东秦岭地区钼矿床的铼-锇同位素年龄及其意义

金属矿床的成矿年龄多年来一直是矿床地质工作者关注的问题之一。中国地质科学院岩矿测试技术研究所建立的铼－锇同位素定年实验室，为研究钼矿床的形成时代提供了新的手段。因辉钼矿是最主要的含铼矿物之一，且基本上不含普通锇，其中所含＾１８７Ｏｓ是由＾１８７Ｒｅ衰变而来，故放射成因＾１８７Ｏｓ的积累是矿物年龄及铼含量的函数。本文采用同位素稀释－等离子体质谱法，测定了东秦岭钼矿带中几个不同类型的大型钼矿床的Ｒｅ－     

Helium, Argon, and Xenon Isotopic Compositions of Ore-formingFluids in Jinding-Baiyangping Polymetallic Deposits,Yunnan, Southwest China

The Jinding superlarge lead and zinc deposit has attracted the attention of geologists of the world and its metallogenesis has long been in dispute. This paper takes the Jinding deposit and the Baiyangping Cu-Ag-Co deposit which was recently found at about 30 km north of Jinding as one ore belt, and, based on researches on the helium, argon, and xenon isotopic compositions of primary inclusions in ore-forming solutions of the main stage, the authors have found that the 3He/4He ratio of the ore-forming fluid is 2.7′ 10- 6 (varying from 0.19 to 1.97 Ra), the 4He/40Ar ratio (0.24- 3.12) is close to the mantle characteristic ratio, and the xenon isotopic composition and evolution show characters of the mantle xenon. The above results reveal the characteristics of mantle source and crust-mantle fluid mixing (mantle helium reaching 32%) and the metallogenic contributions of the deep processes in the Jinding-Baiyangping ore belt.     

Stormflow concentration–discharge dynamics of suspended sediment and dissolved phosphorus in an agricultural watershed

Concentration–discharge (C-Q) relationships are an effective tool for identifying watershed biogeochemical source and transport dynamics over short and long timescales. We examined stormflow C-Q, hysteresis, and flushing patterns of total suspended sediment (TSS) and soluble reactive phosphorus (SRP) in two stream reaches of a severely impaired agricultural watershed in northeastern Wisconsin, USA. The upper watershed reach—draining a relatively flat, row crop-dominated contributing area—showed predominantly anti-clockwise TSS hysteresis during storms, suggesting that particulate materials were mobilized more from distal upland sources than near- and in-channel areas. In contrast, the incised lower watershed reach produced strong TSS flushing responses on the rising limb of storm hydrographs and clockwise hysteresis, signalling rapid mobilization of near- and in-channel materials with increasing event flows. C-Q relationships for SRP showed complex patterns in both the upper and lower reaches, demonstrating largely non-linear chemodynamic C-Q behaviour during events. As with TSS, anti-clockwise SRP hysteresis in the upper reach suggested a delay in the hydrologic connectivity between SRP sources and the stream, with highly variable SRP concentrations during some events. A broad range of clockwise, anti-clockwise, and complex SRP hysteresis patterns occurred in the lower watershed, possibly influenced by in-channel legacy P stores and connection to tile drainage networks in the lower watershed area. Total suspended sediment and SRP responses were also strongly related to precipitation event characteristics including antecedent precipitation, recovery period, and precipitation intensity, highlighting the complexity of stormflow sediment and phosphorus responses in this severely impaired agricultural stream.     

Middle and late Pleistocene glaciations in the Campo Felice Basin (central Apennines, Italy)

The present paper refers to research conducted in the tectonic-karst depression of Campo Felice in the central Apennines (Italy), in which glacial, alluvial and lacustrine sediments have been preserved. Stratigraphic interpretations of sediments underlying the Campo Felice Plain are based on evidence obtained from nine continuous-core boreholes. The boreholes reach a depth of 120 m and provide evidence of five sedimentation cycles separated by erosion surfaces. Each cycle is interpreted as an initial response to a mainly warm stage, characterized by low-energy alluvial and colluvial deposition, pedogenesis, and limited episodes of marsh formation. In turn, a mainly cold stage follows during which a lake formed, and glaciers developed and expanded, leading to deposition of glacial and fluvioglacial deposits. The chronological framework is established by eleven accelerator mass spectrometer ¹⁴C ages and three ³⁹Ar-⁴⁰Ar ages on leucites from interbedded tephra layers. These age determinations indicate five glacial advances that respectively occurred during marine oxygen isotope stages 2, 3-4, 6, 10 and 14.     

