鲁西泰山岩群变质枕状玄武岩岩相学和侵入的奥长花岗岩SHRIMP锆石U-Pb年代学

Petrography of the Metamorphic Pillow Basalt and SHRIMP U-Pb Dating of Zircons from the Intruding Trondhjemite in Archean Taishan "Group",Western Shandong

鲁西泰山岩群柳杭岩组中,典型变质枕状玄武岩出露在济南章丘的团员沟村西一带。本文对变质枕状玄武岩的野外地质和岩相学特征,作了详细描述。电子探针分析表明,岩枕内部既有原生斜长石(An>30),又有绿片岩相变质形成的钠长石(An<10)。侵入柳杭岩组的片麻状奥长花岗岩中的岩浆锆石SHRIMPU-Pb年龄为2707±9Ma,它限制了泰山岩群形成时代不晚于2.71Ga。

Typical metamorphic pillow basalt is widely distributed in the Liuhang ＂Formation＂ of the Taishan ＂Group＂, west of Tuanyuangou village, Zhangqiu, western Shandong Province. The pillows, interstitial filled with silica and carbonate, exhibit blastoporphyritic texture. The cement mainly consists of plagioclase, zoisite, hornblende, chlorite and quartz. The porphyroblasts, ususlly smaller than 0.5mm in size, are mainly composed of plagioclase, zoisite and chlorite. Electron microprobe analysis shows that, in the pillows, most albites （with An 〈 10） in matrix, are formed during green schist facies metamorphism, but some plagioclase phenocrysts （with An 〉30） still remain. A SHRIMP U-Pb zircon age of 2707 ±9Ma was obtained for a gneissic trondhjemite, which intrudes in the Liuhang ＂Formation＂, limiting the formation age of the Taishan ＂Group＂ no younger than 2.71Ga.