Methane-rich fluid inclusions in skarn near the giant REE–Nb–Fe deposit at Bayan Obo, Northern China

We report fluid inclusion data for skarn, formed at the contact between Hercynian granitoids and dolomite of the Proterozoic Bayan Obo Group, in the vicinity of Bayan Obo REE–Nb–Fe deposit, Inner Mongolia, China. Three types of fluid inclusions are identified: two-phase CH₄-rich, three-phase liquid–vapour–solid and two-phase aqueous inclusions. Using microthermometry and laser Raman microprobe analysis to calculate isochores for CH₄-bearing inclusions, we estimate fluid trapping conditions at T=280 to 344 °C and P<1 to 2.3 kbar. Such conditions are compatible with formation of CH₄ inclusions as a result of reaction between graphite in the country rocks (black slate sequence) and fluids derived from magma. The lack of carbonaceous material in the inclusions supports the hypothesis that CH₄ was generated during fluid migration rather than by in situ reaction. In contrast to the skarn, and despite the fact that similar graphite-bearing slates are found in the host rocks, no CH₄-bearing inclusions have been so far reported from Bayan Obo REE ores. We therefore conclude that the skarn-forming fluids in the contact aureole of the Hercynian granitoids were not involved at any stage in the formation of the Bayan Obo deposit.     

Continental crustal growth and the supercontinental cycle: evidence from the Central Asian Orogenic Belt

Studies of supercontinental cycle are mainly concentrated on the assembly, breakup and dispersal of supercontinents, and studies of continental crustal growth largely on the growth and loss (recycling) of the crust. These two problems have long been studied separately from each other. The Paleozoic–Mesozoic granites in the Central Asian Orogenic Belt have commonly positive Nd values, implying large-scale continental crustal growth in the Phanerozoic. They coincided temporally and spatially with the Phanerozoic Pangea supercontinental cycle, and overlapped in space with the P-wave high-V anomalies and calculated positions of subducted slabs for the last 180 Ma, all this suggests that the Phanerozoic Laurasia supercontinental assembly was accompanied by large-scale continental crustal growth in central Asia. Based on these observations, this paper proposes that there may be close and original correlations between a supercontinental cycle, continental crustal growth and catastrophic slab avalanches in the mantle. In this model we suggest that rapid continental crustal growth occurred during supercontinent assembly, whereas during supercontinental breakup and dispersal new additions of the crust were balanced by losses, resulting in a steady state system. Supercontinental cycle and continental crustal growth are both governed by changing patterns of mantle convection.     

Pressure State in Deep Crust and Formation Depth of UHP Metamorphic Rocks

INTRODUCTIONSincethediscoveryofeclogiteswithcoesiteanddia mondinclusionsrelatedtothecontinent continentcollision orogenyenvironment,theultrahigh pressuremetamorphism(UHPM )intheDabie Suluhasarousedgreatinterestinmanygeologists (Liouetal .,1994 ;Xuetal.,1992 ) .Experimentalstudieshaveprovedthatsuchmineralsasdia mond ,coesiteandomphaciteoccurredat 2 - 5GPa (andatthecorrespondingtemperatures) (Stevenetal.,1982 ;MirwaldandMasonne ,1980 ) .However,itdoesnotmeanthatthemetamorphicrockscanbe…     

Time-Frequency Variations of Plio-Pleistocene Foraminiferal Isotopes： A Case Study from Southern South China Sea

The continuous wavelet transform (CWT) analysis reveals the instantaneous variability of the foraminiferal δ18O and δ13C of Site 1143 for the past 5 Ma at the eccentricity, obliquity and precession bands. The cross CWT analysis further demonstrates nonstationary phases of the benthic -δ18O relative to ETP at the three primary Milankovitch bands in the last 5 Ma. The instantaneous phases between benthic -δ18O and δ13C at the precession band display a prominent 128 ka period, probably the cyclicity of the nonstationary climate close to the eccentricity. To explain these nonstationary phases, it is desirable to introduce a nonlinear response model to the global climate system, in which the output has a prominent cycle around 100 ka to match the 128 ka cycle of the instantaneous phase of the δ13C and -δ18O on the precession band.     

