Structural interpretation and hydrocarbon potential of Balkassar oil field,eastern Potwar,Pakistan, using seismic 2D data and petrophysical analysis

The Balkassar oil field is situated in the eastern Potwar sub-basin, lies on the southern flank of Soan syncline in Himalayan collisional regime. The area represents Indo-Pak and Eurasian blocks of Precambrian to recent time. Thrusting and folding of Himalayan, Indo-Pak plate movement and Salt Range uplift form the structural trap in Balkassar sub-surface (Balkassar anticline). On the basis of information from eleven seismic 2D lines and wells data six reflectors well data, four faults were identified and marked. The structural trend is northeast southwest. Interpretation of seismic 2D data reveals that the study area has undergone intense deformation as a consequence of development of thrusts and backthrusts.The Balkassar anticline is bounded by two thrust faults one from southeast and the other from northwest. Time and depth contour models shows that anticline limbs at north-western side are steep as compared to south-eastern limbs. Seismic interpretation indicates the presence of well-developed anticline bounded by three faults in the cover sequence and one fault in basement and thus the structure may act as a trap for hydrocarbons. The petrophysical analysis of Balkassar-OXY-1 well shows about 83.1% hydrocarbons saturation in the reservoir rocks, hence this study suggest that Balkassar Oilfield has potential to produce hydrocarbons.     

Structural styles,hydrocarbon prospects,and potential in the Salt Range and Potwar Plateau,north Pakistan

The Salt Range/Potwar Plateau (SRPP) is part of the Himalayan foreland and an important petroleum province in north Pakistan. The hydrocarbons are commonly produced from stacked Cambrian to Eocene clastic and carbonate reservoirs which have an average thickness of 1 km. These strata are overlain by at least 5 km of Miocene and younger continental molasse sedimentation in the deepest part of the foreland basin. Surface and subsurface (seismic interpretations and borehole data) geology combined with the timing and the patterns of sedimentation has allowed to interpret the deformation as thin skinned, with a detachment in weak Eocambrian evaporates and the development of ramp-and-flat structures, since about 8 Ma. We have reviewed the structural interpretations with new borehole logs, field geology, and reserve estimates in this paper to precisely define oil-field structures with a view on future exploration. As a result of this work, 12 oil fields are classified as three detachment folds, four fault-propagation folds, four pop-ups, and one triangle zone structure. The latter two are identified as better prospects with the last one as the best with estimated reserves of 51 million barrels of oil (MMBO). Hence, the triangle zones along with other ramp-and-flat structures from the North Potwar Deformed Zone (NPDZ) are recognized to provide potential future prospects. Finally, a 40-km-long structural cross section from NPDZ is used to discuss complex deformation of the triangle zone and duplex structures as future potential prospects. About 55 km of shortening across the NPDZ during Plio-Pleistocene time is calculated, which has important bearing on the geometry of prospects, reserve calculations, and the future exploration.     

Physical analog (centrifuge) model investigation of contrasting structural styles in the Salt Range and Potwar Plateau,northern Pakistan

We use scaled physical analog (centrifuge) modeling to investigate along- and across-strike structural variations in the Salt Range and Potwar Plateau of the Himalayan foreland fold-thrust belt of Pakistan. The models, composed of interlayered plasticine and silicone putty laminae, comprise four mechanical units representing the Neoproterozoic Salt Range Formation (basal detachment), Cambrian–Eocene carapace sequence, and Rawalpindi and Siwalik Groups (Neogene molasse), on a rigid base representing the Indian craton. Pre-cut ramps simulate basement faults with various structural geometries.A pre-existing north-dipping basement normal fault under the model foreland induces a frontal ramp and a prominent fault-bend-fold culmination, simulating the Salt Range. The ramp localizes displacement on a frontal thrust that occurs out-of-sequence with respect to other foreland folds and thrusts. With a frontal basement fault terminating to the east against a right-stepping, east-dipping lateral ramp, deformation propagates further south in the east; strata to the east of the lateral ramp are telescoped in ENE-trending detachment folds, fault-propagation folds and pop-up structures above a thick basal detachment (Salt Range Formation), in contrast to translated but less-deformed strata with E–W-trending Salt-Range structures to the west. The models are consistent with Salt Range–Potwar Plateau structural style contrasts being due to basement fault geometry and variation in detachment thickness.     

