Geochemistry and Sr, Nd, Pb isotopic composition of the Central Atlantic Magmatic Province (CAMP) in Guyana and Guinea

The Central Atlantic Magmatic Province (CAMP) is one of the largest igneous provinces on Earth, extending more than 5000 km north to south, on both sides of the Atlantic Ocean. Its emplacement occurred about 200 Ma ago, at the Triassic–Jurassic boundary, and is linked to the initial breakup of Pangaea. Two areas of the province are studied here: French Guyana/Surinam (South America) and Guinea (West Africa), in order to document the petrogenesis and geodynamical significance of high-Ti and low-Ti basaltic magmas from the CAMP.

In Guyana, doleritic and gabbroic dykes are located on the edge of the Guiana Shield, and represent limited volumes of magma. They display low SiO₂ (47–50%), high TiO₂ (2.5–3.5%) and high FeO tholeiitic trends and show variably enriched trace element patterns ((La/Yb)_n=1.5–5.1). Their isotopic signature and ratios of very incompatible elements (εNd_i=+5.8 to +4.2, (⁸⁷Sr/⁸⁶Sr)_i=0.703–0.705, (²⁰⁷Pb/²⁰⁴Pb)_i=15.46–15.64) match a depleted PREMA (prevalent mantle)-like source. Their genesis can be modeled by ca. 15% partial melting of a lherzolite source, and a subsequent limited fractional crystallization (5–10%) or a slight upper crustal assimilation–fractional crystallization (AFC, r=0.1, Proterozoic contaminant). In Guinea, in contrast, huge volumes of CAMP magmas were intruded along the Rockelides suture and the West African craton, forming the Fouta Djalon sills and the Kakoulima laccolith. The laccolith is more than 1000 m thick. These features consist of gabbros, dolerites, diorites and mafic (gabbro) and ultramafic (dunite, wherlite) cumulates. Guinean tholeiites show high SiO₂ (51–58%), low TiO₂ (0.7–1.2%) and FeO trends, with high LILE/HFSE ratios and slight negative Nb–Ta anomalies. Isotopic signatures (εNd_i=+0.4 to −5.3, (⁸⁷Sr/⁸⁶Sr)_i=0.705–0.710, (²⁰⁷Pb/²⁰⁴Pb)_i=15.57–15.66) indicate a more enriched source than for Guyana as well as a higher rate of magma–upper crust interaction through an AFC process (r=0.3, Birimian crust contaminant) and, probably, an additional upper crustal contamination for the most differentiated sample.

This geochemical study supports the prevalence in Guinea, as for other low-Ti CAMP tholeiites, of a lithospheric mantle source, previously enriched during ancient subduction events, and preferentially reactivated in late Triassic times by edge-driven convection between cratonic and mobile belt domains. A larger contribution from a depleted asthenospheric source is required to generate high-Ti tholeiites in Guyana, which may reflect the development of CAMP rifting towards the initiation of the Central Atlantic oceanic crust.     

富含Na+ 、Ca2+、Al3+、Cr3+蒙脱石对垃圾渗滤液中有机物的吸附

由于层间含有高价态金属阳离子的蒙脱石对特定有机物的吸附能力可大大增强,故分别用层间含有Na+、Ca2+、Al3+和Cr3+的蒙脱石对垃圾渗滤液中的有机物进行吸附实验,研究它们吸附苯酚、二甲苯和COD的能力及离子形态对吸附效果的影响.结果表明,含高价金属阳离子的蒙脱石对苯酚和COD的吸附能力较高,吸附能力由小到大的顺序为Na+<Ca2+<Al3+<Cr3+蒙脱石;各种类型蒙脱石对二甲苯的吸附能力相对较低,并且没有一定的规律可循.并对氢键吸附机制进行了探讨.     

Evaluation of shredded tyre chips as sorption media for passive treatment walls

The potential of shredded tyre chips, either on their own or mixed with gravel, to act as a permeable reactive barrier has been examined by carrying out tests for assessing sorption characteristics and establishing their mechanical properties. Sorption–desorption tests have been carried out using free product petrol and paraffin and aqueous phase phenol and cresols.

Compaction and compressibility tests have been carried out to establish optimum tyre–chip mixes in order to optimise the mix in terms of compressibility behaviour. The results demonstrate that tyre chips show significant promise for incorporation in a permeable reactive barrier. The evidence indicates that they would be particularly effective for the retardation of aqueous phase hydrophobic organic contaminants and residual free product. Optimum mixes of 2–6 mm tyre chips and 20 mm gravel, in terms of mechanical stability, will contain just under 10% of tyre chips.     

LINKING SEDIMENT EXPOSURE WITH EFFECTS: MODELING TECHNIQUES, ORGANIC AVAILABILITY AND UPTAKE

1 INTRODUCTION Sediments are the ultimate sink for many hydrophobic contaminants and represent biologically important environmental habitats. Exposure of the sediment-associated contaminants is not only influenced by the fate and transport of sediment but also is influenced by a variety of physical, chemical, and biological processes that involve no net movement of sediments. These processes include pore water transport processes such as advection and diffusion, and sediment mixing process…     

太阳能在处理水、大气及土壤中有机污染物方面的应用

太阳能除作为传统的热源外，还可用于驱动化学过程。本文主要介绍利用光催化氧化技术处理废水、大气及土壤中有机污染物方面的最新进展，正在进行的现场实验、有关的太阳能设施，目前存在的主要困难及未来的应用前景等。     

地表稠油污染物地球化学研究现状

关于石油轻组分对环境的污染问题相对研究较多，而针对稠油污染物的研究则较薄弱。本文着重介绍了目前地表稠油污染物的研究进展，涉及稠油污染的潜在严重性和危害性，其赋存形态、迁移方式和演化机制，以及目前常用的修复方法。进一步开展稠油污染物在地表土壤以及水体中的地球化学特征及演化机制方面的研究工作，将有助于为稠油开采和炼制地区的环境保护和修复治理提供更多的科学依据。