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Rejuvenated volcanism is a worldwide phenomena occurring on many volcanic oceanic islands in all of the major ocean basins (e.g., Samoa, Madeira, Mauritius). This plume-related volcanism follows the main edifice-building stage after a hiatus of variable duration (e.g., 0.6–2 Myrs in Hawai‘i). Hawaiian rejuvenated basalts typically have high MgO contents (>10 wt%) and carry upper mantle xenoliths. Thus, these magmas are assumed to have ascended rapidly through the crust. The basalts erupted along the Koko Rift in Honolulu, Hawai‘i are unusual in their large range in MgO (5.4–11.4 wt%), absence of mantle xenoliths and history of magma mixing. The Koko Rift is the youngest area of rejuvenated volcanism in Hawai‘i (67 ± 2 ka) and its best developed rejuvenation-stage rift system (15-km long rift with 12 major and several minor subaerial and submarine eruptive centers). Here we report on the first systematic petrologic investigation of the Koko Rift basalts to better understand this most recent example of Hawaiian rejuvenated volcanism. New textural and mineral chemical evidence indicates magma was stored along the rift and later mixed to produce the subaerial lavas with 10–11 wt% MgO. The lower MgO (5–6 wt%) subaerial lavas were probably byproducts of the initial hybrid magma, subsequent crystal fractionation and then a second magma mixing event. The absence of mantle xenoliths in Koko Rift lavas and the relatively moderate forsterite contents (84–85%) in the higher MgO lavas may be related to the development of a crustal magma system within the rift. The record of crustal magma storage and crystal fractionation, and two magma mixing episodes in the Koko Rift lavas is unique among Hawaiian rejuvenated volcanism.
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This content will become publicly available on May 1, 2026
Persistent High-Pressure Magma Storage beneath a Near-Ridge Ocean Island Volcano (Isla Floreana, Galápagos)
Abstract Volcanic evolution in ocean island settings is often controlled by variations in the chemistry and volumetric flux of magma from an underlying mantle plume. In locations such as Hawaiʻi or Réunion, this results in predictable variations in magma chemistry, the rate of volcanic activity, and the depth of magma storage with volcanic age and/or distance from the centre of plume upwelling. These systems, however, represent outliers in global plume volcanism due to their high buoyancy flux, frequent eruptions, and large distance from any plate boundary. Most mantle plumes display clear interaction with nearby plate boundaries, influencing the dynamics of solid plume material in the upper mantle and the distribution of melt across regions of active volcanism. Yet, the influence of plume–ridge interaction and plume–ridge distance on the structure, characteristics, and evolution of magma storage beneath ocean island volcanoes remains under constrained. In this study, we consider the evolution of magmatic systems in the Galápagos Archipelago, a region of mantle plume volcanism located 150–250 km south of the Galápagos Spreading Centre (GSC), focusing on the depth of magma storage during the eastward transport of volcanic systems away from the centre of plume upwelling. Geochemical analysis of gabbro xenoliths from Isla Floreana in the southeastern Galápagos suggest that they formed at ~2–2.5 Ma, when the island was located close to the centre of plume upwelling. These nodules, therefore, provide rare insights into the evolution of volcanic systems in the Galápagos Archipelago, tracking variations in the magma system architecture as the Nazca plate carried Isla Floreana eastwards, away from the plume centre. Mineral thermobarometry, thermodynamic modelling, and CO2 fluid inclusion barometry reveal that Isla Floreana’s plume-proximal stage of volcanic activity—recorded in the gabbro xenoliths—was characterized by the presence of high-pressure magma storage (>25 km), below the base of the crust. In fact, we find no petrological evidence that sustained, crustal-level magma storage ever occurred beneath Isla Floreana. Our results contrast with the characteristics of volcanic systems in the western Galápagos above the current centre of plume upwelling, where mid-crust magma storage has been identified. We propose that this change in magmatic architecture of plume-proximal volcanic centres in the Galápagos—from high-pressure mantle storage at 2.5 Ma to mid-crustal storage at the present day—is controlled by the variations in plume–ridge distance. Owing to the northward migration of the GSC, the distance separating the plume stem and GSC is not constant, and was likely <100 km at 2.5 Ma, significantly less than the current plume–ridge distance of 150–250 km. We propose that smaller plume–ridge distances result in greater diversion of plume-material to the GSC, ‘starving’ the eastern Galápagos islands of magma during their initial formation and restricting the ability for these systems to develop long-lived crustal magma reservoirs.
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- PAR ID:
- 10599149
- Publisher / Repository:
- Journal of Petrology
- Date Published:
- Journal Name:
- Journal of Petrology
- Volume:
- 66
- Issue:
- 5
- ISSN:
- 0022-3530
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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