The Davie Fracture Zone and adjacent basins in the offshore Mozambique Margin – A new insights for the hydrocarbon potential

The interpretation of 2-D seismic reflection data provides a modern structural framework including hydrocarbon potential in the present-day stratigraphic and structural traps of both the Davie Fracture Zone and the adjacent Nacala and Angoche basins. Possible stratigraphic traps were identified in submarine fan and channel depositional environments during Cretaceous to Tertiary times. Structural traps are mostly defined within compressional structures formed by a variety of fault-related folds and rift grabens within the Jurassic and Cretaceous successions.The Nacala and Angoche basins form two depressions separated by the Davie compressional zone. This compressional structure is a prominent interior high running approximately north-south. An event of transpression and contraction characterizes the main tectonic setting commonly hosting several detached compressional structures along the western edge of the transform zone.Both basins are associated with the Late Jurassic/Early Cretaceous rifting during the opening of the Mozambique Channel. The Angoche basin is proposed here to have formed by the earliest stage of break-up in mid-Jurassic time. The basin is bounded landward by the Angoche volcanic zone, a dyke swarm branch oriented N64degE forming part of the Karoo and Dronning Maud Land magmatism at c. 180 Ma.Subsequent rifting and break-up led to the drift of East Gondwana southwards along the dextral strike-slip Davie Fracture Zone. At about 150 Ma (Tithonian), East Gondwana appears to have rotated slightly clockwise about a pivot in the proximity of the Angoche basin leading to extension and rifting in the Rovuma basin to the north of the pivot point and compression west of the Davie Fracture Zone to the south. Consequently, the eastern boundary of the Angoche basin was compressed developing a typical growth wedge of massive thrust imbrication structures while extensional tectonics created several depressions and rift-grabens forming the Nacala and Quirimbas basins.Basin stratigraphy is interpreted along seismic reflection lines and correlated to the regional stratigraphic information and wells from the Zambezi Delta and Rovuma basins.     

转换-伸展盆地——莺歌海的演化

在系统研究莺歌海盆地沉降史、变形史、充填史和埋藏史和基础上，确定了莺歌海盆地的演化阶段和分地类型，并建立了转换－－伸展盆地的演化模式，莺歌海盆地演可分为４个主要发展阶段；（１）初始断陷；（２）裂陷；（３）拗陷（４）再次裂陷，盆地的沉降机理是：初始断陷为岩石圈刚性体的简单伸展；裂陷为与先期切断裂带重新活动腾的走滑－－伸展；拗陷走滑－伸展相对较弱，叠加热沉降；再次裂陷以走滑－伸展为离，叠加重力沉降和压     

Dynamic Analysis of Yinggehai Basin through Analogue Modeling

INTRODUCTIONYinggehai basin lies between the Indochina plate and theSouth China plate,it develops along the southeast elongationof the Red River fault zone. Complex structures,hugesediments,ultrahigh pressure and hot fluid diapirs make it aworldwide hot spot.Most of the research work has been donein the Neogene strata and the areas along the edges of thebasin. Because of the huge depth of the sediments,thelimitation of seismic exploration and the special geophysicalposition,it is very h…     

桂北地区丹洲群锆石U-Pb年代学及对华南新元古代裂谷作用期次的启示

桂北地区丹洲群是南华裂谷盆地南段的一套连续裂谷充填沉积,厘定各组沉积时限及区域地层关系,对理解华南新元古代裂谷作用期次具有重要意义。本文利用LA-ICP-MS锆石U-Pb同位素测年,获得丹洲群合桐组二段和拱洞组底部凝灰岩夹层形成年龄分别为801±4 Ma和781±5 Ma。研究表明,丹洲群白竹组和合桐组一段与下江群甲路组和乌叶组、板溪群沧水铺组和马底驿组、西乡群孙家河组及陆良组一段相当,沉积时限为820~800 Ma;合桐组二段与下江群番召组相当,沉积时限为800~780 Ma;拱洞组可与下江群清水江组、平略组和隆里组,板溪群五强溪组中上部和牛牯坪组,西乡群大石沟组中上部和三郎铺组,陆良组二段及澄江组、开建桥组、莲沱组、虹赤村组和上墅组的中上部直接对比,沉积时限为780~725 Ma。华南新元古代裂谷盆地系统的典型地层锆石年龄存在5组高峰,峰值年龄分别为818±2 Ma、802±1 Ma、780±4 Ma、756±4 Ma及728±5 Ma。综合华南新元古代岩浆活动特征及盆地沉积演化过程,确定华南新元古代裂谷作用可分为两期:820~800 Ma和800~725 Ma。此外,华南新元古代岩浆活动与裂谷作用之间存在明显的耦合关系,但各期岩浆活动对各裂谷盆地的影响程度存在差异。     

