Mesozoic tectonic setting of rift basins in eastern North China and implications for destruction of the North China Craton

Abstract

Destruction of the North China Craton (NCC) in the Mesozoic due to subduction of the Paleo-Pacific Plate has attracted a lot of recent interest, with numerous studies focusing on regional tectonics and associated magmatism. Although the peak ages for this event have been established, the timing of its initiation remains poorly understood. In this paper, two rift basins in the northern Hebei Province of China, the Diaoe Basin (DB) and Houcheng Basin (HB), are studied in order to constrain the timing of destruction of the northern margin of the NCC. Both NNE-striking basins developed on Proterozoic basement. The DB is a graben controlled by normal faults on its two margins, and the HB is a half-graben bounded by normal faults on its eastern side. Basin fills include detrital sediments and volcanic rocks, which are (from bottom to top) the Houcheng Formation (Fh), the Zhangjiakou Formation (Fzh), the Shijiayao Formation (Fs), and the Huajiying Formation (Fhj). The Fh is composed mainly of detrital sediments interlayered with andesite in its lower section, and interlayered with felsic volcanics (rhyolite) in its upper section. There exists a transitional change from the Fh to the thick felsic volcanic strata of the Fzh. Geochemically, the andesite layers in the lower Fh were most likely derived from mixing of crust and mantle melts, whereas the felsic rocks were derived from melting of the lower crust. U–Pb dating of zircons by LA-ICP-MS yielded ages for the lower Fh andesites of ca. 165.7Ma in the HB and ca. 157.4Ma in the DB. The felsic rocks at the base of the Fzh yielded ages of ca. 155.1Ma in the HB and ca. 149.2–143.4Ma in the DB. The Fs and Fhj in the DB both yielded similar ages of ca. 136Ma. The development of rift basins, together with the occurrence of massive felsic volcanic rocks, indicates a period of significant extension and thinning of the NCC. The ca. 165.7–155.1Ma age for andesites not only represents the initial timing of crustal extension, but also the timing of thermally induced melting of the lower lithosphere. We conclude, therefore, that the destruction of the northern margin of the NCC started by the Middle Jurassic or earlier.