{"title":"Mn2GeO4中从橄榄石到瓦斯利石结构的转变断层:对深焦距地震物理机制的影响","authors":"","doi":"10.1016/j.tecto.2024.230467","DOIUrl":null,"url":null,"abstract":"<div><p>High-pressure and temperature deformation experiments interfaced with acoustic emission (AE) monitoring have been conducted to study transformational faulting in Mn<sub>2</sub>GeO<sub>4</sub> olivine, which transforms to the β phase, isostructural to wadsleyite. Metastable Mn<sub>2</sub>GeO<sub>4</sub> olivine exhibits a marked embrittlement behavior at temperatures between 800 and 1100 K, emitting numerous AEs. At each temperature, brittle deformation is characterized by a two-stage process: (1) a “preparation” stage with numerous diffusedly located low-magnitude AEs and large <em>b</em> values (>2), and (2) a failure stage where larger-magnitude AEs form a planar distribution with <em>b</em> values about 1. Microstructure analysis reveals extensive kink band development in olivine grains in the recovered samples. Kink band boundaries (KBBs), with a typical thickness of ∼100 nm, are filled with a nanometric β-Mn<sub>2</sub>GeO<sub>4</sub> “gouge”. A dense array of secondary shear localizations is often present within the kink bands, suggesting significant shear deformation therein. The combined observations suggest that faulting in metastable Mn<sub>2</sub>GeO<sub>4</sub> olivine is a self-similar process, from grain-scale to the sample-scale. Both observed embrittlement behavior and the microstructure of metastable Mn<sub>2</sub>GeO<sub>4</sub> olivine are essentially identical to those in Mg<sub>2</sub>GeO<sub>4</sub> olivine we have reported previously, indicating that the physical mechanism of faulting in metastable olivine is insensitive to the specific crystallographic structure of the high-pressure phase. The low <em>b</em> values (about 1) observed in the faulting process in our experiments are similar to those of deep focus earthquakes in cold subduction zones. Our observed mechanism explains deep focus seismicity in cold metastable mantle wedges, provided that the self-similarity assumption holds to geological scales.</p></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":null,"pages":null},"PeriodicalIF":2.7000,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Transformational faulting in Mn2GeO4 from olivine to wadsleyite structure: Implications for physical mechanism of deep-focus earthquakes\",\"authors\":\"\",\"doi\":\"10.1016/j.tecto.2024.230467\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>High-pressure and temperature deformation experiments interfaced with acoustic emission (AE) monitoring have been conducted to study transformational faulting in Mn<sub>2</sub>GeO<sub>4</sub> olivine, which transforms to the β phase, isostructural to wadsleyite. Metastable Mn<sub>2</sub>GeO<sub>4</sub> olivine exhibits a marked embrittlement behavior at temperatures between 800 and 1100 K, emitting numerous AEs. At each temperature, brittle deformation is characterized by a two-stage process: (1) a “preparation” stage with numerous diffusedly located low-magnitude AEs and large <em>b</em> values (>2), and (2) a failure stage where larger-magnitude AEs form a planar distribution with <em>b</em> values about 1. Microstructure analysis reveals extensive kink band development in olivine grains in the recovered samples. Kink band boundaries (KBBs), with a typical thickness of ∼100 nm, are filled with a nanometric β-Mn<sub>2</sub>GeO<sub>4</sub> “gouge”. A dense array of secondary shear localizations is often present within the kink bands, suggesting significant shear deformation therein. The combined observations suggest that faulting in metastable Mn<sub>2</sub>GeO<sub>4</sub> olivine is a self-similar process, from grain-scale to the sample-scale. Both observed embrittlement behavior and the microstructure of metastable Mn<sub>2</sub>GeO<sub>4</sub> olivine are essentially identical to those in Mg<sub>2</sub>GeO<sub>4</sub> olivine we have reported previously, indicating that the physical mechanism of faulting in metastable olivine is insensitive to the specific crystallographic structure of the high-pressure phase. The low <em>b</em> values (about 1) observed in the faulting process in our experiments are similar to those of deep focus earthquakes in cold subduction zones. Our observed mechanism explains deep focus seismicity in cold metastable mantle wedges, provided that the self-similarity assumption holds to geological scales.</p></div>\",\"PeriodicalId\":22257,\"journal\":{\"name\":\"Tectonophysics\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":2.7000,\"publicationDate\":\"2024-08-13\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Tectonophysics\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0040195124002695\",\"RegionNum\":3,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Tectonophysics","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0040195124002695","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
Transformational faulting in Mn2GeO4 from olivine to wadsleyite structure: Implications for physical mechanism of deep-focus earthquakes
High-pressure and temperature deformation experiments interfaced with acoustic emission (AE) monitoring have been conducted to study transformational faulting in Mn2GeO4 olivine, which transforms to the β phase, isostructural to wadsleyite. Metastable Mn2GeO4 olivine exhibits a marked embrittlement behavior at temperatures between 800 and 1100 K, emitting numerous AEs. At each temperature, brittle deformation is characterized by a two-stage process: (1) a “preparation” stage with numerous diffusedly located low-magnitude AEs and large b values (>2), and (2) a failure stage where larger-magnitude AEs form a planar distribution with b values about 1. Microstructure analysis reveals extensive kink band development in olivine grains in the recovered samples. Kink band boundaries (KBBs), with a typical thickness of ∼100 nm, are filled with a nanometric β-Mn2GeO4 “gouge”. A dense array of secondary shear localizations is often present within the kink bands, suggesting significant shear deformation therein. The combined observations suggest that faulting in metastable Mn2GeO4 olivine is a self-similar process, from grain-scale to the sample-scale. Both observed embrittlement behavior and the microstructure of metastable Mn2GeO4 olivine are essentially identical to those in Mg2GeO4 olivine we have reported previously, indicating that the physical mechanism of faulting in metastable olivine is insensitive to the specific crystallographic structure of the high-pressure phase. The low b values (about 1) observed in the faulting process in our experiments are similar to those of deep focus earthquakes in cold subduction zones. Our observed mechanism explains deep focus seismicity in cold metastable mantle wedges, provided that the self-similarity assumption holds to geological scales.
期刊介绍:
The prime focus of Tectonophysics will be high-impact original research and reviews in the fields of kinematics, structure, composition, and dynamics of the solid arth at all scales. Tectonophysics particularly encourages submission of papers based on the integration of a multitude of geophysical, geological, geochemical, geodynamic, and geotectonic methods