Two-Stage Orogenic Cycle of the Eastern Paleo-Asian Ocean from Early Palaeozoic to Early Triassic: Constraints from Magmatic Rocks of the Southeastern Central Asian Orogenic Belt

The evolution of the eastern Paleo-Asian Ocean (PAO) has controlled formation southeastern Central Asian Orogenic Belt (CAOB). However, history and final closure time PAO still remain controversial, which greatly restricts understanding process CAOB. To address these issues, we provide detailed zircon chronology Hf isotope geochemical data Paleozoic to Triassic magmatic rocks in We have identified four periods magmatism as evidenced by: Early Silurian quartz diorites (434.7 Ma), Devonian monzogranites (394.2 Middle Permian granites (260.2–264.5 Ma) Late Permian-Early syenogranite (250.8–253.6 Ma). These features low MgO mantle-compatible elements, are enriched Th, U, K, Pb, Sr, Zr depleted Nb, Ta, La, Ce, P, Ti. belong medium-K calc-alkaline series with εHf(t) values −0.76 2.21, indicating that they may be derived from partial melting mafic lower crust minor contribution mantle magma. high + Nb Ce Y (260–390; 261–461 ppm, respectively), total alkali contents (9.98–10.80; 8.46–9.29 wt.%, saturation temperature (807–840; 810–885 °C). They can classified A-type granites. Monzogranites (between −1.20 +3.34); hence, believe were modified by mantle-derived fluids or melts. Syenogranite (5.49–11.36), suggest juvenile originated mantle. Sr/Y ratios (118–257), (1.42–2.82 ppm), Yb (0.31–0.41 consistent adakite. Considering isotopic (2.99–8.50), thickened crust. Combining results our own previous studies, propose a new model Triassic. It divided into two stages: (1) Cambrian Devonian; (2) first stage is Bainaimiao ocean (secondary basin PAO), closed led arc accretion North China Cratons. second during (~254