Petrogenesis of Jinniu rock mass in Chuzhou area: Melting of delaminated lower crust or mixing of crust and mantle?

The research on Lower Yangtze block in Yeshan area of Chuzhou is very insufficient. Previous researchers held that Jinniu rock mass belongs to marginal facies of Yeshan pluton. In this paper, the authors studied Jinniu pluton. Zircon U-Pb dating indicates that The Jinniu pluton of Yeshan area of Lower Yangtze block was formed at 129±2 Ma, suggesting a product of Early Cretaceous. Zircon Hf isotopic composition has relatively uniform negative εHf(t) values(-2.82——6.52) and old Hf isotopic crustal model ages (1360-1600 Ma). The Jinniu pluton is alkaline(σ:5.08-5.74)), metaluminous rock body(A/CNK:0.803-0.844), which is characterized by relatively strong differentiation between light and heavy rare earth elements, indistinct negative Eu anomalies, enrichment of LREE and LILE, and depletion of HREE and HFSE. Comprehensive comparative study of the Yeshan rock mas shows that the Jinniu rock mass and Yeshan rock mass belong to two different sources of the same period. Regional tectonic evolution characteristics and geochemistry of rocks and Hf isotope characteristics indicate that the source of the Jinniu rock mass seems to have been a mixed product of underplating water-rich basic magma from enriched lithospheric mantle and partially melted ancient lower crust due to the subduction of Paleo-Pacific Plate.