Seismic properties across an amphibolite- to greenschist-facies strain gradient (Neves area, eastern Alps, Italy): New considerations for shear zone imaging
Seismic properties across an amphibolite- to greenschist-facies strain gradient (Neves area, eastern Alps, Italy): New considerations for shear zone imaging
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角闪岩相到绿片岩相应变梯度的地震特性（意大利阿尔卑斯山东部内维斯地区）：剪切带成像的新考虑因素
DOI：
10.1016/j.tecto.2021.229005
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发表时间：
2021
期刊：
影响因子：
2.9
通讯作者：
D. Faulkner
中科院分区：
文献类型：
--
作者：
Thomas Leydier;P. Goncalvès;J. Albaric;H. Leclère;K. Mahan;D. Faulkner
通过地球物理方法检测地壳剪切带的存在和几何形状依赖于我们对控制这些变形岩石的地震特性的内在参数的理解，这些参数在地壳中预期的压力-温度条件范围内。为此，我们的目的是跟踪变化的P波传播速度（VP），各向异性（AVP）和S波分裂（AVS）在整个自然剪切带使用实验和电子背散射衍射方法。五个样品收集在米级剪切带下角闪岩绿片岩相的Neves变质花岗岩（陶恩窗口，东阿尔卑斯山）。随着应变的增加，地震属性表现出非线性演化，这是由于构造、结构和矿物学变化之间的相互作用。地震各向异性的几何形状和大小由强各向异性层状硅酸盐与较少的各向异性但更丰富的石英和斜长石的干涉控制。角闪岩相剪切带边缘（> 500 °C）无主要矿物转化，而以S-C构造发育为特征，VP分布呈正交对称，AVP高达12%，快轴平行于线理，AVSI在平行于C面的两个方向上最大（6%）。绿片岩相（450-500 °C）下的进一步变形导致白云母、白云母和钠长石的显著结晶。主要的六边形对称性发展，具有快VP平面和快S波偏振平面，沿C平面沿着，AVPandAVS超过10%。计算的整个剪切带的弹性张量强调了应变梯度对整个结构的地震特征的重要性。在我们的模型中，大部分地震属性主要由正交对称的原糜棱岩带，而不是由超糜棱岩核心与六角对称（C-平面），这可以解释为什么地震研究剪切带通常涉及一个快速的速度平面倾斜的层边界。
Detecting the presence and geometry of crustal shear zones by geophysical methods relies on our understanding of the intrinsic parameters controlling the seismic properties of these deformed rocks, over the range of pressure-temperature conditions expected in the Earth's crust. To this end, we aimed to track changes in P-wave propagation velocity (VP), anisotropy (AVP) and S-wave splitting (AVS) across a natural shear zone using experimental and electron backscatter diffraction methods. Five samples were collected across a meter-scale shear zone developed under amphibolite- to greenschist-facies in the Neves metagranodiorite (Tauern Window, Eastern Alps). With increasing strain, seismic properties show a non-linear evolution resulting from interactions among structural, textural and mineralogical changes. Geometry and magnitude of seismic anisotropy are controlled by the interference of strongly anisotropic phyllosilicates with less anisotropic but more abundant quartz and plagioclase. The amphibolite-facies shear zone margin (> 500 °C) is free of major mineral transformations, and rather characterized by the development of S-C structure, inducing an orthorhombic symmetry to theVPdistribution and up to 12 %AVP, with the fast axis parallel to lineation.AVSis maximized (6 %) in the two directions parallel to the C-planes. Further deformation under greenschist-facies (450–500 °C) induces significant crystallization of muscovite, chlorite, and albite. A dominant hexagonal symmetry develops, with a fastVPplane and a fast S-wave polarization plane along the C-planes.AVPandAVSexceed 10 %. The computed elastic tensor of the whole shear zone emphasizes the importance of the strain gradient on the seismic signature of the overall structure. In our model, the bulk seismic properties are dominated by the orthorhombic symmetry of the protomylonitic zone rather than by the ultramylonite core with hexagonal symmetry (C-plane), which may explain why seismic studies of shear zones commonly involve a fast velocity plane oblique to the layer boundaries.
陶恩之窗（奥地利东阿尔卑斯山）：新的构造图，包含横截面和构造变质综合
影响因子：
3.1
作者：
Schmid;Scharf;Rosenberg
通讯作者：
Rosenberg