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首页> 外文期刊>Journal of African Earth Sciences >Microstructures and magnetic fabrics of the Ngaoundere granite pluton (Cameroon): Implications to the late-Pan-African evolution of Central Cameroon Shear Zone
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Microstructures and magnetic fabrics of the Ngaoundere granite pluton (Cameroon): Implications to the late-Pan-African evolution of Central Cameroon Shear Zone

机译：Ngaoundere花岗岩岩体（喀麦隆）的微观结构和磁性织物：对喀麦隆中部剪切带晚期泛非演化的影响

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摘要

The Ngaoundere granite pluton, in Central-North Cameroon, located near the Central Cameroon Shear zone (CCSZ), and previously studied for its petrography and geochemistry, is characterized by the absence of macroscopic markers of deformation. In this study, we report microstructures and magnetic fabrics (AMS) of this pluton and discuss the relationship with the Pan-African evolution of the CCSZ. The pluton consists of a porphyritic Hbl-Bt-monzogranite at its rim and a porphyritic biotite-granite at its core, a petrographic distribution denoting a normal zoning pattern, i.e. more silicic toward the centre. As expected, magnetic susceptibilities values also exhibit a zoning pattern in agreement with petrographic zonation. Thermomagnetic data indicate that this pluton is dominantly ferromagnetic in behaviour. As indicated by its microstructures, the pluton has suffered a continuum of deformation from the magmatic state to the high temperature solid-state during magma crystallization and solidification. The magnetic foliations dominantly strike NE-SW and dip moderately to steeply and the lineations mostly plunge shallowly to the NE or SW, roughly parallel to NE-to ENE-trending Central Cameroun Shear Zone (CCSZ). The foliation poles define a girdle pattern with a zone axis (52 degrees/11 degrees) rather close to the best line of the lineations (44 degrees/21 degrees). These fabrics correlate with the structures of the country rocks ascribed by several workers to a regional transpression. Toward the margins of the pluton, particularly the northern one, the lineations tend to rotate from NE to N in azimuth. This change is interpreted as due to strain partitioning, simple shearing with NE-SW extension being relayed by compression toward the northern pluton border. This new magnetic fabric study suggests that the Ngaoundere pluton (poorly dated at c. 575 Ma) was emplaced during the late stages of the CCSZ dextral transpressive movement. It also provides some more constraints on the correlation between the CCSZ system and the shear zone system of NE-Brazil. (C) 2017 Elsevier Ltd. All rights reserved.
机译：喀麦隆中北部的Ngaoundere花岗岩岩体位于喀麦隆中部剪切带（CCSZ）附近，以前对其岩石学和地球化学进行了研究，其特征是没有宏观的变形标志。在这项研究中，我们报告了该子体的微观结构和磁性织物（AMS），并讨论了与CCSZ的泛非演化的关系。岩体的边缘由一个斑状的Hbl-Bt-蒙脱石花岗岩组成，其核心由一个斑状的黑云母-花岗岩构成，岩石学上的分布表明其呈正常的分区模式，即向中心方向呈硅质。不出所料，磁化率值也显示出与岩石学分区一致的分区模式。热磁数据表明，该质子在行为上主要是铁磁的。如其微结构所示，在岩浆结晶和凝固过程中，岩体经历了从岩浆状态到高温固态的连续变形。磁叶主要撞击NE-SW并适度倾斜至陡峭，且线型大多向NE或SW浅陷，大致平行于NE向ENE趋势的中央喀麦隆剪切带（CCSZ）。叶状极点定义了一个腰带图案，其腰带轴（52度/ 11度）非常接近线条的最佳线（44度/ 21度）。这些织物与一些工人归因于区域压迫的乡村岩石结构相关。朝向岩体的边缘，特别是北部，边缘线倾向于从NE旋转到N。这种变化被解释为是由于应变分配，NE-SW延伸的简单剪切通过向北岩体边界的压缩传递。这项新的磁性织物研究表明，在CCSZ右旋超压运动的后期，已植入了Ngaoundere子体（日期大约为575 Ma）。它还为CCSZ系统和NE-巴西剪切带系统之间的相关性提供了更多约束。 （C）2017 Elsevier Ltd.保留所有权利。

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