浙江舟山群岛首次发现二叠纪变质岩

浙江舟山群岛大衢岛及周边若干小岛出露少量变质岩系,包括斜长角闪岩、片麻岩、片岩、大理岩等,以往被归为陈蔡岩群。LAICP-MS锆石U-Pb测年结果表明,黑云斜长片麻岩变质新生锆石或岩浆锆石的变质边年龄在260~270Ma之间,大理岩的变质年龄为261.1±1.3Ma,侵入变质岩的未变形伟晶岩脉年龄为258.0±1.6Ma,表明该套变质岩系的变质时代约为260Ma,不能归入加里东期变质的陈蔡岩群。这是在华南东北缘地区首次发现二叠纪变质岩,为探讨华南东吴运动和全球海西运动,甚至泛大陆的重建提供了重要新信息。

The first discovery of Permian metamorphic rocks in Zhoushan Islands, Zhejiang Province

There are some metaphoric rocks such as amphibolite, genesis, schist and marble exposed in Daqu Island of Zhoushan Is-lands, Zhejiang Province. In the past, they are assigned to Chencai Formation. Nevertheless, new LA-ICP-MS zircon U-Pb analysis yielded the ages of metamorphic neogenic zircon and metamorphic rim in biotite-plagioclase gneiss ranging from 260Ma to 270Ma, whereas the metamorphic age of marble and the formation age of undeformed pegmatite veins which intruded into metamorphic rocks are 261.1±1.3Ma and 258.0±1.6Ma respectively, indicating that the metamorphic age of the rocks in Daqu Island is~260Ma. This is the first reported Permian metamorphic rock on the northeastern margin of South China Block, which may provide some im-portant new information for Dongwu movement in South China, global Hercynian movement and even the Pangaea reconstruction.