Magmatic diapirism of the Fangshan pluton, southwest of Beijing, China

Diapirism as a crustal magma ascent and emplacement mechanism has been increasingly questioned due to lack of unambiguous natural examples. In this paper we report the structure of the Cretaceous Fangshan pluton in the hinterland of the North China Craton, ca. 40 km southwest of Beijing, China. This pluton is a compositionally and texturally concentrically zoned granodiorite with an approximately circular shape. Our detailed structural and petrological investigations reveal a high-temperature shear aureole with pluton-side-up kinematic indicators and a rim syncline around the pluton. In addition, an intensely deformed Archean complex occurs at the northern and southern margins of the pluton requiring at least 4 km upward movement through the 4–5 km thick overlying cover sequence during magma ascent. Based on comparison of stratigraphic units inside and outside the aureole, the bulk wall-rock shortening by ductile flow is estimated to be about 4 km, which is roughly the same as the radius of the pluton. These features are consistent with results of numerous modeling studies and diagnostic criteria of magmatic diapirism, indicating that the Fangshan pluton is a magmatic diapir intruded into a ductile upper crust.