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首页> 外文期刊>Journal of African earth sciences >Field observations, magnetic fabrics and microstructures evidences of syn-kinematic emplacement of the Numba granitic pluton (western Cameroon domain)
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Field observations, magnetic fabrics and microstructures evidences of syn-kinematic emplacement of the Numba granitic pluton (western Cameroon domain)

机译：Numba花岗岩芦苇的Syn-kinematic Pulton（西部喀麦隆域）的磁法织物和微观结构证明

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摘要

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 D-1 event of ENE-WSW to E-W flattening deformation; (2) a D-2 event of sinistral toptowards 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 F-2 folds and (3) a D-3 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 (D-2 Pan-African event) to dextral top-towards east senses of shear movements (D-3 Pan-African event). It can be inferred that the emplacement and the deformation of the NGP was initiated during regional D-2 deformation (dated at 613-585 Ma) when its magnetic fabric was acquired, and it was completely achieved during regional D-3 deformation (dated ca. 585-540 Ma). T-j vs. P-j 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.
机译：N-S细长的泛非洲Numba花岗岩典型芦苇（NGP）载于带状的Biotite Hortblende Gneiss和Amphibolite Country-Rocks，属于喀麦隆中非泛非洲腰带的西方领域。它由Babbroica达克斯的Biotite Hortblende花岗岩和细粒度的生物噻吨花岗岩横切组成。花岗岩的西部边界是米兰化的。花岗岩中记录的结构和微观结构揭示了岩浆，颌下，高至中等温度固态变形。由于多域同形纯磁铁矿颗粒存在，NGP的磁表征显示其铁磁行为。领域和AMS测量证明了研究区域记录了三个变形事件：（1）ENE-WSW的D-1事件到E-W扁平变形; （2）Sinistral的D-2事件TopTowards南部剪切运动的剪切运动，其特征在于乡村岩石中的中等倾角（i）Ne-SW罢工叶; （ii）NNE-SSW通过花岗岩中K-Feldspar甲锭的优选取向标记的NE-SW剧本，（III）低脊柱型NE-SW矿物伸展线辐射与SW Vergence的轴平行“S”形状F-2折叠和（3）D-3对右侧剪切运动的D-3事件开发的狭窄NNE-SSW打击米隆岩走廊。 NGP在Amphibo-Facissic Country-Rock内灌输，并向南方（D-2 Pan-African Event）对南部（D-2 Pan-African事件的相反，以探索剪切运动（D-3 Pan-African Event） ）。可以推断出在收购其磁性织物时在区域D-2变形（在613-585 mA时呈现NGP的施加和变形，并且在区域D-3变形期间完全实现（日期。585-540 mA）。与FLINN图相关的T-J与P-J图表明，具有相当大的剪切部件的主导展平应变状态下的施加。 NGP中记录的不同数据意味着其施加机制指向气球。实际上，具有椭圆形的NGP的东部域表示架构的内部，而其西方结构域表示外部。在椭圆域内部观察到的中等至高倾斜，表明了馈电区的可能位置，并且可以开发与外部部分中的侵入中心的基底eation可以与岩浆流产生。这种同心性易于与内部微结构相关联，该内部微结构从芦苇外部向中心显示中等温度固态，从芦苇外部朝向中心。然后通过膨胀的乡村岩石膨胀，岩浆被燃烧，这是对罪名剪切的岩石。之后，特征在于由右旋剪切特征的变形有助于在芦苇的西部边界处产生NNE-SSW敏感带。

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  • 来源
    《Journal of African earth sciences》 |2020年第12期|104009.1-104009.20|共20页
  • 作者

    Chatue C. Njiki; Njanko T.; Fozing E. M.; Nke B. E. Bella; Seta N.; Njonfang E.;

  • 作者单位

    Univ Dschang Lab Environm Geol POB 67 Dschang Cameroon;

    Univ Dschang Lab Environm Geol POB 67 Dschang Cameroon|DPSP CCAR Minist Sci Res & Innovat POB 1457 Yaounde Cameroon;

    Univ Dschang Lab Environm Geol POB 67 Dschang Cameroon;

    Univ Maroua Lab Geosci & Sustainable Dev POB 814 Maroua Cameroon;

    Univ Ouagadougou Lab Geosci & Min Environm Ouagadougou Burkina Faso;

    Univ Yaounde I Higher Teacher Training Coll Lab Geol POB 47 Yaounde Cameroon;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    AMS; Microstructure; Granite; Pan-African; Cameroon;

    机译：AMS;微观结构;花岗岩;泛非洲;喀麦隆;

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