Comment — Origin of enclaves in S-type granites of the Lachlan Fold Belt

Abstract

The recent passing of Bruce Chappell is a loss to the geochemical– petrological community, and no less to ourselves who grew up (scientifically)with andwere both inspired and provoked by hiswork. Bruce was no stranger to controversy and we believe that we can best honour his memory by scrutinising what may be the last of his contributions to his very considerable scientific legacy — Chappell and Wyborn (2012). Chappell andWyborn (C&W) present the view that S-type granitic rocks commonly contain twomain texturally and chemically different types of enclaves (rock inclusions). The first kind is foliated (schistose to gneissose) metamorphic rocks, commonly rich in biotite and generally of metapelitic composition. The second kind is essentially unfoliated, fine-grained enclaves with poikilitic and commonly porphyritic textures, and sometimes having a marginal reaction zone, in contact with their host granitoid rock. These are commonly called microgranular enclaves. C&W take the position that both these kinds represent forms of restitic material, which they define as any solid remaining when a rock undergoes partial melting. They point out that this does not mean that these enclaves were 100% solid at the time of inclusion in the host magma, however. We are happy with the proffered definition of restite (“pieces of largely solid material remnant from partial melting, which were transported from the source”, Chappell and Wyborn (2012), p. 236), but note that this does not necessarily imply that a restitic enclave must be the restitic counterpart of the particular enclosing granitoid. We also agree that both the microgranular and the schistose enclaves may have contained both crystalline and molten portions. However,