Imprints of modal metasomatism in the post-Deccan subcontinental lithospheric mantle: petrological evidence from an ultramafic xenolith in an Eocene lamprophyre, NW India

Abstract

We report here on the occurrence of an interesting mantle-derived ultramafic xenolith entrained in an Eocene (c. 55 Ma) lamprophyre dyke from the Dongargaon area of the Chhotaudepur alkaline subprovince located within the Narmada Rift Zone, NW India. The mineralogy of the xenolith comprises olivine, clinopyroxene and mica (phlogopite), with the latter occurring essentially as rims around the clinopyroxene. Inclusions of apatite, interstitial sulphide (pyrite) and micron-scale exsolved spinel are widespread. Olivine is forsteritic (Fo85.34), displays little compositional variation and overlaps with that reported from worldwide mantle peridotite xenoliths. Clinopyroxene is a diopside with a compositional range of Wo48.36 En43.83, Fs6.53 and Ac1.27, and is conspicuous by its high CaO (up to 24.4 wt%) and TiO2 (up to 1.6 wt%) content. Clinopyroxene is also compositionally similar to that reported from ‘enriched’ (metasomatized) peridotite xenoliths rather than those that occur in the ‘normal’ (depleted) peridotitic xenoliths. Phlogopites have a high concentration of fluorine (up to 1 wt%), whereas the apatites show an anomalous enrichment of F (up to 5 wt%), as well as enrichment in Sr (SrO up to 1.9 wt%). Our study provides the first direct petrographical evidence for the modal metasomatism in the post-Deccan subcontinental lithospheric mantle (SCLM) from this domain. From the textural and mineralogical assemblage of the xenolith, we infer that a possible olivine + garnet + orthopyroxene assemblage, in the presence of a metasomatic fluid, has given rise to clinopyroxene + phlogopite + spinel. The paragenesis of apatite essentially as inclusions suggests that it to be the earliest crystallized phase during the metasomatic event. Geothermobarometry of the clinopyroxene in the xenolith reveal temperatures of approximately 1200°C and pressures of approximately 12 kb, which are comparable with such data reported from other Deccan-related xenoliths. Preservation of phlogopite and apatite in the ultramafic xenolith imply that some of the readily fusible metasomatized portions in this domain escaped wholesale melting during the eruption of the Deccan Traps, possibly due to the variable thickness of the underlying SCLM.

Magma chamber processes and geodynamic implications of the Pithora pluton, Bastar Craton, Central India

“…The compositional variations of the major minerals such as plagioclase, hornblende, and biotite amongst the host granite, hybrid rock (mixed After repeated analyses, it was found that the error on major element concentrations is <1%, whereas the error on trace elements varied between 3% and 5% (Pandey, Rao, Pandit, Sahoo, & Dhote, 2018).…”

“…A number of natural and synthetic standards were used for calibration. After repeated analyses, it was found that the error on major element concentrations is <1%, whereas the error on trace elements varied between 3% and 5% (Pandey, Rao, Pandit, Sahoo, & Dhote, ). Line scans across the minerals were also conducted to infer the elemental distribution and compositional variation, respectively.…”

Lamprophyres from the Indian shield: A review of their occurrence, petrology, tectonomagmatic significance and relationship with the Kimberlites and related rocks

“…A restricted range in the major oxide composition variation for these lamprophyres suggests they are likely to be a part of a single magmatic episode. Subba Rao et al (1989) have reported Rb-Sr isochron age of the (Madhavan et al, 1998;Madhavan et al, 1992;Upadhyay et al, 2006;Vijaya Kumar and Rathna, 2008); Deccan LIP (Hari et al, 1998;Melluso et al, 2012;Dessai and Vegas, 2010;Pandey et al, 2017c); Mahakoshal (Srivastava and Chalapathi Rao, 2007;Srivastava, 2013) Gondwana Coalfield (Srivastava et al, 2009Chalapathi Rao et al, 2014); Eastern Dharwar Craton (Meshram et al, 2015, Pandey et al, 2018b, Pandey et al, 2017aLanjewar and Randive, 2017). Fig.…”

“…7, 8). Pandey et al (2017aPandey et al ( , 2018b have suggested the presence of a subduction modified mantle wedge in the SCLM beneath EDC, probably, as a result of Neoarchean accretion related Subrahmanyam et al, 1987;Madhavan et al, 1992Madhavan et al, , 1998Ratnakar et al, 1996;Vijaya Kumar and Rathna, 2008), Mahakoshal (Srivastava and Chalapathi Rao, 2007;Srivastava, 2013), Eastern Dharwar Craton (Meshram et al, 2015;Lanjewar and Randive, 2017;Pandey et al, 2017aPandey et al, , b, 2018b, Deccan LIP (Dessai and Vegas, 2010;Pandey et al, 2017c), and Gondwana coalfield (Srivastava et al, 2009;Chalapathi Rao et al, 2014). growth of the Dharwar Craton (Jayananda et al, 2018 and references therein).…”

Lithosphere–asthenosphere interaction and carbonatite metasomatism in the genesis of Mesoproterozoic shoshonitic lamprophyres at Korakkodu, Wajrakarur kimberlite field, Eastern Dharwar Craton, southern India

“…The CAMECA SXFive instrument was operated by SXFive Software at a voltage of 25‐kV current 10 nA for major elements and 40 nA for rare earth elements (REEs) with a LaB 6 filament in the electron gun for generation of electron beam and beam diameter of 1 μm. The natural and synthetic standards used for calibration are same as given in the study of R. Pandey et al (). Counting time for major and minor elements were 10 and 60 s for the REEs.…”