Plastic deformation and development of antigorite crystal preferred orientation in high-pressure serpentinites
Plastic deformation and development of antigorite crystal preferred orientation in high-pressure serpentinites
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DOI：
10.1016/j.epsl.2012.06.049
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发表时间：
2012-10
影响因子：
5.3
通讯作者：
J. Padrón-navarta;A. Tommasi;C. Garrido;V. L. Sánchez‐Vizcaíno
中科院分区：
文献类型：
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作者：
J. Padrón-navarta;A. Tommasi;C. Garrido;V. L. Sánchez‐Vizcaíno
我们通过对来自 Cerro del Almirez 超镁铁质地块（西班牙东南部贝蒂科迪勒拉）的样品进行高分辨率 EBSD 绘图，推断了叶蛇纹石的变形机制。结构关系和相图计算将叶理发育条件限制在高达 600–630°C 和 1.6–1.9GPa 的俯冲前行路径上。变形后，叶蛇纹石在约 100 ℃ 下进行静态退火。 680°C。叶蛇纹石的晶体优选取向 (CPO) 的特征是垂直于叶面的 (001) 极的强排列，以及 [100] 轴和由磁铁矿聚集体伸长定义的宏观线状之间较弱但清晰的平行性。对跨亚晶粒的错误取向的分析表明[010]旋转轴占主导地位，这与[100](001)滑移系统的激活一致。然而，接近平行于（100）的倾斜亚晶界（可能由该系统的刃位错形成）是次要的。大多数亚晶界与 (001) 面近平行。它们被解释为（001）双胞胎，其中持续的粘塑性变形导致双胞胎之间的错误取向略有增加。使用下限方法并考虑不同的变形机制以及基底和非基底滑移系统组对叶蛇纹 CPO 的演化进行建模，结果表明 [100] 和 [010] 最大值的强度反映了叶蛇纹 [100](001) 和 [010](001) 系统的相对强度。其他基础或非基础滑移系统的激活不会显着改变 CPO 模式，但会导致 CPO 浓度降低。 3D 压缩模型更好地再现了天然叶蛇纹石的 CPO。我们认为，高压蛇纹石中广泛存在的强CPO与[hk0](001)上滑移占主导地位的位错蠕变变形以及孪晶的激活相一致，这意味着幂律流变学可以更好地解释俯冲通道和地幔楔深处蛇纹石的力学行为。
We have inferred the deformation mechanisms of antigorite by high-resolution EBSD mapping of samples from Cerro del Almirez ultramafic massif (Betic Cordillera, SE Spain). Textural relations and phase diagram calculations constrain the foliation development conditions to the subduction prograde path at up to 600–630°C and 1.6–1.9GPa. Deformation was followed by static annealing of antigorite at ca. 680°C. The Crystal Preferred Orientation (CPO) of antigorite is characterised by a strong alignment of (001) poles normal to the foliation plane and a weaker, but clear, parallelism between [100] axes and the macroscopic lineation defined by the elongation of magnetite aggregates. Analysis of misorientations across subgrains shows predominance of [010] rotation axis, consistent with activation of the [100](001) slip system. However, tilt subgrain boundaries subparallel to (100), probably formed by edge dislocations of this system, are subsidiary. Most subgrain boundaries are subparallel to (001) planes. They are interpreted as (001) twins wherein continuing viscoplastic deformation resulted in a slight increase of the misorientation between the twins. Modelling of the evolution of the antigorite CPO using a lower bound approach and considering different deformation regimes and sets of basal and non-basal slip systems has shown that intensities of [100] and [010] maxima reflect the relative strength of the antigorite [100](001) and [010](001) systems. Activation of other basal or non-basal slip systems does not change significantly the CPO patterns, but results in less concentrated CPO. 3D transpression models better reproduce the CPO of natural antigorite serpentinites. We propose that the widespread occurrence of strong CPO in high-pressure antigorite serpentinite is consistent with deformation by dislocation creep with dominant glide on [hk0](001), together with the activation of twinning, implying that a power law rheology would better account for the mechanical behaviour of antigorite serpentinite deep in the subduction channel and mantle wedge.