Beishan thermochronology 2022
We report apatite (U-Th)/He thermochronology from the Beishan fold-thrust belt, central Asia. Based on these data, we interpret ~140-133 Ma cooling in the Early Cretaceous to reflect hanging wall exhumation during thrust slip along the Hongqishan thrust in the Hongliudaquan area, southeastern Beishan. And we infer that the normal slip of the Suosuojing fault was responsible for footwall exhumation at ~124‒115 Ma in the Early Cretaceous. The late Mesozoic development of the Beishan fold-thrust belt in central Asia should be a far-field response to the closure of the Mongol‒Okhostk Ocean in the north and the Lhasa‒Qiangtang collision in the south, followed by collapse of thickened crust that triggered the post-thrusting extensional deformation.
Steps to reproduce
Apatite (U-Th)/He dating was conducted in 40Ar/39Ar and (U-Th)/He geochronology laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). After the standard rock crushing and heavy liquid separation procedures, 3-5 relatively euhedral apatite grains free of visible inclusions and internal fractures were selected and measured under a microscope. Each grain was then wrapped in a 1 mm × 1 mm platinum (Pt) capsule and loaded on a drilled oxygen-free copper disk. Helium measurement was performed using fully automatic helium extraction system called Alphachron MK II (Australian Scientific Instrument Pty Limited). After helium extraction, Pt wrapped grains were transferred to Savillex PFA vials and spiked with 230Th-235U solution with known concentration. All the spiked solutions were measured on a Thermo Fisher X-Series II inductively coupled plasma mass spectrometry (ICP-MS). Age calculation was conducted by a java based program named Helioplot (Vermeesch, 2010) and corrected for alpha emission following the procedure of Gautheron et al. (2009) . Durango apatite was used as a reference standard to verify the analytical procedure. Detailed analytical procedure was described in Wu et al., 2016, 2019.