Mid-crustal contact metamorphism around the Chimakurthy mafic-ultramafic complex, Eastern Ghats Belt, India     

Somnath Dasgupta  Jürgen Ehl  Michael M. Raith  Pulak Sengupta  Pranesh Sengupta 《Contributions to Mineralogy and Petrology》1997,129(2-3):182-197

Pelitic rocks were thermally metamorphosed at the contact of the Chimakurthy mafic-ultramafic igneous complex, Eastern Ghats Belt, India. The rocks show progressive change in mineralogy from biotite-sillimanite-quartz-garnet-K-feldspar (association I, 150 m from the intrusive contact) to garnet-spinel-cordierite-K-feldspar-sillimanite (association II, 20–30 m from the intrusive contact) to cordierite-K-feldspar-(cordierite-orthopyroxene-K-feldspar symplectite after osumilite)-spinel-FeTiAl oxides with/without garnet (associations III and IV, 5 m from the intrusive contact), and finally to spinel-orthopyroxene-cordierite-K-feldspar (association V, xenoliths). Oxide mineral clots in associations III and IV resemble emery-type rocks. Initial mineral reactions involved biotite-dehydration melting with partial segregation of the melt. Down-temperature mineral reactions were largely diffusion controlled and preservation of symplectitic and coronitic textures in microdomains is common. Interpretation of reaction textures in relevant petrogenetic grids for the sytems KFMASH and FMAS and combined with geothermobarometry suggest that the pelitic rocks were thermally metamorphosed at c. 6 kbar pressure along a heating-cooling trajectory within the temperature interval between c. 750 °C and c. 1000 °C. Received: 20 October 1996 / Accepted: 17 June 1997  相似文献   

Mixing behavior in quaternary garnet solid solution and an extended Ellis and Green garnet-clinopyroxene geothermometer   总被引：7，自引：0，他引：7  

Pulak Sengupta  Somnath Dasgupta  P. K. Bhattacharya  Y. Hariya 《Contributions to Mineralogy and Petrology》1989,103(2):223-227

Applications of the different formulations of garnet-clinopyroxene geothermometers to crustal granulites and particularly to metamorphosed manganese formations show a wide scatter of estimates. This is primarily related to the uncertainty associated with the formulation of the activity-composition relationship in garnet solid solution besides that in the clinopyroxene solid solution. The largest uncertainty appears to have resulted from the adopted Mg-Mn interaction parameter in garnet which is yet to be experimentally determined. A fresh statistical regression of eleven pairs of garnet and clinopyroxene equilibrated at identical P-T conditions from a manganese formation in India yields W _Mg-Mn ^Gt (=W_Mn-Mg) value of 1600±500 cal/mols. An extension of the Ellis and Green (1979) geothermometer, known to work well in normal granulites, incorporating terms associated with the activity coefficients of the exchangeable cations, now yields consistent temperature estimation from normal granulites as well as from metamorphosed manganese formations. The geothermometer, however, will not work well for garnet having X_Fe0.65 and clinopyroxenes containing appreciable Na, Al and/or Fe³⁺.  相似文献   

Did unusual warming over the mid and higher latitudes play some role in causing the unprecedented failure of the southwest monsoon during July 2002?     

A. K. Srivastava  P. Guhathakurta  M. Rajeevan  S. K. Dikshit  S. R. Kshirsagar 《Meteorology and Atmospheric Physics》2007,96(3-4):193-201

Summary Southwest monsoon rainfall over India during July 2002 was the lowest since instrumental observations of monsoon rainfall began. The present study is an attempt to examine some of the probable causes for this unprecedented rainfall deficit. It is found that mid and higher latitudes in the northern hemisphere were abnormally warm during the spring and summer months. Associated with this unusual warming were two blocking highs, one each to the east and west of the Indian subcontinent. These were separated by an anomalous low (low temperature) just to the north of the subcontinent. This anomalous stationary wave-like configuration was consistently present from March to August and the blocking highs were found to be closer to each other during July. This configuration was apparently responsible for the advection of anomalously dry air over the Indian region during July, which may be one of the causes of the suppressed monsoon flow and, ultimately, rainfall activity.  相似文献   

The Impacts of Three-Dimensional Surface Characteristics on Urban Heat Islands over the Diurnal Cycle   总被引：1，自引：0，他引：1  

Bumseok Chun  Subhrajit Guhathakurta 《The Professional geographer》2017,69(2):191-202

