Magnesian andesite and dacite lavas from Mt. Shasta,northern California: products of fractional crystallization of H<Subscript>2</Subscript>O-rich mantle melts   总被引：2，自引：1，他引：1  

Timothy?L.?GroveEmail author  Michael?B.?Baker  Richard?C.?Price  Stephen?W.?Parman  Linda?T.?Elkins-Tanton  Nilanjan?Chatterjee  Othmar?Müntener 《Contributions to Mineralogy and Petrology》2005,148(5):542-565

Mt. Shasta andesite and dacite lavas contain high MgO (3.5–5 wt.%), very low FeO*/MgO (1–1.5) and 60–66 wt.% SiO₂. The range of major and trace element compositions of the Shasta lavas can be explained through fractional crystallization (~50–60 wt.%) with subsequent magma mixing of a parent magma that had the major element composition of an H₂O-rich primitive magnesian andesite (PMA). Isotopic and trace element characteristics of the Mt. Shasta stratocone lavas are highly variable and span the same range of compositions that is found in the parental basaltic andesite and PMA lavas. This variability is inherited from compositional variations in the input contributed from melting of mantle wedge peridotite that was fluxed by a slab-derived, fluid-rich component. Evidence preserved in phenocryst assemblages indicates mixing of magmas that experienced variable amounts of fractional crystallization over a range of crustal depths from ~25 to ~4 km beneath Mt. Shasta. Major and trace element evidence is also consistent with magma mixing. Pre-eruptive crystallization extended from shallow crustal levels under degassed conditions (~4 wt.% H₂O) to lower crustal depths with magmatic H₂O contents of ~10–15 wt.%. Oxygen fugacity varied over 2 log units from one above to one below the Nickel-Nickel Oxide buffer. The input of buoyant H₂O-rich magmas containing 10–15 wt.% H₂O may have triggered magma mixing and facilitated eruption. Alternatively, vesiculation of oversaturated H₂O-rich melts could also play an important role in mixing and eruption.  相似文献   

Overpressure zone under the Krishna–Godavari offshore basin: geophysical implications for natural hazard in deeper-water drilling     

Rima Chatterjee  Manoj Mukhopadhyay  Suman Paul 《Natural Hazards》2011,57(1):121-132

Accurate knowledge of pore pressure is fundamental to any safe and economic well construction. Here, we present results that are indicative of over pressure zones (OPZ) for five wells drilled under the Krishna–Godavari offshore basin (KGOB) at the Eastern Continental Margin of India (ECMI). OPZ in areas of crustal flexuring can act as potential geohazard while drilling. These wells locate at water depths of 515–1,265 m, where their penetrated-vertical-depth reaches up to 3,960 m in clastic sediments. pore pressure gradient (PPG) and fracture pressure gradient (FPG) are estimated from acoustic log for all five wells, while the Normal Compaction Trend (NCT) and pore pressure are calculated from Miller’s sonic equation. Top of OPZ is indicated by values that are higher than the NCT; departure from NCT is observed at depth intervals of 1,320–2,180 m, 1,700–3,960 m, 1,600–1,880 m, 1,420–2,609 m and 2,080–2,200 m for the respective Wells 1 through 5. The pressure data from Modular Dynamic Tester (MDT) agree well with the pore pressure values obtained from the logs. The Overburden Gradient (OBG), PPG and FPG values increase rather slowly with total depth in deeper-water of KGOB when compared to the wells located in shallow water depth. Consequently, the operating safety margin between PPG and FPG decreases as the water depth increases, and this clearly leads to an increase in the number of casing strings to reach the target depth. Certain basic conclusions on the potentiality of natural hazard for drilling operations are drawn on the basis of these results, but evidently, further studies are warranted to present a more composite picture of OPZ under KGOB.  相似文献   

Arecibo observations of Parkes multibeam pulsars     

N. D. R. Bhat  F. Camilo  J. M. Cordes  D. J. Nice  D. R. Lorimer  S. Chatterjee 《Journal of Astrophysics and Astronomy》2002,23(1-2):53-57

The on-going Parkes multibeam survey has been astoundingly successful (Manchesteret al. 2001), and its discovery of over 600 pulsars has opened up new avenues for probing the Galaxy’s electron content and magnetic field. Here we report on recent observations made with the Arecibo 305-m telescope, where 80 distant, high dispersion measure pulsars (of which 35 are from the multibeam survey) were studied at multiple frequency bands in the range 0.4–2.4 GHz, in order to determine their scattering properties, rotation measures and spectral indices. The results will be used to meet a variety of science goals; viz., creating an improved model of the electron density, mapping out the Galactic magnetic field, and modeling the pulsar population.  相似文献   

Potential and force due to thin disk and spherical galaxies     

Tapan K. Chatterjee 《Astrophysics and Space Science》1987,139(2):243-256

The determination of the potential and force due to a thin exponential model disk galaxy and a polytropicn=4 model spherical galaxy are conducted in the light of the study of collision dynamics.Results indicate that the potential due to the sphere and the disk along its plane are equal at a distance of about 1/3R, whereR is the radius of either configuration. Interior to this distance, the potential due to the sphere is greater than that due to the disk and beyond this distancevice versa.These results are expected to lead to the construction of simple models for galaxies, useful in the study of collision dynamics.  相似文献   

