Petrogenesis and tectonic implications of Late Mesoproterozoic A1- and A2-type felsic lavas from the Huili Group, southwestern Yangtze Block

This paper presents new LA-ICP-MS zircon U-Pb chronology, whole-rock geochemical and zircon Hf isotopic data for the felsic lavas of the Huili Group from the southwestern Yangtze Block. LA-ICP-MS zircon U-Pb dating shows that these rocks were emplaced in Late Mesoproterozoic time (similar to 1028 to 1019 Ma). Relative to typical I-type and S-type granitoids, all the samples are characterized by low Sr and Eu, and high high-field-strength element contents, high TFeO/MgO, enriched rare earth element compositions and negative Eu anomalies, indicating that they share the geochemical signatures of A-type granitoid. They can be further divided into two groups: Group I and Group II. Group I are A(1)-type felsic rocks and were produced by fractional crystallization of alkaline basaltic magmas. The Group II felsic lavas belong to the A(2)-type and were derived by partial melting of a crustal source with mixing of mantle-derived magmas. Both Group I and Group II felsic lavas may erupt in a continental back-arc setting. The coexistence of A(1)- and A(2)-type rocks in the southwestern Yangtze Block suggests that they can occur in the same tectonic setting.