Enriched Subcontinental Lithospheric Mantle in the Northern Part of the South Indian Granulite Terrain: Evidence from Yelagiri and Sevattur Syenite Plutons, Tamil Nadu, South India

In the southern part of the Indian Peninsula, there are a number of alkaline plutons of Proterozoic age. In the northern part of the South Indian granulite terrain, the Yelagiri (syenite, pyroxenite) and Sevattur (syenite, pyroxenite, carbonatite) plutons intrude Archaean epidote-hornblende gneisses. Geochemical and isotopic characteristics of the Yelagiri and Sevattur plutons indicate that the syenitic magmas formed from highly differentiated mantle-derived alkali basalts. The Yelagiri and Sevattur syenites are characterized by evolved Sr and Nd isotopic compositions, pronounced enrichment in LILE and large negative Nb anomalies. Trace element and Sr-Nd isotope characteristics of the Yelagiri and Sevattur syenites are similar to those of the subduction-related alkaline rocks. The scarcity of geological evidence for subduction activity at the time of syenite intrusion during Neoproterozoic does not support a link between the alkaline magmatism and subduction. However, our data are consistent with the model of derivation of the Yelagiri and Sevattur syenites from the subcontinental lithospheric mantle, which was previously enriched by slab derived component. The geochemical and isotopic signatures of other mantle-derived intrusive rocks in the northern part of the South Indian granulite terrain with ages ranging from ca. 2.5 Ga to 0.75 Ga also support the above idea.     

Nonradial oscillations of models of the generalized Roche series

Nonradial oscillations of certain models of the generalized Roche series have been investigated numerically to further understand the nature of the eigen-values and the eigen-functions of the modes of nonradial oscillations of stellar models.     

Effect of Coriolis force on the shapes of rotating stars and stars in binary systems

In this paper an attempt has been made to determine the effect of Coriolis force on the shapes of Roche equipotential surfaces of rotating stars and stars in binary systems. Equations of Roche equipotential surfaces have been obtained for rotating and binary stars which take into account the effects of Coriolis force besides the centrifugal and gravitational forces. Shapes of Roche equipotentials and values of Roche limits are obtained for different values of angular velocity of rotation for rotating stars and for different values of mass ratios for the binary stars. The obtained results have been compared with the corresponding results in which the effect of Coriolis force has not been considered.     

On the Electron density in a coronal hole

Electron density in a coronal hole is rediscussed using the new calculation for the Mgviii 436.62/430.47 density-sensitive theoretical line ratio and with the help of available observations.     

基于激光雷达的自然资源三维动态监测现状与展望

激光雷达作为一种主动的三维遥感观测技术,在不同尺度的土地、矿产、森林、草原、湿地、水、海洋等自然资源的三维动态监测中发挥着越来越重要的作用.本文将在简要介绍激光雷达技术发展现状的基础上,重点阐述激光雷达技术在各类自然资源三维动态监测中的应用现状,同时对激光雷达在自然资源调查中的应用潜力和局限性进行综合分析,最后探讨以激...     

Structural information derived from ambient noise tomography over a hydrocarbon-producing region in the Cachar fold belt,lower Assam,northeast India

Ambient noise tomography is a powerful tool that has found increasing application in reservoir analysis and imaging. The Cachar fold belt in lower Assam, northeast India encompasses several wells under active hydrocarbon production, along with several dry wells. To overcome the lack of active seismic data over the entire fold belt, a passive seismic study was carried out to image the concealed three-dimensional sub-surface structures. The data were recorded from February to November 2011 by a network of 65 wideband seismometers spanning an area of about 40 × 60 km². The data are crosscorrelated in the 2–5 s band, followed by phase-weighted stacking to estimate noise correlation functions with surface wave signatures. The traveltimes picked from the frequency-time analysis are utilized in a tomographic inversion for Rayleigh wave group velocities. The group velocity anomalies have a lateral resolution of ~ 3.5 × 5.5 km² and variations of up to $\pm 20\%$ for each period. The group velocities are in turn inverted for S-wave velocity distribution as a function of depth. The three-dimensional S-wave velocity tomograms reveal the tight anticlines and broad synclines, with high- and low-velocity zones corresponding to structural highs and lows, respectively. The structural interpretation is supported for the part of the region with producing wells and covered by active seismic data, wherein the post-stack time migrated seismic section shows anticlinal and synclinal features similar to those obtained from ambient noise tomography. The structures revealed by ambient noise tomography can help identify zones of interest to be targeted by active seismic surveys in the Cachar fold belt.