生物气CO2还原途径中碳同位素分馏作用研究及应用

地质历史中,CO2/H2还原产甲烷作用对生物气的形成具有十分重要的意义。中国柴达木盆地第四系生物气主要为CO2/H2还原型生物气。笔者以CO2/H2还原生气理论为指导,进行不同初始碳同位素值和不同赋存状态碳源的生物模拟实验,研究CO2/H2还原产气过程中发生的碳同位素分馏作用。实验结果表明,产物中δ13CH4值与底物的δ13C值呈很好的正相关关系;在反应母质过量的情况下,碳源的赋存状态可以影响产物甲烷的碳同位素组成。以游离形式CO2还原产生的甲烷δ13C值,相对于以HCO3-、CO23-离子形式产生的甲烷δ13C值轻。通过柴达木盆地东部第四系生物气田实例分析,探讨了该区生物气的主要底物CO2的来源及赋存状态,对评价盆地生物气资源和有利勘探区预测有重要的参考价值。     

滇西双江县勐库地区退变质榴辉岩中闪石类矿物的成因研究

勐库地区新近发现的退变质榴辉岩中晚期退变质作用形成的闪石类矿物十分丰富,其携带了大量晚期退变质过程中的岩石成因信息。本文通过系统的矿物学研究,鉴定出了3期10种闪石类矿物,其中以镁钙闪石、镁角闪石、铁镁钙闪石、铁韭闪石、透闪石、阳起石等钙质闪石类为主,有少量冻蓝闪石、蓝透闪石等钠-钙闪石类。研究发现,随着退变质过程中时间的推移,角闪石的形成环境逐渐由还原环境向弱氧化环境、氧化环境演变。根据角闪石电子探针成分测试结果计算了相应的温度、压力条件。结合岩相学的资料,将退变质过程分为3期:(1)第1期早阶段为近等温降压过程(p=0.56~0.75 GPa,t=642~709℃),主要形成铁韭闪石、铁镁钙闪石、镁钙闪石;晚阶段为等温降压过程(p=0.39~0.56 GPa,t=619~642℃),主要形成镁钙闪石及少量镁绿钙闪石、铁韭闪石;(2)第2期为降温降压过程(p=0.23~0.42 GPa,t=460~610℃),主要形成镁角闪石、冻蓝闪石及铁角闪石;(3)第3期为近等温降压过程(p=0.09~0.31 GPa,t=350~420℃),主要形成透闪石、阳起石、蓝透闪石等。闪石类的成分变化反映了退变质榴辉岩从地壳底部的角闪石榴辉岩-高压麻粒岩相温压环境向中上地壳角闪岩相、绿片岩相温压环境的渐次退变质作用过程。这与昌宁-孟连构造带上印支期的碰撞造山作用、燕山期的区域性地壳伸展、喜马拉雅期的陆内造山运动具有较好的对应关系。     

桂林地区古人类演化及环境变迁研分

桂林地区曾是古人类活动活跃的地区，据可以断代的古人类洞穴遗址统计，发现桂北地区大部分的洞穴遗址其年代的下限都在距今约7000a 左右，此后古人类离开了洞穴，史前文化也随之发生了重要改变。影响古人类演化的因素鹅很多，究竟是什么原因驱使古人类离开洞穴，改变生活习性，这一问题一直都是困扰考古学界的难题。本文通赤研究桂北地区洞穴遗址的堆积特点，结合洞穴沉积－堆积物的特征及其孢粉记录的古气候信息，探讨了季风气候变化对桂林地区古气候变化的影响作用和气候演变历史，揭示了桂林地区全新世以来的季风气候变化时间序列和突变事件以及对古人类生存环境的影响。距今7000a 左右为中全新世气候适宜期，东亚夏季风强盛，气温升高，桂林地区的降雨增多，一方面由于地下河水位升高，淹没了穴居洞穴，其次是由于降雨增多，导致洞穴湿度增大，从而迫使古人类搬出洞穴。     

Electrical conductivity of K-feldspar at high temperature and high pressure

Electrical conductivity measurements on dry polycrystalline K-feldspar were performed at 1.0 to 3.0 GPa and 873 to 1,173 K with a multi-anvil high-pressure apparatus and the Solartron-1260 Impedance/Gain Phase Analyzer in the frequency range of 10^?1 to 10⁶ Hz. At each temperature the complex impedance displays a perfect semi-circular arc that represents the grain-interior conduction. Under the experimental conditions, electrical conductivity exponentially increases with increasing temperature and slightly decreases with increasing pressure; however, the effect of pressure on the conductivity is less pronounced than that of temperature. The activation enthalpy decreases slightly from 0.99 to 1.02 eV with increasing pressure, and the activation energy and activation volume for K-feldspar are 0.98 eV and 1.46?±?0.17 cm³/mol, respectively. According to these Arrhenius parameters, ionic conduction is proposed to be the dominant conduction mechanism in K-feldspar at high temperatures and pressures, and potassium ions are the charge carriers transporting by an interstitial mechanism. The diffusion coefficient of potassium at high temperatures was calculated from our conductivity data on K-feldspar using Nernst–Einstein equation, and the results were compared with the previous experimental results.     

