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71.
Highly heterogeneous Precambrian basement under the central Deccan Traps, India: Direct evidence from xenoliths in dykes 总被引:1,自引:0,他引:1
Ranjini Ray Anil D. Shukla Hetu C. Sheth Jyotiranjan S. Ray Raymond A. Duraiswami Loyc Vanderkluysen Chandramohan S. Rautela Jyotirmoy Mallik 《Gondwana Research》2008,13(3):375-385
Crustal or mantle xenoliths are not common in evolved, tholeiitic flood basalts that cover huge areas of the Precambrian shields. Yet, the occasional occurrences provide the most direct and unequivocal evidence on basement composition. Few xenolith occurrences are known from the Deccan Traps, India, and inferences about the Deccan basement have necessarily depended on geophysical studies and geochemistry of Deccan lavas and intrusions. Here, we report two basalt dykes (Rajmane and Talwade dykes) from the central Deccan Traps that are extremely rich in crustal xenoliths of great lithological variety (gneisses, quartzites, granite mylonite, felsic granulite, carbonate rock, tuff). Because the dykes are parallel and only 4 km apart, and only a few kilometres long, the xenoliths provide clear evidence for high small-scale lithological heterogeneity and strong tectonic deformation in the Precambrian Indian crust beneath. Measured 87Sr/86Sr ratios in the xenoliths range from 0.70935 (carbonate) to 0.78479 (granite mylonite). The Rajmane dyke sampled away from any of the xenoliths shows a present-day 87Sr/86Sr ratio of 0.70465 and initial (at 66 Ma) ratio of 0.70445. The dyke is subalkalic and fairly evolved (Mg No. = 44.1) and broadly similar in its Sr-isotopic and elemental composition to some of the lavas of the Mahabaleshwar Formation. The xenoliths are comparable lithologically and geochemically to basement rocks from the Archaean Dharwar craton forming much of southern India. As several lines of evidence suggest, the Dharwar craton may extend at least 350–400 km north under the Deccan lava cover. This is significant for Precambrian crustal evolution of India besides continental reconstructions. 相似文献
72.
Remote sensing and GIS application for land quality assessment for coffee growing areas of Karnataka 总被引:2,自引:0,他引:2
G. M. Shalima Devi K. S. Anil Kumar 《Journal of the Indian Society of Remote Sensing》2008,36(1):89-97
An assessment of land quality was carried out for coffee-growing areas of Karnataka using satellite image, toposheets and
soil studies. The investigation focused on monitoring soil processes that control the land quality using satellite data in
order to identify the land qualities that are ideal for coffee-growing; to identify the status of land qualities of coffee-growing
areas using satellite imageries, toposheets and soil resource maps and to characterise land quality using soil studies in
selected areas. The land quality was characterised using climatic data, terrain analysis and soil attributes. From the study
it was observed that coffee growing lands of Gabbugal and Kelagur have best land qualities and coffee-growing areas of Balur
and Nellikkad have moderate land qualities. Satellite image and aerial photographs were successfully used for monitoring the
land quality and its changes in these areas. For optimum utilization of available natural resources on a sustainable basis,
timely and reliable information on soils regarding their nature, extent and spatial distribution along with their potential
and limitations is very important. The efficiency and accuracy of data are improved when remote sensing data products such
as aerial photographs and satellite image are used. 相似文献
73.
The inelastic response of one-storey, asymmetric-plan systems to two excitations is presented and analysed with the objective of identifying the influence of system parameters: uncoupled lateral vibration period, uncoupled torsional-to-lateral frequency ratio, stiffness eccentricity, relative values of the strength and stiffness eccentricities, and yield factor. Furthermore, the influence of yielding on the response of asymmetric-plan systems is examined. In particular, we determine whether the well known relationship between the response of yielding and elastic single-degree-of-freedom (SDF) systems is also applicable to asymmetric-plan systems. 相似文献
74.
