Dispersed intraplate magmatism controlled by pre-existing and plume-induced plate thickness variations

Mantle plumes, the hot upwellings from the Earth’s core-mantle boundary, are thought to trigger surface uplift and the emplacement of large igneous provinces (LIPs). Magmatic centres of many LIPs are scattered over thousands of kilometres. This can be attributed to lateral flow of plume material into thin lithosphere areas, but evidence for such flow is scarce. Here, we examine evidence for this process in different LIPs and at different scales. First, we use the now abundant seismic data and recently developed methods of seismic thermography to map previously unknown plate-thickness variations in the Britain-Ireland part of the North Atlantic Igneous Province, linked to the Iceland Plume. The locations of the ~60 Myr old uplift and magmatism are systematically where the lithosphere is anomalously thin at present. The strong correlation indicates that the hot Iceland Plume material reached this region and eroded its lithosphere, with the thin lithosphere, hot asthenosphere and its decompression melting causing the uplift and magmatism. We demonstrate, further, that the unevenly distributed current intraplate seismicity in Britain and Ireland is also localised in the thin-lithosphere areas and along lithosphere-thickness contrasts. The deep-mantle plume thus appears to have created not only a pattern of thin-lithosphere areas and scattered magmatic centres but, also, lasting mechanical heterogeneity of the lithosphere that controls long-term distributions of deformation, earthquakes and seismic hazard.

At larger scales, recent waveform tomography of different continents shows that lateral variations of the lithospheric thickness exert primary controls on the distributions of LIP magmatism. Joint evidence from tomography and kimberlites reveals the temporal evolution of the lithospheric thickness and indicates where the relevant lithospheric thickness variations pre-dated the LIP and where they are likely to have been changed by the processes that gave rise to the LIP emplacement.

 

References

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