Geochemistry and petrogenesis of lamproites,late cretaceous age,Woodson County,Kansas, U.S.A.

Lamproite sills and their associated sedimentary and contact metamorphic rocks from Woodson County, Kansas have been analyzed for major elements, selected trace elements, and strontium isotopic composition. These lamproites, like lamproites elsewhere, are alkalic (molecular $\text{K}{}_2\text{O + Na}{}_2\text{O}\text{Al}{}_2\text{O}{}_3\text{= 1.6–2.6}$), are ultrapotassic $\text{(}\text{K}{}_2\text{O}\text{Na}{}_2\text{O}\text{= 9.6–150)}$, are enriched in incompatible elements (LREE or light rare-earth elements, Ba, Th, Hf, Ta, Sr, Rb), and have moderate to high initial strontium isotopic compositions (0.7042 and 0.7102). The silica-saturated magma (olivine-hypersthene normative) of the Silver City lamproite could have formed by about 2 percent melting of a phlogopite-garnet lherzolite under high $\text{H}{}_2\text{O}\text{CO}{}_2$ ratios in which the Iherzolite was enriched before melting in the incompatible elements by metasomatism. The Rose Dome lamproite probably formed in a similar fashion although the extreme alteration due to addition of carbonate presumably from the underlying limestone makes its origin less certain. Significant fractional crystallization of phases that occur as phenocrysts (diopside, olivine, K-richterite, and phlogopite) in the Silver City magma and that concentrate Co, Cr, and Sc are precluded as the magma moved from the source toward the surface due to the high abundances of Co, Cr, and Sc in the magma similar to that predicted by direct melting of the metasomatized Iherzolite.Ba and, to a lesser extent, K and Rb and have been transported from the intrusions at shallow depth into the surrounding contact metamorphic zone. The Silver City lamproite has vertical fractionation of some elements due either to volatile transport or to variations in the abundance of phenocrysts relative to groundmass most probably due to flow differentiation although multiple injection or fractional crystallization cannot be conclusively rejected.     

The role of economic sectoral structure as a policy mechanism towards more resilient peripheral regions: the case of South Africa

The role of economic sectoral structure in regional growth and development is widely acknowledged. However, there has been scarce reflection on its role as a policy instrument, particularly for peripheral regions. In reaction, this paper investigates the role of economic sectoral structure as a policy instrument towards more resilient peripheral regions. Through a multiple country policy analysis, the paper determines to what degree economic sectoral structure is reflected in regional development policies of 18 countries with predominantly rural characteristics and lagging regions. Moreover, the role of economic sectoral structure towards more resilient regions is quantified and measured for a specific peripheral region case in South Africa as developing country exhibiting poor economic resilience. The paper highlights related variety as a key ingredient for a region to reach a state of dynamic stability between adaptation and adaptability towards enhanced long-term resilience capacity of the peripheral region. The research concludes that policy focus should support the maintenance of the sectors and industries of comparative advantage on the regional scale, but strongly focus on sectoral comparative advantage within the national scale (if present) to establish a more robust region. This will establish and strengthen the identified peripheral growth centres as centres of national competitiveness and specialisation. Primary policy actions as emanated from the literature and the multiple country policy analysis will promote more efficient sectoral composition as key towards more resilient peripheral regions. It is acknowledged that these policy actions must be informed by a detailed regional economic analysis for different peripheral regions to determine inherent and latent economic potential and link with interdependent industries. This paper will highlight that regional policy should become more explicit by exploiting the role of economic and natural resources as growth engines for the peripheral regional economy in a more effective way through a multi-centred territorial structure.

     

Diagnosing drought using the downstreamness concept: the effect of reservoir networks on drought evolution

To effectively manage hydrological drought, there is an urgent need to better understand and evaluate its human drivers. Using the “downstreamness” concept, we assess the role of a reservoir network in the emergence and evolution of droughts in a river basin in Brazil. In our case study, the downstreamness concept shows the effect of a network of reservoirs on the spatial distribution of stored surface water volumes over time. We demonstrate that, as a consequence of meteorological drought and recovery, the distribution of stored volumes became spatially skewed towards upstream locations, which affected the duration and magnitude of hydrological drought both upstream (where drought was alleviated) and downstream (where drought was aggravated). The downstreamness concept thus appears to be a useful entry point for spatiotemporally explicit assessments of hydrological drought and for determining the likelihood of progression from meteorological drought to a human-modified hydrological drought in a basin.     

Optimization of water allocation in the Shatt al-Arab River under different salinity regimes and tide impact

Wastewater effluents from irrigation and the domestic and industrial sectors have serious impacts in deteriorating water quality in many rivers, particularly in areas under tidal influence. There is a need to develop an approach that considers the impact of human and natural causes of salinization. This study uses a multi-objective optimization–simulation model to investigate and describe the interactions of such impacts in the Shatt al-Arab River, Iraq. The developed model is able to reproduce the salinity distribution in the river given varying conditions. The salinity regime in the river varies according to different hydrological conditions and anthropogenic activities. Due to tidal effects, salinity caused by drainage water is seen to intrude further upstream into the river. The applied approach provides a way to obtain optimal solutions where both river salinity and deficit in water supply can be minimized. The approach is used for exploring the trade-off between these two objectives.     

