华北陆块南缘汝阳群次火山岩SHRIMP锆石U-Pb年龄及其地质意义

华北陆块南缘汝阳群下部的次火山岩一直被看作是与汝阳群同时代的火山喷发夹层。通过研究测得玄武岩SHRIMP锆石U-Pb年龄为213.5±2.4Ma,并在邻近该次火山岩层上部的紫红色泥岩中发现了褪色的角岩化现象,说明该火山岩是晚三叠世沿汝阳群下部顺层侵入的次火山岩岩床。通过对该次火山岩岩石及其地球化学特征的研究,认为该次火山岩起源于有早期俯冲洋壳或陆壳参与再循环的大陆富集型地幔的部分熔融,它与秦岭造山带几乎同时代形成的超高压榴辉岩、埃达克质岩石、高钾钙碱性花岗岩、环斑花岗岩等共同揭示了秦岭造山带自中三叠世全面碰撞造山之后,由碰撞挤压逐渐转变为伸展拉张的深部动力学过程。

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.