The closure time of the easternmost segment of the Solonker-Xar Moron-Changchun-Yanji Suture: determined by the Yangjin’gou Granite Porphyry in the Hunchun Region, northeast China

Abstract

The timing of closure of the paleo-Asian Ocean in northeastern China remains contentious. To investigate this problem and better constrain the final closure time of the paleo-Asian Ocean, we report the geochemical characteristics, zircon U-Pb chronology, and Hf isotopes of the Yangjin’gou granite porphyry in the Hunchun region in the easternmost segment of the Solonker- Xar Moron-Changchun-Yanji Suture (SXCYS). The zircon U-Pb age of the Yangjin’gou granite porphyry is 247.1 ± 1.5 Ma (mean square weighted deviation = 0.7). Initial eHf(t) values are high and positive, ranging from +11.2 to +13.3 with an average of +12.7, and the two-stage Hf isotope model age TDM2 is 520–350 Ma. The geochemical characteristics of the granite porphyry indicate that the rocks belong to the calc-alkaline series and are rich in Si, alkali, and Al, and poor in Ca. These rocks also have a rare-earth element distribution pattern that is smooth and inclined down to the right in spider diagrams, weak negative to positive Eu anomalies (Eu/ Eu* = 0.83–1.01), moderate enrichment of large-ion lithophile elements (e.g., Cs, Ba, Rb, and K) and radioactive incompatible elements (e.g., Th and U), and depletion in high field strength elements (e.g., Ti, Nb, and Ta). The geochemical and isotope data of the rocks indicate that the Yangjin’gou granite porphyry is a high-Ba-Sr granite and that the primitive magma of the Yangjin’gou rocks originated from the partial melting of juvenile crust. Given the location of the Yangjin’gou granite prophyry in the Hunchun region in the easternmost segment of the SXCYS, these rocks are inferred to have formed in a tectonic setting that changed from continental collision to post-collision extension at ~247 Ma, clearly later than the middle Permian closure time of the paleo-Asian Ocean along the middle segment of the North China Craton. The age of ~247 Ma, or a little earlier, represents the closure time of the paleo-Asian Ocean in the easternmost segment of the SXCYS.