萨拉乌苏河流域MGS1层段微量元素记录的全新世千年尺度的气候变化

本文以毛乌素沙漠东南缘萨拉乌苏河流域米浪沟湾剖面MGS1层段为代表,试图通过对其的微量元素分析结果探讨该地全新世千年尺度的气候变化.在分析的14种微量元素中,除Cr和Zn以外的12种元素P、Pb、Rb、Nb、Zr、V、Sr、Cu、Ni、As、Ba、Co含量在MGS1剖面的垂直方向上具有这样的分布规律:元素含量值在沙丘砂...     

http://www.sciencedirect.com/science/article/pii/S1674987113000856

Sulphide inclusions, which represent melts trapped in the minerals of magmatic rocks and xenoliths, provide important clues to the behaviour of immiscible sulphide liquids during the evolution of magmas and the formation of NieCueFe deposits. We describe sulphide inclusions from unique ultramafic clots within mafic xenoliths, from the mafic xenoliths themselves, and from the three silica-rich host plutons in Tongling, China. For the first time, we are able to propose a general framework model for the evolution of sulphide melts during the evolution of mafic to felsic magmas from the upper mantle to the upper crust. The model improves our understanding of the sulphide melt evolution in upper mantle to upper crust magmas, and provides insight into the formation of stratabound skarn-type FeeCu polymetallic deposits associated with felsic magmatism, thus promising to play an important role during prospecting for such deposits.     

Petrogenesis,geochronology, and tectonic significance of granitoids in the Tongshan intrusion,Anhui Province,Middle–Lower Yangtze River Valley,eastern China

The Tongshan copper deposit in Anhui Province is a typical mid-sized skarn and porphyry type deposit in the Anqing–Guichi district along the Middle–Lower Yangtze River Valley, eastern China. The Tongshan intrusion is closely related to this mineralization. The intrusion mainly comprises rocks that are quartz diorite porphyry, quartz monzonite porphyry, and granodiorite porphyry. Plagioclase in these rocks is mostly andesine (An = 31.0–42.9), along with minor oligoclase. Biotite is magnesium-rich [Mg/(Mg + Fe) = 0.52–0.67] and aluminum-poor (Al₂O₃ = 12.32–14.09 wt.%), and can be classified as magnesio-biotite. Hornblende is TiO₂-poor (<1.96 wt.%) and magnesium-rich [Mg/(Mg + Fe) > 0.60], and is magnesio-hornblende or edenite. The SHRIMP zircon U–Pb age of the quartz monzonite porphyry is 145.1 ± 1.2 Ma, which corresponds to the middle Yanshanian period. Whole-rock geochemical results show that the rocks are silica-rich (SiO₂ = 60.23–66.23 wt.%) and alkali-rich (K₂O + Na₂O = 4.97–8.72 wt.%), and low in calcium (CaO = 2.61–5.66 wt.%). Trace element results show enrichments in large ion lithophile element (e.g., K, Rb, and Ba) and depletions in some high field strength elements (e.g., Nb, Ta, P, and Ti). The total rare earth element (REE) content of the rocks is low (ΣREE < 200 μg/g), and they exhibit light REE enrichment [(La/Yb)_N > 10] and small positive Eu anomalies (average δEu = 1.16). These mineralogical, geochronological, and geochemical results show that the intrusion has a mixed crust–mantle source. The Tongshan intrusion was formed by multiple emplacements of crustally contaminated basaltic magma generated by varying degrees of partial melting of enriched lithospheric mantle and lower crust. Hornblende thermobarometry yielded magmatic crystallization temperatures of 652–788 °C and an average crystallization pressure of 1.4 kbar, which corresponds to a depth of approx. 4.7 km. Biotite thermobarometry yielded similar temperatures and lower pressures of 735–775 °C and 0.6 kbar (depth 2.1 km), respectively. The parental magma had a high oxygen fugacity and was produced in a volcanic arc setting related to subduction of the paleo-Pacific plate.     

Glacial and paraglacial history of the Troutbeck Valley,Cumbria, UK: integrating airborne LiDAR,multibeam bathymetry,and geological field mapping

High resolution airborne LiDAR (light detection and ranging) and multibeam bathymetry data, supplemented by geomorphological and geological field mapping are used to derive the glacial and post-glacial history of Troutbeck Valley (English Lake District) at a catchment scale. The results inform wider regional and ice sheet wide glacial reconstructions and demonstrate the effectiveness of an integrated approach combining geomorphological and sedimentological signatures with remote sensing. The holistic catchment approach is used to reconstruct palaeo-ice flow and behaviour of a small part of the last British and Irish Ice Sheet, identifying a series of depositional environments that accompanied both ice advance, ice retreat and post-glacial deposition within the Lake District. Drumlins are mapped in the lower catchment and show multiple regional (wider-extent) ice flow events and a sedimentology consistent with deposition by lodgement processes during the Main Late Devensian Stadial. Other subglacial deposits include till sequences formed under variable basal conditions beneath an advancing ice mass. Retreat features include a suite of recessional moraines formed by still-stands or small readvances of an outlet glacier. Following deglaciation, major sediment redistribution led to formation of a large fan delta via paraglacial and post-glacial fluvial sedimentation. This study indicates that an integrated approach, using geomorphology, sedimentology and remote sensing on a catchment scale, is capable of deriving a more in-depth understanding of regional ice sheet reconstructions and highlights the complexity of palaeo-ice sheet dynamics at a range of spatial scales.     

