Graphic intergrowths of feldspars and quartz in some Czechoslovak pegmatites

Graphic intergrowths of alkali feldspar+quartz, and plagioclase+quartz, occur together in pegmatites in the eastern part of the Czechoslovak Moldanubicum. They form zones between the finer-grained wall zone and the central blocky feldspar+quartz core. The normative Or-Pig-Q compositions of the graphic intergrowths and the Or-Ab-An contents of their feldspars show broad variations generally, but have a restricted range within individual pegmatites. At two localities studied in more detail, coexisting feldspars show gradual changes in composition, from the margins up to the innermost graphic pegmatite, compatible with fractional crystallization along the feldspar solidus-solvus intersection in the Or-Ab-An-Q-H₂O system, at different vapour pressures in different pegmatites. Two models are demonstrated for low and high pressure cases. The feldspar compositions from central blocky zones deviate from the magmatic fractional crystallizations paths; this corresponds with the general assumption that they crystallized from supercritical gaseous fluids.In these and in similar pegmatites, coexisting alkali feldspar+quartz and plagioclase + quartz intergrowths are interpreted as the last products of cotectic crystallization from an ultimately fractionated granitic magma. Positive correlation of Ab solid solution and quartz content in the potassic intergrowths suggests that these characteristics may be indicative of the relative pressure and temperature effective during their crystallization, when compared in pegmatites of the same bulk composition.     

Trace element contents and C-O isotope geochemistry of the different originated magnesite deposits in Lake District (Southwestern Anatolia), Turkey

