The 2018 rift eruption of Kīlauea Volcano presents a superb opportunity to decipher the underlying role of magmatic processes on the behavior and hazards of basaltic volcanoes. Here, we examine the petrogenetic history of the most MgO-rich lavas (~ 7.7–8.7 wt.%) from the voluminous (> 0.8 km³) main phase of this eruption on the volcano’s lower East Rift Zone (LERZ). Our results show that these lavas are compositionally homogeneous, but distinct from recent samples of the Puʻu ʻŌʻō eruption on the middle ERZ (MERZ) and the summit lava lake within Halemaʻumaʻu pit crater. The MgO-rich 2018 LERZ lavas have relatively high K₂O and TiO₂ abundances at a given MgO value, high Nb/Y ratios, and low CaO/TiO₂ and Sr/Zr ratios. These observations preclude a simple hypothesis that the collapse of the caldera in 2018 forced magma from the summit reservoir to erupt directly on the LERZ. Instead, the distinctive chemistry of the MgO-rich 2018 LERZ lavas supports a new model of mixing between three components: (1) olivine-controlled magma, derived from the summit reservoir via Puʻu ʻŌʻō, (2) differentiated magma similar to the earliest lavas from the 2018 rift eruption, and (3) olivine. The differentiated magma was stored within the ERZ since the 1960s. The summit-derived magma (~ 91–95%) accumulated downrift of Puʻu ʻŌʻō and mixed with the differentiated magma (~ 5–9%) over ~ 10 years prior to 2018. This process created a large (> 0.8 km³) magma body within the MERZ that was the direct source of the MgO-rich 2018 LERZ lavas. The magma that was removed from the summit reservoir during the 2018 caldera collapse (up to ~ 0.8 km³) remains within the ERZ, along with any leftover magma from the Puʻu ʻŌʻō and 2018 rift eruptions. The summit reservoir has likely been replenished with magma based on recent lava lake activity within Halemaʻumaʻu from December 2020 to May 2021. Thus, Kīlauea’s plumbing system from the summit to the LERZ may now be flush with magma and primed for a new era of frequent and/or large eruptions.

2018 年基拉韦厄火山的裂谷喷发提供了一个极好的机会来破译岩浆过程对玄武岩火山行为和危害的潜在作用。在这里，我们研究了来自火山下部东裂谷带 (LERZ) 喷发的大量 (> 0.8 km ³ ) 主要阶段的最富含 MgO 的熔岩 (~ 7.7–8.7 wt.%) 的成岩历史。我们的结果表明，这些熔岩在成分上是均质的，但与最近在 ERZ 中部 (MERZ) 和 Halemaʻumaʻu 坑火山口内的山顶熔岩湖上的 Puʻu ʻŌʻō 喷发的样本不同。在给定的 MgO 值下，富含 MgO 的 2018 LERZ 熔岩具有相对较高的 K ₂ O 和 TiO ₂丰度、高 Nb/Y 比率和低 CaO/TiO ₂和 Sr/Zr 比率。这些观察结果排除了一个简单的假设，即 2018 年火山口的坍塌迫使山顶水库的岩浆直接在 LERZ 上喷发。相反，富含 MgO 的 2018 年 LERZ 熔岩的独特化学支持三种成分之间混合的新模型：(1) 橄榄石控制的岩浆，通过 Puʻu ʻŌʻō 来自山顶储层，(2) 类似于最早熔岩的分化岩浆来自 2018 年的裂谷喷发，以及 (3) 橄榄石。自 1960 年代以来，分化的岩浆就储存在 ERZ 中。在 2018 年之前的大约 10 年里，峰顶衍生的岩浆（~ 91-95%）积累了 Puʻu ʻŌʻō 的下游并与分化的岩浆（~ 5-9%）混合。这个过程创造了一个大的（> 0.8 km ³) MERZ 内的岩浆体，它是 2018 年富含 MgO 的 LERZ 熔岩的直接来源。在 2018 年火山口坍塌期间从山顶水库中移除的岩浆（高达约 0.8 km ³）仍留在 ERZ 内，以及来自 Pu'u ʻŌʻō 和 2018 年裂谷喷发的任何剩余岩浆。根据 2020 年 12 月至 2021 年 5 月 Halema'uma'u 内最近的熔岩湖活动，山顶水库很可能被岩浆补充。因此，从山顶到 LERZ 的基拉韦厄管道系统现在可能充满了岩浆，并准备迎接一个频繁和/或大爆发。