Silurian-Devonian Intrusive Rocks and Tectonic Environment in Copulae of Kunlun-Qinling Mountains

Silurian-Devonian magmatic activity was discovered in the copulae of the Kunlun-Qinling mountains by detailed mapping and chronology analysis. Single grain zircon U-Pb dating yielded formation dates of 382-423 Ma in the intrusive rocks, which is Silurian-Devonian. The intrusive bodies are output in stocks, dikes and tectonic slices, which were suffered from later tectonism and evolved in the Kuhai-Saishitang Hercynian mélange belt as tectonic slices. The rock types are quartz-diorite, tonalite, granodiorite and monzonite granite, belonging to typical calc-alkali rocks. The characteristics of trace elements, main elements and tectonic environment discrimination reveal that the rocks were formed in an island arc tectonic environment or a continental margin arc tectonic environment. Some were also formed in a syncollisional tectonic environment, which reflects the stages of the prototethys ocean subduction and later continental crust collision. In that period intrusive rocks are in accordance with the East Kunlun Early Paleozoic magmatic activity zone, so it is suggested that a Silurian-Devonian magmatic arc developed in the copulae between the Kunlun-Qinling mountains, which joins the East Kunlun Early Paleozoic magmatic rock zone to the west. The geological characteristics and tectonic environment of the Silurian-Devonian intrusive rock in the copulae between Kunlun-Qinling Mountains indicated that the Paleotethys archipelagic ocean was formed in back-arc expandation, which was closely related to the close of the prototethys ocean.