•PIC mineral and kimberlite isotopic compositions are similar, implying genetic link.•MARID formed by EM-II-like agent, later modified by interaction with kimberlite.•MARID mineral negative ΔεHfi ...values caused by kimberlite melt infiltration.•Assimilation of MARID material may cause negative ΔεHfi values in kimberlites.
MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks occur as mantle-derived xenoliths in kimberlites and other alkaline volcanic rocks. Both rock types are alkaline and ultramafic in composition. The H2O and alkali metal enrichments in MARID and PIC rocks, reflected in abundant phlogopite, have been suggested to be caused by extreme mantle metasomatism. Radiogenic (Sr–Nd–Hf–Pb) isotope and trace element compositions for mineral separates from MARID (clinopyroxene and amphibole) and PIC (clinopyroxene only) samples derived from Cretaceous kimberlites (Kimberley) and orangeites (Newlands) from South Africa are used here to examine the source(s) of mantle metasomatism. PIC clinopyroxene (n=4) is relatively homogeneous, with narrow ranges in initial isotopic composition (calculated to the emplacement age of the host Bultfontein kimberlite; 87Sr/86Sri: 0.7037–0.7041; εNdi: +3.0 to +3.6; εHfi: +2.2 to +2.5; 206Pb/204Pbi: 19.72–19.94) similar to kimberlite values. This is consistent with PIC rocks representing peridotites modified by intense metasomatic interaction with kimberlite melts.
The MARID clinopyroxene (n=9) and amphibole separates (n=11) studied here display broader ranges in isotope composition (e.g., 87Sr/86Sri: 0.705–0.711; εNdi: −11.0 to −1.0; εHfi: −17.9 to −8.5; 206Pb/204Pbi: 17.33–18.72) than observed in previous studies of MARID rocks. The Nd–Hf isotope compositions of kimberlite-derived MARID samples fall below the mantle array (ΔεHfi between −13.0 and −2.4), a feature reported widely for kimberlites and other alkaline magmas. We propose that such displacements in MARID minerals result from metasomatic alteration of an initial “enriched mantle” MARID composition (i.e., 87Sr/86Sri = 0.711; εNdi = −11.0; εHfi = −17.9; and 206Pb/204Pbi = 17.3) by the entraining kimberlite magma (87Sr/86Sr∼i0.704; εNd∼i+3.3; εHf∼i+2.3; 206Pb/204Pb∼i19.7). A model simulating the flow of kimberlite magma through a mantle column, thereby gradually equilibrating the isotopic and chemical compositions of the MARID wall-rock with those of the kimberlite magma, broadly reproduces the Sr–Nd–Hf–Pb isotope compositions of the MARID minerals analysed here. This model also suggests that assimilation of MARID components could be responsible for negative ΔεHfi values in kimberlites. The isotopic composition of the inferred initial MARID end-member, with high 87Sr/86Sr and low εNd, εHf, and 206Pb/204Pb, resembles those found in orangeites, supporting previous inferences of a genetic link between MARID-veined mantle and orangeites. The metasomatic agent that produced such compositions in MARID rocks must be more extreme than the EM-II mantle component and may relate to recycled material that experienced long-term storage in the lithospheric mantle.
Following the pathways of imperial commerce, blackface minstrel
troupes began to cross the globe in the mid-nineteenth century,
popularizing American racial ideologies as they traveled from
Britain ...to its colonies in the Pacific, Asia, and Oceania, finally
landing in South Africa during the 1860s and 1870s. The first
popular culture export of the United States, minstrel shows
frequently portrayed black characters as noncitizens who were unfit
for democratic participation and contributed to the construction of
a global color line. Chinua Thelwell brings blackface minstrelsy
and performance culture into the discussion of apartheid's
nineteenth-century origins and afterlife, employing a broad archive
of South African newspapers and magazines, memoirs, minstrel songs
and sketches, diaries, and interview transcripts. Exporting Jim
Crow highlights blackface minstrelsy's cultural and social
impact as it became a dominant form of entertainment, moving from
its initial appearances on music hall stages to its troubling
twentieth-century resurgence on movie screens and at public events.
