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1.
This study aims at showing how far pre-existing crustal weaknesses left behind by Proterozoic mobile belts, that pass around cratonic Archean shields (Tanzania Craton to the southeast and Congo Craton to the northwest), control the geometry of the Albertine Rift. Focus is laid on the development of the Lake Albert and Lake Edward/George sub-segments and between them the greatly uplifted Rwenzori Mountains, a horst block located within the rift and whose highest peak rises to >5000 m above mean sea level. In particular we study how the southward propagating Lake Albert sub-segment to the north interacts with the northward propagating Lake Edward/George sub-segment south of it, and how this interaction produces the structures and geometry observed in this section of the western branch of the East African Rift, especially within and around the Rwenzori horst. We simulate behaviour of the upper crust by conducting sandbox analogue experiments in which pre-cut rubber strips of varying overstep/overlap connected to a basal sheet and oriented oblique and/or orthogonal to the extension vector, are placed below the sand-pack. The points of connection present velocity discontinuities to localise deformation, while the rubber strips represent ductile domain affected by older mobile belts. From fault geometry of developing rift segments in plan view and section cuts, we study kinematics resulting from a given set of boundary conditions, and results are compared with the natural scenario. Three different basal model-configurations are used to simulate two parallel rifts that propagate towards each other and interact. Wider overstep (model SbR3) produces an oblique transfer zone with deep grabens (max. 7.0 km) in the adjoining segments. Smaller overlap (model SbR4) ends in offset rift segments without oblique transfer faults to join the two, and produces moderately deep grabens (max. 4.6 km). When overlap doubles the overstep (model SbR5), rifts propagate sub-orthogonal to the extension direction and form shallow valleys (max. 2.9 km). Relative ratios of overlap/overstep between rift segments dictate the kind of transition zone that develops and whether or not a block (like the Rwenzoris) is captured and rotates; hence determining the end-member geometry. Rotation direction is controlled by pre-existing fabrics. Fault orientation, fault kinematics, and block rotation (once in play) reinforce each other; and depending on the local kinematics, different parts of a captured block may rotate with variable velocities but in the same general direction. Mechanical strength anisotropy of pre-structured crust only initially centres fault nucleation and propagation parallel to the grain of weakness of the basement, but at later stages of a protracted period of crustal extension, such boundaries are locally defied. 相似文献
2.
With heights of 4–5 km, the topography of Rwenzori Mountains, a large horst of old crustal rocks located inside a young passive rift system, poses the question “Why are the Rwenzori Mountains so high?”. The Cenozoic Western Rift branch of the East African Rift System is situated within the Late Proterozoic mobile belts between the Archean Tanzania Craton and Congo Craton. The special geological setting of the massif at a rift node encircled by the ends of the northern Western Rift segments of Lake Albert and Lake Edward suggests that the mechanism responsible for the high elevation of the Rwenzoris is related to the rifting process. Our hypothesis is based on the propagation of the rift tips, surrounding the stiff old lithosphere at Rwenzori region, thereby triggering the delamination of the cold and dense mantle lithosphere (ML) root by reducing viscosity and strength of the undermost lower crust. As a result, this unloading induces fast isostatic pop-up of the less dense crustal Rwenzori block. We term this RID—“rift induced delamination of Mantle Lithosphere”. The physical consistency of the RID hypothesis is tested numerically. Viscous flow of 2D models is approximated by a Finite Difference Method with markers in an Eulerian formulation. The equations of conservation of mass, momentum and energy are solved for a multi-component system. Based on laboratory data of appropriate rock samples, a temperature-, pressure- and stress-dependent rheology is assumed. Assuming a simple starting model with a locally heated ML, the ML block between the weakened zones becomes unstable and sinks into the asthenosphere, while the overlying continental crust rises up. Thus, RID seems to be a viable mechanism to explain geodynamically the extreme uplift. Important conditions are a thermal anomaly within the ML, a ductile lower crust with visco-plastic rheology allowing significant strength reduction and lateral density variations. The special situation of a two-sided rifting or offset rift segments to decouple the ML laterally from the surrounding continental lithosphere seems to be most decisive. Further support for the RID mechanism may come from additional crustal thickness and an extensive stress field. Some parameters, such as the excess temperature and yield stress, are very sensitive, small changes determine whether delamination takes place or not. 相似文献
3.
