A Case Study on the petrology and geochemical genesis of Hercynian-Indosinian granite in Hainan Island, China

Granite is a product of crustal melting and intrusion cooling at depths of 10-15km and deeper underground, representing a tectonic environment under certain temperature and pressure conditions. It was exposed to the surface through tectonic uplift and erosion and underwent weathering and alteration. The region in north Hainan island of China is mainly composed of concealed granite, which is generally deeper in the west and shallower in the east, with a maximum depth of over 8km. There is surface exposed granite on the east side. Large areas of Permian-Triassic granite are exposed in the central part of Hainan island and 4615 meters of Fushenre 1 Well in Haikou. Based on extensive field geological surveys and high-precision analysis of major and trace elements in rocks, it is indicated that the granite of the Permian-Triassic period in Hainan Island is mainly composed of biotite diorite granite, with RREs mainly showing a right leaning of LREEs enrichment type. Trace elements are characterized by enrichment of LILEs and relative depletion of high field strength elements, making it a typical island arc type I granite. The northwest southeast trending structure is closely related to the back arc tension background caused by the Pacific westward subduction.