Revisiting the boundary between the Central Asian Orogenic Belt and North China Craton in Alxa area, China: Insights from zircon U-Pb ages and Hf isotopes of Phanerozoic granitoids

•Phanerozoic granitoids are used to constrain the north boundary of the Alxa Block.•The granitoids show juvenile and ancient source provinces with contrasting isotopes.•Tectonic belts with juvenile crust (TDM2 < 1.30 Ga) could be parts of CAOB.•Tectonic belts dominated by ancient crust (TDM2 > 1.30 Ga) belong to the Alxa Block.