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We present an extensive study of rehomogenized olivine‐hosted melt inclusions, olivine phenocrysts, and chromian spinel inclusions to explore the link between geodynamic conditions and the origin and composition of Pliocene–Quaternary intraplate magmatism in Anatolia at Kula, Ceyhan‐Osmaniye, and Karacadağ. Exceptional compositional variability of these products reveals early and incomplete mixing of distinct parental melts in each volcanic center, reflecting asthenospheric and lithospheric mantle sources. The studied primitive magmas consist of (1) two variably enriched ocean island basalt (OIB)‐type melts in Kula; (2) both OIB‐type and plume mid‐ocean ridge basalt (P‐MORB)‐like melts beneath Toprakkale and Üçtepeler (Ceyhan‐Osmaniye); and (3) two variably enriched OIB‐type melts beneath Karacadağ. Estimated conditions of primary melt generation are 23–9 kbar, 75–30 km, and 1415–1215 °C for Kula; 28–19 kbar, 90–65 km, and 1430–1350 °C for Toprakkale; 23–18 kbar, 75–60 km, and 1400–1355 °C for Üçtepeler; and 35–27 kbar, 115–90 km, and 1530–1455 °C for Karacadağ, the deepest levels of which correspond to the depth of the lithosphere‐asthenosphere boundary in all regions. Although magma ascent was likely facilitated by local deformation structures, recent Anatolian intraplate magmatism seems to be triggered by large‐scale mantle flow that also affects the wider Arabian and North African regions. We infer that these volcanics form part of a much wider Arabian‐North African intraplate volcanic province, which was able to invade the Anatolian upper plate through slab gaps., Key Points We present a melt inclusion study of recent primitive Anatolian intraplate magmas at Kula, Ceyhan‐Osmaniye, and KaracadağStudied magmas indicate mixing of two primary melt components, which reflect asthenospheric and lithospheric mantle sourcesAnatolian intraplate magmatism seems to be triggered by large‐scale mantle flow that also affects the wider Arabian and North African region

Background, Aims and Scope. Lakes developing in volcano craters can become highly acidic through the influx of volcanic gases, yielding one of the chemically most extreme natural environments on earth. The Kawah Ijen crater lake in East Java (Indonesia) has a pH < 0.3. It is the source of the extremely acidic and metal-polluted river Banyupahit (45 km). The lake has a significant impact on the river ecosystem as well as on a densely populated area downstream, where agricultural fields are irrigated with water with a pH between 2.5 and 3.5. The chemistry of the river water seemed to have changed over the past decade and the negative effect in the irrigation area increased. A multidisciplinary approach was used to investigate the altered situation and to get insight in the water chemistry and the hydrological processes influencing these alterations. Moreover, a first investigation of the effects of the low pH on ecosystem health and human health was performed. Methods. Water samples were taken at different sites along the river and in the irrigation area. Sampling for macroinvertebrates was performed at the same sites. Samples of soil and crop were taken in the irrigation area. All samples were analysed for metals (using ICP-AES) and other elements, and concentrations were compared to local and international standards. Results and Discussion. The river carries a very high load of SO4, NH4 PO4 Cl, F, Fe, Cu, Pb, Zn, Al and other potentially toxic elements. Precipitation and discharge data over the period of 1980-2000 clearly show that the precipitation on the Ijen plateau influences water chemistry of the downstream river. Metal concentrations in the river water exceed the concentrations mentioned in Indonesian and international quality guidelines, even in the downstream river and the irrigation area. Some metal concentrations are extremely high, especially iron (up to 1,600 mg/l) and aluminium (up to 3,000 mg/l). The food-webs in the acidic parts of the river are highly underdeveloped. No invertebrates were present in the extremely acidic water and, at pH 2.3, only chironomids were found. This also holds true for the river water with pH 3.3 in the downstream area. Agricultural soils in the irrigation area have a pH of 3.9 compared to a pH of 7.0 for soils irrigated with neutral water. Decreased yields of cultivated crops are probably caused by the use of Al containing acidic irrigation water. Increased levels of metals (especially Cd, Co, Ni and Mn) are found in different foodstuffs, but still remain within acceptable ranges. Considering local residents' diets, Cd levels may lead to an increased risk for the human health. Fluoride exposure is of highest concern, with levels in drinking water exceeding guideline values and a lot of local residents suffering from dental fluorosis. Conclusions, Recommendations and Outlook. In short, our data indicate that the Ijen crater lake presents a serious threat to the environment as well as human health and agricultural production. © 2005 ecomed publishers (Verlagsgruppe Hüthig Jehle Rehm GmbH).

