The Ethiopian Rift Valley Lakes host populations of edible fish species including Oreochromis niloticus, Labeobarbus intermedius and Clarias gariepinus, which are harvested also in other tropical countries. We investigated the occurrence of six heavy metals in tissues of these fish species as well as in the waters of Lake Koka and Lake Awassa. Both lakes are affected by industrial effluents in their catchments, making them ideal study sites. Mercury concentrations were very low in the water samples, but concentrations in the fish samples were relatively high, suggesting a particularly high bioaccumulation tendency as compared with the other investigated metals. Mercury was preferentially accumulated in the fish liver or muscle. It was the only metal with species-specific accumulation with highest levels found in the predatory species L. intermedius. Lower mercury concentrations in O. niloticus could be attributed to the lower trophic level, whereas mercury values in the predatory C. gariepinus were unexpectedly low. This probably relates to the high growth rate of this species resulting in biodilution of mercury. Accumulation of lead, selenium, chromium, arsenic and cadmium did not differ between species, indicating that these elements are not biomagnified in the food chain. Values of cadmium, selenium and arsenic were highest in fish livers, while lead and chromium levels were highest in the gills, which could be related to the uptake pathway. A significant impact of the industrial discharges on the occurrence of metals in the lakes could not be detected, and the respective concentrations in fish do not pose a public health hazard.

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The source of fluid-forming veins is of great importance in order to understand the hydraulic system acting in the earth's crust. The study of syntectonic antitaxial veins is one of the few methods by which the opening history can be deduced from rocks, and thus these veins are of primary importance in determining rock kinematics. Antitaxial veins were taken from black shales in two different tectonic settings in the Helvetic Alps, Switzerland, and the Taconic Appalachians, New York State. These syntectonic extension veins are regularly spaced and are oriented sub-normal to bedding. The vein microstructure displays a symmetry around the median line in the centre of the vein, and a symmetry in cathodoluminescence banding parallel to the vein-wall interface, which suggests transport along bedding-parallel dissolution planes from both vein-walls. Antitaxial veins nucleated in transgranular fractures, but evidence for ongoing multiple crack-seal increments is lacking; rather, veins grew continuously keeping close contact to the vein-wall. Radiogenic 87 Sr/ 86 Sr ratios are higher in the surrounding matrix than in the vein, and higher than the corresponding seawater data in all samples. Variations are small and calcite in both the vein and the host rock were derived from the same source of fluid in the Helvetic samples. Mass balance of Sr suggests that the amount of calcite is too small in the surrounding host rock to be derived locally. Stable oxygen compositions are heavier in the host rock than in the veins, with overall low variation in both d 18 O and d 13 C values in the Mesozoic Helvetic samples. Data point to a rock-buffered system, the precipitate most likely derived from an external source. The lower Palaeozoic Appalachian veins have lesser d 18 O values than the host rock, similar to the Helvetic veins. Radiogenic 87 Sr/ 86 Sr data and a large heterogeneity in stable isotope values indicate an open system. Microstructural and isotopic evidence suggests that the antitaxial veins were formed by pervasive fluid flow, with the solute at least partly derived from an external source.

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Fine grained rodingite-like rocks containing epidote, clinozoisite, garnet, chlorite, phengite and titanite occur within antigorite serpentinite boudins from the high-pressure metamorphic Maksyutovo Complex in the Southern Urals. Pseudomorphs after lawsonite, resorption of garnet by chlorite and phengite and stoichiometry suggest the reaction lawsonite + garnet + K-bearing fluid fi clinozoisite + chlorite + phengite, and define a relic assemblage of lawsonite + garnet + chlorite + titanite ± epidote as well as a later post-lawsonite assemblage of clinozoisite + phengite + chlorite + titanite. The reaction lawsonite + titanite fi clinozoisite + rutile + pyrophyllite + H 2 O delimits the maximum stability of former lawsonite + titanite to pressures >13 kbar. P-T conditions of 18-21 kbar ⁄ 520-540°C result, if the average chlorite, Mg-rich garnet rim and average epidote compositions are used as equilibrium compositions of the former lawsonite assemblage. These estimates indicate a similar depth of formation but lower temperatures to those recorded in nearby eclogites. The metamorphic conditions of the lawsonite assemblage are considerably higher than previously suggested and, together with published structural data, support a model in which a normal fault within the Maksyutovo complex acted as the major transport plane of eclogite exhumation.The maximum Si content of phengite and minimum Fe content in clinozoisite constrain the metamorphic conditions of the later pseudomorph assemblage to be >4.5 kbar and <440°C. Rb-Sr isotopic dating of the pseudomorph assemblage results in a formation age of 339 ± 6 and 338 ± 5 Ma, respectively. These results support the recent exhumation models for this complex.