Abstract Composite granitoid plutons record multiple magmatic processes, however, how these processes relate to lithological diversity remain unclear. This study addresses this question through a detailed examination of multiple zircon populations from the Zhongchuan composite pluton in the Western Qinling Orogen, Central China. The Zhongchuan pluton comprises granodiorite, porphyritic monzogranite, biotite monzogranite, muscovite monzogranite and tourmaline monzogranite. Combining zircon textural features, U–Pb ages, Hf-O isotopes and thermometry, three zircon populations were identified, i.e. inherited, autocrystic and antecrystic. Inherited zircon grains from the monzogranites exhibit age-εHf(t) spectra matching that of the detrital zircon from regionally Paleozoic strata, suggesting significant incorporation of metasedimentary protolith. Autocrystic zircon grains from the granodiorite and porphyritic monzogranite mostly exhibit restricted εHf(t) values (−4.5 to − 1.1), similar to those of the zircon from regionally coeval I-type granites, consistent with derivation from a meta-igneous protolith. In contrast, autocrystic zircon grains from the biotite monzogranite, muscovite monzogranite and tourmaline monzogranite show highly variable δ 18O (+8.3 to + 11.3‰) and εHf(t) (−4.9 to + 5.2), indicating an open magmatic system. Particularly, many autocrystic zircon grains from these rocks exhibit εHf(t) values (+1.5 to + 5.2) similar to those of the zircon (εHf(t) = +1.4 to + 5.4) from Triassic diorite, indicating involvement of dioritic magmas. The negative correlation between εHf(t) and Hf for the autocrystic zircon from the muscovite monzogranite and biotite monzogranite further testifies to the mixing of dioritic magmas with the magmas derived from metasedimentary protolith. The tourmaline monzogranite likely incorporated an additional meta-igneous component, as indicated by the lack of a clear εHf(t)-Hf correlation in autocrystic zircon and the similarity of εHf(t) and δ18O values between some autocrystic zircon grains and those from the granodiorite. Antecrystic zircon grains show low Eu/Eu* ratios (0.4) and variable εHf(t) (−5.9 to + 6.9) and δ18O (+7.8 to + 12.4‰) values, reflecting crystallization from deep, heterogeneous mushy magma reservoirs before transporting to a shallow reservoir. Therefore, compositional and lithological diversity of the Zhongchuan composite pluton can be attributed to hybridization of magmas derived from meta-igneous and metasedimentary protoliths and dioritic magmas within trans-crustal mushy magma reservoirs. Our finding highlights the utility of zircon populations in revealing the cryptic mixing processes that contribute to the formation of composite granitoid plutons.
Dou et al. (Tue,) studied this question.