In situ low-U garnet U-Pb dating by LA-SF-ICP-MS and its application in constraining the origin of Anji skarn system combined with Ar-Ar dating and Pb isotopes

•91500 is an ideal reference material for garnet U-Pb dating in spot sizes of 32–16 μm.•Willsboro is not suitable to calibrate the garnets with relatively high common lead.•Anji skarn system (137–138 Ma) has a genetic relationship with fine-grained granite.•Mantle-sourced materials may play an important role to form the Anji skarn system.