Mineral deposit formation in Phanerozoic sedimentary basins of north-east Africa: the contribution of weathering

The intra- and epicontinental basins in north-east Africa (Egypt, Sudan) bear ample evidence of weathering processes repeatedly having contributed to the formation of mineral deposits throughout the Phanerozoic.The relict primary weathering mantle of Pan-African basement rocks consists of kaolinitic saprolite, laterite (in places bauxitic) and iron oxide crust. On the continent, the reaccumulation of eroded weathering-derived clay minerals (mainly kaolinite) occurred predominantly in fluvio-lacustrine environments, and floodplain and coastal plain deposits. Iron oxides, delivered from ferricretes, accumulated as oolitic ironstones in continental and marine sediments. Elements leached from weathering profiles accumulated in continental basins forming silcrete and alunite or in the marine environment contributing to the formation of attapulgite/saprolite and phosphorites.The Early Paleozoic Tawiga bauxitic laterite of northern Sudan gives a unique testimony of high latitude lateritic weathering under global greenhouse conditions. It formed in close spatial and temporal vicinity to the Late Ordovician glaciation in north Africa. The record of weathering products is essentially complete for the Late Cretaceous/Early Tertiary. From the continental sources in the south to the marine sinks in the north, an almost complete line of lateritic and laterite-derived deposits of bauxitic kaolin, kaolin, iron oxides and phosphates is well documented.     

Late Mesozoic rift evolution and crustal extension in the central Songliao Basin,northeastern China: constraints from cross-section restoration and implications for lithospheric thinning

The Songliao Basin, the largest oil-producing basin in China, was the centre of late Mesozoic rifting and lithospheric thinning in northeastern China. However, the rifts are still poorly revealed due to a thick cover of subsidence successions. By structural interpretation and sequential restoration of cross-sections based on new 2D seismic data and well data, this study presents the structural style, basin evolution, and horizontal crustal extension of the central Songliao Basin. We have developed a novel method to retrieve the regional extension principal strains. The results enable an assignment of rifting into two episodes. The earlier episode (ca. 157–130 Ma) was dominated by distributed faulting of numerous planar normal faults trending NNE–SSW, NNW–SSE, or near NS, probably reflecting pre-existing basement fabrics; in contrast, the later episode (ca. 130–102 Ma) was controlled by localized extension along several major listric faults. Horizontal crustal extension during rifting is estimated to have been 11–28 km (10.6%–25.5%), with the long-term average rate varying from 0.20 to 0.51 mm yr^–1. Regional horizontal strains show a gradual evolution from biaxial extension at the beginning of rifting to WNW–ESE uniaxial stretching during the later rifting episode. Brittle crustal extension is interpreted to have been associated with vertical strain due to tectonic stretching, which is estimated to have contributed more in thinning the lower crust than the mantle lithosphere. Accordingly, a two-episode dynamic model is proposed to explain rifting in the Songliao Basin. We suggest that the earlier event was dominated by delamination of the thickened continental lithosphere, whereas the later event was probably controlled by regional crustal detachment due to slab subduction and stagnancy of the Izanagi lithospheric plate.     

A tectonic model for the Tertiary evolution of strike–slip faults and rift basins in SE Asia

Models for the Tertiary evolution of SE Asia fall into two main types: a pure escape tectonics model with no proto-South China Sea, and subduction of proto-South China Sea oceanic crust beneath Borneo. A related problem is which, if any, of the main strike–slip faults (Mae Ping, Three Pagodas and Aliao Shan–Red River (ASRR)) cross Sundaland to the NW Borneo margin to facilitate continental extrusion? Recent results investigating strike–slip faults, rift basins, and metamorphic core complexes are reviewed and a revised tectonic model for SE Asia proposed. Key points of the new model include: (1) The ASRR shear zone was mainly active in the Eocene–Oligocene in order to link with extension in the South China Sea. The ASRR was less active during the Miocene (tens of kilometres of sinistral displacement), with minor amounts of South China Sea spreading centre extension transferred to the ASRR shear zone. (2) At least three important regions of metamorphic core complex development affected Indochina from the Oligocene–Miocene (Mogok gneiss belt; Doi Inthanon and Doi Suthep; around the ASRR shear zone). Hence, Paleogene crustal thickening, buoyancy-driven crustal collapse, and lower crustal flow are important elements of the Tertiary evolution of Indochina. (3) Subduction of a proto-South China Sea oceanic crust during the Eocene–Early Miocene is necessary to explain the geological evolution of NW Borneo and must be built into any model for the region. (4) The Eocene–Oligocene collision of NE India with Burma activated extrusion tectonics along the Three Pagodas, Mae Ping, Ranong and Klong Marui faults and right lateral motion along the Sumatran subduction zone. (5) The only strike–slip fault link to the NW Borneo margin occurred along the trend of the ASRR fault system, which passes along strike into a right lateral transform system including the Baram line.     

