Interaction between mingling mafic and felsic magmas: Its roles in differentiation of a quartz monzonite and MMEs from eastern South China

Abstract

Compositional profiles and mapping of selected mafic microgranular enclaves (MMEs) in Muchen quartz monzonite in eastern South China give constraints on the interaction between mingling mafic and felsic magmas. The intrusion is a typical I-type MME-bearing magnetite-series granitoid in western Pacific. The MMEs and host quartz monzonite are not deformed and have similar magnetic fabrics, which does not support the MMEs are restites or earlier solidified mafic rocks but implies mafic magma globules flowed with felsic magma. The two MMEs represent mafic magma interacting with felsic magma at early and late stage, respectively. The late-stage MME has a Hbl-Bt-Kfs-Pl-Mag assemblage. The early-stage MME has a Cpx-Bt-Kfs-Pl-Mag assemblage with a rim similar to the late-stage MME. Acicular apatite implies rapid cooling of the mafic magmas; however, the similar isotopic ratios and mafic silicate compositions of the MME and quartz monzonite indicate partial equilibrium during magma interactions. Al-in-hornblende estimates the pluton emplacement at ~3.1–3.6 km and therefore the magma mingling-mixing still worked at shallow levels. Most trace element Harker diagrams do not produce linear variation trends and magma mixing cannot solo explain such a pattern. Enrichments of Na2O, REE, Y, Nb, Ta, Ga, Fe3+ and depletions of K2O, Rb, Ba, Sr in the MMEs through diffusion caused noticeable chemical differentiation of both mafic and felsic magmas. Therefore, mass transfer during magma mingling is an important mechanism influencing petrography and chemical compositions of I-type granitoids. Such processes may also extensively occur in the deep hot zones of the continental arc environments.