Reconstruction of magma chamber processes preserved in olivine-phlogopite micro-ijolites from the Oldoinyo Lengai, Tanzania

A detailed petrographic and mineralogical investigation of olivine-phlogopite micro-ijolite xenoliths from Oldoinyo Lengai, Tanzania indicates a complex evolutional history. These xenoliths consist of diverse textural subdomains characterized by minerals ranging from early-formed olivine, through diopside-hosted perovskite and phlogopite, to evolved aegirine-augite and titanite. Thermometry and mineral compositions in the subdomains suggest crystallization temperatures from 1070–970 °C to 850–700 °C at plutonic pressures and SiO2-activities controlled by perovskite-titanite equilibria. Double coronas are a characteristic textural feature of the olivine-phlogopite micro-ijolite, consisting of olivine cores surrounded by an inner clinopyroxene corona and an outer phlogopite corona. These double coronas might have formed during early magma chamber processes, including magma movement to a subsequent chamber resulting in dissolution of olivine with subsequent crystallization and accumulation of diopside and phlogopite. Diopside−aegirine-augite compositional zonation indicates several magma injections followed by cooling periods, during the formation of micro-ijolite groundmass. Mg# (80–83) and Ca (0.1–0.3 in wt%) contents of olivine together with the presence of primary melt inclusions in clinopyroxene, phlogopite, and nepheline indicate a magmatic origin from a possible parental olivine-nephelinite melt. There is evidence for subsolidus, or near-solidus, re-equilibration processes as indicated by the reaction of olivine with titanite forming symplectitic textures of ilmenite and diopside with minor zirconolite. Ti-exchange between phlogopite phenocrysts and other Ti-bearing minerals (perovskite, titanite, magnetite) resulted in ∼750 °C equilibrium temperatures for phlogopite, which are much lower than mafic magmatic (>900 °C) conditions. Calculated subsolidus temperatures suggest crystallization of olivine-phlogopite micro-ijolites over a 10–20 km depth interval

Mechanism of formation of the honeycomb-like structures by the regime of the reversing current (RC) in the second range

Electrodeposition of copper in the hydrogen co-deposition range by the regime of reversing current (RC) in the second range has been investigated by determination of the average current efficiency for hydrogen evolution reaction and by scanning electron (SEM) and optical (OM) microscopic analysis of the obtained deposits. Keeping the cathodic current density, the cathodic and the anodic pulses constant in all experiments, the anodic current density (ja) values were varied: 40, 80, 160, 240 and 320 mA cm−2. The Cu deposits produced by the RC regimes with different anodic current density values were compared with that obtained in a constant galvanostatic regime (DC) at the current density equal to the cathodic current density in the RC regimes. The honeycomb-like structures were formed in the DC regime and by the RC regimes with ja of 40 and 80 mA cm−2. The hole size in them was in the 60–70 μm range. Due to the decrease of quantity of evolved hydrogen with increasing anodic current density, the larger dish-like holes with dendrites at their bottom and shoulder were formed with ja values of 160, 240 and 320 mA cm−2. The maximum number of holes, and hence, the largest specific surface area of the honeycomb-like electrodes was obtained with ja = 80 mA cm−2, that can be ascribed to a suppression of coalescence of neighboring hydrogen bubbles. Application of the RC regime also led to the increase of uniformity of structures, what is concluded by cross section analysis of the formed honeycomb-like electrodes. For the first time, mechanism of Cu electrodeposition in the hydrogen co-deposition range by the RC regime in the second range was proposed and discussed.This is peer-reviewed version of the article: Journal of Electroanalytical Chemistry, 2019, 833, 401-410, [https://doi.org/10.1016/j.jelechem.2018.12.021][http://cer.ihtm.bg.ac.rs/handle/123456789/2986

Fluid infiltration in the lithospheric mantle beneath the Rio Grande Rift, USA: a fluid-inclusion study

Spinel-peridotite xenoliths, hosted in alkali basalts (similar to 15 Ma), were collected from Adam's Diggings in the western margin of the Rio Grande Rift (RGR), New Mexico, USA. We selected five representative spinel-peridotite xenoliths, showing abundant fluid inclusions (FIs). Petrographic observations allowed the distinction of two generations of fluid-inclusion assemblages, both hosted in orthopyroxenes, namely Type-1 (earlier) and Type-2 (later). Both types of fluid inclusions were characterized combining microthermometry, high-resolution Raman micro-spectroscopy, and focused ion beam-scanning electron microscopy. The results of this study indicate that the timing and depth of entrapment, as well as the composition of trapped fluid were different between Type-1 and Type-2 FIs. The earlier fluid infiltration (C-O-N-S) happened before or during formation of exsolution lamellae and was trapped as Type-1 FIs in the cores of orthopyroxenes, whereas the later fluid infiltration (C-O-H-S) was trapped as Type-2 FIs after the formation of the orthopyroxene porphyroclasts with exsolution lamellae. The two fluid percolation events in the Adam's Diggings peridotites indicate the complexity of mantle fluids around the RGR. During ascent of the xenoliths within a basaltic lava, post-entrapment reactions produced magnesite and quartz in Type-1 FIs and magnesite and talc in Type-2 FIs as reaction products of the fluid and its host mineral (orthopyroxene)

C–O–H–S fluids and granitic magma : how S partitions and modifies CO2 concentrations of fluid-saturated felsic melt at 200 MPa

