Petrogenesis of the Post-kinematic Magmatism of the Central Finland Granitoid Complex II; Sources and Magmatic Evolution

The 1·88–1·87 Ga post-kinematic granitoidsof the Central Finland Granitoid Complex (CFGC) provide a keygeochemical link to understanding granite formation in Paleoproterozoicorogenic and post-orogenic terrains. Thickness of the crustand intra-crustal differentiation processes played an importantrole in the formation of three granitoid types that shortlyfollowed the peak of the Svecofennian orogeny. In the easternCFGC, pyroxene-bearing plutons with C-type geochemical affinitiespredominate. These were formed from a mixture of low- to moderate-degreepartial melts (30%) of mafic mantle-derived (basaltic, 49% SiO₂)source rocks and partial melts of pre-existing mafic granulitelower crust at depth. In the western CFGC, high-silica, iron-rich,fluorite-bearing plutons with A-type granite characteristicspredominate. A higher thermal gradient, thinner upper and lowercrust, and significantly more shallow Moho depth resulted inhigher proportions of crustal melts (0·3–0·4vs 0·1–0·2 in the eastern CFGC) incorporatedinto the partial melts of a mafic mantle-derived source. A geochemicalmodel focusing on the Jämsä and Honkajoki plutonsof the post-kinematic suite is presented, constraining the natureof the source rock(s), the degree of partial melting, proportionsof partial melts and fractionation processes involved. KEY WORDS: magmatic evolution; geochemistry; Proterozoic; granite; Finland     

Vertical profiles of biospheric and fossil fuel-derived CO2 and fossil fuel CO2 : CO ratios from airborne measurements of Δ14C, CO2 and CO above Colorado, USA

Measurements of  Δ¹⁴C  in atmospheric CO₂ are an effective method of separating CO₂ additions from fossil fuel and biospheric sources or sinks of CO₂. We illustrate this technique with vertical profiles of CO₂ and  Δ¹⁴C  analysed in whole air flask samples collected above Colorado, USA in May and July 2004. Comparison of lower tropospheric composition to cleaner air at higher altitudes (>5 km) revealed considerable additions from respiration in the morning in both urban and rural locations. Afternoon concentrations were mainly governed by fossil fuel emissions and boundary layer depth, also showing net biospheric CO₂ uptake in some cases. We estimate local industrial CO₂:CO emission ratios using in situ measurements of CO concentration. Ratios are found to vary by 100% and average 57 mole CO₂:1 mole CO, higher than expected from emissions inventories. Uncertainty in CO₂ from different sources was ±1.1 to ±4.1 ppm for addition or uptake of −4.6 to 55.8 ppm, limited by  Δ¹⁴C  measurement precision and uncertainty in background  Δ¹⁴C  and CO₂ levels.     

English Jurassic dasyclads: seaweed indicators of marine climate

Aragonitic chlorophyte (green) algae, typical of the warm seas of the Tethyan area, reached as far north as the present Cotswolds of Southern England in mid-Jurassic times, when conditions made colonisation possible. Few in numbers and species, they appear to show features similar to those of their living descendants found today in warm seas marginal to the tropics, so confirming the Jurassic palaeolatitude arrived at independently from palaeogeographical studies.     

Oxygen Isotope Geochemistry of Oceanic-Arc Lavas

Variations of oxygen isotope ratios in arc-related lavas canconstrain the contributions of subducted crustal igneous rocks,sediments, and fluids to the sub-arc mantle. We have measuredoxygen isotope ratios in 72 arc and back-arc lavas from fiveocean–ocean subduction zone systems using laser-fluorinationanalyses of olivine and other phenocrysts and glass. Eightypercent of our samples have     

Petrogenesis of the Post-kinematic Magmatism of the Central Finland Granitoid Complex I; Radiogenic Isotope Constraints and Implications for Crustal Evolution

Post-kinematic granitoids of the Central Finland Granitoid Complex(CFGC) were emplaced into the Palaeoproterozoic crust of centralFinland shortly after the     

Eelgrass beds and bare substrata – sparid and mugilid composition in contrasting littoral estuarine habitats

