Ridge subduction along convergent plate margins can cause a tear to develop in the underlying slab, which allows the influx of hot sub-slab mantle materials into the mantle wedge. Such a process has a profound influence on the chemistry of Vanuatu arc magmas, but its effect on the genesis of Vanuatu backarc magmas remains to be assessed. Here we present new geochemical data for samples from the Coriolis Troughs (part of the Vanuatu backarc) and combine our new data with published analyses of samples from the entire Vanuatu arc. Many samples from the Coriolis Troughs have major element systematics, chalcophile element systematics and trace element ratios (i.e., Ba/Nb, Th/Nb) that are more similar to the global MORB array than Vanuatu arc samples. These systematics can be attributed to slab rollback prior to ridge subduction, which caused a progressive decline in the proportion of slab fluxes to the mantle source of the Coriolis Trough magmas. As rollback progressed, deep upwelling of enriched mantle components beneath the North Fiji Basin influenced the compositions of the erupted backarc basin magmas. Melting of this enriched mantle source generated the most recent Nifonea Caldera Floor magmas. In contrast to the other recent Coriolis Trough magmas, the Young Lava Plain samples have geochemical characteristics that are comparable to Vanuatu arc magmas. The Young Lava Plain magmas are situated to the southeast of a slab tear. We therefore suggest that influx of hot sub-slab mantle materials through a slab tear caused southeast flow (i.e., mantle flow away from the trench) of sub-arc mantle (i.e., mantle that was enriched by hydrous and oxidising components released from the slab at sub-arc depths) and that this sub-arc mantle source generated the Young Lava Plain magmas. In particular, we suggest that this oxidised source can account for the anomalous chalcophile element signatures of the Young Lava Plain samples compared to the other Coriolis Trough samples. Because all of the Coriolis Trough samples have similar depth-to-slab, we propose that changes in mantle flow patterns caused by ridge subduction and the development of a slab tear can account for the genesis of proximal magmas with comparable ages but distinct compositions.

沿会聚板块边缘的海脊俯冲会导致下伏板片发生撕裂，这使得热的板片下地幔物质流入地幔楔。这一过程对瓦努阿图弧岩浆的化学性质产生了深远的影响，但其对瓦努阿图弧后岩浆成因的影响仍有待评估。在这里，我们展示了科里奥利槽（瓦努阿图后弧的一部分）样品的新地球化学数据，并将我们的新数据与已发表的整个瓦努阿图弧样品的分析相结合。科里奥利槽的许多样品具有主要元素系统、嗜热元素系统和微量元素比率（即 Ba/Nb、Th/Nb），与瓦努阿图弧样品相比，它们更类似于全球 MORB 阵列。这些系统性可归因于山脊俯冲之前的板片回滚，这导致板片通量与科里奥利槽岩浆地幔源的比例逐渐下降。随着回滚的进行，北斐济盆地下方富集地幔成分的深层上升流影响了喷发的弧后盆地岩浆的成分。这种富集地幔源的融化产生了最新的 Nifonea Caldera Floor 岩浆。与其他近期科里奥利槽岩浆相比，年轻熔岩平原样品具有与瓦努阿图弧岩浆相当的地球化学特征。年轻熔岩平原的岩浆位于板片撕裂的东南部。因此，我们认为热的亚板片地幔物质通过板片撕裂流入导致亚弧地幔（即，地幔富含从亚弧深度板块释放的含水和氧化成分），并且这种亚弧地幔源产生了年轻熔岩平原的岩浆。特别是，我们认为，与其他科里奥利槽样品相比，这种氧化源可以解释年轻熔岩平原样品的异常嗜热元素特征。由于所有科里奥利海槽样品的深度与板片深度相似，我们提出由山脊俯冲和板片撕裂的发展引起的地幔流动模式的变化可以解释具有相似年龄但成分不同的近端岩浆的成因。我们认为，与其他科里奥利槽样品相比，这种氧化源可以解释年轻熔岩平原样品的异常嗜热元素特征。由于所有科里奥利海槽样品的深度与板片深度相似，我们提出由山脊俯冲和板片撕裂的发展引起的地幔流动模式的变化可以解释具有相似年龄但成分不同的近端岩浆的成因。我们认为，与其他科里奥利槽样品相比，这种氧化源可以解释年轻熔岩平原样品的异常嗜热元素特征。由于所有科里奥利海槽样品的深度与板片深度相似，我们提出由山脊俯冲和板片撕裂的发展引起的地幔流动模式的变化可以解释具有相似年龄但成分不同的近端岩浆的成因。