浙江道林山新元古代A型花岗岩的发现及其构造意义

道林山岩体侵入于元古宙火山岩和沉积岩中,锆石U-Pb法同位素年龄测定为814Ma和816Ma,形成于晋宁晚期。该岩体主要由钾长石、石英及少量斜长石、黑云母组成,为碱性长石花岗岩,氧化物平均值及NK/A比值与世界A型花岗岩相近,但与M型、S型和I型花岗岩相比,则具有富硅碱而贫钙镁等特点;岩石准铝-过铝质,富含稀土元素和高场强元素,FeO*/MgO比值大,形成于后造山构造环境。该岩体为后造山铝质A型花岗岩,是在晋宁晚期华夏、扬子两大陆块碰撞作用结束后的拉张环境中形成,是华南Rodinia超大陆裂解事件的岩石学记录,揭示了华南Rodinia超大陆裂解始于晋宁晚期(青白口纪),表明江山-绍兴断裂带在晋宁晚期即进入拉张裂解阶段。

Discorery of the Neoproterozoic Daolinshan A-type granite in Zhejiang and its tectonic implications

The Daolinshan granite is intruded into Proterozoic volcanic rocks and sedimentary rocks and has zircon U-Pb ages of 814 and 816 Ma. The granite formed in the late Jinningian Stage. It is alkali feldspar granite composed mainly of alkali feldspar, quartz with small amounts of plagioclase, biotite, and hornblende. Its mean value of oxides and NK/A ratio are close to those of the world's A-type granite, but compared to M-type, S-type and I -type granite, it is rich in silicon and alkalis and poor in calcium and magnesium. The rock is metaluminous to peraluminous and rich in REE and high field strength elements with a high ratio of FeO*/ MgO. The granite pluton formed in a post -orogenic environment and is post-orogenic, aluminous A-type granite. It originated in an extensional environment after the end of the collision of the Yangtze block and Cathaysia block. It is the petrological record of the breakup event of the supercontinent South China Rodinia, revealing that the breakup of the supercontinent in the late Jinningian (Qingbaikouan Period) and so suggesting that the Jiangshan-Shaoxing fault belt had stepped into the stage of extensional breakup in the late Jinningian.