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Sukanta Kumar Das Sanjib Kumar Deb C. M. Kishtawal P. K. Pal 《Theoretical and Applied Climatology》2012,109(1-2):81-94
Seasonal prediction of Indian Summer Monsoon (ISM) has been attempted for the current year 2011 using Community Atmosphere Model (CAM) developed at the National Centre for Atmospheric Research (NCAR). First, 30?years of model climatology starting from 1981 to 2010 has been generated to capture the variability of ISM over the Indian region using 30 seasonal simulations. The simulated model climatology has been validated with different sets of observed climatology, and it was observed that the simulated climatological rainfall is affected by model bias. Subsequently, a bias correction procedure using the Tropical Rainfall Measuring Mission (TRMM) 3B43 rainfall has been proposed. The bias-corrected rainfall climatology shows both spatial and temporal variability of ISM satisfactorily. Further, four sets of 10-member ensemble simulations of ISM 2009 and 2010 have been performed in hindcast mode using observed sea surface temperature (SST) and persistence of April SST anomaly, and it has been found that the bias-corrected model rainfall captures the seasonal variability of ISM reasonably well with some discrepancies in these two contrasting monsoon years. With this positive background, the seasonal prediction of ISM 2011 has been carried out in forecast mode with the assumption of persistence of May SST anomaly from June through September 2011. The model assessment shows an 11% deficiency in All-India Rainfall (AIR) of ISM 2011. In particular, the monthly accumulated rains are predicted to be 101% (17.6?cm), 86% (24.3?cm), 83% (21.0?cm) and 95% (15.5?cm) of normal AIR for the months of June, July, August and September, respectively. 相似文献
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The Dergaon (H5) chondrite: Fall,classification, petrological and chemical characteristics,cosmogenic effects,and noble gas records 总被引：1，自引：0，他引：1
P. N. SHUKLA A. D. SHUKLA V. K. RAI S. V. S. MURTY N. BHANDARI J. N. GOSWAMI A. C. MAZUMDAR P. PHUKON K. DUORAH R. E. GREENWOOD I. A. FRANCHI 《Meteoritics & planetary science》2005,40(4):627-637
Abstract— A multiple fall of a stony meteorite occurred near the town of Dergaon in Assam, India, on March 2, 2001. Several fragments weighing <2 kg and a single large fragment weighing ～10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ～340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. 26Al and 22Na activities as well as the 22Na/26Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low 60Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ～106 cm?2 in samples from the largest fragment to approximately (4–9) × 105 cm?2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ～20 cm for the Dergaon meteorite. 相似文献
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Sukanta Roy Labani Ray Anurup Bhattacharya R. Srinivasan 《International Journal of Earth Sciences》2008,97(2):245-256
The Late Archaean Closepet Granite batholith in south India is exposed at different crustal levels grading from greenschist
facies in the north through amphibolite and granulite facies in the south along a ∼400 km long segment in the Dharwar craton.
Two areas, Pavagada and Magadi, located in the Main Mass of the batholith, best represent the granitoid of the greenschist
and amphibolite facies crustal levels respectively. Heat flow estimates of 38 mW m−2 from Pavagada and 25 mW m−2 from Magadi have been obtained through measurements in deep (430 and 445 m) and carefully sited boreholes. Measurements made
in four boreholes of opportunity in Pavagada area yield a mean heat flow of 39 ± 4 (s.d.) mW m−2, which is in good agreement with the estimate from deep borehole. The study, therefore, demonstrates a clear-cut heat flow
variation concomitant with the crustal levels exposed in the two areas. The mean heat production estimates for the greenschist
facies and amphibolite facies layers constituting the Main Mass of the batholith are 2.9 and 1.8 μW m−3, respectively. The enhanced heat flow in the Pavagada area is consistent with the occurrence of a radioelement-enriched 2-km-thick
greenschist facies layer granitoid overlying the granitoid of the amphibolite facies layer which is twice as thick as represented
in the Magadi area. The crustal heat production models indicate similar mantle heat flow estimates in the range 12–14 mW m−2, consistent with the other parts of the greenstone-granite-gneiss terrain of the Dharwar craton. 相似文献