Till Sachau Daniel Koehn D. Sarah Stamps Michael Lindenfeld 《International Journal of Earth Sciences》2016,105(6):1729-1740
The Rwenzori Mountains in western Uganda form an active rift-transfer zone in the western branch of the East African Rift System. Here we quantify local stress fields in high resolution from field observations of fault structures to shed light on the complex, polyphase tectonics expected in transfer zones. We apply the multiple inverse method, which is optimized for heterogeneous fault-slip data, to the northern and central Rwenzori Mountains. Observations from the northern Rwenzori Mountains show larger heterogeneity than data from the central Rwenzori, including unexpected compressional features; thus the local stress field indicates polyphase transpressional tectonics. We suggest that transpression here is linked to rotational and translational movements of the neighboring Victoria block relative to the Rwenzori block that includes strong overprinting relationships. Stress inversions of data from the central Rwenzori Mountains indicate two distinct local stress fields. These results suggest that the Rwenzori block consists of smaller blocks. 相似文献
4.
D. Koehn K. Link T. Sachau C. W. Passchier K. Aanyu A. Spikings R. Harbinson 《International Journal of Earth Sciences》2016,105(6):1693-1705
This contribution discusses the development of the Palaeoproterozoic Buganda-Toro belt in the Rwenzori Mountains and its influence on the western part of the East African Rift System in Uganda. The Buganda-Toro belt is composed of several thick-skinned nappes consisting of Archaean Gneisses and Palaeoproterozoic cover units that are thrusted northwards. The high Rwenzori Mountains are located in the frontal unit of this belt with retrograde greenschist facies gneisses towards the north, which are unconformably overlain by metasediments and amphibolites. Towards the south, the metasediments are overthrust by the next migmatitic gneiss unit that belongs to a crustal-scale nappe. The southwards dipping metasedimentary and volcanic sequence in the high Rwenzori Mountains shows an inverse metamorphic grade with greenschist facies conditions in the north and amphibolite facies conditions in the south. Early D1 deformation structures are overgrown by cordierite, which in turn grows into D2 deformation, representing the major northwards directed thrusting event. We argue that the inverse metamorphic gradient develops because higher grade rocks are exhumed in the footwall of a crustal-scale nappe, whereas the exhumation decreases towards the north away from the nappe leading to a decrease in metamorphic grade. The D2 deformation event is followed by a D3 E-W compression, a D4 with the development of steep shear zones with a NNE-SSW and SSE-NNW trend including the large Nyamwamba shear followed by a local D5 retrograde event and D6 brittle reverse faulting. The Palaeoproterozoic Buganda-Toro belt is relatively stiff and crosses the NNE-SSW running rift system exactly at the node where the highest peaks of the Rwenzori Mountains are situated and where the Lake George rift terminates towards the north. Orientation of brittle and ductile fabrics show some similarities indicating that the cross-cutting Buganda-Toro belt influenced rift propagation and brittle fault development within the Rwenzori Mountains and that this stiff belt may form part of the reason why the Rwenzori Mountains are relatively high within the rift. 相似文献
5.
Faulting of the lithosphere during extension and related rift-flank uplift: a numerical study 总被引：1，自引：1，他引：0
In this contribution, we present a new model of passive rifting and related rift-flank uplift. The numerical model is based
on a lattice spring network coupled with a viscous particle model so that we can simulate visco-elasto-plastic behaviour with
dynamic fault development. In our model, we show that rift-flank uplift can be achieved best when extension in the crust is
localized and the lower crust is strong so that major rift faults transect the whole crust. Uplift of rift flanks follows
a smooth function whereas down-throw in the rift basin takes place in steps. The geometry of the developing faults has also
an influence on the uplift; in this case, displacement along major rift faults produces higher flanks than distributed displacement
on many faults. Our model also shows that the relative elastic thickness of the crust has only a minor influence on the uplift
since fault depth and elastic thickness are not independent. In addition, we show with a second set of simulations and analytically
that a strain misfit between the upper and lower boundaries of a stretched crust, which is created by the horizontal extension,
leads to an active uplift driven by elastic forces. We compare the numerical simulations, the analytical solution and real
surface data from the Albertine rift in the East African Rift System and show that our new model can reproduce realistic features.