Evolution of Miocene fluvial environments, eastern Potwar plateau, northern Pakistan

The Miocene-Pliocene Siwalik Group records changing fluvial environments in the Himalayan foreland basin. The Nagri and Dhok Pathan Formations of this Group in the eastern Potwar Plateau, northern Pakistan, comprise relatively thick (tens of metres) sandstone bodies and mudstones that contain thinner sandstone bodies (metres thick) and palaeosols. Thick sandstone bodies extend for kilometres normal to palaeoflow, and are composed of large-scale stratasets (storeys) stacked laterally and vertically adjacent to each other. Sandstone bodies represent single or superimposed braided-channel belts, and large-scale stratasets represent channel bars and fills. Channel belts had widths of km, bankfull discharges on the order of 10³ cumecs and braiding parameter up to about 3. Individual channel segments had bankfull widths, maximum depths, and slopes on the order of 10² m, 10¹ m and 10^?4 respectively, and sinuosities around 1-1. These rivers are comparable to many of those flowing over the megafans of the modern Indo-Gangetic basin, and a similar depositional setting is likely. Thin sandstone bodies within mudstone sequences extend laterally for on the order of 10² m and have lobe, wedge, sheet and channel-form geometries: they represent crevasse splays, levees and floodplain channels. Mudstones are relatively bioturbated/disrupted and represent mainly floodbasin and lacustrine deposition. Mudstones and sandstones are extremely disrupted in places, showing evidence of prolonged pedogenesis. These ‘mature’ palaeosols are m thick and extend laterally for km. Lateral and vertical variations in the nature of their horizons apparently depend mainly on deposition rate. The 500 m-thick Nagri Formation has a greater proportion and thicker sandstone bodies than the overlying 700 m-thick Dhok Pathan Formation. The thick sandstone bodies and their large-scale stratasets thicken and coarsen through the Nagri Formation, then thin and fine at the base of the Dhok Pathan Formation. Compacted deposition rates increase with sandstone proportion (0-53 mm/year for Nagri, 0-24 mm/year for Dhok Pathan), and palaeosols are not as well developed where deposition rates are high. Within both formations there are 100 m-scale variations (representing on the order of 10⁵ years) in the proportion and thickness of thick sandstone bodies, and tens-of-m-scale alternations of thick sandstone bodies and mudstone-sandstone strata that represent on the order of 10⁴ years. Formation-scale stratal variations extend across the Potwar Plateau for at least 100 km, although they may be diachronous: however, 100-m and smaller scale variations can only be traced laterally for up to tens of km. Alluvial architecture models indicate that increases in the proportion and thickness of thick sandstone bodies can be explained by increasing channel-belt sizes (mainly), average deposition rate and avulsion frequency on a megafan comparable in size to modern examples. 100-m-scale variations in thick sandstone-body proportion and thickness could result from ‘regional’ shifts in the position of major channels, possibly associated with ‘fan lobes’on a single megafan or with separate megafans. However, such variations could also be related to local changes in subsidence rate or changes in sediment supply to the megafan system. Formation-scale and 100-m-scale stratal variations are probably associated with interelated changes in tectonic uplift, sediment supply and basin subsidence. Increased rates of hinterland uplift, sediment supply and basin subsidence, recorded by the Nagri Formation, may have resulted in diversion of a relatively large river to the area. Alternatively, changing river sizes and sediment supply rates may be related to climate changes affecting the hinterland (possibly linked to tectonic uplift). Climate during deposition of the Siwalik Group was monsoonal. Although the deposits contain no direct evidence for climate change, independent evidence indicates global cooling throughout the Miocene, and the possibility of glacial periods (e.g. around 10-8 Ma, corresponding to base of Nagri Formation). If the higher Himalayas were periodically glaciated, a mechanism would exist for varying sediment supply to megafans on time scales of 10⁴-10⁵ years. Although eustatic sea-level changes are related to global climatic change, they are not directly related to Siwalik stratigraphic changes, because the shoreline was many 100 km away during the Miocene.     

