Geochemistry of volcanic rocks from the Woodlark Basin

EGU2011-12864 The Woodlark Basin east of Papua New Guinea represents one of the few places on Earth where a spreading axis propagates into continental crust. This special tectonic setting allows insights into the evolution of magma composition as continental extension and break-up changes to the formation of ocean crust. We report here geochemical results on samples collected in 2009 from the four segments closest to the continental breakup, from segment 1 which abuts the detachment fault responsible for continental extension on Moresby Seamount in the West, to segment 4, representing mature oceanic crust in the East. A total of 208 glass samples have been analyzed for their major (EMPA) and trace element (LA-ICPMS) compositions. The data show strong E-W variations. Samples ranging from tholeiitic basalt and basaltic andesite to andesite and rhyolite are found on Segment 1. They have generally high alkali values and a wide range of trace element contents and ratios. Segments 2 to 4 magmas in contrast only comprise tholeiitic basalt with lower alkali contents and a more restricted range of trace element chemistry. The geochemical differences between the segments cannot be attributed to differentiation processes alone, and different sources are required. High Ba/La, (La/Sm)N, Rb/Sr, and Th/La on Segment 1 suggest a derivation from an enriched mantle source, while low Nd/Pb and Nb/U suggest that some of the enrichment may also reflect the influence of continental crust during magma genesis. Whether this continental signature is present in the form of recycled material in the mantle or as rafted continental blocks in the axial region is at present unclear. In contrast to rocks from segment 1, trace element compositions of volcanic glasses from segments 2 to 4 show a stronger MORB signature, presumably reflecting more mature spreading in this part of the basin. The influence of continental material appears to be minimal, suggesting that uncontaminated asthenosphere quickly flows into the rift and/or that continental blocks are not retained in the axial region for long time periods following the rifting-spreading transition

On the fluid-mobility of molybdenum, tungsten, and antimony in subduction systems

Molybdenum (Mo) and tungsten (W) have long been regarded as being more or less immobile during slab fluid-induced arc magma generation. Here we characterize about 180 samples of young, predominantly mafic to intermediate tephras and lavas for their Mo, W, and antimony (Sb) concentrations, to examine the fluid-mobility of these elements in subduction systems. Samples were taken along the active arcs of the Chilean Southern Volcanic Zone (SVZ) and the Central American Volcanic Arc (CAVA). When relating Mo, W, and Sb to trace element ratios typically used to constrain the involvement of subduction fluids in magma formation, such as Ba/La or U/Th, Mo, W, and Sb are enriched in the most fluid-influenced, highest-degree melts. W/Mo ratios correlate positively with Pb/Ce, which is established to reflect a recent subduction signal or assimilation of crustal material with an ancient subduction signature, suggesting that subduction processes promote enrichment of W over Mo. This is well expressed at the SVZ and most of the CAVA; while few OIB-type rocks from Central Costa Rica form an opposite trend. Moreover, Mo/W ratios co-vary with Cl contents derived from melt inclusions, indicating that the relative degree of mobilization responds to the composition of the subduction fluid. To evaluate the mobility of Mo, W, and Sb during metamorphism in the slab, eclogites with no or minor metasomatic overprint and a fluid-induced overprint in an eclogite-blueschist sequence were investigated. None of the three elements shows a systematic variability related to metasomatism and the minor variations are interpreted to reflect protolith heterogeneity. This suggests that Mo, W and Sb remain relatively immobile up to depths of 70 km in the subduction zone

Bedeutung zirkulatorischer retinaler Ergebnisse zur Differenzierung des Normaldruckglaukoms vom primären Offenwinkelglaukom

In the given research paper the data of 149 fluorescein angiographies have been evaluated. A comparison between three diagnostic groups (primary open-angle glaucoma, normal tension glaucoma, normal subjects) has been carried out with special reference to patients with glaucoma in order to find out about differences and/or similarities between primary open- angle glaucoma and normal tension glaucoma. Following the aim of examining the pathogenesis of glaucoma desease more closely, clinical and morphological data, parameter of the visual field examination and the fluorescein angiography (arteriovenous passage time, increase in the dilution curve and fluorescein- filling time) have been evaluated. Mechanical and vascular hypotheses about the pathogenesis of glaucoma desease can be found in scientific literature. According to the vascular hypothesis, changes in the perfusion and lesser perfusion of the optic nerve head are considered to be the cause. Wether these come into existence or are a secundary consequence of the increase in intraocular pressure, is still left to discussion. In general the open-angle glaucoma is rather attributed to the mechanical hypothesis while the normal tension glaucoma is attributed to the vascular hypothesis. In this study the retinal circulation was evaluated with the help of the arteriovenous passage time. It was found to be significantly prolonged in glaucoma patients, while there was no significant difference between primary open-angle glaucoma and normal tension glaucoma. To evaluate the blood flow and the blood flow velocity, the increase in the dilution curve and the fluorescein-filling time were used. The latter is considered to be a parameter independent of intensity and quality and is more suitable for the comparison between individuals. Glaucoma patients showed diminished increase and prolonged fluorescein-filling time than the normal subjects. No significant differences could be found between primary open-angle glaucoma and normal tension glaucoma either. Despite the fact that patients with primary open-angle glaucoma showed an increased intraocular pressure when compared with patients with normal tension glaucoma, the diminished perfusion is the same in both groups. These results lead to the assumption, that vascular causes become important in normal tension glaucoma as well as in primary open-angle glaucoma. Thus the evaluation of retinal circulation is important for the examination of glaucoma desease

The human intervertebral disc as a source of DNA for molecular identification

Genetic analyses such as STR-typing are routinely used for identification purposes in forensic casework. Although genotyping techniques only require a minimum amount of DNA to provide a genetic profile, DNA quality differs not only between but also within tissues during ongoing decomposition. Initiated by a recent case where, due to the constitution of the body, preferred tissue was not available or only resulted in a partial and not usable DNA profile, the analysis of intervertebral discs as a source of DNA was considered. As the analysis of this tissue resulted in a high quality DNA profile a further study was performed in which thirty intervertebral discs dissected from bodies in different stages of decay were analyzed. All samples yielded good quality DNA in quantities suitable for STR-based amplification with no or only low degradation indices, resulting in complete genetic profiles. These results demonstrate the robustness of human intervertebral disc tissue as a source of DNA for molecular identification purposes