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21.
Rajesh K. Srivastava 《International Journal of Earth Sciences》2013,102(7):2043-2060
Major and trace element geochemistry of Proterozoic granitoids from the Dirang and Galensiniak Formations, of Lesser and Higher Himalayas, respectively, emplaced in and around Dirang and Tawang regions of the western Arunachal Himalaya, is discussed. In general, these granitoids are massive as well as foliated in nature and are characterized by granitic mineralogical compositions. Porphyritic and hypidiomorphic textures are common in massive type, whereas others show porphyroblastic and foliated textures. Augen structure is also observed in a number of samples. Geochemical and normative compositions together with petrographic features classify them as peraluminous granitoids. Major and trace element geochemistry of most of these granitoids shows granitic nature, while few samples also show monzonitic characteristics. Observed geochemical characters, such as their peraluminous and alkali-calcic/calcic-alkalic nature, crudely defined geochemical patterns, different multi-element and rare-earth element patterns, together with low Mg# (Mg number) of these granitoids suggest their derivation from lower crustal material rather than a mantle source. Multi-element and rare-earth element patterns corroborate their genesis from different crustal melts. It is difficult to explain variations observed in granitoid rocks by partial melting alone; definitely different other processes like migration of melts, magma mixing, assimilation and fractional crystallization also played important role in the genesis of these granitoids. These melts were likely generated at low temperature (730–760 °C) and low pressure (2–5 GPa). The chemical compositions suggest that most of these Paleoproterozoic granitoids are emplaced within the syn-collisional tectonic setting, while few granitoid samples also indicate their volcanic-arc nature. Probably, later group of granitoids are slightly younger to the syn-collisional type. 相似文献
22.
Summary Average SST anomalies of OCT-DEC months for Nino-3 region are predicted using the following parameters – (i) April rain over
Himachal Pradesh, (ii) Darwin pressure change (January–April), (iii) Southern Oscillation Index (Tahiti–Darwin) and (iv) SST
anomalies of Nino-3 region in the month of May. Principal component analysis is used to orthogonalise the predictors before
using them in the regression equation. The first two principal components, which explain nearly 73% of the variance, are used
to fit a regression line. The period 1951–1985 is used as the calibration period for the model and the period 1986–1997 as
the verification period for the forecast.
The Brier score with respect to a reference forecast (persistence) for the independent period is found to be 0.82 which is
indicative of good forecast skill.
Received April 1, 1999 Revised January 17, 2000 相似文献
23.
Satellite altimetry can be used to infer subsurface geological structures analogous to gravity anomaly maps generated through
ship-borne survey. The Eastern offshore was taken up for analysis using Geosat Exact Repeat Mission (ERM) altimeter data.
A methodology is developed to use altimeter data as an aid to offshore hydrocarbon exploration. Processing of altimeter data
involves corrections for various atmospheric and oceanographic effects, stacking and averaging of repeat passes, cross-over
correction, removal of deeper earth and bathymetric effects, spectral analysis and conversion into free-air gravity anomaly.
The final processed results were derived for Eastern offshore in the form of prospecting geoid and gravity anomaly maps and
their spectral components. The highs and lows observed in those maps were derived in terms of a number of prominent megastructures
e.g., gravity linears, 85°E and 90°E ridges, the Andaman trench complex etc. Satellite-derived gravity profiles along 12°N
latitude match well with the existing structures. 相似文献
24.
Abstract. Vein type tungsten mineralization at Degana is genetically and spatially associated with the Degana Granite. The deposit is characterized by pervasive wall rock alteration around the mineralized quartz veins. Laterally three different alteration zones, greisen, silicification and potassic zones, are marked based on the field features, mineral assemblages and geo-chemical characteristics. In the present paper, systematic mineralogical and chemical variation in these alteration zones is reported. Thick mono-mineralic (zinnwaldite) selvages around the veins characterize the deposit. Plagioclase and alkali feldspar are low in the greisen zones while K-feldspar shows more increase than plagioclase in the potassic zone. Quartz is uniformly high in all the alteration zones, but it shows an anomalous value in the silicification zone. Al2 O3 concentration shows initial depletion in greisen zone with gradual increase away from the contact. MgO and FeO are higher in greisen zone than silicification and potassic zones. The potassic zone is characterized by the depletion of Na2 O and higher value of K2 O.