This carefully researched and highly original study demonstrates
that the performance of race in South Africa was inherently
political, contributing to racism and shoring up white racial
identity.
The end of the Archean aeon (3.0–2.5 Ga) was a period of fundamental change in many aspects of the geological record. In Archean cratons, this timespan is marked by a considerable diversification in ...both the nature and petrogenesis of granitoid rocks. In this article, we review the nature, petrogenesis and global evolution of late-Archean granitoids and discuss their geodynamic significance.Late-Archean granitoids can be classified into four groups: (1) volumetrically-dominant and juvenile tonalites, trondhjemites and granodiorites (TTGs), whose geochemistry is consistent with an origin through partial melting of meta-igneous mafic rocks at various pressures; (2) Mg-, Fe- and K-rich, metaluminous (monzo)diorites and granodiorites, referred to as sanukitoids s.l., which derive primarily from hybridization between mantle peridotite and a component rich in incompatible elements; (3) peraluminous and K-rich biotite- and two-mica granites, formed through melting of older crustal lithologies (TTGs and meta-sediments, respectively); and (4) hybrid high-K granites with mixed characteristics from the first three groups.The chronology of granitoid emplacement in late-Archean times is different from one craton to another but, in general, follows a very specific two-stage sequence: (1) a long period (0.2–0.5 Ga) of TTG emplacement; (2) a shorter period (0.02–0.15 Ga) during which all other granitoid types were generated. We propose that this sequence represents the first global subduction–collision cycle in the Earth's history. Although possibly present in the geological record prior to 3.0 Ga, such mechanisms became progressively prevalent on a planetary scale only between 3.0 and 2.5 Ga, indicating that the late-Archean geodynamic changes resulted from the global initiation of “modern-style” plate tectonics. The Archean–Proterozoic transition thus represents a major change in the mechanisms of the Earth's heat loss: before 3.0–2.5 Ga, it took place by large-scale magmatic differentiation characterized by generation of proto-continents that underwent crustal maturation locally, but without obvious cyclic activity on a planetary scale. After this, heat loss became accommodated by plate tectonics and global Wilson subduction–collision cycles. These changes were the consequence of the Earth's cooling, which in turn controlled a number of different parameters locally (thickness, temperature, volume and rheology of the crust). This explains why the changes took place over a short timespan (~ 0.5 Ga) relative to the Earth's history, but at different times and with different characteristics from one craton to another.
The thermobarometric analysis of inclusions in lithospheric diamonds has shown that these diamonds may originate from a wide range of depths, with a global mode at ~175 ± 15 km. Studies based on ...diamond depth distribution at global scale, however, cannot clarify if this mode reflects a real concentration of diamonds, preferential sampling of materials from this level by ascending kimberlites, or simply a statistical distribution within the hard limits imposed by diamond stability, lithosphere thickness and mantle adiabat under typical cratonic thermal regimes. We addressed this problem by comparing depth distributions for peridotitic diamonds from the three localities that have been the most prolific for diamond geobarometry (Cullinan, Kimberley and Voorspoed, South Africa) with those of mantle xenocrysts from the same kimberlite sources. The revised P–T estimates indicate that the diamonds were formed at T higher, equal or lower than the ambient geotherm recorded by the xenocrysts. These conditions may represent old mantle thermal regimes or local thermal perturbations related to infiltration of parental fluids or melts. Nonetheless, the studied diamonds show similar depth distributions for the different localities, with a distinct mode at ⁓180 ± 10 km. The similarity of these distributions with that calculated for peridotitic diamonds worldwide, as well as the lack of systematic correlation with kimberlite sampling efficiency as recorded by mantle xenocrysts, suggests that this mode has genetic significance. Based on observed depth distributions and thermodynamic modeling of COH fluids, diamond-forming processes are predicted to become less efficient with decreasing depth from at least ⁓165 km. In addition, diamond endowment near the base of the lithosphere may be negatively affected by infiltration of carbon-undersaturated melts or fluids after diamond formation. Considering the poor correlation between diamond and xenocryst depth distributions in single kimberlites or kimberlite clusters, even limited xenocryst records from diamond favorable depths (especially from the 160–190 km interval) may correspond to significant diamond potential.