Neoproterozoic granites of the Lajeado intrusive suite,north-center Brazil: A late Ediacaran remelting of a Paleoproterozoic crust

In north-central Brazil, a number of granite plutons, which intrude Paleoproterozoic gneiss-granulite terrains of the Goiás Massif, crop out along a thermal axis parallel to the Transbrasiliano Lineament. Single zircon lead evaporation ages from three granitic bodies span between 552 and 545 Ma. Sm–Nd model ages (T_DM) vary between 2.1 and 1.7 Ga and negative εNd_{(0.55 Ga)} values between −10 and −13 show that Paleoproterozoic crust was involved in the genesis of these granites. These plutons, which form the Lajeado Intrusive Suite are part of an important Ediacaran magmatic event in central-northern of the Tocantins Tectonic Province, composed of metaluminous to slightly peraluminous granites with geochemical characteristics similar to A-type granites, whose crystallization occurred under low water activity during magmatic emplacement. The granitic intrusive bodies are related to a crustal extensional/transtensional tectonic event at the end of the Neoproterozoic. They may have connection with the granitic plutons of similar age (0.56–0.52 Ga) in northwestern Ceará state, on the other side of the Paleozoic Parnaíba Basin in northwest of Borborema Province, along the Transbrasiliano Lineament.     

Trophic ecology and vertical patterns of carbon and nitrogen stable isotopes in zooplankton from oxygen minimum zone regions

The unique physical and biogeochemical characteristics of oxygen minimum zones (OMZs) influence plankton ecology, including zooplankton trophic webs. Using carbon and nitrogen stable isotopes, this study examined zooplankton trophic webs in the Eastern Tropical North Pacific (ETNP) OMZ. δ¹³C values were used to indicate zooplankton food sources, and δ¹⁵N values were used to indicate zooplankton trophic position and nitrogen cycle pathways. Vertically stratified MOCNESS net tows collected zooplankton from 0 to 1000 m at two stations along a north-south transect in the ETNP during 2007 and 2008, the Tehuantepec Bowl and the Costa Rica Dome. Zooplankton samples were separated into four size fractions for stable isotope analyses. Particulate organic matter (POM), assumed to represent a primary food source for zooplankton, was collected with McLane large volume in situ pumps.The isotopic composition and trophic ecology of the ETNP zooplankton community had distinct spatial and vertical patterns influenced by OMZ structure. The most pronounced vertical isotope gradients occurred near the upper and lower OMZ oxyclines. Material with lower δ¹³C values was apparently produced in the upper oxycline, possibly by chemoautotrophic microbes, and was subsequently consumed by zooplankton. Between-station differences in δ¹⁵N values suggested that different nitrogen cycle processes were dominant at the two locations, which influenced the isotopic characteristics of the zooplankton community. A strong depth gradient in zooplankton δ¹⁵N values in the lower oxycline suggested an increase in trophic cycling just below the core of the OMZ. Shallow POM (0–110 m) was likely the most important food source for mixed layer, upper oxycline, and OMZ core zooplankton, while deep POM was an important food source for most lower oxycline zooplankton (except for samples dominated by the seasonally migrating copepod Eucalanus inermis). There was no consistent isotopic progression among the four zooplankton size classes for these bulk mixed assemblage samples, implying overlapping trophic webs within the total size range considered.     

Hα emission from late type be stars

We show here that the Hα flux from late type Be stars can be explained as emission from an HII region formed in the gas envelope around the Be star, by the UV flux emitted by a helium star binary companion. We also discuss the observability of the helium star companions.     

Basaltic and Solution Reference Materials for Iron,Copper and Zinc Isotope Measurements

Iron, Cu and Zn stable isotope systems are applied in constraining a variety of geochemical and environmental processes. Secondary reference materials have been developed by the Institute of Geology, Chinese Academy of Geological Sciences (CAGS), in collaboration with other participating laboratories, comprising three solutions (CAGS‐Fe, CAGS‐Cu and CAGS‐Zn) and one basalt (CAGS‐Basalt). These materials exhibit sufficient homogeneity and stability for application in Fe, Cu and Zn isotopic ratio determinations. Reference values were determined by inter‐laboratory analytical comparisons involving up to eight participating laboratories employing MC‐ICP‐MS techniques, based on the unweighted means of submitted results. Isotopic compositions are reported in per mil notation, based on reference materials IRMM‐014 for Fe, NIST SRM 976 for Cu and IRMM‐3702 for Zn. Respective reference values of CAGS‐Fe, CAGS‐Cu and CAGS‐Zn solutions are as follows: δ⁵⁶Fe = 0.83 ± 0.07 and δ⁵⁷Fe = 1.20 ± 0.13, δ⁶⁵Cu = 0.57 ± 0.06, and δ⁶⁶Zn = ?0.79 ± 0.12 and δ⁶⁸Zn = ?1.65 ± 0.24, respectively. Those of CAGS‐Basalt are δ⁵⁶Fe = 0.15 ± 0.07, δ⁵⁷Fe = 0.22 ± 0.10, δ⁶⁵Cu = 0.12 ± 0.08, δ⁶⁶Zn = 0.17 ± 0.13, and δ⁶⁸Zn = 0.34 ± 0.26 (2s).     

