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3D Modelling from New and Existing Gravity Data of an Intrusive Body in the Northern Part of Kribi-Campo Sub-Basin in Cameroon

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International Journal of Geosciences 2017年第8期8卷 984-1003页

作者： Kue Petou Rokis Malquaire Owona Angue Marie Louise njingti nfor Manguelle-Dicoum Eliezer National Institute of Cartography Yaoundé Cameroon Postgraduate School of Sciences Technologies & Geosciences University of Yaoundé I Yaoundé Cameroon Department of Physics Advanced Teacher Training College University of Yaoundé I Yaoundé Cameroon Department of Physics Faculty of Science University of Yaoundé I Yaoundé Cameroon

A new gravity survey was carried out in the northern part of the onshore Kribi- Campo sub-basin in Cameroon. The data were incorporated to the existing ones and then analyzed and modeled in order to elucidate the subsurface structure of the area. The area is characterized in its north-western part by considerably high positive anomalies indicative of the presence of a dense intrusive body. We find, 1) from the analysis of the gravity residual anomaly map, the high positive anomalies observed are the signature of a shallow dense structure;2) from the multi-scale analysis of the maxima of the horizontal gradient, the structure is confined between depths of 0.5 km and 5 km;3) from the quantitative interpretation of residual anomalies by spectral analysis, the depth to the upper surface of the intrusive body is not uniform, the average depth of the bottom is h1 = 3.6 km and the depths to particular sections of the roof of the intrusion are h2 = 1.6 km and h3 = 0.5 km;4) and the 3D modeling gives results that are suggestive of the presence of contacts between rocks of different densities at different depths and a dense intrusive igneous body in the upper crust of the Kribi zone. From the 3D model the dense intrusive igneous block is surrounded by sedimentary formations to the south-west and metamorphic formations to the north-east. Both formations have a density of about 2.74 g/cm3. The near surface portions of this igneous block lie at a depth range of 0.5 km to 1.5 km while its lower surface has a depth range of 3.6 km to 5.2 km. The shape of the edges and the bottom of the intrusive body are suggestive of the fact that it forms part of a broader structure underlying the Kribi-Campo sub-basin with a great influence on the sedimentary cover.

关键词： Kribi-Campo Sub-Basin Gravity Data 3D Modelling Spectral Analysis Residual Anomaly

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Magnetotelluric Investigation of the Geo-Tectonic Stability of Campo-Ma’an Area in South Cameroon

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International Journal of Geosciences 2017年第12期8卷 1427-1441页

作者： njingti-nfor Owona Angue Marie Louise Clotilde Kue Petou Rokis Malquaire Bisso Dieudonne Piameu Kwagag Joel Postgraduate School of Sciences Technologies&GeosciencesUniversity of Yaounde IYaoundeCameroon Department of Physics Advanced Teacher Training CollegeUniversity of Yaounde IYaoundeCameroon National Institute of Cartography YaoundeCameroon School of Geosciences China University of PetroleumQingdaoChina

The magnetotelluric prospection method has been widely used in Cameroon not only as a reconnaissance method for geophysical investigations but also to determine the nature of the subsurface and the structural settings of the various geological formations in the country that resulted from the global geo-tectonic movements. The present study is aimed at employing the magnetotelluric method to provide evidence on major tectonic dislocations which might have led to the presence of plutonic intrusions in the cratonic structure of the Ntem Complex as well as determining the nature of the contact between the sedimentary Campo Basin and the metamorphic cratonic Ntem Complex. The analyses and interpretations of iso-resistivity maps and geoelectric sections from magnetotelluric data has enabled us to show that tectonic forces at contact between the sedimentary Campo Basin and the metamorphic Ntem Complex were of three different categories: gravity gliding, magmatic upwelling and lateral compressions. The results of the action of these forces were the development of vertical and sub-vertical faulting systems at Craton-Sedimentary Basin contact and subsidence of overburden that appears to have also paved the way for the setting-up of the Ntem River bed and its flood plains. This river bed and its flood plains have been characterized as having a sedimentary deposit depth of 500 m and width of 20 km. Meanwhile, the deep-seated contact faulting systems within the two identified formations have varied fault magnitudes with a maximum of 60 km. The relatively high apparently resistivity values (up to1.0 kΩ•m) for the sedimentary and the very high values for the metamorphic formations (up to and above 10.0 kΩ•m) suggest that the whole area is at present relatively geo-tectonically stable.

