新疆库车新生代前陆褶皱冲断带的变形特征、时代和机制

库车前陆褶皱冲断带自北向南可分为基底冲断带、箱状背斜带、梳状背斜带和挠曲褶皱带,东西方向上可分为西段、中段和东段。本文分段叙述了各变形带的变形特征,指出东段箱状背斜带不发育,秋里塔格山脉(构造带)东延未进入东段,因而总体看自西向东变形强度减弱,地形上趋于夷平。该冲断带的形成经历了两次重大的冲断活动,分别发生在中新世和早(-中)更新世;相应地,该带可分为南、北两个"盆""山"亚系统,两者在地层记录、变形期次和变形机制上尚有若干差异。库车前陆褶皱冲断带的发育,除了受南天山的冲断和向南扩展引起的近南北向挤压应力场控制外,还受到基底断裂在新生代的活化和膏盐层底辟的制约,前者以近北西向的构造变换带及其共轭发育的近北东向断层最为重要,后者既控制了秋里塔格山脉的形成(主要受垂直的挤压应力场作用),也在库车前陆褶皱冲断带东西方向的变形分段中起了重要作用。文章还讨论了变形与地貌发育的关系和在油气勘探中的指导意义。     

黏声介质平面波有限差分叠前深度偏移及在莺歌海盆地的应用

莺琼盆地诸探区中存在底劈现象,深层气源产生的气体沿底劈产生的裂隙通道向上漫溢.漫溢过程中,一是充填在遇到的砂体中形成气藏;二是弥漫在上溢通道中,使得通道中的纵波速度发生变化,进而纵波波阻抗差异变小,反射变弱.另外,通道中气体的存在,会加强地层的吸收衰减,使得地震波振幅变弱、高频成分损失导致同相轴分辨率降低.利用OBC数据进行多波地震勘探和利用黏声介质的叠前深度偏移都是改善模糊区成像质量的重要方法技术.为此,本文提出用黏声介质平面波有限差分法叠前深度偏移成像方法改善气体充填区域的成像质量.黏声介质成像目的是补偿地震波的吸收衰减;平面波偏移成像目的是适应海上单炮数量巨大,提高波动方程叠前深度偏移成像的效率;有限差分法叠前偏移的目的是适应该区浅层气分布局域性极强、Q值的空间变化大的情况.在莺歌海某探区的实际数据上的黏声介质平面波有限差分叠前深度偏移试验证明,本方法是改善模糊区成像质量的较为有效的途径.     

Numerical modelling of rise and fall of a dense layer in salt diapirs

Numerical models are used to study the entrainment of a dense anhydrite layer by a diapir. The anhydrite layer is initially horizontally embedded within a viscous salt layer. The diapir is down-built by aggradation of non-Newtonian sediments ( n = 4, constant temperature) placed on the top of the salt layer. Several parameters (sedimentation rate, salt viscosity, perturbation width and stratigraphic position of the anhydrite layer) are studied systematically to understand their role in governing the entrainment of the anhydrite layer. High sedimentation rates during the early stages of the diapir evolution bury the initial perturbation and, thus, no diapir forms. The anhydrite layer sinks within the buried salt layer. For the same sedimentation rate, increasing viscosity of the salt layer decreases the rise rate of the diapir and reduces the amount (volume) of the anhydrite layer transported into the diapir. Model results show that viscous salt is capable of carrying separate blocks of the anhydrite layer to relatively higher stratigraphic levels. Varying the width of the initial perturbation (in our calculations 400–800 m), from which a diapir triggers, shows that wider diapirs can more easily entrain an embedded anhydrite layer than the narrower diapirs. The anhydrite layer is entrained as long as rise rate of the diapir exceeds the descent rate of the denser anhydrite layer. We conclude that the four parameters mentioned above govern the ability of a salt diapir to entrain an embedded dense layer. However, the model results show that the entrained blocks inevitably sink back if the rise rate of the diapir is less than the rate of descent of the anhydrite layer or the diapir is permanently covered by a stiff overburden in case of high sedimentation rates.     

Sub-seismic scale fracture pattern and in situ permeability data in the chalk atop of the Krempe salt ridge at Lägerdorf, NW Germany: Inferences on synfolding stress field evolution and its impact on fracture connectivity

Chalk is exposed in the Heidestrasse quarry at Lägerdorf, at the top of the NE-SW trending Krempe salt ridge. Structural data indicate the presence of two joint sets, striking almost parallel and perpendicular to the salt ridge, respectively, and of a set of conjugate extensional faults and fault zones striking NW-SE, i.e. almost perpendicular to the salt ridge. Within the overall NW-SE trend of joints and faults, strike variations occur from the massive chalk exposed in the lower half of the quarry, to the overlying layered chalk. A large variability characterizes the normalized spacing of both joint sets, which does not show any clear trend with layer dip. In situ measurements indicate that the cross-sectional permeability of tight joints increases 1-2 orders of magnitude with respect to the undeformed chalk. We propose that joint and fault azimuthal variability resulted from changes through time of the stress ellipsoid at the top of the salt ridge, while joint spacing variability is associated with the weak mechanical influence of bedding in chalk. Azimuthal variability improves fracture connectivity and, hence, permeability and fluid flow.     

