Geology and Bouguer anomalies of Hainan Island and vicinity

Abstract

Northern Hainan Island is part of the Caledonian Cathysian fold system. Central and southern Hainan Island are part of the Variscan southeast maritime terrane. During Late Triassic-Jurassic time (the Indo-Sinian Movement), the Mekong foldbelt collided with the Yangtze terrane. The northwest-dipping subduction zone developed on the southeastern margins of the southeast maritime terrane during Jurassic-Cretaceous time (the Yenshanian Movement). Yenshanian intrusives present in Hainan Island extend northeastward as a magnetic arc across the Chinese continental shelf. Five Bouguer anomaly zones are recognized on Hainan Island. The anomalies in northern and northeastern Hainan Island reflect the thickness of Neogene and Quaternary sediments there, and anomalies in central, northwestern, and southeastern Hainan Island reflect the Variscan tectonic pattern of the region. The Bouguer anomalies increase southward from −20 mgal along the coast to +50 mgal near the edge of the continental shelf, and from +50 mgal to +220 mgal from the continental slope to the abyssal basin.