Vein-stockwork magnesite in the Madenli area, sedimentary huntite-magnesite in the A?a??t?rtar area, and lacustrine hydromagnesite in the Salda Lake area are located in the Bey?ehir-Hoyran and Lycian nappe rocks around Isparta and Burdur, Southwest Anatolia. The aim of this study is to understand trace element contents and carbon-oxygen isotope ratios in different originated magnesite, magnesite bearing huntite, and hydromagnesite deposits. Also, the element contents and isotope ratios of the magnesite occurrences are to compare with each other and similar magnesite occurrences in Turkey and world. It is found that the Madenli magnesite occurrences in the ?arkikaraa?aç ophiolites, A?a??t?rtar magnesite bearing huntite deposits in the lacustrine rocks of the Miocene-Pliocene, and the Salda hydromagnesite deposits in lacustrine basin on the Ye?ilova ophiolites. The paragenesis contains a common carbonate mineral magnesite, less calcite, serpentine, smectite, dolomite, and talc in the Madenli magnesite occurrences, mostly huntite and locally magnesite, dolomite, calcite, illite, quartz, and smectite in the A?a??t?rtar huntite-magnesite occurrences, and only hydromagnesite mineral in the Salda Lake hydromagnesite occurrences. Vein and stockwork Madenli magnesite deposits were recognized by higher total iron oxide concentrations (mean 1.10 wt%) than sedimentary A?a??t?rtar magnesite bearing huntite (mean 0.13 wt%) and lacustrine Salda hydromagnesite (mean 0.22 wt%) deposits. It is suggested that high Fe content (up to 5%) in the magnesite associated with ultramafic rocks than those from sedimentary environments (≤1% Fe). Based on average Ni, Co, Ba, Sr, As and Zr contents in the magnesite deposits, average Ni (134.63 ppm) and Co (15.19 ppm) contents in the Madenli magnesite and Salda hydromagnesite (36.85 ppm for Ni, 3.15 ppm for Co) have higher values than A?a??t?rtar huntite + magnesite (7.67 ppm for Ni and 0.89 ppm for Co). Average Ni-Co contents of these deposits can have close values depending on ophiolite host rock. Average Ba values of the Madenli (108.09 ppm) and A?a??t?rtar (115.88 ppm) areas are higher than those of Salda hydromagnesite (13.15 ppm). Sediment-hosted A?a??t?rtar magnesite-huntite deposits have the highest Sr contents (mean 505.81 ppm) as reasonably different from ultrabasic rock-related Madenli magnesite (mean 38.76 ppm) and Salda hydromagnesite (mean 36.70 ppm). The highest Sr content of sedimentary A?a??t?rtar deposits reveals that Sr is related to carbonate rocks. As and Zr contents have the highest average values (As 52.76 ppm and Zr 9.67 ppm) in the A?a??t?rtar deposits different from Madenli magnesite (As 0.54 ppm and Zr 1.67 ppm) and Salda hydromagnesite (As 0.5 ppm and Zr 2.58 ppm) deposits. High As and Zr concentrations in the A?a??t?rtar magnesite-huntite deposits may come from volcanic rocks in near country rocks. The δ ¹³C (PDB) isotope values vary between ?10.1 and ?11.4‰ in the Madenli magnesite, 7.8 to 8.8‰ for huntite, 1.7 to 8.3‰ for huntite + magnesite and 4.0‰ for limestone + magnesite in the A?a??t?rtar huntite-magnesite deposits, and 4.4 to 4.9‰ for Salda Lake hydromagnesite. The sources of the CO₂ are hydrothermal solutions, meteoric waters, groundwater dissolved carbon released from fresh water carbonates and marine limestone, soil CO₂, and plant C3 in the Madenli magnesite, and may be deep seated metamorphic reactions in limestone and shales of rich in terms of organic matter. The sources of CO₂ in A?a??t?rtar huntite and Salda hydromagnesite were meteoric water, groundwater dissolved inorganic carbon, fresh water carbonates, and marine limestone. The δ ¹⁸O (SMOW) isotope composition ranges from 26.8 to 28.1‰ in the Madenli magnesite, 30.4 to 32.4‰ for huntite and 29.8 to 35.5‰ for huntite + magnesite and 26.9‰ for limestone + magnesite in the A?a??t?rtar area, and 36.4 to 38.2‰ in the Salda Lake hydromagnesite. The Salda Lake hydromagnesite has heavier oxygen isotopic values than others. The sources of oxygen in the Madenli magnesite deposits are hydrothermal solutions, meteoric water, freshwater carbonates, and marine limestone, but the sources of oxygen of the A?a??t?rtar magnesite-huntite are meteoric water, fresh water carbonates, and marine limestone. The Salda Lake hydromagnesite has very high δ¹⁸O isotope values indicating a strong evaporitic environment. Magnesium (Mg⁺²) and silica are released by disintegration of very weathered-serpentinized ultrabasic rocks of all magnesite deposits and from partly dolomite and dolomitic limestone in the A?a??t?rtar magnesite bearing huntite deposits. In the A?a??t?rtar area, calcium (Ca⁺²) for huntite mineralization is provided by surrounding carbonate rocks. Based on isotopic data, host rocks, petrographic properties of the Madenli magnesite can be described as an ultramafic-associated hydrothermal vein mineralization corresponding to “Kraubath type” deposits, but A?a??t?rtar ve Salda Lake deposits are sedimentary mineralization (lacustrine/evaporitic) corresponding to “Bela Stena type” deposits. The estimated temperature using average δ¹⁸O isotope values is about 33.51 °C for Madenli magnesite, 48.33 °C for A?a??t?rtar huntite-magnesite, and 25 °C for Salda hydromagnesite. Based on isotope data, we can be say that the Madenli magnesite, A?a??t?rtar magnesite-huntite, and Salda hydromagnesite occur at low to moderate-low temperature water and alkaline (pH 8.5–10.5) under surface or near-surface conditions.     

