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1.
GEOLOGY AND MINERAL CHEMISTRY OF THE DEOSAI VOLCANICS, BALTISTAN, N. PAKISTAN  相似文献   

2.
The Tertiary collision-related thermal history of the NW Himalaya   总被引：3，自引：0，他引：3  
Garnet‐whole rock Sm‐Nd data are presented for several samples from the Indian plate in the NW Himalaya. These dates, when combined with the P‐T evolution of the Indian plate rocks, allow a thorough reconstruction of the prograde thermal evolution of this region (including the Nanga Parbat Haramosh Massif) during the early Cenozoic. Combining these data with Rb‐Sr mineral separate ages, enables us to constrain the post‐peak cooling history of this region of the Himalaya. The data presented here indicate that the upper structural levels of the cover rocks of the Nanga Parbat Haramosh Massif, and similar rocks in the Kaghan Valley to the south‐west, were buried to pressures of c. 10 kbar and heated to temperatures of c. 650 °C at 46–41 Ma. The burial of the lower structural levels of the cover rocks of the Nanga Parbat Haramosh Massif, to similar depths but at higher temperatures of c. 700 °C, occurred slightly later at 40–36 Ma, synchronous with the imbrication and exhumation of the amphibolite‐ and eclogite‐grade rocks of the Kaghan Valley. In contrast, the cover rocks of the Nanga Parbat Haramosh Massif were not imbricated or exhumed at this time, remaining buried beneath the Kohistan‐Ladakh Island Arc until the syntaxis‐forming event that occurred in the last 10 Myr. The timing of tectonic events in the north‐western Himalaya differs from that experienced by the rocks of the Central Himalaya in that the earliest stage of burial in the NW Himalaya predates that of the Central Himalaya by c. 6 Myr. This difference may result from the diachronous nature of the Indo‐Asian collision or may simply be a reflection of differing timing at different structural levels.  相似文献   

3.
The Nanga Parbat–Haramosh Massif has some of the greatest relief on Earth and highest measured rates of uplift, denudation, and river incision in bedrock. Many studies have sought to understand how its morphology relates to geotectonic evolution and glaciations. However, few catastrophic rock slope failures had been recognised and many of their impacts had been attributed to other processes. Recently more than 150 of these landslides have been found within a 100-km radius of Nanga Parbat (8125 m). New discoveries are reported east, north and west of Nanga Parbat along the Indus streams. Most generated long-run-out rock avalanches that dammed the Indus or its tributaries, some impounding large lakes. They initiated episodes of intermontane sedimentation followed by trenching and removal of sediment. Valley-floor features record a complex interplay of impoundment and sedimentation episodes, superimposition of streams in pre-landslide valley floors, and exhumation of buried features. These findings depart from existing reconstructions of Quaternary events. A number of the rock-avalanche deposits were previously misinterpreted as tills or moraine and their associated lacustrine deposits attributed to glacial lakes. Features up to 1000 m above the Indus, formerly seen as tectonically raised terraces, are depositional features emplaced by landslides, or erosion terraces recording the trenching of valley fill in landslide-interrupted river reaches. Unquestionably, tectonics and glaciation have been important but decisive and misread formative events of the Holocene involve a post-glacial, landslide-fragmented fluvial system. The latter has kept valley developments in a chronic state of disequilibrium with respect to climatic and geotectonic controls. Accepted glacial chronologies are put in doubt, particularly the extent and timing of the last major glaciation. The pace and role processes in the Holocene have been seriously underestimated.  相似文献   

4.
Analysis of fault-striations measured in the Kohistan part of the Indus Suture Zone (NW Himalaya, Pakistan) has been carried out to document dynamic evolution during the brittle stage of the collision of India and Asia. Processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as SSE–NNW compression, E–W compression, radial extension and SSW–NNE compression. The last corresponds to the present-day stress field defined from seismic activity. The earlier stress fields are related to times during the Miocene, when convergence-related stresses were disturbed by the formation of the nearby Nanga Parbat and Indus syntaxes.  相似文献   