冲绳海槽弧后张裂构造及其动力机制讨论

在总结、讨论冲绳海槽弧后张裂构造的地形地貌、地球物理场和动力背景特征的基础上,归纳出海槽北、中、南三段之间的差异,以及它们在陆坡、槽底、岛坡上的不同表现特征.槽底雁行排列的地堑及断层斜切入陆坡,伴随的断块隆眷作用往南加强,使得钓鱼岛一赤尾屿隆起带区别于其北边的陆架外缘隆起带,吕宋岛向台湾的碰撞挤压引起的旋张活动加强了海槽南段的地壳拉张,从北往南岛坡侧都可以追踪出双列岛孤特性.海槽内部构造现象不能为笼统的构造动力背景所能完全解释,需要对各个典型中央地堑的具体深入探测研究.鉴于地堑、地垒、断层以及它们所界定的构造单元和它们内部发生的岩浆作用各有特点,最后讨论了各个地段中央地堑的构造属性、动力要素的差异及变化规律,以期为海槽构造动力的进一步深入研究提供借鉴参考.     

Transtensional tectonics induced by oblique reactivation of previous lithospheric anisotropies during the Late Triassic to Early Jurassic rifting in the Neuquén basin: Insights from analog models

The goal of this study was to determine the main factors that controlled the kinematic evolution and the structural architecture developed during the Late Triassic to Early Jurassic rifting that led to the opening of the Neuquén basin in the southwestern sector of Gondwana. We carried out a series of analog models to simulate an extensional system with a bent geometry similar to the northeastern border of the basin. In different experiments, we varied the extension direction between NNE (N10°E) and NE (N45°E) orientations, inducing rift systems with different degrees of obliquity in each sector of the extended area. We compared the kinematic evolution and the final structural architecture observed in the experiments with data from two selected representative areas of the basin: (1) the Atuel depocenter, situated in the northern Andean sector, and (2) the Entre Lomas area, situated in the northeastern Neuquén Embayment. In both cases, the good match between the field and subsurface data and the results of the analog models supports a NNE orientation of the regional extension (N30°E–N20°E) during the synrift stage. Our experimental results suggest that lithospheric weakness zones of NNW to NW trend could have controlled and localized the extension in the Neuquén basin. These previous anisotropies were linked to the sutures and rheological contrasts generated during the collision of terranes against the southwestern margin of Gondwana during the Paleozoic, as well as further modifications of the thermo-mechanical state of the lithosphere during the Late Paleozoic to Early Mesozoic evolution.     

Asymmetric rifting of the northern Mariana Trough

The evolution of rifting in the northern Mariana Trough was studied, based on single-channel seismic reflection profiles and heat flow. The rift showed structural asymmetry. The northernmost part of the Mariana Trough at 24°N, just south of Minami-Iwojima Island, is now in an incipient rifting stage and shows a half-graben structure. The arc crust just behind the volcanic front is cut by a few major east-dipping normal faults. The major faults extend southward behind the Hiyoshi seamounts around 23°30'N. The rift develops to a full-graben stage at ∼ 23°N, where the width of the trough increases to 80 km. The trough is comprised of several faulted and tilted blocks of island-arc crust. Maximum subsidence occurs along a row of small grabens on the eastern margin of the trough. These grabens are separated by arc volcanoes, and their depths increase southward from 2500 m at 23°20'N to 4500 m at 22°N. The strike of each graben is north-northwest–south-southeast, which is close to the trend of the remnant West Mariana Ridge, but oblique to the active Mariana arc. Crustal extension becomes concentrated along the eastern margin of the trough as rifting progresses. The transition from rifting to sea floor spreading may occur at ∼ 22°N, where the width of the trough is ∼ 120 km. The possible spreading center lies along the southern extension of the grabens on the eastern margin. The period of back-arc rifting before spreading begins is estimated to be less than 3 million years. Heat flow is asymmetric in the rift. High heat flow was observed only in or close to the row of grabens along the eastern margin of the trough. The asymmetric pure shear extension model fits the observed heat flow distribution better than the simple shear extension model.     

