The role of continental lithosphere in the generation of the Karoo volcanic rocks: evidence from combined Nd-and Sr-isotope studies

143Nd/144Nd, 87Sr/86Sr, Sm and Nd analyses are reported on suites of Karoo volcanic rocks from the four sub-areas of Nuanetsi-north Lebombo, south Lebombo, the Central area, and north-west SWA/Namibia. Only seven (12%) of the samples analysed have positive ENd values similar to those found in the majority of recent mantle-derived rocks. Most of the rest have negative ENd (-1.0 to -17.1) and positive ESr, (+3.0 to +240) and thus must contain at least a contribution from source areas which were both old, and had lower Sm/Nd and higher Rh/Sr ratios than the bulk earth

Evolution of the continental lithosphere: evidence from volcanics and xenoliths in southern Africa

The geology of southern Africa offers a rare opportunity to study the evolution of a segment of continental lithosphere because its rocks range in age from 3.6 Ga to recent, and over the last 200 Ma both the upper mantle and the crust have been sampled by Karoo and Tertiary volcanism and as xenoliths in kimberlite pipes

Geochemistry and petrogenesis of the Etendeka volcanic rocks from SWA Namibia

The volcanic rocks of the Etendeka Formation from north-west SWA/Namibia have a present-day coverage of 70,000 km² and comprise a series of interbedded basalts, latites and quartz latites, together with four varieties of intrusive dolerite. Apart from one group of dolerites (regional dolerites) which have mineralogical and geochemical similarities to the Lesotho Formation lavas from the Central area, the Etendeka volcanics differ from all other Karoo volcanics by virtue of their Cretaceous age, stratigraphy, mineralogy, geochemistry, and range in mineralogical, elemental and isotopic compositions for the basaltic rocks

Feeding the Worlth Healthily: the Challenge of Measuring the effects of Agriculture on Health

Agricultural production, food systems and population health are intimately linked. While there is a strong evidence base to inform our knowledge of what constitutes a healthy human diet, we know little about actual food production or consumption in many populations and how developments in the food and agricultural system will affect dietary intake patterns and health. The paucity of information on food production and consumption is arguably most acute in low- and middle-income countries, where it is most urgently needed to monitor levels of under-nutrition, the health impacts of rapid dietary transition and the increasing ‘double burden’ of nutrition-related disease. Food availability statistics based on food commodity production data are currently widely used as a proxy measure of national-level food consumption, but using data from the UK and Mexico we highlight the potential pitfalls of this approach. Despite limited resources for data collection, better systems of measurement are possible. Important drivers to improve collection systems may include efforts to meet international development goals and partnership with the private sector. A clearer understanding of the links between the agriculture and food system and population health will ensure that health becomes a critical driver of agricultural change

Critical methods in international relations: the politics of techniques, devices and acts

Methods have increasingly been placed at the heart of theoretical and empirical research in IR and social sciences more generally. This article explores the role of methods in International Relations and argues that methods can be part of a critical project if reconceptualised away from neutral techniques of organising empirical material and research design. It proposes a two-pronged reconceptualisation of critical methods as devices which enact worlds and acts which disrupt particular worlds. Developing this conceptualisation allows us to foreground questions of knowledge and politics as stakes of method and methodology rather than exclusively of ontology, epistemology or theory. It also allows us to move away from the dominance of scientificity (and its weaker versions of systematicity and rigour) to understand methods as less pure, less formal, messier and more experimental, carrying substantive political visions

The problem of gender categorisation: addressing dilemmas past and present in gender and education research

Developments in the field of gender theory as applied to education since the 1970s are briefly reviewed in order to highlight key challenges and debates around gender categorisation and identification in gender and education. We argue that conundrums of categorisation have haunted, and continue to haunt, the field of gender theory, and empirical applications (such as the case of education) in particular. We explain how we have attempted to address some of the conundrums arising in our own theoretical work, and analyse remaining challenges that we feel the field of education needs to address in order to advance theoretically. Identifying two key tensions underpinning this empirical dilemma of gender categorisation – the tension between agency and determinism in gender identification, and that between gender deconstruction and gender analysis – we seek to weave a path through some of these complex debates, and to indicate ways in which they may be addressed in future work. We argue that in order to avoid essentialism and reification of gender distinction, we need to apply a ‘three-fold’ analysis that incorporates three different elements in our categorisation of gender: spectator perspective; respondent perspective and social context

