Crustal trajectory of sapphirine-bearing granulites from Ganguvarpatti, South India: evidence for an isothermal decompression path   总被引：7，自引：0，他引：7  

A. MOHAN  B. F. WINDLEY 《Journal of Metamorphic Geology》1993,11(6):867-878

Abstract Ganguvarpatti is part of a Precambrian terrane characterized by granulite facies rocks, including charnockites, mafic granulites, sapphirine-bearing granulites, leptynites and gneisses. A sequence of reactions deduced from the multiphase reaction textures provide information on the metamorphic history of this area, as they formed in response to decompression during uplift. Geothermobarometry and constraints from reaction textures define a segment of a P–T path traversed by the granulites of Ganguvarpatti. Near-peak metamorphic conditions of c. 800°C and 8 kbar were succeeded by a symplectitic stage at a significantly lower pressure ( c. 700°C and 4.5 kbar), documenting a nearly isothermal decompression P–T path and rapid uplift ( c. 12 km) followed by cooling. The presence of many fluid inclusions of extremely low density in the charnockites is consistent with a nearly isothermal uplift path. Attainment of a maximum pressure of c. 8 kbar indicates c. 27 km depth of burial during metamorphism. This would imply a total crustal thickness of c. 65–70 km at 2.6–2.5 Ga. Such a profound crustal thickness and a clockwise decompressive P–T path is interpreted as a consequence of tectonic thickening of crust, accomplished by collision tectonics of the southern granulite terrane against the Dharwar craton along the Palghat–Cauvery shear zone via northward subduction.  相似文献   

Concrete evidence & geographically weighted regression: A regional analysis of wealth and the land cover in Massachusetts     

Yelena Ogneva-Himmelberger  Hamil Pearsall  Rahul Rakshit   《Applied geography (Sevenoaks, England)》2009,29(4):478-487

Several studies indicate that there is a positive relationship between green vegetation land cover and wealthy socio-economic conditions in urban areas. The purpose of this research is to test for and explore spatial variation in the relationship between socio-economic and green vegetation land cover across urban, suburban, and rural areas, using geographically weighted regression (GWR). The analysis was conducted at the census block group level for Massachusetts, using Census 2000 data and impervious surface data at 1-m resolution. To explore regional variations in the relationship, four scenarios were generated by regressing each of the following socio-economic variables – median household income, percentage of poverty, percentage of minority population, and median home value – against two environmental variables – percent of impervious surface and population density. GWR results show that there is a considerable spatial variation in the character and the strength of the relationship for each model. There are two main conclusions in this study. First, the impervious surface is generally a strong predictor of the level of wealth as measured by four variables included in the analysis, at the scale of census block group; however, the strength of the relationship varies geographically. Second, GWR, not ordinary least squares technique, should be used for regional scale spatial analysis because it is able to account for local effects and shows geographical variation in the strength of the relationship.  相似文献   

Selection of Test and Reference Areas for the Indian Deepsea Environment Experiment (INDEX)     

Rahul Sharma  B. Nagender Nath 《Marine Georesources & Geotechnology》2000,18(3):177-187

The Indian Deepsea Environment Experiment (INDEX) was conducted in the Central Indian Ocean Basin, to assess the effects of a simulated disturbance on the marine ecosystem and to collect data to predict the effects of large-scale mining. To select the Test and Reference areas for benthic disturbance, detailed studies were carried out for a better understanding of the topgraphic undulations and nodule distribution in five preselected areas of 10 ×10 nautical miles each. Flat topography was one of the important considerations for selection of the areas, because this would allow further dispersion of sediment plume and offer easier maneuverability of the benthic disturber. Relatively low nodule abundances were also preferred, to prevent clogging of the suction device used for resuspension of sediment. On the basis of morphological analysis and nodule distribution, two areas, T1 and A1, were selected as the best suited pair for the disturbance and monitoring experiment.  相似文献   

Prospect for UV observations from the Moon     

Margarita Safonova  Joice Mathew  Rekhesh Mohan  A. G. Sreejith  Jayant Murthy  Noah Brosch  Norbert Kappelmann  Arpit Sharma  Rahul Narayan 《Astrophysics and Space Science》2014,353(2):329-346

Space astronomy in the last 40 years has largely been done from spacecraft in low Earth orbit (LEO) for which the technology is proven and delivery mechanisms are readily available. However, new opportunities are arising with the surge in commercial aerospace missions. We describe here one such possibility: deploying a small instrument on the Moon. This can be accomplished by flying onboard the Indian entry to the Google Lunar X PRIZE competition, Team Indus mission, which is expected to deliver a nearly 30 kgs of payloads to the Moon, with a rover as its primary payload. We propose to mount a wide-field far-UV (130–180 nm) imaging telescope as a payload on the Team Indus lander. Our baseline operation is a fixed zenith pointing but with the option of a mechanism to allow observations of different attitudes. Pointing towards intermediate ecliptic latitude (50^° or above) ensures that the Sun is at least 40^° off the line of sight at all times. In this position, the telescope can cover higher galactic latitudes as well as parts of Galactic plane. The scientific objectives of such a prospective are delineated and discussed.  相似文献   

Mineralogical and ash geochemical studies of coal-mine shale and its hydrocarbon potential: A case study of shale from Makum coalfield,Northeast India     

Rahul Choudhury  Jyotilima Saikia  Binoy K. Saikia 《Journal of the Geological Society of India》2017,90(3):329-334