Our two-layer beam model with strain misfit can also explain why a thick crust in the simulations can have an even higher
rift flank than a thin crust even though the thin crust topography has a higher curvature. We discuss the implications of
our simulations for real rift systems and for the current theory of rift-flank uplift. 相似文献
6.
In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, ‘Riftlink’. The group's focus is the Albertine Rift, the northern part of the western branch of the East African Rift System, and in particular the rising Rwenzori Mountains that stretch along the border of the D.R. Congo and Uganda. Major questions relate to the timing of the formation of the Rwenzori Mountains, and whether the height of these mountains (> 5000 m) relates to rift movements in Neogene times, or represents an old basement block that formed a topographic high long before. Though, at first, research concentrated on the eastern (Ugandan) part of the Albertine Rift and Rwenzori Mountains, it has now moved further to the west to the D.R. Congo. A first field‐campaign, covering the area from northern Lake Edward along the rift shoulder up to the Blue Mountains at Lake Albert, was conducted in summer 2009, in cooperation with the Ruwenzori State University of Butembo. Here, we present a brief overview of the field‐campaign, with impressions gathered on the morphology and geology of the study area. 相似文献
7.
Pietro Passerini Marta Marcucci Giovanni Sguazzoni Leonardo Zan Abdourahman Omar Haga 《地学学报》1991,3(6):607-618
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. 相似文献
8.
Klemens Link Daniel Koehn Matthias G. Barth John V. Tiberindwa Erasmus Barifaijo Kevin Aanyu Stephen F. Foley 《International Journal of Earth Sciences》2010,99(7):1559-1573
Western Uganda is a key region for understanding the development of the western branch of the East African rift system and
its interaction with pre-existing cratonic lithosphere. It is also the site of the topographically anomalous Rwenzori Mountains,
which attain altitudes of >5000 m within the rift. New structural and geochronological data indicate that western Uganda south
and east of the Rwenzori Mountains consists of a WSW to ENE trending fold and thrust belt emplaced by thick-skinned tectonics
that thrust several slices of Proterozoic and Archaean units onto the craton from the south. The presence of Archaean units
within the thrust stack is supported by new Laser-ICP-MS U–Pb age determinations (2637–2584 Ma) on zircons from the Rwenzori
foothills. Repetition of the Paleoproterozoic units is confirmed by mapping the internal stratigraphy where a basal quartzite
can be used as marker layer, and discrete thrust units show distinct metamorphic grades. The thrust belt is partially unconformably
covered by a Neoproterozoic nappe correlated with the Kibaran orogenic belt. Even though conglomerates mark the bottom of
the Kibaran unit, intensive brittle fault zones and pseudotachylites disprove an autochthonous position. The composition of
volcanics in the Toro-Ankole field of western Uganda can be explained by the persistence of a cratonic lithosphere root beneath
the northwardly thrusted Archaean and Palaeoproterozoic rocks of westernmost Uganda. Volcanic geochemistry indicates thinning
of the lithosphere from >140 km beneath Toro-Ankole to ca. 80 km beneath the Virunga volcanic field about 150 km to the south.
We conclude that the western branch of the East African rift system was initiated in an area of thinner lithosphere with Palaeoproterozoic
cover in the Virunga area and has propagated northwards where it now abuts against thick cratonic lithosphere covered by a
thrust belt consisting of gneisses, metasediments and metavolcanics of Neoarchaean to Proterozoic age. 相似文献
9.
