Geoscientist Online

The significance of orogenic andesites (the voluminous andesites formed at convergent plate margins and volcanic arcs) as petrogenetic proxies for the evolution of continental crust has been recognised and established for over three decades. However, their genesis remains highly contentious and is still much debated. The controversy as to whether orogenic andesites are the products of primary melts of mantle and crustal slab materials, or are derived from basaltic mantle melt differentiation in overlying crust within convergent margin environments, remains uncertain and problematic. This Geological Society Special Publication documents the recent research developments undertaken to address this fundamental petrogenetic issue.

Introduced with an overview chapter on the current state of research on orogenic andesites, the volume is broadly divided into three main sections, presenting recent research papers investigating the crustal slab – mantle connection (four papers on the influence of slab fluids, melts and diapirs, their associated melt-rock reactions and melt transfer timescales), and the role of the overriding crust in these systems (eight papers examining crustal melt and magma evolution and their residence times). The final section synthesises the recent research investigating the temporal evolution of orogenic andesites and their contribution to continental crustal growth and development (three papers).

In summary, the volume thoroughly demonstrates that the debate on the origin of andesitic melts at convergent margins (i.e. formation from primary melts of slab or mantle materials versus evolution from basaltic melts at shallower crustal levels) is an active, significant and unresolved research area in igneous petrogenesis. The volume is non-dogmatic and well-balanced on this important issue favouring neither particular genetic viewpoint. Attempting to establish a forum for discussion, the volume successfully promotes the need for new and further research efforts on the petrogenesis of these important and enigmatic rocks and their role in the global geochemical cycles of the Earth.

The editors are to be congratulated on an excellent and significant contribution to the field. This reviewer anticipates that the editors’ stated purpose for the volume to facilitate cross-fertilisation and discussion between researchers proposing these opposite (and potentially irreconcilable) genetic hypotheses and enable the establishment of a mutually holistic model for orogenic andesite petrogenesis, will ultimately be realised.