Seismic Properties of Shear Zones in the Lower Continental Crust

暴露在意大利北部Ivrea-Verbano带和挪威西部卑尔根弧的麻粒岩相地形中的糜棱岩带，分别为下大陆地壳的伸展和挤压断裂带提供了例子。在Ivrea带内，剪切带以Pogallo断裂带糜棱岩和Valle d’ossola麻粒岩域高温剪切带的形式出现。变形超镁质岩也是Ivrea带深部构造层的重要组成部分。卑尔根弧的糜棱岩叠加在斜长杂岩上，具有榴辉岩相矿物学特征。为了验证糜棱岩带引起深部反射的假说，研究了这些带岩石的地震性质。工作的主要阶段是：1)两个地区的抽样方案；2)糜棱岩优选矿物取向研究；3)样品组成的薄片及地球化学研究；4)测定围压为600 MPa时纵波和横波速度的弹性常数张量；4)通过变形和未变形序列构建假设速度剖面。

Mylonite zones exposed within the granulite facies terrains of the Ivrea-Verbano zone, northern Italy, and the Bergen Arc, western Norway, provide examples of fault zones in the lower continental crust of extensional and compressional regimes, respectively. Within the Ivrea zone, the shear zones occur as mylonites of the Pogallo fault zone and as high temperature shear zones in the granulite domain of Valle d'Ossola. Deformed ultramafic rocks are also important constituents of deep structural levels of the Ivrea zone. Mylonites in the Bergen Arc are superimposed on an anorthositic complex and are characterized by an eclogite facies mineralogy. The research investigated the seismic properties of rocks from the these zones in order to evaluate the hypothesis that mylonite zones cause deep crustal reflections. The main phases of the work are 1) a sampling program in both regions; 2) investigation of preferred mineral orientations in the mylonitic rocks; 3) thin section and geochemical study of the composition of samples; 4) determination of the elastic constant tensor by measurement of P- and S-wave velocities at confining pressures up to 600 MPa; 4) construction of hypothetical velocity profiles through deformed and undeformed sequences.