Skip to Main Content
Book Chapter

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

By
Rohit Pandey
Rohit Pandey
EPMA Laboratory, Department of Geology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India
Search for other works by this author on:
N. V. Chalapathi Rao
N. V. Chalapathi Rao
EPMA Laboratory, Department of Geology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India
Search for other works by this author on:
Dinesh Pandit
Dinesh Pandit
EPMA Laboratory, Department of Geology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India
Search for other works by this author on:
Samarendra Sahoo
Samarendra Sahoo
EPMA Laboratory, Department of Geology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India
Search for other works by this author on:
Prashant Dhote
Prashant Dhote
EPMA Laboratory, Department of Geology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India
Search for other works by this author on:
Published:
January 01, 2018

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.

Supplementary material: A table detailing natural and synthetic standards used for calibration is available at https://doi.org/10.6084/m9.figshare.c.3815296

You do not currently have access to this article.
Don't already have an account? Register

Figures & Tables

Contents

Geological Society, London, Special Publications

Large Igneous Provinces from Gondwana and Adjacent Regions

S. Sensarma
S. Sensarma
University of Lucknow, India
Search for other works by this author on:
B. C. Storey
B. C. Storey
University of Canterbury, New Zealand
Search for other works by this author on:
The Geological Society of London
Volume
463
ISBN electronic:
9781786203441
Publication date:
January 01, 2018

GeoRef

References

Related

A comprehensive resource of eBooks for researchers in the Earth Sciences

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

View Article Abstract & Purchase Options

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

Subscribe Now