A new insight into the eastern extension of the Proto-Tethyan margin of Gondwana by Early Paleozoic volcanic rocks in South China

South China is located in a key area of East Gondwana. The volcanic rocks in the unambiguous tectonic setting of Hainan Island were systematically studied based on detailed field, petrological, geochemical, and U-Pb zircon geochronological data. The petrology and geochemistry reveal three types of volcanic rocks, i.e., andesites, NMORB-type metabasalts, and E-MORB-type metabasalts. Their eruption ages are well defined between 446 and 430 Ma. The andesite is characterized by negative Nb, Ta, and Eu anomalies and positive Th and U anomalies. The E-MORB-type metabasalt is characterized by Rb, Ba and Sr depletions, slight Nb and Ta enrichments, and negative Eu anomalies. The N-MORB-type metabasalt has more depleted trace element compositions and is generally enriched in Rb, Ba, and Sr; depleted in Nb and Ta; and it does not exhibit significant Eu anomalies. The whole rock Sr-Nd isotopic analyses show that the andesites, N-MORB-type metabasalts, and E-MORB-type metabasalts have epsilon Nd(t) values of -0.2 to -3.6, +3.7 to +6.8, and + 5.5 to +6.7, respectively. These results suggest that their formation is closely related to the subduction of Proto-Tethyan oceanic crust. These detailed descriptions of the Early Paleozoic volcanic rocks on Hainan Island indicate that South China was likely the eastern extension of the Proto-Tethyan margin and was located on the easternmost periphery of East Gondwana.