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An International Year of Planet Earth-2008 Initiative

Current Issue Technical

Year 2019

Volume 12 (2)

ESI.12.4.2019.13
Geochemistry of Amphibolites associated with Southern Chotanagpur Granite Gneiss Complex around Balrampur, Purulia District, West Bengal
Vidyanand Bhagat and Vikash Kumar*
Abstract

 

The amphibolites associated with southern extremities of Chotanagpur Granite Gneiss Complex (CGGC) of Singhbhum region of eastern Indian Peninsular shield still form a gray area of research. The present study revealed various aspects regarding their mode of occurrence, petromineralogical characteristics as well as chemistry that may eventually throw light on various petrogenic aspects as well as intricate geological problems of the region such as delineation of their protolith, P-T conditions of metamorphism and also the petrotectonic framework of evolution. These are dominantly represented in the field by foliated and non-foliated suites of mafic rocks showing sill-flow morphology that generally occur as linear strips, bands, concordant lenses in the form of oval shaped hills and mounds of variable sizes simultaneously deformed and co-folded with the intercalated metasediments like mica schists, phyllites and quartzites. Petrographically, amphibolites show dominant hornblende-plagioclase mineralogy with traces of relict ophitic to sub-ophitic igneous textures belonging to amphibolite facies rocks. The major and trace including REE data also suggest the ortho- nature of these rocks ranging in composition from basalt to basaltic andesite with mafic to ultramafic character of tholeiitic affinity suggesting their limited range of fractional crystallization. The MORB- and Chondrite- normalized trace element patterns are more or less distinctly spiky showing -ve Nb-Ta-Ti anomaly as well as enrichment of LILEs against HFSEs, all suggesting their island arc set-up of evolution which is also substantiated on tectonomagmatic discrimination plot. The Primitive mantle normalized REE patterns, (La/Sm)N as well as (La/Ce)N ratios > 1 reveal their source related LREE enriched nature. A narrow variation of (Ce/Nd)N ratios (1.38-2.06) along with major element attributes such as Fe2O3/FeO (0.24-0.31), FeO0/MgO (0.79-2.25) as well as Mg number (50-74), too, indicate their comagmatic and uncontaminated nature. Conspicuous absence of volcanic ejectas in the area is of high genetic significance.

 

Keywords:  Amphibolites, CGGC, protolith, tholeiite, island arc affinity, intraarc basin

ESI.12.4.2019.14
Latitudinal Ionospheric Redistribution in Northern Hemisphere during Geomagnetic Storm
Mahesh Parwani1, Roshni Atulkar2, Rafi Ahmad1, P.K. Sharma3 and P.K. Purohit2
Abstract

The region around the Earth, where the magnetic field of the earth, dominates is known as Magnetosphere. The interaction between the solar wind and the magnetosphere gives rise to geomagnetic storms. These storms have deep terrestrial impacts. During the last some decades, our dependency on GPS navigation, communication and other applications has increased many folds, but the reliability of GPS measurements is doubtful especially during geomagnetic storms. Therefore, monitoring and forecasting these storms is imperative to mitigate their impacts.
 
We studied the Ionospheric variability during the four intense geomagnetic storms during the year 2015, a low solar activity period of the 24th solar cycle. The storms chronologically occurred on 17 March, 23 June, 07 October and 20 December. All the storms showed the value of Dst ≤ -100. The storm occurred on 17th of March 2015 was the most intense storm of the existing 24th solar cycle with the value of Dst -223nT. It is called the Saint Patrick’s Day storm.  For the present investigation, we considered three indices viz. Dst, F10.7cm solar flux and AE index. We also applied some statistical tools to study the variability of TEC during geomagnetic storms. We observed TEC variability at three international GNSS Service (IGS) stations at the low, mid and high latitude respectively, namely Mangilao, US (GUUG) at 13.440N & 144.800 E, Urumqi, China (URUM) at 43.820N & 87.600 E and Ny-Alesund, Norway (NYAL) at 78.920N & 11.860 E.
 
It was observed that out of these storms, the Saint Patrick’s Day storm had the deepest impact on the Ionospheric TEC.  It was also seen that during this storm statistical quantities (standard deviation and Average of TEC) also exhibited the highest numeric values. It was observed that low latitudes station showed a higher variation of TEC during the storm period. It was also seen that the Ionospheric TEC had shown synchronized variation with F10.7 solar flux and AE indices during geomagnetic storms.

 

Keywords: Geomagnetic storm, Dst index, AE index, F10.7cm.