P-wave tomography beneath Greenland and surrounding regions-II. Lower mantle

We study the 3-D P-wave velocity (Vp) structure of the lower mantle beneath Greenland and surrounding regions using the latest P-wave arrival-time data. The Greenland Ice Sheet Monitoring Network (GLISN), initiated in 2009, is an international project for seismic observation in these regions, and currently operating 35 seismic stations. We use a new method of global-scale seismic tomography, which sets 3-D grid nodes densely in the study region to enhance the resolution. We invert ~5.8 million arrival times of P, pP and PP waves from 16,257 earthquakes extracted from the ISC-EHB catalog, which were recorded at 12,549 stations in the world.  Our results reveal a hot plume rising from the core-mantle boundary beneath central Greenland, which is named “Greenland plume”. On the other hand, the Iceland plume rises from ~1500 km depth in the lower mantle. At depths < 1500 km, the Iceland plume might be supplied with hot mantle materials through narrow paths from a low-Vp region beneath the North Sea and/or from possible branches of the Greenland plume. We deem that, after the two plumes are joined together in the mantle transition zone (MTZ), the Greenland plume splits mainly into the Jan Mayen and Svalbard plumes in the upper mantle, supplying magmas to the Jan Mayen volcano and the geothermal area in western Svalbard, respectively. Our results also reveal a high-Vp body above the MTZ beneath northeastern Greenland. The lack of active volcanoes in Svalbard is probably due to this body obstructing the flow of the Greenland plume.