Abstract
It has previously been postulated that the Earth's hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can potentially account for the chemical diversity of many continental flood basalts.
Highlights
It has previously been postulated that the Earth’s hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported
The chemical compositions of most Continental flood basalts (CFBs) are dissimilar to ocean island basalts (OIBs)[4] that are associated with hot spots—the surface expressions of mantle plumes[5]
This study suggests that oxygen isotopes, 39Ar/40Ar ages, and other geochemical features of the Chifeng CFBs of East Asia are correlated with distance to the western edge of the stagnant Pacific slab within the mantle transition zone (MTZ)
Summary
Large intracontinental scale, because Cenozoic volcanic rocks in this region (Fig. 1) are associated with stagnant slabs in the MTZ20,21. The Chifeng CFBs are located far from plate boundaries, but were erupted directly above the inferred edge of the Pacific stagnant slab (red dashed line in Fig. 1), and extend about 200 km further to the west. They were mainly (490% volume) erupted between 23.8 and 6.1 Myr ago (Supplementary Figs 1 and 2), producing 100–450-m-thick sheet-like lava flows that cover a total area of 3,000 km[2] (ref 26). Because the above-mentioned features are tightly correlated with the position a6
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