SHRIMP zircon U-Pb age of Ruyang Group subvolcanic rocks on the southern margin of the North China Craton and its geological significance

Subvolcanic rocks of the lower Ruyang Group were formerly regarded as the volcanic eruptive interlayer in the same-aged Ruyang Group on the southern margin of North China Craton. The authors obtained the zircon SHRIMP U-Pb age of 213.5±2.4Ma from the zircon samples among the basalt and discovered the discolored hornfels inside the purple red mudstones near the upper subvolcanic rock layer, which suggests that the subvolcanic sill was concordantly intruded into the lower Ruyang Group during late Triassic. The subvolcanic rocks originated from the early subducted oceanic or continental crusts and was formed by partial melting of recirculated continental enriched mantle, as shown by petrological and geochemical characteristics of subvolcanic rocks. The subvolcanic rocks and the genesis of the same-aged ultrahigh-pressure eclogites, adakitic rock, high-K calc-alkaline granite and rapakivi granite in the Qinling orogenic belt all reveal the gradual deep dynamic process from the colliding extrusion to crustal extension after the whole colliding orogeny of the middle Triassic in Qinling orogenic belt.