A reassessment of models for hydrocarbon generation in the Khibiny nepheline syenite complex, Kola Peninsula, Russia   总被引：2，自引：0，他引：2  

B. Beeskow  P.J. Treloar  A.H. Rankin  T.W. Vennemann  J. Spangenberg 《Lithos》2006,91(1-4):1-18

Although hydrocarbon-bearing fluids have been known from the alkaline igneous rocks of the Khibiny intrusion for many years, their origin remains enigmatic. A recently proposed model of post-magmatic hydrocarbon (HC) generation through Fischer-Tropsch (FT) type reactions suggests the hydration of Fe-bearing phases and release of H₂ which reacts with magmatically derived CO₂ to form CH₄ and higher HCs. However, new petrographic, microthermometric, laser Raman, bulk gas and isotope data are presented and discussed in the context of previously published work in order to reassess models of HC generation. The gas phase is dominated by CH₄ with only minor proportions of higher hydrocarbons. No remnants of the proposed primary CO₂-rich fluid are found in the complex. The majority of the fluid inclusions are of secondary nature and trapped in healed microfractures. This indicates a high fluid flux after magma crystallisation. Entrapment conditions for fluid inclusions are 450–550 °C at 2.8–4.5 kbar. These temperatures are too high for hydrocarbon gas generation through the FT reaction. Chemical analyses of rims of Fe-rich phases suggest that they are not the result of alteration but instead represent changes in magma composition during crystallisation. Furthermore, there is no clear relationship between the presence of Fe-rich minerals and the abundance of fluid inclusion planes (FIPs) as reported elsewhere. δ¹³C values for methane range from − 22.4‰ to − 5.4‰, confirming a largely abiogenic origin for the gas. The presence of primary CH₄-dominated fluid inclusions and melt inclusions, which contain a methane-rich gas phase, indicates a magmatic origin of the HCs. An increase in methane content, together with a decrease in δ¹³C isotope values towards the intrusion margin suggests that magmatically derived abiogenic hydrocarbons may have mixed with biogenic hydrocarbons derived from the surrounding country rocks.  相似文献   

Application of the QUILF thermobarometer to the peralkaline trachytes and pantellerites of the Eburru volcanic complex, East African Rift, Kenya   总被引：1，自引：0，他引：1  

Minghua Ren  Peter A. Omenda  Elizabeth Y. Anthony  John C. White  Ray Macdonald  D.K. Bailey   《Lithos》2006,91(1-4):109-124

The Quaternary Eburru volcanic complex in the south-central Kenya Rift consists of pantelleritic trachytes and pantellerites. The phenocryst assemblage in the trachytes is sanidine + fayalite + ferrohedenbergite + aenigmatite ± quartz ± ilmenite ± magnetite ± pyrrhotite ± pyrite. In the pantellerites, the assemblage is sanidine + quartz + ferrohedenbergite + fayalite + aenigmatite + ferrorichterite + pyrrhotite ± apatite, although fayalite, ferrohedenbergite and ilmenite are absent from more evolved rocks (e.g. with SiO₂ > 71%). QUILF temperature calculations for the trachytes range from 709 to 793 °C and for the pantellerites 668–708 °C, the latter temperatures being among the lowest recorded for peralkaline silicic magmas. The QUILF thermobarometer demonstrates that the Eburru magmas crystallized at relatively low oxidation states (ΔFMQ + 0.5 to − 1.6) for both trachytes and pantellerites. The trachytes and pantellerites evolved along separate liquid lines of descent, the trachytes possibly deriving from a more mafic parent by fractional crystallization and the pantellerites from extreme fractionation of comenditic magmas.  相似文献   

Soil quality changes in land degradation as indicated by soil chemical, biochemical and microbiological properties in a karst area of southwest Guizhou, China   总被引：7，自引：0，他引：7  

Pingjiu Zhang  Lianqing Li  Genxing Pan  Jingchen Ren 《Environmental Geology》2006,51(4):609-619

