Chromium Contents of Standard Rock Samples: A Detailed Investigation by Radiochemical Neutron Activation Analysis

The reported values for the chromium contents of standard acidic rocks show a large spread, making it difficult to assign firm recommended values. A radiochemical neutron activation analysis procedure was developed and its reliability examined critically. The method involves separation of chromium as chromyl chloride by distillation followed by precipitation as barium chromate. The chromium content of a number of international standard rocks has been determined and results obtained are critically reviewed in relation to the available data.     

Discovery of Early Tonian Calc-alkaline and Shoshonitic Metamafic Rocks from the North Purulia Shear Zone, Chhotanagpur Gneissic Complex, Eastern India: Implications of Proterozoic Sub-continental Lithospheric Mantle

Reports of shoshonitic rocks in Precambrian terrains are relatively rare. Pl-Grt amphibolites and Hbl-Bt mafic granulites occurring in the migmatitic gneisses of the Chhotanagpur Gneissic Complex(CGC) show calc-alkaline and shoshonitic characteristics. Relict porphyritic, sub-ophitic and poikilitic textures are noted in these rocks. Their parent magma was emplaced during the waning phase of the regional metamorphism. Geochemically, these metamafics are similar to the Group Ⅲ potassic and ultrapo...     

Petrotectonic framework of granulites from northern part of Chilka Lake area,Eastern Ghats Belt,India: Compressional vis-à-vis transpressional tectonics

Granulite-facies rocks occurring north-east of the Chilka Lake anothosite (Balugan Massif) show a complex metamorphic and deformation history. The M₁–D₁ stage is identified only through microscopic study by the presence of S₁ internal foliation shown by the M₁ assemblage sillimanite–quartz–plagioclase–biotite within garnet porphyroblasts of the aluminous granulites and this fabric is obliterated in outcrop to map-scale by subsequent deformations. S₂ fabric was developed at peak metamorphic condition (M₂–D₂) and is shown by gneissic banding present in all lithological units. S₃ fabric was developed due to D₃ deformation and it is tectonically transposed parallel to S₂ regionally except at the hinge zone of the F₃ folds. The transposed S₂/S₃ fabric is the regional characteristic structure of the area. The D₄ event produced open upright F₄ folds, but was weak enough to develop any penetrative foliation in the rocks except few spaced cleavages that developed in the quartzite/garnet–sillimanite gneiss. Petrological data suggest that the M₄–D₄ stage actually witnessed reactivation of the lower crust by late distinct tectonothermal event. Presence of transposed S₂/S₃ fabric within the anorthosite arguably suggests that the pluton was emplaced before or during the M₃–D₃ event. Field-based large-scale structural analyses and microfabric analyses of the granulites reveal that this terrain has been evolved through superposed folding events with two broadly perpendicular compression directions without any conclusive evidence for transpressional tectonics as argued by earlier workers. Tectonothermal history of these granulites spanning in Neoproterozoic time period is dominated by compressional tectonics with associated metamorphism at deep crust.     

Temporal and spatial variations in the magnitude of completeness for homogenized moment magnitude catalogue for northeast India

Northeast India region is one of the most seismically active areas in the world. Events data for the period 1897–2010, used in this study has been largely compiled from global ISC, NEIC and GCMT databases. Historical seismicity catalogue of Gupta et al (1986) and some events data from the bulletins of India Meteorological Department are also used. Orthogonal regression relations for conversion of body and surface wave magnitudes to M _w,HRVD based on events data for the period 1978–2006 have been derived. An Orthogonal Standard Regression (OSR) relationship has also been obtained for scaling of intensity estimates to M _w,NEIC using 126 global intensity events with intensity VI or greater during the period 1975–2010.     

Simulation of infiltration from porous clay pipe in subsurface irrigation

Abstract

Advances in the traditional method of subsurface porous clay pipe irrigation rely on knowledge of the distribution of water in the soil. Knowing the relationships among the hydraulic and physical parameters in the system is important for both the design and management of the system. To simulate the infiltration from the porous clay pipe and predict the wetted zone geometry in the soil, a computer model is developed herein. Laboratory experiments were conducted on soil samples representing two different soil textures in a specially designed bin to understand the flow phenomenon and to validate the developed model. In a given soil texture, the installation depth of the pipe and the volume of water applied in the soil are the major factors affecting the wetted zone. The relationships among various parameters, namely lateral spacing, installation depth, irrigation run time, hydraulic conductivity of the body of the pipe, and hydraulic head in the system, were established using the developed model.     

Evidences of inclined transpression at the contact between Vinjamuru group and Udayagiri group of Nellore Schist Belt,Andhra Pradesh,India

The Nellore Schist Belt (NSB) is a curvilinear Archaean schist belt, approximately 350 km long and 8–50 km wide. The Nellore Schist Belt is considered to be Neoarchean in age and stratigraphically NSB is classified as the western Udayagiri group (dominated by metasediments) and underlying eastern Vinjamuru group (dominated by metabasalts). There is a long controversy regarding the contact relationship between Udayagiri and Vinjamuru groups. Earlier researchers regarded the contact between two groups as tectonic on the basis of metamorphism. A shear zone and a possible thrust contact between the two groups have also been reported. On the basis of present study, an NNW–SSE trending, westerly dipping inclined transpressional zone is found at the contact between Udayagiri and Vinjamuru groups in the central western part of the NSB. Kinematic analysis of both the hanging wall and foot wall of the westerly dipping thrust zone shows presence of strong S1 schistosity, shear bands and S-C fabric in both strike and dip section along with east-verging overturned fold, westerly dipping inverted beds, suggesting partitioning of non-coaxial deformation in strike-slip and dip-slip component along with a pure shear component. Strike-slip is more prominent in the northern part of the contact than the southern part. The presence of steep to moderate northerly plunging non-orthogonal stretching/mineral elongation lineation all along the contact and clockwise shift of plot of the same in stereo net from its orthogonal position and presence of other kinematic indicators in plan suggests a right lateral strike-slip component. As a whole, it is suggested that Udayagiri group is thrusted over Vinjamuru group along a westerly dipping thrust plane with a right lateral strike-slip motion and simultaneous E–W contraction.