Subsurface lithofacies analysis of the Fluvial Early Permian Warchha Sandstone, Potwar Basin, Pakistan

The Early Permian Warchha Sandstone is well preserved in subsurface in the Potwar Basin and the Punjab Plain of Pakistan. However, this succession is only exposed in the Salt Range, and within this region, only a modest number of the many outcrops are of sufficient quality to enable the preparation of lateral and vertical log profiles. From the subsurface, data from five wells drilled in the Salt Range and Potwar Basin have been analysed. Although they are of restricted coverage, these subsurface data — which take the form of gamma ray logs and well cuttings — provide a valuable addition to the outcrop dataset of the Warchha Sandstone as they provide useful information about vertical textural changes, type and thickness of bedding and the nature of sandbody contacts with underlying strata. Overall, the Warchha Sandstone succession is composed of repeated fining-upwards cycles indicative of a meandering fluvial succession. Sub-components of each cycle are themselves classified into six subsurface sedimentary facies. Through comparison with outcropping parts of the succession, the origin and significance of these subsurface facies can be related to specific architectural elements within the meandering fluvial system responsible for generating the Warchha Sandstone succession.     

Precise Seismic Substructural Model of the Eocene Chorgali Limestone in the Turkwal Oil Field,Central Potwar,Pakistan

The precise seismic substructural interpretation of the Turkwal oil field in the Central Potwar region of district Chakwal of Pakistan has been carried out. The research work was confined to the large fore-thrust that serves as an anticlinal structural trap through ten 2D seismic lines. A precise seismic substructural model of the Eocene Chorgali Limestone with precise orientation of thrust and oblique slip faults shows the presence of a huge fracture, which made this deposit a good reservoir. The abrupt surface changes in dip azimuth for the Eocene Chorgali Limestone verifies the structural trends and also the presence of structural traps in the Turkwal field. The logs of three wells (Turkwal deep X-2, Turkwal-01 and Fimkassar-01) were analyzed for petrophysical studies, well synthetic results and generation of an Amplitude Versus Offset (AVO) model for the area. The AVO model of Turkwal deep X-2 shows abrupt changes in amplitude, which depicts the presence of hydrocarbon content. Well correlation technique was used to define the overall stratigraphic setting and the thickness of the reservoir formation in two wells, Turkwal-01 and Turkwal deep X-2. The Eocene Chorgali Limestone in Turkwal-01 is an upward thrusted anticlinal structure and because of the close position of both wells to the faulted anticlinal structure, its lesser thickness differs compared to Turkwal deep X-2. The overall results confirm that the Turkwal field is comparable to several similar thrust-bound oil-bearing structures in the Potwar basin.     

Crystalline rocks of the Spinatizha area, Pakistan

During the Cretaceous an andesitic arc developed across south Asia facing the Tethys Ocean. Remnants of this arc are preserved in Iran, Afghanistan, and the Chagai Hills and Kohistan, Pakistan. West of the Chaman fault near Spinatizha, Pakistan (33° 33′N, 66° 23′E) a terrain of crystalline rocks is exposed that links the Chagai Hills portion of this arc with the Kandahar portion of it in Afghanistan. Four units are present. (1) The Spinatizha Metamorphic Complex includes orthogneiss, greenschist, amphibolite, metavolcanics, marble and foliated muscovite granite. Extreme variation in rock type and degree of metamorphism characterises the entire complex. It is the oldest unit west of the Chaman fault in Pakistan. (2) The Bazai Ghar Volcanics consist of weakly deformed tuffs, flow breccias, and other coarse-grained pyroclastics of andesitic-arc type. Andesite flows and at least one silicic welded tuff are also present. The Bazai Ghar Volcanics are everywhere separated from the Spinatizha Metamorphic unit by granitic intrusions and a major fault. (3) Both the above units are intruded by a series of calc-alkaline granitic plutons ranging from diorite to granite. The silicic plutons generally intrude the more mafic ones. The Bazai Ghar Volcanics and related intrusions are probably equivalent to the Cretaceous (?) Sinjrani volcanics and the Cretaceous and younger intrusions of the Chagai Hills. (4) Along the fault zone between the volcanic and metamorphic rocks is a small area of previously unknown clastic sedimentary rocks: conglomerates and slates. The unit is of Palaeogene age but cannot yet be correlated with known units. The Spinatizha crystalline terrain extends south along the Chaman fault into Afghanistan and is covered by the Helmund desert to the west. It is the eastern continuation of the calc-alkaline arc terrain of the Chagai Hills dragged by oroclinal flexing into the Chaman transform zone. To the north it connects with the Kandahar volcanic arc. The metamorphic complex may represent the basement on which the arc terrain rests, only exposed due to strong vertical uplift near the Chaman fault.     

