关键词: 早中生代, 闪长质包体, 岩石地球化学, 壳幔岩浆混合作用

Abstract:

The zircon U-Pb ages of 218 Ma and 224 Ma have been obtained from the Dongjiangkou granitoids and their mafic
enclaves, respectively. The disequilibrium magmatic textures can be found in the mafic enclaves, which have some K-feldspars
similar to those of host granitoids and needle-like apatite formed under a quenching condition, indicating a two-end member
magmatic mixing in the early Mesozoic. The two-end member magmatic mixing resulted in similar geochemical compositions and
strong homogenization of Sr-Nd-Pb isotopes between host granitoids and their mafic enclaves. However, Hf isotopic composition
of the mafic enclaves shows a wide range of εHf(t) that varies from -4.58 to 3.31, registering the source features of two-end member
magma. Thus, the positive εHf(t) values (＞10) of zircons from the contemporary mafic enclaves provide evidence that the mafic
magma was derived from the depleted mantle. While, host granitoids with negativeεHf(t ) values (＜10) of zircons were products of
partial melting of the Mid-Proterozoic mantle-derived basic rocks. Since then, the distinct crust- and mantle-derived magmas were
mixed around 224 Ma, resulting in a large number of granitic intrusions with abundant mafic enclaves during the early Mesozoic
in the Qinling orogeny.

Key words: Early Mesozoic；mafic enclave；petro-geochemistry；crust- and mantle-derived magmatic mixing