Experimental Constraint on Ca‐Rich Carbonatite Melt‐Peridotite Interaction and Implications for Lithospheric Mantle Modification Beneath the North China Craton
Xuewen Wang, Junfeng Zhang, Cong Wang, Keqing Zong, Haijin Xu
Abstract
Abstract Melt‐peridotite interaction is the key process causing lithological and mineralogical modification in the lithospheric mantle beneath the North China Craton (NCC). However, the lithology, kinetic, mineral, and melt compositional variations of carbonatite melt‐peridotite reaction are poorly constrained relative to those of silicate melt‐peridotite reaction. Here we report Ca‐rich carbonatite melt‐harzburgite reaction experiments at 3 GPa and 1100–1300°C. The experimental results show that the Ca‐rich carbonatite melt‐harzburgite reaction proceeds by diffusion‐governed rapid infiltration of melt into the harzburgite along grain boundaries, simultaneous dissolution of orthopyroxene and olivine, and precipitation of clinopyroxene. These processes lead to the formation of clinopyroxenite at the melt‐rock interface and melt‐impregnated lherzolite/harzburgite. The reactive infiltration of the melt inside the harzburgite matrix is much faster than the harzburgite dissolution and the growth of the clinopyroxene‐rich layer. The extrapolation of experimental melt infiltration rate to natural conditions suggests that carbonatite‐melt peridotite interaction results in large‐scale mantle metasomatism with various extents of clinopyroxene enrichment, whereas silicate melt‐peridotite interaction forms restricted pyroxenite/garnetite veins. Clinopyroxenes produced by silicate and carbonatite melt‐peridotite reactions show two distinct compositional variation trends. The comparison of published clinopyroxene compositions from 433 natural peridotite samples with the experimentally determined compositional variation trends indicates that carbonatite metasomatism was prevailing in the ancient lithospheric mantle of the NCC before its destruction in the early Cretaceous, while silicate metasomatism was predominant in the juvenile lithospheric mantle since the late Cretaceous. Prolonged ubiquitous carbonatite mantle metasomatism may have led to the destruction of the eastern NCC.