3D modelling of Trompsburg Complex (in South Africa) using 3D focusing inversion of gravity data

Rezaie, Mohammad; Moradzadeh, Ali; Kalate, Ali Nejati; Aghajani, Hamid; Kahoo, Amin Roshandel; Moazam, Sahar

doi:10.1016/j.jafrearsci.2017.03.002

Cited by 10 publications

(5 citation statements)

References 16 publications

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“…Like the Molopo Farms and the Bushveld complexes, this conductor coincides with a large Paleoproterozoic mafic intrusive complex (1.9 Ga, Maier et al., 2003), the Trompsburg Complex (TC, Figure 1). Since it does not have surface exposure, existing knowledge about the complex is limited to gravitational modeling and few borehole measurements (Rezaie et al., 2017). We think the conductor here may be related to the emplacement of the mafic magmas and a metasomatized residue left from the event.…”

Section: Discussionmentioning

confidence: 99%

Probing the Southern African Lithosphere With Magnetotellurics: 2. Linking Electrical Conductivity, Composition, and Tectonomagmatic Evolution

et al. 2022

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The tectonic history of southern Africa includes Archean craton formation, multiple episodes of subduction and rifting and some of the world's most significant magmatic events. These processes left behind a compositional trail that can be observed in xenoliths and measured by geophysical methods. The abundance of kimberlites in southern Africa makes it an ideal place to test and calibrate mantle geophysical interpretations that can then be applied to less well‐constrained regions. Magnetotellurics (MT) is a particularly useful tool for understanding tectonic history because electrical conductivity is sensitive to temperature, bulk composition, accessory minerals, and rock fabric. We produced three‐dimensional MT models of the southern African mantle taken from the SAMTEX MT data set, mapped the properties of ∼36,000 garnet xenocrysts from Group I kimberlites, and compared the results. We found that depleted regions of the mantle are uniformly associated with high electrical resistivities. The conductivity of fertile regions is more complex and depends on the specific tectonic and metasomatic history of the region, including the compositions of metasomatic fluids or melts and the emplacement of metasomatic minerals. The mantle beneath the ∼2.05 Ga Bushveld Complex is highly conductive, probably caused by magmas flowing along a lithospheric weakness zone and precipitating interconnected, conductive accessory minerals such as graphite and sulfides. Kimberlites tend to be emplaced near the edges of the cratons where the mantle below 100 km depth is not highly resistive. Kimberlites avoid strong mantle conductors, suggesting a systematic relationship between their emplacement and mantle composition.

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Section: Discussionmentioning

confidence: 99%

Probing the Southern African Lithosphere With Magnetotellurics: 2. Linking Electrical Conductivity, Composition, and Tectonomagmatic Evolution

et al. 2022

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show abstract

“…Like the Molopo Farms and the Bushveld complexes, this conductor coincides with a large Paleoproterozoic mafic intrusive complex (1.9 Ga, Maier et al, 2003), the Trompsburg Complex (TC, Figure 1). Since it does not have surface exposure, existing knowledge about the complex is limited to gravitational modelling and few borehole measurements (Rezaie et al, 2017). We think the conductor here may be related to the emplacement of the mafic magmas and a metasomatised residue.…”

Section: Kimberleymentioning

confidence: 99%

Probing the southern African lithosphere with magnetotellurics, Part II, linking electrical conductivity, composition and tectono-magmatic evolution.

