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431.
Carbonatites are believed to have crystallized either from mantle-derived primary carbonate magmas or from secondary melts
derived from carbonated silicate magmas through liquid immiscibility or from residual melts of fractional crystallization
of silicate magmas. Although the observed coexistence of carbonatites and alkaline silicate rocks in most complexes, their
coeval emplacement in many, and overlapping initial87Sr/86Sr and143Nd/144Nd ratios are supportive of their cogenesis; there have been few efforts to devise a quantitative method to identify the magmatic
processes. In the present study we have made an attempt to accomplish this by modeling the trace element contents of carbonatites
and coeval alkaline silicate rocks of Amba Dongar complex, India. Trace element data suggest that the carbonatites and alkaline
silicate rocks of this complex are products of fractional crystallization of two separate parental melts. Using the available
silicate melt-carbonate melt partition coefficients for various trace elements, and the observed data from carbonatites, we
have tried to simulate trace element distribution pattern for the parental silicate melt. The results of the modeling not
only support the hypothesis of silicate-carbonate melt immiscibility for the evolution of Amba Dongar but also establish a
procedure to test the above hypothesis in such complexes. 相似文献
432.
433.
Thungyani N. Ovung Jyotisankar Ray Biswajit Ghosh Debabrata Mandal Pallab Dasgupta Madhuparna Paul 《Journal of the Geological Society of India》2017,90(2):154-158
Serpentinization is pervasive in the ultramafic rocks of Manipur ophiolite belt (MOB), Northeastern India. Electron microprobe data of a serpentinite from the Ukhrul-Nungbi sector of MOB shows Ni-rich serpentine mineral (NiO = 33.4-33.9 wt %, SiO2= 37.55-38.96 wt %, MgO= 14.83-16.89 wt %). The composition and X-ray diffraction pattern characterize this Ni-rich serpentine mineral as népouite which is suggested to be a hydrothermal alteration product of NiO-rich olivine in a fore-arc peridotite. The genesis of this NiO-rich olivine is attributed to the melt-rock interaction in a supra-subduction zone setting. 相似文献
434.
Barman Prakash Jade Sridevi Shrungeshwara T. S. Kumar Ashok Bhattacharyya Sanjeev Ray Jagat Dwipendra Jagannathan Saigeetha Jamir Wangshi Menla 《International Journal of Earth Sciences》2017,106(6):2025-2038
International Journal of Earth Sciences - The present study reports the contemporary deformation of the tectonically complex northeast India using 11 years (2002–2013) of GPS... 相似文献
435.
The Dergaon fall represents a shock-melted H4-5(S5) ordinary chondrite which includes at least ten textural varieties of chondrules and belongs to the high chondrule-matrix ratio type.Our study reveals that the chondrules are of diverse mineralogy with variable olivine-pyroxene ratios(Type Ⅱ),igneous melt textures developed under variable cooling rates and formed through melt fractionations from two different melt reservoirs.Based on the experimental analogues,mineralogical associations and phase compositions,it is suggested that the Dergaon chondrules reflect two contrasting environments:a hot,dust-enriched and highly oxidized nebular environment through melting,without significant evaporation,and an arrested reducing environment concomitant with major evaporation loss of alkali and highly volatile trace elements.Coexistence of chlorapatite and merrillite suggests formation of the Dergaon matrix in an acidic accretionary environment.Textural integration and chemical homogenization occurred at ~ 1 atmospheric pressure and a mean temperature of 765 C mark the radiogenic thermal event.Equilibrated shock features(olivine mosaicism,diaplectic plagioclase,polycrystalline troilite) due to an impact-induced thermal event reflect a shock pressure 45 GPa and temperature of 600 C.By contrast,the local disequilibrium shock features(silicate melt veins comprising of olivine crystallites,troilite melt veins and metal droplets) correspond to a shock pressure up to 75 GPa and temperature950 ℃. 相似文献
436.
Kishan Singh Rawat Vinay Kumar Sehgal Sanatan Pradhan Shibendu S. Ray 《Arabian Journal of Geosciences》2017,10(20):445
In this work, we estimated soil moisture (SM) by using dielectric constant properties of soil with radar backscattering coefficient (bc) from simulated annealing techniques of RISAT-1 (radar imaging satellite, based on synthetic aperture radar (SAR) technique) data. We examined the performance of simulated annealing in retrieving SM where the vegetation cover is not very high (NDVI ≈ 0.35 for wheat-dominated area on January 19, 2013).To overcome the land surface model limits on SM estimation accuracy, point measurement spatial coverage limits, and microwave remote sensing spatial-temporal sampling limits, we reduced uncertainties through a combination of these approaches. Near-surface SM measurements from the 5.35-GHz (C-band) channels of RISAT-1 were collocated against ground-truth data (collected during the flight time of RISAT-1 over the study area), to establish SAR-SM relationships for FRS-1(circular horizontal (RH) and circular vertical (RV)) data set of RISAT-1. Comparison with the limited ground-based point (total 24 points) measurements of SM content exhibited a net improvement when near-surface SM observations were assimilated. Comparison of the SM derived from the sigma naught (σ 0) (of RISAT-1 data set FRS-1) using the inversion algorithm with the observed measurements (using time domain reflectometry) of SM showed root mean square error of 0.24, nRMSE = 0.03, R-RMSE = 0.38, MAE = 0.63, NRMSE = 1.02, NSE = 1, d = 0.87, r 2 = 0.65, and RMSE% = 12.79 for RH polarized image while RV polarized image failed each statistical test for predicting good SM with respect to the observed SM. The ability to extract additional information comes at the expense of including more measurements, especially at frequencies lower than the L-band. This approach is therefore intended for future space-borne systems. 相似文献
437.
