scholarly journals Seismic evidence for a thermochemical mantle plume underplating the lithosphere of the Ontong Java Plateau

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Takehi Isse ◽  
Daisuke Suetsugu ◽  
Akira Ishikawa ◽  
Hajime Shiobara ◽  
Hiroko Sugioka ◽  
...  
Keyword(s):  
Mantle Plume ◽  
Upper Mantle ◽  
Seismic Data ◽  
Three Dimensional ◽  
Ontong Java Plateau ◽  
Volcanic Event ◽  
Upper Mantle Structure ◽  
Residual Material ◽  
Passive Seismic ◽  
The Western Pacific

AbstractThe Ontong Java Plateau in the western Pacific Ocean is the world’s largest oceanic plateau. It was formed 122 million years ago by a massive volcanic event that significantly affected Earth’s environment. The cause of the magmatic event remains controversial because the upper mantle structure beneath the plateau is poorly known. Here we use passive seismic data obtained through seafloor observations, alongside existing seismic data, to determine the three-dimensional radially anisotropic shear wave velocity to depths of up to 300 km. We find that the lithosphere–asthenosphere boundary is approximately 40 km deeper beneath the centre of the Ontong Java Plateau than beneath the surrounding seafloor. Based on our results and petrological and rheological constraints, we propose that the lithosphere–asthenosphere boundary has deepened as a result of underplating of dehydrated residual material beneath the pre-existing lithosphere during formation of the Ontong Java Plateau by a thermochemical mantle plume.

Deep electrical structure of northern Alberta (Canada): implications for diamond exploration

2009 ◽  
Vol 46 (2) ◽  
pp. 139-154 ◽  
Author(s):  
Erşan Türkoğlu ◽  
Martyn Unsworth ◽  
Dinu Pana
Keyword(s):  
Subduction Zone ◽  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Three Dimensional ◽  
Diamond Formation ◽  
Magnetotelluric Data ◽  
Diamond Exploration ◽  
Upper Mantle Structure ◽  
Resistivity Model ◽  
Northern Alberta

Geophysical studies of upper mantle structure can provide constraints on diamond formation. Teleseismic and magnetotelluric data can be used in diamond exploration by mapping the depth of the lithosphere–asthenosphere boundary. Studies in the central Slave Craton and at Fort-à-la-Corne have detected conductors in the lithospheric mantle close to, or beneath, diamondiferous kimberlites. Graphite can potentially explain the enhanced conductivity and may imply the presence of diamonds at greater depth. Petrologic arguments suggest that the shallow lithospheric mantle may be too oxidized to contain graphite. Other diamond-bearing regions show no upper mantle conductor suggesting that the correlation with diamondiferous kimberlites is not universal. The Buffalo Head Hills in Alberta host diamondiferous kimberlites in a Proterozoic terrane and may have formed in a subduction zone setting. Long period magnetotelluric data were used to investigate the upper mantle resistivity structure of this region. Magnetotelluric (MT) data were recorded at 23 locations on a north–south profile extending from Fort Vermilion to Utikuma Lake and an east–west profile at 57.2°N. The data were combined with Lithoprobe MT data and inverted to produce a three-dimensional (3-D) resistivity model with the asthenosphere at 180–220 km depth. This model did not contain an upper mantle conductor beneath the Buffalo Head Hills kimberlites. The 3-D inversion exhibited an eastward dipping conductor in the crust beneath the Kiskatinaw terrane that could represent the fossil subduction zone that supplied the carbon for diamond formation. The low resistivity at crustal depths in this structure is likely due to graphite derived from subducted organic material.

Regional Sn velocities and shear velocity in the upper mantle

1973 ◽  
Vol 63 (2) ◽  
pp. 469-475
Author(s):  
Stephen Huestis ◽  
Peter Molnar ◽  
Jack Oliver
Keyword(s):  
Shear Wave ◽  
Western Australia ◽  
Upper Mantle ◽  
Seismic Data ◽  
Shear Velocity ◽  
Apparent Velocity ◽  
Mantle Structure ◽  
Uppermost Mantle ◽  
Seismic Shear ◽  
Upper Mantle Structure

abstract Determinations by various authors of the apparent velocity of the seismic shear wave Sn, which propagates in the uppermost mantle, are presented for several of the Earth's stable regions. Measurements of the velocity over two additional shield areas, India and Western Australia, were made and gave values of 4.72±0.03 km/sec and 4.75-4.87 km/sec, respectively. In general, the Sn velocity is greater than 4.7 km/sec. As the stable regions cover most of the Earth's surface and this velocity is representative of the shear velocity in the uppermost mantle, it is useful as a constraint in inversion of seismic data to determine upper-mantle structure.

CRUSTAL STRUCTURE ON THE EASTERN SEABOARD OF CANADA: STUDIES ON THE CONTINENTAL MARGIN

1966 ◽  
Vol 3 (1) ◽  
pp. 65-76 ◽  
Author(s):  
Charlotte Keen ◽  
B. D. Loncarevic
Keyword(s):  
Continental Shelf ◽  
Upper Mantle ◽  
Seismic Data ◽  
Seismic Refraction ◽  
Ocean Basin ◽  
Mantle Structure ◽  
Upper Mantle Structure ◽  
Gravity Measurements ◽  
Vertical Density ◽  
Eastern Seaboard

The results of several seismic refraction profiles on the continental shelf and slope of the eastern seaboard of Canada are now available. Gravity measurements which begin near the coast of Nova Scotia and end over the abyssal plain have also been made along two tracks perpendicular to the shelf edge. Various models for the crustal and upper mantle structure are presented. A density distribution assumed for each model resulted in a computed gravity field satisfying the observed gravity measurements. The models in agreement with all seismic data suggest that horizontal and vertical density variations occur in the upper mantle down to 100 km. The results indicate a mantle density of 3.42 g/cm3 under the continental shelf and 3.32 g/cm3 under the ocean basin.

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