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1.
The Purulia carbonatite, ‘carbonatite’-‘alkali-pyroxenite’-‘apatite-magnetite rock’ association, is located at Beldih area
of Purulia district, West Bengal and falls within the 100 km long Northern Shear Zone (NSZ). Published literature suggests
that the Purulia carbonatite was formed by the process of liquid immiscibility from under-saturated silicate parent magma.
However, no silica under-saturated rocks like ijolite, nepheline-syenite etc. is known from the area. The trace element geochemistry
(Ba/La, Nb/Th, Nb/Pb and Y/Ce ratios in the present study) also does not support this view. Present study indicates that the
Purulia carbonatite is enriched in ΣREE and incompatible elements but the carbonatite is also poorer in Nb, Th and Pb compared
to the world average of calicocarbonatites. The lower value of Nb is characteristics of carbo(hydro)thermal carbonatite where
carbonatite is associated with alkali-pyroxenite and suggests probable origin of the carbonatite as carbothermal residua evolved
from an unknown parentage. However, the field, petrographic and geochemical data indicate the genesis of this carbonatite
from a primary carbonatitic magma of mantle decent. The 87Sr/86Sr ratio of the carbonatite and apatite separated from the carbonatite (∼0.703) implies primary magmatic derivation of the
Purulia carbonatite. Close similarity of the apatite of the apatite-magnetite rock with the mantle apatite (of type Apatite
B) indicates that they are also of primary magmatic origin. The present work portrays a unique example where primary magmatic
carbonatite is associated with the alkali-pyroxenite. 相似文献
2.
Onset of Hydraulic Fracture Initiation Monitored by Acoustic Emission and Volumetric Deformation Measurements 总被引：2，自引：1，他引：1
Sergey Stanchits Aniket Surdi Patrick Gathogo Eric Edelman Roberto Suarez-Rivera 《Rock Mechanics and Rock Engineering》2014,47(5):1521-1532
In this paper, the results of laboratory studies of fracture initiation, early propagation and breakdown are reported. Three experiments were conducted on a low permeability sandstone block, loaded in a polyaxial test frame, to representative effective in situ stress conditions. The blocks were instrumented with acoustic emission (AE) and volumetric deformation sensors. In two experiments, fluids of different viscosity were injected into the wellbore, fluid injection was interrupted soon after the breakdown pressure had been reached. This allowed us to investigate hydraulic fracture initiation. In the third test, fracture initiation criteria were applied to stop hydraulic fracture propagation significantly earlier, prior to breakdown, and as it propagated a short distance from the wellbore. The analysis of AE results shows an increase in AE activity and a change in the AE spatial correlation, during the fracture initiation. This early stage of fracturing correlates strongly with the onset of rock volumetric deformation, and is confirmed by the analysis of ultrasonic transmission monitoring. The rock microstructure, after the test, was investigated by analysis of scanning electron microscope images. These indicated the development of leak-off zone near the wellbore and a dry hydraulic fracture at the farther distance from the wellbore. 相似文献
3.
The Purulia carbonatite of West Bengal, India is a dyke occurring within the 100 km long South Purulia Shear Zone (SPSZ), which marks the boundary between the Singhbhum Group of Rocks and the Chhotanagpur Granite Gneissic Complex (CGGC). It is composed essentially of calcite with apatite, amphibole, phlogopite, biotite, magnetite and ilmenite as common accessories. Based on optical properties and mineral chemistry two varieties of the amphibole are recognized: magnesiokatophorite and richterite. The latter is characterized by a relatively high content of Si and Na, while the former is enriched in Al and Ca. Such a composition of the amphibole is characteristic for the intermediate to the late stage carbonatite development. These two co-existing amphiboles reflect a sudden variation in total pressure within the magma chamber during the intrusion of the carbonatite dyke. It is inferred that the magnesiokatophorite started crystallizing first along with calcite and apatite. Subsequently, the ascent of carbonatitic magma to a more shallow depth (hypabyssal) resulted in the formation of the richterite. The difference in amphibole composition reflects a variation in the total pressure within the magma chamber that took place during the formation of the Purulia carbonatite. However, an alternative explanation, such as wallrock contamination, or liquid immiscibility, followed by carbonate magma segregation or magma mixing, may also be possible. There is, however, no evidence corroborating such an interpretation. 相似文献
4.
Compositions and petrogenetic significance of the eudialyte group minerals from Sushina,Purulia, West Bengal 总被引：1，自引：0，他引：1
Aniket Chakrabarty Kamal L. Pruseth Amit Kumar Sen 《Journal of the Geological Society of India》2012,79(5):449-459
The eudialyte-group of minerals (EGM) is one of the most important index minerals of the peralkaline (agpaitic) nepheline
syenites. They crystallize in varied physico-chemical conditions ranging from the early-magmatic (orthomagmatic) to late-magmatic
and even in the post-magmatic (hydrothermal) stage. In India, the only agpaitic nepheline syenite gneisses of the Sushina
Hill region contain both late-magmatic as well as hydrothermal eudialytes. Compositionally these are Mn-Nb-Ca rich eudialytes
and are comparable to the other EGM occurrences such as Ilímaussaq (Greenland), Tamazeght (Morocco), Mont-Saint Hilaire (Canada)
and Pilansberg (South Africa). High Mn content (>6.5 wt.%) for both varieties of the Sushina EGM indicates that they are highly
evolved in nature. In terms of the calculated site occupancy, particularly the [M(3)] and [M(2)], the Sushina eudialytes mimic some Pilansberg eudialytes. In addition to the eudialyte, the host nepheline syenite gneiss
also contains an unknown Na-Zr-silicate (NZS) which is often found to be replacing both types of eudialytes. Compositionally
these NZS can be tentatively represented as Na2Zr2S6O17. These NZS are characterized by much higher Zr, but lower Mn and Nb concentrations compared to the associated eudialytes.
