Petrogenesis of carbonatitic lamproitic dykes from Sidhi gneissic complex,Central India

作     者：M.Satyanarayanan D.V.Subba Rao M.L.Renjith S.P.Singh E.V.S.S.K.Babu M.M.Korakoppa 

作者机构：CSIR-National Geophysical Research InstituteHyderabad 500007India Geological Survey of IndiaHyderabad 500068India Department of GeologyBundelkhand UniversityJhansi 284128India NCEGRGeological Survey of IndiaBengaluru 560070India 

出 版 物：《Geoscience Frontiers》 (地学前缘（英文版）)

年 卷 期：2018年第9卷第2期

页      面：531-547页

核心收录：

学科分类：07[理学] 

基　　金：the DST sponsored project vide SERB Grant No.SR/S4/ES-643/2012 the CSIR-NGRI funded project(SHORE PSC0205 WP4.2) 

主　　题：Lamproite Phlogopite Carbonate aggregates Metasomatized mantle Sidhi Gneissic Complex Central India 

摘      要：Petrographic, mineral chemical and whole-rock geochemical characteristics of two newly discovered lamproitic dykes(Dyke 1 and Dyke 2) from the Sidhi Gneissic Complex(SGC), Central India are presented here. Both these dykes have almost similar sequence of mineral-textural patterns indicative of:(1) an early cumulate forming event in a deeper magma chamber where megacrystic/large size phenocrysts of phlogopites have crystallized along with subordinate amount of olivine and clinopyroxene;(2) crystallization at shallow crustal levels promoted fine-grained phlogopite, K-feldspar, calcite and Fe-Ti oxides in the groundmass;(3) dyke emplacement related quench texture(plumose K-feldspar, acicular phlogopites) and finally(4) post emplacement autometasomatism by hydrothermal fluids which percolated as micro-veins and altered the mafic phases. Phlogopite phenocrysts often display resorption textures together with growth zoning indicating that during their crystallization equilibrium at the crystal-melt interface fluctuated multiple times probably due to incremental addition or chaotic dynamic self mixing of the lamproitic magma. Carbonate aggregates as late stage melt segregation are common in both these dykes, however their micro-xenolithic forms suggest that assimilation with a plutonic carbonatite body also played a key role in enhancing the carbonatitic nature of these dykes. Geochemically both dykes are ultrapotassic(K_2 O/Na_2 O: 3.0-9.4) with low CaO, Al_2 O_3 and Na_2 O content and high SiO_2(53.3-55.6 wt.%)and K_2 O/Al_2 O_3 ratio(0.51-0.89) characterizing them as high-silica lamproites. Inspite of these similarities, many other features indicate that both these dykes have evolved independently from two distinct magmas. In dyke 1, phlogopite composition has evolved towards the minette trend(Al-enrichment) from a differentiated parental magma having low MgO, Ni and Cr content; whereas in dyke 2, phlogopite composition shows an evolutionary affinity towards the lamproit