scholarly journals Upper mantle conductivity structure of the back-arc region beneath northeastern China

2001 ◽  
Vol 28 (19) ◽  
pp. 3773-3776 ◽  
Author(s):  
Masahiro Ichiki ◽  
Makoto Uyeshima ◽  
Hisashi Utada ◽  
Zhao Guoze ◽  
Tang Ji ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Northeastern China ◽  
Conductivity Structure ◽  
Mantle Conductivity ◽  
Back Arc

A review of electromagnetic investigations in the Kapuskasing uplift and surrounding regions: electrical properties of key rocks

1994 ◽  
Vol 31 (7) ◽  
pp. 1042-1051 ◽  
Author(s):  
Marianne Mareschal ◽  
Ron D. Kurtz ◽  
Richard C. Bailey
Keyword(s):  
Grain Boundaries ◽  
Upper Mantle ◽  
Field Measurements ◽  
Surface Expression ◽  
High Grade ◽  
Near Surface ◽  
Solid Films ◽  
Conductivity Structure ◽  
Mantle Conductivity ◽  
Detachment Zone

Electromagnetic investigations of the Kapuskasing uplift show that the gross electrical conductivity structure of the present crust is subhorizontal (contrary to the lithology as defined by seismic experiments), with increasing conductivity with depth, a feature common to most continental crusts. The current upper crust of the Chapleau block includes zones of reduced resistivity; the near-surface expression of the Ivanhoe Lake cataclastic zone (< 1 km in depth and 600 m in width), with resistivities of a few hundred ohm metres, is typical of fluid infilling weathered rocks. At least two other zones are less resistive (ρ < 12 kΩ∙m) than the typical upper-crustal Chapleau block (> 40 kΩ∙m), these include a subhorizontal layer at ~ 5 km and a subhorizontal to dipping layer at ~ 2 km. The deeper layer is interpreted as imaging deep fluids (porosities > 0.5%) postdating the uplift. The shallower feature, possibly related to the seismically detected detachment zone dipping at ~ 15° could be imaging conductors such as recent fluids or remnants of solid films precipitated at grain boundaries by more ancient fluids.Auger spectrometry of high-grade rocks exposed near the extrapolated surface expression of the shallower conductor reveals that fragments of graphite films (3–30 nm thick) are commonly found at grain boundaries, whereas traces of sulphur and chlorine are relatively rare. The electrical resistivity of these rocks was measured in laboratory and is lower than normally observed for similar high-grade rocks from other parts of the Canadian shield (5–25 kΩ∙m as opposed to 30–100 kΩ∙m).The Kapuskasing Uplift has opened a new area of research on upper-mantle conductivity structure from surface electromagnetic field measurements, an endeavour believed impossible until now.

Magneto-telluric determination of upper mantle conductivity structure at Victoria, British Columbia

1968 ◽  
Vol 5 (5) ◽  
pp. 1209-1220 ◽  
Author(s):  
B. Caner ◽  
D. R. Auld
Keyword(s):  
Spectral Analysis ◽  
Upper Mantle ◽  
High Resistivity ◽  
Conducting Layer ◽  
Frequency Range ◽  
Tidal Effects ◽  
Conductivity Structure ◽  
Wide Range ◽  
Mantle Conductivity

Magneto-telluric data were obtained at Victoria over a very wide range of periods (2 s to 86 400 s). Only the data up to 15 000 s periods were used for interpretation of conductivity structure, since telluric data at longer periods were dominated by ocean-tidal effects; spectral analysis of one year's data was used to demonstrate the tidal effects. The telluric signals are strongly polarized in the whole frequency range, indicating an anisotropy in surface conductivity.The data indicate the existence of a finite conducting layer 10 ± 3 km thick and resistivity 100–125 ohm-meters, at a depth of 65 ± 5 km. A high resistivity zone (of the order of 4000–5000 ohm-meters) lies below this layer. There is no evidence for any further conducting zones down to a depth of at least 750 km.

scholarly journals A subduction influence on ocean ridge basalts outside the Pacific subduction shield

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Y. Yang ◽  
C. H. Langmuir ◽  
Y. Cai ◽  
P. Michael ◽  
S. L. Goldstein ◽  
...  
Keyword(s):  
Upper Mantle ◽  
The Arctic ◽  
Mantle Flow ◽  
Mantle Heterogeneity ◽  
Gakkel Ridge ◽  
The Pacific ◽  
Mid Ocean Ridge ◽  
The Pacific Ocean ◽  
Back Arc ◽  
Ocean Ridge

AbstractThe plate tectonic cycle produces chemically distinct mid-ocean ridge basalts and arc volcanics, with the latter enriched in elements such as Ba, Rb, Th, Sr and Pb and depleted in Nb owing to the water-rich flux from the subducted slab. Basalts from back-arc basins, with intermediate compositions, show that such a slab flux can be transported behind the volcanic front of the arc and incorporated into mantle flow. Hence it is puzzling why melts of subduction-modified mantle have rarely been recognized in mid-ocean ridge basalts. Here we report the first mid-ocean ridge basalt samples with distinct arc signatures, akin to back-arc basin basalts, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence in this region. This influence can also be identified in Atlantic and Indian mid-ocean ridge basalts but is nearly absent in Pacific mid-ocean ridge basalts. Such a hemispheric-scale upper mantle heterogeneity reflects subduction modification of the asthenospheric mantle which is incorporated into mantle flow, and whose geographical distribution is controlled dominantly by a “subduction shield” that has surrounded the Pacific Ocean for 180 Myr. Simple modeling suggests that a slab flux equivalent to ~13% of the output at arcs is incorporated into the convecting upper mantle.

