SS-LASS Zircon Dating Deciphering Multiple Episodes of Anatexis in a Deeply-Subducted Continental Crust: An Example from Sulu Orogen, China

Abstract

‘Single shot’ laser-ablation split-stream (SS-LASS) technique analyzing unpolished zircon grains makes their thin rims tenable for determination, which thus offers great potential in deciphering the timing of multiple and short-lived episodes of anatexis and metamorphism in deeply-subducted continental crusts. Dominated granitic gneisses in the deeply subducted continental crust undergoing considerable fluid-melt activities persist multistage growth of zircon. Therefore, a comparative study of SS-LASS and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) zircon dating was conducted on the granitic gneisses from the Sulu belt in this study. Zircons mostly show a core-mantle-rim structure with CL-bright rims thinner than 5 µm. For LA-ICP-MS dating, relict magmatic zircon cores yield protolith ages of ca. 756–747 Ma; whereas the dark mantles record synexhumation anatexis at ca. 214 Ma. By contrast, according to the U-Pb dates, trace element features, zircon crystallization temperatures and geological context, SS-LASS zircon petrochronology deciphers three episodes of anatectic events, as follows: (i) the first episode of anatexis at ca. 218–217 Ma dominated by phengite-breakdown melting, likely facilitating the exhumation of the UHP slice from mantle depth; (ii) the second episode of anatexis at ca. 193–191 Ma indicating part of northern Dabie-Sulu belt was still “hot” because of buried in the thickened orogenic crust at that time; (iii) the third episode of anatexis (ca. 162–161 Ma) consistent with the intrusion ages (ca. 161–141 Ma) of the Jurassic to Cretaceous granitoids in this orogen, suggesting the initial collapse of the orogenic root of the Sulu belt occurred at Late Jurassic due to the Izanagi plate initially subducting beneath the margin of Eastern Asia. This study sheds new light upon the utilization of SS-LASS petrochronology deciphering multiple anatectic events in the deeply-subducted continental crust and supports us in better understanding the tectonic evolution of Dabie-Sulu Orogen.