萨拉乌苏河酒坊台剖面末次间冰阶以来的气候环境演化

酒坊台剖面位于萨拉乌苏河流域下游,其中末次间冰阶以来主要为风成砂沉积,间夹砂质古土壤和湖沼相粘土层等,对环境信息有良好的记录。OSL年龄结果表明该剖面顶部记录了末次冰期间冰阶(约52 ka B.P.)以来的气候演化历史。通过对剖面高精度的粒度和磁化率分析,结合Rb、Sr元素含量及其比值综合分析,表明末次冰期间冰阶以来该剖面自上而下可划分为3个主要层段,对应了深海氧同位素MIS 1~3。同时在MIS 3阶段呈现出明显的MIS 3a、3b、3c亚段,结合区域研究资料,表明萨拉乌苏河流域在中—长时间尺度上,对全球性和区域性气候事件有良好的沉积响应。     

Climatic response of Quaternary alluvial deposits in the upper Kali Gandaki valley (West Nepal)

The terraces at the confluence of Kali Gandaki and Miristi Khola (West Nepal) consist of coarse-grained deposits which are considered to be Late Pleistocene to Holocene in age. The stacking pattern of lithofacies is characterised by an alternation of fluvial and debris flow deposits. These periodic changes in sedimentation processes are attributed to climatic variations.Deposits of extended, highly mobile, braided rivers most probably developed under glacial conditions and reflect high sediment supply and high water discharge rates. Deposits of small, only moderately braided river systems evolved during a warmer climate with comparatively low sediment supply and water discharge rates. The mobilisation and redeposition of morainic material by enormous debris flows predominately occurred at the beginning of a warm period and was triggered by earthquakes, glacier lake outburst floods or strong monsoonal rain.     

Multi‐basin depositional framework for moisture‐balance reconstruction during the last 1300 years at Lake Bogoria,central Kenya Rift Valley

Multi‐proxy analysis of sediment cores from five key locations in hypersaline, alkaline Lake Bogoria (central Kenya Rift Valley) has allowed reconstruction of its history of depositional and hydrological change during the past 1300 years. Analyses including organic matter and carbonate content, granulometry, mineralogical composition, charcoal counting and high‐resolution scanning of magnetic susceptibility and elemental geochemistry resulted in a detailed sedimentological and compositional characterization of lacustrine deposits in the three lake basins and on the two sills separating them. These palaeolimnological data were supplemented with information on present‐day sedimentation conditions based on seasonal sampling of settling particles and on measurement of physicochemical profiles through the water column. A new age model based on ²¹⁰Pb, ¹³⁷Cs and ¹⁴C dating captures the sediment chronology of this hydrochemically complex and geothermally fed lake. An extensive set of chronological tie points between the equivalent high‐resolution proxy time series of the five sediment sequences allowed transfer of radiometric dates between the basins, enabling interbasin comparison of sedimentation dynamics through time. The resulting reconstruction demonstrates considerable moisture‐balance variability through time, reflecting regional hydroclimate dynamics over the past 1300 years. Between ca 690 and 950 AD , the central and southern basins of Lake Bogoria were reduced to shallow and separated brine pools. In the former, occasional near‐complete desiccation triggered massive trona precipitation. Between ca 950 and 1100 AD , slightly higher water levels allowed the build‐up of high pCO ₂ leading to precipitation of nahcolite still under strongly evaporative conditions. Lake Bogoria experienced a pronounced highstand between ca 1100 and 1350 AD , only to recede again afterwards. For a substantial part of the time between ca 1350 and 1800 AD , the northern basin was probably disconnected from the united central and southern basins. Throughout the last two centuries, lake level has been relatively high compared to the rest of the past millennium. Evidence for increased terrestrial sediment supply in recent decades, due to anthropogenic soil erosion in the wider Bogoria catchment, is a reason for concern about possible adverse impacts on the unique ecosystem of Lake Bogoria.     

