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Kumar, Santosh
- Chemistry of Clinopyroxenes from Subalkaline and Alkaline Rocks of Phenai Mata Igneous Complex, Baroda District, Gujarat, Western India
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Authors
Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi- 221 005, U.P., IN
1 Department of Geology, Banaras Hindu University, Varanasi- 221 005, U.P., IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 48, No 5 (1996), Pagination: 547-558Abstract
The predominant tholeiitic gabbro-microgranite/granophyre suite has been found in close association with subordinate alkali gabbro-syenite suite at Phenai Mata Igneous Complex (PMIC) (65 Ma). The pyroxene compositions from the selected tholeiitic and alkaline lithotypes of PMIC have been classified and compared to those from alkaline rocks of adjoining complexes. The results indicate that pyroxenes were crystallized in diverse tholeiitic and alkaline parental magmas undergoing differential oxygen fugacity (fO2) and silica activity (aSiO2). The fractionation trend of pyroxenes from tholeiitic rocks of PMIC follows the trend transitional between Ca-poor and Ca-rich augite-ferroaugite trends, though limited iron-enrichment, formed under low fO2. Whereas pyroxenes in alkaline rocks follow the Ca-rich salite-ferrosalite trend at relatively higher fO2 and can be related to those of volcanic and subvolcanic alkaline rocks of adjacent alkaline complex probably representing an analogous alkaline pulse. The pyroxenes of alkaline rocks of PMIC and adjoining area can also be distinguished from those of tholeiitic rocks, having higher Ti and Al contents. An early and strong partitioning of Cr in crystallizing diopside, magnetite and probably chromspinel of tholeiitic and alkaline parental magmas impoverished the pyroxenes (Mg/Mg+Fe1<0.700) of microgranite and syenite in this element during the late stage of crystallization.Keywords
Igneous Petrology, Clinopyroxene, Mineral Chemistry, Alkaline Rocks, Phenai Mata, Gujarat.- Trace and Rare Earth Elements Geochemistry of Alkaline Rocks of Sarnu-Dandali, Harmer, Rajasthan
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Authors
Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, U. P., IN
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, U. P., IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 48, No 6 (1996), Pagination: 663-670Abstract
The alkaline rocks belonging to ijolite series and carbonatites constitute the Sarnu-Dandali igneous complex (68.5 Ma) associated with Precambrian acid volcanics. Trace elements including REE of ten selected Late Cretaceous rock-types viz. melteigite, melanephelinite, phonolite, carbonatite, basalt and Precambrian rhyolites of SDIC have been examined and discussed. The data of alkaline rocks suggest their derivation from an alkaline (ijolitic) magma formed by the partial melting of mantle source. Ba-Sr-REE enriched carbonatites possibly represent an immiscible split from nephelinite. The basalt (Hawaiite) represents a subalkaline magmatic pulse unrelated to alkaline suite. The associated Precambrian rhyolites have formed by a combination of magmatic processes such as partial melting, fractional crystallization and/or magma-mixing.Keywords
Geochemistry, Alkaline Rocks, Sarnu-Dandali, Rajasthan.- Earthquake Swarm Activities after Rains in Peninsular India and a Case Study from Jamnagar
Abstract Views :242 |
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Authors
Sumer Chopra
1,
K. Madhusudhan Rao
1,
B. Sairam
1,
Santosh Kumar
1,
A. K. Gupta
1,
Hardik Patel
1,
M. S. Gadhavi
1,
B. K. Rastogi
1
Affiliations
1 Institute of Seismological Research, Sector-18, Gandhinagar - 382 018, IN
1 Institute of Seismological Research, Sector-18, Gandhinagar - 382 018, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 72, No 2 (2008), Pagination: 245-252Abstract
