Characteristics of pegmatoidal granite exposed near Bayalan,Ajmer district,Rajasthan

The study involves the characterization of pegmatoidal granite, southeast of Beawar, Ajmer district, Rajasthan. Earlier researchers had described this granite as part of the BGC, basement to the Bhim Group of the Delhi Super Group rocks. However, the present study indicates that it is younger than the rocks of Bhim Group of South Delhi Fold Belt, into which it is intrusive. The intrusion is structurally controlled and the outcrop pattern is phacolithic. The granite had intruded post-D₂ deformation of the Delhi orogeny along the axial planes of D₂ folds. The intrusion has also resulted in the formation of a contact aureole about the calc gneisses.     

Tower-Based Greenhouse Gas Measurement Network Design——The National Institute of Standards and Technology North East Corridor Testbed

The North–East Corridor(NEC) Testbed project is the 3rd of three NIST(National Institute of Standards and Technology) greenhouse gas emissions testbeds designed to advance greenhouse gas measurements capabilities. A design approach for a dense observing network combined with atmospheric inversion methodologies is described. The Advanced Research Weather Research and Forecasting Model with the Stochastic Time-Inverted Lagrangian Transport model were used to derive the sensitivity of hypothetical observations to surface greenhouse gas emissions(footprints). Unlike other network design algorithms, an iterative selection algorithm, based on a k-means clustering method, was applied to minimize the similarities between the temporal response of each site and maximize sensitivity to the urban emissions contribution. Once a network was selected, a synthetic inversion Bayesian Kalman filter was used to evaluate observing system performance. We present the performances of various measurement network configurations consisting of differing numbers of towers and tower locations. Results show that an overly spatially compact network has decreased spatial coverage, as the spatial information added per site is then suboptimal as to cover the largest possible area, whilst networks dispersed too broadly lose capabilities of constraining flux uncertainties. In addition, we explore the possibility of using a very high density network of lower cost and performance sensors characterized by larger uncertainties and temporal drift. Analysis convergence is faster with a large number of observing locations, reducing the response time of the filter. Larger uncertainties in the observations implies lower values of uncertainty reduction. On the other hand, the drift is a bias in nature, which is added to the observations and,therefore, biasing the retrieved fluxes.     

A STUDY ON THE DIRECT INTERPRETATION OF DIPOLE SOUNDING RESISTIVITY MEASUREMENTS OVER LAYERED EARTH *

Dipole sounding resistivity measurements over layered earth can be interpreted directly by adapting the procedure given by Koefoed (1968) for Schlumberger system. To carry out the first step of the interpretation leading to the determination of the raised kernel function, partial resistivity functions for the dipole method are derived and given in the form of standard curves. The second step involving the derivation of layering parameters from the kernel being independent of the electrode configurations remains unaltered. The applicability and limitations of the method are discussed.     

Upper-Mantle Fragments from Beneath the Sierra Nevada Batholith: Partial Fusion, Fractional Crystallization, and Metasomatism in a Subduction Related Ancient Lithosphere

Upper-mantle xenoliths in volcanic pipes cutting the axis ofthe Sierra Nevada batholith contain predominantly spinel-bearingperidotites (with sporadic garnet) and garnet websterites. Inspite of the enormous thickness of the Sierran crust, the Sierranupper mantle has not attained the garnet peridotite stabilityfield. The peridotites have forsteritic (Fo_88–92) olivines,Cr-diopsides, Cr-spinels, and magnesian orthopyroxenes (En_88–92).Their texture and compositional characteristics of the coexistingphases indicate that these are fragments of the upper mantlethat had undergone various degrees of partial fusion. The Pconditions of reequilibration and mineralogical characteristicssuggest that the partial fusion was accompanied by diapiricuprise. The REE distribution patterns are nearly chondritic.Garnet websterite xenoliths also contain magnesian and Cr-richphases. Their bulk chemical compositions are like pyroxenitecumulates. The garnet websterites from Big Creek differ fromthose occurring at Pick and Shovel in having more Fe-rich phasesand occasional hydrous minerals. The Pick and Shovel garnetwebsterites are interpreted to be pyroxene-rich, garnet-freecumulates formed by fractional crystallization of melts generatedby partial melting of subcontinental lithosphere at depth 60km. The REE abundance of these xenoliths is consistent withthis mode of origin. Presence of jadeitic clinopyroxenes andF-rich phlogopites, and the LREE- and ⁸⁷Sr/⁸⁶Sr-enriched characterof the garnet websterites from Big Creek may suggest their originas metasomatized upper-mantle garnet peridotites. The latestP-T conditions of equilibration of all garnet-bearing samplesshow that they lie along a nearly adiabatic gradient in therange of 900–1000 C and 18–32 kbar. An isotopically heterogeneous, old (1 b.y.) subcontinental lithosphere,characterized by high ⁸⁷Sr/⁸⁶Sr (0.7044–0.7082), radiogenic²⁰⁶Pb/²⁰⁴Pb (18.86–20.04), ²⁰⁷Pb/²⁰⁴Pb (15.64–15.69)and ²⁰⁸Pb/²⁰⁴Pb (38.69–39.11), and moderate ¹⁴³Nd/¹⁴⁴Nd(0.51234–0.51260; E_Nd–0.35 to –5.8) is consideredto be the source of these rocks. There was a fluid influx froma subducted slab carrying Ba, K, Rb, U, Th, and radiogenic Pbinto the overlying ancient lithosphere.     

Tonian–Ediacaran Tectonometamorphic History of the Sa’al Complex, Sinai (Egypt): Implications for the Tectonostratigraphic Framework of the Northern Arabian–Nubian Shield

The Sa''al Metamorphic Complex (SMC; southern Sinai) encompasses the oldest arc rocks in the Arabian–Nubian Shield, comprising two non-consanguineous metavolcanic successions (the Agramiya Group and the Post-Ra''ayan Formation) separated by the metasediments of the Ra''ayan Formation. It experienced three distinct deformational events (D1–D3) and two low-medium grade regional metamorphic events (M1–M2). The Agramiya Group and the Ra''ayan Formation experienced all tectonometamorphic events (D1–D3 and M1–M2), whereas the Post-Ra''ayan volcanic rocks were only affected by the D3 and M2 events. D1 is an extensional event and is connected to the late Rodinia break-up (~Tonian; 900–870 Ma). The M1 metamorphism variably affected the older Agramiya Group, the rhyolitic tuffs experiencing lower to upper greenschist facies conditions and the basic and intermediate volcanic rocks undergoing amphibolite facies metamorphism. The Ra''ayan Formation metasediments experienced upper greenschist to amphibolite facies metamorphism. The upper greenschist facies M2 affected the youngest Post-Ra''ayan volcanic rocks and other stratigraphic successions. The compressive D2 and D3 events were coeval with the accretion of dismembered terranes in the assembly of Gondwana. D2 can be linked to the Tonian–Cryogenian arc-arc assembly (~880–760 Ma; in Elat and Sinai), whereas D3 and the accompanying M2 is constrained to 622–600 Ma (Ediacaran).     

TRANSFORMATION OF DIPOLE RESISTIVITY SOUNDING MEASUREMENTS OVER LAYERED EARTH BY LINEAR DIGITAL FILTERING *

The technique of linear digital filtering as developed for the direct interpretation of Schlumberger and Wenner soundings (Ghosh 1971) has been applied here for the derivation of the resistivity transform function from the field dipole measurements as the first step in directly interpreting dipole data. Filter coefficients for this transformation have been worked out for the radial-polar, perpendicular and parallel (30°) arrays of dipole sounding. The procedure combines speed with accuracy.