Foreword: Magma generation and evolution in the Earth

A VOLUME IN HONOUR OF THE WORK OF MICHAEL J. O'HARA, ON THE OCCASION OF HIS 70TH BIRTHDAY The 20th century was eventful inall areas of Earth Science. Continental drift and sea-floorspreading became embodied in the theory of plate tectonics,isotopically heterogeneous mantle was recognized as a by-productof plate tectonics, large igneous provinces were identifiedas possibly originating from mantle plumes - the list goes on.One thing these revolutions have in common is the process ofscientific debate - which Mike O'Hara has stimulated vigorouslyin the field of