Forsterite‐bearing type B refractory inclusions from CV3 chondrites: From aggregates to volatilized melt droplets

Abstract– Detailed petrologic and oxygen isotopic analysis of six forsterite‐bearing Type B calcium‐aluminum‐rich inclusions (FoBs) from CV3 chondrites indicates that they formed by varying degrees of melting of primitive precursor material that resembled amoeboid olivine aggregates. A continuous evolutionary sequence exists between those objects that experienced only slight partial melting or sintering through objects that underwent prolonged melting episodes. In most cases, melting was accompanied by surface evaporative loss of magnesium and silicon. This loss resulted in outer margins that are very different in composition from the cores, so much so that in some cases, the mantles contain mineral assemblages that are petrologically incompatible with those in the cores. The precursor objects for these FoBs had a range of bulk compositions and must therefore have formed under varying conditions if they condensed from a solar composition gas. Five of the six objects show small degrees of mass‐dependent oxygen isotopic fractionation in pyroxene, spinel, and olivine, consistent with the inferred melt evaporation, but there are no consistent differences among the three phases. Forsterite, spinel, and pyroxene are ¹⁶O‐rich with Δ¹⁷O ～ ?24‰ in all FoBs. Melilite and anorthite show a range of Δ¹⁷O from ?17‰ to ?1‰.     

The Multiscale TROPIcal CatchmentS critical zone observatory M-TROPICS dataset I: The Nyong River Basin,Cameroon

Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse-gas emissions and carbon budgets from African inland waters. However, long-term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non-stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land-cover and land-use. The latter highlights the need for longer time-series and continued support for CZOs particularly in the humid tropics.     

Fate and tidal transport of butyltin and mercury compounds in the waters of the tropical Bach Dang Estuary (Haiphong, Vietnam)

In this work, two field campaigns were performed in July 2008 (wet season) and March 2009 (dry season) to produce original data on the concentration, partition and distribution of mercury and butyltin compounds along the tropical Bach Dang Estuary located in North Vietnam (Haiphong, Red River Delta). The results demonstrate that mercury and butyltin speciation in the surface waters of this type of tropical estuary is greatly affected by the drastic changes in the seasonal conditions. During high river discharge in the wet season, there was a large estuarine input of total Hg and tributyltin, while the longer residence time of the waters during the dry season promotes increasing MMHg formation and TBT degradation. Although most of the Hg and TBT is transported into the estuary from upstream sources, tidal cycle measurements demonstrate that this estuary is a significant source of TBT and MMHg during the wet (～3kgTBT/day) and dry (～3gMMHg/day) seasons.     

Homogenization of saturated double porous media with Eshelby-like velocity field

In this paper, we focus on strength properties of double porous materials having a Drucker-Prager solid phase at microscale. The porosity consists in two populations of micropores and mesopores saturated with different pressures. To this end, we consider a hollow sphere subjected to a uniform strain rate boundary conditions. For the microscale to mesoscale transition, we take advantage of available results by Maghous et al. (2009), while the meso to macro upscaling is performed by implementing a kinematical limit analysis approach using Eshelby-like trial velocity fields. This two-step homogenization procedure delivers analytical expression of the macroscopic criterion for the considered class of saturated double porous media. This generalizes and improves previous results established by Shen et al. (2014). The results are discussed in terms of the existence or not of effective stresses. Some illustrations are provided.     

A comet impact in AD 536?

Emma Rigby, Melissa Symonds and Derek Ward-Thompson review the evidence for the possibility that a comet may have impacted the Earth in historical times, and discuss the size of the putative comet.     

Flood insurance: the challenge of the uninsured

Increasing concern about flooding and its potentially socially-devastating effects has reinforced the need for an effective mechanism to deal with the recovery of losses from these events. This paper highlights the problem of uninsurance in the UK and the potentially growing number of people who do not have flood insurance. A dual challenge of uninsurance is emerging: those who have been traditionally excluded from insurance cover due to price and a new phenomenon, those who live in high-risk areas who may become cost-prohibited through the introduction of risk-related premiums.     

Discrete-element modelling of extensional fault-propagation folding above rigid basement fault blocks

We employed a discrete‐element technique to investigate the effects of cover strength and fault dip on the style of fault‐propagation folding above a blind normal fault. Deformation in the cover is initially characterised by an upward‐widening monocline that is often replaced, with continued slip on the basement fault, by a single, through‐going fault. Localisation on a single fault produces hangingwall synclines and footwall anticlines as a result of breaching of the earlier monocline and which do not represent ‘drag’ against the fault. As basement fault dip decreases the width of the monocline at the surface increases. Experiments varying the strength of the overburden material illustrate the control that cover strength has on both fault propagation and folding in the cover. Reduction of the strength of the cover results in: (1) the width of the monocline above the fault tip increasing, and (2) more marked footwall thinning and hangingwall thickening of beds. In contrast, an increase in cover strength results in a narrower monocline and rapid propagation of the basement fault into the cover. In multi‐layer (variable strength) experiments simultaneous faulting of competent layers and flow of weaker layers produces complex structural relationships. Faults in the cover die out up and down section and do not link to the basement fault at depth. Similarly, complex macroscopically ductile characteristics such as footwall thinning and hangingwall thickening can be juxtaposed against simple brittle fault cut‐offs. These relationships must be borne in mind when interpreting the field and seismic expression of such structures. We discuss the modelling results in terms of their implications for structural interpretation and the surficial expression of fault‐related folding in extensional settings.     

Hindu nationalism, neo-traditionalism and environmental discourses in India

One of the defining changes India has experienced over the last decade has been the social and political consolidation of the Hindu Right. Critics point to its chauvinist ideologies, the discrimination and violence against religious minorities, and the neglect of the poor. This paper examines the parallels between the discourses of the Hindu Right and those of neo-traditionalist environmentalists. Similarities include gendered and social conservatism; superficial hermeneutic analyses of ancient texts; partial and ‘romantic’ histories; and the essentialisation of science and of East and West. The paper concludes by suggesting that environmental scholars and activists cannot afford to be innocent of the implications of their ideas and assumptions given the social and political contexts of Hindu nationalism in contemporary India.     

Postcolonial environmental justice: Government and governance in India

In this paper, we investigate the context within which struggles for environmental justice are taking place in India. We explore the ways in which postcolonial patterns of government and governance in India affect the ends, the means and the representation of these struggles, focusing on three particular areas: state reform, the judiciary and public interest litigation, and environmental social movements. We argue that India differs from west in the ambitious yet incomplete and contradictory nature of government-sponsored intervention in the environment, and in the particular nature of its public sphere, both of which have been important in shaping struggles for environmental justice. Our wider intention is not merely to catalogue these differences, but to use the Indian material to raise questions about the emphases and implicit assumptions of western environmental justice literature, and reflect on how these may be need reconsideration when working in postcolonial contexts.