Incompatibility between serpentinization and epidote formation in the lower oceanic crust: Evidence from the Oman Drilling Project
Incompatibility between serpentinization and epidote formation in the lower oceanic crust: Evidence from the Oman Drilling Project
复制标题
下洋壳中蛇纹石化与绿帘石形成之间的不相容性：来自阿曼钻探项目的证据
DOI：
10.1111/jmg.12713
复制
发表时间：
2023
影响因子：
3.4
通讯作者：
Tateishi Yamato
中科院分区：
文献类型：
--
作者：
Nozaka Toshio;Tateishi Yamato
绿帘石是一种典型的绿片岩相矿物，在大洋下地壳中普遍存在，而其它指示类似温度条件的矿物如钠长石、阳起石、葡萄石和蛇纹石则普遍存在。为了找到这一现象的原因，我们对国际大陆科学钻探计划（ICDP）阿曼钻探项目采集的阿曼蛇绿岩下地壳岩石进行了岩石学分析。岩相学观察揭示的趋势，正如预期的那样，由斜长石的静态蚀变形成的绿帘石的量随深度而减少。由于矿物组合指示从角闪岩到亚绿片岩相的广泛的温度条件下发生在整个核心没有系统的丰度变化，绿帘石量的减少不能解释的温度条件的差异的蚀变。岩相学观察还表明，绿帘石是不存在或罕见的岩石中含有蛇纹化的橄榄石相比，葡萄石表现出密切的关系与蛇纹化的橄榄石。在含有绿帘石和蛇纹石化橄榄石的特殊样品中，绿帘石与切割或取代斜长石的长石一起出现，覆盖相邻的橄榄石，并与切割网状蛇纹石脉的长石+利蛇纹石脉相连。绿帘石的分布和产状表明其形成与蛇纹石化的主要阶段是脱钩的。切割橄榄石形成网状结构的蛇纹石脉通常是在脉中心带有磁铁矿条带的利蛇纹石，在脉边缘或无磁铁矿脉中具有利蛇纹石-铬铁矿固溶体的成分，表明在蛇纹石化早期阶段具有低硅和低氧电位的化学条件。绿片岩相条件下橄榄石和斜长石蚀变的热力学模型表明，斜长石蚀变形成葡萄石+绿帘石和绿帘石+绿帘石的二氧化硅潜力可能高于橄榄石蛇纹石化。另一方面，葡萄石+绿帘石形成的氧势低于绿帘石+绿帘石形成的氧势，与橄榄石蛇纹石化的氧势相当。通过观察和分析，认为绿帘石的形成受到橄榄石蛇纹石化的抑制，为下洋壳的蚀变提供了还原条件。
It is a general tendency that epidote, which is a typical greenschist facies mineral, is scarce in the lower oceanic crust, in spite of the widespread occurrence of the other minerals indicative of similar temperature conditions such as chlorite, actinolite, prehnite and serpentine. To find the cause of this, we carried out petrological analyses of lower crustal rocks of the Oman ophiolite sampled by the Oman Drilling Project of the International Continental Scientific Drilling Program (ICDP). Petrographic observations revealed the tendency, as expected, that the amount of epidote formed by static alteration of plagioclase decreases with depth. Because mineral assemblages indicative of a wide range of temperature conditions from amphibolite to subgreenschist facies occur throughout the cores without systematic variations of abundance, the decrease of epidote amount cannot be explained by the difference of temperature condition of alteration. Petrographic observations also revealed that epidote is absent or rare in rocks containing serpentinized olivine in contrast to prehnite showing a close association with serpentinization of olivine. In an exceptional sample containing both epidote and serpentinized olivine, epidote occurs with chlorite that cuts or replaces plagioclase, mantles adjacent olivine and is connected with chlorite + lizardite veins cutting mesh‐forming serpentine veins. The distribution and mode of occurrence of epidote suggest decoupling of its formation with the main stage of serpentinization. Serpentine veins cutting olivine to form mesh texture are typically lizardite with magnetite ribbons at vein centres and have compositions of lizardite–cronstedtite solid solution at vein margins or in magnetite‐free veins, suggesting a chemical condition with low silica and low oxygen potentials at an early stage of serpentinization. Thermodynamic modelling for olivine and plagioclase alteration at greenschist facies conditions indicates that silica potential for plagioclase alteration to form prehnite + chlorite and epidote + chlorite could be higher than for olivine serpentinization. On the other hand, oxygen potential for the prehnite + chlorite formation is lower than for the epidote + chlorite formation and is comparable with that for olivine serpentinization. From the observations and analyses, it is concluded that epidote formation is inhibited by olivine serpentinization, which maintains a reducing condition for alteration in the lower oceanic crust.
登录
查看更多内容
箱根火山拉斑斑玄武岩安山岩中共生斜方辉石、红辉石和辉石的成分关系
影响因子：
3.5
作者：
Yasuo Nakamura;I. Kushiro
通讯作者：
I. Kushiro
影响因子：
--
作者：
A. Nicolas;D. Mainprice;F. Boudier
通讯作者：
A. Nicolas;D. Mainprice;F. Boudier
阿曼蛇绿岩干河道吉迪亚剖面绿帘石脉对下洋地壳冷却的制约
影响因子：
3.7
作者：
Bieseler B;Diehl A;Jöns N;Lucassen F;Bach W
通讯作者：
Bach W
日本西南部变质蛇纹岩中滑石的成分变化
影响因子：
0.7
作者：
NOZAKA Toshio;MIYAMOTO Daisuke
通讯作者：
MIYAMOTO Daisuke
DOI：
10.1029/2019jb018877
发表时间：
2020-05
期刊：
Journal of Geophysical Research: Solid Earth
影响因子：
--
作者：
B. Malvoisin;Chang Zhang;O. Müntener;L. Baumgartner;P. Kelemen
通讯作者：
B. Malvoisin;Chang Zhang;O. Müntener;L. Baumgartner;P. Kelemen