Early Cretaceous sedimentary records and tectonic evolution of the Jiaodong Peninsula, Eastern China

Located in the eastern part of Shandong Province, Eastern China, the Jiaodong Peninsula is composed of three units as the Jiaobei terrane in the north, the Sulu orogen in the southeast, and the Early Cretaceous Jiaolai basin... [ view full abstract ]

Located in the eastern part of Shandong Province, Eastern China, the Jiaodong Peninsula is composed of three units as the Jiaobei terrane in the north, the Sulu orogen in the southeast, and the Early Cretaceous Jiaolai basin situated between them. The Sulu orogen, a world-famous ultrahigh-pressure terrane and acknowledged as the eastern extension of the Triassic Qinling-Dabie orogenic belt, is poorly understood in its uplifting-denudation history and the basin-range coupling relationship with peripheral sedimentary basins. This paper investigated the depositional systems and detrital provenances of the Early Cretaceous clastic sediments in the Jiaolai basin as well as in the offshore areas (Lingshan Island and Baxiandun) in the south-cenral Sulu orogen which were found recently, aiming to constrain the tectonic evolution of the Jiaodng Peninsula, especially the Sulu orogen.
The Early Cretaceous sediments in the Jiaolai basin comprise mainly alluvial and fluvial-lacustrine facies clastic rocks and volcanic-volcaniclastic rocks, whereas those in the offshore areas were deepwater turbidites, siltstone-sandstone in fan-delta facies (with paleoslope struck SE-NW), and volcaniclastic-volcanic rocks upward section. The analysis of heavy mineral assemblages from sandstones indicates the detritus were primarily contributed by intermediate-acidic igneous rock and secondarily middle- to high-grade metamorphic rocks. Detrital zircon age populations show prevalent presence of the group of mid-Neoproterozoic (700-900 Ma), indicating detritus derived from source area with affinity to the Yangtze block which includes the Sulu orogen. However, the detrital zircon age data imply the there was also obvious provenance contribution for the fluvial sediments in Jiaolai basin (after 130 Ma) provided by the Jiaobei terrane, which is not detected in the deposits from the offshore areas. These results reflect notable differences in sedimentary environment and detrital provenance between the clastic deposits in the north and south sides of the onshore Sulu orogen, implying the Jiaolai basin and the offshore area would not be a united basin. Instead, they were separated rift basins coupled with adjacent uplifts. The detrital compositions of the Lower Cretaceous in the Jiaodong peninsula show very weak contribution of the UHP metamorphic rocks. It is indicated that the UHP terrane in Sulu orogen did not undergo large-scale exhumation during Jurassic like that in Dabie orogen, and might experience very limited denudation even in the Early Cretaceous under regional extensional background.