The X-ray properties of optically selected z > 0.6 clusters in the European Southern Observatory Distant Cluster Survey

We present XMM–Newton observations of three optically selected   z > 0.6  clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and – unlike other high-redshift, optically selected clusters – are consistent with the T –σ and   L _X–σ  relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by   z ∼ 0.8  .     

Early diagenetic alteration of chlorophyll-a and bacteriochlorophyll-a in a contemporaneous marl ecosystem; Florida Bay

This report covers the analyses of tetrapyrrole pigments in sediments and numerous source biota from northern central Florida Bay. Sediment cores were all carbonate marls and ‘bedrock’ (Pleistocene limestones) was typically at 0.6–1.2 m bsf. (below sea floor). Extraction of the sediments was performed using tetrahydrofuran, shown to be 3–7 times as effective as more common solvents. Surficial sediments were found to contain a pigment distribution indicating a diatomaceous-cyanobacterial biofilm/mat underlain with purple sulfur bacteria as the microphytobenthos. Downhole trends in pigment diagenesis revealed differences due to paleoenvironment. That is, when bacteriochlorophyll-a (BCHLa) plus derivatives were elevated, indicating strong syn-depositional anoxia, the pheophytins-a (PTINsa) were the major chlorophyll-a (CHLa) derivatives. Conversely, when BCHL-a plus derivatives were low, indicating oxic to dys-oxic syn-depositional conditions, then pyropheophorbide-a (pPBIDa) and 13², 17²-cyclopheophorbide-a (CYCLO) were strongly dominant. The generation of cyclopheophorbide in carbonate marls with weakly anoxic to dysoxic syn-depositional conditions may yield an oil-source paleoenvironmental marker for bitumen containing compounds such as bicycloalkanoporphyrins (BiCAPs). Downhole conversions were observed for the following diagenetic steps; CHLa to pheophytin-a (PTINa), PTINa to pyropheophytin-a (pPTINa), pPBIDa to CYCLO, BCHLa to bacteriopheophytin-a (BPTINa), and BPTINa to bacteriopyropheophytin-a (BpPTINa).     

Insights into Li and Li isotope cycling and sub-arc metasomatism from veined mantle xenoliths,Kamchatka

Harzburgitic xenoliths cut by pyroxenite veins from Avachinsky volcano, Kamchatka, are derived from the sub-arc mantle and record element transfer from the slab to the arc. Olivine and orthopyroxene in the harzburgites have Li isotopic compositions (δ⁷Li = +2.8 to +5.6) comparable to estimates of the upper mantle (δ⁷Li ~ +4 ± 2). The pyroxenite veins, which represent modal metasomatism and may therefore provide information about the metasomatic agent, have mantle-normalized trace element characteristics that suggest overprinting of their mantle source by an aqueous, slab-derived fluid. These include relative enrichments of Pb over Ce, U over Th and Sr over Nd. Li is enriched relative to the HREE, and ortho- and clinopyroxene from the veins are in Li elemental and isotopic equilibrium with each other and the surrounding harzburgite. Vein samples (δ⁷Li = +3.0 to +5.0) do not record a significant slab-derived δ⁷Li signature. These observations can be reconciled if slab Li diffusively re-equilibrates in the mantle wedge. Modeling demonstrates that Li equilibration of small (1–2 cm width) veins or melt conduits is achieved at mantle wedge temperatures within 10¹–10⁵ years. We conclude that strongly fractionated Li isotopic signatures cannot be sustained for long periods in the sub-arc mantle, at least at shallow (<70 km) depths. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Large ion lithophile elements in rocks from high-pressure granulite facies terrains

A comparison of K, Rb, Th and U concentrations in granulite facies rocks with those of unmetamorphosed common rock types shows that depletion of these elements in granulites is variable. K/Rb ratios for granulites are generally higher than unmetamorphosed rocks, but K/Rb ratios only reach extreme values when K < 1%. The covariation of K/Rb ratio with K concentration suggests that protolith composition, hence mineralogy, is very important in controlling the degree of Rb depletion in granulites. Felsic granulites exhibiting extreme K/Rb ratios are mainly Archean, reflecting the high abundance of low K felsic rocks in Archean terrains. The Scourian granulites of Scotland all have very high K/Rb ratios and cannot be considered to be representative of granulite facies terrains. It is impossible from this data set to state conclusively whether K is depleted in granulites; K/La ratios of granulites show complete overlap with igneous rocks. Th/U ratios in many granulites are greater than 4, indicating U loss relative to Th. Felsic granulites with low Th/U ratios also have high La/Th ratios, indicating that these granulites have been depleted in Th. The low Th/U ratios of these rocks may reflect retention of Th and U in resistant accessory phases.     