5.
SYNCONVERGENT, DUCTILE N-DIRECTED SHEARING ON THE WESTERN MARGIN OF THE NANGA PARBAT SYNTAXIS, N. PAKISTAN1　BurgJ P ,ChaudryMN ,GhazanfarM ,etal.StructuralevidenceforbackslidingoftheKohistanarcinthecollisionalsystemofnorthwestPakistan[J] .Geology 1996 ,2 4 ( 8) ,739～ 74 2 . 2　ChamberlainCP ,ZeitlerPK ,EricksonE .ConstraintsonthetectonicevolutionofthenorthwesternHimalayafromgeochronologicandpetrologicstudiesofBabusarPass,Pakistan[J] .Journa…  相似文献   

6.
Matthias Kuhle 《GeoJournal》2001,54(2-4):107-396
A continuing prehistoric ice stream network between the Karakorum main crest and the Nanga Parbat massive has been evidenced, which, flowing down from the current Baltoro- and Chogolungma glaciers and filling the Shigar valley as well as the Skardu Basin, has flowed together with the Gilgit valley glacier to a joint Indus parent glacier through the Indus gorge. The ice stream network received an influx by a plateau glacier covering the Deosai plateau, which was connected through outlet glaciers to the ice filling of the Skardu Basin and the Astor glacier at the Nanga Parbat, as well as to the lower Indus glacier. The field observations introduced here in part confirm the results as to the Ice Age glacier surface area of Lydekker, Oestreich and Dainelli, but go beyond it. In additon, a reconstruction of the surface level of this ice stream network and its glacier thicknesses up to the highest regions of the present-day Karakorum valley glaciers has been carried out for the first time. In the area under investigation the Karakorum ice stream network showed three ice cupolas, culminating at an altitude of 6200–6400 m. Between the mountain groups towering 1000–2000 m higher up, they communicated with each other over the transfluence passes in a continuous glacier surface without breaks in slope. In the Braldu- and Basna valley ice thicknesses of 2400–2900 m have been reached. In the Skardu Basin, where the glacier thickness had decreased to c. 1500–1000 m, the ELA at an ice level of 3500-3200 m asl had fallen short to the extent that from here on down the Indus glacier a surface moraine cover has to be suggested. However, 80% of the surface of the ice stream network was devoid of debris and had an albedo of 75-90%. The lowest joint glacier terminus of the ice stream network was situated - as has already been published in 1988 – in the lower Indus valley at 850–800 m asl. The reconstructed maximum extension of the ice stream network has been classified as belonging to the LGM in the wider sense (60–18 Ka BP). Four Late Glacial glacier positions (I–IV), with a decreasing ice filling of the valleys, have been differentiated, which can be locally recognized through polish lines and lateral moraine ledges. The valley (trough-) flanks with their ground moraine covers, oversteepened by glacier abrasion, have been gravitationally destroyed by crumblings, slides and rock avalanches since the deglaciation, so that an interglacial fluvial-, i.e. V-shaped valley relief has been developed from the in part preserved glacial relief. The contrast of the current morphodynamics with regard to the preserved forms is seen as an indication of the prehistorically completely different - namely glacigenic – valley development and the obvious rapidity of this reshaping at still clearly preserved glacial forms provides evidence of their LGM-age. In an additional chapter the lowest ice margin positions, so far unpublished, are introduced, which have been reconstructed for the Hindukush, Central Himalaya and on the eastern margin of Tibet.  相似文献   

7.
The Kohistan Arc Complex is an integral part of the NW Himalayan collision system and is bounded by two major suture zones, the Indus Suture Zone (ISZ) and the Northern Suture in the south and north respectively. Fission‐track analyses on samples collected along the Indus River across the arcuated ISZ in the Besham region are presented here. The footwall yields zircon and apatite fission‐track (FT) ages of ∼23 Ma and ∼3.7 Ma respectively; the hanging wall ages range from 24 to 42 Ma for zircon and ∼10 Ma for apatite. Thus, the change in ISZ kinematics from thrusting to normal faulting was not later than Oligocene and normal faulting on this ISZ segment was still active at least into early Pliocene times. At this time normal faulting had already ended at other ISZ segments, but it was still (or again) active across the ISZ in the Besham region most likely as a local phenomenon caused by the growth of the Indus Syntaxis, a transverse antiform parallel to the Nanga Parbat Syntaxis.  相似文献   

