Geodynamic conditions of evolution of the Tunka Branch in the Baikal Rift System

The Cenozoic paleostress state of the Earth’s crust at the southwestern flank of the Baikal Rift System (Tunka system of basins) is reconstructed. With allowance for known facts about the geologic history of the Tunka system of basins, the evolution of the stress field and its formation conditions are established by comparison of the obtained reconstructions, including the dated stress fields, with the Pleistocene-Holocene deformations in active fault zones and the present-day stress state (seismotectonic deformations calculated from the focal mechanisms of earthquakes). The opening of basins in the NW-SE direction was proceeding in the transtensional regime from the Oligocene to the late Miocene or early Pliocene. At the early-late Pliocene boundary, this process was followed by the transpressional regime with compression in the NW direction. In the late Pliocene, the situation at the southwestern flank changed drastically. Since that time, deformation has occurred in the transpressional regime and the compression axis has been oriented in the NE direction. The alternative models of the evolution of the Tunka system of basins—oblique extension, the transform fracture zone, or a pull-apart system—are considered. Both models are combined in the framework of the suggested stress-field reconstruction. The oblique extension (transtension) was related to the early stages of evolution, whereas a possibility of forming pull-apart basin was existent at the late stages.     

Tectonics,stress state,and geodynamics of the Mesozoic and Cenozoic Rift basins in the Baikal region

The results of geological, structural, tectonic, and geoelectric studies of the dry basins in the Baikal Rift Zone and western Transbaikalia, combined under the term Baikal region, are integrated. Deformations of the Cenozoic sediments related to pulsing and creeping tectonic processes are classified. The efficiency of mapping of the fault-block structure of the territories overlapped by loose and poorly cemented sediments is shown. The faults mapped at the ground surface within the basins are correlated with the deep structure of the sedimentary fill and the surface of the crystalline basement, where they are expressed in warping and zones of low electric resistance. It is established that the kinematics of the faults actively developing in the Late Cenozoic testifies to the relatively stable regional stress field during the Late Pliocene and Quaternary over the entire Baikal region, where the NW-SE-trending extension was predominant. At the local level, the stress field of the uppermost Earth’s crust is mosaic and controlled by variable orientation of the principal stress axes with the prevalence of extension. The integrated tectonophysical model of the Mesozoic and Cenozoic rift basin is primarily characterized by the occurrence of mountain thresholds, asymmetric morphostructure, and block-fault structure of the sedimentary beds and upper part of the crystalline basement. The geological evolution of the Baikal region from the Jurassic to Recent is determined by alternation of long (20–115 Ma) epochs of extension and relatively short (5.3–3.0 Ma) stages of compression. The basins of the Baikal Rift System and western Transbaikalia are derivatives of the same geodynamic processes.     

Basin structures and sediment accumulation in the Baikal Rift Zone: Implications for Cenozoic intracontinental processes in the Central Asian Orogenic Belt

In this paper we present a review of sedimentological, geomorphological, lithological, geochronological and geophysical data from major, minor and satellite basins of the Baikal Rift Zone (BRZ) and discuss various aspects of its evolution. Previously, the most detailed sedimentological data have been obtained from the basins of the central BRZ, e.g., Baikal, Tunka and Barguzin, and have been used by many scientists worldwide. We add new information about the peripheral part and make an attempt to provide a more comprehensive view on BRZ sedimentation stages and environments and their relations to local and regional tectonic events. A huge body of sedimentological data was obtained many years ago by Soviet geologists and therefore is hardly accessible for an international reader. We pay tribute to their efforts to the extent as the format of a journal paper permits. We discuss structural and facial features of BRZ sedimentary sequences for the better understanding of their sedimentation environments. In addition, we review tectono-sedimentation stages, neotectonic features and volcanism of the region. Finally, we consider the key questions of the BRZ evolution from the sedimentological point of view, in particular, correlation of Mesozoic and Cenozoic basins, bilateral growth of the Baikal rift, Miocene sedimentation environment and events at the Miocene/Pliocene boundary, Pliocene and Pleistocene tectonic deformations and sedimentation rates. The data from deep boreholes and surface occurrences of pre-Quaternary sediments, the distribution of the Pleistocene sediments, and the data from the Baikal and Hovsgol lakes sediments showed that 1) BRZ basins do not fit the Mesozoic extensional structures and therefore hardly inherited them; 2) the Miocene stage of sedimentation was characterized by low topography and weak tectonic processes; 3) the rifting mode shifted from slow to fast at ca. 7–5 Ma; 4) the late Pleistocene high sedimentation rates reflect the fast subsidence of basin bottoms.     

