A two-stage evolution of Visakhapatnam-Paradip shelf,east coast of India,from magnetic studies

A detailed analysis of bathymetry and magnetic data of Visakhapatnam-Paradip shelf, east coast of India revealed three major structural lineaments over the shelf/slope of the area. Models derived from the anomalies associated with the trends indicate that trend A represents horst and graben type continental basement while trend B is due to a series of dyke intrusions. Trend C off Chilka lake forms the northward extension of 85°E lineation from deep sea Bengal Fan. A two stage evolution of the eastern continental margin of India has been inferred from the study of this part of the margin, viz., the rift stage evidenced by dyke intrusions of reverse polarity located within the inner part of the shelf and post-rift stage characterized by vertical tectonics in the form of a horst and graben type continental basement. The hotspot related aseismic 85°E ridge further complicated the tectonics of this part of the area.     

High iridium concentration of alkaline rocks of Deccan and implications to K/T boundary

We report here an unusually high concentration of iridium in some alkali basalts and alkaline rocks of Deccan region having an age of about 65Ma, similar to the age of the Cretaceous-Tertiary boundary. The alkali basalts of Anjar, in the western periphery of Deccan province, have iridium concentration as high as 178pg/g whereas the alkaline rocks and basalts associated with the Amba Dongar carbonatite complex have concentrations ranging between 8 and 80 pg/g. Some of these values are more than an order of magnitude higher than the concentration in the tholeiitic basalts of Deccan, indicating the significance of alkaline magmatism in the iridium inventory at the Cretaceous-Tertiary boundary. Despite higher concentration, their contribution to the global inventory of iridium in the Cretaceous-Tertiary boundary clays remains small. The concentration of iridium in fluorites from Amba Dongar was found to be <30 pg/g indicating that iridium is not incorporated during their formation in hydrothermal activity.     

http://www.sciencedirect.com/science/article/pii/S1674987111000855

During the last decades, several integrated studies of Tethyan Jurassic/Cretaceous boundary sections from different countries were published with the objective to indicate problems for the selection of biological, chemical or physical markers suitable for identification of the Jurassic/Cretaceous boundary e the only system boundary within the Phanerozoic still not fixed by GSSP. Drawing the boundary between the Jurassic and Cretaceous systems is a matter of global scale discussions. The problem of proposing possible J/K boundary stratotypes results from lack of a global index fossils, global sea level drop, paleogeographic changes causing development of isolated facies areas, as well as from the effect of Late Cimmerian Orogeny. This contribution summarizes and comments data on J/K boundary interval obtained from several important Tethyan sections and shows still existing problems and discrepancies in its determination.     

Chromium speciation in oxide-type compounds: application to minerals,gems, aqueous solutions and silicate glasses

Cr K-edge XANES spectra were obtained for a variety of Cr-bearing model compounds containing Cr(II), Cr(III), Cr(IV), Cr(V) and Cr(VI), in which the Cr-site symmetry is D4h, Oh and Td. The centroid position of the pre-edge feature is a better indicator of the Cr valence than the edge position. In Cr-rich oxides, higher-energy transitions must be excluded in order to refine a robust valence for Cr. The pre-edge for chromates is not unique and varies as a function of the CrO₄ ^2? moiety distortion, which is often related to Cr-polymerization (monochromate vs. dichromate). Both the analogy with the Mn K-pre-edge information and ab initio FEFF calculations of the pre-edge feature for Cr(III) and Cr(VI) confirm the experimental trends. This methodology is applied to the Cr K-edge pre-edge feature collected in gems (emerald, spinel and ruby), the layered minerals fuchsite and kämmererite, two Cr-bearing aqueous solutions and a set of sodo-calcic silicate glasses used for bottling sparkling white wine. In emerald and fuchsite, the Cr-site is differently distorted than its ruby or spinel counterpart. In a Cr(III)-bearing aqueous solution and sodo-calcic glass, no evidence for Cr(III) with Td and C3v symmetry is detected. However, minor amounts of chromate moieties (most likely monomeric) are detected in a glass synthesized in air. Preliminary spectra for the wine bottle glass suggest that only trace amounts of chromates might possibly be present in these glasses.     