Estimation of the Shale Oil/Gas Potential of a Paleocene–Eocene Succession: A Case Study from the Meyal Area, Potwar Basin, Pakistan

The successful exploration and production of shale-gas resources in the United States and Canada sets a new possible solution towards the energy crisis presently affecting most countries of Asia. This study focuses on the use of well log and 2D seismic data for the characterization of the shale oil/gas potential of a Paleocene–Eocene succession — the Meyal area in the Potwar Basin of Pakistan. Two shaly plays are identified in Paleocene–Eocene strata in well logs using ΔLogR and modified ΔLogR cross-plot techniques. The results indicate that Paleocene shale(the Patala Formation) and the lower shaly part of Eocene limestone(Sakesar Formation) can be potentially mature source rocks. However, the thermal maturity modelling proves that only the Paleocene shale is mature. Our results also suggest that the maturity responses on ΔLogR models for the lower shaly part of the Eocene limestone are due to trapped hydrocarbons in the intra-formational fractures. Petroelastic/petrophysical analysis of the Patala Formation reveals two potential shale oil/gas zones on the basis of Young's modulus, Poisson's ratio, Brittleness index and Total Organic Content at an exploitation depth of 3980–3988 m. This work can provide valuable insight for estimating shale oil/gas potential in highly deformed basins not only in Asia but in other parts of the world.     

青藏高原冻土地球物理勘查方法组合模式

在全球气候日益变暖的情况下,青藏高原多年冻土退化将导致区域水文地质条件发生改变,进而影响到区域水资源循环过程和生态环境,需要开展青藏高原地区冻土地球物理勘查技术方法研究,以实现了解冻土地球物理特征、空间分布信息等.针对以上情况,对地震反射、地震转换波反射、地震折射、探地雷达、音频大地电磁(EH4)、高密度电阻率法这6种技术方法的探测效果进行了对比试验研究.研究结果表明,6种物探技术方法均可探测地层结构、冻土地球物理特征、空间分布信息等,但各种技术方法均存在一定局限性.针对不同目标任务,提出了3种青藏高原冻土地球物理勘查方法组合模式.该组合模式可为今后青藏高原冻土地球物理勘查提供技术支持.     

Seismic attenuation in Jati area,Lower Indus Basin,Pakistan

Reduced amplitude and distorted dispersion of seismic waves caused by attenuation, especially strong attenuation, always degrade the resolution of migrated images. To improve seismic imaging, attenuation must be compensated. This study addresses the factors causing seismic attenuation in Jati Block. Jati Block lies in Lower Indus Basin, Pakistan, approximately 25 mi north of the offshore Indus. Method used for Q factor is empirical equation method. Q factor correlation indicates that there are three major zones of attenuation in Jati block, i.e., zone I (surface to top Khadro), zone II (Upper Goru Formation), and zone III (Lower Goru Formation). Lowest Q value is in zone I, followed by zone II and zone III, respectively. Commonly, Khadro Formation (Basalt) of Paleocene and saucer-shaped igneous intrusion is considered as sources of attenuation. However, surprisingly, Khadro Formation of Paleocene and saucer-shaped igneous intrusion is zone of minimum attenuation and causes minimal transmission loss. Anisotropy analysis is performed to determine cause of attenuation within these zones. Thomson anisotropic parameters are computed for vertical wells using Backus averaging algorithm. These parameters are calibrated using sonic scanner data available for one well. Correlation of Q factor curve with mud log suggests that loose, unconsolidated sands and sand-shale layering are sources of attenuation within zone I. Attenuation in this zone is mostly due to fluid motion relative to the framework of loosely packed grains. Major lithology of Upper Goru Formation is marl. It is a slow formation, and in this formation, P wave loses energy to the formation in what is known as leaky P mode (sonic logging) and is dispersive (seismic). Epsilon (?) value is greater than almost 0.02 throughout Lower Goru Formations, indicating that this formation is strongly anisotropic. Fluctuation of epsilon (?) in Lower Goru Formation also suggests that this formation is causing layer-induced anisotropy. This layer-induced anisotropy in Lower Goru Formation added by dispersive and slow nature of Upper Goru Formation causes rapid attenuation.     

