Geochemical characteristics and tectonic setting of basaltic rocks of the Tamulangou Formation at the northern end of the Da Hinggan Mountains, China

Basaltic rocks of the Late Jurassic Tamulangou Formation in the northern Da Hinggan Mountains are characterized by rich alkalis (K2O+Na2O>5.45%),high K2O (2.15%- 3.75%),high ratios of K2O /Na2O (0.48- 1.12),Th /Ta,Ce/Nb and Ta/Nb and strong enrichment in large- ion lithophile elements (LILE)and light rare earth elements (LREE),belonging to the shoshonitic series. Analysis of the available data indicates that these shoshonitic rocks formed in a continental intraplate set- ting. Geochemical characteristics suggest that the primary magma of these shoshonitic rocks underwent strong crystallization dif- ferentiation and was contaminated with pre- Mesozoic basement materials.