More evidence that the Chicxulub impact predates the K/T mass extinction     

Gerta KELLER  Thierry ADATTE  Wolfgang STINNESBECK  Doris STüBEN  Zsolt BERNER  Utz KRAMAR  Markus HARTING 《Meteoritics & planetary science》2004,39(7):1127-1144

Abstract Yaxcopoil‐1 (Yax‐1), drilled within the Chicxulub crater, was expected to yield the final proof that this impact occurred precisely 65 Myr ago and caused the mass extinction at the Cretaceous‐Tertiary (K/T) boundary. Instead, contrary evidence was discovered based on five independent proxies (sedimentologic, biostratigraphic, magnetostratigraphic, stable isotopic, and iridium) that revealed that the Chicxulub impact predates the K/T boundary by about 300,000 years and could not have caused the mass extinction. This is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest Maastrichtian zone CF1 and is corroborated by magnetostratigraphic chron 29r and characteristic late Maastrichtian stable isotope signals. These results were first presented in Keller et al. (2004). In this study, we present more detailed evidence of the presence of late Maastrichtian planktic foraminifera, sedimentologic, and mineralogic analyses that demonstrate that the Chicxulub impact breccia predates the K/T boundary and that the sediments between the breccia and the K/T boundary were deposited in a normal marine environment during the last 300,000 years of the Cretaceous.  相似文献   

De Sitter type of cosmological model with a self-gravitating nonlinear scalar field     

S. Chatterjee  N. Banerjee 《Astrophysics and Space Science》1987,133(2):383-387

Homogeneous isotropic cosmological solutions are obtained for a de Sitter type of metric in the presence of a self-gravitating scalar field with cubic nonlinearity. Unlike the usual de Sitter case which is indefinitely expanding it is here interestingly found that in the presence of a nonlinear scalar field the model gives a bounce from a maximum of spatial volume. The possibility of bounce from a maximum, however, disappears when a linear scalar field is considered instead.  相似文献   

Interpretation of magnetic fabrics in the Dalma volcanic rocks and associated meta-sediments of the Singhbhum Mobile Belt     

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   

Exhumation of the UHP Tso Morari eclogite as a diapir rising through the mantle wedge     

Nilanjan Chatterjee  Oliver Jagoutz 《Contributions to Mineralogy and Petrology》2015,169(1):1-20

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Bifurcations of dust acoustic solitary waves and periodic waves in an unmagnetized plasma with nonextensive ions     

Asit Saha  Prasanta Chatterjee 《Astrophysics and Space Science》2014,351(2):533-537

Bifurcations of dust acoustic solitary waves and periodic waves in an unmagnetized plasma with q-nonextensive velocity distributed ions are studied through non-perturbative approach. Basic equations are reduced to an ordinary differential equation involving electrostatic potential. After that by applying the bifurcation theory of planar dynamical systems to this equation, we have proved the existence of solitary wave solutions and periodic wave solutions. Two exact solutions of the above waves are derived depending on the parameters. From the solitary wave solution and periodic wave solution, the effect of the parameter (q) is studied on characteristics of dust acoustic solitary waves and periodic waves. The parameter (q) significantly influence the characteristics of dust acoustic solitary and periodic structures.  相似文献   

Geospatial assessment of soil erosion vulnerability at watershed level in some sections of the Upper Subarnarekha river basin, Jharkhand, India   总被引：2，自引：0，他引：2  

Shuvabrata Chatterjee  A. P. Krishna  A. P. Sharma 《Environmental Earth Sciences》2014,71(1):357-374

Undulating landscapes of Chhotanagpur plateau of the Indian state of Jharkhand suffer from soil erosion vulnerability of varying degrees. An investigation was undertaken in some sections of the Upper Subarnarekha River Basin falling within this state. An empirical equation known as Universal Soil Loss Equation (USLE) was utilized for estimating the soil loss. Analysis of remote sensing satellite data, digital elevation model (DEM) and geographical information system (GIS)–based geospatial approach together with USLE led to the soil erosion assessment. Erosion vulnerability assessment was performed by analyzing raster grids of topography acquired from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global DEM data. LANDSAT TM and ETM+ satellite data of March 2001 and March 2011 were used for inferring the land use–land cover characteristics of the watershed for these years, respectively. USLE equation was computed within the GIS framework to derive annual soil erosion rates and also the areas with varying degrees of erosion vulnerability. Erosion vulnerability units thus identified covered five severity classes of erosion ranging from very low (0–5 ton ha^?1 yr^?1) to very severe (> 40 ton ha^?1 yr^?1). Results indicated an overall increase of erosion in the year 2011 as compared to the erosion computed for the year 2001. Maximum soil erosion rate during the year 2001 was found up to 40 ton ha^?1 yr^?1, whereas this went up to 49.80 ton ha^?1 yr^?1 for the year 2011. Factors for the increase in overall erosion could be variation in rainfall, decrease in vegetation or protective land covers and most important but not limited to the increase in built-up or impervious areas as well.  相似文献