This study explores the spatial effects of two- and three-dimensional (2-D, 3-D) urban features in the formation of daytime and nighttime surface urban heat islands (SUHIs) with the help of satellite imagery and LiDAR. Spatially rectified statistical models are used to estimate parameters and understand the spatial spillover effects of urban drivers of SUHIs. In addition, nonlinear relationships among surface temperatures and urban features were included to improve the model fit. The empirical evidence from this study of Atlanta, Georgia, suggests that urban drivers of SUHIs exhibit different and contrasting effects depending on the time of day and their 3-D geometries. The study informs SUHI mitigation efforts by demonstrating that land use policies need to consider the differential effects of land use drivers over the diurnal cycle.  相似文献   

Evidence of Superposed Metamorphism from the Gokavaram Area, Eastern Ghats Belt, and its Relation with the Kemp Land Coast, East Antarctica     

Somnath Dasgupta  Pulak Sengupta  Supratim Pal  Masato Fukuoka 《Gondwana Research》1999,2(2):227

In this paper, we compare the petrological histories of the Kemp Land Coast (east Antarctica), and Gokavaram area (Eastern Ghats), that were supposed to have been juxtaposed. The area around Gokavaram is dominated by different varieties of paragneisses (pelitic, quartzofeldspathic, and calcareous composition) with relatively minor amounts of orthogneisses (mafic, enderbitic, and granitic composition). The rocks were involved in three major phases of deformation, and were finally affected by localised shear movement. On the basis of reaction textures, well preserved in high Mg-Al granulites, and calc-silicate granulites, and geothermobarometric data we deduce a polymetamorphic evolution of the rocks. Following an early M₁ metamorphism culminating at 9.2–9.4 kbar, > 950°C, the rocks cooled nearly isobarically down to 850°C. During a subsequent M₂ metamorphism, near isothermal decompression to 5–6 kbar occurred. This was followed by near isobaric cooling down to 600–650°C. M₃ is a weak amphibolite facies overprint, largely restricted to late shears, which involved hydration as well. Available radiometric data from this area can be interpreted in terms of partial resetting of U-Pb systematics in older sphenes due to M₃ metamorphism at ca. 550 Ma. Despite the absence of sufficient isotopic data on the Eastern Ghats granulites, we document a remarkable similarity in the petrological history of the two supposedly erstwhile neighbours.  相似文献   

The DEEP2 Galaxy Redshift Survey: the relationship between galaxy properties and environment at z∼ 1     

Michael C. Cooper  Jeffrey A. Newman †  Darren J. Croton  Benjamin J. Weiner  Christopher N. A. Willmer  Brian F. Gerke  Darren S. Madgwick †  S. M. Faber  Marc Davis  Alison L. Coil †  Douglas P. Finkbeiner  Puragra Guhathakurta  David C. Koo 《Monthly notices of the Royal Astronomical Society》2006,370(1):198-212

  相似文献   

An HI Survey of Clusters in the Local Universe:     

J.H. van Gorkom  H. Bravo-Alfaro  K.S. Dwarakanath  P. Guhathakurta  B.M. Poggianti  D. Schiminovich  M. Valluri  M. Verheijen  E. Wilcots  A. Zabludoff 《Astrophysics and Space Science》2003,285(1):219-224

We outline the project of multifrequency observation of five clusters of galaxies spanning a redshift between 0.05 and 0.2. The core of the project is an HI survey of clusters accomplished with the VLA in its C configuration, and complemented with GMRT data. The 21 cm imaging is being combined with optical spectroscopy and deep NIR imaging with the aim to obtain a database on galaxy evolution in the nearby universe. We choose a sample of clusters with different degrees of dynamical evolution, some containing an important population of starburst or/and post–starburst galaxies, and a hot intracluster medium with emission in X–ray. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Contrasting parageneses in the manganese silicate-carbonate rocks from Parseoni,Sausar Group,India and their interpretation     

Somnath Dasgupta  Pulak Sengupta  M. Fukuoka  Supriya Roy 《Contributions to Mineralogy and Petrology》1993,114(4):533-538

