The East African Rift system （EARS） provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches, the eastern, magma-rich, and the western, magma-poor, on either sides o...The East African Rift system （EARS） provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches, the eastern, magma-rich, and the western, magma-poor, on either sides of the old thick Tanzanian craton embedded in a younger lithosphere. Data on the pre-rifr, syn-rift and post-rift far-field volcanic and tectonic activity show that the EARS formed in the context of the interaction between a deep mantle plume and a horizontally and vertically heterogeneous lithosphere under far-field tectonic extension. We bring quantitative insights into this evolution by implementing high-resolution 3D thermo-mechanical numerical deformation models of a lithosphere of realistic rheology. The models focus on the central part of the EARS. We explore scenarios of plumelithosphere interaction with plumes of various size and initial position rising beneath a tectonically pre-stretched lithosphere. We test the impact of the inherited rheological discontinuities （suture zones） along the craton borders, of the rheological structure, of lithosphere plate thickness variations, and of physical and mechanical contrasts between the craton and the embedding lithosphere. Our experiments indicate that the ascending plume material is deflected by the cratonic keel and preferentially channeled along one of its sides, leading to the formation of a large rift zone along the eastern side of the craton, with significant magmatic activity and substantial melt amount derived from the mantle plume material. We show that the observed asymmetry of the central EARS, with coeval amagmatic （western） and magmatic （eastern） branches, can be explained by the splitting of warm material rising from a broad plume head whose initial position is slightly shifted to the eastern side of the craton. In that case, neither a mechanical weakness of the contact between the craton and the embedding lithosphere nor the presence of second plume are required to produce simulations that match observations. This result reconciles the passive and active rift models and demonstrates the possibility of development of both magmatic and amagmatic rifts in identical geotectonic environments.展开更多
The East African Rift System(EARS)is located in East Africa,separating into two main branches,the eastern branch and the western branch.It is considered as an intracontinental ridge system,which meets the Red Sea and
The East African Rift extending across Djibouti, Ethiopia and Kenya is characterized by low level of economic development,high level of poverty,increasing population,scarce natural resources(land,water, and environmen...The East African Rift extending across Djibouti, Ethiopia and Kenya is characterized by low level of economic development,high level of poverty,increasing population,scarce natural resources(land,water, and environment),complex and rich ecosystems, increasing desertification and degrading biodiversity, underdeveloped regional trade and market,water resources mainly stored in groundwater and展开更多
On 5th November 2003,the central part of Tanzania (Dodoma),located within the eastern branch of the East African Rift System was struck by an M_s 5.5 earthquake that destroyed a school,a dispensary near its epicenter ...On 5th November 2003,the central part of Tanzania (Dodoma),located within the eastern branch of the East African Rift System was struck by an M_s 5.5 earthquake that destroyed a school,a dispensary near its epicenter and caused a huge crack on the Parliamentary building of Tanzania.This was one of the relatively large earthquakes that affected the area after the M_s 6.1 that occurred north of the Dodoma within the Manyara-Dodoma rift segment in May 7,展开更多
基于地质、地震和钻井资料,对东非阿尔伯特盆地(Lake Albert Basin)的形成演化及构造—沉积地层特征进行了研究,深入分析了盆地石油地质特征,总结其成藏模式及油气富集条件。盆地主要受东非裂谷期构造运动的影响,形成两侧以深大断裂为...基于地质、地震和钻井资料,对东非阿尔伯特盆地(Lake Albert Basin)的形成演化及构造—沉积地层特征进行了研究,深入分析了盆地石油地质特征,总结其成藏模式及油气富集条件。盆地主要受东非裂谷期构造运动的影响,形成两侧以深大断裂为界、狭长(半)地堑的构造格局。沉积地层以新近系碎屑岩为主,岩性多为泥岩、砂岩和砾岩。河流—(扇)三角洲—湖泊沉积体系发育,主要烃源岩为中新统上部富有机质页岩,中新统—上新统河流相、(扇)三角洲相砂岩为主要储层,与细粒湖相泥岩在纵向上形成良好的生储盖匹配。盆地发育大量断块、断背斜等构造圈闭。盆地成藏模式为"凹陷供烃、侧向与垂向复合运移、下生上储",生储盖匹配良好控制垂向上形成多套成藏组合,优质砂体与垂向断层控制油气有效运移,断层控制的构造圈闭是油气聚集的主要场所。展开更多
基金co-funded by a U.S.National Science Foundation(Grant EAR-0538119)to E.Calaisthe Advanced ERC(Grant 290864 RHEOLITH)to E.Burov and A.Koptev+2 种基金the Royal Academy of Netherlands visiting professor grant to E.Burovthe UPMC visiting professor grant to S.Cloetinghperformed on the ERC-funded SGI Ulysse cluster of ISTEP
文摘The East African Rift system （EARS） provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches, the eastern, magma-rich, and the western, magma-poor, on either sides of the old thick Tanzanian craton embedded in a younger lithosphere. Data on the pre-rifr, syn-rift and post-rift far-field volcanic and tectonic activity show that the EARS formed in the context of the interaction between a deep mantle plume and a horizontally and vertically heterogeneous lithosphere under far-field tectonic extension. We bring quantitative insights into this evolution by implementing high-resolution 3D thermo-mechanical numerical deformation models of a lithosphere of realistic rheology. The models focus on the central part of the EARS. We explore scenarios of plumelithosphere interaction with plumes of various size and initial position rising beneath a tectonically pre-stretched lithosphere. We test the impact of the inherited rheological discontinuities （suture zones） along the craton borders, of the rheological structure, of lithosphere plate thickness variations, and of physical and mechanical contrasts between the craton and the embedding lithosphere. Our experiments indicate that the ascending plume material is deflected by the cratonic keel and preferentially channeled along one of its sides, leading to the formation of a large rift zone along the eastern side of the craton, with significant magmatic activity and substantial melt amount derived from the mantle plume material. We show that the observed asymmetry of the central EARS, with coeval amagmatic （western） and magmatic （eastern） branches, can be explained by the splitting of warm material rising from a broad plume head whose initial position is slightly shifted to the eastern side of the craton. In that case, neither a mechanical weakness of the contact between the craton and the embedding lithosphere nor the presence of second plume are required to produce simulations that match observations. This result reconciles the passive and active rift models and demonstrates the possibility of development of both magmatic and amagmatic rifts in identical geotectonic environments.