Structural evolution and asymmetric uplift of the Nanga Parbat syntaxis,Pakistan Himalya

The Nanga Parbat syntaxis, in the NW Himalaya, is a still growing crustal-scale north-trending antiformal structure in the core of which Indian Plate gneisses have been uplifted from beneath the overthrust rocks of the Kohistan island arc. Isotopic and fission track geochronology show that uplift rates within the syntaxis have increased to present day rates of > 6 mm/yr. Uplift has been accommodated by a combination of initial northwest verging thrusting on the western margin of the syntaxis, followed by crustal scale folding within the syntaxis and latterly by dextral reverse faulting on the western margin. This thrusting, folding and faulting is the effect of deformation at the north-western lateral tips of the main Himalayan thrusts where they interfere with the south-southeast verging thrusts of the northwest Himalaya.

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Zusammenfassung Nanga Parbat Konvergenz im nordwestlichen Himalaya ist eine noch im Wachsen begriffene nach Norden streichende antiformale Struktur im Krustenmaßstab. In ihrem Inneren wurden Gneisse der Indischen Platte aus der Nähe der überschobenen Gesteine des Kohistan Inselbogens herausgehoben. Isotopen- und Spaltspurengeochronologie zeigen, daß das Heraushebungsmaß innerhalb der Konvergenz zu der heutigen Rate von > 6 mm/a angestiegen ist. Die Heraushebung hat sich angepaßt an die Kombination von initialer NW-vergenter Überschiebung auf den westlichen Konvergenzrand, die gefolgt wurde von einer krustalen Faltung und lateral von dextraler antithetischer Verwerfung des westlichen Randes. Diese Deckenüberschiebung, Faltung und Verwerfung ist das Resultat der Deformation des nordwestlichen Ausstriches der Himalaya-Hauptüberschiebung, wo sie in Wechselwirkung mit der SSE-vergenten Überschiebung des NW-Himalayas steht.

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Résumé La convergence du Nanga Parbat, dans le nordouest de l'Himalaya, est une structure antiforme d'orientation nord-sud, d'échelle crustale et toujours active; son cur est occupé par des gneiss de la plaque indienne qui ont été soulevés à travers les roches charriées de l'arc insulaire du Kohistan. Les données géochronologiques obtenues à partir des isotopes et des traces de fission montrent que le taux de soulèvement a augmenté dans cette structure jusqu'à la valeur actuelle de plus de 6 mm/an. Le soulèvement s'est effectué par la combinaison d'un charriage initial, à vergence nordouest, sur la bordure ouest de la convergence, suivi d'un plissement d'échelle crustale dans la convergence et, latéralement, d'une fracturation par faille dextre inverse sur sa bordure ouest. Ce charriage, ce plissement et cette fracturation sont l'expression de la déformation à l'extrémité latérale nord-ouest des charriages principaux de l'Himalaya, où ils interfèrent avec les charriages à vergence sud- sud-est de l'Himalaya septentrional.