非洲Muglad多旋回陆内被动裂谷盆地演化及其控油气作用

非洲Muglad盆地经历多旋回陆内被动裂谷发育与叠合演化历史,具有不同于主动裂谷盆地、单旋回被动裂谷盆地以及跨越多个变革期的叠合盆地的演化特征。本文采用叠合盆地研究思路与方法,通过盆地演化过程中关键构造事件识别、盆地演化阶段划分,恢复和重建了各阶段原型盆地;基于不同期次裂谷作用发育程度、叠加过程及叠加方式的时空差异性,划分了不同凹陷的叠合类型,建立了不同叠合类型凹陷油气成藏模式。研究结果表明,受冈瓦纳大陆裂解、非洲大陆周缘大西洋、印度洋、红海张裂等构造事件的影响,该盆地经历了早白垩世Abu Gabra组(简称AG组,下同)沉积期、晚白垩世Darfur群沉积期以及新生代Nayil-Tendi组沉积期三大同裂谷作用阶段。早白垩世盆地原型为多个地堑及半地堑分隔式分布,为与大西洋张开有关的伸展应力场作用产物;晚白垩世Darfur群沉积时期盆地原型为地堑及半地堑继承发育,但沉积中心东移,为与印度洋张开有关的伸展应力场作用产物;新生代Nayil-Tendi组沉积时期原型盆地主要为发育在Kaikang坳陷的地堑、半地堑,为与红海张开有关的伸展应力场作用所致。依据三期裂谷作用在各凹陷的发育程度差异及构造沉降和沉积充填过程的不同,将各凹陷裂谷叠合方式划分为早断型、继承型与活动型三种类型。其中,早断型以Sufyan凹陷最为典型,其构造沉降与沉积充填具有"强-弱-更弱"特征;继承型以Fula凹陷最为典型,其构造沉降与沉积充填具有"强-较强-弱"特征,而活动型以Kaikang坳陷最为典型,其构造沉降与沉积充填具有"强-强-较强"的特征。三期裂谷作用在各凹陷内时空叠合差异控制了各凹陷油气成藏条件及富集规律的不同,早断型凹陷成藏组合以下部成藏组合为主,继承型则以中部成藏组合为主,而活动型凹陷则以上部成藏组合为主。这些多期叠加型被动裂谷盆地研究成果丰富了全球裂谷盆地构造特征与演化及其控油气作用的认识,深化了该类裂谷盆地油气分布规律研究,对于指导下一步勘探部署有重要借鉴意义。     

A tectonic model for the metamorphic evolution of the Basal Gneiss Complex, Western South Norway

A review of currently available information relevant to the Basal Gneiss Complex (BGC) of Western South Norway, combined with the authors'own observations, leads to the following conclusions.
1. Most of the BGC consists of Proterozoic crystalline rocks and probably subordinate Lower Palaeozoic cover.
2. The last major deformation of these rocks was during the Caledonian orogeny and involved large-scale thrusting, recumbent folding and doming. The structural development of the BGC is closely tied in with that of the Caledonian allochthon.
3. The whole eclogite-bearing part of the BGC has suffered a high pressure metamorphism with conditions of between 550°C, 12.5 kbar (Sunnfjord) and about 750°C, 20 kbar (Møre og Romsdal) at the metamorphic climax.
4. This metamorphism was of Caledonian age, probably rather early in the Caledonian tectonic history of the BGC and is considered to have been a rather transient event.
By setting these conclusions in a framework provided by geophysical evidence for the deep structure of the crust in southern Norway we have constructed a geotectonic model to explain the recorded metamorphic history of the BGC. It is suggested that considerable crustal thickening was caused by imbrication of the Baltic plate margin during continental collision with the Greenland plate. This resulted in high pressure metamorphism in the resulting nappe stack. Progradation of the suture caused underthrusting of the Baltic foreland below the eclogite-bearing terrain causing it to emerge at the Earth's surface, aided by tectonic stripping and erosion.
Application of isostacy equations to the model shows that eclogites can be formed by in-situ metamorphism in crustal rocks and reappear at the land surface above a normal thickness of crust in a single orogenic episode of approximately 65-70 Ma duration.     

