Abstract: The Dewulu granodiorite pluton in the West Qinling Orogen contains a series of Au and Cu ore deposits. LA-ICP-MS yielded zircon U-Pb age of 250±1.8 Ma, indicating pluton emplacement occurred in the Early Indosinian. The pluton was found to be weak peraluminous with ASI of 0.9 to 1.0. All samples had high K2O content (2.95%3.52%) and high K2O/Na2O ratio (0.971.10). The granitoids showed high Mg# and compatible elemental content (Cr: (88132)×10-6). Thus, we consider that the Dewulu pluton was formed by the mixing of crust- and mantle-derived magmas. Abundant mafic enclaves occur in the pluton. These gabbro diorite or diorite enclaves had intermediate SiO2 content of 56.17%60.95%. Relative to the host rocks, the mafic enclaves had high Mg# (0.650.67) and low TiO2 content (0.57%0.62%). They were high-K calc-alkaline rocks and had high K2O (1.74%2.43%) and compatible elemental contents (Cr: (212419)×10-6; Ni: (46111)×10-6). They were enriched in LREEs related to HREEs showing intermediate negative Eu anomalies. In the trace element spider diagram, all the enclaves exhibited notable Nb-Ta anomalies. We consider that the Dewulu mafic enclaves are likely derived by partial melting of a potassic lithospheric mantle source, modified by subduction process with subsequent removal of mafic minerals. The Early Indosinian magmatism and associated ore deposits were likely emplaced at an active continental margin in this area.

Key words: granodiorite, mafic enclave, Indosinian, western Qinling, mineralization geotectonic background