A note on chemical composition and origin of ferromanganese oxide coated and uncoated pumice samples from Central Indian Ocean Basin

Pumice are explosive volcanic product, occur as uncoated or coated with ferromanganese (Fe-Mn) oxide and resides in association with ferromanganese nodules on the seabed in Central Indian Ocean Basin (CIOB). The older Fe-Mn oxide coated and younger uncoated pumice clasts were leached with 6N HCl to remove Fe-Mn oxide coatings as well as the calcium carbonate present within the vesicles. The main objective of the present study is to understand the origin of these pumice by utilizing their chemical composition. Both coated and uncoated pumice samples are rhyoliteand medium K calc-alkaline series. Major, trace, rare earth elements (∑REE) concentration and chondrite-normalized REE patterns of both coated and uncoated pumice are nearly similar to each other suggesting a same source. Tectonomagmatic discrimination diagrams (Nb vs Y: Yb vs. Ta), triangular plot (TiO 2 -Zr-Y) and High Field Strength Element ratios (La/Ta- 25; Ta/Hf- 0.2; Nb/Ta- 9; Zr/Nb- 22 and Ba/Ta-1084) indicate volcanic arc origin. These were probably sourced from the nearest Indonesian volcanic arc and drifted to the CIOB by currents.