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We explore crystal growth and magma recharge during the formation of intermediate lavas using bulk rock compositions and zoning patterns and textural variation in plagioclase feldspars from Hasandag volcano in south-central Turkey. Hasandag intermediate lavas formed primarily through fractionation of the observed mineral phases, and also show abundant evidence for magma mixing and thermochemical disequilibrium. Sparse basaltic andesites originated through mixing of observed mafic and felsic lavas rather than fractionation. Plagioclase phenocrysts from all lava types have uniform core (An.sub.~39) and variable rim (An.sub.39-64) compositions, suggesting plagioclase feldspars from a common magma reservoir are present in all erupted lavas. An-rich crystal rims are regularly enriched in Mg, Fe and Ti, indicating mafic recharge and magma mixing. Mixing timescales determined by diffusion modeling of Mg profiles across core-rim boundaries suggest recharge to eruption occurs on the order of up to ~ 45 days. Thermobarometric calculations constrain shallow crustal storage of dacite to 1.5-2 kbar (~ 5 km) and 800-890 °C, with deeper reservoirs for more mafic magmas (up to 35-40 km for basalts). Abundant disequilibrium textures (sieve-textured zones, oscillatory zoning, resorbed and patchy-zoned cores) indicate mobilization of a homogeneous crystal-rich dacitic reservoir by injection of mafic magma. We suggest that incomplete and dynamic physical mixing at shallow crustal levels results in distinct crystal morphologies, some of which record punctuated ascent and storage, while others are erupted rapidly after the influx of new magma., Author(s): Helen Gall [sup.1] [sup.3], Biltan Kürkçüoglu [sup.2], Jacob Cipar [sup.1], Katherine Crispin [sup.1] [sup.4], Tanya Furman [sup.1] Author Affiliations: (1) grid.29857.31, 0000 0001 2097 4281, Department of Geosciences, Pennsylvania [...]

Hf-Pb-Os isotope compositions and highly siderophile element (HSE) abundance variations are used to evaluate the mantle source characteristics and possible effects of differentiation processes in lavas from western Turkey, where the eruption of Late Miocene to Quaternary OIB-type intraplate mafic alkaline lavas followed pre-Middle Miocene convergent margin-type volcanism. Concentrations of Os, Ir, and Ru (IPGE) in the OIB-type intraplate lavas decrease with fractionation for primitive melts (MgO > 10 wt%), suggesting that these elements reside predominantly in olivine and associated HSE retaining trace phases and behave compatibly during olivine-dominated fractionation. Fractional crystallization trends indicate distinctly lower bulk partition coefficients for IPGE in more evolved lavas, possibly reflecting a change in the fractionating assemblages. Pd and Re in the primitive melts display negative correlations with MgO, demonstrating moderately incompatible behavior of these elements during fractionation, while the significantly scattered variation in Pt against MgO may indicate the effects of micronuggets of a Pt-rich alloy. Os-rich alkaline primary lavas (>50 ppt Os) exhibit a limited range of .sup.187Os/.sup.188Os (0.1361-0.1404), with some xenolith-bearing lavas displaying depletions in .sup.187Os/.sup.188Os (0.1131-0.1232), suggesting slight compositional modification of primitive melts through contamination with highly depleted, Os-rich mantle lithosphere. More radiogenic Os isotope ratios (.sup.187Os/.sup.188Os > 0.1954) in the evolved lavas reflect contamination of the magmas by high.sup.187Os/.sup.188Os crustal material during shallow differentiation. The OIB-type lavas show limited variations in Hf and Pb isotopes with .sup.176Hf/.sup.177Hf = 0.282941-0.283051, .sup.206Pb/.sup.204Pb = 18.683-19.091, .sup.207Pb/.sup.204Pb = 15.579-15.646, .sup.208Pb/.sup.204Pb = 38.550-38.993; .sup.176Hf/.sup.177Hf ratios correlate negatively with .sup.208Pb*/.sup.206Pb*, suggesting the effects of similar mantle processes on the evolution of time-integrated Th/U and Lu/Hf. These lavas have distinctly higher .sup.176Hf/.sup.177Hf and lower .sup.208Pb*/.sup.206Pb* than the Early-Middle Miocene lavas of the region, which are interpreted as melts of enriched mantle with an overprint by sediment-derived subduction component. The source region for the OIB-type alkaline melts is interpreted to be a sub-lithospheric reservoir enriched in Hf and Pb isotopes with respect to depleted MORB mantle. Combined evaluation of Hf, Pb, and Os isotopes suggests that the relative enrichment in this domain is related to mixing of ancient oceanic crust with the ambient mantle through long-term plate recycling processes., Author(s): Ercan Aldanmaz[sup.1] , Megan Pickard[sup.2] [sup.7] , Thomas Meisel[sup.3] , Safak Altunkaynak[sup.4] , Kaan Sayit[sup.5] [sup.8] , Pinar Sen[sup.6] , Barry B. Hanan[sup.5] , Tanya Furman[sup.2] Author Affiliations: (1) [...]

Experiments were conducted to determine whether vibrations with frequencies in the sonic to ultrasonic range have any effect on the crystallization of basalt. One-atmosphere melting experiments were done at the QFM buffer on a sample of alkali basalt. A piezoelectric quartz crystal and a function generator were used to generate waves of 1.5 MHz and 150 kHz, and waves were propagated along the platinum quench wire to which the experimental charge was attached. Experiments were conducted at 1182 [degrees] C; at this temperature the sample was about 25% crystalline and contained olivine and plagioclase. Compared to the static control experiments, vibrated experiments produced plagioclase crystals that were less euhedral and had lower aspect ratios. Crystal size distributions for plagioclase were steeper for the vibrated experiments, with a higher population density of smaller crystals. The effect on olivine crystal size distributions was less. If the effect on plagioclase extends to lower vibrational frequencies, it is possible that this phenomenon may occur in magmas prior to eruption. The experimental technique developed to produce vibrations is potentially useful for improving homogeneity of melt and increasing likelihood of achieving mineral-melt equilibrium in partitioning experiments.

The year 1996 witnessed technological advances, and improved research studies and publications on environmental and engineering geology, including biogeochemistry, paleoclimatology, and satellites and remote sensing. The research, technology and publication reports on diverse topics, such as global climate change, interaction of climate and vegetation, ocean circulation and weathering processes are presented. The changing trends in the geosciences fields are discussed.

The melts of metasomatized garnet peridotite are responsible for the formation of mafic alkalic lavas in Rungwe, Tanzania. Minor metasomatic phases in the source area during melting control the geochemical elements of the lava. Carbonatite metasomatism may be the major process. Geochemical analysis of the lava shows the presence of residual garnet in the source for nephelinites. Major rift faults separate volcanoes with varying geochemistry.

The article presents long-term diversity plan in four phases for tracking the increasing diversity in the field of geosciences.