Garnet serves as a key mineral in some granitic rocks, offering unique constraints on melt generation and crustal evolution processes. This study presents an integrated petrological, geochemical, geochronological, and phase equilibrium investigation of garnet-bearing granite from the Chengde area of the Trans-North China Orogen. The garnet exhibits homogeneous major element compositions but distinct trace element zoning patterns, characterized by a decrease in yttrium and heavy rare earth element concentrations from core to rim, which is indicative of growth zoning. Textural evidence of garnet-quartz intergrowth, coupled with trace element variations, documents a multistage growth history involving initial metamorphic nucleation followed by rim development under suprasolidus conditions. Phase equilibrium modeling constrains the garnet formation conditions to 10.7−11.1 kbar and 760−775 °C, similar to thermometric estimates of 685−757 °C. Comprehensive datasets, including whole-rock geochemistry, zircon trace elements, and garnet geochemistry, collectively indicate an S-type granite origin from clay-poor metapelitic sources. Magmatic emplacement occurred at 1886−1875 Ma, followed by metamorphic overprinting at 1855−1802 Ma. These findings highlight the utility of garnet as a robust petrogenetic indicator, providing key insights into peritectic phase entrainment during crustal anatexis. The results significantly advance our understanding of granite formation mechanisms in collisional orogens and elucidate the processes of lower-crustal reworking during Paleoproterozoic orogenesis.
Zhang et al. (Tue,) studied this question.