8.
A sample of banded amphibolite from the western margin of the Nanga Parbat–Haramosh Massif as Sassi has been studied using microstructural and 40Ar/39Ar laserprobe techniques to investigate the relationship between deformation and argon isotope variations in a natural system. Amphibolite-grade deformation occurred during south-directed overthrusting of the Kohistan arc over India along the Main Mantle Thrust and was overprinted by extensional reactivation of the earlier fabric and the formation of biotite-rich shear zones. Subsequent deformation along discrete fine-grained fault zones was characterised by the formation of scapolite, chlorite and K-feldspar, early plastic deformation and later cataclasis. Different minerals developed during this history show a wide range in apparent 40Ar/39Ar ages. Biotite, chlorite and scapolite exhibit much lower concentrations of excess argon, indicating their equilibration in a fluid relatively poor in excess argon. A `true' age of ca. 8 Ma from biotite represents a minimum age for deformation associated with formation of the Nanga Parbat Syntaxis and also precludes Pliocene metamorphism in this area of the syntaxis. Both high- and low-closure temperature minerals (amphiboles and feldspars) record apparent ages which are associated with the incorporation of excess argon within the mineral lattice. Although differential thermal resetting of minerals at different closure temperatures is important, variations in the inherited 40Ar/36Ar ratio throughout the sample is dominated by deformation and fluid infiltration. Consequently it appears that within deforming metamorphic rocks, areas with significantly different argon isotope compositions may be present and need not be homogenised by diffusion. Received: 6 July 1994 / Accepted: 24 December 1996  相似文献   

9.
This article summarizes an exploratory study carried out to investigate the significance of various geomorphic features on the formation of observed knickpoints along the upper Indus River in northern Pakistan. These features include bedrock lithology, active faults, sediment flux from tributary channels, and landslide dams which have blocked the main channel. The knickpoints and their related geomorphic parameters (channel profile, concavity, drainage area and normalized steepness index, etc.) were extracted from Advanced Spaceborne Thermal Emission and Reflection (ASTER) Global Digital Elevation Models (GDEMs) with 30 m resolution using ArcGIS, River Tools, and Matlab software. A total of 251 major and minor knickpoints were extracted from the longitudinal profile along a ~ 750 km reach upstream of Tarbela Reservoir. The identified knickpoints and their respective normalized steepness index (ksn values) were compared with bedrock lithology, mapped faults, regional landslide/rockslide inventory, and the locations of historic landslide dams. The analyses revealed that the knickpoints do not correlate with the bedrock lithology except where major unit boundaries coexist with mapped faults, especially in reaches criss-crossed by active thrust faults in the Nanga Parbat Haramosh (NPHM) region. Neither did the river’s major confluences exhibit any notable knickpoints, but the correlations between knickpoints, mapped landslides, and historic rockslide avalanche dams accounted for approximately 75% of the observed knickpoints, a surprising finding. These observations suggest that more detailed studies aided by high resolution data should be undertaken to further explore the characteristics of knickpoints triggered by tectonic uplift, local fault offset, bedrock erodibility, and landslide/rockslide dams.  相似文献   

10.
High‐grade gneisses (amphibolite–granulite facies) of the Namche Barwa and Gyala Peri massifs, in the eastern Himalayan syntaxis, have been unroofed from metamorphic depths in the late Tertiary–Recent. Rapid exhumation (2–5 mm year?1) has resulted in a pronounced shallow conductive thermal anomaly beneath the massifs and the intervening Tsangpo gorge. The position of the 300 °C isotherm has been estimated from fluid inclusions using CO2–H2O immiscibility phase equilibria to be between 2.5 and 6.2 km depth below surface. Hence, the near‐surface average thermal gradient exceeds 50 °C km?1 beneath valleys, although the thermal gradient is relatively lower beneath the high mountains. The original metamorphic fluid in the gneisses was >90% CO2. This fluid was displaced by incursion of brines from overlying marine sedimentary rocks that have since been largely removed by erosion. Brines can exceed 60 wt% dissolved salts, and include Ca, Na, K and Fe chlorides. These brines were remobilized during the earliest stages of uplift at >500 °C. During exhumation, incursion of abundant topography‐driven surface waters resulted in widespread fracture‐controlled hydrothermal activity and brine dilution down to the brittle–ductile transition. Boiling water was particularly common at shallow levels (<2.5 km) beneath the Yarlung Tsangpo valley, and numerous hot springs occur at the surface in this valley. Dry steam is not a major feature of the hydrothermal system in the eastern syntaxis (in contrast to the western syntaxis at Nanga Parbat), but some dry steam fluids may have developed locally.  相似文献   

