| Abstract:By using the newly introduced GeoLas HD type 193nm ArF excimer laser ablation system and the Agilent 7900 type quadrupole inductively coupled plasma mass spectrometer, we successfully established the method of in-situ garnet U-Pb analytical method by LA-ICP-MS. A U-Pb dating work was carried out on the rodingite rocks form the Late Paleozoic mafic-ultramafic mélange in the northern Hebei Province and the ore-bearing skarn from Makeng iron deposit in southwestern Fujian. It yielded lower intersection ages of 387.6±5.4 Ma (D496-1, MSWD=1.1, N=30) and 409.3±7.8 (D493-1, MSWD=2.0, N=60) Ma for 2 rodingite samples, and 128.6±2.1 Ma (ZK7921-b24, MSWD=2.0, N=60) and 128.7±3.2 Ma (ZK7922-b1, calibration with zircon 91500, MSWD=1.8, N=42) for 2 skarn samples from Makeng deposit. It yielded lower intersection ages of128.7±1.7Ma (PT-b1，MSWD=1.7，N=30) and 132.1±1.3Ma (PT-b1, calibration with zircon 91500, MSWD=1.6, N=30）for a skarn sample from Pantian deposit (except for samples with instructions of calibration with zircon 91500,other samples are calibrated with garnet Willsboro). The garnet U-Pb ages above were consistent with the Sm-Nd isochron ages and previous zircon U-Pb ages within the allowable error range. Garnet U-Pb ages of the skarn samples collected from the Makeng-type deposit showed that the lower intersection and 206Pb/238U ages were consistent using the garnet Willsboro and zircon 91500 as standard samples respectively, which suggested that the matrix effect is small between zircon and garnet minerals. In case of an absence of the standard garnet sample in the laboratory, the zircon 91500 can be used instead. Based on the above research and understanding, an analysis on the application potential of the garnet U-Pb dating method in the geochronological study on skarn-type deposits and rodingite rocks was done. It is considered that the garnet U-Pb dating method has great application and promotion prospects in the chronology study of skarn-type deposits and rodingite rocks, and it is of great importance on the theoretical guidance and practical application. |