Rockfall-Dammed Lakes in the Baikal Region: Evidence from the Past and Prospects for the Future

The mountain province of East Siberia, which includes the Baikal Rift system, is a zone of high tectonic and seismic hazard. Earthquakes and coseismic faulting are dangerous not only by themselves but also as far as they initiate rock collapse and downslope movement of unconsolidated deposits, which may block river valleys and produce rockfall-dammed lakes. Within some rifts of the rift system, evidence of past dammed lakes was discovered that arose instantly, in a geological sense, and flooded large areas of forest. In mountains around some rift basins, small living dammed lakes were encountered, as well as traces of catastrophic debris flows that may have accompanied breaching of earlier collapse-produced dams. Analysis of geomorphological setting in the region, especially in the Muya Rift Basin, revealed conditions favourable to hazardous origination of rockfall-dammed lakes. A large dammed lake may come into existence due to the collapse of bedrock over the narrow antecedent valley of Vitim in the Muya Rift. Preliminary estimates based upon data on the Vitim River discharge showed that the lake might form in as short as 27 days, though the rapidity of its formation, and hence the degree of the risk, can vary as a function of the highly variable amount of summer discharge of the river. Rockfall-dammed lakes may also originate in the floors of Chara and Tunka Rift Basins. Due to their rapid formation, lakes will bring about extensive flooding and cause danger to the taiga, railways and constructions in this populated developing area, and will cause degradation of the permafrost.     

Late Quaternary and current deformation in the western Tunka system of basins: evidence from structural geomorphology and seismology

Integrated seismological and structural geomorphological studies of the western Tunka system of basins in the southwestern Baikal rift show that the historic seismicity reflects the general Late Quaternary evolution trend of structures. Crustal deformation occurs mainly as transpression. Compression follows block boundaries and the northern mountainous borders of basins, whereas extension acts upon basin inner parts which remain in “tectonic shadow” during left-lateral strike-slip motions on W-E faults. Principal stresses inferred from earthquake mechanisms are most often a combination of horizontal NW extension and oblique or vertical compression in the basins and vertical extension with horizontal NE compression in the bordering ridges and along block boundaries. The general deformation style in the region is dominated by strike-slip faulting, and compression (shortening) dominates over extension.     

Style of active intraplate deformation from gravity and seismicity data: the Baikal Rift, Asia

To better understand how active deformation localizes within a continental plate in response to extensional and transtensional tectonics, a combined analysis of high-quality gravity (Bouguer anomaly) and seismicity data is presented consisting of about 35000 earthquakes recorded in the Baikal Rift Zone. This approach allows imaging of deformation patterns from the surface down to the Moho. A comparison is made with heat flow variations in order to assess the importance of lithospheric rheology in the style of extensional deformation. Three different rift sectors can be identified. The southwestern rift sector is characterized by strong gravity and topography contrasts marked by two major crustal faults and diffuse seismicity. Heat flow shows locally elevated values, correlated with recent volcanism and negative seismic P-velocity anomalies. Based on earthquake fault plane solutions and on previous stress field inversions, it is proposed that strain decoupling may occur in this area in response to wrench-compressional stress regime imposed by the India–Asia collision. The central sector is characterized by two major seismic belts; the southernmost one corresponds to a single, steeply dipping fault accommodating oblique extension; in the centre of lake Baikal, a second seismic belt is associated with several dip-slip faults and subcrustal thinning at the rift axis in response to orthogonal extension. The northern rift sector is characterized by a wide, low Bouguer anomaly which corresponds to a broad, high topographic dome and seismic belts and swarms. This topography can be explained by lithospheric buoyancy forces possibly linked to anomalous upper mantle. At a more detailed scale, no clear correlation appears between the surficial fault pattern and the gravity signal. As in other continental rifts, it appears that the lithospheric rheology influences extensional basins morphology. However, in the Baikal rift, the inherited structural fabric combined with stress field variations results in oblique rifting tectonics which seem to control the geometry of southern and northeastern rift basins.     