Geomechanical model for the post-Variscan evolution of the Permocarboniferous–Mesozoic basins in Northeast Germany

The Permocarboniferous basins in Northeast Germany formed on the heterogeneous and eroded parts of the Variscan orogene and its deformed northern foreland. Transtensional tectonic movements and thermal re-equilibration lead to medium-scale crustal fragmentation, fast subsidence rates and regional emplacement of large amounts of mostly acidic volcanics. The later basin formation and differentiation was triggered by reversals of the large-scale stress field and reactivation of prominent zones of weakness like the Elbe Fault System and the Rhenohercynian/Saxothuringian boundary that separate different Variscan basement domains in the area. The geomechanical behaviour of the latter plays an important role for the geodynamic evolution of the medium to large-scale structural units, which we can observe today in three dimensions on structural maps, geophysical recordings and digital models. This study concentrates on an area that comprises the southern Northeast German Basin, the Saale Basin, the Flechtingen High, the Harz Mountains High and the Subhercynian Basin. The presented data include re-evaluations of special geological and structural maps, the most recent interpretation of the DEKORP BASIN 9601 seismic profile and observations of exposed rock sections in Northeast Germany. On the basis of different structural inventories and different basement properties, we distinguish two structural units to the south and one structural unit to the north of the Elbe Fault System. For each unit, we propose a geomechanical model of basin formation and basin inversion, and show that the Rhenohercynian Fold and Thrust Belt domain is deformed in a thin-skinned manner, while the Mid-German Crystalline Rise Domain, which is the western part of the Saxothuringian Zone, rather shows a thick-skinned deformation pattern. The geomechanical model for the unit north to the Elbe Fault System takes account to the fact that the base of the Zechstein beneath the present Northeast German basin shows hardly any evidence for brittle deformation, which indicates a relative stable basement. Our geomechanical model suggests that the Permocarboniferous deposits may have contributed to the structural stiffness by covering small to medium scale structures of the upper parts of the brittle basement. It is further suggested that the pre-Zechstein successions underneath the present Northeast German basin were possibly strengthening during the Cretaceous basin inversion, which resulted in stress transfer to the long-lived master faults, as indicated for example by the shape of the salt domes in the vicinity of the latter faults. Contrary to this, post-Zechstein successions deformed in a different and rather complex way that was strongly biased by intensive salt tectonic movements.     

Tectonic elements controlling the evolution of the Gulf of Saros (northeastern Aegean Sea, Turkey)

Tectonic elements controlling the evolution of the Gulf of Saros have been studied based upon the high-resolution shallow seismic data integrated with the geological field observations. Evolution of the Gulf of Saros started in the Middle to Late Miocene due to the NW–SE compression caused by the counterclockwise movement of the Thrace and Biga peninsulas along the Thrace Fault Zone. Hence, the North Anatolian Fault Zone is not an active structural element responsible for the starting of the evolution of the Gulf of Saros. The compression caused by the rotational movement was compensated by tectonic escape along the pre-existing Ganos Fault System. Two most significant controllers of this deformation are the sinistral Ganos Fault and the dextral northern Saros Fault Zone both extending along the Gulf of Saros. The most important evidences of this movement are the left- and right-oriented shear deformations, which are correlated with structural elements, observed on the land and on the high-resolution shallow seismic records at the sea. Another important line of evidence supporting the evolution of this deformation is that the transgression started in the early-Late Miocene and turned, as a result of regional uplift, into a regression on the Gelibolu Peninsula during the Turolian and in the north of the Saros Trough during the Early Pliocene. The deformation on the Gelibolu Peninsula continued effectively until the Pleistocene. Taking into account the fact that this deformation affected the Late Pleistocene units of the Marmara Formation, the graben formation of the Gulf of Saros is interpreted as a Recent event. However, at least a small amount of compression on the Gelibolu Peninsula is observed. It is also evident that compression ceased at the northern shelf area of the Gulf of Saros.     