Inversion of the satellite observations of the tidally induced magnetic field in terms of 3-D upper-mantle electrical conductivity: Method and synthetic tests

2021 ◽  
Author(s):  
Libor Šachl ◽  
Jakub Velímský ◽  
Javier Fullea
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Upper Mantle ◽  
Spherical Harmonic ◽  
Model Space ◽  
Conductivity Method ◽  
Satellite Gravity ◽  
Compositional Model ◽  
Mantle Conductivity ◽  
The Impact

&lt;p&gt;&lt;span&gt;&lt;span&gt;We have developed and tested a new frequency-domain, spherical harmonic-finite element approach to the inverse problem of global electromagnetic (EM) induction. It is based on the quasi-Newton minimization of data misfit and regularization, and uses the adjoint approach for fast calculation of misfit gradients in the model space. Thus, it allows for an effective inversion of satellite-observed magnetic field induced by tidally driven flows in the Earth's oceans in terms of 3-D structure of the electrical conductivity in the upper mantle.&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; Before proceeding to the inversion of Swarm-derived models of tidal magnetic signatures, we have performed a series of &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;parametric studies&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;, using a 3-D conductivity model WINTERC-e as a testbed.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The WINTERC-e model has been derived using state-of-the-art laboratory conductivity measurements of mantle minerals, and thermal and compositional model of the lithosphere and upper mantle WINTERC-grav. The latter model is based on the inversion of global surface waveforms, satellite gravity and gradiometry measurements, surface elevation, and heat flow data &lt;/span&gt;&lt;span&gt;&lt;span&gt;in a thermodynamically self-consistent framework. &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;Therefore, the WINTERC-e model, independent of any EM data, represents an ideal target for synthetic tests of the 3-D EM inversion.&lt;/span&gt;&lt;/span&gt;&lt;span&gt; &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;&lt;span&gt;We tested the impact of &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;satellite &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;altitude&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;, &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;the truncation degree of the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;spherical-harmonic &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;expansion of the tidal signals, the random&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; noise in data&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;,&lt;/span&gt;&lt;/span&gt;&lt;span&gt; &lt;/span&gt;&lt;span&gt;&lt;span&gt;and &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;of the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;sub-&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;continental conductivity&lt;/span&gt;&lt;/span&gt;&lt;span&gt; &lt;/span&gt;&lt;span&gt;&lt;span&gt;on the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;ability to recover the sub-oceanic upper-mantle conductivity structure.&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; We &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;demonstrate &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;that &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;with &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;suitable regularization &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;we&lt;/span&gt;&lt;/span&gt;&lt;span&gt; &lt;/span&gt;&lt;span&gt;&lt;span&gt;can successfully reconstruct the 3D upper-mantle conductivity below world oceans.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;

Anisotropic upper mantle structures in northeast Asia from Bayesian inversions of ambient noise data

2020 ◽  
Author(s):  
Sang-Jun Lee ◽  
Seongryong Kim ◽  
Junkee Rhie
Keyword(s):  
Upper Mantle ◽  
Joint Inversion ◽  
Northeast Asia ◽  
Three Dimensional ◽  
Japan Sea ◽  
Mantle Dynamics ◽  
Noise Data ◽  
Deep Layers ◽  
Radial Anisotropy ◽  
Back Arc

&lt;p&gt;The northeast Asia region exhibits complex tectonic settings caused by interactions between Eurasian, Pacific, and Philippine Sea plates. Distributed extensional basins, intraplate volcanoes and other heterogeneous features in the region marked results of the tectonic processes, and their mechanisms related to mantle dynamics can be well understood by estimating radial anisotropy in the lithospherie and asthenospherie. We constructed a three-dimensional radial anisotropy model in northeast Asia using hierarchical and transdimensional Bayesian joint inversion techniques with different types of dispersion data up to the depth of the upper mantle (~ 160 km). Thick and deep layers with positive radial anisotropy (V&lt;sub&gt;SH&lt;/sub&gt; &gt; V&lt;sub&gt;SV&lt;/sub&gt;) were commonly found at depths between 70 and 150 km beneath the continental regions. On the other hand, depths and sizes of layers with positive radial anisotropy become shallower and thinner (30 ~ 60 km) respectively beneath regions where experienced the Cenozoic extension. These variations in positive radial anisotropy for different tectonic regions can be understood with the context of extensional geodynamic processes in back arc basins within the East Sea (Japan Sea). Interestingly, the most predominant positive radial anisotropy is imaged along areas with large gradient of the litheosphere-asthnosphere boundary beneath intraplate volcanoes. These observations favor the mechanism of edge-driven convection caused by the difference in lithosphere thickness and localized sublithospheric lateral flow from the continental region to back arc basins.&lt;/p&gt;

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