Increased complexity in volcanic architecture along waning hotspots

Abstract Mantle plumes are key drivers of intraplate volcanism on Earth. Hotspot flux controls the lifetime of volcanism, yet its impact on magma plumbing architecture, composition of erupted products, and eruptive styles remain poorly constrained. Here, we combine geochemistry and geochronology on Earth's longest continental hotspot chain to assess the effect of waning plume activity on pre-eruptive magma transfer, storage, and differentiation. We identify two groups of age-progressive Cenozoic volcanoes across eastern Australia. The Northern volcanoes are older and "long-lived" (3.5–7 Ma activity) and erupted high volumes (>800 km3) of magmas with bimodal compositions, including relatively homogeneous basalts with aphyric texture (~3 vol% phenocrysts). In contrast, the southern volcanic chain splits into two parallel tracks, where volcanoes become "short-lived" (~1.5 Ma or less), erupting <300 km3 of more evolved basalts that show greater compositional and textural complexity (~12 vol% zoned phenocrysts). The inflection point coincides with a change in plate motion, suggesting geodynamic controls on plume flux, which in turn controls plumbing system architecture. Our results suggest waning flux leads to increasingly complex feeder systems and enhanced magma differentiation. Similar trends in hotspot tracks globally suggest that hotspot flux plays a crucial role in the evolution of intraplate volcanoes.