|Title||Magma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz|
|Publication Type||Journal Article|
|Year of Publication||2017|
|Authors||Budd D.A, Troll V.R, Deegan F.M, Jolis E.M, Smith V.C, Whitehouse MJ, Harris C., Freda C., Hilton DR, Halldórsson S.A, Bindeman I.N|
|Type of Article||Article|
|Keywords||canary-islands; gran-canaria; hydrogen isotope; Hydrothermal alteration; Igneous rocks; low-o-18 silicic magmas; merapi volcano; origin; Pb isotope; sunda arc|
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.
|Short Title||Sci Rep|