Provenance Characteristics and Tectonic Implication of the Laiyang Group in Lingshan Island of Riqingwei Basin

Provenance Characteristics and Tectonic Implication of the Laiyang Group in Lingshan Island of Riqingwei BasinJIANG, Yushen and ZHOU, Yaoqi, China University of Petroleum (east)Abstract: Lingshan Island is located on the suture zone of the Sulu orogenic belt and is an important research area of the Riqingwei Basin. There are turbidites of Laiyang Group of Lower Cretaceous, terrigenous clastic rocks of Qingshan Group and igneous rocks in Lingshan Island from top to bottom. There are significant debates about the sedimentary environment, sediment source, and provenance direction of the Laiyang Group sedimentary strata in the Lingshan Island. The stratigraphic features of Lingshan Island section are investigated in detail and analyzed by various methods, and the following conclusions are drawn:(1) Analysis of the sandstone detrital components has shown that the predominant rock type in the study area is lithic feldspathic sandstone with overall low maturity, and the grain composition of sandstone shows that the source rocks may have the characteristics of volcanic rocks, granite and metamorphic rocks. The sedimentary source of the Laiyang Group sandstones in Lingshan Island is relatively close with a short transportation distance and fast sedimentation rate, and is mainly from the cutting of arc-island region, which is affected by tectonic uplift to some extent.(2) The results of paleocurrent analysis show that the ancient water flow in Lingshan Island area is generally oriented in the northwest-southeast direction with an average azimuth of 160 °, suggesting that the sandstone deposits in the study area mainly come from the northern provenance.(3) Analysis of the principal and trace elements in mudstone has revealed that, from bottom to top, there is a trend of change in properties of the source rock from felsic to intermediate, and a trend of decreasing weathering in the source area; The provenance mainly comes from felsic source area, and the overall chemical weathering and recycling degree is low. It is speculated that the clastic materials of mudstone directly come from the strong weathering and deposition of igneous rocks.(4) Results of heavy mineral components analysis have shown that the sedimentary strata in the study area are influenced by source rocks such as acid magmatic rocks and metamorphic rocks to a certain extent, and from the change of heavy mineral characteristics in different horizons, it records the first-stage tectonic uplift movement.Based on the above analysis results and the tectonic position of the study area, it can be concluded that the sedimentary strata of Laiyang Group in Lingshan Island area are influenced to some extent by source rocks such as acid magmatic rocks and metamorphic rocks, and the source rocks are mainly metamorphic sedimentary rocks, intermediate-acid volcanic rocks, metamorphic rocks and sedimentary rocks. The change of provenance reflects a period of tectonic uplift. The main source of provenance in Lingshan Island area is from the Sulu orogenic belt, which may be partly from metamorphic sedimentary rocks of Yangtze platform in the early stage and mainly from Sulu orogenic belt in the later stage.