11.
ABSTRACT The pressure-temperature and temperature-time paths derived for rocks in the Kohistan arc and adjacent Nanga Parbat-Haramosh massif record the dynamics of the collision between the island arc and the Indian plate. Studies of P-T-t paths show that the Kohistan arc was thrust over the Nanga Parbat-Haramosh massif at least 25 Ma ago, but not more than 30–35 Ma ago. Rocks in the Kohistan arc followed decreasing pressure paths, with the early metamorphism beginning at high pressures (9.5 kbar) and later metamorphism occurring at 8.0 kbar. In contrast, rocks in the Nanga Parbat-Haramosh massif (Indian plate) experienced increasing pressure and temperature paths. Prior to thrusting, the massif was at low pressures (4.0 kbar) and low temperatures (450°c). Later, the pressure and temperature increased to 8 kbar and 580°c. The authors interpret the convergence (to approximately the same pressure and temperature) of the P-T paths in the two terranes as being the result of thrusting and thermal equilibration between the thrust sheets. 40Ar/39Ar cooling ages of hornblendes and other geochronological data suggest that the time of peak metamorphism and hence the completion of thickening was approximately 30–35 Ma ago. Temperature-time paths show that after thrusting, during the period 25–10 Ma, the Kohistan arc and Nanga Parbat-Haramosh massif were uplifted at similar rates (0.5 km Ma). However, in the past 10 Ma the Nanga Parbat-Haramosh massif has been uplifted more rapidly than the adjacent Kohistan arc. Rapid uplift has been accommodated by late faults along the edge of the massif.  相似文献   

12.
The Himalayan range is one of the best documented continent-collisional belts and provides a natural laboratory for studying subduction processes. High-pressure and ultrahigh-pressure rocks with origins in a variety of protoliths occur in various settings: accretionary wedge, oceanic subduction zone, subducted continental margin and continental collisional zone. Ages and locations of these high-pressure and ultrahigh-pressure rocks along the Himalayan belt allow us to evaluate the evolution of this major convergent zone.

(1) Cretaceous (80–100 Ma) blueschists and possibly amphibolites in the Indus Tsangpo Suture zone represent an accretionary wedge developed during the northward subduction of the Tethys Ocean beneath the Asian margin. Their exhumation occurred during the subduction of the Tethys prior to the collision between the Indian and Asian continents.

(2) Eclogitic rocks with unknown age are reported at one location in the Indus Tsangpo Suture zone, east of the Nanga Parbat syntaxis. They may represent subducted Tethyan oceanic lithosphere.

(3) Ultrahigh-pressure rocks on both sides of the western syntaxis (Kaghan and Tso Morari massifs) formed during the early stage of subduction/exhumation of the Indian northern margin at the time of the Paleocene–Eocene boundary.

(4) Granulitized eclogites in the Lesser Himalaya Sequence in southern Tibet formed during the Paleogene underthrusting of the Indian margin beneath southern Tibet, and were exhumed in the Miocene.

These metamorphic rocks provide important constraints on the geometry and evolution of the India–Asia convergent zone during the closure of the Tethys Ocean. The timing of the ultrahigh-pressure metamorphism in the Tso Morari massif indicates that the initial contact between the Indian and Asian continents likely occurred in the western syntaxis at 57 ± 1 Ma. West of the western syntaxis, the Higher Himalayan Crystallines were thinned. Rocks equivalent to the Lesser Himalayan Sequence are present north of the Main Central Thrust. Moreover, the pressure metamorphism in the Kaghan massif in the western part of the syntaxis took place later, 7 m.y. after the metamorphism in the eastern part, suggesting that the geometry of the initial contact between the Indian and Asian continents was not linear. The northern edge of the Indian continent in the western part was 300 to 350 km farther south than the area east of the Nanga Parbat syntaxis. Such “en baionnette” geometry is probably produced by north-trending transform faults that initially formed during the Late Paleozoic to Cretaceous Gondwana rifting. Farther east in the southern Tibet, the collision occurred before 50.6 ± 0.2 Ma. Finally, high-pressure to ultrahigh-pressure rocks in the western Himalaya formed and exhumed in steep subduction compared to what is now shown in tomographic images and seismologic data.  相似文献   