•Diamonds may form at T higher, equal or lower than the ambient eruption geotherm.•Similar depth distributions at different localities for peridotitic diamonds.•Poor correlation with xenocryst depth distributions.•The 160–190 km depth interval is the most favorable for diamonds.
Malaria continues to be a disease of massive burden in Africa, and the public health resources targeted at surveillance, prevention, control, and intervention comprise large outlays of expense. ...Malaria transmission is largely constrained by the suitability of the climate for Anopheles mosquitoes and Plasmodium parasite development. Thus, as climate changes, shifts in geographic locations suitable for transmission, and differing lengths of seasons of suitability will occur, which will require changes in the types and amounts of resources.
The shifting geographic risk of malaria transmission was mapped, in context of changing seasonality (i.e. endemic to epidemic, and vice versa), and the number of people affected. A published temperature-dependent model of malaria transmission suitability was applied to continental gridded climate data for multiple future AR5 climate model projections. The resulting outcomes were aligned with programmatic needs to provide summaries at national and regional scales for the African continent. Model outcomes were combined with population projections to estimate the population at risk at three points in the future, 2030, 2050, and 2080, under two scenarios of greenhouse gas emissions (RCP4.5 and RCP8.5).
Estimated geographic shifts in endemic and seasonal suitability for malaria transmission were observed across all future scenarios of climate change. The worst-case regional scenario (RCP8.5) of climate change predicted an additional 75.9 million people at risk from endemic (10-12 months) exposure to malaria transmission in Eastern and Southern Africa by the year 2080, with the greatest population at risk in Eastern Africa. Despite a predominance of reduction in season length, a net gain of 51.3 million additional people is predicted be put at some level of risk in Western Africa by midcentury.
This study provides an updated view of potential malaria geographic shifts in Africa under climate change for the more recent climate model projections (AR5), and a tool for aligning findings with programmatic needs at key scales for decision-makers. In describing shifting seasonality, it was possible to capture transitions between endemic and epidemic risk areas, to facilitate the planning for interventions aimed at year-round risk versus anticipatory surveillance and rapid response to potential outbreak locations.
Falls the Shadow Bentley, Kristina; Nathan, Laurie; Calland, Richard
2013
eBook
Odprti dostop
The gap between the promise of the Constitution and the reality of life for most South Africans is a significant problem that requires urgent attention. This book explores that gap — its causes, its ...meaning and its implications. On the face of it, the Constitution provides for the security of all the people in South Africa and it does this in many compelling ways. Yet the majority of the population are socially, economically, physically and psychologically insecure. This gives rise to troubling questions: What is the nature and extent of the gap between the constitutional promise of security and the reality of people’s lives? Does the gap depend on biological and social criteria such as race, class, gender, health and nationality? What combination of ideas, values, policies and financial and bureaucratic constraints accounts for the gap? And most vitally, what are the implications for human suffering and the potential for conflict and violence? Falls the Shadow tackles these questions in a forthright and rigorous fashion, alerting us to the dimensions and perils of the ‘constitutional shadow’ — a realm of diminished dignity, chronic insecurity and acute political danger.
This open access Regional Reader proposes new ways of theorizing migration in Southern Africa by arguing that traditional western forms of theorizing do not adequately fit the South-South migration ...context. It explores the existing definitions of a ‘migrant’ with a view to conceptualise a definition which will speak to the complexities, envisioning a more inclusive Southern African region. The book investigates the various levels of migration moving from the local (rural to urban and urban to rural) to cross border migration; middle-class versus working-class migrant household livelihoods; livelihoods procurement versus wage earning; social capital (networks) and how they make meaning of their circumstances in a ‘foreign’ space. It also acknowledges the intertwined issues of gender and class as important in analyzing migration processes and the chapters feature both in varying dimensions. As such, the book provides a great resource for students, academics and policy makers.
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