SEISMOLOGY AND GEOLOGY ›› 2012, Vol. ›› Issue (4): 768-781.DOI: 10.3969/j.issn.0253-4967.2012.04.019

• Volcanic hazards and mechanisms • Previous Articles     Next Articles

MINERAL CHEMISTRY OF LAMELLA OLIVINE AND ITS IMPLICATIONS FOR MANTLE RHEOLOGY

SUI Jian-li1, FAN Qi-cheng1, LI Ni1, ZHAO Yong-wei1, DU Xing-xing2   

  1. 1. Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China;
    2. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China
  • Received:2012-07-25 Revised:2012-09-28 Online:2012-12-30 Published:2012-12-28

橄榄石微页理结构的矿物化学及其地幔流变意义

隋建立1, 樊祺诚1, 李霓1, 赵勇伟1, 杜星星2   

  1. 1. 中国地震局地质研究所, 活动构造与火山重点实验室, 北京 100029;
    2. 中国地质科学院地质力学研究所, 北京 100081
  • 基金资助:

    国家自然科学基金(40972048)资助

Abstract:

Olivine creep dominates the major characteristics of mantle rheology. Such ductile deformation affects not only mineral microstructures but also microchemistry of olivines. However,very few works focus on mineral chemistry of these dislocation-rich olivines,because the dislocation structure is too small to be analyzed by electron microprobe. And even these few works led to controversial interpretations on chemical mechanisms of the phenomena,such as exsolution of Fe-Mg olivine,Cottrell cloud and fluid erosion. Here we report two cases of lamellea(in scales of 1μm and over 100μm seperately)olivines in mantle xenoliths from the Halaha River and Chaoer River area,Central Great Xing'an Range. Results of EMP analysis indicate that the lamellae is Fe rich olivine. In response to the arguments against the hypothesis of exsolution and erosion,we discuss the behavior and mechanism of Cottrell cloud in olivine.

Key words: mantle rheology, mineral chemistry of olivine, lamella structure, dislocation, Cottrell cloud

摘要:

橄榄石地幔流变同时包含物理和化学变化,但由于橄榄石位错的宽度通常<0.1μm,较难发现适合电子探针微区分析的样品(>1μm),因此研究较少,并且对其成因机制存在重大分歧,有固溶体出溶、柯氏气团和蚀变反应等多种假说。在东北大兴安岭第四纪火山岩携带的地幔橄榄岩捕虏体中,发现具有地幔流变特征的橄榄石,其中2个样品具有微页理结构,微页理宽度分别为1μm和100μm以上,电子探针研究表明微页理的成分是相对富铁的橄榄石。从矿物成分变化特点可以排除流体蚀变或者岩浆熔体反应的可能性,从固溶体平衡理论的讨论,可以排除Fe-Mg橄榄石固溶体出溶的解释,因此认为元素气团理论的解释更加合理。位错引起橄榄石晶格畸变,从而导致元素选择性富集(Fe富集、Mg亏损),而其他元素不变,这是元素气团的特征,与矿物反应边或者蚀变边明显不同。柯氏气团能显著增强晶体强度,冶金工业普遍采用淬火工艺改善金属性能,而橄榄石位错的成分变化对强度的影响、以及对于地幔流变的影响还需要进一步研究。

关键词: 地幔流变, 橄榄石矿物化学, 微页理结构, 位错, 柯氏气团

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