Geochemistry of the Great Valley Group: an integrated provenance record

Sedimentary geochemistry of fine-grained strata of the Great Valley Group (GVG) in California documents a provenance signal that may better represent unstable, mafic minerals and volcanic clasts within sediment source regions than the provenance signal documented in the petrofacies and detrital zircon analysis of coarser sedimentary fractions. Geochemistry of the GVG provides an overall provenance framework within which to interpret sandstone petrofacies and detrital zircon age signatures. The geochemical signature for all Sacramento Valley samples records an overall continental arc source, with significant variation but no clear spatial or temporal trends, indicating that the geochemical provenance signal remained relatively consistent and homogenized through deposition of Sacramento basin strata. The San Joaquin basin records a distinct geochemical provenance signature that shifted from Early to Late Cretaceous time, with Lower Cretaceous strata recording the most mafic trace element geochemical signature of any GVG samples, and Upper Cretaceous strata recording the most felsic geochemical signature. These provenance results suggest that the early San Joaquin basin received sediment from the southern Sierran foothills terranes and intruding plutons during the Early Cretaceous, with sediment sources shifting east as the southern Sierran batholith was exhumed and more deeply eroded during the Late Cretaceous. The GVG provenance record does not require sediment sources inboard of the arc at any time during GVG deposition, and even earliest Cretaceous drainage systems may not have traversed the arc to link the continental interior with the margin. Because the GVG provenance signature is entirely compatible with sediment sources within the Klamath Mountains, the northern and western Sierran foothills belt, and the main Cretaceous Sierran batholith, the Klamath-Sierran magmatic arc may have formed a high-standing topographic barrier throughout the Cretaceous period.     

The Atmospheric Water Resource over the Qilian-Heihe Valley

On the base of weather station data and the NCEP/NCAR reanalysis data, atmospheric water resource over the Qilian-Heihe Valley was analyzed, and the result shows that, the less water vapor transport source and the divergence of atmospheric stream eld are main cause for resulting in the little water vapor content over the Qilian-Heihe Valley. Annual mean atmospheric water vapor content over the Qilian-Heihe Valley is merely 30% and 40% over the south of the Yangtze River and the middle of North China, respectively. Because of its high elevation and high precipitation e ciency, the Qilian Mountains area has plentiful precipitation. And the lower surface temperature and evaporation make the surface water material gather easily and thus form runo . As for the Heihe Valley, for the low precipitation efficiency, there is little precipitation and its value is corresponded to the surface evaporation. Thus its contribution to the surface water is very small. In the grid of 2.5°×2.5° over the Qilian-Heihe Valley, annual influent and effluent water vapor amount are 668×109 and 650×109 m3, respectively. The net influent water vapor amount is 18×109 m3. The influent water vapor takes on reducing tendency and with an obvious descent in period of the 1970s-1980s. In the recent 40 years, because the air temperature over the Qilian-Heihe Valley is rising and the atmospheric water vapor content is descending, the decrease of precipitation would be inevitable.     

Using fuzzy logic in a Geographic Information System environment to enhance conceptually based prospectivity analysis of Mississippi Valley‐type mineralisation

Geographic Information Systems (GIS) provide an efficient vehicle for the generation of mineral prospectivity maps, which are products of the integration of large geological, geophysical and geochemical datasets that typify modern global‐scale mineral exploration. Conventionally, two contrasting approaches have been adopted, an empirical approach where there are numerous deposits of the type being sought in the analysed mature terrain, or a conceptual approach where there are insufficient known deposits for a statistically valid analysis. There are also a variety of potential methodologies for treatment of the data and their integration into a final prospectivity map. The Lennard Shelf represents the major Mississippi Valley‐type (MVT) province in Australia; however, there are only 13 deposits or major prospects known, making an empirical approach to prospectivity mapping impractical. Instead, a conceptual approach was adopted, where critical features that control the location of MVT deposits on the Lennard Shelf, as defined by widely accepted genetic models, were translated into features related to fluid pathways, depositional traps and fluid outflow zones, which can be mapped in a GIS and categorised as either regional or restricted diagnostic, or permissive criteria. All criteria were derived either directly from geological and structural data, or indirectly from geophysical and geochemical datasets. A fuzzy‐logic approach was adopted for the prospectivity analysis, where each interpreted critical feature of the conceptual model was assigned a weighting between 0 and 1 based on its inferred relative importance and reliability. The fuzzy‐logic method is able to cope with incomplete data, a common problem in regional‐scale exploration datasets. The data were best combined using the gamma operator to produce a fuzzy‐logic map for the prospectivity of MVT deposits on the southeastern Lennard Shelf. Five categories of prospectivity were defined. Importantly, from an exploration viewpoint, the two lowest prospectivity categories occupy ～90% and the highest two categories only 1.6% of the analysed area, yet eight of the 13 known MVT deposits lie in the latter and none in the former: i.e. all lie within ～10% of the area, despite the fact that deposit locations were not used directly in the analysis. The propectivity map also defines potentially mineralised areas in the central southeastern Lennard Shelf and the southern part of the Oscar Ranges, where there are currently no known deposits. Overall, the analysis demonstrates the power of fuzzy‐logic prospectivity mapping on a semi‐regional to regional scale, and emphasises the value of geological data, particularly accurate geological maps, in exploration for hydrothermal mineral deposits that formed late in the evolution of the terrain under exploration.