viii debate of those earlier days has been beautifully summarized by H.
H. Read in his famous "Granite Controversy" (1957). Read's formulation
of the controversy occurred at the time when geochemistry was as a new
and powerful tool. The new techniques opened era during which emerging
an granites were considered mainly from this new viewpoint. Geochemical
signatures have shown that mantle and crustal origins for granites were
both possible, but the debate on how and why granites are emplaced did
not progress much. Meanwhile, structural geology was essentially
geometrical and mechanistic. In the early 70's, the structural approach
began to widen to include solid state physics and fluid dynamics.
Detailed structural maps of granitic bodies were again published, mainly
in France, and analysed in terms of magmatic and plastic flow. The
senior editor of this volume and his students deserve much of the credit
for this new development. Via microstructural and petrofabric studies,
they were able to discriminate between strain in the presence of
residual melt or in the solid-state, and, by systematically measuring
magnetic fabrics (AMS), they have been able to map magmatic foliations
and lineations in ever finer detail, using the internal markers within
granites coming from different tectonic environments. The traditional
debate has been shifted anew. The burning question now seems to be how
the necessary, large-scale or local, crustal extension required for
granite emplacement can be obtained.