Governance, Coordination and Evaluation: the case for an epistemological focus and a return to C.E. Lindblom

While much political science research focuses on conceptualizing and analyzing various forms of governance, there remains a need to develop frameworks and criteria for governance evaluation (Torfing et al 2012). The post-positivist turn, influential in recent governance theory, emphasizes the complexity, uncertainty and the contested normative dimensions of policy analysis. Yet a central evaluative question still arises concerning the capacity of governance networks to facilitate ‘coordination’. The classic contributions of Charles Lindblom, although pre-dating the contemporary governance literature, can enable further elaboration of and engagement with this question. Lindblom’s conceptualisation of coordination challenges in the face of complexity shares with post-positivism a recognition of the inevitably contested nature of policy goals. Yet Lindblom suggests a closer focus on the complex, dynamically evolving, broadly ‘economic’ choices and trade-offs involved in defining and delivery policy for enabling these goals to be achieved and the significant epistemological challenges that they raise for policy-makers. This focus can complement and enrich both post-positivist scholarship and the process and incentives-orientated approaches which predominate in contemporary political science research on coordination in governance. This is briefly illustrated through a short case study evaluating governance for steering markets towards delivering low and zero carbon homes in England

Combined U-Pb and Lu-Hf isotope analyses by laser ablation MC-ICP-MS : methodology and applications

O sistema isotópico Lutécio-Hafnio representa uma das ferramentas mais recentes e poderosas para estudos isotópicos e geocronológicos. Análises combinadas in situ de U-Pb e Lu-Hf sobre zircão pelo LA-MC-ICP-MS permitem caracterizar isotopicamente o magma onde ele cristalizou, fornecendo valiosas informações para estudos de proveniência de sedimento e de evolução crustal. Nesse trabalho descrevemos a sistemática de Lu-Hf pelo LA-MC-ICP-MS implantada no laboratório de Geocronologia da Universidade de Brasília e reportamos os resultados obtidos de repetidas análises de três padrões de zircão: GJ-1 = 0.282022 ± 11 (2SD, n=56), Temora 2 = 0.282693 ± 14 (2SD, n=25) and UQ-Z = 0.282127 ± 33 (2SD, n=11). Foi também caracterizada arazão isotópica 176Hf/177Hf(0.282352 ± 22, 2SD, n=14) de um zircão usado como padrão interno do laboratório. Como aplicação geológica, analisamos dois zircões complexos selecionados a partir de uma amostra de migmatito da Província de Borborema, NE do Brasil. Sobre a base dos dados U-Pb e Lu-Hf foram identificados em ambos os zircões dois eventos de cristalização. Um evento mais antigo de 2.05 Ga nos núcleos herdados, representa um evento magmático Paleoproterozoico bem conhecido na Província Borborema. Um segundo evento de ~ 575 Ma, reconhecido nas bordas, representa um evento magmático-metamórfico Neoproterozóico (Brasiliano). ________________________________________________________________________________________ ABSTRACTThe Lutetium-Hafnium isotopic system represents one of the most innovative and powerful tools for geochronology and isotopic studies. Combined U-Pb and Lu-Hf in situ analyses on zircon by LA-MC-ICP-MS permit to characterize isotopically the host magma from which it crystallized furnishing significant information for sediment provenance and crustal evolution studies. In this paper e describe the Lu-Hf systematic by LA-MC-ICP-MS developed in the laboratory of Geochronology of the University of Brasilia and report the results obtained by repeated analyses of 176Hf/177Hf isotopic ratio of three zircon standards: GJ-1 = 0.282022 ± 11 (n=56), Temora 2 = 0.282693 ± 14 (n=25) and UQZ = 0.282127 ± 33 (n=11). The 176Hf/177Hf ratio (0.282352 ± 22, n=14) of gem quality zircon used as in-house standard have been also characterized. As a geological application, we analyzed two complex zircons selected from a migmatitic rocks from the Borborema Province, NE Brazil. On the basis of U-Pb and Lu-Hf data, two main crystallization events have been identified in both studied zircons. An older event at ca. 2.05 Ga recognized in the inherited cores represents a well-characterized paleoproterozoic magmatic event that affected the whole Borborema Province. A second crystallization event at ~ 575 Ma, recognized at the rims, represents a Neoproterozoic (Brazilian) high grade metamorphic-magmatic event