Focused fluid transfer through the mantle above subduction zones

Volcanic arcs above subduction zones are enriched in volatiles and fluid-mobile elements with respect to mid-oceanic ridge basalts. There is general consensus that this particular subduction zone signature is generated by fluid-induced extraction of these elements from subducted oceanic crust and its sedimentary cover. However, how these fluids are transferred through the mantle wedge to the locus of partial melting and what modification the fluids will experience is unresolved. Here we investigate the interaction of slab fluids with the mantle wedge through a series of high-pressure experiments. We explore two end-member processes of focused and porous reactive flow of hydrous slab melts through the mantle. Transfer by porous flow leads to the formation of hydrous minerals that sequester fluid-mobile elements and residual fluids characterized by trace element patterns inconsistent with typical arc lavas. In contrast, no hydrous minerals are formed in the reaction zone of experiments mimicking focused flow, and the typical trace element signature acquired during fluid extraction from the slab is preserved, indicating that this is an efficient process for element transfer through the mantle wedge.

New online method for water isotope analysis of speleothem fluid inclusions using laser absorption spectroscopy (WS-CRDS)

A new online method to analyse water isotopes of speleothem fluid inclusions using a wavelength scanned cavity ring down spectroscopy (WS-CRDS) instrument is presented. This novel technique allows us simultaneously to measure hydrogen and oxygen isotopes for a released aliquot of water. To do so, we designed a new simple line that allows the online water extraction and isotope analysis of speleothem samples. The specificity of the method lies in the fact that fluid inclusions release is made on a standard water background, which mainly improves the δ D robustness. To saturate the line, a peristaltic pump continuously injects standard water into the line that is permanently heated to 140 °C and flushed with dry nitrogen gas. This permits instantaneous and complete vaporisation of the standard water, resulting in an artificial water background with well-known δ D and δ18O values. The speleothem sample is placed in a copper tube, attached to the line, and after system stabilisation it is crushed using a simple hydraulic device to liberate speleothem fluid inclusions water. The released water is carried by the nitrogen/standard water gas stream directly to a Picarro L1102-i for isotope determination. To test the accuracy and reproducibility of the line and to measure standard water during speleothem measurements, a syringe injection unit was added to the line. Peak evaluation is done similarly as in gas chromatography to obtain &delta D; and δ18O isotopic compositions of measured water aliquots. Precision is better than 1.5 ‰ for δ D and 0.4 ‰ for δ18O for water measurements for an extended range (−210 to 0 ‰ for δ D and −27 to 0 ‰ for δ18O) primarily dependent on the amount of water released from speleothem fluid inclusions and secondarily on the isotopic composition of the sample. The results show that WS-CRDS technology is suitable for speleothem fluid inclusion measurements and gives results that are comparable to the isotope ratio mass spectrometry (IRMS) technique.

Development of a method for analysis of ketamine and norketamine enantiomers in equine brain and cerebrospinal fluid by capillary electrophoresis

Ketamine and norketamine are being transported across the blood brain barrier and are also entering from blood into cerebrospinal fluid (CSF). Enantioselective distributions of these compounds in brain and CSF have never been determined. The enantioselective CE based assay previously developed for equine plasma was adapted to the analysis of these compounds in equine brain via use of an acidic pre-extraction of interferences prior to liquid/liquid extraction at alkaline pH. CSF can be treated as plasma. With 100 mg of brain tissue and 0.5 mL of CSF or plasma, assay conditions for up to 30 nmol/g and 6 μM, respectively, of each enantiomer with LOQs of 0.5 nmol/g and 0.1 μM, respectively, were established and the assays were applied to equine samples. CSF and plasma samples analyzed stemmed from anesthetized patient horses and brain, CSF and plasma were obtained from anesthetized horses that were euthanized with an overdose of pentobarbital. Data obtained indicate that ketamine and norketamine enantiomers are penetrating into brain and CSF with those of ketamine being more favorably transported than norketamine, whereas metabolites of norketamine are hindered. More work is required to properly investigate possible stereoselectivities of the ketamine metabolism and transport of metabolites from blood into brain tissue and CSF.