13.
Hydrothermal activity and mesothermal-styled gold mineralisation occurs near the main topographic divide of most active or young collisional mountain belts. The Southern Alps of New Zealand is used in this study as a model for the mineralising processes. The collisional tectonics results in a two-sided wedge-shaped orogen into which rock is transported horizontally. Upper crustal rocks pass through the orogen and leave the orogen by erosion, whereas lower crustal rocks are deformed into the mountain roots. High relief drives meteoric water flow to near the brittle–ductile transition. Lower to upper greenschist facies metamorphic reactions, driven by deformation at the crustal decollement and in the root, release water-rich fluids that rise through the orogen. Intimate chemical interaction between fluid and rock results in dissolution and later precipitation of gold, arsenic and sulphur. Fluid flow and mineralisation in the topographic divide region is facilitated by a network of steeply dipping faults and associated rock damage zones where oblique strike-slip faults intersect the thrust faults that strike subparallel to the main mountain range.The Nanga Parbat massif of the western Himalaya is an example of an active collisional zone which hosts hydrothermal activity but no gold mineralisation. The lack of gold mineralisation is due to the following factors: CO2-dominated rising metamorphic fluid in dehydrated amphibolite-granulite facies metamorphic rocks does not dissolve gold and arsenic; hot (up to 400 °C) meteoric water confined to fractures in the gneiss limits dissolution of gold and arsenic; low density of hot water/dry steam, and low reduced sulphur content of fluid, restrict solubility of gold and arsenic; absence of fracture networks in the core of the massif and the small volumes of circulating fluid limit metal concentration; and lack of reactive rock compositions limits chemically mediated metal deposition.  相似文献   

14.
The western Himalaya, Karakoram and Tibet are known to be heterogeneous with regard to Pb isotope compositions in K-feldspars, which allows this system to be used as a sediment provenance tool. We used secondary ion mass spectrometry to measure the isotopic character of silt and sand-sized grains from the modern Sutlej and Chenab Rivers, together with Thar Desert sands, in order to constrain their origin. The rivers show a clear Himalayan provenance, contrasting with grains from the Indus Suture Zone, but with overlap to known Karakoram compositions. The desert dunes commonly show 207Pb/204Pb and 206Pb/204Pb values that are much higher than those seen in the rivers, most consistent with erosion from Nanga Parbat. This implies at least some origin from the trunk Indus, probably reworked by summer monsoon winds from the SW, a hypothesis supported by bulk Nd and U-Pb zircon dating. Further data collected from Holocene and Pleistocene sands shows that filled and abandoned channels on the western edge of the Thar Desert were sourced from Himalayan rivers before and at 6-8 ka, but that after that time the proportion of high isotopic ratio grains rose, indicating increased contribution from the Thar Desert dunes prior to ∼4.5 ka when flow ceased entirely. This may be linked to climatic drying, northward expansion of the Thar Desert, or changes in drainage style including regional capture, channel abandonment, or active local Thar tributaries. Our data further show a Himalayan river channel east of the present Indus, close to the delta, in the Nara River valley during the middle Holocene. While this cannot be distinguished from the Indus it is not heavily contaminated by reworking from the desert. The Pb system shows some use as a provenance tool, but is not effective at demonstrating whether these Nara sediments represent a Ghaggar-Hakra stream independent from the Indus. Our study highlights an important role for eolian reworking of floodplain sediments in arid rivers such as the Indus.  相似文献   

