Late Mesozoic tectonic evolution of the Songliao basin, NE China: Evidence from detrital zircon ages and Sr–Nd isotopes

Abstract

The Songliao basin, situated between the Siberian and Sino-Korean (North China) cratons, was tectonically shaped by convergence of the Mongol-Okhotsk and Paleo-Pacific oceans. The lack of isotopic and geochemical data from its sedimentary rocks has hindered a better understanding of the depositional–tectonic history of the basin so far. A continuous sedimentary sequence is preserved in the upper part of the Songliao basin (Denglouku and Quantou formations). These rocks provide clues to depositional processes operating in this region during the late Cretaceous. Dominant zircon populations of the underlying Denglouku Formation are largely Paleozoic (270–250Ma) and Mesozoic (190–170Ma) in age, whereas the overlying Quantou Formation contains mostly older zircon populations of ~1800Ma and ~2500–2900Ma. The youngest detrital zircons place the deposition ages of both rock formations at about ~117Ma and ~103Ma, respectively. The Denglouku Formation is characterized by less negative initial εNd values (−6.3 to −2.8), younger Nd model ages (1.05–1.39Ga) and lower initial 87Sr/86Sr ratios (0.7079 to 0.7088), compared to the Quantou Formation (−12.8, 1.75Ga and 0.7129), confirming that both formations were derived from different source areas. Our data suggest that Paleozoic and Mesozoic magmatic rocks were widespread in the northern periphery of the basin, and served as potential sources of the Denglouku Formation. In the south-east, old basement rocks of the North China craton provided sedimentary material for the Quantou Formation. The south-eastward migration of erosion center(s) in the Songliao basin in the late Mesozoic probably resulted from an abrupt change in basin uplift and subsidence. These processes were driven in response to regional tectonic changes toward an increasing dominance of the Pacific Ocean over the Mongol-Okhotsk Ocean subduction regime.