Mixing of cognate magmas as a process for producing high-silica granites: Insights from Guanmenshan Complex in Liaodong Peninsula, China

Abstract Ascertaining how high-silica granites form is important for understanding why Earth has a high-silica continental crust and how the composition of the continental crust has evolved through time. This study presents a systematic dataset for the petrology, mineralogy, geochronology, and geochemistry of the granite porphyries and related microgranular enclaves and diabases from the Early Cretaceous Guanmenshan Complex (126–123 Ma) in Liaodong Peninsula, North China Craton, to reveal the complex, multi-stage, magmatic evolution in a shallow silicic magma system prior to and during emplacement of high-silica granites. Zircons from the granite porphyries and microgranular enclaves can be classified into two groups: those with dark-CL cores surrounded by light-CL rims, and those comprising entirely light-CL domains, without dark-CL cores. Our results indicate that dark-CL zircon domains with high Th (46–579 ppm), U (120–1274 ppm), and Hf (6709–12,493 ppm) contents and low Ti contents (1.52–7.85 ppm) and Ti-in-zircon temperatures (TTiZ = 622–751 °C) formed from highly evolved magmas, whereas light-CL zircon domains with low Th (14–157 ppm), U (24–236 ppm), and Hf (4749–10,474 ppm) contents and high Ti contents (7.59–29.36 ppm) and Ti-in-zircon temperatures (TTiZ = 748–885 °C) formed from low evolved magmas. These characteristics, combined with the similar U Pb ages and Hf isotopic compositions of the dark-CL zircon cores and light-CL zircon domains and insignificant intra- or inter-grain (87Sr/86Sr)i variations of plagioclase from the granite porphyries and microgranular enclaves, reflect mixing between two cognate magma batches with contrasting evolved signatures. This study presents a model in which the highly evolved magmas were derived from initial interstitial melts that were extracted from a crystal mush leaving behind residual cumulates, whereas the less evolved magmas were the products of re-melting of the cognate cumulates. The diabases likely represent the mafic recharge magma that contributed necessary heat but limited mass to remobilize the cumulate mush, inducing the internal self-mixing and formation of the hybrid high-silica magmas. Feeder-dyke related emplacement of the hybrid magma generated more mafic rocks that became incorporated and dispersed into the high-silica granite porphyries as cognate microgranular enclaves. Our results lend new insights into the important role of cognate magma mixing induced by mafic recharge in generation of high-silica granites.