Early Paleozoic and Late Mesozoic crustal reworking of the South China Block: Insights from Early Silurian biotite granodiorites and Late Jurassic biotite granites in the Guangzhou area of the south-east Wuyi-Yunkai orogeny

The South China Block (SCB) is considered to have undergone extensive reworking of continental crust. However, the processes and mechanisms of this reworking remain uncertain. Here, we investigated Early Silurian (442 Ma) biotite granodiorites and Late Jurassic (164-159 Ma) biotite granites in the Guangzhou area of SE Wuyi-Yunkai orogen (WYO), South China. The biotite granodiorites and biotite granites show major and trace element characteristics similar with crustal-derived melts. They have enriched whole-rock Sr-Nd ((Sr-87/(86)St)(i) = 0.7108-0.7210; epsilon(Nd)(t) = - 11.7 to -7.6) and zircon Hf (epsilon(Hf)(t) = -17.2 to -1.7) isotopic compositions. Early Silurian biotite granodiorites have relatively homogeneous zircon delta O-1(8) values (8.6 parts per thousand-9.3 parts per thousand) while Late Jurassic biotite granites show a wide range of zircon delta O-1(8) values (7.4 parts per thousand-10.6 parts per thousand). We suggest that the Early Silurian biotite granodiorites were formed by partial melting of amphibolites and that the Late Jurassic biotite granites were formed by partial melting of a hybridized crustal source containing metasedimentary rocks with subordinate juvenile crustal rocks. Combining our results with those of previous studies in the SCB, we suggest that Early Paleozoic intracontinental reworking of the SCB can be divided into three stages: crust double-thickening, orogenic collapse, and post-orogenic lithospheric extension. During the Late Ordovician to Early Silurian, Guangzhou area of the SE WYO underwent reworking mainly of middle-lower-crustal rocks in response to crust double-thickening. In addition, during the Late Jurassic, the area underwent reworking mainly of middle-lowercrustal metasedimentary rocks, which was induced by heating from mantle-derived mafic magmas.