Natural and human-induced dissolution and subsidence processes in the salt outcrop of the Cardona Diapir (NE Spain)

The Cardona Diapir in NE Spain, with a salt outcrop about 0.9 km² in area, has a well-developed endokarstic system that used to discharge into the Cardener River. Underground mining for potassium salt carried out from 1930 to 1990 caused significant changes in the topography and hydrology of the diapir. The accumulation of two halite slag heaps, totalling around 10 million tons, locally dammed the surface drainage, creating closed depressions and preferential zones of water recharge. The waters that infiltrated in one of these depressions, largely derived from uncontrolled sewage disposal, led to the generation of a 335-m-long human-induced cave excavated in one of the slag heaps. Moreover, the inflow of freshwater from the surrounding sandstone aquifer, caused by the excavation of a ventilation gallery, resulted in the generation of a 280-m-long cave. In March 1998, the interception of a phreatic conduit by a halite mine gallery 50 m deep caused dramatic changes in the hydrology and geomorphology of the diapir, including: (a) a sudden decline in the piezometric level of the karstic aquifer; (b) the inflow of freshwater and debris from the Cardener River into the endokarstic system and the mine galleries. A tunnel had to be constructed to divert the river flow from the salt outcrop; (c) massive dissolution of salt, creating new cavities and enlarging the pre-existing ones, including both mine galleries or cave passages. The 4,300-m-long Salt Meanders Cave was largely generated by the inrush of water from the Cardener River into the mine galleries; and (d) the generation of a large number of sinkholes in the vicinity of the Cardener River. An inventory of 178 sinkholes has allowed us to estimate minimum probability values of 4.7 and 8 sinkholes/km²·year for time intervals previous and subsequent to the 1998 mine flood event, respectively.     

Emplacement of Proterozoic massif-type anorthosite during regional shortening: evidence from the Bolangir anorthosite complex (Eastern Ghats Province, India)

A study of the 933±32-Ma-old Bolangir massif-type anorthosite complex (Eastern Ghats Province, India) yielded strong evidence for anorthosite emplacement during regional shortening, and thereby new insights in massif-type anorthosite formation. Several lines of evidence strongly suggest synchronism of plutonism and regional deformation. First, structures in the country rocks, which imply N–S-directed shortening accompanied by E–W extension, are mirrored by a E–W trending post-magmatic foliation and N–S trending shear zones in the anorthosite complex. Near the intrusion, the foliation in the country rocks becomes parallel to the contact and an internal marginal foliation, and foliation triple points occur in the country rocks. Second, synshortening dikes inside and outside the anorthosite complex are filled with pluton-related melts. Third, ferrodiorites, which are considered late-stage differentiates of the anorthositic pluton, concentrate in tectonic voids at the pluton margin. Some of these occurrences have been affected by the last increments of the regional deformation, but others transect the same structures. Ascent mechanism and significance of the adjacent terrane boundary of the Eastern Ghats Belt for ascent and emplacement of the Bolangir anorthosite complex are discussed. The results of this study imply that emplacement of Proterozoic massif-type anorthosite is not restricted to extensional settings.     

滇中昆阳群刺穿构造形成机制研究

从昆阳群内刺穿构造时、究分布特征出发，详细研究刺穿体边界特征及其性质，体内物质组成与结构、构造和变质变形特点。分析地质高孔隙流体作用在刺穿构造发生和成长中的地位和作用，提出地层高孔隙流体压力的波动和局部作用是导致刺穿的重要因素，逆冲推覆断裂作用应是继因民组地层岩石水力破裂、破裂作用之后所发生。昆阳群刺穿构造经历了本区地壳岩石圈由拉张体制下的张性破裂、断裂（刺穿）过程向挤压体制下的缩短、增厚过程的转化演化。最后，建立了刺穿构造形成的构造物理过程演化模型。     

底辟热流体上涌的数值模拟及其对早古生代青藏高原柴北缘祁连弧形成的启示

底辟流是研究地球内部物质循环与迁移的重要窗口,其动力学演化过程对于我们认识区域地质构造与演化具有重要意义.本文从热-结构力学的角度,建立三组不同的数值模型,研究底辟流上涌的动力学过程,分析底辟流半径、热-结构耦合、岩浆上涌通道对底辟流上涌过程的影响.该研究对认识早古生代祁连弧的形成过程具有重要启示.数值实验结果表明,底辟流半径越大底辟上涌速度越快;单个底辟很难直接上涌至上地壳底部,柴达木北缘超高压变质带和岩浆弧可能是由于多个底辟流持续上涌,最终发育稳定岩浆通道形成的,并且岩浆通道的形成对于超高压变质岩石的减压时间以及岩浆弧的形成时间均具有重要影响;具有稳定岩浆通道的单个底辟流从地幔深处90 km上涌至壳幔边界的过程中,在水平方向的侵蚀范围要比垂向侵蚀范围大一倍左右,研究结果表明安第斯型底辟流模型可以很好地描述早古生代柴达木北缘祁连弧的形成过程.     

Gas venting that bypasses the feather edge of marine hydrate,offshore Mauritania

Methane can be released from the vast marine hydrate reservoirs that surround continents into oceans and perhaps the atmosphere. But how these pathways work within the global carbon cycle now and during a warmer world is only partially understood. Here we use 3-D seismic data to identify what we interpret to be a gas venting system that bypasses the hydrate stability zone (HSZ) offshore of Mauritania. This venting is manifested by the presence of the acoustic wipe-out (AWO) across a densely faulted succession above a salt diapir and a set of morphological features including a substantial, ∼260 m wide and ∼32 m deep, pockmark at the seabed. The base of the HSZ is marked by a bottom simulating reflector (BSR) which deflects upwards above the diapir, rather than mimicking the seabed. We use a numerical modelling to show that this deflection is caused by the underlying salt diapir. It creates a trapping geometry for gas sealed by hydrate-clogged sediment. After entering the HSZ, some methane accumulated as hydrate in the levees of a buried canyon. Venting in this locality probably reduces the flux of gas to the landward limit of feather edge of hydrate, reducing the volume of gas that would be susceptible for release during a warmer world.