Palaeoproterozoic turbidite deposition in the Liaodong Penisula, northeastern North China craton – Constraints from the Gaojiayu formation of the Liaohe Group

Abstract

The Palaeoproterozoic sedimentary environment is difficult to reconstruct because rocks often experience multiple stages of deformation and metamorphism; however, it is critical to understand the Precambrian evolution of sedimentary basin. In this study, we report two un-metamorphosed sections in the Gaojiayu Formation of the North Liaohe Group, central part of the Jiao-Liao-Ji orogenic belt, eastern North China Craton. Rocks consist of shales, carbonaceous slates, calcareous mudstones and sandstones, marlstones, calcarenites, and brecciated limestones in these sections. Detailed field observations indicate that all kinds of original bedding and syn-depositional structure developed in these rocks. Microscope observations suggest that detritus in rocks predominantly contain feldspars, quartz, and calcites, occasionally with volcanic fragments and pyrites. Palaeocurrent study indicates that the provenance of detritus in rock of these two sections was from NW to SE. Detrital heavy minerals mainly consist of pyrite and hematite, occasionally with barite, which are all from the Li'eryu Formation that contains these minerals in sedimentary layers. The increase of percentages of pyrite in a cross-section indicate that the sedimentary environments transformed from an oxidizing to a reducing depositional environment because the depositional setting became deeper. According to the mafic intrusion dated in this study and regional geochronological data such as the age of underlying volcanic rocks, the depositional age of the Gaojiayu Formation is constrained between 2.17 and 2.16 Ga and 2.11 Ga. Archaean basement (2.5 Ga) is recognized as the major provenance providing clastic materials for the Gaojiayu Formation; volcaniclastic rocks in the Li'eryu Formation were also a significant source. Accordingly, in this paper we interpret the Gaojiayu Formation as turbiditic sedimentary rocks that were deposited in an arc-related abyssal and semi-abyssal environment, probably in an extensional back-arc basin setting. Palaeoproterozoic turbidite deposition combined with a 2.17 Ga volcanic arc developed in the study area, we conclude that the modern trench-arc-basin system may had already existed in the early Palaeoproterozoic and deeply affected the tectonic evolution of the Jiao-Liao-Ji orogenic belt, northeastern North China Craton.