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

Abstract

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 UPb zircon geochronological data. The petrology and geochemistry reveal three types of volcanic rocks, i.e., andesites, N-MORB-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 SrNd isotopic analyses show that the andesites, N-MORB-type metabasalts, and E-MORB-type metabasalts have εNd(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.