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滇东北矿集区小河铅锌矿床构造解析及其控矿模式

小河铅锌矿是滇东北铅锌矿集区内少数几个由北西向主断裂控制的典型铅锌矿床之一,矿化蚀变的空间展布严格受构造控制。为查明其区内构造对矿化蚀变的控制作用特征,通过不同中段大比例尺构造-蚀变岩相学填图,对不同方向构造进行筛分,并对不同中段不同矿(化)体特征和蚀变特征开展了系统的剖析,结果表明：小河铅锌矿床矿化蚀变的岩石组成、类型及结构等相对简单,围岩蚀变以热液白云石化、方解石化、硅化和黄铁矿化为主;矿化主要为闪锌矿化、方铅矿化;该区构造组合形迹反映矿区内存在6期构造体系,分别为加里东期-海西期、印支早-中期、印支晚期-燕山早期、燕山中期、燕山晚期和喜马拉雅期;印支晚期-燕山早期成矿流体沿区内北西向张性-张扭性构造发生大规模运移,在断裂上盘及与之配套的次级断裂、构造破碎带、节理裂隙等构造有利部位成矿,并依次形成以断裂为中心且平面上呈带状展布的矿化蚀变分带：矿化边缘带(Ⅰ)→矿化过渡带(Ⅱ)→矿化中心带(Ⅲ)。最终建立了小河铅锌矿床构造控矿模式。研究成果对同类矿床及川滇黔接壤区的找矿预测具有重要指导意义。     

Fluvial and lacustrine palaeoenvironments of the Miocene Siwalik Group, Khaur area, northern Pakistan

The Miocene Siwalik Group (upsection, the Chinji, Nagri, and Dhok Pathan Formations) in northern Pakistan records fluvial and lacustrine environments within the Himalayan foreland basin. Thick (5 m to tens of metres) sandstones are composed of channel bar and fill deposits of low-sinuousity (1·08–1·19), single-channel meandering and braided rivers which formed large, low-gradient sediment fans (or ‘megafans’). River flow was dominantly toward the south-east and likely perennial. Palaeohydraulic reconstructions indicate that Chinji and Dhok Pathan rivers were small relative to Nagri rivers. Bankfull channel depths of Chinji and Dhok Pathan rivers were generally ≤ 15 m, and up to 33 m for Nagri rivers. Widths of channel segments (including single channels of meandering rivers and individual channels around braid bars) were 320–710 m for Chinji rivers, 320–1050 m for Nagri rivers, and 270–340 m for Dhok Pathan rivers. Mean channel bed slopes were on the order of 0·000056–0·00011. Bankfull discharges of channel segments for Chinji and Dhok Pathan rivers were generally 700–800 m³s^?1, with full river discharges possibly up to 2400 m³s^?1. Bankfull discharges of channel segments for Nagri rivers were generally 1800–3500 m³s^?1, with discharges of some larger channel segments possibly on the order of 9000–32 000 m³s^?1. Full river discharges of some of the largest Nagri braided rivers may have been twice these values. Thin (decimetres to a few metres) sandstones represent deposits of levees, crevasse channels and splays, floodplain channels, and large sheet floods. Laminated mudstones represent floodplain and lacustrine deposits. Lakes were both perennial and short-lived, and likely less than 10 m deep with maximum fetches on the order of a few tens of kilometres. Trace fossils and body fossils within all facies indicate the former existence of terrestrial vertebrates, molluscs (bivalves and gastropods), arthropods (including insects), worms, aquatic fauna (e.g. fish, turtles, crocodiles), trees, bushes, grasses, and aquatic flora. Palaeoenvironmental reconstructions are consistent with previous palaeoclimatic interpretations of monsoonal conditions.     

青藏高原羌塘中部榴辉岩Ar-Ar定年

羌塘榴辉岩产于红脊山-双湖高压变质带中段的片石山地区,是目前青藏高原内部唯一的榴辉岩产地.榴辉岩多硅白云母40 Ar-39 Ar年龄tp=219.3±1.5 Ma;榴辉岩围岩的多硅白云母40 Ar-39 Ar年龄tp=217.2±1.8 Ma,定年结果表明,榴辉岩与围岩经历了相同的高压变质作用,与红脊山-双湖地区蓝闪片岩的高压变质时间是一致的.根据已有高压变质年代学资料,从羌塘的红脊山到双湖、那曲地区的巴青以北、昌都的酉西,直到滇西地区,断续分布长达2000余公里的高压变质带为同一期构造事件的产物,是龙木错-双湖板块缝合带向南延伸到滇西的重要依据.榴辉岩的定年数据进一步揭示,冈瓦纳板块与欧亚(扬子)板块的主体碰撞时间在220 Ma左右,同时也是古特提斯洋消亡的时间记录.     

