Zircon geochronology and geochemistry of pre-Bushveld sills in the eastern Transvaal Supergroup, South Africa

2021 ◽  
Author(s):  
R. Bolhar ◽  
R.G. Cawthorn
Keyword(s):  
South Africa ◽  
Thermal Effects ◽  
Isotope Ratio ◽  
Bushveld Complex ◽  
The Other ◽  
Zircon Geochronology ◽  
Geographic Proximity ◽  
Mafic Rocks ◽  
Different Types ◽  
Transvaal Supergroup

Abstract An extensive suite of sills occurring in the eastern and western Transvaal Supergroup has been termed the Marico Diabase Suite. As a result of their overall geographic proximity to the Bushveld Complex and occurrence in the Transvaal Supergroup they have been assumed to be related to the Bushveld Complex. Previous studies have identified two different types of rocks within this suite, namely the Maruleng and Lydenburg types, based on geochemical and metamorphic characteristics. The Maruleng type has mineralogical (orthopyroxene-bearing) and geochemical affinities with the mafic rocks of the Bushveld Complex, and rocks belonging to this type are much more closely spatially related to the Bushveld Complex. The Lydenburg type, on the other hand, is much more extensive spatially and was emplaced at variable depths within the Transvaal Supergroup. The latter type of rock is variably metamorphosed, far beyond the likely thermal effects arising from emplacement of the Bushveld Complex. Using LA-SF-ICPMS and LA-MC-ICMS for U-Pb-Hf isotope ratio and REE+Ti concentration analysis, we demonstrate that zircon grains from this latter type were subjected to hydrothermal alteration, which caused the introduction of common lead. Despite compositional and isotopic overprinting, an age of 2 083 ± 18 Ma (MSWD = 12, n = 16) is obtained, suggesting a pre-Bushveld in age. We suggest that the original term Marico Diabase Suite encompasses two different events. The Maruleng Suite should be grouped as part of the Bushveld Complex, whereas the Lydenburg Suite should be given a status that is independent from the Bushveld event.

Lithostratigraphy of the Palaeoproterozoic Hekpoort Formation (Pretoria Group, Transvaal Supergroup), South Africa

2020 ◽  
Vol 123 (4) ◽  
pp. 655-668
Author(s):  
N. Lenhardt ◽  
W. Altermann ◽  
F. Humbert ◽  
M. de Kock
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
Sedimentary Rocks ◽  
Type Locality ◽  
Large Igneous Province ◽  
Braided River ◽  
River Systems ◽  
The West ◽  
Igneous Province ◽  
Transvaal Supergroup

Abstract The Palaeoproterozoic Hekpoort Formation of the Pretoria Group is a lava-dominated unit that has a basin-wide extent throughout the Transvaal sub-basin of South Africa. Additional correlative units may be present in the Kanye sub-basin of Botswana. The key characteristic of the formation is its general geochemical uniformity. Volcaniclastic and other sedimentary rocks are relatively rare throughout the succession but may be dominant in some locations. Hekpoort Formation outcrops are sporadic throughout the basin and mostly occur in the form of gentle hills and valleys, mainly encircling Archaean domes and the Palaeoproterozoic Bushveld Complex (BC). The unit is exposed in the western Pretoria Group basin, sitting unconformably either on the Timeball Hill Formation or Boshoek Formation, which is lenticular there, and on top of the Boshoek Formation in the east of the basin. The unit is unconformably overlain by the Dwaalheuwel Formation. The type-locality for the Hekpoort Formation is the Hekpoort farm (504 IQ Hekpoort), ca. 60 km to the west-southwest of Pretoria. However, no stratotype has ever been proposed. A lectostratotype, i.e., the Mooikloof area in Pretoria East, that can be enhanced by two reference stratotypes are proposed herein. The Hekpoort Formation was deposited in a cratonic subaerial setting, forming a large igneous province (LIP) in which short-termed localised ponds and small braided river systems existed. It therefore forms one of the major Palaeoproterozoic magmatic events on the Kaapvaal Craton.

scholarly journals The choice of lucerne varieties in the Netherlands.

