摘要
The Yushugou and Tonghuashan ophiolitic mélange,which occurs in the Kumishi region at the southern margin of the Middle Tianshan Mountains, Xinjiang, consists of mantle peridotite, cumulate pyroxenite, gabbro and anorthosite, diabase dikes and mafic lavas overlain by chert. Geochemical data indicate that the ophiolitic units originated in both MORB and SSZ tectonic settings. U-Pb isotope ages of zircons from the ophiolitic and related rocks record at least four tectonic events related to oceanic spreading and basin closure: 1) ocean basin formation in the Ordovician-Silurian; 2) island arc magmatism in the Silurian; 3) shearing in the Devonian (400 Ma for mylonite); and 4) extensional magmatism of the orogen in the Late Carboniferous (294.8±1.2 Ma for quartz syenite porphyry that formed perpendicular to the direction of subduction and collision).