Post‐Perovskite Phase Transition in the Pyrolitic Lowermost Mantle: Implications for Ubiquitous Occurrence of Post‐Perovskite Above CMB
Yasuhiro Kuwayama, Kei Hirose, Laura Cobden, Mayu Kusakabe, Shigehiko Tateno, Yasuo Ohishi
Abstract
Abstract We conducted in situ high‐pressure and ‐temperature X‐ray diffraction measurements of a pyrolitic mantle material up to 4480 K at 122–166 GPa in a laser‐heated diamond anvil cell. Results demonstrate that the phase transition between bridgmanite and post‐perovskite occurs in pyrolite within the lowermost mantle pressure range even at >4000 K. It suggests the ubiquitous occurrence of post‐perovskite above the core‐mantle boundary, which may be consistent with recent high‐quality seismology data that non‐observations of D” reflections are exceptions. Combining with earlier experiments performed at and below the normal lower‐mantle geotherm, our data show that the bridgmanite + post‐perovskite two‐phase region is ∼5 GPa thick and the d P /d T slope of the boundary is +6.5 ± 2.2 MPa/K, slightly smaller than previous theoretical calculations in MgSiO 3 . The global presence of rheologically weak post‐perovskite at the bottom of the mantle has profound implications in seismology, geodynamics, and heat transfer from the core.