Provenance of Early Cretaceous Laiyang Group in Jiaolai Basin and its significance

Abstract: Using the paleocurrents, gravels composition and detrital zircons age spectrum, the authors analyzed the provenance of Early Cretaceous Laiyang Group in Jiaolai basin and its geological significance. The paleocurrents show a stable northward direction in Wulian-Zhucheng, but gradually change from E-SE at the early stage to W-NW at the late stage in Laiyang-Rushan. Gravels in Wulian-Zhucheng-Jiaozhou comprise mainly granite gneiss, granite, marble and quartzite; in Laiyang-Rushan, however, granites are dominant at the early stage and multiple gravels are present at the late stage. Detrital zircons ages are primarily distributed in the ranges of 110-145 Ma, 150-180 Ma, 200-250 Ma, 600-950 Ma and 1700-2600 Ma, whereas Paleozoic zircons are rarely seen. All these features indicate that there existed three main sources for Early Cretaceous Jiaolai Basin: ① HP-UHP metamorphic rocks and shallow metamorphic complex of Sulu orogen, ② Yanshanian granites (J2-3-K1), and ③ Metamorphic rocks from the Jiaobei uplift. Additionally, the regional difference of provenance is apparent, which suggests the southern part and the northern part of Sulu orogenic belt experienced different orogenic processes. The southern Sulu orogenic belt experienced large-scale uplift and was stable, whereas the northern Sulu orogenic belt was subjected to small-scale uplift and collapsed at the late stage. It is also concluded from the provenance that the ancient landform of Jiaolai basin in the southwest was higher than in the east during the sedimentation of Early Cretaceous Laiyang Group until the late stage of the sedimentation when the east part of the basin was uplifted.