Large-Scale Late Triassic To Early Jurassic High Epsilon(Hf)(T)-Epsilon(Nd)(T) Felsic Rocks In The Ergun Massif (Ne China): Implications For Southward Subduction Of The Mongol-Okhotsk Oceanic Slab And Lateral Crustal Growth

The Manzhouli-Xin Barag right banner are located in the southwest of the Ergun Massif (NE China), the tectonic evolution of these areas are still controversial. In this study, a series of rocks comprising rhyolites (LA-ICP-MS U-Pb zircon ages of 206 +/- 2 Ma and 195 +/- 2 Ma), granodiorites (196 +/- 1 Ma and 190 +/- 1 Ma), and monzogranites (206 +/- 5 Ma and 196 +/- 1 Ma) are newly identified. Whole-rock major and trace element analyses show that these felsic rocks and granites belong to the metaluminous to peraluminous, high-K calc-alkaline series, and can be classified as I-type granites. The zircon in-situ Lu-Hf isotope analyses on rhyolite, granodiorite, and monzogranite, yielded the epsilon(Hf)(t) values that are ranging from of 9.7-12.1, and two-stage model age are in the range of 0.5 Ga to 0.6 Ga, epsilon(Hf)(t) values of 4.4-7.5, 0.8-1.0 Ga, epsilon(Hf)(t) values of 6.0-10.5, 0.6-0.9 Ga, respectively. The whole-rock Sr-Nd isotope analyses on rhyolite, granodiorite, and monzogranite, yielded lower initial Sr-87/Sr-86 ratios (I-Sr) of 0.703374-0.703586, 0.704503-0.704577, 0.704936-0.704379, with medium epsilon(Nd)(t) values of 4.32-4.38, 1.54-2.96, - 0.68 to 2.73, respectively, suggesting that they are derived from the partial melting of a juvenile depleted lower crust. They all show enrichment in the large ion lithophile elements (e.g., Rb, Ba, and K) and depletion in the high field strength elements (e.g., Nb, Ta, and Ti), indicating that they are generated in an Andean-type arc setting and are metasomatized by subduction-slab released fluids or melts with minor crustal contamination. Mainly three magmatic phases: ca. 283-225 Ma, ca. 225-166 Ma, and ca. 166 Ma-114 Ma are identified in the Ergun Massif, and above Late Triassic to Early Jurassic magmatic rocks are related to the second phase, which attribute to the Mongol-Okhotsk ocean southward subduction and lateral crustal growth.