Detrital zircon geochronology of middle Paleozoic to lower Mesozoic strata from Hainan: implications for sedimentary provenance and tectonic evolution of Hainan.

Hainan Island is located at the intersection of the India–Australian, Philippine–Pacific, and Eurasian plates. As a key component of Southeast Asia, constraints on the tectonic evolution of Hainan Island can help researchers to understand the evolutionary process of SE Asia more thoroughly. This study reports 960 new detrital zircon U–Pb ages of 8 samples from the Silurian, Pennsylvanian, and Middle Triassic strata on Hainan. Detrital zircon grains from the Silurian samples yield five dominant age populations of 460–420 Ma, 600–500 Ma, 1200–1000 Ma, 2000–1400 Ma, and 2700–2400 Ma. There are high similarities in age distributions between the Silurian and Pennsylvanian samples, but the Pennsylvanian samples exhibit a special age population of 360–340 Ma. The Middle Triassic samples have a relatively simple detrital zircon age distribution pattern with a dominant age peak at ca. 250 Ma and a subordinate age group of 390–360 Ma. The Silurian strata on Hainan Island mainly receive detritus from the South China Block and Eastern Gondwana, and detrital zircon grains from the Pennsylvanian samples were derived from the recycled strata on Hainan Island except that ca. 350 Ma grains came from the Early Carboniferous bimodal volcanic rocks near the Pennsylvanian sample site. Detrital zircons of the Middle Triassic samples are mainly derived from the ca. 250 Ma collision-related arc materials and the recycled strata. Based on detrital zircon geochronological data and previous results, we proposed a new tectonic model for the late Paleozoic tectonic evolution of Hainan Island. The Carboniferous drifting of Hainan Island northward resulted in a back-arc basin developed on central Hainan Island. At ca. 330 Ma, this back-arc basin turned into an oceanic basin, and this oceanic basin continued to develop during the Early–Middle Permian. Due to the closure of this oceanic basin since the late Middle Permian, the North Hainan finally collided with the South Hainan along the Bangxi–Chenxing tectonic belt and consolidated to form a unified Hainan Island again at ca. 250 Ma. [ABSTRACT FROM AUTHOR]