Özaydın¹,

Selway²,

Griffin³

et al. 2021

Preprint

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The tectonic history of Southern Africa includes Archean formation of cratons, multiple episodes of subduction and rifting and some of the world's most significant magmatic events. These processes left behind a compositional trail that can be observed in xenoliths and measured by geophysical methods. The abundance of kimberlites in southern Africa makes it an ideal place to test and calibrate mantle geophysical interpretations that can then be applied to less well-constrained regions. Magnetotellurics (MT) is a particularly useful tool for understanding tectonic history because electrical conductivity is sensitive to temperature, bulk composition, accessory minerals and rock fabric. We produced three-dimensional MT models of the southern African mantle taken from the SAMTEX MT dataset, mapped the properties of $\sim36000$ garnet xenocrysts from Group I kimberlites, and compared the results. We found that depleted regions of the mantle are uniformly associated with high electrical resistivities. The conductivity of fertile regions is more complex and depends on the specific tectonic and metasomatic history of the region, including the compositions of metasomatic fluids or melts and the emplacement of metasomatic minerals. The mantle beneath the $\sim 2.05$ Ga Bushveld Complex is highly conductive, probably caused by magmas flowing along a lithospheric weakness zone and precipitating interconnected, conductive accessory minerals such as graphite and sulfides. Kimberlites tend to be emplaced near the edges of the cratons where the mantle below 100 km depth is not highly resistive. Kimberlites avoid strong mantle conductors, suggesting a systematic relationship between their emplacement and mantle composition.

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“…(1) Modelled surfaces may be pinned locally with hard data, such as drillhole intersections and reef outcrops; (2) Surfaces may be guided by non-contacting data, such as density contrasts from unconstrained geophysical data inversions [37]; (3) Surfaces may be adjusted by user-defined orientation values, in regions where there are no or only sparse available data [38,39]; (4) Extrapolation away from known or hard data, into areas where there is effectively no data, may be achieved intelligently and logically using trends. Such inputs remove, for example, instances where Merensky and UG2 reefs cross one another; and (5) Directional interpretation bias, inherent in section-based explicit modelling, is minimized.…”

Section: Geomodelling Theorymentioning

confidence: 99%

“…A structural trend was constructed per fault domain, to inform final surface construction trends within each individual domains. These structural trends incorporated field mapping, drillhole contacts, reef contours and geophysical inversion products [37,52,74], which all have disparate or different scales, densities and coverage [75].…”

Section: Construction Of Structural Trendsmentioning

confidence: 99%

Implicit Geomodelling of the Merensky and UG2 Reefs of the Bushveld Complex from Open-Source Data: Implications for the Complex’s Structural History

2020

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The Bushveld Complex (BC) is the world’s largest source of platinum group metals. Extensive studies on the complex have focused on its geochemistry, magma and platinum group mineral genesis, mineral characterization and intrusion mechanisms. However, relatively little work has been undertaken on the overall 3D geometry of the complex, which detracts from the adequate contextualization of such studies. Furthermore, the absence of a broader 3D model of the complex does not permit the identification of structural trends and mineralization patterns. This contribution details the construction of 3D implicitly-modelled Merensky and UG2 Reefs across the Rustenburg Layered Suite of the BC, using Seequent’s Leapfrog software. Multiple open-source and public-domain data sources and modelling workflows were explored to account for disparities in data resolution, data spacing and clustering, and the resolution of model outputs. Key outcomes are (1) a representative, fully-implicit, dynamic geological model of the Merensky and UG2 Reefs over the main chamber of the BC; (2) identification of modelled features that augment the current understanding of the BC’s kinematic history and cumulative deformation; and (3) identification and analysis of subtle geometrical trends and patterns, such as inter-reef spacing and modelled depths, as well as structural domains that may not have been apparent from numerous, more focused or isolated petrological or geochemical studies. It is anticipated that this baseline 3D model will form the foundation for future, possibly localized, dynamic updates as further information becomes available. The addition of proprietary (viz., non-open-source) data, such as 2D seismic sections and 3D seismic surveys, would enhance the overall resolution and quality of such a model and resulting interpretations.

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3D modelling of Trompsburg Complex (in South Africa) using 3D focusing inversion of gravity data

Cited by 10 publications

References 16 publications

Probing the Southern African Lithosphere With Magnetotellurics: 2. Linking Electrical Conductivity, Composition, and Tectonomagmatic Evolution

Probing the Southern African Lithosphere With Magnetotellurics: 2. Linking Electrical Conductivity, Composition, and Tectonomagmatic Evolution

Probing the southern African lithosphere with magnetotellurics, Part II, linking electrical conductivity, composition and tectono-magmatic evolution.

Implicit Geomodelling of the Merensky and UG2 Reefs of the Bushveld Complex from Open-Source Data: Implications for the Complex’s Structural History

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