Migration and tectonic implications of Late Jurassic mafic magmatism in South China

The Jurassic magmatism in the southeastern South China Block has been interpreted as extension-related, yet its tectonic drivers remain unclear. Tectonic models vary between two end-members: (1) Palaeopacific subduction-related; and (2) intracontinental extension-related. This study presents new geochronological and geochemical data for the Late Jurassic mafic rocks in the southeastern South China Block that allow us to differentiate between these tectonic models. The Late Jurassic mafic rocks yielded crystallization ages of 162-157 Ma. Our new geochemical data, together with previously published data, can be divided into three groups: group A with variable epsilon(Nd)(t) (+0.1 to +3.4) and zircon epsilon(Hf)(t) (-4.1 to +15.9) values has slightly negative Nb-Ta anomalies; group B is characterized by negative Nb-Ta anomalies with varying epsilon(Nd)(t) (+1.4 to +1.5) and epsilon(Hf)(t) (-3.0 to +2.6) values; and group C displays significant Nb-Ta anomalies with high epsilon(Nd)(t) (+4.5 to +6.6) and epsilon(Hf)(t) (+6.4 to +14.4) values. The geochemical characteristics suggest that groups A and B are mainly the products of asthenosphere-lithosphere interactions and group C was derived from the asthenosphere. Our new data, together with geological observations, suggest that the Late Jurassic magmatism in the southeastern South China Block probably resulted from asthenospheric upwelling in an intracontinental extension setting due to the far-field effects of the subduction of the Palaeopacific Ocean.