Formation of decollement upwarps during thrusting     

Ashok Kumar Dubey 《地学学报》2004,16(3):91-94

Geometric and kinematic models reveal that rotation of layers during thrusting or development of drag folds produced by movement along listric thrust faults results in the formation of dilation space at the junction of the thrust ramp with the basal decollement. This is accompanied by upwarping of the basement to occupy the available space thereby producing an antiformal structure, which restricts the thrust displacement. The structure is termed a decollement upwarp and examples are cited from the foothill belt of the Himalaya.  相似文献   

Characteristics of spectral aerosol optical depths over India during ICARB     

S. Naseema Beegum  K. Krishna Moorthy  Vijayakumar S. Nair  S. Suresh Babu  S. K. Satheesh  V. Vinoj  R. Ramakrishna Reddy  K. Rama Gopal  K. V. S. Badarinath  K. Niranjan  Santosh Kumar Pandey  M. Behera  A. Jeyaram  P. K. Bhuyan  M. M. Gogoi  Sacchidanand Singh  P. Pant  U. C. Dumka  Yogesh Kant  J. C. Kuniyal  Darshan Singh 《Journal of Earth System Science》2008,117(1):303-313

Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived Ångström parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The Ångström coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from tshe adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the Ångström exponent (α) remained significantly lower (～1) over the Arabian Sea compared to Bay of Bengal (BoB) (～1.4) as revealed by the data respectively from Minicoy and Port Blair. Occurrences of higher values of α, showing dominance of accumulation mode aerosols, over BoB are associated well with the advection, above the boundary layer, of fine particles from the east Asian region during March and April. The change in the airmass to marine in May results in a rapid decrease in α over the BoB.  相似文献   

Late Miocene movement within the Himalayan Main Central Thrust shear zone, Sikkim, north-east India   总被引：7，自引：0，他引：7  

E. J. Catlos  C. S. Dubey  T. M. Harrison  M. A. Edwards 《Journal of Metamorphic Geology》2004,22(3):207-226

In the Sikkim region of north‐east India, the Main Central Thrust (MCT) juxtaposes high‐grade gneisses of the Greater Himalayan Crystallines over lower‐grade slates, phyllites and schists of the Lesser Himalaya Formation. Inverted metamorphism characterizes rocks that immediately underlie the thrust, and the large‐scale South Tibet Detachment System (STDS) bounds the northern side of the Greater Himalayan Crystallines. In situ Th–Pb monazite ages indicate that the MCT shear zone in the Sikkim region was active at c. 22, 14–15 and 12–10 Ma, whereas zircon and monazite ages from a slightly deformed horizon of a High Himalayan leucogranite within the STDS suggest normal slip activity at c. 17 and 14–15 Ma. Although average monazite ages decrease towards structurally lower levels of the MCT shear zone, individual results do not follow a progressive younging pattern. Lesser Himalaya sample KBP1062A records monazite crystallization from 11.5 ± 0.2 to 12.2 ± 0.1 Ma and peak conditions of 610 ± 25 °C and 7.5 ± 0.5 kbar, whereas, in the MCT shear zone rock CHG14103, monazite crystallized from 13.8 ± 0.5 to 11.9 ± 0.3 Ma at lower grade conditions of 525 ± 25 °C and 6 ± 1 kbar. The P–T–t results indicate that the shear zone experienced a complicated slip history, and have implications for the understanding of mid‐crustal extrusion and the role of out‐of‐sequence thrusts in convergent plate tectonic settings.  相似文献   

Geotechnical Susceptibility Constraints on Seismicity of Karewa Group and Its Implication in Quaternary Earthquakes Around Kashmir Valley,India     

R. K. Dubey  Javid Ahmad Dar 《Geotechnical and Geological Engineering》2015,33(3):609-620

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An insight into subterranean flow proposition around Alleppey mudbank coastal sector,Kerala, India: inferences from the subsurface profiles of Ground Penetrating Radar     

V. J. Loveson  R. Dubey  Dinesh Kumar  R. Nigam  S. W. A. Naqvi 《Environmental Earth Sciences》2016,75(20):1361

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Provenance and Palaeoweathering Attributes of Proterozoic Rock Formations from the Son Valley,Central India     

R. K. Dubey  Ravi Shankar 《Journal of the Geological Society of India》2018,91(3):307-314

The characteristics of source rocks and weathering of Palaeoproterozoic phyllitic rock of Mahakoshal Group and Mesoproterozoic shales and siliciclastics of Vindhyan Supergroup exposed in Son Valley, Central India have been investigated by analyzing their chemical compositions. The investigations pertaining to the relationship between major-elements were carried out along Parshoi, Chitrangi, and Markundi areas of Son valley, Central, India. The studied rock strata have been classified into three categories namely phyllitic rocks, shales and sandstone.The A-CN-K ternary diagram, CIW, CIA, MIA, and ICV values indicate about the similar provenance or source rocks subjected to severe chemical weathering, under dry and hot-humid climates in a basic and acidic environment with changing lower to higher PCO₂ of continental flora. Various geochemical discriminantts diagrams, elemental ratios suggest that rocks are derived from post-Archaean-Proterozoic igneous source. The igneous source was mainly granite with a minor contribution of granodioritic rock, in a passive margin setting. The sediments responsible for formation of shale and sandstones were most likely deposited in the interglacial period in between the Mesoproterozoic and Neoproterozoic glacial times. Compositionally the sandstones is distinctive of cratonic environments with their passive continental margin setting. However, the phyllities of Mahakoshal Group suggests their formation under lower weathering conditions in dry climatic conditions which were operating on more intermediate to basic igneous rocks with abundance of mafic minerals.  相似文献   

