合成共存Wadsleyite β-(Mg,Fe)2SiO4和Ringwoodite γ-(Mg,Fe)2SiO4的光学吸收光谱研究

IF 0.5 Q4 MINERALOGY
M. N. Taran
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引用次数: 0

摘要

采用光吸收光谱法研究了环境高压和静水高压条件下(Mg1-xFex)2SiO4、wadsleyite和ringwoodite的α-和β-合成改性。此外,还研究了热退火对晶体的影响。在高达~13 GPa的静水压下,再释放到大气压下,光谱发生变化,晶体颜色也随之发生变化。这清楚地表明一些Fe2+被氧化成Fe3+。在温度高达300℃的空气中退火后,环伍德石和瓦德斯莱石的光谱都发生了变化。Fe2+的电子自旋允许带的强度降低,而紫外区低能吸收边给出的电荷转移电子跃迁O2 -→Fe3+的强度增加。这些晶体化学变化表现为蓝色(菱辉石)和绿色(瓦德斯莱石)颜色的减弱以及伴随而来的淡黄色的增加。Fe2+氧化为Fe3+的作用,在高压下减压以及在相对较低的温度下退火,可以导致两相的解体。因此,这两种矿物起源于深部火山作用或深俯冲带作用后,尚未在近地表条件下得到可靠的鉴定。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Synthetic Co-Existing Wadsleyite β-(Mg,Fe)2SiO4 and Ringwoodite γ-(Mg,Fe)2SiO4: an Optical Absorption Spectroscopy Study
The synthetic high-pressure α- and β-modification of (Mg1–xFex)2SiO4, wadsleyite and ringwoodite, respectively, were studied by optical absorption spectroscopy at ambient and hydrostatic high-pressure conditions. In addition, the effects of thermal annealing on the crystals were investigated. Under hydrostatic compression up to ~13 GPa and then consequent released to atmospheric pressure there were changes in the spectra and related changes in the crystal color. This is a clear indication that some Fe2+ was oxidized to Fe3+. The spectra of both ringwoodite and wadsleyite change after annealing in air at temperatures up to 300 °C. The intensities of electronic spin-allowed bands of Fe2+ decrease and the intensity of the charge-transfer electronic transition O2– → Fe3+, as given by the low-energy absorption edge in the UV region, increases. These crystal-chemical changes are shown by a weakening of the blue (ringwoodite) and green (wadsleyite) colors and a concomitant increase in yellowish tints. The effects of Fe2+ oxidation to Fe3+, upon decompression from high pressures as well as through annealing at relatively low temperatures, can cause the disintegration of both phases. Thus, both minerals have not yet been reliably identified at near surface Earth conditions after originating from deep-seated volcanism or deep subduction zone processes.
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来源期刊
CiteScore
0.70
自引率
0.00%
发文量
18
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