Rungwe in southern Tanzania is an active volcanic centre in the East African Rift System, characterised by Plinian-style explosive eruptions of metaluminous to slightly peralkaline trachytic silica-undersaturated magmas during its late Holocene history. Variations in whole-rock major and trace element compositions of erupted products have been investigated, in combination with electron microprobe data for melt inclusions and phenocrysts comprising sanidine, biotite, clinopyroxene, titanomagnetite, ilmenite, haüyne, titanite, apatite and traces of plagioclase and amphibole. Compositional variations largely reflect fractional crystallisation, with a limited influence of magma mixing. Subtle variations in whole-rock composition and mineralogical characteristics between and within deposits, suggest the existence of a chemically zoned trachytic magma chamber beneath Rungwe. For the two most important studied deposits, the Isongole and Rungwe Pumice, co-existing Fe–Ti oxides constrain pre-eruptive temperature to 915–950 °C and oxygen fugacity to NNO + 0.25–NNO + 0.45. For the Rungwe Pumice, melt inclusions suggest that the melt was water-undersaturated (maximum inferred H2O concentration 5.5 wt.%). In the range of the defined pre-eruptive temperatures, this corresponds to melt viscosities as low as 103.3 Pa · s, i.e. significantly lower than magmas that typically generate highly explosive eruptions. Because no microlites formed in the conduit during ascent, which would have strongly increased the effective magma viscosity, the highly explosive nature of the eruptions may be attributable to a crucial role of exsolved CO2 and S phases, and very high ascent rates.

Multiple sources for ultrapotassic arc magmas from Batu Tara Volcano, Indonesia. 12th Annual V.M. Goldschmidt Conference. Davos-2002, Switzerland, Geochem. Cosmochim. Acta, v. 66, p. A324

Mt. Amiata, a Pleistocene volcanic complex in south Tuscany consists mainly of silicic (62-67 wt.% Si02) lavas and domes, many of which contain abundant metamorphic and mafic igneous inclusions. The results of a detailed geochemical and petrological study indicate a bimodal magmatic system where magma-mixing and wall-rock assimilation were the main pre-eruptive processes in a reservoir underlying the volcano. The metamorphic inclusions are fragments of a contact aureole that formed around the magma chamber in regionally metamorphosed rocks, predominantly schists, gneisses and minor quartzites of the pre-Mesozoic crystalline basement. Aluminous, silica-deficient inclusions that form the largest group, are considered to originate from quartz-poor mica-schists by complex assimilation processes involving extraction of partial melt, interdiffusion between co-existing liquids and mineralliquid reactions. The igneous inclusions represent blobs of hybrid magma, and form, together with some subordinate intermediate lavas and the host lavas an almost complete mixing array, as a result of the inflow of mafic magma into the acid reservoir. Processes of selective chemical exchange superimposed on mixing were probably of little importance. Consequently, the end-members can be identified as an acid Tuscan-type magma of crustal anatectic origin, and a primitive mafic Roman-type magma of the high-K series that is commonly considered to be derived from the upper mantle. This separated origin and the fact that both magmas have some chemical characteristics in common (an enrichment in potassium and a number of related elements) could imply that portions of the lower crust and upper mantle were metasomatized by the same fluid prior to melting.

Climate conditions during Earth’s earliest history were very different from today. Knowledge about this issue is crucial for understanding the development of life on our planet. Billions of years ago, silica-rich rocks formed on the ocean floor, and a small volume is still preserved in surface exposures. They carry traces that provide insight into the properties of ancient seawater. Measuring the proportions of silicon isotopes in these rocks is considered as a promising approach to determine the temperature of seawater that existed long ago. However, application of silicon isotopes is a relatively new research field, and the interpretation of isotope compositions of old as well as recent deposits is hampered by lack of knowledge on the fractionation behavior of the isotopes. The main objective of this research was to expand insights into the fundamental factors that determine the isotope composition of a silica-rich chemical sediment. Through experiments and measurements on deposits from Icelandic hot springs, it has been determined how and to what extent the isotopes fractionate when silica precipitates from a saturated solution. For the first time the influence of temperature on the fractionation behavior has been demonstrated and could be quantitatively constrained. In addition, evidence is provided that properties of the substrate onto which silica is deposited, transformations of the silica minerals after deposition, and provenance of the silica in a seawater basin, are also important factors that influence the ultimate isotope composition of a silica-rich chemical sediment. The results of this research may have significant implications. They enable us to derive more reliable interpretations when using silicon isotopes as tracers of active processes or environmental conditions at the present-day surface, provide a new guideline for the interpretation of isotope data from ancient silica deposits, and question earlier conclusions on the temperature of Precambrian seawater