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Understanding deformation mechanisms in Himalayan rocks is a challenging proposition due to the complex nature of the deformed
rocks and their genesis. Crustal deformation in the Himalayan thrust belt typically occurs in elastico-frictional (EF) or
quasi-plastic (QP) regimes at depths controlled mainly by regional strain-rate and geothermal gradient. However, material
property, grain-size and their progressive changes during deformation are also important controlling factors. We present evidence
of EF deformation from Gondwana rocks developed during the emplacement of one of the frontal horses (Jorthang horse) in the
Lesser Himalayan Duplex (LHD) structure associated with Lesser Himalayan rocks in the footwall of the Ramgarh thrust in the
Rangit window near Jorthang in the Sikkim Himalaya. The rocks in the horse exhibit systematic changes in microand meso-structures
from an undeformed protolith to cataclasite suggesting that it was emplaced under elastico-frictional conditions. Meso- to
micro-scale shear fractures are seen developed in Gondwana sandstone and slate while intercalated fine-grained shale-coal-carbonates
are deformed by cataclastic flow suggesting that material property and grain-size have played an important role in the deformation
of the Jorthang horse. In contrast, the hanging wall schists and quartzites of the Ramgarh thrust exhibit quasi-plastic deformation
structures. This suggests that the Jorthang horse was emplaced under shallower crustal conditions than the antiformally folded
Ramgarh thrust sheet even though the Ramgarh sheet presently overlies the Jorthang horse. 相似文献
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Summary The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces
an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with
the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared
utilising all available upper air data (1977–1986) for each category of the SW monsoon epochs identified by the PCA. These
sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal
components (PCs).
A well defined east-west oriented trough system, extending from about 28° N Latitude/65° E Longitude to 20° N Latitude/90° E
Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to
PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts
associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the
lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC
IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features,
such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric
anticyclones to the south.
The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition,
synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner
by such PCA.
Received July 18, 1997 Revised April 30, 1999 相似文献
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Tapas R. Martha Priyom Roy Ritwik Mazumdar K. Babu Govindharaj K. Vinod Kumar 《Landslides》2017,14(2):697-704
High magnitude earthquakes trigger numerous landslides and their occurrences are mainly controlled by terrain parameters. We created an inventory of 15,551 landslides with a total area of 90.2 km2 triggered by the 2015 Mw 7.8 (Gorkha) and Mw 7.3 (Dolakha) earthquakes in Nepal, through interpretation of very high resolution satellite images (e.g. WorldView, Pleiades, Cartosat-1 and 2, Resourcesat-2). Our spatial analysis of landslide occurrences with ground acceleration, slope, lithology and surface defomation indicated ubiquitous control of steep slope on landslides with ground acceleration as the trigger. Spatial distribution of landslides shows increasing frequency away from the Gorkha earthquake epicentre up to 130 km towards east, dropping sharply thereafter, which is an abnormal phenomenon of coseismic landslides. Landslides are laterally concentrated in three zones which matches well with the seismic rupture evolution of Gorkha earthquake, as reported through teleseismic measurements. 相似文献
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Soumya Mazumdar Ludovico Pinzari Nasser Bagheri Paul Konings Federico Girosi Ian McRae 《Transactions in GIS》2017,21(6):1379-1390
Primary Care is fundamental to a well‐functioning health system. Various geographical small areas including specialized geographies such as Primary Care Service Areas (PCSAs) are used to measure primary care relevant outcomes and services, or to target interventions. PCSAs are small areas, the majority of patients resident in which obtain their primary care services from within the geography. The extent of this self‐sufficiency of use is measured by the Localization Index (LI). PCSAs have been built in the US, Australia and Switzerland using an allocation algorithm, which, while simple and easy to implement, may require the use of various ad‐hoc parameters. In this article we propose an optimization based approach to creating PCSAs, ‐ an approach which has previously been used to generate labour flow regions in Ireland. The approach is data driven, thus requiring a minimal number of ad‐hoc parameters. We compared the resulting PCSAs (or `rPCSAs') with PCSAs generated using the traditional allocation algorithm. We found that rPCSAs were generally larger, offered greater LIs and reflected patient travel patterns better than traditional PCSAs. Accounting for the larger size of rPCSAs showed that rPCSAs offered better LIs than similar sized traditional PCSAs. 相似文献