1953 ◽  
Vol 1 (3) ◽  
pp. 175-185
Author(s):  
W. Scheijgrond
Keyword(s):  
South Africa ◽  
The Netherlands ◽  
Crude Protein ◽  
Dry Matter ◽  
Cold Resistance ◽  
The Other ◽  
Southern Europe ◽  
Different Types ◽  
North And South America ◽  
North And South

Trials were carried out at 2 stations in the Netherlands in the period 1949-51 to compare the amounts of dry matter and crude protein yielded per ha. by 5 different types of lucerne. The Northern French varieties (Du Puits, Flamande Chartain-villiers and Flamande Flandria) gave considerably higher yields of dry matter and protein than Provence or Italian lucerne. A further trial was carried out in the Netherlands in co-operation with O.E.E.C., in which the performances of varieties from Western, Eastern, Central and Southern Europe, North and South America, New Zealand, India and South Africa were compared. The results are tabulated under the following headings: yield in comparative figures, speed of regrowth after winter, earliness of flowering, degree of infestation by grasses and cold-resistance. The Northern French varieties Du Puits, Flamande Flandria, Flamande Chartainvilliers, Flamande Socheville and Flamande C49, gave higher yields of dry matter and crude protein, regrew more rapidly after winter and were less susceptible to infestation by grasses than the other varieties tested. Their cold-resistance was satisfactory. There were no considerable differences in performance between the Northern French varieties tested.-W.J.B. (Abstract retrieved from CAB Abstracts by CABI’s permission)

The use of phosphorus contents in yielding estimates of the proportion of trapped liquid in cumulates of the Upper Zone of the Bushveld Complex

1988 ◽  
Vol 52 (364) ◽  
pp. 81-89 ◽  
Author(s):  
R. Grant Cawthorn ◽  
Kevin L. Walsh
Keyword(s):  
South Africa ◽  
Phosphorus Content ◽  
Bushveld Complex ◽  
Experimental Studies ◽  
Liquid Composition ◽  
Major Influence ◽  
Mafic Rocks ◽  
Interstitial Component ◽  
Basic Rocks

AbstractPhosphorus contents in cumulus rocks occurring close to the level of apatite appearance in the basic rocks of the Bushveld Complex, South Africa, provide a method of calculating the proportion of intercumulus component in these rocks. Previous experimental studies have accurately constrained the phosphorus content of magmas when apatite becomes stable. The ratio of the phosphorus content in the cumulates immediately below the appearance of apatite to this liquid composition defines the proportion of trapped liquid.Application of this method to rocks from the uppermost mafic rocks of the Bushveld Complex leads to the conclusion that there is from 1 to 6 per cent intercumulus component. Many of these rocks are multiphase cumulates and in such rocks estimation of intercumulus component from textural criteria is difficult.If crystals grow In situ on the floor of the magma chamber such small proportions of interstitial component can be produced without appealing to excessive diffusion and circulation of magma through an unconsolidated crystal pile. The geometry of the intrusion as well as its size might have a major influence on the proportion of the liquid ultimately solidifying within a cumulus rock.

Caveats in defining the magmas parental to the mafic rocks of the Bushveld Complex, and the manner of their emplacement: review and commentary

2002 ◽  
Vol 66 (6) ◽  
pp. 815-832 ◽  
Author(s):  
H. V. Eales
Keyword(s):  
South Africa ◽  
Trace Element ◽  
Bushveld Complex ◽  
Bulk Composition ◽  
Trace Element Data ◽  
Mafic Rocks ◽  
Critical Zones ◽  
Derivatives Of ◽  
Western Limb ◽  
Northern Sector

