内蒙古陶海营子地区林西组形成时代 ——来自侵入岩脉LA-ICP-MS锆石U-Pb年龄的证据

长期以来,内蒙古阿鲁科尔沁旗陶海营子地区晚二叠世林西组的沉积时限未得到进一步确认.笔者在对该区林西组典型剖面进行详细野外调查的基础上,对侵入其二段的黑色厚层状细砂岩花岗细晶岩脉中的锆石进行了LA-ICP-MS同位素测定,得到锆石的206Pb/238U年龄加权平均值为242.0Ma±3.7Ma (MSWD=2.8,N=19),表明该细晶岩脉侵位年龄为中三叠世早期.在该剖面林西组二段未有上覆沉积岩系的情况下,该花岗岩脉的侵位年龄可以作为该区林西组沉积上限的间接证据.

The age of Linxi Formation in Taohaiyingzi area, Inner Mongolia: Constraint from the evidence of the LA-ICP-MS zircon U-Pb dating for the intrusive vein

The previous studies of the Linxi Formation in Alukeerqin area show that the Late Permian Linxi Formation should be regarded as the most potential hydrocarbon layer as well as the most potential series of strata for exploration of the Upper Paleozoic in the middle-southern Da Hinggan Mountains; nevertheless, no further data are available concerning the determination of the deposition age of Linxi Formation. LA-ICP-MS zircon U-Pb dating of the intrusive granitic vein yielded an age of 242.0Ma±3.7Ma (MSWD=2.8, N=19), which implies that the emplacement of the dike occurred in the early period of Middle Triassic. The age can be used as indirect evidence of the upper limit of the sedimentation for Linxi Formation in this area.