Late Archaean to Palaeoproterozoic felsic magmatic lithounits exposed in the central part of the Bundelkhand massif have been
mapped and their redox series (magnetite vs ilmenite series) evaluated based on magnetic susceptibility (MS) data. The central
part of Bundelkhand massif comprises of multiple felsic magmatic pulses (∼2600–2200 Ma), commonly represented by coarse grained
granite (CGG-grey granite, CPG-pink granite), medium grained pink granite (MPG), fine grained pink granite (FPG), grey and
pink rhyolites and granite porphyry (GP). However, the pink colour of these felsic rocks is the result of hydrothermal fluid-flushing
leading to potassic alteration of grey granites. MS values of CGG vary from 0.058 to 14.75×10−3 SI with an average of 6.35×10−3 SI, which mostly represent oxidized type, magnetite series (73%) granites involving infracrustal (igneous) source materials.
CPG (av. MS=3.95×10−3 SI) is indeed a pink variety of CGG, the original oxidizing nature of which must have been similar to the bulk of CGG, but
has been moderately to strongly reduced because of distinctly more porphyritic nature together with partial assimilation of
metapelitic (supracrustal) materials, surmicaceous enclaves, carbonaceous material included in the source materials, and to
some extent, induced by hydrothermal and later deformational processes. MPG (av. MS= 1.15×10−3 SI) as lensoidal stock-like bodies intrudes the CPG and represent both magnetite series (18%) and ilmenite series (82%) granites,
which are probably formed by heterogeneous (mixed) source rocks. GP (av. MS=6.26×10−3 SI) occur as dykes (mostly trending NE-SW) intrudes the MPG, CPG and migmatites and bears the nature similar to oxidized
type, magnetite series granite. FPG (av. MS= 0.666×10−3 SI) trending NE-SW occur as lensoid bodies including a large outcrop, is intrusive into both CPG and MPG, and is moderately
to very strongly reduced type, ilmenite series granites, which may be derived by the melting of metapelitic crustal sources.
FPG hosting microgranular (mafic magmatic) enclaves commonly exhibit high MS values (7.31–10.22×10−3 SI), which appear induced by the mixing and mingling of interacting felsic and mafic magmas prevailed in an open system.
Grey (av. MS=10.30×10−3 SI) and pink (av. MS=6.72×10−3 SI) rhyolites represent oxidized type, magnetite series granites, which may have been derived from infracrustal (magmatic)
protoliths. Granite series evaluation of felsic magmatic rocks of central part of Bundelkhand massif strongly suggests their
varied redox conditions (differential oxygen fugacity) mostly intrinsic to magma source regions and partially modified by
hydrothermal and tectonic processes acting upon them. 相似文献
The kinetics of the formation of the purple-colored species between FeIII-EDTA and peroxynitrite were studied as a function of pH (10.4–12.3) at 22°C in aqueous solutions using a stopped-flow technique.
A purple-colored species was immediately formed upon mixing, which had an absorbance maximum at 520 nm. The increase in absorbance
with time could be fit empirically by a power function with two parameters a and b. The power equation determined was absorbance = a*tb, where a increased linearly with pH and the concentration of peroxynitrite, while b almost remained constant with a value of ~0.25. The molar extinction coefficient ε520 nm for the colored species was determined as 13 M−1cm−1, which is much lower than ε520 nm = 520 M−1 cm−1 for the [FeIII(EDTA)O2]3−, a purple species observed in the FeIII–EDTA–H2O2 system. The results of kinetics and spectral measurements of the present study are briefly discussed and compared with those
of the reaction between Fe(III)-EDTA and hydrogen peroxide. 相似文献
In remote sensing the identification accuracy of mangroves is greatly influenced by terrestrial vegetation. This paper deals with the use of specific vegetation indices for extracting mangrove forests using Earth Observing-1 Hyperion image over a portion of Indian Sundarbans, followed by classification of mangroves into floristic composition classes. Five vegetation indices (three new and two published), namely Mangrove Probability Vegetation Index, Normalized Difference Wetland Vegetation Index, Shortwave Infrared Absorption Index, Normalized Difference Infrared Index and Atmospherically Corrected Vegetation Index were used in decision tree algorithm to develop the mangrove mask. Then, three full-pixel classifiers, namely Minimum Distance, Spectral Angle Mapper and Support Vector Machine (SVM) were evaluated on the data within the mask. SVM performed better than the other two classifiers with an overall precision of 99.08%. The methodology presented here may be applied in different mangrove areas for producing community zonation maps at finer levels. 相似文献
During the occurrence of earthquake, the shear wave propagates in the rocks present inside/at the Earth’s crust. The propagation of shear wave may lead to the progression of punch present inside the rock medium. As a result of this, substantial stress accumulated at the vicinity of propagating punch inside rock medium which significantly affects the stability of various geological and human-made structure and, hence, may cause failure of structure. Therefore, the analysis of stress concentration at the vicinity of punch moving due to shear wave propagation has become prominent in the area of seismology. In the present paper, an analytical perspective has been employed to discuss the influence of velocity of moving punch associated with the propagation of shear wave on developed dynamic stress concentration (DSC) in three types of pre-stressed vertical transversely isotropic (VTI) poroelastic media viz. granite (an igneous rock); sandstone (a sedimentary rock); and marble (a metamorphic rock). The closed form expression of DSC for the force of constant intensity has been derived with the aid of Weiner-Hopf technique along with Galilean and two-sided Fourier integral transformations. The noticeable influence of different affecting parameters (viz. velocity of moving punch associated with the shear wave propagation, horizontal compressive/tensile initial stresses, vertical compressive/tensile initial stress, porosity, and anisotropy parameter) on dynamic stress concentration has also been reported. Numerical computation and graphical illustrations have been carried out for the aforementioned three different types of porous rocks to investigate the profound impact of affecting parameters on DSC. Moreover, some noteworthy peculiarities have also been derived from the obtained expression of dynamic stress concentration. 相似文献
