Structural regime and its impact on the mechanism and migration pathways of hydrocarbon seepage in the southern Gulf of Suez rift: An approach for finding new unexplored fault blocks

A Natural active oil seepage occurs at the intersection of the NW-oriented rift coastal fault and a NE-oriented cross fault which bound the southwest dipping Little Zeit tilted fault block at the southwestern side of the Gulf of Suez, Egypt. Detailed surface geological mapping followed by subsurface mapping using aeromagnetic, seismic and borehole data of Ras El Ush oilfield (the nearest oil field to the seepage) provide a reliable hydrocarbon migration pathway model of the area.The proposed model suggests that hydrocarbons migrated upward at the intersection of a NE-oriented and the NW-oriented rift coastal faults where they found their way to the surface. The Nubia Sandstone occurs south of Ras El Ush oilfield in a trap door structure and probably entrapped some of the migrating hydrocarbons while a probable oil-water-contact at −1000 m which resulted into the migration of hydrocarbon through the damage zone of the northeast fault.The original oil in place of the predicted reservoir is estimated to be more than 47.5 MMBO which encourages the design makers for more investigation of this reservoir to increase its certainty and putting it in the plan of the future investments.     

太行山—秦岭中、新生代板内变形及交接转换机制

中—新生代,秦岭是中国大陆中轴隆升的东西向山脉,而太行山为华北地块中部隆升的南北向山脉,两者走向近垂直。为了探讨中-新生代期间同属欧亚板块内部的这两条山脉的隆升历史及其构造应力场转换过程,本文通过对其区域挤压与伸展构造的系统对比分析,结合两带中生代和新生代构造体制转换的对比,最后得出中—新生代期间这两条近垂直山脉由挤压体制转换为伸展体制的时间约为早白垩世晚期;并通过同时代应力场的转换的分析对比,揭示出其挤压变形与古老造山带形成时导致的板内岩石圈不均一性结构有关;而其伸展变形与中国东部弥散性板内裂解密切相关,因而表现出宽裂谷的特征,但其总体构造格局仍受早期基底构造格局影响。总之,板内差异构造变形受早期基底构造格局控制,同时板内不同块体多方位先存边界对板缘动力作用响应存在巨大差异;在筛除板块俯冲的远程效应外,板内自身变形机制可能与板内热—力学结构的不均匀性具有密切联系。     

扬子地块西南缘大红山群变质基性岩的地球化学研究及构造意义

扬子地块西缘近年报道了大量古元古代晚期的地层和侵入岩体,这些地层和岩体的构造环境多数被认为与大陆裂谷相关,而位于扬子西缘的~1.7Ga大红山群一直缺少相关的地球化学证据。本研究对大红山群两种变质基性岩——石榴(斜长)角闪岩(A组)和绿帘斜长角闪岩(B组)的主微量元素进行了地球化学分析,并对其构造环境进行了判别。A、B两组变质基性岩基本具有相似的地球化学性质:主量元素SiO2含量集中于46%~50%,MgO含量较低(5%~6%),但A组FeOT(平均14.28%)远高于B组FeOT(平均3.26%),可能与A组后期发生铁矿化作用有关;两组角闪岩的REE配分模式较一致:A组(La/Yb)N=1.52~4.67和B组(La/Yb)N=1.34~4.50,显示LREE轻微富集,Eu异常、Ce异常均不明显:Eu/Eu*=0.82~1.24,Ce/Ce*=0.93~1.05,两组样品稀土元素特征均具有类似富集型洋中脊玄武岩(E-MORB)的特征;二者的微量元素配分模式也基本一致:相容元素Cr、Co、Ni含量变化较大,不相容元素相对富集,Nb、Ta、Ti负异常不明显,Zr、Hf轻微负异常,其微量元素配分模式区别于岛弧玄武岩和OIB,而与E-MORB较一致。大红山群变质基性岩的地球化学性质可与东川群的基性侵入岩进行类比。A、B两组变质基性岩的原岩为拉斑玄武岩,通过不活动元素构造判别图解推断其构造属性为与富集地幔有关的大陆裂谷环境。变质基性岩中未受陆壳混染样品(Nb/La≈1)的微量、稀土元素地球化学特征显示其岩浆源区可能为富集地幔,结合前人已发表的相关εNd(t)推测大红山群变质基性岩的岩浆源区为不均匀的岩石圈地幔。同样,据扬子西缘相关火山岩的εNd(t)、εHf(t)值推测,扬子西缘1.8~1.5Ga变质火成岩的岩浆源区可能为不均匀的岩石圈地幔。本研究为扬子西缘1.8~1.5Ga大陆裂谷环境的构造岩浆活动提供了新的地球化学证据,大红山群与其同时代火成岩及地层的存在,共同表明了扬子西缘曾在古-中元古代发生了一系列与大陆裂解有关的构造岩浆事件,这期事件是哥伦比亚大陆裂解在扬子西缘的响应。     