The Neo‐Tethyan subduction that operated before the India‐Asia collision resulted in an Andean‐type convergent margin in South Asia and was associated with extensive arc magmatism that formed the Transhimalayan batholiths. Magmatism in the Gangdese Batholith, the largest batholith exposed in the Lhasa terrane of southern Tibet, is considered to have lasted from the early Jurassic to Eocene. However, eastward correlation of the Gangdese Batholith is uncertain because it is truncated by the eastern Himalayan syntaxis. Here, we report new data from the Lohit Batholith, NE India, including: (i) zircon U‐Pb ages of five granitoids from ca. 148 to 96 Ma; and (ii) zircon Hf isotopes of these rocks that yield high and positive εHf(T) values. We argue that the Lohit Batholith is the eastward extension of the Gangdese Batholith, and can be correlated southward to the Wuntho‐Popa arc in West Burma, thus linking a prolonged Neo‐Tethyan magmatic arc system from southern Tibet to Southeast Asia. 相似文献
75.
M. C. Ramadevi S. Seetha Dipankar Bhattacharya B. T. Ravishankar N. Sitaramamurthy G. Meena M. Ramakrishna Sharma Ravi Kulkarni V. Chandra Babu Kumar Brajpal Singh Anand Jain Reena Yadav S. Vaishali B. N. Ashoka Anil Agarwal K. Balaji G. Nagesh Manoj Kumar Dhruti Ranjan Gaan Prashanth Kulshresta Pankaj Agarwal Mathew Sebastian A. Rajarajan D. Radhika Anuj Nandi V. Girish Vivek Kumar Agarwal Ankur Kushwaha Nirmal Kumar Iyer 《Experimental Astronomy》2017,44(1):11-23
Scanning Sky Monitor (SSM) onboard AstroSat is an Xray sky monitor in the soft X-ray band designed with a large field of view to detect and locate transient X-ray sources and alert the astronomical community about interesting phenomena in the X-ray sky. SSM comprises position sensitive proportional counters with 1D coded mask for imaging. There are three detector units mounted on a platform capable of rotation which helps covering about 50% of the sky in one full rotation. This paper discusses the elaborate details of the instrument and few immediate results from the instrument after launch. 相似文献
76.
The monsoon is a large‐scale feature of the tropical atmospheric circulation, affecting people and economies in the world's most densely populated regions. Future trends due to natural variability and human‐induced climate changes are uncertain. Palaeoclimate records can improve our understanding of monsoon dynamics and thereby reduce this uncertainty. Palaeoclimate records have revealed a dramatic decrease in the Asian summer monsoon since the early Holocene maximum 9 ka BP. Here we focus on the last 2 ka, where some records indicate an increasing trend in the summer monsoon. Analysing Globigerina bulloides upwelling records from the Arabian Sea, we find the weakest monsoon occurred 1500 a BP, with an increasing trend towards the present. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
77.
High-speed solar wind streams (HSWS) were identified for solar cycles 22 and 23 (up to 2004). Preliminarily, HSWS were classified
in three groups according to their continuous period of occurrence. In the declining phase of solar cycle 23, 2003 is found
to be anomalous, showing a very large number of HSWS events of long duration (> ten days). We have studied the effect of HSWS
on the cosmic-ray intensity as well as their relationship with geomagnetic disturbance index Ap on yearly, daily, and hourly bases. The yearly average of solar-wind speed was also found to be maximum in 2003. Being within
the declining phase of solar activity, the occurrence of solar flares in 2003 is quite low. In particular during HSWS, no
solar flares have been observed. Associations with cosmic-ray changes do not support the notion that the HSWS are usually
effective in producing significant cosmic-ray decreases. Out of 12 HSWS events observed during the period 2002 (December)
to 2003, four events of significant cosmic-ray decreases at all the stations have been selected for further analysis. The
cosmic-ray intensity has been found to decrease during the first phase of the event (first five days of HSWS) at all three
neutron-monitor stations situated at different latitudes with different cutoff rigidities. The rigidity spectra of observed
decreases in cosmic-ray intensity for these four cases have been found to be significantly different than that of Fds (Forbush
decrease). In two cases the spectra are softer, whereas in the other two they are harder than that of Fds. However, if the
average of all four events is considered together then the spectra of the decrease in cosmic rays during HSWS exactly match
that of Fds. Such a result implies that initially individual events should be considered, instead of combining them together,
as was done earlier. The Ap index is also found to generally increase in the first phase of the event. However, the four events selected on the basis
of cosmic-ray decrease are not always associated with enhanced values of the Ap index. As such, the significance of our study is that further detailed investigations for much longer periods and on an event-by-event
basis is required to understand the effect of coronal-hole-associated HSWS. 相似文献
78.
