MAGMA ASCENT AND ASSEMBLY PRIOR TO THE SODA LAKES ERUPTION, NV

The collapse of a magmatic orogen is associated with widespread extension such as the transition from the Nevadaplano to the Great Basin. With extension different styles of magmatism emerge in the form of decompression melting potentially driven by small-scale convection at the base of the crust. This results in small eruptive centers that often have a short lifetime, suggesting limited magma storage in the crust associated with those eruptive centers. We explore magma storage and ascent at the youngest eruption in Nevada, the Holocene Soda Lakes maar, to investigate if magmas are directly transported from the mantle to the surface.

We use olivine phenocrysts sampled throughout the pyroclastic deposits of the Soda Lakes maar separated for major and trace element analysis. Olivine phenocrysts are advantageous over bulk chemical analyses, as they are not integrating over multiple processes such as assimilation and differentiation. Instead, they provide snapshots of the magmatic evolution prior to eruption. Moreover, their chemistry can potentially be linked to distinct components of the erupted magma.

Olivines from the Soda Lakes pyroclastic deposits are highly variable in major element composition (Fo55-Fo88) with peaks at the primitive end (Fo84-88) and another common composition at ~Fo75. Trace element signatures throughout this large range are consistent with fractional crystallization, which suggests that compositionally distinct and spatially separated magma bodies were involved in an eruption that was initiated by magmas released from the mantle. Thus, small melt pockets may exist throughout the Great Basin where no magmatic activity has yet been recorded.