Publications

Export 2 results:
Sort by: Author Title Type [ Year  (Desc)]
2018
Geiger, H, Troll VR, Jolis EM, Deegan FM, Harris C, Hilton DR, Freda C.  2018.  Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions. Scientific Reports. 8   10.1038/s41598-018-28125-2   AbstractWebsite

The island of Bali in Indonesia is home to two active stratovolcanoes, Agung and Batur, but relatively little is known of their underlying magma plumbing systems. Here we define magma storage depths and isotopic evolution of the 1963 and 1974 eruptions using mineral-melt equilibrium thermobarometry and oxygen and helium isotopes in mineral separates. Olivine crystallised from a primitive magma and has average delta O-18 values of 4.8%. Clinopyroxene records magma storage at the crust-mantle boundary, and displays mantle-like isotope values for Helium (8.62 R-A) and delta O-18 (5.0-5.8%). Plagioclase reveals crystallisation in upper crustal storage reservoirs and shows delta O-18 values of 5.5-6.4%. Our new thermobarometry and isotope data thus corroborate earlier seismic and InSAR studies that inferred upper crustal magma storage in the region. This type of multi-level plumbing architecture could drive replenishing magma to rapid volatile saturation, thus increasing the likelihood of explosive eruptions and the consequent hazard potential for the population of Bali.

2017
Budd, DA, Troll VR, Deegan FM, Jolis EM, Smith VC, Whitehouse MJ, Harris C, Freda C, Hilton DR, Halldorsson SA, Bindeman IN.  2017.  Magma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz. Scientific Reports. 7   10.1038/srep40624   AbstractWebsite

Quartz is a common phase in high-silica igneous rocks and is resistant to post-eruptive alteration, thus offering a reliable record of magmatic processes in silicic magma systems. Here we employ the 75 ka Toba super-eruption as a case study to show that quartz can resolve late-stage temporal changes in magmatic delta O-18 values. Overall, Toba quartz crystals exhibit comparatively high delta O-18 values, up to 10.2%, due to magma residence within, and assimilation of, local granite basement. However, some 40% of the analysed quartz crystals display a decrease in delta O-18 values in outermost growth zones compared to their cores, with values as low as 6.7% (maximum Delta(core-rim) = 1.8%). These lower values are consistent with the limited zircon record available for Toba, and the crystallisation history of Toba quartz traces an influx of a low-delta O-18 component into the magma reservoir just prior to eruption. Here we argue that this late-stage low-delta O-18 component is derived from hydrothermally-altered roof material. Our study demonstrates that quartz isotope stratigraphy can resolve magmatic events that may remain undetected by whole-rock or zircon isotope studies, and that assimilation of altered roof material may represent a viable eruption trigger in large Toba-style magmatic systems.