Precambrian mafic magmatism in the Singhbhum craton,eastern India     

Mihir K. Bose 《Journal of the Geological Society of India》2009,73(1):13-35

The Singhbhum craton has a chequred history of mafic magmatism spanning from early Archaean to Proterozoic. However, lack of adequate isotopic age data put constraints on accurately establishing the history of spatial growth of the craton in which mafic magmatism played a very significant role. Mafic magmatism in the craton spreads from ca.3.3 Ga (oldest “enclaves” of orthoamphibolites) to about 0.1 Ga (‘Newer dolerite’ dyke swarms). Nearly contemporaneous amphibolite and intimately associated tonalitic orthogneiss may represent Archaean bimodal magmatism. The metabasic enclaves are appreciably enriched and do not fulfill the geochemical characteristics of worldwide known early Archaean (>3.0 Ga) mafic magmatism. The enclaves reveal compositional spectrum from siliceous high-magnesian basalt (SHMB) to andesite. However, the occurrence of minor depleted boninitic type within the assemblage has so far been overlooked. High magnesian basalt with boninitic character of Mesoarchaean age is also reported in association with supracrustals from southern fringe of the granitoid cratonic nucleus. The subcontinental lithospheric mantle (SCLM) below the craton is conjectured to have initiated during the early Archaean. Significantly, recurrence of depleted magma types in the craton is observed during the whole span of mafic igneous activity which has been vaguely related to “mantle heterogeneity”, although the alternative model of sequential mantle melting is also being explored. The Singhbhum craton includes the Banded Iron Formation (BIF) associated mafic lavas, MORB-like basic and komatiitic ultrabasic bimodal volcanism — documented as Dalma volcanics, Dhanjori lavas, and the Proterozoic Newer dolerite dykes. Three different types of REE fractionation patterns are observed in the BIF-associated mafic lavas. These are the REE unfractionated type is more depleted than N-MORB and some lavas with boninitic type of REE distribution. MORB-like basic and komatiitic ultrabasic (Dalma volcanics) are emplaced within the Proterozoic Singhbhum Basin (PSB). The vista of magmatism in the basin was controlled by a miniature spreading centre represented by the mid-basinal Dalma volcanic ridge. The volcano-sedimentary basinal domain of Dhanjori emerged at the interface of two subprovinces (viz. the mobile volcano-sedimentary belt of PSB and rigid granite platform) under unique stress environment related to extensional tectonic regime. Trace element distribution in Dhanjori lavas is remarkably similar to that in PSB minor intrusions and lavas (except a Ta spike in the latter). The Proterozoic Newer dolerite dykes within Singhbhum nucleus manifest an unusually wide spam of intrusive activity (ca 2100 Ma to 1100 Ma) and unexpectedly uniform mantle melting behaviour.  相似文献   

The Vaca Muerta mesosiderite: The path under which Fe-Ni alloy ±C phases could have formed     

M. E. Varela  S.-L. Hwang  P. Shen  L. N. Garcia  M. Saavedra  T. Maruoka  M. Bose 《Meteoritics & planetary science》2024,59(3):421-434

The combined SEM and TEM studies on the metal (Fe-Ni alloy ±C) portion of the Vaca Muerta mesosiderite reveal structural and compositional evidence at micro to nanoscale, which sheds light on the solidification of taenite + graphite as a cement, and later solid-state precipitation process for the kamacite formation as grain boundary allotriomorph. Besides, it is proposed that the graphite veinlets formed through a complex partial melting process followed by a solidification toward the final eutectic transient coupled with the solid-state precipitation and later decomposition ordering of taenite. The presence of defects and taenite in graphite signal formation in a liquid environment. The δ¹³C values of graphite in the graphite-rich areas (e.g., ranging from −0.8 ± 1.7‰ to +15.3 ± 2.5‰) suggest a short-circuit diffusion path for C isotope fractionation.  相似文献   

Hydrodynamic characteristics of a lunate shape oscillating propulsor     

Pengfei Liu  Neil Bose   《Ocean Engineering》1999,26(6):325

Research was conducted to study the hydrodynamic efficiency of a foil with aft-swept wing tips. A potential flow based time domain panel method was formulated to predict the performance of a lunate and rectangular foil in large amplitude, unsteady motion. Skin drag was approximated and boundary layer growth and separation were also estimated. Hydrodynamic efficiency was evaluated in terms of propulsive efficiency and thrust coefficient of the foil. Results are presented for a lunate shaped planform and for a rectangular foil. Predictions show that the lunate shaped planform has a substantially higher propulsive efficiency (13% higher) than the rectangular foil under heavy load conditions when the feathering parameter is zero, throughout a range of reduced frequencies (0.2 to 1.8). Under a medium load condition, however, the rectangular foil gave a higher propulsive efficiency at reduced frequencies less than 0.5 and the same efficiency value at a reduced frequency of 1.8. For a practical range of reduced frequencies between 0.5 and 1.0, the lunate tail gave higher propulsive efficiency. The lunate planform gave a lower thrust coefficient at a heavy load and higher thrust at a medium load condition than the rectangular planform for all reduced frequencies.  相似文献   

