The similitude equation in magnetotelluric inversion     

S. E. Dosso  D. W. Oldenburg 《Geophysical Journal International》1991,106(2):507-509

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Reply to ‘Comment on New UPb zircon ages from Tonga (Cameroon): coexisting Eburnean–Transamazonian (2.1 Ga) and Panafrican (0.6 Ga) imprints’ by Sadrack Félix Toteu and Joseph Penaye     

Evine Laure Tanko Njiosseu  Jean Paul Nzenti  Thophile Njanko  Badibanga Kapajika  Anne Ndlec 《Comptes Rendus Geoscience》2005,337(16):77

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Dating prograde fluid pulses during subduction by in situ U–Pb and oxygen isotope analysis     

Laure Gauthiez-Putallaz  Daniela Rubatto  Jörg Hermann 《Contributions to Mineralogy and Petrology》2016,171(2):15

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On the behaviour of the induction arrows over a buried conductive plate — a numerical model study     

A. K. Agarwal  H. W. Dosso 《Physics of the Earth and Planetary Interiors》1990,60(1-4):265-277

Two-dimensional numerical model calculations, employing a finite difference technique, are used to study the behaviour of the induction arrows, for a range of periods, for a conductive plate of (i) semi-infinite and (ii) finite width in uniform and layered resistive hosts. The results for the conductive plate at the surface of the host have application to a uniform-depth ocean, while the results for the plate buried at some depth in the resistive host have application to a conductive sill in a resistive Earth. The numerical results indicate that for a profile over the plate-host vertical interface the in-phase arrows for all periods and locations point towards the conductive plate, while the quadrature arrows at periods near the characteristic period of the model are oppositely directed on either side of the interface so as to point towards each other and towards the interface for nearby locations, both over the conductive plate and the resistive host. Further, the quadrature arrow undergoes a second reversal over the resistive host at a distance from the interface that is somewhat dependent on the period. Thus, at either side of the location of this second reversal, the quadrature induction arrows are again oppositely directed, but pointing away from each other, with the arrows near the interface pointing towards, and the more distant arrows pointing away from the conductive plate. The period range for the quadrature-arrow reversal is characteristic of conductivities and layer depths. The features of the quadrature-arrow sign reversals at and near the interface are in accordance with the earlier laboratory analogue model results of Hebert et al. for the Newfoundland coastal region and Nienaber et al. for a conductive plate in a resistive host.

It is suggested that in practice the sign reversal of the quadrature arrow may aid in locating a conductor-host interface, and that if the conductivity of the host is known, the maximum in the anomalous vertical magnetic field response may permit an approximate determination of the conductive-layer depth.  相似文献   

SrNdPb geochemical morphology between 10° and 17°N on the Mid-Atlantic Ridge: A new MORB isotope signature     

Laure Dosso  Barry B. Hanan  Henri Bougault  Jean-Guy Schilling  Jean-Louis Joron 《Earth and Planetary Science Letters》1991,106(1-4)

Basalts dredged along the Mid-Atlantic Ridge axis between 10°N and 17°N have been studied for their trace element characteristics [1]. To give complementary information on mantle source history and magma genesis, these samples have been analysed for their SrNdPb isotopic compositions. There is a good correlation between the structure of the ridge axis which shows a topographic anomaly centered around 14°N and hygromagmaphile element ratios such as Rb/Sr, (Nb/Zr)_N or Sm/Nd as well as isotopic ratios plotted as a function of latitude. The samples coming from the 14°N topographic high show new MORB SrNd isotopic characteristics which pictured in a classical mantle array diagram, put their representative points close to HIMU sources of ocean islands such as St. Helena, Tubuaïand Mangaia. The 14°N mantle source presents geochemical characteristics which indicate mantle differentiation processes and a mantle history that are more distinct than so far envisaged from typical MORB data. Pb data indicates that the 14°N mantle source cannot be the result of binary mixing between a depleted mantle and a HIMU-type source. Rather, the enriched endmember could itself be a mixture of Walvis-like and HIMU-like materials. The geochimical observations presented favour the model of an incipient ridge-centered plume, in agreement with [1].  相似文献   

A Nd isotopic study of the Kerguelen Islands: Inferences on enriched oceanic mantle sources     

Laure Dosso  V. Rama Murthy 《Earth and Planetary Science Letters》1980,48(2):268-276