Abstract The composition of magmas proposed as parental to the layered suite of the Bushveld Complex, and some models for the manner of their emplacement, are reviewed briefly. Included are some contributions published in South Africa, with which overseas readers might be less familiar. Emphasis is given to the broader features of the cumulates, and the contradictions raised by whole-rock compositional, Sr-isotopic, and trace-element data that cloud their correlation with proposed parental magmas. It is concluded that the Lower, Critical and Main Zones are the derivatives of only two primary magmatic lineages, while a third was added to residual liquids from which the layered rocks above the Pyroxenite Marker were formed. Excessive amounts of olivine and chromium in the cumulates of the Lower and Lower Critical Zones in the northern sector of the Western Limb can seemingly not be accounted for by the composition and volume of the putative magmas. This is attributed to (1) this sector being a proximal facies located close to the original feeder, and/or (2) crystal-charged magma batches, expelled from a lower magma chamber, being periodically injected into and dispersed within the liquids already in place in the Bushveld chamber. Thus, ongoing changes in the bulk composition of the liquids within the chamber would not be reflected in the rinds of earlier, chilled-facies rocks. The expulsion of significant volumes of liquid residua from the chamber during cumulate deposition is not ruled out.

Magma replenishment, and the significance of poikilitic texlures, in the Lower Main Zone of the western Bushveld Complex, South Africa

1998 ◽  
Vol 62 (04) ◽  
pp. 435-450 ◽  
Author(s):  
Andrew A. Mitchell ◽  
Hugh V. Eales ◽  
F. Johan Kruger
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
The Other ◽  
Main Zone ◽  
Initial Ratio ◽  
Sr Isotope ◽  
Isotope Profile ◽  
Compositional Variations ◽  
Partial Resorption ◽  
Magma Replenishment

Abstract Petrographic and compositional variations in the Lower Main Zone (LMZ) of the western Bushveld Complex indicate changing regimes of magma replenishment. The lowermost unit of the LMZ, designated N-I, is an enigmatic sequence of leuconoritic cumulates, characterized primarily by up-sequence increases in both orthopyroxene Mg# and whole-rock Sr isotope initial ratio. The Sr isotope profile of N-I is ascribed to injection and progressive integration of small influxes of fresh magma with high (Main Zone-type) Sr isotope initial ratios. The basal Fe-enrichment in N-I, on the other hand, is ascribed to a separate, later mechanism involving the downward migration of late-stage Fe-rich liquids. The overlying two units, N-II and G-I, delineated chiefly in terms of basal Mg-enrichment of orthopyroxene, are ascribed to injections of fresh magma into the chamber. Poikilitic orthopyroxene grains in the basal parts of both N-II and G-I suggest entrainment and partial resorption of plagioclase grains from the semi-crystalline resident material into which the fresh magma was intruded.

The Final ‘Thank You’

Derrida Today ◽  
2010 ◽  
Vol 3 (1) ◽  
pp. 21-36
Author(s):  
Grant Farred
Keyword(s):  
South Africa ◽  
South African ◽  
Jacques Derrida ◽  
Political Transition ◽  
The Other ◽  
World Cup ◽  
The Core ◽  
Nelson Mandela ◽  
Black President ◽  
The Moment

‘The Final “Thank You”’ uses the work of Jacques Derrida and Friedrich Nietzsche to think the occasion of the 1995 rugby World Cup, hosted by the newly democratic South Africa. This paper deploys Nietzsche's Zarathustra to critique how a figure such as Nelson Mandela is understood as a ‘Superman’ or an ‘Overhuman’ in the moment of political transition. The philosophical focus of the paper, however, turns on the ‘thank yous’ exchanged by the white South African rugby captain, François Pienaar, and the black president at the event of the Springbok victory. It is the value, and the proximity and negation, of the ‘thank yous’ – the relation of one to the other – that constitutes the core of the article. 1

‘Wisselbare Woorde’

2018 ◽  
Author(s):  
Carrol Clarkson
Keyword(s):  
South Africa ◽  
Freedom Of Expression ◽  
The Other ◽  
Frantz Fanon ◽  
Politics Of Representation ◽  
Black Consciousness ◽  
Nadine Gordimer ◽  
Contact Zones ◽  
Critical Problems ◽  
Ethics And Politics

