285-9 Mafic Recharge Primes Mingled Lava Eruption in the Searchlight Magmatic System, Nevada

Abstract:

Mafic recharge can renew the eruptive potential of upper crustal magma reservoirs. Evidence of magma recharge is extensive in the volcanic and plutonic records and includes increased magma temperatures recorded in crystals, pre-eruptive changes in magma isotopic composition recorded in phenocryst rims, mineral disequilibria, magmatic enclaves, and physical and compositional evidence of magma mingling and mixing within upper crustal plutons. However, there are few locations where both the plutonic and volcanic record of a recharge-triggered eruption are preserved. The Miocene Searchlight magmatic system in southern Nevada includes a well-mapped paleo-vertical upper crustal plutonic section, where there is exposure of dikes rooted in mingled gabbro and granite that traverse the pluton towards an overlying, coeval volcanic section. These dikes are phenocryst-rich rhyolite porphyry with abundant mafic enclaves that locally have mafic margins. At least one dike can be traced into the volcanic section, where previous work considering field relations, glass and mineral geochemistry, and mineral textures suggests that it fed a rhyolite porphyry lava flow containing extensive mafic enclaves. This exposure provides a unique opportunity to study a vertically integrated record of eruption triggered by mafic recharge. Here, we present new high-precision U-Pb zircon dates that further demonstrate that the pluton, dike, and eruptive records were contemporaneous, as well as field, petrologic, and geochemical data to better understand the mafic recharge systematics.

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