基于重力和磁力分析,了解班吉磁异常下的地壳结构及其与非洲中部构造巨构的相互作用

IF 2.1 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Journal of Geodynamics Pub Date : 2024-03-01 DOI:10.1016/j.jog.2024.102022
Cyrille Donald Njiteu Tchoukeu , Yvette Poudjom Djomani , Kevin Mickus , Sonia Rousse , Mohamed Sobh , Charles Basseka , Jacques Etame
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引用次数: 0

摘要

就振幅和横向面积而言,中非班吉磁异常(BMA)是地球上最大的大陆磁异常之一。确定班吉磁异常的来源可以加深对中非次区域乃至整个非洲大陆地壳动态的了解。基于磁力和重力分析的导数、二维前向建模和居里等温深度显示:(a) 磁源的底部在 15 至 35 千米之间;(b) BMA 是若干异常的凝聚,这些异常呈东西走向,大致呈东北-西南走向。这些方向与沿中非造山带的泛非区域性剪切带以及刚果克拉通北部边缘的推力片相吻合。磁化深度不超过 35 千米,在中非共和国磁化幅度较小。潜在磁感应强度源的平均密度为 2850 kg/m3,磁感应强度在 0.06 至 0.25 SI 之间。根据解释,BMA 是不连续的中下地壳体的组合,由富含磁性矿物的花岗岩和带状铁质地层组成。重力和磁力模型显示,整个地壳都卷入了泛非碰撞事件,与东非莫桑比克带的情况类似。结合地质和地球化学研究,这些模型增加了刚果克拉通北部边缘地层增生涉及一到两个俯冲带的证据。构造增生造成了沿主要剪切带的地壳再移动,在新新生代晚期岩浆活动期间,这可能在局部促成了富含铁镁矿物的流体循环,从而形成了 BMA 源。
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Understanding the crustal architecture beneath the Bangui magnetic anomaly and its interactions with central African tectonic megastructures based gravity and magnetic analysis

The Bangui magnetic anomaly (BMA) in Central Africa is one of the largest continental magnetic anomalies on Earth in terms of amplitude and lateral size. Determining the sources of the BMA can lead to an increased understanding of the crustal dynamic in the Central African sub-region and the African continent as a whole. Magnetic and gravity analysis-based derivative, two-dimensional forward modelling and a Curie isothermal depth, showed that (a) the bottoms of the magnetic sources were between 15 and 35 km; (b) the BMA is a coalescence of several anomalies that trend E-W and roughly NE-SW. These directions coincide with regional Pan African-aged shear zones along the Central African orogenic belt and to thrust sheets at the northern edge of the Congo Craton. The depth of magnetization does not exceed 35 km with the amplitude of magnetization becoming smaller in the Central African Republic. The potential magnetic susceptibility sources have an average density of 2850 kg/m3 and magnetic susceptibilities between 0.06 and 0.25 SI. The BMA is interpreted to be a combination of middle and lower crustal bodies that are not continuous and consist of magnetic mineral rich granulites and banded iron formations. The gravity and magnetic modelling indicate that the entire crust was involved in the Pan African collisional event similar to what is seen in the Mozambique belt in East Africa. Combined with geological and geochemical studies, the models add evidence that one or two subduction zones were involved in accreting terranes on the northern edge of the Congo Craton. The tectonic accretions caused a crustal remobilization along major shear zones that has locally contributed to a probable circulation of fluids enriched in ferromagnesian minerals during late Neoproterozoic magmatism that created the BMA sources.

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来源期刊
Journal of Geodynamics
Journal of Geodynamics 地学-地球化学与地球物理
CiteScore
4.60
自引率
0.00%
发文量
21
审稿时长
6-12 weeks
期刊介绍: The Journal of Geodynamics is an international and interdisciplinary forum for the publication of results and discussions of solid earth research in geodetic, geophysical, geological and geochemical geodynamics, with special emphasis on the large scale processes involved.
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