Major, trace and platinum-group element geochemistry of Mesoarchean komatiites from the Banasandra greenstone belt, Western Dharwar Craton (southern India): implications for multi-stage plume magmatism in generating compositionally diverse komatiites

ABSTRACT

The early Archean Al-undepleted komatiites (AUK) from two locations (Kunikenahalli, Kodihalli) of the Banasandra greenstone belt in the Western Dharwar Craton are studied for understanding their petrogenesis. The field distribution, mineralogy and geochemistry indicate their cogenetic nature. The samples are mainly cumulates (MgO: 37–45 wt%), now completely serpentinized, while the spinifex zone is obscure. Using geochemical modelling, the MgO content of the primary undifferentiated magma is estimated to be nearly 25 wt%. The depleted LREE values from this study, and the positive ε_Nd values from previous studies suggest that the komatiites are derived from a depleted mantle source. Trace-element and PGE geochemistry eliminate the possibility of crustal contamination and sulphide-saturation in these komatiites after emplacement. Modelling results estimated in this study suggest ~45% melting of a deeper mantle (~6 GPa) to generate the komatiites. Fractionation of olivine (Fo₉₄) from the parental melt and their accumulation formed the mesocumulates in Kodihalli, and the more fractionated orthocumulates in Kunikenahalli. The compositional spectrum from AUK through Al-depleted (ADK) to Al-enriched (AEK) varieties in the Banasandra greenstone belt reported in this study and others, are proposed to be a product of melting of a single mantle plume at different depths.

KEYWORDS:

• Banasandra greenstone belt
• Al-undepleted komatiites
• depleted mantle
• PGE geochemistry
• sulphide saturation

Acknowledgments

K Vishnu is thankful to IISER Bhopal for a research fellowship. Ria Mukherjee wishes to acknowledge IISER Bhopal for financial support to conduct fieldwork and geochemical analysis for this study through an Initiation Research Grant Inst/EES/2018010. Prof. Sarah Jane Barnes is acknowledged for discussion and suggestions regarding MgO modelling. Dr. Pedro Waterton and an anonymous reviewer are thanked and acknowledged for the meticulous and thorough review and detailed comments, which greatly helped to improve the manuscript. Editor-in-chief Prof. Robert Stein is thanked and acknowledged for efficient handling of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2024.2341433

Additional information

Funding

The work was supported by the Indian Institute of Science Education and Research Bhopal [Inst/EES/2018010].