Morphotectonic Appraisal of Yamuna River Basin in Headwater Region: A Relative Active Tectonics Purview     

R. K. Dubey  Gyan Prakash Satyam 《Journal of the Geological Society of India》2018,92(3):346-356

In the present paper integrated appraisals of landform evolution and their geomorphic features, drainage networks across the upper part of Yamuna river basin have been attempted by using various geomorphic indices such as watershed, drainage density (D), drainage texture, stream-gradient index (SL), hypsometric integral (HI), drainage basin asymmetry (AF), mountain front sinuosity (Smf), sinuosity index (SI), valley floor height and width ratio (Vf) and data of historical earthquakes in characterizing the basin in view of relative index of active tectonics (RIAT) on DEM in geographic information systems (GIS) environment to assess the influence of recent tectonics on geomorphologic growth of the basin.The substantiated RIAT classes through some field observations and corroborated by recent seismicity reveal the recent activation of Yamuna tear faults in the basin with delineation of four RIAT classes such as class-1 (inactive 9.8% of the area), class-2 (low active; 16.40% of the area), class-3 (moderately active; 42.38% of the area) and class-4 (very active; 31.62%). The results suggest that the Himalayan frontal thrust (HFT) and Yamuna tear (YT) located in the basin is morphogenic in nature and got activated several times as evidenced by number of seismic activities in the basin and adjoining regions. The incision, and sharp turning of rivers, crenulations and warping of cross beddings/laminations and silt/clay beds and lenses, megascopic and mesoscopic faulting in sediment sequences suggest a very active nature of the HFT and YT till date in association with three prolific microseismogenic weak zones These active discontinuities appear to support the formation and development of different deformational features in sediment sequences which may be indirectly related to subduction and underthrusting of Indian plate under Eurasian plate below the Himalayan mountain chain.  相似文献   

Recession of Milam Glacier,Kumaun Himalaya,Observed via Lichenometric Dating of Moraines     

Kapil Bisht  Yogesh Joshi  Shashi Upadhyay  Poonam Metha 《Journal of the Geological Society of India》2018,92(2):173-176

Glaciers being very sensitive to climate change have been identified as one of the best indicators of climate change and evidences have proved that most of the Himalayan glaciers have receded with an increased rate during the recent past under the influence of global warming. Lichenometric study was carried out on the moraines of Milam glacier (located in Pithoragarh district of Uttarakhand) with the help of lichen species Dimelaena oreina having an average annual growth rate of 1.31 mm. The study revealed that Milam glacier has receded 1450 m in last 69.37 years with an average recession rate of 20.90 m/year. Since lichenometric studies are cost effective and ecofriendly in comparison to carbon dating, satellite and remote sensing based studies and also reliable, hence, it should be promoted in Himalaya which is an abode of glaciers.  相似文献   

Variations of trace gases over the Bay of Bengal during the summer monsoon     

I A Girach  Narendra Ojha  Prabha R Nair  Yogesh K Tiwari  K Ravi Kumar 《Journal of Earth System Science》2018,127(1):15

In situ measurements of near-surface ozone (\(\hbox {O}_{3})\), carbon monoxide (CO), and methane (\(\hbox {CH}_{4})\) were carried out over the Bay of Bengal (BoB) as a part of the Continental Tropical Convergence Zone (CTCZ) campaign during the summer monsoon season of 2009. \(\hbox {O}_{3}\), CO and \(\hbox {CH}_{4}\) mixing ratios varied in the ranges of 8–54 ppbv, 50–200 ppbv and 1.57–2.15 ppmv, respectively during 16 July–17 August 2009. The spatial distribution of mean tropospheric \(\hbox {O}_{3}\) from satellite retrievals is found to be similar to that in surface \(\hbox {O}_{3}\) observations, with higher levels over coastal and northern BoB as compared to central BoB. The comparison of in situ measurements with the Monitoring Atmospheric Composition & Climate (MACC) global reanalysis shows that MACC simulations reproduce the observations with small mean biases of 1.6 ppbv, –2.6 ppbv and 0.07 ppmv for \(\hbox {O}_{3}\), CO and \(\hbox {CH}_{4}\), respectively. The analysis of diurnal variation of \(\hbox {O}_{3}\) based on observations and the simulations from Weather Research and Forecasting coupled with Chemistry (WRF-Chem) at a stationary point over the BoB did not show a net photochemical build up during daytime. Satellite retrievals show limitations in capturing \(\hbox {CH}_{4}\) variations as measured by in situ sample analysis highlighting the need of more shipborne in situ measurements of trace gases over this region during monsoon.  相似文献   

Development of a High Magnification Enlarger     

R P Dubey  N D Christian  K D Mallick 《Journal of the Indian Society of Remote Sensing》1991,19(4):277-286

Visual interpretation forms the basis for many operational applications of remote sensing. Suitable enlargement of remotely sensed data by optical projection is a basic requirement for visual interpretation. High Magnification Enlarger (HME) is a versatile interpretation aid developed for achieving wide-ranging scale transfer and variable-magnification display from a standard 24 cm format transparency. It operates on the principle of optical projection and is configured as a vertical column mounted unit. Low-distortion, high-quality enlarging lenses coupled with accuracy of alignment ensure accurate reproduction of the scale and the finer details from the input image transparency. Maximum user convenience is achieved by motorization of various controls.  相似文献