T. V. Gerya 《Petrology》2013,21(6):550-560
This work presents high-resolution 3D numerical model of transform fault initiation at rifted continental margins. Our petrological-thermomechanical visco-plastic model allows for spontaneous nucleation of oceanic spreading process in a continental rift zone and takes into account new oceanic crust growth driven by decompression melting of the asthenospheric mantle. Numerical model predicts that ridge-transform spreading pattern initiate in several subsequent stages: crustal rifting (0–1.5 Myr), spreading centers nucleation and propagation (1.5–3 Myr), proto-transform fault initiation and rotation (3–5 Myr) and mature ridge-transform spreading (> 5 Myr). Comparison of modeling results with the natural data from the Woodlark Basin suggests that the development of this region closely matches numerical predictions. Similarly to the model, the Moresby (proto-) Transform terminates in the oceanic rather than in the continental crust. This fault associates with a notable topographic depression and formed within 0.5–2 Myr while linking two offset overlapping spreading segments. Model reproduces well characteristic “rounded” contours of the spreading centers as well as the presence of a remnant of the broken continental crustal bridge observed in the Woodlark Basin. Proto-transform fault traces and truncated tip of one spreading center present in the model are also documented in nature. Numerical results are in good agreement with the concept of Taylor et al. (2009) which suggests that spreading segments nucleate en echelon in overlapping rift basins and that transform faults develop as or after spreading nucleates. Our experiments also allow to refine this concept in that (proto)-transform faults may also initiate as oblique rather than only spreading-parallel tectonic features. Subsequent rotation of these faults toward the extension-parallel direction is governed by space accommodation during continued oceanic crust growth within offset ridge-transform intersections. 相似文献
10.
J. Angelier 《Journal of Structural Geology》1985,7(5):605-612
A field analysis of faults and fractures in the Ras Gharib-Ras Gemsa region of the Gulf of Suez shows that the main Late Cenozoic extension occurred perpendicular to the rift axis. Three main types of dip-slip normal faults successively developed as the tilt of blocks bounded by antithetic normal faults increased. Determinations of the amount of extension from structural data are compatible with estimates made using subsidence data through a simplified model of lithospheric stretching. The uplift of rift shoulders is related in chronology and volume to the subsidence of the rift. The geometry of fault patterns and directions of extension suggests that the Late Cenozoic total movement corresponds to a counterclockwise rotation of 4–5° of Sinai relative to Africa, with a pole close to Cairo. 相似文献
11.
12.
《International Geology Review》2012,54(10):867-891
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. 相似文献
13.
Thermal and exhumation history of the central Rwenzori Mountains, Western Rift of the East African Rift System, Uganda 总被引：2，自引：1，他引：1
F. U. Bauer U. A. Glasmacher U. Ring A. Schumann B. Nagudi 《International Journal of Earth Sciences》2010,99(7):1575-1597
The Rwenzori Mountains (Mtns) in west Uganda are the highest rift mountains on Earth and rise to more than 5,000 m. We apply
low-temperature thermochronology (apatite fission-track (AFT) and apatite (U–Th–Sm)/He (AHe) analysis) for tracking the cooling
history of the Rwenzori Mtns. Samples from the central and northern Rwenzoris reveal AFT ages between 195.0 (±8.4) Ma and
85.3 (±5.3) Ma, and AHe ages between 210.0 (±6.0) Ma to 24.9 (±0.5) Ma. Modelled time–temperature paths reflect a protracted
cooling history with accelerated cooling in Permo-Triassic and Jurassic times, followed by a long period of constant and slow
cooling, than succeeded by a renewed accelerated cooling in the Neogene. During the last 10 Ma, differentiated erosion and
surface uplift affected the Rwenzori Mtns, with more pronounced uplift along the western flank. The final rock uplift of the
Rwenzori Mtns that partly led to the formation of the recent topography must have been fast and in the near past (Pliocene
to Pleistocene). Erosion could not compensate for the latest rock uplift, resulting in Oligocene to Miocene AHe ages. 相似文献
14.