15.
Sedimentary basins represent an archive of tectonic events of the hinterland source regions. By determining the variation in sediment lagtime over time, events can be distinguished which may no longer be available as the source has been eroded. In regions characterized by rapid exhumation this is most often the case but the erosion products form a record of these events. Detrital zircon fission‐track ages from sediments of the Siwalik basin, Pakistan, originally presented by Cerveny et al. (New Perspectives in Basin Analysis, Springer‐Verlag, New York, 1988, p. 43), have been reinvestigated and reinterpreted using a revised methodological approach. Detrital age populations were determined from different stratigraphic levels and were correlated through time in order to assess the change in lag time over the stratigraphic section. This information was combined with the many new ages from the hinterland to further interpret events in the source region. The new investigation suggests that steady‐state evolution has not always existed. An overall trend of exhumation increasing by 0.1 mm Myr?1 (from 0.9 to 2.65 mm yr?1) from 18 Ma to the present is evident with a major exception of a net pulse between 11.7 and 10.9 Ma associated with an increase in sedimentation increasingly rich in hornblende. Earlier studies suggested that at this time the source of the sediments was the presently outcropping Kohistan Arc. We are able to demonstrate that this cannot be so but was rather the rapidly exhuming Nanga‐Parbat Haramosh syntaxis (> 2 mm yr?1) coevally with transpressional displacement along the Main Karakorum Thrust, whereby the overlying Kohistan Arc sequences were removed. Furthermore, comparison of our detrital thermochronological data set with another one from the same basin and one from another foreland basin to the east, in NW India suggest that the Himalayan orogenesis was probably not synchronous for the late Early–Middle Miocene. Overall, regions that undergoes today's rapid uplift may be useless to reconstruct earlier phases of exhumation as the levels that may have yielded such info were eroded and deposited into the adjacent basin(s). Such scenario is reproducible in most orogens as in the Himalaya in NW Pakistan stressing the high potential of detrital thermochronological studies to trace hinterland dynamics. Terra Nova, 18, 248–256, 2006  相似文献   

16.
Lasafam Iturrizaga 《GeoJournal》1999,47(1-2):277-339
An abridged version of a geomorphological inventory and typology of Postglacial debris accumulations in High Asia is presented, with selected examples from the Hindu Kush, the Karakoram and the Himalayas. The debris accumulations were surveyed in the course of four research expeditions lasting a total of ten months in selected valley systems of High Asia (the eastern Hindu Kush, the northwestern Karakoram, the Nanga Parbat massif (Pakistan), the Ladakh and Zanskar ranges, the Nun Kun massif, the Kumaon and Garhwal Himalayas with the Kamet, Trisul and Nanda Devi massifs (India) and in the central Himalayas with the Kanjiroba, Annapurna, Manaslu and Makalu massifs (Nepal)). The study areas being widely scattered, a supraregional comparison of the debris accumulations proved possible. The debris accumulations are considered in centre-to-periphery sequences from the mountain interior to the mountain fringes, and in vertical sequences, i.e. altitudinal zones, taking into account their topographical relationship to adjoining elements of the landscape. Supraregional and climate-specific types of debris accumulation are distinguished and it is recognized that the debris accumulations of the Karakoram and the Himalayas resemble each other more closely with increasing elevation. The core of the study is the dominant role played by past glaciation in the formation of Postglacial debris accumulations in the high mountains of Asia. This glacial-history-oriented concept of debris accumulation stands in sharp contrast to previous opinions about the genesis of the debris accumulation landscape in the extreme high mountains of Asia. The study shows that at many places morainic deposits mask extensive portions of the valley sides up to several hundred metres above the valley floor. These moraines are the main debris sources and exert a strong influence on, or even suppress, the purely slope-related formation of debris accumulations. Resedimentation of morainic material in combination with additional talus delivery leads to numerous characteristic composite types of debris accumulations, which are here termed transitional glacial debris accumulations. Various stages in the transition from moraine to slope-related debris accumulations were observed, making it necessary to consider the evolutional element in the development of debris accumulations by taking into account both genetic series of debris accumulations and formations of debris accumulations. A significant proportion of debris accumulations are also due to collapse processes which result from pressure release at the valley sides after deglaciation and occur in the course of glacial trough valleys being transformed into more stable fluvial V-shaped valleys. The residual morainic landscape has left debris accumulations that are basically similar in study areas of different climate – i.e. in the Hindu Kush and the Karakoram on the one hand, and the Himalayas on the other. The age classification of the debris accumulations was based on the location of the slope-derived debris accumulations in relation to the corresponding stages of glaciation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
Mass movements such as landslides in mountainous terrains are natural degradation processes and one of the most important landscape-building factors. Varunawat Parbat overlooking Uttarkashi town witnessed a series of landslides on 23 September 2003 and the debris slides and rock falls continued for 2 weeks. This landslide complex was triggered due to the incessant rainfall prior to the event, and its occurrence led to the blockage of the pilgrim route to Gangotri (source of the Ganges river) and evacuation of thousands of people to safer places. Though there was no loss of lives due to timely evacuation, heavy losses to the property were reported. High-resolution stereoscopic earth observation data were acquired after the incidence to study the landslide in detail with emphasis on the cause of the landslide and mode of failure. Areas along the road and below the Varunawat foothill region are mapped for landslide risk. It was found that the foothill region of the Varunawat Parbat was highly disturbed by man-made activities and houses are dangerously located below steep slopes. The potential zones for landslides along with the existing active and old landslides are mapped. These areas are critical and their treatment with priority is required in order to minimise further landslide occurrences.  相似文献   