碎石桩复合地基检测分析

结合南京钢铁集团新钢铁厂碎石桩复合地基工程实例，从桩身的密实性和连续性、桩体周围土的隆起量以及桩间土挤密效果3个方面对碎石桩复合地基进行检测分析。     

Late Quaternary downcutting rates of the Qianyou River from U/Th speleothem dates, Qinling mountains, China

Dating deposits in caves formed by rivers may yield insight into rates and processes of bedrock incision. Three cave passages at different levels have developed in the walls of the Qianyou River valley in the Qinling mountains, south of the city of Xian, China. Twelve speleothem samples near the position of palaeowater tables in three cave passages are dated by the ²³⁰Th dating method. The results show that the river cut down at the rate of 0.23 ± 0.02 mm/yr from 358,000 ± 38,000 to 247,000 ± 28,000 yr ago, 0.19 ± 0.03 mm/yr from 247,000 ± 28,000 to 118,000 ± 19,000 yr ago, and 0.51 ± 0.08 mm/yr from 118,000 ± 19,000 yr ago until today. These fall very close to the glacial-interglacial transition following marine oxygen isotope stages 10, 8, and 6, respectively. The increase in downcutting rates during the interglacial period is consistent with warm, wet weather, increasing rates of erosion. This may lead us toward an underlying mechanism for modulating incision that is not in a direct response to the presence of headwater glaciers.     

Acidification and Trace Metals of Lakes in Taiwan

One hundred and eighty lakes, ponds and reservoirs in Taiwan, and the offshore islands have been investigated since 1985. Effects such as warming/cooling, mixing, photosynthesis and respiration on pH have been identified. These effects were found to be less profound than those resulting from the geology. Since there is little rain or lake water pH data available prior to 1970, it was necessary to use proxy data in order to ascertain the history of lake acidification. In this study, we present data based on diatoms in a sediment core collected from a lake in the remote subalpine region of southern Taiwan. The acidity of this lake water was found to have increased since 1900. We measured the concentrations of 55 chemical species in lake water samples. In addition, concentrations of 26 chemical species were obtained from sediments. Conductivity, alkalinity (HCO₃ ^?), most other major and minor chemical species, as well as the non sea-salt SO₄/Na ratio in lake water clearly decrease with elevation. Distribution of pH is similar, although the trend is less clear. Distribution of trace metals, however, shows a different trend as anthropogenic pollution, diagenetic reduction and lake acidification are at play.     

乌拉苔草光合速率日变化及日同化量

乌拉苔草沼泽是长白山沟谷湿地的重要类型 ,对其光合速率研究的结果表明 ,乌拉苔草光合速率日变化呈单峰曲线 ,最高峰出现在 1 0时 ,最大值是 1 8.0 7μmol(CO2 ) / (m2 ·s) ;与其该群落伴生的修氏苔草光合速率日变化出现“午休”现象。影响光合速率最大的环境因素是光量子通量密度和叶温 ,呈极显著的正相关 ,其他因素亦多呈正相关 ,环境因子综合影响了乌拉苔草的光合日进程。乌拉苔草光合作用的日总同化量为 1 896 0 1 .2 μmol(CO2 ) /m2 ,是光合能力较强的一种沼泽植物     

以色列解决水资源短缺对我国西北地区水资源开发的启示

以色列解决水资源问题的经验对新时期中国经济社会可持续发展有着现实的借鉴意义。本文分析了以色列的水资源问题及解决措施，结合我国西北地区的实际情况提出了对西北水资源开发的建议和设想。     

从等值线图形获取DAT和GRD格式的数据文件

在盆地模拟研究工作中，需要处理大量的地质数据和地质图件，一方面，随时需要把各种数据变为可视的图形；另一方面，还时常需要从图形中得到研究中所必需的数据，例如，由构造图得到研究区域的深度数据文件。本文介绍一种从等值线图形获取DAT格式和网格化GRD格式的数据文件的方法。