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Tidal variations in the Sundarbans Estuarine System, India 总被引：1，自引：0，他引：1
MEENAKSHI CHATTERJEE D SHANKAR G K SEN P SANYAL D SUNDAR G S MICHAEL ABHISEK CHATTERJEE P AMOL DEBABRATA MUKHERJEE K SUPRIT A MUKHERJEE V VIJITH SIDDHARTHA CHATTERJEE ANWESHA BASU MADHUMITA DAS SARANYA CHAKRABORTI ARAVIND KALLA SURJA KANTA MISRA SOUMYA MUKHOPADHYAY GOPAL MANDAL KANKAN SARKAR 《Journal of Earth System Science》2013,122(4):899-933
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Dwijesh RAY Ranadip BANERJEE Sridhar D IYER Basavaraju BASAVALINGU Subir MUKHOPADHYAY 《《地质学报》英文版》2009,83(6):1122-1135
Abstract: The glass and mineral chemistry of basalts examined from the northern central Indian ridge (NCIR) provides an insight into magma genesis around the vicinity of two transform faults: Vityaz (VT) and Vema (VM). The studied mid-ocean ridge basalts (MORBs) from the outer ridge flank (VT area) and a near-ridge seamount (VM area) reveal that they are moderately phyric plagioclase basalts composed of plagioclase (phenocryst [An60–90] and groundmass [An35–79]), olivine (Fo81–88), diopside (Wo45–51, En25–37, Fs14–24), and titanomagnetite (FeOt ~63.75 wt% and TiO2 ~22.69 wt%). The whole-rock composition of these basalts has similar Mg# [mole Mg/mole(Mg+Fe2+)] (VT basalt: ~0.56–0.58; VM basalt: ~0.57), but differ in their total alkali content (VT basalt: ~2.65; VM basalt: ~3.24). The bulk composition of the magma was gradually depleted in MgO and enriched in FeOt, TiO2, P2O5, and Na2O with progressive fractionation, the basalts were gradually enriched in Y and Zr and depleted in Ni and Cr. In addition, the SREE of magma also increased with fractionation, without any change in the (La/Yb)N value. Glass from the VM seamount shows more fractionated characters (Mg#: 0.56–0.57) compared to the outer ridge flank lava of the VT area (Mg#: 0.63–0.65). This study concludes that present basalts experienced low-pressure crystallization at a relatively shallow depth. The geochemical changes in the NCIR magmas resulted from fractional crystallization at a shallow depth. As a consequence, spinel was the first mineral to crystallize at a pressure >10 kbar, followed by Fe-rich olivine at <10 kbar pressure. 相似文献
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A New Report of Serpentinites from Northern Central Indian Ridge (at 6°S)—An Implication for Hydrothermal Activity 总被引：1，自引：1，他引：0
Serpentinites from the inside corner high (6°38.5'S/ 68°19.34'E) from the Northern Central Indian Ridge (NCIR) are comprised mainly of high Mg-rich lizardite and chrysotile pseudomorphs with varying morphologies.'Mesh rim','window', 'hourglass'and'bastite'are the most common textures displayed by both chrysotile and lizardite.Numerous chrysotile veins in association with cross cutting magnetite veins indicate an advanced stage of serpentinisation.The relatively high abundance of chrysotile and lizardite suggest their close association and formation at a temperature below 250°C. Abundant 'mesh rim' and 'bastite'texture and variegated matrix reveal that the present Serpentinites might have formed due to the interaction of harzburgite and seawater.Positive Eu anomaly (Eu/Eu*up to 3.38), higher La/Sin (up to 4.40) and Nb/La (up to 6.34) ratios suggest substantial hydrothermal influence during the formation of the Serpentinites. 相似文献
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Tectonothermal evolution of the gneiss complex at Salur in the Eastern Ghats Grnaulite Belt of India
Textural relations, thermobarometry and petrogenetic grid considerations in the syn-tectonic granitoid massif and the enveloping metasedimentary gneisses at Salur are consistent with a counter-clockwise P–T –t path for the rocks. The low-P/high-T prograde sector is documented by the pre- to syn-D1 cordierite±orthopyroxene±garnet±spinel–bearing metatexite leucosomes in metapelites. Heating and loading of the rocks (syn- to post-D1) resulted in the formation of garnet+orthopyroxene± cordierite-bearing diatexites, and decomposition of cordierite in metatexite leucosomes to orthopyroxene+sillimanite+biotite+quartz symplectites. Near-peak temperature, 850 °C at 8.0 kbar, was reached syn- to post-D2. Post-peak cooling resulted in the stabilization of coronal grossular and anorthite+calcite symplectites at the expense of scapolite+wollastonite+calcite assemblages in calc-silicate gneisses, and the