Tectonic history of the Huangsong tectonic terrains in the Khanka Massif in the easternmost Central Asian Orogenic Belt: Constraints from detrital zircon U–Pb geochronology

Abstract

The Khanka Massif, as the easternmost micro-massif of the Central Asian Orogenic Belt, its tectonic attributes and Paleozoic tectonic evolution remain controversial. In this paper, we present detrital zircon U–Pb age data for sedimentary rocks from the Huangsong Group, in order to provide constraints in this regard. The Huangsong Group has previously been described as the Precambrian basement of the Khanka Massif, consists of slightly metamorphosed sedimentary rocks, and from bottom to top is divided into the Yangmu and Yanwangdian suites. Unexpectedly, the depositional ages of the Yangmu suite are (from bottom to top) 220–205 Ma, 249–239 Ma, and 509–485 Ma. The depositional ages of the Yanwangdian suite are (from bottom to top) 426–390 Ma and 232–220 Ma. Clearly, the rocks do not have a logical stratigraphic sequence and, therefore, we propose that the “Huangsong Group” represents a stack of tectonic terrains with diverse ages (early Paleozoic to early Mesozoic) rather than a continuous sedimentary sequence. The potential sediment sources were mainly a nearby magmatic arc and batholiths, because the zircons are euhedral–subhedral, exhibit well-developed oscillatory zoning, and have high Th/U ratios. The occurrence of Precambrian detrital zircon grains implies the existence of remnants of Precambrian basement along the western margin of the Khanka Massif in the early Paleozoic. A comparison of magmatism in the regional massifs revealed there was a tectonic affinity between the western margin of the Khanka Massif and eastern margin of the Songnen–Zhangguangcai Range Massif in the Paleozoic. Based on the detrital zircon age populations and trace element contents, we conclude that the western Khanka Massif experienced a change from a stable to an active margin setting during the late Paleozoic, which was caused by subduction of the Paleo-Asian oceanic lithosphere.