Discovery of Late Permian Adakite in Eastern Central Asian Orogenic Belt: Implications for Tectonic Evolution of Paleo-Asian Ocean

Abstract

The Permian to Triassic period represents a pivotal phase in the evolution of the Paleo-Asian Ocean, marked by significant tectonic transitions from subduction, collision, and post-orogenic extension. The timing of closure of the Paleo-Asian Ocean in northeastern China has always been controversial. In this contribution, the petrology, zircon U-Pb geochronology and geochemistry are conducted on granite found in well HFD1, Songliao Basin, eastern part of Central Asian orogenic belt. Zircon U-Pb dating indicates that granite crystallized at 258.9 ± 2.2 Ma, as the product of magmatism occurred in the early Late Permian. The rocks have high SiO2, Al2O3, Na2O content, negative Eu anomaly, light enrichment of rare-earth elements, depletion of heavy rare-earth elements, high Sr (448.29–533.11 ppm, average 499.68 ppm), low Yb (0.49–0.59 ppm, average 0.54 ppm), Y (4.23–5.19 ppm, average 4.49 ppm), and high Sr/Y ratios (98–125, average 112) and can be classified as O-type adakite. This is the first discovery of late Paleozoic adakite in the Songliao Basin and the neighboring areas. The geochemistry of adakite indicates derivation by partial melting of MORB-type subducted oceanic crust, indicating that the subduction of the Paleo-Asian Oceanic lithosphere lasted until at least 258.9 Ma.