ABSTRACT

Mesozoic basalts occur widely in SE China, with two major episodes of activity during the Middle Jurassic and Early Cretaceous. The exact age and mantle source character for the first eruption of basaltic magma during the Jurassic are not well constrained. In this paper we report, for the first time, Re-Os isotope data on these basalts. We sampled the Fankeng basalts in the Yongding basin of southwestern Fujian, SE China and separated the Fe-Ti oxide concentrates in them. Six samples of the Fe-Ti oxide concentrates yield a Re-Os isochron age of 175.4 ± 3.1 Ma with an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.124 ± 0.014, corresponding to an initial γ_Os value of -1.44 at 175.4 Ma. The age suggests that the Fankeng basalts are products of Middle Jurassic magmatism. Both (¹⁸⁷Os/¹⁸⁸Os)_i and γ_Os values are near chondritic. Together with Sm-Nd isotope data of these basalts, we conclude that the Fankeng basaltic magma might be derived from depleted asthenospheric mantle. The near chondritic γ_Os and εNd(T) values may suggest interactions between asthenosphere and lithosphere during early Mesozoic in the area.