Arshan palaeoseismic feature of the Tunka fault (Baikal rift zone,Russia)

The traditional concept of the rift development of flank depressions in the Baikal rift zone is now doubted in view of some indicators for compression deformations identified by the seismogeological and geodetic methods. Besides, the paleoseismological investigations revealed seismogenic strike-slips and reverse faults in the Tunka fault zone that is a major structure-controlling element of the Tunka rift depression. However, a detailed study of the upslope-facing scarp in the Arshan paleoseismogenic structure zone has shown that its formation might be due to rift mechanism of basin formation. Age estimation has been made for the previously unknown pre-historic earthquake whose epicentral area coincides with the western flank of the Arshan paleoseismogenic structure. Judging from previously determined ages of paleoearthquakes, the mean recurrence period for faulting events on the central Tunka fault is 2780–3440 years.     

Evolution of the Academician Ridge Accommodation Zone in the central part of the Baikal Rift, from high-resolution reflection seismic profiling and geological field investigations

 New high-resolution seismic reflection data from the central part of Lake Baikal provide new insight into the structure and stratigraphy of Academician Ridge, a large intra-rift accommodation zone separating the Central and North Baikal basins. Four seismic packages are distinguished above the basement: a thin top-of-basement unit; seismic-stratigraphic unit X; seismic-stratigraphic unit A; and seismic-stratigraphic unit B. Units A and B were cored on selected key locations. The four packages are correlated with a series of deposits exposed on the nearby western shores: the Ularyar Sequence (Oligocene); the Tagay Sequence (Lower to Middle Miocene); the Sasa Sequence (Upper Miocene to Lower Pliocene); the Kharantsy Sequence (Upper Pliocene); and the Nyurga Sequence (Lower Pleistocene). Based on stratal relationships, sedimentary geometries, distribution patterns and principal morphostructural elements – both onshore and offshore – we propose a new palaeogeographic evolution model for the area. In this model progressive tectonic subsidence of the Baikal basins and successive pulses of uplift of various segments of the rift margins lead to: (a) formation of the ridge as a structural and morphological feature separating the Central and North Baikal basins during the Middle to Late Miocene; (b) gradual flooding of the main parts of the ridge and establishment of a lacustrine connection between the two rift basins during the Late Miocene; and (c) total submergence of the top parts of the crest of the ridge during the latest Pleistocene. This new model helps to better constrain numerous phases in the structural evolution of the Baikal Rift, in which the Academician Ridge as an accommodation zone plays a crucial role. Received: 26 November 1999 / Accepted: 12 March 2000     

Pliocene to Quaternary deformation in South East Sayan (Siberia): Initiation of the Tertiary compressive phase in the southern termination of the Baikal Rift System

The South East Sayan area, W of the Lake Baikal is subjected to a very complex tectonic setting where the extensional stress field of the Baikal Rift System meets the compressional stress field generated by the India–Asia collision further south. Using satellite images, aerial photographs, SRTM DEM, field mapping of geomorphological structures, and published neotectonics and geological data we show that most of the relief in the SE Sayan initiated during Late Pliocene–Pleistocene through compressive reactivation of inherited structures. By Late Quaternary, clockwise rotation of the compressive field generated strike–slip faulting and local, secondary extension still within a general compressional stress field. We demonstrate that the formation of the small-scale extensional basins within the East Sayan range is not linked to general the extension in the Baikal Rift System nor to a possible asthenospheric plume acting at the base of the crust but rather to the rotation of small rigid tectonic blocks driven by the compression.     

Petrochemistry of Cenozoic basalts and associated rocks in the Baikal rift zone

The main episode of Cenozoic volcanic activity occurred simultaneously with formation of the Sayan—Baikal uplift, before the rift depressions were initiated. Volcanism and rifting in this region have developed as independent processes, connected with each other only by an ultimate primary mantle energy source. The volcanic regions do not coincide with the rift depressions, except in the Tunka graben.Chemical features of the volcanics show that during the entire period of volcanic activity there was a complex alternation of basaltic lavas of alkaline, intermediate and tholeiitic composition. Both alkaline and subalkaline lavas are distributed over the entire volcanic region, excepting the Tunka depression where tholeiitic lavas are predominant. However, there is neither mineralogical nor chemical evidence for the existence of two separate magma types within the Baikal rift zone.Judging by the presence of high-pressure, lherzolitic megacrysts of clinopyroxene, and to a lesser extent titaniferous biotite and amphibole in alkaline basalts, variations of lava chemistry are connected with high-pressure fractionation of initial melts, which was more complete for sources outside the rift zone. The predominance of tholeiitic lavas in the Tunka depression is likely to have been caused by a higher degree of partial melting and quick ascent of magma to the surface, facilitated by a high geothermal gradient under the depression where crustal extension is taking place.     