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Saurodeep Chatterjee Supriya Mondal Debesh Gain Tapan Kr Baidya Dipanjan Mazumdar 《Journal of Earth System Science》2018,127(6):89
The present work deals with the generations of Fe–Ti oxides and the variation in magnetic fabrics of the Dalma lavas and associated meta-sediments of the Singhbhum Mobile Belt (SMB) in relation to tectonics. Generations of the Fe–Ti oxides are different in meta-sediments and volcanics, the former preserving upliftment related oxidised grains, whereas the latter contains fresh grains prompting towards their upliftment due to plume upwelling before the volcanic eruption. In the meta-sediments, the magnetic fabric has close accordance with \(\hbox {D}_{2}/\hbox {F}_{2}\) event revealing synchronous development with \(\hbox {D}_{2}\). The Dalma thrust developed a sudden break in the homogeneity of the magnetic fabrics of the rocks where the magnetic foliations are all parallel to the Dalma thrust. This also causes \(P_{j}\) to be highest in this sector. The magnetic fabrics of volcanic rocks are different from the meta-sediments and record no signature of deformation. The pattern of distribution of susceptibility axes are in accordance with the subaerial lava flows. However, their \(\hbox {K}_{1}\) and \(\hbox {K}_{2}\) dispersed throughout the periphery with \(\hbox {K}_{3}\) clustering at the centre. This infers towards the fact that although the volcanism took place in a subaerial environment, calm aqueous environment was locally present where the oblate grains settled on the eruption surface with their \(\hbox {K}_{3}\) vertical. 相似文献
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On the Late Neoproterozoic-Early Cambrian Transition Events in Parts of East Gondwanaland 总被引：1，自引：0，他引：1
The East Gondwanaland evolved as a result of break up of the Rodinia supercontinent. The late Neoproterozoic-Early Cambrian geochemical events documented in the rocks of the East Gondwanaland, and Siberia suggest variations in the C, S, and Sr isotopic compositions of the contemporary seawater, and systematic distribution of phosphorite, and evaporite deposits. The geochemical records in the Peninsular India, Himalaya, South China, Iran, and Oman regions have been discussed, and used for establishing late Neoproterozoic links of these widely separated sedimentary basins. 相似文献
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Vol’vach L. N. Vol’vach A.E. Larionov M.G. MacLeod G. C. van den Heever S. P. Wolak P. Olech M. Ipatov A.V. Ivanov D.V. Mikhailov A. G. Mel’nikov A.E. Menten K. Belloche A. Weiss A. Mazumdar P. Schuller F. 《Astronomy Reports》2019,63(1):49-65
Astronomy Reports - The results of long-term monitoring of the Galactic maser source IRAS 18316–0602 (G25.65+1.05) in the water-vapor line at frequency f = 22.235 GHz (616–523... 相似文献
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T. Ramprasad P. Dewangan M.V. Ramana A. Mazumdar S.M. Karisiddaiah E.R. Ramya G. Sriram 《Marine and Petroleum Geology》2011,28(10):1806-1816
The Krishna–Godavari (KG) offshore basin is one of the promising petroliferous basins of the eastern continental margin of India. Drilling in this basin proved the presence of gas hydrate deposits in the shallow marine sediments beyond 750 m water depths, and provided lithologic and stratigraphic information. We obtained multibeam swath bathymetry covering an area of about 4500 km2 in water depths of 280–1800 m and about 1260 line km of high resolution seismic (HRS) records. The general lithology of midslope deposits is comprised of nannofossil-rich clay, nannofossil-bearing clay and foraminifera-bearing clay. The HRS records and bathymetry reveal evidence of slumping and sliding of the upper and midslope sediments, which result in mass transport deposits (MTD) in the northwestern part of the study area. These deposits exhibit 3–9.5 km widths and extend 10–13 km offshore. The boundaries of the MTDs are often demarcated by sharp truncation of finely layered sediments (FLS) and the MTDs are characterized by acoustically transparent zones in the HRS data. Average thickness of recent MTDs varies with depth, i.e., in the upper slope, the thickness is about 45 m, while in the lower slope it is about 60 m, and in deeper offshore locations they attain a maximum thickness of about 90 m. A direct indication for slumping and mass transportation of deposits is provided by the age reversal in 14C AMS dates observed in a sediment core located in the midslope region. Seismic profiling signatures provide indications of fluid/gas movement. We propose that the presence of steep topographic gradients, high sedimentation rates, a regional fault system, diapirism, fluid/gas movement, and neotectonic activity may have facilitated the slumping/sliding of the upper slope sediments in the KG offshore basin. 相似文献