Linking the Paleozoic evolution of Hainan Island to Indochina and Australia: Implication for the paleogeography of the Eastern Tethys Ocean

Abstract

Paleozoic paleogeographic and tectonic evolution of blocks within the eastern Tethyan Orogenic Belt remains ambiguous due to limited and fragmentary geological records. New detrital zircon U-Pb-Hf isotopic analyses integrated with published data from Paleozoic strata in Hainan Island reveal three significant changes in provenance, providing excellent insights into the assembly record with adjacent blocks. Detrital zircon age spectra of early Cambrian strata from Hainan Island yield a major peak at 1.17 Ga, resembling equivalent units from the Kontum Massif (South Indochina) and were likely sourced from Australia. Mid-late Cambrian successions contain a dominantly 1.78–1.40 Ga zircon population sourced from Precambrian rocks on the island. Detrital zircon age spectra of late Ordovician samples yield major age peaks of 0.97 Ga and 0.45 Ga that originated from India and Indochina, respectively. The two provenance shifts in the Cambrian-Ordovician strata are interpreted to result from the consumption of a branch of the Proto-Tethys associated with progressive amalgamation of the Kontum (South Indochina)-Hainan-Australia block and Truong Son (North Indochina)-India-South China block. The late Devonian-early Carboniferous succession encompass significant ca. 368 Ma zircons derived from arc-related rocks that formed during initial subduction of the main Paleo-Tethys Ocean. The lack of ca. 970 Ma Indian-derived zircons within the Devonian-Carboniferous units suggests that Hainan Island rifted away from Gondwana before the late Devonian. Late Paleozoic detrital zircon age pattern of Hainan Island coincides with that of Indochina and North Qiangtang, but is distinct from that of Gondwana and South China, indicating that the coherent Hainan-Indochina-North Qiangtang continental sliver was separated from Gondwana and South China by the main Paleo-Tethys Ocean and the Ailaoshan Ocean, respectively.