MICROGRANULAR ENCLAVES AS INDICATORS OF HYBRIDIZATION PROCESSES IN GRANITOID ROCKS, HERCYNIAN BELT, SPAIN

Many Hercynian granitoids of calc-alkaline composition are characterized by the presence of microgranular enclaves of tonalite to diorite composition. Though some differences in size, shape, and relative abundance of the enclaves are observed between deep-seated, high-level, and subvolcanic plutons, there are considerable similarities in texture, grain size, and composition. In magma interaction zones where basic and silicic magmas mingled, enclaves were generated from the disruption, by convective flow, of synplutonic dykes of basic, fractionated, perhaps hybrid, magmas. Many enclaves can be interpreted as non-consolidated portions of basic magma in thermal equilibrium with the host granitoid. Under such condition, enclaves are easily disaggregated and mixed with the host granitoid, contributing to the hybridization of the latter. The process implies the development of special textures in both enclave and host granitoid, and may be tested by chemical variations and correlations, suggesting that the presence of enclaves, with these particular textures and compositions, may imply that a form of hybridization was involved in the genesis of the host granitoids.