Geochemistry and Tectonic Setting of Mafic Igneous Units in the Neoproterozoic Katangan Basin, Central Africa: Implications for Rodinia Break-up

Geochemical compositions of mafic igneous rocks in the Katangan basin in Central Africa (Democratic Republic of Congo, hereafter Congo, and Zambia) provide the basis for the geodynamic interpretation of the evolution of this Neoproterozoic basin located between the Congo and Kalahari cratons. The Katangan basin is subdivided into five major tectonic units: the Katangan Aulacogen, the External Fold and Thrust Belt, the Domes Region, the Synclinorial Belt and the Katangan High. The metamorphosed mafic igneous rocks investigated occur in the Katangan Aulacogen, the External Fold and Thrust Belt and the Domes Region. The earliest magmatic activity produced continental tholeiites emplaced on Paleoproterozoic crust during the early stages of intraplate break-up. This continental tholeiite magmatism was followed by an association of alkaline and tholeiitic basalts emplaced in the Katangan continental rift and then by tholeiitic basalts with E-MORB affinity marking a young oceanic crust. These volcanic associations mark different stages of evolution from pre-rift continental break-up up to a continental rift similar to the East African rift system and then to a Red Sea type incipient oceanic rift. A similar evolution occurs in the Damaran basin in southwestern Africa, although no pre-rift continental tholeiites have been recorded in this segment of the Pan-African belt system.     

大陆碰撞造山带的流体成分与演化:东喜马拉雅构造结南迦巴瓦岩群高压麻粒岩的流体包裹体研究

位于喜马拉雅东构造结的南迦巴瓦岩群经历了高压麻粒岩相、中压麻粒岩相和角闪岩相三期变质作用.在高压麻粒岩中含有复杂的流体包裹体类型,按照捕获先后顺序有:H2O-CO2±CH4包裹体(Ⅰ型);CO2±CH4±N2包裹体(Ⅱ型);高盐度多相包裹体(Ш型);中.低盐度H2O包裹体(Ⅳ型)和极低密度气体包裹体或"空"包裹体(Ⅴ型).在基性麻粒岩中,被石榴石包裹石英中孤立分布的H2O-CO2 4-CH4包裹体,以及部分沿石榴石晶内裂隙分布的H2-CO2±CH4和H2O包裹体轨迹未穿过围绕石榴石的辉石 斜长石后成合晶冠状体,表明它们有可能是在麻粒岩相变质阶段捕获的.然而,所有流体包裹体的等容线均从麻粒岩相变质峰期P-T区间下方通过,说明麻粒岩相变质峰期捕获的包裹体均受到了不同程度的改造,包括部分爆裂、渗漏和流体-矿物相互作用等.现存的富CO2流体包裹体均具有较低密度,并且往往含有明显数量CH4和N2组分,不可能是麻粒岩相变质峰期捕获的包裹体.根据富CO2包裹体与具有不同相比的H2-CO2包裹体共存推测,大部分CO2包裹体是通过H2O-CO2包裹体中H2O的选择性泄漏而形成的.Ⅲ型高盐度盐水包裹体很可能是角闪岩相退变质过程中捕获的,因其等容线与退变质轨迹近于平行,这些包裹体很可能保存了其在角闪岩相阶段捕获时的原生物理化学特征.沿矿物颗粒裂隙分布的大量Ⅳ型和Ⅴ型包裹体,应该是角闪岩相或更晚期形成的次生包裹体,代表了浅成(近地表)环境的循环流体.与世界许多地区麻粒岩相岩石普遍舍高密度纯CO2流体包裹体不同,南迦巴瓦岩群高压麻粒岩以富含H2O-CO4±CH4和H2O包裹体为特征,这可能与高压麻粒岩与高温麻粒岩产出于不同的构造环境和经历的退变质轨迹有关.     

A critical review of the glaciomarine model for Irish sea deglaciation: evidence from southern Britain,the Celtic shelf and adjacent continental slope

In support of their ‘glaciomarine’ model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach‐face gravels and sands around the shores of the Celtic Sea. Glacial and sea‐level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south‐central Celtic Sea. Relative sea‐levels were lower, and therefore glacio‐isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice‐rafting at a time of high relative sea‐levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation. Copyright © 2001 John Wiley & Sons, Ltd.     

The Lancang River Zone of southwestern Yunnan, China: A questionable location for the active continental margin of Paleotethys

In an attempt to constrain a Late Paleozoic tectono-metamorphic event along the Lancang River Zone, fourteen samples were processed for K/Ar dating on fine mineral fractions and detrital muscovites from this zone in southwestern Yunnan, China. The samples include mica schists, mylonites and gneisses from the Proterozoic Lancang Group and phyllites from the western part of the Simao Basin. In addition, one Ar/Ar analysis was performed on separated phengites from a blueschist of the central part of the Lancang Group. The results reveal a considerable spread of ages; the tectonic evolution of the zone is constrained by the new data, which accentuate two temporally separate, but spatially overlapping events: (i) a Late Carboniferous high-P/low-T metamorphism related to an east-vergent, Late Paleozoic thrust belt, inverting a Devonian to Carboniferous marginal basin of the Yangtze-Platform, and (ii) an upper Permian and Triassic low-P/high-T belt caused by a post-orogenic stage of rifting with distinct petrological and geochemical similarities of the igneous rocks to the Emeishan Large Igneous Province. These results imply that no active continental margin accounts for the subduction of the Paleotethys main branch, proposed to be recorded either along the Lancang River or the Changning-Menglian Belt.     

