Linking Zircon Crystallization to Magmatic Processes in Basalt-Dominated Lava Fields: The Eastern Snake River Plain–Craters of the Moon Testbed.

This article focuses on zircon crystallization and magma evolution in the Eastern Snake River Plain (ESRP) and Craters of the Moon (COM) volcanic fields, which are basalt-dominated systems influenced by the Yellowstone hotspot track. Using U–Pb, U–Th, and (U–Th)/He zircon dating combined with trace element and oxygen-hafnium isotopic analyses, the study demonstrates that most zircons in ESRP rhyolite domes and COM evolved lavas are autocrystic, crystallizing shortly before eruption after extensive fractional crystallization that enriched melt zirconium (Zr). Isotopic data indicate that ESRP magmas assimilated hydrothermally altered felsic rocks with low δ^18O values, whereas COM magmas incorporated Archean crust and unaltered felsic components, reflecting divergent crustal assimilation histories from a similar mantle source. The findings highlight that zircon saturation in mafic magmas requires exceptional conditions of high Zr content achieved through prolonged fractional crystallization, making such zircon-bearing mafic lavas rare globally and emphasizing the need to carefully distinguish autocrystic from xenocrystic zircons in large igneous province studies.