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Contributions to Mineralogy and Petrology 162 (2011): 849-865, doi:10.1007/s00410-011-0628-1.Hydrothermal volatile-solubility and partitioning experiments were conducted with fluid-saturated haplogranitic melt, H2O, CO2, and S in an internally heated pressure vessel at 900°C and 200 MPa; three additional experiments were conducted with iron-bearing melt. The run-product glasses were analyzed by electron microprobe, FTIR, and SIMS; and they contain ≤ 0.12 wt% S, ≤ 0.097 wt.% CO2, and ≤ 6.4 wt.% H2O. Apparent values of log ƒO2 for the experiments at run conditions were computed from the [(S6+)/(S6++S2-)] ratio of the glasses, and they range from NNO-0.4 to NNO+1.4. The C-O-H-S fluid compositions at run conditions were computed by mass balance, and they contained 22-99 mol% H2O, 0-78 mol% CO2, 0-12 mol% S, and < 3 wt% alkalis. Eight S-free experiments were conducted to determine the H2O and CO2 concentrations of melt and fluid compositions and to compare them with prior experimental results for C-O-H fluid-saturated rhyolite melt, and the agreement is excellent. Sulfur partitions very strongly in favor of fluid in all experiments, and the presence of S modifies the fluid compositions, and hence, the CO2 solubilities in coexisting felsic melt. The square of the mole fraction of H2O in melt increases in a linear fashion, from 0.05-0.25, with the H2O concentration of the fluid. The mole fraction of CO2 in melt increases linearly, from 0.0003-0.0045, with the CO2 concentration of C-O-H-S fluids. Interestingly, the CO2 concentration in melts, involving relatively reduced runs (log ƒO2 ≤ NNO+0.3) that contain 2.5-7 mol% S in the fluid, decreases significantly with increasing S in the system. This response to the changing fluid composition causes the H2O and CO2 solubility curve for C-O-H-S fluid-saturated haplogranitic melts at 200 MPa to shift to values near that modeled for C-O-H fluid-saturated, S-free rhyolite melt at 150 MPa. The concentration of S in haplogranitic melt increases in a linear fashion with increasing S in C-O-H-S fluids, but these data show significant dispersion that likely reflects the strong influence of ƒO2 on S speciation in melt and fluid. Importantly, the partitioning of S between fluid and melt does not vary with the (H2O/H2O+CO2) ratio of the fluid. The fluid-melt partition coefficients for H2O, CO2, and S and the atomic (C/S) ratios of the run-product fluids are virtually identical to thermodynamic constraints on volatile partitioning and the H, S, and C contents of pre-eruptive magmatic fluids and volcanic gases for subduction-related magmatic systems thus confirming our experiments are relevant to natural eruptive systems.This research was supported in part by National Science Foundation awards EAR 0308866 and EAR-0836741 to J.D.W

The role of water and compression in the genesis of alkaline basalts: Inferences from the Carpathian-Pannonian region

We present a new model for the formation of Plio-Pleistocene alkaline basalts in the central part of the Carpathian-Pannonian region (CPR). Based on the structural hydroxyl content of clinopyroxene megacrysts, the ‘water’ content of their host basalts is 2.0–2.5 wt.%, typical for island arc basalts. Likewise, the source region of the host basalts is ‘water’ rich (290–660 ppm), akin to the source of ocean island basalts. This high ‘water’ content could be the result of several subduction events from the Mesozoic onwards (e.g. Penninic, Vardar and Magura oceans), which have transported significant amounts of water back to the upper mantle, or hydrous plumes originating from the subduction graveyard beneath the Pannonian Basin. The asthenosphere with such a relatively high ‘water’ content beneath the CPR may have been above the ‘pargasite dehydration’ (90 km) solidi. This means that neither decompressional melting nor the presence of voluminous pyroxenite and eclogite lithologies are required to explain partial melting. While basaltic partial melts have been present in the asthenosphere for a long time, they were not extracted during the syn-rift phase, but were only emplaced at the onset of the subsequent tectonic inversion stage at ~8–5 Ma. We propose that the extraction has been facilitated by evolving vertical foliation in the asthenosphere as a response to the compression between the Adriatic indenter and the stable European platform. The vertical foliation and the prevailing compression effectively squeezed the partial basaltic melts from the asthenosphere. The overlying lithosphere may have been affected by buckling in response to compression, which was probably accompanied by formation of deep faults and deformation zones. These zones formed conduits towards the surface for melts squeezed out of the asthenosphere. This implies that basaltic partial melts could be present in the asthenosphere in cases where the bulk ‘water’ content is relatively high (>~200 ppm) at temperatures exceeding ~1000–1100 °C. These melts could be extracted even under a compressional tectonic regime, where the combination of vertical foliation in the asthenosphere and deep fractures and deformation zones in the folded lithosphere provides pathways towards the surface. This model is also valid for deep seated transpressional or transtensional fault zones in the lithosphere

Thermoanalytical studies on complexes of clotrimazole with cyclodextrins

?-Cyclodextrin and dimethyl-ß-cyclodextrin were used as solubilizing agents for a very poorly water-soluble drug, an imidazole derivative antifungal agent, clotrimazole; with the aim of improving the physicochemical properties of the drug. Solid products were prepared by physical mixing, kneading, precipitation and spray-drying methods in 1:1 and 1:2 drug:cxyclodextrin molar ratios. Drug interactions were studied by thermoanalytical methods such as DSC, DTA, TG and DTG, X-ray diffractometry and Fourier transformation-infrared spectroscopy. The results demonstrated the formation of inclusion complexes in some products.Hungarian Scientific Research Fund: T 026579 T 03250/99This study was supported by the Hungarian National Science Fund (OTKA) (Project number: T 026579) and by the Health Science Council (Project number: T 03250/99). The authors would like to thank Dr. Cs. Novak for his kind contribution. -