用三氧化铬-硫酸溶剂对黑色页岩铼-锇定年方法初探

讨论了铼-锇同位素稀释法测定黑色页岩年龄的溶样方式,比较了王水和不同温度下CrO3-H2SO4的Carius管溶样技术,通过改进流程将铼空白控制在10pg之内,并结合高灵敏度的电感耦合等离子体质谱分析手段,初步研究建立了一种用CrO3-H2SO4溶剂准确测定黑色页岩年龄的方法。     

Iron speciation and isotope fractionation during silicate weathering and soil formation in an alpine glacier forefield chronosequence

The chemical weathering of primary Fe-bearing minerals, such as biotite and chlorite, is a key step of soil formation and an important nutrient source for the establishment of plant and microbial life. The understanding of the relevant processes and the associated Fe isotope fractionation is therefore of major importance for the further development of stable Fe isotopes as a tracer of the biogeochemical Fe cycle in terrestrial environments. We investigated the Fe mineral transformations and associated Fe isotope fractionation in a soil chronosequence of the Swiss Alps covering 150 years of soil formation on granite. For this purpose, we combined for the first time stable Fe isotope analyses with synchrotron-based Fe-EXAFS spectroscopy, which allowed us to interpret changes in Fe isotopic composition of bulk soils, size fractions, and chemically separated Fe pools over time in terms of weathering processes. Bulk soils and rocks exhibited constant isotopic compositions along the chronosequence, whereas soil Fe pools in grain size fractions spanned a range of 0.4‰ in δ⁵⁶Fe. The clay fractions (<2 μm), in which newly formed Fe(III)-(hydr)oxides contributed up to 50% of the total Fe, were significantly enriched in light Fe isotopes, whereas the isotopic composition of silt and sand fractions, containing most of the soil Fe, remained in the range described by biotite/chlorite samples and bulk soils. Iron pools separated by a sequential extraction procedure covered a range of 0.8‰ in δ⁵⁶Fe. For all soils the lightest isotopic composition was observed in a 1 M NH₂OH-HCl-25% acetic acid extract, targeting poorly-crystalline Fe(III)-(hydr)oxides, compared with easily leachable Fe in primary phyllosilicates (0.5 M HCl extract) and Fe in residual silicates. The combination of the Fe isotope measurements with the speciation data obtained by Fe-EXAFS spectroscopy permitted to quantitatively relate the different isotope pools forming in the soils to the mineral weathering reactions which have taken place at the field site. A kinetic isotope effect during the Fe detachment from the phyllosilicates was identified as the dominant fractionation mechanism in young weathering environments, controlling not only the light isotope signature of secondary Fe(III)-(hydr)oxides but also significantly contributing to the isotope signature of plants. The present study further revealed that this kinetic fractionation effect can persist over considerable reaction advance during chemical weathering in field systems and is not only an initial transient phenomenon.     

Navigating through SPASE to heliospheric and magnetospheric data

Virtual observatories have been introduced by the astrophysics community as an environment connecting distributed data sources with a unified interface. The heliophysics community soon recognized that they faced a similar problem of many distributed data sets with varying amount of information about them and several discipline specific virtual observatories have been established. Two of them, the virtual heliospheric observatory (VHO) and the virtual magnetospheric observatory (VMO), share a common architecture design with development efforts oriented towards a structured data search. This paper describes the VHO/VMO middleware and its components from metadata preparation and processing to the user interface.     

Distribution of polycyclic musks in water and particulate matter of the Lippe River (Germany)

The occurrence and distribution of polycyclic musks in the Lippe River system (a tributary of the Rhine River, Germany) was investigated in order to observe the dynamic transport and partitioning of these compounds between aqueous and particulate phases after their discharge into the river by sewage effluents. 1,3,4,6,7,8-Hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[g]-2-benzopyrane (HHCB), 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN), 6-acetyl-1,1,2,3,3,5-hexamethylindane (AHMI) and 4-acetyl-1,1-dimethyl-6-tert.-butylindane (ADBI) concentrations were determined in 19 water and surface sediment samples which were taken from a longitudinal section of the river. HHCB and AHTN were present in each of the water samples at concentrations ranging from <10 to 180 ng l⁻¹ and <10 to 70 ng l⁻¹, respectively. The load of dissolved HHCB and AHTN was calculated on the basis of compound concentrations in water and the corresponding river runoff data and ranged from 3 to 293 g day⁻¹ and from 1 to 108 g day⁻¹, respectively. Increasing loads of HHCB and AHTN along the river reflect a high input of sewage effluents to the densely populated areas along the central part of the river. Decreasing loads at the lower reaches indicate that in the corresponding river sections the rate of removal of musks was higher than the rate of input. Degradation and/or adsorption to particulate matter are processes that might explain this phenomenon. Consequently, high concentrations of HHCB and AHTN were detected in surface sediments from the Lippe River (from 5 to 191 μg kg⁻¹ and from 2 to 1399 μg kg⁻¹, respectively). HHCB/AHTN ratios in sediment samples were lower (average 1.2) than in water samples (average 2.9), suggesting the preferential adsorption of AHTN to particulate matter.     

