Text and Data Mining valid from 2015-08-31
Received: 25 April 2015
Accepted: 31 July 2015
First Online: 31 August 2015
Change Date: 10 September 2015
Change Type: Corrigendum
Change Details: In the version of this Letter originally published, the colour bar for Fig. 1d should have been labelled 'Bulk crustal <i>V</i><sub>p</sub> (km s<sup>-1</sup>)'. This has been corrected in all versions.
: The author declares no competing financial interests.