Petrogenesis and magmatic evolution recorded by zircon for Early Eocene hornblende-rich mafic rocks in Xima area, Tengchong Block

The hornblende-rich mafic rocks exposed in the continental arc is a key object to research differentiation and evolution of arc magmatism in the depth. This paper selected a series of hornblende-rich mafic rocks in Xima area, Tengchong Block to discuss their petrogenesis and evolved process, using the petrography, whole rock major and trace elements, Sr-Nd isotopic compositions, zircon U-Pb dating, Lu-Hf isotopic compositions and trace elements. The age data and isotopic compositions show that the mafic rocks in Xima area are accumulation and differentiation products of homogeneous magma in the Early Eocene (51.2~52.7 Ma). The accumulated minerals of gabbro are dominated by clinopyroxene, plagioclase and magnetite; and the plagioclase, clinopyroxene, titanite and apatite are the major of accumulated minerals for hornblende gabbro. The diorite is predominated by crystallization of crystal-poor evolved melt. The recharge of batch magma resulted in the dissolution and reprecipitation of accumulated minerals during the differentiation, such as plagioclase. The morphology, mineral inclusions and trace element of zircons suggest the early crystallization of plagioclase± orthopyroxene assemblage in the mafic magma could promote the crystallization of zircon in the interaction face between mineral and melt. The wide range of zircon crystallization temperature shows long-time crystallization and the regularvariations of trace elements reflect that zircon crystallized in mafic magma could record crystallization and differentiation processes of mafic magmaefficiently.