Geometry and emplacement of the Late Cretaceous mafic dyke swarms on the islands in Zhejiang Province, Southeast China: Insights from high-resolution satellite images

Abstract

The geology of Zhejiang coastal area in Southeast China is characterized by numerous Late Mesozoic intrusive rocks and widespread mafic dyke swarms, which indicate continental lithospheric extensional eventsduring the Jurassic and Cretaceous. This work is focused on using multisource high-resolution remote sensing images (Worldview2, Geoeye1 and Quickbird2) to identify the geometry, morphology and location of previously undocumented and poorly understood dyke swarms exposed on the islands in Zhejiang Province. The geometry of each dyke is described by its strike, length and thickness. The spatial distribution of the dyke density and crustal dilation are obtained based on the statistics of 774 extracted mafic dykes. Field surveys are performed in some islands in order to analyze the detailed geometric features and assess the interpretative accuracy. The spectral measurement and analysis of mafic dykes are performed as well for remote sensing imagery processing and lithological interpretation. The results show that the frequency distributions of the length and thickness of dykes follow power law curves. The maximum and mean dyke thicknesses are 11.2m and 1.43m, respectively. The crustal dilation of the islands ranges from 0.09% to 7.4%. From the north to the south islands, the dilation decreases gradually. The dyke frequency and density have the same distribution as the dilation. According to 40Ar–39Ar age (Zhongshanjie archipelago) and U–Pb zircon age (Sijiao Island) of the mafic dyke, the dyke swarms on the eastern Zhejiang islands emplaced at around 87–97Ma. The cross-cutting relationships of dykes and host rocks show that the mafic dyke swarms have close spatial correlations with granite. The dykes stretch in various directions whereas the NE-trending dykes dominate. Our research reveals four intrusive events that imply the crustal extension and intermittent variation of the regional stress field in the coastal area of southeastern China in the Late Cretaceous.