Geochemical evidence for provenance and tectonic background from the Palaeogene sedimentary rocks of the East China Sea Shelf Basin

Abstract

The East China Sea Shelf Basin is an important part of the Western Pacific marginal structural domain located in the eastern margin of the Eurasian Plate. Residual sedimentary detritus in the basin has recorded much information on basin composition, plate interaction, continental dynamic environment evolution, and resource response of the Western Pacific region. For studying the Palaeogene clastic rocks obtained from the oil and gas drilling wells of the East China Sea Shelf Basin, through the rock geochemical and mineral compositional analysis, we discuss the sedimentary detritus sources, tectonic background and response to the Western Pacific continental margin tectonic environment evolution. Lithogeochemical analyses of clastic rocks suggest that Palaeocene arenites are characterized by accumulation of volcanic detritus under shallow marine depositional environments, while Eocene and Oligocene arenites are rich in inflexible quartz controlled by an oscillating coastal marine environment and metamorphic crystalline rocks of the Proterozoic Craton in South China. As geochemical compositions of the Palaeogene clastic rocks are largely unaffected by sedimentary recirculation, diagenesis, epigenesis, and chemical weathering, these rocks can be used in provenance tracing. Controlled by the combined remote effects of convergence, collision, and wedging between the Indian and Eurasian plates, and subduction, collision, and back‐arc spreading between the Pacific and Eurasian plates, the East China Sea Shelf Basin showed a tectonic background of both active continental margin and continental island arc in the Palaeocene. The Palaeogene clasts of the Lishui Depression accordingly showed characteristics of recycled orogenic provenance and volcanic arc orogenic provenance, which were mainly Mesozoic volcanic rocks, volcaniclastic rocks and granites from the Zhemin Uplift and Yandang Low Bulge. Along with the Pacific subduction zone passively retreated to the west side of the ancient Ryukyu Island Arc (Diaoyu Island Uplift‐Fold Belt), the source area showed mixed characteristics of recycled orogenic belt, collisional suture and folded overthrust belt, and subduction complex provenance, and the Eocene and Oligocene source rocks were mainly Proterozoic metamorphic quartzite and Mesozoic magmatic igneous rocks from the Haijiao and East Yushan uplifts. The supply of clasts by the Proterozoic cratonic metamorphic rock of South China led to a sharp increase in ancient deposits of source rocks. Copyright © 2016 John Wiley & Sons, Ltd.