Gravity anomaly patterns in the south-central Zimbabwe Archaean craton and their geological interpretation

Ranganai, Rubeni T.; Whaler, Kathy; Ebinger, C. J.

doi:10.1016/j.jafrearsci.2008.01.011

Cited by 16 publications

(30 citation statements)

References 64 publications

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“…In particular, a few dykes of Proterozoic age outcropping northwest of the belt now have clear signatures and appear more continuous than mapped on the surface, extending across and south of the greenstone belt (D2 to D4, FRD, cf Figures 1, 2 and 4). Dykes that have a magnetic expression but are not mapped in the field may be olivine-bearing and tend to weather easily, forming linear depressions filled with overburden [42], making them invisible during field mapping. The dykes appear to fill extensional fractures that also control the drainage pattern in the area [42].…”

Section: Discussionmentioning

confidence: 99%

“…Dykes that have a magnetic expression but are not mapped in the field may be olivine-bearing and tend to weather easily, forming linear depressions filled with overburden [42], making them invisible during field mapping. The dykes appear to fill extensional fractures that also control the drainage pattern in the area [42]. On a regional scale, the one mapped east of the belt (D1, Figure 4) can be seen extending continuously northwards east of, and beyond, the Fort Rixon (FR) belt.…”

Section: Discussionmentioning

confidence: 99%

“…The stratigraphic implications of this "Filabusi model" are that greenstone belts of the Zimbabwe craton perhaps developed within essentially discrete, structurally determined, evolving basins, albeit linked by common, deepseated volcanic processes [13]. This is the autochthonous model preferred for many greenstone belts in the Zimbabwe craton [1,2,6,[12][13][14][15][16][17]. However, Jelsma and Dirks [5] propose another alternative model for the late Archaean evolution of the Zimbabwe craton involving westward stacking of thrust sheets, accommodated by layerparallel shear zones common in several greenstone belts [3,9,13,18].…”

Section: Introductionmentioning

confidence: 99%

“…The regional and structural interpretation used for the Filabusi belt model [11], and the other models, lacks subsurface information that helps discriminate geotectonic models. One of the key factors to understanding the genesis of greenstone belts is a detailed knowledge of their 3D geometry, now commonly provided by geophysics [16,17,[21][22][23][24][25][26]. Because potential field data respond to density and susceptibility changes on surface and at depth, they can be effective in providing clues about the gross structure at depth.…”

Section: Introductionmentioning

confidence: 99%

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Gravity and Aeromagnetic Studies of the Filabusi Greenstone Belt, Zimbabwe Craton: Regional and Geotectonic Implications

Ranganai¹

2012

IJG

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The Filabusi greenstone belt (FGB), Zimbabwe craton, has been geologically remapped relatively recently but its regional tectonic setting and subsurface structure have, until now, remained unresolved. This paper presents gravity and aeromagnetic studies that have been undertaken to provide this important information, and also extend mapping to areas of poor exposure. Several new NNW-trending dykes and structures cutting across the greenstone belt have been revealed, as well as a major extension of one of the metakomatiitic-BIF units, the Shamba Range. ESE-trending dykes identified in the southeast appear on a regional scale to be part of the giant Okavango dyke swarm in northern Botswana. An ~3 km wide NNE-striking magnetic low occurs over the Irisvale-Lancaster shear zone (ILSZ) on the extreme west of the FGB where it roughly marks the boundary with the Bulawayo greenstone belt. Magnetic anomaly trends over ultramafic schists are consistent with strike-slip movement along the ILSZ, and together with the gravity anomalies, support northeasterly directed detachment of the adjacent Fort Rixon belt from the Bulawayo-Filabusi belt. The Bouguer gravity anomaly map shows that the FGB is characterised by a well defined positive anomaly up to 37 mGal, whose symmetry and extent confirm the postulated synclinal structure of the belt. Isolated oval shaped small gravity lows generally correlate with sub-/out-cropping K-rich post-volcanic granite plutons. 2.5D gravity models along three profiles across the greenstone belt show a simple “basin shape” with a possible maximum depth extent of only 4.5 km, compared to an estimated stratigraphic thickness of about 9.0 km. This suggests a truncation at shallow depth of the structurally repeated lithologies. Gravity data and models support the proposed FGB model; deposition of volcanics in an extensional, structurally determined, evolving basin. This autochthonous setting is consistent with other greenstone belts in the Zimbabwe craton and other parts of the world

