Ages, Sources and Tectonic Settings of the Triassic Igneous Rocks in the Easternmost Segment of the East Kunlun Orogen, central China

U-Pb analysis of zircons from igneous rocks in the Elashan Mountain, easternmost segment of the East Kunlun Orogen yielded 252-232 Ma. Geochemically, these rocks are mainly high in SiO2, K2O and K2O+Na2O contents, low in P2O5 and TiO2 contents, depleted in Ba, Sr, P, Ti and enriched in U, Hf, Zr, showing features of I-type granite. The zircon epsilon(Hf)(t) values of the Early Triassic Jiamugeu0027er rhyolite porphyry (252 +/- 3 Ma) are positive (+1.6 to +12.1), suggesting a juvenile crustal source mixing with little old crustal component, and the zircon epsilon(Hf)(t) values of the Middle Triassic Manzhangu0027gang granodiorite (244 +/- 3 Ma) and Dehailong diorite (237+3 Ma) are predominately negative (-8.4 to +1.0), indicating an older crustal source. In comparison, the zircon epsilon(Hf)(t) values of the Late Triassic syenogranites from Suigenu0027ergang (234 +/- 2Ma), Geu0027ermugang (233 +/- 2 Ma) and Yueu0027ergen (232 +/- 3 Ma) plutons vary from -3.8 to +5.0, suggesting a crust-mantle mixing source. From Early-Middle Triassic (252-237 Ma) to Late Triassic (234-232 Ma), the geochemical characteristics of these rocks show the change from a subduction-collision setting to a post-collision or within-plate setting. By comparing of these new age data with 77 zircon U-Pb ages of igneous rocks of the eastern part of East Kunlun orogen from published literatures, we conclude that the igneous rocks of Elashan Mountain and these of the eastern part of East Kunlun Orogen belong to one magmatic belt. All these data indicate that the Triassic magmatic events of the eastern part of East Kunlun Orogen can be divided into three stages: 252-238 Ma, 238-226 Ma and 226-212 Ma. Statistically, the average epsilon(Hf)(t) values of the three-stage igneous rocks show a tendency, from the old to young, from -0.75 +/- 0.25 to lower -2.65 +/- 0.52 and then to -1.22 +/- 0.25, respectively, which reveal the change of their sources. These characteristics can be explained as a crust-mantle mixing source generated in a subductional stage, mainly crust source in a syn-collisional stage and a crust-mantle mixing source (lower crust with mantle-derived underplating magma) in a post-collisional stage. The identification of these three magmatic events in the Elashan Mountain, including all the eastern part of East Kunlun Orogen, provides new evidence for better understanding of the tectonic evolution of the northward subduction and closure of the Paleo-Tethyan (252-238 Ma), the collision of the Songpan-Ganzi block with the southern margin of Qaidam block (238-226 Ma), and the post-collisional setting (226-212 Ma) during the Early Mesozoic period.