Characteristics and Magmatism of Mafic Ultramafic Layered Intrusions

Mafic-ultramafic layered intrusions can occur in various tectonic settings and have typical layered structure and prosodic structure.The magmatisms for layered rocks are mainly gravity differentiation,double-diffusive convection,compaction,assimilation contamination,and magma mixing.Gravitational differentiation well explains the vertical changes of rock types and variations of mineral composition in layered intrusions.Double-diffusive convection and magma mixing play an important role in the formation process of rhythmic beddings.Compaction plays a key role in the late stage of magma evolution for the formation of adcumulatic texture.Assimilation contamination can change the composition of magma,resulting in changes in the composition of magma differentiation.The types of crystal structures depend on the different activities of inter-cumulus liquid and penetration rate of crystal mush,and adcumulatic texture formation requires high permeability.When the inter-cumulus liquid is not active,it is favorable for the formation of ortho-cumulatic texture.Rock association and textures,mineral compositions and change rules are good records for magma differentiation process,magma supplying,and other information,which can be used to discuss the petro-genesis of layered intrusions: temperature and pressure conditions of magma,primitive magma and magmatic evolution.