黄骅坳陷歧北斜坡油气成藏机制与成藏模式

挠曲坡折带油气资源前景广阔,已成为陆相湖盆中的勘探开发与研究热点。由于古地貌或古构造的差异造成多阶挠曲型斜坡地层发生多个折曲变形,同时,由于斜坡结构及构造特征、沉积特征和烃源岩特征等均存在较大的差异,导致复杂的油气分布和油气成藏过程。以多阶挠曲型斜坡——黄骅坳陷歧北斜坡为例,通过研究斜坡形成和演化过程中古地貌和断层耦合下的斜坡结构和构造特征、输导体系、油气运移路径和运移动力等特征,揭示了多阶挠曲斜坡的油气成藏机制。结果表明,歧北斜坡长轴和短轴方向上的古地形、断层及组合样式、砂体成因类型与延伸范围、与烃源岩接触关系、油气运移动力与路径等方面均存在较大差异。长轴方向具有以下特点：以挠曲坡折构造为界,高、中、低斜坡分异;大型断层不发育且三角洲砂体范围局限,中、低斜坡以近源砂体输导为主,砂体连通性好;形成了坡折背景的"缓坡-双边断脊优势-源控型"成藏模式。短轴方向特点为：以滨海断层、港东断层、南大港断层为边界,发育近东西走向的断层坡折构造,次级断层发育,剖面和平面上呈多种组合方式;水下扇砂体连通性好,与一系列断层形成阶梯状输导路径;形成了"近源-阶梯状输导-断控型"成藏模式。     

基于扭矩测量的二维簧片重力梯度仪的设计

基于扭矩测量原理,设计了一个精度为1E的二维簧片重力梯度仪。它的敏感部分是一个簧片悬挂的二维Z形扭摆,用一个高灵敏度的二维电容微位移传感器来检测此摆的二维扭转情况,进而获得摆周围的重力梯度信息。该二维簧片重力梯度仪具有性能稳定、精度高等优点。     

Long wavelength gravity anomalies over India: Crustal and lithospheric structures and its flexure

Long wavelength gravity anomalies over India were obtained from terrestrial gravity data through two independent methods: (i) wavelength filtering and (ii) removing crustal effects. The gravity fields due to the lithospheric mantle obtained from two methods were quite comparable. The long wavelength gravity anomalies were interpreted in terms of variations in the depth of the lithosphere–asthenosphere boundary (LAB) and the Moho with appropriate densities, that are constrained from seismic results at certain points. Modeling of the long wavelength gravity anomaly along a N–S profile (77°E) suggest that the thickness of the lithosphere for a density contrast of 0.05 g/cm³ with the asthenosphere is maximum of ∼190 km along the Himalayan front that reduces to ∼155 km under the southern part of the Ganga and the Vindhyan basins increasing to ∼175 km south of the Satpura Mobile belt, reducing to ∼155–140 km under the Eastern Dharwar craton (EDC) and from there consistently decreasing south wards to ∼120 km under the southernmost part of India, known as Southern Granulite Terrain (SGT).The crustal model clearly shows three distinct terrains of different bulk densities, and thicknesses, north of the SMB under the Ganga and the Vindhyan basins, and south of it the Eastern Dharwar Craton (EDC) and the Southern Granulite Terrain (SGT) of bulk densities 2.87, 2.90 and 2.96 g/cm³, respectively. It is confirmed from the exposed rock types as the SGT is composed of high bulk density lower crustal rocks and mafic/ultramafic intrusives while the EDC represent typical granite/gneisses rocks and the basement under the Vindhyan and Ganga basins towards the north are composed of Bundelkhand granite massif of the lower density. The crustal thickness along this profile varies from ∼37–38 km under the EDC, increasing to ∼40–45 km under the SGT and ∼40–42 km under the northern part of the Ganga basin with a bulge up to ∼36 km under its southern part. Reduced lithospheric and crustal thicknesses under the Vindhyan and the Ganga basins are attributed to the lithospheric flexure of the Indian plate due to Himalaya. Crustal bulge due to lithospheric flexure is well reflected in isostatic Moho based on flexural model of average effective elastic thickness of ∼40 km. Lithospheric flexure causes high heat flow that is aided by large crustal scale fault system of mobile belts and their extensions northwards in this section, which may be responsible for lower crustal bulk density in the northern part. A low density and high thermal regime in north India north of the SMB compared to south India, however does not conform to the high S-wave velocity in the northern part and thus it is attributed to changes in composition between the northern and the southern parts indicating a reworked lithosphere. Some of the long wavelength gravity anomalies along the east and the west coasts of India are attributed to the intrusives that caused the breakup of India from Antarctica, and Africa, Madagascar and Seychelles along the east and the west coasts of India, respectively.     

