Abstract Views :214 |
PDF Views:3
Authors
Affiliations
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: 666-674
Abstract
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.