About 200 shocks were felt and over 50 of M-2 to 4 were located south of Jamnagar in 2006 and same number was felt/located again in 2007 with blast like subterranean sounds soon after heavy rains. Most of the shocks have shallow focal depth of less than 10 km. Some of the tremors have caused cracks in a few houses. During September-October 2006 tremors were confined withm 5 km of Khankotda village which is about 30 km SE of Jamnagar. During August-September 2007 the activity had spread northward up to Jamnagar. Some shocks have occurred about 20-25 km west of this trend faults/lineaments/dykes in the area are studied to identify the causative feature for the tremors. The rainfall data of the district and water level data of nearby observation wells are studied to see any possible relationship with earthquake activity. Data of about hundred cases of swarm type of earthquake sequences in the peninsular India in last several decades are compiled to study their characteristics vis-a-vis monsoons.Keywords
Swarm-Type of Earthquakes, Subterranean Sounds, Saurashtra Seismicity.- Magnetic Susceptibility and Biotite Composition of Granitoids of Amritpur Region, Kumaun Lesser Himalaya: Implication on Granite Series Evaluation and Nature of Felsic Magma
Abstract Views :215 |
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Authors
Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, Uttranchal, IN
1 Department of Geology, Kumaun University, Nainital - 263 002, Uttranchal, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 68, No 4 (2006), Pagination: 666-674Abstract
Felsic magmatism in Amripur and adjoining localities of Kumaun Lesser Himalaya is represented by Palaeoproterozoic (ca 1890 Ma) Bt-Ms granitoids and quartz feldspar porphyries, referred to as Amritpur granitoids (AG) and Amripur porphyry (AP) respectively Magnetic susceptibility( MS) values (range of average ϰ=0062 to 0 522x103 SI) measured for various types of AG correspond to ilmenite-series (reduced type) granites, which are consistent with their peralumnous nature. The MS of AP ranges from 0 399 to 0 912x103 SI with an average MS of 0 528x103 SI, which are typical to ilmenite series granite, although AP represents both metaluminous and peraluminous types Compositions of biotite from Medium-Grained, leucocratic equigranular variety of AG, referred to as Amritpur leucogranite (ALG), are primary in nature, and can be classified as Fe2+ (ferri)biotite enriched in siderophyllite component FeOt/MgO of biotites from AtG vanes from 2 93 to 4 94 which typically crystallized into crustally derived, peraluminous (S-type) felsic magma, with probable 3Fe ⇋ 2AI substitution in biotites during ALG melt evolution but 3Mg⇋2AI substitution cannot be inferred Bulk Fe2O3,/FeO ratio of most AG corresponds to llmenite series (Fe2O3/FeO<O 5) consistent with the observed MS values whereas AP samples equally represent both llmemate and magnetite (Fe2O3/FeO > 0 5) senes. The results strongly favour that the AG magma evolved under reducing environment.Keywords
Palaeoproterozolic Granitoids, llmenite Series, Biotlite Composition, Amritpur, Kumaun Lesser Himalaya.- Microgranular Enclaves in Neoproterozoic Granitoids of South Khasi Hills, Meghalaya Plateau, Northeast India: Field Evidence of Interacting Coeval Mafic and Felsic Magmas
Abstract Views :197 |
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Authors
Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, Uttranchal, IN
2 Directorate of Mineral Resources, RISA Colony, Shillong, Meghalaya, IN
1 Department of Geology, Kumaun University, Nainital - 263 002, Uttranchal, IN
2 Directorate of Mineral Resources, RISA Colony, Shillong, Meghalaya, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 65, No 5 (2005), Pagination: 629-633Abstract
No Abstract.- Pearce Element Ratios Applied to Model Basic Rock Members of Phenai Mata Igneous Complex, Baroda District, Gujarat
Abstract Views :181 |
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Authors
Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, Uttranchal, IN
1 Department of Geology, Kumaun University, Nainital - 263 002, Uttranchal, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 61, No 5 (2003), Pagination: 565-572Abstract
