Geochronological and geochemical of igneous rocks from the Jilin area
We present new geochronological, whole-rock geochemical data, and zircon Hf isotopic data from middle Permian to Middle Jurassic igneous rocks that occur near the Changchun-Yanji Suture in the area of Jilin city. These new data can (1) constrain the timing of magmatism and elucidate the spatio-temporal distribution of magmatism; (2) characterize the petrogenesis of the igneous rocks and their possible sources; and (3) provide new insights into the tectonic setting during magmatism. Together with geological evidence from this area allow us to better understand the transition in the tectonic regime during the Late Paleozoic and Mesozoic. Based on zircon U–Pb ages and geochemical data, the following conclusions are drawn. 1. Middle Permian to Middle Jurassic igneous rocks in the area of Jilin were emplaced during four major phases, at ca. 261 Ma, 253–244 Ma, 183–175 Ma, and 173–164 Ma. 2. The earliest phase of magmatism, at ca. 261 Ma, was generated in an active continental margin by partial melting of juvenile mafic lower crustal material. Magmatism at 253–244 Ma was generated in a continental arc environment by partial melting of juvenile mafic subducted oceanic crust. At 183–175 Ma, monzogranitic and dioritic magmas were generated in a continental arc environment via melting of juvenile lower continental crust and mixing of basaltic magma with crustal melt, respectively. The final stage of magmatism, at 173–164 Ma, formed in an active continental margin, generated by melting of juvenile lower continental crust. 3. Integrated evidence suggests that the closure of the Paleo-Asian Ocean could occur at 244–227 Ma, whereas the timing of tectonic regime transition from the influence of Paleo-Asian Ocean subduction to the subduction of the Paleo-Pacific Ocean occurred between Late Triassic and Early Jurassic (223–185 Ma). 4. The Changchun-Yanji Suture experienced multiple tectonic mode switches from Late Paleozoic to Mesozoic, and was controlled by subduction of the Paleo-Pacific Ocean since Early Jurassic.