文摘The East African Rift System(EARS)is located in East Africa,separating into two main branches,the eastern branch and the western branch.It is considered as an intracontinental ridge system,which meets the Red Sea and
文摘The East African Rift extending across Djibouti, Ethiopia and Kenya is characterized by low level of economic development,high level of poverty,increasing population,scarce natural resources(land,water, and environment),complex and rich ecosystems, increasing desertification and degrading biodiversity, underdeveloped regional trade and market,water resources mainly stored in groundwater and
文摘On 5th November 2003,the central part of Tanzania (Dodoma),located within the eastern branch of the East African Rift System was struck by an M_s 5.5 earthquake that destroyed a school,a dispensary near its epicenter and caused a huge crack on the Parliamentary building of Tanzania.This was one of the relatively large earthquakes that affected the area after the M_s 6.1 that occurred north of the Dodoma within the Manyara-Dodoma rift segment in May 7,
文摘基于地质、地震和钻井资料,对东非阿尔伯特盆地(Lake Albert Basin)的形成演化及构造—沉积地层特征进行了研究,深入分析了盆地石油地质特征,总结其成藏模式及油气富集条件。盆地主要受东非裂谷期构造运动的影响,形成两侧以深大断裂为界、狭长(半)地堑的构造格局。沉积地层以新近系碎屑岩为主,岩性多为泥岩、砂岩和砾岩。河流—(扇)三角洲—湖泊沉积体系发育,主要烃源岩为中新统上部富有机质页岩,中新统—上新统河流相、(扇)三角洲相砂岩为主要储层,与细粒湖相泥岩在纵向上形成良好的生储盖匹配。盆地发育大量断块、断背斜等构造圈闭。盆地成藏模式为"凹陷供烃、侧向与垂向复合运移、下生上储",生储盖匹配良好控制垂向上形成多套成藏组合,优质砂体与垂向断层控制油气有效运移,断层控制的构造圈闭是油气聚集的主要场所。
文摘东非裂谷东支由多个盆地组成,South Lokichar是唯一有油气发现的盆地,目前对于该盆地的石油地质特征及成藏规律仍认识不清,严重制约着东非裂谷东支下一步勘探。本文综合利用钻井、地震、岩芯、薄片以及分析化验等资料,对South Lokichar盆地的构造和地层发育特征、关键成藏条件和影响因素以及成藏规律进行详细分析。研究结果表明:(1) South Lokichar盆地自晚渐新世开始拉张,经历了裂陷I期、裂陷II期及坳陷期三个演化阶段,以裂陷I期沉积序列为主;(2) South Lokichar盆地成藏条件优越,下中新统Lokhone Shale组半深湖-深湖相泥岩为主力烃源岩,生烃指标好,古气候及沉积环境共同控制优质烃源岩的发育;中中新统Lower Auwerwer组为主要目的层系,主要发育扇三角洲相、三角洲相以及湖泊相;扇三角洲前缘及三角洲前缘砂体储集物性最优,浊积砂岩次之,扇三角洲平原砂砾岩体储集物性差;泥质含量是影响储集物性的主要因素。中中新统Middle Auwerwer组泥岩及下中新统Lokhone Shale组泥岩为两套区域盖层;断鼻及断块圈闭为主要的圈闭类型,晚中新世是圈闭形成的关键时期;(3) South Lokichar盆地油气富集平面上呈现"西富东贫"的特点;纵向上油气主要聚集于中中新统Lower Auwerwer组,下中新统Lokhone Shale组次之;Lower Auwerwer组为下生上储的成藏模式,Lokhone Shale组为自生自储式成藏;保存条件是成藏的主控因素;(4) South Lokichar盆地东北部未钻断块圈闭及凹陷带内岩性圈闭具备较好的勘探前景。
