^40Ar／^39Ar dating of Daqingshan thrust

The Daqingshan thrust system is an important part of the western segment of the Mesozoic Yinshan-Yanshan orogenic belt. Therefore, much attention has been paid to the thrusts due also to their large-scale and entirely devel-oped structural elements and typical structural styles. Studies and progress have been concentrated on the ge-ometry, kinematics, dating and dynamic mechanism of the thrust and thrusting. To date, there have been no reliable published isotopic data, however, on the dating…

40Ar/39Ar dating of Daqingshan thrust

The Daqingshan thrust system, to the south of the Shiguai Mesozoic basin, is a complex system of top-to- the-north thrusting tectonic sheets. The thrust system has a complicated evolution due to multi-stage thrusting. In order to date the thrusting events, syntectonic muscovite and bio-tite grains are respectively analyzed with normal 40Ar/39Ar dating and laser 40Ar/39Ar dating, which yield 2 isochron ages, i.e. 193.74 3.88 Ma and 121.6 1.6 Ma. These ages suggest that faults within the Daqingshan thrust system formed dur-ing 2 stages of thrusting, one the early Indosinian and the other the late Yanshanian. The isotopic dating is consistent with field geological relations. Indosinan deformation is evi-denced by top-to-the-north thrusting, with the occurrence of a series of large-scale east-west trending thrust faults and folds, while the Yanshanian thrusting is characterized by top-to-the-NNW thrusting. It is superposed on and modifies early Indosinian thrust faults.