Seismic reflectivity of a finely layered, granulite-facies ductile shear zone in the southern Grenville Province (Quebec)
Seismic reflectivity of a finely layered, granulite-facies ductile shear zone in the southern Grenville Province (Quebec)
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DOI：
10.1016/s0040-1951(97)00133-9
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发表时间：
1997-09
期刊：
影响因子：
2.9
通讯作者：
S. Ji;C. Long;J. Martignole;M. Salisbury
中科院分区：
文献类型：
--
作者：
S. Ji;C. Long;J. Martignole;M. Salisbury
横跨格伦维尔构造省（魁北克，加拿大）麻粒岩相Morin剪切带（MSZ）的Lithoprobe反射剖面54揭示了一个向西倾斜的强反射带。通过详细的野外测绘、主要岩性单元代表性岩石样品的P波速度和密度的实验室测量以及正演合成模拟，对这些反射的起源进行了研究。为了解释测得的地震特性，进行了岩石组构和微结构分析。由速度和密度数据生成的合成地震记录表明，反射波来源于岩性薄层和薄层簇，可能是强烈的构造置换和变质分异的结果。麻粒岩相糜棱岩（含有丰富的硅线石、黑云母或角闪石的糜棱岩除外）的晶格择优取向（LPO）诱导的各向异性非常低，因此不太可能是反射的主要原因。围压对剪切带的反射率没有显著影响，因为反射系数对高达至少600 MPa的压力不敏感。由于薄层团簇的复合反射可引起高反射率，因此某些低折射速度的地壳深部剖面的强反射率可解释为主要长英质岩石中存在薄层基性团簇。
Lithoprobe reflection profile 54 across the granulite-facies Morin shear zone (MSZ) in the Grenville Tectonic Province (Québec, Canada) reveals a west-dipping zone of strong reflections. The origin of these reflections has been investigated by detailed field mapping, laboratory measurements of P-wave velocities and densities of representative rock samples from the main lithological units, and forward synthetic modeling. Petrofabric and microstructural analyses were performed in order to interpret the measured seismic properties. Synthetic seismograms generated from the velocity and density data demonstrate that reflections originate from lithologic thin layers and thin-layer clusters, likely resulted from intensive tectonic transposition and metamorphic differentiation. Lattice-preferred-orientation (LPO)-induced anisotropy of granulite-facies mylonites (except for those containing abundant sillimanite, biotite or amphibole) is very low, and hence unlikely to be the primary cause for reflections. Confining pressure does not significantly affect the reflectivity of the shear zone because the reflection coefficients are not sensitive to pressure up to at least 600 MPa. Since composite reflections of thin-layer clusters can cause high reflectivity, the strong reflectivity from some deep crustal sections with low refraction velocities may be interpreted to be due to the presence of thin-layer, mafic clusters within dominantly felsic rocks.