The common presence of topaz and fluorite as both primary and secondary minerals and fluorine-bearing micas suggest fluorine partitioning in substantial amount between granitic melt and coexisting aqueous fluid phase and higher HF activity during the evolution of hydrothermal fluid. The mutual relationship of the fluorine minerals (topaz and fluorite) in the different alteration zones suggests an increase in the Ca2+ activity and decrease of H+ activity during the fluid evolution from greisenization towards alkali-metasomatised granite and the fluid is assumed to change from low to high activity ratio of Ca2+ /H+. 相似文献
The common presence of topaz and fluorite as both primary and secondary minerals and fluorine-bearing micas suggest fluorine partitioning in substantial amount between granitic melt and coexisting aqueous fluid phase and higher HF activity during the evolution of hydrothermal fluid. The mutual relationship of the fluorine minerals (topaz and fluorite) in the different alteration zones suggests an increase in the Ca
25.
J. N. Hindayar P. Dasarwar S. P. Srivastava N. Thrideep Kumar Murali Mohan S. K. Som 《Journal of the Geological Society of India》2016,88(2):197-205
Understanding the causes of slope development with movement initiation of land sliding requires knowledge on dynamicity, displacement, strain concentration and factor of safety. The 13th mile landslide on Gangtok-Nathula road of the Sikkim Himalaya has seriously affected the Indo-China trade route. To quantify the spatial movement pattern, strain analysis and identification of zones of safety were attempted which indicates that differential movement activity of the landslide zone is co-relatable with differential strain pattern with an overall imprint of the Himalaya collision tectonics. 相似文献
26.
Satyendra Bhandari Rohit Srivastava Vikram Mehta 《Journal of Earth System Science》2016,125(7):1313-1319
This paper presents results of a study of long term trends in the characteristics of the within-season temporal profile of southwest monsoon rainfall over western India during the last five decades in relation to global warming induced regional climate change. In contrast to recent climate change analyses and projections, no significant long-term trends have been observed in this study. Slow decadal scale variations observed are analysed in relation to Pacific Decadal Oscillations (PDO). Daily variations in rainfall anomaly show opposite characteristics during negative and positive phases of PDO. The above-normal rainfall (>25%) is found during the starting phase of monsoon in negative PDO. Over the last decade, i.e., during 2000–2007, the seasonal rainfall amount, as well as seasonal span of southwest monsoon over western India is indicative of a gradual increase. 相似文献
27.
Global Shuttle Radar Topography Mission (SRTM) data products have been widely used in Earth Sciences without an estimation of their accuracy and reliability even though large outliers exist in them. The global 1 arc-sec, 30 m resolution, SRTM C-Band (C-30) data collected in February 2000 has been recently released (2014–2015) outside North America. We present the first global assessment of the vertical accuracy of C-30 data using Ground Control Points (GCPs) from the International GNSS Service (IGS) Network of high-precision static fiducial stations that define the International Terrestrial Reference Frame (ITRF). Large outliers (height error ranging from –1285 to 2306 m) were present in the C-30 dataset and 14% of the data were removed to reduce the root mean square error (RMSE) of the dataset from ~187 to 10.3 m which is close to the SRTM goal of an absolute vertical accuracy of RMSE ~10 m. Globally, for outlier-filtered data from 287 GCPs, the error or difference between IGS and SRTM heights exhibited a non-normal distribution with a mean and standard error of 6.5 ± 0.5 m. Continent-wise, only Australia, North and South America complied with the SRTM goal. At stations where all the X- and C-Band SRTM data were present, the RMSE of the outlier-filtered C-30 data was 11.7 m. However, the RMSE of outlier-included dataset where C- and X-Band data were present was ~233 m. The results suggest that the SRTM data must only be used after regional accuracy analysis and removal of outliers. If used raw, they may produce results that are statistically insignificant with RMSE in 100s of meters. 相似文献
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