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

作　　者：Masayuki Nishi Steeve Gréaux Shigehiko Tateno Yasuhiro Kuwayama Kenji Kawai Tetsuo Irifune Shigenori Maruyama 

机构地区：[1]Geodynamics Research Centre,Ehime University,Ehime 790-8577,Japan [2]Earth-Life Science Institute,Tokyo Institute of Technology,Tokyo 152-8550,Japan [3]Institute for Planetary Materials,Okayama University,Misasa,Tottori 682-0193,Japan [4]Department of Earth Planetary Science,School of Science,University of Tokyo,113-0033 Hongo 7-3-1,Bunkyo,Tokyo,Japan [5]Novosibirsk State University,Pirogova 1,630090,Russia

出　　处：《Geoscience Frontiers》2018年第6期1859-1870,共12页地学前缘（英文版）

基　　金：partially supported by Grant-in-Aid for Scientific Research from the Japanese government to S.M.(JP26106002);M.N,(JP15H05469);S.G.(JP26287105)and T.I.(JP25220712);the Ministry of Education and Science of the Russian Federation to S.M.(14.Y26.31.0018)

摘　　要：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,CaAl_4Si_2O_(11)-rich phase(CAS phase), and SiO_2 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 at660-720 km in 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.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,CaAl_4Si_2O_(11)-rich phase(CAS phase), and SiO_2 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 at660-720 km in 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.

关 键 词：ANORTHOSITE Phase transformation Multi-anvil apparatus Diamond-anvil cell MANTLE dynamics 

分 类 号：P542.5[天文地球—构造地质学] P588[天文地球—地质学]