Acta Petrologica et Mineralogica

Late Triassic basic rocks were discovered in the Xiacangjie area of Songpan-Ganzi terrane, and their petrography, geochemistry and baddeleyite U-Pb chronology were studied. The basic rocks are composed of basalt and diabase, both of which belong to calc-alkaline series with strong alteration, and the formation age of diabase is 208.0±7.0 Ma. La/Nb value is 1.13～1.95, La/Ta value is 7.96～25.79, TiO₂ content is 1.51%～2.22%, and Zr/Nb value is 11.35～16.33, indicating that the magma of the basic rocks originated from the mixed source region of the lithospheric mantle and the asthenosphere mantle. According to the calculation results of the (Yb/Sm)_P-(Tb/Yb)_P model, it is speculated that the basic rocks in the Xiacangjie area may be derived from the partial melting of about 5% of the spinel and garnet transition phase (garnet accounts for about 0~25%) in the lithospheric mantle induced by the asthenospheric materials. Ancient baddeleyites captured in the rocks are found. Light rare earth elements are enriched in the rocks, heavy rare earth elements are depleted, and Nb, Ta and Ti elements are weakly depleted. Combined with the regional geological data, it is considered that Songpan-Garze terrane should have a continental crust basement, and its tectonic environment in the Late Triassic (<211 Ma) was the post-collisional intraplate extension environment.

Late Triassic basic rocks; baddeleyite U-Pb geochronology; Xiacangjie area; Songpan-Ganzi terrane