Pearce element ratio (PER) diagrams were constructed for tholentic gabbro, alkali gabbro, dolerite and tholentic basalt of Phenal Mata Igneous complex (PMIC) Identifying potassium as a conserved element particularly during the course of basic magma(s) differentiation senes The observed variations among the tholentic basalts, dolentes, tholentic and alkali gabbros of PMIC on PER diagrams appear to be commonly controlled by the fractional crystallhzation of plagioclase, chnopyroxene and olivine in variable proportion Tholentic basalts and tholentic gabbros of PMIC could be derived from the same parental magma but proportion of crystallizing phases and even assemblages differ as reflected by their different slopes on PER diagrams The different intercepts with a common slope for tholentic gabbros and dolerites however strongly suggest their similarly involved differentiation mechanism but d1fferent parentage probably formed by slight contamiation of episodic tholentic magma by an alkaline one, which subsequently experienced the same differentation mechanism.Keywords
Pearce Element Ratios, Petrogenesis, Basic rocks, Phenal Mata, Baroda district, Gujarat.- National Seminar on Magmatism, Tectonism and Mineralization (MTM-2007)
Abstract Views :198 |
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Authors
Affiliations
1 Dept. of Geology, Kumaun University, Nainital, IN
1 Dept. of Geology, Kumaun University, Nainital, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 71, No 3 (2008), Pagination: 441-442Abstract
No Abstract.- 5th International Symposium on the Tibetan Plateau and 24th Himalaya-Karakorum-Tibet Workshop
Abstract Views :231 |
PDF Views:135
Authors
Affiliations
1 Kumaun University, Nainital, IN
2 University of Jammu, Jammu, IN
1 Kumaun University, Nainital, IN
2 University of Jammu, Jammu, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 75, No 2 (2010), Pagination: 449-451Abstract
No Abstract.- Magnetic Susceptibility Mapping of Felsic Magmatic Lithounits in the Central Part of Bundelkhand Massif, Central India
Abstract Views :185 |
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Authors
Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
2 Geological Survey of India, Dimapur - 797 112, IN
3 Rolta Academy, MIDC, Marol, Andheri East, Mumbai - 400 093, IN
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
2 Geological Survey of India, Dimapur - 797 112, IN
3 Rolta Academy, MIDC, Marol, Andheri East, Mumbai - 400 093, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 75, No 3 (2010), Pagination: 539-548Abstract
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.Keywords
Magnetic Susceptibility, Magnetite Series, Ilmenite Series, Granitoids, Bundelkhand Massif, Central India.- Mineralogy and Geochemistry of Biotites from Proterozoic Granitoids of Western Arunachal Himalaya: Evidence of Bimodal Granitogeny and Tectonic Affinity
Abstract Views :345 |
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Authors
Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 75, No 5 (2010), Pagination: 715-730Abstract
Felsic magmatic rocks in Kameng corridor of western Arunachal Himalaya are represented by extensively exposed Palaeoproterozoic porphyritic muscovite-biotite granite (GGn) of the Bomdila Group and small stock-like Mesoproterozoic hornblende-biotite granite (HBG) of the Salari Group. Mineralogy and chemical composition of biotites from GGn and HBG have been utilized to understand the nature and tectonic environment of their parental felsic melts. Biotites in GGn (FeOt/MgO=3.1-4.6) are Fe-biotites and have shown affinity with primary biotites co-precipitating with muscovite in a peraluminous (S-type) felsic melt of syn-collisional tectonic environment. Biotites in HBG (FeOt/MgO=1.3-2.2) are transitional between Fe and Mg biotites evolved from Fayalite-Magnetite-Quartz (FMQ) to Nickel-Nickel Oxide (NNO) buffers and are related to primary biotites co-existing with amphibole and other ferromagnesian minerals in a calc-alkaline metaluminous (I-type) felsic melt mostly formed in a subduction setting. Both GGn and HBG biotites exhibit Mg⇌Fe substitution, which is more pronounced in HBG biotites. GGn biotites exhibit 2Al⇌3Fe2+ substitution as expected in peraluminous melt, whereas 3Mg⇌2Al substitution normally expected to operate in metaluminous melt is less pronounced in HBG biotites. GGn biotites are markedly enriched in siderophyllite, and depleted in phlogopite components as compared to HBG biotites, which point to diverse genetic conditions. HBG biotites indicate oxidizing environment of the felsic melt unlike the reducing nature of the porphyritic granite (GGn).Keywords
