Abstract The N–S elongated Pan-African Numba granitic pluton (NGP), hosted in banded biotite hornblende gneiss and amphibolite country-rocks, belongs to the Western Domain of the Pan-African Belt of Central African in Cameroon. It consists of biotite hornblende granite and fine-grained biotite granite crosscut by gabbroic dykes. The western border of the granite is mylonitized. Structures and microstructures recorded in granite reveal magmatic, submagmatic and high- to moderate- temperature solid-state deformations. Magnetic characterisation of the NGP reveals its ferromagnetic behaviour due to the presence of multi-domain automorphic or xenomorphic pure magnetite grains. Field and AMS measurements testify that the study area recorded three deformation events: (1) a D1 event of ENE-WSW to E-W flattening deformation; (2) a D2 event of sinistral top-towards south sense of shear movement characterised by low to moderate dips (i) NE-SW strike foliation in country-rocks; (ii) NNE-SSW to NE-SW strike of magmatic foliation marked by the preferred orientation of K-feldspar megacrysts in granite and (iii) low plunges NE-SW mineral stretching lineation in biotite hornblende gneiss parallel to the axes of SW vergence of "S" shape F2 folds and (3) a D3 event of dextral top-towards east sense of shear movement that developed narrow NNE-SSW strike mylonite corridor. The NGP emplaced in a fracture within an amphibo-gneissic country-rock and has recorded opposite sinistral top-towards south (D2 Pan-African event) to dextral top-towards east senses of shear movements (D3 Pan-African event). It can be inferred that the emplacement and the deformation of the NGP was initiated during regional D2 deformation (dated at 613-585 Ma) when its magnetic fabric was acquired, and it was completely achieved during regional D3 deformation (dated ca. 585-540 Ma). Tj vs. Pj diagram associated with Flinn diagram suggests an emplacement in dominant flattening strain regime with a considerable shear component. The different data recorded in the NGP imply that its emplacement mechanism points to a ballooning. Indeed, the eastern domain of NGP with elliptical shape represents the inner part of the architecture while its western domain represents the outer part. The moderate to high dips observed in the inner part of the elliptical domain suggest the probable location of a feeder zone, and the lineation pointing away from the centre of the intrusion in the outer part may be developed related to the magmatic flow. This concentricity is easily associated with internal microstructures that show moderate-temperature solid-state to submagmatic and magmatic microstructures from the outside of the pluton towards the centre. The magma was then emplaced by ballooning in a gneissic country-rock that was subjected to sinistral shearing. Afterwards, the deformation characterised by a dextral shearing contributed to a generation of a NNE-SSW mylonitic band at the western border of the pluton.

中文翻译：

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Numba 花岗岩岩体（喀麦隆西部地区）同运动侵位的野外观察、磁性织物和微观结构证据

摘要 N-S 拉长的泛非 Numba 花岗岩岩体 (NGP) 位于带状黑云母角闪片麻岩和角闪岩乡村岩石中，属于喀麦隆中非泛非带的西部领域。它由黑云母角闪石花岗岩和细粒黑云母花岗岩被辉长岩脉横切组成。花岗岩的西部边界是糜棱岩化的。花岗岩中记录的结构和微观结构揭示了岩浆、亚岩浆和高温至中温固态变形。由于多畴自晶或异晶纯磁铁矿晶粒的存在，NGP 的磁性表征揭示了其铁磁行为。现场和AMS测量证明研究区记录了三个变形事件：（1）ENE-WSW到EW扁平变形的D1事件；(2) D2 事件的左旋顶部向南的剪切运动，其特征是低至中等倾角 (i) NE-SW 走向在乡村岩石中的叶理；(ii) 岩浆叶理的 NNE-SSW 到 NE-SW 走向，以花岗岩中钾长石巨晶的优先取向为标志；(iii) 黑云母角闪石片麻岩中的低倾角 NE-SW 矿物拉伸线状平行于“S”形 F2 褶皱和 (3) D3 右旋顶部向东切变运动感的事件，其发展为狭窄的 NNE-SSW 撞击糜棱岩走廊。NGP 位于两栖片麻岩乡村岩石内的裂缝中，并记录了相反的左旋顶部向南（D2 泛非事件）和右旋顶部向东的剪切运动感（D3 泛非事件）。可以推断，NGP的就位和变形是在获得其磁性织物时在区域D2变形（日期为613-585 Ma）期间开始的，并且在区域D3变形（日期为585-540）期间完全实现嘛）。与 Flinn 图相关的 Tj 与 Pj 图表明在具有相当大的剪切分量的显着展平应变状态中的就位。NGP 中记录的不同数据意味着其就位机制指向膨胀。事实上，椭圆形 NGP 的东部区域代表建筑的内部，而其西部区域代表外部。在椭圆域内部观察到的中到高的倾角表明可能存在馈线区，外缘背离侵入体中心的线状发育可能与岩浆流动有关。这种同心度很容易与内部微观结构相关联，这些微观结构显示出从岩体外部到中心的中温固态到亚岩浆和岩浆微观结构。然后，岩浆通过在受到左旋剪切的片麻质乡村岩石中膨胀而进入。之后，以右旋剪切为特征的变形导致在岩体西部边界产生 NNE-SSW 糜棱带。这种同心度很容易与内部微观结构相关联，这些微观结构显示出从岩体外部到中心的中温固态到亚岩浆和岩浆微观结构。然后，岩浆通过在受到左旋剪切的片麻质乡村岩石中膨胀而进入。之后，以右旋剪切为特征的变形导致在岩体西部边界产生 NNE-SSW 糜棱带。这种同心度很容易与内部微观结构相关联，这些微观结构显示出从岩体外部到中心的中温固态到亚岩浆和岩浆微观结构。然后，岩浆通过在受到左旋剪切的片麻质乡村岩石中膨胀而进入。之后，以右旋剪切为特征的变形导致在岩体西部边界产生 NNE-SSW 糜棱带。