Variation of the 0+ ion density during low and high solar activity as measured by the SR0SS-C2 satellite

The O⁺ ion density measured by the SROSS-C2 satellite during solar minima (year 1995, F_10.7 = 77) and maxima (year 2000, F_10.7 = 181) has been analyzed for studying diurnal, seasonal, latitudinal and geomagnetic variations. The study region covers an area encompassed between 5-3 5° N latitude and 65-95° E longitude over India at a ~500 km altitude (F2 region). The year 2000 shows significant enhancement in the annual average of O⁺ ion density and attainment of post sunset secondary enhancement compared to 1995. Attributed to photoionization, daytime shows a maximum ionization compared to nighttime. However, attainment of post sunset secondary maxima is attributed to the strong pre-reversal enhancement in the vertical E x B drift. The effect of geomagnetic activity Kp through the E x B drift dynamic movement on O⁺ ion density distribution studies indicates periodicities of seven and nine days in 1995 and 2000, respectively, and polynomial dependency of the O⁺ ion density on geomagnetic activity Kp. Further on, stratification of the O⁺ ion density according to latitude (5-35° N) indicates high density in mid-latitudes (12-24° N) compared to high and low latitudes, except in the winter of 1995, which shows a distinct trend (i.e., density decreases with increasing latitude).     

K-Ar法地质年龄国家一级标准物质ZBH-25黑云母的研制

ZBH-25黑云母采自北京房山花岗闪长岩体.它的40Ar/39Ar阶段加热实验结果表明,40Ar*在矿物晶格中保存均匀稳定,年龄谱平坦,39Ar析出量高达96%,40K-40Ar*同位素体系封闭良好,证明该黑云母结晶以后未受过热扰动.坪年龄为133.0±0.3 Ma,总气体年龄为132.1±0.6 Ma;36Ar/40Ar-39Ar/40Ar反等时线年龄为133.1±1.3 Ma,40Ar/36Ar初始值为293.5±1.6,与大气氩丰度比(295.5±0.5)处于同一范围,表明样品不含过剩氩.激光显微探针单颗粒坪年龄为132.8±0.2Ma,年龄谱和K/Ca谱线平坦,激光熔样总气体年龄为131.3±0.2Ma(图6).这几个Ar-Ar年龄的一致性,说明样品具有良好的均匀性和稳定性,是理想的K-Ar和Ar-Ar法年龄标准物质.对均匀性检验数据进行统计学方法检验,在0.05显著性水平下,证明K和40Ar*的F分布值小于F临界值,说明该样品是均匀的.国内外14个实验室参加了K含量的定值分析,15个实验室参加了40Ar*含量的定值分析,经统计学方法检验,结果显示全部定值数据都服从正态分布并具等精度.在置信概率为0.95时,40Ar*和K含量的相对标准偏差都小于0.5%.两个特性量值定值分析结果的一致值和不确定度分别为40Ar*=1.817±0.013×10-9 mol/g,K=7.60±0.02%,K-Ar年龄(标准值)=132.9±1.3Ma(2σ).此标准物质纯度为98.8%,粒度为0.25-0.63 mm,总重量为5800 g,缩分成最小样品单元共400瓶,每瓶重量为14.5 g.可供我国K-Ar和Ar-Ar法同位素年代学实验室使用120年.     

反射系数K法在地质灾害评价中的应用

应用电阻率测深法探测滑坡和塌陷,采用反射系数K法区分滑坡和塌陷的类型和性质,正确地评价地质灾害,为治理工作提供快速准确的地质依据。     

伊利石层间钾释放的远红外光谱研究

本文介绍了新近研究层间交换的远红外方法，并用该方法研究了金砂伊早石层间交换的性质，随着温度的升高，伊利石的远红外谱段从１０８ｃｍ＾－１向低波数方向偏移，３００Ｃ时为１０７ｃｍ＾－１，５００℃时为１０００ｃｍ＾－１，７００℃时为９８ｃｍ＾－１，同时，伊利石的释钾程度也伴随着增加，远红外谱同释放钾的能力有一清楚对比，因此可以用远红外方法预言伊利石释钾的能力，最后，利用量子化学计算的ＰＭ３方法首次从理论     

热对流成岩作用的基本特征与研究意义

介绍了热对流产生的条件与地质背景,指出火成侵入体、盐丘和活跃断层周围等温线陡倾斜场所易发生热对流成岩作用。综述了岩浆成因热对流的岩石学记录,包括热变质作用、突然升温—逐渐降温的自生矿物组合和相对高温的自生矿物类型,分析了自生伊利石的K/Ar年龄在热对流成岩作用研究中的作用。阐述了热对流成岩作用对盆地动力学、砂岩储层和油气运移研究的意义。