Magnetic fabrics and anisotropy-controlled thrusting in the Kapuskasing Structural Zone, Canada
Magnetic fabrics and anisotropy-controlled thrusting in the Kapuskasing Structural Zone, Canada
复制标题
加拿大卡普斯卡辛构造带的磁性织物和各向异性控制逆冲
DOI：
10.1016/s0040-1951(98)00292-3
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发表时间：
1999
期刊：
影响因子：
2.9
通讯作者：
T. Werner
中科院分区：
文献类型：
--
作者：
G. Borradaile;T. Werner
北方安大略Kapuskasing构造带（KSZ）的太古宙下地壳岩石的磁组构揭示了以前未认识到的、一致定向的矿物定向分布。这些定义了一个剪切穿过不均匀应变扭曲片麻状层理的剪切线理和延伸线理。在麻粒岩相和上部角闪岩相片麻岩中，磁性决定的隐蔽性的反射体与弥散但一致定向的地震反射体近平行。地震反射以前是无法解释的，因为它们一致的方向不符合岩性分层，但我们现在可以把它们归因于首选的矿物方向。磁线理位于地震反射体平面内。边界逆冲断层滞后于磁组构记录的各向异性的低场磁化率（AMS），主要取决于微妙的取向分布的硅酸盐矿物和磁铁矿包裹体。无磁滞剩磁的各向异性隔离了磁铁矿磁组构的成分。这与“全岩”AMS签名略有不同，因为磁铁矿易受后期重结晶或域重排的影响，从而改变其各向异性，以响应非共轴应力历史的后期阶段。AMS和AARM磁线理都是近水平的，分别走向075°和060°。这些与隆升运动学是不相容的，必须反映在深度的古代伸展方向。然而，线理趋势和断层走向的相似性表明，边界逆冲断层通过线理提供的阻力最小的路径向上传播。
Magnetic fabrics of upthrust Archean lower crustal rocks in the Kapuskasing Structural Zone (KSZ), northern Ontario, reveal previously unrecognized, consistently oriented mineral orientation–distributions. These define a schistosity and extension lineation that cuts across the heterogeneously strained contorted gneissic layering. The cryptic, magnetically determined schistosity is subparallel to diffuse but consistently oriented seismic reflectors in granulite and upper amphibolite facies gneisses. The seismic reflections were previously unexplained because their consistent orientation did not conform to lithological layering but we can now attribute them to preferred mineral orientations instead. The magnetic lineation lies within the plane of the seismic reflectors. The bounding thrust fault postdates the magnetic fabrics recorded by anisotropy of low-field magnetic susceptibility (AMS) that are primarily dictated by the subtle orientation distribution of silicate minerals and their magnetite inclusions. Anisotropy of anhysteretic remanence (AARM) isolates the component of magnetic fabric due to magnetite. This differs slightly from the `whole-rock' AMS signature because the magnetite is susceptible to late recrystallization or domain-rearrangement that changes its anisotropy in response to later phases of a noncoaxial stress history. Both AMS and AARM magnetic lineations are subhorizontal, trending 075° and 060°, respectively. These are incompatible with uplift kinematics and must reflect the ancient extension direction at depth. However, the similarity of the lineation trends and the strike of the fault suggest that the boundary thrust propagated upwards across the foliation using the path of least resistance afforded by the lineation.