Anil Sood B. U. Choudhury S. S. Ray S. K. Jalota P. K. Sharma Shushma Panigrahy 《Journal of the Indian Society of Remote Sensing》2009,37(3):483-491
A remote sensing-based approach was applied to study the impact of changes in cropping system on the exploitation of water
resources in two districts namely Ludhiana in central Punjab and Muktsar in South-Western Punjab. Rice-wheat remained dominant
rotation in Ludhiana while cottonwheat rotation was replaced partially by rice-wheat in Muktsar within a span of over five
years (1998–99 to 2003–04). The solo rice-wheat system in Ludhiana district has resulted in large-scale ground water exploitation
as is evident from the faster decline in water table (up to 0.9m year−1) and higher tube-wells density (440 per 1000 ha). As a result, nearly 60 per cent of the total area of Ludhiana district
has the water table depth greater than 10m and in some blocks, it has reached to a depth of 22 m. In Muktsar district, corresponding
rise in water table is 0.2m per year and tube well density is 114 per 1000 ha. Irrigation water associated with paddy cultivation
in Ludhiana and adjoining areas moves laterally through the buried paleo-channels of Sutlaj in the deeper soil profile and
gets accumulated in the basin lands of Muktsar and adjoining areas and causes an extra water flux and subsequent rise in water
table, recorded at 3 to 7m depth. To minimize the hydrological imbalance of the state, it is suggested to diversify some of
the area in the central districts from irrigation water intensive rice-wheat system to less water intensive cropping system. 相似文献
79.
Anirudh Pradhan Anil Kumar Yadav R. P. Singh Vipin Kumar Singh 《Astrophysics and Space Science》2007,312(3-4):145-150
A new class of solutions of Einstein field equations has been investigated for inhomogeneous cylindrically symmetric space-time with string source. To get the deterministic solution, it has been assumed that the expansion (θ) in the model is proportional to the eigen value σ 1 1 of the shear tensor σ i j . Certain physical and geometric properties of the models are also discussed. 相似文献
80.
Anil Kumar Vijayan Takashi Yoshikawa Shigeki Watanabe Hiroaki Sasaki Kazuhiko Matsumoto Sei-Ichi Saito Shigenobu Takeda Ken Furuya 《Journal of Oceanography》2009,65(2):245-258
Regional variations in the contribution of non-photosynthetic pigments (ā
np*) to the total light absorption of phytoplankton (ā
ph*) and its influence on the maximum quantum yield of photosynthesis (φ
m) were investigated. In the western equatorial Pacific, the surface ā
np* : ā
ph* ratio was higher in the western warm pool than that in the upwelling region. This difference appears to be attributable to
severe nitrate depletion and higher percentage of prokaryotes, which can accumulate very high concentrations of zeaxanthin
in the western warm pool. In the subarctic North Pacific, the ā
np* : ā
ph* ratio was expected to be higher in the Alaskan Gyre where the thermocline is sharper and iron limitation may possibly be
more severe than in the Western Subarctic Gyre. However, the ratio was actually higher in the Western Subarctic Gyre, contradictory
to our expectations. This east-west variation appears to be attributable to changes in the taxonomic composition; cyanobacteria
were more abundant in the Western Subarctic Gyre. The values of ā
np* : ā
ph* and its vertical variations were relatively small in the subarctic North Pacific compared to those in the western equatorial
Pacific. These inter-regional variations appear to be attributable to the lower solar radiation intensity, smaller percentage
of cyanobacteria, and relatively strong vertical mixing in the subarctic North Pacific. The spatial variations in ā
np* : ā
ph* significantly influence φ
m. In comparison with φ
m based on the total light absorption (φ
m ph), the values corrected for the contribution of non-photosynthetic pigments (φ
m ps) showed an increase in both the western equatorial Pacific and the subarctic North Pacific. 相似文献