Warm magma storage in a continental rift: Insights from U/Th zircon dating and geochemistry of the Salton Buttes

Abstract

The Salton Rhyolite Buttes, situated within the actively extending Salton Trough, offer a unique opportunity to investigate magma storage conditions in continental rift settings. We present new LA-MC-ICP-MS UTh ages, trace element geochemistry, and Ti-in-zircon thermometry for zircons from all five Salton domes to constrain the timing and nature of past eruptive episodes and magmatic rejuvenation events. Our results reveal a complex history of multiple magmatic and eruptive episodes over the past ∼12,000 years. At Mullet Island, we identify major zircon crystallization events at 11.6 ± 0.6 kyr and 9.8 ± 1.9 kyr, followed by confirmed eruptions between 6 and 8 ka and at 2.3 ka. Obsidian Butte experienced two confirmed eruptions at 1.92 ± 0.06 ka and 5.2 ± 1.2 ka, with significant crystallization periods evidenced by ages of 3.4 ± 0.9 kyr. Rock Hill shows a crystallization event at 4.0 ± 0.9 kyr and a confirmed eruption at 1.8 ± 0.1 ka. The Red Hill domes demonstrate distinct histories: South Red Hill records eruptions at 0.8 ka and 2.5 ± 0.5 ka, with a major crystallization period at 4.7 ± 0.7 kyr, while North Red Hill shows an eruption at 0.8 ka and significant crystallization at 3.1 ± 1.1 kyr. Evidence suggests the presence of a long-lived, interconnected magmatic reservoir that has remained in a warm storage state for over 12,000 years. This finding extends the concept of warm storage, previously documented mainly in arc settings, to continental rift environments. The thin crust, high heat flow, and active extension in the Salton Trough likely facilitate the maintenance of a near-eruptible state over extended periods, even with relatively low magma flux. This has important implications for volcanic hazard assessment and geothermal energy exploration in rift settings. Our study demonstrates that LA-MC-ICP-MS UTh dating can provide high-resolution chronology for young volcanic systems, offering insights into the complex thermal and magmatic evolution of warm storage reservoirs in diverse tectonic environments.