Dynamic causes for the opening of the Baikal Rift Zone: a numerical modelling approach

Previous dynamic models of the Baikal Rift Zone (BRZ) are mostly two-dimensional on vertical plane. In this study, a numerical model of neotectonics in the region on map view was constructed using the adapted PLATES program. The present work is an attempt to test different mechanisms for opening Baikal Rift by comparing the modelled and observed stress and strain rate fields. The following rifting scenarios were tested: (1) pure northwest–southeast extension, (2) pure northeast–southwest compression, (3) oblique rift opening and (4) combined northwest–southeast extension and northeast–southwest compression. The models are calibrated using geologically and GPS-derived strain rates and stress-tensor determinations from fault-slip data and earthquake focal mechanisms. The most successful model requires a combination of NE–SW compression and orthogonal extension. The model results indicate that the present extensional regime in BRZ can be explained by combining the India plate indentation northward into Eurasia, east–west convergence between the North America and Eurasia plates and southeastward extrusion of the Amur plate in northeastern Asia. Predicted fault-slip rates for the best-fit model are consistent with the observed Holocene fault-slip rates in the Lake Baikal region. The generally accepted rotation of the Amur and Mongolia microplates are used as independent constraints for the choice of the best-fit model. These data correlate well with the predicted direction of rotation in our best model.     

GPS-measurements of recent crustal deformation in the junction zone of the rift segments in the central Baikal rift system

Based on multiyear measurements of present-day motions in the central area of the Baikal rift system, new data on the kinematics of horizontal motions, relative horizontal deformation rates, and rotation velocities in the area of junction of the South Baikal, North Baikal, and Barguzin rift basins have been obtained. This area is an intricate structure with two transfer zones: Ol’khon–Svyatoi Nos and Ust’-Barguzin.It is shown that crustal blocks are moving southeastward, normally to the structures of transfer zones and at an acute angle to the Baikal Rift strike, which corresponds to the right-lateral strike-slip extensional faulting along the major structure. The average horizontal velocities increase from 3.0 mm yr–1 in the northern South Baikal basin to 6.5 mm yr–1 in the Barguzin basin. The elongation axes prevailing in the study region are mainly of NW–SE direction. The areas of intense deformations are confined to structures with high seismic activity in the South Baikal and, partly, Barguzin basins. This confirms the existence of a present-day zone of the Earth’s crust destruction in the Baikal rift system, which is the most likely source of strong earthquakes in the future. Two zones with rotations in opposite directions are recognized in the rotation velocity field. Clockwise rotation is typical of structures of N–NE strike (Maloe More basin, southern North Baikal basin, Barguzin Ridge rise). Counterclockwise rotation is determined for NE-striking structures (northern South Baikal basin, southern Barguzin basin). In general, the obtained data show an intricate pattern of present-day horizontal dislocations and deformations in the area of junction of NE- and N–NE-striking rift structures. This suggests left- and right-lateral strike-slip faults, respectively, within them.     

Rifting Attractor Structures in the Baikal Rift System: Location and Effects

The current geodynamics and tectonophysics of the Baikal rift system (BRS) as recorded in lithospheric stress and strain are discussed in the context of self organization of nonlinear dissipative dynamic systems and nonlinear media. The regional strain field inferred from instrumental seismic moment and fault radius data for almost 70,000 M_LH ⩾ 2.0 events of 1968 through 1994 shows a complex pattern with zones of high strain anisotropy in the central part and both flanks of the rift system (the South Baikal, Hovsgöl, and Muya rift basins, respectively). The three zones of local strain anisotropy highs coincide with domains of predominantly vertical stress where earthquakes of different magnitudes are mostly of normal slip geometry. Pulse-like reversals of principal stresses in the high-strain domains appear to be nonlinear responses of the system to subcrustal processes. In this respect, the BRS lithosphere is interpreted in terms of the self organization theory as a geological dissipative system. Correspondingly, the domains of high strain anisotropy and stress change, called rifting attractor structures (RAS), are the driving forces of its evolution. The location and nonlinear dynamics of the rifting attractors have controlled lithospheric stress and strain of the rift system over the period of observations, and the same scenario may have been valid also in the Mesozoic-Cenozoic rifting history. The suggested model of a positive-feedback (fire-like) evolution of nonlinear dynamical systems with rifting attractors opens a new perspective on the current geodynamics and tectonophysics of the Baikal rift system.     