关键词： Magnetotelluric Tectonics Intrusions Gravity-Gliding Upwelling Compression

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Application of Coefficient of Anisotropy to the Geophysical Prospecting of Campo—Ma’an Area of the Ntem Complex in Cameroon

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Open Journal of Geology 2017年第12期7卷 1801-1818页

作者： njingti-nfor Owona Angue Marie Louise Kue Petou Rokis Malquaire Bisso Dieudonné Lando Tsakou Julyo Achille Postgraduate School of Sciences Technologies & Geosciences University of Yaoundé I Yaoundé Cameroon Department of Physics Advanced Teacher Training College University of Yaoundé I Yaoundé Cameroon National Institute of Cartography Yaoundé Cameroon School of Geosciences China University of Petroleum Qingdao China

Audiomagnetotelluric data were acquired for 10 sounding stations in open fields and roads along the main highways from Campo to Ma’an in Cameroon. An application of the coefficients of anisotropy was used to determine the tectonic settings and the nature of the contacts between the sedimentary formation of the Kribi-Campo basin and the cratonic Ntem Complex. The results of this study show that apart from the sedimentary formation, the metamorphic formation in this area comprises two metamorphic blocks: a regional metamorphic block which might be igneous or granitic in nature and composition and seem to be Precambrian and plutonic in origin and a contact or transitional metamorphic block, which might represent schist or gneiss rocks. The contact or transitional metamorphic block might be as a result of a long period of contact between regional metamorphic rocks and rocks of sedimentary formation. These contact/transitional metamorphic rocks which are found sandwiched between rocks of sedimentary formation and rocks of the regional metamorphic block and at varied depths confirm the existence of vertical and sub-vertical contacts between the Kribi-Campo basin and the cratonic Ntem complex. Two types of rock contacts have been identified: a sedimentary-schist contact which is found at the boundary between the sedimentary formation and the transitional metamorphic block and a schist-granite contact between the transitional and regional metamorphic blocks. Two main formations: a sedimentary formation, which is found in the Kribi-Campo sub-basin and the Ntem River bed and its flood plains and the metamorphic formation which includes both the transitional and regional metamorphic rocks have also been identified in the area of study. Subsurface rocks and rock materials have been observed to be highly resistive and occupying almost the entire subsurface in the area of study confirming the high vertical tectonic stability of the Ntem Complex even at contact with the sedimentar

关键词： Anisotropy Telluric Geo-Electric Subsidence Isotropic Vertical Faults Tectonics

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Determination of Structural and Geometrical Parameters of the Kribi-Campo Sedimentary Sub-Basin Using Gravity Data

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International Journal of Geosciences 2017年第9期8卷 1210-1224页

作者： Kue Petou Rokis Malquaire Owona Angue Marie Louise Clotilde njingti nfor Ndougsa-Mbarga Théophile Manguelle-Dicoum Eliezer National Institute of Cartography Yaoundé Cameroon School of Geosciences China University of Petroleum Qingdao China Postgraduate School of Sciences Technologies & Geosciences University of Yaoundé I Yaoundé Cameroon Department of Physics Advanced Teacher Training College University of Yaoundé I Yaoundé Cameroon Department of Physics Faculty of Science University of Yaoundé I Yaoundé Cameroon

In order to produce a more detailed structural and geometrical information, and determine sediments thickness along the Kribi-Campo sub-basin, statistical spectral analysis and horizontal gradient analysis of residual anomalies coupled with the Euler deconvolution approach were applied on the gravity data in the area. The results obtained from the 2D spectral analysis on anomaly grids gave a depth to the basement rocks of the basin from 0.60 km to 3.93 km. This represents the thickness of the sedimentary formations overlying the basement. The interpretation of the spectral analysis results indicated that the potential hydrocarbon field areas are situated between Kribi and Lolabe and at Campo given that those areas have the highest sedimentary thicknesses values. From the analysis of the horizontal gradient, deep faults mainly striking SW-NE have been traced and a structural map of the area has been produced. By applying the Euler deconvolution method to the gravity data, information about the depth and trend of the main subsurface structures have been obtained.