18.
There are five workable coal beds in the Tikak Parbat Formation of the Barail Group in the Makum coalfield, Tinsukia District, Assam. Two of these beds, 18 and 6 m thick, are persistent across the field. The coal is high volatile bituminous B/C, has excellent coking properties, and is of great importance as a blending coal to improve the coking properties of the lower-quality Gondwanan coals.These coals are bimacerites as vitrinertite or trimacerites as duroclarite. Virtrinite predominates with minor amounts of other macerals and minerals. The high percentage of vitrinite indicates that the bark and woody tissues were the dominant contributors to the precursor peat. These peats were strongly decomposed under anaerobic conditions as indicated by the abundance of the collinite type of vitrinite.  相似文献   

19.
We have determined Fe–Mg diffusion coefficients in olivines from different sources (Nanga Parbat, Pakistan and San Carlos, Arizona, USA) at atmospheric pressure as a function of composition, oxygen fugacity (10−5–10−12 Pa) and temperature (700–1200°C) using thin films produced by pulsed laser deposition and RBS to analyze the concentration profiles. We have characterized the nano-scale structure and composition of the thin films annealed at various conditions and shown that the nature of the film (e.g. crystallinity, wetting behavior) depends strongly on the annealing conditions. If these variations are not taken into account in the form of boundary conditions for modeling the diffusion profiles, artifacts would result in the diffusion data. The diffusion coefficients obtained from 75 experiments reveal that (i) between fO2 of 10−5 and 10−10 Pa, diffusion along all three principal crystallographic directions in olivine, [100], [010] and [001], are described by a constant activation energy of ∼200 kJ/mol, precluding any temperature dependence of diffusion anisotropy and change of mechanism of diffusion at temperatures between 950 and 1200°C, (ii) diffusion coefficients increase with oxygen fugacity at fO2 > 10−10 Pa, with an fO2 exponent that lies between 1/4 and 1/7, and (iii) at fO2 below 10−10 Pa, and consequently at temperatures below ∼900°C, diffusion becomes weakly dependent/independent of fO2, indicating a change of diffusion mechanism. Activation energy of diffusion at these conditions is slightly higher, ∼220 kJ/mol. The data, including the change of mechanism, are analyzed in terms of point defect chemistry in Part II of this work to derive an equation that allows calculation of diffusivities in olivine over its entire field of stability. Availability of directly measured data at temperatures down to 700°C imply that for the first time diffusion coefficients can be interpolated, rather than extrapolated, for modeling most natural systems.  相似文献   

20.
Two new palm leaf impressions, cf. Iguanura wallichiana and Palmacites makumensis sp. nov. are described from the Makum Coalfield, Tinsukia District, Assam. They belong to the Tikak Parbat Formation being considered as Late Oligocene (Chattian 28?C23?Myr) in age. Their presence, along with the other known fossil records indicates that CMMT (cold month mean temperature) was not less than 18°C with plenty of rainfall, in the region during the period of deposition.  相似文献   

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