An analytical model of continental rift fault patterns

Two proposed mechanisms of rift initiation are crustal uplift alone and a combination of crustal uplift and regional horizontal extension. A three-dimensional, thick-plate, elastic analysis has been used to model the crustal stress state and the fault patterns associated with these mechanisms. Small ratios of uplift width to crustal thickness (<10) necessitate the thick-plate approach.For the crustal uplift model, the surface fault pattern is characterized by normal faults trending parallel to the major uplift axis at the uplift center and radial normal faults toward the ends of the major uplift axis. Zones of compressional structures (e.g., strikeslip and thrust faults) may develop at the periphery of the uplift. Superposition of regional horizontal tension with the stresses produced by crustal uplift eliminates the compressive stresses at the uplift periphery producing normal faults parallel to the major uplift axis at the uplift center and normal faults perpendicular to the major uplift axis at the uplift periphery.A comparison of these predicted fault patterns with the faults of the Rhine graben suggests that the combination of crustal uplift and regional horizontal extension contributed to the formation of that rift system. The stresses produced by crustal uplift promoted the formation of the central graben and the fan-shaped troughs toward the ends of the major uplift axes, while superposed regional horizontal tension eliminated the large compressive stresses at the uplift periphery promoting the normal faulting and dike intrusions observed on the Rhine graben flanks.     

济阳坳陷构造演化及其大地构造意义

济阳坳陷由负反转盆地、右旋扭张盆地及主动裂谷三个原型叠加而成,并在中、新生代经历了四个演化阶段,三叠纪为板内造山作用阶段,济阳坳陷曾为五条ＮＷ向的以逆冲断层为主的压性构造带占据,早－中侏罗世造山作用结束;晚侏罗世－早始新世为负反转盆地阶段,三叠纪ＮＷ向逆冲断层发生反向伸展;中始新世－渐新世为右旋扭张盆地阶段,ＮＥ,ＥＮＥ向扭张断裂发育,并进而成盆接受沉积,ＮＷ和断裂反向伸展活动受到抑制而渐趋消亡;中新世－全新世为主动裂谷阶段,“拗陷运动”取代“断陷运动”。济阳坳陷构造演化的阶段特征表明了郯庐断裂中、新生代的剪切运动史,即三叠纪右旋剪切,晚侏罗世－早始新世左旋剪切．中始新世－渐新世右旋剪切,中新世－全新世作弱右旋压剪。     

西秦岭地区东昆仑-秦岭断裂系晚新生代左旋走滑历史及其向东扩展

要通过在TM遥感图像解译和野外观测的基础上,描述了东昆仑断裂带东段活动形迹的组成和活动断层地貌特征,阐述了甘南高原西秦岭地区新近纪拉分盆地的沉积-构造特征,提出了该区东昆仑-秦岭断裂系晚新生代左旋走滑伸展-走滑挤压-走滑伸展的3个阶段的构造变形模式。指出,中新世晚期至上新世早期,东昆仑-秦岭断裂系以左旋走滑伸展活动为主,伴随着西秦岭地区拉分盆地的形成和超基性火山岩群的发育。这期左旋走滑伸展活动向东扩展导致了渭河盆地新近纪引张应力方向由早期的NE-SW向转变为晚期的NW—SE向。上新世晚期以来(约3．4Ma以前),东昆仑-秦岭断裂系以左旋走滑挤压活动为主,导致早期拉分盆地的轻微褶皱变形,走滑挤压活动主要集中在东昆仑东段玛沁-玛曲主断裂带上。该期构造变动持续到早更新世,它的向东扩展产生了广泛的地壳形变效应,包括青藏东缘岷山隆起带的快速崛起、华北地区汾-渭地堑系的形成和发展以及郯庐断裂带右旋走滑活动等。中、晚更新世时期,断裂系以走滑伸展变形为主,主要集中在东昆仑断裂带东段3个分支上,地块向东挤出伴随着顺时针旋转。     

Comparison of the ‘strike‐slip’ versus the ‘episodic rift‐sag’ models for the origin of the Isa Superbasin