Late Triassic tectonic inversion in the upper Yangtze Block: Insights from detrital zircon U–Pb geochronology from south‐western Sichuan Basin

The Sichuan Basin and the Songpan‐Ganze terrane, separated by the Longmen Shan fold‐and‐thrust belt (the eastern margin of the Tibetan Plateau), are two main Triassic depositional centres, south of the Qinling‐Dabie orogen. During the Middle–Late Triassic closure of the Paleo‐Tethys Ocean, the Sichuan Basin region, located at the western margin of the Yangtze Block, transitioned from a passive continental margin into a foreland basin. In the meantime, the Songpan‐Granze terrane evolved from a marine turbidite basin into a fold‐and‐thrust belt. To understand if and how the regional sediment routing system adjusted to these tectonic changes, we monitored sediment provenance primarily by using detrital zircon U‐Pb analyses of representative stratigraphic samples from the south‐western edge of the Sichuan Basin. Integration of the results with paleocurrent, sandstone petrology and published detrital zircon data from other parts of the basin identified a marked change in provenance. Early–Middle Triassic samples were dominated by Neoproterozoic (~700–900 Ma) zircons sourced mainly from the northern Kangdian basement, whereas Late Triassic sandstones that contain a more diverse range of zircon ages sourced from the Qinling, Longmen Shan and Songpan‐Ganze terrane. This change reflects a major drainage adjustment in response to the Late Triassic closure of the Paleo‐Tethys Ocean and significant shortening in the Longmen Shan thrust belt and the eastern Songpan‐Ganze terrane. Furthermore, by Late Triassic time, the uplifted northern Kangdian basement had subsided. Considering the eastward paleocurrent and depocenter geometry of the Upper Triassic deposits, subsidence of the northern Kangdian basement probably resulted from eastward shortening and loading of the Songpan‐Ganze terrane over the western margin of the Yangtze Block in response to the Late Triassic collision among Yangtze Block, Yidun arc and Qiangtang terrane along the Ganze‐Litang and Jinshajiang sutures.     

Processes of carbonate precipitation in modern microbial mats

Microbial mats are ecosystems that arguably greatly affected the conditions of the biosphere on Earth through geological time. These laminated organosedimentary systems, which date back to > 3.4 Ga bp, are characterized by high metabolic rates, and coupled to this, rapid cycling of major elements on very small (mm-µm) scales. The activity of the mat communities has changed Earth's redox conditions (i.e. oxidation state) through oxygen and hydrogen production. Interpretation of fossil microbial mats and their potential role in alteration of the Earth's geochemical environment is challenging because these mats are generally not well preserved.Preservation of microbial mats in the fossil record can be enhanced through carbonate precipitation, resulting in the formation of lithified mats, or microbialites. Several types of microbially-mediated mineralization can be distinguished, including biologically-induced and biologically influenced mineralization. Biologically-induced mineralization results from the interaction between biological activity and the environment. Biologically-influenced mineralization is defined as passive mineralization of organic matter (biogenic or abiogenic in origin), whose properties influence crystal morphology and composition. We propose to use the term organomineralization sensu lato as an umbrella term encompassing biologically influenced and biologically induced mineralization. Key components of organomineralization sensu lato are the “alkalinity” engine (microbial metabolism and environmental conditions impacting the calcium carbonate saturation index) and an organic matrix comprised of extracellular polymeric substances (EPS), which may provide a template for carbonate nucleation. Here we review the specific role of microbes and the EPS matrix in various mineralization processes and discuss examples of modern aquatic (freshwater, marine and hypersaline) and terrestrial microbialites.     

Artificial recharge with surface water; a pilot project in Wadi Madoneh, Jordan

Artificial recharge with surface water in Jordan has been discussed at length in several reports and papers, but so far this technique has hardly been applied in the country. This article describes the site selection, design, construction and operation of four small retention structures in Wadi Madoneh during the period 2003–2009. The catchment (37 km²) is located some 20 km east of Amman in a desert region (average annual precipitation is 160 mm). The project is based on a feasibility study conducted in the 1990s. It is shown that in the previous study the retention structures have been largely overdesigned, because of absence of discharge measurements and the negligence of climate change. For this pilot an extensive hydrological study was carried out, based on historical data and contemporary measurements, to derive design parameters for small in-channel dams with a height of 3–6 m. The retention structures are designed to retain the floods in order to slowly release this water for infiltration in the Wadi bed downstream. Four retention structures were installed by a local contractor in 2007. This study shows that virtually all surface runoff from the catchment has ceased which makes the method very effective while the costs are low. Artificial recharge with small retention structures is recommended for application on a larger scale and considered a cheap alternative for other non-conventional water resources supply methods. From experience with vandalism and interaction with the local community, improvements to the design of the dams are recommended.     

Rainfall–interception–evaporation–runoff relationships in a semi-arid catchment,northern Limpopo basin,Zimbabwe

Abstract

Two types of monthly water balance models at basin scale are used: PE models use precipitation and potential evapotranspiration (PET) as their observed input data, whereas P models need only precipitation. Calibration proceeds by comparing model runoff and observed runoff. Calibration is entirely automatic with the exclusion of subjective elements. All models differ only by their actual evapotranspiration equations. PE models from previous papers are generalized essentially by replacing the constant evapotranspiration parameter by a periodic one, thus increasing the number of parameters by two (a “parameter” is an unknown constant to be estimated, and which is a characteristic of the river basin to be described). P models use a periodic “driving force”, which is intended to represent periodicity of hydrological phenomena, normally originating in the (unavailable) PET time series. These eight PE models and three P models are then applied to 55 river basins in 10 countries with widely diverging climates and soil conditions. A marked improvement of model performance in about one third of the basins is due to the introduction of the above mentioned periodic functions. Even when PET data are available it is sometimes useful to consider P models. P models scarcely perform less well than PE models. An engineer, wanting to try out as few models as possible on a given river basin, can restrict his attention to the optimization of two or three models. The paper is an extension of a long effort towards monthly water balance models, and is believed to give a solution in most circumstances.