Tephra glass chemistry provides storage and discharge details of five magma reservoirs which fed the 75 ka Youngest Toba Tuff eruption, northern Sumatra

Abstract

The Youngest Toba Tuff contains five distinct glass populations, identified from Ba, Sr and Y compositions, termed PI (lowest Ba) -PV (highest Ba), representing five compositionally distinct pre-eruptive magma batches that fed the eruption. The PI-PV compositions display systematic changes, with higher FeO, CaO, MgO, TiO 2 and lower incompatible element concentrations in the low-SiO 2 PIV/PV, than the high-SiO 2 PI-PIII compositions. Glass shard abundances indicate PIV and PV were the least voluminous magma batches, and PI and PIII the most voluminous. Pressure estimates using rhyolite-MELTS indicate PV magma equilibrated at~6 km, and PI magma at~3.8 km. Glass population proportions in distal tephra and proximal (caldera-wall) material describe an eruption which commenced by emptying the deepest PIV and PV reservoirs, this being preferentially deposited in a narrow band across southern India (possibly due to jet-stream and/or plinian eruption transport), and as abundant pumice clasts in the lowermost proximal ignimbrites. Later, shallower magma reservoirs erupted, with PI being the most abundant as the eruption ended, sourcing the majority of distal ash from co-ignimbrite clouds (PI-and PIII-dominant), where associated ignimbrites isolated earlier (PIV-and PV-rich) deposits. This study shows how analysis of tephra glass compositional data can yield pre-eruption magma volume estimates, and enable aspects of magma storage conditions and eruption dynamics to be described. Distinguishing between OTT, MTT and YTTIt is not possible to distinguish unequivocally between YTT, OTT or MTT using just major element glass shard chemistry, but they can be separated using glass trace element

Crossing new frontiers: extending tephrochronology as a global geoscientific research tool

“…Another application of tephrochronology is addressed by Pearce et al (2020), who demonstrate through an analysis of tephra-derived glass compositional data that it is possible to reconstruct magma volume estimates and describe aspects of magma storage and eruption dynamics. Pearce et al (2020) used the Youngest Toba Tuff (YTT), produced during the largest known eruption in the Quaternary from the Toba caldera (Sumatra), as an example of how this can be achieved. They collated published (e.g.…”

“…Westgate et al, 2013;Pearce et al, 2014) and previously unpublished glass trace element compositional data, both proximal and distal, from which five distinct populations could be identified in the YTT representing five discrete magma compositions. From these data and the stratigraphic relationships of the deposits, it was possible for Pearce et al (2020) to reconstruct the crustal level of the magma reservoirs, their order of eruption, and their dispersal. Also focussing on Southeast Asia, Bouvet de la Maisonneuve and Bergal-Kuvikas (2020) provide a review of the present knowledge of the volcanic history and tephrochronological potential of the region.…”

“…Another application of tephrochronology is addressed by Pearce et al . (2020), who demonstrate through an analysis of tephra‐derived glass compositional data that it is possible to reconstruct magma volume estimates and describe aspects of magma storage and eruption dynamics. Pearce et al .…”

“…Pearce et al . (2020) used the Youngest Toba Tuff (YTT), produced during the largest known eruption in the Quaternary from the Toba caldera (Sumatra), as an example of how this can be achieved. They collated published (e.g.…”

Magmatic history of the Oldest Toba Tuff inferred from zircon U–Pb geochronology

“…The voluminous YTT rhyolite was likely vented from a melt-rich subvolcanic reservoir located at a depth equivalent to 110-180 MPa 7,21 (or 4-7 km, assuming a mean crustal density of 2.7 g cm −3 ). Judging by the size 43 ; R et al, 2011: Reid et al 44 .…”