Barium isotope evidence for crystal-melt separation in granitic magma reservoirs

•Barium isotopes can be significantly fractionated during granitic magma differentiation.•Albite granites have δ138/134Ba from 0.50‰ to 0.95‰, higher than that of K-feldspar granites (−0.14 to 0.16‰).•K-feldspar (−0.23 to 0.01‰) and biotite (0.73–1.92‰) have lower and higher δ138/134Ba than the whole-rocks, respectively.•Δ138/134BaBiotite-Muscovite vary from −0.98‰ to 1.01‰, reflecting crystal accumulation and repacking.