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| Titel |
Thermal and compositional constrains on the upper mantle beneath the northwestern Pacific imposed by marine magnetotellurics |
| VerfasserIn |
Kiyoshi Baba, Noriko Tada, Tetsuo Matsuno, Hisayoshi Shimizu, Luolei Zhang, Pengfei Liang, Hisashi Utada |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127361
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| Publikation (Nr.) |
 EGU/EGU2016-7227.pdf |
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| Zusammenfassung |
| Oceanic upper mantle beneath the northwestern Pacific has large-scale lateral heterogeneity
that is impossible to attribute to just an age-dependency of the thermal structure based on a
cooling of homogeneous mantle with age. This surprising fact was revealed from seafloor
magnetotelluric (MT) data collected in three areas, northwest (Area A) and southeast (Area
B) of the Shatsky Rise, and off the Bonin Trench (Area C), through the Normal
Oceanic Mantle Project and the Stagnant Slab Project. One-dimensional structures of
electrical conductivity representing each area show significant difference in the
thickness of the upper resistive layer that may be interpreted as cool lithosphere. The
thickness of the layer that is more resistive than 0.01 S m−1 is ∼90 km for Area
A, ∼100 km for Area B, and ∼180 km for Area C. The conductivity below the
resistive layer is similar to ∼0.03 S m−1 for all areas. The thermal structures for
the lithospheric age representing the areas (130, 140, and 147 Ma for Areas A,
B, and C, respectively) predicted from a simple plate cooling model are almost
identical and thus cannot reproduce such variations in electrical conductivity. Then, in
this study, thermal and compositional states of the mantle beneath the three areas
were investigated to discuss the cause of the variations. Combination of five model
parameters, electrical conductivity of crust, mantle potential temperature, thickness of
thermally conductive plate, and H2O and CO2 contents in the asthenospheric mantle
were searched by forward modeling and the χ2 misfit between the MT responses
observed and predicted were assessed with 95% acceptable level. The possibility of
partial melting was taken into account by a self-consistent manner comparing to
the solidus of peridotite that is reduced by H2O and CO2. We assumed that the
mantle conductivity may be represented by the mixture of hydrous olivine and
hydrous carbonated melt. This procedure enables us to discuss how water, carbon,
and/or melt can contribute the electrical conductivity in a range accepted by the
observed data and gives hints to the nature of lithosphere and asthenosphere boundary. |
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