The Changcheng System in Ordos Basin: Detrital zircon SHRIMP U-Pb dating and Hf isotope analysis

The Changcheng System was widely developed in an extensional tectonic setting in the North China Craton after the formation of the Xiong' er Group in the earliest Mesoproterozoic. The internal texture and age histogram of detrital zircons from sedimentary rocks are important for the understanding upon their formation backgrounds and provenance. This paper reports SHRIMP U-Pb ages and Hf isotope analysis of detrital zircons from four (meta-) sedimentary rock samples of the Changcheng System from three cores in the Ordos Basin, western China. According to their internal textures, two types of zircons can be divided, namely magmatic and metamorphic in origin. The detrital zircons have a major age peak at about 1.8 Ga and a minor age peak at similar to 2.5 Ga. The youngest detrital zircon is similar to 1.6Ga in age but with a large error. Zircons have different Hf isotopic compositions, with epsilon(Hf) (t) values ranging from -10.5 to +6.7. Combined with previous work, the main conclusions can be drawn as follows: (1) the bottom boundary age of the Changcheng System in Ordos Basin is younger than 1.7Ga, probably the same as that of the Changcheng System in eastern North China Craton; (2) the detrital sediments of the Changcheng System in Ordos Basin are mainly derived from the Paleoproterozoic Khondalite Belt in the north and/or the Ordos metamorphic basement itself. The zircons with magmatic textures have epsilon(Hf)(t) values of -6.8 similar to +5.2, suggesting that mantle addition to continental crust or mantle-continent mixture occur in the source region; (3) the Changcheng System in the Ordos Basin and eastern North China Craton were formed in similar tectonic settings, such as continental rift or aulacogen.