P-T Conditions and Geothermal Gradients of Gneiss--Enderbite Rocks: Dharmapuri Area, Tamil Nadu, India     

RAO  D. RAMESHWAR; NARAYANA  B. L.; CHARAN  S. N.; NATARAJAN  R. 《Journal of Petrology》1991,32(3):539-554

An investigation of a low- to high-grade transition area inDharmapuri district confirms a continuous section through aformer lower crust, with tonalitic gneisses predominating inthe upper part and enderbites in the lower part. Geothermometry and geobarometry show a prograde metamorphismof 5?5 ? 1?5 kb and 730 ?40 ?C in the transition zone near theorthopyroxene isograd in the north to {small tilde}8? 1?5 kband 775 ? 30 ?C in the south. The progressive increase in metamorphicgrade is demonstrated by the systematic change in mineral compositionsfrom tonalitic gneisses in the north to enderbites in the south.The pressure estimates record a depth of equilibration of mineralsat 14–23 km and 23–33 km in the intermediate andlower parts of the crust, respectively. The presence of suchrocks now at the surface of the continental crust ({small tilde}35 km) could be cited as evidence for this part of the EarlyProterozoic to Late Archean crust having been at least 50–68km thick. The P-T data in this area do not support the division into thewestern high-pressure and eastern low-pressure blocks of thelowland region suggested by earlier workers.  相似文献   

Indus tsangpo suture zone in ladakh—its tectonostratigraphy and tectonics     

V. C. Thakur 《Journal of Earth System Science》1990,99(2):169-185

The Indus Tsangpo suture zone in Ladakh lies between the Phanerozoic sequence of the Zanskar Zone of Tethys Himalaya in the south and Karakoram zone in the north. The five palaeotectonic regimes recognized in the suture zone are: The Indus palaeosubduction complex, the Ladakh magmatic arc, the Indus arc-trench gap sedimentation, the Shyok backarc and the Post-collision molasse sedimentation. The Ladakh magmatic arc, comprising intrusives of the Ladakh plutonic complex and extrusives of the Dras, Luzarmu and Khardung formations, owes its origin to the subduction of the Indian oceanic plate underneath the Tibet-Karakoram block. The Indus Formation, lower Cretaceous to middle Eocene in age, was laid down in a basin between the magmatic arc and the subduction complex. The Shergol and Zildat ophiolitic melange belts exhibit green-schist and blue-schist facies metamorphism and show structural geometry and deformation history dissimilar to that of the underlying and overlying formations. The melange belts and the flysch sediments of the Nindam Formation represent a palaeosubduction complex. The Shyok suture zone consists of tectonic slices of metamorphics of the Pangong Tso Crystallines, Cretaceous to lower Eocene volcanics and sedimentaries, together with ultramafic and gabbro bodies and molasse sediments. This petrotectonic assemblage is interpreted as representing a back-are basin. Post-collision molasse sedimentaries are continental deposits of Neogene age, and they occur with depositional contact transgressing the lithological and structural boundaries. Two metamorphic belts, the Tso Morari crystalline complex and the Pangong Tso Crystallines, flank to the south and north respectively of the Indus suture zone in Eastern Ladakh. Three generations of fold structures and associated penetrative (and linear) structures, showing a similar deformation history of both the metamorphic belts, are developed. The shortening structures developed as a result of collision during the postmiddle Eocene time.  相似文献   

An assessment of Dungale landslide using remotely piloted aircraft system (RPAS), ground penetration radar (GPR), and Slide & RS2 Softwares     

Tandon  Ruchika Sharma  Gupta  Vikram  Venkateshwarlu  Bhimala  Joshi  Pradeep 《Natural Hazards》2022,113(2):1017-1042

Natural Hazards - In the present study, slope stability analysis was done using limit equilibrium method and finite element method of the Dungale landslide situated in the NW Himalaya along Tons...  相似文献   

Major changes in East Asian climate in the mid-Pliocene: Triggered by the uplift of the Tibetan Plateau or global cooling?     

《Journal of Asian Earth Sciences》2013

Since the mid-Pliocene, East Asian climates have experienced significant changes. One view suggests that significant uplift of the Tibetan Plateau during this period could have been responsible for these dramatic changes in the strength of the East Asian monsoon and for Asian interior aridification, while some other authors attribute these changes to the ongoing global cooling and rapid growth of the Arctic ice-sheet. Up to the present, which factor dominates the major changes of East Asian climate in the mid-Pliocene is still a contentious issue. This study presents an analysis of several climate proxies including grain-size, (CaO^* + Na₂O + MgO)/TiO₂ ratio, Na/Ka ratio and dust accumulation rates of the Xifeng Red Clay sequence in the eastern Chinese Loess Plateau and the Xihe Pliocene loess-soil sequence in West Qinling. They reveal that aridity in the continental interior and winter monsoon circulation both intensified, whereas the East Asian summer monsoon showed a weakening rather than intensifying trend since the mid-Pliocene. These changes are also supported by the other multi-proxy records from various regions in East Asia. Previous numerical modeling studies have demonstrated that uplift of the Tibetan Plateau would have simultaneously enhanced continental-scale summer and winter monsoon strength as well as central Asian aridity. The mid-Pliocene climate changes in East Asia are therefore unlikely to be a response to Plateau uplift. On the contrary, our recent modeling results give support to the view that ongoing cooling could have intensified both the aridity of the interior and the strength of the winter monsoon, but weakened the summer monsoon in East Asia.  相似文献   

