Inherited Fabric in an Omphacite Symplectite: Reconstruction of Plastic Deformation under Ultra-High Pressure Conditions
Inherited Fabric in an Omphacite Symplectite: Reconstruction of Plastic Deformation under Ultra-High Pressure Conditions
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DOI：
10.1017/s1431927613001451
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发表时间：
2013-05
影响因子：
2.8
通讯作者：
F. Heidelbach;M. Terry
中科院分区：
文献类型：
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作者：
F. Heidelbach;M. Terry
摘要：我们研究了挪威西部片麻岩地区的榴辉片麻岩，该片麻岩在斯堪的纳造山运动期间作为波罗的海岩石圈的一部分俯冲到劳伦西亚之下。岩石学数据表明，榴辉岩在约 4 GPa 和 800°C 下发生塑性变形，产生强烈的宏观叶理和线理。石榴石在逆行隆起过程中基本保持稳定，而绿辉石则静态转变为由层状透辉石和斜长石组成的辛辉石，以及更等量的角闪石和斜方辉石颗粒。通过电子背散射衍射对晶体择优取向的测量表明，透辉石和角闪石以及斜方辉石与宏观结构以及主体绿辉石的（推测的）取向具有系统的取向关系。链状硅酸盐之间的取向关系非常尖锐，晶型{100}、{010}和⟨001⟩平行。它们的块体纹理显示最大⟨001⟩平行于线理和垂直于线理的{010}和{110}腰棱，最大部分平行于叶理，对应于原始绿辉石的L型纹理，并指示具有纯剪切/简单剪切分量的附加分量的收缩应变。
Abstract We investigated an eclogitic gneiss from the Western Gneiss Region in Norway, which underwent subduction as part of Baltica lithosphere beneath Laurentia during the Scandian orogeny. Petrologic data indicate that the eclogite was deformed plastically at about 4 GPa and 800°C producing a strong macroscopic foliation and lineation. Whereas garnet remained largely stable during the retrograde uplift, omphacite was transformed statically into a symplectite consisting of lamellar diopside and plagioclase with more equant grains of hornblende and orthopyroxene. Measurements of the crystallographic preferred orientation with electron backscatter diffraction show that diopside and hornblende, as well as orthopyroxene, have a systematic orientation relationship with the macroscopic fabric, as well as the (presumed) orientation of the host omphacite. The orientation relationship between the chain silicates is very sharp with the crystallographic forms {100}, {010}, and ⟨001⟩ being parallel. Their bulk texture shows a maximum of ⟨001⟩ parallel to the lineation and girdles of {010} and {110} perpendicular to the lineation with maxima subparallel to the foliation corresponding to an L-type texture of the original omphacite and indicating constrictional strain with an additional component of pure shear/simple shear component.