青藏高原西部叶城-狮泉河地区岩石圈各向异性研究

对青藏高原西部新疆叶城—西藏狮泉河地区宽频地震探测记录到的剪切波进行了各向异性分析,计算结果给出了该地区上地幔各向异性的特征:西昆仑地区各向异性大都沿北东方向分布,总体方向变化不大,各向异性整体走向与青藏高原和塔里木盆地北缘各向异性空间分布一致。由此得出:印度板块向北推进的构造运动是形成本区岩石圈剪切波各向异性的主要原因,青藏高原各地体的各向异性在较大的东西向范围内保持稳定,各地体岩石圈固有的各向异性方向为北东向;作为羌塘地体和拉萨地体的分界线,班公怒江断裂带是主要的地表分界位置,在深部,无论西部剖面还是中部剖面,印度板块岩石圈的各向异性在该断裂带上均没有变化。     

Uplift of the Qinghai-Tibet Plateau: Lithospheric Structure and Structural Geomorphology of the Qinghai-Tibet Plateau

1. IntroductionWith its very thick continental crust (70 kmthick on average, a double norma1 thickness of thecrust), dramatic uplift since the late of thePleistocene (now with an average elevation of 4500-5000 m) and sustained and strong tectonicdeformation, the Qinghai-Tibet Plateau has been oneof the frontier subjects of international geoscienceresearch. With the advent of the 2lst century theQinghai-Tibet Plateau is renowned as a fieldlaboratory of the program of continental dynamics.Peo…     

Structural Attributes of Travertine-Filled Extensional Fissures in the Pamukkale Plateau,Western Turkey

Numerous active and inactive fissure-ridge travertines are located in the hanging wall of the Pamukkale range-front fault, a large normal fault bounding the northeast side of the Denizli Basin. A typical principal fissure-ridge comprises flanking bedded travertines dipping gently away from a nearly vertical, irregular central fissure, partially filled by vertically banded travertine. More complex ridges bear parasitic fissures and associated ridges on their flanks. Fissures roughly follow the long axes of ridge crests, some of them being divided into angular segments and others anastomosing. The traces of fissures are commonly parallel but some are oblique to one another. Fissures vary in width from a few millimeters to 5 m, and range in length from a few meters to a few kilometers.

The widths of central fissures are at a maximum near the midpoints of ridges, but decrease toward both ends, suggesting that they grew in length over time. Lateral fissure development involved the opening of both new and old cracks, some of which propagated into former process zones at crack tips. Fissures increase in width with depth either gradually or in a series of steps, depending on whether there was a uniform rate of fissure dilation during travertine deposition or episodic dilation during fracture propagation. The characteristic irregular morphology of fractures probably reflects extension-fracture propagation in differential stress fields that were weak as a consequence of location near the earth's surface. The fissures probably express a set of subsidiary extension fractures splaying from the Pamukkale range-front fault into its hanging wall.     

帕米尔弧东段逆冲推覆构造特征

帕米尔弧形构造带是青藏高原碰撞挤压表现最明显的地区之一。通过构造剖面和地震剖面解释,认为帕米尔弧东段逆冲推覆构造具有分带性特点,自南西向北东方向可以划分为逆冲推覆构造的根带、中带、锋带与锋前带,相应地发育叠瓦状逆冲断层、冲断褶皱、断层相关褶皱、单斜构造等不同的构造组合。对逆冲推覆锋带中苏盖特和阿克陶生长背斜、生长地层及形成时序分别进行了研究,确定了帕米尔弧形逆冲推覆构造以前展式（背驮式）向前陆方向扩展,逆冲推覆始于上新世,并一直持续到早更新世。弧形构造东西两段逆冲推覆运动方式和地层缩短量有很大差异：西段为与挤压方向垂直的逆冲,而东段为斜冲兼顺时针走滑;西段地层缩短量大于东段。