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Chadwick J.P.,VU University Amsterdam | Chadwick J.P.,Trinity College Dublin | Troll V.R.,Uppsala University | Waight T.E.,Copenhagen University | And 3 more authors.
Contributions to Mineralogy and Petrology | Year: 2013

Recent basaltic-andesite lavas from Merapi volcano contain abundant and varied igneous inclusions suggesting a complex sub-volcanic magmatic system for Merapi volcano. In order to better understand the processes occurring beneath Merapi, we have studied this suite of inclusions by petrography, geochemistry and geobarometric calculations. The inclusions may be classified into four main suites: (1) highly crystalline basaltic-andesite inclusions, (2) co-magmatic enclaves, (3) plutonic crystalline inclusions and (4) amphibole megacrysts. Highly crystalline basaltic-andesite inclusions and co-magmatic enclaves typically display liquid-liquid relationships with their host rocks, indicating mixing and mingling of distinct magmas. Co-magmatic enclaves are basaltic in composition and occasionally display chilled margins, whereas highly crystalline basaltic-andesite inclusions usually lack chilling. Plutonic inclusions have variable grain sizes and occasionally possess crystal layering with a spectrum of compositions spanning from gabbro to diorite. Plagioclase, pyroxene and amphibole are the dominant phases present in both the inclusions and the host lavas. Mineral compositions of the inclusions largely overlap with compositions of minerals in recent and historic basaltic-andesites and the enclaves they contain, indicating a cognate or 'antelithic' nature for most of the plutonic inclusions. Many of the plutonic inclusions plot together with the host basaltic-andesites along fractional crystallisation trends from parental basalt to andesite compositions. Results for mineral geobarometry on the inclusions suggest a crystallisation history for the plutonic inclusions and the recent and historic Merapi magmas that spans the full depth of the crust, indicating a multi-chamber magma system with high amounts of semi-molten crystalline mush. There, crystallisation, crystal accumulation, magma mixing and mafic recharge take place. Comparison of the barometric results with whole rock Sr, Nd, and Pb isotope data for the inclusions suggests input of crustal material as magma ascends from depth, with a significant late addition of sedimentary material from the uppermost crust. The type of multi-chamber plumbing system envisaged contains large portions of crystal mush and provides ample opportunity to recycle the magmatic crystalline roots as well as interact with the surrounding host lithologies. © 2012 Springer-Verlag.

Nuzzo M.,elmholtz Center for Ocean Research Kiel | Nuzzo M.,National Laboratory of Energy and Geology | Nuzzo M.,Faculdadede Ciencias Dauniversidade Of Lisbon | Elvert M.,University of Bremen | And 5 more authors.
Earth and Planetary Science Letters | Year: 2012

Hydrocarbon seeps are ubiquitous at gas-prone Cenozoic deltas such as the Nile Deep Sea Fan (NDSF 22NDSF:Nile Deep Sea Fan.) where seepage into the bottom water has been observed at several mud volcanoes (MVs 33MV: mud volcano.) including North Alex MV (NAMV 44NAMV: North Alex mud volcano.). Here we investigated the sources of hydrocarbon gases and sedimentary organic matter together with biomarkers of microbial activity at four locations of NAMV to constrain how venting at the seafloor relates to the generation of hydrocarbon gases in deeper sediments. At the centre, high upward flux of hot (70°C) hydrocarbon-rich fluids is indicated by an absence of biomarkers of Anaerobic Oxidation of Methane (AOM) and nearly constant methane (CH 4) concentration depth-profile. The presence of lipids of incompatible thermal maturities points to mixing between early-mature petroleum and immature organic matter, indicating that shallow mud has been mobilized by the influx of deep-sourced hydrocarbon-rich fluids. Methane is enriched in the heavier isotopes, with values of δ 13C~-46.6‰ VPDB and δD ~-228‰ VSMOW, and is associated with high amounts of heavier homologues (C 2+) suggesting a co-genetic origin with the petroleum.On the contrary at the periphery, a lower but sustained CH 4 flux is indicated by deeper sulphate-methane transition zones and the presence of 13C-depleted biomarkers of AOM, consistent with predominantly immature organic matter. Values of δ 13C-CH 4~-60‰ VPDB and decreased concentrations of 13C-enriched C 2+ are typical of mixed microbial CH 4 and biodegraded thermogenic gas from Plio-Pleistocene reservoirs of the region. The maturity of gas condensate migrated from pre-Miocene sources into Miocene reservoirs of the Western NDSF is higher than that of the gas vented at the centre of NAMV, supporting the hypothesis that it is rather released from the degradation of oil in Neogene reservoirs. Combined with the finding of hot pore water and petroleum at the centre, our results suggest that clay mineral dehydration of Neogene sediments, which takes place posterior to reservoir filling, may contribute to intense gas generation at high sedimentation rate deltas. © 2012 Elsevier B.V.

Hinrichsen H.-H.,elmholtz Center for Ocean Research Kiel | Kuhn W.,Institute of Oceanography | Peck M.A.,Institute for Hydrobiology and Fisheries Science | Voss R.,elmholtz Center for Ocean Research Kiel
Progress in Oceanography | Year: 2012

We employed coupled 3-D biophysical models to better understand the effects of physical forcing conditions as well as differences in vertical distribution and growth performance on the spatial distribution of larval sprat (. Sprattus sprattus) in the North and the Baltic Sea. Our model simulations analysed the influence of abiotic and biotic forcing variability on larval transport and the seasonal and inter-annual variability in spatial distribution of larvae originating from different spawning areas in each of the two systems. Due to strong spatial and temporal differences in temperature, drift durations differed between the two ecosystems. During cold spring and warm summer periods, drift durations in the Baltic were ∼35 and 15. days, respectively, but were somewhat shorter (30 and 10. d) in the North Sea. Changes in larval feeding rates markedly impacted larval growth rate and stage duration, and, hence, environmental histories experienced by larvae as well as their final distribution. Generally, specific spawning sites were relatively well connected to specific juvenile nursery areas in the Baltic. However, in the North Sea, considerable mixing of sprat populations occurred with frontal areas acted as convergence zones for older larvae originating from different spawning sites. The mixing and/or co-occurrence of 18-mm larvae from different source regions were greatest (least) in the early spring (summer) for larvae at colder (warmer) temperatures having longer (shorter) drift durations. Generally, such high mixing probability would not promote small- or medium-scale population distinctness of North Sea sprat. The results of our coupled hydrodynamic/trophodynamic model simulations provide a baseline in quantifying and understanding larval sprat transport in these different ecosystems and exemplify the extent to which environmental variability (e.g., differences in temperature as well as prey availability) can influence spatial distributions of larval fish. © 2012 Elsevier Ltd.

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