Not only the nutritional status and biological activity but also the soil ecological functioning or soil health has been impacted profoundly by land degradation in the karst area of southwest China where the karst ecosystems are generally considered as extremely vulnerable to land degradation under intensified land-use changes. The objectives of this study are to elucidate the changes in overall soil quality by a holistic approach of soil nutritional, biological activity, and soil health indicators in the karst area as impacted by intense cultivation and vegetation degradation. Topsoil samples were collected on selected eco-tesserae in a sequence of land degradation in a karst area of southwest Guizhou in 2004. The soil nutrient pools of organic carbon (C_org), extractable extracellular carbon (C_ext), total soil nitrogen (N_t), alkali-hydrolyzable nitrogen (N_ah), total phosphorus (P_t), available phosphorus (P_a) were analyzed by wet soil chemistry. The soil biological properties were studied by means of measurements of microbial biomass carbon (both by fumigation–extraction, FE-C_mic, and by calculation from substrate-incubation respiration, SIR-C_mic) of respiration [respiration without addition of substrates, basal respiration (BR), and potential respiration (PR) with substrate-incubation] and of soil enzyme activities (invertase, urease, and alkaline phosphatase). Soil health status was assessed by simple indices of C_mic/C_org and BR/C_mic in conjunction with bacterial community structures determined by polymerase chain reaction and denaturing gradient gel electrophoresis. While the nutritional pool parameters, such as C_org and C_ext, described basically the changes in soil life-supporting capacity with cultivation interference and vegetation declined, those parameters of biological activity such as FE-C_mic, SIR, and SIR-C_mic as well as bacterial community structures measured by molecular method evidenced well the changes in soil functioning for ecosystem health with the land degradation.  相似文献   

Petrology, geochemistry and the mechanisms determining the distribution of platinum-group element and base metal sulphide mineralisation in the Platreef at Overysel, northern Bushveld Complex, South Africa     

David A. Holwell  Iain McDonald 《Mineralium Deposita》2006,41(6):575-598

Platinum-group element (PGE) mineralisation within the Platreef at Overysel is controlled by the presence of base metal sulphides (BMS). The floor rocks at Overysel are Archean basement gneisses, and unlike other localities along the strike of the Platreef where the floor is comprised of Transvaal Supergroup sediments, the intimate PGE–BMS relationship holds strong into the footwall rocks. Decoupling of PGE from BMS is rare and the BMS and platinum-group mineral assemblages in the Platreef and the footwall are almost identical. There is minimal overprinting by hydrothermal fluids; therefore, the mineralisation style present at Overysel may represent the most ‘primary’ style of Platreef mineralisation preserved anywhere along the strike. Chondrite-normalised PGE profiles reveal a progressive fractionation of the PGE with depth into the footwall, with Ir, Ru and Rh dramatically depleted with depth compared to Pt, Pd and Au. This feature is not observed at Sandsloot and Zwartfontein, to the south of Overysel, where the footwall rocks are carbonates. There is evidence from rare earth element abundances and the amount of interstitial quartz towards the base of the Platreef pyroxenites that contamination by a felsic melt derived from partial melting of the gneissic footwall has taken place. Textural evidence in the gneisses suggests that a sulphide liquid percolated down into the footwall through a permeable, inter-granular network that was produced by partial melting around grain boundaries in the gneisses that was induced by the intrusion of the Platreef magma. PGE were originally concentrated within a sulphide liquid in the Platreef magma, and the crystallisation of monosulphide solid solution from the sulphide liquid removed the majority of the IPGE and Rh from it whilst still within the mafic Platreef. Transport of PGE into the gneisses, via downward migration of the residual sulphide liquid, fractionated out the remaining IPGE and Rh in the upper parts of the gneisses leaving a ‘slick’ of disseminated sulphides in the gneiss, with the residual liquid becoming progressively more depleted in these elements relative to Pt, Pd and Au. Highly sulphide-rich zones with massive sulphides formed where ponding of the sulphide liquid occurred due to permeability contrasts in the footwall. This study highlights the fact that there is a fundamental floor rock control on the mechanism of distribution of PGE from the Platreef into the footwall rocks. Where the floor rocks are sediments, fluid activity related to metamorphism, assimilation and later serpentinisation has decoupled PGE from BMS in places, and transport of PGE into the footwall is via hydrothermal fluids. In contrast, where the floor is comprised of anhydrous gneiss, such as at Overysel, there is limited fluid activity and PGE behaviour is controlled by the behaviour of sulphide liquids, producing an intimate PGE–BMS association. Xenoliths and irregular bands of chromitite within the Platreef are described in detail for the first time. These are rich in the IPGE and Rh, and evidence from laurite inclusions indicates they must have crystallised from a PGE-saturated magma. The disturbed and xenolithic nature of the chromitites would suggest they are rip-up clasts, either disturbed by later pulses of Platreef magma in a multi-phase emplacement or transported into the Platreef from a pre-existing source in a deeper staging chamber or conduit.  相似文献   

The chromite deposits associated with ophiolite complexes, Southeastern Desert, Egypt： Petrological and geochemical characteristics and mineralization     

Gehad M. Saleh 《中国地球化学学报》2006,25(4):307-317

1 Introduction The association of massive Fe-Ni-Cu sulfides andchromite is a very unusual feature of podiformchromitites occurring in mantle tectonites of ophioliticcomplexes. It has only been described in theSoutheastern Desert, Egypt, where sulfides a…  相似文献   

