The importance of fractional crystallization and magma mixing in controlling chemical differentiation at Süphan stratovolcano,eastern Anatolia,Turkey

Süphan is a 4,050 m high Pleistocene-age stratovolcano in eastern Anatolia, Turkey, with eruptive products consisting of transitional calc-alkaline to mildly alkaline basalts through trachyandesites and trachytes to rhyolites. We investigate the relative contributions of fractional crystallization and magma mixing to compositional diversity at Süphan using a combination of petrology, geothermometry, and melt inclusion analysis. Although major element chemistry shows near-continuous variation from basalt to rhyolite, mineral chemistry and textures indicate that magma mixing played an important role. Intermediate magmas show a wide range of pyroxene, olivine, and plagioclase compositions that are intermediate between those of basalts and rhyolites. Mineral thermometry of the same rocks yields a range of temperatures bracketed by rhyolite (~750°C) and basalt (~1,100°C). The linear chemical trends shown for most major and trace elements are attributed to mixing processes, rather than to liquid lines of descent from a basaltic parent. In contrast, glassy melt inclusions, hosted by a wide range of phenocryst types, display curved trends for most major elements, suggestive of fractional crystallization. Comparison of these trends to experimental data from basalts and trachyandesites of similar composition to those at Süphan indicates that melt inclusions approximate true liquid lines of descent from a common hydrous parent at pressures of ~500 MPa. Thus, the erupted magmas are cogenetic, but were generated at depths below the shallow, pre-eruptive magma storage region. We infer that chemical differentiation of a mantle-derived basalt occurred in the mid- to lower crust beneath Süphan. A variety of more and less evolved melts with ≥55 wt% SiO₂ then ascended to shallow level where they interacted. The presence of glomerocrysts in many lavas suggests that cogenetic plutonic rocks were implicated in the interaction process. Blending of diverse, but cogenetic, minerals, and melts served to obscure the true liquid lines of descent in bulk rocks. The fact that chemical variation in melt inclusions preserves deep-seated chemical differentiation indicates that inclusions were trapped in phenocrysts prior to shallow-level blending. Groundmass glasses evolved after mixing and display trends that are distinct from those of melt inclusions.     

Crystallization processes beneath the southern Mid-Atlantic Ridge (40–55°S), evidence for high-pressure initiation of crystallization

New major and trace element data are reported for a suite of basalts dredge sampled from the southern MAR (40.6-52.5°S) during cruise 9309 of the R/V Maurice Ewing and cruise 32 of the S.A. Agulhas (51-54.5°S). Samples range from aphyric to moderately porphyritic with plagioclase and olivine the dominant phenocryst and microphenocryst phases. Clinopyroxene occurs rarely as a phenocryst phase. Bulk rock and quench glass samples have major element compositions ranging from moderately primitive (Mg#=68.5) to evolved (Mg#=41.1), with a comparable range in incompatible (Zr=54-232 ppm; Nb=0.8-21 ppm) and highly compatible trace element (Ni=51-289 ppm; Cr=39-949 ppm) abundances. Incompatible trace element ratios (e.g., Zr/Nb=5.9-69; Y/Nb=0.88-29; (La/Sm)_N=0.48-2.9) indicate both enriched and depleted MORB occurring along this section of the MAR, agreeing with along-ridge radiogenic isotope ratio variations delineating compositional influences of the off-axis Discovery, and a so-called LOMU-component, and ridge-centered Shona mantle plumes (Douglass et al. 1999; Douglass and Schilling 2000). Major- and trace-element variations, particularly decreasing CaO/Al₂O₃ ratios and relatively constant Sc abundances with decreasing Mg# suggest crystallization of olivine, plagioclase, and clinopyroxene in most of these basalts prior to eruption. Liquid-lines-of-descent, derived from forward modeling of various reasonable parental magma compositions at pressures between 1 atm-8 kbar, confirm clinopyroxene as an early crystallizing phase, along with olivine and plagioclase, and its pivotal role in the compositional evolution of these basalts. Pressures deduced using algorithms of Grove et al. 1992 and Michael and Cornell 1998 indicate crystallization beneath ridge segments unaffected by mantle plumes occurred predominately at depths of 3-6 kbar (10-20 km). Crystallization beneath ridge segments affected by the Discovery and Shona mantle plumes occurred over a larger pressure range (1 atm-~7 kbar), but predominantly at crustal depths (1 atm-3 kbar), possibly due to more constant magma fluxes and higher temperatures in the crust and lithosphere in these regions favoring the existence and longevity of subaxial magma chambers.     