In this paper we assess two competing tectonic models for the development of the Isa Superbasin (ca 1725–1590 Ma) in the Western Fold Belt of the Mt Isa terrane. In the ‘episodic rift‐sag’ tectonic model the basin architecture is envisaged as similar to that of a Basin and Range province characterised by widespread half‐graben development. According to this model, the Isa Superbasin evolved during three stages of the Mt Isa Rift Event. Stage I involved intracontinental extension, half‐graben development, the emergence of fault scarps and tilt‐blocks, and bimodal volcanism. Stage II involved episodic rifting and sag during intervening periods of tectonic quiescence. Stage III was dominated by thermal relaxation of the lithosphere with transient episodes of extension. Sedimentation was controlled by the development of arrays of half‐grabens bounded by intrabasinal transverse or transfer faults. The competing ‘strike‐slip’ model was developed for the Gun Supersequence stratigraphic interval of the Isa Superbasin (during stage II and the beginning of stage III). According to this model, sinistral movements along north‐northeast‐orientated strike‐slip faults took place, with oblique movements along northwest‐orientated faults. This resulted in the deposition of southeast‐thickening ramp sequences with local sub‐basin depocentres forming to the west and north of north‐northeast‐ and northwest‐trending faults, respectively. It is proposed that dilation zones focused magmatism (e.g. Sybella Granite) and transfer of strike‐slip movement resulted in transient uplift along the western margin of the Mt Gordon Arch. Our analysis supports the ‘episodic rift‐sag’ model. We find that the inferred architecture for the strike‐slip model correlates poorly with the observed structural elements. Interpretation is made difficult because there has been significant modification and reorientation of fault geometry during the Isan Orogeny and these effects need to be removed before any assertion as to the basin structure is made. Strike‐slip faulting does not explain the regional‐scale pattern of basin subsidence. The ‘episodic rift‐sag’ model explains the macroscopic geometry of the Isa Superbasin and is consistent with the detailed sedimentological analysis of basin facies architecture, and the structural history and geometry.     

青藏高原中部第四纪左旋剪切变形的地表地质证据

在青藏铁路的格尔木—拉萨段进行的活动断裂调查发现,在沱沱河—五道梁之间宽约150km的地段内发育了多条由北西西向次级断层左列分布构成的北西西向和北西向左旋张扭性断裂带,在断裂带之间则发育"S"型的北东向裂陷盆地和雁列分布的菱形裂陷盆地,盆地边界断裂也为左旋张扭性质。上述断裂带和裂陷带主要形成于第四纪,它们构成了宽约150km的不均匀的左旋简单剪切变形域,该变形域的整体活动性较弱,属于弱的不均匀剪切变形域。但其中的二道沟断陷盆地是个例外,该盆地边界断裂的垂直活动速率约为0 5mm/a,左旋活动速率介于0 8～1 0mm/a之间。而在整个左旋剪切变形带累计的左旋走滑速率不会超过6mm/a,它们所调节的昆仑山与唐古拉山之间的地壳南北缩短量也可能仅占总缩短量的15%～30%。上述弱剪切变形域与强烈左旋走滑的昆仑断裂系共同构成了高原中部的左旋剪切变形带,它们在印度板块与欧亚板块强烈碰撞的构造动力学背景下,起着调节青藏高原南北向缩短的重要作用。     

东非裂谷系西支构造样式及其对油气成藏的控制作用

基于东非裂谷系西支地震地质综合解释对比研究,发现该生长型裂谷盆地受基底属性影响,主要发育陡断面地堑型盆地结构,沿边界主控断裂走向发育背离型和接近型两类主要调节构造,沿边界主控断裂倾向主要发育地垒式和地堑式两类调节构造。构造样式控制了主要成藏条件：陡断面地堑式裂谷能够形成沉积范围广、厚度大的湖相优质烃源岩;裂谷间走向调节构造属于一级调节带,控制长轴辫状河三角洲的展布;裂谷内错断的边界断裂带属于次级走向调节构造,控制中小型扇三角州的发育。倾向调节构造形成的断鼻、断块圈闭,为该类盆地的主要油气藏类型。     