Geophysical Constraints on the Location and Nature of the North Saharan Flexure in Southern Tunisia

Gravity data, integrated with seismic refraction/reflection data, well data and geological investigations, were used to determine the location of the paleogeographic boundary between the Precambrian Saharan domain and the younger Tunisian Atlas domain. This boundary (North Saharan Flexure or NSF) has not been as clearly defined as it has been to the west in Algeria and Morocco. The gravity data analysis, which included the construction of complete Bouguer and residual gravity anomaly maps, revealed that the Atlasic domain is characterized by relative negative gravity anomalies and numerous linear gravity trends implying a thick and deformed sediment cover. The Saharan domain is characterized by relatively positive gravity anomalies with few gravity trends implying a thin and relatively undeformed sediment cover. An edge-enhancement analysis of the residual gravity anomalies revealed that the NSF is characterized by a series of discontinuous east- and northwest-trending linear anomalies south of 34°N that are not related to the well-known faults within the Gafsa and Accident de Medenine regions. Based on the continuity of the amplitudes of seismic reflection data and the trends of the residual gravity anomalies, the NSF is not an abrupt discontinuity but a series of step faults dipping toward the Atlasic domain. To obtain a more quantitative representation of the southern edge of Tunisian Atlas, a regional gravity model constrained by two wells and seismic reflection/refraction data was constructed along a north-south trending profile which confirms the presence of thicker sediments north of the NSF. Our analysis shows that the NSF has controlled the depositional environment of the sedimentary rocks within the region since at least Triassic time and has acted as a barrier to Atlasic deformation south of the NSF. The NSF is considered an important tectonic feature that has controlled the paleogeographic evolution of the southern margin of the Tethys Ocean, and it continues to be active today based on seismicity hazard studies.     

中国大陆及其邻区岩石层挠曲强度变化和均衡补偿机制

利用中国大陆以及最近与俄罗斯拼接的中亚地区的布格重力和地形数据，采用响应函数和互相关函数技术，结合弹性板挠曲理论，研究了中国大陆及其邻近地区（２５°Ｎ－７０°Ｎ，５０°Ｅ－１４０°Ｅ）的岩石层强度，用现代均衡的观点探讨了研究区的均衡补偿机制．研究结果表明，整个中国大陆及其邻近地区的有效弹性厚度Ｔｅ值为３５ｋｍ．其中，青藏地区Ｔｅ值为８５ｋｍ．西伯利亚西部至乌拉尔Ｔｅ值为７５ｋｍ，天山、塔里木盆地Ｔｅ值为４０ｋｍ，帕米尔高原Ｔｅ值为２５ｋｍ左右，西伯利亚中部、蒙古以及中国东北北部Ｔｅ值为４０ｋｍ，华北Ｔｅ值为２５ｋｍ，华南Ｔｅ值为４０ｋｍ．均衡补偿对于波长大于几千米的地形负荷为局部补偿，对几百公里到１１００ｋｍ的地形负荷为局部补偿和岩石层强度所支持，短波长地形负荷基本上由岩石层强度所支持．     

Buckling of a pervasively faulted lithosphere

We investigated the buckling response of a faulted elastic plate under horizontal compression using the finite element technique to better understand the effect of faults on the elastic behavior of a plate. We studied the effect of changes in fault spacing, depth and dip on the effective Young's modulus, buckling stress and wavelength. Our model consists of a thick elastic plate whose entire upper surface is cut by evenly spaced faults. We impose either an initial sinusoidal deformation with a fixed wavelength or a random deformation to the grid. A fault is represented as a free surface with no resolved shear stress and is allowed to slip in a specified direction using the method of slippery nodes. With the assumption of free slip on the faults, our model results represent an end member case in which the buckling wavelength and buckling stress are minimized by the presence of the faults.In our models, fault depth was varied from 0 to 75% of the plate thickness. As strain increases, the grid deforms by antisymmetric flexural folding and the initial imposed wavelength of deformation is modified such that the new buckling wavelength emerges. Our results show that the effective Young's modulus is a decreasing function of fault depth and an increasing function of fault spacing. In addition, buckling of the plate occurs at a lower stress for greater fault depths. Buckling wavelength is independent of the initial deformation wavelength however, it is modified by the presence of faults. For a plate with closely spaced faults extending through at least 75% of the plate, buckling occurs at a wavelength one half as large as that for a continuous plate. Buckling stress is not independent of the intial deformation wavelength, rather it increases slightly with increasing difference between the initial deformation wavelength and the buckling wavelength.Analytical models that approximate or ignore the effect of faulting can have large errors in calculation of the buckling stress. More importantly, modeling the observed wavelength of deformation in a faulted region with analytical solutions for continuous plates may result in a significant underestimate of elastic thickness. Fault dip does not strongly affect either the effective Young's modulus or the buckling wavelength. Thus, the buckling response should be the same for a plate cut by a low angle fault or a high angle fault.     

实验均衡二十年

回顾了利用响应函数技米研究地球均街己取得的主要成果并提出了研究中值得注意的一些问题。