Cooling kinetics of garnet websterites from the Freychinède orogenic lherzolite massif,French Pyrenees

Clinopyroxene and orthopyroxene megacrysts with lamellar intergrowths of pyroxenes and garnet rarely survive in pyroxenite layers from the exposed spinel-lherzolite massifs because of the emplacement history into the crust. Such features are remarkably preserved in some thick bands (up to 1 m) from the Freychinède ultramafic body (Ariège, French Pyrenees). These bands display a symmetrical zoning from the edges to the centre due to the concurrent decrease of orthopyroxene/clinopyroxene and spinel/garnet modal ratios. Textural and chemical data suggest that the present pyroxenite parageneses resulted from subsolidus recrystallization of magmatic assemblages composed of Al-rich orthopyroxene and clinopyroxene with minor spinel. These primary assemblages were changed by subsolidus recrystallization connected with an isobaric cooling at upper-mantle depth (45–50 km) from solidus temperature (1250°C) down to steady equilibrium temperature (950° C). The primary Al-rich ortho-and clinopyroxenes behaved differently on cooling. In a first stage, orthopyroxene exsolved concomitant Al-rich clinopyroxene and garnet, whereas clinopyroxene exsolved only Al-rich orthopyroxene. The garnet exsolution in clinopyroxene host is delayed to lower temperatures. This multistage process could account for the contrasting shapes of diffusion gradients adjacent to exsolved garnet, which tend to be flat in host-orthopyroxene and steep in host-clinopyroxene. An independent thermal modelling, together with available Al-diffusion data in clinopyroxene, allows us to define a fast magmatic cooling followed by a two-stage subsolidus cooling (35° C/year^-6 from 1250° C to 1050° C and 9° C/year^-6 to 900° C). This matches the contrasted exsolution sequences observed in the pyroxene megacrysts.     

The chemical composition of specular hematite from Tilkerode, Harz, Germany: implications for the genesis of hydrothermal hematite and comparison with the Quadrilátero Ferrífero of Minas Gerais, Brazil

The black shale-hosted selenide vein-type deposit at Tilkerode, eastern Harz, Germany, has specular hematite enclosed in clausthalite (PbSe). The specular hematite has Ti and V in amounts of up to ～1 wt.% TiO₂ and ～3 wt.% V₂O₅, and subordinate, but important, contents of Mo (22–372 ppm) and B (up to 68 ppm). The Tilkerode hematite serves as a reference for hydrothermal hematite formed at relatively low temperatures (<150 °C). The composition of the Tilkerode hematite is compared with that of two generations of specular hematite from itabirite-hosted iron-ore deposits in the Quadrilátero Ferrífero of Minas Gerais, Brazil. The first generation of specular hematite represents an early tectonic hematitisation of dolomitic itabirite at Águas Claras and occurs as fine-grained crystals. Reconnaissance data indicate that the Águas Claras hematite is poorer in Ti and V, relative to the Tilkerode hematite, but has ～5–10 ppm B and ～7–11 ppm Li. The second generation of specular hematite defines the pervasive tectonic foliation of the Gongo Soco iron ore. This hematite has Ti contents of up to ～2 wt.% TiO₂ and subordinate amounts of V (62–367 ppm); its B and Li concentrations are mostly below <2 ppm B and <1 ppm Li. The presence of Ti and B in the Tilkerode hematite can be explained by highly saline, B-bearing fluids that were capable of mobilising otherwise immobile Ti. The Mo signature of the Tilkerode hematite suggests that Mo was derived from the host black shale. In Minas Gerais, B and Li were incorporated into the early tectonic hematite from saline fluids at relatively low temperatures (Águas Claras) and then released during metamorphic hematite growth at higher temperatures, as suggested by the foliation-defining hematite without B–Li signature (Gongo Soco).     

