Mineralogical effects on the detectability of the postperovskite boundary
Name
Grocholski-2012-Mineralogical effect.pdf
Size
578.71 KB
Format
Adobe PDF
Checksum (MD5)
9feccdb67b98f2c3f2a5bfbca6cd8878
Author(s)
Grocholski, Brent
Catalli, Krystle C.
Prakapenka, Vitali
Shim, Sang-Heon Dan
Date Issued
February 2012
Journal
Proceedings of the National Academy of Sciences
Publisher
National Academy of Sciences
Citation
Grocholski, B. et al. “Mineralogical Effects on the Detectability of the Postperovskite Boundary.” Proceedings of the National Academy of Sciences 109.7 (2012): 2275–2279. Copyright ©2012 by the National Academy of Sciences
Version
Final published version
Abstract
The discovery of a phase transition in Mg-silicate perovskite (Pv) to postperovskite (pPv) at lowermost mantle pressure-temperature (P - T) conditions may provide an explanation for the discontinuous increase in shear wave velocity found in some regions at a depth range of 200 to 400 km above the core-mantle boundary, hereafter the D′′ discontinuity. However, recent studies on binary and ternary systems showed that reasonable contents of Fe[superscript 2+] and Al for pyrolite increase the thickness (width of the mixed phase region) of the Pv - pPv boundary (400–600 km) to much larger than the D′′ discontinuity (≤ 70 km). These results challenge the assignment of the D′′ discontinuity to the Pv - pPv boundary in pyrolite (homogenized mantle composition). Furthermore, the mineralogy and composition of rocks that can host a detectable Pv → pPv boundary are still unknown. Here we report in situ measurements of the depths and thicknesses of the Pv → pPv transition in multiphase systems (San Carlos olivine, pyrolitic, and midocean ridge basaltic compositions) at the P - T conditions of the lowermost mantle, searching for candidate rocks with a sharp Pv - pPv discontinuity. Whereas the pyrolitic mantle may not have a seismologically detectable Pv → pPv transition due to the effect of Al, harzburgitic compositions have detectable transitions due to low Al content. In contrast, Al-rich basaltic compositions may have a detectable Pv - pPv boundary due to their distinct mineralogy. Therefore, the observation of the D′′ discontinuity may be related to the Pv → pPv transition in the differentiated oceanic lithosphere materials transported to the lowermost mantle by subducting slabs.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1073/pnas.1109204109