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The Abor volcanics of the continental flood basalt affinity are extensively exposed in different parts of the Siang valley. These are associated with Yinkiong Group of rocks of Paleocene–Eocene age and represent syn-sedimentary volcanism in a rift setting. Subsequent folding and thrusting of the Siyom and Rikor sequences above the Yinkiong Group of rocks represent changes from syn-to-post collisional brittle-ductile tectonic episodes. Mylonitic Abor volcanics in the thrust contacts are studied at several locations in the north and south of Puging in the Siang valley. Both the Abor volcanics and associated Rikor and Yinkiong Group of rocks preserve meso to micro-scale fabric asymmetries indicating that the thrust contacts are shear zones of brittle-ductile nature containing mylonitic textures of high shear strain. Two distinct hitherto unrecognised shear zones in the north and south of Puging are named as North Puging Shear Zone (NPSZ) and South Puging Shear Zone (SPSZ). The kinematic indicators along the thrust contact indicate oblique slip thrusting of the Rikor and Siyom thrust sheets above the Yinkiong Group of rocks. This paper provides field evidence proving that the compression due the Burmese plate made oblique slip thrusting and zones of mylonitised volcanics possible and associated metasediments were formed. The kinematic indicators in the NPSZ and SPSZ respectively indicate top-to-SSE and top-to-NNW sense of shears. 相似文献
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Mildly deformed granitoids exposed around Bilgi in the northernmost part of the eastern Dharwar craton are divided into two
groups viz. granodiorites and monzogranites. The granodiorites contain microgranular enclaves and amphibolite xenoliths, and
show low-Al TTG affinity with high SiO2 (71–74 %), Na2O, Y and Sr/Y, moderate to moderately high Mg#, Cr and Ni, low to moderate LILE, and low Nb and Ta. However, compared to similar
TTGs from different cratons the Bilgi granodiorites have distinctly higher K2O, K2O/Na2O, Rb and lower REE and Th. The amphibolite xenoliths are characterized by variable enrichment of K2O, Rb, Ba and Th and depletion of Ti, Zr and P compared to MORB. The microgranular enclaves are quartz diorite to granodiorite
in composition with high Mg, Ni and Cr, and compared to MORB, are enriched in LILE and depleted in Ti and Y. The monzogranites,
compared to the granodiorites, display higher SiO2, K2O and Rb with lower Mg#, although still maintaining the high Na2O, Ni and Cr and low REE character.
The Bilgi granodiorites are explained as transitional TTGs late synkinematic with respect to regional deformation. Geochemical
signatures and regional geological set up suggest that they are probably derived from partial melting of a highly depleted
slab material (metabasalt) followed by variable contamination or assimilation of intermediate crustal rocks in a subduction
zone set up. Late stage fluid activity on the granodioritic magma is probably responsible for the generation of monzogranites.
The amphibolite xenoliths predate the granodiorites and possibly represent fragments of a schist belt carried away by the
granitic magma. They are probably island arc basalt derived from mantle source that has been metasomatized by slab-derived
fluids. The microgranular enclaves are coeval with the Bilgi granodiorites and also likely to be island arc magmas derived
from mantle variably enriched in slab-derived and within-plate components. 相似文献
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TTG(Tonalite-Trondhjemite-Granodiorite) gneisses,a major component of Precambrian continental crust,play a significant role in understanding the process and mechanism of the crustal evolution in the early periods of the Earth. In terms of field occurrence,there are two kinds of Archean TTGs in the NCC(North China Craton): intercalated and non-intercalated TTGs. In this contribution,we make a comprehensive comparison of these two types of TTGs from the typical areas(Lushan and Hengshan) in the NCC with an aim to constrain their petrogenesis. The results suggest that they have similar mineral assemblages of Pl + Qtz + Bt ± Amp ± Kfs but different field appearances and geochemical compositions,thus probably reflecting different source materials and tectonic settings. Differences in the contents of characteristic elements,such as Sr,REE and HFSE,suggest that the nonintercalated TTGs in Hengshan were generated at deeper levels than those of intercalated TTGs in Lushan. Constraints from element contents and geochemical modeling results are consistent with derivation from dual sources involving both garnet amphibolite and rutile-bearing eclogite residues for the non-intercalated TTGs in Hengshan,whereas the compositions of intercalated TTGs in Lushan indicate that they were formed by partial melting with amphibolite to garnet-amphibolite residues. Moreover,accumulation of plagioclase is also required in the petrogenesis of intercalated TTGs in Lushan,at least for part of them. In addition,the non-intercalated TTGs in Hengshan display distinctly higher Mg O,Mg#,Cr and Ni values and lower SiO_2 average contents compared to the intercalated TTGs in Lushan. These features suggest that the former magma,at least a part,might have interacted with the mantle wedge during ascent. Considering all the above factors and in combination with the whole-rock Nd and zircon Hf isotopic data,it is suggested that the non-intercalated TTGs in Hengshan were produced by partial melting of subducted slab contaminated by the overlying mantle wedge at deeper levels and high pressures,whereas the intercalated TTGs in Lushan were generated by melting of the thickened lower crust at lower pressures and shallower depths. The tectonic settings of the two types of TTGs shed new light on the growth of the NCC. 相似文献