河南桐柏围山城地区主要侵入岩年代学与地球化学特征

河南省桐柏围山城地区位于华北板块与扬子板块之间的秦岭造山带与大别造山带的衔接部位,本文对产于该区的主要侵入岩体开展了锆石SHRIMP测年和岩石地球化学特征研究。总共对8件样品开展了SHRIMP测年,其中产于破山银矿区的云斜煌岩获得的锆石SHRIMP测年结果为461.8 ± 9.7 Ma,MSWD＝1.10,表明其形成于加里东中期。在桃园岩体及其南部混染带内产出的变辉长岩、石英闪长岩、花岗闪长岩和黑云母花岗岩共获得了6组年龄数据,分别是431.7 ± 8.3 Ma （MSWD＝0.76）、432.3 ± 7.5Ma （MSWD＝0.45）、470.3 ± 8.3Ma（MSWD＝1.3）、431.5 ± 8.2 Ma（MSWD＝1.6）、433 ± 11 Ma（MSWD＝1.8）和426.7 ± 9.1 Ma（MSWD＝1.6）,说明桃园岩体是加里东晚期岩浆侵位产物。梁湾岩体花岗闪长岩和二长花岗岩的锆石SHRIMP测年结果分别为132.5 ± 2.3Ma （MSWD＝1.5）和137.0 ± 3.4Ma （MSWD＝1.9）,为燕山中期。锆石SHRIMP测年结果表明,围山城地区主要侵入岩的岩浆活动集中在三个时期,分别是460-470Ma,430Ma和135Ma。侵入岩体的岩石地球化学研究结果表明,与加里东晚期花岗岩相比,燕山中期花岗岩明显富K、Nb和Rb贫Na和Y。Pb-Sr-Nd同位素示踪研究表明,加里东晚期花岗岩明显富含放射性成因Pb,其206Pb/204Pb值为19.342～19.712,平均值19.512,（87Sr/86Sr）i值较低,变化于0.70211~0.704899,εNd (t)值均为正值,变化范围为+3.55～+7.53,显示成岩物质来源较深,可能来自亏损地幔;而燕山中期花岗岩的放射性成因Pb含量低,206Pb/204Pb值为17.278～17.492,平均值17.370, （87Sr/86Sr）i值相对较高,为0.707004~0.716968,εNd (t)值均为较大负值,变化范围为-16.95～-9.76,显示成岩物质来源较浅,可能来自下地壳。围山城地区加里东晚期花岗岩与燕山中期花岗岩岩石地球化学特征上的差别与它们形成时所处的大地构造环境有关,加里东晚期花岗岩形成于弧后环境,而燕山中期花岗岩则形成于华北与扬子两大板块碰撞后的岩石圈减薄与伸展构造环境。     

Hydro-climatic trends in the Abay/Upper Blue Nile basin,Ethiopia

Trends of the three hydro-meteorological variables precipitation, temperature and stream flow, represented by 13, 12, and 9 gauging stations, respectively, within the Abay/Upper Blue Nile basin have been studied to support water management in the region. The Trends were evaluated over different time periods depending on data availability at the stations. The statistical Mann–Kendall and Pettitt tests have been used to assess trends and change points respectively. The tests have been applied to mean annual, monthly, seasonal, 1- and 7-days annual minimum and maximum values for streamflow, while mean annual, monthly and seasonal timescales were applied to meteorological variables. The results are heterogeneous and depict statistically significant increasing/decreasing trends. Besides, it showed significant abrupt change of point upward/downward shift for streamflow and temperature time series. However, precipitation time series did not show any statistically significant trends in mean annual and seasonal scales across the examined stations.Increasing trends in temperature at different weather stations for the mean annual, rainy, dry and small rainy seasons are apparent. The mean temperature at Bahir Dar – typical station in the Lake Tana sub basin, has been increasing at the rate of about 0.5 °C/decade, 0.3 °C/decade in rainy season (June–September), 0.6 °C/decade in small rainy season (March–May), and 0.6 °C/decade in dry season (October–February). Other stations in the Abay/Upper Blue Nile show comparable results. Overall it is found that trends and change point times varied considerably across the stations and catchment to catchment. Identified significant trends can help to make better planning decisions for water management. However, the cause attributes to the observed changes in hydro-meteorological variables need further research. In particular the combined effects of land use/land cover change and climate variability on streamflow of Abay/Blue Nile basin and its tributaries needs to be understood better.