Seagrass beds serve as nursery grounds for many fish species and often play an important role in the juvenile stages of economically and recreationally important fishes. The eelgrass Zostera capensis is the dominant submerged macrophyte in permanently open South African estuaries and occupies large intertidal and subtidal areas within the Knysna system. The primary objective of this study was to compare the occurrence of sparids and mugilids in eelgrass and nearby bare sediment areas using sampling with seine nets. The hypothesis that was tested is that mugilids are dominant in unvegetated areas of the Knysna Estuary littoral whereas sparids predominate within eelgrass beds located in the same zone. The results indicate that the family Mugilidae is better represented at unvegetated sites when compared to members of the family Sparidae, with the exception of Lithognathus lithognathus, but that the dominant three sparids and dominant two mugilids were most abundant in sparse eelgrass beds that included both bare and vegetated areas within this habitat type. The main fish species responsible for the separation of fish assemblages associated with unvegetated sites versus those associated with vegetated areas were Rhabdosargus holubi, Liza dumerili, Liza richardsonii, Lithognathus lithognathus, Sarpa salpa and Diplodus capensis, with R. holubi, S. salpa and D. capensis being mainly attracted to eelgrass habitats and L. dumerili, L. richardsonii and L. lithognathus having a stronger affinity for bare areas. This finding confirms a previous estuarine study in the nearby Swartvlei lake littoral, which found that sparids dominated areas where aquatic macrophytes were extensive and that mugilids became more prevalent at those same sites when the macrophytes underwent complete senescence. The length-frequency distributions of some sparid and mugilid species differed considerably between eelgrass and bare sediment areas, whereas those of other species showed little or no difference between these two habitat types.     

河北承德黑山铁矿床热液成矿特征及流体包裹体研究

黑山大型钒钛磁铁矿矿床产于大庙斜长岩杂岩体中,是承德地区最重要的"大庙式"岩浆型铁矿床。笔者在矿区野外地质观察过程中发现,穿插于斜长岩中的铁磷矿脉、磁铁矿硫化物矿脉有热液成矿作用的显示,表明黑山铁矿床成因除传统认为的岩浆期结晶、熔离、矿浆贯入成矿作用外,还有热液期的成矿作用发生。本文对热液成矿期铁磷矿石中磷灰石和矿化蚀变石英中的流体包裹体进行了显微测温和激光拉曼光谱分析。结果表明,磷灰石中原生包裹体可以分为气液两相包裹体、含子矿物包裹体、含液态CO2三相包裹体、单液相、单气相包裹体5类,均一温度主要集中于180～420℃,盐度主要集中于6.2%～38.9%NaCleq,流体包裹体气相成分主要为CO2、N2和CH4,液相成分主要为H2O,固相成分主要为方解石、石盐、白云石及铁氧化物子矿物。石英中流体包裹体类型和成分与磷灰石中的类似,但固相成分未发现石盐和不透明金属子矿物,均一温度变化于149～422℃,盐度变化于5.7%～22.9%NaCleq。成矿流体为CaCl2-NaCl-H2O-CO2体系,均一温度和盐度呈现正相关连续渐变的特征。铁磷矿石的磷灰石中原生包裹体为流体包裹体,盐度高,子矿物种类复杂,组成中富含CO2和CH4等,这些特征显示成矿流体以岩浆热液为主;成矿机理可能与大气降水对岩浆热液的稀释有关。     

江西铜坑嶂钼矿和红山铜矿含矿斑岩锆石U-Pb定年及其地质意义

江西铜坑嶂钼矿和红山铜矿是在武夷山成矿带中最近发现的两个斑岩型矿床。本文利用LA-ICP-MS锆石U-Pb定年方法对铜坑嶂花岗斑岩和红山含矿花岗斑岩分别进行了年代学研究,获得铜坑嶂岩体中花岗斑岩的锆石年龄为138±1Ma,代表斑岩体侵位的年龄;红山矿区含矿斑岩的锆石年龄,分作两期,分别为99Ma和49Ma,两期不同的年龄可能代表了两期热事件。研究表明,铜坑嶂钼矿的成岩成矿时代均发生在白垩纪,其岩浆作用与成矿作用基本吻合。综合前人资料,认为铜坑嶂钼矿区的斑岩和红山铜矿区的斑岩可能分别形成于大陆弧后伸展带和岩石圈伸展环境。     

Rock Weathering Processes in Antarctica: A Comparison of Some Recent Studies with Those from the Northern Hemisphere

A review of some recent studies on rock weathering in Antarctica has revealed that Antarctic weathering research has a significant contribution to make to the ongoing debate about rock weathering in cold climates. Largely conducted in the field rather than the laboratory as in the Northern Hemisphere, it demonstrates that whilst all weathering processes can occur in Antarctica this is highly localised and dependent on the particular micro‐environment. Freeze‐thaw, for example, is not the most dominant process in many parts of Antarctica. The right combination of rock temperature and moisture can mean that salt, insolation, hydration or even chemical weathering can predominate.