Volcano-Pluton Connections in Silicic Magmatic Systems: Insights from southeast Iceland and southern Nevada

Abstract

This study aims at understanding the processes by which silicic magmas are generated, how silicic magmatic systems evolve and how they are terminated, and the link between magmatic processes at depth and eruptive centers on the Earth’s surface. We present evidence for volcano-pluton connections from two perspectives: the evolution of a plutonic silicic system, as recorded in the mineral zircon, at the Austurhorn Intrusive Complex (AIC), SE Iceland, and the death throes of a silicic magmatic system, as indicated by field relationships and geochemistry, in the Highland Range Silicic Volcanic Sequence (HRSVS), S Nevada. The two systems preserve a striking record of the complex interactions that take place between mafic and felsic magmas both in an intrusive (AIC) and an extrusive (HRSVS) setting, and we emphasize that both are part of greater systems that preserve intrusive as well as extrusive components. From our results, we conclude that zircon at Austurhorn records a long and complex magmatic history characterized by multiple episodes of mafic magma recharge into a dominantly felsic magma reservoir. Their elemental compositions form a coherent low-Hf and low-U/Yb array, consistent with fractional crystallization, that falls within the field established by Carley et al (2010) for silicic rocks from other tectonic settings. We establish a U-Pb intrusion age for the AIC at 6.45±0.04 Ma, and a major mafic recharge event at 5.99±0.6 Ma. At the Highland Range, we interpret the capping mingled lava (CML), rhyolite porphyries, and andesite dike and lavas to be derived from nearby Searchlight Pluton. Our results suggest an origin of the CML by mingling of porphyry-like rhyolite and andesite magmas, and the CML is the last silicic unit exposed in the HRSVS, thus marking the death of the HR-SLP silicic magmatic system.