Repacking-Driven Compaction in the Spirit Mountain Batholith, Southern Nevada.

This article focuses on mechanical phase separation by repacking-accommodated compaction in the Spirit Mountain Batholith (SMB), a Miocene granitic pluton in the Colorado River extensional corridor. Through geochemical analyses, plagioclase compositional mapping, and textural studies, the research identifies a near-linear unmixing trend between crystal-rich cumulates and SiO2-rich interstitial melt, indicating melt loss at depth and melt accumulation near the top of the batholith. Trace element modeling, supported by rhyolite-MELTS simulations, estimates a minimum trapped melt fraction of about 30%, consistent with maximum packing fractions from compaction experiments, and suggests that gravity-driven repacking can extract a ~3.5 km thick melt lens within approximately 30,000 years. The study concludes that the SMB formed through repeated sill injections over ~2 million years, undergoing partial crystallization followed by mechanical phase separation driven primarily by gravity-induced crystal-melt segregation.