Circum-Cratonic Triassic Syenite Province of North China Craton Reveals Heterogeneous Lithospheric Mantle Related to Dual Subduction

Subduction-induced metasomatism may increase heterogeneity in the subcontinental lithospheric mantle (SCLM) over time. Syenite and its relevant varieties are typically derived from the most metasomatized portions of the SCLM and thus provide a key to decipher its heterogeneity. The only circum-cratonic syenite province in the world, the Late Triassic belt around North China craton, is unique and offers an opportunity to investigate heterogeneity of the SCLM right before its destruction in the Mesozoic. New and previous data of whole-rock Sr-Nd and zircon in situ Hf-O isotopes of syenite intrusions encircling the craton indicate two distinct types of metasomatism characterized by an alteration of juvenile or ancient materials. The spatiotemporally distinct sources can be discriminated by melts from oceanic slabs subducting beneath much of North China followed by deep subduction of South China craton only in the south. This unique setting of a circum-cratonic syenite belt proves in a single case study that subduction-induced metasomatism may cause craton-scale SCLM heterogeneity.