The Rajahmundry Trap Basalts(RTB) are erupted through fault-controlled fissures in the Krishna-Godavari Basin(K-G Basin) of Godavari Triple Junction,occurring as a unique outcrop sandwiched between Cretaceous and Tertiary sediments along the east coast of India.Detailed geochemical studies have revealed that RTB are mid-Ti(1.74-1.92) to high-Ti(2.04-2.81) basalts with a distinct quartz tholeiitic parentage.MgO(6.2-13.12 wt.%),Mg#(29-50) and Zr(109-202 ppm) suggest that these basalts evolved by fractional crystallization during the ascent of the parent magma along deep-seated fractures.Moderate to high fractionation of HREE,as indicated by(Gd/Yb)N ratios(1.71-2.31) of RTB,suggest their generation through 3-5%melting of a Fe-rich mantle corresponding to the stability fields of spinel and garnet peridotite at depths of 60-100 km.Low K2O/P2O5(0.26-1.26),high TiO2/P2O5(6.74-16.79),La/Nb(0.89-1.45),Nb/Th > 8(8.35-13),negative anomalies at Rb reflect minimum contamination by granitic continental crust.(Nb/La)PM ratios(0.66-1.1) of RTB are attributed to endogenic contamination resulted through recycling of subducted oceanic slab into the mantle.Pronounced Ba enrichment with relative depletion in Rb indicates assimilation of Infra- and Inter-trappean sediments of estuarine to shallow marine character.Geochemical compositions such as Al2O3/TiO2(3.88-6.83),medium to high TiO2(1.74-2.81 wt.%).positive Nb anomalies and LREE enrichment of these RTB attest to their mantle plume origin and indicate the generation of parent magma from a plume-related enriched mantle source with EM 1signature.Ba/Th(46-247),Ba/La(3.96-28.51) and Th/Nb(0.08-0.13) ratios suggest that the source enrichment process was marked by recycling of subduction-processed oceanic crust and lithospheric components into the mantle.Zr/Hf(37-41) and Zr/Ba(0.51-3.24) indicate involvement of an asthenospheric mantle source.The Rajahmundry basalts show affinity towards FOZO(focal zone mantle) and PSCL(post-Archaean subcontinental lithosphere) which reflect mixing between asthenospheric and lithospheric mantle components in their source.Origin of RTB magma is attributed to plume-lithosphere interaction and the upward movement of melt is facilitated by intrabasinal deep-seated faults in the K-G Basin. 相似文献
Several volumetrically minor \(\sim \)2.8 Ga anorogenic granites and rhyolites occur along the marginal part of the Singhbhum craton whose origin and role in crustal evolution are poorly constrained. This contribution presents petrographic, geochemical, zircon U–Pb and trace element, and mineral chemical data on such granites exposed in the Pala Lahara area to understand their petrogenesis and tectonic setting. The Pala Lahara granites are calc-alkaline, high-silica rocks and define a zircon U–Pb age of 2.79 Ga. These granites are ferroan, weakly metaluminous, depleted in Al, Ca and Mg and rich in LILE and HFSE. They are classified as A2-type granites with high Y/Nb ratios. Geochemical characteristics (high \(\hbox {SiO}_{2}\) and \(\hbox {K}_{2}\hbox {O}\), very low MgO, Mg#, Cr, Ni and V, negative Eu anomaly, flat HREE and low Sr/Y) and comparison with melts reported by published experimental studies suggest an origin through high-temperature, shallow crustal melting of tonalitic/granodioritic source similar to the \(\sim \)3.3 Ga Singhbhum Granite. Intrusion of the Pala Lahara granites was coeval with prominent mafic magmatism in the Singhbhum craton (e.g., the Dhanjori mafic volcanic rocks and NNE–SSW trending mafic dyke swarm). It is suggested that the \(\sim \)2.8 Ga A-type granites in the Singhbhum craton mark a significant crustal reworking event attendant to mantle-derived mafic magmatism in an extensional tectonic setting. 相似文献
Natural Hazards - National capital of India, Delhi is under moderate to high seismic hazard due to active regional faults such as the Mahendragarh fault, the Delhi Haridwar fault, the Sohna fault,... 相似文献
Sea levels of different atmosphere–ocean general circulation models (AOGCMs) respond to climate change forcing in different ways, representing a crucial uncertainty in climate change research. We isolate the role of the ocean dynamics in setting the spatial pattern of dynamic sea-level (ζ) change by forcing several AOGCMs with prescribed identical heat, momentum (wind) and freshwater flux perturbations. This method produces a ζ projection spread comparable in magnitude to the spread that results from greenhouse gas forcing, indicating that the differences in ocean model formulation are the cause, rather than diversity in surface flux change. The heat flux change drives most of the global pattern of ζ change, while the momentum and water flux changes cause locally confined features. North Atlantic heat uptake causes large temperature and salinity driven density changes, altering local ocean transport and ζ. The spread between AOGCMs here is caused largely by differences in their regional transport adjustment, which redistributes heat that was already in the ocean prior to perturbation. The geographic details of the ζ change in the North Atlantic are diverse across models, but the underlying dynamic change is similar. In contrast, the heat absorbed by the Southern Ocean does not strongly alter the vertically coherent circulation. The Arctic ζ change is dissimilar across models, owing to differences in passive heat uptake and circulation change. Only the Arctic is strongly affected by nonlinear interactions between the three air-sea flux changes, and these are model specific.