Origin of ash in the Central Indian Ocean Basin and its implication for the volume estimate of the 74,000 year BP Youngest Toba eruption

A controversy exists about the origin of ash in the Central Indian Ocean Basin (CIOB). In situ silicic volcanism and Indonesian arc volcanism have been proposed as sources of ash in the basin. We present here the detailed morphology and chemical composition (ten major, 20 trace and 14 rare earth elements (REE)) of glass shards from eight sediment cores in the CIOB to gain insights and provide new estimates of ash volume. The glass shards are of rhyolitic composition with a strong negative Europium anomaly, and show a bubble wall junction-type morphology suggesting a magmatic type of eruption. Major, trace and REE composition and morphology of the shards suggest Youngest Toba Tuff (YTT) of similar to 74 ka of Northern Sumatra as the source for the ash. The YTT shards have higher Ca, K, Al, Cs, Ba, Ta, Th, U and heavy REE and lower Fe, Rb, Sr, Y and light REE compared to Middle Toba Tuff, and higher Si, K, Hf and light REE, and lower Ti, Fe, Mn, Mg, Ca, Na, Rb, Sr, Y, Nb, Th, U and heavy REE compared to Oldest Toba Tuff. The YTT covers a new minimum area of similar to 3.2 x 10(6) km(2) in the CIOB and increases additional ash volume by 160 km(3) to the earlier volume (350 km(3)) reported. The new occurrence of YTT from the CIOB, South China Sea and Arabian Sea suggests significant increase in ash volume, and climatic implications need to be reassessed.