Two distinct varieties of eudialyte and NZS indicate subtle changes in the alkalinity during their formations. The formation
of the late-magmatic as well as hydrothermal eudialyte essentially took place at somewhat elevated pH conditions. The replacement
or alteration of eudialytes by NZS indicates a decreasing pH condition. In terms of the chemical composition the late-magmatic
eudialytes can be represented as a solid-solution series between the kentbrooksite-taseqite-aqualite while the hydrothermal
eudialyte represents solid-solution between kentbrooksitetaseqite -Ce-zirsilite. 相似文献
5.
6.
In this paper, a wavelet-fi ltered genetic-neuro-fuzzy(WGNF) control system design framework for response control of a highway bridge under various earthquake loads is discussed. The WGNF controller is developed by combining fuzzy logic, discrete wavelet transform, genetic algorithms, and neural networks for use as a control algorithm. To evaluate the performance of the WGNF algorithm, it is tested on a highway bridge equipped with hydraulic actuators. It controls the actuators installed on the abutments of the highway bridge structure. Various earthquakes used as input signals include an artifi cial earthquake, the El-Centro, Kobe, North Palm Springs, Turkey Bolu, Chi-Chi, and Northridge earthquakes. It is proved that the WGNF control system is effective in mitigating the vibration of the highway bridge under a variety of seismic excitation. 相似文献
7.
Natural Hazards - The present study focused on the recent flood inundation (July 2020) that occurred in the lower Indo-Gangetic-Brahmaputra plains (IGBP) using concurrent C-band Sentinel-1A... 相似文献
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9.
Aniket Chakrabarty Kamal L. Pruseth Amit Kumar Sen 《Journal of the Geological Society of India》2011,77(1):12-16
Eudialyte is a group of hydrated silicate minerals essentially consisting of Na and Zr with a very complex crystal structure,
and generally associated with alkaline rocks. The complexity of the eudialyte structure can be understood from the fact that
Na alone exist in five distinct sites and extensive solid solubility can occur in almost all cation sites, sometimes one element
occupying multiple sites to the extent of exclusion of other elements. Structurally, eudialyte can be represented as Na15[M
1
]6[M
2]3Zr3[M
3
](Si25O73)(O,OH,H2O)3X2 (Johnsen and Grice, 1999), where M
1
and M
2
sites are occupied by Ca, Mn and Fe, M
3
by Nb and X by OH, Cl and F. In addition, cations like Al, Hf, W, Ta, Sr, Ba and various REEs get incorporated into the eudialyte
structure by substitution, and additional site vacancies even may develop in order to maintain electrical neutrality. Eudialyte,
approximately of the composition Na9Ca8Mn3Nb(Zr,Ce)3Si25O73(OH)2, has hydrothermally replaced albite in the nepheline syenite gneiss exposed south of the Sushina hill of Purulia district,
West Bengal. The eudialyte contains ≈2.25 atom% Zr and 0.75 atom% Nb. In addition to eudialyte in nepheline syenite, an unknown
Na-Zr silicate (NZS) has also replaced the albite crystals. The NZS contains ≈ 7 atom% Zr with a possible empirical formula
of Na12Zr11Si36O95(OH)10. Surface exposures of these rocks are limited at Sushina hill, yet a detailed and systematic investigation on this enigmatic
rock is warranted for they may turn out to be a resource for Zr. 相似文献
10.
The Purulia carbonatite, ‘carbonatite’-‘alkali-pyroxenite’-‘apatite-magnetite rock’ association, is located at Beldih area of Purulia district, West Bengal and falls within the 100 km long Northern Shear Zone (NSZ). Published literature suggests that the Purulia carbonatite was formed by the process of liquid immiscibility from under-saturated silicate parent magma. However, no silica under-saturated rocks like ijolite, nepheline-syenite etc. is known from the area. The trace element geochemistry (Ba/La, Nb/Th, Nb/Pb and Y/Ce ratios in the present study) also does not support this view. Present study indicates that the Purulia carbonatite is enriched in ΣREE and incompatible elements but the carbonatite is also poorer in Nb, Th and Pb compared to the world average of calicocarbonatites. The lower value of Nb is characteristics of carbo(hydro)thermal carbonatite where carbonatite is associated with alkali-pyroxenite and suggests probable origin of the carbonatite as carbothermal residua evolved from an unknown parentage. However, the field, petrographic and geochemical data indicate the genesis of this carbonatite from a primary carbonatitic magma of mantle decent. The 87Sr/86Sr ratio of the carbonatite and apatite separated from the carbonatite (～0.703) implies primary magmatic derivation of the Purulia carbonatite. Close similarity of the apatite of the apatite-magnetite rock with the mantle apatite (of type Apatite B) indicates that they are also of primary magmatic origin. The present work portrays a unique example where primary magmatic carbonatite is associated with the alkali-pyroxenite. 相似文献
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