resetting of cation exchange temperatures at 700–750 °C. Near-isothermal decompression at c. 700–750 °C is manifested by the decomposition of garnet porphyroblasts in the granitoid gneisses to plagioclase+orthopyroxene/ilmenite/biotite two-phase coronas and restabilization of cordierite at garnet margins in metapelites. Subsequent low-P, near-isobaric cooling led to the overprinting of granulite facies assemblages by muscovite+calcite assemblages, and further resetting of cation exchange thermometers to lower temperatures c. 600 °C. The tectonothermal evolution of the Salur gneiss complex vis-a-vis the Eastern Ghats Belt is therefore consistent with high degrees of lower crustal melting, followed by prograde heating of the cover rocks due to magma invasion synchronous with crustal compression, and finally thermal relaxation over a protracted period punctuated by tectonic/erosional denudation of the thickened crust. 相似文献
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Upper-mantle xenoliths in volcanic pipes cutting the axis ofthe Sierra Nevada batholith contain predominantly spinel-bearingperidotites (with sporadic garnet) and garnet websterites. Inspite of the enormous thickness of the Sierran crust, the Sierranupper mantle has not attained the garnet peridotite stabilityfield. The peridotites have forsteritic (Fo88–92) olivines,Cr-diopsides, Cr-spinels, and magnesian orthopyroxenes (En88–92).Their texture and compositional characteristics of the coexistingphases indicate that these are fragments of the upper mantlethat had undergone various degrees of partial fusion. The Pconditions of reequilibration and mineralogical characteristicssuggest that the partial fusion was accompanied by diapiricuprise. The REE distribution patterns are nearly chondritic.Garnet websterite xenoliths also contain magnesian and Cr-richphases. Their bulk chemical compositions are like pyroxenitecumulates. The garnet websterites from Big Creek differ fromthose occurring at Pick and Shovel in having more Fe-rich phasesand occasional hydrous minerals. The Pick and Shovel garnetwebsterites are interpreted to be pyroxene-rich, garnet-freecumulates formed by fractional crystallization of melts generatedby partial melting of subcontinental lithosphere at depth 60km. The REE abundance of these xenoliths is consistent withthis mode of origin. Presence of jadeitic clinopyroxenes andF-rich phlogopites, and the LREE- and 87Sr/86Sr-enriched characterof the garnet websterites from Big Creek may suggest their originas metasomatized upper-mantle garnet peridotites. The latestP-T conditions of equilibration of all garnet-bearing samplesshow that they lie along a nearly adiabatic gradient in therange of 900–1000 C and 18–32 kbar. An isotopically heterogeneous, old (1 b.y.) subcontinental lithosphere,characterized by high 87Sr/86Sr (0.7044–0.7082), radiogenic206Pb/204Pb (18.86–20.04), 207Pb/204Pb (15.64–15.69)and 208Pb/204Pb (38.69–39.11), and moderate 143Nd/144Nd(0.51234–0.51260; ENd–0.35 to –5.8) is consideredto be the source of these rocks. There was a fluid influx froma subducted slab carrying Ba, K, Rb, U, Th, and radiogenic Pbinto the overlying ancient lithosphere. 相似文献
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RAY Durbar BANERJEE Ranadip MAZUMDER Anin PAROPKARI Anil L. MUKHOPADHYAY Subir BALAKRISHNAN Srinivasan 《海洋学报(英文版)》2018,37(4):22-33
Polymetallic sulfides from two hydrothermal chimneys and talus deposit from the Vienna Woods field of Manus Basin were studied for mineralogy, elemental composition, and S-isotope ratio to understand their evolution. The factors including the nature of source fluid, mineral paragenesis, and related geochemical processes have been discussed. Mineralogy and elemental concentration of Cu and Fe-rich large chimney at the central part of this hydrothermal field was completely different from the smaller Zn-rich peripheral chimney and Fe-rich talus deposit, suggesting the variable degree of alterations generate physico-chemically different source fluids responsible for these hydrothermal structures. Similarly, S-isotope ratios also indicate chemically diverse fluids and different modes of precipitation were involved in their evolution. Distinct mineral zonings and associated elemental and isotopic compositions within individual deposit confirm paragenetic shifts were involved during their growth process. 相似文献
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