Felsic dyke swarms from central Inner Mongolian: Implications for the Triassic tectonic setting in the southeast Central Asian Orogenic Belt.

This work presents the whole-rock elemental geochemistry and Sr − Nd isotopes and zircon Hf − O isotopes for dikes from Tagaolemiao and Tuilamamiao, the southern margin of the southeast Central Asian Orogenic Belt (SE CAOB), to explore their origin and dynamic setting. Zircon U − Pb dating reveals that the Tagaolemiao dikes emplaced at ca. 242 Ma and the Tuilamamiao dikes emplaced at ca. 250 Ma, which postdated the Late Permian magmatic lull and convergent events in the SE CAOB. Dikes from the two areas are I-type rhyolitic rocks and exhibit high SiO 2 , low MgO, and low Cr, Co, and Ni contents. The Tagaolemiao dikes have depleted zircon Hf (ε Hf (t) = +3.75 to +9.82), whole-rock Sr − Nd (I Sr (t) = 0.704340–0.704855; ε Nd (t) = +1.3 to +2.1) isotopic composition and variable zircon δ18O values (4.88–7.29‰), and were derived from the mixing melts of the juvenile crust and depleted mantle. In contrast, the dikes from Tuilamamiao show negative zircon ε Hf (t) (−2.33 to −10.85) and whole-rock ε Nd (t) (−6.7 to −15.5) values, low I Sr (t) (0.706640–0.708208) and high δ18O (6.38–7.61‰) values, which originated from the partial melting of the old continental lower crust. The Triassic dyke swarms from this work indicate the SE CAOB switched into an intra-continental extension tectonic setting after the Paleozoic long-term accretion-convergence. • Early-Middle dikes were derived from the thickened lower crust. • Triassic dyke swarms reveal an intra-continental extension setting. • Vigorous mantle perturbation is important to the Triassic tectonics in the SE CAOB. [ABSTRACT FROM AUTHOR]