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Title: Mineralogical effects on the detectability of the postperovskite boundary

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{double_prime} discontinuity. However, recent studies on binary and ternary systems showed that reasonable contents of Fe{sup 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{double_prime} discontinuity ({le} 70 km). These results challenge the assignment of the D{double_prime} discontinuity to the Pv - pPv boundary in pyrolite (homogenized mantle composition). Furthermore, the mineralogy and composition of rocks that can host a detectable Pv {yields} pPv boundary are still unknown. Here we report in situ measurements of the depths and thicknesses of the Pv {yields} 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 Pvmore » {yields} 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{prime} discontinuity may be related to the Pv {yields} pPv transition in the differentiated oceanic lithosphere materials transported to the lowermost mantle by subducting slabs.« less

Authors:
; ; ;  [1]
  1. UC
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
DOE - OTHERNSF
OSTI Identifier:
1036338
Resource Type:
Journal Article
Journal Name:
Proc. Natl. Acad. Sci. USA
Additional Journal Information:
Journal Volume: 109; Journal Issue: (7) ; 02, 2012; Journal ID: ISSN 0027-8424
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

Grocholski, Brent, Catalli, Krystle, Shim, Sang-Heon, Prakapenka, Vitali, and MIT). Mineralogical effects on the detectability of the postperovskite boundary. United States: N. p., 2017. Web. doi:10.1073/pnas.1109204109.
Grocholski, Brent, Catalli, Krystle, Shim, Sang-Heon, Prakapenka, Vitali, & MIT). Mineralogical effects on the detectability of the postperovskite boundary. United States. https://doi.org/10.1073/pnas.1109204109
Grocholski, Brent, Catalli, Krystle, Shim, Sang-Heon, Prakapenka, Vitali, and MIT). Tue . "Mineralogical effects on the detectability of the postperovskite boundary". United States. https://doi.org/10.1073/pnas.1109204109.
@article{osti_1036338,
title = {Mineralogical effects on the detectability of the postperovskite boundary},
author = {Grocholski, Brent and Catalli, Krystle and Shim, Sang-Heon and Prakapenka, Vitali and MIT)},
abstractNote = {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{double_prime} discontinuity. However, recent studies on binary and ternary systems showed that reasonable contents of Fe{sup 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{double_prime} discontinuity ({le} 70 km). These results challenge the assignment of the D{double_prime} discontinuity to the Pv - pPv boundary in pyrolite (homogenized mantle composition). Furthermore, the mineralogy and composition of rocks that can host a detectable Pv {yields} pPv boundary are still unknown. Here we report in situ measurements of the depths and thicknesses of the Pv {yields} 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 {yields} 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{prime} discontinuity may be related to the Pv {yields} pPv transition in the differentiated oceanic lithosphere materials transported to the lowermost mantle by subducting slabs.},
doi = {10.1073/pnas.1109204109},
url = {https://www.osti.gov/biblio/1036338}, journal = {Proc. Natl. Acad. Sci. USA},
issn = {0027-8424},
number = (7) ; 02, 2012,
volume = 109,
place = {United States},
year = {2017},
month = {5}
}