No abstract

A set of samples including porphyritic rhyolite, rhyo-trachyte, trachyte and basalt was collected in the Tram Tau district, Tu Le Mesozoic Basin, in NW Viet Nam for analysis for major, trace, elemental and Rb-Sr and Sm-Nd isotopic compositions. The volcanic rocks are alkaline and highly enriched in trace elements including rare earth elements (REEs). However, primitive mantle and chondrite trace element normalized patterns expose strong negative anomalies for Ba, Sr, Eu and Ti, possibly reflecting fractional crystallization of plagioclase (for Sr and Eu), pyroxene, and especially amphibole (for Ba and Ti). The measured Sr ratio of 0.703 would occur, respectively, at 3÷4% and 2÷5% to generate the observed strontium isotopic ratios in the Tram Tau volcanic rocks.