Abstract:
This paper conducted detailed investigations of the lithological assemblages and stratigraphy of the Zhongtiao Group and the Danshanshi Group in Zhongtiao Mountain region, Trans-North China Orogen (NTCO), North China Craton. The Zhongtiao Group comprises of a suit of metamorphic sedimentary rocks, consisting of multicyclic sedimentary rocks composed of clastic rocks, mudstones and carbonate rocks. The geochemical characteristics of the metamorphic sandstone show that the Zhongtiao group experienced a transition from early relative stability to late activity. Detrital zircons from the Zhongtiao Group and SIMS U-Pb analyses of zircon grains from an intercalated amphibolite indicate that they were deposited ~2.1Ga and formed in a back-arc basin of active continental margin. The Danshanshi Group is a series of conglomerates and sandstones forming a molasse basin during the collisional orogeny stage at approximately 1.85 Ga. Taken together, we present a brief scenario for the evolution of the sedimentary basin in Zhongtiao mountain region. From approximately 2.1Ga, the estward-directed subduction of the ocean between Western block and Eastern block, back-arc basin (Zhongtiao Group) developed behind the arc that located in the west margin of Estern block, resulting in the deposition of the Zhongtiao Group in the back-arc basin on the western margin of the Estern block. Starting from approximately 1.85 Ga, the ocean between Western block and Eastern block closed, resulting in the collision of the two blocks along TNCO, the Zhongtiao Back-arc basin underwent fold deformation and is finally transformed into a retro-arc foreland fold-and-thrust belt. The Danshanshi foreland molasse basin is formed overlying this foreland fold-and-thrust belt. Such a shift from the back-arc basins to foreland basins in the Late Paleoproterozoic supports the model that the collision between Eastern and Western blocks occurred at ~1.85Ga.