Deccan basalts     

Mihir K. Bose 《Lithos》1972,5(2):131-145

The Deccan basalts now cover an area of c. 500,000 sq. km in central and western India. The lava pile varies in thickness from c. 2000 metres in western India to c. 100–200 metres in central India, exposing the upper and lower horizons of the volcanics respectively. The salient mineralogical and chemical characters of the basalts are reviewed. Dominantly the basalts are tholeiitic while minor alkalic variants in western India represent the closing phase of volcanic activity. The diversification of the magma to the west is associated with thickening of the lava pile and increase of heat flow. The ultrabasic flows (picrite basalts) are products of fractionation of the source magma of olivine tholeiitic composition. The minor acid variants (e.g. rhyolites, pitchstones, felsites, etc.) are possibly residual liquids of the ascending magma.  相似文献   

Mineral reactions and geothermobarometry in a suite of granulite facies rocks from Paderu, Eastern Ghats granulite belt: A reappraisal of the P-T trajectory     

Supratim Pal  Sankar Bose 《Journal of Earth System Science》1997,106(3):77-89

High Mg-Al spinel-sapphirine granulites, orthopyroxene-bearing quartzofeldspathic granulites, two pyroxene-bearing mafic granulites and metapelitic gneisses are exposed around Paderu, Eastern Ghats Belt. Geothermobarometry in orthopyroxene-bearing quartzofeldspathic granulites and mafic granulites indicate near isobaric cooling through 90°C from ca. 720°C to 630°C, at 8.0 kbar. However, signatures of ultrahigh temperature metamorphism are recorded from the mineralogy and reaction textures in the high Mg-Al granulites. Mineral reactions deduced in this work, when combined with others described by Lalet al (1987) from the same area and plotted in an appropriate petrogenetic grid in the system FMASO indicate an ACW path comprising a high dT/dP prograde arm reaching P_max − T_max = 9.5 kbar, ∼ 1000°C, followed by near-isobaric cooling down to 9 kbar, 900°C and subsequent decompressive reworking.  相似文献   

Sensitivity of AUV response to variations in hydrodynamic parameters     

Doug Perrault  Neil Bose  Siu O&#x;Young  Christopher D. Williams 《Ocean Engineering》2003,30(6):779-811

The sensitivity of the response of a typical AUV to changes in hydrodynamic parameters is examined. The analysis is primarily performed using a computer model of an axi-symmetric vehicle typical of many AUVs in service today. The vehicle used is the Canadian Self-Contained Off-the-shelf Underwater Testbed (C-SCOUT), designed and built by graduate and work term students. The fully nonlinear computer model is based on Newton–Euler equations of motion, and uses the component build-up method to describe the excitation forces. The hydrodynamic parameters are varied in a series of simulations with the computer model; the response being analyzed for specific performance indicators.  相似文献   

Petrology of the nepheline syenite of Mount Girnar, India     

Mihir K. Bose 《Lithos》1971,4(4):357-366

Hypersolvus nepheline syenite and haplosyenite, in close spatial and temporal association with lamprophyric rock, occur as small intrusions in the gabbrodiorite pluton of Mount Girnar, Gujrat, Western India. The syenite crystallized in a relatively dry condition from a residual liquid following crystallization of lamprophyric rock with profuse hydrous mafic phases. Distribution of some of the more common trace elements with respect to the major elements in the syenites has been interpreted.  相似文献   

Wave propagation in marine sediments and water saturated soils     

S. K. Bose 《Pure and Applied Geophysics》1962,52(1):27-40

Summary A unification of the theories of Biot and Weiskopf has been made to form the suitable equations of motion for porous water saturated soils and marine sediments. It has been shown that the velocities of the body waves depend on the direction of propagation. In the vertical direction there are three, one distortional and two dilatational waves. In the horizontal direction there are two dilatational and two distortional waves. Finally, propagation of Love waves and Rayleigh waves have been discussed. Suitable potential functions have been derived to find the frequency equation for Rayleigh waves.  相似文献   

Controls on the geometry of tails around rigid circular inclusions: insights from analogue modelling in simple shear     

Santanu Bose  Fernando O. Marques   《Journal of Structural Geology》2004,26(12):2145-2156