干涉合成孔径雷达（INSAR）复图像配准方法   总被引：1，自引：0，他引：1  

单世铎  赵拥军 《测绘学院学报》2005,22(2):131-133

合成孔径雷达干涉测量技术是使用图像中的相位信息来提取高精度的数字地面高程模型。精确的图像配准是合成孔径雷达干涉技术提取数字高程模型的关键步骤之一，配准质量将直接影响提取的地面高程的精度。配准按照其精度分为粗配准和精配准。文中采用基于幅度互相关函数法完成图像的粗配准。在粗配准的基础上，使用最小二乘配准算法进一步提高配准的精度。实际数据处理表明，配准精度能够满足INSAR数据处理的要求。  相似文献   

基于复小波变换的SAR图像斑点滤波方法   总被引：1，自引：0，他引：1  

张春华许素芹  陶荣华陈标 《测绘学院学报》2005,22(4):269-271

斑点噪声的存在使得SAR图像的应用受到较大的限制.文中首先介绍了SAR图像斑点噪声模型以及几种常用的SAR斑点噪声抑制方法;然后对小波变换斑点噪声滤波方法进行分析,提出了基于二元树复小波变换的SAR图像滤波方法.实验比较表明,二元树复小波变换抑制SAR斑点噪声效果明显,较小波变换更具有优越性.  相似文献   

岩石复电阻率Dias模型及其参数求取方法   总被引：4，自引：0，他引：4  

丁柱  童茂松  潘涛 《物探化探计算技术》2005,27(2):135-137

Dias模型是众多描述岩石复电阻率的频散特性模型中的一种,它不但参数少,且可由这些参数导出具有特定物理意义的参数。针对Dias模型参数的求取及反演解的不确定性评价,这里提出了一种模拟退火阻尼最小二乘联合反演方法。该方法首先将参数求解空间离散化,利用模拟退火找到全局最优解区间,然后利用阻尼最小二乘法在解空间进行求解。该方法有效地克服了原来两种方法的反演速度慢、反演结果依赖于初值的缺点,并实现了对反演结果多解性的评价。研究结果表明,对于岩石复电阻率数据的处理解释,Dias模型的使用比传统的Cole模型及其变形更具有潜在的优势。  相似文献   

近百年中国东部夏季降水的时空变率   总被引：4，自引：0，他引：4  

Li Xiaodong  Zhu Yafen  Qian Weihong 《大气科学进展》2002,19(6):1055-1068

利用中国东部25°N以北28个站1880-1999年夏季季降水序列,用旋转复经验正交函数（RCEOF）方法,研究了中国东部地区百年干湿的时空演变规律。结果表明,夏季降水空间变率大值区依次为:长江中下游地区、淮河流域、江南、华北、西南及东北。除西南外的5个关键区大体上反映了从6月到8月夏季雨带自南向北椎进所滞留的地区。旋转空间位相分布揭示了长江中下游地区、江南、东北的旱涝异常主要表现为驻波振动特征;而淮河流域、华北、西南地区显示出降水异常信号具有部分的行波特征。尤其第4空间模显示出旱涝异常信号从东北南部可沿着黄淮下游传到长江下游地区。对于近百年中国东部地区夏季于湿变化,长江中下游地区、淮河流域、华北及东北四个地区都存在20-25年时间尺度的周期振荡;长江中下游地区及华北地区都存在准60年时间尺度的振荡周期;东北地区主要表现出36年时间尺度的振荡周期;淮河流域存在明显的70-80年时间尺度的振荡周期;华北地区存在的11年时间尺度的振荡周期恰好与太阳黑子活动的11年周期相一致。在年代际时间尺度（包括次年代际时间尺度）上,长江中下游、淮河流域及华北地区的夏季降水的变化与太阳活动有显著的正相关。  相似文献   

复杂介质结构中折射界面的哈格多恩原理波前成像   总被引：6，自引：4，他引：6       下载免费PDF全文

徐朝繁  张先康  朱金芳  段永红  田晓峰  潘纪顺 《地震地质》2002,24(4):542-548

在城市活断层探测中 ,浅层结构常常表现为强烈的非均匀性 ,界面横向强烈起伏 ,层内速度变化较大 ,传统的基于平界面均匀层模型的折射资料处理方法不能适用。研究开发能应用于复杂介质结构中折射资料处理的方法就显得十分必要。文中基于惠更斯原理 ,用波前扩张法对波场作正演计算 ,根据哈格多恩折射波前成像原理 ,在lecomte算法和Hole有限差分计算程序的基础上 ,开发出 1种复杂介质结构中折射资料的处理方法与软件 ,并用此方法处理了福州城市活断层折射探测试验中在义序完成的 2条折射剖面资料。结果表明 :探测区浅层为 3层结构 ,分别为盖层、强风化层和基岩。基岩顶界面的埋深约为 5 8～ 5 2m ,盖层P波速度变化较大  相似文献