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High Pressure Response of Rutile Polymorphs and Its Significance for Indicating the Subduction Depth of Continental Crust
Author(s) -
Dawei MENG,
Xiuling WU,
Xiaoyu FAN,
Zhengjie ZHANG,
Hong CHEN,
Xin MENG,
Jianping ZHENG
Publication year - 2008
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2008.tb00586.x
Subject(s) - coesite , metamorphism , rutile , omphacite , geology , eclogite , mineralogy , diamond , materials science , geochemistry , subduction , composite material , paleontology , tectonics
α‐PbO 2 ‐type TiO 2 (TiO 2 ‐II) is an important index mineral for ultrahigh‐pressure metamorphism. After the discovery of a natural high‐pressure phase of titanium oxide with α‐PbO 2 ‐structure in omphacite from coesite‐bearing eclogite at Shima in the Dabie Mountains, China, a nano‐scale (<2 nm) α‐PbO 2 ‐type TiO 2 has been identified through electron diffraction and high‐resolution transmission electron microscopy in coesite‐bearing jadeite quartzite at Shuanghe in the Dabie Mountains. The crystal structure is orthorhombic with lattice parameters a = 4.58times10 −1 nm, b = 5.42times10 −1 nm, c = 4.96times10 −1 nm and space group Pbcn. The analysis results reveal that rutile {011} R twin interface is a basic structural unit of α‐PbO 2 ‐type TiO 2 . Nucleation of α‐PbO 2 ‐type TiO 2 lamellae is caused by the displacement of one half of the titanium cations within the {011} R twin slab. This displacement reduces the Ti‐O‐Ti distance and is favored by high pressure. The identification of α‐PbO 2 ‐type TiO 2 in coesite‐bearing jadeite quartzite from Shuanghe, Dabie Mountains, provides a new and powerful evidence of ultrahigh‐pressure metamorphism at 4–7 GPa, 850°C‐900°C, and implies a burial of continental crustal rocks to 130–200 kilometers depth or deeper. The α‐PbO 2 ‐type TiO 2 may be a useful indicator of the pressure and temperature in the diamond stability field.