Zircon U-Pb dating of cretaceous adakitic volcanic rocks in the eastern part of North Dabie Mountains

Mesozoic volcanic rocks in the eastern part of the North Dabie Mountains are rich in Na (Na2O = 4.03%, Na2O/K2O = 1.31), Sr (865 μg/g) and Ba (1361 μg/g), and high in Sr/Y ratio (66.1) but low in Nb, Y and HREE. They have experienced strong fractionation of REE [ (La/Yb)N = 26.6], and are similar to adakite in geochemical characteristics. The U-Pb dating of zircon from the volcanic rocks is (129.2 ± 2.6) Ma, belonging to Early Cretaceous. These rocks are similar to the volcanic rocks of North Huaiyang not only in age and rare-earth element and trace element geochemistry, but also in the formation temperature and pressure of the minerals. The results indicated that the delamination of mountain root and underplating of mafic-ultramafic magma had happened in the Dabie orogen before Early Cretaceous. Mesozoic magmatism was intense in the North Dabie Mountains, including the intrusion of mafic-ultramafic magma, uplifting of gneiss dome, explosion of volcanic rocks and intrusion of granitic magma. The Mesozoic volcanic rocks in the eastern part of the North Dabie Mountains may be one part of the Mesozoic volcano-intrusive complex belt of North Huaiyang. The existence of Mesozoic volcanic remnant cap means the denudation of the Dabie orogenic belt was not very strong since Early Cretaceous.