Foundationitem:UndertheauspicesoftheNationalNaturalScienceFoundationofChina(No.49601007)1IntroductionThehlemelineoftilepaperisanexPlorahonofthetenns'sustainablecihes',whichweremuchinevidCnceatHabitatIIheldatIStanbulinJunel996(UNCHtheUnitedNationConferenceonHumanSettlements).ttisexPlorahoniscompletelynottotracethefashionofthewordsthemselves,rathertoviewthefactSthat,ontheonehand,IniningciheshavebeenplaytngsuchacrucialroletoChina'snahonalsocio-economyasChinahasbeingcontributedtotheglob… 相似文献
438.
Vera A. FERNANDES Ray BURGESS Grenville TURNER 《Meteoritics & planetary science》2000,35(6):1355-1364
Abstract— The laser 40Ar‐39Ar dating technique has been applied to the Dar al Gani (DaG) 262 lunar meteorite, a polymict highland regolith breccia, to determine the crystallisation age and timing of shock events experienced by this meteorite. Laser stepped‐heating analyses of three dominantly feldspathic fragments (DaG‐1, DaG‐2, and DaG‐3) revealed the presence of trapped Ar, mostly released at intermediate and high temperatures, with an 40Ar/36Ar value of ~2.8. Trapped Ar is most likely released from melt glass present as small veins within the fragments. The 40Ar‐39Ar ages determined for the three fragments are ~3.0 Ga for DaG‐1 and DaG‐2 and 2.0 Ga for DaG‐3 and probably relate to major impact events. Laser spot analyses were performed on a feldspathic clast, an impact crystalline melt basalt (ICMB), and the matrix in a polished section of DaG 262. The feldspathic and ICMB clasts have low contents of trapped Ar compared with that in the matrix. The feldspathic clast shows a wide range of ages from 3.0 to 1.7 Ga similar to those obtained by stepped heating. The younger age is interpreted as a minimum age for the last major event that assembled this meteorite. The ICMB shows two age clusters at 3.37 and 3.07 Ga, where the older age may be that of the impact event that formed the impact melt. Several cosmic‐ray exposure (CRE) ages were obtained as expected for a polymict regolith breccia. The CRE ages are 106 and 141 Ma for the feldspathic clast and the ICMB, respectively. One of the feldspathic fragments, DaG‐2, shows a range between 200–400 Ma. These CRE ages, which are similar to those determined for returned samples of the lunar regolith, indicate that the different components of DaG 262 experienced preexposure prior to assemblage of the meteorite. 相似文献
439.
T.P. Ray 《Astrophysics and Space Science》2000,272(1-3):115-125
After briefly reviewing observations of molecular outflows from young stars, we discuss current ideas as to how they might
be accelerated. Broadly speaking it is thought that such outflows represented either deflected accreted gas, or ambient material
that has been pushed by a poorly collimated wind or accelerated by a highly collimated jet. Observations tend to favour the
latter model, with jets being the clear favourite at least for the youngest flows. Jets from young stars may accelerate ambient
gas either through the development of a boundary layer, where ambient and jet material are turbulently mixed, or at the working
surface of the jet, i.e. the bow shock, via the prompt entrainment mechanism. Recently, we (Downes and Ray, 1999) have investigated,
through simulations, the efficiency of prompt entrainment in jets from young stars as a means of accelerating ambient molecular
gas without causing dissociation. Prompt entrainment was found to be very poor at transferring momentum from the jet to its surroundings in both the case
of ``heavy' (not surprizingly) but also ``equi-density' (with respect to the ambient environment) jets. Moreover the transfer
efficiency decreases with increasing density as the bow shock takes on a more aerodynamic shape. Models, however, in which
jets are the ultimate prime movers, do have the advantage that they can reproduce several observational features of molecular
outflows. In particular a power law relationship for mass versus velocity, similar to what is observed, is predicted by the
simulations and the so-called ``Hubble Law' for molecular outflows is naturally explained. Pulsing of the jet, i.e. varying
its velocity, is found to have little effect on the momentum transfer efficiency at least for the dynamically young jets we
have studied.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
440.
Jie?BaoEmail author Zhangshuan?Hou Jaideep?Ray Maoyi?Huang Laura?Swiler Huiying?Ren 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(8):2213-2231
In this study, we focus on a hydrogeological inverse problem specifically targeting monitoring soil moisture variations using tomographic ground penetrating radar (GPR) travel time data. Technical challenges exist in the inversion of GPR tomographic data for handling non-uniqueness, nonlinearity and high-dimensionality of unknowns. We have developed a new method for estimating soil moisture fields from crosshole GPR data. It uses a pilot-point method to provide a low-dimensional representation of the relative dielectric permittivity field of the soil, which is the primary object of inference: the field can be converted to soil moisture using a petrophysical model. We integrate a multi-chain Markov chain Monte Carlo (MCMC)–Bayesian inversion framework with the pilot point concept, a curved-ray GPR travel time model, and a sequential Gaussian simulation algorithm, for estimating the dielectric permittivity at pilot point locations distributed within the tomogram, as well as the corresponding geostatistical parameters (i.e., spatial correlation range). We infer the dielectric permittivity as a probability density function, thus capturing the uncertainty in the inference. The multi-chain MCMC enables addressing high-dimensional inverse problems as required in the inversion setup. The method is scalable in terms of number of chains and processors, and is useful for computationally demanding Bayesian model calibration in scientific and engineering problems. The proposed inversion approach can successfully approximate the posterior density distributions of the pilot points, and capture the true values. The computational efficiency, accuracy, and convergence behaviors of the inversion approach were also systematically evaluated, by comparing the inversion results obtained with different levels of noises in the observations, increased observational data, as well as increased number of pilot points. 相似文献