Electrical-hydraulic conductivity model for a weathered-fractured aquifer system of Olbanita,Lower Baringo Basin,Kenya Rift

Groundwater yield in the Kenya Rift is highly unsustainable owing to geological variability. In this study, field hydraulic characterization was performed by using geo-electric approaches. The relations between electrical-hydraulic (eh) conductivities were modeled hypothetically and calibrated empirically. Correlations were based on the stoch-astic models and field-scale hydraulic parameters were contingent on pore-level parameters. By considering variation in pore-size distributions over eh conduction interval, the relations were scaled-up for use at aquifer-level. Material-level electrical conductivities were determined by using Vertical Electrical Survey and hydraulic conductivities by analyzing aquifer tests of eight boreholes in the Olbanita aquifer located in Kenya rift. VES datasets were inverted by using the computer code IP2Win. The main result is that ln T=0.537 (ln Fa)+3.695; the positive gradient indicating eh conduction through poresurface networks and a proxy of weathered and clayey materials. An inverse (1/F-K) correlation is observed. Hydraulic parameters determined using such approaches may possibly contri-bute significantly towards sustainable yield management and planning of groundwater resources.     

Hydrothermal mineralization along submarine rift zones,Hawaii

This is the first article to describe mineralization of midplate submarine rift zones and hydrothermal manganese oxide mineralization of midplate volcanic edifices. Hydrothermal Mn oxides were recovered from submarine extensions of two Hawaiian rift zones, along Haleakala and Puna Ridges. These Mn oxides form two types of deposits, metallic stratiform layers in volcaniclastic rocks and cement for clastic rocks; both deposit types are composed of todorokite and bimessite. Thin Fe‐Mn crusts that coat some rocks formed by a combination of hydrogenetic and hydrothermal processes and are composed of δ‐MnO₂. The stratiform layers have high Mn contents (mean 40%) and a large fractionation between Mn and Fe (Fe/Mn = 0.04). Unlike most other hydrothermal Mn oxide deposits, those from Hawaiian rift zones are enriched in the trace metals Zn, Co, Ba, Mo, Sr, V, and especially Ni (mean 0.16%). Metals are derived from three sources: mafic and ultramafic rocks leached by circulating hydrothermal fluids, clastic material (in Mn‐cemented sandstone), and seawater that mixed with the hydrothermal fluids. Mineralization on Haleakala Ridge occurred sometime during the past 200 to 400 ka, when the summit was at a water depth of more than 1,000 m. Hydrothermal circulation was probably driven by heat produced by intrusion of dikces, magma reservoirs, and flow of magma through axial and lateral conduits. The supply of seawater to ridge interiors must be extensive because of their high porosity and permeability. Precipitation of Mn oxide below the seafloor is indicated by its occurrence as cement, growth textures that show mineralizing fluids were introduced from below, and pervasive replacement of original matrix of clastic rocks.     

云南易门狮子山铜矿基性侵入岩地球化学特征及其地质意义

针对云南易门狮子山铜矿区基性侵入岩体(以矿区1237m中段层状辉长岩为例)的岩石学和地球化学特征分析,结果表明:SiO2,Na2O和K2O的平均质量分数分别为47.06%,3.91%,2.17%,σ(里特曼指数)平均为9.9;微量元素表现为大离子亲石元素K,Rb,Th明显富集,Sr,Ta,Nb,Yb,Cr,Y等元素亏损,显示了大陆裂谷玄武岩的特征;稀土元素总量为178.60×10-6～404.50×10-6,Eu负异常不明显(0.73～0.97),轻稀土元素富集(LREE/HREE=7.05～16.59,(La/Yb)N=6.56～36.94);研究还认为狮子山基性侵入岩是在大陆初始裂谷背景下形成的,属于深源玄武质岩浆演化形成,可能有壳源物质的混入。     

