http://www.sciencedirect.com/science/article/pii/S1674987111000594

A new model is suggested for the history of the Baikal Rift,in deviation from the classic two-stage evolution scenario,based on a synthesis of the available data from the Baikal Basin and revised correlation between tectonic-lithological-stratigraphic complexes(TLSC) in sedimentary sections around Lake Baikal and seismic stratigraphic sequences(SSS) in the lake sediments.Unlike the previous models,the revised model places the onset of rifting during Late Cretaceous and comprises three major stages which are subdivided into several substages.The stages and the substages are separated by events of tectonic activity and stress reversal when additional compression produced folds and shear structures.The events that mark the stage boundaries show up as gaps,unconformities,and deformation features in the deposition patterns. The earliest Late Cretaceous-Oligocene stage began long before the India-Eurasia collision in a setting of diffuse extension that acted over a large territory of Asia.The NW-SE far-field pure extension produced an NE-striking half-graben oriented along an old zone of weakness at the edge of the Siberian craton.That was already the onset of rift evolution recorded in weathered lacustrine deposits on the Baikal shore and in a wedge-shaped acoustically transparent seismic unit in the lake sediments.The second stage spanning Late Oligocene-Early Pliocene time began with a stress change when the effect from the Eocene India-Eurasia collision had reached the region and became a major control of its geodynamics.The EW and NE transpression and shear from the collisional front transformed the Late Cretaceous half-graben into a U-shaped one which accumulated a deformed layered sequence of sediments.Rifting at the latest stage was driven by extension from a local source associated with hot mantle material rising to the base of the rifted crust.The asthenospheric upwarp first induced the growth of the Baikal dome and the related change from finer to coarser molasse deposition.With time,the upwarp became a more powerful stress source than the collision,and the stress vector returned to the previous NW-SE extension that changed the rift geometry back to a half-graben. The layered Late Pliocene-Quaternary subaerial tectonic-lithological-stratigraphic and the Quaternary submarine seismic stratigraphic units filling the latest half-graben remained almost undeformed.The rifting mechanisms were thus passive during two earlier stages and active during the third stage. The three-stage model of the rift history does not rule out the previous division into two major stages but rather extends its limits back into time as far as the Maastrichtian.Our model is consistent with geological, stratigraphic,structural,and geophysical data and provides further insights into the understanding of rifting in the Baikal region in particular and continental rifting in general.     

钾质火成岩,橄榄粗玄岩与金矿的直接与间接的联系

世界上许多低温到中温热液和斑岩型Ａｕ±Ｃｕ产出与钾质火成岩和橄榄粗玄岩相关或产于其中。容矿岩体多以高卤族元素如Ｃｌ和Ｆ、大离子亲石元素和贫高场强元素为特征。与钾质火成岩套有关的成矿作用往往限于三类构造环境：晚期大洋岛弧、大陆弧和后碰撞弧。晚期大洋岛弧的实例有巴布亚新几内亚Ｌｉｌｉｒ岛中更新世的Ｌａｄｏｌａｍ金矿床，斐济ＶｉｔｉＬｅｖｕ上新世的Ｅｍｐｅｒｏｒ金矿和澳大利亚新南威尔士奥陶纪Ｇｏｏｎｕｍｂｌａ斑岩铜金矿床。大陆弧的实例包括中生代一新生代智利安第斯山脉的许多低温金和斑岩型Ｃｕ－Ａｕ矿床。后碰撞弧的一个实例是中新世巴布亚新几内亚的Ｐｏｒｇｅｒａ金矿床。对于这些晚期大洋岛弧、大陆弧和后碰撞弧中与金一铜矿床有关的钾质火成岩，其云母斑晶中ＣＬ的含量与同构造环境非高钾岩石相比特别高。大洋岛弧中矿化钾质火成岩的云母斑晶中似乎以十分高的ＣＬ和Ｆ为特征。     

技术加网方法

技术加网方法［德］Ｄ．ＭｏｒｇｃｎｓｔｅｒｎＩ，所有各种加阿方法的出发点通常是一个设计方案。在该方案中对要加同的带有灰度值或颜色的面状和线状要素是按色谱识别的。对于每一灰度值将按设计方案来制作一张面状蒙片。对于颜色值则通常称色片。这两种复盖方法称为蒙...     