The origin of the highly differentiated igneous rocks of the Kerguelen Islands and the nature of their source regions have been investigated by a Nd isotopic study. The Nd isotopic compositions of syenites and granites are identical to those of gabbros and basalts and indicate a common source. The isotopic data preclude the involvement ofold continental crustal material in the genesis of these granitic and alkalic rocks. The data from the Kerguelen samples greatly extend the Nd-Sr isotopic correlation observed for uncontaminated basalts from the oceanic mantle. The large Nd isotopic variations in the Kerguelen samples could be explained by mixing of deep mantle material brought up by a plume and the upper oceanic mantle or by heterogeneities in the lower mantle. An important finding of this study is that there are enriched mantle sources under the oceanic regions. These enriched sources may be ancient in age and are compatible with the 2-b.y. age inferred from the Pb isotope data of these samples. Earth models in future must incorporate this feature of the oceanic mantle in a consideration of mantle-crust evolutionary relationships.  相似文献   

An analogue model study of electromagnetic induction in the eastern coastal region of North America     

H.W. Dosso  W. Nienaber  J.A. Wright  J.P. Greenhouse  R.C. Bailey 《Physics of the Earth and Planetary Interiors》1980,23(1):13-30

The behavior of electric and magnetic field variations over the eastern coastal region of North America is studied using a scaled laboratory electromagnetic analogue model. The model source frequency used simulates a period of 1 h in the geophysical scale. The results indicate that deflection and conductive channelling of induced electric current is important for both the E-polarization (northeast-southwest direction of the electric field of the source) and the H-polarization (northwest-southeast) of the source field. In the model, conductive channelling occurs through the Strait of Belle Isle, Cabot Strait, and in the St. Lawrence River. Current deflection is particularly prevalent around the southeast coast of Newfoundland for both E- and H-polarization, and around the northeast coastline of Nova Scotia for E-polarization. The model results also show current deflection by cape and bay coastal features, as well as by ocean depth contours.A comparison of model measurements for the cases of a uniform source field and a line current source indicate that the nature of the source field has a measurable but surprisingly small effect on the vertical to horizontal magnetic field ratio for both E- and H-polarizations, and negligible effect on the magnetotelluric ratio for coastal regions.The model fields in coastal regions were found to be strongly influenced by induced currents, deflected and channelled by the coastline and ocean bathymetry, and were dependent on the nature and particularly the polarization of the source field. Thus, along the complex coastline of eastern North America, a wide range of electric and magnetic field values should be expected. In some regions the coast effect, measured by the vertical to horizontal magnetic field ratio at the coast, could be expected to be extremely small or absent, while in other regions the ratio could approach a value as large as unity for variations of 1 h period.  相似文献   

Electromagnetic induction in the San Juan Bay region of Vancouver Island     

G.H. Chan  H.W. Dosso  L.K. Law 《Physics of the Earth and Planetary Interiors》1981,27(2):114-121

The response of the electric and magnetic field variations over the San Juan Bay region of Vancouver Island is studied using a scaled laboratory analogue model. The laboratory frequencies simulate periods of 10 and 100 s in the geophysical problem. The model results indicate that, for both E- and H-polarization of the source field, induced current in the ocean is deflected around Cape Flattery and channelled into the Juan de Fuca Strait. With increasing period, the proportion of current channelled into the Strait decreases sharply. Induced current in the strait is also funnelled into San Juan Bay, a finger-shaped bay ca. 4 km wide and 7.5 km long, for both polarizations of the source field. The effect of the Bay on the field response is confined to the local region, within approximately 6 km of the centre of the Bay. Good agreement between field station and analogue model H_z results was obtained for the San Juan Bay. The behaviour of the Parkinson arrow for these two stations is examined with the aid of the analogue model results.  相似文献   

A numerical study of the topographic effect on electromagnetic fields in a three-dimensional conductivity model     

V. Ramaswamy  F. W. Jones  H. W. Dosso 《Pure and Applied Geophysics》1976,114(4):653-662

Summary The topographic effect on electromagnetic fields in a three-dimensional conductivity model is investigated using a finite-difference numerical method. The model is that of a conducting block buried in the host Earth beneath a conducting hill. The altitude effect as well as the effect of conductivity of the hill has been studied by comparing the results for the field components at the surface of the hill with those at the surface of a flat half-space. The results indicate that both altitude and the hill conductivity influence the behaviour of the electromagnetic fields. For certain traverses beyond the edge of the block, it is seen that the variations in some field components are mainly due to the topographic effect and that the contribution from the block itself is negligible.  相似文献   

Mesoscale distribution of zooplankton biomass in the northeast Atlantic Ocean determined with an Optical Plankton Counter: Relationships with environmental structures     

Jean-Philippe Labat  Stephane Gasparini  Laure Mousseau  Louis Prieur  Marc Boutoute  Patrick Mayzaud   《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1742-1756

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