阿尔金断裂与祁连山北缘断裂的交汇部位是阿尔金断裂向东扩展的新破裂生长点,两断裂构造与新生的红柳峡断裂构成似三联点构造。破裂生长点附近的最新构造变形表现为:阿尔金断裂的旋转隆升和向北扩展;祁连山北缘断裂的逆冲推覆兼右旋走滑;红柳峡断裂的挤压拖曳弯曲,它们共同受制于青藏高原的强烈隆升和向外扩张作用。推测阿尔金断裂自西而东的破裂扩展就是似三联点构造逐一形成而又被切割贯通的过程。阿尔金断裂以蠕滑活动为主,2002年玉门地震与祁连山北缘逆冲断裂及其伴生的调节断层的活动相关。 相似文献
15.
Devana Chasma is a rift system on Venus formed in association with the Beta Regio and Phoebe Regio volcanic highlands, which are interpreted as mantle plumes. We present a new analysis of a 2500-km-long segment of Devana. Based on the rift topography, the horizontal extension across the rift boundary faults is 3–9 km. This is a lower bound on the total rift extension because the altimetry does not resolve the topographic relief across the numerous faults that are visible in radar images of the rift floor. The total extension across Devana is approximately 20 km, similar in magnitude to continental rift systems on Earth. Rift flank elevations are up to 3.1 km in the regions nearest the mantle plumes and decay strongly with increasing distance from the plumes, indicating a strong thermal component to the rift flank topography, unlike the situation usually reported for terrestrial rifts. As on Earth, there is also a flexural uplift component to the flank topography. Rift depths are up to 2.5 km below the surrounding plains, with considerable along-strike variability. There is a 600 km lateral offset along Devana Chasma near the mid-point between the two mantle plumes. Devana most likely formed as two distinct rifts due to the horizontal stresses created by outflow from the upwelling plumes. The offset zone formed as a result of the interaction between the two rift tips, which requires that upwelling at the two mantle plumes overlapped in time. 相似文献
16.
Martha Withjack 《Tectonophysics》1979,53(1-2)
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. 相似文献
17.
海拉尔盆地为典型的小型断陷湖盆,具有"下断上凹"的二元结构,"洼槽控油、隆起带控油"特征明显。本文在系统研究构造演化特征的基础上,分析了不同类型隆起带形成演化历史及对油气的控制作用。研究表明,海拉尔盆地构造演化历经了5个阶段:即铜钵庙组山间盆地、南一段和南二段被动裂陷盆地、南三段和南四段主动裂陷盆地、大磨拐河组-伊敏组断-坳转化盆地和青元岗组坳陷盆地。经历了3期强烈变形和2期强烈改造,被动裂陷的走滑作用导致反向断层及其下盘翘倾隆起,形成"长期淋滤造储、近洼不整合输导、反向断层遮挡" 的成藏有利条件,最终成为被动裂陷层序有利油气富集区带。主动裂陷伸展作用形成小型滚动背斜和中央隆起带,小型滚动背斜带形成"小而肥"构造油藏,而中央隆起带形成典型的复式油气聚集带。南屯组沉积末期构造反转,导致部分中央背斜带隆升剥蚀,断裂切割破碎,进而导致大气水下渗淋滤,有效改造基岩潜山储层,成为基岩潜山油藏的富集带。伊敏组沉积末期,形成正反转断层和反转期活动的正断层两种调整型断层,将早期聚集在断陷构造层的油气调整到大磨拐河组,聚集在反转构造及其边部,形成次生油气聚集带。 相似文献
18.
