Timing and implications for the late Mesozoic geodynamic settings of eastern North China Craton: Evidences from K–Ar dating age and sedimentary–structural characteristics records of Lingshan Island, Shandong Province

Abstract

The Lingshan Island in Shandong Province in the eastern North China Craton, well known for the Late Mesozoic multi-scale slide-slump structures is related to paleo-earthquake. Terrigenous clastic rocks, volcanic clastic rocks and volcanic lavas are extensively exposed in the Lingshan Island and its adjacent regions of the Shandong Province, which led to fierce debates on their ages, sedimentary characteristics and tectono-sedimentary evolution. In this contribution, we present the characteristics of the Late Mesozoic stratigraphy in the Lingshan Island. Whole-rock K–Ar dating of dyke at Beilaishi and rhyolites at Laohuzui of the Lingshan Island yielded ages of 159 Ma and $106\hbox {–}92\hbox { Ma}$ which coincides with the Laiyang Period rifting and the Qingshan Period rifting in the Jiaolai Basin, respectively. On the basis of the analysis to the Late Mesozoic sedimentary environment of ‘flysch’ and ‘molasse’-like formations as well as tectonic stress fields reconstruction, four episodes of the tectono-sedimentary evolution were established in the Lingshan Island and its adjacent regions in the eastern North China Craton. They consist of two episodes of extensional events for the syn-rift, and two episodes of compression events for the inversion of the post-rift. The entire episodes can be summarized as follows: (1) the first syn-rift NW–SE extension in Laiyang Period can be identified by the ‘flysch’ formation (Unit 1) and by emplacement of the NE-trending dyke in the Laiyang Group. This syn-rift episode can be related to the NW–SE post-orogenic extension resulted from the gravity collapse of the thickened lithosphere along the Sulu Orogen. (2) The first post-rift NW–SE inversion, which was caused by the NW-directed subduction of Izanaqi Plate, can be well documented by the ‘X’ type conjugate joints as well as slide slump folds in Unit 1. (3) The second syn-rift NW–SE extension in Qingshan Period is characterized by rhyolite rocks (Unit 2). This syn-rift episode can be considered to be associated with lithospheric delamination of the thickened lithosphere in the eastern North China Craton. And finally, (4) the second post-rift NW–SE inversion which resulted from the subduction of the Pacific Plate under the eastern North China Craton in the NW direction at the end of the Qingshan Period is recorded by ‘molasse’-like formation (Unit 3).

Appendix

A1. Sample preparation and analytical procedure for K–Ar

Four ‘fresh’ hornblende and biotite-bearing samples suitable for K–Ar dating were taken from surface outcrop at four sites in Lingshan Island. Sample locations are shown in figure 2. Dated specimens include diorite-porphyrite dyke and rhyolite whole rocks. These rocks were crushed with a rotary mill and sieved, and the 60–80 mesh size fraction was retained for pre-processing. The sieved fraction was washed ultrasonically in distilled water to exclude powder residue, and then dried in an oven ($50{^{\circ }}\hbox {C}$).

Potassium was analyzed by flame photometry using a 2000 ppm Cs buffer (Nagao and Itaya 1988; Itaya 1991). The multiple runs of geochemical standards reference samples ZBH-25 and TC-18 showed that accuracy and reproducibility were with 2%. Argon was analyzed by isotope dilution at Key Laboratory of Orogenic Belts and Crustal Evolution (Peking University) using a 15 cm radius sector type mass spectrometer with a single collector system (VSS-RGA-10). Mass discrimination was atmospheric argon several times each day. Physical constants used in the calculation of K–Ar ages are $\lambda =5.543\times 10^{-10}\hbox {yr}^{-1}$, $^{40}\hbox {K}/\hbox {K}=1.167\times 10^{-4}$ (Steiger and Jäger 1977).