Crustal structure above the Iceland mantle plume imaged by the ICEMELT refraction profile

• Published in: Geophysical Journal International
• Main Authors: Darbyshire, Fiona A., Bjarnason, Ingi Þorleifur, White, Robert S., Flóvenz, Ólafur G.
• Other Authors: Raunvísindastofnun (HÍ), Science Institute (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 1998
• Subjects: Crustal structure; Iceland; Mantle plume; Seismic refraction; Jarðskorpa; Jarðmöttull; Jarðskjálftar; Jarðeðlisfræði; glacier; Vatnajökull
• Online Access: https://hdl.handle.net/20.500.11815/568; https://doi.org/10.1046/j.1365-246X.1998.00701.x

The crustal structure of central Iceland is modelled using data from a 310 km long refraction profile shot during summer 1995. The profile traversed Iceland from the Skagi Peninsula on the north coast (surface rocks of age 8.5–0.8 Myr) to the southeast coast (surface rocks of age 8.5–3.3 Myr), crossing central Iceland (surface rocks of age 3.3–0 Myr) over the glacier Vatnajökull, below which the locus of the Iceland mantle plume is currently centred. The crustal thickness is 25 km at the north end of the profile, increasing to 38–40 km beneath southern central Iceland. The upper crust is characterized by seismic P-wave velocities from 3.2 to approximately 6.4 km s−1. At the extreme ends of the profile, the upper crust can be modelled by a two-layered structure, within which seismic velocity increases with depth, with a total thickness of 5–6 km. The central highlands of Iceland have a single unit of upper crust, with seismic velocity increasing continuously with depth to almost 10 km below the surface. Below the central volcanoes of northern Vatnajökull, the upper crust is only 3 km thick. The lower-crustal velocity structure is determined from rays that turn at a maximum depth of 24 km below central Iceland, where the seismic velocity is 7.2 km s−1. Below 24 km depth there are no first-arriving turning rays. The Moho is defined by P-and S-wave reflections observed from the shots at the extreme ends of the profile.P- to S-wave velocity ratios give a Poisson's:of 0.26 in the upper crust and 0.27 in the lower crust, indicating that, even directly above the centre of the mantle plume, the crust is well below the solidus temperature. We thank Rob Staples for assistance and many helpful discussions. This work is funded by the Natural Environment Research Council (NERC) and National Science Foundation research grants; FD is supported by NERC. Instruments were loaned by the University of Cambridge, the University of Iceland, the NERC Geophysical Equipment Pool, the PASSCAL instrument pool, the Lamont-Doherty Earth ...