山东新泰孟家屯岩组锆石特征及其年代学意义

Characters of Zircons in the Mengjiatun Formation in Xintai of Shandong and Their Chronological Significance

本文借助于离子探针技术(SHRIMP Ⅱ),对孟家屯岩组的石榴子石石英岩、含十字石石榴黑云母片岩、斜长角闪岩,以及孟家屯岩组的围岩条带状黑云斜长片麻岩(原岩为英云闪长岩)等进行了锆石年代学测定,并结合阴极发光和背散射电子图像反映出的锆石形态和微区特征,得出不同锆石微区的年龄。经分析有几组年龄值,分别为:2742 Ma和2717 Ma,2695 Ma,2642～2620 Ma。结合笔者其他的研究分析,它们分别代表孟家屯岩组源区岩石年龄、英云闪长岩的侵入年龄、变质作用年龄。在此基础上,较为完整的论述了孟家屯岩组演化历史。本文的同位素年代学资料为鲁西孟家屯岩组最新的资料,尤其是首次获得了孟家屯岩组准确的源区岩石年龄,并且准确地限定了孟家屯岩组的形成时代。对研究孟家屯岩组,以及泰山岩群和整个鲁西的地质演化历史有重要的意义。

Zircons in the garnet quartzite, staurolite-bearing garnet-biotite schist, amphibolite, and banded biotite plagiogneiss are dated by means of SHRIM n , and the shape and micro-texture of the zircons observed with CL and BSE. Ages of 2742 Ma, 2717 Ma, 2695 Ma, and 2642 - 2620 Ma are obtained in different micro-regions of the minerals. These ages are the age of the protolith of the Mengjiatun Formation, eruption age of tonalite, and age of the main metamorphic stage. The evolution of the Mengjiatun Formation is reconstructed. The most important result is the age of the protolith, which confines the sedimentation age of the Mengjiatun Formation. These results are significant in studying the Mengjiatun Formation, Taishan Group, and the geological evolution of western Shandong.