Intraplate seismotectonic features of North China

Intraplate earthquakes in North China are characterized by shallow depth, large magnitude and high frequency. Obviously, the zonal distribution of earthquakes is closely related to recent active faults and Cenozoic graben and rift systems.The active faults are mainly oriented NNE with right-lateral movements, and partially oriented NW with left-lateral movements.The Hetao-Yinchuan graben, Fenhe-Weihe graben and North China Plain rift systems often reflect crustal thinning and mantle uplift.According to the data concerning crustal deformation, particularly the movement patterns of faulting, crustal taphrogenesis and earthquake surface rupture, it is suggested that a shearing-extension mechanism could be considered as a cause of the formation of seismotectonic structures in North China since the Early Cenozoic Era.Graben and rift systems also developed in Northeast and South China. They formed earlier than the graben and rift systems in North China, however, and their activity has decreased during the Quaternary period. It is reasonable that the seismicity in Northeast and South China is not as strong as that in North China.     

华北新构造：印欧碰撞远场效应与太平洋俯冲地幔上涌之间的相互作用

作为大陆内部典型的伸展断陷区和强震活动区,华北地区处于东部太平洋板块俯冲构造和西部印欧大陆碰撞构造的双重大地构造背景之下,其新构造运动相当复杂:西部沿鄂尔多斯地块周缘两个地堑盆地系引张伸展断陷作用、中部太行山块体的局部断陷和整体隆升、东部华北平原区和渤海湾海域区的区域沉降,南缘沿秦岭构造带的左旋走滑拉张活动,东缘沿郯庐断裂带的右旋挤压走滑活动。这些不同类型的断裂构造在晚新生代的阶段性活动,产生了复杂的构造地貌组合特征。综合研究发现,华北晚新生代经历了3期伸展断陷-挤压隆升演化阶段:新近纪晚期(10～2.5 Ma)、早中更新世和晚更新世以来。地壳引张应力方向或NW-SE、或NE-SW向;地块隆升导致湖盆的消亡,挤压应力方向为NE-SW至W-E向。研究认为,华北地区新构造受两个岩石圈构造过程的相互影响:印欧碰撞产生的远程效应和东部岩石圈地幔的上涌。一方面,青藏高原东北缘地块的持续推挤及其构造应力向东的传递导致鄂尔多斯地块反时针旋转和秦岭山地的向东挤出逃逸,这个挤出构造动力学统治了华北地区晚新生代的引张伸展、斜张走滑和挤压变形。尤其是,新近纪晚期强烈的NW-SE向地壳伸展变形与青藏东缘挤出造山作用同步(10～9 Ma至4.2 Ma);上新世末期(约2.5 Ma)、晚更新世早期(约200～70 ka)和晚更新世晚期—全新世(约20 ka以来)3次构造挤压事件与青藏高原东缘构造事件基本对应。另一方面,岩石圈地幔上涌主导了华北东部平原区的区域地壳沉降,同时伴随着早、中更新世的5期幔源火山活动。这两个岩石圈构造作用力此消彼长,深刻统治着华北地区新构造与现今活动构造以及地震构造。     

Mesozoic transtensional basin history of the Eastern Cordillera, Colombian Andes: Inferences from tectonic models

