College of Earth Sciences, Jilin University, Changchun 130061, China

The authors presented geochronology and geochemical data of diorites from Nancha gold deposit in Tonghua region, with the aim to constraining its formation age, magma source and tectonic setting. LA-ICP-MS U-Pb dating results of zircons from the diorites indicate that the rocks were formed in the Middle Jurassic (171±2 Ma, MSWD=1.19). Geochemically, these rocks have SiO₂ concentrations of 52.52%-54.90%, K₂O of 2.14%-3.84%, Na₂O of 3.17%-3.35%, MgO of 7.43%-9.34% and high Mg^# of 68.57-72.57. These rocks are characterized by enrichment in large ion lithophile elements(LILE, such as K, Ba, Rb and Sr)and light rare earth elements (LREE), relatively depletion in high field strength elements (HFSE, such as Ta, Nb, Ti and Zr), and heavy rare earth elements (HREE). These characteristics suggest that primary magma of the rocks were derived from the partial melting of mantle with miner crustal contamination, which may related to partial melting of mantle wedge by addition of sediment melt from subducting oceanic crust. Based on former and present studies, the authors consider that the Nancha ore deposit high-Mg diorites were formed in compressional structural setting which is similar to volcanic arc. It could be related to the subduction of the Paleo-Paci-fic plate beneath the Eurasian continent.