川滇西部上新世以来构造地貌:断裂控制的盆地发育及对于远程陆内构造过程的约束 总被引：4，自引：0，他引：4
青藏高原隆升、周边地貌形成是新生代时期印度-欧亚板块碰撞后的重要响应。在滇西北地区发育了一系列由晚新生代(上新世以来)活动断裂所控制的盆地,例如宾川盆地、洱海盆地、鹤庆盆地、弥渡盆地等。宾川盆地是近南北向程海左行走滑断裂在走滑剪切作用下产生的北西向正断层和北东向走滑断层共同作用而形成的一个较大的拉分盆地。洱海盆地是由两组陡立的共轭张剪性(Transtensional)断层组限定的,为一伸展断陷盆地,总体上反映了近E-W向的区域伸展。滇西北地区发育的其它晚新生代盆地,如弥渡盆地、鹤庆盆地、剑川盆地等,也为区域走滑断裂及其分支断裂所控制,并且这些分支断裂在区域上为一组NE-SW和NW-SE向的共轭正断裂,反映了该区域近E-W向的伸展。将藏东南三江地区发育的活动断裂按照其走向分为三组:(1)NW-SE走向的断裂,如红河断裂、无量山-营盘山断裂等;(2)近N-S向断裂系,以程海断裂、小江断裂等为代表;(3)NE-SW走向的断裂,如丽江-剑川断裂、鹤庆-洱源断裂和南定河断裂等。这些断裂的震源机制解表明地震断裂活动性或者是走滑性质或者是伸展属性,它们的组合型式也揭示出藏东南三江地区在上新世以来表现为近E-W向的伸展。区域上,在藏东北部地区发育的断层构造组合普遍反映了以近E-W向挤压为主导的应力场。推测这一现象为上新世以来藏东地区上地壳围绕喜马拉雅东构造结做顺时针旋转所致,区域上受印度-欧亚会聚过程中印度板块顺时针旋转诱发的差异性应力场制约。 相似文献
19.
Farshad Jamali Khaled Hessami Manoochehr Ghorashi 《Journal of Asian Earth Sciences》2011,40(4):1015-1025
This paper uses high-resolution images and field investigations, in conjunction with seismic reflection data, to constrain active structural deformation in the Kashan region of Central Iran. Offset stream beds and Qanats indicate right-lateral strike slip motion at a rate of about 2 mm/yr along the NW–SE trending Qom-Zefreh fault zone which has long been recognized as one of the major faults in Central Iran. However, the pattern of drainage systems across the active growing folds including deep incision of stream beds and deflected streams indicate uplift at depth on thrust faults dipping SW beneath the anticlines. Therefore, our studies in the Kashan region indicate that deformation occurs within Central Iran which is often considered to behave as a non-deforming block within the Arabia–Eurasia collision zone. The fact that the active Qom-Zefreh strike-slip fault runs parallel to the active folds, which overlie blind thrust faults, suggests that oblique motion of Arabia with respect to Eurasia is partitioned in this part of Central Iran. 相似文献
20.
印度与欧亚板块碰撞以来东喜马拉雅构造结的演化 总被引：14，自引：0，他引：14
在野外填图,构造观察及前人研究的基础上,本文识别并描述了东喜马拉雅构造结中的推覆断裂、正断裂及走滑断裂、背斜(形)和向斜(形)等构造类型,讨论了这些构造位置及与印度板块挤入,印支地块旋转的关系,还探讨了东喜马拉雅构造结对印度板块持续向北推挤下的特殊应变调节方式。在印度大陆部分,东喜马拉雅构造结由3个向外逐渐变新的构造结组成,即北东向的南迦巴瓦峰复式背斜、北西向的桑复式向斜及北东向的阿萨母复式向斜。上述3个构造结是协调印度板块的挤入、喜马拉雅弧的扩展及印支地块的旋转的构造。在欧亚大陆内部的冈底斯岛弧,在派区及阿尼桥走滑断裂协调下,高喜马拉雅结晶岩的基底挤入冈底斯岛弧内部,在大拐弯顶端形成向上的挤出构造。在南迦巴瓦峰构造结的北西侧,由于掀斜式抬升及重力滑动,使得冈底斯盖层与结晶基底脱耦,上盘盖层沿东久向北西方向滑动。在南迦巴瓦峰构造结北东侧,由于印支地块的挤出和旋转,形成一系列的北西向走滑断裂,如实皆断裂、嘉黎-高黎贡断裂、澜沧江断裂及红河断裂等。 相似文献