Early Paleozoic Paleo-Asian Ocean subduction in the southern Beishan, Gansu: Evidence of zircon U−Pb age and geochemical records from Mingshujing adakitic pluton

The southern Beishan has an important tectonic position and a complex tectonic evolution history, which restricts the research on the tectonic attribution of the Beishan orogenic belt. The Mingshujing adakitic pluton is located in the south of Beishan, Gansu, to the west of Huitong Mountain, and the lithology is mainly adamellite, syenogranite, granodiorite, quartz diorite, etc. The LA−ICP−MS ages of the adamellite, syenogranite, granodiorite zircons of the Mingshujing adakitic pluton are 423.4±3.4 Ma, 425.4±2.3 Ma and 437.8±3.5 Ma, respectively, which represent the crystallization age of the pluton. The content of SiO₂ is mostly higher than 56% (55.53% ~ 64.42%), Al₂O₃ is larger than 15% (15.1% ~ 17.79%), MgO is mostly less than 3%, and all are less than 6% (2.07% ~ 3.5%). The content of Y and Yb is relatively low. At the same time, no Eu anomaly or only weak negative Eu anomaly can be observed, REE distribution patterns show strong REE segregation and belong to the type of enriched LREE, and there exist very prominent negative Nb anomaly and positive Sr anomaly in the trace element spidergram. The petrogeochemistry has similar characteristics to that of adakite. Based on the regional geological background, it is believed that the Silurian adakitic pluton in the southern Beishan were formed in the volcanic arc environment of the active continent margin, and which may be the products of the northward subducting magmatism of the Silurian paleo-Asian oceanic crust in Beishan Mountains, at the same time, there was a massive continental accretion. The identification of adakitic pluton in the Mingshujing provides an important basis for the early Paleozoic tectonic evolution of the Beishan Orogenic Belt.