Backstripping analysis and forward modeling of 162 stratigraphic columns and wells of the Eastern Cordillera (EC), Llanos, and Magdalena Valley shows the Mesozoic Colombian Basin is marked by five lithosphere stretching pulses. Three stretching events are suggested during the Triassic–Jurassic, but additional biostratigraphical data are needed to identify them precisely. The spatial distribution of lithosphere stretching values suggests that small, narrow (<150 km), asymmetric graben basins were located on opposite sides of the paleo-Magdalena–La Salina fault system, which probably was active as a master transtensional or strike-slip fault system. Paleomagnetic data suggesting a significant (at least 10°) northward translation of terranes west of the Bucaramanga fault during the Early Jurassic, and the similarity between the early Mesozoic stratigraphy and tectonic setting of the Payandé terrane with the Late Permian transtensional rift of the Eastern Cordillera of Peru and Bolivia indicate that the areas were adjacent in early Mesozoic times. New geochronological, petrological, stratigraphic, and structural research is necessary to test this hypothesis, including additional paleomagnetic investigations to determine the paleolatitudinal position of the Central Cordillera and adjacent tectonic terranes during the Triassic–Jurassic. Two stretching events are suggested for the Cretaceous: Berriasian–Hauterivian (144–127 Ma) and Aptian–Albian (121–102 Ma). During the Early Cretaceous, marine facies accumulated on an extensional basin system. Shallow-marine sedimentation ended at the end of the Cretaceous due to the accretion of oceanic terranes of the Western Cordillera. In Berriasian–Hauterivian subsidence curves, isopach maps and paleomagnetic data imply a (>180 km) wide, asymmetrical, transtensional half-rift basin existed, divided by the Santander Floresta horst or high. The location of small mafic intrusions coincides with areas of thin crust (crustal stretching factors >1.4) and maximum stretching of the subcrustal lithosphere. During the Aptian–early Albian, the basin extended toward the south in the Upper Magdalena Valley. Differences between crustal and subcrustal stretching values suggest some lowermost crustal decoupling between the crust and subcrustal lithosphere or that increased thermal thinning affected the mantle lithosphere. Late Cretaceous subsidence was mainly driven by lithospheric cooling, water loading, and horizontal compressional stresses generated by collision of oceanic terranes in western Colombia. Triassic transtensional basins were narrow and increased in width during the Triassic and Jurassic. Cretaceous transtensional basins were wider than Triassic–Jurassic basins. During the Mesozoic, the strike-slip component gradually decreased at the expense of the increase of the extensional component, as suggested by paleomagnetic data and lithosphere stretching values. During the Berriasian–Hauterivian, the eastern side of the extensional basin may have developed by reactivation of an older Paleozoic rift system associated with the Guaicáramo fault system. The western side probably developed through reactivation of an earlier normal fault system developed during Triassic–Jurassic transtension. Alternatively, the eastern and western margins of the graben may have developed along older strike-slip faults, which were the boundaries of the accretion of terranes west of the Guaicáramo fault during the Late Triassic and Jurassic. The increasing width of the graben system likely was the result of progressive tensional reactivation of preexisting upper crustal weakness zones. Lateral changes in Mesozoic sediment thickness suggest the reverse or thrust faults that now define the eastern and western borders of the EC were originally normal faults with a strike-slip component that inverted during the Cenozoic Andean orogeny. Thus, the Guaicáramo, La Salina, Bitúima, Magdalena, and Boyacá originally were transtensional faults. Their oblique orientation relative to the Mesozoic magmatic arc of the Central Cordillera may be the result of oblique slip extension during the Cretaceous or inherited from the pre-Mesozoic structural grains. However, not all Mesozoic transtensional faults were inverted.     

K-rich mantle metasomatism control of localization and initiation of lithospheric strike-slip faulting

ABSTRACT A conceptual model is proposed in which bulk transtension, or local transtension during bulk simple shear (resulting from mantle anisotropy contrasts or lithosphere rheology contrasts), of heterogeneously enriched lithospheric mantle, triggers localized K-rich magmatism, which focuses strain and causes nucleation of lithosphere-scale transtensional or strike-slip shear zones. Transtension-triggered magmatism is most likely to be located at sites of maximum metasomatism of the lithospheric mantle. Magma-generated fractures propagate upwards, nucleating zones of lithospheric weakness, which focus shear in narrow transcurrent faults or at basin margins. In this way, magmatism controls fault timing and location. Although volcanism will be coeval with fault development and volcanoes will appear fault-controlled, counterintuitively, our model suggests that faults are, in a sense, volcano-controlled. We suggest that this new transtension – K-rich magmatism – transcurrent faulting association represents a hitherto unrecognized genetic relationship as significant as, for example, the ocean island magma series.     