Distribution of Palaeozoic tectonic superimposed unconformities in the Tarim Basin,NW China: significance for the evolution of palaeogeomorphology and sedimentary response

Seismic and drilling well data were used to examine the occurrence of multiple stratigraphic unconformities in the Tarim Basin, NW China. The Early Cambrian, the Late Ordovician and the late Middle Devonian unconformities constitute three important tectonic sequence boundaries within the Palaeozoic succession. In the Tazhong, Tabei, Tadong uplifts and the southwestern Tarim palaeo‐uplift, unconformities obviously belong to superimposed unconformities. A superimposed unconformity is formed by superimposition of unconformities of multiple periods. Areas where superimposed unconformities develop are shown as composite belts of multiple tectonic unconformities, and as higher uplift areas of palaeo‐uplifts in palaeogeomorphologic units. The contact relationship of unconformities in the lower uplift areas is indicative of truncation‐overlap. A slope belt is located below the uplift areas, and the main and secondary unconformities are characterized by local onlap reflection on seismic profiles. The regional dynamics controlled the palaeotectonic setting of the Palaeozoic rocks in the Tarim Basin and the origin and evolution of the basin constrained deposition. From the Sinian to the Cambrian, the Tarim landmass and its surrounding areas belonged to an extensional tectonic setting. Since the Late Ordovician, the neighbouring north Kunlun Ocean and Altyn Ocean was transformed from a spreading ocean basin to a closed compressional setting. The maximum compression was attained in the Late Ordovician. The formation of a tectonic palaeogeomorphologic evolution succession from a cratonic margin aulacogen depression to a peripheral foreland basin in the Early Caledonian cycle controlled the deposition of platform, platform margin, and deep‐water basin. Tectonic uplift during the Late Ordovician resulted in a shallower basin which was followed by substantial erosion. Subsequently, a cratonic depression and peripheral or back‐arc foreland basin began their development in the Silurian to Early–Middle Devonian interval. In this period, the Tabei Uplift, the Northern Depression and the southern Tarim palaeo‐uplift showed obvious control on depositional systems, including onshore slope, shelf and deep‐water basin. The southern Tarim Plate was in a continuous continental compressional setting after collision, whereas the southern Tianshan Ocean began to close in the Early Ordovician and was completely closed by the Middle Devonian. At the same time, further compression from peripheral tectonic units in the eastern and southern parts of the Tarim Basin led to the expansion of palaeo‐uplift in the Late Devonian–Early Carboniferous interval, and the connection of the Tabei Uplift and Tadong Uplift, thus controlling onshore, fluvial delta, clastic coast, lagoon‐bay and shallow marine deposition. Copyright © 2015 John Wiley & Sons, Ltd.     

A sedimentological model for the continental Upper Triassic Tadrart Ouadou Sandstone Member: recording an interplay of climate and tectonics (Argana Valley; South‐west Morocco)

The continental Upper Triassic Tadrart Ouadou Sandstone Member was deposited in an extensional setting on the Pangaean continent, strongly influenced by a low‐latitude climatic regime (10° to 20° north). Complex interaction of basin subsidence and climatically driven processes led to high facies variability and a lack of correlatable units across the Argana Valley exposures. A process‐orientated approach integrating detailed facies with architectural element analysis was undertaken, which resulted in a multistage depositional model for the Tadrart Ouadou Sandstone Member. The basin‐scale model shows that basal alluvial fan and braided river systems are confined to the centre of the Argana Valley exposures. Aeolian deposits occur throughout the sequence, but dominate in the north. After a phase of playa deposition, prominent basin‐wide fluvial incision of up to 8 m marks the onset of perennial fluvial flow. These well‐sorted, internally complex and locally highly amalgamated fluvial sandstones are widespread throughout the basin and are focused in a north to south (south‐west) flowing channel system. After a final stage of aeolian sedimentation, sandstone deposition of the Tadrart Ouadou Sandstone Member in the Argana Valley is terminated rapidly by the onlap of lacustrine mudstones of the Sidi Mansour Member. The study revealed that, except for one pronounced period of perennial conditions, sedimentation is controlled largely by ephemeral fluvial flow, alternating ground water tables, deflation processes and periods with limited periodic local run‐off. The study highlights that facies architecture in the basin is the result of complex interaction of local syn‐sedimentary tectonics and the climatic regime within the basin, but also the climate of the catchment area to the east. The data suggest a proximal to mid‐distal basin setting in the rain‐shadow to the west of a mountain range (Massif Ancien), which exerted a strong control on the depositional environments of Triassic deposits exposed in this part of South‐west Morocco.     

