HF-ND ISOTOPE CONSTRAINTS ON THE MANTLE SOURCE CHARACTERISTICS FOR THE TENGCHONG VOLCANICS FROM SE TIBETAN PLATEAU
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 in primitive mantle-normalized trace element spider diagram. Preliminary Hf and Nd isotope results indicate that the Tengchong volcanics plot between mantle igneous rock array and seawater array, around the zircon-free sediments arrays, in the εHf versus εNd diagram. This implies that the sediment component in the mantle source for Tengchong volcanic rocks was mature clay sediments or mudstones rather than other sediments such as sandstones. This interpretation from Hf-Nd isotope systematics is consistent with the conclusion on mantle source characteristics based on 238U-230Th isotope disequilibrium data of the Tengchong volcanics. Finally, new constraints on the mantle source rocks from Hf-Nd isotope systematics in Tengchong might exemplify the characteristics of the source rocks for older widespread post-collisional volcanism in other areas of the Tibetan Plateau.