关键词： Sediment Thickness Spectral Analysis Horizontal Gradient Structural Map Kribi-Campo Sub-Basin Gravity Data

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Determination of the Structural Lineaments in the Kribi-Campo-Ma’an Area from a Multi-Scale Analysis of Gravity Data Using the HGM and Euler 3D Deconvolution Approaches

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International Journal of Geosciences 2016年第9期7卷 1122-1143页

作者： Owona Angue Marie Louise Clotilde Assembe Stephane Patrick njingti nfor Ngoh Jean Daniel Ndougsa Mbarga Theophile Kue Petou Rokis Bisso Dieudonné Department of Physics Advanced Teacher Training College University of Yaoundé I Yaoundé Cameroon Postgraduate School of Sciences Technologies & Geosciences University of Yaoundé I Yaoundé Cameroon Department of Physics Faculty of Science University of Bamenda Bambili Cameroon

With the aim to produce a detailed structural map and then enhance the geological information of the south-western Cameroon, a field gravity study is carried out in the Kribi-Campo-Ma’an area (SW Cameroon). This study area is assumed to undergo pending active tectonics as witnessed by several earthquakes [1]. Besides, the area has been affected by some shears that gave rise to many major faults including the Kribi-Campo Fault (KCF). This N-S lineament is an active fault corresponding to the NW margin of the CC [2] [3] and related to the development of the Kribi-Campo basin. The gravity data analysis enables to highlight many deeply-seated structural features trending in the NE, NNE, N-S, NNW, NW and E-W directions in this region. The NW-SE trend is more strongly developed than the other identified trends and could have deeply affected the major NNE structure. The NNE-SSW to N-S fractures and faults which are local relays of the Kribi-Campo fault are related to the Kribi shear zone. The fairly good clustering observed on local maxima of the horizontal gradient magnitude enables to suggest that the contacts outlined have vertical to subvertical dips. However, a probable interpretation of these features is that they are vertical to subvertical faults which follow the aforementioned directions. The location of the study area in the gulf of Guinea suggests that it sustains tectonics related both to the equatorial and the south Atlantic oceans opening.

关键词： Gravity Anomaly Lineament Kribi-Campo Fault Dip

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Quantitative Interpretation of Gravity Anomalies in the Kribi-Campo Sedimentary Basin (South Cameroon) Based on Spectral Analysis and 2.5D Modelling: Structural Implications

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Open Journal of Earthquake Research 2020年第3期9卷 240-254页

作者： Kue Petou Rokis Malquaire Owona Angue Marie Louise Clotilde njingti nfor Eloundou Essama Lionel Mioumnde Arthur Paterne Kue Negham Martine Clémence Manguelle-Dicoum Eliezer Weiqi Song Department of Geophysics School of Geosciences China University of Petroleum (East China) Qinqdao China Postgraduate School of Sciences Technologies & Geosciences University of Yaoundé I Yaoundé Cameroon National Institute of Cartography Yaoundé Cameroon Department of Physics Advanced Teacher Training College University of Yaoundé I Yaoundé Cameroon Department of Physics University of Yaoundé I Yaoundé Cameroon Laboratory of Ore Processing Institute of Geological and Mining Research Yaoundé Cameroon Department of Geography University of Dschang Dschang Cameroon

Ground gravity survey was recently carried out in the Lolabe-Campo area, which constitutes the southern onshore portion of the Kribi-Campo sub-basin in South Cameroon. The obtained gravity data were processed and interpreted in order to elucidate the subsurface geology of the area in which preliminary studies highlighted the presence of an intrusive igneous body. In order to determine the nature and the characteristics of this body, spectral analysis, ideal body solution and 2.5D modelling methods were applied to the gravity data. The results suggest that the emplacement, breaking up and separation of the intrusive igneous body were the outcome of two tectonic events corresponding to an upward vertical translational tectonic movement followed by an anticlockwise rotational faulting tectonic movement. From a density contrast of 0.13 g·cmǅ, the two isolated bodies have an estimated density of 2.80 g·cmǅ which is comparatively higher than the average density of 2.67 g·cmǅ of the autochthonous rocks. These two blocks are completely surrounded by both sedimentary and metamorphic formations and are confined between the depths of 0.6 km and 3.5 km. The highly dense nature of the rocks and their location around the Atlantic Ocean led to the conclusion that the two intrusive bodies are composed principally of gabbro. The disposition and shape of the open zone resulting from the separation of the blocks are suggestive of a trap for the accumulation of hydrocarbons and mineral resources.

关键词： Spectral Analysis Ideal Body 2.5D Modelling Formation Depth Intrusive Blocks

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