Geoid height versus topography of the Northern Ninetyeast Ridge: implications on crustal compensation     

S. Rajesh  T. J. Majumdar 《Marine Geophysical Researches》2009,30(4):251-264

In this paper we focused on understanding the isostatic compensation of the Ninetyeast Ridge in the overall context of the Bay of Bengal oceanic lithosphere and the interaction of the ridge system with the north Andaman subduction zone from north of 7–18°N. This region is characterized by the initial interaction of the Kerguelen hotspot with the Bay of Bengal oceanic lithosphere. We used satellite altimeter-derived marine geoid, as it should comprehensively reflect the compensations caused by large spatial wavelength dominated deeper anomaly sources in a hotspot affected lithospheric load like the Ninetyeast Ridge. Our analyses of the geoid-to-topography ratio (GTR), residual geoid, gravity-to-topographic kernel and upward continuation of anomalies show the existence of two different types of source compensation bodies beneath the northern (12–18°N) and southern (7–12°N) Ninetyeast Ridge. In the northern region, the geoid to topography ratio varies from 0.63 ± 0.05 to 0.44 ± 0.03, while in the southern region it ranges from 1.34 ± 0.09 to 1.31 ± 0.07 which resulted in a north to south increase in the apparent compensation depth from ~9 to 28 km. The presence of a shallow Moho, low GTR, broader gravity to topography kernel and the absence of a ridge anomaly from the mantle density dominated upward continued anomaly at z = 300 km indicates that at the northern segment the underplated low density crustal melt is the dominant isostatic compensating body. However, at the southern ridge segment the high GTR, strong gravity-to-topography kernel and the subsistence of the anomaly at long wavelengths, even at z = 300 km represents the existence of large volumes of hotspot related underplated dense material as the source of compensation. The proximity of the dense source compensating body of the southern Ninetyeast Ridge to the Andaman subduction zone affected the regional mantle driven density gradient flow, as observed from the z = 300 km continued gravity anomaly. The existence of a southern Ninetyeast Ridge in such a transpressional regime has caused the formation of a forearc sliver at its eastern flank, which is a major crustal deformational structure developed as a result of ridge-trench collision.  相似文献   

Multiple hazard mapping (MHM) for vulnerability assessment in Pali Gad watershed using geospatial tools     

Priti Kaushik  P. K. Joshi  Xuefei Yang 《Journal of the Indian Society of Remote Sensing》2005,33(3):441-445

  相似文献   

Landsat imagery analysis and field studies in the Kullu and Chauhar valleys,Himachal Pradesh,India     

A. K. Nagar  R. S. Rawat 《Journal of the Indian Society of Remote Sensing》1989,17(2):27-40

The rough terrain between the Gogar Dhar (Mandi-Brot rise) and the Kullu-Larji valley is geologically unexplored. This paper brings out for the first time the geology and regional tectonic set-up of the area on the basis of LANDSAT imagery interpretation and field checks. Image analysis of about 3700 sq. km area and field observations along selected sections of the area reveal that the area mainly comprises mica-chlorite schists, quartzites and phyllites i.e. low to medium grade Chail metamorophics with acid and basic intrusions within them. Structually the rocks are arranged in the form of a NNW-SSE trending faulted synclinorium, the axis of which passes through Daggi Dhar. The western flank of the synclinorium is more strongly folded. Granitoids and basics show concordent relations with the country rocks. Two belts of granitoids are found occupying the cores of the folds on both the limbs of the synclinorium. Along the Uhl river (in the Chauhar valley) and the Kullu valley passes the Chail thrust separating the Chail metamorphics from the rocks of the outer carbonate belt and the traps of the Mandi unit, and the inner carbonate belt of the Larji window zone respectively. The area is dissected into blocks by cross cutting, deep-seated major faults of three generations. The fold and fault systems have prominent control over the geomorphology including the drainage patterns and landforms of the area. The present area is a typical case of inverted relief, anticlinal valleys and synclinal hills being the main geomorphic features developed due to structural control. The change in the course of the Beas River between Mandi and Pandoh is a typical case of structural control on the present drainage system.  相似文献   

Evolution of Quaternary alluvial fans and terraces in the intramontane Pinjaur Dun, Sub-Himalaya, NW India: interaction between tectonics and climate change   总被引：2，自引：0，他引：2  