Helium-argon isotopic tracing for the Pb-Zn-Ag polymetallic ore deposits in the central-south segment of the Da Hinggan Ling Range

In recent years big strides have been made in the exploration of ores in the central-south segment of the Da Hinggan Ling Range, though some debates still exist on the metallogenesis and sources of ore-forming materials. Pyrite and other sulfides in direct relation to the Pb-Zn-Ag ore deposits were chosen for the He and Ar isotopic analysis of ore-forming fluids, and the first He and Ar isotope data have been obtained from the study region. ^3He/^4He ratios in 14 samples collected from 7 mining districts are 2.17×10^-6-12.52×10^-6, averaging 6.86×10^-6 and their R/Ra ratios are 1.56-9.01 Ra, averaging 4.37 Ra. By projecting the data points onto the ^3He-^4He concentrations diagram, all the points fall near the mantle helium area. The calculated mantle-source helium ratios are within the range of 19.58%-76.96%, with an average of 49.52%. Argon isotopic characteristics are close to those of mantle source, indicating that the ore-forming material was transport upwards via the multi-stage evolution of mantle plume and concentrated as ores in the favorable loci of mantle branch structures.     

A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt

1IntroductionThe northern segment of the South LancangjiangBelt refers to the terrain about200km east of theYunxian-Lingcang granite in the South LancangjiangBelt(Fig.1).During the seventh Five-Year Plan peri-od,Mo Xuanxue et al.(1993)undertook the resear…     

鄂尔多斯盆地纳岭沟铀矿床绿泥石特征及地质意义

纳岭沟铀矿床位于鄂尔多斯盆地北部,具有明显的后期热液作用的特征,矿体空间展布主要受控于绿色-灰色砂岩的过渡界面,与绿泥石化的蚀变砂岩关系密切。通过对纳岭沟铀矿床不同颜色砂岩中的绿泥石进行详细的岩相学研究和电子探针化学成分分析,依据绿泥石的成因与共生矿物的关系,识别出绿泥石主要的3种类型:填隙物型绿泥石,片状与黄铁矿共生型绿泥石以及黑云母蚀变型绿泥石;同时通过绿泥石的Fe-Si图解确定了纳岭沟铀矿床不同颜色砂岩中的绿泥石主要为铁镁绿泥石和密绿泥石。根据Al/(Fe+Mg+Al)-Mg/(Fe+Mg)的关系图解确定出不同颜色砂岩中的绿泥石具有铁镁质流体和泥质两种来源,通过绿泥石中主要阳离子与镁的关系图解和计算得出的绿泥石形成温度共同确定出绿泥石是多期次的中低温热液流体作用的产物。综合研究表明,纳岭沟铀矿床的绿泥石形成至少经历了温度稍高的还原性流体和温度稍低的氧化性流体等两个期次的流体作用,稍高温的还原性流体与成矿关系更为重要。与绿泥石形成有关的热液流体作用不仅带入了部分铀,还促进了铀的活化和运移。     

Diurnal Variations of Carbon Dioxide, Methane, and Nitrous Oxide Vertical Fluxes in a Subtropical Estuarine Marsh on Neap and Spring Tide Days

Measuring fluxes of greenhouse gases (GHGs) is fundamental to estimating their impact on global warming. We examined diurnal variations of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) vertical fluxes in a tidal marsh ecosystem. Measurements were recorded on neap and spring tide days in April and September 2010 in the Shanyutan wetland of the Min River estuary, southeast China. Here, we define a positive flux as directing into the atmosphere. CH₄ fluxes on the diurnal scale were positive throughout, and CH₄ emissions into the atmosphere on neap tide days were higher than on spring tide days. CH₄ releases from the marsh ecosystem on neap tide days were higher in the daytime; however, on spring tide days, daily variations of CH₄ emissions were more complex. The marsh ecosystem plays a twofold role in both releasing and assimilating CO₂ and N₂O gases on the diurnal scale. Average CO₂ fluxes were positive on the daily scale both on neap and spring days and were greater on the neap tide days than on spring tide days. Diurnal variations of N₂O fluxes fluctuated more. Over the diurnal period, soil temperature markedly controlled variations of CH₄ emissions compared to other soil factors, such as salinity and redox potential. Tidal water height was a key factor influencing GHGs fluxes at the water–air interface. Compared with N₂O, the diurnal course of CO₂ and CH₄ fluxes in the marsh ecosystem appeared to be directly controlled by marsh plants. These results have implications for sampling and scaling strategies for estimating GHGs fluxes in tidal marsh ecosystems.     

浙江省海岛沿岸水域微生物生态分布

文章报道了浙江海岛沿岸水域中异养细菌、氨化细菌和反硝化细菌的数量分布及异养细菌的种群组成。结果表明：本调查海区异养细菌的数量较多，其数量分布范围在２．０４×１０４～８．３６×１０６个／ｄｍ３之间；氨化细菌数量分布范围在３．０×１０３～１．１×１０６个／ｄｍ３之间；反硝化细菌的数量分布范围在３．０×１０２～１．１－１０６个／ｄｍ３之间。细菌的数量与环境中营养盐的浓度之间存在密切关系。在不同的海区异养细菌的种群组成存在一定的差异，在浙北海区，革兰氏阴性菌所占比例为４１．６％，在浙中海区为４６．９％，在浙南海区为６４．９％。