Latest erosional incision in river valleys of southern East Siberia

Examples of the geological and geomorphic framework of river valleys in the Tunka rift basin (Baikal rift system) and in the Irkutsk amphitheater (Siberian craton) have been used to show that horizontal and vertical motions of tectonic units in southern East Siberia are superposed with periodic movements. In the latter, the waves of slow uplift are attendant with erosional incision events, whereas during the subsidence cycles the incised valleys become filled with mainly alluvial sediments. The latest incision events in the area occurred in the past 70 kyr.     

Cretaceous deformation history of the middle Tan-Lu fault zone in Shandong Province, eastern China

Based on field analysis of fault-slip data from different rock units of the Cretaceous basins along the middle part of the Tan-Lu fault zone (Shandong Province, eastern China), we document polyphase tectonic stress fields and address the changes in sense of motion of the Tan-Lu fault zone during the Cretaceous. The Cretaceous deformation history of the Tan-Lu fault zone can be divided into four main stages. The first stage, during the earliest Cretaceous, was dominated by N-S extension responsible for the formation of the Jiaolai basin. We interpret this extension to be related to dextral strike-slip pull-apart opening guided by the Tan-Lu fault zone. The second stage, during the middle Early Cretaceous, was overwhelmingly rift-dominated and characterized by widespread silicic to intermediate volcanism, normal faulting and basin subsidence. It was at this stage that the Tan-Lu-parallel Yi-Shu Rift was initiated by E-W to WNW-ESE extension. The tectonic regime then changed during the late Early Cretaceous to NW-SE-oriented transpression, causing inversion of the Early Cretaceous rift basin and sinistral slip along the Tan-Lu fault zone. During the Late Cretaceous, dextral activation of the Tan-Lu fault zone resulted in pull-apart opening of the Zhucheng basin, which was subsequently deformed by NE-SW compression. This deformation chronology of the Tan-Lu fault zone and the associated Cretaceous basins allow us to constrain the regional kinematic models as related to subduction along the eastern margin of Asia, or related to collision in the Tibet region.     

Basic tectonic features of the Knipovich Ridge (North Atlantic) and its neotectonic evolution

The geological and geophysical data primarily on the structure of the upper sedimentary sequence of the northern Knipovich Ridge (Norwegian-Greenland Basin) that were obtained during Cruise 24 of the R/V Akademik Nikolai Strakhov are considered. These data indicate that the recent kinematics of the northern Knipovich Ridge is determined by dextral strike-slip displacements along the Molloy Fracture Zone (315° NW). This stress field is superimposed by a system related to rifting and latitudinal opening of rifts belonging to the ridge proper. Thus, the structural elements formed under the effect of two stress fields are combined in this district. Several stages of tectonic movements are definable. The first stage (prior to 500 ka ago) is marked by the dominant normal faults, which are overlain by the lower and upper sedimentary sequences. The second stage (prior to 120–100 ka ago) is characterized by development of normal and reverse faults, which displace the lower sequence and are overlain by the upper sequence. Both younger and older structural features reveal peaks of tectonic activity separated by intermediate quiet periods 50–60 ka long. The stress field of the regional strike-slip faulting is realized in numerous oblique NE-trending normal and normal-strike-slip faults that divide the rift valley and its walls into the segments of different sizes. Their strike (20°–30° NE) is consistent with a system of secondary antithetic sinistral strike-slip faults. The system of depressions located 40 km west of the rift valley axis may be considered a paleorift zone that is conjugated at 78°07′ N and 5°20′ W with the NW-trending fault marked by the main dextral offset. The stress field that existed at this stage was identical to the recent one. The rift valley axis migrated eastward to its present-day position approximately 2 Ma ago (if the spreading rate of ～0.7 cm/yr is accepted). The obtained data substantially refine the understanding of the initial breakup of continents with the formation of oceanic structural elements. The neotectonic stage is characterized by combination of different stress fields that resulted in the formation of a complex system of tectonic structural units, including those located beyond the recent extension zone along the rift axis of the Knipovich Ridge. The tectonic deformations occurred throughout the neotectonic stage as discrete recurrent events.     