The tectonic and geomagnetic significance of paleomagnetic observations from volcanic rocks from central Afar, Africa

Deformation throughout Afar over the past 2 myr has been characterized by widespread and intense crustal fragmentation that results from inhomogeneous extension across the region. In eastern Afar, this situation has evolved to localized extension associated with the westward propagation of the Gulf of Aden/Gulf of Tadjurah seafloor spreading system into the Asal–Ghoubbet Rift. During the gradual process of rift propagation and localization, crustal blocks in eastern Afar sustained clockwise rotations of 11°. To better understand the processes of rift propagation and localization and how they affect the rest of Afar, we have collected and analyzed over 400 oriented paleomagnetic samples from 67 lava flows from central and southern Afar. Unlike eastern Afar, the mean paleomagnetic direction from central Afar indicates that vertical-axis rotations are statistically insignificant (3.6°±4.4°), though small clockwise rotations (<8°) are permitted. Thus, propagation and localization in central Afar have not had the same influence in causing crustal block rotations or, perhaps more likely, have not reached the same stage of evolution as seen in eastern Afar. In addition, several of the lava flows record intriguing geomagnetic field behavior associated with polarity transitions, excursions, or large secular variation events. Interestingly, the transitional or anomalous virtual geomagnetic poles (VGPs) tend to cluster in two nearly antipodal regions, one in the northern Pacific Ocean and the other in the southwest Indian Ocean. One lava flow has recorded both of the antipodal transitional components, with the two components residing in magnetic minerals with unblocking temperatures above and below 500°C, respectively. Reheating and partial remagnetization by the overlying flow cannot explain either of the transitional directions because both differ significantly from that of the reversely magnetized overlying flow. The high-temperature component gives a VGP in the northern Pacific, whereas the lower-temperature component gives a nearly antipodal VGP south of Cape Town, South Africa. Hence, the configuration of the geomagnetic field appears to have jumped nearly instantaneously from a northern-hemisphere transitional state to a southern-hemisphere one during this normal-to-reverse polarity transition.     

Aspects of Rift Valley faulting and volcanicity in North Tanzania: report of a Geologists’ Association Field Meeting in 2008

The African Rift Valleys results from Neogene-Recent breakup up the African Plate due to continental extension. Compared with the western sector, in the eastern or Gregory Rift Valley the fracturing is accompanied by a large amount of volcanic activity and, in northern Tanzania, the volcanic rocks are relatively young compared with those in Ethiopia and Kenya where the products of the earliest stages of mantle melting are buried beneath older, more-extensive volcanic formations. The volcanic rocks vary from Pliocene and early Pleistocene intraplate basalts and trachytes to late Pleistocene/Holocene nephelinites and carbonatites.     

中国大陆东部晚中生代裂陷作用的表现形式及其幕式扩展

晚中生代期间，岩石圈的深部过程和构造应力场由左旋压扭（Ｊ２－Ｊ３）到右旋张扭（Ｊ３－Ｋ１）的反转变格导致了中国大陆东部大规模的裂陷作用，表现为广泛的火山岩喷发、花岗岩浆侵位、大规模ＮＮＥ向含油气断陷盆地系和变质核杂岩的发育。根据地质和地球物理资料探讨了这期裂陷作用的运动学体制。利用计算机模拟研究了裂陷盆地的充填演化过程，结果表明边界同沉积断层沉降速率的变化是盆地发育演化的重要特征之一，并由此导致了断陷盆地的幕式扩展