This is a contribution to IGCP 497 and IGCP 597. Financial support for this work was supplied by Research Project ODRE II ("Oroclines and Delamination: Relations and Effects") No. CGL2009-1367 from the Spanish Ministry of Science and Innovation. JFS wishes to acknowledge financial support from project CONSOLIDER CGL2007-65338-C02-01/BTE by the Spanish ministry of Science and Technology. STJ thanks NSERC for a Discovery Grant. JBM acknowledges the continuing support of N.S.E.R.C., Canada. We acknowledge the critical reviews by G. Mohn and an anonymous reviewer, which helped to improve the final version of this paper.