AN EXAMPLE OF A THERMALLY METAMORPHOSED AGGLUTINATE

A single fragment from an Apollo 16 soil appears to be a soil agglutinate that has experienced thermal metamorphism. Its texture is similar to that observed in many of the samples of recrystallized polymict breccias collected in the lunar highlands. Debris blankets, consisting largely of mineral and lithic clasts and derived from highland bedrock by major impacts, are less likely than agglutinate-rich soil from the highland megaregolith to be the progenitor of this class of recrystallized rocks.     

Rayleigh waves in granular medium

Summary The wave velocity equation in the form of a ninth order determinantal expression is derived appropriate to Rayleigh type waves in a granular half-space supporting a different granular layer. The calssical frequency equation when both media are elastic has been deduced as a particular case by limiting process.     

Surface winds in The Arabian Sea from MSMR — an Empirical approach

Multi-channel Scanning Microwave Radiometer (MSMR) onboard 1RS P4 (Oceansat I) measured Brightness Temperature data of the different bands are found sensitive to the surface and the overlying atmosphere to different degrees. A judicious combination of multi-channel data can provide such oceanic/atmospheric parameters as surface wind speed, sea surface temperature, water vapour in the marine atmosphere, etc. This paper highlights results obtained in relation to surface wind speed. Co-location and concurrence of several ocean data buoys in the Arabian Sea with MSMR observations allowed empirical construction of D-matrix coefficients for surface wind speed. With both MSMR and the Arabian Sea buoys functioning for the period of one and a half year (June, 1999 to December, 2000) without interruptions provided a large database. All channels are found to exhibit moderate sensitivity to surface wind speed. MSMR data in the immediate vicinity (within 150 km) of the buoy locations and within a time window of one hour were used. A multi-channel linear equation for surface wind speed was subsequently derived. The equation was subjected to tests with independent data set for the period January - June 2001 over the Arabian Sea and found to be moderately accurate. The empirical equation is expected to be useful for regional applications over the Arabian Sea and over regions closer to west coasts, which might have been flagged out in the operational geophysical data stream. An interesting subset of data revealed the wind signatures of the May 2001 cyclone in the Arabian Sea.     

Prediction of sub-surface subsidence movements due to underground coal mining

Summary The theoretical model of the relationship between sub-surface and surface subsidence movements proposed earlier by the authors of this paper is briefly described and further tested against another case history example. Using this model, the magnitudes of the maximum subsidence, tilt and horizontal strain at sub-surface horizons between the ground surface and seam level are predicted in terms of the magnitudes of the corresponding components at the surface due to the extraction of subcritical panels with a wide range of width-depth ratios and the results presented in the form of nomographs and tables. These graphs and tables could be used to estimate the maximum subsidence, tilt and horizontal strain at any chosen sub-surface horizon associated with the extraction of a subcritical panel from the known corresponding maximum values at the surface.The proposed theoretical model can also be used to predict sub-surface subsidence components at any point within the zone influenced by the extraction of a panel from the corresponding surface subsidence components which may be obtained from field measurements or pre-calculated using any existing method of surface subsidence prediction. As an example, the profiles of surface and sub-surface subsidence at various horizons between the ground surface and the seam level resulting from the extraction of an assumed sub-critical longwall panel are predicted using the theoretical model together with the empirical method of surface subsidence prediction. The pattern of sub-surface subsidence movements in the strata overlying the panel is examined.     

Chhotanagpur granite gneiss in relation to the schistose rocks around Murhu,Ranchi district,Bihar: a structural approach

Structural analysis of the Chhotanagpur gneiss and the adjoining schistose rocks of the Singhbhum Group indicates perfect conformity in their structures on macroscopic, mesoscopic and microscopic scales. This precludes the possibility of the gneissic rocks having intruded into the deformed and metamorphozed schistose rocks. The observed features can be best explained by considering the gneissic rocks as the basement and the schistose rocks as the cover, both deformed and metamorphozed together. However, this does not exclude the possibility of the gneissic rocks being reactivated and intruding elsewhere.     

Selection of optimum frequency of a wind scatterometer

The problem of selecting the optimum operating frequency of a scatterometer, used for remote sensing of sea surface wind speed has been addressed by applying the criteria of maximum sensitivity of backscattering coefficient to wind speed as well as its correlation with wind speed. The backscattering coefficient values for sea surface were computed by the two-scale scattering theory. To compute the atmospheric transmittance, 753 clear sky atmospheres over Indian Ocean were used. While the correlation coefficient was uniform (0.94) throughout the frequency range of 1 to 30GHz, only frequencies above 5GHz were found sensitive enough to yield a wind speed accuracy of ±2msec⁻¹ and better, the accuracy improving with frequency.     

Quasi-specular sea scatter with modified reflection coefficient

The paper deals with the relationship between the sea surface wind speed (U) and the backscattering coefficient (σ⁰) for microwave frequencies and quasi specular range of angles. Valenzuela’s effective reflection coefficient based on the theory of scattering of electromagnetic waves from rought dielectric surfaces has been introduced in the expression of backscattering coefficient and the final result compared with the σ⁰-U relationship derived fromSEASAT scatterometer and concurrent sea truth data.     

Geochemistry of braunite and associated phases in metamorphosed non-calcareous manganese ores of India

In the metamorphosed manganese oxide ores of India, braunite is ubiquitous in all assemblages from chlorite to sillimanite grades. Chemical analyses of braunite from different prograde assemblages confirm the presence of a fixed R²⁺ (=Mn²⁺+Mg+Ca) SiO₃ molecule in the mineral. Element partitioning between coexisting braunite and bixbyite indicates a near-ideal mixing of Fe⁺³/ -Mn⁺³ in the phases. This also indicates that braunite became relatively ferrian while equilibrating with associated phases such as bixbyite, hollandite and jacobsite during prograde reactions. Petrogenetic studies show that as a general trend, prograde lower oxide phases appeared by deoxidation of higher oxide phases. But braunite, a more reduced phase than bixbyite, appeared early from deoxidation of pyrolusite in presence of quartz. Bixbyite could appear later from the reacting pyrolusite-braunite-quartz assemblage. Inferred mineral reaction paths and the general trend of pro-grade deoxidation reactions suggest that the composition of ambient fluid phase was internally buffered during metamorphism.