NARAYANAPANICKER SURESH  TRILOKI N. BAGATI  ROHTASH KUMAR  VIKRAM C. THAKUR 《Sedimentology》2007,54(4):809-833

Quaternary alluvial fans in the tectonically active Pinjaur Dun, an intramontane valley in the Sub‐Himalaya, were deposited in front of the Nalagarh Thrust and were influenced both by tectonics and glacial climate fluctuations. The surface morphology indicates that an earlier set of first‐order fans (Qf1) became entrenched and onlapped by a series of second‐order fans (Qf2). The younger fan segments were then cut by a pair of terraces (T1 and T2). Quartz optically stimulated luminescence dating establishes that the Qf1 aggradational phase was initiated before 96·5 ± 25·3 ka and terminated after 83·7 ± 16·3 ka. This was followed by a period of incision, before Qf2 fan deposition started at 72·4 ± 13·4 ka and continued until 24·5 ± 4·9 ka. Sediment was deposited on the T1 (upper) and T2 (lower) terraces at 16·3 ± 2·1 and 4·5 ka, respectively, recording a return to overall degradation punctuated by minor deposition on terraces. The period of incision separating the younger and older fan deposits coincided with enhanced SW monsoon precipitation. The subsequent development of the Qf2 fans and their progradation until 20 ka suggest erosional unloading of the thrust hangingwall during a tectonically quiescent phase. Toe cutting, deposition of axial river and lacustrine facies, and retreat of Qf2 around 45 ka, indicate fanward shift of the axial river due to tilting of the valley towards the NE in response to reactivation of the Nalagarh Thrust. The cessation of Qf2 deposition around 20 ka and the onset of through‐fan entrenchment suggest reduced sediment supply but relatively high stream power during the last glacial maxima (LGM). The prolonged stream incision since the cessation of Qf2 deposition, with only minor depositional phases at 16·3 ± 2·1 and 4·5 ka, resulted from high water discharge and low sediment input during intensification of the SW monsoon and vegetation changes in the hinterland.  相似文献   

Retrieval of EVI from Oceansat 2 Data and Comparison with MODIS Derived EVI     

A. K. Mishra 《Journal of the Indian Society of Remote Sensing》2014,42(4):877-883

The vegetation index is derived using many remote sensing sensors. Vegetation Index is extensively used and remote sensing has become the primary data source. Number of vegetation indices (VIs) have been developed during the past decades in order to assess the state of vegetation qualitatively and quantitatively. Analysis of vegetation indices has been carried out by many investigators scaling from regional level to global level using the remote sensing data of varying spatial, temporal and radiometric resolutions. There are as many as 14 VIs in use. Globally operational algorithms for generation of NDVI have utilized digital counts, at sensor radiances, ‘normalized’ reflectance (top of the atmosphere), and more recently, partially atmospheric corrected (ozone absorption and molecular scattering) reflectance. Presently NDVI and EVI are standard MODIS data products which are widely used by the scientific community for environmental studies. The OCM sensor in Oceansat 2 is designed for ocean colour studies. The OCM sensor has been used for studying ocean phytoplankton, suspended sediments and aerosol optical depth by many investigators. In addition to its capability of studying the ocean surface, OCM sensor has also the potential to study the land surface features. In a past EVI has been retrieved using OCM sensor of Oceansat 1. However, there is slight change in the band width of Oceansat 2—OCM sensor compared with OCM of Oceansat 1 sensor. In the present paper an attempt has been made to derive EVI using Oceansat 2 OCM sensor and the results have been compared with MODIS data. The enhanced vegetation index (EVI) is calculated using the reflectance values obtained after removing molecular scattering and ozone absorption component from the total radiance detected by the sensor. The band-2, Band-3, band-6 and band-8 corresponding to Blue, Red and Infrared part of the visible spectrum have been used to determine EVI. The result shows that Oceansat 2 derived EVI and MODIS derived EVI are well correlated.  相似文献   

The plate coupling in the Tokai District,the Central Japan,inferred from the different data using triangular dislocation elements     

Tadafumi Ochi  Teruyuki Kato 《Tectonophysics》2011,497(1-4):15-22

We estimate interseismic coupling on the subducting plate interface in the Tokai area, central Japan, by inverting two geodetic data sets. The data record surface motion between March 1996 to May 2000; one represents vertical motion deduced from the leveling observations and the other is the horizontal velocity field deduced from GPS observations. In the inversion, we employed the analytical solutions of surface displacement due to a triangular dislocation element embedded in a homogeneous elastic half space in order to represent the curved plate interface. The vertical data show that the most strongly coupled portion of the subduction interface is concentrated beneath Omaezaki Cape, while the horizontal data show strongest coupling in the shallower region of the subducting plate interface. The estimated maximum value of coupling from the horizontal data is 40 mm/year, while that from vertical data is 25 mm/year.  相似文献