Proterozoic Granitoids, Biotite Chemistry, Tectonomagmatism, Western Arunachal, Himalaya.- Petrography and Major Elements Geochemistry of Microgranular Enclaves and Neoproterozoic Granitoids of South Khasi, Meghalaya: Evidence of Magma Mixing and Alkali Diffusion
Abstract Views :216 |
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Authors
Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
2 Department of Geology, Patkai Christian College, Chumukedima, Patkai - 797 103, IN
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
2 Department of Geology, Patkai Christian College, Chumukedima, Patkai - 797 103, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 76, No 4 (2010), Pagination: 345-360Abstract
Neoproterozoic (690±19 Ma) felsic magmatism in the south Khasi region of Precambrian northeast Indian shield, referred to as south Khasi granitoids (SKG), contains country-rock xenoliths and microgranular enclaves (ME). The mineral assemblages (pl-hbl-bt-kf-qtz-mag) of the ME and SKG are the same but differ in proportions and grain size. Modal composition of ME corresponds to quartz monzodiorite whereas SKG are quartz monzodiorite, quartz monzonite and monzogranite. The presence of acicular apatite, fine grains of mafic-felsic minerals, resorbed maficfelsic xenocrysts and ocellar quartz in ME strongly suggest magma-mixed and undercooled origin for ME. Molar Al2O3/CaO+Na2O+K2O (A/CNK) ratio of ME (0.68-0.94) and SKG (0.81-1.00) suggests their metaluminous (I-type) character. Linear to sub-linear variations of major elements (MgO, Fe2O3t, P2O5, TiO2, MnO and CaO against SiO2) of ME and SKG and two-component mixing model constrain the origin of ME by mixing of mafic and felsic magmas in various proportions, which later mingled and undercooled as hybrid globules into cooler felsic (SKG) magma. However, rapid diffusion of mobile elements from felsic to mafic melt during mixing and mingling events has elevated the alkali contents of some ME.Keywords
Neoproterozoic Granitoids, Microgranular Enclaves, Magma-Mixing, South Khasi, Meghalaya.- Petrology and Geochemistry of the Mafic Dyke Rocks from Precambrian Almora Crystallines of Kumaun Lesser Himalaya
Abstract Views :214 |
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Authors
Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 76, No 5 (2010), Pagination: 437-452Abstract
Mafic dykes of Almora region intrude the Precambrian crystalline rocks of Kumaun Lesser Himalaya. Mafic dykes exhibit fine grained margin and medium to coarse grained core, melanocratic, low to highly ferromagnetic (MS=0.85-38.58×10-3SI) in nature commonly showing subophitic to ophitic textures with ol-pl-cpx-hbl-bt-mt-ap-sp assemblage, and modally correspond to leucogabbro and olivinegabbro (sensu stricto). Olivine (Fo61-Fo33), clinopyroxene (Wo46-En42-Fs22 to Wo40-En36-Fs15) and plagioclase (An58-An12) have crystallized in the temperature range of ca 1400-980°C at pressure <2 kbar in an olivine tholeiitic basalt parent. Low acmite (Napfu=0.033-0.025), (Mg#=0.64-0.82), Ti-Al contents of clinopyroxenes and their evolution along enstatite-ferrosilite join (i.e. Mg⇀Fe substitution) strongly suggest tholeiitic nature of mafic dyke melt with changing activities of alumina and silica. Clinopyroxene compositions of mafic dykes differ markedly as compared to those observed for adjoining Bhimtal volcanics but closely resemble to that crystallized in tholeiitic melts of Deccan province. Observed Cr vs. Mg# variation, enriched LILE (Sr, Ba)-LREE and positive Eu-anomaly of the studied mafic dykes are indicative of fractional crystallization of olivine-clinopyroxene-plagioclase from a crustally-contaminated tholeiitic basalt magma derived from enriched mantle source. The mafic dykes of Almora are geochemically identical to mafic dykes of Nainital, but are unrelated to Precambrian mafic volcanic flow and dykes of NW Himalaya and dykes of Salma and Rajmahal regions.Keywords
Petrology, Geochemistry, Mafic Dykes, Almora, Kumaun Lesser Himalaya.- Typology and Geochemistry of Microgranular Enclaves Hosted in Malanjkhand Granitoids, Central India
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Authors
Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
2 Hindustan Copper Limited, Malanjkhand, Balaghat - 481 116, IN
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
2 Hindustan Copper Limited, Malanjkhand, Balaghat - 481 116, IN