No abstract

Sector-zoned clinopyroxene is common in igneous rocks, but has been overlooked in the study of magmatic processes. Whilst concentric zoning is commonly used as a record of physicochemical changes in the melt feeding crystal growth, clinopyroxene is also highly sensitive to crystallisation kinetics. In sector-zoned crystals, the fidelity of compositional changes as recorders of magma history is dubious and the interplay between thermodynamic and kinetic controls remains poorly understood. Here we combine electron probe and laser ablation micro-chemical maps of titanaugite crystals from Mt. Etna (Sicily, Italy) to explore the origin of sector zoning at the major and trace element levels, and its implications for the interpretation of magmatic histories. Elemental maps afford the possibility to revisit sector zoning from a spatially controlled perspective. The most striking observation is a clear decoupling of elements into sectors vs. concentric zones within single crystals. Most notably, Al-Ti enrichments and Si-Mg depletions in the prism sectors {1 0 0}, {1 1 0} and {0 1 0} relative to the hourglass (or basal) sectors {À1 1 1} correlate with enrichments in rare earth elements and highly charged high field strength elements due to cation exchanges driven by kinetic effects. In contrast, transition metals (Cr, Ni, Sc) show little partitioning into sectors and strong enrichments in concentric zones following resorbed surfaces, interpreted as evidence of mafic recharge and magma mixing. Our results document that kinetic partitioning has minor effects on the compositional variations of cations with low charge relative to the ideal charge/radius of the structural site they occupy in the clinopyroxene lattice. We suggest that this may be due to a lower efficiency in charge balance mechanisms compared to highly charged cations. It follows that compatible metals such as Cr can be considered trustworthy recorders of mafic intrusions and eruption triggers even in sector-zoned crystals. We also observe that in alkaline systems where clinopyroxene crystallisation takes place at nearequilibrium conditions, sector zoning should have little effect on Na-Ca partitioning and in turn, on the application of experimentally calibrated thermobarometers. Our data show that whilst non-sector-zoned crystals form under relatively stagnant conditions, sector zoning develops in response to low degrees of undercooling, such as during slow magma ascent. Thus, we propose that the chemistry of sector-zoned crystals can provide information on magma history, eruption triggers, and possibly ascent rates.

Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of 13C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars.

Very little is known on the occurrence and abundance in the environment of dicarboxylated metabolites (CAPECs) of A9PE surfactants. We have monitored monthly CAPECs and the other A9PE metabolites in effluents of five activated sludge sewage treatment plants (STPs) for 4 months. The analytical procedure is based on solid-phase extraction with a Carbograph 4 cartridge and liquid chromatography−mass spectrometry (MS) with an electrospray (ES) interface. On extracting 25 and 250 mL of respectively untreated and treated sewage samples, analyte recoveries ranged between 87 and 93% with RSDs no larger than 10%. Unexpectedly, data averaged on 20 samples of treated sewages showed that CAPECs were the dominant products of the A9PE biotransformation, accounting for 66% of all the metabolites leaving the plants. As a total, CA8PEC and CA6PEC represented 87% of the CAPEC class. On the average, CAPEC amounts having one ethoxy unit (CAPE2Cs) were almost double those of species having only a phenoxy acid moiety (CAPE1Cs). CAPEC species having more than four ethoxy units were never detected during our survey.

A simple and rapid method able to determine residues of 12 sulfonamide (SAs) antibacterials in cattle and trout muscle tissues is presented. This method is based on the matrix solid-phase dispersion technique with hot water as extractant followed by liquid chromatography-mass spectrometry (LC-MS). The LC-MS instrumentation was equipped with an electrospray source and a single quadrupole. After 0.8 g of a flesh sample containing the analytes is deposited on sand (crystobalite), this material is packed into an extraction cell. SAs are extracted by flowing 4 mL of water through the cell heated at 80 degrees C. A 0.5-mL aliquot of the bovine tissue extract is then directly injected into the LC column, while the fish tissue extract is filtered prior to LC-MS analysis. MS data acquisition was performed in the positive-ion mode and monitoring at least three ions for each target compound. Confirmatory ions were produced by the in-source collision-induced dissociation process. At the tolerance levels issued by the EU and U.S. Food and Drug Administration, i.e., 100 ppb, recovery of the analytes in bovine and trout muscle tissues was 75-98% with RSDs ranging between 1 and 8%. Estimated limits of quantification (S/N = 10) were 6-15 ppb for SAs in bovine muscle tissue and 3-13 ppb in trout fillet. When trying to reduce the analysis time by using a short chromatographic run time, severe ion signal suppression was experienced for the early-eluted SAs. This effect was traced to competition effects by polar endogenous coextractives, maybe proteinaceous species, which are eluted in the first part of the chromatographic run. This unwelcome effect was removed by simply adopting more selective chromatographic conditions.