Magnetic properties and paleointensity of pseudotachylytes from the Sudbury structure, Canada: Petrologic control
Magnetic properties and paleointensity of pseudotachylytes from the Sudbury structure, Canada: Petrologic control
复制标题
DOI：
10.1016/j.tecto.2004.10.015
复制
发表时间：
2005-06
期刊：
影响因子：
2.9
通讯作者：
N. Nakamura;Yuhya Iyeda
中科院分区：
文献类型：
--
作者：
N. Nakamura;Yuhya Iyeda
由于假玄武玻璃是通过粉碎和摩擦熔化的组合产生的，它可以记录环境地球的磁场作为从摩擦熔化冷却期间的热剩磁。为了测试确定古强度的可靠性，Coe修改的Thellier方法进行了一个小套件的伪玄武玻璃体在大位移断层带从北部范围萨德伯里影响结构。本文所研究的假玄武玻璃按其原岩岩性可分为两类：片麻岩成因的假玄武玻璃和花岗岩成因的假玄武玻璃。岩石学观察证实，在片麻岩成因的假玄武玻璃中存在大量的细粒磁铁矿包裹体和粗粒钛磁铁矿，并伴有钛铁矿片层的出溶。在花岗岩成因的假玄武玻璃中，发现了多畴磁铁矿的分散分布。虽然花岗岩类成因的假玄武玻璃不能估计的古强度，片麻岩成因的假玄武玻璃产生弱的古强度值，这是与以前的古强度数据从苏长岩在萨德伯里火成杂岩。这些结果表明，原岩岩石学控制了假玄武玻璃中的磁性矿物学和作为古地球磁场记录器的可靠性。
Since a pseudotachylyte is generated through a combination of comminution and frictional melting, it may record an ambient Earth's magnetic field as a thermal remanence during the cooling from friction melt. To test the reliability of determining the paleointensity, the Coe-modified Thellier method was carried out on a small suite of pseudotachylytes in large-displacement fault zones from the North-range Sudbury impact structure. Pseudotachylytes studied here are classified into two types in their protolith lithology: gneiss-origin and granitoid-origin pseudotachylyte. Petrologic observations confirm the presence of abundant fine-grained magnetite inclusions and coarse-grained titanomagnetites with exsolved ilmenite lamella in gneiss-origin pseudotachylyte. In granitoid-origin pseudotachylyte, we found a scatter distribution of multidomain magnetite. Although the granitoid-origin pseudotachylyte fails to estimate the paleointensity, the gneiss-origin pseudotachylytes yield weak paleointensity values, which are consistent with previous paleointensity data from the norite in Sudbury Igneous Complex. These results suggest that the protolith petrology controls a magnetic mineralogy in pseudotachylytes and the reliability as recorder of ancient Earth's magnetic field.