Nutrient Dynamics in Vegetated and Unvegetated Areas of a Southern Everglades Mangrove Creek

Flow-through flumes were used to quantify net areal fluxes of nutrients in the fringe mangrove zone of lower Taylor River in the southern Everglades National Park. We also quantified net areal fluxes along the open water portion of the channel to determine the relative importance of either zone (vegetated vs. unvegetated) in the regulation of nutrient exchange in this system. Taylor River's hydrology is driven mainly by precipitation and wind, as there is little influence of tide. Therefore, quarterly samplings of the vegetated and unvegetated flumes were slated to include typical wet season and dry season periods, as well as between seasons, over a duration of two years. Concentrations of dissolved and total organic carbon (DOC and TOC) were highest during the wet season and similar to one another throughout the study, reflecting the low particulate loads in this creek. Dissolved inorganic nitrogen (nitrate+nitrite+ammonium) was 10–15% of the total nitrogen (TN) content, with NO−x and NH+4 showing similar concentration ranges over the 2-year study. Soluble reactive phosphorus (SRP) was usually <0·05μM, while total phosphorus (TP) was typically an order of magnitude higher. Net areal fluxes were calculated from nutrient concentration change over the length of the flumes. Most flux occurred in the vegetated zone. Dissolved inorganic nitrogen and DOC were usually taken up from the water column; however, we saw no seasonal pattern for any constituent over the course of this study. Total nutrients (TOC, TN, and TP) showed little net exchange and, like SRP, had fluxes that shifted irregularly throughout the study. Despite the lack of a clear seasonal pattern, there was a great deal of consistency between vegetated flumes, especially for NO−x and NH+4, and fluxes in the vegetated flumes were generally in the same direction (import, export, or no net flux) during a given sampling. These findings suggest that the fringe mangrove zone is of considerable importance in regulating nutrient dynamics in lower Taylor River. Furthermore, the influence of this zone may at times extend into northeast Florida Bay, as the bay is the primary recipient of water and nutrients during the wet season.     

Dating the lower crust by ion microprobe

Ion microprobe UThPb ages of zircons from granulite facies lower crustal xenoliths from north Queensland, Australia, correlate well with the ages of major orogenic episodes manifest at the earth's surface. About half of the xenoliths contain Proterozoic zircons which are similar in age to the episodes of high-grade metamorphism of the older surface rocks. All the xenoliths contain late Paleozoic zircons which show a real 100 Ma range in²⁰⁶Pb²³⁸/U ages (from 320 to 220 Ma), which is attributed to granulite facies metamorphism followed by slow cooling in the deep crust. The Paleozoic zircon ages coincide in time with the prolonged episode of eruption of voluminous felsic ash-flows and intrusion of high-level granites in this region (320-270 Ma). Mineral and melt inclusions in the zircons provide clues to the origin of some of the xenoliths, and coupled with the age information, can be used to infer the geological processes operating in the lower crust. The zircons from two mafic xenoliths contain felsic and intermediate melt inclusions implying at least a two-stage history for these rocks, involving either partial melting of a more felsic protolith or crystal accumulation from an evolved melt. Some of the zircons from the felsic xenoliths contain CO₂-rich fluid inclusions, indicating that those zircons grew during high-grade metamorphism. The isotopic and chemical data for the whole rock xenoliths show that they originate from a segment of the lower crust which is a heterogeneous mixture of supracrustal and mafic, mantle-derived, lithologies. The major orogenic event responsible for the formation of that crust occurred in the late Paleozoic, when Proterozoic supracrustal rocks were emplaced into the lower crust, possibly along thin-skinned thrust slices. This was accompanied by intrusion of high-temperature, mantle-derived melts which caused partial melting of pre-existing crust. The most likely setting for such tectonism is a continental margin subduction zone.     

A lithium isotopic study of sub-greenschist to greenschist facies metamorphism in an accretionary prism,New Zealand

To investigate the behavior of Li during low-grade metamorphism and fluid flux in an accretionary prism we measured the Li concentrations ([Li]) and isotopic compositions (δ⁷Li) of sub-greenschist and greenschist-facies Otago Schist composites, as well as cross-cutting quartz veins, which are interpreted to have precipitated from slab-derived fluids. The average [Li] of sub-greenschist facies composites (41 ± 13 μg/g, 2σ) is statistically distinct (97% confidence level, student t test) to that of greenschist facies composites (34 ± 9 μg/g, 2σ), which have experienced mass addition of silica in the form of quartz veins having [Li] between 0.4–2.3 μg/g. A linear regression of the correlation between [Li] and calculated mass additions suggests that the depletion of [Li] in greenschist facies composites is due to both dilution from the addition of the quartz veins, as well as metamorphic dehydration. The [Li] of both groups of composites correlates with their CIA (Chemical Index of Alteration) values (50–58), which are low, consistent with the inferred graywacke protolith of the Otago Schist. The δ⁷Li of sub-greenschist and greenschist facies composites are remarkably constant, with an average δ⁷Li of 0.2 ± 1.7 (2σ) and ?0.5 ± 1.9 (2σ), respectively, and comparable to that of the average upper continental crust. Thus, metamorphism has had no discernable effect on δ⁷Li in these samples. The Li isotopic signature of the schists is similar to that seen in pelitic sedimentary rocks and likely reflects the δ⁷Li of the protoliths. The surprisingly light δ⁷Li of the quartz veins (?2.8 to ?1.4) likely records kinetic fractionation associated with Li ingress into the veins from surrounding wallrock.An isotopic equilibrium fluid flow model indicates that: 1) if the [Li] of slab-derived fluids is less than a few μg/g, the δ⁷Li of the overlying lithologies (i.e., the schists) is not significantly influenced by the fluid flux, regardless of the δ⁷Li of the fluids, 2) the slab-derived fluids will have heavy δ⁷Li of > + 10 after reacting with the prism sediments during their ascent, and 3) the [Li] of the slab-derived fluids is likely in the range of 0 < [Li] ≤ 41(μg/g). Thus, isotopically heavy slab-derived fluids that traverse sediments in accretionary prisms may leave little trace in the rocks and their surface compositional characteristics will reflect the net result of their interaction with the sediments of the prism.