Trace Element and Hf-Nd Isotope Constraints on the Origin of Young Tengchong Volcanic Rocks, SE Tibetan Plateau

Abstract

Hafnium and neodymium isotope systematics in mafic volcanic rocks provide useful information about mantle source characteristics and processes. Hf and Nd isotope arrays are useful for identifying the types of subducted sediments involved in enriched mantles. The Tengchong volcanic field is located in Yunnan Province and is one of two active volcanic fields on the Tibetan Plateau. Although a great deal of geochemical and petrological research has been conducted to investigate the origin of these volcanoes, application of combined Hf and Nd isotopes to study their mantle source characteristics has not been accomplished previously. In this study, Hf and Nd isotopic compositions together with major and trace element concentrations are reported for the four active volcanoes in the Tengchong volcanic field, including Heikongshan, Dayingshan, Maanshan, and Laoguipo volcanoes. All studied samples have LREE enriched patterns. They are depleted in high field strength elements Ti, Nb, and Ta. Hf and Nd isotope results indicate that the Tengchong volcanics plot between the mantle igneous rock and seawater arrays. This implies that the enriched component in the mantle source for the Tengchong volcanic rocks was mature clay sediments or mudstones rather than other sediments such as sandstones. New constraints on the mantle source rocks from Hf-Nd isotope systematics in Tengchong can serve as a reference for interpreting the characteristics of the source rocks for older widespread post-collisional volcanism in other areas of the Tibetan Plateau.