Palaeomagnetic and rock magnetic study of charnockites from Tamil Nadu,India, and the ‘Ur’ protocontinent in Early Palaeoproterozoic times     

S. Mondal  J.D.A. Piper  L. Hunt  G. Bandyopadhyay  S. Basu Mallik 《Journal of Asian Earth Sciences》2009,34(4):493-506

Palaeomagnetic and magnetomineralogical results are reported from charnockites in basement terrane at the eastern sector of the WSW–ENE granulite belt of South India. Magnetite is the dominant ferromagnet identified by rock magnetic and optical study; it is present in several phases including large homogeneous titanomagnetites and disseminated magnetite in microfractures linked to growth stages ranging from primary charnockite formation to uplift decompression and exhumation within the interval ～2500–2100 Ma. Several components of magnetization are resolved by thermal demagnetization and summarized by four pole positions; in the northern (Pallavaram) sector these are P1 (33°N, 99°E, dp/dm = 8/9°) and P2 (79°N, 170°E, dp/dm = 3/6°), and in the southern (Vandallur) sector they are V1 (23°N, 116°E, dp/dm = 8/9°) and V2 (26°S, 136°E, dp/dm = 5/10°). These magnetizations are linked to uplift cooling of the basement and unblocking temperature spectra suggest acquisition sequences P1 → P2 and V1 → V2 in each case implying movement of the shield from higher to lower palaeolatitudes sometime between 2500 and 2100 Ma. Palaeomagnetic poles from the cratonic nuclei of Africa, Australia and India all identify motion from higher to lower palaeolatitudes in Early Palaeoproterozoic times, and this is dated ～2400 and ～2200 Ma in the former two shields. The corresponding apparent polar wander (APW) segments match the magnetization record within the charnockite basement terranes of southern India to yield a preliminary reconstruction of the ‘Ur’ protocontinent, the oldest surviving continental protolith with origins prior to 3000 Ma. Although subject to later relative movements these nuclei seem to have remained in proximity until the Mesozoic break-up of Gondwana.  相似文献   

Aquifer Response in the Ultramafic Field Area of Sukhinda Valley — Orissa (India)     

I. Radhakrishna  T. Venkateswarlu 《Ground water》1980,18(5):479-485

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Palaeomagnetism and ages of dolerite dykes in Karimnagar District, Andhra Pradesh, India   总被引：1，自引：0，他引：1  

Y. V. Subba Rao  I. V. Radhakrishna Murthy 《Geophysical Journal International》1985,82(2):331-337

Summary. Results of palaeomagnetic investigations of three dolerite dykes in Karimnagar District, Andhra Pradesh, India are reported. The remanent magnetic directions of specimens from one dyke, called A, fall into two groups, one with a positive inclination and the other with a negative inclination, indicating two intrusions. For dykes B and C, the remanent magnetic directions show a negative inclination. The pole positions for all these dykes are close to those for the Gwalior Traps, whose age is 1830±200 Myr. It is inferred that these dykes were emplaced over a short span of time around the Gwalior Trap period, which may represent a phase of multiple igneous activity.  相似文献   

Simulation of chloride migration rates in Paleo Pennar Delta Region, Coastal Andhra Pradesh, India   总被引：1，自引：0，他引：1  

M. V. R. Chowdary  I. Radhakrishna 《Environmental Geology》1998,36(1-2):109-117

 Quaternary alluvial aquifers in the paleo Pennar delta region of Andhra Pradesh (Long. 80°0′ and 80°12′; Lat. 14°40′ and 14°20′) constitute an important coastal strip, with potential fresh groundwater resources and several well fields in operation. The lineament patterns and traces of paleo channels provide basic information on the configuration and boundaries of paleo delta and the possible neotectonic movements in the region. The paleo delta region is essentially characterized by freshwater aquifer systems at the near-surface depths, (up to 50 m from ground level) with transmissivity values in the system ranging from 1200 to 2500 m²/day. This groundwater system has been subjected to heavy draft situation over the last two decades, parlicularly near the outer rim of the delta where an unlined brackish-water canal runs parallel to the coast imparting chloride contamination to the adjoining fresh aquifers. A two-dimensional solute transport model solution was applied to assess chloride migration rates inland under different hydraulic stresses, combining finite difference solution of flow equation and the method of characteristic solution of solute transport equation. Groundwater flow and chloride migration patterns/rates were obtained for different simulated stress events in the delta system, and measures required to protect the freshwater resources ara outlined. Received: 2 January 1997 · Accepted: 4 November 1997  相似文献   

