THE 400-KM SEISMIC DISCONTINUITY AND THE PROPORTION OF OLIVINE IN THE EARTHS UPPER MANTLE
The 400-km seismic discontinuity has traditionally been ascribed to the isochemical transformation of α-olivine to the β-modified-spinel structure in a mantle of peridotitic bulk composition1-6. It has recently been proposed7,8 that the observed seismic velocity increase at 400km depth is too abrupt...
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| Format: | Journal article |
| Language: | English |
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1986
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| _version_ | 1797080001696235520 |
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| author | Bina, C Wood, B |
| author_facet | Bina, C Wood, B |
| author_sort | Bina, C |
| collection | OXFORD |
| description | The 400-km seismic discontinuity has traditionally been ascribed to the isochemical transformation of α-olivine to the β-modified-spinel structure in a mantle of peridotitic bulk composition1-6. It has recently been proposed7,8 that the observed seismic velocity increase at 400km depth is too abrupt and too small to result from a phase change in olivine but instead requires that the transition zone be chemically distinct in bulk composition from the uppermost mantle. By requiring phase relations in the Mg2SiO4-Fe2SiO4 system to be internally consistent thermodynamically, we find that the α-β transition in olivine of mantle (Mg0.9Fe0.1) 2SiO4 composition is extremely sharp, occurring over a depth interval (isothermal) of ∼6 km. The magnitude of the predicted velocity increase is in agreement with that observed seismically9,10 if the transition zone is composed of ∼60-70% olivine. Thus, our results indicate that seismic velocities across the 400-km discontinuity are consistent with a transition zone of homogeneous peridotitic composition and do not require chemical stratification. © 1986 Nature Publishing Group. |
| first_indexed | 2024-03-07T00:53:52Z |
| format | Journal article |
| id | oxford-uuid:8756e394-7e6d-4485-817c-8a82a070afce |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T00:53:52Z |
| publishDate | 1986 |
| record_format | dspace |
| spelling | oxford-uuid:8756e394-7e6d-4485-817c-8a82a070afce2022-03-26T22:10:05ZTHE 400-KM SEISMIC DISCONTINUITY AND THE PROPORTION OF OLIVINE IN THE EARTHS UPPER MANTLEJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:8756e394-7e6d-4485-817c-8a82a070afceEnglishSymplectic Elements at Oxford1986Bina, CWood, BThe 400-km seismic discontinuity has traditionally been ascribed to the isochemical transformation of α-olivine to the β-modified-spinel structure in a mantle of peridotitic bulk composition1-6. It has recently been proposed7,8 that the observed seismic velocity increase at 400km depth is too abrupt and too small to result from a phase change in olivine but instead requires that the transition zone be chemically distinct in bulk composition from the uppermost mantle. By requiring phase relations in the Mg2SiO4-Fe2SiO4 system to be internally consistent thermodynamically, we find that the α-β transition in olivine of mantle (Mg0.9Fe0.1) 2SiO4 composition is extremely sharp, occurring over a depth interval (isothermal) of ∼6 km. The magnitude of the predicted velocity increase is in agreement with that observed seismically9,10 if the transition zone is composed of ∼60-70% olivine. Thus, our results indicate that seismic velocities across the 400-km discontinuity are consistent with a transition zone of homogeneous peridotitic composition and do not require chemical stratification. © 1986 Nature Publishing Group. |
| spellingShingle | Bina, C Wood, B THE 400-KM SEISMIC DISCONTINUITY AND THE PROPORTION OF OLIVINE IN THE EARTHS UPPER MANTLE |
| title | THE 400-KM SEISMIC DISCONTINUITY AND THE PROPORTION OF OLIVINE IN THE EARTHS UPPER MANTLE |
| title_full | THE 400-KM SEISMIC DISCONTINUITY AND THE PROPORTION OF OLIVINE IN THE EARTHS UPPER MANTLE |
| title_fullStr | THE 400-KM SEISMIC DISCONTINUITY AND THE PROPORTION OF OLIVINE IN THE EARTHS UPPER MANTLE |
| title_full_unstemmed | THE 400-KM SEISMIC DISCONTINUITY AND THE PROPORTION OF OLIVINE IN THE EARTHS UPPER MANTLE |
| title_short | THE 400-KM SEISMIC DISCONTINUITY AND THE PROPORTION OF OLIVINE IN THE EARTHS UPPER MANTLE |
| title_sort | 400 km seismic discontinuity and the proportion of olivine in the earths upper mantle |
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