Neotectonic and volcanic characteristics of the Karasu fault zone (Anatolia,Turkey): The transition zone between the Dead Sea transform and the East Anatolian fault zone

The Karasu Rift (Antakya province, SE Turkey) has developed between east-dipping, NNE-striking faults of the Karasu fault zone, which define the western margin of the rift and west-dipping, N–S to N20°–30°E-striking faults of Dead Sea Transform fault zone (DST) in the central part and eastern margin of the rift. The strand of the Karasu fault zone that bounds the basin from west forms a linkage zone between the DST and the East Anatolian fault zone (EAFZ). The greater vertical offset on the western margin faults relative to the eastern ones indicates asymmetrical evolution of the rift as implied by the higher escarpments and accumulation of extensive, thick alluvial fans on the western margins of the rift. The thickness of the Quaternary sedimentary fill is more than 465 m, with clastic sediments intercalated with basaltic lavas. The Quaternary alkali basaltic volcanism accompanied fluvial to lacustrine sedimentation between 1.57 ± 0.08 and 0.05 ± 0.03 Ma. The faults are left-lateral oblique-slip faults as indicated by left-stepping faulting patterns, slip-lineation data and left-laterally offset lava flows and stream channels along the Karasu fault zone. At Hacılar village, an offset lava flow, dated to 0.08 ± 0.06 Ma, indicates a rate of left-lateral oblique slip of approximately 4.1 mm·year^–1. Overall, the Karasu Rift is an asymmetrical transtensional basin, which has developed between seismically active splays of the left-lateral DST and the left-lateral oblique-slip Karasu fault zone during the neotectonic period.     

Processing and interpretation of the gravity field of the East African Rift: implication for crustal extension

Compilation of new and existing gravity data were undertaken to assess the nature of the crust beneath the East African Rift System. Using 3D gravity modeling code crustal model of gravity profiles across two sectors of the rift were computed. The results are discussed in light of the structure of the rift system.The results of the 3D modeling of gravity profiles across the two rift zones revealed northward thinning of the crust. The maximum crustal attenuation occurs beneath the Afar depression, indicating the Afar rift undergoes an intense fragmentation of the crust resulting from faulting and magmatic activity. However, our computed crustal thickness below the Afar depression falls within an upper bound compared to elsewhere below tectonically active rift zones. This can be explained in terms of crustal accretion resulting from an impact of the Afar mantle plume since 30 Ma ago.The residual gravity obtained using high-cut filtering techniques reveals significant density contrast between the northern and southern sectors of the rift. The northern part of the rift is characterized by regular patterns of positive gravity anomalies, which can be interpreted in terms of a zone of crustal thinning through which relatively dense materials have intruded the overlying crust. In contrast, south of the Main Ethiopian Rift, the anomalies are characterized by random patterns and low amplitudes. The along-rift-axis variation in gravity anomalies implies that the style of crustal deformation changed progressively, beginning with regionally distributed crustal deformation, such as the one we observe within the more juvenile and wider southern segment of the rift, to localized deformation within the active and narrow rift zones of the northern sector of the Ethiopian Rift. We suggest that the key parameters controlling along-rift-axis variation in gravity anomalies are the rate of crustal extension, faulting and magmatic activities.     

Strike-slip faults parallel to crustal spreading axes: data from Iceland and the Afar Depression

Slickenside studies in regions of crustal spreading such as Iceland and the Afar Depression, East Africa, reveal that a significant number of faults parallel and close to rift axes are strike-slip rather than normal. Therefore, the pattern of brittle deformation in these regions does not conform to the classic two-dimensional schemes of oceanic tectonics and pre-oceanic rifting. Dip-slip and strike-slip faulting presumably alternated along or in the vicinity of spreading axes, indicate a varying stress field and a combination of transverse and longitudinal movements. In Iceland, strike-slip faults parallel to rifts are observed both west and east of the rift system as well as in a median area between overlapping rifts; the mechanisms proposed for their origin include accommodation of oblique convergence or divergence of crustal sections due to variations of spreading directions along axis and the interaction of overlapping rifts. In the Afar Depression this kind of fault is recorded west of the rift of Asal and can be imputed to reflect an interaction among rifts in the vicinity of the Afar triple junction. Rift-parallel strike-slip faults cannot however be assumed to be a feature of all crustal spreading axes due to the peculiarity of the examined regions: both of them are hot-spot areas and the Afar Depression lies at a triple junction.     

