Timing of closure of the Jilin-Heilongjiang Ocean: constraints from zircon U-Pb and Ar-Ar dating of the Heilongjiang Complex in NE China

There has much debate over the timing of the overlap and transition between the closure of the Palaeo-Asian Ocean and the initiation of subduction of the Palaeo-Pacific Ocean. This geological process is recorded by the Jilin-Heilongjiang high-pressure metamorphic belt located at the easternmost end of the Central Asian Orogenic Belt. To address this issue, we investigated the Heilongjiang Complex exposed in the Yilan and Huanan regions using geological and geochemical analyses combined with laser ablation inductively coupled plasma mass spectrometry zircon U-Pb and Ar-Ar isotopic dating. Our geochemical studies indicate that the protoliths of the Yilan blueschist consist of subalkaline basalt formed in an ocean island environment. The zircon U-Pb analyses yielded zircon crystallization ages of 247 +/- 4, 259 +/- 3, 252 +/- 5 and 266 +/- 3 Ma. The Ar-Ar analyses yielded phengite ages of 185 +/- 2 and 177 +/- 2 Ma for a mica schist and a muscovite-albite schist in the Huanan area, respectively. Our findings indicate that the opening of the Jilin-Heilongjiang Ocean occurred during the late Permian to early Triassic (266-247 Ma) and its subduction occurred during the early Triassic to early Jurassic (247-185 Ma). These results provide new constraints on the timing of the overlap and transition between the closure of the Palaeo-Asian Ocean and the initiation of subduction of the Palaeo-Pacific Ocean.