Petrology and geochemistry of the Chuanwulu alkaline complex in South Tianshan: Constraints on petrogenesis and tectonic setting
南天山川乌鲁碱性杂岩体的岩石学和地球化学特征及其岩石成因

The Chuanwulu alkaline complex is located in the Kuokesayanling region in the west sector of the South Tianshan orogenic belt. The complex is spatially and genetically associated with the Cu, Au polymetallic ore deposits. It consists of gabbro-diorite at early stage, monzonite-syenite at main stage and alkaline granite porphyry dyke at late stage. They have distinct mineral and chemical compositions. From early to late stage, SiO2changes from 50.52% to 70.64%, where total alkali contents increase at SiO2<61.69% but decreases at SiO2 >61.69%. Most samples are of alkaline affinities based on the SiO2-AR diagram, and display a trend from metaluminous to peralikine. The primitive mantle normalized trace element diagrams are characterized by the enrichment of the LILE relative to HFSE, and Rb, Ba, Th and Sr enrichment coupled with negative Nb, Ta, P and Ti anomolies. They exhibit a relative enrichment of LREE with (La/Yb)N ratios of 14.13~25.09 as well as very slightly positive or negative Eu anomalies. The petrological observations and geochemical variations suggest that the Chuanwulu alkaline complex was produced by magma mixing. Mafic magma was derived from hydrous lithospheric mantle while felsic magma is produced by partial melting of water-saturated intermediate rocks in middle and lower continental crust. The complex was likely formed under an extension setting in response to a post-collision tectonic environment.