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扬子地块西缘的河口群长期以来被认为是早元古代的火山—沉积地层,这种认识缺乏高精度同位素年龄的支持。为精确标定河口群的时代,采用激光剥蚀等离子体质谱(LA-ICP-MS)对川西南拉拉铜矿区河口群中的石英角斑岩进行锆石U-Pb定年。结果表明所有锆石均为岩浆锆石,单点分析结果均为谐和年龄,锆石207Pb/206Pb加权平均年龄为1722±25Ma(2σ,MSWD=0.5,n=11)。由此认为河口群浅变质火山—沉积岩系的精确沉积时代为1722±25Ma,为早元古代晚期的火山—沉积地层。
The estuarine group at the western margin of the Yangtze block has long been considered to be an Early Proterozoic volcano-sedimentary formation lacking the support of high-precision isotopic ages. In order to accurately calibrate the estuaries, zircon U-Pb dating of quartz horn porphyries in the estuarine region of the Lara copper deposit in southwestern Sichuan Province was performed by laser ablation plasmon resonance mass spectrometry (LA-ICP-MS). The results show that all zircons are magmatic zircons, and the single point analysis results are all in harmony age. The 207Pb / 206Pb zircon weighted average age is 1722 ± 25Ma (2σ, MSWD = 0.5, n = 11). Therefore, the precise depositional age of the shallow-metamorphic volcanic-sedimentary rocks in the estuary group is 1722 ± 25Ma, which is the volcano-sedimentary formation of the Early Early Proterozoic.