Die großen Gräben: Harmonische Strukturen in einer disharmonisch struierten Erdkruste

A system of intracontinental grabens extends over Western Europe, the Levant and East Africa. Small crustal segments framed by elevated shoulders are sunken along parallel escarpments and disintegrated by antithetic normal faults. The shoulders are risen up as outward tilted blocks and thought to form a closed vault at the base of the crust, corresponding to the wedge block of the graben. Underneath the Rhinegraben exists, as detected by seismic refraction measurements, a pillow-shaped body of material with P-wave velocities of 7.4 to 7.9 km/sec, intercalated between crust and mantle. The taphrogenesis of all larger grabens is assumed to be induced by the formation and growth of subcrustal swells of this type. Also the specific graben volcanism is thought to be connected with the intruded laccolithic body of mantle-derived material. The tensional breakup and the faulting of the warped crustal masses was favoured by the gravity slide of the crust which was uncoupled from the substratum by the intercalated magmatic layer. Along the Red Sea Rift the crust tore completely releasing the basaltic substratum in the inner graben. The pattern of its magnetic anomalies leads to the assumption that the pillow body is recruited by simatic dike injections according to the principle of sea-floor spreading. Therefore, there is a great conformity between the intercontinental and the mid-oceanic rift systems. The supplies of mantle material along the Mid-Atlantic and the Carlsberg Rift are related to the drift of the continental frames. The mid-oceanic rift systems in their medial position to the framing continental margins correspond to the intracontinental graben swarm, equidistant from both fronts of circum-Pacific tectonics. A reciprocating action is presumed between the ascending masses along the rift zones and the suction of masses along the deep-sea trenches and geosynclines. The observed crustal movements imply an equilibrant plastic flow within the upper mantle, probably impelled by mechanical convection currents. The continental unbalance between the Pacific and the anti-Pacific hemisphere is discussed as causing mantle currents. Within this interplay between crust and mantle and between continents and ocean floors, the oceanic crust had obtained harmonical features moulded directly by the deduced mobility. The continental crust, however, is passively stressed, its rocks are affected by heterogeneous deformations from which the continents got its polygenetic multiform fabric.     

塔里木盆地南部塘古孜巴斯坳陷发现晚新生代伸展构造

通过认真、系统的地震资料解释,在塔里木盆地南部的塘古孜巴斯坳陷及周缘首次发现晚新生代正断层。在塘古孜巴斯坳陷内部发现的晚新生代正断层走向为北西-南东向,剖面上组合成地堑或堑-垒构造,与巴楚隆起东北缘所发育的晚新生代正断层相似。塘古孜巴斯坳陷西北缘发现的两条晚新生代正断层走向为北东-南西,剖面组合成一地堑构造,与阿瓦提凹陷西北缘沙井子断裂带上发育的晚新生代张扭性正断层带走向一致,但不具备张扭性变形特征。正断层形成于上新世晚期(约3 Ma),持续演化至更新世早期(约2 Ma)。正断层的活动时间也与阿瓦提凹陷周缘的晚新生代正断层一致。它们形成于一个区域性弱伸展构造应力场内,代表印度-亚洲碰撞远程效应下,塔里木盆地脉式挤压(-冲断)过程中的一个构造间歇期。     

Neotectonic and volcanic characteristics of the Karasu fault zone (Anatolia,Turkey): The transition zone between the Dead Sea transform and the East Anatolian fault zone

Abstract

The Karasu Rift (Antakya province, SE Turkey) has developed between east-dipping, NNE-striking faults of the Karasu fault zone, which define the western margin of the rift and westdipping, N-S to N20°-30°E-striking faults of Dead Sea Transform fault zone (DST) in the central part and eastern margin of the rift. The strand of the Karasu fault zone that bounds the basin from west forms a linkage zone between the DST and the East Anatolian fault zone (EAFZ). The greater vertical offset on the western margin faults relative to the eastern ones indicates asymmetrical evolution of the rift as implied by the higher escarpments and accumulation of extensive, thick alluvial fans on the western margins of the rift. The thickness of the Quaternary sedimentary fill is more than 465 m, with clastic sediments intercalated with basaltic lavas. The Quaternary alkali basaltic volcanism accompanied fluvial to lacustrine sedimentation between 1.57 ± 0.08 and 0.05 ± 0.03 Ma. The faults are left-lateral oblique-slip faults as indicated by left-stepping faulting patterns, slip-lineation data and left-laterally offset lava flows and stream channels along the Karasu fault zone. At Hacilar village, an offset lava flow, dated to 0.08 ± 0.06 Ma, indicates a rate of leftlateral oblique slip of approximately 4.1 mm?year^?1. Overall, the Karasu Rift is an asymmetrical transtensional basin, which has developed between seismically active splays of the left-lateral DST and the left-lateral oblique-slip Karasu fault zone during the neotectonic period. © 2001 Éditions scientifiques et médicales Elsevier SAS     