We used analogue modelling to investigate the factors controlling tail geometry in porphyroclast systems. Results show that: (1) σ inclusions can develop in both slipping and non-slipping modes, but δ-inclusions only form in the latter. (2) σ inclusions develop when the mantle production rate is constant and the mantle is transected by the separatrix. δ inclusions form when the mantle is initially outside the separatrix and later comes inside this line. (3) In the slipping mode, the wedge-shaped tail of σ-inclusions always has a straight external surface parallel to the shear plane, whereas in the non-slipping mode the external surface is curved inwards (external embayments). (4) Together with earlier theoretical results, σ- and δ inclusions always show stair-stepping of tails when embedded in a viscous matrix under homogeneous simple shear deformation. (5) Maximum stair-stepping occurs in the slipping mode and is at least equal to the inclusion diameter. If our models bear significant similarity to nature, then (i) the straight or curved character of σ-inclusions could mean that they had, respectively, a slipping or non-slipping interface with the surrounding recrystallized matrix, and (ii) δ-inclusions may result from shear deformation under retrogressive metamorphic conditions in thrust systems.  相似文献   

Penecontemporaneous dolomitization in the Precambrian Bhander Limestone,Rajasthan, India — A petrographic attestation     

Bose  Pradip K. 《International Journal of Earth Sciences》1979,68(2):680-695

Dolomitization in the Precambrian Bhander Limestones around Bhainsrorgarh, Rajasthan was largely penecontemporaneous with deposition in tidally influenced evaporating pans. Regardless of the circumstantial evidence relating to the environment, prelithification dolomitization is evident independently from intimate control of the depositional fabric on the process, swerving of calcite laminae around dolomite porphyrotopes, and streaming of mica flakes around dolospars. Penecontemporaneity of this dolomitization is inferred from its confinement within selected lamina/e or bed/s, leaving the adjacent laminae or beds completely unaffected, plastic deformation and occasional mechanical failure of seams of pallisade calcite crystals infilling shrinkage cracks, formation of thin dolomitized crusts at lamina-top surfaces and its downward gradation to primary calcmicrite by gradual depletion of dolomite concentration and erosion of such crusts prior to deposition of overlying sediments.In modern settings penecontemporaneous dolomite crystals are usually less than 5 micron size but in present case they are mostly much coarser. This coarsening presumably arises from epitaxial growth on initially micron-sized dolomites.There are, of course, partly overlapping phases in dolomitization. Epigenetic dolomitization operated in a subordinate scale and has sometimes been manifested as passive precipitation in voids.

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Zusammenfassung Dolomitization in the Precambrian Bhander Limestone around Bhainsrorgarh, Rajaszeitig mit der Sedimentation in Gezeiten-beeinflußten Evaporit-Becken. Über diesen Hinweis aus dem Ablagerungsmilieu hinaus ist eine Dolomitisierung vor der Lithifikation auch aus dem Gefüge zu erkennen. Hierzu gehören Dolomitkristalle, die von Kalzitkrusten umhüllt sind, sowie die Anordnung von Glimmerblättchen um Dolomite. Synsedimentäre Dolomitisierung wird weiterhin belegt durch die Beeinflussung bestimmter Sedimentlagen und durch die Überlagerung von ungestörten Sedimenten, die Füllung von Schrumpfungsrissen mit Pallisaden-Kalzit nach der Dolomitbildung, sowie die Kristallisation von Dolomitkrusten an Sedimentoberflächen und deren Aufarbeitung.Rezenten Beobachtungen nach sind synsedimentäre Dolomite meist sehr feinkörnig; die hier gefundenen größeren Dolomite werden auf ein späteres epitaxiales Überwachsen zurückgeführt. Darüber hinaus gibt es auch später Dolomitisierungsphasen von untergeordneter Bedeutung.

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Résumé La dolomitisation du calcaire précabrien du Bhander dans le Rajasthan se produit en même temps que la sédimentation dans des vases d'évaporation influencé par les marées. A partir de cette indication relative au milieu du depôt, une dolomitisation est aussi discernable dans les textures, avant la lapidification. A ceci appartiennent les cristaux dolomitiques qui sont enveloppés de croûtes de calcite, ainsi la disposition de paillettes de mica autour des dolomites. La dolomitisation synsédimentaire sera encore complexée par l'influence de certaines couches de sédiments par le recouvrement de sédiments qui n'ont pas été dérangés, par le remplissage de craquelures de compaction par de la calcite en palissade après la formation de la dolomite ainsi que la cristallisation des croûtes de dolomite à la surface des sédiments et leur remeniement. D'après de récentes observations, les dolomites synsédimentaires sont la plupart à grain très fin. Les dolomites les plus grandes qui ont été trouvées ici, doivent être attribuées à un gonflement épitaxique plus tarif. En outre, il y a aussi des phases de la dolomitisaitons tardives qui n'ont qu'une signification secondaire.

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