Ward, Jack F.1; Rosenbaum, Gideon1; Ubide, Teresa1; Wu, Jonny2; Caulfield, John T. 1,3; Sandiford, Mike4; Gürer, Derya1
1School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Australia, 2Department of Earth and Atmospheric Sciences, University of Houston, Houston, USA, 3Central Analytical Research Facility, Institute for Future Environments, Queensland University of Technology, Brisbane, Australia, 4School of Earth Sciences, University of Melbourne, Melbourne, Australia
East Asia contains many Holocene volcanic centres, several of which are located far (between 600 and 1500 km) from the Pacific and Philippine Sea plate subduction zones. The origin of these intraplate volcanoes, which include Jeju, Ulleungdo, Tianchi, Jingbohu, Erkeshan and Wudalianchi, remains enigmatic. Geodynamic processes proposed to explain the occurrence of the East Asian Holocene intraplate volcanoes include mantle plume activity, subduction processes with slab fluid involvement, and subduction processes without slab fluid involvement. Here, we evaluate a variety of geophysical datasets and a compilation of geochemical data to assess the feasibility of these mechanisms. High-resolution tomography data provide no evidence for the rise of deep-seated mantle plumes. Instead, the tomographic and seismic data highlight the stagnation of the Pacific slab at the 660 km discontinuity below Tianchi, Longgang, Jingbohu, Erkeshan and Wudalianchi. The geophysical data also provide evidence for the stagnation of the Philippine Sea slab at the 410 km discontinuity below Jeju and Ulleungdo. Although the intraplate volcanoes appear to be located above subducted slabs, the geochemical data do not provide evidence for melt generation due to slab metasomatism. Instead, the intraplate volcanoes are alkaline in composition and display primitive mantle normalised trace element characteristics comparable to those shown by ocean island basalts. In light of the absence of evidence for plume activity or slab metasomatism, we suggest that convective upwellings occurring at the edges of the Pacific and Philippine Sea slabs may be responsible for Holocene intraplate volcanism in East Asia. Because it is likely that the Pacific and Philippine Sea slabs have been stagnant in the mantle transition zone for millions of years, we speculate that slab-edge convection and volcanism may be driven by regional-scale tectonic events. We conclude by discussing possible Neogene–Quaternary tectonic events that may have contributed to the occurrence of East Asian Holocene intraplate volcanism.
Jack Ward is a PhD student at the School of Earth and Environmental Sciences, The University of Queensland. He uses geophysical and geochemical data to better understand the processes that cause anomalous subduction-related magmatism.