Evaluation of the boundary layer depth in semi-arid region of India     

Manoj Kumar  Chinmay Mallik  Anil Kumar  N.C. Mahanti  A.M. Shekh 《Dynamics of Atmospheres and Oceans》2010,49(2-3):96-107

The annual variation in Planetary Boundary Layer (PBL) height is determined from the profiles of conserved thermodynamic variables, i.e. virtual potential temperature θ_v, equivalent potential temperature θ_e and saturated equivalent potential temperature θ_es, using radiosonde data at Anand (23°35′N, 72°55′E, 45.1 m a.s.l.), India. Out of all the variables, the θ_v profile seems to provide the most reasonable estimate of the PBL height. This has been supplemented by T–Phi gram analysis for specific days. The analysis has been done for 00, 03, 06, 09 and 12 GMT for the 14th and 15th day of each month in the year 1997 based on LASPEX-97 data. In winters the height of boundary layer is very low due to subsidence and radiation cooling while heights in pre-monsoon months exhibit large variations.  相似文献   

Foreword     

B. P. Radhakrishna 《Journal of the Geological Society of India》2010,75(1):1-1

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Changing trends of scientific practices in India in the twenty-first century     

B. P. Radhakrishna 《Journal of the Geological Society of India》2010,75(6):779-782

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Paul K. Sims (1918–2011)     

B. P. Radhakrishna  S. Viswanathan 《Journal of the Geological Society of India》2012,79(1):96-97

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Do we lack in ‘scientific temper’?     

B. P. Radhakrishna 《Journal of the Geological Society of India》2009,74(2):151-157

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Grain-size variation in the Kavaratti lagoon sediments,Lakshadweep, Arabian Sea     

T.K. Mallik 《Marine Geology》1976,20(1):57-75

The Lakshadweep are a group of coral atolls enclosing lagoons and submerged reefs and banks in the Arabian Sea off the western coast of India. The sediments in the lagoons consist of corals, halimeda, shells of gastropods, pelecypods, foraminifera, ostracods, etc. derived from the breaking up of the reefs by mechanical processes such as waves, winds, currents, etc. To study the grain-size characteristics of these calcareous sediments in the lagoons, 50 samples were analysed and the grain-size parameters were calculated. The mean of the samples range from ?1.538 to 2.161, standard deviation from 0.935 to 1.859, skewness from ?1.051 to 1.635 and kurtosis from 2.068 to 4.402. The sediments range from coarse sand and gravel to very fine sand size in general and usually are well sorted. A bimodal to polymodal character is present in the sediments due to mixing of a number of heterogeneous constituents. The coarser sediments consist of corals and a good amount of halimeda occurs in the 0 (1 mm) to ?1 (2 mm) phi class. Foraminifera predominantly occur in the interval 1 (0.5 mm) to 0 (1 mm) phi. In the range 1 (0.5 mm) to 2 (0.25 mm) phi, corals are again important, while in the sizes finer than 2 phi (0.25 mm), all the constituents predominate. The size distribution was compared with those obtained at other places such as Barracuda Keys, Gulf of Aqaba, Isla Perez and Lower Florida Keys. The present grain-size variation is not only controlled by the composition of the calcareous sediments but is also modified by the different transporting agents, such as waves, winds, currents, etc. Different energy conditions also exist in the lagoon. Mean transport direction seems to be roughly towards the SSE and saltation is an important mode of transport.  相似文献