Percolation of Dioritic Melts Through Ultramafic Cumulate Mushes Forms High-Mg Intermediate Igneous Rocks

Percolation of dioritic melts through ultramafic cumulate mushes and their reaction and hybridization have been documented in some arcs, but the impact of the processes on the compositions of arc igneous rocks is not yet fully understood. Here, we investigate the petrogenesis of meladiorites from the ca. 200 Ma Cuijiu Igneous Complex in the eastern Gangdese Arc, southern Tibet. The meladiorites are pervasively intruded by normal diorite dykes and show geochemical affinities with high-Mg intermediate igneous rocks, and their amphibole is characterized by low-Mg core and high-Mg rim. Our new data, together with published data, demonstrate that the meladiorites resulted from hybridization of an ultramafic cumulate mush (∼30%–∼50%) with percolating normal dioritic melts (∼50%–∼70%), and that dissolution-crystallization and chemical diffusion dominated the hybridization. We propose that percolation of dioritic melts through ultramafic cumulate mushes is a viable way to form hybrid high-Mg intermediate igneous rocks.