Physical Properties, Morphology and Petrological Characteristics of Pumices from the Central Indian Ocean Basin

About 400 pumice clasts collected from the Central Indian Ocean Basin (CIOB) were studied for their morphology and were classified based on their shape and size. A majority of the samples range between <1 cm and 36 cm and in the Zinggs shape diagram plot in the equant and oblate fields. The Corey Shape Factor for most of the samples is close to 0.7, which is common for volcaniclastic material. The physical properties such as density, specific gravity, void ratio, porosity, moisture content and degree of saturation, were determined for 30 pumice samples. Density varies from 0.21 to 0.74 g/cm3 specific gravity 1.84 to 3.27, void ratio 2.21 to 10.67, porosity 67% to 91%, moisture content during sinking 0.44 to 2.35 and degree of saturation varies from 26.5% to 86%. Binocular and electron microscopy studies reveal that 60% of the vesicles are elongated, 30% are spherical and 10% are fibrous. Petrography of the pumices exhibits vitrophyric texture with phenocrysts of feldspars and clinopyroxenes. X-ray diffractrogram and mineral analyses confirm plagioclase to be a major phase, while quartz and orthoclase are not uncommon. Todorokite is commonly present in the ferromanganese oxide coating present over some of the pumices. This paper also delves into some details concerning the controversial origin of the pumices and glass shards in the CIOB.     

土地利用与土地覆盖变化

文章概要介绍国际地圈－生物圈计划的核心计划之一－土地利用与土地覆盖变化的科学计划。阐述了该计划的形成历史，科学目标以及主要研究内容，指出ＬＵＣＣ研究目的是改善对全球土地利用和土地覆盖变化动态过程的认识，以着重提高替土地覆盖变化的能力。     

二维构造电阻率法有限元模拟中离散波数选择方法的研究

本文对两个异性点电源电场情况下转换电位函数φ(x,λ,z)的性态进行了分析,提出了选择离散波数的基本原则。文中所举算例表明,本文提出的方法是可行的.     

利用多光谱数据编绘怀俄明州山前地带白垩系页岩岩相图

岩相是最小的岩性单元,它能在盆地分析中用于确定沉积环境和古地理.它可指示单一的沉积事件,并可依颜色、结构、成分和沉积为造来决定.岩相图的编绘依赖于调查者在野外的判别,这对于巨厚而单一的页岩层系而言是特别困难的.我们发现热红外(8~14μm)和陆地卫星可见光一近红外图象提供了区分怀俄明州温德河与比格霍恩盆地Cody页岩层系的方法.用热红外和可见光一近红外图象与常规野外工作及实验室技术相结合,提供了怀俄明州山前地带36Ma年前发生的有关海平面变动的新认识.     

多米尼群和蓬戈拉群(南非德兰士瓦)底部前寒武纪古土壤的化学和矿物特征

我们研究了发现于(元古宙最下部)多米尼群及(太古宇)蓬戈拉群的沉积岩与下伏花岗岩(南非德兰士瓦)之间的蚀变带。该蚀变带有一过渡的下部界线,原生火成矿物向上到与上覆沉积岩接触处全部渐次破坏。Ca、Mg、Na、P和Mn在该带往上逐渐流失。化学和矿物变化以及可用的地层证据都与这些带所形成的古土壤是28—30亿年前前寒武纪风化作用产物的解释完全符合。古土壤形成后又遭到交代作用和变质作用。眼下古土壤中见到的绢云母可能是原始泥土经低温钾交代作用形成的。前蓬戈拉群古土壤中的红柱石可能由保存地下水流和钾交代作用的不透水带中的原始泥土经变质而生成。调查了三个地方的多米尼古土壤。除铁的性状外,上述三个地点的风化作用结果相似。有一处丧失了20％的铁,而另一处竟失去了75％和80％的原始铁含量。铁丧失量的差异可能是由于在颗粒大小和地形的活动中土壤通气量及大气圈气体的扩散所发生的变化所致。铁丧失量的变化可以用于把某些制约条件放在前寒武纪大气圈的组分上。受多米尼古土壤(上覆含铀砾岩)施加影响的特定制约条件,需要化学风化和温室效应,并可能存在扩散性的光化学氧化剂,氧分压和二氧化碳气体分压的可能范围:PO_2为0.02％到0.5 PAL(现代大气圈水平),PCO_2为5—30 PAL。