Synthesis of inverse ringwoodite sheds light on the subduction history of Tibetan ophiolites

Luca Bindi; William L Griffin; Wendy R Panero; Ekaterina Sirotkina; Andrey Bobrov; Tetsuo Irifune

doi:10.1038/s41598-018-23790-9

Synthesis of inverse ringwoodite sheds light on the subduction history of Tibetan ophiolites

Sci Rep. 2018 Apr 3;8(1):5457. doi: 10.1038/s41598-018-23790-9.

Authors

Luca Bindi^{1

2}, William L Griffin³, Wendy R Panero⁴, Ekaterina Sirotkina^{5

6}, Andrey Bobrov^{5

6

7}, Tetsuo Irifune^{8

9}

Affiliations

¹ Dipartimento di Scienze della Terra, Università di Firenze, Via La Pira 4, I-50121, Florence, Italy. luca.bindi@unifi.it.
² CNR-Istituto di Geoscienze e Greorisorse, Via La Pira 4, I-50121, Florence, Italy. luca.bindi@unifi.it.
³ ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia.
⁴ School of Earth Sciences, Ohio State University, Columbus, Ohio, USA.
⁵ Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, Moscow, 119991, Russia.
⁶ Department of Petrology, Geological Faculty, Moscow State University, Moscow, 119991, Russia.
⁷ Institute of Experimental Mineralogy of Russian Academy of Sciences, Chernogolovka, 142432, Russia.
⁸ Geodynamics Research Center, Ehime University, Matsuyama, 790-8577, Japan.
⁹ Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, 152-8550, Japan.

Abstract

Tibetan ophiolites are shallow mantle material and crustal slabs that were subducted as deep as the mantle transition zone, a conclusion supported by the discovery of high-pressure phases like inverse ringwoodite in these sequences. Ringwoodite, Mg₂SiO₄, exhibits the normal spinel structure, with Mg in the octahedral A site and Si in the tetrahedral B site. Through A and B site-disorder, the inverse spinel has four-coordinated A cations and the six-coordinated site hosts a mixture of A and B cations. This process affects the density and impedance contrasts across the boundaries in the transition zone and seismic-wave velocities in this portion of the Earth. We report the first synthesis at high pressure (20 GPa) and high temperature (1600 °C) of a Cr-bearing ringwoodite with a completely inverse-spinel structure. Chemical, structural, and computational analysis confirm the stability of inverse ringwoodite and add further constraints to the subduction history of the Luobusa peridotite of the Tibetan ophiolites.