Carrol Clarkson’s chapter wrestles with the contentious question of Coetzee’s relation to the Black Consciousness Movement in South Africa of the 1970s and early 1980s, which took its philosophical bearings from Frantz Fanon and found expression in the writings of Steve Biko. Clarkson focuses on the ways in which Coetzee departed from the ideas about writing and resistance that were circulating in his contemporary South Africa, particularly as articulated by novelist Nadine Gordimer. Clarkson discusses two related literary-critical problems: an ethics and politics of representation, and an ethics and politics of address, showing how Coetzee explores a tension between freedom of expression and responsibility to the other. In the slippage from saying to addressing we are led to further thought about modes and sites of consciousness—and hence accountabilities—in the interlocutory contact zones of the post-colony. The chapter invites a sharper appreciation of what a postcolonial philosophy might be.

scholarly journals Private retirement resorts in South Africa: Guidelines for wellness and sustainability in the long term.

2013 ◽  
Vol 32 (1) ◽  
Author(s):  
Andries C. Hauptfleisch
Keyword(s):  
South Africa ◽  
Knowledge Base ◽  
Quantitative Data ◽  
Qualitative Data ◽  
Well Being ◽  
The Other ◽  
Literature Study ◽  
Optimal Profile

Unsubsidised private retirement resorts in South Africa developed during the last three decades present residents with many challenges. There is no existing generally accepted knowledge base or guidelines to serve this sensitive market. The research objective was to establish which elements are experienced by residents of retirement resorts as satisfactory and which as problematic. A literature study was also undertaken. Quantitative as well as qualitative data were obtained by means of structured questionnaires, interviews and a seminar. The results reported pertain to eight resorts in the east of Pretoria, four in Bloemfontein and two in Knysna. The study is currently being extended to other centres. The quantitative data is arranged in order of the priorities set by the biggest group (Pretoria), with the other groups in comparison. So the research was based on the sourcing of quantitative and qualitative data, as well as on descriptive evaluations. The results offer insightful knowledge and guidelines towards establishing an optimal profile for the development of long-term sustainable private retirement resorts. The implications and value of this study are that both developers of retirement resorts and prospective residents are provided with guidelines to better equip them to evaluate a specific retirement resort with regard to the sustainable well- being of residents long-term.

Comparative Surface Imaging Study of Multifocal Diffractive Intraocular Lenses

2021 ◽  
Author(s):  
Hyeck Soo Son ◽  
Jung Min Lee ◽  
Ramin Khoramnia ◽  
Chul Young Choi
Keyword(s):  
Imaging Study ◽  
The Other ◽  
Intraocular Lenses ◽  
Optical Surface ◽  
Diffractive Optic ◽  
Atomic Force ◽  
Acceptable Range ◽  
Different Types ◽  
Concentric Pattern

Abstract Purpose To analyse and compare the surface topography and roughness of three different types of diffractive multifocal IOLs. Methods Using scanning electron microscope (SEM, Inspect F, 5.0 KV, maximum magnification up to 20,000) and atomic force microscope (AFM, Park Systems, XE-100, non-contact, area profile comparison, 10 × 10 µm, 40 × 40 µm), the surface quality of the following diffractive IOLs was studied: the AcrySof IQ PanOptix (Alcon, USA), the AT LARA 829MP (Carl Zeiss Meditec, Germany), and Tecnis Symfony (Johnson&Johnson Vision, USA). The measurements were made over three representative areas (central non-diffractive optic, central diffractive optic, and diffractive step) of each IOL. Roughness profile in terms of mean arithmetic roughness (Ra) and root-mean-squared roughness (Rq) values were obtained and compared statistically. Results In SEM examination, all IOLs showed a smooth optical surface without any irregularities at low magnification. At higher magnification, Tecnis Symfony showed unique highly regular, concentric, and lineate structures in the diffractive optic area which could not be seen in the other studied diffractive IOLs. The differences in the measured Ra and Rq values of the Tecnis Symfony were statistically significant compared to the other models (p < 0.05). Conclusion Various different topographical traits were observed in three diffractive multifocal IOLs. The Ra values of all studied IOLs were within an acceptable range. Tecnis Symfony showed statistically significant higher surface Ra values at both central diffractive optic and diffractive step areas. Furthermore, compared to its counterparts, Tecnis Symfony demonstrated highly ordered, concentric pattern in its diffractive surfaces.

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