Reworking of a granitic continental crust : from anatexis to granite magma

The continental crust, which started to form about 4 Ga ago, is petrologically very diverse. The main hypothesis that this research examines is that diversity is produced through anatexis of the continental crust resulting in the formation of granite magmas, which can eventually be transferred to shallower levels and form plutons there. This study uses field and microstructural observations combined with mineral and whole-rock composition to understand when and how a granitic continental crust, in the southern São Francisco Craton, Brazil, became petrologically diverse. The Kinawa migmatite represents a former Archean leucogranodiorite that has been reworked in a shear zone at upper amphibolite facies conditions (<730°C and 0.5-0.6 GPa). A wide variety of rocks were produced in this process, including three types of diatexite (grey, schlieren and homogenous), a series of leucosomes and minor amphibolites, metatexites and grey gneisses. Grey diatexites are residual with a microstructure consistent with H2O-fluxed melting (degree of partial melting ~0.35-0.40) via the reaction Pl + Kfs + Qz + H2O = melt. Schlieren diatexites alternate residuum-rich domains with leucocratic quartzofeldspathic domains. Homogeneous diatexites have the highest SiO2 and K2O contents and are coarse-grained, leucocratic rocks. Leucosomes are small but abundant rocks bodies that vary in compositions from tonalite to alkali-feldspar granite. Homogeneous diatexites, quartzo-feldspathic domains from the schlieren diatexites and leucosomes have, in different parts, plagioclase-dominated and K-feldspar-dominated framework microstructures. They are interpreted as melt-rich rocks and some of them contain evidence of tectonic compaction. In the active shear zone setting of the migmatite shearenhanced compaction, both during melting and crystallisation, provided an essentially continuous driving force for the segregation of melt from solids, and generated the petrological diversity observed in the mig