D" Reflection Polarities Inform Lowermost Mantle Mineralogy
Abstract Polarities of seismic reflections at the discontinuity atop the D" region (PdP and SdS) indicate the sign of the velocity contrast across the D" reflector. Recent studies found PdP polarities matching and opposite those of P and PcP. While anisotropy could explain this behavior, w...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Wiley
2022-10-01
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| Series: | Geochemistry, Geophysics, Geosystems |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2021GC010325 |
| _version_ | 1797638051582705664 |
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| author | C. Thomas L. J. Cobden A. R. T. Jonkers |
| author_facet | C. Thomas L. J. Cobden A. R. T. Jonkers |
| author_sort | C. Thomas |
| collection | DOAJ |
| description | Abstract Polarities of seismic reflections at the discontinuity atop the D" region (PdP and SdS) indicate the sign of the velocity contrast across the D" reflector. Recent studies found PdP polarities matching and opposite those of P and PcP. While anisotropy could explain this behavior, we find that the ratio of the change in S wave velocity over change in P wave velocity (R‐value) can influence polarity behavior of D" reflected P waves. For R‐values exceeding 3, the P wave reverses polarity in the absence of anisotropy while S wave polarity is not influenced by the R‐value. Using sets of one million models for normal mantle and MORB with varying minerals and processes across the boundary, we carry out a statistical analysis (Linear Discriminant Analysis) finding that there is a marked difference in mantle mineralogy to explain R‐values larger and smaller than 3, respectively. Based on our results we can attribute different mineralogy to a number of cases. In particular, we find that when velocities increase across D" and polarities of PdP and SdS are opposite the post‐perovskite phase transition is still the best explanation whereas MORB is the best explanation when PdP and SdS are the same. When the velocities are decreasing, the post‐perovskite phase transition within MORB is the best explanation if PdP and SdS polarities are the same but if PdP and SdS are opposite, our results indicate that primordial material or mantle enriched in bridgmanite can explain the polarity behavior, further constraining mineralogy within the large low seismic velocity provinces. |
| first_indexed | 2024-03-11T12:57:08Z |
| format | Article |
| id | doaj.art-04e0c13acede4d32a058ae8e3112838a |
| institution | Directory Open Access Journal |
| issn | 1525-2027 |
| language | English |
| last_indexed | 2024-03-11T12:57:08Z |
| publishDate | 2022-10-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj.art-04e0c13acede4d32a058ae8e3112838a2023-11-03T16:56:07ZengWileyGeochemistry, Geophysics, Geosystems1525-20272022-10-012310n/an/a10.1029/2021GC010325D" Reflection Polarities Inform Lowermost Mantle MineralogyC. Thomas0L. J. Cobden1A. R. T. Jonkers2Institut für Geophysik Westfälische Wilhelms‐Universität Münster Münster GermanyDepartment of Earth Sciences Universiteit Utrecht Utrecht The NetherlandsInstitut für Geophysik Westfälische Wilhelms‐Universität Münster Münster GermanyAbstract Polarities of seismic reflections at the discontinuity atop the D" region (PdP and SdS) indicate the sign of the velocity contrast across the D" reflector. Recent studies found PdP polarities matching and opposite those of P and PcP. While anisotropy could explain this behavior, we find that the ratio of the change in S wave velocity over change in P wave velocity (R‐value) can influence polarity behavior of D" reflected P waves. For R‐values exceeding 3, the P wave reverses polarity in the absence of anisotropy while S wave polarity is not influenced by the R‐value. Using sets of one million models for normal mantle and MORB with varying minerals and processes across the boundary, we carry out a statistical analysis (Linear Discriminant Analysis) finding that there is a marked difference in mantle mineralogy to explain R‐values larger and smaller than 3, respectively. Based on our results we can attribute different mineralogy to a number of cases. In particular, we find that when velocities increase across D" and polarities of PdP and SdS are opposite the post‐perovskite phase transition is still the best explanation whereas MORB is the best explanation when PdP and SdS are the same. When the velocities are decreasing, the post‐perovskite phase transition within MORB is the best explanation if PdP and SdS polarities are the same but if PdP and SdS are opposite, our results indicate that primordial material or mantle enriched in bridgmanite can explain the polarity behavior, further constraining mineralogy within the large low seismic velocity provinces.https://doi.org/10.1029/2021GC010325seismologywave polaritystatisticsthermochemical modelingD |
| spellingShingle | C. Thomas L. J. Cobden A. R. T. Jonkers D" Reflection Polarities Inform Lowermost Mantle Mineralogy Geochemistry, Geophysics, Geosystems seismology wave polarity statistics thermochemical modeling D |
| title | D" Reflection Polarities Inform Lowermost Mantle Mineralogy |
| title_full | D" Reflection Polarities Inform Lowermost Mantle Mineralogy |
| title_fullStr | D" Reflection Polarities Inform Lowermost Mantle Mineralogy |
| title_full_unstemmed | D" Reflection Polarities Inform Lowermost Mantle Mineralogy |
| title_short | D" Reflection Polarities Inform Lowermost Mantle Mineralogy |
| title_sort | d reflection polarities inform lowermost mantle mineralogy |
| topic | seismology wave polarity statistics thermochemical modeling D |
| url | https://doi.org/10.1029/2021GC010325 |
| work_keys_str_mv | AT cthomas dreflectionpolaritiesinformlowermostmantlemineralogy AT ljcobden dreflectionpolaritiesinformlowermostmantlemineralogy AT artjonkers dreflectionpolaritiesinformlowermostmantlemineralogy |