天水地区主要活动断裂特征与氡气测试成果分析

断层氡气释放强度、范围、成分等的变化可以用来分析评价活动断层的相对活动性。研究了天水地区主要活动断裂的基本特征,并对这些断裂进行了氡气测试与分析。结果表明:西秦岭北缘断裂带的活动性为强—极强;礼县—罗家堡断裂的活动性为强;礼县—积石峡断裂的活动性为强—中等;清水断裂活动性为中等。该结果与活断层的活动强度较吻合,说明氡气测试成果可以作为一种断裂活动性的评价方法。      

Nature and timing of the Solonker suture of the Central Asian Orogenic Belt: insights from geochronology and geochemistry of basic intrusions in the Xilin Gol Complex,Inner Mongolia,China

The Solonker suture zone of the Central Asian Orogenic Belt (CAOB) records the final closure of the Paleo-Asian Ocean. The nature and timing of final collision along the Solonker suture has long been controversial, partly because of an incomplete record of isotopic ages and differing interpretations of the geological environments of key tectonic units. The Xilin Gol Complex, consisting of strongly deformed gneisses, schists and amphibolites, is such a key tectonic unit within the CAOB. Lenticular or quasi-lamellar amphibolites are dispersed throughout the complex, intercalated with biotite–plagioclase gneiss. Both rock types experienced amphibolite-facies metamorphism. The protolith of the amphibolite is a basic rock that intruded into the biotite–plagioclase gneiss at 319 ± 4 Ma based on LA-ICPMS zircon U–Pb dating. The basic intrusion was sourced from a modified magma that experienced crystal fractionation and was admixed with slab-derived fluids. The slab-derived fluids, which formed during Early Paleozoic oceanic subduction along the north-dipping Sonidzuoqi–Xilinhot subduction zone, mixed with the magma source and produced subduction-related geochemical signatures superimposed on volcanic arc chemistry. After Early Paleozoic oceanic subduction and arc-continent collision, a transient stage of extension occurred between 313 and 280 Ma in the Sonidzuoqi–Xilinhot area. Deformation and recrystallization during the switch from compression to extension and reheating by the later magmatic intrusions reset the isotope systems of minerals in the Xilin Gol Complex, recorded by a 312.2 ± 1.5 Ma biotite ⁴⁰Ar/³⁹Ar age from biotite–plagioclase gneiss, a 309 ± 12 Ma zircon intercept age and a 307.5 ± 3.5 Ma hornblende ⁴⁰Ar/³⁹Ar age from amphibolites in the complex. There was an arc/forearc-related marine basin at the southern margin of the Xilin Gol Complex during the Permian. The closure of the oceanic basin led to Late Paleozoic–Middle Triassic north-dipping subduction beneath the Xilin Gol Complex and induced the amphibolite-facies metamorphism of the complex. The final suturing of the Solonker zone occurred from 269 to 231 Ma. This latest amphibolite-facies metamorphism with pressures of 0.31–0.39 GPa and temperatures of 620–660 °C was recorded at 263.4 ± 1.4 Ma to the Xilin Gol Complex, as indicated by the hornblende ⁴⁰Ar/³⁹Ar age from the amphibolites, as well as several zircon ages of 260 ± 3–231 ± 3 Ma. The Xilin Gol Complex documented the progressive accretion of a single, long-lived subduction system at the southern margin of the south Mongolian microcontinent from the Early Paleozoic (~452 Ma) to Middle Triassic (~231 Ma). The CAOB shows protracted collision prior to final suturing.     