从地壳上地幔构造看大陆岩石圈伸展与裂解

本篇讨论大陆岩石圈拆沉、伸展与裂解作用过程。由于大陆岩石圈厚度大而且很不均匀,产生裂谷的机制比较复杂。大陆碰撞远程效应的触发,岩石圈拆沉,以及板块运动的不规则性和地球应力场方向转折,都可能产生岩石圈断裂和大陆裂谷。岩石圈拆沉为在重力作用下"去陆根"的作用过程,演化过程可分为大陆根拆离、地壳伸展和岩石圈地幔整体破裂三个阶段。大陆碰撞带、俯冲的大陆和大洋板块、克拉通区域岩石圈,都可能产生岩石圈拆沉。大陆岩石圈调查表明,拉张区可见地壳伸展、岩石圈拆离、软流圈上拱和热沉降;它们是大陆岩石圈伸展与裂解早期的主要表现。从初始拉张的盆岭省到成熟的张裂省,拆离后地壳伸展成复式地堑,下地壳幔源玄武岩浆侵位,断裂带贯通并切穿整个岩石圈,表明地壳伸展进入成熟阶段。中国东北松辽盆地和西欧北海盆地曾处于成熟的张裂省。岩石圈破裂为岩浆侵位提供了阻力很小的通道网。岩浆侵位作用伴随岩石圈破裂和热流体上涌,成熟的张裂省可发展成大陆裂谷。多数的大陆裂谷带并没有发展成威尔逊裂谷带和洋中脊,普通的大陆裂谷要演化为威尔逊裂谷带,必须有来自软流圈的长期和持续的热流和玄武质岩浆的供应。威尔逊裂谷带岩石圈地幔和软流圈为地震低速带,其根源可能与来自地幔底部的地幔热羽流有关。     

Structural and Stratigraphic Evolution of the Rio Grande Rift,Northern New Mexico and Southern Colorado

The well-known Pliocene to Quaternary Rio Grande rift of northern New Mexico and southern Colorado is distinctly different from the Miocene rift, especially in structural style. Prior to approximately 21 Ma, there was little extension or rift-basin development. Uppermost Oligocene and Lower Miocene strata were deposited as broad volcaniclastic aprons, with no significant evidence of syn-depositional faulting, in contrast to younger deposits. The only documented areas of extensional faulting and stratal rotation older than 21 Ma occur within or close to magmatic centers. Early rift basins (21-10 Ma) developed as half grabens progressively tilted in hanging walls of normal faults that primarily reactivated Laramide (Eocene) reverse faults: (1) the San Luis basin tilted eastward as the Sangre de Cristo normal fault reactivated westward-dipping Laramide reverse faults; (2) the Tesuque basin tilted westward as normal faults reactivated eastward-dipping Laramide reverse faults of Sierra Nacimiento and related features; and (3) the Belen basin experienced complex tilting as diverse normal faults reactivated variably dipping Laramide reverse faults. Some of these early-rift faults remain active, whereas others became inactive starting near 10 Ma, as new faults broke across Laramide and early-rift features. The Embudo transfer zone linked normal faults along the east side of the San Luis basin to the Pajarito, La Bajada, San Francisco, and Rincon fault zones at this time. Normal faults along the northwest side of the Miocene Tesuque basin became inactive at the same time that rapid uplift of the Sandia Mountains as a footwall block began at about 10 Ma. This shifting of normal-fault activity resulted in reversal of tilt direction from westward for the Miocene Tesuque basin to eastward for the modern Albuquerque basin. Uplift and erosion of early-rift deposits along the northwest side of the Albuquerque basin have resulted.