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Gravity and Aeromagnetic Studies of the Filabusi Greenstone Belt, Zimbabwe Craton: Regional and Geotectonic Implications

Ranganai¹

2012

IJG

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“…For example, Taylor and McLennan [1986] argued that the mafic rocks of Archaean greenstone belts were the dominant Archaean rock type; they concluded from a study of the distribution of heat-producing elements in Archaean sediments that the bulk Archaean crust was a mixture of a 67% mafic greenstone belt component and a 33% felsic TTG component. This view is rejected here for it has become clear since the work of Taylor and McLennan [1986] that although in some cratons greenstone belts outcrop over a relatively large surface area, they are relatively shallow structures [De Wit and Ashwal, 1997;Stettler et al, 1995;Ranganai et al, 2008] and so must make up only a small component of the total volume of the Archaean crust. Here we argue that the major part of the Archaean middle continental crust and in some cases the Archaean lower continental crust [Rollinson and Tarney, 2005] is TTG in composition.…”

Section: Average Composition Of Archaean Continental Crustmentioning

confidence: 99%

Secular evolution of the continental crust: Implications for crust evolution models

Rollinson

2008

Geochem Geophys Geosyst

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[1] The present-day flux from mantle to crust is basaltic and yet the average composition of the continental crust is andesitic. This is the crust composition paradox. A new solution to this paradox is proposed whereby the secular evolution in the composition of the continental crust reflects a changing flux from mantle to crust over time. Thus it is proposed that the present-day composition of the continental crust is a time-integrated average. Crustal growth curves show that 48-54% of the continental crust was formed by the end of the Archaean. A mass balance model based upon a tonalite-trondhjemite-granodiorite compositional model for the Archaean continental crust shows that the post-Archaean mantle to crust flux was predominantly basaltic and likely a mix of arc-plume basalts. Trace element modeling, however, reveals that additional processes also contributed to the average crust composition. Balancing Y, Ho, and Yb concentrations requires a garnetiferous mafic granulite lower Archaean crust, which in turn drives the post-Archaean flux toward a high mg # andesite. This suggests that there was a slab melt contribution to the continents, in addition to basalt. An excess of fluid mobile elements in the continental crust can be explained either by the addition of a slab melt or small fraction melts. A deficiency in Sr requires that the post-Archaean crustal composition has been modified by erosion. Both Archaean and post-Archaean continental crust contain contributions from basalt and a slab melt. In the Archaean crust the slab melt contribution is dominant. In the post-Archaean crust the basaltic contribution is dominant.

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Integration of Geophysical and Geological Data of Kimberlites in Narayanpet–Maddur Field, Andhra Pradesh, India

Vani

Lakshmi

Ramakrishnarao³

et al. 2013

Proceedings of 10th International Kimberlite Conference

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Gravity anomaly patterns in the south-central Zimbabwe Archaean craton and their geological interpretation

Cited by 16 publications

References 64 publications

Gravity and Aeromagnetic Studies of the Filabusi Greenstone Belt, Zimbabwe Craton: Regional and Geotectonic Implications

Gravity and Aeromagnetic Studies of the Filabusi Greenstone Belt, Zimbabwe Craton: Regional and Geotectonic Implications

Secular evolution of the continental crust: Implications for crust evolution models

Integration of Geophysical and Geological Data of Kimberlites in Narayanpet–Maddur Field, Andhra Pradesh, India

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