Multiple Sources of Metals of Mineralization in Lower Cambrian Black Shales of South China: Evidence from Geochemical and Petrographic Study

Black shales of the Lower Cambrian Niutitang Formation in southern China (Huangjiawan mine, Zunyi region, northern part of the Guizhou Province) host regionally distributed stratiform polymetallic Ni‐Mo‐platinum group elements (PGE)‐Au phosphate‐ and sulfide‐rich ores. These are confined to a ≥0.2‐m thick ore horizon composed of mineralized bodies of algal onkolites, phosphate nodules, and sulfide and shale clasts in a mineralized phosphate‐ and organic matter‐rich matrix. Compared to footwall and hanging wall shales, the ore bed is strongly enriched in Ni (up to 100‐fold), As (up to 97‐fold), Mo (up to 95‐fold), Sb (up to 67‐fold), Rh (up to 49‐fold), Cu (up to 37‐fold), Pd (up to 33‐fold), Ru (up to 24‐fold), Zn (up to 23‐fold), Pt (up to 21‐fold), Ir (up to 15‐fold), Co (up to 14‐fold), and Pb (up to 13‐fold). Even footwall and hanging wall black shales are significantly enriched by Mo (21‐fold) and Ni (12‐fold) but depleted in Cr in comparison to average Cambrian black shale. Organic matter is represented by separate accumulations dispersed in the rock matrix or as biotic bitumen droplets and veinlets in ore clasts. Similar organic carbon (C_org) values in an ore bed and enclosing footwall and hanging wall shales of little mineralization indicate that metal accumulation was not controlled only by biogenic productivity and organic matter accumulation rate. Evaporitic conditions during sedimentation of the basal part of the Niutitang Formation were documented by an occurrence of preserved Ni‐, V‐, Cr‐, and Cu‐enriched phosphate‐rich hardground with halite and anhydrite pseudomorphs on the paleosurface of the underlying Neoproterozoic carbonates. Neoproterozoic black shales of the Doushantuo Formation are characterized by increased metal concentrations. Comparison of metal abundances in both hardground and Doushantuo black shales indicate that black shales could have become a source of metal‐rich hardground during weathering. The polymetallic Ni‐Mo‐PGE sulfide‐rich ore bed is interpreted to represent a remnant of shallow‐water hardground horizon rich in metals, which originated in a sediment‐starved, semi‐restricted, seawater environment. During the Early Cambrian transgression an influx of fresh seawater and intensive evaporation, together with the hydrothermal enrichment of seawater in a semi‐restricted basin, resulted in the formation of dense metalliferous brines; co‐precipitation of metals together with phosphates and sulfides occurred at or above the oxic–anoxic sediment interface. Metal‐enriched hardground was disintegrated by the action of waves or bottom currents and deposited in a deeper part of the anoxic basin. Contemporaneously with the formation of a polymetallic Ni‐Mo‐PGE‐Au sulfide ore bed, economic sedimentary exhalative (SEDEX)‐type barite deposits were forming in a stratigraphically and geotectonically similar setting. The results of geochemical study at the Shang Gongtang SEDEX‐type Ba deposit indicate that concentrations of Ag, As, Cr, Cu, Fe, Mn, Ni, Pb, Sb, V, Zn and other metals decrease from top of the barite body toward the hanging wall black shale. Lower Cambrian black shales of the Niutitang Formation above the barite body also display similar element abundances as Neoproterozoic black shales of the Doushantuo Formation, developed in the footwall of the barite body. But the geochemical composition of the sulfide layer is different from the Ni‐Mo ore bed, showing only elevated Pb, Cu, Ni and Mo values. It is suggested that hydrothermal brines at Shang Gongtang might have leached metals from footwall Neoproterozoic sequences and became, after mixing with normal seawater, an additional source of Ag, Cr, Cu, Pb, Sb, Zn, Ni, PGE, V and other metals.