New Evidence of Indosinian Magmatic Activity and Revelation of Old Ages in Binbalechagan, Inner Mongolia

摘要

Field geological survey has revealed that Binbalechagan batholith is not composed of a single rock body. This paper has selected fine grained porphyritic syenogranites (FPSG) in the batholith for the isotope chronological study. By LA-MC-ICPMS U-Pb dating of 28 zircons, weighted mean age of 217.3 ± 9.9 Ma (MSWD = 0.076) was obtained from FPSG. Since the characteristics of these zircons are in accordance with those of typical magmatic zircon, the result can represent the diagenetic age of FPSG. The research confirmed the existence of Indosinian magmatic activities in the area. In addition, 425 ± 5 Ma was obtained from one zircon in which black inclusions were found, and this age is believed to be a mixed one, indicating that there might be an old massif at the age of > 425Ma in the area of Binbalechagan.