TY - JOUR

T1 - High-pressure phase transitions of anorthosite crust in the Earth's deep mantle

AU - Nishi, Masayuki

AU - Gréaux, Steeve

AU - Tateno, Shigehiko

AU - Kuwayama, Yasuhiro

AU - Kawai, Kenji

AU - Irifune, Tetsuo

AU - Maruyama, Shigenori

PY - 2018/11/1

Y1 - 2018/11/1

N2 - We investigated phase relations, mineral chemistry, and density of lunar highland anorthosite at conditions up to 125 GPa and 2000 K. We used a multi-anvil apparatus and a laser-heated diamond-anvil cell for this purpose. In-situ X-ray diffraction measurements at high pressures and composition analysis of recovered samples using an analytical transmission electron microscope showed that anorthosite consists of garnet, CaAl4Si2O11-rich phase (CAS phase), and SiO2 phases in the upper mantle and the mantle transition zone. Under lower mantle conditions, these minerals transform to the assemblage of bridgmanite, Ca-perovskite, corundum, stishovite, and calcium ferrite-type aluminous phase through the decomposition of garnet and CAS phase at around 700 km depth. Anorthosite has a higher density than PREM and pyrolite in the upper mantle, while its density becomes comparable or lower under lower mantle conditions. Our results suggest that ancient anorthosite crust subducted down to the deep mantle was likely to have accumulated at 660-720 km depth without coming back to the Earth's surface. Some portions of the anorthosite crust might have circulated continuously in the Earth's deep interior by mantle convection and potentially subducted to the bottom of the lower mantle when carried within layers of dense basaltic rocks.

AB - We investigated phase relations, mineral chemistry, and density of lunar highland anorthosite at conditions up to 125 GPa and 2000 K. We used a multi-anvil apparatus and a laser-heated diamond-anvil cell for this purpose. In-situ X-ray diffraction measurements at high pressures and composition analysis of recovered samples using an analytical transmission electron microscope showed that anorthosite consists of garnet, CaAl4Si2O11-rich phase (CAS phase), and SiO2 phases in the upper mantle and the mantle transition zone. Under lower mantle conditions, these minerals transform to the assemblage of bridgmanite, Ca-perovskite, corundum, stishovite, and calcium ferrite-type aluminous phase through the decomposition of garnet and CAS phase at around 700 km depth. Anorthosite has a higher density than PREM and pyrolite in the upper mantle, while its density becomes comparable or lower under lower mantle conditions. Our results suggest that ancient anorthosite crust subducted down to the deep mantle was likely to have accumulated at 660-720 km depth without coming back to the Earth's surface. Some portions of the anorthosite crust might have circulated continuously in the Earth's deep interior by mantle convection and potentially subducted to the bottom of the lower mantle when carried within layers of dense basaltic rocks.

KW - Anorthosite

KW - Diamond-anvil cell

KW - Mantle dynamics

KW - Multi-anvil apparatus

KW - Phase transformation

KW - SYSTEM

KW - HIGH-TEMPERATURE

KW - GARNET

KW - SUBDUCTION

KW - X-RAY-DIFFRACTION

KW - THERMAL EQUATION

KW - CONTINENTAL-CRUST

KW - EQUATION-OF-STATE

KW - SOLID-SOLUTION

KW - GPA

UR - http://www.scopus.com/inward/record.url?scp=85035100506&partnerID=8YFLogxK

U2 - 10.1016/j.gsf.2017.10.002

DO - 10.1016/j.gsf.2017.10.002

M3 - Article

AN - SCOPUS:85035100506

VL - 9

SP - 1859

EP - 1870

JO - Geoscience Frontiers

JF - Geoscience Frontiers

SN - 1674-9871

IS - 6

ER -