This two-stage model for evolution of the Rio Grande rift in north-central New Mexico and southern Colorado is fundamentally different from previous two-stage models, which described Oligo-Miocene volcaniclastic aprons as “early rift deposits,” and related them to extensional structures. Rather, development of half grabens began around 21 Ma, with dominance of negative inversion of Laramide reverse and thrust faults. Regional change in extension direction led to the abandonment of some faults and the initiation of new faults at 10-8 Ma in the Rio Grande rift. The biggest change occurred in the Tesuque basin, as the western boundary fault became inactive during growth of the Jemez volcanic field, and the Sandia Mountains began their rapid rise as the northern Albuquerque basin tilted to the east. Continued regional uplift, and integration and incision of the Rio Grande and tributaries, have occurred during the last 5 million years, with the course of the river tending to follow the downdropped side of each modern half graben.     

Dynamics Analysis of the Baiyun Sag in the Pearl River Mouth Basin,North of the South China Sea

The Baiyun sag is a deep one developing on the slope of the Pearl River Mouth Basin. It occurs as a composite graben horizontally, and is composed of two sub-sags versus one low uplift. Vertically, the sedimentary architecture could be divided into three layers, i.e. the faulted layer on the bottom, the faulted-ductile stretching layer in the middle and the draping layer on the top. The main rifting stage of the sag is supposed to be characterized by ductile extension and thinning of the crust. The special deformation pattern is probably attributed to the fact that the Baiyun sag is located in the transfer zone of the pre-existing weak zone, which made the sag a strongly deformed area, characterized by the greatly thinned lithosphere and active magmatism. The highly rising mantle under the Baiyun sag should be an important mechanism responsible for the ductile deformation, which caused partial melting of the upper mantle. Upweiling to the upper crust and the sedimentary layers, the partial melting materials accommodated extensional strain and caused non-faulted vertical subsidence. Magma was collected under the transfer zone after the first stage of rifting, and transferred laterally in a direction perpendicular to the extension to the ENE and WSW parts of the sag and upwelled along the NW-trending basal faults, where WNW-trending shear faults developed in swarms. The faulting activity and sedimentation history of the Baiyun sag may have been affected by the ocean ridge jump around 24 Ma and the cessation of sea floor spreading around 16 Ma.     

Geometry and architecture of faults in a syn-rift normal fault array: The Nukhul half-graben, Suez rift, Egypt

The geometry and architecture of a well exposed syn-rift normal fault array in the Suez rift is examined. At pre-rift level, the Nukhul fault consists of a single zone of intense deformation up to 10 m wide, with a significant monocline in the hanging wall and much more limited folding in the footwall. At syn-rift level, the fault zone is characterised by a single discrete fault zone less than 2 m wide, with damage zone faults up to approximately 200 m into the hanging wall, and with no significant monocline developed. The evolution of the fault from a buried structure with associated fault-propagation folding, to a surface-breaking structure with associated surface faulting, has led to enhanced bedding-parallel slip at lower levels that is absent at higher levels. Strain is enhanced at breached relay ramps and bends inherited from pre-existing structures that were reactivated during rifting. Damage zone faults observed within the pre-rift show ramp-flat geometries associated with contrast in competency of the layers cut and commonly contain zones of scaly shale or clay smear. Damage zone faults within the syn-rift are commonly very straight, and may be discrete fault planes with no visible fault rock at the scale of observation, or contain relatively thin and simple zones of scaly shale or gouge. The geometric and architectural evolution of the fault array is interpreted to be the result of (i) the evolution from distributed trishear deformation during upward propagation of buried fault tips to surface faulting after faults breach the surface; (ii) differences in deformation response between lithified pre-rift units that display high competence contrasts during deformation, and unlithified syn-rift units that display low competence contrasts during deformation, and; (iii) the history of segmentation, growth and linkage of the faults that make up the fault array. This has important implications for fluid flow in fault zones.