The Genesis of A‐Type Granites in Lower Yangtze River Belt: Evidence From Calcium Isotopes.

A‐type granite is a favorable rock for the study of crustal evolution, crust‐mantle interaction and metallogenesis. However, the origin of A‐type granite remains controversial. In this study, we report high‐precision Ca isotopic compositions of a co‐genetic suite of A‐type granites from the Lower Yangtze River Belt (LYRB) in eastern China. Our results show that the δ44/40Ca of the A‐type granites ranges from 0.55 ± 0.11‰ to 1.44 ± 0.06‰, and is negatively correlated with CaO, Sr and Ba contents and Eu/Eu*, indicating that the Ca isotope fractionation of A‐type granites is dominated by plagioclase and potassium feldspar. There is kinetic fractionation of Ca isotopes during A‐type granite magma evolution. Sample BSL‐7, the least evolved sample, revealed that it had a low δ44/40Ca of 0.59‰, which is significantly lower than that of the upper continental crust (δ44/40Ca = 0.71–0.72‰) and the bulk silicate earth (δ44/40Ca = 0.94‰). The low δ44/40Ca can be best explained by partial melting of the enriched mantle metasomatized by subduction material. Combined with the geodynamic background of the LYRB, we propose that the formation of A‐type granites in the LYRB originates from partial melting of the enriched mantle, triggered by early Cretaceous ridge subduction of the Pacific and Izanagi plates. Plain Language Summary: A‐type granite is an important rock type in the study of continental evolution. However, the genesis of A‐type granite has been debated. We try to constrain the origin of A‐type granites by Ca isotopes. The Ca isotopic composition of plagioclase and potassium feldspar in A‐type granites is obviously different, which makes Ca isotopes can be used to trace the magmatic evolution of A‐type granites. In addition, the Ca isotope compositions of different magma source areas vary widely. Therefore, Ca isotopes have great potential to restrict the source feature of A‐type granite magmas. Key Points: The fractionation of Ca isotopes of A‐type granites is dominated by plagioclase and potassium feldsparThere is kinetic fractionation of calcium isotopes during A‐type granite magma evolutionThe ridge subduction model can well explain the genesis of A‐type granites in the LYRB [ABSTRACT FROM AUTHOR]