Textures Induced by the Coesite-Stishovite Transition and Implications for the Visibility of the X-Discontinuity
The coesite-stishovite phase transition is considered the most plausible candidate to explain the X-discontinuity observed at around 300 km depth in a variety of tectonic settings. Here, we investigate the microstructure in SiO2 across the coesite-stishovite transition in uniaxial compression experi...
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FB/Einrichtung: | FB 14: Geowissenschaften |
Dokumenttypen: | Artikel |
Medientypen: | Text |
Erscheinungsdatum: | 2022 |
Publikation in MIAMI: | 31.10.2023 |
Datum der letzten Änderung: | 31.10.2023 |
Angaben zur Ausgabe: | [Electronic ed.] |
Quelle: | Geochemistry, Geophysics, Geosystems 23 (2022) 10, e2022GC010544, 1-14 |
Schlagwörter: | coesite-stishovite transition; microstructures; multigrain crystallography; X-discontinuity; reflection coefficients; mantle heterogeneities |
Fachgebiet (DDC): | 550: Geowissenschaften, Geologie |
Lizenz: | CC BY 4.0 |
Sprache: | English |
Förderung: | Finanziert über die DEAL-Vereinbarung mit Wiley 2019-2022. Förderer: Deutsche Forschungsgemeinschaft / Projektnummer: 390989765 Förderer: Agence Nationale de la Recherche / Projektnummer: ANR-17-CE31-0025 Förderer: European Commission / Projektnummer: 730872 Förderer: German Academic Exchange Service / Projektnummer: PHC40555PC |
Format: | PDF-Dokument |
URN: | urn:nbn:de:hbz:6-68968629816 |
Weitere Identifikatoren: | DOI: 10.17879/18978548921 |
Permalink: | https://nbn-resolving.de/urn:nbn:de:hbz:6-68968629816 |
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Onlinezugriff: | 10.1029_2022GC010544.pdf |
The coesite-stishovite phase transition is considered the most plausible candidate to explain the X-discontinuity observed at around 300 km depth in a variety of tectonic settings. Here, we investigate the microstructure in SiO2 across the coesite-stishovite transition in uniaxial compression experiments. We apply the multigrain crystallography technique (MGC) in a laser-heated diamond-anvil cell (LH-DAC) to identify the seismic signature of the transition and the amount of SiO2 in the mantle. While coesite displays weak lattice-preferred orientations (LPO) before the transition, stishovite develops strong LPO characterized by the alignment of [112] axes parallel to the compression direction. However, LPO has little effect on the impedance contrast across the transition, which is up to 8.8% for S-waves in a mid-ocean ridge basalt (MORB) composition at 300 km depth along a normal mantle geotherm, 10 GPa-1700 K. Therefore, 10–50 vol.% of a MORB component, corresponding to 0.6–3.2 vol.% SiO2, mechanically mixed with the pyrolytic mantle would be required to explain the range of impedance (and velocity) contrasts observed for the X-discontinuity. Based on the reflection coefficients computed for the coesite-stishovite transition, we show that the incidence angle or epicentral distance is critical for the detection of silica-containing lithologies in the upper mantle, with highest detection probabilities for small incidence angles. The intermittent visibility of the X-discontinuity may thus be explained by the seismic detectability of the coesite-stishovite transition rather than by absence of the transition or chemical heterogeneities in some specific tectonic settings.