Alkaline rocks and carbonatites of Amba Dongar and adjacent areas, Deccan Alkaline Province, Gujarat, India. 2. Complexly zoned clinopyroxene phenocrysts

Rock, N. M. S.; Gwalani, L.G.; Griffin, Brendan

doi:10.1007/bf01159723

Cited by 17 publications

(18 citation statements)

References 21 publications

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“…Similar within plate alkaline affinity has also been envisaged in terms of SiO 2 vs. Al 2 O 3 diagram (figure 16c) of clinopyroxene. Projection of clinopyroxene compositions in EnAc-Fs diagram maintains close affinity for those of alkaline rocks from Deccan Volcanic Province (figure 9d) (Rock et al 1994;Kumar 1996). Thus, tectonic discrimination diagrams involving clinopyroxene chemistry consistently point out a within plate alkaline affinity for the parental magma.…”

Section: Evaluation Of Tectonic Settingmentioning

confidence: 72%

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Evaluation of phase chemistry and petrochemical aspects of Samchampi-Samteran differentiated alkaline complex of Mikir Hills, northeastern India

et al. 2010

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The Samchampi-Samteran alkaline complex occurs as a plug-like pluton within the Precambrian granite gneisses of Mikir Hills, Assam, northeastern India and it is genetically related to Sylhet Traps. The intrusive complex is marked by dominant development of syenite within which ijolitemelteigite suite of rocks is emplaced with an arcuate outcrop pattern. Inliers of alkali pyroxenite and alkali gabbro occur within this ijolite-melteigite suite of rocks. The pluton is also traversed by younger intrusives of nepheline syenite and carbonatite. Development of sporadic, lumpy magnetite ore bodies is also recorded within the pluton. Petrographic details of the constituent lithomembers of the pluton have been presented following standard nomenclatorial rules. Overall pyroxene compositions range from diopside to aegirine augite while alkali feldspars are typically orthoclase and plagioclase in syenite corresponds to oligoclase species. Phase chemistry of nepheline is suggestive of Na-rich alkaline character of the complex. Biotite compositions are typically restricted to a uniform compositional range and they belong to 'biotite' field in the relevant classification scheme. Garnets (developed in syenite and melteigite) typically tend to be Ti-rich andradite, which on a closer scan can be further designated as melanites. Opaque minerals mostly correspond to magnetite. Use of Lindsley's pyroxene thermometric method suggests an equilibration temperature from ∼ 450 • -600 • C for melteigite/alkali gabbro and ∼ 400 • C for syenite. Critical assessment of other thermometric methods reveals a temperature of equilibration of ∼ 700 • -1350 • C for ijolite-melteigite suite of rocks in contrast to a relatively lower equilibration temperature of ∼ 600 • C for syenite. Geobarometric data based on pyroxene chemistry yield an equilibration pressure of 5.32-7.72 kb for ijolite, melteigite, alkali pyroxenite, alkali gabbro and nepheline syenite. The dominant syenite member of the intrusive plug records a much higher (∼ 11 kb) equilibration pressure indicating a deeper level of intrusion. Major oxide variations of constituent lithomembers with respect to differentiation index (D.I.) corroborate a normal magmatic differentiation. A prominent role of liquid immiscibility is envisaged from field geological, petrographic and petrochemical evidences. Tectonic discrimination diagrams involving clinopyroxene chemistry strongly suggest within plate alkaline affinity for the parental magma which is in conformity with the regional plume tectonics.

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Section: Evaluation Of Tectonic Settingmentioning

confidence: 72%

“…(d) Projection of clinopyroxene compositions of different lithotypes from Samchampi-Samteran complex in terms of En-Ac-Fs components. Clinopyroxene compositions from alkaline and tholeiitic rocks of Deccan volcanic province are also shown in the diagram (Rock et al 1994;Kumar 1996).…”

Section: Role Of Liquid Immiscibilitymentioning

confidence: 99%

Evaluation of phase chemistry and petrochemical aspects of Samchampi-Samteran differentiated alkaline complex of Mikir Hills, northeastern India

et al. 2010

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“…Table 2). It is quite distinct in its chemistry from the diopside reported from Murud Janjira lamprophyres (Wo 47-50 En 33-39 Fs 10-19 ; Melluso et al, 2002;Dessai and Viegas, 2010), Phenai mata and Panwad-Kawant lamprophyres (Wo 52-56 En 25-44 Fs 4-11 ; Rock et al, 1994) and Chhaktalao lamprophyres (Wo 48-48 En 35-37 Fs 13-14 ; Hari, 1998) from the Deccan LIP. CUL clinopyroxene shows very good positive correlation between Al and Ti implying a fractionation trend (Electronic supplementary Fig.…”

Section: Petrography and Mineral Chemistrymentioning

confidence: 92%

Petrogenesis of lamprophyres from Chhota Udepur area, Narmada rift zone, and its relation to Deccan magmatism

Rao

Das

2012

Journal of Asian Earth Sciences

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“…In terms of Ac-En-Fs ternary components, clinopyroxenes are strongly depleted in acmite component and evolved along En-Fs join (MgFe substitution) which is a characteristic feature of clinopyroxene crystallization in a tholeiitic (subalkaline) melt (Fig.6). A remarkable feature of clinopyroxenes of mafic dyke is that their Ac-En-Fs components do not relate to clinopyroxenes of Precambrian Bhimtal volcanics but appear compositionally similar to that of tholeiitic basalt of Deccan Traps (Rock et al 1994;Kumar, Fig.3. Plagioclase compositions (o) of the mafic dykes in terms of Ab-An-Or components (Deer et al 1966).…”

Section: Classification and Compositional Variation Of Clinopyroxenementioning

confidence: 99%

Petrology and geochemistry of the mafic dyke rocks from precambrian almora crystallines of Kumaun Lesser Himalaya

Singh

Kumar

2010

J Geol Soc India

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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 -3 SI) 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 (Fo 61 -Fo 33 ), clinopyroxene (Wo 46 -En 42 -Fs 22 to Wo 40 -En 36 -Fs 15 ) and plagioclase (An 58 -An 12 ) have crystallized in the temperature range of ca1400-980 o C at pressure <2 kbar in an olivine tholeiitic basalt parent. Low acmite (Na pfu =0.033-0.025), (Mg # =0.64-0.82), Ti-Al contents of clinopyroxenes and their evolution along enstatite-ferrosilite join (i.e. MgFe 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.

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Alkaline rocks and carbonatites of Amba Dongar and adjacent areas, Deccan Alkaline Province, Gujarat, India. 2. Complexly zoned clinopyroxene phenocrysts

Cited by 17 publications

References 21 publications

Evaluation of phase chemistry and petrochemical aspects of Samchampi-Samteran differentiated alkaline complex of Mikir Hills, northeastern India

Evaluation of phase chemistry and petrochemical aspects of Samchampi-Samteran differentiated alkaline complex of Mikir Hills, northeastern India

Petrogenesis of lamprophyres from Chhota Udepur area, Narmada rift zone, and its relation to Deccan magmatism

Petrology and geochemistry of the mafic dyke rocks from precambrian almora crystallines of Kumaun Lesser Himalaya

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