Mn silicate-carbonate rocks at Parseoni occur as conformable lenses within metapelites and calc-silicate rocks of the Precambrian Sausar Group, India. The host rocks are estimated to have been metamorphosed at uppermost P-T conditions of 500–550°C and 3–4 kbar. The Mn-rich rocks contain appreciable Fe, reflected in the occurrence of magnetite₍₁₎ (MnO 1%), magnetite₍₂₎ (MnO 15%) and magnetite₍₃₎ (MnO 10%). Two contrasting associations of pyroxmangite, with and without tephroite, developed in the Mn silicate-carbonate rocks under isothermal-isobaric conditions. The former assemblage formed in relatively Fe-rich bulk compositions and equilibrated with a metamorphic fluid having a low X _{CO 2} (<0.2), and the latter equilibrated with a CO₂-rich fluid. Rhodochrosite+magnetite₍₁₎+quartz protoliths produced the observed mineral assemblages on metamorphism. Partitioning of major elements between coexisting phases is somewhat variable. Fe shows preference for tephroite over pyroxmangite at the ambient physical conditions of metamorphism. Oxygen fugacity during metamorphism was monitored at or near the QFM buffer in tephroite bearing domains, and the fluid composition was buffered by mineral reactions in respective domains. As compared to other metamorphosed Mn deposits of the Sausar Group, the Mn silicate-carbonate rocks at Parseoni were, therefore, metamorphosed at much lower f _{O 2} through complex mineral-fluid interactions.  相似文献   

Latitudinal variability of large-scale coronal temperature and its association with the density and the global magnetic field     

M. Guhathakurta  R. R. Fisher 《Solar physics》1994,152(1):181-188

In this paper we utilize the latitude distribution of the coronal temperature during the period 1984–1992 that was derived in a paper by Guhathakurta et al, 1993, utilizing ground-based intensity observations of the green (5303 Fe XIV) and red (6374 Fe X) coronal forbidden lines from the National Solar Observatory at Sacramento Peak, and estabish its association with the global magnetic field and the density distributions in the corona. A determination of plasma temperature,T, was estimated from the intensity ratio Fe X/Fe XIV (whereT is inversely proportional to the ratio), since both emission lines come from ionized states of Fe, and the ratio is only weakly dependent on density. We observe that there is a large-scale organization of the inferred coronal temperature distribution that is associated with the large-scale, weak magnetic field structures and bright coronal features; this organization tends to persist through most of the magnetic activity cycle. These high-temperature structures exhibit time-space characteristics which are similar to those of the polar crown filaments. This distribution differs in spatial and temporal characterization from the traditional picture of sunspot and active region evolution over the range of the sunspot cycle, which are manifestations of the small-scale, strong magnetic field regions.affiliated to USRA  相似文献   

Effects of Salinity and Mangrove Detritus on Desorption of Metals from Brackish Water Desorption of Metals from Brackish Water and Shrimp     

Himadri Guhathakurta  Anilava Kaviraj 《洁净——土壤、空气、水》2004,32(6):411-418

Desorption and bioaccumulation of Cd, Zn, and Pb were studied using naturally contaminated sediment from a brackish water pond in the Sunderban Biosphere Reserve in India. Pattern of desorption of the metals from the sediment and bioaccumulation in fingerlings of the teleost Oreochromis mossambicusand postlarvae of the shrimp Penaeus monodon were studied as a function of salinity and loading of detritus of a mangrove plant. Effects of both salinity and loading of detritus on bioaccumulation of the metals were studied under two conditions: either the animals were allowed free access to the sediment or access was denied. Ninety‐six hour experiments showed that desorption of Cd and Pb from sediment into water increased with salinity of the medium while desorption of Zn decreased. Salinity of the medium also had a significant effect on the bioaccumulation of metals by fish; Cd and Pb accumulation decreased in saline medium while the accumulation of Zn increased. Conditions of access to sediment had no effect on the bioaccumulation of metals by fish; effect of interaction between salinity and access condition was also insignificant. The access conditions, however, significantly influenced accumulation of metal by the shrimp postlarvae. The effect of interaction between salinity and access condition was insignificant in influencing the bioaccumulation of all metals except Zn. The accumulation of Zn increased as a function of the salinity of the medium when shrimp postlarvae were allowed access to the sediment. Desorption of metals from sediment to water were below detection limits when detritus of a mangrove plant was added to the medium. Both the level of detritus and the conditions of access influenced accumulation of metals by fish, but the effect of interaction between the two factors were found to be insignificant. Shrimp postlarvae showed net accumulation only of Pb in the presence of detritus and the accumulation of Pb increased when the larvae were separated from the sediment. The results are important in understanding the mobility of metals between solid and aqueous phases in brackish water environments that experience periodic fluctuations in salinity and fluxes of organic load in the form of mangrove detritus.  相似文献