Control of the Shift in Subduction Direction on Upper Plate Tectonic Extension and Gold Mineralization: A Case Study From the Early Cretaceous Jiaodong Peninsula, Eastern China

The subduction of the Paleo-Pacific plate, and tectonic extension and mineralization in the upper plate, has been extensively studied in the last decades. How plate interactions along plate margins contributed to the upper plate processes, however, remains controversial. This study focuses on the Queshan Metamorphic Core Complex (MCC) and the Songjiagou gold deposit in the northern Jiaodong Peninsula, southeastern North China Craton, to uncover the processes of and factors on Early Cretaceous tectonic extension and gold mineralization. It is shown that the Queshan MCC experienced early nearly east-west and late northwest-southeast extensional stress fields, with a critical transition between 123 and 119 Ma. During 136-119 Ma, the average cooling rate of the lower plate exceeded 17.5 degrees C/Myr, but decreased rapidly to 3.5 degrees C/Myr after 119 Ma. Formation of the Songjiagou gold deposit is shown to occur in two distinct stages, that is, weak emplacement of gold-bearing fluids along the northeast-southwest fault from 122 to 118 Ma, and large-scale fluid activities between 118 and 116 Ma. A detachment fault zone, formed during the rapid exhumation of the Queshan MCC due to near east-west extension, and a brittle fracture system, created under northwest-southeast extension, contributed to a fracture network that connect the middle and upper crust. This network facilitated the migration of hydrothermal fluids and precipitation of gold from the fluids. The Songjiagou deposit exemplifies the major gold mineralization event of around 120 Ma in the Jiaodong Peninsula. During this period, the Paleo-Pacific plate shifted from westward to northwestward subduction. It is suggested that changes in subduction direction caused tectonic extension in the upper plate. The latter triggered reopening of pre-existing fault systems, which enabled gold-bearing fluids in the big mantle wedge to ascend rapidly from deep sources to the shallow crust, thereby driving large-scale gold mineralization in the Jiaodong Peninsula.