Apatite, a powerful geochemical tool for understanding the evolution of volatile and trace elements in magmatic systems, is a common accessory phase in Icelandic rocks. Torfajökull, a historically active Icelandic volcano erupting apatite‐bearing magmas, exhibits a unique compositional history; from more‐evolved peralkaline rhyolites (Pleistocene) to less‐evolved metaluminous rhyolites (Holocene). Geochemical analyses of apatites and volcanic glasses from five eruptions spanning Torfajökull’s rhyolitic history (384ka to 1477 CE) contribute new insights into the volatile (H-F-Cl-S) and rare earth element (REE) evolution of the system. Some of the apatites contain exceptionally high REE compositions (≤20 wt% REE2O3), with concentrations decreasing over time. This temporal trend corresponds to changing magma compositions and saturation of different REE‐bearing phases, as mafic–felsic magma mingling becomes more prominent. Volcanic glass and apatite compositions indicate increasing volatile abundances in magmas through time. Sulfur concentrations are low in apatite (20–100 μg g−1), as is expected in reduced systems, with the exception of elevated sulfur in apatite from the 67ka eruption (20–570 μg g−1). Magma oxidation induced by volcanic degassing (further exemplified by Cl–OH contents in apatite), perhaps explains this signature. The success of this apatite‐focused investigation of Torfajökull reveals the potential of apatite to elucidate magmatic and volcanic processes in Iceland.
Apatite as a Monitor of Dynamic Magmatic Evolution at Torfajökull Volcanic Center, Iceland
Connors, L., T. L. Carley, and A. Fiege (2021) "Apatite as a Monitor of Dynamic Magmatic Evolution at Torfajökull Volcanic Center, Iceland." In F. Vetere (ed.), Dynamic Magma Evolution, pp. 61-88. Washington, D.C.: American Geophysical Union