Early Jurassic I-type garnet leucogranite in the Siguniangshan pluton, eastern margin of the Songpan-Ganze terrane (NE Tibet), and its tectonic implications

•For the first time, the ~185 Ma leucogranite was discovered in northeastern Tibet.•The ~185 Ma garnet leucogranite was a highly evolved peraluminous I-type granite.•Three magmatic events occurred in the Siguniangshan pluton during ~204–185 Ma.•Source of the leucogranite is the Neoproterozoic basement or early-formed intrusions.•Rapid uplift and extra shear heating along the decollement promoted partial melting.