as those exposed in the Panamint Range.…”

Section: Discussionmentioning

confidence: 99%

Electrical conductivity images of Quaternary faults and Tertiary detachments in the California Basin and Range

Park

Wernicke

2003

Tectonics

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Comparison of an electrical resistivity section derived from magnetotelluric (MT) data to a geologic section extending eastward from the Sierra Nevada near latitude 36°20′N shows that the crust is dominated by steeply dipping conductive features that correlate with active strike‐slip faults. While there is a subhorizontal conductor at a depth ∼20 km beneath some of the profile, it is broken by vertical structures associated with the active strike‐slip faults. The continuous subhorizontal anomalies in the lower crust typically observed in extensional regions are therefore absent in the resistivity section. The present‐day strike‐slip tectonic regime as indicated by geodetic data in this part of the Basin and Range is not producing features that could be inferred to indicate subhorizontal shear zones resulting from lateral crustal flow during extension. Because the Miocene tectonic regime resulted in the formation of metamorphic core complexes and thus was accompanied by such flow, the present regime appears to represent a fundamental transition in the mode of crustal deformation in the region. A serendipitous result of our study was the identification on resistivity sections of carbonate aquifers in the upper crust. Comparison of resistivities from the MT section to measured fluid resistivities from springs and boreholes suggests that the aquifers must be heterogeneous, with more saline brines occupying the deepest portions of the carbonates.

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“…In the following a similar impedance phase anisotropy, determined in a narrow extensional basin of the Neogene Pannonian Basin, will be compared to that one described by Mareschal et al (1995) from the Archean craton.…”

mentioning

confidence: 99%

“…The magnetotelluric sounding method (Cagniard, 1953) which provides the distribution of the electric resistivity in the depth recently showed a great progress in all aspects-data acquisition, processing and interpretation-enabling Mareschal et al (1995), too to get very precise phase values and from these a more exact structural model than was earlier possible.…”

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confidence: 99%

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Magnetotelluric Phase Anisotropy above Extensional Structures of the Neogene Pannonian Basin

Ádám

1997

J. geomagn. geoelec

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Neogene extensional forces generated narrow rift zones (deep subbasins) in the Pannonian Basin, among others one of the deepest, the 7 km deep Bdkes graben. Above this structure strong magnetotelluric (MT) phase anisotropy (phase-deviation in two orthogonal directions) has been observed indicating the upwelling of the partially molten asthenosphere. This upwelling is certainly the first to prove the validity of the deep mantle structure of Buck's extensional narrow rift model by an electromagnetic method.A geotectonic relation will also be pointed out between the causes of MT phase anisotropy in cratonic and orogenic belts.

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Archaean cratonic roots, mantle shear zones and deep electrical anisotropy

Cited by 130 publications

References 29 publications

Velocity–conductivity relationships for mantle mineral assemblages in Archean cratonic lithosphere based on a review of laboratory data and Hashin–Shtrikman extremal bounds

Velocity–conductivity relationships for mantle mineral assemblages in Archean cratonic lithosphere based on a review of laboratory data and Hashin–Shtrikman extremal bounds

Electrical conductivity images of Quaternary faults and Tertiary detachments in the California Basin and Range

Magnetotelluric Phase Anisotropy above Extensional Structures of the Neogene Pannonian Basin

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