Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
Volume 122, Issue 7, Pages 4900-4917Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2017JB014339
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Funding
- Ministry of Science and Technology of Taiwan, Republic of China [CDA-106-M02, MOST 103-2112-M-001-001-MY3, 105-2116-M-001-024, AS-102-CDA-M02]
- Geophysics Program of the U.S. National Science Foundation
- CSEDI Program of the U.S. National Science Foundation
- Visiting Professorship Program of the Institute for Study of the Earth's Interior, Okayama University
- HPSTAR Center
- Cutting-Edge Research Club of the National Cheng Kung University (NCKU)
- JSPS KAKENHI [26287135]
- National Science Foundation [EAR-0622171]
- Department of Energy [DE-FG02-94ER14466, DE-AC02-06CH11357]
- 263 DOE-BES [DE-AC02-06CH11357]
- Academia Sinica
- Grants-in-Aid for Scientific Research [26287135] Funding Source: KAKEN
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Complex seismic, thermal, and chemical features have been reported in Earth's lowermost mantle. In particular, possible iron enrichments in the large low shear-wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, altering the lower mantle dynamics and heat flux across core-mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure-induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermal conductivity of Fe-bearing bridgmanite to 120 GPa using optical pump-probe spectroscopy. The conductivity of Fe-bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure-induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid-lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.
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