Moho depths and three-dimensional velocity structure of the crust and upper mantle beneath the Baikal region,from local tomography

We studied the 3D velocity structure of the crust and uppermost mantle beneath the Baikal region using tomographic inversion of ∼25,000 P and S arrivals from more than 1200 events recorded by 86 stations of three local seismological networks. Simultaneous iterative inversion with a new source location algorithm yielded 3D images of P and S velocity anomalies in the crust and upper mantle, a 2D model of Moho depths, and corrections to source coordinates and origin times. The resolving power of the algorithm, its stability against variations in the starting model, and the reliability of the final results were checked in several tests. The 3D velocity structure shows a well-pronounced low-velocity zone in the crust and uppermost mantle beneath the southwestern flank of the Baikal rift which matches the area of Cenozoic volcanism and a high velocity zone beneath the Siberian craton. The Moho depth pattern fits the surface tectonic elements with thinner crust along Lake Baikal and under the Busiyngol and Tunka basins and thicker crust beneath the East Sayan and Transbaikalian mountains and under the Primorsky ridge on the southern craton border.     

Redefined crustal structure of the Buchan Rift,northeast Victoria: evidence from potential field modelling of newly acquired land-based gravity data

The Buchan Rift, in northeastern Victoria, is a north–south-trending basin, which formed in response to east–west crustal extension in the Early Devonian. The rift is filled mostly with Lower Devonian volcanic and volcaniclastic rock of the Snowy River Volcanics. Although the structure and geometry of the Buchan Rift and its major bounding faults are well mapped at the surface, a discrepancy exists between the surface distribution of the thickest rift fill and its expected potential field response. To investigate this variation, two new detailed land-based gravity surveys, which span the rift and surrounding basement rocks in an east–west orientation, have been acquired and integrated with pre-existing government data. Qualitative interpretation of the observed magnetic data suggests the highly magnetic rocks of the Snowy River Volcanics have a wider extent at depth than can be mapped at the surface. Forward modelling of both land-based gravity data and aeromagnetic data supports this interpretation. With the Snowy River Volcanics largely confined within the Buchan Rift, resolved geometries also allow for the interpretation of rift boundaries that are wider at depth. These geometries are unusual. Unlike typical basin inversions that involve reactivation of rift-dipping faults, the bounding faults of the Buchan Rift dip away from the rift axis and thus appear unrelated to the preceding rifting episode. Limited inversion of previous extensional rift faults to deform the rift-fill sequences (e.g. Buchan Synclinorium) appears to have been followed by the initiation of new reverse faults in outboard positions, possibly because the relatively strong igneous rift fill began to act as a rigid basement ramp during continued E–W crustal shortening in the Middle Devonian Tabberabberan Orogeny. Overthrusting of the rift margins by older sediments and granite intrusions of the adjacent Tabberabbera and Kuark zones narrowed the exposed rift width at surface. This scenario may help explain the steep-sided geometries and geophysical expressions of other rift basins in the Tasmanides and elsewhere, particularly where relatively mechanically strong basin fill is known or suspected.     

Review of the tectonics of the Levant Rift system: the structural significance of oblique continental breakup

The Levant Rift system is an elongated series of structural basins that extends for more than 1000 km from the northern Red Sea to southern Anatolia. The system consists of three major segments, the Jordan Rift in the south, El Gharb–Kara-Su Rift in the north, and the Lebanese Fault splay in between. The rifted parts of this structural system are accompanied by intensively uplifted margins that mirror-image the basinal pattern, namely, the deeper the basin—the higher its margins, and vice versa. Uplifts also occur along the fault splay section. The Jordan Rift comprises axial basins that diminish in size from the south northwards, and are separated from each other by shallow threshold zones along the axis of the rift, where the margins are also subdued. The Lebanese Fault splay consists of five faults that emerge from the northern edge of the Jordan Rift and trend like a fan between the north and the northeast. One of these faults connects the Jordan and El Gharb–Kara-Su rifts. The Levant Rift and its uplifted margins started to develop in the middle-late Miocene, and most of the structural development occurred in the Plio-Pleistocene.The Levant Rift system is characterized by its oblique displacement, and evidence for both dip-slip and strike-slip displacement was measured on its faults. Earthquakes also indicate that same mixed pattern, some of them show strike-slip offset, and others normal. It is generally conceded that the amount of normal offset along the boundary faults of the Rift system reaches 8–10 km, but the lateral displacement is disputed, and offsets ranging from 11 to 107 km were suggested. Assessment of the available data led us to suggest that the sinistral offset along the Levant Rift system is approximately 10–20 km. The similarity between the vertical and the lateral displacements, the basin and threshold structural pattern of the Rift, model experiments in oblique rifting, as well as the significant tectonic resemblance to the Red Sea and the East African rifts, indicate that the Levant Rift is the product of continental breakup, and it is probably an emerging oceanic spreading center.