Post-collisional talc-alkaline lamprophyres from the Kadiri greenstone belt: Evidence for the Neoarchean convergence-related evolution of the Eastern Dharwar Craton and its schist belts

Pandey, Ashutosh and Rao, Chalapathi NV and Chakrabarti, Ramananda and Pankaj, Praveer and Pandit, Dinesh and Pandey, Rohit and Sahoo, Samarendra (2018) Post-collisional talc-alkaline lamprophyres from the Kadiri greenstone belt: Evidence for the Neoarchean convergence-related evolution of the Eastern Dharwar Craton and its schist belts. In: LITHOS, 320 . pp. 105-117.

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Abstract

Lamprophyres from the greenstone belts play a crucial role in deciphering tectonic and geodynamic processes operating during the Archean. This study presents a comprehensive mineralogical and geochemical study of three lamprophyre dykes with talc-alkaline to shoshonitic affinities from the Neoarchean Kadiri schist belt, eastern Dharwar craton, southern India. These rocks display porphyritic-panidiomorphic texture, typical of the lamprophyres with amphibole (magnesio-hornblende) as phenocrysts, biotite as microphenocrysts and feldspar, epidote, titanite and apatite confined to the groundmass. Alteration of biotite to chlorite is observed along with mild deformation in the amphibole phenocrysts. Based on mineralogy and major oxide geochemistry, these rocks are classified as the talc-alkaline lamprophyres. Higher Ba/Nb and low Nb/La points to their derivation from an enriched lithospheric mantle source and higher Th/Yb ratio along with negative TNT (Ti-Nb-Ta) and Zr-Hf anomalies on the primitive mantle (PM) normalized multi-element diagram indicates dehydrated fluids from the foundering slab could be the possible metasomatic agent. Fractionated HREE ratios (Gd-N/Yb-N >1.9) and higher Sm-N/Yb-N suggests that the source region lies in the garnet stability field. Higher than PM Rb/Sr along with positive correlation between K/La and Rb/La reveals presence of metasomatic phlogopite in the source region. Strong negative initial epsilon Nd along with radiogenic (87) Sr/(86) Sr ratios further support an enriched mantle reservoir involved in their genesis. Non-modal batch melting (1-5%) of a mixed source (phlogopite-garnet peridotite) assuming 5% mixing of subducted sediment with ambient mantle wedge (depleted mantle) satisfies the multi-element concentration pattern shown by the Kadiri lamprophyres. The source enrichment can be linked to the accretion-related growth of Dharwar craton and its schist belts during Neoarchean. Our study shows that a majority of lamprophyres associated with the Archean greenstone belts display a shoshonitic character; this highlights the role of subduction-related processes in the growth and evolution of the greenstone belts (C) 2018 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Publication:	LITHOS
Publisher:	ELSEVIER SCIENCE BV
Additional Information:	Copyright for this articles belongs to ELSEVIER SCIENCE BV
Keywords:	Calc-alkaline lamprophyres; Greenstone belts; Enriched mantle; Kadiri schist belt; Dharwar craton
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences
Date Deposited:	24 Jan 2019 06:18
Last Modified:	24 Jan 2019 06:18
URI:	http://eprints.iisc.ac.in/id/eprint/61392

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