微乳液介质—DBH-PF光度法测定食品中微量锗的研究

以阳离子型 O/ W CTMAB/ n- C5H11OH/ n- C7H16/ H2 O微乳液为介质 ,进行 Ge( IV) - DBH- PF的分光光度法测定 ,ε510 nm=2 .18× 10 5L· mol-1.cm-1,建立了高灵敏测定食品中微量锗的新方法 ,锗量在每 2 5m L 0～ 7.0μg范围内符合比尔定律 ,方法选择性好 ,试样无需萃取分离 ,可快速测定     

Observed vs. predicted variability in non-algal suspended particulate matter concentration in the English Channel in relation to tides and waves

The study of water clarity is essential to understand variability in biological production, particularly in coastal seas. The spatial and temporal variability of non-algal suspended particulate matter (SPM) in surface waters of the English Channel was investigated and related to local forcing by means of a large satellite dataset covering the study area with a spatial resolution of 1.2 km and a daily temporal resolution. This analysed dataset is a time series of non-algal SPM images derived from MODIS and MERIS remote-sensing reflectance by application of an IFREMER semi-analytical algorithm over the period 2003–2009. In a first step, the variability of time series of MODIS images was analysed through temporal autocorrelation functions. Then, non-algal SPM concentrations were assessed in terms of site-specific explanatory variables such as tides, wind-generated surface-gravity wave amplitudes and chlorophyll-a (Chl-a), based on three statistical models with fitting parameters calibrated on a dataset of merged MERIS/MODIS images gathered from 2007 to 2009 over the whole English Channel. Correlogram analysis and the first model highlight the local patterns of the influence of the tide, especially the neap–spring cycle, on non-algal surface SPM. Its effect is particularly strong in the central and eastern English Channel and in the western coastal areas. The second model shows that waves prevail as driver at the entrance of the English Channel. The most sophisticated of the three statistical models, although involving only three explanatory variables—the tide, waves and Chl-a—is able to estimate non-algal surface SPM with a coefficient of determination reaching 70% at many locations.     

Land use change increases flood hazard: a multi-modelling approach to assess change in flood characteristics driven by socio-economic land use change scenarios

Natural Hazards - We analysed in the work how change in land use/land cover influences on flood characteristics (frequency and magnitude) using a model inter-comparison approach, statistical...     

40Ar/39Ar temporal framework for the Alleret maar lacustrine sequence (French Massif-Central): Volcanological and paleoclimatic implications

The Alleret maar (Massif Central, France) is part of the few Western European early middle Pleistocene lacustrine sequences. In the AL3 core several new ash layers were recovered in the 10 first meters of the sedimentary filling. We obtained three ⁴⁰Ar/³⁹Ar ages, which range from 683 ± 5 ka (MSWD: 1.2, n = 17) to 722 ± 6 ka (MSWD: 3.2, n = 18). All the studied ash layers belong to the Super-Besse eruptive cycle of the Sancy volcano. Based on the chronostratigraphy that we have derived we estimate that the age of the main eruption could correspond to the Sancy volcano caldera formation at 725 ka close to the end of MIS 18 and that the Super-Besse explosive episode duration lasted only about 40 ka. The time framework we build evidences that the Alleret lacustrine sequence represents a time interval of probably 180 ka spanning from MIS 18 to MIS 14. This sequence offers the first well constrained comparison between terrestrial environmental history and that preserved in marine sediments during the Mid-Pleistocene Revolution.     

ESR/U-series dating of teeth recovered from well-stratigraphically age-controlled sequences from Northern France

During the last two decades, extensive road-construction works in Northern France have allowed the discovery of numerous Middle Palaeolithic sites. Geological and multidisciplinary studies performed on these localities allowed the establishment of a precise chronostratigraphical and biostratigraphical framework of regional significance, which could be correlated to the global marine palaeoclimatic scale. Each human occupation layer has been linked to this regional framework, thus providing a stratigraphical age-control for the Middle Palaeolithic human settlements of this area.At the same time, a program of geochronological studies was developed using TL, OSL, U-series, ESR and, as often as possible, ESR/U-series methods. Hence, bones and teeth recovered from archaeological sites of Savy, Ault, Caours, Gentelles and La Celle-sur-Seine, were analyzed and the results compared to the chronostratigraphical ages. The age results are generally in good agreement with the geological data while bones and dental tissues display in some cases U-series ages higher that the EU-ESR ones, suggesting U-loss phenomena.