松辽盆地大庆长垣中浅层断层形成演化的新模式

松辽盆地油气集中富集的中浅层断层十分发育,不同反射界面断层发育存在差异,前人认为是多期构造活动的结果。本文应用先存构造条件下断层作用模式,利用三维地震资料,对中浅层的断裂系统重新进行构造解析。结果表明,①松辽盆地大庆长垣中浅层断裂系统按照错断层位、断距、延伸长度、走向可划分为8个类型;②T_2、T_1、T_(06)反射层断层的平均走向分别为322°、320°和316°,断层平均走向从下往上存在逆时针旋转的变化趋势;③大庆长垣自中浅层形成以来,构造应力机制由泉头组—明水组沉积时期的伸展应力机制转变为明水组沉积末期的走滑应力机制,但构造应力场的主应力方向没有发生改变;④研究区复杂的断裂系统是在构造应力场主应力方向保持相对稳定的条件下、在递进变形过程中逐渐形成的。该断层形成演化的新模式更合理地揭示了松辽盆地中浅层断层发育规律和成因机制,对研究区进一步的勘探开发有指导意义。     

塔西南齐姆根楔形构造与走滑构造叠加两阶段演化模式

塔里木盆地西南缘逆冲带由西部近东西方向的喀什逆冲构造带和东部近东西方向柯克亚—和田逆冲构造带以及中间喀什—叶城走滑断层系组成,而北西—南东走向的喀什—叶城走滑断层带及其东侧齐姆根构造则为呈北东方向凸出的弧形构造。齐姆根弧形构造在地表地质和地震剖面均表现为向盆地方向倾斜的单斜形态。而且在塔西南地区,该弧形构造上从白垩系到新近系地层厚度明显大于东西两侧逆冲带同时代地层厚度,表现为异常增厚的特征。为了探讨齐姆根弧形构造特征及地层厚度异常增厚等原因,依据前人的地表地质填图成果,以及塔里木盆地西南缘齐姆根地区及邻区完成的二维地震资料及钻井资料成果,对该区地震剖面资料进行详细的构造解释,提出齐姆根弧形构造单斜之下存在3个隐伏逆冲构造楔形体,即棋盘楔形构造、齐姆根楔形构造和英吉沙楔形构造。地震剖面解释的生长地层指出棋盘楔形构造形成最早,为上新世阿图什组沉积时期;其次发育齐姆根楔形构造,为更新世西域组底部沉积时期;最晚发育英吉沙楔形构造,时间大约在更新世西域组中?上段沉积时期,据此认为齐姆根中深层逆冲构造位移扩展方式为前展式。而且地震剖面解释上也揭示了白垩系到新近系地层厚度异常增厚发育的构造部位及发育规律,说明地层异常厚度变化受区域构造控制,其时间大约为更新世西域组沉积时期。该时期对应于喀什—叶城走滑断层系活动时期,据此我们推测由于走滑断层系区域侧向挤压作用以及东西两侧发育的逆冲构造带起到了限制阻挡作用,三者联合之下造成了齐姆根单斜上含软弱层的各时代地层被挤压屈曲形成弧形形态构造,在弧形构造发育期间岩层之间层间滑脱加厚可导致地层厚度异常增厚。综合前面认识,最后提出齐姆根弧形构造为叠加构造发育地区,经历了早、晚两期构造叠加变形：早期为逆冲楔形构造发育阶段,晚期为走滑作用改造及弧形构造形成阶段。而且沿着齐姆根弧形构造走向,弧形构造北西侧翼部单斜发生逆时针旋转,而弧形构造南东侧翼部单斜发生顺时针旋转,并得到已有古地磁数据支持,属于旋转弧构造类型。该认识支持了帕米尔东侧局部弧形构造是在早期发育的逆冲推覆构造基础上,逐渐叠加有晚期发育的左旋走滑断层而形成弧形构造。