The mineralogy and geochemical studies of the coal-mine shale collected from the Tirap opencast coal-mine (Makum coalfield, Northeast India) are reported in this paper. Thermo-chemical conversion (pyrolysis) of coal-mine shale has been studied to see its hydrocarbon potential. A combined approach using X-Ray diffraction (LTA-XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrophotometer (EDS), X-ray fluorescence spectrometry (XRF), thermogravimetry-derivative and differential thermogravimetric (TG-DTG and DTA) analysis is made to obtain new information on the mineralogical and geochemical studies of a coal-mine shale (CMS) sample. Gas chromatography-mass spectrometry (GC-MS) analysis is performed to evaluate the quality of the liquid fraction (tar) obtained after pyrolysis at 600°C. The shale sample is dominated by quartz, clay minerals (kaolinite and illite), sulphate bearing phase like gypsum with minor proportion of anatase, probably as artifacts of the plasma-ashing process. GC-MS analysis illustrates the presence of highly oxygenated organic components (M.W. around 94-108) and high molecular weight (M.W. 256) cyclic sulphur (e.g. octathiocane with molecular formula S₈) compounds along with the complex N-containing organic sulphur compounds (M.W. around 255-486) in the tar produced.  相似文献   

Satellite-based technique for nowcasting of thunderstorms over Indian region     

Suman Goyal  Ashish Kumar  M Mohapatra  L S Rathore  S K Dube  Rahul Saxena  R K Giri 《Journal of Earth System Science》2017,126(6):79

India experiences severe thunderstorms during the months, March–June. But these systems are not predicted well, mainly due to the absence of mesoscale observational network over Indian region and the expert system. As these are short lived systems, the nowcast is attempted worldwide based on satellite and radar observations. Due to inadequate radar network, satellite plays the dominant role for nowcast of these thunderstorms. In this study, a nowcast based algorithm ForTracc developed by Vila et al. (Weather Forecast 23:233–245, 2008) has been examined over the Indian region using Infrared Channel \((10.8~\upmu \hbox {m})\) of INSAT-3D for prediction of Mesoscale Convective Systems (MCS). In this technique, the current location and intensity in terms of Cloud Top Brightness Temperature (CTBT) of the MCS are extrapolated. The purpose of this study is to validate this satellite-based nowcasting technique for Convective Cloud Clusters that helps in optimum utilization of satellite data and improve the nowcasting. The model could predict reasonably the minimum CTBT of the convective cell with average absolute error (AAE) of \({<}7\hbox { K}\) for different lead periods (30–180 min). However, it was underestimated for all the lead periods of forecasts. The AAE in the forecasts of size of the cluster varies from about \(3\times 10^{4}\hbox { km}^{2}\) for 30-min forecast to \(7\times 10^{4}\hbox { km}^{2}\) for 120-min forecast. The mean absolute error in prediction of size is above 31–38% of actual size for different lead periods of forecasts from 30 to 180 min. There is over estimation in prediction of size for 30 and 60 min forecasts (17% and 2.6% of actual size of the cluster, respectively) and underestimation in 90 to 180-min forecasts (–2.4% to –28%). The direct position error (DPE) based on the location of minimum CTBT ranges from 70 to 144 km for 30–180-min forecast respectively.  相似文献   

Dynamics of sea-ice biogeochemistry in the coastal Antarctica during transition from summer to winter     

Suhas Shetye  Babula Jena  Rahul Mohan 《地学前缘(英文版)》2017,8(3):507-516

The seasonality of carbon dioxide partial pressure(pCO_2).air-sea CO_2 fluxes and associated environmental parameters were investigated in the Antarctic coastal waters.The in-situ survey was carried out from the austral summer till the onset of winter[January 2012,February 2010 and March 2009) in the Enderby Basin.Rapid decrease in pCO_2 was evident under the sea-ice cover in January,when both water column and sea-ice algal activity resulted in the removal of nutrients and dissolved inorganic carbon(DIC) and increase in pH.The major highlight of this study is the shift in the dominant biogeochemical factors from summer to early winter.Nutrient limitation(low Si/N),sea-ice cover,low photosynthetically active radiation(PAR),deep mixed layer and high upwelling velocity contributed towards higher pCO_2during March(early winter).CO_2 fluxes suggest that the Enderby Basin acts as a strong CO_2 sink during January(-81 mmol m~2 d~(-1)),however it acts as a weak sink of CO_2 with-2.4 and-1.7 mmol m~(-2) d~(-1)during February and March,respectively.The present work,concludes that sea ice plays a dual role towards climate change,by decreasing sea surface PCO_2 in summer and enhancing in early winter.Our observations emphasize the need to address seasonal sea-ice driven CO_2 flux dynamics in assessing Antarctic contributions to the global oceanic CO_2 budget.  相似文献   

Measurement of Hubble constant: were differences in secondary distance indicators apparent as early as the HST Key Project?     

Rahul Kumar Thakur  Shashikant Gupta  Rahul Nigam  PK Thiruvikraman 《天文和天体物理学研究(英文版)》2021,(3):97-106

Different measurements of the Hubble constant(H₀)are not consistent,and a tension between the CMB based methods and cosmic distance ladder based methods has been observed.Measurements from various distance based methods are also inconsistent.To aggravate the problem,the same cosmological probe(TypeⅠa SNe for instance)calibrated through different methods also provides different values of H₀.We compare various distance ladder based methods through the already available unique data obtained from the Hubble Space Telescope(HST).Our analysis is based on parametric(t-test)as well as non-parametric statistical methods such as the Mann-Whitney U test and Kolmogorov-Smirnov test.Our results show that different methods provide different values of H₀ and the differences are statistically significant.The biases in the calibration would not account for these differences as the data have been taken from a single telescope with a common calibration scheme.The unknown physical effects or issues with the empirical relations of distance measurement from different probes could give rise to these differences.  相似文献