Geochronology of the Middle Triassic Andesites in Mohe'ertu Area, Inner Mongolia, China, and Its Implications

摘要

The Mohe'ertu Middle Triassic andesitic rocks were first recognized in the middle east of the Xing'anlling-Mongolia Orogenic Belt (XMOB) on the south of the Siberrian paleo-plate through our filed works. These rocks are composed of basaltic andesite and trachyandesite. Two representative samples were dated by LA-MC-ICP-MS. Zircon U-Pb dating results show that the crystallization ages of the andesites are between 234.8±3.2Ma (lσ, MSWD=0.84) and 231.4±1.2 Ma (lσ, MSWD=2.5), which belong to the Middle Triassic. Combined these data with previously regional age data, we conclude that the andesites were formed in post-collisional extension tectonic setting within the XMOB, and they can be treated as new volcanic evidences formagmatic evolution in the Middle Triassic.