江苏茅山推覆构造带的分析与研究

溧水地区与宜(兴)—溧(阳)地区的地层区划,跨扬子与江南两个地层区,两者以江南深断裂为界。宜溧地区中、新生代地层的分布特征,中生代火山杂岩系的分布特征,都充分反映了江南深断裂对地层、构造、火山岩浆岩活动的控制作用。茅山楔状冲断体构造的研究采用了历年来溧水地区与宜(兴)—溧(阳)地区的有关成果地质资料,展开了茅山推覆构造带的分析与研究,发现了茅山楔状冲断体构造是经燕山晚期两次推覆构造造山运动(茅山运动)而造就的后展式(上叠式)推覆构造。为观其整体,同时对推覆构造带的前缘挤压带、后缘拉张带、根部隆起带作了简述。茅山推覆构造造山运动期,充分表现了新华夏系构造的特点。先是造成了晚白垩系浦口组(K2p)与下伏地层早白垩系葛村组(K1g)及以前各地层的区域性不整合(浦口运动),后来又造成了新生代下第三系泰州组(E1t)与下伏地层晚白垩系赤山组(K2c)及以前各地层的区域性不整合(泰州运动),可见其影响范围很广,又以江南深断裂为背景,其构造意义必然深远。     

裂谷盆地深层石油地质特征与油气成藏条件

裂谷盆地是指沉积盆地在地质历史演变的某个阶段经历了裂谷时期的盆地。裂谷盆地深层在中国一般是指裂谷盆地中含油气层段埋深>3 500 m的地层,国外则指埋深>4 000 m的地层。中国东部具深层油气田的裂谷盆地主要是中、新生代盆地;全球裂谷盆地深层的大油气藏主要分布于白垩系,其次是上古生界;深层油气藏的储层形式多样,有孔隙型、裂缝型、溶洞-裂缝型及孔隙-裂缝型等;深层油气田的油气运移方向以垂向为主,圈闭则大多以岩性或与断裂有关的构造岩性圈闭为主。其次,盐岩体的活动对圈闭的形成亦十分重要,其类型则以复合型为主。     

Structural architecture of the northern composite terrane, the Eastern Ghats Mobile Belt, India: Implications for Gondwana tectonics

New data from structural mapping and tectonic evaluation in the northern parts of the Eastern Ghats Mobile Belt (EGMB-north) involving the interpretation of satellite images, field traverses, critical outcrop mapping and kinematic studies of macro- as well as microstructures of the shear zone rocks together with the geometry and disposition of Gondwana basins led to, for the first time, the elucidation of post-Grenvillian structural architecture of the terrane. This helps in assessing the sequence of successive tectonothermal events that were responsible for the origin and progressive evolution of the Permo-Carboniferous coal bearing sediments along the Mahanadi rift that forms significant in the reconstruction models of east Gondwana.The composite terrane of high-grade metamorphic rocks (EGMB-north), strikes E–W in contrast to the regional NE–SW trend of the EGMB. The structural architecture obtained from this study is controlled by the boundary shear zones and associated link shear zones. The dextral kinematic displacements along the Northern Boundary Shear Zone (NBSZ) as well as the Mahanadi Shear Zone (MSZ) and Koraput–Sonapur–Rairakhol Shear Zone (KSRSZ) were derived from multi-scale field based structural observations. A N–S structural cross-section presents a crustal-scale ‘flower structure’ across the composite terrane exposing different domains displaying distinctive internal structures with widely varying different geological evolution history and strain partitioning, separated by crustal-scale shear zones. Deep seismic imaging and gravity signatures support ‘flower structure’ model. The pervasive first formed gneissic fabrics were continuously reworked and partitioned into a series of E–W, crustal-scale shear zones.The Neoproterozoic regional dextral transpressional tectonics along the shear zones and their repeated reactivation could be responsible for initiation and successive evolution of Gondwana basins and different episodes of sedimentation. Available geochronological data shows that the structural architecture presented here is post-Grenvillian, which has been repeatedly reactivated through long-lived transpressional tectonics. The composite terrane is characterized by all the typical features of an oblique convergent orogen with transpressional kinematics in the middle to lower crust. The kinematic changes from transpression to transtensional stresses were found to be associated with global geodynamics related to the transformation from Rodinia to Gondwana configuration.     

伊通盆地莫里青断陷地温地压系统与油气成藏关系

基于地温和地压实测数据及声波测井资料等,利用地温-地压系统的原理,对伊通盆地莫里青断陷的地温场、压力场及温压系统特征进行了剖析,并从油气生成、保存及分布角度探讨了温压系统与油气成藏的关系。研究表明,断陷内各区带地温梯度较高,有利于有机质的成熟与烃类生成;泥岩欠压实段主要出现在双阳组,强化了油气的封闭作用;斜坡带泥岩不发育异常压力,以毛细管压力封闭为主;莫里青断陷发育弱高压型复式温压系统,上下2套温压系统流体能量相差较小,油气垂向运聚活动很少,深部弱高压型温压系统内部最有利于油气富集成藏,双阳组含油气系统是最重要的勘探对象。